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Sample records for jahn-teller glass formation

  1. Cyclopropenyl Anions: Carbon Tunneling or Diradical Formation? A Contest between Jahn-Teller and Hund.

    PubMed

    Kozuch, Sebastian

    2015-07-14

    The π bond shifting (automerization) by carbon tunneling of cyclopropenyl anions was computationally analyzed by the small curvature tunneling methodology. Similar to other antiaromatic cases, the process is hindered by substituents departing from planarity, since these groups must be realigned along with the π bond shifting. With hydrogens as substituents the tunneling is extremely fast, in a case of both heavy and light atom tunneling. But, with more massive substituents (such as Me and F), and especially with longer groups (such as CN), the tunneling probability is reduced or even virtually canceled. The automerization of triphenylcyclopropyl anion by tunneling was supposed to be impossible due to the high mass of the phenyl groups. However, it was found that the ground state of this species is actually a D3h aromatic triplet, a single-well system that cannot undergo automerization. For this and other systems with π acceptor groups, the superposition of states that generates the second-order Jahn-Teller distortion is diminished, and by Hund's rule, the triplet results in the ground state.

  2. Jahn-Teller Effect: Its History and Applicability

    DOE R&D Accomplishments Database

    Teller, E.

    1981-08-31

    The interactions between Teller, Renner, Jahn and Landau which led to the formulation of the Jahn-Teller effect are discussed. The applicability of Jahn-Teller type of theory to superconductivity and the explanation proposed by the use of Goldstone particles are assessed.

  3. Jahn-Teller effect: its history and applicability

    SciTech Connect

    Teller, E.

    1981-08-31

    The interactions between Teller, Renner, Jahn and Landau which led to the formulation of the Jahn-Teller effect are discussed. The applicability of Jahn-Teller type of theory to superconductivity and the explanation proposed by the use of Goldstone particles are assessed.

  4. Reactions of trivacant Wells-Dawson heteropolytungstates. Ionic strength and Jahn-Teller effects on formation in multi-iron complexes.

    PubMed

    Anderson, Travis M; Zhang, Xuan; Hardcastle, Kenneth I; Hill, Craig L

    2002-05-06

    Reaction of alpha-P(2)W(15)O(56)(12-) and Fe(III) in a saturated NaCl solution produces a trisubstituted Wells-Dawson structure with three low-valent metals, alpha-(Fe(III)Cl)(2)(Fe(III)OH(2))P(2)W(15)O(59)(11-) (1). Dissolution of this species into 1 M NaBr (Br(-) is non-coordinating) gives the triaquated species alpha-(Fe(III)OH(2))(3)P(2)W(15)O(59)(9-) (2). Ionic strength values of 1 M or greater are necessary to avoid decomposition of 1 or 2 to the conventional sandwich-type complex, alpha beta beta alpha-(Fe(III)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(12-) (3). If the pH is greater than 5, a new triferric sandwich, alpha alpha beta alpha-(NaOH(2))(Fe(III)OH(2))Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (4), forms rather than 3. Like the previously reported Wells-Dawson-derived sandwich-type structures with three metals in the central unit ([TM(II)Fe(III)(2)(P(2)W(15)O(56))(P(2)TM(II)(2)W(13)O(52))],(16-) TM = Cu, Co), this complex has a central alpha-junction and a central beta-junction. Thermal studies suggest that 4 is more stable than 3 over a wide range of temperatures and pH values. The intrinsic Jahn-Teller distortion of d-electron-containing metal ions incorporated into the external sites of the central multi-metal unit impacts the stoichiometry of their incorporation (with a consequent change in the inter-POM-unit connectivity, where POM = polyoxometalate). Reaction of non-distorting Ni(II) with the diferric lacunary sandwich-type POM alpha alpha alpha alpha-(NaOH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(16-) (5) produces alpha beta beta alpha-(Ni(II)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (6), a Wells-Dawson sandwich-type structure with two Ni(II) and two Fe(III) in the central unit. All structures are characterized by (31)P NMR, IR, UV-vis, magnetic susceptibility, and X-ray crystallography. Complexes 4 and 6 are highly selective and effective catalysts for the H(2)O(2)-based epoxidation of alkenes.

  5. Jahn-Teller and pseudo-Jahn-Teller effects in trifluoromethane radical cation

    NASA Astrophysics Data System (ADS)

    Ghanta, Susanta

    2016-08-01

    Jahn-Teller (JT) and pseudo-Jahn-Teller (PJT) effects in the ground, first and second excited electronic states of the trifluoromethane radical cation are theoretically examined here. Extensive ab initio computation of electronic potential energy surfaces and their coupling surfaces are performed. Full quantum dynamics are obtained by both time-independent and time-dependent quantum mechanical methods. This system belongs to (E+A)⊗e JT-PJT family. Our results compare well with the experimental data. JT interactions are fairly strong in the second excited B˜2 E electronic state and the PJT interaction between A˜2A2 - B˜2 E electronic states is stronger which cause an increase of the spectral line density of the vibronic spectrum.

  6. Andrew Liehr and the structure of Jahn-Teller surfaces

    NASA Astrophysics Data System (ADS)

    Chibotaru, Liviu F.; Iwahara, Naoya

    2017-05-01

    The present article is an attempt to draw attention to a seminal work by Andrew Liehr “Topological aspects of conformational stability problem” [1, 2] issued more than half century ago. The importance of this work stems from two aspects of static Jahn-Teller and pseudo-Jahn-Teller problems fully developed by the author. First, the work of Liehr offers an almost complete overview of adiabatic potential energy surfaces for most known Jahn-Teller problems including linear, quadratic and higher-order vibronic couplings. Second, and most importantly, it identifies the factors defining the structure of Jahn-Teller surfaces. Among them, one should specially mention the minimax principle stating that the distorted Jahn-Teller systems tend to preserve the highest symmetry consistent with the loss of their orbital degeneracy. We believe that the present short reminiscence not only will introduce a key Jahn-Teller scientist to the young members of the community but also will serve as a vivid example of how a complete understanding of a complex problem, which the Jahn-Teller effect certainly was in the beginning of 1960s, can be achieved.

  7. Jahn-Teller crystals - new class of smart materials

    NASA Astrophysics Data System (ADS)

    Kaplan, M. D.; Zimmerman, G. O.

    2017-05-01

    Jahn-Teller crystals represent a promising class in the search for new smart materials. Jahn- Teller multiferroics are of a special interest. We show that the properties of these crystals are not only “of interest for future applications”, but are already used and protected by various patents. Special attention is paid to some new results on magnetic shape memory effects in dielectrics because the physics of the corresponding materials is not yet completely clarified.

  8. Optimized unconventional superconductivity in a molecular Jahn-Teller metal.

    PubMed

    Zadik, Ruth H; Takabayashi, Yasuhiro; Klupp, Gyöngyi; Colman, Ross H; Ganin, Alexey Y; Potočnik, Anton; Jeglič, Peter; Arčon, Denis; Matus, Péter; Kamarás, Katalin; Kasahara, Yuichi; Iwasa, Yoshihiro; Fitch, Andrew N; Ohishi, Yasuo; Garbarino, Gaston; Kato, Kenichi; Rosseinsky, Matthew J; Prassides, Kosmas

    2015-04-01

    Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above T c is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C60 (3-) electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller-active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of T c with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

  9. The Jahn-Teller and pseudo Jahn-Teller effect in materials science

    NASA Astrophysics Data System (ADS)

    Bersuker, I. B.

    2017-05-01

    Defining materials science as a translation from microscopic foundations of matter to macroscopic performance in applications, this mostly review paper is devoted to the special features of matter with Jahn-Teller (JT) and pseudo JT (PJT) centers that makes it outstanding in the search of novel properties and applications as novel materials. There are three kinds of problems in this respect. The first is related to the difficulties in the use of computer simulation of observable properties (a methodology widely employed in materials science) in application to systems with dynamic JT and PJT effects. The second is due to the specifics of such systems in interaction with external perturbations, which contribute with a strong orientational effect that enhances the observable properties by orders of magnitude. The third kind of problems relevant to materials science is in the use of the JT and PJT effects in revealing the origin of structural properties of a relevant polyatomic system and working out methods to influence them in designing novel materials. The paper formulates these problems and provides for examples that demonstrate their importance. For the second group of problems, illustrative examples include flexoelectricity, permittivity, and electrostriction in systems with dynamical JT and PJT centers, and it is shown that the latter enhance the observable properties by several orders of magnitude. Also related to this group of problems are the magnetic-dielectric bistabilities in molecular systems and solids induced by JT and PJT effect, illustrated on molecules like CuF3 and crystals of the type LiCuO2. The third group of problems is shown by the already multiply used application of the PJTE to reveal the origin of distortions of planar configuration in 2D (graphene-like) and quasi-2D materials and to work out methods of restoration of their planar configurations by means of external perturbations.

  10. Optimized unconventional superconductivity in a molecular Jahn-Teller metal

    PubMed Central

    Zadik, Ruth H.; Takabayashi, Yasuhiro; Klupp, Gyöngyi; Colman, Ross H.; Ganin, Alexey Y.; Potočnik, Anton; Jeglič, Peter; Arčon, Denis; Matus, Péter; Kamarás, Katalin; Kasahara, Yuichi; Iwasa, Yoshihiro; Fitch, Andrew N.; Ohishi, Yasuo; Garbarino, Gaston; Kato, Kenichi; Rosseinsky, Matthew J.; Prassides, Kosmas

    2015-01-01

    Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above Tc is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C603– electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller–active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of Tc with interfulleride separation, demonstrating molecular electronic structure control of superconductivity. PMID:26601168

  11. Cooperative Jahn-Teller phase transition of icosahedral molecular units

    NASA Astrophysics Data System (ADS)

    Nasrollahi, Seyed H.; Vvedensky, Dimitri D.

    2017-02-01

    Non-linear molecules undergo distortions when the orbital degeneracy of the highest occupied level is lifted by the Jahn-Teller effect. If such molecules or clusters of atoms are coupled to one another, the system may experience a cooperative Jahn-Teller effect (CJTE). In this paper, we describe a model of how the CJTE leads to the crystallization of the disordered phase. The model Hamiltonian is based on a normal mode decomposition of the clusters in order to maintain the symmetry labels. We take account of the electron-strain and the electron-phonon couplings and, by displacing the coordinates of the oscillators, obtain a term that explicitly couples the Jahn-Teller centers, enabling us to perform a mean-field analysis. The calculation of the free energy then becomes straightforward, and obtaining phase diagrams in various regimes follows from the minimization of this free energy. The results show that the character of the phase transition may change from strong to weak first order and even to second-order, depending on the coupling to the vibrational modes. Taken together, these results may serve as a paradigm for crystallization near the transition temperature, where the atoms tend to form clusters of icosahedral symmetry.

  12. Electric Field Control of Jahn-Teller Distortions in Bulk Perovskites.

    PubMed

    Varignon, Julien; Bristowe, Nicholas C; Ghosez, Philippe

    2016-02-05

    The Jahn-Teller distortion, by its very nature, is often at the heart of the various electronic properties displayed by perovskites and related materials. Despite the Jahn-Teller mode being nonpolar, we devise and demonstrate, in the present Letter, an electric field control of Jahn-Teller distortions in bulk perovskites. The electric field control is enabled through an anharmonic lattice mode coupling between the Jahn-Teller distortion and a polar mode. We confirm this coupling and quantify it through first-principles calculations. The coupling will always exist within the Pb2_{1}m space group, which is found to be the favored ground state for various perovskites under sufficient tensile epitaxial strain. Intriguingly, the calculations reveal that this mechanism is not only restricted to Jahn-Teller active systems, promising a general route to tune or induce novel electronic functionality in perovskites as a whole.

  13. The Jahn-Teller plus pseudo-Jahn-Teller vibronic problem in the C3 radical and its topological implications.

    PubMed

    Rocha, C M R; Varandas, A J C

    2016-02-14

    The combined Jahn-Teller plus pseudo-Jahn-Teller [(E'+A1')⊗e'] problem is discussed for the tricarbon radical (C3) by means of ab initio calculations at the multireference configuration interaction level of theory. For the (1)E' electronic state arising from a e'(2) valence configuration, three additional symmetry-equivalent C2v seams are found to lie in close proximity to the D3h symmetry-required seam over the entire range of the breathing coordinate here considered. As the perimeter of the molecule increases, the C2v disjoint seams approach the D3h one almost linearly and ultimately coalesce with it at Q1 = 5.005 a0, thence forming an intersection node or confluence. By further increasing the size of the molecular triangle, the C2v seams get rotated by ±π in the g-h plane. A three-state vibronic Hamiltonian is also proposed to model locally the title system and shown to accurately mimic the calculated data over the region close to the minimum energy crossing point. No net geometric phase effect is observed when the associated electronic wave functions are adiabatically transported along closed paths encircling the four singularity points. For all paths enclosing the intersection node, the sign reversal criterion is shown to be not fulfilled, even for infinitesimal loops. The results so obtained are expected to be valid for other ring systems experiencing similar topological attributes.

  14. The Jahn-Teller plus pseudo-Jahn-Teller vibronic problem in the C3 radical and its topological implications

    NASA Astrophysics Data System (ADS)

    Rocha, C. M. R.; Varandas, A. J. C.

    2016-02-01

    The combined Jahn-Teller plus pseudo-Jahn-Teller [ ( E ' + A1 ' ) ⊗ e ' ] problem is discussed for the tricarbon radical (C3) by means of ab initio calculations at the multireference configuration interaction level of theory. For the 1E' electronic state arising from a e'2 valence configuration, three additional symmetry-equivalent C2v seams are found to lie in close proximity to the D3h symmetry-required seam over the entire range of the breathing coordinate here considered. As the perimeter of the molecule increases, the C2v disjoint seams approach the D3h one almost linearly and ultimately coalesce with it at Q1 = 5.005 a0, thence forming an intersection node or confluence. By further increasing the size of the molecular triangle, the C2v seams get rotated by ±π in the g-h plane. A three-state vibronic Hamiltonian is also proposed to model locally the title system and shown to accurately mimic the calculated data over the region close to the minimum energy crossing point. No net geometric phase effect is observed when the associated electronic wave functions are adiabatically transported along closed paths encircling the four singularity points. For all paths enclosing the intersection node, the sign reversal criterion is shown to be not fulfilled, even for infinitesimal loops. The results so obtained are expected to be valid for other ring systems experiencing similar topological attributes.

  15. Synchronization of networked Jahn-Teller systems in SQUIDs

    NASA Astrophysics Data System (ADS)

    Gül, Yusuf

    2016-06-01

    We consider the nonlinear effects in a Jahn-Teller (JT) system of two coupled resonators interacting simultaneously with a flux qubit using coupled SQUIDs. A two-frequency description of JT system that inherits the networked structure of both nonlinear Josephson junctions and harmonic oscillators is employed to describe the synchronous structures in a multifrequency scheme. Eigenvalue spectrum is used to show the switch between the effective single mode and two mode configuration in terms of frequency difference. The Rabi supersplitting is investigated by the spectral response of JT systems in different coupling regimes. Second-order coherence functions are employed to investigate antibunching effects in resonator mode. Synchronous structure between correlations of privileged mode and qubit is obtained in localization-delocalization and photon blockade regime controlled by the population imbalance.

  16. Jahn-Teller distortion driven magnetic polarons in magnetite

    NASA Astrophysics Data System (ADS)

    Huang, H. Y.; Chen, Z. Y.; Wang, R.-P.; de Groot, F. M. F.; Wu, W. B.; Okamoto, J.; Chainani, A.; Singh, A.; Li, Z.-Y.; Zhou, J.-S.; Jeng, H.-T.; Guo, G. Y.; Park, Je-Geun; Tjeng, L. H.; Chen, C. T.; Huang, D. J.

    2017-06-01

    The first known magnetic mineral, magnetite, has unusual properties, which have fascinated mankind for centuries; it undergoes the Verwey transition around 120 K with an abrupt change in structure and electrical conductivity. The mechanism of the Verwey transition, however, remains contentious. Here we use resonant inelastic X-ray scattering over a wide temperature range across the Verwey transition to identify and separate out the magnetic excitations derived from nominal Fe2+ and Fe3+ states. Comparison of the experimental results with crystal-field multiplet calculations shows that the spin-orbital dd excitons of the Fe2+ sites arise from a tetragonal Jahn-Teller active polaronic distortion of the Fe2+O6 octahedra. These low-energy excitations, which get weakened for temperatures above 350 K but persist at least up to 550 K, are distinct from optical excitations and are best explained as magnetic polarons.

  17. Persistence of Jahn Teller distortion in high pressure metallic phase of LaMnO3

    SciTech Connect

    Baldini, Maria; Struzhkin, Viktor V.; Goncharov, Alexander F.; Postorino, P.; Mao, Wendy L.

    2011-02-11

    High pressure, low temperature Raman measurements performed on LaMnO{sub 3} up to 34 GPa provide the first experimental evidence for the persistence of the Jahn-Teller distortion over the entire stability range of the insulating phase. This result resolves the ongoing debate about the nature of the pressure driven insulator to metal transition (IMT), demonstrating that LaMnO{sub 3} is not a classical Mott insulator. The formation of domains of distorted and regular octahedra, observed from 3 to 34 GPa, sheds new light on the mechanism behind the IMT suggesting that LaMnO{sub 3} becomes metallic when the fraction of undistorted octahedra domains increases beyond a critical threshold.

  18. Zeeman interaction and Jahn-Teller effect in the Γ8 multiplet

    NASA Astrophysics Data System (ADS)

    Iwahara, Naoya; Vieru, Veacheslav; Ungur, Liviu; Chibotaru, Liviu F.

    2017-08-01

    We present a thorough analysis of the interplay of magnetic moment and the Jahn-Teller effect in the Γ8 cubic multiplet. We find that in the presence of the dynamical Jahn-Teller effect, the Zeeman interaction remains isotropic, whereas the g and G factors can change their signs. The static Jahn-Teller distortion also can change the sign of these g factors as well as the nature of the magnetic anisotropy. Combining the theory with state-of-the-art ab initio calculations, we analyzed the magnetic properties of Np4 + and Ir4 + impurity ions in a cubic environment. The calculated g factors of the Np4 + impurity agree well with experimental data. The ab initio calculation predicts a strong Jahn-Teller effect in Ir4 + ion in the cubic environment and the strong vibronic reduction of g and G factors.

  19. Chemically induced Jahn-Teller ordering on manganite surfaces.

    PubMed

    Gai, Zheng; Lin, Wenzhi; Burton, J D; Fuchigami, K; Snijders, P C; Ward, T Z; Tsymbal, Evgeny Y; Shen, J; Jesse, Stephen; Kalinin, Sergei V; Baddorf, Arthur P

    2014-07-24

    Physical and electrochemical phenomena at the surfaces of transition metal oxides and their coupling to local functionality remains one of the enigmas of condensed matter physics. Understanding the emergent physical phenomena at surfaces requires the capability to probe the local composition, map order parameter fields and establish their coupling to electronic properties. Here we demonstrate that measuring the sub-30-pm displacements of atoms from high-symmetry positions in the atomically resolved scanning tunnelling microscopy allows the physical order parameter fields to be visualized in real space on the single-atom level. Here, this local crystallographic analysis is applied to the in-situ-grown manganite surfaces. In particular, using direct bond-angle mapping we report direct observation of structural domains on manganite surfaces, and trace their origin to surface-chemistry-induced stabilization of ordered Jahn-Teller displacements. Density functional calculations provide insight into the intriguing interplay between the various degrees of freedom now resolved on the atomic level.

  20. Jahn-Teller distortion and magnetic ordering in layered nickelates

    NASA Astrophysics Data System (ADS)

    Johannes, Michelle; Mazin, Igor; Bernstein, Noam

    2006-03-01

    One of the long-standing challenges in the theory of layered nickelates is that NaNiO2 is antiferromagnetic and has a strong Jahn-Teller induced orbital ordering, while LiNiO2 has none. A variety of hypothesis have been proposed to explain this mystery: a difference in Li/Na ionic radii, differences in the underlying electronic structure, the zero-point motion of Li ions, etc. One of the most viable propositions is that the difference is due to the presence of Na2^+ ions (1% or more) on the Li sites. It remains unclear whether the magnetic interaction of Na2^+ with the in-plane Na3^+ is strong enough to cancel the Li-assisted antiferromagnetic superexchange even for 1% of Na2^+, and what effect it has on orbital ordering. We provide quantitative arguments, based on first principles calculations and atomistic simulations, that spin and orbital orderings are unrelated, and that both are destroyed (the latter in a rather unusual way) by Na2^+ impurities, but for entirely separate reasons.

  1. Crystal structure, ferromagnetostructural behavior and evidence of cooperative Jahn-Teller interactions of the complex [CuL]Cl·H 2O (L= N-glycyl-2(aminomethyl)benzimidazol), synthesized by a novel simple method of peptide bond formation.

    NASA Astrophysics Data System (ADS)

    García-Orozco, Ivan; Tapia-Benavides, Antonio Rafael; Alvarez-Toledano, Cecilio; Toscano, Ruben A.; Ramírez-Rosales, Daniel; Zamorano-Ulloa, Rafael; Reyes-Ortega, Yasmi

    2002-01-01

    [CuL]Cl·H 2O 1 (L= N-glycyl-2(aminomethyl)benzimidazol) compound crystallizes in the orthorhombic space group Pna2 1 with unit cell parameters a=7.140(5) Å, b=17.621(5) Å, c=9.941(5) Å. Its structure shows that the copper(II) ion is tetra coordinated with a square planar geometry. The ligand acts as a tridentate and the chloride ion is the fourth ligand. Symmetry related units stack into helicoidal columns along the ā direction producing weakly bonded strips with dihedral angles of 2.6° between two consecutive molecular planes. UV/VIS spectrum of 1 shows one broad and weak band at 622 nm, characteristic of d-d transitions, indicative of low local Cu(II) symmetry. X band ESR spectra of 1 at 300 and 77 K are axial exchange narrow lines with g∥=2.135 and g⊥=2.028. However, the axial spectrum at 6.4 K shows an increment Δ g∥=0.076(6) and Δ g⊥=0.028(4) which suggests a cooperative Jahn-Teller interactions between complexes via the hydrogen-bonding network. Magnetic susceptibility data at 18-300 K and fitted to the modified Bleany-Bowers equation indicate a weak ferromagnetic coupling with 2J≅+17 cm-1, which is compatible with the helium temperature ESR results and with the helicoidal stacking into columns of the molecules along the a-axis with 78.9° Cu'-Cl'-Cu and 81.2° Cu'-N( 1)-Cu bonds angles. The synthesis is a novel, simple and efficient method: in aqueous conditions and heterogeneous phase with basic copper(II) carbonate, which carries out the formation of the stable peptide bond.

  2. Jahn-Teller and spin-orbit coupling effects in transition-metal trifluorides

    NASA Astrophysics Data System (ADS)

    Mondal, Padmabati; Opalka, Daniel; Poluyanov, Leonid V.; Domcke, Wolfgang

    2011-08-01

    The effects of linear and higher-order Jahn-Teller couplings as well as spin-orbit coupling in orbitally degenerate electronic states of the transition-metal trifluorides MnF 3 and CoF 3 have been systematically explored with multi-configuration ab initio methods. The adiabatic potential-energy surfaces of low-lying 5E' and 5E″ states have been calculated with the CASSCF method. The spin-orbit coupling is described by matrix elements of the Breit-Pauli operator with nonrelativistic CASSCF wave functions. The Jahn-Teller coupling parameters of the Jahn-Teller active in-plane bending and stretching modes have been determined up to sixth order and fourth order, respectively, in the normal-mode expansion. Vibronic spectra have been computed, employing a Jahn-Teller Hamiltonian up to sixth order in the degenerate bending mode and fourth order in the degenerate stretching mode. These results represent the first ab initio study of the dynamical Jahn-Teller effect in transition-metal trifluorides with inclusion of spin-orbit coupling.

  3. Pseudo-Jahn-Teller origin of the low barrier hydrogen bond in N2H7+

    NASA Astrophysics Data System (ADS)

    García-Fernández, P.; García-Canales, L.; García-Lastra, J. M.; Junquera, J.; Moreno, M.; Aramburu, J. A.

    2008-09-01

    The microscopic origin and quantum effects of the low barrier hydrogen bond (LBHB) in the proton-bound ammonia dimer cation N2H7+ were studied by means of ab initio and density-functional theory (DFT) methods. These results were analyzed in the framework of vibronic theory and compared to those obtained for the Zundel cation H5O2+. All geometry optimizations carried out using wavefunction-based methods [Hartree-Fock, second and fourth order Möller-Plesset theory (MP2 and MP4), and quadratic configuration interaction with singles and doubles excitations (QCISD)] lead to an asymmetrical H3N-H+⋯NH3 conformation (C3v symmetry) with a small energy barrier (1.26kcal/mol in MP4 and QCISD calculations) between both equivalent minima. The value of this barrier is underestimated in DFT calculations particularly at the local density approximation level where geometry optimization leads to a symmetric H3N⋯H+⋯NH3 structure (D3d point group). The instability of the symmetric D3d structure is shown to originate from the pseudo-Jahn-Teller mixing of the electronic A1g1 ground state with five low lying excited states of A2u symmetry through the asymmetric α2u vibrational mode. A molecular orbital study of the pseudo-Jahn-Teller coupling has allowed us to discuss the origin of the proton displacement and the LBHB formation in terms of the polarization of the NH3 molecules and the transfer of electronic charge between the proton and the NH3 units (rebonding). The parallel study of the H5O2+ cation, which presents a symmetric single-well structure, allows us to analyze why these similar molecules behave differently with respect to proton transfer. From the vibronic analysis, a unified view of the Rudle-Pimentel three-center four-electron and charge transfer models of LBHBs is given. Finally, the large difference in the N-N distance in the D3d and C3v configurations of N2H7+ indicates a large anharmonic coupling between α2u-α1g modes along the proton

  4. Photoluminescence properties of Jahn-Teller transition-metal ions

    NASA Astrophysics Data System (ADS)

    Sanz-Ortiz, Marta N.; Rodríguez, Fernando

    2009-09-01

    This work investigates the influence of electron-phonon coupling associated with E ⊗e and T ⊗e Jahn-Teller (JT) effect in different transition-metal (TM) ions on de-excitation phenomena through nonradiative multiphonon relaxation, i.e., photoluminescence (PL) quenching. We developed a configurational curve model which is able to predict from the absorption spectrum whether a given JT-TM ion is PL or quenched. The prediction is made on the basis of an adapted Dexter-Klick-Russell parameter for JT systems, defined in terms of spectroscopic parameters through ΛJT=αΔeabs/Eabs, where Δeabs refers to the splitting of the parent octahedral Eg states by the JT distortion in E ⊗e (α =3/4) or T ⊗e (α =1/4), and Eabs is the energy of the first absorption band involving electronic transition between Eg and T2g. We show that PL in any JT-TM ion occurs whenever ΛJT<0.1 or is quenched if ΛJT>0.2. This result is noteworthy since it allows us to establish structural requirements for the JT-TM ion and the host crystal to be PL. Although PL properties of materials containing TM ions depend on a variety of structural factors such as the electronic configuration, the site symmetry, and the crystal field produced by neighboring atoms, the present model achieves this goal through a simple spectroscopic parameter: ΛJT. In this work we correlated the PL properties of different sixfold-coordinated JT systems such as Ti3+, Cu2+, Mn3+, Cr2+, Fe2+, Co3+, and Ni3+ in halides and oxides with ΛJT obtained from their respective absorption spectra. From this analysis we conclude that depending on the nature of the JT coupling and its strength, PL is either strongly favored or quenched in T ⊗e while it is mostly quenched in E ⊗e systems due to the larger JT distortion.

  5. Jahn-Teller effect for short-lived states: Study of the complex potential energy surfaces

    NASA Astrophysics Data System (ADS)

    Feuerbacher, Sven; Cederbaum, Lorenz S.

    2004-07-01

    The Jahn-Teller effect for bound electronic states has been investigated for many decades. In contrast, nothing is known regarding its occurrence for short-lived electronic states. Here we investigate the linear and the quadratic E⊗e Jahn-Teller effect for degenerate resonance states with special regard to the complex potential energy surfaces. We find many new phenomena for both the real and imaginary parts of the potential energy surfaces including additional minima and intersections. Possible simplifications of the equations describing the adiabatic potential energy surfaces are discussed. We also briefly investigate other Jahn-Teller effects in linear approximation. The theoretical concepts are exemplified by calculating ab initio data for the degenerate Π*-type resonance states of the tris(boramethyl)amin anion along two different doubly degenerate vibrational modes.

  6. Angular-overlap calculation of the Jahn-Teller stabilization energie for f-orbital degeneracies

    SciTech Connect

    Warren, K.D.

    1980-03-01

    The angular-overlap model is applied to the calculation of the linear Jahn-Teller coupling constants for f-orbital degeneracies. The MX/sub 6/, O/sub h/, chromophore is treated as representative of the highest symmetry commonly occurring in the lanthanide and actinide series, and it is shown that, even when spin-orbit effects are taken into account, 5f orbital degeneracies may lead to significant Jahn-Teller stabilization energies. The operation of this effect for F/sup 1/ GAMMA/sub 8/ states is considered. 2 tables.

  7. Flattening a puckered cyclohexasilane ring by suppression of the pseudo-Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Pokhodnya, Konstantin; Olson, Christopher; Dai, Xuliang; Schulz, Douglas L.; Boudjouk, Philip; Sergeeva, Alina P.; Boldyrev, Alexander I.

    2011-01-01

    We report the experimental and theoretical characterization of neutral Si6X12 (X = Cl, Br) molecules that contain D3d distorted six-member silicon rings due to a pseudo-Jahn-Teller (PJT) effect. Calculations show that filling the intervenient molecular orbitals with electron pairs of adduct suppresses the PJT effect in Si6X12, with the Si6 ring becoming planar (D6h) upon complex formation. The stabilizing role of electrostatic and covalent interactions between positively charged silicon atoms and chlorine atoms of the subject [Si6Cl14]2- dianionic complexes is discussed. The reaction of Si6Cl12 with a Lewis base (e.g., Cl-) to give planar [Si6Cl14]2- dianionic complexes presents an experimental proof that suppression of the PJT effect is an effective strategy in restoring high Si6 ring symmetry. Additionally, the proposed pathway for the PJT suppression has been proved by the synthesis and characterization of novel compounds containing planar Si6 ring, namely, [nBu4N]2[Si6Cl12I2], [nBu4N]2[Si6Br14], and [nBu4N]2[Si6Br12I2]. This work represents the first demonstration that PJT effect suppression is useful in the rational design of materials with novel properties.

  8. Jahn Teller effect of cations in water: The cupric ion in water

    SciTech Connect

    Halley, J.W.; Wang, X.R.; Curtiss, L.A.

    1993-02-01

    We report a molecular dynamics model for the Jahn Teller effect in the solvation shell of a cation in solution in an aqueous liquid. We apply the model to the cupric ion and compare results with results of neutron scattering experiments on copper chlorate solutions. We conclude that the original interpretation of the experiments in terms of a Jan Teller effect may require modification.

  9. Jahn Teller effect of cations in water: The cupric ion in water

    SciTech Connect

    Halley, J.W. . School of Physics and Astronomy); Wang, X.R. . Dept. of Physics); Curtiss, L.A. )

    1993-02-01

    We report a molecular dynamics model for the Jahn Teller effect in the solvation shell of a cation in solution in an aqueous liquid. We apply the model to the cupric ion and compare results with results of neutron scattering experiments on copper chlorate solutions. We conclude that the original interpretation of the experiments in terms of a Jan Teller effect may require modification.

  10. Seams near seams: the Jahn-Teller effect in the 1E" state of N3+.

    PubMed

    Dillon, Joseph J; Yarkony, David R

    2007-03-28

    The (1)E(") electronic state of cyclic N(3) (+) arising from the singly excited electron configuration e('3)e(") is studied using multireference configuration interaction wave functions and a quadratic Jahn-Teller Hamiltonian determined from those calculations. It is shown that these two states have both a symmetry-required seam of conical intersections at D(3h) geometries and three proximal symmetry equivalent C(2v) seams, located on a circle with radius rho(0) from the D(3h) intersection. rho(0), a function of Q(s), the breathing mode, is quite small but only attains a value of zero at Q(s) (crit)=1.252 A, resulting in a confluence or intersection node of the three C(2v) seams with the D(3h) seam. At this point only, g= parallelg(Q(s)) parallel, the norm of half the energy difference gradient, the linear Jahn-Teller term, vanishes and the intersection is of the Renner-Teller type. The close proximity of the previously unreported C(2v) seams to the D(3h) seam over the range of Q(s) considered is a consequence of the small values of g, compared to the quadratic Jahn-Teller term. The present analysis has important implications in the study of Jahn-Teller effects in ring systems and provides insight into a recent report that characterized this D(3h) seam as a Renner-Teller or glancing intersection.

  11. Interplay Between Structural, Jahn-Teller, and Magnetic States of Slightly Doped Lanthanum Manganites

    NASA Astrophysics Data System (ADS)

    Golenishchev-Kutuzov, V. A.; Golenishchev-Kutuzov, A. V.; Kalimullin, R. I.; Semennikov, A. V.

    2016-12-01

    By combining the results of elastic moduli, electrical resistivity, and magnetization measurements for La_{1-x}SrxMnO3 ( x = 0.125, x = 0.15, and x = 0.175), we have constructed a phase diagram that describes the structural, magnetic, transport properties and the relationships among them as a function of the composition and temperature (140-340 K). The local, intermediate, and cooperative Jahn-Teller distortions of the octahedral structural units MnO6 have been studied. It is common for these distortions to be observed using probes of intermediate structures (domains or super-cells), but they are absent in the averaged crystallographic structure. In the cooperative Jahn-Teller distorted phase, the macroscopic sample length is temperature dependent. We presume that the structural transitions from the cooperative Jahn-Teller phase to the charge ordering phase at low temperatures (150 and 180 K at x = 0.125 and x = 0.15) are due to the increase in the spontaneous magnetization with the conservation of the local deformations of separate octahedra. The agreement between the types of the orbital ordering and the local, intermediate, and Jahn-Teller cooperative distortions of octahedra was established.

  12. The vibrational Jahn-Teller effect in E⊗e systems

    NASA Astrophysics Data System (ADS)

    Thapaliya, Bishnu P.; Dawadi, Mahesh B.; Ziegler, Christopher; Perry, David S.

    2015-10-01

    The Jahn-Teller theorem is applied in the vibrational context where degenerate high-frequency vibrational states (E) are considered as adiabatic functions of low-frequency vibrational coordinates (e). For CH3CN and Cr(C6H6)(CO)3, the global minimum of the non-degenerate electronic potential energy surface occurs at the C3v geometry, but in CH3OH, the equilibrium geometry is far from the C3v reference geometry. In the former cases, the computed spontaneous Jahn-Teller distortion is exceptionally small. In methanol, the vibrational Jahn-Teller interaction results in the splitting of the degenerate E-type CH stretch into what have been traditionally assigned as the distinct ν2 and ν9 vibrational bands. The ab initio vibrational frequencies are fit precisely by a two-state high-order Jahn-Teller Hamiltonian (Viel and Eisfeld, 2004). The presence of vibrational conical intersections, including 7 for CH3OH, has implications for spectroscopy, for geometric phase, and for ultrafast localized non-adiabatic energy transfer.

  13. Model study of coexistence of Jahn-Teller distortion, antiferromagnetism and superconductivity in iron pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Pradhan, B.; Goi, S. K.; Behera, Srikanta; Parida, P. K.; Mishra, R. N.

    2016-12-01

    We have proposed a theoretical model for the coexistence of superconductivity (SC), antiferromagnetism (AFM) and Jahn-Teller (JT) effect in the mean field approximation for iron based superconductors. The model is solved by using Zubarev's double-time Green's function technique to get their selfconsistent gap equations. Then these gap equations are solved numerically.

  14. Jahn-Teller / Kondo Interplay in a Three-Terminal Quantum Dot

    NASA Astrophysics Data System (ADS)

    Toonen, R. C.; Qin, H.; Huettel, A. K.; Goswami, S.; van der Weide, D. W.; Eberl, K.; Blick, R. H.

    2006-03-01

    The Jahn-Teller effect is the spontaneous geometric distortion of a nonlinear molecular entity. The Kondo effect, an expression of asymptotic freedom, arises from the hybridization between localized states of a magnetic impurity and the itinerant states of its environment. The interplay of these two phenomena has attracted the attention of theorists studying the growth and interactions of heavy-fermion systems. Because of the technical difficulties associated with probing isolated impurities in bulk materials, this composite effect has remained experimentally unexplored. We have investigated co-tunneling transport phenomena in a three-terminal quantum dot with triangular symmetry. Our measurements of anomalous spectral signatures reveal interplay between the Jahn-Teller and Kondo effects. This discovery suggests a means of controlling the correlation of spatially separated pairs of entangled electrons (EPR pairs)---a necessary condition for the physical realization of a quantum computer (DiVincenzo's 7th requirement).

  15. Time-dependent Jahn-Teller problem: phonon-induced relaxation through conical intersection.

    PubMed

    Pae, Kaja; Hizhnyakov, Vladimir

    2014-12-21

    A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E⊗e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.

  16. The electronic spectrum of SiH4: Jahn-Teller Rydberg series

    NASA Astrophysics Data System (ADS)

    Velasco, A. M.; Lavín, C.; Sánchez de Merás, A. M. J.; Sánchez Marín, J.

    2011-12-01

    The aim of the present theoretical work is to provide data necessary for a better understanding of the electronic spectrum of the silane molecule, which is affected by the Jahn-Teller effect. By selecting an adequate distorted C2v geometry of SiH4, the three lower Koopmans ionization potentials are evaluated with the equation of motion coupled cluster of singles and doubles method. Vertical excitation energies for the different Rydberg series converging to the three Jahn-Teller components are inferred from ab initio coupled cluster linear response calculations. Absorption oscillator strengths for dipole-allowed electronic transitions are also determined with the molecular-adapted quantum defect orbital methodology. Predictions of new spectroscopic data on SiH4 are reported.

  17. Time-dependent Jahn-Teller problem: Phonon-induced relaxation through conical intersection

    SciTech Connect

    Pae, Kaja Hizhnyakov, Vladimir

    2014-12-21

    A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E⊗e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.

  18. A variational treatment of some excited e ⊗ ɛ jahn-teller states

    NASA Astrophysics Data System (ADS)

    Ballhausen, C. J.

    1982-12-01

    Using a simple variational treatment for the first-order Jahn-Teller coupling, E ⊗ ɛ, all the pairs of states for which i=( v+ 1/2), v=0,1,2 … are to first order vertically displaced in energy with an energy difference of one vibrational quantum. An analytical expression is given for the reduced matrix element of Child and Longuet-Higgins.

  19. The Quantization of the E ⊗ e Jahn-Teller Hamiltonian.

    PubMed

    Arvanitidis, Athanasios G; Vandaele, Eva R J; Szopa, Marek; Ceulemans, Arnout

    2017-09-18

    The E ⊗ e Jahn-Teller Hamiltonian in the Bargmann-Fock representation gives rise to a system of two coupled first-order differential equations in the complex field, which may be rewritten in the Birkhoff standard form. General leapfrog recurrence relations are derived, from which the quantized solutions of these equations can be obtained. The results are compared to the analogous quantization scheme for the Rabi Hamiltonian.

  20. Jahn-Teller effects in transition-metal compounds with small charge-transfer energy

    NASA Astrophysics Data System (ADS)

    Mizokawa, Takashi

    2013-04-01

    We have studied Jahn-Teller effects in Cs2Au2Br6, ACu3Co4O12(A=Ca or Y), and IrTe2 in which the ligand p-to-transition-metal d charge-transfer energy is small or negative. The Au+/Au3+ charge disproportionation of Cs2Au2Br6 manifests in Au 4f photoemission spectra. In Cs2Au2Br6 with negative Δ and intermediate U, the charge disproportionation can be described using effective d orbitals constructed from the Au 5d and Br 4p orbitals and is stabilized by the Jahn-Teller distortion of the Au3+ site with low-spin d8 configuration. In ACu3Co4O12, Δs for Cu3+ and Co4+ are negative and Us are very large. The Zhang-Rice picture is valid to describe the electronic state, and the valence change from Cu2+/Co4+ to Cu3+/Co3+ can be viewed as the O 2p hole transfer from Co to Cu or d9 + d6L → d9L + d6. In IrTe2, both Δ and U are small and the Ir 5d and Te 5p electrons are itinerant to form the multi-band Fermi surfaces. The ideas of band Jahn-Teller transition and Peierls transition are useful to describe the structural instabilities.

  1. PREFACE: XXIst International Symposium on the Jahn-Teller Effect 2012

    NASA Astrophysics Data System (ADS)

    Koizumi, Hiroyasu

    2013-04-01

    (The PDF contains the full conference program, the list of sponsors and the conference poster.) The 21st International Symposium on the Jahn-Teller effect was held at the University of Tsukuba, Japan, from 26-31 August 2012. People from 23 different countries participated and the number of registered participants was 118. In this symposium, the phrase 'Jahn-Teller effect' was taken to have a rather broad meaning. We discussed the Jahn-Teller and pseudo Jahn-Teller distortions. We also discussed general vibronic problems, and the problems associated with the conical intersections of the potential energy surfaces. As is indicated in the subtitle of the present symposium, 'Physics and Chemistry of Symmetry Breaking', a number of different topics concerning symmetry breaking were also extensively discussed. In particular, we had many discussions on magnetism, ferroelectricity, and superconductivity. A subtle but important problem that was dealt with was the appearance of multi-valuedness in the use of multi-component wave functions. In the Jahn-Teller problems, we almost always use the multi-component wave functions, thus, the knowledge of the proper handling of multi-valuedness is very important. Digital computers are not good at dealing with multi-valuedness, but we need to somehow handle it in our calculations. A very well known example of successful handling is found in the problem of the molecular system with the conical intersection: we cannot obtain the solution that satisfies the single-valuedness of wave functions (SVWF) just using the potential energy surface generated by a package program, and solving the Schrödinger equation with the quantum Hamiltonian constructed from the classical counterpart by replacing the classical variables with the corresponding operators; however, if a gauge potential is included and the double-valuedness of the electronic wave functions around the conical intersections is taken into account, the solution that satisfies the SVWF

  2. The Jahn Teller and pseudo-Jahn Teller effect in the dark Ãstate of the nitrate radical NO3

    NASA Astrophysics Data System (ADS)

    Takematsu, Kana; Robichaud, David; Okumura, Mitchio; Stanton, John

    2007-03-01

    Despite its apparent simple molecular structure, the lowest electronic states of the nitrate radical NO3 remain poorly understood. In particular, the three lowest states of the radical provide a benchmark for testing models of the Jahn-Teller (JT) and pseudo-JT effects. The dark Ãstate of NO3 undergoes strong JT distortion, suggesting that models with only linear and quadratic vibronic couplings are inadequate. We present cavity ringdown (CRD) and integrated cavity output (ICOS) spectra of the forbidden A&˜circ; ^2E"<-X&˜circ; ^2A2' transition (preliminary report in Deev, et. al. J.Chem. Phys., 2005. 122:224305) and compare them to a simulation based on a model Hamiltonian developed by Koppel, Domcke and Cederbaum that incorporates both JT and PJT couplings. New insights into the pseudo-JT effect among the lowest states are gained by examination of intensity-borrowing mechanisms for the observed vibronic bands.

  3. A Genuine Jahn-Teller System with Compressed Geometry and Quantum Effects Originating from Zero-Point Motion.

    PubMed

    Aramburu, José Antonio; García-Fernández, Pablo; García-Lastra, Juan María; Moreno, Miguel

    2016-07-18

    First-principle calculations together with analysis of the experimental data found for 3d(9) and 3d(7) ions in cubic oxides proved that the center found in irradiated CaO:Ni(2+) corresponds to Ni(+) under a static Jahn-Teller effect displaying a compressed equilibrium geometry. It was also shown that the anomalous positive g∥ shift (g∥ -g0 =0.065) measured at T=20 K obeys the superposition of the |3 z(2) -r(2) ⟩ and |x(2) -y(2) ⟩ states driven by quantum effects associated with the zero-point motion, a mechanism first put forward by O'Brien for static Jahn-Teller systems and later extended by Ham to the dynamic Jahn-Teller case. To our knowledge, this is the first genuine Jahn-Teller system (i.e. in which exact degeneracy exists at the high-symmetry configuration) exhibiting a compressed equilibrium geometry for which large quantum effects allow experimental observation of the effect predicted by O'Brien. Analysis of the calculated energy barriers for different Jahn-Teller systems allowed us to explain the origin of the compressed geometry observed for CaO:Ni(+) . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. First-principles study of the dynamic Jahn-Teller distortion of the neutral vacancy in diamond

    NASA Astrophysics Data System (ADS)

    Prentice, Joseph C. A.; Monserrat, Bartomeu; Needs, R. J.

    2017-01-01

    First-principles density functional theory methods are used to investigate the structure, energetics, and vibrational motions of the neutral vacancy defect in diamond. The measured optical absorption spectrum demonstrates that the tetrahedral Td point group symmetry of pristine diamond is maintained when a vacancy defect is present. This is shown to arise from the presence of a dynamic Jahn-Teller distortion that is stabilized by large vibrational anharmonicity. Our calculations further demonstrate that the dynamic Jahn-Teller-distorted structure of Td symmetry is lower in energy than the static Jahn-Teller distorted tetragonal D2 d vacancy defect, in agreement with experimental observations. The tetrahedral vacancy structure becomes more stable with respect to the tetragonal structure by increasing temperature. The large anharmonicity arises mainly from quartic vibrations, and is associated with a saddle point of the Born-Oppenheimer surface and a minimum in the free energy. This study demonstrates that the behavior of Jahn-Teller distortions of point defects can be calculated accurately using anharmonic vibrational methods. Our work will open the way for first-principles treatments of dynamic Jahn-Teller systems in condensed matter.

  5. Dopant-induced stabilization of rhombohedral LiMn O2 against Jahn-Teller distortion

    NASA Astrophysics Data System (ADS)

    Prasad, R.; Benedek, R.; Thackeray, M. M.

    2005-04-01

    Dopants introduced into layered LiMnO2 , a candidate cathode material for lithium batteries, tend to suppress the Jahn-Teller-effect-driven monoclinic distortion (symmetry C2/m ) in favor of the layered rhombohedral structure (R3¯m) , which has superior Li insertion/extraction cycling properties. First-principles calculations, within the Local-Spin-Density-Approximation Generalized-Gradient-Approximation (LSDA-GGA) framework, implemented in the VASP code, are performed for 3d transition-metal, as well as Mg, Zn, Al, and N dopants, in order to assess their relative effectiveness in stabilizing the R3¯m symmetry. At the concentration x=0.25 , the selected cation dopants (with the exception of Co and Fe) are found to adopt the same oxidation state (divalent or trivalent) in both monoclinic and rhombohedral structures. Transition metals earlier than Fe are trivalent, whereas those later than Co are divalent. Co in monoclinic LiMnO2 exhibits (stable) trivalent and (metastable) divalent states that are only narrowly different in energy. Fe is trivalent in the monoclinic structure, but is mixed valent in the rhombohedral structure. Divalent dopants (which oxidize a neighboring Mn to the [non-Jahn-Teller-active] 4+ oxidation state) promote rhombohedral structure stabilization to a greater extent than trivalent dopants. Within the class of divalent dopants, the filled shell systems Mg and Zn are more effective than those with partially filled eg shells. Within the class of trivalent dopants, those with partially filled t2g shells are more effective than those with filled or empty shells. Breathing mode (Q1) and Jahn-Teller active ( Q2 , Q3 ) phonon coordinates of transition metal octahedra are analyzed.

  6. A Practical Computational Approach to Study Molecular Instability Using the Pseudo-Jahn-Teller Effect.

    PubMed

    García-Fernández, Pablo; Aramburu, Jose Antonio; Moreno, Miguel; Zlatar, Matija; Gruden-Pavlović, Maja

    2014-04-08

    Vibronic coupling theory shows that the cause for spontaneous instability in systems presenting a nondegenerate ground state is the so-called pseudo-Jahn-Teller effect, and thus its study can be extremely helpful to understand the structure of many molecules. While this theory, based on the mixing of the ground and excited states with a distortion, has been long studied, there are two obscure points that we try to clarify in the present work. First, the operators involved in both the vibronic and nonvibronic parts of the force constant take only into account electron-nuclear and nuclear-nuclear interactions, apparently leaving electron-electron repulsions and the electron's kinetic energy out of the chemical picture. Second, a fully quantitative computational appraisal of this effect has been up to now problematic. Here, we present a reformulation of the pseudo-Jahn-Teller theory that explicitly shows the contributions of all operators in the molecular Hamiltonian and allows connecting the results obtained with this model to other chemical theories relating electron distribution and geometry. Moreover, we develop a practical approach based on Hartree-Fock and density functional theory that allows quantification of the pseudo-Jahn-Teller effect. We demonstrate the usefulness of our method studying the pyramidal distortion in ammonia and its absence in borane, revealing the strong importance of the kinetic energy of the electrons in the lowest a2″ orbital to trigger this instability. The present tool opens a window for exploring in detail the actual microscopic origin of structural instabilities in molecules and solids.

  7. Impurities in noncubic crystals: stabilization mechanisms for Jahn-Teller ions in layered perovskites.

    PubMed

    García-Lastra, J M; Aramburu, J A; Barriuso, M T; Moreno, M

    2004-11-26

    Mechanisms responsible for the local geometry around Jahn-Teller impurities in K2NiF4 type lattices are shown to be different from those generating the warping in cubic crystals. The present density functional theory calculations reveal that the elastic anisotropy of the host lattice (visible for closed shell impurities) and the electric field created by the rest of lattice ions upon active electrons make it possible to have d(9) ions in an elongated geometry but with a A(1g) ground state. The puzzling difference between equilibrium geometries for Cu2+ and Ni+ in layered perovskites can reasonably be understood.

  8. Competing Jahn-Teller distortions and ferrimagnetic ordering in the geometrically frustrated system N i1 -xC uxC r2O4

    NASA Astrophysics Data System (ADS)

    Reehuis, M.; Tovar, M.; Többens, D. M.; Pattison, P.; Hoser, A.; Lake, B.

    2015-01-01

    with a disordered spin-liquid-like or a reentrant-spin-glass-like state. This paper provides insight into the interplay between the Jahn-Teller effect, geometrical frustration, and long-range magnetic order in these complex systems.

  9. Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of hexafluorobenzene: The Jahn-Teller effect and vibrational analysis

    NASA Astrophysics Data System (ADS)

    Kwon, Chan Ho; Kim, Myung Soo

    2004-06-01

    One-photon mass-analyzed threshold ionization (MATI) spectrum of hexafluorobenzene was obtained by using vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The ionization energy of hexafluorobenzene determined from the position of the 0-0 band was 9.9108±0.0006 eV. To aid the spectral analysis, the Jahn-Teller coupling parameters for four e2g modes of C6F6+ in the ground electronic state were calculated from the topographical data of the potential energy surface obtained at the density functional theory (DFT) level. These were used in the initial calculation of the energies of the Jahn-Teller states and upgraded through the multimode fit to the experimental data. Excellent agreement between the experimental and calculated frequencies was achieved. The vibrations which are not linear Jahn-Teller active were observed and could be assigned by referring to the frequencies obtained at the DFT level.

  10. Stability of Jahn-Teller distortion ordering in LaM n1 -xS cxO3

    NASA Astrophysics Data System (ADS)

    Cuartero, V.; Blasco, J.; Subías, G.; García, J.; Meneghini, C.; Aquilanti, G.

    2015-09-01

    We have investigated the role of M n3 + Jahn-Teller distortion in driving ferromagnetism in the LaM n1 -xS cxO3 series. The replacement of Mn by Sc in LaMn O3 decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the LaSc O3 sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in LaMn O3 into a nearly regular one in LaSc O3 . Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc K edges reveal the stability of both Jahn-Teller distorted Mn O6 octahedron and nearly regular Sc O6 octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted Mn O6 octahedra spatially ordered as in LaMn O3 and nearly regular Sc O6 octahedra. This result contrasts with the pseudocubic phase and the appearance of regular Mn O6 octahedra in LaM n1 -xG axO3 for x >0.5 . Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the M n3 + atom is allocated. Besides, a ferromagnetic ground state is observed for x >0.5 in both series independently of the presence (or not) of Jahn-Teller distortions around M n3 + , which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in LaM n1 -xBxO3 (B =Sc or Ga) .

  11. Effect of Jahn-Teller distortion on the short range magnetic order in copper ferrite

    NASA Astrophysics Data System (ADS)

    Abdellatif, M. H.; Innocenti, Claudia; Liakos, Ioannis; Scarpellini, Alice; Marras, Sergio; Salerno, Marco

    2017-02-01

    Copper ferrite of spinel crystal structure was synthesized in the form of nano-particles using citrate-gel auto-combustion method. The sample morphology and composition were identified using scanning electron microscopy, X-ray diffraction, and X-ray spectroscopy. The latter technique reveals an inverse spinel structure with Jahn-Teller tetragonal distortion. The static magnetization was measured using vibrating sample magnetometer. Magnetic force microscopy was used in combination with the magnetization data to demonstrate the finite size effect of the magnetic spins and their casting behavior due to the introduction of copper ions in the tetrahedral magnetic sub-lattices, which results in tetragonal distorting the spinel structure of the copper ferrite. The magnetic properties of materials are a result of the collective behavior of the magnetic spins, and magnetic force microscopy can probe the collective behavior of the magnetic spins in copper ferrite, yet providing a sufficient resolution to map the effects below the micrometer size scale, such as the magnetic spin canting. A theoretical study was done to clarify the finite size effect of Jahn-Teller distortion on the magnetic properties of the material. When the particles are in the nano-scale, below the single domain size, their magnetic properties are very sensitive to their size change.

  12. Dynamical Jahn-Teller effect and Berry phase in positively charged fullerenes: Basic considerations

    NASA Astrophysics Data System (ADS)

    de Los Rios, Paolo; Manini, Nicola; Tosatti, Erio

    1996-09-01

    We study the Jahn-Teller effect of positive fullerene ions 2C+60 and 1C2+60. The aim is to discover if this case, in analogy with the negative ion, possesses a Berry phase or not, and what are the consequences on dynamical Jahn-Teller quantization. Working in the linear and spherical approximation, we find no Berry phase in 1C2+60, and presence/absence of Berry phase for coupling of one L=2 hole to an L=4/L=2 vibration. We study in particular the special equal-coupling case (g2=g4), which is reduced to the motion of a particle on a five-dimensional sphere. In the icosahedral molecule, the final outcome assesses the presence and/or absence of a Berry phase of π for the hu hole coupled to Gg/Hh vibrations. Some qualitative consequences on ground- state symmetry, low-lying excitations, and electron emission from C60 are spelled out.

  13. Medium effect on the Jahn-Teller distortions of the tetramethylallene radical cation

    SciTech Connect

    Qin, X.Z.; Trifunac, A.D. )

    1991-08-22

    The Jahn-Teller distortion of the delocalized {pi}-radical cation tetramethylallene{sm bullet}{sup +} (TMA{sm bullet}{sup +}) was found to be medium dependent. TMA{sup {sm bullet}} was studied in liquid hydrocarbons (195-295 K) by time-resolved fluorescence-detected magnetic resonance (FDMR) spectroscopy and in freon matrices (80-160 K) and zeolite Na-Y (80-298 K) by EPR spectroscopy. The observed coupling constants for the twelve protons of the four methyl groups of the radical cation are 11.3, 8.1, and 14.4 G, respectively. AM1 and INDO calculations suggest that different coupling constants can be explained by different twist angles in TMA{sup {sm bullet}+}. It is suggested that interaction between TMA{sup {sm bullet}+} and the chlorine or fluorine atoms of freon matrices or between TMA{sup {sm bullet}+} and the sodium atoms of the zeolite can influence the charge and spin distribution in the radical cation so that the structures that differ from that found in hydrocarbon solution can be stabilized. This is the first example of a Jahn-Teller-active radical cation that has been studied in several media.

  14. Rotationally resolved photoelectron spectroscopic study of the Jahn-Teller effect in allene

    NASA Astrophysics Data System (ADS)

    Schulenburg, A. M.; Merkt, F.

    2009-01-01

    The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of allene (C3H4) and perdeuterated allene have been recorded from the first adiabatic ionization energy up to 2200 cm-1 of internal energy in the cations at a resolution sufficient to observe the full rotational structure. The intensity distributions in the spectra are dominated by vibrational progressions in the torsional mode, which were analyzed in the realm of a two-dimensional model of the E ⊗(b1⊕b2) Jahn-Teller effect in the allene cation [C. Woywod and W. Domcke, Chem. Phys. 162, 349 (1992)]. Whereas the rotational structure of the transitions to the lowest torsional levels (00 and 41) are regular and can be qualitatively analyzed in terms of a simple orbital ionization model, the rotational structure of the spectra of the 42 and 43 levels are strongly perturbed. The photoelectron spectrum of C3H4 also reveals several weak vibrational bands in the immediate vicinity of these levels that are indicative of (ro)vibronic perturbations. A slight broadening of the transitions to the 41 levels compared to that of the vibronic ground state and the increase of the number of sharp features in the rotational structure of the spectrum of the 42 level point at the importance of large-amplitude motions not considered in previous treatments of the Jahn-Teller effect in the allene cation.

  15. Rotational Parameters from Vibronic Eigenfunctions of Jahn-Teller Active Molecules

    NASA Astrophysics Data System (ADS)

    Garner, Scott M.; Miller, Terry A.

    2017-06-01

    The structure in rotational spectra of many free radical molecules is complicated by Jahn-Teller distortions. Understanding the magnitudes of these distortions is vital to determining the equilibrium geometric structure and details of potential energy surfaces predicted from electronic structure calculations. For example, in the recently studied {\\widetilde{A}^2E^{''} } state of the NO_3 radical, the magnitudes of distortions are yet to be well understood as results from experimental spectroscopic studies of its vibrational and rotational structure disagree with results from electronic structure calculations of the potential energy surface. By fitting either vibrationally resolved spectra or vibronic levels determined by a calculated potential energy surface, we obtain vibronic eigenfunctions for the system as linear combinations of basis functions from products of harmonic oscillators and the degenerate components of the electronic state. Using these vibronic eigenfunctions we are able to predict parameters in the rotational Hamiltonian such as the Watson Jahn-Teller distortion term, h_1, and compare with the results from the analysis of rotational experiments.

  16. Jahn-Teller assisted polaronic hole hopping as a charge transport mechanism in CuO nanograins

    NASA Astrophysics Data System (ADS)

    Younas, M.; Nadeem, M.; Idrees, M.; Akhtar, M. J.

    2012-04-01

    Impedance spectroscopy has been employed to investigate the dielectric and electric transport phenomena in sol-gel synthesized CuO nanograins. Semiconducting features of the grains and grain boundaries have been endorsed to the thermal activation of the localized charge carriers. On cooling below 303 K, a transition from Jahn-Teller polaron hopping mechanism to the Mott's variable range hopping mechanism has been observed owing to random potential fluctuations among localized sites. Activation energies for conduction and relaxation processes at grain boundaries provide strong signatures for the involvement of Jahn-Teller adiabatic small polarons as a charge transport mechanism in CuO nanograins.

  17. Jahn-Teller stabilization energies for ZnS:Mn and ZnSe:Mn excited states obtained by the angular overlap model

    NASA Astrophysics Data System (ADS)

    Stavrev, K. K.; Kynev, K. D.; Nikolov, G. St.

    1988-06-01

    Linear Jahn-Teller coupling constants are obtained by the angular overlap model. A comparison with the data published recently [Parrot et al., J. Chem. Phys. 87, 1463 (1987)] is made in order to demonstrate the considerable improvement in the calculated Jahn-Teller coefficients when the parameters of the angular overlap model are extracted from a spectral analysis of the systems under consideration.

  18. Jahn-Teller Coupling in the Methoxy Radical: Insights Into the Infrared Spectrum of Molecules with Vibronic Coupling

    NASA Astrophysics Data System (ADS)

    Johnson, Britta; Sibert, Edwin

    2015-06-01

    The ground tilde{X}^2E vibrations of the methoxy radical have intrigued both experimentalists and theorists alike due to the presence of a conical intersection at the C3v molecular geometry. This conical intersection causes methoxy's vibrational spectrum to be strongly influenced by Jahn-Teller coupling which leads to large amplitude vibrations and extensive mixing of the two lowest electronic states. The spectrum is further complicated due to spin-orbit and Fermi couplings. The standard diabatic normal mode quantum numbers are poor labels due to this vibronic mixing. Using the potential energy force field and calculated spectra of the methoxy radical by Nagesh and Sibert^1 as a starting point, we look to develop a method for assigning states to a spectrum with vibronic coupling. We simplify the analysis by considering only the lowest two e modes of methoxy (the rock and the bend). When we include first-order Jahn-Teller coupling between these two modes in a new zero-order Hamiltonian, we are able to use an expanded version of the linear Jahn-Teller quantum numbers to assign the states.^2 This zeroth order representation is nontrivial; therefore, we study the properties of its eigenstates using correlation diagrams with respect to the strength of the Jahn-Teller coupling constant. [^1] Nagesh, J.; Sibert, E. L. J. Phys. Chem. A 2012, 116, 3846-3855. [^2] Barckholtz, T. A.; Miller, T. A. Int. Revs. in Phys. Chem. 1998, 17, 435-524.

  19. Orbital Ordering in Frustrated Jahn-Teller Systems with 90° Exchange

    NASA Astrophysics Data System (ADS)

    Mostovoy, M. V.; Khomskii, D. I.

    2002-11-01

    We show that superexchange interactions in frustrated Jahn-Teller systems with transition metal ions connected by the 90° metal-oxygen-metal bonds (e.g., NaNiO2, LiNiO2, and ZnMn2O4) are much different from those in materials with the 180° bonds. In the 90°-exchange systems spins and orbitals are decoupled: the spin exchange is much weaker than the orbital one and it is ferromagnetic for all orbital states. Though the mean-field orbital ground state is strongly degenerate, quantum orbital fluctuations select particular ferro-orbital states. We explain the orbital and magnetic ordering observed in NaNiO2 and show that LiNiO2 is not a spin-orbital liquid.

  20. Orbital ordering in frustrated Jahn-Teller systems with 90 degrees exchange.

    PubMed

    Mostovoy, M V; Khomskii, D I

    2002-11-25

    We show that superexchange interactions in frustrated Jahn-Teller systems with transition metal ions connected by the 90 degrees metal-oxygen-metal bonds (e.g., NaNiO2, LiNiO2, and ZnMn2O4) are much different from those in materials with the 180 degrees bonds. In the 90 degrees -exchange systems spins and orbitals are decoupled: the spin exchange is much weaker than the orbital one and it is ferromagnetic for all orbital states. Though the mean-field orbital ground state is strongly degenerate, quantum orbital fluctuations select particular ferro-orbital states. We explain the orbital and magnetic ordering observed in NaNiO2 and show that LiNiO2 is not a spin-orbital liquid.

  1. Nonadiabaticity in a Jahn-Teller system probed by absorption and resonance Raman scattering.

    PubMed

    Pae, K; Hizhnyakov, V

    2013-03-14

    A theory of absorption and resonance Raman scattering of impurity centers in crystals with E⊗e-type Jahn-Teller effect in the excited state is presented. The vibronic interaction with non-totally symmetric local or pseudolocal modes and with a continuum of bath modes (phonons) is considered. A number of specific quantum effects, such as the nonadiabaticity-induced enhancement of the Raman scattering at high-energy excitation, the size effect of the final state, the interference of different channels of scattering, the Fermi resonances in the conical intersection, and others, were shown to become apparent in the calculated spectra. The vibronic interaction with phonons essentially determines the structure of the spectra.

  2. Proposal for observing dynamic Jahn-Teller effect by single solid-state defects

    NASA Astrophysics Data System (ADS)

    Xiao, Xing; Zhao, Nan

    2016-10-01

    The Jahn-Teller effect (JTE) widely exists in polyatomic systems including organic molecules, nano-magnets, and solid-state defects. Detecting the JTE at single-molecule level can provide unique properties about the detected individual object. However, such measurements are challenging because of the weak signals associated with a single quantum object. Here, we propose that the dynamic JTE of single defects in solids can be observed with nearby quantum sensors. With numerical simulations, we demonstrate the real-time monitoring of JT axis jumps between different stable configurations of single substitutional nitrogen defect centers (P1 centers) in diamond. This is achieved by measuring the spin coherence of a single nitrogen-vacancy (NV) center near the P1 center with the double electron-electron resonance technique. Our work extends the ability of NV center as a quantum probe to sense the rich physics in various electron-vibrational coupled systems.

  3. Jahn-Teller versus quantum effects in the spin-orbital material LuVO3

    DOE PAGES

    Skoulatos, M.; Toth, S.; Roessli, B.; ...

    2015-04-13

    In this article, we report on combined neutron and resonant x-ray scattering results, identifying the nature of the spin-orbital ground state and magnetic excitations in LuVO3 as driven by the orbital parameter. In particular, we distinguish between models based on orbital-Peierls dimerization, taken as a signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor of the latter. In order to solve this long-standing puzzle, polarized neutron beams were employed as a prerequisite in order to solve details of the magnetic structure, which allowed quantitative intensity analysis of extended magnetic-excitation data sets. The results of this detailed study enabledmore » us to draw definite conclusions about the classical versus quantum behavior of orbitals in this system and to discard the previous claims about quantum effects dominating the orbital physics of LuVO3 and similar systems.« less

  4. Pseudo Jahn-Teller versus Renner-Teller effects in the instability of linear molecules

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Bersuker, Isaac B.; Zou, Wenli; Boggs, James E.

    2010-11-01

    It is shown that for linear molecules in degenerate states the Renner-Teller effect (RTE) is not the only (and not even the main) source of bending instability; the pseudo Jahn-Teller effect (PJTE) is most important in the bending. Numerical estimates demonstrate that π- σ interactions with a limited number of excited states does not solve the problem. For a Π term with two perturbations a general formula of combined RTE plus PJTE is derived which does not involve excited states explicitly. It shows that the PJTE lowers the curvature of the energy surface in the direction of bending and contributes also to its splitting. By means of ab initio calculations the contributions of the RTE and PJTE to the bending instability are estimated for HBF, HNN, HCO, BH 2, NH 2, and AlH 2 molecules. The PJTE influence is significantly larger than the RTE one. This result may be similarly important for nonlinear systems.

  5. Jahn-Teller coupling and magnetic ground state in vanadium spinels^1

    NASA Astrophysics Data System (ADS)

    Chern, Gia-Wei; Tchernyshyov, Oleg

    2008-03-01

    The interplay of orbital, lattice, and spin degrees of freedom in vanadium spinels has attracted much interest among researchers. The V^3+ ion has two electrons occupying three degenerate t2g orbitals and is thus Jahn-Teller active. It also has a total spin S=1 in accordance with Hund's rules. Moreover, the V^3+ ions sitting on the B-site of spinel form a pyrochlore lattice, the interactions between these localized spin and orbital degrees of freedom are thus geometrically frustrated [1]. Here we present a theoretical model for the ground states of vanadium spinels. We view all of the vanadates (Cd, Zn, Mg on the one hand and Mn on the other) within the same model in which the influence of Mn is simulated by a magnetic field. In the case of MnV2O4, our calculation yields a ground state with antiferro-orbital ordering accompanied by a tetragonal structural distortion with lattice constants a=b>c. In addition, the V spins develop an orthogonal antiferromagnetic order in the ab plane on top of a ferromagnetic moment along the c axis. The results are consistent with a recent experimental characterization of MnV2O4 [2]. In particular, we will discuss the important role played by cooperative Jahn-Teller interaction and spin-orbital coupling in stabilizing the orthogonal spin configuration. [1] O. Tchernyshyov, Phys. Rev. Lett., 93, 157206 (2004). [2] V. O. Garlea et al., cond-mat/0711.1844. ,1NSF Grant No. DMR-0348679

  6. Quantifying the Effects of Higher Order Jahn-Teller Coupling Terms on a Quadratic Jahn-Teller Hamiltonian in the Case of NO_3 and Li_3.

    NASA Astrophysics Data System (ADS)

    Tran, Henry; Stanton, John F.; Miller, Terry A.

    2016-06-01

    The Jahn-Teller (JT) effect represents an enormous complication in the understanding of many molecules. We have been able to assign ˜20 vibronic bands in the tilde{A}^2E'' ← tilde{X}^2A_2' transition of NO_3 and determine the linear and quadratic JT coupling terms for ν_3 and ν_4, indicating strong and weak JT coupling along these modes respectively. It was found that the experimental results quantitatively disagree with ones determined from a vibronic Hamiltonian based on high-level ab-initio theory. Typical analyses of experimental data use the quadratic JT Hamiltonian because limited measured levels tend to allow fitting only to coupling terms up to quadratic JT coupling. Hence, these analyses may neglect key contributions from cubic and quartic terms. To quantify this limitation, we have fit artificial spectra calculated with up to fourth order terms in the potential using a quadratic JT Hamiltonian and analyzed the results. The parameters chosen for this analysis are determined from ab-initio potentials for the tilde{A} state of NO_3 and tilde{X} state of Li_3 to gain further insight on these molecules. Our initial results concerning the limitations of the quadratic JT Hamiltonian will be presented. T. Codd, M.-W. Chen, M. Roudjane, J. F. Stanton, and T. A. Miller. Jet cooled cavity ringdown spectroscopy of the tilde{A}^2E'' ← tilde{X}^2A'_2 Transition of the NO_3 Radical. J. Chem. Phys., 142:184305, 2015

  7. CuN6 Jahn-Teller centers in coordination frameworks comprising fully condensed Kuratowski-type secondary building units: phase transitions and magneto-structural correlations.

    PubMed

    Grzywa, Maciej; Denysenko, Dmytro; Hanss, Jan; Scheidt, Ernst-Wilhelm; Scherer, Wolfgang; Weil, Matthias; Volkmer, Dirk

    2012-04-14

    The metal-organic framework [Cu(ta)(2)] (Hta = 1H-1,2,3-triazole), containing Jahn-Teller active Cu(II) ions and 1,2,3-triazolate ligands, is prepared under solvothermal reaction conditions. The compound shows a reversible phase transition from the tetragonal crystal system (α-[Cu(ta)(2)]: space group I4(1)/amd (no. 141), a = 11.8447(7) Å, c = 18.9782(13) Å, V = 2662.6(3) Å(3)) to the cubic crystal system (β-[Cu(ta)(2)]: space group Fd3m (no. 227), a = 17.4416(15) Å, V = 5305.9(8) Å(3)) within the temperature range of 120-160 °C. Both [Cu(ta)(2)] polymorphs have identical bonding topologies that might be described as fully condensed Kuratowski-type pentanuclear secondary building units of local T(d) point group symmetry in which four Cu(II) ions occupy the vertices of an imaginary tetrahedron. α-[Cu(ta)(2)], as opposed to the high-temperature β-phase, shows a strong tetragonal Jahn-Teller distortion of CuN(6) coordination octahedra. The compounds are characterized by elemental and thermogravimetric analyses, single crystal and powder X-ray diffraction, FTIR-, UV-vis and fluorescence spectroscopy. Magnetic susceptibility investigations reveal two different Cu(II) sites at a ratio of 1 : 2, in agreement with the solid state structure of [Cu(ta)(2)]. At low temperatures the formation of antiferromagnetically coupled Cu(II) dimers is observed, leading to a spin frustration of roughly 1/3 of all magnetically active Cu(II) sites.

  8. A valence bond analysis of electronic degeneracies in Jahn-Teller systems: low-lying states of the cyclopentadienyl radical and cation.

    PubMed

    Zilberg, Shmuel; Haas, Yehuda

    2002-09-11

    The lowest doublet electronic state of the cyclopentadienyl radical (CPDR) and the lowest singlet state of the cyclopentadienyl cation (CPDC) are distorted from the highly symmetric D(5h) structure due to the Jahn-Teller effect. A valence bond analysis based on the phase-change rule of Longuet-Higgins reveals that in both cases the distortion is due to the first-order Jahn-Teller effect. It is shown that, while for the radical an isolated Jahn-Teller degeneracy is expected, in the case of the cation the main Jahn-Teller degeneracy is accompanied by five satellite degeneracies. The method offers a chemically oriented way for identifying the distortive coordinates.

  9. Jahn-Teller effect in LiMn2O4: influence on charge ordering, magnetoresistance and battery performance.

    PubMed

    Ragavendran, K; Xia, H; Mandal, P; Arof, A K

    2017-01-18

    The phase transition near room temperature in LiMn2O4 was studied using thermal expansion measurements, and directly compared with the electrochemical performance of the material. Studies based on thermal expansion indicate the onset of a first-order phase transition at Tc ∼ 220 K for the nearly half-doped material, with [Mn(3+)]/[Mn(4+)] ≈ 1. The Tc shifts to a higher temperature, ∼290 K, and signatures for Verwey-type charge ordering at 290 K can be observed when the fraction of Jahn-Teller Mn(3+) in LiMn2O4 is increased, i.e., [Mn(3+)]/[Mn(4+)] > 1. These studies show that the first-order phase transition near room temperature in LiMn2O4 is associated with charge ordering, which ultimately is a consequence of the Jahn-Teller effect. In addition, the Jahn-Teller effect is proven to be an important cause of magnetoresistance and electrochemical capacity fading in LiMn2O4. Electrochemical measurements show that both materials, either with a Tc ∼ 220 K or Tc ∼ 290 K, exhibit capacity fading to almost the same extent. Electrochemical capacity retention is observed only in nanosized LiMn2O4, for which the phase transition anomalies are completely absent.

  10. Microscopic Insight into the Isosymmetric Jahn-Teller Bond Axis Reorientation in Na3MnF6

    NASA Astrophysics Data System (ADS)

    Charles, Nenian; Rondinelli, James

    2014-03-01

    Using first-principles density functional theory calculations, we investigate the hydrostatic pressure-induced spontaneous reorientation of the Jahn-Teller bond axis in the fluoride cryolite Na3MnF6. We find a first-order isosymmetric transition occurs between crystallographically equivalent monoclinic structures at approximately 2.15 GPa, consistent with earlier experimental studies. Analogous calculations for Na3ScF6 show no evidence of a transition up to 6.82 GPa. Mode crystallography analysis of the pressure-dependent structures in the vicinity of the transition reveals a clear evolution of the Jahn-Teller bond distortions in cooperation with an asymmetrical stretching of the equatorial fluorine atoms in the MnF6 octahedral units. We identify a change in orbital occupancy of the eg manifold in the d4 Jahn-Teller active Mn(III) to be responsible for the transition, which stabilizes one monoclinic P21/n variant over the other. From our results, we conjecture that the same transition may be accessible in epitaxially grown thin films of Na3MnF6 with a modest biaxial tensile strain.

  11. Raman phonon study of Jahn-Teller distortion in Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Drichko, Natalia; Broholm, Collin; Kimura, Kenta; Ishii, Rieko; Nakatsuju, Satoru

    2013-03-01

    The frustrated magnet Ba3CuSb2O9 does not exhibit either structural or magnetic ordering down to the lowest measured temperatures and is of great current interest as a spin-liquid candidate. It has been proposed recently that the lack of ordering is due to a static or dynamic Jahn-Teller distortion that leads to orbital disorder. We use phonon Raman scattering at temperatures between 20 and 380 K to investigate Jahn-Teller distortion in crystals with different Sb:Cu stoichiometry. We focus on phonons in the range of 500-800 cm-1 attributable to oxygen vibrations. In addition to signatures of the strong disorder due to Cu-Sb site mixing present in these materials, we observe mode-splitting due to a static Jahn-Teller distortion below 200 K in samples that undergo a transition to an orthorhombic phase. In contrast, samples that remain hexagonal to the lowest temperatures do not show such mode splitting. We are thankful to O. Tchernyshyov and Zihao Hao for discussions. This work was supported in part by the U.S. DoE, Office of Basic Energy Science, DMSE under Award DE-FG02-08ER46544 and H. Blewett Fellowship from APS

  12. Structural ground states of (A ,A')Cr2O4(A = Mg, Zn; A' = Co, Cu) spinel solid solutions: Spin-Jahn-Teller and Jahn-Teller effects

    NASA Astrophysics Data System (ADS)

    Kemei, Moureen C.; Moffitt, Stephanie L.; Darago, Lucy E.; Seshadri, Ram; Suchomel, Matthew R.; Shoemaker, Daniel P.; Page, Katharine; Siewenie, Joan

    2014-05-01

    We examine the effect of small amounts of magnetic substituents in the A sites of the frustrated spinels MgCr2O4 and ZnCr2O4. Specifically, we look for the effects of spin and lattice disorder on structural changes accompanying magnetic ordering in these compounds. Substitution of Co2+ on the nonmagnetic Zn2+ site in Zn1-xCoxCr2O4 where 0 < x ≤ 0.2 completely suppresses the spin-Jahn-Teller distortion of ZnCr2O4 although these systems remain frustrated, and magnetic ordering occurs at very low temperatures of T < 20 K. On the other hand, the substitution of Jahn-Teller active Cu2+ for Mg2+ and Zn2+ in Mg1-xCuxCr2O4 and Zn1-xCuxCr2O4 where 0 < x ≤ 0.2 induce Jahn-Teller ordering at temperatures well above the Néel temperatures of these solid solutions, and yet spin interactions remain frustrated with long-range magnetic ordering occurring below 20 K without any further lattice distortion. The Jahn-Teller distorted solid solutions Mg1-xCuxCr2O4 and Zn1-xCuxCr2O4 adopt the orthorhombic Fddd structure of ferrimagnetic CuCr2O4. Total neutron scattering studies of Zn1-xCuxCr2O4 suggest that there are local AO4 distortions in these Cu2+-containing solid solutions at room temperature and that these distortions become cooperative when average structure distortions occur. Magnetism evolves from compensated antiferromagnetism in MgCr2O4 and ZnCr2O4 to uncompensated antiferromagnetism with substitution of magnetic cations on the nonmagnetic cation sites of these frustrated compounds. The sharp heat capacity anomalies associated with the first-order spin-Jahn-Teller transitions of MgCr2O4 and ZnCr2O4 become broad in Mg1-xCuxCr2O4, Zn1-xCoxCr2O4, and Zn1-xCuxCr2O4 when x > 0. We present a temperature-composition phase diagram summarizing the structural ground states and magnetic properties of the studied spinel solid solutions.

  13. Using EPR spectroscopy to go from the Jahn-Teller effect to nuclear waste disposal

    NASA Astrophysics Data System (ADS)

    Boatner, L. A.

    2003-02-01

    Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique for elucidating the fundamental solid-state-chemical and crystal-field ground-state electronic properties of rare-earth and actinide ions that are incorporated into single-crystal host materials. In the case of rare-earth or rare-earth-like ions that are characterized by a degenerate orbital doublet ground state when placed in a cubic crystal field, EPR has proven to be an extremely valuable approach to the study of various manifestations of the Jahn-Teller (J-T) effect. The contributions of EPR spectroscopy to the study of the J-T effect in ions such as La 2+, Y 2+ and Sc 2+ include the discovery of quadrupolar effects in J-T systems and a verification of Frank Ham's theory of the dynamic J-T effect. Such basic studies can often have unforeseen consequences—like leading to the discovery of new scintillators for gamma-ray detection or the development of a matrix for the disposal of radioactive waste.

  14. Pseudo Jahn-Teller effect in oxepin, azepin, and their halogen substituted derivatives

    NASA Astrophysics Data System (ADS)

    Ilkhani, Ali Reza

    2017-09-01

    Oxepin and azepin are heterocyclic compounds with a seven-membered ring, which are present in the main skeleton of many anti-depressive drugs. Planar configuration instability due to the pseudo Jahn-Teller effect (PJTE) in oxepin, azepin and six their halogen substituted derivatives were investigated as an original PJTE study. Optimization and the following frequency calculations in these two series illuminated that all of these eight compounds were unstable in high-symmetry planar (with C 2 v symmetry) configuration and their structures were puckered to lower C s symmetry stable geometry. Moreover, the vibronic coupling interaction between 1 A 1 ground and the first 1 B 1 excited states via (1 A 1 + 1 A 1 ' + 1 B 1) ⊗ b 1 and (1 A 1 + 1 B 1 + 1 A 1 ' ) ⊗ b 1 PJTE problems were the reasons for the symmetry breaking phenomenon and non-planarity of the seven-member ring in those series. Finally, numerical fitting of the adiabatic potential energy surface (APES) cross-sections along the b 1 puckering coordination was employed to estimate the vibronic coupling constants of PJTE problems for all the considered compounds.

  15. Quantum friction of pseudorotation in Jahn-Teller system: Passage through conical intersection

    NASA Astrophysics Data System (ADS)

    Pae, Kaja; Hizhnyakov, Vladimir

    2016-08-01

    A theoretical study of the relaxation of an excited impurity center with strong E × e-type Jahn-Teller effect, caused by the emission of phonons to the bulk, is presented. The dependence of the passing the system through the conical intersection of the potential surface on the momentum of the pseudorotation is figured out. An analytical description of the quantum states of the conical intersection (Slonczewski resonances) is given. It is found that for realistic vibronic interactions with phonons, the characteristic time of the energy loss is several tenths of mean periods of phonons, i.e., it is in the picosecond range. It is also found that there is a finite probability of the speeding-up of the pseudorotation of the system at the intermediate stage of relaxation. In particular, this probability increases close to the Slonczewski resonances. During the relaxation, the system may change the direction of the pseudomoment; the probability of such a change also increases near the resonances.

  16. PBE+U calculations of the Jahn-Teller effect in PrO2

    NASA Astrophysics Data System (ADS)

    Tran, Fabien; Schweifer, Johannes; Blaha, Peter; Schwarz, Karlheinz; Novák, Pavel

    2008-02-01

    The Jahn-Teller distortion in praseodymium dioxide (PrO2) has been studied using density functional theory with the PBE+U functional for the exchange-correlation energy. Various possible distortions were suggested based on recent neutron diffraction experiments [C. H. Gardiner , Phys. Rev. B 70, 024415 (2004)]. We could identify the most likely distorted structure with a magnitude of the distortion in very good agreement with the experiment. This structure is the one with the lowest total energy and the corresponding calculated electronic and magnetic properties agree well with the experiment. We investigated the dependency of various properties on the Coulomb parameter Ueff=U-J and suggest Ueff=6eV as the most appropriate value, for which about 1.65 4f electrons (one localized plus 0.65 delocalized) per Pr atom are found. We also show that magnetism (antiferromagnetism or ferromagnetism) has only a minor influence on the energy and magnitude of the distortion, which is consistent with the fact that the Néel temperature (13.5K) is much smaller than the temperature of 120K below which the distortion is observed.

  17. Symmetry-adapted excited states for the T1u⊗hg Jahn-Teller system

    NASA Astrophysics Data System (ADS)

    Qiu, Q. C.; Dunn, J. L.; Bates, C. A.

    2001-08-01

    Jahn-Teller (JT) systems typically contain a set of equivalent-energy wells in the lowest adiabatic potential-energy surface (APES). Quantum-mechanical tunneling between these wells (the dynamic JT effect) must be allowed for by taking appropriate symmetrized combinations of oscillator-type states associated with the wells. It is important to be able to describe the excited states of such systems for a number of reasons. One particular reason is that they are required for the calculation of second-order vibronic reduction factors, which in turn are useful for modeling experimental data using effective Hamiltonians. In this paper, projection-operator techniques are used to obtain general expressions for the symmetry-adapted excited states of the icosahedral T1u⊗hg JT system for the case of D5d minima in the APES. Analytical expressions for the states and their energies for one-phonon excitation are given explicitly. The energies of a selection of states with two-phonon excitations are also obtained and plotted. The results obtained in this paper are applicable to the C-60 molecule.

  18. Dynamic Jahn-Teller viewpoint for generation mechanism of asymmetric modes of coherent phonons

    NASA Astrophysics Data System (ADS)

    Kayanuma, Yosuke; Nakamura, Kazutaka G.

    2017-03-01

    We propose a dynamic Jahn-Teller approach to elucidate the generation mechanism of asymmetric modes of coherent phonons induced in crystals by irradiation with a short optical pulse in the opaque energy region. This is a natural extension of the impulsive excitation model of symmetric modes to multi dimensions in the configuration coordinate space. We show that the two generation mechanisms of coherent phonons coexist in this case, namely the impulsive absorption (IA) mechanism and impulsive stimulated Raman scattering (ISRS) mechanism. The dependence of the phonon amplitude on the polarization of the pump pulse is exactly the same in IA and ISRS processes and is in agreement with the prediction of the argument based on Raman tensors. The dependence of the excitation efficiency of the coherent phonons on the frequency of the pump pulse is calculated using a simplified model of the optical response function of the crystal. Generally, the IA mechanism predominates in the opaque region, although ISRS makes a comparable contribution to phonon generation in the near-edge opaque region. The initial phase of the coherent phonon is always cosine-like in IA but depends on the excitation frequency in ISRS.

  19. Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Wang, Ya; Bersuker, Isaac B.

    2016-03-01

    We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g‑b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted.

  20. Reexamination of the origin of the pseudo Jahn-Teller puckering instability in silicene.

    PubMed

    Soto, J R; Molina, B; Castro, J J

    2015-03-28

    Silicene, the graphene-like crystal formed by the Si hexagonal lattice, presents a periodic buckled structure whose origin is due to the pseudo Jahn-Teller instability on each of its planar six membered rings. This has been attributed to the coupling of the planar D6h ground state with the first b2g excited state through a b2g vibrational mode. Here we show, by explicitly calculating the vibronic coupling constants through a complete study of the PJT effect, that the vibronic coupling of the ground state with only one excited state to explain the planar instability is inconsistent with the linear multilevel PJT effect theory. It is also shown that in order to have consistency, the PJT model should include the next excited state, which is symmetry compatible coupled to the puckering mode. This is done by the analysis, based on DFT and TDDFT calculations, of the vibronic instability of the ground state of hexasilabenzene, the basic silicon hydrogenated hexagonal ring unit defining silicene.

  1. Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues.

    PubMed

    Liu, Yang; Wang, Ya; Bersuker, Isaac B

    2016-03-21

    We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g-b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted.

  2. Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues

    PubMed Central

    Liu, Yang; Wang, Ya; Bersuker, Isaac B.

    2016-01-01

    We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g−b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted. PMID:26996445

  3. Further studies of anisotropy in the T1u⊗hg Jahn-Teller system

    NASA Astrophysics Data System (ADS)

    Qiu, Q. C.; Dunn, J. L.; Bates, C. A.; Liu, Y. M.

    1998-08-01

    In the linear T1u⊗hg Jahn-Teller system, the adiabatic potential energy surface (APES) is a trough. However, in real systems, quadratic coupling will be present, which warps the APES to give wells of either D3d or D5d symmetry. The degeneracy of the vibrations within the wells is also lifted. This anisotropy has recently been investigated in the T1u⊗hg system, and expressions for the frequencies in both types of wells obtained in the strong coupling limit using the method of Öpik and Pryce. A scale transformation procedure was then used to incorporate these results into expressions for the states in the wells and their associated energies. However, this calculation did not allow for second-order perturbation effects and is only valid in the strong coupling limit. In this paper, a revised scale transformation procedure is developed for the D5d wells, which allows expressions for the anisotropic frequencies to be obtained without employing the Öpik and Pryce procedure. An expression is obtained for the phonon overlap that is correct to second-order and is not restricted to the strong coupling limit. Results are then obtained for the ground-state energies and inversion splitting. For D3d wells, the previous results are improved by application of a modified scale transformation procedure and overlaps correct to second order obtained. The results obtained in this paper are of interest in studies of the C-60 anion state of the C60 molecule, which is known to occupy a T1u orbital ground state.

  4. A Local Approach to Solid State Problems: Pseudo Jahn-Teller origin of Ferroelectricity and Multiferroicity

    NASA Astrophysics Data System (ADS)

    Bersuker, I. B.

    2013-04-01

    This is a partially review paper in which, in continuation of previous work, it is shown that in perovskite crystals of ABO3 type the spontaneous polarization is triggered by local vibronic interactions, the pseudo Jahn-Teller effect (PJTE). The driving force of the latter is added covalency by distortion, which is essentially of local (chemical) origin. The local origin of polar instability in crystals is confirmed by the theorem of structural instability proved earlier. For crystals of BaTiO3 type local PJT interactions of the metal ion with the oxygen environment results in a peculiar adiabatic potential energy surface (APES) which has eight trigonal [111] type minima, twelve [110] type saddle points between them, six higher in energy [100] type saddle points at the top of the barrier connecting four minima, and a maximum at the cubic symmetry. The temperature dependence of the free energy with this potential explains the origin of all the four phases in such crystals; only the lowest rhombohedral phase is fully ordered, the other two ones at higher temperatures are partially disordered, and the paraelectric phase is fully (three-dimensionally) disordered. For BaTiO3 this picture is confirmed by numerical estimates and ab initio DFT calculations. An important further development of this theory was reached recently by showing that not only B ions with electronic d0 configurations are subject to the PJTE instability to produce ferroelectricity in perovskite crystals ("the d0 mystery"), but some other specific dn configurations with unpaired electrons may be dipolar active too, the crystal being thus both magnetic and ferroelectric (multiferroic), and the necessary conditions for such multiferroicity are formulated for the whole d0-dn variety of perovskites. Moreover, the condition of multiferroicity was shown to depend also on the spin state, high-spin or low-spin, which in conditions of spin crossover leads to a magnetic-ferroelectric crossover that can be

  5. Percolation features of cooperative Jahn-Teller systems: Ising EFT framework

    NASA Astrophysics Data System (ADS)

    Moujaes, Elie A.; Abou Ghantous, Michel

    2014-08-01

    Elastic exchange between two nearest Jahn-Teller (JT) centers in two or three dimensional dense crystals, can give an ordered macroscopic distortion known as cooperative JT effect (CJTE). A very diluted JT crystal does not show this effect. In the dynamic JT effect (DJTE), tunneling between different equivalent distorted wells has a pronounced influence on the CJTE. We investigate this phenomenon using a progressive increase in the concentration of these centers in the JT crystals, based on a bond percolation vector spin analogy technique within the framework of effective field theory (EFT). Mean field theory (MFT) was extensively used in previous studies of CJTE; however it neither includes correlation between JT centers in the lattice due to the complexity of the distortion field in the crystal nor the effect of tunneling between wells. We resort to an alternative procedure, by describing a JT center as a pseudo-spin vector , induced to represent the degenerate JT-distorted states, where two nearest JT centers interact via an elastic exchange described by an Ising type spin interaction. The DJTE is considered to be similar to an elastic transverse field term in the Hamiltonian portraying the effect of tunneling between equivalent wells in the adiabatic potential energy surface (APES). We will be particularly discussing S = 1, S = 3/2 and S = 5/2 spin cases, where 2 S + 1 wells in the APES are present and what JT systems they actually represent, with a percolative mechanism applied to the interactions between different JT centers. The different lattices are distinguished by their coordination numbers. Strong tunneling effects can suppress the CJTE and lead to a new state of criticality. Generalizations to higher spin systems will be obtained using a scaling technique. For the relevant distortions, we determine single site correlations, the macroscopic average distortion describing a structural phase transition and the elastic isothermal susceptibility as a

  6. Phase stability and Jahn-Teller distortion in doped lithiated manganese oxides: A LSDA+U study

    NASA Astrophysics Data System (ADS)

    Prasad, Rajendra; Nath Shukla, Nitya; Benedek, Roy

    2006-03-01

    We discuss how the rhombohedral phase of lithiated manganese oxide can be stabilized by doping with various impurities. Our study is based on LSDA+U calculations as implemented in the VASP code. We have considered rhombohedral and monoclinic phases using a supercell of 16 atoms. Our results are based on total energy calculations for 25% dopant concentration and pure lithiated manganese oxide. Several dopants such as Co, Fe, Ni, Mg and Zn are considered. We find that oxidation state of the dopant plays an important role in suppressing the Jahn-Teller distortion. Divalent impurities are found to be most effective. The effect of including U in the calculation is discussed.

  7. Jahn-Teller-like origin of the tetragonal distortion in disordered Fe-Pd magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Opahle, Ingo; Koepernik, Klaus; Nitzsche, Ulrike; Richter, Manuel

    2009-02-01

    The electronic structure and magnetic properties of disordered FexPd100-x alloys (50Jahn-Teller-like effect, which allows the system to reduce its band energy in a narrow composition range. Prospects for an optimization of the alloys' properties by adding third elements are discussed.

  8. Ultrasonic evaluation of the Jahn-Teller effect parameters. Application to ZnSe:Cr2 +

    NASA Astrophysics Data System (ADS)

    Gudkov, V. V.; Bersuker, I. B.; Zhevstovskikh, I. V.; Korostelin, Yu V.; Landman, A. I.

    2011-03-01

    A method is constructed that uses ultrasonic experiments to evaluate the parameters of the Jahn-Teller (JT) effect in impurity centers in crystals. The method is based on measurements of temperature dependent attenuation and phase velocity and does not require assumptions about mechanisms of relaxation. The results are illustrated by measurements performed on the impurity system ZnSe:Cr2 + , in which the Cr2 + ion has a threefold degenerate T term in the ground state, subject to the T\\otimes (e+t_2) JT problem. Ultrasound propagation anomalies show that the main JT distortions of the tetrahedral environment of the Cr2 + ion are of tetragonal E type and hence the lowest branch of the adiabatic potential energy surface (APES) is formed in accordance with the T\\otimes e problem. With dopant concentration 3.8 × 1018 cm - 3 the modulus of the constant of linear vibronic coupling to tetragonal E type vibrations is determined by two independent experiments: |FE| = 5.49 × 10 - 5 dyn revealed from attenuation measurements, while a slightly different value |FE| = 5.57 × 10 - 5 dyn emerges from phase velocity measurements. Contributions of other active vibronic modes to the elastic modulus Cl = (C11 + C12 + 2C44)/2 are analyzed and it is shown that the influence of the totally symmetric mode is negligible. Using additional information about this system obtained from independent sources, we also estimated the primary force constant in the E direction (KE≈(1.4-4.2) × 104 dyn cm - 1) and orthorhombic and trigonal saddle points of the APES in the five-dimensional space of the tetragonal and trigonal coordinates, their stabilization energies being EJTO≈81-450 cm - 1 and EJTT≈48-417 cm - 1, respectively (the variations of the KE, EJTO and EJTT values are due to different literature data for EJTE). With these data the APES of the JT linear T\\otimes (e+t_2) problem for the Cr2 + ion in the ZnSe:Cr2 + system is revealed.

  9. Jahn-Teller coupling and fragmentation after core-shell excitation in CF{sub 4} investigated by partial-ion-yield spectroscopy

    SciTech Connect

    Guillemin, Renaud; Stolte, Wayne C.; Lindle, Dennis W.; Piancastelli, Maria Novella

    2010-10-15

    We investigate fragmentation processes induced by core-level photoexcitation in CF{sub 4} at both the carbon and fluorine K edges by means of partial-ion-yield spectroscopy. The molecule CF{sub 4} is a textbook example of systems in which Jahn-Teller coupling strongly manifests itself in the photoabsorption spectrum. Spectral features related to Jahn-Teller and quasi-Jahn-Teller splitting are observed, and important differences in the fragmentation pathways are revealed depending on the symmetries of the core-excited states. We interpret these experimental observations on the grounds of symmetry lowering from the T{sub d} to the C{sub 3v} point group as well as preferential orientation with respect to the polarization vector of the incident radiation.

  10. Local ordering of Jahn-Teller orbitals in LiNiO2 by neutron powder diffraction

    NASA Astrophysics Data System (ADS)

    Chung, Jae-Ho; Egami, Takeshi; Shamoto, Shin-Ichi; Proffen, Thomas; Ghorayeb, Andre

    2004-03-01

    The orbital state of LiNiO2 has been controversial, since there is no signature of long-range Jahn-Teller distortion, unlike NaNiO2 that shows ferromagnetic orbital order. We have neutron pair distribution function analysis to reveal important features, such as the local J-T distortion, the sharp oxygen-oxygen distance correlations, and unusual temperature dependence. These observations can be explained by a local ordering of Ni^3+ Jahn-Teller orbitals, where three neighboring 3d_z^2-r^2/3 orbitals share an oxygen site to form a trimer. Under this arrangement, it is expected that a medium-range elastic field will induce a curvature on NiO2 layers, which frustrates long-range order and is consistent with the systematic peak broadening observed in the neutron diffraction profiles. We propose that this local ordering is the basis for the complex magnetic properties observed in this material.

  11. Spontaneous Orbital-Selective Mott Transitions and the Jahn-Teller Metal of A3C60

    NASA Astrophysics Data System (ADS)

    Hoshino, Shintaro; Werner, Philipp

    2017-04-01

    The alkali-doped fullerides A3C60 are half-filled three-orbital Hubbard systems which exhibit an unconventional superconducting phase next to a Mott insulator. While the pairing is understood to arise from an effectively negative Hund coupling, the highly unusual Jahn-Teller metal near the Mott transition, featuring both localized and itinerant electrons, has not been understood. This property is consistently explained by a previously unrecognized phenomenon: the spontaneous transition of multiorbital systems with negative Hund coupling into an orbital-selective Mott state. This symmetry-broken state, which has no ordinary orbital moment, is characterized by an orbital-dependent two-body operator (the double occupancy) or an orbital-dependent kinetic energy and may be regarded as a diagonal-order version of odd-frequency superconductivity. We propose that the recently discovered Jahn-Teller metal phase of Rbx Cs3 -xC60 is an experimental realization of this novel state of matter.

  12. Teaching the Jahn-Teller Theorem: A Simple Exercise That Illustrates How the Magnitude of Distortion Depends on the Number of Electrons and Their Occupation of the Degenerate Energy Level

    ERIC Educational Resources Information Center

    Johansson, Adam Johannes

    2013-01-01

    Teaching the Jahn-Teller theorem offers several challenges. For many students, the first encounter comes in coordination chemistry, which can be difficult due to the already complicated nature of transition-metal complexes. Moreover, a deep understanding of the Jahn-Teller theorem requires that one is well acquainted with quantum mechanics and…

  13. Teaching the Jahn-Teller Theorem: A Simple Exercise That Illustrates How the Magnitude of Distortion Depends on the Number of Electrons and Their Occupation of the Degenerate Energy Level

    ERIC Educational Resources Information Center

    Johansson, Adam Johannes

    2013-01-01

    Teaching the Jahn-Teller theorem offers several challenges. For many students, the first encounter comes in coordination chemistry, which can be difficult due to the already complicated nature of transition-metal complexes. Moreover, a deep understanding of the Jahn-Teller theorem requires that one is well acquainted with quantum mechanics and…

  14. Using Extended Huckel Theory as a Platform to Introduce Jahn-Teller Distortion: The Spontaneous Distortion of 1,3,5,7-Cyclooctatetraene from a Perfect Octagon

    ERIC Educational Resources Information Center

    Sohlberg, Karl; Liu, Xiang

    2013-01-01

    Herein, a slightly enhanced version of extended Huckel molecular orbital theory is applied to demonstrate the spontaneous distortion of 1,3,5,7-cyclooctatetraene from a perfect octagon, a consequence of the Jahn-Teller effect. The exercise is accessible to students who have been introduced to basic quantum mechanics and extended Huckel molecular…

  15. Dynamics of photo-induced changes in the elastic characteristics of lithium niobate crystals doped with Jahn-Teller Fe2+ ions

    NASA Astrophysics Data System (ADS)

    Golenishchev-Kutuzov, A. V.; Golenishchev-Kutuzov, V. A.; Kalimullin, R. I.; Semennikov, A. V.

    2017-02-01

    The effect of admixture Jahn-Teller Fe2+ ions on the elastic characteristics of lithium niobate was studied. The appearance of photostrains and a change in elastic moduli under the influence of laser radiation was established, thus enabling the creation of device elements with optically controlled elastic characteristics.

  16. Using Extended Huckel Theory as a Platform to Introduce Jahn-Teller Distortion: The Spontaneous Distortion of 1,3,5,7-Cyclooctatetraene from a Perfect Octagon

    ERIC Educational Resources Information Center

    Sohlberg, Karl; Liu, Xiang

    2013-01-01

    Herein, a slightly enhanced version of extended Huckel molecular orbital theory is applied to demonstrate the spontaneous distortion of 1,3,5,7-cyclooctatetraene from a perfect octagon, a consequence of the Jahn-Teller effect. The exercise is accessible to students who have been introduced to basic quantum mechanics and extended Huckel molecular…

  17. Jahn-Teller distortion in the phosphorescent excited state of three-coordinate Au(I) phosphine complexes.

    PubMed

    Barakat, Khaldoon A; Cundari, Thomas R; Omary, Mohammad A

    2003-11-26

    DFT calculations were used to optimize the phosphorescent excited state of three-coordinate [Au(PR3)3]+ complexes. The results indicate that the complexes rearrange from their singlet ground-state trigonal planar geometry to a T-shape in the lowest triplet luminescent excited state. The optimized structure of the exciton contradicts the structure predicted based on the AuP bonding properties of the ground-state HOMO and LUMO. The rearrangement to T-shape is a Jahn-Teller distortion because an electron is taken from the degenerate e' (5dxy, 5dx2-y2) orbital upon photoexcitation of the ground-state D3h complex. The calculated UV absorption and visible emission energies are consistent with the experimental data and explain the large Stokes' shifts while such correlations are not possible in optimized models that constrained the exciton to the ground-state trigonal geometry.

  18. Jahn-Teller versus quantum effects in the spin-orbital material LuVO3

    SciTech Connect

    Skoulatos, M.; Toth, S.; Roessli, B.; Enderle, M.; Habicht, K.; Sheptyakov, D.; Cervellino, A.; Freeman, P. G.; Reehuis, M.; Stunault, A.; McIntyre, G. J.; Tung, L. D.; Marjerrison, C.; Pomjakushina, E.; Brown, P. J.; Khomskii, D. I.; Rüegg, Ch.; Kreyssig, A.; Goldman, A. I.; Goff, J. P.

    2015-04-13

    In this article, we report on combined neutron and resonant x-ray scattering results, identifying the nature of the spin-orbital ground state and magnetic excitations in LuVO3 as driven by the orbital parameter. In particular, we distinguish between models based on orbital-Peierls dimerization, taken as a signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor of the latter. In order to solve this long-standing puzzle, polarized neutron beams were employed as a prerequisite in order to solve details of the magnetic structure, which allowed quantitative intensity analysis of extended magnetic-excitation data sets. The results of this detailed study enabled us to draw definite conclusions about the classical versus quantum behavior of orbitals in this system and to discard the previous claims about quantum effects dominating the orbital physics of LuVO3 and similar systems.

  19. Pulsed magnetic field synchrotron X-ray powder diffraction of the Jahn-Teller distortion in TbVO4

    NASA Astrophysics Data System (ADS)

    Vanacken, J.; Frings, P.; Detlefs, C.; Duc, F.; Lorenzo, J. E.; Nardone, M.; Billette, J.; Zitouni, A.; Bras, W.; Rikken, G.

    2006-11-01

    X-ray powder diffraction experiments under pulsed magnetic fields were carried out at the DUBBLE beam line at the ESRF. A mobile generator delivered 110 kJ to the load coil, which was sufficient to generate peak fields of 30 T. A liquid He flow cryostat allowed us to vary the sample temperature accurately between 8 K and 300 K. Powder diffraction patterns of TbVO4 were recorded in a broad temperature range using 21 keV monochromatic X-rays and an on-line image plate detector. We present results on the suppression of the Jahn-Teller structural distortion in TbVO4by to the magnetic field.

  20. Ab initio calculation of spin-orbit coupling for an NV center in diamond exhibiting dynamic Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Thiering, Gergő; Gali, Adam

    2017-08-01

    Point defects in solids may realize solid state quantum bits. The spin-orbit coupling in these point defects plays a key role in the magneto-optical properties that determine the conditions of quantum bit operation. However, experimental data and methods do not directly yield these highly important data, particularly for such complex systems where the dynamic Jahn-Teller (DJT) effect damps the spin-orbit interaction. Here, we show for an exemplary quantum bit, the nitrogen-vacancy (NV) center in diamond, that ab initio supercell density functional theory provides a quantitative prediction for the spin-orbit coupling damped by DJT. We show that DJT is responsible for the multiple intersystem crossing rates of the NV center at cryogenic temperatures. Our results pave the way toward optimizing solid state quantum bits for quantum information processing and metrology applications.

  1. Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal

    DOE PAGES

    Katayama, Naoyuki; Kimura, Kenta; Han, Yibo; ...

    2015-07-13

    With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose-Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Furthermore, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc2S4. To confirm this exotic ground state, experimentsmore » based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn-Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn-Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. Lastly, we discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state.« less

  2. Stability of Jahn-Teller distortion in LaMnO{sub 3} under pressure: An x-ray absorption study

    SciTech Connect

    Ramos, Aline Y.; Tolentino, Helio C. N.; Souza-Neto, Narcizo M.; Itie, Jean-Paul; Morales, Liliana; Caneiro, Alberto

    2007-02-01

    The local environment of manganese atoms in LaMnO{sub 3} under pressure up to 15.3 GPa has been studied by x-ray absorption spectroscopy. For pressures below 8 GPa, no change is detected within the MnO{sub 6} octahedra. Above this pressure a continuous reduction of the long Mn-O distance takes place, however, the octahedral distortion persists over the whole pressure range. At 15.3 GPa the average Jahn-Teller splitting of the distances is reduced by about one-third, indicating that a total removal of the local Jahn-Teller distortion would occur only for pressures around 30 GPa, where metallization is reported to take place. A hysteresis in the long distance reduction is observed down to ambient pressure, suggesting the coexistence of MnO{sub 6} distorted and undistorted units.

  3. The Phase Transitions in Double Tungstate in Extremely Low-Dimensional and Low-Symmetry Compounds with Cooperative Jahn-Teller Effect

    DTIC Science & Technology

    2001-01-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADPO 11897 TITLE: The Phase Transitions in Double Tungstate in Extremely...report: ADP011865 thru ADP011937 UNCLASSIFIED Invited Paper The phase transitions in double tungstate - in extremely low-dimensional and low-symmetry...Warsaw, Poland ABSTRACT The rare earth double tungstates are of special interest because of manifestation of cooperative Jahn-Teller effect (CJTE) for low

  4. Pseudo-Jahn-Teller and relaxation-rate analyses of a model for the hydride ion at the E' 4 center in alpha quartz

    NASA Astrophysics Data System (ADS)

    Georgiev, M.; Manov, A.

    1988-02-01

    Calculated cluster data on the energy vs hydride-ion displacement for the E' 4 center, as reported by Isoya, Weil, and Halliburton, are re-analyzed in terms of the Pseudo-Jahn-Teller effect. Realistic values are obtained of the vibronic-mixing parameters giving credibility to our interpretation. Relaxation rates are computed of hydrogen transfer between two opposite off-center sites.

  5. Dependence of the Jahn-Teller distortion in LaMn 1-x ScxO3 on the isovalent Mn-site substitution

    NASA Astrophysics Data System (ADS)

    Subías, G.; Cuartero, V.; Blasco, J.; García, J.; Meneghini, C.; Aquilanti, G.

    2016-05-01

    We investigated the relative importance of removing the Mn3+ Jahn-Teller distortion in driving ferromagnetism in LaMn1-xScxO3 combining x-ray powder diffraction and x-ray absorption spectroscopy at the Mn and Sc K-edges. By increasing the Sc content, the orthorhombic distortion of the Pbnm cell in LaMnO3 decreases but the unit-cell remains slightly distorted in LaScO3. Besides, the nearly tetragonal-distorted MO6 in LaMnO3 continuously evolves into a nearly regular one in LaScO3. On the other hand, x-ray absorption spectra show that the MnO6 octahedron remains Jahn-Teller distorted and the ScO6 octahedron is nearly regular along the whole series. Moreover, the ordering of the Mn3+ Jahn-Teller distortion is not disrupted in the ab plane for any Sc concentration. This contrasts with the Ga- substituted compounds, where a regular MnO6 is found for x>0.5. However, both LaMn0.5Sc0.5O3 and LaMn0.5Ga0.5O3 show ferromagnetic behavior independently of the presence (or not) of Jahn-Teller distorted Mn3+. Thus, our results point to the Mn-sublattice dilution as the main effect in driving ferromagnetism in these manganites over local structure effects previously proposed by the spin flipping or the vibronic superexchange models.

  6. Manifestation of the Jahn-Teller active vibrations in the vibronic spectra of tetracoordinate Cu 2+, Ni 2+ and Zn 2+ chlorides

    NASA Astrophysics Data System (ADS)

    Trendafilova, N.; Nikolov, G. St.; Kellner, R.; Mikosch, H.; Bauer, G.; Bogatchev, G.

    1990-11-01

    An attempt is made to track the changes in the vibrational modes that are Jahn-Teller active of some pseudotetrahedral MCl 42- ions. The infrared and Raman spectra of powder (Et 4N) 2MCl 4, M=Ni, Cu, Zn and of Cu- and Ni-doped (Et 4N) 2ZnCl 4 were recorded both at room temperature and at 77, 100 and 170 K. The room temperature spectra show that for NiCl 42- and CuCl 42- if present the Jahn-Teller distortions are dynamically averaged and the transitions can be accounted for as intrasheet vibronic transitions. The low-temperature spectra however show splittings that are indicative of a low symmetry field thus suggestingthat at 77 K the NiCl 42- and CuCl 42- are vibronically stabilized in a static C 2v field. The doped compound spectra reveal that the Zn matrix effect overrides the static Jahn-Teller distortions present in the free ion spectra. In the CuCl 42- spectrum a band at 2700 cm -1 with side bands + v(a 1), - v(t 2s) was detected and it was assigned to the 2B 2g→ 2B 1g transition arising from the split 2T 2 term in D 2h site symmetry.

  7. First-Principles Study of the Jahn-Teller Distortion in the Ti1-XVXH2 and Zr1-XNbxH2 Alloys

    NASA Astrophysics Data System (ADS)

    Quijano, Ramiro; de Coss, Romeo; Singh, David

    2008-03-01

    The transition metal dihydrides TiH2 and ZrH2 present the fluorite structure (CaF2) at high temperature but undergoes a tetragonal distortion with c/a<1 at low temperature. Electronic band structure calculations have shown that TiH2 and ZrH2 in the cubic phase display a very flat band at the Fermi level. Thus the low temperature tetragonal distortion has been associated to a Jahn-Teller effect. In order to understand the role of band filling in controlling the structural instability of the transition metal dihydrides, we have performed a first-principles total energy study of the Ti1-XVxH2 and Zr1-xNbxH2 alloys. The calculations were performed using FP-LAPW method within the (DFT) and we use the GGA for exchange correlation functional energy. The critical concentration for which the Jahn-Teller effect is suppressed, was determined from the evolution of the tetragonal-cubic energy barrier. We discuss the electronic mechanism of the structural-instability, in terms of the band filling. From the obtained results we conclude that the tetragonal distortion in TiH2 and ZrH2 is not produced only by a Jahn-Teller Effect. This research was supported by Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grant No. 43830-F.

  8. Effects of Spin-Orbit Coupling on Covalent Bonding and the Jahn-Teller Effect Are Revealed with the Natural Language of Spinors.

    PubMed

    Zeng, Tao; Fedorov, Dmitri G; Schmidt, Michael W; Klobukowski, Mariusz

    2011-09-13

    The orbital-based natural language describing the complexity of chemistry ( Stowasser , R. ; Hoffmann , R. J. Am. Chem. Soc. 1999 , 121 , 3414 ) was extended by us recently to the definition of spin-orbit natural spinors ( Zeng , T. et al. J. Chem. Phys. 2011 , 134 , 214107 ). This novel method gives chemical insights into the role of spin-orbit coupling in covalent bonding and in the Jahn-Teller effect. The natural spinors are used to explain antibonding spin-orbit effects on TlH and Tl2: it is found that the spin-orbit induced charge transfer from the bonding to the nonbonding or antibonding orbitals has a large effect on the bond strength. The natural spinors are also used to explain the spin-orbit quenching of the Jahn-Teller effect in WF5: the spin-orbit interaction can stabilize the totally symmetric electron distribution so that the high-symmetry molecular structure becomes more stable than its distortions. A general discussion of the role of the spin-orbit coupling in covalent bonding and Jahn-Teller effect is given in terms of the competition between the rotational nature of the spin-orbit coupling and the directionality of the two effects. The natural spinors offer the advantage of providing a simple and clear pictorial explanation for the profound relativistic spin-dependent interactions in chemistry often appearing as a black box answer.

  9. Numerical Estimation of the Pseudo-Jahn-Teller Effect Using Nonadiabatic Coupling Integrals in Monocyclic and Bicyclic Conjugated Molecules.

    PubMed

    Koseki, Shiro; Toyota, Azumao; Muramatsu, Takashi; Asada, Toshio; Matsunaga, Nikita

    2016-12-29

    The pseudo-Jahn-Teller (pJT) effect in monocyclic and bicyclic conjugated molecules was investigated by using the state-averaged multiconfiguration self-consistent field (MCSCF) method, together with the 6-31G(d,p) basis sets. Following the perturbation theory, the force constant along a normal mode Q is given by the sum of the classical force constant and the vibronic contribution (VC) resulting from the interaction of the ground state with excited states. The latter is given as the sum of individual contributions arising from vibronic interactions between the ground state and excited states. In the present work, each VC was calculated on the basis of nonadiabatic coupling (NAC) integrals. Furthermore, the classical force constant was estimated by taking advantage of the VC and the force constant obtained by vibrational analyses. For pentalene and heptalene, the present method seems to overestimate the VC in absolute value because of the small energy gap between the ground state and the lowest excited state. However, we are confident that the VC and the classical force constant for the other molecules are reasonable in magnitude in comparison with available literature information. Thus, it is proved that the present method is applicable and useful for numerical estimation of pJT effect.

  10. Density functional theory study of the multimode Jahn-Teller problem in the open-shell corannulenes and coronenes

    NASA Astrophysics Data System (ADS)

    Andjelković, Ljubica; Gruden-Pavlović, Maja; Zlatar, Matija

    2015-10-01

    Analysis of the multimode Jahn-Teller (JT) distortion in anions and cations of corannulene and coronene is presented, combining multideterminantal-DFT (MD-DFT) and Intrinsic Distortion Path (IDP) methods. The JT distortion is derived from the sum of contributions of all possible JT active normal modes. The Csbnd C stretching modes play the most important role in the stabilization of the systems, in all investigated species, pushing the nuclei toward the minima on the potential energy surface. The further inspection of the IDP revealed that the relaxation of the geometry arrives in the final part of the path and is encountered by the softest vibrational modes. The same trend was observed in cyclopentadienyl radical, benzene anion, benzene cation and fullerene ions. This gives microscopic origin into the mechanism of the distortion and provides general behavior of the JT effect in these similar molecules. Moreover, MD-DFT and IDP, as fast and fully non-empirical approaches, can be considered as a reliable tool for better understanding of the JT effect.

  11. Time-resolved luminescence from Jahn-Teller split states of self-trapped excitons in PbWO4

    NASA Astrophysics Data System (ADS)

    Itoh, Minoru; Sakurai, Takaaki

    2006-06-01

    This paper reports the observation of time-resolved luminescence from a self-trapped exciton (STE) localized at tetrahedral (WO4)2- complex anion in PbWO4 . The results clearly reveal that the STE luminescence is composed of three emission bands peaking at 407, 425, and 450nm . Such a composite nature is explained well by assuming that the lowest triplet states of the STE split into three sublevels owing to the symmetry lowering from Td to C3v due to the Jahn-Teller effect. This assumption is in accordance with the theoretical prediction of Bacci [M. Bacci, S. Porcinai, E. Mihóková, M. Nikl, and K. Polák, Phys. Rev. B 64, 104302 (2001); M. Bacci, E. Mihóková, and L. S. Schulman, ibid. 66, 132301 (2002)]. The decay curve of each component and its temperature dependence are investigated in the range of 77to300K . These results are discussed on the basis of an adiabatic potential energy diagram of the triplet STE state. Time-resolved luminescence spectra are also measured for Mo-doped PbWO4 crystals. From a comparison with the spectra of undoped PbWO4 crystals, the Mo-related luminescence is clearly separated from the intrinsic luminescence due to STEs.

  12. THz and infrared excitation spectrum below the Jahn-Teller transition in Sr3Cr2O8

    NASA Astrophysics Data System (ADS)

    Wang, Zhe; Schmidt, Michael; Günther, Axel; Schaile, Sebastian; Pascher, Nikola; Mayr, Franz; Goncharov, Yurii; Krug von Nidda, Hans-Albrecht; Loidl, Alois; Quintero-Castro, Diana; Islam, A. T. M. N.; Lake, Bella; Deisenhofer, Joachim

    2012-02-01

    We report on optical excitations observed recently in Sr3Cr2O8 by THz and infrared spectroscopy. Low-energy excitations below 3 THz are detected by THz time domain spectroscopy. These excitations can be divided into two different classes according to the temperature-dependent properties. One is emergent right below the Jahn-Teller transition temperature, which is determined by specific heat measurement to occur at 285 K [1, 2]. The other appears only below 100 K, where the fluctuations are sufficiently suppressed, consistent with the temperature dependence of low-energy Raman modes [3]. Infrared transmission measurements reveal a broad crystal-field excitation, which can be associated with an electronic transition from E to T2 orbital states. [4pt] [1] Zhe Wang et al., Phys. Rev. B 83, 201102 (2011) [0pt] [2] D. L. Quintero-Castro et al., Phys. Rev. B 81, 014415 (2010) [0pt] [3] D. Wulferding et al., Phys. Rev. B 84, 064419 (2011)

  13. Dielectric anomaly and structural change related to the Jahn-Teller transition in DyVO4

    NASA Astrophysics Data System (ADS)

    Kishimoto, Kazumasa; Ishikura, Taishi; Nakamura, Hiroyuki; Wakabayashi, Yusuke; Kimura, Tsuyoshi

    2010-03-01

    RVO4 system has been studied as dielectrics for several decades. Among them, DyVO4 having Dy^3+ ( 4f^9) and V^5+ (3d^0) ions shows the Jahn-Teller (JT) transition at TD =14 K due to the interaction between 4f electrons on Dy sites and the lattice. As a result, the lattice distorts from the I41amd tetragonal to the Imma orthorhombic structure and ferroquadrupolar ordering occurs below TD. We measured the dielectric constant of a single crystal of DyVO4 and observed a distinct dielectric anomaly around TD. To clarify the origin of the dielectric anomaly, we performed detailed single crystal structure analyses. Our results suggest that the JT distortion shifts the position of oxygen ions relative to a V ion and then local polarization of a VO4 tetrahedron is induced below TD. We also report the structural domain control causing remarkable magnetocapacitance effects by applying a relatively small magnetic field (˜0.1 T), which is attributed to the strong spin-orbit coupling of Dy 4f electrons.

  14. Model of the interplay of band Jahn-Teller effect with magnetic order mediated by exchange interactions

    NASA Astrophysics Data System (ADS)

    Reddy, G. Gangadhar; Ramakanth, A.; Ghatak, S. K.; Behera, S. N.; Nolting, W.; Rao, T. Venkatappa

    2006-10-01

    A model calculation is presented with the aim to study the interplay between magnetic and structural transitions. The model consists of an orbitally doubly degenerate conduction band and a periodic array of local moments. The band electrons interact with the local spins via the s-f interaction. The interaction of the band electrons with phonons is introduced by including band Jahn-Teller (J-T) interaction. The model Hamiltonian, including the above terms, is solved for the single particle Greens function. In doing this an ansatz for self-energy of electrons, which was developed earlier, has been utilized. The quasiparticle density of states (QDOS) and hence the orbital populations are calculated treating the ferromagnetism of local moments in the mean field approximation. The critical value of electron-phonon interaction (G) for the appearance of the band J-T distortion is higher in the ferromagnetic state. The strain appears at a critical temperature (Ts) when G is greater than the critical value. The onset of ferromagnetism at TC (

  15. Contribution of Jahn-Teller and charge transfer excitations to the photovoltaic effect of manganite/titanite heterojunctions

    NASA Astrophysics Data System (ADS)

    Ifland, Benedikt; Hoffmann, Joerg; Kressdorf, Birte; Roddatis, Vladimir; Seibt, Michael; Jooss, Christian

    2017-06-01

    The effect of correlation effects on photovoltaic energy conversion at manganite/titanite heterojunctions is investigated. As a model system we choose a heterostructure consisting of the small polaron absorber Pr0.66Ca0.34MnO3 (PCMO) epitaxially grown on single-crystalline Nb-doped SrTi0.998Nb0.002O3 (STNO) substrates. The high structural and chemical quality of the interfaces is proved by detailed characterization using high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) studies. Spectrally resolved and temperature-dependent photovoltaic measurements show pronounced contributions of both the Jahn-Teller (JT) excitations and the charge transfer (CT) transitions to the photovoltaic effect at different photon energies. A linear temperature dependence of the open-circuit voltage for an excitation in the PCMO manganite is only observed below the charge-ordering temperature, indicating that the diffusion length of the photocarrier exceeds the size of the space charge region. The photovoltaic response is compared to that of a heterojunction of lightly doped Pr0.05Ca0.95MnO3 (CMO)/STNO, where the JT transition is absent. Here, significant contributions of the CT transition to the photovoltaic effect set in below the Neel temperature. We conclude that polaronic correlations and ordering effects are essentials for photovoltaic energy conversion in manganites.

  16. On the Jahn-Teller effect in the X∼2E electronic ground state of CH3F+

    NASA Astrophysics Data System (ADS)

    Sarkar, Rudraditya; Rajagopala Reddy, S.; Mahapatra, S.; Köppel, H.

    2017-01-01

    In view of recent experimental and theoretical developments, we revisit our earlier theoretical studies (Mahapatra et al., 2004, 2005) on the Jahn-Teller effect in the degenerate X∼2E electronic ground state of CH3F+. The electronic potential energy surfaces and the coupling surfaces are re-calculated employing state-of-the-art ab initio quantum chemistry methods. The vibronic Hamiltonian, constructed with the aid of multimode vibronic coupling theory and symmetry selection rules, is systematically extended to higher order in the Taylor series expansion and the parameters are carefully revised in the present study. First principles quantum dynamics study is carried out to calculate the vibronic eigenvalue spectrum of this degenerate electronic state of CH3F+. The vibronic energy levels are assigned and compared with the experimental pulsed-field-ionization zero-electron-kinetic energy (PFI-ZEKE) and one photon ZEKE spectra of CH3F+ and also with the earlier theoretical results reported in the literature.

  17. The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure

    NASA Astrophysics Data System (ADS)

    Kyono, Atsushi; Gramsch, Stephen A.; Yamanaka, Takamitsu; Ikuta, Daijo; Ahart, Muhtar; Mysen, Bjørn O.; Mao, Ho-Kwang; Hemley, Russell J.

    2012-02-01

    The crystal structure of chromite FeCr2O4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch-Murnaghan equation of state (EoS) based on the P-V data gives: K 0 = 209 (13) GPa, K' = 4.0 (fixed), and V 0 = 588 (1) Å3. The FeO4 tetrahedra and CrO6 octahedra are compressed isotropically with pressure with their Fe-O and Cr-O bond distances decreasing from 1.996 (6) to 1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe2+ cation is more compressible than the octahedral site occupied by the Cr3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K 0 = 147 (9) GPa, K' = 4.0 (fixed), V 0 = 4.07 (1) Å3 and K 0 = 275 (24) GPa, K' = 4.0 (fixed), V 0 = 10.42 (2) Å3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd-{overline{3}} m) to a tetragonal structure (space group I41 /amd). At the phase transition boundary, the two Cr-O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr-O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5° to 106.6 (7)°, which generates a "stretched" tetrahedral geometry. It is proposed that the Jahn-Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral

  18. Suppression of Jahn-Teller Distortions and Origin of Piezochromism and Thermochromism in Cu-Cl Hybrid Perovskite.

    PubMed

    Gupta, Sunny; Pandey, Tribhuwan; Singh, Abhishek Kumar

    2016-07-05

    While pressure-induced changes in the electronic, magnetic, and optical properties of Cu-Cl hybrid perovskites have been studied intensively, the correlation between these properties and pressure-induced structural changes is still vaguely understood. Here, by first-principles calculations on a model system (EDBE)[CuCl4] (EDBE = 2,2'-(ethylenedioxy)bis(ethylammonium)) (a Cu-Cl hybrid perovskite), we correlate the evolution of a series of exciting physical properties with pressure while resolving some of the long-standing debates on the fundamental electronic nature of this important class of material. The material shows two structural phase transitions and an anisotropy in compressibility with increasing pressure. After a critical pressure of 17 GPa, the structure becomes highly symmetric, thereby suppressing the Jahn-Teller distortions. At zero pressure, mapping the optical transitions with the Laporte selection rules, lower and higher energy excitations are found to be of Mott-Hubbard (MH) and charge transfer (CT) type, respectively, signifying the material to be a Mott insulator. The material shows a red shift in the charge transfer band edge with increasing pressure and temperature, demonstrating the piezochromism and the thermochromism, respectively. Piezochromism originates from the changes in mixing of Cl-Cu p-d states, while thermochromism is due to broadening of conduction band states, thereby showing different electronic and structural evolution with pressure and temperature. Furthermore, the magnetic ordering in the material was found to be stable up to higher pressures, making pressure a tool to tune the electronic property without perturbing the magnetic property.

  19. The E⊗e dynamic Jahn-Teller problem: A new insight from the strong coupling limit

    NASA Astrophysics Data System (ADS)

    Sato, Tohru; Chibotaru, Liviu F.; Ceulemans, Arnout

    2005-02-01

    Correct boundary conditions for the E⊗e dynamic Jahn-Teller problem are considered explicitly for the first time to obtain approximate analytical solutions in the strong coupling limit. Numerical solutions for the decoupled equations using the finite difference method are also presented. The numerical solutions for the decoupled equations exhibit avoided crossings in the weak coupling region, which explains the oscillating behavior of the solutions obtained by Longuet-Higgins et al. for the coupled equations. The obtained analytical energy expressions show improved agreement with the numerical calculations as compared with the previous treatment in which the potentials were assumed to be harmonic. We demonstrate that the pseudorotational energy j2/(2g2), where g is the dimensionless vibronic coupling constant, and j total angular momentum: j=±1/2,±3/2,…, in the conventional strong coupling expression for the vibronic levels of the lower sheet is exact. Non-Hermitian first-order perturbation theory gives the energy which is correct up to 1/g4. The asymptotic behavior of the wave function at the origin does not influence the corrected energy up to order of 1/g4. At the same time the treatment of the upper sheet with correct boundary conditions gives solutions which are entirely different from the corresponding Slonczewski's solutions. Besides, the correct boundary conditions enable us to evaluate the nonadiabatic coupling between the lower and upper potential sheets. The energy correction due to the nonadiabatic coupling is estimated to be of order 1/g6.

  20. Interaction of spin-orbital-lattice degrees of freedom: Vibronic state of the corner-sharing-tetrahedral frustrated spin system HoBaFe4O7 by dynamical Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Kamazawa, Kazuya; Ishikado, Motoyuki; Ohira-Kawamura, Seiko; Kawakita, Yukinobu; Kakurai, Kazuhisa; Nakajima, Kenji; Sato, Masatoshi

    2017-03-01

    A powder inelastic neutron-scattering study of HoBaFe4O7 (HBFO) revealed characteristic magnetic excitations associated with geometrical spin frustration. Dispersionless excitations in energy (ω ) and wave-vector (Q ) space are observed at several discrete energies. Some of them can be attributed to crystal-field excitations of Ho3 + in octahedral symmetry, but the others are explained instead by the vibronic state of the Fe2 + dynamical Jahn-Teller effect with orbit-spin coupling, indicating interaction among the spin, the orbital, and the lattice degree of freedom. The antiferromagnetic HBFO lattice has cubic symmetry, and both Fe2 + and Fe3 + reside on corner-sharing tetrahedra with a number ratio of 3:1. Even though Fe2 + is a Jahn-Teller active ion in tetrahedral symmetry, the system does not exhibit any static lattice distortion to the lowest temperature studied (4 K). The observed excitations can be understood by considering the dynamical interaction among spin-orbital-lattice degrees of freedom, indicating that spin fluctuation due to the frustration effect induces the dynamical Jahn-Teller effect, although in most cases a Jahn-Teller active ion Fe2 + takes the static Jahn-Teller effect in a magnetic oxide system.

  1. Jahn-Teller effect in CH2DO∕CHD2O(X̃(2)E): vibronic coupling of all vibrational modes.

    PubMed

    Shao, Zhuo; Mo, Yuxiang

    2013-06-28

    For the Jahn-Teller active methoxy radical CH3O∕CD3O(X̃(2)E), only the degenerate vibrational modes break the C3v geometric symmetry. For the isotopologues CH2DO∕CHD2O, all their normal vibrational motions break the C3v geometric symmetry, which results in a splitting of the adiabatic potential energy surfaces (APESs), that is, all vibrational modes are Jahn-Teller active. Therefore, each fundamental vibrational energy level of CH2DO∕CHD2O splits into two levels due to a combination of Jahn-Teller and spin-orbit interactions. In this work we report an ab initio calculation of the spin-vibronic energy levels of CH3O∕CH2DO∕CHD2O∕CD3O using a diabatic model. The APESs were calculated at the UCCSD(T)-F12a∕cc-pVQ(T)Z-F12a level. The vibronic parameters in the diabatic model Hamiltonian of CD3O were first determined using the least-squares fitting to the APESs. The vibronic parameters of the other three isotopologues were derived from those of CD3O using the Duschinsky rotation method. The calculated spin-vibronic energy splittings for the vibrational ground states of CH3O∕CH2DO∕CHD2O∕CD3O are 61.8∕73.5∕70.2∕54.5 cm(-1), respectively, in good agreement with the reported experimental results.

  2. First-principle investigation of Jahn-Teller distortion and topological analysis of chemical bonds in LiNiO{sub 2}

    SciTech Connect

    Chen Zhenlian; Zou Huamin; Zhu Xiaopeng; Zou Jie; Cao Jiefeng

    2011-07-15

    First-principle GGA+U calculations were performed on the undistorted rhombohedral R3-bar m model, the collinear Jahn-Teller distorted monoclinic C2/m model, and six non-collinear Jahn-Teller distortion ordering models of LiNiO{sub 2}. The zigzag and C2/m models are found to be the most stable and the next most stable structural models, respectively. An energy gap appears for the C2/m and zigzag structures, whereas no energy gap appears for the R3-bar m structure. Topological analyses were performed on the R3-bar m, C2/m and zigzag models using the atoms-in-molecules theory and the electron localization function. The results show that the Ni-O interaction is the transit closed-shell interaction, in which the net electron transfer occurs from the Ni ion to the ligand O ions. The Ni-O bond possesses the {sigma} dative bond character and is polarized toward the O ions. In the distorted structures, the bonding electrons around the oxygen atom are strongly polarized toward the long Ni-O bond. - Graphical abstract: Isosurfaces of the difference charge density and the electron localization function for the zigzag structure of LiNiO{sub 2}. Highlights: > Using ELF and AIM, topological analyses were carried out on different structures. > The zigzag Jahn-Teller distortion ordering is the most stable structure. > Semiconductor gap emerges in the C2/m and zigzag structures. > The Ni-O bonds are dative bonds. > In the distorted structures, bond electrons accumulate in the long Ni-O bond basins.

  3. Jahn-Teller distortion and magnetic transitions in perovskite RMnO3 ( R=Ho , Er, Tm, Yb, and Lu)

    NASA Astrophysics Data System (ADS)

    Tachibana, Makoto; Shimoyama, Tomotaka; Kawaji, Hitoshi; Atake, Tooru; Takayama-Muromachi, Eiji

    2007-04-01

    The perovskite RMnO3 ( R=Ho , Er, Tm, Yb, and Lu) were prepared under high pressure and studied with heat capacity and synchrotron x-ray powder diffraction measurements. The temperature interval between the antiferromagnetic transition and the first-order transition to the presumably E -type structure narrows with the decreasing ionic radius of R , and almost closes for R=Lu . Combined with the data for the larger rare earth R , the results show intricate relationship between the complex magnetic phase diagram and significant increase of Jahn-Teller distortion found for the smallest members of RMnO3 .

  4. Quadratic coupling treatment of the Jahn-Teller effect in the triply-degenerate electronic state of CH4(+): can one account for floppiness?

    PubMed

    Mondal, T; Varandas, A J C

    2012-12-07

    The Jahn-Teller (JT) coupling effects in the triply degenerate ground electronic state of methane radical cation are investigated theoretically within a quadratic vibronic coupling approach. The underlying potential energy surfaces over the two-dimensional space of nuclear coordinates, subject to the T(2) ⊗ (e + t(2) + t(2)) Jahn-Teller effect, are established from extensive ab initio calculations using the multi-reference configuration interaction method and then employed to determine the various parameters of a diabatic Hamiltonian of this system. Our previous investigation [T. Mondal and A. J. C. Varandas, J. Chem. Phys. 135, 174304 (2011)], relying on the linear vibronic coupling approach augmented by only a diagonal second-order term of the totally symmetric mode, are extended here by including all possible quadratic coupling constants of JT active e and t(2) modes. Inclusion of these quadratic couplings is found to be important to reproduce correctly the broad vibrational structure and for a better description of dynamical JT effect in the first vibronic band of this radical cation. The impact of large amplitude motions (which are responsible for floppiness of the molecule) on the vibronic structure and dynamics of the first photoelectron band have been examined via readjustment of their linear coupling parameters up to ±10%.

  5. Symmetry breaking in the planar configurations of disilicon tetrahalides: Pseudo-Jahn-Teller effect parameters, hardness and electronegativity.

    PubMed

    Kouchakzadeh, Ghazaleh; Nori-Shargh, Davood

    2015-11-21

    CCSD(T), MP2, LC-BLYP, LC-ωPBE and B3LYP methods with the Def2-TZVPP basis set and natural bond orbital (NBO) interpretations were performed to investigate the correlations between the Pseudo-Jahn-Teller Effect (PJTE) parameters [i.e. vibronic coupling constant values (F), energy gaps between reference states (Δ) and the primary force constant (K0)], structural and configurational properties, global hardness, global electronegativity, natural bond orders, stabilization energies associated with electron delocalizations and natural atomic charges of disilicon tetrafluoride (1), disilicon tetrachloride (2), disilicon tetrabromide (3) and disilicon tetraiodide (4). All levels of theory showed the trans-bent (C2h) configurations as the energy minimum structures of compounds 1-4, and the flap angles between the X2Si planes and the Si=Si bonds in the distorted (C2h) configurations decrease from compound 1 to compound 4. The negative curvatures of the ground state electronic configurations and the positive curvatures of the excited states of the adiabatic potential energy surfaces (APESs) which resulted from the mixing of the ground Ag and excited B2g states are due to the PJTE (i.e. PJT(Ag + B2g) ⊗ b2g problem). Contrary to the usual expectation, with the decrease of the energy gaps between reference states (Δ), the PJTE stabilization energy, E(PJT), decreases from compound 1 to compound 4. The canonical molecular orbital (CMO) analysis revealed that the contributions of the ψ(HOMO)(b3u) and ψL(UMO)(b1u) molecular orbitals in the vibronic coupling constant (F) decrease from compound 1 to compound 4. This fact clearly justifies the decrease of the vibronic coupling constant (F) and the primary force constant (the force constant without the PJTE) values on going from compound 1 to compound 4, leading to the decrease of the negative curvatures of the ground state electronic configuration curves of their corresponding APESs. The results obtained showed that the

  6. The modulation of Jahn-Teller coupling by elastic and binding strain perturbations-a novel view on an old phenomenon and examples from solid-state chemistry.

    PubMed

    Reinen, Dirk

    2012-04-16

    Cations in 6-coordination with orbitally degenerate E(g) ground states, such as Cu(2+) and low-spin Co(2+), play an important role in coordination chemistry-in particular, in modern complex biochemistry. The stereochemistry and the binding properties within the basic polyhedra are the subject of pronounced modifications due to vibronic coupling in such cases, but may be also significantly influenced by what is usually called an imposed strain. The latter effect makes allowance for the general observation that the host sites into which the Jahn-Teller unstable centers are substituted are seldom of O(h) symmetry and built from six equal ligands. Hence, the finally observed molecular and binding structure of the pseudo-octahedral complex is the result of the combined action of vibronic coupling and strain. The closer analysis of host-site strain effects demands to distinguish between elastic strain components, which modify the force constant of the vibronically active (here, ε(g)) vibration, and binding strain perturbations, which take account of possibly present ligands with different binding properties. A symmetry-met semiempirical strain model on such a basis is presented and a corresponding formulation within the vibronic coupling formalism is given, on the molecular level. Well-established model examples of Cu(2+) in octahedral fluoride coordination in various host solids, where a great variety of experimental results is available, are given. The derived parameters allow a detailed characterization of the structural and energy qualities of the Jahn-Teller centers, and might help to steer these properties in cases where synthesis strategies are needed. The proposed strain concept is more complex than that of Ham [F. S. Ham, Electron Paramagnetic Resonance; Plenum Press: New York, 1972; F. S. Ham, Phys. Rev. 1965, A138, 1727]; the advantage is that it is directly tied to the structure and energy of the Jahn-Teller complex in focus, although more data (experimental

  7. Lattice Distortion, Polaron Conduction, and Jahn-Teller Effect on teh Magnetoresistance of La(sub 0.7)Ca(sub 0.5)CoO(sub 3) Epitaxial Films

    NASA Technical Reports Server (NTRS)

    Yeh, N. C.; Vasquez, R. P.; Beam, D. A.; Fu, C. C.; Huynh, H.; Beach, G.

    1996-01-01

    In summary, we have investigated the role of lattice distortion, polaron conduction and Jahn-Teller coupling in the occurrence of the colossal negative magnetoresistance in perovskite oxides. We conclude that larger lattice distortion gives rise to larger zero-field resistivity and larger magnitude of negative magnetoresistance.

  8. Anomalous multi-order Raman scattering in LaMnO3: a signature of quantum lattice effects in a Jahn-Teller crystal.

    PubMed

    Kovaleva, N N; Kusmartseva, O E; Kugel, K I; Maksimov, A A; Nuzhnyy, D; Balbashov, A M; Demikhov, E I; Dejneka, A; Trepakov, V A; Kusmartsev, F V; Stoneham, A M

    2013-04-17

    The multi-order Raman scattering is studied up to fourth order for a detwinned LaMnO3 crystal. Based on a comprehensive data analysis of the polarization-dependent Raman spectra, we show that the anomalous features in the multi-order scattering could be the sidebands on the low-energy mode at about 25 cm(-1). We suggest that this low-energy mode stems from the tunneling transition between the potential energy minima arising near the Jahn-Teller Mn(3+) ion due to the lattice anharmonicity and that the multi-order scattering is activated by this low-energy electronic motion. The sidebands are dominated by the oxygen contribution to the phonon density-of-states, however, there is an admixture of an additional component, which may arise from coupling between the low-energy electronic motion and the vibrational modes.

  9. Anomalous multi-order Raman scattering in LaMnO3: a signature of quantum lattice effects in a Jahn-Teller crystal

    NASA Astrophysics Data System (ADS)

    Kovaleva, N. N.; Kusmartseva, O. E.; Kugel, K. I.; Maksimov, A. A.; Nuzhnyy, D.; Balbashov, A. M.; Demikhov, E. I.; Dejneka, A.; Trepakov, V. A.; Kusmartsev, F. V.; Stoneham, A. M.

    2013-04-01

    The multi-order Raman scattering is studied up to fourth order for a detwinned LaMnO3 crystal. Based on a comprehensive data analysis of the polarization-dependent Raman spectra, we show that the anomalous features in the multi-order scattering could be the sidebands on the low-energy mode at about 25 cm-1. We suggest that this low-energy mode stems from the tunneling transition between the potential energy minima arising near the Jahn-Teller Mn3+ ion due to the lattice anharmonicity and that the multi-order scattering is activated by this low-energy electronic motion. The sidebands are dominated by the oxygen contribution to the phonon density-of-states, however, there is an admixture of an additional component, which may arise from coupling between the low-energy electronic motion and the vibrational modes.

  10. Charge disproportionation and Jahn-Teller distortion in LiNiO2 and NaNiO2: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Chen, Hungru; Freeman, Colin L.; Harding, John H.

    2011-08-01

    Density functional theory calculations have been performed on three potential ground-state configurations of LiNiO2 and NaNiO2. These calculations show that, whereas NaNiO2 shows the expected cooperative Jahn-Teller distortion (and therefore a crystal structure with C2/m symmetry), LiNiO2 shows at least two possible crystal structures very close in energy (within 3 meV/formula unit): P21/c and P2/c. Moreover, one of them (P2/c) shows charge disproportionation of the (expected) Ni3+ cations into Ni2+ and Ni4+. We discuss the implications of this complex ground state for the interpretation of the available electron and neutron structure data, its electronic and complex magnetic behavior.

  11. Towards a model of a dynamical Jahn-Teller coupling at very low temperatures in Tb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Bonville, P.; Gukasov, A.; Mirebeau, I.; Petit, S.

    2014-02-01

    We present an interpretation of zero-field energy integrated ("diffuse") neutron scattering and of high-field magnetization data at very low temperature in the frustrated pyrochlore system Tb2Ti2O7. This material has antiferromagnetic exchange interactions, and it is expected to have an Ising character at low temperature. Contrary to expectations, it shows no magnetic ordering down to 0.05 K, being thus labeled a "spin liquid." However, the ground state in Tb2Ti2O7 is not a mere fluctuating moment paramagnet but, as demonstrated by very recent experiments, a state where the electronic degrees of freedom are hybridized with the phononic variables in an unconventional way. We show here that, by approximating this complex and still unraveled electron-phonon interaction by a dynamic Jahn-Teller coupling, one can account rather well for the diffuse neutron scattering and the low-temperature isothermal magnetization.

  12. Impact of Jahn-Teller active Mn3+ on strain effects and phase transitions in Sr0.65Pr0.35MnO3

    NASA Astrophysics Data System (ADS)

    Tan, Teck-Yee; Kennedy, Brendan J.; Zhou, Qingdi; Ling, Christopher D.; Miiller, Wojciech; Howard, Christopher J.; Carpenter, Michael A.; Knight, Kevin S.

    2012-03-01

    The mixed-valence manganite Sr0.65Pr0.35MnO3 has been prepared and its crystal and magnetic structure investigated between 7 and 1200 K using high-resolution powder neutron diffraction. The structural and lattice parameter data have been used to determine the octahedral tilting and spontaneous strains associated with the structural, electronic, and magnetic phase transitions. At room temperature, the structure is tetragonal and is characterized by cooperative out-of-phase tilts of the MnO6 octahedra about the c axis and a large Jahn-Teller-type distortion due to the presence of Mn3+. The sample exhibits a reversible phase transition from the cubic Pm3¯m perovskite to a tetragonal I4/mcm structure at 750 K. The Pm3¯m ↔ I4/mcm phase transition is continuous, and the tetragonal strain, which is dominated by the Jahn-Teller-type distortion of the MnO6 octahedra, exhibits an unusual et0.5 ∝ (Tc - T) temperature dependence. At low temperatures, a C-type antiferromagnetic structure develops with a Neel temperature TN of 250 K. The Mn magnetic moment at 7 K is 2.99(2) μB/Mn. The magnetic ordering introduces additional tetragonal strain, and this strain shows the expected quadratic dependence on the magnetic moment at low temperatures. An increase in the octahedral tilt angle at TN demonstrates an effective coupling between the magnetic ordering process and octahedral tilting.

  13. Electron spin relaxation in pseudo-Jahn-Teller low-symmetry Cu(II) complexes in diaqua(L-aspartate)Zn(II).H(2)O crystals.

    PubMed

    Hoffmann, S K; Hilczer, W; Goslar, J; Massa, M M; Calvo, R

    2001-11-01

    Low-temperature (4-55 K) pulsed EPR measurements were performed with the magnetic field directed along the z-axis of the g-factor of the low-symmetry octahedral complex [(63)Cu(L-aspartate)(2)(H2O)2] undergoing dynamic Jahn-Teller effect in diaqua(L-aspartate)Zn(II) hydrate single crystals. Spin-lattice relaxation time T(1) and phase memory time T(M) were determined by the electron spin echo (ESE) method. The relaxation rate 1/T(1) increases strongly over 5 decades in the temperature range 4-55 K. Various processes and mechanisms of T(1)-relaxation are discussed, and it is shown that the relaxation is governed mainly by Raman relaxation processes with the Debye temperature Theta(D)=204 K, with a detectable contribution from disorder in the doped Cu(2+) ions system below 12 K. An analytical approximation of the transport integral I(8) is given in temperature range T=0.025-10Theta(D) and applied for computer fitting procedures. Since the Jahn-Teller distorted configurations differ strongly in energy (delta(12)=240 cm(-1)), there is no influence of the classical vibronic dynamics mechanism on T(1). Dephasing of the ESE (phase relaxation) is governed by instantaneous diffusion and spectral diffusion below 20 K with resulting rigid lattice value 1/T(0)(M)=1.88 MHz. Above this temperature the relaxation rate 1/T(M) increases upon heating due to two mechanisms. The first is the phonon-controlled excitation to the first excited vibronic level of energy Delta=243 cm(-1), with subsequent tunneling to the neighbor potential well. This vibronic-type dynamics also produces a temperature-dependent broadening of lines in the ESEEM spectra. The second mechanism is produced by the spin-lattice relaxation. The increase in T(M) is described in terms of the spin packets forming inhomogeneously broadened EPR lines.

  14. Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal

    SciTech Connect

    Katayama, Naoyuki; Kimura, Kenta; Han, Yibo; Nasu, Joji; Drichko, Natalia; Nakanishi, Yoshiki; Halim, Mario; Ishiguro, Yuki; Satake, Ryuta; Nishibori, Eiji; Yoshizawa, Masahito; Nakano, Takehito; Nozue, Yasuo; Wakabayashi, Yusuke; Ishihara, Sumio; Hagiwara, Masayuki; Sawa, Hiroshi; Nakatsuji, Satoru

    2015-07-13

    With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose-Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Furthermore, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc2S4. To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn-Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn-Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. Lastly, we discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state.

  15. Orbital Ordering and the Cooperative Jahn-Teller Effect in Single Crystals of the Magnetic Perovskite La7/8Sr1/8MnO3

    NASA Astrophysics Data System (ADS)

    Gordon, I.; Wagner, P.; Moshchalkov, V. V.; Bruynseraede, Y.; Pinsard, L.; Revcolevschi, A.

    In the low-doped magnetic perovskite La7/8Sr1/8MnO3, a strong coupling exists between crystal structure and magnetic and electronic properties. At room temperature, the material is in a paramagnetic-semiconducting state, showing a dynamic Jahn-Teller (DJT) ordering of the Mn3+ ions. Below TJT=269 K however, the crystal goes into a cooperative Jahn-Teller (CJT) state, exhibiting antiferrodistorsive orbital ordering of the MnO6 octahedra. This leads to an increase in resistivity by a factor of 2 and to a drop of the paramagnetic susceptibility by about 20% [Physica B 155 (1989) 362; Phys. Rev. Lett. 71 (1993) 2331]. Around TC=188 K, a ferromagnetic transition occurs while the CJT effect becomes gradually weaker. Below TC the sample is metallic-like and shows a considerable colossal negative magnetoresistance (CMR) effect. Finally, the material goes into a charge-ordered, insulating state below TCO=147 K where the CJT effect completely vanishes. When crossing the phase boundary from the DJT to the CJT state, the resistivity shows a jump-like increase by a factor of roughly 2.15. This results from a frustration of the charge transport at the onset of orbital ordering. By assuming that each Mn4+ ion is surrounded only by Mn3+ nearest-neighbors and by taking into account only charge transport along the principal axes, the square-diagonals and the cube-diagonals, we are able to calculate a jump ratio of 2.26, corresponding well to the experimental value. The CJT transition also causes a sudden decrease in the magnetic moment, which has been studied by performing field-dependent SQUID measurements around TJT. Since the crystal is in a paramagnetic state around TJT, the magnetization M scales with the Brillouin function [beta](J), where J is the spin of small ferromagnetic clusters. Fitting the magnetization data with the Brillouin function results in a CJT-induced shrinking of magnetic clusters from roughly four Mn ions to three Mn ions. These cluster sizes can also be

  16. The role of Jahn-Teller distortion in insulator to semiconductor phase transition in organic-inorganic hybrid compound (p-chloroanilinium)2CuCl4 at high pressure.

    PubMed

    Ghalsasi, Pallavi; Garg, Nandini; Deo, M N; Garg, Alka; Mande, Hemant; Ghalsasi, Prasanna; Sharma, Surinder M

    2015-12-28

    (p-Chloroanilinium)2CuCl4(C2H14Cl6CuN2) is from an important family of organic-inorganic layered hybrid compounds which can be a possible candidate for multiferroicity. In situ high pressure FTIR, Raman and resistivity measurements on this compound indicate the weakening of Jahn-Teller distortion and the consequent removal of puckering of the CuCl6(4-) octahedra within the layer. These effects trigger insulator to semiconductor phase transition along with a change in the sample colour from yellow to dark red. This article explains the crucial role of the anisotropic volume reduction of the CuCl6(4-) octahedron (caused due to the quenching of Jahn-Teller distortion) in the observed insulator to semiconductor phase transition.

  17. Cavity ringdown spectrum of the forbidden A~2E''<--X~2A2' transition of NO3: Evidence for static Jahn-Teller distortion in the A~ state

    NASA Astrophysics Data System (ADS)

    Deev, Andrei; Sommar, Jonas; Okumura, Mitchio

    2005-06-01

    The Jahn-Teller effect in the first two excited states of the nitrate radical NO3 has yet to be experimentally elucidated. In this paper, direct evidence of strong Jahn-Teller interactions in the à state is presented from the first complete absorption spectrum of the ÃE″2←X˜A2'2 transition of NO3 in the gas phase in the region 5900-9000cm-1, at moderate resolution (0.15cm-1). The observed spectrum is consistent with Herzberg-Teller selection rules, and reveals strong linear and quadratic Jahn-Teller interactions in the à state. Several of the vibronic bands have been tentatively assigned, including ν2,ν3, an irregular progression in ν4, and combination bands involving ν1. Our assignments are consistent with the previous works of Weaver et al. [A. Weaver, D. W. Arnold, S. E. Bradforth, and D. M. Neumark, J. Chem. Phys. 94, 1740 (1991)] and Hirota et al. [E. Hirota, T. Ishiwata, K. Kawaguchi, M. Fujitake, N. Ohashi, and I. Tanaka, J. Phys. Chem. 107, 2829 (1997)] The band origin is not observed, in accord with the selection rules, but is determined to be T0=7064cm-1 from the observation of the 410 hot band at 6695.7cm-1. Rotational contour analysis of this band indicates that the upper state is an asymmetric rotor, establishing that NO3 undergoes static Jahn-Teller distortion in the ground vibrational level of the à state.

  18. Spin-lattice coupling, Jahn-Teller effect and the influence of the measurement rate in La{sub 0.7}Ca{sub 0.3−x}Sr{sub x}MnO{sub 3} manganites

    SciTech Connect

    Burrola-Gándara, L. A.; Elizalde Galindo, J. T.; Sáenz-Hernández, R. J.; Santillán-Rodríguez, C. R.; Lardizabal-Gutiérrez, D.; Pizá-Ruiz, P.; Matutes-Aquino, J. A.

    2016-05-15

    This work presents a study of how the magnetic and temperature variables, as well as the measurement rate, affect magnetic and structural phase transitions for La{sub 0.7}Ca{sub 0.3−x}Sr{sub x}MnO{sub 3} (x=0.15, 0.08, 0.07 and 0.06) manganites. A single phase rhombohedral crystal structure for Sr{sub 0.15} compound and a single phase orthorhombic crystal structure for Sr{sub 0.08}, Sr{sub 0.07}, and Sr{sub 0.06} compounds were identified by X ray diffraction. The Curie temperature adjustment to room temperature was reached for Sr{sub 0.07} sample, in which a Jahn-Teller transition was observed. This Jahn-Teller transition showed a susceptible response to 0.5, 1, 2, 3, 5 and 7 K/min measurement rates, and was revealed without measurement sequence at 234, 257, 196, 233, 245 and 238 K respectively in thermomagnetic curves (10 mT). Also, Curie temperature increases sequentially around 2 K for the same measurement rates. To avoid magnetic field effect, a differential scanning calorimetry for Sr{sub 0.07} sample was obtained in the same temperature region, for 2, 3, 5, 7 K/min showing the Jahn-Teller phase transition at 225 K and a vibrational like behavior in the heat flux below 225 K, for all the temperature rates. The latter, is related to the static to dynamic Jahn-Teller transition. Furthermore, Curie temperature appears around 284 K.

  19. Crystallographic, Electronic, and Magnetic Properties of Rock Salt Superstructure Sulfide Lu2CrS4 with Jahn-Teller Distortion.

    PubMed

    Tezuka, Keitaro; Wakeshima, Makoto; Nozawa, Masataka; Oshikane, Keita; Ohoyama, Kenji; Shan, Yue Jin; Imoto, Hideo; Hinatsu, Yukio

    2015-10-19

    A new chromium(II) sulfide, Lu2CrS4, with a novel structure was prepared by a solid-state reaction. The powder X-ray diffraction pattern could be indexed as a tetragonal system, with a = 7.46373(2) Å, c = 22.6338(2) Å, and space group I4̅2d (No. 122). Rietveld analysis of the pattern provided the crystal structure consisting of CrS6 and LuS6 octahedra sharing edges and apexes and revealed a rock salt superstructure with new cation (vacancy) arrangements. The electrical resistivity indicates semiconducting behavior. The magnetic susceptibility and specific heat measurements showed that the Cr ions are in the high-spin d(4) configuration and that their magnetic moments ordered antiferromagnetically at 55 K. The basic antiferromagnetic structure was determined using powder neutron diffraction data at 10 K. The band structure calculations demonstrate that the densities of states of Cr 3d electrons split into two spin-up eg bands because of Jahn-Teller distortion.

  20. An EPR investigation of the dynamic Jahn-Teller effect in SrCl2:y(2 plus) and SrCl2:Sc(2 plus)

    NASA Technical Reports Server (NTRS)

    Herrington, J. R.; Estle, T. L.; Boatner, L. A.

    1972-01-01

    EPR spectra have been observed for SrCl2:Y(2+) and SrCl2:Sc(2+) at liquid helium temperatures. At 1.2 K the spectra were dominated by anisotropic hyperfine patterns whose lineshapes and angular dependences were explained using second order solutions of the effective Hamiltonian for an isolated 2Eg state split by large random internal strains. Pronounced asymmetries in some of the strin produced lineshapes for Srcl2:Sc(2+) are shown to result from second order terms in the solution of the effective Hamiltonian. Coexisting with the anisotropic hyperfine patterns are weak nearly isotropic hyperfine patterns with typical lineshapes. Variations in the apparent intensity of lines in these weak hyperfine patterns as functions of the applied magnetic field direction and temperature imply that these lines result from averaging by vibronic relaxation of a portion of the anisotropic pattern. The effective Hamiltonian parameters for SrCl2:La(2+), SrCl2:y(2+), and SrCl2:SC(2+) are analyzed in terms of crystal field theory modified to include a dynamic Jahn-Teller effect.

  1. Valence and spin states in delafossite AgNiO2 and the frustrated Jahn-Teller system ANiO2 (A=Li,Na)

    NASA Astrophysics Data System (ADS)

    Kang, J.-S.; Lee, S. S.; Kim, G.; Lee, H. J.; Song, H. K.; Shin, Y. J.; Han, S. W.; Hwang, C.; Jung, M. C.; Shin, H. J.; Kim, B. H.; Kwon, S. K.; Min, B. I.

    2007-11-01

    Electronic structures of delafossite oxides AgNi1-xCoxO2 and the frustrated Jahn-Teller (JT) system ANiO2 (A=Li,Na) have been investigated by employing soft x-ray absorption spectroscopy and photoemission spectroscopy (PES). It is found that Ni ions are in the Ni2+-Ni3+ mixed-valent states and that the low-spin (LS) Ni3+ component increases from LiNiO2 to AgNiO2 and NaNiO2 , in agreement with the presence of the JT transition in NaNiO2 and the absence of the JT transition in LiNiO2 and AgNiO2 . In AgNi1-xCoxO2 , the Ni3+ component increases with x , while Co ions are in the LS Co3+ states for all x , which is consistent with the metallic nature for low values of x . A good agreement is found between the measured PES spectra and the calculated local spin density approximation (LSDA) electronic structures of AgNiO2 and AgCoO2 , but the pseudogap feature in PES of AgNiO2 is not described by the LSDA.

  2. Bcc and Fcc transition metals and alloys: a central role for the Jahn-Teller effect in explaining their ideal and distorted structures.

    PubMed

    Lee, Stephen; Hoffmann, Roald

    2002-05-01

    Transition metal elements, alloys, and intermetallic compounds often adopt the body centered cubic (bcc) and face centered cubic (fcc) structures. By comparing quantitative density functional with qualitative tight-binding calculations, we analyze the electronic factors which make the bcc and fcc structures energetically favorable. To do so, we develop a tight-binding function, DeltaE(star), a function that measures the energetic effects of transferring electrons within wave vector stars. This function allows one to connect distortions in solids to the Jahn-Teller effect in molecules and to provide an orbital perspective on structure determining deformations in alloys. We illustrate its use by considering first a two-dimensional square net. We then turn to three-dimensional fcc and bcc structures, and distortions of these. Using DeltaE(star), we rationalize the differences in energy of these structures. We are able to deduce which orbitals are responsible for instabilities in seven to nine valence electron per atom (e(-)/a) bcc systems and five and six e(-)/a fcc structures. Finally we demonstrate that these results account for the bcc and fcc type structures found in both the elements and binary intermetallic compounds of group 4 through 9 transition metal atoms. The outline of a theory of metal structure deformations based on loss of point group operation rather than translational symmetry is presented.

  3. Pseudo-Jahn-Teller Distortion in Two-Dimensional Phosphorus: Origin of Black and Blue Phases of Phosphorene and Band Gap Modulation by Molecular Charge Transfer.

    PubMed

    Chowdhury, Chandra; Jahiruddin, Sheik; Datta, Ayan

    2016-04-07

    Phosphorene (Pn) is stabilized as a layered material like graphite, yet it possess a natural direct band gap (Eg = 2.0 eV). Interestingly, unlike graphene, Pn exhibits a much richer phase diagram which includes distorted forms like the stapler-clip (black Pn, α form) and chairlike (blue Pn, β form) structures. The existence of these phases is attributed to pseudo-Jahn-Teller (PJT) instability of planar hexagonal P6(6-) rings. In both cases, the condition for vibronic instability of the planar P6(6-) rings is satisfied. Doping with electron donors like tetrathiafulvalene and tetraamino-tetrathiafulvalene and electron acceptors like tetracyanoquinodimethane and tetracyanoethylene convert blue Pn into N-type and black Pn into efficient P-type semiconductors, respectively. Interestingly, pristine blue Pn, an indirect gap semiconductor, gets converted into a direct gap semiconductor on electron or hole doping. Because of comparatively smaller undulation in blue Pn (with respect to black Pn), the van der Waals interactions between the dopants and blue Pn is stronger. PJT distortions for two-dimensional phosphorus provides a unified understanding of structural features and chemical reactivity in its different phases.

  4. Origin of warping in the E⊗e Jahn-Teller problem: Quadratic vibronic coupling versus anharmonicity and application to NaCl: Rh2+ and triangular molecules

    NASA Astrophysics Data System (ADS)

    García-Fernández, P.; Bersuker, I. B.; Aramburu, J. A.; Barriuso, M. T.; Moreno, M.

    2005-05-01

    A general method is suggested which allows one to separate the quadratic, cubic, and pseudo Jahn-Teller contributions to the warping of the adiabatic potential energy surface (APES) of the E⊗e problem employing ab initio calculations. Numerical results were obtained for NaCl:Rh2+ in a cluster approximation and triangular molecules (Na3,K3,Cu3,Ag3) using density functional theory (DFT) and multireference second-order perturbation theory (CASPT2) methods. A largely unexpected result is that the contribution of cubic anharmonicity to the energy barrier between the minima of the lower and upper branches of the APES is dominant in all the systems and amounts for not less than 60% of the total. Another feature is that the three different contributions mentioned above may have different signs, thus either enhancing or diminishing each other, affecting in different ways the lower and upper branches of the APES. Other details of the numerical results are also analyzed.

  5. Symmetry-adapted excited states for the T{sub 1u}(direct-product)h{sub g} Jahn-Teller system

    SciTech Connect

    Qiu, Q. C.; Dunn, J. L.; Bates, C. A.

    2001-08-15

    Jahn-Teller (JT) systems typically contain a set of equivalent-energy wells in the lowest adiabatic potential-energy surface (APES). Quantum-mechanical tunneling between these wells (the dynamic JT effect) must be allowed for by taking appropriate symmetrized combinations of oscillator-type states associated with the wells. It is important to be able to describe the excited states of such systems for a number of reasons. One particular reason is that they are required for the calculation of second-order vibronic reduction factors, which in turn are useful for modeling experimental data using effective Hamiltonians. In this paper, projection-operator techniques are used to obtain general expressions for the symmetry-adapted excited states of the icosahedral T{sub 1u}(direct-product)h{sub g} JT system for the case of D{sub 5d} minima in the APES. Analytical expressions for the states and their energies for one-phonon excitation are given explicitly. The energies of a selection of states with two-phonon excitations are also obtained and plotted. The results obtained in this paper are applicable to the C{sub 60}{sup -} molecule.

  6. Virtual free ion magnetism and the absence of Jahn-Teller distortion in a linear two-coordinate complex of high-spin iron(II).

    PubMed

    Reiff, William M; LaPointe, Anne M; Witten, Edward H

    2004-08-25

    Mössbauer spectroscopy and dc magnetization measurements have been used to characterize the low temperature magnetism of a rigorously linear, two-coordinate complex of high-spin Fe(II), Fe[(C(Si(CH3)3]2 (1). The local C-Fe-C chromophore of 1 exhibits novel slow, single-ion paramagnetic relaxation and fully resolved magnetic hyperfine splitting of its zero field Mössbauer spectrum over the range approximately 100 to approximately 50K. The hyperfine field at 4.2 K is 152 T! This is the largest magnetic hyperfine field observed for iron to date regardless of spin, oxidation state, or coordination environment. This observation is attributable to the large unquenched orbital angular momentum corresponding to the degenerate ground (dxy, dx2-y2) orbital pair of 1 in local Dinfinityh symmetry. Maintenance of the ground-state degeneracy is required by the Jahn-Teller theorem leading to the unprecedented result that the magnitude of the magnetic moment of 1's 5Deltag ground state is essentially that of the parent free ion (5D4) ground term.

  7. Ti3+ on Nb site: A paramagnetic Jahn-Teller center in vacuum-reduced LiNbO3:Mg:Ti single crystals

    NASA Astrophysics Data System (ADS)

    Corradi, G.; Zaritskii, I. M.; Hofstaetter, A.; Polgár, K.; Rakitina, L. G.

    1998-10-01

    An axial EPR signal observed in vacuum annealed LiNbO3 single crystals doped with 8 mol % Mg and 0.05 mol % Ti has been attributed to Ti3+ on Nb site. The g tensor components (g||=1.760+/-0.005 and g⊥=1.786+/-0.005 for T=5 K and g||=g⊥=1.893+/-0.005 for T=74 K), resulting in outstandingly low values of the orbital reduction factor (from k=0.16 to 0.13), can be explained by a dynamic pseudo-Jahn-Teller effect. The vibronic coupling of the center is much stronger than that reported for other nd1 centers with similar trigonally distorted octahedral coordination in LiNbO3 like the Ti3+ on Li site and trapped Nb4+ polarons on both cation sites. Stronger coupling for ions on or near the Nb site is understood as a result of smaller trigonal splitting of the ground state due to the more central position of the Nb site in the oxygen octahedron. Electron transfer from the observed Ti3+ center to lattice niobiums, resulting in Nb4+ trapped polarons, has been stimulated by illumination in the near UV region. The average energy difference of the involved Ti4+/3+ and Nb5+/4+ donor levels has been estimated to be 70+/-23 meV depending also on the distance of compensating Mg2+ ions on nearby Li sites.

  8. Ba3(Cr0.97(1)Te0.03(1))2TeO9: in Search of Jahn-Teller Distorted Cr(II) Oxide

    SciTech Connect

    Li, Manrong; Deng, Zheng; Lapidus, Saul H.; Stephens, Peter W.; Segre, Carlo U.; Croft, Mark; Sena, Robert Paria; Hadermann, Joke; Walker, David; Greenblatt, Martha

    2016-10-17

    A novel 6H - type hexagonal perovskite Ba 3 (Cr 0.97(1) Te 0.03 (1 ) ) 2 TeO 9 was prepared at high pressure (6 GPa) and temperature ( 1 773 K). Both transmission electron microscopy and synchrotron powder x - ray diffraction data demonstrate that Ba 3 (Cr 0.97(1) Te 0.03(1) ) 2 TeO 9 crystallize s in P6 3 / mmc with face - shared (Cr 0.97(1) Te 0.03(1) )O 6 octahedral pairs interconnected with TeO 6 octahedra via corner - sharing. Structure analysis shows a mixed Cr 2+ /Cr 3+ valence state with ~ 10% Cr 2+ . The existence of Cr 2+ in Ba 3 (Cr 2+ 0.10(1) Cr 3+ 0.87(1) Te 6+ 0.03 ) 2 TeO 9 is further evidenced by x - ray absorption near edge spectr oscopy . Magnetic properties measurements show a paramagnetic response down to 4 K and a small glassy - state curvature at low temperature. In this work, the o ctahedral Cr 2+ O 6 component is stabilized in an oxide material for the first time ; the expected Jahn - Teller distortion of high - spin ( d 4 ) Cr 2+ is not found , which is attributed to the small proportion of Cr 2+ (~ 10%) and the face - sharing arrangement of CrO 6 octahedral pairs, that structu rally dis favor axial distortion.

  9. Cooperative Jahn-Teller effect in a 2D mesoscopic C{60/n-} system with D5d symmetry adsorbed on buffer layers using Ising EFT model

    NASA Astrophysics Data System (ADS)

    Abou Ghantous, M.; Moujaes, E. A.; Dunn, J. L.; Khater, A.

    2012-06-01

    Fullerene molecules adsorbed on surfaces often show macroscopic average distortions. As charged ions C60n- are known to be Jahn-Teller (JT) active, it is suggested that these distortions could be a manifestation of cooperative JT effects (CJTE) due to interactions between neighbouring fullerene ions. In order to understand the distortion properties it is necessary to take correlations between different distortions into account. However, this can't easily be done in the mean field approximation usually used to describe the CJTE. We therefore propose an alternative procedure to describe 2D mesoscopic islands of C60 ions in which a pseudo vector spin overrightarrow{S} is evoked to represent degenerate JT-distorted states when the quadratic JT coupling is considered. This approach is analogous to methods used for 2D magnetic systems. We then use the differential operator technique in effective field theory within the Ising approach. We include the effects of weak surface interactions and dynamic motion between equivalent distortions via terms equivalent to anisotropy and a transverse field in magnetism respectively. For distortions to D5d symmetry, we determine single site correlations as a function of temperature, the macroscopic average distortion describing a structural phase transition, and the isothermal response function. Phase diagrams are presented for relevant cases of the system parameters.

  10. Jahn-Teller effect in van der Waals complexes; Ar-C6H6+ and Ar-C6D6+

    NASA Astrophysics Data System (ADS)

    van der Avoird, Ad; Lotrich, Victor F.

    2004-06-01

    The two asymptotically degenerate potential energy surfaces of argon interacting with the X˜ 2E1g ground state benzene+ cation were calculated ab initio from the interaction energy of the neutral Ar-benzene complex given by Koch et al. [J. Chem. Phys. 111, 198 (1999)] and the difference of the geometry-dependent ionization energies of the complex and the benzene monomer computed by the outer valence Green's function method. Coinciding minima in the two potential surfaces of the ionic complex occur for Ar on the C6v symmetry axis of benzene+ (the z axis) at ze=3.506 Å. The binding energy De of 520 cm-1 is only 34% larger than the value for the neutral Ar-benzene complex. The higher one of the two surfaces is similar in shape to the neutral Ar-benzene potential, the lower potential is much flatter in the (x,y) bend direction. Nonadiabatic (Jahn-Teller) coupling was taken into account by transformation of the two adiabatic potentials to a two-by-two matrix of diabatic potentials. This transformation is based on the assumption that the adiabatic states of the Ar-benzene+ complex geometrically follow the Ar atom. Ab initio calculations of the nonadiabatic coupling matrix element between the adiabatic states with the two-state-averaged CAS-SCF(5,6) method confirmed the validity of this assumption. The bound vibronic states of both Ar-C6H6+ and Ar-C6D6+ were computed with this two-state diabatic model in a basis of three-dimensional harmonic oscillator functions for the van der Waals modes. The binding energy D0=480 cm-1 of the perdeuterated complex agrees well with the experimental upper bound of 485 cm-1. The ground and excited vibronic levels and wave functions were used, with a simple model dipole function, to generate a theoretical far-infrared spectrum. Strong absorption lines were found at 10.1 cm-1 (bend) and 47.9 cm-1 (stretch) that agree well with measurements. The unusually low bend frequency is related to the flatness of the lower adiabatic potential in the

  11. High-pressure behavior of cuprospinel CuFe2O4: Influence of the Jahn-Teller effect on the spinel structure

    DOE PAGES

    Kyono, Atsushi; Gramsch, Stephen A.; Nakamoto, Yuki; ...

    2015-08-14

    The Jahn-Teller-effect at Cu2+ in cuprospinel CuFe2O4 was investigated using high-pressure, single crystal synchrotron x-ray diffraction (XRD) techniques at beamline BL10A at the Photon Factory, KEK, Japan. Six data sets were collected in the pressure range from ambient to 5.9 GPa at room temperature. Structural refinements based on the data were performed at 0.0, 1.8, 2.7, and 4.6 GPa. The unit cell volume of cuprospinel decreases continuously from 590.8 (6) Å3 to 579.5 (8) Å3 up to 3.8 GPa. Leastsquares fitting to a third-order Birch-Murnaghan equation of state yields zero-pressure volume V0 = 590.7 (1) Å3 and bulk modulus K0more » = 188.1 (4.4) GPa with K’ fixed at 4.0. The crystal chemical composition determined by electron-probe analysis and x-ray site-occupancy refinement is represented as [Cu0.526Fe0.474][6][Cu0.074Fe1.926]O4. Most of the Cu2+ are preferentially distributed onto the tetrahedral (T) site of the spinel structure. At 4.6 GPa, a cubic-tetragonal phase transition is indicated by a splitting of the a axis of the cubic structure into a smaller a axis and a longer c axis, with unit cell parameters a = 5.882 (1) Å and c = 8.337 (1) Å. The tetragonal crystal structure with space group I41/amd was refined to R1 = 0.0182 and wR2 = 0.0134 using observed 35 x-ray reflections. At the T site, the tetrahedral O-T-O bond angles along the c-axis direction of the unit cell decreases slightly from 109.47 ° to 108.7 (4) °, which generates a stretched tetrahedral geometry along the c-axis. The cubic-totetragonal transition induced by the Jahn-Teller effect at Cu2+ is attributable to the angular distortion at the tetrahedral site. At the octahedral (M) site, on the other hand, the two M-O bonds parallel to the caxis are shortened with respect to the four M-O bonds parallel to the ab-plane, which are lengthened as a result of the phase transition, leading to a compressed octahedral geometry along the c-axis. With the competing distortions between the

  12. High-pressure behavior of cuprospinel CuFe2O4: Influence of the Jahn-Teller effect on the spinel structure

    SciTech Connect

    Kyono, Atsushi; Gramsch, Stephen A.; Nakamoto, Yuki; Sakata, Masafumi; Kato, Masato; Tamura, Tomoya; Yamanaka, Takamitsu

    2015-08-14

    The Jahn-Teller-effect at Cu2+ in cuprospinel CuFe2O4 was investigated using high-pressure, single crystal synchrotron x-ray diffraction (XRD) techniques at beamline BL10A at the Photon Factory, KEK, Japan. Six data sets were collected in the pressure range from ambient to 5.9 GPa at room temperature. Structural refinements based on the data were performed at 0.0, 1.8, 2.7, and 4.6 GPa. The unit cell volume of cuprospinel decreases continuously from 590.8 (6) Å3 to 579.5 (8) Å3 up to 3.8 GPa. Leastsquares fitting to a third-order Birch-Murnaghan equation of state yields zero-pressure volume V0 = 590.7 (1) Å3 and bulk modulus K0 = 188.1 (4.4) GPa with K’ fixed at 4.0. The crystal chemical composition determined by electron-probe analysis and x-ray site-occupancy refinement is represented as [Cu0.526Fe0.474][6][Cu0.074Fe1.926]O4. Most of the Cu2+ are preferentially distributed onto the tetrahedral (T) site of the spinel structure. At 4.6 GPa, a cubic-tetragonal phase transition is indicated by a splitting of the a axis of the cubic structure into a smaller a axis and a longer c axis, with unit cell parameters a = 5.882 (1) Å and c = 8.337 (1) Å. The tetragonal crystal structure with space group I41/amd was refined to R1 = 0.0182 and wR2 = 0.0134 using observed 35 x-ray reflections. At the T site, the tetrahedral O-T-O bond angles along the c-axis direction of the unit cell decreases slightly from 109.47 ° to 108.7 (4) °, which generates a stretched tetrahedral geometry along the c-axis. The cubic-totetragonal transition induced by the Jahn-Teller effect at Cu2+ is attributable to the angular distortion at the tetrahedral site. At the octahedral (M) site, on the other hand, the two M-O bonds parallel to the caxis are shortened with respect to the four M-O bonds parallel to

  13. The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure

    SciTech Connect

    Kyono, Atsushi; Gramsch, Stephen A; Yamanaka, Takamitsu; Ikuta, Daijo; Ahart, Muhtar; Mysen, Bjørn O; Mao, Ho-kwang; Hemley, Russell J

    2012-03-15

    a 'stretched' tetrahedral geometry. It is proposed that the Jahn-Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn-Teller effect observed in this structure and its role in the pressure-induced phase transition.

  14. Pseudo Jahn-Teller origin of puckering in cyclohexahomoatomic molecules E6 (E = S, Se, Te) and restoring S6 planar ring configuration

    NASA Astrophysics Data System (ADS)

    Ilkhani, Ali Reza

    2015-10-01

    The pseudo Jahn-Teller effect (PJTE) is employed to explore the origin of the puckering structure of cyclohexasulfur (S6), cyclohexaselenium (Se6) and cyclohexatellurium (Te6) and their nondegenerate and degenerate vibronic excited states and their planar structure instabilities have investigated. The ab initio geometry optimization and frequency calculations show that all these cyclohexahomoatomic molecules chose D6h symmetry in the planar configuration, and according the S6 and Se6 experimental structure, the chair form of the molecules is stable structure. The vibronic coupling between the ground state 1A1g and excited state 1B2g is the cause of chair puckering in all these series compounds and the numerical solutions of the PJTE (1A1g+1B2g)⊗b2g problems describe their instability. The adiabatic potential energy surfaces (APES) cross sections of low-lying electronic states along the b2g puckering normal coordinates have calculated by the state-average complete active space self-consistent field (SA-CASSCF) method. The calculation results show that, the chair puckering instability in the S6 from unstable planar configuration with D6h symmetry to a stable D3d distorted geometry, is stronger than others, whereas it is weaker in Te6. Additionally, coordination two canions (X = H+, He2+) to the S6 chair structure restore the planarity of S6 puckered ring in the S6X2 systems, although the D6h symmetry in S6 planar ring configuration changes to the Cs symmetry in the systems.

  15. Pseudo Jahn-Teller origin of ferroelectric instability in BaTiO3 type perovskites: The Green's function approach and beyond

    NASA Astrophysics Data System (ADS)

    Polinger, V.; Garcia-Fernandez, P.; Bersuker, I. B.

    2015-01-01

    The local origin of dipolar distortions in ABO3 perovskite crystals is reexamined by means of a novel approach, the Green's function method augmented by DFT computations. The ferroelectric distortions are shown to be induced by the pseudo Jahn-Teller effect (PJTE). The latter involves vibronic hybridization (admixture) of the ground state to same-spin opposite-parity excited electronic bands. Similar to numerous molecular calculations, the PJT approach provides a deeper insight into the nature of chemical bonding in the octahedral cluster [BO6] and, in particular, reveals the local origin of its polar instability. This allows predicting directly which transition ions can create ferroelectricity. In particular, the necessary conditions are established when an ABO3 perovskite crystal with an electronic dn configuration of the complex ion [BO6] can possess both proper ferroelectric and magnetic properties. Distinguished from the variety of cluster approaches to local properties, the Green's function method includes the influence of the local vibronic-coupling perturbation on the whole crystal via the inter-cell interaction responsible for creation of electronic and vibrational bands. Calculated Green's functions combined with the corresponding numeric estimates for the nine electronic bands, their density of states, and the local adiabatic potential energy surface (APES) confirm the eight-minimum form of this surface and feasibility of the PJT origin of the polar instability in BaTiO3. We show also that multicenter long-range dipole-dipole interactions critically depend on the PJTE largely determining the magnitude of the local dipoles. DFT calculations for the bulk crystal and its clusters confirm that the dipolar distortions are of local origin, but become possible only when their influence on (relaxation of) the whole lattice is taken into account. The results are shown to be in full qualitative and semiquantitative agreement with the experimental data for this

  16. Incorporation of Jahn-Teller Cu(2+) Ions into Magnetoelectric Multiferroic MnWO4: Structural, Magnetic, and Dielectric Permittivity Properties of Mn1-xCuxWO4 (x ≤ 0.25).

    PubMed

    Patureau, Pascaline; Josse, Michaël; Dessapt, Rémi; Mevellec, Jean-Yves; Porcher, Florence; Maglione, Mario; Deniard, Philippe; Payen, Christophe

    2015-11-16

    Polycrystalline samples of Mn1-xCuxWO4 (x ≤ 0.5) have been prepared by a solid-state synthesis as well as from a citrate synthesis at moderate temperature (850 °C). The goal is to study changes in the structural, magnetic, and dielectric properties of magnetoelectric type-II multiferroic MnWO4 caused by replacing Jahn-Teller-inactive Mn(2+) (d(5), S = 5/2) ions with Jahn-Teller-active Cu(2+) (d(9), S = 1/2) ions. Combination of techniques including scanning electron microscopy, powder X-ray and neutron diffraction, and Raman spectroscopy demonstrates that the polycrystalline samples with low copper content 0 ≤ x ≤ 0.25 are solid solution that forms in the monoclinic P2/c space group. Rietveld analyses indicate that Cu atoms substitutes for Mn atoms at the Mn crystallographic site of the MnWO4 structure and suggest random distributions of Jahn-Teller-distorted CuO6 octahedra in the solid solution. Magnetic susceptibility reveals that only 5% of Cu substitution suppresses the nonpolar collinear AF1 antiferromagnetic structure observed in pure MnWO4. Type-II multiferroicity survives a weak Cu substitution rate (x < 0.15). Multiferroic transition temperature and Néel temperature increase as the amount of Cu increases. New trends in some of the magnetic properties and in dielectric behaviors are observed for x = 0.20 and 0.25. Careful analysis of the magnetic susceptibility reveals that the incorporation of Cu into MnWO4 strengthens the overall antiferromagnetic interaction and reduces the magnetic frustration.

  17. The Jahn-Teller effect in the lower electronic states of benzene cation. III. The ground-state vibrations of C6H6+ and C6D6+

    NASA Astrophysics Data System (ADS)

    Burrill, Andrew B.; Chung, You K.; Mann, Heather A.; Johnson, Philip M.

    2004-05-01

    New mass analyzed threshold ionization (MATI) spectra of the molecules C6H6+ and C6D6+ have been collected using tunable vacuum ultraviolet (VUV) single photon excitation from the neutral ground state and also using two-photon excitation through the 61 vibration of the 1B2u S1 state. Emphasis was placed on obtaining accurate relative intensities of the vibrational lines in order to use this information in the vibronic analysis. The MATI spectra collected from VUV (S0 originating state), triplet (T1), and resonant two photon (S1) excitation schemes were compared with Jahn-Teller calculations employing the classical model of Longuet-Higgins and Moffitt to obtain the Jahn-Teller coupling parameters of 3 of the 4 linearly active modes (e2g modes 6-9 in Wilson's notation). Franck-Condon factors, including the effects of geometry changes, were calculated from the vibronic wave functions and used to identify the lines in the various spectra. It is found that most of the lines with substantial intensity can be understood using only the modes 1, 6, 8, and 9. Weaker peaks are due to various non-e2g modes, but these do not derive intensity through Jahn-Teller coupling. When the effects of geometry change were included, simulations of the spectra from the calculated vibrational energies and intensities were close to the experimental spectra. This verifies the applicability of the model to the understanding of the vibrational structure of this type of molecule, but some variations indicate directions for further improvement of the model.

  18. Jahn-Teller Effect in the Phonon Properties of Defective SrTiO3 from First Principles

    SciTech Connect

    Evarestov, Robert; Blokhin, Evgeny; Gryaznov, D.; Kotomin, Eugene Alexej; Merkle, R.; Maier, Joachim

    2012-05-17

    Using a hybrid density functional theory method combined with linear combination of atomic orbitals basis set and periodic supercell approach, the atomic, electronic structure, and phonon properties were calculated for SrTiO3 containing either Fe4+ substituting host Ti4+ ions or neutral oxygen vacancies Vo. For both defects, the Jahn–Teller effect occurs, thus reducing the cubic symmetry of a perfect crystal and leading to the appearance of both Raman- and infrared-active vibrational modes. The calculated phonon densities of states and group-theoretical analysis of defect-induced phonon frequencies were used for the interpretation of the relevant experimental data, once defect-induced local modes are identified. The temperature dependence of the Vo formation energy based on the calculated Gibbs free energy was also compared with experiments, and the phonon contribution therein estimated.

  19. Multiconfiguration Self-Consistent Field Study on Formonitrile Imine and N-Substituted Nitrile Imines HCN2-R: Energy Component Analysis of the Pseudo-Jahn-Teller Effect.

    PubMed

    Toyota, Azumao; Muramatsu, Takashi; Koseki, Shiro

    2017-03-23

    Stable geometrical structures for formonitrile imine (1) and N-substituted nitrile imines HCN2-R (R = Li, BeH, BH2, CH3, CN, CCH, C6H5, NH2, OH, and F) (2-11) were examined by using the multiconfiguration self-consistent-field (MCSCF) method followed by second-order configuration interaction (SOCI) calculations and second-order multiconfiguration quasi-degenerate perturbation theory (MCQDPT2) calculations, together with the aug-cc-pVTZ basis sets. The results show that 1 suffers a pseudo-Jahn-Teller (JT) distortion from a linear C∞v structure to a C1 structure via a planar bent Cs structure. Each of the others is found to undergo pseudo-JT distortion from a symmetrical structure to a planar bent Cs structure for 2, 3, and 7 and to a C1 structure for 4, 5, 6, 8, 9, 10, and 11. At the stationary structures of 1-11, the structural characteristics were briefly discussed in terms of allenic and propargylic. To elucidate the nature of pseudo-JT distortions, energy component analyses were carried out at the MCSCF+SOCI level of theory at all of the stationary structures for the relevant molecules. In most of the molecules examined, pseudo-JT stabilizations were classified into two groups, one in which the stability arises from a lowering of the energy of the attractive term Ven and the other in which the stability results from a lowering of the energy of the repulsive terms Vnn and Vee. In addition to the above two groups, it was also found that the following three groups are responsible for the pseudo-JT stabilizations in a certain stage of the structural changes. Namely, one is a lowering of the energy of the term Vee observed in 6, another is a lowering of the energy of the terms Vee and Ven observed in 9-11, and the other is a lowering of the energy of the terms Ven and Vnn observed in 10. These energetic behaviors were accounted in terms of an elongation or a contraction of the molecular skeleton, a migration of electrons from one part of the molecule to other parts

  20. Origin of small barriers in Jahn-Teller systems: quantifying the role of 3d-4s hybridization in the model system NaCl:Ni+.

    PubMed

    Barriuso, M T; Ortiz-Sevilla, B; Aramburu, J A; García-Fernández, P; García-Lastra, J M; Moreno, M

    2013-08-19

    Despite its relevance, the microscopic origin of the energy barrier, B, between the compressed and elongated geometries of Jahn-Teller (JT) systems is not well understood yet because of a lack of quantitative data about its various contributions. Seeking to clear up this matter, we have carried out both periodic and cluster ab initio calculations on the model system NaCl:Ni(+). This system is particularly puzzling because, according to experimental data, its barrier is much smaller than that for other d(9) and d(7) ions in similar lattices. All calculations performed on the model system lead, in fact, to values |B| ≤ 160 cm(-1), which are certainly smaller than B = 500 cm(-1) derived for NaCl:M(2+) (M = Ag, Rh) or B = 1024 cm(-1) obtained for KCl:Ag(2+). As a salient feature, analysis of calculations carried out as a function of the Qθ (∼3z(2) - r(2)) coordinate unveils the microscopic origin of the barrier. It is quantitatively proven that the elongated geometry observed for NaCl:Ni(+) is due to the 3d-4s vibronic admixture, which is slightly larger than the anharmonicity in the eg JT mode that favors a compressed geometry. The existence of these two competing mechanisms explains the low value of B for the model system, contrary to cases where the complex formed by d(9) or d(7) ions is elastically decoupled from the host lattice. Although the magnitude of B for NaCl:Ni(+) is particularly small, the tunneling splitting, 3Γ, is estimated to be below 9 cm(-1), thus explaining why the coherence is easily destroyed by random strains and thus a static JT effect is observed experimentally. As a main conclusion, the barrier in JT systems cannot be understood neglecting the tiny changes of the electronic density involved in small distortions. The present calculations reasonably explain the experimental g tensor of NaCl:Ni(+), pointing out that the d-d transitions in NiCl6(5-) are much smaller than those for CuCl6(4-) and the optical electronegativity of Ni(+) is only

  1. Nonadiabatic effects in a generalized Jahn-Teller lattice model: Heavy and light polarons, pairing, and the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Majerníková, Eva; Riedel, J.; Shpyrko, S.

    2002-05-01

    The self-consistent ground state polaron potential of one-dimensional lattice of two-level molecules with spinless electrons and two dispersionless phonon modes with linear coupling and quantum phonon-assisted (nonadiabatic) transitions between the levels is found anharmonic in phonon displacements. As a function of these, the potential shows a crossover from two nonequivalent broad minima to a single narrow minimum which correspond to the positions of the levels in the ground state. Generalized variational approach respecting the mixing of levels (reflection) via a variational parameter implies prominent nonadiabatic effects: (i) In the limit of the symmetric E⊗e Jahn-Teller situation they cause transition between the regime of the predominantly one-level ``heavy'' polaron and a ``light'' polaron oscillating between the levels due to phonon assistance with almost vanishing polaron displacement. Vanishing polaron selflocalization implies enhancement of the electron transfer due to decrease of the ``heavy'' polaron mass (undressing) at the point of the transition. There can occur pairing of ``light'' polarons due to exchange of virtual phonons. Continuous transition to new energy ground state close to the transition from ``heavy'' polaron phase to ``light'' (bi)polaron phase occurs. In the ``heavy'' phase, we have found anomalous (anharmonic) enhancements of quantum fluctuations of the phonon coordinate, conjugated momentum and their product in the ground state as functions of the effective coupling which reach their maxima at E⊗e JT symmetry. They decrease rapidly to their harmonic values as soon as the ``light'' phase is stabilized. (ii) Nonadiabatic dependence of the polaron mass (Debye-Waller screening) on the optical phonon frequency appears. (iii) The contribution of Rabi oscillations to the transfer enhances significantly quantum shift of the insulator-metal transition line to higher values of the critical effective electron-phonon coupling supporting so

  2. Magnetic structure of the high-density single-valent eg Jahn-Teller system LaMn7O12

    NASA Astrophysics Data System (ADS)

    Prodi, Andrea; Gilioli, Edi; Cabassi, Riccardo; Bolzoni, Fulvio; Licci, Francesca; Huang, Qingzhen; Lynn, Jeff W.; Affronte, Marco; Gauzzi, Andrea; Marezio, Massimo

    2009-02-01

    We studied the structural and physical properties of powder samples of the high-pressure LaMn7O12 compound by means of neutron diffraction, dc magnetization, specific-heat, and dc electrical resistivity measurements. Our structural refinement shows that LaMn7O12 is the counterpart with quadruple perovskite structure of the well-known simple-perovskite LaMnO3 because both compounds are single-valent Mn3+ systems sharing a similar pseudocubic network of buckled corner-sharing MnO6 octahedra distorted by the Jahn-Teller (JT) effect. Besides this similarity, LaMn7O12 exhibits the following structural differences: (i) a monoclinic I2/m , instead of orthorhombic Pnma , structure; (ii) a much larger buckling of the MnO6 octahedra, corresponding to a Mn-O-Mn bond angle as small as ψ=180°-ϕ=136° . At TN,B=78K , the neutron data show evidence of an antiferromagnetic (AFM) structure of the octahedral Mn3+ ions ( B sites), which consists of ferromagnetically coupled antiferromagnetic ac planes. This structure, commonly referred to as C type, markedly differs from the A -type structure of LaMnO3 , which consists of antiferromagnetically coupled ferromagnetic ac planes. We argue that this difference may be due not only to the different buckling, because the magnetic superexchange interaction is sensitive to ϕ , but also to the existence of two distinct JT distorted B sites, a characteristic feature of the quadruple perovskite structure not found in LaMnO3 . A further feature of this structure is the presence of a pseudocubic sublattice of JT Mn3+ ions with square coordination ( A' site) in addition to the B -site sublattice. At TN,A'=21K , the A' sublattice of LaMn7O12 is found to form a second AFM structure consisting of AFM coupled ferromagnetic planes. This additional ordering appears to occur independently of that of the B sublattice. Finally, we observed a thermally activated insulating behavior of the resistivity similar to that previously reported for LaMnO3 , which

  3. Pseudo Jahn-Teller effect and natural bond orbital analysis of structural properties of tetrahydridodimetallenes M2H4, (M = Si, Ge, and Sn).

    PubMed

    Nori-Shargh, Davood; Mousavi, Seiedeh Negar; Boggs, James E

    2013-02-21

    The structural properties of ethene (1) and tetrahydridodimetallenes M(2)H(4) [M = Si (2), Ge (3), and Sn (4)] have been examined by means of CCSD(T)/Def2-TZVPP, MP4(SDTQ)/Def2-TZVPP, and B3LYP/Def2-TZVPP levels of theory and natural bond orbital analysis (NBO) interpretations. The results obtained showed the expected planar ground state structure for compound 1 (D(2h) symmetry) but trans-bent ground state structures for compounds 2-4 (C(2h) symmetry). The distortions of the high-symmetry configurations of compounds 2-4 are due to the pseudo Jahn-Teller effect (PJTE), which is the only source of instability of high-symmetry configurations in nondegenerate states. The distortions are due to the mixing of the ground A(g) and excited B(2g) states [i.e., HOMO(B(3u)) → LUMO + 3(B(1u)) for compound 1, HOMO(B(3u)) → LUMO + 2(B(1u)) for compound 2, and HOMO(B(3u)) → LUMO + 1(B(1u)) for compounds 3 and 4]. Importantly, the higher-lying B(1g), B(2u), and B(2g) states are not involved in the PJT interactions. The energy gaps between reference states (Δ) in the undistorted configurations decrease from compound 1 to compound 4, and the PJT stabilization energies increase. Therefore, the primary force constant of the ground state in the Q((b2g)) direction (K(0)) decreases from compound 1 to compound 4. This fact can be justified by the valence isoelectronic systems of these compounds (having similar vibronic coupling constants, F). For the purpose of more chemical transparency, the NBO results were analyzed, and their relation to the PJT interactions has been revealed. The NBO analysis showed that stabilization energy associated with π(M-H) (b(u)) → σ*(M═M) (b(u)) electron delocalization (i.e., the mixing of the distorted b(u) molecular orbitals along the b(2g) bending distortions) increases from compound 1 to compound 4. Also, by using the hybridized orbitals obtained, an n parameter is defined. The NBO results revealed that the n values in the mean hybrid orbitals

  4. Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal

    NASA Astrophysics Data System (ADS)

    Zhevstovskikh, I. V.; Bersuker, I. B.; Gudkov, V. V.; Averkiev, N. S.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Shakurov, G. S.; Ulanov, V. A.; Surikov, V. T.

    2016-06-01

    A methodology is worked out to retrieve the numerical values of all the main parameters of the six-dimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from the ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propagation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60 K for the wave propagating along the [110] direction, for both the longitudinal and the shear modes, the latter with two polarizations along the [001] and [1 1 ¯ 0 ] axes, respectively. We show that these anomalies are due to the ultrasound relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the experimental findings is based on the T2 g⊗(eg+t2 g) JTE problem including the linear and the quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis, we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states. To our knowledge, such a based-on-experimental-data numerical reconstruction of the APES

  5. Geometrical and electronic structure of the molybdenum and tungsten halides MX3 and MX4 (M = Mo, W; X = F, Cl): Jahn-Teller effect and spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Sliznev, Valery V.; Belova, Natalya V.

    2017-03-01

    The ground and lower-lying excited electronic states of MX3 and MX4 (M = Mo, W; X = F, Cl) molecules were systematically studied by the complete active space self-consistent field (CASSCF) and multiconfigurational quasi-degenerate second-order perturbation (XMCQDPT2) methods. Scalar-relativistic effects and spin-orbit coupling were taken into account employing the third-order Douglas-Kroll-Hess (DKH) Hamiltonian and full Breit-Pauli operator. The ground orbital state of MoF3 and MoCl3 complexes is quadruplet 4A2‧ state in the equilibrium configuration with D3h symmetry. If the spin-orbit interaction is taken into account the calculations result in two 4E1/2 and 4E3/2 spin-orbit states with 11-14 cm-1 energy differences instead of one 4A2‧ state. Spin-orbit interaction quenches the Jahn-Teller effect in 2E″ ground orbital state of WF3 complex in D3h configuration, and C2v configuration with (4E1/2 + 4E3/2) spin-mixed state corresponds to the minimum on the PES. The WCl3 complex reveals strong interaction of the spin-orbit states of different multiplicity. For WCl3 complex the configuration with D3h symmetry corresponds to the minimum on the PES for four lowest spin-mixed electronic states. The MoF4, MoCl4 and WCl4 complexes possess the tetrahedral equilibrium configuration with 3A2 orbital electronic state. If the spin-orbit interaction is taken into account the ground state changes to the threefold degenerated 3T2 spin-orbit state with weak Jahn-Teller effect. In the case of WF4 complex the strong Jahn-Teller effect has been discovered in the first excited 1E singlet electronic state of the tetrahedral structure, and D2d configuration with 1A1 electronic state possesses the lowest energy. The comparison with available experimental data has been performed. The tendencies in molecular parameters of complexes studied were analyzed.

  6. Investigations of the spin-Hamiltonian parameters and defect structure due to Jahn-Teller effect for the tetragonal Nb4+ center in cubic Cs2ZrCl6 crystal

    NASA Astrophysics Data System (ADS)

    Wu, Xiao-Xuan; Zheng, Wen-Chen

    2015-06-01

    The spin-Hamiltonian parameters (g factors g//, ?, and hyperfine structure constants A//, ?) of the tetragonally compressed Nb4+ center in cubic Cs2ZrCl6 crystal are calculated from two theoretical methods: one is the complete diagonalization (of energy matrix) method and another is the perturbation theory method. Both methods are based on the two-spin-orbit-parameter model where the contributions to spin-Hamiltonian parameters from the spin-orbit parameter of central dn ion (in the conventional crystal field theory) and that of ligand ion via covalence effect are contained. The calculated results from the two methods are in reasonable agreement with the experimental values. The tetragonal distortion of (NbCl6)2- octahedral cluster due to the Jahn-Teller effect for Nb4+ at the cubic Zr4+ site in Cs2ZrCl6 is also acquired. The results are discussed.

  7. Density functional theory analysis of the interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction, and spin-orbit coupling in Ca3CoMO6 (M = Co, Rh, Ir).

    PubMed

    Zhang, Yuemei; Kan, Erjun; Xiang, Hongjun; Villesuzanne, Antoine; Whangbo, Myung-Hwan

    2011-03-07

    In the isostructural oxides Ca(3)CoMO(6) (M = Co, Rh, Ir), the CoMO(6) chains made up of face-sharing CoO(6) trigonal prisms and MO(6) octahedra are separated by Ca atoms. We analyzed the magnetic and electronic properties of these oxides on the basis of density functional theory calculations including on-site repulsion and spin-orbit coupling, and examined the essential one-electron pictures hidden behind results of these calculations. Our analysis reveals an intimate interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction, and spin-orbit coupling in governing the magnetic and electronic properties of these oxides. These oxides undergo a Jahn-Teller distortion, but their distortions are weak, so that their trigonal-prism Co(n+) (n = 2, 3) ions still give rise to strong easy-axis anisotropy along the chain direction. As for the d-state split pattern of these ions, the electronic and magnetic properties of Ca(3)CoMO(6) (M = Co, Rh, Ir) are consistent with d(0) < (d(2), d(-2)) < (d(1), d(-1)) but not with (d(2), d(-2)) < d(0) < (d(1), d(-1)). The trigonal-prism Co(3+) ion in Ca(3)Co(2)O(6) has the L = 2 configuration (d(0))(1)(d(2), d(-2))(3)(d(1), d(-1))(2) because of the metal-metal interaction between adjacent Co(3+) ions in each Co(2)O(6) chain, which is mediated by their z(2) orbitals, and the spin-orbit coupling of the trigonal-prism Co(3+) ion. The spins in each CoMO(6) chain of Ca(3)CoMO(6) prefer the ferromagnetic arrangement for M = Co and Rh but the antiferromagnetic arrangement for M = Ir. The octahedral M(4+) ion of Ca(3)CoMO(6) has the (1a)(1)(1e)(4) configuration for M = Rh but the (1a)(2)(1e)(3) configuration for M = Ir, which arises from the difference in the spin-orbit coupling of the M(4+) ions and the Co···M metal-metal interactions.

  8. Effects of Lattice Distortion and Jahn-Teller Coupling on the Magnetoresistance of La(sub 0.7)Ca(sub 0.3)MnO(sub 3) and La(sub 0.5)Ca(sub 0.5)CoO(sub 3) Epitaxial Films

    NASA Technical Reports Server (NTRS)

    Yeh, N. C.; Vasquez, R. P.; Beam, D. A.; Fu, C. C.; Huynh, J.; Beach, G.

    1996-01-01

    Studies of La(sub 0.7)Ca(sub 0.3)MnO(sub 3) epitaxial films on substrates with a range of lattice constants reveal two dominant contributions to the occurence of colossal negative magnetoresistance (CMR) in these manganites:...We therefore suggest that lattice polaron conduction associated with Jahn-Teller coupling is essential for the occurence of CMR, and that lattice distortion further enhances the CMR effect in the manganites.

  9. The study of the influence of Jahn-Teller coupling and low symmetry strain on the anomalous electron paramagnetic resonance spectrum of titanium(III) doped CsAl(SO4)2ṡ12H2O

    NASA Astrophysics Data System (ADS)

    Tregenna-Piggott, Philip L. W.; Noble, Christopher J.; Pilbrow, John R.

    2000-08-01

    The controversial EPR spectrum of titanium(III) as an impurity in cesium aluminum sulphate alum has been re-examined using conventional CW- and a novel pulsed-EPR technique, which monitors the nutation frequency as a function of field. The CW-spectra display a high degree of structure, which is interpreted as arising from chemically distinct titanium(III) species. The two-dimensional nutation spectrum maps the g∥ vs g⊥ relation from just one crystal orientation, and to far greater precision than available from CW-EPR. This novel technique shows that the origin of the linewidths observed for some of the EPR lines is inhomogeneous broadening, the nature of which can be described adequately only in the two-dimensional nutation spectrum. Calculations of g∥ vs g⊥ have been undertaken by numerical diagonalization of the vibronic Hamiltonian. It is found that the relationship between g∥ and g⊥ can be modeled only by assuming that the titanium(III) ions are subject to both dynamic Jahn-Teller coupling and low symmetry strain. Furthermore, it is shown that the calculated g∥ vs g⊥ relation is strongly dependent upon the nature of the vibronic interaction assumed. An excellent reproduction of the experimental data is obtained, using parameters consistent with those employed to model the susceptibility data of the isostructural cesium titanium sulphate alum.

  10. Sr3Bi2(SeO3)6·H2O: A novel anionic layer consisting of second-order Jahn-Teller (SOJT) distortive cations

    NASA Astrophysics Data System (ADS)

    Ahn, Hyun Sun; Lee, Eun Pyo; Chang, Hong-Young; Lee, Dong Woo; Ok, Kang Min

    2015-01-01

    A new layered bismuth selenite hydrate material, Sr3Bi2(SeO3)6·H2O has been synthesized through a hydrothermal reaction using SrCO3, Bi2O3, SeO2, and water as reagents. The crystal structure of the reported material has been determined by single crystal X-ray diffraction analysis. The anionic layered framework of Sr3Bi2(SeO3)6·H2O consists of polyhedra of second-order Jahn-Teller (SOJT) distortive cations, Bi3+ and Se4+. Attributable to the variable and asymmetric coordination geometry of the constituent cations, a rich structural chemistry including uni-dimensional bands and linkers is observed in the layer. The material is thermally stable up to about 390 °C and starts decomposing due to the sublimation of SeO2 above the temperature. The UV-vis diffuse reflectance spectrum suggests a band gap of 3.3 eV. Elemental analysis, infrared spectrum, local dipole moment calculations, and electronic structure calculations are also reported.

  11. Highly stable cooperative distortion in a weak Jahn-Teller d2 cation: perovskite-type ScVO3 obtained by high-pressure and high-temperature transformation from bixbyite.

    PubMed

    Castillo-Martínez, Elizabeth; Bieringer, Mario; Shafi, Shahid P; Cranswick, Lachlan M D; Alario-Franco, Miguel Ángel

    2011-06-08

    A novel ScVO(3) perovskite phase has been synthesized at 8 GPa and 1073 K from the cation-disordered bixbyite-type ScVO(3). The new perovskite has orthorhombic symmetry at room temperature, space group Pnma, and lattice parameters a = 5.4006(2) Å, b = 7.5011(2) Å, and c = 5.0706(1) Å with Sc(3+) and V(3+) ions fully ordered on the A and B sites of the perovskite cell. The vanadium oxygen octahedra [V-O(6)] display cooperative Jahn-Teller (JT) type distortions, with predominance of the tetragonal Q(3) over the orthorhombic Q(2) JT modes. The orthorhombic perovskite shows Arrhenius-type electrical conductivity and undergoes a transition to triclinic symmetry space group P-1 close to 90 K. Below 60 K, the magnetic moments of the 4 nonequivalent vanadium ions undergo magnetic long-range ordering, resulting in a magnetic superstructure of the perovskite cell with propagation vector (0.5, 0, 0.5). The magnetic moments are confined to the xz plane and establish a close to zigzag antiferromagnetic mode.

  12. Influence of Jahn-Teller Cu2+ (3d9) ion on structural and magnetic properties of Al-Cr co-substituted CuFe2O4

    NASA Astrophysics Data System (ADS)

    Tanna, A. R.; Trivedi, U. N.; Chhantbar, M. C.; Joshi, H. H.

    2013-11-01

    Four specimens of two compositions of the spinel oxide system CuAlxCrxFe2-2xO4 with x = 0.2 and 0.6 have been synthesized by double sintering ceramic technique with different thermal history i.e. quenched and slow-cooled. X-ray diffractometry has confirmed that tetragonal distortion is present in slow-cooled sample, while it is absent in quenched sample. The lower value of saturation moment compared to Neel's moment for each composition is explained by invoking random canting of spins model. Hyperfine interaction parameters: nuclear hyperfine field, quadrupole splitting (shifts), isomer shift and Fe3+ ion distribution are deduced through computer simulation of Mössbauer spectra. 57Fe Mössbauer spectra recorded at room temperature show the effect of magnetic dilution of inter-sublattice ( A- B) interaction (frustration) more in case of quenched-sample compared to slow-cooled one. FTIR spectra also corroborate the influence of Jahn-Teller (J-T) distortion of octahedral void arising due to larger Cu2+ ion occupancy at octahedral sites. The force constants are also estimated from FTIR spectra.

  13. Pseudo Jahn-Teller origin of instability of planar configurations of hexa-heterocycles. Application to compounds with 1,2- and 1,4-C4X2 skeletons (X = O, S, Se, Te)

    NASA Astrophysics Data System (ADS)

    Ilkhani, Ali R.; Hermoso, Willian; Bersuker, Isaac B.

    2015-10-01

    The driving force of symmetry breaking in planar molecular-ring systems in nondegenerate states is the pseudo Jahn-Teller effect (PJTE), and the knowledge of the mechanism of the latter allows one to manipulate the molecular properties, in particular, by restoring the planar configuration. We explore the PJTE induced structural nonplanarity in a series of 12 hexa-heterocycles with a C4X2 skeleton, 1,2- and 1,4-dichalcogenins with X = O, S, Se, Te, and a variety of ligands (H, F, Cl, Br). All the structures are optimized in both distorted equilibrium and unstable planar configurations, and the vibrational frequencies of the latter are evaluated. Then the energy profiles of the ground and several excited states in the planar configuration along the coordinate of instability are calculated, the excited states producing the instability of the ground state via the PJTE are revealed, and the vibronic coupling constants are estimated by means of fitting the solutions of the secular equations to the corresponding energy profiles.

  14. Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba2M(VO4)2(OH), M = V(3+), Mn(3+), and Fe(3+), with Interesting Jahn-Teller and Spin-Liquid Behavior.

    PubMed

    Sanjeewa, Liurukara D; McGuire, Michael A; Garlea, Vasile O; Hu, Longyu; Chumanov, George; McMillen, Colin D; Kolis, Joseph W

    2015-07-20

    A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V(3+), Mn(3+), and Fe(3+)), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, β = 113.07(3)°, V = 408.51(2) Å(3). The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn-Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.

  15. Glass formation in microgravity

    NASA Technical Reports Server (NTRS)

    Ray, C. S.; Day, D. E.

    1987-01-01

    An account is given of containerless glass-forming experiments conducted aboard the Space Shuttle in 1985, using a single-axis acoustic levitator furnace apparatus. An attempt was made to obtain quantitative evidence for the suppression of heterogeneous nucleation/crystallization in containerless melts under microgravity conditions, as well as to study melt homogenization in the absence of gravity-driven convection and assess the feasibility of laser fusion target glass microsphere preparation with a microgravity apparatus of the present type. A ternary calcia-gallia-silica glass thus obtained indicated a 2-3-fold increase in glass-formation tendency for this material composition in microgravity, by comparison with 1g.

  16. Glass formation in microgravity

    NASA Technical Reports Server (NTRS)

    Ray, C. S.; Day, D. E.

    1987-01-01

    An account is given of containerless glass-forming experiments conducted aboard the Space Shuttle in 1985, using a single-axis acoustic levitator furnace apparatus. An attempt was made to obtain quantitative evidence for the suppression of heterogeneous nucleation/crystallization in containerless melts under microgravity conditions, as well as to study melt homogenization in the absence of gravity-driven convection and assess the feasibility of laser fusion target glass microsphere preparation with a microgravity apparatus of the present type. A ternary calcia-gallia-silica glass thus obtained indicated a 2-3-fold increase in glass-formation tendency for this material composition in microgravity, by comparison with 1g.

  17. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La1-xCaxMnO3

    DOE PAGES

    Shatnawi, Mouath; Bozin, Emil S.; Mitchell, J. F.; ...

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO6 octahedra across the OR transition at TS~720 K. The study utilizedmore » explicit two-phase PDF structural modeling, revealing that away from TMI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO3. The results hence do not support the percolative scenario for the MI transition in La1–xCaxMnO3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.« less

  18. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La1-xCaxMnO3

    SciTech Connect

    Shatnawi, Mouath; Bozin, Emil S.; Mitchell, J. F.; Billinge, Simon J. L.

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO6 octahedra across the OR transition at TS~720 K. The study utilized explicit two-phase PDF structural modeling, revealing that away from TMI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO3. The results hence do not support the percolative scenario for the MI transition in La1–xCaxMnO3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.

  19. Phase Transition and Second Harmonic Generation in Thiophosphates Ag2Cd(P2S6) and AgCd3(PS4)S2 Containing Two Second-Order Jahn-Teller Distorted Cations.

    PubMed

    Fan, Yu-Hang; Jiang, Xiao-Ming; Liu, Bin-Wen; Li, Shu-Fang; Guo, Wei-Huan; Zeng, Hui-Yi; Guo, Guo-Cong; Huang, Jin-Shun

    2017-01-03

    Two new phases in the Ag-Cd-P-S system containing two second-order Jahn-Teller (SOJT) distorted d(10) cations (Cd(2+) and Ag(+)), namely, Ag2Cd(P2S6) (1) and AgCd3(PS4)S2 (2), are obtained via medium-temperature solid-state synthesis. Compound 1 exhibits a two-dimensional layered structure and undergoes a first-order structural phase transition at approximately 280 °C. This outcome can be ascribed to the significant mismatch in the expansion coefficients between Cd-S (Ag-S) and P-P (P-S) bonds evaluated through bond valence theory. The three-dimensional non-centrosymmetric (NCS) framework of 2 is constructed by two types of tetrahedral layers consisting of corner-shared CdS4, AgS4, and PS4 tetrahedra. Compound 2 exhibits second harmonic generation (SHG) intensity of 0.45 times that of commercial AgGaS2 (AGS) at a laser irradiation of 1.85 μm and an optical band gap of 2.56 eV, and no intrinsic vibrational absorption of chemical bonds is observed in the range of 2.5-18.2 μm. Both phase transition in 1 and SHG properties in 2 are closely related to the SOJT distorted d(10) cations and diverse phosphorus-sulfur polyanions (PaSb)(n-), which together can easily result in NCS distorted structures and interesting properties.

  20. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La1-xCaxMnO3

    SciTech Connect

    Shatnawi, Mouath; Bozin, Emil S.; Mitchell, J. F.; Billinge, Simon J. L.

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO6 octahedra across the OR transition at TS~720 K. The study utilized explicit two-phase PDF structural modeling, revealing that away from TMI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO3. The results hence do not support the percolative scenario for the MI transition in La1–xCaxMnO3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.

  1. Glass formation - A contemporary view

    NASA Technical Reports Server (NTRS)

    Uhlmann, D. R.

    1983-01-01

    The process of glass formation is discussed from several perspectives. Particular attention is directed to kinetic treatments of glass formation and to the question of how fast a given liquid must be cooled in order to form a glass. Specific consideration is paid to the calculation of critical cooling rates for glass formation, to the effects of nucleating heterogeneities and transients in nucleation on the critical cooling rates, to crystallization on reheating a glass, to the experimental determination of nucleation rates and barriers to crystal nucleation, and to the characteristics of materials which are most conducive to glass formation.

  2. Orbital Dimer Model for the Spin-Glass State in Y2 Mo2 O7

    NASA Astrophysics Data System (ADS)

    Thygesen, Peter M. M.; Paddison, Joseph A. M.; Zhang, Ronghuan; Beyer, Kevin A.; Chapman, Karena W.; Playford, Helen Y.; Tucker, Matthew G.; Keen, David A.; Hayward, Michael A.; Goodwin, Andrew L.

    2017-02-01

    The formation of a spin glass generally requires that magnetic exchange interactions are both frustrated and disordered. Consequently, the origin of spin-glass behavior in Y2 Mo2 O7 —in which magnetic Mo4 + ions occupy a frustrated pyrochlore lattice with minimal compositional disorder—has been a longstanding question. Here, we use neutron and x-ray pair-distribution function (PDF) analysis to develop a disorder model that resolves apparent incompatibilities between previously reported PDF, extended x-ray-absorption fine structure spectroscopy, and NMR studies, and provides a new and physical explanation of the exchange disorder responsible for spin-glass formation. We show that Mo4 + ions displace according to a local "two-in-two-out" rule on each Mo4 tetrahedron, driven by orbital dimerization of Jahn-Teller active Mo4 + ions. Long-range orbital order is prevented by the macroscopic degeneracy of dimer coverings permitted by the pyrochlore lattice. Cooperative O2 - displacements yield a distribution of Mo-O-Mo angles, which in turn introduces disorder into magnetic interactions. Our study demonstrates experimentally how frustration of atomic displacements can assume the role of compositional disorder in driving a spin-glass transition.

  3. Orbital Dimer Model for the Spin-Glass State in Y2Mo2O7

    DOE PAGES

    Thygesen, Peter M. M.; Paddison, Joseph A. M.; Zhang, Ronghuan; ...

    2017-02-08

    The formation of a spin glass generally requires that magnetic exchange interactions are both frustrated and disordered. Consequently, the origin of spin-glass behavior in Y2Mo2O7-in which magnetic Mo4+ ions occupy a frustrated pyrochlore lattice with minimal compositional disorder-has been a longstanding question. Here, we use neutron and x-ray pair-distribution function (PDF) analysis to develop a disorder model that resolves apparent incompatibilities between previously reported PDF, extended x-rayabsorption fine structure spectroscopy, and NMR studies, and provides a new and physical explanation of the exchange disorder responsible for spin-glass formation. We show that Mo4+ ions displace according to a local "two-in-two-out" rulemore » on each Mo4 tetrahedron, driven by orbital dimerization of Jahn-Teller active Mo4+ ions. Long-range orbital order is prevented by the macroscopic degeneracy of dimer coverings permitted by the pyrochlore lattice. Cooperative O2- displacements yield a distribution of Mo-O-Mo angles, which in turn introduces disorder into magnetic interactions. In conclusion, our study demonstrates experimentally how frustration of atomic displacements can assume the role of compositional disorder in driving a spin-glass transition.« less

  4. Orbital Dimer Model for the Spin-Glass State in Y_{2}Mo_{2}O_{7}.

    PubMed

    Thygesen, Peter M M; Paddison, Joseph A M; Zhang, Ronghuan; Beyer, Kevin A; Chapman, Karena W; Playford, Helen Y; Tucker, Matthew G; Keen, David A; Hayward, Michael A; Goodwin, Andrew L

    2017-02-10

    The formation of a spin glass generally requires that magnetic exchange interactions are both frustrated and disordered. Consequently, the origin of spin-glass behavior in Y_{2}Mo_{2}O_{7}-in which magnetic Mo^{4+} ions occupy a frustrated pyrochlore lattice with minimal compositional disorder-has been a longstanding question. Here, we use neutron and x-ray pair-distribution function (PDF) analysis to develop a disorder model that resolves apparent incompatibilities between previously reported PDF, extended x-ray-absorption fine structure spectroscopy, and NMR studies, and provides a new and physical explanation of the exchange disorder responsible for spin-glass formation. We show that Mo^{4+} ions displace according to a local "two-in-two-out" rule on each Mo_{4} tetrahedron, driven by orbital dimerization of Jahn-Teller active Mo^{4+} ions. Long-range orbital order is prevented by the macroscopic degeneracy of dimer coverings permitted by the pyrochlore lattice. Cooperative O^{2-} displacements yield a distribution of Mo-O-Mo angles, which in turn introduces disorder into magnetic interactions. Our study demonstrates experimentally how frustration of atomic displacements can assume the role of compositional disorder in driving a spin-glass transition.

  5. Pseudo Jahn-Teller distortion for a tricyclic carbon sulfide (C6S8) and its suppression in S-oxygenated dithiine (C4H4(SO2)2)

    NASA Astrophysics Data System (ADS)

    Pratik, Saied Md.; Chowdhury, Chandra; Bhattacharjee, Rameswar; Jahiruddin, Sk.; Datta, Ayan

    2015-10-01

    The tricyclic carbon-sulfide, C6S8 molecule containing two S-atoms in the 1,4-position of the central six-membered ring and one disulfide (Ssbnd S) and one thione (Cdbnd S) bond on the five membered rings on its either side (1) possesses a "butterfly flapping" type distorted ground state in the gas-phase and also in β-phase of the crystal. For the isolated molecule, better consideration of the S…S non-bonding interactions in the dithiine ring in the bent form at the M06-2X/6-31+G(d,p) level leads to a significant barrier for inversion of 2.4 kcal/mol which is 2-3 times more than that previously obtained by Weber and Dolg at the B3LYP/cc-pVTZ level due to underestimation of dispersion interactions at the B3LYP level. The origin of the distortion leading to lowering of symmetry for 1 (C2h → C2) is traced to vibronic mixing between the ground state (Ag) and the low lying excited states of Au symmetry through the au normal mode, a (1Ag + 1Au + 2Au + 3Au) × au pseudo Jahn-Teller effect (PJTE) problem. Based on fitting of the ground state APES to the lowest root of the 4 × 4 secular determinant, we calculate the linear vibronic coupling constants (F0i) between the relevant states. Similar in class to 1, the S-oxygenated derivative of dithiine, C4H4(SO2)2 (2) unlike most other dithiines, remains planar. The absence of the butterfly-type puckered structure in 2 is traced to the enhanced gap (Δ0) and very small vibronic coupling (F01) between the ground and PJT active state along the au distortion which suppress the PJT instability. Considering the separation of the occupied molecular orbital (OMO) and unoccupied molecular orbitals (UMO) energy levels provide a qualitative understanding for the contrasting behavior of 1 and 2. In effect, the PJT effect is shown to be a fruitful and general tool to describe the presence or lack of molecular distortion.

  6. Investigation of dielectric relaxation, Jahn-Teller distortion, and magnetic ordering in Y substituted Pr{sub 1−x}Y{sub x}MnO{sub 3} (0.1 ≤ x ≤ 0.4)

    SciTech Connect

    Yadav, Ruchika Elizabeth, Suja; Nair, Harikrishnan S.; Kumar, Amit; Yusuf, S. M.; Adiga, Shilpa

    2015-03-07

    We report structural, magnetic, and dielectric properties of the perovskite compound Pr{sub 1−x}Y{sub x}MnO{sub 3} (0.1 ≤ x ≤ 0.4) studied using dc magnetization, ac susceptibility, neutron powder diffraction, and dielectric techniques. These compounds crystallize in orthorhombic space group (Pnma) in the temperature range 5–300 K. The Mn-O-Mn bond angle decreases with the Y substitution along with an increase in the Jahn-Teller distortion. The Jahn-Teller distortion for Pr{sub 0.9}Y{sub 0.1}MnO{sub 3} shows an anomalous change near 50 K, below which it falls sharply. Neutron powder diffraction patterns of all reported compositions at low temperature constitute additional magnetic Bragg peaks that suggest magnetic ordering. Magnetic reflections were indexed in the nuclear lattice with the propagation vector k = (0, 0, 0). Rietveld refinement of powder patterns conform to A type antiferromagnetic ordering where moments are aligned ferromagnetically in a–c plane and coupled nearly antiferromagnetically along b-axis resulting in a net ferromagnetic component along the b-direction. The antiferromagnetic transition temperature was deduced from dc magnetization and ac susceptibility data. The transition temperature decreases by nearly 22 K (from 81 K to 59 K) as yttrium content (x) increases from 0.1 to 0.4. Measurements reveal strong frequency dispersion in dielectric constant and dielectric loss. Activation energy and relaxation time are estimated from the Arrhenius plot. It is further shown that relaxation behaviour is altered with yttrium doping concentration.

  7. From spin induced ferroelectricity to dipolar glasses: Spinel chromites and mixed delafossites

    SciTech Connect

    Maignan, A.

    2012-11-15

    Magnetoelectric multiferroics showing coupling between polarization and magnetic order are attracting much attention. For instance, they could be used in memory devices. Metal-transition oxides are provided several examples of inorganic magnetoelectric multiferroics. In the present short review, spinel and delafossite chromites are described. For the former, an electric polarization is evidenced in the ferrimagnetic state for ACr{sub 2}O{sub 4} polycrystalline samples (A=Ni, Fe, Co). The presence of a Jahn-Teller cation such as Ni{sup 2+} at the A site is shown to yield larger polarization values. In the delafossites, substitution by V{sup 3+} at the Cr or Fe site in CuCrO{sub 2} (CuFeO{sub 2}) suppresses the complex antiferromagnetic structure at the benefit of a spin glass state. The presence of cation disorder, probed by transmission electron microscopy, favors relaxor-like ferroelectricity. The results on the ferroelectricity of ferrimagnets and insulating spin glasses demonstrate that, in this research field, transition-metal oxides are worth to be studied. - Graphical abstract: Electric polarization as a function of temperature is measured up to T{sub C} in three chromite ferrimagnetic spinels. Largest values are reached for spinels with Jahn-Teller cations at the A site (Ni or Fe). Highlights: Black-Right-Pointing-Pointer Electric polarization is evidenced in the ferrimagnetic state of the chromite spinels. Black-Right-Pointing-Pointer Jahn-Teller cations at the A site of these spinels lead to larger polarization values. Black-Right-Pointing-Pointer Vanadium substituted at the Cr (or Fe) site of delafossites changes the antiferromagnetic state to spin glass. Black-Right-Pointing-Pointer Electric polarization is not the result of magnetic ordering but magnetic disordering in Cr or Fe delafossites. Black-Right-Pointing-Pointer Relaxor-type ferroelectricity or spin induced ferroelectricity can be observed in the delafossites.

  8. Nanogratings formation in multicomponent silicate glasses

    NASA Astrophysics Data System (ADS)

    Lancry, M.; Zimmerman, F.; Desmarchelier, R.; Tian, J.; Brisset, F.; Nolte, S.; Poumellec, B.

    2016-03-01

    We demonstrate the formation of porous nanogratings in various oxide glasses including TiO2-doped silica, GeO2 and alumino-borosilicate by near-IR femtosecond laser radiation. ULE and GeO2 glasses exhibit similar birefringence to pure silica, whereas Borofloat 33 reveals twice weaker amplitude. Using quantitative birefringence measurements, small-angle X-ray scattering and scanning electron microscopy, we correlate birefringence and porous nanolayers formation according to laser repetition rate and glass composition. We show that heat accumulation is a crucial parameter limiting the glass decomposition and thus nanogratings formation.

  9. Bubble formation in additive manufacturing of glass

    NASA Astrophysics Data System (ADS)

    Luo, Junjie; Gilbert, Luke J.; Peters, Daniel C.; Bristow, Douglas A.; Landers, Robert G.; Goldstein, Jonathan T.; Urbas, Augustine M.; Kinzel, Edward C.

    2016-05-01

    Bubble formation is a common problem in glass manufacturing. The spatial density of bubbles in a piece of glass is a key limiting factor to the optical quality of the glass. Bubble formation is also a common problem in additive manufacturing, leading to anisotropic material properties. In glass Additive Manufacturing (AM) two separate types of bubbles have been observed: a foam layer caused by the reboil of the glass melt and a periodic pattern of bubbles which appears to be unique to glass additive manufacturing. This paper presents a series of studies to relate the periodicity of bubble formation to part scan speed, laser power, and filament feed rate. These experiments suggest that bubbles are formed by the reboil phenomena why periodic bubbles result from air being trapped between the glass filament and the substrate. Reboil can be detected using spectroscopy and avoided by minimizing the laser power while periodic bubbles can be avoided by a two-step laser melting process to first establish good contact between the filament and substrate before reflowing the track with higher laser power.

  10. Symmetry and degeneracy manifolds in Jahn-Teller molecules

    NASA Astrophysics Data System (ADS)

    Mead, C. A.

    2013-04-01

    We consider problems in dealing with molecular systems of n identical nuclei. One problem is that of finding suitable internal coordinates. For n <= 4, these can be simply the internuclear distances. For n > 4, it is shown that, with perhaps one exception, there is no internal coordinate system that treats all nuclei equivalently. We also consder the properties of conical intersections between two Born-Oppenheimer electronic energy surfaces, in particular the problem of identifying the two coordinates that remove the degeneracy to first order in the near neighborhoods of symmetry manifolds.

  11. Spin-singlet state formation in the cluster Mott insulator GaNb4S8 studied by μSR and NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Waki, T.; Kajinami, Y.; Tabata, Y.; Nakamura, H.; Yoshida, M.; Takigawa, M.; Watanabe, I.

    2010-01-01

    Muon spin relaxation (μSR) and nuclear magnetic resonance experiments revealed that the spin-singlet state with an excitation gap of ˜200K is realized from S=1/2Nb4 tetrahedral clusters in a cluster Mott insulator GaNb4S8 . The intercluster cooperative phenomenon to the singlet state at TS=32k is triggered by intracluster Jahn-Teller type structural instability developed from ˜3TS . Referring to the lattice symmetry, the formation of Nb8 octamer ( Nb4-Nb4 bond) is suggested.

  12. The formation kinetics of lunar glasses

    NASA Technical Reports Server (NTRS)

    Uhlmann, D. R.; Handwerker, C. A.; Onorato, P. I. K.; Salomaa, R.; Goncz, D.

    1978-01-01

    The kinetic treatment of crystallization and glass formation, involving the construction of time-temperature-transformation curves (TTT) corresponding to a given degree of crystallinity, is extended to permit the description of crystallization of a body initially cooled to a glassy state. The key assumption is that if at any time and temperature a crystallite is smaller than the critical size corresponding to that temperature, it will melt completely and can be ignored in any further calculations of the crystal distribution. This approach is used to predict the temperature of maximum crystallization rate for the matrix composition of lunar breccia 67975; results are shown to be in excellent agreement with experiment. Theoretical results obtained for anorthite indicate a barrier to nucleation in the range of 75 kT when the ratio of the undercooling to the liquidus temperature is 0.2. Measured nucleation barriers for the 67975 matrix composition are in the range of 42 to 45 kT.

  13. Dimethylammonium copper formate [(CH3)2NH2]Cu(HCOO)3: A metal-organic framework with quasi-one-dimensional antiferromagnetism and magnetostriction

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing; Jain, Prashant; Choi, Kwang-Yong; van Tol, Johan; Cheetham, Anthony K.; Kroto, Harold W.; Koo, Hyun-Joo; Zhou, Haidong; Hwang, Jungmin; Choi, Eun Sang; Whangbo, Myung-Hwan; Dalal, Naresh S.

    2013-06-01

    Metal-organic frameworks (MOFs) can exhibit many interesting properties such as multiferroic behavior, dipolar glass, gas storage, and protonic conductivity. Here we report that dimethylammonium copper formate (DMACuF) [(CH3)2NH2]Cu(HCOO)3, a cation templated nonporous MOF with perovskite topology, exhibits strong one-dimensional (1D) antiferromagnetism with a Néel temperature, TN, of 5.2 K. These conclusions are derived from detailed magnetic susceptibility, heat capacity, dielectric constant, and high-frequency electron paramagnetic resonance measurements as well as density functional theory (DFT) calculations. The magnetic susceptibility exhibits a broad maximum at ˜50 K, suggesting low-dimensional magnetism; heat capacity measurements show a Néel temperature of 5.2 K. The magnetization versus field data at 1.8 K shows a spin-flop transition at Hsf ˜ 1.7 T. The ratio TN/J=6.5×10-2, where J is the near-neighbor exchange constant (77.4 K), and the small value (2 K) of the interchain coupling suggests that DMACuF is close to an ideal 1D magnet. In this three-dimensional crystal lattice, the 1D magnetic behavior is made possible by the Jahn-Teller distortion of the 3d9 Cu2+ ions. Temperature dependence of the electron paramagnetic resonance field and the linewidth exhibits critical broadening for temperatures below 50 K, following a behavior quite characteristic of 1D spin systems. DFT calculations show that [(CH3)2NH2]Cu(HCOO)3 has a magnetic structure in which 1D antiferromagnetic chains parallel to the c direction are weakly coupled ferromagnetically, supporting the thermomagnetic and EPR results. Dielectric measurements under applied magnetic fields of 0-7 T reveal a kink at the TN, a clear indication of magnetostriction behavior.

  14. Film formation of CdSe quantum dot embedded phosphate glass on an FTO glass substrate

    NASA Astrophysics Data System (ADS)

    Han, Karam; Kim, Yoon Hwa; Im, Won Bin; Chung, Woon Jin

    2015-07-01

    A thick film with CdSe quantum dot (QD) embedded glass was formed on a fluorine-doped tin oxide (FTO) glass substrate. Phosphate glasses with different CdO and ZnSe concentrations were synthesized, and the heat treatment conditions were varied to determine the appropriate QD and film formation conditions. Phosphate glass with 1 mol. % CdO and 1.5 mol. % ZnSe showed controlled crystallization of CdSe QDs when they were heat treated at 550℃ for 1 hr. Absorption spectra and Raman spectroscopy identified the QD formation. Precursor glass was ground into powder and pasted onto FTO only and TiO2/FTO glass substrates via the screen printing method. Glass film embedded with QDs was successfully formed after sintering, thus demonstrating its potential for film applications. [Figure not available: see fulltext.

  15. Orbital and spin interplay in spin-gap formation in pyroxene ATi Si2 O6 (A=Na,Li)

    NASA Astrophysics Data System (ADS)

    Hikihara, Toshiya; Motome, Yukitoshi

    2004-12-01

    Interplay between orbital and spin degrees of freedom is theoretically studied for the phase transition to the spin-singlet state with lattice dimerization in pyroxene titanium oxides ATiSi2O6 (A=Na,Li) . For the quasi-one-dimensional spin- 1/2 systems, we derive an effective spin-orbital-lattice coupled model in the strong correlation limit with explicitly taking account of the t2g orbital degeneracy and investigate the model by numerical simulation as well as the mean-field analysis. We find a nontrivial feedback effect between orbital and spin degrees of freedom; as temperature decreases, development of antiferromagnetic spin correlations changes the sign of orbital correlations from antiferro- to ferro-type, and finally, the ferro-type orbital correlations induce the dimerization and the spin-singlet formation. As a result of this interplay, the system undergoes a finite-temperature transition to the spin-dimer and orbital-ferro-ordered phase concomitant with the Jahn-Teller lattice distortion. The numerical results for the magnetic susceptibility show a deviation from the Curie-Weiss behavior and well reproduce the experimental data. The results reveal that the Jahn-Teller energy scale is considerably small and the orbital and spin exchange interactions play a decisive role in the pyroxene titanium oxides.

  16. Aerodynamic levitation, supercooled liquids and glass formation

    DOE PAGES

    Benmore, C. J.; Weber, J. K. R.

    2017-05-04

    Containerless processing or ‘levitation’ is a valuable tool for the synthesis and characterization of materials, particularly at extreme temperatures and under non-equilibrium conditions. The method enables formation of novel glasses, amorphous phases, and metastable crystalline forms that are not easily accessed when nucleation and growth can readily occur at a container interface. Removing the container enables the use of a wide variety of process atmospheres to modify a materials structure and properties. In the past decade levitation methods, including acoustic, aerodynamic, electromagnetic, and electrostatic, have become well established sample environments at X-ray synchrotron and neutron sources. This article briefly reviewsmore » the methods and then focuses on the application of aerodynamic levitation to synthesize and study new materials. This is presented in conjunction with non-contact probes used to investigate the atomic structure and to measure the properties of materials at extreme temperatures. The use of aerodynamic levitation in research using small and wide-angle X-ray diffraction, XANES, and neutron scattering are discussed in the context of technique development. The use of the containerless methods to investigate thermophysical properties is also considered. We argue that structural motifs and in the liquid state can potentially lead to the fabrication of materials, whose properties would differ substantially from their well known crystalline forms.« less

  17. Crystal nucleation and glass formation in metallic alloy melts

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1984-01-01

    Homogeneous nucleation, containerless solidification, and bulk formation of metallic glasses are discussed. Homogeneous nucleation is not a limiting factor for metallic glass formation at slow cooling rates if the reduced glass transition temperature is high enough. Such glasses can be made in bulk if heterogeneous nucleants are removed. Containerless processing eleminates potential sources of nucleants, but as drop tube experiments on the Pd-Si alloys show, the free surface may still be a very effective heterogeneous nucleant. Combination of etching and heating in vacuum or fluxing can be effective for cleaning fairly large ingots of nucleants. Reduced gravity processing has a potentially useful role in the fluxing technique, for example to keep large metallic ingots surrounded by a low density, low fluidity flux if this proved difficult under ground conditions. For systems where heterogeneous nucleants in the bulk of the ingot need gravity to segregate to the flux-metal interface, reduced gravity processing may not be appropriate for bulk glass formation.

  18. Formation of bulk metallic glass by fluxing

    NASA Technical Reports Server (NTRS)

    Kui, H. W.; Turnbull, D.; Greer, A. L.

    1984-01-01

    Bulk specimens (0.4-4 g mass) of the alloy Pd40Ni40P20 have been undercooled consistently to the glass state, with no detectable superficial crystallinity, in a molten flux of dehydrated boron oxide. The minimum dimension of the most massive glass specimen, so formed, was 1.0 cm. The absence of crystallinity in the specimens was confirmed by X-ray diffraction, scanning electron microscopy, and calorimetry.

  19. Role of Alloying Additions in Glass Formation and Properties of Bulk Metallic Glasses

    PubMed Central

    Chen, Na; Martin, Laura; Luzguine-Luzgin, Dmitri V.; Inoue, Akihisa

    2010-01-01

    Alloying addition, as a means of improving mechanical properties and saving on costs of materials, has been applied to a broad range of uses and products in the metallurgical fields. In the field of bulk metallic glasses (BMGs), alloying additions have also proven to play effective and important roles in promoting glass formation, enhancing thermal stability and improving plasticity of the materials. Here, we review the work on the role of alloying additions in glass formation and performance improvement of BMGs, with focus on our recent results of alloying additions in Pd-based BMGs. PMID:28883386

  20. Kinetic criteria of glass formation and the pressure dependence of the glass transition temperature.

    PubMed

    Schmelzer, Jürn W P

    2012-02-21

    An overview on different attempts of formulation of kinetic criteria of glass formation is given. It is analyzed which of the characteristic time scales-time of observation, time of relaxation, and time of change of external parameters-have to be employed to appropriately develop such criteria. Based on this analysis, a general model-independent kinetic criterion for glass formation is formulated. As a first consequence, it is shown that it is not-as often claimed-the Deborah number which governs glass formation. Based on this general kinetic criterion for glass formation, general expressions for the dependence of the glass transition temperature on pressure (and vice versa) are obtained being essentially ratios of the partial derivatives of the appropriate relaxation times with respect to pressure and temperature, respectively. Employing, as examples, further two different (free volume and entropy based) models for the description of viscous flow and relaxation, respectively, relations similar but, in general, not identical to the classical Ehrenfest relations describing second-order equilibrium phase transitions are obtained. In this way, it can be explained why one of the Ehrenfest's relations is usually fulfilled in glass transition and the other not and why the Prigogine-Defay ratio in glass transition is not equal to one as this is the case with Ehrenfest's ratio in second-order equilibrium phase transitions. © 2012 American Institute of Physics

  1. Formation of Colloidal Nanocellulose Glasses and Gels.

    PubMed

    Nordenström, Malin; Fall, Andreas; Nyström, Gustav; Wågberg, Lars

    2017-09-26

    Nanocellulose (NC) suspensions can form rigid volume-spanning arrested states (VASs) at very low volume fractions. The transition from a free-flowing dispersion to a VAS can be the result of either an increase in particle concentration or a reduction in interparticle repulsion. In this work, the concentration-induced transition has been studied with a special focus on the influence of the particle aspect ratio and surface charge density, and an attempt is made to classify these VASs. The results show that for these types of systems two general states can be identified: glasses and gels. These NC suspensions had threshold concentrations inversely proportional to the particle aspect ratio. This dependence indicates that the main reason for the transition is a mobility constraint that, together with the reversibility of the transition, classifies the VASs as colloidal glasses. If the interparticle repulsion is reduced, then the glasses can transform into gels. Thus, depending on the preparation route, either soft and reversible glasses or stiff and irreversible gels can be formed.

  2. Tuning polymer glass formation with additives and ions

    NASA Astrophysics Data System (ADS)

    Simmons, David

    2015-03-01

    A polymer's glass transition and associated dynamic and mechanical properties are among the most important factors determining its performance in engineering applications. For this reason, decades of research have aimed to establish methods of tuning polymers' glass formation behavior. Here I describe molecular simulations providing new insight into two approaches to altering a polymer's glass formation behavior: introduction of small-molecule diluents; and introduction of charged moieties to form an ionomer. In the first case, we explore how diluent molecular properties control modifications to the host polymer's glass transition and mechanical response. Results indicate that diluents can induce a rich array of effects, necessitating development of an expanded classification beyond the usual plasticizer/antiplasticizer dichotomy. In the second case, simulations indicate that ionomer glass formation is indistinguishable from that in polymer nanocomposites, in contrast to the longstanding assumption that covalent grafting of chains to ionic aggregates in these systems leads to a qualitatively distinct effect. Taken together, these results provide new guidance towards the rational understanding and control of polymer glass-formation in a range of materials. In collaboration with Jayachandra Hari Mangalara and Dihui Ruan, The University of Akron. This material is based in part on work supported by the W.M. Keck Foundation.

  3. Substrate effects on glass formation in simple monatomic supercooled liquids

    NASA Astrophysics Data System (ADS)

    Hoang, Vo Van; Thoa, Dao Kim; Odagaki, Takashi; Qui, Le Ngoc

    2015-02-01

    Glass formation in simple monatomic supercooled liquids on substrate is studied via molecular dynamics simulations. We find that glass formation in thin films on substrate exhibits a 'heterogeneous' behavior, i.e. solidlike atoms initiate/enhance simultaneously in the near substrate region and in the interior of the system, then solidlike domain grows outward to the free surface. Substrate causes strong layering of the near substrate region of liquid and glass. Layering is enhanced with decreasing temperature and layering region exhibits a glassy behavior instead of crystalline one. We find that structure and dynamics of liquid and glass in the near substrate region is different from those of the remaining part of thin films. This means that thin films formed on substrate can be divided into three distinct parts: near substrate region, interior and free surface region. We find a significant amount of liquidlike atoms even at T

  4. Glass formation, properties and structure of soda-yttria-silica glasses

    NASA Technical Reports Server (NTRS)

    Angel, Paul W.; Hann, Raiford E.

    1992-01-01

    The glass formation region of the soda yttria silicate system was determined. The glasses within this region were measured to have a density of 2.4 to 3.1 g/cu cm, a refractive index of 1.50 to 1.60, a coefficient of thermal expansion of 7 x 10(exp -6)/C, softening temperatures between 500 and 780 C, and Vickers hardness values of 3.7 to 5.8 GPa. Aqueous chemical durability measurements were made on select glass compositions while infrared transmission spectra were used to study the glass structure and its effect on glass properties. A compositional region was identified which exhibited high thermal expansion, high softening temperatures, and good chemical durability.

  5. Glass formation, properties, and structure of soda-yttria-silicate glasses

    NASA Technical Reports Server (NTRS)

    Angel, Paul W.; Hann, Raiford E.

    1991-01-01

    The glass formation region of the soda yttria silicate system was determined. The glasses within this region were measured to have a density of 2.4 to 3.1 g/cu cm, a refractive index of 1.50 to 1.60, a coefficient of thermal expansion of 7 x 10(exp -6)/C, softening temperatures between 500 and 780 C, and Vickers hardness values of 3.7 to 5.8 GPa. Aqueous chemical durability measurements were made on select glass compositions while infrared transmission spectra were used to study the glass structure and its effect on glass properties. A compositional region was identified which exhibited high thermal expansion, high softening temperatures, and good chemical durability.

  6. Study of the glass formation of high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin C.; Kaukler, William F.; Rolin, Terry

    1992-01-01

    A number of compositions of ceramic oxide high T(sub c) superconductors were elevated for their glass formation ability by means of rapid thermal analysis during quenching, optical, and electron microscopy of the quenched samples, and with subsequent DSC measurements. Correlations between experimental measurements and the methodical composition changes identified the formulations of superconductors that can easily form glass. The superconducting material was first formed as a glass; then, with subsequent devitrification, it was formed into a bulk crystalline superconductor by a series of processing methods.

  7. Quantifying the origin of metallic glass formation

    PubMed Central

    Johnson, W. L.; Na, J. H.; Demetriou, M. D.

    2016-01-01

    The waiting time to form a crystal in a unit volume of homogeneous undercooled liquid exhibits a pronounced minimum τX* at a ‘nose temperature' T* located between the glass transition temperature Tg, and the crystal melting temperature, TL. Turnbull argued that τX* should increase rapidly with the dimensionless ratio trg=Tg/TL. Angell introduced a dimensionless ‘fragility parameter', m, to characterize the fall of atomic mobility with temperature above Tg. Both trg and m are widely thought to play a significant role in determining τX*. Here we survey and assess reported data for TL, Tg, trg, m and τX* for a broad range of metallic glasses with widely varying τX*. By analysing this database, we derive a simple empirical expression for τX*(trg, m) that depends exponentially on trg and m, and two fitting parameters. A statistical analysis shows that knowledge of trg and m alone is therefore sufficient to predict τX* within estimated experimental errors. Surprisingly, the liquid/crystal interfacial free energy does not appear in this expression for τX*. PMID:26786966

  8. Quantifying the origin of metallic glass formation

    NASA Astrophysics Data System (ADS)

    Johnson, W. L.; Na, J. H.; Demetriou, M. D.

    2016-01-01

    The waiting time to form a crystal in a unit volume of homogeneous undercooled liquid exhibits a pronounced minimum τX* at a `nose temperature' T* located between the glass transition temperature Tg, and the crystal melting temperature, TL. Turnbull argued that τX* should increase rapidly with the dimensionless ratio trg=Tg/TL. Angell introduced a dimensionless `fragility parameter', m, to characterize the fall of atomic mobility with temperature above Tg. Both trg and m are widely thought to play a significant role in determining τX*. Here we survey and assess reported data for TL, Tg, trg, m and τX* for a broad range of metallic glasses with widely varying τX*. By analysing this database, we derive a simple empirical expression for τX*(trg, m) that depends exponentially on trg and m, and two fitting parameters. A statistical analysis shows that knowledge of trg and m alone is therefore sufficient to predict τX* within estimated experimental errors. Surprisingly, the liquid/crystal interfacial free energy does not appear in this expression for τX*.

  9. Potassium Chloride Nanowire Formation Inside a Microchannel Glass Array

    SciTech Connect

    Zhang, Daqing; Moore, Sam; Wei, Jiang; Alkhateeb, Abudullah I.; Gangadean, Dev; Mahmood, Hasan; Lantrips, Justin; McIlroy, David N.; LaLonde, Aaron D.; Norton, M G.; Young, James S.; Wang, Chong M.

    2005-06-27

    The synthesis of KCl nanowires has been achieved by atomic layer deposition inside high aspect ratio channels of microchannel glass. The average diameter of the KCl nanowires is 250 nm, with a minimum observed diameter of 50 nm, and lengths up to 5 {micro}m. The Cl precursor was TaCl5, while the source of K was determined to be impurities in the microchannel glass substrate. The process for KCl nanowire formation is a three-step chemical process that simultaneously etches K from the substrate concomitant with the formation of chlorine gas. It is postulated that the curvature of the channels may influence the diameters of the KCl nanowires.

  10. Structural Relaxation of 3-Dimensionally Confined Polymer Glasses: Isobaric versus Isochoric Glass Formation

    NASA Astrophysics Data System (ADS)

    Guo, Yunlong; Zhang, Chuan; Priestley, Rodney

    2011-03-01

    We have measured the glassy-state structural relaxation of aqueous suspended polystyrene (PS) nanoparticles and the corresponding silica-capped PS nanoparticles via modulated differential scanning calorimetry. Suspended and capped-PS nanoparticles undergo glass formation and subsequent physical aging under isobaric and isochoric conditions, respectively. To account for glass transition temperature (Tg) changes with confinement, physical aging measurements were performed at a constant value of Tg minus Ta, where Ta is the aging temperature. With deceasing diameter, aqueous suspended PS nanoparticles exhibited enhanced physical aging rates in comparison to bulk PS. At all values of Tg minus Ta investigated, capped-PS nanoparticles aged at reduced rates compared to the corresponding aqueous suspended PS nanoparticles. Due to differences in paths to glass formation, suspended and capped-PS nanoparticles aged to different apparent equilibrium states. We captured the physical aging behavior of all nanoparticles via the Tool, Narayanaswamy, and Moynihan (TNM) model of structural relaxation.

  11. The formation of crystals in glasses containing rare earth oxides

    NASA Astrophysics Data System (ADS)

    Fadzil, Syazwani Mohd; Hrma, Pavel; Crum, Jarrod; Siong, Khoo Kok; Ngatiman, Mohammad Fadzlee; Said, Riduan Mt

    2014-02-01

    Korean spent nuclear fuel will reach the capacity of the available temporary storage by 2016. Pyroprocessing and direct disposal seems to be an alternative way to manage and reuse spent nuclear fuel while avoiding the wet reprocessing technology. Pyroprocessing produces several wastes streams, including metals, salts, and rare earths, which must be converted into stabilized form. A suitable form for rare earth immobilization is borosilicate glass. The borosilicate glass form exhibits excellent durability, allows a high waste loading, and is easy to process. In this work, we combined the rare earths waste of composition (in wt%) 39.2Nd2O3-22.7CeO2-11.7La2O3-10.9PrO2-1.3Eu2O3-1.3Gd2O3-8.1Sm2O3-4.8Y2O3 with a baseline glass of composition 60.2SiO2-16.0B2O3-12.6Na2O-3.8Al2O3-5.7CaO-1.7ZrO2. Crystallization in waste glasses occurs as the waste loading increases. It may produce complicate glass processing and affect the product quality. To study crystal formation, we initially made glasses containing 5%, 10% and 15% of La2O3 and then glasses with 5%, 10% and 15% of the complete rare earth mix. Samples were heat-treated for 24 hours at temperatures 800°C to 1150°C in 50°C increments. Quenched samples were analyzed using an optical microscope, scanning electron microscope with energy dispersive spectroscopy, and x-ray diffraction. Stillwellite (LaBSiO5) and oxyapatite (Ca2La8Si6O26) were found in glasses containing La2O3, while oxyapatite (Ca2La8Si6O26 and NaNd9Si6O26) precipitated in glasses with additions of mixed rare earths. The liquidus temperature (TL) of the glasses containing 5%, 10% and 15% La2O3 were 800°C, 959°C and 986°C, respectively; while TL was 825°C, 1059°C and 1267°C for glasses with 5%, 10% and 15% addition of mixed rare earth oxides. The component coefficients TB2O3, TSiO2, TCaO, and TRE2O3 were also evaluated using a recently published study.

  12. The kinetics of lunar glass formation, revisited

    NASA Technical Reports Server (NTRS)

    Klein, L. C.; Uhlmann, D. R.

    1976-01-01

    The nucleation frequency of Lunar Composition 70019, a lithified soil breccia from the center of a small crater in the Taurus-Littrow Valley, is determined using a relation that describes nucleation throughout the volume of a liquid together with measurements of the time required at temperatures of 780 to 930 C to obtain sensibly crystalline bodies. Curves indicating the time required at a given temperature to reach a particular fraction crystallized are shown to have the general form predicted by kinetic analysis. Nucleation frequencies are evaluated by applying such analysis to a curve representing the transition between glassy material and material with a sensible degree of crystallinity. The results obtained are found to be in excellent agreement with the values expected from the classical theory of homogeneous nucleation, indicating that such nucleation represents the dominant contribution to crystal formation, at least over the range of undercoolings covered (250 to 400 C).

  13. The formation of crystals in glasses containing rare earth oxides

    SciTech Connect

    Fadzil, Syazwani Mohd; Hrma, Pavel; Crum, Jarrod; Siong, Khoo Kok; Ngatiman, Mohammad Fadzlee; Said, Riduan Mt

    2014-02-12

    Korean spent nuclear fuel will reach the capacity of the available temporary storage by 2016. Pyroprocessing and direct disposal seems to be an alternative way to manage and reuse spent nuclear fuel while avoiding the wet reprocessing technology. Pyroprocessing produces several wastes streams, including metals, salts, and rare earths, which must be converted into stabilized form. A suitable form for rare earth immobilization is borosilicate glass. The borosilicate glass form exhibits excellent durability, allows a high waste loading, and is easy to process. In this work, we combined the rare earths waste of composition (in wt%) 39.2Nd{sub 2}O{sub 3}–22.7CeO{sub 2}–11.7La{sub 2}O{sub 3}–10.9PrO{sub 2}–1.3Eu{sub 2}O{sub 3}–1.3Gd{sub 2}O{sub 3}–8.1Sm{sub 2}O{sub 3}–4.8Y{sub 2}O{sub 3} with a baseline glass of composition 60.2SiO{sub 2}–16.0B{sub 2}O{sub 3}–12.6Na{sub 2}O–3.8Al{sub 2}O{sub 3}–5.7CaO–1.7ZrO{sub 2}. Crystallization in waste glasses occurs as the waste loading increases. It may produce complicate glass processing and affect the product quality. To study crystal formation, we initially made glasses containing 5%, 10% and 15% of La{sub 2}O{sub 3} and then glasses with 5%, 10% and 15% of the complete rare earth mix. Samples were heat-treated for 24 hours at temperatures 800°C to 1150°C in 50°C increments. Quenched samples were analyzed using an optical microscope, scanning electron microscope with energy dispersive spectroscopy, and x-ray diffraction. Stillwellite (LaBSiO{sub 5}) and oxyapatite (Ca{sub 2}La{sub 8}Si{sub 6}O{sub 26}) were found in glasses containing La{sub 2}O{sub 3}, while oxyapatite (Ca{sub 2}La{sub 8}Si{sub 6}O{sub 26} and NaNd{sub 9}Si{sub 6}O{sub 26}) precipitated in glasses with additions of mixed rare earths. The liquidus temperature (T{sub L}) of the glasses containing 5%, 10% and 15% La{sub 2}O{sub 3} were 800°C, 959°C and 986°C, respectively; while T{sub L} was 825°C, 1059°C and 1267°C for glasses

  14. Glass formation and properties in the gallia-calcia system

    NASA Technical Reports Server (NTRS)

    Whichard, G.; Day, D. E.

    1984-01-01

    The critical cooling rate for glass formation was measured for five compositions in the Ga2O3-CaO system and varied from a low of (315 + or - 85) C/s for a eutectic melt containing 37.5 mol pct Ga2O3 to a high of (840 + or - 60) C/s for a melt containing 52 mol pct Ga2O3. The density and refractive index both increased with increasing Ga2O3 content, but the crystallization temperature and microhardness varied only slightly. The IR spectra of these glasses suggest that both GaO4 tetrahedra and GaO6 octahedra are present.

  15. Glass formation and thermodynamics of supercooled monatomic liquids.

    PubMed

    Hoang, Vo Van; Odagaki, Takashi

    2011-06-02

    Atomic mechanism of glass formation of a supercooled simple monatomic liquid with Lennard-Jones-Gauss (LJG) interatomic potential is studied by molecular dynamics (MD) simulation. Supercooled and glassy states are obtained by cooling from the melt. Glassy state obtained at low temperatures is annealed for very long time, on the order of microsecond, and we find that glassy state remains unchanged and that the long-lived glassy state of a simple monatomic system in three dimensions is realized. We analyze the spatiotemporal properties of solid-like and liquid-like atoms that are defined by the Lindemann-like freezing criterion. The number of solid-like atoms, distributed throughout the liquid, increases with decreasing temperature toward glass transition and they form clusters. In the deeply supercooled region, almost all solid-like atoms form a single percolation cluster and its characteristic size increases sharply on further cooling. Glass formation in supercooled liquid occurs when a single percolation cluster of solid-like atoms involves a majority of atoms to form a relatively rigid solid phase. We also obtain several physical quantities of the system, including temperature dependence of mass density, Lindemann ratio, incoherent intermediate scattering function, α-relaxation time, evolution of radial distribution function, and local bond-pair orders detected by Honeycutt-Andersen analysis. We identify three characteristic temperatures related to the vitrification: a temperature at which crossover from liquid-like to solid-like dynamics occurs on cooling, the glass transition temperature, and the Vogel-Fulcher-Tammann temperature. Behavior of liquid-like atoms in glassy state has been analyzed and discussed.

  16. Glass formation, chemical properties and surface analysis of Cu-based bulk metallic glasses.

    PubMed

    Qin, Chunling; Zhao, Weimin; Inoue, Akihisa

    2011-01-01

    This paper reviews the influence of alloying elements Mo, Nb, Ta and Ni on glass formation and corrosion resistance of Cu-based bulk metallic glasses (BMGs). In order to obtain basic knowledge for application to the industry, corrosion resistance of the Cu-Hf-Ti-(Mo, Nb, Ta, Ni) and Cu-Zr-Ag-Al-(Nb) bulk glassy alloy systems in various solutions are reported in this work. Moreover, X-ray photoelectron spectroscopy (XPS) analysis is performed to clarify the surface-related chemical characteristics of the alloy before and after immersion in the solutions; this has lead to a better understanding of the correlation between the surface composition and the corrosion resistance.

  17. Glass Formation, Chemical Properties and Surface Analysis of Cu-Based Bulk Metallic Glasses

    PubMed Central

    Qin, Chunling; Zhao, Weimin; Inoue, Akihisa

    2011-01-01

    This paper reviews the influence of alloying elements Mo, Nb, Ta and Ni on glass formation and corrosion resistance of Cu-based bulk metallic glasses (BMGs). In order to obtain basic knowledge for application to the industry, corrosion resistance of the Cu–Hf–Ti–(Mo, Nb, Ta, Ni) and Cu–Zr–Ag–Al–(Nb) bulk glassy alloy systems in various solutions are reported in this work. Moreover, X-ray photoelectron spectroscopy (XPS) analysis is performed to clarify the surface-related chemical characteristics of the alloy before and after immersion in the solutions; this has lead to a better understanding of the correlation between the surface composition and the corrosion resistance. PMID:21731441

  18. Structures of late transition metal monoxides from Jahn-Teller instabilities in the rock salt lattice.

    PubMed

    Derzsi, Mariana; Piekarz, Przemysław; Grochala, Wojciech

    2014-07-11

    Most late transition metal (LTM) monoxides crystallize in other than a rock salt structure, which is so common in the earlier transition metal monoxides. Here we present theoretical evidence based on density functional theory that an electron-phonon coupling involving a single soft mode in the cubic cell is responsible for the onset of the experimentally observed structures of the late transition metal monoxides.

  19. Transition from Orbital Liquid to Jahn-Teller Insulator in Orthorhombic Perovskites RTiO3

    NASA Astrophysics Data System (ADS)

    Cheng, J.-G.; Sui, Y.; Zhou, J.-S.; Goodenough, J. B.; Su, W. H.

    2008-08-01

    Following the same strategy used for RVO3, thermal conductivity measurements have been made on a series of single-crystal perovskites RTiO3 (R=La,Nd,…,Yb). Results reveal explicitly a transition from an orbital liquid to an orbitally ordered phase at a magnetic transition temperature, which is common for both the antiferromagnetic and ferromagnetic phases in the phase diagram of RTiO3. This spin/orbital transition is consistent with the mode softening at TN in antiferromagnetic LaTiO3 and is supported by an anomalous critical behavior at Tc in ferromagnetic YTiO3.

  20. Jahn-Teller-induced femtosecond electronic depolarization dynamics of the nitrogen-vacancy defect in diamond

    PubMed Central

    Ulbricht, Ronald; Dong, Shuo; Chang, I-Ya; Mariserla, Bala Murali Krishna; Dani, Keshav M.; Hyeon-Deuk, Kim; Loh, Zhi-Heng

    2016-01-01

    Single-photon emission from the nitrogen-vacancy defect in diamond constitutes one of its many proposed applications. Owing to its doubly degenerate 3E electronic excited state, photons from this defect can be emitted by two optical transitions with perpendicular polarization. Previous measurements have indicated that orbital-selective photoexcitation does not, however, yield photoluminescence with well-defined polarizations, thus hinting at orbital-averaging dynamics even at cryogenic temperatures. Here we employ femtosecond polarization anisotropy spectroscopy to investigate the ultrafast electronic dynamics of the 3E state. We observe subpicosecond electronic dephasing dynamics even at cryogenic temperatures, up to five orders of magnitude faster than dephasing rates suggested by previous frequency- and time-domain measurements. Ab initio molecular dynamics simulations assign the ultrafast depolarization dynamics to nonadiabatic transitions and phonon-induced electronic dephasing between the two components of the 3E state. Our results provide an explanation for the ultrafast orbital averaging that exists even at cryogenic temperatures. PMID:27848938

  1. Time-dependent pseudo Jahn-Teller effect: Phonon-mediated long-time nonadiabatic relaxation

    SciTech Connect

    Vaikjärv, Taavi Hizhnyakov, Vladimir

    2014-02-14

    Our system under theoretical consideration is an impurity center in a solid. We are considering the time evolution of the center in a quasi-degenerate electronic state. Strict quantum mechanical treatment of non-adiabadicity of the state is used. The phonon continuum is taken into account in addition to the vibration responsible for the main vibronic interaction. To describe the dynamics of the excited state a master equation has been used. The theoretical considerations are illustrated by the calculations of the long-time evolution of vibrations of the center, influenced by the emission of phonons to the bulk.

  2. Smectite Formation from Basaltic Glass Under Acidic Conditions on Mars

    NASA Technical Reports Server (NTRS)

    Peretyazhko, T. S.; Sutter, B.; Morris, R. V.; Agresti, D. G.; Le, L.; Ming, D. W.

    2015-01-01

    Massive deposits of phyllosilicates of the smectite group, including Mg/Fe-smectite, have been identified in Mars's ancient Noachian terrain. The observed smectite is hypothesized to form through aqueous alteration of basaltic crust under neutral to alkaline pH conditions. These pH conditions and the presence of a CO2-rich atmosphere suggested for ancient Mars were favorable for the formation of large carbonate deposits. However, the detection of large-scale carbonate deposits is limited on Mars. We hypothesized that smectite deposits may have formed under acidic conditions that prevented carbonate precipitation. In this work we investigated formation of saponite at a pH of approximately 4 from Mars-analogue synthetic Adirondack basaltic glass of composition similar to Adirondack class rocks located at Gusev crater. Hydrothermal (200º Centigrade) 14 day experiments were performed with and without 10 millimoles Fe(II) or Mg under anoxic condition [hereafter denoted as anoxic_Fe, anoxic_Mg and anoxic (no addition of Fe(II) or Mg)] and under oxic condition [hereafter denoted as oxic (no addition of Fe(II) or Mg)]. Characterization and formation conditions of the synthesized saponite provided insight into the possible geochemical conditions required for saponite formation on Mars.

  3. Crater Formation Above Salt Caverns: Piston vs Hour-glass

    NASA Astrophysics Data System (ADS)

    Berest, P.

    2016-12-01

    Conditions leading to crater formation above salt caverns are discussed. In most cases, at the end of leaching, the cavern roof had reached the top of the salt formation, allowing direct contact between brine and marl (or argillite) layers that compose the overburden of the salt formation. These layers are prone to weathering when in contact with saturated brine. Stoping takes place, and the cavern roof rises through the overburden. This process may be several years or dozens of years long. In Lorraine salt formations, stoping stops when the rising cavern top reaches a competent layer, the Beaumont Dolomite. Operators then lower cavern-brine pressure to trigger collapse. A rigid cylinder of rock (a "piston") drops into the cavern, and a crater whose initial edges are vertical is created. Cavern drop is more abrupt when the cavern top is filled partly with air. The contour of the piston is circular, as a circle is the shape such that the ratio between perimeter and area is minimal. In other cases, for instance in Kansas, the cavern rises until the uppermost keystone in the bedrock at shallow depth is breached, permitting loose materials to flow into the cavern through a relatively narrow hole at the bottom of the sink hole, as in an hour glass.

  4. Gaining Thermodynamic Insight From Distinct Glass Formation Kinetics of Structurally Similar Organic Compounds.

    PubMed

    Kalra, Arjun; Luner, Paul; Taylor, Lynne S; Byrn, Stephen R; Li, Tonglei

    2017-06-23

    Thermodynamic and kinetic aspects of crystallization of 12 structurally similar organic compounds were investigated from the supercooled liquid state by calorimetric and rheologic measurements. Based on their crystallization behaviors, these compounds were divided into 3 categories: stable glass formers, poor glass formers, and good glass formers with poor stability on reheating. Correlation was sought between thermodynamic quantities and glass formation based on nucleation and crystal growth theories. Larger values of enthalpy of fusion and melting point were found to correlate with poor glass-forming ability. Conversely, lower entropy of fusion was found to correlate with glass formation. Examination of kinetic aspects of glass formation revealed 2 important facets of good glass formers, that is, rapid increase in viscosity on supercooling and high melting point viscosity compared with non-glass formers. A broader relationship was sought between entropy of fusion and glass formation by including several glass formers from literature. Our analysis indicated that good glass formers tend to have an entropy of fusion closer to 0.3 J cm(-3) K(-1). The structural similarity of the compounds in this study provides insights regarding the nature of intermolecular interactions responsible for the observed effect on entropy of fusion, viscosity, and crystallization kinetics. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  5. Examining the role of canister cooling conditions on the formation of nepheline from nuclear waste glasses

    SciTech Connect

    Christian, J. H.

    2015-09-01

    Nepheline (NaAlSiO₄) crystals can form during slow cooling of high-level waste (HLW) glass after it has been poured into a waste canister. Formation of these crystals can adversely affect the chemical durability of the glass. The tendency for nepheline crystallization to form in a HLW glass increases with increasing concentrations of Al₂O₃ and Na₂O.

  6. Apparatus and process to enhance the uniform formation of hollow glass microspheres

    SciTech Connect

    Schumacher, Ray F

    2013-10-01

    A process and apparatus is provided for enhancing the formation of a uniform population of hollow glass microspheres. A burner head is used which directs incoming glass particles away from the cooler perimeter of the flame cone of the gas burner and distributes the glass particles in a uniform manner throughout the more evenly heated portions of the flame zone. As a result, as the glass particles are softened and expand by a released nucleating gas so as to form a hollow glass microsphere, the resulting hollow glass microspheres have a more uniform size and property distribution as a result of experiencing a more homogenous heat treatment process.

  7. Probing Toluene and Ethylbenzene Stable Glass Formation using Inert Gas Permeation

    SciTech Connect

    Smith, R. Scott; May, Robert A.; Kay, Bruce D.

    2015-09-01

    Inert gas permeation is used to investigate the formation of stable glasses of toluene and ethylbenzene. The effect of deposition temperature (Tdep) on the kinetic stability of the vapor deposited glasses is determined using Kr desorption spectra from within sandwich layers of either toluene or ethylbenzene. The results for toluene show that the most stable glass is formed at Tdep = 0.92 Tg, although glasses with a kinetic stability within 50% of the most stable glass were found with deposition temperatures from 0.85 to 0.95 Tg. Similar results were found for ethylbenzene, which formed its most stable glass at 0.91 Tg and formed stable glasses from 0.81 to 0.96 Tg. These results are consistent with recent calorimetric studies and demonstrate that the inert gas permeation technique provides a direct method to observe the onset of molecular translation motion that accompanies the glass to supercooled liquid transition.

  8. Theoretical Studies of the Spin Hamiltonian Parameters and Local Distortions for Cu2+ in Alkaline Earth Lead Zinc Phosphate Glasses

    NASA Astrophysics Data System (ADS)

    Wang, Bo-Kun; Wu, Shao-Yi; Yuan, Zi-Yi; Liu, Zi-Xuan; Jiang, Shi-Xin; Liu, Zheng; Yao, Zi-Jian; Teng, Bao-Hua; Wu, Ming-He

    2016-08-01

    The spin Hamiltonian parameters and local structures are theoretically studied for Cu2+-doped alkaline earth lead zinc phosphate (RPPZ, R=Mg, Ca, Sr, and Ba) glasses based on the high-order perturbation calculations for a tetragonally elongated octahedral 3d9 cluster. The relative elongation ratios are found to be ρ≈3.2%, 4.4%, 4.6%, and 3.3% for R=Mg, Ca, Sr, and Ba, respectively, because of the Jahn-Teller effect. The whole decreasing crystal-field strength Dq and orbital reduction factor k from Mg to Sr are ascribed to the weakening electrostatic coulombic interactions and the increasing probability of productivity of nonbridge oxygen (and hence increasing Cu2+-O2- electron cloud admixtures) under PbO addition, respectively, with increasing alkali earth ionic radius. The anomalies (the largest Dq and the next highest k among the systems) for R=Ba are attributed to the cross linkage of this large cation in the network. The overall increasing order (Mg≤Baglasses containing copper dopants.

  9. Spectroscopic investigation of a new hybrid glass formed by the interaction between croconate ion and calcium polyphosphate.

    PubMed

    de Oliveira, Carlos Ivan R; de Oliveira, Luiz Fernando C; Dias Filho, Francisco A; Messaddeq, Younes; Ribeiro, Sidney J L

    2005-07-01

    In this work, a new organic-inorganic hybrid material has been synthesized by the incorporation of croconate ion into a calcium polyphosphate coacervate. The hybrid so obtained was characterized by means of electronic and vibrational spectroscopies. The material is a homogeneous mixture described by a structural model, which includes helical chains of polyphosphate ions, where the calcium ion occupies the internal vacancies of the structure. The croconate ion appears to be occupying the regions outside the polymeric structure, surrounded by several water molecules. The electronic spectrum of the incorporated material shows a broad band peaking at the same wavelength region (363 nm) observed for the aqueous solution of croconate ion, and manifesting the Jahn-Teller effect as evidenced by the doublet structure of the band. The infrared spectrum is widely dominated by the absorption bands of the polyphosphate ion and the appearance of the carbonyl stretching band at ca. 1550 cm(-1) indicates the presence of croconate ion incorporated in the structure. The Raman spectrum of the material shows several vibrational bands related to the oxocarbon moiety; most of them are shifted in comparison with the free ion. These shifts can be understood in terms of strong hydrogen bonding interactions between water molecules and the oxocarbon moiety. The low temperature methodology proposed here can be well used in the preparation of new phosphate glasses containing organic moieties opening the route to an entirely new class of hybrid glasses.

  10. Bulk Formation of Metallic Glasses and Amorphous Silicon from the Melt

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1985-01-01

    By using metallic glass compositions with a high relative glass transition temperature, such as Pd40Ni40P20, homogeneous nucleation also becomes negligible. Large (5g) masses of this alloys were obtained using a molten B2O3 flux. Presently, bulk glass formation in iron based glasses is being investigated. It is expected that if an undercooling of about 250K can be achieved in a Ge or Si melt, formation of the amorphous semiconductor phase (rather than the crystal) may be kinetically favored. The volumetric behavior of undercooled liquid Ga droplet dispersion is investigated by dilatometry. A theoretical model (both analytical and numerical) was developed for transient nucleation in glass forming melts. The model, originally designed for isothermal conditions, was extended to continuous quenching. It is being applied to glass formation in various metallic and oxide systems. A further refinement will be the inclusion of diffusion controlled interfacial rearrangements governing the growth of the crystal embryos.

  11. Bulk Formation of Metallic Glasses and Amorphous Silicon from the Melt

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1985-01-01

    By using metallic glass compositions with a high relative glass transition temperature, such as Pd40Ni40P20, homogeneous nucleation also becomes negligible. Large (5g) masses of this alloys were obtained using a molten B2O3 flux. Presently, bulk glass formation in iron based glasses is being investigated. It is expected that if an undercooling of about 250K can be achieved in a Ge or Si melt, formation of the amorphous semiconductor phase (rather than the crystal) may be kinetically favored. The volumetric behavior of undercooled liquid Ga droplet dispersion is investigated by dilatometry. A theoretical model (both analytical and numerical) was developed for transient nucleation in glass forming melts. The model, originally designed for isothermal conditions, was extended to continuous quenching. It is being applied to glass formation in various metallic and oxide systems. A further refinement will be the inclusion of diffusion controlled interfacial rearrangements governing the growth of the crystal embryos.

  12. Metastable Ice and Glass Formation in Atmospherically Relevant Aqueous Droplets

    NASA Astrophysics Data System (ADS)

    Murray, B. J.; Moehler, O.

    2008-12-01

    In this presentation an X ray diffraction study of homogeneous nucleation and the subsequent crystallisation of ice in aqueous organic acid solution droplets will be presented. Aqueous citric acid solutions have been chosen as a model system and are thought to be representative of organic material found in many upper tropospheric aerosols. It will be shown that the metastable cubic form of ice can nucleate, crystallise and is stabilised in citric acid solution droplets which freeze homogeneously below about 219 K. Cubic ice is only produced when ammonium bisulphate solution droplets freeze below about 183 K. This solute dependence is related to the viscosity and glass forming ability of the respective aqueous solutions. Experiments were also performed with more concentrated citric acid solution droplets, in which ice should nucleate at lower temperatures. It is found that ice crystallisation is inhibited below ~198 K in citric acid solution droplets. These droplets most likely formed ultra-viscous liquids or glassy material rather than crystallise. In order to test the impact of glassy particles on cloud formation, glassy citric acid particles were recently produced within the AIDA cloud simulation chamber in Karlsruhe Germany. Preliminary results suggest glassy citric acid aerosol do not produce an ice cloud via a homogeneous freezing route. In fact, ice particle production is markedly suppressed.

  13. Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation

    PubMed Central

    Fredholm, Yann C.; Karpukhina, Natalia; Brauer, Delia S.; Jones, Julian R.; Law, Robert V.; Hill, Robert G.

    2012-01-01

    Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO2–P2O5–CaO–Na2O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. PMID:21993007

  14. Effects of phosphate buffer in parenteral drugs on particle formation from glass vials.

    PubMed

    Ogawa, Toru; Miyajima, Makoto; Wakiyama, Naoki; Terada, Katsuhide

    2013-01-01

    The characteristics of inorganic particles generated in glass vials filled with phosphate buffer solutions were investigated. During storage, particles were visually detected in the phosphate buffer solution in particular glass vials which pass compendial tests of containers for injectable drugs. These particles were considered to be different from ordinal glass delamination, which has been reported in a number of papers because the particles were mainly composed of Al, P and O, but not Si. The formation of the particles accelerated at higher storage temperatures. Among the surface treatments tested for the glass vials, sulfur treatment showed a protective effect on the particle formation in the vials, whereas the SiO(2) coating did not have any protective effects. It was found that the elution ratio of Al and Si in the solution stored in the glass vials after the heating was similar to the ratio of Al and Si in borosilicate glass. However, the Al concentration decreased during storage (5°C, 6 months), and consequently, particle formation was observed in the solution. Adding citrate, which is a chelating agent for Al, effectively suppressed the particle formation in the heated solution. When 50 ppb and higher concentrations of Al ion were added to the phosphate buffer solution, the formation of white particles containing Al, P and O was detected. It is suggested that a phosphate buffer solution in a borosilicate glass vial has the ability to form particles due to interactions with the Al that is eluted from the glass during storage.

  15. Universal non-Landau, self-organized, lattice disordering percolative dopant network sub-T(c) phase transition in ceramic superconductors.

    PubMed

    Phillips, J C

    2009-09-15

    Ceramic superconductors (cuprates, pnictides, etc.) exhibit universal features in both T(c)(max) and in their planar lattice disordering measured by EXAFS, as reflected by three phase transitions. The two highest temperature transitions are known to be associated with formation of Jahn-Teller pseudogaps and superconductive gaps, with corresponding Landau order parameters, but no new gap is associated with the third transition below T(c), and its origin is mysterious. It is argued that the third subT(c) transition is a dopant glass transition, which is remarkably similar to topological transitions previously observed in chalcogenide and oxide alloy network glasses (like window glass).

  16. Pregrowth and Biofilm formation of Bacillus subtilis on Glass Studied via AFM, SEM and Optical Microsopy

    NASA Astrophysics Data System (ADS)

    Stutzman, Sydney; Otte, Michelle; Calabrese, Joseph; Senevirathne, Reshani; Senevirathne, Indrajith

    2014-03-01

    Lock Haven University of Pennsylvania - Research into surface adhesion properties and the selectivity of bacteria towards glass will provide a better understanding of biofilm formation and how this formation will in turn effect hospital and laboratory settings. Investigation was focused on quantifying the selectivity of non-pathogenic B. subtilis - on soda lime glass substrates. Standardized Corning 2947-75X25 microscope glass slides were used as the surface for bacterial attachment and facilitation of preliminary growth and formation of biofilms. Observations will be discussed both quantitatively and qualitatively. Structure morphology was investigated via Atomic Force Microscopy, Scanning Electron Microscopy and complemented with Optical Microscopy.

  17. Glass formation and Raman spectra of CaO-SiO2 glasses towards the orthosilicate limit

    NASA Astrophysics Data System (ADS)

    Retsinas, A.; Kalampounias, A. G.; Papatheodorou, G. N.

    2016-12-01

    A series of silicate glasses formed in the binary system (1-X)CaO-XSiO2with silica mole fractions X ranging from 0.61to 0.38have been prepared using container-less aerodynamic levitation techniques and CO2-laser heating. Glasses with X<0.45were prepared for the first time but, no glass formation was possible at compositions X<0.38. Ambient temperature polarized and depolarized Raman spectra were measured for all these glasses. Qi-speciation analysis of the isotropic Raman spectra shows that near X∼0.38the predominant structures present are the SiO44- tetrahedra and the single bridged Q1species. Oxygen bridging was present at all compositions studied while at X<0.45 small amounts of free oxygen anions was present. The data are compared with the resent NMR measurements obtained with the same glass samples used in the present study. Stokes and anti-Stokes Raman spectra were measured in low frequencies revealing the Boson peak (BP) at ∼50 and ∼70 cm-1 for the corresponding polarized and depolarized configurations. On the Stokes side the BP frequencies exhibit a fictional shift due to contributions from the low frequency vibrational modes of the glass.

  18. THE IMPACT OF KINETICS ON NEPHELINE FORMATION IN NUCLEAR WASTE GLASSES

    SciTech Connect

    Amoroso, J.

    2011-03-07

    Sixteen glass compositions were selected to study the potential impacts of the kinetics of nepheline formation in high-level nuclear waste (HLW) glass. The chosen compositions encompassed a relatively large nepheline discriminator (ND) range, 0.40-0.66, and included a relatively broad range, and amount of, constituents including high aluminum and high boron concentrations. All glasses were fabricated in the laboratory and subsequently exposed to six different cooling treatments. The cooling treatments consisted of three 'stepped' profiles and their corresponding 'smooth' profiles. Included in the cooling treatment was the Defense Waste Processing Facility (DWPF) canister centerline cooling (CCC) profile in addition to a 'faster' and a 'slower' total cooling line. After quenching and heat treating, x-ray diffraction confirmed the type and amount of any resultant crystallization. The target compositions were shown to be consistent with the measured compositions. Two quenched glasses and several treated glasses exhibited minor amounts of spinel and spinel-like phases. Nepheline was not observed in any of the quenched glasses but was observed in many of the treated glasses. The amount of nepheline ranged from approximately 2wt% to 30wt% for samples cooled over shorter times and longer times respectively. Differences were observed in the amount of nepheline crystallization after smooth and stepped cooling and increased with total cooling time. In some glasses, nepheline crystallization appeared to be directly proportional to total cooling time while the total amount of nepheline crystallization varied, suggesting that the nepheline crystallization rate was independent of (or at least faster than) cooling rate but, varied depending on the glass composition. On the contrary, in another glass, nepheline crystallization appeared to be inversely proportional to cooling rate. The high alumina glasses, predicted to form nepheline according to the ND, did not precipitate

  19. Investigation of the local structure of Cu2+ ions doped in alkali lead tetraborate glasses by their electron paramagnetic resonance and optical spectra

    NASA Astrophysics Data System (ADS)

    Wu, Ying; Chen, Zhi

    2014-06-01

    The local structure of the Cu2+ centers in alkali lead tetraborate glasses was theoretically studied based on the optical spectra data and high-order perturbation formulas of the spin Hamiltonian parameters (electron paramagnetic resonance g factors g∥, g⊥ and hyperfine structure constants A∥, A⊥) for a 3d9 ion in a tetragonally elongated octahedron. In these formulas, the relative axial elongation of the ligand O2- octahedron around the Cu2+ due to the Jahn-Teller effect is taken into account by considering the contributions to the g factors from the tetragonal distortion which is characterized by the tetragonal crystal-field parameters Ds and Dt. From the calculations, the ligand O2- octahedral around Cu2+ is determined to suffer about 19.2% relative elongation along the C4 axis of the alkali lead tetraborate glass system, and a negative sign for A∥ and a positive sign for A⊥ for these Cu2+ centers are suggested in the discussion.

  20. Formation of gallium arsenide nanostructures in Pyrex glass.

    PubMed

    Howlader, Matiar M R; Zhang, Fangfang; Deen, M Jamal

    2013-08-09

    In this paper, we report on a simple, low-cost process to grow GaAs nanostructures of a few nm diameter and ∼50 nm height in Pyrex glass wafers. These nanostructures were grown by sequential plasma activation of GaAs and Pyrex glass surfaces using a low-temperature hybrid plasma bonding technology in air. Raman analyses of the activated surfaces show gallium oxide and arsenic oxide, as well as suppressed non-bridging oxygen with aluminate and boroxol chains in glass. The flow of alkaline ions toward the cathode and the replacement of alkaline ions by Ga and As ions in glass result in the growth of GaAs nanostructures in nanopores/nanoscratches in glass. These nanopores/nanoscratches are believed to be the origin of the growth of the nanostructures. It was found that the length of the GaAs nanostructures may be controlled by an electrostatic force. Cross-sectional observation of the bonded interface using high-resolution transmission electron microscopy confirms the existence of the nanostructures. A possible application of the nanostructures in glass is a filtration system for biomolecules.

  1. Entropy Theory of Polymer Glass-Formation in Variable Spatial Dimension

    NASA Astrophysics Data System (ADS)

    Xu, Wen-Sheng; Douglas, Jack; Freed, Karl

    The importance of packing frustration is broadly appreciated to be an important aspect of glass-formation. Recently, great interest has focused on using spatial dimensionality () as a theoretical tool for exploring this and other aspects of glass-forming liquids. We explore glass-formation in variable based on the generalized entropy theory, a synthesis of the Adam-Gibbs model with direct computation of the configurational entropy of polymer fluids using an established analytical statistical thermodynamic model. We find that structural relaxation in the fluid state asymptotically becomes Arrhenius in the limit and that the fluid transforms upon sufficient cooling above a critical dimension near into a dense amorphous state with a finite positive residual configurational entropy. The GET also predicts the variation with of measures of fragility and of the characteristic temperatures of glass-formation demarking the onset , middle , and end , of the broad glass transition. Direct computations of the isothermal compressibility and thermal expansion coefficient, which are physical measures of packing frustration, demonstrate that these fluid properties strongly correlate with the fragility of glass-formation. Back to three dimensions, we deduce apparently universal relationships between , a measure of the breadth of the glass-formation and both the isothermal compressibility and thermal expansion coefficient of polymer melts at .

  2. Glass formation, glass fragility, molecular mobility and longevity of germplasm stored at cryogenic temperatures.

    USDA-ARS?s Scientific Manuscript database

    Cryogenic storage of living specimens presupposes that viability can be maintained indefinitely when aqueous glasses are formed and maintained. Indeed, constrained mobility within glassy matrices is a thermodynamic barrier to many chemical and physical reactions. However, impeding molecular mobili...

  3. Glass formation in a mixture of hard disks and hard ellipses.

    PubMed

    Xu, Wen-Sheng; Duan, Xiaozheng; Sun, Zhao-Yan; An, Li-Jia

    2015-06-14

    We present an event-driven molecular dynamics study of glass formation in two-dimensional binary mixtures composed of hard disks and hard ellipses, where both types of particles have the same area. We demonstrate that characteristic glass-formation behavior appears upon compression under appropriate conditions in such systems. In particular, while a rotational glass transition occurs only for the ellipses, both types of particles undergo a kinetic arrest in the translational degrees of freedom at a single density. The translational dynamics for the ellipses is found to be faster than that for the disks within the same system, indicating that shape anisotropy promotes the translational motion of particles. We further examine the influence of mixture's composition and aspect ratio on the glass formation. For the mixtures with an ellipse aspect ratio of k = 2, both translational and rotational glass transition densities decrease with increasing the disk concentration at a similar rate, and hence, the two glass transitions remain close to each other at all concentrations investigated. By elevating k, however, the rotational glass transition density diminishes at a faster rate than the translational one, leading to the formation of an orientational glass for the ellipses between the two transitions. Our simulations imply that mixtures of particles with different shapes emerge as a promising model for probing the role of particle shape in determining the properties of glass-forming liquids. Furthermore, our work illustrates the potential of using knowledge concerning the dependence of glass-formation properties on mixture's composition and particle shape to assist in the rational design of amorphous materials.

  4. Glass formation and properties of Ge-Te-BiI3 far infrared transmitting chalcohalide glasses.

    PubMed

    Sun, Jie; Nie, Qiuhua; Wang, Xunsi; Dai, Shixun; Xu, Tiefeng; Wang, Guoxiang

    2011-09-01

    A novel series of Ge-Te-BiI(3) chalcogenide glasses were prepared by traditional melt-quenching method and the glass-forming region was determined. Properties measurements including density, Vis-NIR and infrared (IR) transmission spectra with FTIR, XRD, DSC were adopted to analyze the composition, structure and performance of the Ge-Te-BiI3 glass system. Based on the metallization criterion and band gap energy theory, the relationships between energy gap, metallization criterion and glass composition was investigated. The results show that with the addition of BiI3, the glasses-forming ability and thermal stability are improved. The values of energy band gap and metallization criterion are within the range of 0.627-0.343 eV and 0.177-0.131, respectively. These series of glasses have wide optical transmission window from 2.2 to 25 μm and can offer an alternative solution for far infrared transmitting applications. Copyright © 2011 Elsevier B.V. All rights reserved.

  5. Glass formation and crystallization of high lead content PbO-B2O3 compositions

    NASA Technical Reports Server (NTRS)

    Weinberg, Michael C.; Smith, Gary L.; Neilson, George F.

    1986-01-01

    The glass-forming and undercooling ability of PbO-B2O3 melts in the 2PbO.B2O3 to 4PbO.B2O3 composition range were studied. The glass formation propensities were investigated as a function of cooling rate and sample mass. A qualitative investigation of the crystallization process(es) preventing glass formation was made, and it was concluded that under normal circumstances heterogeneous nucleation was the common occurrence. Hence, it was concluded that such compositions are prime candidates for containerless experiments aboard the Space Shuttle.

  6. Formation and Properties of Laser-Induced Periodic Surface Structures on Different Glasses.

    PubMed

    Gräf, Stephan; Kunz, Clemens; Müller, Frank A

    2017-08-10

    The formation and properties of laser-induced periodic surface structures (LIPSS) was investigated on different technically relevant glasses including fused silica, borosilicate glass, and soda-lime-silicate glass under irradiation of fs-laser pulses characterized by a pulse duration τ = 300 fs and a laser wavelength λ = 1025 nm. For this purpose, LIPSS were fabricated in an air environment at normal incidence with different laser peak fluence, pulse number, and repetition frequency. The generated structures were characterized by using optical microscopy, scanning electron microscopy, focused ion beam preparation and Fast-Fourier transformation. The results reveal the formation of LIPSS on all investigated glasses. LIPSS formation on soda-lime-silicate glass is determined by remarkable melt-formation as an intra-pulse effect. Differences between the different glasses concerning the appearing structures, their spatial period and their morphology were discussed based on the non-linear absorption behavior and the temperature-dependent viscosity. The findings facilitate the fabrication of tailored LIPSS-based surface structures on different technically relevant glasses that could be of particular interest for various applications.

  7. Quasi-containerless glass formation method and apparatus

    NASA Technical Reports Server (NTRS)

    Naumann, Robert J. (Inventor); Ethridge, Edwin C. (Inventor)

    1987-01-01

    Glass rods or fibers are prepared from a polycrystalline rod by heating a short section of the rod in a first furnace to form a molten zone of the rod, heating a second short section of the rod in a second furnace to form a second molten zone and gradually moving the furnaces apart from one another to form an elongated molten float zone, which is cooled in its midsection to produce a glass rod between the molten zones. In another embodiment a single moving furnace assembly and a precursor rod with compositional gradient sections, are used, and the moving furnace traverses the rod so that the molten portion is drawn out to a degree whereby a fiber of ultrapure glass is formed.

  8. Formation of nanostructured metallic glass thin films upon sputtering.

    PubMed

    Ketov, Sergey V; Joksimovic, Rastko; Xie, Guoqiang; Trifonov, Artem; Kurihara, Kazue; Louzguine-Luzgin, Dmitri V

    2017-01-01

    Morphology evolution of the multicomponent metallic glass film obtained by radio frequency (RF) magnetron sputtering was investigated in the present work. Two modes of metallic glass sputtering were distinguished: smooth film mode and clustered film mode. The sputtering parameters, which have the most influence on the sputtering modes, were determined. As a result, amorphous Ni-Nb thin films with a smooth surface and nanoglassy structure were deposited on silica float glass and Si substrates. The phase composition of the target appeared to have a significant influence on the chemical composition of the deposited amorphous thin film. The differences in charge transport and nanomechanical properties between the smooth and nanoglassy Ni-Nb film were also determined.

  9. Computation assisted design of favored composition for ternary Mg-Cu-Y metallic glass formation.

    PubMed

    Wang, Q; Li, J H; Liu, B X

    2015-06-14

    With the aid of ab initio calculations, a realistic interatomic potential was constructed for the Mg-Cu-Y ternary system under the proposed formalism of smoothed and long-range second-moment approximation of tight-binding. Taking the potential as the starting base, an atomistic computation/simulation route was developed for designing favored and optimized compositions for Mg-Cu-Y metallic glass formation. Simulations revealed that the physical origin of metallic glass formation is the collapse of crystalline lattice when solute concentration exceeds a critical value, thus leading to predict a hexagonal region in the Mg-Cu-Y composition triangle, within which metallic glass formation is energetically favored. It is proposed that the hexagonal region can be defined as the intrinsic glass formation region, or quantitative glass formation ability of the system. Inside the hexagonal region, the driving force for formation of each specific glassy alloy was further calculated and correlated with its forming ability in practice. Calculations pinpointed the optimized stoichiometry in the Mg-Cu-Y system to be Mg64Cu16Y20, at which the formation driving force reaches its maximum, suggesting that metallic glasses designed to have compositions around Mg64Cu16Y20 are most stable or easiest to obtain. The predictions derived directly from the atomistic simulations are supported by experimental observations reported so far in the literature. Furthermore, Honeycutt-Anderson analysis indicated that pentagonal bipyramids (although not aggregating to form icosahedra) dominate in the local structure of the Mg-Cu-Y metallic glasses. A microscopic picture of the medium-range packing can then be described as an extended network of the pentagonal bipyramids, entangled with the fourfold and sixfold disclination lines, jointly fulfilling the space of the metallic glasses.

  10. A deep water turbidity origin for the Altuda Formation (Capitanian, Permian), Northwest Glass Mountains, Texas

    USGS Publications Warehouse

    Haneef, Mohammad; Rohr, D.M.; Wardlaw, B.R.

    2000-01-01

    The Altuda Formation (Capitanian) in the northwestern Glass Mountains is comprised of thin, even bedded limestones, dolostones, mixed clastic-carbonates, and silt/sandstones interbedded with basin-ward dipping wedge-shaped clinoforms of the Captian Limestone. The formation is characterized by graded bedding, planar laminations, flame structures, contorted/convolute bedding, horizontal branching burrows, and shelf-derived normal marine fauna. A detailed study of the Altuda Formation north of Old Blue Mountain, Glass Mountains, reveals that the formation in this area was deposited by turbidity currents in slope to basinal settings.

  11. Investigation of ruthenium dioxide formation mechanisms in containment glass synthesized by liquid feed

    SciTech Connect

    Sawada, K.; Shimada, T.; Sako, N.; Enokida, Y.; Schuller, S.; Angeli, F.; Charpentier, T.

    2013-07-01

    The presenting paper focuses on the structural configuration of ruthenium in vitreous matrices with the objective of obtaining more insight into ruthenium incorporation and solubilization mechanisms in borosilicate glasses. To determine the structural effect of an increasing RuO{sub 2} in a borosilicate glass, a series of glass samples were selected from a benchmark composition. {sup 11}B NMR shows that the borate network is influenced by the presence of RuO{sub 2} in the glass: the addition of 2% RuO{sub 2} in a borosilicate glass led to a significant rise of BO{sub 4}. RuO{sub 2} precipitated in the glass does not seem to be the cause of this modification because when RuO{sub 2} increase there is no further change of BO{sub 4} fraction. This effect can be therefore attributed to RuO{sub 2} dissolved in the glass. RuO{sub 2} is known to have a very low solubility in borosilicate glasses (50 to 2000 ppm depending on the temperature, sodium concentration and conditions of synthesis). The link between the ruthenium and the borated network is not yet clearly identified, however, assumptions can be made such as the formation of Ru-O-B when a sufficient quantity of Ru is add (> 400 ppm). Ruthenium could play the role of silicon in increasing the possibility of bridging bond formation with boron coordination number IV.

  12. Glass formation and crystallization in high-temperature glass-ceramics and Si3N4

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III

    1991-01-01

    The softening of glassy grain boundaries in ceramic matrix composites and Si3N4 at high temperatures reduces mechanical strength and the upper-use temperature. By crystallizing this glass to a more refractory crystalline phase, a material which performs at higher temperatures may result. Three systems were examined: a cordierite composition with ZrO2 as a nucleating agent; celsian compositions; and yttrium silicate glasses both in bulk and intergranular in Si3N4. For the cordierite compositions, a series of metastable phases was obtained. The crystallization of these compositions was summarized in terms of metastable ternary isothermal sections. Zircon formed at the expense of ZrO2 and spinel. In SiC composites, the transformations were slower. In celsian, two polymorphs were crystallized. One phase, hexacelsian, which always crystallized, even when metastable, had an undesirable volume change. The other phase, celsian, was very difficult to crystallize. In yttrium silicate bulk glasses, similar in composition to the intergranular glass in Si3N4, a number of polymorphs of Y2Si2O7 were crystallized. The conditions under which these polymorphs formed are compared with crystallization in Si3N4.

  13. Thermal dehydration of magnesium acetate tetrahydrate: formation and in situ crystallization of anhydrous glass.

    PubMed

    Koga, Nobuyoshi; Suzuki, Yasumichi; Tatsuoka, Tomoyuki

    2012-12-13

    The kinetics and mechanism of the thermal dehydration of magnesium acetate tetrahydrate were investigated as a typical example of the glass formation process via the thermal decomposition of solids. Formation of an intermediate fluid phase was identified as the characteristic phenomenon responsible for the formation of anhydrous glass. Thermal dehydration from the surface fluid layer regulates the zero-order-like rate behavior of the mass-loss process with an apparent activation energy E(a) ≈ 70-80 kJ mol(-1). Because of variations in the mechanism of release of the water vapor with changes in the reaction temperature range, the mass-loss behavior is largely dependent on the particle size of the sample and heating conditions. The formation of hollow anhydrous glass is the novel finding of the present study. The mechanism of formation is discussed in terms of complementary interpretations of the morphological changes and kinetic behavior of the thermal dehydration. On further heating, the as-produced anhydrous glass exhibits a glass transition phenomenon at approximately 470 K with an E(a) ≈ 550-560 kJ mol(-1), and subsequently crystallizes via the three-dimensional growth of nuclei controlled by diffusion. The crystallization process is characterized by an E(a) ≈ 280 kJ mol(-1) and an enthalpy change ΔH = -13.3 kJ mol(-1), resulting in the formation of smaller, rounded particles of crystalline anhydrate.

  14. Does fragility of glass formation determine the strength of Tg-nanoconfinement effects?

    NASA Astrophysics Data System (ADS)

    Mangalara, Jayachandra Hari; Marvin, Michael D.; Wiener, Nicholas R.; Mackura, Mark E.; Simmons, David S.

    2017-03-01

    Nanoscale confinement has been shown to alter the glass transition and associated mechanical and transport properties of glass-forming materials. Inspired by expected interrelations between nanoconfinement effects, cooperative dynamics in supercooled liquids, and the "fragility" (or temperature-abruptness) of the glass transition, it is commonly expected that nanoconfinement effects on Tg should be more pronounced for more fragile glass formers. Here we employ molecular dynamics simulations of glass formation in the bulk and under nanoconfinement of model polymers in which we systematically tune fragility by several routes. Results indicate that a correlation between fragility and the strength of nanoconfinement effects is weak to modest at best when considering all systems but can appear to be stronger when considering a subset of systems. This outcome is consistent with a reanalysis of the Adam-Gibbs theory of glass formation indicating that fragility does not necessarily track in a universal way with the scale of cooperative motion in glass-forming liquids. Finally, we find that factors such as composition gradients or variability in measurement sensitivity to different parts of the dynamic gradient have the potential to significantly confound efforts to identify trends in Tg-nanoconfinement effects with variables such as fragility, emphasizing the importance of employing diverse data sets and multiple metrologies in the study of this problem.

  15. Limited surface mobility inhibits stable glass formation for 2-ethyl-1-hexanol.

    PubMed

    Tylinski, M; Beasley, M S; Chua, Y Z; Schick, C; Ediger, M D

    2017-05-28

    Previous work has shown that vapor-deposition can prepare organic glasses with extremely high kinetic stabilities and other properties that would be expected from liquid-cooled glasses only after aging for thousands of years or more. However, recent reports have shown that some molecules form vapor-deposited glasses with only limited kinetic stability when prepared using conditions expected to yield a stable glass. In this work, we vapor deposit glasses of 2-ethyl-1-hexanol over a wide range of deposition rates and test several hypotheses for why this molecule does not form highly stable glasses under normal deposition conditions. The kinetic stability of 2-ethyl-1-hexanol glasses is found to be highly dependent on the deposition rate. For deposition at Tsubstrate = 0.90 Tg, the kinetic stability increases by 3 orders of magnitude (as measured by isothermal transformation times) when the deposition rate is decreased from 0.2 nm/s to 0.005 nm/s. We also find that, for the same preparation time, a vapor-deposited glass has much more kinetic stability than an aged liquid-cooled glass. Our results support the hypothesis that the formation of highly stable 2-ethyl-1-hexanol glasses is inhibited by limited surface mobility. We compare our deposition rate experiments to similar ones performed with ethylcyclohexane (which readily forms glasses of high kinetic stability); we estimate that the surface mobility of 2-ethyl-1-hexanol is more than 4 orders of magnitude less than that of ethylcyclohexane at 0.85 Tg.

  16. Probing Toluene and Ethylbenzene Stable Glass Formation Using Inert Gas Permeation.

    PubMed

    Smith, R Scott; May, R Alan; Kay, Bruce D

    2015-09-17

    Inert gas permeation is used to investigate the formation of stable glasses of toluene and ethylbenzene. The effect of deposition temperature (T(dep)) on the kinetic stability of the vapor deposited glasses is determined using Kr desorption spectra from within sandwich layers of either toluene or ethylbenzene. The results for toluene show that the most stable glass is formed at T(dep) = 0.92 T(g), although glasses with a kinetic stability within 50% of the most stable glass were found with deposition temperatures from 0.85 to 0.95 T(g). Similar results were found for ethylbenzene, which formed its most stable glass at 0.91 T(g) and formed stable glasses from 0.81 to 0.96 T(g). These results are consistent with recent calorimetric studies and demonstrate that the inert gas permeation technique provides a direct method to observe the onset of molecular translation motion that accompanies the glass to supercooled liquid transition.

  17. A model for foam formation, stability, and breakdown in glass-melting furnaces.

    PubMed

    van der Schaaf, John; Beerkens, Ruud G C

    2006-03-01

    A dynamic model for describing the build-up and breakdown of a glass-melt foam is presented. The foam height is determined by the gas flux to the glass-melt surface and the drainage rate of the liquid lamellae between the gas bubbles. The drainage rate is determined by the average gas bubble radius and the physical properties of the glass melt: density, viscosity, surface tension, and interfacial mobility. Neither the assumption of a fully mobile nor the assumption of a fully immobile glass-melt interface describe the observed foam formation on glass melts adequately. The glass-melt interface appears partially mobile due to the presence of surface active species, e.g., sodium sulfate and silanol groups. The partial mobility can be represented by a single, glass-melt composition specific parameter psi. The value of psi can be estimated from gas bubble lifetime experiments under furnace conditions. With this parameter, laboratory experiments of foam build-up and breakdown in a glass melt are adequately described, qualitatively and quantitatively by a set of ordinary differential equations. An approximate explicit relationship for the prediction of the steady-state foam height is derived from the fundamental model.

  18. Glass formation and the third harmonic generation of Cu2Se-GeSe2-As2Se3 glasses

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Klymovych, O. S.; Myronchuk, G. L.; Zamuruyeva, O. V.; Zmiy, O. F.; Alahmed, Z. A.; Chyský, J.; Bila, Jiri; Kamarudin, H.

    2014-10-01

    We have performed the investigation of the nonlinear optical properties namely the third harmonic generation (THG) of the glass-formation region in the Cu2Se-GeSe2-As2Se3 system. The samples were synthesized by direct single-temperature method from high-purity elementary substances. We have found that the value of disorder parameter Δ depends on the composition of the glassy alloys. The measurements show that increasing the Cu2Se concentration leads to increased slope of the absorption edge, which may be explained by the decrease of the height of random potential relief for the electrons in the tails of the state density which border the band edges. A very sharp increase in the THG at low temperature was observed. Significant enhancement in THG was obtained with decreasing the energy gap, which agreed well with the nonlinear optical susceptibilities obtained from other glasses.

  19. Glass formation and structure of calcium antimony phosphate glasses and those doped with tellurium oxide

    NASA Astrophysics Data System (ADS)

    Li, Jun; Zhang, Yin; Nian, Shangjiu; Wu, Zhenning; Cao, Weijing; Zhou, Nianying; Wang, Danian

    2017-03-01

    An approximate glass-forming region in the P2O5-Sb2O3-CaO ternary system was determined. The properties and structure of two compositional series of (A) (75- x)P2O5- xSb2O3-25CaO ( x = 20, 25, 30, 35 mol%) and (B) 45P2O5-30Sb2O3-(25- x)CaO- xTeO2 ( x = 5, 10, 15, 20 mol%) were studied systematically. Thermal properties were investigated by means of differential scanning calorimetry (DSC). The densities of all samples were measured by Archimedes' method using distilled water as the immersion liquid. The water durability of the glasses was described by their dissolution rate (DR) in the distilled water at 90 °C for some time periods. Density, thermal stability and water durability were improved with the addition of Sb2O3 and TeO2. Structural studies were carried out by X-ray diffraction (XRD), infrared spectroscopy and Raman spectroscopy. The phosphate chain depolymerization occurred with the increase of Sb2O3 and the Q2 structural units transformed to the Q1 and Q0 structural units with the addition of TeO2.

  20. Modeling Multiple Time Scales during Glass Formation with Phase-Field Crystals

    SciTech Connect

    Berry, Joel; Grant, Martin

    2011-04-29

    The dynamics of glass formation in monatomic and binary liquids are studied numerically using a microscopic field theory for the evolution of the time-averaged atomic number density. A stochastic framework combining phase-field crystal free energies and dynamic density functional theory is shown to successfully describe several aspects of glass formation over multiple time scales. Agreement with mode coupling theory is demonstrated for underdamped liquids at moderate supercoolings, and a rapidly growing dynamic correlation length is found to be associated with fragile behavior.

  1. Formation of periodic structures on glass with laser irradiation

    NASA Astrophysics Data System (ADS)

    Peng, Ying Zi; An, Cheng Wu; Wu, Dong Jiang; Hong, Ming Hui; Lu, Yong Feng; Chong, Tow Chong

    2003-07-01

    Regular and tidy periodic structures hae been directly induced on glasses using a CW CO2 laser beam with linear polarization. It is experimentally shown that precise periodic structures with the period of several microns can be formed by means of well-set laser parameters. The orientation of the periodic structures formed is the same as that of the laser polarization no matter what the scanning direction is. The occurrence of periodic structures is very sensitive to laser power level and scanning velocity. To obtain appropriate periodic patterns, a combined condition of laser energy and scanning velocity must be satisfied. The period, width and height of the structures are dependent on processing parameters. An interesting phenomenon is that the period decreases with increasing scanning velocity. Permanent relieves with periods, widths and heights varied with the laser parameters are also studied.

  2. Crystallization behavior and glass formation of selected lunar compositions.

    NASA Technical Reports Server (NTRS)

    Scherer, G.; Hopper, R. W.; Uhlmann, D. R.

    1972-01-01

    The kinetics of crystal growth have been determined over a wide range of temperature, from 800 to 1219 C, for lunar compositions 14259 and 14310. At all temperatures for both compositions the extent of crystal growth is found to be a linear function of time. For both materials, the growth rate versus temperature relations exhibit the form generally found with glass-forming materials. At all temperatures measured, the crystal growth rate of composition 14259 is smaller than that of composition 14310. The maximum growth rate for both compositions occurs at a temperature of about 1120 C. The growth rate data are combined with viscosity data obtained on the same compositions to construct the reduced growth rate versus undercooling relations.

  3. The formation of silver metal nanoparticles by ion implantation in silicate glasses

    NASA Astrophysics Data System (ADS)

    Vytykacova, S.; Svecova, B.; Nekvindova, P.; Spirkova, J.; Mackova, A.; Miksova, R.; Böttger, R.

    2016-03-01

    It has been shown that glasses containing silver metal nanoparticles are promising photonics materials for the fabrication of all-optical components. The resulting optical properties of the nanocomposite glasses depend on the composition and structure of the glass, as well as on the type of metal ion implanted and the experimental procedures involved. The main aim of this article was to study the influence of the conditions of the ion implantation and the composition of the glass on the formation of metal nanoparticles in such glasses. Four various types of silicate glasses were implanted with Ag+ ions with different energy (330 keV, 1.2 MeV and 1.7 MeV), with the fluence being kept constant (1 × 1016 ions cm-2). The as-implanted samples were annealed at 600 °C for 1 h. The samples were characterised in terms of: the nucleation of metal nanoparticles (linear optical absorption), the migration of silver through the glass matrix during the implantation and post-implantation annealing (Rutherford backscattering spectroscopy), and the oxidation state of silver (photoluminescence in the visible region).

  4. Metallic glass formation at the interface of explosively welded Nb and stainless steel

    NASA Astrophysics Data System (ADS)

    Bataev, I. A.; Hokamoto, K.; Keno, H.; Bataev, A. A.; Balagansky, I. A.; Vinogradov, A. V.

    2015-07-01

    The interface between explosively welded niobium and stainless steel SUS 304 was studied using scanning electron microscopy, transmission electron microscopy and energy dispersive X-Ray spectroscopy. The wavy interface along which vortex zones were located was observed. The vortex zones formed due to the mixing of materials typically had amorphous structure. Inoue's criteria of glass formation were used to explain this result. The effect of the composition, cooling rate and pressure on the glass formation are discussed. The conditions of deformation, heating, and cooling as well as shockwaves propagation were numerically simulated. We show that the conditions of vortex zone formation resemble the conditions of rapid solidification processes. In contrast to the "classical" methods of rapid solidification of melt, the conditions of metastable phase formation during explosive welding are significantly complicated by the fluctuations of composition and pressure. Possible metastable structures formation at the interface of some common explosively joined materials is predicted.

  5. Heterogeneous-nucleation and glass-formation studies of 56Ga2O3-44CaO

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin C.; Curreri, Peter A.; Pline, David

    1987-01-01

    Glass formation and heterogeneous crystallization are described for the reluctant-glass-forming 56Ga2O3-44CaO eutectic composition. The times and temperatures for nucleation at various cooling rates and experimental conditions were measured and empirical continuous-cooling-crystallization boundaries were constructed for various heterogeneous nucleation processes. A definition for an empirical critical cooling rate to form a glass from reluctant borderline glass formers is proposed, i.e., the cooling rate that results in glass formation in 95 percent of the quenching experiments.

  6. Chemical influence on β-relaxations and the formation of molecule-like metallic glasses.

    PubMed

    Yu, Hai Bin; Samwer, Konrad; Wang, Wei Hua; Bai, Hai Yang

    2013-01-01

    Secondary (also known as Johari-Goldstein or β-) relaxations are an intrinsic feature of supercooled liquids and glasses. They are important in many respects but the underlying mechanisms are not well understood. A long-standing puzzle is why some glasses show β-relaxations as pronounced peaks, whereas others as unobvious excess wings. Here we demonstrate that these different behaviours are related to the fluctuations of chemical interactions by using prototypical systems of metallic glasses. A general rule is summarized: pronounced β-relaxations are associated with systems where all the atomic pairs have large similar negative values of enthalpy of mixing, whereas positive or significant fluctuations in enthalpy of mixing suppress β-relaxations. The emerging physical picture is that strong and comparable interactions among all the constituting atoms maintain string-like atomic configurations for the excitations of β-events and can be considered as the formation of molecule-like metallic glasses.

  7. Advances in the generalized entropy theory of glass-formation in polymer melts

    NASA Astrophysics Data System (ADS)

    Dudowicz, Jacek; Douglas, Jack F.; Freed, Karl F.

    2014-12-01

    The generalized entropy theory (GET) of polymeric glass-forming liquids is reformulated into a computationally simpler and more natural formalism than the original version of this theory. The new theoretical framework greatly facilitates establishing essential trends in the dependence of the segmental relaxation time τ, fragility, characteristic temperatures of glass-formation, etc., on the combined influences of monomer molecular structure, chain rigidity, and cohesive interaction strength. Special attention is placed on the estimating the parameters of the phenomenological Vogel-Fulcher-Tammann relations for describing segmental relaxation in diverse liquids in the low temperature range of glass-formation, Tg > T > Tc (or Tg < T < Tg + 100 K), where Tg and Tc are, respectively, the glass transition temperature and the crossover temperature separating the high and low temperature regimes of glass-formation. Finally, we discuss how the molecular energetic interaction parameters of the GET can be estimated from experimental data. Illustrative calculations are performed for the stiffness factor σ and the cohesive energy density u as a first step in this direction.

  8. Fluoride-containing bioactive glasses: effect of glass design and structure on degradation, pH and apatite formation in simulated body fluid.

    PubMed

    Brauer, Delia S; Karpukhina, Natalia; O'Donnell, Matthew D; Law, Robert V; Hill, Robert G

    2010-08-01

    Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in particular, dental applications for caries inhibition. Melt-derived glasses in the system SiO(2)-P(2)O(5)-CaO-Na(2)O with increasing amounts of CaF(2) were prepared by keeping network connectivity and the ratio of all other components constant. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid at 37 degrees C over up to 2 weeks were investigated. Crystal phases formed in SBF were characterized using infrared spectroscopy, X-ray diffraction with Rietveld analysis and solid-state nuclear magnetic resonance spectroscopy ((19)F and (31)P MAS-NMR). Results show that incorporation of fluoride resulted in a reduced pH rise in aqueous solutions compared to fluoride-free glasses and in formation of fluorapatite (FAp), which is more chemically stable than hydroxyapatite or carbonated hydroxyapatite and therefore is of interest for dental applications. However, for increasing fluoride content in the glass, fluorite (CaF(2)) was formed at the expense of FAp. Apatite formation could be favoured by increasing the phosphate content in the glass, as the release of additional phosphate into the SBF would affect supersaturation in the solution and possibly favour formation of apatite.

  9. Formation of plasma induced surface damage in silica glass etching for optical waveguides

    NASA Astrophysics Data System (ADS)

    Choi, D. Y.; Lee, J. H.; Kim, D. S.; Jung, S. T.

    2004-06-01

    Ge, B, P-doped silica glass films are widely used as optical waveguides because of their low losses and inherent compatibility with silica optical fibers. These films were etched by ICP (inductively coupled plasma) with chrome etch masks, which were patterned by reactive ion etching (RIE) using chlorine-based gases. In some cases, the etched surfaces of silica glass were very rough (root-mean square roughness greater than 100 nm) and we call this phenomenon plasma induced surface damage (PISD). Rough surface cannot be used as a platform for hybrid integration because of difficulty in alignment and bonding of active devices. PISD reduces the etch rate of glass and it is very difficult to remove residues on a rough surface. The objective of this study is to elucidate the mechanism of PISD formation. To achieve this goal, PISD formation during different etching conditions of chrome etch mask and silica glass was investigated. In most cases, PISD sources are formed on a glass surface after chrome etching, and metal compounds are identified in theses sources. Water rinse after chrome etching reduces the PISD, due to the water solubility of metal chlorides. PISD is decreased or even disappeared at high power and/or low pressure in glass etching, even if PISD sources were present on the glass surface before etching. In conclusion, PISD sources come from the chrome etching process, and polymer deposition on these sources during the silica etching cause the PISD sources to grow. In the area close to the PISD source there is a higher ion flux, which causes an increase in the etch rate, and results in the formation of a pit.

  10. Compositional landscape for glass formation in metal alloys.

    PubMed

    Na, Jong Hyun; Demetriou, Marios D; Floyd, Michael; Hoff, Andrew; Garrett, Glenn R; Johnson, William L

    2014-06-24

    A high-resolution compositional map of glass-forming ability (GFA) in the Ni-Cr-Nb-P-B system is experimentally determined along various compositional planes. GFA is shown to be a piecewise continuous function formed by intersecting compositional subsurfaces, each associated with a nucleation pathway for a specific crystalline phase. Within each subsurface, GFA varies exponentially with composition, wheres exponential cusps in GFA are observed when crossing from one crystallization pathway to another. The overall GFA is shown to peak at multiple exponential hypercusps that are interconnected by ridges. At these compositions, quenching from the high-temperature melt yields glassy rods with diameters exceeding 1 cm, whereas for compositions far from these cusps the critical rod diameter drops precipitously and levels off to 1 to 2 mm. The compositional landscape of GFA is shown to arise primarily from an interplay between the thermodynamics and kinetics of crystal nucleation, or more precisely, from a competition between driving force for crystallization and liquid fragility.

  11. Studies of the Local Distortions and the EPR Parameters for Cu2+ in xLi2O-(30-x)Na2O-69·5B2O Glasses

    NASA Astrophysics Data System (ADS)

    Ding, Chang-Chun; Wu, Shao-Yi; Kuang, Min-Quan; Hu, Xian-Fen; Li, Guo-Liang

    2016-03-01

    The local distortions and electron paramagnetic resonance (EPR) parameters for Cu2+ in lithium sodium borate (LNB) glasses xLi2O·(30-x)·Na2O·69.5B2O3 (5≤x≤25 mol%) are theoretically studied at various concentrations x in a consistent way. Owing to the Jahn-Teller effect, the [CuO6]10- clusters are found to experience the significant tetragonal elongations of 16% along C4 axis. Despite the nearly unchanging observed g factors, measured d-d transition band (or cubic field parameter Dq) shows remarkable linear increases with concentration x, whose influences on g‖ and g⊥ are actually cancelled by the linearly increasing covalency factor N and relative elongation ratio η with x. The almost unvarying hyperfine structure constants are attributed to the fact that the influences of the linearly increasing N and the linearly decreasing core polarisation constant κ largely cancel one another. The microscopic mechanisms of the above concentration dependences for these quantities are illustrated from mixed alkali effect (modification of B2O3 network by transforming some BO3 units into BO4 ones with variations in modifier Li2O concentration).

  12. Spin glass behavior in frustrated quantum spin system CuAl2O4 with a possible orbital liquid state.

    PubMed

    Nirmala, R; Jang, Kwang-Hyun; Sim, Hasung; Cho, Hwanbeom; Lee, Junghwan; Yang, Nam-Geun; Lee, Seongsu; Ibberson, R M; Kakurai, K; Matsuda, M; Cheong, S-W; Gapontsev, V V; Streltsov, S V; Park, Je-Geun

    2017-04-05

    CuAl2O4 is a normal spinel oxide having quantum spin, S  =  1/2 for Cu(2+). It is a rather unique feature that the Cu(2+) ions of CuAl2O4 sit at a tetrahedral position, not like the usual octahedral position for many oxides. At low temperatures, it exhibits all the thermodynamic evidence of a quantum spin glass. For example, the polycrystalline CuAl2O4 shows a cusp centered at ~2 K in the low-field dc magnetization data and a clear frequency dependence in the ac magnetic susceptibility while it displays logarithmic relaxation behavior in a time dependence of the magnetization. At the same time, there is a peak at ~2.3 K in the heat capacity, which shifts towards a higher temperature with magnetic fields. On the other hand, there is no evidence of new superlattice peaks in the high-resolution neutron powder diffraction data when cooled from 40 to 0.4 K. This implies that there is no long-ranged magnetic order down to 0.4 K, thus confirming a spin glass-like ground state for CuAl2O4. Interestingly, there is no sign of structural distortion either although Cu(2+) is a Jahn-Teller active ion. Thus, we claim that an orbital liquid state is the most likely ground state in CuAl2O4. Of further interest, it also exhibits a large frustration parameter, f  =  |θ CW/T m| ~ 67, one of the largest values reported for spinel oxides. Our observations suggest that CuAl2O4 should be a rare example of a frustrated quantum spin glass with a good candidate for an orbital liquid state.

  13. Influence of the Substrate on the Formation of Metallic Glass Coatings by Cold Gas Spraying

    NASA Astrophysics Data System (ADS)

    Henao, John; Concustell, Amadeu; Dosta, Sergi; Cinca, Núria; Cano, Irene G.; Guilemany, Josep M.

    2016-06-01

    Cold gas spray technology has been used to build up coatings of Fe-base metallic glass onto different metallic substrates. In this work, the effect of the substrate properties on the viscoplastic response of metallic glass particles during their impact has been studied. Thick coatings with high deposition efficiencies have been built-up in conditions of homogeneous flow on substrates such as Mild Steel AISI 1040, Stainless Steel 316L, Inconel 625, Aluminum 7075-T6, and Copper (99.9%). Properties of the substrate have been identified to play an important role in the viscoplastic response of the metallic glass particles at impact. Depending on the process gas conditions, the impact morphologies show not only inhomogeneous deformation but also homogeneous plastic flow despite the high strain rates, 108 to 109 s-1, involved in the technique. Interestingly, homogenous deformation of metallic glass particles is promoted depending on the hardness and the thermal diffusivity of the substrate and it is not exclusively a function of the kinetic energy and the temperature of the particle at impact. Coating formation is discussed in terms of fundamentals of dynamics of undercooled liquids, viscoplastic flow mechanisms of metallic glasses, and substrate properties. The findings presented in this work have been used to build up a detailed scheme of the deposition mechanism of metallic glass coatings by the cold gas spraying technology.

  14. Effect of calcium phosphate glass on bone formation in calvarial defects of Sprague-Dawley rats.

    PubMed

    Moon, Hyun-Ju; Kim, Kyoung-Nam; Kim, Kwang-Mahn; Choi, Seong-Ho; Kim, Chong-Kwan; Kim, Kee-Deog; LeGeros, Racquel Z; Lee, Yong-Keun

    2006-09-01

    The purpose of this study was to investigate the bone regenerative effect of calcium phosphate glass in vivo. We prepared two different sizes of calcium phosphate glass powder using the system CaO-CaF2-P2O5-MgO-ZnO; the particle size of the powders were 400 microm and 40 microm. 8 mm calvarial critical-sized defects were created in 60 male Sprague-Dawley rats. The animals were divided into 3 groups of 20 animals each. Each defect was filled with a constant weight of 0.5 g calcium phosphate glass powder mixed with saline. As controls, the defect was left empty. The rats were sacrificed 2 or 8 weeks after postsurgery, and the results were evaluated using radiodensitometric and histological studies; they were also examined histomorphometrically. When the bigger powders with 400 microm particle were grafted, the defects were nearly completely filled with new-formed bone in a clean healing condition after 8 week. When smaller powders with 40 microm particle were transplanted, new bone formation was even lower than the control group due to a lot of inflammatory cell infiltration. It was concluded that the prepared calcium phosphate glass enhanced the new bone formation in the calvarial defect of Sprague-Dawley rats and it is expected to be a good potential materials for hard tissue regeneration. The particle size of the calcium phosphate was crucial; 400 microm particles promoted new bone formation, while 40 microm particles inhibited it because of severe inflammation.

  15. Generalized entropy theory of glass-formation in fully flexible polymer melts

    NASA Astrophysics Data System (ADS)

    Xu, Wen-Sheng; Douglas, Jack F.; Freed, Karl F.

    2016-12-01

    The generalized entropy theory (GET) offers many insights into how molecular parameters influence polymer glass-formation. Given the fact that chain rigidity often plays a critical role in understanding the glass-formation of polymer materials, the GET was originally developed based on models of semiflexible chains. Consequently, all previous calculations within the GET considered polymers with some degree of chain rigidity. Motivated by unexpected results from computer simulations of fully flexible polymer melts concerning the dependence of thermodynamic and dynamic properties on the cohesive interaction strength (ɛ), the present paper employs the GET to explore the influence of ɛ on glass-formation in models of polymer melts with a vanishing bending rigidity, i.e., fully flexible polymer melts. In accord with simulations, the GET for fully flexible polymer melts predicts that basic dimensionless thermodynamic properties (such as the reduced thermal expansion coefficient and isothermal compressibility) are universal functions of the temperature scaled by ɛ in the regime of low pressures. Similar scaling behavior is also found for the configurational entropy density in the GET for fully flexible polymer melts. Moreover, we find that the characteristic temperatures of glass-formation increase linearly with ɛ and that the fragility is independent of ɛ in fully flexible polymer melts, predictions that are again consistent with simulations of glass-forming polymer melts composed of fully flexible chains. Beyond an explanation of these general trends observed in simulations, the GET for fully flexible polymer melts predicts the presence of a positive residual configurational entropy at low temperatures, indicating a return to Arrhenius relaxation in the low temperature glassy state.

  16. Generalized entropy theory of glass-formation in fully flexible polymer melts.

    PubMed

    Xu, Wen-Sheng; Douglas, Jack F; Freed, Karl F

    2016-12-21

    The generalized entropy theory (GET) offers many insights into how molecular parameters influence polymer glass-formation. Given the fact that chain rigidity often plays a critical role in understanding the glass-formation of polymer materials, the GET was originally developed based on models of semiflexible chains. Consequently, all previous calculations within the GET considered polymers with some degree of chain rigidity. Motivated by unexpected results from computer simulations of fully flexible polymer melts concerning the dependence of thermodynamic and dynamic properties on the cohesive interaction strength (ϵ), the present paper employs the GET to explore the influence of ϵ on glass-formation in models of polymer melts with a vanishing bending rigidity, i.e., fully flexible polymer melts. In accord with simulations, the GET for fully flexible polymer melts predicts that basic dimensionless thermodynamic properties (such as the reduced thermal expansion coefficient and isothermal compressibility) are universal functions of the temperature scaled by ϵ in the regime of low pressures. Similar scaling behavior is also found for the configurational entropy density in the GET for fully flexible polymer melts. Moreover, we find that the characteristic temperatures of glass-formation increase linearly with ϵ and that the fragility is independent of ϵ in fully flexible polymer melts, predictions that are again consistent with simulations of glass-forming polymer melts composed of fully flexible chains. Beyond an explanation of these general trends observed in simulations, the GET for fully flexible polymer melts predicts the presence of a positive residual configurational entropy at low temperatures, indicating a return to Arrhenius relaxation in the low temperature glassy state.

  17. Simulation of an atomistic dynamic field theory for monatomic liquids: freezing and glass formation.

    PubMed

    Berry, Joel; Elder, K R; Grant, Martin

    2008-06-01

    We examine a phase field crystal model for simple liquid-solid systems consisting of a free energy functional related to the Ramakrishnan-Yussouff free energy of classical density functional theory and an equation of motion capable of describing long-time-scale behavior in the deeply supercooled regime. The thermodynamics and dynamics of freezing and glass formation in this model system are studied through large-scale three-dimensional Langevin simulations. At low cooling rates bcc crystals are formed by nucleation and growth from the melt. At large cooling rates no clear glass transition is observed, but a kinetically driven first-order transition from supercooled liquid to a disordered glasslike solid does occur. Despite the peculiarities of the transition, the structure and properties of the resulting disordered solid are shown to strongly resemble those of a typical glass. Consequences of pseudocritical behavior and heterogeneity near the liquid spinodal are also discussed.

  18. Protein aggregation and particle formation in prefilled glass syringes.

    PubMed

    Gerhardt, Alana; Mcgraw, Nicole R; Schwartz, Daniel K; Bee, Jared S; Carpenter, John F; Randolph, Theodore W

    2014-06-01

    The stability of therapeutic proteins formulated in prefilled syringes (PFS) may be negatively impacted by the exposure of protein molecules to silicone oil-water interfaces and air-water interfaces. In addition, agitation, such as that experienced during transportation, may increase the detrimental effects (i.e., protein aggregation and particle formation) of protein interactions with interfaces. In this study, surfactant-free formulations containing either a monoclonal antibody or lysozyme were incubated in PFS, where they were exposed to silicone oil-water interfaces (siliconized syringe walls), air-water interfaces (air bubbles), and agitation stress (occurring during end-over-end rotation). Using flow microscopy, particles (≥2 μm diameter) were detected under all conditions. The highest particle concentrations were found in agitated, siliconized syringes containing an air bubble. The particles formed in this condition consisted of silicone oil droplets and aggregated protein, as well as agglomerates of protein aggregates and silicone oil. We propose an interfacial mechanism of particle generation in PFS in which capillary forces at the three-phase (silicone oil-water-air) contact line remove silicone oil and gelled protein aggregates from the interface and transport them into the bulk. This mechanism explains the synergistic effects of silicone oil-water interfaces, air-water interfaces, and agitation in the generation of particles in protein formulations.

  19. Thermochromic effects in a Jahn-Teller active CuCl(4-)6 layered hybrid system.

    PubMed

    Caretta, A; Miranti, R; Arkenbout, A H; Polyakov, A O; Meetsma, A; Hidayat, R; Tjia, M O; Palstra, T T M; van Loosdrecht, P H M

    2013-12-18

    The hybrid material copper (II) tetrachloro-bis(phenyl ethyl ammonium) (C6H5CH2CH2NH3)2CuCl4, or PEACuCl, has been investigated by temperature-dependent spectroscopic absorption experiments. The absorption bands observed in the near-infrared region (1.3-1.9 eV) generally exhibit redshifts with increasing temperature. The temperature-induced energy shifts of the spectral components are shown to be consistently related to temperature-induced Cu-Cl bond length changes. Additionally, the thermochromic color change is caused by a charge transfer band edge redshifting (in the visible region 2.0-2.8 eV) with increasing temperature. By comparison with similar Cu-based systems, it is suggested that this shift is caused by broadening and strengthening of the band.

  20. Thermochromic effects in a Jahn-Teller active {{CuCl}}_{6}^{4-} layered hybrid system

    NASA Astrophysics Data System (ADS)

    Caretta, A.; Miranti, R.; Arkenbout, A. H.; Polyakov, A. O.; Meetsma, A.; Hidayat, R.; Tjia, M. O.; Palstra, T. T. M.; van Loosdrecht, P. H. M.

    2013-12-01

    The hybrid material copper (II) tetrachloro-bis(phenyl ethyl ammonium) (C6H5CH2CH2NH3)2CuCl4, or PEACuCl, has been investigated by temperature-dependent spectroscopic absorption experiments. The absorption bands observed in the near-infrared region (1.3-1.9 eV) generally exhibit redshifts with increasing temperature. The temperature-induced energy shifts of the spectral components are shown to be consistently related to temperature-induced Cu-Cl bond length changes. Additionally, the thermochromic color change is caused by a charge transfer band edge redshifting (in the visible region 2.0-2.8 eV) with increasing temperature. By comparison with similar Cu-based systems, it is suggested that this shift is caused by broadening and strengthening of the band.

  1. Bone formation in calvarial defects of Sprague-Dawley rats by transplantation of calcium phosphate glass.

    PubMed

    Moon, Hyun-Ju; Kim, Kyoung-Nam; Kim, Kwang-Mahn; Choi, Seong-Ho; Kim, Chong-Kwan; Kim, Kee-Deog; LeGeros, Racquel Z; Lee, Yong-Keun

    2005-09-01

    The purpose of this study was to investigate the bone-regenerative effect of calcium phosphate glass in vivo. We prepared amorphous calcium phosphate glass powder having a mean particle size of 400 microm in the system CaO-CaF2-P2O5-MgO-ZnO. Calvarial critical-sized defects (8 mm) were created in 60 male Sprague-Dawley rats. The animals were divided into an experimental group and control group of 30 animals each. Each defect was filled with a constant weight of 0.5 g calcium phosphate glass powder mixed with saline. As a control, the defect was left empty. The rats were sacrificed 2, 4, or 8 weeks postsurgery, and the results evaluated using radiodensitometric and histological studies; they were also examined histomorphometrically. When the calcium phosphate glass powders with 400-microm particles were grafted, the defects were nearly completely filled with new-formed bone in a clean healing condition after 8 weeks. It was observed that the prepared calcium phosphate glass enhanced new bone formation in the calvarial defect of Sprague-Dawley rats and could be expected to have potential for use as a hard tissue regeneration material.

  2. Characterization and Glass Formation of JSC-1 Lunar and Martian Soil Simulants

    NASA Astrophysics Data System (ADS)

    Ray, Chandra S.; Reis, Signo T.; Sen, Subhayu

    2008-01-01

    The space exploration mission of NASA requires human and robotic presence for long duration beyond the low earth orbit (LEO), especially on Moon and Mars. Developing a human habitat or colony on these planets would require a diverse range of materials, whose applications would range from structural foundations, (human) life support, (electric) power generation to components for scientific instrumentations. A reasonable and cost-effective approach for fabricating the materials needed for establishing a self-sufficient human outpost would be to primarily use local (in situ) resources on these planets. Since ancient times, glass and ceramics have been playing a vital role on human civilization. A long term project on studying the feasibility of developing glass and ceramic materials has been undertaken using Lunar and Martian soil simulants (JSC-1) as developed by Johnson Space Center. The first step in this on-going project requires developing a data base on results that fully characterize the simulants to be used for further investigations. The present paper reports characterization data of both JSC-1 Lunar and JSC Mars-1 simulants obtained up to this time via x-ray diffraction analysis, scanning electron microscopy, thermal analysis (DTA, TGA) and chemical analysis. The critical cooling rate for glass formation for the melts of the simulants was also measured in order to quantitatively assess the glass forming tendency of these melts. The importance of the glasses and ceramics developed using in-situ resources for constructing human habitats on Moon or Mars is discussed.

  3. Characterization and Glass Formation of JSC-1 Lunar and Martian Soil Simulants

    NASA Technical Reports Server (NTRS)

    Sen, Subhayu

    2008-01-01

    The space exploration mission of NASA requires long duration presence of human being beyond the low earth orbit (LEO), especially on Moon and Mars. Developing a human habitat or colony on these planets would require a diverse range of materials, whose applications would range from structural foundations, (human) life support, (electric) power generation to components for scientific instrumentation. A reasonable and cost-effective approach for fabricating the materials needed for establishing a self-sufficient human outpost would be to primarily use local (in situ) resources on these planets. Since ancient times, glass and ceramics have been playing a vital role on human civilization. A long term project on studying the feasibility of developing glass and ceramic materials using Lunar and Martian soil simulants (JSC-1) as developed by Johnson Space Center has been undertaken. The first step in this on-going project requires developing a data base on results that fully characterize the simulants to be used for further investigations. The present paper reports characterization data of both JSC-1 Lunar and JSC Mars-1 simulants obtained up to this time via x-ray diffraction analysis, scanning electron microscopy, thermal analysis (DTA, TGA) and chemical analysis. The critical cooling rate for glass formation for the melts of the simulants was also measured in order to quantitatively assess the glass forming tendency of these melts. The importance of the glasses and ceramics developed using in-situ resources for constructing human habitats on Moon or Mars is discussed.

  4. Characterization and Glass Formation of JSC-1 Lunar and Martian Soil Simulants

    NASA Technical Reports Server (NTRS)

    Sen, Subhayu

    2008-01-01

    The space exploration mission of NASA requires long duration presence of human being beyond the low earth orbit (LEO), especially on Moon and Mars. Developing a human habitat or colony on these planets would require a diverse range of materials, whose applications would range from structural foundations, (human) life support, (electric) power generation to components for scientific instrumentation. A reasonable and cost-effective approach for fabricating the materials needed for establishing a self-sufficient human outpost would be to primarily use local (in situ) resources on these planets. Since ancient times, glass and ceramics have been playing a vital role on human civilization. A long term project on studying the feasibility of developing glass and ceramic materials using Lunar and Martian soil simulants (JSC-1) as developed by Johnson Space Center has been undertaken. The first step in this on-going project requires developing a data base on results that fully characterize the simulants to be used for further investigations. The present paper reports characterization data of both JSC-1 Lunar and JSC Mars-1 simulants obtained up to this time via x-ray diffraction analysis, scanning electron microscopy, thermal analysis (DTA, TGA) and chemical analysis. The critical cooling rate for glass formation for the melts of the simulants was also measured in order to quantitatively assess the glass forming tendency of these melts. The importance of the glasses and ceramics developed using in-situ resources for constructing human habitats on Moon or Mars is discussed.

  5. A photo-oxidation mechanism for patterning and hologram formation in conjugated polymer/glass composites

    NASA Astrophysics Data System (ADS)

    Levi, Ofer; Perepelitsa, Galina; Davidov, Dan; Shalom, Shoshy; Benjamin, Iris; Neumann, Ronny; Agranat, Aharon J.; Avny, Yair

    2000-08-01

    Improved diffraction efficiency was observed in holograms stored in disordered conjugated polymer/glass composites. The conjugated polymers used were alkoxy substituted poly(phenylenevinylne) analogs and the glass matrices were zirconia-organosilica xerogels. Investigation of the mechanism of hologram formation revealed evidence of a photochromic process consisting of light induced photo-oxidation (bleaching) of the embedded conjugated polymer resulting in the formation of an absorption grating and a phase grating. Investigation of the hologram formation revealed that the process was oxygen dependent. Oxygen removal increases hologram formation time by more than an order of magnitude and halves the total hologram efficiency. The oxygen dependence was also highly correlated with photobleaching of the samples and beam interaction of the writing beams. The chemical transformations upon photobleaching were shown by infrared and Raman spectroscopy to involve chain scission and oxidation of the polymer at the vinylic position of the conjugated polymer. Film preparation of the composites was optimized showing a tenfold improvement in the holographic properties compared to our previous results. The optimized treatment method allows for a high, >20%, diffraction efficiency, η, to be obtained for the 2.5-μm-thick polymer/glass films. Light sensitivity was compared for several polymer/glass composites and was correlated to the absorption curves and holographic diffraction efficiency showing that the new composites and film preparation techniques are promising for holographic materials sensitive in the blue and ultraviolet spectral regions. A method of information fixing by preventing oxygen entry to the composite film resulted in a fourfold increase of the erasure time. These findings suggest that holograms can be fixed for a long term by nonoxygen permeable coating, applied after hologram formation.

  6. Structural aspects of glass-formation in Ni-Nb melts

    SciTech Connect

    Holland-Moritz, D.; Yang, F.; Gegner, J.; Meyer, A.; Hansen, T.; Ruiz-Martín, M. D.

    2014-05-28

    We report on investigations of the static structure factors of glass-forming Ni{sub 59.5}Nb{sub 40.5} alloy melts by combination of the containerless processing technique of electrostatic levitation with neutron diffraction. By application of the isotopic substitution method, the full set of partial structure factors was determined. The short-range order in liquid Ni{sub 59.5}Nb{sub 40.5} is characterized by a large nearest neighbor coordination number of Z{sub NN} = 14.3 and a chemical short-range order with an affinity for the formation of heterogeneous Nb-Ni nearest neighbors. The structure factors observed here in the liquid state closely resemble those reported for amorphous Nb-Ni solids. The comparison with earlier results on the short-range structure in Zr-based glass-forming melts suggests that a large local density of packing, chemical order, and structural frustration are, amongst others, common structural properties of these metallic glass-forming systems, which favor glass-formation.

  7. Evolutions of Molecular Oxygen Formation and Sodium Migration in Xe Ion Irradiated Borosilicate Glasses

    SciTech Connect

    Chen, Liang; Zhang, Duofei F.; Lv, Peng; Zhang, Jiandong; Du, Xing; Yuan, Wei; Nan, Shuai; Zhu, Zihua; Wang, Tieshan

    2016-07-23

    The modifications of a commercial borosilicate glass induced by Xe ion irradiation have been studied by Raman spectroscopy and ToF-SIMS depth profiling. A decrease in the average Si–O–Si angle, an increase in the population of three-membered rings and an increase of the glass polymerization are evidenced. The molecular oxygen appears in the irradiated glasses after the irradiation fluence reaches approximately 1015 ions/cm2. The O2 concentration decreaseswith the depth of irradiated glass at the ion fluence of 2 × 1016 ions/cm2. A sodiumdepleted layer at the surface and a depleted zone at around the penetration depth of 5 MeV Xe ions are observed. The thickness of the sodium depleted layer increases with the irradiation fluence. Moreover, comparing with previous results after electron and Ar ion irradiation, it can be concluded that the nuclear energy deposition can partially inhibit the formation of molecular oxygen and increase the threshold value of electron energy deposition for the molecular oxygen formation.

  8. Glass formation and cluster evolution in the rapidly solidified monatomic metallic liquid Ta under high pressure

    NASA Astrophysics Data System (ADS)

    Jiang, Dejun; Wen, Dadong; Tian, Zean; Liu, Rangsu

    2016-12-01

    Molecular dynamics (MD) simulations have been performed to examine the glass formation and cluster evolution during the rapid solidification of monatomic metallic liquid Ta under high pressure. The atomic structures in the systems are characterized by the radical distribution function (RDF), Honeycutt-Anderson (H-A) bond-type index method and cluster-type index method (CTIM). It is observed that the defective icosahedra play the critical role in the formation of Ta monatomic metallic glasses (MGs) rather than (12 0 12 0) perfect icosahedra, which have been identified as the basic local atomic units in many multi-component MGs. With the increase of pressure P, the fraction of icosahedral type clusters decreases remarkably in Ta MGs, while the fraction of bcc type clusters rises evidently. The evolution of vitrification degree (DSRO or DMRO) of the rapidly cooled metal Ta system further reveals that a higher pressure P is disadvantageous to the formation of Ta monatomic MGs. The weaker glass forming ability (GFA) of liquid metal Ta obtained under higher pressure P can be contributed to the decrease of DSRO or DMRO which is induced by increasing high pressure P to some extent.

  9. Recrystallized Impact Glasses of the Onaping Formation and the Sudbury Igneous Complex, Sudbury Structure, Ontario, Canada

    NASA Technical Reports Server (NTRS)

    Dressler, B. O.; Weiser, T.; Brockmeyer, P.

    1996-01-01

    The origin of the Sudbury Structure and of the associated heterolithic breccias of the Onaping Formation and the Sudbury Igneous Complex have been controversial. While an impact origin of the structure has gained wide acceptance over the last 15 years, the origin of the recrystallized Onaping Formation glasses and of the igneous complex is still being debated. Recently the interpretation of the breccias of the Onaping Formation as suevitic fall-back impact breccias has been challenged. The igneous complex is interpreted either as a differentiated impact melt sheet or as a combination of an upper impact melt represented by the granophyre, and a lower, impact-triggered magmatic body consisting of the norite-sublayer formations. The Onaping Formation contains glasses as fluidal and nonfluidal fragments of various shapes and sizes. They are recrystallized, and our research indicates that they are petrographically heterogeneous and span a wide range of chemical compositions. These characteristics are not known from glasses of volcanic deposits. This suggests an origin by shock vitrification, an interpretation consistent with their association with numerous and varied country rock clasts that exhibit microscopic shock metamorphic features. The recrystallized glass fragments represent individual solid-state and liquid-state vitrified rocks or relatively small melt pods. The basal member lies beneath the Gray and Black members of the Onaping Formation and, where not metamorphic, has an igneous matrix. Igneous-textured melt bodies occur in the upper two members and above the Basal Member. A comparison of the chemical compositions of recrystallized glasses and of the matrices of the Basal Member and the melt bodies with the components and the bulk composition of the igneous complex is inconclusive as to the origin of the igneous complex. Basal Member matrix and Melt Bodies, on average, are chemically similar to the granophyre of the Sudbury Igneous Complex, suggesting that

  10. Application of the entropy theory of glass formation to poly(α-olefins)

    NASA Astrophysics Data System (ADS)

    Stukalin, Evgeny B.; Douglas, Jack F.; Freed, Karl F.

    2009-09-01

    The entropy theory of glass formation, which has previously been developed to describe general classes of polymeric glass-forming liquids, is extended here to model the thermodynamic and dynamic properties of poly(α-olefins). By combining this thermodynamic theory with the Adam-Gibbs model (which relates the configurational entropy to the rate of structural relaxation), we provide systematic computations for all four characteristic temperatures (TA, Tc, Tg, T0), governing the position and breadth of the glass transition, and the fragility parameters (D,m) describing the strength of the temperature dependence of the structural relaxation time, where TA is the temperature below which the relaxation is non-Arrhenius, Tc is the crossover or empirical mode-coupling temperature, Tg is the glass transition temperature, and T0 is the temperature at which the extrapolated relaxation time diverges. These temperatures and fragility parameters are evaluated as a function of molar mass, pressure, and the length n of the α-olefin side chains. The nearest neighbor interaction energy and local chain rigidities are found to strongly influence the four characteristic temperatures and the low temperature fragility. We also observe an "internal plasticization" of the poly(α-olefins) wherein the fragility decreases as the number n of "flexible" side group units increases. Our computations provide solid support for a pressure counterpart of the Vogel-Fulcher-Tammann relation. The entropy theory of glass formation predicts systematic changes in fragility with chain stiffness, cohesive energy, polymerization index, and side chain length, and qualitative trends in these parameters are discussed.

  11. Porous wall hollow glass microspheres as a medium or substrate for storage and formation of novel materials

    DOEpatents

    Wicks, George G; Serkiz, Steven M.; Zidan, Ragaiy; Heung, Leung K.

    2014-06-24

    Porous wall hollow glass microspheres are provided as a template for formation of nanostructures such as carbon nanotubes, In addition, the carbon nanotubes in combination with the porous wall hollow glass microsphere provides an additional reaction template with respect to carbon nanotubes.

  12. Sulphate incorporation and glass formation in phosphate systems for nuclear and toxic waste immobilization

    SciTech Connect

    Bingham, P.A. Hand, R.J.

    2008-07-01

    Glass formation and the capacity for sulphur incorporation have been investigated within the systems P{sub 2}O{sub 5}-Al{sub 2}O{sub 3}-Na{sub 2}O-Fe{sub 2}O{sub 3} and P{sub 2}O{sub 5}-Fe{sub 2}O{sub 3}-R{sub y}O (R = Li, Na, K, Mg, Ca, Ba, Pb). Linear relationships have been identified linking log [SO{sub 3}] with the oxide ion activity, which can be represented to varying degrees by normalized cation field strength index {sigma}(z/a{sup 2}), theoretical optical basicity {lambda}{sub th}, oxygen to phosphorus molar ratio [O]/[P], or P{sub 2}O{sub 5} content. When prepared under oxidizing conditions only basic, highly depolymerized phosphate glasses for which {sigma}(z/a{sup 2}) < {approx}1.2; {lambda}{sub th} > {approx}0.5; [O]/[P] > {approx}3.8; or P{sub 2}O{sub 5} content <{approx}40 mol% can incorporate levels of sulphur that could be considered useful from a waste immobilization perspective. Data for several phosphate and borosilicate glasses suggest that the {sigma}(z/a{sup 2}) scale provides the best residual fitting error and that if glasses are considered within their familial limits, this can provide a useful methodology for predicting sulphur capacity.

  13. Formation of nanostructures in Eu3+ doped glass-ceramics: an XAS study.

    PubMed

    Pellicer-Porres, J; Segura, A; Martínez-Criado, G; Rodríguez-Mendoza, U R; Lavín, V

    2013-01-16

    We describe the results of x-ray absorption experiments carried out to deduce structural and chemical information in Eu(3+) doped, transparent, oxyfluoride glass and nanostructured glass-ceramic samples. The spectra were measured at the Pb and Eu-L(III) edges. The Eu environment in the glass samples is observed to be similar to that of EuF(3). Complementary x-ray diffraction experiments show that thermal annealing creates β-PbF(2) type nanocrystals. X-ray absorption indicates that Eu ions act as seeds in the nanocrystal formation. There is evidence of interstitial fluorine atoms around Eu ions as well as Eu dimers. X-ray absorption at the Pb-L(III) edge shows that after the thermal treatment most lead atoms form a PbO amorphous phase and that only 10% of the lead atoms remain available to form β-PbF(2) type nanocrystals. Both x-ray diffraction and absorption point to a high Eu content in the nanocrystals. Our study suggests new approaches to the oxyfluoride glass-ceramic synthesis in order to further improve their properties.

  14. Recent advances with generalized entropy theory of glass-formation in polymers

    NASA Astrophysics Data System (ADS)

    Freed, Karl

    The generalized entropy theory (GET) of glass-formation in polymers is a combination of the lattice cluster theory (LCT) for the configurational entropy density with the Adam-Gibbs (AG) theory for the structural relaxation time. A greatly simplified form of the GET (whose expression for the free energy is roughly double that of Flory-Huggins theory) accurately reproduces the four characteristic temperatures of glass-formation (the onset, crossover, glass transition, and Kauzmann temperatures) of the full GET to within 4K for a series of models of polymers composed of semi-flexible chains having the structure of poly(n-alpha olefins). The theory is now simple enough to be used in courses in polymer physics. Although the successes of the GET provide a strong validation of the final form of the AG theory provided the configurational entropy is used, the physical basis of the AG theory has remained an enigma. Hence, we have developed a new, more general, statistical mechanical derivation of AG theory that explains the previously perplexing observations that the string-like elementary excitations have the mass and temperature dependence of systems undergoing equilibrium self-assembly. This work is supported by the (U.S.) Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE- SC0008631.

  15. Formation and evolution of ultrashort pulse-induced nanogratings in Borosilicate glass

    NASA Astrophysics Data System (ADS)

    Zimmermann, F.; Plech, Anton; Richter, S.; Tünnermann, Andreas; Nolte, S.

    2014-05-01

    The versatility of ultrashort laser pulses as a tool for laser materials processing has augmented particular interest in the past decade. Especially birefringent modifications, so-called nanogratings, have found to exhibit tremendous potential for manifold photonic functionalities. These self-assembling structures, orienting always perpendicular to the laser polarization, have been up to now extensively studied in bulk fused silica. Commonly it is assumed that the formation of nanogratings is actually limited to anomalous glasses like silica or slightly doped silica. However, we recently found that even in glasses like borosilicate or BK7 nanogratings can be observed within certain parameter regimes. Here we present an extensive study of the fundamental constituents of nanogratings in bulk borosilicate glass using small angle X-ray scattering (SAXS) in combination with focused ion beam milling (FIB) and scanning electron microscopy (SEM). The irradiation produces void-like sheets (10-20 nm wide) as well as elongated cracks of up to 400 nm. In contrast to nanogratings in fused silica, borosilicate shows a significant smaller optical retardance. The cumulative action of several hundreds of laser pulses lead to the formation of individual grating planes with a period of about 60 nm (at an inscribing laser wavelength of 800 nm) while the well-known λ/2n (n-refractive index) period is prevented. This has never been observed for ultrashort pulse induced nanogratings so far.

  16. Accelerated Leach Testing of GLASS (ALTGLASS): I. Informatics approach to high level waste glass gel formation and aging

    DOE PAGES

    Jantzen, Carol M.; Trivelpiece, Cory L.; Crawford, Charles L.; ...

    2017-02-18

    Glass corrosion data from the ALTGLASS™ database were used to determine if gel compositions, which evolve as glass systems corrode, are correlated with the generation of zeolites and subsequent increase in the glass dissolution rate at long times. The gel compositions were estimated based on the difference between the elemental glass starting compositions and the measured elemental leachate concentrations from the long-term product consistency tests (ASTM C1285) at various stages of dissolution, ie, reaction progress. A well-characterized subset of high level waste glasses from the database was selected: these glasses had been leached for 15-20 years at reaction progresses upmore » to ~80%. The gel composition data, at various reaction progresses, were subjected to a step-wise regression, which demonstrated that hydrogel compositions with Si*/Al* ratios of <1.0 did not generate zeolites and maintained low dissolution rates for the duration of the experiments. Glasses that formed hydrogel compositions with Si^*/Al^* ratios ≥1, generated zeolites accompanied by a resumption in the glass dissolution rate. Finally, the role of the gel Si/Al ratio, and the interactions with the leachate, provides the fundamental understanding needed to predict if and when the glass dissolution rate will increase due to zeolitization.« less

  17. Effect of variable valence impurities on the formation of bismuth-related optical centres in a silicate glass

    SciTech Connect

    Galagan, B I; Denker, B I; Lili Hu; Sverchkov, S E; Shulman, I L; Dianov, Evgenii M

    2012-10-31

    We have studied the effect of variable valence impurities (cerium and iron) on the formation of bismuth-related IR luminescence centres and the optical loss between 1000 and 1300 nm in a magnesium aluminosilicate glass. The results demonstrate that additional doping of the glass with ceria leads to effective bleaching in a wide spectral range, including the luminescence range of the bismuth centres. At the same time, ceria reduces the concentration of luminescence centres. Gamma irradiation of the glass bleached by cerium restores the luminescence centres but leads to a background loss in a wide spectral range. Iron is shown to be a very harmful impurity in bismuth-doped active media: even trace levels of iron prevent the formation of bismuth-related active centres in the glass and produce a strong, broad absorption band centred near 1 {mu}m. (luminescence of glasses)

  18. A New DTA Method for Measuring Critical Cooling Rate for Glass Formation

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Reis, Signo T.; Brow, Richard K.; Holand, Wolfram; Rheinberger, Volker

    2004-01-01

    A new differential thermal analysis (DTA) experimental method has been developed to determine the critical cooling rate for glass formation, R(sub c). The method, which is found especially suitable for melts that, upon cooling, have a small heat of crystallization or a very slow crystallization rate, has been verified using a 38Na2O-62SiO2 (mol%) melt with a known R(sub c) (-approx. 19 C/min), then used to determine R(sub c) for two complex lithium silicate glass forming melts. The new method is rapid, easy to conduct and yields values for R(sub c) that are in excellent agreement with the R(sub c)-values measured by standard DTA techniques.

  19. A New DTA Method for Measuring Critical Cooling Rate for Glass Formation

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Reis, Signo T.; Brow, Richard K.; Holand, Wolfram; Rheinberger, Volker

    2004-01-01

    A new differential thermal analysis (DTA) experimental method has been developed to determine the critical cooling rate for glass formation, R(sub c). The method, which is found especially suitable for melts that, upon cooling, have a small heat of crystallization or a very slow crystallization rate, has been verified using a 38Na2O-62SiO2 (mol%) melt with a known R(sub c) (-approx. 19 C/min), then used to determine R(sub c) for two complex lithium silicate glass forming melts. The new method is rapid, easy to conduct and yields values for R(sub c) that are in excellent agreement with the R(sub c)-values measured by standard DTA techniques.

  20. Mechanisms of microhole formation on glasses by an abrasive slurry jet

    SciTech Connect

    Wang, J.; Nguyen, T.; Pang, K. L.

    2009-02-15

    Abrasive jet micromachining is considered as a promising precision processing technology for brittle materials such as silicon substrates and glasses that are increasingly used in various applications. In this paper, the mechanisms of microhole formation on brittle glasses by an abrasive slurry jet are studied based on the viscous flow and erosion theories. It is shown that the hole cross section is characterized by a ''W'' shape and can be classified into three zones caused, respectively, by jet direct impact, viscous flow, and turbulent flow induced erosion. An analysis of the surface morphology shows that ductile-mode erosion is dominant. The effect of process parameters on material removal is studied which shows that increasing the pressure and erosion time increases the hole depth, but has little effect on the hole diameter.

  1. Communication: The simplified generalized entropy theory of glass-formation in polymer melts

    SciTech Connect

    Freed, Karl F.

    2015-08-07

    While a wide range of non-trivial predictions of the generalized entropy theory (GET) of glass-formation in polymer melts agree with a large number of observed universal and non-universal properties of these glass-formers and even for the dependence of these properties on monomer molecular structure, the huge mathematical complexity of the theory precludes its extension to describe, for instance, the perplexing, complex behavior observed for technologically important polymer films with thickness below ∼100 nm and for which a fundamental molecular theory is lacking for the structural relaxation. The present communication describes a hugely simplified version of the theory, called the simplified generalized entropy theory (SGET) that provides one component necessary for devising a theory for the structural relaxation of thin polymer films and thereby supplements the first required ingredient, the recently developed Flory-Huggins level theory for the thermodynamic properties of thin polymer films, before the concluding third step of combining all the components into the SGET for thin polymer films. Comparisons between the predictions of the SGET and the full GET for the four characteristic temperatures of glass-formation provide good agreement for a highly non-trivial model system of polymer melts with chains of the structure of poly(n-α olefins) systems where the GET has produced good agreement with experiment. The comparisons consider values of the relative backbone and side group stiffnesses such that the glass transition temperature decreases as the amount of excess free volume diminishes, contrary to general expectations but in accord with observations for poly(n-alkyl methacrylates). Moreover, the SGET is sufficiently concise to enable its discussion in a standard course on statistical mechanics or polymer physics.

  2. Communication: The simplified generalized entropy theory of glass-formation in polymer melts.

    PubMed

    Freed, Karl F

    2015-08-07

    While a wide range of non-trivial predictions of the generalized entropy theory (GET) of glass-formation in polymer melts agree with a large number of observed universal and non-universal properties of these glass-formers and even for the dependence of these properties on monomer molecular structure, the huge mathematical complexity of the theory precludes its extension to describe, for instance, the perplexing, complex behavior observed for technologically important polymer films with thickness below ∼100 nm and for which a fundamental molecular theory is lacking for the structural relaxation. The present communication describes a hugely simplified version of the theory, called the simplified generalized entropy theory (SGET) that provides one component necessary for devising a theory for the structural relaxation of thin polymer films and thereby supplements the first required ingredient, the recently developed Flory-Huggins level theory for the thermodynamic properties of thin polymer films, before the concluding third step of combining all the components into the SGET for thin polymer films. Comparisons between the predictions of the SGET and the full GET for the four characteristic temperatures of glass-formation provide good agreement for a highly non-trivial model system of polymer melts with chains of the structure of poly(n-α olefins) systems where the GET has produced good agreement with experiment. The comparisons consider values of the relative backbone and side group stiffnesses such that the glass transition temperature decreases as the amount of excess free volume diminishes, contrary to general expectations but in accord with observations for poly(n-alkyl methacrylates). Moreover, the SGET is sufficiently concise to enable its discussion in a standard course on statistical mechanics or polymer physics.

  3. Synthesis, Direct Formation under High Pressure, Structure, and Electronic Properties of LiNbO3-type Oxide PbZnO3.

    PubMed

    Mori, Daisuke; Tanaka, Kie; Saitoh, Hiroyuki; Kikegawa, Takumi; Inaguma, Yoshiyuki

    2015-12-07

    A novel LiNbO3-type (LN-type) lead zinc oxide, PbZnO3, was successfully synthesized under high pressure and temperature. Rietveld structure refinement using synchrotron powder X-ray diffraction (XRD) data demonstrated that LN-type PbZnO3 crystallized into a trigonal structure with a polar space group (R3c). The bond valence sum estimated from the interatomic distances indicated that the sample possesses a Pb(4+)Zn(2+)O3 valence state. Polarization could evolve as a result of the repulsion between constituent cations because PbZnO3 does not contain a stereochemical 6s(2) cation or a Jahn-Teller active d(0) cation. Distortion of ZnO6 octahedra resulting from cation shift is comparable with that of d(0) TiO6 in ZnTiO3 and MnTiO3 with LN-type oxides, which leads to stabilization of the polar structure. PbZnO3 exhibited metallic behavior and temperature-independent diamagnetic character. In situ XRD measurement revealed that the formation of LN-type PbZnO3 occurred directly without the formation of a perovskite phase, which is unusual among LN-type materials obtained by high-pressure synthesis.

  4. Smectite Formation From Basaltic Glass in the Presence of Sulfuric Acid on Mars

    NASA Astrophysics Data System (ADS)

    Peretyazhko, T.; Niles, P. B.; Sutter, B.; Morris, R. V.; Ming, D. W.

    2016-12-01

    Phyllosilicates of the smectite group detected in Noachian and early Hesperian terrains on Mars were hypothesized to form under neutral to alkaline conditions. These pH conditions and the presence of a CO2-rich atmosphere during the Noachian and early Hesperian should have been favorable for the formation of large carbonate deposits. However, large-scale carbonate deposits have not been detected on Mars. Recent orbital and landed missions have detected phyllosilicates co-existing with minerals that usually form under acidic conditions including jarosite and alunite. The occurrence of sulfates co-existing with phyllosilicates minerals on Mars and absences of large-scale carbonate in Noachian terrains indicate that phyllosilicate formation under sulfuric acid conditions was at least locally important. The pH effect and the nature of phyllosilicate minerals forming during acid-sulfate weathering of basalt remain unknown. We investigated formation of smectite minerals in the presence of sulfuric acid from Mars-analogue, glass-rich, basalt simulant. Hydrothermal (200º C) 14 d experiments were performed with addition of sulfuric acid of variable concentration at a pH range from 1.8 to 8.4. Sulfuric acid did not suppress smectite formation and gradual acid neutralization during basalt weathering led to montmorillonite formation at pH 3 followed by saponite at pH 4 and higher. Smectite formed through glass phase alteration and was accompanied by precipitation of calcium sulfate (anhydrite). Similar smectite and sulfate formation under acid sulfate conditions may have occurred in near-surface hydrothermal areas near magma bodies on Mars.

  5. Induced rupture of vesicles adsorbed on glass by pore formation at the surface-bilayer interface.

    PubMed

    Kataoka-Hamai, Chiho; Yamazaki, Tomohiko

    2015-02-03

    Supported lipid bilayers (SLBs) are often formed by spontaneous vesicle rupture and fusion on a solid surface. A well-characterized rupture mechanism for isolated vesicles is pore nucleation and expansion in the solution-exposed nonadsorbed area. In contrast, pore formation in the adsorbed bilayer region has not been investigated to date. In this work, we studied the detailed mechanisms of asymmetric rupture of giant unilamellar vesicles (GUVs) adsorbed on glass using fluorescence microscopy. Asymmetric rupture is the pathway where a rupture pore forms in a GUV near the edge of the glass-bilayer interface with high curvature and then expansion of the pore yields a planar bilayer patch. We show that asymmetric rupture occasionally resulted in SLB patches bearing a defect pore. The defect formation probability depended on lipid composition, salt concentration, and pH. Approximately 40% of negatively charged GUVs under physiological conditions formed pore-containing SLB patches, while negatively charged GUVs at low salt concentration or pH 4.0 and positively charged GUVs exhibited a low probability of defect inclusion. The edge of the defect pore was either in contact with (on-edge) or away from (off-edge) the edge of the planar bilayer. On-edge pores were predominantly formed over off-edge defects. Pores initially formed in the glass-adsorbed region before rupture, most frequently in close contact with the edge of the adsorbed region. When a pore formed near the edge of the adsorbed area or when the edge of a pore reached that of the adsorbed area by pore expansion, asymmetric rupture was induced from the defect site. These induced rupture mechanisms yielded SLB patches with an on-edge pore. In contrast, off-edge pores were produced when defect pore generation and subsequent vesicle rupture were uncoupled. The current results demonstrate that pore formation in the surface-adsorbed region of GUVs is not a negligible event.

  6. Interplay between spinodal decomposition and glass formation in proteins exhibiting short-range attractions.

    PubMed

    Cardinaux, Frédéric; Gibaud, Thomas; Stradner, Anna; Schurtenberger, Peter

    2007-09-14

    We investigate the competition between spinodal decomposition and dynamical arrest using aqueous solutions of the globular protein lysozyme as a model system for colloids with short-range attractions. We show that quenches below a temperature Ta lead to gel formation as a result of a local arrest of the protein-dense phase during spinodal decomposition. The rheological properties of these gels allow us to use centrifugation experiments to determine the local densities of both phases and to precisely locate the gel boundary and the attractive glass line close to and within the unstable region of the phase diagram.

  7. CO2 Photoreduction by Formate Dehydrogenase and a Ru-Complex in a Nanoporous Glass Reactor.

    PubMed

    Noji, Tomoyasu; Jin, Tetsuro; Nango, Mamoru; Kamiya, Nobuo; Amao, Yutaka

    2017-02-01

    In this study, we demonstrated the conversion of CO2 to formic acid under ambient conditions in a photoreduction nanoporous reactor using a photosensitizer, methyl viologen (MV(2+)), and formate dehydrogenase (FDH). The overall efficiency of this reactor was 14 times higher than that of the equivalent solution. The accumulation rate of formic acid in the nanopores of 50 nm is 83 times faster than that in the equivalent solution. Thus, this CO2 photoreduction nanoporous glass reactor will be useful as an artificial photosynthesis system that converts CO2 to fuel.

  8. Formation of metallic and metallic-glass hollow spheres and their solidification characteristics

    NASA Technical Reports Server (NTRS)

    Lee, M. C.

    1985-01-01

    Various metals and metallic glass systems have bene processed into hollow spheres with sizes ranging from 3 mm to 440 microns in diameter. The technique for the formation of the large hollow spheres, in general, is based on the fluid-dynamic instability of a hollow annular jet. A refined technique has also been developed for microshell formation, in which discrete bubbles are injected into the stream of the molten material and individually 'flushed' out at a frequency related to the Rayleigh jet instability. The surfaces of those spheres of all sizes exhibit a range of contrasting solidification behaviors and characteristics. Metal shells of varying materials, sizes, aspect ratios, sphericity and concentricity have many useful and novel applications.

  9. Alkylated glass partition allows formation of solvent-free lipid bilayer by Montal-Mueller technique.

    PubMed

    Batishchev, Oleg V; Indenbom, Andrey V

    2008-11-01

    Formation of bilayer lipid membrane (BLM) by Montal-Mueller technique across a small aperture in a partition film traditionally requires coating of the aperture with a hydrophobic substance, often just an organic solvent. However, we demonstrate here that the most effective coating is not strictly hydrophobic but rather provides water/oil repellent properties. BLM were formed from diphytanoylphosphatidylcholine (DPhPC) on small 0.1-0.8 mm apertures made in specially prepared alkylated glass coverslips. The coverslips were either fluorosiliconized by 3,3,3-Trifluoropropyl-trimethoxysilane, which reduces adsorption of DPhPC in addition to creation of hydrophobic surface, or silanized, which promote adsorption of DPhPC. At fluorosiliconized surfaces stable BLM were formed. Specific capacitance of these BLM was 0.86 microF/cm(2)+/-5%, while their lateral tension was estimated as 4.3+/-0.4 mN/m. BLM were stable for hours under moderate voltage applied. At silanized surfaces stable BLM were formed only in acidic medium (3 glass can be robustly used for formation of model lipid membranes under physiological conditions.

  10. Protein-adsorption and Ca-phosphate formation on chitosan-bioactive glass composite coatings

    NASA Astrophysics Data System (ADS)

    Wagener, V.; Boccaccini, A. R.; Virtanen, S.

    2017-09-01

    In the last years, chitosan-bioactive glass (BG) composites have been developed and investigated as bioactive coatings for orthopedic applications. The increase of bioactivity occurs due to the stimulation of calcium-phosphate/hydroxyapatite formation on the surface while the coating is degrading. In the present work, protein adsorption and its influence on calcium-phosphate precipitation was studied for the first time on such composite coatings. The experiments involved coating of 316L stainless steel substrates with chitosan (Ch) and chitosan-bioactive glass (Ch-BG) and immersion of the coated samples in two different bovine serum albumin (BSA) containing solutions, namely DI H2O (with pH adjusted to about 7.2 with diluted NaOH) and simulated body fluid (SBF). In order to investigate the influence of protein adsorption on calcium-phosphate precipitation, samples were also immersed in DI H2O and in SBF without BSA. Samples were analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Surface analysis revealed that adsorption of BSA takes place on all studied samples and that protein adsorption is influenced by the presence of Ca2+ and PO43- ions. Bioactivity in the form of hydroxyapatite pre-stage formation is significantly increased on Ch-BG composite coating as compared with bare stainless steel surface. However, calcium-phosphate precipitation in SBF is reduced by the presence of BSA.

  11. Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

    PubMed

    Möncke, D; Kamitsos, E I; Palles, D; Limbach, R; Winterstein-Beckmann, A; Honma, T; Yao, Z; Rouxel, T; Wondraczek, L

    2016-09-28

    A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn(2+) enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb(2+) and Bi(3+) induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was

  12. Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties

    NASA Astrophysics Data System (ADS)

    Möncke, D.; Kamitsos, E. I.; Palles, D.; Limbach, R.; Winterstein-Beckmann, A.; Honma, T.; Yao, Z.; Rouxel, T.; Wondraczek, L.

    2016-09-01

    A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined

  13. Atomistic modeling to investigate the favored composition for metallic glass formation in the Ca-Mg-Ni ternary system.

    PubMed

    Zhao, S; Li, J H; An, S M; Li, S N; Liu, B X

    2017-05-17

    A realistic interatomic potential was first constructed for the Ca-Mg-Ni system and then applied to Monte Carlo simulations to predict the favored composition for metallic glass formation in the ternary system. The simulations not only predict a hexagonal composition region, within which the Ca-Mg-Ni metallic glass formation is energetically favored, but also pinpoint an optimized sub-region within which the amorphization driving force, i.e. the energy difference between the solid solution and disordered phase, is larger than that outside. The simulations further reveal that the physical origin of glass formation is the solid solution collapsing when the solute atom exceeds the critical solid solubility. Further structural analysis indicates that the pentagonal bi-pyramids dominate in the optimized sub-region. The large atomic size difference between Ca, Mg and Ni extends the short-range landscape and facilitates the development of a hybridized packing model in the medium-range, and eventually enhancing the glass formation in the system. The predictions are well supported by the experimental observations reported so far, and could be of help for designing the ternary glass formation.

  14. High-throughput Exploration of Glass Formation via Laser Deposition and the Study of Heterogeneous Microstructure in a Bulk Metallic Glass Alloy

    NASA Astrophysics Data System (ADS)

    Tsai, Peter T.

    Bulk metallic glasses are a relatively novel class of engineering alloys characterized by a "disordered" atomic structure devoid of long-range translational symmetry. Compared to crystalline alloys, the confluence of metallic bonding and amorphous structure imbues bulk metallic glasses with a unique set of properties that makes them particularly attractive for a wide variety of structural applications. Such properties include exceptional yield strengths, high elastic resilience, resistance to corrosion, and in particular, the unparalleled ability among metals to be thermoplastically formed across a wide range of length scales when heated above the glass transition temperature. Formation of metallic glass from a molten liquid depends on whether cooling is sufficiently rapid to bypass crystallization and vitrify into an amorphous solid; for a given alloy composition, the ease with which full vitrification can occur upon cooling from the liquid state is termed the alloy's "glass forming ability". Unfortunately, relatively few excellent glass formers have been reported in the vast, multicomponent composition space in which they reside. The apparent slowness of progress may be attributed largely to the inefficiency of the one-at-a-time experimental approach to discovery and design. In this thesis work, a high-throughput combinatorial methodology was developed to expedite the discovery process of new bulk metallic glasses. Laser deposition was used to fabricate continuously-graded composition libraries of Cu-Zr and Cu-Zr-Ti alloys. By processing the libraries with a range of laser heat input, the best glass formers in each alloy system could be efficiently and systematically deduced. Furthermore, instrumented nanoindentation performed on the libraries enabled rapid evaluation of mechanical property trends. Despite boasting high strengths, monolithic bulk metallic glasses generally suffer from an intrinsic lack of damage tolerance compared to other high performance alloys

  15. Radiation effects in moist-air systems and the influence of radiolytic product formation on nuclear waste glass corrosion

    SciTech Connect

    Wronkiewicz, D.J.; Bates, J.K.; Buck, E.C.; Hoh, J.C.; Emery, J.W.; Wang, L.M.

    1997-07-01

    Ionizing radiation may affect the performance of glass in an unsaturated repository site by interacting with air, water vapor, or liquid water to produce a variety of radiolytic products. Tests were conducted to examine the effects of radiolysis under high gas/liquid ratios. Results indicate that nitrate is the predominant radiolytic product produced following both gamma and alpha radiation exposure, with lesser amounts of nitrite and carboxylic acids. The formation of nitrogen acids during exposure to long-lived, alpha-particle-emitting transuranic elements indicates that these acids may play a role in influencing nuclear waste form reactions in a long-term unsaturated disposal scenario. Experiments were also conducted with samples that simulate the composition of Savannah River Plant nuclear waste glasses. Radiolytic product formation in batch tests (340 m{sup {minus}1}, 90 C) resulted in a small increase in the release rates of many glass components, such as alkali and alkaline earth elements, although silicon and uranium release rates were slightly reduced indicating an overall beneficial effect of radiation on waste form stability. The radiolytic acids increased the rate of ion exchange between the glass and the thin film of condensate, resulting in accelerated corrosion rates for the glass. The paragenetic sequence of alteration phases formed on both the irradiated and nonirradiated glass samples reacted in the vapor hydration tests matches closely with those developed during volcanic glass alteration in naturally occurring saline-alkaline lake systems. This correspondence suggests that the high temperatures used in these tests have not changed the underlying glass reaction mechanism relate to that which controls glass reactions under ambient surficial conditions.

  16. Devitrification properties of vapor-deposited ethylcyclohexane glasses and interpretation of the molecular mechanism for formation of vapor-deposited glasses.

    PubMed

    Ramos, Sergio Luis L M; Chigira, Atsuko K; Oguni, Masaharu

    2015-03-12

    We constructed an adiabatic calorimeter adapted for the preparation and in situ thermal characterization of vapor-deposited glasses and reported the investigation of the enthalpic states and dynamic properties of ethylcyclohexane (ECH) glasses prepared by vapor deposition in the temperature range of (0.71-0.96)Tg,liq; Tg,liq = (101 ± 1) K is the calorimetric glass transition temperature of the bulk liquid. It was verified that the ECH glasses deposited at temperatures immediately below Tg,liq were characterized by lower enthalpies and higher devitrification temperatures (Tdev), as compared to the glass obtained by supercooling the bulk liquid. The deposition temperature (TD) expected to yield experimentally the entity with the highest Tdev and the lowest enthalpic state was estimated to be 0.93Tg,liq. A model potentially elucidating the fundamental mechanism of formation and devitrification for the glasses prepared via the physical vapor deposition method as a function of TD was proposed. The fundamental point is that the glass is formed by deposition in a molecule-by-molecule fashion and the molecule deposited is frozen in a certain configuration determined by its being itself on the surface. For amorphous entities prepared at a TD much lower than Tg,liq, the surface molecule is frozen mostly as they are deposited. For the entity deposited at TD = 0.93Tg,liq in the case of ECH, the surface molecule is mobile immediately after the deposition to look for its stable configuration only on account of the intermolecular interactions with the molecules beneath and in the same surface layer as itself and freezes in a certain reasonably stable configuration; the molecules below the surface layer have already frozen in and get more stabilization energy through the additional interactions with the surface molecules. As a result, the intermolecular interaction of the molecules accumulated in such a way is stronger than that in the bulk liquid glass. It is argued that this is

  17. Enhanced osteoprogenitor elongated collagen fiber matrix formation by bioactive glass ionic silicon dependent on Sp7 (osterix) transcription.

    PubMed

    Varanasi, Venu G; Odatsu, Tetsurou; Bishop, Timothy; Chang, Joyce; Owyoung, Jeremy; Loomer, Peter M

    2016-10-01

    Bioactive glasses release ions, those enhance osteoblast collagen matrix synthesis and osteogenic marker expression during bone healing. Collagen matrix density and osteogenic marker expression depend on osteogenic transcription factors, (e.g., Osterix (OSX)). We hypothesize that enhanced expression and formation of collagen by Si(4+) depends on enhanced expression of OSX transcription. Experimental bioactive glass (6P53-b) and commercial Bioglass(TM) (45S5) were dissolved in basal medium to make glass conditioned medium (GCM). ICP-MS analysis was used to measure bioactive glass ion release rates. MC3T3-E1 cells were cultured for 20 days, and gene expression and extracellular matrix collagen formation was analyzed. In a separate study, siRNA was used to determine the effect of OSX knockdown on impacting the effect of Si(4+) on osteogenic markers and matrix collagen formation. Each bioactive glass exhibited similar ion release rates for all ions, except Mg(2+) released by 6P53-b. Gene expression results showed that GCM markedly enhanced many osteogenic markers, and 45S5 GCM showed higher levels of expression and collagen matrix fiber bundle density than 6P53-b GCM. Upon knockdown of OSX transcription, collagen type 5, alkaline phosphatase, and matrix density were not enhanced as compared to wild type cells. This study illustrates that the enhancement of elongated collagen fiber matrix formation by Si(±) depends on OSX transcription. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2604-2615, 2016.

  18. Biofilm formation affects surface properties of novel bioactive glass-containing composites.

    PubMed

    Hyun, Hong-Keun; Salehi, Satin; Ferracane, Jack L

    2015-12-01

    This study investigated the effects of bacterial biofilm on the surface properties of novel bioactive glass (BAG)-containing composites of different initial surface roughness. BAG (65 mol% Si; 4% P; 31% Ca) and BAG-F (61% Si; 31% Ca; 4% P; 3% F; 1% B) were synthesized by the sol-gel method and micronized (size ∼0.1-10 μm). Composites with 72wt% total filler load were prepared by replacing 15% of the silanized Sr glass with BAG, BAG-F, or silanized silica. Specimens (n=10/group) were light-cured and divided into 4 subgroups of different surface roughness by wet polishing with 600 and then up to 1200, 2400, or 4000 grit SiC. Surface roughness (SR), gloss, and Knoop microhardness were measured before and after incubating in media with or without a Streptococcus mutans (UA 159) biofilm for 2 weeks. Results were analyzed with ANOVA/Tukey's test (α=0.05). The SR of the BAG-containing composites with the smoothest surfaces (2400/4000 grit) increased in media or bacteria; the SR of the roughest composites (600 grit) decreased. The gloss of the smoothest BAG-containing composites decreased in bacteria and media-only, but more in media-alone. The microhardness of all of the composites decreased with exposure to media or bacteria, with BAG-containing composites affected more than the control. Exposure to bacterial biofilm and its media produced enhanced roughness and reduced gloss and surface microhardness of highly polished dental composites containing a bioactive glass additive, which could affect further biofilm formation, as well as the esthetics, of restorations made from such a material. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  19. Network topology for the formation of solvated electrons in binary CaO-Al2O3 composition glasses.

    PubMed

    Akola, Jaakko; Kohara, Shinji; Ohara, Koji; Fujiwara, Akihiko; Watanabe, Yasuhiro; Masuno, Atsunobu; Usuki, Takeshi; Kubo, Takashi; Nakahira, Atsushi; Nitta, Kiyofumi; Uruga, Tomoya; Weber, J K Richard; Benmore, Chris J

    2013-06-18

    Glass formation in the CaO-Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO-Al2O3 glasses using combined density functional theory-reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O-Ca and O-Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al-O is stronger than that of Ca-O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71-74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass.

  20. Network topology for the formation of solvated electrons in binary CaO–Al2O3 composition glasses

    PubMed Central

    Akola, Jaakko; Kohara, Shinji; Ohara, Koji; Fujiwara, Akihiko; Watanabe, Yasuhiro; Masuno, Atsunobu; Usuki, Takeshi; Kubo, Takashi; Nakahira, Atsushi; Nitta, Kiyofumi; Uruga, Tomoya; Weber, J. K. Richard; Benmore, Chris J.

    2013-01-01

    Glass formation in the CaO–Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO–Al2O3 glasses using combined density functional theory–reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O–Ca and O–Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al–O is stronger than that of Ca–O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71–74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass. PMID:23723350

  1. The Formation of Boundary Clinopyroxenes and Associated Glass Veins in Type B1 CAIs

    SciTech Connect

    Paque, J M; Beckett, J R; Ishii, H A; Toppani, A; Burnett, D S; Teslich, N; Dai, Z R; Bradley, J P

    2008-05-18

    We used focused ion beam thin section preparation and scanning transmission electron microscopy (FIB/STEM) to examine the interfacial region between spinel and host melilite for three spinel grains, two from the mantle and one from the core of an Allende type B1 inclusion, and a second pair of spinel grains from a type B1 inclusion from the Leoville carbonaceous chondrite. The compositions of boundary clinopyroxenes decorating spinel surfaces are generally consistent with those of coarser clinopyroxenes from the same region of the inclusion, suggesting little movement of spinels between mantle and core regions after the formation of boundary clinopyroxenes. The host melilite displays no anomalous compositions near the interface, and anorthite or other late-stage minerals are not observed, suggesting that crystallization of residual liquid was not responsible for the formation of boundary clinopyroxenes. Allende spinels display either direct spinel-melilite contact or an intervening boundary clinopyroxene between the two phases. In the core, boundary clinopyroxene is mantled by a thin (1-2 {micro}m thick) layer of normally zoned (X{sub Ak} increasing away from the melilite-clinopyroxene contact) melilite with X{sub Ak} matching that of the host melilite at the melilite-melilite contact. In the mantle, X{sub Ak} near boundary spinels is constant. Spinels in a Leoville type B1 inclusion are more complex with boundary clinopyroxene, as observed in Allende, but also variable amounts of glass ({approx}1 {micro}m width), secondary calcite, perovskite, and an unknown Mg-, Al-, OH-rich and Ca-, Si-poor crystalline phase that may be a layered double hydrate. Glass compositions are consistent to first order with a precursor consisting mostly of Mg-carpholite or sudoite with some aluminous diopside. One possible scenario of formation for the glass veins is that open system alteration of melilite produced a porous, hydrated aggregate of Mg-carpholite or sudoite + aluminous

  2. Side-group size effects on interfaces and glass formation in supported polymer thin films

    NASA Astrophysics Data System (ADS)

    Xia, Wenjie; Song, Jake; Hsu, David D.; Keten, Sinan

    2017-05-01

    Recent studies on glass-forming polymers near interfaces have emphasized the importance of molecular features such as chain stiffness, side-groups, molecular packing, and associated changes in fragility as key factors that govern the magnitude of Tg changes with respect to the bulk in polymer thin films. However, how such molecular features are coupled with substrate and free surface effects on Tg in thin films remains to be fully understood. Here, we employ a chemically specific coarse-grained polymer model for methacrylates to investigate the role of side-group volume on glass formation in bulk polymers and supported thin films. Our results show that bulkier side-groups lead to higher bulk Tg and fragility and are associated with a pronounced free surface effect on overall Tg depression. By probing local Tg within the films, however, we find that the polymers with bulkier side-groups experience a reduced confinement-induced increase in local Tg near a strongly interacting substrate. Further analyses indicate that this is due to the packing frustration of chains near the substrate interface, which lowers the attractive interactions with the substrate and thus lessens the surface-induced reduction in segmental mobility. Our results reveal that the size of the polymer side-group may be a design element that controls the confinement effects induced by the free surface and substrates in supported polymer thin films. Our analyses provide new insights into the factors governing polymer dynamics in bulk and confined environments.

  3. Phase formation and mechanical properties of Cu-Zr-Ti bulk metallic glass composites

    NASA Astrophysics Data System (ADS)

    Kim, Byoung Jin; Yun, Young Su; Kim, Won Tae; Kim, Do Hyang

    2016-11-01

    The effect of the type of the crystalline phase and its volume fraction on the mechanical property of Cu50Zr50-xTix alloys (x = 0-10) bulk metallic glass composites has been investigated in this study. Up to 6 at% of Ti, B19' phase particles distributed in the glassy matrix, while at 8 and 10% of Ti, B2 phase particles are retained in the glass matrix due to suppression of the eutectoid transformation of B2 phase and by avoidance of martensitic transformation of B2 into B19'. The volume fraction of crystalline phase is strongly dependent on the cooling rate. The larger volume fraction of the crystalline phases results in the lower yield stress, the higher plastic strain, and the more pronounced work hardening behavior. At the crystalline volume fraction below 30%, the variation of the yield strength can be described by the rule of mixture model (ROM), while at the crystalline volume fraction higher than 50% by the load-bearing model (LBM). At the crystal fractions between 30 and 50%, there is a yield strength drop and a transition from the ROM to the LBM. This transition is due to the formation of the crystalline structural framework at higher crystal fraction.

  4. The processes of modified microareas formation in the bulk of porous glasses by laser radiation

    NASA Astrophysics Data System (ADS)

    Kostyuk, G. K.; Sergeev, M. M.; Yakovlev, E. B.

    2015-06-01

    The possibility of the formation of modified microareas (MAs) with changed optical properties in the bulk of porous glasses (PGs) with laser radiation is investigated. A laser module of continuous action with wavelength λ = 800 nm and power P = 120 mW was used as the source of radiation. The material used in the experiment was PG of 94.73 SiO2-4.97 B2O3-0.30 Na2O. A model that describes the processes taking place under laser radiation that lead to a modification of the glass is proposed. Our evaluation results based on experimental data are given. The results of an additional PG plate of the same composition impregnated with glycerol—a substance with a high degree of polarizability—during exposure experiments are also given. A fiber laser of continuous action with wavelength λ = 1070 nm and power P = 16.5 W was used as a source of radiation.

  5. Non-textured laser modification of silica glass surface: Wettability control and flow channel formation

    NASA Astrophysics Data System (ADS)

    Aono, Yuko; Hirata, Atsushi; Tokura, Hitoshi

    2016-05-01

    Local wettability of silica glass surface is modified by infrared laser irradiation. The silica glass surface exhibits hydrophobic property in the presence of sbnd CF3 or sbnd (CH3)2 terminal functional groups, which are decomposed by thermal treatment, and degree of the decomposition depends on the applied heat. Laser irradiation can control the number of remaining functional groups according to the irradiation conditions; the contact angle of deionized water on the laser modified surfaces range from 100° to 40°. XPS analysis confirms that the variation in wettability corresponds to the number of remaining sbnd CF3 groups. The laser irradiation achieves surface modification without causing any cracks or damages to the surface, as observed by SEM and AFM; moreover, surface transparency to visible light and surface roughness remains unaffected. The proposed method is applied to plane flow channel systems. Dropped water spreads only on the hydrophilic and invisible line modified by the laser irradiation without formation of any grooves. This indicates that the modified line can act as a surface channel. Furthermore, self-transportation of liquid is also demonstrated on a channel with gradually-varied wettability along its length. A water droplet on a hydrophobic side is self-transported to a hydrophilic side due to contact-angle hysteresis force without any actuators or external forces.

  6. Formation of alkali-metal nanoparticles in alkali-silicate glasses under electron irradiation and thermal processing

    NASA Astrophysics Data System (ADS)

    Bochkareva, E. S.; Sidorov, A. I.; Ignat'ev, A. I.; Nikonorov, N. V.; Podsvirov, O. A.

    2017-02-01

    Experiments and numerical simulation show that the irradiation of alkali-containing glasses using electrons at an energy of 35 keV and the subsequent thermal processing at a temperature above the vitrification point lead to the formation of spherical metal (lithium, sodium, and potassium) nanoparticles with oxide sheaths that exhibit plasmon resonances in the visible spectral range. Glasses containing two alkali metals exhibit mutual effect of metals on the formation of nanoparticles with two compositions due to the difference of ion radii and mobilities of metal ions.

  7. Formation of cylindrical micro-lens array on fused silica glass surface using CO2 laser assisted reshaping technique

    NASA Astrophysics Data System (ADS)

    Choi, Hun-Kook; Ahsan, Md. Shamim; Yoo, Dongyoon; Sohn, Ik-Bu; Noh, Young-Chul; Kim, Jin-Tae; Jung, Deok; Kim, Jin-Hyeok; Kang, Ho-Min

    2015-12-01

    This paper demonstrates the laser assisted formation of plano-convex cylindrical and flat-top curved micro-lens array on fused silica glass surface. Initially, femtosecond laser pulses are irradiated on the sample glass to fabricate periodic linear micro-gratings on the glass surface. Afterwards, we reshape the micro-gratings by several times irradiation of a CO2 laser beam by focusing the laser beam on top of the micro-gratings. As a consequence, plano-convex cylindrical micro-lens array with a period varying from 20 to 40 μm are formed on fused silica glass surface. However, flat-top curved gratings' array is observed on the glass surface for a gratings' period of 50 μm. The fabricated micro-lenses show great consistency in size and shape throughout the sample area. Furthermore, we analyze the formation mechanism of micro-lens array on glass surface using the CO2 laser assisted reshaping technique. The proposed reshaping technique exhibits great potential for forming a large variety of micro-lens arrays on the surface of various transparent materials.

  8. Microfacies and depositional environment of the Word Formation (Permian) Glass Mountains, Texas

    SciTech Connect

    Rathjen, J.D. . Dept. of Geological Sciences)

    1993-02-01

    The Word Formation (Permian) crops out in the Glass Mountains of West Texas. The Word is composed of clastics in the southwest, carbonates in the northeast, and a transitional zone of alternating carbonates and clastics separating the two extreme facies. Sediment thickness ranges from 457 meters in the southwest to 91 meters in the northeast. Measured sections and petrographic data have identified six microfacies from the transitional and eastern facies of the Word. These are southwest to northeast: (1) Peloidal Packstones, (2) Bioclastic Wackestones/Packstones, (3) Whole Fossil Wackestones/Packstones, (4) Bioturbated Wackestones, (5) Fusulinid-Crinoid Packstones, and from the eastern facies, (6) Dolostones. Petrographic data indicate that a shallow water lagoonal environment existed in the southwest. This lagoonal environment grades into a more fossiliferous normal marine environment toward the northeast. In the northeast, a very shallow water shelf environment existed which was periodically subaerially exposed, dolomitizing the sediments.

  9. Isotopic Effect on the Gel and Glass Formation of a Charged Colloidal Clay: Laponite.

    PubMed

    Marques, Flavio Augusto de Melo; Angelini, Roberta; Ruocco, Giancarlo; Ruzicka, Barbara

    2017-04-04

    The time evolution of both dynamic and static structure factors of a charged colloidal clay, Laponite, dispersed in both $H_2O$ and $D_2O$ solvents has been investigated through multi angle Dynamic Light Scattering (DLS) and Small Angle X-ray Scattering (SAXS) as a function of weight concentration. The aging phenomenology and the formation of arrested states, both gel and glass, are preserved in $D_2O$ while the dynamics is slowed down with respect to water. These findings are important to understand the role played by the solvent in the interparticle interactions and for techniques such as neutron scattering and nuclear magnetic resonance that permit to extend the accessible scattering vectors and timescales.

  10. Experimental investigation of biofilm formation within a glass porous medium in the presence of carbon dioxide

    NASA Astrophysics Data System (ADS)

    Sygouni, Varvara; Manariotis, Ioannis D.; Chrysikopoulos, Constantinos V.

    2013-04-01

    Capturing CO2 emissions and storing them in properly selected deep geologic formations is considered a promising solution for the reduction of CO2 in the atmosphere. However, if CO2 leakage occurs from geologic storage formations due to permeability increases caused by rock-brine-supercritical CO2 geochemical reactions or reactivation of existing fractures, the impact to groundwater quality could be significant. Dissolved CO2 in groundwater can decrease the pH, which in turn can solubilize undesired heavy metals from the solid matrix with profound and severe implications to public health. Consequently, it is essential to fully understand the potential impact of CO2 to shallow groundwater systems. In this study, a series of visualization experiments in a glass-etched micromodel were performed in order to estimate the effect of CO2 on biofilm formation. All biofilms were developed using Pseudomonas (P.) Putida. Synthetic water saturated with CO2 was injected through the micromodel through an inlet port, and CO2 was measured at the outlet port. The transient growth of the biofilm was monitored by taking high-resolution digital photographs at various times, and the effect of CO2 on biofilm growth was estimated. Furthermore, transient changes of effective permeability and porosity were measured and the effect of solution chemistry (e.g. pH, ionic strength, redox potential) on the rate of biofilm growth was evaluated.

  11. The influence of sodium nanoparticles formation on luminescent properties of fluorophosphate glasses containing molecular clusters and quantum dots of lead selenide

    NASA Astrophysics Data System (ADS)

    Lipatova, Zh. O.; Kolobkova, E. V.; Sidorov, A. I.; Nikonorov, N. V.

    2016-08-01

    The influence of sodium nanoparticles and secondary heat treatment conditions on the spectralluminescent characteristics of fluorophosphate glasses with PbSe molecular clusters and quantum dots is studied. Experiments with glasses containing no sodium nanoparticles show that their thermal treatment leads to the formation of molecular clusters with subsequent formation of quantum dots having an intense luminescence. The results of numerical simulation for glasses with sodium nanoparticles shows that heat treatment leads to formation of a sodium fluoride shell on the nanoparticles surface. It is shown that quenching of the luminescence of PbSe molecular clusters and quantum dots takes place in these glasses.

  12. Glass formation and the third harmonic generation of Cu{sub 2}Se–GeSe{sub 2}–As{sub 2}Se{sub 3} glasses

    SciTech Connect

    Reshak, A. H.; Klymovych, O. S.; Zmiy, O. F.; Myronchuk, G. L.; Zamuruyeva, O. V.; Alahmed, Z. A.; Chyský, J.; Bila, Jiri; Kamarudin, H.

    2014-10-14

    We have performed the investigation of the nonlinear optical properties namely the third harmonic generation (THG) of the glass-formation region in the Cu{sub 2}Se–GeSe{sub 2}–As{sub 2}Se{sub 3} system. The samples were synthesized by direct single-temperature method from high-purity elementary substances. We have found that the value of disorder parameter Δ depends on the composition of the glassy alloys. The measurements show that increasing the Cu{sub 2}Se concentration leads to increased slope of the absorption edge, which may be explained by the decrease of the height of random potential relief for the electrons in the tails of the state density which border the band edges. A very sharp increase in the THG at low temperature was observed. Significant enhancement in THG was obtained with decreasing the energy gap, which agreed well with the nonlinear optical susceptibilities obtained from other glasses.

  13. Discovery of Critical Oxygen Content for Glass Formation in Zr80Pt20 Melt Spun Ribbons

    SciTech Connect

    D.J. Sordelet; E.A. Rozhkova; X. Yang; M.J. Kramer

    2004-09-30

    Zr{sub 80}Pt{sub 20} alloys may form meta-stable quasicrystals either during devitrification of an amorphous phase or directly upon cooling from a liquid depending on processing conditions. To date, little attention has been given to the role of oxygen on the glass formation or devitrification behavior of Zr-Pt and similar alloys. This study reveals that oxygen content during melt spinning indeed strongly influences the formation of the as-quenched structure. A critical amount of oxygen was found to be required to form amorphous ribbons at a fixed quench rate. At lower oxygen levels (i.e., <500 ppm mass), a fully crystallized is formed; the structure is composed mainly of meta-stable {beta}-Zr with a small fraction of a quasicrystalline phase. At higher oxygen levels, the as-quenched structure transitions to a fully amorphous structure ({approx}1000 ppm mass), and with further oxygen addition forms a mixture of amorphous and quasicrystalline ({approx}1500 ppm mass) or crystalline phases (>2500 ppm mass). Details regarding the structure of the meta-stable {beta}-Zr phase in the low-oxygen ribbons are provided along with a discussion of the structural similarity between this phase and the quasicrystal structure that formed in this alloy.

  14. On the Formation of Nanobubbles in Vycor Porous Glass during the Desorption of Halogenated Hydrocarbons

    PubMed Central

    Mitropoulos, A. C.; Stefanopoulos, K. L.; Favvas, E. P.; Vansant, E.; Hankins, N. P.

    2015-01-01

    Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of ‘ink-bottle’ pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary. PMID:26047466

  15. Yielding of glass under shear: A directed percolation transition precedes shear-band formation

    NASA Astrophysics Data System (ADS)

    Shrivastav, Gaurav Prakash; Chaudhuri, Pinaki; Horbach, Jürgen

    2016-10-01

    Under external mechanical loading, glassy materials, ranging from soft matter systems to metallic alloys, often respond via formation of inhomogeneous flow patterns, during yielding. These inhomogeneities can be precursors to catastrophic failure, implying that a better understanding of their underlying mechanisms could lead to the design of smarter materials. Here, extensive molecular dynamics simulations are used to reveal the emergence of heterogeneous dynamics in a binary Lennard-Jones glass, subjected to a constant strain rate. At a critical strain, this system exhibits for all considered strain rates a transition towards the formation of a percolating cluster of mobile regions. We give evidence that this transition belongs to the universality class of directed percolation. Only at low shear rates, the percolating cluster subsequently evolves into a transient (but long-lived) shear band with a diffusive growth of its width. Finally, the steady state with a homogeneous flow pattern is reached. In the steady state, percolation transitions also do occur constantly, albeit over smaller strain intervals, to maintain the stationary plastic flow in the system.

  16. On the Formation of Nanobubbles in Vycor Porous Glass during the Desorption of Halogenated Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Mitropoulos, A. C.; Stefanopoulos, K. L.; Favvas, E. P.; Vansant, E.; Hankins, N. P.

    2015-06-01

    Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of ‘ink-bottle’ pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary.

  17. Influence of biofilm formation on the optical properties of novel bioactive glass-containing composites.

    PubMed

    Hyun, Hong-Keun; Ferracane, Jack L

    2016-09-01

    Bioactive glass (BAG) has been suggested as a possible additive for dental restorative materials because of its antimicrobial effect and potential for promoting apatite formation in body fluids. The purpose of this study was to investigate the effects of bacterial biofilm on the change of colorimetric value and translucency of novel BAG-containing composites having different initial surface roughness. Composites with 72wt% total filler load were prepared by replacing 15% of the silanized Sr glass with BAG (65 mol % Si; 4% P; 31% Ca), BAG-F (61% Si; 31% Ca; 4% P; 3% F; 1% B), or silanized silica. Light-cured discs of 2-mm thickness (n=10/group) were divided into 4 different surface roughness subgroups produced by wet polishing with 600 and then up to 1200, 2400, or 4000 grit SiC. CIE L*a*b* were measured and the color difference and translucency parameter (TP) were calculated before and after incubating in media with or without a Streptococcus mutans (UA 159) biofilm for 2 wks (no agitation). Results were analyzed using ANOVA/Tukey's test (α=0.05). All the color differences for BAG and BAG-F composite showed significant decreases with bacterial biofilm compared to media-only. The mean TP (SD) of BAG and BAG-F composite before aging [10.0 (2.8) and 8.5 (1.4)] was higher than that of the control composite [4.9 (0.8)], while the change in TP with aging was greater compared to the control with or without bacteria. BAG-F composites with the smoothest surfaces showed a greater decrease in TP under bacterial biofilm compared to the BAG composite. Highly polished dental composites containing bioactive glass additives may become slightly rougher and show reduced translucency when exposed to bacterial biofilms, but do not discolor any more than control composites that do not contain the BAG. Copyright © 2016 The Academy of Dental Materials. All rights reserved.

  18. Formation of metallic cation-oxygen network for anomalous thermal expansion coefficients in binary phosphate glass.

    PubMed

    Onodera, Yohei; Kohara, Shinji; Masai, Hirokazu; Koreeda, Akitoshi; Okamura, Shun; Ohkubo, Takahiro

    2017-05-31

    Understanding glass structure is still challenging due to the result of disorder, although novel materials design on the basis of atomistic structure has been strongly demanded. Here we report on the atomic structures of the zinc phosphate glass determined by reverse Monte Carlo modelling based on diffraction and spectroscopic data. The zinc-rich glass exhibits the network formed by ZnOx (averaged x<4) polyhedra. Although the elastic modulus, refractive index and glass transition temperature of the zinc phosphate glass monotonically increase with the amount of ZnO, we find for the first time that the thermal expansion coefficient is very sensitive to the substitution of the phosphate chain network by a network consisting of Zn-O units in zinc-rich glass. Our results imply that the control of the structure of intermediate groups may enable new functionalities in the design of oxide glass materials.

  19. Formation of metallic cation-oxygen network for anomalous thermal expansion coefficients in binary phosphate glass

    PubMed Central

    Onodera, Yohei; Kohara, Shinji; Masai, Hirokazu; Koreeda, Akitoshi; Okamura, Shun; Ohkubo, Takahiro

    2017-01-01

    Understanding glass structure is still challenging due to the result of disorder, although novel materials design on the basis of atomistic structure has been strongly demanded. Here we report on the atomic structures of the zinc phosphate glass determined by reverse Monte Carlo modelling based on diffraction and spectroscopic data. The zinc-rich glass exhibits the network formed by ZnOx (averaged x<4) polyhedra. Although the elastic modulus, refractive index and glass transition temperature of the zinc phosphate glass monotonically increase with the amount of ZnO, we find for the first time that the thermal expansion coefficient is very sensitive to the substitution of the phosphate chain network by a network consisting of Zn-O units in zinc-rich glass. Our results imply that the control of the structure of intermediate groups may enable new functionalities in the design of oxide glass materials. PMID:28561027

  20. Effects of halogen substitutions on the formation of copper colloids by hydrogen reduction in sodium borate glasses

    NASA Astrophysics Data System (ADS)

    Edson, Daniel Lee

    2002-01-01

    The substitution of small amounts of halogens (< 1 mol%) for oxygen in sodium borate glasses with 10 to 35 mol% soda that contain 0.1 or 0.2 wt% CuO dramatically influences the ligand environment around copper in these glasses and the formation of copper colloids during hydrogen treatment near Tg. The suppression of copper colloid formation in glasses that contain halogen ions has not previously been reported. The interaction of halogen ions and copper depends on the identity of the halogen ion, the ratio of the molar concentrations halogen to copper ions and the soda content of the glass. The heavier halogen ions, Cl, Br and I, preferentially associate with copper ions in the melt. Four bromine ions associate with each cupric ion, reducing it to the cuprous state. The reduction power of the ions increases in the order Cl- < Br- < I-. Cl, Br and I associate with cupric ions in combination with oxygen ions in the glass. These mixed anion complexes, which probably contain multiple halogen ions, give rise to intense charge transfer absorption bands in the UV-Vis spectra which cause a color change in the glass. The concentration of the mixed anion complexes is very small and depends on the ratio of halogen to copper. The reduction of cupric ions has been separated from the growth of copper colloids during hydrogen reduction through use of the ESR. The reduction of cupric ions by hydrogen is described by the tarnishing model. The presence of Cl, Br and I completely prevents the formation of copper colloids during hydrogen reduction near Tg. CuBr nanoparticles form in glasses with ratios of Br:Cu of 1:1 or 2:1. Support for the view that cuprous ions are the diffusing species in these glasses following hydrogen reduction is presented, with a requirement that hydrogen be present at the growing nuclei to further reduce the ion to the atomic state. Bonding between mobile cuprous ions and halogen ions is suggested to slow or prevent the formation of copper colloids and the

  1. Accelerated formation of sodium depletion layer on soda lime glass surface by corona discharge treatment in hydrogen atmosphere

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Keiga; Ikeda, Hiroshi; Sakai, Daisuke; Funatsu, Shiro; Uraji, Keiichiro; Yamamoto, Kiyoshi; Suzuki, Toshio; Harada, Kenji; Nishii, Junji

    2014-05-01

    Formation of a sodium depletion layer on a soda lime glass surface was accelerated efficiently using a corona discharge treatment in H2 atmosphere. One origin of such acceleration was the preferential generation of H+ with a larger mobility at an anode needle end with a lower applied voltage than that in air. The second origin was the applied voltage across the glass plate during the corona discharge treatment, which was estimated theoretically as 2.7 times higher than that in air. These two effects doubled the depletion layer thickness compared with that in air.

  2. Hydroxyapatite formation on sol-gel derived poly(ε-caprolactone)/bioactive glass hybrid biomaterials.

    PubMed

    Allo, Bedilu A; Rizkalla, Amin S; Mequanint, Kibret

    2012-06-27

    Investigation of novel biomaterials for bone regeneration is based on the development of scaffolds that exhibit bone-bonding ability, biocompatibility, and sufficient mechanical strength. In this study, using novel poly (ε-caprolactone)/bioactive glass (PCL/BG) hybrids with different organic/inorganic ratios, the effects of BG contents on the in vitro bone-like hydroxyapatite (HA) formation, mechanical properties, and biocompatibility were investigated. Rapid precipitation of HA on the PCL/BG hybrid surfaces were observed after incubating in simulated body fluid (SBF) for only 6 h, as confirmed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and inductively coupled plasma atomic emission spectroscopy (ICPS). The ICPS elemental analysis results were further analyzed in terms of the Ca(2+) and PO4(3-) which were consumed to form the apatite layer. The results revealed that the rate and total amount of HA deposition decreased with an increase in PCL content. The compressive modulus and strength of the PCL/BG hybrids increased with the decrease in PCL content. The highest values were achieved at the lowest PCL content (10 wt %) and were around, 90 MPa and 1.4 GPa, respectively. To evaluate the cytotoxicity of PCL/BG bioactive hybrids, MC3T3-E1 osteoblast-like cells were cultured for up to 72 h. Our data indicated that whereas initial cell attachment was marginally lower than the control tissue culture poly styrene (TCPS) surface, the hybrid materials promoted cell growth in a time-dependent manner. Cell viability within the different PCL/BG hybrid samples appeared to be influenced by compositional differences whereby higher PCL contents correlated with slight reduction in cell viability. Taken together, this study adds important new information to our knowledge on hydroxyapatite formation, mechanical properties, and cytotoxic effects of PCL/BG hybrids prepared by the sol-gel process

  3. On the formation of Na nanoparticles in femtosecond-laser irradiated glasses

    SciTech Connect

    Jiang Nan; Su Dong; Spence, John C. H.; Qiu Jianrong

    2010-03-15

    This work discusses the response of Na to both high-energy electrons and femtosecond-laser (fs-laser) pulses in the soda-lime glass. The evidence for different responses of Na to high-energy electron irradiation between glasses with and without fs-laser irradiation suggests that the chemical and/or physical states of Na in the fs-laser irradiated glass are different from those in the original glass. Fs-laser pulses in the glass may be able to neutralize Na, which may form clusters. These results suggest that close attention should be paid to the defects associated with Na when optical or physical data are interpreted in fs-laser irradiated Na glasses.

  4. Secondary caries formation in vitro around glass ionomer-lined amalgam and composite restorations.

    PubMed

    Dionysopoulos, P; Kotsanos, N; Papadogianis, Y

    1996-08-01

    The aim of this in vitro secondary caries study was to examine the glass-ionomer liner's effect on wall-lesion inhibition when a conventional and a light-cured glass ionomer liner was placed under amalgam and composite resin restorations. Class V preparations in extracted upper premolars were used and ten restorations were used for each of the following groups: (i) two layers of copal varnish and amalgam; (ii) conventional glass-ionomer and amalgam; (iii) light-cured glass-ionomer and amalgam; (iv) bonding agent and light-cured composite resin; (v) conventional glass-ionomer, bonding agent and light-cured composite resin; (vi) light-cured glass-ionomer, extended 0.3 mm short of the enamel margin bonding agent and light-cured composite resin; and (vii) light-cured glass-ionomer, extended 1 mm short of the enamel margin, bonding agent and light-cured composite resin. The teeth were thermocycled and artificial caries were created using an acid-gel. The results of this study showed that artificial recurrent caries can be reduced significantly (P < 0.05) with a glass-ionomer liner under amalgam restorations. The results also showed that when the light-cured glass-ionomer liner was placed 0.3 mm from the cavosurface margin under composite resin restoration, the artificial recurrent caries reduced significantly (P < 0.05).

  5. Thermodynamic Origins of Shear Band Formation and the Universal Scaling Law of Metallic Glass Strength

    NASA Astrophysics Data System (ADS)

    Liu, Y. H.; Liu, C. T.; Wang, W. H.; Inoue, A.; Sakurai, T.; Chen, M. W.

    2009-08-01

    We report a universal scaling law, τy=3R(Tg-RT)/V, that uncovers an inherent relationship of the yield strength τy with the glass transition temperature Tg and molar volume V of metallic glasses. This equation is derived from fundamental thermodynamics and validated by various metallic glasses with well-defined yielding. The linearity between τy and Tg demonstrates the intrinsic correlation between yielding and glass-liquid transition, which contributes to the basic understanding of the strength and deformation of glassy alloys.

  6. Proposed thermodynamic method to predict the glass formation of the ternary transition metal systems.

    PubMed

    Wang, T L; Li, J H; Liu, B X

    2009-04-14

    By considering the energetic competition between the crystalline solid solution and glass phase, a thermodynamic method is proposed to predict/determine the glass forming range of a ternary metal system and in terms of the dynamics, the parameter gamma(ABC)* is further defined to search for a proper alloy with superior glass forming ability in the system. 10 more ternary/binary metal systems, e.g. the Cu-Zr-Ti and Cu-Hf-Ti systems, were studied and the predicted alloys of superior glass forming ability match well with those reported from experimental observations.

  7. Formation temperature of ultra-stable glasses and application to ethylbenzene

    NASA Astrophysics Data System (ADS)

    Tournier, Robert F.

    2015-11-01

    Ultra-stable thin glass films are obtained when they are deposited at a temperature Td below the glass transition temperature Tg. An enthalpy excess Δɛ × ΔHm is frozen during deposition inducing an isothermal liquid-glass transition temperature Tsg equal to Td and a liquid-to-liquid transition temperature Tgf above Tg depending on Δɛ. The enthalpy excess, the ultra-stable glass enthalpy saving, and the optimum deposition temperature Tsg leading to the maximum density, are predicted for ethylbenzene, knowing only the molar melting heat ΔHm of crystals, their melting temperature Tm, Tg, and the specific heat jump at Tg.

  8. Formation of carbon vacancy in 4H silicon carbide during high-temperature processing

    NASA Astrophysics Data System (ADS)

    Ayedh, H. M.; Bobal, V.; Nipoti, R.; Hallén, A.; Svensson, B. G.

    2014-01-01

    As-grown and pre-oxidized silicon carbide (SiC) samples of polytype 4H have been annealed at temperatures up to 1950 °C for 10 min duration using inductive heating, or at 2000 °C for 30 s using microwave heating. The samples consisted of a n-type high-purity epitaxial layer grown on 4° off-axis ⟨0001⟩ n+-substrate and the evolution of the carbon vacancy (VC) concentration in the epitaxial layer was monitored by deep level transient spectroscopy via the characteristic Z1/2 peak. Z1/2 appears at ˜0.7 eV below the conduction band edge and arises from the doubly negative charge state of VC. The concentration of VC increases strongly after treatment at temperatures ≥ 1600 °C and it reaches almost 1015 cm-3 after the inductive heating at 1950 °C. A formation enthalpy of ˜5.0 eV is deduced for VC, in close agreement with recent theoretical predictions in the literature, and the entropy factor is found to be ˜5 k (k denotes Boltzmann's constant). The latter value indicates substantial lattice relaxation around VC, consistent with VC being a negative-U system exhibiting considerable Jahn-Teller distortion. The microwave heated samples show evidence of non-equilibrium conditions due to the short duration used and display a lower content of VC than the inductively heated ones. Finally, concentration-versus-depth profiles of VC favour formation in the "bulk" of the epitaxial layer as the prevailing process and not a Schottky type process at the surface.

  9. Formation of Nanoporous Anodic Alumina by Anodization of Aluminum Films on Glass Substrates.

    PubMed

    Lebyedyeva, Tetyana; Kryvyi, Serhii; Lytvyn, Petro; Skoryk, Mykola; Shpylovyy, Pavlo

    2016-12-01

    Our research was aimed at the study of aluminum films and porous anodic alumina (PAA) films in thin-film РАА/Al structures for optical sensors, based on metal-clad waveguides (MCWG). The results of the scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies of the structure of Al films, deposited by DC magnetron sputtering, and of PAA films, formed on them, are presented in this work.The study showed that the structure of the Al films is defined by the deposition rate of aluminum and the thickness of the film. We saw that under anodization in 0.3 M aqueous oxalic acid solution at a voltage of 40 V, the PAA film with a disordered array of pores was formed on aluminum films 200-600 nm thick, which were deposited on glass substrates with an ultra-thin adhesive Nb layer. The research revealed the formation of two differently sized types of pores. The first type of pores is formed on the grain boundaries of aluminum film, and the pores are directed perpendicularly to the surface of aluminum. The second type of pores is formed directly on the grains of aluminum. They are directed perpendicularly to the grain plains. There is a clear tendency to self-ordering in this type of pores.

  10. Biomimetic formation of apatite on the surface of porous gelatin/bioactive glass nanocomposite scaffolds

    NASA Astrophysics Data System (ADS)

    Mozafari, Masoud; Rabiee, Mohammad; Azami, Mahmoud; Maleknia, Saied

    2010-12-01

    There have been several attempts to combine bioactive glasses (BaGs) with biodegradable polymers to create a scaffold material with excellent biocompatibility, bioactivity, biodegradability and toughness. In the present study, the nanocomposite scaffolds with compositions based on gelatin (Gel) and BaG nanoparticles in the ternary SiO 2-CaO-P 2O 5 system were prepared. In vitro evaluations of the nanocomposite scaffolds were performed, and for investigating their bioactive capacity these scaffolds were soaked in a simulated body fluid (SBF) at different time intervals. The scaffolds showed significant enhancement in bioactivity within few days of immersion in SBF solution. The apatite formation at the surface of the nanocomposite samples confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) analyses. In vitro experiments with osteoblast cells indicated an appropriate penetration of the cells into the scaffold's pores, and also the continuous increase in cell aggregation on the bioactive scaffolds with increase in the incubation time demonstrated the ability of the scaffolds to support cell growth. The SEM observations revealed that the prepared scaffolds were porous with three dimensional (3D) and interconnected microstructure, pore size was 200-500 μm and the porosity was 72-86%. The nanocomposite scaffold made from Gel and BaG nanoparticles could be considered as a highly bioactive and potential bone tissue engineering implant.

  11. Electroless porous silicon formation applied to fabrication of boron-silica-glass cantilevers

    NASA Astrophysics Data System (ADS)

    Teva, J.; Davis, Z. J.; Hansen, O.

    2010-01-01

    This work describes the characterization and optimization of anisotropic formation of porous silicon in large volumes (0.5-1 mm3) of silicon by an electroless wet etching technique. The main goal is to use porous silicon as a sacrificial volume for bulk micromachining processes, especially in cases where etching of the full wafer thickness is needed. The porous silicon volume is formed by a metal-assisted etching in a wet chemical solution composed of hydrogen peroxide (30%), hydrofluoric acid (40%) and ethanol. This paper focuses on optimizing the etching conditions in terms of maximizing the etching rate and reproducibility of the etching. In addition to that, a study of the morphology of the pore that is obtained by this technique is presented. The results from the characterization of the process are applied to the fabrication of boron-silica-glass cantilevers that serve as a platform for bio-chemical sensors. The porous silicon volume is formed in an early step of the fabrication process, allowing easy handling of the wafer during all of the micromachining processes in the process flow. In the final process step, the porous silicon is quickly etched by immersing the wafer in a KOH solution.

  12. In-situ observation of bubble formation at silicon melt-silica glass interface

    NASA Astrophysics Data System (ADS)

    Minami, Toshiro; Maeda, Susumu; Higasa, Mitsuo; Kashima, Kazuhiko

    2011-03-01

    The generation mechanism of pinhole defects in the Czochralski (CZ)-grown silicon (Si) single crystals was clarified by in-situ observations of bubble formation at the interface between Si melt and a silica glass crucible in a small experimental apparatus. The nucleation and growth of bubbles were facilitated by creating small cavities on the inner wall of the crucible. Si melting was conducted in an argon (Ar) atmosphere, and the pressure was maintained at either 100 Torr or close to a vacuum (no Ar-gas flow). It was found that in the presence of Ar, bubbles formed in the cavities immediately after the cavities came in contact with the melt. However, no bubbles formed in a vacuum in the experimental apparatus. These results indicate that the bubbles formed in the cavities are largely filled with Ar, and the initial bubble volumes are nearly comparable with those of the cavities. In an initial stage of expansion of a bubble, estimated volumes changed nearly in accordance with the Boyle-Charles law. Further, participation of SiO gas in bubble growth may explain the deviation of the bubble volume from the theoretical value anticipated if only Ar gas was involved in the bubble growth.

  13. In vitro surface reaction layer formation and dissolution of calcium phosphate cement-bioactive glass composites.

    PubMed

    Liu, Changsheng; Chen, Chien-Wen; Ducheyne, Paul

    2008-09-01

    Composites of hydrated calcium phosphate cement (CPC) and bioactive glass (BG) containing Si were immersed in vitro to study the effect of chemical composition on surface reaction layer formation and dissolution/precipitation behavior. The solutions used were 0.05 M tris hydroxymethyl aminomethane/HCl (tris buffer), tris buffer supplemented with plasma electrolyte (TE) with pH 7.4 at 37 degrees C, and this solution complemented with 10% newborn bovine serum (TES). The post-immersion solutions were analyzed for changes in Ca, PO(4) and Si concentrations. The reacted surfaces were analyzed using Fourier transform infrared (FTIR), and scanning electron microscopy with energy dispersive x-ray analysis. The sample weight variations after immersion were also determined. The results showed that the composition of the bioactive composite CPCs greatly affected their behavior in solution and the formation of apatite bioactive surface reaction layers. After immersion in the TE solution, Ca ions were taken up by all samples during the entire immersion duration. Initially, the P ion concentration increased sharply, and then decreased. This reaction pattern reveals the formation of an amorphous calcium phosphate layer on the surface of these composite CPCs. FTIR revealed that the layer was, in fact, poorly crystallized Ca-deficient carbonate apatite. The thickness of the layer was 12-14 microm and it was composed of rod-like apatite with directional arrangement. For immersion in the TES solution, the Ca and Si ion concentrations showed a similar behavior to that in TE, but the release rate of Si ions was higher. FTIR revealed that after TES immersion, not only did the typical, poorly crystallized, Ca-deficient carbonated apatite form, as it did in TE, but also the serum proteins co-adsorbed on the surface and thereby affected the surface reaction layer formation. A thinner apatite layer was formed and was composed of a micro-porous layer comprising rounded particles in a glue

  14. Effects of minor Sn addition on the glass formation and properties of Fe-metalloid metallic glasses with high magnetization and high glass forming ability

    NASA Astrophysics Data System (ADS)

    Shi, Minjie; Liu, Zengqian; Zhang, Tao

    2015-03-01

    Effects of minor Sn addition on the glass-forming ability (GFA) as well as thermal, magnetic, and mechanical properties of Fe-P-C-B-Si bulk metallic glasses (BMGs) with compositions of Fe80-xSnxP9C8B2Si1 (x=0, 1, 2 and 3 at%) were investigated. The minor Sn substitution for Fe effectively enhances the GFA. The fully glassy rods can be produced up to 3 and 3.5 mm in diameter for the alloys with 1 and 2 at% Sn addition, respectively. Moreover, these Sn-containing BMGs exhibit good soft magnetic properties including high saturation magnetization (Ms) of 1.46-1.51 T, low coercivity (Hc) of 3.8-5.0 A/m and good mechanical properties, i.e., high fracture strength (σf) above 3.2 GPa and limited plastic strain (εp) above 0.4%. The combination of large GFA, good soft magnetic and mechanical properties as well as low cost makes the Fe-Sn-P-C-B-Si BMGs promising as soft magnetic materials for industrial applications.

  15. Development of fusogenic glass surfaces that impart spatiotemporal control over macrophage fusion: Direct visualization of multinucleated giant cell formation.

    PubMed

    Faust, James J; Christenson, Wayne; Doudrick, Kyle; Ros, Robert; Ugarova, Tatiana P

    2017-06-01

    Implantation of synthetic material, including vascular grafts, pacemakers, etc. results in the foreign body reaction and the formation of multinucleated giant cells (MGCs) at the exterior surface of the implant. Despite the long-standing premise that fusion of mononucleated macrophages results in the formation of MGCs, to date, no published study has shown fusion in context with living specimens. This is due to the fact that optical-quality glass, which is required for the majority of live imaging techniques, does not promote macrophage fusion. Consequently, the morphological changes that macrophages undergo during fusion as well as the mechanisms that govern this process remain ill-defined. In this study, we serendipitously identified a highly fusogenic glass surface and discovered that the capacity to promote fusion was due to oleamide contamination. When adsorbed on glass, oleamide and other molecules that contain long-chain hydrocarbons promoted high levels of macrophage fusion. Adhesion, an essential step for macrophage fusion, was apparently mediated by Mac-1 integrin (CD11b/CD18, αMβ2) as determined by single cell force spectroscopy and adhesion assays. Micropatterned glass further increased fusion and enabled a remarkable degree of spatiotemporal control over MGC formation. Using these surfaces, we reveal the kinetics that govern MGC formation in vitro. We anticipate that the spatiotemporal control afforded by these surfaces will expedite studies designed to identify the mechanism(s) of macrophage fusion and MGC formation with implication for the design of novel biomaterials. Copyright © 2017 Elsevier Ltd. All rights reserved.

  16. Rare earth dependent formation of PbF2 nanocrystals and its effect on the emission properties in oxyfluoride glasses

    NASA Astrophysics Data System (ADS)

    Kim, Kyoung Hoon; Choi, Yong Gyu; Im, Won Bin; Chung, Woon Jin

    2013-03-01

    Oxyfluoride glasses doped with rare earth ions (Dy3+, Er3+ or Ho3+) were fabricated, and their visible and near infrared emissions were evaluated before and after the formation of β-PbF2 nanocrystals. Upon heat treatment of the parent glass to precipitate β-PbF2 nanocrystals, both the intensity and lifetime of radiative emissions from the Dy3+ ion were improved conspicuously, whereas changes in the emissions from Er3+ and Ho3+ turned out to be relatively insignificant. In addition to the hypersensitive nature of some 4 f↔4 f transitions of Dy3+, its spatial distribution inside the heat-treated oxyfluoride samples is believed to be responsible for this interesting observation. Our finding thus exemplifies the chemical effects of rare earth ions on the formation of nanocrystals via heat treating oxyfluoride glasses. Various probes including X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and Judd-Ofelt analysis were applied to elucidate the rare earth dependence of the fluoride nanocrystals within the oxyfluoride glasses.

  17. Bulk formation of metallic glasses and amorphous silicon from the melt

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1984-01-01

    Procedures and compositions for producing metallic glasses in bulk at slow cooling rates were investigated. An attempt was made to form the amorphous phase of the tetrahedrally coordinated elements (Si or Ge) by undercooling the melt. The crystal nucleation behavior of pure liquids and glass formers were examined.

  18. Formation of cylindrical micro-lens array in fused silica glass using laser irradiations

    NASA Astrophysics Data System (ADS)

    Choi, Hun-Kook; Ahsan, Md. Shamim; Yoo, Dongyoon; Sohn, Ik-Bu; Noh, Young-Chul; Kim, Jin Tae; Jung, Deok; Kim, Jin Hyeok

    2013-12-01

    In this article, we report the development of plano-convex cylindrical micro-lens array on the surface of fused silica glass using laser processing technology. Initially, femtosecond laser pulses are irradiated on the target fused silica glass substrate to pattern periodic micro-grooves. Afterwards, laser beam from CO2 laser source is applied several times on the previously micro-patterned fused silica glass surface, the purpose of which is to polish the micro-patterned glass surface. As a consequence, periodic plano-convex cylindrical micro-lens array is evolved on the glass surface. The micro-lens array shows great consistency in size and shape throughout the sample area. We also investigate various optical properties of the micro-lenses evolved glass substrates including the diffraction pattern and diffraction efficiency of light. The glass sample comprising cylindrical micro-lens array can diffract light with moderate diffraction efficiency. We strongly believe that, it is possible to engineer cylindrical micro-lens array on the surface of a variety of transparent materials including glasses and polymers over a large area.

  19. Alteration of Basaltic Glass to Mg/Fe-Smectite under Acidic Conditions: A Potential Smectite Formation Mechanism on Mars

    NASA Technical Reports Server (NTRS)

    Peretyazhko, Tanya; Sutter, Brad; Ming, Douglas W.

    2014-01-01

    Phyllosilicates of the smectite group including Mg- and Fe-saponite and Fe(III)-rich nontronite have been identified on Mars. Smectites are believed to be formed under neutral to alkaline conditions that prevailed on early Mars. This hypothesis is supported by the observation of smectite and carbonate deposits in Noachian terrain on Mars. However, smectite may have formed under mildly acidic conditions. Abundant smectite formations have been detected as layered deposits hundreds of meters thick in intracrater depositional fans and plains sediments, while no large deposits of carbonates are found. Development of mildly acidic conditions at early Mars might allow formation of smectite but inhibit widespread carbonate precipitation. Little is known regarding the mechanisms of smectite formation from basaltic glass under acidic conditions. The objective of this study was to test a hypothesis that Mars-analogue basaltic glass alters to smectite minerals under acidic conditions (pH 4). The effects of Mg and Fe concentrations and temperature on smectite formation from basaltic glass were evaluated. Phyllosilicate synthesis was performed in batch reactors (Parr acid digestion vessel) under reducing hydrothermal conditions at 200 C and 100 C. Synthetic basaltic glass with a composition similar to that of the Gusev crater rock Adirondack (Ground surface APXS measurement) was used in these experiments. Basaltic glass was prepared by melting and quenching procedures. X-ray diffraction (XRD) analysis indicated that the synthesized glass was composed of olivine, magnetite and X-ray amorphous phase. Samples were prepared by mixing 250 mg Adirondack with 0.1 M acetic acid (final pH 4). In order to study influence of Mg concentration on smectite formation, experiments were performed with addition of 0, 1 and 10 mM MgCl2. After 1, 7 and 14 day incubations the solution composition was analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and the altered glass and formed

  20. Computer Modeling of Thermal Convection in Melts to Explain Glass Formation in Low Gravity and on Earth

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Ramachandran, Narayanan

    2006-01-01

    Experiments conducted up to this time on glass forming melts in the low gravity environment of space show that glasses prepared in low-g are more chemically homogeneous and more resistant to crystallization than the comparable glasses prepared at 1-g on Earth. This result is somewhat surprising and opposite to the accepted concept on glass formation for a melt. A hypothesis based on "shear thinning" of a melt, a decrease in viscosity with increasing shear stress, is proposed as an explanation for the observed low-gravity results. This paper describes detailed simulation procedures to test the role of thermal convection in introducing shear stress in glass forming melts, using a lithium disilcate melt as a model. The simulation system in its idealized version consists of a cylinder that is heated at one end and cooled at the other with gravity acting in a transverse direction to the thermal gradient. The side wall of the cylinder is assumed to be insulating. The governing equations of motion and energy are solved using variable properties for viscosity (Arrehenius and non-Arrehenius behaviors) and density (constant and temperature dependent). Other parametric variables in the calculations include gravity level and gravity vector orientation. The shear stress in the system are then computed as a function of gravity from the calculated values of maximum melt velocity, and its effect on melt viscosity (shear thinning) is predicted. Also included and discussed are the modeling efforts related to other potential convective processes in glass forming melts and their possible effects on melt viscosity.

  1. Examining metallic glass formation in LaCe:Nb by ion implantation

    DOE PAGES

    Sisson, Richard; Reinhart, Cameron; Bridgman, Paul; ...

    2017-01-01

    In order to combine niobium (Nb) with lanthanum (La) and cerium (Ce), Nb ions were deposited within a thin film of these two elements. According to the Hume-Rothery rules, these elements cannot be combined into a traditional crystalline metallic solid. The creation of an amorphous metallic glass consisting of Nb, La, and Ce is then investigated. Amorphous metallic glasses are traditionally made using fast cooling of a solution of molten metals. In this paper, we show the results of an experiment carried out to form a metallic glass by implanting 9 MeV Nb 3+ atoms into a thin film ofmore » La and Ce. Prior to implantation, the ion volume distribution is calculated by Monte Carlo simulation using the SRIM tool suite. As a result, using multiple methods of electron microscopy and material characterization, small quantities of amorphous metallic glass are indeed identified.« less

  2. Examining metallic glass formation in LaCe:Nb by ion implantation

    SciTech Connect

    Sisson, Richard; Reinhart, Cameron; Bridgman, Paul; Jevremovic, Tatjana

    2017-01-01

    In order to combine niobium (Nb) with lanthanum (La) and cerium (Ce), Nb ions were deposited within a thin film of these two elements. According to the Hume-Rothery rules, these elements cannot be combined into a traditional crystalline metallic solid. The creation of an amorphous metallic glass consisting of Nb, La, and Ce is then investigated. Amorphous metallic glasses are traditionally made using fast cooling of a solution of molten metals. In this paper, we show the results of an experiment carried out to form a metallic glass by implanting 9 MeV Nb 3+ atoms into a thin film of La and Ce. Prior to implantation, the ion volume distribution is calculated by Monte Carlo simulation using the SRIM tool suite. As a result, using multiple methods of electron microscopy and material characterization, small quantities of amorphous metallic glass are indeed identified.

  3. From Glass Formation to Icosahedral Ordering by Curving Three-Dimensional Space

    NASA Astrophysics Data System (ADS)

    Turci, Francesco; Tarjus, Gilles; Royall, C. Patrick

    2017-05-01

    Geometric frustration describes the inability of a local molecular arrangement, such as icosahedra found in metallic glasses and in model atomic glass formers, to tile space. Local icosahedral order, however, is strongly frustrated in Euclidean space, which obscures any causal relationship with the observed dynamical slowdown. Here we relieve frustration in a model glass-forming liquid by curving three-dimensional space onto the surface of a 4-dimensional hypersphere. For sufficient curvature, frustration vanishes and the liquid "freezes" in a fully icosahedral structure via a sharp "transition." Frustration increases upon reducing the curvature, and the transition to the icosahedral state smoothens while glassy dynamics emerge. Decreasing the curvature leads to decoupling between dynamical and structural length scales and the decrease of kinetic fragility. This sheds light on the observed glass-forming behavior in Euclidean space.

  4. Durability of SRP Waste Glass - Effects of Pressure and Formation of Surface Layers

    SciTech Connect

    Wicks, G.G.

    2001-10-17

    This report discusses results of an assessment of pressure at anticipated storage temperature on the chemical durability of Savannah River Plant waste glass. Surface interactions were also examined and corrosion mechanisms discussed.

  5. Formation of void array inside transparent and absorptive glasses by femtosecond laser irradiation.

    PubMed

    Jang, Wooyoung; Kim, Daejin; Kim, Taehong; Moon, Ayoung; Lim, Ki-Soo; Lee, Myeongkyu; Sohn, Ik-Bu

    2012-06-01

    We demonstrate self-fabrication of void arrays in a fused silica transparent in the visible and a color-filter borosilicate glass strongly absorptive at 800 nm using tightly focused Ti-sapphire femtosecond laser pulses at 1 kHz without scanning. The period, the size, the number of voids, and the length of the aligned void structure were controlled by changing the laser pulse energy, and the position of the focal point inside two materials. The void arrays were observed by an optical microscope and also estimated by an optical diffraction experiment. The void size and period were smaller in the absorptive glass than in the transparent glass. The submicrometer-sized void was observed by a scanning electron microscope. The smaller and clearer void arrays were formed in the color filter than the fused silica glass. With increasing the laser focal depth, the void-array length increased in the fused silica and decreased in the color filter.

  6. Electron irradiation effect on bubble formation and growth in a sodium borosilicate glass

    SciTech Connect

    Chen, X.; Birtcher, R. C.; Donnelly, S. E.

    2000-02-08

    In this study, the authors studied simultaneous and intermittent electron irradiation effects on bubble growth in a simple sodium borosilicate glass during Xe ion implantation at 200 C. Simultaneous electron irradiation increases the average bubble size in the glass. This enhanced diffusion is also shown by the migration of Xe from bubbles into the matrix when the sample is irradiated by an electron beam after the Xe implantation.

  7. Trace phase formation, crystallization kinetics and crystallographic evolution of a lithium disilicate glass probed by synchrotron XRD technique

    PubMed Central

    Huang, Saifang; Huang, Zhaohui; Gao, Wei; Cao, Peng

    2015-01-01

    X-ray diffraction technique using a laboratory radiation has generally shown limitation in detectability. In this work, we investigated the in situ high-temperature crystallization of a lithium disilicate glass-ceramic in the SiO2–Li2O–CaO–P2O5–ZrO2 system with the aid of synchrotron radiation. The formation of lithium metasilicate and other intermediate phases in trace amount was successfully observed by synchrotron X-ray diffraction (SXRD). The crystallization mechanism in this glass was thus intrinsically revised to be the co-nucleation of lithium metasilicate and disilicate, instead of the nucleation of lithium disilicate only. The phase content, crystallite size and crystallographic evolutions of Li2Si2O5 in the glass-ceramic as a function of annealing temperature were studied by performing Rietveld refinements. It is found that the growth of Li2Si2O5 is constrained by Li2SiO3 phase at 580–700°C. The relationship between the crystallographic evolution and phase transition was discussed, suggesting a common phenomenon of structural response of Li2Si2O5 along its c axis to other silicon-related phases during glass crystallization. PMID:25778878

  8. In-situ probing of metallic glass formation and crystallization upon heating and cooling via fast differential scanning calorimetry

    NASA Astrophysics Data System (ADS)

    Pogatscher, S.; Uggowitzer, P. J.; Löffler, J. F.

    2014-06-01

    The crystallization of small-scale Au-based metallic glass samples was investigated by fast differential scanning calorimetry. Rapid cooling and heating makes possible in-situ probing of glass formation from the supercooled liquid state or direct transition from the glassy state to the equilibrium liquid and, thereby, the determination of a critical cooling (Φc ˜ 600 Ks-1) and heating rate (Φh ˜ 6 × 103 Ks-1) for crystallization. Crystallization kinetics was studied in the whole supercooled liquid region by linear heating and isothermal calorimetry. We show that the temperature dependence of crystal growth is reflected in a "Kissinger plot" for Au49Ag5.5Pd2.3Cu26.9Si16.3 and compares well with a model for crystal growth in a glassy system. Linear heating and isothermal measurements after heating the glass show that its crystallization is always growth-controlled up to its temperature of melting. In contrast, for a low degree of direct undercooling from the equilibrium liquid isothermal crystallization is nucleation-controlled, whereas it is again growth-controlled at large undercooling. The overall crystallization behavior of the metallic glass is presented in a complete time-temperature-transformation map on cooling and, so far not accessible, on heating after various cooling procedures.

  9. Comparison of Acid Titration, Conductivity, Flame Photometry, ICP-MS, and Accelerated Lamellae Formation Techniques in Determining Glass Vial Quality.

    PubMed

    Fujimori, Kiyoshi; Lee, Hans; Sloey, Christopher; Ricci, Margaret S; Wen, Zai-Qing; Phillips, Joseph; Nashed-Samuel, Yasser

    2016-01-01

    Certain types of glass vials used as primary containers for liquid formulations of biopharmaceutical drug products have been observed with delamination that produced small glass like flakes termed lamellae under certain conditions during storage. The cause of this delamination is in part related to the glass surface defects, which renders the vials susceptible to flaking, and lamellae are formed during the high-temperature melting and annealing used for vial fabrication and shaping. The current European Pharmacopoeia method to assess glass vial quality utilizes acid titration of vial extract pools to determine hydrolytic resistance or alkalinity. Four alternative techniques with improved throughput, convenience, and/or comprehension were examined by subjecting seven lots of vials to analysis by all techniques. The first three new techniques of conductivity, flame photometry, and inductively coupled plasma mass spectrometry measured the same sample pools as acid titration. All three showed good correlation with alkalinity: conductivity (R(2) = 0.9951), flame photometry sodium (R(2) = 0.9895), and several elements by inductively coupled plasma mass spectrometry [(sodium (R(2) = 0.9869), boron (R(2) = 0.9796), silicon (R(2) = 0.9426), total (R(2) = 0.9639)]. The fourth technique processed the vials under conditions that promote delamination, termed accelerated lamellae formation, and then inspected those vials visually for lamellae. The visual inspection results without the lot with different processing condition correlated well with alkalinity (R(2) = 0.9474). Due to vial processing differences affecting alkalinity measurements and delamination propensity differently, the ratio of silicon and sodium measurements from inductively coupled plasma mass spectrometry was the most informative technique to assess overall vial quality and vial propensity for lamellae formation. The other techniques of conductivity, flame photometry, and accelerated lamellae formation

  10. Effect of chain stiffness on the competition between crystallization and glass-formation in model unentangled polymers

    NASA Astrophysics Data System (ADS)

    Nguyen, Hong T.; Smith, Tyler B.; Hoy, Robert S.; Karayiannis, Nikos Ch.

    2015-10-01

    We map out the solid-state morphologies formed by model soft-pearl-necklace polymers as a function of chain stiffness, spanning the range from fully flexible to rodlike chains. The ratio of Kuhn length to bead diameter (lK/r0) increases monotonically with increasing bending stiffness kb and yields a one-parameter model that relates chain shape to bulk morphology. In the flexible limit, monomers occupy the sites of close-packed crystallites while chains retain random-walk-like order. In the rodlike limit, nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, the competition between random-walk-like and nematic chain ordering produces glass-formation; the range of kb over which this occurs increases with the thermal cooling rate | T ˙ | implemented in our molecular dynamics simulations. Finally, values of kb between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. Our results should provide a useful initial step in a coarse-grained modeling approach to systematically determining the effect of chain stiffness on the crystallization-vs-glass-formation competition in both synthetic and colloidal polymers.

  11. Defect formation of gamma irradiated MoO3-doped borophosphate glasses

    NASA Astrophysics Data System (ADS)

    Abdelghany, A. M.; Ouis, M. A.; Azooz, M. A.; EllBatal, H. A.

    2013-10-01

    Borophosphate glasses of the basic composition (50P2O5, 30B2O3, 20Na2O mol%) containing different doping molybdenum oxide percents (0.16-0.98) were prepared by melting and annealing method. Infrared and UV-visible absorption spectroscopic measurements before and after gamma irradiation were carried out. The base undoped borophosphate glass reveals strong UV absorption bands but with no visible bands and these UV bands are related to unavoidable trace iron impurities contaminated within the raw materials used for the preparation of this glass. The introduction of MoO3 (in doping ratio) into this glass produces an additional UV band and a broad visible band and their intensities increase with the MoO3 content. These additional bands are related to both Mo6+ and Mo5+ ions. The base undoped borophosphate glass shows retardation effect towards gamma irradiation. Gamma irradiation produces marked changes in the UV-visible spectra of Mosbnd O3-doped glasses. Such changes can be related to the production of induced defects from photochemical reactions and the generation of positive holes. Infrared absorption spectrum of the undoped borophosphate glass reveals complex vibrational bands due to the presence of both phosphate groups beside borate groups with triangular and tetrahedrally coordinated units. The introduction of MoO3 causes some limited variations in the FTIR spectra. Gamma irradiation produces minor changes in the intensities of some IR bands. Such changes are related to the changes in the bond angles and/or bond lengths of few structural groups upon irradiation while the main structural groups remain unchanged in their number and position.

  12. Glass transition and composite formation in InF{sub 3}-containing oxyfluoroniobate system

    SciTech Connect

    Savchenko, N. N.; Ignatieva, L. N.; Marchenko, Yu. V.; Bouznik, V. M.

    2016-05-18

    The glasses in the system MnNbOF{sub 5}-BaF{sub 2}-InF{sub 3} have been firstly synthesized and studied. The thermal parameters of these glasses are analyzed. It was stated that glass of the composition 40MnNbOF{sub 5}-40BaF{sub 2}-20InF{sub 3} is the most thermal stable in the system under study. By X-ray analysis the compositions of the crystalline phases obtained at the glass thermal treatment were determined: the main phases are Ba{sub 3}In{sub 2}F{sub 12} and BaNbOF{sub 5}. By Raman and IR spectra analysis it was stated that the networks of glasses in the system are built by the structural type of the glasses in NbO{sub 2}F-BaF{sub 2} system: (NbO{sub n}F{sub m}) polyhedra joined oxygen bridges. Indium trifluoride forms InF{sub 6} polyhedra, which are embeded between oxyfluoroniobate ions, forming a common networks or forms its own layers from InF{sub 6} polyhedra. IR-spectroscopy method showed that at devitrification of the sample 30MnNbOF{sub 5}-50BaF{sub 2}-20InF{sub 3} the band position and shape change in going from glass state to crystalline. The bands in the range 900–700 cm{sup −1} shift into the low-frequency range and transformed into narrow peaks characteristic for the crystalline state. It was determined that for this sample the IR-spectroscopy method fixes the presence of the crystalline phases at 340°C without time of exposure, despite the fact that X-ray analysis shows an amorphous state for this sample at the same temperature. It was suggested, that controlling the composition and conditions of annealing of the glasses it can be obtain the transparent glass-ceramics of definite composition.

  13. Bioactive glasses with improved processing. Part 1. Thermal properties, ion release and apatite formation.

    PubMed

    Groh, Daniel; Döhler, Franziska; Brauer, Delia S

    2014-10-01

    Bioactive glasses, particularly Bioglass® 45S5, have been used to clinically regenerate human bone since the mid-1980s; however, they show a strong tendency to undergo crystallization upon heat treatment, which limits their range of applications. Attempts at improving their processing (by reducing their tendency to crystallize) have included increasing their silica content (and thus their network connectivity), incorporating intermediate oxides or reducing their phosphate content, all of which reduce glass bioactivity. Therefore, bioactive glasses known for their good processing (e.g. 13-93) are considerably less bioactive. Here, we investigated if the processing of 45S5 bioactive glass can be improved while maintaining its network connectivity and phosphate content. The results show that, by increasing the calcium:alkali cation ratio, partially substituting potassium for sodium (thereby making use of the mixed alkali effect) and adding small amounts of fluoride, bioactive glasses can be obtained which have a larger processing window (suggesting that they can be processed more easily, allowing for sintering of scaffolds or drawing into fibres) while degrading readily and forming apatite in aqueous solution within a few hours.

  14. NEPHELINE FORMATION POTENTIAL IN SLUDGE BATCH 4 AND ITS IMPACT ON DURABILITY: SELECTING GLASSES FOR A PHASE 3 STUDY

    SciTech Connect

    Fox, K

    2006-01-27

    Savannah River National Laboratory's frit development effort for SB4 is being driven by the most current CBU option for this sludge, referred to as Case 15C Blend 1. Candidate frits have been identified for this option via a paper study approach developed by Peeler and Edwards with the intent of down-selecting to a set of key frits whose operating windows (i.e., WL intervals that meet PCCS MAR criteria) are robust to and/or selectively optimal for this sludge option. The primary frits that appear attractive on paper (i.e., down-selected via the paper study) are now being incorporated into this experimental study. The potential for the formation of a nepheline primary crystalline phase is an important factor in frit development for SB4, due to the high Al{sub 2}O{sub 3} content of this sludge. Based upon earlier work by Li et al., glasses that do not satisfy the constraint: (SiO{sub 2}/SiO{sub 2} + Na{sub 2}O + Al{sub 2}O{sub 3}) > 0.62 where the oxides are expressed as mass fractions in the glass, will precipitate nepheline as their primary crystalline phase, hindering the durability of the glass. Based on the most recent compositional projection from the CBU for SB4 (Case 15C Blend 1), 16 glasses have been selected to complement the earlier work by continuing the investigation into the ability of the above constraint to predict the occurrence of a nepheline primary crystalline phase for SB4 glasses and into the impact of such phases on the durability of the SB4 glasses. Glasses were selected to cover WLs which tightly bound the nepheline discriminator value of 0.62, with the intent of refining this value to a level of confidence where it can be incorporated into offline administrative controls and/or the PCCS to support SME acceptability decisions. In addition, glass specimens at WLs of 35 and 40% will be prepared and analyzed to contribute needed data to the ComPro{trademark} database in anticipation of a variability study for SB4. The glasses in Table 4-3 are to

  15. Formation of Al-doped ZnO thin films on glass by sol-gel process and characterization

    NASA Astrophysics Data System (ADS)

    Shahid, M. U.; Deen, K. M.; Ahmad, A.; Akram, M. A.; Aslam, M.; Akhtar, W.

    2016-02-01

    In this study, pure ZnO and Al-doped ZnO thin films were developed on glass by sol-gel process followed by drying and annealing in air at 170 and 400 °C, respectively. The surface morphology and structural characteristics were determined through scanning electron microscopy, atomic force microscopy and X-ray diffraction. The Fourier transform infrared spectroscopy validated the formation of Al-doped ZnO film on glass substrate. It was evaluated that 1 at% aluminum (Al) doping in ZnO film showed low electrical resistivity and higher charge carrier concentration due to uniformly dispersed regular shape crystallites as compared to pure ZnO and 2 at% `Al'-doped thin films.

  16. Formation of metallic nanoislands in the process of electron irradiation of a thin gold film on glass

    NASA Astrophysics Data System (ADS)

    Komissarenko, F. E.; Zhukov, M. V.; Mukhin, I. S.; Golubok, A. O.; Sidorov, A. I.

    2017-02-01

    It has been demonstrated experimentally that the local irradiation of a thin gold film on glass with electrons with an energy of 5 keV led to an increase in the thickness of the irradiated area. When the film was subjected to local irradiation with electrons with an energy of 25 keV, the irradiated region became thinner and a gold ring was formed along the perimeter of this region. At high densities of the electron current, thickened regions of the film assumed the shape of fractal nanostructures. The observed effects were induced by the formation of a negative charge region on the surface of glass (or in the bulk of it) and the migration of positive gold ions into this region.

  17. The central role of broken bond-bending constraints in promoting glass formation in the oxides.

    PubMed

    Zhang, M; Boolchand, P

    1994-11-25

    A glass network of N atoms with n(1) of the atoms with a coordination number of 1, and m(2) of the atoms with a coordination number of 2 about which the bond-angle constraint is broken, will in general display a stiffness threshold (rigidity percolation threshold) when the average coordination increases to a critical value (r)(c) = 2.4 - 0.4 (n(1) - m(2))/N. Silica and sodium tellurate glasses provide model examples for which this general relation predicts the observed rigidity percolation threshold; this relation predicts the percolation threshold only if one includes broken bond-bending constraints due to bridging oxygen in the former network and nonbridging oxygen in the latter network. The rigidity percolation threshold in (Na(2)O)x,(TeO(2))1-x glasses observed to occur near x approximately 0.18 in tellurium-125 Lamb-Mössbauer factor measurments.

  18. Glass formation development and testing for the vitrification of cesium-loaded Crystalline Silicotitanate (CST)

    SciTech Connect

    Andrews, M.K.

    1997-07-01

    As part of a joint project between the Oak Ridge National Laboratory (ORNL) and the Savannah River Technology Center (SRTC), Melton Valley Storage Tank supernate will be passed through a column of crystalline silicotitanate (CST) sorbent at ORNL. The cesium-loaded CST sorbent will subsequently be shipped to the SRTC for vitrification in a joule-heated melter. The CST sorbent contains significant quantities of titanium which historically have been difficult to incorporate into the glass structure. Therefore, crucible studies were performed to develop a glass formulation that could be processed in the SRTC shielded cells melter. Additional tests were conducted to increase the waste loading and optimize the composition. These studies showed that waste loadings up to 60 wt percent CST could be obtained. The results of the crucible melts were used to determine the liquidus temperature, viscosity, and durability of the glass waste form. This paper will present the results of the formulation efforts.

  19. Effect of Etching Condition on the Formation of Bioactive Surface of Hydroxyapatite-Glass-Titanium Composite

    NASA Astrophysics Data System (ADS)

    Ban, Seiji; Maruno, Shigeo; Hasegawa, Jiro

    1991-07-01

    X-ray diffraction study shows that an etching solution of 3% HF and 5% HNO3 is the most suitable solution for preparing a bioactive surface layer of HA-glass-titanium composite, since the glass is removed, a great number of HA particles are exposed, and little CaF2 is produced by the etching. Anodic polarization measurement demonstrates that the 3-min etching gives an electrochemically active surface of the composites. These results and SEM observations suggest that this solution provides an adequate surface of the composite for the dental and medical implants.

  20. Design rules for rational control of polymer glass formation behavior and mechanical properties with small molecular additives

    NASA Astrophysics Data System (ADS)

    Mangalara, Jayachandra Hari; Simmons, David

    Small molecule additives have long been employed to tune polymers' glass formation, mechanical and transport properties. For example, plasticizers are commonly employed to suppress polymer Tg and soften the glassy state, while antiplasticizers, which stiffen the glassy state of a polymer while suppressing its Tg, are employed to enhance protein and tissue preservation in sugar glasses. Recent literature indicates that additives can have a wide range of possible effects, but all of these have not been clearly understood and well appreciated. Here we employ molecular dynamics simulations to establish design rules for the selection of small molecule additives with size, molecular stiffness, and interaction energy chosen to achieve targeted effects on polymer properties. We furthermore find that a given additive's effect on a polymer's Tg can be predicted from its Debye-Waller factor via a function previously found to describe nanoconfinement effects on the glass transition. These results emphasize the potential for a new generation of targeted molecular additives to contribute to more targeted rational design of polymers. We acknowledge the Keck Foundation and the Ohio Supercomputing Center for financial and computational support of this effort, respectively.

  1. Formation of a macro-porous SiO2 layer as an anti-reflective coating on glass substrates.

    PubMed

    Park, No-Kuk; Kim, Yong Sul; Kim, Min Jung; Lee, Tae Jin; Lee, Seung Hyun; Lee, Seung Hun

    2013-11-01

    A macro-porous silica layer, consisting of a silica layer with macro-sized pores, was formed as an antireflective material on glass substrates. The silica layer and macro-pores were formed by the oxidative thermal decomposition of tetra-ethylorthorsilicate (TEOS) used as the precursor and polystyrene (PS) spherical beads used as the polymer template for the macro-pores at high temperatures. The size of pores was determined by the size of PS beads in the antireflective agent solution. The size of the PS spherical beads can be controlled by changing the concentration of styrene monomer, and the porosity of the macro pore in the silica layer could be controlled by the TEOS/PS ratio. The optimal thermal treating temperature for the formation of a macro-porous silica layer was found to be 650 degrees C. The size of the spherical type macro pores formed in the silica layer on the glass substrate was 100-150 nm. UV-Vis spectrophotometry confirmed the improved antireflective properties of the glass substrate with the macro-porous silica layer.

  2. Formation of Fe/mg Smectite Under Acidic Conditions from Synthetic Adirondack Basaltic Glass: an Analog to Fe/mg Smectite Formation on Mars

    NASA Technical Reports Server (NTRS)

    Sutter, B.; Peretyazhko, T.; Morris, R. V.; Ming, D. W.

    2014-01-01

    Smectite has been detected as layered material hundreds of meters thick, in intracrater depositional fans, in plains sediments, and deposits at depth on Mars. If early Mars hosted a dense CO2 atmosphere, then extensive carbonate should have formed in the neutral/alkaline conditions expected for smectite formation. However, large carbonate deposits on Mars have not been discovered. Instead of neutral to moderately alkaline conditions, early Mars may have experienced mildly acidic conditions that allowed for Fe/Mg smectite formation but prevented widespread carbonate formation. The objective of this work is to demonstrate that Fe(II)/Mg saponite and nontronite can form in mildly acidic solutions (e.g., pH 4). Synthetic basaltic glass (< 53 microns) of Adirondack rock class composition was exposed to pH 4 (acetic acid buffer) and N2 purged (anoxic) solutions amended with 0 and 10 mM Mg or Fe(II). Basaltic glass in these solutions was heated to 200 C in batch reactors for 1, 7, and 14 days. X-ray diffraction analysis of reacted materials detected the presence of phyllosilicates as indicated by a approx. 15.03-15.23Angstroms (001) peak. Smectite was confirmed as the phyllosilicate after treatments with glycerol and KCl and heating to 550 C. Trioctahedral saponite was confirmed by the presence of a 4.58 to 4.63 Angstroms (02l) and 1.54Angstroms (060) peaks. Saponite concentration was highest, as indicated by XRD peak intensity, in the 10 mM Mg treatment followed by the 0 mM and then 10 mM Fe(II) treatments. This order of sapontite concentration suggests that Fe(II) additions may have a role in slowing the kinetics of saponite formation relative to the other treatments. Nontronite synthesis was attempted by exposing Adirondack basaltic glass to pH 4 oxic solutions (without N2 purge) at 200 C for 14 days. X-ray diffraction analysis indicated that mixtures of trioctahedral (saponite) and dioctahedral (nontronite) may have formed in these experiments based on the 02l and 060

  3. Formation of Fe/Mg Smectite under acidic conditions from synthetic Adirondack Basaltic Glass: An Analog to Fe/Mg Smectite Formation on Mars.

    NASA Astrophysics Data System (ADS)

    Sutter, B.; Peretyazhko, T.; Morris, R. V.; Ming, D. W.

    2014-12-01

    Smectite has been detected as layered material hundreds of meters thick, in intracrater depositional fans, in plains sediments, and deposits at depth on Mars. If early Mars hosted a dense CO2 atmosphere, then extensive carbonate should have formed in the neutral/alkaline conditions expected for smectite formation. However, large carbonate deposits on Mars have not been discovered. Instead of neutral to moderately alkaline conditions, early Mars may have experienced mildly acidic conditions that allowed for Fe/Mg smectite formation but prevented widespread carbonate formation. The objective of this work is to demonstrate that Fe(II)/Mg-saponite and nontronite can form in mildly acidic solutions (e.g., pH 4). Synthetic basaltic glass (< 53 μm) of Adirondack rock class composition was exposed to pH 4 (acetic acid buffer) and N2 purged (anoxic) solutions amended with 0 and 10 mM Mg or Fe(II). Basaltic glass in these solutions was heated to 200ºC in batch reactors for 1, 7, and 14 days. X-ray diffraction analysis of reacted materials detected the presence of phyllosilicates as indicated by a ~15.03-15.23Ǻ (001) peak. Smectite was confirmed as the phyllosilicate after treatments with glycerol and KCl and heating to 550°C. Trioctahedral saponite was confirmed by the presence of a 4.58 to 4.63 Ǻ (02l) and 1.54Ǻ (060) peaks. Saponite concentration was highest, as indicated by XRD peak intensity, in the 10 mM Mg treatment followed by the 0 mM and then 10 mM Fe(II) treatments. This order of sapontite concentration suggests that Fe(II) additions may have a role in slowing the kinetics of saponite formation relative to the other treatments. Nontronite synthesis was attempted by exposing Adirondack basaltic glass to pH 4 oxic solutions (without N2 purge) at 200ºC for 14 days. X-ray diffraction analysis indicated that mixtures of trioctahedral (saponite) and dioctahedral (nontronite) may have formed in these experiments based on the 02l and 060 peaks. Mössbauer analysis

  4. Effect of Jahn-Teller ion in zinc sodium sulphate hexahydrate: a case of low hyperfine coupling constant for Cu(II) ion

    NASA Astrophysics Data System (ADS)

    Naidu, K. C.; Shiyamala, C.; Mithira, S.; Natarajan, B.; Venkatesan, R.; Rao, P. S.

    2005-06-01

    Single crystal electron paramagnetic resonance (EPR) studies of Cu(II) doped zinc sodium sulphate hexahydrate are carried out from room temperature (RT) to 123 K. The RT spectra show unresolved hyperfine lines and hence angular variation studies are also carried out at 123 K to obtain spin Hamiltonian parameters. The spin Hamiltonian parameters calculated from the 123 K spectra are: g(11)=2.039, g(22)=2.232, g(33)=2.394, A(11)=5.64 mT, A(22)=4.20 mT, and A(33)=7.94 mT. The g-matrix values at RT and 123 K have matched fairly well with each other. The low hyperfine value (A(33)), obtained at 123 K, has been explained by considering considerable admixture of d(x 2-y 2) ground state with d(z 2) excited state and the delocalization of the unpaired spin density onto the ligands. The admixture coefficients of ground state wave function are: a=0.346, b=0.935, c=0.055, d=0.040, e=-0.040, where a and b correspond to admixture coefficients for d(z 2) and d(x 2-y 2), respectively. Angular variation of Cu(II) resonances in the three orthogonal axes shows that the impurity has entered a substitutional site in the host lattice in place of Zn(II). Bonding parameters, kappa=0.295, P=245.4x10(-4), alpha(2)=0.709, alpha=0.8421 and alpha'=0.6034, have also been calculated to fully characterize the EPR.

  5. An unusual stable mononuclear Mn(III) bis-terpyridine complex exhibiting Jahn-Teller compression: electrochemical synthesis, physical characterisation and theoretical study.

    PubMed

    Romain, Sophie; Duboc, Carole; Neese, Frank; Rivière, Eric; Hanton, Lyall R; Blackman, Allan G; Philouze, Christian; Leprêtre, Jean-Claude; Deronzier, Alain; Collomb, Marie-Noëlle

    2009-01-01

    The mononuclear manganese bis-terpyridine complex [Mn(tolyl-terpy)(2)](X)(3) (1(X)(3); X=BF(4), ClO(4), PF(6); tolyl-terpy=4'-(4-methylphenyl)-2,2':6',2"-terpyridine), containing Mn in the unusual +III oxidation state, has been isolated and characterised. The 1(3+) ion is a rare example of a mononuclear Mn(III) complex stabilised solely by neutral N ligands. Complex 1(3+) is obtained by electrochemical oxidation of the corresponding Mn(II) compound 1(2+) in anhydrous acetonitrile. Under these conditions the cyclic voltammogram of 1(2+) exhibits not only the well-known Mn(II)/Mn(III) oxidation at E(1/2)=+0.91 V versus Ag/Ag(+) (+1.21 V vs. SCE) but also a second metal-based oxidation process corresponding to Mn(III)/Mn(IV) at E(1/2)=+1.63 V (+1.93 V vs. SCE). Single crystals of 1(PF(6))(3)2 CH(3)CN were obtained by an electrocrystallisation procedure. X-ray analysis unambiguously revealed its tetragonally compressed octahedral geometry and high-spin character. The electronic properties of 1(3+) were investigated in detail by magnetic measurements and theoretical calculations, from which a D value of +4.82 cm(-1) was precisely determined. Density functional and complete active space self consistent field ab initio calculations both correctly predict a positive sign of D, in agreement with the compressed tetragonal distortion observed in the X-ray structure of 1(PF(6))(3)2 CH(3)CN. The different contributions to D were calculated, and the results show that 1) the spin-orbit coupling part (+2.593 cm(-1)) is predominant compared to the spin-spin interaction (+1.075 cm(-1)) and 2) the excited triplet states make the dominant contribution to the total D value.

  6. Thermochromism, the Alexandrite effect, and dynamic Jahn-Teller distortions in Ho2Cu(TeO3)2(SO4)2.

    PubMed

    Lin, Jian; Diefenbach, Kariem; Cross, Justin N; Babo, Jean-Marie; Albrecht-Schmitt, Thomas E

    2013-11-18

    A 3d-4f heterobimetallic material with mixed anions, Ho2Cu(TeO3)2(SO4)2, has been prepared under hydrothermal conditions. Ho2Cu(TeO3)2(SO4)2 exhibits both thermochromism and the Alexandrite effect. Variable temperature single crystal X-ray diffraction and UV-vis-NIR spectroscopy reveal that changes in the Cu(II) coordination geometry result in negative thermal expansion of axial Cu-O bonds that plays a role in the thermochromic transition of Ho2Cu(TeO3)2(SO4)2. Magnetic studies reveal an effective magnetic moment of 14.97 μB. which has a good agreement with the calculated value of 15.09 μB.

  7. Local and Cooperative Jahn-Teller Effect and Resultant Magnetic Properties of M2AgF4 (M = Na-Cs) Phases.

    PubMed

    Kurzydłowski, Dominik; Jaroń, Tomasz; Ozarowski, Andrew; Hill, Stephen; Jagličić, Zvonko; Filinchuk, Yaroslav; Mazej, Zoran; Grochala, Wojciech

    2016-11-07

    The crystal structure, magnetic properties, heat capacity, and Raman spectra of double-perovskite M2AgF4 (M = K, K3/4Rb1/4, K1/2Rb1/2, K1/4Rb3/4, and Rb) phases have been examined, adding to the body of previous results for the M = Na, Cs derivatives. The results suggest that double-perovskite K2AgF4 adopts a disordered orthorhombic Bmab structure with an antiferrodistortive arrangement of the elongated and tilted [AgF6] octahedra rather than the structure with the ferrodistortive arrangement of compressed octahedra, as suggested previously (Mazej, Z.; Goreshnik, E.; Jagličić, Z.; Gaweł, B.; Łasocha, W.; Grzybowska, D.; Jaroń, T.; Kurzydłowski, D.; Malinowski, P. J.; Koźmiński, W.; Szydłowska, J.; Leszczyński, P. J.; Grochala, W. KAgF3, K2AgF4 and K3Ag2F7: important steps towards a layered antiferromagnetic fluoroargentate(II). CrystEngComm 2009, 11, 1702-1710). A re-examination of the previously collected single-crystal X-ray diffraction data confirms the current structure assignment, and it is also in agreement with recent theoretical calculations. High-field electron paramagnetic resonance spectra reaffirm the presence of elongated [AgF6] octahedra in the crystal structure of all M2AgF4 phases studied. The local structure of the M = K derivative is most complex, with regions of the sample that are quite orthorhombically distorted, whereas other regions more closely resemble the tetragonal phase. The mixed-cation K/Rb phases are also inhomogeneous, containing regions of the pure K compound and regions of another high-symmetry phase (likely tetragonal) of a mixed (Rb-richer) compound with unknown composition. The temperature-resolved phase diagram of all K/Rb phases has been established and positioned within the entire M = Na, K, Rb, Cs series.

  8. Formation of budesonide/α-lactose glass solutions by ball-milling

    NASA Astrophysics Data System (ADS)

    Dudognon, E.; Willart, J. F.; Caron, V.; Capet, F.; Larsson, T.; Descamps, M.

    2006-04-01

    The possibility to obtain amorphous budesonide stabilised by blending with an excipient characterised by a higher glass transition temperature, namely α-lactose, has been studied. We carried out the mixing of the two compounds at room temperature by ball-milling. The four obtained blends (containing, respectively, 10, 30, 50 and 70% w of budesonide) are X-ray amorphous and exhibit a single glass transition located between the ones of pure milled crystalline compounds. This revealed that the two amorphous phases are miscible whatever the composition and sufficiently mixed to relax as a whole. Ball-milling thus appears as a powerful tool to form amorphous molecular alloys with enhanced stability properties.

  9. Formation of silver nanoparticles inside a soda-lime glass matrix in the presence of a high intensity Ar{sup +} laser beam

    SciTech Connect

    Niry, M. D.; Khalesifard, H. R.; Mostafavi-Amjad, J.; Ahangary, A.; Azizian-Kalandaragh, Y.

    2012-02-01

    Formation and motion of the silver nanoparticles inside an ion-exchanged soda-lime glass in the presence of a focused high intensity continuous wave Ar{sup +} laser beam (intensity: 9.2 x 10{sup 4} W/cm{sup 2}) have been studied in here. One-dimensional diffusion equation has been used to model the diffusion of the silver ions into the glass matrix, and a two-dimensional reverse diffusion model has been introduced to explain the motion of the silver clusters and their migration toward the glass surface in the presence of the laser beam. The results of the mentioned models were in agreement with our measurements on thickness of the ion-exchange layer by means of optical microscopy and recorded morphology of the glass surface around the laser beam axis by using a Mirau interferometer. SEM micrographs were used to extract the size distribution of the migrated silver particles over the glass surface.

  10. The Formation of the Second-Order Nonlinearity in Thermally Poled Fused Silica Glass

    DTIC Science & Technology

    2007-11-02

    NONIINEARITY IN THERMALLY POLED FUSED SILICA GLASS 6. AUTHOR(S) THOMAS GUSTAVE ALLEY 5. FUNDING NUMBERS 7. PERFORMING ORGANIZATION NAME(S) AND...ADDRESS(ES) The University of New Mexico 8. PERFORMING ORGANIZATION REPORT NUMBER 98-020D 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES...self- organized , photoinduced, second-order nonlinearity. The most widely accepted explanation attributes the nonlinearity to an asymmetric

  11. Formation and Structure of AL(PO3)3 System Glasses,

    DTIC Science & Technology

    1982-08-06

    only the systems con- taining LiF or MgF2 that formed glass. 3) In the four-component systems that only contained NaF, KF, Ca?2 , SrF2 , or BaF2...a joining effect upon networks. Other single valued and dual valued chemicals such as NaF, KF, CaF2, SrF2 9 and BaF2 , belong to the out- er part of

  12. Origin of an Isothermal R -Martensite Formation in Ni-rich Ti-Ni Solid Solution: Crystallization of Strain Glass

    NASA Astrophysics Data System (ADS)

    Ji, Yuanchao; Wang, Dong; Ding, Xiangdong; Otsuka, Kazuhiro; Ren, Xiaobing

    2015-02-01

    We report that R martensite isothermally forms with time in a solution-treated Ti48.7Ni51.3 single crystal. This abnormal formation originates from the growth of a short-range ordered R phase with time, i.e., the "crystallization" of strain glass. The established time-composition-temperature Ti-Ni diagram shows a time evolution of the R phase and composition-temperature phase diagram. The presence or absence of the R phase in this new diagram, as well as in other conditions (like doping Fe or aging), is explained in a unified framework of free-energy landscape. Our finding suggests a new mechanism for the isothermal martensite formation, which could be applied to other metal and ceramic martensitic systems to find new phases and novel properties.

  13. Formation of luminescent and nonluminescent silver nanoparticles in silicate glasses by near-infrared femtosecond laser pulses and subsequent thermal treatment: the role of halogenides

    NASA Astrophysics Data System (ADS)

    Klyukin, Dmitry A.; Dubrovin, Victor D.; Pshenova, Alisa S.; Putilin, Sergey E.; Shakhverdov, Teimur A.; Tsypkin, Anton N.; Nikonorov, Nikolay V.; Sidorov, Alexander I.

    2016-06-01

    It is shown experimentally that the near-infrared femtosecond laser irradiation and subsequent thermal treatment of silver-containing silicate glasses result in the formation of luminescent silver molecular clusters (MCs) and silver nanoparticles (NPs). In glasses doped also with halides (mostly Br), the nonluminescent silver NPs are formed because of the presence of halogenide shells on their surfaces, whereas, in glasses with no Br ions, the luminescent silver nanoparticles provides an emission in the 600- to 750-nm range. Two possible mechanisms of luminescence of glass with silver NPs are considered: (i) luminescence of silver NPs without halogenide shell and (ii) the luminescence of silver MCs Agm (m=1 to 4) remaining even after the formation of silver NPs.

  14. Calculation of alloying effect on formation enthalpy of TiCu intermetallics from first-principles calculations for designing Ti-Cu-system metallic glasses

    NASA Astrophysics Data System (ADS)

    Shirasawa, Naoya; Takigawa, Yorinobu; Uesugi, Tokuteru; Higashi, Kenji

    2016-01-01

    The effect of alloying on the formation enthalpy of TiCu intermetallics was investigated via first-principles calculations to propose a new design method for Ti-Cu-system metallic glasses. The calculation results showed good agreement with the reported experimental results that Ni, Pd, Sn and Zr improve this system's glass-forming ability. According to the calculation results, a Ti-Zr-Cu-Ga system was designed as a potential new bulk Ti-based metallic glass, and a bulk sample with a 2-mm diameter was fabricated.

  15. Effect of aluminum on the formation of silver metal quantum dots in sol-gel derived alumino-silicate glass film.

    PubMed

    Kim, Bok Hyeon; Son, Dong Hoon; Ju, Seongmin; Jeong, Chaehwan; Boo, Seongjae; Kim, Cheol Jin; Hanl, Won-Taek

    2006-11-01

    The effect of aluminum incorporation on silver metal quantum dots formation in the alumino-silicate glass film processed by sol-gel process was investigated. The sol-gel derived glass was coated onto the silica glass plate by spin coating with the mixture solution of tetraethyl orthosilicate (TEOS), C2H5OH, H2O, AgNO3, Al(NO3)3. 39H2O, and HNO3 with the molar ratios of Ag/Si = 0.12 and Al/Si varying from 0 to 0.12. The formation of the silver metal quantum dots was confirmed by the measurements of the UV/VIS optical spectra, the X-ray diffraction patterns, and the transmission electron microscope images. While the radius of silver metal quantum dots increased with the increase of aluminum concentration, the concentration of the silver metal quantum dots decreased. The formation of the silver metal quantum dots was found strongly suppressed by incorporation of aluminum ions in the glass. The change in the glass structure due to the aluminum incorporation was investigated by the analysis of the Raman spectra. The silver ions in the glass contributed to form stable (Al:Ag)O4 tetrahedra by pairing with aluminum ions and thus clustering of silver metal quantum dots was hindered.

  16. The peculiarity of the formation of zinc films on a glass substrate

    SciTech Connect

    Tomaev, V. V.; Polishchuk, V. A.; Borisov, E. N.

    2016-06-17

    Thin Nanocrystalline films of the zinc have been fabricated by thermal spraying on the glass substrate. Morphologies and structure of the films had been investigated by the methods X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). It is found that the surface of the films has a different types of the nanocrystals zinc. Were detected intergrowths of two or more the nanocrystals, hexagonal shape. Using the theory of homogeneous and heterogeneous nucleation of a new phase, had been evaluated the geometrical and thermodynamic parameters nanocrystals zinc.

  17. Short-pulse laser formation of monatomic metallic glass in tantalum nanowire

    NASA Astrophysics Data System (ADS)

    Gan, Yong; Sun, Zheng; Shen, Yaogen

    2017-01-01

    The short-pulse laser heating of a tantalum nanowire is simulated by a hybrid method coupling the two-temperature model into the molecular dynamics. It is shown that the monatomic metallic glasses can be formed by short-pulse lasers. The critical cooling rate for vitrifying the pure metallic liquids in tantalum nanowire is estimated to be on the order of 1013 K s-1. Further simulations with different laser parameters and heated spot size are performed, demonstrating that the short-pulse laser quenching is a robust and promising alternative to the vitrification of monatomic metallic liquids into glassy state.

  18. The formation of frangipane horizons and their influence on physical-chemical properties of soils from glass houses

    NASA Astrophysics Data System (ADS)

    Filipov, F.; Bulgariu, D.; Avarvarei, I.

    2009-04-01

    The pedological, mineralogical and geochemical studies performed by as on soils (s.s hortic antrosols) from Iasi (Copou glass house), Barlad and Bacau glass houses have show that, in most of cases, the profile of hortic antrosols have the following compositions: Aho-AC-C or Ck, and Aho-B/C or Ck, respectively. In function of parental material nature and specific exploitation technologies, can appear the diagnostic horizons of association (hiposalic-sc, hiponatric-ac etc.) and / or of transition (A/B, A/C, C/A, A+C, ABk etc.). Specific for soils from glass houses are intense modifications of soil profile, large variability of mineralogy and chemistry, salinization processes (by progressive accumulation of soluble salts) at superior horizons level and formation, at 50 cm depth, of a compact and impermeable horizon (frangipane horizon). From chemical point of view, the hortic antrosols are generally characterized by high values of saturation in bases, of accessible phosphorus and of ratio between humic and fulvic acids (organic matter is dominant in intense humified fraction). Regarding the formation conditions, the mineralogy and geochemistry of frangipane horizons, in this moment, in literature are not too many data. In case of studied soils, the frangipane horizons appear in specific forms, where their structure, morphology and chemistry varied in large limits. In hortic antrosols where are formed, the frangipane horizons determined a sever pedogeochemical segregation. Thus, the horizons situated above to the frangipane horizon evolutes in weak oxidant conditions, weak acid-neutral pH (5.87 - 6.95), high salinity and humidity, intense biological activity; while the horizons situated below to the frangipane horizon evolutes in weak reduction conditions, neutral - weak alkaline pH (7.61 - 8.04), reduced salinity and humidity, weak biological activity. This determined an important differentiation of micro-elements and organic compounds dynamic, evidenced by the

  19. Composition-dependent stability of the medium-range order responsible for metallic glass formation

    DOE PAGES

    Zhang, Feng; Ji, Min; Fang, Xiao-Wei; ...

    2014-09-18

    The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. Furthermore, we focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. These results show that a Bergman-type motifmore » with crystallization-resisting icosahedral symmetry is energetically most favorable in the composition range 0.63 < xCu < 0.68, and is the underlying motif for one of the three optimal glass-forming ranges observed experimentally for this binary system (Li et al., 2008). This work establishes an energy-based methodology to evaluate specific medium-range structural motifs which compete with stable crystalline nuclei in deeply undercooled liquids.« less

  20. Composition-dependent stability of the medium-range order responsible for metallic glass formation

    SciTech Connect

    Zhang, Feng; Ji, Min; Fang, Xiao-Wei; Sun, Yang; Wang, Cai-Zhuang; Mendelev, Mikhail I.; Kramer, M. J.; Napolitano, Ralph E.; Ho, Kai-Ming

    2014-09-18

    The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. Furthermore, we focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. These results show that a Bergman-type motif with crystallization-resisting icosahedral symmetry is energetically most favorable in the composition range 0.63 < xCu < 0.68, and is the underlying motif for one of the three optimal glass-forming ranges observed experimentally for this binary system (Li et al., 2008). This work establishes an energy-based methodology to evaluate specific medium-range structural motifs which compete with stable crystalline nuclei in deeply undercooled liquids.

  1. Formation of hollow microcylinders from sputtered erbium-doped glass films

    NASA Astrophysics Data System (ADS)

    Krishnaswamy, Madhu; McMullin, James N.; Keyworth, B. P.; Broughton, James N.

    1997-05-01

    A planar sputter-deposited erbium-doped glass ridge was re- shaped into a hollow microcylinder using only photolithography, wet-etching and annealing. It is believed that selective build-up of gas is primarily responsible for this phenomenon, which is similar to glass-blowing. Other factors, such as the width and depth of the original ridge, the adhesion of the ridge to the underlying surface and the duration of the anneal, influence the eventual shape of the hollow microcylinder. By varying the processing parameters, a wide range of microcylinder shapes and sizes were obtained: circular and semi-circular profiles with 9.0 micrometers diameter or flatter 'tunnel-shaped' profiles ranging u pt o 25 micrometers in height and 100 micrometers in width. Microcylinders up to 1 cm long were fabricated. Water was sen to enter these hollow devices through capillary action. He-Ne light propagation through the hollow portion of the device was observed. These observations confirm that the microcylinders are hollow over their entire length. Hollow microcylinders or microchannels may find application in microfluidics and micro-optics.

  2. Specific heat of hydrated lysozyme, water's contribution to its dynamics, and criteria for glass formation of biomaterials

    NASA Astrophysics Data System (ADS)

    Tombari, Elpidio; Johari, G. P.

    2013-09-01

    Previous studies of the dynamics of hydrated proteins had shown a feature resembling an exceptionally broad glass-softening endotherm. Its onset temperature, denoted as Tg, was indefinable in one calorimetric study of hydrated lysozyme and was in the 148-218 K range in another study, depending upon hydration. Other methods reported this Tg as ˜170 K. We argue that glass-formation of biomaterials should be studied by measuring a property on both the cooling and heating paths and it should be ascertained (i) that there is thermal hysteresis of the measured property, (ii) that the real and imaginary components of a dynamic property obey the Kramers-Kronig relations, and (iii) that there is an effect of annealing that is consistent with the glass phenomenology. We report the real and imaginary components of the dynamic specific heat, Cp' and Cp″, of dry and two hydrated lysozyme samples on the cooling and the heating paths as well as the effects of annealing and changing the frequency. For the most hydrated (34.6 g water per 100 g lysozyme) sample, Cp,app does not show thermal hysteresis in the 160-230 K range, Cp' varies in a sigmoid-shape manner with T while Cp″ remains close to zero, and there is no effect of annealing. We interpret these findings in terms of continuous development of ice-like aggregates of immobile H2O as more H-bonds form on cooling, and continuous deterioration of the aggregates on heating. As the equilibrium constant between the aggregates and mobile H2O increases on cooling, configurational degrees of freedom of H2O molecules and lysozyme segments decrease. Consequently, the net change in enthalpy is small but the change in Cp is large. Mobility of the lysozyme segments still depends upon the mobility of H2O molecules.

  3. Specific heat of hydrated lysozyme, water's contribution to its dynamics, and criteria for glass formation of biomaterials.

    PubMed

    Tombari, Elpidio; Johari, G P

    2013-09-14

    Previous studies of the dynamics of hydrated proteins had shown a feature resembling an exceptionally broad glass-softening endotherm. Its onset temperature, denoted as T(g), was indefinable in one calorimetric study of hydrated lysozyme and was in the 148-218 K range in another study, depending upon hydration. Other methods reported this T(g) as ~170 K. We argue that glass-formation of biomaterials should be studied by measuring a property on both the cooling and heating paths and it should be ascertained (i) that there is thermal hysteresis of the measured property, (ii) that the real and imaginary components of a dynamic property obey the Kramers-Kronig relations, and (iii) that there is an effect of annealing that is consistent with the glass phenomenology. We report the real and imaginary components of the dynamic specific heat, C(p)' and C(p)", of dry and two hydrated lysozyme samples on the cooling and the heating paths as well as the effects of annealing and changing the frequency. For the most hydrated (34.6 g water per 100 g lysozyme) sample, C(p,app) does not show thermal hysteresis in the 160-230 K range, C(p)' varies in a sigmoid-shape manner with T while C(p)" remains close to zero, and there is no effect of annealing. We interpret these findings in terms of continuous development of ice-like aggregates of immobile H2O as more H-bonds form on cooling, and continuous deterioration of the aggregates on heating. As the equilibrium constant between the aggregates and mobile H2O increases on cooling, configurational degrees of freedom of H2O molecules and lysozyme segments decrease. Consequently, the net change in enthalpy is small but the change in C(p) is large. Mobility of the lysozyme segments still depends upon the mobility of H2O molecules.

  4. Glass Formation in Simulated High-Density Al2O3·2SiO2

    NASA Astrophysics Data System (ADS)

    Hoang, Vo Van

    Glass formation in octahedral phase of Al2O3·2SiO2 has been investigated via Molecular Dynamics (MD) simulation in a model containing 3025 atoms with the Born-Mayer type pair potentials under periodic boundary conditions. The system has been cooled from 7000 K to 350 K at a cooling rate γ = 4.375×1013 K/s and at a fixed density of 4.00 g/cm3 corresponding to the octahedral network structure phase of the system. Glass transition temperature Tg has been obtained via temperature dependence of the system potential energy. Evolution of structure upon cooling from the melt has been found and discussed. Structural properties of an amorphous model obtained at the temperature of 350 K have been analyzed in detail through the partial radial distribution functions (PRDF), coordination number distributions, bond-angle distributions and interatomic distances, compared with those for the model at the same temperature and density obtained by compression of the initial 2.60 g/cm3 amorphous one. The local environment of oxygen and the problem of triclusters in high-density phase has been calculated and discussed.

  5. Bulk formation of a metallic glass - Pd40Ni40P20

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Greer, A. L.; Turnbull, D.

    1982-01-01

    Molten spheroids of Pd40Ni40P20, of up to 0.53-cm minor diameter, were slowly cooled (1.4 K/s) on a fused silica surface under 10 to the -6 torr vacuum to a form which was entirely glassy except for some superficial crystallinity comprising less than 0.5% of the volume. The occurrence of crystallization was eliminated by subjecting the specimens to surface etching followed by a succession of heating and cooling cycles. The absence of crystallization in bulk was confirmed by X-ray diffraction, transmission electron microscopy, and calorimetry. Using the last technique, the heat of crystallization of the glass was measured to be 5.3 + or - 0.3 kJ/g atom.

  6. Dynamical arrest, percolation, gelation, and glass formation in model nanoparticle dispersions with thermoreversible adhesive interactions.

    PubMed

    Eberle, Aaron P R; Castañeda-Priego, Ramón; Kim, Jung M; Wagner, Norman J

    2012-01-24

    We report an experimental study of the dynamical arrest transition for a model system consisting of octadecyl coated silica suspended in n-tetradecane from dilute to concentrated conditions spanning the state diagram. The dispersion's interparticle potential is tuned by temperature affecting the brush conformation leading to a thermoreversible model system. The critical temperature for dynamical arrest, T*, is determined as a function of dispersion volume fraction by small-amplitude dynamic oscillatory shear rheology. We corroborate this transition temperature by measuring a power-law decay of the autocorrelation function and a loss of ergodicity via fiber-optic quasi-elastic light scattering. The structure at T* is measured using small-angle neutron scattering. The scattering intensity is fit to extract the interparticle pair-potential using the Ornstein-Zernike equation with the Percus-Yevick closure approximation, assuming a square-well interaction potential with a short-range interaction (1% of particle diameter). (1) The strength of attraction is characterized using the Baxter temperature (2) and mapped onto the adhesive hard sphere state diagram. The experiments show a continuous dynamical arrest transition line that follows the predicted dynamical percolation line until ϕ ≈ 0.41 where it subtends the predictions toward the mode coupling theory attractive-driven glass line. An alternative analysis of the phase transition through the reduced second virial coefficient B(2)* shows a change in the functional dependence of B(2)* on particle concentration around ϕ ≈ 0.36. We propose this signifies the location of a gel-to-glass transition. The results presented herein differ from those observed for depletion flocculated dispersion of micrometer-sized particles in polymer solutions, where dynamical arrest is a consequence of multicomponent phase separation, suggesting dynamical arrest is sensitive to the physical mechanism of attraction.

  7. Mono and sequential ion irradiation induced damage formation and damage recovery in oxide glasses: Stopping power dependence of the mechanical properties

    NASA Astrophysics Data System (ADS)

    Mir, A. H.; Monnet, I.; Toulemonde, M.; Bouffard, S.; Jegou, C.; Peuget, S.

    2016-02-01

    Simple and complex borosilicate glasses were irradiated with single and double ion beams of light and heavy ions over a broad fluence and stopping power range. As a result of the heavy ion irradiation (U, Kr, Au), the hardness was observed to diminish and saturate after a decrease by 35 ± 1%. Unlike slow and swift heavy ion irradiation, irradiation with light ions (He,O) induced a saturation hardness decrease of 18 ± 1% only. During double ion beam irradiation; where glasses were first irradiated with a heavy ion (gold) and then by a light ion (helium), the light ion irradiation induced partial damage recovery. As a consequence of the recovery effect, the hardness of the pre-irradiated glasses increased by 10-15% depending on the chemical composition. These results highlight that the nuclear energy loss and high electronic energy loss (≥4 keV/nm) result in significant and similar modifications whereas light ions with low electronic energy loss (≤1 keV/nm) result in only mild damage formation in virgin glasses and recovery in highly pre-damaged glasses. These results are important to understand the damage formation and recovery in actinide bearing minerals and in glasses subjected to self-irradiation by alpha decays.

  8. Effect of geometrical constraint condition on the formation of nanoscale twins in the Ni-based metallic glass composite

    SciTech Connect

    Lee, M H; Kim, B S; Kim, D H; Ott, R T; Sansoz, F; Eckert, J

    2014-04-25

    We investigated the effect of geometrically constrained stress-strain conditions on the formation of nanotwins in alpha-brass phase reinforced Ni59Zr20Ti16Si2Sn3 metallic glass (MG) matrix deformed under macroscopic uniaxial compression. The specific geometrically constrained conditions in the samples lead to a deviation from a simple uniaxial state to a multi-axial stress state, for which nanocrystallization in the MG matrix together with nanoscale twinning of the brass reinforcement is observed in localized regions during plastic flow. The nanocrystals in the MG matrix and the appearance of the twinned structure in the reinforcements indicate that the strain energy is highly confined and the local stress reaches a very high level upon yielding. Both the effective distribution of reinforcements on the strain enhancement of composite and the effects of the complicated stress states on the development of nanotwins in the second-phase brass particles are discussed.

  9. The evaluation of Candida albicans biofilms formation on silicone catheter, PVC and glass coated with titanium dioxide nanoparticles by XTT method and ATPase assay.

    PubMed

    Haghighi, F; Mohammadi, Sh R; Mohammadi, P; Eskandari, M; Hosseinkhani, S

    2012-01-01

    Lots of Candida albicans infections involve in biofilm formation on medical devices. This kind of biofilm can impede antifungal therapy and complicates the treatment of infectious diseases particularly in field of chronic diseases associated with implanted devices. This study has investigated the influence of treating silicone catheter, PVC and glass coated with Titanium dioxide (TiO2) nanoparticles on attachment of C. albicans. In this study TiO2 nanoparticles were synthesized from precursor TiCl4 and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) which showed TiO2 nanoparticles are 70-100 nm in size. In the simplest model of biofilms formation, C. albicans isolates (ATCC10231) and (ATCC 76615) were grown on the surface of small disks of catheter, PVC and glass in a flat-bottomed 12-well plates and evaluated biofilm formation using ATP bioluminescence and tetrazolium salt (XTT) reduction assays. In addition, morphology of C. albicans biofilms after 48 h incubation was observed by SEM. Results indicated that there is a statistical difference between mean of coated samples especially catheter and glass before and after TiO2 nanoparticles coating (p<0.05). In SEM analysis, C. albicans biofilm was more aggregated on the surface of glass and catheter than PVC and control groups and after treatment by these nanoparticles, catheter and glass both showed most significant decrease of C. albicans attachment in comparison to the control groups (Fig. 4, Ref. 23).

  10. Can alteration experiments on impact melts from El'gygytgyn and volcanic glasses shed new light on the formation of the Martian surface?

    NASA Astrophysics Data System (ADS)

    Hellevang, Helge; Dypvik, Henning; Kalleson, Elin; Pittarello, Lidia; Koeberl, Christian

    2013-07-01

    This investigation involved three specimens: an altered felsic sample of impactite from the ICDP El'gygytgyn drill core D1c, and two reference volcanics from Iceland, namely a rhyolitic glass and a basaltic glass. The goal of this work was to better understand the alteration of impact melt and volcanic glass, and to apply the results to an investigation of alteration processes below the surface of Mars. Hydrothermal batch alteration experiments with the El'gygytgyn sample showed formation of various silica phases such as cristobalite, opal, and quartz. According to geochemical modeling, zeolites were also expected, but zeolite minerals already present in the impactite prior to the experiment may have masked possible experimental zeolite growth. Basaltic glass was altered to smectite, talc, and opal. The accompanying numerical modeling gave results that were similar or comparable to the laboratory experiments. Rhyolitic glass was kinetically more stable than basaltic glass, and showed only minor formation of calcite and feldspar during the 3-week experiment. The study showed that closed-system isochemical alteration of both siliceous and mafic glasses and melts results in the formation of smectites and zeolites. Therefore, to link alteration features on Mars to specific physical conditions, the exact identity of the mineral phases present in surface rocks must be known. Moreover, our simulations on closed-system isochemical alteration showed that the fraction of zeolites and silica formed relative to smectite depends on the source mineral altered. Therefore, fractions of these mineral groups present in the Martian soil may be used to better predict source rock characteristics.

  11. Formation of nanostructures at the glass-carbon surface exposed to laser radiation

    SciTech Connect

    Abramov, D V; Gerke, M N; Kucherik, A O; Kutrovskaya, S V; Prokoshev, V G; Arakelyan, S M

    2007-11-30

    An experimental technique for obtaining nanostructures in the field of high-power laser radiation at the surface of carbon materials is developed. A specific feature of this technique is the formation of liquid carbon inside the region of laser action in the sample exposed to radiation in air at a pressure of {approx}1 atm. Several types of nanostructures (quasi-domains and nanopeaks) are detected in the laser cavern and beyond the range of laser action. Mechanisms of formation of such structures are proposed. The formation of quasi-domains is related to crystallisation of the melt. The nanopeak groups are formed outside the laser action region during the deposition of hot vapours of the material escaping from this region. The dependences of the variation in morphological properties of the nanostructures on the duration of laser action and the radii of typical cavern zones on the laser radiation power are obtained. (interaction of laser radiation with matter. laser plasma)

  12. Formation and characterization of hydrophobic glass surface treated by atmospheric pressure He/CH4 plasma

    NASA Astrophysics Data System (ADS)

    Noh, Sooryun; Youn Moon, Se

    2014-01-01

    Atmospheric pressure helium plasmas, generated in the open air by 13.56 MHz rf power, were applied for the glass surface wettability modification. The plasma gas temperature, measured by the spectroscopic method, was under 400 K which is low enough to treat the samples without thermal damages. The hydrophobicity of the samples determined by the water droplet contact angle method was dependent on the methane gas content and the plasma exposure time. Adding the methane gas by a small amount of 0.25%, the contact angle was remarkably increased from 10° to 83° after the 10 s plasma treatment. From the analysis of the treated surface and the plasma, it was shown that the deposition of alkane functional groups such as C-H stretch, CH2 bend, and CH3 bend was one of the contributing factors for the hydrophobicity development. In addition, the hydrophobic properties lasted over 2 months even after the single treatment. From the results, the atmospheric pressure plasma treatment promises the fast and low-cost method for the thermally-weak surface modification.

  13. Glass Formation and Primary Solidification in Nd2Fe14B with TiC Additions

    NASA Astrophysics Data System (ADS)

    McCallum, R. W.; Willard, M. A.; Dennis, K. W.; Kramer, M. J.; Branagan, D. J.

    1996-03-01

    In bulk permanent magnets, the extrinsic properties relating to the microstructure determine the level of hard magnetic properties that is actually achieved. Alloy additions which affect the solidification behavior of the melt and then form precipitates which pin grain boundaries and therefor control grain size should be valuable in producing the uniform microstructure required for good magnetic properties. The addition of TiC to 2-14-1 results in a factor of three reduction of the quench rate required to produce amorphous material. In addition, the crystallization temperature of the glass is enhanced leading to enhanced nucleation and finer grain size during crystallization. Given the affect of TiC additions to the stochiometric melt, it is not surprising that the additions affect the range of primary solidification of the 2-14-1 phase. When TiC is added to the limit of liquid solubility, the limit 2-14-1 primary solidification is move farther from the stochiometric composition in the Nd rich region. Work at the Ames Laboratory, was supported by the U. S. Department of Energy under contract No. W-7405-ENG-82.

  14. Thermodynamic prediction of glass formation tendency, cluster-in-jellium model for metallic glasses, ab initio tight-binding calculations, and new density functional theory development for systems with strong electron correlation

    SciTech Connect

    Yao, Yongxin

    2009-01-01

    Solidification of liquid is a very rich and complicated field, although there is always a famous homogeneous nucleation theory in a standard physics or materials science text book. Depending on the material and processing condition, liquid may solidify to single crystalline, polycrystalline with different texture, quasi-crystalline, amorphous solid or glass (Glass is a kind of amorphous solid in general, which has short-range and medium-range order). Traditional oxide glass may easily be formed since the covalent directional bonded network is apt to be disturbed. In other words, the energy landcape of the oxide glass is so complicated that system need extremely long time to explore the whole configuration space. On the other hand, metallic liquid usually crystalize upon cooling because of the metallic bonding nature. However, Klement et.al., (1960) reported that Au-Si liquid underwent an amorphous or “glassy” phase transformation with rapid quenching. In recent two decades, bulk metallic glasses have also been found in several multicomponent alloys[Inoue et al., (2002)]. Both thermodynamic factors (e.g., free energy of various competitive phase, interfacial free energy, free energy of local clusters, etc.) and kinetic factors (e.g., long range mass transport, local atomic position rearrangement, etc.) play important roles in the metallic glass formation process. Metallic glass is fundamentally different from nanocrystalline alloys. Metallic glasses have to undergo a nucleation process upon heating in order to crystallize. Thus the short-range and medium-range order of metallic glasses have to be completely different from crystal. Hence a method to calculate the energetics of different local clusters in the undercooled liquid or glasses become important to set up a statistic model to describe metalllic glass formation. Scattering techniques like x-ray and neutron have widely been used to study the structues of metallic glasses. Meanwhile, computer simulation

  15. Formation and spectral probing of transparent oxyfluoride glass-ceramics containing (Eu2+, Eu3+:BaGdF5) nano-crystals

    NASA Astrophysics Data System (ADS)

    Biswas, Kaushik; Balaji, S.; Karmakar, Prantik; Annapurna, K.

    2015-01-01

    In the present study, we report the formation of transparent glass-ceramics containing BaGdF5 nanocrystals under optimum ceramization of SiO2-BaF2-K2O-Sb2O3-GdF3-Eu2O3 based oxyfluoride glass and the energy transfer mechanisms in Eu2+ → Eu3+ and Gd3+ → Eu3+ has been interpreted through luminescence study. The modification of local environment surrounding dopant ion in glass and glass ceramics has been studied using Eu3+ ion as spectral probe. The optimum ceramization temperature was determined from the differential scanning calorimetry (DSC) thermogram which revealed that the glass transition temperature (Tg), the crystallization onset temperature (Tx), and crystallization peak temperature (Tp) are 563 °C, 607 °C and 641 °C, respectively. X-ray diffraction pattern of the glass-ceramics sample displayed the presence of cubic BaGdF5 phase (JCPDS code: 24-0098). Transmission electron microscopy image of the glass-ceramics samples revealed homogeneous distribution of spherical fluoride nanocrystals ranging 5-15 nm in size. The emission transitions from the higher excited sates (5DJ, J = 1, 2, and 3) as well as lowered asymmetry ratio of the 5D0 → 7F2 transition (forced electric dipole transition) to that of the 5D0 → 7F1 transition (magnetic dipole) of Eu3+ in the glass-ceramics when compared to glass sample demonstrated the incorporation of dopant Eu3+ ions into the cubic BaGdF5 nanocrystals with higher local symmetry with enhanced ionic nature. The presence of absorption bands of Eu2+ ions and Gd3+ ions present in the glass matrix or fluoride nanocrystals in the excitation spectra of Eu3+ by monitoring emission at 614 nm indicated energy transfer from (Eu2+ → Eu3+) and (Gd3+ → Eu3+) in both glass and glass-ceramics samples.

  16. Multispectroscopic methodology to study Libyan desert glass and its formation conditions.

    PubMed

    Gomez-Nubla, Leticia; Aramendia, Julene; Fdez-Ortiz de Vallejuelo, Silvia; Alonso-Olazabal, Ainhoa; Castro, Kepa; Zuluaga, Maria Cruz; Ortega, Luis Ángel; Murelaga, Xabier; Madariaga, Juan Manuel

    2017-03-27

    Libyan desert glass (LDG) is a melt product whose origin is still a matter of controversy. With the purpose of adding new information about this enigma, the present paper analyzes the inner part of LDG specimens and compares them with the results of LDG surfaces. An integrated analytical methodology was used combining different techniques such as Raman spectroscopy, in point-by-point and imaging modes, scanning electron microscopy with X-ray microanalysis (SEM-EDS), energy-dispersive micro X-ray fluorescence spectrometry (μ-EDXRF), electron probe micro analyzer (EPMA), and optical cathodoluminescence (Optical-CL). According to our results, flow structures of the melt and the amorphous nature of the matrix could be discerned. Moreover, the observed displacement of Raman bands, such as in the cases of quartz and zircon, and the identification of certain compounds such as coesite (the most clarifying phase of high pressures), α-cristobalite, gypsum, anhydrite, corundum, rutile, amorphous calcite, aragonite, and calcite allowed us to know that LDGs could be subjected to shock pressures between 6 and more than 30 GPa, and temperatures between 300 and 1470 °C. The differences of temperature and pressure would be provoked by different cooling processes during the impact. Besides, in most cases the minerals corresponding to high pressure and temperatures were located in the inner part of the LDGs, with some exceptions that could be explained because they were trapped subsequently to the impact; there was more than one impact or heterogeneous cooling.Furthermore, nitrogen and oxygen gases were identified inside bubbles, which could have been introduced from the terrestrial atmosphere during the meteorite impact.These data helped us to clarify some clues about the origin of these enigmatic samples.

  17. The role of superheating in the formation of Glass Mountain obsidians (Long Valley, CA) inferred through crystallization of sanidine

    NASA Astrophysics Data System (ADS)

    Waters, Laura E.; Andrews, Benjamin J.

    2016-10-01

    The Glass Mountain obsidians (Long Valley, CA) are crystal poor (<8 vol%) and highly evolved (high SiO2, low Sr), and therefore, their formation required extremely efficient separation of melts from a crystal-rich source. A petrologic and experimental investigation of the mineral phases in Glass Mountain lavas identifies conditions under which phenocrysts grew and the driving mechanism for crystallization, which places constraints on the possible processes that generated the obsidians. The obsidian in this study (GM-11) is saturated in nine phases (sanidine + quartz + plagioclase + titanomagnetite + ilmenite + zircon + apatite + allanite + biotite), and results of high-resolution SEM compositional mapping and electron microprobe analysis reveal that individual sanidine crystals are normally zoned and span a range of compositions (Or40-78). Sanidines have a "granophyric" texture, characterized by intergrowths of quartz and sanidine. Mineral phases in the natural sample are compared to H2O-saturated phase equilibrium experiments conducted in cold-seal pressure vessels, over a range of conditions (700-850 °C; 75-225 MPa), and all are found to be plausible phenocrysts. Comparison of sanidine compositions from the natural sample with those grown in phase equilibrium experiments demonstrates that sanidine in the natural sample occurs in a reduced abundance. Further comparison with phase equilibrium experiments suggests that sanidine compositions track progressive loss of dissolved melt water (±cooling), suggesting that crystallization in the natural obsidian was driven predominantly by degassing resulting from decompression. It is paradoxical that an effusively (slowly) erupted lava should contain multiple phenocryst phases, including sanidine crystals that span a range of compositions with granophyric textures, and yet remain so crystal poor. To resolve this paradox, it is necessary that the solidification mechanism (degassing or cooling) that produced the sanidine

  18. Effects of Al2O3, B2O3, Na2O, andSiO(2) on nepheline formation in borosilicate glasses: chemical and physical correlations

    SciTech Connect

    Li, Hong; Hrma, Pavel R.; Vienna, John D.; Qian, Maoxu; Su, Yali; Smith, Donald E.

    2003-12-01

    Raman spectroscopic technique was applied to study complex borosilicate glasses to elucidate Al2O3, B2O3, Na2O, and SiO2 effects on the network structure evolution with an emphasis on the nepheline formation tendency in the glasses. An origin of the observed Raman band near 850 cm-1 in the quenched glass samples was elucidated by studying the quenched and slowly cooled samples using a variety of spectroscopic methods. The results suggested that the characteristic Raman band near 850 cm-1 was closely related to the nepheline-like nanocrystals formed in the quenched glass samples. Composition models for both the characteristic Raman band intensity and liquidus were developed. The two models provide a consistent outcome that increase in B2O3 and SiO2 decreases the Raman band intensity, or nepheline formation tendency, and liquidus, whereas increase Al2O3 and Na2O increases the Raman band intensity, or nepheline formation tendency, and liquidus temperture.

  19. Properties of glass, oil's formation...how to explain it? The secret is to amaze!

    NASA Astrophysics Data System (ADS)

    Merlino, Silvia; Evangelista, Rosaria; Bianucci, Marco; Mantovani, Carlo; Gambarelli, Licia

    2013-04-01

    The design and testing of numerous routes for teaching and dissemination of topics in physics, biology, geology and energy is born from a collaboration between teachers and researchers that lasted for many years in Parma, Italy. These projects are implemented by the association "Parma Casa della Scienza", which promotes the dissemination of scientific culture in schools and among the public. The main purpose of the association is to create a science center in Parma, offering also training opportunities on techniques for teaching science. The funds for the projects come from European competitions and Cariparma Foundation. Currently the association is proposing laboratory activities, with the widespread diffusion of 20 educational programs, included in school curricula. The approach is informal and aims at the stimulation of curiosity and surprise. Students who participate arise so spontaneously in an attitude of research - action, working directly on the phenomena under study. This avoids the clichés of standard passive listening. Our work is a constant search for ideas, ways and means to demonstrate, for the purposes of school education, how useful is the game and the interaction with the phenomena, many of which are usually only seen in books and not lived with awareness. Two in particular are the educational proposals that we would like to present , relating to content of great importance that are rarely addressed in the context of schooling completed First Path: explains the physico-chemical properties and structural properties of glassy materials; enters the details of the molecular structure of "amorphous solid" contrasting it with that of crystalline solid; llustrates the process of formation; gives reason for its peculiar properties from which derive extreme flexibility of working and the many optical properties. This is achieved through the actual processing of a fluid "pseudo glassy" realized at low temperatures, which simulates the processes described

  20. Mechanism of Phase Formation in the Batch Mixtures for Slag-Bearing Glass Ceramics - 12207

    SciTech Connect

    Stefanovsky, Sergey V.; Stefanovsky, Olga I.; Malinina, Galina A.

    2012-07-01

    Slag surrogate was produced from chemicals by heating to 900 deg. C and keeping at this temperature for 1 hr. The product obtained was intermixed with either sodium di-silicate (75 wt.% waste loading) or borax (85 wt.% slag loading). The mixtures were heat-treated within a temperature range of 25 to 1300 deg. C. The products were examined by X-ray diffraction and infrared spectroscopy. The products prepared at temperatures of up to 1000 deg. C contained both phase typical of the source slag and intermediate phases as well as phases typical of the materials melted at 1350 deg. C such as nepheline, britholite, magnetite and matrix vitreous phase. Vitrification process in batch mixtures consisting of slag surrogate and either sodium di-silicate or sodium tetraborate runs through formation of intermediate phases mainly silico-phosphates capable to incorporate Sm as trivalent actinides surrogate. Reactions in the batch mixtures are in the whole completed by ∼1000 deg. C but higher temperatures are required to homogenize the products. If in the borate-based system the mechanism is close to simple dissolution of slag constituents in the low viscous borate melt, then in the silicate-based system the mechanism was found to be much complicated and includes re-crystallization during melting with segregation of newly-formed nepheline type phase. (authors)

  1. Spin Glass Freezing and Ferromagnetic Cluster Formation in LiNiO_2

    NASA Astrophysics Data System (ADS)

    van Duijn, Joost; Gaulin, Bruce; Park, Sungil; Lee, Seung-Hun; Copley, John

    2003-03-01

    LiNiO2 displays a layered structure that consists of alternating triangular nets of magnetic Ni and non-magnetic Li ions. Its magnetic properties have been a longstanding source of debate, having been proposed as a candidate for many exotic magnetic ground states. Recent detailed characterization studies have shown that some Ni ions always occupy sites in the Li layers and vice versa. We have carried out inelastic neutron scattering studies on a well characterized sample of LiNiO2 using the new Disk Chopper Spectrometer at NIST. Diffuse inelastic scattering is observed in the forward direction and around (1,0,0) in reciprocal space, indicative of short range, dynamic ferromagnetic order. Spin freezing is directly observed by a decrease in the inelastic scattering and concomitant increase in the elastic scattering below ˜15 K, consistent with bulk susceptibility measurements. Our neutron measurements are interpreted as arising from ferromagnetic correlations within the triangular net and 3D ferromagnetic clusters surrounding Ni sites within the Li sublattice. Such ferromagnetic clusters interupt the formation of a 3D Neel state in which ferromagnetic sheets stack antiferromagnetically, as is believed to be the case in NaNiO2.

  2. Velocity autocorrelation functions of particles and clusters in liquids. A possible criterion for correlation length of incipient glass formation

    NASA Astrophysics Data System (ADS)

    Variyar, Jayasankar E.; Kivelson, Daniel; Lynden-Bell, R. M.

    1992-12-01

    We have carried out molecular-dynamics simulations over a range of densities in two and three dimensions for particles that interact through soft repulsive potentials. We have also carried out calculations of the corresponding systems in which all particles except a tagged particle and its neighbors within a certain distance are frozen. Velocity autocorrelation functions for a single particle, for clusters containing the particle, and for the velocity of the particle relative to an embedding cluster were obtained. The single-particle velocity autocorrelation function can be resolved into correlation functions describing the local rattling in a cage or a cluster, the motion of the cluster itself, and a small cross-correlation term; the function for the single particle is sensitive to the structure of the fluid over a much shorter time scale than are those of clusters, and the shape of the single-particle velocity autocorrelation function comes primarily from rattling motion within a cage. We show that the velocity autocorrelation functions of clusters are probably better probes than that for the single particle for investigating incipient glass formation since they can be used to establish a correlation length which increases when a liquid is cooled. The dynamics of clusters at a given state point depend upon their sizes, and the nature of their motions changes qualitatively from ``rattling'' for small to ``diffusional'' for large clusters, the ``critical'' size at which the change occurs increasing with decreasing temperature. A simple model for this cluster behavior is presented.

  3. Oxidation of Al-containing austenitic stainless steels as related to the formation of strong glass-ceramic to metal seals

    SciTech Connect

    Moddeman, W.E.; Birkbeck, J.C.; Bowling, W.C.; Burke, A.R.; Cassidy, R.T.

    1996-08-01

    In glass-ceramic to metal seals used in pyrotechnic actuators and ignitors, Ni-based alloys and Al-containing austenitic stainless steels are used. Metal attack by the glass is severe if Ni based alloys are used, less so for the Al-containing alloys. In this paper, lithia-alumina-silica glass-ceramic was sealed to Al-containing alloys that were first oxidized prior to sealing (preoxidation). Results show that this preoxidation substantially reduces the probability of glass/metal reactions during seal formation, thus improving the overall quality of the interface without loss of seal bond strength. Mechanism of surface oxide formation of these Al- containing steels is discussed. Auger data show the composition of the resulting oxides to be a function of oxidation temperature. There are two theories on the oxidation mechanism: (1) oxidation occurring at the air/oxide interface (Abderrazik et al, 1987), and (2) oxidation taking place at the oxide/metal interface (Hindam and Smeltzer, 1980). To test the theories, oxidation of the Al-containing alloys was carried out, first in pure oxygen-16, and then followed by pure oxygen-18. SIMS showed no layered structure, but did show a mixture of oxides. Thus, the oxidation mechanism is not simple and must be allowing oxygen to have access at all stages of the oxidation process.

  4. Effect of configuration factor on gap formation in hybrid composite resin, low-shrinkage composite resin and resin-modified glass ionomer.

    PubMed

    Boroujeni, Parvin M; Mousavinasab, Sayyed M; Hasanli, Elham

    2015-05-01

    Polymerization shrinkage is one of the important factors in creation of gap between dental structure and composite resin restorations. The aim of this study was to evaluate the effect of configuration factor (C-factor) on gap formation in a hybrid composite resin, a low shrinkage composite resin and a resin modified glass ionomer restorative material. Cylindrical dentin cavities with 5.0 mm diameter and three different depths (1.0, 2.0 and 3.0 mm) were prepared on the occlusal surface of 99 human molars and the cavities assigned into three groups (each of 33). Each group contained three subgroups depend on the different depths and then cavities restored using resin modified glass ionomer (Fuji II LC Improved) and two type composite resins (Filtek P90 and Filtek Z250). Then the restorations were cut into two sections in a mesiodistal direction in the middle of restorations. Gaps were measured on mesial, distal and pulpal floor of the cavities, using a stereomicroscope. Data analyses using Kruskal-Wallist and Mann-Whitney tests. Increasing C-factor from 1.8 to 3.4 had no effect on the gap formation in two type composite resins, but Fuji II LC Improved showed significant effect of increasing C-factor on gap formation. Taken together, when C-factor increased from 1.8 up to 3.4 had no significant effect on gap formation in two tested resin composites. Although, Filtek P90 restorations showed smaller gap formation in cavities walls compared to Filtek Z250 restorations. High C-factor values generated the largest gap formation. Silorane-based composite was more efficient for cavity sealing than methacrylate-based composites and resin modified glass ionomer. © 2014 Wiley Publishing Asia Pty Ltd.

  5. Formation and atomic configuration of binary metallic glasses studied by ion beam mixing and molecular dynamics simulation

    SciTech Connect

    Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Liu, B. X.

    2007-06-15

    Metallic glasses are obtained in an immiscible Ag-Nb system with overall composition ranging from 25 to 90 at. % of Nb by ion beam mixing. Interestingly, the diffraction analysis shows that the formed Nb-rich metallic glass features are two distinct atomic configurations. In atomistic modeling, an n-body Ag-Nb potential is derived, under the assistance of ab initio calculation, and then applied in molecular dynamics simulations. An atomic configuration is discovered, i.e., an icositetrahedral ordering, and as well as an icosahedral ordering observed in the Ag-Nb metallic glasses and in some previously reported systems. Simulations confirm that the two dominate local atomic packing units are formed through a structural phase transition from the Nb-based bcc and fcc solid solutions, respectively, suggesting a concept of structural heredity that the crystalline structure of the constituent metals play a decisive role in determining the atomic structure of the resultant metallic glasses.

  6. Innovative approach to the design of low-cost Zr-based BMG composites with good glass formation.

    PubMed

    Cheng, Jia-Lin; Chen, Guang; Liu, Chain-Tsuan; Li, Yi

    2013-01-01

    The high manufacturing cost for metallic glasses hampers actual commercial applications of this class of fascinating materials. In this letter, the effect of oxygen impurity on the glass forming ability and tensile properties of Zr-BMG composites were studied. Our results have demonstrated that oxygen was absorbed and concentrated only in the precipitated β-Zr phase, leading that the remainder molten metal retains good glass forming ability. The high oxygen concentration in the β-Zr phase induces a significant solid-solution strengthening effect, this resulting in an enhanced strength of the BMG composites without sacrificing their overall ductility. Based on this alloying strategy, we have successfully developed the low-cost Zr-based BMG composites with excellent tensile properties and good glass forming ability, using the low grade industrial raw materials processed under industrial vacuum systems. This finding is expected to greatly cut down the manufacturing cost and greatly promote the commercial applications of the BMG composites.

  7. Characterization of Free Volume Changes Associated with Shear Band Formation in Zr- and Cu-Based Bulk Metallic Glasses

    SciTech Connect

    Flores, K M; Glade, S C; Asoka-Kumar, P; Kanungo, B

    2003-11-14

    The free volume model for flow in metallic glasses predicts a significant increase in free volume at the onset of plastic deformation. The details of these structural changes are unclear, however, particularly during strain localization in shear bands. In this study, the free volume changes associated with inhomogeneous plastic deformation of a Cu-based bulk metallic glass were examined using positron annihilation spectroscopy (PAS). PAS results indicated that there was a distribution of free volume site sizes in both the as-quenched and rolled glasses, and that the concentration of larger sites increased with deformation. Differential scanning calorimetry (DSC) was also used to observe the glass transition behaviors of Cu- and Zr-based glasses after rolling and annealing. Annealing resulted in an increase in the height of the endothermic glass transition peak, consistent with structural relaxation relative to the as-quenched material. Deformation resulted in both a lower endothermic peak height and an earlier and deeper exothermic peak associated with structural relaxation, indicating a more disordered structure with more free volume.

  8. Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. I. The formation of the ppσ-network.

    PubMed

    Zhugayevych, Andriy; Lubchenko, Vassiliy

    2010-12-21

    Semiconductor glasses exhibit many unique optical and electronic anomalies. We have put forth a semiphenomenological scenario [A. Zhugayevych and V. Lubchenko, J. Chem. Phys. 133, 234504 (2010)] in which several of these anomalies arise from deep midgap electronic states residing on high-strain regions intrinsic to the activated transport above the glass transition. Here we demonstrate at the molecular level how this scenario is realized in an important class of semiconductor glasses, namely chalcogen and pnictogen containing alloys. Both the glass itself and the intrinsic electronic midgap states emerge as a result of the formation of a network composed of σ-bonded atomic p-orbitals that are only weakly hybridized. Despite a large number of weak bonds, these ppσ-networks are stable with respect to competing types of bonding, while exhibiting a high degree of structural degeneracy. The stability is rationalized with the help of a hereby proposed structural model, by which ppσ-networks are symmetry-broken and distorted versions of a high symmetry structure. The latter structure exhibits exact octahedral coordination and is fully covalently bonded. The present approach provides a microscopic route to a fully consistent description of the electronic and structural excitations in vitreous semiconductors.

  9. Hydrothermal Alteration of Glass from Underground Nuclear Tests: Formation and Transport of Pu-clay Colloids at the Nevada National Security Site

    SciTech Connect

    Zavarin, M.; Zhao, P.; Joseph, C.; Begg, J.; Boggs, M.; Dai, Z.; Kersting, A. B.

    2015-05-27

    The testing of nuclear weapons at the Nevada National Security Site (NNSS), formerly the Nevada Test Site (NTS), has led to the deposition of substantial quantities of plutonium into the environment. Approximately 2.8 metric tons (3.1×104 TBq) of Pu were deposited in the NNSS subsurface as a result of underground nuclear testing. While 3H is the most abundant anthropogenic radionuclide deposited in the NNSS subsurface (4.7×106 TBq), plutonium is the most abundant from a molar standpoint. The only radioactive elements in greater molar abundance are the naturally occurring K, Th, and U isotopes. 239Pu and 240Pu represent the majority of alpha-emitting Pu isotopes. The extreme temperatures associated with underground nuclear tests and the refractory nature of Pu results in most of the Pu (98%) being sequestered in melted rock, referred to as nuclear melt glass (Iaea, 1998). As a result, Pu release to groundwater is controlled, in large part, by the leaching (or dissolution) of nuclear melt glass over time. The factors affecting glass dissolution rates have been studied extensively. The dissolution of Pu-containing borosilicate nuclear waste glasses at 90ºC has been shown to lead to the formation of dioctahedral smectite colloids. Colloid-facilitated transport of Pu at the NNSS has been observed. Recent groundwater samples collected from a number of contaminated wells have yielded a wide range of Pu concentrations from 0.00022 to 2.0 Bq/L. While Pu concentrations tend to fall below the Maximum Contaminant Level (MCL) established by the Environmental Protection Agency (EPA) for drinking water (0.56 Bq/L), we do not yet understand what factors limit the Pu concentration or its transport behavior. To quantify the upper limit of Pu concentrations produced as a result of melt glass dissolution and determine the nature of colloids and Pu associations, we performed a 3 year nuclear melt glass dissolution experiment

  10. Nepheline Formation Potential in Sludge Batch 4 (SB4) and Its Impact on Durability: Selecting Glasses for a Phase 2 Study

    SciTech Connect

    Peeler, D

    2005-08-15

    The likelihood for the formation of nepheline in Sludge Batch 4 (SB4) glass systems and the potential impact of nepheline on the durability of these systems is part of the frit development efforts for SB4. The effect of crystallization on glass durability is complex and depends on several interrelated factors including the change in residual glass composition, the formation of internal stress or microcracks, and the preferential attack at the glass-crystal interface. Perhaps one of the most significant effects is the type and extent (or fraction) of crystallization and the change to the residual glass composition. A strong increase in glass dissolution (or decrease in durability) has been observed in previous studies in glasses that formed aluminum-containing crystals, such as NaAlSiO{sub 4} (nepheline) and LiAlSi{sub 2}O{sub 6}, and crystalline SiO{sub 2}. Although it is well known that the addition of Al{sub 2}O{sub 3} to borosilicate glasses enhances the durability of the waste form (through creation of network-forming tetrahedral Na{sup +}-[AlO{sub 4/2}]{sup -} pairs), the combination of high Al{sub 2}O{sub 3} and Na{sub 2}O can lead to the formation of nepheline (NaAlSiO{sub 4}). Given the projected high concentration of Al{sub 2}O{sub 3} in SB4 and the potential use of a high Na{sub 2}O based frit to improve melt rate and a high Na{sub 2}O sludge due to settling problems, the potential formation of nepheline in various SB4 systems continues to be assessed. The most recent compositional projections from the Closure Business Unit (CBU) for SB4 may be framed around three decision areas: the sodium molarity of the sludge (at values of 1M Na and 1.6M Na), the SB3 heel that will be included in the batch (expressed in inches of SB3 sludge with values of 0, 40, and 127''), and the introduction of an ARP stream into the sludge (which is represented by six options: no ARP, ARPa, ARPe, ARPk, ARPm, and ARPv). Candidate frits are being identified for these options via a

  11. Formation of hydroxyapatite onto glasses of the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives.

    PubMed

    Agathopoulos, S; Tulyaganov, D U; Ventura, J M G; Kannan, S; Karakassides, M A; Ferreira, J M F

    2006-03-01

    New bioactive glasses with compositions based on the CaO-MgO-SiO(2) system and additives of B(2)O(3), P(2)O(5), Na(2)O, and CaF(2) were prepared. The in vitro mineralization behaviour was tested by immersion of powders or bulk glasses in simulated body fluid (SBF). Monitoring of ionic concentrations in SBF and scanning electron microscopy (SEM) observations at the surface of the glasses were conducted over immersion time. Raman and infrared (IR) spectroscopy shed light on the structural evolution occurring at the surface of the glasses that leads to formation of hydroxyapatite.

  12. Containerless synthesis of interesting glasses

    NASA Technical Reports Server (NTRS)

    Weinberg, Michael C.

    1990-01-01

    One aspect of containerless glass experimentation was thoroughly examined: glass forming ability. It is argued that although containerless processing will abet glass formation, other ground-based methods can do the job better. However, these methods have limitations, such as sample dimensions and concomitant ability to make property measurements. Most importantly, perhaps, is the observation that glass properties are a function of preparation procedure. Thus, it seems as though there still is an argument for use of containerless processing for glass forming.

  13. Formation of an ensemble of silver nanoparticles in the process of surface evaporation of glass optical waveguides doped with silver ions by the radiation of a pulsed CO{sub 2} laser

    SciTech Connect

    Egorov, V I; Sidorov, A I; Nashchekin, A V

    2015-09-30

    It is shown that pulsed irradiation (a wavelength of 10.6 μm and an energy density of 0.6 – 8.5 J cm{sup -2}) of glass with a waveguide layer containing silver ion leads to the formation of a ring, surrounding the irradiated zone and consisting of silver nanoparticles deposited on the glass surface. The possible process of formation of silver nanoparticles under laser irradiation is discussed. (optics and technology of nanostructures)

  14. Effects of soda-lime-silica waste glass on mullite formation kinetics and micro-structures development in vitreous ceramics.

    PubMed

    Marinoni, Nicoletta; D'Alessio, Daniela; Diella, Valeria; Pavese, Alessandro; Francescon, Ferdinando

    2013-07-30

    The effects of soda-lime waste glass, from the recovery of bottle glass cullet, in partial replacement of Na-feldspar for sanitary-ware ceramic production are discussed. Attention is paid to the mullite growth kinetics and to the macroscopic properties of the final output, the latter ones depending on the developed micro-structures and vitrification grade. Measurements have been performed by in situ high temperature X-ray powder diffraction, scanning electron microscopy, thermal dilatometry, water absorption and mechanical testing. Glass substituting feldspar from 30 to 50 wt% allows one (i) to accelerate the mullite growth reaction kinetics, and (ii) to achieve macroscopic features of the ceramic output that comply with the latest technical requirements. The introduction of waste glass leads to (i) a general saving of fuel and reduction of the CO2-emissions during the firing stage, (ii) a preservation of mineral resources in terms of feldspars, and (iii) an efficient management of the bottle glass refuse by readdressing a part of it in the sanitary-ware manufacturing.

  15. Atomic-scale models of early-stage alkali depletion and SiO2-rich gel formation in bioactive glasses.

    PubMed

    Tilocca, Antonio

    2015-01-28

    Molecular dynamics simulations of Na(+)/H(+)-exchanged 45S5 Bioglass® models reveal that a large fraction of the hydroxyl groups introduced into the proton-exchanged, hydrated glass structure do not initially form covalent bonds with Si and P network formers but remain free and stabilised by the modifier metal cations, whereas substantial Si-OH and P-OH bonding is observed only at higher Na(+)/H(+) exchange levels. The strong affinity between free OH groups and modifier cations in the highly fragmented 45S5 glass structure appears to represent the main driving force for this effect. This suggests an alternative direct route for the formation of a repolymerised silica-rich gel in the early stages of the bioactive mechanism, not considered before, which does not require sequential repeated breakings of Si-O-Si bonds and silanol condensations.

  16. Ectopic bone formation by gel-derived bioactive glass-poly-L-lactide-co-glycolide composites in a rabbit muscle model.

    PubMed

    Filipowska, Joanna; Cholewa-Kowalska, Katarzyna; Wieczorek, Jarosław; Semik, Danuta; Dąbrowski, Zbigniew; Łączka, Maria; Osyczka, Anna M

    2017-01-17

    In this study we aimed to assess the in vivo osteoinductive properties of two composite scaffolds made of PLGA (poly-L-lactide-co-glycolide) and two types of gel-derived bioactive glasses, namely a high silica S2 bioactive glass (S2-PLGA composites) or high lime A2 bioactive glass (A2-PLGA composites). To achieve that, the potential of the composites to induce ectopic bone formation in a rabbit muscle has been examined along with the control PLGA scaffold. Cylinder-like scaffolds of 7  ×  3 mm (width  ×  height) were implanted into pouches created in the latissimus dorsi muscle of 18 New Zealand rabbits. The tissue sections were obtained at 6, 12 or 24 weeks post-surgery (six rabbits per each time point) and stained with hematoxylin-eosin. The process of wound healing, the formation of collagen-rich connective tissue and its transition to cartilage were examined by Sirius red and Alcian blue histological stainings. We also performed immunohistochemical verification of the presence of osteoblast- and osteoclast- like cells in the vicinity of the scaffolds. A typical foreign body reaction and wound healing process was observed for all implanted scaffolds. Osteoblast- and osteoclast-like cells were observed in the vicinity of the scaffolds as determined by the immunohistochemical staining for Osteocalcin, BMP-2 and Cathepsin K. Compared to plain PLGA scaffolds, numerous osteoblast-like cells were observed 12 weeks post implantation near the composites and the scaffolds gradually degraded as bone formation proceeded. S2-PLGA and A2-PLGA composites display osteoinductive properties in vivo. Furthermore, they are more effective at inducing ectopic bone formation in a rabbit muscle compared to plain PLGA. Thus these SBG-PLGA composite scaffolds have potential for clinical applications in dental and/or orthopedic-bone tissue engineering.

  17. Formation of molecular glasses and the aggregation in solutions for lanthanum(III), calcium(II), and yttrium(III) complexes of octanoyl-DL-alaninate.

    PubMed

    Naren, Gerile; Masuda, Rie; Iida, Masayasu; Harada, Masafumi; Kurosu, Hiromichi; Suzuki, Toshiharu; Kimura, Takayoshi

    2008-04-07

    Octanoylalaninato-metal (metal = calcium(II), yttrium(III), lanthanum(III), and zinc(II)) complexes were prepared and the first three metal complexes were found to readily form transparent and stable molecular glasses from methanol and chloroform solutions. The process of glass formation from solution was studied in detail. The effect of the central metal ions on the formation of glassy states was remarkable: the lanthanum and calcium complexes assumed glassy or crystalline states depending on the isolation method and the yttrium complex had a large tendency to assume an amorphous state, whereas the zinc complex did not assume a pure and stable glassy-state. The glass transition temperatures were 50 degrees C for the yttrium complex and 70-75 degrees C for the lanthanum and calcium complexes when these complexes are monohydrates prepared by a solvent-cast method, whereas they increase by 10-30 degrees for the hemihydrates which were obtained by an annealing treatment at 110 degrees C. The coordinated water was eliminated from the solid above the glass transition temperature. The glassy state was regarded as a result of the self-aggregation of the metal complex in solution by an entanglement of the methylene chains with one another. SAXS showed the presence of two disordered bilayer structures with 2.2 nm and 4.5 nm periods in the glassy states. The structures of the molecular assemblies in the solid states and solutions were compared by SAXS and NMR studies. EXAFS studies confirmed the coordination numbers of oxygen atoms around the yttrium and lanthanum atoms in the glassy states for the yttrium and lanthanum complexes to be about 7.

  18. Technologies for Use in the Formation of a Differentiated Structure in Iron Billets Used in Glass Molds

    NASA Astrophysics Data System (ADS)

    Leushin, I. O.; Chistyakov, D. G.

    2016-09-01

    Causes for the failure of pig iron press molds that are parts of a glass mold are described. Criteria for differentiating the structure of pig iron are established. Ways of obtaining a differentiated structure of a casting product are outlined. A heat treatment regime for the billets is determined.

  19. Synchrotron X-ray diffraction to detect glass or ice formation in the vitrified bovine cumulus-oocyte complexes and morulae.

    PubMed

    Anzar, Muhammad; Grochulski, Pawel; Bonnet, Brennan

    2014-01-01

    Vitrification of bovine cumulus-oocyte complexes (COCs) is not as successful as bovine embryos, due to oocyte's complex structure and chilling sensitivity. Synchrotron X-ray diffraction (SXRD), a powerful method to study crystal structure and phase changes, was used to detect the glass or ice formation in water, tissue culture medium (TCM)-199, vitrification solution 2 (VS2), and vitrified bovine COCs and morulae. Data revealed Debye's rings and peaks associated with the hexagonal ice crystals at 3.897, 3.635, 3.427, 2.610, 2.241, 1.912 and 1.878 Å in both water and TCM-199, whereas VS2 showed amorphous (glassy) appearance, at 102K (-171°C). An additional peak of sodium phosphate monobasic hydrate (NaH2PO4.H2O) crystals was observed at 2.064 Å in TCM-199 only. All ice and NaH2PO4.H2O peaks were detected in the non-vitrified (control) and vitrified COCs, except two ice peaks (3.145 and 2.655 Å) were absent in the vitrified COCs. The intensities of majority of ice peaks did not differ between the non-vitrified and vitrified COCs. The non-vitrified bovine morulae in TCM-199 demonstrated all ice- and NaH2PO4.H2O-associated Debye's rings and peaks, found in TCM-199 alone. There was no Debye's ring present in the vitrified morulae. In conclusion, SXRD is a powerful method to confirm the vitrifiability of a solution and to detect the glass or ice formation in vitrified cells and tissues. The vitrified bovine COCs exhibited the hexagonal ice crystals instead of glass formation whereas the bovine morulae underwent a typical vitrification.

  20. Synchrotron X-Ray Diffraction to Detect Glass or Ice Formation in the Vitrified Bovine Cumulus-Oocyte Complexes and Morulae

    PubMed Central

    Anzar, Muhammad; Grochulski, Pawel; Bonnet, Brennan

    2014-01-01

    Vitrification of bovine cumulus-oocyte complexes (COCs) is not as successful as bovine embryos, due to oocyte's complex structure and chilling sensitivity. Synchrotron X-ray diffraction (SXRD), a powerful method to study crystal structure and phase changes, was used to detect the glass or ice formation in water, tissue culture medium (TCM)-199, vitrification solution 2 (VS2), and vitrified bovine COCs and morulae. Data revealed Debye's rings and peaks associated with the hexagonal ice crystals at 3.897, 3.635, 3.427, 2.610, 2.241, 1.912 and 1.878 Å in both water and TCM-199, whereas VS2 showed amorphous (glassy) appearance, at 102K (−171°C). An additional peak of sodium phosphate monobasic hydrate (NaH2PO4.H2O) crystals was observed at 2.064 Å in TCM-199 only. All ice and NaH2PO4.H2O peaks were detected in the non-vitrified (control) and vitrified COCs, except two ice peaks (3.145 and 2.655 Å) were absent in the vitrified COCs. The intensities of majority of ice peaks did not differ between the non-vitrified and vitrified COCs. The non-vitrified bovine morulae in TCM-199 demonstrated all ice- and NaH2PO4.H2O-associated Debye's rings and peaks, found in TCM-199 alone. There was no Debye's ring present in the vitrified morulae. In conclusion, SXRD is a powerful method to confirm the vitrifiability of a solution and to detect the glass or ice formation in vitrified cells and tissues. The vitrified bovine COCs exhibited the hexagonal ice crystals instead of glass formation whereas the bovine morulae underwent a typical vitrification. PMID:25536435

  1. Nanodot and nanocrystal pattern formation and luminescent properties of BiB 3O 6 glasses after moderate energy ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Plaza, J. L.; Martínez, O.; Hortelano, V.; Bensalah, H.; Diéguez, E.

    2012-02-01

    In this work we study the nanopatterning effect on the surface of BIBO glasses by means of Ion Beam Sputtering (IBS), using moderate energy (<5 kV) Ar ions. The analysis, changing the energy of the Ar ions, has demonstrated the formation of nanodots, nanorripples, and nanopyramids. We have also analysed the dependence of the nanopatterns on the sample thickness for the same experimental conditions. The sizes of the nanodots have been analysed by AFM, while their optical properties studied by means of μ-Raman/μ-photoluminescence techniques.

  2. Effect of hydrothermal condition on the formation of multi-component oxides of Ni-based metallic glass under high temperature water near the critical point

    DOE PAGES

    Kim, J. S.; Kim, S. Y.; Kim, D. H.; ...

    2015-07-01

    The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni59Zr20Ti16Si2Sn3 metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO3, ZrTiO4 and ZrSnO4 ternary oxide phases observed on the surface of metallic glass at below glass transition temperature and the morphology of oxide phasesmore » changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.« less

  3. Effect of hydrothermal condition on the formation of multi-component oxides of Ni-based metallic glass under high temperature water near the critical point

    SciTech Connect

    Kim, J. S.; Kim, S. Y.; Kim, D. H.; Ott, R. T.; Kim, H. G.; Lee, M. H.

    2015-07-01

    The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni59Zr20Ti16Si2Sn3 metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO3, ZrTiO4 and ZrSnO4 ternary oxide phases observed on the surface of metallic glass at below glass transition temperature and the morphology of oxide phases changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.

  4. Effect of hydrothermal condition on the formation of multi-component oxides of Ni-based metallic glass under high temperature water near the critical point

    SciTech Connect

    Kim, J. S.; Lee, M. H.; Kim, S. Y.; Kim, D. H.; Ott, R. T.; Kim, H. G.

    2015-07-15

    The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni{sub 59}Zr{sub 20}Ti{sub 16}Si{sub 2}Sn{sub 3} metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO{sub 3}, ZrTiO{sub 4} and ZrSnO{sub 4} ternary oxide phases observed on the surface of metallic glass at below glass transition temperature and the morphology of oxide phases changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.

  5. Effect of hydrothermal condition on the formation of multi-component oxides of Ni-based metallic glass under high temperature water near the critical point

    NASA Astrophysics Data System (ADS)

    Kim, J. S.; Kim, S. Y.; Kim, D. H.; Ott, R. T.; Kim, H. G.; Lee, M. H.

    2015-07-01

    The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni59Zr20Ti16Si2Sn3 metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO3, ZrTiO4 and ZrSnO4 ternary oxide phases observed on the surface of metallic glass at below glass transition temperature and the morphology of oxide phases changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.

  6. The Grism Lens-Amplified Survey from Space (GLASS). V. Extent and Spatial Distribution of Star Formation in z ~ 0.5 Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Vulcani, Benedetta; Treu, Tommaso; Schmidt, Kasper B.; Poggianti, Bianca M.; Dressler, Alan; Fontana, Adriano; Bradač, Marusa; Brammer, Gabriel B.; Hoag, Austin; Huang, Kuan-Han; Malkan, Matthew; Pentericci, Laura; Trenti, Michele; von der Linden, Anja; Abramson, Louis; He, Julie; Morris, Glenn

    2015-12-01

    We present the first study of the spatial distribution of star formation in z ˜ 0.5 cluster galaxies. The analysis is based on data taken with the Wide Field Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We illustrate the methodology by focusing on two clusters (MACS 0717.5+3745 and MACS 1423.8+2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as a field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 108-1011 M⊙ and star formation rates in the range 1-20 M⊙ yr-1. Both in clusters and in the field, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside-out growth. In ˜20% of the cases, the Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc. We investigate trends with the hot gas density as traced by the X-ray emission, and with the surface mass density as inferred from gravitational lens models, and find no conclusive results. The diversity of morphologies and sizes observed in Hα illustrates the complexity of the environmental processes that regulate star formation. Upcoming analysis of the full GLASS data set will increase our sample size by almost an order of magnitude, verifying and strengthening the inference from this initial data set.

  7. THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). V. EXTENT AND SPATIAL DISTRIBUTION OF STAR FORMATION IN z ∼ 0.5 CLUSTER GALAXIES

    SciTech Connect

    Vulcani, Benedetta; Treu, Tommaso; Malkan, Matthew; Abramson, Louis; Schmidt, Kasper B.; Poggianti, Bianca M.; Dressler, Alan; Fontana, Adriano; Pentericci, Laura; Bradac, Marusa; Hoag, Austin; Huang, Kuan-Han; He, Julie; Brammer, Gabriel B.; Trenti, Michele; Linden, Anja von der; Morris, Glenn

    2015-12-01

    We present the first study of the spatial distribution of star formation in z ∼ 0.5 cluster galaxies. The analysis is based on data taken with the Wide Field Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We illustrate the methodology by focusing on two clusters (MACS 0717.5+3745 and MACS 1423.8+2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as a field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 10{sup 8}–10{sup 11} M{sub ⊙} and star formation rates in the range 1–20 M{sub ⊙} yr{sup −1}. Both in clusters and in the field, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside-out growth. In ∼20% of the cases, the Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc. We investigate trends with the hot gas density as traced by the X-ray emission, and with the surface mass density as inferred from gravitational lens models, and find no conclusive results. The diversity of morphologies and sizes observed in Hα illustrates the complexity of the environmental processes that regulate star formation. Upcoming analysis of the full GLASS data set will increase our sample size by almost an order of magnitude, verifying and strengthening the inference from this initial data set.

  8. The effects of 3D bioactive glass scaffolds and BMP-2 on bone formation in rat femoral critical size defects and adjacent bones.

    PubMed

    Liu, Wai-Ching; Robu, Irina S; Patel, Rikin; Leu, Ming C; Velez, Mariano; Chu, Tien-Min Gabriel

    2014-08-01

    Reconstruction of critical size defects in the load-bearing area has long been a challenge in orthopaedics. In the past, we have demonstrated the feasibility of using a biodegradable load-sharing scaffold fabricated from poly(propylene fumarate)/tricalcium phosphate (PPF/TCP) loaded with bone morphogenetic protein-2 (BMP-2) to successfully induce healing in those defects. However, there is limited osteoconduction observed with the PPF/TCP scaffold itself. For this reason, 13-93 bioactive glass scaffolds with local BMP-2 delivery were investigated in this study for inducing segmental defect repairs in a load-bearing region. Furthermore, a recent review on BMP-2 revealed greater risks in radiculitis, ectopic bone formation, osteolysis and poor global outcome in association with the use of BMP-2 for spinal fusion. We also evaluated the potential side effects of locally delivered BMP-2 on the structures of adjacent bones. Therefore, cylindrical 13-93 glass scaffolds were fabricated by indirect selective laser sintering with side holes on the cylinder filled with dicalcium phosphate dehydrate as a BMP-2 carrier. The scaffolds were implanted into critical size defects created in rat femurs with and without 10 μg of BMP-2. The x-ray and micro-CT results showed that a bridging callus was found as soon as three weeks and progressed gradually in the BMP group while minimal bone formation was observed in the control group. Degradation of the scaffolds was noted in both groups. Stiffness, peak load and energy to break of the BMP group were all higher than the control group. There was no statistical difference in bone mineral density, bone area and bone mineral content in the tibiae and contralateral femurs of the control and BMP groups. In conclusion, a 13-93 bioactive glass scaffold with local BMP-2 delivery has been demonstrated for its potential application in treating large bone defects.

  9. Measuring the specific surface area of natural and manmade glasses: effects of formation process, morphology, and particle size

    SciTech Connect

    Papelis, Charalambos; Um, Wooyong; Russel, Charles E.; Chapman, Jenny B.

    2003-03-28

    The specific surface area of natural and manmade solid materials is a key parameter controlling important interfacial processes in natural environments and engineered systems, including dissolution reactions and sorption processes at solid-fluid interfaces. To improve our ability to quantify the release of trace elements trapped in natural glasses, the release of hazardous compounds trapped in manmade glasses, or the release of radionuclides from nuclear melt glass, we measured the specific surface area of natural and manmade glasses as a function of particle size, morphology, and composition. Volcanic ash, volcanic tuff, tektites, obsidian glass, and in situ vitrified rock were analyzed. Specific surface area estimates were obtained using krypton as gas adsorbent and the BET model. The range of surface areas measured exceeded three orders of magnitude. A tektite sample had the highest surface area (1.65 m2/g), while one of the samples of in situ vitrified rock had the lowest surf ace area (0.0016 m2/g). The specific surface area of the samples was a function of particle size, decreasing with increasing particle size. Different types of materials, however, showed variable dependence on particle size, and could be assigned to one of three distinct groups: (1) samples with low surface area dependence on particle size and surface areas approximately two orders of magnitude higher than the surface area of smooth spheres of equivalent size. The specific surface area of these materials was attributed mostly to internal porosity and surface roughness. (2) samples that showed a trend of decreasing surface area dependence on particle size as the particle size increased. The minimum specific surface area of these materials was between 0.1 and 0.01 m2/g and was also attributed to internal porosity and surface roughness. (3) samples whose surface area showed a monotonic decrease with increasing particle size, never reaching an ultimate surface area limit within the particle

  10. Biofilm Formation and Adaptation by Pseudomonas fluorescens on both Biotite and Glass Coupons Under Varying Fe-Nutrient Availability

    NASA Astrophysics Data System (ADS)

    Grant, M.; Helms, G. L.; Shi, Z.; Thomashow, L.; Keller, C. K.; Harsh, J. B.

    2014-12-01

    We isolated an efficient weathering strain of Pseudomonas fluorescens from the rhizosphere of a White Pine (Pinus strobus) seedling. We grew it in a drip-flow biofilm reactor using both Fe-abundant and Fe-deficient media on either a glass or biotite coupon. Our working hypothesis was that the bacterium would respond to Fe deficiency by enhancing biotite weathering through an increase in the relative amount of polysaccharides in the biofilm compared to the Fe-abundant treatment. Because Fe is necessary for biofilm development, we hypothesized that biomass production on the biotite surface would exceed that on a Fe-free glass slide only in the Fe-deficient medium. We quantified total biomass, specific number of viable cells (SNVC), and the concentrations of K, Mg, and Fe in the biofilm. High-resolution magic angle spinning proton nuclear magnetic resonance (HR-MAS 1H-NMR) spectroscopy was used to characterize the biofilm matrix in terms of relative biofilm constituent concentrations. Compared with biofilms grown on glass, biofilms grown on biotite had higher total biomass and SNVC irrespective of Fe supply, with a near doubling of both the biofilm biomass from 0.43 to 0.76 mg cm-2 and SNVC from 1.52 × 107 to 3.24 × 107 CFU cm-2 mg-1 when Fe was deficient, and an increase in biomass from 1.94 to 2.46 mg cm-2 and in SNVC from 8.39 × 107 to 1.96 × 108 CFU cm-2 mg-1 when Fe was sufficient. Similarly with Fe deficient, the cation concentrations in biofilms grown on biotite vs. glass increased 2.14 and 2.46 times for K and Mg, respectively, and 7.01 times for Fe. When Fe was sufficient, the concentrations of cations increased 1.24, 2.07, and 3.77 times for K, Mg, and Fe, respectively. Based on NMR spectra, no significant change in biofilm chemistry occurred between the glass and biotite systems whether Fe was deficient or not. However, we did observe an increase in the ratio of the integrated areas corresponding to the carbohydrate and protein NMR regions, increasing

  11. Use of a Routh-Russel deformation map to achieve film formation of a latex with a high glass transition temperature.

    PubMed

    Gonzalez, Edurne; Paulis, María; Barandiaran, María Jesús; Keddie, Joseph L

    2013-02-12

    In the film formation of latex, particle deformation can occur by processes of wet sintering, dry sintering, or capillary action. When latex films dry nonuniformly and when particles deform and coalesce while the film is still wet, a detrimental skin layer will develop at the film surface. In their process model, Routh and Russel proposed that the operative particle deformation mechanism can be determined by the values of control parameters on a deformation map. Here, the film formation processes of three methyl methacrylate/butyl acrylate copolymer latexes with high glass transition temperatures (T(g)), ranging from 45 to 64 °C, have been studied when heated by infrared radiation. Adjusting the infrared (IR) power density enables the film temperature, polymer viscosity, and evaporation rate during latex film formation to be controlled precisely. Different polymer particle deformation mechanisms have been demonstrated for the same latex under a variety of film formation process conditions. When the temperature is too high, a skin layer develops. On the other hand, when the temperature is too low, particles deform by dry sintering, and the process requires extended time periods. The deduced mechanisms can be interpreted and explained by the Routh-Russel deformation maps. Film formation of hard (high T(g)) coatings is achieved without using coalescing aids that emit volatile organic compounds (VOCs), which is a significant technical achievement.

  12. Containerless processing of fluoride glass

    NASA Technical Reports Server (NTRS)

    Doremus, Robert H.

    1990-01-01

    Ground-based experiments on glass formation, crystallization, surface tension, vaporization, and chemical durability of a zirconium-barium-lanthanum (ZBL) fluoride glass are summarized. In a container large, columnar grains grew out from the container-glass interface during cooling. The main crystalline phase was alpha BaZrF6. A ZBL glass sphere was levitated acoustically during Shuttle flight STS-11. The glass was melted and then cooled while being levitated (containerless). Crystallization in the recovered sample was very fine and mainly beta BaZr2F10, showing the influence of the container on the nucleation and microstructure of crystallization in the glass. Glass formation should be easier for a containerless glass than in a container.

  13. Containerless processing of fluoride glass

    NASA Technical Reports Server (NTRS)

    Doremus, Robert H.

    1990-01-01

    Ground-based experiments on glass formation, crystallization, surface tension, vaporization, and chemical durability of a zirconium-barium-lanthanum (ZBL) fluoride glass are summarized. In a container large, columnar grains grew out from the container-glass interface during cooling. The main crystalline phase was alpha BaZrF6. A ZBL glass sphere was levitated acoustically during Shuttle flight STS-11. The glass was melted and then cooled while being levitated (containerless). Crystallization in the recovered sample was very fine and mainly beta BaZr2F10, showing the influence of the container on the nucleation and microstructure of crystallization in the glass. Glass formation should be easier for a containerless glass than in a container.

  14. β-Irradiation Effects on the Formation and Stability of CaMoO4 in a Soda Lime Borosilicate Glass Ceramic for Nuclear Waste Storage.

    PubMed

    Patel, Karishma B; Boizot, Bruno; Facq, Sébastien P; Lampronti, Giulio I; Peuget, Sylvain; Schuller, Sophie; Farnan, Ian

    2017-02-06

    Molybdenum solubility is a limiting factor to actinide loading in nuclear waste glasses, as it initiates the formation of water-soluble crystalline phases such as alkali molybdates. To increase waste loading efficiency, alternative glass ceramic structures are sought that prove resistant to internal radiation resulting from radioisotope decay. In this study, selective formation of water-durable CaMoO4 in a soda lime borosilicate is achieved by introducing up to 10 mol % MoO3 in a 1:1 ratio to CaO using a sintering process. The resulting homogeneously dispersed spherical CaMoO4 nanocrystallites were analyzed using electron microscopy, X-ray diffraction (XRD), Raman and electron paramagnetic resonance (EPR) spectroscopies prior to and post irradiation, which replicated internal β-irradiation damage on an accelerated scale. Following 0.77 to 1.34 GGy of 2.5 MeV electron radiation CaMoO4 does not exhibit amorphization or significant transformation. Nor does irradiation induce glass-in-glass phase separation in the surrounding amorphous matrix, or the precipitation of other molybdates, thus proving that excess molybdenum can be successfully incorporated into a structure that it is resistant to β-irradiation proportional to 1000 years of storage without water-soluble byproducts. The CaMoO4 crystallites do however exhibit a nonlinear Scherrer crystallite size pattern with dose, as determined by a Rietveld refinement of XRD patterns and an alteration in crystal quality as deduced by anisotropic peak changes in both XRD and Raman spectroscopy. Radiation-induced modifications in the CaMoO4 tetragonal unit cell occurred primarily along the c-axis indicating relaxation of stacked calcium polyhedra. Concurrently, a strong reduction of Mo(6+) to Mo(5+) during irradiation is observed by EPR, which is believed to enhance Ca mobility. These combined results are used to hypothesize a crystallite size alteration model based on a combination of relaxation and diffusion

  15. Nanoscale bit formation in highly (111)-oriented ferroelectric thin films deposited on glass substrates for high-density storage media.

    SciTech Connect

    Kim, D. H.; Kim, Y. K.; Hong, S.; Kim, Y.; Baik, S.

    2011-04-21

    PbTiO{sub 3} (PTO) ferroelectric films on Pt(111) bottom electrode layers covering Ta/glass were prepared using pulsed laser deposition. X-ray diffraction patterns revealed that the PTO films were preferentially (111)-oriented. The films were highly crystalline and had a smooth surface with root mean square (RMS) roughness of 1.5 nm. Ferroelectric properties of the PTO films were characterized using piezoresponse force microscopy (PFM). PFM techniques achieved ferroelectric polarization bits with a minimum width of 22 nm, which corresponds to a potential recording density of 1.3 Tbit/in{sup 2} in ferroelectric storage devices.

  16. Morphology and interphase formation in epoxy/PMMA/glass fiber composites: effect of the molecular weight of the PMMA.

    PubMed

    Olmos, D; Bagdi, K; Mózcó, J; Pukánszky, B; González-Benito, J

    2011-08-01

    In this work ternary composites based on an epoxy thermoset modified with a thermoplastic polymer and reinforced with glass fibers were prepared. The aim of this study is to analyze the influence of the molecular weight of the thermoplastic polymer on the final morphologies. To obtain tailor made interphases four poly(methylmethacrylate), PMMA, which differ in their molecular weight (34,000, 65,000, 76,000 and 360,000 g/mol) were chosen to modify the epoxy resin. The amount of PMMA in the composites was fixed to 5 wt.%. Neat polymer matrices (epoxy-PMMA without fibers) were also prepared for comparison. To study all systems dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used. Although all the systems showed the typical phase separation in the epoxy/PMMA blend, DMA experiments revealed a new phase with more restricted mobility when the glass fibers are present. The amount of this phase increases as molecular weight of PMMA does. The morphologies as well as the fracture surface in the immediate surroundings of the fibers were found to be different from those observed further away from the surface of the fiber, suggesting therefore that, in this case, different fracture mechanism operates. These observations allow us to conclude that an interphase with specific properties is formed. This interphase is based on a polymer or a polymer blend (epoxy-PMMA) enriched in the component with lower mobility. Copyright © 2011 Elsevier Inc. All rights reserved.

  17. Solubilities and Glass Formation in Aqueous Solutions of the Sodium Salts of Malonic Acid With and Without Ammonium Sulfate.

    PubMed

    Kissinger, Jared A; Buttke, Lukas G; Vinokur, Anastasiya I; Guzei, Ilia A; Beyer, Keith D

    2016-06-02

    The solubility of sodium hydrogen malonate and sodium malonate in water both with and without ammonium sulfate present has been studied using differential scanning calorimetry and infrared spectroscopy. The crystals that form from sodium hydrogen malonate/water solutions were determined to be sodium hydrogen malonate monohydrate by single-crystal X-ray diffractometry. The crystals formed in sodium malonate/water solutions were determined to be sodium malonate monohydrate, a compound whose structure had not been previously known. When ammonium sulfate is added to these respective aqueous systems, the precipitation solids contain sodium sulfate decahydrate under low to moderate ammonium concentrations and lecontite (NaNH4SO4·2H2O) under high ammonium concentrations, which can be found under dry atmospheric conditions. Thus, it appears the presence of malonate and hydrogen malonate ions does not significantly affect the precipitation of inorganic salts in these systems. The glass transition temperatures of all solutions were also determined, and it was observed that the addition of ammonium sulfate slightly lowers the glass transition temperature in these solutions.

  18. Designing new biocompatible glass-forming Ti75-x Zr10 Nbx Si15 (x = 0, 15) alloys: corrosion, passivity, and apatite formation.

    PubMed

    Abdi, Somayeh; Oswald, Steffen; Gostin, Petre Flaviu; Helth, Arne; Sort, Jordi; Baró, Maria Dolors; Calin, Mariana; Schultz, Ludwig; Eckert, Jürgen; Gebert, Annett

    2016-01-01

    Glass-forming Ti-based alloys are considered as potential new materials for implant applications. Ti75 Zr10 Si15 and Ti60 Zr10 Nb15 Si15 alloys (free of cytotoxic elements) can be produced as melt-spun ribbons with glassy matrix and embedded single β-type nanocrystals. The corrosion and passivation behavior of these alloys in their homogenized melt-spun states have been investigated in Ringer solution at 37°C in comparison to their cast multiphase crystalline counterparts and to cp-Ti and β-type Ti-40Nb. All tested materials showed very low corrosion rates as expressed in corrosion current densities icorr  < 50 nA/cm(2). Electrochemical and surface analytical studies revealed a high stability of the new alloys passive states in a wide potential range. This corresponds to low passive current densities ipass  = 2 ± 1 µA/cm(2) based on the growth of oxide films with thickness d <10 nm. A homogeneous constituent distribution in the melt-spun alloys is beneficial for stable surface passivity. The addition of Nb does not only improve the glass-forming ability and the mechanical properties but also supports a high pitting resistance even at extreme anodic polarization up to 4V versus SCE were oxide thickness values of d ∼35 nm are reached. With regard to the corrosion properties, the Nb-containing nearly single-phase glassy alloy can compete with the β-type Ti-40Nb alloy. SBF tests confirmed the ability for formation of hydroxyapatite on the melt-spun alloy surfaces. All these properties recommend the new glass-forming alloys for application as wear- and corrosion-resistant coating materials for implants.

  19. The formation of supercooled brines, viscous liquids, and low-temperature perchlorate glasses in aqueous solutions relevant to Mars

    NASA Astrophysics Data System (ADS)

    Toner, J. D.; Catling, D. C.; Light, B.

    2014-05-01

    Salt solutions on Mars can stabilize liquid water at low temperatures by lowering the freezing point of water. The maximum equilibrium freezing-point depression possible, known as the eutectic temperature, suggests a lower temperature limit for liquid water on Mars; however, salt solutions can supercool below their eutectic before crystallization occurs. To investigate the magnitude of supercooling and its variation with salt composition and concentration, we performed slow cooling and warming experiments on pure salt solutions and saturated soil-solutions of MgSO4, MgCl2, NaCl, NaClO4, Mg(ClO4)2, and Ca(ClO4)2. By monitoring solution temperatures, we identified exothermic crystallization events and determined the composition of precipitated phases from the eutectic melting temperature. Our results indicate that supercooling is pervasive. In general, supercooling is greater in more concentrated solutions and with salts of Ca and Mg. Slowly cooled MgSO4, MgCl2, NaCl, and NaClO4 solutions investigated in this study typically supercool 5-15 °C below their eutectic temperature before crystallizing. The addition of soil to these salt solutions has a variable effect on supercooling. Relative to the pure salt solutions, supercooling decreases in MgSO4 soil-solutions, increases in MgCl2 soil-solutions, and is similar in NaCl and NaClO4 soil-solutions. Supercooling in MgSO4, MgCl2, NaCl, and NaClO4 solutions could marginally extend the duration of liquid water during relatively warm daytime temperatures in the martian summer. In contrast, we find that Mg(ClO4)2 and Ca(ClO4)2 solutions do not crystallize during slow cooling, but remain in a supercooled, liquid state until forming an amorphous glass near -120 °C. Even if soil is added to the solutions, a glass still forms during cooling. The large supercooling effect in Mg(ClO4)2 and Ca(ClO4)2 solutions has the potential to prevent water from freezing over diurnal and possibly annual cycles on Mars. Glasses are also

  20. Glass sealing

    SciTech Connect

    Brow, R.K.; Kovacic, L.; Chambers, R.S.

    1996-04-01

    Hernetic glass sealing technologies developed for weapons component applications can be utilized for the design and manufacture of fuel cells. Design and processing of of a seal are optimized through an integrated approach based on glass composition research, finite element analysis, and sealing process definition. Glass sealing procedures are selected to accommodate the limits imposed by glass composition and predicted calculations.

  1. Realization of a Zachariasen glass

    NASA Astrophysics Data System (ADS)

    Phillips, J. C.

    1983-07-01

    Recent experimental and theoretical studies of oxide and chalcogenide network glasses have shown that their molecular structure is predominantly that of a frozen liquid of partially polymerized clusters. The formation of continuous random networks is predicted at critical compositions by the topological theory of network glass formation. The predicted compositions are in good agreement with recent data on Sn xGe 1- x(S or Se) 2 ternary chalcogenide glass alloys.

  2. Glass Formation of n-Butanol: Coarse-grained Molecular Dynamics Simulations Using Gay-Berne Potential Model

    NASA Astrophysics Data System (ADS)

    Xie, Gui-long; Zhang, Yong-hong; Huang, Shi-ping

    2012-04-01

    Using coarse-grained molecular dynamics simulations based on Gay-Berne potential model, we have simulated the cooling process of liquid n-butanol. A new set of GB parameters are obtained by fitting the results of density functional theory calculations. The simulations are carried out in the range of 290-50 K with temperature decrements of 10 K. The cooling characteristics are determined on the basis of the variations of the density, the potential energy and orientational order parameter with temperature, whose slopes all show discontinuity. Both the radial distribution function curves and the second-rank orientational correlation function curves exhibit splitting in the second peak. Using the discontinuous change of these thermodynamic and structure properties, we obtain the glass transition at an estimate of temperature Tg=120±10 K, which is in good agreement with experimental results 110±1 K.

  3. Studies on color-center formation in glass utilizing measurements made during 1 to 3 MeV electron irradiation

    NASA Technical Reports Server (NTRS)

    Swyler, K. J.; Levy, P. W.

    1976-01-01

    The coloring of NBS 710 glass was studied using a facility for making optical absorption measurements during and after electron irradiation. The induced absorption contains three Gaussian shaped bands. The color center growth curves contain two saturating exponential and one linear components. After irradiation the coloring decays can be described by three decreasing exponentials. At room temperature both the coloring curve plateau and coloring rate increases with increasing dose rate. Coloring measurements made at fixed dose rate but at increasing temperature indicate: (1) The coloring curve plateau decreases with increasing temperature and coloring is barely measurable near 400 C. (2) The plateau is reached more rapidly as the temperature increases. (3) The decay occurring after irradiation cannot be described by Arrhenius kinetics. At each temperature the coloring can be explained by simple kinetics. The temperature dependence of the decay can be explained if it is assumed that the thermal untrapping is controlled by a distribution of activation energies.

  4. Properties Of Soda/Yttria/Silica Glasses

    NASA Technical Reports Server (NTRS)

    Angel, Paul W.; Hann, Raiford E.

    1994-01-01

    Experimental study of glass-formation compositional region of soda/ yttria/silicate system and of selected physical properties of glasses within compositional region part of continuing effort to identify glasses with high coefficients of thermal expansion and high softening temperatures, for use as coatings on superalloys and as glass-to-metal seals.

  5. Polarons in endohedral Li+@C60- dimers and in 1D and 2D crystals

    NASA Astrophysics Data System (ADS)

    Kawazoe, Yoshiyuki; Belosludov, Vladimir R.; Zhdanov, Ravil K.; Belosludov, Rodion V.

    2017-10-01

    The electron charge distribution and polaron formation on the carbon sites of dimer clusters Li+@C60- and of 1D or 2D Li+@C60- periodic systems are studied with the use of the generalized Su-Schrieffer-Heeger model with respect to the intermolecular and intramolecular degrees of freedom. The charge distributions over the molecular surface and Jahn-Teller bond distortions of carbon atoms are calculated using the self-consistent iterative methods. Polarons formed in periodic 1D and 2D systems (chains and planar layers) as well as in dimer cluster system are examined. In the periodic systems polaron formation may be described by the cooperative Jahn-Teller effect. Orientation of the polarons on the molecule surface depends on the doping of the system, moreover, electron doping changes the energy levels in the system.

  6. Lattice vacancies in silicon film exposed to external electric field

    NASA Astrophysics Data System (ADS)

    Mao, Yuliang; Caliste, Damien; Pochet, Pascal

    2013-07-01

    Density functional calculations based on wavelet basis set are performed to investigate the structure, internal electric-charge distribution, and formation energy of lattice vacancies in silicon film under electric fields. It was found that the formation energies of vacancies both in JT⊥ (Jahn-Teller distortion orthogonal to electric field) and JT‖ (Jahn-Teller distortion parallel to electric field) distortions are decreased with the increasing of field strength, due to the charge polarization in the whole space of silicon film. For the split vacancy, it can lower its energy by moving further away from the split space to form a tetragonal JT⊥ vacancy under electric field. Our results also demonstrate the importance of the potential fluctuations induced by the electric fields on the charge redistribution within the vacancy defects.

  7. Mapping the spatial distribution of star formation in cluster galaxies at z ~0.5 with the Grism Lens-Amplified Survey from Space (GLASS)

    NASA Astrophysics Data System (ADS)

    Vulcani, B.; Treu, T.; Schmidt, K. B.; Poggianti, B. M.; Dressler, A.; Fontana, A.; Bradač, M.; Brammer, G. B.; Hoag, A.; Huang, K.; Malkan, M.; Pentericci, L.; Trenti, M.; von der Linden, A.; Abramson, L.; He, J.; Morris, G.

    2016-06-01

    What physical processes regulate star formation in dense environments? Understanding why galaxy evolution is environment dependent is one of the key questions of current astrophysics. I will present the first characterization of the spatial distribution of star formation in cluster galaxies at z~0.5, and compare to a field control sample, in order to quantify the role of different physical processes that are believed to be responsible for shutting down star formation (Vulcani et al. 2015, Vulcani et al. in prep). The analysis makes use of data from the Grism Lens-Amplified Survey from Space (GLASS), a large HST cycle-21 program targeting 10 massive galaxy clusters with extensive HST imaging from CLASH and the Frontier Field Initiative. The program consists of 140 primary and 140 parallel orbits of near-infrared WCF3 and optical ACS slitless grism observations, which result in 3D spectroscopy of hundreds of galaxies. The grism data are used to produce spatially resolved maps of the star formation density, while the stellar mass density and optical surface brightness are obtained from multiband imaging. I will describe quantitative measures of the spatial location and extent of the star formation rate. I will show that both in clusters and in the field, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside out growth. The Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc. I will also correlate the properties of the Hα maps to the cluster global properties, such as the hot gas density, and the surface mass density. The characterization of the spatial distribution of Halpha provides a new window, yet poorly exploited, on the mechanisms that regulate star formation and morphological

  8. Effect of Process Parameters on Formation and Aggregation of Nanoparticles Prepared with a Shirasu Porous Glass Membrane.

    PubMed

    Seo, Jeong-Woong; Kim, Kyung-Jin; Kim, Su-Hyeon; Hwang, Kyu-Mok; Seok, Su Hyun; Park, Eun-Seok

    2015-01-01

    The objectives of this study were to prepare itraconazole (ITZ) nanoparticles using a Shirasu porous glass (SPG) membrane and to characterize the effects of diverse preparation parameters on the physical stability of nanoparticles. SPG membrane technology was used for the antisolvent precipitation method. The preparation of nanoparticles was carried out over a wide range of continuous-phase factors (type of surfactant, surfactant concentration), dispersed-phase factors (solvent type, solvent volume used to dissolve ITZ), and technical factors (pressure, membrane pore size, stirring speed in the continuous phase, temperature). Improved physical stability of nanoparticles was observed when surfactant with a lower molecular weight and higher hydrophilic segment ratio was used. The water miscibility of the solvent also had an effect on the physical stability. N,N-Dimethylacetamide contributed to creating a well-rounded shape and narrow size distribution due to high miscibility. Concentration of the surfactant and solvent volume used for dissolving ITZ were related to instability of nanoparticles, resulting from depletion attraction and Ostwald ripening. In addition to these factors, technical factors changed the environment surrounding ITZ nanoparticles, such as the physicochemical equilibrium between surfactant and ITZ nanoparticles. Therefore, the appropriate continuous-phase factors, dispersed-phase factors, and technical factors should be maintained for stabilizing ITZ nanoparticles.

  9. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite.

    PubMed

    Li, Yuelin; Walko, Donald A; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephan; Zheng, Hong; Mitchell, J F

    2015-12-16

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, La0.99Sr2.01Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  10. Evidence of Photo-induced Dynamic Competition of Metallic and Insulating Phase in a Layered Manganite.

    SciTech Connect

    Li, Yuelin; Walko, Donald A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephan; Zheng, Hong; Mitchell, J. F.

    2015-12-16

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time- dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  11. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

    DOE PAGES

    Li, Yuelin; Walko, Daonld A.; Li, Qing'an; ...

    2015-11-17

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitationmore » modulates the local competition between the metallic and the insulating phases.« less

  12. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

    SciTech Connect

    Li, Yuelin; Walko, Daonld A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephen; Zheng, Hong; Mitchell, J. F.

    2015-11-17

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  13. Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for iodine mediated particle formation in the marine boundary layer

    NASA Astrophysics Data System (ADS)

    Murray, B. J.; Haddrell, A. E.; Peppe, S.; Davies, J. F.; Reid, J. P.; O'Sullivan, D.; Price, H. C.; Kumar, R.; Saunders, R. W.; Plane, J. M. C.; Umo, N. S.; Wilson, T. W.

    2012-09-01

    Iodine oxide particles are known to nucleate in the marine boundary layer where gas phase molecular iodine and organoiodine species are produced by macroalgae. These ultra-fine particles may then grow through the condensation of other materials to sizes where they may serve as cloud condensation nuclei. There has been some debate over the chemical identity of the initially nucleated particles. In laboratory simulations, hygroscopic measurements have been used to infer that they are composed of insoluble I2O4, while elemental analysis of laboratory generated particles suggests soluble I2O5 or its hydrated form iodic acid, HIO3 (I2O5·H2O). In this paper we explore the response of super-micron sized aqueous iodic acid solution droplets to varying humidity using both Raman microscopy and single particle electrodynamic traps. These measurements reveal that the propensity of an iodic acid solution droplet to crystallise is negligible on drying to ~0% relative humidity (RH). On applying mechanical pressure to these droplets they shatter in a manner consistent with an ultra-viscous liquid or a brittle glass. Water retention in amorphous material at low RH is important for understanding the hygroscopic growth of aerosol particles and uptake of other condensable material. Subsequent water uptake between 10 and 20% RH causes their viscosity to reduce sufficiently that the cracked droplets flow and merge. The persistence of iodic acid solution in an amorphous state, rather than a crystalline state, suggests they will more readily accommodate other condensable material and are therefore more likely to grow to sizes where they may serve as cloud condensation nuclei. On increasing the humidity to ~90% the mass of the droplets only increases by ~20% with a corresponding increase in radius of only 6%, which is remarkably small for a highly soluble material. We suggest that the small growth factor of aqueous iodic acid solution droplets is consistent with the small aerosol growth

  14. Low-temperature formation of high-quality gate oxide by ultraviolet irradiation on spin-on-glass

    NASA Astrophysics Data System (ADS)

    Usuda, R.; Uchida, K.; Nozaki, S.

    2015-11-01

    Although a UV cure was found to effectively convert a perhydropolysilazane (PHPS) spin-on-glass film into a dense SiOx film at low temperature, the electrical characteristics were never reported in order to recommend the use of PHPS as a gate-oxide material that can be formed at low temperature. We have formed a high-quality gate oxide by UV irradiation on the PHPS film, and obtained an interface midgap trap density of 3.4 × 1011 cm-2 eV-1 by the UV wet oxidation and UV post-metallization annealing (PMA), at a temperature as low as 160 °C. In contrast to the UV irradiation using short-wavelength UV light, which is well known to enhance oxidation by the production of the excited states of oxygen, the UV irradiation was carried out using longer-wavelength UV light from a metal halide lamp. The UV irradiation during the wet oxidation of the PHPS film generates electron-hole pairs. The electrons ionize the H2O molecules and facilitate dissociation of the molecules into H and OH-. The OH- ions are highly reactive with Si and improve the stoichiometry of the oxide. The UV irradiation during the PMA excites the electrons from the accumulation layer, and the built-in electric field makes the electron injection into the oxide much easier. The electrons injected into the oxide recombine with the trapped holes, which have caused a large negative flat band voltage shift after the UV wet oxidation, and also ionize the H2O molecules. The ionization results in the electron stimulated dissociation of H2O molecules and the decreased interface trap density.

  15. Glass formation and magnetic properties in the Co and Fe-based amorphous alloy with small Mo or Nb additions

    NASA Astrophysics Data System (ADS)

    Jo, Hye-In; Choi-Yim, Haein

    2012-02-01

    The ferromagnetic metallic glass alloys in the Co-Fe-B-Si-M (M = Mo or Nb) system were investigated. Ingots of [(Co1- x Fe x )0.75B0.2Si0.05]96Mo4 ( x = 0, 0.2, 0.5, 0.8, 1.0) and [(Co1- x Fe x )0.75 B0.2Si0.05]96Nb4 ( x = 0, 0.2, 0.5, 0.8, 1.0) alloys were cast into about 30 µm-thick ribbons by using a melt spinning method. As-spun ribbons were identified as being fully amorphous by using X-ray diffraction (XRD). The thermal stability parameters, such as the supercooled liquid region (Δ T x = T g - T x ) and the exothermic heat (Δ H Exo ), were measured by using differential scanning calorimetry (DSC). For Co-Fe-B-Si-Mo alloys, Δ T x and Δ H Exo were in the range of 41.4-81.7 K and 23.40-104.21 J/g, and for Co-Fe-B-Si-Nb alloys, Δ T x and Δ H Exo were in the range of 60.4-88.0 K and 18.45-62.05 J/g, respectively. These glassy ribbons also exhibited semi-hard magnetic properties, i.e., a coercive force ( H c ) of 67.26-100.68 Oe and a saturation magnetization ( M s ) of 341.288-746.176 emu·cm3.

  16. Low-temperature formation of high-quality gate oxide by ultraviolet irradiation on spin-on-glass

    SciTech Connect

    Usuda, R.; Uchida, K.; Nozaki, S.

    2015-11-02

    Although a UV cure was found to effectively convert a perhydropolysilazane (PHPS) spin-on-glass film into a dense SiO{sub x} film at low temperature, the electrical characteristics were never reported in order to recommend the use of PHPS as a gate-oxide material that can be formed at low temperature. We have formed a high-quality gate oxide by UV irradiation on the PHPS film, and obtained an interface midgap trap density of 3.4 × 10{sup 11 }cm{sup −2} eV{sup −1} by the UV wet oxidation and UV post-metallization annealing (PMA), at a temperature as low as 160 °C. In contrast to the UV irradiation using short-wavelength UV light, which is well known to enhance oxidation by the production of the excited states of oxygen, the UV irradiation was carried out using longer-wavelength UV light from a metal halide lamp. The UV irradiation during the wet oxidation of the PHPS film generates electron-hole pairs. The electrons ionize the H{sub 2}O molecules and facilitate dissociation of the molecules into H and OH{sup −}. The OH{sup −} ions are highly reactive with Si and improve the stoichiometry of the oxide. The UV irradiation during the PMA excites the electrons from the accumulation layer, and the built-in electric field makes the electron injection into the oxide much easier. The electrons injected into the oxide recombine with the trapped holes, which have caused a large negative flat band voltage shift after the UV wet oxidation, and also ionize the H{sub 2}O molecules. The ionization results in the electron stimulated dissociation of H{sub 2}O molecules and the decreased interface trap density.

  17. Biosilica-glass formation using enzymes from sponges [silicatein]: Basic aspects and application in biomedicine [bone reconstitution material and osteoporosis

    NASA Astrophysics Data System (ADS)

    Wang, Shun-Feng; Wang, Xiao-Hong; Gan, Lu; Wiens, Matthias; Schröder, Heinz C.; Müller, Werner E. G.

    2011-09-01

    In the last 15 years biomineralization, in particular biosilicification (i.e., the formation of biogenic silica, SiO2), has become an exciting source of inspiration for the development of novel bionic approaches, following "Nature as model". Among the silica forming organisms there are the sponges that have the unique property to catalyze their silica skeletons by a specific enzyme termed silicatein. In the present review we summarize the present state of knowledge on silicatein-mediated "biosilica" formation in marine sponges, the involvement of further molecules in silica metabolism and their potential application in biomedicine. Recent advancements in the production of bone replacement material and in the potential use as a component in the treatment of osteoporosis are highlighted.

  18. Synthesis, cytotoxicity, and hydroxyapatite formation in 27-Tris-SBF for sol-gel based CaO-P2O5-SiO2-B2O3-ZnO bioactive glasses

    PubMed Central

    Kaur, Gurbinder; Pickrell, G.; Kimsawatde, G.; Homa, D.; Allbee, H. A.; Sriranganathan, N.

    2014-01-01

    CaO-P2O5-SiO2-B2O3-ZnO bioactive glasses were prepared via an optimized sol–gel method. The current investigation was focused on producing novel zinc based calcium phosphoborosilicate glasses and to evaluate their mechanical, rheological, and biocompatible properties. The morphology and composition of these glasses were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The particle size, mechanical and flexural strength was also determined. Furthermore, the zeta potential of all the glasses were determined to estimate their flocculation tendency. The thermal analysis and weight loss measurements were carried out using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) respectively. For assessing the in-vitro bioactive character of synthesized glasses, the ability for apatite formation on their surface upon their immersion in simulated body fluid (SBF) was checked using SEM and pH measurements. MTS assay cytotoxicity assay and live-dead cell viability test were conducted on J774A.1 cells murine macrophage cells for different glass concentrations. PMID:24637634

  19. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation.

    PubMed

    Starr, Francis W; Douglas, Jack F; Sastry, Srikanth

    2013-03-28

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the "mosaic" length of the RFOT model relaxes the conventional assumption that the "entropic droplets" are compact. We also confirm the

  20. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation

    PubMed Central

    Starr, Francis W.; Douglas, Jack F.; Sastry, Srikanth

    2013-01-01

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the “mosaic” length of the RFOT model relaxes the conventional assumption that the “entropic droplets” are compact. We also confirm

  1. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation

    NASA Astrophysics Data System (ADS)

    Starr, Francis W.; Douglas, Jack F.; Sastry, Srikanth

    2013-03-01

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the "mosaic" length of the RFOT model relaxes the conventional assumption that the "entropic droplets" are compact. We also confirm the

  2. Comment on ``Pseudo-Jahn Teller and TICT-models: a photophysical comparison of meta-and para-DMABN derivatives'' [Chem. Phys. Lett. 305 (1999) 8] The PICT model for dual fluorescence of aminobenzonitriles

    NASA Astrophysics Data System (ADS)

    Zachariasse, Klaas A.

    2000-03-01

    Due to the larger admixture of charge transfer (CT) in the intramolecular charge transfer (ICT) state than in the locally excited (LE) state of dual fluorescent molecules such as 4-(dimethylamino)benzonitrile, the radiative rate constant kf'(ICT) is smaller than kf(LE), irrespective of the ICT molecular structure. The validity of the TICT or PICT model can therefore not be tested with these data. The absence of dual fluorescence for 4-(methylamino)benzonitrile, 3-(dimethylamino)benzonitrile and two dicyano- N, N-dimethylanilines, which cannot be explained by the TICT hypothesis, is caused by their large energy gap Δ E(S 1, S 2), which prevents the ICT state from becoming lower in energy than LE.

  3. Plagioclase zonation styles in hornblende gabbro inclusions from Little Glass Mountain, Medicine Lake volcano, California: Implications for fractionation mechanisms and the formation of composition gaps

    USGS Publications Warehouse

    Brophy, J.G.; Dorais, M.J.; Donnelly-Nolan, J.; Singer, B.S.

    1997-01-01

    The rhyolite of Little Glass Mountain (73-74% SiO2) is a single eruptive unit that contains inclusions of quenched andesite liquid (54-61% SiO2) and partially crystalline cumulate hornblende gabbro (53-55% SiO2). Based on previous studies, the quenched andesite inclusions and host rhyolite lava are related to one another through fractional crystallization and represent an example of a fractionation-generated composition gap. The hornblende gabbros represent the cumulate residue associated with the rhyolite-producing and composition gap-forming fractionation event. This study combines textural (Nomarski Differential Interference Contrast, NDIC, imaging), major element (An content) and trace element (Mg, Fe, Sr, K, Ti, Ba) data on the style of zonation of plagioclase crystals from representative andesite and gabbro inclusions, to assess the physical environment in which the fractionation event and composition gap formation took place. The andesite inclusions (54-61% SiO2) are sparsely phyric with phenocrysts of plagioclase, augite and Fe-oxide??olivine, +/-orthopyroxene, +/-hornblende set within a glassy to crystalline matrix. The gabbro cumulates (53-55% SiO2) consist of an interconnected framework of plagioclase, augite, olivine, orthopyroxene, hornblende and Fe-oxide along with highly vesicular interstitial glass (70-74% SiO2). The gabbros record a two-stage crystallization history of plagioclase + olivine + augite (Stage I) followed by plagioclase+orthopyroxene + hornblende + Fe-oxide (Stage II). Texturally, the plagioclase crystals in the andesite inclusions are characterized by complex, fine-scale oscillatory zonation and abundant dissolution surfaces. Compositionally (An content) the crystals are essentially unzoned from core-to-rim. These features indicate growth within a dynamic (convecting?), reservoir of andesite magma. In contrast, the plagioclase crystals in the gabbros are texturally smooth and featureless with strong normal zonation from An74 at the

  4. Transient nucleation in glasses

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.

    1991-01-01

    Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

  5. Glass recycling

    SciTech Connect

    Dalmijn, W.L.; Houwelingen, J.A. van

    1995-12-31

    Glass recycling in the Netherlands has grown from 10,000 to 300,000 tonnes per annum. The various advantages and problems of the glass cycle with reference to the state of the art in the Netherlands is given. Special attention is given to new technologies for the automated sorting of cullet with detection systems. In Western Europe the recycling of glass has become a success story. Because of this, the percentage of glass cullet used in glass furnaces has increased. To meet the quality demands of the glass industry, automated sorting for the removal of stones, non-ferrous metals and other impurities had to be developed and incorporated in glass recycling plants. In Holland, Germany and other countries, the amount of glass collected has reached a level that color-sorting becomes necessary to avoid market saturation with mixed cullet. Recently, two systems for color-sorting have been developed and tested for the separation of bottles and cullet in the size range of 20--50 mm. With the increased capacity of the new glass recycling plants, 120,000--200,000 tpy, the quality systems have also to be improved and automated. These quality control systems are based on the automated sorting technology developed earlier for the glass recycling plants. The data obtained are automatically processed and printed. The sampling system and its relation to the theory of Gy will be described. Results of both developments in glass recycling plants will be described.

  6. Glass Artworks

    NASA Technical Reports Server (NTRS)

    1988-01-01

    Several NASA technologies have played part in growth and cost containment of studio glass art, among them a foam type insulation developed to meet a need for lightweight material that would reduce flame spread in aircraft fire. Foam comes in several forms and is widely used by glass artists, chiefly as an insulator for the various types of ovens used in glass working. Another Spinoff is alumina crucibles to contain molten glass. Before alumina crucibles were used, glass tanks were made of firebrick which tended to erode under high temperatures and cause impurities; this not only improved quality but made the process more cost effective. One more NASA technology that found its way into glass art working is a material known as graphite board, a special form of graphite originally developed for rocket motor applications. This graphite is used to exact compound angles and creates molds for poured glass artworks of dramatic design.

  7. Bioactive glass in tissue engineering

    PubMed Central

    Rahaman, Mohamed N.; Day, Delbert E.; Bal, B. Sonny; Fu, Qiang; Jung, Steven B.; Bonewald, Lynda F.; Tomsia, Antoni P.

    2011-01-01

    This review focuses on recent advances in the development and use of bioactive glass for tissue engineering applications. Despite its inherent brittleness, bioactive glass has several appealing characteristics as a scaffold material for bone tissue engineering. New bioactive glasses based on borate and borosilicate compositions have shown the ability to enhance new bone formation when compared to silicate bioactive glass. Borate-based bioactive glasses also have controllable degradation rates, so the degradation of the bioactive glass implant can be more closely matched to the rate of new bone formation. Bioactive glasses can be doped with trace quantities of elements such as Cu, Zn and Sr, which are known to be beneficial for healthy bone growth. In addition to the new bioactive glasses, recent advances in biomaterials processing have resulted in the creation of scaffold architectures with a range of mechanical properties suitable for the substitution of loaded as well as non-loaded bone. While bioactive glass has been extensively investigated for bone repair, there has been relatively little research on the application of bioactive glass to the repair of soft tissues. However, recent work has shown the ability of bioactive glass to promote angiogenesis, which is critical to numerous applications in tissue regeneration, such as neovascularization for bone regeneration and the healing of soft tissue wounds. Bioactive glass has also been shown to enhance neocartilage formation during in vitro culture of chondrocyte-seeded hydrogels, and to serve as a subchondral substrate for tissue-engineered osteochondral constructs. Methods used to manipulate the structure and performance of bioactive glass in these tissue engineering applications are analyzed. PMID:21421084

  8. Enzymatically induced formation of neodymium hexacyanoferrate nanoparticles on the glucose oxidase/chitosan modified glass carbon electrode for the detection of glucose.

    PubMed

    Sheng, Qinglin; Luo, Kai; Zheng, Jianbin; Zhang, Hongfang

    2008-11-15

    The formation of neodymium hexacyanoferrate (NdHCF) nanoparticles (NPs) on the surface of glucose oxidase/chitosan (GOx/CHIT) modified glass carbon electrode induced by enzymatic reaction was described and characterized. CHIT can be used not only as enzyme immobilizer, but also to provide active sites for NPs growth. Results showed that the optimized conditions of the GOx/CHIT film induced NdHCF NPs for the biosensing of glucose were 1.0mM Nd(3+) and 20.0mM Fe(CN)(6)(3-). The biocatalyzed generation of NdHCF NPs enabled the development of an electrochemical biosensor for glucose. The calculated apparent Michaelis-Menten constant was 7.5mM. The linear range for glucose detection was 0.01-10.0mM with the correlation coefficient of 0.9946, and the detection limit was 5 microM (S/N=3). Furthermore, this system avoids the interferences of other species during the biosensing process and can be used for the determination of glucose in human plasma samples.

  9. Marginal gap formation and fluoride release of resin-modified glass-ionomer cement: effect of silanized spherical silica filler addition.

    PubMed

    Tjandrawinata, Rosalina; Irie, Masao; Suzuki, Kazuomi

    2004-09-01

    The purpose of this study was to investigate the effects of silanized spherical silica fillers (SF) on the immediate and 24-hour marginal gaps of resin-modified glass-ionomer cement (RMGIC) in tooth cavities. In correlation with marginal gap formation in the tooth cavity, these influencing factors were also examined: marginal gap and setting shrinkage of cement in the Teflon mold, as well as the shear bond strength to tooth substrate. Moreover in correlation with caries prevention, fluoride release was examined too. In this investigation, the fillers were mixed into the RMGIC powder (Fuji II LC EM). Untreated spherical silica filler (UF)-added RMGIC was used as a comparison. When compared with the control (i.e., original RMGIC), the addition of SF significantly decreased immediate marginal gap in tooth cavities and setting shrinkage in Teflon mold up to 63% and 66% respectively. Fluoride release was significantly reduced too. Apart from these results, this study showed that addition of 5 wt% SF increased the shear bond strength to human enamel and dentin.

  10. Glass Research

    NASA Technical Reports Server (NTRS)

    Weinberg, M. C.

    1985-01-01

    Research efforts span three general areas of glass science: glass refining, gel-derived glasses, and nucleation and crystallization of glasses. Gas bubbles which are present in a glass product are defects which may render the glass totally useless for the end application. For example, optical glasses, laser host glasses, and a variety of other specialty glasses must be prepared virtually defect free to be employable. Since a major mechanism of bubble removal, buoyant rise, is virtually inoperative in microgravity, glass fining will be especially difficult in space. On the other hand, the suppression of buoyant rise and the ability to perform containerless melting experiments in space allows the opportunity to carry out several unique bubble experiments in space. Gas bubble dissolution studies may be performed at elevated temperatures for large bubbles with negligible bubble motion. Also, bubble nucleation studies may be performed without the disturbing feature of heterogeneous bubble nucleation at the platinum walls. Ground based research efforts are being performed in support of these potential flight experiments.

  11. International Congress on Glass XII

    SciTech Connect

    Doremus, R H; LaCourse, W C; Mackenzie, J D; Varner, J R; Wolf, W W

    1980-01-01

    A total of 158 papers are included under nine headings: structure and glass formation; optical properties; electrical and magnetic properties; mechanical properties and relaxation; mass transport; chemical durability and surfaces; nucleation; crystallization; and glass ceramics; processing; and automatic controls. Separate abstracts were prepared for eight papers; four of the remaining papers had been processed previously for the data base. (DLC)

  12. Glass corrosion in natural environment

    NASA Technical Reports Server (NTRS)

    Thorpe, Arthur N.

    1989-01-01

    A series of studies of the effects of solutes which appear in natural aqueous environments, specifically Mg and Al, under controlled conditions, permit characterization of the retardation of silicate glass leaching in water containing such solutes. In the case of Mg the interaction with the glass appears to consist of exchange with alkali ions present in the glass to a depth of several microns. The effect of Al can be observed at much lower levels, indicating that the mechanism in the case of Al involves irreversible formation of aluminosilicate species at the glass surface.

  13. Compositional effects on the formation of a calcium phosphate layer and the response of osteoblast-like cells on polymer-bioactive glass composites.

    PubMed

    Lu, Helen H; Tang, Amy; Oh, Seong Cheol; Spalazzi, Jeffrey P; Dionisio, Kathie

    2005-11-01

    Biodegradable polymer-ceramic composites are attractive systems for bone tissue engineering applications. These composites have the combined advantages of the component phases, as well as the inherent ease in optimization where desired material properties can be tailored in a well-controlled manner. This study focuses on the optimization of a polylactide-co-glycolide (PLAGA) and 45S5 bioactive glass (BG) composite for bone tissue engineering. The first objective is to examine the effects of composition or overall BG content on the formation of a Ca-P layer on the PLAGA-BG composite. It is expected that with increasing BG content (0%, 10%, 25%, 50% by weight), the required incubation time in a simulated body fluid (SBF) for the composite to form a detectable surface Ca-P layer will decrease. Both the kinetics and the chemistry will be determined using SEM+EDAX, FTIR, and mu-CT methods. Solution phosphorous and calcium concentrations will also be measured. The second objective of the study is to determine the effects of BG content on the maturation of osteoblast-like cells on the PLAGA-BG composite. It is hypothesized that mineralization will increase with increasing BG content, and the composite will support the proliferation and differentiation of osteoblasts. Specifically, cell proliferation, alkaline phosphatase activity and mineralization will be monitored as a function of BG content (0%, 10%, 50% by weight) and culturing time. It was found that the kinetics of Ca-P layer formation and the resulting Ca-P chemistry were dependent on BG content. The response of human osteoblast-like cells to the PLAGA-BG composite was also a function of BG content. The 10% and 25% BG composite supported greater osteoblast growth and differentiation compared to the 50% BG group. The results of this study suggest that there is a threshold BG content which is optimal for osteoblast growth, and the interactions between PLAGA and BG may modulate the kinetics of Ca-P formation and the

  14. 2012 Problem 13: Misty Glass

    NASA Astrophysics Data System (ADS)

    Huang, Shan; Li, Xiao; Gao, Wenli; Zhou, Huijun

    2015-10-01

    Based on diffraction theory, we propose a model to explain the formation of colorful rings created by a misty glass. The model is verified by examining the relation between the size of the ring and size of the droplets.

  15. Glass formation and structure in the MgSiO{sub 3}-Mg{sub 2}SiO{sub 4} pseudobinary system: From degraded networks to ioniclike glasses

    SciTech Connect

    Kalampounias, A. G.; Nasikas, N. K.; Papatheodorou, G. N.

    2009-09-21

    A series of glasses xMgO-(1-x)SiO{sub 2} with compositions from enstatite MgSiO{sub 3} (x=0.5) to forsterite Mg{sub 2}SiO{sub 4} (x=0.667) in mole fraction intervals of x{approx_equal}0.02 have been prepared by containerless levitation techniques and CO{sub 2} laser heating. Polarized and depolarized Raman spectra measured at ambient conditions for all these glasses show systematic and smooth band intensity changes with composition. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged SiO{sub 4} tetrahedra (Q{sup i}, species analysis) undoubtedly shows that bridging oxygens are present in all glasses studied even in the limit of the forsterite composition where bridged Si{sub 2}O{sub 7}{sup 6-} ionic dimers are formed. Furthermore the relative amounts of the Q{sup i} species change smoothly with composition while at high MgO content 'free' oxygens are present presumably forming Mg-O-Mg bridges, which contribute to the glass stability at these compositions. Raman spectra measurements at different temperature below T{sub g} show small alterations in the Q{sup i} species in the MgSiO{sub 3} region while no changes were observed in the Mg{sub 2}SiO{sub 4} region. The Boson peak frequency is practically invariant on both composition and temperature and this is in contrast to the systematics followed by most silicate glasses. It is suggested that at compositions near the forsterite ioniclike glasses are formed arising from a very fragile liquid.

  16. Perspective: The glass transition

    NASA Astrophysics Data System (ADS)

    Biroli, Giulio; Garrahan, Juan P.

    2013-03-01

    We provide here a brief perspective on the glass transition field. It is an assessment, written from the point of view of theory, of where the field is and where it seems to be heading. We first give an overview of the main phenomenological characteristics, or "stylised facts," of the glass transition problem, i.e., the central observations that a theory of the physics of glass formation should aim to explain in a unified manner. We describe recent developments, with a particular focus on real space properties, including dynamical heterogeneity and facilitation, the search for underlying spatial or structural correlations, and the relation between the thermal glass transition and athermal jamming. We then discuss briefly how competing theories of the glass transition have adapted and evolved to account for such real space issues. We consider in detail two conceptual and methodological approaches put forward recently, that aim to access the fundamental critical phenomenon underlying the glass transition, be it thermodynamic or dynamic in origin, by means of biasing of ensembles, of configurations in the thermodynamic case, or of trajectories in the dynamic case. We end with a short outlook.

  17. The formation of nanocrystalline ZrO2 nuclei in a Li2O-Al2O3-SiO2 glass - a combined XANES and TEM study.

    PubMed

    Kleebusch, Enrico; Patzig, Christian; Krause, Michael; Hu, Yongfeng; Höche, Thomas; Rüssel, Christian

    2017-09-07

    The high economic importance of glass ceramics based on Li2O/Al2O3/SiO2 (LAS) is mainly due to their low coefficients of thermal expansion (CTE), which make these materials suitable candidates for a number of applications. The exact mechanism of the crystallization processes in LAS glasses is still not fully understood. The present work focuses on the formation and development of nanocrystalline ZrO2 within an LAS base composition which contains only ZrO2 as nucleating agent. Using a combination of transmission electron microscopy and X-ray absorption spectroscopy techniques, the temporal evolution of the ZrO2 nanocrystal formation is described. It is found that the formation of ZrO2 is initiated by liquid-liquid phase separation droplets with high Zr content, which eventually evolve into the nanocrystalline ZrO2 precipitations. This process is accompanied by a gradual change of the coordination of the tetravalent Zr ions from sixfold in the glass to eightfold in the crystals. The diameters of the ZrO2 crystals stay well below 4 nm, even at late stages. The degree of crystallization at each step of the crystallization process is deduced, and from that, the Avrami coefficient n is determined to be n ≈ 1, which describes a barrier-limited crystal growth process.

  18. Self-assembly and glass-formation in a lattice model of telechelic polymer melts: Influence of stiffness of the sticky bonds.

    PubMed

    Xu, Wen-Sheng; Freed, Karl F

    2016-06-07

    Telechelic polymers are chain macromolecules that may self-assemble through the association of their two mono-functional end groups (called "stickers"). A deep understanding of the relation between microscopic molecular details and the macroscopic physical properties of telechelic polymers is important in guiding the rational design of telechelic polymer materials with desired properties. The lattice cluster theory (LCT) for strongly interacting, self-assembling telechelic polymers provides a theoretical tool that enables establishing the connections between important microscopic molecular details of self-assembling polymers and their bulk thermodynamics. The original LCT for self-assembly of telechelic polymers considers a model of fully flexible linear chains [J. Dudowicz and K. F. Freed, J. Chem. Phys. 136, 064902 (2012)], while our recent work introduces a significant improvement to the LCT by including a description of chain semiflexibility for the bonds within each individual telechelic chain [W.-S. Xu and K. F. Freed, J. Chem. Phys. 143, 024901 (2015)], but the physically associative (or called "sticky") bonds between the ends of the telechelics are left as fully flexible. Motivated by the ubiquitous presence of steric constraints on the association of real telechelic polymers that impart an additional degree of bond stiffness (or rigidity), the present paper further extends the LCT to permit the sticky bonds to be semiflexible but to have a stiffness differing from that within each telechelic chain. An analytical expression for the Helmholtz free energy is provided for this model of linear telechelic polymer melts, and illustrative calculations demonstrate the significant influence of the stiffness of the sticky bonds on the self-assembly and thermodynamics of telechelic polymers. A brief discussion is also provided for the impact of self-assembly on glass-formation by combining the LCT description for this extended model of telechelic polymers with the

  19. Potentially improved glasses from space environment

    NASA Technical Reports Server (NTRS)

    Nichols, R.

    1977-01-01

    The benefits of processing glasses in a low-gravity space environment are examined. Containerless processing, the absence of gravity driven convection, and lack of sedimentation are seen as potential advantages. Potential applications include the formation of glass-ceramics with a high content of active elements for ferromagnetic devices, the production of ultrapure chalcogenide glasses for laser windows and IR fiber optics, and improved glass products for use in optical systems and laser fusion targets.

  20. GLASS FIBER REINFORCED PLASTICS,

    DTIC Science & Technology

    Contents: Fibrous glass fillers Binders used in the glass plastic industry Method of manufacturing glass plastics and glass plastic articles Properties of fiberglass Primary areas for use of glass fibre reinforced plastics