Sample records for jahn-teller lattice distortions

  1. Suppression of the cooperative Jahn-Teller distortion and its effect on the Raman octahedra-rotation modes of TbM n1 -xF exO3

    NASA Astrophysics Data System (ADS)

    Vilarinho, R.; Passos, D. J.; Queirós, E. C.; Tavares, P. B.; Almeida, A.; Weber, M. C.; Guennou, M.; Kreisel, J.; Moreira, J. Agostinho

    2018-04-01

    This work reports the changes in structure and lattice dynamics induced by substituting the Jahn-Teller-active M n3 + ion by the Jahn-Teller-inactive F e3 + in TbM n1 -xF exO3 over the full composition range. The structural analysis reveals that the amplitude of the cooperative Jahn-Teller distortion decreases linearly from x =0 (pure TbMn O3 ) to x =0.5 , where it is completely suppressed. We then correlate this evolution with the behavior of the Raman modes across the solid solution. In particular, we show that the Raman modes associated with the rotation of octahedra, whose wave number is commonly considered to scale linearly with the tilt angles in orthorhombic Pnma perovskites, are also sensitive to the amplitude of the Jahn-Teller distortion.

  2. 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.

  3. Dynamical Jahn Teller distortion in single crystals of Cu(II) doped magnesium potassium phosphate hexahydrate: a variable temperature EPR study

    NASA Astrophysics Data System (ADS)

    PrabhuKantan, A.; Velavan, K.; Venkatesan, R.; Sambasiva Rao, P.

    2003-05-01

    Single crystal electron paramagnetic resonance (EPR) studies on Cu(II)-doped magnesium potassium phosphate hexahydrate have been carried out at room temperature. The temperature dependence of g and A values has been obtained for the polycrystalline sample and the ground state is unambiguously identified. These results indicate the existence of a dynamic Jahn-Teller distortion for Cu(II) ion. The g and A tensor direction cosines are evaluated and compared with Mg-O directions, which confirms that Cu(II) enters substitutionally in the lattice.

  4. The Jahn-Teller distortion influenced ferromagnetic order in Pr1-xLaxMnO3

    NASA Astrophysics Data System (ADS)

    He, Feifei; Mao, Zhongquan; Tang, Lingyun; Zhang, Jiang; Chen, Xi

    2018-06-01

    The structural and magnetic properties of Pr1-xLaxMnO3 (0 ≤ x ≤ 1) polycrystalline powders are investigated. A structural phase transition from a large Jahn-Teller (J-T) distorted orthorhombic structure to a small J-T distorted orthorhombic phase is found at x = 0.70, while the LaMnO3 is showed to have a rhombohedral structure. All the samples exhibit ferromagnetic ordering, and meanwhile, a reentrant spin glass behavior at low temperature. The relationship between J-T distortions and the ferromagnetic order is discussed.

  5. 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.

  6. Ab initio EPR parameters for dangling-bond defect complexes in silicon: Effect of Jahn-Teller distortion

    NASA Astrophysics Data System (ADS)

    Pfanner, Gernot; Freysoldt, Christoph; Neugebauer, Jörg; Gerstmann, Uwe

    2012-05-01

    A dangling bond (db) is an important point defect in silicon. It is realized in crystalline silicon by defect complexes of the monovacancy V with impurities. In this work, we present spin-polarized density-functional theory calculations of EPR parameters (g and hyperfine tensors) within the GIPAW formalism for two kinds of db defect complexes. The first class characterizes chemically saturated db systems, where three of the four dangling bonds of the isolated vacancy are saturated by hydrogen (VH3) or hydrogen and oxygen (hydrogen-oxygen complex, VOH). The second kind of db consists of systems with a Jahn-Teller distortion, where the vacancy includes either a substitutional phosphorus atom (the E center, VP) or a single hydrogen atom (VH). For all systems we obtain excellent agreement with available experimental data, and we are therefore able to quantify the effect of the Jahn-Teller distortion on the EPR parameters. Furthermore we study the influence of strain to obtain further insights into the structural and electronic characteristics of the considered defects.

  7. 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.

  8. 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.

  9. 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

  10. Dynamical Jahn-Teller effect of fullerene anions

    NASA Astrophysics Data System (ADS)

    Liu, Dan; Iwahara, Naoya; Chibotaru, Liviu F.

    2018-03-01

    The dynamical Jahn-Teller effect of C60n - anions (n =1 -5) is studied using the numerical diagonalization of the linear pn⊗8 d Jahn-Teller Hamiltonian with the currently established coupling parameters. It is found that in all anions the Jahn-Teller effect stabilizes the low-spin states, resulting in the violation of Hund's rule. The energy gain due to the Jahn-Teller dynamics is found to be comparable to the static Jahn-Teller stabilization. The Jahn-Teller dynamics influences the thermodynamic properties via strong variation of the density of vibronic states with energy. Thus the large vibronic entropy in the low-spin states enhances the effective spin gap of C603 - quenching the spin crossover. From the calculations of the effective spin gap as a function of the Hund's rule coupling, we found that the latter should amount 40 ±5 meV in order to cope with the violation of Hund's rule and to reproduce the large spin gap. With the obtained numerical solutions, the matrix elements of electronic operators for the low-lying vibronic levels and the vibronic reduction factors are calculated for all anions.

  11. 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.

  12. 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…

  13. Dynamic Jahn-Teller effect in the parent insulating state of the molecular superconductor Cs₃C₆₀.

    PubMed

    Klupp, Gyöngyi; Matus, Péter; Kamarás, Katalin; Ganin, Alexey Y; McLennan, Alec; Rosseinsky, Matthew J; Takabayashi, Yasuhiro; McDonald, Martin T; Prassides, Kosmas

    2012-06-19

    The 'expanded fulleride' Cs(3)C(60) is an antiferromagnetic insulator in its normal state and becomes a molecular superconductor with T(c) as high as 38 K under pressure. There is mounting evidence that superconductivity is not of the conventional BCS type and electron-electron interactions are essential for its explanation. Here we present evidence for the dynamic Jahn-Teller effect as the source of the dramatic change in electronic structure occurring during the transition from the metallic to the localized state. We apply infrared spectroscopy, which can detect subtle changes in the shape of the C(60)3- ion due to the Jahn-Teller distortion. The temperature dependence of the spectra in the insulating phase can be explained by the gradual transformation from two temperature-dependent solid-state conformers to a single one, typical and unique for Jahn-Teller systems. These results unequivocally establish the relevance of the dynamic Jahn-Teller effect to overcoming Hund's rule and forming a low-spin state, leading to a magnetic Mott-Jahn-Teller insulator.

  14. 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.

  15. Jahn-Teller distortion of Mn3+-occupied octahedra in red beryl from Utah indicated by optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Fridrichová, Jana; Bačík, Peter; Ertl, Andreas; Wildner, Manfred; Dekan, Július; Miglierini, Marcel

    2018-01-01

    Red beryl from Utah is chemically homogeneous and contains only Fe < 0.163, Mn < 0.018, and Mg < 0.016 apfu. Channel sites contain only up to Cs 0.011, K 0.009, Rb 0.004, and Na 0.004 apfu. This suggests only very slight tetrahedral (Cs,K,Rb)Li□-1Be-1 substitution, octahedral Na(Fe2+,Mg)□-1Al-1 substitution can be excluded. Fe and Mn are trivalent as documented by Mössbauer spectroscopy and optical absorption spectroscopy. Red beryl optimized formula is ∼[(Cs,Rb,K)0.02□0.98]Σ1.00□1.00(Al1.79Fe3+0.16Mn3+0.02Ti4+0.02Mg0.01)Σ2.00Be3(Si6O18). Location of Mn3+ was estimated to the octahedral Al3+ site, other choices are improbable due to the bond-length requirements. No Mn3+-induced Jahn-Teller structural distortion was detected due to site symmetry restrictions and small Mn3+ content. However, optical spectroscopy shows broad band at ∼7190 cm-1 assigned to the excited level of the spin-allowed pseudo-tetragonal split E ground state of elongated six-fold Mn3+ coordination. Crystal field calculations indicate that the local Mn3+ environment complies well with crystal chemical expectations for Jahn-Teller distorted Mn3+O6 octahedra.

  16. Multimode Jahn-Teller effect in bulk systems: A case of the N V 0 center in diamond

    DOE PAGES

    Zhang, Jianhua; Wang, Cai -Zhuang; Zhu, Zizhong; ...

    2018-04-15

    Here, the multimode Jahn-Teller (JT) effect in a bulk system of a neutral nitrogen-vacancy (NV 0) center in diamond is investigated via first-principles density-functional-theory calculations and the intrinsic distortion path (IDP) method. The adiabatic potential energy surface of the electronic ground state of the NV 0 center is calculated based on the local spin-density approximation. Our calculations confirm the presence of the dynamic Jahn-Teller effect in the ground 2E state of the NV 0 center. Within the harmonic approximation, the IDP method provides the reactive path of JT distortion from unstable high-symmetry geometry to stable low-symmetry energy minimum geometry, andmore » it describes the active normal modes participating in the distortion. We find that there is more than one vibrational mode contributing to the distortion, and their contributions change along the IDP. Several vibrational modes with large contributions to JT distortion, especially those modes close to 44 meV, are clearly observed as the phonon sideband in photoluminescence spectra in a series of experiments, indicating that the dynamic Jahn-Teller effect plays an important role in the optical transition of the NV 0 center.« less

  17. Multimode Jahn-Teller effect in bulk systems: A case of the N V0 center in diamond

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhua; Wang, Cai-Zhuang; Zhu, Zizhong; Liu, Qing Huo; Ho, Kai-Ming

    2018-04-01

    The multimode Jahn-Teller (JT) effect in a bulk system of a neutral nitrogen-vacancy (N V0 ) center in diamond is investigated via first-principles density-functional-theory calculations and the intrinsic distortion path (IDP) method. The adiabatic potential energy surface of the electronic ground state of the N V0 center is calculated based on the local spin-density approximation. Our calculations confirm the presence of the dynamic Jahn-Teller effect in the ground 2E state of the N V0 center. Within the harmonic approximation, the IDP method provides the reactive path of JT distortion from unstable high-symmetry geometry to stable low-symmetry energy minimum geometry, and it describes the active normal modes participating in the distortion. We find that there is more than one vibrational mode contributing to the distortion, and their contributions change along the IDP. Several vibrational modes with large contributions to JT distortion, especially those modes close to 44 meV, are clearly observed as the phonon sideband in photoluminescence spectra in a series of experiments, indicating that the dynamic Jahn-Teller effect plays an important role in the optical transition of the N V0 center.

  18. Multimode Jahn-Teller effect in bulk systems: A case of the N V 0 center in diamond

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Jianhua; Wang, Cai -Zhuang; Zhu, Zizhong

    Here, the multimode Jahn-Teller (JT) effect in a bulk system of a neutral nitrogen-vacancy (NV 0) center in diamond is investigated via first-principles density-functional-theory calculations and the intrinsic distortion path (IDP) method. The adiabatic potential energy surface of the electronic ground state of the NV 0 center is calculated based on the local spin-density approximation. Our calculations confirm the presence of the dynamic Jahn-Teller effect in the ground 2E state of the NV 0 center. Within the harmonic approximation, the IDP method provides the reactive path of JT distortion from unstable high-symmetry geometry to stable low-symmetry energy minimum geometry, andmore » it describes the active normal modes participating in the distortion. We find that there is more than one vibrational mode contributing to the distortion, and their contributions change along the IDP. Several vibrational modes with large contributions to JT distortion, especially those modes close to 44 meV, are clearly observed as the phonon sideband in photoluminescence spectra in a series of experiments, indicating that the dynamic Jahn-Teller effect plays an important role in the optical transition of the NV 0 center.« less

  19. The effect of band Jahn-Teller distortion on the magnetoresistivity of manganites: a model study.

    PubMed

    Rout, G C; Panda, Saswati; Behera, S N

    2011-10-05

    We present a model study of magnetoresistance through the interplay of magnetisation, structural distortion and external magnetic field for the manganite systems. The manganite system is described by the Hamiltonian which consists of the s-d type double exchange interaction, Heisenberg spin-spin interaction among the core electrons, and the static and dynamic band Jahn-Teller (JT) interaction in the e(g) band. The relaxation time of the e(g) electron is found from the imaginary part of the Green's function using the total Hamiltonian consisting of the interactions due to the electron and phonon. The calculated resistivity exhibits a peak in the pure JT distorted insulating phase separating the low temperature metallic ferromagnetic phase and the high temperature paramagnetic phase. The resistivity is suppressed with the increase of the external magnetic field. The e(g) electron band splitting and its effect on magnetoresistivity is reported here. © 2011 IOP Publishing Ltd

  20. 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.

  1. Thermal and composition driven phase transition in the co-operative Jahn-Teller distorted Zn1-xCuxCr2O4 spinel

    NASA Astrophysics Data System (ADS)

    Saraswathy, S.; Kalavathi, S.; Rajamadhavan, R.; Asuvathraman, R.

    2018-04-01

    Phase pure poly crystalline powder samples of spinel compounds with formula Zn1-xCuxCr2O4 have been synthesized. It is found that for a critical concentration of Cu with x=0.58 cubic structure of the parent ZnCr2O4 transforms into a tetragonal structure. The well-known co-operative Jahn-Teller effect induces the structural transition and the observed variation of lattice parameters as a function of Cu substitution displays the role of strain. Thermally driven destruction of the co-operative Jahn-Teller effect and the resultant reverting back to cubic structure is observed to complete at 850 K and 373 K in pristine CuCr2O4 and Zn0.4Cu0.6Cr2O4. A first order transition observed for Zn0.4Cu0.6Cr2O4 is at variance with the continuous transition observed in the literature for Mg0.46Cu0.54Cr2O4.

  2. 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

  3. 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.

  4. 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.

  5. Absence of Jahn-Teller transition in the hexagonal Ba 3CuSb 2O 9 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

  6. The Phenalenyl Free Radical - a Jahn-Teller D3H PAH

    NASA Astrophysics Data System (ADS)

    O'Connor, G. D.; Troy, T. P.; Roberts, D. A.; Chalyavi, N.; Fückel, B.; Crossley, M. J.; Nauta, K.; Schmidt, T. W.; Stanton, J. F.

    2012-06-01

    After benzene and naphthalene, the smallest polycyclic aromatic hydrocarbon bearing six-membered rings is the threefold-symmetric phenalenyl radical. Despite the fact that it is so fundamental, its electronic spectroscopy has not been rigorously scrutinized, in spite of growing interest in graphene fragments for molecular electronic applications. Here we used complementary laser spectroscopic techniques to probe the jet-cooled phenalenyl radical in vacuo. Its spectrum reveals the interplay between four electronic states that exhibit Jahn-Teller and pseudo-Jahn-Teller (Herzberg-Teller) vibronic coupling. The coupling mechanism has been elucidated by the application of various ab initio quantum-chemical techniques.

  7. First order phase transitions resulted from collective Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Rosenfeld, E. V.

    2018-01-01

    Generally, in case of the collective Jahn-Teller effect, a high-symmetry structure of a matrix in which quantum systems with degenerate ground state are inserted becomes distorted. This usually smooth transition can become abrupt only if the matrix by itself is a trigger and JTE merely activates its switching. It is shown in this paper that proper insertion into matrix of quantum systems with the singlet ground state and degenerate excited state leads to the formation of a new metastable state of the whole system and a stepwise appearance of JTE. Using nanotechnology, a matrix of any nature can be transformed into trigger in this way if one manages to synthesize and insert into it proper quantity of quantum JT-active centers with appropriate energy spectrum.

  8. 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.

  9. 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…

  10. GMX approximation for the linear E ⊗ ɛ Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Mancini, Jay D.; Fessatidis, Vassilios; Bowen, Samuel P.

    2006-02-01

    A newly developed generalized moments expansion (GMX) based on the t-expansion of Horn and Weinstein is applied to a linear E ⊗ ɛ Jahn-Teller system. Comparisons are made with other moments schemes as well a coupled cluster approximation.

  11. Jahn-Teller effect versus Hund's rule coupling in C60N-

    NASA Astrophysics Data System (ADS)

    Wehrli, S.; Sigrist, M.

    2007-09-01

    We propose variational states for the ground state and the low-energy collective rotator excitations in negatively charged C60N- ions (N=1,…,5) . The approach includes the linear electron-phonon coupling and the Coulomb interaction on the same level. The electron-phonon coupling is treated within the effective mode approximation which yields the linear t1u⊗Hg Jahn-Teller problem whereas the Coulomb interaction gives rise to Hund’s rule coupling for N=2,3,4 . The Hamiltonian has accidental SO(3) symmetry which allows an elegant formulation in terms of angular momenta. Trial states are constructed from coherent states and using projection operators onto angular momentum subspaces which results in good variational states for the complete parameter range. The evaluation of the corresponding energies is to a large extent analytical. We use the approach for a detailed analysis of the competition between Jahn-Teller effect and Hund’s rule coupling, which determines the spin state for N=2,3,4 . We calculate the low-spin-high-spin gap for N=2,3,4 as a function of the Hund’s rule coupling constant J . We find that the experimentally measured gaps suggest a coupling constant in the range J=60-80meV . Using a finite value for J , we recalculate the ground state energies of the C60N- ions and find that the Jahn-Teller energy gain is partly counterbalanced by the Hund’s rule coupling. In particular, the ground state energies for N=2,3,4 are almost equal.

  12. Experimental investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part II. Vibrational analysis of the A 2E"3-X 2E"2 electronic transition.

    PubMed

    Sioutis, Ilias; Stakhursky, Vadim L; Tarczay, György; Miller, Terry A

    2008-02-28

    Laser-induced fluorescence (LIF) and laser-excited dispersed fluorescence (LEDF) spectra of the cycloheptatrienyl (tropyl) radical C7H7 have been observed under supersonic jet-cooling conditions. Assignment of the LIF excitation spectrum yields detailed information about the A-state vibronic structure. The LEDF emission was collected by pumping different vibronic bands of the A 2E"3<--X 2E"2 electronic spectrum. Analysis of the LEDF spectra yields valuable information about the vibronic levels of the X 2E"2 state. The X- and A-state vibronic structures characterize the Jahn-Teller distortion of the respective potential energy surfaces. A thorough analysis reveals observable Jahn-Teller activity in three of the four e'3 modes for the X 2E"2 state and two of the three e'1 modes for the A 2E"3 state and provides values for their deperturbed vibrational frequencies as well as linear Jahn-Teller coupling constants. The molecular parameters characterizing the Jahn-Teller interaction in the X and A states of C7H7 are compared to theoretical results and to those previously obtained for C5H5 and C6H6+.

  13. Pseudo Jahn-Teller effect in control and rationalization of chemical transformations in two-dimensional compounds

    NASA Astrophysics Data System (ADS)

    Gorinchoy, N. N.; Bersuker, I. B.

    2017-05-01

    We show that the pseudo Jahn-Teller effect (PJTE) is instrumental in predicting and rationalizing structural changes in chemical transformations of two-dimensional (2D) molecular systems by means of analyzing the symmetries and electron occupation of the ground and lowest excited electronic states and the energy gap between them, subject to their PJT coupling along the main distortion coordinates. Special attention is paid to rationalizing the PJTE origin of non-planarity of 2D compounds and to the restoration of their planar configurations. Examples of two series of 1,2- and 1,4-dithiin containing tricyclic compounds (carbon sulfide, thianthrene, and antracene and their derivatives) are used to demonstrate in detail the mechanism of (1) enhancement and suppression of the PJTE distortions (puckering) in redox processes, and (2) PJTE induced symmetry breaking and restoration of the planar configuration by chemical substitutions.

  14. 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.

  15. 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.

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

    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 LuVO 3 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 studymore » 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 LuVO 3 and similar systems.« less

  17. The Jahn-Teller effect in (hu+)2⊗hg systems

    NASA Astrophysics Data System (ADS)

    Hands, Ian D.; Diery, Wajood A.; Dunn, Janette L.; Bates, Colin A.

    2007-07-01

    A general consideration is made of the vibronic coupling in a (hu+)2⊗hg Jahn-Teller system, that is to say, a system in which two holes of Hu symmetry are coupled to vibrations of hg symmetry. We find that the resulting high-spin states may undergo spontaneous distortion into species exhibiting one of the following four possible symmetries: D5 d, D3 d, D2 h or C2 h. The system may be viewed as a first approximation to a C602+ ion, but our intention here is to make a general consideration of the model without application to any specific molecular system. Coulombic interactions between holes, which must be important in real systems, are therefore ignored throughout. However, they could be included in the model, if required, using the method described in an earlier work [I.D. Hands, J.L. Dunn, W.A. Diery, C.A. Bates, Phys. Rev. B 73 (2006) 115435]. For each of the different symmetry types, projection operators are used to create symmetry-adapted states (SASs) that give a good account of the states of the system over a wide range of coupling strengths. These SASs are used, in turn, to derive energies for the vibronic states.

  18. The temperature dependence of the pressure switching of Jahn Teller deformation in the deuterated ammonium copper Tutton salt

    NASA Astrophysics Data System (ADS)

    Augustyniak, Maria A.; Krupski, Marcin

    1999-09-01

    The pressure switch of the Jahn-Teller deformation direction in (ND 4) 2Cu(SO 4) 2·6D 2O was investigated in the temperature range 130-320 K. Below 295 K, the new, pressure-induced phase, is stable under ambient pressure. Switching back is observed on heating to above 297 K. In the range 150-295 K a strong temperature dependence of the switching pressure (from 24 to 450 MPa) is observed. Below 150 K, the switching process is slow and a coexistence of two phases is observed. We conclude that the switch of the Cu(D 2O) 6 complex deformation direction is the Jahn-Teller response to the changes in the hydrogen bond system.

  19. On the important role of the anti-Jahn-Teller effect in underdoped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Kamimura, Hiroshi; Matsuno, Shunichi; Mizokawa, Takashi; Sasaoka, Kenji; Shiraishi, Kenji; Ushio, Hideki

    2013-04-01

    In this paper it is shown that the "anti-Jahn-Teller effect" plays an essential role in giving rise to a small Fermi surface of Fermi pockets above Tc and d-wave superconductivity below Tc in underdoped cuprates. In the first part of the present paper, we review the latest developments of the model proposed by Kamimura and Suwa, which bears important characteristics born from the interplay of Jahn-Teller Physics and Mott Physics. It is shown that the feature of Fermi surfaces in underdoped LSCO is the Fermi pockets in the nodal region constructed by doped holes under the coexistence of a metallic state and of the local antiferromagnetic order. In the antinodal region in the momentum space, there are no Fermi surfaces. Then it is discussed that the phonon-involved mechanism based on the Kamimura-Suwa model leads to the d-wave superconductivity. In particular, it is shown that the origin of strong electron-phonon interactions in cuprates is due to the anti-Jahn-Teller effect. In the second part a recent theoretical result on the energy distribution curves (EDCs) of angle-resolved photoemission spectroscopy (ARPES) below Tc is discussed. It is shown that the feature of ARPES profiles of underdoped cuprates consists of a coherent peak in the nodal region and the real transitions of photoexcited electrons from occupied states below the Fermi level to a free-electron state above the vacuum level in the antinodal region, where the latter transitions form a broad hump. From this feature, the origin of the two distinct gaps observed by ARPES is elucidated without introducing the concept of the pseudogap. Finally, a remark is made on the phase diagram of underdoped cuprates.

  20. Anisotropic orbital occupation and Jahn-Teller distortion of orthorhombic YMnO{sub 3} epitaxial films: A combined experimental and theoretical study on polarization-dependent x-ray absorption spectroscopy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Haw, Shu-Chih; Chen, Shin-Ann; National Synchrotron Radiation Research Center

    2014-04-21

    The b-axis oriented orthorhombic YMnO{sub 3} (o-YMnO{sub 3}) epitaxial films on a YAlO{sub 3} (010) substrate were fabricated with pulsed-laser deposition. The anisotropic orbital occupation and Jahn-Teller (JT) distortion of an o-YMnO{sub 3} film were investigated with polarization-dependent x-ray absorption spectra and configuration-interaction multiplet-cluster calculations. A significant energy difference, ∼3.8 eV, for the main white line along E//b and E//a in polarization-dependent Mn K-edge spectra of o-YMnO{sub 3} indicates an extraordinary JT distortion and significant anisotropic Mn–O bonding within the ab plane in the o-YMnO{sub 3} film. Most importantly, although the orbital occupation of 3d electrons in o-YMnO{sub 3} filmsmore » is almost the same as that in single crystalline o-DyMnO{sub 3}, the JT distortion of o-YMnO{sub 3} films is larger than that of single crystalline o-DyMnO{sub 3}, deduced from the multiplet calculations. We speculate that this JT distortion predominantly contributes to the origin of the cycloidal spin deformation in bulk o-YMnO{sub 3}, because of a suppressed nearest-neighbor superexchange interaction and an enhanced next-nearest-neighbor superexchange interaction. These complementary results provide insight into the origin of the E-type magnetic configuration of o-YMnO{sub 3}.« less

  1. Jahn-Teller effect in molecular electronics: quantum cellular automata

    NASA Astrophysics Data System (ADS)

    Tsukerblat, B.; Palii, A.; Clemente-Juan, J. M.; Coronado, E.

    2017-05-01

    The article summarizes the main results of application of the theory of the Jahn-Teller (JT) and pseudo JT effects to the description of molecular quantum dot cellular automata (QCA), a new paradigm of quantum computing. The following issues are discussed: 1) QCA as a new paradigm of quantum computing, principles and advantages; 2) molecular implementation of QCA; 3) role of the JT effect in charge trapping, encoding of binary information in the quantum cell and non-linear cell-cell response; 4) spin-switching in molecular QCA based on mixed-valence cell; 5) intervalence optical absorption in tetrameric molecular mixed-valence cell through the symmetry assisted approach to the multimode/multilevel JT and pseudo JT problems.

  2. Modulation of Jahn-Teller effect on magnetization and spontaneous electric polarization of CuFeO2

    NASA Astrophysics Data System (ADS)

    Xiao, Guiling; Xia, Zhengcai; Wei, Meng; Huang, Sha; Shi, Liran; Zhang, Xiaoxing; Wu, Huan; Yang, Feng; Song, Yujie; Ouyang, Zhongwen

    2018-03-01

    CuFe0.99Mn0.01O2 and CuFe0.99Co0.01O2 single crystal samples are grown by a floating zone technique and their magnetization and spontaneous electric polarization have been investigated. Similarly with pure CuFeO2, an obviously anisotropic magnetization and spontaneous electric polarization were observed in the both doped samples, and their phase transition critical fields and temperatures are directly doping ion dependent. Considering the different d-shell configuration and ionic size between Mn3+, Co3+ and Fe3+ ions, in which the Mn3+ ion with Jahn-Teller (J-T) effect has different distortion on the geometry frustration from both of Fe3+ and Co3+ ion. Since for Mn3+ ion, the orbital splitting results from the low-symmetry J-T distortion in a crystal-field environment leads to a distorted MnO6 octahedron, which different from undistorted FeO6 and CoO6 octahedrons. The strain between distorted and undistorted octahedrons produces different effects on the spin reorientation transition and spontaneous electric polarization. Although the pure CuFeO2 has a very strong and robust frustration, the presence of the strain due to the random distribution of distorted MnO6 octahedron and undistorted CoO6 (FeO6) octahedrons leads to its spin reorientation transitions and spontaneous electric polarization different from CuFeO2.

  3. Vibrational and Nonadiabatic Coherence in 2D Electronic Spectroscopy, the Jahn-Teller Effect, and Energy Transfer

    NASA Astrophysics Data System (ADS)

    Jonas, David M.

    2018-04-01

    Femtosecond two-dimensional (2D) Fourier transform spectroscopy generates and probes several types of coherence that characterize the couplings between vibrational and electronic motions. These couplings have been studied in molecules with Jahn-Teller conical intersections, pseudo-Jahn-Teller funnels, dimers, molecular aggregates, photosynthetic light harvesting complexes, and photosynthetic reaction centers. All have closely related Hamiltonians and at least two types of vibrations, including one that is decoupled from the electronic dynamics and one that is nonadiabatically coupled. Polarized pulse sequences can often be used to distinguish these types of vibrations. Electronic coherences are rapidly obscured by inhomogeneous dephasing. The longest-lived coherences in these systems arise from delocalized vibrations on the ground electronic state that are enhanced by a nonadiabatic Raman excitation process. These characterize the initial excited-state dynamics. 2D oscillation maps are beginning to isolate the medium lifetime vibronic coherences that report on subsequent stages of the excited-state dynamics.

  4. 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.

  5. Quantifying the effects of higher order coupling terms on fits using a second order Jahn-Teller Hamiltonian

    NASA Astrophysics Data System (ADS)

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

    2018-01-01

    The limitations associated with the common practice of fitting a quadratic Hamiltonian to vibronic levels of a Jahn-Teller system have been explored quantitatively. Satisfactory results for the prototypical X∼2E‧ state of Li3 are obtained from fits to both experimental spectral data and to an "artificial" spectrum calculated by a quartic Hamiltonian which accurately reproduces the adiabatic potential obtained from state-of-the-art quantum chemistry calculations. However the values of the Jahn-Teller parameters, stabilization energy, and pseudo-rotation barrier obtained from the quadratic fit differ markedly from those associated with the ab initio potential. Nonetheless the RMS deviations of the fits are not strikingly different. Guidelines are suggested for comparing parameters obtained from fits to experiment to those obtained by direct calculation, but a principal conclusion of this work is that such comparisons must be done with a high degree of caution.

  6. Jahn-Teller transition in TiF3 investigated using density-functional theory

    NASA Astrophysics Data System (ADS)

    Perebeinos, Vasili; Vogt, Tom

    2004-03-01

    We use first-principles density-functional theory to calculate the electronic and magnetic properties of TiF3 using the full-potential-linearized augmented-plane-wave method. The local density approximation (LDA) predicts a fully saturated ferromagnetic metal and finds degenerate energy minima for high- and low-symmetry structures. The experimentally observed Jahn-Teller phase transition at Tc=370 K cannot be driven by the electron-phonon interaction alone, which is usually described accurately by the LDA. Electron correlations beyond the LDA are essential to lift the degeneracy of the singly occupied Ti t2g orbital. Although the on-site Coulomb correlations are important, the direction of the t2g-level splitting is determined by dipole-dipole interactions. The LDA+U functional predicts an aniferromagnetic insulator with an orbitally ordered ground state. The input parameters U=8.1 eV and J=0.9 eV for the Ti 3d orbital were found by varying the total charge on the TiF2-6 ion using the molecular NRLMOL code. We estimate the Heisenberg exchange constant for spin 1/2 on a cubic lattice to be approximately 24 K. The symmetry lowering energy in LDA+U is about 900 K per TiF3 formula unit.

  7. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La 1-xCa xMnO 3

    DOE PAGES

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

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO 3 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 MnO 6 octahedra across the OR transition at T S~720 K.more » The study utilized explicit two-phase PDF structural modeling, revealing that away from T MI 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 CaMnO 3. The results hence do not support the percolative scenario for the MI transition in La 1–xCa xMnO 3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO 3 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

  8. High-pressure behavior of cuprospinel CuFe 2O 4: 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 Cu 2+ in cuprospinel CuFe 2O 4 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) Å 3 to 579.5 (8) Å 3 up to 3.8 GPa. Leastsquares fitting to a third-order Birch-Murnaghan equation of state yields zero-pressure volume V 0 = 590.7more » (1) Å 3 and bulk modulus K 0 = 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 [Cu 0.526Fe 0.474] [6][Cu 0.074Fe 1.926]O 4. Most of the Cu 2+ 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 I4 1/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 Cu 2+ 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

  9. Observation of a quadrupole interaction for cubic imperfections exhibiting a dynamic Jahn-Teller effect.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    The observation and interpretation of weak EPR transitions, identified as 'forbidden' transitions, establish the existence of a new type of quadrupole interaction for cubic-symmetry imperfections. This interaction is simply a consequence of the ground-vibronic-state degeneracy. The signs as well as the magnitudes of the quadrupole-coupling coefficients are determined experimentally. These data agree well with the predictions of crystal field theory modified to account for a weak-to-moderate vibronic interaction (i.e., a dynamic Jahn-Teller effect).

  10. α-ScVSe2O8, β-ScVSe2O8, and ScVTe2O8: new quaternary mixed metal oxides composed of only second-order Jahn-Teller distortive cations.

    PubMed

    Kim, Yeong Hun; Lee, Dong Woo; Ok, Kang Min

    2013-10-07

    Three new quaternary scandium vanadium selenium/tellurium oxides, α-ScVSe2O8, β-ScVSe2O8, and ScVTe2O8 have been synthesized through hydrothermal and standard solid-state reactions. Although all three reported materials are stoichiometrically similar, they exhibit different crystal structures: α-ScVSe2O8 has a three-dimensional framework structure consisting of ScO6, VO6, and SeO3 groups. β-ScVSe2O8 reveals another three-dimensional framework composed of ScO7, VO5, and SeO3 polyhedra. ScVTe2O8 shows a layered structure with ScO6, VO4, and TeO4 polyhedra. Interestingly, the constituent cations, that is, Sc(3+), V(5+), Se(4+), and Te(4+) are all in a distorted coordination environment attributable to second-order Jahn-Teller (SOJT) effects. Complete characterizations including infrared spectroscopy, elemental analyses, thermal analyses, dipole moment calculation, and the magnitudes of out-of-center distortions for the compounds are reported. Transformation reactions suggest that α-ScVSe2O8 may change to β-ScVSe2O8, and then to Sc2(SeO3)3·H2O under hydrothermal conditions.

  11. EPR Studies of orthorhombic Jahn-Teller effect in single crystal of ferroelectric Cu(II):Cd2(NH4)2 (SO4)3

    NASA Astrophysics Data System (ADS)

    Benson, Yerima; de, Dilip

    In this paper we report the first EPR observation and theoretical explanation of orthorhombic Jahn-Teller effect in Cu(II) doped single crystal of ferroelectric cadmium ammonium sulphate: Cu(II):Cd2(NH4)2 (SO4)3 . The isotropic EPR spectra of the 2D ion (in regular octahedral symmetry) at higher temperature becomes anisotropic at low temperature with clear manifestation of orthorhombic g and hyperfine tensors at 15 K. The static Jahn-Teller(JT) effect can only be explained theoretically by assuming the three JT potential wells energetically inequivalent, unlike the potential wells in most of the Cu(II) doped crystalline materials where JT effect manifests. The measured splitting of the JT potential wells in this ferroelectric crystal fall in the sub millimeter wave region pointing to possible application of the material.

  12. Unconventional high-Tc superconductivity in fullerides.

    PubMed

    Takabayashi, Yasuhiro; Prassides, Kosmas

    2016-09-13

    A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. © 2016 The Author(s).

  13. Generalized Born-Oppenheimer treatment of Jahn-Teller systems in Hilbert spaces of arbitrary dimension: theory and application to a three-state model potential.

    PubMed

    Varandas, A J C; Sarkar, B

    2011-05-14

    Generalized Born-Oppenheimer equations including the geometrical phase effect are derived for three- and four-fold electronic manifolds in Jahn-Teller systems near the degeneracy seam. The method is readily extendable to N-fold systems of arbitrary dimension. An application is reported for a model threefold system, and the results are compared with Born-Oppenheimer (geometrical phase ignored), extended Born-Oppenheimer, and coupled three-state calculations. The theory shows unprecedented simplicity while depicting all features of more elaborated ones.

  14. Local lattice distortion in high-entropy alloys

    NASA Astrophysics Data System (ADS)

    Song, Hongquan; Tian, Fuyang; Hu, Qing-Miao; Vitos, Levente; Wang, Yandong; Shen, Jiang; Chen, Nanxian

    2017-07-01

    The severe local lattice distortion, induced mainly by the large atomic size mismatch of the alloy components, is one of the four core effects responsible for the unprecedented mechanical behaviors of high-entropy alloys (HEAs). In this work, we propose a supercell model, in which every lattice site has similar local atomic environment, to describe the random distributions of the atomic species in HEAs. Using these supercells in combination with ab initio calculations, we investigate the local lattice distortion of refractory HEAs with body-centered-cubic structure and 3 d HEAs with face-centered-cubic structure. Our results demonstrate that the local lattice distortion of the refractory HEAs is much more significant than that of the 3 d HEAs. We show that the atomic size mismatch evaluated with the empirical atomic radii is not accurate enough to describe the local lattice distortion. Both the lattice distortion energy and the mixing entropy contribute significantly to the thermodynamic stability of HEAs. However the local lattice distortion has negligible effect on the equilibrium lattice parameter and bulk modulus.

  15. Phase Separation and d Electronic Orbitals on Cyclic Degradation in Li-Mn-O Compounds: First-Principles Multiscale Modeling and Experimental Observations.

    PubMed

    Kim, Duho; Lim, Jin-Myoung; Park, Min-Sik; Cho, Kyeongjae; Cho, Maenghyo

    2016-07-06

    A combined study involving experiments and multiscale computational approaches is conducted to propose a theoretical solution for the suppression of the Jahn-Teller distortion which causes severe cyclic degradation. As-synthesized pristine and Al-doped Mn spinel compounds are the focus to understand the mechanism of the cyclic degradation in terms of the Jahn-Teller distortion, and the electrochemical performance of the Al-doped sample shows enhanced cyclic performance compared with that of the pristine one. Considering the electronic structures of the two systems using first-principles calculations, the pristine spinel suffers entirely from the Jahn-Teller distortion by Mn(3+), indicating an anisotropic electronic structure, but the Al-doped spinel exhibits an isotropic electronic structure, which means the suppressed Jahn-Teller distortion. A multiscale phase field model in nanodomain shows that the phase separation of the pristine spinel occurs to inactive Li0Mn2O4 (i.e., fully delithiated) gradually during cycles. In contrast, the Al-doped spinel does not show phase separation to an inactive phase. This explains why the Al-doped spinel maintains the capacity of the first charge during the subsequent cycles. On the basis of the mechanistic understanding of the origins and mechanism of the suppression of the Jahn-Teller distortion, fundamental insight for making tremendous cuts in the cyclic degradation could be provided for the Li-Mn-O compounds of Li-ion batteries.

  16. Distorted allotropes of bi-benzene: vibronic interactions and electronic excitations

    NASA Astrophysics Data System (ADS)

    Krasnenko, V.; Boltrushko, V.; Hizhnyakov, V.

    2017-05-01

    Bi-benzene - chemically bound two benzene molecules in stuck position is studied both analytically and numerically. There are several allotropes of bi-benzene having different geometry. The reason of the existence of sundry distorted structures is the pseudo-Jahn-Teller effect. The parameters of vibronic couplings causing distortions are found. For the calculation of these parameters both, the vibronic coupling of carbon atoms in different C6 rings and the vibronic coupling in the rings are considered. The contribution of the distortion of C6-planes to the latter coupling is also found. The energies of all the electronic states of π-electrons in all bi-benzene allotropes are determined by using the calculated vibronic interaction parameters.

  17. Magneto-structural correlation in Co0.8Cu0.2Cr2O4 cubic spinel

    NASA Astrophysics Data System (ADS)

    Kumar, Ram; Rayaprol, S.; Siruguri, V.; Xiao, Y.; Ji, W.; Pal, D.

    2018-05-01

    Neutron and X-ray diffraction, magnetic susceptibility, and specific heat measurements have been used to investigate the magneto-structural phase transitions in 20% Cu substituted multiferroic CoCr2O4 spinel. The Jahn-Teller active Cu2+ ion in the tetrahedral A-site of the spinel configuration induces the Jahn-Teller distortion slightly above the Néel temperature. In this compound, we observe a Jahn-Teller distortion of the crystal structure at 90 K. It was further observed that the high temperature cubic (Fd 3 ‾ m) structure coexists with the low temperature orthorhombic (Fddd) structure till the lowest temperature of measurement.

  18. Acoustic Properties of Crystals with Jahn-Teller Impurities: Elastic Moduli and Relaxation Time. Application to SrF2:Cr2+

    NASA Astrophysics Data System (ADS)

    Averkiev, Nikita S.; Bersuker, Isaac B.; Gudkov, Vladimir V.; Zhevstovskikh, Irina V.; Sarychev, Maksim N.; Zherlitsyn, Sergei; Yasin, Shadi; Shakurov, Gilman S.; Ulanov, Vladimir A.; Surikov, Vladimir T.

    2017-11-01

    A new approach to evaluate the relaxation contribution to the total elastic moduli for crystals with Jahn-Teller (JT) impurities is worked out and applied to the analysis of the experimentally measured ultrasound velocity and attenuation in SrF2:Cr2+. Distinguished from previous work, the background adiabatic contribution to the moduli, important for revealing the impurity relaxation contribution, is taken into account. The temperature dependence of the relaxation time for transitions between the equivalent configurations of the JT centers has been obtained, and the activation energy for the latter in SrF2:Cr2+, as well as the linear vibronic coupling constant have been evaluated.

  19. On the Mechanism of D-Wave High TC Superconductivity by the Interplay of Jahn-Teller Physics and Mott Physics

    NASA Astrophysics Data System (ADS)

    Ushio, H.; Matsuno, S.; Kamimura, H.

    2011-01-01

    In the present paper we will discuss two important roles of the interplay of Jahn-Teller physics and Mott physics. One is the small Fermi surface. The "Fermi arcs" observed in ARPES should be one of the edges of small Fermi pockets, based on the Kamimura-Suwa model (K-S model). This prediction is consistent with ARPES results by Tanaka et al. Another is the mechanism of superconductivity in cuprates. This can be explained by the interplay of strong electron-phonon interactions and local AF order. It is shown that the characteristic phase difference of wave functions between up- and down-spin carriers in the presence of the local AF order leads to the superconducting gap of dx2-y2 symmetry even in the phonon-involved mechanism.

  20. Design of Mott and topological phases on buckled 3d-oxide honeycomb lattices

    NASA Astrophysics Data System (ADS)

    Pentcheva, Rossitza

    The honeycomb lattice, as realized e.g. in graphene, has rendered a robust platform for innovative science and potential applications. A much richer generalization of this lattice arises in (111)-oriented bilayers of perovskites, adding the complexity of the strongly correlated, multiorbital nature of electrons in transition metal oxides. Based on first principles calculations with an on-site Coulomb repulsion, here we provide trends in the evolution of ground states versus band filling in (111)-oriented (La XO3)2 /(LaAlO3)4 superlattices, with X spanning the entire 3d transition metal series. The competition between local quasi-cubic and global triangular symmetry triggers unanticipated broken symmetry phases, with mechanisms ranging from Jahn-Teller distortion, to charge-, spin-, and orbital-ordering. LaMnO3 and LaCoO3 bilayers, where spin-orbit coupling opens a sizable gap in the Dirac-point Fermi surface, emerge as much desired oxide-based Chern insulators, the latter displaying a gap capable of supporting room-temperature applications Further realizations of the honeycomb lattice and geometry patterns beyond the perovskite structure will be addressed. Research supported by the DFG, SFB/TR80.

  1. Free H₂ rotation vs Jahn-Teller constraints in the nonclassical trigonal (TPB)Co-H₂ complex.

    PubMed

    Gunderson, William A; Suess, Daniel L M; Fong, Henry; Wang, Xiaoping; Hoffmann, Christina M; Cutsail, George E; Peters, Jonas C; Hoffman, Brian M

    2014-10-22

    Proton exchange within the M-H2 moiety of (TPB)Co(H2) (Co-H2; TPB = B(o-C6H4P(i)Pr2)3) by 2-fold rotation about the M-H2 axis is probed through EPR/ENDOR studies and a neutron diffraction crystal structure. This complex is compared with previously studied (SiP(iPr)3)Fe(H2) (Fe-H2) (SiP(iPr)3 = [Si(o-C6H4P(i)Pr2)3]). The g-values for Co-H2 and Fe-H2 show that both have the Jahn-Teller (JT)-active (2)E ground state (idealized C3 symmetry) with doubly degenerate frontier orbitals, (e)(3) = [|mL ± 2>](3) = [x(2) - y(2), xy](3), but with stronger linear vibronic coupling for Co-H2. The observation of (1)H ENDOR signals from the Co-HD complex, (2)H signals from the Co-D2/HD complexes, but no (1)H signals from the Co-H2 complex establishes that H2 undergoes proton exchange at 2 K through rotation around the Co-H2 axis, which introduces a quantum-statistical (Pauli-principle) requirement that the overall nuclear wave function be antisymmetric to exchange of identical protons (I = 1/2; Fermions), symmetric for identical deuterons (I = 1; Bosons). Analysis of the 1-D rotor problem indicates that Co-H2 exhibits rotor-like behavior in solution because the underlying C3 molecular symmetry combined with H2 exchange creates a dominant 6-fold barrier to H2 rotation. Fe-H2 instead shows H2 localization at 2 K because a dominant 2-fold barrier is introduced by strong Fe(3d)→ H2(σ*) π-backbonding that becomes dependent on the H2 orientation through quadratic JT distortion. ENDOR sensitively probes bonding along the L2-M-E axis (E = Si for Fe-H2; E = B for Co-H2). Notably, the isotropic (1)H/(2)H hyperfine coupling to the diatomic of Co-H2 is nearly 4-fold smaller than for Fe-H2.

  2. Orbital effects in cobaltites by neutron scattering

    NASA Astrophysics Data System (ADS)

    Louca, Despina

    2005-03-01

    The orbital degree of freedom can play a central role in the physics of transition metal perovskite oxides because of its intricate coupling with other degrees of freedom such as spin, charge and lattice. In this talk the case of La1-xSrxCoO3 will be presented. Using elastic and inelastic neutron scattering, we investigated the thermal evolution of the local atomic structure and lattice dynamics in the pure sample and with the addition of charge carriers as the system crosses over from a paramagnetic insulator to a ferromagnetic metal. In LaCoO3, the thermal activation of the Co ions from a nonmagnetic ground state to an intermediate spin state gives rise to orbital degeneracy. This leads to Jahn-Teller distortions that are dynamical in nature. Doping stabilizes the intermediate spin configuration of the Co ions in the paramagnetic insulating phase. Evidence for local static Jahn-Teller distortions is observed but without long-range ordering. The size of the JT lattice is proportional to the amount of charge. However, with cooling to the metallic phase, static JT distortions disappear for x <= 30 %, the percolation limit. This coincides with narrowing of two modes at φ=22,nd,4,eV in the phonon spectrum in which we argue is due to localized dynamical JT fluctuations^1. The implications of the orbital effects to the structural and magnetic properties will be discussed. ^1D. Louca and J. L. Sarrao, Phys. Rev. Lett. 91, 155501 (2003).

  3. Ba 3 (Cr 0.97(1) Te 0.03(1) ) 2 TeO 9 : in Search of Jahn–Teller Distorted Cr(II) Oxide

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Man-Rong; Deng, Zheng; Lapidus, Saul H.

    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+more » . 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.« less

  4. Effect of pressure on the tetragonal distortion in TiH2: a first-principles study

    NASA Astrophysics Data System (ADS)

    de Coss, R.; Quijano, R.; Singh, D. J.

    2009-03-01

    The transition metal dihydride TiH2 present the fluorite structure (CaF2) at high temperature but undergoes a tetragonal distortion with c/a<1 at low temperature. Early electronic band structure calculations have shown that TiH2 in the cubic phase display a nearly flat double degenerated band at the Fermi level. Thus the low temperature tetragonal distortion has been associated to a Jahn-Teller effect. Nevertheless, recently we have show that the instability of fcc-TiH2 is likely to be related with a van Hove singularity. In the present work, we have performed ab-initio calculations of the electronic structure and the tetragonal distortion for TiH2 under pressure (0-30 GPa). We found that the fcc-fct energy barrier and the tetragonal distortion increases with pressure. The evolution of the tetragonal distortion is analyzed in terms of the electronic band structure. This research was supported by Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grant No. 49985.

  5. 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.

  6. Proton NMR studies of the electronic structure of ZrH/sub x/

    NASA Technical Reports Server (NTRS)

    Attalla, A.; Bowman, R. C., Jr.; Craft, B. D.; Venturini, E. L.; Rhim, W. K.

    1982-01-01

    The proton spin lattice relaxation times and Knight shifts were measured in f.c.c. (delta-phase) and f.c.t. (epsilon-phase) ZrH/sub x/ for 1.5 or = to x or = to 2.0. Both parameters indicate that N(E/sub F/) is very dependent upon hydrogen content with a maximum occurring at ZrH1 83. This behavior is ascribed to modifications in N(E/sub F/) through a fcc/fct distortion in ZrH/sub x/ associated with a Jahn-Teller effect.

  7. 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

  8. Spin and orbital disordering by hole doping in P r1 -xC axV O3

    NASA Astrophysics Data System (ADS)

    Reehuis, M.; Ulrich, C.; Abdala, P. M.; Pattison, P.; Khaliullin, G.; Fujioka, J.; Miyasaka, S.; Tokura, Y.; Keimer, B.

    2016-09-01

    High-resolution powder x-ray diffraction and single-crystal neutron diffraction were used to investigate the crystal structure and magnetic ordering of the compound P r1 -xC axV O3 (0 ≤x ≤0.3 ), which undergoes an insulator-to-metal transition for x ˜0.23 . Since the ionic radii of P r3 + and C a2 + are almost identical and structural disorder is minimal, P r1 -xC axV O3 is a good model system for the influence of hole doping on the spin and orbital correlations in transition metal oxides. The end member PrV O3 is a Mott-Hubbard insulator, which exhibits a structural phase transition at TS=180 K from an orthorhombic to a monoclinic structure with space groups Pbnm and P 21/b , respectively. This transition is associated with the onset of orbital ordering and strong Jahn-Teller distortions of the V O6 octahedra. Antiferromagnetic C -type order with vanadium moments oriented in the a b plane is observed below TN=140 K . Upon cooling, the vanadium moments induce a progressive magnetic polarization of the praseodymium sublattice, resulting in a ferrimagnetic structure with coexisting modes (Cx, Fy) and (Fx, Cy). In the insulating range of the P r1 -xC axV O3 phase diagram, Ca doping reduces both the orbital and magnetic transition temperatures so that TS=108 K and TN=95 K for x =0.20 . The Jahn-Teller distortions and ordered vanadium moments also decrease upon doping. In a metallic sample with x =0.30 , Jahn-Teller distortions and long-range orbital ordering are no longer observable, and the average crystal structure remains orthorhombic down to low temperature. However, broadening of some lattice Bragg reflections indicate a significant increase in lattice strain. Antiferromagnetic short-range order with a weak ordered moment of 0.14(3) μB per vanadium atom could still be observed on the vanadium site below T ˜60 K . We discuss these observations in terms of doping-induced spin-orbital polaron formation.

  9. On the nature of the phase transition in uranium dioxide

    NASA Astrophysics Data System (ADS)

    Gofryk, K.; Mast, D.; Antonio, D.; Shrestha, K.; Andersson, D.; Stanek, C.; Jaime, M.

    Uranium dioxide (UO2) is by far the most studied actinide material as it is a primary fuel used in light water nuclear reactors. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. UO2 crystalizes in the face-centered-cubic fluorite structure and is a Mott-Hubbard insulator with well-localized uranium 5 f-electrons. In addition, below 30 K, a long range antiferromagnetic ordering of the electric-quadrupole of the uranium moments is observed, forming complex non-collinear 3-k magnetic structure. This transition is accompanied by Jahn-Teller distortion of oxygen atoms. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion. Here we present results of our extensive thermodynamic investigations on well-characterized and oriented single crystals of UO2+x (x = 0, 0.033, 0.04, and 0.11). By focusing on the transition region under applied magnetic field we are able to study the interplay between different competing interactions (structural, magnetic, and electrical), its dynamics, and relationship to the oxygen content. We will discuss implications of these results. Work supported by the Department of Energy, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division.

  10. Tensile Strain Effects on the Magneto-transport in Calcium Manganese Oxide Thin Films: Comparison with its Hole-doped Counterpart

    NASA Astrophysics Data System (ADS)

    Lawson, Bridget; Neubauer, Samuel; Chaudhry, Adeel; Hart, Cacie; Ferrone, Natalie; Houston, David; Yong, Grace; Kolagani, Rajeswari

    Magnetoresistance properties of the epitaxial thin films of doped rare earth manganites are known to be influenced by the effect of bi-axial strain induced by lattice mismatch with the substrate. In hole-doped manganites, the effect of both compressive and tensile strain is qualitatively consistent with the expected changes in unit cell symmetry from cubic to tetragonal, leading to Jahn-Teller strain fields that affect the energy levels of Mn3 + energy levels. Recent work in our laboratory on CaMnO3 thin films has pointed out that tetragonal distortions introduced by tensile lattice mismatch strain may also have the effect of modulating the oxygen content of the films in agreement with theoretical models that propose such coupling between strain and oxygen content. Our research focuses on comparing the magneto-transport properties of hole-doped manganite LaCaMnO3 thin films with that of its electron doped counter parts, in an effort to delineate the effects of oxygen stoichiometry changes on magneto-transport from the effects of Jahn-Teller type strain. Towson University Office of Undergraduate Research, Fisher Endowment Grant and Undergraduate Research Grant from the Fisher College of Science and Mathematics, Seed Funding Grant from the School of Emerging technologies and the NSF Grant ECCS 112856.

  11. Ne matrix spectra of the sym-C6Br3F3+ radical cation

    USGS Publications Warehouse

    Bondybey, V.E.; Sears, T.J.; Miller, T.A.; Vaughn, C.; English, J.H.; Shiley, R.S.

    1981-01-01

    The electronic absorption and laser excited, wavelength resolved fluorescence spectra of the title cation have been observed in solid Ne matrix and vibrationally analysed. The vibrational structure of the excited B2A2??? state shows close similarity to the parent compound. The X2E??? ground state structure is strongly perturbed and irregular owing to a large Jahn-Teller distortion. The data are analysed in terms of a recently developed, sophisticated multimode Jahn-Teller theoretical model. We have generated the sym-C6Br3F3+ cations in solid Ne matrix and obtained their wavelength resolved emission and absorption spectra. T ground electronic X2E??? state exhibits an irregular and strongly perturbed vibrational structure, which can be successfully modeled using sophisticated multimode Jahn-Teller theory. ?? 1981.

  12. 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 HCN 2 -R (R = Li, BeH, BH 2 , CH 3 , CN, CCH, C 6 H 5 , NH 2 , 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 C 1 structure via a planar bent C s structure. Each of the others is found to undergo pseudo-JT distortion from a symmetrical structure to a planar bent C s structure for 2, 3, and 7 and to a C 1 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 V en and the other in which the stability results from a lowering of the energy of the repulsive terms V nn and V ee . 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 V ee observed in 6, another is a lowering of the energy of the terms V ee and V en observed in 9-11, and the other is a lowering of the energy of the terms V en and V nn 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

  13. Ab initio theory of spin-orbit coupling for quantum bits in diamond exhibiting dynamic Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Gali, Adam; Thiering, Gergő

    Dopants in solids are promising candidates for implementations of quantum bits for quantum computing. In particular, the high-spin negatively charged nitrogen-vacancy defect (NV) in diamond has become a leading contender in solid-state quantum information processing. The initialization and readout of the spin is based on the spin-selective decay of the photo-excited electron to the ground state which is mediated by spin-orbit coupling between excited states states and phonons. Generally, the spin-orbit coupling plays a crucial role in the optical spinpolarization and readout of NV quantum bit (qubit) and alike. Strong electron-phonon coupling in dynamic Jahn-Teller (DJT) systems can substantially influence the effective strength of spin-orbit coupling. Here we show by ab initio supercell density functional theory (DFT) calculations that the intrinsic spin-orbit coupling is strongly damped by DJT effect in the triplet excited state that has a consequence on the rate of non-radiative decay. This theory is applied to the ground state of silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in their negatively charged state that can also act like qubits. We show that the intrinsic spin-orbit coupling in SiV and GeV centers is in the 100 GHz region, in contrast to the NV center of 10 GHz region. Our results provide deep insight in the nature of SiV and GeV qubits in diamond. EU FP7 DIADEMS project (Contract No. 611143).

  14. Structure and Stability of Carboxylate Complexes. 20. Diaqua Bis(methoxyacetato) Complexes of Nickel(II), Copper(II), and Zinc(II): A Structural Study of the Dynamic Pseudo-Jahn-Teller Effect.

    PubMed

    Prout, Keith; Edwards, Alison; Mtetwa, Victor; Murray, Jon; Saunders, John F.; Rossotti, Francis J. C.

    1997-06-18

    The crystal structure of trans-diaquabis(methoxyacetato)copper(II), C(6)H(14)O(8)Cu, has been determined by neutron diffraction at 4.2 K (monoclinic, P2(1)/n, a = 6.88(1), b = 7.19(1), c = 9.77(2) Å, gamma = 95.7(1) degrees, (Z = 2)) and by X-ray diffraction at 125, 165, 205, 240, 265, 295, and 325 K. These measurements show that there is no phase change in the temperature range 4.2-325 K. The copper(II) coordination at 4.2 K is a tetragonally distorted elongated rhombic octahedron (Cu-OOC 1.955(1), Cu-OMe 2.209(1), and Cu-OH(2) 2.031(2) Å). As the temperature increases to 325 K, the Cu-OOC bonds shorten slightly to 1.934(5) Å, the Cu-OMe bonds shorten more markedly to 2.137(4) Å, and Cu-OH(2) lengthens to 2.155(6) Å to give a tetragonally distorted compressed rhombic octahedron. For comparison the structure of the isomorphous nickel(II) complex (monoclinic, P2(1)/n, a = 6.633(1), b = 7.192(1), c = 10.016(2) Å, gamma = 98.30(2) degrees, (Z = 2)) has been redetermined at 295 K and the structure of the analogous zinc(II) complex (orthorhombic, F2dd, a = 7.530(1), b = 13.212(1), c = 21.876(2) Å (Z = 8)) has also been determined. The nickel(II) complex has an almost regular trans (centrosymmetric) octahedral coordination (Ni-OOC 2.022(1), Ni-OMe 2.043(1), and Ni-OH(2) 2.077(2) Å). However, zinc(II) has a very distorted octahedral coordination with the zinc atom on a 2-fold axis with the water molecules and the methoxy ligators cis and the carboxylate ligators trans (Zn-OOC 1.985(1), Zn-OMe 2.304(2), and Zn-OH(2) 2.038(2) Å). The variation in the dimensions of the copper(II) coordination sphere is discussed in terms of static (low temperature) and planar dynamic (high temperature) pseudo-Jahn-Teller effects.

  15. New Baxter phase in the Ashkin-Teller model on a cubic lattice

    NASA Astrophysics Data System (ADS)

    Santos, J. P.; Rosa, D. S.; Sá Barreto, F. C.

    2018-02-01

    The mean field theory results are obtained from the Bogoliubov inequality for the spin-1/2 Ashkin-Teller model on a cubic lattice for different cluster sizes. The phase diagram, magnetization and free energy are obtained. From those expressions we observed a new phase in the model. Denoted in the course of this work by Baxter(2) this new phase presents 〈 S 〉 ≠ 〈 σ 〉 ≠ 0. The phase transitions between the Baxter(2) and the others well known phases for the model are studied and classified.

  16. 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.

  17. Local probe studies on lattice distortions and electronic correlations in manganites

    NASA Astrophysics Data System (ADS)

    Lopes, Armandina Maria Lima

    Nesta tese apresenta-se um estudo experimental das distorcoes locais e correlacoes electronicas em oxidos magneticos com magnetoresistencia colossal. A tecnica de sonda local - Correlacao Angular Perturbada - e utilizada em amostras caracterizadas quanto as suas propriedades macroscopicas nomeadamente propriedades estruturais, magneticas e electricas, tendo em vista a obtencao de informacao microscopica relevante via gradiente de campo electrico e campo magnetico hiperfino, focando em particular os seguintes aspectos: -Distorcoes de rede e agregados de polaroes no sistema LaMnO3+Delta. E apresentado um estudo dos gradientes de campo electrica e campo magnetico hiperfino em amostras representativas do sistema LaMnO3+Delta, correlacionando estas propriedades locais com a caracterizacao das propriedades macroscopicas, efectuada nas mesmas amostras. Desta forma, foi possivel estudar a natureza microscopica das distorcoes polaronicas. Foi dada especial atencao ao composto com composicao LaMnO3.12 uma vez que este e um sistema padrao de uma manganite ferromagnetica-isoladora que apresenta uma transicao estrutural romboedrica (R)-ortorrombica (O) perto da temperatura ambiente. O estudo revelou que agregados de distorcoes locais sobrevivem ate 776 K, na fase de estrutura media mais simetrica (romboedrica), onde, por simetria, os octaedros MnO6 deveriam ser regulares. Estas distorcoes sao semelhantes as observadas no sistema LaMnO3 onde os octaedros MnO6 apresentam uma distorcao Jahn-Teller colectiva. Com a diminuicao da temperatura observa-se um aumento continuo destes agregados. Abaixo de uma temperatura critica estas distorcoes relaxam acomodando-se numa estrutura com reduzidas distorcoes Jahn-teller. Verificou-se tambem que a transicao estrutural (macroscopica) pode ser entendida como uma transicao de percolacao dos ambientes microscopicos. -Coexistencia das ordens electrica e magnetica no sistema Pr1-xCaxMnO3. E apresentado o primeiro estudo de gradiente de campo

  18. Lattice distortions in GaN on sapphire using the CBED-HOLZ technique.

    PubMed

    Sridhara Rao, D V; McLaughlin, K; Kappers, M J; Humphreys, C J

    2009-09-01

    The convergent beam electron diffraction (CBED) methodology was developed to investigate the lattice distortions in wurtzite gallium nitride (GaN) from a single zone-axis pattern. The methodology enabled quantitative measurements of lattice distortions (alpha, beta, gamma and c) in transmission electron microscope (TEM) specimens of a GaN film grown on (0,0,0,1) sapphire by metal-organic vapour-phase epitaxy. The CBED patterns were obtained at different distances from the GaN/sapphire interface. The results show that GaN is triclinic above the interface with an increased lattice parameter c. At 0.85 microm from the interface, alpha=90 degrees , beta=8905 degrees and gamma=11966 degrees . The GaN lattice relaxes steadily back to hexagonal further away from the sapphire substrate. The GaN distortions are mainly confined to the initial stages of growth involving the growth and the coalescence of 3D GaN islands.

  19. One Dimensional(1D)-to-2D Crossover of Spin Correlations in the 3D Magnet ZnMn 2O 4

    DOE PAGES

    Disseler, S. M.; Chen, Y.; Yeo, S.; ...

    2015-12-08

    In this paper we report on the intriguing evolution of the dynamical spin correlations of the frustrated spinel ZnMn 2O 4. Inelastic neutron scattering and magnetization studies reveal that the dynamical correlations at high temperatures are 1D. At lower temperature, these dynamical correlations become 2D. Surprisingly, the dynamical correlations condense into a quasi 2D Ising-like ordered state, making this a rare observation of two dimensional order on the spinel lattice. Remarkably, 3D ordering is not observed down to temperatures as low as 300 mK. This unprecedented dimensional crossover stems from frustrated exchange couplings due to the huge Jahn-Teller distortions aroundmore » Mn 3+ ions on the spinel lattice.« less

  20. Aggregate frequency width, nuclear hyperfine coupling and Jahn-Teller effect of Cu2+ impurity ion ESR in SrLaAlO4 dielectric resonator at 20 millikelvin

    NASA Astrophysics Data System (ADS)

    Hosain, M. A.; Le Floch, J.-M.; Krupka, J.; Tobar, M. E.

    2018-01-01

    The impurity paramagnetic ion, Cu2+ substitutes Al in the SrLaAlO4 single crystal lattice, this results in a CuO6 elongated octahedron, and the resulting measured g-factors satisfy four-fold axes variation condition. The aggregate frequency width of the electron spin resonance with the required minimum level of impurity concentration has been evaluated in this single crystal SrLaAlO4 at 20 millikelvin. Measured parallel hyperfine constants, A\\Vert Cu , were determined to be -155.7×10-4~cm-1, ~ -163.0×10-4~cm-1, ~ -178.3×10-4~cm-1 and -211.1×10-4~cm-1 at 9.072~GHz~(WGH4, 1, 1) for the nuclear magnetic quantum number M_I=+\\frac{3}{2}, +\\frac{1}{2}, -\\frac{1}{2} , and -\\frac{3}{2} respectively. The anisotropy of the hyperfine structure reveals the characteristics of the static Jahn-Teller effect. The second-order-anisotropy term, ˜ (\\fracspin{-orbit~coupling}{10D_q}){\\hspace{0pt}}2 , is significant and cannot be disregarded, with the local strain dominating over the observed Zeeman-anisotropy-energy difference. The Bohr electron magneton, β=9.23× 10-24 JT-1 , (within -0.43% so-called experimental error) has been found using the measured spin-Hamiltonian parameters. Measured nuclear dipolar hyperfine structure parameter P\\Vert=12.3×10-4~cm-1 shows that the mean inverse third power of the electron distance from the nucleus is < r-3_q>≃ 5.23 a.u. for Cu2+ ion in the substituted Al3+ ion site assuming nuclear electric quadruple moment Q=-0.211 barn.

  1. Giant ferrimagnetism and polarization in a mixed metal perovskite metal-organic framework

    NASA Astrophysics Data System (ADS)

    Rout, Paresh C.; Srinivasan, Varadharajan

    2018-01-01

    Perovskite metal-organic frameworks (MOFs) have recently emerged as potential candidates for multiferroicity. However, the compounds synthesized so far possess only weak ferromagnetism and low polarization. Additionally, the very low magnetic transition temperatures (Tc) also pose a challenge to the application of the materials. We have computationally designed a mixed metal perovskite MOF—[C(NH2)3] [(Cu0.5Mn0.5) (HCOO) 3] —that is predicted to have magnetization two orders of magnitude larger than its parent ([C (NH2)3] [Cu (HCOO) 3] ), a significantly larger polarization (9.9 μ C /cm2), and an enhanced Tc of up to 56 K, unprecedented in perovskite MOFs. A detailed study of the magnetic interactions revealed a mechanism leading to the large moments as well as the increase in the Tc. Mixing a non-Jahn-Teller ion (Mn2 +) into a Jahn-Teller host (Cu2 +) leads to competing lattice distortions which are directly responsible for the enhanced polarization. The MOF is thermodynamically stable as evidenced by the computed enthalpy of formation and can likely be synthesized. Our work represents a first step towards rational design of multiferroic perovskite MOFs through the largely unexplored mixed metal approach.

  2. Perovskite-structure TlMnO₃: a new manganite with new properties.

    PubMed

    Yi, Wei; Kumagai, Yu; Spaldin, Nicola A; Matsushita, Yoshitaka; Sato, Akira; Presniakov, Igor A; Sobolev, Alexey V; Glazkova, Yana S; Belik, Alexei A

    2014-09-15

    We synthesize a new member of the AMnO3 perovskite manganite family (where A is a trivalent cation)--thallium manganite, TlMnO3--under high-pressure (6 GPa) and high-temperature (1500 K) conditions and show that the structural and magnetic properties are distinct from those of all other AMnO3 manganites. The crystal structure of TlMnO3 is solved and refined using single-crystal X-ray diffraction data. We obtain a triclinically distorted structure with space group P1̅ (No. 2), Z = 4, and lattice parameters a = 5.4248(2) Å, b = 7.9403(2) Å, c = 5.28650(10) Å, α = 87.8200(10)°, β = 86.9440(10)°, and γ = 89.3130(10)° at 293 K. There are four crystallographic Mn sites in TlMnO3 forming two groups based on the degree of their Jahn-Teller distortions. Physical properties of insulating TlMnO3 are investigated with Mössbauer spectroscopy and resistivity, specific heat, and magnetization measurements. The orbital ordering, which persists to the decomposition temperature of 820 K, suggests A-type antiferromagnetic ordering with the ferromagnetic planes along the [-101] direction, consistent with the measured collinear antiferromagnetism below the Néel temperature of 92 K. Hybrid density functional calculations are consistent with the experimentally identified structure, insulating ground state, and suggested magnetism, and show that the low symmetry originates from the strongly Jahn-Teller distorted Mn(3+) ions combined with the strong covalency of the Tl(3+)-O bonds.

  3. Lattice distortion and electron charge redistribution induced by defects in graphene

    DOE PAGES

    Zhang, Wei; Lu, Wen -Cai; Zhang, Hong -Xing; ...

    2016-09-14

    Lattice distortion and electronic charge localization induced by vacancy and embedded-atom defects in graphene were studied by tight-binding (TB) calculations using the recently developed three-center TB potential model. We showed that the formation energies of the defects are strongly correlated with the number of dangling bonds and number of embedded atoms, as well as the magnitude of the graphene lattice distortion induced by the defects. Lastly, we also showed that the defects introduce localized electronic states in the graphene which would affect the electron transport properties of graphene.

  4. Quasi-Particle Relaxation and Quantum Femtosecond Magnetism in Non-Equilibrium Phases of Insulating Manganites

    NASA Astrophysics Data System (ADS)

    Perakis, Ilias; Kapetanakis, Myron; Lingos, Panagiotis; Barmparis, George; Patz, A.; Li, T.; Wang, Jigang

    We study the role of spin quantum fluctuations driven by photoelectrons during 100fs photo-excitation of colossal magneto-resistive manganites in anti-ferromagnetic (AFM) charge-ordered insulating states with Jahn-Teller distortions. Our mean-field calculation of composite fermion excitations demonstrates that spin fluctuations reduce the energy gap by quasi-instantaneously deforming the AFM background, thus opening a conductive electronic pathway via FM correlation. We obtain two quasi-particle bands with distinct spin-charge dynamics and dependence on lattice distortions. To connect with fs-resolved spectroscopy experiments, we note the emergence of fs magnetization in the low-temperature magneto-optical signal, with threshold dependence on laser intensity characteristic of a photo-induced phase transition. Simultaneously, the differential reflectivity shows bi-exponential relaxation, with fs component, small at low intensity, exceeding ps component above threshold for fs AFM-to-FM switching. This suggests the emergence of a non-equilibrium metallic FM phase prior to establishment of a new lattice structure, linked with quantum magnetism via spin/charge/lattice couplings for weak magnetic fields.

  5. Possible bicollinear nematic state with monoclinic lattice distortions in iron telluride compounds

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bishop, Christopher B.; Herbrych, Jacek W.; Dagotto, Elbio R.

    2017-07-15

    Here, iron telluride (FeTe) is known to display bicollinear magnetic order at low temperatures together with a monoclinic lattice distortion. Because the bicollinear order can involve two different wave vectors (π/2,π/2) and (π/2,–π/2), symmetry considerations allow for the possible stabilization of a nematic state with short-range bicollinear order coupled to monoclinic lattice distortions at a T S higher than the temperature T N where long-range bicollinear order fully develops. As a concrete example, the three-orbital spin-fermion model for iron telluride is studied with an additional coupling ˜λ 12 between the monoclinic lattice strain and an orbital-nematic order parameter with Bmore » 2g symmetry. Monte Carlo simulations show that with increasing ˜λ 12 the first-order transition characteristic of FeTe splits and bicollinear nematicity is stabilized in a (narrow) temperature range. In this new regime, the lattice is monoclinically distorted and short-range spin and orbital order breaks rotational invariance. A discussion of possible realizations of this exotic state is provided.« less

  6. Strain doping: Reversible single-axis control of a complex oxide lattice via helium implantation

    DOE PAGES

    Guo, Hangwen; Dong, Shuai; Rack, Philip D.; ...

    2015-06-25

    We report on the use of helium ion implantation to independently control the out-of-plane lattice constant in epitaxial La 0.7Sr 0.3MnO 3 thin films without changing the in-plane lattice constants. The process is reversible by a vacuum anneal. Resistance and magnetization measurements show that even a small increase in the out-of-plane lattice constant of less than 1% can shift the metal-insulator transition and Curie temperatures by more than 100 °C. Unlike conventional epitaxy-based strain tuning methods which are constrained not only by the Poisson effect but by the limited set of available substrates, the present study shows that strain canmore » be independently and continuously controlled along a single axis. This permits novel control over orbital populations through Jahn-Teller effects, as shown by Monte Carlo simulations on a double-exchange model. As a result, the ability to reversibly control a single lattice parameter substantially broadens the phase space for experimental exploration of predictive models and leads to new possibilities for control over materials’ functional properties.« less

  7. Structural change and charge ordering correlated ultrasonic anomalies in La1-xCaxMnO3 (x=0.5,0.83) perovskite

    NASA Astrophysics Data System (ADS)

    Zheng, R. K.; Zhu, C. F.; Xie, J. Q.; Li, X. G.

    2001-01-01

    Ultrasonic sound velocity and attenuation have been measured in polycrystalline manganese oxide La1-xCaxMnO3 (x=0.5,0.83,1.0) at a frequency of 10 MHz. For x=0.5, on cooling down from high temperature, a slight softening of the sound velocity above the charge ordering transition temperature TCO and dramatic stiffening below TCO coincided with big attenuation peaks for both longitudinal and transverse waves were observed. It was found that these ultrasonic anomalies near TCO are correlated with the fine structure (i.e., the lattice parameters) change caused by the Jahn-Teller effect. For x=0.83, the sound velocity starts to soften dramatically with decreasing temperature from higher temperature to TS (180 K), and stiffens dramatically below TS. The large softening and stiffening of the sound velocity accompanied by a big attenuation peak are strongly correlated with a cubic-to-tetragonal structural phase transition at TS, which is confirmed by the low-temperature powder x-ray diffraction measurements. It is suggested that this structural phase transition be due to the Jahn-Teller distortion of the Mn3+O6 octahedra and related to the charge ordering transition. For CaMnO3, the anomaly in sound velocity is small.

  8. Perspectives of disproportionation driven superconductivity in strongly correlated 3d compounds.

    PubMed

    Moskvin, A S

    2013-02-27

    Disproportionation in 3d compounds can give rise to an unconventional electron-hole Bose liquid with a very rich phase diagram, from a Bose metal, to a charge ordering insulator and an inhomogeneous Bose-superfluid. Optimal conditions for disproportionation driven high-T(c) superconductivity are shown to be realized only for several Jahn-Teller d(n) configurations that permit the formation of well defined local composite bosons. These are the high-spin d(4), low-spin d(7), and d(9) configurations given the octahedral crystal field, and the d(1), high-spin d(6) configurations given the tetrahedral crystal field. The disproportionation reaction has a peculiar 'anti-Jahn-Teller' character lifting the bare orbital degeneracy. Superconductivity in the d(4) and d(6) systems at variance with d(1), d(7), and d(9) systems implies unavoidable coexistence of the spin-triplet composite bosons and the magnetic lattice. We argue that unconventional high-T(c) superconductivity, observed in quasi-2d cuprates with tetragonally distorted CuO(6) octahedra and iron-based layered pnictides/chalcogenides with tetrahedrally coordinated Fe(2+) ions presents a key argument to support the fact that the disproportionation scenario is at work in these compounds.

  9. Lattice distortions in complex oxides and their relation to the thermal properties

    NASA Astrophysics Data System (ADS)

    Srivastava, Archana; Gaur, N. K.

    2018-05-01

    We have investigated the various lattice distortions in complex oxides Ca1-xLaxMnO3 and its effect on elastic and thermal properties of these perovskite manganites, especially Debye temperature of these complex oxides. The revealed data on Bulk modulus and Debye temperature studied as a function of lattice distortions using a novel atomistic approach of Atom in Molecules(AIM) theory and Modified Rigid Ion Model (MRIM) are in closer agreement with the available experimental data for some concentrations (x) of Ca1-xLaxMnO3. We demonstrate that the distortions introduced due to electron concentration, size mismatch and JT effects are the dominant factor, whereas charge mismatch and buckling of Mn-O-Mn angle influence the thermal properties to a lesser degree in the ferromagnetic state.

  10. Orbital symmetry fingerprints for magnetic adatoms in graphene

    NASA Astrophysics Data System (ADS)

    Uchoa, Bruno; Yang, Ling; Tsai, S.-W.; Peres, N. M. R.; Castro Neto, A. H.

    2014-01-01

    In this paper, we describe the formation of local resonances in graphene in the presence of magnetic adatoms containing localized orbitals of arbitrary symmetry, corresponding to any given angular momentum state. We show that quantum interference effects which are naturally inbuilt in the honeycomb lattice in combination with the specific orbital symmetry of the localized state lead to the formation of fingerprints in differential conductance curves. In the presence of Jahn-Teller distortion effects, which lift the orbital degeneracy of the adatoms, the orbital symmetries can lead to distinctive signatures in the local density of states. We show that those effects allow scanning tunneling probes to characterize adatoms and defects in graphene.

  11. Lattice distortion in hcp rare gas solids

    NASA Astrophysics Data System (ADS)

    Grechnev, A.; Tretyak, S. M.; Freiman, Yu. A.

    2010-04-01

    The lattice distortion parameter δ ≡c/a-√8/3 has been calculated as a function of molar volume for the hcp phases of He, Ar, Kr, and Xe. Results from both semi-empirical potentials and density functional theory are presented. Our study shows that δ is negative for helium in the entire pressure range. For Ar, Kr, and Xe δ changes sign from negative to positive as the pressure increases, growing rapidly in magnitude at higher pressures.

  12. The Synthesis and Characterization of Some Fluoride Perovskites: An Undergraduate Experiment in Solid State Chemistry.

    ERIC Educational Resources Information Center

    Langley, Richard H.; And Others

    1984-01-01

    Describes a senior-level experiment dealing with the synthesis and characterization of a perovskite. Since most perovskites are cubic, their characterization by x-ray diffraction is simplified. In addition, magnetic ordering may be observed and the effects of a Jahn-Teller distortion seen. (JN)

  13. Topological magnetic phase in LaMnO3 (111) bilayer

    NASA Astrophysics Data System (ADS)

    Weng, Yakui; Huang, Xin; Yao, Yugui; Dong, Shuai

    Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as Hubbard type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO3 (111) bilayer sandwiched in LaScO3 barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO3 (111) bilayer just stays at the Dirac point, rendering a semi-metal (graphene-like) which is also a half-metal (different from graphene nor previous studied LaNiO3 (111) bilayer). The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice (~ 1 . 7 meV) than the undistorted one (~11 meV).

  14. Topological magnetic phase in LaMnO3 (111) bilayer

    NASA Astrophysics Data System (ADS)

    Weng, Yakui; Huang, Xin; Yao, Yugui; Dong, Shuai

    2015-11-01

    Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as the Hubbard-type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO3 (111) bilayer sandwiched in LaScO3 barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO3 (111) bilayer just stays at the Dirac point, rendering a semimetal (graphenelike) which is also a half metal [different from graphene or the previously studied LaNiO3 (111) bilayer]. The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice (˜1.7 meV) than the undistorted one (˜11 meV). Therefore, to suppress the lattice distortion can be helpful to enhance the robustness of the topological phase in perovskite (111) bilayers.

  15. Pseudo Jahn-Teller coupling in trioxides XO3(0,1,-1) with 22 and 23 valence electrons

    NASA Astrophysics Data System (ADS)

    Grein, Friedrich

    2013-05-01

    D3h and C2v geometries and energies, vertical excitation energies, as well as minimal energy paths as function of the O1(z)-X-O2 angle α were obtained for XO3(0,1,-1) (X = B, Al, Ga; C, Si, Ge; N, P, As; S, Se) molecules and ions with 22 and 23 valence electrons (VE), using density functional theory (DFT), coupled cluster with single and double substitutions with noniterative triple excitations (CCSD(T)), equation of motion (EOM)-CCSD, time-dependent DFT, and multi-reference configuration interaction methods. It is shown that pseudo Jahn-Teller (PJT) coupling increases as the central atom X becomes heavier, due to decreases in excitation energies. As is well known for CO3, the excited 1E' states of the 22 VE systems SiO3, GeO3; NO_3 ^ +, PO3+, AsO3+; BO3-, AlO3-, GaO3- have strong vibronic coupling with the 1A1' ground state via the e' vibrational modes, leading to a C2v minimum around α = 145°. For first and second row X atoms, there is an additional D3h minimum (α = 120°). Interacting excited states have minima around 135°. In the 23 VE systems CO3-, SiO3-; NO3, PO3; SO3+, coupling of the excited 2E' with the 2A2' ground state via the e' mode does not generate a C2v state. Minima of interacting excited states are close to 120°. However, due to very strong PJT coupling, a double-well potential is predicted for GeO3-, AsO3, and SeO3+, with a saddle point at D3h symmetry. Interaction of the b2 highest occupied molecular orbital with the b2 lowest unoccupied molecular orbital, both oxygen lone pair molecular orbitals, is seen as the reason for the C2v stabilization of 22 VE molecules.

  16. Nodeless vibrational amplitudes and quantum nonadiabatic dynamics in the nested funnel for a pseudo Jahn-Teller molecule or homodimer

    NASA Astrophysics Data System (ADS)

    Peters, William K.; Tiwari, Vivek; Jonas, David M.

    2017-11-01

    The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between

  17. Nodeless vibrational amplitudes and quantum nonadiabatic dynamics in the nested funnel for a pseudo Jahn-Teller molecule or homodimer.

    PubMed

    Peters, William K; Tiwari, Vivek; Jonas, David M

    2017-11-21

    The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between

  18. Eu/RG absorption and excitation spectroscopy in the solid rare gases: state dependence of crystal field splitting and Jahn-Teller coupling.

    PubMed

    Byrne, Owen; McCaffrey, John G

    2011-03-28

    Absorption spectroscopy recorded for annealed samples of matrix-isolated atomic europium reveals a pair of thermally stable sites in Ar and Kr while a single site exists in Xe. Plots of the matrix shifts of the visible s → p bands versus host polarizability, allowed the association of the single site in Xe and the blue sites in Ar and Kr. On the basis of the similar ground state bond lengths expected for the Eu-rare gas (RG) diatomics and the known Na-RG molecules, the blue sites are attributed to Eu occupancy in the smaller tetra-vacancy while the red sites are proposed to arise from hexa-vacancy sites. Both sites are of cubic symmetry, consistent with the pronounced Jahn-Teller structure present on the y(8)P ← a(8)S(7/2) transition for these bands in the three hosts studied. Site-selective excitation spectroscopy has been used to reanalyze complex absorption spectra previously published by Jakob et al. [Phys. Lett. A 57, 67 (1976)] for the near-UV f → d transitions. On the basis that a pair of thermally stable sites exist in solid argon, the occurrence of crystal field splitting has been identified to occur for the J ≥ 5/2 level of the (8)P state when isolated in these two sites with cubic symmetry. From a detailed lineshape analysis, the magnitude of the crystal field splittings on the J = 5/2 level in Ar is found to be 105 and 123 cm(-1) for the red and blue sites, respectively.

  19. Effects of Mn substitution on the thermoelectric properties of the electron-doped perovskite Sr1-xLaxTiO3

    NASA Astrophysics Data System (ADS)

    Okuda, T.; Hata, H.; Eto, T.; Nishina, K.; Kuwahara, H.; Nakamura, M.; Kajimoto, R.

    2014-12-01

    We have tried to improve the n-type thermoelectric properties of the electron- doped Perovskite Sr1-xLaxTiO3 by a Mn substitution. The 1 ~ 2 % Mn substitution enhances the Seebeck coefficient (S) and reduces the thermal conductivity (κ) by about 50 % at room temperature (RT) without largely increasing the resistivity for the 5 % electron-doped SrTiO3. Consequently, the power factor at RT keeps a large value comparable to that of Bi2Te3 and the dimensionless figure-of-merits at RT increases twofold by the slight Mn substitution. Such a large reduction of κ at RT is perhaps due to the effect of Jahn-Teller active Mn3+ ions, around which dynamical local lattice distortion may occur.

  20. Theoretical Study of the Jahn-Teller effect in CH3CN+ (X2E) and CD3CN+ (X2E): multimode spin-vibronic energy level calculations.

    PubMed

    Zhang, Shiyang; Mo, Yuxiang

    2009-10-15

    The spin-vibronic energy levels for CH(3)CN(+)(X(2)E) and CD(3)CN(+)(X(2)E) have been calculated using a diabatic model including multimode vibronic couplings and spin-orbit interaction without adjusting any parameter. The diabatic potential energy surfaces are represented by the Taylor expansions including linear, quadratic and bilinear vibronic coupling terms. The normal coordinates used in the Taylor expansion were expressed by the mass-weighted Cartesian coordinates. The adiabatic potential energy surfaces for CH(3)CN(+) and CD(3)CN(+) were calculated at the level of CASPT2/cc-pvtz, and the spin-orbit coupling constant was calculated at the level of MRCI/CAS/cc-pvtz. The spin-orbit energy splittings for the ground vibrational states of CH(3)CN(+)(X(2)E) and CD(3)CN(+)(X(2)E) are 20 and 16 cm(-1), respectively, which are resulted from the quenching of the spin-orbit coupling strength of 51 cm(-1). The calculated spin-vibronic levels are in good agreement with the experimental data. The calculation results show that the Jahn-Teller effects in CH(3)CN(+)(X(2)E) and CD(3)CN(+)(X(2)E) are essential to understand their spin-vibronic energy structure.

  1. Magnetic properties of a quasi-two-dimensional S =1/2 Heisenberg antiferromagnet with distorted square lattice

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hironori; Tamekuni, Yusuke; Iwasaki, Yoshiki; Otsuka, Rei; Hosokoshi, Yuko; Kida, Takanori; Hagiwara, Masayuki

    2017-06-01

    We successfully synthesize single crystals of the verdazyl radical α -2 ,3 ,5 -Cl3 -V. Ab initio molecular orbital calculations indicate that the two dominant antiferromagnetic interactions, J1 and J2 (α =J2/J1≃0.56 ), form an S =1 /2 distorted square lattice. We explain the magnetic properties based on the S =1 /2 square lattice Heisenberg antiferromagnet using the quantum Monte Carlo method, and examine the effects of the lattice distortion and the interplane interaction contribution. In the low-temperature regions below 6.4 K, we observe anisotropic magnetic behavior accompanied by a phase transition to a magnetically ordered state. The electron spin resonance signals exhibit anisotropic behavior in the temperature dependence of the resonance field and the linewidth. We explain the frequency dependence of the resonance fields in the ordered phase using a mean-field approximation with out-of-plane easy-axis anisotropy, which causes a spin-flop phase transition at approximately 0.4 T for the field perpendicular to the plane. Furthermore, the anisotropic dipole field provides supporting information regarding the presence of the easy-axis anisotropy. These results demonstrate that the lattice distortion, anisotropy, and interplane interaction of this model are sufficiently small that they do not affect the intrinsic behavior of the S =1 /2 square lattice Heisenberg antiferromagnet.

  2. Magnetization and heat-capacity measurements on Zn1-xCrxTe

    NASA Astrophysics Data System (ADS)

    Pekarek, T. M.; Luning, J. E.; Miotkowski, I.; Crooker, B. C.

    1994-12-01

    We have taken magnetization and calorimetric measurements on Zn1-xCrxTe (x=0.003). The heat-capacity measurements show a Schottky peak indicating an energy-level splitting of 3.1 K between the ground and first excited states. Above 1.5 K we observe additional heat capacity, which indicates the presence of additional low-energy vibronic excitations. The magnetization data reveal a small anisotropy (~7%) with the (111) direction giving the largest value. The magnetization data were fit with a model including a static Jahn-Teller distortion proposed previously in these materials [J. T. Vallin, G. A. Slack, S. Roberts, and A. E. Hughes, Phys. Rev. B 2, 4313 (1970)]. Reasonable agreement was found with the data for a spin-orbit parameter of -59 cm-1 and a Jahn-Teller energy of 320 cm-1.

  3. Vibronic Analysis for widetilde{B} - widetilde{X} Transition of Isopropoxy Radical

    NASA Astrophysics Data System (ADS)

    Chhantyal-Pun, Rabi; Miller, Terry A.

    2013-06-01

    Alkoxy radicals are important intermediates in combustion and atmospheric chemistry. Alkoxy radicals are also of significant spectroscopic interest for the study of Jahn Teller and pseudo Jahn Teller effects, involving the widetilde{X} and widetilde{A} states. The Jahn Teller effect has been studied in methoxy. Substitution of one or two hydrogens by methyl groups transforms the interaction to a pseudo Jahn Teller effect in ethoxy and isopropoxy. Previously, moderate resolution scans have been obtained for widetilde{B} - widetilde{X} and widetilde{B} - widetilde{A} transition systems, the latter observable at higher temperature. These measurements have shown that the widetilde{X} and widetilde{A} states of isopropoxy are separated by only 60.7(7) cm^{-1} which indicates a strong pseudo Jahn Teller effect in the widetilde{X} state. Such pseduo Jahn Teller coupling should also introduce additional bands into the widetilde{B} - widetilde{X} spectrum and a number of weaker transitions have been observed which may be caused by such effects. In this talk we present a vibronic analysis for the widetilde{B} - widetilde{X} transition based on the experimental results and also the results from recent quantum chemistry calculations.

  4. Bicollinear antiferromagnetic order, monoclinic distortion, and reversed resistivity anisotropy in FeTe as a result of spin-lattice coupling

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2016-09-08

    The bicollinear antiferromagnetic order experimentally observed in FeTe is shown to be stabilized by the coupling g ~ 12 between monoclinic lattice distortions and the spin-nematic order parameter with B 2g symmetry, within a three-orbital spin-fermion model studied with Monte Carlo techniques. A finite but small value of g ~ 12 is required, with a concomitant lattice distortion compatible with experiments, and a tetragonal-monoclinic transition strongly first order. Remarkably, the bicollinear state found here displays a planar resistivity with the reversed puzzling anisotropy discovered in transport experiments. Orthorhombic distortions are also incorporated, and phase diagrams interpolating between pnictides and chalcogenidesmore » are presented. Here, we conclude that the spin-lattice coupling we introduce is sufficient to explain the challenging properties of FeTe.« less

  5. Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material

    DOE PAGES

    Li, Junjie; Wang, Xuan; Zhou, Haidong; ...

    2016-07-29

    Here, we report a direct and real time measurement of photoinduced structure phase transition in single crystal La 0.84Sr 0.16MnO 3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. Furthermore, the fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion followingmore » the photo-excitation. We attribute the slow process to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.« less

  6. Structural analysis of LaVO3 thin films under epitaxial strain

    NASA Astrophysics Data System (ADS)

    Meley, H.; Karandeep, Oberson, L.; de Bruijckere, J.; Alexander, D. T. L.; Triscone, J.-M.; Ghosez, Ph.; Gariglio, S.

    2018-04-01

    Rare earth vanadate perovskites exhibit a phase diagram in which two different types of structural distortions coexist: the strongest, the rotation of the oxygen octahedra, comes from the small tolerance factor of the perovskite cell (t = 0.88 for LaVO3) and the smaller one comes from inter-site d-orbital interactions manifesting as a cooperative Jahn-Teller effect. Epitaxial strain acts on octahedral rotations and crystal field symmetry to alter this complex lattice-orbit coupling. In this study, LaVO3 thin film structures have been investigated by X-ray diffraction and scanning transmission electron microscopy. The analysis shows two different orientations of octahedral tilt patterns, as well as two distinct temperature behaviors, for compressive and tensile film strain states. Ab initio calculations capture the strain effect on the tilt pattern orientation in agreement with experimental data.

  7. Nonequilibrium phase transitions in isotropic Ashkin-Teller model

    NASA Astrophysics Data System (ADS)

    Akıncı, Ümit

    2017-03-01

    Dynamic behavior of an isotropic Ashkin-Teller model in the presence of a periodically oscillating magnetic field has been analyzed by means of the mean field approximation. The dynamic equation of motion has been constructed with the help of a Glauber type stochastic process and solved for a square lattice. After defining the possible dynamical phases of the system, phase diagrams have been given and the behavior of the hysteresis loops has been investigated in detail. The hysteresis loop for specific order parameter of isotropic Ashkin-Teller model has been defined and characteristics of this loop in different dynamical phases have been given.

  8. Lattice dynamics of A Sb2O6 (A =Cu , Co) with trirutile structure

    NASA Astrophysics Data System (ADS)

    Maimone, D. T.; Christian, A. B.; Neumeier, J. J.; Granado, E.

    2018-03-01

    Raman spectroscopy experiments on single crystals of CuSb2O6 and CoSb2O6 quasi-one-dimensional antiferromagnets with trirutile crystal structure were performed, with a focus on the first material. The observed Raman-active phonon modes and previously reported infrared-active modes were identified with the aid of ab initio lattice dynamics calculations. The structural transition between monoclinic β -CuSb2O6 and tetragonal α -CuSb2O6 phases at Ts=400 K is manifested in our spectra by a "repulsion" of two accidentally quasidegenerate symmetric modes below Ts, caused by a phonon mixing effect that is only operative in the monoclinic β -CuSb2O6 phase due to symmetry restrictions. Also, two specific phonons, associated with CuO6 octahedra rotation and with a Jahn-Teller elongation mode, soften and broaden appreciably as T →Ts . A crossover from a displacive to an order-disorder transition at Ts is inferred.

  9. Local lattice distortion in NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys investigated by synchrotron X-ray diffraction

    DOE PAGES

    Tong, Yang; Jin, Ke; Bei, Hongbin; ...

    2018-05-26

    Severe lattice distortion is presumptively considered as a core effect of high-entropy alloys, but quantitative measurements are still missing. Here, we demonstrate that the lattice distortion in high-entropy alloys can be quantitatively analyzed based on pair distribution function obtained from synchrotron X-ray diffraction. By applying this method to equiatomic NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys, we found that the local lattice distortion in the NiCoCr (0.23%) and FeCoNiCrMn (0.24%) alloys are comparable while negligible in the FeCoNiCr alloy (0.04%). Furthermore, the origin of local lattice distortion in the NiCoCr and FeCoNiCrMn concentrated alloys was discussed.

  10. Local lattice distortion in NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys investigated by synchrotron X-ray diffraction

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tong, Yang; Jin, Ke; Bei, Hongbin

    Severe lattice distortion is presumptively considered as a core effect of high-entropy alloys, but quantitative measurements are still missing. Here, we demonstrate that the lattice distortion in high-entropy alloys can be quantitatively analyzed based on pair distribution function obtained from synchrotron X-ray diffraction. By applying this method to equiatomic NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys, we found that the local lattice distortion in the NiCoCr (0.23%) and FeCoNiCrMn (0.24%) alloys are comparable while negligible in the FeCoNiCr alloy (0.04%). Furthermore, the origin of local lattice distortion in the NiCoCr and FeCoNiCrMn concentrated alloys was discussed.

  11. Lattice distortion mechanism study of TiO2 nanoparticles during photocatalysis degradation and reactivation

    NASA Astrophysics Data System (ADS)

    Wu, Wenhui; Xue, Xudong; Jiang, Xudong; Zhang, Yupeng; Wu, Yichu; Pan, Chunxu

    2015-05-01

    In this paper, the photocatalytic process of TiO2 (P25) is directly characterized by using a positron annihilation lifetime spectroscopy (PALS), high-resolution transmission electron microscopy (HRTEM), Photoluminescence spectroscopy (PL) and UV Raman spectroscopy (Raman). The experimental results reveal that: 1) From PALS measurements, because τ1 and τ2 values and their intensity (I1 and I2) assigned to the different size and amounts of defects, respectively, their variations indicate the formation of different types and amounts of defects during the absorption and degradation. 2) HRTEM observations show that the lattice images become partly blurring when the methylene blue is fully degradated, and clear again after exposed in the air for 30 days. According to the results, we propose a mechanism that the lattice distortion induces the defects as electron capture sites and provides energy for improving photocatalytic process. Meanwhile, the lattice distortion relaxation after exposing in the air for 30 days perfectly explains the gradual deactivation of TiO2, because the smaller vacancy defects grow and agglomerate through the several photocatalytic processes. The instrumental PL and Raman are also used to analyze the samples and approved the results of PALS and HRTEM.

  12. Contribution of Lattice Distortion to Solid Solution Strengthening in a Series of Refractory High Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Chen, H.; Kauffmann, A.; Laube, S.; Choi, I.-C.; Schwaiger, R.; Huang, Y.; Lichtenberg, K.; Müller, F.; Gorr, B.; Christ, H.-J.; Heilmaier, M.

    2018-03-01

    We present an experimental approach for revealing the impact of lattice distortion on solid solution strengthening in a series of body-centered-cubic (bcc) Al-containing, refractory high entropy alloys (HEAs) from the Nb-Mo-Cr-Ti-Al system. By systematically varying the Nb and Cr content, a wide range of atomic size difference as a common measure for the lattice distortion was obtained. Single-phase, bcc solid solutions were achieved by arc melting and homogenization as well as verified by means of scanning electron microscopy and X-ray diffraction. The atomic radii of the alloying elements for determination of atomic size difference were recalculated on the basis of the mean atomic radii in and the chemical compositions of the solid solutions. Microhardness (μH) at room temperature correlates well with the deduced atomic size difference. Nevertheless, the mechanisms of microscopic slip lead to pronounced temperature dependence of mechanical strength. In order to account for this particular feature, we present a combined approach, using μH, nanoindentation, and compression tests. The athermal proportion to the yield stress of the investigated equimolar alloys is revealed. These parameters support the universality of this aforementioned correlation. Hence, the pertinence of lattice distortion for solid solution strengthening in bcc HEAs is proven.

  13. a Zero-Order Picture of the Infrared Spectrum for the Methoxy Radical: Assignment of States

    NASA Astrophysics Data System (ADS)

    Johnson, Britta; Sibert, Edwin

    2016-06-01

    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 vibronic coupling which leads to large amplitude vibrations and extensive mixing of the two lowest electronic states. This coupling combined with spin-orbit and Fermi couplings greatly complicates the assignments of states. Using the potential force field and calculated spectra of Nagesh and Sibert1,2, we assign quantum numbers to the infrared spectrum. When the zero-order states are the diabatic normal mode states, there is sufficient mode mixing that the normal mode quantum numbers are poor labels for the final states. We define a series of zero-order Hamiltonians which include additional coupling elements beyond the normal mode picture but still allow for the assignment of Jahn-Teller quantum numbers. In methoxy, the two lowest frequency e} modes, the bend (q_5) and the rock (q_6), are the modes with the strongest Jahn-Teller coupling. In general, a zero-order Hamiltonian which includes first-order Jahn-Teller coupling in q_6 is sufficient for most states of interest. Working in a representation which includes first-order Jahn-Teller coupling in q_6, we identify states in which additional coupling elements must be included; these couplings include first-order Jahn-Teller coupling in q_5, higher order Jahn-Teller coupling in q_5 and q_6, and, in the dueterated case, Jahn-Teller coupling which is modulated by the corresponding a modes. [^1] Nagesh, J.; Sibert, E. L. J. Phys. Chem. A 2012, 116, 3846-3855. Lee, Y.F.; Chou, W.T.; Johnson, B.A.; Tabor, D.P. ; Sibert, E.L.; Lee, Y.P. J. Mol. Spectrosc. 2015, 310, 57-67. Barckholtz, T. A.; Miller, T. A. Int. Revs. in Phys. Chem. 1998, 17, 435-524.

  14. Phonon triggered rhombohedral lattice distortion in vanadium at high pressure

    DOE PAGES

    Antonangeli, Daniele; Farber, Daniel L.; Bosak, Alexei; ...

    2016-08-19

    In spite of the simple body-centered-cubic crystal structure, the elements of group V, vanadium, niobium and tantalum, show strong interactions between the electronic properties and lattice dynamics. Further, these interactions can be tuned by external parameters, such as pressure and temperature. We used inelastic x-ray scattering to probe the phonon dispersion of single-crystalline vanadium as a function of pressure to 45 GPa. Our measurements show an anomalous high-pressure behavior of the transverse acoustic mode along the (100) direction and a softening of the elastic modulus C44 that triggers a rhombohedral lattice distortion occurring between 34 and 39 GPa. Lastly, ourmore » results provide the missing experimental confirmation of the theoretically predicted shear instability arising from the progressive intra-band nesting of the Fermi surface with increasing pressure, a scenario common to all transition metals of group V.« less

  15. Intrinsic Local Distortions and charge carrier behavior in CMR manganites and cobaltites

    NASA Astrophysics Data System (ADS)

    Bridges, Frank

    2010-03-01

    We compare and contrast the local structure and electronic configurations in two oxide systems La1-xSrxCoO3 (LSCO) and La1-yCayMnO3 (LCMO). Although these oxides may appear quite similar they have rather different properties. At x=0, LaCoO3 (LCO) has unusual magnetic properties - diamagnetic at low T but developing a moment near 100K. The Sr doped LSCO materials show ferromagnetism for x > 0.2. For LCO, one of the possible spin state configurations called the intermediate spin (IS) state (S=1), should be Jahn-Teller (JT) active, while the low spin (S=0) and high spin (S=2) states have no JT distortion. Early local structure measurements suggested a JT distortion was present in LCO and therefore supported an IS spin model. However we find no evidence for any significant JT distortion (and hence no support for the IS model) for a range of bulk and nanoparticle cobaltites La1-xSrxCoO3, x = 0 - 0.35. In contrast there are large JT distortions in the manganites LCMO, 0.2 < x < 0.5 (Mn-O bonds), for which CMR behavior is observed. We have shown that the JT distortions in the manganites depend on both temperature T and magnetic field B, and from the B-field dependence, propose the size and nature of the polarons in LCMO. We also present Co K-edge XANES data that shown no significant shift of the edge for the cobaltites as the Sr concentration increases from x =0 to 0.35 indicating essentially no change in the electronic configuration about Co; consequently, the holes introduced via Sr doping appear to go primarily into the O bands. In contrast there is a large shift of the Mn K-edge with Ca doping indicating a change in the average Mn valence, and a corresponding change in the Mn electronic configuration. We briefly discuss some possible models.

  16. Lattice distortions and local compressibility around trivalent rare-earth impurities in fluorites

    NASA Astrophysics Data System (ADS)

    Tovar, M.; Ramos, C. A.; Fainstein, C.

    1983-10-01

    We have calculated the lattice distortions around trivalent rare-earth dilute impurities, occupying substitutionally metal sites in fluorites. Explicit results are given for the equilibrium positions of the nearest fluorine ligands, R, the induced electric dipole moments, and the local hydrostatic strains for MF2 (M=Cd, Ca, Sr, Pb, and Ba). These results are used to study the impurity-ligand distance dependence of the fourth-order cubic-crystal-field parameter, b4, for Gd3+ and the isoelectronic ion Eu2+. Comparison is made with the change of b4 with hydrostatic stress using the calculated local compressibility of the lattice. A consistent description of the experimental data is obtained assuming b4~R-m with m~10.

  17. Jahn–Teller Assisted Na Diffusion for High Performance Na Ion Batteries

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Xin; Wang, Yan; Wu, Di

    2016-08-30

    Na energy storage technology is strategically attractive for large scale applications such as grid energy storage. Here, we show in this paper that there is a clear relation between the Jahn$-$Teller activity of a transition metal ion at the end of charge and the mobility of Na in a cathode material. This is particularly important as mobility at the end of charge limits the capacity of current materials. Consequently, by using this classical piece of physics in the battery world, it is possible to create higher capacity Na-cathode materials. Even more exciting is that the ideal element to impart thismore » effect on cathodes is Fe, which is the least expensive of the transition metal oxides and can therefore enable low cost cathode materials.« less

  18. Ab initio study of dynamical E × e Jahn-Teller and spin-orbit coupling effects in the transition-metal trifluorides TiF3, CrF3, and NiF3

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    Multiconfiguration ab initio methods have been employed to study the effects of Jahn-Teller (JT) and spin-orbit (SO) coupling in the transition-metal trifluorides TiF3, CrF3, and NiF3, which possess spatially doubly degenerate excited states (ME) of even spin multiplicities (M = 2 or 4). The ground states of TiF3, CrF3, and NiF3 are nondegenerate and exhibit minima of D3h symmetry. Potential-energy surfaces of spatially degenerate excited states have been calculated using the state-averaged complete-active-space self-consistent-field method. SO coupling is described by the matrix elements of the Breit-Pauli operator. Linear and higher order JT coupling constants for the JT-active bending and stretching modes as well as SO-coupling constants have been determined. Vibronic spectra of JT-active excited electronic states have been calculated, using JT Hamiltonians for trigonal systems with inclusion of SO coupling. The effect of higher order (up to sixth order) JT couplings on the vibronic spectra has been investigated for selected electronic states and vibrational modes with particularly strong JT couplings. While the weak SO couplings in TiF3 and CrF3 are almost completely quenched by the strong JT couplings, the stronger SO coupling in NiF3 is only partially quenched by JT coupling.

  19. Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti4+) Doping

    PubMed Central

    Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

    2015-01-01

    The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti4+-doped VO2 (TixV1-xO2) system. It was observed that the TC of TixV1-xO2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in TixV1-xO2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials. PMID:25950809

  20. GdPtPb: A noncollinear antiferromagnet with distorted kagome lattice

    DOE PAGES

    Manni, S.; Bud'ko, Sergey L.; Canfield, Paul C.

    2017-08-24

    In the spirit of searching for Gd-based, frustrated, rare earth magnets, we have found antiferomagnetism (AF) in GdPtPb, which crystallizes in the ZrNiAl-type structure that has a distorted kagome lattice of Gd triangles. Single crystals were grown and investigated using structural, magnetic, transport, and thermodynamic measurements. GdPtPb orders antiferromagnetically at 15.5 K, arguably with a planar, noncollinear structure. The high temperature magnetic susceptibility data reveal an “anti-frustration” behavior having a frustration parameter, |f| = |Θ|/T N = 0.25, which can be explained by mean field theory within a two-sublattice model. Here, the study of the magnetic phase diagram down tomore » T = 1.8K reveals a change of magnetic structure through a metamagnetic transition at around 20 kOe and the disappearance of the AF ordering near 140 kOe. In total, our work indicates that GdPtPb can serve as an example of a planar, noncollinear AF with a distorted kagome magnetic sublattice.« less

  1. Lattice distortion of square iron nitride monolayers induced by changing symmetry of substrate

    NASA Astrophysics Data System (ADS)

    Hattori, Takuma; Iimori, Takushi; Miyamachi, Toshio; Komori, Fumio

    2018-04-01

    Rectangular iron nitride monatomic layers are fabricated on the threefold symmetric Cu(111) substrate by taking advantage of the stability of the square nitride film. Two different ordered structures are observed on the Cu(111) substrate by scanning tunneling microscopy after annealing at 510 K and 580 K. Their chemical composition and lattice symmetry are investigated by x-ray photoelectron spectroscopy and low energy electron diffraction. The monolayer film prepared at 580 K is a distorted Fe2N monolayer analogous to a ferromagnetic square Fe2N monolayer with a clock reconstruction on the Cu(001) substrate. The lattice deformation of the square Fe2N monolayer is induced by using Cu(111) with threefold symmetry.

  2. 3D lattice distortions and defect structures in ion-implanted nano-crystals

    DOE PAGES

    Hofmann, Felix; Robinson, Ian K.; Tarleton, Edmund; ...

    2017-04-06

    The ability of Focused Ion Beam (FIB) techniques to cut solid matter at the nano-scale revolutionized the study of material structure across the life-, earth- and material sciences. But a detailed understanding of the damage caused by the ion beam and its effect on material properties remains elusive. We examine this damage in 3D using coherent X-ray diffraction to measure the full lattice strain tensor in FIB-milled gold nano-crystals. We also found that even very low ion doses, previously thought to be negligible, cause substantial lattice distortions. At higher doses, extended self-organized defect structures appear. Combined with detailed numerical calculations,more » these observations allow fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.« less

  3. 3D lattice distortions and defect structures in ion-implanted nano-crystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hofmann, Felix; Robinson, Ian K.; Tarleton, Edmund

    The ability of Focused Ion Beam (FIB) techniques to cut solid matter at the nano-scale revolutionized the study of material structure across the life-, earth- and material sciences. But a detailed understanding of the damage caused by the ion beam and its effect on material properties remains elusive. We examine this damage in 3D using coherent X-ray diffraction to measure the full lattice strain tensor in FIB-milled gold nano-crystals. We also found that even very low ion doses, previously thought to be negligible, cause substantial lattice distortions. At higher doses, extended self-organized defect structures appear. Combined with detailed numerical calculations,more » these observations allow fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.« less

  4. The trigonal prism in coordination chemistry.

    PubMed

    Cremades, Eduard; Echeverría, Jorge; Alvarez, Santiago

    2010-09-10

    Herein we analyze the accessibility of the trigonal-prismatic geometry to metal complexes with different electron configurations, as well as the ability of several hexadentate ligands to favor that coordination polyhedron. Our study combines i) a structural database analysis of the occurrence of the prismatic geometry throughout the transition-metal series, ii) a qualitative molecular orbital analysis of the distortions expected for a trigonal-prismatic geometry, and iii) a computational study of complexes of several transition-metal ions with different hexadentate ligands. Also the tendency of specific electron configurations to present a cis bond-stretch Jahn-Teller distortion is analyzed.

  5. Ferro-Lattice-Distortions and Charge Fluctuations in Superconducting LaO 1- x F x BiS 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Athauda, Anushika; Hoffmann, Christina; Aswartham, Saicharan

    2017-05-15

    Competing ferroelectric and charge density wave states have been proposed to exist in the electron–phonon coupled LaO1-xFxBiS2 superconductor. The lattice instability is proposed to arise from unstable phonon modes that can break the crystal symmetry. Using single crystal diffraction, a superlattice pattern is observed, that arises from coherent in-plane displacements of the sulfur atoms in the BiS2 superconducting planes. The distortions morph into coordinated ferrodistortive patterns with displacements in the x- and y-directions, that alternate along the c-axis. Diffuse scattering is observed along the (H0L) plane due to stacking faults but not along the (HH0) plane. The ferro-distortive pattern remainsmore » in the superconducting state upon fluorine doping, but the displacements are diminished in magnitude. Moreover, we find that the in-plane distortions give rise to disorder where the (00L) reflections become quite broad. It is possible that charge carriers can get trapped in the lattice deformations reducing the effective number of carriers available for pairing.« less

  6. Lattice-mediated magnetic order melting in TbMnO 3

    DOE PAGES

    Baldini, Edoardo; Kubacka, Teresa; Mallett, Benjamin P. P.; ...

    2018-03-15

    Recent ultrafast magnetic-sensitive measurements have revealed a delayed melting of the long-range cycloid spin order in TbMnO 3 following photoexcitation across the fundamental Mott-Hubbard gap. The microscopic mechanism behind this slow transfer of energy from the photoexcited carriers to the spin degrees of freedom is still elusive and not understood. Here, we address this problem by combining spectroscopic ellipsometry, ultrafast broadband optical spectroscopy, and ab initio calculations. Upon photoexcitation, we observe the emergence of a complex collective response, which is due to high-energy coherent optical phonons coupled to the out-of-equilibrium charge density. This response precedes the magnetic order melting andmore » is interpreted as the fingerprint of the formation of anti-Jahn-Teller polarons. We propose that the charge localization in a long-lived self-trapped state hinders the emission of magnons and other spin-flip mechanisms, causing the energy transfer from the charge to the spin system to be mediated by the reorganization of the lattice. In conclusion, we provide evidence for the coherent excitation of a phonon mode associated with the ferroelectric phase transition.« less

  7. Lattice-mediated magnetic order melting in TbMnO 3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Baldini, Edoardo; Kubacka, Teresa; Mallett, Benjamin P. P.

    Recent ultrafast magnetic-sensitive measurements have revealed a delayed melting of the long-range cycloid spin order in TbMnO 3 following photoexcitation across the fundamental Mott-Hubbard gap. The microscopic mechanism behind this slow transfer of energy from the photoexcited carriers to the spin degrees of freedom is still elusive and not understood. Here, we address this problem by combining spectroscopic ellipsometry, ultrafast broadband optical spectroscopy, and ab initio calculations. Upon photoexcitation, we observe the emergence of a complex collective response, which is due to high-energy coherent optical phonons coupled to the out-of-equilibrium charge density. This response precedes the magnetic order melting andmore » is interpreted as the fingerprint of the formation of anti-Jahn-Teller polarons. We propose that the charge localization in a long-lived self-trapped state hinders the emission of magnons and other spin-flip mechanisms, causing the energy transfer from the charge to the spin system to be mediated by the reorganization of the lattice. In conclusion, we provide evidence for the coherent excitation of a phonon mode associated with the ferroelectric phase transition.« less

  8. Piezomagnetism and magnetoelastic memory in uranium dioxide

    DOE PAGES

    Jaime, M.; Saul, A.; Salamon, M.; ...

    2017-07-24

    Uranium dioxide (UO 2) is a prime nuclear fuel and perhaps the most thoroughly studied actinide material to date. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. The magnetic state of this cubic material is characterized by a non- collinear antiferromagnetic structure and multidomain Jahn-Teller distortions that could be behind novel thermal properties. Here we show that single crystals of UO 2, subjected to magnetic fields up to 95 T in the magnetic state, exhibit the abrupt appearance of positive linear magnetostriction leading to a trigonal distortion. Upon reversal ofmore » the field the linear term also reverses sign, a hallmark of piezomagnetism. The switching phenomenon occurs at ± 18 T and persists during subsequent field reversals, demonstrating robust magneto-elastic memory. This is the first example of piezomagnetism in an actinide spin system and the magneto-elastic memory loop here is nearly an order of magnitude wider in field than those previously observed, making UO 2 the hardest piezomagnet known. The possibility of an inverse phase with reduced magnetocrystalline anisotropy is considered to explain these effects.« less

  9. Piezomagnetism and magnetoelastic memory in uranium dioxide

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jaime, M.; Saul, A.; Salamon, M.

    Uranium dioxide (UO 2) is a prime nuclear fuel and perhaps the most thoroughly studied actinide material to date. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. The magnetic state of this cubic material is characterized by a non- collinear antiferromagnetic structure and multidomain Jahn-Teller distortions that could be behind novel thermal properties. Here we show that single crystals of UO 2, subjected to magnetic fields up to 95 T in the magnetic state, exhibit the abrupt appearance of positive linear magnetostriction leading to a trigonal distortion. Upon reversal ofmore » the field the linear term also reverses sign, a hallmark of piezomagnetism. The switching phenomenon occurs at ± 18 T and persists during subsequent field reversals, demonstrating robust magneto-elastic memory. This is the first example of piezomagnetism in an actinide spin system and the magneto-elastic memory loop here is nearly an order of magnitude wider in field than those previously observed, making UO 2 the hardest piezomagnet known. The possibility of an inverse phase with reduced magnetocrystalline anisotropy is considered to explain these effects.« less

  10. Enhanced vibronic interaction caused by local lattice symmetry lowering in the (Fe, Mg)As2 ternary system

    NASA Astrophysics Data System (ADS)

    Pishtshev, A.; Rubin, P.

    2018-04-01

    By means of periodic density functional theory (DFT) electronic structure calculations, we investigate iron-site doping effects in a structural model of bulk FeAs2. Simulations performed within the projector augmented-wave method-Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) functional scheme reveal that the impacts of the two stoichiometric substitutions Fe → Mg and Fe → Ni are radically different with respect to the structural and electronic behavior of the dopants. In particular, unlike the Ni dopant, the Mg dopant incorporated in FeAs2 occupies a noncentral equilibrium position characterized by an off-center displacement from the reference higher-symmetry position. Analysis of the respective electron and vibrational factors allows us to explain this result in terms of the local pseudo Jahn-Teller effect (pJTE). On the basis of DFT calculations, we deduce which electron orbitals and lattice vibrational modes are appropriate for promoting the local instability at the origin of the pJTE. Quantitative evaluations of the pJTE parameters performed within the polyatomic formalism of an effective tight-binding model show that it is just the enhanced vibronic interaction in the Mg-[FeAs6] cluster that is responsible for the local lattice symmetry breaking.

  11. Perils of Neglecting Lattice Relaxation in the Pressure Dependence of Deep Luminescence Bands in Wide Gap Semiconductors

    NASA Astrophysics Data System (ADS)

    Iota, V.; Weinstein, B. A.

    1998-03-01

    Deep defect states are often assumed to be insensitive to pressure because of their localized atomic-like character. In apparent conflict with this, experiments on widegap II-VI materials find that the pressure shifts of many 'midgap' photoluminescence (PL) bands associated with large-lattice-relaxation defects are more rapid than the shift of the bandgap(B. Weinstein, T. Ritter, et. al., Phys. Stat. Sol. (b) 198), 167 (1996). To study this, we measured the effects of pressure on the PL and PL-excitation (PLE) bands arising from the Zn-vacancy (V_Zn) and the P_Se deep acceptor centers in ZnSe. Using the observed pressure variation of the Stokes shifts and the established 1 atm. configuration coordinate (CC) models( D.Y. Jeon, H.P Gislason, G.D. Watkins, Phys. Rev. B 48), 7872 (1993), we were able to infer quantitative CC-diagrams at any pressure. Our results show that the pressure dependence of the lattice relaxation contributes a substantial fraction (several meV/kbar) to the overall shift of the PL-bands, and, hence, must be included. For the case of the V_Zn, simple calculations of the Jahn-Teller splitting using dangling-bond orbitals support this conclusion. figures

  12. Optimum inhomogeneity of local lattice distortions in La2CuO4+y

    PubMed Central

    Poccia, Nicola; Ricci, Alessandro; Campi, Gaetano; Fratini, Michela; Puri, Alessandro; Gioacchino, Daniele Di; Marcelli, Augusto; Reynolds, Michael; Burghammer, Manfred; Saini, Naurang Lal; Aeppli, Gabriel; Bianconi, Antonio

    2012-01-01

    Electronic functionalities in materials from silicon to transition metal oxides are, to a large extent, controlled by defects and their relative arrangement. Outstanding examples are the oxides of copper, where defect order is correlated with their high superconducting transition temperatures. The oxygen defect order can be highly inhomogeneous, even in optimal superconducting samples, which raises the question of the nature of the sample regions where the order does not exist but which nonetheless form the “glue” binding the ordered regions together. Here we use scanning X-ray microdiffraction (with a beam 300 nm in diameter) to show that for La2CuO4+y, the glue regions contain incommensurate modulated local lattice distortions, whose spatial extent is most pronounced for the best superconducting samples. For an underdoped single crystal with mobile oxygen interstitials in the spacer La2O2+y layers intercalated between the CuO2 layers, the incommensurate modulated local lattice distortions form droplets anticorrelated with the ordered oxygen interstitials, and whose spatial extent is most pronounced for the best superconducting samples. In this simplest of high temperature superconductors, there are therefore not one, but two networks of ordered defects which can be tuned to achieve optimal superconductivity. For a given stoichiometry, the highest transition temperature is obtained when both the ordered oxygen and lattice defects form fractal patterns, as opposed to appearing in isolated spots. We speculate that the relationship between material complexity and superconducting transition temperature Tc is actually underpinned by a fundamental relation between Tc and the distribution of ordered defect networks supported by the materials. PMID:22961255

  13. Underlying theory of a model for the Renner-Teller effect in tetra-atomic molecules: X(2)Πu electronic state of C2H2(+).

    PubMed

    Perić, M; Jerosimić, S; Mitić, M; Milovanović, M; Ranković, R

    2015-05-07

    In the present study, we prove the plausibility of a simple model for the Renner-Teller effect in tetra-atomic molecules with linear equilibrium geometry by ab initio calculations of the electronic energy surfaces and non-adiabatic matrix elements for the X(2)Πu state of C2H2 (+). This phenomenon is considered as a combination of the usual Renner-Teller effect, appearing in triatomic species, and a kind of the Jahn-Teller effect, similar to the original one arising in highly symmetric molecules. Only four parameters (plus the spin-orbit constant, if the spin effects are taken into account), which can be extracted from ab initio calculations carried out at five appropriate (planar) molecular geometries, are sufficient for building up the Hamiltonian matrix whose diagonalization results in the complete low-energy (bending) vibronic spectrum. The main result of the present study is the proof that the diabatization scheme, hidden beneath the apparent simplicity of the model, can safely be carried out, at small-amplitude bending vibrations, without cumbersome computation of non-adiabatic matrix elements at large number of molecular geometries.

  14. Research on the optical spectra, g factors and defect structures for two tetragonal Y²+ centers in the irradiated CaF₂: Y crystal.

    PubMed

    Zheng, Wen-Chen; Mei, Yang; Yang, Yu-Guang; Liu, Hong-Gang

    2012-11-01

    Based on the defect models that the tetragonal Y(2+) (1) center in the irradiated CaF(2): Y crystal is due to Y(2+) at Ca(2+) site associated with a nearest interstitial F(-) ion along C(4) axis and the tetragonal Y(2+) (2) center is Y(2+) at Ca(2+) site where the tetragonal distortion is caused by the static Jahn-Teller effect, the two optical spectral bands and anisotropic g factors for both tetragonal Y(2+) centers are calculated. The calculations are made by using two methods based on the cluster approach, one is the complete diagonalization (of energy matrix) method (CDM) and another is the perturbation theory method (PTM). The calculated results for each Y(2+) center from CDM and PTM coincide and show reasonable agreement with the experimental values. The calculated isotropic g factor for Y(2+) (2) center at higher temperature owing to the dynamical Jahn-Teller effect is also consistent with the observed value. The defect structures (i.e., tetragonal distortion) of the two Y(2+) centers are obtained from the calculation. It appears that both theoretical methods can be applied to explain the optical and EPR data, to study the defect model and to determine the defect structures for d(1) ions in crystals. Copyright © 2012 Elsevier B.V. All rights reserved.

  15. Active hydrogen evolution through lattice distortion in metallic MoTe2

    NASA Astrophysics Data System (ADS)

    Seok, Jinbong; Lee, Jun-Ho; Cho, Suyeon; Ji, Byungdo; Kim, Hyo Won; Kwon, Min; Kim, Dohyun; Kim, Young-Min; Oh, Sang Ho; Wng Kim, Sung; Lee, Young Hee; Son, Young-Woo; Yang, Heejun

    2017-06-01

    Engineering surface atoms of transition metal dichalcogenides (TMDs) is a promising way to design catalysts for efficient electrochemical reactions including the hydrogen evolution reaction (HER). However, materials processing based on TMDs, such as vacancy creation or edge exposure, for active HER, has resulted in insufficient atomic-precision lattice homogeneity and a lack of clear understanding of HER over 2D materials. Here, we report a durable and effective HER at atomically defined reaction sites in 2D layered semimetallic MoTe2 with intrinsic turnover frequency (TOF) of 0.14 s-1 at 0 mV overpotential, which cannot be explained by the traditional volcano plot analysis. Unlike former electrochemical catalysts, the rate-determining step of the HER on the semimetallic MoTe2, hydrogen adsorption, drives Peierls-type lattice distortion that, together with a surface charge density wave, unexpectedly enhances the HER. The active HER using unique 2D features of layered TMDs enables an optimal design of electrochemical catalysts and paves the way for a hydrogen economy.

  16. Note: Is it symmetric or not?

    PubMed

    Stanton, John F

    2013-07-28

    The reasons by which a molecule might distort from an idealized high symmetry configuration (for example, D3h for the nitrate radical) in a quantum-chemical computation are well-known, but briefly reviewed here in light of considerable recent debate on the BNB molecule. The role of the pseudo-Jahn-Teller effect in such cases is emphasized, as is the ultimate relevance and proper interpretation of the title question in cases where the adiabatic potential energy surface is extremely flat.

  17. Bis(6-meth-oxy-2-{[tris-(hydroxy-meth-yl)-meth-yl]-imino-meth-yl}phenolato)-copper(II) dihydrate.

    PubMed

    Zhang, Xiutang; Wei, Peihai; Dou, Jianmin; Li, Bin; Hu, Bo

    2009-01-08

    In the title compound, [Cu(C(12)H(16)NO(5))(2)]·2H(2)O, the Cu(II) ion adopts a trans-CuN(2)O(4) octa-hedral geometry arising from two N,O,O'-tridentate 6-meth-oxy-2-{[tris-(hydroxy-meth-yl)meth-yl]-imino-meth-yl}phenolate ligands. The Jahn-Teller distortion of the copper centre is unusally small. In the crystal structure, O-H⋯O hydrogen bonds, some of which are bifurcated, link the component species.

  18. Effect of dynamics on the elastic softening of vacancies in Si

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shirai, Koun; Ishisada, Jun

    2014-02-21

    Recently, elastic softening at temperatures below 20 K has been observed in nondoped floating zone silicon. From the experimental analysis, it has been suggested that this softening is caused by an intrinsic vacancy defect through the Jahn-Teller (JT) effect. We have theoretically studied the relations between softening and the vacancies. The ground state of the JT distortion is stiff. However, by considering atomistic dynamical and anharmonic effects, it is found that low-energy excitations exist in the E-mode distortion and that different polarizations of the E-distortion can be easily interchanged. The calculated energy barriers for the reorientation of JT distortions aremore » consistent with other experiments and calculations. This low-lying mode can be the cause of softening in the elastic responses.« less

  19. Lattice-mediated magnetic order melting in TbMnO3

    NASA Astrophysics Data System (ADS)

    Baldini, Edoardo; Kubacka, Teresa; Mallett, Benjamin P. P.; Ma, Chao; Koohpayeh, Seyed M.; Zhu, Yimei; Bernhard, Christian; Johnson, Steven L.; Carbone, Fabrizio

    2018-03-01

    Recent ultrafast magnetic-sensitive measurements [Johnson et al., Phys. Rev. B 92, 184429 (2015), 10.1103/PhysRevB.92.184429; Bothschafter et al., Phys. Rev. B 96, 184414 (2017), 10.1103/PhysRevB.96.184414] have revealed a delayed melting of the long-range cycloid spin order in TbMnO3 following photoexcitation across the fundamental Mott-Hubbard gap. The microscopic mechanism behind this slow transfer of energy from the photoexcited carriers to the spin degrees of freedom is still elusive and not understood. Here, we address this problem by combining spectroscopic ellipsometry, ultrafast broadband optical spectroscopy, and ab initio calculations. Upon photoexcitation, we observe the emergence of a complex collective response, which is due to high-energy coherent optical phonons coupled to the out-of-equilibrium charge density. This response precedes the magnetic order melting and is interpreted as the fingerprint of the formation of anti-Jahn-Teller polarons. We propose that the charge localization in a long-lived self-trapped state hinders the emission of magnons and other spin-flip mechanisms, causing the energy transfer from the charge to the spin system to be mediated by the reorganization of the lattice. Furthermore, we provide evidence for the coherent excitation of a phonon mode associated with the ferroelectric phase transition.

  20. Evidence for Jahn-Teller distortions at the antiferromagnetic transition in LaTiO3.

    PubMed

    Hemberger, J; Krug von Nidda, H-A; Fritsch, V; Deisenhofer, J; Lobina, S; Rudolf, T; Lunkenheimer, P; Lichtenberg, F; Loidl, A; Bruns, D; Büchner, B

    2003-08-08

    LaTiO3 is known as a Mott insulator which orders antiferromagnetically at T(N)=146 K. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At T(N) significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.

  1. Controlling the orbital sequence in individual Cu-phthalocyanine molecules.

    PubMed

    Uhlmann, C; Swart, I; Repp, J

    2013-02-13

    We report on the controlled change of the energetic ordering of molecular orbitals. Negatively charged copper(II)phthalocyanine on NaCl/Cu(100) undergoes a Jahn-Teller distortion that lifts the degeneracy of two frontier orbitals. The energetic order of the levels can be controlled by Au and Ag atoms in the vicinity of the molecule. As only one of the states is occupied, the control of the energetic order is accompanied by bistable changes of the charge distribution inside the molecule, rendering it a bistable switch.

  2. Nanoscale orbital excitations and the infrared spectrum of a molecular Mott insulator: A15-Cs3C60.

    PubMed

    Naghavi, S S; Fabrizio, M; Qin, T; Tosatti, E

    2016-10-14

    The quantum physics of ions and electrons behind low-energy spectra of strongly correlated molecular conductors, superconductors and Mott insulators is poorly known, yet fascinating especially in orbitally degenerate cases. The fulleride insulator Cs 3 C 60 (A15), one such system, exhibits infrared (IR) spectra with low temperature peak features and splittings suggestive of static Jahn-Teller distortions with a breakdown of orbital symmetry in the molecular site. That is puzzling, since there is no detectable static distortion, and because the features and splittings disappear upon modest heating, which they should not. Taking advantage of the Mott-induced collapse of electronic wavefunctions from lattice-extended to nanoscale localized inside a caged molecular site, we show that the unbroken spin and orbital symmetry of the ion multiplets explains the IR spectrum without adjustable parameters. This demonstrates the importance of a fully quantum treatment of nuclear positions and orbital momenta in the Mott insulator sites, dynamically but not statically distorted. The observed demise of these features with temperature is explained by the thermal population of a multiplet term whose nuclear positions are essentially undistorted, but whose energy is very low-lying. That term is in fact a scaled-down orbital excitation analogous to that of other Mott insulators, with the same spin 1/2 as the ground state, but with a larger orbital momentum of two instead of one.

  3. Assigning the low lying vibronic states of CH3O and CD3O

    NASA Astrophysics Data System (ADS)

    Johnson, Britta A.; Sibert, Edwin L.

    2017-05-01

    The assignment of lines in vibrational spectra in strongly mixing systems is considered. Several low lying vibrational states of the ground electronic X˜ 2E state of the CH3O and CD3O radicals are assigned. Jahn-Teller, spin-orbit, and Fermi couplings mix the normal mode states. The mixing complicates the assignment of the infrared spectra using a zero-order normal mode representation. Alternative zero-order representations, which include specific Jahn-Teller couplings, are explored. These representations allow for definitive assignments. In many instances it is possible to plot the wavefunctions on which the assignments are based. The plots, which are shown in the adiabatic representation, allow one to visualize the effects of various higher order couplings. The plots also enable one to visualize the conical seam and its effect on the wavefunctions. The first and the second order Jahn-Teller couplings in the rocking motion dominate the spectral features in CH3O, while first order and modulated first order couplings dominate the spectral features in CD3O. The methods described here are general and can be applied to other Jahn-Teller systems.

  4. The effect of external magnetic field on the Raman peaks in manganites

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sahu, A. K., E-mail: ajitsahu@seemantaengg.ac.in; Rout, G. C.

    2014-04-24

    We report here a microscopic theoretical model study exhibiting the effect of external magnetic field on the Raman excitation peaks in the CMR manganite system. The Hamiltonian consists of Jahn-Teller (J-T) distortion in e{sub g} band, the double exchange interaction and the Heisenberg spin-spin interaction. Further the phonons are coupled to e{sub g} band electrons, J-T distorted e{sub g} band and the double exchange interaction. The Raman spectral intensity is calculated from the imaginary part of the phonon Green function. The spectra exhibits three peaks besides a very weak high energy peak. The magnetic field effect on these peaks aremore » reported.« less

  5. A tight binding model study of tunneling conductance spectra of spin and orbitally ordered CMR manganites

    NASA Astrophysics Data System (ADS)

    Panda, Saswati; Sahoo, D. D.; Rout, G. C.

    2018-04-01

    We report here a tight binding model for colossal magnetoresistive (CMR) manganites to study the pseudo gap (PG) behavior near Fermi level. In the Kubo-Ohata type DE model, we consider first and second nearest neighbor interactions for transverse spin fluctuations in core band and hopping integrals in conduction band, in the presence of static band Jahn-Teller distortion. The model Hamiltonian is solved using Zubarev's Green's function technique. The electron density of states (DOS) is found out from the Green's functions. We observe clear PG near Fermi level in the electron DOS.

  6. A binuclear Mn(III) complex of a scorpiand-like ligand displaying a single unsupported Mn(III)-O-Mn(III) bridge.

    PubMed

    Blasco, Salvador; Cano, Joan; Clares, M Paz; García-Granda, Santiago; Doménech, Antonio; Jiménez, Hermas R; Verdejo, Begoña; Lloret, Francesc; García-España, Enrique

    2012-11-05

    The crystal structure of a binuclear Mn(III) complex of a scorpiand-like ligand (L) displays an unsupported single oxo bridging ligand with a Mn(III)-O-Mn(III) angle of 174.7°. Magnetic susceptibility measurements indicate strong antiferromagnetic coupling between the two metal centers. DFT calculations have been carried out to understand the magnetic behavior and to analyze the nature of the observed Jahn-Teller distortion. Paramagnetic (1)H NMR has been applied to rationalize the formation and magnetic features of the complexes formed in solution.

  7. Novel effect of spin dynamics with suppression of charge and orbital ordering in Nd0.5Ca0.5MnO3 under the influence of ac electric field

    NASA Astrophysics Data System (ADS)

    Sarwar, T.; Qamar, A.; Nadeem, M.

    2017-07-01

    Dynamics of spin ordering in the manganite Nd0.5Ca0.5MnO3 have been investigated in this paper. It was observed that the complex mixed magnetic ordering in pellets is comprised of antiferromagnetic ordering at 160 K (TN) and complete charge ordering at 250 K (TCO). Under ac field, appearance of unstable ferromagnetic correlations is observed above TCO, which is badly frustrated due to strong spin disorder induced by Jahn Teller distortions. Impedance measurements reveal the spin glass like scenario, suppressing the strong antiferromagnetic and charge ordering states below TN.

  8. Structural phase transition of as-synthesized Sr-Mn nanoferrites by annealing temperature

    NASA Astrophysics Data System (ADS)

    Amer, M. A.; Meaz, T. M.; Attalah, S. S.; Ghoneim, A. I.

    2015-11-01

    The Sr0.2Mn0.8Fe2O4 nanoparticle ferrites were synthesized by the co-precipitation method and annealed at different temperatures T. XRD, TEM, FT-IR, VSM and Mössbauer techniques were used to characterize the samples. This study proved that the structural phase of nanoferrites was transformed from cubic spinel for T≤500 °C to Z-type hexagonal for T≥700 °C. The structural transformation was attributed to Jahn-Teller effect of the Mn3+ ions and/or atomic disorder existed in the crystal lattice. The obtained spectra and parameters for the samples were affected by the transformation process. The lattice constant a showed a splitting to a and c for T>500 °C. The lattice constant c, grain and crystallite size R, strain, octahedral B-site band position and force constant, Debye temperature, coercivity Hc, remnant magnetization, squareness and magnetic moment, spontaneous magnetization and hyperfine magnetic fields showed increase against T. The lattice constant a, distortion and dislocation parameters, specific surface area, tetrahedral A-site band position and force constant, threshold frequency, Young's and bulk moduli, saturation magnetization Ms, area ratio of B-/A-sites, A-site line width were decreased with T. Experimental and theoretical densities, porosity, Poison ratio, stiffness constants, rigidity modulus, B-site line width and spontaneous magnetization showed dependence on T, whereas Ms and Hc proved dependence on R.

  9. High pressure effects on a trimetallic Mn(II/III) SMM.

    PubMed

    Prescimone, Alessandro; Sanchez-Benitez, Javier; Kamenev, Konstantin V; Moggach, Stephen A; Lennie, Alistair R; Warren, John E; Murrie, Mark; Parsons, Simon; Brechin, Euan K

    2009-09-28

    A combined study of the high pressure crystallography and high pressure magnetism of the complex [Mn3(Hcht)2(bpy)4](ClO4)3.Et2O.2MeCN (1.Et2O.2MeCN) (H3cht is cis,cis-1,3,5-cyclohexanetriol) is presented in an attempt to observe and correlate pressure induced changes in its structural and physical properties. At 0.16 GPa the complex 1.Et2O.2MeCN loses all associated solvent in the crystal lattice, becoming 1. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making the magnetic exchange between the manganese ions weaker. No significant variations are observed in the Jahn-Teller axis of the only Mn(III) present in the structure. High pressure dc chiMT plots display a gradual decrease in both the low temperature value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|.

  10. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Krasnenko, V.; Boltrushko, V.; Hizhnyakov, V.

    Chemically bound states of benzene molecules with graphene are studied both analytically and numerically. The states are formed by switching off intrabonds of π-electrons in C{sub 6} rings to interbonds. A number of different undistorted and distorted structures are established both with aligned and with transversal mutual orientation of benzene and graphene. The vibronic interactions causing distortions of bound states are found, by using a combination of analytical and numerical considerations. This allows one to determine all electronic transitions of π-electrons without explicit numerical calculations of excited states, to find the conical intersections of potentials, and to show that themore » mechanism of distortions is the pseudo-Jahn-Teller effect. It is found that the aligned distorted benzene molecule placed between two graphene sheets makes a chemical bond with both of them, which may be used for fastening of graphene sheets together.« less

  11. Electronic instability and change of crystalline phase in compounds of the V3Si type at low temperature

    NASA Technical Reports Server (NTRS)

    Labbe, J.; Friedel, J.

    1978-01-01

    In V3Si, the V atoms form an array of dense linear chains; a tight-binding approximation in one dimension was used to describe the d electrons. The electronic energy calculated by this method was reduced when the lattice is deformed. This lead to a band type of the Jahn Teller effect, which may explain the cubic to tetragonal transition which was observed at low temperatures. The theory can be extended to other superconductors of the V3X type when X=Ga, Ge, Sn, etcetera, or NB3SN.

  12. 3D lattice distortions and defect structures in ion-implanted nano-crystals

    PubMed Central

    Hofmann, Felix; Tarleton, Edmund; Harder, Ross J.; Phillips, Nicholas W.; Ma, Pui-Wai; Clark, Jesse N.; Robinson, Ian K.; Abbey, Brian; Liu, Wenjun; Beck, Christian E.

    2017-01-01

    Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga+), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology. PMID:28383028

  13. 3D lattice distortions and defect structures in ion-implanted nano-crystals.

    PubMed

    Hofmann, Felix; Tarleton, Edmund; Harder, Ross J; Phillips, Nicholas W; Ma, Pui-Wai; Clark, Jesse N; Robinson, Ian K; Abbey, Brian; Liu, Wenjun; Beck, Christian E

    2017-04-06

    Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga + ), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology.

  14. Molecular geometry of vanadium dichloride and vanadium trichloride: a gas-phase electron diffraction and computational study.

    PubMed

    Varga, Zoltán; Vest, Brian; Schwerdtfeger, Peter; Hargittai, Magdolna

    2010-03-15

    The molecular geometries of VCl2 and VCl3 have been determined by computations and gas-phase electron diffraction (ED). The ED study is a reinvestigation of the previously published analysis for VCl2. The structure of the vanadium dichloride dimer has also been calculated. According to our joint ED and computational study, the evaporation of a solid sample of VCl2 resulted in about 66% vanadium trichloride and 34% vanadium dichloride in the vapor. Vanadium dichloride is unambiguously linear in its 4Sigma(g)+ ground electronic state. For VCl3, all computations yielded a Jahn-Teller-distorted ground-state structure of C(2v) symmetry. However, it lies merely less than 3 kJ/mol lower than the 3E'' state (D(3h) symmetry). Due to the dynamic nature of the Jahn-Teller effect in this case, rigorous distinction cannot be made between the planar models of either D(3h) symmetry or C(2v) symmetry for the equilibrium structure of VCl3. Furthermore, the presence of several low-lying excited electronic states of VCl3 is expected in the high-temperature vapor. To our knowledge, this is the first experimental and computational study of the VCl3 molecule.

  15. Electronic structure and energetics of the tetragonal distortion for TiH2, ZrH2 and HfH2: a first principles study

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Quijano, Ramiro; DeCoss, Romeo; Singh, David J

    2009-01-01

    The electronic structure and energetics of the tetragonal distortion for the fluorite-type dihydrides TiH{sub 2}, ZrH{sub 2}, and HfH{sub 2} are studied by means of highly accurate first-principles total-energy calculations. For HfH{sub 2}, in addition to the calculations using the scalar relativistic (SR) approximation, calculations including the spin-orbit coupling have also been performed. The results show that TiH{sub 2}, ZrH{sub 2}, and HfH{sub 2} in the cubic phase are unstable against tetragonal strain. For the three systems, the total energy shows two minima as a function of the c/a ratio with the lowest-energy minimum at c/a < 1 in agreementmore » with the experimental observations. The band structure of TiH{sub 2}, ZrH{sub 2}, and HfH{sub 2} (SR) around the Fermi level shows two common features along the two major symmetry directions of the Brillouin zone, {Lambda}?L and {Lambda}?K, a nearly flat doubly degenerate band, and a van Hove singularity, respectively. In cubic HfH{sub 2} the spin-orbit coupling lifts the degeneracy of the partially filled bands in the {Lambda}?L path, while the van Hove singularity in the {Lambda}?K path remains unchanged. The density of states of the three systems in the cubic phase shows a sharp peak at the Fermi level. We found that the tetragonal distortion produces a strong reduction in the density of states at the Fermi level resulting mainly from the splitting of the doubly-degenerate bands in the {Lambda}?L direction and the shift of the van Hove singularity to above the Fermi level. The validity of the Jahn-Teller model in explaining the tetragonal distortion in this group of dihydrides is discussed.« less

  16. Ferromagnetism in LaCoO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhou, Shiming; Shi, Lei; Zhao, Jiyin; He, Laifa; Yang, Haipeng; Zhang, Shangming

    2007-11-01

    We have investigated the structural and magnetic properties of LaCoO3 nanoparticles prepared by a sol-gel method. A ferromagnetic order with TC˜85K has been observed in the nanoparticles. The infrared spectra give evidence for a stabilizing of higher spin state and a reduced Jahn-Teller distortion in the nanoparticles with respect to the bulk LaCoO3 , which is consistent with the recent reports in the strained films [Phys. Rev. B 75, 144402 (2007)] and proposed to be the possible origin of the observed ferromagnetic order in LaCoO3 .

  17. Spin dynamics and orbital state in LaTiO3

    PubMed

    Keimer; Casa; Ivanov; Lynn; Zimmermann; Hill; Gibbs; Taguchi; Tokura

    2000-10-30

    A neutron scattering study of the Mott-Hubbard insulator LaTiO3 ( T(N) = 132 K) reveals a spin wave spectrum that is well described by a nearest-neighbor superexchange constant J = 15.5 meV and a small Dzyaloshinskii-Moriya interaction ( D = 1.1 meV). The nearly isotropic spin wave spectrum is surprising in view of the absence of a static Jahn-Teller distortion that could quench the orbital angular momentum, and it may indicate strong orbital fluctuations. A resonant x-ray scattering study has uncovered no evidence of orbital order in LaTiO3.

  18. Specific features of the structural and magnetic states of a Zn1 - x Ni x Se crystal ( x = 0.0025) at low temperatures

    NASA Astrophysics Data System (ADS)

    Dubinin, S. F.; Sokolov, V. I.; Parkhomenko, V. D.; Teploukhov, S. G.; Gruzdev, N. B.

    2008-12-01

    The magnetic state and the structure of a Zn1 - x Ni x Se ( x = 0.0025) bulk crystal were studied at low temperatures. It is revealed that the magnetic and crystal structures below T ≅ 15 K are dependent on the cooling rate of this dilute semiconductor. For example, on fast cooling to 4.2 K, about 10% hexagonal ferromagnetic phase is formed in the crystal. During heating, the phase disappears at T ≅ 15 K. The results obtained are discussed with allowance for the specific features of the Jahn-Teller distortions in this compound.

  19. Different Effects of Al Substitution for Mn or Fe on the Structure and Electrochemical Properties of Na0.67Mn0.5Fe0.5O2 as a Sodium Ion Battery Cathode Material.

    PubMed

    Wang, Huibo; Gao, Rui; Li, Zhengyao; Sun, Limei; Hu, Zhongbo; Liu, Xiangfeng

    2018-05-07

    P2-type layered oxides based on the elements Fe and Mn have attracted great interest as sodium ion battery (SIB) cathode materials owing to their inexpensive metal constituents and high specific capacity. However, they suffer from rapid capacity fading and complicated phase transformations. In this study, we modulate the crystal structure and optimize the electrochemical performances of Na 0.67 Mn 0.5 Fe 0.5 O 2 by Al doping for Mn or Fe, respectively, and the roles of Al in the enhancement of the rate capability and cycling performance are unraveled. (1) The substitution of Al for Mn or Fe decreases the lattice parameters a and c but enlarges d spacing and lengthens Na-O bonds, which enhances Na + diffusion and rate capability especially for Na 0.67 Mn 0.5 Fe 0.47 Al 0.03 O 2 . (2) Al doping reduces the thickness of TMO 2 and strengthens TM-O/O-O bonding. This enhances the layered structure stability and the capacity retention. (3) Al doping mitigates Mn 3+ and Jahn-Teller distortion, mitigating the irreversible phase transition. (4) Al doping also alleviates the lattice volume variation and the structure strain. This further improves the stability of the layered structure and the cycling performances particularly in the case of Al doping for Fe. The in-depth insights into the roles of Al substitution might be also useful for designing high-performance cathode materials for SIBs through appropriate lattice doping.

  20. Local distortion and EPR parameters of copper(II) in borate glasses

    NASA Astrophysics Data System (ADS)

    Kuang, Min-Quan; Wang, Li-Dan; Duan, Shu-Kai

    2017-12-01

    The EPR parameters (g and A tensors) of the paramagnetic Cu2+ sites in CaB4O7, LiCaBO3, Li2B4O7, KLiB4O7 glasses are well explained by utilizing the fourth-order perturbation formulas for 3 d9 ions in the tetragonally elongated octahedral [CuO6]10- clusters. The magnitude of the local distortion for the [CuO6]10- clusters suffering the Jahn-Teller effect is denoted by the relative elongation ratio ρ which is proportional to the ratio Δg///Δg⊥ (Δg//= g//-gs and Δg⊥ = g⊥-gs). The g isotropies giso (=(g//+2g⊥)/3) undergo an linear increase with the decline of the covalecny of the glass systems (i.e., the augment of the orbital reduction factor k). The signs of the hyperfine structure constants are determined by computing the quantitative contributions arising from the isotropic and anisotropic copper 3d-3s (4s) orbital admixtures indicated by the core polarization constant κ and the reduction factor H, respectively. The above correlations are proved to be available for analogous borate glasses doping with copper ions, e.g., MRbB4O7 (M = Li, Na and K), 90M2B4O7·9PbO·CuO (M = Li, Na and K), 10MO·30ZnO·60B2O3 (M = Mg, Ca and Sr) and xLi2O·(30-x)Na2O·69.5B2O3 (5 ≤ x ≤ 25 mol%), and all the results are discussed.

  1. Structural and dynamical properties of the V(3+) ion in dilute aqueous solution: An ab initio QM/MM molecular dynamics simulation.

    PubMed

    Kritayakornupong, Chinapong

    2009-12-01

    A hybrid ab initio QM/MM molecular dynamics simulation at the Hartree-Fock level has been performed to investigate structural and dynamical parameters of the V(3+) ion in dilute aqueous solution. A distorted octahedral structure with the average V(3+)-O distance of 1.99 A is evaluated from the QM/MM simulation, which is in good agreement with the X-ray data. Several structural parameters such as angular distribution functions, theta- and tilt-angle distributions have been determined to obtain the full description of the hydration structure of the hydrated V(3+). The Jahn-Teller distortions of the V(3+) ion are pronounced in the QM/MM simulation. The mean residence time of 14.5 ps is estimated for the ligand exchange processes in the second hydration shell. (c) 2009 Wiley Periodicals, Inc.

  2. Role of lattice distortion on diffuse phase transition temperatures in Bi0.5Na0.5TiO3-BaTiO3 [BNBTO] solid solutions

    NASA Astrophysics Data System (ADS)

    Pradhan, Lagen Kumar; Pandey, Rabichandra; Kumar, Sunil; Supriya, Sweety; Kar, Manoranjan

    2018-04-01

    Effect of lattice distortion on diffuse phase transition in BNBTO solid solutions near Morphotropic phase boundary (MPB) has been investigated. Solid solutions of (Bi0.5Na0.5)1-xBaxTiO3 (with mole % of x= 0.04, 0.05, 0.06, 0.07 and 0.08) were prepared by the planetary ball mill method in ethanol medium. Rietveld refinement technique with rhombohedral (R3c) and tetragonal (P4bm) crystal symmetry has been employed for structural as well as phase analysis of the solid solutions. Both rhombohedral and tetragonal lattice distortion (c/a) tends toward the pseudo-cubic crystal symmetry with the increase of mole fraction of Ba2+ near MPB (x= 6 mole %). Also, the average crystallite size and grain size decrease with increase of mole fraction of Ba2+ in BNT ceramic are due to larger ionic radius of Ba2+ and grain boundary pinning process in the solid solutions respectively. Additionally, depolarization temperature (Td) and maximum temperature (Tm) reduces due to the lattice distortion of both the phases in BNBTO solid solutions, which is explained extensively. Significant increase of dielectric constant has been observed near MPB composition (x=6%) in BNBTO solid solutions.

  3. Coupled ferroelectric polarization and magnetization in spinel FeCr2S4

    PubMed Central

    Lin, L.; Zhu, H. X.; Jiang, X. M.; Wang, K. F.; Dong, S.; Yan, Z. B.; Yang, Z. R.; Wan, J. G.; Liu, J.-M.

    2014-01-01

    One of the core issues for multiferroicity is the strongly coupled ferroelectric polarization and magnetization, while so far most multiferroics have antiferromagnetic order with nearly zero magnetization. Magnetic spinel compounds with ferrimagnetic order may be alternative candidates offering large magnetization when ferroelectricity can be activated simultaneously. In this work, we investigate the ferroelectricity and magnetism of spinel FeCr2S4 in which the Fe2+ sublattice and Cr3+ sublattice are coupled in antiparallel alignment. Well defined ferroelectric transitions below the Fe2+ orbital ordering termperature Too = 8.5 K are demonstrated. The ferroelectric polarization has two components. One component arises mainly from the noncollinear conical spin order associated with the spin-orbit coupling, which is thus magnetic field sensitive. The other is probably attributed to the Jahn-Teller distortion induced lattice symmetry breaking, occuring below the orbital ordering of Fe2+. Furthermore, the coupled ferroelectric polarization and magnetization in response to magnetic field are observed. The present work suggests that spinel FeCr2S4 is a multiferroic offering both ferroelectricity and ferrimagnetism with large net magnetization. PMID:25284432

  4. Bond-length fluctuations and the spin-state transition in LCoO3 (L=La, Pr, and Nd)

    NASA Astrophysics Data System (ADS)

    Yan, J.-Q.; Zhou, J.-S.; Goodenough, J. B.

    2004-04-01

    The temperature dependence of thermal conductivity, κ(T), and magnetic susceptibility, χ(T), have been measured on single crystals of LCoO3 (L=La, Pr, Nd) grown by the floating-zone method. The susceptibility measurement shows a progressive stabilization of the low-spin (LS) state of Co(III) with decreasing size of the L3+ ion, and the population of excited intermediate-spin (IS) or high-spin (HS) state Co(III) ions begins to increase at 200 K and 300 K for PrCoO3 and NdCoO3 compared with 35 K in LaCoO3. The low-temperature Curie-Weiss paramagnetic susceptibility of LCoO3 is an intrinsic property arising from surface cobalt and, possibly, a LS ground state bearing some IS character caused by the virtual excitation to the IS state. The transition from a LS to a IS/HS state introduces bond-length fluctuations that suppress the phonon contribution to κ(T) below 300 K. The suppressed κ(T) could be further reduced by dynamic Jahn-Teller distortions associated with the IS/HS species. A smooth transition in ρ(T) and α(T) and a nearly temperature independent α(T)≈20 μV/K above 600 K do not support a thermally induced, homogeneous Mott-Hubbard transition model for the high-temperature transition of LaCoO3 from an insulating to a conductive state. A two-phase process is proposed for the interval 300 KJahn-Teller distortions that may be dynamic.

  5. Thermo physical Properties of Multiferroic Rare Earth Manganite GdMnO3

    NASA Astrophysics Data System (ADS)

    Choithrani, Renu; Gaur, N. K.

    2008-04-01

    We have investigated the thermophysical properties of multiferroic rare earth manganite GdMnO3 in the temperature range 15 K⩽T⩽300 K. We have applied interatomic potential to study the Specific heat (C) as a function of temperature. The calculated Specific heat values are closer to the available experimental data. At room temperature, the orthorhombic GdMnO3 phase is indicative of a strong Jahn-Teller distortion. In addition, we have reported the cohesive energy (φ), molecular force constant (f), compressibility (β), Restrahalen frequency (ν0), Debye temperature (ΘD) and Groneisen parameter (γ) at temperature 15 K⩽T⩽300 K.

  6. Magnetostructural Properties of Colossal Magnetoresistance Manganites Under External Magnetic Fields and Uniaxial Pressure

    NASA Astrophysics Data System (ADS)

    Kaplan, Michael; Zimmerman, George

    2002-03-01

    In the colossal magnetoresistance manganites the transport and magnetostructural properties are tightly connected [1,2]. Many magnetic field induced structural phase transitions and anomalous magnetoacoustical properties continue to be discovered in various manganite derivatives. Nevertheless the mechanism of structural transitions and microscopic theory of corresponding anomalous properties are still to be completely understood. Here we present a microscopic model of magnetic field and uniaxial pressure induced structural phase transitions in lightly doped manganites. The model is based on the cooperative Jahn-Teller effect which takes into account the Mn3+-ground doublet and excited triplet electronic states. Numerous calculations for different orientation magnetic field suggest the explanations of the origin of the structural transitions and of the measured magnetostriction data. The calculations for the two-sublattice antiferrodistortive crystals under uniaxial pressure support the idea of metaelasticity - a property typical for Jahn-Teller antiferroelastics. 1.Y. Tokura, ed. Colossal Magnetoresistance Oxides. Gordon & Breach, London, 2000. 2.M. Kaplan, G. Zimmerman, eds. Vibronic Interactions: Jahn-Teller Effect in Crystal and Molecules. NATO Science Series, Dordrecht/Boston/London, 2001

  7. Substrate-dependent structural and CO sensing properties of LaCoO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Liu, Haifeng; Sun, Hongjuan; Xie, Ruishi; Zhang, Xingquan; Zheng, Kui; Peng, Tongjiang; Wu, Xiaoyu; Zhang, Yanping

    2018-06-01

    LaCoO3 thin films were grown on different (0 0 1) oriented LaAlO3, SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 by the polymer assisted deposition method, respectively. All the LaCoO3 thin films are in epitaxial growth on these substrates, with tetragonal distortion of CoO6 octahedrons. Due to different in-plane lattice mismatch, the LaCoO3 film on LaAlO3 has the largest tetragonal distortion of CoO6 octahedrons while the film grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 has the smallest tetragonal distortion. The relative contents of the surface absorbed oxygen species are found to increase for the LaCoO3 epitaxial films grown on (0 0 1) oriented (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3 and LaAlO3 substrates, sequentially. The film sensors exhibit good CO sensing properties at 150 °C, and the LaCoO3 film on LaAlO3 shows the highest response but the film on (LaAlO3)0.3(Sr2AlTaO6)0.7 shows the lowest. It reveals that the larger degree of Jahn-Teller-like tetragonal distortion of CoO6 octahedrons may greatly improve the surface absorbing and catalytic abilities, corresponding to more excellent CO sensing performance. The present study suggests that the formation of epitaxial films is an efficient methodology for controlling the octahedral distortion and thereby improving the gas sensing performance of perovskite transition metal oxides.

  8. Ultrafast optically induced ferromagnetic/anti-ferromagnetic phase transition in GdTiO3 from first principles

    NASA Astrophysics Data System (ADS)

    Khalsa, Guru; Benedek, Nicole A.

    2018-03-01

    Epitaxial strain and chemical substitution have been the workhorses of functional materials design. These static techniques have shown immense success in controlling properties in complex oxides through the tuning of subtle structural distortions. Recently, an approach based on the excitation of an infrared active phonon with intense midinfrared light has created an opportunity for dynamical control of structure through special nonlinear coupling to Raman phonons. We use first-principles techniques to show that this approach can dynamically induce a magnetic phase transition from the ferromagnetic ground state to a hidden antiferromagnetic phase in the rare earth titanate GdTiO3 for realistic experimental parameters. We show that a combination of a Jahn-Teller distortion, Gd displacement, and infrared phonon motion dominate this phase transition with little effect from the octahedral rotations, contrary to conventional wisdom.

  9. Specific features of nonvalent interactions in orthorhombic perovskites

    NASA Astrophysics Data System (ADS)

    Serezhkin, V. N.; Pushkin, D. V.; Serezhkina, L. B.

    2014-07-01

    It is established that isostructural orthorhombic perovskites ABO3 (sp. gr. Pnma in different systems, no. 62, Z = 4), depending on the specificity of nonvalent interactions (which determine the combinatorial-topological type of the Voronoi-Dirichlet polyhedra (VDPs) of four basis atoms), are divided into ten different stereotypes. It is shown by the example of 259 perovskites belonging to the DyCrO3 stereotype that VDP characteristics can be used to quantitatively estimate the distortion of BO6 octahedra, including that caused by the Jahn-Teller effect. It is found that one of the causes of the distortion of the coordination polyhedra of atoms in the structure of orthorhombic perovskites is heteroatomic metal-metal interactions, for which the interatomic distances are much shorter than the sum of the Slater radii of A and B atoms.

  10. Zero kinetic energy photoelectron spectroscopy of triphenylene.

    PubMed

    Harthcock, Colin; Zhang, Jie; Kong, Wei

    2014-06-28

    We report vibrational information of both the first electronically excited state and the ground cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited electronic state S1 of the neutral molecule is of A1' symmetry and is therefore electric dipole forbidden in the D3h group. Consequently, there are no observable Franck-Condon allowed totally symmetric a1' vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E' third electronically excited state S3. The assignment of all vibrational bands as e' symmetry is based on comparisons with calculations using the time dependent density functional theory and spectroscopic simulations. When an electron is eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to C2v and resulting in two nearly degenerate electronic states of A2 and B1 symmetry. Here we follow a crude treatment by assuming that all e' vibrational modes resolve into b2 and a1 modes in the C2v molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm(-1). The observed ZEKE spectra contain a consistent pattern, with a cluster of transitions centered near the same vibrational level of the cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much more extensive calculations, which will be performed in the future.

  11. Off-Centre Effects in the Triplet Relaxed Excited State of Ga+ Centres in CsBr:Ga Crystal

    NASA Astrophysics Data System (ADS)

    Kalder, K.; Korrovits, V.; Nagirnyi, V.; Stolovits, A.; Zazubovich, S.; Babin, V.

    1997-06-01

    Spectra, polarization and decay kinetics of the triplet and singlet emission of Ga+ centres in CsBr:Ga crystals have been studied in the temperature range of 0.1 to 400 K. It has been found that the triplet AX and AT emission bands coincide. Two slow components have been observed in the decay kinetics of each emission at T < 1.5 K and explained by the tunnel splitting of the metastable minima of the corresponding triplet relaxed excited state. It points to the off-centre displacement of a Ga+ ion from a crystal lattice site both in the tetragonal (T) and in the trigonal (X) Jahn-Teller minima.

  12. Charge localization and ordering in A 2 Mn 8 O 16 hollandite group oxides: Impact of density functional theory approaches

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kaltak, Merzuk; Fernandez-Serra, Marivi; Hybertsen, Mark S.

    The phases of A 2Mn 8O 16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3d electrons are more explicitly considered with the DFT + Umore » approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn 3+ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Lastly, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.« less

  13. Charge localization and ordering in A 2 Mn 8 O 16 hollandite group oxides: Impact of density functional theory approaches

    DOE PAGES

    Kaltak, Merzuk; Fernandez-Serra, Marivi; Hybertsen, Mark S.

    2017-12-01

    The phases of A 2Mn 8O 16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3d electrons are more explicitly considered with the DFT + Umore » approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn 3+ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Lastly, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.« less

  14. Spin-phonon coupling and high-pressure phase transitions of RMnO 3 (R=Ca and Pr): An inelastic neutron scattering and first-principles study

    DOE PAGES

    Mishra, S. K.; Gupta, M. K.; Mittal, R.; ...

    2016-06-22

    Here, we report inelastic neutron scattering measurements over 7–1251 K in CaMnO 3 covering various phase transitions, and over 6–150 K in PrMnO 3 covering the magnetic transition. The excitations around 20 meV in CaMnO 3 and at 17 meV in PrMnO 3 at low temperatures are found to be associated with magnetic origin. We observe coherent magnetic neutron scattering in localized regions in reciprocal space and show it to arise from long-range correlated magnetic spin-waves below the magnetic transition temperature (TN) and short-range stochastic spin-spin fluctuations above T N. In spite of the similarity of the structure of themore » two compounds, the neutron inelastic spectrum of PrMnO 3 exhibits broad features at 150 K unlike well-defined peaks in the spectrum of CaMnO 3. This might result from the difference in the nature of interactions in the two compounds (magnetic and Jahn-Teller distortion). Ab initio phonon calculations have been used to interpret the observed phonon spectra. The ab initio calculations at high pressures show that the variations of Mn-O distances are isotropic for CaMnO 3 and highly anisotropic for PrMnO 3. The calculation in PrMnO 3 shows the suppression of Jahn-Teller distortion and simultaneous insulator-to-metal transition. It appears that this transition may not be associated with the occurrence of the tetragonal phase above 20 GPa as reported in the literature, since the tetragonal phase is found to be dynamically unstable, although it is found to be energetically favored over the orthorhombic phase above 20 GPa. CaMnO 3 does not show any phase transition up to 60 GPa.« less

  15. Charge localization and ordering in A2Mn8O16 hollandite group oxides: Impact of density functional theory approaches

    NASA Astrophysics Data System (ADS)

    Kaltak, Merzuk; Fernández-Serra, Marivi; Hybertsen, Mark S.

    2017-12-01

    The phases of A2Mn8O16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3 d electrons are more explicitly considered with the DFT + U approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn3 + centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Finally, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.

  16. Role of 5f electrons in the structural stability of light actinide (Th-U) mononitrides under pressure.

    PubMed

    Modak, P; Verma, Ashok K

    2016-03-28

    Pressure induced structural sequences and their mechanism for light actinide (Th-U) mononitrides were studied as a function of 5f-electron number using first-principles total energy and electronic structure calculations. Zero pressure lattice constants, bulk module and C11 elastic module vary systematically with 5f-electron number implying its direct role on crystal binding. There is a critical 5f-electron number below which the system makes B1-B2 and above it B1-R3̄m-B2 structural sequence under pressure. Also, the B1-B2 transition pressure increases with increasing 5f-electron number whereas an opposite trend is obtained for the B1-R3̄m transition pressure. The ascending of N p anti-bonding states through the Fermi level at high pressure is responsible for the structural instability of the system. Above the critical 5f-electron number in the system a narrow 5f-band occurs very close to the Fermi level which allows the system to lower its symmetry via band Jahn-Teller type lattice distortion and the system undergoes a B1-R3̄m phase transition. However, below the critical 5f-electron number this mechanism is not favorable due to a lack of sufficient 5f-state occupancy and thus the system undergoes a B1-B2 phase transition like other ionic solids.

  17. Experimental and theoretical identification of the Fe(vii) oxidation state in FeO4.

    PubMed

    Lu, Jun-Bo; Jian, Jiwen; Huang, Wei; Lin, Hailu; Li, Jun; Zhou, Mingfei

    2016-11-16

    The experimentally known highest oxidation state of iron has been determined to be Fe(vi) so far. Here we report a combined matrix-isolation infrared spectroscopic and theoretical study of two interconvertible iron oxide anions: a dioxoiron peroxide complex [(η 2 -O 2 )FeO 2 ] - with a C 2v -structure and a tetroxide FeO 4 - with a D 2d tetrahedral structure, which are formed by co-condensation of laser-ablated iron atoms and electrons with O 2 /Ar mixtures at 4 K. Quantum chemistry theoretical studies indicate that the Jahn-Teller distorted tetroxide FeO 4 - anion is a d 1 species with hereto the highest iron formal oxidation state Fe(vii).

  18. Response functions for dimers and square-symmetric molecules in four-wave-mixing experiments with polarized light

    NASA Astrophysics Data System (ADS)

    Smith, Eric Ryan; Farrow, Darcie A.; Jonas, David M.

    2005-07-01

    Four-wave-mixing nonlinear-response functions are given for intermolecular and intramolecular vibrations of a perpendicular dimer and intramolecular vibrations of a square-symmetric molecule containing a doubly degenerate state. A two-dimensional particle-in-a-box model is used to approximate the electronic wave functions and obtain harmonic potentials for nuclear motion. Vibronic interactions due to symmetry-lowering distortions along Jahn-Teller active normal modes are discussed. Electronic dephasing due to nuclear motion along both symmetric and asymmetric normal modes is included in these response functions, but population transfer between states is not. As an illustration, these response functions are used to predict the pump-probe polarization anisotropy in the limit of impulsive excitation.

  19. Large-scale phase separation with nano-twin domains in manganite spinel (Co,Fe,Mn){sub 3}O{sub 4}

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Horibe, Y., E-mail: horibe@post.matsc.kyutech.ac.jp; Takeyama, S.; Mori, S.

    The effect of Mn concentration on the formation of nano-domain structures in the spinel oxide (Co,Fe,Mn){sub 3}O{sub 4} was investigated by electron diffraction, bright-, and dark-field imaging technique with transmission electron microscopy. Large scale phase separation with nano-twin domains was observed in Co{sub 0.6}Fe{sub 1.0}Mn{sub 1.4}O{sub 4}, in contrast to the highly aligned checkerboard nano-domains in Co{sub 0.6}Fe{sub 0.9}Mn{sub 1.5}O{sub 4}. Diffusion of the Mn{sup 3+} ions with the Jahn-Teller distortions is suggested to play an important role in the formation of checkerboard nano-domain structure.

  20. DFT calculations of the structures and vibrational spectra of the [Fe(bpy) 3] 2+ and [Ru(bpy) 3] 2+ complexes

    NASA Astrophysics Data System (ADS)

    Alexander, Bruce D.; Dines, Trevor J.; Longhurst, Rayne W.

    2008-09-01

    Structures of the [M(bpy) 3] 2+ complexes (M = Fe and Ru) have been calculated at the B3-LYP/DZVP level. IR and Raman spectra were calculated using the optimised geometries, employing a scaled quantum chemical force field, and compared with an earlier normal coordinate analysis of [Ru(bpy) 3] 2+ which was based upon experimental data alone, and the use of a simplified model. The results of the calculations provide a highly satisfactory fit to the experimental data and the normal coordinate analyses, in terms of potential energy distributions, allow a detailed understanding of the vibrational spectra of both complexes. Evidence is presented for Jahn-Teller distortion in the 1E MLCT excited state.

  1. Nanoscale strain mapping in battery nanostructures

    NASA Astrophysics Data System (ADS)

    Ulvestad, A.; Cho, H. M.; Harder, R.; Kim, J. W.; Dietze, S. H.; Fohtung, E.; Meng, Y. S.; Shpyrko, O. G.

    2014-02-01

    Coherent x-ray diffraction imaging is used to map the local three dimensional strain inhomogeneity and electron density distribution of two individual LiNi0.5Mn1.5O4-δ cathode nanoparticles in both ex-situ and in-situ environments. Our reconstructed images revealed a maximum strain of 0.4%. We observed different variations in strain inhomogeneity due to multiple competing effects. The compressive/tensile component of the strain is connected to the local lithium content and, on the surface, interpreted in terms of a local Jahn-Teller distortion of Mn3+. Finally, the measured strain distributions are discussed in terms of their impact on competing theoretical models of the lithiation process.

  2. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bhattacharyya, Swarnendu, E-mail: swarnendu.bhattacharyya@ch.tum.de; Domcke, Wolfgang, E-mail: wolfgang.domcke@ch.tum.de; Dai, Zuyang

    A diabatic three-sheeted six-dimensional potential-energy surface has been constructed for the ground state and the lowest excited state of the PH{sub 3}{sup +} cation. Coupling terms of Jahn-Teller and pseudo-Jahn-Teller origin up to eighth order had to be included to describe the pronounced anharmonicity of the surface due to multiple conical intersections. The parameters of the diabatic Hamiltonian have been optimized by fitting the eigenvalues of the potential-energy matrix to ab initio data calculated at the CASSCF/MRCI level employing the correlation-consistent triple-ζ basis. The theoretical photoelectron spectrum of phosphine and the non-adiabatic nuclear dynamics of the phosphine cation have beenmore » computed by propagating nuclear wave packets with the multiconfiguration time-dependent Hartree method. The theoretical photoelectron bands obtained by Fourier transformation of the autocorrelation function agree well with the experimental results. It is shown that the ultrafast non-radiative decay dynamics of the first excited state of PH{sub 3}{sup +} is dominated by the exceptionally strong Jahn-Teller coupling of the asymmetric bending vibrational mode together with a hyperline of conical intersections with the electronic ground state induced by the umbrella mode. Time-dependent population probabilities have been computed for the three adiabatic electronic states. The non-adiabatic Jahn-Teller dynamics within the excited state takes place within ≈5 fs. Almost 80% of the excited-state population decay to the ground state within about 10 fs. The wave packets become highly complex and delocalized after 20 fs and no further significant transfer of electronic population seems to occur up to 100 fs propagation time.« less

  3. A2TiF 5· nH 2O ( A=K, Rb, or Cs; n=0 or 1): Synthesis, structure, characterization, and calculations of three new uni-dimensional titanium fluorides

    NASA Astrophysics Data System (ADS)

    Jo, Vinna; Woo Lee, Dong; Koo, Hyun-Joo; Ok, Kang Min

    2011-04-01

    Three new uni-dimensional alkali metal titanium fluoride materials, A2TiF 5· nH 2O ( A=K, Rb, or Cs; n=0 or 1) have been synthesized by hydrothermal reactions. The structures of A2TiF 5· nH 2O have been determined by single-crystal X-ray diffraction. The Ti 4+ cations have been reduced to Ti 3+ during the synthesis reactions. All three A2TiF 5· nH 2O materials contain novel 1-D chain structures that are composed of the slightly distorted Ti 3+F 6 corner-sharing octahedra attributable to the Jahn-Teller distortion. The coordination environment of the alkali metal cations plays an important role to determine the degree of turning in the chain structures. Complete structural analyses, Infrared and UV-vis diffuse reflectance spectra, and thermal analyses are presented, as are electronic structure calculations.

  4. Magnetic structure and local lattice distortion in giant negative thermal expansion material Mn3Cu1-xGexN

    NASA Astrophysics Data System (ADS)

    Iikubo, S.; Kodama, K.; Takenaka, K.; Takagi, H.; Shamoto, S.

    2010-11-01

    Magnetic and local structures in an antiperovskite system, Mn3Cu1-xGexN, with a giant negative thermal expansion have been studied by neutron powder diffraction measurement. We discuss (1) an importance of an averaged cubic crystal structure and a ΓG5g antiferromagnetic spin structure for the large magneto-volume effect (MVE) in this itinerant electron system, (2) an unique role of a local lattice distortion well described by the low temperature tetragonal structure of Mn3GeN for the broadening of MVE.

  5. Temperature-dependent and anisotropic optical response of layered Pr0.5Ca1.5MnO4 probed by spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Majidi, M. A.; Thoeng, E.; Gogoi, P. K.; Wendt, F.; Wang, S. H.; Santoso, I.; Asmara, T. C.; Handayani, I. P.; van Loosdrecht, P. H. M.; Nugroho, A. A.; Rübhausen, M.; Rusydi, A.

    2013-06-01

    We study the temperature dependence as well as anisotropy of optical conductivity (σ1) in the pseudocubic single crystal Pr0.5Ca1.5MnO4 using spectrocopic ellipsometry. Three transition temperatures are observed and can be linked to charge-orbital (TCO/OO˜320 K), two-dimensional-antiferromagnetic (2D-AFM) (˜200 K), and three-dimensional AFM (TN˜125 K) orderings. Below TCO/OO, σ1 shows a charge-ordering peak (˜0.8 eV) with a significant blue shift as the temperature decreases. Calculations based on a model that incorporates a static Jahn-Teller distortion and assumes the existence of a local charge imbalance between two different sublattices support this assignment and explain the blue shift. This view is further supported by the partial spectral weight analysis showing the onset of optical anisotropy at TCO/OO in the charge-ordering region (0.5-2.5 eV). Interestingly, in the charge-transfer region (2.5-4 eV), the spectral weight shows anomalies around the T2D-AFM that we attribute to the role of oxygen-p orbitals in stabilizing the CE-type magnetic ordering. Our result shows the importance of spin, charge, orbital, and lattice degrees of freedom in this layered manganite.

  6. Nanoclustering phase competition induces the resistivity hump in colossal magnetoresistive manganites

    NASA Astrophysics Data System (ADS)

    Pradhan, Kalpataru; Yunoki, Seiji

    2017-12-01

    Using a two-band double-exchange model with Jahn-Teller lattice distortions and superexchange interactions, supplemented by quenched disorder, at an electron density n =0.65 , we explicitly demonstrate the coexistence of the n =1 /2 -type (π ,π ) charge-ordered and the ferromagnetic nanoclusters above the ferromagnetic transition temperature Tc in colossal magnetoresistive (CMR) manganites. The resistivity increases due to the enhancement of the volume fraction of the charge-ordered and the ferromagnetic nanoclusters upon decreasing the temperature down to Tc. The ferromagnetic nanoclusters start to grow and merge, and the volume fraction of the charge-ordered nanoclusters decreases below Tc, leading to the sharp drop in the resistivity. By applying a small external magnetic field h , we show that the resistivity above Tc increases, as compared with the case when h =0 , a fact that further confirms the coexistence of the charge-ordered and the ferromagnetic nanoclusters. In addition, we show that the volume fraction of the charge-ordered nanoclusters decreases upon increasing the bandwidth, and consequently the resistivity hump diminishes for large bandwidth manganites, in good qualitative agreement with experiments. The obtained insights from our calculations provide a complete pathway to understand the phase competition in CMR manganites.

  7. Ab initio DFT+U study of He atom incorporation into UO(2) crystals.

    PubMed

    Gryaznov, Denis; Heifets, Eugene; Kotomin, Eugene

    2009-09-07

    We present and discuss results of the density functional theory (DFT) for perfect UO(2) crystals with He atoms in octahedral interstitial positions therein. We have calculated basic bulk crystal properties and He incorporation energies into the low temperature anti-ferromagnetic UO(2) phase using several exchange-correlation functionals within the spin-polarized local density (LDA) and generalized gradient (GGA) approximations. In all DFT calculations we included the on-site correlation corrections using the Hubbard model (DFT+U approach). We analysed a potential crystalline symmetry reduction from tetragonal down to orthorhombic structure and confirmed the presence of the Jahn-Teller effect in a perfect UO(2). We discuss also the problem of a conducting electronic state arising when He is placed into a tetragonal antiferromagnetic phase of UO(2) commonly used in defect modelling. Consequently, we found a specific monoclinic lattice distortion which allowed us to restore the semiconducting state and properly estimate He incorporation energies. Unlike the bulk properties, the He incorporation energy strongly depends on several factors, including the supercell size, the use of spin polarization, the exchange-correlation functionals and on-site correlation corrections. We compare our results for the He incorporation with the previous shell model and ab initio DFT calculations.

  8. Enhanced photocatalytic activity of Te-doped Bi{sub 2}MoO{sub 6} under visible light irradiation: Effective separation of photogenerated carriers resulted from inhomogeneous lattice distortion and improved electron capturing ability

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, Shuguang, E-mail: csustcsg@yahoo.com; Li, Yuhan; Wu, Zixu

    Te-doped Bi{sub 2}MoO{sub 6} photocatalyst was hydrothermally synthesized, and nonmetal atoms Te were homogeneously incorporated into Bi{sub 2}MoO{sub 6} lattice with the substitution of Te{sup 4+} to Mo{sup 6+}. With increasing Te-doping concentration in Bi{sub 2}MoO{sub 6}, no detectable band-gap narrowing but more and more severe inhomogeneous lattice distortions were determined. The activity of Bi{sub 2}MoO{sub 6} photocatalyst was evaluated through methylene blue degradation under visible light irradiation (λ>410 nm) and was greatly enhanced by Te-doping. When Te-doped Bi{sub 2}MoO{sub 6} was synthesized at Te/Mo molar ratio of 7.5%, a maximum first-order rate constant of methylene blue degradation was obtained.more » The inhomogeneous lattice distortion generated an internal dipole moment, and the holes generated with the substitution of Te{sup 4+} to Mo{sup 6+} acted as the capturing centers of photogenerated electrons, thus the effective separation of photogenerated carriers was facilitated to result in a relatively high concentration of holes on the surface of Te-doped Bi{sub 2}MoO{sub 6} to be favorable for the efficient methylene blue degradation. - Graphical abstract: With the substitution of Te{sup 4+} to Mo{sup 6+}, effective separation of photogenerated carriers resulted from inhomogeneous lattice distortion and improved electron capturing ability is achieved to be responsible for enhanced photocatalytic activity of Te-doped Bi{sub 2}MoO{sub 6}. - Highlights: • Nonmetal Te is incorporated into Bi{sub 2}MoO{sub 6} with the substitution of Te{sup 4+} to Mo{sup 6+}. • Revealing inhomogeneous lattice distortion and improved electron capturing ability. • Effective separation of photogenerated carriers in Te-doped Bi{sub 2}MoO{sub 6} is achieved. • The mechanism of methylene blue degradation over Te-doped Bi{sub 2}MoO{sub 6} is proposed.« less

  9. Local Lattice Distortion in the Giant Negative Thermal Expansion Material Mn3Cu1-xGexN

    NASA Astrophysics Data System (ADS)

    Iikubo, S.; Kodama, K.; Takenaka, K.; Takagi, H.; Takigawa, M.; Shamoto, S.

    2008-11-01

    Giant negative thermal expansion is achieved in antiperovskite manganese nitrides when the sharp volume change associated with magnetic ordering is broadened by substitution. In this Letter, we address the unique role of the ‘‘magic” element, Ge, for such broadening in Mn3Cu1-xGexN. We present evidence for a local lattice distortion well described by the low-temperature tetragonal (T4) structure of Mn3GeN for a range of x, where the overall structure remains cubic. This structural instability shows a strong correlation with the broadness of the growth of the ordered magnetic moment and, hence, is considered to trigger the broadening of the volume change.

  10. Effect of severe plastic deformation on the structure and crystal-lattice distortions in the Ni3(Al, X) ( X = Ti, Nb) intermetallic compound

    NASA Astrophysics Data System (ADS)

    Kazantseva, N. V.; Pilyugin, V. P.; Danilov, S. E.; Kolosov, V. Yu.

    2015-05-01

    A systematic combined study of crystal lattice distortions caused by doping and by severe plastic deformation (SPD) of Ti- and Nb-doped Ni3Al intermetallic compound has been carried out using methods of X-ray diffraction, electron microscopy, and electrical-resistance measurements. The degree of imperfection of the alloys has been estimated based on the results obtained by all three methods. The degree of structural perfection of niobium-doped crystals was found to be higher than in the case of Ti doping. The character of stresses (tensile stresses after doping; and compressive stresses after SPD) in the crystal lattice has been established and their values have been calculated. A significant increase in the density of dislocations, point defects, and lattice curvature has been found after SPD. A nanocrystalline structure is formed in these alloys, but no complete disordering of the intermetallic phase is observed.

  11. Edward Teller

    Science.gov Websites

    physics, astrophysics, and statistical mechanics. Lawrence Livermore [National Laboratory] physicist Mort towering figures of 20th-century physics. ... Although his early training was in chemical physics and spectroscopy, Teller has made substantial contributions to such diverse fields as nuclear physics, plasma

  12. Investigations of the local distortions and EPR parameters for Cu2+ in xNa2 O-(30-x)K2 O-70B2 O3 (5 ≤ x ≤ 25 mol%) glasses.

    PubMed

    Zhang, Zhen-Ya; Wu, Shao-Yi; Zhang, Fu; Zhang, Cheng-Xi; Qin, Rui-Jie; Gao, Han

    2018-03-01

    The local distortions and electron paramagnetic resonance parameters for Cu 2+ in the mixed alkali borate glasses xNa 2 O-(30-x)K 2 O-70B 2 O 3 (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na 2 O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO 6 ] 10- clusters show significant tetragonal elongation ratios p ~19% along the C 4 axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu 2+ with the variation of the composition of Na 2 O. Copyright © 2017 John Wiley & Sons, Ltd.

  13. Anomalous double-stripe charge ordering in β -NaFe2O3 with double triangular layers consisting of almost perfect regular Fe4 tetrahedra

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shintaro; Ueda, Hiroaki; Michioka, Chishiro; Yoshimura, Kazuyoshi; Nakamura, Shin; Katsufuji, Takuro; Sawa, Hiroshi

    2018-05-01

    The physical properties of the mixed-valent iron oxide β -NaFe2O3 were investigated by means of synchrotron radiation x-ray diffraction, magnetization, electrical resistivity, differential scanning calorimetry, 23Na NMR, and 57FeM o ̈ssbauer measurements. This compound has double triangular layers consisting of almost perfect regular Fe4 tetrahedra, which suggests geometrical frustration. We found that this compound exhibits an electrostatically unstable double-stripe-type charge ordering, which is stabilized by the cooperative compression of Fe3 +O6 octahedra, owing to a valence change and Fe2 +O6 octahedra due to Jahn-Teller distortion. Our results indicate the importance of electron-phonon coupling for charge ordering in the region of strong charge frustration.

  14. Synchrotron radiation-based 61Ni Mössbauer spectroscopic study of Li(Ni1/3Mn1/3Co1/3)O2 cathode materials of lithium ion rechargeable battery

    NASA Astrophysics Data System (ADS)

    Segi, Takashi; Masuda, Ryo; Kobayashi, Yasuhiro; Tsubota, Takayuki; Yoda, Yoshitaka; Seto, Makoto

    2016-12-01

    Layered rocksalt type oxides, such as Li(Ni1/3Mn1/3Co1/3)O2, are widely used as the cathode active materials of lithium-ion rechargeable batteries. Because the nickel ions are associated with the role of the charge compensation at discharge and charge, the 61Ni Mössbauer measurements at 6 K using synchrotron radiation were performed to reveal the role of Ni. The Ni ions of the active materials play two roles for the redox process between the charge and discharge states of lithium-ion batteries. Half of the total Ni ions change to the low-spin Ni3+ with Jahn-Teller distortion from the Ni2+ ions of the discharge state. The remainder exhibit low-spin state divalent Ni ions.

  15. Spontaneous electric polarization in the B-site magnetic spinel GeCu2O4

    NASA Astrophysics Data System (ADS)

    Yanda, Premakumar; Ghara, Somnath; Sundaresan, A.

    2018-04-01

    We report the observation of a spontaneous electric polarization at the antiferromagnetic ordering temperature (TN ∼ 33 K) of Cu2+ ions in the B-site magnetic spinel GeCu2O4, synthesized at high pressure and high temperature. This compound is known to crystallize in a tetragonal structure (space group I41/amd) due to Jahn-Teller distortion of Cu2+ ions and exhibit a collinear up-up-down-down (↑↑↓↓) antiferromagnetic spin configuration below TN. We found a clear dielectric anomaly at TN, where an electric polarization appears in the absence of applied magnetic field. The electric polarization is suppressed by applied magnetic fields, which demonstrates that the compound GeCu2O4 is a type-II multiferroic.

  16. High pressure synthesis, crystal growth and magnetic properties of TiOF

    NASA Astrophysics Data System (ADS)

    Cumby, J.; Burchell, M. B.; Attfield, J. P.

    2018-06-01

    Polycrystalline samples of TiOF have been prepared at 1300 °C and 8 GPa, with small single crystals grown at the same conditions. The crystal structure remains tetragonal rutile-type down to at least 90 K (space group P42/mnm, a = 4.6533 (2) Å and c = 3.0143 (2) Å at 90 K) and the Ti(O,F)6 octahedra are slightly compressed, consistent with Jahn-Teller distortion of 3d1 Ti3+. Diffuse scattering reveals disordered structural correlations that may arise from local cis-order of oxide anions driven by covalency. TiOF is paramagnetic down to 5 K and observation of a small paramagnetic moment and a substantial Pauli term indicates that the d-electrons are partially delocalised.

  17. Elastic moduli of the distorted Kagome-lattice ferromagnet Nd3Ru4Al12

    NASA Astrophysics Data System (ADS)

    Suzuki, Takashi; Mizuno, Takuyou; Takezawa, Kohki; Kamikawa, Shuhei; Andreev, Alexander V.; Gorbunov, Denis I.; Henriques, Margarida S.; Ishii, Isao

    2018-05-01

    The distorted kagome-lattice compound Nd3Ru4Al12 has the hexagonal structure. This compound is reported as a ferromagnet in which spins are aligned along the c-axis with the Curie temperature TC = 39 K . The nature of localized f-electrons is expected in Nd3Ru4Al12, and magnetic anisotropy can be attributed to a crystal electric field (CEF) effect. We performed ultrasonic measurements on a Nd3Ru4Al12 single-crystalline sample in order to investigate the phase transition at TC and the CEF effect. All longitudinal and transverse elastic moduli increase monotonically with decreasing temperature, and no clear elastic softening due to a quadrupole interaction is detected under the hexagonal CEF. This result is in contrast to an isomorphic compound Dy3Ru4Al12 with a remarkable elastic softening of the transverse modulus C44. At the ferromagnetic phase transition, the moduli show obvious elastic anomalies, suggesting characteristic couplings between a strain and a magnetic order parameter.

  18. Enhanced photocatalytic activity of Te-doped Bi2MoO6 under visible light irradiation: Effective separation of photogenerated carriers resulted from inhomogeneous lattice distortion and improved electron capturing ability

    NASA Astrophysics Data System (ADS)

    Chen, Shuguang; Li, Yuhan; Wu, Zixu; Wu, Baoxin; Li, Haibin; Li, Fujin

    2017-05-01

    Te-doped Bi2MoO6 photocatalyst was hydrothermally synthesized, and nonmetal atoms Te were homogeneously incorporated into Bi2MoO6 lattice with the substitution of Te4+ to Mo6+. With increasing Te-doping concentration in Bi2MoO6, no detectable band-gap narrowing but more and more severe inhomogeneous lattice distortions were determined. The activity of Bi2MoO6 photocatalyst was evaluated through methylene blue degradation under visible light irradiation (λ>410 nm) and was greatly enhanced by Te-doping. When Te-doped Bi2MoO6 was synthesized at Te/Mo molar ratio of 7.5%, a maximum first-order rate constant of methylene blue degradation was obtained. The inhomogeneous lattice distortion generated an internal dipole moment, and the holes generated with the substitution of Te4+ to Mo6+ acted as the capturing centers of photogenerated electrons, thus the effective separation of photogenerated carriers was facilitated to result in a relatively high concentration of holes on the surface of Te-doped Bi2MoO6 to be favorable for the efficient methylene blue degradation.

  19. Evidence of Photo-induced Dynamic Competition of Metallic and Insulating Phase in a Layered Manganite.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Yuelin; Walko, Donald A.; Li, Qing'an

    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 lasermore » excitation modulates the local competition between the metallic and the insulating phases.« less

  20. 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, LaSr 2Mn 2O 7, 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 wherebymore » the laser excitation modulates the local competition between the metallic and the insulating phases.« less

  1. Weak ferromagnetism in a high-pressure phase of FeTiO3 with polar lattice distortion

    NASA Astrophysics Data System (ADS)

    Varga, Tamas; Mitchell, John; Fennie, Craig; Streiffer, Stephen; Hong, Seungbum; Park, Moonkyu; Gopalan, Venkatraman; Kumar, Amit; Vlahos, Eftihia; Sanehira, Takeshi; Wang, Yanbin

    2009-03-01

    Today's challenge in multiferroics is to identify materials in which polarization and magnetization -- normally considered contraindicated properties - are strongly coupled. Recent density functional theory calculations have predicted that the family of compounds MTiO3 (M = Mn, Fe, Ni) are promising candidates where a polar lattice distortion can induce weak ferromagnetism. The crucial insight is that while the equilibrium one-atmosphere structure of these is ilmenite, they must be transformed to a closely related LiNbO3-type structure. We have prepared the corresponding FeTiO3 phase at 18 GPa and 1200 ^oC. It shows a sharp antiferromagnetic (AF) transition at 111.5 K. FeTiO3 also displays ferroelectric domains, and weak ferromagnetism coincident with the AF transition. Possible coupling between its polarization and weak ferromagnetism is discussed based on results of piezoelectric force microscopy (PFM), second harmonic generation (SHG), dielectric, and polarization measurements.

  2. Tuning the Curie temperature of epitaxial Nd0.6Sr0.4MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bhat, Shwetha G.; Kumar, P. S. Anil

    2018-02-01

    NdxSr1-xMnO3 (0.2 ≤ x ≤ 0.5) systems are widely studied in magnetism, popular for high colossal magnetoresistance and are ferromagnetic oxides with TC ranging from 200 K to 300 K. Recently, many of such compounds are re-visited for exploring the correlation of spin, charge and lattice degrees of freedom. Although, manganite thin films are the ideal candidates for studying the electron-correlation effects, the puzzle of obtaining a high quality epitaxial thin films of NdxSr1-xMnO3 are still unsolved contrary to its sister compound LaxSr1-xMnO3. Hence, in this study, we demonstrate the growth of best quality of Nd0.6Sr0.4MnO3 (NSMO) epitaxial thin films. This is evident from the TC and a sharp insulator-to-metal transition (IMT) coinciding at as high as ∼255 K against the bulk TC (∼270 K). It is the highest reported TC in Nd0.6Sr0.4MnO3 thin films to date. Moreover, as-deposited films with in situ oxygen annealing are not enough to relax the lattice of NSMO films due to the significant Jahn-Teller distortion in the film. With ex situ annealing processes alongside the various deposition and in situ annealing conditions, we have extensively studied the growth of epitaxial NSMO thin films on LaAlO3 (0 0 1) and SrTiO3 (0 0 1) to investigate the evolution of lattice and its one-to-one correspondence with the magnetism and the electrical properties of thin films. Accordingly, the enhanced magnetization, reduced resistivity and the higher TC and IMT of the NSMO films obtained from our extensive growth analysis looks promising for the future applications across the TC and IMT.

  3. Ab initio study of the ground state surface of Cu3

    NASA Technical Reports Server (NTRS)

    Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Walch, Stephen P.; Laskowski, Bernard C.

    1986-01-01

    The ground state surface of the metallic trimer Cu3 is investigated theoretically. Relativistic and correlation effects are taken into account in ab initio computations, which are calibrated against analogous computations for the 1Sigma(g)+ state of Cu2; the results are presented in tables and analyzed. The Cu3 ground state is found to have a 2B2 C(2v) structure with angle greater than 60 deg, lying 59/cm below a 2A1 C(2v) geometry and 280/cm below the D(3h) equilateral geometry. These findings are shown to be in good agreement with the experimental measurements of Rohlfing and Valentini (1986) and their analysis (in terms of a Jahn-Teller distortion of 2E-prime equilateral-triangle geometry) by Truhlar et al. (1986).

  4. Coupled Electronic and Magnetic Phase Transition in the Infinite-Layer Phase LaSrNiRuO4.

    PubMed

    Patino, Midori Amano; Zeng, Dihao; Bower, Ryan; McGrady, John E; Hayward, Michael A

    2016-09-06

    Topochemical reduction of the ordered double perovskite LaSrNiRuO6 with CaH2 yields LaSrNiRuO4, an extended oxide phase containing infinite sheets of apex-linked, square-planar Ni(1+)O4 and Ru(2+)O4 units ordered in a checkerboard arrangement. At room temperature the localized Ni(1+) (d(9), S = (1)/2) and Ru(2+) (d(6), S = 1) centers behave paramagnetically. However, on cooling below 250 K the system undergoes a cooperative phase transition in which the nickel spins align ferromagnetically, while the ruthenium cations appear to undergo a change in spin configuration to a diamagnetic spin state. Features of the low-temperature crystal structure suggest a symmetry lowering Jahn-Teller distortion could be responsible for the observed diamagnetism of the ruthenium centers.

  5. The vibronic level structure of the cyclopentadienyl radical

    NASA Astrophysics Data System (ADS)

    Ichino, Takatoshi; Wren, Scott W.; Vogelhuber, Kristen M.; Gianola, Adam J.; Lineberger, W. Carl; Stanton, John F.

    2008-08-01

    The 351.1 nm photoelectron spectrum of the cyclopentadienide ion has been measured, which reveals the vibronic structure of the X~ 2E1'' state of the cyclopentadienyl radical. Equation-of-motion ionization potential coupled-cluster (EOMIP-CCSD) calculations have been performed to construct a diabatic model potential of the X~ 2E1'' state, which takes into account linear Jahn-Teller effects along the e2' normal coordinates as well as bilinear Jahn-Teller effects along the e2' and ring-breathing a1' coordinates. A simulation based on this ab initio model potential reproduces the spectrum very well, identifying the vibronic levels with linear Jahn-Teller angular momentum quantum numbers of +/-1/2. The angular distributions of the photoelectrons for these vibronic levels are highly anisotropic with the photon energies used in the measurements. A few additional weak photoelectron peaks are observed when photoelectrons ejected parallel to the laser polarization are examined. These peaks correspond to the vibronic levels for out-of-plane modes in the ground X~ 2E1'' state, which arise due to several pseudo-Jahn-Teller interactions with excited states of the radical and quadratic Jahn-Teller interaction in the X~ 2E1'' state. A variant of the first derivative of the energy for the EOMIP-CCSD method has been utilized to evaluate the strength of these nonadiabatic couplings, which have subsequently been employed to construct the model potential of the X~ 2E1'' state with respect to the out-of-plane normal coordinates. Simulations based on the model potential successfully reproduce the weak features that become conspicuous in the 0° spectrum. The present study of the photoelectron spectrum complements a previous dispersed fluorescence spectroscopic study Miller and co-workers [J. Chem. Phys. 114, 4855 (2001); 4869 (2001) Miller and co-workers [J. Chem. Phys.114, 4869 (2001)] to provide a detailed account of the vibronic structure of X~ 2E1'' cyclopentadienyl. The electron

  6. Orbital ordering-driven ferromagnetism in LaCoO3 nanowires

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Fan, Hong Jin

    2010-09-01

    The structure and magnetic properties of LaCoO3 nanowires are investigated as a function of the diameter in the temperature range of 5-300 K. Ferromagnetism below 85 K is observed in these nanowires, in agreement with the recent observations in LaCoO3 epitaxial thin films and nanoparticles. With the diameter of nanowires decreasing, the unit-cell volume increases, while both the global and local structural distortions lessen, accompanied by the gradual enhancement of ferromagnetism. The structure analysis reveals that LaCoO3 nanowires exhibit a monoclinic distorted structure with I2/a space group in the entire investigated temperature range. Different from bulks, there is no clear spin-state transition occurring with temperature in LaCoO3 nanowires. There exists a noticeable Jahn-Teller (JT) distortion in the nanowires even at the lowest temperature, namely, orbital-ordered JT active Co3+ ions with intermediate-spin (IS) state persist at low temperatures, which is not observed in bulk LaCoO3. These results indicate that the ferromagnetism in the nanowires is driven by the orbital ordering of IS Co3+.

  7. Griffiths' inequalities for Ashkin-Teller model

    NASA Technical Reports Server (NTRS)

    Lee, C. T.

    1973-01-01

    The two Griffiths' (1967) inequalities for the correlation functions of Ising ferromagnets with two-body interactions, and two other inequalities obtained by Kelly and Sherman (1968) and by Sherman (1969) are shown to hold not only for the Ashkin-Teller (1943) model but also for a generalized Ashkin-Teller model (Kihara et al., 1954) with many-body interactions involving arbitrary clusters of particles. A cluster of particles is understood to mean a collection of pairs of particles rather than a group of particles. The four generalized inequalities under consideration are presented in the form of theorems, and a new inequality is obtained.

  8. Effect of lattice distortion on uranium magnetic moments in U4Ru7Ge6 studied by polarized neutron diffraction

    NASA Astrophysics Data System (ADS)

    Vališka, Michal; Klicpera, Milan; Doležal, Petr; Fabelo, Oscar; Stunault, Anne; Diviš, Martin; Sechovský, Vladimír

    2018-03-01

    In a cubic ferromagnet, small spontaneous lattice distortions are expected below the Curie temperature, but the phenomenon is usually neglected. This study focuses on such an effect in the U4Ru7Ge6 compound. Based on DFT calculations, we propose a lattice distortion from the cubic I m -3 m space group to a lower, rhombohedral, symmetry described by the R -3 m space group. The strong spin-orbit coupling of the uranium ions plays an essential role in lowering the symmetry, giving rise to two different U sites (U1 and U2). Using polarized neutron diffraction in applied magnetic fields of 1 and 9 T in the ordered state (1.9 K ) and in the paramagnetic state (20 K ), we bring convincing experimental evidence of this splitting of the U sites, with different magnetic moments. The data have been analyzed both by maximum entropy calculations and by a direct fit in the dipolar approximation. In the ordered phase, the μL/μS ratio of the orbital and spin moments on the U2 site is remarkably lower than for the free U3 + or U4 + ion, which points to a strong hybridization of the U 5 f wave functions with the 4 d wave functions of the surrounding Ru. On the U1 site, the μL/μS ratio exhibits an unexpectedly low value: the orbital moment is almost quenched, like in metallic α -uranium. As a further evidence of the 5 f -4 d hybridization in the U4Ru7Ge6 system, we observe the absence of a magnetic moment on the Ru1 site, but a rather large induced moment on the Ru2 site, which is in closer coordination with both U positions. Very similar results are obtained at 20 K in the ferromagnetic regime induced by the magnetic field of 9 T . This shows that applying a strong magnetic field above the Curie temperature also leads to the splitting of the uranium sites, which further demonstrates the intimate coupling of the magnetic ordering and structural distortion. We propose that the difference between the magnetic moment on the U1 and U2 sites results from the strong spin

  9. Jet cooled cavity ringdown spectroscopy of the A ˜ 2 E ″ ← X ˜ 2 A2 ' transition of the NO3 radical

    NASA Astrophysics Data System (ADS)

    Codd, Terrance; Chen, Ming-Wei; Roudjane, Mourad; Stanton, John F.; Miller, Terry A.

    2015-05-01

    The A ˜ 2 E ″ ← X ˜ 2 A2 ' spectrum of NO3 radical from 7550 cm-1 to 9750 cm-1 has been recorded and analyzed. Our spectrum differs from previously recorded spectra of this transition due to jet-cooling, which narrows the rotational contours and eliminates spectral interference from hot bands. Assignments of numerous vibronic features can be made based on both band contour and position including the previously unassigned 30 1 band and several associated combination bands. We have analyzed our spectrum first with an independent anharmonic oscillator model and then by a quadratic Jahn-Teller vibronic coupling model. The fit achieved with the quadratic Jahn-Teller model is excellent, but the potential energy surface obtained with the fitted parameters is in only qualitative agreement with one obtained from ab initio calculations.

  10. Teller Award Acceptance Speech (LIRPP Vol. 12)

    NASA Astrophysics Data System (ADS)

    McCrory, Robert L.

    2016-10-01

    It is indeed an honor to receive an award named for such an accomplished and famous physicist who is present with us today, Dr. Edward Teller. In thinking over what to say on this occasion, I noted that the Teller Award was given for pioneering research in controlled fusion, in controlling fusion for the benefit of mankind. I think everyone in this audience certainly would agree that this lofty goal is truly one of the unconquered, grand challenges in applied physics...

  11. Occupational Noise Exposure among Toll Tellers at Toll Plaza in Malaysia

    NASA Astrophysics Data System (ADS)

    Azmi, Sharifah Nadya Syed; Dawal, Siti Zawiah Md; Ya, Tuan Mohammad Yusoff Shah Tuan; Saidin, Hamidi

    2010-10-01

    Toll tellers working at toll plaza have potential of exposure to high noise from the vehicles especially for the peak level of sound emitted by the heavy vehicles. However, occupational exposures in this workplace have not been adequately characterized and identified. Occupational noise exposure among toll tellers at toll plaza was assessed using Sound Level Meter, Noise Dosimeter and through questionnaire survey. These data were combined to estimate the work shift exposure level and health impacts to the toll tellers by using statistical analysis. Noise Dosimeter microphone was located at the hearing zone of the toll teller which working inside the toll booth and full-period measurements were collected for each work shift. The measurements were taken at 20 toll booths from 6.00 am to 2.00 pm for 5 days. 71 respondents participated in the survey to identify the symptoms of noise induced hearing loss and other health related problems among toll tellers. Results of this study indicated that occupational noise exposure among toll tellers for Mean Continuous Equivalent Level, Leq was 79.2±1.4 dB(A), Mean Maximum Level, Lmax was 107.8±3.6 dB(A) and Mean Peak Level, Lpeak was 136.6±9.9 dB. The Peak Level reported statistically significantly at 140 dB, the level of TLV recommended by ACGIH. The research findings indicated that the primary risk exposure to toll tellers comes from noise that emitted from heavy vehicles. Most of the toll tellers show symptoms of noise induced hearing loss and annoyed by the sources of noise at the toll plaza.

  12. Exotic s-wave superconductivity in alkali-doped fullerides.

    PubMed

    Nomura, Yusuke; Sakai, Shiro; Capone, Massimo; Arita, Ryotaro

    2016-04-20

    Alkali-doped fullerides (A3C60 with A = K, Rb, Cs) show a surprising phase diagram, in which a high transition-temperature (Tc) s-wave superconducting state emerges next to a Mott insulating phase as a function of the lattice spacing. This is in contrast with the common belief that Mott physics and phonon-driven s-wave superconductivity are incompatible, raising a fundamental question on the mechanism of the high-Tc superconductivity. This article reviews recent ab initio calculations, which have succeeded in reproducing comprehensively the experimental phase diagram with high accuracy and elucidated an unusual cooperation between the electron-phonon coupling and the electron-electron interactions leading to Mott localization to realize an unconventional s-wave superconductivity in the alkali-doped fullerides. A driving force behind the exotic physics is unusual intramolecular interactions, characterized by the coexistence of a strongly repulsive Coulomb interaction and a small effectively negative exchange interaction. This is realized by a subtle energy balance between the coupling with the Jahn-Teller phonons and Hund's coupling within the C60 molecule. The unusual form of the interaction leads to a formation of pairs of up- and down-spin electrons on the molecules, which enables the s-wave pairing. The emergent superconductivity crucially relies on the presence of the Jahn-Teller phonons, but surprisingly benefits from the strong correlations because the correlations suppress the kinetic energy of the electrons and help the formation of the electron pairs, in agreement with previous model calculations. This confirms that the alkali-doped fullerides are a new type of unconventional superconductors, where the unusual synergy between the phonons and Coulomb interactions drives the high-Tc superconductivity.

  13. Dirac fermions and pseudomagnetic fields in two-dimensional electron gases with triangular antidot lattices

    NASA Astrophysics Data System (ADS)

    Li, Yun-Mei; Zhou, Xiaoying; Zhang, Yan-Yang; Zhang, Dong; Chang, Kai

    2017-07-01

    We investigate theoretically the electronic properties of two-dimensional electron gases (2DEGs) with regular and distorted triangular antidot lattices. We show that the triangular antidot lattices embedded in 2DEGs behave like artificial graphene and host Dirac fermions. By introducing the Wannier representation, we obtain a tight-binding Hamiltonian including the second-nearest-neighboring hopping, which agrees well with the numerically exact solutions. Based on the tight-binding model, we find that spatially nonuniform distortions of the antidot lattices strongly modify the electronic structures, generate pseudomagnetic fields and the well-defined Landau levels. In contrast to graphene, we can design the nonuniform distortions to generate various configurations of pseudomagnetic fields. We show that the snake orbital states arise by designing the ±B pseudomagnetic field configuration. We find that the disorders of antidot lattices during fabrication would not affect the basic feature of the Dirac electrons, but they lead to a reduction in conductance in strong disorder cases.

  14. 12 CFR 205.16 - Disclosures at automated teller machines.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Disclosures at automated teller machines. 205.16 Section 205.16 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.16 Disclosures at automated teller machines. (a...

  15. Occasional Addresses by Edward Teller at Conferences of Laser Interaction and Related Plasma Phenomena (LIRPP)

    NASA Astrophysics Data System (ADS)

    Hora, Heinrich; Miley, George H.

    2016-10-01

    The following sections are included: * Futurology of High Intensity Lasers (LIRPP Vol. 3A) * Lecture in Connection with the Edward Teller Medal Award (LIRPP Vol. 10) * Photo of the First Recipients of the Edward Teller Medal in 1991 * Photos from the Edward Teller Medal Celebration in 1997 * Photo with Participants of the LIRPP No. 12 Conference, 1995 * Photo with Edward Teller Medalists at IFSA01, Kyoto, 2001 * Keynote Address: The Edward Teller Lecture (LIRPP Vol. 11) * Keynote Address: Dr. Edward Teller (LIRPP Vol. 12) * Teller Award Presentation and Keynote Address (LIRPP Vol. 13) * Laudations of Awardees 1991-1995 (LIRPP Vol. 13) * Laudations of Awardees 1999-2003

  16. Universal Teller Curriculum Guide.

    ERIC Educational Resources Information Center

    DuPage Area Vocational Education Authority, Addison, IL.

    This curriculum guide has been designed to provide the teacher with a basis for planning a comprehensive program in the career field of universal teller, and to allow the teacher and learner maximum flexibility. The teaching or instruction, in both educational and financial institutions, can be accomplished through large formal groups, small…

  17. Role of distortion in the hcp vs fcc competition in rare-gas solids

    NASA Astrophysics Data System (ADS)

    Krainyukova, N. V.

    2011-05-01

    As a prototype of an initial or intermediate structure between hcp and fcc lattices we consider a distorted bcc crystal. We calculate the temperature and pressure dependences of the lattice parameters for the heavier rare gas solids Ar, Kr, Xe in a quasiharmonic approximation with Aziz potentials, and confirm earlier predictions that the hcp structure predominates over fcc in the bulk within wide ranges of P and T. The situation is different for confined clusters with up to 105 atoms, where, owing to the specific surface energetics and terminations, structures with five-fold symmetry made up of fcc fragments are dominant. As a next step we consider the free relaxation of differently distorted bcc clusters, and show that two types (monoclinic and orthorhombic) of initial distortion are a driving force for the final hcp vs fcc configurations. Possible energy relationships between the initial and final structures are obtained and analyzed.

  18. Role of cooperative structural distortions in the metal--insulator transitions of perovskite ferrates

    NASA Astrophysics Data System (ADS)

    Cammarata, Antonio; Rondinelli, James

    2012-02-01

    Transition-metal oxides within the perovskite crystal family exhibit strong electron--electron correlation effects that coexist with complex structural distortions, leading to metal-insulator (MI) transitions. Using first-principles density functional calculations, we investigate the effects of cooperative octahedral rotations and dilations/contractions on the charge-ordering MI-transition in CaFeO3. By calculating the evolution in the lattice phonons, which describe the different octahedral distortions present in the low-symmetry monoclinic phase of CaFeO3 with increasing electron correlation, we show that the MI-transition results from a complex interplay between these modes and correlation effects. We combine this study with group theoretical tools to disentangle the electron--lattice interactions by computing the evolution in the low-energy electronic band structure with the lattice phonons, demonstrating the MI-transition in CaFeO3 proceeds through a symmetry-lowering transition driven by a cooperative three-dimensional octahedral dilation/contraction pattern. Finally, we suggest a possible route by which to control the charge ordering by fine-tuning the electron--lattice coupling.

  19. Magneto-elastic coupling across the first-order transition in the distorted kagome lattice antiferromagnet Dy3Ru4Al12

    PubMed Central

    Henriques, M.S.; Gorbunov, D.I.; Kriegner, D.; Vališka, M.; Andreev, A.V.; Matěj, Z.

    2018-01-01

    Structural changes through the first-order paramagnetic-antiferromagnetic phase transition of Dy3Ru4Al12 at 7 K have been studied by means of X-ray diffraction and thermal expansion measurements. The compound crystallizes in a hexagonal crystal structure of Gd3Ru4Al12 type (P63/mmc space group), and no structural phase transition has been found in the temperature interval between 2.5 and 300 K. Nevertheless, due to the spin-lattice coupling the crystal volume undergoes a small orthorhombic distortion of the order of 2×10-5 as the compound enters the antiferromagnetic state. We propose that the first-order phase transition is not driven by the structural changes but rather by the exchange interactions present in the system. PMID:29445250

  20. Elastic properties of iron-based superconductor SrFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Horikoshi, Keita; Imai, Jo; Nakanishi, Yoshiki; Nakamura, Mitsuteru; Kobayashi, Tatsuya; Adachi, Toru; Miyasaka, Shigeki; Tajima, Setsuko; Yoshizawa, Masahito

    2018-05-01

    We have measured the transverse elastic constants C44 and C66 of iron-based superconductor SrFe2(As1-xPx)2 (Sr122) single crystals as a function of temperature. Under-doped samples show elastic anomalies towards the structural/magnetic transition temperature. Optimal sample shows an upturn at the superconducting transition temperature in both C44 and C66. These behavior is similar to Ba122, while only C66 shows anomaly for Ba122. The elastic anomalies were analyzed by Jahn-Teller formula, and it was found that the Jahn-Teller energy of C44 is much larger than that of C66. This indicates that monoclinic structural fluctuations exist inherently in Sr122 in addition to the known tetragonal fluctuations. Co-existence of these diverse fluctuations and their cooperation are a key to investigate the mechanism and properties of superconductivity in iron based superconductors.

  1. Rotational and Fine Structure of Pseudo-Jahn Molecules with C_1 Symmetry

    NASA Astrophysics Data System (ADS)

    Liu, Jinjun

    2016-06-01

    It has been found in our previous works that rotational and fine-structure analysis of spectra involving nearly degenerate electronic states may aid in interpretation and analysis of the vibronic structure, specifically in the case of pseudo-Jahn-Teller (pJT) molecules with C_s symmetry. The spectral analysis of pJT derivatives (isopropoxy and cyclohexoxy of a prototypical JT molecule (the methoxy radical) allowed for quantitative determination of various contributions to the energy separation between the nearly degenerate electronic states, including the relativistic spin-orbit (SO) effect, the electrostatic interaction, and their zero-point energy difference. These states are coupled by SO and Coriolis interactions, which can also be determined accurately in rotational and fine structure analysis. Most recently, the spectroscopic model for rotational analysis of pJT molecules has been extended for analysis of molecules with C_1 symmetry, i.e., no symmetry. This model includes the six independently determinable components of the spin-rotation (SR) tensor and the three components of the SO and Coriolis interactions. It has been employed to simulate and fit high-resolution laser-induced fluorescence (LIF) spectra of jet-cooled alkoxy radicals with C_1 symmetry, including the 2-hexoxy and the 2-pentoxy radicals, as well as previously recorded LIF spectrum of the trans-conformer (defined by its OCCC dihedral angle) of the 2-butoxy radical. Although the LIF spectra can be reproduced by using either the SR constants or SO and Coriolis constants, the latter simulation offers results that are physically more meaningful whereas the SR constants have to be regarded as effective constants. Furthermore, we will review the SO and Coriolis constants of alkoxy radicals that have been investigated, starting from the well-studied methoxy radical (CH_3O). J. Liu, D. Melnik, and T. A. Miller, J. Chem. Phys. 139, 094308 (2013) J. Liu and T. A. Miller, J. Phys. Chem. A 118, 11871

  2. Effects of strain on ferroelectric polarization and magnetism in orthorhombic HoMnO3

    NASA Astrophysics Data System (ADS)

    Iuşan, Diana; Yamauchi, Kunihiko; Barone, Paolo; Sanyal, Biplab; Eriksson, Olle; Profeta, Gianni; Picozzi, Silvia

    2013-01-01

    We explore how the ferroelectric polarization of antiferromagnetic E-type orthorhombic HoMnO3 can be increased, by investigating the effects of in-plane strain on both the magnetic properties and the ferroelectric polarization, using combined density functional theory calculations and a model Hamiltonian technique. Our results show that the net polarization is strongly enhanced under compressive strain, due to an increase of the elec-tronic contribution to the polarization. In contrast, the ionic contribution is found to decrease. We identify the electron-lattice coupling, due to Jahn-Teller (JT) distortions, and its response to strain, to be responsible for the observed behavior. The JT-induced orbital ordering of occupied Mn-eg1 electrons in alternating 3x2-r23y2-r2 orbital states in the unstrained structure, changes under in-plane compressive strain to a mixture with x2-z2y2-z2 states. The asymmetric hopping of eg electrons between Mn ions along zigzag spin chains (typical of the AFM-E spin configuration) is therefore enhanced under strain, explaining the large value of the polarization. Using a degenerate double-exchange model including electron-phonon interaction, we reproduce the change in the orbital ordering pattern. In this picture, the orbital ordering change is related to a change of the Berry phase of the eg electrons. This causes an increase of the electronic contribution to the polarization.

  3. P2-type Na2/3Mn1-xAlxO2 cathode material for sodium-ion batteries: Al-doped enhanced electrochemical properties and studies on the electrode kinetics

    NASA Astrophysics Data System (ADS)

    Pang, Wei-Lin; Zhang, Xiao-Hua; Guo, Jin-Zhi; Li, Jin-Yue; Yan, Xin; Hou, Bao-Hua; Guan, Hong-Yu; Wu, Xing-Long

    2017-07-01

    Recently, sodium-ion batteries (SIBs) have been considered as the promising alternative for lithium-ion batteries. Although layered P2-type transition metal oxides are an important class of cathode materials for SIBs, there are still some hurdles for the practical applications, including low specific capacity as well as poor cycling and rate properties. In this study, the electrochemical properties of layered Mn-based oxides have been effectively improved via Al doping, which cannot only promote the formation of layered P2-type structure in the preparation processes but also stabilize the lattice during the successive Na-intercalation/deintercalation due to suppression of the Jahn-Teller distortion of Mn3+. Among the as-prepared series of Na2/3Mn1-xAlxO2 (x = 0, 1/18, 1/9, and 2/9), Na2/3Mn8/9Al1/9O2 with x = 1/9 exhibits the optimal doping effect with the best electrochemical properties, in terms of the highest specific capacity of 162.3 mA h g-1 at 0.1 C, the highest rate capability, and the best cycling stability in comparison to the undoped Na2/3MnO2 and the other two materials with different Al-doped contents. Both cyclic voltammetry at varied scan rates and galvanostatic intermittent titration technique disclose the optimal electrode kinetics (the highest Na-diffusion coefficient) of the best Na2/3Mn8/9Al1/9O2.

  4. Chemical Pressure Effects in Layered Manganites

    NASA Astrophysics Data System (ADS)

    Moritomo, Yutaka; Maruyama, Yousuke; Nakamura, Arao

    1998-03-01

    Lattice effects on the magnetic and transport properties have been investigated for layered-type doped mangaites. The insulator-to-metal transition temperature for La_1.2Sr_1.8Mn_2O7 (T_C=130 K) is significantly suppressed with chemical substitution of the trivalent La^3+ ions to smaller Nd^3+ (or Sm^3+) ions(Y. Moritomo et al), Phys. Rev. B56(1997)R7057. Similarly, the charge-ordering temperature for La_0.5Sr_1.5MnO4 (T_CO=230 K) is suppresses with chemical substitution(Y. Moritomo et al), Phys. Rev. B56, in press. Systematic x-ray as well as neutron diffraction measurements have revealed that above chemical pressure enhances the static Jahn-Teller distortion of the MnO6 octahedra in both the system. We will explain the suppressions of TC and T_CO in terms of the increasing d_3z^2-r^2 character in the occupied eg state. Our observation indicates that the chemical pressure effects are qualitatively different between the cubic and layered manganites systems. The authors are grateful to K. Ohoyama and M. Ohashi for their help in neutron diffraction measurements, and to S. Mori for his help in electron diffraction measurements. This work was supported by a Grant-In-Aid for Scientific Research from the Ministry of Education, Science, Sport and Culture and from PRESTO, Japan Scienece and Technology Corporation (JST), Japan.

  5. Spin crossover in the CsFeII[CrIII(CN)6] Prussian blue analog: Phonons and thermodynamics from hybrid functionals

    NASA Astrophysics Data System (ADS)

    Middlemiss, Derek S.; Portinari, Damiano; Grey, Clare P.; Morrison, Carole A.; Wilson, Chick C.

    2010-05-01

    Solid-state lattice-dynamics calculations within the hybrid density-functional approach are applied to the study of the thermally induced Fe2+ lowspin(LS;S=0)↔highspin(HS;S=2) crossover (SCO) in the extended network of the CsFe[Cr(CN)6] Prussian blue analog. The variations in the thermodynamic parameters defining the SCO transition with the Fock exchange content (F0) of the functional are obtained and discussed, where, in keeping with the findings of previous studies of isolated complexes, it is found that an admixture F0≈14% provides reliable values. The transition is shown to be dominated by the entropy difference, ΔS , associated with the softening of low-frequency vibrational (vib) modes in the HS state, as has been suggested previously for a wide range of SCO materials, more than half of ΔSvib deriving from modes with wave numbers of 250cm-1 or less. Analysis of the influence of the spectroscopic selection rules upon the apparent SCO thermodynamics reveals that determinations based solely upon infrared or Raman frequencies, or upon their combination, lead to significant errors. The effect upon the SCO transition of the electronic entropy associated with the degenerate Fe2+ HS (eg2t2g4) configurations is also detailed, evidence for the existence of an associated dynamic Jahn-Teller distortion being presented. Optimized structures, bulk moduli, Γ -point vibrational frequencies, and crystal-field energy models are discussed for all relevant spin states.

  6. Structural Characterization of Biogenic Manganese Oxides Produced in Sea Water

    NASA Astrophysics Data System (ADS)

    Webb, S. M.; Bargar, J. R.; Tebo, B. M.

    2003-12-01

    Manganese oxides have been coined as the "scavengers of the sea" and play important roles in both marine and freshwater systems. Natural manganese oxide nanoparticles and grain coatings are ubiquitous in the environment and profoundly impact the quality of sediments via their ability to degrade and sequester contaminants. These oxides are believed to form dominantly via oxidation of Mn(II) by marine and freshwater bacteria and have extremely high sorptive capacities for heavy metals. We have used XANES, EXAFS, and synchrotron (SR)-XRD techniques to study biogenic manganese oxides produced by spores of the marine Bacillus sp., strain SG-1 in seawater as a function of reaction time under fully in-situ conditions. The primary biogenic solid-phase Mn oxide product is a hexagonal layered phyollomanganate with an oxidation state similar to that in delta-MnO2. XRD data show the biooxides to have a phyllomanganate 10 basal plane spacing, suggesting the interlayer is hydrated and contains calcium. As the experiment continues, the initial biooxide changes to show triclinic symmetry. Fits to these EXAFS spectra suggest the octahedral layers have low Mn octahedral site vacancies in the lattice and the latyers bend to accommodate Jahn-Teller distortions creating the change in symmetry. The oxides observed in this study as models of Mn(II) bio-oxidation may be representative of the most abundant manganese oxide phase suspended in the oxic and sub-oxic zones of the oceanic water column.

  7. Surface Meteorology at Teller Site Stations, Seward Peninsula, Alaska, Ongoing from 2016

    DOE Data Explorer

    Bob Busey; Bob Bolton; Cathy Wilson; Lily Cohen

    2017-12-05

    Meteorological data are currently being collected at two locations at the Teller Site, Seward Peninsula. Teller Creek Station near TL_BSV (TELLER BOTTOM METEOROLOGICAL STATION) Station is located in the lower watershed in a tussock / willow transition zone and co-located with continuous snow depth measurements and subsurface measurements. Teller Creek Station near TL_IS_5 (TELLER TOP METEOROLOGICAL STATION) Station is located in the upper watershed and co-located with continuous snow depth measurements and subsurface measurements. Two types of data products are provided for these stations: First, meteorological and site characterization data grouped by sensor/measurement type (e.g., radiation or soil pit temperature and moisture). These are *.csv files. Second, a Data Visualization tool is provided for quick visualization of measurements over time at a station. Download the *_Visualizer.zip file, extract, and click on the 'index.html' file. Data values are the same in both products.

  8. Structural instability of the CoO 4 tetrahedral chain in SrCoO 3-δ thin films

    DOE PAGES

    Glamazda, A.; Choi, Kwang-yong; Lemmens, P.; ...

    2015-08-31

    Raman scattering experiments together with detailed lattice dynamic calculations are performed to elucidate crystallographic and electronic peculiarities of SrCoO 3-δ films. We observe that the 85 cm -1 phonon mode involving the rotation of a CoO 4 tetrahedron undergoes a hardening by 21 cm -1 when the temperature is decreased. In addition, new phonon modes appear at 651.5 and 697.6 cm -1 . The latter modes are attributed to the Jahn-Teller activated modes. Upon cooling from room temperature, all phonons exhibit an exponential-like increase of intensity with a characteristic energy of about 103–107 K. We attribute this phenomenon to anmore » instability of the CoO 4 tetrahedral chain structure, which constitutes a key ingredient to understand the electronic and structural properties of the brownmillerite SrCoO 2.5.« less

  9. Manifestation of Crystal Lattice Distortions in the IR Reflection Spectra of Abrasion-Treated ZnSe Ceramics

    NASA Astrophysics Data System (ADS)

    Sitnikova, V. E.; Dunaev, A. A.; Mamalimov, R. I.; Pakhomov, P. M.; Khizhnyak, S. D.; Chmel, A. E.

    2017-07-01

    The Fourier IR reflection spectra of ZnSe ceramics prepared by hot pressing (HP), physical vapor deposition (PVD), and PVD combined with hot isostatic pressing (HIP) are presented. The optical constants of polished and dry-ground specimens were used for comparison. The grinding treatment simulated the erosion of the outer surface of optical elements made of zinc selenide under the influence of solid dust particles and deposits. In the polished specimens residual stresses showed up in the IR reflection spectra of the ZnSePVD and ZnSeHIP ceramics, which had well-defined orientation of grains, but were not present in the spectra of the ZnSeHIP ceramics as a result of mutual compensation of the stresses in the randomly oriented grains of the material. The stresses, which appeared as a shift of the absorption bands calculated by the Kramers-Kronig method, increased significantly after abrasive treatment of the specimens. For all the treated ceramics the intensity of the absorption bands resulting from the anharmonicity of the vibrations in the distorted crystal lattice increased by several times. The last effect also depends on the production prehistory of the ceramics.

  10. Structures and chemical properties of silicene: unlike graphene.

    PubMed

    Jose, Deepthi; Datta, Ayan

    2014-02-18

    The discovery of graphene and its remarkable and exotic properties have aroused interest in other elements and molecules that form 2D atomic layers, such as metal chalcogenides, transition metal oxides, boron nitride, silicon, and germanium. Silicene and germanene, the Si and Ge counterparts of graphene, have interesting fundamental physical properties with potential applications in technology. For example, researchers expect that silicene will be relatively easy to incorporate within existing silicon-based electronics. In this Account, we summarize the challenges and progress in the field of silicene research. Theoretical calculations have predicted that silicene possesses graphene-like properties such as massless Dirac fermions that carry charge and the quantum spin Hall effect. Researchers are actively exploring the physical and chemical properties of silicene and tailoring it for wide variety of applications. The symmetric buckling in each of the six-membered rings of silicene differentiates it from graphene and imparts a variety of interesting properties with potential technological applications. The pseudo-Jahn-Teller (PJT) distortion breaks the symmetry and leads to the buckling in silicenes. In graphene, the two sublattice structures are equivalent, which does not allow for the opening of the band gap by an external electric field. However, in silicene where the neighboring Si atoms are displaced alternatively perpendicular to the plane, the intrinsic buckling permits a band gap opening in silicene in the presence of external electric field. Silicene's stronger spin orbit coupling than graphene has far reaching applications in spintronic devices. Because silicon prefers sp(3) hybridization over sp(2), hydrogenation is much easier in silicene. The hydrogenation of silicene to form silicane opens the band gap and increases the puckering angle. Lithiation can suppress the pseudo-Jahn-Teller distortion in silicene and hence can flatten silicene's structure

  11. Photochemical water oxidation by crystalline polymorphs of manganese oxides: structural requirements for catalysis.

    PubMed

    Robinson, David M; Go, Yong Bok; Mui, Michelle; Gardner, Graeme; Zhang, Zhijuan; Mastrogiovanni, Daniel; Garfunkel, Eric; Li, Jing; Greenblatt, Martha; Dismukes, G Charles

    2013-03-06

    Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ≫ λ-MnO2, where the latter is derived from spinel LiMn2O4 following partial Li(+) removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and λ-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration e(g)(1) which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface.

  12. Reactive Orthotropic Lattice Diffuser for Noise Reduction

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R. (Inventor)

    2016-01-01

    An orthotropic lattice structure interconnects porous surfaces of the flap with internal lattice-structured perforations to equalize the steady pressure field on the flap surfaces adjacent to the end and to reduce the amplitude of the fluctuations in the flow field near the flap end. The global communication that exists within all of the perforations provides the mechanism to lessen the pressure gradients experienced by the end portion of the flap. In addition to having diffusive effects (diffusing the incoming flow), the three-dimensional orthogonal lattice structure is also reactive (acoustic wave phase distortion) due to the interconnection of the perforations.

  13. Magnetic properties of the Fe{sup II} spin crossover complex in emulsion polymerization of trifluoroethylmethacrylate using poly(vinyl alcohol)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Suzuki, Atsushi, E-mail: suzuki@mat.usp.ac.j; Iguchi, Motoi; Oku, Takeo

    2010-04-15

    Influence of chemical substitution in the Fe{sup II} spin crossover complex on magnetic properties in emulsion polymerization of trifluoroethylmethacrylate using poly(vinyl alcohol) as a protective colloid was investigated near its high spin/low spin (HS/LS) phase transition. The obvious bi-stability of the HS/LS phase transition was considered by the identification of multiple spin states between the quintet (S=2) states to single state (S=0) across the excited triplet state (S=1). Magnetic parameters of gradual shifts of anisotropy g-tensor supported by the molecular distortion of the spin crossover complex would arise from a Jahn-Teller effect regarding ligand field theory on the basis ofmore » a B3LYP density functional theory using electron spin resonance (ESR) spectrum and X-ray powder diffraction. - Graphical abstract: AFM surface image of the emulsion particles with the spin crossover complex.« less

  14. Magnetic phase transition in layered inorganic-organic hybrid (C12H25NH3)2CuCl4

    NASA Astrophysics Data System (ADS)

    Bochalya, Madhu; Kumar, Sunil; Kanaujia, Pawan K.; Prakash, G. Vijaya

    2018-05-01

    Inorganic-organic (IO) hybrids are material systems which have become an interesting theme of research for physicist and chemists recently due to the possibility of engineering specific magnetic, thermal or optoelectronic properties by playing around with the transition metal, halides and the organic components. Our experiments on (C12H25NH3)2CuCl4 show that the system exhibits a long range ferromagnetic order below ˜11 K. In such an inorganic-organic hybrid system, Jahn-Teller distortion of the copper ions results into a weak ferromagnetic order as compared to the antiferromagnetic spin-spin exchange in the pure inorganic CuCl2 compound. Moreover, this particular hybrid system also exhibits photoluminescence when excited below absorption maximum related to charge transfer peak though the effect is much weaker as compared to that in extensively studied other MX4-based (M = Sn, Pb; X = Cl, Br, I) counterparts.

  15. Neutron diffraction study of layered Ni dioxides: Ag2NiO2

    NASA Astrophysics Data System (ADS)

    Nozaki, Hiroshi; Sugiyama, Jun; Janoschek, Marc; Roessli, Bertrand; Pomjakushin, Vladimir; Keller, Lukas; Yoshida, Hiroyuki; Hiroi, Zenji

    2008-03-01

    In order to elucidate the antiferromagnetic (AF) nature of hexagonal Ag2NiO2 with TN = 56 K and to know the mechanism of the structural phase transition of TS~270 K, neutron powder diffraction patterns have been measured in the temperature range between 1.5 and 330 K. One magnetic Bragg peak indexed as \\frac {1}{3}~\\frac {1}{3}~0 is clearly observed below TN, confirming the formation of long-range AF order, reported by a muon-spin spectroscopy measurement. The weak intensity of the magnetic peak also suggests the two-dimensional nature of the AF order, but the spin structure is still unknown. In addition, the precise structural analysis of the data between 160 and 330 K shows that only the cH-axis length changes drastically at TS, which suggests the appearance of local Jahn-Teller distortion below TS.

  16. Present knowledge of electronic properties and charge transport of icosahedral boron-rich solids

    NASA Astrophysics Data System (ADS)

    Werheit, Helmut

    2009-06-01

    B12 icosahedra or related structure elements determine the different modifications of elementary boron and numerous boron-rich compounds from α-rhombohedral boron with 12 to YB66 type with about 1584 atoms per unit cell. Typical are well-defined high density intrinsic defects: Jahn-Teller distorted icosahedra, vacancies, incomplete occupancies, statistical occupancies and antisite defects. The correlation between intrinsic point defects and electron deficiencies solves the discrepancy between theoretically predicted metal and experimentally proved semiconducting character. The electron deficiencies generate split-off valence states, which are decisive for the electronic transport, a superposition of band-type and hopping-type conduction. Their share depends on actual conditions like temperature or pre-excitation. The theoretical model of bipolaron hopping is incompatible with numerous experiments. Technical application of the typically p-type icosahedral boron-rich solids requires suitable n-type counterparts; doping and other possibilities are discussed.

  17. Lattice distortion and strain relaxation in epitaxial thin films of multiferroic TbMnO3 probed by X-ray diffractometry and micro-Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Stender, D.; Medarde, M.; Lippert, T.; Wokaun, A.; Schneider, C. W.

    2013-08-01

    A detailed structural XRD analysis of (1 1 0)-oriented TbMnO3 thin films grown on (1 1 0)-YAlO3 substrates shows the co-existence of a strained and relaxed "sublayer" within the films due to strain relaxation during epitaxial growth by pulsed laser deposition. The substrate-film lattice mismatch yields a compressive strain anisotropy along the two in-plane directions, i.e. [1 -1 0] and [0 0 1] and a monoclinic distortion. A further manifestation of the growth-induced strain is the hardening of Raman active modes as a result of changed atomic motions along the [1 -1 0] and [0 0 1] directions.

  18. Angle-resolved photoelectron spectroscopy of cyclopropane

    NASA Astrophysics Data System (ADS)

    Keller, P. R.; Taylor, J. W.; Carlson, Thomas A.; Whitley, T. A.; Grimm, F. A.

    1985-10-01

    The angular distribution parameter, β, determined for the valence orbitals (IP < 18 eV) of cyclopropane in the 10-30 eV photon energy range using dispersed polarized synchrotron radiation. The energy dependence of β for photoelectron energies between, 2 and 10 eV above threshold was found to be similar to those found previously for other σ orbitals. The effects of Jahn-Teller splitting on β for the 3e' orbital were found to be small but definitely present. The overall shape and magnitude of the β( hv) curve are, however, sufficiently for the different Jahn-Teller components that, for purposes of orbital assignments using β( hv) curves the shape and magnitude of the curves can be considered associated only with the initial state. Resonance photoionization features at a photon ener of ≈ 18 eV were observed in the 3e' and 3a' 1 orbitals and tentatively assigned to autoionization.

  19. Structural phase transition, Néel temperature enhancement, and persistent magneto-dielectric coupling in Cr-substituted Mn3O4

    NASA Astrophysics Data System (ADS)

    Dwivedi, G. D.; Kumar, Abhishek; Yang, K. S.; Chen, B. Y.; Liu, K. W.; Chatterjee, Sandip; Yang, H. D.; Chou, H.

    2016-05-01

    Structural phase transition and Néel temperature (TN) enhancement were observed in Cr-substituted Mn3O4 spinels. Structural, magnetic, and dielectric properties of (Mn1-xCrx)3O4 (where x = 0.00, 0.10, 0.20, 0.25, 0.30, 0.40, and 0.50) were investigated. Cr-substitution induces room temperature structural phase transition from tetragonally distorted I41/amd (x = 0.00) to cubic Fd 3 ¯ m (x = 0.50). TN is found to increase from 43 K (x = 0.00) to 58 K (x = 0.50) with Cr-substitution. The spin ordering-induced dielectric anomaly near TN ensures that magneto-dielectric coupling persists in the cubic x = 0.50 system. X-ray absorption spectra reveal that Cr exists in a trivalent oxidation state and prefers the octahedral (Oh)-site, replacing Mn3+. Due to a reduction in the Jahn-Teller active Mn3+ cation and an increase in the smaller Cr3+ cation, the system begins to release the geometrical frustration by lowering its degeneracy. Consequently, a phase transition, from distorted tetragonal structure to the more symmetric cubic phase, occurs.

  20. Concomitant Ordering and Symmetry Lowering

    ERIC Educational Resources Information Center

    Boo, William O. J.; Mattern, Daniell L.

    2008-01-01

    Examples of concomitant ordering include magnetic ordering, Jahn-Teller cooperative ordering, electronic ordering, ionic ordering, and ordering of partially-filled sites. Concomitant ordering sets in when a crystal is cooled and always lowers the degree of symmetry of the crystal. Concomitant ordering concepts can also be productively applied to…

  1. Lattice distortion and stripelike antiferromagnetic order in Ca10(Pt3As8)(Fe2As2)5

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sapkota, Aashish; Tucker, Gregory S; Ramazanoglu, Mehmet

    2014-09-01

    Ca10(Pt3As8)(Fe2As2)5 is the parent compound for a class of Fe-based high-temperature superconductors where superconductivity with transition temperatures up to 30 K can be introduced by partial element substitution. We present a combined high-resolution high-energy x-ray diffraction and elastic neutron scattering study on a Ca10(Pt3As8)(Fe2As2)5 single crystal. This study reveals the microscopic nature of two distinct and continuous phase transitions to be very similar to other Fe-based high-temperature superconductors: an orthorhombic distortion of the high-temperature tetragonal Fe-As lattice below TS=110(2) K followed by stripelike antiferromagnetic ordering of the Fe moments below TN=96(2) K. These findings demonstrate that major features of themore » Fe-based high-temperature superconductors are very robust against variations in chemical constitution as well as structural imperfection of the layers separating the Fe-As layers from each other and confirms that the Fe-As layers primarily determine the physics in this class of material.« less

  2. A Theoretical Investigation of the Structure and Reactivity of the Molecular Constituents of Oil Sand and Oil Shale

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Parish, Carol A.

    molecular-based energy storage devices as well as magnetically controllable liquid marbles. 3-5 We have been investigating the small molecule encapsulation properties of POSS and discovered some interesting symmetry breaking processes that need to be better understood in order to use POSS in advanced materials. We have investigated this symmetry breaking mechanism in POSS monocations Si8O12(C(CH3)3)8+ and Si8O12Cl8+, using density functional theory (DFT) and group theory. Under Oh symmetry, these ions possess 2T2g and 2Eg electronic states, respectively, and undergo different symmetry breaking mechanisms. The ground states of Si 8O 12(C(CH 3) 3) 8 + and Si 8O 12Cl 8 + belong to the C 3v and D 4h point groups and are characterized by Jahn-Teller stabilization energies of 3959 and 1328 cm-1, respectively, at the B3LYP/def2-SVP level of theory. The symmetry distortion mechanism in Si 8O 12Cl 8 + is Jahn-Teller type, whereas in Si 8O 12(C(CH 3) 3) 8 + the distortion is a combination of both Jahn-Teller and pseudo-Jahn-Teller effects. The distortion force acting in Si 8O 12(C(CH 3) 3) 8 + is mainly localized on one Si-(tert-butyl) group while in Si 8O 12Cl 8 + it is distributed over the oxygen atoms. The main distortion forces acting on the Si8O12 core arise from the coupling between the electronic state and the vibrational modes; identified as 9t 2g+1e g+3a 2u for the Si 8O 12(C(CH 3) 3) 8 + and 1e g+2e g for Si 8O 12Cl 8 +. This work was published in the Journal of Physical Chemistry A, 2015, 119, 4237-4243.« less

  3. Role of chemically and thermally induced crystal lattice distortion in enhancing the Seebeck coefficient in complex tellurides

    DOE PAGES

    Levin, E. M.; Iowa State Univ., Ames, IA; Kramer, M. J.; ...

    2016-07-14

    Composition and crystal structure of complex materials can significantly change the Seebeck effect, i.e., heat to electrical energy conversion, which is utilized in thermoelectric materials. Despite decades of studies of various thermoelectric materials and their application, the fundamental understanding of this effect still is limited. One of the most efficient groups of thermoelectric materials is based on GeTe, where Ge is replaced by [Ag + Sb], i.e., Ag xSb xGe 50-2xTe 50 alloys, traditionally shown as (GeTe) m(AgSbTe 2) 100-m (TAGS-m series). Here, in this article, we report on the discovery of two unique phenomena in TAGS materials attributed tomore » the effects from [Ag + Sb] atoms: (i) a linear relation between the Seebeck coefficient and rhombohedral lattice distortion, and (ii) resonance-like temperature-induced behavior of the contribution to the Seebeck coefficient produced by [Ag + Sb] atoms. Finally, our findings show that heat to electrical energy conversion strongly depends on the temperature- and compositionally-induced rhombohedral to cubic transformation where [Ag + Sb] atoms play a crucial mediating role.« less

  4. Rectification of elemental image set and extraction of lens lattice by projective image transformation in integral imaging.

    PubMed

    Hong, Keehoon; Hong, Jisoo; Jung, Jae-Hyun; Park, Jae-Hyeung; Lee, Byoungho

    2010-05-24

    We propose a new method for rectifying a geometrical distortion in the elemental image set and extracting an accurate lens lattice lines by projective image transformation. The information of distortion in the acquired elemental image set is found by Hough transform algorithm. With this initial information of distortions, the acquired elemental image set is rectified automatically without the prior knowledge on the characteristics of pickup system by stratified image transformation procedure. Computer-generated elemental image sets with distortion on purpose are used for verifying the proposed rectification method. Experimentally-captured elemental image sets are optically reconstructed before and after the rectification by the proposed method. The experimental results support the validity of the proposed method with high accuracy of image rectification and lattice extraction.

  5. Heptacopper(II) and dicopper(II)-adenine complexes: synthesis, structural characterization, and magnetic properties

    DOE PAGES

    Leite Ferreira, B. J. M.; Brandão, Paula; Dos Santos, A. M.; ...

    2015-07-13

    The syntheses, crystal structures, and magnetic properties of two new copper(II) complexes with molecular formulas [Cu 7(μ 2-OH 2) 6(μ 3-O) 6(adenine) 6(NO 3) 26H 2O (1) and [Cu 2(μ 2-H 2O) 2(adenine) 2(H 2O) 4](NO 3) 42H 2O (2) are reported. We composed the heptanuclear compound of a central octahedral CuO 6 core sharing edges with six adjacent copper octahedra. In 2, the copper octahedra shares one equatorial edge. In both compounds, these basic copper cluster units are further linked by water bridges and bridging adenine ligands through N3 and N9 donors. All copper(II) centers exhibit Jahn-Teller distorted octahedralmore » coordination characteristic of a d 9 center. Our study of the magnetic properties of the heptacopper complex revealed a dominant ferromagnetic intra-cluster interaction, while the dicopper complex exhibits antiferromagnetic intra-dimer interactions with weakly ferromagnetic inter-dimer interaction.« less

  6. Enhanced magnetic anisotropies of single transition-metal adatoms on a defective MoS2 monolayer.

    PubMed

    Cong, W T; Tang, Z; Zhao, X G; Chu, J H

    2015-03-23

    Single magnetic atoms absorbed on an atomically thin layer represent the ultimate limit of bit miniaturization for data storage. To approach the limit, a critical step is to find an appropriate material system with high chemical stability and large magnetic anisotropic energy. Here, on the basis of first-principles calculations and the spin-orbit coupling theory, it is elucidated that the transition-metal Mn and Fe atoms absorbed on disulfur vacancies of MoS2 monolayers are very promising candidates. It is analysed that these absorption systems are of not only high chemical stabilities but also much enhanced magnetic anisotropies and particularly the easy magnetization axis is changed from the in-plane one for Mn to the out-of-plane one for Fe by a symmetry-lowering Jahn-Teller distortion. The results point out a promising direction to achieve the ultimate goal of single adatomic magnets with utilizing the defective atomically thin layers.

  7. Dynamically fluctuating electric dipole moments in fullerene-based magnets.

    PubMed

    Kambe, Takashi; Oshima, Kokichi

    2014-09-19

    We report here the direct evidence of the existence of a permanent electric dipole moment in both crystal phases of a fullerene-based magnet--the ferromagnetic α-phase and the antiferromagnetic α'-phase of tetra-kis-(dimethylamino)-ethylene-C60 (TDAE-C60)--as determined by dielectric measurements. We propose that the permanent electric dipole originates from the pairing of a TDAE molecule with surrounding C60 molecules. The two polymorphs exhibit clear differences in their dielectric responses at room temperature and during the freezing process with dynamically fluctuating electric dipole moments, although no difference in their room-temperature structures has been previously observed. This result implies that two polymorphs have different local environment around the molecules. In particular, the ferromagnetism of the α-phase is founded on the homogeneous molecule displacement and orientational ordering. The formation of the different phases with respect to the different rotational states in the Jahn-Teller distorted C60s is also discussed.

  8. Evolution of the magnetic and structural properties of Fe 1 - x Co x V 2 O 4

    DOE PAGES

    Sinclair, R.; Ma, Jie; Cao, H. B.; ...

    2015-10-12

    The magnetic and structural properties of single-crystal Fe 1-xCo xV 2O 4 samples have been investigated by performing specific heat, susceptibility, neutron diffraction, and x-ray diffraction measurements. As the orbital-active Fe 2+ ions with larger ionic size are gradually substituted by the orbital-inactive Co 2+ ions with smaller ionic size, the system approaches the itinerant electron limit with decreasing V-V distance. Then, various factors such as the Jahn-Teller distortion and the spin-orbital coupling of the Fe 2+ ions on the A sites and the orbital ordering and electronic itinerancy of the V 3+ ions on the B sites compete withmore » each other to produce a complex magnetic and structural phase diagram. Finally, this phase diagram is compared to those of Fe 1-xMn xV 2O 4 and Mn 1-xCo xV 2O 4 to emphasize several distinct features.« less

  9. Prediction of Intrinsic Ferromagnetic Ferroelectricity in a Transition-Metal Halide Monolayer

    NASA Astrophysics Data System (ADS)

    Huang, Chengxi; Du, Yongping; Wu, Haiping; Xiang, Hongjun; Deng, Kaiming; Kan, Erjun

    2018-04-01

    The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems. On the basis of first-principles calculations, we reveal that a charged CrBr3 monolayer exhibits in-plane multiferroicity, which is ensured by the combination of orbital and charge ordering as realized by the asymmetric Jahn-Teller distortions of octahedral Cr - Br6 units. As an example, we further show that (CrBr3)2Li is a ferromagnetic ferroelectric multiferroic. The explored phenomena and mechanism of multiferroics in this 2D system not only are useful for fundamental research in multiferroics but also enable a wide range of applications in nanodevices.

  10. Frequency effects on charge ordering in Y0.5Ca0.5MnO3 by impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Sarwar, Tuba; Qamar, Afzaal; Nadeem, Muhammad

    2015-02-01

    In this work, structural and electrical properties of Y0.5Ca0.5MnO3 are investigated by employing X-ray diffraction and impedance spectroscopy, respectively. Applied ac electric field showed the charge ordering transition temperature around 265 K and below this temperature the heteromorphic behavior of the sample is discussed in the proximity of TCO. With frequency effects the volume of robust charge orbital ordering (COO) domains diminishes due to different competing phases along with Jahn Teller distortions. Comprehensive melting and collapse of charge orbital ordering occurs below TN(125 K), where a colossal drop in the value of impedance is observed. The change in profile of modulus plane plots determines the spreading of relaxation time of intermingled phases. Hopping mechanism is elaborated in terms of strong electron phonon coupling. Variable range hopping model and Arrhenius model are used to discuss the short and long range hopping between Mn3+ and Mn4+ channels assessing the activation energy Ea.

  11. Correlation between microstructure and electrical transport properties of La0.7(Ba1-xCax)0.3MnO3 (x = 0 and 0.03) synthesized by sol-gel

    NASA Astrophysics Data System (ADS)

    Kurniawan, Budhy; Winarsih, Suci; Imaduddin, Agung; Manaf, Azwar

    2018-03-01

    In this paper, we reported the correlation of structure, microstructure, and electrical transport properties of polycrystalline La0.7(Ba1-xCax)0.3MnO3 (x = 0 and 0.03). The materials were synthesized by sol-gel method. These materials have interesting electronic and magnetic properties which are heavily affected by the degree of crystallographic mismatch between the La and Mn sites. By tuning these sites, the double exchange (DE) and Coulomb interactions among Mn ions can be artificially controlled. La0.7Ba0.3MnO3 is one of the strong candidates for application because it has high magnetoresistance and magnetocaloric properties. Doped Ca to the La0.7Ba0.3MnO3 is aimed for reducing its transition temperature to near room temperature and increasing the magnetoresistance and magnetocaloric properties of this material. Jahn-Teller distortion can be linked to core-shell model with the result of percolation model.

  12. Pinning of topological solitons at extrinsic defects in a quasi one-dimensional charge density wave

    NASA Astrophysics Data System (ADS)

    Razzaq, Samad; Wippermann, Stefan; Tae Hwan Kim Collaboration; Han Woong Yeom Collaboration

    Quasi one-dimensional (1D) electronic systems are known to exhibit exotic physical phenomena, such as, e.g., Jahn Teller distortions, charge density wave (CDW) formation and non-Fermi liquid behavior. Solitonic excitations of the charge density wave ordered ground state and associated topological edge states in atomic wires are presently the focus of increasing attention. We carried out a combined ab initio and scanning tunneling microscopy (STM) study of solitonic and non-solitonic phase defects in the In/Si(111) atomic wire array. While free solitons move too fast to be imaged directly in STM, they can become trapped at extrinsic de- fects within the wire. We discuss the detailed atomistic structure of the responsible extrinsic defects and trapped solitons. Our study highlights the key role of coupled theory-experimental investigations in order to understand also the elusive fast moving solitons. S. W. gratefully acknowledges financial support from the German Research Foundation (DFG), Grant No. FOR1700.

  13. Prediction of Intrinsic Ferromagnetic Ferroelectricity in a Transition-Metal Halide Monolayer.

    PubMed

    Huang, Chengxi; Du, Yongping; Wu, Haiping; Xiang, Hongjun; Deng, Kaiming; Kan, Erjun

    2018-04-06

    The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems. On the basis of first-principles calculations, we reveal that a charged CrBr_{3} monolayer exhibits in-plane multiferroicity, which is ensured by the combination of orbital and charge ordering as realized by the asymmetric Jahn-Teller distortions of octahedral Cr─Br_{6} units. As an example, we further show that (CrBr_{3})_{2}Li is a ferromagnetic ferroelectric multiferroic. The explored phenomena and mechanism of multiferroics in this 2D system not only are useful for fundamental research in multiferroics but also enable a wide range of applications in nanodevices.

  14. Impact of hole doping on spin transition in perovskite-type cobalt oxides.

    PubMed

    Che, Xiangli; Li, Liping; Hu, Wanbiao; Li, Guangshe

    2016-06-28

    Series of perovskite PrCo1-xNixO3-δ (x = 0-0.4) were prepared and carefully investigated to understand the spin state transition driven by hole doping and further to reveal the effect of spin state transition on electronic conduction. It is shown that with increasing doping level, the transition temperature Ts for Co(3+) ions from low-spin (LS) to intermediate-spin (IS) reduces from 211.9 K for x = 0 to 190.5 K for x = 0.4. XPS and FT-IR spectra demonstrate that hole doping promoted this transition due to a larger Jahn-Teller distortion. Moreover, a thermal activation of spin disorder caused by thermal population of the spin states for Co ions has a great impact on the electrical transport of these perovskite samples. This work may shed light on the comprehension of spin transition in cobalt oxides through hole doping, which is promising for finding new strategies of enhancing electronic conduction, especially for energy and catalysis applications.

  15. Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kim, Honggyu; Marshall, Patrick B.; Ahadi, Kaveh

    The lattice response of a prototype Mott insulator, SmTiO 3, to hole doping is investigated with atomic-scale spatial resolution. SmTiO 3 films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO 3-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. In conclusion, themore » results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed.« less

  16. Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

    DOE PAGES

    Kim, Honggyu; Marshall, Patrick B.; Ahadi, Kaveh; ...

    2017-11-02

    The lattice response of a prototype Mott insulator, SmTiO 3, to hole doping is investigated with atomic-scale spatial resolution. SmTiO 3 films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO 3-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. In conclusion, themore » results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed.« less

  17. Redox non-innocence of thioether crowns: spectroelectrochemistry and electronic structure of formal nickel(III) complexes of aza-thioether macrocycles.

    PubMed

    Stephen, Emma; Huang, Deguang; Shaw, Jennifer L; Blake, Alexander J; Collison, David; Davies, E Stephen; Edge, Ruth; Howard, Judith A K; McInnes, Eric J L; Wilson, Claire; Wolowska, Joanna; McMaster, Jonathan; Schröder, Martin

    2011-09-05

    The Ni(II) complexes [Ni([9]aneNS(2)-CH(3))(2)](2+) ([9]aneNS(2)-CH(3)=N-methyl-1-aza-4,7-dithiacyclononane), [Ni(bis[9]aneNS(2)-C(2)H(4))](2+) (bis[9]aneNS(2)-C(2)H(4)=1,2-bis-(1-aza-4,7-dithiacyclononylethane) and [Ni([9]aneS(3))(2)](2+) ([9]aneS(3)=1,4,7-trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni(III) products, which have been characterized by X-ray crystallography, UV/Vis and multi-frequency EPR spectroscopy. The single-crystal X-ray structure of [Ni(III)([9]aneNS(2)-CH(3))(2)](ClO(4))(6)·(H(5)O(2))(3) reveals an octahedral co-ordination at the Ni centre, while the crystal structure of [Ni(III)(bis[9]aneNS(2)-C(2)H(4))](ClO(4))(6)·(H(3)O)(3)·3H(2)O exhibits a more distorted co-ordination. In the homoleptic analogue, [Ni(III)([9]aneS(3))(2)](ClO(4))(3), structurally characterized at 30 K, the Ni-S distances [2.249(6), 2.251(5) and 2.437(2) Å] are consistent with a Jahn-Teller distorted octahedral stereochemistry. [Ni([9]aneNS(2)-CH(3))(2)](PF(6))(2) shows a one-electron oxidation process in MeCN (0.2 M NBu(4)PF(6), 293 K) at E(½)=+1.10 V versus Fc(+)/Fc assigned to a formal Ni(III)/Ni(II) couple. [Ni(bis[9]aneNS(2)-C(2)H(4))](PF(6))(2) exhibits a one-electron oxidation process at E(½)=+0.98 V and a reduction process at E(½)=-1.25 V assigned to Ni(II)/Ni(III) and Ni(II)/Ni(I) couples, respectively. The multi-frequency X-, L-, S-, K-band EPR spectra of the 3+ cations and their 86.2% (61)Ni-enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6%, 42.8% and 37.2% Ni character in [Ni([9]aneNS(2)-CH(3))(2)](3+), [Ni(bis[9]aneNS(2)-C(2)H(4))](3+) and [Ni([9]aneS(3))(2)](3+), respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S-thioether centres. EPR spectra for [(61)Ni([9]aneS(3))(2)](3+) are consistent with a dynamic Jahn-Teller distortion in this compound. Copyright

  18. 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.

  19. Near-infrared photoabsorption by C60 dianions in a storage ring.

    PubMed

    Kadhane, U; Andersen, J U; Bonderup, E; Concina, B; Hvelplund, P; Suhr Kirketerp, M-B; Liu, B; Nielsen, S Brøndsted; Panja, S; Rangama, J; Støchkel, K; Tomita, S; Zettergren, H; Hansen, K; Sundén, A E K; Canton, S E; Echt, O; Forster, J S

    2009-07-07

    We present a detailed study of the electronic structure and the stability of C(60) dianions in the gas phase. Monoanions were extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were then stored in an electrostatic ring, and their near-infrared absorption spectrum was measured by observation of laser induced electron detachment. From the time dependence of the detachment after photon absorption, we conclude that the reaction has contributions from both direct electron tunneling to the continuum and vibrationally assisted tunneling after internal conversion. This implies that the height of the Coulomb barrier confining the attached electrons is at least approximately 1.5 eV. For C(60)(2-) ions in solution electron spin resonance measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C(60)(2-) ions is singlet. The observed spectrum corresponds to an electronic transition from a t(1u) lowest unoccupied molecular orbital (LUMO) of C(60) to the t(1g) LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule, and a main absorption band at 10,723 cm(-1) corresponds to a transition between the Jahn-Teller ground states. Also transitions from pseudorotational states with 200 cm(-1) and (probably) 420 cm(-1) excitation are observed. We argue that a very broad absorption band from about 11,500 cm(-1) to 13,500 cm(-1) consists of transitions to so-called cone states, which are Jahn-Teller states on a higher potential-energy surface, stabilized by a pseudorotational angular momentum barrier. A previously observed, high-lying absorption band for C(60)(-) may also be a transition to a cone state.

  20. The strength of electron electron correlation in Cs3C60

    NASA Astrophysics Data System (ADS)

    Baldassarre, L.; Perucchi, A.; Mitrano, M.; Nicoletti, D.; Marini, C.; Pontiroli, D.; Mazzani, M.; Aramini, M.; Riccó, M.; Giovannetti, G.; Capone, M.; Lupi, S.

    2015-10-01

    Cs3C60 is an antiferromagnetic insulator that under pressure (P) becomes metallic and superconducting below Tc = 38 K. The superconducting dome present in the T - P phase diagram close to a magnetic state reminds what found in superconducting cuprates and pnictides, strongly suggesting that superconductivity is not of the conventional Bardeen-Cooper-Schrieffer (BCS) type We investigate the insulator to metal transition induced by pressure in Cs3C60 by means of infrared spectroscopy supplemented by Dynamical Mean-Field Theory calculations. The insulating compound is driven towards a metallic-like behaviour, while strong correlations survive in the investigated pressure range. The metallization process is accompanied by an enhancement of the Jahn-Teller effect. This shows that electronic correlations are crucial in determining the insulating behaviour at ambient pressure and the bad metallic nature for increasing pressure. On the other hand, the relevance of the Jahn-Teller coupling in the metallic state confirms that phonon coupling survives in the presence of strong correlations.

  1. Removal of Lattice Imperfections that Impact the Optical Quality of Ti:Sapphire using Advanced Magnetorheological Finishing Techniques

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Menapace, J A; Schaffers, K I; Bayramian, A J

    2008-02-26

    Advanced magnetorheological finishing (MRF) techniques have been applied to Ti:sapphire crystals to compensate for sub-millimeter lattice distortions that occur during the crystal growing process. Precise optical corrections are made by imprinting topographical structure onto the crystal surfaces to cancel out the effects of the lattice distortion in the transmitted wavefront. This novel technique significantly improves the optical quality for crystals of this type and sets the stage for increasing the availability of high-quality large-aperture sapphire and Ti:sapphire optics in critical applications.

  2. Unconventional high-Tc superconductivity in fullerides

    PubMed Central

    Takabayashi, Yasuhiro; Prassides, Kosmas

    2016-01-01

    A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc. However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter—the overlap between the outer wave functions of the constituent molecules—is controlled by the C603− molecular electronic structure via the on-molecule Jahn–Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott–Jahn–Teller state through chemical or physical pressurization yields an unconventional Jahn–Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen–Cooper–Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn–Teller and Fermi liquid metal when the Jahn–Teller distortion melts. This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’. PMID:27501971

  3. Superconductivity and fast proton transport in nanoconfined water

    NASA Astrophysics Data System (ADS)

    Johnson, K. H.

    2018-04-01

    A real-space molecular-orbital density-wave description of Cooper pairing in conjunction with the dynamic Jahn-Teller mechanism for high-Tc superconductivity predicts that electron-doped water confined to the nanoscale environment of a carbon nanotube or biological macromolecule should superconduct below and exhibit fast proton transport above the transition temperature, Tc ≅ 230 K (-43 °C).

  4. Revolving scanning transmission electron microscopy: correcting sample drift distortion without prior knowledge.

    PubMed

    Sang, Xiahan; LeBeau, James M

    2014-03-01

    We report the development of revolving scanning transmission electron microscopy--RevSTEM--a technique that enables characterization and removal of sample drift distortion from atomic resolution images without the need for a priori crystal structure information. To measure and correct the distortion, we acquire an image series while rotating the scan coordinate system between successive frames. Through theory and experiment, we show that the revolving image series captures the information necessary to analyze sample drift rate and direction. At atomic resolution, we quantify the image distortion using the projective standard deviation, a rapid, real-space method to directly measure lattice vector angles. By fitting these angles to a physical model, we show that the refined drift parameters provide the input needed to correct distortion across the series. We demonstrate that RevSTEM simultaneously removes the need for a priori structure information to correct distortion, leads to a dramatically improved signal-to-noise ratio, and enables picometer precision and accuracy regardless of drift rate. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. A variational theory of Hall effect of Anderson lattice model: Application to colossal magnetoresistance manganites (Re1-x Ax MnO3)

    NASA Astrophysics Data System (ADS)

    Panwar, Sunil; Kumar, Vijay; Singh, Ishwar

    2017-10-01

    An anomalous Hall constant RH has been observed in various rare earth manganites doped with alkaline earths namely Re1-xAxMnO3 (where Re = La, Pr, Nd etc., and A = Ca, Sr, Ba etc.) which exhibit colossal magnetoresistance (CMR), metal- insulator transition and many other poorly understood phenomena. We show that this phenomenon of anomalous Hall constant can be understood using two band (ℓ-b) Anderson lattice model Hamiltonian alongwith (ℓ-b) hybridization recently studied by us for manganites in the strong electron-lattice Jahn-Teller (JT) coupling regime an approach similar to the two - fluid models. We use a variational method in this work to study the temperature variation of Hall constant RH (T) in these compounds. We have already used this variational method to study the zero field electrical resistivity ρ (T) and magnetic susceptibility of doped CMR manganites. In the present study, we find that the Hall constant RH (T) reduces with increasing magnetic field parameters h&m and the metal-insulator transition temperature (Tρ) shifts towards higher temperature region. We have also observed the role of the model parameters e.g. local Coulomb repulsion U, Hund's rule coupling JH between eg spins and t2g spins, ferromagnetic nearest neighbor exchange coupling JF between t2g core spins and hybridization Vk between ℓ-polarons and d-electrons on Hall constant RH (T) of these materials at different magnetic fields. Here we find that RH (T) for a particular value of h and m shows a rapid initial increase, followed by a sharp peak at low temperature say 50 K in our case and a slow decrease at high temperatures, resembling with the key feature of many CMR compounds like La0.8Ba0.2 MnO3.The magnitude of RH (T) reduces and the anomaly (sharp peak) in RH becomes broader and shifts towards higher temperature region on increasing Vk or JH or doping x and even vanishes on further increasing these parameters. Our results of anomalous Hall constant (RH) have same

  6. 12 CFR 328.4 - Prohibition against receiving deposits at same teller station or window as noninsured institution.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... teller station or window as noninsured institution. 328.4 Section 328.4 Banks and Banking FEDERAL DEPOSIT... Prohibition against receiving deposits at same teller station or window as noninsured institution. (a) Prohibition. An insured depository institution may not receive deposits at any teller station or window where...

  7. Determination of lattice parameters, strain state and composition in semipolar III-nitrides using high resolution X-ray diffraction

    NASA Astrophysics Data System (ADS)

    Frentrup, Martin; Hatui, Nirupam; Wernicke, Tim; Stellmach, Joachim; Bhattacharya, Arnab; Kneissl, Michael

    2013-12-01

    In group-III-nitride heterostructures with semipolar or nonpolar crystal orientation, anisotropic lattice and thermal mismatch with the buffer or substrate lead to a complex distortion of the unit cells, e.g., by shearing of the lattice. This makes an accurate determination of lattice parameters, composition, and strain state under assumption of the hexagonal symmetry impossible. In this work, we present a procedure to accurately determine the lattice constants, strain state, and composition of semipolar heterostructures using high resolution X-ray diffraction. An analysis of the unit cell distortion shows that four independent lattice parameters are sufficient to describe this distortion. Assuming only small deviations from an ideal hexagonal structure, a linear expression for the interplanar distances dhkl is derived. It is used to determine the lattice parameters from high resolution X-ray diffraction 2ϑ-ω-scans of multiple on- and off-axis reflections via a weighted least-square fit. The strain and composition of ternary alloys are then evaluated by transforming the elastic parameters (using Hooke's law) from the natural crystal-fixed coordinate system to a layer-based system, given by the in-plane directions and the growth direction. We illustrate our procedure taking an example of (112¯2) AlκGa1-κN epilayers with Al-contents over the entire composition range. We separately identify the in-plane and out-of-plane strains and discuss origins for the observed anisotropy.

  8. Theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena

    NASA Astrophysics Data System (ADS)

    Jin, Yongmei M.; Wang, Yu U.; Ren, Yang

    2015-12-01

    Pre-martensitic phenomena, also called martensite precursor effects, have been known for decades while yet remain outstanding issues. This paper addresses pre-martensitic phenomena from new theoretical and experimental perspectives. A statistical mechanics-based Grüneisen-type phonon theory is developed. On the basis of deformation-dependent incompletely softened low-energy phonons, the theory predicts a lattice instability and pre-martensitic transition into elastic-phonon domains via 'phonon spinodal decomposition.' The phase transition lifts phonon degeneracy in cubic crystal and has a nature of phonon pseudo-Jahn-Teller lattice instability. The theory and notion of phonon domains consistently explain the ubiquitous pre-martensitic anomalies as natural consequences of incomplete phonon softening. The phonon domains are characterised by broken dynamic symmetry of lattice vibrations and deform through internal phonon relaxation in response to stress (a particular case of Le Chatelier's principle), leading to previously unexplored new domain phenomenon. Experimental evidence of phonon domains is obtained by in situ three-dimensional phonon diffuse scattering and Bragg reflection using high-energy synchrotron X-ray single-crystal diffraction, which observes exotic domain phenomenon fundamentally different from usual ferroelastic domain switching phenomenon. In light of the theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena, currently existing alternative opinions on martensitic precursor phenomena are revisited.

  9. Theoretical Studies of Relaxation and Optical Properties of Polymers

    NASA Astrophysics Data System (ADS)

    Jin, Bih-Yaw

    1993-01-01

    This thesis is composed of two parts. In the part one, the empirical correlation between the logarithm of tunneling splittings and the temperature at which the spin-lattice relaxation time is minimum for methyl groups in different molecular crystals is explained successfully by taking multiphonon processes into account. We show that one phonon transitions dominate in the low barrier limit. However, in the intermediate barrier range and high barrier limit, it is necessary to include multiphonon processes. We also show that the empirical correlation depends only logarithmically on the details of the phonon bath. In the part two, we have investigated the optical and relaxation properties of conjugated polymers. The connection between the vibronic picture of Raman scattering and the third order perturbation approach in solid state physics is clarified in chapter 2. Starting from the Kramers -Heissenberg-Dirac formula for Raman scattering, we derive expressions for the Condon and Herzberg-Teller terms from a simple two-level system to a two-band system, i.e. polyacetylene, by using traditional vibronic picture. Both the Condon and Herzberg-Teller terms contribute to two-band processes, while three-band processes consist only of Herzberg-Teller terms in the solid state limit. Close to resonance the Condon term dominates and converges to the usual solid state result. In the off-resonance region the Herzberg -Teller term is comparable to Condon term for both small molecule and solid state system. In chapter 3, we will concentrate on the lattice relaxation of the lowest optically allowed 1B_ {u} state, especially, the effect of electron correlation on the excited state geometric relaxation for finite polyenes. We have examined the competition between electron-electron interaction and electron-phonon coupling on the formation of localized lattice distortion in the 1B_{u} state for finite polyene with chain length up to 30 double bonds. The chain length dependence of the

  10. Synthesis, structure and properties of blödite-type solid solutions, Na2Co1-x Cu x (SO4)2·4H2O (0 < x ≤ 0.18), and crystal structure of synthetic kröhnkite, Na2Cu(SO4)2·2H2O

    NASA Astrophysics Data System (ADS)

    Marinova, Delyana; Wildner, Manfred; Bancheva, Tsvetelina; Stoyanova, Radostina; Georgiev, Mitko; Stoilova, Donka G.

    2018-03-01

    Based on different experimental methods—crystallization processes in aqueous solutions, infrared spectroscopy, single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) and TG-DTA-DSC measurements—it has been established that copper ions are included in sodium cobalt sulfate up to about 18 mol%, thus forming limited solid solutions Na2Co1-x Cu x (SO4)2·4H2O (0 < x ≤ 0.18) with a blödite-type structure. In contrast, cobalt ions are not able to accept the coordination environment of the copper ions in the strongly distorted Cu(H2O)2O4 octahedra, thus resulting in the crystallization of Co-free kröhnkite. The solid solutions were characterized by vibrational and EPR spectroscopy. DSC measurements reveal that the copper concentration increase leads to increasing values of the enthalpy of dehydration (ΔH deh) and decreasing values of the enthalpy of formation (ΔH f). The crystal structures of synthetic kröhnkite, Na2Cu(SO4)2·2H2O, as well as of three Cu2+-bearing mixed crystals of Co-blödite, Na2Co1-x Cu x (SO4)2·4H2O with x (Cu) ranging from 0.03 to 0.15, have been investigated from single-crystal X-ray diffraction data. The new data for the structure of synthetic kröhnkite facilitated to clarify structural discrepancies found in the literature for natural kröhnkite samples, traced back to a mix-up of lattice parameters. The crystal structures of Co-dominant Na2Co1-x Cu x (SO4)2·4H2O solid solutions reveal a comparatively weak influence of the Jahn-Teller-affected Cu2+ guest cations up to the maximum content of x (Cu) = 0.15. The response of the MO2(H2O)4 octahedral shape by increased bond-length distortion with Cu content is clear cut (but limited), mainly concerning the M-OH2 bond lengths, whereas other structural units are hardly affected. However, the specific type of imposed distortion seems to play an important role impeding higher Cu/Co replacement ratios.

  11. Lasing in topological edge states of a one-dimensional lattice

    NASA Astrophysics Data System (ADS)

    St-Jean, P.; Goblot, V.; Galopin, E.; Lemaître, A.; Ozawa, T.; Le Gratiet, L.; Sagnes, I.; Bloch, J.; Amo, A.

    2017-10-01

    Topology describes properties that remain unaffected by smooth distortions. Its main hallmark is the emergence of edge states localized at the boundary between regions characterized by distinct topological invariants. Because their properties are inherited from the topology of the bulk, these edge states present a strong immunity to distortions of the underlying architecture. This feature offers new opportunities for robust trapping of light in nano- and micrometre-scale systems subject to fabrication imperfections and environmentally induced deformations. Here, we report lasing in such topological edge states of a one-dimensional lattice of polariton micropillars that implements an orbital version of the Su-Schrieffer-Heeger Hamiltonian. We further demonstrate that lasing in these states persists under local deformations of the lattice. These results open the way to the implementation of chiral lasers in systems with broken time-reversal symmetry and, when combined with polariton interactions, to the study of nonlinear phenomena in topological photonics.

  12. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jian, Tian; Lopez, Gary V.; Wang, Lai-Sheng, E-mail: Lai-Sheng-Wang@brown.edu

    We report the observation of a manganese-centered tubular boron cluster (MnB{sub 16}{sup −}), which is characterized by photoelectron spectroscopy and ab initio calculations. The relatively simple pattern of the photoelectron spectrum indicates the cluster to be highly symmetric. Ab initio calculations show that MnB{sub 16}{sup −} has a Mn-centered tubular structure with C{sub 4v} symmetry due to first-order Jahn-Teller effect, while neutral MnB{sub 16} reduces to C{sub 2v} symmetry due to second-order Jahn-Teller effect. In MnB{sub 16}{sup −}, two unpaired electrons are observed, one on the Mn 3d{sub z{sup 2}} orbital and another on the B{sub 16} tube, making itmore » an unusual biradical. Strong covalent bonding is found between the Mn 3d orbitals and the B{sub 16} tube, which helps to stabilize the tubular structure. The current result suggests that there may exist a whole class of metal-stabilized tubular boron clusters. These metal-doped boron clusters provide a new bonding modality for transition metals, as well as a new avenue to design boron-based nanomaterials.« less

  13. Structural evolution of the methane cation in subfemtosecond photodynamics

    NASA Astrophysics Data System (ADS)

    Mondal, T.; Varandas, A. J. C.

    2015-07-01

    An ab initio quantum dynamics study has been performed to explore the structural rearrangement of ground state CH 4+ in subfemtosecond resolved photodynamics. The method utilizes time-dependent wave-packet propagation on the X ˜ 2 T 2 electronic manifold of the title cation in full dimensionality, including nonadiabatic coupling of the three electronic sheets. Good agreement is obtained with recent experiments [Baker et al., Science 312, 424 (2006)] which use high-order harmonic generation to probe the attosecond proton dynamics. The novel results provide direct theoretical support of the observations while unravelling the underlying details. With the geometrical changes obtained by calculating the expectation values of the nuclear coordinates as a function of time, the structural evolution is predicted to begin through activation of the totally symmetric a1 and doubly degenerate e modes. While the former retains the original Td symmetry of the cation, the Jahn-Teller active e mode conducts it to a D2d structure. At ˜1.85 fs, the intermediate D2d structure is further predicted to rearrange to local C2v minimum geometry via Jahn-Teller active bending vibrations of t2 symmetry.

  14. High-Resolution Laser Spectroscopy of Free Radicals in Nearly Degenerate Electronic States

    NASA Astrophysics Data System (ADS)

    Liu, Jinjun

    2017-06-01

    Rovibronic structure of molecules in orbitally degenerate electronic states including Renner-Teller (RT) and Jahn-Teller (JT) active molecules has been extensively studied. Less is known about rotational structure of polyatomic molecules in nearly degenerate states, especially those with low (e.g., C_s) symmetry that are subject to the pseudo-Jahn-Teller (pJT) effect. In the case of free radicals, the unpaired electron further complicates energy levels by inducing spin-orbit (SO) and spin-rotation (SR) splittings. Asymmetric deuteration or methyl substitution of C_{3v} free radicals such as CH_3O, CaCH_3, and CaOCH_3 lowers the molecular symmetry, lifts the vibronic degeneracy, and reduces the JT effect to the pJT effect. New spectroscopic models are required to reproduce the rovibronic structure and simulate the experimentally obtained spectra of pJT-active free radicals. It has been found that rotational and fine-structure analysis of spectra involving nearly degenerate states may aid in vibronic analysis and interpretation of effective molecular constants. Especially, SO and Coriolis interactions that couple the two states can be determined accurately from fitting the experimental spectra. Coupling between the two electronic states also affects the intensities of rotational and vibronic transitions. The study on free radicals in nearly degenerate states provides a promising avenue of research which may bridge the gap between symmetry-induced degenerate states and the Born-Oppenheimer (BO) limit of unperturbed electronic states.

  15. Pressure–Temperature Phase Diagram Reveals Spin–Lattice Interactions in Co[N(CN) 2 ] 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Musfeldt, J. L.; O’Neal, K. R.; Brinzari, T. V.

    2017-04-07

    Diamond anvil cell techniques, synchrotron-based infrared and Raman spectroscopies, and lattice dynamics calculations are combined with prior magnetic property work to reveal the pressure–temperature phase diagram of Co[N(CN)2]2. The second-order structural boundaries converge on key areas of activity involving the spin state exposing how the pressure-induced local lattice distortions trigger the ferromagnetic → antiferromagnetic transition in this quantum material.

  16. Raman study of transition-metal oxides with perovskite-like structure

    NASA Astrophysics Data System (ADS)

    Kolev, Nikolay Iliev

    ordering and freezing of the Jahn-Teller distortions in a superstructure. Polarized Raman spectra confirmed their usefulness in studying thin films and their properties.

  17. Orbital Dimer Model for the Spin-Glass State in Y 2 Mo 2 O 7

    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 Y 2Mo 2O 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-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 Mo 4+ ions displace accordingmore » 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. 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

  18. DOE Office of Scientific and Technical Information (OSTI.GOV)

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

    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 2Mo 2O 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-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 Mo 4+ ions displace accordingmore » 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. 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

  19. Structure and reactivity of a mononuclear gold(II) complex

    NASA Astrophysics Data System (ADS)

    Preiß, Sebastian; Förster, Christoph; Otto, Sven; Bauer, Matthias; Müller, Patrick; Hinderberger, Dariush; Hashemi Haeri, Haleh; Carella, Luca; Heinze, Katja

    2017-12-01

    Mononuclear gold(II) complexes are very rare labile species. Transient gold(II) species have been suggested in homogeneous catalysis and in medical applications, but their geometric and electronic structures have remained essentially unexplored: even fundamental data, such as the ionic radius of gold(II), are unknown. Now, an unprecedentedly stable neutral gold(II) complex of a porphyrin derivative has been isolated, and its structural and spectroscopic features determined. The gold atom adopts a 2+2 coordination mode in between those of gold(III) (four-coordinate square planar) and gold(I) (two-coordinate linear), owing to a second-order Jahn-Teller distortion enabled by the relativistically lowered 6s orbital of gold. The reactivity of this gold(II) complex towards dioxygen, nitrosobenzene and acids is discussed. This study provides insight on the ionic radius of gold(II), and allows it to be placed within the homologous series of nd9 Cu/Ag/Au divalent ions and the 5d8/9/10 Pt/Au/Hg 'relativistic' triad in the periodic table.

  20. Structural and catalytic characterization of a heterovalent Mn(II)Mn(III) complex that mimics purple acid phosphatases.

    PubMed

    Smith, Sarah J; Riley, Mark J; Noble, Christopher J; Hanson, Graeme R; Stranger, Robert; Jayaratne, Vidura; Cavigliasso, Germán; Schenk, Gerhard; Gahan, Lawrence R

    2009-11-02

    The binuclear heterovalent manganese model complex [Mn(II)Mn(III)(L1)(OAc)(2)] ClO(4) x H(2)O (H(2)L1 = 2-(((3-((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino)-methyl)phenol) has been prepared and studied structurally, spectroscopically, and computationally. The magnetic and electronic properties of the complex have been related to its structure. The complex is weakly antiferromagnetically coupled (J approximately -5 cm(-1), H = -2J S(1) x S(2)) and the electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectra identify the Jahn-Teller distortion of the Mn(III) center as predominantly a tetragonal compression, with a significant rhombic component. Electronic structure calculations using density functional theory have confirmed the conclusions derived from the experimental investigations. In contrast to isostructural M(II)Fe(III) complexes (M = Fe, Mn, Zn, Ni), the Mn(II)Mn(III) system is bifunctional possessing both catalase and hydrolase activities, and only one catalytically relevant pK(a) (= 8.2) is detected. Mechanistic implications are discussed.

  1. Crystal Growth of the S =1/2 Antiferromagnet K2PbCu(NO2)6 Elpasolite

    NASA Astrophysics Data System (ADS)

    Dong, Lianyang; Besara, Tiglet; Siegrist, Theo

    The elpasolite K2PbCu(NO2)6is known for its two structural transitions at 281 K and 273 K. Single crystals of K2PbCu(NO2)6 have been grown in aqueous solution, but the rapid nucleation rate and convective transport renders it difficult to obtain large high quality single crystals. We developed a gel method to grow K2PbCu(NO2)6 Elpasolite with sizes up to 5x5x5 mm3, suitable for neutron diffraction measurements. Susceptibility measurements clearly show that the Jahn-Teller distortions at 286K and 273K with associated orbital ordering produce a linear chain Heisenberg antiferromagnetic system. The intrachain interaction strength has been derived from a Bonner-Fisher analysis that yielded a value of 5.4K. This work was supported by the National Science Foundation, under award DMR-1534818. A portion of this work has been performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement.

  2. Habit plane-driven P2-type manganese-based layered oxide as long cycling cathode for Na-ion batteries

    NASA Astrophysics Data System (ADS)

    Luo, Rui; Wu, Feng; Xie, Man; Ying, Yao; Zhou, Jiahui; Huang, Yongxin; Ye, Yusheng; Li, Li; Chen, RenJie

    2018-04-01

    Layered transition metal oxides are considered to be promising candidates as cathode materials for sodium-ion batteries. Herein, a facile solid-state reaction is developed to synthesize hexagons plate-like Na0.67Ni0.25Mn0.75O2+δ (denoted as P2-NNM) material with habit plane formed. The structure of this layered oxide is characterized by XRD, HR-TEM and SAED. The layered material delivers a high reversible capacity of 91.8 mAh g-1 at 0.2 C with a capacity retention of 94.4 % after 280 cycles, superior rate capability and long cycle life (84.2 % capacity retention after 1000 cycle). Ni2+ is an active ion and Ni doping alleviates the Jahn-Teller distortion, and Mn3+/Mn4+ coexist as Mn4+ is desired from the stability perspective. Particularly, CV and XPS results confirm these results. Moreover, the electrode exhibits a quasi-solid-solution reaction during the sodium extraction and insertion. This contribution demonstrates that P2-NNM is a promising cathode electrode for rechargeable long-life sodium-ion batteries.

  3. First iron and cobalt(II) hexabromoclathrochelates: structural, magnetic, redox, and electrocatalytic behavior.

    PubMed

    Dolganov, Alexander V; Belov, Alexander S; Novikov, Valentin V; Vologzhanina, Anna V; Romanenko, Galina V; Budnikova, Yulia G; Zelinskii, Genrikh E; Buzin, Michail I; Voloshin, Yan Z

    2015-02-07

    Template condensation of dibromoglyoxime with n-butylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded iron and cobalt(ii) hexabromoclathrochelates. The paramagnetic cobalt clathrochelate was found to be a low-spin complex at temperatures below 100 K, with a gradual increase in the effective magnetic moment at higher temperatures due to the temperature 1/2↔3/2 spin crossover and a gap caused by the structure phase transition. The multitemperature X-ray and DSC studies of this complex and its iron(ii)-containing analog also showed temperature structural transitions. The variation of an encapsulated metal ion's radius, electronic structure and spin state caused substantial differences in the geometry of its coordination polyhedron; these differences increase with the decrease in temperature due to Jahn-Teller distortion of the encapsulated cobalt(ii) ion with an electronic configuration d(7). As follows from CV and GC data, these cage iron and cobalt complexes undergo both oxidation and reduction quasireversibly, and showed an electrocatalytic activity for hydrogen production in different producing systems.

  4. What is the valence of Mn in GaMnN?

    NASA Astrophysics Data System (ADS)

    Nelson, Ryky; Berlijn, Tom; Moreno, Juana; Jarrell, Mark; Ku, Wei

    2014-03-01

    Motivated by the potential high Curie temperature of GaMnN, we investigate the controversial Mn-valence in this diluted magnetic semiconductor. From a first-principles Wannier functions analysis of the high energy Hilbert space we find unambiguously the charge state of Mn to be close to 2 + (d5), but in a mixed spin configuration with average magnetic moments of 4 μB. Using more extended Wannier orbitals to capture the lower-energy physics, we further demonstrate the feasibility of both the effective d4 description (appropriate to deal with the local magnetic moment and Jahn-Teller distortion), and the effective d5 description (relevant to study long-range magnetic order). Our derivation highlights the general richness of low-energy sectors in interacting many-body systems and the generic need for multiple effective descriptions, and advocates for a diminished relevance of atomic valence measured by various experimental probes. This research is supported in part by LA-SiGMA, NSF Award Number #EPS-1003897. TB was supported by DOE CMCSN and as a Wigner Fellow at the Oak Ridge National Laboratory.

  5. Unusual behavior of uranium dioxide at high magnetic fields. Part I

    NASA Astrophysics Data System (ADS)

    Gofryk, K.; Jaime, M.; Zapf, V.; Harrison, N.; Saul, A.; Radtke, G.; Lashley, J. C.; Salamon, M.; Andersson, A. D.; Stanek, C.; Durakiewicz, T.; Smith, J. L.

    UO2 is a Mott-Hubbard insulator with well-localized 5 f-electrons and its crystal structure is the face-centered-cubic fluorite. It experiences a first-order antiferromagnetic phase transition at 30.8 K to a non-collinear antiferromagnetic structure that remains a topic of debate. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion of oxygen atoms. Despite extensive experimental and theoretical efforts the nature of the competing degrees of freedom and their couplings (such as spin-phonon coupling) are still unclear. Here we present results of our extensive thermodynamic investigations, on well-characterized and oriented single crystals of UO2, focusing on magnetization M(T,H) measurements in DC and pulsed magnetic fields to up 65 T at the NHMFL. Work supported by the Department of Energy, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division. The NHMFL Pulsed Field Facility is supported by the NSF, the U.S. D.O.E., and the State of Florida through NSF cooperative Grant DMR.

  6. Task clarification, performance feedback, and social praise: Procedures for improving the customer service of bank tellers

    PubMed Central

    Crowell, Charles R.; Anderson, D. Chris; Abel, Dawn M.; Sergio, Joseph P.

    1988-01-01

    Customer service for bank tellers was defined in terms of 11 verbal behavior categories. An audio-recording system was used to track the occurrence of behaviors in these categories for six retail banking tellers. Three behavior management interventions (task clarification, performance feedback, and social praise), applied in sequence, were designed to improve overall teller performance with regard to the behavioral categories targeted. Clarification was accomplished by providing clear delineation of the various target categories, with specific examples of the behaviors in each. Feedback entailed presentation of ongoing verbal and visual information regarding teller performance. Praise consisted of verbal recognition of teller performance by branch managers. Results showed that clarification effects emerged quickly, producing an overall increase in desired behaviors of 12% over baseline. Feedback and praise effects occurred more gradually, resulting in overall increases of 6% and 7%, respectively. A suspension of all procedures led to a decline in overall performance, whereas reinstatement of feedback and praise was again accompanied by performance improvement. These findings extend the generality of behavior management applications and help to distinguish between possible antecedent and consequent effects of performance feedback. PMID:16795713

  7. Science and Technology Review, July-August 1998: Celebrating Edward Teller at 90

    DOE R&D Accomplishments Database

    Smart, J.

    1998-07-01

    On the occasion of Edward Teller's 90th birthday, Science and Technology Review (S&TR) has the pleasure of honoring Lawrence Livermore's co-founder and most influential scientist. Teller is known for his inventive work in physics, his concepts leading to thermonuclear explosions, and his strong stands on such issues as science education, the nation's strategic defense, the needs for science in the future, and sharing scientific information. The articles in this issue also show him, as always, tirelessly moving forward with his new and changing interests.

  8. Reconnaissance for radioactive deposits in the vicinity of Teller and Cape Nome, Seward Peninsula, Alaska, 1946-47

    USGS Publications Warehouse

    White, Max Gregg; West, W.S.; Matzko, J.J.

    1953-01-01

    Placer-mining areas and bedrock exposures near Teller on the Seward Peninsula, Alaska, were investigated in June and July, 1946, for possible sources of radioactive materials. The areas that were investigated are: Dese Creek, southeast of Teller; Bluestone River basin, south and southeast of Teller; Sunset Creek and other small streams flowing south into Grantley Harbor, northeast of Teller; and, also northeast of Teller, Swanson Creek and its tributaries, which flow north into the Agiapuk River basin. No significant amount of radioactive material was found, either in the stream gravels or in the bedrock of any of the areas. A heavy-mineral fraction obtained from a granite boulder probably derived from a bench gravel on Gold Run contains 0. 017 percent equivalent uranium, but the radioactivity is due to allanite and zircon. The types of bedrock tested include schist, slate, and greenstone. Readings on fresh surfaces of rock were the same as, or only slightly above the background count. The maximum radioactivity in stream concentrates is 0. 004 percent equivalent uranium in a sluice concentrate from Sunset Creek.

  9. 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≤Ba

  10. Polaron melting and ordering as key mechanisms for colossal resistance effects in manganites

    PubMed Central

    Jooss, Ch.; Wu, L.; Beetz, T.; Klie, R. F.; Beleggia, M.; Schofield, M. A.; Schramm, S.; Hoffmann, J.; Zhu, Y.

    2007-01-01

    Polarons, the combined motion of electrons in a cloth of their lattice distortions, are a key transport feature in doped manganites. To develop a profound understanding of the colossal resistance effects induced by external fields, the study of polaron correlations and the resulting collective polaron behavior, i.e., polaron ordering and transition from polaronic transport to metallic transport is essential. We show that static long-range ordering of Jahn–Teller polarons forms a polaron solid which represents a new type of charge and orbital ordered state. The related noncentrosymmetric lattice distortions establish a connection between colossal resistance effects and multiferroic properties, i.e., the coexistence of ferroelectric and antiferromagnetic ordering. Colossal resistance effects due to an electrically induced polaron solid–liquid transition are directly observed in a transmission electron microscope with local electric stimulus applied in situ using a piezo-controlled tip. Our results shed light onto the colossal resistance effects in magnetic field and have a strong impact on the development of correlated electron-device applications such as resistive random access memory (RRAM). PMID:17699633

  11. Gamow–Teller resonances in the {sup 118}Sb compound nucleus: Puzzles of an experiment in Sarov

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Urin, M. H., E-mail: urin@theor.mephi.ru

    2016-03-15

    Contradictory data on the observation of Gamow–Teller resonances in the {sup 118}Sb compound nucleus are discussed along with the available interpretation of these data and planned experimental and theoretical investigations into Gamow–Teller resonances in a number of antimony isotopes.

  12. Microscopic origin of lattice contraction and expansion in undoped rutile TiO2 nanostructures

    NASA Astrophysics Data System (ADS)

    Santara, Batakrushna; Giri, P. K.; Imakita, Kenji; Fujii, Minoru

    2014-05-01

    We have investigated the microscopic origin of lattice expansion and contraction in undoped rutile TiO2 nanostructures by employing several structural and optical spectroscopic tools. Rutile TiO2 nanostructures with morphologies such as nanorods, nanopillars and nanoflowers, depending upon the growth conditions, are synthesized by an acid-hydrothermal process. Depending on the growth conditions and post-growth annealing, lattice contraction and expansion are observed in the nanostructures and it is found to correlate with the nature and density of intrinsic defects in rutile TiO2. The change in lattice volume correlates well with the optical bandgap energy. Irrespective of growth conditions, theTiO2 nanostructures exhibit strong near infrared (NIR) photoluminescence (PL) at 1.43 eV and a weak visible PL, which are attributed to the Ti interstitials and O vacancies, respectively, in rutile TiO2 nanostructures. Further, ESR study reveals the presence of singly ionized oxygen vacancy defects. It is observed that lattice distortion depends systematically on the relative concentration and type of defects such as oxygen vacancies and Ti interstitials. XPS analyses revealed a downshift in energy for both Ti 2p and O 1s core level spectra for various growth conditions, which is believed to arise from the lattice distortions. It is proposed that the Ti4+ interstitial and F+ oxygen vacancy defects are primarily responsible for lattice expansion, whereas the electrostatic attraction between Ti4+ interstitial and O2- interstitial defects causes the lattice contraction in the undoped TiO2 nanostructures. The control of lattice parameters through the intrinsic defects may provide new routes to achieving novel functionalities in advanced materials that can be tailored for future technological applications.

  13. Lattice Vibrations Boost Demagnetization Entropy in Shape Memory Alloy

    DOE PAGES

    Stonaha, Paul J.; Manley, Michael E.; Bruno, Nick; ...

    2015-10-07

    Magnetocaloric (MC) materials present an avenue for chemical-free, solid state refrigeration through cooling via adiabatic demagnetization. We have used inelastic neutron scattering to measure the lattice dynamics in the MC material Ni 45Co 5Mn 36.6In 13.4. Upon heating across TC, the material exhibits an anomalous increase in phonon entropy of 0.17 0.04 k_B/atom, which is nine times larger than expected from conventional thermal expansion. We find that the phonon softening is focused in a transverse optic phonon, and we present the results of first-principle calculations which predict a strong coupling between lattice distortions and magnetic excitations.

  14. One of My Favorite Assignments: Automated Teller Machine Simulation.

    ERIC Educational Resources Information Center

    Oberman, Paul S.

    2001-01-01

    Describes an assignment for an introductory computer science class that requires the student to write a software program that simulates an automated teller machine. Highlights include an algorithm for the assignment; sample file contents; language features used; assignment variations; and discussion points. (LRW)

  15. Identifying the Distribution of Al 3+ in LiNi 0.8 Co 0.15 Al 0.05 O 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Trease, Nicole M.; Seymour, Ieuan D.; Radin, Maxwell D.

    2016-11-22

    The doping of Al into layered Li transition metal (TM) oxide cathode materials, LiTMO 2, is known to improve the structural and thermal stability, although the origin of the enhanced properties is not well understood. The effect of aluminum doping on layer stabilization has been investigated using a combination of techniques to measure the aluminum distribution in layered LiNi 0.8Co 0.15Al 0.05O 2 (NCA) over multiple length scales with 27Al and 7Li MAS NMR, local electrode atom probe (APT) tomography, X-ray and neutron diffraction, DFT, and SQUID magnetic susceptibility measurements. APT ion maps show a homogenous distribution of Ni, Co,more » Al and O 2 throughout the structure at the single particle level in agreement with the high-temperature phase diagram. 7Li and 27Al NMR indicates that the Ni 3+ ions undergo a dynamic Jahn-Teller (JT) distortion. 27Al NMR spectra indicate that the Al reduces the strain associated with the JT distortion, by preferential electronic ordering of the JT long bonds directed toward the Al 3+ ion. The ability to understand the complex atomic and orbital ordering around Al 3+ demonstrated in the current method will be useful for studying the local environment of Al 3+ in a range of transition metal oxide battery materials.« less

  16. Identifying the Distribution of Al 3+ in LiNi 0.8 Co 0.15 Al 0.05 O 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Trease, Nicole M.; Seymour, Ieuan D.; Radin, Maxwell D.

    2016-10-07

    The doping of Al into layered Li transition metal (TM) oxide cathode materials, LiTMO 2, is known to improve the structural and thermal stability, although the origin of the enhanced properties is not well understood. We have investigated the effect of aluminum doping on layer stabilization using a combination of techniques to measure the aluminum distribution in layered LiNi 0.8Co 0.15Al 0.05O 2 (NCA) over multiple length scales with 27Al and 7Li MAS NMR, local electron atom probe (LEAP) tomography, X-ray and neutron diffraction, DFT, and SQUID magnetic susceptibility measurements. LEAP tomographic maps show a homogenous distribution of Ni, Co,more » Al and O 2 throughout the structure at the particle level in agreement with the hightemperature phase diagram. 7Li and 27Al NMR indicates that the Ni 3+ ions undergo a dynamic Jahn-Teller (JT) distortion. 27Al NMR spectra indicate that the Al reduces the strain associated with the JT distortion, by preferential electronic ordering of the JT long bonds directed toward the Al 3+ ion. Our ability to understand the complex atomic and orbital ordering around Al 3+ demonstrated in the current method will be useful for studying the local environment of Al 3+ in a range of transition metal oxide battery materials.« less

  17. Ashkin-Teller criticality and weak first-order behavior of the phase transition to a fourfold degenerate state in two-dimensional frustrated Ising antiferromagnets

    NASA Astrophysics Data System (ADS)

    Liu, R. M.; Zhuo, W. Z.; Chen, J.; Qin, M. H.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.

    2017-07-01

    We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses. Furthermore, a similar behavior of the transition to the fourfold single-stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the fourfold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior.

  18. Theoretical study of orbital ordering induced structural phase transition in iron pnictides

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jena, Sushree Sangita, E-mail: sushree@iopb.res.in; Rout, G. C., E-mail: gcr@iopb.res.in; Panda, S. K., E-mail: skp@iopb.res.in

    2016-05-06

    We attribute the structural phase transition (SPT) in the parent compounds of the iron pnictides to orbital ordering. Due to anisotropy of the d{sub xz} and d{sub yz} orbitals in the xy plane, orbital ordering makes the orthorhombic structure more favorable and thus inducing the SPT. We consider a one band model Hamiltonian consisting of first and second-nearest-neighbor hopping of the electrons. We introduce Jahn-Tellar (JT) distortion in the system arising due to the orbital ordering present in this system. We calculate the electron Green’s function by using Zuvareb’s Green’s function technique and hence calculate an expression for the temperaturemore » dependent lattice strain which is computed numerically and self-consistently. The temperature dependent electron specific heat is calculated by minimizing the free energy of the system. The lattice strain is studied by varying the JT coupling and elastic constant of the system. The structural anomaly is studied through the electron occupation number and the specific heat by varying the physical parameters like JT coupling, lattice constant, chemical potential and hopping integrals of the system.« less

  19. Structural and magnetic properties of Nd0.67Ba0.33MnO3 manganites with partial replacement of Fe and Cu at Mn-site

    NASA Astrophysics Data System (ADS)

    Sudakshina, B.; Arun, B.; Chandrasekhar, K. Devi; Yang, H. D.; Vasundhara, M.

    2018-06-01

    We have investigated the structural and magnetic properties of Nd0.67Ba0.33MnO3 manganite and partial replacement of Mn with Fe and Cu compounds followed by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and vibrating sample magnetometer (VSM). The Rietveld refinement of XRD indicates orthorhombic crystal structure with I-mma space group for all the compounds and thus obtained lattice parameters confirm the presence of co-operative Jahn-Teller effect. XRD and XAS spectra results suggests the existence of Fe3+ in Fe-substituted compound where as a mixed state of Cu2+ and Cu3+ ions in the Cu-substituted compound. The ferromagnetic (FM) to paramagnetic (PM) transition and magnetic moment is found to decrease upon the substitution of Fe and Cu atoms because of the suppression of double exchange interaction. The theoretically obtained and experimentally determined values of effective PM moment and saturation magnetic moment confirms the presence of inhomogeneous magnetic states containing FM and antiferromagnetic clusters in all the studied compounds.

  20. Quantum phase diagram of distorted J 1 - J 2 Heisenberg S  =  1/2 antiferromagnet in honeycomb lattice: a modified spin wave study

    NASA Astrophysics Data System (ADS)

    Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid

    2016-10-01

    Using the modified spin wave method, we study the {{J}1}-{{J}2} Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S  =  1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter \\barα={{J}2}/{{J}1} : (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for 0≤slant \\barα≲ 0.207 , (2) a magnetically gapped disordered state for 0.207≲ \\barα≲ 0.369 , preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for 0.396≲ \\barα≤slant 1 . We also explore the phase diagram of a distorted {{J}1}-{{J}2} model with S  =  1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.

  1. Mesoscopic Elastic Distortions in GaAs Quantum Dot Heterostructures.

    PubMed

    Pateras, Anastasios; Park, Joonkyu; Ahn, Youngjun; Tilka, Jack A; Holt, Martin V; Reichl, Christian; Wegscheider, Werner; Baart, Timothy A; Dehollain, Juan Pablo; Mukhopadhyay, Uditendu; Vandersypen, Lieven M K; Evans, Paul G

    2018-05-09

    Quantum devices formed in high-electron-mobility semiconductor heterostructures provide a route through which quantum mechanical effects can be exploited on length scales accessible to lithography and integrated electronics. The electrostatic definition of quantum dots in semiconductor heterostructure devices intrinsically involves the lithographic fabrication of intricate patterns of metallic electrodes. The formation of metal/semiconductor interfaces, growth processes associated with polycrystalline metallic layers, and differential thermal expansion produce elastic distortion in the active areas of quantum devices. Understanding and controlling these distortions present a significant challenge in quantum device development. We report synchrotron X-ray nanodiffraction measurements combined with dynamical X-ray diffraction modeling that reveal lattice tilts with a depth-averaged value up to 0.04° and strain on the order of 10 -4 in the two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. Elastic distortions in GaAs/AlGaAs heterostructures modify the potential energy landscape in the 2DEG due to the generation of a deformation potential and an electric field through the piezoelectric effect. The stress induced by metal electrodes directly impacts the ability to control the positions of the potential minima where quantum dots form and the coupling between neighboring quantum dots.

  2. Reduced Lattice Thermal Conductivity of Fe-bearing Bridgmanite in Earth's Deep Mantle

    NASA Astrophysics Data System (ADS)

    Hsieh, W. P.; Deschamps, F.; Okuchi, T.; Lin, J. F.

    2017-12-01

    Complex seismic and thermo-chemical features have been revealed in Earth's lowermost mantle. Particularly, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, which, in turn, may alter the lower mantle dynamics and heat flux across core-mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure-induced lattice distortion in bridgmanite could affect its lattice thermal conductivity, but this effect remains largely unknown. Here we report our measurements of the lattice thermal conductivity of Fe-bearing and (Fe,Al)-bearing bridgmanites to 120 GPa using optical pump-probe spectroscopy. The thermal conductivity of Fe-bearing bridgmanite increases monotonically with pressure, but drops significantly around 45 GPa presumably due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000-km depth. Modeling of our results applied to the LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that, while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.

  3. Direct characterization of photoinduced lattice dynamics in BaFe2As2

    PubMed Central

    Gerber, S.; Kim, K. W.; Zhang, Y.; Zhu, D.; Plonka, N.; Yi, M.; Dakovski, G. L.; Leuenberger, D.; Kirchmann, P.S.; Moore, R. G.; Chollet, M.; Glownia, J. M.; Feng, Y.; Lee, J.-S.; Mehta, A.; Kemper, A. F.; Wolf, T.; Chuang, Y.-D.; Hussain, Z.; Kao, C.-C.; Moritz, B.; Shen, Z.-X.; Devereaux, T. P.; Lee, W.-S.

    2015-01-01

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe–As–Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands. PMID:26051704

  4. Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in γ -Fe nanoparticles

    NASA Astrophysics Data System (ADS)

    Augustyns, V.; van Stiphout, K.; Joly, V.; Lima, T. A. L.; Lippertz, G.; Trekels, M.; Menéndez, E.; Kremer, F.; Wahl, U.; Costa, A. R. G.; Correia, J. G.; Banerjee, D.; Gunnlaugsson, H. P.; von Bardeleben, J.; Vickridge, I.; Van Bael, M. J.; Hadermann, J.; Araújo, J. P.; Temst, K.; Vantomme, A.; Pereira, L. M. C.

    2017-11-01

    γ -Fe and related alloys are model systems of the coupling between structure and magnetism in solids. Since different electronic states (with different volumes and magnetic ordering states) are closely spaced in energy, small perturbations can alter which one is the actual ground state. Here, we demonstrate that the ferromagnetic state of γ -Fe nanoparticles is associated with a tetragonal distortion of the fcc structure. Combining a wide range of complementary experimental techniques, including low-temperature Mössbauer spectroscopy, advanced transmission electron microscopy, and synchrotron radiation techniques, we unambiguously identify the tetragonally distorted ferromagnetic ground state, with lattice parameters a =3.76 (2 )Å and c =3.50 (2 )Å , and a magnetic moment of 2.45(5) μB per Fe atom. Our findings indicate that the ferromagnetic order in nanostructured γ -Fe is generally associated with a tetragonal distortion. This observation motivates a theoretical reassessment of the electronic structure of γ -Fe taking tetragonal distortion into account.

  5. Swelling Mechanisms of UO2 Lattices with Defect Ingrowths

    PubMed Central

    Günay, Seçkin D.

    2015-01-01

    The swelling that occurs in uranium dioxide as a result of radiation-induced defect ingrowth is not fully understood. Experimental and theoretical groups have attempted to explain this phenomenon with various complex theories. In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method. Based on their resemblance to experimental data, the simulation results presented here show that fission induces only oxygen Frenkel pairs while alpha particle irradiation results in both oxygen and uranium Frenkel pair defects. Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects. It is shown that obstruction type Frenkel pairs are responsible for both fission- and alpha-particle-induced lattice swelling. Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects. Additionally, at high concentrations, some of the obstruction type uranium Frenkel pairs formed diatomic and triatomic structures with oxygen ions in their octahedral cages, increasing the slope of the linear dependence. PMID:26244777

  6. Comment on "Histories and Horoscopes: The Ethnographer as Fortune-Teller."

    ERIC Educational Resources Information Center

    Luttrell, Wendy

    1998-01-01

    Explores the analogy of the researcher as fortune teller and the parallels between research histories and horoscopes and discusses the tension between what the subject is and what he or she is imagined to be by others. (SLD)

  7. Soil Physical, Chemical, and Thermal Characterization, Teller Road Site, Seward Peninsula, Alaska, 2016

    DOE Data Explorer

    Graham, David; Kholodov, Alexander; Wilson, Cathy; Moon, Ji-Won; Romanovsky, Vladimir; Busey, Bob

    2018-02-05

    This dataset provides the results of physical, chemical, and thermal characterization of soils at the Teller Road Site, Seward Peninsula, Alaska. Soil pits were dug from 7-14 September 2016 at designated Intensive Stations 2 through 9 at the Teller Road MM 27 Site. This dataset includes field observations and descriptions of soil layers or horizons, field measurements of soil volumetric water content, soil temperature, thermal conductivity, and heat capacity. Laboratory measurements of soil properties include gravimetric water content, bulk density, volumetric water content, and total carbon and nitrogen.

  8. Lattice vibrations boost demagnetization entropy in a shape-memory alloy

    NASA Astrophysics Data System (ADS)

    Stonaha, P. J.; Manley, M. E.; Bruno, N. M.; Karaman, I.; Arroyave, R.; Singh, N.; Abernathy, D. L.; Chi, S.

    2015-10-01

    Magnetocaloric (MC) materials present an avenue for chemical-free, solid-state refrigeration through cooling via adiabatic demagnetization. We have used inelastic neutron scattering to measure the lattice dynamics in the MC material N i45C o5M n36.6I n13.4 . Upon heating across the Curie temperature (TC) , the material exhibits an anomalous increase in phonon entropy of 0.22 ±0.04 kB/atom , which is ten times larger than expected from conventional thermal expansion. This transition is accompanied by an abrupt softening of the transverse optic phonon. We present first-principles calculations showing a strong coupling between lattice distortions and magnetic excitations.

  9. First-principles calculation of the effects of tetragonal distortions on the Gilbert damping parameter of Co2MnSi

    NASA Astrophysics Data System (ADS)

    Pradines, B.; Arras, R.; Calmels, L.

    2017-05-01

    We present an ab initio study of the influence of the tetragonal distortion, on the static and dynamic (Gilbert damping parameter) magnetic properties of a Co2MnSi crystal. This tetragonal distortion can for instance be due to strain, when Co2MnSi is grown on a substrate with a small lattice mismatch. Using fully relativistic Korringa-Kohn-Rostoker (KKR) calculations, in conjunction with the coherent potential approximation (CPA) to describe atomic disorder and the linear response formalism to compute the Gilbert damping parameter, we show that a tetragonal distortion can substantially change the properties of Co2MnSi, in a way which depends on the kind of atomic disorder.

  10. Microstructural, Magnetic, and Optical Properties of Pr-Doped Perovskite Manganite La0.67Ca0.33MnO3 Nanoparticles Synthesized via Sol-Gel Process

    NASA Astrophysics Data System (ADS)

    Xia, Weiren; Wu, Heng; Xue, Piaojie; Zhu, Xinhua

    2018-05-01

    We report on microstructural, magnetic, and optical properties of Pr-doped perovskite manganite (La1 - xPrx)0.67Ca0.33MnO3 (LPCMO, x = 0.0-0.5) nanoparticles synthesized via sol-gel process. Structural characterizations (X-ray and electron diffraction patterns, (high resolution) TEM images) provide information regarding the phase formation and the single-crystalline nature of the LPCMO systems. X-ray and electron diffraction patterns reveal that all the LPCMO samples crystallize in perovskite crystallography with an orthorhombic structure ( Pnma space group), where the MnO6 octahedron is elongated along the b axis due to the Jahn-Teller effect. That is confirmed by Raman spectra. Crystallite sizes and grain sizes were calculated from XRD and TEM respectively, and the lattice fringes resolved in the high-resolution TEM images of individual LPCMO nanoparticle confirmed its single-crystalline nature. FTIR spectra identify the characteristic Mn-O bond stretching vibration mode near 600 cm- 1, which shifts towards high wavenumbers with increasing post-annealing temperature or Pr-doping concentration, resulting in further distortion of the MnO6 octahedron. XPS revealed dual oxidation states of Mn3+ and Mn4+ in the LPCMO nanoparticles. UV-vis absorption spectra confirm the semiconducting nature of the LPCMO nanoparticles with optical bandgaps of 2.55-2.71 eV. Magnetic measurements as a function of temperature and magnetic field at field cooling and zero-field cooling modes, provided a Curie temperature around 230 K, saturation magnetization of about 81 emu/g, and coercive field of 390 Oe at 10 K. Such magnetic properties and the semiconducting nature of the LPCMO nanoparticles will make them as suitable candidate for magnetic semiconductor spintronics.

  11. Microstructural, Magnetic, and Optical Properties of Pr-Doped Perovskite Manganite La0.67Ca0.33MnO3 Nanoparticles Synthesized via Sol-Gel Process.

    PubMed

    Xia, Weiren; Wu, Heng; Xue, Piaojie; Zhu, Xinhua

    2018-05-04

    We report on microstructural, magnetic, and optical properties of Pr-doped perovskite manganite (La 1 - x Pr x ) 0.67 Ca 0.33 MnO 3 (LPCMO, x = 0.0-0.5) nanoparticles synthesized via sol-gel process. Structural characterizations (X-ray and electron diffraction patterns, (high resolution) TEM images) provide information regarding the phase formation and the single-crystalline nature of the LPCMO systems. X-ray and electron diffraction patterns reveal that all the LPCMO samples crystallize in perovskite crystallography with an orthorhombic structure (Pnma space group), where the MnO 6 octahedron is elongated along the b axis due to the Jahn-Teller effect. That is confirmed by Raman spectra. Crystallite sizes and grain sizes were calculated from XRD and TEM respectively, and the lattice fringes resolved in the high-resolution TEM images of individual LPCMO nanoparticle confirmed its single-crystalline nature. FTIR spectra identify the characteristic Mn-O bond stretching vibration mode near 600 cm - 1 , which shifts towards high wavenumbers with increasing post-annealing temperature or Pr-doping concentration, resulting in further distortion of the MnO 6 octahedron. XPS revealed dual oxidation states of Mn 3+ and Mn 4+ in the LPCMO nanoparticles. UV-vis absorption spectra confirm the semiconducting nature of the LPCMO nanoparticles with optical bandgaps of 2.55-2.71 eV. Magnetic measurements as a function of temperature and magnetic field at field cooling and zero-field cooling modes, provided a Curie temperature around 230 K, saturation magnetization of about 81 emu/g, and coercive field of 390 Oe at 10 K. Such magnetic properties and the semiconducting nature of the LPCMO nanoparticles will make them as suitable candidate for magnetic semiconductor spintronics.

  12. Electronic and magnetic properties of RMnO3/AMnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Yu, Rong; Yunoki, Seiji; Dong, Shuai; Dagotto, Elbio

    2009-09-01

    The ground-state properties of RMnO3/AMnO3 (RMO/AMO) heterostructures (with R=La,Pr,… , a trivalent rare-earth cation and A=Sr,Ca,… , a divalent alkaline cation) are studied using a two-orbital double-exchange model including the superexchange coupling and Jahn-Teller lattice distortions. To describe the charge transfer across the interface, the long-range Coulomb interaction is taken into account at the mean-field level, by self-consistently solving the Poisson’s equation. The calculations are carried out numerically on finite clusters. We find that the state stabilized near the interface of the heterostructure is similar to the state of the bulk compound (R,A)MO at electronic density close to 0.5. For instance, a charge and orbitally ordered CE state is found at the interface if the corresponding bulk (R,A)MO material is a narrow-to-intermediate bandwidth manganite. But instead the interface regime accommodates an A-type antiferromagnetic state with a uniform x2-y2 orbital order, if the bulk (R,A)MO corresponds to a wide bandwidth manganite. We argue that these results explain some of the properties of long-period (RMO)m/(AMO)n superlattices, such as (PrMnO3)m/(CaMnO3)n and (LaMnO3)m/(SrMnO3)n . We also remark that the intermediate states in between the actual interface and the bulklike regimes of the heterostructure are dependent on the bandwidth and the screening of the Coulomb interaction. In these regions of the heterostructures, states are found that do not have an analog in experimentally known bulk phase diagrams. These new states of the heterostructures provide a natural interpolation between magnetically ordered states that are stable in the bulk at different electronic densities.

  13. Visual Display Terminal use in Iranian bank tellers: Effects on job stress and insomnia.

    PubMed

    Giahi, Omid; Shahmoradi, Behzad; Barkhordari, Abdullah; Khoubi, Jamshid

    2015-01-01

    Visual Display Terminals (VDTs) are equipments in many workplaces which their use may increase the risk of visual, musculoskeletal and mental problems including insomnia. To determine the relationship between duration of daily VDT use and insomnia among the Iranian bank tellers. We randomly selected 382 bank tellers working with VDT. Quality of sleep and stress information were collected by Athens Insomnia Scales (AIS) and Demand-Control Model (DCM) model respectively. Out of 382 participants, 127 (33.2%) had sleep complaints and 255 (66.8%) had no sleep disorders. Moreover, the insomnia symptoms' score were significantly high in the participants having more than 6 hours of daily VDT use after adjusting for multiple confounding factors (P <  0.001). There was no significant relationship between stress and insomnia. It seems that the low levels of stress and job satisfaction reduce the impact of VDT on sleep quality in tellers who worked less than 6 hours per day.

  14. Distortion of 3D SU8 photonic structures fabricated by four-beam holographic lithography withumbrella configuration.

    PubMed

    Zhu, Xuelian; Xu, Yongan; Yang, Shu

    2007-12-10

    We present a quantitative study of the distortion from a threeterm diamond-like structure fabricated in SU8 polymer by four-beam holographic lithography. In the study of the refraction effect, theory suggests that the lattice in SU8 should be elongated in the [111] direction but have no distortion in the (111) plane, and each triangular-like hole array in the (111) plane would rotate by ~30 degrees away from that in air. Our experiments agree with the prediction on the periodicity in the (111) plane and the rotation due to refraction effect, however, we find that the film shrinkage during lithographic process has nearly compensated the predicted elongation in the [111] direction. In study of photonic bandgap (PBG) properties of silicon photonic crystals templated by the SU8 structure, we find that the distortion has decreased quality of PBG.

  15. Star wars and strategic defense initiatives: work activity and health symptoms of unionized bank tellers during work reorganization.

    PubMed

    Seifert, A M; Messing, K; Dumais, L

    1997-01-01

    Work activity and health symptoms of bank tellers whose work was undergoing reorganization were examined during a university-union study of the health effects of work in women's traditional jobs. Data were gathered through collective and individual interviews, analysis of work activity, and a questionnaire administered to 305 tellers. Employees worked in a standing posture over 80 percent of the time. More than two-thirds frequently suffered pain in back, legs, and feet. The average teller had been involved in 3.7 robberies as a direct victim and six as a witness. Work required feats of memory and concentration. In order to meet job demands, tellers engaged in supportive activities and teamwork. The introduction of individualized objectives threatened the employees' ability to collaborate and induced distress. More than twice as many tellers as other female workers in Québec experience psychological distress (Ilfeld scale), related to: robbery during the past two years (odds ratio = 1.7; confidence interval = 1.0-2.9); difficult relations with superiors (O.R. = 2.6; C.I. = 1.3-5.3); and full-time work (O.R. = 2.3; C.I. = 1.3-3.9). Diverse methods enriched the analysis, and union participation allowed the proposal of concrete correction measures.

  16. 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.

  17. Direct characterization of photoinduced lattice dynamics in BaFe 2As 2

    DOE PAGES

    Gerber, S.; Kim, K. W.; Zhang, Y.; ...

    2015-06-08

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe 2As 2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe–As–Fe bond angle. We directly quantify the coherent latticemore » dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands.« less

  18. Spin-state blockade in Te6+-substituted electron-doped LaCoO3

    NASA Astrophysics Data System (ADS)

    Tomiyasu, Keisuke; Koyama, Shun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi

    2015-03-01

    Perovskite-type LaCoO3 (Co3+: d6) is a rare inorganic material with sensitive and characteristic responses among low, intermediate, and high spin states. For example, in insulating nonmagnetic low-spin states below about 20 K, light hole doping (Ni substitution) induces much larger magnetization than expected; over net 10μB/hole (5μB/Ni) for 1μB/hole (1μB/Ni), in which the nearly isolated dopants locally change the surrounding Co low-spin states to magnetic ones and form spin molecules with larger total spin. Further, the former is isotropic, whereas the latter exhibits characteristic anisotropy probably because of Jahn-Teller distortion. In contrast, for electron doping, relatively insensitive spin-state responses were reported, as in LaCo(Ti4+) O3, but are not clarified, and are somewhat controversial. Here, we present macroscopic measurement data of another electron-doped system LaCo(Te6+) O3 and discuss the spin-state responses. This study was financially supported by Grants-in-Aid for Young Scientists (B) (No. 22740209 and 26800174) from the MEXT of Japan.

  19. Two-dimensional La2/3Sr4/3MnO4 Manganite Films Probed by Epitaxial Strain and Cation Ordering

    NASA Astrophysics Data System (ADS)

    Nelson-Cheeseman, Brittany; Santos, Tiffany; Bhattacharya, Anand

    2010-03-01

    Dimensionality is known to play a central role in the properties of strongly correlated systems. Here we investigate magnetism and transport in thin films of the Ruddlesden-Popper n=1 phase, La1-xSr1+xMnO4. Within this material, the MnO6-octahedra form two-dimensional perovskite sheets separated by an extra rocksalt layer. By fabricating high quality thin films with ozone-assisted molecular beam epitaxy, we study how the effects of epitaxial strain and intentional cation ordering, known as digital synthesis, influence the properties of this 2-dimensional manganite. For example, at the same Mn^3+:Mn^4+ ratio (2:1) as its fully spin-polarized 3D manganite counterpart, this two dimensional analog at x=1/3 only displays a spin glass phase below 20K in bulk. This is believed to result from a competition between superexchange and double exchange, as well as disordered Jahn-Teller distortions. However, in our films we find weak ferromagnetic order up to much higher temperatures in addition to a low temperature spin glass phase. We will discuss how strain and cation order effect the presence of this weak ferromagnetism.

  20. Mapping chemical/structural order in double perovskite Sr2-xGdxMnTiO6 by atomic resolution electron microscopy

    NASA Astrophysics Data System (ADS)

    Alvarez, Inmaculada; Biskup, Neven; Lopez, Maria; Garcia-Hernandez, Mar; Veiga, Luisa; Varela, Maria; UCM Collaboration; ORNL Collaboration; CSIC Collaboration

    2013-03-01

    We report on visualizing the chemical and structural order of double perovskite Sr2-xGdxMnTiO6. The antisite disorder of Mn and Ti is detected even at atomic scale at all x, resulting in Mn-rich and Ti-rich regions. For x ?0.75, the majority of manganese ions are in Mn3+ state and are centered in Jahn-Teller distorted MnO6octahedra. The Fourier transformation of atomic resolution images along the [110] zone axis reveals a superstructure that corresponds to the tilting of oxygen octahedra and that doubles the unit cell along [001]c. This superstructure is spatially inhomogeneous and coincides with the regions where B-site ion (Mn/Ti) is displaced along the [110] direction. We discuss these findings in the frame of possible local ferroelectricity and in the light of strong electroresistance observed in Sr1.25Gd0.75MnTiO6. Research at ORNL supported by the U.S. DOE-BES, Materials Sciences and Engineering Division, and also by ORNL's ShaRE User Program (sponsored by DOE-BES). Research at UCM supported by the ERC Starting Investigator Award and MAT2010-20117.

  1. Investigations on the Local Structures and the Spin Hamiltonian Parameters for Cu2+ in (90-x)TeO2-10GeO2-xWO3 Glasses

    NASA Astrophysics Data System (ADS)

    Feng, Chun-Rong; Jian, Jun; Chen, Xiao-Hong; Du, Quan; Wang, Ling

    2017-12-01

    The local structures and the spin Hamiltonian parameters (SHPs) for Cu2+ in (90-x)TeO2-10GeO2-xWO3 glasses are theoretically investigated at various WO3 concentrations (x=7.5, 15, 22.5 and 30 mol%). Subject to the Jahn-Teller effect, the [CuO6]10- groups are found to experience the small or moderate tetragonal elongation distortions (characterised by the relative tetragonal elongation ratios ρ≈0.35-3.09%) in C4 axis. With only three adjusted coefficients a, b and ω, the relevant model parameters (Dq, k and ρ) are described by the Fourier type and linear functions, respectively, and the measured concentration dependences of the d-d transition bands and SHPs are reproduced. The maximum of g∥ and the minimum of |A∥| at x=15 mol% are illustrated from the abrupt decrease of the copper-oxygen electron cloud admixtures or covalency and the obvious decline of the copper 3d-3s (4s) orbital admixtures due to the decreasing electron cloud density around oxygen ligands spontaneously bonding with Cu2+ and Te4+ (W6+), respectively.

  2. Spontaneous symmetry breaking by double lithium adsorption in polyacenes

    NASA Astrophysics Data System (ADS)

    Ortiz, Yenni. P.; Seligman, Thomas H.

    2010-12-01

    We show that adsorption of one lithium atom to polyacenes, i.e. chains of linearly fused benzene rings, will cause such chains to be slightly deformed. If we adsorb a second identical atom on the opposite side of the same ring, this deformation is dramatically enhanced despite the fact that a symmetric configuration seems possible. We argue, that this may be due to an instability of the Jahn-Teller type possibly indeed to a Peierls instability.

  3. Spontaneous symmetry breaking by double lithium adsorption in polyacenes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ortiz, Yenni. P.; Seligman, Thomas H.; Centro Internacional de Ciencias, Cuernavaca, Morelos

    2010-12-23

    We show that adsorption of one lithium atom to polyacenes, i.e. chains of linearly fused benzene rings, will cause such chains to be slightly deformed. If we adsorb a second identical atom on the opposite side of the same ring, this deformation is dramatically enhanced despite the fact that a symmetric configuration seems possible. We argue, that this may be due to an instability of the Jahn-Teller type possibly indeed to a Peierls instability.

  4. Renner-Teller effects in the photoelectron spectra of CNC, CCN, and HCCN.

    PubMed

    Coudert, Laurent H; Gans, Bérenger; Garcia, Gustavo A; Loison, Jean-Christophe

    2018-02-07

    The line intensity of photoelectron spectra when either the neutral or cationic species display a Renner-Teller coupling is derived and applied to the modeling of the photoelectron spectra of CNC, CCN, and HCCN. The rovibronic energy levels of these three radicals and of their cations are investigated starting from ab initio results. A model treating simultaneously the bending mode and the overall rotation is developed to deal with the quasilinearity problem in CNC + , CCN + , and HCCN and accounts for the large amplitude nature of their bending mode. This model is extended to treat the Renner-Teller coupling in CNC, CCN, and HCCN + . Based on the derived photoelectron line intensity, the photoelectron spectra of all three molecules are calculated and compared to the experimental ones.

  5. Structure-activity correlations in a nickel-borate oxygen evolution catalyst.

    PubMed

    Bediako, D Kwabena; Lassalle-Kaiser, Benedikt; Surendranath, Yogesh; Yano, Junko; Yachandra, Vittal K; Nocera, Daniel G

    2012-04-18

    An oxygen evolution catalyst that forms as a thin film from Ni(aq)(2+) solutions containing borate electrolyte (Ni-B(i)) has been studied by in situ X-ray absorption spectroscopy. A dramatic increase in catalytic rate, induced by anodic activation of the electrodeposited films, is accompanied by structure and oxidation state changes. Coulometric measurements correlated with X-ray absorption near-edge structure spectra of the active catalyst show that the nickel centers in activated films possess an average oxidation state of +3.6, indicating that a substantial proportion of nickel centers exist in a formal oxidation state of Ni(IV). In contrast, nickel centers in nonactivated films exist predominantly as Ni(III). Extended X-ray absorption fine structure reveals that activated catalyst films comprise bis-oxo/hydroxo-bridged nickel centers organized into sheets of edge-sharing NiO(6) octahedra. Diminished long-range ordering in catalyst films is due to their ostensibly amorphous nature. Nonactivated films display a similar oxidic nature but exhibit a distortion in the local coordination geometry about nickel centers, characteristic of Jahn-Teller distorted Ni(III) centers. Our findings indicate that the increase in catalytic activity of films is accompanied by changes in oxidation state and structure that are reminiscent of those observed for conversion of β-NiOOH to γ-NiOOH and consequently challenge the long-held notion that the β-NiOOH phase is a more efficient oxygen-evolving catalyst. © 2012 American Chemical Society

  6. Spin-orbit coupling, strong correlation, and insulator-metal transitions: The J eff = 3 2 ferromagnetic Dirac-Mott insulator Ba 2 NaOsO 6

    DOE PAGES

    Gangopadhyay, Shruba; Pickett, Warren E.

    2015-01-15

    The double perovskite Ba 2NaOsO 6 (BNOO), an exotic example of a very high oxidation state (heptavalent) osmium d1 compound and also uncommon by being a ferromagnetic open d-shell (Mott) insulator without Jahn-Teller (JT) distortion, is modeled using a density functional theory based hybrid functional incorporating exact exchange for correlated electronic orbitals and including the large spin-orbit coupling (SOC). The experimentally observed narrow-gap ferromagnetic insulating ground state is obtained, but only when including spin-orbit coupling, making this a Dirac-Mott insulator. The calculated easy axis along [110] is in accord with experiment, providing additional support that this approach provides a realisticmore » method for studying this system. The predicted spin density for [110] spin orientation is nearly cubic (unlike for other directions), providing an explanation for the absence of JT distortion. An orbital moment of –0.4μ B strongly compensates the +0.5μ B spin moment on Os, leaving a strongly compensated moment more in line with experiment. Remarkably, the net moment lies primarily on the oxygen ions. An insulator-metal transition, by rotating the magnetization direction with an external field under moderate pressure, is predicted as one consequence of strong SOC, and metallization under moderate pressure is predicted. In conclusion, a comparison is made with the isostructural, isovalent insulator Ba 2LiOsO 6, which, however, orders antiferromagnetically.« less

  7. Vibronic eigenstates and the geometric phase effect in the 2E″ state of NO3.

    PubMed

    Eisfeld, Wolfgang; Viel, Alexandra

    2017-01-21

    The 2 E″ state of NO 3 , a prototype for the Jahn-Teller effect, has been an enigma and a challenge for a long time for both experiment and theory. We present a detailed theoretical study of the vibronic quantum dynamics in this electronic state, uncovering the effects of tunnelling, geometric phase, and symmetry. To this end, 45 vibronic levels of NO 3 in the 2 E″ state are determined accurately and analyzed thoroughly. The computation is based on a high quality diabatic potential representation of the two-sheeted surface of the 2 E″ state developed by us [W. Eisfeld et al., J. Chem. Phys. 140, 224109 (2014)] and on the multi-configuration time dependent Hartree approach. The vibrational eigenstates of the NO 3 - anion are determined and analyzed as well to gain a deeper understanding of the symmetry properties of such D 3h symmetric systems. To this end, 61 eigenstates of the NO 3 - anion ground state are computed using the single sheeted potential surface of the 1 A 1 state published in the same reference quoted above. The assignments of both the vibrational and vibronic levels are discussed. A simple model is proposed to rationalize the computed NO 3 spectrum strongly influenced by the Jahn-Teller couplings, the associated geometric phase effect, and the tunnelling. Comparison with the available spectroscopic data is also presented.

  8. Teller Training Module: Off-Line Banking System. High-Technology Training Module.

    ERIC Educational Resources Information Center

    Lund, Candyce J.

    This teller training module on offline banking systems is intended to be part of a postsecondary financial applications course. The module contains the following sections: module objective; specific objective; content--electronic audit machine key functions, practice packet--sample bank transactions and practicing procedures, and…

  9. Detailed relationship between local structure, polarons, and magnetizationfor La1-xCaxMnO3 (0.21≤x≤0.45)

    NASA Astrophysics Data System (ADS)

    Bridges, F.; Downward, L.; Neumeier, J. J.; Tyson, T. A.

    2010-05-01

    We present detailed local structure measurements (using the extended x-ray absorption fine structure technique) for the colossal magnetoresistive material La1-xCaxMnO3 (0.21distortions of the Mn-O bonds are parameterized using σ , the width of the Mn-O pair-distribution function (PDF). After subtracting thermal phonon contributions, we show that the contributions to σ2 from polaron and Jahn-Teller (JT) distortions, σJT/polaron2 , are a universal function of the magnetization, independent of how the magnetization is achieved via changes in temperature or magnetic field. However this universal behavior is only observed for Bfields≥2T , likely as a result of domain canting in low B fields. The resulting curve is well described by two straight lines with significantly different slopes. These regimes represent two distinctly differ distortions of the oxygen octahedra about the Mn. For low magnetizations up to ˜65% of the theoretical maximum magnetization, MT , the slope is low and the distortion removed as the sample becomes magnetized is small—we argue this arises from polarons which have a low distortion around two (or possibly three) Mn sites. At high magnetizations large distortions per Mn site are removed as these sites become magnetized. The data are also analyzed in terms of a two Mn-O peak distribution using experimental standards for Mn-O. The results agree well with recent neutron PDF results but not with some earlier results. We discuss the limitations of assuming a two peak distribution in view of the two distortions needed to describe the Mn-O distortions as a function of T and B for B≥2T . It is likely that there is a distribution of longer bonds. Finally we show that with increasing B field, the Mn-Mn peak also has a small B -field-induced change—a measure at the unit cell level of magnetostriction but find that there is no observable B -field-induced change in the Mn

  10. Proton-Proton Fusion and Tritium β Decay from Lattice Quantum Chromodynamics

    NASA Astrophysics Data System (ADS)

    Savage, Martin J.; Shanahan, Phiala E.; Tiburzi, Brian C.; Wagman, Michael L.; Winter, Frank; Beane, Silas R.; Chang, Emmanuel; Davoudi, Zohreh; Detmold, William; Orginos, Kostas; Nplqcd Collaboration

    2017-08-01

    The nuclear matrix element determining the p p →d e+ν fusion cross section and the Gamow-Teller matrix element contributing to tritium β decay are calculated with lattice quantum chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor-symmetric value of the quark masses, corresponding to a pion mass of mπ˜806 MeV . The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within 2 σ of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated p p →d e+ν transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be L1 ,A=3.9 (0.2 )(1.0 )(0.4 )(0.9 ) fm3 at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.

  11. Anomalous Centrifugal Distortion in NH_2

    NASA Astrophysics Data System (ADS)

    Martin-Drumel, Marie-Aline; Pirali, Olivier; Coudert, L. H.

    2017-06-01

    The NH2 radical spectrum, first observed by Herzberg and Ramsay, is dominated by a strong Renner-Teller effect giving rise to two electronic states: the bent X ^{2}B_1 ground state and the quasi-linear A ^{2}A_1 excited state. The NH2 radical has been the subject of numerous high-resolution investigations and its electronic and ro-vibrational transitions have been measured. Using synchrotron radiation, new rotational transitions have been recently recorded and a value of the rotational quantum number N as large as 26 could be reached. In the X ^{2}B_1 ground state, the NH2 radical behaves like a triatomic molecule displaying spin-rotation splittings. Due to the lightness of the molecule, a strong coupling between the overall rotation and the bending mode arises whose effects increase with N and lead to the anomalous centrifugal distortion evidenced in the new measurements.^d In this talk the Bending-Rotation approach developed to account for the anomalous centrifugal distortion of the water molecule is modified to include spin-rotation coupling and applied to the fitting of high-resolution data pertaining to the ground electronic state of NH2. A preliminary line position analysis of the available data^{c,d} allowed us to account for 1681 transitions with a unitless standard deviation of 1.2. New transitions could also be assigned in the spectrum recorded by Martin-Drumel et al.^d In the talk, the results obtained with the new theoretical approach will be compared to those retrieved with a Watson-type Hamiltonian and the effects of the vibronic coupling between the ground X ^{2}B_1 and the excited A ^{2}A_1 electronic state will be discussed. Herzberg and Ramsay, J. Chem. Phys. 20 (1952) 347 Dressler and Ramsay, Phil. Trans. R. Soc. A 25 (1959) 553 Hadj Bachir, Huet, Destombes, and Vervloet, J. Molec. Spectrosc. 193 (1999) 326 McKellar, Vervloet, Burkholder, and Howard, J. Molec. Spectrosc. 142 (1990) 319 Morino and Kawaguchi, J. Molec. Spectrosc. 182 (1997) 428

  12. 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.

  13. Magnetoelastic couplings in the distorted diamond-chain compound azurite

    NASA Astrophysics Data System (ADS)

    Cong, Pham Thanh; Wolf, Bernd; Manna, Rudra Sekhar; Tutsch, Ulrich; de Souza, Mariano; Brühl, Andreas; Lang, Michael

    2014-05-01

    We present results of ultrasonic measurements on a single crystal of the distorted diamond-chain compound azurite Cu3(CO3)2(OH)2. Pronounced elastic anomalies are observed in the temperature dependence of the longitudinal elastic mode c22 which can be assigned to the relevant magnetic interactions in the system and their couplings to the lattice degrees of freedom. From a semiquantitative analysis of the magnetic contribution to c22 the magnetoelastic coupling G =∂J2/∂ɛb can be estimated, where J2 is the intradimer coupling constant and ɛb the strain along the intrachain b axis. We find an exceptionally large coupling constant of |G |˜ 3650 K highlighting an extraordinarily strong sensitivity of J2 against changes of the b-axis lattice parameter. These results are complemented by measurements of the hydrostatic pressure dependence of J2 by means of thermal expansion and magnetic susceptibility measurements performed both at ambient and finite hydrostatic pressure. We propose that a structural peculiarity of this compound, in which Cu2O6 dimer units are incorporated in an unusually stretched manner, is responsible for the anomalously large magnetoelastic coupling.

  14. Half-metallicity and tetragonal distortion in semi-Heusler alloy FeCrSe

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Huang, H. M., E-mail: smilehhm@163.com; Luo, S. J.; Yao, K. L.

    2014-01-28

    Full-potential linearized augmented plane wave methods are carried out to investigate the electronic structures and magnetic properties in semi-Heusler alloy FeCrSe. Results show that FeCrSe is half-metallic ferromagnet with the half-metallic gap 0.31 eV at equilibrium lattice constant. Calculated total magnetic moment of 2.00μ{sub B} per formula unit follows the Slater-Pauling rule quite well. Two kinds of structural changes are used to investigate the sensitivity of half-metallicity. It is found that the half-metallicity can be retained when lattice constant is changed by −4.56% to 3.52%, and the results of tetragonal distortion indicate the half-metallicity can be kept at the range ofmore » c/a ratio from 0.85 to 1.20. The Curie temperature, cohesive energy, and heat of formations of FeCrSe are also discussed.« less

  15. Size- and pressure-controlled ferromagnetism in LaCoO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Fita, I.; Markovich, V.; Mogilyansky, D.; Puzniak, R.; Wisniewski, A.; Titelman, L.; Vradman, L.; Herskowitz, M.; Varyukhin, V. N.; Gorodetsky, G.

    2008-06-01

    Magnetic properties of nanocrystalline LaCoO3 with particle size of 25, 30, 32, and 38 nm, prepared by the citrate method, were investigated in temperature range 2-320 K, magnetic field up to 50 kOe, and under hydrostatic pressure up to 11 kbar. All nanoparticles exhibit weak ferromagnetism below TC≈85K , in agreement with recent observation on LaCoO3 particles and tensile thin films. It was found that with decreasing particle size, i.e., with increasing the surface to volume ratio, the unit-cell volume increases monotonically due to the surface effect. The ferromagnetic moment increases as well, simultaneously with lattice expansion, whereas TC remains nearly unchanged. On the other hand, an applied hydrostatic pressure suppresses strongly the ferromagnetic phase leading to its full disappearance at 10 kbar, while the TC does not change visibly under pressure. It appears that the ferromagnetism in LaCoO3 nanoparticles is controlled by the unit-cell volume. This clear correlation suggests that the nature of ferromagnetic ground state of LaCoO3 is likely related to orbitally ordered Jahn-Teller active Co3+ ions with intermediate-spin (IS) state, which may persist in the expanded lattice at low temperatures. A robust orbital order presumed among the IS Co3+ species can explain the very stable TC observed for LaCoO3 samples prepared under different conditions: single crystal powders, nanoparticles, and thin films.

  16. Minor Distortions with Major Consequences: Correcting Distortions in Imaging Spectrographs

    PubMed Central

    Esmonde-White, Francis W. L.; Esmonde-White, Karen A.; Morris, Michael D.

    2010-01-01

    Projective transformation is a mathematical correction (implemented in software) used in the remote imaging field to produce distortion-free images. We present the application of projective transformation to correct minor alignment and astigmatism distortions that are inherent in dispersive spectrographs. Patterned white-light images and neon emission spectra were used to produce registration points for the transformation. Raman transects collected on microscopy and fiber-optic systems were corrected using established methods and compared with the same transects corrected using the projective transformation. Even minor distortions have a significant effect on reproducibility and apparent fluorescence background complexity. Simulated Raman spectra were used to optimize the projective transformation algorithm. We demonstrate that the projective transformation reduced the apparent fluorescent background complexity and improved reproducibility of measured parameters of Raman spectra. Distortion correction using a projective transformation provides a major advantage in reducing the background fluorescence complexity even in instrumentation where slit-image distortions and camera rotation were minimized using manual or mechanical means. We expect these advantages should be readily applicable to other spectroscopic modalities using dispersive imaging spectrographs. PMID:21211158

  17. Effect of temperature on the electronic instability and the crystalline phase change at low temperature of V3Si type compounds

    NASA Technical Reports Server (NTRS)

    Labbe, J.; Friedel, J.

    1977-01-01

    Equations assuming a Jahn-Teller type effect for the d band electrons in V3Si compounds are given, and the results of free-energy change calculations by using some approximations based on these equations are depicted. The tetragonal structure is converted to cubic as the temperature rises past T sub m which is calculated as 13 K. by the Batterman-Barrett method and is measured to be 20-5 K. Other parameters such as change of C sub p with temperature are predicted better.

  18. Flexible 2D Crystals of Polycyclic Aromatics Stabilized by Static Distortion Waves.

    PubMed

    Meissner, Matthias; Sojka, Falko; Matthes, Lars; Bechstedt, Friedhelm; Feng, Xinliang; Müllen, Klaus; Mannsfeld, Stefan C B; Forker, Roman; Fritz, Torsten

    2016-07-26

    The epitaxy of many organic films on inorganic substrates can be classified within the framework of rigid lattices which helps to understand the origin of energy gain driving the epitaxy of the films. Yet, there are adsorbate-substrate combinations with distinct mutual orientations for which this classification fails and epitaxy cannot be explained within a rigid lattice concept. It has been proposed that tiny shifts in atomic positions away from ideal lattice points, so-called static distortion waves (SDWs), are responsible for the observed orientational epitaxy in such cases. Using low-energy electron diffraction and scanning tunneling microscopy, we provide direct experimental evidence for SDWs in organic adsorbate films, namely hexa-peri-hexabenzocoronene on graphite. They manifest as wave-like sub-Ångström molecular displacements away from an ideal adsorbate lattice which is incommensurate with graphite. By means of a density-functional-theory based model, we show that, due to the flexibility in the adsorbate layer, molecule-substrate energy is gained by straining the intermolecular bonds and that the resulting total energy is minimal for the observed domain orientation, constituting the orientational epitaxy. While structural relaxation at an interface is a common assumption, the combination of the precise determination of the incommensurate epitaxial relation, the direct observation of SDWs in real space, and their identification as the sole source of epitaxial energy gain constitutes a comprehensive proof of this effect.

  19. Flexible 2D Crystals of Polycyclic Aromatics Stabilized by Static Distortion Waves

    PubMed Central

    2016-01-01

    The epitaxy of many organic films on inorganic substrates can be classified within the framework of rigid lattices which helps to understand the origin of energy gain driving the epitaxy of the films. Yet, there are adsorbate–substrate combinations with distinct mutual orientations for which this classification fails and epitaxy cannot be explained within a rigid lattice concept. It has been proposed that tiny shifts in atomic positions away from ideal lattice points, so-called static distortion waves (SDWs), are responsible for the observed orientational epitaxy in such cases. Using low-energy electron diffraction and scanning tunneling microscopy, we provide direct experimental evidence for SDWs in organic adsorbate films, namely hexa-peri-hexabenzocoronene on graphite. They manifest as wave-like sub-Ångström molecular displacements away from an ideal adsorbate lattice which is incommensurate with graphite. By means of a density-functional-theory based model, we show that, due to the flexibility in the adsorbate layer, molecule–substrate energy is gained by straining the intermolecular bonds and that the resulting total energy is minimal for the observed domain orientation, constituting the orientational epitaxy. While structural relaxation at an interface is a common assumption, the combination of the precise determination of the incommensurate epitaxial relation, the direct observation of SDWs in real space, and their identification as the sole source of epitaxial energy gain constitutes a comprehensive proof of this effect. PMID:27014920

  20. Sun Oven Grown Cuprates Superconductivity and Periodic Lattice Distortions PLD

    NASA Astrophysics Data System (ADS)

    Acrivos, Juana V.; Chidvinadze, J. G.; Gulanova, D. D.; Loy, D.

    2011-03-01

    Bi 1.7 Pb 0.3 Sr 2 Ca n-1 Cu n O4 + 2 n + δ identified by the layer heavy element composition with substitution, s (2 s :2:n-1:n > 2) cuprates grown by green chemistry, transition temperatures to superconductivity Tc = 87 to 150K are related to their structure. Enhanced XRD at energies near but below the Cu K, and Pb and Bi L3-edges for pure n=2, 3 phases show Darwin shaped preferred [HKL] reflections that identify the magnitude of the allowed transition moment from the core state to extended unoccupied states determined by the electron density symmetry in that plane, confirmed by XAS of 3 μ m thick films. Weak PLD are still detected, but the stability gained by substitution of Bi by Pb is the formation of nearly symmetric Pb8 cubes in (2s : 2 : 1 : 2)13 and (2s < formula > < ? TeX super-lattices. The preferred 2D [HKL] reflection planes play the same role in the chemical activity of 3D solids as the linear bonds do in molecular reactions, governed by scattering dependent on the electron density symmetry in their highest and lowest unoccupied states. Supported by US NSF, Dreyfus, DOE Laboratories SSRL-SLAC, STUC-Ukraine and Georgia NSF.

  1. GeneStoryTeller: a mobile app for quick and comprehensive information retrieval of human genes

    PubMed Central

    Eleftheriou, Stergiani V.; Bourdakou, Marilena M.; Athanasiadis, Emmanouil I.; Spyrou, George M.

    2015-01-01

    In the last few years, mobile devices such as smartphones and tablets have become an integral part of everyday life, due to their software/hardware rapid development, as well as the increased portability they offer. Nevertheless, up to now, only few Apps have been developed in the field of bioinformatics, capable to perform fast and robust access to services. We have developed the GeneStoryTeller, a mobile application for Android platforms, where users are able to instantly retrieve information regarding any recorded human gene, derived from eight publicly available databases, as a summary story. Complementary information regarding gene–drugs interactions, functional annotation and disease associations for each selected gene is also provided in the gene story. The most challenging part during the development of the GeneStoryTeller was to keep balance between storing data locally within the app and obtaining the updated content dynamically via a network connection. This was accomplished with the implementation of an administrative site where data are curated and synchronized with the application requiring a minimum human intervention. Database URL: http://bioserver-3.bioacademy.gr/Bioserver/GeneStoryTeller/. PMID:26055097

  2. Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle: Reduced Conductivity of Fe-Bridgmanite

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo

    Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core-mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure-induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermalmore » conductivity of Fe-bearing bridgmanite to 120 GPa using optical pump-probe spectroscopy. The conductivity of Fe-bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.« less

  3. Influence of the Renner-Teller Coupling in CO+H Collision Dynamics

    NASA Astrophysics Data System (ADS)

    Ndengue, Steve Alexandre; Dawes, Richard

    2017-06-01

    Carbon monoxide is after molecular hydrogen the second most abundant molecule in the universe and an important molecule for processes occurring in the atmosphere, hydrocarbon combustion and the interstellar medium. The rate coefficients of CO in collision with dominant species like H, H_2, He, etc are necessary to understand the CO emission spectrum or to model combustion chemistry processes. The inelastic scattering of CO with H has been intensively studied theoretically in the past decades,^1 mostly using the so-called WKS PES^6 developed by Werner et al. or recently a modified version by Song et al.^2 Though the spectroscopic agreement of the WKS surface with experiment is quite good, so far the studies of scattering dynamics have neglected coupling to an electronic excited state. We present new results on a set of HCO surfaces of the ground and the excited Renner-Teller coupled electronic states^3 with the principal objective of studying the influence of the Renner-Teller coupling on the inelastic scattering of CO+H. Our calculations done using the MCTDH^4 algorithm in the 0-2 eV energy range allow evaluation of the contribution of the Renner-Teller coupling on the rovibrationally inelastic scattering and discuss the relevance and reliability of the calculations. References:} 1. N. Balakrishnan, M. Yan and A. Dalgarno, Astrophys. J. 568, 443 (2002); B.C. Shepler et al, Astron. & Astroph. 475, L15 (2007); L. Song et al, J. Chem. Phys. 142, 204303 (2015); K.M. Walker et al, Astroph. J. 811, 27 (2015). 2. L. Song et al, Astrophys. J. 813, 96 (2015). 3. H.-M. Keller et al, J. Chem. Phys. 105, 4983 (1996). 4. S. Ndengue, R. Dawes and H. Guo, J. Chem. Phys. 144, 244301 (2016). 5. M.H. Beck et al., Phys. Rep. 324, 1 (2000).

  4. Raman dispersion spectroscopy on the highly saddled nickel(II)-octaethyltetraphenylporphyrin reveals the symmetry of nonplanar distortions and the vibronic coupling strength of normal modes

    NASA Astrophysics Data System (ADS)

    Schweitzer-Stenner, Reinhard; Stichternath, Andreas; Dreybrodt, Wolfgang; Jentzen, Walter; Song, Xing-Zhi; Shelnutt, John A.; Nielsen, Ole Faurskov; Medforth, Craig J.; Smith, Kevin M.

    1997-08-01

    -displacements, whereas the |Q>-state is subject to A2g, B1g, and B2g displacements of its equilibrium configuration. While the former is induced by the combined effect of ruffling and saddling, the latter arises from Jahn-Teller coupling within the degenerate states.

  5. Time-of-flight neutron powder diffraction study on the third row transition metal hexafluorides WF6, OsF6, and PtF6

    NASA Astrophysics Data System (ADS)

    Marx, R.; Seppelt, K.; Ibberson, R. M.

    1996-05-01

    A neutron diffraction study on the third-row transition metal hexafluorides MF6 (M≡W, Os, Pt) has been performed using the high resolution neutron powder diffractometer (HRPD) at the spallation source ISIS, England. The previously unknown structures of the low-temperature phases of OsF6 and PtF6 are reported. WF6, OsF6, and PtF6, which exhibit a (5dt2g)0, (5dt2g)2, and (5dt2g)4 electronic configuration, respectively, are found to be isostructural and crystallize in the UF6 structure, space group Pmnb, (No. 62). The geometry of the MF6 molecules is to good approximation octahedral for each compound, the mean M-F bond length increasing only slightly from 182.5 (W) to 185.0 (Pt). For WF6 deviations from ideal octahedral geometry are only marginally significant [181.8(2) to 183.2(2) pm] and may be interpreted on the basis of packing effects. Deviations for the d2 complex OsF6 are somewhat larger [181.5(2) to 184.4(3) pm] and may be assumed to be caused by packing effects essentially the same as for WF6, in addition to a first-order Jahn-Teller effect arising from the (5dt2g)2 electronic configuration. While eliminating the effects of packing by a comparison of individual M-F bond lengths for WF6 and OsF6, the OsF6 molecule shows to have D4h symmetry with two apical M-F bonds about 1.8 pm longer than the four equatorial bonds as a result of the Jahn-Teller distortion. Only small deviations from ideal octahedral geometry [184.4(3) to 185.8(3) pm] are found for the d4 complex PtF6. Within the series W to Pt a substantial shortening of the F...F van der Waals contact distances is observed. This shortening more than compensates for the increase in the M-F bond lengths and leads to unit cell volumes and cell parameters decreasing continuously from W to Pt. The variation of F...F contact distances and M-F bond lengths may be rationalized in terms of polarization of the F-ligands in the field of the highly charged nuclei of the central atoms which are only incompletely

  6. Enantiopure distorted ribbon-shaped nanographene combining two-photon absorption-based upconversion and circularly polarized luminescence.

    PubMed

    Cruz, Carlos M; Márquez, Irene R; Mariz, Inês F A; Blanco, Victor; Sánchez-Sánchez, Carlos; Sobrado, Jesús M; Martín-Gago, José A; Cuerva, Juan M; Maçôas, Ermelinda; Campaña, Araceli G

    2018-04-28

    Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of ca. 2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a [5]carbohelicene moiety. This system is shown to combine two-photon absorption and circularly polarized luminescence and a remarkably long emission lifetime of 21.5 ns. The [5]helicene is responsible for the chiroptical activity while the push-pull geometry and the extended network of sp 2 carbons are factors favoring the nonlinear absorption. Electronic structure theoretical calculations support the interpretation of the results.

  7. Ferroelectric and paraelectric Ba0.5Sr0.5TiO3 film structure distortions at room temperature and their effects on tunable microwave properties

    NASA Astrophysics Data System (ADS)

    Alldredge, L. M. B.; Chang, Wontae; Qadri, Syed B.; Kirchoefer, Steven W.; Pond, Jeffrey M.

    2007-05-01

    Sputter-deposited Ba0.5Sr0.5TiO3 films on (001) MgO were characterized for their dielectric properties with different lattice structures. With varying Ar :O2 ratios during deposition, the films showed either in-plane (ca) tetragonal distortions, significantly affecting the dielectric constant and tunability. The dielectric constant exhibited clear hysteresis with dc bias at room temperature, indicating that the films were ferroelectric. The relationship between the dielectric properties and the distortions was the reverse of that observed in films deposited by pulsed laser deposition. The anisotropic in-plane dielectric behavior can be understood by relating polarization to film distortions and to the presence of permanent dipoles.

  8. Removal of Lattice Imperfections that Impact the Optical Quality of Ti:Sapphire using Advanced Magnetorheological Finishing Techniques

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Menapace, J A; Schaffers, K I; Bayramian, A J

    2007-10-09

    Ti:sapphire has become the premier lasing medium material for use in solid-state femtosecond high-peak power laser systems because of its wide wavelength tuning range. With a tuneable range from 680 to 1100 nm, peaking at 800 nm, Ti:sapphire lasing crystals can easily be tuned to the required pump wavelength and provide very high pump brightness due to their good beam quality and high output power of typically several watts. Femtosecond lasers are used for precision cutting and machining of materials ranging from steel to tooth enamel to delicate heart tissue and high explosives. These ultra-short pulses are too brief tomore » transfer heat or shock to the material being cut, which means that cutting, drilling, and machining occur with virtually no damage to surrounding material. Furthermore, these lasers can cut with high precision, making hairline cuts of less than 100 microns in thick materials along a computer-generated path. Extension of laser output to higher energies is limited by the size of the amplification medium. Yields of high quality large diameter crystals have been constrained by lattice distortions that may appear in the boule limiting the usable area from which high quality optics can be harvested. Lattice distortions affect the transmitted wavefront of these optics which ultimately limits the high-end power output and efficiency of the laser system, particularly when operated in multi-pass mode. To make matters even more complicated, Ti:sapphire is extremely hard (Mohs hardness of 9 with diamond being 10) which makes it extremely difficult to accurately polish using conventional methods without subsurface damage or significant wavefront error. In this presentation, we demonstrate for the first time that Magnetorheological finishing (MRF) can be used to compensate for the lattice distortions in Ti:sapphire by perturbing the transmitted wavefront. The advanced MRF techniques developed allow for precise polishing of the optical inverse of lattice

  9. Reducing Field Distortion in Magnetic Resonance Imaging

    NASA Technical Reports Server (NTRS)

    Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob

    2010-01-01

    A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

  10. Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses

    NASA Astrophysics Data System (ADS)

    Haglund, Peter; Frostevarg, Jan; Powell, John; Eriksson, Ingemar; Kaplan, Alexander F. H.

    2018-03-01

    Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.

  11. Theoretical formulation of optical conductivity of La0.7Ca0.3MnO3 exhibiting paramagnetic insulator - ferromagnetic metal transition

    NASA Astrophysics Data System (ADS)

    Satiawati, L.; Majidi, M. A.

    2017-07-01

    A theory of high-energy optical conductivity of La0.7Ca0.3MnO3 has been proposed previously. The proposed theory works to explain the temperature-dependence of the optical conductivity for the photon energy region above ˜0.5 eV for up to ˜22 eV, but fails to capture the correct physics close to the dc limit in which metal-insulator transition occurs. The missing physics at the low energy has been acknowledged as mainly due to not incorporating phonon degree of freedom and electron-phonon interactions. In this study, we aim to complete the above theory by proposing a more complete Hamiltonian incorporating additional terms such as crystal field, two modes of Jahn-Teller vibrations, and coupling between electrons and the two Jahn-Teller vibrational modes. We solve the model by means of dynamical mean-field theory. At this stage, we aim to derive the analytical formulae involved in the calculation, and formulate the algorithmic implementation for the self-consistent calculation process. Our final goal is to compute the density of states and the optical conductivity for the complete photon energy range from 0 to 22 eV at various temperatures, and compare them with the experimental data. We expect that the improved model preserves the correct temperature-dependent physics at high photon energies, as already captured by the previous model, while it would also reveal ferromagnetic metal - paramagnetic insulator transition at the dc limit.

  12. Theoretical study of the local structures and the EPR parameters for RLNKB glasses with VO2+ and Cu2+ dopants

    NASA Astrophysics Data System (ADS)

    Ding, Chang-Chun; Wu, Shao-Yi; Wu, Li-Na; Zhang, Li-Juan; Peng, Li; Wu, Ming-He; Teng, Bao-Hua

    2018-02-01

    The electron paramagnetic resonance (EPR) parameters and local structures for impurities VO2+ and Cu2+ in RO-Li2O-Na2O-K2O-B2O3 (RLNKB; R = Zn, Mg, Sr and Ba) glasses are theoretically investigated by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral 3d1 and tetragonally elongated octahedral 3d9 clusters, respectively. The VO2+ and Cu2+ dopants are found to undergo the tetragonal compression (characterized by the negative relative distortion ratios ρ ≈ -3%, -0.98%, -1% and -0.8% for R = Zn, Mg, Sr and Ba) and elongation (characterized by the positive relative distortion ratios ρ ≈ 29%, 17%, 16% and 28%), respectively, due to the Jahn-Teller effect. Both dopants show similar overall decreasing trends of cubic field parameter Dq and covalency factor N with decreasing electronegativity of alkali earth cation R. The conventional optical basicities Λth and local optical basicities Λloc are calculated for both systems, and the local Λloc are higher for Cu2+ than for VO2+ in the same RLNKB glass, despite the opposite relationship for the conventional Λth. This point is supported by the weaker covalency or stronger ionicity for Cu2+ than VO2+ in the same RLNKB system, characterized by the larger N in the former. The above comparative analysis on the spectral and local structural properties would be helpful to understand structures and spectroscopic properties for the similar oxide glasses with transition-metal dopants of complementary electronic configurations.

  13. Ab Initio Ligand Field Molecular Mechanics and the Nature of Metal-Ligand π-Bonding in Fe(II) 2,6-di(pyrazol-1-yl)pyridine Spin Crossover Complexes.

    PubMed

    Deeth, Robert J; Halcrow, Malcolm A; Kershaw Cook, Laurence J; Raithby, Paul R

    2018-04-06

    A ligand field molecular mechanics (LFMM) force field has been constructed for the spin states of [Fe(bpp) 2 ] 2+ (bpp=2,6-di(pyrazol-1-yl)pyridine) and related complexes. A new charge scheme is employed which interpolates between partial charges for neutral bpp and protonated [H 3 bpp] 3+ to achieve a target metal charge. The LFMM angular overlap model (AOM) parameters are fitted to fully ab initio d orbital energies. However, several AOM parameter sets are possible. The ambiguity is resolved by calculating the Jahn-Teller distortion mode for high spin, which indicates that in [Fe(bpp) 2 ] 2+ pyridine is a π-acceptor and pyrazole a weak π-donor. The alternative fit, assumed previously, where both ligands act as π-donors leads to an inconsistent distortion. LFMM optimisations in the presence of [BF 4 ] - or [PF 6 ] - anions are in good agreement with experiment and the model also correctly predicts the spin state energetics for 3-pyrazolyl substituents where the interactions are mainly steric. However, for 4-pyridyl or 4-pyrazolyl substituents, LFMM only treats the electrostatic contribution which, for the pyridyl substituents, generates a fair correlation with the spin crossover transition temperatures, T 1/2 , but in the reverse sense to the dominant electronic effect. Thus, LFMM generates its smallest spin state energy difference for the substituent with the highest T 1/2 . One parameter set for all substituted bpp ligands is insufficient and further LFMM development will be required. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. New functional materials AC3B4O12 (Review)

    NASA Astrophysics Data System (ADS)

    Vasil'ev, A. N.; Volkova, O. S.

    2007-11-01

    The physical properties of perovskites of the type AC3B4O12, whose structure derives from simple perovskites ABO3, are reviewed. The A position is subject to strong structural distortions and splits into two new positions A and C. In the structure of AC3B4O12 vacancies and any cations with a large radius, irrespective of their charge state, can be present in the icosahedral environment of A: Na +, Cd2+, Ca2+, Sr2+, Y3+, Ln3+, and Nd4+. The C position in the square environment of oxygen can be occupied only by the Jahn-Teller cations Cu2+ and Mn3+. Transition and nontransition metal ions—Mn3+, Fe3+, Al3+, Cr3+, Ti4+, Mn4+, Ge4+, Ru4+, Ir4+, Ta5+, Nb5+, Ta5+, Sb5+—can occupy the B position in an octahedral environment. Some members of the family of complex perovskites possess properties which are characteristic for systems with heavy fermions; collinear and noncollinear magnetic structures with high ordering temperatures occur in these materials; tunneling magnetoresistance and high permittivity are observed. The diversity and unique properties make these materials attractive for practical applications.

  15. An Angular Overlap Model for Cu(II) Ion in the AMOEBA Polarizable Force Field

    PubMed Central

    Xiang, Jin Yu; Ponder, Jay W.

    2014-01-01

    An extensible polarizable force field for transition metal ion was developed based on AMOEBA and the angular overlap model (AOM) with consistent treatment of electrostatics for all atoms. Parameters were obtained by fitting molecular mechanics (MM) energies to various ab initio gas-phase calculations. The results of parameterization were presented for copper (II) ion ligated to water and model fragments of amino acid residues involved in the copper binding sites of type 1 copper proteins. Molecular dynamics (MD) simulations were performed on aqueous copper (II) ion at various temperatures, as well as plastocyanin (1AG6) and azurin (1DYZ). Results demonstrated that the AMOEBA-AOM significantly improves the accuracy of classical MM in a number of test cases when compared to ab initio calculations. The Jahn-Teller distortion for hexa-aqua copper (II) complex was handled automatically without specifically designating axial and in-plane ligands. Analyses of MD trajectories resulted in a 6-coordination first solvation shell for aqueous copper (II) ion and a 1.8ns average residence time of water molecules. The ensemble average geometries of 1AG6 and 1DYZ copper binding sites were in general agreement with X-ray and previous computational studies. PMID:25045338

  16. Electronic Structure of Ethynyl Substituted Cyclobutadienes

    NASA Astrophysics Data System (ADS)

    Emmert, Frank Lee Emmert, III; Thompson, Stephanie J.; Slipchenko, Lyudmila V.

    2011-06-01

    We investigated the effects of ethynyl substitution on the electronic structure of cyclobutadiene. These species are involved in Bergman Cyclization reactionsand are possible intermediates in the formation of fullerenes and graphite sheets. Prediction of the electronic energy of cyclobutadiene is challenging for single-reference ab initio methods such as HF, MP2 or DFT because of Jahn-Teller distortions and the diradical character of the singlet state. We determined the vertical and adiabatic singlet-triplet energy splittings, the natural charges and spin densities in substituted cyclobutadienes, using the equations of motion spin flip coupled cluster with single and double excitations (EOM-SF-CCSD) method that accurately describes diradical states. The adiabatic singlet-triplet gaps decrease upon substituent addition, but the singlet state is always lower in energy. However, we found that the results are affected by spin-contamination of the reference state and deteriorate when an unrestricted HF reference is employed. O. L. Chapman, C. L. McIntosh, J. Pacansky, "Cyclobutadiene" J. Am. Chem. Soc. 1973, 95, (2), 614-617. N. S. Goroff, "Mechanism of Fullerene Formation." Acc. Chem. Res. 1996, 29, (2), 77-83. L.V. Slipchenko and A.I. Krylov, "Singlet-triplet gaps in diradicals by the Spin-Flip approach: A benchmark study", J. Chem. Phys. 2002, 117, 4694-4708.

  17. Ba3CuOs2O9 and Ba3ZnOs2O9, a comparative study

    NASA Astrophysics Data System (ADS)

    Feng, Hai L.; Jansen, Martin

    2018-02-01

    Polycrystalline samples of Ba3CuOs2O9 and Ba3ZnOs2O9 were synthesized by solid-state reactions. Ba3CuOs2O9 crystallizes in Cmcm, while Ba3ZnOs2O9 adopts the hexagonal space group P63/mmc. Both the crystal structures consist of face-sharing Os-centered octahedra forming dimer-like Os2O9 units, which are interconnected by corner-sharing CuO6, or ZnO6 octahedra, respectively. In Ba3CuOs2O9, the CuO6 octahedra show a characteristic Jahn-Teller distortion. Both, Ba3CuOs2O9 and Ba3ZnOs2O9, are electrically insulating. Magnetic and specific heat measurements confirm that Ba3CuOs2O9 is antiferromagnetically ordered below 47 K. Analysis of the magnetic data indicated that its magnetic properties are dominated by Cu2+ ions. The magnetic susceptibility of Ba3ZnOs2O9 is weakly temperature-dependent with a broad maximum ≈ 280 K, indicating the presence of strong exchange interactions within the Os2O9 dimer. The residual magnetic susceptibility at low temperatures also suggests the presence of appreciable exchange coupling between the dimers.

  18. Negative Ion Photoelectron Spectroscopy Confirms the Prediction that D-3h Carbontrioxide (CO 3) Has a Singlet Ground State

    DOE PAGES

    Hrovat, David; Hou, Gao-Lei; Chen, Bo; ...

    2015-11-13

    The CO 3 radical anion (CO 3 •–) has been formed by electrospraying carbonate dianion (CO 3 2–) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO 3 •– shows that, unlike trimethylenemethane [C(CH 2) 3], carbontrioxide (CO 3) has a singlet ground state. From the NIPE spectrum, the electron affinity of CO 3 was determined to be EA = 4.06 ± 0.03 eV, and the singlet-triplet energy difference was found to be ΔEST = - 17.8 ± 0.9 kcal/mol. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO 3 aremore » very close in energy, a prediction that is confirmed by the relative intensities of the bands in the NIPE spectrum of CO 3 •–. The 560 cm -1 vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as 3A 1, in which both unpaired electrons reside in σ MOs, rather than 3A 2, in which one unpaired electron occupies the b 2 σ MO, and the other occupies the b 1 π MO.« less

  19. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bazante, Alexandre P., E-mail: abazante@chem.ufl.edu; Bartlett, Rodney J.; Davidson, E. R.

    The benzene radical anion is studied with ab initio coupled-cluster theory in large basis sets. Unlike the usual assumption, we find that, at the level of theory investigated, the minimum energy geometry is non-planar with tetrahedral distortion at two opposite carbon atoms. The anion is well known for its instability to auto-ionization which poses computational challenges to determine its properties. Despite the importance of the benzene radical anion, the considerable attention it has received in the literature so far has failed to address the details of its structure and shape-resonance character at a high level of theory. Here, we examinemore » the dynamic Jahn-Teller effect and its impact on the anion potential energy surface. We find that a minimum energy geometry of C{sub 2} symmetry is located below one D{sub 2h} stationary point on a C{sub 2h} pseudo-rotation surface. The applicability of standard wave function methods to an unbound anion is assessed with the stabilization method. The isotropic hyperfine splitting constants (A{sub iso}) are computed and compared to data obtained from experimental electron spin resonance experiments. Satisfactory agreement with experiment is obtained with coupled-cluster theory and large basis sets such as cc-pCVQZ.« less

  20. Synthesis and characterization of cathode materials for lithium ion-rechargeable batteries

    NASA Astrophysics Data System (ADS)

    Nieto Ramos, Santander

    Lithium intercalation materials are of special interest for cathodes in rechargeable lihium-ion batteries, because they are capable of reversibly intercalating lithium ions without altering the main unit. We developed a novel solution-based route for the synthesis of these lithium intercalates oxides. The first part of this work was devoted to the optimization of chemical solution process parameters in order to correlate their electrochemical properties. It was found that the lattice parameters and the crystallite size increase, whereas the lattice strain decreases with the increase in calcinations temperature. Powders annealed at 700°C for 15 h yielded best electrochemical performance. The electrochemical performance of substituted Li1.2Mn2O 4, Li1.2Mn1.8O4, Li1.2Cr 0.05Mn1.95O4, and Li1.2Cr0.05 Mn1.75O4 spinel electrodes in lithium cell has been studied. The electrochemical data showed that the Li and Cr dopant effect improves the cycleablility of spinel LiMn2O4 electrodes. The second part of this dissertation was devoted to improve the rate capabilities of these cathode materials by growing nano-size cathode particles and also by cation co-doping. Though the discharge capacity of these nano-crystalline cathodes was equivalent to their microcrystalline counterpart, these exhibited capacity fading in the 4V range. Through a combined X-ray diffraction, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses, we correlated the observed capacity fading with the onset of Jahn-Teller (J-T) distortion toward the end of the discharge in the cut-off limit between 4.2 and 3.2V. It was postulated that J-T distortion is the dominant fading mechanism of these nano-crystalline cathodes then by increasing the average oxidation state of the Mn ion in a virgin lithium manganate cathode, the onset of such distortion towards the end of the discharge could be delayed, and therefore, the cycleability of these cathodes could be improved. By synthesizing lithium

  1. Spontaneous symmetry breaking and strong deformations in metal adsorbed graphene sheets

    NASA Astrophysics Data System (ADS)

    Jalbout, A. F.; Ortiz, Y. P.; Seligman, T. H.

    2013-03-01

    We study the adsorption of Li to graphene flakes simulated as aromatic molecules. Surprisingly the out of plane deformation is much stronger for the double adsorption from both sides to the same ring than for a single adsorption, although a symmetric solution seems possible. We thus have an interesting case of spontaneous symmetry breaking. While we cannot rule out a Jahn Teller deformation with certainty, this explanation seems unlikely and other options are discussed. We find a similar behavior for boron-nitrogen sheets, and also for other light alkalines as adsorbants.

  2. Origin of Spinel Nanocheckerboards via First Principles

    NASA Astrophysics Data System (ADS)

    Kornbluth, Mordechai; Marianetti, Chris A.

    2015-06-01

    Self-organizing nanocheckerboards have been experimentally fabricated in Mn-based spinels but have not yet been explained with first principles. Using density-functional theory, we explain the phase diagram of the ZnMnxGa2 -xO4 system and the origin of nanocheckerboards. We predict total phase separation at zero temperature and then show the combination of kinetics, thermodynamics, and Jahn-Teller physics that generates the system's observed behavior. We find that the {011 } surfaces are strongly preferred energetically, which mandates checkerboard ordering by purely geometrical considerations.

  3. Investigation of Gamow Teller transition properties in 56-64Ni isotopes using QRPA methods

    NASA Astrophysics Data System (ADS)

    Cakmak, Sadiye; Nabi, Jameel-Un; Babacan, Tahsin

    2018-02-01

    Weak rates in nickel isotopes play an integral role in the dynamics of supernovae. Electron capture and β-decay of nickel isotopes, dictated by Gamow-Teller transitions, significantly alter the lepton fraction of the stellar matter. In this paper we calculate Gamow-Teller (GT) transitions for isotopes of nickel, Ni6456-, using QRPA methods. The GT strength distributions were calculated using four different QRPA models. Our results are also compared with previous theoretical calculations and measured strength distributions wherever available. Our investigation concluded that amongst all RPA models, the pn-QRPA(C) model best described the measured GT distributions (including total GT strength and centroid placement). It is hoped that the current investigation of GT properties would prove handy and may lead to a better understanding of the presupernova evolution of massive stars.

  4. Formal verification of automated teller machine systems using SPIN

    NASA Astrophysics Data System (ADS)

    Iqbal, Ikhwan Mohammad; Adzkiya, Dieky; Mukhlash, Imam

    2017-08-01

    Formal verification is a technique for ensuring the correctness of systems. This work focuses on verifying a model of the Automated Teller Machine (ATM) system against some specifications. We construct the model as a state transition diagram that is suitable for verification. The specifications are expressed as Linear Temporal Logic (LTL) formulas. We use Simple Promela Interpreter (SPIN) model checker to check whether the model satisfies the formula. This model checker accepts models written in Process Meta Language (PROMELA), and its specifications are specified in LTL formulas.

  5. Restoring the lattice of Si-based atom probe reconstructions for enhanced information on dopant positioning.

    PubMed

    Breen, Andrew J; Moody, Michael P; Ceguerra, Anna V; Gault, Baptiste; Araullo-Peters, Vicente J; Ringer, Simon P

    2015-12-01

    The following manuscript presents a novel approach for creating lattice based models of Sb-doped Si directly from atom probe reconstructions for the purposes of improving information on dopant positioning and directly informing quantum mechanics based materials modeling approaches. Sophisticated crystallographic analysis techniques are used to detect latent crystal structure within the atom probe reconstructions with unprecedented accuracy. A distortion correction algorithm is then developed to precisely calibrate the detected crystal structure to the theoretically known diamond cubic lattice. The reconstructed atoms are then positioned on their most likely lattice positions. Simulations are then used to determine the accuracy of such an approach and show that improvements to short-range order measurements are possible for noise levels and detector efficiencies comparable with experimentally collected atom probe data. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. Imaging nanoscale lattice variations by machine learning of x-ray diffraction microscopy data

    DOE PAGES

    Laanait, Nouamane; Zhang, Zhan; Schlepütz, Christian M.

    2016-08-09

    In this paper, we present a novel methodology based on machine learning to extract lattice variations in crystalline materials, at the nanoscale, from an x-ray Bragg diffraction-based imaging technique. By employing a full-field microscopy setup, we capture real space images of materials, with imaging contrast determined solely by the x-ray diffracted signal. The data sets that emanate from this imaging technique are a hybrid of real space information (image spatial support) and reciprocal lattice space information (image contrast), and are intrinsically multidimensional (5D). By a judicious application of established unsupervised machine learning techniques and multivariate analysis to this multidimensional datamore » cube, we show how to extract features that can be ascribed physical interpretations in terms of common structural distortions, such as lattice tilts and dislocation arrays. Finally, we demonstrate this 'big data' approach to x-ray diffraction microscopy by identifying structural defects present in an epitaxial ferroelectric thin-film of lead zirconate titanate.« less

  7. Imaging nanoscale lattice variations by machine learning of x-ray diffraction microscopy data

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Laanait, Nouamane; Zhang, Zhan; Schlepütz, Christian M.

    In this paper, we present a novel methodology based on machine learning to extract lattice variations in crystalline materials, at the nanoscale, from an x-ray Bragg diffraction-based imaging technique. By employing a full-field microscopy setup, we capture real space images of materials, with imaging contrast determined solely by the x-ray diffracted signal. The data sets that emanate from this imaging technique are a hybrid of real space information (image spatial support) and reciprocal lattice space information (image contrast), and are intrinsically multidimensional (5D). By a judicious application of established unsupervised machine learning techniques and multivariate analysis to this multidimensional datamore » cube, we show how to extract features that can be ascribed physical interpretations in terms of common structural distortions, such as lattice tilts and dislocation arrays. Finally, we demonstrate this 'big data' approach to x-ray diffraction microscopy by identifying structural defects present in an epitaxial ferroelectric thin-film of lead zirconate titanate.« less

  8. Simultaneous effects of pressure and temperature on donor binding energy in Pöschl-Teller quantum well

    NASA Astrophysics Data System (ADS)

    Hakimyfard, Alireza; Barseghyan, M. G.; Duque, C. A.; Kirakosyan, A. A.

    2009-12-01

    In the frame of the variational method and the effective-mass approximation, the effects of hydrostatic pressure and temperature on the binding energy for donor impurities in the Pöschl-Teller quantum well are studied. The binding energy dependencies on the width of the quantum well, the hydrostatic pressure, the impurity position, the temperature, and the parameters of the confining potential are reported. The results show that the binding energy increases (decreases) with the increasing of the hydrostatic pressure (temperature). It is also found that, associated with the symmetry breaking in the Pöschl-Teller quantum well, and depending on the impurity position, the binding energy can increase or decrease.

  9. From lattice Hamiltonians to tunable band structures by lithographic design

    NASA Astrophysics Data System (ADS)

    Tadjine, Athmane; Allan, Guy; Delerue, Christophe

    2016-08-01

    Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

  10. Detection and Rectification of Distorted Fingerprints.

    PubMed

    Si, Xuanbin; Feng, Jianjiang; Zhou, Jie; Luo, Yuxuan

    2015-03-01

    Elastic distortion of fingerprints is one of the major causes for false non-match. While this problem affects all fingerprint recognition applications, it is especially dangerous in negative recognition applications, such as watchlist and deduplication applications. In such applications, malicious users may purposely distort their fingerprints to evade identification. In this paper, we proposed novel algorithms to detect and rectify skin distortion based on a single fingerprint image. Distortion detection is viewed as a two-class classification problem, for which the registered ridge orientation map and period map of a fingerprint are used as the feature vector and a SVM classifier is trained to perform the classification task. Distortion rectification (or equivalently distortion field estimation) is viewed as a regression problem, where the input is a distorted fingerprint and the output is the distortion field. To solve this problem, a database (called reference database) of various distorted reference fingerprints and corresponding distortion fields is built in the offline stage, and then in the online stage, the nearest neighbor of the input fingerprint is found in the reference database and the corresponding distortion field is used to transform the input fingerprint into a normal one. Promising results have been obtained on three databases containing many distorted fingerprints, namely FVC2004 DB1, Tsinghua Distorted Fingerprint database, and the NIST SD27 latent fingerprint database.

  11. A statistical analysis of the elastic distortion and dislocation density fields in deformed crystals

    DOE PAGES

    Mohamed, Mamdouh S.; Larson, Bennett C.; Tischler, Jonathan Z.; ...

    2015-05-18

    The statistical properties of the elastic distortion fields of dislocations in deforming crystals are investigated using the method of discrete dislocation dynamics to simulate dislocation structures and dislocation density evolution under tensile loading. Probability distribution functions (PDF) and pair correlation functions (PCF) of the simulated internal elastic strains and lattice rotations are generated for tensile strain levels up to 0.85%. The PDFs of simulated lattice rotation are compared with sub-micrometer resolution three-dimensional X-ray microscopy measurements of rotation magnitudes and deformation length scales in 1.0% and 2.3% compression strained Cu single crystals to explore the linkage between experiment and the theoreticalmore » analysis. The statistical properties of the deformation simulations are analyzed through determinations of the Nye and Kr ner dislocation density tensors. The significance of the magnitudes and the length scales of the elastic strain and the rotation parts of dislocation density tensors are demonstrated, and their relevance to understanding the fundamental aspects of deformation is discussed.« less

  12. Investigating the Human Computer Interaction Problems with Automated Teller Machine Navigation Menus

    ERIC Educational Resources Information Center

    Curran, Kevin; King, David

    2008-01-01

    Purpose: The automated teller machine (ATM) has become an integral part of our society. However, using the ATM can often be a frustrating experience as people frequently reinsert cards to conduct multiple transactions. This has led to the research question of whether ATM menus are designed in an optimal manner. This paper aims to address the…

  13. Old Father Story Teller: Grandfather Stories of the Pueblo Native American Indians.

    ERIC Educational Resources Information Center

    Velarde, Pablita

    Pablita Velarde, renowned artist and lecturer, recalls some of the Tewa legends handed down orally through the generations. She heard her grandfather and great-grandfather relate these tales on cold winter evenings at Santa Clara Pueblo when she was a child. The six stories told by Old Father Story Teller are "The Stars," which ties the…

  14. Limited distortion in LSB steganography

    NASA Astrophysics Data System (ADS)

    Kim, Younhee; Duric, Zoran; Richards, Dana

    2006-02-01

    It is well known that all information hiding methods that modify the least significant bits introduce distortions into the cover objects. Those distortions have been utilized by steganalysis algorithms to detect that the objects had been modified. It has been proposed that only coefficients whose modification does not introduce large distortions should be used for embedding. In this paper we propose an effcient algorithm for information hiding in the LSBs of JPEG coefficients. Our algorithm uses parity coding to choose the coefficients whose modifications introduce minimal additional distortion. We derive the expected value of the additional distortion as a function of the message length and the probability distribution of the JPEG quantization errors of cover images. Our experiments show close agreement between the theoretical prediction and the actual additional distortion.

  15. Spontaneous structural distortion of the metallic Shastry-Sutherland system Dy B4 by quadrupole-spin-lattice coupling

    NASA Astrophysics Data System (ADS)

    Sim, Hasung; Lee, Seongsu; Hong, Kun-Pyo; Jeong, Jaehong; Zhang, J. R.; Kamiyama, T.; Adroja, D. T.; Murray, C. A.; Thompson, S. P.; Iga, F.; Ji, S.; Khomskii, D.; Park, Je-Geun

    2016-11-01

    Dy B4 has a two-dimensional Shastry-Sutherland (Sh-S) lattice with strong Ising character of the Dy ions. Despite the intrinsic frustrations, it undergoes two successive transitions: a magnetic ordering at TN=20 K and a quadrupole ordering at TQ=12.5 K . From high-resolution neutron and synchrotron x-ray powder diffraction studies, we have obtained full structural information on this material in all phases and demonstrate that structural modifications occurring at quadrupolar transition lead to the lifting of frustrations inherent in the Sh-S model. Our paper thus provides a complete experimental picture of how the intrinsic frustration of the Sh-S lattice can be lifted by the coupling to quadrupole moments. We show that two other factors, i.e., strong spin-orbit coupling and long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in metallic Dy B4 , play an important role in this behavior.

  16. Jahn-Teller effect on the [TiF 4F 4F int] 6-(C 4v) and [NiF 4F 4F int] 7-(C 4v) clusters embedded into SrF 2 crystals

    NASA Astrophysics Data System (ADS)

    Ulanov, V. A.; Zhiteitcev, E. R.; Varlamov, A. G.

    2007-07-01

    By means of EPR method the associative [TiF 4F 4F int] 6-(C 4v) and [NiF 4F 4F int] 7-(C 4v) centers were revealed in the fluorite type SrF 2:Ti and SrF 2:Ni crystals grown by Bridgman method in helium atmosphere containing some amount of a fluorine gas. It was found that at low temperatures the local structures of these associative centers were exposed to a static rhombic distortion. The reasons of such distortions were accounted for by the assumption that the E ⊗ ( b1 + b2) vibronic interaction became effective due to that the ground orbital states of the [TiF 4F 4F int] 6-(C 4v) and [NiF 4F 4F int] 7-(C 4v) centers occurred to be doubly degenerated.

  17. Highly anisotropic exchange interactions of j eff = 1 2 iridium moments on the fcc lattice in La 2 B IrO 6   ( B = Mg , Zn )

    DOE PAGES

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; ...

    2016-06-20

    Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $$_2$$ZnIrO$$_6$$ and La$$_2$$MgIrO$$_6$$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

  18. Cosmological Distortions in Redshift Space

    NASA Astrophysics Data System (ADS)

    Ryden, Barbara S.

    1995-05-01

    The long-sought value of q_0, the deceleration parameter, remains elusive. One method of finding q_0 is to measure the distortions of large scale structure in redshift space. If the Hubble constant changes with time, then the mapping between redshift space and real space is nonlinear, even in the absence of peculiar motions. When q_0 > -1, structures in redshift space will be distorted along the line of sight; the distortion is proportional to (1 + q_0 ) z in the limit that the redshift z is small. The cosmological distortions at z <= 0.2 can be found by measuring the shapes of voids in redshift surveys of galaxies (such as the upcoming Sloane Digital Sky Survey). The cosmological distortions are masked to some extent by the distortions caused by small-scale peculiar velocities; it is difficult to measure the shape of a void when the fingers of God are poking into it. The cosmological distortions at z ~ 1 can be found by measuring the correlation function of quasars as a function of redshift and of angle relative to the line of sight. Finding q_0 by measuring distortions in redshift space, like the classical methods of determining q_0, is simple and elegant in principle but complicated and messy in practice.

  19. Robust distortion correction of endoscope

    NASA Astrophysics Data System (ADS)

    Li, Wenjing; Nie, Sixiang; Soto-Thompson, Marcelo; Chen, Chao-I.; A-Rahim, Yousif I.

    2008-03-01

    Endoscopic images suffer from a fundamental spatial distortion due to the wide angle design of the endoscope lens. This barrel-type distortion is an obstacle for subsequent Computer Aided Diagnosis (CAD) algorithms and should be corrected. Various methods and research models for the barrel-type distortion correction have been proposed and studied. For industrial applications, a stable, robust method with high accuracy is required to calibrate the different types of endoscopes in an easy of use way. The correction area shall be large enough to cover all the regions that the physicians need to see. In this paper, we present our endoscope distortion correction procedure which includes data acquisition, distortion center estimation, distortion coefficients calculation, and look-up table (LUT) generation. We investigate different polynomial models used for modeling the distortion and propose a new one which provides correction results with better visual quality. The method has been verified with four types of colonoscopes. The correction procedure is currently being applied on human subject data and the coefficients are being utilized in a subsequent 3D reconstruction project of colon.

  20. Grain refinement and Lattice Imperfections in Commercial Aluminum Alloy Processed by Severe Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Charfeddine, Saifeddine; Zehani, Karim; Besais, Lotfi; Korchef, Atef

    2014-08-01

    In the present work, investigations on the microstructure of an aluminum alloy that had been subjected to severe plastic deformation (SPD) by equal channel angular pressing (ECAP), filing and ball milling, were carried out using X-ray diffraction and scanning electron microscopy. SPD leads to lattice distortions, increased dislocation density and an intensive refinement of the microstructure. The refinement and lattice imperfections of the material are greatly affected by the deformation modes and loading performance occurring during SPD. During the milling, the dislocation annihilation increases at higher strains thereby resulting in a smaller crystallite size. After ECAP, the material manifests a strong shear texture and anisotropy of the deformation behavior. Strain anisotropy is less pronounced in filed and ball milled powder particles.

  1. Possible origin of photoconductivity in La0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Sagdeo, P. R.; Choudhary, R. J.; Phase, D. M.

    2010-01-01

    The effect of photon energy on the density of states near Fermi level of pulsed laser deposited La0.7Ca0.3MnO3 thin film has been studied to investigate the possible origin of change in the conductivity of these manganites upon photon exposure. For this purpose the photoelectron spectroscopy measurements were carried out using CSR beamline (BL-2) on Indus-1 synchrotron radiation source. The valance band spectra were measured at room temperature with photon energy ranging from 40 to 60 eV. We could see huge change in the density of states near Fermi level and this change is observed to be highest at 56 eV which is due to the resonance between Mn 3p to Mn 3d level. Our results suggest that the probability of electron transfer from deep Mn 3p level to Mn 3d-eg level is higher than that of Mn 3d-t2g level. It appears that this transfer of electron from deep Mn level to Mn 3d-eg level not only modifies the density of state near Fermi level but also changes the mobility of electrons by modifying the electron lattice coupling due to presence of Mn+3 Jahn-Teller ion.

  2. Structure-related frustrated magnetism of nanosized polyoxometalates: aesthetics and properties in harmony.

    PubMed

    Kögerler, Paul; Tsukerblat, Boris; Müller, Achim

    2010-01-07

    The structural versatility characterizing polyoxometalate chemistry, in combination with the option to deliberately use well-defined building blocks, serves as the foundation for the generation of a large family of magnetic clusters, frequently comprising highly symmetric spin arrays. If the spin centers are coupled by antiferromagnetic exchange, some of these systems exhibit spin frustration, which can result in novel magnetic properties of purely molecular origins. We discuss here the magnetic properties of selected nanosized polyoxometalate clusters featuring spin triangles as their magnetic 'building blocks' or fragments. This includes unique porous Keplerate clusters of the type {(Mo)Mo(5)}(12)M(30) (M = Fe(III), Cr(III), V(IV)) with the spin centers defining a regular icosidodecahedron and the {V(15)As(6)}-type cluster sphere containing a single equilateral spin triangle; these species are widely discussed and studied in the literature for their role in materials science as molecular representations of Kagomé lattices and in relation to quantum computing, respectively. Exhibiting fascinating and unique structural features, these magnetic molecules allow the study of the implications of frustrated spin ordering. Furthermore, this perspective covers the impact of spin frustration on the degeneracy of the ground state and related problems, namely strong magnetic anisotropy and the interplay of antisymmetric exchange and structural Jahn-Teller effects.

  3. Search for multipolar instability in URu2Si2 studied by ultrasonic measurements under pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Yanagisawa, T.; Mombetsu, S.; Hidaka, H.; Amitsuka, H.; Cong, P. T.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Huang, K.; Kanchanavatee, N.; Janoschek, M.; Maple, M. B.; Aoki, D.

    2018-04-01

    The elastic properties of URu2Si2 in the high magnetic field region above 40 T, over a wide temperature range from 1.5 to 120 K, were systematically investigated by means of high-frequency ultrasonic measurements. The investigation was performed at high magnetic fields to better investigate the innate bare 5 f -electron properties, since the unidentified electronic thermodynamic phase of unknown origin, the so-called "hidden order" (HO), and associated hybridization of conduction and f electrons (c -f hybridization) are suppressed at high magnetic fields. From the three different transverse modes we find contrasting results; both the Γ4(B2 g) and Γ5(Eg) symmetry modes C66 and C44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Γ3(B1 g) symmetry mode (C11-C12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Γ3(B1 g) lattice instability in URu2Si2 . However, the results from this work cannot be explained by using existing crystalline electric field schemes applied to the quadrupolar susceptibility in a local 5 f2 configuration. Instead, we present an analysis based on a band Jahn-Teller effect.

  4. Lattice surgery on the Raussendorf lattice

    NASA Astrophysics Data System (ADS)

    Herr, Daniel; Paler, Alexandru; Devitt, Simon J.; Nori, Franco

    2018-07-01

    Lattice surgery is a method to perform quantum computation fault-tolerantly by using operations on boundary qubits between different patches of the planar code. This technique allows for universal planar code computation without eliminating the intrinsic two-dimensional nearest-neighbor properties of the surface code that eases physical hardware implementations. Lattice surgery approaches to algorithmic compilation and optimization have been demonstrated to be more resource efficient for resource-intensive components of a fault-tolerant algorithm, and consequently may be preferable over braid-based logic. Lattice surgery can be extended to the Raussendorf lattice, providing a measurement-based approach to the surface code. In this paper we describe how lattice surgery can be performed on the Raussendorf lattice and therefore give a viable alternative to computation using braiding in measurement-based implementations of topological codes.

  5. Crystallization of a Keplerate-type polyoxometalate into a superposed kagome-lattice with huge channels.

    PubMed

    Saito, Masaki; Ozeki, Tomoji

    2012-09-07

    Crystal structures of two Sr(2+) salts of the Keplerate-type polyoxometalate, [Mo(VI)(72)Mo(V)(60)O(372)(CH(3)COO)(30)(H(2)O)(72)](42-), have been determined by single crystal X-ray diffraction. One compound exhibits a superposed kagome-lattice with huge channels whose diameters measure approximately 3.0 nm, while the arrangement of the Keplerate anions in the other compound approximates to a distorted cubic close packing.

  6. Electronic structures of filled tetrahedral semiconductors LiMgN and LiZnN: conduction band distortion

    NASA Astrophysics Data System (ADS)

    Yu, L. H.; Yao, K. L.; Liu, Z. L.

    2004-12-01

    The band structures of the filled tetrahedral semiconductors LiMgN and LiZnN, viewed as the zinc-blende (MgN) - and (ZnN) - lattices partially filled with He-like Li + ion interstitials, were studied using the full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The conduction band distortions of LiMgN and LiZnN, compared to their “parent” zinc-blende analog AlN and GaN, are discussed. It was found that the insertion of Li + ions at the interstitial sites near the cation or anion pushes the conduction band minimum of the X point in the Brillouin zone upward, relative to that of the Γ point, for both (MgN) - and (ZnN) - lattices (the valence band maximum is at Γ for AlN, GaN, LiMgN, and LiZnN), which provides a method to convert a zinc-blende indirect gap semiconductor into a direct gap material, but the conduction band distortion of the β phase (Li + near the cation) is quite stronger than that of the α phase (Li + near the anion). The total energy calculations show the α phase to be more stable than the β phase for both LiMgN and LiZnN. The Li-N and Mg-N bonds exhibit a strong ionic character, whereas the Zn-N bond has a strong covalent character in LiMgN and LiZnN.

  7. Excitations and relaxation dynamics in multiferroic GeV4S8 studied by terahertz and dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Reschke, S.; Wang, Zhe; Mayr, F.; Ruff, E.; Lunkenheimer, P.; Tsurkan, V.; Loidl, A.

    2017-10-01

    We report on THz time-domain spectroscopy on multiferroic GeV4S8 , which undergoes orbital ordering at a Jahn-Teller transition at 30.5 K and exhibits antiferromagnetic order below 14.6 K. The THz experiments are complemented by dielectric experiments at audio and radio frequencies. We identify a low-lying excitation close to 0.5 THz, which is only weakly temperature dependent and probably corresponds to a molecular excitation within the electronic level scheme of the V4 clusters. In addition, we detect complex temperature-dependent behavior of a low-lying phononic excitation, closely linked to the onset of orbitally driven ferroelectricity. In the high-temperature cubic phase, which is paramagnetic and orbitally disordered, this excitation is of relaxational character becomes an overdamped Lorentzian mode in the orbitally ordered phase below the Jahn-Teller transition, and finally appears as well-defined phonon excitation in the antiferromagnetic state. Abrupt changes in the real and imaginary parts of the complex dielectric permittivity show that orbital ordering appears via a structural phase transition with strong first-order character and that the onset of antiferromagnetic order is accompanied by significant structural changes, which are of first-order character, too. Dielectric spectroscopy documents that at low frequencies, significant dipolar relaxations are present in the orbitally ordered, paramagnetic phase only. In contrast to the closely related GaV4S8 , this relaxation dynamics that most likely mirrors coupled orbital and polar fluctuations does not seem to be related to the dynamic processes detected in the THz regime.

  8. Perturbatively deformed defects in Pöschl-Teller-driven scenarios for quantum mechanics

    NASA Astrophysics Data System (ADS)

    Bernardini, Alex E.; da Rocha, Roldão

    2016-07-01

    Pöschl-Teller-driven solutions for quantum mechanical fluctuations are triggered off by single scalar field theories obtained through a systematic perturbative procedure for generating deformed defects. The analytical properties concerning the quantum fluctuations in one-dimension, zero-mode states, first- and second-excited states, and energy density profiles are all obtained from deformed topological and non-topological structures supported by real scalar fields. Results are firstly derived from an integrated λϕ4 theory, with corresponding generalizations applied to starting λχ4 and sine-Gordon theories. By focusing our calculations on structures supported by the λϕ4 theory, the outcome of our study suggests an exact quantitative correspondence to Pöschl-Teller-driven systems. Embedded into the perturbative quantum mechanics framework, such a correspondence turns into a helpful tool for computing excited states and continuous mode solutions, as well as their associated energy spectrum, for quantum fluctuations of perturbatively deformed structures. Perturbative deformations create distinct physical scenarios in the context of exactly solvable quantum systems and may also work as an analytical support for describing novel braneworld universes embedded into a 5-dimensional gravity bulk.

  9. On Traveling Waves in Lattices: The Case of Riccati Lattices

    NASA Astrophysics Data System (ADS)

    Dimitrova, Zlatinka

    2012-09-01

    The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.

  10. Group III Acceptors with Shallow and Deep Levels in Silicon Carbide: ESR and ENDOR Studies

    NASA Astrophysics Data System (ADS)

    Il'in, I. V.; Uspenskaya, Yu. A.; Kramushchenko, D. D.; Muzafarova, M. V.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.

    2018-04-01

    Results of investigations of Group III acceptors (B, Al, and Ga) in crystals of silicon carbide using the most informative electron spin resonance and electron nuclear double resonance methods are presented. Structural models of the acceptors with shallow and deep levels are considered. In addition to the data obtained earlier, studies using high-frequency magnetic resonance were obtained, which allowed revealing orthorhombic deviations from the axial symmetry for the deep acceptors; theoretical analysis explains experimentally found shifts of g factors for the deep acceptors arising due to the orthorhombic deviations, which appear probably due to the Jahn-Teller effect.

  11. Comment on 'Ground state of octahedral platinum hexafluoride'

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gabuda, S. P.; Kozlova, S. G.

    2009-05-15

    It is shown that the principal results of a recent work by Alvarez-Thon et al. [Phys. Rev. A 77, 034502 (2008)] are in conflict with earlier work of the present authors [JETP Lett. 73, 35 (2001)] and also with a well known result concerning magnetic properties, NMR, and Jahn-Teller effect in the systems possessing even number of d electrons. This can be attributed to the fact that Alvarez-Thon et al. did not account for the influence of {sup 19}F and {sup 195}Pt nuclear magnetic moments and vibronic interactions on the wave function of PtF{sub 6} molecules.

  12. Vibrational overtone spectra of metallocenes: effect of the coordinating metal on the CH bond lengths

    NASA Astrophysics Data System (ADS)

    Billinghurst, Brant E.; Gough, Kathleen M.

    2003-03-01

    The first through third overtone spectra of ferrocene, ruthenocene, nickelocene, cobaltocene, dicyclopentadienyl magnesium and sodium cyclopentadienyl are examined with particular attention to the CH stretching of the cyclopentadienyl. Using semi-empirical correlations between CH bond length and CH stretching frequencies in each overtone region, we have determined that the type of metal atom within a metallocene complex has little effect on the CH bond length in the cyclopentadienyl. The only exception is cobaltocene where there is evidence that the Jahn-Teller effect results in several different CH bond lengths. Evidence that bis(cyclopentadienyl) magnesium is not ionic has been observed.

  13. Transition from orbital liquid to Jahn-Teller insulator in orthorhombic perovskites RTiO3.

    PubMed

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

    2008-08-22

    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 T_{N} in antiferromagnetic LaTiO3 and is supported by an anomalous critical behavior at T_{c} in ferromagnetic YTiO3.

  14. Analysis of Brown camera distortion model

    NASA Astrophysics Data System (ADS)

    Nowakowski, Artur; Skarbek, Władysław

    2013-10-01

    Contemporary image acquisition devices introduce optical distortion into image. It results in pixel displacement and therefore needs to be compensated for many computer vision applications. The distortion is usually modeled by the Brown distortion model, which parameters can be included in camera calibration task. In this paper we describe original model, its dependencies and analyze orthogonality with regard to radius for its decentering distortion component. We also report experiments with camera calibration algorithm included in OpenCV library, especially a stability of distortion parameters estimation is evaluated.

  15. Dianionic Titanyl and Vanadyl (Cation+ )2 [MIV O(Pc4- )]2- Phthalocyanine Salts Containing Pc4- Macrocycles.

    PubMed

    Konarev, Dmitri V; Kuzmin, Alexey V; Khasanov, Salavat S; Litvinov, Alexey L; Otsuka, Akihiro; Yamochi, Hideki; Kitagawa, Hiroshi; Lyubovskaya, Rimma N

    2018-06-18

    In this study, the titanyl and vanadyl phthalocyanine (Pc) salts (Bu 4 N + ) 2 [M IV O(Pc 4- )] 2- (M=Ti, V) and (Bu 3 MeP + ) 2 [M IV O(Pc 4- )] 2- (M=Ti, V) with [M IV O(Pc 4- )] 2- dianions were synthesized and characterized. Reduction of M IV O(Pc 2- ) carried out with an excess of sodium fluorenone ketyl in the presence of Bu 4 N + or Bu 3 MeP + is exclusive to the phthalocyanine centers, forming Pc 4- species. During reduction, the metal +4 charge did not change, implying that Pc is an non-innocent ligand. The Pc negative charge increase caused the C-N(pyr) bonds to elongate and the C-N(imine) bonds to alternate, thus increasing the distortion of Pc. Jahn-Teller effects are significant in the [eg(π*)] 2 dianion ground state and can additionally distort the Pc macrocycles. Blueshifts of the Soret and Q-bands were observed in the UV/Vis/NIR when M IV O(Pc 2- ) was reduced to [M IV O(Pc . 3- )] . - and [M IV O(Pc 4- )] 2- . From magnetic measurements, [Ti IV O(Pc 4- )] 2- was found to be diamagnetic and (Bu 4 N + ) 2 [V IV O(Pc 4- )] 2- and (Bu 3 MeP + ) 2 [V IV O(Pc 4- )] 2- were found to have magnetic moments of 1.72-1.78 μ B corresponding to an S=1/2 spin state owing to V IV electron spin. As a result, two latter salts show EPR signals with V IV hyperfine coupling. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Artificial solid electrolyte interphase for aqueous lithium energy storage systems

    PubMed Central

    Zhi, Jian; Yazdi, Alireza Zehtab; Valappil, Gayathri; Haime, Jessica; Chen, Pu

    2017-01-01

    Aqueous lithium energy storage systems address environmental sustainability and safety issues. However, significant capacity fading after repeated cycles of charge-discharge and during float charge limit their practical application compared to their nonaqueous counterparts. We introduce an artificial solid electrolyte interphase (SEI) to the aqueous systems and report the use of graphene films as an artificial SEI (G-SEI) that substantially enhance the overall performance of an aqueous lithium battery and a supercapacitor. The thickness (1 to 50 nm) and the surface area (1 cm2 to 1 m2) of the G-SEI are precisely controlled on the LiMn2O4-based cathode using the Langmuir trough–based techniques. The aqueous battery with a 10-nm-thick G-SEI exhibits a discharge capacity as high as 104 mA·hour g−1 after 600 cycles and a float charge current density as low as 1.03 mA g−1 after 1 day, 26% higher (74 mA·hour g−1) and 54% lower (1.88 mA g−1) than the battery without the G-SEI, respectively. We propose that the G-SEI on the cathode surface simultaneously suppress the structural distortion of the LiMn2O4 (the Jahn-Teller distortion) and the oxidation of conductive carbon through controlled diffusion of Li+ and restricted permeation of gases (O2 and COx), respectively. The G-SEI on both small (~1 cm2 in 1.15 mA·hour cell) and large (~9 cm2 in 7 mA·hour cell) cathodes exhibit similar property enhancement, demonstrating excellent potential for scale-up and manufacturing. PMID:28913426

  17. On relative distortion in fingerprint comparison.

    PubMed

    Kalka, Nathan D; Hicklin, R Austin

    2014-11-01

    When fingerprints are deposited, non-uniform pressure in conjunction with the inherent elasticity of friction ridge skin often causes linear and non-linear distortions in the ridge and valley structure. The effects of these distortions must be considered during analysis of fingerprint images. Even when individual prints are not notably distorted, relative distortion between two prints can have a serious impact on comparison. In this paper we discuss several metrics for quantifying and visualizing linear and non-linear fingerprint deformations, and software tools to assist examiners in accounting for distortion in fingerprint comparisons. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  18. The giant Gamow-Teller resonance states

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshio

    1982-04-01

    The mean energy of the giant Gamow-Teller resonance state (GTS) is studied, which is defined by the non-energy-weighted and the linearly energy-weighted sum of the strengths for ΣAi = 1 τi- σi- Using Bohr and Mottelson's hamiltonian with the ξl· σ force, the difference between the mean energies of GTS and the isobaric analog state (IAS) is expressed as E GTS -E IAS,≈ 2<π¦Σ Ai=1ξ il i· σ i¦π>/ (3T 0-4(k τ-k στ) T 0. The observed energy systematics is well explained by kτ- kστ≈ 4/ A MeV . The relationship between the mean energies and the excitation energies of the collective states in the random phase approximation for charge-exchange excitations is discussed in a simple model. From the excitation energy systematics of GTS, the values of kστ and the Migdal parameter g' are estimated to be about k στ = {(16-24)}/{A}MeV and g' = 0.49-0.72 , respectively.

  19. Chirality in distorted square planar Pd(O,N)2 compounds.

    PubMed

    Brunner, Henri; Bodensteiner, Michael; Tsuno, Takashi

    2013-10-01

    Salicylidenimine palladium(II) complexes trans-Pd(O,N)2 adopt step and bowl arrangements. A stereochemical analysis subdivides 52 compounds into 41 step and 11 bowl types. Step complexes with chiral N-substituents and all the bowl complexes induce chiral distortions in the square planar system, resulting in Δ/Λ configuration of the Pd(O,N)2 unit. In complexes with enantiomerically pure N-substituents ligand chirality entails a specific square chirality and only one diastereomer assembles in the lattice. Dimeric Pd(O,N)2 complexes with bridging N-substituents in trans-arrangement are inherently chiral. For dimers different chirality patterns for the Pd(O,N)2 square are observed. The crystals contain racemates of enantiomers. In complex two independent molecules form a tight pair. The (RC) configuration of the ligand induces the same Δ chirality in the Pd(O,N)2 units of both molecules with varying square chirality due to the different crystallographic location of the independent molecules. In complexes and atrop isomerism induces specific configurations in the Pd(O,N)2 bowl systems. The square chirality is largest for complex [(Diop)Rh(PPh3 )Cl)], a catalyst for enantioselective hydrogenation. In the lattice of two diastereomers with the same (RC ,RC) configuration in the ligand Diop but opposite Δ and Λ square configurations co-crystallize, a rare phenomenon in stereochemistry. © 2013 Wiley Periodicals, Inc.

  20. Frequency modulation television analysis: Distortion analysis

    NASA Technical Reports Server (NTRS)

    Hodge, W. H.; Wong, W. H.

    1973-01-01

    Computer simulation is used to calculate the time-domain waveform of standard T-pulse-and-bar test signal distorted in passing through an FM television system. The simulator includes flat or preemphasized systems and requires specification of the RF predetection filter characteristics. The predetection filters are modeled with frequency-symmetric Chebyshev (0.1-db ripple) and Butterworth filters. The computer was used to calculate distorted output signals for sixty-four different specified systems, and the output waveforms are plotted for all sixty-four. Comparison of the plotted graphs indicates that a Chebyshev predetection filter of four poles causes slightly more signal distortion than a corresponding Butterworth filter and the signal distortion increases as the number of poles increases. An increase in the peak deviation also increases signal distortion. Distortion also increases with the addition of preemphasis.

  1. Speckle in the diffraction patterns of Hendricks-Teller and icosahedral glass models

    NASA Technical Reports Server (NTRS)

    Garg, Anupam; Levine, Dov

    1988-01-01

    It is shown that the X-ray diffraction patterns from the Hendricks-Teller model for layered systems and the icosahedral glass models for the icosahedral phases show large fluctuations between nearby scattering wave vectors and from sample to sample, that are quite analogous to laser speckle. The statistics of these fluctuations are studied analytically for the first model and via computer simulations for the second. The observability of these effects is discussed briefly.

  2. AES Cardless Automatic Teller Machine (ATM) Biometric Security System Design Using FPGA Implementation

    NASA Astrophysics Data System (ADS)

    Ahmad, Nabihah; Rifen, A. Aminurdin M.; Helmy Abd Wahab, Mohd

    2016-11-01

    Automated Teller Machine (ATM) is an electronic banking outlet that allows bank customers to complete a banking transactions without the aid of any bank official or teller. Several problems are associated with the use of ATM card such card cloning, card damaging, card expiring, cast skimming, cost of issuance and maintenance and accessing customer account by third parties. The aim of this project is to give a freedom to the user by changing the card to biometric security system to access the bank account using Advanced Encryption Standard (AES) algorithm. The project is implemented using Field Programmable Gate Array (FPGA) DE2-115 board with Cyclone IV device, fingerprint scanner, and Multi-Touch Liquid Crystal Display (LCD) Second Edition (MTL2) using Very High Speed Integrated Circuit Hardware (VHSIC) Description Language (VHDL). This project used 128-bits AES for recommend the device with the throughput around 19.016Gbps and utilized around 520 slices. This design offers a secure banking transaction with a low rea and high performance and very suited for restricted space environments for small amounts of RAM or ROM where either encryption or decryption is performed.

  3. The Rovibronic Spectra of the Cyclopentadienyl Radical

    NASA Astrophysics Data System (ADS)

    Sharma, Ketan; Miller, Terry A.; Stanton, John F.; Nesbitt, David

    2017-06-01

    Cyclopentadienyl (Cp) radical has been subject to numerous studies for the greater part of half a century. Experimental work has involved photo-electron spectroscopy, laser induced fluorescence excitation and emission, infrared absorption spectroscopy, and recently rotationally resolved spectra in the CH stretch region taken at JILA. Even more theoretical works appear in the literature, but substantial advances in computation have occurred since their completion. Cp's highly symmetric (D_{5h}) structure and doubly degenerate electronic ground (˜{X}^2E_1^{''}), which is subject to linear Jahn-Teller distortion, have been a great motivation for work on it. We have commenced new computational work to obtain a broad understanding of the electronic, vibrational, and rotational, i.e. rovibronic, structure of the Cp radical as revealed by its spectra, with particular emphasis on the new infrared spectra. The goal is to guide experiments and their analyses and reconcile results from spectroscopy and quantum chemistry calculations. T. Ichino, et al. J. Chem. Phys. 129, 084310 (2008) L. Yu, S. C. Foster, J. M. Williamson, M. C. Heaven and T. A. Miller J. Phys. Chem. 92, 4263 (1988) B. E. Applegate, A. J. Bezant and T. A. Miller J. Chem. Phys 114, 4869 (2001) D. Leicht, M. Kaufmann, G. Schwaab, and M. Havenith J. Chem. Phys. 145, 7 (2016), 074304.

  4. Composition-dependent properties and phase stability of Fe-Pd ferromagnetic shape memory alloys: A first-principles study

    NASA Astrophysics Data System (ADS)

    Li, Chun-Mei; Hu, Yan-Fei

    2017-12-01

    The composition-dependent properties and their correlation with the phase stability of Fe75+xPd25-x (- 10.0 ≤x ≤10.0 ) alloys are systematically investigated by using first-principles exact muffin-tin orbitals (EMTO)-coherent potential approximation (CPA) calculations. It is shown that the martensitic transformation (MT) from L 12 to body-centered-tetragonal (bct) occurs in the ordered alloys with about -5.0 ≤x ≤10.0 . In both the L 12 and bct phases, the evaluated a and c/a agree well with the available experimental data; the average magnetic moment per atom increases whereas the local magnetic moments of Fe atoms, dependent on both their positions and the structure of the alloy, decrease with increasing x. The tetragonal shear elastic constant of the L 12 phase ( C ' ) decreases whereas that of the bct phase (Cs) increases with x. The tetragonality of the martensite ( |1 -c /a | ) increases whereas its energy relative to the austenite with a negative value decreases with Fe addition. All these effects account for the increase of MT temperature (TM) with x. The MT from L 12 to bct is finally confirmed originating from the splitting of Fe 3d Eg and T2 g bands upon tetragonal distortion due to the Jahn-Teller effect.

  5. Crystal and magnetic structure of the La1-xCaxMnO3 compound (0.11⩽x⩽0.175)

    NASA Astrophysics Data System (ADS)

    Pissas, M.; Margiolaki, I.; Papavassiliou, G.; Stamopoulos, D.; Argyriou, D.

    2005-08-01

    We studied the crystal and magnetic structure of the La1-xCaxMnO3 compound for (0.11⩽x⩽0.175) using stoichiometric samples. For x<0.13 the system’s ground state is insulating canted antiferromagnetic. For 0.13⩽x⩽0.175 below the Jahn-Teller transition temperature (TJT) the crystal structure undergoes a monoclinic distortion. The crystal structure can be described with P21/c space group which permits two Mn sites. The unit-cell strain parameter s=2(a-c)/(a+c) increases for Ta>b/2) structure.

  6. Ligand field photofragmentation spectroscopy of [Ag(L)N]2+ complexes in the gas phase: experiment and theory.

    PubMed

    Guan, Jingang; Puskar, Ljiljana; Esplugas, Ricardo O; Cox, Hazel; Stace, Anthony J

    2007-08-14

    Experiments have been undertaken to record photofragmentation spectra from a series of [Ag(L)N]2+ complexes in the gas phase. Spectra have been obtained for silver(II) complexed with the ligands (L): acetone, 2-pentanone, methyl-vinyl ketone, pyridine, and 4-methyl pyridine (4-picoline) with N in the range of 4-7. A second series of experiments using 1,1,1,3-fluoroacetone, acetonitrile, and CO2 as ligands failed to show any evidence of photofragmentation. Interpretation of the experimental data has come from time-dependent density functional theory (TDDFT), which very successfully accounts for trends in the spectra in terms of subtle differences in the properties of the ligands. Taking a sample of three ligands, acetone, pyridine, and acetonitrile, the calculations show all the spectral transitions to involve ligand-to-metal charge transfer, and that wavelength differences (or lack of spectra) arise from small changes in the energies of the molecular orbitals concerned. The calculations account for an absence in the spectra of any effects due to Jahn-Teller distortion, and they also reveal structural differences between complexes where the coordinating atom is either oxygen or nitrogen that have implications for the stability of silver(II) compounds. Where possible, comparisons have also been made with the physical properties of condensed phase silver(II) complexes.

  7. Tailoring of magnetic orderings in Fe substituted GdMnO3 bulk samples towards room temperature

    NASA Astrophysics Data System (ADS)

    Pal, A.; Dhana Sekhar, C.; Venimadhav, A.; Murugavel, P.

    2017-10-01

    The evolution of various magnetic ordering has been studied for the orthorhombic perovskite GdMn1-x Fe x O3 (0  ⩽  x  ⩽  0.7) system to obtain its comprehensive magnetic phase diagram. We observed that the substitution of Fe in GdMnO3 increases the antiferromagnetic Neel temperature (T N) from 40 K to above 400 K and importantly induces a spin-reorientation transition (T SR) for x  ⩾  0.4. These transitions are close to room temperature at x  =  0.5 and then gradually separated at a higher x value. The static orbital ordering induced by the Jahn-Teller distortion seems to play an important role in changing the T N. The variations of spin-reorientation ordering along with the competition between the magnetic orderings as a function of the composition were discussed with respect to antisymmetric exchange interactions and Mn3+ single-ion anisotropy in detail. In addition, the correlation between structural and magnetic properties suggests that the subtle structural change at composition x  =  0.4 may affect the magnetic ordering. The observed tunable T SR and T N in GdMn1-x Fe x O3 could add a practical value for these compositions in fields like spintronics and sensors.

  8. Investigation of the charge-orbital ordering mechanism in single-layered Pr0.5Ca1.5MnO4

    NASA Astrophysics Data System (ADS)

    Rangkuti, C. N.; Majidi, M. A.

    2018-04-01

    Motivated by the experimental study of half-doped single-layered Pr0.5Ca1.5MnO4 showing charge, orbital, and spin orderings [1], we propose a model to theoretically study the system to explain such ordering phenomena. The ground state electron configuration reveals that the charges form a checkerboard pattern with alternating Mn3+/Mn4+ sites, while the orbitals are aligned in zigzag chains [1, 2]. We calculate the ground state energy of this system to find the most preferable configuration by comparing three types of configurations (charge-unordered, charge-ordered, and charge-orbital-ordered states). The calculations are based on a tight-binding model representing effective electron hoppings among Mn ions in MnO2-plane. We take into account the horizontally- and vertically-oriented orbital and spin degrees of freedom at Mn sites. We assume that the hopping integral values depend on the relative orientation between the corresponding orbitals of adjacent Mn ions. The interaction terms we incorporate into our effective Hamiltonian include inter-orbital, intra-orbital Hubbard repulsions, and Jahn-Teller distortion [2]. We absorb the exchange interaction between spins into local self-energy that we calculate within dynamical mean field algorithm [2]. Within our model we show a circumstance in which the charge-orbital ordered configuration has the lowest energy, consistent with the ground state ordering revealed by the experimental data.

  9. Charge versus orbital-occupancy ordering in manganites

    NASA Astrophysics Data System (ADS)

    Luo, Weidong; Varela, Maria; Tao, Jing; Pennycook, Stephen J.; Pantelides, Sokrates T.

    2006-03-01

    It is generally assumed that density-functional theory (DFT) in the local-spin-density approximation (LSDA) or the generalized- gradient approximation (GGA) is not adequate to describe mixed- valence manganites. Here we report benchmark DFT/GGA calculations for the ground-state structural, electronic and magnetic properties for both undoped and doped CaMnO3 and find the results to be in excellent agreement with available data, including new atomic-resolution Z-contrast imaging and electron-energy loss spectra. More specifically, we found that the DFT results predict two inequivalent Mn atoms in both 0.33 and 0.5 electron-doped CaMnO3, in agreement with experimental evidence of Mn^+3/Mn^+4 oxidation state ordering. The inequivalent Mn atoms are marked by their distinctive orbital occupancies, dissimilar local Jahn-Teller distortion and different magnetic moments from DFT calculations. We also show that the spherically integrated charges associated with the two inequivalent Mn atoms are the same, and they are actually the same as in the Mn metal. This charge neutrality with different orbital occupancies is the result of self-consistency and atomic relaxations in the crystal. We conclude that DFT without additional correlations can account for the observed properties of oxidation-state ordering in this system. The impact of the results on other mixed-valence systems will be discussed.

  10. Effects of rare-earth size on the electronic structure of La1−xLuxVO3.

    PubMed

    Chen, B; Laverock, J; Newby, D; McNulty, J F; Smith, K E; Glans, P-A; Guo, J-H; Qiao, R-M; Yang, W-L; Lees, M R; Tung, L D; Singh, R P; Balakrishnan, G

    2015-03-18

    The electronic structure of La(1-x)Lu(x)VO(3)(x = 0, 0.2, 0.6 and 1) single crystals has been investigated using soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy, and resonant soft x-ray inelastic scattering to study the effects of rare-earth size. The x-ray absorption and emission spectra at the O K-edge present a progressive evolution with R-site cation, in agreement with local spin density approximation calculations. This evolution with R, together with the temperature dependence of the O K-edge spectra, is attributed to changes in the crystal structure of La(1-x)Lu(x)VO(3). The crystal-field dd. excitations probed by resonant inelastic x-ray scattering at the V L(3)-edge exhibit an increase in energy and enhanced intensity with the decrease of R-site ionic radius, which is mainly attributed to the increased tilting magnitude of the VO(6) octahedra. Upon cooling to ~95 K, the dd* excitations are prominently enhanced in relative Intensity, in agreement with the formation of the Jahn.Teller distortion int he orbital ordering phase. Additionally, the dd* transitions of the mixed compounds are noticeably suppressed with respect to those of the pure compounds, possibly owing to the formation of C-type orbital ordering induced by large R-site size variances.

  11. Characterization of oxygen defects in diamond by means of density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Thiering, Gergő; Gali, Adam

    2016-09-01

    Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce oxygen contamination in diamond, however, the incorporation of oxygen into diamond crystal and the nature of oxygen-related point defects are largely unknown. Oxygen may be potentially interesting as a source of quantum bits or it may interact with other point defects which are well established solid state qubits. Here we employ plane-wave supercell calculations within density functional theory, in order to characterize the electronic and magneto-optical properties of various oxygen-related defects. Besides the trivial single interstitial and substitutional oxygen defects we also consider their complexes with vacancies and hydrogen atoms. We find that oxygen defects are mostly electrically active and introduce highly correlated orbitals that pose a challenge for density functional theory modeling. Nevertheless, we are able to identify the fingerprints of substitutional oxygen defect, the oxygen-vacancy and oxygen-vacancy-hydrogen complexes in the electron paramagnetic resonance spectrum. We demonstrate that first principles calculations can predict the motional averaging of the electron paramagnetic resonance spectrum of defects that are subject to Jahn-Teller distortion. We show that the high-spin neutral oxygen-vacancy defect exhibits very fast nonradiative decay from its optical excited state that might hinder applying it as a qubit.

  12. Atomic-scale understanding of non-stoichiometry effects on the electrochemical performance of Ni-rich cathode materials

    NASA Astrophysics Data System (ADS)

    Kong, Fantai; Liang, Chaoping; Longo, Roberto C.; Zheng, Yongping; Cho, Kyeongjae

    2018-02-01

    As the next-generation high energy capacity cathode materials for Li-ion batteries, Ni-rich oxides face the problem of obtaining near-stoichiometric phases due to excessive Ni occupying Li sites. These extra-Ni-defects drastically affect the electrochemical performance. Despite of its importance, the fundamental correlation between such defects and the key electrochemical properties is still poorly understood. In this work, using density-functional-theory, we report a comprehensive study on the effects of non-stoichiometric phases on properties of Ni-rich layered oxides. For instance, extra-Ni-defects trigger charge disproportionation reaction within the system, alleviating the Jahn-Teller distortion of Ni3+ ions, which constitutes an important reason for their low formation energies. Kinetic studies of these defects reveal their immobile nature, creating a "pillar effect" that increases the structural stability. Ab initio molecular dynamics revealed Li depletion regions surrounding extra-Ni-defects, which are ultimate responsible for the arduous Li diffusion and re-intercalation, resulting in poor rate performance and initial capacity loss. Finally, the method with combination of high valence cation doping and ion-exchange synthesis is regarded as the most promising way to obtain stoichiometric oxides. Overall, this work not only deepens our understanding of non-stoichiometric Ni-rich layered oxides, but also enables further optimizations of high energy density cathode materials.

  13. Generic distortion model for metrology under optical microscopes

    NASA Astrophysics Data System (ADS)

    Liu, Xingjian; Li, Zhongwei; Zhong, Kai; Chao, YuhJin; Miraldo, Pedro; Shi, Yusheng

    2018-04-01

    For metrology under optical microscopes, lens distortion is the dominant source of error. Previous distortion models and correction methods mostly rely on the assumption that parametric distortion models require a priori knowledge of the microscopes' lens systems. However, because of the numerous optical elements in a microscope, distortions can be hardly represented by a simple parametric model. In this paper, a generic distortion model considering both symmetric and asymmetric distortions is developed. Such a model is obtained by using radial basis functions (RBFs) to interpolate the radius and distortion values of symmetric distortions (image coordinates and distortion rays for asymmetric distortions). An accurate and easy to implement distortion correction method is presented. With the proposed approach, quantitative measurement with better accuracy can be achieved, such as in Digital Image Correlation for deformation measurement when used with an optical microscope. The proposed technique is verified by both synthetic and real data experiments.

  14. Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

    DOE PAGES

    McGuire, Michael A.; Cao, Huibo; Chakoumakos, Bryan C.; ...

    2014-11-18

    Here we report structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature T SR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropymore » of the atomic displacement parameters for Bi with increasing temperature above T SR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. Finally, the identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.« less

  15. Elastic and anelastic relaxations associated with the incommensurate structure of Pr0.48Ca0.52MnO3

    NASA Astrophysics Data System (ADS)

    Carpenter, Michael A.; Howard, Christopher J.; McKnight, Ruth E. A.; Migliori, Albert; Betts, Jon B.; Fanelli, Victor R.

    2010-10-01

    The elastic and anelastic properties of a polycrystalline sample of Pr0.48Ca0.52MnO3 have been investigated by resonant ultrasound spectroscopy, as a function of temperature (10-1130 K) and magnetic field strength (0-15 T). Marked softening of the shear modulus as the Pnma↔incommensurate phase transition at ˜235K in zero field is approached from either side is consistent with pseudoproper ferroelastic character, driven by an order parameter with Γ3+ symmetry associated with Jahn-Teller ordering. This is accompanied by an increase in attenuation just below the transition point. The attenuation remains relatively high down to ˜80K , where there is a distinct Debye peak. It is attributed to coupling of shear strain with the Γ3+ order parameter which, in turn, controls the repeat distance of the incommensurate structure. Kinetic data extracted from the Debye peak suggest that the rate-controlling process could be related to migration of polarons. Elastic softening and stiffening as a function of magnetic field at constant temperatures between 177 and ˜225K closely resembles the behavior as a function of temperature at 0, 5, and 10 T and is consistent with thermodynamically continuous behavior for the phase transition in both cases. This overall pattern can be rationalized in terms of linear/quadratic coupling between the Γ3+ order parameter and an order parameter with Σ1 or Σ2 symmetry. It is also consistent with a dominant role for spontaneous strains in determining the strength of coupling, evolution of the incommensurate microstructure, and equilibrium evolution of the Jahn-Teller ordered structure through multicomponent order-parameter space.

  16. Electron-spin-resonance studies of 12CH3F + , 13CH3F + , and 12CH2DF + in neon matrices at 4 K: Comparison with theoretical calculations

    NASA Astrophysics Data System (ADS)

    Knight, Lon B., Jr.; Gregory, Brian W.; Hill, Devon W.; Arrington, C. A.; Momose, Takamasa; Shida, Tadamasa

    1991-01-01

    Various isotopic forms of the methyl fluoride cation 12CH3F+, 13CH3F+, and 12CH2DF+ have been generated by photoionization at 16.8 eV and separately by electron bombardment at 50 eV. The first electron-spin-resonance (ESR) results are reported for this radical cation which was isolated in neon matrices at 4 K. The measured A tensors or nuclear hyperfine parameters were compared with the results obtained from various computational approaches. Surprising observations were the large amounts of spin density on the methyl group, especially the hydrogen atoms, and the extreme differences in the deuterated spectra compared to the nondeuterated case. The presence of a single D atom apparently acts to prevent dynamic Jahn-Teller averaging which makes the methyl hydrogens equivalent on the ESR time scale. Such a dramatic Jahn-Teller effect has been previously observed for the similar methane cations CH+4 and CH2D+2. The magnetic parameters for CH2DF+ in neon at 4 K are gX=2.0032(5), gY=2.0106(8), and gZ=2.0120(5); for H: AX = 483(1), AY=476(1), and AZ=483(1) MHz; for D: ‖AX‖=5.0(3), ‖AY‖<3, and ‖AZ‖=7.1(3) MHz; for 19F : AX=965(1), AY=-130(2), and AZ=-166(1) MHz. For CH3F+, the g tensor and 19F A tensor were similar to those above but the H atoms were equivalent with values of AX=317(1), AY=323(2), and AZ=312 MHz.

  17. The ÖX˜ absorption of vinoxy radical revisited: Normal and Herzberg-Teller bands observed via cavity ringdown spectroscopy

    NASA Astrophysics Data System (ADS)

    Thomas, Phillip S.; Chhantyal-Pun, Rabi; Kline, Neal D.; Miller, Terry A.

    2010-03-01

    The ÖX˜ electronic absorption spectrum of vinoxy radical has been investigated using room temperature cavity ringdown spectroscopy. Analysis of the observed bands on the basis of computed vibrational frequencies and rotational envelopes reveals that two distinct types of features are present with comparable intensities. The first type corresponds to "normal" allowed electronic transitions to the origin and symmetric vibrations in the à state. The second type is interpreted in terms of excitations to asymmetric à state vibrations, which are only vibronically allowed by Herzberg-Teller coupling to the B˜ state. Results of electronic structure calculations indicate that the magnitude of the Herzberg-Teller coupling is appropriate to produce vibronically induced transitions with intensities comparable to those of the normal bands.

  18. Enhanced optical design by distortion control

    NASA Astrophysics Data System (ADS)

    Thibault, Simon; Gauvin, Jonny; Doucet, Michel; Wang, Min

    2005-09-01

    The control of optical distortion is useful for the design of a variety of optical system. The most popular is the F-theta lens used in laser scanning system to produce a constant scan velocity across the image plane. Many authors have designed during the last 20 years distortion control corrector. Today, many challenging digital imaging system can use distortion the enhanced their imaging capability. A well know example is a reversed telephoto type, if the barrel distortion is increased instead of being corrected; the result is a so-called Fish-eye lens. However, if we control the barrel distortion instead of only increasing it, the resulting system can have enhanced imaging capability. This paper will present some lens design and real system examples that clearly demonstrate how the distortion control can improve the system performances such as resolution. We present innovative optical system which increases the resolution in the field of view of interest to meet the needs of specific applications. One critical issue when we designed using distortion is the optimization management. Like most challenging lens design, the automatic optimization is less reliable. Proper management keeps the lens design within the correct range, which is critical for optimal performance (size, cost, manufacturability). Many lens design presented tailor a custom merit function and approach.

  19. Image distortion analysis using polynomial series expansion.

    PubMed

    Baggenstoss, Paul M

    2004-11-01

    In this paper, we derive a technique for analysis of local distortions which affect data in real-world applications. In the paper, we focus on image data, specifically handwritten characters. Given a reference image and a distorted copy of it, the method is able to efficiently determine the rotations, translations, scaling, and any other distortions that have been applied. Because the method is robust, it is also able to estimate distortions for two unrelated images, thus determining the distortions that would be required to cause the two images to resemble each other. The approach is based on a polynomial series expansion using matrix powers of linear transformation matrices. The technique has applications in pattern recognition in the presence of distortions.

  20. Designing shape-memory Heusler alloys from first-principles

    NASA Astrophysics Data System (ADS)

    Siewert, M.; Gruner, M. E.; Dannenberg, A.; Chakrabarti, A.; Herper, H. C.; Wuttig, M.; Barman, S. R.; Singh, S.; Al-Zubi, A.; Hickel, T.; Neugebauer, J.; Gillessen, M.; Dronskowski, R.; Entel, P.

    2011-11-01

    The phase diagrams of magnetic shape-memory Heusler alloys, in particular, ternary Ni-Mn-Z and quarternary (Pt, Ni)-Mn-Z alloys with Z = Ga, Sn, have been addressed by density functional theory and Monte Carlo simulations. Finite temperature free energy calculations show that the phonon contribution stabilizes the high-temperature austenite structure while at low temperatures magnetism and the band Jahn-Teller effect favor the modulated monoclinic 14M or the nonmodulated tetragonal structure. The substitution of Ni by Pt leads to a series of magnetic shape-memory alloys with very similar properties to Ni-Mn-Ga but with a maximal eigenstrain of 14%.

  1. Isotropic Kink and Quasiparticle Excitations in the Three-Dimensional Perovskite Manganite La_{0.6}Sr_{0.4}MnO_{3}.

    PubMed

    Horiba, Koji; Kitamura, Miho; Yoshimatsu, Kohei; Minohara, Makoto; Sakai, Enju; Kobayashi, Masaki; Fujimori, Atsushi; Kumigashira, Hiroshi

    2016-02-19

    In order to reveal the many-body interactions in three-dimensional perovskite manganites that show colossal magnetoresistance, we performed an in situ angle-resolved photoemission spectroscopy on La_{0.6}Sr_{0.4}MnO_{3} and investigated the behavior of quasiparticles. We observed quasiparticle peaks near the Fermi momentum in both the electron and the hole bands, and clear kinks throughout the entire hole Fermi surface in the band dispersion. This isotropic behavior of quasiparticles and kinks suggests that polaronic quasiparticles produced by the coupling of electrons with Jahn-Teller phonons play an important role in the colossal magnetoresistance properties of the ferromagnetic metallic phase of three-dimensional manganites.

  2. Stereo depth distortions in teleoperation

    NASA Technical Reports Server (NTRS)

    Diner, Daniel B.; Vonsydow, Marika

    1988-01-01

    In teleoperation, a typical application of stereo vision is to view a work space located short distances (1 to 3m) in front of the cameras. The work presented here treats converged camera placement and studies the effects of intercamera distance, camera-to-object viewing distance, and focal length of the camera lenses on both stereo depth resolution and stereo depth distortion. While viewing the fronto-parallel plane 1.4 m in front of the cameras, depth errors are measured on the order of 2cm. A geometric analysis was made of the distortion of the fronto-parallel plane of divergence for stereo TV viewing. The results of the analysis were then verified experimentally. The objective was to determine the optimal camera configuration which gave high stereo depth resolution while minimizing stereo depth distortion. It is found that for converged cameras at a fixed camera-to-object viewing distance, larger intercamera distances allow higher depth resolutions, but cause greater depth distortions. Thus with larger intercamera distances, operators will make greater depth errors (because of the greater distortions), but will be more certain that they are not errors (because of the higher resolution).

  3. Anisotropy and multiband superconductivity in Sr 2 RuO 4 determined by small-angle neutron scattering studies of the vortex lattice [Anisotropy and multiband superconductivity in Sr 2 RuO 4

    DOE PAGES

    Kuhn, S. J.; Morgenlander, W.; Louden, E. R.; ...

    2017-11-14

    Despite numerous studies the exact nature of the order parameter in superconducting Sr 2RuO 4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001> and also a symmetry changemore » to a distorted triangular symmetry for fields close to <100>.The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr 2RuO 4. Lastly, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.« less

  4. Anisotropy and multiband superconductivity in Sr 2 RuO 4 determined by small-angle neutron scattering studies of the vortex lattice [Anisotropy and multiband superconductivity in Sr 2 RuO 4

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kuhn, S. J.; Morgenlander, W.; Louden, E. R.

    Despite numerous studies the exact nature of the order parameter in superconducting Sr 2RuO 4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001> and also a symmetry changemore » to a distorted triangular symmetry for fields close to <100>.The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr 2RuO 4. Lastly, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.« less

  5. Mixed valence transition metal 2D-oxides: Comparison between delafossite and crednerite compounds

    NASA Astrophysics Data System (ADS)

    Martin, Christine; Poienar, Maria

    2017-08-01

    Transition metal oxides offer large opportunities to study relationships between structures and properties. Indeed these compounds crystallize in numerous frameworks corresponding to different dimensionalities and, accordingly, show a huge variety of properties (as high Tc superconductivity, colossal magnetoresistivity, multiferroicity..). The control of the oxidation state of the transition metal, via the monitoring of the oxygen content, is of prime importance to understand and optimize the properties, due to the strong coupling that exists between the lattice and the charges and spins of the transition metals. In this large playground for chemists, we reinvestigated several 2D-compounds derived from delafossite structure. Considering this paper as a very short review, we report here the results obtained on CuMO2 compounds (with M = Cr, Mn or Mn+Cu) by using a combination of techniques, as X-ray, neutrons and/or electrons diffraction on poly-crystals for structural characterisations that are correlated with electrical and/or magnetic properties. The complementarity of studies is also addressed by the synthesis and characterization of single crystals in addition to poly-crystals. Moreover the comparison of the structures of similar Cr and Mn based oxides highlights the crucial role of the Jahn-Teller effect of trivalent manganese to lift the degeneracy, which is responsible of the magnetic frustration in CuCrO2.

  6. Anharmonic rattling vibrations effects in the ESR of Er 3+ doped SmB 6 Kondo insulator

    DOE PAGES

    Lesseux, G. G.; Rosa, P. F. S.; Fisk, Z.; ...

    2017-01-23

    We report X-band Electron Spin Resonance (ESR) experiments on ≈ 0.2% and ≈ 0.7 % Er 3+ doped SmB 6 at low temperature (4 K - 40 K). The crystal field ground state of Er 3+ in SmB 6 is a Γ 8 quartet with a nearby Γ 6 excited doublet. The angular dependence of the resonances is not consistent with transitions between pure cubic crystal field states. The data were interpreted in terms of a dynamic Jahn-Teller (JT) effect by a coupling to Γ 3 vibrational modes, which we propose to originate from the rattling of the small Ermore » 3+ ions in the large SmB6 cage. Our data show an anisotropic pair of E and E’ resonances at g ≈ 4.4 and two nearly isotropic signals at g ≈ 5.8, one intense and narrow (A vibrational mode) and the other broad and faint, which we attribute to Er 3+ ions at lattice sites which are strongly affected by strain, defects and/or extrinsic Al impurities that inhibits the JT effects. Our results are in general consistent with those previously reported by Sturm et al. In addition to the angular dependence of the lines, we discuss the intensities, g-values and the linewidths of the Er 3+ transitions as a function of temperature.« less

  7. Influence of the manganese and cobalt content on the electrochemical performance of P2-Na0.67MnxCo1-xO2 cathodes for sodium-ion batteries.

    PubMed

    Hemalatha, K; Jayakumar, M; Prakash, A S

    2018-01-23

    The resurgence of sodium-ion batteries in recent years is due to their potential ability to form intercalation compounds possessing a high specific capacity and energy density comparable to existing lithium systems. To comprehend the role of cobalt substitution in the structure and electrochemical performance of Na 0.67 MnO 2 , the solid solutions of P2-Na 0.67 Mn x Co 1-x O 2 (x = 0.25, 0.5, 0.75) are synthesized and characterized. The XRD-Rietveld analysis revealed that the Co-substitution in Na 0.67 MnO 2 decreases lattice parameters 'a' and 'c' resulting in the contraction of MO 6 octahedra and the enlargement of inter-layer 'd' spacing. XPS indicates that the isovalent cobalt substitution in Na 0.67 MnO 2 results in the partial/complete replacement of Jahn-Teller active trivalent manganese to form low-spin complexes of better structural stability. The Na-ion diffusion coefficient, D Na + , derived from cyclic voltammetry and impedance spectroscopy, confirmed the enhanced mass transport in Co-rich phases compared to Mn-rich phases. Furthermore, higher diffusion coefficient values are observed for Co 3+ /Co 4+ than for their Mn 3+ /Mn 4+ redox processes. In addition, Co-rich phases exhibit a high structural stability and superior capacity retention, whereas Mn-rich phases discharge higher capacities.

  8. Spin-lattice coupling mediated multiferroicity in (ND 4) 2FeCl 5 • D 2O

    DOE PAGES

    Tian, Wei; Cao, Huibo; Wang, Jincheng; ...

    2016-12-07

    In this paper, we report a neutron diffraction study of the multiferroic mechanism in (ND 4) 2FeCl 5 • D 2O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at T N = 7.3 K, followed by a second transition to an IC cycloidal spin state at T FE = 6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both oddmore » and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at T FE, thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed, indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND 4) 2FeCl 5 • D 2O.« less

  9. Two-level structural sparsity regularization for identifying lattices and defects in noisy images

    DOE PAGES

    Li, Xin; Belianinov, Alex; Dyck, Ondrej E.; ...

    2018-03-09

    Here, this paper presents a regularized regression model with a two-level structural sparsity penalty applied to locate individual atoms in a noisy scanning transmission electron microscopy image (STEM). In crystals, the locations of atoms is symmetric, condensed into a few lattice groups. Therefore, by identifying the underlying lattice in a given image, individual atoms can be accurately located. We propose to formulate the identification of the lattice groups as a sparse group selection problem. Furthermore, real atomic scale images contain defects and vacancies, so atomic identification based solely on a lattice group may result in false positives and false negatives.more » To minimize error, model includes an individual sparsity regularization in addition to the group sparsity for a within-group selection, which results in a regression model with a two-level sparsity regularization. We propose a modification of the group orthogonal matching pursuit (gOMP) algorithm with a thresholding step to solve the atom finding problem. The convergence and statistical analyses of the proposed algorithm are presented. The proposed algorithm is also evaluated through numerical experiments with simulated images. The applicability of the algorithm on determination of atom structures and identification of imaging distortions and atomic defects was demonstrated using three real STEM images. In conclusion, we believe this is an important step toward automatic phase identification and assignment with the advent of genomic databases for materials.« less

  10. Two-level structural sparsity regularization for identifying lattices and defects in noisy images

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Xin; Belianinov, Alex; Dyck, Ondrej E.

    Here, this paper presents a regularized regression model with a two-level structural sparsity penalty applied to locate individual atoms in a noisy scanning transmission electron microscopy image (STEM). In crystals, the locations of atoms is symmetric, condensed into a few lattice groups. Therefore, by identifying the underlying lattice in a given image, individual atoms can be accurately located. We propose to formulate the identification of the lattice groups as a sparse group selection problem. Furthermore, real atomic scale images contain defects and vacancies, so atomic identification based solely on a lattice group may result in false positives and false negatives.more » To minimize error, model includes an individual sparsity regularization in addition to the group sparsity for a within-group selection, which results in a regression model with a two-level sparsity regularization. We propose a modification of the group orthogonal matching pursuit (gOMP) algorithm with a thresholding step to solve the atom finding problem. The convergence and statistical analyses of the proposed algorithm are presented. The proposed algorithm is also evaluated through numerical experiments with simulated images. The applicability of the algorithm on determination of atom structures and identification of imaging distortions and atomic defects was demonstrated using three real STEM images. In conclusion, we believe this is an important step toward automatic phase identification and assignment with the advent of genomic databases for materials.« less

  11. Chemical complexity induced local structural distortion in NiCoFeMnCr high-entropy alloy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Fuxiang; Tong, Yang; Jin, Ke

    In order to study chemical complexity-induced lattice distortion in high-entropy alloys, the static Debye–Waller (D-W) factor of NiCoFeMnCr solid solution alloy is measured with low temperature neutron diffraction, ambient X-ray diffraction, and total scattering methods. Here, the static atomic displacement parameter of the multi-element component alloy at 0 K is 0.035–0.041 Å, which is obvious larger than that of element Ni (~0 Å). The atomic pair distance between individual atoms in the alloy investigated with extended X-ray absorption fine structure (EXAFS) measurements indicates that Mn has a slightly larger bond distance (~0.4%) with neighbor atoms than that of others.

  12. Chemical complexity induced local structural distortion in NiCoFeMnCr high-entropy alloy

    DOE PAGES

    Zhang, Fuxiang; Tong, Yang; Jin, Ke; ...

    2018-06-16

    In order to study chemical complexity-induced lattice distortion in high-entropy alloys, the static Debye–Waller (D-W) factor of NiCoFeMnCr solid solution alloy is measured with low temperature neutron diffraction, ambient X-ray diffraction, and total scattering methods. Here, the static atomic displacement parameter of the multi-element component alloy at 0 K is 0.035–0.041 Å, which is obvious larger than that of element Ni (~0 Å). The atomic pair distance between individual atoms in the alloy investigated with extended X-ray absorption fine structure (EXAFS) measurements indicates that Mn has a slightly larger bond distance (~0.4%) with neighbor atoms than that of others.

  13. Infrared spectroscopy of ionized corannulene in the gas phase.

    PubMed

    Alvaro Galué, Héctor; Rice, Corey A; Steill, Jeffrey D; Oomens, Jos

    2011-02-07

    The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H(2), and C(2)H(x) losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp(3) hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C(5v) geometry induced by the Jahn-Teller effect as a consequence of the degenerate (2)E(1) ground electronic state. As indicated by the calculations, the five equivalent C(s) minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm(-1) region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

  14. Structure refinements of members in the brownmillerite solid solution series Ca{sub 2}Al{sub x}(Fe{sub 0.5}Mn{sub 0.5}){sub 2-x}O{sub 5+{delta}} with 1/2{<=}x{<=}4/3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stoeber, Stefan, E-mail: stefan.stoeber@geo.uni-halle.de; Redhammer, Guenther; Schorr, Susan

    2013-01-15

    Four different brownmillerite solid solutions Ca{sub 2}Al{sub x}(Fe{sub 0.5}Mn{sub 0.5}){sub 2-x}O{sub 5+{delta}} with 1/2{<=}x{<=}4/3 were synthesized by a solid oxide ceramic method. The phases crystallize either in a primitive centered orthorhombic cell with space group Pnma or in a body centered cell with space group I2mb dependent on the aluminum concentration present in the solid solution. Mn{sup 3+} ions occupy exclusively site 4a coordinated by six oxygen anions. Increasing Mn{sup 3+} concentrations cause a remarkable distortion of the octahedron and indirectly of the tetrahedron, resulting in twisted and tilted octahedral layers as well as buckled tetrahedral chains. The influences aremore » discussed on the site 4a of trivalent manganese due to its Jahn-Teller activity, with regard to the occupation of octahedron and tetrahedron with different sized iron and aluminum ions. - Graphical Abstract: The coupled substitution Fe{sup 3+}>Mn{sup 3+}+Fe{sup 3+} <=>2 Al{sup 3+} in brownmillerite phases (Ca{sub 2}(Fe{sub 0.5}Mn{sub 0.5}){sub 2-x}Al{sub x}O{sub 5+{delta}}) changes predominantly their structural properties, which is essential for the hydration performance of the calcium aluminate cement, where brownmillerites occur as clinker phases. Highlights: Black-Right-Pointing-Pointer We present structural data of four Ca-Al-Fe-Mn-brownmillerites. Black-Right-Pointing-Pointer Mn{sup 3+}-ions occupy exclusively the octahedrally coordinated site 0,0,0. Black-Right-Pointing-Pointer Bonds and angles of the octahedrally coordinated site are distorted strongly. Black-Right-Pointing-Pointer Mn{sup 3+}-ions influence indirectly the shape of the tetrahedron. Black-Right-Pointing-Pointer Mn{sup 3+}-ions stabilize Pnma instead of I2mb in Ca-Al-Fe-Mn-brownmillerites.« less

  15. Understanding Two Different Structures in the Dark Stable State of the Oxygen‐Evolving Complex of Photosystem II: Applicability of the Jahn–Teller Deformation Formula

    PubMed Central

    Shoji, Mitsuo; Isobe, Hiroshi; Tanaka, Ayako; Fukushima, Yoshimasa; Kawakami, Keisuke; Umena, Yasufumi; Kamiya, Nobuo; Nakajima, Takahito

    2017-01-01

    Abstract Tanaka et al. (J. Am. Chem. Soc., 2017, 139, 1718) recently reported the three‐dimensional (3D) structure of the oxygen evolving complex (OEC) of photosystem II (PSII) by X‐ray diffraction (XRD) using extremely low X‐ray doses of 0.03 and 0.12 MGy. They observed two different 3D structures of the CaMn4O5 cluster with different hydrogen‐bonding interactions in the S1 state of OEC keeping the surrounding polypeptide frameworks of PSII the same. Our Jahn–Teller (JT) deformation formula based on large‐scale quantum mechanics/molecular mechanics (QM/MM) was applied for these low‐dose XRD structures, elucidating important roles of JT effects of the MnIII ion for subtle geometric distortions of the CaMn4O5 cluster in OEC of PSII. The JT deformation formula revealed the similarity between the low‐dose XRD and damage‐free serial femtosecond X‐ray diffraction (SFX) structures of the CaMn4O5 cluster in the dark stable state. The extremely low‐dose XRD structures were not damaged by X‐ray irradiation. Implications of the present results are discussed in relation to recent SFX results and a blue print for the design of artificial photocatalysts for water oxidation. PMID:29577075

  16. Multiscale quantification of tissue spiculation and distortion for detection of architectural distortion and spiculated mass in mammography

    NASA Astrophysics Data System (ADS)

    Lao, Zhiqiang; Zheng, Xin

    2011-03-01

    This paper proposes a multiscale method to quantify tissue spiculation and distortion in mammography CAD systems that aims at improving the sensitivity in detecting architectural distortion and spiculated mass. This approach addresses the difficulty of predetermining the neighborhood size for feature extraction in characterizing lesions demonstrating spiculated mass/architectural distortion that may appear in different sizes. The quantification is based on the recognition of tissue spiculation and distortion pattern using multiscale first-order phase portrait model in texture orientation field generated by Gabor filter bank. A feature map is generated based on the multiscale quantification for each mammogram and two features are then extracted from the feature map. These two features will be combined with other mass features to provide enhanced discriminate ability in detecting lesions demonstrating spiculated mass and architectural distortion. The efficiency and efficacy of the proposed method are demonstrated with results obtained by applying the method to over 500 cancer cases and over 1000 normal cases.

  17. Distortions in Judged Spatial Relations.

    ERIC Educational Resources Information Center

    Stevens, Albert

    1978-01-01

    Distortions in judgments of relative geographical relations were observed, particularly when the locations were in different geographical or political units. Subjects distorted the judged relation to conform with the relation of the superordinate political unit. A model for the hierachical storage of spatial information is presented. (Author/RD)

  18. Lattice effects on ferromagnetism in perovskite ruthenates

    PubMed Central

    Cheng, J.-G.; Zhou, J.-S.; Goodenough, John B.

    2013-01-01

    Ferromagnetism and its evolution in the orthorhombic perovskite system Sr1–xCaxRuO3 have been widely believed to correlate with structural distortion. The recent development of high-pressure synthesis of the Ba-substituted Sr1–yBayRuO3 makes it possible to study ferromagnetism over a broader phase diagram, which includes the orthorhombic Imma and the cubic phases. However, the chemical substitutions introduce the A-site disorder effect on Tc, which complicates determination of the relationship between ferromagnetism and structural distortion. By clarifying the site disorder effect on Tc in several unique series of ruthenates in which the average bond length 〈A–O〉 remains the same but the bond-length variance varies, we are able to demonstrate a parabolic curve of Tc versus mean bond length 〈A–O〉. A much higher Tc ∼ 177 K than that found in orthorhombic SrRuO3 can be obtained from the curve at a bond length 〈A–O〉, which makes the geometric factor t = 〈A–O〉/(√2〈Ru–O〉) ∼ 1. This result reveals not only that the ferromagnetism in the ruthenates is extremely sensitive to the lattice strain, but also that it has an important implication for exploring the structure–property relationship in a broad range of oxides with perovskite or a perovskite-related structure. PMID:23904477

  19. Lattice strain induced multiferroicity in PZT-CFO particulate composite

    NASA Astrophysics Data System (ADS)

    Pradhan, Lagen Kumar; Pandey, Rabichandra; Kumar, Rajnish; Kar, Manoranjan

    2018-02-01

    Lead Zirconate Titanate [Pb(Zr0.52Ti0.48)O3/PZT] and Cobalt Ferrite [CoFe2O4/CFO] based multiferroic composites [(1-x)PZT-(x)CFO] with (x = 0.10-0.40) have been prepared to study its magnetoelectric (ME) and multiferroic properties. X-ray diffraction method along with the Rietveld refinement technique reveals that the crystal symmetries corresponding to PZT and CFO exist independently in the composites. The effect of interfacial strain on lattice distortion in PZT has been observed. It is well correlated with the magnetoelectric coupling of the composites. Dispersion behavior of dielectric constant with frequency can be explained by the modified Debye model. Different relaxation phenomena have been observed in PZT-CFO particulate composites. The ferroelectric properties of composites decrease with the increase in percentage of CFO in the composite. Both saturation (Ms) and remanent (Mr) magnetization increase with the increase in CFO content in the composite. The maximum ME coupling was found to be 1.339 pC/cm2 Oe for the composition (0.80) PZT-(0.20) CFO at the application of maximum magnetic field of 50 Oe. The multiferroic properties in CFO-PZT can be explained by the lattice strain at the CFO-PZT interfaces.

  20. Transverse spin structure of the nucleon from lattice-QCD simulations.

    PubMed

    Göckeler, M; Hägler, Ph; Horsley, R; Nakamura, Y; Pleiter, D; Rakow, P E L; Schäfer, A; Schierholz, G; Stüben, H; Zanotti, J M

    2007-06-01

    We present the first calculation in lattice QCD of the lowest two moments of transverse spin densities of quarks in the nucleon. They encode correlations between quark spin and orbital angular momentum. Our dynamical simulations are based on two flavors of clover-improved Wilson fermions and Wilson gluons. We find significant contributions from certain quark helicity flip generalized parton distributions, leading to strongly distorted densities of transversely polarized quarks in the nucleon. In particular, based on our results and recent arguments by Burkardt [Phys. Rev. D 72, 094020 (2005)], we predict that the Boer-Mulders function h(1/1), describing correlations of transverse quark spin and intrinsic transverse momentum of quarks, is large and negative for both up and down quarks.

  1. JWST ISIM Distortion Analysis Challenge

    NASA Technical Reports Server (NTRS)

    Cifie, Emmanuel; Matzinger, Liz; Kuhn, Jonathan; Fan, Terry

    2004-01-01

    Very tight distortion requirements are imposed on the JWST's ISM structure due to the sensitivity of the telescope's mirror segment and science instrument positioning. The ISIM structure is a three dimensional truss with asymmetric gusseting and metal fittings. One of the primary challenges for ISIM's analysis team is predicting the thermal distortion of the structure both from the bulk cooldown from ambient to cryo, and the smaller temperature changes within the cryogenic operating environment. As a first cut to estimate thermal distortions, a finite element model of bar elements was created. Elements representing joint areas and metal fittings use effective properties that match the behavior of the stack-up of the composite tube, gusset and adhesive under mechanical and thermal loads. These properties were derived by matching tip deflections of a solid model simplified T-joint. Because of the structure s asymmetric gusseting, this effective property model is a first attempt at predicting rotations that cannot be captured with a smeared CTE approach. In addition to the finite element analysis, several first order calculations have been performed to gauge the feasibility of the material design. Because of the stringent thermal distortion requirements at cryogenic temperatures, a composite tube material with near zero or negative CTE is required. A preliminary hand analysis of the contribution of the various components along the distortion path between FGS and the other instruments, neglecting second order effects were examined. A plot of bounding tube longitudinal and transverse CTEs for thermal stability requirements was generated to help determine the feasibility of meeting these requirements. This analysis is a work in progress en route to a large degree of freedom hi-fidelity FEA model for distortion analysis. Methods of model reduction, such as superelements, are currently being investigated.

  2. Inference Control Mechanism for Statistical Database: Frequency-Imposed Data Distortions.

    ERIC Educational Resources Information Center

    Liew, Chong K.; And Others

    1985-01-01

    Introduces two data distortion methods (Frequency-Imposed Distortion, Frequency-Imposed Probability Distortion) and uses a Monte Carlo study to compare their performance with that of other distortion methods (Point Distortion, Probability Distortion). Indications that data generated by these two methods produce accurate statistics and protect…

  3. GeneStoryTeller: a mobile app for quick and comprehensive information retrieval of human genes.

    PubMed

    Eleftheriou, Stergiani V; Bourdakou, Marilena M; Athanasiadis, Emmanouil I; Spyrou, George M

    2015-01-01

    In the last few years, mobile devices such as smartphones and tablets have become an integral part of everyday life, due to their software/hardware rapid development, as well as the increased portability they offer. Nevertheless, up to now, only few Apps have been developed in the field of bioinformatics, capable to perform fast and robust access to services. We have developed the GeneStoryTeller, a mobile application for Android platforms, where users are able to instantly retrieve information regarding any recorded human gene, derived from eight publicly available databases, as a summary story. Complementary information regarding gene-drugs interactions, functional annotation and disease associations for each selected gene is also provided in the gene story. The most challenging part during the development of the GeneStoryTeller was to keep balance between storing data locally within the app and obtaining the updated content dynamically via a network connection. This was accomplished with the implementation of an administrative site where data are curated and synchronized with the application requiring a minimum human intervention. © The Author(s) 2015. Published by Oxford University Press.

  4. Low distortion laser welding of cylindrical components

    NASA Astrophysics Data System (ADS)

    Kittel, Sonja

    2011-02-01

    Automotive components are for the most part cylindrical and thus the weld seams are of radial shape. Radial weld seams are usually produced by starting at a point on the component's surface rotating the component resulting in an overlap zone at the start/end of the weld. In this research, it is shown that the component's distortion strongly depends on the overlap of weld start and end. A correlation between overlap zone and distortion is verified by an experimental study. In order to reduce distortion generated by the overlap zone a special optics is used which allows shaping the laser beam into a ring shape which is then focused on the cylindrical surface and produces a radial ring weld seam simultaneously by one laser pulse. In doing this, the overlap zone is eliminated and distortion can be reduced. Radial weld seams are applied on precision samples and distortion is measured after welding. The distortion of the precision samples is measured by a tactile measuring method and a comparison of the results of welding with the ring optics to reference welds is done.

  5. A survey of ab initio conical intersections for the H+H2 system

    NASA Astrophysics Data System (ADS)

    Halász, Gábor; Vibók, Ágnes; Mebel, Alexander M.; Baer, Michael

    2003-02-01

    In this article we present a survey of the various conical intersections which govern potential transitions between the three lower electronic states for the title molecular system. It was revealed that these three states, for a given fixed HH distance, RHH, usually form four conical intersections: two, between the two lower states and two, between the two upper states. One of the four is the well known equilateral D3h ci and the others are, essentially, C2v cis: One of them is located on the symmetry line perpendicular to the HH axis (just like the D3h ci) and the other two are located on both sides of this symmetry line and in this way form the ci-twins. The study was carried out for four RHH-values, namely, RHH=0.74, 0.5417, 0.52, and 0.4777 Å. It was also established that there exists one single RHH-value designated as R˜HH, located in the interval {0.52, 0.53 Å}, for which all four cis coalesce to become one kind of "super" ci which couples the three states. The numerical study was carried out employing the line integral approach for groups of two and three states. As for the two-state calculations we found that all D3h-cis, at close proximity, are circular (ordinary) Jahn-Teller-type cis, whereas all C2v-cis, at close proximity, are elliptic Jahn-Teller cis [Chem. Phys. Lett 354, 243 (2002)]. Particular attention is given to the 3-state quantization of the nonadiabatic coupling matrix. The quantization is found to be fulfilled in all situations as long as the regions in configuration space are not too far from the relevant cis. In the Discussion and Conclusion we discuss, among other subjects, the possibility to diabatize the adiabatic potential matrix.

  6. Lattice relaxation in oxide heterostructures: LaTiO3/SrTiO3 superlattices.

    PubMed

    Okamoto, Satoshi; Millis, Andrew J; Spaldin, Nicola A

    2006-08-04

    Local density approximation + Hubbard U and many-body effective Hamiltonian calculations are used to determine the effects of lattice relaxation in LaTiO3/SrTiO3 superlattices. Large ferroelectric-like distortions of the TiO6 octahedra are found, which substantially affect the Ti d-electron density, bringing the calculated results into good agreement with experimental data. The relaxations also change the many-body physics, leading to a novel symmetry-breaking-induced ordering of the xy orbitals, which does not occur in bulk LaTiO3, or in the hypothetical unrelaxed structure.

  7. Detection of chromatic and luminance distortions in natural scenes.

    PubMed

    Jennings, Ben J; Wang, Karen; Menzies, Samantha; Kingdom, Frederick A A

    2015-09-01

    A number of studies have measured visual thresholds for detecting spatial distortions applied to images of natural scenes. In one study, Bex [J. Vis.10(2), 1 (2010)10.1167/10.2.231534-7362] measured sensitivity to sinusoidal spatial modulations of image scale. Here, we measure sensitivity to sinusoidal scale distortions applied to the chromatic, luminance, or both layers of natural scene images. We first established that sensitivity does not depend on whether the undistorted comparison image was of the same or of a different scene. Next, we found that, when the luminance but not chromatic layer was distorted, performance was the same regardless of whether the chromatic layer was present, absent, or phase-scrambled; in other words, the chromatic layer, in whatever form, did not affect sensitivity to the luminance layer distortion. However, when the chromatic layer was distorted, sensitivity was higher when the luminance layer was intact compared to when absent or phase-scrambled. These detection threshold results complement the appearance of periodic distortions of the image scale: when the luminance layer is distorted visibly, the scene appears distorted, but when the chromatic layer is distorted visibly, there is little apparent scene distortion. We conclude that (a) observers have a built-in sense of how a normal image of a natural scene should appear, and (b) the detection of distortion in, as well as the apparent distortion of, natural scene images is mediated predominantly by the luminance layer and not chromatic layer.

  8. Prediction of transmission distortion for wireless video communication: analysis.

    PubMed

    Chen, Zhifeng; Wu, Dapeng

    2012-03-01

    Transmitting video over wireless is a challenging problem since video may be seriously distorted due to packet errors caused by wireless channels. The capability of predicting transmission distortion (i.e., video distortion caused by packet errors) can assist in designing video encoding and transmission schemes that achieve maximum video quality or minimum end-to-end video distortion. This paper is aimed at deriving formulas for predicting transmission distortion. The contribution of this paper is twofold. First, we identify the governing law that describes how the transmission distortion process evolves over time and analytically derive the transmission distortion formula as a closed-form function of video frame statistics, channel error statistics, and system parameters. Second, we identify, for the first time, two important properties of transmission distortion. The first property is that the clipping noise, which is produced by nonlinear clipping, causes decay of propagated error. The second property is that the correlation between motion-vector concealment error and propagated error is negative and has dominant impact on transmission distortion, compared with other correlations. Due to these two properties and elegant error/distortion decomposition, our formula provides not only more accurate prediction but also lower complexity than the existing methods.

  9. The prevalence of cognitive distortion in depressed adolescents.

    PubMed

    Marton, P; Kutcher, S

    1995-01-01

    This study examined the prevalence of cognitive distortion in depressed adolescents. Ninety-four consecutive depressed adolescent psychiatric outpatients were administered the Beck Depression Inventory, the Dysfunctional Attitude Scale, the Interpersonal Dependency Inventory and the Maudsley Personality Inventory. Depressed patients who scored above a threshold for cognitive distortion were compared to those who fell below the threshold. Of the depressed patients, 47.4% were found to meet the severity criteria for cognitive distortion, while the remaining 52.6% were found to be below the severity threshold. Cognitive distortion was associated with more severe symptoms of depression, lack of social self confidence and greater introversion. These results do not support the hypothesis that cognitive distortion is universal in clinical depression. However, they do suggest that cognitive distortion is associated with more severe depression.

  10. The prevalence of cognitive distortion in depressed adolescents.

    PubMed Central

    Marton, P; Kutcher, S

    1995-01-01

    This study examined the prevalence of cognitive distortion in depressed adolescents. Ninety-four consecutive depressed adolescent psychiatric outpatients were administered the Beck Depression Inventory, the Dysfunctional Attitude Scale, the Interpersonal Dependency Inventory and the Maudsley Personality Inventory. Depressed patients who scored above a threshold for cognitive distortion were compared to those who fell below the threshold. Of the depressed patients, 47.4% were found to meet the severity criteria for cognitive distortion, while the remaining 52.6% were found to be below the severity threshold. Cognitive distortion was associated with more severe symptoms of depression, lack of social self confidence and greater introversion. These results do not support the hypothesis that cognitive distortion is universal in clinical depression. However, they do suggest that cognitive distortion is associated with more severe depression. PMID:7865499

  11. Temperature distortion generator for turboshaft engine testing

    NASA Technical Reports Server (NTRS)

    Klann, G. A.; Barth, R. L.; Biesiadny, T. J.

    1984-01-01

    The procedures and unique hardware used to conduct an experimental investigation into the response of a small-turboshaft-engine compression system to various hot gas ingestion patterns are presented. The temperature distortion generator described herein uses gaseous hydrogen to create both steady-state and time-variant, or transient, temperature distortion at the engine inlet. The range of transient temperature ramps produced by the distortion generator during the engine tests was from less than 111 deg K/sec (200 deg R/sec) to above 611 deg K/sec (1100 deg R/sec); instantaneous temperatures to 422 deg K (760 deg R) above ambient were generated. The distortion generator was used to document the maximum inlet temperatures and temperature rise rates that the compression system could tolerate before the onset of stall for various circumferential distortions as well as the compressor system response during stall.

  12. Theoretical studies of the local structures and spin Hamiltonian parameters for Cu2+ in alkaline earth alumino borate glasses

    NASA Astrophysics Data System (ADS)

    Guo, Jia-Xing; Wu, Shao-Yi; Kuang, Min-Quan; Peng, Li; Wu, Li-Na

    2018-01-01

    The local structures and spin Hamiltonian parameters are theoretically studied for Cu2+ in alkaline earth alumino borate (XAB, X = Mg, Ca and Sr) glasses by using the perturbation calculations for tetragonally elongated octahedral 3d9 groups. The [CuO6]10- groups are subject to the large relative tetragonal elongation ratios of 15.4%, 13.4% and 13.0% for MgAB, CaAB and SrAB glasses, respectively, arising from the Jahn-Teller effect. The decreasing cubic field parameter Dq, orbital reduction factor k and relative elongation ratio with the increase of the radius of alkaline earth ion X from Mg to Ca or Sr are analyzed for the studied systems in a uniform way.

  13. Charge and orbital orders and structural instability in high-pressure quadruple perovskite CeCuMn6O12

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Matsushita, Yoshitaka; Katsuya, Yoshio; Tanaka, Masahiko; Yamaura, Kazunari; Belik, Alexei A.

    2018-02-01

    We prepared a quadruple perovskite CeCuMn6O12 under high-pressure and high-temperature conditions at 6 GPa and about 1670 K and investigated its structural, magnetic and transport properties. CeCuMn6O12 crystallizes in space group Im-3 above T CO  =  297 K below this temperature, it adopts space group R-3 with the 1:3 (Mn4+:Mn3+) charge and orbital orders. Unusual compressed Mn3+O6 octahedra are realized in CeCuMn6O12 similar to CaMn7O12 with the  -Q 3 Jahn-Teller distortion mode. Below about 90 K, structural instability takes place with phase separation and the appearance of competing phases; and below 70 K, two R-3 phases coexist. CeCuMn6O12 exhibits a ferromagnetic-like transition below T C  =  140 K, and it is a semiconductor with the magnetoresistance reaching about  -40% at 140 K and 70 kOe. We argued that the valence of Ce is  +3 in CeCuMn6O12 with the Ce3+(C{{u}2+}Mn23+ )(Mn33+M{{n}4+} )O12 charge distribution in the charge-ordered R-3 phase and Ce3+(C{{u}2+}Mn23+ )(Mn43.25+ )O12 in the charge-disordered Im-3 phase.

  14. Enhanced charge ordering transition in doped CaFeO3 through steric templating

    NASA Astrophysics Data System (ADS)

    Jiang, Lai; Saldana-Greco, Diomedes; Schick, Joseph T.; Rappe, Andrew M.

    2014-06-01

    We report a density functional theory investigation of B-site doped CaFeO3, a prototypical charge ordered perovskite. At 290 K, CaFeO3 undergoes a metal-insulator transition and a charge disproportionation reaction 2Fe4+→Fe5++Fe3+. We observe that when Zr dopants occupy a (001) layer, the band gap of the resulting solid solution increases to 0.93 eV due to a two-dimensional Jahn-Teller-type distortion, where FeO6 cages on the xy plane elongate along x and y alternatively between neighboring Fe sites. Furthermore, we show that the rock-salt ordering of the Fe5+ and Fe3+ cations can be enhanced when the B-site dopants are arranged in a (111) plane due to a collective steric effect that facilitates the size discrepancy between the Fe5+O6 and Fe3+O6 octahedra and therefore gives rise to a larger band gap. The enhanced charge disproportionation in these solid solutions is verified by rigorously calculating the oxidation states of the Fe cations with different octahedral cage sizes. We therefore predict that the corresponding transition temperature will increase due to the enhanced charge ordering and larger band gap. The compositional, structural, and electrical relationships exploited in this paper can be extended to a variety of perovskites and nonperovskite oxides, providing guidance in the structural manipulation of electrical properties of functional materials.

  15. In situ XAFS and micro-XAFS studies on LiNi 0.8Co 0.15Al 0.05O 2 cathode material for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Nonaka, T.; Okuda, C.; Seno, Y.; Nakano, H.; Koumoto, K.; Ukyo, Y.

    We have applied in situ X-ray absorption fine structure (XAFS) and in situ micro-XAFS techniques to study LiNi 0.8Co 0.15Al 0.05O 2 cathode materials in Li-ion coin cells that show various levels of capacity fading: fresh cell, cycle tested cell and aging tested cell. The change in the oxidation state and local structure of Ni and Co during charge has been investigated. Ni and Co K-edge X-ray absorption near edge structure (XANES) show that the Ni oxidation state is converted from Ni 3+ to Ni 4+ upon charging, whereas the Co oxidation state hardly changes. Ni K-edge extended X-ray absorption fine structure (EXAFS) reveals that the Jahn-Teller distorted NiO 6 octahedron turns into the symmetric octahedron upon charging, which is consistent with the change in the Ni oxidation state. Ni K-edge micro-XANES show that the oxidation of Ni proceeds homogeneously in a grain of LiNi 0.8Co 0.15Al 0.05O 2 within the special resolution of ∼2 μm, and proceeds independently of the grain size. All the behaviors of Ni and Co observed in these experiments for the fresh cell remain unchanged after the capacity fade is induced by cycle tests or aging tests, which demonstrates the considerable stability of the LiNi 0.8Co 0.15Al 0.05O 2 cathode material.

  16. Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wolloch, M.; Gruner, M. E.; Keune, W.

    2016-11-01

    We present phonon dispersions, element-resolved vibrational density of states (VDOS) and corresponding thermodynamic properties obtained by a combination of density functional theory (DFT) and nuclear resonant inelastic x-ray scattering (NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and thin epitaxial films. We see distinct differences in the VDOS of the antiferromagnetic (AF) and ferromagnetic (FM) phases, which provide a microscopic proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a particular sensitivity to the slight tetragonal distortions present in epitaxial films, which is not encountered in the AF phase. This results in a notablemore » change in lattice entropy, which is important for the comparison between thin film and bulk results. Our calculations confirm the recently reported lattice instability in the AF phase. The imaginary frequencies at the X point depend critically on the Fe magnetic moment and atomic volume. Analyzing these nonvibrational modes leads to the discovery of a stable monoclinic ground-state structure, which is robustly predicted from DFT but not verified in our thin film experiments. Specific heat, entropy, and free energy calculated within the quasiharmonic approximation suggest that the new phase is possibly suppressed because of its relatively smaller lattice entropy. In the bulk phase, lattice vibrations contribute with the same sign and in similar magnitude to the isostructural AF-FM phase transition as excitations of the electronic and magnetic subsystems demonstrating that lattice degrees of freedom need to be included in thermodynamic modeling.« less

  17. Leaf Mass Area, Leaf Carbon and Nitrogen Content, Kougarok Road and Teller Road, Seward Peninsula, Alaska, 2016

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shawn Serbin; Alistair Rogers; Kim Ely

    Carbon, Nitrogen and Leaf Mass Area of leaves sampled from locations on the Kougarok Rd (transect A) and Teller Rd NGEE Arctic study sites, Seward Peninsula, Alaska. Species include: Alnus viridis spp. fruticosa, Arctostaphylos rubra, Betula glandulosa, Chamerion latifolium, Petasites frigidus, Salix alaxensis, Salix glauca, Salix pulchra, Salix richardsonii and Vaccinium uliginosum.

  18. Microwave background distortions from domain walls

    NASA Technical Reports Server (NTRS)

    Goetz, Guenter; Noetzold, Dirk

    1990-01-01

    Domain walls arising in a cosmic phase transition after decoupling were recently proposed as seeds for the formation of large scale structure. The distortion induced in the microwave background radiation is calculated in dependence of the wall thickness, surface density, scalar field potential, cosmic redshift and the velocity of the wall. It was found that the maximal redshift distortion for both spherical and planar walls is of the order pi G sigma H(sup -1)(sub 0), where sigma is the surface energy density and H(sup -1)(sub 0) the Hubble parameter. It was also found that, for a wall thickness smaller than the horizon, walls can be treated as infinitely thin, i.e., the redshift distortion is independent of the wall thickness and the specific form of the scalar potential. For planar walls moving with a Lorentz-factor gamma the redshift distortion is enhanced by gamma cubed.

  19. Nonlinear dust-lattice waves: a modified Toda lattice

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cramer, N. F.

    Charged dust grains in a plasma interact with a Coulomb potential, but also with an exponential component to the potential, due to Debye shielding in the background plasma. Here we investigate large-amplitude oscillations and waves in dust-lattices, employing techniques used in Toda lattice analysis. The lattice consists of a linear chain of particles, or a periodic ring as occurs in experimentally observed dust particle clusters. The particle motion has a triangular waveform, and chaotic motion for large amplitude motion of a grain.

  20. Area of Lattice Polygons

    ERIC Educational Resources Information Center

    Scott, Paul

    2006-01-01

    A lattice is a (rectangular) grid of points, usually pictured as occurring at the intersections of two orthogonal sets of parallel, equally spaced lines. Polygons that have lattice points as vertices are called lattice polygons. It is clear that lattice polygons come in various shapes and sizes. A very small lattice triangle may cover just 3…

  1. Plasticity and Awareness of Bodily Distortion

    PubMed Central

    Zantedeschi, Marta

    2016-01-01

    Knowledge of the body is filtered by perceptual information, recalibrated through predominantly innate stored information, and neurally mediated by direct sensory motor information. Despite multiple sources, the immediate prediction, construction, and evaluation of one's body are distorted. The origins of such distortions are unclear. In this review, we consider three possible sources of awareness that inform body distortion. First, the precision in the body metric may be based on the sight and positioning sense of a particular body segment. This view provides information on the dual nature of body representation, the reliability of a conscious body image, and implicit alterations in the metrics and positional correspondence of body parts. Second, body awareness may reflect an innate organizational experience of unity and continuity in the brain, with no strong isomorphism to body morphology. Third, body awareness may be based on efferent/afferent neural signals, suggesting that major body distortions may result from changes in neural sensorimotor experiences. All these views can be supported empirically, suggesting that body awareness is synthesized from multimodal integration and the temporal constancy of multiple body representations. For each of these views, we briefly discuss abnormalities and therapeutic strategies for correcting the bodily distortions in various clinical disorders. PMID:27630779

  2. Reflector surface distortion analysis techniques (thermal distortion analysis of antennas in space)

    NASA Technical Reports Server (NTRS)

    Sharp, R.; Liao, M.; Giriunas, J.; Heighway, J.; Lagin, A.; Steinbach, R.

    1989-01-01

    A group of large computer programs are used to predict the farfield antenna pattern of reflector antennas in the thermal environment of space. Thermal Radiation Analysis Systems (TRASYS) is a thermal radiation analyzer that interfaces with Systems Improved Numerical Differencing Analyzer (SINDA), a finite difference thermal analysis program. The programs linked together for this analysis can now be used to predict antenna performance in the constantly changing space environment. They can be used for very complex spacecraft and antenna geometries. Performance degradation caused by methods of antenna reflector construction and materials selection are also taken into consideration. However, the principal advantage of using this program linkage is to account for distortions caused by the thermal environment of space and the hygroscopic effects of the dry-out of graphite/epoxy materials after the antenna is placed into orbit. The results of this type of analysis could ultimately be used to predict antenna reflector shape versus orbital position. A phased array antenna distortion compensation system could then use this data to make RF phase front corrections. That is, the phase front could be adjusted to account for the distortions in the antenna feed and reflector geometry for a particular orbital position.

  3. Graphite distortion ``C`` Reactor. Final report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wood, N.H.

    1962-02-08

    This report covers the efforts of the Laboratory in an investigation of the graphite distortion in the ``C`` reactor at Hanford. The particular aspects of the problem to be covered by the Laboratory were possible ``fixes`` to the control rod sticking problem caused by VSR channel distortion.

  4. Effects of Distortion on Mass Flow Plug Calibration

    NASA Technical Reports Server (NTRS)

    Sasson, Jonathan; Davis, David O.; Barnhart, Paul J.

    2015-01-01

    A numerical, and experimental investigation to study the effects of flow distortion on a Mass Flow Plug (MFP) used to control and measure mass-flow during an inlet test has been conducted. The MFP was first calibrated using the WIND-US flow solver for uniform (undistorted) inflow conditions. These results are shown to compare favorably with an experimental calibration under similar conditions. The effects of distortion were investigated by imposing distorted flow conditions taken from an actual inlet test to the inflow plane of the numerical simulation. The computational fluid dynamic (CFD) based distortion study only showed the general trend in mass flow rate. The study used only total pressure as the upstream boundary condition, which was not enough to define the flow. A better simulation requires knowledge of the turbulence structure and a specific distortion pattern over a range of plug positions. It is recommended that future distortion studies utilize a rake with at least the same amount of pitot tubes as the AIP rake.

  5. Personality retesting for managing intentional distortion.

    PubMed

    Ellingson, Jill E; Heggestad, Eric D; Makarius, Erin E

    2012-05-01

    Self-report personality questionnaires often contain validity scales designed to flag individuals who intentionally distort their responses toward a more favorable characterization of themselves. Yet, there are no clear directives on how scores on these scales should be used by administrators when making high-stakes decisions about respondents. Two studies were conducted to investigate whether administrator-initiated retesting of flagged individuals represents a viable response to managing intentional distortion on personality questionnaires. We explored the effectiveness of retesting by considering whether retest responses are more accurate representations of a flagged individual's personality characteristics. A comparison of retest scores to a baseline measure of personality indicated that such scores were more accurate. Retesting should only work as a strategy for dealing with intentional distortion when individuals choose to respond more accurately the second time. Thus, we further explored the emotional reaction to being asked to retest as one possible explanation of why individuals who engage in intentional distortion respond more accurately upon retest.

  6. The Generation of Harmonic Distortion and Distortion Products in a Computational Model of the Cochlea

    NASA Astrophysics Data System (ADS)

    Meaud, Julien; Li, Yizeng; Grosh, Karl

    2011-11-01

    It is generally agreed that the nonlinear response of the cochlea is due to the forward transduction of the outer hair cell (OHC) hair bundle (HB) and subsequent alteration of the active force applied to the cochlear structures, including the basilar membrane (BM). A mechanical-acoustical-electrical model of the cochlea with three-dimensional fluid representation, and feedback from OHC somatic motility coupled to nonlinear HB mechanotransduction is used to predict nonlinear distortion of the BM response to acoustic stimulus. An efficient alternating frequency time scheme is implemented to solve for the nonlinear stationary dynamics of the cochlea. The model is used to predict the location of maximum generation of nonlinear distortion during pure tone and two-tone stimulation as well as the propagation of the distortion components on the BM.

  7. FSD: Frequency Space Differential measurement of CMB spectral distortions

    NASA Astrophysics Data System (ADS)

    Mukherjee, Suvodip; Silk, Joseph; Wandelt, Benjamin D.

    2018-07-01

    Although the cosmic microwave background (CMB) agrees with a perfect blackbody spectrum within the current experimental limits, it is expected to exhibit certain spectral distortions with known spectral properties. We propose a new method Frequency Space Differential (FSD) to measure the spectral distortions in the CMB spectrum by using the inter-frequency differences of the brightness temperature. The difference between the observed CMB temperature at different frequencies must agree with the frequency derivative of the blackbody spectrum in the absence of any distortion. However, in the presence of spectral distortions, the measured inter-frequency differences would also exhibit deviations from blackbody that can be modelled for known sources of spectral distortions like y and μ. Our technique uses FSD information for the CMB blackbody, y, μ, or any other sources of spectral distortions to model the observed signal. Successful application of this method in future CMB missions can provide an alternative method to extract spectral distortion signals and can potentially make it feasible to measure spectral distortions without an internal blackbody calibrator.

  8. Distortion improvement of capsule endoscope image

    NASA Astrophysics Data System (ADS)

    Mang, Ou-Yang; Huang, Shih-Wei; Chen, Yung-Lin; Lin, Chu-Hsun; Lin, Tai-Yung; Kuo, Yi-Ting

    2007-02-01

    Distortion exists in the present capsule endoscope image resulting from the confined space and the wide-angle requirement [8]. Based on the previous two lens works, the optimal design had obtained that the field of view was about 86 degrees , and MTF was about 18% at 100 lp/mm, but distortion would go to -26%. It's difficult to add another lens on the 7mm optical path between the dome and imaging lenses for improving distortion. In order to overcome this problem, we intend to design the optical dome as another optical lens. The original dome is transparent and has an equal thickness, namely without refracting light almost. Our objective in this paper is to design the inner curvature of the dome and associate two aspheric imaging lenses in front of the CMOS sensors to advance the distortion with maintaining field of view and MTF under the same capsule volume. Furthermore, the paper proposes the real object plane of intestine is nearly a curved surface rather than an ideal flat surface. Taking those reasons under consideration, we design three imaging lenses with curved object plane and obtain the field of view is about 86 degrees , MTF is about 26% at 100 lp/mm, and the distortion improve to -7.5%. Adding the dome lens is not only to enhance the image quality, but also to maintain the tiny volume requirement.

  9. Symmetry and lattice mismatch induced strain accommodation near and away from correlated perovskite interfaces

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vailionis, A.; Boschker, H.; Max Planck Institute for Solid State Research, 70569 Stuttgart

    2014-09-29

    Distinct MnO{sub 6} octahedral distortions near and away from the La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/SrTiO{sub 3}(001) (LSMO/STO) interface are quantified using synchrotron x-ray diffraction and dynamical x-ray diffraction simulations. Three structural regions of stress accommodation throughout the film thickness were resolved: near the LSMO/STO interface, intermediate region farther from the interface, and the main layer away from the interface. The results show that within the first two unit cells stress is accommodated by the suppression of octahedral rotations in the film, leading to the expansion of the c-axis lattice parameter. Farther from the interface film structure acquires octahedral tilts similar tomore » thicker perovskite films under tensile stress, leading to a reduced c-axis parameter. We demonstrate that these regions are related to two different strain coupling mechanisms: symmetry mismatch at the interface and lattice mismatch in the rest of the film. The findings suggest new routes for strain engineering in correlated perovskite heterostructures.« less

  10. (In) Sensitivity to spatial distortion in natural scenes

    PubMed Central

    Bex, Peter J.

    2010-01-01

    The perception of object structure in the natural environment is remarkably stable under large variation in image size and projection, especially given our insensitivity to spatial position outside the fovea. Sensitivity to periodic spatial distortions that were introduced into one quadrant of gray-scale natural images was measured in a 4AFC task. Observers were able to detect the presence of distortions in unfamiliar images even though they did not significantly affect the amplitude spectrum. Sensitivity depended on the spatial period of the distortion and on the image structure at the location of the distortion. The results suggest that the detection of distortion involves decisions made in the late stages of image perception and is based on an expectation of the typical structure of natural scenes. PMID:20462324

  11. Gamow-Teller transitions and neutron-proton-pair transfer reactions

    NASA Astrophysics Data System (ADS)

    Van Isacker, P.; Macchiavelli, A. O.

    2018-05-01

    We propose a schematic model of nucleons moving in spin-orbit partner levels, j = l ± 1/2, to explain Gamow-Teller and two-nucleon transfer data in N = Z nuclei above 40Ca. Use of the LS coupling scheme provides a more transparent approach to interpret the structure and reaction data. We apply the model to the analysis of charge-exchange, 42Ca(3He,t)42Sc, and np-transfer, 40Ca(3He,p)42Sc, reactions data to define the elementary modes of excitation in terms of both isovector and isoscalar pairs, whose properties can be determined by adjusting the parameters of the model (spin-orbit splitting, isovector pairing strength and quadrupole matrix element) to the available data. The overall agreement with experiment suggests that the approach captures the main physics ingredients and provides the basis for a boson approximation that can be extended to heavier nuclei. Our analysis also reveals that the SU(4)-symmetry limit is not realized in 42Sc.

  12. Spectral distortions of the cosmic microwave background

    NASA Technical Reports Server (NTRS)

    Adams, Fred C.; Mcdowell, Jonathan C.; Freese, Katherine; Levin, Janna

    1989-01-01

    Recent experiments indicate that the spectrum of the cosmic microwave background deviates from a pure blackbody; here, spectral distortions produced by cosmic dust are considered. The main result is that cosmic dust in conjunction with an injected radiation field (perhaps produced by an early generation of very massive stars) can explain the observed spectral distortions without violating existing cosmological constraints. In addition, it is shown that Compton y-distortions can also explain the observed spectral shape, but the energetic requirements are more severe.

  13. High-resolution study of Gamow-Teller excitations in the 42Ca(3He,t )42Sc reaction and the observation of a "low-energy super-Gamow-Teller state"

    NASA Astrophysics Data System (ADS)

    Fujita, Y.; Fujita, H.; Adachi, T.; Susoy, G.; Algora, A.; Bai, C. L.; Colò, G.; Csatlós, M.; Deaven, J. M.; Estevez-Aguado, E.; Guess, C. J.; Gulyás, J.; Hatanaka, K.; Hirota, K.; Honma, M.; Ishikawa, D.; Krasznahorkay, A.; Matsubara, H.; Meharchand, R.; Molina, F.; Nakada, H.; Okamura, H.; Ong, H. J.; Otsuka, T.; Perdikakis, G.; Rubio, B.; Sagawa, H.; Sarriguren, P.; Scholl, C.; Shimbara, Y.; Stephenson, E. J.; Suzuki, T.; Tamii, A.; Thies, J. H.; Yoshida, K.; Zegers, R. G. T.; Zenihiro, J.

    2015-06-01

    To study the Gamow-Teller (GT) transitions from the Tz=+1 nucleus 42Ca to the Tz=0 nucleus 42Sc, where Tz is the z component of isospin T , we performed a (p ,n )-type (3He,t ) charge-exchange reaction at 140 MeV/nucleon and scattering angles around 0∘. With an energy resolution of 29 keV, states excited by GT transitions (GT states) could be studied accurately. The reduced GT transition strengths B (GT) were derived up to the excitation energy of 13 MeV, assuming the proportionality between the cross sections at 0∘ and B (GT) values. The main part of the observed GT transition strength is concentrated in the lowest 0.611-MeV, Jπ=1+ GT state. All the other states at higher energies are weakly excited. Shell-model calculations could reproduce the gross feature of the experimental B (GT) distribution, and random-phase-approximation calculations including an attractive isoscalar interaction showed that the 0.611-MeV state has a collective nature. It was found that this state has all of the properties of a "low-energy super-Gamow-Teller state." It is expected that low-lying Jπ=1+ GT states have T =0 in the Tz=0 nucleus 42Sc. However, T =1 states are situated in a higher energy region. Assuming an isospin-analogous structure in A =42 isobars, analogous T =1 , 1+ states are also expected in 42Ca. Comparing the (3He 42,tCa) 42Sc and 42Ca(p ,p') spectra measured at 0∘, candidates for T =1 GT states could be found in the 10 -12 -MeV region of 42Sc. They were all weakly excited. The mass dependence of the GT strength distributions in Sc isotopes is also discussed.

  14. Enhancement of tetragonal anisotropy and stabilisation of the tetragonal phase by Bi/Mn-double-doping in BaTiO3 ferroelectric ceramics

    PubMed Central

    Yabuta, Hisato; Tanaka, Hidenori; Furuta, Tatsuo; Watanabe, Takayuki; Kubota, Makoto; Matsuda, Takanori; Ifuku, Toshihiro; Yoneda, Yasuhiro

    2017-01-01

    To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti4+ sites for donor doping of Bi3+ into the Ba2+ site. Because addition of La3+ instead of Bi3+ showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn3+ in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi3+. PMID:28367973

  15. Neutron and X-ray studies in suppressing orbital order in FeV2 O4 with Cr doping

    NASA Astrophysics Data System (ADS)

    Reig-I-Plessis, Dalmau; Wen, Zhangsu; Thaler, Alexander; Garlea, Vasile O.; Zhou, Haidong; Ruff, Jacob; MacDougall, Gregory

    2015-03-01

    FeV2O4 is a spinel compound with an orbitally active V3+ cation on a frustrated pyrochlore sublattice and Jahn-Teller active Fe3+ on a diamond sublattice. Previous studies show that this material has three structural and two magnetic transitions, and that orbital order leads to coupling between the spin and lattice degrees-of-freedom. The opposite end of the doping series is the multiferroic, FeCr2O4, which has spin, but no orbital degree of freedom on the Cr3+ and only two structural transitions. Although both materials show a higher temperature collinear ferrimagnetic state and a non-collinear phase at lower temperature, the physics must be different since the canting transition in FeV2O4 is associated with the orbital order at the lowest structural transition. In this talk, I will present the results of synchrotron X-ray and neutron powder diffraction studies of the structural and magnetic transitions in the doping series FeV2-xCrxO4. Specifically, I will comment on the doping-temperature phase diagram we extract from these measurements, and the region of co-existence between distinct non-collinear spin orders which exist at finite doping. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-FG02-07ER46453.

  16. Lattice-cell orientation disorder in complex spinel oxides

    DOE PAGES

    Chen, Yan; Cheng, Yongqiang; Li, Juchuan; ...

    2016-11-07

    Transition metal (TM) substitution has been widely applied to change complex oxides crystal structures to create high energy density electrodes materials in high performance rechargeable lithium-ion batteries. The complex local structure in the oxides imparted by the TM arrangement often impacts their electrochemical behaviors by influencing the diffusion and intercalation of lithium. Here, a major discrepancy is demonstrated between the global and local structures of the promising high energy density and high voltage LiNi 0.5Mn 1.5O 4 spinel cathode material that contradicts the existing structural models. A new single-phase lattice-cell orientation disorder model is proposed as the mechanism for themore » local ordering that explains how the inhomogeneous local distortions and the coherent connection give rise to the global structure in the complex oxide. As a result, the single-phase model is consistent with the electrochemical behavior observation of the materials.« less

  17. Strong potential wave functions with elastic channel distortion

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Macek, J.; Taulbjerg, K.

    1989-06-01

    The strong-potential Born approximation is analyzed in a channel-distorted-wave approach. Channel-distorted SPB wave functions are reduced to a conventional form in which the standard off-energy-shell factor /ital g/ has been replaced by a modified factor ..gamma.., which represents a suitable average of /ital g/ over the momentum distribution of the distorted-channel function. The modified factor is evaluated in a physically realistic model for the distortion potential, and it is found that ..gamma.. is well represented by a slowly varying phase factor. The channel-distorted SPB approximation is accordingly identical to the impulse approximation if the phase variation of ..gamma.. can bemore » ignored. This is generally the case in applications to radiative electron capture and to a good approximation for ordinary capture at not too small velocities.« less

  18. Glancing-incidence focussed ion beam milling: A coherent X-ray diffraction study of 3D nano-scale lattice strains and crystal defects

    DOE PAGES

    Hofmann, Felix; Harder, Ross J.; Liu, Wenjun; ...

    2018-05-11

    Here, this study presents a detailed examination of the lattice distortions introduced by glancing incidence Focussed Ion Beam (FIB) milling. Using non-destructive multi-reflection Bragg coherent X-ray diffraction we probe damage formation in an initially pristine gold micro-crystal following several stages of FIB milling. These experiments allow access to the full lattice strain tensor in the micro-crystal with ~25 nm 3D spatial resolution, enabling a nano-scale analysis of residual lattice strains and defects formed. Our results show that 30 keV glancing incidence milling produces fewer large defects than normal incidence milling at the same energy. However the resulting residual lattice strainsmore » have similar magnitude and extend up to ~50 nm into the sample. At the edges of the milled surface, where the ion-beam tails impact the sample at near-normal incidence, large dislocation loops with a range of Burgers vectors are formed. Further glancing incidence FIB polishing with 5 keV ion energy removes these dislocation loops and reduces the lattice strains caused by higher energy FIB milling. However, even at the lower ion energy, damage-induced lattice strains are present within a ~20 nm thick surface layer. These results highlight the need for careful consideration and management of FIB damage. They also show that low-energy FIB-milling is an effective tool for removing FIB-milling induced lattice strains. This is important for the preparation of micro-mechanical test specimens and strain microscopy samples.« less

  19. Glancing-incidence focussed ion beam milling: A coherent X-ray diffraction study of 3D nano-scale lattice strains and crystal defects

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hofmann, Felix; Harder, Ross J.; Liu, Wenjun

    Here, this study presents a detailed examination of the lattice distortions introduced by glancing incidence Focussed Ion Beam (FIB) milling. Using non-destructive multi-reflection Bragg coherent X-ray diffraction we probe damage formation in an initially pristine gold micro-crystal following several stages of FIB milling. These experiments allow access to the full lattice strain tensor in the micro-crystal with ~25 nm 3D spatial resolution, enabling a nano-scale analysis of residual lattice strains and defects formed. Our results show that 30 keV glancing incidence milling produces fewer large defects than normal incidence milling at the same energy. However the resulting residual lattice strainsmore » have similar magnitude and extend up to ~50 nm into the sample. At the edges of the milled surface, where the ion-beam tails impact the sample at near-normal incidence, large dislocation loops with a range of Burgers vectors are formed. Further glancing incidence FIB polishing with 5 keV ion energy removes these dislocation loops and reduces the lattice strains caused by higher energy FIB milling. However, even at the lower ion energy, damage-induced lattice strains are present within a ~20 nm thick surface layer. These results highlight the need for careful consideration and management of FIB damage. They also show that low-energy FIB-milling is an effective tool for removing FIB-milling induced lattice strains. This is important for the preparation of micro-mechanical test specimens and strain microscopy samples.« less

  20. Additive lattice kirigami

    PubMed Central

    Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.

    2016-01-01

    Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes. PMID:27679822

  1. Additive lattice kirigami.

    PubMed

    Castle, Toen; Sussman, Daniel M; Tanis, Michael; Kamien, Randall D

    2016-09-01

    Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes.

  2. Appraisal distortions and intimate partner violence: gender, power, and interaction.

    PubMed

    Whiting, Jason B; Oka, Megan; Fife, Stephen T

    2012-06-01

    In relationships characterized by control, abuse, or violence, many appraisal distortions occur including denial and minimization. However, the nature of the distortion varies depending on the individual's role in the relationship (i.e., abuser or victim). Reducing these distortions is an important component in treatment success and involves accepting responsibility for actions and attributions. This study used constructivist grounded theory methods to explore the following questions: (1) What are the types of distortions that are used by individuals who have been in violent or abusive relationships? (2) What are the gender and power differences in the appraisal distortions used? (3) What are the functions and interactions of the distortions in the relationship dynamics? Qualitative analysis of interviews with 29 individuals who had been in abusive relationships found that there were several types of distortions used by participants, but there were differences in the function of the distortion, depending on the individual's role in the abuse. These generally corresponded to power and gender, where the male as perpetrator used different distortions (or used similar distortions for different reasons) than did the female as victim. Suggestions for research as well as treatment implications for both offenders and survivors of abuse are given. © 2012 American Association for Marriage and Family Therapy.

  3. Restoring 2D content from distorted documents.

    PubMed

    Brown, Michael S; Sun, Mingxuan; Yang, Ruigang; Yun, Lin; Seales, W Brent

    2007-11-01

    This paper presents a framework to restore the 2D content printed on documents in the presence of geometric distortion and non-uniform illumination. Compared with textbased document imaging approaches that correct distortion to a level necessary to obtain sufficiently readable text or to facilitate optical character recognition (OCR), our work targets nontextual documents where the original printed content is desired. To achieve this goal, our framework acquires a 3D scan of the document's surface together with a high-resolution image. Conformal mapping is used to rectify geometric distortion by mapping the 3D surface back to a plane while minimizing angular distortion. This conformal "deskewing" assumes no parametric model of the document's surface and is suitable for arbitrary distortions. Illumination correction is performed by using the 3D shape to distinguish content gradient edges from illumination gradient edges in the high-resolution image. Integration is performed using only the content edges to obtain a reflectance image with significantly less illumination artifacts. This approach makes no assumptions about light sources and their positions. The results from the geometric and photometric correction are combined to produce the final output.

  4. Effects of Visual Feedback Distortion on Gait Adaptation: Comparison of Implicit Visual Distortion Versus Conscious Modulation on Retention of Motor Learning.

    PubMed

    Kim, Seung-Jae; Ogilvie, Mitchell; Shimabukuro, Nathan; Stewart, Trevor; Shin, Joon-Ho

    2015-09-01

    Visual feedback can be used during gait rehabilitation to improve the efficacy of training. We presented a paradigm called visual feedback distortion; the visual representation of step length was manipulated during treadmill walking. Our prior work demonstrated that an implicit distortion of visual feedback of step length entails an unintentional adaptive process in the subjects' spatial gait pattern. Here, we investigated whether the implicit visual feedback distortion, versus conscious correction, promotes efficient locomotor adaptation that relates to greater retention of a task. Thirteen healthy subjects were studied under two conditions: (1) we implicitly distorted the visual representation of their gait symmetry over 14 min, and (2) with help of visual feedback, subjects were told to walk on the treadmill with the intent of attaining the gait asymmetry observed during the first implicit trial. After adaptation, the visual feedback was removed while subjects continued walking normally. Over this 6-min period, retention of preserved asymmetric pattern was assessed. We found that there was a greater retention rate during the implicit distortion trial than that of the visually guided conscious modulation trial. This study highlights the important role of implicit learning in the context of gait rehabilitation by demonstrating that training with implicit visual feedback distortion may produce longer lasting effects. This suggests that using visual feedback distortion could improve the effectiveness of treadmill rehabilitation processes by influencing the retention of motor skills.

  5. Compensating for pneumatic distortion in pressure sensing devices

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.; Leondes, Cornelius T.

    1990-01-01

    A technique of compensating for pneumatic distortion in pressure sensing devices was developed and verified. This compensation allows conventional pressure sensing technology to obtain improved unsteady pressure measurements. Pressure distortion caused by frictional attenuation and pneumatic resonance within the sensing system makes obtaining unsteady pressure measurements by conventional sensors difficult. Most distortion occurs within the pneumatic tubing which transmits pressure impulses from the aircraft's surface to the measurement transducer. To avoid pneumatic distortion, experiment designers mount the pressure sensor at the surface of the aircraft, (called in-situ mounting). In-situ transducers cannot always fit in the available space and sometimes pneumatic tubing must be run from the aircraft's surface to the pressure transducer. A technique to measure unsteady pressure data using conventional pressure sensing technology was developed. A pneumatic distortion model is reduced to a low-order, state-variable model retaining most of the dynamic characteristics of the full model. The reduced-order model is coupled with results from minimum variance estimation theory to develop an algorithm to compensate for the effects of pneumatic distortion. Both postflight and real-time algorithms are developed and evaluated using simulated and flight data.

  6. Radial line method for rear-view mirror distortion detection

    NASA Astrophysics Data System (ADS)

    Rahmah, Fitri; Kusumawardhani, Apriani; Setijono, Heru; Hatta, Agus M.; Irwansyah, .

    2015-01-01

    An image of the object can be distorted due to a defect in a mirror. A rear-view mirror is an important component for the vehicle safety. One of standard parameters of the rear-view mirror is a distortion factor. This paper presents a radial line method for distortion detection of the rear-view mirror. The rear-view mirror was tested for the distortion detection by using a system consisting of a webcam sensor and an image-processing unit. In the image-processing unit, the captured image from the webcam were pre-processed by using smoothing and sharpening techniques and then a radial line method was used to define the distortion factor. It was demonstrated successfully that the radial line method could be used to define the distortion factor. This detection system is useful to be implemented such as in Indonesian's automotive component industry while the manual inspection still be used.

  7. Dual tunneling-unit scanning tunneling microscope for length measurement based on crystalline lattice

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, H.; Higuchi, T.; Nishioki, N.

    1997-01-01

    A dual tunneling-unit scanning tunneling microscope (DTU STM) was developed for nm order length measurement with wide scan range. The crystalline lattice of highly oriented pyrolitic graphite (HOPG) was used as reference scale. A reference unit was set up on top of a test unit. The reference sample holder and the probe tip of test unit were attached to one single XY scanner on either surface, while the test sample holder was open. This enables simultaneous acquisition of wide images of HOPG and test sample. The length in test sample image was measured by counting the number of HOPG lattices.more » An inchworm actuator and an impact drive mechanism were introduced to roughly position probe tips. The XY scanner was designed to be elastic to eliminate image distortion. Some comparison experiments using two HOPG chips were carried out in air. The DTU STM is confirmed to be a stable and more powerful device for length measurement which has nanometer accuracy when covering a wide scan range up to several micrometers, and is capable of measuring comparatively large and heavy samples. {copyright} {ital 1997 American Vacuum Society.}« less

  8. Bilateral Symmetry of Distortions of Tactile Size Perception.

    PubMed

    Longo, Matthew R; Ghosh, Arko; Yahya, Tasneem

    2015-01-01

    The perceived distance between touches on the limbs is generally bigger for distances oriented across the width of the limb than for distances oriented along the length of the limb. The present study aimed to investigate the coherence of such distortions of tactile size perception across different skin surfaces. We investigated distortions of tactile size perception on the dorsal and palmar surfaces of both the left and right hands as well as the forehead. Participants judged which of two tactile distances felt larger. One distance was aligned with the proximodistal axis (along the body), the other with the mediolateral axis (across the body). Clear distortions were found on all five skin surfaces, with stimuli oriented across the width of the body being perceived as farther apart than those oriented along the length of the body. Consistent with previous results, distortions were smaller on the palmar than on the dorsal hand surface. Distortion on the forehead was intermediate between the dorsal and palmar surfaces. There were clear correlations between distortion on the left and right hands, for both the dorsal and palmar skin surfaces. In contrast, within each hand, there was no significant correlation between the two skin surfaces. Distortion on the forehead was not significantly correlated with that on any of the other skin surfaces. These results provide evidence for bilaterally symmetric representations underlying tactile size perception. © The Author(s) 2015.

  9. Effects of deterministic surface distortions on reflector antenna performance

    NASA Technical Reports Server (NTRS)

    Rahmat-Samii, Y.

    1985-01-01

    Systematic distortions of reflector antenna surfaces can cause antenna radiation patterns to be undesirably different from those of perfectly smooth reflector surfaces. In this paper, a simulation model for systematic distortions is described which permits an efficient computation of the effects of distortions in the reflector pattern. The model uses a vector diffraction physical optics analysis for the determination of both the co-polar and cross-polar fields. An interpolation scheme is also presented for the description of reflector surfaces which are prescribed by discrete points. Representative numerical results are presented for reflectors with sinusoidally and thermally distorted surfaces. Finally, comparisons are made between the measured and calculated patterns of a slowly-varying distorted offset parabolic reflector.

  10. Distortion Properties of GaN Switches at High-Temperatures

    NASA Astrophysics Data System (ADS)

    Kameche, Mohamed

    2006-08-01

    The origins of HEMT distortion in passive control applications as SPST switch are presented in this paper. Also, this paper describes the change of the AlGaN/GaN HEMT switch distortion properties (second-and third distortion intercept points) over a wide range of temperature. The results indicate that the change in second-and third-order distortion intercept points is smaller (about 2dBm) over a wide range of temperature from -50 to +300°C. A comparison of the GaN-based HEMT switch with InP-and GaAs-HEMT switches shows that the GaN technology generates lower distortion than its InP and GaAs technologies counterpart.

  11. Enhanced way of securing automated teller machine to track the misusers using secure monitor tracking analysis

    NASA Astrophysics Data System (ADS)

    Sadhasivam, Jayakumar; Alamelu, M.; Radhika, R.; Ramya, S.; Dharani, K.; Jayavel, Senthil

    2017-11-01

    Now a days the people's attraction towards Automated Teller Machine(ATM) has been increasing even in rural areas. As of now the security provided by all the bank is ATM pin number. Hackers know the way to easily identify the pin number and withdraw money if they haven stolen the ATM card. Also, the Automated Teller Machine is broken and the money is stolen. To overcome these disadvantages, we propose an approach “Automated Secure Tracking System” to secure and tracking the changes in ATM. In this approach, while creating the bank account, the bank should scan the iris known (a part or movement of our eye) and fingerprint of the customer. The scanning can be done with the position of the eye movements and fingerprints identified with the shortest measurements. When the card is swiped then ATM should request the pin, scan the iris and recognize the fingerprint and then allow the customer to withdraw money. If somebody tries to break the ATM an alert message is given to the nearby police station and the ATM shutter is automatically closed. This helps in avoiding the hackers who withdraw money by stealing the ATM card and also helps the government in identifying the criminals easily.

  12. Evaluation of Spin Hamiltonian Parameters and Local Structure of Cu2+-doped Ion in xK2SO4-(50 - x)Na2SO4-50ZnSO4 Glasses with Various K2SO4 Concentrations

    NASA Astrophysics Data System (ADS)

    Ding, Ch.-Ch.; Wu, Sh.-Y.; Xu, Y.-Q.; Zhang, L.-J.; He, J.-J.

    2018-03-01

    The spin Hamiltonian parameters (SHPs), i.e., g factors and hyperfine structure constants, and local structures are theoretically studied by analyzing tetragonally elongated 3d9 clusters for Cu2+ in xK2SO4-(50 - x)Na2SO4-50ZnSO4 glasses with various K2SO4 concentrations x. The concentration dependences of the SHPs are attributed to the parabolic decreases of the cubic field parameter Dq, orbital reduction factor k, relative tetragonal elongation ratio τ, and core polarization constant κ with x. The [CuO6]10- clusters are found to undergo significant elongations of about 17% due to the Jahn-Teller effect. The calculated cubic field splittings and the SHPs at various concentrations agree well with the experimental data.

  13. Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials

    DOE PAGES

    Neukirch, Amanda J.; Nie, Wanyi; Blancon, Jean-Christophe; ...

    2016-05-25

    Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. In spite of the remarkable progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. High on the list of unexplained phenomena are very modest mobilities despite low charge carrier effective masses. Moreover, experiments elucidate unique degradation of photocurrent affecting stable operation of perovskite solar cells. These puzzles suggest that, while ionic hybrid perovskite devices may have efficiencies on par with conventional Si and GaAs devices, they exhibit more complicated charge transport phenomena. Wemore » report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using both periodic boundary conditions and isolated structures. Using the hybrid density functional theory, we found that volumetric strain in a CsPbI 3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI 3 (MA = CH 3NH 3) cluster, both volumetric strain and MA reorientation effects lead to larger binding energies at around 600 and 1300 meV for holes and electrons, respectively. Such large reorganization energies suggest appearance of small polarons in organometallic perovskite materials. Furthermore, the fact that both volumetric lattice strain and MA molecular rotational degrees of freedom can cooperate to create and stabilize polarons indicates that in order to mitigate this problem, formamidinium (FA = HC(NH 2) 2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.« less

  14. What makes an automated teller machine usable by blind users?

    PubMed

    Manzke, J M; Egan, D H; Felix, D; Krueger, H

    1998-07-01

    Fifteen blind and sighted subjects, who featured as a control group for acceptance, were asked for their requirements for automated teller machines (ATMs). Both groups also tested the usability of a partially operational ATM mock-up. This machine was based on an existing cash dispenser, providing natural speech output, different function menus and different key arrangements. Performance and subjective evaluation data of blind and sighted subjects were collected. All blind subjects were able to operate the ATM successfully. The implemented speech output was the main usability factor for them. The different interface designs did not significantly affect performance and subjective evaluation. Nevertheless, design recommendations can be derived from the requirement assessment. The sighted subjects were rather open for design modifications, especially the implementation of speech output. However, there was also a mismatch of the requirements of the two subject groups, mainly concerning the key arrangement.

  15. Systems and methods for mirror mounting with minimized distortion

    NASA Technical Reports Server (NTRS)

    Antonille, Scott R. (Inventor); Wallace, Thomas E. (Inventor); Content, David A. (Inventor); Wake, Shane W. (Inventor)

    2012-01-01

    A method for mounting a mirror for use in a telescope includes attaching the mirror to a plurality of adjustable mounts; determining a distortion in the mirror caused by the plurality adjustable mounts, and, if the distortion is determined to be above a predetermined level: adjusting one or more of the adjustable mounts; and determining the distortion in the mirror caused by the adjustable mounts; and in the event the determined distortion is determined to be at or below the predetermined level, rigidizing the adjustable mounts.

  16. Dinuclear metallacycles with single M-O(H)-M bridges [M = Fe(II), Co(II), Ni(II), Cu(II)]: effects of large bridging angles on structure and antiferromagnetic superexchange interactions.

    PubMed

    Reger, Daniel L; Pascui, Andrea E; Foley, Elizabeth A; Smith, Mark D; Jezierska, Julia; Ozarowski, Andrew

    2014-02-17

    The reactions of M(ClO4)2·xH2O and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) in the presence of triethylamine lead to the formation of monohydroxide-bridged, dinuclear metallacycles of the formula [M2(μ-OH)(μ-Lm)2](ClO4)3 (M = Fe(II), Co(II), Cu(II)) or [M2(μ-OH)(μ-Lm*)2](ClO4)3 (M = Co(II), Ni(II), Cu(II)). With the exception of the complexes where the ligand is Lm and the metal is copper(II), all of these complexes have distorted trigonal bipyramidal geometry around the metal centers and unusual linear (Lm*) or nearly linear (Lm) M-O-M angles. For the two solvates of [Cu2(μ-OH)(μ-Lm)2](ClO4)3, the Cu-O-Cu angles are significantly bent and the geometry about the metal is distorted square pyramidal. All of the copper(II) complexes have structural distortions expected for the pseudo-Jahn-Teller effect. The two cobalt(II) complexes show moderate antiferromagnetic coupling, -J = 48-56 cm(-1), whereas the copper(II) complexes show very strong antiferromagnetic coupling, -J = 555-808 cm(-1). The largest coupling is observed for [Cu2(μ-OH)(μ-Lm*)2](ClO4)3, the complex with a Cu-O-Cu angle of 180°, such that the exchange interaction is transmitted through the dz(2) and the oxygen s and px orbitals. The interaction decreases, but it is still significant, as the Cu-O-Cu angle decreases and the character of the metal orbital becomes increasingly d(x(2)-y(2)). These intermediate geometries and magnetic interactions lead to spin Hamiltonian parameters for the copper(II) complexes in the EPR spectra that have large E/D ratios and one g matrix component very close to 2. Density functional theory calculations were performed using the hybrid B3LYP functional in association with the TZVPP basis set, resulting in reasonable agreement with the experiments.

  17. Interior of a charged distorted black hole

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Abdolrahimi, Shohreh; Frolov, Valeri P.; Shoom, Andrey A.

    We study the interior of a charged, nonrotating distorted black hole. We consider static and axisymmetric black holes, and focus on a special case when an electrically charged distorted solution is obtained by the Harrison-Ernst transformation from an uncharged one. We demonstrate that the Cauchy horizon of such a black hole remains regular, provided the distortion is regular at the event horizon. The shape and the inner geometry of both the outer and inner (Cauchy) horizons are studied. We demonstrate that there exists a duality between the properties of the horizons. Proper time of a free fall of a testmore » particle moving in the interior of the distorted black hole along the symmetry axis is calculated. We also study the property of the curvature in the inner domain between the horizons. Simple relations between the 4D curvature invariants and the Gaussian curvature of the outer and inner horizon surfaces are found.« less

  18. 76 FR 6640 - Advantage Life Products, Inc., and B-Teller, Inc. (n/k/a CA Goldfields, Inc.), Order of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-07

    ..., Inc. (n/k/a CA Goldfields, Inc.), Order of Suspension of Trading February 3, 2011. It appears to the... current and accurate information concerning the securities of B-Teller, Inc. (n/k/a CA Goldfields, Inc...(k) of the Securities Exchange Act of 1934, that trading in the securities of the above-listed...

  19. Correction of amplitude-phase distortion for polarimetric active radar calibrator

    NASA Astrophysics Data System (ADS)

    Lin, Jianzhi; Li, Weixing; Zhang, Yue; Chen, Zengping

    2015-01-01

    The polarimetric active radar calibrator (PARC) is extensively used as an external test target for system distortion compensation and polarimetric calibration for the high-resolution polarimetric radar. However, the signal undergoes distortion in the PARC, affecting the effectiveness of the compensation and the calibration. The system distortion compensation resulting from the distortion of the amplitude and phase in the PARC was analyzed based on the "method of paired echoes." Then the correction method was proposed, which separated the ideal signals from the distorted signals. Experiments were carried on real radar data, and the experimental results were in good agreement with the theoretical analysis. After the correction, the PARC can be better used as an external test target for the system distortion compensation.

  20. Ultrafast diffraction conoscopy of the structural phase transition in VO2: Evidence of two lattice distortions

    NASA Astrophysics Data System (ADS)

    Kumar, Nardeep; Rúa, Armando; Fernández, Félix E.; Lysenko, Sergiy

    2017-06-01

    Photoinduced phase transitions in complex correlated systems occur very rapidly and involve the interplay between various electronic and lattice degrees of freedom. For these materials to be considered for practical applications, it is important to discover how their phase transitions take place. Here we use a novel ultrafast diffraction conoscopy technique to study the evolution of vanadium dioxide (VO2) from biaxial to uniaxial symmetry. A key finding in this study is an additional relaxation process through which the phase transition takes place. Our results show that the biaxial monoclinic crystal initially, within the first 100-300 fs, transforms to a transient biaxial crystal, and within the next 300-400 fs converts into a uniaxial rutile crystal. The characteristic times for these transitions depend on film morphology and are presumably altered by misfit strain. We take advantage of Landau phenomenology to describe the complex dynamics of VO2 phase transition in the femtosecond regime.