Unusual Crystallization Behavior Close to the Glass Transition

NASA Astrophysics Data System (ADS)

Desgranges, Caroline; Delhommelle, Jerome

2018-03-01

Using molecular simulations, we shed light on the mechanism underlying crystal nucleation in metal alloys and unravel the interplay between crystal nucleation and glass transition, as the conditions of crystallization lie close to this transition. While decreasing the temperature of crystallization usually results in a lower free energy barrier, we find an unexpected reversal of behavior for glass-forming alloys as the temperature of crystallization approaches the glass transition. For this purpose, we simulate the crystallization process in two glass-forming Copper alloys, Ag6 Cu4 , which has a positive heat of mixing, and CuZr, characterized by a large negative heat of mixing. Our results allow us to identify this unusual behavior as directly correlated with a nonmonotonic temperature dependence for the formation energy of connected icosahedral structures, which are incompatible with crystalline order and impede the development of the crystal nucleus, leading to an unexpectedly larger free energy barrier at low temperature. This, in turn, promotes the formation of a predominantly closed-packed critical nucleus, with fewer defects, thereby suggesting a new way to control the structure of the crystal nucleus, which is of key importance in catalysis.

Formation of crystal-like structures and branched networks from nonionic spherical micelles

NASA Astrophysics Data System (ADS)

Cardiel, Joshua J.; Furusho, Hirotoshi; Skoglund, Ulf; Shen, Amy Q.

2015-12-01

Crystal-like structures at nano and micron scales have promise for purification and confined reactions, and as starting points for fabricating highly ordered crystals for protein engineering and drug discovery applications. However, developing controlled crystallization techniques from batch processes remain challenging. We show that neutrally charged nanoscale spherical micelles from biocompatible nonionic surfactant solutions can evolve into nano- and micro-sized branched networks and crystal-like structures. This occurs under simple combinations of temperature and flow conditions. Our findings not only suggest new opportunities for developing controlled universal crystallization and encapsulation procedures that are sensitive to ionic environments and high temperatures, but also open up new pathways for accelerating drug discovery processes, which are of tremendous interest to pharmaceutical and biotechnological industries.

Temperature-dependent μ-Raman investigation of struvite crystals.

PubMed

Prywer, Jolanta; Kasprowicz, D; Runka, T

2016-04-05

The effect of temperature on the vibrational properties of struvite crystals grown from silica gels was systematically studied by μ-Raman spectroscopy. The time-dependent Raman spectra recorded in the process of long time annealing of struvite crystal at 353 K do not indicate structural changes in the struvite crystal with the time of annealing. The temperature-dependent Raman spectra recorded in the range 298-423 K reveal a phase transition in struvite at about 368 K. Above this characteristic temperature, some of bands assigned to vibrations of the PO4 and NH4 tetrahedra and water molecules observed in the Raman spectra in low temperatures (orthorhombic phase) change their spectral parameters or disappear, which indicates a transition to a higher symmetry structure of struvite in the range of high temperatures. Copyright © 2016 Elsevier B.V. All rights reserved.

Shear induced structures in crystallizing cocoa butter

NASA Astrophysics Data System (ADS)

Mazzanti, Gianfranco; Guthrie, Sarah E.; Sirota, Eric B.; Marangoni, Alejandro G.; Idziak, Stefan H. J.

2004-03-01

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear from the melt in temperature controlled Couette cells, at final crystallization temperatures of 17.5^oC, 20^oC and 22.5^oC in Beamline X10A of NSLS. The formation of phase X was observed at low shear rates (90 s-1) and low crystallization temperature (17.5^oC), but was absent at high shear (720 s-1) and high temperature (20^oC). The d-spacing and melting point suggest that this new phase is a mixture rich on two of the three major components of cocoa butter. We also found that, contrary to previous reports, the transition from phase II to phase V can happen through the intermediate phase IV, at high shear rates and temperature.

Structure determination of an integral membrane protein at room temperature from crystals in situ

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

Axford, Danny; Foadi, James; Imperial College London, London SW7 2AZ

2015-05-14

The X-ray structure determination of an integral membrane protein using synchrotron diffraction data measured in situ at room temperature is demonstrated. The structure determination of an integral membrane protein using synchrotron X-ray diffraction data collected at room temperature directly in vapour-diffusion crystallization plates (in situ) is demonstrated. Exposing the crystals in situ eliminates manual sample handling and, since it is performed at room temperature, removes the complication of cryoprotection and potential structural anomalies induced by sample cryocooling. Essential to the method is the ability to limit radiation damage by recording a small amount of data per sample from many samplesmore » and subsequently assembling the resulting data sets using specialized software. The validity of this procedure is established by the structure determination of Haemophilus influenza TehA at 2.3 Å resolution. The method presented offers an effective protocol for the fast and efficient determination of membrane-protein structures at room temperature using third-generation synchrotron beamlines.« less

The topological pressure-temperature phase diagram and crystal structures of the dimorphic system spiperone.

PubMed

Robert, B; Perrin, M-A; Coquerel, G; Céolin, R; Rietveld, I B

2016-03-01

The topological pressure-temperature phase diagram for the dimorphism of spiperone, a potent neuroleptic drug, has been constructed using literature data and improved crystal structures obtained with new crystallographic data from single-crystal X-ray diffraction at various temperatures. It is inferred that form II, which is the more dense form and exhibits the lower melting temperature, becomes the more stable phase under pressure. Under ambient conditions, form I is more stable. Copyright © 2015 Académie Nationale de Pharmacie. Published by Elsevier Masson SAS. All rights reserved.

“Skin-Core-Skin” Structure of Polymer Crystallization Investigated by Multiscale Simulation

PubMed Central

Ruan, Chunlei

2018-01-01

“Skin-core-skin” structure is a typical crystal morphology in injection products. Previous numerical works have rarely focused on crystal evolution; rather, they have mostly been based on the prediction of temperature distribution or crystallization kinetics. The aim of this work was to achieve the “skin-core-skin” structure and investigate the role of external flow and temperature fields on crystal morphology. Therefore, the multiscale algorithm was extended to the simulation of polymer crystallization in a pipe flow. The multiscale algorithm contains two parts: a collocated finite volume method at the macroscopic level and a morphological Monte Carlo method at the microscopic level. The SIMPLE (semi-implicit method for pressure linked equations) algorithm was used to calculate the polymeric model at the macroscopic level, while the Monte Carlo method with stochastic birth-growth process of spherulites and shish-kebabs was used at the microscopic level. Results show that our algorithm is valid to predict “skin-core-skin” structure, and the initial melt temperature and the maximum velocity of melt at the inlet mainly affects the morphology of shish-kebabs. PMID:29659516

Generalization of soft phonon modes

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

Rudin, Sven P.

Soft phonon modes describe a collective movement of atoms that transform a higher-symmetry crystal structure into a lower-symmetry crystal structure. Such structural transformations occur at finite temperatures, where the phonons (i.e., the low-temperature vibrational modes) and the static perfect crystal structures provide an incomplete picture of the dynamics. In this paper, principal vibrational modes (PVMs) are introduced as descriptors of the dynamics of a material system withmore » $N$ atoms. The PVMs represent the independent collective movements of the atoms at a given temperature. Molecular dynamics (MD) simulations, here in the form of quantum MD using density functional theory calculations, provide both the data describing the atomic motion and the data used to construct the PVMs. The leading mode, $${\\mathrm{PVM}}_{0}$$, represents the $3N$-dimensional direction in which the system moves with greatest amplitude. For structural phase transitions, $${\\mathrm{PVM}}_{0}$$ serves as a generalization of soft phonon modes. At low temperatures, $${\\mathrm{PVM}}_{0}$$ reproduces the soft phonon mode in systems where one phonon dominates the phase transformation. In general, multiple phonon modes combine to describe a transformation, in which case $${\\mathrm{PVM}}_{0}$$ culls these phonon modes. Moreover, while soft phonon modes arise in the higher-symmetry crystal structure, $${\\mathrm{PVM}}_{0}$$ can be equally well calculated on either side of the structural phase transition. Finally, two applications demonstrate these properties: first, transitions into and out of bcc titanium, and, second, the two crystal structures proposed for the $${\\beta}$$ phase of uranium, the higher-symmetry structure of which stabilizes with temperature.« less

Generalization of soft phonon modes

DOE PAGES

Rudin, Sven P.

2018-04-27

Soft phonon modes describe a collective movement of atoms that transform a higher-symmetry crystal structure into a lower-symmetry crystal structure. Such structural transformations occur at finite temperatures, where the phonons (i.e., the low-temperature vibrational modes) and the static perfect crystal structures provide an incomplete picture of the dynamics. In this paper, principal vibrational modes (PVMs) are introduced as descriptors of the dynamics of a material system withmore » $N$ atoms. The PVMs represent the independent collective movements of the atoms at a given temperature. Molecular dynamics (MD) simulations, here in the form of quantum MD using density functional theory calculations, provide both the data describing the atomic motion and the data used to construct the PVMs. The leading mode, $${\\mathrm{PVM}}_{0}$$, represents the $3N$-dimensional direction in which the system moves with greatest amplitude. For structural phase transitions, $${\\mathrm{PVM}}_{0}$$ serves as a generalization of soft phonon modes. At low temperatures, $${\\mathrm{PVM}}_{0}$$ reproduces the soft phonon mode in systems where one phonon dominates the phase transformation. In general, multiple phonon modes combine to describe a transformation, in which case $${\\mathrm{PVM}}_{0}$$ culls these phonon modes. Moreover, while soft phonon modes arise in the higher-symmetry crystal structure, $${\\mathrm{PVM}}_{0}$$ can be equally well calculated on either side of the structural phase transition. Finally, two applications demonstrate these properties: first, transitions into and out of bcc titanium, and, second, the two crystal structures proposed for the $${\\beta}$$ phase of uranium, the higher-symmetry structure of which stabilizes with temperature.« less

Artificial crystals with 3d metal and palladium particles subjected to high-temperature heat treatment

NASA Astrophysics Data System (ADS)

Rinkevich, A. B.; Nemytova, O. V.; Perov, D. V.; Samoylovich, M. I.; Kuznetsov, E. A.

2018-04-01

High-temperature heat treatment has valuable impact on the structure and physical properties of artificial crystals with 3d metal and palladium particles. Artificial crystals are obtained by means of introduction of particles into the interspherical voids of opal matrices. The magnetic properties are studied at the temperatures ranging from 2 to 300 K and in fields up to 350 kOe. Microwave properties are investigated in the millimeter frequency range. The complex dielectric permittivity of several nanocomposites is measured. The influence of heat treatment up to 960 °C on the structure of artificial crystals is clarified.

Control of morphology and crystal purity of InP nanowires by variation of phosphine flux during selective area MOMBE

NASA Astrophysics Data System (ADS)

Kelrich, A.; Dubrovskii, V. G.; Calahorra, Y.; Cohen, S.; Ritter, D.

2015-02-01

We present experimental results showing how the growth rate, morphology and crystal structure of Au-catalyzed InP nanowires (NWs) fabricated by selective area metal organic molecular beam epitaxy can be tuned by the growth parameters: temperature and phosphine flux. The InP NWs with 20-65 nm diameters are grown at temperatures of 420 and 480 °C with the PH3 flow varying from 1 to 9 sccm. The NW tapering is suppressed at a higher temperature, while pure wurtzite crystal structure is preferred at higher phosphine flows. Therefore, by combining high temperature and high phosphine flux, we are able to fabricate non-tapered and stacking fault-free InP NWs with the quality that other methods rarely achieve. We also develop a model for NW growth and crystal structure which explains fairly well the observed experimental tendencies.

Room-temperature serial crystallography at synchrotron X-ray sources using slowly flowing free-standing high-viscosity microstreams.

PubMed

Botha, Sabine; Nass, Karol; Barends, Thomas R M; Kabsch, Wolfgang; Latz, Beatrice; Dworkowski, Florian; Foucar, Lutz; Panepucci, Ezequiel; Wang, Meitian; Shoeman, Robert L; Schlichting, Ilme; Doak, R Bruce

2015-02-01

Recent advances in synchrotron sources, beamline optics and detectors are driving a renaissance in room-temperature data collection. The underlying impetus is the recognition that conformational differences are observed in functionally important regions of structures determined using crystals kept at ambient as opposed to cryogenic temperature during data collection. In addition, room-temperature measurements enable time-resolved studies and eliminate the need to find suitable cryoprotectants. Since radiation damage limits the high-resolution data that can be obtained from a single crystal, especially at room temperature, data are typically collected in a serial fashion using a number of crystals to spread the total dose over the entire ensemble. Several approaches have been developed over the years to efficiently exchange crystals for room-temperature data collection. These include in situ collection in trays, chips and capillary mounts. Here, the use of a slowly flowing microscopic stream for crystal delivery is demonstrated, resulting in extremely high-throughput delivery of crystals into the X-ray beam. This free-stream technology, which was originally developed for serial femtosecond crystallography at X-ray free-electron lasers, is here adapted to serial crystallography at synchrotrons. By embedding the crystals in a high-viscosity carrier stream, high-resolution room-temperature studies can be conducted at atmospheric pressure using the unattenuated X-ray beam, thus permitting the analysis of small or weakly scattering crystals. The high-viscosity extrusion injector is described, as is its use to collect high-resolution serial data from native and heavy-atom-derivatized lysozyme crystals at the Swiss Light Source using less than half a milligram of protein crystals. The room-temperature serial data allow de novo structure determination. The crystal size used in this proof-of-principle experiment was dictated by the available flux density. However, upcoming developments in beamline optics, detectors and synchrotron sources will enable the use of true microcrystals. This high-throughput, high-dose-rate methodology provides a new route to investigating the structure and dynamics of macromolecules at ambient temperature.

The Effect of Acidity Coefficient on Crystallization Behavior of Blast Furnace Slag Fibers

NASA Astrophysics Data System (ADS)

Tian, Tie-Lei; Zhang, Yu-Zhu; Xing, Hong-wei; Li, Jie; Zhang, Zun-Qian

2018-01-01

The chemical structure of mineral wool fiber was investigated by using Fourier Transform Infrared Spectroscopy (FTIR). Next, the glass transition temperature and the crystallization temperature of the fibers were studied. Finally, the crystallization kinetics of fiber was studied. The results show that the chemical bond structure of fibers gets more random with the increase of acidity coefficient. The crystallization phases of the fibers are mainly melilites, and also a few anorthites and diopsides. The growth mechanism of the crystals is three dimensional. The fibers with acidity coefficient of 1.2 exhibit the best thermal stability and is hard to crystallize as it has the maximum aviation energy of crystallization kinetics.

Debranching and temperature-cycled crystallization of waxy rice starch and their digestibility.

PubMed

Zeng, Feng; Ma, Fei; Gao, Qunyu; Yu, Shujuan; Kong, Fansheng; Zhu, Siming

2014-11-26

Slowly digestible starch (SDS) was obtained through debranched waxy rice starch and subsequent crystallization under isothermal and temperature-cycled conditions. Temperature-cycled crystallization of dual 4/-20 °C produced a higher yield of SDS product than isotherm crystallization. Crystal structure of SDS products changed from A-type to a mixture of B and V-type X-ray diffraction patterns. The relative crystallinity was higher in the temperature-cycled samples than that of isotherm. Attenuated total reflectance Fourier transform infrared spectroscopy suggested that the peripheral regions of isothermal storage starch were better organized than temperature-cycles. Temperature cycling induced higher onset temperature for melting of crystals than isothermal storage under a differential scanning calorimeter. The cycled temperature storage induced a greater amount of SDS than the isothermal storage. Copyright © 2014 Elsevier Ltd. All rights reserved.

Reduced-temperature crystallization of thin amorphous Fe80B20 films studied via empirical modeling of extended x-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Harris, V. G.; Oliver, S. A.; Ayers, J. D.; Das, B. N.; Koon, N. C.

1996-04-01

The evolution of the local atomic environment around Fe atoms in very thin (15 nm), amorphous, partially crystallized and fully crystallized films of Fe80B20 was studied using extended x-ray absorption fine structure (EXAFS) measurements. The relative atomic fraction of each crystalline phase present in the annealed samples was extracted from the Fe EXAFS data by a least-squares fitting procedure, using data collected from t-Fe3B, t-Fe2B, and α-Fe standards. The type and relative fraction of the crystallization products follows the trends previously measured in Fe80B20 melt-spun ribbons, except for the fact that crystallization temperatures are ≊200 K lower than those measured in bulk equivalents. This greatly reduced crystallization temperature may arise from the dominant role of surface nucleation sites in the crystallization of very thin amorphous films.

Apparatus for growing HgI.sub.2 crystals

DOEpatents

Schieber, Michael M.; Beinglass, Israel; Dishon, Giora

1978-01-01

A method and horizontal furnace for vapor phase growth of HgI.sub.2 crystals which utilizes controlled axial and radial airflow to maintain the desired temperature gradients. The ampoule containing the source material is rotated while axial and radial air tubes are moved in opposite directions during crystal growth to maintain a desired distance and associated temperature gradient with respect to the growing crystal, whereby the crystal interface can advance in all directions, i.e., radial and axial according to the crystallographic structure of the crystal. Crystals grown by this method are particularly applicable for use as room-temperature nuclear radiation detectors.

Crystal growth, structural, low temperature thermoluminescence and mechanical properties of cubic fluoroperovskite single crystal (LiBaF3)

NASA Astrophysics Data System (ADS)

Daniel, D. Joseph; Ramasamy, P.; Ramaseshan, R.; Kim, H. J.; Kim, Sunghwan; Bhagavannarayana, G.; Cheon, Jong-Kyu

2017-10-01

Polycrystalline compounds of LiBaF3 were synthesized using conventional solid state reaction route and the phase purity was confirmed using powder X-ray diffraction technique. Using vertical Bridgman technique single crystal was grown from melt. Rocking curve measurements have been carried out to study the structural perfection of the grown crystal. The single peak of diffraction curve clearly reveals that the grown crystal was free from the structural grain boundaries. The low temperature thermoluminescence of the X-ray irradiated sample has been analyzed and found four distinguishable peaks having maximum temperatures at 18, 115, 133 and 216 K. Activation energy (E) and frequency factor (s) for the individual peaks have been studied using Peak shape method and the computerized curve fitting method combining with the Tmax- TStop procedure. Nanoindentation technique was employed to study the mechanical behaviour of the crystal. The indentation modulus and Vickers hardness of the grown crystal have values of 135.15 GPa and 680.81 respectively, under the maximum indentation load of 10 mN.

Low-Temperature Crystal Structures of the Hard Core Square Shoulder Model.

PubMed

Gabriëlse, Alexander; Löwen, Hartmut; Smallenburg, Frank

2017-11-07

In many cases, the stability of complex structures in colloidal systems is enhanced by a competition between different length scales. Inspired by recent experiments on nanoparticles coated with polymers, we use Monte Carlo simulations to explore the types of crystal structures that can form in a simple hard-core square shoulder model that explicitly incorporates two favored distances between the particles. To this end, we combine Monte Carlo-based crystal structure finding algorithms with free energies obtained using a mean-field cell theory approach, and draw phase diagrams for two different values of the square shoulder width as a function of the density and temperature. Moreover, we map out the zero-temperature phase diagram for a broad range of shoulder widths. Our results show the stability of a rich variety of crystal phases, such as body-centered orthogonal (BCO) lattices not previously considered for the square shoulder model.

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.

Effects of thermo-order-mechanical coupling on band structures in liquid crystal nematic elastomer porous phononic crystals.

PubMed

Yang, Shuai; Liu, Ying

2018-08-01

Liquid crystal nematic elastomers are one kind of smart anisotropic and viscoelastic solids simultaneously combing the properties of rubber and liquid crystals, which is thermal sensitivity. In this paper, the wave dispersion in a liquid crystal nematic elastomer porous phononic crystal subjected to an external thermal stimulus is theoretically investigated. Firstly, an energy function is proposed to determine thermo-induced deformation in NE periodic structures. Based on this function, thermo-induced band variation in liquid crystal nematic elastomer porous phononic crystals is investigated in detail. The results show that when liquid crystal elastomer changes from nematic state to isotropic state due to the variation of the temperature, the absolute band gaps at different bands are opened or closed. There exists a threshold temperature above which the absolute band gaps are opened or closed. Larger porosity benefits the opening of the absolute band gaps. The deviation of director from the structural symmetry axis is advantageous for the absolute band gap opening in nematic state whist constrains the absolute band gap opening in isotropic state. The combination effect of temperature and director orientation provides an added degree of freedom in the intelligent tuning of the absolute band gaps in phononic crystals. Copyright © 2018 Elsevier B.V. All rights reserved.

Ordered iron aluminide alloys having an improved room-temperature ductility and method thereof

DOEpatents

Sikka, Vinod K.

1992-01-01

A process is disclosed for improving the room temperature ductility and strength of iron aluminide intermetallic alloys. The process involves thermomechanically working an iron aluminide alloy by means which produce an elongated grain structure. The worked alloy is then heated at a temperature in the range of about 650.degree. C. to about 800.degree. C. to produce a B2-type crystal structure. The alloy is rapidly cooled in a moisture free atmosphere to retain the B2-type crystal structure at room temperature, thus providing an alloy having improved room temperature ductility and strength.

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

Aliev, Ziya S., E-mail: ziyasaliev@gmail.com; Institute of Physics, ANAS, H.Javid ave. 131, AZ1143 Baku; Donostia International Physics Center

Single crystals of the ternary copper compounds CuTlS and CuTlSe have been successfully grown from stoichiometric melt by using vertical Bridgman-Stockbarger method. The crystal structure of the both compounds has been determined by powder and single crystal X-Ray diffraction. They crystallize in the PbFCl structure type with two formula units in the tetragonal system, space group P4/nmm, a=3.922(2); c=8.123(6); Z=2 and a=4.087(6); c=8.195(19) Å; Z=2, respectively. The band structure of the reported compounds has been analyzed by means of full-potential linearized augmented plane-wave (FLAPW) method based on the density functional theory (DFT). Both compounds have similar band structures and aremore » narrow-gap semiconductors with indirect band gap. The resistivity measurements agree with a semiconductor behavior although anomalies are observed at low temperature. - Graphical abstract: The crystal structures of CuTl and CuTlSe are isostructural with the PbFCl-type and the superconductor LiFeAs-type tetragonal structure. The band structure calculations confirmed that they are narrow-gap semiconductors with indirect band gaps of 0.326 and 0.083 eV. The resistivity measurements, although confirming the semiconducting behavior of both compounds exhibit unusual anomalies at low temperatures. - Highlights: • Single crystals of CuTlS and CuTlSe have been successfully grown by Bridgman-Stockbarger method. • The crystal structure of the both compounds has been determined by single crystal XRD. • The band structure of the both compounds has been analyzed based on the density functional theory (DFT). • The resistivity measurements have been carried out from room temperature down to 10 K.« less

RH-temperature phase diagrams of hydrate forming deliquescent crystalline ingredients.

PubMed

Allan, Matthew; Mauer, Lisa J

2017-12-01

Several common deliquescent crystalline food ingredients (including glucose and citric acid) are capable of forming crystal hydrate structures. The propensity of such crystals to hydrate/dehydrate or deliquesce is dependent on the environmental temperature and relative humidity (RH). As an anhydrous crystal converts to a crystal hydrate, water molecules internalize into the crystal structure resulting in different physical properties. Deliquescence is a solid-to-solution phase transformation. RH-temperature phase diagrams of the food ingredients alpha-d-glucose and citric acid, along with sodium sulfate, were produced using established and newly developed methods. Each phase diagram included hydrate and anhydrate deliquescence boundaries, the anhydrate-hydrate phase boundary, and the peritectic temperature (above which the hydrate was no longer stable). This is the first report of RH-temperature phase diagrams of glucose and citric acid, information which is beneficial for selecting storage and processing conditions to promote or avoid hydrate formation or loss and/or deliquescence. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structural and magnetic investigations of single-crystalline neodymium zirconate pyrochlore Nd2Zr2O7

NASA Astrophysics Data System (ADS)

Hatnean, M. Ciomaga; Lees, M. R.; Petrenko, O. A.; Keeble, D. S.; Balakrishnan, G.; Gutmann, M. J.; Klekovkina, V. V.; Malkin, B. Z.

2015-05-01

We report structural and magnetic properties studies of large high-quality single crystals of the frustrated magnet Nd2Zr2O7 . Powder x-ray diffraction analysis confirms that Nd2Zr2O7 adopts the pyrochlore structure. Room-temperature x-ray diffraction and time-of-flight neutron-scattering experiments show that the crystals are stoichiometric in composition with no measurable site disorder. The temperature dependence of the magnetic susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits to the magnetic susceptibility data using a Curie-Weiss law reveal a ferromagnetic coupling between the Nd moments. Magnetization versus field measurements show a local Ising anisotropy along the <111 > axes of the Nd3 + ions in the ground state. Specific heat versus temperature measurements in zero applied magnetic field indicate the presence of a thermal anomaly below T ˜7 K, but no evidence of magnetic ordering is observed down to 0.5 K. The experimental temperature dependence of the single-crystal bulk dc susceptibility and isothermal magnetization are analyzed using crystal field theory and the crystal field parameters and exchange coupling constants determined.

Filtering properties of Thue-Morse nano-photonic crystals containing high-temperature superconductor

NASA Astrophysics Data System (ADS)

Talebzadeh, Robabeh; Bavaghar, Mehrdad

2018-05-01

In this paper, we introduced new design of quasi-periodic layered structures by choosing order two of ternary Thue-Morse structure. We considered Superconductor-dielectric photonic crystal with mirror symmetric as (ABSSAB)N(BASSBA)N composed of two kinds of nano-scale dielectric layers (A and B) and high-temperature superconductor layers where N is the number of period. This structure is assumed to be the free space. By using the transfer matrix method and the two fluid model, we theoretically study the transmission spectrum of ternary Thue-Morse superconducting photonic crystals with mirror symmetry and introduce this structure as a narrow optical filter. We showed that transmission peak so-called defect mode appears itself inside the transmission spectrum of suggested structure as same as defective layered structure. Also, we analyzed the influence of various related parameters such as the operating temperature of superconductor layer on position of defect mode. The redshift of defect mode with increasing the operating temperature was observed.

Ordered distribution of I and Cl in the low-temperature crystal structure of mutnovskite, Pb{sub 4}As{sub 2}S{sub 6}ICl: An X-ray single-crystal study

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

Bindi, Luca; Garavelli, Anna; Pinto, Daniela

2008-02-15

To study the temperature-dependent structural changes and to analyze the crystal chemical behavior of the halogens as a function of temperature, a crystal of the recently discovered mineral mutnovskite, ideally Pb{sub 2}AsS{sub 3}(I,Cl,Br), has been investigated by X-ray single-crystal diffraction methods at 300 and 110 K. At room temperature (RT) mutnovskite was confirmed to possess a centrosymmetric structure-type, space group Pnma, while at low temperature (110 K) it adopts a non-centrosymmetric orthorhombic structure-type, space group Pnm2{sub 1}, with a=11.5394(9) A, b=6.6732(5) A, c=9.3454(7) A, V=719.64(9) A{sup 3} and Z=2. Mutnovskite reconverts to the centrosymmetric-type upon returning to RT thus indicatingmore » that the phase transition is completely reversible in character. The refinement of the LT-structure leads to a residual factor R=0.0336 for 1827 independent observed reflections [F{sub o}>4{sigma}(F{sub o})] and 80 variables. The crystal structure of cooled mutnovskite is topologically identical to that observed at RT and the slight structural changes occurring during the phase transition Pnma{yields}Pnm2{sub 1} are mainly restricted to the coordination polyhedra around Pb. The structure solution revealed that I and Cl are ordered into two specific sites. Indeed, the unique mixed (I,Cl) position in the RT-structure (Wyckoff position 4c) transforms into two 2a Wyckoff positions in the LT-structure hosting I and Cl, respectively. - Graphical abstract: In the crystal structure of mutnovskite at 110 K the two halogens I and Cl are ordered into two specific sites and only slight changes in the coordination environment around Pb atoms occur during the phase transition Pnma{yields}Pnm2{sub 1} from the RT-structure to the LT-structure. Two kinds of layers alternating along a are present in the LT-structure: Layer I contains Cl atoms and [001] columns of Pb1 and Pb4 prisms, layer II contains I atoms and [001] columns of Pb2 and Pb3 prisms.« less

Low carrier semiconductor like behavior in Lu3Ir4Ge13 single crystal

NASA Astrophysics Data System (ADS)

Kumar, Anil; Matteppanavar, Shidaling; Thamizhavel, A.; Ramakrishnan, S.

2018-04-01

Single crystal of Lu3Ir4Ge13 crystallizing in the Yb3Rh4Sn13-type cubic crystal structure has been grown by Czochralski method in a tetra-arc furnace. In this paper we report on the crystal structure, magnetic and transport properties of Lu3Ir4Ge13. The analysis of the powder x-ray diffraction (XRD) studies revealed that Lu3Ir4Ge13 crystallizes in a cubic structure with the space group Pm-3n, no. 223. The lattice parameter was obtained from the Rietveld refinement of the room temperature XRD data which amounts to 8.904 (3) Å with low R factors. The temperature dependence of the resistivity exhibited semiconductor like behavior till 1.8 K, with a broad hump around 15 - 62 K. This hump was observed in both warming and cooling cycle with a very small hysteresis, it may be due to the existence of structural transition from high - low symmetry. The temperature dependent magnetization data shows the diamagnetic behavior with an anomaly around 70 K, which is well supported by the derivative of resistivity data.

Changes in the Electrical Conductivity and Catalytic Property of Vanadium Iron Borophosphate Glasses with Crystallization

NASA Astrophysics Data System (ADS)

Cha, Jaemin; Jeong, Hwajin; Ryu, Bongki

2018-05-01

Glasses were prepared in the V2O5-P2O5-B2O3 system containing Fe2O3 and were crystallized to examine the changes in the structure, as well as the catalytic and the electrical properties. The glasses were annealed in a graphite mold at a temperature above the glass transition temperature for 1 h and were heat-treated at the crystallization temperature for 1 h, 6 h and 12 h, respectively. Fourier-transform infrared spectroscopy (FTIR) was employed to analyze the structural changes of the V-O bonds after crystallization while the X-ray photoelectron spectroscopy (XPS) analysis indicated a decrease in V5+ and an increase in V4+ amounts. The X-ray diffraction (XRD) analysis indicated that a new crystalline phase of non-stoichiometric Fe0.12V2O5 was formed after 1 h of heat treatment. Structural changes induced by the crystallization were analyzed by determining the molecular volume from the sample density. The conductivity and the catalytic property were examined based on the migration of V and Fe ions exhibiting different valence states with crystallization. Both the conductivity and the catalytic property improved after the samples had been crystallized at the crystallization peak temperature ( T p). Furthermore, as compared to the sample heat treated for 1 h, the conductance and catalytic properties were improved for samples crystallized at T p for 6 h and 12 h.

Ultrasonic acoustic levitation for fast frame rate X-ray protein crystallography at room temperature.

PubMed

Tsujino, Soichiro; Tomizaki, Takashi

2016-05-06

Increasing the data acquisition rate of X-ray diffraction images for macromolecular crystals at room temperature at synchrotrons has the potential to significantly accelerate both structural analysis of biomolecules and structure-based drug developments. Using lysozyme model crystals, we demonstrated the rapid acquisition of X-ray diffraction datasets by combining a high frame rate pixel array detector with ultrasonic acoustic levitation of protein crystals in liquid droplets. The rapid spinning of the crystal within a levitating droplet ensured an efficient sampling of the reciprocal space. The datasets were processed with a program suite developed for serial femtosecond crystallography (SFX). The structure, which was solved by molecular replacement, was found to be identical to the structure obtained by the conventional oscillation method for up to a 1.8-Å resolution limit. In particular, the absence of protein crystal damage resulting from the acoustic levitation was carefully established. These results represent a key step towards a fully automated sample handling and measurement pipeline, which has promising prospects for a high acquisition rate and high sample efficiency for room temperature X-ray crystallography.

Ultrasonic acoustic levitation for fast frame rate X-ray protein crystallography at room temperature

NASA Astrophysics Data System (ADS)

Tsujino, Soichiro; Tomizaki, Takashi

2016-05-01

Increasing the data acquisition rate of X-ray diffraction images for macromolecular crystals at room temperature at synchrotrons has the potential to significantly accelerate both structural analysis of biomolecules and structure-based drug developments. Using lysozyme model crystals, we demonstrated the rapid acquisition of X-ray diffraction datasets by combining a high frame rate pixel array detector with ultrasonic acoustic levitation of protein crystals in liquid droplets. The rapid spinning of the crystal within a levitating droplet ensured an efficient sampling of the reciprocal space. The datasets were processed with a program suite developed for serial femtosecond crystallography (SFX). The structure, which was solved by molecular replacement, was found to be identical to the structure obtained by the conventional oscillation method for up to a 1.8-Å resolution limit. In particular, the absence of protein crystal damage resulting from the acoustic levitation was carefully established. These results represent a key step towards a fully automated sample handling and measurement pipeline, which has promising prospects for a high acquisition rate and high sample efficiency for room temperature X-ray crystallography.

Ultrasonic acoustic levitation for fast frame rate X-ray protein crystallography at room temperature

PubMed Central

Tsujino, Soichiro; Tomizaki, Takashi

2016-01-01

Increasing the data acquisition rate of X-ray diffraction images for macromolecular crystals at room temperature at synchrotrons has the potential to significantly accelerate both structural analysis of biomolecules and structure-based drug developments. Using lysozyme model crystals, we demonstrated the rapid acquisition of X-ray diffraction datasets by combining a high frame rate pixel array detector with ultrasonic acoustic levitation of protein crystals in liquid droplets. The rapid spinning of the crystal within a levitating droplet ensured an efficient sampling of the reciprocal space. The datasets were processed with a program suite developed for serial femtosecond crystallography (SFX). The structure, which was solved by molecular replacement, was found to be identical to the structure obtained by the conventional oscillation method for up to a 1.8-Å resolution limit. In particular, the absence of protein crystal damage resulting from the acoustic levitation was carefully established. These results represent a key step towards a fully automated sample handling and measurement pipeline, which has promising prospects for a high acquisition rate and high sample efficiency for room temperature X-ray crystallography. PMID:27150272

Temperature insensitive curvature sensor based on cascading photonic crystal fiber

NASA Astrophysics Data System (ADS)

Fu, Guangwei; Li, Yunpu; Fu, Xinghu; Jin, Wa; Bi, Weihong

2018-03-01

A temperature insensitive curvature sensor is proposed based on cascading photonic crystal fiber. Using the arc fusion splicing method, this sensor is fabricated by cascading together a single-mode fiber (SMF), a three layers air holes structure of photonic crystal fiber (3PCF), a five layers air holes structure of photonic crystal fiber (5PCF) and a SMF in turn. So the structure SMF-3PCF-5PCF-SMF can be obtained with a total length of 20 mm. During the process of fabrication, the splicing machine parameters and the length of each optical fiber are adjusted to obtain a high sensitivity curvature sensor. The experimental results show that the curvature sensitivity is -8.40 nm/m-1 in the curvature variation range of 0-1.09 m-1, which also show good linearity. In the range of 30-90 °C, the temperature sensitivity is only about 3.24 pm/°C, indicating that the sensor is not sensitive to temperature. The sensor not only has the advantages of easy fabricating, simple structure, high sensitivity but also can solve the problem of temperature measurement cross sensitivity, so it can be used for different areas including aerospace, large-scale bridge, architectural structure health monitoring and so on.

Growth Temperature Dependence of Morphology of GaN Single Crystals in the Na-Li-Ca Flux Method

NASA Astrophysics Data System (ADS)

Wu, Xi; Hao, Hangfei; Li, Zhenrong; Fan, Shiji; Xu, Zhuo

2018-02-01

In this paper, the effect of growth temperature on the morphology and transparency of the GaN crystals obtained by the Li-Ca-added Na Flux method was studied. Addition of Li-Ca was attempted to control the growth habit and further improve transparency of GaN crystals. The samples with wurtzite structure of GaN were confirmed by the x-ray powder diffraction analysis. GaN single crystal with maximum size of about 6 mm was grown at 750°C. As the growth temperature was increased from 700°C to 850°C, the morphology of the crystals changed from pyramid to prism, and their surfaces became smooth. It was found that high growth temperature was beneficial to obtain a transparent crystal, but the evaporation of sodium would suppress its further growth. The E 2 (high) mode in the Raman spectra was at 568 cm-1, and the full-width at half-maximum values of this peak for the crystals obtained at 700°C, 750°C, 800°C, and 850°C were 7.5 cm-1, 10.3 cm-1, 4.4 cm-1, and 4.0 cm-1, respectively. It indicates that all the crystals are stress free and the transparent crystal grown at high temperature has high structural quality or low impurity concentrations.

Swinging Symmetry, Multiple Structural Phase Transitions, and Versatile Physical Properties in RECuGa3 (RE = La-Nd, Sm-Gd).

PubMed

Subbarao, Udumula; Rayaprol, Sudhindra; Dally, Rebecca; Graf, Michael J; Peter, Sebastian C

2016-01-19

The compounds RECuGa3 (RE = La-Nd, Sm-Gd) were synthesized by various techniques. Preliminary X-ray diffraction (XRD) analyses at room temperature suggested that the compounds crystallize in the tetragonal system with either the centrosymmetric space group I4/mmm (BaAl4 type) or the non-centrosymmetric space group I4mm (BaNiSn3 type). Detailed single-crystal XRD, neutron diffraction, and synchrotron XRD studies of selected compounds confirmed the non-centrosymmetric BaNiSn3 structure type at room temperature with space group I4mm. Temperature-dependent single-crystal XRD, powder XRD, and synchrotron beamline measurements showed a structural transition between centro- and non-centrosymmetry followed by a phase transition to the Rb5Hg19 type (space group I4/m) above 400 K and another transition to the Cu3Au structure type (space group Pm3̅m) above 700 K. Combined single-crystal and synchrotron powder XRD studies of PrCuGa3 at high temperatures revealed structural transitions at higher temperatures, highlighting the closeness of the BaNiSn3 structure to other structure types not known to the RECuGa3 family. The crystal structure of RECuGa3 is composed of eight capped hexagonal prism cages [RE4Cu4Ga12] occupying one rare-earth atom in each ring, which are shared through the edge of Cu and Ga atoms along the ab plane, resulting in a three-dimensional network. Resistivity and magnetization measurements demonstrated that all of these compounds undergo magnetic ordering at temperatures between 1.8 and 80 K, apart from the Pr and La compounds: the former remains paramagnetic down to 0.3 K, while superconductivity was observed in the La compound at T = 1 K. It is not clear whether this is intrinsic or due to filamentary Ga present in the sample. The divalent nature of Eu in EuCuGa3 was confirmed by magnetization measurements and X-ray absorption near edge spectroscopy and is further supported by the crystal structure analysis.

VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

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

Rao Popuri, Srinivasa; University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac; National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara

2014-05-01

Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversiblemore » intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.« less

Itinerant Antiferromagnetism in FeMnP 0.8Si 0.2

DOE PAGES

Sales, Brian C.; Susner, Michael A.; Conner, Benjamin S.; ...

2015-09-25

Compounds based on the Fe 2P structure have continued to attract interest because of the interplay between itinerant and localized magnetism in a noncentrosymmetric crystal structure, and because of the recent developments of these materials for magnetocaloric applications. We report the growth and characterization of millimeter-sized single crystals of FeMnP 0.8Si 0.2 with the Fe 2P structure. Single-crystal x-ray diffraction, magnetization, resistivity, and Hall and heat capacity data are reported. The crystals exhibit itinerant antiferromagnetic order below 158 K with no hint of ferromagnetic behavior in the magnetization curves and with the spins ordered primarily in the ab plane. Themore » room-temperature resistivity is close to the Ioffe-Regel limit for a metal. Single-crystal x-ray diffraction indicates a strong preference for Mn to occupy the larger pyramidal 3g site. The cation site preference in the as-grown crystals and the antiferromagnetism were not changed after high-temperature anneals and a rapid quench to room temperature« less

Structural transformation of crystallized debranched cassava starch during dual hydrothermal treatment in relation to enzyme digestibility.

PubMed

Boonna, Sureeporn; Tongta, Sunanta

2018-07-01

Structural transformation of crystallized debranched cassava starch prepared by temperature cycling (TC) treatment and then subjected to annealing (ANN), heat-moisture treatment (HMT) and dual hydrothermal treatments of ANN and HMT was investigated. The relative crystallinity, lateral crystal size, melting temperature and resistant starch (RS) content increased for all hydrothermally treated samples, but the slowly digestible starch (SDS) content decreased. The RS content followed the order: HMT → ANN > HMT > ANN → HMT > ANN > TC, respectively. The HMT → ANN sample showed a larger lateral crystal size with more homogeneity, whereas the ANN → HMT sample had a smaller lateral crystal size with a higher melting temperature. After cooking at 50% moisture, the increased RS content of samples was observed, particularly for the ANN → HMT sample. These results suggest that structural changes of crystallized debranched starch during hydrothermal treatments depend on initial crystalline characteristics and treatment sequences, influencing thermal stability, enzyme digestibility, and cooking stability. Copyright © 2018 Elsevier Ltd. All rights reserved.

Does Z' equal 1 or 2? Enhanced powder NMR crystallography verification of a disordered room temperature crystal structure of a p38 inhibitor for chronic obstructive pulmonary disease.

PubMed

Widdifield, Cory M; Nilsson Lill, Sten O; Broo, Anders; Lindkvist, Maria; Pettersen, Anna; Svensk Ankarberg, Anna; Aldred, Peter; Schantz, Staffan; Emsley, Lyndon

2017-06-28

The crystal structure of the Form A polymorph of N-cyclopropyl-3-fluoro-4-methyl-5-[3-[[1-[2-[2-(methylamino)ethoxy]phenyl]cyclopropyl]amino]-2-oxo-pyrazin-1-yl]benzamide (i.e., AZD7624), determined using single-crystal X-ray diffraction (scXRD) at 100 K, contains two molecules in the asymmetric unit (Z' = 2) and has regions of local static disorder. This substance has been in phase IIa drug development trials for the treatment of chronic obstructive pulmonary disease, a disease which affects over 300 million people and contributes to nearly 3 million deaths annually. While attempting to verify the crystal structure using nuclear magnetic resonance crystallography (NMRX), we measured 13 C solid-state NMR (SSNMR) spectra at 295 K that appeared consistent with Z' = 1 rather than Z' = 2. To understand this surprising observation, we used multinuclear SSNMR ( 1 H, 13 C, 15 N), gauge-including projector augmented-wave density functional theory (GIPAW DFT) calculations, crystal structure prediction (CSP), and powder XRD (pXRD) to determine the room temperature crystal structure. Due to the large size of AZD7624 (ca. 500 amu, 54 distinct 13 C environments for Z' = 2), static disorder at 100 K, and (as we show) dynamic disorder at ambient temperatures, NMR spectral assignment was a challenge. We introduce a method to enhance confidence in NMR assignments by comparing experimental 13 C isotropic chemical shifts against site-specific DFT-calculated shift distributions established using CSP-generated crystal structures. The assignment and room temperature NMRX structure determination process also included measurements of 13 C shift tensors and the observation of residual dipolar coupling between 13 C and 14 N. CSP generated ca. 90 reasonable candidate structures (Z' = 1 and Z' = 2), which when coupled with GIPAW DFT results, room temperature pXRD, and the assigned SSNMR data, establish Z' = 2 at room temperature. We find that the polymorphic Form A of AZD7624 is maintained at room temperature, although dynamic disorder is present on the NMR timescale. Of the CSP-generated structures, 2 are found to be fully consistent with the SSNMR and pXRD data; within this pair, they are found to be structurally very similar (RMSD 16 = 0.30 Å). We establish that the CSP structure in best agreement with the NMR data possesses the highest degree of structural similarity with the scXRD-determined structure (RMSD 16 = 0.17 Å), and has the lowest DFT-calculated energy amongst all CSP-generated structures with Z' = 2.

High-Temperature Formation Phases and Crystal Structure of Hot-Pressed Thermoelectric CuGaTe2 with Chalcopyrite-Type Structure

NASA Astrophysics Data System (ADS)

Fujii, Yosuke; Kosuga, Atsuko

2017-11-01

Polycrystalline CuGaTe2 with a chalcopyrite-type structure consolidated by hot-pressing is a potential candidate as a medium-temperature thermoelectric (TE) material. However, its high-temperature formation phases have rarely been reported to date. Here, we investigated the temperature-dependent formation phases and crystal structure at 300-800 K of hot-pressed CuGaTe2. From synchrotron x-ray diffraction data and crystal structure analysis of the heating and cooling processes, it was clarified that a certain amount of impurity phases, such as Te and CuTe, precipitated from the CuGaTe2 matrix when the temperature was increased (to 500-650 K). This is the temperature range where CuGaTe2 has been reported to show high TE performance. After CuGaTe2 was heated to 800 K, such impurity phases remained, even when cooled to room temperature. They also affected the tetragonal distortion and the x-coordinate of Te in the CuGaTe2 matrix, probably due to deficiencies of Cu and Te in the matrix. Our results reveal detailed information on the formation phases of CuGaTe2 at high temperature and thus provide insight for evaluation of its high-temperature stability and transport properties.

High-Temperature Formation Phases and Crystal Structure of Hot-Pressed Thermoelectric CuGaTe2 with Chalcopyrite-Type Structure

NASA Astrophysics Data System (ADS)

Fujii, Yosuke; Kosuga, Atsuko

2018-06-01

Polycrystalline CuGaTe2 with a chalcopyrite-type structure consolidated by hot-pressing is a potential candidate as a medium-temperature thermoelectric (TE) material. However, its high-temperature formation phases have rarely been reported to date. Here, we investigated the temperature-dependent formation phases and crystal structure at 300-800 K of hot-pressed CuGaTe2. From synchrotron x-ray diffraction data and crystal structure analysis of the heating and cooling processes, it was clarified that a certain amount of impurity phases, such as Te and CuTe, precipitated from the CuGaTe2 matrix when the temperature was increased (to 500-650 K). This is the temperature range where CuGaTe2 has been reported to show high TE performance. After CuGaTe2 was heated to 800 K, such impurity phases remained, even when cooled to room temperature. They also affected the tetragonal distortion and the x-coordinate of Te in the CuGaTe2 matrix, probably due to deficiencies of Cu and Te in the matrix. Our results reveal detailed information on the formation phases of CuGaTe2 at high temperature and thus provide insight for evaluation of its high-temperature stability and transport properties.

Continuous-wave mid-infrared photonic crystal light emitters at room temperature

NASA Astrophysics Data System (ADS)

Weng, Binbin; Qiu, Jijun; Shi, Zhisheng

2017-01-01

Mid-infrared photonic crystal enhanced lead-salt light emitters operating under continuous-wave mode at room temperature were investigated in this work. For the device, an active region consisting of 9 pairs of PbSe/Pb0.96Sr0.04Se quantum wells was grown by molecular beam epitaxy method on top of a Si(111) substrate which was initially dry-etched with a two-dimensional photonic crystal structure in a pattern of hexagonal holes. Because of the photonic crystal structure, an optical band gap between 3.49 and 3.58 µm was formed, which matched with the light emission spectrum of the quantum wells at room temperature. As a result, under optical pumping, using a near-infrared continuous-wave semiconductor laser, the device exhibited strong photonic crystal band-edge mode emissions and delivered over 26.5 times higher emission efficiency compared to the one without photonic crystal structure. The output power obtained was up to 7.68 mW (the corresponding power density was 363 mW/cm2), and a maximum quantum efficiency reached to 1.2%. Such photonic crystal emitters can be used as promising light sources for novel miniaturized gas-sensing systems.

Crystal structure and crystal growth of the polar ferrimagnet CaBaFe4O7

NASA Astrophysics Data System (ADS)

Perry, R. S.; Kurebayashi, H.; Gibbs, A.; Gutmann, M. J.

2018-05-01

Magnetic materials are a cornerstone for developing spintronic devices for the transport of information via magnetic excitations. To date, relatively few materials have been investigated for the purpose of spin transport, mostly due to the paucity of suitable candidates as these materials are often chemically complex and difficult to synthesize. We present the crystal growth and a structure solution on the high-temperature crystal structure of the layered, polar ferrimagnet CaBaFe4O7 , which is a possible new contender for spintronics research. The space group is identified as P 3 by refinement of single crystal and powder neutron diffraction data. At 400 K, the trigonal lattice parameters are a =11.0114 (11 )Å and c =10.330 (3 )Å . The structure is similar to the low-temperature phase with alternating layers of triangular and Kagome-arranged Fe-O tetrahedra. We also present details of the crystal growth by traveling solvent method.

Charge-transport in tin-iodide perovskite CH3NH3SnI3: origin of high conductivity.

PubMed

Takahashi, Yukari; Obara, Rena; Lin, Zheng-Zhong; Takahashi, Yukihiro; Naito, Toshio; Inabe, Tamotsu; Ishibashi, Shoji; Terakura, Kiyoyuki

2011-05-28

The structural and electrical properties of a metal-halide cubic perovskite, CH(3)NH(3)SnI(3), have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity.

Relation between the structural parameters of metallic glasses at the onset crystallization temperatures and threshold values of the effective diffusion coefficients

NASA Astrophysics Data System (ADS)

Tkatch, V. I.; Svyrydova, K. A.; Vasiliev, S. V.; Kovalenko, O. V.

2017-08-01

Using the results of differential scanning calorimetry and X-ray diffractometry, an analysis has been carried out of the initial stages of the eutectic and primary mechanisms of crystallization of a series of metallic glasses based on Fe and Al with the established temperature dependences of the effective diffusion coefficients. Analytical relationships, which relate the volume density of crystallites formed in the glasses at the temperatures of the onset of crystallization with the values of the effective diffusion coefficients at these temperatures have been proposed. It has been established that, in the glasses, the crystallization of which begins at the lower boundary of the threshold values of the effective diffusion coefficients ( 10-20 m2/s), structures are formed with the volume density of crystallites on the order of 1023-1024 m-3 and, at the upper boundary (10-18 m2/s), of the order of 1018 and 1020 m-3 in the glasses that are crystallized via the eutectic and primary mechanisms, respectively. Good agreement between the calculated and experimental estimates indicates that the threshold values of the effective diffusion coefficients are the main factors that determine the structure of glasses at the initial stages of crystallization.

Construction of hydrophobic wood surfaces by room temperature deposition of rutile (TiO2) nanostructures

Treesearch

Rongbo Zheng; Mandla A. Tshabalala; Qingyu Li; Hongyan Wang

2015-01-01

A convenient room temperature approach was developed for growing rutile TiO2 hierarchical structures on the wood surface by direct hydrolysis and crystallization of TiCl3 in saturated NaCl aqueous solution.The morphology and the crystal structure of TiO2 coated on the wood surface were characterized...

Structural and Functional Mechanisms of Adaptations of WrbA in Extremophilic Organisms

DTIC Science & Technology

2010-05-11

organisms adapt to high temperature. A model of the thermophilic enzyme was constructed based on the crystal Structure of the mesophilie counterpart to...binding for the thermophilic enzyme was independent of ligand concentration. Comparison of enzyme activities between the two proteins with a variety of...extremophilic organisms adapt to high temperature. A model of the thermophilic enzyme was constructed based on the crystal structure of the mesophilic

The 15-K neutron structure of saccharide-free concanavalin A.

PubMed

Blakeley, M P; Kalb, A J; Helliwell, J R; Myles, D A A

2004-11-23

The positions of the ordered hydrogen isotopes of a protein and its bound solvent can be determined by using neutron crystallography. Furthermore, by collecting neutron data at cryo temperatures, the dynamic disorder within a protein crystal is reduced, which may lead to improved definition of the nuclear density. It has proved possible to cryo-cool very large Con A protein crystals (>1.5 mm3) suitable for high-resolution neutron and x-ray structure analysis. We can thereby report the neutron crystal structure of the saccharide-free form of Con A and its bound water, including 167 intact D2O molecules and 60 oxygen atoms at 15 K to 2.5-A resolution, along with the 1.65-A x-ray structure of an identical crystal at 100 K. Comparison with the 293-K neutron structure shows that the bound water molecules are better ordered and have lower average B factors than those at room temperature. Overall, twice as many bound waters (as D2O) are identified at 15 K than at 293 K. We note that alteration of bound water orientations occurs between 293 and 15 K; such changes, as illustrated here with this example, could be important more generally in protein crystal structure analysis and ligand design. Methodologically, this successful neutron cryo protein structure refinement opens up categories of neutron protein crystallography, including freeze-trapped structures and cryo to room temperature comparisons.

Crystal structure and vibrational spectra of piperazinium bis(4-hydroxybenzenesulphonate) molecular-ionic crystal

NASA Astrophysics Data System (ADS)

Marchewka, M. K.; Pietraszko, A.

2008-02-01

The piperazinium bis(4-hydroxybenzenesulphonate) crystallizes from water solution at room temperature in P2 1/ c space group of monoclinic system. The crystals are built up of doubly protonated piperazinium cations and ionized 4-hydroxybenzenesulphonate anions that interact through weak hydrogen bonds of O-H⋯O and N-H⋯O type. Mutual orientation of anions is determined by non-conventional hydrogen bonds of C-H⋯π type. Room temperature powder FT IR and FT Raman measurements were carried out. The vibrational spectra are in full agreement with the structure obtained from X-ray crystallography. The big single crystals of the title salt can be grown.

The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.

2001-01-01

Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study, we show that possible conformational changes induced by heating are stable and apparently non-reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for four weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 hours at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.

The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.; Rose, M. Franklin (Technical Monitor)

2000-01-01

Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study we show that possible conformational changes induced by heating are stable and apparently non- reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for 4 weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 h at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.

Protein crystal growth in microgravity: Temperature induced large scale crystallization of insulin

NASA Technical Reports Server (NTRS)

Long, Marianna M.; Delucas, Larry J.; Smith, C.; Carson, M.; Moore, K.; Harrington, Michael D.; Pillion, D. J.; Bishop, S. P.; Rosenblum, W. M.; Naumann, R. J.

1994-01-01

One of the major stumbling blocks that prevents rapid structure determination using x-ray crystallography is macro-molecular crystal growth. There are many examples where crystallization takes longer than structure determination. In some cases, it is impossible to grow useful crystals on earth. Recent experiments conducted in conjuction with NASA on various Space Shuttle missions have demonstrated that protein crystals often grow larger and display better internal molecular order than their earth-grown counterparts. This paper reports results from three Shuttle flights using the Protein Crystallization Facility (PCF). The PCF hardware produced large, high-quality insulin crystals by using a temperature change as the sole means to affect protein solubility and thus, crystallization. The facility consists of cylinders/containers with volumes of 500, 200, 100, and 50 ml. Data from the three Shuttle flights demonstrated that larger, higher resolution crystals (as evidenced by x-ray diffraction data) were obtained from the microgravity experiments when compared to earth-grown crystals.

Cryo-cooling in macromolecular crystallography: advantages, disadvantages and optimization.

PubMed

Juers, Douglas H; Matthews, Brian W

2004-05-01

The flash-cooling of crystals in macromolecular crystallography has become commonplace. The procedure makes it possible to collect data from much smaller specimens than was the case in the past Also, flash-cooled crystals are much less prone to radiation damage than their room-temperature counterparts, allowing data to be accumulated over extended periods of time. Notwithstanding the attractiveness of the technique, it does have potential disadvantages. First, better methods need to be developed to prevent damage to crystals on freezing. There is also a risk that structures determined at low temperature may suggest conclusions based on aspects of the structure that are not necessarily relevant at room temperature.

Structure, dielectric and electric properties of diisobutylammonium hydrogen sulfate crystal

NASA Astrophysics Data System (ADS)

Bednarchuk, Tamara J.; Kinzhybalo, Vasyl; Markiewicz, Ewa; Hilczer, Bożena; Pietraszko, Adam

2018-02-01

Diisobutylammonium hydrogen sulfate, a new organic-inorganic hybrid compound, was successfully synthesized and three structural phases in 298-433 K temperature range were revealed by differential scanning calorimetry and X-ray powder diffraction studies. Single crystal X-ray diffraction data were used to describe the crystal structures in each particular case. In phase III (below 336/319 K on heating/cooling) the crystal arrangement appears to be within the triclinic symmetry with P-1 space group. During heating in the 336-339 K region (and 319-337 K on cooling) the crystal exists in the phase II, characterized by monoclinic symmetry with P21/c space group. Consequently, above 339 K (during heating, and 337 K during cooling temperature sequences), i.e. in phase I the crystal exhibits orthorhombic symmetry (Cmce space group). Ferroelastic domain structure was observed in phase III. These phase boundaries (III→II and II→I) were accompanied by the presence of small anomalies, apparent in the dielectric permittivity and electric conductivity experimental data. Fast proton transport with activation energy of 0.23 eV was observed in the high temperature phase I and related to phonon assisted proton diffusion conditioned by disorder of diisobutylammonium (diba) cations, as well as by high thermal displacements of oxygen and sulfur atoms of hydrogen sulfate anion (hs).

Time lapse microscopy of temperature control during self-assembly of 3D DNA crystals

NASA Astrophysics Data System (ADS)

Conn, Fiona W.; Jong, Michael Alexander; Tan, Andre; Tseng, Robert; Park, Eunice; Ohayon, Yoel P.; Sha, Ruojie; Mao, Chengde; Seeman, Nadrian C.

2017-10-01

DNA nanostructures are created by exploiting the high fidelity base-pairing interactions of double-stranded branched DNA molecules. These structures present a convenient medium for the self-assembly of macroscopic 3D crystals. In some self-assemblies in this system, crystals can be formed by lowering the temperature, and they can be dissolved by raising it. The ability to monitor the formation and melting of these crystals yields information that can be used to monitor crystal formation and growth. Here, we describe the development of an inexpensive tool that enables direct observation of the crystal growth process as a function of both time and temperature. Using the hanging-drop crystallization of the well-characterized 2-turn DNA tensegrity triangle motif for our model system, its response to temperature has been characterized visually.

Characterization of LaF 3 coatings prepared at different temperatures and rates

NASA Astrophysics Data System (ADS)

Yu, Hua; Shen, Yanming; Cui, Yun; Qi, Hongji; Shao, JianDa; Fan, ZhengXiu

2008-01-01

LaF 3 thin films were prepared by thermal boat evaporation at different substrate temperatures and various deposition rates. X-ray diffraction (XRD), Lambda 900 spectrophotometer and X-ray photoelectron spectroscopy (XPS) were employed to study crystal structure, transmittance and chemical composition of the coatings, respectively. Laser-induce damage threshold (LIDT) was determined by a tripled Nd:YAG laser system with a pulse width of 8 ns. It is found that the crystal structure became more perfect and the refractive index increased gradually with the temperature rising. The LIDT was comparatively high at high temperature. In the other hand, the crystallization status also became better and the refractive index increased when the deposition rate enhanced at a low level. If the rate was super rapid, the crystallization worsened instead and the refractive index would lessen greatly. On the whole, the LIDT decreased with increasing rate.

New structure type in the mixed-valent compound YbCu4Ga8.

PubMed

Subbarao, Udumula; Gutmann, Matthias J; Peter, Sebastian C

2013-02-18

The new compound YbCu(4)Ga(8) was obtained as large single crystals in high yield from reactions run in liquid gallium. Preliminary investigations suggest that YbCu(4)Ga(8) crystallizes in the CeMn(4)Al(8) structure type, tetragonal space group I4/mmm, and lattice constants are a = b = 8.6529(4) Å and c = 5.3976(11) Å. However, a detailed single-crystal XRD revealed a tripling of the c axis and crystallizing in a new structure type with lattice constants of a = b = 8.6529(4) Å and c = 15.465(1) Å. The structural model was further confirmed by neutron diffraction measurements on high-quality single crystal. The crystal structure of YbCu(4)Ga(8) is composed of pseudo-Frank-Kasper cages occupying one ytterbium atom in each ring which are shared through the corner along the ab plane, resulting in a three-dimensional network. The magnetic susceptibility of YbCu(4)Ga(8) investigated in the temperature range 2-300 K showed Curie-Weiss law behavior above 100 K, and the experimentally measured magnetic moment indicates mixed-valent ytterbium. Electrical resistivity measurements show the metallic nature of the compound. At low temperatures, variation of ρ as a function of T indicates a possible Fermi-liquid state at low temperatures.

Thermal tuning on band gaps of 2D phononic crystals considering adhesive layers

NASA Astrophysics Data System (ADS)

Zhou, Xiaoliang; Chen, Jialin; Li, Yuhang; Sun, Yuxin; Xing, Yufeng

2018-02-01

Phononic crystals are very attractive in many applications, such as noise reduction, filters and vibration isolation, due to their special forbidden band gap structures. In the present paper, the investigation of tunable band gaps of 2D phononic crystals with adhesive layers based on thermal changing is conducted. Based on the lumped-mass method, an analytical model of 2D phononic crystals with relatively thin adhesive layers is established, in which the in-plane and out-of-plane modes are both in consideration. The adhesive material is sensitive to temperature so that the band structure can be tuned and controlled by temperature variation. As temperature increases from 20 °C-80 °C, the first band gap shifts to the frequency zone around 10 kHz, which is included by the audible frequency range. The results propose an important guideline for applications, such as noise suppression using the 2D phononic crystals.

Empirical temperature-dependent intermolecular potentials determined by data mining from crystal data

NASA Astrophysics Data System (ADS)

Hofmann, D. W. M.; Kuleshova, L. N.

2018-05-01

Modern force fields are accurate enough to describe thermal effects in molecular crystals. Here, we have extended our earlier approach to discrete force fields for various temperatures to a force field with a continuous function. For the parametrisation of the force field, we used data mining on experimental structures with the temperature as an additional descriptor. The obtained force field can be used to minimise energy at a finite temperature and for molecular dynamics with zero-K potentials. The applicability of the method has been demonstrated for the prediction of crystal density, temperature density gradients and transition temperature.

Fluorescence XAS using Ge PAD: Application to High-Temperature Superconducting Thin Film Single Crystals

NASA Astrophysics Data System (ADS)

Oyanagi, H.; Tsukada, A.; Naito, M.; Saini, N. L.; Zhang, C.

2007-02-01

A Ge pixel array detector (PAD) with 100 segments was used in fluorescence x-ray absorption spectroscopy (XAS) study, probing local structure of high temperature superconducting thin film single crystals. Independent monitoring of individual pixel outputs allows real-time inspection of interference of substrates which has long been a major source of systematic error. By optimizing grazing-incidence angle and azimuthal orientation, smooth extended x-ray absorption fine structure (EXAFS) oscillations were obtained, demonstrating that strain effects can be studied using high-quality data for thin film single crystals grown by molecular beam epitaxy (MBE). The results of (La,Sr)2CuO4 thin film single crystals under strain are related to the strain dependence of the critical temperature of superconductivity.

Polyamides based on the renewable monomer, 1,13-tridecane diamine I: synthesis and characterization of nylon 13,T

DOE PAGES

He, Jie; Samanta, Satyabrata; Selvakumar, Sermadurai; ...

2013-06-01

Nylon 13,T was successfully synthesized and chemical composition, thermal properties, crystal structure, and moisture absorption characterized. Melting temperature and glass transition temperature were determined to be 263 °C and 90 °C, respectively, while the equilibrium melting temperature was determined to be 289 °C. Characterization of the crystallization kinetics showed that nylon 13,T exhibits very fast crystallization compared to the industrially important nylons, nylon 6 and nylon 6,6. In addition, the moisture absorption of nylon 13,T was dramatically lower than nylon 6 and nylon 6,6 which is consistent with the much lower amide content of nylon 13,T. The crystal structure wasmore » determined to be pseudohexagonal.« less

Low-Ca pyroxenes from LL group chondritic meteorites: Crystal structural studies and implications for their thermal histories

NASA Astrophysics Data System (ADS)

Artioli, G.; Davoli, G.

1994-12-01

Crystal structural refinements of one orthorhombic (Pbca) and two monoclinic (P21/c) single crystals, from chondrules of low-Ca pyroxenes from unequilibrated chondritic meteorites of the LL group, were carried out. The intracrystalline Fe-Mg distribution between the M1 and M2 crystallographic sites of the Parnallee (LL-3) orthoenstatite is suggestive of very rapid cooling, whereas both the structural state and intracrystalline Fe-Mg distribution in the Soko Banja (LL-4) and Jolomba (LL-6) clinoenstaties indicate rapid cooling from the high temperature polymorphs, with no significant re-equilibration at lower temperatures. These results imply that thermal metamorphism in the parent body, if present, was insufficient to allow re-equilibration of the pyroxene minerals to low temperature, ordered crystal structures. The data also indicate that, assuming low or mild pressure and shock effects, there is no well defined correlation between equilibrium temperature of the mineral phases and the alleged petrologic type of the meteorites. This evidence is consistent with a rubble pile model for the parent body accretional history, or with an onion shell model with very low thermal peak metamorphism, as is assumed for a very small object.

Effect of gallium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni-Mn-Ga alloys

NASA Astrophysics Data System (ADS)

Belosludtseva, E. S.; Kuranova, N. N.; Marchenkova, E. B.; Popov, A. G.; Pushin, V. G.

2016-04-01

The effect of gallium alloying on the structure, the phase composition, and the properties of quasibinary Ni50Mn50- z Ga z (0 ⩽ z ⩽ 25 at %) alloys is studied over a wide temperature range. The influence of the alloy composition on the type of crystal structure in high-temperature austenite and martensite and the critical martensitic transformation temperatures is analyzed. A general phase diagram of the magnetic and structural transformations in the alloys is plotted. The temperature-concentration boundaries of the B2 and L21 superstructures in the austenite field, the tetragonal L10 (2 M) martensite, and the 10 M and 14 M martensite phases with complex multilayer crystal lattices are found. The predominant morphology of martensite is shown to be determined by the hierarchy of the packets of thin coherent lamellae of nano- and submicrocrystalline crystals with planar habit plane boundaries close to {011} B2. Martensite crystals are twinned along one of the 24 24{ {011} }{< {01bar 1} rangle _{B2}} "soft" twinning shear systems, which provides coherent accommodation of the martensitic transformation-induced elastic stresses.

Temperature Dependence of Density, Viscosity and Electrical Conductivity for Hg-Based II-VI Semiconductor Melts

NASA Technical Reports Server (NTRS)

Li, C.; Ban, H.; Lin, B.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The relaxation phenomenon of semiconductor melts, or the change of melt structure with time, impacts the crystal growth process and the eventual quality of the crystal. The thermophysical properties of the melt are good indicators of such changes in melt structure. Also, thermophysical properties are essential to the accurate predication of the crystal growth process by computational modeling. Currently, the temperature dependent thermophysical property data for the Hg-based II-VI semiconductor melts are scarce. This paper reports the results on the temperature dependence of melt density, viscosity and electrical conductivity of Hg-based II-VI compounds. The melt density was measured using a pycnometric method, and the viscosity and electrical conductivity were measured by a transient torque method. Results were compared with available published data and showed good agreement. The implication of the structural changes at different temperature ranges was also studied and discussed.

High pressure phase transitions in lawsonite at simultaneous high pressure and temperature: A single crystal study

NASA Astrophysics Data System (ADS)

O'Bannon, E. F., III; Vennari, C.; Beavers, C. C. G.; Williams, Q. C.

2015-12-01

Lawsonite (CaAl2Si2O7(OH)2.H2O) is a hydrous mineral with a high overall water content of ~11.5 wt.%. It is a significant carrier of water in subduction zones to depths greater than ~150 km. The structure of lawsonite has been extensively studied under room temperature, high-pressure conditions. However, simultaneous high-pressure and high-temperature experiments are scarce. We have conducted synchrotron-based simultaneous high-pressure and temperature single crystal experiments on lawsonite up to a maximum pressure of 8.4 GPa at ambient and high temperatures. We used a natural sample of lawsonite from Valley Ford, California (Sonoma County). At room pressure and temperature lawsonite crystallizes in the orthorhombic system with Cmcm symmetry. Room temperature compression indicates that lawsonite remains in the orthorhombic Cmcm space group up to ~9.0 GPa. Our 5.0 GPa crystal structure is similar to the room pressure structure, and shows almost isotropic compression of the crystallographic axes. Unit cell parameters at 5.0 GPa are a- 5.7835(10), b- 8.694(2), and c- 13.009(3). Single-crystal measurements at simultaneous high-pressure and temperature (e.g., >8.0 GPa and ~100 oC) can be indexed to a monoclinic P-centered unit cell. Interestingly, a modest temperature increase of ~100 oC appears to initiate the orthorhombic to monoclinic phase transition at ~0.6-2.4 GPa lower than room temperature compression studies have shown. There is no evidence of dehydration or H atom disorder under these conditions. This suggests that the orthorhombic to monoclinic transition could be kinetically impeded at 298 K, and that monoclinic lawsonite could be the dominant water carrier through much of the depth range of upper mantle subduction processes.

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

Bugaris, Daniel E.; Malliakas, Christos D.; Han, Fei

A new polymorph of the RE 2Ru 3Ge 5 (RE = Pr, Sm, Dy) compounds has been grown as single crystals via an indium flux. These compounds crystallize in tetragonal space group P4/mnc with the Sc 2Fe 3Si 5-type structure, having lattice parameters a = 11.020(2) Å and c = 5.853(1) Å for RE = Pr, a = 10.982(2) Å and c = 5.777(1) Å for RE = Sm, and a = 10.927(2) Å and c = 5.697(1) Å for RE = Dy. These materials exhibit a structural transition at low temperature, which is attributed to an apparent charge densitymore » wave (CDW). Both the high-temperature average crystal structure and the low-temperature incommensurately modulated crystal structure (for Sm 2Ru 3Ge 5 as a representative) have been solved. The charge density wave order is manifested by periodic distortions of the onedimensional zigzag Ge chains. From X-ray diffraction, charge transport (electrical resistivity, Hall effect, magnetoresistance), magnetic measurements, and heat capacity, the ordering temperatures (T CDW) observed in the Pr and Sm analogues are ~200 and ~175 K, respectively. The charge transport measurement results indicate an electronic state transition happening simultaneously with the CDW transition. X-ray absorption near-edge spectroscopy (XANES) and electronic band structure results are also reported.« less

Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural study.

PubMed

Albert, Stéphanie; Pillet, Sébastien; Lecomte, Claude; Pradel, Annie; Ribes, Michel

2008-02-01

A temperature-dependent structural investigation of the substituted argyrodite Ag(7)GeSe(5)I has been carried out on a single crystal from 15 to 475 K, in steps of 50 K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the F\\bar 43m space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram-Charlier development of the Debye-Waller factors for iodine and silver, and (ii) a split-atom model for Ag(+) ions. An increased delocalization of the mobile d(10) Ag(+) cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined.

Crystal structure and thermal expansion of a CsCe 2Cl 7 scintillator

DOE PAGES

Zhuravleva, M.; Lindsey, A.; Chakoumakos, B. C.; ...

2015-04-06

Here we used single-crystal X-ray diffraction data to determine crystal structure of CsCe 2Cl 7. It crystallizes in a P112 1/b space group with a = 19.352(1) Å, b = 19.352(1) Å, c = 14.838(1) Å, γ = 119.87(2) ° , and V = 4818.6(5) Å 3. Differential scanning calorimetry measurements combined with the structural evolution of CsCe 2Cl 7 via X-ray diffractometry over a temperature range from room temperature to the melting point indicates no obvious intermediate solid-solid phase transitions. The anisotropy in the average linear coefficient of thermal expansion of the a axis (21.3 10 -6/ °C) withmore » respect to the b and c axes (27.0 10 -6/ °C) was determined through lattice parameter refinement of the temperature dependent diffraction patterns. Lastly, these findings suggest that the reported cracking behavior during melt growth of CsCe 2Cl 7 bulk crystals using conventional Bridgman and Czochralski techniques may be largely attributed to the anisotropy in thermal expansion.« less

Accessing protein conformational ensembles using room-temperature X-ray crystallography

PubMed Central

Fraser, James S.; van den Bedem, Henry; Samelson, Avi J.; Lang, P. Therese; Holton, James M.; Echols, Nathaniel; Alber, Tom

2011-01-01

Modern protein crystal structures are based nearly exclusively on X-ray data collected at cryogenic temperatures (generally 100 K). The cooling process is thought to introduce little bias in the functional interpretation of structural results, because cryogenic temperatures minimally perturb the overall protein backbone fold. In contrast, here we show that flash cooling biases previously hidden structural ensembles in protein crystals. By analyzing available data for 30 different proteins using new computational tools for electron-density sampling, model refinement, and molecular packing analysis, we found that crystal cryocooling remodels the conformational distributions of more than 35% of side chains and eliminates packing defects necessary for functional motions. In the signaling switch protein, H-Ras, an allosteric network consistent with fluctuations detected in solution by NMR was uncovered in the room-temperature, but not the cryogenic, electron-density maps. These results expose a bias in structural databases toward smaller, overpacked, and unrealistically unique models. Monitoring room-temperature conformational ensembles by X-ray crystallography can reveal motions crucial for catalysis, ligand binding, and allosteric regulation. PMID:21918110

Growth of a New Ternary BON Crystal on Si(100) by Plasma-Assisted MOCVD and Study on the Effects of Fed Gas and Growth Temperature

NASA Astrophysics Data System (ADS)

Chen, G. C.; Lee, S.-B.; Boo, J.-H.

A new ternary BOxNy crystal was grown on Si(100) substrate at 500°C by low-frequency (100 kHz) radio-frequency (rf) derived plasma-assisted MOCVD with an organoborate precursor. The as-grown deposits were characterized by SEM, TED, XPS, XRD, AFM and FT-IR. The experimental results showed that BOxNy crystal was apt to be formed at N-rich atmosphere and high temperature. The decrease of hydrogen flux in fed gases was of benefit to form BON crystal structure. The crystal structure of BOxNy was as similar to that of H3BO3 in this study.

The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography

DOE PAGES

Edlund, Petra; Takala, Heikki; Claesson, Elin; ...

2016-10-19

Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived frommore » conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. As a result, the study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.« less

The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography

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

Edlund, Petra; Takala, Heikki; Claesson, Elin

Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived frommore » conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. As a result, the study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.« less

Crystal growth and electronic structure of low-temperature phase SrMgF{sub 4}

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

Atuchin, Victor V.; Functional Electronics Laboratory, Tomsk State University, Tomsk 634050; Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, Novosibirsk 630090

2016-04-15

Using the vertical Bridgman method, the single crystal of low temperature phase SrMgF{sub 4} is obtained. The crystal is in a very good optical quality with the size of 10×7×5 mm{sup 3}. Detailed photoemission spectra of the element core levels are determined by a monochromatic AlKa (1486.6 eV) X-ray source. Moreover, the first-principles calculations are performed to investigate the electronic structure of SrMgF{sub 4}. A good agreement between experimental and calculated results is achieved. It is demonstrated that almost all the electronic orbitals are strongly localized and the hybridization with the others is very small, but the Mg–F bonds covalencymore » is relatively stronger than that of Sr–F bonds. - Graphical abstract: Large size of low-temperature phase SrMgF{sub 4} crystal was obtained (right) and its electronic structure was investigated by X-ray photoelectron spectroscopy and first-principles calculation (left). - Highlights: • Large size single crystal of low-temperature phase SrMgF{sub 4} is obtained. • Electronic structure of SrMgF{sub 4} is measured by X-ray photoelectron spectroscopy. • Partial densities of states are determined by first-principles calculation. • Good agreement between experimental and calculated results is achieved. • Strong ionic characteristics of chemical bonds are exhibited in SrMgF{sub 4}.« less

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

Cebe, Peggy; Partlow, Benjamin P.; Kaplan, David L.

Using fast scanning calorimetry (FSC), we investigated the glass transition and crystal melting of samples of B. mori silk fibroin containing Silk I and/or Silk II crystals. Due to the very short residence times at high temperatures during such measurements, thermal decomposition of silk protein can be significantly suppressed. FSC was performed at 2000 K/s using the Mettler Flash DSC1 on fibroin films with masses around 130–270 ng. Films were prepared with different crystalline fractions (ranging from 0.26 to 0.50) and with different crystal structures (Silk I, Silk II, or mixed) by varying the processing conditions. These included water annealingmore » at different temperatures, exposure to 50% MeOH in water, or autoclaving. The resulting crystal structure was examined using wide angle X-ray scattering. Degree of crystallinity was evaluated from Fourier transform infrared (FTIR) spectroscopy and from analysis of the heat capacity increment at the glass transition temperature. Silk fibroin films prepared by water annealing at 25 °C were the least crystalline and had Silk I structure. FTIR and FSC studies showed that films prepared by autoclaving or 50% MeOH exposure were the most crystalline and had Silk II structure. Intermediate crystalline fraction and mixed Silk I/Silk II structures were found in films prepared by water annealing at 37 °C. FSC results indicate that Silk II crystals exhibit endotherms of narrower width and have higher mean melting temperature Tm(II) = 351 ± 2.6 °C, compared to Silk I crystals which melt at Tm(I) = 292 ± 3.8 °C. Films containing mixed Silk I/Silk II structure showed two clearly separated endothermic peaks. Evidence suggests that the two types of crystals melt separately and do not thermally interconvert on the extremely short time scale (0.065 s between onset and end of melting) of the FSC experiment.« less

Crystallization characteristics of iron-rich glass ceramics prepared from nickel slag and blast furnace slag

NASA Astrophysics Data System (ADS)

Wang, Zhong-Jie; Ni, Wen; Li, Ke-Qing; Huang, Xiao-Yan; Zhu, Li-Ping

2011-08-01

The crystallization process of iron-rich glass-ceramics prepared from the mixture of nickel slag (NS) and blast furnace slag (BFS) with a small amount of quartz sand was investigated. A modified melting method which was more energy-saving than the traditional methods was used to control the crystallization process. The results show that the iron-rich system has much lower melting temperature, glass transition temperature ( T g), and glass crystallization temperature ( T c), which can result in a further energy-saving process. The results also show that the system has a quick but controllable crystallization process with its peak crystallization temperature at 918°C. The crystallization of augite crystals begins from the edge of the sample and invades into the whole sample. The crystallization process can be completed in a few minutes. A distinct boundary between the crystallized part and the non-crystallized part exists during the process. In the non-crystallized part showing a black colour, some sphere-shaped augite crystals already exist in the glass matrix before samples are heated to T c. In the crystallized part showing a khaki colour, a compact structure is formed by augite crystals.

The Effect of Temperature and Solution pH on the Nucleation of Tetragonal Lysozyme Crystals

NASA Technical Reports Server (NTRS)

Judge, Russell A.; Jacobs, Randolph S.; Frazier, Tyralynn; Snell, Edward H.; Pusey, Marc L.

1999-01-01

Part of the challenge of macromolecular crystal growth for structure determination is obtaining crystals with a volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature, and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over 1 week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable, however, was pH; crystal numbers changed by two orders of magnitude over the pH range 4.0-5.2. Crystal size also varied with solution conditions, with the largest crystals obtained at pH 5.2. Having optimized the crystallization conditions, we prepared a batch of crystals under the same initial conditions, and 50 of these crystals were analyzed by x-ray diffraction techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.

Magnetism and structure of a half-metallic Heusler compound Co-Mn-Cr-Si

NASA Astrophysics Data System (ADS)

Huh, Yung; Joshi, Swarangi; Jain, Sanmati; Pathak, Ojas; Kharel, Parashu

Half metallic ferromagnetic Heusler compounds have a potential in the development of spintronic devices for its high spin polarization at the Fermi level and lattice structure compatibility. Heusler compounds based on cobalt are considered a good candidate for room temperature half-metals due to their high Curie temperature. Co2CrSi is one of such predicted half-metal, but it is meta-stable and difficult to synthesize in the desired crystal structure. We have successfully synthesized a Heusler compound Co2Mn0.5Cr0.5Si by using arc melting and rapid quenching followed by thermal treatment under high vacuum to control any parasitic contamination. Crystal X-ray diffraction pattern shows the samples crystallize in a cubic Heusler structure with some degrees of structural disorder. Curie temperatures of the prepared samples are observed well beyond room temperature near 900 K. Magnetic anomalies present in as-prepared samples are cleared, and its magnetic properties are improved by thermal treatment. This research is supported by Academic and Scholarly Excellence Funds, and Research/Scholarship Support Fund, South Dakota State University.

In-situ crystallization of GeTe\\GaSb phase change memory stacked films

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

Velea, A., E-mail: alin.velea@psi.ch; National Institute of Materials Physics, RO-077125 Magurele, Ilfov; Borca, C. N.

2014-12-21

Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C,more » the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples.« less

Rechargeable solid state neutron detector and visible radiation indicator

DOEpatents

Stowe, Ashley C.; Wiggins, Brenden; Burger, Arnold

2017-05-23

A radiation detection device, including: a support structure; and a chalcopyrite crystal coupled to the support structure; wherein, when the chalcopyrite crystal is exposed to radiation, a visible spectrum of the chalcopyrite crystal changes from an initial color to a modified color. The visible spectrum of the chalcopyrite crystal is changed back from the modified color to the initial color by annealing the chalcopyrite crystal at an elevated temperature below a melting point of the chalcopyrite crystal over time. The chalcopyrite crystal is optionally a .sup.6LiInSe.sub.2 crystal. The radiation is comprised of neutrons that decrease the .sup.6Li concentration of the chalcopyrite crystal via a .sup.6Li(n,.alpha.) reaction. The initial color is yellow and the modified color is one of orange and red. The annealing temperature is between about 450 degrees C. and about 650 degrees C. and the annealing time is between about 12 hrs and about 36 hrs.

Electronic structures and abnormal phonon behaviors of cobalt-modified Na0.5Bi0.5TiO3-6%BaTiO3 single crystals

NASA Astrophysics Data System (ADS)

Huang, T.; Zhang, P.; Xu, L. P.; Chen, C.; Zhang, J. Z.; Hu, Z. G.; Luo, H. S.; Chu, J. H.

2016-10-01

Optical properties, electronic structures, and structural variations of x wt% cobalt (Co) doped Na0.5Bi0.5TiO3-6%BaTiO3 (x=0%, 0.5%, 0.8%) single crystals have been studied by temperature-dependent optical ellipsometry and Raman spectra from 250 to 650 K. Based on the temperature evolution of electronic transitions (Ecp1 and Ecp2) and the phonon modes involving Ti-O vibrations, two critical temperature points exhibit an increasing trend with Co dopants, which are related to structural variations for ferroelectric to anti-ferroelectric, and anti-ferroelectric to paraelectric transition, respectively. Additionally, distinguishing abnormal phonon behaviors can be observed from Raman spectra for the crystal of x=0.5% and 0.8%, which show reverse frequency shift of the modes involving Ti-O vibration. It can be ascribed to different relative concentration of Co2+ and Co3+ in the crystals, which has been confirmed by X-ray Photoelectron Spectroscopy data.

Fluorescence X-ray absorption spectroscopy using a Ge pixel array detector: application to high-temperature superconducting thin-film single crystals.

PubMed

Oyanagi, H; Tsukada, A; Naito, M; Saini, N L; Lampert, M O; Gutknecht, D; Dressler, P; Ogawa, S; Kasai, K; Mohamed, S; Fukano, A

2006-07-01

A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle theta and adjusting the azimuthal angle phi, smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr)2CuO4 thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO6 octahedron) in (La,Sr)2CuO4 thin films grown on LaSrAlO4 and SrTiO3 substrates is uniaxially distorted changing the tetragonality by approximately 5 x 10(-3) in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.

The phase transition of Pb8F14I2.

PubMed

Weil, Matthias

2017-01-01

The reversible phase transition of Pb 8 F 14 I 2 is of continuous type and takes place at about 107 °C as monitored by temperature-dependent single crystal and powder X-ray diffraction measurements, optical microscopy, and differential scanning calorimetry. The low-temperature ferroelastic phase crystallizes in the orthorhombic crystal system (23 °C, Bmmb , Z  = 2, a  = 6.0699(6) Å, b  = 6.0165(6) Å, c  = 25.077(2) Å, 1487 structure factors, 41 parameter, R ( F 2 ) = 0.0346, wR ( F 2 ) = 0.0771) and changes its symmetry to the tetragonal crystal system into the high-temperature paraelastic phase (130 °C, I 4/ mmm , Z  = 1, a  = 4.2667(12) Å, c  = 25.388(7) Å, 430 structure factors, 303 parameter, R ( F 2 ) = 0.0575, wR ( F 2 ) = 0.1564). Group-subgroup relationships between the two structures and a hypothetical intermediate structure are presented.

Phonon conductivity metrics for compact, linked-cage, layered, and filled-cage crystals, using ab initio, molecular dynamics and Boltzmann transport treatments

NASA Astrophysics Data System (ADS)

Huang, Baoling

Atomic-level thermal transport in compact, layered, linked-cage, and filled-cage crystals is investigated using a multiscale approach, combines the ab initio calculation, molecular dynamics (MD), Boltzman transport equations (BTE), and the kinetic theory. These materials are of great interests in energy storage, transport, and conversion. The structural metrics of phonon conductivity of these crystals are then explored. An atomic structure-based model is developed for the understanding the relationship between the atomic structure and phonon transport in compact crystals at high temperatures. The elemental electronegativity, element mass, and the arrangement of bonds are found to be the dominant factors to determine the phonon conductivity. As an example of linked-cage crystals, the phonon conductivity of MOF-5 is investigated over a wide temperature range using MD simulations and the Green-Kubo method. The temperature dependence of the thermal conductivity of MOF-5 is found to be weak at high temperatures, which results from the suppression of the long-range acoustic phonon transport by the special linked-cage structure. The mean free path of the majority of phonons in MOF-5 is limited by the cage size. The phonon and electron transport in layered Bi2Te3 structure are investigated using the first-principle calculations, MD, and BTE. Strong anisotropy has been found for both phonon and electron transport due to the special layered structure. The long-range acoustic phonons dominate the phonon transport with a strong temperature and direction dependence. Temperature dependence of the energy gap and appropriate modelling of relaxation times are found to be important for the prediction of the electrical transport in the intrinsic regime. The scattering by the acoustic, optical, and polar-optical phonons are found to dominate the electron transport. For filled skutterudite structure, strong coupling between the filler and the host is found, which contradicts the traditional "rattler" concept. The interatomic bonds of the host are significantly affected by the filler. It is shown that without changing the interatomic potentials for the host, the filler itself can not result in a lower phonon conductivity for the filled structure. It is also found that the behavior of partially-filled skutterudites can be better understood by treating the partially-filled structure as a solid solution of the empty structure and fully-filled structure. The combination of theoretical-analysis methods used in this work, provides for comparative insight into the role of atomic structure on the phonon transport in a variety of crystals used in energy storage, transport, and conversion.

Neutron Transmission of Single-crystal Sapphire Filters

NASA Astrophysics Data System (ADS)

Adib, M.; Kilany, M.; Habib, N.; Fathallah, M.

2005-05-01

An additive formula is given that permits the calculation of the nuclear capture, thermal diffuse and Bragg scattering cross-sections as a function of sapphire temperature and crystal parameters. We have developed a computer program that allows calculations of the thermal neutron transmission for the sapphire rhombohedral structure and its equivalent trigonal structure. The calculated total cross-section values and effective attenuation coefficient for single-crystalline sapphire at different temperatures are compared with measured values. Overall agreement is indicated between the formula and experimental data. We discuss the use of sapphire single crystal as a thermal neutron filter in terms of the optimum cystal thickness, mosaic spread, temperature, cutting plane and tuning for efficient transmission of thermal-reactor neutrons.

Low temperature structural transformation in T[Ni(CN){sub 4}].xpyz with x=1,2; T=Mn,Co,Ni,Zn,Cd; pyz=pyrazine

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

Rodriguez-Hernandez, J.; Instituto de Ciencia y Tecnologia de Materiales, Universidad de La Habana; Lemus-Santana, A.A.

2010-01-15

The materials under study are pillared solids T[Ni(CN){sub 4}].xpyz with one and two (x=1,2) pyrazine (pyz) molecules and where T=Mn, Co, Ni, Zn, Cd. Stimulated by their structural features and potential role as prototype of porous solids for hydrogen storage, the structural stability under cryogenic conditions for this series of pillared solids was studied. At low temperature, in the 100-200 K range, the occurrence of a reversible structural transformation was found. For T=Mn, Co, Zn, Cd, with x=2, the structural transformation was observed to occur around 185 K, and the low temperature phase crystallizes with a monoclinic unit cell (spacemore » group Pc). This structure change results from certain charge redistribution on cooling within the involved ligands. For T=Ni with x=1, both the low and high temperature phases crystallize with unit cells of tetragonal symmetry, within the same space group but with a different unit cell volume. In this case the structure change is observed around 120 K. Above that temperature the rotational states for the pyrazine molecule are thermally excited and all the pyrazine molecules in the structure become equivalent. Under this condition the material structure is described using a smaller structural unit. The structural study using X-ray powder diffraction data was complemented with calorimetric and Raman spectroscopy measurements. For the low temperature phases the crystal structures were solved from Patterson methods and then refined using the Rietveld method. - Graphical abstract: Low temperature ordered structure for pyrazine in T[Ni(CN){sub 4}].pyz.« less

High-energy-resolution monochromator for nuclear resonant scattering of synchrotron radiation by Te-125 at 35.49 keV

NASA Astrophysics Data System (ADS)

Imai, Yasuhiko; Yoda, Yoshitaka; Kitao, Shinji; Masuda, Ryo; Higashitaniguchi, Satoshi; Inaba, Chika; Seto, Makoto

2007-09-01

We have developed a high-resolution monochromator (HRM) for the measurement of nuclear resonant scattering (NRS) of synchrotron radiation by Te-125 at 35.49 keV using the backscattering of sapphire (9 1 -10 68). HRMs for nuclei with excitation energies less than 30 keV have been successfully developed using high angle diffractions by silicon crystals. Nearly perfect silicon crystal, however, is not suitable for high efficient HRMs at higher energy regions because the symmetry of the crystal structure is high and the Debye-temperature is low. Therefore, we used high quality synthetic sapphire crystal, which has low symmetry of crystal structure and high Debye-temperature. The temperature of the crystal was precisely controlled around 218 K to diffract synchrotron radiation with a Bragg angle of π/2 - 0.52 mrad. Energy was tuned by changing the crystal temperature under the condition of constant diffraction angle. Energy resolution was measured by detecting nuclear forward scattering by Te-125 in enriched TeO II. The relative energy resolution of 2.1×10 -7 is achieved, that is 7.5 meV in energy bandwidth. This HRM opens studies on element-specific dynamics and electronic state of substances containing Te-125.

Synthesis of formamidinium lead iodide perovskite bulk single crystal and its optical properties

NASA Astrophysics Data System (ADS)

Zheng, Hongge; Duan, Junjie; Dai, Jun

2017-07-01

Formamidinium lead iodide (FAPbI3) is a promising hybrid perovskite material for optoelectronic devices. We synthesized bulk single crystal FAPbI3 by a rapid solution crystallization method. X-ray diffraction (XRD) was performed to characterize the crystal structure. Temperature-dependent photoluminescence (PL) spectra of the bulk single crystal FAPbI3 were measured from 10 to 300 K to explain PL recombination mechanism. It shows that near band edge emission blueshifts with the temperature increasing from 10 to 120 K and from 140 K to room temperature, a sudden emission band redshift demonstrates near 140 K because of the phase transition from orthorhombic phase to cubic phase. From the temperature-dependent PL spectra, the temperature coefficients of the bandgap and thermal activation energies of FAPbI3 perovskite are fitted.

Hot plate annealing at a low temperature of a thin ferroelectric P(VDF-TrFE) film with an improved crystalline structure for sensors and actuators.

PubMed

Mahdi, Rahman Ismael; Gan, W C; Abd Majid, W H

2014-10-14

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

Blue phase liquid crystal phase transition for cyano compound chiral nematic liquid crystal mixtures with three two-ring core structures and chiral dopant concentrations

NASA Astrophysics Data System (ADS)

Shin, Jaesun; Kim, Beomjong; Jung, Wansu; Fahad, Mateen; Park, SangJin; Hong, Sung-Kyu

2017-05-01

Blue phase (BP) temperature range of a chiral nematic liquid crystal (LC) mixture is dependent upon the host nematic LC chemical structure and chiral dopant concentration. In this study, we investigated BP phase transition behaviour and helical twisting power (HTP) using three chiral dopant concentrations of cyano compound chiral nematic LC mixtures incorporating three two-ring core structures in the host nematic LCs. The effect of the host nematic LC core structure, HTP and chiral dopant concentrations were considered on BP temperature ranges, for two types of complete BPI and BPII without isotropic phase (Iso) and two types of coexistence state of BPI+Iso and BPII+Iso.

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

Kinetics of nucleation and crystallization in poly(e-caprolactone) (PCL)

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

Zhuravlev, Evgeny; Schmelzer, Jurn; Wunderlich, Bernhard

2011-01-01

The recently developed differential fast scanning calorimetry (DFSC) is used for a new look at the crystal growth of poly(3-caprolactone) (PCL) from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity using heating rates from 50 to 50,000 K/s. The crystal nucleation and crystallization halftimes were determined simultaneously. The obtained halftimes cover a range from 3 102 s (nucleation at 215 K) to 3 109 s (crystallization at 185 K). After attempting to analyze the experiments with the classicalmore » nucleation and growth model, developed for systems consisting of small molecules, a new methodology is described which addresses the specific problems of crystallization of flexible linear macromolecules. The key problems which are attempted to be resolved concern the differences between the structures of the various entities identified and their specific role in the mechanism of growth. The structures range from configurations having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms in the temperature range from the glass transition to equilibrium melting for increasingly perfect and larger crystals. The mechanisms and kinetics of growth involve also a detailed understanding of the interaction with the surrounding rigid-amorphous fraction (RAF) in dependence of crystal size and perfection.« less

Magnetic properties of GdMnO3 nanoparticles embedded in mesoporous silica

NASA Astrophysics Data System (ADS)

Tajiri, Takayuki; Mito, Masaki; Deguchi, Hiroyuki; Kohno, Atsushi

2018-05-01

Perovskite manganite GdMnO3 nanoparticles were synthesized using mesoporous silica as a template, and their magnetic properties and crystal structure were investigated. Powder X-ray diffraction data indicated successful synthesis of the GdMnO3 nanoparticles, with mean particle sizes of 13.9 and 20.9 nm. The lattice constants for the nanoparticles were slightly different from those for the bulk material and varied with the particle size. The magnetic transition temperatures for the nanoparticles were higher than those of the bulk crystal. The synthesized GdMnO3 nanoparticles exhibited superparamagnetic behaviors: The blocking temperature, coercive field, and transition temperature depended on the particle size. Magnetic measurements and crystal structure analysis suggest that the changes in the magnetic properties for GdMnO3 nanoparticles can be attributed to the modulation of the crystallographic structure.

Single Crystal Growth, Resistivity, and Electronic Structure of the Weyl Semimetals NbP and TaP

DOE PAGES

Sapkota, Deepak; Mukherjee, Rupam; Mandrus, David

2016-12-06

We have successfully synthesized niobium monophosphide and tantalum monophosphide crystals by a chemical vapor transport technique. We report resistivity vs. temperature of both materials in the temperature range from 2 K to 300 K. We have also performed electronic structure calculations and present the band structure and density of states of these two compounds. The calculations show that both compounds are semimetals, as their conduction and valence bands overlap near the Fermi energy.

EPR study of free radical in gamma-irradiated bis(cyclopentadienyl)zirconium dichloride single crystal

NASA Astrophysics Data System (ADS)

Caliskan, Betul; Caliskan, Ali Cengiz

2017-06-01

Bis(cyclopentadienyl)zirconium dichloride (BCZD; zirconocene dichloride) single crystals were exposed to 60Co-γ irradiation at room temperature. The irradiated single crystals were investigated between 125 and 470 K by electron paramagnetic resonance spectroscopy. The spectra of the crystals were found to be temperature independent. The paramagnetic center was attributed to the cyclopentadienyl radical. The g values of the radiation damage center observed in BCZD single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.

Boron Arsenide and Boron Phosphide for High Temperature and Luminescent Devices. [semiconductor devices - crystal growth/crystal structure

NASA Technical Reports Server (NTRS)

Chu, T. L.

1975-01-01

The crystal growth of boron arsenide and boron phosphide in the form of bulk crystals and epitaxial layers on suitable substrates is discussed. The physical, chemical, and electrical properties of the crystals and epitaxial layers are examined. Bulk crystals of boron arsenide were prepared by the chemical transport technique, and their carrier concentration and Hall mobility were measured. The growth of boron arsenide crystals from high temperature solutions was attempted without success. Bulk crystals of boron phosphide were also prepared by chemical transport and solution growth techniques. Techniques required for the fabrication of boron phosphide devices such as junction shaping, diffusion, and contact formation were investigated. Alloying techniques were developed for the formation of low-resistance ohmic contacts to boron phosphide. Four types of boron phosphide devices were fabricated: (1) metal-insulator-boron phosphide structures, (2) Schottky barriers; (3) boron phosphide-silicon carbide heterojunctions; and (4) p-n homojunctions. Easily visible red electroluminescence was observed from both epitaxial and solution grown p-n junctions.

Growth of NBT-BT single crystals by flux method and their structural, morphological and electrical characterizations

NASA Astrophysics Data System (ADS)

Kanuru, Sreenadha Rao; Baskar, K.; Dhanasekaran, R.; Kumar, Binay

2016-05-01

In this paper, one of the important, eco-friendly polycrystalline material, (1-x)(Na0.5Bi0.5)TiO3 (NBT) - xBaTiO3 (BT) of different compositions (x=0.07, 0.06 and 0.05 wt%) around the morphotropic phase boundary (MPB) were synthesized by solid state reaction technique. And the single crystals with 13×7×7 mm3, 12×12×7 mm3 and 10×7×4 mm3 dimensions were grown by self flux method. The morphology, crystal structure and unit-cell parameters have been studied and the monoclinic phase has been identified for 0.07 wt% of BT. Higher BT concentration changes the crystal habit and the mechanism has been studied clearly. Raman spectroscopy at room-temperature confirms the presence of functional groups. The quality of the as grown single crystals was examined by high resolution x-ray diffraction analysis. The dielectric properties of the as grown crystals were investigated in the frequency range of 20 Hz-2 MHz from room temperature to 450 °C. The broad dielectric peak and frequency dispersion demonstrates the relaxor behavior of grown crystals. The dielectric constant (εr), transition temperature (Tm), and depolarization temperature (Td) of the grown crystals are found to be comparatively good. The diffusive factor (γ) from Curie-Weiss law confirms the as grown NBT-BT single crystals are relaxor in nature.

Point defect disorder in high-temperature solution grown Sr6Tb0.94Fe1.06(BO3)6 single crystals

NASA Astrophysics Data System (ADS)

Velázquez, M.; Péchev, S.; Duttine, M.; Wattiaux, A.; Labrugère, C.; Veber, Ph.; Buffière, S.; Denux, D.

2018-08-01

New Sr6Tb0.94Fe1.06(BO3)6 single crystals were obtained from lithium borate high-temperature solution growth under controlled atmosphere. Their average crystal structure was found to adopt the trigonal R-3 space group with lattice parameters a = 12.2164 Å and c = 9.1934 Å. A combined multiscale characterization approach, involving diffuse reflectance, X-ray photoelectron (XPS) and Mössbauer spectroscopies, was undertaken to establish the exact nature of the point defect disorder in this crystal structure. The FeTb× antisite disorder in the Sr6Tb0.94Fe1.06(BO3)6 single crystals is different from the kind of point defect disorder known to exist in the powder phase material counterpart. The absence of Tb4+ cations in the crystal lattice was established by XPS, and that of any phase transition down to 4 K was checked by specific heat measurements. The magnetic susceptibility curve was found to follow a Curie-Weiss behaviour in the 4-354 K temperature range.

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

Mohri, Maryam, E-mail: mmohri@ut.ac.ir; Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe; Nili-Ahmadabadi, Mahmoud

The crystallization of Ni-rich/NiTiCu bi-layer thin film deposited by magnetron sputtering from two separate alloy targets was investigated. To achieve the shape memory effect, the NiTi thin films deposited at room temperature with amorphous structure were annealed at 773 K for 15, 30, and 60 min for crystallization. Characterization of the films was carried out by differential scanning calorimetry to indicate the crystallization temperature, grazing incidence X-ray diffraction to identify the phase structures, atomic force microscopy to evaluate surface morphology, scanning transmission electron microscopy to study the cross section of the thin films. The results show that the structure ofmore » the annealed thin films strongly depends on the temperature and time of the annealing. Crystalline grains nucleated first at the surface and then grew inward to form columnar grains. Furthermore, the crystallization behavior was markedly affected by composition variations. - Highlights: • A developed bi-layer Ni45TiCu5/Ni50.8Ti was deposited on Si substrate and crystallized. • During crystallization, The Ni{sub 45}TiCu{sub 5} layer is thermally less stable than the Ni-rich layer. • The activation energy is 302 and 464 kJ/mol for Cu-rich and Ni-rich layer in bi-layer, respectively.« less

Polymer Deposition from a Quasi-Vapor Phase as a New Route to Access a Wide Temperature Range for Crystallization

NASA Astrophysics Data System (ADS)

Jeong, Hyuncheol; Arnold, Craig; Priestley, Rodney

Polymer crystallization is strongly governed by kinetics where crystallization temperature (Tc) plays an important role in determining materials properties. Due to the high entropic barrier required for reorganization, the long-chain molecules typically form folded-chain crystals, whose thickness and thermal stability decrease as Tc is lowered. Interesting questions remain regarding crystallization in the deeply supercooled regime. This is partially due to the difficulty in accessing the low Tc range without nucleation. For a strong crystal-former like polyethylene (PE), cooling from a melt or solution always confronts the onset of nucleation at a high Tc followed by rapid crystal growth. Here, we introduce an alternative approach to grow polymer crystals via Matrix Assisted Pulsed Laser Evaporation (MAPLE). This methodology achieves the crystallization of polymers from a quasi-vapor phase at a controlled temperature, allowing for the study of the empirical relationship between Tc and crystal structure over a wide range of Tc. With PE as a model polymer, we investigated the morphological and thermal properties of crystals grown over a wide temperature range down to 120 °C below bulk crystallization point.

Structural Variation of LaMnO3+δ by Oxygen Nonstoichiometry

NASA Astrophysics Data System (ADS)

Niwa, Eiki; Maeda, Hiroki; Hashimoto, Takuya; Mizusaki, Junichiro

2013-07-01

The relationship between oxygen content and crystal structure of LaMnO3+δ, which is mother phase of cathode material for solid oxide fuel cells, has been investigated by X-ray diffraction, thermogravimetry and iodometric titration. It was confirmed that LaMnO3+δ with different oxygen content can be prepared by controlling sintering temperature in static air. Crystal system of LaMnO3.17±0.02 and LaMnO3.13±0.01 at room temperature was rhombohedral with space group of Rbar {3}c, whereas crystal structure of LaMnO3.08±0.01 was orthorhombic whose space group was proposed to be Pmna (No. 53). With increase of oxygen content in LaMnO3+δ, molar volume decreased and higher crystal symmetry was obtained.

Searching the Cambridge Structural Database for polymorphs.

PubMed

van de Streek, Jacco; Motherwell, Sam

2005-10-01

In order to identify all pairs of polymorphs in the Cambridge Structural Database (CSD), a method was devised to automatically compare two crystal structures. The comparison is based on simulated powder diffraction patterns, but with special provisions to deal with differences in unit-cell volumes caused by temperature or pressure. Among the 325,000 crystal structures in the Cambridge Structural Database, 35,000 pairs of crystal structures of the same chemical compound were identified and compared. A total of 7300 pairs of polymorphs were identified, of which 154 previously were unknown.

The Effect of Temperature and Solution pH on Tetragonal Lysozyme Nucleation Kinetics

NASA Technical Reports Server (NTRS)

Judge, Russell A.; Jacobs, Randolph S.; Frazier, Tyralynn; Snell, Edward H.; Pusey, Marc L.

1998-01-01

Part of the challenge of macromolecular crystal growth for structure determination is obtaining an appropriate number of crystals with a crystal volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over one week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions, Duplicate experiments indicate the reproducibility of the technique, Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable however, was pH, where crystal numbers changed by two orders of magnitude over the pH range 4.0 to 5.2. Crystal size varied also with solution conditions, with the largest crystals being obtained at pH 5.2. Having optimized the crystallization conditions, a batch of crystals were prepared under exactly the same conditions and fifty of these crystals were analyzed by x-ray techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.

Crystal structure, electronic structure, and photoluminescent properties of SrMoO{sub 4}:Tb{sup 3+} phosphors

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

Park, Sung Wook; Moon, Byung Kee; Jeong, Jung Hyun, E-mail: jhjeong@pknu.ac.kr

2015-10-15

Highlights: • SrMoO{sub 4}:Tb{sup 3+} phosphor samples were synthesized at different temperatures. • The crystal and electronic structures, and luminescence properties were studied. • The excitation peak shifts to red with increasing the sintering temperature. • The luminescence mechanism of SrMoO{sub 4}:Tb{sup 3+} was suggested. - Abstract: The experimental and theoretical studies of the optical properties of SrMoO{sub 4}:Tb{sup 3+} phosphors were carried out. The structural, optical, and electronical properties of the phosphors were systematically studied. The phosphor samples were crystallized at different temperatures via a sol–gel method. Excitation spectra of SrMoO{sub 4}:Tb{sup 3+} powder samples exhibited gradual red shiftmore » and luminescent intensity changed with increasing the sintering temperature. Such spectral changes depend strongly on the crystallographic properties such as lattice parameters and crystallinity. The shift of the excitation spectra is mainly ascribed to the covalent bond interaction between Mo−O bonds. An energy band model was demonstrated to describe the luminescence mechanism in the material.« less

Low temperature structural variations of Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}-7%BaTiO{sub 3} single crystal: Evidences from optical ellipsometry and Raman scattering

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

Huang, T.; Guo, S.; Xu, L. P.

2015-06-14

Optical properties and structural variations of Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}-7%BaTiO{sub 3} (NBT-7%BT) single crystal have been studied by temperature-dependent optical ellipsometry and Raman spectroscopy from 4.2 to 300 K. The second derivative of the complex dielectric functions reveals two interband transitions (E{sub cp1} and E{sub cp2}) located at about 3.49 and 4.25 eV, respectively. Depending on the temperature evolution of electronic transitions, structural variations appear near 60, 150, and 240 K, respectively. These anomalies are also well illustrated from the low-frequency phonon modes involving vibrations of Bi. The low-temperature structural variations of NBT-7%BT crystal can be associated with instability of the crystalline latticemore » driven by off-centered Bi ions, followed by the variations of polarizability of the unit cells.« less

Structural complexity of simple Fe 2O 3 at high pressures and temperatures

DOE PAGES

Bykova, Elena; Dubrovinsky, L.; Dubrovinskaia, N.; ...

2016-02-11

Although chemically very simple, Fe 2O 3 is known to undergo a series of enigmatic structural, electronic and magnetic transformations at high pressures and high temperatures. So far, these transformations have neither been correctly described nor understood because of the lack of structural data. Here we report a systematic investigation of the behaviour of Fe 2O 3 at pressures over 100 GPa and temperatures above 2,500 K employing single crystal X-ray diffraction and synchrotron Mössbauer source spectroscopy. Crystal chemical analysis of structures presented here and known Fe(II, III) oxides shows their fundamental relationships and that they can be described bymore » the homologous series nFeO·mFe 2O 3. Decomposition of Fe 2O 3 and Fe 3O 4 observed at pressures above 60 GPa and temperatures of 2,000 K leads to crystallization of unusual Fe 5O 7 and Fe 25O 32 phases with release of oxygen. Lastly, our findings suggest that mixed-valence iron oxides may play a significant role in oxygen cycling between earth reservoirs.« less

Phase Diagram of Kob-Andersen-Type Binary Lennard-Jones Mixtures

NASA Astrophysics Data System (ADS)

Pedersen, Ulf R.; Schrøder, Thomas B.; Dyre, Jeppe C.

2018-04-01

The binary Kob-Andersen (KA) Lennard-Jones mixture is the standard model for computational studies of viscous liquids and the glass transition. For very long simulations, the viscous KA system crystallizes, however, by phase separating into a pure A particle phase forming a fcc crystal. We present the thermodynamic phase diagram for KA-type mixtures consisting of up to 50% small (B ) particles showing, in particular, that the melting temperature of the standard KA system at liquid density 1.2 is 1.028(3) in A particle Lennard-Jones units. At large B particle concentrations, the system crystallizes into the CsCl crystal structure. The eutectic corresponding to the fcc and CsCl structures is cutoff in a narrow interval of B particle concentrations around 26% at which the bipyramidal orthorhombic PuBr3 structure is the thermodynamically stable phase. The melting temperature's variation with B particle concentration at two constant pressures, as well as at the constant density 1.2, is estimated from simulations at pressure 10.19 using isomorph theory. Our data demonstrate approximate identity between the melting temperature and the onset temperature below which viscous dynamics appears. Finally, the nature of the solid-liquid interface is briefly discussed.

Study of Polymer Crystallization by Physical Vapor Deposition

NASA Astrophysics Data System (ADS)

Jeong, Hyuncheol

When a polymer is confined under the submicron length scale, confinement size and interfaces can significantly impact the crystallization kinetics and resulting morphology. The ability to tune the morphology of confined polymer systems is of critical importance for the development of high-performance polymer microelectronics. The wisdom from the research on confined crystallization suggests that it would be beneficial to have a processing route in which the crystallization of polymers is driven by interface and temperature effects at a nanometer-scale confinement. In practice, for atomic and small-molecular systems, physical vapor deposition (PVD) has been recognized as the most successful processing route for the precise control of the film structure at surface utilizing confinement effects. While standard PVD technologies are not generally applicable to the deposition of the chemically fragile macromolecules, the development of matrix-assisted pulsed laser evaporation (MAPLE) now enables the non-destructive PVD of high-molecular weight polymers. In this thesis work, we investigated the use of MAPLE for the precise control of the crystallization of polymer films at a molecular level. We also sought to decipher the rules governing the crystallization of confined polymers, by using MAPLE as a tool to form confined polymer systems onto substrates with a controlled temperature. We first explored the early stages of film growth and crystallization of poly(ethylene oxide) (PEO) at the substrate surface formed by MAPLE. The unique mechanism of film formation in MAPLE, the deposition of submicron-sized polymer droplets, allowed for the manifestation of confinement and substrate effects in the crystallization of MAPLE-deposited PEO. Furthermore, we also focused on the property of the amorphous PEO film formed by MAPLE, showing the dependence of polymer crystallization kinetics on the thermal history of the amorphous phase. Lastly, we probed how MAPLE processing affected the semi-crystalline structure in MAPLE-deposited polyethylene (PE) films. Depositing PE at various temperatures remarkably allowed for the tunability of the melting temperature and crystallinity of the PE films, thus manipulating the semi-crystalline structure. By comparing the structure of PE formed by different processing routes, i.e., MAPLE and melt-crystallization, we discussed how processing routes affect the development of semi-crystalline phase in polymer films.

Immersion Freezing of Aluminas: The Effect of Crystallographic Properties on Ice Nucleation

NASA Astrophysics Data System (ADS)

King, M.; Chong, E.; Freedman, M. A.

2017-12-01

Atmospheric aerosol particles serve as the nuclei for heterogeneous ice nucleation, a process that allows for ice to form at higher temperatures and lower supersaturations with respect to ice. This process is essential to the formation of ice in cirrus clouds. Heterogeneous ice nucleation is affected by many factors including the composition, crystal structure, porosity, and surface area of the particles. However, these factors are not well understood and, as such, are difficult to account for in climate models. To test the effects of crystal structure on ice nucleation, a system of transition aluminas (Al2O3) that differ only in their crystal structure, despite being compositionally similar, were tested using immersion freezing. Particles were immersed in water and placed into a temperature controlled chamber. Freezing events were then recorded as the chamber was cooled to negative 30 °. Alpha-alumina, which is a member of the hexagonal crystal system, showed a significantly higher temperature at which all particles froze in comparison to other samples. This supports the hypothesis that, since a hexagonal crystal structure is the lowest energy state for ice, hexagonal surface structures would best facilitate ice nucleation. However, a similar sample of hexagonal chi-alumina did not show the same results. Further analysis of the samples will be done to characterize surface structures and composition. These conflicting data sets raise interesting questions about the effect of other surface features, such as surface area and porosity, on ice nucleation.

Flow-induced crystallization in isotactic polypropylene

NASA Astrophysics Data System (ADS)

Hamad, Fawzi Ghassan

Brief intervals of strong flow stretch chains in a semicrystalline polymer melt, which results in an increase in the nuclei number density and a transformation of the crystal structure. This flow-induced crystallization (FIC) phenomenon is explored in this study using highly isotactic polypropylene (iPP) samples. Using one synthesized and five commercial linear isotactic polypropylene samples, we investigate the FIC behavior by imposing shear onto these samples in a rotational rheometer. Equipped with a good temperature control and flexible shear protocol, we apply different temperature and flow conditions. The magnitude of the FIC effect varies with basic processing parameters (shear rate, specific work, crystallization temperature, and shearing temperature) and material properties (totalistic, molecular weight distribution, and particle concentration in the polymer). The scope of this study is to systematically investigate the influences of these parameters on FIC. The FIC effects that are investigated in this dissertation are: crystallization kinetics, persistence time of flow-induced nuclei, and crystal morphology. The crystallization time was measured in the rheometer by monitoring the onset of crystallization after quenching samples sheared above Tm. These samples were subsequently used to study their flow-induced nuclei persistence time and crystal morphology. The lifetime of flow-induced nuclei was determined by measuring the time required to return from FIC back to quiescent crystallization using a differential scanning calorimeter. The crystal morphology was imaged using polarized optical microscopy and atomic force microscopy. We investigated the influence of specific work on the three FIC characteristics, and found three regimes that are separated by the critical work ( Wc) and the saturation work (Wsat) thresholds. Below the critical work threshold, the morphology is composed of mostly spherulite crystals, which keep a constant volume, and a small fraction of rice grain (anisotropic) crystals. The number of rice grain crystals increases with specific work, speeding up the crystallization time of the semicrystalline polymer. At critical work, spherulite formation stops, and the morphology consists only of rice grain structures. This morphology allows the sample to crystallize at higher temperatures when cooling at 5 C/min, with the sheared sample crystallizing at 129C compared to the unsheared sample at 113C. . Shearing isotactic polypropylene at higher temperatures reduced the FIC effect after subsequent quenching. Generally speaking, shearing at higher temperatures results in slower crystallization, but surprisingly, the influence of temperature is rather weak. Flow-induced crystallization persists even when shear is applied well above the equilibrium melting temperature (187C), finally weakening above the Hoffman-Weeks temperature (210C). This is likely due to the long lifetime of flow- induced precursors (crystallize to form rice grains), which remain stable at temperatures below 210C and only start to disappear slowly in prolonged annealing at temperatures above 210C (diminishing the FIC effect). Tacticity was found to govern the maximum nuclei number density in sheared samples; samples with lower isotactic content show a stronger FIC effect. Similarly, it was found that the concentration of particulates (mainly catalyst residue) are crucially important to FIC, samples with lower amounts of particles lowering the FIC nuclei number density. Data shows that the rate at which the crystallization time changes correlates with the prominence of the high molecular weight tail. A sample with a higher molecular weight tail in its distribution exhibits a faster change in crystallization time as a function of specific work. Similarly, increasing the molecular weight of the added component in a blend induces a larger change in the FIC behavior. (Abstract shortened by ProQuest.).

Electrical properties of crystallized 30B2O3-70V2O5 glass

NASA Astrophysics Data System (ADS)

Gwoo, Donggun; Kim, Taehee; Han, Kyungseok; Choi, Wongyu; Kim, Jonghwan; Ryu, Bongki

2013-05-01

30B2O3-70V2O5 binary-system glass was prepared, and variations in structural and electrical property were examined using crystallization. While different related research studies exist, few have evaluated the variations in the structure and properties with changes in the crystallization rate. 30B2O3-70V2O5 glass was annealed in the graphite mold above the glass transition temperature for 2 h and heat-treated at each crystallization temperature for 3 h. 30B2O3-70V2O5 glass showed predominantly electronic conductive characteristic. FTIR was preferentially used for analyzing the structural changes of B-O bond after crystallization, while XRD was utilized to verify the inferred changes in the structure array (BO3 + V2O5 ↔ BO4 + 2VO2). Structural changes induced by heat treatment were confirmed by analyzing the molecular volume determined from the sample density, and conductance was measured to correlate structural and property changes. Conductivity is discussed based on the migration of vanadate ions with different valence states because of the increase in VO2 crystallinity at 130°C, which, however, was not observed at 170°C. After VO2 structures were reinforced, a 1.8-fold increase in conductance was observed (as compared to the annealed sample) after crystallization at 130°C for 3 h.

High Temperature Stability of Binary Microstructures Derived from Liquid Precursors

DTIC Science & Technology

1994-06-30

isopropoxide , Ti(OC3H7 )4 was stirred into the solution under nitrogen to produce a composition with a 1:1 Pb:Ti ratio. The solution was then boiled and...This program has emphasized two topics: 1) the crystallization of metastable, solid- solution structures, their partitioning into equilibrium structures...structural ceramics and their composites, and 2) the formation of single crystal thin films via spin coating single crystal substrates with solution

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–xK x)Fe 2As 2 single crystal with x = 0.24

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

Liu, Yong; Tanatar, Makariy A.; Timmons, Erik

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–xK x)Fe 2As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–xK x)Fe 2As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~more » 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–xK x)Fe 2As 2 single crystal with x = 0.24

DOE PAGES

Liu, Yong; Tanatar, Makariy A.; Timmons, Erik; ...

2016-11-09

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–xK x)Fe 2As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–xK x)Fe 2As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~more » 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

Growth, structural, optical, thermal and mechanical properties of cytosinium hydrogen selenite: A novel nonlinear optical single crystal

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

Jaikumar, P.; Sathiskumar, S.; Balakrishnan, T., E-mail: balacrystalgrowth@gmail.com

Highlights: • Growth of bulk single crystals of cytosinium hydrogen selenite (CHS) is reported. • Dielectric constant of CHS is measured as a function of Frequency and temperature. • Lower cut off value of UV–vis-NIR spectrum of CHS crystal is observed at 210 nm. • Meyer’s index value of CHS crystal calculated identifies it as a soft material. • Powder SHG efficiency of CHS is about 1.5 times that of KDP crystal. - Abstract: A novel nonlinear optical single crystal of cytosinium hydrogen selenite was grown from aqueous solution of cytosinium hydrogen selenite by slow solvent evaporation method at roommore » temperature. The structural properties of grown crystal have been studied by single crystal and powder X-ray diffraction analysis. Presence of various functional groups was identified from Fourier transform infrared spectroscopy. The optical transmittance and absorbance spectra were recorded by UV–vis-NIR spectrometer and the grown crystal possesses good transparency in the entire visible region. The dielectric constant and dielectric loss of the crystal were calculated as a function of frequency at different temperatures. The mechanical strength of the cytosinium hydrogen selenite crystal was estimated using Vicker’s microhardness tester. Etch patterns of the cytosinium hydrogen selenite crystal were obtained using distilled water as etchant for different etching time. Second harmonic generation efficiency tested using Nd:YAG laser is about 1.5 times that of KDP.« less

Crystal structure across the β to α phase transition in thermoelectric Cu 2–xSe

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

Eikeland, Espen; Blichfeld, Anders B.; Borup, Kasper A.

Here, the crystal structure uniquely imparts the specific properties of a material, and thus provides the starting point for any quantitative understanding of thermoelectric properties. Cu 2–xSe is an intensely studied high performing, non-toxic and cheap thermoelectric material, and here for the first time, the average structure of β-Cu 2–xSe is reported based on analysis of multi-temperature single-crystal X-ray diffraction data. It consists of Se–Cu layers with additional copper between every alternate layer. The structural changes during the peculiar zT enhancing phase transition mainly consist of changes in the inter-layer distance coupled with subtle Cu migration. Just prior to themore » transition the structure exhibits strong negative thermal expansion due to the reordering of Cu atoms, when approached from low temperatures. The phase transition is fully reversible and group–subgroup symmetry relations are derived that relate the low-temperature β-phase to the high-temperature α-phase. Weak superstructure reflections are observed and a possible Cu ordering is proposed. The structural rearrangement may have a significant impact on the band structure and the Cu rearrangement may also be linked to an entropy increase. Both factors potentially contribute to the extraordinary zT enhancement across the phase transition.« less

Crystal structure across the β to α phase transition in thermoelectric Cu 2–xSe

DOE PAGES

Eikeland, Espen; Blichfeld, Anders B.; Borup, Kasper A.; ...

2017-06-13

Here, the crystal structure uniquely imparts the specific properties of a material, and thus provides the starting point for any quantitative understanding of thermoelectric properties. Cu 2–xSe is an intensely studied high performing, non-toxic and cheap thermoelectric material, and here for the first time, the average structure of β-Cu 2–xSe is reported based on analysis of multi-temperature single-crystal X-ray diffraction data. It consists of Se–Cu layers with additional copper between every alternate layer. The structural changes during the peculiar zT enhancing phase transition mainly consist of changes in the inter-layer distance coupled with subtle Cu migration. Just prior to themore » transition the structure exhibits strong negative thermal expansion due to the reordering of Cu atoms, when approached from low temperatures. The phase transition is fully reversible and group–subgroup symmetry relations are derived that relate the low-temperature β-phase to the high-temperature α-phase. Weak superstructure reflections are observed and a possible Cu ordering is proposed. The structural rearrangement may have a significant impact on the band structure and the Cu rearrangement may also be linked to an entropy increase. Both factors potentially contribute to the extraordinary zT enhancement across the phase transition.« less

Growth and characterization of Na2Mo2O7 crystal scintillators for rare event searches

NASA Astrophysics Data System (ADS)

Pandey, Indra Raj; Kim, H. J.; Kim, Y. D.

2017-12-01

Disodium dimolybdate (Na2Mo2O7) crystals were grown using the Czochralski technique. The thermal characteristics of the compound were analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements. The crystal structure of the grown sample was confirmed using X-ray diffraction (XRD). Luminescence properties were measured at room and low temperatures, using a light emitting diode (LED) source. Very weak luminescence was observed at room temperature; however, the luminescence intensity was enhanced at low temperatures. The crystal's transmittance spectrum was measured for estimating its optical quality and energy band gap. The grown crystal exhibited a luminescence light yield of 55% compared with CaMoO4 crystals at 10 K, when excited by a 280-nm-wavelength LED source, but does not have the drawbacks of radioactive Ca isotopes. These results suggest that at cryogenic temperatures, Na2Mo2O7 crystal scintillators are promising for the detection of dark matter and neutrinoless double beta decay of 100Mo.

Structural disorder and elementary magnetic properties of triangular lattice ErMgGaO 4 single crystals

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

Cevallos, F. Alex; Stolze, Karoline; Cava, Robert J.

The single crystal growth, structure, and basic magnetic properties of ErMgGaO 4 are reported. The structure consists of triangular layers of magnetic ErO 6 octahedra separated by a double layer of randomly occupied non-magnetic (Ga,Mg)O 5 bipyramids. The Er atoms are positionally disordered. Magnetic measurements parallel and perpendicular to the c axis of a single crystal reveal dominantly antiferromagnetic interactions, with a small degree of magnetic anisotropy. A weighted average of the directional data suggests an antiferromagnetic Curie Weiss temperature of approximately -30 K. Below 10 K the temperature dependences of the inverse susceptibilities in the in-plane and perpendicular-to planemore » directions are parallel, indicative of an isotropic magnetic moment at low temperatures. In conclusion, no sign of magnetic ordering is observed above 1.8 K, suggesting that ErMgGaO 4 is a geometrically frustrated magnet.« less

Catalytic thermal barrier coatings

DOEpatents

Kulkarni, Anand A.; Campbell, Christian X.; Subramanian, Ramesh

2009-06-02

A catalyst element (30) for high temperature applications such as a gas turbine engine. The catalyst element includes a metal substrate such as a tube (32) having a layer of ceramic thermal barrier coating material (34) disposed on the substrate for thermally insulating the metal substrate from a high temperature fuel/air mixture. The ceramic thermal barrier coating material is formed of a crystal structure populated with base elements but with selected sites of the crystal structure being populated by substitute ions selected to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a higher rate than would the base compound without the ionic substitutions. Precious metal crystallites may be disposed within the crystal structure to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a lower light-off temperature than would the ceramic thermal barrier coating material without the precious metal crystallites.

Structural disorder and elementary magnetic properties of triangular lattice ErMgGaO 4 single crystals

DOE PAGES

Cevallos, F. Alex; Stolze, Karoline; Cava, Robert J.

2018-03-23

The single crystal growth, structure, and basic magnetic properties of ErMgGaO 4 are reported. The structure consists of triangular layers of magnetic ErO 6 octahedra separated by a double layer of randomly occupied non-magnetic (Ga,Mg)O 5 bipyramids. The Er atoms are positionally disordered. Magnetic measurements parallel and perpendicular to the c axis of a single crystal reveal dominantly antiferromagnetic interactions, with a small degree of magnetic anisotropy. A weighted average of the directional data suggests an antiferromagnetic Curie Weiss temperature of approximately -30 K. Below 10 K the temperature dependences of the inverse susceptibilities in the in-plane and perpendicular-to planemore » directions are parallel, indicative of an isotropic magnetic moment at low temperatures. In conclusion, no sign of magnetic ordering is observed above 1.8 K, suggesting that ErMgGaO 4 is a geometrically frustrated magnet.« less

Coupling of Crystal Structure and Magnetism in the Layered, Ferromagnetic Insulator CrI 3

DOE PAGES

McGuire, Michael A.; Dixit, Hemant; Cooper, Valentino R.; ...

2014-12-23

Here, we examine the crystallographic and magnetic properties of single crystals of CrI 3, an easily cleavable, layered and insulating ferromagnet with a Curie temperature of 61 K. Our X-ray diffraction studies reveal a first-order crystallographic phase transition occurring near 210–220 K upon warming, with significant thermal hysteresis. The low-temperature structure is rhombohedral (Rmore » $$\\bar{3}$$, BiI 3-type) and the high-temperature structure is monoclinic (C2/m, AlCl 3-type). Evidence for coupling between the crystallographic and magnetic degrees of freedom in CrI 3 was found; we observed an anomaly in the interlayer spacing at the Curie temperature and an anomaly in the magnetic susceptibility at the structural transition. First-principles calculations reveal the importance of proper treatment of the long-ranged interlayer forces, and van der Waals density functional theory does an excellent job of predicting the crystal structures and their relative stability. Our calculations suggest that the ferromagnetic order found in the bulk material may persist into monolayer form, suggesting that CrI 3 and other chromium trihalides may be promising materials for spintronic and magnetoelectronic research.« less

Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved

NASA Astrophysics Data System (ADS)

Cassar, Daniel R.; Lancelotti, Ricardo F.; Nuernberg, Rafael; Nascimento, Marcio L. F.; Rodrigues, Alisson M.; Diz, Luiza T.; Zanotto, Edgar D.

2017-07-01

The diffusion mechanisms controlling viscous flow, structural relaxation, liquid-liquid phase separation, crystal nucleation, and crystal growth in multicomponent glass-forming liquids are of great interest and relevance in physics, chemistry, materials, and glass science. However, the diffusing entities that control each of these important dynamic processes are still unknown. The main objective of this work is to shed some light on this mystery, advancing the knowledge on this phenomenon. For that matter, we measured the crystal growth rates, the viscosity, and lead diffusivities in PbSiO3 liquid and glass in a wide temperature range. We compared our measured values with published data covering 16 orders of magnitude. We suggest that above a certain temperature range Td (1.2Tg-1.3Tg), crystal growth and viscous flow are controlled by the diffusion of silicon and lead. Below this temperature, crystal growth and viscous flow are more sluggish than the diffusion of silicon and lead. Therefore, Td marks the temperature where decoupling between the (measured) cationic diffusivity and the effective diffusivities calculated from viscosity and crystal growth rates occurs. We reasonably propose that the nature or size of the diffusional entities controlling viscous flow and crystal growth below Td is quite different; the slowest is the one controlling viscous flow, but both processes require cooperative movements of some larger structural units rather than jumps of only one or a few isolated atoms.

Nucleated Poly(L-lactic acid) with N, N‧-oxalyl bis(benzoic acid) dihydrazide

NASA Astrophysics Data System (ADS)

Tian, Liang-Liang; Cai, Yan-Hua

2018-04-01

One of the major challenges in the field of Poly(L-lactic acid) (PLLA) is the enhancement of crystallization. In the present work, the evaluation of the influence of N, N‧-oxalyl bis(benzoic acid) dihydrazide (TBOD), as a novel organic nucleating agent, on the non-isothermal crystallization, melting behavior, and thermal stability of PLLA was performed using differential scanning calorimeter and thermogravimetric analysis. Non-isothermal crystallization measurement revealed that TBOD had an excellent accelerating effect for the crystallization of PLLA in cooling, and upon the addition of 3 wt% TBOD, PLLA exhibited the highest onset crystallization temperature and the crystallization peak temperature, as well as the largest non-isothermal crystallization enthalpy. In particular, when the TBOD concentration was 1 wt% ∼ 3 wt%, the onset crystallization temperatures were higher than the theoretical ceiling temperature of crystallization, thoroughly demonstrating the powerful crystallization promoting ability of TBOD. Additionally, the non-isothermal crystallization behavior of PLLA/TBOD depended on the TBOD concentration, cooling rate as well as the final melting temperature. The melting behavior of PLLA/TBOD after non-isothermal crystallization further confirmed the effect of TBOD on the crystallization process and crystal structure of PLLA, and the appearance of the double melting peaks during melting stages was attribute to the melting-recrystallization. For melting behavior after isothermal crystallization, the crystallization temperature and crystallization time significantly affected the melting behavior of PLLA/TBOD. The addition of TBOD could not change the thermal decomposition profile of the PLLA, but the thermal stability did not regularly decrease with increasing of TBOD concentration, indicating that there might exist intermolecular interaction between PLLA and TBOD.

Shear sensitive monomer-polymer laminate structure and method of using same

NASA Technical Reports Server (NTRS)

Singh, Jag J. (Inventor); Eftekhari, Abe (Inventor); Parmar, Devendra S. (Inventor)

1993-01-01

Monomer cholesteric liquid crystals have helical structures which result in a phenomenon known as selective reflection, wherein incident white light is reflected in such a way that its wavelength is governed by the instantaneous pitch of the helix structure. The pitch is dependent on temperature and external stress fields. It is possible to use such monomers in flow visualization and temperature measurement. However, the required thin layers of these monomers are quickly washed away by a flow, making their application time dependent for a given flow rate. The laminate structure according to the present invention comprises a liquid crystal polymer substrate attached to a test surface of an article. A light absorbing coating is applied to the substrate and is thin enough to permit bonding steric interaction between the liquid crystal polymer substrate and an overlying liquid crystal monomer thin film. Light is directed through and reflected by the liquid crystal monomer thin film and unreflected light is absorbed by the underlying coating. The wavelength of the reflected light is indicative of the shear stress experienced by the test surface. Novel aspects of the invention include its firm bonding of a liquid crystal monomer to a model and its use of a coating to reduce interference from light unreflected by the monomer helical structure.

Cubic-to-tetragonal structural phase transition in Rb1-xCsxCaF3 solid solutions: Thermal expansion and EPR studies

NASA Astrophysics Data System (ADS)

Lahoz, F.; Villacampa, B.; Alcalá, R.; Marquina, C.; Ibarra, M. R.

1997-04-01

The influence of crystal mixing on the structural phase transitions in Rb1-xCsxCaF3 (0=0.44. This transition shows a weak first-order component in the x=0 and 0.1 samples, which is progressively smeared out for x>0.1, indicating a spatial distribution of the critical temperature in those crystals with high ionic substitution rate. In RbCaF3 , another structural phase transition was observed at 20 K with a thermal hysteresis between 20 and 40 K. This transition has not been found in any of the mixed crystals.

Crystals of Janus colloids at various interaction ranges

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

Preisler, Z.; Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht; Vissers, T.

We investigate the effect of interaction range on the phase behaviour of Janus particles with a Kern-Frenkel potential. Specifically, we study interaction ranges Δ = 0.1σ, 0.3σ, 0.4σ, 0.5σ with σ the particle diameter, and use variable box shape simulations to predict crystal structures. We found that changing the interaction range beyond 0.2σ drastically increases the variety of possible crystal structures. In addition to close-packed structures, we find body-centered tetragonal and AA-stacked hexagonal crystals, as well as several lamellar crystals. For long interaction ranges and low temperatures, we also observe an extremely large number of metastable structures which compete withmore » the thermodynamically stable ones. These competing structures hinder the detection of the lowest-energy crystal structures, and are also likely to interfere with the spontaneous formation of the ground-state structure. Finally, we determine the gas-liquid coexistence curves for several interaction ranges, and observe that these are metastable with respect to crystallization.« less

Homogenous Nucleation and Crystal Growth in a Model Liquid from Direct Energy Landscape Sampling Simulation

NASA Astrophysics Data System (ADS)

Walter, Nathan; Zhang, Yang

Nucleation and crystal growth are understood to be activated processes involving the crossing of free-energy barriers. Attempts to capture the entire crystallization process over long timescales with molecular dynamic simulations have met major obstacles because of molecular dynamics' temporal constraints. Herein, we circumvent this temporal limitation by using a brutal-force, metadynamics-like, adaptive basin-climbing algorithm and directly sample the free-energy landscape of a model liquid Argon. The algorithm biases the system to evolve from an amorphous liquid like structure towards an FCC crystal through inherent structure, and then traces back the energy barriers. Consequently, the sampled timescale is macroscopically long. We observe that the formation of a crystal involves two processes, each with a unique temperature-dependent energy barrier. One barrier corresponds to the crystal nucleus formation; the other barrier corresponds to the crystal growth. We find the two processes dominate in different temperature regimes. Compared to other computation techniques, our method requires no assumptions about the shape or chemical potential of the critical crystal nucleus. The success of this method is encouraging for studying the crystallization of more complex

Mechanochemical synthesis of N-salicylidene­aniline: thermosalient effect of polymorphic crystals

PubMed Central

Mittapalli, Sudhir; Sravanakumar Perumalla, D.

2017-01-01

Polymorphs of the dichloro derivative of N-salicylideneaniline exhibit mechanical responses such as jumping (Forms I and III) and exploding (Form II) in its three polymorphs. The molecules are connected via the amide N—H⋯O dimer synthon and C—Cl⋯O halogen bond in the three crystal structures. A fourth high-temperature Form IV was confirmed by variable-temperature single-crystal X-ray diffraction at 180°C. The behaviour of jumping exhibited by the polymorphic crystals of Forms I and III is due to the layered sheet morphology and the transmission of thermal stress in a single direction, compared with the corrugated sheet structure of Form II such that heat dissipation is more isotropic causing blasting. The role of weak C—Cl⋯O interactions in the thermal response of molecular crystals is discussed. PMID:28512571

[Effect of annealing temperature on the crystallization and spectroscopic response of a small-molecule semiconductor doped in polymer film].

PubMed

Yin, Ming; Zhang, Xin-Ping; Liu, Hong-Mei

2012-11-01

The crystallization properties of the perylene (EPPTC) molecules doped in the solid film of the derivative of polyfluorene (F8BT) at different annealing temperatures, as well as the consequently induced spectroscopic response of the exciplex emission in the heterojunction structures, were studied in the present paper. Experimental results showed that the phase separation between the small and the polymer molecules in the blend film is enhanced with increasing the annealing temperature, which leads to the crystallization of the EPPTC molecules due to the strong pi-pi stacking. The size of the crystal phase increases with increasing the annealing temperature. However, this process weakens the mechanisms of the heterojunction configuration, thus, the total interfacial area between the small and the polymer molecules and the amount of exciplex are reduced significantly in the blend film. Meanwhile, the energy transfer from the polymer to the small molecules is also reduced. As a result, the emission from the exciplex becomes weaker with increasing the annealing temperature, whereas the stronger emission from the polymer molecules and from the crystal phase of the small molecules can be observed. These experimental results are very important for understanding and tailoring the organic heterojunction structures. Furthermore, this provides photophysics for improving the performance of photovoltaic or solar cell devices.

Effects of temperature changes and stress loading on the mechanical and shape memory properties of thermoplastic materials with different glass transition behaviours and crystal structures.

PubMed

Iijima, Masahiro; Kohda, Naohisa; Kawaguchi, Kyotaro; Muguruma, Takeshi; Ohta, Mitsuru; Naganishi, Atsuko; Murakami, Takashi; Mizoguchi, Itaru

2015-12-01

To investigate the effects of temperature changes and stress loading on the mechanical and shape memory properties of thermoplastic materials with different glass transition behaviours and crystal structures. Five thermoplastic materials, polyethylene terephthalate glycol (Duran®, Scheu Dental), polypropylene (Hardcast®, Scheu Dental), and polyurethane (SMP MM®, SMP Technologies) with three different glass transition temperatures (T g) were selected. The T g and crystal structure were assessed using differential scanning calorimetry and X-ray diffraction. The deterioration of mechanical properties by thermal cycling and the orthodontic forces during stepwise temperature changes were investigated using nanoindentation testing and custom-made force-measuring system. The mechanical properties were also evaluated by three-point bending tests; shape recovery with heating was then investigated. The mechanical properties for each material were decreased significantly by 2500 cycles and great decrease was observed for Hardcast (crystal plastic) with higher T g (155.5°C) and PU 1 (crystalline or semi-crystalline plastic) with lower T g (29.6°C). The Duran, PU 2, and PU 3 with intermediate T g (75.3°C for Duran, 56.5°C for PU 2, and 80.7°C for PU 3) showed relatively stable mechanical properties with thermal cycling. The polyurethane polymers showed perfect shape memory effect within the range of intraoral temperature changes. The orthodontic force produced by thermoplastic appliances decreased with the stepwise temperature change for all materials. Orthodontic forces delivered by thermoplastic appliances may influence by the T g of the materials, but not the crystal structure. Polyurethane is attractive thermoplastic materials due to their unique shape memory phenomenon, but stress relaxation with temperature changes is expected. © The Author 2015. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Long Periodic Structure of a Room-Temperature Ionic Liquid by High-Pressure Small-Angle X-Ray Scattering and Wide-Angle X-Ray Scattering: 1-Decyl-3-Methylimidazolium Chloride.

PubMed

Abe, Hiroshi; Hamaya, Nozomu; Koyama, Yoshihiro; Kishimura, Hiroaki; Takekiyo, Takahiro; Yoshimura, Yukihiro; Wakabayashi, Daisuke; Funamori, Nobumasa; Matsuishi, Kiyoto

2018-04-23

The Bragg reflections of 1-decyl-3-methylimidazolium chloride ([C 10 mim][Cl]), a room-temperature ionic liquid, are observed in a lowly scattered wavevector (q) region using high-pressure (HP) small-angle X-ray scattering methods. The HP crystal of [C 10 mim][Cl] was characterized by an extremely long periodic structure. The peak position at the lowest q (1.4 nm -1 ) was different from that of the prepeak observed in the liquid state (2.3 nm -1 ). Simultaneously, Bragg reflections at high-q were detected using HP wide-angle X-ray scattering. The longest lattice constant was estimated to be 4.3 nm using structural analysis. The crystal structure of HP differed from that of the low-temperature (LT) crystal and the LT liquid crystal. With increasing pressure, Bragg reflections in the high-q component became much broader, and were accompanied by phase transition, although those in the low-q component were observed to be relatively sharp. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, Crystal Structure, and Magnetic Properties of the YbFeTi2O7 Compound

NASA Astrophysics Data System (ADS)

Drokina, T. V.; Petrakovskii, G. A.; Molokeev, M. S.; Velikanov, D. A.

2018-03-01

We report on the synthesis conductions and results of experimental investigations of the crystal structure and magnetic properties of a new magnetic compound YbFeTi2O7. According to the X-ray diffractometry data, the crystal structure of the investigated compound is described by the rhombic space group Pcnb with unit cell parameters of a = 9.8115(1) Å, b = 13.5106(2) Å, and c = 7.31302(9) Å and atomic disordering in the distribution of iron ions Fe3+ over five structural sites. The magnetic measurements in the lowtemperature region revealed a kink in the temperature dependence of the magnetic moment and its dependence on the sample magnetic prehistory. The experimental results obtained suggest that with a decrease in temperature the sample passes from the paramagnetic state to the spin-glass-like magnetic state characterized by a freezing temperature of T f = 4.5 K at the preferred antiferromagnetic exchange coupling in the sample spin system. The chemical pressure variation upon replacement of rare-earth ion R by Yb in the RFeTi2O7 system does not change the crystal lattice symmetry and magnetic state.

Magnetic structure and phase stability of the van der Waals bonded ferromagnet Fe 3-xGeTe 2

DOE PAGES

May, Andrew F.; Calder, Stuart A.; Cantoni, Claudia; ...

2016-01-08

The magnetic structure and phase diagram of the layered ferromagnetic compound Fe 3GeTe 2 have been investigated by a combination of synthesis, x-ray and neutron diffraction, high-resolution microscopy, and magnetization measurements. Single crystals were synthesized by self-flux reactions, and single-crystal neutron diffraction finds ferromagnetic order with moments of 1.11(5)μ B/Fe aligned along the c axis at 4 K. These flux-grown crystals have a lower Curie temperature T c ≈ 150 K than crystals previously grown by vapor transport (T c = 220 K). The difference is a reduced Fe content in the flux-grown crystals, as illustrated by the behavior observedmore » in a series of polycrystalline samples. As Fe content decreases, so do the Curie temperature, magnetic anisotropy, and net magnetization. Furthermore, Hall-effect and thermoelectric measurements on flux-grown crystals suggest that multiple carrier types contribute to electrical transport in Fe 3–xGeTe 2 and structurally similar Ni 3–xGeTe 2.« less

Evidence for monoclinic distortion in the ground state phase of underdoped La 1.95Sr 0.05CuO 4: A single crystal neutron diffraction study

DOE PAGES

Singh, Anar; Schefer, Jurg; Sura, Ravi; ...

2016-03-24

The existing controversy about the symmetry of the crystal structure of the ground state of the critical doped La 1.95Sr 0.05CuO 4 has been resolved by analyzing the single crystal neutron diffraction data collected between 5 and 730 K. We observed small but significant intensities for "forbidden" reflections given by extinction rules of the orthorhombic Bmab space group at low temperatures. A careful investigation of neutron diffraction data reveals that the crystal structure of La 1.95Sr 0.05CuO 4 at 5 K is monoclinic with B2/m (2/m 1 1) space group. The monoclinic structure emerges from the orthorhombic structure in amore » continuous way; however, the structure is stable below similar to 120K which agrees with other observed phenomena. Lastly, our results on symmetry changes are crucial for the interpretation of physical properties also in other high temperature superconductors with similar structures.« less

Evidence for monoclinic distortion in the ground state phase of underdoped La{sub 1.95}Sr{sub 0.05}CuO{sub 4}: A single crystal neutron diffraction study

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

Singh, Anar, E-mail: singhanar@gmail.com; Schefer, Jürg; Frontzek, Matthias

2016-03-28

The existing controversy about the symmetry of the crystal structure of the ground state of the critical doped La{sub 1.95}Sr{sub 0.05}CuO{sub 4} has been resolved by analyzing the single crystal neutron diffraction data collected between 5 and 730 K. We observed small but significant intensities for “forbidden” reflections given by extinction rules of the orthorhombic Bmab space group at low temperatures. A careful investigation of neutron diffraction data reveals that the crystal structure of La{sub 1.95}Sr{sub 0.05}CuO{sub 4} at 5 K is monoclinic with B2/m (2/m 1 1) space group. The monoclinic structure emerges from the orthorhombic structure in a continuous way;more » however, the structure is stable below ∼120 K which agrees with other observed phenomena. Our results on symmetry changes are crucial for the interpretation of physical properties also in other high temperature superconductors with similar structures.« less

Features of the structural states of KNbO{sub 3} single crystals before and after fast-neutron irradiation

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

Stash, A. I., E-mail: astas@yandex.ru; Ivanov, S. A.; Stefanovich, S. Yu.

Neutron irradiation is a unique tool for forming new structural states of ferroelectrics, which cannot be obtained by conventional methods. The inf luence of the irradiation by two doses of fast neutrons (F = 1 × 10{sup 17} and 3 × 10{sup 17} cm{sup –2}) on the structure and properties of KNbO{sub 3} single crystals has been considered for the first time. The developed method for taking into account the experimental correction to the diffuse scattering has been used to analyze the structural changes occurring in KNbO{sub 3} samples at T = 295 K and their correlations with the behaviormore » of dielectric and nonlinear optical characteristics. The irradiation to the aforementioned doses retains the KNbO{sub 3} polar structure, shifting Т{sub Ð}¡ to lower temperatures and significantly affecting only the thermal parameters and microstructure of single crystals. Neutron irradiation with small atomic displacements provides a structure similar to the high-temperature modification of an unirradiated KNbO{sub 3} crystal.« less

Local structure of Ge2Sb2Te5 during crystallization under pressure

NASA Astrophysics Data System (ADS)

Roscioni, O. M.; Branicio, P. S.; Kalikka, J.; Zhou, X.; Simpson, R. E.

2018-04-01

The role of stress on the crystallization process of the phase change data storage material, Ge2Sb2Te5, is studied. When thin Ge2Sb2Te5 films are capped with Si3N4, stress is generated in the Ge2Sb2Te5 layer which causes the crystallization temperature to increase. Si3N4 films of 25 nm thickness increase the crystallization temperature from 446 K to 464 K. We show that stress predominantly destabilizes voids and increases the number of Ge-Sb and homopolar bonds in the vicinity of Ge atoms, and this makes the crystallization less probable, thus resulting in the increase in the measured temperature.

High pressure high temperature devitrification of Fe78B13Si9 metallic glass with simultaneous x-ray structural characterization

NASA Astrophysics Data System (ADS)

Stemshorn, Andrew K.; Vohra, Yogesh K.; Smith, Spencer J.

2018-06-01

Changes in bulk crystallization behavior following devitrification at high pressure are investigated for a Fe78B13Si9 composition metallic glass using in-situ energy dispersive x-ray powder diffraction. Crystallization with time was evaluated for a series of measurements to a maximum pressure of 5.63 ± 0.15 GPa for the Fe78B13Si9 glass. Pressure was found to strongly affect onset bulk crystallization temperature Tx. Crystallization at each pressure was found to progress in two stages. In the first stage, α-Fe precipitates and in the second Fe2B forms while α-Fe continues to crystallize. Complementary high pressure room temperature studies were conducted.

Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations.

PubMed

van de Streek, Jacco; Neumann, Marcus A

2010-10-01

This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 A either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect.

On melt solutions for the growth of CaTiO3 crystals

NASA Astrophysics Data System (ADS)

Klimm, Detlef; Schmidt, Max; Wolff, Nora; Guguschev, Christo; Ganschow, Steffen

2018-03-01

When calcium titanate crystals are grown from stoichiometric melts, they crystallize in the cubic perovskite structure. Upon cooling to room temperature they undergo subsequent phase transitions to tetragonal and orthorhombic modifications. These phase transitions are disruptive and result in severely damaged crystals. This paper presents differential thermal analysis data for several prospective solvents, with the aim to identify a system offering the possibility to perform crystal growth of undistorted CaTiO3 crystals by crystallizing them significantly below the melting point directly in the low temperature modification. From mixtures CaF2:TiO2:CaTiO3 = 3:1:1 (molar ratio) the growth of undistorted, at least millimeter-sized CaTiO3 crystals is possible.

Crystal Structure Studies of Low-Ca Pyroxenes from LL-Group Chondritic Meteorites

NASA Astrophysics Data System (ADS)

Artioli, G.; Davoli, G.; Sighinolfi, G. P.

1993-07-01

One orthorhombic (Pbca) and two monoclinic (P2(sub)1/c) single crystals of low-Ca pyroxenes were extracted from unequilibrated chondritic meteorites of the LL-group. The results of the crystal structure refinements performed using x-ray diffraction data indicate that: (1) the intracrystalline Fe-Mg distribution over the M1 and M2 crystallographic sites of the Parnallee (LL-3) orthoenstatite is consistent with a temperature of 960 degrees C for the closure of the exchange equilibrium process; and (2) the structural state and intracristalline Fe-Mg order in the Soko Banja (LL-4) and Jolomba (LL-6) clinoenstatites indicate a closing temperature of at least 1000-1100 degrees C, with no significant reequilibration at lower temperatures. The present data represent the first detailed crystallographic investigation of pyroxenes from LL-chondrites and support the hypothesis that the chondrule pyroxenes bear a distinct memory of rapid cooling in the solar nebular and that thermal metamorphism in the parent body, if present, was totally unsufficient to allow reequilibration of the pyroxene minerals to the low-temperature ordered crystal structures. The data also indicate that, assuming low or mild pressure and shock effects, there is no well-defined correlation between equilibrium temperature of the mineral phases and the alleged petrologic type of the meteorites. This evidence is consistent with a rubble-pile model for the parent body accretional history, or with an onion-shell model with very low thermal-peak metamorphism, as it is assumed for a very small object.

Low-temperature nanodoping of protonated LiNbO3 crystals by univalent ions

NASA Astrophysics Data System (ADS)

Borodin, Yu. V.

2015-01-01

In the nanocomposite model developed here, crystals are treated as subordinate aggregate of pro- ton-selected structural elements, their blocks, and proton-containing quantum sublattices with preferred transport effects separating them. The formation of stratified reversible hexagonal structures is accompanied with protonation and formation of a dense network of H-bonds ensuring the nanocomposite properties. Nanodoping with H+ ions occurs during processing of crystals and glasses in melts as well as in aqueous solutions of Ag, Tl, Rb, and Cs salts. The isotope exchange H+ ↔ D+ and ion exchange H+ ↔ M+ lead to nanodoping of protonated materials with D+ and M+ ions. This is manifested especially clearly in Li-depleted nonequilibrium LiNbO3 and LiTaO3 crystals. Low-temperature proton-ion nanodoping over superlattices is a basically new approach to analysis of the structure and properties of extremely nonequilibrium materials.

Anomalous heat transfer in two polymorphs of para-bromobenzophenone

NASA Astrophysics Data System (ADS)

Romantsova, O. O.; Horbatenko, Yu. V.; Krivchikov, A. I.; Korolyuk, O. A.; Vdovichenko, G. A.; Zloba, D. I.; Pyshkin, O. S.

2017-03-01

The thermal conductivity of a polycrystalline sample of monoclinic polymorph of para-bromobenzophenone in the T = 3-320 K temperature range was measured using steady-state linear heat flow. The temperature dependences of thermal conductivity are presented as the sum of two independent contributions: a contribution that corresponds to the thermal conductivity of an orientationally ordered crystal structure, and a new additional thermally activated contribution that manifests itself above 130 K. A comparison is made with the data on the thermal conductivity of a single crystal triclinic polymorph of para-bromobenzophenone. It is established that the contribution corresponding to the thermal conductivity of the orientationally ordered crystal structure depends on the molecular crystal packing, and the characteristic activation energy of the thermal activation contribution, which is caused by the intramolecular vibrations of the C-Br bond, does not depend on the grain size or on the structure of the sample.

Order-disorder phase transitions and their influence on the structure and vibrational properties of new hybrid material: 2-Amino-4-methyl-3-nitropyridinium trifluoroacetate

NASA Astrophysics Data System (ADS)

Lorenc, J.; Bryndal, I.; Syska, W.; Wandas, M.; Marchewka, M.; Pietraszko, A.; Lis, T.; Mączka, M.; Hermanowicz, K.; Hanuza, J.

2010-08-01

New organic-organic salt, 2-amino-4-methyl-3-nitropyridinium trifluoroacetate, has been synthesised and characterised by FT-IR, FT-Raman, DSC and single crystal X-ray crystallography. The 2-amino-4-methyl-3-nitropyridinium trifluoroacetate undergoes a reversible phase transition at ˜162 K. The X-ray structures, vibrational spectra and quantum chemical DFT calculations (B3LYP/6-31G(d,p) approach) have been analysed for high-temperature and low-temperature modifications of the compound, which both crystallize in orthorhombic space group Pbca with two non-equivalent cations and two anions in the asymmetric unit. Their crystal and molecular structures have been compared and the role of the intermolecular interactions in these crystals has been analysed. The mechanisms of the phase transition have been proposed.

Crystal structure and vibrational spectra of melaminium arsenate

NASA Astrophysics Data System (ADS)

Anbalagan, G.; Marchewka, M. K.; Pawlus, K.; Kanagathara, N.

2015-01-01

The crystals of the new melaminium arsenate (MAS) [C3H7N6+ṡH2AsO4-] were obtained by the slow evaporation of an aqueous solution at room temperature. Single crystal X-ray diffraction analysis reveals that the crystal belongs to triclinic system with centro symmetric space group P-1. The crystals are built up from single protonated melaminium residues and single dissociated arsenate H2AsO4- anions. The protonated melaminium ring is almost planar. A combination of ionic and donor-acceptor hydrogen-bond interactions linking together the melaminium and arsenate residues forms a three-dimensional network. Vibrational spectroscopic analysis is reported on the basis of FT-IR and FT-Raman spectra recorded at room temperature. Hydrogen bonded network present in the crystal gives notable vibrational effect. DSC has also been performed for the crystal shows no phase transition in the studied temperature range (113-293 K).

Tunable two-dimensional photonic crystals using liquid crystal infiltration

NASA Astrophysics Data System (ADS)

Leonard, S. W.; Mondia, J. P.; van Driel, H. M.; Toader, O.; John, S.; Busch, K.; Birner, A.; Gösele, U.; Lehmann, V.

2000-01-01

The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal E7 was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 μm and a band gap wavelength range of 3.3-5.7 μm. After infiltration, the band gap for the H polarized field shifted dramatically to 4.4-6.0 μm while that of the E-polarized field collapsed. As the sample was heated to the nematic-isotropic phase transition temperature of the liquid crystal (59 °C), the short-wavelength band edge of the H gap shifted by as much as 70 nm while the long-wavelength edge was constant within experimental error. Band structure calculations incorporating the temperature dependence of the liquid crystal birefringence can account for our results and also point to an escaped-radial alignment of the liquid crystal in the nematic phase.

Crystal Structure Variations of Sn Nanoparticles upon Heating

NASA Astrophysics Data System (ADS)

Mittal, Jagjiwan; Lin, Kwang-Lung

2018-04-01

Structural changes in Sn nanoparticles during heating below the melting point have been investigated using differential scanning calorimetry (DSC), x-ray diffraction (XRD) analysis, electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). DSC revealed that the heat required to melt the nanoparticles (28.43 J/g) was about half compared with Sn metal (52.80 J/g), which was attributed to the large surface energy contribution for the nanoparticles. ED and XRD analyses of the Sn nanoparticles revealed increased intensity for crystal planes having large interplaner distances compared with regular crystal planes with increasing heat treatment temperature (HTT). HRTEM revealed an increase in interlayer spacing at the surface and near joints between nanoparticles with the HTT, leading to an amorphous structure of nanoparticles at the surface at 220°C. These results highlight the changes that occur in the morphology and crystal structure of Sn nanoparticles at the surface and in the interior with increase of the heat treatment temperature.

Combinatorial and High Throughput Discovery of High Temperature Piezoelectric Ceramics

DTIC Science & Technology

2011-10-10

the known candidate piezoelectric ferroelectric perovskites. Unlike most computational studies on crystal chemistry, where the starting point is some...studies on crystal chemistry, where the starting point is some form of electronic structure calculation, we use a data driven approach to initiate our...experimental measurements reported in the literature. Given that our models are based solely on crystal and electronic structure data and did not

Preferential Stereocomplex Crystallization in Enantiomeric Blends of Cellulose Acetate-g-Poly(lactic acid)s with Comblike Topology.

PubMed

Bao, Jianna; Han, Lili; Shan, Guorong; Bao, Yongzhong; Pan, Pengju

2015-10-01

Although stereocomplex (sc) crystallization is highly effective for improving the thermal resistance of poly(lactic acid) (PLA), it is much less predominant than homocrystallization in high-molecular-weight (HMW) poly(l-lactic acid)/ poly(d-lactic acid) (PLLA/PDLA) racemic blends. In this contribution, the sc crystallization of HMW PLLA/PDLA racemic blends was facilitated by using comblike PLAs with cellulose acetate as the backbone. Competing crystallization kinetics, polymorphic crystalline structure, and structural transition of comblike PLLA/PDLA blends with a wide range of MWs were investigated and compared with the corresponding linear/comblike and linear blends. The HMW comblike blend is preferentially crystallized in sc polymorphs and exhibits a faster crystallization rate than does the corresponding linear blend. The sc crystallites are predominantly formed in nonisothermal cold crystallization and isothermal crystallization at temperatures above 120 °C for the comblike blends. Except for the facilitated sc formation in primary crystallization, synchrotron radiation WAXD analysis indicates that the presence of a comblike component also facilitates the transition or recrystallization from homocrystallite (hc) to sc crystallite upon heating. Preferential sc formation of comblike blends is probably attributable to the favorable interdigitation between enantiomeric branches and the increased mobility of polymer segments. After crystallization under the same temperature, the comblike blends, which mainly contain sc crystallites, show smaller long periods and thinner crystalline lamellae than do the corresponding PLLA with homocrystalline structures.

Specific Features of the Domain Structure of BaTiO3 Crystals during Thermal Heating and Cooling

NASA Astrophysics Data System (ADS)

Kiselev, D. A.; Ilina, T. S.; Malinkovich, M. D.; Sergeeva, O. N.; Bolshakova, N. N.; Semenova, E. M.; Kuznetsova, Yu. V.

2018-04-01

This paper presents the results of the study of the domain structure of barium titanate crystals in a wide temperature range including the Curie point ( T C) using the polarization-optical method in the reflected light and the force microscopy of the piezoelectric response. It is shown that a new a-c domain structure forms during cyclic heating of the crystal above T C and subsequent cooling to the ferroelectric phase. The role of uncompensated charges appeared on the crystal surface during the phase transition and their influence on the formation of the domain structure during cooling are discussed.

Crystal structure and superconductivity in atomic hydrogen: Deformation between I41/amd and Fddd

NASA Astrophysics Data System (ADS)

Ishikawa, T.; Nagara, H.; Oda, T.; Suzuki, N.; Shimizu, K.

2017-10-01

We investigated crystal structures of solid metallic hydrogen using the potential energy surface trekking for structure search. We applied this technique to a tetragonal I41/amd structure at pressures of 500 and 600 GPa and obtained the transformation into multiple orthorhombic Fddd structures, which are formed by distortions in the ab plane of I41/amd. The potential barriers are easily surmounted by few trekking steps, which indicates that in solid metallic hydrogen crystal structure is softened with respect to the distortion and is easily fluctuated among the I41/amd and Fddd structures. Calculated superconducting critical temperatures show 269 K for I41/amd and 263 K for Fddd at 500 GPa. The structures are softened and the electron-phonon coupling are enhanced with pressurization to 600 GPa. As the results, the superconducting critical temperature is increased to 281 K for I41/amd, whereas it is decreased to 252 K for Fddd owing to its larger phonon softening than that of I41/amd.

Temperature-dependent dielectric functions and interband critical points of sulfur-rich TlIn(S1-xSex)2 layered solid solution crystals

NASA Astrophysics Data System (ADS)

Gomonnai, O. O.; Gordan, O.; Guranich, P. P.; Slivka, A. G.; Gomonnai, A. V.; Zahn, D. R. T.

2017-12-01

Real and imaginary parts of the dielectric function of TlIn(S1-xSex)2 (x = 0.05, 0.08, 0.25) single crystals were determined in the spectral range from 1 to 5 eV within a temperature interval 140-293 K from spectroscopic ellipsometry measurements. The energies of interband transitions (critical points) of the TlIn(S1-xSex)2 crystals were obtained from the second derivative of the real and imaginary parts of dielectric function. Structural phase transitions are behind the observed change of electronic band structure.

Surface and electronic structure of Bi-Ca-Sr-Cu-O superconductors studied by LEED, UPS and XPS

NASA Astrophysics Data System (ADS)

Shen, Z.-X.; Lindberg, P. A. P.; Wells, B. O.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Eom, C. B.; Kapitulnik, A.; Geballe, T. H.; Soukiassian, P.

1989-02-01

Single crystal and polycrystalline samples of Bi2CaSr2Cu2O8 have been studied by various surface sensitive techniques, including low energy electron diffraction (LEED), ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). The surface structure of the single crystals was characterized by LEED to be consistent with that of the bulk structure. Our data suggest that Bi2CaSr2Cu2O8 single crystals are very stable in the ultrahigh vacuu. No change of XPS spectra with temperature was observed. We have also studied the electronic structure of Bi2Sr2CuO6, which has a lower superconducting transition temperature Tc. Comparing the electronic structure of the two Bi-Ca-Sr-Cu-O superconductors, an important difference in the density of states near EF was observed which seems to be related to the difference in Tc.

Temperature dependence of single-crystal elastic constants of flux-grown alpha-GaPO(4).

PubMed

Armand, P; Beaurain, M; Rufflé, B; Menaert, B; Papet, P

2009-06-01

The lattice parameter change with respect to temperature (T) has been measured using high-temperature powder X-ray diffraction techniques for high-temperature flux-grown GaPO(4) single crystals with the alpha-quartz structure. The lattice and the volume linear thermal expansion coefficients in the temperature range 303-1173 K were computed from the X-ray data. The percentage linear thermal expansions along the a and c axes at 1173 K are 1.5 and 0.51, respectively. The temperature dependence of the mass density rho of flux-grown GaPO(4) single crystals was evaluated using the volume thermal expansion coefficient alpha(V)(T) = 3.291 x 10(-5) - 2.786 x 10(-8) [T] + 4.598 x 10(-11)[T](2). Single-crystal high-resolution Brillouin spectroscopy measurements have been carried out at ambient pressure from 303 to 1123 K to determine the elastic constants C(IJ) of high-temperature flux-grown GaPO(4) material. The single-crystal elastic moduli were calculated using the sound velocities via the measured Brillouin frequency shifts Deltanu(B). These are, to our knowledge, the highest temperatures at which single-crystal elastic constants of alpha-GaPO(4) have been measured. Most of the room-temperature elastic constant values measured on flux-grown GaPO(4) material are higher than the ones found for hydrothermally grown GaPO(4) single crystals. The fourth-order temperature coefficients of both the Brillouin frequency shifts T(nuB)((n)) and the single-crystal elastic moduli T(C(IJ))((n)) were obtained. The first-order temperature coefficients of the C(IJ) are in excellent agreement with previous reports on low-temperature hydrothermally grown alpha-GaPO(4) single crystals, while small discrepancies in the higher-order temperature coefficients are observed. This is explained in terms of the OH content in the GaPO(4) network, which is an important parameter in the crystal thermal behavior.

Towards TiO2 nanotubes modified by WO3 species: influence of ex situ crystallization of precursor on the photocatalytic activities of WO3/TiO2 composites

NASA Astrophysics Data System (ADS)

Sun, Hui; Dong, Bohua; Su, Ge; Gao, Rongjie; Liu, Wei; Song, Liang; Cao, Lixin

2015-09-01

TiO2 nanotubes (TNT) crystallized at different temperatures were loaded with WO3 hydrate through the reaction between (NH4)6W7O24·6H2O and an aqueous solution of HCl. The photocatalytic activities of nanocomposites firstly increase and then decrease as a function of the crystallized temperature of the TNT precursor. The structural, morphologic and optical properties of WO3/TiO2 nanocomposites were also investigated in this study. The samples, initially anatase titania (573 K-773 K), presented phase transition to rutile titania at 873 K. With the crystallized temperature increasing, an evolution of samples morphology changing from nanotube-like structure to nanorod-like structure was observed. Meanwhile, the absorption edge of samples exhibited a red shift, and correspondingly their band gap decreased. Consistent with x-ray diffraction diffractograms, the existence of rutile titania as an impurity in the precursor TNT, crystallized at higher than 873 K, depressed photocatalytic activity evidently. As a result, the degradation rate of methyl orange (MO) increased with the samples crystallinity firstly, and then reduced due to the appearance of rutile titania. In our experimental conditions, the optimal photocatalytic activity was achieved for the sample crystalized at 773 K. Its degradation rate could reach 98.76% after 90 min UV light irradiation.

Effect of Structural Relaxation on the In-Plane Electrical Resistance of Oxygen-Underdoped ReBaCuO (Re = Y, Ho) Single Crystals

NASA Astrophysics Data System (ADS)

Vovk, Ruslan V.; Vovk, Nikolaj R.; Dobrovolskiy, Oleksandr V.

2014-05-01

The effect of jumpwise temperature variation and room-temperature storing on the basal-plane electrical resistivity of underdoped ReBaCuO (Re = Y, Ho) single crystals is investigated. Reducing the oxygen content has been revealed to lead to the phase segregation accompanied by both, labile component diffusion and structural relaxation in the sample volume. Room-temperature storing of single crystals with different oxygen hypostoichiometries leads to a substantial widening of the rectilinear segment in in conjunction with a narrowing of the temperature range of existence of the pseudogap state. It is established that the excess conductivity obeys an exponential law in a broad temperature range, while the pseudogap's temperature dependence is described satisfactory in the framework of the BCS-BEC crossover theory. Substituting yttrium with holmium essentially effects the charge distribution and the effective interaction in CuO planes, thereby stimulating disordering processes in the oxygen subsystem. This is accompanied by a notable shift of the temperature zones corresponding to transitions of the metal-insulator type and to the regime of manifestation of the pseudogap anomaly.

A Novel High-Sensitivity, Low-Power, Liquid Crystal Temperature Sensor

PubMed Central

Algorri, José Francisco; Urruchi, Virginia; Bennis, Noureddine; Sánchez-Pena, José Manuel

2014-01-01

A novel temperature sensor based on nematic liquid crystal permittivity as a sensing magnitude, is presented. This sensor consists of a specific micrometric structure that gives considerable advantages from other previous related liquid crystal (LC) sensors. The analytical study reveals that permittivity change with temperature is introduced in a hyperbolic cosine function, increasing the sensitivity term considerably. The experimental data has been obtained for ranges from −6 °C to 100 °C. Despite this, following the LC datasheet, theoretical ranges from −40 °C to 109 °C could be achieved. These results have revealed maximum sensitivities of 33 mVrms/°C for certain temperature ranges; three times more than of most silicon temperature sensors. As it was predicted by the analytical study, the micrometric size of the proposed structure produces a high output voltage. Moreover the voltage's sensitivity to temperature response can be controlled by the applied voltage. This response allows temperature measurements to be carried out without any amplification or conditioning circuitry, with very low power consumption. PMID:24721771

Cracking a chemical conundrum

NASA Astrophysics Data System (ADS)

Adams, James M.; Ivanov, Alexandre S.; Johnson, Mark R.; Stride, John A.

2004-07-01

An everyday laboratory chemical, hexamethylbenzene (HMB) has assumed an important role in the history of molecular structure and crystallography. It was one of the first organic crystal structures to be solved and provided direct experimental proof for the hypothesis of planarity in aromatic systems. Very soon after this, HMB was found to undergo a phase transition at 117K, resulting in crystal shattering. Since then, many attempts have been made to obtain the low-temperature structure, but none have succeeded until now. Making use of the unique properties of the neutron, we have performed powder diffraction measurements to obtain the low-temperature crystal structure and inelastic measurements to determine the dynamics of the system. These experiments have been augmented by the use of ab initio calculations and molecular modelling to obtain a complete picture of HMB in the solid state.

Thermal response, catalytic activity, and color change of the first hybrid vanadate containing Bpe guest molecules.

PubMed

Fernández de Luis, Roberto; Urtiaga, M Karmele; Mesa, José L; Larrea, Edurne S; Iglesias, Marta; Rojo, Teófilo; Arriortua, María I

2013-03-04

Four isomorphic compounds with formula [{Co2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoBpe 1; [{CoNi(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoNiBpe 2; [{Co0.6Ni1.4(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiCoBpe 3; and [{Ni2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiBpe 4, have been obtained by hydrothermal synthesis. The crystal structures of CoBpe 1 and NiBpe 4 were determined by single-crystal X-ray diffraction (XRD). The Rietveld refinement of CoNiBpe 2 and NiCoBpe 3 XRD patterns confirms that those are isomorphic. The compounds crystallize in the P1̅ space group, exhibiting a crystal structure constructed from inorganic layers pillared by Bpe ligands. The crystal structure contains intralayer and interlayer channels, in which the crystallization water molecules and Bpe guest molecules, respectively, are located. The solvent molecules establish a hydrogen bonding network with the coordinated water molecules. Thermodiffractometric and thermogravimetric studies showed that the loss of crystallization and coordinated water molecules takes place at different temperatures, giving rise to crystal structure transformations that involve important reduction of the interlayer distance, and strong reduction of crystallinity. The IR, Raman, and UV-vis spectra of the as-synthesized and heated compounds confirm that the structural building blocks and octahedral coordination environment of the metal centers are maintained after the structural transformations. The color change and reversibility of the water molecules uptake/removal were tested showing that the initial color is not completely recovered when the compounds are heated at temperatures higher than 200 °C. The thermal evolution of the magnetic susceptibility indicates one-dimensional antiferromagnetic coupling of the metal centers at high temperatures. For NiCoBpe 3 and NiBpe 4 compounds magnetic ordering is established at low temperatures, as can be judged by the maxima observed in the magnetic susceptibilities. CoNiBpe 2 was proved as catalyst being active for cyanosilylation reactions of aldehydes.

Multi-temperature study of potassium uridine-5'-monophosphate: electron density distribution and anharmonic motion modelling.

PubMed

Jarzembska, Katarzyna N; Řlepokura, Katarzyna; Kamiński, Radosław; Gutmann, Matthias J; Dominiak, Paulina M; Woźniak, Krzysztof

2017-08-01

Uridine, a nucleoside formed of a uracil fragment attached to a ribose ring via a β-N1-glycosidic bond, is one of the four basic components of ribonucleic acid. Here a new anhydrous structure and experimental charge density distribution analysis of a uridine-5'-monophosphate potassium salt, K(UMPH), is reported. The studied case constitutes the very first structure of a 5'-nucleotide potassium salt according to the Cambridge Structural Database. The excellent crystal quality allowed the collection of charge density data at various temperatures, i.e. 10, 100, 200 and 300 K on one single crystal. Crystal structure and charge density data were analysed thoroughly in the context of related literature-reported examples. Detailed analysis of the charge density distribution revealed elevated anharmonic motion of part of the uracil ring moiety relatively weakly interacting with the neighbouring species. The effect was manifested by alternate positive and negative residual density patterns observed for these atoms, which `disappear' at low temperature. It also occurred that the potassium cation, quite uniformly coordinated by seven O atoms from all molecular fragments of the UMPH - anion, including the O atom from the ribofuranose ring, can be treated as spherical in the charge density model which was supported by theoretical calculations. Apart from the predominant electrostatic interactions, four relatively strong hydrogen bond types further support the stability of the crystal structure. This results in a compact and quite uniform structure (in all directions) of the studied crystal, as opposed to similar cases with layered architecture reported in the literature.

Synthesis, crystal structure and high temperature phase transition in the new organic-inorganic hybrid [N(C4H9)4]3Zn2Cl7H2O crystals

NASA Astrophysics Data System (ADS)

Ben Gzaiel, Malika; Oueslati, Abderrazek; Lhoste, Jérôme; Gargouri, Mohamed; Bulou, Alain

2015-06-01

The present paper accounts for the synthesis, crystal structure, differential scanning calorimetry and vibrational spectroscopy of a new compound tri-tetrabutylammonium heptachloro-dizincate (I) grown at room temperature by slow evaporation of aqueous solution. From X-ray diffraction data collected at room temperature, it is concluded that it crystallizes in the monoclinic system (P21/n space group) containing ZnCl42- and ZnCl3H2O1- tetrahedra. The atomic arrangement can be described by an alternation of organic and organic-inorganic layers stacked along the c direction. Differential scanning calorimetry (DSC) in the range 250-450 K disclosed a reversible structural phase transition of order-disorder type at 358 K, prior to the melting at 395 K. The temperature dependence of the Raman spectra of [N(C4H9)4]3Zn2Cl7H2O single crystals was studied in the spectral range 100-3500 cm-1 and for temperatures between 300 and 386 K. The most important changes are observed for the line at 261 cm-1 issued from ν1(ZnCl4). The analysis of the wavenumber, intensity and the line width based on an order-disorder model allowed to obtain information relative to the activation energy and the correlation length. The decrease of the activation energy with increasing temperature has been interpreted in term of a change in the re-orientation motion of the anionic parts. The assumption of cluster fluctuations also allowed the critical exponents to be obtained for the transition δ = 0.011 and the correlation length ξ0 = 598 Å.

Self-assembled ordered structures in thin films of HAT5 discotic liquid crystal.

PubMed

Morales, Piero; Lagerwall, Jan; Vacca, Paolo; Laschat, Sabine; Scalia, Giusy

2010-05-20

Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical microscopy, revealing large-scale ordered structures substantially different from those typically observed in standard samples of the same material. Thin and very long fibrils of planar-aligned liquid crystal were found, possibly formed as a result of an intermediate lyotropic nematic state arising during the solvent evaporation process. Moreover, in sufficiently thin films the crystallization seems to be suppressed, extending the uniform order of the liquid crystal phase down to room temperature. This should be compared to the bulk situation, where the same material crystallizes into a polymorphic structure at 68 °C.

Crystal Structure and Transport Properties of Oxygen-Deficient Perovskite Sr 0.9Y 0.1CoO 3-δ

DOE PAGES

Yang, Tianrang; Mattick, Victoria F.; Chen, Yan; ...

2018-01-29

The present work reports a systematic study on temperature-dependent local crystal structure, oxygen stoichiometry, and electrical/electrochemical properties of an oxygen-deficient Sr 0.9Y 0.1CoO 3-δ (SYC10) perovskite using variable-temperature neutron diffraction (VTND), thermal gravimetric analysis, and electrical/electrochemical methods, respectively. The VTND reveals that the crystal symmetry of SYC10 remains P4/mmm tetragonal up to 900 °C. The tetragonal symmetry reflects the net effects of temperature and oxygen stoichiometry on crystal symmetry. The observed p-type electronic conductivity behavior originates from the charge-ordering between the two distinctive Co-sites. The partial oxide-ion conductivity and diffusivity obtained from oxygen permeation measurements are 2.3 × 10 –2more » S cm –1 and 7.98 × 10–8 cm 2/s at 800 °C in air, respectively. The electrochemical oxygen reduction reaction kinetics of the SYC10 cathode is primarily limited by the charge-transfer process at low temperatures (600–650 °C) and oxide-ion migration from the cathode into the electrolyte at high temperatures (700–800 °C).« less

Ba(1-x)Sr(x)Zn2Si2O7--A new family of materials with negative and very high thermal expansion.

PubMed

Thieme, Christian; Görls, Helmar; Rüssel, Christian

2015-12-15

The compound BaZn2Si2O7 shows a high coefficient of thermal expansion up to a temperature of 280 °C, then a transition to a high temperature phase is observed. This high temperature phase exhibits negative thermal expansion. If Ba(2+) is successively replaced by Sr(2+), a new phase with a structure, similar to that of the high temperature phase of BaZn2Si2O7, forms. At the composition Ba0.8Sr0.2Zn2Si2O7, this new phase is completely stabilized. The crystal structure was determined with single crystal X-ray diffraction using the composition Ba0.6Sr0.4Zn2Si2O7, which crystallizes in the orthorhombic space group Cmcm. The negative thermal expansion is a result of motions and distortions inside the crystal lattice, especially inside the chains of ZnO4 tetrahedra. Dilatometry and high temperature X-ray powder diffraction were used to verify the negative thermal expansion. Coefficients of thermal expansion partially smaller than -10·10(-6) K(-1) were measured.

Crystal Structure and Transport Properties of Oxygen-Deficient Perovskite Sr 0.9Y 0.1CoO 3-δ

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

Yang, Tianrang; Mattick, Victoria F.; Chen, Yan

The present work reports a systematic study on temperature-dependent local crystal structure, oxygen stoichiometry, and electrical/electrochemical properties of an oxygen-deficient Sr 0.9Y 0.1CoO 3-δ (SYC10) perovskite using variable-temperature neutron diffraction (VTND), thermal gravimetric analysis, and electrical/electrochemical methods, respectively. The VTND reveals that the crystal symmetry of SYC10 remains P4/mmm tetragonal up to 900 °C. The tetragonal symmetry reflects the net effects of temperature and oxygen stoichiometry on crystal symmetry. The observed p-type electronic conductivity behavior originates from the charge-ordering between the two distinctive Co-sites. The partial oxide-ion conductivity and diffusivity obtained from oxygen permeation measurements are 2.3 × 10 –2more » S cm –1 and 7.98 × 10–8 cm 2/s at 800 °C in air, respectively. The electrochemical oxygen reduction reaction kinetics of the SYC10 cathode is primarily limited by the charge-transfer process at low temperatures (600–650 °C) and oxide-ion migration from the cathode into the electrolyte at high temperatures (700–800 °C).« less

A low-temperature polymorph of m-quinquephenyl.

PubMed

Gomes, Ligia R; Howie, R Alan; Low, John Nicolson; Rodrigues, Ana S M C; Santos, Luís M N B F

2012-12-01

A low-temperature polymorph of 1,1':3',1'':3'',1''':3''',1''''-quinquephenyl (m-quinquephenyl), C(30)H(22), crystallizes in the space group P2(1)/c with two molecules in the asymmetric unit. The crystal is a three-component nonmerohedral twin. A previously reported room-temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993). Chem. Commun. pp. 1795-1797] also crystallizes with two molecules in the asymmetric unit in the space group P-1. The unit-cell volume for the low-temperature polymorph is 4120.5 (4) Å(3), almost twice that of the room-temperature polymorph which is 2102.3 (6) Å(3). The molecules in both structures adopt a U-shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit-cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C-H...π interactions.

The stability of a crystal with diamond structure for patchy particles with tetrahedral symmetry.

PubMed

Noya, Eva G; Vega, Carlos; Doye, Jonathan P K; Louis, Ard A

2010-06-21

The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values of the range of the potential, with the aim of investigating the conditions under which a diamond crystal can be formed. We find that the diamond phase is never stable for our longer-ranged potential. At low temperatures and pressures, the fluid freezes into a body-centered-cubic solid that can be viewed as two interpenetrating diamond lattices with a weak interaction between the two sublattices. Upon compression, an orientationally ordered face-centered-cubic crystal becomes more stable than the body-centered-cubic crystal, and at higher temperatures, a plastic face-centered-cubic phase is stabilized by the increased entropy due to orientational disorder. A similar phase diagram is found for the shorter-ranged potential, but at low temperatures and pressures, we also find a region over which the diamond phase is thermodynamically favored over the body-centered-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centered-cubic solid explains why it is stable even though the enthalpy of the latter phase is lower. Some preliminary studies on the growth of the diamond structure starting from a crystal seed were performed. Even though the diamond phase is never thermodynamically stable for the longer-ranged model, direct coexistence simulations of the interface between the fluid and the body-centered-cubic crystal and between the fluid and the diamond crystal show that at sufficiently low pressures, it is quite probable that in both cases the solid grows into a diamond crystal, albeit involving some defects. These results highlight the importance of kinetic effects in the formation of diamond crystals in systems of patchy particles.

Atomistic insights into the nanosecond long amorphization and crystallization cycle of nanoscale G e2S b2T e5 : An ab initio molecular dynamics study

NASA Astrophysics Data System (ADS)

Branicio, Paulo S.; Bai, Kewu; Ramanarayan, H.; Wu, David T.; Sullivan, Michael B.; Srolovitz, David J.

2018-04-01

The complete process of amorphization and crystallization of the phase-change material G e2S b2T e5 is investigated using nanosecond ab initio molecular dynamics simulations. Varying the quench rate during the amorphization phase of the cycle results in the generation of a variety of structures from entirely crystallized (-0.45 K/ps) to entirely amorphized (-16 K/ps). The 1.5-ns annealing simulations indicate that the crystallization process depends strongly on both the annealing temperature and the initial amorphous structure. The presence of crystal precursors (square rings) in the amorphous matrix enhances nucleation/crystallization kinetics. The simulation data are used to construct a combined continuous-cooling-transformation (CCT) and temperature-time-transformation (TTT) diagram. The nose of the CCT-TTT diagram corresponds to the minimum time for the onset of homogenous crystallization and is located at 600 K and 70 ps. That corresponds to a critical cooling rate for amorphization of -4.5 K/ps. The results, in excellent agreement with experimental observations, suggest that a strategy that utilizes multiple quench rates and annealing temperatures may be used to effectively optimize the reversible switching speed and enable fast and energy-efficient phase-change memories.

In-Situ Crystallization of a Lithium Disilicate Glass--Effect of Pressure on Crystal Growth Rate

NASA Technical Reports Server (NTRS)

Fuss, T.; Ray, C. S.; Lesher, C. E.; Day, D. E.

2006-01-01

Crystallization of a Li2O.2SiO2 (LS2) glass subjected to a uniform hydrostatic pressure of 4.5 GPa and 6 GPa was investigated up to a temperature of 750 C. The density of the compressed glass is about 2% greater at 4.5 GPa than at 1 atm and, depending upon the processing temperature, up to 10% greater at 6 GPa. Crystal growth rates investigated as a function of temperature and pressure show that lithium disilicate crystal growth is an order of magnitude slower at 4.5 GPa than 1 atm resulting in a shift of +45 C (plus or minus 10 C) in the growth rate curve at high pressure compared to 1 atm condition. At 6 GPa lithium disilicate crystallization is suppressed entirely, while a new high pressure lithium metasilicate crystallizes at temperatures 95 C (plus or minus 10 C) higher than those reported for lithium disilicate crystallization at 1 atm. The decrease in crystal growth rate with increasing pressure for lithium disilicate glass up to 750 C is related to an increase in viscosity with pressure associated with fundamental changes in glass structure accommodating densification.

Biomimetic and Aggregation-Driven Crystallization Route for Room-Temperature Material Synthesis: Growth of β-Ga2O3 Nanoparticles Using Peptide Assemblies as Nanoreactors

PubMed Central

Lee, Sang-Yup; Gao, Xueyun; Matsui, Hiroshi

2008-01-01

The room temperature synthesis of β-Ga2O3 nanocrystal was examined by coupling two biomimetic crystallization techniques, the enzymatic peptide nano-assembly templating and the aggregation-driven crystallization. The catalytic template of peptide assembly nucleated and mineralized primary β-Ga2O3 crystals, and then fused them to grow single-crystalline and monodisperse nanoparticles in the cavity of the peptide assembly at room temperature. In this work, the peptide assembly was exploited as a nano-reactor with an enzymatic functionality catalyzing the hydrolysis of gallium precursors. In addition, the characteristic ring-structure of peptide assembly is expected to provide an efficient dehydration pathway and the crystallization control over the surface tension, which are advantageous for the β-Ga2O3 crystal growth. This multifunctional peptide assembly could be applied for syntheses of a variety of nanomaterials that are kinetically difficult to grow at room temperature. PMID:17302413

Friction and wear of tin and tin alloys from minus 100 C to 150 C

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1975-01-01

Sliding friction experiments were conducted with an iron (110) single-crystal pin sliding on single and polycrystalline tin and tin alloys. Specimens were examined at various ambient temperatures from -100 to 150 C. Applied loads varied from 1 to 50 grams, and sliding velocity was constant at 0.7 mm/min. Results indicate that the crystal transformation of tin influences the friction coefficient. Friction was higher for the diamond structure (gray tin) than it was for the body-centered tetragonal structure (white tin). Bismuth arrested the crystal transformation, which resulted in constant friction over the temperature range -100 to 150 C. Both copper and aluminum enhanced the kinetics of transformation, with aluminum producing a nearly twofold change in friction with the crystal transformation.

Lead(ii) soaps: crystal structures, polymorphism, and solid and liquid mesophases.

PubMed

Martínez-Casado, F J; Ramos-Riesco, M; Rodríguez-Cheda, J A; Redondo-Yélamos, M I; Garrido, L; Fernández-Martínez, A; García-Barriocanal, J; da Silva, I; Durán-Olivencia, M; Poulain, A

2017-07-05

The long-chain members of the lead(ii) alkanoate series or soaps, from octanoate to octadecanoate, have been thoroughly characterized by means of XRD, PDF analysis, DSC, FTIR, ssNMR and other techniques, in all their phases and mesophases. The crystal structures at room temperature of all of the members of the series are now solved, showing the existence of two polymorphic forms in the room temperature crystal phase, different to short and long-chain members. Only nonanoate and decanoate present both forms, and this polymorphism is proven to be monotropic. At higher temperature, these compounds present a solid mesophase, defined as rotator, a liquid crystal phase and a liquid phase, all of which have a similar local arrangement. Since some lead(ii) soaps appear as degradation compounds in oil paintings, the solved crystal structures of lead(ii) soaps can now be used as fingerprints for their detection using X-ray diffraction. Pair distribution function analysis on these compounds is very similar in the same phases and mesophases for the different members, showing the same short range order. This observation suggests that this technique could also be used in the detection of these compounds in disordered phases or in the initial stages of formation in paintings.

Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts

NASA Technical Reports Server (NTRS)

Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK

1987-01-01

The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.

Temperature and saturation dependence in the vapor sensing of butterfly wing scales.

PubMed

Kertész, K; Piszter, G; Jakab, E; Bálint, Zs; Vértesy, Z; Biró, L P

2014-06-01

The sensing of gasses/vapors in the ambient air is the focus of attention due to the need to monitor our everyday environment. Photonic crystals are sensing materials of the future because of their strong light-manipulating properties. Natural photonic structures are well-suited materials for testing detection principles because they are significantly cheaper than artificial photonic structures and are available in larger sizes. Additionally, natural photonic structures may provide new ideas for developing novel artificial photonic nanoarchitectures with improved properties. In the present paper, we discuss the effects arising from the sensor temperature and the vapor concentration in air during measurements with a photonic crystal-type optical gas sensor. Our results shed light on the sources of discrepancy between simulated and experimental sensing behaviors of photonic crystal-type structures. Through capillary condensation, the vapors will condensate to a liquid state inside the nanocavities. Due to the temperature and radius of curvature dependence of capillary condensation, the measured signals are affected by the sensor temperature as well as by the presence of a nanocavity size distribution. The sensing materials used are natural photonic nanoarchitectures present in the wing scales of blue butterflies. Copyright © 2014 Elsevier B.V. All rights reserved.

[Effect of crystallization temperature of palm oil on its crystallization. IV. The influence of tripalmitoylglycerol (PPP) on the crystallization of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-glycerol (POO)].

PubMed

Mihara, Hiroaki; Ishiguro, Takashi; Fukano, Hidenori; Taniuchi, Shigeyuki; Ogino, Keizo

2007-01-01

Triacylglycerin in Palm Oil contains POP (1,3-dipalmitoyl-2-oleoyl-glycerol) at 30%, POO (1,2-dioleoyl-3-palmitoyl-glycerol) at 20% and PPP (tripalmitoylglycerol) at 5%. The crystallization temperature of PPP is high and the rates of crystal nuclear formation and growth are fast. It is thus considered that PPP may have some effect on the manner or mode of Palm Oil. Examination was thus made to clarify how PPP may affect the crystallization of POP and POO by differential scanning calorimetry (DSC) and X ray diffractometry (XRD) conducted on PPP/POP and PPP/POO mixtures. High and low temperature peaks were noted to appear on the DSC crystallization curve for either of these mixtures. The high temperature peak was considered possibly due to PPP, and the low temperature peak, to POP or POO. DSC isothermal analysis indicated the rate of crystal growth of either mixture to exceed that of pure of POP or POO. Crystal mixture structure was also seen to be complicated than either compound in pure form. The present findings thus clearly indicate that clarification should be made of the effects of high melting point triacylglycerin, such as PPP, on the crystallization of Palm Oil.

Growth of InAs/InP core-shell nanowires with various pure crystal structures.

PubMed

Gorji Ghalamestani, Sepideh; Heurlin, Magnus; Wernersson, Lars-Erik; Lehmann, Sebastian; Dick, Kimberly A

2012-07-20

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (∼500 °C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460 °C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.

Temperature Dependence of the Luminescence Decay Time of a PbWO4 Scintillator

NASA Astrophysics Data System (ADS)

Shi, Chao-shu; Deng, Jie; Han, Zheng-fu; Xie, Zhi-jian; Liao, Jing-ying; G, Zimmerer; J, Beker; M, Kamada; M, Runne; A, Schröder

1998-06-01

Experimental results are given for the temperature dependence of the decay time of the emission at 430 nm from PbWO4 crystal under vacuum-ultraviolet (82 nm) photon excitation in the temperature range of 80-300 K. The structures in the curve are interpreted for the first time by studying the thermoluminescence of PbWO4, which originates from the traps in the crystal.

Superconductivity at 5 K in quasi-one-dimensional Cr-based KCr3As3 single crystals

NASA Astrophysics Data System (ADS)

Mu, Qing-Ge; Ruan, Bin-Bin; Pan, Bo-Jin; Liu, Tong; Yu, Jia; Zhao, Kang; Chen, Gen-Fu; Ren, Zhi-An

2017-10-01

Recently a new family of Cr-based A2Cr3As3 (A =K , Rb, Cs) superconductors was reported, which own a rare quasi-one-dimensional (Q1D) crystal structure with infinite (Cr3As3) 2 - chains and exhibit intriguing superconducting characteristics possibly derived from spin-triplet electron pairing. The crystal structure of A2Cr3As3 is actually a slight variation of the hexagonal TlFe3Te3 prototype, although they have different lattice symmetry. Here we report superconductivity in a 133-type KCr3As3 compound that belongs to the latter structure. The single crystals of KCr3As3 were prepared by the deintercalation of K ions from K2Cr3As3 crystals which were grown from a high-temperature solution growth method, and it owns a centrosymmetric lattice in contrast to the noncentrosymmetric K2Cr3As3 . After annealing at a moderate temperature, the KCr3As3 crystals show superconductivity at 5 K revealed by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The discovery of this KCr3As3 superconductor provides a different structural instance to study the exotic superconductivity in these Q1D Cr-based superconductors.

Bridgman growth of lead potassium niobate crystals

NASA Astrophysics Data System (ADS)

Fan, Shiji; Sun, Renying; Lin, Yafang; Wu, Jindi

1999-03-01

Lead potassium niobate Pb 2KNb 5O 15 (PKN) crystals with tetragonal tungsten bronze (TTB) structure have been grown by the modified Bridgman (BR) method. Nearly sealed Pt crucibles and small temperature gradients in the Bridgman furnace can limit volatilization of PbO and cracking of as-grown PKN crystals. Transparent PKN crystals of 1 inch diameter by ˜2 inch length with brownish color have been grown successfully at a crucible lowering rate <0.5 mm/h and a temperature gradient of 10-15°C/cm across the solid-liquid interface. Coupling between twins and growth directions of the crystal is also discussed.

Glass formation and crystallization in the alumina-silica-lanthanum phosphate system for ceramics composites

NASA Astrophysics Data System (ADS)

Guo, Shuling

The formation, structure, and dynamics of glasses in the alumina-silica-lanthanum phosphate system and their crystallization were investigated as a function of composition. These are of interest because of their potential as precursors for synthesizing ceramic-matrix-composites via co-crystallization of lanthanum monazite and either mullite or alumina into finely mixed microstructures. The glasses were characterized by X-Ray Diffraction (XRD), Raman spectroscopy, Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electron Energy Loss Spectrometry (EELS). Glass formation from rapidly quenched liquids was easiest and most consistent for compositions containing silica, such as for mullitemonazite compositions, and more difficult for alumina-monazite compositions. For mullite-monazite glasses, the glass transition temperatures increased linearly from 845°C to 906°C with increasing mullite content. An analysis of the glass structure indicated a network consisting of corner-linked aluminate, silicate and phosphate tetrahedra where aluminum played a central role of separating silicon and phosphorous. It was hypothesized that the glass network consisted of domains of aluminum silicate network edged by phosphate tetrahedra. A maximum in the crystallization temperature was attributed to the complexity of the glass network. At relatively mullite-rich compositions, simultaneous and cooperative crystallization of lanthanum phosphate and mullite correlated with the highest crystallization temperatures, and the lowest activation energies of crystallization. This was preceded by amorphous phase segregation in the glass at lower temperatures. An intermediate phase of lanthanum phosphate was discovered with an orthorhombic unit cell. For compositions of high phosphate contents, lanthanum phosphate precipitated first at about 900°C leaving an essentially pure mullite glass. Mullite crystallized at about 1000°C, matching the conditions for crystallizing pure mullite glass. The phosphate phase transformed to monazite at even higher temperatures. No amorphous phase segregation was observed in these cases. Microstructures were correlated with nucleation and growth conditions such that the continuous and isolated phases could be manipulated. Optimum nucleation temperatures were close to the glass transition temperature. Conditions were identified for forming a continuous boundary phase of monazite that isolated mullite grains, which is desired for fabricating ceramic-matrix-composites.

Crystal structure determination of new antimitotic agent bis(p-fluorobenzyl)trisulfide.

PubMed

An, Haoyun; Hu, Xiurong; Gu, Jianming; Chen, Linshen; Xu, Weiming; Mo, Xiaopeng; Xu, Wanhong; Wang, Xiaobo; Xu, Xiao

2008-01-01

The purpose of this research was to investigate the physical characteristics and crystalline structure of bis(p-fluorobenzyl)trisulfide, a new anti-tumor agent. Methods used included X-ray single crystal diffraction, X-ray powder diffraction (XRPD), Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetric (DSC) and thermogravimetric (TG) analyses. The findings obtained with X-ray single crystal diffraction showed that a monoclinic unit cell was a = 12.266(1) A, b = 4.7757(4) A, c = 25.510(1) A, beta = 104.25(1) degrees ; cell volume = 1,448.4(2) A(3), Z = 4, and space group C2/c. The XRPD studies of the four crystalline samples, obtained by recrystallization from four different solvents, indicated that they had the same diffraction patterns. The diffraction pattern stimulated from the crystal structure data is in excellent agreement with the experimental results. In addition, the identical FT-IR spectra of the four crystalline samples revealed absorption bands corresponding to S-S and C-S stretching as well as the characteristic aromatic substitution. Five percent weight loss at 163.3 degrees C was observed when TG was used to study the decomposition process in the temperature range of 20-200 degrees C. DSC also allowed for the determination of onset temperatures at 60.4(1)-60.7(3) degrees C and peak temperatures at 62.1(3)-62.4(3) degrees C for the four crystalline samples studied. The results verified that the single crystal structure shared the same crystal form with the four crystalline samples investigated.

High-temperature solution growth and characterization of (1-x)PbTiO3-xBi(Zn2/3Nb1/3)O3 piezo-/ferroelectric single crystals

NASA Astrophysics Data System (ADS)

Paterson, Alisa R.; Zhao, Jinyan; Liu, Zenghui; Wu, Xiaoqing; Ren, Wei; Ye, Zuo-Guang

2018-03-01

Complex perovskite PbTiO3-Bi(Me‧Me″)O3 solid solutions represent new materials systems that possess a higher Curie temperature (TC) than the relaxor-PbTiO3 solid solutions, and are useful for potential applications. To this end, novel ferroelectric single crystals of the (1-x)PbTiO3-xBi(Zn2/3Nb1/3)O3 (PT-BZN) solid solution were successfully grown by the high-temperature solution growth (HTSG) method. Powder X-ray diffraction shows that the symmetry of the grown crystals is tetragonal. The dielectric permittivity and optical domain structures were characterized by dielectric measurements and polarized light microscopy, respectively, as a function of temperature, revealing a first-order ferroelectric-paraelectric phase transition at a TC of 436 ± 2 °C. Based on the TC, the average composition of the crystal platelet was estimated to be 0.58PT-0.42BZN. Piezoresponse force microscopy measurements of the phase and amplitude as a function of voltage reveal the complex polar domain structure and demonstrate the ferroelectric switching behaviour of these materials. These results suggest that the PT-BZN single crystals indeed form a new family of high TC piezo-/ferroelectric materials which are potentially useful for the fabrication of electromechanical transducers for high-temperature applications.

Structure of Ce2RhIn8: an example of complementary use of high-resolution neutron powder diffraction and reciprocal-space mapping to study complex materials.

PubMed

Moshopoulou, E G; Ibberson, R M; Sarrao, J L; Thompson, J D; Fisk, Z

2006-04-01

The room-temperature crystal structure of the heavy fermion antiferromagnet Ce2RhIn8, dicerium rhodium octaindide, has been studied by a combination of high-resolution synchrotron X-ray reciprocal-space mapping of single crystals and high-resolution time-of-flight neutron powder diffraction. The structure is disordered, exhibiting a complex interplay of non-periodic, partially correlated planar defects, coexistence and segregation of polytypic phases (induced by periodic planar ;defects'), mosaicity (i.e. domain misalignment) and non-uniform strain. These effects evolve as a function of temperature in a complicated way, but they remain down to low temperatures. The room-temperature diffraction data are best represented by a complex mixture of two polytypic phases, which are affected by non-periodic, partially correlated planar defects, differ slightly in their tetragonal structures, and exhibit different mosaicities and strain values. Therefore, Ce2RhIn8 approaches the paracrystalline state, rather than the classic crystalline state and thus several of the concepts of conventional single-crystal crystallography are inapplicable. The structural results are discussed in the context of the role of disorder in the heavy-fermion state and in the interplay between superconductivity and magnetism.

Control of Partial Coalescence of Self-Assembled Metal Nano-Particles across Lyotropic Liquid Crystals Templates towards Long Range Meso-Porous Metal Frameworks Design

PubMed Central

Dumée, Ludovic F.; Lemoine, Jean-Baptiste; Ancel, Alice; Hameed, Nishar; He, Li; Kong, Lingxue

2015-01-01

The formation of purely metallic meso-porous metal thin films by partial interface coalescence of self-assembled metal nano-particles across aqueous solutions of Pluronics triblock lyotropic liquid crystals is demonstrated for the first time. Small angle X-ray scattering was used to study the influence of the thin film composition and processing conditions on the ordered structures. The structural characteristics of the meso-structures formed demonstrated to primarily rely on the lyotropic liquid crystal properties while the nature of the metal nano-particles used as well as the their diameters were found to affect the ordered structure formation. The impact of the annealing temperature on the nano-particle coalescence and efficiency at removing the templating lyotropic liquid crystals was also analysed. It is demonstrated that the lyotropic liquid crystal is rendered slightly less thermally stable, upon mixing with metal nano-particles and that low annealing temperatures are sufficient to form purely metallic frameworks with average pore size distributions smaller than 500 nm and porosity around 45% with potential application in sensing, catalysis, nanoscale heat exchange, and molecular separation. PMID:28347094

Synthesis, crystal structure, vibrational spectroscopy and photoluminescence of new hybrid compound containing chlorate anions of stanate (II)

NASA Astrophysics Data System (ADS)

Lassoued, Mohamed Saber; Abdelbaky, Mohammed S. M.; Lassoued, Abdelmajid; Meroño, Rafael Mendoza; Gadri, Abdellatif; Ammar, Salah; Ben Salah, Abdelhamid; García-Granda, Santiago

2017-08-01

The present work aimed at studying a new organic-inorganic bis (4-amino quinolinium) hexachloro stanate (II) dihydrate compound. It was prepared and characterized by single crystal X-ray diffraction, X-ray powder, Hirshfeld surface, Spectroscopy measurement, thermal study and photoluminescence properties. It was found to crystallize in the monoclinic system (P21/c space group) with the following lattice parameters: a = 7.2558(6) Å, b = 13.4876(5) Å, c = 17.2107(13) Å, β = 102.028 (12)°. Its crystal structure was determined and refined down to an R value of 0.06 and a wR value of 0.087. The structure consisted of two different alternating organic-inorganic layers. The crystal packing was stabilized by Nsbnd H⋯Cl and Osbnd H⋯Cl hydrogen bonds and π-π interactions. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D finger plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. The X-ray powder is in agreement with the X-ray structure. Scanning electronic microscopy (SEM) was carried out. Furthermore, the room temperature Infra Red (IR) spectrum of the title compound was analyzed on the basis of data found in the literature. Solid state 13C NMR spectrum shows ten signals, confirming the solid state structure determined by X-ray diffraction. Thermal analysis shows two anomalies at 380 and 610 °C. The optical properties of the crystal were studied using optical absorption UV-visible and photoluminescence (PL) spectroscopy, which were investigated at room temperature.

Temperature-resolved study of three [M(M'O4)4(TBPO)4] complexes (MM' = URe, ThRe, ThTc).

PubMed

Helliwell, Madeleine; Collison, David; John, Gordon H; May, Iain; Sarsfield, Mark J; Sharrad, Clint A; Sutton, Andrew D

2006-02-01

The crystal structures of the title complexes were measured at several temperatures between room temperature and 100 K. Each sample shows reversible crystal-to-crystal phase transitions as the temperature is varied. The behaviour of [U(ReO4)4(TBPO)4] (I) and [Th(ReO4)4(TBPO)4] (II) (TBPO = tri-n-butylphosphine oxide) is very similar; at room temperature, crystals of (I) and (II) are isostructural, with space group I42m, and reducing the temperature to 100 K causes a lowering of the space-group symmetry to C-centred cells, space groups Cc for (I) and Cmc2(1) for (II). The variation of lattice symmetry of [Th(TcO4)4(TBPO)4] (III) was found to be somewhat different, with the body-centred cubic space group, I43m, occurring at 293 K, a reduction of symmetry at 230 K to the C-centred orthorhombic space group, Cmc2(1), and a further transition to the primitive orthorhombic space group, Pbc2(1), below 215 K. Elucidation of the correct space-group symmetry and the subsequent refinement was complicated in some cases by the twinning by pseudo-merohedry that arises from the lowering of the space-group symmetry, occurring as the temperature is reduced. All three of the crystal structures determined at room temperature have high atomic displacement parameters, particularly of the (n)Bu groups, and (III) shows disorder of some of the O atoms. The structures in the space group Cmc2(1), show some disorder of nBu groups, but are otherwise reasonably well ordered; the structures of (I) in Cc and (III) in Pbc2(1) are ordered, even to the ends of the alkyl chains. Inter-comparison of the structures measured below 293 K, using the program OFIT from the SHELXTL package, showed that generally, they are remarkably alike, with weighted r.m.s. deviations of the M, M' and P atoms of less than 0.1 A, as are the 293 K structures of (I) and (II) with their low-temperature counterparts. However, the structure of (III) measured in the space group Cmc2(1) is significantly different from both the structure of (III) at 293 K and that found below 215 K, with weighted r.m.s. deviations of the Th, Tc and P atoms of 0.40 and 0.37 A, respectively. An extensive network of weak intra- and intermolecular C-H...O hydrogen bonds found between the atoms of the nBu and [M'O4] groups probably influences the packing and the overall geometry of the molecules.

Effect of the temperature-rate parameters of directional solidification on the structure formation in high-temperature materials

NASA Astrophysics Data System (ADS)

Svetlov, I. L.; Neiman, A. V.

2017-03-01

The effect of the temperature gradient and the crystal growth rate on the structure formation in nickel and niobium superalloys is studied under the conditions of the flat, cellular, dendritic, or dendritic-cellular configuration of a solidification front during directional solidification.

Magnetic and Crystal Structure of α-RuCl3

NASA Astrophysics Data System (ADS)

Sears, Jennifer

The layered honeycomb material α-RuCl3 has been proposed as a candidate material to show significant bond-dependent Kitaev type interactions. This has prompted several recent studies of magnetism in this material that have found evidence for multiple magnetic transitions in the temperature range of 8-14 K. We will present elastic neutron scattering measurements collected using a co-aligned array of α-RuCl3 crystals, identifying zigzag magnetic order within the honeycomb planes with an ordering temperature of ~8 K. It has been reported that the ordering temperature depends on the c axis periodicity of the layered structure, with ordering temperatures of 8 and 14 K for three and two-layer periodicity respectively. While the in-plane magnetic order has been identified, it is clear that a complete understanding of magnetic ordering and interactions will depend on the three dimensional structure of the crystal. Evidence of a structural transition at ~150 K has been reported and questions remain about the structural details, in particular the stacking of the honeycomb layers. We will present x-ray diffraction measurements investigating the low and high temperature structures and stacking disorder in α-RuCl3. Finally, we will present inelastic neutron scattering measurements of magnetic excitations in this material. Work done in collaboration with K. W. Plumb (Johns Hopkins University), J. P. Clancy, Young-June Kim (University of Toronto), J. Britten (McMaster University), Yu-Sheng Chen (Argonne National Laboratory), Y. Qiu, Y. Zhao, D. Parshall, and J. W. Lynn (NCNR).

Tunable alumina 2D photonic-crystal structures via biomineralization of peacock tail feathers

NASA Astrophysics Data System (ADS)

Jiang, Yonggang; Wang, Rui; Feng, Lin; Li, Jian; An, Zhonglie; Zhang, Deyuan

2018-04-01

Peacock tail feathers with subtle periodic nanostructures exhibit diverse striking brilliancy, which can be applied as natural templates to fabricate artificial photonic crystals (PhCs) via a biomineralization method. Alumina photonic-crystal structures are successfully synthesized via an immersion and two-step calcination process. The lattice constants of the artificial PhCs are greatly reduced compared to their natural matrices. The lattice constants are tunable by modifying the final annealing conditions in the biomineralization process. The reflection spectra of the alumina photonic-crystal structures are measured, which is related to their material and structural parameters. This work suggests a facile fabrication process to construct alumina PhCs with a high-temperature resistance.

Thermo-Physical Properties of B2O3-Containing Mold Flux for High Carbon Steels in Thin Slab Continuous Casters: Structure, Viscosity, Crystallization, and Wettability

NASA Astrophysics Data System (ADS)

Park, Jun-Yong; Kim, Gi Hyun; Kim, Jong Bae; Park, Sewoong; Sohn, Il

2016-08-01

The effect of B2O3 on the thermo-physical properties of commercial mold fluxes, including the viscosity, crystallization behavior, and wettability, was investigated. Viscosity was measured using the rotating spindle method, and CCT (continuous cooling transformation) diagrams were obtained to investigate the crystallization behavior at various cooling rates using CLSM (confocal laser scanning microscope). The wettability of the fluxes was determined by measuring the contact angles at 1573 K (1300 °C) using the digital images generated by the sessile drop method and were used to calculate the surface tension, interfacial tension, and work of adhesion for Flux A (existing flux) and B (modified flux). These thermo-physical properties were correlated with the structural analysis obtained using FT-IR (Fourier transform-infrared), Raman and MAS-NMR (magic angle spin-nuclear magnetic resonance) spectroscopy. In addition, DTA (differential thermal analysis) was performed on the samples to measure the liquidus temperatures. Higher B2O3 concentrations resulted in lower liquidus temperatures, consequently decreasing the viscosity, the break temperature, and the crystallization temperature. However, B2O3 addition accelerated crystal growth owing to the higher diffusion kinetics of the cations, which also reduced the size of the liquid/solid co-existing region.

Self-assembled novel multi-porphyrin micro-crystals as a photocatalyst for 2,4,6-trinitrotoluene degradation

NASA Astrophysics Data System (ADS)

Hikal, Walid M.

In this thesis I have presented the findings of my research pursued during my Ph.D. study. Following the findings that 2,4,6-trinitrotoluene binds to porphyrins at room temperature and could be photoctalytically degraded using porphyrin solutions and visible light, the purpose of this work was to determine the nature of the binding between the two species and develop a solid porphyrin-based photocatalyst for TNT degradation. C1TPP porphyrin is found to be able to bind to TNT via 1.94 kcal/mole hydrogen bonds at room temperature and hydrophobic bonds at higher temperatures. Photocatalytic solid porphyrin crystalline structures have been developed using two oppositely charged, commercially available, and low cost porphyrins in presence and absence of PAMAM generation 4 (G4) dendrimer, by self-assembly at room temperature without acidification. Solid porphyrin crystals were characterized by means of optical microscopy, UV-visible spectroscopy, fluorescence spectroscopy, and powder X-ray diffraction. A hypothetical model for the structure of the crystals is proposed. The porphyrin crystals show photocatalytic capabilities; illumination of the crystals in a 2,4,6-trinitrotoluene solution by visible light results in degradation of TNT and the intermediates have been determined using high pressure liquid chromatography (HPLC) and gas chromatography (GC).

Investigation of phase transitions in LiK 1- x(NH 4) xSO 4 mixed crystal

NASA Astrophysics Data System (ADS)

Freire, P. T. C.; Paraguassu, W.; Silva, A. P.; Pilla, O.; Teixeira, A. M. R.; Sasaki, J. M.; Mendes Filho, J.; Guedes, I.; Melo, F. E. A.

1999-02-01

We present Raman scattering results on LiK 1- x(NH 4) xSO 4 mixed crystal for temperatures between 100 and 300 K. We observed that in this temperature range the crystal undergoes two different phase transitions, which we call Bansal and Tomaszewski phase transitions. The introduction of ammonium ions in the potassium sites increases the C 66→C 3v4 (Bansal) phase transition temperature and decreases the Tomaszewski phase transition temperature. Finally, the most impressive effect of the presence of ammonium impurity in the LiKSO 4 structure is the decrease in the temperature hysteresis of Bansal phase transition and the almost complete destruction of hysteresis in the Tomaszewski phase transition, leading to a high temperature range of stability of the trigonal phase.

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

Ozkendir, Osman Murat, E-mail: ozkendir@gmail.com

Highlights: • Crystal and electronic structure properties of Nd{sub x}Ti{sub 1−x}BO{sub 2+d} structure were investigated. • New crystal structures for Nd–Ti complexes are determined. • Distortions in the crystal structure were observed as a result of Boron shortage. • Prominent change in electronic properties of the samples with the increasing Nd amount. - Abstract: Neodymium substituted TiBO{sub 3} samples were investigated according to their crystal, electric and electronic properties. Studies were conducted by X-ray absorption fine structure spectroscopy (XAFS) technique for the samples with different substitutions in the preparation processes. To achieve better crystal structure results during the study, XRDmore » pattern results were supported by extended-XAFS (EXAFS) analysis. The electronic structure analysis were studied by X-ray absorption near-edge structure spectroscopy (XANES) measurements at the room temperatures. Due to the substituted Nd atoms, prominent changes in crystal structure, new crystal geometries for Nd-Ti complexes, phase transitions in the crystals structure were detected according to the increasing Nd substitutions in the samples. In the entire stages of the substitutions, Nd atoms were observed as governing the whole phenomena due to their dominant characteristics in Ti geometries. Besides, electrical resistivity decay was determined in the materials with the increasing amount of Nd substitution.« less

Low-temperature x-ray crystal structure analysis of the cage-structured compounds M Be13 (M =La,Sm, and U)

NASA Astrophysics Data System (ADS)

Hidaka, Hiroyuki; Nagata, Ryoma; Tabata, Chihiro; Shimizu, Yusei; Miura, Naoyuki; Yanagisawa, Tatsuya; Amitsuka, Hiroshi

2018-05-01

The beryllides M Be13 (M = rare earths and actinides) crystallize in a NaZn13-type cubic structure, which can be categorized as a cage-structured compound. In this study, powder x-ray diffraction measurements have been performed on LaBe13,SmBe13, and UBe13 in the temperature range between 7 and 300 K in order to investigate their crystallographic characteristics systematically. They keep the NaZn13-type cubic structure down to the lowest temperature. We estimated their Debye temperature to be 600-750 K from analyses of the temperature dependence of a lattice parameter, being in good agreement with the values reported previously. Rietveld refinements on the obtained powder patterns revealed that the M atom in the 8 a site is located in an almost ideal snub cube formed by 24 BeII atoms in the 96 i site, whose caged structure is unchanged even at the low temperatures. In addition, it is argued from the temperature variation of an isotropic mean-square displacement parameter that the M Be13 compounds commonly have a low-energy phonon mode, which can be described by a model assuming an Einstein oscillation of the M atom with a characteristic temperature of ˜160 K.

Fabrication and characterization of poly(L-lactic acid) gels induced by fibrous complex crystallization with solvents

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

Matsuda, Yasuhiro; Fukatsu, Akinobu; Wang, Yangyang

2014-01-01

Complex crystal induced gelation of poly(L-lactic acid) (PLLA) solutions was studied for a series of solvents, including N,N-dimethylformamide (DMF). By cooling the solutions prepared at elevated temperatures, PLLA gels were produced in solvents that induced complex crystals ( -crystals) with PLLA. Fibrous structure of PLLA in the gel with DMF was observed by polarizing optical microscopy, field emission electron microscopy, and atomic force microscopy. Upon heating, the crystal form of PLLA in the DMF gel changed from -crystal to a-crystal, the major crystal form in common untreated PLLA films, but the morphology and high elastic modulus of the gel remainedmore » until the a-crystal dissolved at higher temperature. In addition, a solvent exchanging method was developed, which allowed PLLA gels to be prepared in other useful solvents that do not induce -crystals without losing the morphology and mechanical properties.« less

Structural analysis of as-deposited and annealed low-temperature gallium arsenide

NASA Astrophysics Data System (ADS)

Matyi, R. J.; Melloch, M. R.; Woodall, J. M.

1993-04-01

The structure of GaAs grown at low substrate temperatures (LT-GaAs) by molecular beam epitaxy has been studied using high resolution X-ray diffraction methods. Double crystal rocking curves from the as-deposited LT-GaAs show well defined interference fringes, indicating a high level of structural perfection. Triple crystal diffraction analysis of the as-deposited sample showed significantly less diffuse scattering near the LT-GaAs 004 reciprocal lattice point compared with the substrate 004 reciprocal lattice point, suggesting that despite the incorporation of approximately 1% excess arsenic, the epitaxial layer had superior crystalline perfection than did the GaAs substrate. Triple crystal scans of annealed LT-GaAs showed an increase in the integrated diffuse intensity by approximately a factor of three as the anneal temperature was increased from 700 to 900°C. Analogous to the effects of SiO2 precipitates in annealed Czochralski silicon, the diffuse intensity is attributed to distortions in the epitaxial LT-GaAs lattice by arsenic precipitates.

Analyzing multistep homogeneous nucleation in vapor-to-solid transitions using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Tanaka, Kyoko K.; Diemand, Jürg; Tanaka, Hidekazu; Angélil, Raymond

2017-08-01

In this paper, we present multistep homogeneous nucleations in vapor-to-solid transitions as revealed by molecular dynamics simulations on Lennard-Jones molecules, where liquidlike clusters are created and crystallized. During a long, direct N V E (constant volume, energy, and number of molecules) involving the integration of (1.9 -15 )× 106 molecules in up to 200 million steps (=4.3 μ s ), crystallization in many large, supercooled nanoclusters is observed once the liquid clusters grow to a certain size (˜800 molecules for the case of T ≃0.5 ɛ /k ). In the simulations, we discovered an interesting process associated with crystallization: the solid clusters lost 2-5 % of their mass during crystallization at low temperatures below their melting temperatures. Although the crystallized clusters were heated by latent heat, they were stabilized by cooling due to evaporation. The clusters crystallized quickly and completely except at surface layers. However, they did not have stable crystal structures, rather they had metastable structures such as icosahedral, decahedral, face-centered-cubic-rich (fcc-rich), and hexagonal-close-packed-rich (hcp-rich). Several kinds of cluster structures coexisted in the same size range of ˜1000 -5000 molecules. Our results imply that multistep nucleation is a common first stage of condensation from vapor to solid.

Transfiguring structural, optical and dielectric properties of cadmium thiourea acetate crystal by the addition of L-threonine for laser assisted device applications

NASA Astrophysics Data System (ADS)

Kulkarni, Rupali B.; Anis, Mohd; Hussaini, S. S.; Shirsat, Mahendra D.

2018-03-01

Present investigation reports the growth of pure and L-threonine (LT) doped cadmium thiourea acetate (CTA) crystals by slow solution evaporation technique followed by structural, optical and dielectric characterization studies. A bulk single crystal of LT-CTA has been grown at temperature 38 °C. The single crystal x-ray diffraction technique has been employed to confirm the structural parameters of pure and LT doped CTA crystals. The increase in optical transparency of LT-CTA crystal was ascertained in the range of 200 to 900 nm using UV-visible spectral analysis. The widened optical band gap of the LT-CTA crystal is found to be 4.7 eV. Pure and doped crystals are subjected to FT-IR analysis to indicate the presence of functional groups quantitatively. Appreciable enhancement in second harmonic generation (SHG) efficiency of LT-CTA crystal with reference to parent CTA was confirmed from Kurtz-Perry SHG test (1.31 times of CTA crystal). The assertive influence of LT on electrical properties of grown crystals has been investigated in the temperature range 35 °C-120 °C. Electronic purity and the color centered photoluminescence emission nature of pure and IA-CTA crystals were justified by luminescence analysis. With the aid of single beam Z-scan analysis, the Kerr lensing nonlinearity was identified and the magnitude of TONLO parameters has been determined. The cubic susceptibility (χ3) and figure of merit (FOM) was found to be 4.81 × 10-4esu and 978.35. Results vitalize LT-CTA for laser stabilization systems.

Solubility- and temperature-driven thin film structures of polymeric thiophene derivatives for high performance OFET applications

NASA Astrophysics Data System (ADS)

LeFevre, Scott W.; Bao, Zhenan; Ryu, Chang Y.; Siegel, Richard W.; Yang, Hoichang

2007-09-01

It has been shown that high charge mobility in solution-processible organic semiconductor-based field effect transistors is due in part to a highly parallel π-π stacking plane orientation of the semiconductors with respect to gate-dielectric. Fast solvent evaporation methods, generally, exacerbate kinetically random crystal orientations in the films deposited, specifically, from good solvents. We have investigated solubility-driven thin film structures of thiophene derivative polymers via spin- and drop-casting with volatile solvents of a low boiling point. Among volatile solvents examined, marginal solvents, which have temperature-dependent solubility for the semiconductors (e.g. methylene chloride for regioregular poly(3-alkylthiophene)s), can be used to direct the favorable crystal orientation regardless of solvent drying time, when the temperature of gate-dielectrics is held to relatively cooler than the warm solution. Grazing-incidence X-ray diffraction and atomic force microscopy strongly support that significant control of crystal orientation and mesoscale morphology using a "cold" substrate holds true for both drop and spin casting. The effects of physiochemical post-modificaiton on film crystal structures and morphologies of poly(9,9-dioctylfluorene-co-bithiophene) have also been investigated.

Chiral discrimination in cyclodextrin complexes of amino acid derivatives: beta-cyclodextrin/N-acetyl-L-phenylalanine and N-acetyl-D-phenylalanine complexes.

PubMed

Alexander, Jennifer M; Clark, Joanna L; Brett, Tom J; Stezowski, John J

2002-04-16

In a systematic study of molecular recognition of amino acid derivatives in solid-state beta-cyclodextrin (beta-CD) complexes, we have determined crystal structures for complexes of beta-cyclodextrin/N-acetyl-L-phenylalanine at 298 and 20 K and for N-acetyl-D-phenylalanine at 298 K. The crystal structures for the N-acetyl-L-phenylalanine complex present disordered inclusion complexes for which the distribution of guest molecules at room temperature is not resolvable; however, they can be located with considerable confidence at low temperature. In contrast, the complex with N-acetyl-D-phenylalanine is well ordered at room temperature. The latter complex presents an example of a complex in this series in which a water molecule is included deeply in the hydrophobic torus of the extended dimer host. In an effort to understand the mechanisms of molecular recognition giving rise to the dramatic differences in crystallographic order in these crystal structures, we have examined the intermolecular interactions in detail and have examined insertion of the enantiomer of the D-complex into the chiral beta-CD complex crystal lattice.

High-temperature magnetostructural transition in van der Waals-layered α - MoCl 3

DOE PAGES

McGuire, Michael A.; Yan, Jiaqiang; Lampen-Kelley, Paula; ...

2017-11-07

Here, the crystallographic and magnetic properties of the cleavable 4d 3 transition metal compound α–MoCl 3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagneticmore » at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.« less

High-temperature magnetostructural transition in van der Waals-layered α -MoCl3

NASA Astrophysics Data System (ADS)

McGuire, Michael A.; Yan, Jiaqiang; Lampen-Kelley, Paula; May, Andrew F.; Cooper, Valentino R.; Lindsay, Lucas; Puretzky, Alexander; Liang, Liangbo; KC, Santosh; Cakmak, Ercan; Calder, Stuart; Sales, Brian C.

2017-11-01

The crystallographic and magnetic properties of the cleavable 4 d3 transition metal compound α -MoCl3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagnetic at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.

Synthesis and X-ray crystal structure determination of N- p-methylphenyl-4-benzoyl-3,4-diphenyl-2-azetidinone

NASA Astrophysics Data System (ADS)

Kabak, Mehmet; Şenöz, Hülya; Elmali, Ayhan; Adar, Vildan; Svoboda, Ingrid; Dušek, Michal; Fejfarová, Karla

2010-12-01

The title compound, C29H23NO2, has been characterized by single-crystal X-ray diffraction at two different temperatures (303 K and 120 K) and wavelengths (Mo K α and Cu K α). The non-centrosymmetric hexagonal crystal structure contains four-membered planar β-lactam ring with an unusually long C-C bond. The β-lactam ring is almost planar.

Crystal structure and phase transformations of calcium yttrium orthophosphate, Ca 3Y(PO 4) 3

NASA Astrophysics Data System (ADS)

Fukuda, Koichiro; Iwata, Tomoyuki; Niwa, Takahiro

2006-11-01

Crystal structure and phase transformations of calcium yttrium orthophosphate Ca 3Y(PO 4) 3 were investigated by X-ray powder diffraction, selected-area electron diffraction, transmission electron microscopy and optical microscopy. The high-temperature phase is isostructural with eulytite, cubic (space group I4¯3d) with a=0.983320(5) nm, V=0.950790(8) nm 3, Z=4 and D x=3.45 Mg m -3. The crystal structure was refined with a split-atom model, in which the oxygen atoms are distributed over two partially occupied sites. Below the stable temperature range of eulytite, the crystal underwent a martensitic transformation, which is accompanied by the formation of platelike surface reliefs. The inverted crystal is triclinic (space group P1) with a=1.5726(1) nm, b=0.84267(9) nm, c=0.81244(8) nm, α=109.739(4)°, β=90.119(5)°, γ=89.908(7)°, V=1.0134(1) nm 3, Z=4 and D x=3.24 Mg m -3. The crystal grains were composed of pseudo-merohedral twins. The adjacent twin domains were related by the pseudo-symmetry mirror planes parallel to {101¯} with the composition surface {101¯}. When the eulytite was cooled relatively slowly from the stable temperature range, the decomposition reaction of Ca 3Y(PO 4) 3→ β-Ca 3(PO 4) 2+YPO 4 occurred.

Diffusion-controlled and "diffusionless" crystal growth near the glass transition temperature: relation between liquid dynamics and growth kinetics of seven ROY polymorphs.

PubMed

Sun, Ye; Xi, Hanmi; Ediger, M D; Richert, Ranko; Yu, Lian

2009-08-21

The liquid dynamics of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, named ROY for its red, orange, and yellow crystal polymorphs, was characterized by dielectric spectroscopy and differential scanning calorimetry. Four of these polymorphs show fast "diffusionless" crystal growth at low temperatures while three others do not. ROY was found to be a typical fragile organic liquid. Its alpha relaxation process has time-temperature superposition symmetry across the viscous range (tau(alpha)=100 s-100 ns) with the width of the relaxation peak characterized by a constant beta(KWW) of 0.73. No secondary relaxation peak was observed, even with glasses made by fast quenching. For the polymorphs not showing fast crystal growth in the glassy state, the growth rate has a power-law relation with tau(alpha), u proportional to tau(alpha)(-xi), where xi approximately = 0.7. For the polymorphs showing fast crystal growth in the glassy state, the growth is so fast near and below the glass transition temperature T(g) that thousands of molecular layers can be added to the crystalline phase during one structural relaxation time of the liquid. In the glassy state, this mode of growth slows slightly over time. This slowdown is not readily explained by the effect of physical aging on the thermodynamic driving force of crystallization, the glass vapor pressure, or the rate of structural relaxation. This study demonstrates that from the same liquid or glass, the growth of some polymorphs is accurately described as being limited by the rate of structural relaxation or bulk diffusion, whereas the growth of other polymorphs is too fast to be under such control.

Effects of Vacancy Cluster Defects on Electrical and Thermodynamic Properties of Silicon Crystals

PubMed Central

Huang, Pei-Hsing; Lu, Chi-Ming

2014-01-01

A first-principle plane-wave pseudopotential method based on the density function theory (DFT) was employed to investigate the effects of vacancy cluster (VC) defects on the band structure and thermoelectric properties of silicon (Si) crystals. Simulation results showed that various VC defects changed the energy band and localized electron density distribution of Si crystals and caused the band gap to decrease with increasing VC size. The results can be ascribed to the formation of a defect level produced by the dangling bonds, floating bonds, or high-strain atoms surrounding the VC defects. The appearance of imaginary frequencies in the phonon spectrum of defective Si crystals indicates that the defect-region structure is dynamically unstable and demonstrates phase changes. The phonon dispersion relation and phonon density of state were also investigated using density functional perturbation theory. The obtained Debye temperature (θ D) for a perfect Si crystal had a minimum value of 448 K at T = 42 K and a maximum value of 671 K at the high-temperature limit, which is consistent with the experimental results reported by Flubacher. Moreover, the Debye temperature decreased with increases in the VC size. VC defects had minimal effects on the heat capacity (C v) value when temperatures were below 150 K. As the temperature was higher than 150 K, the heat capacity gradually increased with increasing temperature until it achieved a constant value of 11.8 cal/cell·K. The heat capacity significantly decreased as the VC size increased. For a 2 × 2 × 2 superlattice Si crystal containing a hexagonal ring VC (HRVC10), the heat capacity decreased by approximately 17%. PMID:24526923

Morphological, spectroscopic and thermal studies of samarium chloride coordinated single crystal grown by slow evaporation method

NASA Astrophysics Data System (ADS)

Slathia, Goldy; Raina, Bindu; Gupta, Rashmi; Bamzai, K. K.

2018-05-01

The synthesis of samarium chloride coordinated single crystal was carried out at room temperature by slow evaporation method. The crystal possesses a well defined hexagonal morphology with six symmetrically equivalent growth sectors separated by growth boundaries. The theoretical morphology has been established by structural approach using Bravaise-Friedele-Donnaye-Harker (BFDH) law. Fourier transform infra red spectroscopy was carried in order to study the geometry and structure of the crystal. The detailed thermogravimetric analysis elucidates the thermal stability of the complex.

In-situ study on growth units of Ba2Mg(B3O6)2 crystal

NASA Astrophysics Data System (ADS)

Lv, X. S.; Sun, Y. L.; Tang, X. L.; Wan, S. M.; Zhang, Q. L.; You, J. L.; Yin, S. T.

2013-05-01

BMBO (Ba2Mg(B3O6)2 crystal) is an excellent birefringent crystal and a potential stimulated Raman scattering (SRS) crystal. In this paper, high temperature Raman spectroscopy was used to in-situ study the melt structure near a BMBO crystal-melt interface. [B3O6]3- groups were found in this region. The result reveals that both of BaO bonds and MgO bonds are the weak bonds in the BMBO crystal structure. During the melting process, the crystal structure broke into Ba2+ ions, Mg2+ ions and [B3O6]3- groups. Our experimental results confirmed that the well-developed faces of BMBO crystals are the (001), (101) and (012) faces. Based on attachment energy theory, the crystal growth habit was discussed. The (001) (101) and (012) crystal faces linked by the weak BaO bonds and MgO bonds have smaller attachment energies and slower growth rates, and thus present in the final morphology. The (012) crystal face has a multi-terrace structure, which suggests that BMBO crystal grows with a layer-by-layer mode.

A variable temperature EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 170 GHz: zero-field splitting parameter and its absolute sign.

PubMed

Misra, Sushil K; Andronenko, Serguei I; Chand, Prem; Earle, Keith A; Paschenko, Sergei V; Freed, Jack H

2005-06-01

EPR measurements have been carried out on a single crystal of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) at 170-GHz in the temperature range of 312-4.2K. The spectra have been analyzed (i) to estimate the spin-Hamiltonian parameters; (ii) to study the temperature variation of the zero-field splitting (ZFS) parameter; (iii) to confirm the negative absolute sign of the ZFS parameter unequivocally from the temperature-dependent relative intensities of hyperfine sextets at temperatures below 10K; and (iv) to detect the occurrence of a structural phase transition at 4.35K from the change in the structure of the EPR lines with temperature below 10K.

Co-crystal formation between two organic solids on the surface of Titan

NASA Astrophysics Data System (ADS)

Cable, M. L.; Vu, T. H.; Maynard-Casely, H. E.; Hodyss, R. P.

2017-12-01

Laboratory experiments of Titan molecular materials, informed by modeling, can help us to understand the complex and dynamic surface processes occurring on this moon at cryogenic temperatures. We previously demonstrated that two common organic materials on Titan, ethane and benzene, form a unique and stable co-crystalline structure at Titan surface temperatures. We have now characterized a second co-crystal that is stable on Titan, this time between two solids: acetylene and ammonia. The co-crystal forms within minutes at Titan surface temperature, as evidenced by new Raman spectral features in the lattice vibration and C-H bending regions. In addition, a red shift of the C-H stretching mode suggests that the acetylene-ammonia co-crystal is stabilized by a network of C-H···N interactions. Thermal stability studies indicate that this co-crystal remains intact to >110 K, and experiments with liquid methane and ethane reveal the co-crystal to be resistant to fluvial or pluvial exposure. Non-covalently bound structures such as these co-crystals point to far more complex surface interactions than previously believed on Titan. New physical and mechanical properties (deformation, plasticity, density, etc.), differences in storage of key species (i.e., ethane versus methane), variations in surface transport and new chemical gradients can all result in diverse surface features and chemistries of astrobiological interest.

Effect of crystals and fibrous network polymer additives on cellular morphology of microcellular foams

NASA Astrophysics Data System (ADS)

Miyamoto, Ryoma; Utano, Tatsumi; Yasuhara, Shunya; Ishihara, Shota; Ohshima, Masahiro

2015-05-01

In this study, the core-back foam injection molding was used for preparing microcelluar polypropylene (PP) foam with either a 1,3:2,4 bis-O-(4-methylbenzylidene)-D-sorbitol gelling agent (Gel-all MD) or a fibros network polymer additive (Metablen 3000). Both agent and addiive could effectively control the celluar morphology in foams but somehow different ways. In course of cooling the polymer with Gel-all MD in the mold caity, the agent enhanced the crystal nucleation and resulted in the large number of small crystals. The crystals acted as effective bubble nucleation agent in foaming process. Thus, the agent reduced the cell size and increased the cell density, drastically. Furthermore, the small crystals provided an inhomogenuity to the expanding cell wall and produced the high open cell content with nano-scale fibril structure. Gell-all as well as Metablene 3000 formed a gel-like fibrous network in melt. The network increased the elongational viscosity and tended to prevent the cell wall from breaking up. The foaming temperature window was widened by the presence of the network. Especially, the temperature window where the macro-fibrous structure was formed was expanded to the higher temperature. The effects of crystal nucleating agent and PTFE on crystals' size and number, viscoelsticity, rheological propreties of PP and cellular morphology were compared and thorougly investigated.

Dew Point Calibration System Using a Quartz Crystal Sensor with a Differential Frequency Method.

PubMed

Lin, Ningning; Meng, Xiaofeng; Nie, Jing

2016-11-18

In this paper, the influence of temperature on quartz crystal microbalance (QCM) sensor response during dew point calibration is investigated. The aim is to present a compensation method to eliminate temperature impact on frequency acquisition. A new sensitive structure is proposed with double QCMs. One is kept in contact with the environment, whereas the other is not exposed to the atmosphere. There is a thermal conductivity silicone pad between each crystal and a refrigeration device to keep a uniform temperature condition. A differential frequency method is described in detail and is applied to calibrate the frequency characteristics of QCM at the dew point of -3.75 °C. It is worth noting that frequency changes of two QCMs were approximately opposite when temperature conditions were changed simultaneously. The results from continuous experiments show that the frequencies of two QCMs as the dew point moment was reached have strong consistency and high repeatability, leading to the conclusion that the sensitive structure can calibrate dew points with high reliability.

Structural features of single crystals of LuB{sub 12} upon a transition to the cage-glass phase

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

Bolotina, N. B., E-mail: nb-bolotina@mail.ru; Verin, I. A.; Shitsevalova, N. Yu.

2016-03-15

The unit-cell parameters of dodecaboride LuB{sub 12}, which undergoes a transition to the cage-glass phase, have been determined for the first time in the temperature range of 50–75 K by X-ray diffraction, and the single-crystal structure of this compound is established at 50 K. Nonlinear changes in the unit-cell parameters correspond to anomalies in the physical properties near the glass-transition temperature T* ~ 50–70 K. This compound has cubic symmetry at room temperature, and it is reduced to tetragonal symmetry at lower temperatures. Based on the X-ray diffraction data and relying on the physical properties of the crystals, the structuremore » model, in which a small part (~15%) of Lu atoms are displaced from the 2a sites at the centers of the B{sub 24} cuboctahedra to the 16n sites of sp. gr. I4/mmm, seems preferable.« less

Formation of Helically Structured Chitin/CaCO3 Hybrids through an Approach Inspired by the Biomineralization Processes of Crustacean Cuticles.

PubMed

Matsumura, Shunichi; Kajiyama, Satoshi; Nishimura, Tatsuya; Kato, Takashi

2015-10-01

Chitin/CaCO3 hybrids with helical structures are formed through a biomineralization-inspired crystallization process under ambient conditions. Liquid-crystalline chitin whiskers are used as helically ordered templates. The liquid-crystalline structures are stabilized by acidic polymer networks which interact with the chitin templates. The crystallization of CaCO3 is conducted by soaking the templates in the colloidal suspension of amorphous CaCO3 (ACC) at room temperature. At the initial stage of crystallization, ACC particles are introduced inside the templates, and they crystallize to CaCO3 nanocrystals. The acidic polymer networks induce CaCO3 crystallization. The characterization of the resultant hybrids reveals that they possess helical order and homogeneous hybrid structures of chitin and CaCO3 , which resemble the structure and composition of the exoskeleton of crustaceans. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Snynthesis and magnetization of BaLn2O4 (Ln = lanthanide)

NASA Astrophysics Data System (ADS)

Lundberg, Matthew

The BaLn2O4 family has been synthesized successfully as single crystals by the flux-growth method. The phases crystallize in the CaV2O4 structure prototype in space group Pnma (# 62). The structure has been studied using single-crystal x-ray diffraction, and stoichiometry confirmed with EDS, and the unit cell parameters and atomic positions have been determined for the whole lanthanide series (with the exception of the Lu compound). The effects of the lanthanide ionic radius on the atomic positions in the unit cell has been studied in terms of fractional atomic coordinates, bond lengths and angles, and bond valence sums. Magnetic measurements have been performed on the series with the exception of the La, Eu, and Lu members in the form of susceptibility versus temperature. The crystals all show signs of geometric antiferromagnetic frustration with the Neel temperatures significantly below the temperature predicted by the Weiss constant. Additionally some members of the family, namely BaCe2O4, BaNd2O4, BaPr 2O4, BaSm2O4, BaTb2O 4, and BaYb2O4 show significant crystal field splitting, that causes deviation from Currie-Weiss behavior.

Defect-induced local variation of crystal phase transition temperature in metal-halide perovskites.

PubMed

Dobrovolsky, Alexander; Merdasa, Aboma; Unger, Eva L; Yartsev, Arkady; Scheblykin, Ivan G

2017-06-26

Solution-processed organometal halide perovskites are hybrid crystalline semiconductors highly interesting for low-cost and efficient optoelectronics. Their properties are dependent on the crystal structure. Literature shows a variety of crystal phase transition temperatures and often a spread of the transition over tens of degrees Kelvin. We explain this inconsistency by demonstrating that the temperature of the tetragonal-to-orthorhombic phase transition in methylammonium lead triiodide depends on the concentration and nature of local defects. Phase transition in individual nanowires was studied by photoluminescence microspectroscopy and super-resolution imaging. We propose that upon cooling from 160 to 140 K, domains of the crystal containing fewer defects stay in the tetragonal phase longer than highly defected domains that readily transform to the high bandgap orthorhombic phase at higher temperatures. The existence of relatively pure tetragonal domains during the phase transition leads to drastic photoluminescence enhancement, which is inhomogeneously distributed across perovskite microcrystals.Understanding crystal phase transition in materials is of fundamental importance. Using luminescence spectroscopy and super-resolution imaging, Dobrovolsky et al. study the transition from the tetragonal to orthorhombic crystal phase in methylammonium lead triiodide nanowires at low temperature.

Room-temperature spin-orbit torque in NiMnSb

NASA Astrophysics Data System (ADS)

Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

2016-09-01

Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

Crystal Structure Characterization of Thin Layer Zinc Oxide

NASA Astrophysics Data System (ADS)

Doyan, Aris; Susilawati; Azizatul Fitri, Siti; Ahzan, Sukainil

2017-05-01

In this research the characterization of the crystal structure of a thin layer of ZnO (zinc oxide) were synthesized by sol - gel method and spin coating deposited on a glass substrate. The samples were divided into three sol concentrations of 0.1, 0.3, 0.5 Molar and two deposition temperature is 350 °C, and 550 °C. UV-Vis. spectrophotometer results showed that in the spectrum of visible light (wavelength range 300-800 nm) has a transmittance value of which increases with increasing concentration and temperature deposition of zinc oxide, otherwise the value of the absorption and the band gap energy decreases with the addition of concentration and deposition temperature. The transmittances value of the highest and lowest absorption was 93.5% and 0.03 is at a concentration of 0.1 M and zinc oxide deposition temperature of 550 °C, with a value of band gap energy of 2.98 eV. The XRD results showed that the zinc oxide crystal orientation in the field of 013 with a crystal grain size 14.4472 nm. SEM results showed the surface morphology of zinc oxide such as rod-like.

Optimization of single crystals of solid electrolytes with tysonite-type structure (LaF3) for conductivity at 293 K: 2. Nonstoichiometric phases R 1- y M y F3- y ( R = La-Lu, Y; M = Sr, Ba)

NASA Astrophysics Data System (ADS)

Sorokin, N. I.; Sobolev, B. P.; Krivandina, E. A.; Zhmurova, Z. I.

2015-01-01

Single crystals of fluorine-conducting solid electrolytes R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y ( R = La-Lu, Y) with a tysonite-type structure (LaF3) have been optimized for room-temperature conductivity σ293 K. The optimization is based on high-temperature measurements of σ( T) in two-component nonstoichiometric phases R 1 - y M y F3 - y ( M = Sr, Ba) as a function of the MF2 content. Optimization for thermal stability is based on studying the phase diagrams of MF2- RF3 systems ( M = Sr, Ba) and the behavior of nonstoichiometric crystals upon heating when measuring temperature dependences σ( T). Single crystals of many studied R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y phases have σ293 K values large enough to use these materials in solid-state electrochemical devices (chemical sensors, fluorine-ion batteries, accumulators, etc.) operating at room temperature.

Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Crx(Rh1-yRuy)7-xB3 (x=0.88-1; y=0-1) with Th7Fe3-type structure

NASA Astrophysics Data System (ADS)

Misse, Patrick R. N.; Mbarki, Mohammed; Fokwa, Boniface P. T.

2012-08-01

Powder samples and single crystals of the new complex boride series Crx(Rh1-yRuy)7-xB3 (x=0.88-1; y=0-1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region.

Dielectric and electromechanical properties of rare earth calcium oxyborate piezoelectric crystals at high temperatures.

PubMed

Yu, Fapeng; Zhang, Shujun; Zhao, Xian; Yuan, Duorong; Qin, Lifeng; Wang, Qing-Ming; Shrout, Thomas R

2011-04-01

The electrical resistivity, dielectric, and electromechanical properties of ReCa(4)O(BO(3))(3) (ReCOB; Re = Er, Y, Gd, Sm, Nd, Pr, and La) piezoelectric crystals were investigated as a function of temperature up to 1000 °C. Of the studied crystals, ErCOB and YCOB were found to possess extremely high resistivity (p): p > 3 × 10(7) ω.cm at 1000 °C. The property variation in ReCOB crystals is discussed with respect to their disordered structure. The highest electromechanical coupling factor κ(26) and piezoelectric coefficient d(26) at 1000°C, were achieved in PrCOB crystals, with values being on the order of 24.7% and 13.1 pC/N, respectively. The high thermal stability of the electromechanical properties, with variation less than 25%, together with the low dielectric loss (<46%) and high mechanical quality factor (>1500) at elevated temperatures of 1000 °C, make ErCOB, YCOB, and GdCOB crystals promising for ultrahigh temperature electromechanical applications. © 2011 IEEE

Inorganic pyrophosphatase crystals from Thermococcus thioreducens for X-ray and neutron diffraction.

PubMed

Hughes, Ronny C; Coates, Leighton; Blakeley, Matthew P; Tomanicek, Steve J; Langan, Paul; Kovalevsky, Andrey Y; García-Ruiz, Juan M; Ng, Joseph D

2012-12-01

Inorganic pyrophosphatase (IPPase) from the archaeon Thermococcus thioreducens was cloned, overexpressed in Escherichia coli, purified and crystallized in restricted geometry, resulting in large crystal volumes exceeding 5 mm3. IPPase is thermally stable and is able to resist denaturation at temperatures above 348 K. Owing to the high temperature tolerance of the enzyme, the protein was amenable to room-temperature manipulation at the level of protein preparation, crystallization and X-ray and neutron diffraction analyses. A complete synchrotron X-ray diffraction data set to 1.85 Å resolution was collected at room temperature from a single crystal of IPPase (monoclinic space group C2, unit-cell parameters a=106.11, b=95.46, c=113.68 Å, α=γ=90.0, β=98.12°). As large-volume crystals of IPPase can be obtained, preliminary neutron diffraction tests were undertaken. Consequently, Laue diffraction images were obtained, with reflections observed to 2.1 Å resolution with I/σ(I) greater than 2.5. The preliminary crystallographic results reported here set in place future structure-function and mechanism studies of IPPase.

X-ray transparent microfluidic chip for mesophase-based crystallization of membrane proteins and on-chip structure determination

DOE PAGES

Khvostichenko, Daria S.; Schieferstein, Jeremy M.; Pawate, Ashtamurthy S.; ...

2014-08-21

Crystallization from lipidic mesophase matrices is a promising route to diffraction-quality crystals and structures of membrane proteins. The microfluidic approach reported here eliminates two bottlenecks of the standard mesophase-based crystallization protocols: (i) manual preparation of viscous mesophases and (ii) manual harvesting of often small and fragile protein crystals. In the approach reported here, protein-loaded mesophases are formulated in an X-ray transparent microfluidic chip using only 60 nL of the protein solution per crystallization trial. The X-ray transparency of the chip enables diffraction data collection from multiple crystals residing in microfluidic wells, eliminating the normally required manual harvesting and mounting ofmore » individual crystals. In addition, we validated our approach by on-chip crystallization of photosynthetic reaction center, a membrane protein from Rhodobacter sphaeroides, followed by solving its structure to a resolution of 2.5 Å using X-ray diffraction data collected on-chip under ambient conditions. A moderate conformational change in hydrophilic chains of the protein was observed when comparing the on-chip, room temperature structure with known structures for which data were acquired under cryogenic conditions.« less

X-ray Transparent Microfluidic Chip for Mesophase-Based Crystallization of Membrane Proteins and On-Chip Structure Determination

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

Khvostichenko, Daria S.; Schieferstein, Jeremy M.; Pawate, Ashtamurthy S.

2014-10-01

Crystallization from lipidic mesophase matrices is a promising route to diffraction-quality crystals and structures of membrane proteins. The microfluidic approach reported here eliminates two bottlenecks of the standard mesophase-based crystallization protocols: (i) manual preparation of viscous mesophases and (ii) manual harvesting of often small and fragile protein crystals. In the approach reported here, protein-loaded mesophases are formulated in an X-ray transparent microfluidic chip using only 60 nL of the protein solution per crystallization trial. The X-ray transparency of the chip enables diffraction data collection from multiple crystals residing in microfluidic wells, eliminating the normally required manual harvesting and mounting ofmore » individual crystals. We validated our approach by on-chip crystallization of photosynthetic reaction center, a membrane protein from Rhodobacter sphaeroides, followed by solving its structure to a resolution of 2.5 Å using X-ray diffraction data collected on-chip under ambient conditions. A moderate conformational change in hydrophilic chains of the protein was observed when comparing the on-chip, room temperature structure with known structures for which data were acquired under cryogenic conditions.« less

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

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

Prokhorov, I. A., E-mail: igor.prokhorov@mail.ru; Ralchenko, V. G.; Bolshakov, A. P.

2013-12-15

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likelymore » due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.« less

Comparing two tetraalkylammonium ionic liquids. II. Phase transitions.

PubMed

Lima, Thamires A; Paschoal, Vitor H; Faria, Luiz F O; Ribeiro, Mauro C C; Ferreira, Fabio F; Costa, Fanny N; Giles, Carlos

2016-06-14

Phase transitions of the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N1114][NTf2], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N1444][NTf2], were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, and Raman spectroscopy. XRD and Raman spectra were obtained as a function of temperature at atmospheric pressure, and also under high pressure at room temperature using a diamond anvil cell (DAC). [N1444][NTf2] experiences glass transition at low temperature, whereas [N1114][NTf2] crystallizes or not depending on the cooling rate. Both the ionic liquids exhibit glass transition under high pressure. XRD and low-frequency Raman spectra provide a consistent physical picture of structural ordering-disordering accompanying the thermal events of crystallization, glass transition, cold crystallization, pre-melting, and melting. Raman spectra in the high-frequency range of some specific cation and anion normal modes reveal conformational changes of the molecular structures along phase transitions.

Low temperature time resolved photoluminescence in ordered and disordered Cu2ZnSnS4 single crystals

NASA Astrophysics Data System (ADS)

Raadik, Taavi; Krustok, Jüri; Kauk-Kuusik, M.; Timmo, K.; Grossberg, M.; Ernits, K.; Bleuse, J.

2017-03-01

In this work we performed time-resolved micro-photoluminescence (TRPL) studies of Cu2ZnSnS4 (CZTS) single crystals grown in molten KI salt. The order/disorder degree of CZTS was varied by the thermal post treatment temperature. Photoluminescence spectra measured at T=8 K showed an asymmetric band with a peak position of 1.33 eV and 1.27 eV for partially ordered and disordered structures, respectively. Thermal activation energies were found to be ET (PO) =65±9 meV for partially ordered and ET (PD) =27±4 meV for partially disordered. These low activation energy values indicating to the defect cluster recombination model for both partially ordered and disordered structures. TRPL was measured for both crystals and their decay curves were fitted with a stretched exponential function, in order to describe the charge carriers' recombination dynamics at low temperature.

Defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

NASA Astrophysics Data System (ADS)

Li, Dong-Xiang; Qin, Xiu-Bo; Zheng, Li-Rong; Li, Yu-Xiao; Cao, Xing-Zhong; Li, Zhuo-Xin; Yang, Jing; Wang, Bao-Yi

2013-03-01

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane. By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+—VO defect complexes (or clusters) have been identified in annealed crystals at a high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. In addition, excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.

Fiber structure formation in melt spinning of bio-based aliphatic co-polyesters

NASA Astrophysics Data System (ADS)

Qin, Qing; Takarada, Wataru; Kikutani, Takeshi

2015-05-01

High-speed melt spinning of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) with the 3-hydroxyhexanoate composition of 5.4 mol% was carried out. Melting temperature of this polymer is 141.5°C. It has been reported that PHBH fibers of good appearance can be prepared through the melt spinning process only when extrusion temperature is lower than the melting temperature of pure PHB (176 °C). The high-speed melt spinning experiment in this study revealed that the crystallization of PHBH proceeded at high take-up velocities even when the extrusion temperature was higher than the melting temperature of PHB. This result is considered to be due to the enhancement of crystallization through the application of high tensile stress to the molten polymer in the spinning line. As-spun fibers showed sufficiently high mechanical properties. On the other hand, crystalline orientation of α-form crystal increased with an increase in the take-up velocity and the existence of a small amount of β-form crystals was detected at high take-up velocities. This is another indication for the occurrence of crystallization under high tensile stress.

Semicrystalline polyamide engineering thermoplastics based on the renewable monomer, 1,9-nonane diamine: Thermal properties and water absorption

DOE PAGES

Kugel, Alex; He, Jie; Samanta, Satyabrata; ...

2012-08-27

Here, a series of poly(1,9-nonamethylene adipamide-co-1,9-nonamethylene terephthalamide) copolymers were produced using melt polymerization and the thermal properties, crystal structure, and moisture uptake characterized. The results confirmed that the copolymers exhibit isomorphism. As expected, glass transition temperature and the apparent melting temperature increased with increasing terephthalmide content. Using the difference in the apparent melting temperature to the crystallization temperature as a measure of relative crystallization rate, it was observed that crystallization rate decreased as the terephthalamide content of the copolymer was increased from 0 to 50 mole percent but then sharply increased when increased beyond 50 mole percent. This behavior maymore » be the result of extensive inter- and intramolecular interactions in the melt associated with terephthalmide units in the polymer chain that nucleate crystallization upon cooling below the equilibrium melting temperature. Comparing the thermal properties of copolymers possessing an excess of terephthalmide units to the commodity polyamide Nylon 6,6, it is believed that these copolymers may have utility as partially renewable engineering thermoplastics.« less

Multi-wavelength laser emission in dye-doped photonic liquid crystals.

PubMed

Wang, Chun-Ta; Lin, Tsung-Hsien

2008-10-27

Multi-wavelength lasing in a dye-doped cholesteric liquid crystal (CLC) cell is demonstrated. By adding oversaturated chiral dopant, the multi-photonic band CLC structure can be obtained with non-uniform chiral solubility. Under appropriate excitation, multi-wavelength lasing can be achieved with a multi-photonic band edge CLC structure. The number of lasing wavelengths can be controlled under various temperature processes. Nine wavelength CLC lasings were observed simultaneously. The wavelength range covers around 600-675nm. Furthermore, reversible tuning of multi-wavelength lasing was achieved by controlling CLC device temperature.

Pressure relaxation and diffusion of vacancies in rapidly grown helium crystals

NASA Astrophysics Data System (ADS)

Birchenko, A. P.; Mikhin, N. P.; Rudavskii, E. Ya.; Smirnov, S. N.; Fysun, Ya. Yu.

2018-04-01

An experimental study of the features of pressure relaxation in rapidly grown crystals of a diluted solid solution 3He-4He, at temperatures above 1.3 K, was performed. A cylindrical cell with capacitive pressure sensors at the ends was used for measurements. It was found that, when the helium crystals were grown at cooling rates ≳4 mK/s, the difference in pressure ΔP registered by the sensors at 1.3 K reached 2.4 bars. The ΔP value decreased with subsequent stepwise increase in temperature, but reached zero only after thorough annealing at the premelting temperatures. The kinetics of pressure changes at the sample ends at different temperatures was recorded. The results obtained were interpreted within the framework of the structural relaxation model based on the monovacancy diffusion mechanism. The proposed model made it possible to explain the dependence of ΔP on the time and temperature recorded in the experiment, as well as to determine the activation energy of the structural relaxation process and the diffusion coefficient of vacancies. The details of the vacancy model are described in the Appendix.

Structural, mechanical, electrical and optical properties of a new lithium boro phthalate NLO crystal synthesized by a slow evaporation method

NASA Astrophysics Data System (ADS)

Mohanraj, K.; Balasubramanian, D.; Jhansi, N.

2017-11-01

A new non-linear optical (NLO) single crystal of lithium boro phthalate (LiBP) was grown by slow solvent evaporation technique. The powder sample was subjected to powder X-ray diffraction (PXRD) to find its crystalline nature and the crystal structure of the grown crystal was determined using single crystal X-ray (SXRD) diffraction analysis. The Fourier Transform Infrared (FTIR) spectrum was recorded for grown crystal to identify the various functional groups present in the compound. The mechanical property of the LiBP single crystal was studied using Vickers microhardness tester. The dielectric constant and dielectric loss measurements were carried out for the grown crystal at various temperatures. The grown crystal was subjected to UV-Visible Spectral Studies to analyze the linear optical behavior of the grown crystal. The Kurtz-Perry Powder technique was employed to measure the Second Harmonic Generation efficiency of the grown crystal.

Local structure of the SnTe topological crystalline insulator: Rhombohedral distortions emerging from the rocksalt phase

NASA Astrophysics Data System (ADS)

Mitrofanov, K. V.; Kolobov, A. V.; Fons, P.; Krbal, M.; Shintani, T.; Tominaga, J.; Uruga, T.

2014-10-01

AIVBVI crystals are believed to possess a rhombohedral (ferroelectric) structure at low temperature that changes to the rocksalt (paraelectric) structure above the Curie temperature. For GeTe it has been recently demonstrated that locally the structure retains the subsets of the shorter and longer bonds across the ferroelectric-to-paraelectric transition despite acquiring the cubic structure on average. Nothing is known about the existence of local distortions in SnTe, a prototypical topological crystalline insulator, where the crystal symmetry plays a crucial role. In this work we report the results of x-ray absorption measurements. We find that the structure is locally rhombohedrally distorted, and the distortions increase at T >100K, breaking the rocksalt average symmetry. Our density functional theory simulations performed at 0 K indicate that the role of spin-orbit coupling in the formation of the local structure of SnTe at low temperature is negligibly small. The small stochastic distortions do not affect the intrinsic band inversion of SnTe.

Evaluation of the effect of roasting process on the energy transition and the crystalline structures of Arabica, Robusta, and Liberica coffee from Jambi Indonesia

NASA Astrophysics Data System (ADS)

Perdana, B. M.; Manihuruk, R.; Ashyar, R.; Heriyanti; Sutrisno

2018-04-01

The effect of the roasting process has been evaluated to determine of the energy transition and the crystalline structure of three types of coffee, Arabica, Robusta, and Liberica coffee both green and roasted coffee with the roasted temperature at 200°C and 230°C. The crystalline structure of the coffee was evaluated with X-ray powder diffraction (XRD). The result exposes that the three types of green coffee showed that an amorphous structure whereas the roasted coffee denotes a crystal structure of sucrose. The varied temperature in the roasting process leads to changes in the crystal structure shown by the peak shift of 2θ for all types of coffee. The added cations, such as Fe2+, Ca2+, and Mg2+ ions on Liberica coffee induced of changes in the crystal structures, which are assigned by the peak shift, that imply of metal ions of the sucrose complexes happened in the solution, except for the addition of Mg2+ ion.

The densification, crystallization and mechanical properties of allylhydridopolycarbosilane-derived silicon carbide

NASA Astrophysics Data System (ADS)

Moraes, Kevin V.

Allylhydridopolycarbosilane is a precursor of growing importance in the fabrication of silicon carbide ceramics. However, prior to this study few details were available about the processing-structure-property relationships for this material. In Part 1 of this study the processes of densification and microstructural transformation of the partially pyrolysed amorphous AHPCS-SiC was investigated in the temperature region of 800°C to 1600°C. In Part 2 of this study, mechanical properties, specifically fracture toughness (K1c) and Vickers hardness, were measured on bulk specimens in the temperature range of 1000°C to 1600°C. A combination of X-Ray diffraction (XRD), Transmission Electron Microscopy (TEM), 29Si Nuclear Magnetic Resonance (NMR) and micro Raman spectroscopy, along with simultaneous Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) were used to follow the structural transformation of the partially pyrolysed AHPCS-SiC on several length scales between the temperature of 800 to 1600°C. It was determined that the rate of densification of amorphous AHPCS-SiC, partially pyrolysed to 600°C, depends on the surface to volume ratio. Calculations were preformed that suggested that nucleation of the SiC crystals should occur preferentially on the surface of the powder particles rather than in the bulk. However, TEM on samples heat-treated to 1600°C did not show a preponderance of crystals on the surface of the particles compared to their bulk. Crystallization of beta-SiC occurs at ca. 1250°C, as determined by DSC and supported by NMR and electron diffraction. The average size of the beta-SiC crystallites, as determined by XRD, was ca. 5 nm at 1600°C. Prior to the crystallization of beta-SiC, Raman spectroscopy indicates the presence of carbon clusters in the otherwise amorphous matrix. These carbon clusters have predominantly sp3 bonding at 1100°C that gradually converts to predominantly sp 2 bonded carbon at higher temperatures, with average basal plane sizes of 20--25 A between 1100 in addition to 1600°C. The amorphous structure formed at temperatures below the crystallization temperature is unstable. It is seen from DSC that amorphous AHPCS-SiC undergoes two distinct exothermic events: a broad, irreversible, exotherm that corresponds to structural relaxation and chemical condensation and a second, much sharper, exotherm that corresponds to crystallization. Fracture toughness values measured on cold-pressed and infiltrated AHPCS-SiC samples were in the range of 1.4 to 1.67 MPam1/2. It appears that toughness increases with increasing heat treatment temperature. The Vickers hardness at 10 N was ca. 8.7 to 12.6 MPa. The Vickers hardness does not appear to vary significantly with the heat-treatment temperature.

Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4

NASA Astrophysics Data System (ADS)

Carnicom, Elizabeth M.; Klimczuk, Tomasz; von Rohr, Fabian; Winiarski, Michal J.; Kong, Tai; Stolze, Karoline; Xie, Weiwei; Kushwaha, Satya K.; Cava, Robert J.

2017-08-01

The growth and characterization of CePtIn4, stabilized by 10% Zn substitution for In, is reported. The new material is orthorhombic, space group Cmcm (No. 63), with lattice parameters a = 4.51751(4) Å, b = 16.7570(2) Å, and c = 7.36682(8) Å, and the refined crystal composition has 10% of Zn substituted for In, i.e., the crystals are CePt(In0.9Zn0.1)4. Crystals were grown using a self-flux method: only growths containing Zn yielded CePtIn4 crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic temperature-dependent magnetic susceptibilities for single crystals show that Zn-stabilized CePtIn4 orders magnetically at ˜1.9 K. High-temperature Curie-Weiss fits indicate an effective moment of ˜2.49 μB/Ce and a directionally averaged Weiss-temperature of approximately -31 K. Specific heat data shows a peak consistent with the ordering temperature seen in the magnetic susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no superconducting transition down to 0.14 K.

Structured laser gain-medium by new bonding for power micro-laser

NASA Astrophysics Data System (ADS)

Kausas, Arvydas; Zheng, Lihe; Taira, Takunori

2017-02-01

In this work, we have compared the Q-switched performance of single rod crystal to a newly developed distributed face cooling structure. This structure was made by surface activated bonding technology and allowed to combine transparent heatsink to a gain crystal at room temperature. The Sapphire and Nd3+:YAG crystal plates were combined in this fashion to produce eight crystal chip which was further used to obtain Q-switch pulses with Cr4+:YAG crystal as saturable absorber. Energy of 9 mJ and pulse duration of 815 ps were achieved. Although the energy obtained with single rod system was 10 mJ, the degradation of the beam prevents such crystal to be used in further applications. This is the first demonstration of distributed face cooling system outperformed conventionally single rod system.

The effect of thermal history on crystalline structure and mechanical properties of β-nucleated isotactic polypropylene

NASA Astrophysics Data System (ADS)

Tian, Yefei; Zhou, Jian; Feng, Jiachun

2018-04-01

The effect of thermal history on β-nucleated iPP was systematically investigated by comparing the variance of crystalline microstructures and mechanical property of stepwise crystallized sample and annealed sample, which experienced different thermal history. The mechanical property tests exhibit that that the toughness of stepwise crystallized sample and annealed sample were both decreased compared to control sample, while the tensile strength of the stepwise crystallized sample increased slightly. Structure investigation showed that the α-relaxation peak, which is related to the assignment of chains in rigid amorphous phase, moved to the high temperature region for stepwise crystallized sample, while it moved to the low temperature region for annealed sample. The results indicated the weakening in rigid amorphous fraction (RAF) and the increase in lamellar thickness of β-iPP after stepwise crystallization treatment. For annealed sample, the RAF strengthened and lamellar thickness decreased slightly after thermal treatment. A mechanism of crystalline microstructures evolution of restricted area between the main lamellar under different treatments was proposed.

A novel inert crystal delivery medium for serial femtosecond crystallography

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

Conrad, Chelsie E.; Basu, Shibom; James, Daniel

Serial femtosecond crystallography (SFX) has opened a new era in crystallography by permitting nearly damage-free, room-temperature structure determination of challenging proteins such as membrane proteins. In SFX, femtosecond X-ray free-electron laser pulses produce diffraction snapshots from nanocrystals and microcrystals delivered in a liquid jet, which leads to high protein consumption. A slow-moving stream of agarose has been developed as a new crystal delivery medium for SFX. It has low background scattering, is compatible with both soluble and membrane proteins, and can deliver the protein crystals at a wide range of temperatures down to 4°C. Using this crystal-laden agarose stream, themore » structure of a multi-subunit complex, phycocyanin, was solved to 2.5 Å resolution using 300 µg of microcrystals embedded into the agarose medium post-crystallization. The agarose delivery method reduces protein consumption by at least 100-fold and has the potential to be used for a diverse population of proteins, including membrane protein complexes.« less

A novel inert crystal delivery medium for serial femtosecond crystallography

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

Conrad, Chelsie E.; Basu, Shibom; James, Daniel

Serial femtosecond crystallography (SFX) has opened a new era in crystallography by permitting nearly damage-free, room-temperature structure determination of challenging proteins such as membrane proteins. In SFX, femtosecond X-ray free-electron laser pulses produce diffraction snapshots from nanocrystals and microcrystals delivered in a liquid jet, which leads to high protein consumption. A slow-moving stream of agarose has been developed as a new crystal delivery medium for SFX. It has low background scattering, is compatible with both soluble and membrane proteins, and can deliver the protein crystals at a wide range of temperatures down to 4°C. Using this crystal-laden agarose stream, themore » structure of a multi-subunit complex, phycocyanin, was solved to 2.5Å resolution using 300µg of microcrystals embedded into the agarose medium post-crystallization. The agarose delivery method reduces protein consumption by at least 100-fold and has the potential to be used for a diverse population of proteins, including membrane protein complexes.« less

A novel inert crystal delivery medium for serial femtosecond crystallography

DOE PAGES

Conrad, Chelsie E.; Basu, Shibom; James, Daniel; ...

2015-06-30

Serial femtosecond crystallography (SFX) has opened a new era in crystallography by permitting nearly damage-free, room-temperature structure determination of challenging proteins such as membrane proteins. In SFX, femtosecond X-ray free-electron laser pulses produce diffraction snapshots from nanocrystals and microcrystals delivered in a liquid jet, which leads to high protein consumption. A slow-moving stream of agarose has been developed as a new crystal delivery medium for SFX. It has low background scattering, is compatible with both soluble and membrane proteins, and can deliver the protein crystals at a wide range of temperatures down to 4°C. Using this crystal-laden agarose stream, themore » structure of a multi-subunit complex, phycocyanin, was solved to 2.5 Å resolution using 300 µg of microcrystals embedded into the agarose medium post-crystallization. The agarose delivery method reduces protein consumption by at least 100-fold and has the potential to be used for a diverse population of proteins, including membrane protein complexes.« less

The Effect of Solution Conditions on the Nucleation Kinetics of Tetragonal Lysozyme Crystals

NASA Technical Reports Server (NTRS)

Judge, Russell A.; Baird, James K.; Pusey, Marc L.

1998-01-01

An understanding of protein crystal nucleation rates and the effect of solution conditions upon them, is fundamental to the preparation of protein crystals of the desired size and shape for X-ray diffraction analysis. The ability to predict the effect of supersaturation, temperature, pH and precipitant concentration on the number and size of crystals formed is of great benefit in the pursuit of protein structure analysis. In this study we experimentally examine the effect of supersaturation, temperature, pH and sodium chloride concentration on the nucleation rate of tetragonal chicken egg white lysozyme crystals. In order to do this batch crystallization plates were prepared at given solution concentrations and incubated at three different temperatures over the period of one week. The number of crystals per well with their size and dimensions were recorded and correlated against solution conditions. Duplicate experiments indicate the reproducibility of the technique. Although it is well known that crystal numbers increase with increasing supersaturation, large changes in crystal number were also correlated against solution conditions of temperature, pH and salt concentration over the same supersaturation ranges. Analysis of these results enhance our understanding of the effect of solution conditions such as the dramatic effect that small changes in charge and ionic strength can have on the number of tetragonal lysozyme crystals that form and grow in solution.

Structural transition and enhanced phase transition properties of Se doped Ge2Sb2Te5 alloys

NASA Astrophysics Data System (ADS)

Vinod, E. M.; Ramesh, K.; Sangunni, K. S.

2015-01-01

Amorphous Ge2Sb2Te5 (GST) alloy, upon heating crystallize to a metastable NaCl structure around 150°C and then to a stable hexagonal structure at high temperatures (>=250°C). It has been generally understood that the phase change takes place between amorphous and the metastable NaCl structure and not between the amorphous and the stable hexagonal phase. In the present work, it is observed that the thermally evaporated (GST)1-xSex thin films (0 <= x <= 0.50) crystallize directly to the stable hexagonal structure for x >= 0.10, when annealed at temperatures >= 150°C. The intermediate NaCl structure has been observed only for x < 0.10. Chemically ordered network of GST is largely modified for x >= 0.10. Resistance, thermal stability and threshold voltage of the films are found to increase with the increase of Se. The contrast in electrical resistivity between the amorphous and crystalline phases is about 6 orders of magnitude. The increase in Se shifts the absorption edge to lower wavelength and the band gap widens from 0.63 to 1.05 eV. Higher resistance ratio, higher crystallization temperature, direct transition to the stable phase indicate that (GST)1-xSex films are better candidates for phase change memory applications.

Crystal structure and superconducting properties of KSr2Nb3O10

NASA Astrophysics Data System (ADS)

Kawaguchi, T.; Horigane, K.; Itoh, Y.; Kobayashi, K.; Horie, R.; Kambe, T.; Akimitsu, J.

2018-05-01

We performed X-ray diffraction (XRD) and DC magnetic susceptibility measurements to elucidate the crystal structure and superconducting properties of KSr2Nb3O10. From the diffraction pattern indexing, it was found that KSr2Nb3O10 crystallizes with monoclinic symmetry, space group P21/m(11). We succeeded in preparing high temperature (HT) and low temperature (LT) phases of KSr2Nb3O10 powder samples synthesized by a conventional solid state reaction and an ion-exchange reaction, respectively. Superconductivity was observed at 4 K by Li intercalation and it was found that the superconducting volume fraction of the LT phase ( 1.4%) is clearly larger than that of the HT phase (0.07%).

Prediction study of structural, elastic and electronic properties of FeMP (M = Ti, Zr, Hf) compounds

NASA Astrophysics Data System (ADS)

Tanto, A.; Chihi, T.; Ghebouli, M. A.; Reffas, M.; Fatmi, M.; Ghebouli, B.

2018-06-01

First principles calculations are applied in the study of FeMP (M = Ti, Zr, Hf) compounds. We investigate the structural, elastic, mechanical and electronic properties by combining first-principles calculations with the CASTEP approach. For ideal polycrystalline FeMP (M = Ti, Zr, Hf) the shear modulus, Young's modulus, Poisson's ratio, elastic anisotropy indexes, Pugh's criterion, elastic wave velocities and Debye temperature are also calculated from the single crystal elastic constants. The shear anisotropic factors and anisotropy are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal.

Effects of dry etching processes on exciton and polariton characteristics in ZnTe

NASA Astrophysics Data System (ADS)

Sun, J. H.; Xie, W. B.; Shen, W. Z.; Ogawa, H.; Guo, Q. X.

2003-12-01

We have employed temperature-dependent reflection spectra to study the effects of reactive ion etching (RIE) on the exciton and polariton characteristics in ZnTe crystals exposed to CH4/H2 gases under different rf plasma powers. Classic exciton-polariton theory has been used to calculate the reflection spectra. By comparing with an as-grown ZnTe crystal and the temperature-dependent behavior, we are able to identify the excitons and RIE-induced polariton structures in these dry etched ZnTe crystals. An increase of the rf plasma power will lead to an increase of defect density in the surface damage layers, resulting in a decrease of the photon energies of the observed exciton and polariton structures.

Characterization of Anodic Aluminum Oxide Membrane with Variation of Crystallizing Temperature for pH Sensor.

PubMed

Yeo, Jin-Ho; Lee, Sung-Gap; Jo, Ye-Won; Jung, Hye-Rin

2015-11-01

We fabricated electrolyte-dielectric-metal (EDM) device incorporating a high-k Al2O3 sensing membrane from a porous anodic aluminum oxide (AAO) using a two step anodizing process for pH sensors. In order to change the properties of the AAO template, the crystallizing temperature was varied from 400 degrees C to 700 degrees C over 2 hours. The structural properties were observed by field emission scanning electron microscopy (FE-SEM). The pH sensitivity increased with an increase in the crystallizing temperature from 400 degrees C to 600 degrees C. However at 700 degrees C, deformation occurred. The porous AAO sensor with a crystallizing temperature of 600 degrees C displayed the good sensitivity and long-term stability and the values were 55.7 mV/pH and 0.16 mV/h, respectively.

Crystallization of DNA-coated colloids

PubMed Central

Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

2015-01-01

DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids. PMID:26078020

Metal — Insulator Transition-like in Nano-Crystallized Ni-Fe-Zr Metallic Glasses

NASA Astrophysics Data System (ADS)

Hamed, F.; Obaidat, I. M.; Benkraouda, M.

2007-08-01

Ni-Fe-Zr based Metallic glassy ribbons were prepared by melt spinning technique. The compositional and structural integrity of the melt spun ribbons were verified by means of X-ray diffraction, SEM, EDX and DSC. 5 to 7 cm long ribbons of Ni-Fe-Zr based metallic glasses with different compositions were sealed inside quartz ampoules under vacuum. The sealed metallic glassy ribbons were nano-crystallized at 973 K for varying periods of time. The temperature dependence of the electrical resistivity of the nano-crystallized samples had been investigated over the temperature range 25-280 K. The crystallized ribbons at 973 K for periods for less than 4 hours displayed insulating electrical behavior like at low temperatures, while those annealed for more than 4 hours showed metallic behavior like. Nonlinear I-V characteristics were also observed at low temperatures for samples annealed for less than four hours.

Novel carbon-ion fuel cells. Final report, October 1, 1993--September 30, 1996

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

Cocks, F.H.

1997-01-01

Mixed lanthanide dicarbides having the fluorite crystal structure have been synthesized using the elemental lanthanide metals and elemental carbon that was 99.9% pure carbon-13 isotope. A two step process of first, arc furnace melting of the components, followed by an annealing step in a high vacuum furnace, was adopted as the standard method of fabricating small cast ingots of the dicarbides. The crystal structure of the various lanthanide dicarbides produced were confirmed by x-ray diffraction under protective atmospheres at both room temperature at Duke University and at high temperature at Oak Ridge National Laboratory. After more than 15 combinations ofmore » cerium or lanthanum with dopants were tried, low temperature x-ray diffraction showed that Ce{sub .5}Er{sub .5}C{sub 2} had been successfully stabilized and had the desired fluorite crystal structure at room temperature. The fluorite crystal structure lanthanide dicarbide cast ingots were further prepared by having flat and clean surfaces ground onto their surfaces by high-speed milling machines inside argon gas atmosphere gloveboxes. The surfaces thus created were then coated with carbon-12 by the arc evaporation method under low pressure argon gas. The coated ingots were then allowed to have carbon diffusion occur from the surface coating of carbon-12 into the ingot of dicarbide that had been synthesized from carbon-13. After the diffusion run, the cast ingots were slit down the axis perpendicular to the carbon coating. The fracture surface created was then squared and polished by high,speed milling in a glove box with a argon atmosphere. The high diffusion co-efficient of carbon in lanthanide dicarbides having the fluorite crystal structure would make possible the manufacture of a carbon-ion electrolyte for use in a battery or a fuel cell that could consume solid carbon as it`s feedstock.« less

In Situ High Temperature High Pressure MAS NMR Study on the Crystallization of AlPO 4 -5

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

Zhao, Zhenchao; Xu, Suochang; Hu, Mary Y.

2016-01-28

A damped oscillating crystallization process of AlPO4-5 at the presence of small amount of water is demonstrated by in situ high temperature high pressure multinuclear MAS NMR. Crystalline AlPO4-5 is formed from an intermediate semicrystalline phase via continuous rearrangement of the local structure of amorphous precursor gel. Activated water catalyzes the rearrangement via repeatedly hydrolysis and condensation reaction. Strong interactions between organic template and inorganic species facilitate the ordered rearrangement. During the crystallization process, excess water, phosphate, and aluminums are expelled from the precursor. The oscillating crystallization reflects mass transportation between the solid and liquid phase during the crystallization process.more » This crystallization process is also applicable to AlPO4-5 crystallized in the presence of a relatively large amount of water.« less

Highly reproducible alkali metal doping system for organic crystals through enhanced diffusion of alkali metal by secondary thermal activation.

PubMed

Lee, Jinho; Park, Chibeom; Song, Intek; Koo, Jin Young; Yoon, Taekyung; Kim, Jun Sung; Choi, Hee Cheul

2018-05-16

In this paper, we report an efficient alkali metal doping system for organic single crystals. Our system employs an enhanced diffusion method for the introduction of alkali metal into organic single crystals by controlling the sample temperature to induce secondary thermal activation. Using this system, we achieved intercalation of potassium into picene single crystals with closed packed crystal structures. Using optical microscopy and Raman spectroscopy, we confirmed that the resulting samples were uniformly doped and became K 2 picene single crystal, while only parts of the crystal are doped and transformed into K 2 picene without secondary thermal activation. Moreover, using a customized electrical measurement system, the insulator-to-semiconductor transition of picene single crystals upon doping was confirmed by in situ electrical conductivity and ex situ temperature-dependent resistivity measurements. X-ray diffraction studies showed that potassium atoms were intercalated between molecular layers of picene, and doped samples did not show any KH- nor KOH-related peaks, indicating that picene molecules are retained without structural decomposition. During recent decades, tremendous efforts have been exerted to develop high-performance organic semiconductors and superconductors, whereas as little attention has been devoted to doped organic crystals. Our method will enable efficient alkali metal doping of organic crystals and will be a resource for future systematic studies on the electrical property changes of these organic crystals upon doping.

The effect of adding CTAB template in ZSM-5 synthesis

NASA Astrophysics Data System (ADS)

Widayat, Widayat; Annisa, Arianti Nuur

2017-11-01

In general, ZSM-5 synthesis is performed using a hydrothermal process that takes place at high temperature and high pressure (> 373 K,> 1 bar). The synthesis of ZSM-5 is influenced by the organic template used. The organic template serves as a determinant of the zeolite crystal structure formation. CTAB is an easily found organic template and the price is cheap so the production cost of ZSM-5 synthesis would be more efficient. In this research, ZSM-5 is synthesized by varying temperature and crystallization time. The result showed the optimal condition of ZSM-5 synthesis was at 363 K for the crystallization temperature with 8 hours of crystallization time. The crystalline product had 60.07% of crystallinity with an aluminosilicate composition of 72% w/w.

The Preparation and Characterization of Natrolite Synthetized by Purified Attapulgite

NASA Astrophysics Data System (ADS)

Li, H. J.; Zhou, X. D.; Zhang, J. M.; Wu, X. Y.; Gao, H. B.

2017-06-01

This paper mainly researched the hydrothermal synthesis of Natrolite, using amorphous silicon source from the purified attapulgite. The effects of silicon source, silicon aluminum ratio, crystallization time and crystallization temperature on the synthesis of natrolite were investigated. The results showed that the optimal synthesis condition of natrolite was: Hydrothermal activated ATP with NaOH was silicon source, silicon aluminum ratio was 10:1, crystallization time lasted to 72h and crystallization temperature was 150°C, the template was removed by calcining 8 hours at 550°C. The structural formula of obtained natrolite is Na2Al2Si3O10•2H2O.

Effects of Pressure-shift Freezing on the Structural and Physical Properties of Gelatin Hydrogel Matrices

PubMed Central

Kim, Byeongsoo; Gil, Hyung Bae; Min, Sang-Gi; Lee, Si-Kyung; Choi, Mi-Jung

2014-01-01

This study investigates the effects of the gelatin concentration (10-40%, w/v), freezing temperatures (from -20℃ to -50℃) and freezing methods on the structural and physical properties of gelatin matrices. To freeze gelatin, the pressure-shift freezing (PSF) is being applied at 0.1 (under atmospheric control), 50 and 100 MPa, respectively. The freezing point of gelatin solutions decrease with increasing gelatin concentrations, from -0.2℃ (10% gelatin) to -6.7℃ (40% gelatin), while the extent of supercooling did not show any specific trends. The rheological properties of the gelatin indicate that both the storage (G') and loss (G") moduli were steady in the strain amplitude range of 0.1-10%. To characterize gelatin matrices formed by the various freezing methods, the ice crystal sizes which were being determined by the scanning electron microscopy (SEM) are affected by the gelatin concentrations. The ice crystal sizes are affected by gelatin concentrations and freezing temperature, while the size distributions of ice crystals depend on the freezing methods. Smaller ice crystals are being formed with PSF rather than under the atmospheric control where the freezing temperature is above -40℃. Thus, the results of this study indicate that the PSF processing at a very low freezing temperature (-50℃) offers a potential advantage over commercial atmospheric freezing points for the formation of small ice crystals. PMID:26760743

Crystal Structure and Theoretical Analysis of Green Gold Au 30 (S- t Bu) 18 Nanomolecules and Their Relation to Au 30 S(S- t Bu) 18

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

Dass, Amala; Jones, Tanya; Rambukwella, Milan

We report the complete X-ray crystallographic structure as determined through single crystal X-ray diffraction and a thorough theoretical analysis of the green gold Au30(S-tBu)18. While the structure of Au30S(S-tBu)18 with 19 sulfur atoms has been reported, the crystal structure of Au30(S-tBu)18 without the μ3-sulfur has remained elusive until now, though matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) data unequivocally shows its presence in abundance. The Au30(S-tBu)18 nanomolecule is not only distinct in its crystal structure but has unique temperature dependent optical properties. Structure determination allows a rigorous comparison and an excellent agreement with theoreticalmore » predictions of structure, stability, and optical response.« less

Structural, magnetic, magneto-caloric and Mössbauer spectral study of Tb{sub 2}Fe{sub 17} compound synthesized by arc melting

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

Charfeddine, S.; LVMU, Centre National de Recherches en Sciences des Matériaux, Technopole de Borj-Cédria, BP 73 Soliman 8027; Zehani, K.

We have synthesized the intermetallic Tb{sub 2}Fe{sub 17} compound in hexagonal crystal structure by arc-melting without annealing. X-ray diffraction pattern has been refined by Rietveld method. The crystal structure is hexagonal with P6{sub 3}/mmc space group (Th{sub 2}Ni{sub 17}-type). The Mössbauer spectrum of Tb{sub 2}Fe{sub 17} compound has been analyzed with seven magnetic sextets assigned to the inequivalent crystallographic sites. The temperature dependence of magnetization data revealed that Tb{sub 2}Fe{sub 17} exhibits a second-order ferromagnetic to paramagnetic phase transition in the vicinity of Curie temperature (T{sub C}=412 K). The relative cooling power around the magnetic transition and the Arrott plotsmore » are also reported. - Graphical abstract: A 3D surface showing the temperature and applied magnetic field dependencies of the magnetization for Tb{sub 2}Fe{sub 17} compound (left). Rietveld analysis of the XRD pattern (right). Crystal structure for the hexagonal P6{sub 3}/mmc Tb{sub 2}Fe{sub 17} (bottom). Display Omitted - Highlights: • Tb{sub 2}Fe{sub 17} single-phase synthesized by simple arc-melting without any heat treatment. • The crystal structure is hexagonal with P6{sub 3}/mmc space group. • The magnetic entropy change of the sample was determined by Maxwell relation. • Hyperfine parameters, magnetic and magnetocaloric properties were studied.« less

Pin-Hole Free Perovskite Film for Solar Cells Application Prepared by Controlled Two-Step Spin-Coating Method

NASA Astrophysics Data System (ADS)

Bahtiar, A.; Rahmanita, S.; Inayatie, Y. D.

2017-05-01

Morphology of perovskite film is a key important for achieving high performance perovskite solar cells. Perovskite films are commonly prepared by two-step spin-coating method. However, pin-holes are frequently formed in perovskite films due to incomplete conversion of lead-iodide (PbI2) into perovskite CH3NH3PbI3. Pin-holes in perovskite film cause large hysteresis in current-voltage curve of solar cells due to large series resistance between perovskite layer-hole transport material. Moreover, crystal structure and grain size of perovskite crystal are also other important parameters for achieving high performance solar cells, which are significantly affected by preparation of perovskite film. We studied the effect of preparation of perovskite film using controlled spin-coating parameters on crystal structure and morphological properties of perovskite film. We used two-step spin-coating method for preparation of perovskite film with varied spinning speed, spinning time and temperature of spin-coating process to control growth of perovskite crystal aimed to produce high quality perovskite crystal with pin-hole free and large grain size. All experiment was performed in air with high humidity (larger than 80%). The best crystal structure, pin-hole free with large grain crystal size of perovskite film was obtained from film prepared at room temperature with spinning speed 1000 rpm for 20 seconds and annealed at 100°C for 300 seconds.

Temperature effects on the band gaps of Lamb waves in a one-dimensional phononic-crystal plate (L).

PubMed

Cheng, Y; Liu, X J; Wu, D J

2011-03-01

This study investigates the temperature-tuned band gaps of Lamb waves in a one-dimensional phononic-crystal plate, which is formed by alternating strips of ferroelectric ceramic Ba(0.7)Sr(0.3)TiO(3) and epoxy. The sensitive and continuous temperature-tunability of Lamb wave band gaps is demonstrated using the analyses of the band structures and the transmission spectra. The width and position of Lamb wave band gaps shift prominently with variation of temperature in the range of 26 °C-50 °C. For example, the width of the second band gap increases from 0.066 to 0.111 MHz as the temperature is increased from 26 °C to 50 °C. The strong shift promises that the structure could be suitable for temperature-tuned multi-frequency Lamb wave filters. © 2011 Acoustical Society of America

Cubic-to-tetragonal structural phase transition in Rb{sub 1{minus}x}Cs{sub x}CaF{sub 3} solid solutions: Thermal expansion and EPR studies

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

Lahoz, F.; Villacampa, B.; Alcala, R.

1997-04-01

The influence of crystal mixing on the structural phase transitions in Rb{sub 1{minus}x}Cs{sub x}CaF{sub 3} (0{lt}x{lt}1) fluoroperovskite crystals has been studied by thermal expansion and EPR measurements of Ni{sup 2+} and Ni{sup 3+} paramagnetic probes. A cubic-to-tetragonal phase transition has been detected in crystals with x=0, 0.1, 0.21, 0.27, and 0.35. The critical temperature and the tetragonal distortion decrease as x increases. No transition was observed for x{ge}0.44. This transition shows a weak first-order component in the x=0 and 0.1 samples, which is progressively smeared out for x{gt}0.1, indicating a spatial distribution of the critical temperature in those crystals withmore » high ionic substitution rate. In RbCaF{sub 3}, another structural phase transition was observed at 20 K with a thermal hysteresis between 20 and 40 K. This transition has not been found in any of the mixed crystals.« less

On the synthesis of AlPO4-21 molecular sieve by vapor phase transport method and its phase transformation to AlPO4-15 molecular sieve

NASA Astrophysics Data System (ADS)

Shao, Hui; Chen, Jingjing; Chen, Xia; Leng, Yixin; Zhong, Jing

2015-04-01

An experimental design was applied to the synthesis of AlPO4-21 molecular sieve (AWO structure) by vapor phase transport (VPT) method, using tetramethylguanidine (TMG) as the template. In this study, the effects of crystallization time, crystallization temperature, phosphor content, template content and water content in the synthesis gel were investigated. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy (FT-IR). Microstructural analysis of the crystal growth in vapor synthetic conditions revealed a revised crystal growth route from zeolite AlPO4-21 to AlPO4-15 in the presence of the TMG. Homogenous hexagonal prism AlPO4-21 crystals with size of 7 × 3 μm were synthesized at a lower temperature (120 °C), which were completely different from the typical tabular parallelogram crystallization microstructure of AlPO4-21 phase. The crystals were transformed into AlPO4-21 phase with higher crystallization temperature, longer crystallization time, higher P2O5/Al2O3 ratio and higher TMG/Al2O3 ratio.

Crystal structure of tin(IV) chloride octa­hydrate

PubMed Central

Hennings, Erik; Schmidt, Horst; Voigt, Wolfgang

2014-01-01

The title compound, [SnCl4(H2O)2]·6H2O, was crystallized according to the solid–liquid phase diagram at lower temperatures. It is built-up of SnCl4(H2O)2 octa­hedral units (point group symmetry 2) and lattice water mol­ecules. An intricate three-dimensional network of O—H⋯O and O—H⋯Cl hydrogen bonds between the complex molecules and the lattice water molecules is formed in the crystal structure. PMID:25552971

The molecular and crystal structure of dextrans: a combined electron and X-ray diffraction study. II. A low temperature, hydrated polymorph.

PubMed

Guizard, C; Chanzy, H; Sarko, A

1985-06-05

The crystal and molecular structure of a dextran hydrate has been determined through combined electron and X-ray diffraction analysis, aided by stereochemical model refinement. A total of 65 hk0 electron diffraction intensities were measured on frozen single crystals held at the temperature of liquid nitrogen, to a resolution limit of 1.6 A. The X-ray intensities were measured from powder patterns recorded from collections of the single crystals. The structure crystallizes in a monoclinic unit cell with parameters a = 25.71 A, b = 10.21 A, c (chain axis) = 7.76 A and beta = 91.3 degrees. The space group is P2(1) with b axis unique. The unit cell contains six chains and eight water molecules, with three chains of the same polarity and four water molecules constituting the asymmetric unit. Along the chain direction the asymmetric unit is a dimer residue; however, the individual glucopyranose residues are very nearly related by a molecular 2-fold screw axis. The conformation of the chain is very similar to that in the anhydrous structure, but the chain packing differs in the two structures in that the rotational positions of the chains about the helix axes (the chain setting angles) are considerably different. The chains still pack in the form of sheets that are separated by water molecules. The difference in the chain setting angles between the anhydrous and hydrate structures corresponds to the angle between like unit cell axes observed in the diffraction diagrams recorded from hybrid crystals containing both polymorphs. Despite some beam damage effects, the structure was determined to a satisfactory degree of agreement, with the residuals R''(electron diffraction) = 0.258 and R(X-ray) = 0.127.

Structural analysis of β-glucosidase mutants derived from a hyperthermophilic tetrameric structure

PubMed Central

Nakabayashi, Makoto; Kataoka, Misumi; Mishima, Yumiko; Maeno, Yuka; Ishikawa, Kazuhiko

2014-01-01

β-Glucosidase from Pyrococcus furiosus (BGLPf) is a hyperthermophilic tetrameric enzyme which can degrade cellooligosaccharides to glucose under hyperthermophilic conditions and thus holds promise for the saccharification of lignocellulosic biomass at high temperature. Prior to the production of large amounts of this enzyme, detailed information regarding the oligomeric structure of the enzyme is required. Several crystals of BGLPf have been prepared over the past ten years, but its crystal structure had not been solved until recently. In 2011, the first crystal structure of BGLPf was solved and a model was constructed at somewhat low resolution (2.35 Å). In order to obtain more detailed structural data on BGLPf, the relationship between its tetrameric structure and the quality of the crystal was re-examined. A dimeric form of BGLPf was constructed and its crystal structure was solved at a resolution of 1.70 Å using protein-engineering methods. Furthermore, using the high-resolution crystal structural data for the dimeric form, a monomeric form of BGLPf was constructed which retained the intrinsic activity of the tetrameric form. The thermostability of BGLPf is affected by its oligomeric structure. Here, the biophysical and biochemical properties of engineered dimeric and monomeric BGLPfs are reported, which are promising prototype models to apply to the saccharification reaction. Furthermore, details regarding the oligomeric structures of BGLPf and the reasons why the mutations yielded improved crystal structures are discussed. PMID:24598756

Self-assembly of nematic liquid crystal elastomer filaments

NASA Astrophysics Data System (ADS)

Wei, Wei-Shao; Xia, Yu; Yang, Shu; Yodh, A. G.

In this work we investigate the self-assembly of nematic liquid crystal polymer (NLCP) filaments and their corresponding cross-linked elastomer structures. Specifically, by fine-tuning surfactant concentration, prepolymer chain length, and temperature within a background aqueous phase we can generate filaments composed of oligomerized LC monomers. Filaments with narrowly dispersed diameters ranging from one hundred nanometers to a few micrometers can be obtained. Using polarization optical microscopy, we show that the nematic LCs within the filaments have an escaped radial structure. After photo-cross-linking, nematic liquid crystal elastomer filaments are obtained with well-maintained directors and smooth surface structure. Since these materials are elastomers, the size and mechanical and optical response of the filaments can be ''tuned'' near the nematic to isotropic phase transition temperature. This work is supported by NSF DMR16-07378, PENN MRSEC Grant DMR11-20901, and NASA Grant NNX08AO0G.

Method of forming a joint

DOEpatents

Butt, Darryl Paul; Cutler, Raymond Ashton; Rynders, Steven Walton; Carolan, Michael Francis

2006-08-22

A method of joining at least two sintered bodies to form a composite structure, including providing a first multicomponent metallic oxide having a perovskitic or fluorite crystal structure; providing a second sintered body including a second multicomponent metallic oxide having a crystal structure of the same type as the first; and providing at an interface a joint material containing at least one metal oxide containing at least one metal identically contained in at least one of the first and second multicomponent metallic oxides. The joint material is free of cations of Si, Ge, Sn, Pb, P and Te and has a melting point below the sintering temperatures of both sintered bodies. The joint material is heated to a temperature above the melting point of the metal oxide(s) and below the sintering temperatures of the sintered bodies to form the joint. Structures containing such joints are also disclosed.

Temperature driven structural-memory-effects in carbon nanotubes filled with Fe3C nano crystals

NASA Astrophysics Data System (ADS)

Boi, Filippo S.; Zhang, Xiaotian; Corrias, Anna

2018-02-01

We report the observation of novel temperature-driven structural-memory-effects in carbon nanotubes (CNTs) filled with Fe3C nano-crystals. These structural-transitions were measured by means of temperature (T) dependent x-ray diffraction (XRD) in the T-range from 298 K to 12 K. A clear reversible 2θ-shift in the 002-peak of the graphitic-CNTs-walls is found with the decrease of the temperature. As determined by Rietveld refinement, such 2θ-shift translates in a not previously reported decrease in the value of the CNT graphitic c-axis with the decrease of the temperature (from 298 K to 12 K). Also, a clear reversible 2θ-shift in the 031 and 131 diffraction-peaks of Fe3C is observed within the same T-range. Rietveld refinements confirm the existence of such memory-effect and also reveal a gradual decrease of the 010-axis of Fe3C with the decrease of the temperature. These observations imply that the observed structural-memory-effect is a characteristic of CNTs when Fe3C is the encapsulated ferromagnet. The generality of such memory-effects was further confirmed by additional measurements performed on other types of CNTs characterized by continuous Fe3C-filling. XRD measurements in the T-range from 298 K to 673 K revealed also an unusual reversible decrease of the Fe3C-peak intensities with the increase of the temperature. These observations can have important implications on the magnetic data recording applications of these nanostructures by helping in better understanding the unusual temperature-dependent magnetic instabilities of iron-based nano-crystals which have been recently reported in literature.

Dry-growth of silver single-crystal nanowires from porous Ag structure

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

Chen, Chuantong, E-mail: chenchuantong@sanken.osaka-u.ac.jp; Nagao, Shijo; Jiu, Jinting

A fabrication method of single crystal Ag nanowires in large scale is introduced without any chemical synthesis in wet processes, which usually generates fivefold twinned nanowires of fcc metals. Dense single-crystal nanowires grow on a mechanically polished surface of micro-porous Ag structure, which is created from Ag micro-particles. The diameter and the length of the nanowires can be controlled simply by changing the temperature and the time of the heating during the nanowire growth in air. Unique growth mechanism is described in detail, based on stress-induced migration accelerated by the micro-porous structure where the origin of Ag nanowires growth ismore » incubated. Transmission electron microscopy analysis on the single crystal nanowires is also presented. This simple method offered an alternative preparation for metallic nanowires, especially with the single crystal structure in numerous applications.« less

Synthesis and structural study of N-isopropenylbenzimidazolone

NASA Astrophysics Data System (ADS)

Mondieig, D.; Negrier, Ph.; Leger, J. M.; Lakhrissi, L.; El Assyry, A.; Lakhrissi, B.; Essassi, E. M.; Benali, B.; Boucetta, A.

2015-05-01

The synthesis and the crystal structure of the N-isopropenylbenzimidazolone (C10H10N2O) are presented. The synthesis was performed by Meth-Cohen method by reaction of o-phenylenediamine with ethyl acetoacetate in refluxed xylene. The single crystal structure was determined at room temperature by means of X-rays diffraction. The crystal system is monoclinic, with space group C2/c and eight molecules per unit cell. The unit cell dimensions are: a = 15.978(1) Å, b = 6.100(2) Å, c = 18.222(2) Å, β = 90.16(1)° and V = 1776.0(6) Å3.

A Few Good Crystals Please

NASA Technical Reports Server (NTRS)

Judge, Russell A.; Snell, Edward H.

1999-01-01

Part of the challenge of macromolecular crystal growth for structure determination is obtaining an appropriate number of crystals with a crystal volume suitable for X-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of solution conditions on the nucleation rate and final crystal size of two crystal systems; tetragonal lysozyme and glucose isomerase. Batch crystallization plates were prepared at given solution concentration and incubated at set temperatures over one week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Duplicate experiments indicate the reproducibility of the technique. Results for each system showing the effect of supersaturation, incubation temperature and solution pH on nucleation rates will be presented and discussed. In the case of lysozyme, having optimized solution conditions to produce an appropriate number of crystals of a suitable size, a batch of crystals were prepared under exactly the same conditions. Fifty of these crystals were analyzed by x-ray techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.

Polymer-stabilized liquid crystal blue phases.

PubMed

Kikuchi, Hirotsugu; Yokota, Masayuki; Hisakado, Yoshiaki; Yang, Huai; Kajiyama, Tisato

2002-09-01

Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260-326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10(-4) s for the stabilized blue phases at room temperature.

Method and apparatus for conducting structural health monitoring in a cryogenic, high vibration environment

NASA Technical Reports Server (NTRS)

Qing, Xinlin (Inventor); Beard, Shawn J. (Inventor); Li, Irene (Inventor)

2013-01-01

Sensors affixed to various such structures, where the sensors can withstand, remain affixed, and operate while undergoing both cryogenic temperatures and high vibrations. In particular, piezoelectric single crystal transducers are utilized, and these sensors are coupled to the structure via a low temperature, heat cured epoxy. This allows the transducers to monitor the structure while the engine is operating, even despite the harsh operating conditions. Aspects of the invention thus allow for real time monitoring and analysis of structures that operate in conditions that previously did not permit such analysis. A further aspect of the invention relates to use of piezoelectric single crystal transducers. In particular, use of such transducers allows the same elements to be used as both sensors and actuators.

In situ X-ray data collection and structure phasing of protein crystals at Structural Biology Center 19-ID

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

Michalska, Karolina; Tan, Kemin; Chang, Changsoo

A prototype of a 96-well plate scanner forin situdata collection has been developed at the Structural Biology Center (SBC) beamline 19-ID, located at the Advanced Photon Source, USA. The applicability of this instrument for protein crystal diffraction screening and data collection at ambient temperature has been demonstrated. Several different protein crystals, including selenium-labeled, were used for data collection and successful SAD phasing. Without the common procedure of crystal handling and subsequent cryo-cooling for data collection atT= 100 K, crystals in a crystallization buffer show remarkably low mosaicity (<0.1°) until deterioration by radiation damage occurs. Data presented here show that cryo-coolingmore » can cause some unexpected structural changes. Based on the results of this study, the integration of the plate scanner into the 19-ID end-station with automated controls is being prepared. With improvement of hardware and software,in situdata collection will become available for the SBC user program including remote access.« less

Non-linear thermal evolution of the crystal structure and phase transitions of LaFeO{sub 3} investigated by high temperature X-ray diffraction

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

Selbach, Sverre M.; Tolchard, Julian R.; Fossdal, Anita

2012-12-15

The crystal structure, anisotropic thermal expansion and structural phase transition of the perovskite LaFeO{sub 3} has been studied by high-temperature X-ray diffraction from room temperature to 1533 K. The structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R3{sup Macron }c structure of LaFeO{sub 3} is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes. Non-linear lattice expansion across the antiferromagnetic to paramagnetic transition of LaFeO{sub 3} at T{sub N}=735 K was compared to the corresponding behavior of the ferroelectric antiferromagnet BiFeO{sub 3} to gain insight tomore » the magnetoelectric coupling in BiFeO{sub 3}, which is also multiferroic. The first order phase transition of LaFeO{sub 3} from Pbnm to R3{sup Macron }c was observed at 1228{+-}9 K, and a subsequent transition to Pm3{sup Macron }m was extrapolated to occur at 2140{+-}30 K. The stability of the Pbnm and R3{sup Macron }c polymorphs of LaFeO{sub 3} is discussed in terms of the competing enthalpy and entropy of the two crystal polymorphs and the thermal evolution of the polyhedral volume ratio V{sub A}/V{sub B}. - Graphical abstract: Aniostropic thermal evolution of the lattice parameters and phase transition of LaFeO{sub 3}. Highlights: Black-Right-Pointing-Pointer The crystal structure of LaFeO{sub 3} is studied by HTXRD from RT to 1533 K. Black-Right-Pointing-Pointer A non-linear expansion across the Neel temperature is observed for LaFeO{sub 3}. Black-Right-Pointing-Pointer The ratio V{sub A}/V{sub B} is used to rationalize the thermal evolution of the structure.« less

Magnetic and magnetostrictive behavior of Dy 3+ doped CoFe 2O 4 single crystals grown by flux method

NASA Astrophysics Data System (ADS)

Kambale, Rahul C.; Song, K. M.; Won, C. J.; Lee, K. D.; Hur, N.

2012-02-01

We studied the effect of Dy 3+ content on the magnetic properties of cobalt ferrite single crystal. The single crystals of CoFe 1.9Dy 0.1O 4 were grown by the flux method using Na 2B 4O 7.10 H 2O (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction analysis at room temperature confirmed the spinel cubic structure with lattice constant a=8.42 Å of the single crystals. The compositional analysis endorses the presence of constituents Co, Fe and Dy elements after sintering at 1300 °C within the final structure. The magnetic hysteresis measurements at various temperatures viz. 10 K, 100 K, 200 K and 300 K reveal the soft ferrimagnetic nature of the single crystal than that of for pure CoFe 2O 4. The observed saturation magnetization ( Ms) and coercivity ( Hc) are found to be lower than that of pure CoFe 2O 4 single crystal. The magnetostriction ( λ) measurement was carried out along the [001] direction. The magnetic measurements lead to conclude that the present single crystals can be used for magneto-optic recording media.

High-temperature/high-pressure x-ray diffraction: Recent developments

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

Schiferl, D.; Johnson, S.W.; Zinn, A.S.

1989-01-01

We have developed two Merrill-Bassett diamond-anvil cells for specialized high-temperature uses. The first is constructed largely of rhenium to provide uniform, constant P and T on the order of 20 GPa at 1200 K for extended periods. The second is for single-crystal x-ray diffraction, but can be heated to 630 K at 20 GPa to grow single-crystal samples which cannot be produced at room temperature. With this cell, the crystal structure of /var epsilon/-O/sub 2/ was shown to be monoclinic with a = 3.649 A, b = 5.493 A, c = 7.701 A, and /Beta/ = 116.11/degree/ at 19.7 GPa.more » 15 refs.« less

Understanding the structure of chocolate

NASA Astrophysics Data System (ADS)

Schenk, H.; Peschar, R.

2004-10-01

Crystallization of cocoa-butter in the β phase from the melt under static conditions is only possible using the memory effect of cocoa-butter. Under all other conditions polymorphs with lower melting temperatures develop, whereas the β phase is the preferred one in chocolate. SAXS experiments proved 1,3-distearoyl-2-oleoylglycerol seeds with triple chain-length packing initiate the β-crystallization. Models for the different phases may be based on the crystal structure determinations of triacylglycerols. A new, patented, way of chocolate making is in development in which the traditional tempering process is replaced by another pre-crystallization process. The process is based on the use of seed crystals in the liquid phase and driven by a feedback system.

Early structural development in melt-quenched polymer PTT from atomistic molecular dynamic simulations

NASA Astrophysics Data System (ADS)

Hsieh, Min-Kang; Lin, Shiang-Tai

2009-12-01

Molecular dynamics simulations are performed to study the initial structural development in poly(trimethylene terephthalate) (PTT) when quenched below its melting point. The development of local ordering has been observed in our simulations. The thermal properties, such as the glass transition temperature (Tg) and the melting temperature (Tm), determined from our simulations are in reasonable agreement with experimental values. It is found that, between these two temperatures, the number of local structures quickly increases during the thermal relaxation period soon after the system is quenched and starts to fluctuate afterwards. The formation and development of local structures is found to be driven mainly by the torsional and van der Waals forces and follows the classical nucleation-growth mechanism. The variation of local structures' fraction with temperature exhibits a maximum between Tg and Tm, resembling the temperature dependence of the crystallization rate for most polymers. In addition, the backbone torsion distribution for segments within the local structures preferentially reorganizes to the trans-gauche-gauche-trans (t-g-g-t) conformation, the same as that in the crystalline state. As a consequence, we believe that such local structural ordering could be the baby nuclei that have been suggested to form in the early stage of polymer crystallization.

[Effects of annealing temperature on the structure and optical properties of ZnMgO films prepared by atom layer deposition].

PubMed

Sun, Dong-Xiao; Li, Jin-Hua; Fang, Xuan; Chen, Xin-Ying; Fang, Fang; Chu, Xue-Ying; Wei, Zhi-Peng; Wang, Xiao-Hua

2014-07-01

In the present paper, we report the research on the effects of annealing temperature on the crystal quality and optical properties of ZnMgO films deposited by atom layer deposition(ALD). ZnMgO films were prepared on quartz substrates by ALD and then some of the samples were treated in air ambient at different annealing temperature. The effects of annealing temperature on the crystal quality and optical properties of ZnMgO films were characterized by X-ray diffraction (XRD), photoluminescence (PL) and ultraviolet-visible (UV-Vis) absorption spectra. The XRD results showed that the crystal quality of ZnMgO films was significantly improved when the annealing temperature was 600 degrees C, meanwhile the intensity of(100) diffraction peak was the strongest. Combination of PL and UV-Vis absorption measurements showed that it can strongly promote the Mg content increasing in ZnMgO films and increase the band gap of films. So the results illustrate that suitable annealing temperature can effectively improve the crystal quality and optical properties of ZnMgO films.

Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Hyatt, Mark J.; Drummond, Charles H., III

1991-01-01

Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glass transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder X ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structural transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Hyatt, Mark J.; Drummond, Charles H., III

1991-01-01

Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glasss transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder x ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structure transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

Molecular reorientation of a nematic liquid crystal by thermal expansion

PubMed Central

Kim, Young-Ki; Senyuk, Bohdan; Lavrentovich, Oleg D.

2012-01-01

A unique feature of nematic liquid crystals is orientational order of molecules that can be controlled by electromagnetic fields, surface modifications and pressure gradients. Here we demonstrate a new effect in which the orientation of nematic liquid crystal molecules is altered by thermal expansion. Thermal expansion (or contraction) causes the nematic liquid crystal to flow; the flow imposes a realigning torque on the nematic liquid crystal molecules and the optic axis. The optical and mechanical responses activated by a simple temperature change can be used in sensing, photonics, microfluidic, optofluidic and lab-on-a-chip applications as they do not require externally imposed gradients of temperature, pressure, surface realignment, nor electromagnetic fields. The effect has important ramifications for the current search of the biaxial nematic phase as the optical features of thermally induced structural changes in the uniaxial nematic liquid crystal mimic the features expected of the biaxial nematic liquid crystal. PMID:23072803

Crystallization Behavior of A Bulk Amorphous Mg62Cu26Y12 Alloy

NASA Astrophysics Data System (ADS)

Wu, Shyue-Sheng; Chin, Tsung-Shune; Su, Kuo-Chang

1994-07-01

The crystallization temperature, the associated activation energy and the crystallized structure of a bulk amorphous Mg62Cu26Y12 alloy with a diameter of 2.5 mm were studied. It possesses a one-step crystallization behavior. The crystallization reaction was found to be represented by: AM(MG62Cu26Y12)→Mg2Cu+MgY+CuY+Mg, ( Tx=188°C, Eac=134 kJ/mol) where AM represents the amorphous state, T x the crystallization temperature at an infinitesimal heating rate, and E ac the associated activation energy. The amount of crystalline phases were found to be Mg2Cu:MgY:CuY=76:17:7. The Mg phase is identifiable only by high resolution electron microscopy, not by X-ray diffraction. The crystallization leads to a sharp rise in electrical resistivity which is reversed to those of iron-based amorphous alloys.

Optical, Structural, and Thermal Properties of Cerium-Doped Zinc Borophosphate Glasses.

PubMed

Choi, Su-Yeon; Ryu, Bong-Ki

2015-11-01

In this study, we verify the relationship between the optical properties and structure of cerium-doped zinc borophosphate glasses that have concurrence of non-bridging oxygen (NBO) and bridging oxygen (BO), Ce3+ and Ce4+, and BO3 structure and BO4 structure. We prepared cerium-doped zinc borophosphate glass with various compositions, given by xCeO2-(100-x)[50ZnO-10B2O3 -40P2O5] (x = 1 mol% to 6 mol%), and analyzed their optical band energy, glass transition temperature, crystallization temperature, density, and molar volume. Some of the techniques used for analysis were Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In the investigated glasses, the optical band gap energy decreased from 3.28 eV to 1.73 eV. From these results, we can deduce the changes when transitions occur from BO to NBO, from Ce3+ to Ce4+, and from the BO3 structure to the BO4 structure with increasing CeO2 content using FT-IR and XPS analysis. We also verified the changes in structural and physical properties from quantitative properties such as glass transition temperature, crystallization temperature, density, and molar volume.

Effect of sintering temperature on physical, structural and optical properties of wollastonite based glass-ceramic derived from waste soda lime silica glasses

NASA Astrophysics Data System (ADS)

Almasri, Karima Amer; Sidek, Hj. Ab Aziz; Matori, Khamirul Amin; Zaid, Mohd Hafiz Mohd

The impact of different sintering temperatures on physical, optical and structural properties of wollastonite (CaSiO3) based glass-ceramics were investigated for its potential application as a building material. Wollastonite based glass-ceramics was provided by a conventional melt-quenching method and followed by a controlled sintering process. In this work, soda lime silica glass waste was utilized as a source of silicon. The chemical composition and physical properties of glass were characterized by using Energy Dispersive X-ray Fluorescence (EDXRF) and Archimedes principle. The Archimedes measurement results show that the density increased with the increasing of sintering temperature. The generation of CaSiO3, morphology, size and crystal phase with increasing the heat-treatment temperature were examined by field emission scanning electron microscopy (FESEM), Fourier transforms infrared reflection spectroscopy (FTIR), and X-ray diffraction (XRD). The average calculated crystal size gained from XRD was found to be in the range 60 nm. The FESEM results show a uniform distribution of particles and the morphology of the wollastonite crystal is in relict shapes. The appearance of CaO, SiO2, and Ca-O-Si bands disclosed from FTIR which showed the formation of CaSiO3 crystal phase. In addition to the calculation of the energy band gap which found to be increased with increasing sintering temperature.

Crystal structure and low-energy Einstein mode in ErV{sub 2}Al{sub 20} intermetallic cage compound

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

Winiarski, Michał J., E-mail: mwiniarski@mif.pg.gda.pl; Klimczuk, Tomasz

Single crystals of a new ternary aluminide ErV{sub 2}Al{sub 20} were grown using a self-flux method. The crystal structure was determined by powder X-ray diffraction measurements and Rietveld refinement, and physical properties were studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. These measurements reveal that ErV{sub 2}Al{sub 20} is a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment μ{sub eff} =9.27(1) μ{sub B} and Curie-Weiss temperature Θ{sub CW} =−0.55(4) K. The heat capacity measurements show a broad anomaly at low temperatures that is attributed to the presence of a low-energy Einstein mode withmore » characteristic temperature Θ{sub E} =44 K, approximately twice as high as in the isostructural ‘Einstein solid’ VAl{sub 10.1}. - Graphical abstract: A low-energy Einstein mode is observed in a novel intermetallic cage compound ErV{sub 2}Al{sub 20} by specific heat and resistivity measurements. - Highlights: • Single crystals of a new compound ErV{sub 2}Al{sub 20} were grown by self-flux method. • Crystal structure is reported, based on powder x-ray diffraction. • ErV{sub 2}Al{sub 20} is a Curie-Weiss paramagnet. • Low-energy ‘rattling’ phonon mode (Θ{sub E}=44 K) is found in specific heat measurements.« less

Room temperature syntheses, crystal structures and properties of two new heterometallic polymers based on 3-ethoxy-2-hydroxybenzaldehyde ligand

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

Zhang, Shu-Hua, E-mail: zsh720108@163.com; Zhao, Ru-Xiao; Li, Gui

Two new heterometallic coordination polymers [ZnNa(ehbd){sub 2}(N{sub 3})]{sub n} (1) and [Cu{sub 3}Na{sub 2}(ehbd){sub 2}(N{sub 3}){sub 6}]{sub n} (2) (Hehbd is 3-ethoxy-2-hydroxybenzaldehyde) have been synthesized under room temperature and structurally characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. Complex 1 crystallizes in the orthorhombic space group Pbca, showing a one-dimensional (1-D) chain. Complex 2 crystallizes in the triclinic space group Pī, constructing a heterometallic 2D layer structure. Luminescent properties and magnetic properties have been studied for 1 and 2, respectively and the fluorescence quantum yield of 1 is 0.077. - Highlights: • Two novel complexes 1more » and 2 have been synthesized. • Complex 1 represents a novel qualitative change of luminescence property. • Complex 2 displays ferromagnetic interaction through symmetric μ{sub 1,1}–N{sub 3} bridges. • Complex 2 displays anti-ferromagnetic interaction through asymmetric μ{sub 1,1}–N{sub 3} bridges.« less

Growth and dielectric, mechanical, thermal and etching studies of an organic nonlinear optical L-arginine trifluoroacetate (LATF) single crystal

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

Arjunan, S.; Department of Physics, Presidency College, Chennai 600005; Mohan Kumar, R.

2008-08-04

L-arginine trifluoroacetate, an organic nonlinear optical material, has been synthesized from aqueous solution. Bulk single crystal of dimension 57 mm x 5 mm x 3 mm has been grown by temperature lowering technique. Powder X-ray diffraction studies confirmed the monoclinic structure of the grown L-arginine trifluoroacetate crystal. Linear optical property of the grown crystal has been studied by UV-vis spectrum. Dielectric response of the L-arginine trifluoroacetate crystal was analysed for different frequencies and temperatures in detail. Microhardness study on the sample reveals that the crystal possesses relatively higher hardness compared to many organic crystals. Thermal analyses confirmed that the L-argininemore » trifluoroacetate material is thermally stable upto 212 deg. C. The etching studies have been performed to assess the perfection of the L-arginine trifluoroacetate crystal. Kurtz powder second harmonic generation test confirms the nonlinear optical properties of the as-grown L-arginine trifluoroacetate crystal.« less

Room temperature aluminum antimonide radiation detector and methods thereof

DOEpatents

Lordi, Vincenzo; Wu, Kuang Jen J.; Aberg, Daniel; Erhart, Paul; Coombs, III, Arthur W; Sturm, Benjamin W

2015-03-03

In one embodiment, a method for producing a high-purity single crystal of aluminum antimonide (AlSb) includes providing a growing environment with which to grow a crystal, growing a single crystal of AlSb in the growing environment which comprises hydrogen (H.sub.2) gas to reduce oxide formation and subsequent incorporation of oxygen impurities in the crystal, and adding a controlled amount of at least one impurity to the growing environment to effectively incorporate at least one dopant into the crystal. In another embodiment, a high energy radiation detector includes a single high-purity crystal of AlSb, a supporting structure for the crystal, and logic for interpreting signals obtained from the crystal which is operable as a radiation detector at a temperature of about 25.degree. C. In one embodiment, a high-purity single crystal of AlSb includes AlSb and at least one dopant selected from a group consisting of selenium (Se), tellurium (Te), and tin (Sn).

The impact of N,N-dimethyldodecylamine N-oxide (DDAO) concentration on the crystallisation of sodium dodecyl sulfate (SDS) systems and the resulting changes to crystal structure, shape and the kinetics of crystal growth.

PubMed

Summerton, Emily; Hollamby, Martin J; Zimbitas, Georgina; Snow, Tim; Smith, Andrew J; Sommertune, Jens; Bettiol, Jeanluc; Jones, Christopher; Britton, Melanie M; Bakalis, Serafim

2018-05-19

At low temperatures stability issues arise in commercial detergent products when surfactant crystallisation occurs, a process which is not currently well-understood. An understanding of the phase transition can be obtained using a simple binary SDS (sodium dodecyl sulfate) + DDAO (N,N-dimethyldodecylamine N-oxide) aqueous system. It expected that the crystallisation temperature of an SDS system can be lowered with addition of DDAO, thus providing a route to improve detergent stability. Detergent systems are typically comprised of anionic surfactants, non-ionic surfactants and water. This study explores the crystallisation of a three component system consisting of sodium dodecyl sulfate (SDS), N,N-dimethyldodecylamine N-oxide (DDAO), and water using wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC) and confocal Raman microscopy. The presence of DDAO lowered the crystallisation temperature of a 20 wt% SDS system. For all aqueous mixtures of SDS + DDAO at low temperatures, SDS hydrated crystals, SDS.1/2H 2 O or SDS·H 2 O, formed. SDS hydrates comprising of layers of SDS separated by water layers. DDAO tended to reside in the vicinity of these SDS crystals. In the absence of DDAO an additional intermediary hydrate structure, SDS.1/8H 2 O, formed whereas for mixed SDS + DDAO systems no such structure was detected during crystallisation. Copyright © 2018. Published by Elsevier Inc.

The Effects of ph on Structural and Optical Characterization of Iron Oxide Thin Films

NASA Astrophysics Data System (ADS)

Tezel, Fatma Meydaneri; Özdemir, Osman; Kariper, I. Afşin

In this study, the iron oxide thin films have been produced by chemical bath deposition (CBD) method as a function of pH onto amorphous glass substrates. The surface images of the films were investigated with scanning electron microscope (SEM). The crystal structures, orientation of crystallization, crystallite sizes, and dislocation density i.e. structural properties of the thin films were analyzed with X-ray diffraction (XRD). The optical band gap (Eg), optical transmission (T%), reflectivity (R%), absorption coefficient (α), refraction index (n), extinction coefficient (k) and dielectric constant (ɛ) of the thin films were investigated depending on pH, deposition time, solution temperature, substrate temperature, thickness of the films by UV-VIS spectrometer.

Room-temperature serial crystallography using a kinetically optimized microfluidic device for protein crystallization and on-chip X-ray diffraction

PubMed Central

Heymann, Michael; Opthalage, Achini; Wierman, Jennifer L.; Akella, Sathish; Szebenyi, Doletha M. E.; Gruner, Sol M.; Fraden, Seth

2014-01-01

An emulsion-based serial crystallographic technology has been developed, in which nanolitre-sized droplets of protein solution are encapsulated in oil and stabilized by surfactant. Once the first crystal in a drop is nucleated, the small volume generates a negative feedback mechanism that lowers the supersaturation. This mechanism is exploited to produce one crystal per drop. Diffraction data are measured, one crystal at a time, from a series of room-temperature crystals stored on an X-ray semi-transparent microfluidic chip, and a 93% complete data set is obtained by merging single diffraction frames taken from different unoriented crystals. As proof of concept, the structure of glucose isomerase was solved to 2.1 Å, demonstrating the feasibility of high-throughput serial X-ray crystallography using synchrotron radiation. PMID:25295176

Structural characterization and physicochemical features of new hybrid compound containing chlorate anions of cadmate (II)

NASA Astrophysics Data System (ADS)

Lassoued, Mohamed Saber; Abdelbaky, Mohammed S. M.; Lassoued, Abdelmajid; Gadri, Abdellatif; Ammar, Salah; Ben Salah, Abdelhamid; García-Granda, Santiago

2017-08-01

The present paper reports the synthesis of a single crystal of a new organic-inorganic hybrid compound, with the formula (C6H14N2) CdCl4·H2O, by slow evaporation method at room temperature. It was characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Hirshfeld surface, spectroscopy measurement, thermal study and photoluminescence (PL) properties. A preliminary SCXRD structural analysis revealed that it crystallized in the monoclinic system (space group P21/c) with the following unit cell parameters: a = 12.95823(16) Å, b = 14.92449(16) Å, c = 7.13838(9) Å and β = 103.2108(12)° with Z = 4. The refinement converged to R = 0.0164 and ωR = 0.0393. Its atomic arrangement can be described as an alternation of organic and inorganic layers along the a-axis. The crystal packing was governed by the N-H⋯Cl and O-H⋯Cl hydrogen bonding interaction between the 1.2-diammoniumcyclohexane cations, the [CdCl42n-]n anions and water molecule. The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing the relative contribution of these interactions in the crystal structure quantitatively. Furthermore, the room temperature infrared (IR) spectrum of the title compound was recorded and analyzed on the basis of data found in the literature. Besides, the thermal analysis studies were performed, but no phase transition was found in the temperature range between 30 and 450 °C. The optical and PL properties of the compound were investigated in the solid state at room temperature and exhibited three bands at 225, 268 and 315 nm and a strong fluorescence at 443 nm.

High-frequency dielectric study of proustite crystals Ag3AsS3

NASA Astrophysics Data System (ADS)

Bordovsky, V. A.; Gunia, N. Yu; Castro, R. A.

2014-12-01

The dielectric properties of the crystals proustite in the frequency of 106-109 Hz and a temperature range of 173 to 473 K were studied. The dispersion of the dielectric parameters indicates the existence of non-Debye relaxation mechanism correlates with structural changes in the phase transition region. The charge transfer is temperature activated with an activation energy of 2.40 ± 0.01 eV.

Regulation of Silk Material Structure by Temperature-Controlled Water Vapor Annealing

PubMed Central

Hu, Xiao; Shmelev, Karen; Sun, Lin; Gil, Eun-Seok; Park, Sang-Hyug; Cebe, Peggy; Kaplan, David L.

2011-01-01

We present a simple and effective method to obtain refined control of the molecular structure of silk biomaterials through physical temperature-controlled water vapor annealing (TCWVA). The silk materials can be prepared with control of crystallinity, from a low content using conditions at 4°C (alpha-helix dominated silk I structure), to highest content of ~60% crystallinity at 100°C (beta-sheet dominated silk II structure). This new physical approach covers the range of structures previously reported to govern crystallization during the fabrication of silk materials, yet offers a simpler, green chemistry, approach with tight control of reproducibility. The transition kinetics, thermal, mechanical, and biodegradation properties of the silk films prepared at different temperatures were investigated and compared by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), uniaxial tensile studies, and enzymatic degradation studies. The results revealed that this new physical processing method accurately controls structure, in turn providing control of mechanical properties, thermal stability, enzyme degradation rate, and human mesenchymal stem cell interactions. The mechanistic basis for the control is through the temperature controlled regulation of water vapor, to control crystallization. Control of silk structure via TCWVA represents a significant improvement in the fabrication of silk-based biomaterials, where control of structure-property relationships is key to regulating material properties. This new approach to control crystallization also provides an entirely new green approach, avoiding common methods which use organic solvents (methanol, ethanol) or organic acids. The method described here for silk proteins would also be universal for many other structural proteins (and likely other biopolymers), where water controls chain interactions related to material properties. PMID:21425769

Phase transition in crystalline benzil : an infrared study of vibrational excitons.

NASA Astrophysics Data System (ADS)

Le Roy, A.; Et-Tabti, O.; Guérin, R.

1993-03-01

The molecular crystal of benzil, [C 6 H 5 CO] 2, is known to undergo a phase transition at T c = 84 K. The phase transition is from a high temperature trigonal phase with space group D 43 (P3 121) to a low temperature monoclinic phase with space group C 32 (C 2). This paper reports a study of the exciton structure of the infrared bands of benzil as a function of temperature in the vicinity of T c = 84 K. The benzil molecule belongs to the C 2 molecular point group. Group theoretical analysis of the exciton structure of infrared bands predicts two components for molecular B modes and one component for molecular A modes in the high temperature phase. Below T c all the internal modes of benzil are expected to split into two components. Our experimental results show that the A molecular modes are resolved in a doublet structure in the low temperature phase whereas only one component is observed above T c. The doublet structure of infrared bands is studied as a function of temperature in the vicinity of T c. These splittings of crystal states in the low temperature phase are found to be described by a ¦T c - T¦ β law. The temperature dependence of the doublet structure of internal B modes is also studied below and above T c.

Concerted ligand exchange and the roles of counter anions in the reversible structural switching of crystalline peptide metallo-macrocycles.

PubMed

Miyake, Ryosuke; Shionoya, Mitsuhiko

2014-06-02

To understand reversible structural switching in crystalline materials, we studied the mechanism of reversible crystal-to-crystal transformation of a tetranuclear Ni(II) macrocycle consisting of artificial β-dipeptides. On the basis of detailed structural analyses and thermodynamic measurements made in a comparison of pseudo-isostructural crystals (NO3 and BF4 salts), we herein discuss how ligand-exchange reactions take place in the crystal due to changes in water content and temperature. Observations of the structural transformation of NO3 salt indicated that a pseudo crystalline phase transformation takes place through concerted ligand-exchange reactions at the four Ni(II) centers of the macrocycle with hydrogen bond switching. A mechanism for this ligand exchange was supported by IR spectroscopy. Thermodynamic measurements suggested that the favorable compensation relationship of the enthalpy changes due to water uptake and structural changes are keys to the reversible structural transformation. On the basis of a comparison with the pseudo-isostructural crystals, it is apparent that the crystal packing structure and the types of counter anions are important factors for facilitating reversible ligand exchange with single crystallinity.

Remote Sensing of Crystal Shapes in Ice Clouds

NASA Technical Reports Server (NTRS)

van Diedenhoven, Bastiaan

2017-01-01

Ice crystals in clouds exist in a virtually limitless variation of geometries. The most basic shapes of ice crystals are columnar or plate-like hexagonal prisms with aspect ratios determined by relative humidity and temperature. However, crystals in ice clouds generally display more complex structures owing to aggregation, riming and growth histories through varying temperature and humidity regimes. Crystal shape is relevant for cloud evolution as it affects microphysical properties such as fall speeds and aggregation efficiency. Furthermore, the scattering properties of ice crystals are affected by their general shape, as well as by microscopic features such as surface roughness, impurities and internal structure. To improve the representation of ice clouds in climate models, increased understanding of the global variation of crystal shape and how it relates to, e.g., location, cloud temperature and atmospheric state is crucial. Here, the remote sensing of ice crystal macroscale and microscale structure from airborne and space-based lidar depolarization observations and multi-directional measurements of total and polarized reflectances is reviewed. In addition, a brief overview is given of in situ and laboratory observations of ice crystal shape as well as the optical properties of ice crystals that serve as foundations for the remote sensing approaches. Lidar depolarization is generally found to increase with increasing cloud height and to vary with latitude. Although this variation is generally linked to the variation of ice crystal shape, the interpretation of the depolarization remains largely qualitative and more research is needed before quantitative conclusions about ice shape can be deduced. The angular variation of total and polarized reflectances of ice clouds has been analyzed by numerous studies in order to infer information about ice crystal shapes from them. From these studies it is apparent that pristine crystals with smooth surfaces are generally inconsistent with the data and thus crystal impurity, distortion or surface roughness is prevalent. However, conclusions about the dominating ice shapes are often inconclusive and contradictory and are highly dependent on the limited selection of shapes included in the investigations. Since ice crystal optical properties are mostly determined by the aspect ratios of the crystal components and their microscale structure, it is advised that remote sensing applications focus on the variation of these ice shape characteristics, rather than on the macroscale shape or habit. Recent studies use databases with nearly continuous ranges of crystal component aspect ratio and-or roughness levels to infer the variation of ice crystal shape from satellite and airborne remote sensing measurements. Here, the rationale and results of varying strategies for the remote sensing of ice crystal shape are reviewed. Observed systematic variations of ice crystal geometry with location, cloud height and atmospheric state suggested by the data are discussed. Finally, a prospective is given on the future of the remote sensing of ice cloud particle shapes.

Crystal structures and infrared spectra of two Fe-bearing hydrous magnesium silicates synthesized at high temperature and pressure

NASA Technical Reports Server (NTRS)

Yang, H.; Prewitt, C. T.; Liu, Z.

2002-01-01

The synthesis and characterization of Fe-bearing phase E and phase E' demonstrate that the phase E-type structures can be rather compliant and complex, and that as we further explore the temperature-pressure-composition space, other types of structures that are similar to or related to the structure of phase E may be discovered.

Nanoscale-driven crystal growth of hexaferrite heterostructures for magnetoelectric tuning of microwave semiconductor integrated devices.

PubMed

Hu, Bolin; Chen, Zhaohui; Su, Zhijuan; Wang, Xian; Daigle, Andrew; Andalib, Parisa; Wolf, Jason; McHenry, Michael E; Chen, Yajie; Harris, Vincent G

2014-11-25

A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25-40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals was found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ∼150 K for Co2Y ferrite, compared to 5-10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on a wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.

High-pressure crystal structures of an insensitive energetic crystal: 1,1-diamino-2,2-dinitroethene

DOE PAGES

Dreger, Zbigniew A.; Stash, Adam I.; Yu, Zhi -Gang; ...

2015-12-03

Understanding the insensitivity/stability of insensitive high explosive crystals requires detailed structural information at high pressures and high temperatures of interest. Synchrotron single crystal x-ray diffraction experiments were used to determine the high-pressure structures of 1,1-diamino-2,2-dinitroethene (FOX-7), a prototypical insensitive high explosive. The phase transition around 4.5 GPa was investigated and the structures were determined at 4.27 GPa (α’-phase) and 5.9 GPa (ε-phase). The α’-phase (monoclinic, P2 1/ n), structurally indistinguishable from the ambient α-phase, transforms to the new ε-phase (triclinic, P1). The most notable features of the ε-phase, compared to the α’-phase, are: formation of planar layers and flattening ofmore » molecules. Density functional theory (DFT-D2) calculations complemented the experimental results. Furthermore, the results presented here are important for understanding the molecular and crystalline attributes governing the high-pressure insensitivity/stability of insensitive high explosive crystals.« less

High-pressure crystal structures of an insensitive energetic crystal: 1,1-diamino-2,2-dinitroethene

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

Dreger, Zbigniew A.; Stash, Adam I.; Yu, Zhi -Gang

Understanding the insensitivity/stability of insensitive high explosive crystals requires detailed structural information at high pressures and high temperatures of interest. Synchrotron single crystal x-ray diffraction experiments were used to determine the high-pressure structures of 1,1-diamino-2,2-dinitroethene (FOX-7), a prototypical insensitive high explosive. The phase transition around 4.5 GPa was investigated and the structures were determined at 4.27 GPa (α’-phase) and 5.9 GPa (ε-phase). The α’-phase (monoclinic, P2 1/ n), structurally indistinguishable from the ambient α-phase, transforms to the new ε-phase (triclinic, P1). The most notable features of the ε-phase, compared to the α’-phase, are: formation of planar layers and flattening ofmore » molecules. Density functional theory (DFT-D2) calculations complemented the experimental results. Furthermore, the results presented here are important for understanding the molecular and crystalline attributes governing the high-pressure insensitivity/stability of insensitive high explosive crystals.« less

Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: Scavenger of free radicals

NASA Astrophysics Data System (ADS)

Fezai, Ramzi; Hemissi, Hanene; Mezni, Ali; Rzaigui, Mohamed

2017-12-01

Single crystal of the hybrid compound [p-(F)C6H4NH3]6P6O18·2H2O has been grown with sizes up to 0.65 × 0.45 × 0.3 mm3 by the slow evaporation method. The crystal structure of this material was determined by single crystal X-ray diffraction. It crystallizes in the triclinic space group P 1 bar with the lattice parameters a = 10.16(3) Å, b = 15.87(3) Å, c = 16.36(4) Å, α = 80.93(2)°, β = 85.92(18)°, γ = 85.31(2)°, V = 2591.1(12) Å3 and Z = 2. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a, c) planes. The cohesion of the structure is essentially ensured by a hydrogen bonding network as well as electrostatic and Van Der Waals interactions and also F…F interactions so as to increase the stability of the 3D-network. The effect of the nature of the substituent in para-position with respect to amine group on obtained structures and on other studied properties was discussed. Crystal symmetry is confirmed by 31P MAS-NMR. Furthermore, IR characteristics and thermal analysis are given. The luminescent properties of this material have been carried out at room temperature based on UV absorption spectroscopy data. AC conductivity of this compound has been investigated by means of impedance spectroscopy measurements in the 303-383 K temperature range. The antioxidant study was determined, in vitro, using 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical and reducing power and with ascorbic acid as a control. X-rays structural results are correlated with electrical and antioxidant findings.

Temperature dependence of Fe/++/ crystal field spectra - Implications to mineralogical mapping of planetary surfaces

NASA Technical Reports Server (NTRS)

Sung, C.-M.; Singer, R. B.; Parkin, K. M.; Burns, R. G.; Osborne, M.

1977-01-01

Results are reported of Fe(++) crystal field spectral measurements for olivines and pyroxenes up to 400 C. The results are correlated with crystal structure data at elevated temperatures, and the validity of remote-sensed identifications of minerals on hot surfaces of the moon and Mercury is assessed. Two techniques were used to obtain spectra of minerals at elevated temperatures using a spectrophotometer. One employed a diamond cell assembly or a specially designed sample holder to measure polarized absorption spectra of heated single crystals. For the other technique, a sample holder was designed to attach to a diffuse reflectance accessory to produce reflectance spectra of heated powdered samples. Polarized absorption spectra of forsterite at 20-400 C are shown in a graph. Other graphs show the temperature dependence of Fe(++) crystal field bands in olivines, the diffuse reflectance spectra of olivine at 40-400 C, the polarization absorption spectra of orthopyroxene at 30-400 C, the diffuse reflectance spectra of pigeonite at 40-400 C, and unpolarized absorption spectra of lunar pyroxene from Apollo 15 rock 15058.

A novel fabrication of Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell micro/nanocrystals from Cu{sub 2}O temples and enhanced photocatalytic activities

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

Li, Junqi, E-mail: sfmlab@163.com; Sun, Long; Yan, Ying

2016-08-15

Highlights: • The Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell crystals maintained the same morphology with template. • The crystals exhibit enhanced photocatalytic activity than the pure Cu{sub 2}O crystals. • The photocatalytic activity of different R crystals is diverse from each other. • A possible formation mechanism has been proposed. - Abstract: Uniform and monodispersed Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell micro/nanocrystals have been synthesized successfully at room temperature via a simple chemical etching reaction, using Cu{sub 2}O as sacrificial template. The structure and properties of the crystals were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM),more » X-ray photoelectron spectra (XPS). The photocatalytic activity of the Cu{sub 2}O@Cu{sub 7}S{sub 4} crystals was evaluated by photocatalytic decolorization of MeO (methyl orange) aqueous solution at ambient temperature under visible-light irradiation. The results show that the as-prepared Cu{sub 2}O@Cu{sub 7}S{sub 4} crystals revealed core-shell structure, which maintained the same morphology with corresponding template and were composed of cuboctahedron Cu{sub 7}S{sub 4} shell and active Cu{sub 2}O core. Due to the unique Cu{sub 2}O@Cu{sub 7}S{sub 4} core-shell structure, the crystals exhibit enhanced photocatalytic activity than that of the pure Cu{sub 2}O crystals, and the photocatalytic activity of different R crystals is diverse from each other. A possible formation mechanism has been proposed.« less

Structural versus electrical properties of an organic-inorganic hybrid material based on sulfate

NASA Astrophysics Data System (ADS)

Ben Rached, Asma; Guionneau, Philippe; Lebraud, Eric; Mhiri, Tahar; Elaoud, Zakaria

2017-01-01

A new organo-sulfate compound is obtained by slow evaporation at room temperature and is characterized by powder and single-crystal X-ray diffraction (XRD) at variable temperatures. The benzylammonium monohydrogenosulfate of formula C6H5CH2NH3+. HSO4-, denoted (BAS), crystallizes in the monoclinic system P21/c space group with the following parameters at room temperature: a=5.623(5)Å, b=20.239(5) Å, c=8.188(5)Å, β=94.104(5)°. The crystal structure consists of infinite parallel two-dimensional planes built by HSO4- anions and C6H5CH2NH3+ cations interconnected by strong O-H….. O and N-H….. O hydrogen bonds. A phase transition is detected at 350 K by differential scanning calorimetry (DSC) and confirmed by powder XRD. Conductivity measurements using the impedance spectroscopy technique allow to determine the conductivity relaxation parameters associated with the H+ conduction from an analysis of the M"/M"max spectrum measured in a wide temperature range. Transport properties of this material appear to be due to an H+ ion hopping mechanism.

Dew Point Calibration System Using a Quartz Crystal Sensor with a Differential Frequency Method

PubMed Central

Lin, Ningning; Meng, Xiaofeng; Nie, Jing

2016-01-01

In this paper, the influence of temperature on quartz crystal microbalance (QCM) sensor response during dew point calibration is investigated. The aim is to present a compensation method to eliminate temperature impact on frequency acquisition. A new sensitive structure is proposed with double QCMs. One is kept in contact with the environment, whereas the other is not exposed to the atmosphere. There is a thermal conductivity silicone pad between each crystal and a refrigeration device to keep a uniform temperature condition. A differential frequency method is described in detail and is applied to calibrate the frequency characteristics of QCM at the dew point of −3.75 °C. It is worth noting that frequency changes of two QCMs were approximately opposite when temperature conditions were changed simultaneously. The results from continuous experiments show that the frequencies of two QCMs as the dew point moment was reached have strong consistency and high repeatability, leading to the conclusion that the sensitive structure can calibrate dew points with high reliability. PMID:27869746

Structure of an LiKSO 4 single crystal studied by 7Li and 39K NMR at low temperature

NASA Astrophysics Data System (ADS)

Lim, A. R.; Jeong, S.-Y.

2000-09-01

The 7Li and 39K nuclear magnetic resonances in an LiKSO 4 single crystal grown by the slow evaporation method have been investigated using a Bruker FT nuclear magnetic resonance (NMR) spectrometer. From the experimental data, the quadrapole coupling constant and asymmetry parameter were determined at room temperature and low temperature, respectively. Unlike the case at 300 K, the 7Li NMR line consists of three sets at 180 K, while 39K nucleus exhibits six sets for the rotation around the three crystallographic axes. The three resonance lines of 7Li and 39K at low temperature can be explained by the existence of three kinds of twin domain, rotated with respect to each other by 120° around the c-axis. The three resonance lines are also related to the crystallographic mirror plane. Structure of ferroelastic LiKSO 4 crystals at 180 K can be directly inferred from the domain pattern obtained by 7Li and 39K NMR. The above results show that the equations of the twin boundaries belong to the mm2 F6 mm ferroelastic species. Therefore, the symmetry of phases III and II is given by orthorhombic structure with Cmc2 1 ( mm2) and hexagonal structural with P6 3mc (6 mm), respectively.

Highly Conducting Molecular Crystals.

NASA Astrophysics Data System (ADS)

Whitehead, Roger James

Available from UMI in association with The British Library. Requires signed TDF. As the result of a wide ranging effort towards the preparation of new electrically conducting molecular crystals, high quality samples were prepared of the organic radical-ion salt (TMTSF)_2SbCl _2F_4 {bis-tetramethyltetraselenafulvalene-dichlorotetrafluoroantimonate(V) }. A collaborative effort to investigate the electronic and structural properties of this material has yielded the necessary depth of information required to give a satisfactory understanding of its rather complicated behaviour. The combination of x-ray structural studies with d.c. transport, reflectance and magnetic measurements has served to underline the importance of crystalline perfection, electronic dimensionality and conduction electron correlation in determining the materials overall behaviour. This thesis describes the method of preparation and characterization of (TMTSF)_2SbCl _2F_4 and the experimental arrangements used to determine the temperature dependence of its ambient pressure electrical conductivity, thermopower and electron spin resonance spectra. The crystal structure and optical reflectance measurements at room temperature are also presented. The results into a study of the low temperature diffraction pattern are described along with the temperature dependence in the static magnetic susceptibility and in the conductivity behaviour under elevated hydrostatic pressures. These findings are rationalized by reference to other materials which show similar behaviour in their electronic and/or structural properties, and also to the various theoretical models currently enjoying favour.

Temperature Dependent Surface Structures and Electronic Properties of Organic-Inorganic Hybrid Perovskite Single Crystals

NASA Astrophysics Data System (ADS)

Jao, M.-H.; Teague, M. L.; Huang, J.-S.; Tseng, W.-S.; Yeh, N.-C.

Organic-inorganic hybrid perovskites, arising from research of low-cost high performance photovoltaics, have become promising materials not only for solar cells but also for various optoelectronic and spintronic applications. An interesting aspect of the hybrid perovskites is that their material properties, such as the band gap, can be easily tuned by varying the composition, temperature, and the crystalline phases. Additionally, the surface structure is critically important for their optoelectronic applications. It is speculated that different crystalline facets could show different trap densities, thus resulting in microscopically inhomogeneous performance. Here we report direct studies of the surface structures and electronic properties of hybrid perovskite CH3NH3PbI3 single crystals by scanning tunneling microscopy and spectroscopy (STM/STS). We found long-range spatially homogeneous tunneling conductance spectra with a well-defined energy gap of (1.55 +/- 0.1) eV at 300 K in the tetragonal phase, suggesting high quality of the single crystals. The energy gap increased to (1.81 +/- 0.1) eV in the orthorhombic phase, below the tetragonal-to-orthorhombic phase transition temperature at 150 K. Detailed studies of the temperature evolution in the spatially resolved surface structures and local density of states will be discussed to elucidate how these properties may influence the optoelectronic performance of the hybrid perovskites. We thank the support from NTU in Taiwan and from NSF in the US.

Special Features of the Structure of Single-Crystal Refractory Nickel Alloy Under Directed Crystallization

NASA Astrophysics Data System (ADS)

Bondarenko, Yu. A.; Echin, A. B.; Surova, V. A.; Kolodyazhnyi, M. Yu.

2017-05-01

The effect of the conditions of directed crystallization (the temperature gradient and the crystallization rate) on the dendrite spacing, on the size of the particles of the hardening γ'-phase in the arms and arm spaces of the dendrites, on the volume fraction and size of the pores, on the size of the particles of the eutectic γ/γ'-phase, and on the features of dendritic segregation in a single-crystal castable refractory alloy is studied.

Influence of growth temperature on properties of zirconium dioxide films grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Kukli, Kaupo; Ritala, Mikko; Aarik, Jaan; Uustare, Teet; Leskela, Markku

2002-08-01

ZrO2 films were grown by atomic layer deposition from ZrCl4 and H2O or a mixture of H2O and H2O2 on Si(100) substrates in the temperature range of 180-600 degC. The films were evaluated in the as-deposited state, in order to follow the effect of deposition temperature on the film quality. The rate of crystal growth increased and the content of residual impurities decreased with increasing temperature. The zirconium-to-oxygen atomic ratio, determined by ion-beam analysis, corresponded to the stoichiometric dioxide regardless of the growth temperature. The effective permittivity of ZrO2 in Al/ZrO2/Si capacitor structures increased from 13-15 in the films grown at 180 degC to 19 in the films grown at 300-600 degC, measured at 100 kHz. The permittivity was relatively high in the crystallized films, compared to the amorphous ones, but rather insensitive to the crystal structure. The permittivity was higher in the films grown using water. The leakage current density tended to be lower and the breakdown field higher in the films grown using hydrogen peroxide.

How Sensitive Is the Elasticity of Hydroxyapatite-Nanoparticle-Reinforced Chitosan Composite to Changes in Particle Concentration and Crystallization Temperature?

PubMed

Wang, Kean; Liao, Kin; Goh, Kheng Lim

2015-10-10

Hydroxyapatite (HA) nanoparticle-reinforced chitosan composites are biocompatible and biodegradable structural materials that are used as biomaterials in tissue engineering. However, in order for these materials to function effectively as intended, e.g., to provide adequate structural support for repairing damaged tissues, it is necessary to analyse and optimise the material processing parameters that affect the relevant mechanical properties. Here we are concerned with the strength, stiffness and toughness of wet-spun HA-reinforced chitosan fibres. Unlike previous studies which have addressed each of these parameters as singly applied treatments, we have carried out an experiment designed using a two-factor analysis of variance to study the main effects of two key material processing parameters, namely HA concentration and crystallization temperature, and their interactions on the respective mechanical properties of the composite fibres. The analysis reveals that significant interaction occurs between the crystallization temperature and HA concentration. Starting at a low HA concentration level, the magnitude of the respective mechanical properties decreases significantly with increasing HA concentration until a critical HA concentration is reached, at around 0.20-0.30 (HA mass fraction), beyond which the magnitude of the mechanical properties increases significantly with HA concentration. The sensitivity of the mechanical properties to crystallization temperature is masked by the interaction between the two parameters-further analysis reveals that the dependence on crystallization temperature is significant in at least some levels of HA concentration. The magnitude of the mechanical properties of the chitosan composite fibre corresponding to 40 °C is higher than that at 100 °C at low HA concentration; the reverse applies at high HA concentration. In conclusion, the elasticity of the HA nanoparticle-reinforced chitosan composite fibre is sensitive to HA concentration and crystallization temperature, and there exists a critical concentration level whereby the magnitude of the mechanical property is a minimum.

Exchange-Hole Dipole Dispersion Model for Accurate Energy Ranking in Molecular Crystal Structure Prediction.

PubMed

Whittleton, Sarah R; Otero-de-la-Roza, A; Johnson, Erin R

2017-02-14

Accurate energy ranking is a key facet to the problem of first-principles crystal-structure prediction (CSP) of molecular crystals. This work presents a systematic assessment of B86bPBE-XDM, a semilocal density functional combined with the exchange-hole dipole moment (XDM) dispersion model, for energy ranking using 14 compounds from the first five CSP blind tests. Specifically, the set of crystals studied comprises 11 rigid, planar compounds and 3 co-crystals. The experimental structure was correctly identified as the lowest in lattice energy for 12 of the 14 total crystals. One of the exceptions is 4-hydroxythiophene-2-carbonitrile, for which the experimental structure was correctly identified once a quasi-harmonic estimate of the vibrational free-energy contribution was included, evidencing the occasional importance of thermal corrections for accurate energy ranking. The other exception is an organic salt, where charge-transfer error (also called delocalization error) is expected to cause the base density functional to be unreliable. Provided the choice of base density functional is appropriate and an estimate of temperature effects is used, XDM-corrected density-functional theory is highly reliable for the energetic ranking of competing crystal structures.

Rotating lattice single crystal architecture on the surface of glass

DOE PAGES

Savytskii, D.; Jain, H.; Tamura, N.; ...

2016-11-03

Defying the requirements of translational periodicity in 3D, rotation of the lattice orientation within an otherwise single crystal provides a new form of solid. Such rotating lattice single (RLS) crystals are found, but only as spherulitic grains too small for systematic characterization or practical application. Here we report a novel approach to fabricate RLS crystal lines and 2D layers of unlimited dimensions via a recently discovered solid-to-solid conversion process using a laser to heat a glass to its crystallization temperature but keeping it below the melting temperature. The proof-of-concept including key characteristics of RLS crystals is demonstrated using the examplemore » of Sb 2S 3 crystals within the Sb-S-I model glass system for which the rotation rate depends on the direction of laser scanning relative to the orientation of initially formed seed. Lattice rotation in this new mode of crystal growth occurs upon crystallization through a well-organized dislocation/disclination structure introduced at the glass/ crystal interface. Implications of RLS growth on biomineralization and spherulitic crystal growth are noted.« less

Low-temperature crystallization of anodized TiO2 nanotubes at the solid-gas interface and their photoelectrochemical properties

NASA Astrophysics Data System (ADS)

Liu, Jing; Liu, Zhaoyue; Zhang, Tierui; Zhai, Jin; Jiang, Lei

2013-06-01

TiO2 nanotubular arrays formed by electrochemical anodization have attracted significant attention for photoelectrochemical applications that utilize solar energy. However, the as-anodized TiO2 nanotubes are amorphous, and need to be crystallized by high-temperature thermal annealing. Herein, we describe a low-temperature hydrothermal solid-gas route to crystallize TiO2 nanotubes. In this process, the as-anodized TiO2 hydroxo nanotubes are dehydrated to yield anatase phase via solid-gas interface reaction in an autoclave at a temperature of less than 180 °C. The solid-gas interface reaction alleviates the collapse of as-anodized TiO2 nanotubes during hydrothermal process efficiently. Compared with the common thermal annealing at the same temperature but at atmospheric pressure, the hydrothermal route improves the photocurrent density of TiO2 nanotubes by ~10 times in KOH electrolyte. The duration of the hydrothermal reaction has a substantial effect on the photoelectrochemical properties of TiO2 nanotubes, which is ascribed to the synergetic effect between the crystallization and structural evolution. Electron donors can further suppress the charge recombination in the low-temperature crystallized TiO2 nanotubes and boost the photocurrent density by ~120%.TiO2 nanotubular arrays formed by electrochemical anodization have attracted significant attention for photoelectrochemical applications that utilize solar energy. However, the as-anodized TiO2 nanotubes are amorphous, and need to be crystallized by high-temperature thermal annealing. Herein, we describe a low-temperature hydrothermal solid-gas route to crystallize TiO2 nanotubes. In this process, the as-anodized TiO2 hydroxo nanotubes are dehydrated to yield anatase phase via solid-gas interface reaction in an autoclave at a temperature of less than 180 °C. The solid-gas interface reaction alleviates the collapse of as-anodized TiO2 nanotubes during hydrothermal process efficiently. Compared with the common thermal annealing at the same temperature but at atmospheric pressure, the hydrothermal route improves the photocurrent density of TiO2 nanotubes by ~10 times in KOH electrolyte. The duration of the hydrothermal reaction has a substantial effect on the photoelectrochemical properties of TiO2 nanotubes, which is ascribed to the synergetic effect between the crystallization and structural evolution. Electron donors can further suppress the charge recombination in the low-temperature crystallized TiO2 nanotubes and boost the photocurrent density by ~120%. Electronic supplementary information (ESI) available: Morphology images of TiO2 nanotubular arrays crystallized by hydrothermal solid-liquid reaction at 130 °C, 160 °C and 180 °C for 4 h. Cross-sectional image of TiO2 nanotubular arrays prepared by anodizing Ti foil at 20 V for 20 min in 0.5 wt% HF solution followed by drying in air at 100 °C for 1 h; Photocurrent density-potential curves of TiO2 nanotubular arrays crystallized by thermal annealing at 450 °C and atmospheric pressure for 4 h. See DOI: 10.1039/c3nr01286g

Characterization of crystal forms of β-estradiol thermal analysis, Raman microscopy, X-ray analysis and solid-state NMR

NASA Astrophysics Data System (ADS)

Variankaval, N. E.; Jacob, K. I.; Dinh, S. M.

2000-08-01

The structure and select crystalline properties of a common drug (estradiol) used in a transdermal drug delivery system are investigated. Four different crystal forms of estradiol (EA, EC, ED and EM) were prepared in the laboratory and characterized by thermal analysis, optical microscopy, Raman microspectroscopy, and solid-state NMR. Variable temperature X-ray studies were carried out on form A (EA) to determine whether the crystal structure changed as a function of temperature. These four forms exhibited different thermal behavior. EA and EC had similar melting points. This study clearly shows that water cannot be released from the crystal lattice of EA unless melting is achieved, and exposing EA to temperatures below the melting point only results in a partial release of hydrogen bonded water. EC was prepared by melting EA and subsequently cooling it to room temperature. Form EC was anhydrous, as it did not exhibit water loss, as opposed to EA, which had about 3.5% water in its crystal structure. ED was very difficult to prepare and manifested itself only as a mixture with EC. Its melting point was about 10°C lower than that of EC. It is thought to be an unstable form due to its simultaneous occurrence with EC and the inability to isolate it. EM is a solvate of methanol, not a polymorph. Its melting point was similar to EA and EC. From thermogravimetry/differential thermal analysis and differential scanning calorimetry data, it was apparent that estradiol formed a hemisolvate with methanol. All four forms had different morphologies. Raman microscopy was carried out on the different crystal forms. The spectra of EC and ED were almost identical. Thermal analysis revealed that this is due to the highly unstable nature of ED and its tendency to either convert spontaneously to EC or occur in mixtures with it.

Synthesis, crystal structure and luminescent properties of a new pyrochlore type tungstate CsGa0.333W1.667O6

NASA Astrophysics Data System (ADS)

Zhao, Dan; Zhao, Ji; Fan, Yun-Chang; Ma, Zhao; Zhang, Rui-Juan; Liu, Bao-Zhong

2018-06-01

High temperature solution reaction leads to a new tungstate compound CsGa0.333W1.667O6, whose structure was determined by single-crystal X-ray diffraction analysis. The results show that it crystallizes in pyrochlore structure with cubic space group Fd-3m and a = 10.2529 (13) Å. In this structure, Ga and W atoms are in a statistical disorder manner. The self-activated luminescent properties CsGa0.333W1.667O6 were studied. Under the excitation of 323 nm, the emission spectrum exhibits a blue emission centered at 466 nm with the chromaticity coordinates (0.1838, 0.1814).

Vibrational spectroscopic studies of an organic non-linear optical crystal 8-hydroxyquinolinium picrate

NASA Astrophysics Data System (ADS)

Krishna Kumar, V.; Nagalakshmi, R.

2007-04-01

8-Hydroxyquinolinium picrate (8-HQP) was synthesized by the addition of equimolar quantities of 8-hydroxyquinoline (8-HQ) and picric acid (PA). Single crystals were grown from N, N dimethyl formamide (DMF) by restricted evaporation method at room temperature. The solubility of 8-HQP was determined in different solvents at various temperatures. The structural characterization of the grown crystals was carried out by X-ray diffraction. Vibrational modes were classified on the basis of group theoretical analysis and the spectral bands were compared with those of parent compounds in order to propose a tentative assignment by recording FT-IR, FT-Raman and polarized Raman spectra in different crystal orientations. The crystal possess lower cut-off at 230 nm and good transparency as confirmed by optical transmittance studies.

Crystal structure and phase transitions of sodium potassium niobate perovskites

NASA Astrophysics Data System (ADS)

Tellier, J.; Malic, B.; Dkhil, B.; Jenko, D.; Cilensek, J.; Kosec, M.

2009-02-01

This paper presents the crystal structure and the phase transitions of K xNa 1- xNbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100-800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic-tetragonal and tetragonal-cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

The Conformational Flexibility of the Acyltransferase from the Disorazole Polyketide Synthase Is Revealed by an X-ray Free-Electron Laser Using a Room-Temperature Sample Delivery Method for Serial Crystallography

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

Mathews, Irimpan I.; Allison, Kim; Robbins, Thomas

The crystal structure of the trans-acyltransferase (AT) from the disorazole polyketide synthase (PKS) was determined at room temperature to a resolution of 2.5 Å using a new method for sample delivery directly into an X-ray free-electron laser. A novel sample extractor efficiently delivered limited quantities of microcrystals directly from the native crystallization solution into the X-ray beam at room temperature. The AT structure revealed important catalytic features of this core PKS enzyme, including the occurrence of conformational changes around the active site. The implications of these conformational changes on polyketide synthase reaction dynamics are discussed.

The Conformational Flexibility of the Acyltransferase from the Disorazole Polyketide Synthase Is Revealed by an X-ray Free-Electron Laser Using a Room-Temperature Sample Delivery Method for Serial Crystallography

DOE PAGES

Mathews, Irimpan I.; Allison, Kim; Robbins, Thomas; ...

2017-08-23

The crystal structure of the trans-acyltransferase (AT) from the disorazole polyketide synthase (PKS) was determined at room temperature to a resolution of 2.5 Å using a new method for sample delivery directly into an X-ray free-electron laser. A novel sample extractor efficiently delivered limited quantities of microcrystals directly from the native crystallization solution into the X-ray beam at room temperature. The AT structure revealed important catalytic features of this core PKS enzyme, including the occurrence of conformational changes around the active site. The implications of these conformational changes on polyketide synthase reaction dynamics are discussed.

Crystal structure and magnetic properties of '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' containing residual {alpha}-Fe prepared by low-temperature ammonia nitridation

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

Yamashita, S.; Masubuchi, Y.; Nakazawa, Y.

2012-10-15

Slight enhancement of saturation magnetization to 219 A m{sup 2} kg{sup -1} was observed from 199 A m{sup 2} kg{sup -1} for the original {alpha}-Fe on the intermediate nitrided mixture of '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' with residual {alpha}-Fe among the low temperature ammonia nitridation products under 5 T magnetic field at room temperature. The value changed not linearly against the yield as had been expected. Crystal structure refinement indicated that the phase similar to {alpha} Prime Prime -Fe{sub 16}N{sub 2} had deviations on its lattice constants and positional parameters, compared to previously reported values for {alpha} Prime Primemore » -Fe{sub 16}N{sub 2}. Spin-polarized total energy calculations were performed using the projector-augmented wave method as implemented in the Vienna ab-initio simulation package (VASP) to calculate magnetic moment on the refined crystal structure of the intermediate '{alpha} Prime Prime -Fe{sub 16}N{sub 2}'. The calculations supported the observed magnetization enhancement in the intermediate nitridation product. - Graphical abstract: Crystal structural parameters slightly change in the intermediate nitrided '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' from those in {alpha} Prime Prime -Fe{sub 16}N{sub 2} to show the magnetization maxima in the mixture of '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' and the residual {alpha}-F. Highlights: Black-Right-Pointing-Pointer Larger magnetization was observed than the value of Fe{sub 16}N{sub 2} on its intermediate nitrided mixture with residual {alpha}-Fe. Black-Right-Pointing-Pointer The enhancement was related to the crystal structural deviation from Fe{sub 16}N{sub 2} on the intermediate nitride. Black-Right-Pointing-Pointer It was supported by spin-polarized total energy calculation using the deviated structure.« less

Prediction of the As-Cast Structure of Al-4.0 Wt Pct Cu Ingots

NASA Astrophysics Data System (ADS)

Ahmadein, Mahmoud; Wu, M.; Li, J. H.; Schumacher, P.; Ludwig, A.

2013-06-01

A two-stage simulation strategy is proposed to predict the as-cast structure. During the first stage, a 3-phase model is used to simulate the mold-filling process by considering the nucleation, the initial growth of globular equiaxed crystals and the transport of the crystals. The three considered phases are the melt, air and globular equiaxed crystals. In the second stage, a 5-phase mixed columnar-equiaxed solidification model is used to simulate the formation of the as-cast structure including the distinct columnar and equiaxed zones, columnar-to-equiaxed transition, grain size distribution, macrosegregation, etc. The five considered phases are the extradendritic melt, the solid dendrite, the interdendritic melt inside the equiaxed grains, the solid dendrite, and the interdendritic melt inside the columnar grains. The extra- and interdendritic melts are treated as separate phases. In order to validate the above strategy, laboratory ingots (Al-4.0 wt pct Cu) are poured and analyzed, and a good agreement with the numerical predictions is achieved. The origin of the equiaxed crystals by the "big-bang" theory is verified to play a key role in the formation of the as-cast structure, especially for the castings poured at a low pouring temperature. A single-stage approach that only uses the 5-phase mixed columnar-equiaxed solidification model and ignores the mold filling can predict satisfactory results for a casting poured at high temperature, but it delivers false results for the casting poured at low temperature.

Structural variations and dielectric properties of (Bi1-xL ax ) 2Si O5 (0 ≤x ≤0.1 ): Polycrystallines synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses

NASA Astrophysics Data System (ADS)

Taniguchi, Hiroki; Tatewaki, Shingo; Yasui, Shintaro; Fujii, Yasuhiro; Yamaura, Jun-ichi; Terasaki, Ichiro

2018-04-01

This paper focuses on effects of isovalent La substitution on the crystal structure and dielectric properties of ferroelectric B i2Si O5 . Polycrystalline samples of (Bi1-xL ax ) 2Si O5 are synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses with a composition range of 0 ≤x ≤0.1 . The crystal structure changes from monoclinic to tetragonal with increasing La-substitution rate x at room temperature. This structural variation stems from the change in orientation of Si O4 tetrahedra that form one-dimensional chains when they are in the ordered configuration, thus suggesting that lone-pair electrons play an important role in sustaining one-dimensional chains of Si O4 tetrahedra. Synchronizing with the disordering of Si O4 chains, ferroelectric phase transition temperature of (Bi1-xL ax ) 2Si O5 sharply decreases as x increases, and ferroelectricity finally vanishes at around x =0.03 . The present results demonstrate that lone-pair electrons of Bi play an important role in the ferroelectricity of B i2Si O5 through propping the ordered structure of one-dimensional Si O4 chains with stereochemical activity. Furthermore, an additional phase transition has been first discovered in the low-temperature region of (Bi1-xL ax ) 2Si O5 with x ≤0.01 , where the ordered one-dimensional Si O4 chains remain.

A novel organic nonlinear optical crystal: Creatininium succinate

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

Thirumurugan, R.; Anitha, K., E-mail: singlecerystalxrd@gmail.ciom

2015-06-24

A novel organic material complex of creatininium succinate (CS) has been synthesized and single crystals were grown by the reaction of creatinine and succinic acid from aqueous solution by employing the technique of slow evaporation at room temperature. The structure of the grown crystal has been elucidated using single crystal X-ray diffraction analysis and the structure was refined by least-squares method to R = 0.027 for 1840 reflections. FT-IR spectral investigation has been carried out to identify the various functional groups in the title compound. UV–Vis transmission was carried out which shows the crystal has a good optical transmittance inmore » the visible region with lower cutoff wavelength around 220 nm. Nonlinear optical property of the crystal was confirmed by Kurtz-Perry powder technique.« less

Structure and high-pressure behavior of 2,5-di-(4-aminophenyl)-1,3,4-oxadiazole

NASA Astrophysics Data System (ADS)

Franco, Olga; Orgzall, Ingo; Reck, Günter; Stockhause, Sabine; Schulz, Burkhard

2005-06-01

The crystalline structures of two modifications of a compound containing the oxadiazole ring, 2,5-di-(4-aminophenyl)-1,3,4-oxadiazole (DAPO) were determined. One of these modifications contains water molecules in the crystal structure, which is observed for the first time for an oxadiazole crystal. Both crystals show an orthorhombic structure. The water free modification, DAPO I, belongs to the space group Pbca (61) and has the lattice parameters: a=13.461(5), b=7.937(3) and c=22.816(8) Å (CCDC 246608). The water containing pseudo-polymorph, DAPO II, has the space group Cmcm (63) and the lattice parameters: a=16.330(5), b=12.307(2) and c=6.9978(14) Å (CCDC 246609). To gain information on the inter molecular interactions within the crystals, X-ray experiments under compression at ambient temperature and under heating at vacuum conditions were performed. Neither DAPO I nor DAPO II undergo phase transitions in the ressure range up to 5 GPa, as could be concluded from X-ray and Raman experiments. X-ray and calorimetric studies indicate that DAPO II dehydrates into DAPO I under increasing temperature. Structural considerations suggest a two-stage process. The compression behavior of both substances is well described by the Murnaghan equation of state (MEOS) and the values of the bulk modulus and its pressure derivative are determined for these crystals. Additionally, in the case of DAPO I, also the thermal expansion coefficient α0 was measured.

Crystal and Vibrational Structure of Energetic 3,5-dinitro 1,3,5-oxadiazinane (DOD) by Single Crystal X-ray Diffractometry and Raman Spectroscopy

DTIC Science & Technology

2018-03-19

calculations using a temperature of 298 K. 15. SUBJECT TERMS 3,5-dinitro-1,3,5-oxadiazinane (DOD), X-ray crystallography , Raman, energetic material...X-ray analysis. 2.2 Characterization X-ray Crystallography . DOD crystals were characterized with a SuperNova, Dualflex, EosS2 diffractometer using

The Surface Layer of a Crystal and Its Specific Role in the Process of Melt Formation

NASA Astrophysics Data System (ADS)

Sobolev, R. N.

2018-04-01

A crystal becomes melted in a few stages. The structure of the crystal surface differs from that of its interior. Therefore, as its interior is gradually involved in the melting process, the phase transition temperature becomes higher. The melting point becomes constant when all atoms have the same number of unsaturated bonds.

Optical Characterization of Lead Monoxide Films Grown by Laser-Assisted Deposition

NASA Astrophysics Data System (ADS)

Baleva, M.; Tuncheva, V.

1994-05-01

The Raman spectra of PbO films, grown by laser-assisted deposition (LAD) at different substrate temperatures are investigated. The spectra of the films, deposited on amorphous, single crystal quartz and polycrystal PbTe substrates, are compared with the Raman spectra of tetragonal and orthorhombic powder samples. The phonon frequencies determined in our experiment with powder samples coincide fairly well with those obtained by Adams and Stevens, J. Chem. Soc., Dalton Trans., 1096 (1977). Thus the Raman spectra of the powder samples presented in this paper can be considered as unambiguous characteristics of the two different PbO crystal phases. It was concluded that the Raman scattering may serve as a tool for identification of PbO films and their crystal modifications. On the basis of this investigation it was concluded that the film structure changes from orthorhombic to tetragonal with increased substrate temperature, and that the nature of the substrate influences the crystal structure of the films. On the basis of the Raman spectra of the β-PbO films with prevailing (001) orientation of crystallization, an assignment of the modes is proposed.

Melt Flow before Crystal Seeding in Cz Si Growth with Transversal MF

NASA Astrophysics Data System (ADS)

Iizuka, Masaya; Mukaiyama, Yuji; Demina, S. E.; Kalaev, V. V.

2017-06-01

Industrial Cz growth of Si crystal of 300 mm and higher diameter usually requires DC magnetic fields (MFs) to suppress turbulence in the melt. We present 3D unsteady analysis of melt turbulent convection in an industrial Cz system coupled with the effect of the transversal MF for different argon gas flow rates for the stage before crystal seeding. We have performed detailed 2D axisymmetric modeling of global heat transfer in the whole Cz furnace. Radiative heat fluxes obtained in 2D modeling have been used in detailed 3D steady and unsteady modeling of crystallization zone. LES method is applied as a predictive approach for modeling of turbulent flow of silicon melt. We have obtained flow structure and temperature distribution in the melt, which were different from previously reported data. We have observed a well-fixed dark spike which includes low temperature melt area on the melt free surface in MF cases. These results indicates that MF and argon flow rate conditions are important to achieve stable positioning of the dark spike on the melt free surface for optimized crystal seeding without uncontrollable meltdown and single crystal structure loss.

Structural, mechanical and light yield characterisation of heat treated LYSO:Ce single crystals for medical imaging applications

NASA Astrophysics Data System (ADS)

Mengucci, P.; André, G.; Auffray, E.; Barucca, G.; Cecchi, C.; Chipaux, R.; Cousson, A.; Davì, F.; Di Vara, N.; Rinaldi, D.; Santecchia, E.

2015-06-01

Five single crystals of cerium-doped lutetium yttrium oxyorthosilicate (LYSO:Ce) grown by the Czochralski method were submitted to structural characterisation by X-ray (XRD) and neutron (ND) diffraction, scanning (SEM) and transmission (TEM) electron microscopy and energy dispersive microanalysis (EDS). The Ultimate Tensile Strength (UTS), the Young Modulus (YM) and the Light Yield (LY) of the samples were also measured in order to correlate the mechanical and the optical behaviour of the crystals with the characteristics of their microstructure. Two of the samples analysed were also heat treated at 300 °C for 10 h to evidence possible variations induced by the temperature in the optical and mechanical response of the crystals. Results showed that the mean compositional variations evidenced by the structural analyses do not affect the mechanical and optical behaviour of the samples. On the contrary, the thermal treatment could induce the formation of coherent spherical particles (size 10 to 15 nm), not uniformly distributed inside the sample, that strongly reduce the UTS and YM values, but it does not affect the optical response of the crystal. This latter result was attributed to the low value of the heating temperature (300 °C) that is not sufficiently high to induce annealing of the oxygen vacancies traps that are responsible of the deterioration of the scintillation properties of the LYSO:Ce crystals. This study was carried out in the framework of the Crystal Clear Collaboration (CCC).

Synthesis, crystal structure and characterization of a new organic-inorganic hybrid material 4-(ammonium methyl) pipyridinium hexachloro stanate (II) trihydrate

NASA Astrophysics Data System (ADS)

Lassoued, Mohamed Saber; Abdelbaky, Mohammed S. M.; Lassoued, Abdelmajid; Ammar, Salah; Gadri, Abdellatif; Ben Salah, Abdelhamid; García-Granda, Santiago

2018-03-01

The present paper undertakes the study of (C6H16N2) SnCl6·3H2O which is a new hybrid compound. It was prepared and characterized by single crystal X-ray diffraction, X-ray powder, Hirshfeld surface, Spectroscopy measurement, thermal study and photoluminescence properties. The single crystal X-ray diffraction studies revealed that the compound crystallizes in monoclinic Cc space group with cell parameters a = 8.3309(9) Å, b = 22.956(2) Å, c = 9.8381(9) Å, β = 101.334(9) ° and Z = 4. The atomic arrangement shows an alternation of organic and inorganic entities. The cohesion between these entities is performed via Nsbnd H⋯Cl, Nsbnd H⋯O, Osbnd H⋯Cl and Osbnd H⋯O hydrogen bonding to form a three-dimensional network. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D finger plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. The X-ray powder is in agreement with the X-ray structure. Scanning electron microscope (SEM) was carried out. Furthermore, the room temperature infrared (IR) spectrum of the title compound was recorded and analyzed on the basis of data found in the literature. Solid state 13C NMR spectrum shows four signals, confirming the solid state structure determined by X-ray diffraction. Besides, the thermal analysis studies were performed, but no phase transition was found in the temperature range between 30 and 450 °C. The optical and PL properties of the compound were investigated in the solid state at room temperature and exhibited three bands at 348 and 401 cm-1 and a strong fluorescence at 480 nm.

Comparing two tetraalkylammonium ionic liquids. II. Phase transitions

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

Lima, Thamires A.; Paschoal, Vitor H.; Faria, Luiz F. O.

Phase transitions of the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N{sub 1114}][NTf{sub 2}], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N{sub 1444}][NTf{sub 2}], were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, and Raman spectroscopy. XRD and Raman spectra were obtained as a function of temperature at atmospheric pressure, and also under high pressure at room temperature using a diamond anvil cell (DAC). [N{sub 1444}][NTf{sub 2}] experiences glass transition at low temperature, whereas [N{sub 1114}][NTf{sub 2}] crystallizes or not depending on the cooling rate. Both the ionic liquids exhibit glass transition under high pressure. XRD and low-frequency Raman spectra provide a consistent physical picturemore » of structural ordering-disordering accompanying the thermal events of crystallization, glass transition, cold crystallization, pre-melting, and melting. Raman spectra in the high-frequency range of some specific cation and anion normal modes reveal conformational changes of the molecular structures along phase transitions.« less

Structural defects caused by swift ions in fluorite single crystals

NASA Astrophysics Data System (ADS)

Assylbayev, Ruslan; Lushchik, Aleksandr; Lushchik, Cheslav; Kudryavtseva, Irina; Shablonin, Evgeni; Vasil'chenko, Evgeni; Akilbekov, Abdirash; Zdorovets, Maxim

2018-01-01

A comparative study of radiation damage caused by the irradiation of oxygen-free calcium fluoride single crystals with ∼GeV 132Xe or 209Bi heavy ions, 100-keV light hydrogen ions (protons) or X-rays at room temperature has been performed. Optical absorption in a wide spectral region from NIR to VUV (1.5-10.5 eV), its dependence on stepwise preheating of the irradiated CaF2 crystals to a certain temperature as well as thermally stimulated luminescence accompanying the main annealing stages have been analyzed. It is shown that in addition to different F-type aggregates, Ca colloids and trifluorine quasi-molecules, complex and temperature stable structural defects responsible for VUV absorption (in particular, the 9.8 eV band) are induced in CaF2 only after irradiation with swift heavy ions. The origin and tentative creation mechanisms of such defects as well as the features of the used irradiation types are considered.

Superheating Suppresses Structural Disorder in Layered BiI3 Semiconductors Grown by the Bridgman Method

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

Johns, Paul M.; Sulekar, Soumitra; Yeo, Shinyoung

2016-01-01

The susceptibility of layered structures to stacking faults is a problem in some of the more attractive semiconductor materials for ambient-temperature radiation detectors. In the work presented here, Bridgman-grown BiI3 layered single crystals are investigated to understand and eliminate this structural disorder, which reduces radiation detector performance. The use of superheating gradients has been shown to improve crystal quality in non-layered semiconductor crystals; thus the technique was here explored to improve the growth of BiI3. When investigating the homogeneity of non-superheated crystals, highly geometric void defects were found to populate the bulk of the crystals. Applying a superheating gradient tomore » the melt prior to crystal growth improved structural quality and decreased defect density from the order of 4600 voids per cm3 to 300 voids per cm3. Corresponding moderate improvements to electronic properties also resulted from the superheat gradient method of crystal growth. Comparative measurements through infrared microscopy, etch-pit density, x-ray rocking curves, and sheet resistivity readings show that superheat gradients in BiI3 growth led to higher quality crystals.« less

Temperature induced phase transformations and negative electrocaloric effect in (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric single crystal

NASA Astrophysics Data System (ADS)

Zhuo, Fangping; Li, Qiang; Yan, Qingfeng; Zhang, Yiling; Wu, Hong-Hui; Xi, Xiaoqing; Chu, Xiangcheng; Cao, Wenwu

2017-10-01

Temperature induced phase transitions and electrocaloric effect (ECE) of (Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals have been comprehensively studied. Based on the in situ evolution of domain structures and dielectric properties of the PLZST crystals, the phase transitions during heating are in the sequence of orthorhombic antiferroelectric → rhombohedral ferroelectric → cubic paraelectric. Coexistence of the negative and positive ECEs has been achieved in the PLZST single crystals. A negative ECE value of -1.26 °C and enhanced electrocaloric strength of -0.21 K mm/kV near the Curie temperature have been obtained. A modified Landau model gives a satisfactory description of the experimentally observed unusual ECE. Moreover, a temperature-electric field phase diagram is also established based on theoretical analysis. Our results will help people understand better the electrocaloric family, particularly on the negative and/or positive effect in antiferroelectrics and ferroelectrics.

Heat capacity, resistivity, and angular dependent magnetization studies of single crystal Nd 1 + ϵ Fe 4 B 4 for ϵ ≈ 1 7

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

Conner, Benjamin S.; Susner, Michael A.; UES Inc., Beavercreek, OH

Advances in crystal growth have allowed for synthesis of large single crystals of Nd 1+ϵFe 4B 4, a well-known phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd 1+ϵFe 4B 4 sample with a distribution of ϵ that skews towards the solubility limit of Nd near ϵ ≈ 17. Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previouslymore » reported values in the Nd 1+ϵFe 4B 4 system. Here, we also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed.« less

Heat capacity, resistivity, and angular dependent magnetization studies of single crystal Nd 1 + ϵ Fe 4 B 4 for ϵ ≈ 1 7

DOE PAGES

Conner, Benjamin S.; Susner, Michael A.; UES Inc., Beavercreek, OH; ...

2017-04-04

Advances in crystal growth have allowed for synthesis of large single crystals of Nd 1+ϵFe 4B 4, a well-known phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd 1+ϵFe 4B 4 sample with a distribution of ϵ that skews towards the solubility limit of Nd near ϵ ≈ 17. Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previouslymore » reported values in the Nd 1+ϵFe 4B 4 system. Here, we also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed.« less

Crystal structure, phase transition and structural deformations in iron borate (Y0.95Bi0.05)Fe3(BO3)4 in the temperature range 90-500 K.

PubMed

Smirnova, Ekaterina S; Alekseeva, Olga A; Dudka, Alexander P; Artemov, Vladimir V; Zubavichus, Yan V; Gudim, Irina A; Bezmaterhykh, Leonard N; Frolov, Kirill V; Lyubutin, Igor S

2018-04-01

An accurate X-ray diffraction study of (Y 0.95 Bi 0.05 )Fe 3 (BO 3 ) 4 single crystals in the temperature range 90-500 K was performed on a laboratory diffractometer and used synchrotron radiation. It was established that the crystal undergoes a diffuse structural phase transition in the temperature range 350-380 K. The complexity of localization of such a transition over temperature was overcome by means of special analysis of systematic extinction reflections by symmetry. The transition temperature can be considered to be T str ≃ 370 K. The crystal has a trigonal structure in the space group P3 1 21 at temperatures of 90-370 K, and it has a trigonal structure in the space group R32 at 375-500 K. There is one type of chain formed by the FeO 6 octahedra along the c axis in the R32 phase. When going into the P3 1 21 phase, two types of nonequivalent chains arise, in which Fe atoms are separated from the Y atoms by a different distance. Upon lowering the temperature from 500 to 90 K, a distortion of the Y(Bi)O 6 , FeO 6 , B(2,3)O 3 coordination polyhedra is observed. The distances between atoms in helical Fe chains and Fe-O-Fe angles change non-uniformly. A sharp jump in the equivalent isotropic displacement parameters of O1 and O2 atoms within the Fe-Fe chains and fluctuations of the equivalent isotropic displacement parameters of B2 and B3 atoms were observed in the region of structural transition as well as noticeable elongation of O1, O2, B2, B3, Fe1, Fe2 atomic displacement ellipsoids. It was established that the helices of electron density formed by Fe, O1 and O2 atoms may be structural elements determining chirality, optical activity and multiferroicity of rare-earth iron borates. Compression and stretching of these helices account for the symmetry change and for the manifestation of a number of properties, whose geometry is controlled by an indirect exchange interaction between iron cations that compete with the thermal motion of atoms in the structure. Structural analysis detected these changes as variations of a number of structural characteristics in the c unit-cell direction, that is, the direction of the helices. Structural results for the local surrounding of the atoms in (Y 0.95 Bi 0.05 )Fe 3 (BO 3 ) 4 were confirmed by EXAFS and Mössbauer spectroscopies.

Phase transformations in SrAl2Si2O8 glass

NASA Technical Reports Server (NTRS)

Drummond, Charles H., III; Bansal, Narottam P.

1992-01-01

Bulk glass of SrAl2Si2O8 composition crystallized at temperatures below 1000 C into hexacelsian, a hexagonal phase which undergoes a reversible, rapid transformation to an orthorhombic phase at 758 C, and at higher temperatures crystallized as celsian, a monoclinic phase. The glass transition temperature and crystallization onset temperature were determined to be 883 C and 1086 C, respectively, from DSC at a heating rate of 20 C/min. Thermal expansion of the various phases and density and bend strengths of cold isostatically pressed glass powder bars, sintered at various temperatures, were measured. The kinetics of the hexacelsian-to-celsian transformation for SrAl2Si2O8 were studied. Hexacelsian flakes were isothermally heat treated at temperatures from 1025-1200 C for various times. Avrami plots were determined by quantitatively measuring the amount of monoclinic celsian formed at various times using x ray diffraction. The Avrami constant was determined to be 1.1, suggesting a diffusionless, one dimensional transformation mechanism. The activation energy was determined from an Arrhenius plot of 1n k vs. 1/T to be 125 kilocal/mole. This value is consistent with a mechanism which transforms the layered hexacelsian structure to a three dimensional framework celsian structure and involves the breaking of Si-O bonds.

Optical properties of Mn 2+ in KCaF 3 single crystal

NASA Astrophysics Data System (ADS)

Mazurak, Z.; Ratuszna, A.; Daniel, Ph.

1999-02-01

It is known that the spectroscopic properties of 3d impurities in crystals are very sensitive to the environment of the ion and can be changed considerably by using different matrices. The crystal structure of KCaF 3 has been previously determined by the Rietveld profile method. At room temperature, KCa 1- xMn xF 3 ( x<0.1) crystallizes in monoclinic C2 h ( B2 1/ m) symmetry. The local geometries around Mn 2+ in this crystals, in their ground and excited states, are the primary properties that govern the spectroscopic behavior of these systems, which enjoy of fundamental and technological interest. The present work reports the absorption and luminescence spectra of the Mn 2+-doped KCaF 3 (fluoroperovskite). The luminescence spectra recorded over a range of temperatures are dominated by wide bands, corresponding to the 4T 1(G)→ 6A 1(G), Mn 2+ transition. The lifetime ( τ= f( T)) of the first excited state 4T 1(G) was measured as a function of temperature. The lifetime of the Mn 2+ emission, in this crystal have been found to be temperature independent ( τ<7 μs). The absorption and emission spectra of Mn 2+ (3d 5) in KCaF 3 are analyzed using a C4 crystal-field hamiltonian. The calculated energy levels are in good agreement with those obtained experimentally. The resulting crystal-field parameters Bnm are a good representation of the crystal-field interactions of Mn 2+ in KCaF 3.

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

NASA Astrophysics Data System (ADS)

Kalkan, B.; Edwards, T. G.; Raoux, S.; Sen, S.

2013-08-01

The structural, thermodynamic, and kinetic aspects of the transformations between the metastable amorphous and crystalline phases of GaSb are investigated as a function of pressure at ambient temperature using synchrotron x-ray diffraction experiments in a diamond anvil cell. The results are consistent with the hypothesis that the pressure induced crystallization of amorphous GaSb into the β-Sn crystal structure near ˜5 GPa is possibly a manifestation of an underlying polyamorphic phase transition between a semiconducting, low density and a metallic, high density amorphous (LDA and HDA, respectively) phases. In this scenario, the large differences in the thermal crystallization kinetics between amorphous GaSb deposited in thin film form by sputtering and that prepared by laser melt quenching may be related to the relative location of the glass transition temperature of the latter in the pressure-temperature (P-T) space with respect to the location of the critical point that terminate the LDA ↔ HDA transition. The amorphous → β-Sn phase transition is found to be hysteretically reversible as the β-Sn phase undergoes decompressive amorphization near ˜2 GPa due to the lattice instabilities that give rise to density fluctuations in the crystal upon decompression.

Single crystal growth, magnetic and thermal properties of perovskite YFe0.6Mn0.4O3 single crystal

NASA Astrophysics Data System (ADS)

Xie, Tao; Shen, Hui; Zhao, Xiangyang; Man, Peiwen; Wu, Anhua; Su, Liangbi; Xu, Jiayue

2016-11-01

High quality YFe0.6Mn0.4O3 single crystal was grown by floating zone technique using a four-mirror-image-furnace under flowing air. Powder X-ray diffraction gives well evidence that the specimen has an orthorhombic structure, with space group Pbnm. Temperature dependence of the magnetizations of YFe0.6Mn0.4O3 single crystal were studied under ZFC and FC modes in the temperature range from 5 K to 400 K. A clear spin reorientation transition behavior (Γ4→Γ1) is observed in the temperature range of 322-316 K, due to the substitution of Mn at the Fe site of YFeO3. Its Néel temperature is around 385 K. Moreover, the spin reorientation is verified by the change of magnetic hysteresis loops of the sample along [001] axis in the temperature range of 50-385 K. The thermal properties of the sample were measured by the differential scanning calorimeter (DSC) from 300 K to 500 K, which also clearly appear anomaly in the spin reorientation region.

Synthesis and temperature dependent Raman studies of large crystalline faces topological GeBi4Te7 single crystal

NASA Astrophysics Data System (ADS)

Mal, Priyanath; Bera, G.; Turpu, G. R.; Srivastava, Sunil K.; Das, Pradip

2018-05-01

We present a study of structural and vibrational properties of topological insulator GeBi4Te7. Modified Bridgeman technique is employed to synthesize the single crystal with relatively large crystalline faces. Sharp (0 0 l) reflection confirms the high crystallinity of the single crystal. We have performed temperature dependent Raman measurement for both parallel and perpendicular to crystallographic c axis geometry. In parallel configuration we have observed seven Raman modes whereas in perpendicular geometry only four of these are identified. Appearance and disappearance of Raman modes having different intensities for parallel and perpendicular to c measurement attribute to the mode polarization. Progressive blue shift is observed with lowering temperature, reflects the increase in internal stress.

Electrical characteristics of organic perylene single-crystal-based field-effect transistors

NASA Astrophysics Data System (ADS)

Lee, Jin-Woo; Kang, Han-Saem; Kim, Min-Ki; Kim, Kihyun; Cho, Mi-Yeon; Kwon, Young-Wan; Joo, Jinsoo; Kim, Jae-Il; Hong, Chang-Seop

2007-12-01

We report on the fabrication of organic field-effect transistors (OFETs) using perylene single crystal as the active material and their electrical characteristics. Perylene single crystals were directly grown from perylene powder in a furnace using a relatively short growth time of 1-3 h. The crystalline structure of the perylene single crystals was characterized by means of a single-crystal x-ray diffractometer. In order to place the perylene single crystal onto the Au electrodes of the field-effect transistor, a polymethlymethacrylate thin layer was spin-coated on top of the crystal surface. The OFETs fabricated using the perylene single crystal showed a typical p-type operating mode. The field-effect mobility of the perylene crystal based OFETs was measured to be ˜9.62×10-4 cm2/V s at room temperature. The anisotropy of the mobility implying the existence of different mobilities when applying currents in different directions was observed for the OFETs, and the existence of traps in the perylene crystal was found through the measurements of the temperature-dependent mobility at various operating drain voltages.

Synthesis, growth, structural, spectroscopic and optical studies of a semiorganic NLO crystal: zinc guanidinium phosphate.

PubMed

Suvitha, A; Murugakoothan, P

2012-02-01

The semi-organic nonlinear optical (NLO) crystal, zinc guanidinium phosphate (ZGuP) has been grown through synthesis between zinc sulphate, guanidine carbonate and orthophosphoric acid from its aqueous solution by slow solvent evaporation technique. Solubility of the synthesized material has been determined for various temperatures using water as solvent. The grown crystal has been characterized by powder X-ray diffraction to confirm the crystal structure. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopy technique. (1)H and (13)C FT-NMR have been recorded to elucidate the molecular structure. The optical absorption study confirms the suitability of the crystal for device applications. The second harmonic generation (SHG) efficiency of ZGuP is found to be 1.825 times that of potassium dihydrogen phosphate (KDP). Thermal behavior of the grown crystals has been studied by thermogravimetric and differential thermal analysis. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. Copyright © 2011 Elsevier B.V. All rights reserved.

Concentration and structure inhomogeneities in GaSb(Si) single crystals grown at different heat and mass transfer conditions

NASA Astrophysics Data System (ADS)

Serebryakov, Yu. A.; Prokhorov, I. A.; Vlasov, V. N.; Korobeynikova, E. N.; Zakharov, B. G.; Shul'pina, I. L.; Marchenko, M. P.; Fryazinov, I. V.

2007-06-01

Results of ground-based experiments on crystallization of gallium antimonide on the POLIZON facility carried out within the framework of space experiment preparation aboard FOTON satellite are submitted. Technical and technological opportunities of suppression of disturbing factors for improvement of quality of grown crystals in space are substantiated. Features of formation of concentration and structure inhomogeneities in GaSb:Si crystals grown under non-stationary and stationary convection conditions are investigated. Experimental data about structure and dopant distribution inhomogeneities are discussed taking into account results of numerical researches of GaSb:Si crystallization. Also earlier received results of modeling of GaSb:Te crystallization under close temperature conditions are used. Correlation between computational and experimental data is shown. The data on intensity of flows close to crystallization front are received at which non-stationary or stationary conditions of crystallization are realized. The forecast for space conditions is made. The influence of a rotating magnetic field on convection in melt for application in space experiment projected is investigated.

Dynamic Properties of DNA-Programmable Nanoparticle Crystallization.

PubMed

Yu, Qiuyan; Zhang, Xuena; Hu, Yi; Zhang, Zhihao; Wang, Rong

2016-08-23

The dynamics of DNA hybridization is very important in DNA-programmable nanoparticle crystallization. Here, coarse-grained molecular dynamics is utilized to explore the structural and dynamic properties of DNA hybridizations for a self-complementary DNA-directed nanoparticle self-assembly system. The hexagonal close-packed (HCP) and close-packed face-centered cubic (FCC) ordered structures are identified for the systems of different grafted DNA chains per nanoparticle, which are in good agreement with the experimental results. Most importantly, the dynamic crystallization processes of DNA hybridizations are elucidated by virtue of the mean square displacement, the percentage of hybridizations, and the lifetime of DNA bonds. The lifetime can be modeled by the DNA dehybridization, which has an exponential form. The lifetime of DNA bonds closely depends on the temperature. A suitable temperature for the DNA-nanoparticle crystallization is obtained in the work. Moreover, a too large volume fraction hinders the self-assembly process due to steric effects. This work provides some essential information for future design of nanomaterials.

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

Han, Fei; Wan, Xiangang; Phelan, Daniel

ZrCuSi 2-type CePd 1-xBi 2 crystals were obtained from excess Bi flux. Magnetic susceptibility measurements reveal that CePd 1-xBi 2 is a highly anisotropic antiferromagnet with transition temperature at 6 K, and a magnetic-field-induced metamagnetic transition at 5 T. An enhanced Sommerfeld coefficient of γ of 0.199 J-mol-Ce -1K -2 obtained from specific heat measurements suggests a moderate Kondo effect in CePd 1-xBi 2. In addition to the antiferromagnetic peak the resistivity curve shows a shoulder-like behavior which could be attributed to the presence of Kondo effect and crystal-electric-field effects in this compound. Magnetoresistance and Hall effect measurements suggest anmore » interplay between Kondo and crystal-electric-field effects which reconstructs the Fermi surface topology of CePd 1-xBi 2 around 75 K. Electronic structure calculations reveal the Pd vacancies are important to the magnetic structure and enhance the crystal-electric-field effects which quench the orbital moment of Ce at low temperatures.« less

Melt structure and self-nucleation of ethylene copolymers

NASA Astrophysics Data System (ADS)

Alamo, Rufina G.

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. These studies have been carried out by DSC, x-ray, TEM and optical microscopy on a large number of model, narrow, and broad copolymers with different comonomer types and contents. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and lower the nucleation barrier. Diffusion of all sequences to a randomized melt state is a slow process, restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. Self-seeds dissolve above a critical melt temperature that demarcates homogeneity of the copolymer melt. There is a critical threshold level of crystallinity to observe the effect of melt memory on crystallization rate, thus supporting the correlation between melt memory and the change in melt structure during copolymer crystallization. Unlike binary blends, commercial ethylene-1-alkene copolymers with a range in inter-chain comonomer composition between 1 and about 15 mol % display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. With decreasing the initial melt temperature, broadly distributed copolymers show enhanced crystallization followed by a decrease of crystallization rate. The inversion demarcates the onset of liquid-liquid phase separation (LLPS) and a reduction of self-nuclei due to the strong thermodynamic drive for molecular segregation inside the binodal. The strong effect of melt memory on crystallization rate can be used to identify liquid-liquid phase separation in broadly distributed copolymers, and offers strategies to control the state of copolymer melts in ways of technological relevance for melt processing of LLDPE and other random olefin copolymers. References: B. O. Reid, et al., Macromolecules 46, 6485-6497, 2013 H. Gao, et al., Macromolecules 46, 6498-6506, 2013 A. Mamun et al., Macromolecules 47, 7958-7970, 2014 X. Chen et al., Macromol. Chem. Phys. 216, 1220 -1226, 2015 M. Ren et al., Macromol. Symp. 356, 131-141, 2015 Work supported by the NSF (DMR1105129).

High-Temperature Stable Anatase Titanium Oxide Nanofibers for Lithium-Ion Battery Anodes.

PubMed

Lee, Sangkyu; Eom, Wonsik; Park, Hun; Han, Tae Hee

2017-08-02

Control of the crystal structure of electrochemically active materials is an important approach to fabricating high-performance electrodes for lithium-ion batteries (LIBs). Here, we report a methodology for controlling the crystal structure of TiO 2 nanofibers by adding aluminum isopropoxide to a common sol-gel precursor solution utilized to create TiO 2 nanofibers. The introduction of aluminum cations impedes the phase transformation of electrospun TiO 2 nanofibers from the anatase to the rutile phase, which inevitably occurs in the typical annealing process utilized for the formation of TiO 2 crystals. As a result, high-temperature stable anatase TiO 2 nanofibers were created in which the crystal structure was well-maintained even at high annealing temperatures of up to 700 °C. Finally, the resulting anatase TiO 2 nanofibers were utilized to prepare LIB anodes, and their electrochemical performance was compared to pristine TiO 2 nanofibers that contain both anatase and rutile phases. Compared to the electrode prepared with pristine TiO 2 nanofibers, the electrode prepared with anatase TiO 2 nanofibers exhibited excellent electrochemical performances such as an initial Coulombic efficiency of 83.9%, a capacity retention of 89.5% after 100 cycles, and a rate capability of 48.5% at a current density of 10 C (1 C = 200 mA g -1 ).

Structural Properties Characterized by the Film Thickness and Annealing Temperature for La2O3 Films Grown by Atomic Layer Deposition.

PubMed

Wang, Xing; Liu, Hongxia; Zhao, Lu; Fei, Chenxi; Feng, Xingyao; Chen, Shupeng; Wang, Yongte

2017-12-01

La 2 O 3 films were grown on Si substrates by atomic layer deposition technique with different thickness. Crystallization characteristics of the La 2 O 3 films were analyzed by grazing incidence X-ray diffraction after post-deposition rapid thermal annealing treatments at several annealing temperatures. It was found that the crystallization behaviors of the La 2 O 3 films are affected by the film thickness and annealing temperatures as a relationship with the diffusion of Si substrate. Compared with the amorphous La 2 O 3 films, the crystallized films were observed to be more unstable due to the hygroscopicity of La 2 O 3 . Besides, the impacts of crystallization characteristics on the bandgap and refractive index of the La 2 O 3 films were also investigated by X-ray photoelectron spectroscopy and spectroscopic ellipsometry, respectively.

The magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS3

NASA Astrophysics Data System (ADS)

Wildes, A. R.; Simonet, V.; Ressouche, E.; Ballou, R.; McIntyre, G. J.

2017-11-01

The magnetic properties and magnetic structure are presented for CoPS3, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Néel temperature of TN ∼120 K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2 K and 300 K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Single-crystal neutron diffraction shows that the magnetic propagation vector is k  =  (0 1 0) with the moments mostly along the {a} axis and with a small component along the {c} axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent 2β = 0.60 +/- 0.01 for T > 0.9~TN .

Structural Evolution of Silicon Oxynitride Fiber Reinforced Boron Nitride Matrix Composite at High Temperatures

NASA Astrophysics Data System (ADS)

Zou, Chunrong; Li, Bin; Zhang, Changrui; Wang, Siqing; Xie, Zhengfang; Shao, Changwei

2016-02-01

The structural evolution of a silicon oxynitride fiber reinforced boron nitride matrix (Si-N-Of/BN) wave-transparent composite at high temperatures was investigated. When heat treated at 1600 °C, the composite retained a favorable bending strength of 55.3 MPa while partially crystallizing to Si2N2O and h-BN from the as-received amorphous structure. The Si-N-O fibers still performed as effective reinforcements despite the presence of small pores due to fiber decomposition. Upon heat treatment at 1800 °C, the Si-N-O fibers already lost their reinforcing function and rough hollow microstructure formed within the fibers because of the accelerated decomposition. Further heating to 2000 °C led to the complete decomposition of the reinforcing fibers and only h-BN particles survived. The crystallization and decomposition behaviors of the composite at high temperatures are discussed.

Reversal of spontaneous magnetization and spontaneous exchange bias for Sm1-xYxCrO3: The effect of Y doping

NASA Astrophysics Data System (ADS)

Zhang, Hongguang; Wang, Jianhua; Xie, Liang; Fu, Dexiang; Guo, Yanyan; Li, Yongtao

2017-11-01

We report the crystal and electronic structures and magnetic properties of non-magnetic Y3+ ion doped SmCrO3 crystals. Structural distortion and electronic structure variation are caused by cation disorder due to Y doping. Although the spin moment of Sm3+ is diluted by nonmagnetic Y ions, spin reorientation continues to exist, and the temperature-dependent magnetization reversal effect and the spontaneous exchange bias effect under zero field cooling are simultaneously induced below Neel temperature. Significantly, the method of doping promotes the achievement of temperature dependent tunable switching of magnetization and sign of a spontaneous exchange bias from positive to negative. Our work provides more tunable ways to the sign reversal of magnetization and exchange bias, which have potential application in designing magnetic random access memory devices, thermomagnetic switches and spin-valve devices.

Simulation and Experimental Studies on Grain Selection and Structure Design of the Spiral Selector for Casting Single Crystal Ni-Based Superalloy.

PubMed

Zhang, Hang; Xu, Qingyan

2017-10-27

Grain selection is an important process in single crystal turbine blades manufacturing. Selector structure is a control factor of grain selection, as well as directional solidification (DS). In this study, the grain selection and structure design of the spiral selector were investigated through experimentation and simulation. A heat transfer model and a 3D microstructure growth model were established based on the Cellular automaton-Finite difference (CA-FD) method for the grain selector. Consequently, the temperature field, the microstructure and the grain orientation distribution were simulated and further verified. The average error of the temperature result was less than 1.5%. The grain selection mechanisms were further analyzed and validated through simulations. The structural design specifications of the selector were suggested based on the two grain selection effects. The structural parameters of the spiral selector, namely, the spiral tunnel diameter ( d w ), the spiral pitch ( h b ) and the spiral diameter ( h s ), were studied and the design criteria of these parameters were proposed. The experimental and simulation results demonstrated that the improved selector could accurately and efficiently produce a single crystal structure.

Simulation and Experimental Studies on Grain Selection and Structure Design of the Spiral Selector for Casting Single Crystal Ni-Based Superalloy

PubMed Central

Zhang, Hang; Xu, Qingyan

2017-01-01

Grain selection is an important process in single crystal turbine blades manufacturing. Selector structure is a control factor of grain selection, as well as directional solidification (DS). In this study, the grain selection and structure design of the spiral selector were investigated through experimentation and simulation. A heat transfer model and a 3D microstructure growth model were established based on the Cellular automaton-Finite difference (CA-FD) method for the grain selector. Consequently, the temperature field, the microstructure and the grain orientation distribution were simulated and further verified. The average error of the temperature result was less than 1.5%. The grain selection mechanisms were further analyzed and validated through simulations. The structural design specifications of the selector were suggested based on the two grain selection effects. The structural parameters of the spiral selector, namely, the spiral tunnel diameter (dw), the spiral pitch (hb) and the spiral diameter (hs), were studied and the design criteria of these parameters were proposed. The experimental and simulation results demonstrated that the improved selector could accurately and efficiently produce a single crystal structure. PMID:29077067

Reply to “Structural and magnetic behavior of the cubic oxyfluoride SrFeO{sub 2}F studied by neutron diffraction”

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

Clemens, Oliver, E-mail: oliver.clemens@kit.edu; Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen; Berry, Frank J.

2015-03-15

In this article we comment on the results published by Thompson et al. (, J. Solid State Chem. 219 (2014) 173–178) on the crystal structure of SrFeO{sub 2}F, who claim the compound to crystallize in the cubic space group Pm-3m. We give a more detailed explanation of the determination of our previously reported structural model with Imma symmetry (Clemens et al., J. Solid State Chem. 206 (2013) 158–169), with addition of variable temperature XRD measurements with high counting time to provide unambiguous evidence for the Imma model being correct for our sample. - Graphical abstract: The crystal structure of SrFeO{submore » 2}F is discussed with regards to previous reports. - Highlights: • SrFeO{sub 2}F was synthesized by polymer based fluorination of SrFeO{sub 3}. • Evaluation of the diffraction data shows a pseudocubic cell metric. • Superstructure reflections at low d-spacings indicate deviation from cubic symmetry. • The phase transition temperature from orthorhombic to cubic was determined using variable temperature X-ray diffraction. • Results published by Thompson et al. are critically discussed with respect to those observations.« less

Tunable bandgap in hybrid perovskite CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) single crystals and photodetector applications

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

Wang, L.; Duan, R. F.; Huang, F.

We report the synthesis of CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) (X=Cl and I) single crystals via a stepwise temperature control approach. High-quality CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) crystals with a tunable bandgap from 1.92 eV to 2.53 eV have been prepared successfully in this way. And further experiments revealed the influence of halogen content and preparation temperature on the structural and optical properties of these crystals. It is observed that chlorine can lower the critical nucleation energy, which results in crystallizing at lower temperature with the chlorine content increasing, while the nucleation energy increases slowly with increasing iodine content. Moreover,more » in contrast to Frank–van der Merwe growth with low heating rate, high heating rate leads to a mass of small size single crystals and Stranski-Krastanov growth. The single crystals with tunable band gap and impressive characteristics enable us to fabricate high performance photodetectors for different wavelengths.« less

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.

Self-propagating high-temperature synthesis and luminescent properties of ytterbium doped rare earth (Y, Sc, Lu) oxides nanopowders

NASA Astrophysics Data System (ADS)

Permin, D. A.; Novikova, A. V.; Balabanov, S. S.; Gavrishchuk, E. M.; Kurashkin, S. V.; Savikin, A. P.

2018-04-01

This paper describes a comparative study of structural and luminescent properties of 5%Yb-doped yttrium, scandium, and lutetium oxides (Yb:RE2O3) powders and ceramics fabricated by self-propagating high-temperature synthesis. According to X-ray diffractometry and electron microscopy the chosen method ensures preparation of low-agglomerated cubic Ctype crystal structured powders at one step. No crucial differences in luminescence spectra were found the Yb:RE2O3 powders and ceramics. It was shown that the emission lifetimes of the Yb:RE2O3 powders are lowered by crystal structure defects, while its values for ceramics samples are compared to that of monocrystals and more influenced by rare earth impurities.

Strong, Ductile, and Thermally Stable bcc-Mg Nanolaminates.

PubMed

Pathak, Siddhartha; Velisavljevic, Nenad; Baldwin, J Kevin; Jain, Manish; Zheng, Shijian; Mara, Nathan A; Beyerlein, Irene J

2017-08-15

Magnesium has attracted attention worldwide because it is the lightest structural metal. However, a high strength-to-weight ratio remains its only attribute, since an intrinsic lack of strength, ductility and low melting temperature severely restricts practical applications of Mg. Through interface strains, the crystal structure of Mg can be transformed and stabilized from a simple hexagonal (hexagonal close packed hcp) to body center cubic (bcc) crystal structure at ambient pressures. We demonstrate that when introduced into a nanocomposite bcc Mg is far more ductile, 50% stronger, and retains its strength after extended exposure to 200 C, which is 0.5 times its homologous temperature. These findings reveal an alternative solution to obtaining lightweight metals critically needed for future energy efficiency and fuel savings.

Preparation and Delivery of Protein Microcrystals in Lipidic Cubic Phase for Serial Femtosecond Crystallography.

PubMed

Ishchenko, Andrii; Cherezov, Vadim; Liu, Wei

2016-09-20

Membrane proteins (MPs) are essential components of cellular membranes and primary drug targets. Rational drug design relies on precise structural information, typically obtained by crystallography; however MPs are difficult to crystallize. Recent progress in MP structural determination has benefited greatly from the development of lipidic cubic phase (LCP) crystallization methods, which typically yield well-diffracting, but often small crystals that suffer from radiation damage during traditional crystallographic data collection at synchrotron sources. The development of new-generation X-ray free-electron laser (XFEL) sources that produce extremely bright femtosecond pulses has enabled room temperature data collection from microcrystals with no or negligible radiation damage. Our recent efforts in combining LCP technology with serial femtosecond crystallography (LCP-SFX) have resulted in high-resolution structures of several human G protein-coupled receptors, which represent a notoriously difficult target for structure determination. In the LCP-SFX technique, LCP is recruited as a matrix for both growth and delivery of MP microcrystals to the intersection of the injector stream with an XFEL beam for crystallographic data collection. It has been demonstrated that LCP-SFX can substantially improve the diffraction resolution when only sub-10 µm crystals are available, or when the use of smaller crystals at room temperature can overcome various problems associated with larger cryocooled crystals, such as accumulation of defects, high mosaicity and cryocooling artifacts. Future advancements in X-ray sources and detector technologies should make serial crystallography highly attractive and practicable for implementation not only at XFELs, but also at more accessible synchrotron beamlines. Here we present detailed visual protocols for the preparation, characterization and delivery of microcrystals in LCP for serial crystallography experiments. These protocols include methods for conducting crystallization experiments in syringes, detecting and characterizing the crystal samples, optimizing crystal density, loading microcrystal laden LCP into the injector device and delivering the sample to the beam for data collection.

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

Ben Smida, Youssef; Marzouki, Riadh; Georges, Samuel

A new sodium cobalt (II) arsenate Na{sub 4}Co{sub 7}(AsO{sub 4}){sub 6} has been synthesized by a solid-state reaction and its crystal structure determined from single crystal X-ray diffraction data. It crystallizes in the monoclinic system, space group C2/m, with a=10.7098(9) Å, b=14.7837(9) Å, c=6.6845(7) Å, and β=105.545(9)°. The structure is described as a three-dimensional framework built up of corner-edge sharing CoO{sub 6}, CoO{sub 4} and AsO{sub 4} polyhedra, with interconnecting channels along [100] in which the Na{sup +} cations are located. The densest ceramics with relative density of 94% was obtained by ball milling and optimization of sintering temperature, andmore » its microstructure characterized by scanning electron microscopy. The electrical properties of the ceramics were studied over a temperature interval from 280 °C to 560 °C using the complex impedance spectroscopy over the range of 13 MHz–5 Hz. The ionic bulk conductivity value of the sample at 360 °C is 2.51 10{sup −5} S cm{sup −1} and the measured activation energy is Ea=1 eV. The sodium migration pathways in the crystal structure were investigated computationally using the bond valence site energy (BVSE) model and classical molecular dynamics (MD) simulations. - Graphical abstract: Correlation between crystal structure, microstructure and ionic conductivity . Display Omitted - Highlights: • A new arsenate Na{sub 4}Co{sub 7}(AsO{sub 4}){sub 6} was prepared by solid state reaction. • Its crystal structure was determined by powder X-ray diffraction. • Na{sup +} ionic conductivity was probed by complex impedance spectroscopy. • Na{sup +} conduction pathways were modeled by bond-valence method and molecular dynamics.« less

Self-powdering and nonlinear optical domain structures in ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3} crystals formed in glass

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

Tsukada, Y.; Honma, T.; Komatsu, T., E-mail: komatsu@mst.nagaokaut.ac.j

Ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3}, (GMO), crystals are formed through the crystallization of 21.25Gd{sub 2}O{sub 3}-63.75MoO{sub 3}-15B{sub 2}O{sub 3} glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50-500 {mu}m spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called 'self-powdering phenomenon during crystallization' in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and amore » spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO{sub 4}){sup 2-} tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals. - Graphical abstract: This figure shows the polarized optical photograph at room temperature for a particle (piece) obtained by a heat treatment of the glass at 590 deg. C for 2 h in an electric furnace in air. This particle was obtained through the self-powdering behavior in the crystallization of glass. The periodic domain structure is observed. Ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3} crystals are formed in the particle, and second harmonic generations are detected, depending on the domain structure.« less

Exploration on anion ordering, optical properties and electronic structure in K3WO3F3 elpasolite

NASA Astrophysics Data System (ADS)

Atuchin, V. V.; Isaenko, L. I.; Kesler, V. G.; Lin, Z. S.; Molokeev, M. S.; Yelisseyev, A. P.; Zhurkov, S. A.

2012-03-01

Room-temperature modification of potassium oxyfluorotungstate, G2-K3WO3F3, has been prepared by low-temperature chemical route and single crystal growth. Wide optical transparency range of 0.3-9.4 μm and forbidden band gap Eg=4.32 eV have been obtained for G2-K3WO3F3 crystal. Meanwhile, its electronic structure has been calculated with the first-principles calculations. The good agreement between the theorectical and experimental results have been achieved. Furthermore, G2-K3WO3F3 is predicted to possess the relatively large nonlinear optical coefficients.

Study, selection, and preparation of solid cationic conductors. [characteristics of solid electrolytes for rechargeable high energy and high power density batteries

NASA Technical Reports Server (NTRS)

Roth, W. L.; Muller, O.

1974-01-01

Crystal chemical principles and transport theory have been used to predict structures and specific compounds which might find application as solid electrolytes in rechargeable high energy and high power density batteries operating at temperatures less than 200 C. Structures with 1-, 2-, and 3-dimensional channels were synthesized and screened by nuclear magnetic resonance, dielectric loss, and conductivity. There is significant conductivity at room temperature in some of the materials but none attain a level that is comparable to beta-alumina. Microwave and fast pulse methods were developed to measure conductivity in powders and in small crystals.

Crystallization, melting, and structure of water nanoparticles at atmospherically relevant temperatures.

PubMed

Johnston, Jessica C; Molinero, Valeria

2012-04-18

Water nanoparticles play an important role in atmospheric processes, yet their equilibrium and nonequilibrium liquid-ice phase transitions and the structures they form on freezing are not yet fully elucidated. Here we use molecular dynamics simulations with the mW water model to investigate the nonequilibrium freezing and equilibrium melting of water nanoparticles with radii R between 1 and 4.7 nm and the structure of the ice formed by crystallization at temperatures between 150 and 200 K. The ice crystallized in the particles is a hybrid form of ice I with stacked layers of the cubic and hexagonal ice polymorphs in a ratio approximately 2:1. The ratio of cubic ice to hexagonal ice is insensitive to the radius of the water particle and is comparable to that found in simulations of bulk water around the same temperature. Heating frozen particles that contain multiple crystallites leads to Ostwald ripening and annealing of the ice structures, accompanied by an increase in the amount of ice at the expense of the liquid water, before the particles finally melt from the hybrid ice I to liquid, without a transition to hexagonal ice. The melting temperatures T(m) of the nanoparticles are not affected by the ratio of cubic to hexagonal layers in the crystal. T(m) of the ice particles decreases from 255 to 170 K with the particle size and is well described by the Gibbs-Thomson equation, T(m)(R) = T(m)(bulk) - K(GT)/(R - d), with constant K(GT) = 82 ± 5 K·nm and a premelted liquid of width d = 0.26 ± 0.05 nm, about one monolayer. The freezing temperatures also decrease with the particles' radii. These results are important for understanding the composition, freezing, and melting properties of ice and liquid water particles under atmospheric conditions. © 2012 American Chemical Society

Tuning the functional properties of PMN-PT single crystals via doping and thermoelectrical treatments

NASA Astrophysics Data System (ADS)

Luo, Laihui; Dietze, Matthias; Solterbeck, Claus-Henning; Luo, Haosu; Es-Souni, Mohammed

2013-12-01

Single crystals based on solid solutions of lead-magnesium-niobate (PMN) and lead titanate (PT) have emerged as highly promising multifunctional systems combining piezoelectric, pyroelectric, and electro-optic properties that surpass by far those of the best known lead-zirkonium-titanate ceramics. In this paper we present new findings on how the phase transition temperature and the dielectric and ferroelectric properties can be tuned depending on crystal composition, orientation, and thermoelectrical treatment. Mn-doped and pure 0.72PbMg1/3Nb2/3O3-0.28PbTiO3 (0.72PMN-0.28PT) single crystals with ⟨111⟩ and ⟨001⟩ orientations were investigated. A special attention was devoted to field cooling (FC), i.e., cooling under electric field from different temperatures. The results illustrate different findings that were not reported before: the Curie temperature, i.e., ferroelectric-paraelectric transition temperature, is enhanced after field cooling of the Mn-doped, ⟨001⟩-oriented crystal while such a shift is not observed in the ⟨111⟩-oriented and the non-doped crystals. In addition, substantial polarization suppression occurs in the Mn-doped crystals upon FC from high temperature regardless of orientation. Based on piezoforce microscopy of the domain structure that shows suppression of domain growth following field cooling from 200 °C, we propose a mechanism for polarization suppression based on domain pinning by charged defects. The practical importance of our results lies in showing the opportunity offered by a proper choice of crystal composition and poling conditions for tuning the functional properties of PMN-PT single crystals for a specific application. This should contribute to the understanding of their properties towards advanced sensor and transducers devices.

Hydrothermal Synthesis, Crystal Structure, and Photoluminescent Properties of Li[UO2(CH3COO)3]3[Co(H2O)6

NASA Astrophysics Data System (ADS)

AlDamen, Murad A.; Juwhari, Hassan K.; Al-zuheiri, Aya M.; Alnazer, Louy A.

2017-12-01

Single crystal of Li[UO2(CH3COO)3]3[Co(H2O)6] was prepared and found to crystallize in the monoclinic crystal system in the sp. gr. C2/ c, with Z = 2, and unit cell parameters a = 22.1857(15) Å, b = 13.6477(8) Å, c = 15.6921(10) Å, β = 117.842(9)°, V = 4201.3(4) Å3. The crystal was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The single crystal X-ray diffraction analysis revealed that the crystal has a lamellar structure in which a cobalt hydrate is sandwiched within the Li[UO2(CH3COO)3]3 2- chains. Furthermore, the room temperature photoluminescence spectrum of the complex was investigated in the solid state.

Hydrothermal synthesis, crystal structure, luminescent and magnetic properties of a new mononuclear GdIII coordination complex

NASA Astrophysics Data System (ADS)

Coban, Mustafa Burak

2018-06-01

A new GdIII coordination complex, {[Gd(2-stp)2(H2O)6].2(4,4'-bipy).4(H2O)}, complex 1, (2-stp = 2-sulfoterephthalate anion and 4,4'-bipy = 4,4'-bipyridine), has been synthesized by hydrothermal method and characterized by elemental analysis, solid state UV-Vis and FT-IR spectroscopy, single-crystal X-ray diffraction, solid state photoluminescence and variable-temperature magnetic measurements. The crystal structure determination shows that GdIII ions are eight coordinated and adopt a distorted square-antiprismatic geometry. Molecules interacting through intra- and intermolecular (O-H⋯O, O-H⋯N) hydrogen bonds in complex 1, give rise to 3D hydrogen bonded structure and the discrete lattice 4,4'-bipy molecules occupy the channel of the 3D structure. π-π stacking interactions also exist 4,4'-bipy-4,4'-bipy and 4,4'-bipy-2-stp molecule rings in 3D structures. Additionally, solid state photoluminescence properties of complex 1 at room temperature have been investigated. Under the excitation of UV light (at 349 nm), the complex 1 exhibited green emissions (at 505 nm) of GdIII ion in the visible region. Furthermore, Variable-temperature magnetic susceptibility and isothermal magnetization as function of external magnetic field studies reveal that complex 1 displays possible antiferromagnetic interaction.

Structural study of polymorphism in methylprednisolone aceponate

NASA Astrophysics Data System (ADS)

Knyazev, A. V.; Somov, N. V.; Shipilova, A. S.; Gusarova, E. V.; Knyazeva, S. S.; Stepanova, O. V.; Chuprunov, E. V.

2017-08-01

The crystal structures of methylprednisolone aceponate were determined by X-ray diffraction analysis at temperatures 90 K and 150 K: space group P212121, a = 14.8592(2), b = 19.6844(5), c = 26.1626(4) Å, Z = 12; R = 0.0598 (T = 90 K); space group P212121, a = 6.57348(14), b = 14.8295(3), c = 26.2214(5) Å, Z = 4; R = 0.0518 (T = 150 K). Features of structural changes in the phase transition were revealed. The abrupt change in the unit cell parameters in the phase transition was shown by low-temperature X-ray powder. The methods of degree of invariance of crystal electron density and molecular Voronoi-Dirichlet polyhedra were used for the analysis of polymorphism in methylprednisolone aceponate. The atomic structure at 90 K have a translational pseudosymmetry of electron density η = 0.329(1). The decrease of number of intermolecular contacts in the high-temperature modification due to rupture of intermolecular non-valence contacts C/O was observed.

Effect of Te doping on FeSe superconductor synthesized by powder-in-tube

NASA Astrophysics Data System (ADS)

Imaduddin, A.; Nisa, K.; Yudanto, S. D.; Nugraha, H.; Siswayanti, B.

2017-04-01

FeSe is a superconducting material, which has the simplest crystal structure among the Fe-based superconductors. It has no arsenic element, which is very harmful to the human body. In this study, we analyzed the effects of milling time and Te doping on FeSe superconductors. The synthesis of the samples were carried out using powder-in-tube method in a SS304 stainless steel tube. After the pressing process, followed by the sintering process at 500° C for 20 hours, the samples were removed from the tubes. Later, we analyzed its crystal structures, surfaces morphology and the superconductivity properties. Δ-FeSe phase (hexagonal, non-superconductor) and β-FeSe (tetragonal, superconductor) were formed in the samples, including minor phases of Fe and Fe3Se4. Te doping changed the crystal structure from β-FeSe and Δ-FeSe into FeSe0.5Te0.5. In addition, the onset critical temperature (TC, onset) shifted to higher temperature.

Structure of free radicals in irradiated acetyl-L-leucine single crystals at 77 K

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

Almanov, G.A.; Bogdanchikov, G.A.; Usov, O.M.

1988-09-01

By using the EPR method, two types of radicals are observed, which are formed in acetyl-L-leucine single crystals irradiated at 77K. These are alkyl type radicals (CH/sub 3/)/sub 2/CCH/sub 2/CH(NHCOCH/sub 3/)COOH and peptide group radicals. When the crystals are defrozen to room temperatures, the radicals of the second type disappear without formation of paramagnetic particles. Two possible structures of the peptide group radicals were studied by the INDO method. On defreezing to room temperature, the alkyl group radical is retained, while the peptide radical disappears without formation of paramagnetic particles. For the protonated form of the anion-radical, a better agreementmore » is observed between the theoretically calculated and the experimentally obtained HFI constants. The quantum chemical analysis of the possible structures of the peptide group radicals indicates that the formation of the protonated form of the anion-radical is energetically favorable.« less

Bioprospecting for microbial products that affect ice crystal formation and growth.

PubMed

Christner, Brent C

2010-01-01

At low temperatures, some organisms produce proteins that affect ice nucleation, ice crystal structure, and/or the process of recrystallization. Based on their ice-interacting properties, these proteins provide an advantage to species that commonly experience the phase change from water to ice or rarely experience temperatures above the melting point. Substances that bind, inhibit or enhance, and control the size, shape, and growth of ice crystals could offer new possibilities for a number of agricultural, biomedical, and industrial applications. Since their discovery more than 40 years ago, ice nucleating and structuring proteins have been used in cryopreservation, frozen food preparation, transgenic crops, and even weather modification. Ice-interacting proteins have demonstrated commercial value in industrial applications; however, the full biotechnological potential of these products has yet to be fully realized. The Earth's cold biosphere contains an almost endless diversity of microorganisms to bioprospect for microbial compounds with novel ice-interacting properties. Microorganisms are the most appropriate biochemical factories to cost effectively produce ice nucleating and structuring proteins on large commercial scales.

Transition to collapsed tetragonal phase in CaFe2As2 single crystals as seen by 57Fe Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Bud'ko, Sergey L.; Ma, Xiaoming; Tomić, Milan; Ran, Sheng; Valentí, Roser; Canfield, Paul C.

2016-01-01

Temperature dependent measurements of 57Fe Mössbauer spectra on CaFe2As2 single crystals in the tetragonal and collapsed tetragonal phases are reported. Clear features in the temperature dependencies of the isomer shift, relative spectra area, and quadrupole splitting are observed at the transition from the tetragonal to the collapsed tetragonal phase. From the temperature dependent isomer shift and spectral area data, an average stiffening of the phonon modes in the collapsed tetragonal phase is inferred. The quadrupole splitting increases by ˜25 % on cooling from room temperature to ˜100 K in the tetragonal phase and is only weakly temperature dependent at low temperatures in the collapsed tetragonal phase, in agreement with the anisotropic thermal expansion in this material. In order to gain microscopic insight about these measurements, we perform ab initio density functional theory calculations of the electric field gradient and the electron density of CaFe2As2 in both phases. By comparing the experimental data with the calculations we are able to fully characterize the crystal structure of the samples in the collapsed-tetragonal phase through determination of the As z coordinate. Based on the obtained temperature dependent structural data we are able to propose charge saturation of the Fe-As bond region as the mechanism behind the stabilization of the collapsed-tetragonal phase at ambient pressure.

Crystal structure of new AsS{sub 2} compound

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

Bolotina, N. B., E-mail: bolotina@ns.crys.ras.ru; Brazhkin, V. V.; Dyuzheva, T. I.

2013-01-15

AsS{sub 2} single crystals have been obtained for the first time from an As{sub 2}S{sub 3} melt at pressures above 6 GPa and temperatures above 800 K in the As{sub 2}S{sub 3} {yields} AsS + AsS{sub 2} reaction. The monoclinic structure of the new high-pressure phase is solved by X-ray diffraction analysis and compared to the structure of high-pressure AsS phase, which was studied previously.

Intrinsic crystal phase separation in the antiferromagnetic superconductor Rb(y)Fe(2-x)Se2: a diffraction study.

PubMed

Yu Pomjakushin, V; Krzton-Maziopa, A; Pomjakushina, E V; Conder, K; Chernyshov, D; Svitlyk, V; Bosak, A

2012-10-31

The crystal and magnetic structures of the superconducting iron-based chalcogenides Rb(y)Fe(2-x)Se(2) have been studied by means of single-crystal synchrotron x-ray and high-resolution neutron powder diffraction in the temperature range 2-570 K. The ground state of the crystal is an intrinsically phase-separated state with two distinct-by-symmetry phases. The main phase has the iron vacancy ordered √5 × √5 superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have √5 × √5-type of ordering and has a smaller in-plane lattice constant a and larger tetragonal c-axis and can be well described by assuming the parent average vacancy disordered structure (I4/mmm space group) with the refined stoichiometry Rb(0.60(5))(Fe(1.10(5))Se)(2). The minority phase amounts to 8-10% mass fraction. The unit cell volume of the minority phase is 3.2% smaller than the one of the main phase at T = 2 K and has quite different temperature dependence. The minority phase merges with the main vacancy ordered phase on heating above the phase separation temperature T(P) = 475 K. The spatial dimensions of the phase domains strongly increase above T(P) from 1000 to >2500 Å due to the integration of the regions of the main phase that were separated by the second phase at low temperatures. Additional annealing of the crystals at a temperature T = 488 K, close to T(P), for a long time drastically reduces the amount of the minority phase.

Statistical Fine Structure in Inhomogeneously Broadened Absorption Lines in Solids.

DTIC Science & Technology

1987-12-22

the inhomogeneously broadened zero-phonon SijSo (0-0) absorption of pentacene molecules in crystals of p-terphenyl at liquid helium temperatures. SFS...structure (SFS) in the inhomogeneously broadened zero-phonon S, +- So (0-0) absorption of pentacene molecules in crystals of p-terphenyl at liquid helium...tile large multiplicity of local environments. Inhomogeneously broadened absorption lines are usually treated as smooth, Gaussian profiles. In recent

Crystal cryocooling distorts conformational heterogeneity in a model Michaelis complex of DHFR

PubMed Central

Keedy, Daniel A.; van den Bedem, Henry; Sivak, David A.; Petsko, Gregory A.; Ringe, Dagmar; Wilson, Mark A.; Fraser, James S.

2014-01-01

Summary Most macromolecular X-ray structures are determined from cryocooled crystals, but it is unclear whether cryocooling distorts functionally relevant flexibility. Here we compare independently acquired pairs of high-resolution datasets of a model Michaelis complex of dihydrofolate reductase (DHFR), collected by separate groups at both room and cryogenic temperatures. These datasets allow us to isolate the differences between experimental procedures and between temperatures. Our analyses of multiconformer models and time-averaged ensembles suggest that cryocooling suppresses and otherwise modifies sidechain and mainchain conformational heterogeneity, quenching dynamic contact networks. Despite some idiosyncratic differences, most changes from room temperature to cryogenic temperature are conserved, and likely reflect temperature-dependent solvent remodeling. Both cryogenic datasets point to additional conformations not evident in the corresponding room-temperature datasets, suggesting that cryocooling does not merely trap pre-existing conformational heterogeneity. Our results demonstrate that crystal cryocooling consistently distorts the energy landscape of DHFR, a paragon for understanding functional protein dynamics. PMID:24882744

Spin-glass polyamorphism induced by a magnetic field in LaMnO3 single crystal

NASA Astrophysics Data System (ADS)

Eremenko, V. V.; Sirenko, V. A.; Baran, A.; Čižmár, E.; Feher, A.

2018-05-01

We present experimental evidence of field-driven transition in spin-glass state, similar to pressure-induced transition between amorphous phases in structural and metallic glasses, attributed to the polyamorphism phenomena. Cusp in temperature dependences of ac magnetic susceptibility of weakly disordered LaMnO3 single crystal is registered below the temperature of magnetic ordering. Frequency dependence of the cusp temperature proves its spin-glass origin. The transition induced by a magnetic field in spin-glass state, is manifested by peculiarity in dependence of cusp temperature on applied magnetic field. Field dependent maximum of heat capacity is observed in the same magnetic field and temperature range.

The low temperature synthesis, characterization and properties of ferroelectrics

NASA Astrophysics Data System (ADS)

Xu, Jie

2000-10-01

PZT 50:50 xerogels prepared by two different sol-gel routes crystallized in a similar fashion to give a mixture of tetragonal and rhombohedral at high temperature (1000°C). Both the diffraction and EXAFS data suggest that the compositional inhomogeneity of the samples prepared by the two routes is similar. The crystallization of CZT gels is complicated. Crystalline CaCO 3 was always detected in the dry gels regardless of the sample composition and preparation methods. At intermediate temperatures a fluorite related phase was always formed and it transformed to perovskite at higher temperatures. The EXAFS data suggest that perovskite CZT samples prepared using alkoxide sol-gel chemistry may not be random solid solutions. All the solution processed ZrTiO4 materials crystallized in the range 600--700°C. The KTN samples prepared using a conventional alkoxide sol-gel route crystallized completely to perovskite at lower temperatures than those prepared using prehydrolyzed precursors. The EXAFS data for the KTN samples prepared using a conventional alkoxide sol-gel route are consistent with a random distribution of tantalum and niobium in the solid solution. However, materials prepared using the inhomogeneous sol-gel route and by the direct reaction of mixed oxides were shown to be compositionally inhomogeneous. The heterogeneity could not be removed by regrinding and heating the mixed oxide samples several times. K2Ta4-xNbxO11 (x = 0, 2, 4) samples were prepared using alkoxide sol-gel chemistry and their crystallization was examined by powder X-ray diffraction. A Rietveld structure analysis of the pyrochlore formed from a gel with bulk composition K2Ta 2Nb2O11 indicated that it was rich in potassium relative to the bulk sample. On heating to high temperatures tetragonal tungsten bronzes were formed. A Rietveld analysis was also performed for K2Ta 2Nb2O11 with tetragonal tungsten bronze structure. The defect pyrochlores "AgTaO3" and GaTaO 3 were synthesized by ion-exchange using pyrochlore KTaO3 as a starting material. The structures of the pyrochlores were examined using the Rietveld method. The pyrochlore-to-perovskite transformations were also explored.

Synthesis, structure and characterization of a hybrid centrosymmetric material (4-dimethylaminopyridinium nitrate gallic acid monohydrate) well-designed for non-linear optics

NASA Astrophysics Data System (ADS)

Ennaceur, Nasreddine; Jalel, Boutheina; Henchiri, Rokaya; Cordier, Marie; Ledoux-Rak, Isabelle

2018-01-01

Hybrid material: 4-Dimethylaminopyridinium nitrate gallic acid monohydrate abbreviated DNGA monohydrate has been successfully synthesized by slow evaporation method at room temperature. X-ray diffraction (XRD) on a single crystal showed that the latter was crystallized in P-1 space group. Likewise, thermal analyses demonstrated the stability of our crystal up to 80 °C. Besides, the analysis of the infrared spectrum (FTIR), allowed us to confirm the presence of the different groups present in the structure. Furthermore, by studying the UV-Visible spectrum, the transparency of our crystal was proven. Despite the fact that of having a centrosymmetric structure, the nonlinear optical properties of our single crystal, which was tested by Kurtz-Perry technique, proved that its second harmonic generation efficiency was 1.22 times more than that of KDP (potassium dihydrogen phosphate) single crystal. This nonlinear optical behavior of the studied compound was also determined through the calculations of polarizability and first hyperpolarizability values.

Effect of temperature on terahertz photonic and omnidirectional band gaps in one-dimensional quasi-periodic photonic crystals composed of semiconductor InSb.

PubMed

Singh, Bipin K; Pandey, Praveen C

2016-07-20

Engineering of thermally tunable terahertz photonic and omnidirectional bandgaps has been demonstrated theoretically in one-dimensional quasi-periodic photonic crystals (PCs) containing semiconductor and dielectric materials. The considered quasi-periodic structures are taken in the form of Fibonacci, Thue-Morse, and double periodic sequences. We have shown that the photonic and omnidirectional bandgaps in the quasi-periodic structures with semiconductor constituents are strongly depend on the temperature, thickness of the constituted semiconductor and dielectric material layers, and generations of the quasi-periodic sequences. It has been found that the number of photonic bandgaps increases with layer thickness and generation of the quasi-periodic sequences. Omnidirectional bandgaps in the structures have also been obtained. Results show that the bandwidths of photonic and omnidirectional bandgaps are tunable by changing the temperature and lattice parameters of the structures. The generation of quasi-periodic sequences can also change the properties of photonic and omnidirectional bandgaps remarkably. The frequency range of the photonic and omnidirectional bandgaps can be tuned by the change of temperature and layer thickness of the considered quasi-periodic structures. This work will be useful to design tunable terahertz PC devices.

Disentangling the surface and bulk electronic structures of LaOFeAs

DOE PAGES

Zhang, P.; Ma, J.; Qian, T.; ...

2016-09-20

We performed a comprehensive angle-resolved photoemission spectroscopy study of the electronic band structure of LaOFeAs single crystals. We found that samples cleaved at low temperature show an unstable and very complicated band structure, whereas samples cleaved at high temperature exhibit a stable and clearer electronic structure. Using in situ surface doping with K and supported by first-principles calculations, we identify both surface and bulk bands. Our assignments are confirmed by the difference in the temperature dependence of the bulk and surface states.

Crystal structure of the true Nasicon: Na/sub 3/Zr/sub 2/Si/sub 2/PO/sub 12/

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

Boilot, J.P.; Collin, G.; Colomban, P.

For the first time, the results of single crystal determination of the true Nasicon are given. The structure refinement yielded the following composition: Na/sub 3.09(8)/Zr/sub 2.01(1)/P/sub 0.91/Si/sub 2.09/O/sub 12/. Evidence of the total occupancy of the Zr octahedron is found, displaying that only the Si/P non-stoichiometry mechanism is present in the Nasicon crystal. For the two temperatures which have been investigated (R.T. and 623K), the structures are very close to that of the Nasicon analog: Na/sub 3/Sc/sub 2/P/sub 3/O/sub 12/. However the Si/P substitution prevents the sodium long range ordering even in the monoclinic low temperature phase and therefore themore » cross over to the rhombohedral symmetry only involves very small atomic displacements. For both structures, a new sodium position (mid-Na) is displayed in the conduction channel, intermediate between the usual Na(1) and Na(2) sites.« less

Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH 3NH 3) 2CdX 4 (X = Cl, Br, I)

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

Roccanova, Rachel; Ming, Wenmei; Whiteside, Vincent R.

Here, we report the synthesis, crystal and electronic structures, as well as optical properties of the hybrid organic–inorganic compounds MA 2CdX 4 (MA = CH 3NH 3; X = Cl, Br, I). MA 2CdI 4 is a new compound, whereas, for MA 2CdCl 4 and MA 2CdBr 4, structural investigations have already been conducted but electronic structures and optical properties are reported here for the first time. Single crystals were grown through slow evaporation of MA 2CdX 4 solutions with optimized conditions yielding mm-sized colorless (X = Cl, Br) and pale yellow (X = I) crystals. Single crystal and variablemore » temperature powder X-ray diffraction measurements suggest that MA 2CdCl 4 forms a 2D layered perovskite structure and has two structural transitions at 283 and 173 K. In contrast, MA 2CdBr 4 and MA 2CdI 4 adopt 0D K 2SO 4-derived crystal structures based on isolated CdX 4 tetrahedra and show no phase transitions down to 20 K. The contrasting crystal structures and chemical compositions in the MA 2CdX 4 family impact their air stabilities, investigated for the first time in this work; MA 2CdCl 4 is air-stable, whereas MA 2CdBr 4 and MA 2CdI 4 partially decompose when left in air. Optical absorption measurements suggest that MA 2CdX 4 have large optical band gaps above 3.9 eV. Room temperature photoluminescence spectra of MA 2CdX 4 yield broad peaks in the 375–955 nm range with full width at half-maximum values up to 208 nm. These PL peaks are tentatively assigned to self-trapped excitons in MA 2CdX 4 following the crystal and electronic structure considerations. The bands around the Fermi level have small dispersions, which is indicative of high charge localization with significant exciton binding energies in MA 2CdX 4. On the basis of our combined experimental and computational results, MA 2CdX 4 and related compounds may be of interest for white-light-emitting phosphors and scintillator applications.« less

Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH 3NH 3) 2CdX 4 (X = Cl, Br, I)

DOE PAGES

Roccanova, Rachel; Ming, Wenmei; Whiteside, Vincent R.; ...

2017-11-02

Here, we report the synthesis, crystal and electronic structures, as well as optical properties of the hybrid organic–inorganic compounds MA 2CdX 4 (MA = CH 3NH 3; X = Cl, Br, I). MA 2CdI 4 is a new compound, whereas, for MA 2CdCl 4 and MA 2CdBr 4, structural investigations have already been conducted but electronic structures and optical properties are reported here for the first time. Single crystals were grown through slow evaporation of MA 2CdX 4 solutions with optimized conditions yielding mm-sized colorless (X = Cl, Br) and pale yellow (X = I) crystals. Single crystal and variablemore » temperature powder X-ray diffraction measurements suggest that MA 2CdCl 4 forms a 2D layered perovskite structure and has two structural transitions at 283 and 173 K. In contrast, MA 2CdBr 4 and MA 2CdI 4 adopt 0D K 2SO 4-derived crystal structures based on isolated CdX 4 tetrahedra and show no phase transitions down to 20 K. The contrasting crystal structures and chemical compositions in the MA 2CdX 4 family impact their air stabilities, investigated for the first time in this work; MA 2CdCl 4 is air-stable, whereas MA 2CdBr 4 and MA 2CdI 4 partially decompose when left in air. Optical absorption measurements suggest that MA 2CdX 4 have large optical band gaps above 3.9 eV. Room temperature photoluminescence spectra of MA 2CdX 4 yield broad peaks in the 375–955 nm range with full width at half-maximum values up to 208 nm. These PL peaks are tentatively assigned to self-trapped excitons in MA 2CdX 4 following the crystal and electronic structure considerations. The bands around the Fermi level have small dispersions, which is indicative of high charge localization with significant exciton binding energies in MA 2CdX 4. On the basis of our combined experimental and computational results, MA 2CdX 4 and related compounds may be of interest for white-light-emitting phosphors and scintillator applications.« less

Ge K-Edge Extended X-Ray Absorption Fine Structure Study of the Local Structure of Amorphous GeTe and the Crystallization

NASA Astrophysics Data System (ADS)

Maeda, Yoshihito; Wakagi, Masatoshi

1991-01-01

The local structure and crystallization of amorphous GeTe (a-GeTe) were examined by means of Ge K-edge EXAFS. In a-GeTe, both Ge-Ge and Ge-Te bonds were observed to exist in nearest neighbors of Ge. The average coordination number around Ge is 3.7, which is close to the tetrahedral structure. A random covalent network (RCN) model seems to be suitable for the local Structure. After a-GeTe crystallizes at 129°C, the Ge-Ge bond disappears and the Ge-Te bond length increases considerably. As temperature rises, in a-GeTe the Debye-Waller factor of the Ge-Te bond increases greatly, while that of the Ge-Ge bond increases only slightly. At the crystallization, it is found that the fluctuation of the Ge-Te bond length plays a major role in the change of the local structure and bonding state around Ge.

Medium-range structure and glass forming ability in Zr–Cu–Al bulk metallic glasses

DOE PAGES

Zhang, Pei; Maldonis, Jason J.; Besser, M. F.; ...

2016-03-05

Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr–Cu–Al bulk metallic glass (BMG) alloys. Both Zr 50Cu 35Al 15 and Zr 50Cu 45Al 5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr 50Cu 35Al 15, the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T g, than in Zr 50Cu 45Al 5. Variable resolution fluctuation microscopy of the MRO clusters show that in Zr 50Cu 35Al 15more » on sub-Tg annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Furthermore, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures.« less

Electron paramagnetic resonance study of radiation-induced paramagnetic centers in succinic anhydride single crystal

NASA Astrophysics Data System (ADS)

Caliskan, Betul; Caliskan, Ali Cengiz; Er, Emine

2017-09-01

Succinic anhydride single crystals were exposed to 60Co-gamma irradiation at room temperature. The irradiated single crystals were investigated at 125 K by Electron Paramagnetic Resonance (EPR) Spectroscopy. The investigation of EPR spectra of irradiated single crystals of succinic anhydride showed the presence of two succinic anhydride anion radicals. The anion radicals observed in gamma-irradiated succinic anhydride single crystal were created by the scission of the carbon-oxygen double bond. The structure of EPR spectra demonstrated that the hyperfine splittings arise from the same radical species. The reduction of succinic anhydride was identified which is formed by the addition of an electron to oxygen of the Csbnd O bond. The g values, the hyperfine structure constants and direction cosines of the radiation damage centers observed in succinic anhydride single crystal were obtained.

Radiation-induced hydroxyl addition to purine molecules: EPR and ENDOR study of hypoxanthine hydrochloride monohydrate single crystals.

PubMed

Tokdemir, Sibel; Nelson, William H

2005-06-01

Three radical species were detected in an EPR/ENDOR study of X-irradiated hypoxanthine.HCl.H2O single crystals at room temperature: RI was identified as the product of net H addition to C8, RII was identified as the product of net H addition to C2, and RIII was identified as the product of OH addition to C8. The observed set of radicals was the same for room-temperature irradiation as for irradiation at 10 K followed by warming the crystals to room temperature; however, the C2 H-addition and C8 OH-addition radicals were not detectable after storage of the crystals for about 2 months at room temperature. Use of selectively deuterated crystals permitted unique assignment of the observed hyperfine couplings, and results of density functional theory calculations on each of the radical structures were consistent with the experimental results. Comparison of these experimental results with others from previous crystal-based systems and model system computations provides insight into the mechanisms by which the biologically important purine C8 hydroxyl addition products are formed. The evidence from solid systems supports the mechanism of net water addition to one-electron oxidized purine bases and demonstrates the importance of a facial approach between the reactants.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

DOE PAGES

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh; ...

2017-04-14

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Liquid crystal 'blue phases' with a wide temperature range.

PubMed

Coles, Harry J; Pivnenko, Mikhail N

2005-08-18

Liquid crystal 'blue phases' are highly fluid self-assembled three-dimensional cubic defect structures that exist over narrow temperature ranges in highly chiral liquid crystals. The characteristic period of these defects is of the order of the wavelength of visible light, and they give rise to vivid specular reflections that are controllable with external fields. Blue phases may be considered as examples of tuneable photonic crystals with many potential applications. The disadvantage of these materials, as predicted theoretically and proved experimentally, is that they have limited thermal stability: they exist over a small temperature range (0.5-2 degrees C) between isotropic and chiral nematic (N*) thermotropic phases, which limits their practical applicability. Here we report a generic family of liquid crystals that demonstrate an unusually broad body-centred cubic phase (BP I*) from 60 degrees C down to 16 degrees C. We prove this with optical texture analysis, selective reflection spectroscopy, Kössel diagrams and differential scanning calorimetry, and show, using a simple polarizer-free electro-optic cell, that the reflected colour is switched reversibly in applied electric fields over a wide colour range in typically 10 ms. We propose that the unusual behaviour of these blue phase materials is due to their dimeric molecular structure and their very high flexoelectric coefficients. This in turn sets out new theoretical challenges and potentially opens up new photonic applications.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

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

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Unusual structural phase transition in [N(C2H5)4][N(CH3)4][ZnBr4

NASA Astrophysics Data System (ADS)

Krawczyk, Monika K.; Ingram, Adam; Cach, Ryszard; Czapla, Zbigniew; Czupiński, Olaf; Dacko, Sławomir; Staniorowski, Piotr

2018-04-01

The new hybrid organic-inorganic crystal [N(C2H5)4][N(CH3)4][ZnBr4] was grown and its physical properties and structural phase transition are presented. On the basis of thermal analysis (DSC (differential scanning calorimetry), DTA (differential thermal analysis), DTG), X-ray structural, dilatometric and dielectric studies as well as optical observation, the reversible first-order phase transition at 490/488 K on heating and cooling run, respectively, has been found. An appearance of domain structure of ferroelastic type gives evidence for an untypical lowering of crystal symmetry during the phase transition. At room temperature, the satisfying crystal structure solution was found in the tetragonal system, in the P?21m space group.

Silicon crystals: Process for manufacturing wafer-like silicon crystals with a columnar structure

NASA Technical Reports Server (NTRS)

Authier, B.

1978-01-01

Wafer-like crystals suitable for making solar cells are formed by pouring molten Si containing suitable dopants into a mold of the desired shape and allowing it to solidify in a temperature gradient, whereby the large surface of the melt in contact with the mold is kept at less than 200 D and the free surface is kept at a temperature of 200-1000 D higher, but below the melting point of Si. The mold can also be made in the form of a slit, whereby the 2 sides of the mold are kept at different temperatures. A mold was milled in the surface of a cylindrical graphite block 200 mm in diameter. The granite block was induction heated and the bottom of the mold was cooled by means of a water-cooled Cu plate, so that the surface of the mold in contact with one of the largest surfaces of the melt was held at approximately 800 D. The free surface of the melt was subjected to thermal radiation from a graphite plate located 2 mm from the surface and heated to 1500 D. The Si crystal formed after slow cooling to room temperature had a columnar structure and was cut with a diamond saw into wafers approximately 500 mm thick. Solar cells prepared from these wafers had efficiencies of 10 to 11%.

Growth of NH4Cl Single Crystal from Vapor Phase in Vertical Furnace

NASA Astrophysics Data System (ADS)

Nigara, Yutaka; Yoshizawa, Masahito; Fujimura, Tadao

1983-02-01

A pure and internally stress-free single crystal of NH4Cl was grown successfully from the vapor phase. The crystal measured 1.6 cmφ× 2 cm and had the disordered CsCl structure, which was stable below 184°C. The crystal was grown in an ampoule in a vertical furnace, in which the vapor was efficiently transported both by diffusion and convection. In line with the growth mechanism of a single crystal, the temperature fluctuation (°C/min) on the growth interface was kept smaller than the product of the temperature gradient (°C/cm) and the growth rate (cm/min). The specific heat of the crystal was measured around -31°C (242 K) during cooling and heating cycles by AC calorimetry. The thermal hysteresis (0.4 K) obtained here was smaller than that (0.89 K) of an NH4Cl crystal grown from its aqueous solution with urea added as a habit modifier.

Survey and analysis of crystal polymorphism in organic structures

PubMed Central

Kaur, Ramanpreet

2018-01-01

With the intention of producing the most comprehensive treatment of the prevalence of crystal polymorphism among structurally characterized materials, all polymorphic compounds flagged as such within the Cambridge Structural Database (CSD) are analysed and a list of crystallographically characterized organic polymorphic compounds is assembled. Classifying these structures into subclasses of anhydrates, salts, hydrates, non-hydrated solvates and cocrystals reveals that there are significant variations in polymorphism prevalence as a function of crystal type, a fact which has not previously been recognized in the literature. It is also shown that, as a percentage, polymorphic entries are decreasing temporally within the CSD, with the notable exception of cocrystals, which continue to rise at a rate that is a constant fraction of the overall entries. Some phenomena identified that require additional scrutiny include the relative prevalence of temperature-induced phase transitions among organic salts and the paucity of polymorphism in crystals with three or more chemical components. PMID:29765601

The Conformational Flexibility of the Acyltransferase from the Disorazole Polyketide Synthase Is Revealed by an X-ray Free-Electron Laser Using a Room-Temperature Sample Delivery Method for Serial Crystallography

PubMed Central

Allison, Kim; Robbins, Thomas; Lyubimov, Artem Y.; Uervirojnangkoorn, Monarin; Brunger, Axel T.; Khosla, Chaitan; DeMirci, Hasan; McPhillips, Scott E.; Hollenbeck, Michael; Soltis, Michael; Cohen, Aina E.

2017-01-01

The crystal structure of the trans-acyltrans-ferase (AT) from the disorazole polyketide synthase (PKS) was determined at room temperature to a resolution of 2.5 Å using a new method for the direct delivery of the sample into an X-ray free-electron laser. A novel sample extractor efficiently delivered limited quantities of microcrystals directly from the native crystallization solution into the X-ray beam at room temperature. The AT structure revealed important catalytic features of this core PKS enzyme, including the occurrence of conformational changes around the active site. The implications of these conformational changes for polyketide synthase reaction dynamics are discussed. PMID:28832129

Crystal structure, electronic structure, optical and scintillation properties of self-activated Cs 4YbI 6 [Crystal structure, optical and scintillation properties of self-activated Cs 4YbI 6

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

Wu, Yuntao; Chakoumakos, Bryan C.; Shi, Hongliang

A self-activated Cs 4YbI 6 single crystal was grown by the vertical Bridgman method. Crystal structure refinements verified the phase purity and the trigonal crystal system with a space group of more » $$\\bar{R}$$3 c. By using differential scanning calorimetry, the melting and crystallization points were determined to be 550 and 510 °C, respectively. Luminescence and scintillation properties were systematically studied. Upon ultraviolet light (360 nm) excitation, the Cs 4YbI 6 crystal exhibits bluish-green emission centered at 450 and 480 nm due to spin-allowed and spin-forbidden transitions of Yb 2+ activators. The lifetimes of the corresponding emission bands at room temperature are tens and hundreds of nanoseconds, respectively. X-ray excited radioluminescence spectrum is dominated by the spin-forbidden transition of Yb 2+ at 480 nm. The absolute light yield is 2700 ± 200 photons/MeV with a principal scintillation decay time of 33 ns. In conclusion, the physical explanation for the low light yield observed is proposed from experimental and theoretical insights.« less

Crystal structure, electronic structure, optical and scintillation properties of self-activated Cs 4YbI 6 [Crystal structure, optical and scintillation properties of self-activated Cs 4YbI 6

DOE PAGES

Wu, Yuntao; Chakoumakos, Bryan C.; Shi, Hongliang; ...

2018-05-14

A self-activated Cs 4YbI 6 single crystal was grown by the vertical Bridgman method. Crystal structure refinements verified the phase purity and the trigonal crystal system with a space group of more » $$\\bar{R}$$3 c. By using differential scanning calorimetry, the melting and crystallization points were determined to be 550 and 510 °C, respectively. Luminescence and scintillation properties were systematically studied. Upon ultraviolet light (360 nm) excitation, the Cs 4YbI 6 crystal exhibits bluish-green emission centered at 450 and 480 nm due to spin-allowed and spin-forbidden transitions of Yb 2+ activators. The lifetimes of the corresponding emission bands at room temperature are tens and hundreds of nanoseconds, respectively. X-ray excited radioluminescence spectrum is dominated by the spin-forbidden transition of Yb 2+ at 480 nm. The absolute light yield is 2700 ± 200 photons/MeV with a principal scintillation decay time of 33 ns. In conclusion, the physical explanation for the low light yield observed is proposed from experimental and theoretical insights.« less

Brownmillerite Ca 2 Co 2 O 5 : Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal Structural Transitions

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

Zhang, Junjie; Zheng, Hong; Malliakas, Christos D.

2014-11-20

We synthesized Ca 2Co 2O 5 in the brownmillerite form using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4×0.8×0.5 mm 3 were obtained. At room temperature, Ca 2Co 2O 5 crystallizes as a fully ordered brownmillerite variant in the orthorhombic space group Pcmb (No. 57) with unit cell parameters a=5.28960(10) Å, b=14.9240(2) Å, and c=10.9547(2) Å. Furthermore, with decreasing temperature, it undergoes re-entrant sequence of first-order structural phase transitions (Pcmb→ P2/c11→ P121/m1→ Pcmb) that is unprecedented among brownmillerites, broadening the family of space groups available to these materials and challenging current approaches for sortingmore » the myriad variants of brownmillerite structures. Magnetic susceptibility data indicate antiferromagnetic ordering in Ca 2Co 2O 5 occurs near 240 K, corroborated by neutron powder diffraction. Below 140 K, Ca 2Co 2O 5 shows a weak ferromagnetic component directed primarily along the b axis, and it also exhibits thermal and magnetic history dependence in magnetization.« less

Metal-loaded pollucite-like aluminophosphates: dissymmetrisation of crystal structures and physical properties

NASA Astrophysics Data System (ADS)

Shvanskaya, L. V.; Yakubovich, O. V.; Koshelev, A. V.; Vasiliev, A. N.

2018-02-01

Two aluminophosphate analogues of the mineral pollucite with the general formula Cs2(M,Al)3P3O12 (where M = Cu or Mn) have been synthesized by high-temperature flux and structurally characterized using the single-crystal X-ray diffraction. Both samples crystallize in cubic I4132 space group, Z = 8, with a = 13.5911(5) and a = 13.8544(7) for Cu- and Mn-loaded phases, respectively. Their framework structures are based on the ANA-type topology and exhibit the partial ordering of the metal (M/Al) and phosphorus (P) cations over the tetrahedral sites. The regular changes in cell dimensions and volumes in the row Cs2(Cu,Al)3P3O12→Cs2(Mn,Al)3P3O12 obviously correspond to increasing radii of the transition metal. The crystal chemical analysis of both pollucite-like phases show correlations between the difference in the radii size of tetrahedral cations and the degree of distortion of flexible ANA-type framework due to decreasing of the intertetrahedral angles (T-O-T). Magnetic susceptibility measurements indicate that both compounds are paramagnets in the temperature range of 2-300 K.

Structural characterization of oxidized titanium surfaces

NASA Astrophysics Data System (ADS)

Jobin, M.; Taborelli, M.; Descouts, P.

1995-05-01

Oxidized titanium surfaces resulting from various processes have been structurally characterized by means of scanning force microscopy, x-ray photoemission spectroscopy (XPS), x-ray diffraction, and electron energy-loss spectroscopy (EELS) with losses in the 0-100 eV range. It has been found that the surface morphology has a granular structure for electropolished titanium and for titanium evaporated on mica at low substrate temperature (570 K), but changes to flat terraces for the films evaporated at higher temperature (770 K). Angular-dependent XPS has revealed the presence of a Ti2O3 suboxide at the Ti/TiO2 interface for electropolished titanium. Dry oxidation has been performed at 770 and 970 K on both weakly and highly crystallized evaporated titanium films oriented along (0001). In the case of underlying crystallized metallic titanium, the resulting TiO2 films are crystallized with the anatase (004) orientation for oxidation at 770 K and with rutile (200) orientation for oxidation at 970 K. EELS spectra interpreted in terms of the molecular orbitals of a (TiO6)8- cluster show that the local octahedral environment of titanium atoms is preserved on native oxides, even if these oxides are not crystallized.

Phase field modeling of rapid crystallization in the phase-change material AIST

NASA Astrophysics Data System (ADS)

Tabatabaei, Fatemeh; Boussinot, Guillaume; Spatschek, Robert; Brener, Efim A.; Apel, Markus

2017-07-01

We carry out phase field modeling as a continuum simulation technique in order to study rapid crystallization processes in the phase-change material AIST (Ag4In3Sb67Te26). In particular, we simulate the spatio-temporal evolution of the crystallization of a molten area of the phase-change material embedded in a layer stack. The simulation model is adapted to the experimental conditions used for recent measurements of crystallization rates by a laser pulse technique. Simulations are performed for substrate temperatures close to the melting temperature of AIST down to low temperatures when an amorphous state is involved. The design of the phase field model using the thin interface limit allows us to retrieve the two limiting regimes of interface controlled (low temperatures) and thermal transport controlled (high temperatures) dynamics. Our simulations show that, generically, the crystallization velocity presents a maximum in the intermediate regime where both the interface mobility and the thermal transport, through the molten area as well as through the layer stack, are important. Simulations reveal the complex interplay of all different contributions. This suggests that the maximum switching velocity depends not only on material properties but also on the precise design of the thin film structure into which the phase-change material is embedded.

Structural, quantum chemical, vibrational and thermal studies of a hydrogen bonded zwitterionic co-crystal (nicotinic acid: pyrogallol)

NASA Astrophysics Data System (ADS)

Prabha, E. Arockia Jeya Yasmi; Kumar, S. Suresh; Athimoolam, S.; Sridhar, B.

2017-02-01

In the present work, a new co-crystal of nicotinic acid with pyrogallol (NICPY) has been grown in the zwitterionic form and the corresponding structural, vibrational, thermal, solubility and anti-cancer characteristics have been reported. The single crystal X-ray diffraction analysis confirms that the structural molecular packing of the crystal stabilized through N-H⋯O and O-H⋯O hydrogen bond. The stabilization energy of the hydrogen bond motifs were calculated in the solid state. Vibrational spectral studies such as Fourier transform-infrared (FT-IR) and FT-Raman were adopted to understand the zwitterionic co-crystalline nature of the compound, which has been compared with theoretically calculated vibrational frequencies. The thermal stability of the grown co-crystal was analyzed by TG/DTA study. The solubility of the NICPY co-crystal was investigated in water at different temperature and compared with that of the nicotinic acid, which is the parent compound of NICPY co-crystal. The grown crystals were treated with human cervical cancer cell line (HeLa) to analyze the cytotoxicity of NICPY crystals and compared with the parent compound, which shows that NICPY has moderate activity against human cervical cancer cell line.

Fundamental Studies of Crystal Growth of Microporous Materials

NASA Technical Reports Server (NTRS)

Singh, Ramsharan; Doolittle, John, Jr.; Payra, Pramatha; Dutta, Prabir K.; George, Michael A.; Ramachandran, Narayanan; Schoeman, Brian J.

2003-01-01

Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (a) Nature of the molecular units responsible for the crystal nuclei formation; (b) Nature of the nuclei and nucleation process; (c) Growth process of the nuclei into crystal; (d) Morphological control and size of the resulting crystal; (e) Surface structure of the resulting crystals; and (f) Transformation of frameworks into other frameworks or condensed structures.

First Protein Crystallization Experiments on The International Space Station: Sweet Success in Space With Thaumatin

NASA Technical Reports Server (NTRS)

Kundrot, Craig E.; Barnes, Cindy L.; Snell, Eddie H.; Achari, Aniruddha; Whitaker, Ann F. (Technical Monitor)

2001-01-01

We determined the room temperature 1.2 A structure of thaumatin using a crystal grown in the first protein crystallization experiment conducted aboard the International Space Station (ISS). The crystals were grown in the Enhanced Gaseous Nitrogen Dewar (EGN) developed by Alexander McPherson and co-workers. EGN transports frozen solutions contained in tygon tubing in a liquid nitrogen Dewar to ISS where the tubes then thaw. Batch, free interface diffusion (FID), or vapor diffusion crystallization occurs after thawing. EGN was flown to the ISS on STS-106 on September 8, 2000. This was a "risk mitigation" flight that tested EGN performance and the process of conducting experiments on ISS. We focused on how to map a hanging drop crystallization recipe to the EGN FID method. Thaumatin was chosen as the test system. Three series of crystallization recipes were set-up. Each series tested different volume ratios of protein-rich solution to precipitant-rich solution. The series differed from each other by fixing either the protein concentration or the amount of protein in the solutions. Upon return of the samples to Earth on October 24 by STS-92, bubbles that spanned the diameter of the tubing were observed in all tubes. Such bubbles interrupt liquid-liquid diffusion and force vapor diffusion equilibration to occur instead. Nonetheless, crystals grew in 9 of 30 tubes. Many large crystals were grown, the largest being 2.0 x 1.1 x 1.0 cubic mm. The largest crystal was used to collect data at room temperature on beamline 7-1 of the Stanford Synchrotron Radiation Source to a maximum resolution of 1.2 A. The structure was refined anisotropically using SHELX with a data to parameter ratio of 4.5 to give an R(sub factor) of 15.8% (R(sub free) = 18.2%) for ail reflections without generated hydrogens. This refinement is proceeding. Comparisons of this 1.2 A microgravity structure to previous reports of the thaumatin structure at 1.75 A and to ground control crystals will be presented.

Effects of structural imperfection on gelatinization characteristics of amylopectin starches with A- and B-type crystallinity.

PubMed

Genkina, Natalia K; Wikman, Jeanette; Bertoft, Eric; Yuryev, Vladimir P

2007-07-01

The aim of the present work was to investigate the effect of physical structures on the properties of starch granules. Starches with a high amylopectin content possessing A- and B-type crystallinity were chosen for the study. The gelatinization temperature decreased in the following order: maize (A) > potato (B) > wheat (A) > barley (A), which did not reflect a correlation with the type of crystallinity. Low values of gelatinization temperature were accompanied with high free surface energy of the crystallites. It is proposed that these data are caused by different types of imperfections in starch crystals. Annealing resulted in an enhancement of the gelatinization temperature and a decrease of the free surface energy of the crystallites for all starches reflecting a partial improvement of crystalline perfection. A limited acid hydrolysis (lintnerization) of the starches decreased the gelatinization temperature because of a partial disruption of the crystalline lamellae and an increase of the amount of defects on the edges of the crystallites. Annealing of the lintnerized starches improved the structure of maize and potato starch, giving them similar structural and physicochemical parameters, which was opposite the behavior of the annealed sample from wheat. The possible nature of removable and nonremovable defects inside the crystalline region of the starch granules is discussed. It is concluded that, besides the allomorphic A- and B-types of crystal packing, physical defects in the crystals possess a major impact on starch gelatinization.

Annealing of gallium nitride under high-N 2 pressure

NASA Astrophysics Data System (ADS)

Porowski, S.; Jun, J.; Krukowski, S.; Grzegory, I.; Leszczynski, M.; Suski, T.; Teisseyre, H.; Foxon, C. T.; Korakakis, D.

1999-04-01

GaN is the key material for blue and ultraviolet optoelectronics. It is a strongly bonded wurztite structure semiconductor with the direct energy gap 3.5 eV. Due to strong bonding, the diffusion processes require high temperatures, above 1300 K. However at this temperature range at ambient pressure, GaN becomes unstable and dissociates into Ga and N 2. Therefore high pressure of N 2 is required to study the diffusion and other annealing related processes. We studied annealing of bulk GaN nitride single crystals grown under high pressure and also annealing of homo- and heteroepitaxial GaN layers grown by MOCVD technique. Annealing at temperatures above 1300 K influences strongly the structural and optical properties of GaN crystals and layers. At this temperature diffusion of the Mg and Zn acceptors have been observed. In spite of very interesting experimental observations the understanding of microscopic mechanisms of these processes is limited.

Predicting Molecular Crystal Properties from First Principles: Finite-Temperature Thermochemistry to NMR Crystallography.

PubMed

Beran, Gregory J O; Hartman, Joshua D; Heit, Yonaton N

2016-11-15

Molecular crystals occur widely in pharmaceuticals, foods, explosives, organic semiconductors, and many other applications. Thanks to substantial progress in electronic structure modeling of molecular crystals, attention is now shifting from basic crystal structure prediction and lattice energy modeling toward the accurate prediction of experimentally observable properties at finite temperatures and pressures. This Account discusses how fragment-based electronic structure methods can be used to model a variety of experimentally relevant molecular crystal properties. First, it describes the coupling of fragment electronic structure models with quasi-harmonic techniques for modeling the thermal expansion of molecular crystals, and what effects this expansion has on thermochemical and mechanical properties. Excellent agreement with experiment is demonstrated for the molar volume, sublimation enthalpy, entropy, and free energy, and the bulk modulus of phase I carbon dioxide when large basis second-order Møller-Plesset perturbation theory (MP2) or coupled cluster theories (CCSD(T)) are used. In addition, physical insight is offered into how neglect of thermal expansion affects these properties. Zero-point vibrational motion leads to an appreciable expansion in the molar volume; in carbon dioxide, it accounts for around 30% of the overall volume expansion between the electronic structure energy minimum and the molar volume at the sublimation point. In addition, because thermal expansion typically weakens the intermolecular interactions, neglecting thermal expansion artificially stabilizes the solid and causes the sublimation enthalpy to be too large at higher temperatures. Thermal expansion also frequently weakens the lower-frequency lattice phonon modes; neglecting thermal expansion causes the entropy of sublimation to be overestimated. Interestingly, the sublimation free energy is less significantly affected by neglecting thermal expansion because the systematic errors in the enthalpy and entropy cancel somewhat. Second, because solid state nuclear magnetic resonance (NMR) plays an increasingly important role in molecular crystal studies, this Account discusses how fragment methods can be used to achieve higher-accuracy chemical shifts in molecular crystals. Whereas widely used plane wave density functional theory models are largely restricted to generalized gradient approximation (GGA) functionals like PBE in practice, fragment methods allow the routine use of hybrid density functionals with only modest increases in computational cost. In extensive molecular crystal benchmarks, hybrid functionals like PBE0 predict chemical shifts with 20-30% higher accuracy than GGAs, particularly for 1 H, 13 C, and 15 N nuclei. Due to their higher sensitivity to polarization effects, 17 O chemical shifts prove slightly harder to predict with fragment methods. Nevertheless, the fragment model results are still competitive with those from GIPAW. The improved accuracy achievable with fragment approaches and hybrid density functionals increases discrimination between different potential assignments of individual shifts or crystal structures, which is critical in NMR crystallography applications. This higher accuracy and greater discrimination are highlighted in application to the solid state NMR of different acetaminophen and testosterone crystal forms.

Effect of surface modification of cellulose nanocrystal on nonisothermal crystallization of poly(β-hydroxybutyrate) composites.

PubMed

Chen, Jianxiang; Wu, Defeng; Tam, Kam C; Pan, Keren; Zheng, Zhigong

2017-02-10

Ring-opening polymerization of l-lactide from cellulose nanocrystal (CNC) surface yielded polylactide-grafted CNC (CNC-g-PLA). The structure and chemical composition of the CNC-g-PLA were characterized by FT-IR, 1 H NMR, XPS and XRD. The crystallization behavior and lamellar structure of poly(β-hydroxybutyrate) (PHB) in the presence of pristine CNC and CNC-g-PLA were elucidated via DSC and SAXS, and Babinet's reciprocity theory was applied. Crystallization kinetics were further analyzed using Ozawa, Mo and Kissinger models. In the presence of pristine CNC, nucleation of PHB crystals led to an increase in the crystallization temperature (T c ) of PHB; while CNC-g-PLA acted as antinucleation agent, resulting in a remarkable reduction in T c of PHB. Accordingly, the composite with pristine CNC possessed a higher crystallization rate than neat PHB, while CNC-g-PLA displayed the lowest crystallization rate. However, the lamellar structure of PHB was not affected by the presence of pristine and modified CNCs, and almost identical crystallization activation energies as the neat PHB were observed, indicating that nucleation is dominant during PHB crystallization, instead of crystal growth. This study offers a promising approach of using pristine and modified CNCs to control the crystallization of biodegradable aliphatic polyesters. Copyright © 2016 Elsevier Ltd. All rights reserved.

Wavelength and bandwidth tunable photonic stopband of ferroelectric liquid crystals.

PubMed

Ozaki, Ryotaro; Moritake, Hiroshi

2012-03-12

The chiral smectic C phase of ferroelectric liquid crystals (FLCs) has a self-assembling helical structure which is regarded as a one-dimensional pseudo-photonic crystal. It is well known that a stopband of a FLC can be tuned in wavelength domain by changing temperature or electric field. We here have demonstrated an FLC stopband with independently tunable wavelength and bandwidth by controlling temperature and incident angle. At highly oblique incidence, the stopband does not have polarization dependence. Furthermore, the bandwidth at highly oblique incidence is much wider than that at normal incidence. The mechanism of the tunable stopband is clarified by considering the reflection at oblique incidence.

Serial Femtosecond Crystallography of G Protein-Coupled Receptors

PubMed Central

Liu, Wei; Wacker, Daniel; Gati, Cornelius; Han, Gye Won; James, Daniel; Wang, Dingjie; Nelson, Garrett; Weierstall, Uwe; Katritch, Vsevolod; Barty, Anton; Zatsepin, Nadia A.; Li, Dianfan; Messerschmidt, Marc; Boutet, Sébastien; Williams, Garth J.; Koglin, Jason E.; Seibert, M. Marvin; Wang, Chong; Shah, Syed T.A.; Basu, Shibom; Fromme, Raimund; Kupitz, Christopher; Rendek, Kimberley N.; Grotjohann, Ingo; Fromme, Petra; Kirian, Richard A.; Beyerlein, Kenneth R.; White, Thomas A.; Chapman, Henry N.; Caffrey, Martin; Spence, John C.H.; Stevens, Raymond C.; Cherezov, Vadim

2014-01-01

X-ray crystallography of G protein-coupled receptors and other membrane proteins is hampered by difficulties associated with growing sufficiently large crystals that withstand radiation damage and yield high-resolution data at synchrotron sources. Here we used an x-ray free-electron laser (XFEL) with individual 50-fs duration x-ray pulses to minimize radiation damage and obtained a high-resolution room temperature structure of a human serotonin receptor using sub-10 µm microcrystals grown in a membrane mimetic matrix known as lipidic cubic phase. Compared to the structure solved by traditional microcrystallography from cryo-cooled crystals of about two orders of magnitude larger volume, the room temperature XFEL structure displays a distinct distribution of thermal motions and conformations of residues that likely more accurately represent the receptor structure and dynamics in a cellular environment. PMID:24357322

Growth, structural, optical and surface analysis of piperazinium tartrate: A NLO single crystal

NASA Astrophysics Data System (ADS)

Gupta, Apurva; Raseel Rahman M., K.; Nair, Lekha

2018-05-01

Single crystal of piperazinium tartrate (PPZT) was grown by the slow evaporation solution growth technique at room temperature. Crystallinity of grown crystal was examined by powder X-ray diffraction. High transparency and wide band gap were observed in the UV-Visible spectroscopic studies. Intense and broad emissions were observed in the blue region, as that is indicated by photoluminescence spectroscopy. The quality of the grown PPZT single crystals were analyzed by the etching studies using the water as the etchant.

L-Nitroargininium picrate

NASA Astrophysics Data System (ADS)

Apreyan, R. A.; Fleck, M.; Atanesyan, A. K.; Sukiasyan, R. P.; Petrosyan, A. M.

2015-12-01

L-Nitroargininium picrate has been obtained from an aqueous solution containing equimolar quantities of L-nitroarginine and picric acid by slow evaporation. Single crystal was grown by evaporation method. Crystal structure was determined at room temperature. The salt crystallizes in monoclinic crystal system (space group P21). Vibrational spectra and thermal properties were studied. Second harmonic generation efficiency measured by powder method is found to be four times higher than in L-nitroarginine, which in turn is ten times more efficient than KDP (KH2PO4).

Hydroxyl migration disorders the surface structure of hydroxyapatite nanoparticles

NASA Astrophysics Data System (ADS)

Cheng, Xiajie; Wu, Hong; Zhang, Li; Ma, Xingtao; Zhang, Xingdong; Yang, Mingli

2017-09-01

The surface structure of nano-hydroxyapatite (HAP) was investigated using a combined simulated annealing and molecular dynamics method. The stationary structures of nano-HAP with 4-7 nm in diameter and annealed under different temperatures were analyzed in terms of pair distribution function, structural factor, mean square displacement and atomic coordination number. The particles possess different structures from bulk crystal. A clear radial change in their atomic arrangements was noted. From core to surface the structures change from ordered to disordered. A three-shell model was proposed to describe the structure evolution of nano-HAP. Atoms in the core zone keep their arrangements as in crystal, while atoms in the surface shell are in short-range order and long-range disorder, adopting a typically amorphous structure. Atoms in the middle shell have small displacements and/or deflections but basically retain their original locations as in crystal. The disordered shell is about 1 nm in thickness, in agreement with experimental observations. The disordering mainly stems from hydroxyl migration during which hydroxyls move to the surface and bond with the exposed Ca ions, and their left vacancies bring about a rearrangement of nearby atoms. The disordering is to some extent different for particles unannealed under different temperatures, resulting from fewer number of migrated hydroxyls at lower temperatures. Particles with different sizes have similar surface structures, and their surface energy decreases with increasing size. Moreover, the surface energy is reduced by hydroxyl migration because the exposed Ca ions on the surface are ionically bonded with the migrated hydroxyls. Our calculations proposed a new structure model for nano-HAP, which indicates a surface structure with activities different from those without surface reorganization. This is particularly interesting because most bioactivities of biomaterials are dominated by their surface activity.

Ferroelectric performances and crystal structures of (Pb, La)(Zr, Ti, Nb)O{sub 3}

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

Kitamura, Naoto; Division of Ecosystem Research, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510; Mizoguchi, Takuma

2014-02-15

In this study, we focused on Nb and La substituted Pb(Zr, Ti)O{sub 3}: i.e., (Pb, La)(Zr, Ti, Nb)O{sub 3}. As for the samples, dependences of ferroelectric properties on La and Nb compositions were examined. In addition, the crystal structures were analyzed by the Rietveld method, and then a relationship between the metal compositions and the crystal structures were discussed. From P–E hysteresis loop measurements, it was found that the remanant polarization of Pb(Zr, Ti)O{sub 3} was increased by both the La and Nb substitutions although the heavy substitution of La had an undesirable effect. It was also indicated that themore » Curie temperature decreased with increasing La content. The Rietveld analysis using synchrotron X-ray diffraction patterns demonstrated that the structure distortion was relaxed by the La and Nb substitutions. Such a change in the crystals was well consistent with the harmful effects on the Curie temperature and the remanent polarization by the heavy La substitution. - Graphical abstract: Rietveld refinement pattern of 2 mol% PbSiO{sub 3}-added Pb{sub 0.95}La{sub 0.05}Zr{sub 0.50}Ti{sub 0.45}Nb{sub 0.05}O{sub 3} (synchrotron X-ray diffraction). Display Omitted - Highlights: • (Pb,La)(Zr,Ti,Nb)O{sub 3} were successfully synthesized. • Remanant polarization of Pb(Zr,Ti)O{sub 3} was improved by substitutions of La and Nb. • Crystal structures of (Pb,La)(Zr,Ti,Nb)O{sub 3} were refined and the distortions were estimated.« less

Crystallization of a Li2O2SiO2 Glass under High Hydrostatic Pressures

NASA Technical Reports Server (NTRS)

Fuss, T.; Day, D. E.; Lesher, C. E.; Ray, C. S.

2004-01-01

The crystallization behavior of a Li2O.2SiO2 (LS2) glass subjected to a uniform hydrostatic pressure of 4.5 or 6 GPa was investigated between 550 and 800 C using XRD, IR, Raman, TEM, NMR, and DTA. The density of the glass subjected to 6 GPa was between 2.52 plus or minus 0.01 and 2.57 plus or minus 0.01 grams per cubic centimeters, depending upon the processing temperatures, and was higher than that of the stoichiometric LS2 crystals, 2.46 plus or minus 0.01 grams per cubic centimeter. Thus, crystallization in 6 GPa glass occurred in a condition of negative volume dilatation, deltaV = V(sub glass) - V(sub crystal), while that for the 4.5 GPa glass occurred in the condition deltaV greater than 0. For deltaV greater than 0, which also includes the control glass at ambient (one atmosphere) pressure, the glasses always crystallize Li2Si2O5 (orthorhombic, Ccc2) crystals, but for deltaV less than 0 (6 GPa), the glasses crystallize Li2SiO3 crystals with a slightly deformed structure. The crystal growth rate vs. temperature curve moved to higher temperature with increasing pressure, and was independent of the sign of deltaV. These results for the effect of hydrostatic pressure on the crystallization of LS2 glass were discussed from thermodynamic considerations.

High pressure floating zone growth and structural properties of ferrimagnetic quantum paraelectric BaFe 12O 19

DOE PAGES

Cao, Huibo B.; Zhao, Zhiying Y.; Lee, Minseong; ...

2015-06-24

High quality single crystals of BaFemore » $$_{12}$$O$$_{19}$$ were grown with the floating zone technique in flowing oxygen atmosphere of 100 atm. BaFe$$_{12}$$O$$_{19}$$ melts incongruently in atmospheric oxygen. High oxygen pressure above 50 atm modifies the melting behavior to be congruent, which allows for the crystal growth with the crucible-free floating zone technique. Single crystal neutron diffraction were measured to determine the nuclear and magnetic structures at 4 K and 295 K. At both temperatures, there exist local electric dipoles formed by the off-mirror-plane displacements of magnetic Fe$$^{3+}$$ ions at the bypyramidal sites. The displacement at 4 K is about half of that at room temperature. The temperature dependence of specific heat shows no anomaly associated with the long range polar ordering in the temperature range of 1.90-300~K. The inverse dielectric constant along the c-axis shows a $T^2$ temperature dependence below 20 K and then following by a plateau below 10 K, recognized as quantum paraelectric features. Further cooling below 1.4 K, the upturn region was clearly revealed and indicates BaFe$$_{12}$$O$$_{19}$$ is a critical quantum paraelectric system with Fe$$^{3+}$$ ions playing roles for both magnetic and electric dipoles.« less

Modeling two-dimensional crystals and nanotubes with defects under stress

NASA Astrophysics Data System (ADS)

Dietel, Jürgen; Kleinert, Hagen

2009-06-01

We calculate analytically the phase diagram of a two-dimensional planar crystal and its wrapped version with defects under external homogeneous stress as a function of temperature using a simple elastic square lattice model that allows for defect formation. The temperature dependence turns out to be very weak. The results are relevant for recent stress experiments on carbon nanotubes at high temperatures. Under increasing stress, we find a crossover regime which we identify with a cracking transition that is almost independent of temperature. Furthermore, we find an almost stress-independent melting point. In addition, we derive an enhanced ductility with relative strains before cracking between 200% and 400%, in agreement with carbon nanotube experiments. The specific values depend on the Poisson ratio and the angle between the external force and the crystal axes. We give arguments that the results for carbon nanotubes should be not much different from these results in spite of the different lattice structures.

Estimation of the engineering elastic constants of a directionally solidified superalloy for finite element structural analysis

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali; Kalluri, Sreeramesh

1991-01-01

The temperature-dependent engineering elastic constants of a directionally solidified nickel-base superalloy were estimated from the single-crystal elastic constants of nickel and MAR-MOO2 superalloy by using Wells' method. In this method, the directionally solidified (columnar-grained) nickel-base superalloy was modeled as a transversely isotropic material, and the five independent elastic constants of the transversely isotropic material were determined from the three independent elastic constants of a cubic single crystal. Solidification for both the single crystals and the directionally solidified superalloy was assumed to be along the (001) direction. Temperature-dependent Young's moduli in longitudinal and transverse directions, shear moduli, and Poisson's ratios were tabulated for the directionally solidified nickel-base superalloy. These engineering elastic constants could be used as input for performing finite element structural analysis of directionally solidified turbine engine components.

Vapor-Deposited Glasses with Long-Range Columnar Liquid Crystalline Order

DOE PAGES

Gujral, Ankit; Gomez, Jaritza; Ruan, Shigang; ...

2017-10-04

Anisotropic molecular packing, particularly in highly ordered liquid crystalline arrangements, has the potential for optimizing performance in organic electronic and optoelectronic applications. Here we show that physical vapor deposition can be used to prepare highly organized glassy solids of discotic liquid crystalline systems. Using grazing incidence X-ray scattering, atomic force microscopy, and UV–vis spectroscopy, we compare three systems: a rectangular columnar liquid crystal, a hexagonal columnar liquid crystal, and a nonmesogen. The packing motifs accessible by vapor deposition are highly organized for the liquid crystalline systems with columns propagating either in-plane or out-of-plane depending upon the substrate temperature during deposition.more » As a result, the structures formed at a given substrate temperature can be understood as resulting from partial equilibration toward the structure of the equilibrium liquid crystal surface during the deposition process.« less

Thermoelectric clathrates of type I.

PubMed

Christensen, Mogens; Johnsen, Simon; Iversen, Bo Brummerstedt

2010-01-28

Thermoelectric clathrates hold significant promise for high temperature applications with zT values exceeding 1.3. The inorganic clathrates have been shown to be both chemically and thermally stable at high temperatures, and high performance can be obtained from both single crystals and processed powders. The clathrates also show excellent compatibility factors in segmented module applications. For a materials chemist it is furthermore of great importance that the clathrates exhibit a very rich chemistry with the ability for substitution of many different elements. This allows delicate tuning of both the crystal structure as well as the physical properties. With all these assets, it is not surprising that clathrates have been intensely investigated in the thermoelectric community during the past decade. The present perspective provides a review of the many studies concerned with the synthesis, crystal structure and thermoelectric properties of clathrates with emphasis on the type I clathrate.

Vapor-Deposited Glasses with Long-Range Columnar Liquid Crystalline Order

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

Gujral, Ankit; Gomez, Jaritza; Ruan, Shigang

Anisotropic molecular packing, particularly in highly ordered liquid crystalline arrangements, has the potential for optimizing performance in organic electronic and optoelectronic applications. Here we show that physical vapor deposition can be used to prepare highly organized glassy solids of discotic liquid crystalline systems. Using grazing incidence X-ray scattering, atomic force microscopy, and UV–vis spectroscopy, we compare three systems: a rectangular columnar liquid crystal, a hexagonal columnar liquid crystal, and a nonmesogen. The packing motifs accessible by vapor deposition are highly organized for the liquid crystalline systems with columns propagating either in-plane or out-of-plane depending upon the substrate temperature during deposition.more » As a result, the structures formed at a given substrate temperature can be understood as resulting from partial equilibration toward the structure of the equilibrium liquid crystal surface during the deposition process.« less

Ion Conduction Path and Low-Temperature Form:. Argyrodite-Type Superionic Conductors

NASA Astrophysics Data System (ADS)

Onoda, M.; Wada, H.; Sato, A.; Ishii, M.

2007-01-01

The structures of the orthorhombic room-temperature phase of Cu8GeS6 (phase II) and the monoclinic low-temperature phase of Ag7TaS6 (phase II) have been successfully refined based on X-ray diffraction data from 12-fold twinned (Cu8GeS6 II) and 24-fold twinned (Ag7TaS6 II) crystals. Respectively among 6 major and 6 minor twin domains of Cu8GeS6 II, or among 12 major and 12 minor twin domains of Ag7TaS6 II, the argyrodite-type frameworks, GeS6 or TaS6, can be superposed to each other in principle, and only Cu-Cu or Ag-Ag network directions differ. At higher temperature, the crystals were considered to be 2-fold twinned crystals of superionic-conductor phase I with a space group F 43m. On cooling, each domain transforms into 6 domains of orthorhombic Cu8GeS6 II or 12 domains of monoclinic Ag7TaS6 II. Superposed projections along 6 directions of the structure of Cu8GeS6 II and along 12 directions of the structure of Ag7TaS6 II seem to show approximate expressions for Cu-ion and Ag-ion conduction paths in superionic-conductor phases, Cu8GeS6 I and Ag7TaS6I.

Structure, phase transitions, and isotope effects in [(CH3)4N]2PuCl6

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

Wilson, Richard E.

2015-11-02

The single crystal X-ray diffraction structure of [(CH3)4N]2PuCl6 is presented for the first time, resolving long standing confusion and speculation regarding the structure of this compound in the literature. A temperature dependent study of this compound shows that the structure of [(CH3)4N]2PuCl6 undergoes no fewer than two phase transitions between 100 and 360 K. The phase of [(CH3)4N]2PuCl6 at room temperature is Fd-3c a = 26.012(3) Å. At 360 K, the structure is in space group Fm-3m with a = 13.088(1) Å. The plutonium octahedra and tetramethylammonium cations undergo a rotative displacement and the degree of rotation varies with temperature,more » giving rise to the phase transition from Fm-3m to Fd-3c as the crystal is cooled. Synthesis and structural studies of the deuterated salt [(CD3)4N]2PuCl6 suggest that there is an isotopic effect associated with this phase transition as revealed by a changing transition temperature in the deuterated versus protonated compound indicating that the donor-acceptor interactions between the tetramethylammonium cations and the hexachloroplutonate anions are driving the phase transformation.« less

Synthesis and crystal structure of the solid solution Co3(SeO3)3-x(PO3OH)x(H2O) involving crystallographic split positions of Se4+ and P5+.

PubMed

Zimmermann, Iwan; Johnsson, Mats

2013-10-21

Three new cobalt selenite hydroxo-phosphates laying in the solid solution Co3(SeO3)3-x(PO3OH)x(H2O), with x = 0.8, x = 1.0, and x = 1.2 are reported. Single crystals were obtained by hydrothermal synthesis and the crystal structure was determined by single crystal X-ray diffraction. The structure can be described as a 3D framework having selenite and hydroxo-phosphate groups protruding into channels in the crystal structure. Se(4+) and P(5+) share a split position in the structure so that either SeO3 groups having a stereochemically active lone pair or tetrahedrally coordinated PO3OH groups are present. The OH-group is thus only present when the split position is occupied by P(5+). The crystal water is coordinated to a cobalt atom and TG and IR measurements show that the water and hydroxyl groups leave the structure at unusually high temperatures (>450 °C). Magnetic susceptibility measurements show antiferromagnetic coupling below 16 K and a magnetic moment of 4.02(3) μB per Co atom was observed.

A revisit to the temperature dependence of electrical resistivity of α - Titanium at low temperatures

NASA Astrophysics Data System (ADS)

Sharath Chandra, L. S.; Mondal, R.; Thamizhavel, A.; Dhar, S. K.; Roy, S. B.

2017-09-01

The temperature dependence of resistivity ρ(T) of a polycrystalline sample and a single crystal sample (current along the [0001] direction) of α - Titanium (Ti) at low temperatures is revisited to understand the electrical charge transport phenomena in this hexagonal closed pack metal. We show that the ρ(T) in single crystal Ti can be explained by considering the scattering of electrons due to electron-phonon, electron-electron, inter-band s-d and electron-impurity interactions, whereas the ρ(T) of polycrystalline Ti could not be explained by these interactions alone. We observed that the effects of the anisotropy of the hexagonal structure on the electronic band structure and the phonon dispersion need to be taken into account to explain ρ(T) of polycrystalline Ti. Two Debye temperatures corresponding to two different directions for the electron-phonon interactions and inter-band s-d scattering are needed to account the observed ρ(T) in polycrystalline Ti.

Synthesis, structure, optical, photoluminescence and magnetic properties of K2[Co(C2O4)2(H2O)2]·4H2O

NASA Astrophysics Data System (ADS)

Narsimhulu, M.; Hussain, K. A.

2018-06-01

The synthesis, crystal structure, optical, photoluminescence and magnetic behaviour of potassium bis(oxalato)cobaltate(II)tertrahydrate{K2[Co(C2O4)2(H2O)2]·4H2O} are described. The compound was grown at room temperature from mixture of aqueous solutions by slow evaporation method. The X-ray crystallographic data showed that the compound belongs to the monoclinic crystal system with P21/n space group and Z = 4. The UV-visible diffuse absorbance spectra exhibited bands at 253, 285 and 541 nm in the visible and ultraviolet regions. The optical band gap of the compound was estimated as 3.4 eV. At room temperature, an intense photoluminescence was observed from this material around 392 nm when it excited at 254 nm. The variable temperature dc magnetic susceptibility measurements exposed paramagnetic behaviour at high temperatures and antiferromagnetic ordering at low temperatures.

High resolution x-ray diffraction analysis of annealed low-temperature gallium arsenide

NASA Astrophysics Data System (ADS)

Matyi, R. J.; Melloch, M. R.; Woodall, J. M.

1992-05-01

High resolution x-ray diffraction methods have been used to characterize GaAs grown at low substrate temperatures by molecular beam epitaxy and to examine the effects of post-growth annealing on the structure of the layers. Double crystal rocking curves from the as-deposited epitaxial layer show well-defined interference fringes, indicating a high level of structural perfection despite the presence of excess arsenic. Annealing at temperatures from 700 to 900 °C resulted in a decrease in the perpendicular lattice mismatch between the GaAs grown at low temperature and the substrate from 0.133% to 0.016% and a decrease (but not total elimination) of the visibility of the interference fringes. Triple-crystal diffraction scans around the 004 point in reciprocal space exhibited an increase in the apparent mosaic spread of the epitaxial layer with increasing anneal temperature. The observations are explained in terms of the growth of arsenic precipitates in the epitaxial layer.

H/D isotopic recognition and temperature effects in IR spectra of hydrogen-bonded cyclic dimers in crystals: 3-Methylcinnamic acid and 4-phenylbutyric acid

NASA Astrophysics Data System (ADS)

Hachuła, Barbara; Jabłońska-Czapla, Magdalena; Flakus, Henryk T.; Nowak, Maria; Kusz, Joachim

2015-01-01

In the present work, the experimental and theoretical study of the nature of the inter-hydrogen bond interactions in two different carboxylic acids, 3-methylcinnamic acid (3MCA) and 4-phenylbutyric acid (4PBA), were reported. The polarized IR spectra of 3MCA and 4PBA crystals were recorded at the frequency ranges of the νOsbnd H and νOsbnd D bands. The spectral properties of 3MCA and 4PBA interpreted with the aid of the calculations based on the "strong-coupling" model. The differences in the spectral properties of the two different dimeric systems in the crystals provide a valuable information about the existence of a direct relationship between the crystal spectral properties in IR and the electronic structure of the molecular systems. In 3MCA crystals strong vibrational exciton interactions favor a "tail-to-head" (TH)-type Davydov coupling widespread via the π-electrons, whereas in 4PBA crystals a weak "through-space" (SS) exciton coupling is responsible for a "side-to-side"-type coupling. The relative contribution of each individual exciton coupling mechanism in IR spectra generation strongly depends on temperature and molecular electronic structure. The H/D isotopic recognition effect, depending on a non-random distribution of protons and deuterons in the crystal hydrogen bridges, was also analyzed.

H/D isotopic recognition and temperature effects in IR spectra of hydrogen-bonded cyclic dimers in crystals: 3-methylcinnamic acid and 4-phenylbutyric acid.

PubMed

Hachuła, Barbara; Jabłońska-Czapla, Magdalena; Flakus, Henryk T; Nowak, Maria; Kusz, Joachim

2015-01-05

In the present work, the experimental and theoretical study of the nature of the inter-hydrogen bond interactions in two different carboxylic acids, 3-methylcinnamic acid (3MCA) and 4-phenylbutyric acid (4PBA), were reported. The polarized IR spectra of 3MCA and 4PBA crystals were recorded at the frequency ranges of the νO-H and νO-D bands. The spectral properties of 3MCA and 4PBA interpreted with the aid of the calculations based on the "strong-coupling" model. The differences in the spectral properties of the two different dimeric systems in the crystals provide a valuable information about the existence of a direct relationship between the crystal spectral properties in IR and the electronic structure of the molecular systems. In 3MCA crystals strong vibrational exciton interactions favor a "tail-to-head" (TH)-type Davydov coupling widespread via the π-electrons, whereas in 4PBA crystals a weak "through-space" (SS) exciton coupling is responsible for a "side-to-side"-type coupling. The relative contribution of each individual exciton coupling mechanism in IR spectra generation strongly depends on temperature and molecular electronic structure. The H/D isotopic recognition effect, depending on a non-random distribution of protons and deuterons in the crystal hydrogen bridges, was also analyzed. Copyright © 2014 Elsevier B.V. All rights reserved.

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

Zhang, Pei; Maldonis, Jason J.; Besser, M. F.

Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr–Cu–Al bulk metallic glass (BMG) alloys. Both Zr 50Cu 35Al 15 and Zr 50Cu 45Al 5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr 50Cu 35Al 15, the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T g, than in Zr 50Cu 45Al 5. Variable resolution fluctuation microscopy of the MRO clusters show that in Zr 50Cu 35Al 15more » on sub-Tg annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Furthermore, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures.« less

Protein crystal growth in microgravity review of large scale temperature induction method: Bovine insulin, human insulin and human α-interferon

NASA Astrophysics Data System (ADS)

Long, Marianna M.; Bishop, John Bradford; Delucas, Lawrence J.; Nagabhushan, Tattanhalli L.; Reichert, Paul; Smith, G. David

1997-01-01

The Protein Crystal Growth Facility (PCF) is space-flight hardware that accommodates large scale protein crystal growth experiments using temperature change as the inductive step. Recent modifications include specialized instrumentation for monitoring crystal nucleation with laser light scattering. This paper reviews results from its first seven flights on the Space Shuttle, the last with laser light scattering instrumentation in place. The PCF's objective is twofold: (1) the production of high quality protein crystals for x-ray analysis and subsequent structure-based drug design and (2) preparation of a large quantity of relatively contaminant free crystals for use as time-release protein pharmaceuticals. The first three Shuttle flights with bovine insulin constituted the PCF's proof of concept, demonstrating that the space-grown crystals were larger and diffracted to higher resolution than their earth-grown counterparts. The later four PCF missions were used to grow recombinant human insulin crystals for x-ray analysis and continue productions trials aimed at the development of a processing facility for crystalline recombinant a-interferon.

Strong, Ductile, and Thermally Stable bcc-Mg Nanolaminates

DOE PAGES

Pathak, Siddhartha; Velisavljevic, Nenad; Baldwin, Jon Kevin Scott; ...

2017-08-15

Magnesium has attracted attention worldwide because it is the lightest structural metal. However, a high strength-to-weight ratio remains its only attribute, since an intrinsic lack of strength, ductility and low melting temperature severely restricts practical applications of Mg. Through interface strains, the crystal structure of Mg can be transformed and stabilized from a simple hexagonal (hexagonal close packed hcp) to body center cubic (bcc) crystal structure at ambient pressures. Here, we demonstrate that when introduced into a nanocomposite bcc Mg is far more ductile, 50% stronger, and retains its strength after extended exposure to 200°C, which is 0.5 times itsmore » homologous temperature. These findings reveal an alternative solution to obtaining lightweight metals critically needed for future energy efficiency and fuel savings.« less

[Spectrum studies on titania photocatalysts].

PubMed

Su, W; Fu, X; Wei, K; Zhang, H; Lin, H; Wang, X; Li, D

2001-02-01

The nano-sized TiO2 photocatalysts were prepared by sol-gel method and characterized by FTIR spectroscopy, FT-Raman spectroscopy and diffuse reflectance spectroscopy(DRS). Photocatalytic degradation of oleic acid over the TiO2 catalysts was investigated. The result showed that calcination temperature has strong effect on crystal structure, energy band structure, optical adsorption and photocatalytic activity of the TiO2 catalysts. It was found that the TiO2 photocatalyst calcined at 400 degrees C has the best apparent optical adsorption, the biggest band edge position and the highest photoactivity. The effect of calcination temperature on photocatalytic activity of TiO2 catalysts has been ascribed to the changes in structure and optical property of catalyst such as crystal size, content of rutile, residual NO3-, and band-edge position of light adsorption.

Static high pressure studies on Nd and Sc

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

Akella, J.; Xu, J.; Smith, G.S.

1985-06-24

We have investigated the crystal structural transformations in neodymium and scandium up to 4.0 GPa pressure and at room temperature, in a diamond-anvil high pressure apparatus. Nd has a double hexagonal-close packed (dhcp) structure at ambient pressure and temperature. Then it transforms to a face-centered cubic (fcc) structure at 3.8 GPa, which further transforms to a triple hexagonal-close packed structure (thcp) at about 18.0 GPa. In scandium we observed only one transformation from the hexagonal-close packed (hcp) structure at room temperature to a tetragonal structure. This transformation occurs between 19.0 and 23.2 GPa pressure.

Crystalline, Glassy and Polymeric Electrolytes:. Similarities and Differences in Ionic Transport Mechanisms

NASA Astrophysics Data System (ADS)

Souquet, Jean Louis

2006-06-01

Ionocovalent crystals or glasses as well as molten salts or salt polymer complexes are currently studied as electrolytes for high energy density batteries. Their large Red/Ox stability range results from their thermodynamic or kinetic characteristics. For all these electrolytes, charge carriers are the consequence of local deviations from electroneutrality, identified as point defects for ionic crystals or partial dissociation in disordered structures. The charge carriers formation derives from a similar activated process. The main difference comes from the migration process, which depends on the dynamic properties of the surrounding medium. When the structural relaxation time is large, an activated process, mainly enthalpic, prevails for charge carriers migration. It is the usual case for ionic crystals or glasses. In the liquid or overcooled liquid states, the structural relaxation time of the medium is shorter that the time required for the activated migration process to occur and a local reorganization of the medium vanishes the energy barrier and provides the free volume necessary to ionic migration. In that case, the migration is mainly an entropic process. The configurational entropy necessary to this process decreases with temperature and vanishes at the so called ideal glass transition temperature which can be estimated by extrapolation of the transport properties or of the thermodynamic characteristics of the medium. However, at the experiment time scale, this configurational entropy disappears at a somewhat higher temperature, the glass transition temperature at which the structural relaxation time corresponds to the measurement time. Some glass forming ionic melts studied in a large temperature scale, over and below the glass transition temperature, evidence the two, enthalpic and entropic, migration mechanisms, allowing the determination of the thermodynamic characteristics of the charge carriers formation and migration. Some recent results indicate that entropic process, associated to long scale deformations, may also exist in crystalline structures.

Antiferromagnetic defect structure in LaNi O 3 – δ single crystals

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

Wang, Bi -Xia; Rosenkranz, Stephan; Rui, X.

Here, the origins of the metal-insulator and magnetic transitions exhibited by perovskite rare-earth nickelates, RNiO 3 (where R is a rare-earth element), remain open issues, with charge disproportionation, magnetic interactions, and lattice response across multiple length scales being among the many possible origins. Recently, growth of single crystals of LaNiO 3, which is the only member of these compounds that remains metallic in its ground state, has been reported, opening a new chapter in the investigation of the perovskite nickelates. Here, using a combination of magnetometry, heat capacity, and neutron scattering on as-grown and purposely reduced LaNiO 3–δ crystals, wemore » show that both antiferromagnetic and ferromagnetic phases with a Néel temperature of ~152 K and a Curie temperature of ~225 K can be induced by reduction of the oxygen content. Transmission electron microscopy shows that these phases are characterized by ordered oxygen vacancy defect structures that exist as dilute secondary phases in as-grown crystals despite growth in partial oxygen pressures up to at least 130 bar. The demonstration of antiferromagnetism resulting from oxygen vacancy ordered structures implies that stoichiometry must be explicitly considered when interpreting the bulk properties of LaNiO 3–δ single crystals; accordingly, the implications of our results for putative oxygen-stoichiometric LaNiO 3 are discussed.« less

Structural, thermal, laser damage, photoconductivity, NLO and mechanical properties of modified vertical Bridgman method grown AgGa0.5In0.5Se2 single crystal

NASA Astrophysics Data System (ADS)

Vijayakumar, P.; Ramasamy, P.

2016-08-01

AgGa0.5In0.5Se2 single crystal was grown using modified vertical Bridgman method. The structural perfection of the AgGa0.5In0.5Se2 single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. The structural and compositional uniformities of AgGa0.5In0.5Se2 were studied using Raman scattering spectroscopy at room temperature. The FWHM of the Γ1 (W1) and Γ5L (Γ15) measured at different regions of the crystal confirms that the composition throughout its length is fairly uniform. Thermal properties of the as-grown crystal, including specific heat, thermal diffusivity and thermal conductivity have been investigated. The multiple shot surface laser damage threshold value was measured using Nd:YAG laser. Photoconductivity measurements with different temperatures have confirmed the positive photoconducting behavior. Second harmonic generation (SHG) on powder samples has been measured using the Kurtz and Perry technique and the results display that AgGa0.5In0.5Se2 is a phase-matchable NLO material. The hardness behavior has been measured using Vickers micro hardness measurement and the indentation size effect has been observed. The classical Meyer's law, propositional resistance model and modified propositional resistance model have been used to analyse the micro hardness behavior.

Antiferromagnetic defect structure in LaNi O3 -δ single crystals

NASA Astrophysics Data System (ADS)

Wang, Bi-Xia; Rosenkranz, S.; Rui, X.; Zhang, Junjie; Ye, F.; Zheng, H.; Klie, R. F.; Mitchell, J. F.; Phelan, D.

2018-06-01

The origins of the metal-insulator and magnetic transitions exhibited by perovskite rare-earth nickelates, RNiO3 (where R is a rare-earth element), remain open issues, with charge disproportionation, magnetic interactions, and lattice response across multiple length scales being among the many possible origins. Recently, growth of single crystals of LaNiO3, which is the only member of these compounds that remains metallic in its ground state, has been reported, opening a new chapter in the investigation of the perovskite nickelates. Here, using a combination of magnetometry, heat capacity, and neutron scattering on as-grown and purposely reduced LaNi O3 -δ crystals, we show that both antiferromagnetic and ferromagnetic phases with a Néel temperature of ˜152 K and a Curie temperature of ˜225 K can be induced by reduction of the oxygen content. Transmission electron microscopy shows that these phases are characterized by ordered oxygen vacancy defect structures that exist as dilute secondary phases in as-grown crystals despite growth in partial oxygen pressures up to at least 130 bar. The demonstration of antiferromagnetism resulting from oxygen vacancy ordered structures implies that stoichiometry must be explicitly considered when interpreting the bulk properties of LaNi O3 -δ single crystals; accordingly, the implications of our results for putative oxygen-stoichiometric LaNiO3 are discussed.

Structures and phase transitions of the A7PSe6 (A = ag, Cu) argyrodite-type ionic conductors. III. alpha-Cu7PSe6

PubMed

Gaudin; Petricek; Boucher; Taulelle; Evain

2000-12-01

The crystal structure of the third polymorph of the Cu(7)PSe(6) argyrodite compound, alpha-Cu(7)PSe(6), heptacopper phosphorus hexaselenide, is determined by means of single-crystal diffraction from twinned crystals and X-ray powder diffraction, with the help of extensive NMR measurements. In the low-temperature form, i.e. below the last phase transition, alpha-Cu(7)PSe(6) crystallizes in orthorhombic symmetry, space group Pna2(1), with a = 14.3179 (4), b = 7.1112 (2), c = 10.1023 (3) A, V = 1028.590 (9) A(3) (deduced from powder data, T = 173 K) and Z = 4. Taking into account a twinning by reticular merohedry, the refinement of the alpha-Cu(7)PSe(6) structure leads to the residual factors R = 0.0466 and wR = 0.0486 for 127 parameters and 3714 observed, independent reflections (single-crystal data, T = 173 K). A full localization of the Cu(+)d(10) element is reached with one twofold-, one threefold- and five fourfold-coordinated Cu atoms. The observation of two phase transitions for Cu(7)PSe(6), to be compared with only one for Ag(7)PSe(6), is attributed to the d(10) element stability in a low coordination environment, copper being less prone to lower coordination sites than silver, especially at low temperature.

Aging-driven decomposition in zolpidem hemitartrate hemihydrate and the single-crystal structure of its decomposition products.

PubMed

Vega, Daniel R; Baggio, Ricardo; Roca, Mariana; Tombari, Dora

2011-04-01

The "aging-driven" decomposition of zolpidem hemitartrate hemihydrate (form A) has been followed by X-ray powder diffraction (XRPD), and the crystal and molecular structures of the decomposition products studied by single-crystal methods. The process is very similar to the "thermally driven" one, recently described in the literature for form E (Halasz and Dinnebier. 2010. J Pharm Sci 99(2): 871-874), resulting in a two-phase system: the neutral free base (common to both decomposition processes) and, in the present case, a novel zolpidem tartrate monohydrate, unique to the "aging-driven" decomposition. Our room-temperature single-crystal analysis gives for the free base comparable results as the high-temperature XRPD ones already reported by Halasz and Dinnebier: orthorhombic, Pcba, a = 9.6360(10) Å, b = 18.2690(5) Å, c = 18.4980(11) Å, and V = 3256.4(4) Å(3) . The unreported zolpidem tartrate monohydrate instead crystallizes in monoclinic P21 , which, for comparison purposes, we treated in the nonstandard setting P1121 with a = 20.7582(9) Å, b = 15.2331(5) Å, c = 7.2420(2) Å, γ = 90.826(2)°, and V = 2289.73(14) Å(3) . The structure presents two complete moieties in the asymmetric unit (z = 4, z' = 2). The different phases obtained in both decompositions are readily explained, considering the diverse genesis of both processes. Copyright © 2010 Wiley-Liss, Inc.

Antiferromagnetic defect structure in LaNi O 3 – δ single crystals

DOE PAGES

Wang, Bi -Xia; Rosenkranz, Stephan; Rui, X.; ...

2018-06-12

Here, the origins of the metal-insulator and magnetic transitions exhibited by perovskite rare-earth nickelates, RNiO 3 (where R is a rare-earth element), remain open issues, with charge disproportionation, magnetic interactions, and lattice response across multiple length scales being among the many possible origins. Recently, growth of single crystals of LaNiO 3, which is the only member of these compounds that remains metallic in its ground state, has been reported, opening a new chapter in the investigation of the perovskite nickelates. Here, using a combination of magnetometry, heat capacity, and neutron scattering on as-grown and purposely reduced LaNiO 3–δ crystals, wemore » show that both antiferromagnetic and ferromagnetic phases with a Néel temperature of ~152 K and a Curie temperature of ~225 K can be induced by reduction of the oxygen content. Transmission electron microscopy shows that these phases are characterized by ordered oxygen vacancy defect structures that exist as dilute secondary phases in as-grown crystals despite growth in partial oxygen pressures up to at least 130 bar. The demonstration of antiferromagnetism resulting from oxygen vacancy ordered structures implies that stoichiometry must be explicitly considered when interpreting the bulk properties of LaNiO 3–δ single crystals; accordingly, the implications of our results for putative oxygen-stoichiometric LaNiO 3 are discussed.« less

Preparation and characterization of superfine ammonium perchlorate (AP) crystals through ceramic membrane anti-solvent crystallization

NASA Astrophysics Data System (ADS)

Ma, Zhenye; Li, Cheng; Wu, Rujun; Chen, Rizhi; Gu, Zhenggui

2009-10-01

In this paper, a novel ceramic membrane anti-solvent crystallization (CMASC) method was proposed for the safe and rapid preparation ammonium perchlorate (AP) crystals, in which the acetone and ethyl acetate were chosen as solvent and anti-solvent, respectively. Comparing with the conventional liquid anti-solvent crystallization (LASC), CMASC which successfully introduces ceramic membrane with regular pore structure to the LASC as feeding medium, is favorable to control the rate of feeding rate and, therefore, to obtain size and morphology controllable AP. Several kinds of micro-sized AP particles with different morphology were obtained including polyhedral-like, quadrate-like to rod-like. The effect of processing parameters on the crystal size and shape of AP crystals such as volume ratio of anti-solvent to solvent, feeding pressure and crystallization temperature were investigated. It is found that higher volume ratio of anti-solvent to solvent, higher feeding pressure and higher temperature result in smaller particle size. Scaning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the resulting AP crystals. The nucleation and growth kinetic of the resulting AP crystals were also discussed.

Phase transition studied by 7Li nuclear magnetic resonance in LiXSO4 (X = K, Rb, Cs and NH4) single crystals

NASA Astrophysics Data System (ADS)

Lim, Ae Ran; Choh, Sung Ho; Jeong, Se-Young

2000-11-01

The temperature dependences of 7Li nuclear magnetic resonance in LiXSO4 (X = K, Rb, Cs, and NH4) single crystals grown by the slow evaporation method have been investigated by employing a Bruker FT NMR spectrometer. From the experimental data, the nuclear quadrupole constant, the asymmetry parameter and the principal axes of the EFG tensor were determined, and the results were compared with the crystal structure. The temperature dependences of the quadrupole parameters were explained with a single torsional mode of the Li-O bond by the Bayer theory. All the LiO4 tetrahedra in four different crystals showed torsional motion about the X-axis of the EFG tensor. Based on these results, the differences in atomic weight of X in the LiXSO4 single crystals are responsible for the differences in the torsional angular frequencies.

Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth.

PubMed

Utsumi, Wataru; Saitoh, Hiroyuki; Kaneko, Hiroshi; Watanuki, Tetsu; Aoki, Katsutoshi; Shimomura, Osamu

2003-11-01

The synthesis of large single crystals of GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue-light-emitting diodes and lasers. Although high-quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N(2) at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melting of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred at about 2,220 degrees C, and decreasing the temperature allowed the GaN melt to crystallize to the original structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.

Use of anomolous thermal imaging effects for multi-mode systems control during crystal growth

NASA Technical Reports Server (NTRS)

Wargo, Michael J.

1989-01-01

Real time image processing techniques, combined with multitasking computational capabilities are used to establish thermal imaging as a multimode sensor for systems control during crystal growth. Whereas certain regions of the high temperature scene are presently unusable for quantitative determination of temperature, the anomalous information thus obtained is found to serve as a potentially low noise source of other important systems control output. Using this approach, the light emission/reflection characteristics of the crystal, meniscus and melt system are used to infer the crystal diameter and a linear regression algorithm is employed to determine the local diameter trend. This data is utilized as input for closed loop control of crystal shape. No performance penalty in thermal imaging speed is paid for this added functionality. Approach to secondary (diameter) sensor design and systems control structure is discussed. Preliminary experimental results are presented.

Low-Threshold Lasing from 2D Homologous Organic-Inorganic Hybrid Ruddlesden-Popper Perovskite Single Crystals.

PubMed

Raghavan, Chinnambedu Murugesan; Chen, Tzu-Pei; Li, Shao-Sian; Chen, Wei-Liang; Lo, Chao-Yuan; Liao, Yu-Ming; Haider, Golam; Lin, Cheng-Chieh; Chen, Chia-Chun; Sankar, Raman; Chang, Yu-Ming; Chou, Fang-Cheng; Chen, Chun-Wei

2018-05-09

Organic-inorganic hybrid two-dimensional (2D) perovskites have recently attracted great attention in optical and optoelectronic applications due to their inherent natural quantum-well structure. We report the growth of high-quality millimeter-sized single crystals belonging to homologous two-dimensional (2D) hybrid organic-inorganic Ruddelsden-Popper perovskites (RPPs) of (BA) 2 (MA) n-1 Pb n I 3 n+1 ( n = 1, 2, and 3) by a slow evaporation at a constant-temperature (SECT) solution-growth strategy. The as-grown 2D hybrid perovskite single crystals exhibit excellent crystallinity, phase purity, and spectral uniformity. Low-threshold lasing behaviors with different emission wavelengths at room temperature have been observed from the homologous 2D hybrid RPP single crystals. Our result demonstrates that solution-growth homologous organic-inorganic hybrid 2D perovskite single crystals open up a new window as a promising candidate for optical gain media.

Photonic crystal fiber modal interferometer based on thin-core-fiber mode exciter.

PubMed

Miao, Yinping; Ma, Xixi; Wu, Jixuan; Song, Binbin; Zhang, Hao; Liu, Bo; Yao, Jianquan

2015-11-10

A thin-core-fiber excited photonic crystal fiber modal interferometer has been proposed and experimentally demonstrated. By employing a thin-core fiber as the mode exciter, both of the core and cladding modes propagate in the photonic crystal fiber and interfere with each other. The experimental results show that the transmission dips corresponding to different-order modes have various strain responses with opposite shift directions. The strain sensitivity could be improved to 58.57  pm/με for the applied strain from 0 to 491 με by utilizing the wavelength interval between the dips with opposite shift directions. Moreover, due to the pure silica property of the employed photonic crystal fiber, the proposed fiber modal interferometer exhibits a low-temperature sensitivity of about 0.56  pm/°C within a temperature range from 26.4°C (room temperature) to 70°C. Additionally, the proposed fiber modal interferometer has several advantages, such as good stability, compact structure, and simple fabrication. Therefore, it is more applicable for strain measurement with reducing temperature cross-sensitivity.

Crystallization kinetics, optical and dielectric properties of Li2OṡCdOṡBi2O3ṡSiO2 glasses

NASA Astrophysics Data System (ADS)

Rani, Saroj; Sanghi, Sujata; Ahlawat, Neetu; Agarwal, Ashish

2015-10-01

Crystallization kinetics, optical absorption and electrical behavior of lithium cadmium silicate glasses with different amount of bismuth oxide were investigated using non-isothermal crystallization approach, UV-VIS-NIR spectroscopy and impedance spectroscopy, respectively. These glasses were synthesized by normal melt quenching technique. Variation in physical properties, viz. density, molar volume with Bi2O3:SiO2 ratio were related to the structural changes occurring in the glasses. The glass transition temperature (Tg), crystalline peak temperature (Tp) and melting temperature (Tm) of these glasses were determined using differential scanning calorimeter at various heating rates. The dependence of Tg and Tp on heating rate has been used for the determination of the activation energy of glass transition and crystallization. Thermal stability parameters have revealed high stability of the glass prepared with 40 mol% of Bi2O3 content. The crystallization kinetics for the glasses was studied by using the Kissinger and modified Ozawa equations. Appearance of a sharp cut-off and a wide and reasonable transmission in VIS-NIR region makes these glasses suitable for IR transmission window. The cut-off wavelength, optical band gap and Urbach's energy have been analyzed and discussed in terms of changes in the glass structure. By analyzing the impedance spectra, the ac and dc conductivities, activation energy for dc conduction (Edc) and for relaxation (EM″) were calculated. The results obtained from dc conductivity confirm the network forming role of Cd2+ ion in the glasses. The scaling of the conductivity spectra has been used to interpret the temperature dependence of the relaxation dynamics. The observed conductivity spectra follows power law with exponent 's' which decreases with temperature and satisfies the correlated barrier hopping (CBH) model. The perfect overlying of normalized plots of electrical modulus on a single 'master curve' depicts temperature as well as composition independent dynamical process at several frequencies.

Growth and piezoelectric properties of Ca3Nb(Al0.5Ga0.5)3Si2O14 crystals with langasite structure

NASA Astrophysics Data System (ADS)

Xiong, Kainan; Zheng, Yanqing; Tu, Xiaoniu; Jiang, Bohan; Cao, Shuoliang; Shi, Erwei

2017-06-01

Piezoelectric crystals Ca3Nb(Al0.5Ga0.5)3Si2O14 (CNAGS) with langasite structure have been successfully grown by Czochralski method. In this work, the crystal structure, quality, chemical composition, piezoelectric properties, electric resistivity and optical properties of the as-grown crystals were characterized. The full width at half-maximum (FWHM) of the rocking curve of CNAGS was found to be 23″. The chemical compositions of CNAGS crystals are very close to that of initial compositions. At room temperature, the piezoelectric coefficients d11 and d14 of CNAGS crystals are 4.12 pC/N and -5.03 pC/N, and the electromechanical coupling coefficients k12 and k26 are also determined as 11.6% and 18.3%, respectively. The electric resistivity of as-growth crystal was found to be on the order of 2×108 Ω cm at 500 °C and 1×106 Ω cm at 800 °C. And the transmittances of CNAGS crystals were found to be over 80% in the wavelength range of 700-2700 nm.

Evolution of molecular crystal optical phonons near structural phase transitions

NASA Astrophysics Data System (ADS)

Michki, Nigel; Niessen, Katherine; Xu, Mengyang; Markelz, Andrea

Molecular crystals are increasingly important photonic and electronic materials. For example organic semiconductors are lightweight compared to inorganic semiconductors and have inexpensive scale up processing with roll to roll printing. However their implementation is limited by their environmental sensitivity, in part arising from the weak intermolecular interactions of the crystal. These weak interactions result in optical phonons in the terahertz frequency range. We examine the evolution of intermolecular interactions near structural phase transitions by measuring the optical phonons as a function of temperature and crystal orientation using terahertz time-domain spectroscopy. The measured orientation dependence of the resonances provides an additional constraint for comparison of the observed spectra with the density functional calculations, enabling us to follow specific phonon modes. We observe crystal reorganization near 350 K for oxalic acid as it transforms from dihydrate to anhydrous form. We also report the first THz spectra for the molecular crystal fructose through its melting point.

The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film

PubMed Central

Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

2016-01-01

Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

Molecular dynamics study on the evolution of interfacial dislocation network and mechanical properties of Ni-based single crystal superalloys

NASA Astrophysics Data System (ADS)

Li, Nan-Lin; Wu, Wen-Ping; Nie, Kai

2018-05-01

The evolution of misfit dislocation network at γ /γ‧ phase interface and tensile mechanical properties of Ni-based single crystal superalloys at various temperatures and strain rates are studied by using molecular dynamics (MD) simulations. From the simulations, it is found that with the increase of loading, the dislocation network effectively inhibits dislocations emitted in the γ matrix cutting into the γ‧ phase and absorbs the matrix dislocations to strengthen itself which increases the stability of structure. Under the influence of the temperature, the initial mosaic structure of dislocation network gradually becomes irregular, and the initial misfit stress and the elastic modulus slowly decline as temperature increasing. On the other hand, with the increase of the strain rate, it almost has no effect on the elastic modulus and the way of evolution of dislocation network, but contributes to the increases of the yield stress and tensile strength. Moreover, tension-compression asymmetry of Ni-based single crystal superalloys is also presented based on MD simulations.

Magnetic and thermal properties of amorphous TbFeCo alloy films

NASA Astrophysics Data System (ADS)

Wang, Ke; Dong, Shuo; Huang, Ya; Qiu, Yuzhen

2017-07-01

Amorphous TbFeCo material with perpendicular magnetic anisotropy is currently attracting more attention for potential applications in spintronic devices and logic memories. We systematically investigate magnetic, structural, thermal, optical and electrical properties of TbFeCo alloy films. It shows out-of-plane easy axis of the films turns into in-plane orientation after annealing. Significant increase in saturation magnetization in the temperature range between 400 and 450 °C is revealed by thermomagnetic measurements. The occurrence of crystallization and oxidation at high temperatures is confirmed by X-ray diffraction measurements. Pronounced changes in optical reflectance and sheet resistance are observed with temperature, in line with structural relaxation and change. The activation barriers for crystallization and oxidation are determined to be 1.01 eV and 0.83 eV, respectively, for FeCo-rich and Tb-rich samples. Better thermal stability against crystallization and oxidation is demonstrated in the FeCo-rich sample than the Tb-rich type. Our results provide some useful information for the alloy used in device fabrication.

Temperature and field induced strain measurements in single crystal Gd 5Si 2Ge 2

DOE PAGES

McCall, S. K.; Nersessian, N.; Carman, G. P.; ...

2016-03-29

The first-order magneto-structural transformation that occurs in Gd 5Si 2Ge 2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd 5Si 2.05Ge 1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of –8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of –8500 ppm, +900 ppm and +2300 ppm were measured along the a,more » b and c axes, respectively. Furthermore, using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.« less

TaRh2B2 and NbRh2B2: Superconductors with a chiral noncentrosymmetric crystal structure.

PubMed

Carnicom, Elizabeth M; Xie, Weiwei; Klimczuk, Tomasz; Lin, Jingjing; Górnicka, Karolina; Sobczak, Zuzanna; Ong, Nai Phuan; Cava, Robert J

2018-05-01

It is a fundamental truth in solid compounds that the physical properties follow the symmetry of the crystal structure. Nowhere is the effect of symmetry more pronounced than in the electronic and magnetic properties of materials-even the projection of the bulk crystal symmetry onto different crystal faces is known to have a substantial impact on the surface electronic states. The effect of bulk crystal symmetry on the properties of superconductors is widely appreciated, although its study presents substantial challenges. The effect of a lack of a center of symmetry in a crystal structure, for example, has long been understood to necessitate that the wave function of the collective electron state that gives rise to superconductivity has to be more complex than usual. However, few nonhypothetical materials, if any, have actually been proven to display exotic superconducting properties as a result. We introduce two new superconductors that in addition to having noncentrosymmetric crystal structures also have chiral crystal structures. Because the wave function of electrons in solids is particularly sensitive to the host material's symmetry, crystal structure chirality is expected to have a substantial effect on their superconducting wave functions. Our two experimentally obtained chiral noncentrosymmetric superconducting materials have transition temperatures to superconductivity that are easily experimentally accessible, and our basic property characterization suggests that their superconducting properties may be unusual. We propose that their study may allow for a more in-depth understanding of how chirality influences the properties of superconductors and devices that incorporate them.

Crystal structure and magnetism of the FexNi8-xSi3 materials, 0 ≤ x ≤ 8

NASA Astrophysics Data System (ADS)

Gallus, Simone; Haddouch, Mohammed Ait; Chikovani, Mamuka; Perßon, Jörg; Voigt, Jörg; Friese, Karen; Senyshyn, Anatoliy; Grzechnik, Andrzej

2018-02-01

The crystal structure and magnetic properties of the materials FexNi8-xSi3 with 0 ≤ x ≤ 8 have been investigated to estimate any possible magnetocaloric effect and compare it to that in known magnetocalorics. Two structural ranges could be identified in this system by X-ray and neutron diffraction. The structure of the samples with 0 ≤ x ≤ 4 is related to the trigonal structure of Ni31Si12. Doubled c lattice parameters compared to the one in Ni31Si12 are observed in the samples with x = 2 and x = 3. The average structure of Fe2Ni6Si3 has been determined by X-ray single-crystal diffraction. The compounds with the compositions 5 ≤ x ≤ 8 crystallize in cubic Fe3Si-type structure. Magnetic measurements have shown that the compound Fe3Ni5Si3 displays a phase transition close to room temperature. However, its magnetocaloric effect is much smaller than the one in the promising magnetocaloric materials.

Synthesis, growth, structural and optical studies of organic nonlinear optical material--piperazine-1,4-diium bis 2,4,6-trinitrophenolate.

PubMed

Suguna, S; Anbuselvi, D; Jayaraman, D; Nagaraja, K S; Jeyaraj, B

2014-11-11

Piperazine-1,4-diium bis 2,4,6-trinitrophenolate is one of the useful organic materials with nonlinear optical (NLO) and pharmaceutical applications. The material was grown by slow evaporation solution growth method at room temperature. The crystal system and lattice parameters were identified by single crystal XRD analysis. The grown material crystallizes in monoclinic system with P21/n space group. The main functional groups NH2, NO2, CN, CC, and phenolic 'O' atom were identified using FTIR analysis. The protons and carbons of grown crystal with various chemical environments were studied by 1H and 13C NMR spectroscopy to confirm the molecular structure. The optical properties of the crystal were studied by UV-vis-NIR spectroscopy and the transmission 100% range starts from 532 nm onwards. The optical band gap was measured as 2.63 eV from the plot of (αhν)2 versus hν. The thermal stability was detected at 304.1°C using TG-DTA analysis. The dielectric studies of the sample were carried out at different temperatures in the frequency range from 50 Hz to 5 MHz to establish the dielectric nature of the crystal. Photoconductivity measurements were carried out on the grown crystal. The Second Harmonic Generation (SHG) of the crystal was tested to confirm the nonlinear optical property. Copyright © 2014 Elsevier B.V. All rights reserved.

Formation of Polymer Networks for Fast In-Plane Switching of Liquid Crystals at Low Temperatures

NASA Astrophysics Data System (ADS)

Yu, Byeong-Hun; Song, Dong Han; Kim, Ki-Han; Wok Park, Byung; Choi, Sun-Wook; Park, Sung Il; Kang, Sung Gu; Yoon, Jeong Hwan; Kim, Byeong Koo; Yoon, Tae-Hoon

2013-09-01

We formed a polymer structure to enable fast in-plane switching of liquid crystals at low temperatures. The problem of the inevitable slow response at low temperatures was reduced by the formation of in-cell polymer networks in in-plane switching (IPS) cells. The electro-optic characteristics of polymer-networked IPS cells were measured at temperatures ranging from -10 to 20 °C. The turn-on and turn-off times of an IPS cell were reduced by 44.5 and 47.2% at -10 °C by the formation of polymer networks. We believe that the proposed technology can be applied to emerging display devices such as mobile phones and automotive displays that may be used at low temperatures.

Crystal structure and magnetic properties of Mn substituted ludwigite Co 3O 2BO 3

NASA Astrophysics Data System (ADS)

Knyazev, Yu. V.; Ivanova, N. B.; Kazak, N. V.; Platunov, M. S.; Bezmaternykh, L. N.; Velikanov, D. А.; Vasiliev, А. D.; Ovchinnikov, S. G.; Yurkin, G. Yu.

2012-03-01

The needle shape single crystals Co3-x MnxO2BO3 with ludwigite structure have been prepared. According to the X-ray diffraction data the preferable character of distinct crystallographic positions occupation by Mn ions is established. Magnetization field and temperature dependencies are measured. Paramagnetic Curie temperature value Θ=-100 K points out the predominance of antiferromagnetic interactions. Spin-glass magnetic ordering takes the onset at TN=41 K. The crystallographic and magnetic properties of Co3O2BO3:Mn are compared with the same for the isostructural analogs Co3O2BO3 and CoO2BO3:Fe.

The crystal and magnetic structures of Sr 2LaFe 3O 8

NASA Astrophysics Data System (ADS)

Battle, P. D.; Gibb, T. C.; Lightfoot, P.

1990-02-01

The crystal and magnetic structures of the anion-deficient perovskite Sr 2LaFe 3O 8 (space group Pmma, a = 5.5095(1), b = 11.8845(5), c = 5.6028(1)AÅ) have been refined from X-ray and neutron powder diffraction data collected at room temperature. The crystal structure consists of layers of octahedral (O) and tetrahedral (T) iron-oxygen polyhedra arranged in the stacking sequence … OOTOOT … perpendicular to theyˆaxis of the unit cell. The magnetic structure is that of a G-type antiferromagnet with ordered magnetic moments of 3.77(5) and 3.15(11) μ B at the octahedral and tetrahedral sites, respectively. The low moment at the tetrahedral site is consistent with the observed disorder and magnetic anisotropy.

Lifetimes and spatio-temporal response of protein crystals in intense X-ray microbeams

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

Warkentin, Matthew A.; Atakisi, Hakan; Hopkins, Jesse B.

Serial synchrotron-based crystallography using intense microfocused X-ray beams, fast-framing detectors and protein microcrystals held at 300 K promises to expand the range of accessible structural targets and to increase overall structure-pipeline throughputs. To explore the nature and consequences of X-ray radiation damage under microbeam illumination, the time-, dose- and temperature-dependent evolution of crystal diffraction have been measured with maximum dose rates of 50 MGy s −1 . At all temperatures and dose rates, the integrated diffraction intensity for a fixed crystal orientation shows non-exponential decays with dose. Non-exponential decays are a consequence of non-uniform illumination and the resulting spatial evolution of diffracted intensitymore » within the illuminated crystal volume. To quantify radiation-damage lifetimes and the damage state of diffracting crystal regions, a revised diffraction-weighted dose (DWD) is defined and it is shown that for Gaussian beams the DWD becomes nearly independent of actual dose at large doses. An apparent delayed onset of radiation damage seen in some intensity–dose curves is in fact a consequence of damage. Intensity fluctuations at high dose rates may arise from the impulsive release of gaseous damage products. Accounting for these effects, data collection at the highest dose rates increases crystal radiation lifetimes near 300 K (but not at 100 K) by a factor of ∼1.5–2 compared with those observed at conventional dose rates. Improved quantification and modeling of the complex spatio-temporal evolution of protein microcrystal diffraction in intense microbeams will enable more efficient data collection, and will be essential in improving the accuracy of structure factors and structural models.« less

Lifetimes and spatio-temporal response of protein crystals in intense X-ray microbeams

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

Warkentin, Matthew A.; Atakisi, Hakan; Hopkins, Jesse B.

Serial synchrotron-based crystallography using intense microfocused X-ray beams, fast-framing detectors and protein microcrystals held at 300 K promises to expand the range of accessible structural targets and to increase overall structure-pipeline throughputs. To explore the nature and consequences of X-ray radiation damage under microbeam illumination, the time-, dose- and temperature-dependent evolution of crystal diffraction have been measured with maximum dose rates of 50 MGy s –1. At all temperatures and dose rates, the integrated diffraction intensity for a fixed crystal orientation shows non-exponential decays with dose. Non-exponential decays are a consequence of non-uniform illumination and the resulting spatial evolution ofmore » diffracted intensity within the illuminated crystal volume. To quantify radiation-damage lifetimes and the damage state of diffracting crystal regions, a revised diffraction-weighted dose (DWD) is defined and it is shown that for Gaussian beams the DWD becomes nearly independent of actual dose at large doses. An apparent delayed onset of radiation damage seen in some intensity–dose curves is in fact a consequence of damage. Intensity fluctuations at high dose rates may arise from the impulsive release of gaseous damage products. Accounting for these effects, data collection at the highest dose rates increases crystal radiation lifetimes near 300 K (but not at 100 K) by a factor of ~1.5–2 compared with those observed at conventional dose rates. As a result, improved quantification and modeling of the complex spatio-temporal evolution of protein microcrystal diffraction in intense microbeams will enable more efficient data collection, and will be essential in improving the accuracy of structure factors and structural models.« less

Lifetimes and spatio-temporal response of protein crystals in intense X-ray microbeams

DOE PAGES

Warkentin, Matthew A.; Atakisi, Hakan; Hopkins, Jesse B.; ...

2017-10-13

Serial synchrotron-based crystallography using intense microfocused X-ray beams, fast-framing detectors and protein microcrystals held at 300 K promises to expand the range of accessible structural targets and to increase overall structure-pipeline throughputs. To explore the nature and consequences of X-ray radiation damage under microbeam illumination, the time-, dose- and temperature-dependent evolution of crystal diffraction have been measured with maximum dose rates of 50 MGy s –1. At all temperatures and dose rates, the integrated diffraction intensity for a fixed crystal orientation shows non-exponential decays with dose. Non-exponential decays are a consequence of non-uniform illumination and the resulting spatial evolution ofmore » diffracted intensity within the illuminated crystal volume. To quantify radiation-damage lifetimes and the damage state of diffracting crystal regions, a revised diffraction-weighted dose (DWD) is defined and it is shown that for Gaussian beams the DWD becomes nearly independent of actual dose at large doses. An apparent delayed onset of radiation damage seen in some intensity–dose curves is in fact a consequence of damage. Intensity fluctuations at high dose rates may arise from the impulsive release of gaseous damage products. Accounting for these effects, data collection at the highest dose rates increases crystal radiation lifetimes near 300 K (but not at 100 K) by a factor of ~1.5–2 compared with those observed at conventional dose rates. As a result, improved quantification and modeling of the complex spatio-temporal evolution of protein microcrystal diffraction in intense microbeams will enable more efficient data collection, and will be essential in improving the accuracy of structure factors and structural models.« less

Lifetimes and spatio-temporal response of protein crystals in intense X-ray microbeams

DOE PAGES

Warkentin, Matthew A.; Atakisi, Hakan; Hopkins, Jesse B.; ...

2017-10-13

Serial synchrotron-based crystallography using intense microfocused X-ray beams, fast-framing detectors and protein microcrystals held at 300 K promises to expand the range of accessible structural targets and to increase overall structure-pipeline throughputs. To explore the nature and consequences of X-ray radiation damage under microbeam illumination, the time-, dose- and temperature-dependent evolution of crystal diffraction have been measured with maximum dose rates of 50 MGy s −1 . At all temperatures and dose rates, the integrated diffraction intensity for a fixed crystal orientation shows non-exponential decays with dose. Non-exponential decays are a consequence of non-uniform illumination and the resulting spatial evolution of diffracted intensitymore » within the illuminated crystal volume. To quantify radiation-damage lifetimes and the damage state of diffracting crystal regions, a revised diffraction-weighted dose (DWD) is defined and it is shown that for Gaussian beams the DWD becomes nearly independent of actual dose at large doses. An apparent delayed onset of radiation damage seen in some intensity–dose curves is in fact a consequence of damage. Intensity fluctuations at high dose rates may arise from the impulsive release of gaseous damage products. Accounting for these effects, data collection at the highest dose rates increases crystal radiation lifetimes near 300 K (but not at 100 K) by a factor of ∼1.5–2 compared with those observed at conventional dose rates. Improved quantification and modeling of the complex spatio-temporal evolution of protein microcrystal diffraction in intense microbeams will enable more efficient data collection, and will be essential in improving the accuracy of structure factors and structural models.« less

Alternative approaches used to assess structural changes of natural zircon caused by heat treatment

NASA Astrophysics Data System (ADS)

Huong, L. T. T.; Thuyet, N. T. M.; Phan, T. L.; Tran, N.; Toan, D. N.; Thang, P. D.; Huy, B. T.

2018-03-01

It is known that large changes in the crystal structure of zircon (ZrSiO4) can be assessed through the linewidth of the characteristic Raman mode (Δν3) at 1008 cm-1. However, the use of Δν3 to assess small changes caused by heat treatment at temperatures below its decomposition temperature of 1670 °C is difficult. The present work points out that the combination of X-ray diffraction (XRD) analyses, and photoluminescence (PL) and Raman (RS) measurements with different excitation wavelengths is an effective approach to solve the above problem. In this context, we have selected natural zircon containing some rare-earth (RE) impurities, and then studied the changes in its crystal structure caused by heat treatment at temperatures Tan=400-1600 °C. XRD analyses reveal that small modifications of the unit-cell parameters occur as Tan>600 °C. Taking the intensity ratios of the ν3 mode to RE-related emissions (Iν3/IRE) or the PL intensity ratios between RE-related emissions into consideration, the similar results in good agreement with the XRD analyses are also found. We believe that the small structural changes are related to the migration and redistribution of defects and impurities, and re-crystallization of zircon. This could be further confirmed though the relation between paramagnetic and ferromagnetic signals when Tan changes.

Superconductivity versus structural phase transition in the closely related Bi 2Rh 3.5S 2 and Bi 2Rh 3S 2

DOE PAGES

Kaluarachchi, Udhara S.; Xie, Weiwei; Lin, Qisheng; ...

2015-05-19

Single crystals of Bi 2Rh 3S 2 and Bi 2Rh 3.5S 2 were synthesized by solution growth, and the crystal structures and thermodynamic and transport properties of both compounds were studied. In the case of Bi 2Rh 3S 2, a structural first-order transition at around 165 K is identified by single-crystal diffraction experiments, with clear signatures visible in resistivity, magnetization, and specific heat data. No superconducting transition for Bi 2Rh 3S 2 was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi 2Rh 3.5S 2; however, bulk superconductivity with a criticalmore » temperature, T c ≈ 1.7 K, was observed. The Sommerfeld coefficient γ and the Debye temperature (Θ D) were found to be 9.41 mJ mol –1K –2 and 209 K, respectively, for Bi 2Rh 3S 2, and 22 mJ mol –1K –2 and 196 K, respectively, for Bi 2Rh 3.5S 2. As a result, the study of the specific heat in the superconducting state of Bi 2Rh 3.5S 2 suggests that Bi 2Rh 3.5S 2 is a weakly coupled, BCS superconductor.« less

Evidence for the quasi-two dimensional behavior of the vortex structure in Bi 2Sr 2CaCu 2O 8 single crystals

NASA Astrophysics Data System (ADS)

Pastoriza, H.; Arribere, A.; Goffman, M. F.; de la Cruz, F.; Mitzi, D. B.; Kapitulnik, A.

1994-02-01

AC susceptibility and dc magnetization measurements on Bi 2Sr 2CaCu 2O 8 (BSCCO) single crystals in a wide range of temperatures clearly show that below the dc irreversibility line the vortex system loss the long range order in the c direction. The susceptibility data taken at 7 Hz show the different nature of two dissipation peaks: One related to the interplane currents at temperatures well below the dc irreversibility line and the other associated with the intraplane ones at temperatures above that line. In this sense the irreversibility line corresponds to the temperature where quasi-two dimensional vortices are depinned.

Crystal Structure and Magnetic Properties of New Cubic Quaternary Compounds RT2Sn2Zn18 (R = La, Ce, Pr, and Nd, and T = Co and Fe)

NASA Astrophysics Data System (ADS)

Isikawa, Yosikazu; Mizushima, Toshio; Ejiri, Jun-ichi; Kitayama, Shiori; Kumagai, Keigou; Kuwai, Tomohiko; Bordet, Pierre; Lejay, Pascal

2015-07-01

The new cubic quaternary intermetallic compounds RT2Sn2Zn18 (R = La, Ce, Pr, and Nd, and T = Co and Fe) were synthesized by the mixture-metal flux method using Zn and Sn. The crystal structure was investigated by powder X-ray diffraction and with a four-circle X-ray diffractometer using single crystals. The space group of the compounds is Fdbar{3}m (No. 227). The rare-earth atom is at the cubic site which is the center of a cage composed of Zn and Sn atoms. The crystal structure is the same as the CeCr2Al20-type crystal structure except the atoms at the 16c site, i.e., the Zn atoms at the 16c site are completely replaced by Sn atoms, indicating that the compounds are crystallographically new ordered quaternary compounds. The lattice parameter a and the physical properties of the magnetic susceptibility χ, the magnetization M, and the specific heat C of these cubic caged compounds were investigated. LaCo2Sn2Zn18 and LaFe2Sn2Zn18 are enhanced Pauli paramagnets that originate from the Co and Fe itinerant 3d electrons. CeCo2Sn2Zn18 and CeFe2Sn2Zn18 are also enhanced Pauli paramagnets that originate from both the 3d electrons and Ce 4f electrons. PrCo2Sn2Zn18 and PrFe2Sn2Zn18 are nonmagnetic materials with huge values of C divided by temperature, which indicates that the ground state of Pr ions is a non-Kramers' doublet. NdCo2Sn2Zn18 and NdFe2Sn2Zn18 are magnetic materials with the Néel temperatures of 1.0 and 3.8 K, respectively. All eight compounds have large magnetic moments of Co/Fe in the paramagnetic temperature region, and thus their magnetic moments are inferred to be magnetically frustrating owing to the pyrochlore lattice in the low-temperature region.

The significance of temperature dependence on the piezoelectric energy harvesting by using a phononic crystal

NASA Astrophysics Data System (ADS)

Aly, Arafa H.; Nagaty, Ahmed; Khalifa, Zaki; Mehaney, Ahmed

2018-05-01

In this study, an acoustic energy harvester based on a two-dimensional phononic crystal has been constructed. The present structure consists of silicon cylinders in the air background with a polyvinylidene fluoride cylinder as a defect to confine the acoustic energy. The presented energy harvester depends on the piezoelectric effect (using the piezoelectric material polyvinylidene fluoride) that converts the confined acoustic energy to electric energy. The maximum output voltage obtained equals 170 mV. Moreover, the results revealed that the output voltage can be increased with increasing temperature. In addition, the effects of the load resistance and the geometry of the piezoelectric material on the output voltage have been studied theoretically. Based on these results, all previous studies about energy harvesting in phononic structures must take temperature effects into account.

Thermal conductivity of solid monohydroxyl alcohols in polyamorphous states

NASA Astrophysics Data System (ADS)

Krivchikov, A. I.; Korolyuk, O. A.; Sharapova, I. V.

2012-01-01

New measurements of the thermal conductivity of solid ethyl alcohol C2H5OH in the interval from 2 K to the melting temperature are presented. An annealing effect in the thermal conductivity of the orientationally ordered phase of the alcohol has been observed over a wide range of temperatures. This phase was obtained as a result of an irreversible first-order phase transition from an orientationally disordered crystal with a cubic structure at T = 109 K. The thermal conductivity was observed to increase as the monoclinic lattice changed from a less stable phase to a more stable one. The growth may be due to the improved quality of the completely ordered crystal. A comparative analysis of the temperature dependences of the thermal conductivity κ(T) is made for the solid monohydroxyl alcohols CH3OH, C2H5OH, С2D5OD, C3H7OH, and C4H9OH in their disordered orientational and structural states. At low temperatures the thermal conductivity of the series of monohydroxyl structural glasses of the alcohols increases linearly with the mass of the alcohol molecule.

Direct measurement of the low temperature spin state transitions in La1-xSrxCoO3 (0.05 < x < 0.3)

NASA Astrophysics Data System (ADS)

Gulec, A.; Klie, R. F.

2014-12-01

Sr-doped LaCoO3 has a complex magnetic phase diagram, which is believed to be directly correlated to changes in the crystal structure and ordering of the Co3+ spin states. In this work, we study the low temperature Co3+-ion spin state transitions in Sr-doped LaCoO3 around the critical doping concentration where a metal to insulator transition has been observed using electron energy-loss spectroscopy of the O K-edge combined with the Co L-edge fine structure. We measure the local spin state of the Co3+-ions and we demonstrate that the Co3+ spin-state transition only occurs in La0.95Sr0.05CoO3 single-crystal materials in the temperature range accessible by LN2 in-situ cooling, while no structural symmetry change is observed. The presence of this low-temperature spin-state transition in La1-xSrxCoO3 (x < 0.17) has been proposed as the origin of the percolative magnetic ordering in doped LaCoO3.

Single crystal Ce doped scintillator material with garnet structure sensitive to gamma ray and neutron radiation

NASA Astrophysics Data System (ADS)

Solodovnikov, D.; Weber, M. H.; Haven, D. T.; Lynn, K. G.

2012-08-01

A mixed garnet scintillator host material is obtained from the melt—Yttrium Gadolinium Gallium Aluminum Garnet (YGGAG). In addition to the high thermal and chemical stability and radiation hardness found in garnet crystals, it offers sensitivity to neutrons due to the presence of Gd atoms, has lower melting temperature than yttrium aluminum garnet, and similar crystallization behavior suitable for growth of large volume crystals. Crystals of YGGAG doped with Ce of 10×10×10 mm3 have already demonstrated energy resolution of 10% at 662 keV.

Transition to collapsed tetragonal phase in CaFe 2As 2 single crystals as seen by 57Fe Mössbauer spectroscopy

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

Bud'ko, Sergey L.; Ma, Xiaoming; Tomić, Milan

Temperature dependent measurements of 57Fe Mössbauer spectra on CaFe 2As 2 single crystals in the tetragonal and collapsed tetragonal phases are reported. Clear features in the temperature dependencies of the isomer shift, relative spectra area, and quadrupole splitting are observed at the transition from the tetragonal to the collapsed tetragonal phase. From the temperature dependent isomer shift and spectral area data, an average stiffening of the phonon modes in the collapsed tetragonal phase is inferred. The quadrupole splitting increases by ~25% on cooling from room temperature to ~100 K in the tetragonal phase and is only weakly temperature dependent atmore » low temperatures in the collapsed tetragonal phase, in agreement with the anisotropic thermal expansion in this material. In order to gain microscopic insight about these measurements, we perform ab initio density functional theory calculations of the electric field gradient and the electron density of CaFe 2As 2 in both phases. By comparing the experimental data with the calculations we are able to fully characterize the crystal structure of the samples in the collapsed-tetragonal phase through determination of the As z coordinate. Furthermore, based on the obtained temperature dependent structural data we are able to propose charge saturation of the Fe-As bond region as the mechanism behind the stabilization of the collapsed-tetragonal phase at ambient pressure.« less

Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

NASA Astrophysics Data System (ADS)

Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

2017-01-01

GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.