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Lattice Vibrations (lattice + vibration)
Selected AbstractsAtomistic Simulation of the Lattice Constants and Lattice Vibrations in LnM4Al8 (Ln: Nd, Sm; M: Cr, Mn, Cu, Fe).CHEMINFORM, Issue 39 2003Yan-mei Kang No abstract is available for this article. [source] Single-crystal Raman study of erythrite, Co3(AsO4)2·8H2OJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2004Wayde N. Martens Abstract Single-crystal Raman and infrared spectra of natural and synthetic erythrite, Co3(AsO4)2·8H2O, are reported and compared with the spectra polycrystalline, synthetic annabergite, Ni3(AsO4)2·8H2O, and hörnesite, Mg3(AsO4)2·8H2O. Factor group analysis and single-crystal considerations were used to interpret the experimental data. The Raman spectra of erythrite reveal the ,1 arsenate stretching vibration at 850 cm,1 (Ag) with the corresponding infrared band at 821 cm,1 (Bu). The ,3 antisymmetric vibration is split into three components, observed at 796 (Ag), 788 (Ag) and 803 (Bg) cm,1. The ,2 symmetric bending modes are observed at 375 (Ag) and 385 (Bg) cm,1. The ,4 bending modes are predicted to split into three bands which are observed at 441 (Ag), 446 (Bg) and 457 (Ag) cm,1. Lattice vibrations are found at 112 (Ag), 124 (Bg), 145 (Ag), 157 (Bg), 165 (Ag), 179 (Ag), 189 (Ag), 191 (Bg), 201 (Bg), 210 (Ag), 227 (Ag), 250 (Ag), 264 (Ag), 264 (Ag), 280 (Bg), 302 (Bg), 321 (Bg) and 338 cm,1(Ag). Hydroxyl stretching modes are observed at 3050, 3218, 3333, 3449 and 3479 cm,1 in the infrared spectrum. Raman-active hydroxyl bands are detected at 3009 (Bg), 3052 (Ag), 3190 (Bg) 3203 (Bg), 3281 (Ag) and 3310 (Bg), 3436 (Bg) and 3443 (Ag) cm,1. Infrared hydroxyl bands at 3050 and 3218 cm,1 are from water type II, short hydrogen bonding distances, and the bands at 3449 and 3479 cm,1 are due to water I, long hydrogen bonding distances. Water bending modes are detected in the infrared spectrum at 1571, 1621, 1641 and 1682 cm,1, but owing to the inherent weak Raman scattering cross-section of water these could not be detected in the Raman spectra. Copyright © 2004 John Wiley & Sons, Ltd. [source] Phonons in the Kondo insulator YbB12PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004K. S. Nemkovski Abstract We have studied the phonon excitations in the Kondo insulator YbB12 by means of inelastic neutron scattering. The excitation spectra extended up to the energy of 130 meV that is connected with boron "molecules" vibrations mainly. The specific shape of phonon dispersion curves for low frequency lattice vibration has been found. It could be explained by weak bounding of Yb ions in the lattice. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ab initio crystal structure predictions for flexible hydrogen-bonded molecules.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2001Part III. Abstract In crystal structure predictions possible structures are usually ranked according to static energy. Here, this criterion has been replaced by the free energy at any temperature. The effects of harmonic lattice vibrations were found by standard lattice-dynamical calculations, including a rough estimate of the effects of thermal expansion. The procedure was tested on glycol and glycerol, for which accurate static energies had been obtained previously (Part II of this series). It was found that entropy and zero-point energy give the largest contribution to free energy differences between hypothetical crystal structures, adding up to about 3 kJ/mol for the structures with lowest energy. The temperature-dependent contribution to the energy and the effects of thermal expansion showed less variation among the structures. The overall accuracy in relative energies was estimated to be a few kJ/mol. The experimental crystal structure for glycol corresponded to the global free energy minimum, whereas for glycerol it ranked second at 1 kJ/mol. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 816,826, 2001 [source] Using terahertz pulsed spectroscopy to quantify pharmaceutical polymorphism and crystallinityJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2005Clare J. Strachan Abstract Terahertz pulsed spectroscopy (TPS) is a new technique that is capable of eliciting rich information when investigating pharmaceutical materials. In solids, it probes long-range crystalline lattice vibrations and low energy torsion and hydrogen bonding vibrations. These properties make TPS potentially an ideal tool to investigate crystallinity and polymorphism. In this study four drugs with different solid-state properties were analyzed using TPS and levels of polymorphism and crystallinity were quantified. Carbamazepine and enalapril maleate polymorphs, amorphous, and crystalline indomethacin, and thermotropic liquid crystalline and crystalline fenoprofen calcium mixtures were quantified using partial least-squares analysis. Root-mean-squared errors of cross validation as low as 0.349% and limits of detection as low as approximately 1% were obtained, demonstrating that TPS is an analytical technique of potential in quantifying solid-state properties of pharmaceutical compounds. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:837,846, 2005 [source] Raman spectroscopic study of the uranyl selenite mineral marthozite Cu[(UO2)3(SeO3)2O2]·8H2OJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2008Ray L. Frost Abstract The mineral marthozite, a uranyl selenite, has been characterised by Raman spectroscopy at 298 K. The bands at 812 and 797 cm,1 were assigned to the symmetric stretching modes of the (UO2)2+ and (SeO3)2, units, respectively. These values gave the calculated UO bond lengths in uranyl of 1.799 and/or 1.814 Å. Average UO bond length in uranyl is 1.795 Å, inferred from the X-ray single crystal structure analysis of marthozite by Cooper and Hawthorne. The broad band at 869 cm,1 was assigned to the ,3 antisymmetric stretching mode of the (UO2)2+ (calculated UO bond length 1.808 Å). The band at 739 cm,1 was attributed to the ,3 antisymmetric stretching vibration of the (SeO3)2, units. The ,4 and the ,2 vibrational modes of the (SeO3)2, units were observed at 424 and 473 cm,1. Bands observed at 257, and 199 and 139 cm,1 were assigned to OUO bending vibrations and lattice vibrations, respectively. OH···O hydrogen bond lengths were inferred using Libowiztky's empirical relation. The infrared spectrum of marthozite was studied for complementation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Thermal Conductivity of Monazite-Type REPO4 (RE=La, Ce, Nd, Sm, Eu, Gd)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Aibing Du Low-thermal conductivity ceramics in monazite-type REPO4 (RE=La, Ce, Nd, Sm, Eu, Gd) ceramics are expected to have potential in structural (refractories, thermal insulator) and nuclear applications. To this end, the present study determines their thermal conductivities and examines how differences of the rare earth ions change their thermal conductivity at different temperatures. The results show that their conductivities are remarkably low from 25° to 1000°C. In addition, different conductivity variation mechanisms exist that change gradually upon altering from LaPO4 to GdPO4 at low and high temperatures. At relatively lower temperatures (,400°C), the thermal conductivities of all the REPO4 ceramics decrease nearly at first, reach a minimum value, and then rise with gradual altering from LaPO4 to GdPO4. It may be due to the combined effects of the increase of both the anharmonicities in lattice vibrations and the bond strength. As the temperature increases, the conductivity trends become obscure, and the conductivities of the monazite-type REPO4 approach their minimum thermal conductivities when the temperature is above 800°C. [source] Electrical conductivity of vanadium dioxide switching channelPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2010A. Pergament Abstract The electrical conductivity of the switching channel of vanadium dioxide thin-film sandwich structures is studied over a wide temperature range (15,300,K). It is shown that the electrical resistance of the channel varies with temperature as R,,,exp(aT,,,b/T) in the high-temperature region (above 70,K). The experimental results are discussed from the viewpoint of the small polaron hopping conduction theory which takes into account the influence of thermal lattice vibrations onto the resonance integral. [source] Luminescence and vibrational properties of erbium-implanted nanoporous GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008C. B. Soh Abstract Implantation of erbium (Er) into GaN is useful in creating selected areas to emit at the green, yellow and infrared wavelengths. Enhanced erbium activation is obtained when erbium is implanted into porous GaN formed by electrochemical etching than into as-grown GaN. This is due to the increase in surface areas for light extraction and the availability of more free surfaces to accommodate strain when it is annealed. Furnace annealing at 1100 °C for 30 mins in nitrogen gives rise to higher band-edge photoluminescence intensity. Apart from the host GaN phonon modes, we have also observed disorder-induced lattice vibrations at 170, 200 and 350-365 cm,1 from Er-implanted porous GaN. The E2 (high) mode of GaN also shifts towards higher energy at higher annealing temperatures, indicative of more erbium occupying the VGa site (ionic radii of Er > Ga) and hence increasing the compressive stress in the GaN crystal lattice. The prominent defect-induced local vibrational modes in Er-doped nanoporous GaN are also observed in ultraviolet resonant Raman scattering. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New approach to the theory of lattice vibrations of random alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004V. S. VinogradovArticle first published online: 16 NOV 200 Abstract The theory of vibrational excitations of random alloys is presented, which takes into account the scattering of excitations on n -impurity complexes (clusters) and is capable to describe complex structure of their spectra. The essential feature of the theory consists in two-stage disorder averaging procedure. First, theory equations are averaged and Fourier transformed over the coordinate characterizing the cluster position as a whole. Then they are averaged over inter-impurity distances in the cluster. The derivation of the Green function equations is carried out both in the version similar to average-t-matrix approximation (ATA) and in that similar to coherent potential approximation (CPA). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phonons and Raman spectra of lithiated titanate Li0.5TiO2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004R. Baddour-Hadjean Abstract Raman spectra of the electrochemically lithiated TiO2 anatase evidence that Li intercalation induces complex spectral features in the high wavenumber range. These modes can be assigned to the stretching vibrations of Li-O valence bonds. Two theoretical approaches are used to describe the vibrations of Li atoms within the TiO2 lattice. First, the quantum-mechanical calculations of molecular clusters imitating the Li...TiO2 system, which showed formation of covalent Li-O bonds and allowed an estimation of their force constants. Second, the lattice dynamics simulation which enabled to predict the whole spectrum of Li-phonons and their interaction with TiO2 lattice vibrations. Complex structure of the observed Raman spectra is explained by multiplicity of the Li positions. This results in multiple Raman bands originated from the Li atom vibrations covering a wide frequency range from 450 up to 950 cm,1. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||