Debye Temperature (debye + temperature)

Distribution by Scientific Domains

Selected Abstracts

Studies on multiphased mixed crystals of NaCl, KCl and KI

M. Priya
Abstract Multiphased mixed crystals of NaCl, KCl and KI were grown by the melt method, for the first time. Densities and refractive indices of all the grown crystals were determined and used for the estimation of the composition in the crystal. Atomic absorption spectroscopic measurements were done to estimate the metal atom contents in the crystal. Lattice parameters and thermal parameters (Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency) were determined from the X-ray powder diffraction data. DC and AC electrical measurements were done at various temperatures ranging from 40 to 150°C. Activation energies were also estimated. The observed lattice parameters showed that the system exhibits three phases each nearly corresponds to NaCl, KCl and KI. The thermal and electrical parameters show a highly nonlinear bulk composition dependence. Results are reported. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thermal expansion and atomic displacement parameters of cubic KMgF3 perovskite determined by high-resolution neutron powder diffraction

I. G. Wood
The structure of KMgF3 has been determined by high-resolution neutron powder diffraction at 4.2,K, room temperature and at 10,K intervals from 373,K to 1223,K. The material remains cubic at all temperatures. The average volumetric coefficient of thermal expansion in the range 373,1223,K was found to be 7.11,(3) × 10,5,K,1. For temperatures between 4.2 and 1223,K, a second-order Grüneisen approximation to the zero-pressure equation of state, with the internal energy calculated via a Debye model, was found to fit well, with the following parameters: ,D = 536,(9),K, Vo = 62.876,(6),Å3, = 6.5,(1) and (VoKo/,,) = 3.40,(2) × 10,18,J, where ,D is the Debye temperature, Vo is the volume at T = 0, is the first derivative with respect to pressure of the incompressibility (Ko) and ,, is a Grüneisen parameter. The atomic displacement parameters were found to increase smoothly with T and could be fitted using Debye models with ,D in the range 305,581,K. At 1223,K, the displacement of the F ions was found to be much less anisotropic than that in NaMgF3 at this temperature. [source]

A stationary-wave model of enzyme catalysis

Carlo Canepa
Abstract An expression for the external force driving a system of two coupled oscillators in the condensed phase was derived in the frame of the Debye theory of solids. The time dependence and amplitude of the force is determined by the size of the cell embedding the coupled oscillators and its Debye temperature (,D). The dynamics of the driven system of oscillators were followed in the two regimes of (a) low ,D and cell diameter, as a model of liquid water, and (b) large ,D and cell diameter, as a model of the core of a protein. The response in potential energy of the reference oscillator was computed for all possible values of the internal parameters of the system under investigation. For protein cores, the region in the parameter space of high maximum potential energy of the reference oscillator is considerably extended with respect to the corresponding simulation for water. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

Temperature dependence of elastic parameters and internal frictions for MnCu20Ni5Fe2 alloy

Mikio Fukuhara
Abstract Using ultrasonics, MnCu20Ni5Fe2 (M2052) alloy's acoustic characteristics were observed in order to understand its high damping properties. Longitudinal and shear wave velocities, eight kinds of elastic parameters, and dilational and shear internal frictions were simultaneously measured as functions of temperature in cooling and heating runs between 218 and 373 K in M2052 alloy. A valley in Young and shear moduli, Debye temperature and internal friction peaks at around 345 K showed a M2052 fcc/fct trans-formation, accompanied by volume-nonpreserving lattice softening. The increment of dilational friction in the low temperature can be interpreted as boundary effect of the misfit domain, associated with nonharmonity of potential between pairs of atoms. The M2052 alloy shows highest elasticity below 300 K, indicating large resistance for volume-preserving distortion. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Phase transition and elasticity of CdO under pressure

Feng Peng
Abstract First-principles calculations of the crystal structures, and phase transition, and elastic properties of cadmium oxide (CdO) have been carried out with the plane-wave pseudopotential within the generalized gradient approximation in the frame of density functional theory method. The calculated values (for crystal structures) are in good agreement with experimental data as well as with some of the existing model calculations. For CsCl-type CdO, the dependence of the elastic constants cij, the aggregate elastic modulus (B, G, E), and the elastic anisotropy on the pressure have been investigated. Moreover, the pressure dependences of the Poisson ratio, Debye temperature, and the compressional and shear elastic wave velocities have been investigated for the first time. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

First-principles calculations of transition phase and thermodynamic properties of CdO

Liping Yao
Abstract The transition phase of CdO from NaCl-type (B 1) structure to CsCl-type (B 2) structure is investigated by ab initio plane-wave pseudopotential density-functional theory, and the thermodynamic properties of the B 1 and B 2 structures under high pressure and temperature are obtained through the quasiharmonic Debye model. The transition phase from B 1 structure to B 2 structure occurs at a pressure of 83.1 GPa, which agrees well with other calculated values. Moreover, the relationship of the relative volume V /V0, and the Debye temperature , and the heat capacity CV with the pressure P and temperature T are also successfully obtained. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Elastic and thermal properties of ,-plutonium

Hans Siethoff
Abstract It has been demonstrated in recent experimental and theoretical studies, that ,-Pu exhibits highly anisotropic phonon properties. The present paper indicates, that properties related to low-energy phonons such as Debye temperature and activation energy of self-diffusion do not reflect these anisotropies, and obey the same laws as other face-centred cubic metals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Isotope and disorder effects in the Raman spectra of LiHxD1,x crystals

V. G. Plekhanov
Most of the physical properties of a solid depend on its isotopic composition in some way or another. Scientific interest, technological promise and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled crystals. A great number of stable isotopes and well-developed methods for their separation have made it possible to grow crystals of C, LiH, ZnO, ZnSe, CuCl, GaN, GaAs, CdS, Cu2O, Si, Ge and ,-Sn with a controllable isotopic composition. Among these compounds, LiH possesses the largest value of the isotope effect. The great number of theoretical and experimental data suggest that the isotopic composition of a crystal lattice exerts some influence on the vibrational properties of crystals. These effects are fairly large and can be readily measured by modern experimental techniques (ultrasound, Brillouin and Raman scattering and neutron scattering). In addition, crystals of different isotopic compositions possess different Debye temperatures. This difference between an LiH crystal and its deuterated analogue exceeds a 100 K. Very pronounced and general effects of isotopic substitution are observed in phonon spectra. The scattering lines in isotopically mixed crystals are not only shifted (the shift of LO lines exceeds 100 cm,1) but are also broadened. This broadening is related to the isotopic disorder of the crystal lattice. It is shown that the degree of a change in the scattering potential is different for different isotopic mixed crystals. In the case of germanium and diamond crystals, phonon scattering is weak, which allows one to apply successfully the coherent potential approximation (CPA) for describing the shift and broadening of scattering lines. In the case of lithium hydride, the change in the scattering potential is so strong that it results in phonon localization, which is directly observed in experiments. The common nature of the isotopic and disorder effects in a wide range of crystals is emphasized. Copyright © 2001 John Wiley & Sons, Ltd. [source]

On Lindemann's Melting Criterion

H.-J. Hoffmann
Schmelzen; Schmelztemperatur; Schmelzkriterium; Lindemann-Kriterium Abstract Lindemann's empirical melting criterion is applied using data of the solid chemical elements. The respective expression which depends on the melting temperature, the molar mass and the molar volume correlates fairly well with the Debye temperatures. However, it seems incapable to predict inversely the melting temperatures with the other parameters given. Thus, Lindemann's criterion has no empirical relevance in addition to its scientific deficits. Über das Schmelzkriterium von Lindemann Das empirische Schmelzkriterium nach Lindemann wird an Hand von Daten der festen chemischen Elemente geprüft. Der betreffende Ausdruck, der von Schmelztemperatur, Molmasse und Molvolumen abhängt, korreliert recht gut mit der Debye-Temperatur. Es gelingt jedoch nicht mit befriedigender Genauigkeit, die Schmelztemperaturen aus der Umkehrung dieses Ausdrucks bei gegebenen anderen Parametern vorherzusagen. Neben den anderen bekannten Mängeln hat das Lindemann-Kriterium somit auch keine empirische Vorhersagekraft. [source]

Moments of phonon density of states spectra and characteristic phonon temperatures of wide band gap materials

Roland Pässler
Abstract We have re-digitized a variety of phonon density of states (PDOS) spectra, that have been published by different researchers for the wide band gap materials diamond, SiC, BN, AlN, GaN, ZnO, ZnS, and ZnSe, including calculations of the respective first- and second-order moments. Notwithstanding the obvious differences in concrete shapes of spectra presented for one and the same material by different authors, the respective magnitudes of estimated moments have been found in most cases to be nearly the same (to within uncertainties of some few%). Anticipated differences between phonon temperatures, ,eff, that are effective in controlling the observable temperature dependences of fundamental energy gaps and the respective average phonon temperatures, ,P, are seen to be throughout smaller than ±10%. The estimated high-temperature limits of Debye temperatures, ,D(,), are found to be significantly higher (by factors of order 1.4) than ,P. As a remarkable heuristic finding revealed by our numerical and analytical studies we can further state that, for SiC, AlN, GaN, ZnO, ZnS, and ZnSe, the individual ,D(,) values are nearly equal (within ±5%) to the respective average optical (LO/TO) phonon temperatures pertaining to the upper sections of the corresponding PDOS spectra. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]