Debye model

About: Debye model is a research topic. Over the lifetime, 7462 publications have been published within this topic receiving 133987 citations.

Ultrasonic studies on network structure of ternary TeO2–WO3–K2O glass system

Abstract: Longitudinal and shear ultrasonic velocities were measured in different compositions of the glass system (TeO 2 ) 80 –(WO 3 ) (20− x ) –(K 2 O) x using pulse echo technique. Measurements were carried out at 6 MHz frequency and at room temperature. Elastic moduli and some other physical parameters such as, glass transition temperature, Debye temperature, softening temperature, and fugacity have been calculated. Results indicated that these parameters depend upon the alkali oxide modifier (K 2 O) content i.e., glass composition. Quantitative analysis has been carried out, in order to obtain more informations about the structure of these glasses, based on bond compression model, and ring deformation model, i.e., the cation-anion bond of each oxide.

Theoretical study of alloy phase stability in the Cd-Mg system

Abstract: A theoretical study of thermodynamic properties and of the phase diagram for crystalline hcp-based Cd-Mg alloys is presented. Many first-principles studies of phase diagrams for metallic alloys have considered only configurational contributions to the free energy, which arise from the effects of substitutional disorder on the entropy and enthalpy. In this paper, the additional effects of the vibrational free energy, the electronic entropy, and the energy associated with structural relaxations on the thermodynamic properties and calculated phase equilibria for Cd-Mg alloys are studied. Ground-state properties and the densities of states of stable and metastable Cd-Mg compounds with hcp-based structures have been calculated with the linear muffin-tin orbital (LMTO) method. The results of these LMTO calculations are combined with the cluster variation method to calculate the configurational free energy and electronic entropy of ordered and disordered alloys from first principles. The vibrational free energy is treated using the Debye model; the configurational dependence of the Debye temperature is obtained semiempirically from experimentally measured entropies of formation in combination with the results of the LMTO calculations. The energy associated with structural relaxations is estimated from experimentally measured lattice parameters and elastic constants. We find that, although the configurational free energy is the largest component of the total alloy free energy, nonconfigurational effects contribute significantly to thermodynamic properties, and hence appreciably affect the calculated Cd-Mg phase diagram.

THERMAL EXPANSION OF MODIFIED SPINEL, β-Mg2SiO4

Abstract: Thermal expansion of β-Mg2SiO4 (modified spinel; orthorhombic symmetry) was measured by the X-ray powder diffraction method in the temperature range between 20°C and 800°C. Gruneisen's theory of thermal expansion was applied to the linear and volume expansion data, and thermal expansion coefficients were obtained to be αa=9.14, αb=5.46, αc=5.92, and αv=20.6 in unit of 10-6/K, at 293K. Gruneisen's parameter γG=1.26 was obtained by assuming the Debye temperature to be 952K. The magnitude of volume expansion coefficient of β-Mg2SiO4 is located between those of γ- and α-phases. β-Mg2SiO4 is found to be a significantly anisotropic material both in thermal expansion and elasticity.

Phonon density of states and heat capacity of La 3 − x Te 4

Abstract: The phonon density of states (DOS) of La_(3−x)Te_4 compounds (x=00,018,032) was measured at 300, 520, and 780 K, using inelastic neutron scattering A significant stiffening of the phonon DOS and a large broadening of features were observed upon introduction of vacancies on La sites (increasing x) Heat-capacity measurements were performed at temperatures 185 ≤ T ≤ 1200 K and were analyzed to quantify the contributions of phonons and electrons The Debye temperature and the electronic coefficient of heat capacity determined from these measurements are consistent with the neutron-scattering results, and with previously reported first-principles calculations Our results indicate that La vacancies in La_(3−x)Te_4 strongly scatter phonons and this source of scattering appears to be independent of temperature The stiffening of the phonon DOS induced by the introduction of vacancies is explained in terms of the electronic structure and the change in bonding character The temperature dependence of the phonon DOS is captured satisfactorily by the quasiharmonic approximation