Debye model

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

A First-Principles Calculation on Structural, Electronic, Magnetic, Mechanical, and Thermodynamic Properties of SrAmO3

Abstract: For the first time, the americium-based perovskite SrAmO3 has been studied with respect to its structural, electronic, magnetic, mechanical, and thermodynamic properties The study has been carried within the well-known density functional theory (DFT) using different approximations such as local spin density approximation (LSDA), generalized gradient approximation (GGA), LSDA + U, GGA + U In order to check for the stable ground state, optimization was performed for non-magnetic, ferromagnetic, and anti-ferromagnetic phases, and the compound was found to be stable in the ferromagnetic phase The spin magnetic moment was obtained with different exchange correlations and was found to be an integer which is one of the consequences of half-metallic nature The half-metallic nature of SrAmO3 was also confirmed from spin-polarised band structure calculations using GGA, GGA + U, and mBJ, showing metallic nature in spin-up states and semi-conducting in spin-down states The elastic constants, Young modulus, shear modulus, Poisson ratio, and anisotropic factor were also calculated SrAmO3 was found to establish ductile and anisotropic nature Debye temperature was predicted to be 353 K from elastic constants The thermodynamic properties, like variation of specific heat capacity, thermal expansion, and entropy, were studied in the temperature range of 0 to 600 K

First principle study of elastic and thermodynamic properties of FeB4 under high pressure

Abstract: The elastic properties, elastic anisotropy, and thermodynamic properties of the lately synthesized orthorhombic FeB4 at high pressures are investigated using first-principles density functional calculations. The calculated equilibrium parameters are in good agreement with the available experimental and theoretical data. The obtained normalized volume dependence of high pressure is consistent with the previous experimental data investigated using high-pressure synchrotron x-ray diffraction. The complete elastic tensors and crystal anisotropies of the FeB4 are also determined in the pressure range of 0–100 GPa. By the elastic stability criteria and vibrational frequencies, it is predicted that the orthorhombic FeB4 is stable up to 100 GPa. In addition, the calculated B/G ratio reveals that FeB4 possesses brittle nature in the range of pressure from 0 to 100 GPa. The calculated elastic anisotropic factors suggest that FeB4 is elastically anisotropic. By using quasi-harmonic Debye model, the compressibility, bulk modulus, the coefficient of thermal expansion, the heat capacity, and the Gruneisen parameter of FeB4 are successfully obtained in the present work.

The thermal expansion of gold: point defect concentrations and pre-melting in a face-centred cubic metal.

Abstract: On the basis of ab initio computer simulations, pre-melting phenomena have been suggested to occur in the elastic properties of hexagonal close-packed iron under the conditions of the Earth's inner core just before melting. The extent to which these pre-melting effects might also occur in the physical properties of face-centred cubic metals has been investigated here under more experimentally accessible conditions for gold, allowing for comparison with future computer simulations of this material. The thermal expansion of gold has been determined by X-ray powder diffraction from 40 K up to the melting point (1337 K). For the entire temperature range investigated, the unit-cell volume can be represented in the following way: a second-order Gruneisen approximation to the zero-pressure volumetric equation of state, with the internal energy calculated via a Debye model, is used to represent the thermal expansion of the `perfect crystal'. Gold shows a nonlinear increase in thermal expansion that departs from this Gruneisen–Debye model prior to melting, which is probably a result of the generation of point defects over a large range of temperatures, beginning at T/Tm > 0.75 (a similar homologous T to where softening has been observed in the elastic moduli of Au). Therefore, the thermodynamic theory of point defects was used to include the additional volume of the vacancies at high temperatures (`real crystal'), resulting in the following fitted parameters: Q = (V0K0)/γ = 4.04 (1) × 10−18 J, V0 = 67.1671 (3) A3, b = (K0′ − 1)/2 = 3.84 (9), θD = 182 (2) K, (vf/Ω)exp(sf/kB) = 1.8 (23) and hf = 0.9 (2) eV, where V0 is the unit-cell volume at 0 K, K0 and K0′ are the isothermal incompressibility and its first derivative with respect to pressure (evaluated at zero pressure), γ is a Gruneisen parameter, θD is the Debye temperature, vf, hf and sf are the vacancy formation volume, enthalpy and entropy, respectively, Ω is the average volume per atom, and kB is Boltzmann's constant.

Monte Carlo simulation of cross-plane thermal conductivity of nanostructured porous silicon films

Abstract: This paper presents a Monte Carlo (MC) modeling of heat conduction in heavily doped (p+ and n+) porous silicon (PS) films known as mesoporous silicon (meso-PS). A three-dimensional pore network generator is developed to better reproduce the structure of low porosity (fv<50%) meso-PS. The submicron scale heat conduction modeled by the Boltzman transport equation is simulated using the MC method in which the nonlinear phonon dispersion curves of bulk silicon and the phonon lifetime dependent on temperature, frequency, and polarization are taken into account. The proposed method has been applied to predict the effect of the porosity (10%–47%), pore sizes (10–20nm), pore arrangement (p+- and n+-type), temperature (50–500K), and film thickness (50nm–1μm) on the cross-plane thermal conductivity of meso-PS films. Moreover, the simulation results enable to deduce the scattering mean free path (MFP) of phonons in the PS and the scattering MFP due to phonon-pore wall interaction. At room temperature, the thermal co...