Second-order and third-order elastic constants of B95 aluminum alloy and B95/nanodiamond composite

All independent second-order and third-order elastic constants in B95 aluminum alloy and B95/nanodiamond composite have been determined. To determine the second-order elastic constants, the densities and velocities of longitudinal and shear bulk acoustic waves in the materials under study have been measured. To quantitatively characterize the nonlinear elastic properties, the third-order elastic constants (TOECs) of B95 alloy and B95/nanodiamond composite have been determined. The Thurston-Brugger method has been used to experimentally determine the TOECs. For this purpose, the relative changes in the bulk wave velocity have been experimentally measured depending on the uniaxial compression applied to the samples under study and all independent TOECs have been calculated. The elastic wave velocities have been measured by the ultrasonic pulse method at a frequency of 10 MHz. The results obtained have been discussed.     

Dimensional resonances of elastic and magnetoelastic vibrations in two layered structure

Peculiarities of dimensional resonances of elastic and magnetoelastic waves in bi-layered insulator structure: ferromagnetic film–non-magnetic elastic substrate have been investigated. Dependences of resonant frequencies of vibration modes upon thicknesses of magnetic and non-magnetic layers, elastic and magnetoelastic parameters, applied magnetic field have been calculated. The presence of peculiarities of resonant frequencies harmonics behavior with change of magnetic layer thickness have been shown.     

Ab initio investigation of the pressure influence on elastic properties of the GaS layered compound

From first principles, in the pressure range of 0–20 GPa, taking into account the structural phase transition at 3 GPa, all independent elastic constants of GaS compound have been calculated. From obtained data, the pressure dependences of the velocities of propagation of elastic waves in different symmetry directions have been determined. The values of averaged elastic moduli, Young’s modulus and Poisson’s ratio and their pressure dependence have also been calculated..     

EuS高压相变及其弹性和热力学性质

采用平面波赝势密度泛函理论,利用第一性原理的方法研究了EuS的晶体结构、高压相变以及弹性性质．计算结果和实验值以及前人利用不同计算模型得到的理论值相吻合．研究了EuS的弹性常数、弹性模量和弹性的各向异性等力学性质随压力变化的趋势．同时研究了泊松比、德拜温度及纵波和横波的弹性波速随压力的变化趋势．基于德拜模型,进而研究了EuS在0～800 K和0～60 GPa下相变前后的热膨胀系数、热熔、Grüneisen参数等热力学性质．     

Constantes élastiques des phases cristallographiques ordonnées et désordonnées de PtCo

The elastic constants of the PtCo (1:1) alloy in the ordered and disordered states have been measured between 298 and 4.2 K by the superposition method. The Debye temperatures have been deduced. The influence of the magnetic domains on the absolute values of the elastic constants has been also studied. The room temperature values of the magnetoelastic constants of the disordered phase have been determined from the elastic constants and the magnetostriction coefficients.     

A first-principles study on the structural and elastic properties and the equation of state of wurtzite-type cadmium selenide under pressure

A first-principles investigation on the crystal structural and elastic properties and the equation of state of wurtzite-type cadmium selenide (w-CdSe) has been conducted using the plane-wave pseudo-potential density functional theory and the quasi-harmonic Debye model. The elastic constants, the aggregate elastic moduli, the elastic anisotropy, and Poisson's ratio under pressure have been investigated. Our calculated equilibrium lattice constants, the elastic constants, and the aggregate elastic moduli at zero pressure are in good agreement with the experimental data and other theoretical results. The variations in the compressional and shear elastic wave velocities with pressure at zero temperature up to pressure 2.7 GPa have been studied; the computed Debye temperature at zero pressure and zero temperature is in reasonable agreement with the result of Bonello et al., In addition, the equation of state of w-CdSe in the pressure range of 0–2.7 GPa and up to a temperature of 900 K has also been obtained.     

Concentration dependences of the elastic constants of the two-dimensional graphene-silicene system

The concentration dependences of the elastic constants of the two-dimensional Si _x C_{1 − x} system have been investigated with the use of the Harrison bonding-orbital method and the Keating model. The central and non-central force constants and the Grüneisen parameter have been considered by means of the bonding-orbital method. All quantities under consideration have been shown to exhibit a nonlinear behavior during the transition from graphene to silicene. A nontrivial role of the short-range repulsion has been discussed. The second-order and third-order elastic constants, the pressure dependences of the second-order elastic constants, as well as the Poisson’s ratio and Young’s modulus have been investigated in the Keating model. It has been found that the elastic constants and Young’s modulus change almost linearly upon the transition from graphene to silicene, whereas the other quantities under consideration exhibit nonlinearity.     

Effects of pressure on structural,electronic, and mechanical properties of α,β,and γ uranium

The first-principles methods have been employed to calculate the structural, electronic, and mechanical properties of the α, β, and γ phases of uranium under pressure up to 100 GPa. The electronic structure has been viewed in forms of density of states and band structure. The mechanical stability of metal U in the α, β, and γ phases have been examined.The independent elastic constants, polycrystalline elastic moduli, as well as Poisson's ratio have been obtained. Upon compression, the elastic constants, elastic moduli, elastic wave velocities, and Debye temperature of α phase are enhanced pronouncedly. The value of B/G illustrates that α and γ phases are brittle in ground state.     

Second-order and third-order elastic constants of B4C ceramics

The linear and nonlinear elastic properties of B₄C boron carbide ceramics have been studied. The second-order elastic constants and other parameters of the theory of elasticity in the linear approximation have been calculated based on the experimentally measured density and velocity values of longitudinal and shear bulk acoustic waves in the samples. The Thurston-Brugger method has been used to determine the third-order elastic constants of B₄C. To achieve this, we have measured the relative changes of the longitudinal and shear bulk acoustic wave velocities depending on the uniaxial compression applied to the sample.     

Calculated elastic constants of dilute alloys based on bcc metals

The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for a number of dilute alloys based on Mo, Nb, W, Ta and V.     

Elastic properties of graphene: The Keating model

The elastic properties of graphene have been described in terms of the Keating model. It has been shown that the two-dimensional structure of graphene is described by two independent elastic constants, like an isotropic solid. The Young’s modulus and the Poisson’s ratio have been determined. The results are compared with the experimental data obtained for graphite.     

α-AlPO4晶体弹性温度特性的研究

研究了用缓慢升温法生长的α-AlPO₄晶体的弹性温度特性。测量采用传输法,测温范围为-30—150℃;用最小二乘法拟合弹性-温度曲线;用电子计算机处理数据。给出了弹性常数c_ij和s_ij(i,j=1,2,…,6)的温度特性方程以及T₀=25℃时的一级、二级和三级温度系数。 关键词：     

Anomales elastisches Verhalten von Eis bei tiefen Temperaturen

The temperature dependence of the longitudinal elastic constants of ice single crystals has been measured by an ultrasonic pulse-echo method. With heating, resp. cooling rates less than a critical value, deviations to lower values of the elastic constants have been observed. The time dependence of the anomaly has been studied at fixed temperatures. Limiting values of the elastic constants have been reached after sufficiently long time; the maximum of these values was observed at about 105°K. The findings are interpreted as representing a phase transition within the protonic structure.     

Effects of self-consistent dynamics of dislocations in the elastic field of a planar mesodefect

The self-consistent dynamics of a dislocation ensemble in an elastic field of a planar mesodefect has been considered within the kinetic approach. The effective Airy stress function for a planar mesodefect, which takes into account the screening effect of a system of distributed dislocation charges, has been obtained. Coordinate dependences of the stress tensor components and the dislocation charge density for the considered screened system have been found. Its elastic energy and misorientation of the regions adjacent to the planar mesodefect have been calculated.     

First-Principles Study of Structural,Elastic and Electronic Properties of OsSi

First-principles study of structural, elastic, and electronic properties of the B20 structure OsSi has been reported using the plane-wave pseudopotential density functional theory method. The calculated equilibrium lattice and elastic constants are in good agreement with the experimental data and other theoretical results. The dependence of the elastic constants, the aggregate elastic modulus, the deviation from the Cauchy relation, the elastic wavevelocities in different directions and the elastic anisotropy on pressure have been obtained and discussed. This could be the first quantitative theoretical prediction of the elastic properties under high pressure of OsSi compound. Moreover, the electronic structure calculations show that OsSi is a degenerate semiconductor with the gap value of 0.68 eV, which is higher than theexperimental value of 0.26 eV. The analysis of the PDOS reveals that hybridization between Os d and Si p states indicates a certain covalency of the Os-Si bonds.     

The elastic and inelastic scattering of 33 MeV polarized 3He from oxygen and iron isotopes

Angular distributions of differential cross sections and analysing powers have been measured for elastic and inelastic scattering of polarized 33 MeV ³He from ¹⁷O, ¹⁸O, ⁵⁴Fe and ⁵⁶Fe targets. The elastic data have been analysed to deduce the optical model parameters. The inelastic scattering together with the elastic scattering have been interpreted in terms of a macroscopic model within a coupled-channels framework. From this analysis the deformation parameters, β, were deduced.     

Temperature dependent ultrasonic properties of aluminium nitride

Hexagonal wurtzite structured aluminium nitride has been characterized by the theoretical calculation of ultrasonic attenuation, ultrasonic velocity, higher order elastic constants, thermal relaxation time, acoustic coupling constants and other related parameters in temperature range 200-800 K for wave propagation along the unique axis of the crystal. Higher order elastic constants of AlN at different temperatures are calculated using Lennard-Jones potential for the determination of ultrasonic attenuation. A decrease in ultrasonic velocity with temperature has been predicted, which is caused by reduction in higher order elastic constants with temperature. The temperature dependent ultrasonic properties have been discussed in correlation with higher order elastic constants, thermal relaxation time, thermal conductivity, acoustic coupling constants and thermal energy density. Anomalous behaviour of the attenuation is found at 400 K. On the basis of attenuation, the ductility and performance of AlN have been studied.     

First-Principles Calculations of Structural,Elastic and ElectronicProperties of Tetragonal HfO2under Pressure

Structural, elastic and electronic properties of tetragonal HfO₂ at applied hydrostatic pressure up to 50 GPa have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated ground-state properties are in good agreement with previous theoretical and experimental data. Six independent elastic constants of tetragonal HfO₂ have been calculated at zero pressure and high pressure. From the obtained elastic constants, the bulk, shear and Young's modulus, Poisson's coefficients, acoustic velocity and Debye temperature have been calculated at the applied pressure. Band structure shows that tetragonal HfO₂ is an indirect band gap. The variation of the gap versus pressure is well fitted to a quadratic function.     

First-principles calculations on elasticity of under pressure

First-principles calculations of the crystal structure and the elastic properties of OsN₂ have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values are in very good agreement with experimental data as well as with some of the existing model calculations. The dependence of the elastic constants c_ij, the aggregate elastic moduli (B,G,E), Poisson’s ratio, and the elastic anisotropy on pressure has been investigated. Moreover, the variation of the Debye temperature and the compressional and shear elastic wave velocities with pressure P up to 60 GPa at 0 K have been investigated for the first time.