Pressure Dependence Of Elastic Constants Research Articles

Pressure dependence of elastic constants using Landau free energy and a numerical modeling analysis of W-InN

ABSTRACT In this work, we study the pressure dependence of elastic constants of wurtzite indium nitride semiconductor based on Landau free energy expansion. Elastic constants are obtained as functions pressure up to second order. We have also evaluated the bulk modulus (B) and anisotropies of compressibility and shear for wurtzite indium nitride as functions of pressure. Agreement with previously obtained results based on first-principles calculations is found to be satisfactory.

Inverse-perovskites Sc3GaX (X = B, C, N): A comprehensive theoretical investigation at ambient and elevated pressures

We have made a comprehensive theoretical investigation of structural, mechanical, thermophysical, electronic, optical, thermodynamical and vibrational properties of inverse-perovskites Sc3GaX (X = B, C, N) as a function of pressure using density functional theory (DFT). Pressure dependent elastic constants are studied as regards mechanical stability, ductility, machinability and anisotropy of moduli. At ambient pressure, the density of states (DOS) at Fermi level of Sc3GaB is almost twice than that of Sc3GaC or Sc3GaN. This explains the predicted superconductivity of Sc3GaB. The nature of chemical bonding is studied via charge density distribution map. Calculated phonon dispersions exhibit dynamic stability of these compounds. The temperature and pressure dependent thermodynamic properties of Sc3GaB and Sc3GaN are investigated for the first time using quasi-harmonic Debye model. Debye and melting temperatures increase with increasing pressure which indicate that our studied compounds could be used for possible devices in harsh environments. Calculated minimum thermal conductivities of the compounds are much smaller than the optimum value (1.25 Wm−1K−1) up to 20 GPa. Hence the compounds are promising TBC materials over the entire pressure range considered. Optical properties of the compounds indicated several practical usefulness including the potential to be employed as coating materials to prevent solar heating.

Equation-of-state-constrained pressure dependence of x-ray elastic constants of gold for stress components calculation in a high-pressure anvil apparatus

In the resolution of the large divergence between pressure calculated by way of axial stress components from elastic constants and pressure determined by an equation of state, a 2nd order pressure dependency of elastic constants is introduced. Incorporating results from the equation of state and ultrasonic measurements in the literature, we determined the pressure dependency of x-ray elastic constants of gold and established functions for the calculation of macro-stress components from its macro-strain counterparts. The precision of stress components through these functions is estimated to be at 1% level. The determination of stress components, including crucial shear components, through analysis of an x-ray diffraction image, is demonstrated.

Thermal properties and pressure-dependent elastic constants of cadmium stannate as a substrate for MEMS: An ab initio study

Silicon carbide (SiC) has become a suitable replacement to silicon as a substrate for manufacture of microelectromechanical systems (MEMS) that operate in harsh environmental conditions, owing to its better mechanical properties such as excellent wear resistance. However, just like silicon, SiC is also brittle, a property that limits its application as a substrate for manufacture of flexible MEMS. In this study, we explored the thermal properties as well as the pressure-dependent elastic constants of cadmium stannate (Cd2SnO4) for the first time within the quantum espresso code. The result showed that the elastic constants of SiC are much higher than those of Cd2SnO4. The properties of SiC were found to be more sensitive to the applied pressure compared those of Cd2SnO4, implying that it is less mechanically and thermally stable with the applied pressure compared to Cd2SnO4, and therefore, less appealing compared to Cd2SnO4 for the manufacture of most MEMS.

The mechanical, dynamical, thermodynamical properties and elastic anisotropies of cubic YbAu compound under pressure

The structural, elastic, vibrational, electronic and thermodynamic properties of thermodynamically important YbAu in B2 structure under pressure have been investigated by performing first principles method using DFT. The calculated lattice parameter and equilibrium volume are in good agreement with the experimental values. Zero pressure elastic constants and pressure-dependent elastic constants are positive up to 30 GPa. The resulting elastic constants are stable mechanically as they meet the Born stability condition, which makes the YbAu compound stable in nature. B/G ratio shows that the YbAu has a brittle nature while Poisson’s ratio (ν) values show that an ionic bond nature. The presented phonon dispersion curves and one-phonon DOS also confirms that this compound is stable dynamically. The electronic structure and metallic nature have been analysed quantitatively from band structure and density of states. To better illustrate the nature of bonding and charge transfer, we have studied the charge density plots and mulliken charge analysis. Also, the thermodynamic properties have been investigated under temperature and high pressure. The pressure effects on the volume of YbAu are found to be greater than the temperature effects. • Pressure effect on the structural, elastic, vibrational and electronic properties of YbAu compound was investigated using DFT. • Electronic band structure and density of state calculations revealed that YbAu is metallic in nature. • The elastic anisotropy was visualized in detail by plotting the directional dependence. • The thermodynamic properties were investigated under temperature and high pressure.

Ab initio study of the pressure dependence of mechanical and thermodynamic properties of GeB2O4 (B = Mg, Zn and Cd) spinel crystals

Ab initio full-potential (linearized) augmented plane-wave plus local orbitals (FP-(L)APW + lo) calculations are performed to study the hydrostatic pressure dependence of the mechanical and thermodynamics properties of GeMg2O4, GeZn2O4, and GeCd2O4 cubic spinels. The calculated equilibrium structural parameters using both the local density approximation and the generalized gradient approximation are well consistent with the available theoretical and experimental data in the literature. The monocrystalline elastic constants are predictet using the energy-strain scheme. The polycrystalline elastic moduli are determined from the monocrystalline elastic constants through the Voigt-Reuss-Hill approximations. To understand the mechanical behavior of the investigated compounds, assessments of their mechanical stability, ductility/brittleness, sound velocities, elastic anisotropy, pressure-dependent elastic constants, and Debye temperature are made. Regarding thermodynamic properties, temperature dependence of the lattice parameter, bulk modulus, isochoric and isobaric heat capacities, volume thermal expansion coefficient, and Debye temperature at different fixed pressures are explored through the quasi-harmonic Debye model coupled with the FP-(L)APW + lo approach.

Pressure-Dependent Elastic, Mechanical, and Ultrasonic Analysis of CaAuBi Compound

The Lennard-Jones potential model is used to investigate the effects of pressure on the elastic and ultrasonic properties of CaAuBi half-Heusler compound. Potential model technique approaches is used to evaluate second- and third-order elastic constants of CaAuBi compound at various pressures (0-15 GPa). The pressure dependence of elastic constants is studied and it has been observed that the elastic constants of the half-Heusler CaAuBi compound increase monotonically as pressure is increased. The hexagonal half-Heusler CaAuBi compound is mechanically stable at different pressures according to Born's elastic stability criteria. The Voigt-Reuss-Hill method was used to compute elastic parameters such as Young's modulus Y, shear modulus G, bulk modulus B, and Poisson's ratio ν under various pressures. For the provided pressure range, the second-order elastic constants were also utilized to determine ultrasonic velocities along with z-axis at various angles. The half-Heusler CaAuBi compound's hardness, ultrasonic attenuation, melting temperature, and anisotropy are also determined. The computation have been also satisfactory in estimating the thermal conductivity k(min) and Debye average velocity under varied pressure. Keywords: elastic properties, thermal conductivity, ultrasonic properties, thermo-physical properties.

Thermal Properties and Pressure-Dependent Elastic Constants of Cadmium Stannate as a Substrate for Mems: An Ab Initio Study

Thermal Properties and Pressure-Dependent Elastic Constants of Cadmium Stannate as a Substrate for Mems: An Ab Initio Study

First-Principles Elastic and Anisotropic Characteristics of Structure-H Gas Hydrate under Pressure

Evaluating gas hydrates properties contributes valuably to their large-scale management and utilization in fundamental science and applications. Noteworthy, structure-H (sH) gas hydrate lacks a comprehensive characterization of its structural, mechanical, and anisotropic properties. Anisotropic and pressure dependent properties are crucial for gas hydrates’ detection and recovery studies. The objective of this work is the determination of pressure-dependent elastic constants and mechanical properties and the direction-dependent moduli of sH gas hydrates as a function of guest composition. First-principles DFT computations are used to evaluate the mechanical properties, anisotropy, and angular moduli of different sH gas hydrates under pressure. Some elastic constants and moduli increase more significantly with pressure than others. This introduces variations in sH gas hydrate’s incompressibility, elastic and shear resistance, and moduli anisotropy. Young’s modulus of sH gas hydrate is more anisotropic than its shear modulus. The anisotropy of sH gas hydrates is characterized using the unit cell elastic constants, anisotropy factors, and the angular dependent moduli. Structure-properties composition correlations are established as a function of pressure. It is found that compressing filled sH gas hydrates increases their moduli anisotropy. Differences in atomic bonding across a crystal’s planes can be expected in anisotropic structures. Taken together the DFT-based structure–properties–composition relations for sH gas hydrates provide novel and significant material physics results for technological applications.

Structural and elastic properties of TlInSe2 at high pressure

The results of the structural study of chain-like structured TlInSe2 compound using powder synchrotron X-ray diffraction (XRD) experiments under the pressures up to P = 30.53 GPa and a first principle analysis of structural and elastic properties under the pressures up to P = 50 GPa are reported. The XRD data show the stability of the tetragonal phase in the whole investigated pressure range. Density Functional Theory (DFT) calculations also evidence that at zero pressure the lowest energy structure of TlInSe2 is tetragonal (space symmetry group I4/mcm). At pressures above P ≥ 38 GPa the symmetry of the lowest energy structure changes to face-centered cubic one (Fm-3m). It was shown that the experimentally and theoretically obtained pressure dependences of lattice parameters in tetragonal phase are in good agreement. The pressure dependences of elastic constants, acoustic wave velocities and other elastic parameters, such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio have been calculated.

First Principles Study on the Structural, Elastic, Electronic and Optical Properties of Cubic ‘Half-Heusler’ Alloy RuVAs Under Pressure

The pressure effect (0 to 40 GPa) on the structural, elastic, electronic, and optical properties of half-metallic compound RuVAs has been investigated employing the DFT based on the first-principles method. The CASTEP computer code is used for this investigation. The calculated lattice parameter show slide deviation from the synthesized and other theoretical data. The normalized lattice parameter and volume are decreased with increasing pressure. The zero pressure elastic constants and also the pressure-dependent elastic constants are positive up to 40 GPa and satisfy the Born stability condition which ensured that the compound RuVAs is stable in nature. At zero pressure, the electronic band gap of 0.159 eV is observed from the band structure calculations which ensured the semimetallic nature of RuVAs. No band gap is observed in the electronic band structure at 40 GPa which indicates the occurrence of phase transition of compound RuVAs at this pressure. We have calculated the value of bulk modulus B, shear modulus G, Young’s modulus E, Pugh ratio B/G, Poisson’s ratio ν and anisotropy factor A of this compound by using the Voigt-Reuss-Hill (VRH) averaging scheme under pressure. The bulk modulus shows a linear response to pressure so that the hardness of this material is increased with increasing pressure. Furthermore, the optical properties such as reflectivity, absorptivity, conductivity, dielectric constant, refractive index, and loss function of RuVAs were evaluated and discussed under pressure up to 40 GPa.

Pressure effect on core structures and yield behaviors of screw superdislocations in FeAl

The core structure and the mobility of [111] screw superdislocations are investigated under hydrostatic pressures by comprehensive atomic simulations in B2–FeAl. The pressure dependence of elastic constants and lattice parameter of FeAl is also revealed. The result indicates that the [111] screw superdislocation dissociates on the (11¯0) plane under different pressures, and the separation increases with the decrease of external pressures. It is interesting to find that the consecutive transformation of core configurations takes place under different pressures. The quantitative analysis confirms that the core transformation is determined by the system energy optimization. Furthermore, the simulation results demonstrate that the operation of <111> {112} and <111> {110} slip systems and the corresponding yield stresses of dissociated screw superdislocations have strong dependence on the variation of external pressures.

Structural, mechanical, and thermodynamic properties of R-3m ReB4 under high pressure

The structural, mechanical, and thermodynamic properties of R-3m ReB4 under high pressure were investigated by using the density functional theory in combination with the quasi-harmonic Debye model in this work. The calculated structure parameters and bulk moduli of R-3m ReB4 at zero pressure are in good agreement with previous theoretical data. The calculated single crystal elastic constants and phonon spectra revealed that R-3m ReB4 is mechanically and dynamically stable at least 100 GPa. The pressure dependence of elastic constants and elastic modulus (B, G, and E) have been determined. Based on the obtained elastic modulus, two theoretical models were used to predict the Vickers hardness of R-3m ReB4. Furthermore, through plotting the directional dependent of bulk moduli, Young’s moduli, and shear moduli, the elastic anisotropy has been investigated in detail. Moreover, using the quasi-harmonic Debye model, some basic thermodynamical quantities such as the heat capacity, Gruneisen parameter, and the thermal expansion coefficients of R-3m ReB4 were explored under high temperature and high pressure. The obtained results can provide valuable reference for future synthesis and application R-3m ReB4 material.

DFT study on phase transition behavior and mechanical properties of HgSe polymorphs under high pressure

Total energy calculations based on density functional theory are performed for HgSe in the ambient and pressure induced phases. The electronic exchange and correlation effects are described by employing the generalized gradient approximation together with the projector augmented wave potentials. The equation of state parameters and the phase transition paths are obtained from the energy-volume landscape and enthalpy versus pressure data, correspondingly. The observed phase transition sequence of HgSe as ZB → Cinnabar → RS → Cmcm and the final transition from Cmcm to CsCl structure predicted by the other theoretical study are confirmed by our calculations. The pressure dependence of elastic constants of the structures considered in this study is reported. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Debye temperature as isotropic mechanical properties are evaluated for HgSe polymorphs. Our calculations of energy band structure reveal the inverted band structure evoking that HgSe in ZB phase is a semimetal.

Phonon, elastic and thermodynamic properties of L12 phase Rh3Zr under pressure from first-principles

The phonon, elastic and thermodynamic properties of L12 phase Rh3Zr have been investigated by density functional theory approach combining with quasi-harmonic approximation model. The relaxed lattice parameters of L12 phase Rh3Zr at zero pressure are in good agreement with the experiment. To judge the stability of L12 phase Rh3Zr under high pressure, the phonon band structure has been studied. The results show that L12 phase Rh3Zr possesses dynamical stability in the pressure range from 0[Formula: see text]GPa to 80[Formula: see text]GPa due to the absence of imaginary frequencies. The pressure dependences of elastic constants [Formula: see text] have been analyzed. All the elastic constants of Rh3Zr in a wide pressure range (0–80[Formula: see text]GPa) meet general mechanical conditions, suggesting that L12 phase Rh3Zr is mechanically stable under pressure up to 80[Formula: see text]GPa. L12 phase Rh3Zr exhibits ductility under high pressure and the pressure can improve the ductility from the results of the value of [Formula: see text] and Poisson’s ratio [Formula: see text]. Hence, it is obvious that the mechanical properties of Rh3Zr can be improved under high pressure. Moreover, we have obtained the thermodynamic properties using the quasi-harmonic Debye model. We note that the effect of the temperature on the Debye temperature [Formula: see text] is smaller than that of the pressure. We believe that our result will be a good guidance to future works and applications.

The structural, elastic, electronic and dynamical properties of chalcopyrite semiconductor BeGeAs2 from first-principles calculations

First-principles calculations for the structural, elastic, electronic and vibrational properties of BeGeAs2 with chalcopyrite structure have been reported in the frame work of the density functional theory. The calculated ground state properties are in good agreement with the available data. By considering the electronic band structure and electronic density of states calculation, it is found that this compound is a semiconductor which confirmed the previous work. Single-crystal elastic constants and related properties such as Young’s modulus, Poisson ratio, shear modulus and bulk modulus have been predicted using the stress–finite strain technique. It can be seen from the calculated elastic constants that this compound is mechanically stable in the chalcopyrite structure. Pressure dependences of elastic constants and band gap are also reported. Finally, the phonon dispersion curves and total and partial density of states were calculated and discussed. The calculated phonon frequencies BeGeAs2 are positive, indicating the dynamical stability of the studied compound.

A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

We have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation drag limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions.This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.

Temperature and Pressure Dependence of Elastic Constants and Related Parameters for InP Semiconductor

Based on the empirical pseudo-potential method (EPM), the symmetric and anti-symmetric pseudo-potential form factors have been adjusted to match the calculated energy gaps of InP with the corresponding experimental values. The adjusted symmetrical and anti-symmetrical form factors at G(1,1,1) have been used to calculate the polarity of the considered material. The elastic constants C 11, C 12 and C 44 of InP have been obtained. The knowledge of these constants helps us to determine their related elastic parameters such as bulk (Bu), shear (Cs) and Young’s (Y0) moduli. Other important parameters such as Poisson’s ratio (σ ), linear compressibility (C0 ), Cauchy ratio (Ca) , Born ratio (B0), isotropy factor (A ), bond stretching (α ), bond binding force (β ) and internal strain parameter (ζ ) for InP have also been calculated. The variation of all studied quantities with temperature and pressure has been investigated. Our results show a good agreement with the available experimental data. Most of our data may be taken as references especially for high values of temperature and pressure.

Effect of pressure on structural, electronic, mechanical and optical properties of ruthenium diboride with oP12-type structure

The structural parameters, electronic, elastic, hardness and optical properties of oP12-type RuB2 (Space group Pnma, No: 62) are investigated by means of density functional theory method within local-density approximation as a function of pressure. It is shown that the results at 0 GPa pressure are in good agreement with related theoretical and experimental data. The pressure dependence of elastic constants, special bond lengths, Mulliken bond populations, hardness, energy band gaps, charge densities and optical properties such as dielectric function, absorption coefficient, reflectivity function, extinction coefficient, refractive index, energy loss spectrum of oP12-type RuB2 have been investigated. It is observed that the oP12-type RuB2 compound exhibits anisotropic compressibility under hydrostatic pressure: c-direction is more compressible than a- and b-directions, due to the different bond stiffness and bond angle changes. From calculated partial density of states, Mulliken populations and 2D/3D electron densities, the nature of chemical bonding for RuB2 can be recognized as a combination of partially covalent, ionic and metallic bonds. The calculated hardness value shows that oP12- type RuB2 is hard material.

Density functional investigation on electronic structure and elastic properties of BeX at high pressure

We present an ab initio calculations to investigate the structural, electronic and elastic properties of BeX (X = Co, Ni, Cu and Pd) intermetallic compounds using full potential linearized augmented plane wave method. The exchange correlation energy is described in generalized gradient approximations. The ground-state properties such as lattice parameter (a 0), bulk modulus (B) and pressure derivative of bulk modulus (B’) have been determined. The band structure and density of states histograms are plotted which reveal the metallic nature for all the four compounds. A special attention has been paid to the determination of the second order elastic constants. By calculating bulk-to-shear modulus ratio (B/G H) and Cauchy pressure (C 12–C 44), ductility or brittleness of these intermetallics is determined. Pressure dependences of elastic constants and sound wave velocities including Debye temperature are also investigated.