Ground state parameters,electronic properties and elastic constants of CaMg3:DFT study

The present study aims to investigate the equation of state(EOS)parameters of CaMg3 in aReCh(D09),AIFR(DO3),CU3A11(LI2)and CuTi3(L60)structures,using full potential linear muffin-tin orbitals(FP-LMTO)approach based on the density functional theory(DFT).The local density approximation(LDA)and the generalized gradient approximation(GGA)were both applied for the exchange-correlation potential term.The calculated equation of slate parameters at equilibrium,in general,agreed well with the available data of the literature.The calculations showed that under compression CaMg3 transforms from DO3 to DO9 at about 29.96GPa,and 25.1 GPa using LDA and GGA,respectively.The elastic constants C,y,aggregate moduli,Vickers hardness,sound velocity,and Debye temperature of CaMg3 in D03 structure were also reported,discussed and analyzed.Using LDA(GGA),the calculated values of Hv andθD were found at around 5.80GPa(5.93GPa)and 393.44 K(389.91 K),respectively.Electronic band structure,total density of states(TDOS)as well as the partial density of states(PDOS)have been also obtained.The electronic band structure confirms the metallic behavior of CaMg3 in DO3 phase,the valence bands are dominated by the maximum contribution of‘d’like states of Ca in the energy ranging from 2 to 3 eV for GGA,and from 4.5 to 5 eV for LDA,respectively.

Mechanical, piezoelectric and some thermal properties of(B3) BP under pressure

Some compounds of group III-V semiconductor materials exhibit very good piezoelectric,mechanical,and thermal properties and their use in surface acoustic wave(SAW) devices operating specially at GHz frequencies.These materials have been appreciated for a long time due to their high acoustic velocities,which are important parameters for active microelectromechanical systems(MEMS) devices.For this object,first-principles calculations of the anisotropy and the hydrostatic pressure effect on the mechanical,piezoelectric and some thermal properties of the(B3) boron phosphide are presented,using the density functional perturbation theory(DFPT).The independent elastic and compliance constants,the Reuss modulus,Voigt modulus,and the shear modulus,the Kleinman parameter,the Cauchy and Born coefficients,the elastic modulus,and the Poisson ratio for directions within the important crystallographic planes of this compound under pressure are obtained.The direct and converse piezoelectric coefficients,the longitudinal,transverse,and average sound velocity,the Debye temperature,and the Debye frequency of(B3) boron phosphide under pressure are also presented and compared with available experimental and theoretical data of the literature.