Elastic and lattice dynamical properties of ternary strontium chalcogenide alloys

The structural and elastic properties, and lattice dynamics of the ternary alloys SrS1−xSexSrS1−xSex, SrS1−xTexSrS1−xTex and SrSe1−xTexSrSe1−xTex have been studied using first principles calculations. The density functional perturbation theory (DFPT) and the virtual crystal approximation (VCA) are employed. The variation of the structural parameters, the elastic constants, the optical and acoustic phonon frequencies at the high symmetry points ΓΓ, X and L, the electronic and static dielectric constants, the Born effective charge are studied as a function of the concentration (x). All these properties follow a quadratic law in x   and the values of the bowing parameters for SrS1−xTexSrS1−xTex are larger than for the other two alloys. The structural and elastic properties for simple cubic supercells with x=0.25, 0.5, and 0.75 have been computed and they are in good agreement with those obtained from VCA.