Elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 under pressure

Abstract

The elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 have been calculated using the full potential linearized augmented plane wave based on density functional theory. Exchange and correlation effects are taken into account by a generalized gradient approximation and an orbital independent modified Becke–Johnson potential coupled with generalized gradient approximation. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. The results are in good agreement with the available theoretical and experimental data. The elastic properties such as elastic constants, shear modulus, Young modulus, Poisson’s ratio, $$B/G$$ ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and specific heat have been calculated. The pressure dependence of the elastic moduli has been also evaluated. Furthermore, elastic anisotropic properties for KCaF 3 have been analyzed in the pressure range of 0–40 GPa by calculating directional dependence of the Young’s moduli in the crystal. From calculations of the electronic properties, it is found that the band gap is 10.4 (6.1) eV at the $$R$$ – $$\Gamma $$ direction in the Brillouin zone using modified Becke–Johnson potential coupled with generalized gradient approximation (generalized gradient approximation). The variation of the band gap versus pressure is well fitted to a quadratic function. The calculations show that indirect $$R$$ – $$\Gamma $$ to direct $$\Gamma $$ – $$\Gamma $$ band gap transition occurs at 20 GPa. Moreover, optical properties, such as the dielectric function, refractive index and extinction index, have been calculated for radiation up to 35 eV.