Investigation of the structural, mechanical, dynamical and thermal properties of CsCaF3 and CsCdF3

Abstract

The structural, mechanical, dynamical and thermal properties of CsCaF3 and CsCdF3 are presented by using an ab initio pseudopotential method and a linear response scheme, within the generalized gradient approximation. The obtained structural and mechanical properties are in good agreement with other available theoretical and experimental studies. The calculated elastic constants of these materials obey the cubic stability conditions. It has been found that CsCaF3 is brittle whereas CsCdF3 has ductile manner. The full phonon dispersion curves of these materials are reported for the first time in the literature. We have found that calculated phonon modes are positive along the all symmetry directions, indicating that these materials are dynamically stable at the cubic structure. The obtained zone-center phonon modes for CsCaF3 (IR data) are found to be 83 (98) cm(-1), 104 (115) cm(-1), 120 cm(-1), 180 (192) cm(-1), 231 (250.5) cm(-1), 361 (374) cm(-1), 446 (449) cm(-1). Also, we have calculated internal energy, Helmholtz free energy, constant-volume specific heat, entropy and Debye temperature as function of temperature. At the 300 K, specific heats are calculated to be 113.36 J mol(-1) K-1 and 115.58 J mol(-1) K-1 for CsCaF3 and CsCdF3, respectively, which are lower than Doulong-Petit limit (12 472 J mol(-1) K-1).