Interplay between the B-sites’ valence states and phonon dynamics in the Ca3BO (B= Si, Ge, Sn, and Pb) antiperovskites

Abstract

Antiperovskites have emerged as an interesting family of compounds thanks to their outstanding properties that range from magnetically frustrated structures to superconductivity and thermoelectricity. Here, is presented a study, based on first-principles calculations in the framework of density functional theory, of the electronic valence characteristics and the phonon dynamics of the ${\text{Ca}}_{3}B\text{O}$ antiperovskite oxides with $B=$ Si, Ge, Sn, and Pb. This paper shows that, as the $B$-site is larger, the most stable phase is the high-symmetry $Pm\bar{3}m$ phase. Nevertheless, unstable modes appear for $B=$ Si and Ge, inducing group-to-subgroup phase transitions explaining their $Pnma$ orthorhombic low-temperature ground state. In correlation with the reversed-perovskite structure, our findings based on the Bader charges analysis suggest negative valence states in the $B$-sites. As such, based on the vibrational analysis and Goldschmidt’s tolerance factor, it is estimated the ionic $B^{(4-\delta )-}$ radii size range is in agreement with the phonon dynamics of the presented family.