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

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.