Potassium-rich antiperovskites K3HTe and K3FTe and their structural relation to lithium and sodium counterparts.

ABSTRACT

Unlike perovskite oxides, antiperovskites M3HCh and M3FCh (M = Li, Na; Ch = S, Se, Te) mostly retain their ideal cubic structure over a wide range of compositions owing to anionic size flexibility and low-energy phonon modes that promote their ionic conductivity. In this study, we show the synthesis of potassium-based antiperovskites K3HTe and K3FTe and discuss the structural features in comparison with lithium and sodium analogues. It is shown experimentally and theoretically that both compounds maintain a cubic symmetry and can be prepared at ambient pressure, in contrast to most of the reported M3HCh and M3FCh which require high pressure synthesis. A systematic comparison of a series of cubic M3HTe and M3FTe (M = Li, Na, K) revealed that telluride anions contract in the order of K, Na, Li, with a pronounced contraction in the Li system. This result can be understood in terms of the difference in charge density of alkali metal ions as well as the size flexibility of Ch anions, contributing to the stability of the cubic symmetry.