Potassium-rich antiperovskites K 3 HTe and K 3 FTe and their structural relation to lithium and sodium counterparts.

Unlike perovskite oxides, antiperovskites M 3 HCh and M 3 FCh (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 K 3 HTe and K 3 FTe 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 M 3 HCh and M 3 FCh which require high pressure synthesis. A systematic comparison of a series of cubic M 3 HTe and M 3 FTe (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.