Unusual structure and chemical behavior of potassium-indium under pressure

Abstract

Pressure has become a powerful tool in obtaining unconventional compounds with fascinating properties. Alkali metal trielides have drawn significant attention, because of their structural characters and broad applications. In this article, we have extensively explored the structural phase diagram and properties of K–In compounds under high pressure. It is found that with the pressure up to 40 GPa, the stoichiometries of K4In, K3In, K2In, KIn, KIn3 and KIn4 are thermodynamically stable. Particularly, the predicted K–In compounds contain a rich variety of polyindium form with covalent bonding pattern, e.g., In2 units, zigzag chains, six rings (In6 units) and cage. The In-rich compounds (P6/mmm-KIn2, C2/m-KIn4 and R-3m-KIn4) and four K-rich compounds (Cmca-K2In, Cm-K3In, C2/m-K4In and Pnma-K4In) exhibit metallic feature. However, the occupations of states near the Fermi level of these structures are distinct. For In-rich and K-rich compositions, the majority of the occupied states come from the In-p states and K-d states, respectively, which may be related to the ratio of K/In in these compounds. Our results enable an opportunity to understand the structures and properties of K–In compounds.