A New Perspective and Design Principle for Halide Perovskites: Ionic Octahedron Network (ION)

The metal halide ionic octahedron, [MX₆] (M = metal cation, X = halide anion), is considered to be the fundamental building block and functional unit of metal halide perovskites. By representing the metal halide ionic octahedron in halide perovskites as a super ion/atom, the halide perovskite can be described as an extended ionic octahedron network (ION) charge balanced by selected cations. This new perspective of halide perovskites based on ION enables the prediction of different packing and connectivity of the metal halide octahedra based on different solid-state lattices. In this work, a new halide perovskite Cs₈Au_3.5In_1.5Cl₂₃ was discovered on the basis of a BaTiO₃-lattice ION {[InCl₆][AuCl₅][Au/InCl₄]₃}^8-, which is assembled from three different ionic octahedra [InCl₆], [AuCl₆], and [Au/InCl₆] and balanced by positively charged Cs cations. The success of this ION design concept in the discovery of Cs₈Au_3.5In_1.5Cl₂₃ opens up a new venue for the rational design of new halide perovskite materials.