K2.64Cs0.36SiF7: a new fluorosilicate with a trans-perovskite structure

Abstract

A new oxygen-free fluorosilicate, namely K_2.64Cs_0.36SiF₇ was synthesized via a high-temperature method. It crystallizes in a tetragonal system with the P4/mbm space group. The cell parameters of K_2.64Cs_0.36SiF₇ are found to be a = 7.768(4) Å and c = 5.560(6) Å. Single crystal X-ray diffraction shows that it has a trans-perovskite structure built by the [SiF₆] and [FK₄(K_0.64/Cs_0.36)₂] octahedra. By a structural analysis, the disorder place and the disorder ratio of K_2.64Cs_0.36SiF₇ is different from other M₃SiF₇ (M = K⁺, Rb⁺, Cs⁺, and NH₄⁺) compounds. The ultraviolet cut-off edge of K_2.64Cs_0.36SiF₇ is shorter than 190 nm, and the band gap is 6.0 eV. Structure–property relationships were further illuminated via the first-principles calculation methods.