Modulation of perovskite-related frameworks induced by alkaline earth metals in phosphate fluorides A2MPO4F (A = K, Rb; M = Ba, Ca)

Abstract

A new phosphate fluoride, Rb₂CaPO₄F, was synthesized from a high temperature solution. Single-crystal X-ray diffraction analysis indicates that Rb₂CaPO₄F belongs to the Pnma space group of the orthorhombic system. It exhibits an intricate three dimensional (3D) framework that consists of 1D infinite zig-zag [FRb₂Ca]_∞ chains interlinked by isolated PO₄ tetrahedra. The 1D chains are composed of plane-sharing F-centered [FRb₄Ca₂] octahedra. Meanwhile, we also obtained another phosphate fluoride K₂CaPO₄F, which is isostructural with Rb₂CaPO₄F. Moreover, the effect of the cation size on the framework structures of A₂CaPO₄F (A = K, Rb) and K₂BaPO₄F is discussed in detail. In addition, the UV-Vis-NIR diffuse reflectance spectra and the infrared spectra were measured to determine their cut-off edge and the anionic group, respectively. The first-principles theoretical studies were also conducted to aid in the understanding of the electronic structures and linear optical properties.