KSb(BeF3)F3: a totally fluorine strategy for achieving wide bandgap and large birefringence

Abstract

Herein, a novel antimony fluoroberyllate, KSb(BeF₃)F₃, exhibiting a distinctive 1D [BeF₃]_∞⁻ polyanion chain, has been successfully synthesized using a totally fluorine strategy. Innovatively, by introducing a Be–F bond with a large electronegativity difference and completely eliminating the suspended oxygen atoms in the structure, KSb(BeF₃)F₃ exhibits a large optical bandgap (5.3 eV). Furthermore, KSb(BeF₃)F₃ shows a large birefringence (0.11@546 nm), larger than that of other reported alkali/alkaline earth metal oxysalts with tetrahedral units only, showing that the reported compound is a potential practical short-wave ultraviolet birefringent material. First principles theoretical studies reveal that the excellent properties originate from the cooperation of the 1D infinite [BeF₃]_∞⁻ polyanion chains and SbF₆ octahedra. The totally fluorine strategy we adopted not only resulted in a novel structure, which facilitated the diversification of structural types of the antimony-based materials, but also achieved the bandgap tuning of the materials.