K4Sb(SO4)3Cl: The first apatite-type sulfate ultraviolet nonlinear optical material with sharply enlarged birefringence

Abstract

Abstract Owing to the close relationship of composition-structure-property, material properties can generally be altered or even tuned through specific structural evolution. Here, we report a new compound, the first nocentrosymmetric (NCS) apatite-type antimony sulfate K4Sb(SO4)3Cl, which was successfully synthesized by mineral-inspired cosubstitution using centrosymmetric (CS) Ca5(PO4)3F as the prototype. The introduction of Sb3+ cations with stereochemical activity lone pair not only induced the crystal structure symmetry transformation, but also dramatically enhanced the birefringence. The title compound K4Sb(SO4)3Cl exhibits a markedly enlarged birefringence which is about 17 times that of its parent phase Ca5(PO4)3F ( 0.004@546 nm). This strategy will guide the discovery of new structure-driven functional materials in the future.