[RbSr3X][(BS3)2] (X = Cl, Br): two salt-inclusion thioborates with large birefringence and structure transformation from centrosymmetric to asymmetric

Abstract

[RbSr₃X][(BS₃)₂] (X = Cl, Br), two salt-inclusion chalcogenides with planar [BS₃] as anionic units, were obtained. Structure analysis indicates that the size effect of halogens may adjust the arrangement between the [BS₃] units and further lead to the CS-to-NCS structure transformation. Experimental characterizations reveal that they have wide bandgaps (3.64–3.70 eV), large birefringence (0.136–0.144) and high LIDT (12–14 × AgGaS₂). This work indicates that the thioborate family is a rich source to explore structure chemistry and promising infrared functional materials.