LiSrSbS₃: parallel configurations of lone pair electrons inducing a large birefringence

Enhancement of birefringence is significant since the birefringent materials can create and control polarized light and be used extensively in various advanced optical systems. By optimizing the arrangement of [SbS₃] units with stereo-chemical active lone pair electrons, a new quaternary thioantimonate LiSrSbS₃ with a large birefringence has been successfully synthesized by a high temperature solid-state reaction method. LiSrSbS₃ crystallizes in the monoclinic space group of P2₁/c. In the structure, the isolated infinite [LiS₄] chains and zigzag [SrS₆] chains are alternately connected with each other to compose a three-dimensional (3D) framework, and the isolated pyramid [SbS₃] units are located between them. To analyze the source of large birefringence, the electronic structure and optical properties of LiSrSbS₃ were further investigated by the first-principles method, and the results show that the optimized arrangement [SbS₃] trigonal pyramid induces a large birefringence.