Design and synthesis of Ba3SiSe5 with suitable birefringence modulated via MIV atoms in the Ba–MIV–Q (MIV = Si, Ge; Q = S, Se) system

A new ternary Ba-based selenide, Ba3SiSe5, was synthesized by a high-temperature solid-state method. It crystallizes in the centrosymmetric space group Pnma (no. 62) of the orthorhombic system. The structure of the title compound consists of unique Se(4)Ba layers and discrete SiSe4 tetrahedra. The structure and computational properties of Ba3SiSe5 are systematically studied together with those of the Ba–MIV–Q (MIV = Si, Ge; Q = S, Se) system, and show an interesting difference in dimensions formed by one of the crystallographic Ba atoms and MIVQ4 tetrahedra, as well as optical property transformations modulated by MIV atoms. First principles methods were employed to obtain a better understanding of the relationship between structures and properties. Ba3SiSe5 maintains a moderate birefringence of 0.044@1064 nm and the real space atom cutting method indicates that the SiSe4 tetrahedra make the major contribution to its birefringence.