BaLa4(SiS4)2(BS3)2: Structurally Ordered Thioborate-Thiosilicate Obtained by Adjusting the Cationic Size

Thioborates are of interest as nonlinear optical materials, birefringent materials, and solid-state electrolytes. Under the dilemma that all known thioborate-thiosilates are disordered structures with co-occupied atomic sites, the first structurally ordered thioborate-thiosilicate, BaLa4(SiS4)2(BS3)2, has been successfully obtained by adjusting the cationic size. It features a novel 3D tunnel network assembled by La-B-S chains and La-Si-S bilayers. In addition, BaLa4(SiS4)2(BS3)2 exhibits good chemical and thermal stability (up to 880 °C), wide light transmission range (0.4-11 μm), wide band gap (3.25 eV), moderate birefringence (0.076 @ 546 nm), and high laser-induced damage threshold (6 × AgGaS2). Theoretical calculations showed that the [BS3]3- functional group is the main contributor to birefringence. This work enriches the structure types of thioborate-thiosilicate and expands insights into mixed anionic thioborates.