Stereochemically active lone pair-induced large optical anisotropy in a novel infrared birefringent crystal Ba 2 La 2 Sb 4 S 10 (S 2 )

The first compound Ba 2 La 2 Sb 4 S 10 (S 2 ) in the Ba–La–Sb–S system was successfully synthesized via a vacuum high-temperature solution method, exhibiting large birefringence (0.53 at 1064 nm) induced by the stereochemically active lone pair effect.