Ba2M(C3N3O3)2 (M = Mg, Ca): potential UV birefringent materials with strengthened optical anisotropy originating from the (C3N3O3)3− group

Abstract

Demands for UV birefringent materials are growing dramatically owing to the rapid development of ultraviolet technology. Here, a new family of UV birefringent materials, Ba₂Mg(C₃N₃O₃)₂ (BMCY) and Ba₂Ca(C₃N₃O₃)₂ (BCCY), have been successfully discovered. It is the first time that the excellent birefringent properties of cyanurates have been studied. These materials exhibit an extremely large birefringence (Δn = 0.728–0.351 and 0.771–0.346 from 230 nm to 800 nm for BMCY and BCCY, respectively), much larger than that of the commercial UV birefringent crystal α-BaB₂O₄ (α-BBO) (Δn = 0.12@532 nm). Our study indicates that the impressive optical properties of BMCY and BCCY stem from the strengthened optical anisotropy of the planar (C₃N₃O₃)³⁻ group compared with the isoelectronic (B₃O₆)³⁻ group. Besides, its congruent-melting properties make it feasible to grow a bulk crystal by the Bridgman–Stockbarger technique. The extraordinary properties of BMCY and BCCY may shed light on a new path to explore birefringent materials for practical application.