NaGaI3O9F: a new alkali metal gallium iodate combined with IO3− and IO3F2− units

Birefringent crystals are very important optical materials, which are widely used in the fields of optics and communication. In this work, we reported a new iodate, NaGaI3O9F, synthesized by mild hydrothermal method. NaGaI3O9F crystallized in the monoclinic space group P21/c (No. 14) and it featured a novel ∞[Ga2(IO3F)2(IO3)4]2− layer stacked with Na+ cations located in the void maintaining charge balance. Notably, IO3− and IO3F2− anionic units appeared in the same time in the A–Ga–I–O/F (A = alkali metal) system. According to the experimental characterization and theoretical calculations, NaGaI3O9F showed a wide bandgap (4.27 eV) and large birefringence (Δnexp ∼ 0.203, Δncal = 0.197 at 1064 nm), indicating its potential use as a birefringent material.