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

Abstract

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 (Δn_exp ∼ 0.203, Δn_cal = 0.197 at 1064 nm), indicating its potential use as a birefringent material.