Synthesis, Structure, Characterization, and Calculation of a Noncentrosymmetric Fluorine-Containing Indium Iodate, Ba[InF3(IO3)2]

Iodates capable of exhibiting large second-harmonic-generation (SHG) response, wide transparent windows, and ease in crystal growth are an ideal materials class for the design of mid-infrared (IR) nonlinear optical (NLO) crystals. In previous research, we have presented a new strategy for effectively designing noncentrosymmetric iodates on the basis of the structure-directing properties of d0 transition-metal (TM) oxide fluoride anions. However, due to the d–d electronic transition of TM cations, the band gaps of these TM-containing iodates are relatively small. In this study, we substituted TM cations of β-Ba[VFO2(IO3)2] (BVIF) with In3+ cations and successfully synthesized the first F–-containing indium iodate, Ba[InF3(IO3)2]. It has a similar structure and exhibits an SHG response equivalent with that of BVIF. Remarkably, however, the band gap of Ba[InF3(IO3)2] is larger than that of BVIF. The analysis of the structure–property relationship indicates that the enlarged band gap mainly originates from the removal of TM cations. In addition, due to the strong anisotropic polarization of the [IO3]− groups, Ba[InF3(IO3)2] can also exhibit a large birefringence (0.172@1064 nm), which not only is helpful for the phase-matching ability of Ba[InF3(IO3)2] in a wide wavelength range but also suggests that Ba[InF3(IO3)2] may be a potential birefringent crystal.