CsZrF<sub>4</sub>(IO<sub>3</sub>): The First Polar Zirconium Iodate with <i>cis</i>-[ZrO<sub>2</sub>F<sub>6</sub>] Polyhedra Inducing Optimized Balance of Large Band Gap and Second Harmonic Generation
Lin Lin, Xingxing Jiang, Chao Wu, Zheshuai Lin, Zhipeng Huang, Mark G. Humphrey, Chi Zhang
Abstract
The development of d0 transition-metal (TM) iodates is of critical importance because these iodates are promising candidates for second-order nonlinear optical (NLO) materials with excellent optical properties and rich functional and structural diversity. In this work, the first polar zirconium iodate CsZrF4(IO3) has been synthesized via a facile hydrothermal reaction. It features an unusual linear chain structure comprised of edge-sharing cis-[ZrO2F6] polyhedra and [IO3] groups. The newly developed cis-[ZrO2F6] polyhedra are structure-directing, inducing alignment of the [IO3] groups and playing a decisive role in the macroscopic polarity of the crystal structure. Crystalline CsZrF4(IO3) displays a large optical band gap (4.26 eV, the largest value among the d0-TM iodate family), a strong second-harmonic generation response (4.5 × KH2PO4), a broad transparency window extending from the UV to the mid-IR region (0.29–5.8 μm), and a high laser damage threshold. First-principles calculations suggest that the cis-[ZrO2F6] polyhedra and [IO3] groups make dominant contributions to the large band gap and SHG response simultaneously. This study shows that high coordination number d0-TM oxide-fluoride polyhedra afford a new paradigm for the development of efficient NLO materials.