Functional Materials Design via Structural Regulation Originated from Ions Introduction: A Study Case in Cesium Iodate System

Tailored structural regulation to achieve novel compounds with special properties is very attractive and important for functional material design. In this paper, CsIO3 was selected as a maternal structure and three new derivatives, namely, CsIO2F2, Cs3(IO2F2)3·H2O, and Cs­(IO2F2)2·H5O2, were successfully prepared by introducing different units (F–, H2O, H5O2+, and IO2F2–) under hydrothermal condition for the first time. Then, the structural transformations were schematically analyzed and the corresponding properties originated from ions introduction were investigated. Therein, noncentrosymmetric CsIO3 and CsIO2F2 exhibit good nonlinear optical properties with large second-harmonic generation (SHG) effects (15 × and 3 × KH2PO4), wide band gaps (4.2 and 4.5 eV), wide transmittance ranges (∼0.27–5.5 μm), and high laser damage thresholds (15 × and 20 × AgGaS2, respectively), which shows that they are potential nonlinear optical materials in near-ultraviolet to mid-infrared. To further analyze the structure–properties relationship, the first-principles calculations are applied to explore the origins of the optical properties, such as birefringences and SHG responses. Moreover, the protonated (H5O2)+ cations in Cs­(IO2F2)2·H5O2 imply that it may feature enhanced conductivity, which was tentatively verified by the resistivity tests via the conventional dc four-probe method. The study case of structural regulation realized by ions introduction in this work may give a feasible guidance for functional materials design.