Explorations of New Second-Order Nonlinear Optical Materials in the Potassium Vanadyl Iodate System

Four new potassium vanadyl iodates based on lone-pair-containing IO3 and second-order Jahn−Teller distorted VO5 or VO6 asymmetric units, namely, α-KVO2(IO3)2(H2O) (Pbca), β-KVO2(IO3)2(H2O) (P212121), K4[(VO)(IO3)5]2(HIO3)(H2O)2·H2O (P1), and K(VO)2O2(IO3)3 (Ima2) have been successfully synthesized by hydrothermal reactions. α-KVO2(IO3)2(H2O) and β-KVO2(IO3)2(H2O) exhibit two different types of 1D [VO2(IO3)2]− anionic chains. Neighboring VO6 octahedra in the α-phase are corner-sharing into a 1D chain with the IO3 groups attached on both sides of the chain in a uni- or bidentate bridging fashion, whereas those of VO5 polyhedra in the β-phase are bridged by IO3 groups into a right-handed helical chain with remaining IO3 groups being grafted unidentately on both sides of the helical chain. The structure of K4[(VO)(IO3)5]2(HIO3)(H2O)2·H2O contains novel isolated [(VO)(IO3)5]2− units composed of one VO6 octahedron linked to five IO3 groups and one terminal O2− anion. The structure of K(VO)2O2(IO3)3 exhibits a 1D [(VO)2O2(IO3)3]− chain in which neighboring VO6 octahedra are interconnected by both oxo and bridging iodate anions. Most interestingly, three of four compounds are noncentrosymmetric (NCS), and K(VO)2O2(IO3)3 displays a very strong second-harmonic generation response of about 3.6 × KTP, which is phase matchable. It also has high thermal stability, a wide transparent region and moderate hardness as well as an excellent growth habit. Thermal analyses and optical and ferroelectric properties as well as theoretical calculations have also been performed.