Series of New Alkali Metal Hafnium-Based Iodates A₂Hf(IO₃)₆ (A = K, Rb, Cs) and Isomorphic Ba₂Zn(IO₃)₆ with Large Birefringence

Iodate is an important class of optoelectronic functional materials, however, only a few hafnium-based iodates have been reported at present. Herein, a series of alkali metal hafnium-based iodates A2Hf(IO3)6 (A = K, Rb, Cs) and isomorphic Ba2Zn(IO3)6 were synthesized by the hydrothermal method. These four crystals all crystallized in the trigonal system with an R3¯ space group. Both Hf4+ and Zn2+ are six-coordinated with six IO3– groups, forming a petal-shaped arrangement. Based on millimeter-sized crystals, their ultraviolet cutoff edges were measured as 329–347 and 288 nm, respectively. Theoretical calculation shows that they possess a large birefringence of 0.092–0.111@1064 nm. This work not only provides potential birefringent materials but also enriches the iodate system.