Hydrothermal Synthesis And Crystal Growth Of Hydrated Borates And Iodates As Nonlinear Optical Materials

The last 50 years great advances have been seen in the field of borates. A large number of compounds have been discovered and synthesized. Some of these compounds have non-centrosymmetric structures, which have been applied successfully as nonlinear optical crystals. Among them, hydrated borates: i.e. Potassium Pentaborate (KB5O8·4H2O) is the pioneer vacuum ultraviolet frequency-doubling crystal which is possible to produce phase-matched second-harmonic generation (SHG) at wavelengths as short as 216.8nm. Orthorhombic Calcium Triborate Hydrate (2CaO·3B2O3·H2O) has been proposed as a potential nonlinear optical material.Metal iodates contain isolated [IO3]- groups which has a lone pair to form non-centrosymmetric structure. Metal iodates have been shown to exhibit pyroelectric, piezoelectric, and second-harmonic generation properties. The [IO3]- groups in some metal iodates orient perfectly parallel, which leads to large nonlinear optical coefficients.Hydrothermal synthetic methods and Solution evaporation methods are commonly adopted in producing hydrated inorganic compounds. In this paper Sr2B11O16(OH)5 H2O and NaIO3·H2O single crystals have been prepared by these two crystal growth methods. And Ga(IO3)3 has been synthesized by a precursor route. Powder SHG test confirmed the nonlinear optical property of the three compounds.Thermal stability of crystalline Sr2B11O16(OH)5 H2O has been determined by differential thermal analysis (DTA) and thermogravimetry (TG). It shows that our hydrated crystal contains 2.26 water molecules, which does not agree with the natural mineral reported previously. Based upon its crystal structure, which is built by [B5O8(OH)]2- polyanions forming two infinite sheets interlinked by Sr cations, we speculate that the structure can host another water molecule in the voids. So the best molecular formula to describe our crystal may be put forward as Sr2B11O16(OH)5 nH2O, with n = 2.26.