New materials for infrared non-linear optics.: Syntheses, structural characterisations, second harmonic generation and optical transparency of M(IO3)3 metallic iodates

Two new phases alpha-In(IO3)(3) and beta-In(IO3)(3) have been synthesised by evaporation of concentrated nitric acid solution containing metallic salts and sources of iodate. Single crystal structures reveal an acentric three-dimensional network for alpha-In(IO3)(3) and a centrosymmetric two-dimensional network for beta-In(IO3)(3). Temperature-dependent X-ray powder diffraction experiments shows the transformation of alpha-In(IO3)(3) to beta-In(IO3)(3) at 365 degrees C. The phase transition is not reversible. alpha-In(IO3)(3) is the kinetically favoured phase whereas beta-In(IO3)(3) is the thermodynamically stable phase. alpha-In(IO3)(3) is isomorphic to Cr(IO3)(3), Fe(IO3)(3) and Ga(IO3)(3) and crystallises in space group P6(3) ( no. 173) with a = 9.541( 1) angstrom and c = 5.266( 1) angstrom. Structural relationships among the anhydrous non-centrosymmetric metallic iodates M(IO3)(3) (M = Cr, Fe, In, Ga), M(IO3)(2) (M = Mg, Mn, Co, Ni, Zn) and alpha-LiIO3 are described. Structural analogies between these metallic iodates allow us to prepare solid solutions as In1-xFex(IO3)(3) and In1-xCrx(IO3)(3). Luminescence of the In1-xCrx(IO3)(3) phases has been observed. DSC analyses of beta-In(IO3)(3) and Ga(IO3)(3) show that they decompose at 535 degrees C and 525 degrees C respectively. Fe(IO3)(3), Ga(IO3)(3) and alpha-In(IO3)(3) generate second harmonics and have high non-linear coefficients and high optical damage thresholds in powder form. Furthermore, they do not absorb up to 12 mm. Consequently, they possess a large domain of transparency from visible light to the beginning of the far-infrared, including three atmospheric transparency windows. They are particularly interesting for potential applications in quadratic non-linear optics in atmospheric transparency bands II and III.