New materials for infrared non linear optic. Syntheses, structural characterisations, second harmonic generation and optical transparency of M(IO3)3 metallic iodates.
Résumé
Two new phases a-In(IO3)3 and b-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 a-In(IO3)3 and a centrosymmetric two-dimensional network for b-In(IO3)3. Temperature-dependent X-ray powder diffraction experiments shows the transformation of a-In(IO3)3 to b-In(IO3)3 at 365 uC. The phase transition is not reversible. a-In(IO3)3 is the kinetically favoured phase whereas b-In(IO3)3 is the thermodynamically stable phase. a-In(IO3)3 is isomorphic to Cr(IO3)3, Fe(IO3)3 and Ga(IO3)3 and crystallises in space group P63 (no. 173) with a = 9.541(1) A° and c = 5.266(1) A° . 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 a-LiIO3 are described. Structural analogies between these metallic iodates allow us to prepare solid solutions as In12xFex(IO3)3 and In12xCrx(IO3)3. Luminescence of the In12xCrx(IO3)3 phases has been observed. DSC analyses of b-In(IO3)3 and Ga(IO3)3 show that they decompose at 535 uC and 525 uC respectively. Fe(IO3)3, Ga(IO3)3 and a-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.