New iodate materials as potential laser matrices.: Preparation and characterisation of α-M(IO3)3 (M = Y, Dy) and β-M(IO3)3 (M = Y, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er).: Structural evolution as a function of the Ln3+ cationic radius

Anhydrous yttrium iodate presents polymorphism; two crystalline phases are obtained under hydrothermal conditions. alpha-Y(IO3)(3) crystallises in the monoclinic space-group P2(1)/c with a three-dimensional structure, whereas beta-Y(IO3)(3) crystallises in the monoclinic space-group P2(1)/n with a two-dimensional structure. The lattice parameters are a = 7.038(1) angstrom, b = 8.466(1) angstrom, c = 13.317(1) angstrom, 99.65(1)degrees, V = 782.3(2) angstrom(3), Z = 4 for alpha-Y(IO3)(3) and a = 8.685(1) angstrom, b = 5.964(1) angstrom, c = 14.958(1) angstrom, beta = 96.99(2)degrees, V = 769.0(2) angstrom(3), Z = 4 for beta-Y(IO3)(3). The a-form is isostructural with a-Dy(IO3)(3) studied in this work and a-Ln(IO3)(3) (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Th, Ho, Er, Tm, Yb, and Lu) already studied. The beta-forrn is isostructural with D-Ln(IO3)(3) (Ln = Ce, Pr, Nd, Eu, Gd, Th, Dy, Ho and Er) studied in this work. The structural evolutions as a function of the Ln(3+) cationic radius are studied. alpha-Y(IO3)(3) and beta-Y(IO3)(3) present good thermal stability since they decompose at 600 degrees C. They are transparent up to 11.5 mu m and they have good optical damage thresholds on powder. (C) 2007 Elsevier Masson SAS. All rights reserved.