Phase transitions and high-temperature crystal chemistry of polymorphous modifications of Cs2(UO2)2(MoO4)

Phase transitions and thermal deformations of α- and β-Cs 2(UO2)2(MoO4)3 were studied by high-temperature X-ray diffraction analysis. In heating of α-Cs2(UO2)2(MoO4)3 to 625 ± 25°C, the reconstructive phase transition α → β proceeds. β -Cs2(UO2)2(MoO 4)3 is stable up to 700 ±25°C. The thermal expansion of both phases is sharply anisotropic: α11 = 10 × 10-6, α22 = 33 × 10-6, α 33 = 10 × 10-6, αV = 53 × 10-6 deg-1 for α -Cs(UO2) 2(MoO4)3 and α11 = 13 × 10-6, α33 = 3 × 10-6, αV = 31 × 10-6 deg-1 for β-Cs2 (UO2)2 (MoO4) 3. The anisotropy of thermal expansion is explained by features of the crystal structure of the compounds. © 2004 MAIK Nauka/ Interperiodica"."