X-ray and thermal studies of mixed valent uranium molybdates

Abstract

Thermal expansion behavior of U 2MoO 8, β-UMo 2O 8, UMo 5O 16, UMo 7O 22 and UMo 10O 32 was studied in vacuum between 298 K and 873 K using high temperature X-ray diffractometer. The compounds were synthesized by solid state route, reacting UO 2, MoO 2 and/or MoO 3 in required molar proportions in sealed evacuated quartz ampoules at desired temperatures. Studies of oxidation behavior of all mixed valent uranium molybdates were carried out using thermogravimetry in dry air up to 973 K. Oxidation states of uranium and molybdenum were proposed based on their oxidation behavior. X-ray diffraction data of all the uranium molybdates were indexed on orthorhombic system. From ambient to 873 K, lattice parameters and cell volume of U 2MoO 8, β-UMo 2O 8 and UMo 7O 22 showed positive thermal expansion whereas UMo 5O 16 and UMo 10O 32 showed negative axial as well as volume thermal expansion up to 873 K.