Combustion synthesis and thermal expansion measurements of the rare earth-uranium ternary oxides RE6UO12 (RE = La, Nd and Sm)

Rare earth-uranium ternary oxides were synthesized by a solution combustion route. The starting materials were the corresponding metal nitrates and urea. In these preparations, the metal nitrates act as oxidizer and urea as fuel. Highly exothermic decomposition of the metal nitrate-urea complexes on heating at about 500 K leads to a combustion process yielding RE6UO12 fine powders. Thermal expansion measurements of these compounds were carried out in the temperature range of 298-1173 K by high temperature X-ray powder diffractometry. The observed axial thermal expansion behaviour is explained on the basis of the crystal chemistry of the compounds. (C) 2000 Elsevier Science B.V. All rights reserved.