Synthesis, Characterization and Crystal Chemistry of Uranium and Cerium Doped Yttrium Titanate Pyrochlore: A Potential Waste Immobilization Matrix

Uranium and cerium doped yttrium titanate pyrochlores Y 2-x A x Ti 2 O 7±δ (A = U or Ce) were synthesized by gel combustion method. The Rietveld analysis of these pyrochlores showed that due to the large charge heterogeneity, uranium cannot be incorporated to a large extent at the intended A site of the pyrochlore in air atmosphere causing separation into brannerite phase containing yttrium and yttria stabilized UO 2+x . Studies also showed that more than 10 mole% U could be accommodated at A site when reducing conditions were used. Unlike uranium, 15 mole% of Ce could be doped at A site as a single phase in air atmosphere. The observations in the crystal chemistry of these pyrochlores were confirmed by XRD, SEM, Raman and XPS. The gamma irradiation of these pyrochlores showed good radiation stability which was confirmed by XRD and PALS. PALS also confirmed uranium doping is preferably taking place at B site in oxidizing conditions. The thermo-physical properties of these pyrochlores were evaluated by HT-XRD and DSC.