Phase relationships in the UO2- BaO-ZrO2-MoO x system

The pseudoquaternary system UO2-BaO-ZrO2-MoO x (where x = 0, 2, 3) was studied in the temperature range 1480°C-1600°C at oxygen pressures corresponding to reducing (x=0) and oxidizing (x=2,3) conditions for molybdenum. Ternary BaO-ZrO2- MoOx compositions were mixed with UO2 in proportion of 80 wt% UO2. In reducing conditions (pO2=10-16 atm), Mo0 is in equilibrium with the U1-xZr xO2 matrix and the Ba(ZrUMo)O3 perovskite phase. In oxidizing conditions (pO2 =10-9 atm), BaO reacts preferably with MoO3 giving the scheelite BaMoO4 phase. For Ba/Mo1, the perovskite phase is replaced by a new uranate phase of composition Ba2(U 1-x Zrx)3O9+y with y