THERMODYNAMIC STUDY ON THE (U1-YER(Y))O2+ -X SOLID-SOLUTIONS/

The oxygen potentials of (U1-yEry)O2+/-x solid solutions were measured by means of a thermogravimetric method in the range of 1200 approxima tely 1500-degrees-C and 10(-13) less-than-or-equal-to p(O2) less-than- or-equal-to 10(-4) atmosphere for y = 0.06 and y = 0.20, respectively. The lattice parameters of the stoichiometric (U1-yEry)O2 were also me asured by the least-squares method in the range of y = 0.01 to y = 0.3 3. The lattice parameter decreases linearly with an increase in the er bium concentration. The change of the lattice parameter can be express ed in a linear equation of y as a(angstrom) = 5.4695 - 0.220y for 0 le ss-than-or-equal-to y less-than-or-equal-to 0.33. The DELTAG(O2)BAR ha s been found to undergo an abrupt increase in the range of - 270 to - 360 kJ/mol for y = 0.06 and - 220 to - 320 kJ/mol for y = 0.20 respect ively in the temperature range of 1200 approximately 1500-degrees-C. B oth DELTAS(O2)BAR and DELTAH(O2)BAR for (U1-yEry)O2+/-x showed sharp m axima at about the O/M ratio of 2.005, irrespective of erbium content, but the minimum peaks of the DELTAS(O2)BAR and DELTAH(O2)BAR were sho wn only for y = 0.20 at O/M = 1.995.