Thermodynamic study on the (U1-yEry)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∝1500 C and 10-13 ≤pO2≤10-4 atmosphere for y=0.06 and y=0.20, respectively. The lattice parameters of stoichiometric (U1-yEry)O2 were also measured by the least-squares method in the range of y=0.01 to y=0.33. The lattice parameter decreases linearly with an increase in the erbium concentration. The change of the lattice parameter can be expressed in a linear equation of y as a(A)=5.4695-0.220y for 0≤y≤0.33. The Δanti GO2 has 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 respectively in the temperature range of 1200∝1500 C. Both Δanti SO2 and Δanti HO2 for (U1-yEry)O2±x showed sharp maxima at about the O/M ratio of 2.005, irrespective of erbium content, but the minimum peaks of the Δanti SO2 and Δanti HO2 were shown only for y=0.20 at O/M=1.995. (orig.)