Oxygen potentials of (U,Gd)Osub(2+-x) solid solutions in the temperature range 1000-15000C

Oxygen potentials of Usub(0.86)Gdsub(0.14)Osub(2+-x) and Usub(0.73)Gdsub(0.27)Osub(2+-x) solid solutions, together with UOsub(2+x), have been measured at 1000, 1300 and 15000C by using a thermogravimetric technique. The results at 10000C show good agreement with the results of a previous solid electrolyte galvanic cell measurement. The oxygen potentials for the solid solutions increase positively with increasing Gd content. Stable hypostoichiometric phases are seen at the oxygen potentials below -65 and -50 kcal/mol between 1000 and 15000C for Usub(0.86)Gdsub(0.14)O2 and Usub(0.73)Gdsub(0.27)O2, respectively. From the oxygen partial pressure dependence of x, models for the defect structure in hyper- and hypostoichiometric solid solutions are suggested. (orig.)