DEFECT STRUCTURES OF U1-YERYO2+ -X SOLID-SOLUTIONS/

The nonstoichiometry x in U1-yEryO2+/-x was determined by thermogravim etry under the controlled oxygen partial pressure of CO2/CO mixture ga s. The oxygen potentials corresponding to various x values of U1-yEryO 2+/-x solid solutions were measured with an electrolyte oxygen sensor in a range 10(-14) less than or equal to pO2 less than or equal to 10 (-3) at 1200-1500 degrees C for UO2, y = 0.02, 0.06 and 0.20 solid sol utions. Defect equilibrium equations were derived, and the relations o f x versus p(O2) were obtained using the mass action law. The dominan t defect species in a specified region were determined by fitting the calculated curve of log x value log p(O2) to the experimental data fo r each theoretical model. The calculated curve for the (2:1:2)(m') and (Er'U-.)(x) clusters in hyperstoichiometry and that for the (2Er'V-O) (dec)(x) cluster in hypostoichiometry were in good agreement with the present experimental results.