Thermal expansion and solubility limits of plutonium-doped lanthanum zirconates

Plutonium-doped and undoped lanthanum zirconates were prepared by solid state reaction. The solubility limit of Pu in La2Zr2O7 was studied by X-ray diffraction, and the solubility limits of Pu in pyrochlore-type phase prepared in air, vacuum and Ar–8%H2 atmospheres were determined to be 10, 35 and 100 mol%, respectively. The compound with 80 mol% Pu prepared in air and the compounds with 80 and 100 mol% Pu prepared in vacuum showed single fluorite-type phases. Thermal expansion coefficients of (La1−xPux)2Zr2O7+y (x=0, 0.05, 0.10 and 0.80) were also measured by high-temperature X-ray diffraction at temperatures between room temperature and 1273 K in air and He–8%H2 atmospheres and were found to increase with increasing Pu content. The dependence of the linear thermal expansion coefficients on Pu content is discussed from the point of view of the radii of both tetravalent Pu in air and trivalent Pu in He–8%H2.