Thermal expansion and solubility limits of plutonium-doped lanthanum zirconates

Plutonium-doped and undoped lanthanum zirconates were prepared by solid sta te reaction. The solubility limit of Pu in La2Zr2O7 was studied by X-ray di ffraction, and the solubility limits of Pu in pyrochlore-type phase prepare d in air, vacuum and Ar-8%H-2 atmospheres were determined to be 10, 35 and 100 mol%, respectively. The compound with 80 mol% Pu prepared in air and th e compounds with 80 and 100 mol% Pu prepared in vacuum showed single fluori te-type phases. Thermal expansion coefficients of (La1-xPux)(2)Zr2O7+y (x = 0, 0.05, 0.10 and 0.80) were also measured by high-temperature X-ray diffr action at temperatures between room temperature and 1273 K in air and He-8% H-2 atmospheres and were found to increase with increasing Pu content. The dependence of the linear thermal expansion coefficients on Pu content is di scussed from the point of view of the radii of both tetravalent Pu in air a nd trivalent Pu in He-8%H2. (C) 2001 Elsevier Science B.V. All rights reser ved.