Re-evaluation of the phase relationship between plutonium and zirconium dioxides

The phase relationship between ZrO2 and PuO2 was examined in a low PuO2 con tent region, from 3.1 to 11.2 mol% PuO2, at temperatures between 1273 K and 1473 K, by high temperature X-ray diffractometry. The measurements were ca rried out in air. At 1273 K, the samples in this composition range consiste d of two phases, monoclinic and cubic. Another phase, tetragonal, was obser ved at 1373 K. The low temperature monoclinic phase disappeared at 1473 K. It was confirmed that the monoclinic phase disappears around 1463 K; the di sappearance temperature does not depend on the composition of the sample. I t was, thus, inferred that there should be a eutectoid line in the phase di agram. Though the eutectoid point is not clear, the PuO2 content at the poi nt should be less than 3.1 mol%. (C) 2001 Elsevier Science Ltd. All rights reserved.