Oxidation/reduction studies on ZryU1−yO2+x and delineation of a new orthorhombic phase in U–Zr–O system

In this communication, we report the oxidation and reduction behavior of fluorite type solid solutions in U–Zr–O. The maximum solubility of ZrO2 in UO2 lattice could be achieved with a mild oxidizing followed by reducing conditions. The role of valency state of U is more dominating in controlling the unit cell parameters than the incorporated interstitial oxygen in the fluorite lattice. The controlled oxidation studies on U–Zr–O solid solutions led to the delineation of a new distorted fluorite lattice at the U:Zr=2:1 composition. The detailed crystal structure analysis of this ordered composition Zr0.33U0.67O2.33 (ZrU2O7) has been carried from the powder XRD data. This phase crystallizes in an orthorhombically distorted fluorite type lattice with unit cell parameters: a=5.1678(2), b=5.4848(2), c=5.5557(2) Å and V=157.47(1) Å3 (Space group: Cmcm, No. 63). The metal ions have distorted cubical polyhedra with anion similar to the fluorite structure. The excess anions are occupied in the interstitial (empty cubes) of the fluorite unit cell. The crystal structure and chemical analyses suggest approximately equal fractions of U4+ and U6+ in this compound. The details of the thermal stability as well as kinetics of formation and oxidation of ZrU2O7 are also studied using thermogravimetry.

Local surrounding of M ions in Zr0.33U0.67O2.33.Figure optionsDownload as PowerPoint slide