Further insights into the chemistry of the Bi–U–O system

Abstract

Cubic fluorite-type phases have been reported in the U^IVO₂–Bi₂O₃ system for the entire compositional range, but an unusual non-linear variation of the lattice parameter with uranium substitution has been observed. In the current extensive investigation of the uranium(IV) oxide–bismuth(III) oxide system, this behaviour of the lattice parameter evolution with composition has been confirmed and its origin identified. Even under inert atmosphere at 800 °C, U^IV oxidises to U^V/U^VI as a function of the substitution degree. Thus, using a combination of three methods (XRD, XANES and Raman) we have identified the formation of the BiU^VO₄ and Bi₂U^VIO₆ compounds, within this series. Moreover, we present here the Rietveld refinement of BiU^VO₄ at room temperature and we report the thermal expansion of both BiU^VO₄ and Bi₂U^VIO₆ compounds.