Oxygen potential of hypo-stoichiometric La-doped UO2

The oxygen potential of hypo-stoichiometric (U0.8La0.2)O2−x was measured as a function of oxygen-to-metal ratio (2 − x) in the temperature range from 1173 K to 1473 K. Compared with uranium oxides doped with other lanthanides, e.g. Lu, Er, Gd and Nd, the relationship between ΔG¯O2 and the oxygen-to-metal ratio obtained for this sample showed almost the same trend, and for the relatively large oxygen non-stoichiometry x, its significance was comparable with that of (U0.8Gd0.2)O2−x  . However, the detailed variation of ΔH¯O2 and ΔS¯O2 was different among these uranium oxides, especially in the near O/M = 2.0 region. Furthermore, the oxygen defect structure was evaluated from the relationship between log PO2PO2 and log x  , and ΔG¯O2 value of lanthanide-doped uranium oxide was discussed in terms of lanthanide ionic radius.

► The oxygen potential of hypo-stoichiometric La-doped urania was evaluated from 1173 K to 1473 K. ► The relationship between oxygen partial pressure and non-stoichiometry was analyzed in detail. ► The oxygen defect structure was estimated to be a single oxygen vacancy or a vacancy complex. ► The oxygen potential of La-doped urania was discussed in terms of lanthanide ionic radius.