Non-stoichiometry, electrical conductivity and defect structure of hyper-stoichiometric UO2+x at 1000 deg. C

The oxygen non-stoichiometry (x) and electrical conductivity (σ) of hyper-stoichiometric UO2+x have been measured as a function of partial pressure (PO2) at 1000 deg. C by a solid-state coulometric titration technique and a dc 4-probe method, respectively. Both of the properties were found to be proportional to PO21/2 at the high oxygen partial pressure regime, and PO21/5 at the low oxygen partial pressure regime. These PO2-dependencies of the non-stoichiometry and the electrical conductivity are well explained with the (2:2:2) cluster model: (2Oia2Oib2VO)' and (2Oia2Oib2VO)'''' are predominant at high and low PO2, respectively. The electron-hole mobility of UO2+x at 1000 deg. C has been determined by the combination of the non-stoichiometry and electrical conductivity combined on the basis of the (2:2:2) cluster model