Non-stoichiometry, electrical conductivity and defect structure of hyper-stoichiometric UO 2+x at 1000°C

Abstract

The oxygen non-stoichiometry ( x) and electrical conductivity ( σ) of hyper-stoichiometric UO 2+ x have been measured as a function of partial pressure ( P O 2 ) at 1000°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 P O 2 1/2 at the high oxygen partial pressure regime, and P O 2 1/5 at the low oxygen partial pressure regime. These P O 2 -dependencies of the non-stoichiometry and the electrical conductivity are well explained with the (2:2:2) cluster model: (2O i a 2O i b 2V O) ′ and (2O i a 2O i b 2V O) ″″ are predominant at high and low P O 2 , respectively. The electron–hole mobility of UO 2+ x at 1000°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.