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

The oxygen non-stoichiometry (x) and electrical conductivity (sigma) of hyp er-stoichiometric UO2+x have been measured as a function of partial pressur e (Po-2) at 1000 degrees C by a solid-state coulometric titration technique and a dc 4-probe method, respectively. Both of the properties were found t o be proportional to P-O2(1/2) at the high oxygen partial pressure regime, and P-O2(1/5) at the low oxygen partial pressure regime. These P-O2-depende ncies of the non-stoichiometry and the electrical conductivity are well exp lained with the (2:2:2) cluster model: (2O(i)(a)2O(i)(h)2V(O))' and (2O(i)( a)2O(i)(h)2V(O))"" are predominant at high and low P-O2, respectively. The electron-hole mobility of at 1000 degrees C has been determined by the comb ination of the non-stoichiometry and electrical conductivity combined on th e basis of the (2:2:2) cluster model. (C) 2000 Elsevier Science B.V. All ri ghts reserved.