Electrical conductivity of (Er,U)O2+x and (Ce,U)O2+x Original Research Article

The electrical conductivity (σ) of (EryU1−y)O2+x (y=0.06, 0.20) and (CeyU1−y)O2+x (y=0.05, 0.15, 0.25) has been measured as a function of oxygen partial pressure in the temperature range of 1100≤T/°C≤1300 by a d.c. 4-probe method. Both of the oxides exhibited Po2-regions where the electrical conductivity is independent of oxygen partial pressure, which indicates that doped Er and Ce exist as trivalent cations on uranium sites and fix the hole concentration by acting as electron acceptors, i.e. [hradical dot]=[Er′U] and [hradical dot]=[Ce′U], respectively. It is considered that strong oxidization tendency of uranium and reduction tendency of cerium simultaneously render the cerium ions exist exclusively as Ce3+ in the uranium dioxide. The electron–hole mobility of (EryU1−y)O2+x and (CeyU1−y)O2+x in the Po2 region where σ is constant has been calculated by the combination of the electrical conductivity and charge carrier concentration; the activation energy (EH) of each oxide has been obtained from the temperature dependence of the mobility. Small polaron hopping conduction mechanism was confirmed by small magnitude of the mobility (0.018–0.052 cm2 V−1 s−1) and the activation energy (0.12–0.22 eV).