Electrical conductivity of polycrystalline uranium dioxide

The electrical impedance of a disc-shaped sample of polycrystalline UO2 has been measured over a frequency range of 10 Hz to 10 MHz at temperatures between 108 and 380 K. Three distinct regions in the impedance profiles were observed; these have been associated with the region near the metallic electrodes, with the bulk material and with the grain boundaries. Activation energies for conduction have been determined in each of the three regions [0.17, 0.13 and 0.29 eV for the electrode, bulk and grain boundary contributions, respectively]. The impedance response has been modelled using a two-phase microstructure and an effective medium treatment. At low temperatures the boundary region is less conducting than the grain interior. However, at ambient temperatures and above, the boundary region dominates and electrical conduction takes place primarily through the boundaries.