Partial electronic and ionic conduction in nanocrystalline ceria: role of space charge

The total electrical conductivities of Gd-doped (0.15 mol%) and nominally pure nanocrystalline CeO2−x ceramics (∼30 nm grain size) were measured by impedance spectroscopy as a function of temperature and oxygen partial pressure. Careful separation of the partial ionic and electronic contributions using an electronically blocking cell allowed for a clear distinction between potential explanations. It is shown that unlike competing models the space charge model explains all the experimental features not only qualitatively but also quantitatively.