In the present study, the effect of the addition of boron on the electrical conduction properties of nanocrystalline cerium oxide (CeO(2)) was investigated. Pellets consisting of pure CeO(2) and a mixture of CeO(2) and 10 mol.% of boron oxide (B-CeO(2) samples) were sintered at 800 degrees C as well as 1100 degrees C and their electrical conduction properties investigated by impedance spectroscopy at different temperatures and oxygen partial pressures. The nanocrystalline B-CeO(2) samples exhibit a higher electronic grain boundary conductivity and higher activation energy compared to a pure CeO(2) sample (1.41 eV for B-CeO(2) vs. 1.21 eV for pure CeO(2)). According to electron energy-loss spectroscopy analysis, (i) boron can be detected only at the grain boundaries and (ii) cerium cations are lightly reduced at the grain boundaries. The results are consistent with both the formation of a space charge layer with a positive space charge potential but also with conduction along a glassy cerium-boron-oxide phase. (C) 2010 Elsevier B.V. All rights reserved.