CeNbO4 + delta has been synthesized by both solid state and wet chemical routes and characterized with respect to electrical conductivity and oxygen stoichiometry between 900 degrees C and 1100 degrees C and pO(2) from 1 bar to 0.002 bar. CeNbO4 + delta was shown to exhibit mixed conductivity with oxygen interstitials and electron holes being the major charge carriers. The activation energies for chemical diffusion (D-chem) and surface exchange coefficient (k(chem)), determined by electrical relaxation measurements, were 55.8 +/- 3.7 and 198 +/- 20 kJ/mol, respectively. Finally, both D-chem and k(chem) were reduced with decreasing partial pressure of oxygen. (c) 2008 Elsevier B.V. All rights reserved.