Electrical conductivity of the oxygen-deficient rutile CrNbO4-delta

Reduction of CrNbO4 under 5% H-2/Ar at different temperatures has been carried out to obtain oxygen-deficient rutiles aiming for mixed ionic and electronic conductivities. Decomposition is observed at temperatures above 950 degrees C. Hence, the more reduced rutile that could be obtained corresponds to that obtained at 950 degrees C which has the composition CrNbO3.96. When compared with CrNbO4, the reduced product exhibits an electrical conductivity between three and four orders of magnitude higher. Both bulk and grain boundary conductivities are enhanced upon reduction. The small amount of vacancies generated by reduction does not induce oxygen conductivity. However, the presence of the corresponding small amount of Nb(IV) in the rutile affects strongly the electrical properties. This is likely related to the structural characteristics of rutile that allow for strong Nb-Nb interactions. On the other hand, no evidence of protonic conductivity has been found. (C) 2008 Elsevier Masson SAS. All rights reserved.