Electronic conductivity of Ce0.8Gd0.2-xPrxO2-δ and influence of added CoO

Doped ceria and ceria based solid oxide solutions show a unique combination of oxygen ion mobility, electronic conductivity, and high catalytic activity for redox reactions. In this work, the minority conductivity of electrons has been measured directly as a function of the composition of ceria-praseodymia based solid solutions in order to maximize the electronic conductivity without depressing the oxygen ion mobility. The influence of Co as well as the Gd/Pr dopant ratio on the electronic conductivity of ceria-praseodymia pellets was studied for the compositions Ce0.8Gd0.2-xPrxO2-delta (0.05 <= x <= 0.15) with and without an additional Co content of 0.02 with respect to the formula. The Hebb-Wagner polarization technique was used with ion-blocking microcontacts. In the temperature range 700-800 degrees C, the presence of high amounts of praseodymium increases the p-type conductivity by a factor of more than 10 for oxygen partial pressures higher than 10(-10) bar. Co-doped ceria-gadolinia-praseodyinia solid solutions showed a further increase of the electronic conductivities in a partial pressure range where the Co-free materials showed the minimum of the electronic conductivities. It is assumed that the effect of the additional cobalt doping is due to electronic short circuits along the grain boundaries via segregated CoO. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim