The influence of alumina on the microstructure and grain boundary conductivity of yttria-doped zirconia

The influence of alumina additions on grain boundary electrical conductivity of yttria-doped zirconia has been investigated by impedance spectroscopy. The results have been interpreted taking into account the microstructural and microchemical characterizations. Experiments have been conducted on polycrystals sintered from powders prepared through two different processing routes. Samples with the cleaner microstructure and no evidence for grain boundary glassy films show the highest conductivities, which decrease in the presence of alumina additions. On the contrary, alumina additions (≤2 mol%) lead to an increase of conductivity of samples showing grain boundary glassy films. These results have been attributed to a change in the glassy phase wettability due to the higher amount of Al found in the glassy phases in the presence of alumina additions. The same grain boundary activation energy found for the different samples suggests that only “clean” grain boundaries contribute to the transport processes.