Electrical conductivity of cubic-YSZ/Al2O3 composites at high temperatures

In order to improve the mechanical properties of YSZ, to be used as electrolyte in SOFC, its composite ceramics have been suggested as possible candidates. The present paper reports electrical conductivity measurements, performed by the complex impedance spectroscopy technique on cubic yttria stabilized zirconia (7.54mol% Y2O3)/alumina (5-10-15wt%) composite ceramics. The experiments, performed at constant oxygen partial pressure (0.21 atm) in the temperature range 523-1123 K, allow separation of the bulk and the grain boundary electrical resistance. In all specimens, the bulk conduction process presents a mechanism variation at about 870 K. At higher temperatures the activation energy decreases with increasing the A1(2)O(3) content, while the behaviour is opposite at the lower temperatures. The total conductivity shows only one slope, in the temperature range investigated, with activation energies increasing with the Al2O3 content. Grain boundary conductivities present a change in the slope of the Arrhenius plots. The results are compared with those obtained on polycrystalline YSZ (7.54mol% Y2O3) specimens.