Microstructure-conductivity correlation for hot-pressed 8YSZ powders

oarse 8YSZ powders destined for plasma spray deposition were obtained from three different suppliers (Hochrhein, Magnesium Elektron, Unitec). Their ionic conductivities were measured by impedance spectroscopy on pellets prepared by vacuum hot pressing. Density was adequate for one powder (Unitec, 95%) but poor for the other two (73-80%). For the latter samples, conductivity was a factor of 1.5 below reference values for pure dense 8YSZ, owing to their porosity. For the former samples, however, the conductivity was a factor > 3 below 8YSZ reference values. An additional resistance, responsible for this large discrepancy, appeared in the impedance response and is ascribed to the distinct microstructure at intergranular zones within these otherwise dense samples.