Samples of yttria-stabilized material were prepared by hot isostatic pressing, tape casting, vacuum plasma spraying, and calendering. The ionic conductivities of these samples were measured by using impedance spectroscopy, 4-point probe methods, current interruption techniques and the van der Pauw technique. The tape-cast and hot-pressed samples exhibited high, and very reproducible, conductivities. The vacuum plasma sprayed samples exhibited an anisotropy in their conductivity; with the cross-plane value being several times lower than the in-plane value. A simple model which was based upon the porous microstructure of these samples could explain this observation. Sintering of the plasma sprayed samples minimized the anisotropy and significantly improved the conductivity. The calendered samples also exhibited a similar anisotropy in conductivity when they were inadequately sintered.

J.Van Herle, A.J.McEvoy, K.R.Thampi: Journal of Materials Science, 1994, 29[14], 3691-701