The effect of grain boundary phases upon the resistivity of zirconia-based electrolyte systems was investigated by means of impedance spectroscopy and microstructural analyses. The effect of the sintering temperature upon the grain boundary and intra-grain resistivities of seven ZrO2-Y2O3 systems with various impurity and Y2O3 contents was determined. For each system, 6 to 8 sintering temperatures between 1200 and 1700C were used. The changes in the intra-grain resistivity with increasing sintering temperature were small and were related mainly to densification of the ceramic. The grain boundary resistivity exhibited a complex behavior which varied with the impurity content. The resistivity versus sintering temperature plots exhibited inflections or peaks. This type of behavior was attributed to the composition, location and wetting properties of the boundary phases. All of these changed according to the sintering temperature and atmosphere, the cooling rate from the sintering temperature, the subsequent heat treatment, and the amount and type of impurity in the starting powder. It was found that the activation energy for O-ion conduction across grain boundaries was independent of the impurity content and of the nature of the glassy phase. It was shown that O-ion conduction across grain boundaries took place via direct grain/grain contact, rather than via the intermediate grain boundary glassy phase; which had an extremely low O-ion conductivity.

S.P.S.Badwal: Solid State Ionics, 1995, 76[1-2], 67-80