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Abstract. The effect of alumina additions on the ionic conductivity and mechanical properties of 3 and 8 mol% Y203-ZrO 2 compositions has been investigated. Such materials are of interest for use in fuel cells and other similar applications. Sintered specimens were characterised by XRD, SEM, impedance spectroscopy, four -probe DC conductivity and mechanical strength measurements. Alumina additions had no affect on the conductivity degradation behaviour at 1000 ~ and the activation energy but resulted in an increase in the strength of 8 mol% Y203 -ZrO2 composition by about 25%. However, a significant drop in the ionic conductivity well above what could be accounted for by the decrease in the volume fraction of the conducting phase, was observed.

The grain-boundary resistivity of tetragonal zirconia polycrystals, which had undergone creep with different applied compressive loads and at different temperatures, has been measured with impedance spectroscopy. A stress exponent of unity was determined from strain rate versus stress data. The grain-boundary resistivity decreased significantly with increasing stress at a constant creep temperature indicating squeezing out of the glassy phase from interfaces between grains. This, however, had no effect on the activation energy for the grain-boundary resistivity. [

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