Long term stability of yttria and scandia doped zirconia electrolytes

The decrease of the intrinsic electrical conductivity of various yttria and scandia doped zirconia electrolyte tapes was examined during long time exposure at 950degreesC by four-point dc measurements. Different sintering profiles were applied to determine influence of phase composition and microstructure on degradation rate. The investigated specimen showed a degradation rate of 16-38 % during the first 1000 hours, whereas the degradation rate decreased exponentially by time. For the 8YSZ specimen it was found that samples sintered below 1500degreesC exhibited a significantly higher degradation than the specimen sintered at higher temperature. Degradation of 3YSZ specimen was somewhat lower and was accompanied with an increase of the tetragonal phase at expense of the cubic phase. In case of 4SSZ only slight change of the conductivity was observed after 2000 h of annealing. Although samples sintered according to a rate controlled sintering profile showed a slightly higher conductivity than conventionally sintered samples not much difference in degradation behavior was observed.