Grain-boundary effect in zirconia stabilized with yttria and calcia by electrical measurements

Six samples of mixed Y2O3/CaO doped ZrO2 electrolytes, with the same nominal chemical composition of (ZrO2)0.90–(Y2O3)0.04–(CaO)0.06, were sintered at 1600 °C for 2, 4, 6, 8, 10 and 15 h, respectively, to make the grain size differ from sample to sample. The grain-boundary conductivity of each sample was measured using complex impedance method in the temperature range from 673 to 1073 K and experimental results were analyzed according to the Arrhenius equation. It was found that variation in grain size can produce large change in the activation energy for grain-boundary conduction, Egb, and there exists a particular grain size at which Egb reaches a maximum. Such an experimental phenomenon was then analyzed based on two existing models, the constriction resistance model and the brick layer model, and a possible explanation was proposed.