Electrical conductivity of Sc2O3-ZrO2 compositions by 4-probe d.c. and 2-probe complex impedance techniques

The ionic conductivities of several samples in the Sc₂O₃-ZrO₂ system (Sc₂O₃: ～ 8 mol %) have been measured using 4-probe d.c. and 2-probe complex impedance dispersion techniques. Samples which contained monoclinic zirconia showed hysteresis effects and S-shaped Arrhenius conductivity plots. This behaviour was assigned to the m-ZrO₂ ? t-ZrO₂ transformation. In samples which were free of monoclinic ZrO₂, contributions from the grain boundary resistance were relatively small. The Arrhenius plots of their conductivity showed a distinct change in the slope around 600° C towards higher activation energy and this was attributed to vacancy trapping. The 4-probe d.c. data could be fitted to an equation of the formρ=A ₁ T exp (E ₁/RT)+A ₂ T exp (E ₂/RT). The process which dominated the conduction mechanism at lower temperatures had an activation energy of 130 to 140 kJ mol^?1. The activation energy for the migration of oxygen ion vacancies within the bulk of the grain was 64 to 70 kJ mol^?1.