Effect of dopant concentration on electrical conductivity in the Sc2O3-ZrO2 system

Electrical conductivity measurements have been made as a function of dopant concentration (4 to 8 mol% Sc₂O₃) in the scandia-zirconia system, All the compositions studied had a tetragonal structure. The hombohedral phase was present only in samples prepared from mechanical mixtures of Sc₂O₃ and ZrO₂. In specimens prepared by coprecipitation, no phase lines were observed and the monoclinic zirconia (m-ZrO₂) phase was present for only Sc₂O₃ contents 5 mol %. The conductivity of Sc₂O₃-ZrO₂ decreased continuously with time up to 300 h anneal time between 700 and 1000° C. X-ray diffraction of coprecipated specimens of 7.8 mol % Sc₂O₃-ZrO₂ composition annealed at 1000° C (28 days), 750° C (42 days) or 460° C (189 days) did not reveal any changes to account for this. However, transmission electron microscopy showed that changes associated with the formation of very fine precipitates had occurred. The activation energy for conduction in the low-temperature region decreased monotonically with decrease in the scandia content. Jumps in the conductivity curves and hysterisis effects were observed in specimens containing m-ZrO₂.