THE ELECTRICAL PROPERTIES OF ALUMINA AT HIGH TEMPERATURES

The ionic transport number and the d-c. electrical conductivity of single-crystal and polycrystalline alumina have been studied between 1 000 °K and 1 750 °K at an oxygen partial pressure of 0.2 atm. The ionic transport number was determined by the galvanic-cell e.m.f. measurements; the electrical conductivity was measured by the three-terminal method.It was found that alumina is a mixed conductor, being predominantly an ionic conductor at temperatures below 1 100 °K and predominantly electronic at temperatures higher than 1 600 °K. The activation energies found for the electrical conductivity of the single-crystal and polycrystalline specimens are 0.8 eV and 2.4 eV respectively in the ionic range and 3.0 eV and 3.7 eV in the electronic range.