Electrical Properties of Single‐Crystal and Polycrystalline Alumina at High Temperatures

The electrical conductivity of single‐crystal and polycrystalline aluminum oxide has been measured over the temperature range 1300° to 1750°C. and at oxygen partial pressures of 10° to 10 −10 atmospheres. Alumina exhibits p‐ type conductivity at high oxygen pressures and n ‐type conductivity at low oxygen pressures. The variation of conductivity with temperature depends on the specimen purity, oxygen pressure, and temperature level. Activation energies varying between 2.6 and 5.8 e.v. were found. The conductivity of alumina does not result from any single simple process over wide ranges of temperature and oxygen partial pressure. Apparently intrinsic conduction is found for single crystals at temperatures above 1600°C.