Electronic and Ionic Conductivity in Single Crystals of MgO

Abstract

The electrical conductivity and relative fractions of ionic and electronic conductivity of single crystals of MgO were measured between 1000° and 1500°C. The results resolve conflicting observations of electronic and ionic conductivity of previous investigations in that MgO is shown to exhibit both kinds of conductivity in this temperature range. The nature of the charge carriers depends on temperature, the surrounding oxygen pressure, and the purity of the crystal. The following conditions favor predominant electronic conductivity: (1) high temperatures (>1300°C), (2) high (1 atm) or very low (<10—6 atm) oxygen partial pressures, (3) contamination, specifically Li, was found to increase the relative electronic fraction. Conversely, low temperatures (<1300°C), intermediate (10—4 to 10—5) oxygen partial pressures, and probably high purity favor predominant ionic transport. The electronic conductivity observed at the higher temperatures most likely results from point defects created in thermodynamic equilibrium.