Ionic Conductivity and Magnesium Vacancy Mobility in Magnesium Oxide

The dc conductivity and ionic transference number of MgO single crystals doped with Al, Fe, and Sc were measured as a function of temperature (1200° to 1600°C) and oxygen pressure (10 −1 to 10 −13 MPa). Magnesium oxide is a mixed conductor with its ionic component directly proportional to the trivalent solute concentration. The activation energy for ionic conduction equals 202 kj/mol and is independent of the specific trivalent solute used. This behavior results from a defect structure for a single trivalent solute for which the charge balance condition is 2[ V Mg '] =[ I Mg ], where [ V Mg ”] is the Mg vacancy concentration and [ I Mg ] the trivalent solute concentration. At lower temperatures and high Sc concentrations, effects attributed to Sc ionvacancy association are observed. Ionic conduction results from Mg vacancy motion with a diffusion coefficient of V Mg ' given by image Deduced values of the Mg‐ion diffusion coefficient lead to the conclusion that the scatter in the published D Mg data largely results from differences in impurity content.