Quantitative modeling of the point defect structures of Fe-doped MgO and MgSiO sub 3 perovskite

Many physical and chemical processes in ceramics, such as diffusion, electrical conduction, and solid-state deformation, involve the motion of point defects. Because point defect concentrations in crystals are governed by the laws of thermodynamics, they can be quantitatively determined. In this paper we review recent progress on quantitative point defect concentration modeling in ceramics and minerals. Specific models for MgO and MgSiO{sub 3} perovskite that contain Fe as a dominant impurity are discussed. Both materials are believed to be abundant in the Earth's lower mantle and strongly control its properties. For MgO, the model indicates that electrical conduction involves Fe{sup 3+} on Mg sites (Fe{sub Mg}), electrons, and magnesium vacancies. The threshold concentration of Fe in MgO above which other defects are affected strongly depends on oxygen fugacity and temperature. For MgSiO{sub 3} perovskite, the strong influence of temperature, pressure, and oxygen activity on defect populations is shown and its importance relative to incongruous experimental results is discussed. 16 refs., 5 figs.