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Many transition metal oxides possess intermediate values of electrical conductivity (10−2−102 (Ω-cm)−1) which exhibit Arrhenius behavior with small (≤ 0.5 eV) activation energies. It can be demonstrated that the mobility in such materials is often activated, e.g., conduction is via small polaron hopping (Mason 1988). Among these are the simple oxides of iron and various iron-containing complex oxides, e.g., spinels, olivines, etc. Such materials have both geological and technological importance. The electrical properties are closely related to defect phenomena in these materials, e.g., point defect formation, multi-site exchange reactions, solid solution, etc. The equations below are completely general for all the materials and phenomena considered. A more thorough treatment is given in (Mason 1987). |
