Electronic Conduction and Thermopower of Magnetite and Iron-Aluminate Spinels

Electrical-conductivity and thermoelectric-power measurements of magnetite and iron-aluminate spinels at high temperatures confirm a small-polaron model of electronic conduction. Electrical properties corroborate the previously established cation distribution and defect model. Iron cations become randomly distributed between sublattices at the highest temperature. An n-to-p transition therefore occurs at the 50%Fe₃O₄-50%FeAl₂O₄ composition. Cation distribution and defect equilibria appear to be independent of composition.