Defect Structure, Charge Transport Mechanisms, and Strain Effects in Sr4Fe6O12+δ Epitaxial Thin Films

The defect structure and charge transport mechanisms of layered perovskite-related structure Sr4Fe6O12+δ in the form of epitaxial thin films are studied as a function of temperature, oxygen partial pressure, and the type of substrate upon which they were grown. Values for the band gap, oxidation, and reduction enthalpies are extracted by fitting the experimental data to a defect model assuming a high oxygen deficiency. The electrical conductivity was dominated by p-type and n-type electronic conductivity at high and low oxygen partial pressures, respectively, with no evidence of a measurable ionic conductivity. Specimens cooled to below 400 °C after being annealed at different pO2’s at elevated temperatures exhibited an activated conductivity whose activation energy Ea increased from ∼0.2 eV to ∼1.0 eV as the pO2 at which the specimens were annealed decreased from 1 atm to 10−4 atm. These data, which are also examined with respect to the different epitaxial strains induced by selecting substrates with dif...