Electrical and thermal transport properties of (La,Ca)(Cr,Co)O 3

Abstract

DC electrical conductivity and Seebeck data as functions of temperature and oxygen activity were used to explain the electrical and thermal transport properties of (La,Ca) (Cr,Co)O 3. The electrical conductivity data of La(Cr,Co)O 3 suggested that it depends upon Co content. At Co concentrations less than 20 mol%, Co acted as traps for the carriers and decreased the electrical conductivity of the compositions at temperatures less than 900 °C. As the Co concentration increased to above 20 mol%, electrical conductivity increased significantly due to a connecting path of available Co sites. Additional Ca substitution for La increased the electrical conductivity in accordance with Verway's principle. Defect models derived from the electrical conductivity data were found to relate the carrier concentrations to the Ca, Co and oxygen vacancy concentrations. The measured Seebeck coefficients were found to be positive even for the most reducing conditions, indicating that (La,Ca)(Cr,Co)O 3 compositions with Co ≤ 0.3 and Ca ≤ 0.3 were as stable as LaCrO 3. The Heikes formula was adopted to interpret the Seebeck coefficient results. These results indicated that electrical conduction in La(Cr,Co)O 3 and (La,Ca)(Cr,Co)O 3 occurs via the non-adiabatic and adiabatic small polaron mechanisms, respectively.