ELECTRICAL AND THERMAL TRANSPORT-PROPERTIES OF (LA,CA)(CR,CO)O-3

DC electrical conductivity and Seebeck data as functions of temperatur e 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 C o concentrations less than 20 mol%, Co acted as traps for the carriers and decreased the electrical conductivity of the compositions at temp eratures less than 900 degrees C. As the Co concentration increased to above 20 mol%, electrical conductivity increased significantly clue t o 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 d ata 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 less than or equal to 0 .3 and Ca less than or equal to 0.3 were as stable as LaCrO3. The Heik es formula was adopted to interpret the Seebeck coefficient results. T hese 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 pol aron mechanisms, respectively.