Electrical resistivity and thermopower of (La1−xSrx)MnO3 and (La1−xSrx)CoO3 at elevated temperatures

Electrical resistivity and Seebeck (S) measurements were performed on (La1−xSrx)MnO3 (0.02⩽x⩽0.50) and (La1−xSrx)CoO3 (0⩽x⩽0.15) in air up to 1073 K. (La1−xSrx)MnO3 (x⩽0.35) showed a metal-to-semiconductor transition; the transition temperature almost linearly increased from ∼250 to ∼390 K with increasing Sr content. The semiconductor phase above the transition temperature showed negative values of S. (La1−xSrx)CoO3 (0⩽x⩽0.10) showed a semiconductor-to-metal transition at ∼500 K. Dominant carriers were holes for the samples of x⩾0.02 above room temperature. LaCoO3 showed large negative values of S below ca. 400 K, indicative of the electron conduction in the semiconductor phase.