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

Electrical resistivity and Seebeck (S) measurements were performed on (La(1-x)Sr(x))MnO(3) (0.02 less than or equal to x less than or equal to 0.50) and (La(1-x)Sr(x))CoO(3) (0 less than or equal to x less than or equal to 0.15) in air up to 1073 K. (La(1-x)Sr(x))MnO(3) (x less than or equal to 0.35) showed a metal-to-semiconductor transition; the transition temperature almost linearly increased from similar to 250 to similar to 390 K with increasing Sr content. The semiconductor phase above the transition temperature showed negative values of S. (La(1-x)Sr(x))CoO(3) (0 less than or equal to x less than or equal to 0.10) showed a semiconductor-to-metal transition at similar to 500 K. Dominant carriers were holes for the samples of x greater than or equal to 0.02 above room temperature. LaCoO(3) showed large negative values of S below ca. 400 K, indicative of the electron conduction in the semiconductor phase. (C) 2000 Elsevier Science Ltd. All rights reserved.