Thermoelectric properties and figure of merit of perovskite-type Sr1−xLaxSnO3 ceramics

The thermoelectric properties of perovskite-type Sr1−xLaxSnO3 ceramics with x=0.01-0.05 were evaluated from the Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ measured at high temperatures. The La-doped ceramics were n-type semiconductors exhibiting thermally activated electrical conduction behaviors in the temperature range of 473-1073 K. Eelectron carriers were introduced into the conduction band from doped La atoms up to x=0.03, which was the solubility limit of La at Sr site. The temperature dependence of the κ values for the ceramics was unaffected by both the La content and the microstructures. Estimations of the electronic thermal conductivities by the Wiedemann-Franz law revealed that the phonon thermal conductivities were dominant for all ceramics. The dimensionless figure of merit ZT increased with increasing temperature for all ceramics and reached 0.02-0.05 at 1073 K. In contrast to cubic Ba1−xLaxSnO3 ceramics, bending of the Sn-O-Sn bonds due to octahedral tilting distortion in Sr1−xLaxSnO3 lowered the electron mobility, decreasing the power factor S2σ and ZT values, although it effectively reduced the phonon mean free path, decreasing the κ values.