Effect of microstructure on the thermoelectric performance of La1−xSrxCoO3

• Electrical and thermal transport properties are affected by the microstructure in La1−xSrxCoO3 polycrystalline materials.
• Coarse/fine grain size distribution enhances the Seebeck coefficient.
• Porosity reduces the thermal conductivity in La1−xSrxCoO3 polycrystalline samples.
• The combination of large/small grain ratio distribution with the high porosity may result to the enhancement of the thermoelectric performance of the material.

We present a case where the microstructure has a profound effect on the thermoelectric properties of oxide compounds. Specifically, we have investigated the effect of different sintering treatments on La1−xSrxCoO3 samples synthesized using the Pechini method. We found that the samples, which are dense and consist of inhomogeneously-mixed grains of different size, exhibit both higher Seebeck coefficient and thermoelectric figure of merit than the samples, which are porous and consist of grains with almost identical size. The enhancement of Seebeck coefficient in the dense samples is attributed to the so-called “energy-filtering” mechanism that is related to the energy barrier of the grain boundary. On the other hand, the thermal conductivity for the porous compounds is significantly reduced in comparison to the dense compounds. It is suggested that a fine-manipulation of grain size ratio combined with a fine-tuning of porosity could considerably enhance the thermoelectric performance of oxides.

The enhancement of the dimensionless thermoelectric figure ZT of merit is presented for two equally Sr-doped LaCoO3 compounds, possessing different microstructure, indicating the effect of the latter to the thermoelectric performance of the La1−xSrxCoO3 solid solution.Figure optionsDownload as PowerPoint slide