Tailoring the electrical and thermal transport properties of LaCoO3 ceramic by band engineering and Fermi energy optimization via isovalent Al-substitution for thermoelectric application

Abstract

Recognizing high performance thermoelectric (TE) ceramics is challenging due to high thermal conductivity and interdependent electrical and thermal transport properties. Herein we report the strategy of isovalent Al substitution in LaCoO3, which resulted in the enhancement of electrical conductivity by band engineering and increased charge carrier mobility via effective mass and Fermi energy optimization. The Al substitution in LaCoO3 not only enhances the electrical transport properties but also decrease the lattice thermal conductivity through enhanced phonon scattering originated from the lattice strain induced by huge mass fluctuation of Co and substituted Al atom. The results indicate that the electrical conductivity increase with increasing the Al substitution and the maximum value of 642 S cm−1 was observed at 753 K and the maximum power factor (73.3 µW m−1K−2) was achieved at 703 K for the sample LaCo0.97Al0.03O3. The Al-substitution enhanced the charge carrier mobility from 0.21 cm2 V−1 s−1 to 51.6 cm2 V−1 s−1 by decreasing the effective mass from 28.76*me to 12.76*me. The decreased carrier concentration with Al substitution is due to the upward shift of Fermi energy towards the conduction band. The lowest thermal conductivity value (0.87 W m−1K−1) was obtained at 303 K for the sample LaCo0.95Al0.05O3. The lattice thermal conductivity of LaCo0.95Al0.05O3 (1.259 W m−1K−1) was reduced about 48% when compared with pure LaCoO3 (2.437 W m−1K−1) at 753 K. The present work reveals the importance of decoupling the electrical and thermal transport properties in achieving high performance TE ceramics.