Enhanced thermoelectric efficiency in Bi-substituted La0.95Sr0.05CoO3

Abstract

We present the results of a comprehensive investigation of electric and thermal transport properties of polycrystalline Bi-substituted La0.95− xBi xSr0.05CoO3 for LBSCO-0, 1, and 2. The electrical resistivity reflects the semiconducting nature with n-type to p-type transition ∼52 K for LBSCO-1 and LBSCO-2 samples. In the low temperature region, the dominant transport mechanism is found to be variable range hopping with the hopping range decreasing with increasing temperature from 95 to 20 Å. The substitution of higher atomic weight element Bi at the La site drastically affects the overall thermal conductivity by reducing the lattice contribution (∼0.12 W/m-K at 50 K) and also enhancing the Seebeck coefficient ( S ∼ 354  μV/K). The increase in the resistivity and Seebeck coefficient for the Bi-substituted system is related to the decrease in the available charge carrier concentration (∼5.12 × 1020 cm−3). The overall variation in the Seebeck coefficient depicts a complex nature with a large decreasing trend below 50 K followed by an in-depth analysis of the Debye temperature (∼470 K) and e– ph coupling. These findings suggest that the Bi-substituted LBSCO system has phonon-mediated charge transport via the phonon drag effect below 50 K. Notably, we found a large increment in ZT ∼ 0.17 at room temperature for LBSCO-2 compositions that is one-order larger than pristine undoped LBSCO-0 and even higher than the other existing cobaltite-based thermoelectric choice.