Entropy-stabilized perovskite oxide Ba0.1Ca0.1La0.05Sr0.75Ti0.85Nb0.15O3 with improved thermoelectric performance for high-temperature waste heat recovery

Abstract

SrTiO₃ (STO) is a well-known n-type thermoelectric material with high Seebeck coefficient, but it exhibits low electrical conductivity and high thermal conductivity, resulting in poor thermoelectric figure of merit (zT). In this work, an entropy stabilization approach is employed to enhance electrical transport in an STO-based system. The polycrystalline ceramic composition (Ba_0.1Ca_0.1La_0.05Sr_0.75)(Ti_0.85Nb_0.15)O₃ (BCLSTN) has been synthesized via the solid-state reaction route and densified using spark plasma sintering (SPS). Structural, microstructural, and compositional analyses confirm the incorporation of donor ions La³⁺ and Nb⁵⁺ at the A and B-sites, respectively, thereby contributing additional electrons. Additionally, the isovalent doping of Ba and Ca at the Sr-site has been found to weaken the Anderson localization of electrons present in the material. This results in enhancement of electron mobility, leading the charge carriers to attain the itinerant state. As a result, the BCLSTN ceramic exhibits high electrical conductivity, which is 29.4 and 7.7 times improvement at 323 K compared to SrTi_0.85Nb_0.15O₃ (STN) and La_0.07Sr_0.93Ti_0.93Nb_0.07O₃ (LSTN) compositions, respectively. A maximum Seebeck coefficient −166 µV K⁻¹ has been attained, giving rise to an improved power factor of about 218% and 132% enhancement compared to STN and LSTN compositions, respectively. Consequently, entropy engineering not only improves the electrical transport but also prevents the rise in lattice thermal conductivity owing to multiple cations occupying A- and B-sites. As a result, zT of BCLSTN shows a significant improvement of ∼149% and 98% compared to that of STN and LSTN, respectively. Moreover, an all n-type thermoelectric prototype module has been fabricated, which has shown staggering power output and power density of 95.5 mW and 2902 W m⁻², respectively.