Double perovskite Pr₂CoFeO₆ thermoelectric oxide: Roles of Sr-doping and Micro/nanostructuring

Owing to their excellent thermal stability, non-toxicity, and low cost, oxide-based thermoelectric materials have considerably expanded research interests and industrial application. Here, we, for the first time, report a new-type Pr₂CoFeO₆ oxide-based thermoelectric materials from both theoretical and experimental aspects. Our first-principles calculation results indicate that Pr₂CoFeO₆ is a p-type semiconductor with narrow bandgap. The experimental thermoelectric evaluation shows that pristine Pr₂CoFeO_6, synthesized by a combination of sol–gel method and conventional sintering, has a peak figure of merit, ZT of 0.015 at 773 K with a high positive Seebeck coefficient of 250 μV K⁻¹ and very low thermal conductivity of 0.7 W m⁻¹ K⁻¹ at this temperature. Further Sr²⁺ doping on Pr-sites (Pr³⁺) enhances the carrier concentration from 4.03 × 10¹⁴ cm⁻³ to 5.22 × 10¹⁷ cm⁻³, contributing to an improved power factor up to 46 μW m⁻¹ K⁻². Besides, Sr-doping induces point defects in the matrix and further suppresses the thermal conductivity to 0.58 W m⁻¹ K⁻¹, leading to a promising ZT up to 0.05 at 673 K in Pr_1.8Sr_0.2CoFeO₆, which is significantly improved by 233% compared to pristine Pr₂CoFeO₆. We also predict that a high ZT of > 0.2 can be achieved by the optimization of carrier density, band engineering, and energy filtering, which is comparable to many other oxide-based thermoelectric materials.