Terbium Ion Doping in Ca ₃Co ₄O ₉: A Step towards High-Performance Thermoelectric Materials

Abstract

The potential of thermoelectric materials to generate electricity from the waste heat can play a key role in achieving a global sustainable energy future. In order to proceed in this direction, it is essential to have thermoelectric materials that are environmentally friendly and exhibit high figure of merit, ZT. Oxide thermoelectric materials are considered ideal for such applications. High thermoelectric performance has been reported in single crystals of Ca ₃Co ₄O ₉. However, for large scale applications single crystals are not suitable and it is essential to develop high-performance polycrystalline thermoelectric materials. In polycrystalline form, Ca ₃Co ₄O ₉ is known to exhibit much weaker thermoelectric response than in single crystal form. Here, we report the observation of enhanced thermoelectric response in polycrystalline Ca ₃Co ₄O ₉ on doping Tb ions in the material. Polycrystalline Ca _3−xTb _xCo ₄O ₉ (x = 0.0–0.7) samples were prepared by a solid-state reaction technique. Samples were thoroughly characterized using several state of the art techniques including XRD, TEM, SEM and XPS. Temperature dependent Seebeck coefficient, electrical resistivity and thermal conductivity measurements were performed. A record ZT of 0.74 at 800 K was observed for Tb doped Ca ₃Co ₄O ₉ which is the highest value observed till date in any polycrystalline sample of this system.