Impurity Removal Leading to High-Performance CoSb3-Based Skutterudites with Synergistic Carrier Concentration Optimization and Thermal Conductivity Reduction

Abstract

Thermoelectric properties of CoSb₃-based skutterudites are greatly determined by the removal of detrimental impurities, such as (Fe/Co)Sb₂, (Fe/Co)Sb, and Sb. In this study, we use a facile temperature gradient zone melting (TGZM) method to synthesize high-performance CoSb₃-based skutterudites by impurity removal. After removing metallic or semimetallic impurities (Fe/Co)Sb, (Fe/Co)Sb₂, and Sb, the carrier concentration of TGZM-Ce_0.75Fe₃CoSb₁₂ can be reduced to 1.21 × 10²⁰ cm^-3 and the electronic thermal conductivity dramatically reduced to 0.7 W m^-1 K^-1 at 693 K. Additionally, removing these impurities also effectively reduces the lattice thermal conductivity from 7.2 W m^-1 K^-1 of cast-Ce_0.75Fe₃CoSb₁₂ to 1.02 W m^-1 K^-1 of TGZM-Ce_0.75Fe₃CoSb₁₂ at 693 K. As a consequence, TGZM-Ce_0.75Fe₃CoSb₁₂ approaches a high power factor of 11.7 μW cm^-1 K^-2 and low thermal conductivity of 1.72 W m^-1 K^-1 at 693 K, leading to a peak zT of 0.48 at 693 K, which is 10 times higher than that of cast-Ce_0.75Fe₃CoSb₁₂. This study indicates that our facile TGZM method can effectively synthesize high-performance CoSb₃-based skutterudites by impurity removal and set up a solid foundation for further development.

Keywords: CoSb3; synthesis; temperature gradient zone melting; thermal conductivity; thermoelectric.