Outstanding thermoelectric performance of n-type half-Heusler V(Fe1−xCox)Sb compounds at room-temperature

Abstract The effects of cobalt substitution at the Fe-site on the crystal structure, electronic structure and thermoelectric (TE) properties of half-Heusler (HH) V(Fe 1 − x Co x )Sb compounds are investigated. Crystal structural analysis using powder X-ray diffraction clarified that all compounds have d e f i c i e n t HH structures (Huang et al., C h e m . M a t e r ., 32, 5173-5181, 2020). With Co-substitution at the Fe 4 c sites, defects are observed in the V 4 a and Fe 4 c sites, and a small amount of Fe atoms enter into 4 d sites, which is normally vacant in an i d e a l HH structure. The deficient HH structures of the V(Fe 1 − x Co x )Sb compounds are supported by electronic structural analysis using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). All compounds exhibit n -type behaviour in both calculations and experiments with deficient HH structures. The absolute value of the Seebeck coefficient | S | , decreases with an increase in the cobalt content x . The tendency of the experimental | S | value to decrease corresponds well with the | S | determined by KKR-CPA calculations. Cobalt substitution acts as an electron dopant that effectively tunes the carrier concentration. The optimised carrier concentration of 2.1 × 10 20 cm − 3 leads to the highest power factor of 5.7 × 10 − 3 W/K 2 m at room temperature for the V(Fe 0.99 Co 0.01 )Sb compound. The V(Fe 1 − x Co x )Sb compounds are thus potential candidates as n -type TE materials for power generation near room temperature.