Strategic Design and Mechanistic Understanding of Vacancy‐Filling Heusler Thermoelectric Semiconductors

Abstract

Doping narrow‐gap semiconductors is a well‐established approach for designing efficient thermoelectric materials. Semiconducting half‐Heusler (HH) and full‐Heusler (FH) compounds have garnered significant interest within the thermoelectric field, yet the number of exceptional candidates remains relatively small. It is recently shown that the vacancy‐filling approach is a viable strategy for expanding the Heusler family. Here, a range of near‐semiconducting Heuslers, TiFe _x Cu _y Sb, creating a composition continuum that adheres to the Slater‐Pauling electron counting rule are theoretically designed and experimentally synthesized. The stochastic and incomplete occupation of vacancy sites within these materials imparts continuously changing electrical conductivities, ranging from a good semiconductor with low carrier concentration in the endpoint TiFe _0.67Cu _0.33Sb to a heavily doped p‐type semiconductor with a stoichiometry of TiFe _1.00Cu _0.20Sb. The optimal thermoelectric performance is experimentally observed in the intermediate compound TiFe _0.80Cu _0.28Sb, achieving a peak figure of merit of 0.87 at 923 K. These findings demonstrate that vacancy‐filling Heusler compounds offer substantial opportunities for developing advanced thermoelectric materials.

Abstract

By filling a defined amount of Cu atoms to the tetrahedral interstices, the multiphase TiFeSb alloy is stabilized into TiFe _x Cu _y Sb semiconductors with the HH‐like structure. Owing to the enhanced Seebeck coefficient and reduced thermal conductivity, TiFe _0.80Cu _0.28Sb achieves a thermoelectric figure of merit of 0.87 at 923 K.