Enhanced Thermoelectric Performance in Vacancy-filling Heuslers due to Kondo-like Effect.

In efforts to improve thermoelectric efficiency, various tactics have been employed with considerable success to decouple intertwined material attributes. However, the integration of magnetism, derived from the unique spin characteristic that other methods cannot replicate, has been comparatively underexplored and presents an ongoing intellectual challenge. Our previous research has shown that vacancy-filling Heuslers offer a highly adaptable framework for modulating thermoelectric properties. Here, we demonstrate how intrinsic magnetic-electrical-thermal coupling can enhance the thermoelectric performance in a vacancy-filling Heusler alloy. Our materials, Nb 0.75 Ti 0.25 FeCr x Sb with 0 ≤ x ≤ 0.1, feature a fraction of magnetic Cr ions that randomly occupy the vacancy sites of the Nb 0.75 Ti 0.25 FeSb half-Heusler matrix. These alloys achieve a remarkable thermoelectric figure-of-merit (zT) of 1.21 at 973 K, owing to the increased Seebeck coefficient and decreased thermal conductivity. The mechanism is primarily due to the introduction of magnetism, which increases the density-of-states effective mass (reaching levels up to 15 times that of a free electron's mass) and simultaneously reduces the electronic thermal conductivity. Mass and strain-field fluctuations in the vacancy-filling Heuslers further reduce the lattice thermal conductivity. Even higher zT values can potentially be achieved by carefully balancing electron mobility and effective mass. Our work underscores the substantial prospects for exploiting magnetic-electrical-thermal synergies in cutting-edge thermoelectric materials. This article is protected by copyright. All rights reserved.