Pivotal role of Sb vacancies in quaternary half-Heusler thermoelectrics

Abstract

Half-Heusler compounds are promising high-temperature thermoelectric materials due to their high figure of merit and excellent mechanical properties. The capability of the Heusler structure to accommodate a large variety of different elements allows for a vast phase space of substitutions and compositions. The quaternary half-Heuslers (also known as “double half-Heuslers”) with stoichiometry have sparked particular interest as a route to lower the lattice thermal conductivity and enhance thermoelectric performance. Here, we unveil the pivotal role of intrinsic defects, namely Sb vacancies, in nominally stoichiometric X(Ni_0.5Fe_0.5)Sb quaternary half-Heuslers, where X = Ti, Zr, Hf. Sb vacancies naturally occur during synthesis and can switch the conduction behavior from intrinsic n-type to p-type. To control the formation of Sb vacancies, we developed a sophisticated synthesis method, which we argue will be crucial for rational design of n- and p-type quaternary half-Heusler thermoelectrics.