Alloyed triple half-Heuslers: a route toward high-performance thermoelectrics with intrinsically low lattice thermal conductivity

Abstract

Half-Heusler (HH) alloys have been extensively studied as ternary systems with various intriguing physical properties since their discovery around a century ago. Particularly, HH semiconductors show promising potential as high-temperature thermoelectric materials due to their excellent electrical properties, while their high thermal conductivities restrict their further development and application. In this work, alloyed triple HH (THH) alloys Ti(Fe_0.5+xCo_0.25Cu_0.25−x)Sb (x = 0, 0.025, 0.05, 0.075) with intrinsically low lattice thermal conductivities have been successfully designed and synthesized based on a valence balanced strategy. All the samples are homogeneous single phase, crystalizing in the cubic MgAgAs-type structure with the space group F3m. Fe/Co/Cu distributes randomly on the 4c site, leading to greatly enhanced point-defect phonon scattering and thus significantly lower lattice thermal conductivity than conventional 18-electron HHs and double HH TiFe_0.5Ni_0.5Sb. Meanwhile, the electrical transport properties can be feasibly optimized by partial substitution of Cu with Fe. As a result, a peak zT value of 0.71 has been realized for the sample with x = 0.025 in the temperature range of 900 to 1024 K, demonstrating the potential of alloyed THH compounds as high-performance thermoelectric materials.