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Among the various TE materials, the half-Heusler compounds are particularly promising for applications due to their decent higher-temperatures zT together with other advantages such as mechanical and thermal robustness, non-toxicity, and employment of low-cost and earth-abundant elements, 4–13 etc. κ tot has contributions from both the electronic ( κ e) and the lattice ( κ L) parts, i.e., κ tot = κ e + κ L. In general, higher zT corresponds to better material performance. The performance of a TE material is characterized by its figure-of-merit ( zT), where S, σ, T, and κ tot are the Seebeck coefficient, the electrical conductivity, the absolute temperature, and the total thermal conductivity, respectively. The large-scale application potential of TE technology is greatly hindered by the limited material properties, therefore, it is vitally important to improve the performance of TE materials. However, the current application of TE technology is restricted only within niche fields where reliability outweighs conversion efficiency. They are noise-free, maintenance-free, and emission-free. 2 In comparison to other competing technologies, TE devices perform reliably due to their solid-state nature. Introduction By interconverting between heat and electricity, thermoelectric (TE) technology is potentially applicable under special scenarios such as active cooling 1 or powering the nodes of the internet of things (IoT). This work advances the understanding of phonon transport properties in half-Heusler compounds, and thus provides a guideline for subsequently improving their thermoelectric properties.ġ. Furthermore, through a combination of experimental and first-principle approaches, we reveal that the intensified point-defect phonon scattering originates from the formation of Co/4d Frenkel-pair defects as a result of charge-compensation effects. Herein, we show that point-defect scattering has been the major effective mechanism for phonon scattering other than the intrinsic phonon–phonon interaction for ZrCoSb and possibly other HH compounds. To date, the lattice thermal conductivity of optimized half-Heusler compounds remains well above the amorphous limit, thus meriting the importance of unveiling their phonon-transport features as well as the individual contributing mechanisms in scattering phonon. This is particularly essential for certain thermoelectric materials such as half-Heusler compounds due to their intrinsic high lattice thermal conductivity. Enhancing the phonon scattering has been one of the most widely studied strategies to advance the thermoelectric materials’ figure-of-merit ( zT) as it avoids the complications in optimizing the intertwined electronic transport properties. Broader context Solid-state thermoelectric technology has attracted great research interest in recent years for potential applications in thermal management and power generation. Our work systematically depicts the phonon scattering profile of HH compounds and illuminates subsequent material optimizations. Induced by the charge-compensation effect, the formation of Co/4d Frenkel point defects is responsible for the drastic reduction of lattice thermal conductivity in ZrCoSb 1− xSn x. In this work, however, we show that point-defect scattering has been the dominant mechanism for phonon scattering other than the intrinsic phonon–phonon interaction for ZrCoSb and possibly many other HH compounds. Various mechanisms were reported with claimed effectiveness to enhance the phonon scattering of HH compounds including grain-boundary scattering, phase separation, and electron–phonon interaction. Their only drawback is the remaining-high lattice thermal conductivity. Half-Heusler (HH) compounds are among the most promising thermoelectric (TE) materials for large-scale applications due to their superior properties such as high power factor, excellent mechanical and thermal reliability, and non-toxicity. E-mail: b Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA c Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China d Department of Materials and Earth Sciences, Technical University of Darmstadt, Darmstadt, 64287, Germany e Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA f Institute of Materials Science, Technical University of Dresden, Dresden, 01062, Germany g Institute of Applied Physics, Technical University of Dresden, Dresden, 01062, Germany * a a Leibniz Institute for Solid State and Materials Research, Dresden, 01069, Germany. Sci., 2020, 13, 5165-5176 Unveiling the phonon scattering mechanisms in half-Heusler thermoelectric compounds †