Direct Observation of Inherent Atomic‐Scale Defect Disorders responsible for High‐Performance Ti1−xHfxNiSn1−ySby Half‐Heusler Thermoelectric Alloys

Structural defects often dominate the electronic‐ and thermal‐transport properties of thermoelectric (TE) materials and are thus a central ingredient for improving their performance. However, understanding the relationship between TE performance and the disordered atomic defects that are generally inherent in nanostructured alloys remains a challenge. Herein, the use of scanning transmission electron microscopy to visualize atomic defects directly is described and disordered atomic‐scale defects are demonstrated to be responsible for the enhancement of TE performance in nanostructured Ti1−xHfxNiSn1−ySby half‐Heusler alloys. The disordered defects at all atomic sites induce a local composition fluctuation, effectively scattering phonons and improving the power factor. It is observed that the Ni interstitial and Ti,Hf/Sn antisite defects are collectively formed, leading to significant atomic disorder that causes the additional reduction of lattice thermal conductivity. The Ti1−xHfxNiSn1−ySby alloys containing inherent atomic‐scale defect disorders are produced in one hour by a newly developed process of temperature‐regulated rapid solidification followed by sintering. The collective atomic‐scale defect disorder improves the zT to 1.09 ± 0.12 at 800 K for the Ti0.5Hf0.5NiSn0.98Sb0.02 alloy. These results provide a promising avenue for improving the TE performance of state‐of‐the‐art materials. Disordered defects at all atomic sites induce a local composition fluctuation, effectively scattering phonons and improving power factors. Direct observation of atomic‐scale defect disorders clarifies an enhancement of thermoelectric performance originating from a significant reduction of thermal conductivity in half‐Heulser alloys. The collective atomic‐scale defect disorder improves the zT to 1.09 ± 0.12 at 800 K for the Ti0.5Hf0.5NiSn0.98Sb0.02 alloy.