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

5 years ago

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

Young-Min Kim, Kyu Hyoung Lee, Hyeona Mun, Ki Sung Kim, Jucheol Park, Albina Y. Borisevich, Sung Wng Kim, Jisoo Kim

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.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201702091