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We herein report the significantly improved thermoelectric performance of n-type Bi2Te2.7Se0.3 polycrystalline bulks through band structure engineering achieved by Au-doping. The Seebeck coefficient can be increased for both Bi2Te2.7Se0.3 and Cu-intercalated Bi2Te2.7Se0.3 bulks by doping Au on the Bi site, either due to the addition of the resonant state or the enhancement of density of states (DOS) effective mass md*. Theoretical calculations combined with experimental measurements showed that band engineering connected with chemical potential tuning results in higher DOS at the bottom of the conduction band and increases the md* from ∼0.88m0 (Bi2Te2.7Se0.3) to ∼1.06m0 (Cu0.008Bi1.99Au0.01Te2.7Se0.3). As a consequence, a peak thermoelectric figure of merit ZT∼0.91 was obtained at 320 K for Cu0.008Bi1.99Au0.01Te2.7Se0.3, which is ∼40% and ∼25% enhancement in comparison with Bi2Te2.7Se0.3 and Cu0.008Bi2Te2.7Se0.3, respectively. [ABSTRACT FROM AUTHOR]

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 Ti 1- x Hf x NiSn 1- y Sb y 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 Ti 1- x Hf x NiSn 1- y Sb y 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 Ti 0.5 Hf 0.5 NiSn 0.98 Sb 0.02 alloy. These results provide a promising avenue for improving the TE performance of state-of-the-art materials., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)