ICT2014 Abstracts

Obtaining high performance thermoelectric (TE) materials is the central theme in the direct thermal-to-electric energy conversion. In this talk we introduce atomic scale point defect engineering as a new strategy to simultaneously optimize the electrical properties and lattice thermal conductivity of TE materials. Three typical TE materials are selected as paradigms to demonstrate the applicability of this new approach, such Bi₂Te₃ based alloys, Mg₂(Si,Sn) solid solutions and ZrNiSn based half-Heusler alloys.

Intrinsic point defects play an important role in enhancing TE properties. In (Bi,Sb)₂(Te,Se)₃ solid solutions, we engineer antisite defects and donor-like effect by tuning formation energy of point defects and hot deformation. As a result, a record value of the figure of merit ZT ~ 1.2 at 445 K was obtained for n-type polycrystalline Bi₂Te_2.3Se_0.7 alloys, and a high ZT of ~ 1.3 at 380 K for p-type polycrystalline Bi_0.3Sb_1.7Te₃ alloys. Also we enahnce the TE properties of Mg₂(Si,Sn) via synergistically implementing Sb dopants, Mg vacancies, and Mg interstitials in Mg₂Si_0.4Sn_0.6-xSb_x. Sb doping facilitates the formation of Mg vacancies at high doping ratios (x > 0.1). A state-of-the-art figure of merit ZT> 1.1 was attained at 750 K. Point defects change the band structure of ZrNiSn based half-Heusler alloys. Although normally considered an ordered compound, the ZrNiSn displays many transport characteristics of a disordered alloy. We found that, similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits a charge transport dominated by alloy scattering. The unexpected transport phenomenon can be explained by the atomic disorder in this system. The influence of the disordering and defects in crystal structure on the electron transport process has been quantitatively analyzed. These results demonstrate the promise of point defect engineering as a new strategy in optimizing TE properties.