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A3: High temperature materials

 The intrinsic disorder related alloy scattering in unsubstituted ZrNiSn half-Heusler thermoelectric materials

Hanhui Xie,1 Heng Wang,2 Chenguang Fu,1 Yintu Liu,1 G. Jeffrey Snyder,*2 Xinbing Zhao1 and Tiejun Zhu*1
1 State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, China2 Materials Science, California Institute of Technology,  USA

The intrinsic structural disorder dramatically affects the thermal and electronic transport in semiconductors. Although normally considered an ordered compound, the half-Heusler ZrNiSn displays many transport characteristics of a disordered alloy. Similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits charge transport dominated by alloy scattering, as demonstrated in this work. The unexpected importance of disorder scattering, even in ZrNiSn which is normally considered fully ordered, can be explained by the disorder on the Ni/vacancy site recently found by XRD in this half-Heusler system. 

The influence of the disordering and defects in crystal structure on the electron transport process has been quantitatively analyzed in ZrNiSn1-xSbx with carrier concentration nH ranging from 5.0´1019 to 2.3´1021 cm-3 by changing Sb dopant content. The optimized carrier concentration nH » 3 - 4´1020cm-2 results in ZT » 0.8 at 875K. This work suggests that MNiSn (M = Hf, Zr, Ti) and perhaps most other half-Heusler thermoelectric materials should be considered highly disordered especially when trying to understand the electronic and phonon structure.