Wenhao Fan,Shaoping Chen,Bo Zeng,Qiang Zhang,Qingsen Meng,Wenxian Wang,Zuhair A. Munir
Solid solutions of Mg2Si0.6Sn0.4–xBix with 0 ≤ x ≤ 0.03 were prepared by a one-step synthesis and consolidation method, using MgH2 as a starting material. The thermoelectric properties of these samples were evaluated over the temperature range 300–775 K. Figure of merit, zT, values were determined over this range for all compositions and found to increase with temperature reaching a value of 1.36 at 775 K for samples with x = 0.02. Examination of the components of the total thermal conductivity showed that the bipolar thermal conductivity is suppressed by an increase in the band gap, resulting from solid solution formation, and by low minority carrier mobility. The suppression of the bipolar thermal conductivity is believed to be the consequence of charged grain boundaries.
Here, we report a peak ZT of 1.85 at 873 K for sulfur and Pb codoped polycrystalline SnSe by boosting electrical transport properties while suppressing the lattice thermal conductivity. Compared with single sulfur doped samples, the carrier concentration is improved 1 order of magnitude by Pb incorporation, thereby contributing to improved electrical conductivity and power factor. Moreover, the introduction of sulfur and Pb suppresses the bipolar thermal conductivity by enlarging the band gap. The lattice thermal conductivity significantly decreased as low as 0.13 W m–1 K–1 at 873 K due to the synergic approach involving suppressing bipolar thermal conductivity, large mass fluctuation induced by sulfur incorporation, and nanoprecipitates. We demonstrate that the combination of tailoring band structure, suppressing bipolar thermal conductivity, and introducing large mass fluctuation contributes to the high thermoelectric performance in SnSe. The high performance was achieved through boosting electrical transport properties while maintaining ultralow thermal conductivity. Our findings offer a new strategy for achieving high performance thermoelectric materials.
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