4 years ago

Three-Stage Inter-Orthorhombic Evolution and High Thermoelectric Performance in Ag-Doped Nanolaminar SnSe Polycrystals

Three-Stage Inter-Orthorhombic Evolution and High Thermoelectric Performance in Ag-Doped Nanolaminar SnSe Polycrystals
Shixue Dou, Peng Qin, Lijuan Zhang, Zhen Li, Zhenhua Ge, Qiao Sun, Jianli Wang, Zhenxiang Cheng
The ultrahigh thermoelectric performance of SnSe-based single crystals has attracted considerable interest in their polycrystalline counterparts. However, the temperature-dependent structural transition in SnSe-based thermoelectric materials and its relationship with their thermoelectric performance are not fully investigated and understood. In this work, nanolaminar SnSe polycrystals are prepared and characterized in situ using neutron and synchrotron powder diffraction measurements at various temperatures. Rietveld refinement results indicate that there is a complete inter-orthorhombic evolution from Pnma to Cmcm by a series of layer slips and stretches along the a- and b-axes over a 200 K temperature range. This phase transition leads to drastic enhancement of the carrier concentration and phonon scattering above 600 K. Moreover, the unique nanolaminar structure effectively enhances the carrier mobility of SnSe. Their grain and layer boundaries further improve the phonon scattering. These favorable factors result in a high ZT of 1.0 at 773 K for pristine SnSe polycrystals. The thermoelectric performances of polycrystalline SnSe are further improved by p-type and n-type dopants (i.e., doped with Ag and SnCl2, respectively), and new records of ZT are achieved in Ag0.015Sn0.985Se (ZT of 1.3 at 773 K) and SnSe0.985Cl0.015 (ZT of 1.1 at 773 K) polycrystals. The complete inter-orthorhombic evolution and the nanolaminar structure significantly influencing the thermoelectric performance of SnSe polycrystals via promoting carrier mobility and simultaneously strengthening the phonon scattering is revealed for the first time. A new record of ZT = 1.3 is obtained at 773 K for Ag-doped nanolaminar SnSe polycrystals.

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

DOI: 10.1002/aenm.201700573

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