Preparation and thermoelectric transport properties of BiSe and Sb-doped BiSe single crystals

Abstract

<p indent="0mm">Exploring high thermoelectric performance in single crystal materials with intrinsic low lattice thermal conductivity has become an important field for thermoelectric research. BiSe, as a member of (Bi₂Se₃)_{<italic>m</italic>}(Bi₂)_{<italic>n</italic>} series superlattice compounds, has a very low intrinsic thermal conductivity due to the existence of Bi₂ bilayer in its layered crystal structure. Moreover, it is a new and promising thermoelectric material due to the non-toxic and environmentally friendly chemical compositions. The special layered structure of BiSe makes its thermoelectric transport properties significantly anisotropic. In this paper, BiSe single crystal was prepared by Bridgman method, and its anisotropic thermoelectric transport properties were investigated. The results show that the sample has higher conductivity and thermal conductivity in the in-plane direction, while the lower Seebeck coefficient makes the thermoelectric figure of merit <italic>ZT</italic> value in this direction lower than that in the interlamellar direction. The maximum values of <italic>ZT</italic> in the two directions are 0.11 <sc>(573 K)</sc> and 0.16 <sc>(623 K),</sc> respectively. Compared with polycrystalline BiSe, the single crystal sample exhibits lower electric transport performance, which can be attributed to the difference of scattering coefficient. The carrier concentration of BiSe single crystal is regulated by Sb doping, which effectively improves the Seebeck coefficient of the samples and optimizes the electrical transport performance. In the meanwhile, Sb doping can produce lattice distortion and reduce the lattice thermal conductivity. The final <italic>ZT</italic> value of Bi_0.8Sb_0.2Se single crystal increases by about 1 fold, reaching 0.34 <sc>(573 K)</sc> in the interlamellar direction and 0.20 <sc>(573 K)</sc> in the in-plane direction.