Thermoelectric transport properties in Bi-doped SnTe–SnSe alloys

Abstract

Numerous endeavors have been made to advance thermoelectric SnTe for potential applications. Effective strategies focus on the manipulation of transport properties, including valence band convergence, resonate state, and defect engineering. It has been demonstrated that alloying trivalent Bi or chalcogenide SnSe alone in SnTe can trigger an inherent enhancement of thermoelectric performance. However, what the critical role in the transport valence band co-doping Bi and Se in SnTe plays is still unclear. Particularly, fully evaluating the effect of band convergence on the carrier concentration-dependent weighted mobility, which dominates the electronic performance, is primary and essential for designing excellent thermoelectric materials. Here, we report that Bi doping in SnTe–SnSe alloys can derive a distinct decrease in the energy offset between the two valence bands, thus improving the density-of-state effective mass by only slightly deteriorating the mobility. The well-established theoretical model reveals that the Bi-doping-induced band convergence and the optimized carrier concentration actually enhance the weighted mobility, contributing to the improvement of electronic performance. Moreover, the Debye–Callaway model demonstrates the origin of the reduced lattice thermal conductivity. The present results confirm the potential of transport engineering in promoting thermoelectric performance.

Remarkable Improvement of Thermoelectric Figure-of-Merit in SnTe through In Situ-Created Te Nanoinclusions

“…Various strategies have been employed to improve the Seebeck coefficient of SnTe including electronic band engineering, optimization of the carrier concentration, and introduction of the resonance states in the valence band. 4,5 Additionally, by employing cumulative approaches such as improving the power factor through band convergence, 6,7 energy filtering, and lowering of lattice thermal conductivity by introducing endotaxial precipitation resulted in huge improvement in ZT of SnTe. 8−14 The study by Brebrick and Strauss shows that the Seebeck coefficient of SnTe shows a very anomalous dependence on the carrier concentration because of the existence of two valence bands.…”

“…Such an unfavorable trend of thermoelectric parameters results in very low figure-of-merit ( ZT ) ≪ 1 for pristine SnTe. Various strategies have been employed to improve the Seebeck coefficient of SnTe including electronic band engineering, optimization of the carrier concentration, and introduction of the resonance states in the valence band. , Additionally, by employing cumulative approaches such as improving the power factor through band convergence, , energy filtering, and lowering of lattice thermal conductivity by introducing endotaxial precipitation resulted in huge improvement in ZT of SnTe. − The study by Brebrick and Strauss shows that the Seebeck coefficient of SnTe shows a very anomalous dependence on the carrier concentration because of the existence of two valence bands. With an increasing carrier concentration, the Fermi level crosses three regions: the I-light hole valence band (L band), II-light hole (L) and partial heavy hole (∑) bands, and III-L band and ∑ bands.…”

Manipulating the Solubility of SnSe in SnTe by Br Doping for Improving the Thermoelectric Performance

“…The Debye–Callaway model with strain field and quality variations is used to better explain the contribution of various phonon scattering sources to the lattice thermal conductivity following the doping of Se and Br, as illustrated in Figure e. , The lattice thermal conductivity is calculated as , where κ l pure is the lattice thermal conductivity of Sn 1.03 Te, κ l calc is the calculated lattice thermal conductivity of defect materials, and u is the disorder scaling parameter (the detailed information is provided in the Supporting Information). The experimental lattice thermal conductivity is basically consistent with the prediction, which reveals that the Se substitution defect dominates the phonon scattering process.…”

Tuning valley degeneracy with band inversion

“…To induce multiple carrier pockets in SnTe, we suggest alloying the compound with either SnSe or SnS. While SnSe and SnS natively crystallize in the layered orthorhombic Pnma structure, 36,37 single-phase alloys between SnTe and SnSe in the rock-salt structure have been reported, 38,39 indicating that the rock-salt crystal structure can be maintained up to a solubility limit. Given that the s-and p-orbital energies of Se and S are lower than those of Te, 40 we would expect the Sns/anion-p interaction to strengthen since the atomic orbital energies will be closer, resulting in an increase in the energy of the L + 6 state.…”