Abstract: As a typical (IV-VI)_x(V₂VI₃)_y compound, the tetradymite-like layered SnSb₂Te₄-based compounds have attracted increasing attention in the thermoelectric community owing to the intrinsically low lattice thermal conductivity. Nevertheless, the effect of cations disorder on the inherent physical characteristics remains puzzling, and its inferior Seebeck coefficient is the bottleneck to achieving high thermoelectric performance. In this work, the thermoelectric properties of polycrystalline In_xSn_1-xSb₂(Te_1-ySe_y)₄ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.15) samples are comprehensively investigated. In conjunction with the calculated band structure and experimental results, the Seebeck coefficient and power factor are markedly improved after the introduction of indium and selenium, which originates from the combined effects of the emergent resonant states and converged valence bands along with optimal carrier concentration. Additionally, compared with the ordered lattice structure, the disordered cations occupancy in SnSb₂Te₄ further strengthens lattice anharmonicity and reduces phonon group velocity verified by first-principles calculations, securing intrinsically low lattice thermal conductivity. Finally, a record zT value of ∼0.6 at 670 K and an average zT of ∼0.4 between 320 and 720 K are obtained in the In_0.1Sn_0.9Sb₂Te_3.4Se_0.6 sample, being one of the highest zT values among SnSb₂Te₄-based materials. This work not only demonstrates that SnSb₂Te₄-based compounds are promising thermoelectric candidates, but also provides guidance for the promotion of thermoelectric performance in a broad temperature range.

Key words: Thermoelectric, SnSb₂Te₄, Lattice anharmonicity, Resonant level, Band Convergence