Synergistic Enhancement of Thermoelectric Performance in SnBi₄Se₇ via Dual Defect Engineering and Band Structure Modulation

The ternary layered compound SnBi4Se7, with its unique layered structure and complex intrinsic defects, offers a promising material platform for thermoelectric research. However, performance enhancement is limited by detrimentally high vacancy defects and strong electron–phonon coupling. This study develops an Sn-self-flux-assisted synthesis strategy combining rapid melt-quenching and postannealing. This approach enables successful syntheses of a series of solid solutions of Sn1.2+0.05xBi4(Se7–xTex) allowing synergistic Sn (Bi-site) and Te (Se-site) substitution. Interestingly, excess Sn content plays a dual role in enhancing thermoelectric performance: it promotes the formation of antisite defects (SnBi), enhancing the Seebeck coefficient from −49.85 to −63.31 μV K–1, and it simultaneously compensates for cation vacancies, optimizing lattice plainification and reducing carrier scattering. Furthermore, strategic Te doping at Se sites effectively suppresses electron–phonon scattering, resulting in an electrical conductivity increase from 710.71 to 1452.37 S cm–1. Through these synergistic effects, the optimized Sn1.4Bi4(Se3Te4) sample achieves a peak thermoelectric figure of merit (ZT) of approximately 0.48 at 623 K─representing a 2.7-fold enhancement compared to the undoped material (ZT = 0.18). These results demonstrate successful decoupling of electrical and thermal transport through defect engineering, offering a new strategy for the development of high-performance thermoelectric materials.