Thermoelectric transport evolution and effective-mass enhancement in solid solution alloys between GeBi2Te4 and SnBi2Te4

초록

GeBi2Te4 and SnBi2Te4 are layered tellurides with the same natural-superlattice structure and both are of interest as near-room-temperature thermoelectric materials. In this study, the electrical and thermal transport properties of Ge1-xSnxBi2Te4 solid-solution alloys (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were systematically investigated. A complete single-phase solid solution was formed over the entire composition range. With increasing Sn content, the Hall carrier concentration nH increased from 3.20 × 1019–1.40 × 1020 cm−3 at x = 0.6 and then decreased at higher Sn contents, while the density-of-states effective mass md* also increased from 0.79 to 1.68 m0 at x = 0.6 before decreasing to 1.21 m0 at x = 1. The power factor gradually increased with increasing Sn content, i.e. from 0.72 to 0.95 mWm−1K−2 at 300 K. This continuous and moderate enhancement in power factor is driven by the synergistic interplay between the md* enhancement that mitigates the degradation of the Seebeck coefficient at lower Sn contents (x ≤ 0.6) and the subsequent mobility recovery that boosts electrical conductivity in the Sn-rich regime (x > 0.6). In contrast to the moderate electronic transport changes, the bipolar-corrected lattice thermal conductivity κlatt was lowest for the x = 0.4 composition over the entire measured temperature range, reaching 0.48 W m−1 K−1 at 300 K. Consequently, the gradual increase of the power factor, combined with the suppressed κlatt in the intermediate solid-solution-alloy compositions, produced the most favorable thermoelectric performance near x = 0.4 – 0.6, with the highest thermoelectric figure of merit zT of 0.37 obtained at 350 K for x = 0.4, ~60% higher than that of pristine GeBi2Te4 (zT = 0.23 at 350 K). These results show that Ge/Sn solid-solution alloying in Ge1-xSnxBi2Te4 provides only moderate overall changes in electronic transport, but effectively suppresses lattice thermal conduction and thereby improves the thermoelectric performance of this natural-superlattice system. © 2026 Elsevier B.V.

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