Multifunctional GeMnTe₂ Synergistically Optimizes Thermoelectric Properties of SnTe-In₂Te₃ Alloys

SnTe-In₂Te₃ alloys ensure excellent electrical properties in the whole temperature region due to the resonant level. Nevertheless, temperature-sensitive resonance states and single phonon scattering restrict further improvement of thermoelectric performance. Consequently, it is anticipated that additional electrically independent scattering sources should be introduced to impede phonon transport. Here, the SnTe-In₂Te₃-GeMnTe₂ alloy is prepared by further solidifying cubic GeMnTe₂, which demonstrates multiple modulation effects. The highly redissolved Mn²⁺ promotes the valence band convergence, enhances the Seebeck coefficient at higher temperature, and balances the possible weakened resonance level effect at higher carrier concentrations, and a high average power factor (1.94 mW m^-1 K^-2) is realized over the entire temperature range. Additionally, compensatory vacancies, substitutions, and Ge/Mn precipitates are easily constructed with GeMnTe₂ alloying, leading to a further reduction in lattice thermal conductivity, which reaches κ_l ∼ 0.6 W m^-1 K^-1 at 850 K. Ultimately, a high peak zT of ∼1.25 (850 K) and a zT_ave of 0.72 (300-850 K) are realized in (SnTe)_2.91(In₂Te₃)_0.03(Ge_0.5Mn_0.5Te)_1.2, and the maximum thermoelectric conversion efficiency of ∼2.8% (ΔT ∼ 450 K) is achieved. The present results indicate multiple effects of GeMnTe₂ in enhancing the thermoelectric performance of SnTe-In₂Te₃ alloys.