Vacancy Suppression and Resonant Level Rendering Extraordinary Power Factor in Sn_0.99In_0.01Te/Tourmaline Composite

SnTe, as a potential medium-temperature thermoelectric material, reaches a maximum power factor (PF) usually above 750 K, which is not conducive to continuous high-power output in practical applications. In this study, PF is maintained at high values between 18.5 and 25 µW cm^-1 K^-2 for Sn_0.99In_0.01Te-x wt% tourmaline samples within the temperature range of 323 to 873 K, driving the highest PF_eng of 1.2 W m^-1 K^-1 and PF_ave of 22.5 µW cm^-1 K^-2, over 2.5 times that of pristine SnTe. Such an extraordinary PF is attributed to the synergy of resonant levels and Sn vacancy suppression. Specifically, the Seebeck coefficient increases dramatically, reaching 88 µV K^-1 at room temperature. Meanwhile, by Sn vacancy suppression, carrier concentration, and mobility are optimized to ≈10¹⁹ cm^-3 and 740 cm² V^-1 s^-1, respectively. With the tourmaline compositing, Sn vacancies are further suppressed and the thermal conductivity simultaneously decreases, with the minimum lattice thermal conductivity of 0.9 W m^-1 K^-1. Finally, the zT value ≈0.8 is obtained in the Sn_0.99In_0.01Te sample. The peak of the power output density reaches 0.89 W cm^-2 at a temperature difference of 600 K. Such SnTe alloys with high and "temperature-independent" PF will offer an option for realizing high output power in thermoelectric devices.