Ultralow Lattice Thermal Conductivity in SnTe by Manipulating the Electron–Phonon Coupling

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SnTe has been regarded as an environment-friendly alternative of PbTe thermoelectrics, although its performance is limited by its high thermal conductivity, partly owing to its high carrier concentration. In SnTe + x AgSbSe 2, we observe a significant decrease of the total thermal conductivity from 3.37 to 1.27 W m –1 K –1 at 850 K, even though the hole concentration is at a high level of 10 21 cm –3 . With the increase of the AgSbSe 2 fraction, both the electrical and thermal conductivities decrease to their minima at x = 20%, and then they start to increase simultaneously, indicating strong electron–phonon coupling. By applying the first-principles calculations, it is unraveled that the minimum of thermal conductivity is due to the nonmonotonic dependence of electron–phonon coupling on the lattice constant. At x = 20%, a ZT value of 0.95 at 850 K is achieved, accompanied by an ultralow lattice thermal conductivity. This study reveals that tuning the electron–phonon coupling could be an efficient way to improve the thermoelectric performance, if it is constrained within the process of intravalley scattering.