Strong lattice anharmonicity securing intrinsically low lattice thermal conductivity and high performance thermoelectric SnSb2Te4 via Se alloying

Seeking a material with intrinsically low lattice thermal conductivity is crucial for screening high-performance thermoelectric (TE) materials. Here, the TE properties of SnSb2(Te1-xSex)4 (0 <= x <= 0.25) samples are systematically investigated for the first time. An intrinsically ultralow lattice thermal conductivity (similar to 0.56 W m(-1) K-1 at 320 K and similar to 0.46 W m(-1) K-1 at 720 K) has been observed in SnSb2Te4, which can be ascribed to the weak chemical bonding as well as the bond anharmonicity verified by first-principles calculations. Furthermore, alloying with Se enables the remarkable increase in the Seebeck coefficients, resulting from the optimized carrier concentrations due to the enlarged formation energy of intrinsic SnSb-type antisite defects along with the simultaneous enhancement of density-of-states effective mass from the convergence of multiple carrier pockets. As a result, a peak zT value of 0.5 at 720 K and a significant improvement in average zT (similar to 200%) in SnSb2(Te0.75Se0.25)(4) are achieved. This work not only demonstrates the potential of SnSb2Te4-based compounds for practical TE applications, but also provides an insightful guidance to improve TE performance by defect and electronic band engineering.