| Summary: | Herein, we report the synthesis, structural and microstructural characterization, and thermoelectric properties of AgSn<i><sub>m</sub></i>[Sb<sub>0.8</sub>Bi<sub>0.2</sub>]Te<sub>2+<i>m</i></sub> and Br-doped telluride systems. These compounds were prepared by solid-state reaction at high temperature. Powder X-ray diffraction data reveal that these samples exhibit crystal structures related to the NaCl-type lattice. The microstructures and morphologies are investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). Positive values of the Seebeck coefficient (S) indicate that the transport properties are dominated by holes. The S of undoped AgSn<i><sub>m</sub></i>[Sb<sub>0.8</sub>Bi<sub>0.2</sub>]Te<sub>2+<i>m</i></sub> ranges from +40 to 57 μV·K<sup>−1</sup>. Br-doped samples with <i>m</i> = 2 show S values of +74 μV·K<sup>−1</sup> at RT, and the Seebeck coefficient increases almost linearly with increasing temperature. The total thermal conductivity (<i>κ</i><sub>tot</sub>) monotonically increases with increasing temperature (10–300 K). The <i>κ</i><sub>tot</sub> values of undoped AgSn<i><sub>m</sub></i>[Sb<sub>0.8</sub>Bi<sub>0.2</sub>]Te<sub>2+<i>m</i></sub> are ~1.8 W m<sup>−1 </sup>K<sup>−1</sup> (<i>m</i> = 4) and ~1.0 W m<sup>−1</sup> K<sup>−1</sup> (<i>m</i> = 2) at 300 K. The electrical conductivity (<i>σ</i>) decreases almost linearly with increasing temperature, indicating metal-like behavior. The ZT value increases as a function of temperature. A maximum ZT value of ~0.07 is achieved at room temperature for the Br-doped phase with <i>m</i> = 4.
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