Structural Characterization and Thermoelectric Properties of Br-Doped AgSn[Sb_0.8Bi_0.2]Te₂₊ Systems

Herein, we report the synthesis, structural and microstructural characterization, and thermoelectric properties of AgSn[Sb_0.8Bi_0.2]Te₂₊ 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[Sb_0.8Bi_0.2]Te₂₊ ranges from +40 to 57 μV·K^-1. Br-doped samples with m = 2 show S values of +74 μV·K^-1 at RT, and the Seebeck coefficient increases almost linearly with increasing temperature. The total thermal conductivity (κ_tot) monotonically increases with increasing temperature (10-300 K). The κ_tot values of undoped AgSn[Sb_0.8Bi_0.2]Te₂₊ are ~1.8 W m^-1 K^-1 (m = 4) and ~1.0 W m^-1 K^-1 (m = 2) at 300 K. The electrical conductivity (σ) 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 m = 4.