High Thermoelectric Performance in Electron-Doped AgBi₃S₅ with Ultralow Thermal Conductivity

We report electron-doped AgBi₃S₅ as a new high-performance nontoxic thermoelectric material. This compound features exceptionally low lattice thermal conductivities of 0.5-0.3 W m⁻¹ K⁻¹ in the temperature range of 300-800 K, which is ascribed to its unusual vibrational properties: "double rattling" phonon modes associated with Ag and Bi atoms. Chlorine doping at anion sites acts as an efficient electron donor, significantly enhancing the electrical properties of AgBi₃S₅. In the carrier concentration range (5 × 10¹⁸-2 × 10¹⁹ cm⁻³) investigated in this study, the trends in Seebeck coefficient can be reasonably understood using a single parabolic band model with the electron effective mass of 0.22 me (me is the free electron mass). Samples of 0.33% Cl-doped AgBi₃S₅ prepared by spark plasma sintering show a thermoelectric figure of merit of ∼1.0 at 800 K.