Charge Compensation Modulation of the Thermoelectric Properties in AgSbTe₂ via Mn Amphoteric Doping

In thermoelectric research, the introduction of a dopant can suppress lattice thermal conductivity (κ₁) through phonon scattering and optimize the power factor (PF) by changing the behavior of carriers, which are the key prerequisites for high thermoelectric performance. However, the electrical thermal conductivity (κ_e) can also increase with the increase of electrical conductivity (σ), which may override the optimization in PF and be detrimental to the improvement of final ZT. In this work, we highlight an amphoteric doping method by using Mn atoms to substitute both Ag and Sb atoms in AgSbTe₂. The Mn_Sb positive doping in p-type AgSbTe₂ can improve the σ through increasing the hole concentration while maintaining a relative high Seebeck coefficient (S), thus substantially improving the PF. On the other hand, the Mn_Ag negative doping can introduce electrons into the matrix, which will recombine with the major hole carriers and lead to a decrease of σ to suppress exorbitant κ_e induced by the Mn_Sb doping. The combination of the both functions by Mn amphoteric doping can further improve the thermoelectric property through charge compensation modulation. By virtue of amphoteric doping, though σ is decreased, PF is further optimized because of increased S, while the total thermal conductivity (κ_total) is further decreased due to suppressed κ_e and additional phonon scattering, which are beneficial for the improvement of the final ZT value. As a result, 5 mol % Mn_Ag-Mn_Sb amphoteric doping AgSbTe₂ sample achieves a maximum ZT value of ∼0.74 at 550 K, which is higher than that of the pristine sample and other Mn monodoped counterparts. The present work suggests charge compensation modulation via amphoteric doping as an effective avenue to simultaneously achieve low thermal conductivity and high power factor for better thermoelectric performance.