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 (kappa(1)) (PF) by changing the behavior of carriers, which are the key through phonon scattering and optimize the power factor prerequisites for high thermoelectric performance. However, the electrical thermal conductivity (kappa(e)) can also increase with the increase of electrical conductivity (sigma), which may override the optimization in PF and be detrimental to the improve- ment 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 sigma 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 sigma decrease of a to suppress exorbitant kappa(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 sigma is decreased, PF is further optimized because of increased S, while the total thermal conductivity (kappa(total)) is further decreased due to suppressed ice 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 similar to 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.