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

Abstract

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 (κe) 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 MnSb 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 MnAg 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 κe induced by the MnSb 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 (κtotal) is further decreased due to suppressed κe and additional phonon scattering, which are beneficial for the improvement of the final ZT value. As a result, 5 mol % MnAg-MnSb 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.