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 (κ 1 ) 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 AgSbTe 2 . The Mn Sb positive doping in p-type AgSbTe 2 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 AgSbTe 2 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.

High-Performance Thermoelectric Energy Conversion: A Tale of Atomic Ordering in AgSbTe2

“…Left arrow indicates increasing disorder. Comparison of thermoelectric figure of merit, zT, of 6 mol % Cd-doped AgSbTe 2 [3] with other (b) AgSbTe 2 -based thermoelectrics ,,,− and (c) metal chalcogenide-based state-of-the-art thermoelectric materials. ,,− (d) Comparison of device figure of merit, ZT dev , of 6 mol % Cd-doped AgSbTe 2 [3] with state-of-the-art thermoelectric materials. ,,,,,− Panels a, c, and d are adapted with permission from ref . Copyright 2021 The American Association for the Advancement of Science.…”

“…Li et al have investigated the effect of Mn substitution in AgSbTe 2, but the approach is different from other groups because they have chosen an amphoteric doping approach . They have replaced both Ag and Sb atoms with Mn atoms in AgSbTe 2 and studied the effect on thermoelectric properties.…”

“…However, greater than 5 mol % of Mn alloying in Sb site increases the total thermal conductivity by enhancing electronic thermal conductivity (κ e ). On the other hand, the replacement of Ag by Mn introduces excess electrons in the system (negative Mn Ag dopant), which recombines with the holes (the dominant charge carriers) and reduces the electrical conductivity . Mn Ag –Mn Sb amphoteric doped sample has lower electrical conductivity because of reduced hole concentration due to charge compensation.…”

Defect Compensation Weakening Induced Mobility Enhancement in Thermoelectric BiTeI by Iodine Deficiency

“…For example, the “ // ” direction κ of pristine BiTeI (S1) is ∼0.63 Wm −1 K −1 at 300 K and decreases to ∼0.43 Wm −1 K −1 at 545 K. Meanwhile, like the electrical conductivity, the thermal conductivity also demonstrates strong anisotropy between two measured directions, during which the “ // ” direction κ is much lower that of “ ⊥ ” direction since the lamellar stacked microstructure along this direction will strongly hinder the propagation of phonons. According to the Wiedemann−Franz relation, κ e is equal to LσT, [49] where L is the Lorenz number obtained by fitting the respective Seebeck coefficient values [50,51] . Based on the calculated L (shown in Figure S3a and S3b), we can obtain the electronic and lattice part of thermal conductivity.…”

“…According to the WiedemannÀ Franz relation, k e is equal to LσT, [49] where L is the Lorenz number obtained by fitting the respective Seebeck coefficient values. [50,51] Based on the calculated L (shown in Figure S3a and S3b), we can obtain the electronic and lattice part of thermal conductivity. As shown in Figure S3c and S3d, k l is very similar to k since k e contributes very small proportion to k. Upon introduction of I deficiency, k e increases due to the increase of σ.…”