Achieving a High Thermoelectric Performance of Tetrahedrites by Adjusting the Electronic Density of States and Enhancing Phonon Scattering

Abstract

Recently, many researchers have focused on tetrahedrite-based compounds due to their intrinsic low thermal conductivity; however, their thermoelectric performance is limited by the lower power factor. In this case, using Ge doping on Sb sites, the power factor is obviously enhanced due to an increment in carrier concentration and density of states; simultaneously, the thermal conductivity is substantially suppressed by atomic defects. Also, ZnO nanoparticles are introduced in the Ge-doped compounds to further weaken the thermal conductivity. As a result, the maximum dimensionless figure of merit (ZT) of ∼1.0 is obtained for the Cu12Sb3.96Ge0.04S13-0.5 wt % ZnO sample at 750 K, which is ∼72% larger than that of Cu12Sb4S13. All results indicate that suitable elemental doping combined with the incorporation of the nanophase is a very promising approach for Cu12Sb4S13 tetrahedrites to improve the thermoelectric performance.

Thermoelectric Cu12Sb4S13‐Based Synthetic Minerals with a Sublimation‐Derived Porous Network

“…The Cu 3 SbS 4 second-phase impurity was eliminated after annealing. As demonstrated by the X-ray diffraction (XRD) pattern (Figure 1d), all of the diffraction peaks of unannealed samples and annealed samples were well-indexed to tetrahedrite crystalline phase (PDF#42-0561) except for a small amount of impurity phase Cu 3 SbS 4 (PDF#35-0581) found in unannealed samples, which is consistent with previously reported works; [22,35,36,46] however, no recognizable diffraction peak of the Cu 3 SbS 4 phase was detected in the annealed samples, indicating that the annealing process facilitated the transformation of Cu 3 SbS 4 phase into pure Cu 12 Sb 4 S 13 phase; thus, the XRD peaks of AD 0 vol% showed a clear shift. The carrier mobility of the annealed samples might be improved due to compensation for intrinsic vacancies after this process.…”

“…b) Comparison of zT ave (the cold‐ and hot‐side temperatures of 323 and 723 K, respectively) and maximum zT max of tetrahedrites with different compositions. [ 28,32,35,36,58 ] c) Schematic of a segmented single‐leg; the low‐ and high‐temperature materials are Cu 0.001 Bi 0.3 Sb 1.699 Te 3 and porous AP 0.7 vol%, respectively. d) The predicted conversion efficiency (η) in the temperature range of 300–723 K based on the zT values.…”

“…According to the Debye-Callaway and EMT model, the reduction of κ L may be ascribed to the synergistic effect between the absence of a thermal conduction medium and phonon scattering from pore interfaces, dislocations, and precipitates. The enhanced weighted mobility was ascribed to the solution of impurity Cu 3 SbS 4 phase, which compensated for intrinsic vacancies and because Cu [28,32,35,36,58] value of 1.15 at 723 K was achieved in the porous AP 0.7 vol% sample, which increased by 47.8% compared with the dense tetrahedrite. Importantly, the average zT of 0.69 calculated at a temperature difference of 400 K for the AP 0.7 vol% sample was also competitive among reported tetrahedrite compounds.…”

“…[32][33][34] Nevertheless, the chemical composition of natural tetrahedrite (Cu 12−x (Zn,Fe) x (Sb,As) 4 S 13 , 0 ≤ x ≤ 2) is relatively fixed, making it extremely difficult to adjust into an optimum range for thermoelectricity; [34] therefore, many researchers have investigated the thermoelectric properties of synthetic tetrahedrites prepared by melting reactions or mechanical alloying, [21][22][23][24]35] but some serious problems remain in synthetic tetrahedrites: i) secondary phase Cu 3 SbS 4 should be minimized because it acts as an impurity that can lead to the formation of additional scattering centers for charge carriers. [36] Annealing treatment may be an effective strategy to achieve this goal; ii) the bulk tetrahedrites synthesized by mechanical alloying have poor mechanical properties and gradually break into pieces in the air, which may be suppressed by the use of micropores to absorb internal expansion. [35] Additionally, porous interfaces, which are possibly more stable than nanoprecipitates at high temperatures, may facilitate phonon scattering and decrease the lattice thermal conductivity of tetrahedrite.…”

Thermoelectric Cu–S-Based Materials Synthesized via a Scalable Mechanochemical Process

“…To enhance its thermoelectric performance, doping of mechanochemically synthesized Cu 12 Sb 4 S 13 is a promissing possibility as can be seen from papers published recently, see e.g. [81][82][83][84][85] .…”