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Thermoelectric (TE) materials-based devices are valuable for translating heat into electricity, but the cost is largely driven by the use of purified metals required for efficient TE performance. This study focuses on tetrahedrite materials, which are cost-effective due to their abundance in copper ore mining waste and status as one of the most widespread sulfosalts on Earth. The research investigates the effects of co-doping and iso-valent doping on the TE properties of p-type tetrahedrite samples, specifically Cu 10 Mn 2 Sb 4 S 11 Se 2 (Sample A) and Cu 10 MnZnSb₄S 11 Se 2 (Sample B). These samples were synthesized using hot pressing at 773 K and compared with the existing pristine compound (Cu 10 Mn 2 Sb 4 S 13). Doping with Mn and Zn (1:1) at the Cu site was found to optimize carrier concentration and enhance phonon scattering, leading to an improved power factor. Additionally, the Se substitution at the S site also introduced band degeneracy, further increasing the power factor. Further, sample B exhibited the highest Seebeck coefficient (∼300 μV/K) at 650 K, in comparison to Sample A (∼225 μV/K) and the pristine compound (∼250 μV/K). On the other hand, Sample A demonstrated significantly higher electrical conductivity (∼0.76 × 10⁴ S/m at 650 K), ∿ three times greater than that of the other prepared samples. Notably, the power factor of Sample A (∼0.389 mW/mK2 at 650 K) was more than twice that of Sample B (∼0.141 mW/mK2) and the pristine compound (∼0.160 mW/mK2). These findings suggest that dual-site substitution at the Cu and S positions presents a promising strategy to augment the TE performance of tetrahedrite compounds. [Display omitted] • The p-type tetrahedrites compounds sample-A (Cu 10 Mn 2 Sb 4 S 11 Se 2) and sample-B (Cu 10 MnZnSb4S 11 Se 2) were successfully synthesized employing a hot press at 773K. • Doping at the Cu site with a 1:1 ratio of Mn and Zn optimizes carrier concentration and enhances phonon scattering, resulting in an improved power factor. • Se substitution at the S site introduced band degeneracy, further increasing the power factor. • Notably, the power factor of Sample A (∼0.39 mW/mK2 at 650 K) was more than twice that of Sample B (∼0.14 mW/mK2). [ABSTRACT FROM AUTHOR]

Tetrahedrites, a class of naturally‐occurring sulfosalts, recently emerged as interesting thermoelectric materials due to their semiconducting electronic properties combined with glass‐like thermal transport. Here, we demonstrate that the high thermoelectric performance of synthetic tetrahedrites can be maintained while being mixed with tetrahedrite minerals. The combination of ball‐milling and spark plasma sintering yields chemically‐homogeneous, dense polycrystalline samples with thermoelectric performance equivalent to those obtained in purely synthetic compounds with peak ZT values of ∼0.6 at 623 K. While ball‐milling significantly lowers the crystallite size, a complete solid solution between both types of tetrahedrites is only achieved through the sintering process. Not only do these findings confirm interesting prospects for the direct use of natural ores in the preparation of tetrahedrites, but they also further evidence the importance of the chemical compositions of the two initial tetrahedrites on the optimization of the thermoelectric properties of the final compound. [ABSTRACT FROM AUTHOR]

With global warming and rising energy demands, it is important now than ever to transit to renewable energy systems. Thermoelectric (TE) devices can present a feasible alternative to generate clean energy from waste heat. However, to become attractive for large-scale applications, such devices must be cheap, efficient, and based on ecofriendly materials. In this study, the potential of novel silicide-tetrahedrite modules for energy generation was examined. Computer simulations based on the finite element method (FEM) and implicit finite difference method (IFDM) were performed. The developed computational models were validated against data measured on a customized system working with commercial TE devices. The models were capable of predicting the TEGs' behavior with low deviations ( ≤ 10%). IFDM was used to study the power produced by the silicide-tetrahedrite TEGs for different Δ T between the sinks, whereas FEM was used to study the temperature distributions across the testing system in detail. To complement these results, the influence of the electrical and thermal contact resistances was evaluated. High thermal resistances were found to affect the devices Δ T up to ~15%, whereas high electrical contact resistances reduced the power output of the silicide-tetrahedrite TEGs by more than ~85%. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of dually substituted Cu12−xInxSb4S12.8Se0.2 tetrahedrites are studied in temperature range from 300 to 723 K. The results indicate that dual substitution of In for Cu and Se for S not only causes the enhancement of thermopower S but also gives rise to a significant decrease in lattice thermal conductivity κL. An ultralow κL ≈0.2 W m−1 K−1 is obtained at 723 K in Cu11.95In0.05Sb4S12.8Se0.2 sample due to the enhanced phonon scattering mainly by point defects. Consequently, a high figure of merit ZTmax ≈1.0 is achieved in Cu11.95In0.05Sb4S12.8Se0.2 sample, which is ≈56% larger than that of pristine Cu12Sb4S13, indicating that dual substitution is effective in boosting the thermoelectric properties of tetrahedrites. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) materials-based devices are useful in converting heat into electricity. The cost of thermoelectric materials is mainly incurred from the purified pure metals used to make the efficient TE device. In the current study, tetrahedrite materials are considered due to their low cost, as these materials are abundant in mining waste of copper ores and also the most extensive sulfosalt on earth. Hence, to add value addition to mine waste materials, the composite approach has been employed to integrate the natural tetrahedrite (mine waste/tailings product) materials with synthetically developed tetrahedrite materials in the lab for the current investigation. Further, the optimum quantity of mine waste addition is optimized by the systematic investigation of TE performance with varying the mine waste percentage addition to the synthetic tetrahedrite. The p-type synthetic Cu 10 FeZnSb 4 S 13 (Sample-A) tetrahedrite compound and 70 (Cu 10 FeZnSb 4 S 13) + 30 (natural/mine waste) (Sample-B) have been synthesized employing hot-press at 773 K along with the pristine (Cu 10 Fe 2 Sb 4 S 13) tetrahedrite compound. Moreover, the Seebeck coefficient is increased by 36 % (220 μV/K to 300 μV/K) for Sample-B, as compared to sample A and it is ∿ 2 times higher as compared to the pristine compound. The power factor is increased by ∿ 3 times that of the Sample-A (0.05 mW/mK2 to 0.15 mW/mK2). In addition, the thermal conductivity of Sample-B compound was further reduced by 30 % than Sample-A (0.98 W/mK to 0.69W/mK) and ∿ 44 % more than the pristine compound. Finally, the zT of Sample-B increased to almost 3 times than Sample-A (0.05–0.15). [Display omitted] • The p-type tetrahedrites compounds Sample-A (Cu 10 FeZnSb 4 S 13) and Sample-B [70 Cu 10 FeZnSb 4 S 13 + 30 (natural minerals/mine waste)] have been successfully synthesized employing hot press at 773 K. • Higher effective mass and energy filtering phenomena significantly enhanced the Seebeck coefficient of Sample-B by ∿36 % as compared to Sample-A. • The power factor of Sample-B has been increased by ∿ 3 times as that of Sample-A (0.05 mW/mK2 to 0.15 mW/mK2). • The zT of Sample-B tetrahedrites composite increased to ≈ 3 times of pristine Sample-A. [ABSTRACT FROM AUTHOR]

Tetrahedrites, due to their promising thermoelectric properties, are one of the materials being investigated for use in thermoelectric generators. One problem is the lack of n-type tetrahedrites, which would be beneficial for the design of tetrahedrite thermoelectric modules. Preliminary theoretical studies have shown that elements from groups I and II can be introduced into the structural voids of tetrahedrite, acting as donor dopants, and should enable n-type conductivity. Therefore, in this work, an attempt was made to obtain and study magnesium-doped tetrahedrites. A series of samples, MgxCu12Sb4S13, with different magnesium contents were obtained and their phase and chemical compositions were characterized. It was observed that the structural changes occurring upon doping indicate that Mg atoms are likely to be embedded in the structural voids. The experimental studies have been supported by electronic structure calculations indicating that the most likely location of Mg is in the structural voids at the 6b Wyckoff position. Seebeck coefficient and resistivity measurements showed that doping with Mg reduces the concentration of holes, which is consistent with the predicted donor character of the dopant. However, the introduction of magnesium in sufficient amounts to achieve n-type conductivity was not successful. [ABSTRACT FROM AUTHOR]

With global warming and rising energy demands, it is important now than ever to transit to renewable energy systems. Thermoelectric (TE) devices can present a feasible alternative to generate clean energy from waste heat. However, to become attractive for large-scale applications, such devices must be cheap, efficient, and based on ecofriendly materials. In this study, the potential of novel silicide-tetrahedrite modules for energy generation was examined. Computer simulations based on the finite element method (FEM) and implicit finite difference method (IFDM) were performed. The developed computational models were validated against data measured on a customized system working with commercial TE devices. The models were capable of predicting the TEGs’ behavior with low deviations (≤10%). IFDM was used to study the power produced by the silicide-tetrahedrite TEGs for different ΔT between the sinks, whereas FEM was used to study the temperature distributions across the testing system in detail. To complement these results, the influence of the electrical and thermal contact resistances was evaluated. High thermal resistances were found to affect the devices ΔT up to ~15%, whereas high electrical contact resistances reduced the power output of the silicide-tetrahedrite TEGs by more than ~85%.

Manganese-doped tetrahedrites, with Cu11Mn1Sb4S13 composition and synthesized by the solid-state method, were hot-pressed at temperatures ranging between 788 K and 848 K. The structure, microstructure, phase purity and thermoelectric properties of the materials were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and density studies. According to the XRD analysis, all the hot-pressed materials presented a main tetrahedrite phase. However, very small amounts of chalcostibite (CuSbS2) were detected by SEM–EDS. While keeping the pressure constant at 60 MPa, an increase in density with hot-pressing temperature was observed, reaching a maximum relative density of 97% for the samples hot-pressed at 848 K. Measurements of the electrical transport properties indicated higher thermal conductivity, electrical conductivity and Seebeck coefficient for the denser samples, with a greater power factor leading to an increase of > 10% in the figure of merit ( zT ) relative to the less dense materials. [ABSTRACT FROM AUTHOR]

Most of the energy produced is lost, mainly as waste heat. Thermoelectricity, which can directly convert heat into electricity, is seen with huge potential to recover part of such heat. However, to be widely used, it is necessary to be based on cheap, available, non-toxic, stable and easy-to-produce good thermoelectric materials. Here we present an overview of the potential of Cu–S based synthetic minerals for thermoelectric applications. In particular, we focus on tetrahedrites, which are world spread minerals with Cu10M2Sb4Si3 (M = Cu, Mn, Fe, Co, Ni, Zn) general formula that show high potential for thermoelectrics. An overview of their properties are presented, with emphasis on those relevant for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Optimization and analysis of novel thermoelectric module is proposed in this research paper. The simulation for four thermoelectric modules were performed in COMSOL Multiphysics 5.4 software and detailed analysis of these thermoelectric modules were carried out. The three thermoelectric modules showed the efficiency and power output above-average thermoelectric modules. It also indicated that lead telluride based thermoelectric modules could be used in isolated areas due to toxicity of lead whereas tetrahedrite based thermoelectric module could be used in non-isolated areas due to its non-toxic properties. The proposed thermoelectric modules can be utilized in applications such as industries, deep space explorations, automobiles, thermal power plants, renewable electricity generation, hybrid renewable systems, etc. in an economically viable manner. [ABSTRACT FROM AUTHOR]

Tetrahedrite-based thermoelectric materials have received much attention in recent years due to their good thermoelectric performance and earth-abundance. The parent compound Cu12Sb4S13 exhibits a high power factor and low lattice thermal conductivity. Further enhancement of the thermoelectric figure of merit ZT is expected in substituted compounds, primarily at the Cu site Cu12-xMxSb4S13. In this work we have studied the impact of substitution effects on thermoelectric properties using density-functional theory electronic structure calculations in combination with calculation of electrical transport properties by the BoltzTrap program. [ABSTRACT FROM AUTHOR]

Samples with Cu12−xCoxSb4S13−ySey (0 ≤ x ≤ 2, 0 ≤ y ≤ 1) nominal compositions were prepared by melting the elements under vacuum, followed by slow cooling. The phases formed in this process were identified and characterized by powder x-ray diffraction and scanning electron microscopy observations, complemented with energy-dispersive spectroscopy. All samples have tetrahedrite as the major phase (> 78 vol.%). However, minority phases like skinnerite and chalcostibite are usually also observed, the number and volume of them increasing with the increase of cobalt content. Measurements of electrical resistivity and Seebeck coefficient showed that these materials can present large power factors, with the Cu11.5Co0.5Sb4S12Se sample having a room temperature value higher than 200 μW K−2 m−1. [ABSTRACT FROM AUTHOR]

Materials with ultralow thermal conductivity are crucial to many technological applications, including thermoelectric energy harvesting, thermal barrier coatings, and optoelectronics. Liquid-like mobile ions are effective at disrupting phonon propagation, hence suppressing thermal conduction. However, high ionic mobility leads to the degradation of liquid-like thermoelectric materials under operating conditions due to ion migration and metal deposition at the cathode, hindering their practical application. Here, a new type of behavior, incipient ionic conduction, which leads to ultralow thermal conductivity, while overcoming the issues of degradation inherent in liquid-like materials, is identified. Using neutron spectroscopy and molecular dynamics (MD) simulations, it is demonstrated that in tetrahedrite, an established thermoelectric material with a remarkably low thermal conductivity, copper ions, although mobile above 200 K, are predominantly confined to cages within the crystal structure. Hence the undesirable migration of cations to the cathode can be avoided. These findings unveil a new approach for the design of materials with ultralow thermal conductivity, by exploring systems in which incipient ionic conduction may be present., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

A Cu 12 Sb 3.6 Bi 0.4 S 10 Se 3 glass was prepared by melt spinning and crystallized by heat treatments at selected temperatures, the total preparation procedure taking less than one day. The sample characterization by powder X-ray diffraction, scanning and transmission electron microscopy complemented with EDS indicate the formation of compact materials, with a tetrahedrite relative weight fraction higher than 90% when treated at temperatures close to the crystallization peaks (∼200° C). Selenium enters the tetrahedrite structure, while bismuth precipitates in submicron and nanosized spherical shape phases depleted in copper and enriched in antimony, sulfur and selenium (when compared with the matrix composition). The characterization of electrical transport properties (electrical resistivity and Seebeck coefficient) indicate a behavior similar to that obtained by other methods on Cu 12 Sb 4 S 13 , with a maximum power factor of ∼400 μW/K 2 m at room temperature. [ABSTRACT FROM AUTHOR]

Computational inverse design and consequent experimental results allow for the identification of new tetrahedrite-mineral compositions as promising absorber candidates in drift-based thin-film solar cells. In device simulations, cell efficiencies above 20% are modeled with absorber layers as thin as 250 nm. These new compositions thus open opportunities for realization of a new class of high-efficiency thin-film solar cell. [ABSTRACT FROM AUTHOR]

We present the study of the effect of Te substitution on the thermoelectric properties for Sb in CuSbTeS tetrahedrite compounds with x ranging from 0.2 to 1.5 in the temperature range of room temperature to 723 K. Powder x-ray diffraction and electron microscopy results indicate a successful homogenous substitution without the alteration of the crystal structure or the introduction of secondary phases. Thermoelectric property measurements show that the excess electrons from Te during the substitution fill the unoccupied levels near the top of the valence bands in pure CuSbS compound, moving the Fermi level closer to the top of the valence bands. This leads to an enhancement in thermopower but also to an increase in electrical resistivity. Overall, the reduction in total thermal conductivity gives rise to improved ZT values in all substituted samples. The highest ZT value obtained in this study is 0.92 at 723 K for x = 1, which is comparable to that of other p-type bulk thermoelectric materials. [ABSTRACT FROM AUTHOR]

• CdI 2 and LiI as fluxes were used for synthesis-growth of tetrahedrite crystals. • Cu 10-x Li x Cd 2 Sb 4 S 13 solid solution formed if LiI as flux was used. • PL bands with maxima at 1.08 eV (CdI 2 -flux) and at 1.16 eV (LiI-flux) were measured. • The thermal quenching E A of PL bands were 88±6 (CdI 2 -flux) and 199±7 meV (LiI-flux). • V oc = 506 mV, j sc = 4.46 mA/cm2, FF = 50%, η = 1.13% - with tetrahedrite grown in LiI. Synthesis of Cd-substituted tetrahedrite Cu 10 Cd 2 Sb 4 S 13 (TH Cd) monograin powders are performed by the molten salt synthesis-growth method using two different fluxes: CdI 2 and LiI. The X-ray diffraction (XRD) data of the materials indicates that mainly single phase of tetrahedrite Cu 10 Cd 2 Sb 4 S 13 compound is formed in both flux salts. XRD pattern of TH Cd crystals grown in LiI reveals a shift of all diffraction peaks, lower CdS content and a smaller lattice parameter values in comparison with those formed in CdI 2. Energy dispersive X-ray spectroscopy reveals stoichiometric composition of Cu 10 Cd 2 Sb 4 S 13 crystals grown in CdI 2 and Cu-poor grown in LiI. Analysis by Atomic Absorption Spectroscopy confirms the incorporation of Li into TH Cd crystals at the level of 6.7 × 1020 at/cm3. The photoluminescence (PL) study of Cu 10 Cd 2 Sb 4 S 13 microcrystals at T = 10 K shows single broad asymmetric photoluminescence bands with the maxima at around 1.08 and 1.16 eV for materials grown respectively in CdI 2 and LiI. The thermal quenching activation energy of this PL band is E A = 88±6 and 199±7 meV for TH Cd crystals grown in CdI 2 and LiI, respectively. Changes in the lattice parameters, composition and shift in PL maximum give evidences of Li incorporation from LiI into the crystal lattice of TH Cd forming Cu 10-x Li x Cd 2 Sb 4 S 13 solid solution. [ABSTRACT FROM AUTHOR]

This contribution deals with the mechanochemical synthesis, characterization, and thermoelectric properties of tetrahedrite-based materials, Cu12-xMxSb4S13 (M = Fe2+, Zn2+, Cd2+; x = 0, 1.5, 2). High-energy mechanical milling allows obtaining pristine and substituted tetrahedrites, after short milling under ambient conditions, of stoichiometric mixtures of the corresponding commercially available binary sulfides, i.e., Cu2S, CuS, Sb2S3, and MS (M = Fe2+, Zn2+, Cd2+). All the target materials but those containing Cd were obtained as single-phase products; some admixture of a hydrated cadmium sulfate was also identified by XRD as a by-product when synthesizing Cu10Cd2Sb4S13. The as-obtained products were thermally stable when firing in argon up to a temperature of 350–400 °C. Overall, the substitution of Cu(II) by Fe(II), Zn(II), or Cd(II) reduces tetrahedrites' thermal and electrical conductivities but increases the Seebeck coefficient. Unfortunately, the values of the thermoelectric figure of merit obtained in this study are in general lower than those found in the literature for similar samples obtained by other powder processing methods; slight compositional changes, undetected secondary phases, and/or deficient sintering might account for some of these discrepancies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel affordable n-silicide/p-tetrahedrite thermoelectric module concept proposed. • Detailed validated multiphysics analysis done, TEG geometry optimization performed. • Pairs with optimal geometry preliminarily manufactured, assembled, characterized. • Power density/efficiency predictions: up to 5 kW/m2/5% (temperatures up to 620 K). • Affordable, non-toxic, performing generators enable viable industrial heat recovery. Thermoelectric (TE) generators allow the direct conversion of heat into electricity without moving parts and with little maintenance needs if carefully designed. However, their high cost per unit power produced has prevented their widespread use in waste heat recovery applications. The use of earth-abundant, affordable, non-toxic and performant TE materials such as n-silicide and p-tetrahedrite for TE generators is assessed in the present analysis. A full multiphysics model was used to optimize the geometry of an n-p TE pair/module using these materials and assess its performance. The approach taken implemented the matched load condition automatically and a broad range of conditions was tested and discussed. Several pairs with the optimal geometry were preliminarily manufactured, assembled and characterized. The experimental results were compared against the predictions, allowing to validate the multiphysics model. Power densities up to 5 kW/m2 were predicted for temperatures between 290 K and 620 K, with efficiencies up to 5%. If modules with such performance could be manufactured with electric contact resistances comparable to those found in currently available commercial modules, then a door to the viable recovery of waste heat in industrial and automotive applications could be opened. [ABSTRACT FROM AUTHOR]

Pores in a solid can effectively reduce thermal conduction, but they are not favored in thermoelectric materials due to simultaneous deterioration of electrical conductivity. Conceivably, creating a porous structure may endow thermoelectric performance enhancement provided that overwhelming reduction of electrical conductivity can be suppressed. This work demonstrates such an example, in which a porous structure is formed leading to a significant enhancement in the thermoelectric figure of merit (zT). By a unique BiI 3 sublimation technique, pore networks can be introduced into tetrahedrite Cu 12 Sb 4 S 13 -based materials, accompanied by changes in their hierarchical structures. The addition of a small quantity of BiI 3 (0.7 vol%) results in a ≈72% reduction in the lattice thermal conductivity, whereas the electrical conductivity is improved due to unexpected enhanced carrier mobility. As a result, an enhanced zT of 1.15 at 723 K in porous tetrahedrite and a high conversion efficiency of 6% at ΔT = 419 K in a fabricated segmented single-leg based on this porous material are achieved. This work offers an effective way to concurrently modulate the electrical and thermal properties during the synthesis of high-performance porous thermoelectric materials., (© 2021 Wiley-VCH GmbH.)

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 Cu 12 Sb 3.96 Ge 0.04 S 13 -0.5 wt % ZnO sample at 750 K, which is ∼72% larger than that of Cu 12 Sb 4 S 13 . All results indicate that suitable elemental doping combined with the incorporation of the nanophase is a very promising approach for Cu 12 Sb 4 S 13 tetrahedrites to improve the thermoelectric performance.

Thermoelectric devices convert heat flow to charge flow, providing electricity. Materials for highly efficient devices must satisfy conflicting requirements of high electrical conductivity and low thermal conductivity. Thermal conductivity in caged compounds is known to be suppressed by a large vibration of guest atoms, so-called rattling, which effectively scatters phonons. Here, the crystal structure and phonon dynamics of tetrahedrites (Cu,Zn) 12 (Sb,As) 4 S 13 are studied. The results reveal that the Cu atoms in a planar coordination are rattling. In contrast to caged compounds, chemical pressure enlarges the amplitude of the rattling vibration in the tetrahedrites so that the rattling atom is squeezed out of the planar coordination. Furthermore, the rattling vibration shakes neighbors through lone pairs of the metalloids, Sb and As, which is responsible for the low thermal conductivity of tetrahedrites. These findings provide a new strategy for the development of highly efficient thermoelectric materials with planar coordination., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)