Ball milling as an effective route for the preparation of doped bornite: synthesis, stability and thermoelectric properties

Bornite, Cu5FeS4, is a naturally-occuring mineral with an ultralow thermal conductivity and potential for thermoelectric power generation. We describe here a new, easy and scalable route to synthesise bornite, together with the thermoelectric behaviour of manganese-substituted derivatives, Cu5Fe1-xMnxS4 (0 ≤ x ≤ 0.10). The electrical and thermal transport properties of Cu5Fe1-xMnxS4 (0 ≤ x ≤ 0.10), which are p-type semiconductors, were measured from room temperature to 573 K. The stability of bornite was investigated by thermogravimetric analysis under inert and oxidising atmospheres. Repeated measurements of the electrical transport properties confirm that bornite is stable up to 580 K under an inert atmosphere, while heating to 890 K results in rapid degradation. Ball milling leads to a substantial improvement in the thermoelectric figure of merit of unsusbtituted bornite (ZT = 0.55 at 543 K), when compared to bornite prepared by conventional high-temperature synthesis (ZT < 0.3 at 543 K). Manganese-substituted samples have a ZT comparable to that of unsubstituted bornite

The impact of manganese substitution on the structure and properties of tetrahedrite

The crystal structure of the tetrahedrites Cu12-xMnxSb4S13 (x = 0, 1) has been studied by powder neutron diffraction between room temperature and 773 K. At all temperatures investigated, manganese exclusively occupies tetrahedral sites, while the trigonal-planar sites contain only copper. In situ diffraction data confirm the stability of the tetrahedrite phase up to 773 K, with no evidence of copper mobility at elevated temperatures. Analysis of atomic displacement parameters indicate that there are low-energy vibrations associated with the trigonal-planar and the tetrahedral copper cations. The Einstein temperatures for the copper cations range between 79 and 91 K. Manganese substitution increases the electrical resistivity and the Seebeck coefficient, while the thermal conductivity is reduced. This results in a modest improvement in the thermoelectric figure of merit for Cu12MnSb4S13, which reaches ZT=0.56 at 573 K

The influence of mobile copper ions on the glass-like thermal conductivity of copper-rich tetrahedrites

Tetrahedrites are promising p-type thermoelectric materials for energy recovery. We present here the first investigation of the structure and thermoelectric properties of copper-rich tetrahedrites, Cu12+xSb4S13 (0 0 consist of two tetrahedrite phases. In-situ neutron diffraction data demonstrate that on heating, the two tetrahedrite phases coalesce into a single tetrahedrite phase at temperatures between 493 and 553 K, and that this transition shows marked hysteresis on cooling. Our structural data indicate that copper ions become mobile above 393 K. Marked changes in the temperature dependence of the electrical and thermal transport properties of the copper-rich phases occur at the onset of copper mobility. Excess copper leads to a significant reduction in the total thermal conductivity, which for the nominal composition Cu14Sb4S13 reaches a value as low as 0.44 W m-1K-1 at room temperature, and to thermoelectric properties consistent with phonon liquid electron crystal (PLEC) behaviour

Issues and opportunities from Peltier effect in functionally-graded colusites: from SPS temperature modeling to enhanced thermoelectric performances

International audienceThe quaternary sulphide V-Sn colusite, Cu 26 V 2 Sn 6 S 32 , is one of the most promising costefficient thermoelectric materials to date because of the low toxicity, wide availability and low cost of the composing elements. Recent studies have demonstrated the potential of this environmentally-friendly material and its transport properties are now well understood. In the present work, we take the next step of producing large quantities of optimised V-Sn colusite using industrial-grade precursors and investigating the effect of Spark Plasma Sintering (SPS) in the production of large cylindrical pucks of up to 30 mm in diameter and 10 mm in thickness. In the process, we identified and solved several key issues including the generation of temperature gradients during SPS, porosity and defect formation. The generation of radial and axial temperature gradients within the sample during SPS has been modeled using modified Fourier and Ohm laws and confirmed experimentally thanks to the T SPS-dependent transport properties of V-Sn colusite and EDS analysis. We demonstrate that large pucks of colusite with enhanced thermoelectric properties can be produced using a combination of SPS and High-temperature Isostatic Press (HIP). Overall, our work experimentally and theoretically demonstrates that the production of both homogeneous and functionally-graded bulk materials can be easily up-scaled through a careful control of the SPS conditions

Issues and opportunities from Peltier effect in functionally-graded colusites: from SPS temperature modeling to enhanced thermoelectric performances

International audienceThe quaternary sulphide V-Sn colusite, Cu 26 V 2 Sn 6 S 32 , is one of the most promising costefficient thermoelectric materials to date because of the low toxicity, wide availability and low cost of the composing elements. Recent studies have demonstrated the potential of this environmentally-friendly material and its transport properties are now well understood. In the present work, we take the next step of producing large quantities of optimised V-Sn colusite using industrial-grade precursors and investigating the effect of Spark Plasma Sintering (SPS) in the production of large cylindrical pucks of up to 30 mm in diameter and 10 mm in thickness. In the process, we identified and solved several key issues including the generation of temperature gradients during SPS, porosity and defect formation. The generation of radial and axial temperature gradients within the sample during SPS has been modeled using modified Fourier and Ohm laws and confirmed experimentally thanks to the T SPS-dependent transport properties of V-Sn colusite and EDS analysis. We demonstrate that large pucks of colusite with enhanced thermoelectric properties can be produced using a combination of SPS and High-temperature Isostatic Press (HIP). Overall, our work experimentally and theoretically demonstrates that the production of both homogeneous and functionally-graded bulk materials can be easily up-scaled through a careful control of the SPS conditions

Copper‐Rich Thermoelectric Sulfides: Size‐Mismatch Effect and Chemical Disorder in the [TS4]Cu6 Complexes of Cu26T2Ge6S32 (T=Cr, Mo, W) Colusites

International audienceHerein, we investigate the Mo and W substitution for Cr in synthetic colusite, Cu26Cr2Ge6S32. Primarily, we elucidate the origin of extremely low electrical resistivity which does not compromise the Seebeck coefficient and leads to outstanding power factors of 1.94 mW m−1 K−2 at 700 K in Cu26Cr2Ge6S32. We demonstrate that the abnormally long iono‐covalent T–S bonds competing with short metallic Cu–T interactions govern the electronic transport properties of the conductive “Cu26S32” framework. We address the key role of the cationic size‐mismatch at the core of the mixed tetrahedral–octahedral complex over the transport properties. Two essential effects are identified: 1) only the tetrahedra that are directly bonded to the [TS4]Cu6 complex are significantly distorted upon substitution and 2) the major contribution to the disorder is localized at the central position of the mixed tetrahedral–octahedral complex, and is maximized for x=1, i.e. for the highest cationic size‐variance, σ2

Ordered sphalerite derivative Cu 5 Sn 2 S 7 : a degenerate semiconductor with high carrier mobility in the Cu–Sn–S diagram

International audienceRegardless of the complexity of the phase diagram of the Cu–Sn–S system, several compositions near the prototypical mohite Cu2SnS3 have arisen as potential non-toxic, earth-abundant and cost-efficient photovoltaic and thermoelectric materials. In this work, we revisited the Cu2+xSn1−xS3 system and discovered a monoclinic (C2) ordered sphalerite derivative member, Cu5Sn2S7. Using a combination of synchrotron diffraction and spectroscopy, transmission electron microscopy, precession-assisted electron diffraction tomography, Mössbauer spectroscopy, first principles calculations and transport properties measurements, we discuss the structure–thermoelectric properties relationships and clarify the interesting crystal chemistry in this system. The ternary sulfide Cu5Sn2S7 exhibits a degenerate semiconducting behavior with exceptionally high hole mobility originating from the interplay between atomic ordering and charge delocalization

Ordered sphalerite derivative Cu 5 Sn 2 S 7 : a degenerate semiconductor with high carrier mobility in the Cu–Sn–S diagram

International audienceThe discovery of the monoclinic Cu 5 Sn 2 S 7 phase adds a high mobility member to the Cu–Sn–S diagram and demonstrates how the crystal structure can be advantageously manipulated to design novel compositions for energy-oriented applications