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Current high-performance thermoelectric materials require elaborate doping and synthesis procedures, particularly in regard to the artificial structure, and the underlying thermoelectric mechanisms are still poorly understood. Here, we report that a natural chalcopyrite mineral, Cu1+x Fe1-x S2 , obtained from a deep-sea hydrothermal vent can directly generate thermoelectricity. The resistivity displayed an excellent semiconducting character, and a large thermoelectric power and high power factor were found in the low x region. Notably, electron-magnon scattering and a large effective mass was detected in this region, thus suggesting that the strong coupling of doped carriers and antiferromagnetic spins resulted in the natural enhancement of thermoelectric properties during mineralization reactions. The present findings demonstrate the feasibility of thermoelectric energy generation and electron/hole carrier modulation with natural materials that are abundant in the Earth's crust.

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The well-documented formation of amorphous bands in boron carbide (B 4 C) under contact loading has been identified in the literature as one of the possible mechanisms for its catastrophic failure. To mitigate amorphization, Si-doping was suggested by an earlier computational work, which was further substantiated by an experimental study. However, there have been discrepancies between theoretical and experimental studies, about Si replacing atom/s in B 12 icosahedra or the C-B-C chain. Dense single phase Si-doped boron carbide is produced through a conventional scalable route. A powder mixture of SiB 6 , B 4 C, and amorphous boron is reactively sintered, yielding a dense Si-doped boron carbide material.A combined analysis of Rietveld refinement on XRD pattern coupled with electron density difference Fourier maps and DFT simulations were performed in order to investigate the location of Si atoms in boron carbide lattice. Si atoms occupy an interstitial position, between the icosahedra and the chain. These Si atoms are bonded to the chain end C atoms and result in a kinked chain. Additionally, these Si atoms are also bonded to the neighboring equatorial M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT2 B atom of the icosahedra, which is already bonded to the C atom of the chain, forming a bridge like geometry. Si atoms are found to reside around the chain, resulting in a kinked chain. These Si atoms lie close to boron atom of the neighboring icosahedra. Owing to this bonding, distance suggests weak bonding and Si is anticipated to stabilize the icosahedra through electron donation, which is expected to help in mitigating stress-induced amorphization. Possible supercell structures are suggested along with the most plausible structure for Si-doped boron carbide.

International audienceWe report for the first time the thermoelectric properties of CuCr2-xSbxS4 (0.22 <= x <= 0.5). Although CuCr2S4 has been reported to be a metallic compound, addition of Sb shifts the material toward the semiconductor side. This is confirmed by band structure calculations of CuCr2-xSbxS4 (x = 0, 0.25, 0.5) models. Increasing Sb content enhances the power factor. However, beyond x = 0.3, further Sb addition lowers the electrical conductivity and power factor. A very interesting point is the simultaneous increase of the Seebeck coefficient as well as the electrical conductivity with increasing temperature, which acts like a variable range hopping (VRH) compounds but possesses much better properties than those having VRH. Samples were annealed for 48 h prior to thermoelectric properties measurements to have a reliable dimensionless figure of merit (ZT). An attractive ZT of 0.43 is obtained at similar to 650 degrees C. The attractive thermoelectric properties we discovered by driving a metal compound into a semiconductor make this compound an interesting thermoelectric material especially because of the cheap constituent elements compared to those of typical state-of-the-art thermoelectric materials. Furthermore, this material is stable up to 650 degrees C at least, a relatively high temperature for sulfides. Additionally, we discovered a miscibility gap in this solid solution close to an Sb content of 0.15; although a detailed study dedicated entirely to this miscibility gap would be required, it will encourage the researchers to further explore this system

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