Gabin Guélou

A copper-containing oxytelluride as a promising thermoelectric material for waste heat recovery

The new thermoelectric material BiOCuTe exhibits an electrical conductivity of 224 S cm−1 and a Seebeck coefficient of +186 μV K−1 at 373 K, together with an extremely low lattice thermal conductivity of ∼0.5 W m−1 K−1. This results in a ZT of 0.42 at 373 K, which increases to 0.66 at the maximum temperature investigated, 673 K.

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

Bornite, Cu5FeS4, is a naturally-occurring mineral with an ultralow thermal conductivity and potential for thermoelectric power generation. We describe here a new, easy and scalable route for synthesising 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 unsubstituted 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.

Up-scaled synthesis process of sulphur-based thermoelectric materials

The scale up of Spark Plasma Sintering (SPS) for the consolidation of large square monoliths (50 × 50 × 3 mm3) of thermoelectric materials is demonstrated and the properties of the fabricated samples compared with those from laboratory scale SPS. The SPS processing of n-type TiS2 and p-type Cu10.4Ni1.6Sb4S13 produces highly dense compacts of phase pure material. Electrical and thermal transport property measurements reveal that the thermoelectric performance of the consolidated n- and p-type materials is comparable with that of material processed using laboratory scale SPS, with ZT values that approach 0.75 and 0.35 at 700 K for Cu10.4Ni1.6Sb4S13 and TiS2, respectively. Mechanical properties of the consolidated materials show that large-scale SPS processing produces highly homogeneous materials with hardness and elastic moduli that deviate little from values obtained on materials processed on the laboratory scale. More generally, the process described in this paper is a promising way to produce high performance thermoelectric materials with square geometry, specifically required for thermoelectric device production.

Synthesis and Physical Properties of Layered Copper Oxytellurides Sr2TMCu2Te2O2 (TM = Mn, Co, Zn)

We synthesized a new series of layered copper oxytellurides Sr2TMCu2Te2O2 with variation in transition metal (TM = Mn, Co, and Zn) elements. These compounds are the first example having alternately stacked anti-fluorite Cu2Te2 and perovskite-like TM-oxide layers. Owing to the longer ionic radius of Te compared to those of Se and S, they exhibit larger lattice parameters than isostructural sulfides and selenides. First principles band structure calculation for the Zn compound as a representative reveals a semiconducting direct band gap of ∼1.7 eV and the Co compound shows a comparable band gap in the diffuse reflectance measurement result. From the thermoelectric property study, we determined a power factor of ∼70 μW m−1 K−2 and a figure of merit ZT of ∼0.045 at 770 K for the Co compound, which encourages further improvement in thermoelectric response by applying various enhancement methods. In terms of the magnetic properties, a signature of antiferromagnetic order is observed in the Co and Mn compounds. The present results not only highlight the structural flexibility of the system to tune the physical properties but also suggest that the replacement of the blocking layer can be a new way to improve the thermoelectric performance of layered copper oxychalcogenides.