Synthèse, caractérisation et mise en forme de nouveaux matériaux thermoélectriques à base de ZnSb

Abstract : The heat loss from different sources at different scales (microprocessors, cars, houses, factories) is an almost untapped source of energy. The conversion of this thermal energy into electrical energy is possible through the use of thermoelectric generators. However at the present time their use is not widespread due to their low efficiency, toxicity and because of the cost of the existing materials. The aim of this thesis that follows the DFT calculations previously made during Kinga Niedziolka’s thesis, (University of Montpellier, 2014) was to obtain new efficient thermoelectric materials based on ZnSb relying on the calculation results. Based on the calculations and in agreement with the industrial partner Hutchinson, aluminum (1 % at. in substitution of Zn), tellurium (1 % at. in substitution of Sb), titanium (1 % at. in substitution of Zn) and yttrium (1 % at. in substitution of Zn) were selected as dopants. The objective, was to synthesize and characterize the materials which were calculated as n type semiconductors (electron conduction). The materials were synthesized by melting, quenching and annealing. They were obtained in the form of polycrystalline ingots. They were characterized by X-ray diffraction, scanning electron microscopy and EDS and WDS microanalysis. Their shaping for thermoelectric characterization was then developed. The technique of Spark Plasma Sintering (SPS) was chosen to this aim and we achieved very interesting densities of around 98% for all doped materials. Thermoelectric characterizations were carried out up to 600 K by means of a ZEM-3 type apparatus. Only tellurium doped materials with the most promising results were thoroughly studied. However, the thermoelectric characterization of the synthesized doped materials didn’t show the expected transition to an n-type conduction. However, progress was made regarding ZnSb as a p-type material. The optimization of the mechanical alloying process led to a very promising ZnSb material. The analyses of this material by transmission electron microscopy and XPS analysis led to the identification of some precipitates which give rise to improved thermoelectric properties compared to existing p-type ZnSb. Furthermore the obtained material has a high thermal stability reinforcing its interest compared to other materials for applications in the same temperature range.
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Romain Pothin. Synthèse, caractérisation et mise en forme de nouveaux matériaux thermoélectriques à base de ZnSb. Matériaux. Université Montpellier, 2016. Français. ⟨NNT : 2016MONTT231⟩. ⟨tel-01816008⟩

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