Contribution à l'étude des propriétés thermoélectriques de vitrocéramiques et verres de chalcogénures semi-conducteurs

Abstract : Thermoelectrics are materials capable of converting thermal energy into electrical energy through Seebeck effect, and vice-versa through Peltier effect. By using these two phenomena, it becomes possible to salvage heat loss from most human activities (industries, cars,…) or on the other side, to efficiently and silently produce cold. To obtain an efficient material, it is necessary to look for materials that simultaneously possess a low electrical resistivity, a low thermal conductivity and a high thermoelectric power alpha (or Seebeck coefficient). In other words, it is possible to show that we need to optimize the figure of merit ZT = alpha2.T/rho.lambda (a ZT as high as 1 can be considered as efficient). Chalcogenide glasses, due to favorably disordered structures, exhibit a naturally low thermal conductivity, but have a too high electrical resistivity (oppositely to classical thermoelectrics of which we seek to lower the thermal conductivity). In this work, two strategies were set up into lowering electrical resistivity and then further enhance the thermoelectric performance of chalcogenide glasses. Focusing on telluride glasses, we firstly tried to modify their composition and add metallic elements such as copper. Substituting Te par Se in the ternary system Cu-As-Te allowed increasing their thermal stability. For vitreous materials, we finally obtained a maximal ZT around 0.1 at 375K, for the compound Cu30As10Te54Se6. The second solution consists in partially crystallizing these glasses: by taking advantage of the favorable properties of each phase (the low thermal conductivity of the glassy phase and the low electrical resistivity of the crystalline phase), the figure of merit can be raised. By optimizing glass-ceramics of composition Cu15As30Te55, a ZT close to 0.2 at 375K has been obtained. However, predicting how the thermoelectric properties evolve with crystalline fraction or microstructure is complex. That led us to set up a transport model for two-phases composites, giving finally some insights to further improve these materials.
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Jean-Baptiste Vaney. Contribution à l'étude des propriétés thermoélectriques de vitrocéramiques et verres de chalcogénures semi-conducteurs. Autre. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0115⟩. ⟨tel-01750909⟩

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