Électrodéposition et caractérisations de nanofils thermoélectriques Bi0,5Sb1,5Te3 dans des matrices mésoporeuses en polycarbonate

Abstract : Bismuth chalcogenides are the best thermoelectric materials at room temperature. Nanostructuring is a promising approach to improve their efficiency which is currently limited. The aim of this work is the template synthesis of p-type Bi0,5Sb1,5Te3 nanowires by electrodeposition in polycarbonate mesoporous membranes. Firstly, comparative study of diffusion coefficients of BiIII, SbIII and TeIV cations was done on planar electrode. More specifically, the diffusion processes occurring during the deposition into the pores were studied, the membranes acting as an array of recessed ultramicro-electrodes. The cation concentrations in the synthesis electrolytes were then adjusted and related electrochemical systems have been investigated. Consequently, several deposition potentials have been defined leading to the synthesis of BixSbyTez nanowires. Composition, morphology and crystallinity of the nanostructures were systematically studied by Transmission Electron Microscopy equipped with an EDS system, for three types of membranes with different pore diameters and densities. The targeted composition Bi0,5Sb1,5Te3 was almost obtained for antimony enriched electrolytes. In best synthesis conditions, nanowires are polycrystalline and textured. High Resolution TEM images exhibit local defects like twin boundaries. Moreover, thermoelectric properties of array of nanowires were investigated. In particular the Seebeck coefficient, the internal resistance and the output power were studied as function of synthesis parameters. It appears that nanowires fabricated in commercial membranes exhibit positive Seebeck coefficients of about +300 µV/K. The results show that internal resistances are governed by the filling rate of mesoporous membranes
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Jonathan Schoenleber. Électrodéposition et caractérisations de nanofils thermoélectriques Bi0,5Sb1,5Te3 dans des matrices mésoporeuses en polycarbonate. Autre. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0137⟩. ⟨tel-01750987⟩

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