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Structures et propriétés de transports de chalcogénures complexes

Abstract : This work has been focused on synthetizing and characterising chalcogenide compounds. Most new, those compounds show complex structures or where disorder bring complexity. The first part of this manuscript is dedicated to the study of the new single-cristalline Ba0.5Cr5Se8 and of the related polycristalline solid-solution BaxCr5Se8 (0.5 ≤ x ≤ 0.55). This compound is part of the pseudo-hollandite family. Its cristalline structure has been resolved by means of single-crystal X-ray diffraction, a lowering of symetryis observed compared to usual pseudo-hollandites. All antiferromagnetic, the compounds exhibit a transition at 58 K, the magnetic structure has been resolved using neutron diffraction on polycrystal and is twice the cristalline one along b and c. Thermoelectric properties of the compounds have been studied and a maximum ZT of 0.12 is observed at 800 K for Ba0.5Cr5Se8. The second section has first focused on a similar structure to the previous one, TlIn5Se8. Although too resistive to be interesting, two new compounds have been studied: TlIn4.8Cr0.2Se8 and Tl0.98In13.12Se16.3Te2.7. The latter quaternary exhibits static disorder on specific crystallographic sites. The last chapter highlights compounds from the lamellar compound MnPSe3 family, with the particularity to possess P2 pairs. The structure of the new In2Ge2Te6 has been resolved and thermoelectric properties of the InSiTe3, Cr2Si2Te6, Cr2Ge2Te6 and In2Ge2Te6 have been studied. Stacking faults were observed in In2Ge2Te6 and explain the impact on the phonon mean free path. All the compounds whose thermoelectric properties have been studied exhibit low thermal conductivity, below 1 W.m-1.K-1 for most of them. ZTs of 0.18 at 673 K and 0.43 at 773 K were found for In2Ge2Te6 and Cr2Ge2Te6.
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Submitted on : Friday, December 15, 2017 - 3:56:04 PM
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  • HAL Id : tel-01665219, version 1

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Robin Lefevre. Structures et propriétés de transports de chalcogénures complexes. Chimie organique. Normandie Université, 2017. Français. ⟨NNT : 2017NORMC225⟩. ⟨tel-01665219⟩

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