Équilibres oxydo-réducteurs dans les dichalcogénures de platine et de palladium. Influence de la pression sur la redistribution du nuage électronique

Abstract : This thesis deals with the analysis of the electronic structure of dichalcogenides of platinum and palladium, solid state compounds which adopt peculiar structural arrangements. A preliminary study at ambient pressure is realized on the PtQ2 (Q = O, S, Se, Te) family which adopts the polymeric CdI2 type structure with a low c/a ratio. Thanks to ab initio calculations, we are able to identify the factors responsible for this value. An electronic transfer from anionic to cationic bands leads to a decrease of the c parameter while orbital and geometric factors induce the increase of the a parameter. Then, PtO2, only stable lamellar oxide, was examined. We show that the electronic count is responsible for the structural arrangement. The partial electronic transfer for PtTe2 shows that the chalcogenides charge balance has to be redefined. The strong combination between p and d orbitals, evidenced by calculations, prevents us to determine a charge balance for PtTe2 and PdTe2 which can be written Pt3+(Te-1,5)2 and Pd2+(Te-1)2 atr ambient pressure. In the case of PtTe2, high pressure does not induce an electronic transfer but a rearrangement. The same phenomenon is observed for PdSe2. This compound undergoes a phase transition from the PdS2- to the pyrite-type structure without electronic transfer but with a cooperative Jahn-Teller distorsion. The influence of temperature was finally studied and shows strong structural rearrangements in the pyrite-type structure.
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Theses
Matériaux. Université de Nantes, 2004. Français
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Submitted on : Monday, November 22, 2004 - 3:20:18 PM
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Céline Sortais-Soulard. Équilibres oxydo-réducteurs dans les dichalcogénures de platine et de palladium. Influence de la pression sur la redistribution du nuage électronique. Matériaux. Université de Nantes, 2004. Français. 〈tel-00007453〉

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