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Synthèses, études structurales et propriétés magnétiques dans des phosphates et des vanadates de formulation AIA'IIBVO4 (A : alcalin, Ag, Cu ; A' : Cd, Cu, Mn, Mg ; B : P, V)

Abstract : Contrary to their homologous LiMPO4 (M: transition metal) which crystallize with the olivine type structure, the vanadates LiMVO4 crystallize with the spinel type structure or Na2CrO4 type structure. In general, few compounds crystallize with this last structural type. This is due to the strong steric constraints existing within this structure. Thus the study of the substitution of cadmium for lithium in the LiCdVO4 compound highlighted the existence of modulated structures for compositions (Li1 xCdx/2)CdVO4 (0,4 < x ≤ 2/3). The structures of these compounds were solved in the superspace formalism. The study of the homologous system with sodium (Na1 xCdx/2)CdVO4 (0 ≤ x ≤ 1) did not allow modulated phases to be isolated. The substitution of cadmium for sodium generates strong steric constraints which are at the origin of a structural transition from Na2CrO4 type structure to maricite type structure. This transition made it possible to extend the system until the limiting compound (Cd1/2)CdVO4 (x = 1).
In order to extend our comprehension of the structural differences between phosphates and vanadates of general formula AA' BO4 (A : alkali and d10 cation, A' : transition metal, B : P et V), the AMnPO4 and AMnVO4 series were studied and this made it possible to synthesize and characterize the new AMnVO4 compounds with A: Cu, Na, Ag, K, Rb and AMnPO4 with A: Rb and Ag. A very surprising result was obtained with the new compound KMnVO4, which crystallizes in a new oxygen-deficient perovskite type structure.
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Hamdi Ben Yahia. Synthèses, études structurales et propriétés magnétiques dans des phosphates et des vanadates de formulation AIA'IIBVO4 (A : alcalin, Ag, Cu ; A' : Cd, Cu, Mn, Mg ; B : P, V). Matériaux. Université Sciences et Technologies - Bordeaux I, 2006. Français. ⟨tel-00129401⟩

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