Sol-gel processing and structural study of europium-doped hybrid materials

Abstract

The thermal, morphological and conducting properties of macromolecular organic-inorganic networks synthesized by the sol-gel process and containing a wide concentration range of europium trifluoromethanesulfonate, Eu(CF ₃ SO ₃ ) ₃ , have been investigated. The hybrid matrix, U(2000), of these materials, classed as ureasils, includes a siliceous backbone and short polyether-based segments. The link between these components is made by urea bridges. The behaviour of the doped ureasils is significantly better than that of previously characterized electrolytes based on poly(ethylene oxide), PEO. The essentially amorphous character of the hybrid host contributes to an improved transparency and moderate conductivities of certain electrolytes at room temperature (ca. 5×10 ^–6 Ω ^–1 cm ^–1 ). DSC, XRD and FTIR measurements show that the formation of a high-melting crystalline complex results from the coordination of the Eu ³⁺ ions by the ether oxygens of the organic moieties at composition n=5 [where n represents the molar ratio of (OCH ₂ CH ₂ ) units per Eu ³⁺ ion]. The results obtained for samples with n≥20 suggest that in this range of composition the principal effect of the polyether chains is to exert a plasticizing influence, as the coordination of the cations by the urea linkages is favored.