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Zusammenfassung:
Orange-colored crystals of the oxoferrate tellurate K12+6xFe6Te4-xO27 [x=0.222(4)] were synthesized in a potassium hydroxide hydroflux with a molar water-base ratio n(H2O)/n(KOH) of 1.5 starting from Fe(NO3)(3) . 9H(2)O, TeO2 and H2O2 at about 200 degrees C. By using (NH4)(2)TeO4 instead of TeO2, a fine powder consisting of microcrystalline spheres of K12+6xFe6Te4-xO27 was obtained. K12+6xFe6Te4-xO27 crystallizes in the acentric cubic space group I4? 3d. [(FeO5)-O-III] pyramids share their apical atoms in [Fe2O9] groups and two of their edges with [(TeO6)-O-VI] octahedra to form an open framework that consists of two loosely connected, but not interpenetrating, chiral networks. The flexibility of the hinged oxometalate network manifests in a piezoelectric response similar to that of LiNbO3.The potassium cations are mobile in channels that run along the directions and cross in cavities acting as nodes. The ion conductivity of cold-pressed pellets of ball-milled K12+6xFe6Te4-xO27 is 2.3x10(-4) S . cm(-1) at room temperature. Magnetization measurements and neutron diffraction indicate antiferromagnetic coupling in the [Fe2O9] groups.
