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• W745008943 abstract "Various compounds with host structures based on geomaterials have been preparedusing solid state methods (900-1200 0c), low pressure hydrothermal conditions (<220°C, <1800 psi) or using purpose-built high pressure equipment <800°C, < 5500Opsi).Each material was characterized using various combinations of powder X-ray andneutron diffraction, single crystal X -ray diffraction, IR spectroscopy, Mossbauerspectroscopy and magnetometry.The iron end member, danalite, of the helvite family of minerals with the formulaFeg[BeSi04]6S2 has been prepared for the first time. Isovalent substitution of thesulphide anion has allowed both selenide and telluride materials to be prepared.These compounds crystallize with the sodalite structure in the space group P-43n andexhibit an ordered framework constructed from alternating Be04 and Si04 tetrahedracontaining a tetrahedral cluster of iron(II) ions around a central chalcogenide.Mossbauer measurements curiously show that, despite an elongated tetrahedralgeometry of three oxide and one cha1cogenide around the iron ions, the valence andlattice contribution to the isomer shift oppose each other leading to zero quadrupolemoment at room temperature for the sulphide material. Magnetic and polarizedneutron experiments show that the interactions within the tetrahedral metal clusters ofdivalent ions are predominantly antiferromagnetic. In the sulphide, the clustersbehave as totally isolated clusters showing no magnetic interaction across the cages.As the distance between the clusters shortens, as in the case of the selenide, threedimensionalinteractions between the clusters are observed. A systematic study of anextensive series of compounds in the helvite series, (Mn,Fe,Zn,Co)8[BeSi04]6X2;X =S, Se and Te has been carried out. All diffraction data of the compounds have beenrefmed using the Rietve1d method and very accurate structural parameters obtained.Correlations between parameters such as the beryllium and silicon tilt angles,framework bond angle and bond lengths as well as the IR absorptions have beendrawn for the beryllosilicate sodalite frameworks. The theoretical maximum andminimum cell parameters for a sodalite framework, based on ordered Be04 and Si04tetrahedra, has been determined.Transition metal boracites with the formula M3B7013X; M = Co, Zn, Mn, X = Cl, Brand I have been prepared using a borate flux. Their stoichiometries have beendetermined using the Mohr method and Rietveld refinement of powder X-raydiffraction data. In contrast to compounds prepared using hydrothermal methods, thehalide site is not heavily substituted by hydroxide. A temperature dependant study ofMg3B7013CIo.78(OH)o.22 is also presented. Magnetic measurements have confirmeddual weak ferromagnetic and antiferromagnetic properties in the iodide materialsA series of LnSF and Ln2AF4S2 materials have been synthesized using hightemperature sealed tube methods. The missing member of the LnSF series, DySF, hasbeen prepared for the first time. Precise structural data on the LnAF4S2 compoundswhere Ln = La, Ce, Dy and Er have been gleaned from the Rietveld refinement ofpowder diffraction data. . In contrast to previous studies, the lanthanide has beenshown as preferentially distributed over the two LnlCa sites and the fluoride displacedfrom a special site to allow pseudo seven coordination for the smaller lanthanides.High-pressure methods have failed to produce the calciurnlgermanium based zeolitessuch as gismondine or the unusual mineral, bemalite. A new complex phosphate ofthe formula NaMllf;(P207 )2(P301O), containing the triphosphate unit, has been preparedat high pressure and the structure determined using single crystal methods. Usinglow pressure hydothermal methods, the full series of lanthanide hydroxide Ln(OH)3have been prepared. Structure refinement has shown a contraction in the Ln-O bonddistance as the series is transversed." @default.
• W745008943 created "2016-06-24" @default.
• W745008943 creator A5074080321 @default.
• W745008943 date "2004-01-01" @default.
• W745008943 modified "2023-09-24" @default.
• W745008943 title "Preparation and characterisation of complex metal chalcogenides and halides" @default.
• W745008943 hasPublicationYear "2004" @default.
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