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  • 1
    Digitale Medien
    Digitale Medien
    Citrate Route to Sn-Doped BaTi4O9 with Microwave Dielectric Properties (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Highly reactive and nanometer-sized (30–50 nm) Sn-doped BaTi4O9 (BaTi4-xSnxO9; x = 0.0–0.03) powders have been prepared by the citrate-precursor method. The effect of Sn substitution on the crystallization and microwave dielectric properties has also been investigated on the basis of microstructure and crystal structure. Addition of a small amount of SnO2 resulted in a lowering of the sintering temperature of BaTi4O9, and at 1250–1300°C for 2–5 h, dense compounds with a theoretical density up to 99% could be obtained. The Sn-doped BaTi4O9 materials were found to have excellent microwave dielectric properties with epsilonr = 34–37, Q = 8300–8900 at 11 GHz and tauf = 3.6–16.1 ppm/°C.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02756.x
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  • 2
    Digitale Medien
    Digitale Medien
    Local structure analysis of Ti species stabilized in ion exchangeable layer solids by X-ray absorption spectroscopy (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 728-730 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Nano-sized titanium dioxides are incorporated into the interlayer spaces of ion-exchangeable layered perovskites, H1-xCa2-xLaxNb3O10 (x=0.00̃.75), by replacing the interlayer protons with positively charged TiO2 nano-sol particles or basic titanium glycolate complex (titanatrane). Powder X-ray diffraction analysis, UV-Vis absorption spectroscopy, thermogravimetric analysis, and N2 adsorption-desorption isotherm measurements show that quantum sized TiO2 particles are stabilized inbetween perovskite lattices to form micropores (SBET= 371̃10 m2/g). X-ray absorption spectroscopy at the Ti K-edge was used for investigating the local environment around Ti atoms constituting the interlayer pillars. According to the XANES spectra, the 'as-pillared' Ti species have the same local environments with those of precursory species, which subsequently converted into TiO2 clusters with rutile and anatase-like local structures when TiO2 nano-sol particles and titanatrane are used as pillaring species, respectively. It is also found that the local environment of TiO2 remains almost constant irrespective of the layer charge density, while the TiO2 pillar content and the microporosity increase with the latter.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S090904950100022X
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  • 3
    Digitale Medien
    Digitale Medien
    Ion exchange and fixation of rare-earth cation into expandable tetrasilicic fluorine mica (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 731-733 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Rare-earth cation (Nd3+) are incorporated into the interlayer spaces between the silicate layers of synthetic fluorine mica, Na0.665Mg2.68(Si3.98Al0.02)O10.02F1.98, by conventional ion exchange reaction. Subsequent migration of the interlayer cations upon calcination into the vacant octahedra of 2:1 layers is followed by powder X-ray diffraction, diffuse-reflectance UV spectroscopy, and X-ray absorption spectroscopy as a function of calcination temperature. It is found from the spectroscopic analyses that the interlayer cations start to migrate into the octahedral vacant sites from 400°C through the hexagonal siloxane ring of the tetrahedral silicate layers. According to the Nd LIII-edge XANES spectra, the normalized absorption intensity gradually decreases while the FWHM increases with temperature, suggesting that the bonding character of rare-earth cations and silicate lattices evolves from ionic to covalent as the calcination temperature increases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049501000188
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  • 4
    Digitale Medien
    Digitale Medien
    XAFS study of copper species stabilized in the interlayer space of layered perovskite oxides (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 734-736 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: New intercalation compounds with Cu2+ ions in the interlayer of layered perovskite oxides, OA1-xCa2-xLaxNb3O10 (OA = n-octylammonium ion, 0 ≤ x 〈 1), have been prepared by ion-exchange reaction, and characterized by means of XRD and XAS. For the detail elucidation of the fine structure of the Cu K-edge XANES spectra, polarized XAS was applied for the [Cu(en)2]2+ and Cu2+ ions intercalated to the single crystal. According to the XANES and EXAFS spectra measured at Cu K-edge, copper ions are four-coordinated. In addition, XANES spectra have shown that the charge transfer from host layer to intercalated ions influences on the chemical state of copper ion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049500014539
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  • 5
    Digitale Medien
    Digitale Medien
    Preparation and Adsorption Properties of Mesoporous Pillared Clays with Silica Sol (1998)
    Springer
    Journal of porous materials 5 (1998), S. 111-119 
    Details
    ISSN: 1573-4854
    Schlagwort(e): pillared clays ; intercalation ; microporosity ; mesoporosity ; organic template
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract New mesoporous silica-pillared montmorillonites were prepared by the post-intercalation of bulky organic cations into silica sol exchanged montmorillonites. Pillared clays with SiO2-Fe2O3 sol were first prepared, followed by the dissolution of iron oxide (or hydroxide) from the pillars with hydrochloric acid. A portion of the interlayered sol particles were then replaced with organic cations which led to a rearrangement of silica sol particles between the silicate layers. The removal of the organics by burning resulted in mesoporous sol pillared clays with an average pore size of more than 20 Å in diameter. The BET specific surface area increased to as high as 950 m2/g in these mesoporous pillared clays.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009685118854
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