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  • 1
    Electronic Resource
    Electronic Resource
    A novel intergrowth structure between ReO3-type and tetragonal tungsten bronze-type in the Zr/Nb/W/O system (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 917-922 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The intergrowth structure of a zirconium niobium tungsten oxide has been determined by transmission electron microscopy methods. Electron diffraction patterns reveal the parameters of the monoclinic lattice: a = 19.0, b = 3.9 and c = 13.8 Å; β = 93.5°. Additional reflections in higher-order Laue zones indicate the presence of a diagonal glide plane, leading to a larger unit cell. A structure model of composition ZrnNb8−2nW12+nO56 (0.5 〈 n 〈 1) has been derived from high-resolution lattice images. Alternating slabs of ReO3-type and of tetragonal tungsten bronze structure are intergrown coherently. Two five-membered rings of MO6 octahedra belonging to adjacent tetragonal tungsten bronze subcells are connected by having two octahedra in common. For the first time, this arrangement of double pentagons is observed in a regular structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768196006891
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  • 2
    Electronic Resource
    Electronic Resource
    Order and Disorder in Niobium Tungsten Oxides of the Tetragonal Tungsten Bronze Type (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 240-249 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Two superstructures of the TTB type (tetragonal tungsten bronze) exist in the system Nb2O5/WO3. They are caused by an ordered arrangement of pentagonal tunnels filled with metal–oxygen strings. Besides the well known 4:9 phase (Nb8W9O47), which has a tripled b axis, evidence for a new orthorhombic structure, Nb6W8O39 (a = b = 27.3 Å), has been found. The oxidation products of Nb7W10O47 and Nb4W13O47 frequently comprise less-ordered arrangements of filled tunnels, causing diffuse scattering. In Nb7W10O47.5 the electron diffraction patterns (along [001]) of many crystal fragments show circular diffuse scattering, which appears around the main reflections of the TTB substructure with two distinct radii (r*). r* \simeq 0.33a* indicates the predominance of 4:9-type domains, whereas r* \simeq 0.41a* corresponds to Nb6W8O39. In Nb4W13O49 the diffuse scattering pattern is cross-shaped; this is due to the presence of long slabs of diamond-linked pentagonal columns. Structure models for these particular states of order have been derived from high-resolution transmission electron microscopy images. Some general principles for the formation of the different arrangements are deduced. Apparently, two distinct types of link between the filled pentagonal tunnels are important features which lead to the stability of these structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876819701971X
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  • 3
    Electronic Resource
    Electronic Resource
    Structural Characterization of Vanadiumphosphate Catalysts Generated under Ammoxidation Conditions (1998)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 278-281 (Apr. 1998), p. 660-665 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/03/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.278-281.660.pdf
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  • 4
    Electronic Resource
    Electronic Resource
    The Synthesis and Structure of Nanocrystalline Spinel Ferrite Produced by High-Energy Ball-Milling Method (1996)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 235-238 (Oct. 1996), p. 139-144 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/02/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.235-238.139.pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Zur Präparation und Struktur gemischtvalenter Niob-Wolframoxide der Zusammensetzung (Nb,W)17O47 (1995)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 621 (1995), S. 799-806 
    Details
    ISSN: 0044-2313
    Keywords: Nb8W9O47 ; niobium tungsten oxides ; mixed valency ; electron microscopy ; HRTEM ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation and Structure of Niobium Tungsten Oxides (Nb,W)17O47 with Mixed ValencyThe formal substitution of 2Nb5+ by Nb4+ or W4+, respectively, and W6+ leads to tungsten niobium oxides (Nb,W)17O47 with mixed valency. The phases Nb8-nW9+nO47 with n = 1 to 5 could be obtained by heating (1 250°) mixtures of NbO2 or WO2, respectively, with Nb2O5 and WO3. The products crystallize with the structure of Nb8W9O47. This is proved by X-ray powder diffraction and transmission electron microscopy. A further decrease of the Nb-content results in two-phase products.
    Notes: Durch formale Substitution von je zwei Nb5+ durch Nb4+ (bzw. W4+) und W6+ sind - ausgehend von Nb8W9O47 - gemischtvalente Niob-Wolframoxide unterschiedlicher Nb/W-Verhältnisse denkbar, von denen Zusammensetzungen Nb8-nW9+nO47 mit n = 1 bis 5 durch isothermes Erhitzen (1 250°C) der entsprechenden Gemenge von NbO2 (bzw. WO2) mit Nb2O5 und WO3 phasenrein dargestellt werden konnten. Diese Produkte kristallisieren alle in der Struktur des Nb8W9O47 und sind somit als Mischphase (0 ≤ n ≤ 5) aufzufassen, wie die röntgenographische (Pulvermethode) und durchstrahlungs-elektronenmikroskopische Untersuchung belegt. Präparate mit niedrigerem Nb-Gehalt (n 〉 5) erhielten wir dagegen nicht mehr phasenrein.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19956210517
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  • 6
    Electronic Resource
    Electronic Resource
    Präparation und transmissionselektronenmikroskopische Charakterisierung quaternärer Niob-Wolframoxide des Titans, Zirconiums und Hafniums (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 990-996 
    Details
    ISSN: 0044-2313
    Keywords: Quaternary niobium tungsten oxides ; tetragonal tungsten bronzes ; intergrowth structures ; HRTEM ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation and Transmission Electron Microscopy Investigation of Quaternary Niobium Tungsten Oxides of Titanium, Zirconium, and HafniumStarting with the phases in the pseudobinary system tem Nb2O5/WO3, the formal substitution of 2 Nb5+ by M4+ and W6+ provides a possibility to prepare quaternary niobium tungsten oxides of the same structure. For the first time, MNb6W10O47 (M = Ti, Zr, Hf) and M2Nb4W11O47 (M = Ti, Hf) were obtained. They crystallize in the threefold TTB-type (tetragonal tungsten bronze) superstructure of the 4:9 phase (Nb8W9O47). However, transmission electron microscopic investigations of ZrNb6W10O47 revealed the presence of another quaternary phase that exhibits a novel intergrowth structure between TTB type and ReO3 type. In W-richer samples, Zr-containing crystals with the structure of the 2 :7 phase (Nb4W7O31) occur. The sample of composition Zr2Nb4W11O47 crystallizes in a disordered TTB structure with microdomains of the ReO3 type.
    Notes: Ausgehend von den im pseudobinären System Nb2O5/WO3 bekannten Phasen bietet die formale Substitution von je 2 Nb5+ durch M4+ und W6+ eine Möglichkeit zur gezielten Synthese quaternärer Niob-Wolframoxide gleicher Struktur. So wurden erstmals die Phasen MNb6W10O47 (M = Ti, Zr, Hf) und M2Nb4W11O47 (M = Ti, Hf) erhalten, die alle isotyp zur 4 : 9-Phase (Nb8W9O47) in einer dreifachen Überstruktur der tetragonalen Wolframbronzen (TTB) kristallisieren. Bei der Untersuchung röntgenographisch einphasiger Proben von ZrNb6W10O47 im Transmissions-Elektronenmikroskop wurden Kristallite einer weiteren quaternären Phase mit einer Intergrowth-Struktur gefunden, die Bauelemente des TTB- und des ReO3-Typs in einer zuvor noch nicht beobachteten Weise kombiniert. Mit dieser Methode ließen sich in W-reicheren Präparaten Zr-haltige Kristallite mit der Struktur der 2:7-Phase (Nb4W7O31) identifizieren. Für die Zusammensetzung Zr2Nb4W11O47 wird davon abweichend eine wenig geordnete TTB-Struktur mit Mikrodomänen des ReO3-Typs beobachtet.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.199762301155
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