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  • 1
    Electronic Resource
    Electronic Resource
    Determination by X-ray diffraction of interstitial concentrations of vanadium ions in disordered VOx (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 387-395 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Integrated intensities were measured from VOx single crystals with x = 0.80, 0.94, 1.01, 1.11 and 1.25. A least-squares refinement was carried out for the scale factor and the isotropic temperature factors of vanadium and oxygen ions for each composition, for a range of interstitial vanadium contents. The R values after the refinement were 0.04-0.05. There are vanadium ions at tetrahedral interstitial sites, the concentration of which changes from 0-0.5% to 3% with composition x; this confirms quantitatively previous studies which employed dynamical electron diffraction effects. The temperature factors of vanadium (BV) and oxygen (BO) increase with x; BV = 1.02-1.38 Å2 and BO = 0.58-1.24 Å2. The composition dependence of the overall temperature factor is similar to that of the lattice parameter. The 002 structure factor for electrons U002 and the critical voltage Ec at which the second-order Kikuchi line disappears were calculated for VO0.82 and VO1.20, using the individual temperature factors determined by this study. The 002 structure factors measured by the critical-voltage and the intersecting-Kikuchi-line method [Watanabe, Andersson, Gjønnes & Terasaki (1974). Acta Cryst. A30, 772-776] were in agreement within less than 2%. The results support the idea that the ionic state of the cation lies between neutral and singly ionized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476000922
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  • 2
    Electronic Resource
    Electronic Resource
    The defect structure of VOx. I. The ordered phase, VO1.30 (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 745-756 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Integrated X-ray intensities were obtained from a single crystal of VO1.30 annealed below the ordering transition. The space group is I41/amd, and the unit-cell contents are V51.6O64. The atomic arrangement is similar to that proposed by Andersson & Gjönnes [Acta Chem. Scand. (1970), 24, 2250-2252], but there are more vanadium vacancies and interstitial ions. The latter are surrounded by four vacancies as in the defect structure of FexO. The oxygen ions around an interstitial vanadium ion are displaced away from it; oxygen and vanadium ions on the octahedrally coordinated sites exhibit strongly correlated displacements. There are anisotropic electron density distributions at vanadium ions near a vacancy. These effects indicate that the order--disorder transition is not due to a Jahn-Teller effect, but instead is a result of a long-range cooperative interaction, presumably due to the semi-metallic nature of this oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773947900173X
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  • 3
    Electronic Resource
    Electronic Resource
    Short-range order in Ni3Fe (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1-7 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Short-range order parameters were obtained for a single crystal of 62Ni3Fe quenched from above Tc. These are the first absolute measurements of diffuse elastic neutron scattering complete enough to separate the effects of local order and atomic displacements (up to quadratic terms) and indicate that neutrons are ideally suited for such studies. The results are compared to those obtained with X-rays. The short-range order intensity of Ni3Fe is similar in shape to that for Cu3Au but in this alloy it is due to the plate-like nature of ordered domains, not the antiphase domain boundaries which are present in such regions in Cu3Au.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480000010
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray diffraction study of Zr(Ca,Y)O2−x. II. Local ionic arrangements (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 520-530 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Above the 1300 K transition and in the defect fluorite phase, there is diffuse X-ray scattering which is similar for both Ca- and Y-stabilized zirconias. This is largely due to ionic displacements from the average structure, principally oxygen ions displaced locally in (100) directions. It has been proposed that some of this scattering is due to fine precipitates of ZrCa4O9 or ZrY4O9. The quantitative analysis of this diffuse scattering reported here does indeed indicate some similarities to this phase; in particular the stabilizing ions form rods in the ({\bar 3}{\bar 3}2) directions similar to those in the precipitate. However, in this compound the stabilizing ion is a second neighbor to an oxygen-ion vacancy, whereas the present results indicate that these tend to be first neighbors. This is the first direct evidence for this association in these materials. This probably occurs to reduce local distortions and to provide local charge balance. It is concluded that the diffuse intensity is from locally ordered regions, not precipitates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480001179
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  • 5
    Electronic Resource
    Electronic Resource
    Distortion-induced scattering due to vacancies in NbC0.72 (1988)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 167-176 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The diffuse X-ray (and electron) scattering from NbC0.72, previously thought to be due to vacancy octahedra, is shown to be dominated by the scattering due to mean-square atomic displacements with wave vectors near the Brillouin-zone boundary. The atomic displacements are similar to those produced by an optical phonon. On the basis of the sign and amplitude of the displacement parameters a model for the environment around a carbon vacancy is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387010043
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  • 6
    Electronic Resource
    Electronic Resource
    Vacancy–strain coupling in ordered TiO (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 556-561 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of the partially ordered phase of TiO has been examined with a single crystal. While the space group is that first determined from powder X-ray diffraction and electron diffraction by Watanabe, Castle, Jostons & Malin [Acta Cryst. (1967). 23, 307-313], (B2/m), the average structure is somewhat different. There are waves of Ti and O ion vacancies every third (100) plane in the [010] direction of the monoclinic structure. The amplitude of the wave is twice as large for the Ti ion vacancies as for the O ion vacancies. There is no appreciable concentration of interstitial Ti ions in either the ordered phase or the disordered (cubic) phase. The ordering temperature Tc is 1026 (2)°C. The monoclinic angle is directly proportional to the square of the order parameter associated with vacancy ordering. A mean-field theory is developed that includes vacancy-vacancy and vacancy-electron interactions, and vacancy-strain coupling. This theory explains the main features of the order-disorder transition in this material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478001199
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  • 7
    Electronic Resource
    Electronic Resource
    The defect structure of VOx. II. Local ionic arrangements in the disordered phase (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 975-989 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In VOx (0.8 〈 x 〈 1.3), there are large numbers of cation and anion vacancies and interstitial vanadium ions. To determine the local arrangements of these defects, X-ray diffuse scattering was measured in absolute units with single crystals of VOx (x = 0.89, 1.17 and 1.28). For x 〉 1, the interstitials are present near vacancy clusters, similar to the defect arrays found in the semiconductor FexO. For x 〈 1, there are few interstitials, but an increased concentration of anion vacancies. The anion and cation vacancies are arranged (so as to minimize the electrostatic energy) in rows along (110) directions with alternating vacancy-rich and vacancy-deficient { 111 } layers. Some portions of this vacancy arrangement resemble that found in metallic TiOx. VOx behaves like a semimetal for x 〈 1, but a semiconductor for x 〉 1, and the present results, when compared to the defect structures in TiOx and FexO, show that the nature of the bonding between cations and anions controlling the conduction mechanism is reflected in the defect structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479002175
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  • 8
    Electronic Resource
    Electronic Resource
    A structural study of the alloy Cu3Au above its critical temperature (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 597-614 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Absolute measurements of the diffuse intensity in a volume in reciprocal space have been made at six temperatures ranging from 2°C above Tc to 930°C. The Warren short-range order parameters were obtained after correcting for the intensity due to atomic displacements in a more complete manner than in earlier studies. As a result the short-range order parameters are considerably smaller than in these earlier investigations. The (previously disputed) specific heat anomalies in Cu3Au above Tc and the L12 phase have been shown to be associated with unusual changes in diffuse X-ray scattering vs temperature. From studies of the scattering distributions, computer simulation and pair potentials obtained with the Warren short-range order parameters, the anomaly at 600°C appears to be due to the disappearance of DO22-like fluctuations, whereas above 850°C, CuPt-like fluctuations develop. There are premonitory effects just above Tc; there is a large increase in the Debye-Waller factor, in the total intensity due to quadratic terms in atomic displacements, and an apparent change in the sign of average first-neighbor displacement. The long-range oscillations in the interatomic potentials determined from the diffuse-scattering data fit the Friedel potential only approximately. The electron-to-atom ratio in Cu3Au was found to be ̃0.97, in agreement with results on Cu alloys by other methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476001277
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  • 9
    Electronic Resource
    Electronic Resource
    Clustering in Fe–3.9at.%Mo (1971)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 27 (1971), S. 97-109 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The diffuse X-ray scattering from a single crystal of Fe-3.9 at. % Mo has been measured at room temperature. A volume in reciprocal space was explored, which was chosen so that the intensity due to local order could be separated from the effects of different atomic sizes of the species and first-order thermal diffuse scattering making use of the symmetry of these contributions according to a theory by Boric & Sparks. The Warren local order parameters have been derived and used in a computer program to generate the corresponding atomic distributions. The Mo atoms formed clusters on the average 7 to 8 Mo atoms in size, the clustered regions having about twice the Mo concentration as the average alloy composition. The largest clusters contained about 40 Mo atoms. The shapes of all these regions were irregular. An analysis of the scattering due solely to the differences in atomic size of Fe and Mo indicates that the Fe atoms are displaced from lattice points by about 0.001 Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739471000226
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  • 10
    Electronic Resource
    Electronic Resource
    Equations for diffuse scattering from materials with multiple sublattices (1975)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 31 (1975), S. 635-645 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: General equations are presented for the diffuse scattering due to local ionic arrangements and displacements in systems with more than one ion per lattice point. Up to fourth-order terms are included. These are placed in a form easy to evaluate in specific cases; examples are given of a solid-solution oxide, and an oxide with vacant sites. Methods for employing these equations for the separation of the various contributions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739475001362
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