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  • 1
    Electronic Resource
    Electronic Resource
    Neutron diffraction of a complex of 1,8-bis(dimethylamino)naphthalene with 1,2-dichloromaleic acid (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 691-696 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A neutron study of the crystalline complex of 1,8-bis(dimethylamino)naphthalene (DMAN) with 1,2-dichloromaleic acid (ClMH2) has been carried out at 100 K using the Laue time-of-flight technique. The moieties are planar. The neutron data indicate that both [N—H...N]+ and [O—H...O]− hydrogen bonds in the complex are asymmetric. There are significant differences between the neutron and X-ray temperature factors, C—H, N—H and O—H bond lengths. There is a strong correlation between the neutron and X-ray temperature factors for non-H atoms and no correlation for H-atom temperature factors. According to the neutron data the involvement of a given H atom in a weak C—H...O hydrogen bond can be correlated with the ratio of equivalent temperature factors of the H and non-H atoms to which they are attached.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768196003023
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  • 2
    Electronic Resource
    Electronic Resource
    High-temperature phases of NaNbO3 and NaTaO3 (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 24-30 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The high-temperature phases of the perovskites sodium niobate, NaNbO3, and sodium tantalate, NaTaO3, have been re-examined using the high-resolution powder diffractometer HRPD at the ISIS neutron spallation source; the two materials show the same sequence of phases with tilted octahedra. Diffraction patterns were measured every 5 K allowing structural changes with temperature within a single phase to be determined for the first time. Previous structure determinations within one phase had been performed at a single temperature only. The octahedra are tilted about pseudocubic \langle100\rangle directions and are also deformed; the magnitude of the deformation is shown to be proportional to the square of the angle of tilt as expected from a phenomenological theory applied to such transitions. The structures of NaNbO3 between 753 and 793 K and of NaTaO3 below 758 K are not as reported in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876819800963X
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  • 3
    Electronic Resource
    Electronic Resource
    Distortion Characteristics Across the Structural Phase Transition in (Cu1−xZnx)WO4 (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 102-112 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Rietveld analysis of neutron powder diffraction data on the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution has enabled the comparison of microscopic and macroscopic order parameters associated with the P2/c–P\overline 1 structural phase transition. The macroscopic spontaneous strain, calculated from the lattice parameters, conforms well with a second-order Landau model. Furthermore, this is also true of the symmetry-related atomistic M—O order parameter and the quadratic elongation of the MO6 octahedra. It is clear that the Jahn–Teller effect, associated with the divalent Cu cation, is the driving force for the phase transition and the excess elongation evident in the M—O(2) bond giving rise to the non-symmetry predicted strain element e22. The existence of a large region of order parameter saturation at the copper-rich end of the solid solution is also associated with the MO6 elongation and the breakdown of the homogeneous strain field of the zinc solute atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768196010403
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  • 4
    Electronic Resource
    Electronic Resource
    Crystal Structure Solution from Neutron Powder Diffraction Data by a new Monte Carlo Approach Incorporating Restrained Relaxation of the Molecular Geometry (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 968-974 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: We report the development of a new aspect of the Monte Carlo method for crystal structure solution from powder diffraction data and demonstrate the advantages of this new approach by applying it to solve the low-temperature crystal structure (phase II) of perdeuterated pyrene from neutron powder diffraction data. In previous applications of our Monte Carlo technique, the structural fragment was constrained to have a standard geometry throughout the calculation, whereas in the new approach, restrained relaxation of the structural fragment from standard geometry is considered for each structure sampled during the calculation. The new approach gives rise to a substantially improved discrimination (in terms of the weighted profile R factor Rwp) between the correct structure solution and incorrect structures sampled during the Monte Carlo calculation [for the calculation with standard geometry of the structural fragment, Rwp ranged from circa 27.5–30% for `wrong' structures to 21.2% for the best structure solution (i.e. discrimination 6̃.3%); for the calculation with relaxation of the geometry of the structural fragment, Rwp ranged from circa 24–26% for `wrong' structures to 11.6% for the best structure solution (i.e. discrimination 1̃2.4%)]. The work reported here represents the first application of the Monte Carlo method for structure solution using neutron powder diffraction data; the new methodology (applicable to both neutron and X-ray powder diffraction data) represents a substantial enhancement of the scope and potential of the method, particularly for cases in which the discrimination in Rwp between the correct structure solution and incorrect structure solutions is expected to be inherently small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897004548
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  • 5
    Electronic Resource
    Electronic Resource
    Rb3H(SeO4)2 at 4K by Neutron Powder Diffraction (1996)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 1061-1063 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270195011085
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of olivine cooling rates from metal-cation ordering (1996)
    [s.l.] : Nature Publishing Group
    Nature 381 (1996), S. 407-409 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] It has been recognized for some time that non-equilibrium cation ordering in minerals might provide a means to measure rock cooling rates, from early work on Mg/Fe ordering in amphi-boles6 and extensive studies of pyroxenes7'8 to more recent analysis of Al/Si ordering in alkali feldspars9. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/381407a0
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature evolution between 50 K and 320 K of the thermal expansion tensor of gypsum derived from neutron powder diffraction data (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 477-483 
    Details
    ISSN: 1432-2021
    Keywords: Key words gypsum ; thermal expansion tensor ; Rietveld analysis ; neutron powder diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The unit cell parameters, extracted from Rietveld analysis of neutron powder diffraction data collected between 4.2 K and 320 K, have been used to calculate the temperature evolution of the thermal expansion tensor for gypsum for 50 ≤ T ≤ 320 K. At 300 K the magnitudes of the principal axes are α 11  = 1.2(6) × 10−6 K−1, α 22  = 36.82(1) × 10−6 K−1 and α 33  = 25.1(5) × 10−6 K−1. The maximum axis, α 22 , is parallel to b, and using Institution of Radio Engineers (IRE) convention for the tensor orthonormal basis, the axes α 11 and α 33 have directions equal to (−0.979, 0, 0.201) and (0.201, 0, 0.979) respectively. The orientation and temperature dependent behaviour of the thermal expansion tensor is related to the crystal structure in the I2/a setting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050210
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  • 8
    Electronic Resource
    Electronic Resource
    Octahedral cation ordering in olivine at high temperature. II: an in situ neutron powder diffraction study on synthetic MgFeSiO4 (Fa50) (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 630-637 
    Details
    ISSN: 1432-2021
    Keywords: Key words Olivine ; Order/disorder ; High temperature cation partitioning ; Neutron diffraction (powder)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The partitioning of Fe and Mg between the M1 and M2 octahedral sites of olivine has been investigated by in situ time-of-flight neutron powder diffraction. The degree of M-cation order was determined from direct measurements of site occupancies in a synthetic sample of Fo50Fa50 heated to 1250 °C at the Fe-FeO oxygen buffer. Fe shows slight preference for M1 at temperatures below about 600 °C, progressively disordering on heating to this temperature. Above 630 °C, the temperature at which site preferences cross over (T cr), Fe preferentially occupies M2, becoming progressively more ordered into M2 on increasing temperature. The cation-ordering behaviour is discussed in relation to the temperature dependence of the M1 and M2 site geometries, and it is suggested that vibrational entropy, crystal field effects and changes in bond characteristics play a part in the cross-over of partitioning behaviour. The temperature dependence of site ordering is modelled using a Landau expansion of the free energy of ordering of the type ΔG = −hQ + gTQ +   (T − T c)Q 2 +   Q 4, with a/h = 0.00406 K−1, b/h = 2.3, T c = 572 K and g/h = 0.00106 K−1. These results suggest that the high-temperature ordering behaviour across the forsterite-fayalite join will have a bearing on the activity-composition relations of this important rock-forming mineral, and indicate that Fe-Mg olivine solid solutions become less ideal as temperature increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690000109
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  • 9
    Electronic Resource
    Electronic Resource
    Neutron powder diffraction study of the scintillator material ZnWO4 (1996)
    Springer
    Journal of materials science 31 (1996), S. 2873-2877 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract With a view to the technological applications of ZnWO4 crystals, we have performed Rietveld profile refinement of medium-resolution, time-of-flight, neutron powder diffraction data of synthetic ZnWO4 to improve the quality of the current crystal structure derived from single crystal X-ray techniques that produced a final solution with an R factorof only 10%. The new structural data for ZnWO4, monoclinic space group P2/c, lattice parameters of 0.469263(5), 0.572129(7), 0.492805(5) nm for a, b and c respectively, and a β angle of 90.6321(9) ° with two formula units per unit cell. The ZnO6 octahedra contain 3 pairs of Zn-O bonds of 0.2026(2), 0.2090(2) and 0.2227(3) nm and the WO6 octahedra contain 3 pairs of W-O bonds 0.1789(2), 0.1914(2) and 0.2133(3) nm. These new data confirm the basic structure of ZnWO4 and provide accurate off-centring magnitudes for the Zn and W cations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00355995
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  • 10
    Electronic Resource
    Electronic Resource
    Koordinationszahl 4 oder 6 für Lithium??: Die Kristallstruktur von wasserfreiem Lithiumpermanganat, Li[MnO4] (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 1419-1425 
    Details
    ISSN: 0044-2313
    Keywords: Lithium permanganate, Li[MnO4] ; preparation ; crystal structure ; neutron powder data ; MAPLE calculation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Coordination Number 4 or 6 for Lithium?: The Crystal Structure of Lithium Permanganate, Li[MnO4]Waterless 7Li[MnO4] was obtained by dehydration of 7Li[MnO4] · 3 D2O at 60°C above P4O10 in vacuum as violet powder.The structure determination by neutron diffraction measurements via pulsed polychromatic neutron source [time-of-flight powder diffractometer; profile-R-value = 2.1%, Bragg-R-value = 7.4%] confirms the space group Cmcm with a = 551.402(8), b = 839.754(15), c = 635.911(10) pm (Z = 4); parameters see text. The crystal structure of Li[MnO4] corresponds to the CrVO4-type with coordination number 6 for lithium and 4 for manganese.The Madelung Part of Lattice Energie, MAPLE, the Effective Coordination Numbers, ECoN and the charge distribution were calculated and discussed.
    Notes: Durch Trocknung von 7Li[MnO4] · 3 D2O bei 60°C über P4O10 im Vakuum wurde wasserfreies 7Li[MnO4] als violettes Pulver erhalten.Die Strukturaufklärung mittels Neutronenbeugungsmessungen im gepulsten polychromatischen Neutronenstrahl [Flugzeitdiffraktometer; Profil-R-Wert = 2,1%, Bragg-R-Wert = 7,4%] belegt die Raumgruppe Cmcm mit a = 551,402(8), b = 839,754(15), c = 635,911(10)pm (Z = 4); Parameter siehe Text. Die Kristallstruktur von Li[MnO4] entspricht dem CrVO4-Typ mit der Koordinationszahl 6 für Lithium und 4 für Mangan.Der Madelunganteil der Gitterenergie, MAPLE, Effektive Koordinationszahlen, ECoN und die Ladungsverteilung wurden berechnet und diskutiert.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19936190817
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