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  • 1
    Electronic Resource
    Electronic Resource
    A priori estimates of errors in intensities for imperfectly spherical crystals (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 78-82 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A priori estimates of errors in intensities for spheres arising from non-sphericity in crystal shape may now be readily determined from a recently published table of (1/A*)(∂A*/∂μR) values [Flack & Vincent (1978). Acta Cryst. A34, 489-491] using an expression given by Jeffery & Rose [Acta Cryst. (1964), 17, 343-350]. However, a new relationship between σ(R) and σ(r) is determined. The effects of crystal radius, non-sphericity and wavelength on intensity errors are discussed. The importance to the selection of crystals for electron density measurements is stressed. Universal curves of σ(r)/r, the error due to non-sphericity, against μr calculated for a range of intensity errors at θ = 0 and 45 ° are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000140
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  • 2
    Electronic Resource
    Electronic Resource
    Intensity errors due to beam inhomogeneity and imperfectly spherical crystals (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 795-802 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An analysis of the intensity errors from imperfectly spherical crystals with an inhomogeneous incident X- ray beam is presented. The crystals are considered to have either no absorption or strong absorption. The inhomogeneity of the incident beam profile is represented by three possible models: (a) a Lorentzian, (b) a Gaussian and (c) a second-order Taylor series expansion. The results are compared with intensities for electron density studies from five crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479001819
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  • 3
    Electronic Resource
    Electronic Resource
    On the polarization factor for crystal-monochromated X-radiation. III. A weighting scheme for products (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 620-624 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The minimum-variance weighting scheme for calculating the weighted mean of a quality for the following unusual case is analysed. The quantity is derived from the product of two independent quantities for each of the which a set of data is available. All the products between the two sets of data are taken into consideration. The application to measurements of the polarization state of X-radiation is outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480001301
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  • 4
    Electronic Resource
    Electronic Resource
    Electron-density studies of metal–metal bonds. I. The deformation density of Ti2O3 at 295 K (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 803-808 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The electron-density distribution in Ti2O3 at room temperature has been determined from single-crystal X-ray diffraction data. The deformation maps show maxima of 0.15 e Å-3 between the Ti atoms sharing a common face of O-atom octahedra, and maxima of 0.18 e Å-3 between the O atoms and their four nearest Ti neighbours. These observations support the general view concerning the bonding in Ti2O3 and correlate well with the results of theoretical band-structure calculations. In particular, they confirm the existence of a metal-metal bond which is directed parallel to the ternary axis and is responsible for the anomalously low c/a ratio of this compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480001611
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  • 5
    Electronic Resource
    Electronic Resource
    On the polarization factor for crystal-monochromated X-radiation. I. Assessment of errors (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 610-614 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The relation between the parameter c describing the degree of perfection of a crystal monochromator and the polarization ratio K is established. The influence of the incorrect assumption that a monochromator is always ideally mosaic on the polarization factor is discussed in terms of the systematic errors that may be introduced into X-ray data from the neglect to consider it as otherwise. Emphasis is given to a comparison of the errors for the two most common spectrometer geometries which provides some illuminating results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480003907
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  • 6
    Electronic Resource
    Electronic Resource
    Electron-density studies of metal–metal bonds. I. The deformation density of V2O3 at 295 K (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 808-813 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The charge-density distribution in V2O3 differs from that in Ti2O3 mainly with respect to the deformation of the metal atoms. The V atoms show a positive deformation of up to 0.1 e Å-3 perpendicular to c in a plane containing three nearest V-atom sites across the edges of the surrounding O-atom octahedra, and a negative deformation of up to 0.3 e Å-3 parallel to c between the nearest V-atom site across the faces of the O-atom octahedra. These observations are in accordance with theoretical band-structure calculations and confirm the existence of an eπ metal-metal bond which is directed across the common edges of the metal-centred O-atom octahedra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480013101
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  • 7
    Electronic Resource
    Electronic Resource
    Absorption-weighted mean path lengths for spheres (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 489-491 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Accurate values ( ̃0.05%) of the absorption-weighted mean path lengths for spheres as a function of μR and θ have been calculated by differentiation of the table of values of absorption corrections [Dwiggins (1975). Acta Cryst. A31, 395-396].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478001059
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  • 8
    Electronic Resource
    Electronic Resource
    The relation between the structures proposed for parawollastonite, β-CaO.SiO2 (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 938-941 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The two structures proposed for monoclinic parawollastonite [Tolliday (1958). Nature (London), 182, 1012-1013; Trojer (1968). Z. Kristallogr. 80, 291- 308] are in fact identical within the limits of experimental error. The nature of the relationship is discussed and it is shown that the equivalence is due to the specialized values of the y coordinates of all atoms in the structure. A review of the data sets used in the structure determinations, which allows a decision to be made on the true space group, is also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479002096
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  • 9
    Electronic Resource
    Electronic Resource
    Absorption and extinction corrections: standard tests (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 682-686 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The standard-test tables of values of transmission factors and {\bar T}, the absorption-weighted mean path lengths, given by Cahen & Ibers [J. Appl. Cryst. (1972), 5, 298-299; J. Appl. Cryst. (1973), 6, 244] and Alcock [Acta Cryst. (1974), A30, 332-335] have been corrected and extended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480001386
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  • 10
    Electronic Resource
    Electronic Resource
    Testing for serial correlation in intensity data (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 495-496 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An example of the use of the Durbin-Watson d statistic to test for positive and negative serial correlation is presented. It is found that the diffractometer data tested do not suffer from serial correlation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480001040
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