ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • International Union of Crystallography (IUCr)
  • 1980-1984  (5,963)
  • 1945-1949  (204)
  • 1925-1929
Collection
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1-7 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 54-57 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: X-ray investigations of Eu2+-rich precipitates in NaCl single crystals have revealed the presence of two phases. Phase A of chemical formula EuCl2 with a CaF2-type structure and lattice parameter a = 6.969 (2) Å preserves strictly the orientation of the matrix lattice. Phase B with the lattice parameter a = 7.47 (1) Å and tentative formula EuCl2.2NaCl, containing Eu2+ ions and charge-compensating cation vacancies, is localized at subgrain boundaries and is thermally less stable than phase A.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 68-74 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The present paper deals with the finding and the estimation of negative quartets. The use of symmetry is also discussed and the results obtained for four structures of increasing size are reported. Conditional probability distributions using magnitudes contained in the second representation of the quartets provides improved estimates of their phases.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 116-122 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The concept of disorientation, previously used for studying the statistical distribution of the relative orientation of identical cubic crystals, is defined in this work for any two lattices. Using the proposed definition, an algorithm is presented, allowing all the known relative orientations between the two lattices to be conveniently classed. As an example, a unified classification of the numerous mutual orientations of the Al and CuAl2 crystals is suggested. The unit quaternion method used by Grimmer [Acta Cryst. (1974), A30, 685-688] for identical cubic lattices is here proved efficient for discussing the pair axis/angle disorientations in more complicated cases: cubic 1/cubic 2; tetragonal 1/tetragonal 2; hexagonal 1/hexagonal 2; cubic/tetragonal; cubic/orthorhombic and cubic/hexagonal. The general expressions of equivalent quaternions are given for any point group of lattice 1 or lattice 2.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 122-126 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The controversial space-group problem of spinel, MgAl2O4, whether it is Fd3m or F{\bar 4}3m, was studied by electron diffraction. It was confirmed that the appearance of 'forbidden reflections' such as {200} was caused by the double reflection process of reflections with high indices on the non-zero-order Laue zone. Consequently, the space group of spinel is Fd3m, and the assignment of the space group to F{\bar 4}3m is ruled out. The change of space group from F{\bar 4}3m to Fd3m associated with a phase transition, proposed by Mishra & Thomas [Acta Cryst. (1977), A33, 678], can also be explained by double diffraction: the magnitudes of primary reflections with high indices rapidly decrease due to the increase of the Debye-Waller factors at elevated temperatures.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 143-146 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It is pointed out that there is some uncertainty as to the correct behaviour of the integrated reflectivity as a function of the degree of asymmetry for the scattering of X-rays from imperfect crystals in the extremely asymmetric Bragg case. Numerical calculations based on the Takagi-Taupin equations are exemplified and indicate that the integrated reflectivity for such crystals tends asymptotically to the perfect-crystal result in the asymmetric limits, the perfect-crystal result, in turn, tends to the kinematical value at these limits, as has been shown previously. In addition, comments are offered on the relevance of the present work to the study of highly imperfect crystals by section topography, and in particular to the study of the near-surface grain-boundary structure of crystals.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 147-148 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The mean Debye-Waller parameter {\bar {\it B}}of TlCl has been determined by double- as well as triple-axis neutron diffraction for a powder sample. Thermal diffuse scattering (TDS) corrections have also been made to the intensity of the diffraction peaks obtained by these techniques. TDS was found negligible in the triple-axis diffraction pattern as expected. The {\bar {\it B}} values thus found are 3.08 ± 0.43 and 3.07 ± 0.22 Å2, respectively, for double- and triple-axis methods. These values are in good agreement with those found by recent X- ray diffraction measurements.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 157-158 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 171-177 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Based on the new energy-transfer equations [Kato (1976). Acta Cryst. A32, 458-466; Kato (1979). Acta Cryst. A35, 9-16] the integrated intensities (II) are calculated. Since the energy-transfer equations have physical meanings different from the traditional ones originally given by Darwin [Philos. Mag. (1922), 43, 800-824] and extended by Hamilton [Acta Cryst. (1957), 10, 629-634], the method of calculating (II) must be modified, particularly in the case of a wide incident beam. Since the modified method does not include the angular integration, it is much simpler than the traditional method. Thus, the analytically rigorous expressions of (II) can be obtained for parallel-sided crystals including absorption, and for any diffraction conditions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 190-193 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: High-resolution electron microscopy can be used to differentiate between two structural models of long-period ordered alloys. These models differ in the nature of the disorder as seen in the stacking irregularities which can have planar boundaries as exemplified by Ag3Mg or wavy boundaries as in AuCu II. In the composition range 22-27 at.% Mg, Ag3Mg is built up with a regular arrangement of two kinds of structural layers, 1 or 2 L12 cells in thickness. Some stacking disorder exists, but this alloy can be locally described using a space-group notation and has the character of being an infinitely adaptative structure. High-resolution images have been used to show the perfect planarity of the boundaries in Ag3Mg, thus demonstrating the way in which disorder is accommodated in this alloy.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 333-333 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 334-334 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 344-350 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Retention of known geometry, with regard to mean atomic positions, has proved useful in the refinement of macromolecules. In structures with a paucity of diffraction data and large displacements of the atoms from their mean positions, it is also of value to restrain the thermal factors to be consistent with known stereochemistry. This paper presents a technique for accomplishing this by restraining the variances of the interatomic distributions (which are functions of the mean atomic positions and the thermal parameters) to suitably small values. This procedure allows meaningful anisotropic refinement of macromolecules to be carried out with low-resolution diffraction data. Anisotropic thermal parameters obtained in this way should prove useful in understanding the dynamics of the biological functions of macromolecules.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 353-356 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: From careful measurement and indexing of the powder diffraction patterns obtained for pure dicalcium silicate, unit-cell parameter vs temperature plots have been obtained covering the β and α' dicalcium silicate phases. It is found that these phases are all closely related, the temperature variations, for example, being gradual from 293 K (the β phase) and more discontinuous between 993 and 1043 K corresponding to the β = α'L transition. Our conclusions lead to a simplified dicalcium silicate transformation scheme which requires that there is no phase differentiation within the β-phase regime.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 372-378 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The ordered domain structure present in the α-phase Cu-Al alloys investigated by Epperson, Ffirnrohr & Ortiz [Acta Cryst. (1978), A34, 667-681] is determined by an extension of the computer method developed recently by Epperson [J. Appl. Cryst. (1979), 12, 351-356] for analyzing a Gehlen-Cohen type simulated structure for a binary, f.c.c., locally ordered alloy in terms of nearest-neighbor atomic configurations. The dominant ordered feature of the more concentrated of these alloys is the existence of randomly dispersed Boric-Sparks tetrahedra; that is, four nearest-neighbor Al atoms arranged tetrahedrally about a Cu atom. The majority of these tetrahedra are isolated; however, as many as three or four are occasionally found to be joined in fragments of a Cu3Au-type antiphase-shift structure. This extended ordered structure also incorporates the Cu3Au-type ring configuration, another principal characteristic structural feature of these Cu-Al alloys. As a typical example, a Cu-14.76 at.% Al alloy quenched from 923 K and annealed for 1580 h at 423 K was found to contain 87 such locally ordered regions in an 8000-atom model. Of these 'domains', 74 were isolated tetrahedra and the remainder consisted of pairs of tetrahedra joined such that their central atoms were mutual second-nearest neighbors. For this alloy and heat treatment, the locally ordered regions of this type amount to about 14 volume % of the microstructure and contain 32% of the Al in the alloy. The average (spherical) domain size is only 3.4 Å. Not only are the locally ordered regions very small, but there are also perceptible imperfections in the packing sequence.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 470-475 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method of using quartets and quintets in the direct-methods program MULTAN is described with several successful applications.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 330-330 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 331-332 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 334-334 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 496-496 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In Agarwal [Acta Cryst. (1978), A34, 791-809], equation (61) should read: c3 = 2Cm1 Cm2. All information is given in the Abstract.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 499-500 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 502-502 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 520-530 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 573-578 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Some algorithms have been derived to calculate the expected values of one-phase seminvariants of first rank in space groups up to orthorhombic by a probabilistic approach [Giacovazzo (1978). Acta Cryst. A34, 562-576]. The method has been tested on several known structures. The results show how the method can secure a very reliable estimate for a limited number of one-phase seminvariants which can be used from the initial stages of phase determination. In addition, the estimated values can be used as a good figure of merit to select the correct K2 solution in a multisolution procedure.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 600-604 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Extinction effects in white-beam X-ray and neutron diffraction are considered following the formulation developed for monochromatic-beam diffraction by Becker & Coppens [Acta Cryst. (1974), A30, 129-147]. In white-beam diffraction, a small deviation of the wavelength from the Bragg condition Δλ is a variable which represents the line profile of the diffraction peaks, so that by using the new parameter Δλ the theory is converted to one in white-beam diffraction. It is shown that for a convex crystal, primary extinction yp agrees with the results calculated already for monochromatic diffraction. The same relation is shown to hold in secondary extinction ys. It is concluded that extinction theory derived for monochromatic diffraction is applicable without any modification in white-beam diffraction.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 620-624 
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 653-656 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Direct methods are applied to difference-structure factors for a structure containing one or more heavy atoms at known special or pseudo-special positions, such that the heavy atoms do not contribute to several reflection parity groups. Phases of reflections in these parity groups, represented by symbols, are analysed by the sign-correction method. Phases as well as amplitudes of the difference-structure factors are refined by the general DIRDIF procedure as described previously.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 74-82 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A phase relationship involving triplet and quartet contributions is given. It is able to take account of the correlation between triplet and quartet relations. The information exploited by the formula is discussed and compared with that exploited by phase relationships arising from the properties of the Fourier transform of periodic positive functions. In particular, the information contained in a Karle-Hauptman determinant of low order is briefly considered.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 57-67 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Two approximations that are commonly used to describe the scattering of high-energy electrons are the first Born approximation (kinematic approximation) and the closely related 'weak phase-object' approximation. The quantitative domains of validity for the use of these two scattering approximations for structural analysis of organic crystals are evaluated numerically in terms of resolution, crystal thickness and incident electron energy. The resulting calculations show how progressively important dynamical scattering effects lead to an increasingly large contribution to the R value in a structure factor analysis. Alternatively, the results show that an increasing dissimilarity is produced between the structure inferred from electron microscope images and the correct structure. The results also show that the actual images (and the structure inferred from the images) remain qualitatively similar to the projected Coulomb potential, even though dynamical scattering effects may lead to a large quantitative dissimilarity relative to the correct structure.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 96-103 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of sodium chloride has been studied by gas-phase electron diffraction using photographic plates designed for high-temperature work [Kakumoto, Ino, Kodera & Kakinoki (1977). J. Appl. Cryst. 10, 100-103]. The molecular structure at about 1130 K has been determined by an analysis based on the new complex scattering factors for Na+ and Cl- calculated recently by the present authors. The radial distribution function shows the existence of a considerable amount of dimer molecules in the vapor. The structures of the monomer and dimer have been analyzed by a least-squares method assuming that the dimer is of a planar diamond shape: for monomer ra(Na--Cl) = 2.392 ± 0.028, for dimer ra(Na-Cl) = 2.515 ± 0.017, ra(Cl-Cl) = 3.893 ± 0.021 Å, ∠ClNaCl = 101.4 ± 0.8°. The present study indicates that the Na--Cl distance of the dimer is longer than that of the monomer and the determined structure parameters differ appreciably from existing theoretical predictions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 741-746 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The cation distribution of the compounds (Fe0,5Ta0,5)O2 and (Fe0,45Nb0,53)O2 has been redetermined by the combined use of neutron and X-ray powder diffraction. Analysis of the powder patterns showed that the compounds are isostructural, their structure being of the rutile-type AO2. The cations are statistically distributed. There exists no partial ordering, neither of Fe and Ta nor of Fe and Nb. Neutron diffraction patterns taken at 4.2 K showed only one magnetic reflection, which is strongly broadened. The magnetic structure of (Fe0.5Ta0.5)O2 is of MnF2-type, whereas (Fe0.45Nb0.53)O2 orders in the BEY-structure. Profile analysis of these broadened reflections was carried out with the convolution integral of a Gaussian with a Lorentzian function, from which correlation lengths could be derived.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 156-156 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The Abstract by Modlin & Rodgers [Acta Cryst. (1978), A34, S4, 381] was submitted without the knowledge of the present author, who was not aware of its content. Only preliminary discussions and work on certain aspects of a research programme had taken place at the time that the Abstract was submitted. The conclusions claimed in the last sentence had not been arrived at.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 155-156 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The scattering factors of the 1s22s22p6 core for K+ and Cl- have been calculated from analytical wave functions and also with one-term Gaussian representations. These scattering factors, together with the experimental structure factors, have been used to obtain, by difference Fourier inversion, the valence-electron charge distributions of KCl in the [100], [110] and [111] directions. By comparison, a very simple one-term Gaussian representation has been shown to yield reliable results.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 157-157 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In Bertaut & Dulac [Acta Cryst. (1972), 28, 580-588], for clerical reasons an error has crept in so that the numerical moment values of y and z components of Cr1 are to be interchanged. One should read in the Abstract and in relation (8.9): Sz(Cr1) = -0.73 (instead of -0.45); sy(Cr1) = 0.45 (instead of + 0.73).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 819-826 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: All geometric units in crystal structures of space groups P{\bar 4}3m, I{\bar 4}3m, Pn3m, F{\bar 4}3m and Fd3m possess point group {\bar 4}3m. These units may be vacant, or may contain one or more atoms. In units containing more atoms than one, the atoms form one or a collection of these polyhedra: tetrahedron, truncated tetrahedron, octahedron, cuboctahedron or truncated octahedron; the last two may be distorted. Therefore, a formula that lists the consecutive polyhedra starting from the center of the unit can be used for the tabulation of these crystal structures. Only structures of Cu2O type are known in Pn3m and typical structures of the other four space groups are tabulated.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 830-830 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The equivalence relationships for general planes (or reflexions) in Laue class {\bar 3}1m are different from those for Laue class {\bar 3}m1. Table 3.5.1 of International Tables for X-ray Crystallography [(1969). Vol. I. Birmingham: Kynoch Press] makes no allowance for these differences. The necessary corrections are given.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 834-834 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 835-836 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 836-836 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 851-856 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: New twin domains of thickness of the order of a few micrometres can be created in KClO3 crystals by applying a small uniaxial stress. The observed domain structure can be explained by postulating a hypothetical prototype phase of symmetry 4/mmm. The magnitude of spontaneous strain, σs, for the room-temperature monoclinic phase, computed on the basis of the postulated tetragonal prototype, has an exceptionally large value of 0.257. Further, σs varies linearly as the square root of temperature, implying a mean-field-like behaviour. However, presumably because of the very large spontaneous strain, attempts to move the domain walls back and forth by applying uniaxial stress (at room temperature) have not yet been successful, and the question asked in the title may be a matter of definition.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 198-205 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A systematic theoretical analysis is made of the kinds of structural irregularity which occur in biological systems. The theoretical problems investigated were: (1) the precise meaning of the term 'paracrystal' when applied to biological systems such as tropomyosin tactoids, collagen fibrils, keratin and the myelin sheath of nerve; (2) the relationship between the paracrystal and liquid-theory descriptions of disorder which have recently been applied to the structure of collagen fibrils; (3) how structural irregularity affects the diffraction patterns (X-ray, neutron and electron) which are commonly used to investigate the structure of these systems experimentally. The conclusions are: (I) paracrystalline disorder of the first kind refers to a spatially disordered crystal but for biological systems it would generally be impracticable to distinguish this from thermal disorder; (2) paracrystalline disorder of the second kind provides a conceptually clumsy method for describing liquid-like systems; (3) paracrystal models are not strictly valid for finite systems; (4) modern liquid theory, as applied, for example, to the structure of the collagen fibrils, provides an elegant and economical alternative to paracrystal theory for disorder of the second kind; (5) the presence of peaks in diffraction patterns from biological systems does not necessarily imply that the system has very much regularity, i.e. it is not evidence for the existence of a lattice.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 228-237 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Ternary oxides AMO2, A2MO3 and A5MO6 with monovalent A and tri-, tetra- or hepta-valent M metals can exhibit order/disorder transitions with about 20 superstructures of the NaC1 lattice. Some structures can be related to AM, A2M and A5M alloys with a larger distortion of the lattice due to stronger interactions between metal atoms. In ternary oxides about 30 short-range order configurations are selected for the first, second and third shell of metal atoms in applying Pauling's electrovalence rule. Stable configurations are characterized by the strength of Coulomb interactions and by a high point symmetry of the M atoms. Mainly disordered ternary oxides can vary stoichiometrically with a frequent occurrence of vacancies or with partial occupation of tetrahedral interstices by A atoms.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 259-265 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A statistical distribution of ions M in lattices or partial lattices ∞[A1 - xMxLm] of mixed crystals being assumed, the probability functions PJ(V)(x) for single coordination polyhedra MLn (j = 1), pairs (j = 2) and larger clusters of MLn groups (j 〉 2) in 1D (v = 2) and v-connected 2D systems (v = 3, 4, 6) are calculated. On raising the connecting number v, increasing cluster probabilities are distinctly shifted to lower concentrations x of the foreign ion M. For a relation between the numerical values P(x) and experimental results, the mixed-crystal series (BaF)2[Zn1 - xCuxF4] of a four-connected 2D structure is given as an illustrative example.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 282-287 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Oriented specimens of biomembranes give distinct X-ray diffraction patterns of circular symmetry along the equatorial plane. In order to interpret such a diffraction pattern, properties of the radial autocorrelation function were examined in detail in conjunction with electron-density distribution and applied. The radial autocorrelation function, which is the Fourier-Bessel transform of an intensity function with circular symmetry, is the radial projection of a two- dimensional autocorrelation function and can be interpreted in terms of Fourier components of electron-density projection along the membrane normal. Some useful information is obtainable on the structure of the scatterer: (i) the approximate size of the X-ray scatterer; (ii) judgement of crystalline or non-crystalline arrangement of molecules; (iii) the existence of a regular arrangement of the electron-density fluctuations in a projection along the membrane normal; (iv) the rotational symmetry element existing in the scatterer if any.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 299-303 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The pressure dependence of the lattice parameters of PdZn having an L10-type structure has been measured up to 24 GPa (240 kbar) with a diamond-anvil-type cell and sodium chloride as an internal-pressure marker. The axial ratio c/a, which was originally 0.814 (1) [between the two extreme values 1.00 and 0.707 (= 1/ \sqrt{2}) for this type of structure], does not decrease but increases with increasing pressure and after reaching 0.822 at 10 GPa it remains almost constant on further compression. The equation of state has been derived for the L10-type structure assuming pairwise interactions between like atoms and between unlike atoms and comparison is made between the calculated and observed compression curves of the a and c axes. The anisotropy in the lattice compressibility leads to a considerably larger interatomic potential for the unlike atom pair than for the like atom pair.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 442-450 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Formulas are derived extending several semi-empirical absorption-correction methods to diffractometers operating in Weissenberg geometries, with particular attention paid to flat-cone geometry. These formulas are useful for a variety of instruments using both area and linear position-sensitive detectors. While a complete data set can sometimes be corrected using a single absorption reflection, it was found that the best corrections are usually obtained by considering two absorption reflections rather than one. A discussion of the optimum choice of absorption correction when a crystal has at least a twofold symmetry axis is presented. The accuracy of the methods and the limits of applicability have been examined by computer simulations.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 436-442 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Both real and imaginary components of the anomalous X-ray scattering were measured by single-crystal diffraction experiments with synchrotron radiation at wavelengths through the region of the three L absorption edges of cesium, the first such experiment for any element at the L edges. Near the L3 edge f' varies between -26.7 and -13.9 and f" between 4.0 and 16.1 electrons in a wavelength interval of 0.008 Å. Similar but smaller changes occur near the L2 edge, and still smaller ones at L1. Fine structure in the f" curve corresponds to that observed in an absorption curve and also, by a dispersion relation, to fine structure in the f' curve. These effects offer promise as a substitute for isomorphous replacement for solving the phase problem for macromolecular crystal structure. Similar experiments with cobalt near the K edge give f' values in agreement with measurements by other workers for nickel and copper by different methods at corresponding wavelengths; the lowest value observed is f' = -7.5 electrons.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1065-1070 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A systematic investigation of the effect of phase errors of different types on E maps is presented. Both random and systematic errors have been considered with distributions depending in different ways on the resolution of the data. Considerably large random errors can be tolerated without great loss of structural information in the E maps, while smaller systematic errors have greater destructive effects. These effects are explained by the introduction and analysis of a phase-error function.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1072-1088 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1093-1093 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1094-1094 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 904-915 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Based on accurate X-ray diffraction intensity data collected from spherically shaped single crystals, net atomic charges and electron density distributions have been studied for MnO, Mn2SiO4, Mg2Si2O6, LiAlSi2O6 and CaMgSi2O6. Examination of various procedures for determining atomic charges in a given structure has led to the conclusion that the following approach appears to be most reliable. (1) For cations: the number of electrons in the sphere of radius ER, effective distribution radius, which is defined according to the characteristics of radial distribution functions or difference-Fourier maps, is calculated. (2) For oxygen atoms: with the cation charges fixed at the values obtained from the above procedure and the total charge of the crystal constrained to be neutral, oxygen charges are estimated from least-squares refinements using atomic scattering factors. The final charges of atoms examined are less ionic than the corresponding formal ones: those of Li, O, Mg, Al, Si, Ca and Mn are respectively + 0.7 (1), -1.1 to -1.5, + 1.4 (1) to + 1.8, + 2.4(1), + 2.2 (1) to + 2.6, + 1.4 (2) and + 1.2 (1) to + 1.6 e. Residual electron densities between Si and O have been clearly observed in difference-Fourier maps after charge refinements for crystals of LiAlSi2O6, CaMgSi2O6 and Mg2Si2O6.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 937-944 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Beu, Musil & Whitney [Acta Cryst. (1962), 15, 1292-1301; Acta Cryst. (1963), 16, 1241-1242] proposed a maximum-likelihood method of estimating the lattice parameters of cubic, tetragonal and hexagonal crystals, and a method of testing the hypothesis that systematic errors had been satisfactorily accounted for. The use of maximum likelihood is unnecessary, and open to some objection. The argument is therefore rewritten in the more familiar least-squares form, and is generalized to cover the remaining crystal systems. Only if systematic errors are absent is it legitimate to estimate standard deviations of parameters from the differences of observed and calculated Bragg angles. With minor modifications the results are applicable to structural parameters also.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 945-946 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: If dispersive atoms are present the structure factor of a centrosymmetric crystal is not purely real, and the probability distribution of the modulus of the structure factor becomes P(F)dF = ( 2F/μ) exp (-ΣF2/μ2)I0(SF2/μ2)dF, where Io is the modified Bessel function of zero order, Σ is the sum of the squares of the moduli of the atomic scattering factors, S is the modulus of the sum of their squares, and μ is (Σ2 - S2)1/2. For a non-centrosymmetric crystal the form of the distribution is not altered, but Σ must be defined as in the preceding sentence.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 975-978 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The comparison of molecular structures is facilitated by a combination of graphical and numerical techniques. Conversion to a molecular reference frame makes the linear relationships between the molecules or fragments easily visualized, and can be used to produce diagrams clearly displaying the molecular similarities and differences.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1002-1013 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The results of experiments in which an anomalous form of the Pendellösung fringes has been discovered together with a classical one are presented. The general theory of X-ray spherical-wave diffraction has been constructed taking into account the change of phase relationships for radiation propagating in vacuum. An explanation of the observed experimental results and classification of possible manifestations of the Pendellösung effect are given. New data concerning the previously discovered phenomenon of focusing are presented.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 989-996 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The results of an investigation of the polarization coefficient of X-ray radiation diffracted in real crystals are given. The form of the angular dependence of the polarization coefficient in the range of the Bragg reflection is found to be qualitatively different in the cases of primary and secondary extinction. It allows the unambiguous identification of the type of extinction in the crystal. On the basis of the experimental data analysis of the polarization coefficients for silicon and germanium crystals with different dislocation densities, it is shown that the mosaic model of a crystal is suitable for describing X-ray scattering in real crystals if the dislocation density is higher than 104 mm-2 and in practice only primary extinction is present in mosaic crystals. An expression is given for the primary extinction factor for the mosaic crystal, obtained on the basis of the solution of the Takagi-Taupin equations for finite crystals. This expression was used for the analysis of the LiF and NaF structure factors measured by different authors. The effective size which was obtained for the domains appeared to be physically reasonable and to be directly connected with the value of the dislocation density in the crystal.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1025-1030 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Pendellösung intensity beats of white radiation diffracted from parallel-sided single-crystal wafers of silicon were measured by a solid-state detector. After a few corrections, the extremum positions in the beat were measured to evaluate the atomic scattering factors for various reflections. The scattering factor shows a dependence on wavelength, λ, which can be interpreted by the anomalous dispersion term, f', as calculated by Cromer [Acta Cryst. (1965), 18, 17-23]. The obtained values of the atomic scattering factor expressed as linear functions of wavelength are listed with those at λ = 0.5594 Å for comparison with the data so far obtained with Ag Kα1 and wedge crystals. The values for 111 and 220 reflections in the present experiment, 10.59 and 8.40, were almost the same as Tanemura & Kato's [Acta Cryst. (1972), A28, 69-80], 10.664 and 8.463, respectively.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1050-1057 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The direct-analysis formalism of Kurki-Suonio [e.g. Isr. J. Chem. (1977). 16, Nos. 2-3, 115-123, 132-136] is modified to apply to the calculation of nuclear distributional moments 〈xλyμzv〉, which are linear combinations of the multipole moments 〈rkylmp〉. They are integrated from the radical coefficients of the corresponding multipole terms through Gaussian and difference series procedures. An application to the thermal neutron diffraction structure factors of Merisalo & Larsen [Acta Cryst. (1977). A33, 351-354] on zinc indicates that the moment 〈x2〉 agrees with the anharmonic result of Merisalo & Larsen 〈z2〉 does not show discrepancy with the value based on harmonic assumption. The existence of the third-order component in the nuclear smearing function and, due to this, anharmonicity of thermal motion is well established, but the magnitude of 〈x3〉 is not accurately defined on the basis of the present data. The ratios of the fourth and second moments do not reveal deviation from harmonic thermal smearing.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1071-1071 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Corrections are given to §§ 4.3 and 4.4 of International Tables for X-ray Crystallography [Vol. I (1969), Birmingham: Kynoch Press].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1090-1091 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1091-1091 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1095-1095 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1096-1096 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 211-219 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: For explaining diamagnetic effects observed in condensed aromatic compounds, their molecular diamagnetic anisotropies must be known. A method is proposed which, on the basis of relatively accurate structural data and of two experimental crystal anisotropies, allows the determination of molecular anisotropies in the plane and perpendicular to it. For monoclinic compounds whose magnetic tensor has no revolution symmetry, it is necessary to correct to first order the orientation of the principal magnetic axes of the crystal with respect to revolution symmetry. The proposed method is applied and discussed in the case of ten condensed aromatic compounds which crystallize in the orthorhombic and monoclinic systems. It yields, in some cases, molecular anisotropies very different from those suggested by different authors. One very simplified model produces results which fit in with the molecular anisotropies obtained as long as the arrangement of the rings is not too complex.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 219-226 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Diffuse X-ray scattering in Li3N has been investigated in the range 293 to 880 K with monochromatic Mo Kα radiation. Crystal and film were fixed during the exposure. Diffuse intensity in the form of rods and discs was found. It increased with increasing temperature but without change of its features. The diffuse intensity distribution was calculated for various temperatures on the basis of an anisotropic shell model. Good agreement with the experimental results was achieved. The anharmonic effects detected in the difference electron density were studied taking into account split positions for the Li ions. This simulation leads to only minor changes in the calculated intensity distribution which indicates that the diffuse intensity of Li3N is mainly caused by harmonic lattice vibrations.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 641-653 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Within certain good approximations the probability distribution function (p.d.f.) used to describe mosaic-block orientation in secondary-extinction models is exactly analogous to the p.d.f. for atomic thermal motion in the harmonic approximation. Use is made of this relationship to explain carefully, with the aid of several diagrams, certain distinctions and relationships common to both p.d.f.'s - which if not properly understood can lead (and have led) to some important confusions. For example, if the three-dimensional p.d.f. is Gaussian, surfaces of constant probability density are ellipsoidal (e.g. the thermal-vibration ellipsoid); but the scattering process 'sees' this p.d.f. as a one-dimensional projection, the half-width of which lies on a fourth-order surface (shaped, for example, like a peanut shell). For extinction it is shown explicitly that the form of this projected one-dimensional function is independent of experimental conditions (e.g. collimation), and that an earlier form [Coppens & Hamilton (1970), Acta Cryst. A26, 417-425], still commonly used and tested, is always incorrect. Apart from the intentional restriction of the detailed analysis of secondary extinction to type I extinction (in which mosaic-block orientation is the dominant effect), the approximations adopted are shown to have a wide range of validity. The (unusual) conditions under which the approximations may be sufficiently invalid to produce detectable effects are examined qualitatively in relation to the possibility of experimental investigations.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 697-704 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A numerical method is developed for calculating the thermal diffuse scattering (TDS) correction from phonon inelastic scattering in a neutron diffraction pattern measured by the time-of-flight method. The correction is evaluated for a nickel powder spectrum at room temperature. It is shown to be more important than had been suggested previously. It gives rise to a reduction of the apparent Debye-Waller factor by about 10%. It may also lead to the appearance of the higher-order Debye-Waller factor previously ascribed to anharmonicity.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 732-734 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A simple method is given for deriving the triclinic-cell parameters from three general reflections by vertical or horizontal measurements on upper-level films.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 739-740 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 740-740 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 267-268 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Recent experimental measurements have revealed systematic differences between measured values of f' and those calculated by the method of Cromer & Liberman [J. Chem. Phys. (1970), 53, 1891-1898] when the incident X-ray is near to and on the long-wavelength side of an edge. The source of the discrepancy has been identified and some previously published values of f' are corrected. These corrections also apply to Table 2.3.1 in International Tables for X-ray Crystallography, Vol. IV [(1974), Birmingham: Kynoch Press].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 269-269 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 796-800 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Derivative lattices are related to one another by transformation matrices having rational elements. A simple algorithm for finding these matrices consists in testing if the scalar products of the vectors defining two arbitrary primitive cells of two lattices can be exactly or approximately related by equations with rational coefficients. A rational relationship indicates that two or more lattices have a number of geometrical features in common such as common superlattices, sublattices, etc. The algorithm can, therefore, be applied to a variety of crystallographic problems such as the study of twinning, the indexing of powder patterns, single-crystal diffractometry and the critical evaluation of crystal data. Five examples are discussed in detail.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 916-921 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A neutron diffraction study of Debye-Waller factors has been performed on ThC and ThC0.77 powder samples at 4 and 250 K on the high-resolution diffractometers D1A and D1B of HFR (Grenoble); 25 diffraction lines were resolved and analysed with wavelength λ = 1.21 Å on D 1A, and 22 lines with λ = 1.28 Å on D1B. In the case of ThC, it is shown that the results (BTh = 0.07 ± 0.05 Å2 and BC = 0.40 ± 0.08 Å2 at 4 K; BTh = 0.32 ± 0.08 Å2 and BC = 0.68 ± 0.08 Å2 at 250 K) are mainly due to the thermal vibrations. For ThC0.77, we find BTh = 0.23 ± 0.03 Å2 and BC = 0.47 ± 0.05 Å2 at 4 K, and BTh = 0.48 ± 0.04 Å2 and BC = 0.69 ± 0.05 Å2 at 250 K. The enhancements of the Debye-Waller factors compared to the stoichiometric case are attributed to the static distortions induced by the presence of 23% vacancies in the carbon sublattice. The mean-square static displacements of thorium and carbon atoms are found to be about 1% of the lattice parameter \sqrt{\langle \Delta x^{2}\rangle _{\rm Th} = 0.08 ± 0.03 Å and \sqrt{\langle \Delta x^{2}\rangle _{\rm c}\simeq _{\rm Th} 0.05 ± 0.03 Å.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 966-974 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It has been observed that the reflectivity of the (110) planes of a quartz lamina can be increased by submitting it to a static or alternating electric field. Measurements have been performed on 2.5 and 6 mm thick plates using a curved-crystal spectrometer with DuMond geometry. Photon energies were in the range 50 to 300 keV. Under the proper conditions, the increase in reflectivity is accompanied by negligible loss in resolution. The effects are explained by the occurrence of a quasi-mosaicity.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 77
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 996-1001 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Small-angle scattering experiments of horse-spleen ferritin solutions have been performed at various wavelengths near the K absorption edge of iron, using synchrotron radiation from the storage ring DORIS. The anomalous dispersion of the atomic form factor f as described by f' and if” has been monitored by the dependence of the radius of gyration R and the absorption coefficient μ respectively. There is a 4% increase of R at the absorption edge. The relative full half width of this peak of 0.0016 corresponding to 1 1 eV of the energy scale reflects the drastic variation of f' by 7 electrons. The predictable relation between R and has been verified by the Kramers-Kronig relation. As small-angle scattering is primarily influenced by f', best advantage from anomalous dispersion in small-angle scattering can be taken by measurements very near the absorption edges.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 78
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1017-1025 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The theory of representations has been used to obtain probabilistic estimates of the two-phase variants and seminvariants for the non-centrosymmetric space groups up to orthorhombic. Some practical applications show that the phase estimations can be useful in direct procedures, mostly for those crystal structures in which the enantiomorph definition is difficult.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 79
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1041-1043 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In MX2-type structures atoms are always in a sandwich form with an M atom surrounded by two X atoms. The orientation of the M atom is always determined by the two X atoms, e.g. an M atom with γ orientation will always have two X atoms in A and B (or B and A) orientations around it. Therefore, by representing both X atoms by one M atom, the calculation can be reduced to one third of the original since the summation in the structure-factor calculation over all atoms will reduce to the summation over M atoms only. How this can be done is examined in the paper.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 80
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 335-342 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Owing to progress in lattice-dynamical computing routines, free-energy calculations for perfect molecular crystals are no longer prohibitive in the quasi-harmonic approximation. Thus the consistent derivation of an equilibrium conformation at various temperatures and pressures, and even the stability range of various phases, may become a routine possibility, starting from semi-empirical potentials only. An example of such conformational calculations is given and discussed for the tetragonal phase of adamantane at 163 and 1 K. The effect of vibrational energy (even zero-point) and entropy upon molecular orientation and position in the unit cell is shown not to be negligible by several examples. This precludes the possibility of calculating the cell parameters on free-energy grounds and the molecular coordinates by considering the minimum packing energy. For crystals with molecules fixed by symmetry, the quasi-harmonic approximation becomes particularly appropriate, since in this case for any unit cell the first derivatives of energy with respect to any molecular shift are zero. Some critical steps of such calculations are examined and discussed, especially in connection with converging processes. No particular problem is encountered in sampling the Brillouin zone, because only a limited number of points is necessary. Convergence of lattice sums to obtain packing energy is more critical, although for most practical purposes a maximum packing distance of 15 Å is sufficient. The real difficulties of these calculations consist in the need of considering many degrees of freedom at once, and also in the inadequacy of present-day semi-empirical potentials.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 81
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 361-364 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: All 20 independent third-order elastic constants (TOEC) of orthorhombic calcium formate, Ca(HCOO)2, Ca2+. C2H2O2-4, space group Pcab, have been determined with the aid of stress-induced shifts of ultrasonic resonance frequencies. Longitudinal and transverse effects possess negative values indicating the high stability of calcium formate over a wide pressure range. The anisotropy of TOEC, characterized by --c111 〉 --c333 〉 --c222, corresponds with the anisotropy of second-order elastic constants (c11 〉 c33 〉 c22). The value 5.22 for the pressure derivative of the inverse bulk compressibility coincides with the quasi- invariant value of ca 5 observed in most stable cubic crystals so far investigated. There exists a pronounced departure from third-order Cauchy relations: the 'transverse' constants exceed the corresponding 'shear' components considerably in absolute magnitude in accordance with the behaviour of the second-order Cauchy relations. These effects are explained as originating from the non-centrosymmetric formate ions. A comparison of TOEC of calcium formate and cubic calcium fluoride confirms the typical contribution of the formate ions to the third-order elastic behaviour.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 82
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 281-286 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A synthetic pyroxenoid of nominal composition MnFeSi2O6 has been produced in the glassy state and examined by high-resolution electron microscopy after periods of annealing of from two to sixteen hours at 1070 K. Initially highly defective structures exhibiting large chain repeat distances are produced, but on further annealing the five-tetrahedra chain repeat of rhodonite predominates. (110)-type stacking faults are frequently observed. In most eases these faults involve considerable disruption of the lattice, but in certain instances the stacking fault displacement is equal to the rhodonite lattice repeat and the faults are visible only if the chain periodicity varies. In the latter case, the structure shows a two-dimensional ability to accommodate defects, and models for this, involving chain breaking and/or chain branching, are proposed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 83
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 286-292 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: This article contains a table of the groups of combined geometrical and color-permutational symmetry operations that leave a certain kind of three-colored, three-dimensionally periodic object apparently unchanged. The asymmetric units - 'motifs' - of the object are all either geometrically congruent to, or are mirror images of, one another. Each motif has a 'color' representing a scalar quality of some kind, and three different colors of motifs are assumed to occur in the object. Two types of three-colored space groups exist: type I in which all of the geometrical lattice translations leave all the motifs unchanged in color, and type II in which at least one of the geometrical lattice translations requires a permutation of the three colors in order to restore the original appearance. There are 88 three-colored space groups of type I, and 341 of type II. Type I can belong only to the trigonal, hexagonal and cubic systems; type II can belong to any system, except the cubic. A notation for the three-colored, three-dimensional space groups is proposed. It is based on similar principles to those used in the article on colored point groups by Harker [Acta Cryst. (1976), A32, 133-139].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 84
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 309-314 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The Fourier transform of a finite coiled coil containing an integral number of repeat units is evaluated analytically. The special cases where the coiled coil reduces either to a pure helix or to a toroidal helix are specifically included.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 85
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 324-331 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Two of the magnetic superlattice Bragg reflections of a single crystal of hematite (Fe2O3) have been measured by diffraction of X-rays produced from a conventional source, and compared to the intensities expected from the photon-spin scattering. Several orientations of the spins relative to the beams have been realized by rotating the crystal and by changing its temperature through the Morin (spin-flip) transition; in some of the measurements, the polarization produced by the monochromator was enhanced and this produced a visible asymmetry in the dependence of the intensities on the spin direction. The variations of the intensities during these changes of configuration are characteristic of magnetic scattering; the observed variations, as well as the absolute intensities, agree with the theory apart from some discrepancies. These may be due to intense multiple-scattering effects, and to some possible anomalies in the spin direction near the sample surface. As an application of this technique, changes of the direction of magnetization when a magnetic field is applied to the weakly ferromagnetic room-temperature phase have been investigated.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 86
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 407-413 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It has been found that the crystallization of oxyhaemoglobin from polyethylene glycol solutions [Grabowski et al. (1978). Biochem. J. 171, 277-279] yields at least three different forms of isomorphous crystals (P21212, a = 96.66, b = 97.88, c = 65.40 Å). 3.5 Å resolution data have been collected for two of the three identified forms. The orientations and positions of the αβ haemoglobin dimers within the asymmetric units of these crystals have been established by the molecular replacement method with computing techniques different from those used by Ward, Wishner, Lattman & Love [J. Mol. Biol. (1975), 98, 161-171] in their studies of human deoxyhaemoglobin crystals obtained from polyethylene glycol solutions. The calculations have been performed also with diffraction data from deoxyhaemoglobin and fluoromethaemoglobin + inositol hexaphosphate crystallized from polyethylene glycol by Fermi & Perutz [J. Mol. Biol. (1977), 144, 421-431]. In all cases, the individual dimers have been positioned independently and it is shown that, in the methods using a fast rotation function, three- and multidimensional residual-type translation functions may be directly applied to the structure determination of those complex structures in which the structure of only one of the two subunits present in the asymmetric unit is known. It is also shown that in all crystals studied the haemoglobin dimers are arranged in the \cal Y conformation, which seems to exclude the possibility of the full oxygenation of haemoglobin crystallized from polyethylene glycol solutions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 87
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 430-436 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A simple computer program for the simulation and analysis of X-ray back-reflection Laue photographs of a single crystal with any structure and orientation has been developed in Fortran IV. Comparison of computer plots of the calculated patterns with the photographs enables rapid identification of approximate orientation. The program may ultimately be used to index an orientation from the identification of at least three spots from the photographs. The procedure incorporating use of the program requires only minimal knowledge of crystallography or computer methods.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 88
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 153-162 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Theoretical expressions for the complementary cumulative function of the Bijvoet ratio X applicable to a truncated data set are worked out for a non-centrosymmetric crystal containing P anomalous scatterers in the unit cell [P = 1 and many (MN and MC cases)] besides a large number of normal scatterers. These expressions contain the truncation limit yt as a parameter of the distribution. The results obtained are used to discuss the effect of data truncation arising from the non-observability of extremely weak reflections on the measurability of Bijvoet differences.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 89
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 566-572 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Long one-dimensional magic-integer sequences are used to express the phases of 10-20 primary reflexions. The magic-integer representation of phases is extended to other secondary reflexions through strong triple- phase relationships involving one secondary and two primary reflexions. In the MAGEX procedure multiple magic-integer representations of the secondaries are sought and the error involved in their subsequent use in a conventional ψ map is much reduced. In view of the large number of primary reflexions the indices of the terms included in the ψ map are large and maps may be computed at up to 220 points. Further reflexions, in batches of ten or so, may be added to the initial set by the further use of magic integers and small-scale maps. When the base of estimated phases is sufficiently large then the phase information is extended by the controlled use of the tangent formula. Examples of the successful application of MAGEX are described.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 90
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 578-584 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: FeSiF6.6H2O above 240 K is described following the structural model previously proposed for MgSiF6.6H2O above 300 K: periodic antiphase built on the ordered monoclinic cell of the low-temperature form. In the present case a progressive ordering is observed and the antiphase boundaries are no longer planar but exhibit steps which lead to a mean boundary canted with respect to the c hexagonal axis (space group P3). Above 240 K a phase transformation occurs with a threefold twinning and a significant lattice deformation. The monoclinic cell (P21/c) is described.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 91
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 594-604 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A technique for improving the precision of crystal data collected on films or with electronic position-sensitive detectors is proposed. The extent of each medium or strong reflection is computed independently, after smoothing and filtering the individual intensities, producing a variable 'dynamic mask'. A method of calculating universal background profiles, which preserves the data and limits the necessary storage, is introduced. The method was applied to data collected with X-ray precession and oscillation techniques and to neutron data collected with a fiat-cone diffractometer equipped with a linear detector. In all cases substantial improvement in the precision of weaker reflections was observed. The overall quality of the data was particularly enhanced in the neutron diffraction case.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 92
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 145-153 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Mixed crystals Pb3(PO4)2--Pb3(AsO4)2 are ferroelastic at low temperatures. The phase diagram contains three different phases a (paraelastic), \tt b and \tt c (both ferroelastic). The transformation \tt a-\tt b is first order for Pb3(PO4)2 and approaches second-order behaviour with increasing As content. The spontaneous strains and the birefringence follow approximately a Curie-Weiss law, with a corresponding order-parameter exponent β = ¼. The mutual high-temperature phases give diffuse X-ray reflections due to inelastic scattering. The soft-mode model is discussed for these results.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 93
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A comparison of the two methods available for describing the puckering of five-membered rings - the Altona-Sundaralingam (A-S) [Altona & Sundaralingam (1972). J. Am. Chem. Soc. 94, 8205-8212] pseudorotation parameters τm, P and the Cremer-Pople (C-P) [Cremer & Pople (1975). J. Am. Chem. Soc. 97, 1354-1358] puckering parameters q, φ - shows that they are the same for all practical purposes but both have minor shortcomings. In the A-S method, the value of τm is somewhat dependent on the choice of the origin atom, while in the C-P method the normal to the mean plane, rather than being fixed, precesses as the ring puckering changes. We present here an exact procedure for obtaining the A-S parameters τm, P that correspond to the amplitude and phase of the Fourier wave of period 4π/5, thus making τm independent of the origin atom. Formulae are also given for the estimation of the standard deviations in the A-S and C-P parameters.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 94
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 426-430 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Rotation and translation functions in reciprocal space, commonly used to find the orientation of a known molecular fragment and/or its position in the unit cell, are all identical or closely related to the function Q(R,t) = 〈|Eh|2|Ehp(R,t)|2〉h, where |Eh| is the observed normalized structure factor and Ehp(R,t) is the normalized structure factor for the partial structure, calculated for orientation R and position t. In this paper, this function is derived from statistical considerations without referring to a Patterson synthesis. From the centrosymmetric and noncentrosymmetric probability density functions, Q(R,t) = 1 + 2p2 and Q(R,t) = 1 + p2 are obtained, respectively, where p2 is the fraction of atoms (scattering power) that has been placed in the correct orientation and position in the unit cell. Alternative search functions, for instance using |Eh|4 instead of |Eh|2, are discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 95
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 697-701 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: For b.c.c. vanadium metal the integrated intensities of 80 independent reflections were measured by using a spherically shaped single crystal 0.241 (3) mm in diameter with Ag Kα radiation. It was confirmed that there are very small differences in integrated intensities between paired reflections, and these differences can be measured significantly beyond the experimental error. The ratios of the paired reflections are small than those obtained from platy crystals [Weiss & DeMarco (1965). Phys. Rev. A. 140, 1223-1225] but are in good agreement with those recalculated recently by means of the APW method [Wakoh & Kubo (1980). J. Phys. F. 10, 2707-2715].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 96
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 711-722 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: 19 absolute atomic scattering factors were measured for imperfect copper single crystals with an accuracy of the order of ±0.05 electrons for reflections with sin θ/λ ≤ 0.7 Å-1. This data set is of significantly higher accuracy than those measured earlier with X-rays for imperfect single crystals. The experimental form factors for low momentum transfer are significantly smaller than the free-atom values. The corresponding deformation density shows a small pile up of charge between nearest-neighbour atoms. At the present level of experimental accuracy, none of the available band-structure calculations provides a satisfactory description of the measured form factors over the whole range of momentum transfer where effects due to bonding can be expected.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 97
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 625-636 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A complete list of (3 + 1)-dimensional superspace groups is presented. These groups describe the symmetry of incommensurate crystal structures with a one-dimensional modulation. A short discussion is given of applications. Extinction rules and Bravais types are tabulated in order to facilitate the determination of the superspace-group symmetry.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 98
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 642-644 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: To overcome the disadvantages of a small starting set in MULTAN a technique is described whereby a large number of phases are given random values with low weights and then refined by a weighted tangent formula. The effectiveness of the process depends quite critically on assigning suitable weights to phase estimates and on a fairly tight control of the refinement. Examples of the application of the method are given for a number of structures, many of which are difficult to solve by direct methods.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 636-641 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A formula has been derived for the mean-square error in the phases of crystal reflections determined through the multiwavelength anomalous scattering method. The error is written in terms of a simple function of the positions in the complex plane of the 'centres' corresponding to the different wavelengths. For the case of three centres, the mean-square error is inversely proportional to the area of the triangle formed by them. The theoretical values are in good agreement with those obtained by earlier workers from computer simulations. The present method makes it easier to optimize the number and the actual wavelengths to be employed in the multiwavelength method. The maximum benefits of this method are expected in experiments employing synchrotron radiation or neutrons.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 100
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 645-649 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The absolute values of all the nine elastic constants of acenaphthene single crystals, C12H10, belonging to the orthorhombic system, have been determined by the photographic method from the measurement of the intensities of thermal diffuse scattering observed in a series of Laue photographs taken with monochromatized Cu Kα radiation having no higher harmonics of λKα. The direct beam was recorded photographically after being absorbed through nickel foils of known thickness, its intensity being reduced by a factor of 106. Diffuse scattering domains near the reciprocal-lattice nodes 400, 080, 004, 105, 014 and 072 were investigated extensively. The diffusely scattered intensities were corrected for the general scattering, polarization and skew factors. Corrections for absorption, divergence and second-order diffuse scattering were found negligible. The values of the elastic constants in units of GN m-2, with e.s.d.'s in parentheses, are C11 = 11.05 (50); C22 = 10.26 (30); C33 = 9.40 (23); C44 = 4.25 (08); C55 = 3.69 (07); C66 = 4.87 (10); C12 = -1.93 (20); C13 = 3.34 (12); C23 = 2.34 (13). The accuracy of experimentally determined values of the elastic constants is discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...