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![[Cover illustration]](/a/issues/1999/02/01/graphics/coverill.gif) |
Cover illustration: One quadrant of each of four fibre diffraction patterns from disordered polynucleotide fibres. The patterns were calculated for fibres with disorder as follows. Upper left: crystalline (no disorder); upper right: noncrystalline (completely disordered); lower left: discrete rotational disorder and correlated lattice disorder; lower right: random screw disorder. See Stroud & Millane [Acta Cryst. (1996), A52, 812-829]. |
Acta Cryst. (1999). A55, 105-111 [ doi:10.1107/S0108767398003705 ]
Synopsis: A method to otain the crystal potential from the scattering matrix in high-energy electron diffraction is proposed.
Online March 1999
Acta Cryst. (1999). A55, 112-118 [ doi:10.1107/S0108767398006977 ]
Synopsis: A method for determining crystal structures directly from dynamical transmission electron diffraction patterns is given. This solves the phase problem.
Online March 1999
Acta Cryst. (1999). A55, 119-126 [ doi:10.1107/S0108767398006989 ]
Synopsis: Simulations of the transmission of 200 keV electrons through and beyond `atomic focuser' crystals establish the conditions for using such crystals to obtain ultra-high-resolution electron micrographs of thin samples.
Online March 1999
Acta Cryst. (1999). A55, 127-132 [ doi:10.1107/S0108767398006990 ]
Synopsis: Diffraction techniques using both X-rays and electrons are used to obtain bond lengths and geometry, and spectroscopic techniques of electron energy-loss spectroscopy and nuclear magnetic resonance to obtain information on energy levels and local environment of the titanium and oxygen atoms in lithium titanium silicate and lithium titanium germanate.
Online March 1999
Acta Cryst. (1999). A55, 133-142 [ doi:10.1107/S0108767398007533 ]
Synopsis: Green's-function techniques are used to obtain a real-space-series solution for elastic reflection high-energy electron diffraction from a crystalline surface. A renormalized perturbation expansion due to potential self-scattering is developed for the local real-space Green's function.
Online March 1999
Acta Cryst. (1999). A55, 143-159 [ doi:10.1107/S0108767398008617 ]
Synopsis: A coordinate-space, multislice description of electron scattering from crystals with correlated atomic displacements is constructed. It is used to find expressions for high-resolution electron-microscope images of crystals with static displacements (as in modulated structures) or dynamical displacements (as generated by photons) and, in particular, to determine the translational symmetry of these images.
Online March 1999
Acta Cryst. (1999). A55, 160-167 [ doi:10.1107/S0108767398008630 ]
Synopsis: Methods to retrieve the electron scattering potential under dynamical diffraction conditions using measurements at two closely spaced voltages are proposed. A non-linear refinement procedure is required when only diffracted intensities are available, a more direct method can be implemented using the full complex exit-surface wave function.
Online March 1999
Acta Cryst. (1999). A55, 168-177 [ doi:10.1107/S0108767398008642 ]
Synopsis: The structure of a novel type of boron nitride whisker was determined by transmission electron microscopy. The whiskers were found to be helical cones with a square-like apical defect.
Online March 1999
Acta Cryst. (1999). A55, 178-187 [ doi:10.1107/S0108767398008769 ]
Synopsis: A method of developing a detailed model of the structure of network solids from diffraction data is presented. The method refines a prediction based on first-principles molecular dynamics with the reduced density function determined from diffraction data.
Online March 1999
Acta Cryst. (1999). A55, 188-196 [ doi:10.1107/S0108767398008903 ]
Synopsis: Quantitative convergent-beam electron diffraction is used to determine structure factors and three-phase structure invariants. The refinements are based on centre-disc intensities only.
Online March 1999
Acta Cryst. (1999). A55, 197-203 [ doi:10.1107/S0108767398009003 ]
Synopsis: Using the three-beam approximation to the many-beam diffraction equations of electron diffraction, expressions are derived for the coefficient of reflection from a crystal surface and for the depth of penetration of the primary beam into the bulk. The expressions are used to analyse the increase in reflectivity that occurs when a surface resonance condition is established.
Online March 1999
Acta Cryst. (1999). A55, 204-211 [ doi:10.1107/S0108767398011325 ]
15-375 KSynopsis: Cell parameters were determined from the ratio of lines joining conic intersections on divergent-beam photographs. The results were compared with ratios from computer-generated divergent-beam patterns to assess the usefulness of the technique.
Online March 1999
Acta Cryst. (1999). A55, 212-215 [ doi:10.1107/S0108767398011337 ]
Synopsis: A simple but sufficiently accurate expression is obtained for the exit wave of a crystal in zone-axis orientation. The exit wave at each atom column can be parametrized with only one parameter, which is a function of the projected `weight' of the column.
Online March 1999
Acta Cryst. (1999). A55, 216-219 [ doi:10.1107/S0108767398012598 ]
Synopsis: The algebra is given for the recovery of phase and amplitude for centrosymmetric and noncentrosymmetric cases from a three-beam convergent-beam electron diffraction pattern. The algebra is available in Mathematica format.
Online March 1999
Acta Cryst. (1999). A55, 220-227 [ doi:10.1107/S0108767398013944 ]
Synopsis: The structures of the alloy phases Nb2Zrx-2O2x+1 are reviewed and their observed disorder discussed. It is suggested their behaviour can be modelled by a lattice of frustrated XY-type spins (rotations) of the oxygen ion nets.
Online March 1999
Acta Cryst. (1999). A55, 228-233 [ doi:10.1107/S0108767398014093 ]
Synopsis: A new model of high-Tc superconductivity is presented based upon the pairing of holes in real space, the pairing mechanism being magnetic exchange coupling. It is suggested that the CuO2 planes have regions of two different charge densities.
Online March 1999
Acta Cryst. (1999). A55, 234-245 [ doi:10.1107/S0108767398014810 ]
Synopsis: A model is proposed that explains the origin of the bright contrast of dislocation walls consisting of edge dislocation dipoles in electron channelling contrast images (ECCI) of fatigued crystals, when the incident beam is parallel to the edge dislocations.
Online March 1999
Acta Cryst. (1999). A55, 246-257 [ doi:10.1107/S0108767398010824 ]
Synopsis: Pattern simulations for three-beam and six-beam X-ray diffraction are presented using multislice calculations based on Moodie & Wagenfeld's formulation of the X-ray equations, which factorize Maxwell's equations into Dirac format, using circular-polarization bases.
Online March 1999
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