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January 1998 issue
Cover illustration: Power spectrum of a high-resolution electron-microscopy image of NiAl <110>. The image calculation includes a realistic phonon spectrum by coupling the `molecular dynamics' and `multislice' simulation techniques. The diffuse background, satellite peaks and bands mirror the effect of thermal diffuse scattering and correlated atom vibrations. Courtesy of G. Möbus, T. Gemming and P. Gumbsch.
international union of crystallography
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research papers
An exact nonperturbative inversion method is described for transmission electron diffraction which allows crystal structure factors to be obtained directly from the intensities of multiply scattered Bragg beams.
A procedure for the determination of the primary and secondary modes necessary for the symmetry-mode analysis of structural phase transitions is presented. The method only requires the use of International Tables for Crystallography, Vol. A.
Single crystals of the incommensurate organic salt hexamine sebacate present satellites up to sixth order. In the superspace approach, two refinement models based respectively on programs MSR and JANA are compared.
A method is described for estimating the structure amplitudes of unmeasured reflections using a Patterson map computed with the measured data. Conditions for implementing the original idea, first put forward by Karle & Hauptman in 1964, are significantly improved.
Electron ptychography is used to form an image at a resolution of three times the conventional limit of the microscope used. The accuracy of the experimental procedure is examined.
The theory of three-dimensional and multiple scattering effects in electron ptychography is developed. Calculations indicate how these affect the interpretation of experimental results.
The X-ray propagation process in a crystal containing a thin buried layer is detailed. Direct consequences on the analysis of X-ray standing waves and reflectivity measurements are pointed out.
The influence of thermal diffuse scattering on HREM simulations is found to be very tiny, proven by molecular-dynamics-simulated time series of frozen phonons in an NiAl crystal.
This paper shows that crystal structure refinement using electron diffraction data gives reliable results and good R values if the dynamical diffraction theory is used for the calculated intensities.
Approximate methods for treating dynamical scattering effects in integrated electron diffraction intensities from unknown structures are described. (hk0) structure factors of AlmFe are determined ab initio from a combination of CBED and integrated intensities.
Analytical expressions for ψ profiles are obtained by using the boundary-value Green-function technique. The results indicate a strong dependence on the crystal shape.
Using the boundary-value Green-function technique in the solution of the Takagi–Taupin equations, it is shown how absorption, resonant scattering and polarization affect the dynamical interactions and cause changes of ψ profiles.
The concepts of statistical dynamical theory are implemented in the Takagi–Taupin equations. Using the boundary-value Green-function technique, analytical solutions for the coherent diffracted power is obtained and the influence on ψ profiles is discussed.
short communications
Erratum to Acta Cryst. (1997), A 53, 445–455.
