Showing papers on "Electron backscatter diffraction published in 1981"

The application of convergent-beam electron diffraction to the detection of small symmetry changes accompanying phase transformations I. General and methods

Abstract: This paper considers the origins of convergent-beam diffraction patterns (CBDPs) and the particular uses of high-order Laue zone (holz) lines which are a feature of these patterns. Small changes in the arrangement of the holz lines, corresponding to changes in the lattice parameter and symmetry of the crystal giving rise to them, are discussed, and a technique for their simulation described. The advantages and limitations of the convergent-beam diffraction technique are considered.

Structural studies of graphite intercalation compounds using ( 0 0 l ) x-ray diffraction

Abstract: Analysis of the ($00l$) x-ray diffractograms of graphite intercalation compounds reveals important structural information concerning these compounds. In particular, the in-plane intercalate density is observed to depart from the commonly accepted stoichiometric values. This result has important implications concerning various structural phase transformations that have been reported in these materials. The application of Fourier synthesis to the ($00l$) integrated intensities yields the projected structure of the intercalate layer onto the $c$ axis. A least-squares refinement program RFINE4 was used to analyze the ($00l$) integrated intensities, yielding in-plane intercalate densities, Debye-Waller temperature factors, and various layer separations. The graphite-graphite layer separations were found to be not significantly different from the values for pristine graphite. Connections of the results of ($00l$) x-ray diffraction with other structural-analysis techniques such as electron diffraction and electron microscopy are discussed.

Electron diffraction and microscopy studies of the structure of grain boundaries in silicon

Abstract: The diffraction effects expected from the periodic structure of twist boundaries in Si are determined by an examination of the reciprocal lattice of these boundaries. Methods of analysis are developed to distinguish between the real diffraction spots due to the periodic boundary structure and those due to double diffraction effects. The electron microscope images from the boundaries studied in Si bicrystals were frequently found to be complex and contained moire fringes which provided no information on the actual boundary structure. By analysing the electron diffraction patterns from these boundaries for the presence of new diffraction spots it is possible to show that all the Σ1 [001], Σ1 [111] and Σ3 [111] twist boundaries examined have a periodic structure.

A neutron diffraction investigation of some ??-sialons

Abstract: Neutron diffraction measurements have been made on β′-sialons having chemical compositions Si6-zAlzOzN8-z, where Z=2.0, 2.9 and 4.0. The powder diffraction patterns have been recorded for sample temperatures of 300 K and 4.2 K, and the profile refinement method has been used in the data analysis. The unit-cell dimensions and the atomic co-ordinates were found to vary in a regular way with composition. The values of scattering amplitude per atomic site obtained using the refinement method provide evidence of a preferential replacement of nitrogen by oxygen on specific crystallographic sites, and an indication of a small vacancy concentration on the metal-atom sites.

Crystal structure analysis of Ca4YFe5O13 by combining 1 MeV high‐resolution electron microscopy with convergent‐beam electron diffraction

Abstract: By combining 1 MeV high-voltage-high-resolution electron microscopy with convergent-beam electron diffraction (CBED), the crystal structure of a perovskite-related compound, Ca4YFe5O13, is determined. The crystal has orthorhombic symmetry with lattice parameters a = 5.46, b = 37.4 and c = 5.54 A. The space group is determined to be centrosymmetric Pnma by selecting the point group from the CBED patterns. The structure images taken from two principle-axis directions, which are interpreted on the basis of the calculated images, reveal that the structure consists of a succession of the stacking of FeO6 octahedra (O layer) and FeO4 tetrahedra (T layer) and is represented by the stacking sequence of ...OTOOTOTOOTO... along the b axis repeated at intervals of 37.4 A. It is shown that the Ca4YFe5O13 crystal structure can be described in terms of unit-cell-level twinning of Ca2Fe2O5.

Electron Diffraction and Microscopy Techniques for Studying Grain-Boundary Structure

Abstract: Electron microscopy and diffraction techniques for studying grain-boundary structure are reviewed. The experimental conditions for applying strong-beam, weak-beam, and lattice imaging and electron diffraction are described and examples from recent studies in ceramics, semiconductors, and metals are used to illustrate the information that these techniques provide. It is demonstrated that electron diffraction can be used to study both the periodic nature of the boundary layer and its thickness. A particularly valuable feature of weak-beam imaging is that it can provide information on the details of the dislocation structure of the boundary, whereas strong-beam imaging can be used to determine the rigid-body translation between neighboring grains across special boundaries; these translations can be significantly smaller than the resolution of the microscope. Finally, lattice imaging can provide information on the location of dislocations and steps in the boundary.

X-Ray and Neutron Diffraction Studies on Amorphous Transitionmetal—Boron Alloys (Fe-B,Co-B,Ni-B)

Abstract: The atomic-scale structure of the amorphous metallic alloys Fe80B20, Co81·5B18·5, and Ni81·5B18·5 was investigated by X-ray- and neutron-diffraction covering a wide range of the ratio (fmetal/fboron) of the scattering factors of both components. The structure factors S (q) show a pronounced dependence on the ratio fmetal/fboron . In the cases of a small ratio an additional peak near q = 21.5 nm-1 appears in the structure factors from which a definite distance between B-B atoms, which are separated by metal atoms, is deduced. The corresponding structure factors show only weak oscillations in the range of the second and third maxima, which are followed by increased amplitudes at larger q's. By Fourier-transformation radial distribution curves were evaluated, from which the distances between the metal-metal-, the metal-boron-, and the boron-boron-atoms and the coordination numbers are extracted. From the splitted first maximum of the radial distribution function in the cases of small ratio fmetal/fboron also partial coordination numbers could be obtained. The results suggest some kind of short range order between the metal and the boron atoms.

X-Ray Diffraction on Electrolyte Solutions in the Low Angle Range

Abstract: Abstract Aqueous cobalt, nickel, zinc, cadmium and aluminium-chloride, -nitrate, -sulphate and PhAsCl solutions at 25 °C were studied by small angle X-ray diffraction. The scattered intensities of chloride, nitrate and CdSO4 solutions show the so-called \"prepeak\". The concentration dependence of the peak positions is discussed.

Gas-flame, high-temperature apparatus for single-crystal X-ray diffraction studies

Abstract: A new high-temperature gas-flame heater utilizing three different kinds of gases has been constructed for single-crystal diffractometry and for photography. The whole system of the heater consists of a burner and gas controller. The temperature control of the heater is carried out by changing the ratio of the flow rates of propane, oxygen and nitrogen gases; the third gas plays a role in increasing blower pressure of the flame and reducing fluctuation of the sample temperature. The heater can thus stably provide a temperature ranging from about 1000°C up to about 2000°C within a deviation of ± 20 °C. The burner has at its end a nozzle head in which Ave holes are so opened that gas flowing through the holes converges to a point 10 mm distant from the head. An accessory device is described which facilitates measuring directly the sample temperatures during the collection of reflection intensities with the single-crystal difTractometer.

The Molecular Structure of Benzotrifluoride as Studied by Gas Electron Diffraction

Abstract: Abstract The molecular structure of benzotrifluoride has been studied by electron diffraction. The geometry of the carbon ring is essentially regular hexagonal. The bond configuration of the trifluoromethyl group considerably departs from the regular tetrahedral arrangement. The following values were obtained for bond lengths (rg) and bond angles: r(C-C)ring- 139.7 ±0.3 pm (mean value), r(Cmethyl-Cphenyl) = 150.4 ± 0.4 pm, r(C-F) = 134.5 ±0.3 pm, r(C-H) = 109.9 ± 0.5 pm and ∢ C-C-F = 111.9 ± 0.1°. The electron diffraction data are in agreement with nearly free rotation of the -CF3 group around the Cmethyi-Cphenyi axis

A fitting method for X-ray diffraction profiles

Abstract: A fitting method is proposed for X-ray diffraction profiles which requires only a small number of parameters.