B. Buras

X-ray energy-dispersive diffractometry using synchrotron radiation

The special features of X-ray energy-dispersive powder and single-crystal diffraction using synchrotron radiation are discussed on the basis of experiments performed at the Deutsches Elektronen-Synchrotron, DESY. The method is shown to be of particular value for fast structure identifications, experiments for which large scattering vectors are important, studies of phase transformations and chemical reactions at elevated temperatures and high-pressure studies. Studies of time-dependent phenomena using pulsed external fields are discussed.

Relations between integrated intensities in crystal diffraction methods for X-rays and neutrons

In addition to the classical experimental methods of crystal diffraction a number of new methods have become available using the time-of-flight technique for neutrons and energy-dispersive detectors for X- rays. It is shown that there are simple relations between the formulae for the integrated intensities of the different methods, and that the intensity formulae for all the methods can be simply generated, provided that one of them is derived in the usual way. Formulae are given for the powdered crystal and the ideally imperfect crystal in the kinematical approximation as well as for the large perfect crystal in the framework of the dynamical theory.

X-ray energy-dispersive powder diffractometry using synchrotron radiation

Abstract The results of a test using synchrotron radiation in X-ray energy-dispersive powder diffractometry are reported and discussed

Neutron diffraction study of magnetic ordering in Cd1−xMnxTe

Abstract Neutron diffraction experiments were performed on Cd1−xMnxTe crystals for x=0.40, 0.60, 0.63, 0.65 and 0.70. Magnetic Bragg scattering was observed at low temperatures for x⩾0.60 corresponding to the Type III antiferromagnetic ordering of a f.c.c. sub-lattice. The Neel temperatures decreasing with x were determined and the critical concentration xc was estimated.

A spectrometer for X-ray energy-dispersive diffraction using synchrotron radiation

Describes a white-beam X-ray energy-dispersive diffractometer built for Hasylab in Hamburg, FRG, using the synchrotron radiation from the electron storage ring DORIS. The following features of the instrument are discussed: horizontal or vertical scattering plane, collimators, sample environment, remote control of the goniometer, data acquisition, energy-sensitive detectors using small-area and large-area detector crystals, modes of operation, powder and single crystal diffraction. An example is given from a high-pressure study of YbH2 using a diamond anvil cell.

A Neutron Scattering Study of Lattice Dynamics of HgTe and HgSe

The dispersion relations for the acoustic and optic phonons in HgTe and for the acoustic phonons in HgSe were determined by neutron inelastic scattering in three high symmetry directions. The effect of the free-carrier screening of the long-range electric field of LO phonons in HgTe was observed. The formalism of the rigid ion model is used for numerical calculations of the phonon dispersion relations and the phonon densities of states in HgTe and HgSe.

Optimum resolution in X-ray energy-dispersive diffractometry

The resolution problem in X-ray energy-dispersive diffractometry is discussed. It is shown that for a given characteristic of the solid-state detector system and a given range of interplanar spacings, an optimum scattering angle can be easily found for any divergence of the incident and scattered beams.

Influence of the incident beam on integrated intensities in X-ray energy-dispersive diffractometry

Polarization measurements of the primary X-ray beam produced by thick copper and tungsten anodes are reported and formulas derived for integrated intensities of Bragg reflections in energy-dispersive diffractometry with the polarization of the primary beam taken into account. It was found that for an angle of 45° between the scattering plane and the plane containing the electron beam and the primary beam, the influence of polarization vanishes, while it increases as the angle changes from 45° to either 0 or 90°. For the latter values, the influence of polarization is considerable at high photon energies and at scattering angles close to 90°.

Energy-dispersive spectroscopic methods applied to X-ray diffraction in single crystals

Two single-crystal energy-dispersive crystallographic methods (the fixed-crystal method and the rotating-crystal method) are described and investigated. Formulae for integrated intensities are derived for mosaic and perfect single crystals. Experimental results and a comparison between measured and calculated integrated intensities for a perfect germanium crystal are given. Special features and possible applications of the methods are discussed.

Quantitative structural studies by means of the energy-dispersive method with X-rays from a storage ring

Test experiments were made using the X-ray energy-dispersive method at the storage ring DORIS (Hamburg) working in the single-bunch mode. It is shown that the spectral distribution of the incident beam calculated from the storage-ring parameters is in very good agreement with that derived from measured diffraction patterns of known substances, and thus it can be used for structural studies. This is illustrated with results of profile-fitting refinement applied to urea (CH4N2O) and naphthalene (C10H8). It is also shown that because of an improved detector system and the time structure of the radiation emitted from the storage ring one is able to record 7 × 104 photons per second and obtain reliable patterns in times of the order of 1  s.