Four-unit-cell superstructure in the optimally doped YBa2Cu3O6.92 superconductor

Diffuse x-ray scattering measurements reveal that the optimally doped YBa2Cu3O6.92 superconductor is intrinsically modulated due to the formation of a kinetically limited 4-unit-cell superlattice, q(0)=(1/4, 0, 0), along the shorter Cu-Cu bonds. The superlattice consists of large anisotropic displacements of Cu, Ba, and O atoms, respectively, which are correlated over approximately 3-6 unit cells in the ab plane, and appears to be consistent with the presence of an O-ordered "ortho-IV" phase. Long-range strains emanating from these modulated regions generate an inhomogeneous lattice which may play a fundamentally important role in the electronic properties of yttrium-barium-copper-oxides.

In situ synchrotron study of phase transformation behaviors in bulk metallic glass by simultaneous diffraction and small angle scattering

We have used a new approach involving simultaneous diffraction and small angle scattering to study the amorphous-to-crystalline phase transformation in Zr-based bulk metallic glass. In situ, time-resolved data provided the first direct demonstration of a phase separation prior to crystallization. There is evidence that nucleation and growth of the crystalline phase occur in separate stages, with different kinetics. Our data support the view that crystalline nucleation is achieved via short-range diffusion of small atoms (e.g., Ni), whereas the growth is dictated by long-range diffusion.

High-energy diffuse scattering on the 1-ID beamline at the advanced photon source

This paper reports on experiments in which high-energy (65.35 keV) X-rays were used to record the detailed diffuse diffraction patterns of a number of ceramic materials. The methodology has enabled a greater q-range to be explored (up to sintheta/lambda approximately 0.97) than is possible with laboratory-based experiments, with better q-space resolution and increased sensitivity, thus allowing previously unseen detail in diffraction patterns to be recorded. In all, 11 sections of data have been collected for Ca-CSZ, eight for Y-CSZ and six for wüstite.

Separating the recrystallization and deformation texture components by high-energy X-rays

High-energy synchrotron diffraction offers great potential for experimental study of recrystallization kinetics. Measurements on partially recrystallized samples using a monochromatic high-energy synchrotron beam show that recrystallized grains generate sharp diffraction spots, whereas the intensity from the deformed matrix varies smoothly along the Debye–Scherrer rings. Based on these observations, a method has been developed to separate the recrystallization texture components from those originating from the deformation matrix. The validity of this method is demonstrated with partially recrystallized interstitial-free steel.

High-energy X-ray diffuse scattering using Weissenberg flat-cone geometry. Erratum

In the paper by Butleret al.[J. Appl. Cryst.(2000),33, 1046–1050], Figures 3 and 4 on pages 1047 and 1048 reproduced poorly. Revised versions of these pages are available in the online version of this erratum, which is available throughCrystallography Journals Online.

High-energy X-ray diffuse scattering using Weissenberg flat-cone geometry

A technique for the measurement of diffuse X-ray scattering on individual reciprocal-space planes using high-energy X-ray photons is described. The method is demonstrated using a disordered crystal of the compound TlSbOGeO4and compared to data collected with a sealed-tube Cu anode source. Measurements were made on a synchrotron undulator beamline at an energy of 45 keV using Weissenberg flat-cone geometry and a storage phosphor (image) plate to detect the scattered X-rays. Advantages of the method include: extension of the accessible diffraction space to both higherandlower wavevectors, the ability to use crystals of irregular shape without the need for complicated absorption corrections, less need to prepare sample surfaces carefully, and the ability to filter fluorescence simply.

Experimental characterization of APS undulator A at high photon energies (50-200 keV)

The considerable intensity of Advanced Photon Source (APS) undulator A as a source of high-energy X-rays permits the performance of numerous types of experiments that require such photon energies. Measured and calculated properties, in the 50-200 keV range, of the X-ray beam from undulator A, installed in sector 1 of the APS, are presented. The flux spectra observed at various gaps agree well with calculations that incorporate the actual magnetic field within the device and the emittance and energy spread of the stored positrons. The field errors and energy spread cause the X-ray beam to lose undulator radiation properties at high energies, as seen in the smeared-out spectral harmonics and increased beam divergence, giving resemblance to a low-K wiggler source. Owing to the wiggler-like behavior in this photon-energy range, the optimal operating condition for undulator A is in the vicinity of the closed-gap setting, corresponding to a maximum critical energy.