Acquisition of Powder Diffraction Data with Synchrotron Radiation

Abstract

Aust. J. Phys., 1988,41,117-31 During the past year, a dedicated triple-axis powder diffractometer has been in routine operation at the Brookhaven National Synchrotron Light Source as a user-oriented facility. The diffractometer is designed to allow easy interchange between energy-dispersive and monochromatic beam experiments. In the latter mode of operation, high resolution data have been collected for a variety of samples with the use of the crystal-analyser technique, and in several cases these data sets have been used successfully for structure solution and Rietveld refinement. Several aspects of data acquisition at a synchrotron beam-line are described, and some of the different types of scattering geometry which have been used are discussed. Simple expressions are given for the instrumental resolution function expressed as the angular variation of peak widths for each of these. The peak shapes observed for a reference sample of Si on the present triple-axis instrument are well described by the convolution of Gaussian and Lorentzian functions, and the angular dependence of the Gaussian component is in excellent agreement with the corresponding calculated instrumental function. One of the most important considerations for each type of experiment is the necessary compromise between intensity Ilnd resolution over a wide range of scattering angles, and some of the available options are discussed. In particular, the use of Ge (440) and LiF(400) analyser crystals gives a focussing minimum at relatively high angles (28 ::::: 50· at 1·54 A), a highly desirable feature for Rietveld analysis of complex structures. Absolute intensities from reference samples of Si and Ce02 are calculated for these and several other scattering configurations involving both fiat-plate and capillary geometry to illustrate this compromise.

Synthesis and structure of a stuffed derivative of α-quartz, Mg0.5AlSiO4

“…Our refinements proceeded as follows: after the scale factor and four radial distribution function (RDF) background terms (needed to model the background from the capillary glass) had converged, specimen displacement and lattice parameters were added and optimized. Sixteen additional background terms were then added, and the peak profiles were fitted by refining isotropic and anisotropic broadening parameters and a Gaussian particle size coefficient in a pseudo-Voigt function (Thompson et al 1987;Cox et al 1988;Finger et al 1994). On convergence of the preceding parameters, atomic positions and isotropic temperature factors for Mg, Al/Si, and O were refined.…”

Effect of vanadium ion implantation on the crystallization kinetics and phase transformation of electrospun TiO2 nanofibers

“…According to Eq. 6, a near-parallel beam is incident on the sample and then diffracted by the sample [37,38]:…”

Structural and defect analysis of V-alloyed C15 NbCr2 from high resolution synchrotron X-ray powder diffraction

“…X-ray peak shapes re¯ect the grain size and microstrain in powder samples (Cox et al 1988). It can be seen from tables 2 and 3 that C15 Nb 33 Cr 42 V 25 exhibits a noticeable component of Gaussian contribution in its pseudo-Voigt peak shape function, whereas C15 NbCr 2 shows a predominant Lorentzian contribution.…”