A new technique for angle-dispersive powder diffraction using an energy-dispersive setup and synchrotron radiation

Abstract

A new diffraction technique for combined angle- and energy-dispersive structural analysis and refinement (CAESAR), by collecting angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation, is introduced. By step scanning a well calibrated SSD over a limited 2θ range, a series of one-dimensional energy-dispersive data (intensityversusenergy) are obtained as a function of 2θ. The entire intensity (Int) data set consists of several thousand channels covering a range of photon energies,E(up to ∼150 keV), at each of the ∼1000 2θ steps, forming a 2–4 mega-element two-dimensional array, Int(E, 2θ). These intensity data are then regrouped according to photon energies, which are defined in the multichannel SSD as individual channels, yielding a large number of intensityversus2θ (angle-dispersive) data sets, Int(E= const., 2θ), each of which corresponds to a given photon energy or wavelength. The entire data set, selected subsets or composite scans can be used for multiple data set Rietveld refinement. Data collected both on α-Al2O3(a NIST diffraction standard) at ambient conditions and on a mixture of MgO and Au at high pressure were analyzed using the Rietveld technique, with varying schemes of data treatment. Furthermore, it is demonstrated that data within certain energy bands (ΔE/E= ±10%) may be binned together to improve counting statistics in a composite angle-dispersive scan, even when collected with much coarser scan steps of 0.1 or 0.2°. This technique is useful for high-pressure as well as general purpose powder diffraction studies that have limited X-ray access to the sample using synchrotron radiation. Several advantages are discussed.