High-pressure angle-dispersive powder diffraction using an energy-dispersive setup and white synchrotron radiation

Abstract

A new powder diffraction technique has been applied to collect high-pressure angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation, with the multi-anvil apparatus SPEED-1500 at SPring-8. By scanning a well-calibrated SSD over a given 2θ range at a predetermined step size, a series of one-dimensional (1D) energy dispersive data (intensity, Int, versus energy, E) are obtained as a function of 2θ. The entire intensity dataset Int (2 θ, E ) consists of 4048 energy bins, covering photon energies (E) up to ~ 160 keV at 600 2θ steps, forming a large two-dimensional (2D) array. These intensity data are regrouped according to photon-energy bins, which are defined by individual channels in the multi-channel analyzer, yielding a large number of intensity-versus-2θ (angle-dispersive) datasets, Int(E = const ., 2 θ ), each of which corresponds to a given photon energy or wavelength. Experimental data obtained on a mixture of MgO and Au to 20 GPa are used to demonstrate the feasibility of this technique. The entire dataset, selected subsets or composite scans can be used for Rietveld refinement. Data subsets are selected to simulate coarse step scans. Our analysis indicates that data within certain energy bins (up to ~ 10%) may be binned together to improve counting statistics and to permit 2θ scans at 0.1–0.2° steps, without losing angular resolution. This will allow much faster data collection within about 10 min. Our test results indicate that at photon energy of ~80 keV, the angular resolution Δ θ / θ (in terms of refined FWHM) is about 0.006 within a 2θ range from 3 to 10°. This new technique is useful for high-pressure and general-purpose powder diffraction studies that have limited X-ray access to the sample using synchrotron radiation. Several advantages are discussed .