Chapter 16 - High-pressure angle-dispersive powder diffraction using an energy-dispersive setup and white synchrotron radiation

Abstract

The chapter discusses a new powder diffraction technique that collects high-pressure angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation, with the multi-anvil apparatus, SPring-Eight Energy Dispersive system with a hydraulic ram of 1500 ton (SPEED-1500). SPEED-1500 is a double-stage multi-anvil apparatus, where the first stage is a large DIA-type cubic anvil apparatus, employing WC anvils with a truncation 342 Y. Wang et ah edge length of 26 mm. The second-stage anvil assembly consists of eight sintered diamond cubic anvils containing Si as the binding material and are much less opaque to X-rays than those using Co as binding material. The double-stage system of SPEED-1500 is capable of generating simultaneous P-T conditions of 35 GPa and 2800 K, when sintered diamond anvils are used for the second stage; the Combined Angle-and Energy-dispersive Structural Analysis and Refinement (CAESAR) technique will make routine structural refinement possible at these conditions. Many attempts have been made to perform monochromatic diffraction using various high-pressure devices. For example, step-scan angle-dispersive diffraction (ADD) studies have been carried out using the multi-anvil press (MAP), where a monochromator is used to select a narrow band of energies from the incoming radiation, and a point detector (sometimes with a crystal analyzer) is scanned at a given step size in 2θ to collect diffracted intensity. The main disadvantage of this technique is that, like conventional ID Step-scan techniques, the scan is limited to a specific direction and does not integrate most or all of the available diffracted signals, as a 2D detector does. Effects of poor counting statistics can be minimized by oscillating the sample. In fact, sample oscillation is frequently practiced in the DAC with energy-dispersive diffraction (EDD) technique. \\