Recent developments in research on disordered materials using high energy x-ray diffraction

High-energy x-ray diffraction is generally considered to involve incident beam energies in excess of 60 keV. At these energies the photons act as a bulk probe and scattering experiments may be carried out in transmission geometry. Although the Pair Distribution Function (PDF) technique has been used to investigate the structure of disordered materials since the early days of x-ray diffraction, high-energy x-ray PDF has extensively expanded the technique's capabilities. The large penetration depth and low absorption of high-flux, high-energy synchrotron x-rays compared to conventional laboratory based x-ray sources, has allowed the investigation of materials in complex sample environments in real time. The resulting pair distribution function yields information on the average local and intermediate range structure in liquid, glassy and nano-crystalline materials at the atomic level, providing a measurement that can be directly compared to theory and molecular dynamics or Monte Carlo simulations. For example, the structure of nano-crystalline cements have recently been characterized using Reverse Monte Carlo simulations applied to high energy PDF data. Developments in instrumentation through the use of large area detectors have provided the ability to perform fast (typically 100ms) measurements on meta-stable liquid states in high temperature ceramics. In addition, micro-focused (20 micron) high-energy x-ray beams are able to easily penetrate diamond anvil cells to enable studies of the structure of dense glasses at high pressures of several GPa.