Abstract
Over the 100 years since the discovery of the diffraction of X-rays by crystals, structure determination based on the analysis of Bragg peaks has grown into a very precise, widely applicable, and definitive tool. This conventional crystallography is based on the assumption that a crystal consists of a three-dimensional array of identical units. Real materials, however, only approximate this ideal and their diffraction patterns contain, in addition to sharp Bragg peaks, a weak continuous background known as diffuse scattering. Diffuse scattering occurs when there are departures of any kind from the ideal lattice. The properties of many important materials are dependent not simply on the average crystal structure yielded by the Bragg analysis but are often crucially dependent on the departures from ideality (disorder) that can only be revealed by analysis of the diffuse scattering. Diffuse scattering has been known and studied since the very earliest days of crystallography but because of the generally very low intensities and the diversity of effects that can give rise to it, the field has largely remained the realm of a relatively few specialist research groups. However, in recent years with the advent of synchrotron sources, latest high-resolution and high-dynamic-range X-ray pixel detectors and powerful computers for analysis and modelling, the problems that limited development of diffuse scattering methods have now largely been solved. Current methods are now capable of tackling virtually any disorder problem to yield details of structure and dynamics that goes far beyond the confines of the average unit cell description of structure. In this paper, we outline how diffuse scattering methods developed over the course of a century since the birth of X-ray crystallography and review the wide range of different areas and materials to which the methods have been applied.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes on contributors
Richard Welberry completed his Ph.D. in Chemical Crystallography in Dame Kathlein Lonsdale's Laboratory at University College London in 1970. After five years postdoctoral research at University College Cardiff he moved to Australia in 1975 to join the staff of the Research School of Chemistry at the Australian National University, initially as Fellow but subsequently as full Professor. He is now Professor Emeritus. The focus of his research has been on the development of methods and strategies to measure, interpret and analyse diffuse X-ray scattering. He has pioneered the use of large-scale computer simulations to model disordered systems of all kinds and has applied the methods to a wide range of different materials including organic molecular crystals, pharmaceuticals, inclusion compounds, non-stoichiometric inorganic materials and ceramics, minerals, piezoelectric materials, QCs, zeolites and proteins.
Thomas Weber received his Ph.D. in Mineralogy from Ludwig-Maximilians University in Munich in 1998. After three years of postdoctoral research at the University of Berne, he joined the Laboratory of Crystallography at ETH Zurich in 2001. His research focus is on the further development of methods and software for a better understanding of real structure and properties of disordered crystals. Other research interests include higher dimensional modelling of aperiodic crystals, development of novel diffraction methods and solid-state reactions in 3D polymers.
ORCID
T.R. Welberry http://orcid.org/0000-0002-6906-9191