REFLECTIONS ON THE FIRST CENTURY OF X-RAY DIFFRACTION

X-ray diffraction (XRD) was discovered in 1912 by von Laue and colleagues, and shortly thereafter the (father and son) Braggs solved the first crystal structures, of halite and diamond, using XRD. These remarkable achievements were recognized by two Nobel prizes, and they completely changed our views of solids, paving the way for a structure-based understanding of material behavior. Most early XRD data were measured on readily available minerals, memorialized in the 1937 volume “Atomic Structure of Minerals” by W.L. Bragg. Since then, XRD has become the favored method for characterizing the structure of solids and has proven to be invaluable in studying all ordered solids. The first XRD data were measured on another planet, Mars, on the centennial of the discovery and it is interesting to speculate what von Laue and the Braggs would think about the last century’s changes. Much has transpired since 1912; recordings went from ionization chambers, to film, to a variety of electronic detectors, and now to position-sensitive detectors on instruments ranging from portable diffraction devices to synchrotrons, on samples down to sub-mg size, with measurement times down to picoseconds. Laboratory XRD instruments now offer resolution and measurement times achievable only with a synchrotron two decades ago. Lab-based XRD instruments routinely provide data allowing multi-component (>10 phases) quantitative analyses and accurate and precise unit-cell parameter determinations. Information on partially ordered and disordered phases can also be obtained from X-ray scattering (not diffraction) data.

Perhaps the greatest advances of our generation include the development of commercially available automated diffractometers in the late 1970’s, which paved the way for tremendous advances in computer analysis of diffraction and scattering data. Data can now be routinely collected in a lab in a matter of seconds as a function of variable sample environment (T, P, etc.), with comparable data analysis times in many cases for complex structures and multi-component mixtures. These developments make the most advanced diffraction experiments accessible to all, but they also pave the way for an increasing amount of “black-box” science. Unlike instrumentation and software, the underlying physics is the same as it was a century ago.