30 years of Rietveld refinement

100 people queuing outside the lecture theatre were unable to get in to hear Hugo Rietveld, inventor of Rietveld Refinement that revolutionised powder diffraction. Hugo outlined development of the method from his early days at the U. of Western Australia to work on neutron structures of uranium compounds and heavy metal ceramics at the Netherlands Energy Research Foundation ECN in Petten .

A. Hewat took up the neutron story showing how primitive the original diffractometers were, even at the new European High Flux Reactor (ILL). Today’s instruments have large position sensitive detectors capable of collecting all available neutrons. Powder diffraction, has had more impact than most other neutron techniques, from the study of charge reservoirs in oxide superconductors, to the structures of giant magneto-resistive ceramics.

F. Izumi showed how incommensurable structures could be refined, and described a new computer program, REMEDY combining Rietveld and Maximum Entropy techniques to increase real space resolution. He gave examples of complex spin-ladder oxide superconductors, and other inorganic materials.

D. Louer described the contribution of automatic indexing and structure solution from powders to the transformation of the study of solid state chemistry.

Finally, A. Fitch showed how increased resolution from high intensity synchrotron radiation reveals the precise line positions needed for automatic indexing, and crystal symmetry and superstructure identification. Synchrotron radiation has become a very powerful tool for the almost automatic solution of unknown structures from very small quantities of powder, and an ideal complement to neutron Rietveld refinement.

Alan Hewat