Neutron scattering’s influence on crystallography

Abstract

Picture a group of X-ray diffractionists pontificating in the Crystallography Forum; the buffoon amongst them asks: “What has neutron diffraction done for us?” Aside from being a poor parody of a well-known scene from a Monty Python film, this question does contain an element of truth. In the hundred years since the discoveries of von Laue and the Braggs, X-ray crystallography has been remarkably successful in providing extensive and reliable tools and methods for understanding many aspects of crystal structure and behavior. There are, of course, particular experiments where neutrons offer significant advantages over X-rays. These advantages are well known to us all: dramatically different dependence of the scattering factors on atomic number and isotope, no dependence of the nuclear scattering factor on angle, larger penetration, sensitive to unpaired spins, and energies comparable to lattice and magnetic excitations. But what has neutron scattering contributed to the science of crystallography? With the ringing out of 2014 as the UNESCO International Year of Crystallography, it is timely to reflect on the various aspects of crystallography where neutrons have led the way [1]. These aspects include the development of counter diffractometers, automation, and electronic position-sensitive detectors, most areas of magnetism, the study of incommensurate structures, the Rietveld method to analyse powder diffraction patterns, total pattern refinement, powder diffraction in materials discovery, standard libraries of amino acids and peptides, strain scanning, extreme sample environments of many forms, and operando in situ experiments. Potted histories of several of these aspects, especially those with connection to the neutron scattering activities at Lucas Heights, will be presented.