The complementary use of X-ray and neutron diffraction in the study of crystals

Neutrons and X-rays interact differently with atoms in crystals. While X-rays primarily give information on electron distributions, neutrons report on nuclear positions, and, through the spin interaction, are sensitive to magnetic structure. These and other differences have been exploited for many years in, for example, X-N difference studies and in determining magnetic structure. The major differences in available X-ray and neutron incident-beam intensities have also influenced the ways in which the two probes are exploited; not only are neutron sources inherently weaker, but this disadvantage is heightened by the weaker neutron-nucleus interaction. Advances in sources of both types, coupled with developments in instrumentation, have enabled not only the relative strengths to be exploited more effectively, but also some of the respective weaknesses in both techniques to be at least partially overcome. After outlining the main relevant advantages of X-rays and neutrons, and specifically of pulsed spallation neutron sources, this paper will discuss some of the scientific areas in which these various advantages are being increasingly exploited with advanced sources and instrumentation. Although the examples focus in particular on studies of structure and disorder in powder samples, including work at high pressures, some attention is given to hydrogen location in, and diffuse scattering from, single crystals. Finally, a personal forward look towards possible future developments is offered.