Imaging Nanoscale Disorder in Reciprocal Space

Correlated defects are responsible for the functional properties of many materials that underpin energy-related technologies. Single-crystal diffuse scattering using x-rays or neutrons is a powerful probe of short-range order in crystalline lattices, but its use has been limited by the experimental challenge of collecting data over a sufficiently large volume of reciprocal space and the theoretical challenge of modeling the results. However, instrumental and computational advances at both x-ray and neutron sources now allow the efficient measurement and rapid transformation of reciprocal space data into three-dimensional pair distribution functions, providing model-independent images of nanoscale disorder in real space. By eliminating Bragg peaks before the transformation, 3D-∆PDF measurements image defect-defect correlations directly, displaying only the probabilities of interatomic vectors that deviate from the average structure. I will give examples of the use of this method to probe the structure and correlation length of order-disorder transitions in intercalation compounds, the length scale and dimensionality of nematic correlations in iron arsenides, and the defect correlations in a superionic thermoelectric.
This work was supported by the U.S. Department of Energy, Materials Science and Engineering Division.