Over the past five years, the use of pair distribution function (PDF) methods to study local structure has become increasingly prominent in the mainstream materials chemistry literature. Because the technique is sensitive not only to the average (long-range) material structure but also to any local distortions away from the average structure, PDF measurements provide a valuable means of studying local structure in a way that is inherently consistent with traditional crystallographic refinement. In this article, we review the ways in which PDF methods are being used to determine local structure-property relationships in a range of materials of particular currency within the materials chemistry community.

We use a combination of neutron and X-ray total scattering measurements together with pair distribution function (PDF) analysis to characterise the variation in local structure across the orbital order-disorder transition in LaMnO3. Our experimental data are inconsistent with a conventional order-disorder description of the transition, and reflect instead the existence of a discontinuous change in local structure between ordered and disordered states. Within the orbital-ordered regime, the neutron and X-ray PDFs are best described by a local structure model with the same local orbital arrangements as those observed in the average (long-range) crystal structure. We show that a variety of meaningfully-different local orbital arrangement models can give fits of comparable quality to the experimental PDFs collected within the disordered regime; nevertheless, our data show a subtle but consistent preference for the anisotropic Potts model proposed in Phys Rev. B 79, 174106 (2009). The key implications of this model are electronic and magnetic isotropy together with the loss of local inversion symmetry at the Mn site. We conclude with a critical assessment of the interpretation of PDF measurements when characterising local symmetry breaking in functional materials.

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