Functional materials are designed to exhibit complexity on various levels. Their high physical properties may emerge from structural modulations caused by, for example, short range order, microstructural defects, surface layers, spatial heterogeneity, time-dependent excited states. As domains of distinct structural properties become smaller or shorter-lived, conventional structural determination techniques fall short of capturing these key fluctuations in time and space. The need to study materials in their real environment also adds to the challenge of obtaining accurate diffraction data.
Here we present some developments in high-energy x-ray powder diffraction that have helped understanding functional materials through experiments in-situ/operando, often combined with high spatial or time resolution. Besides easing absorption-related problems like low signal and beam-induced sample degradation, high-energy x-rays allow atomic-scale structural analysis through Pair Distribution Function. High photon flux and µm-sized beams help obtaining 3D diffraction maps of inhomogeneous materials in a few minutes. Instrumentation developments can now extend 3D diffraction to the structural response on the milli- to microsecond timescales to external fields, making structural studies truly multidimensional.