Far-From-Equilibrium Processing of Materials under Extreme Conditions

International audienceHigh energy ball milling and exposure to energetic heavy ion beams are two material processing methods that rapidly impart enormous amounts of energy into small volumes, yielding disordered material states that are otherwise inaccessible. The innovative strategy of this project involves the application of neutron total scattering experiments, coupled with advanced modeling, to investigate the nature of the structural disorder in far-from-equilibrium processed complex oxides over a range of lengthscales. This approach presents a significant improvement over conventional long-range characterization techniques, using X-ray and electron probes, that are less sensitive to anion sublattices and the unique aperiodic, short-range structural features produced by extreme processing conditions. Using pyrochlore and other fluorite-derived oxides as model systems, we show that defect behavior in chemically disordered (equilibrium) and mechanically milled and ion irradiated ceramics (far-from-equilibrium) is far more complex than previously thought. We demonstrate that locally ordered structural motifs are arranged such that the average, long-range structure does not represent the actual atomic configuration (1). The disordering process appears to be decoupled across structural length scales, proceeding locally at different rates than over longer length scales (2). This finding is important as the formation of disorder is inherent to many energy-related applications under which materials must perform in harsh conditions, such as nuclear materials as well as electrolyte and catalyst materials. In this contribution, we show that by using these oxides as model systems, we produce well-defined metastable phases with a variety of disorder and defect structures (3, 4). Systematic analysis of the structural behavior with coupled experiments and modeling identifies the underlying processes that drive the formation of intricate disorder across all material length scales. This research helps to build a robust atomic- and mesoscale understanding of highly defective and disordered phases but will also show how far-from-equilibrium processing techniques can be used to induce specific atomic arrangements and tailor physical properties (e.g., oxygen transport) to enhance functionality in technological applications (e.g., solid oxide fuel cells).1. E. C. O’Quinn et al., Sci. Adv. 6, 1–8 (2020).2. E. C. O’Quinn et al., J. Mater. Chem. A. 9, 16982–16997 (2021). 3. E. C. O’Quinn et al., J. Mater. Sci. 53, 13400–13410 (2018).4. C-K. Chung et al., Acta Mater. 181, 309–317 (2019)