Advanced characterization technique for mechanochemically synthesized materials: neutron total scattering analysis
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Materials that adopt the pyrochlore (A2B2O7) structure show promise for use in a variety of energy-related applications such as immobilization of actinide-rich nuclear waste and oxide fuel cells. Mechanochemical synthesis, a combination of milling and high-temperature treatment, has been successfully applied to fabricate many different pyrochlore compositions. High-resolution neutron total scattering experiments were used to gain fundamental insight into the structural details of milled Er2Ti2O7 pyrochlore and the subsequent evolution under high-temperature treatment. The milling process creates a highly disordered structure in which local atomic ordering is present that is significantly different than the observed long-range behavior. Thermal annealing leads to a complex defect recovery scheme with a gradual local rearrangement from a weberite-type atomic ordering to a pyrochlore phase independent of the sharp long-range crystallization process. Annealing of the milled sample up to 1200 °C does not reproduce the local structure of the same pyrochlore sample prepared by solid-state synthesis. This indicates that despite both samples possessing identical long-range structures, local defects induced by the milling process persist to very high temperatures. These findings provide a direct insight into the mechanochemical synthesis of pyrochlore oxides and help to better elucidate the structural properties of highly disordered complex oxides under extreme conditions from the local atomic arrangement to the macroscale.
This work was supported as part of the Materials Science of Actinides, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0001089. The research at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. AFF thanks Conacyt (Mexico) for its continuous financial support on pyrochlore research at his lab. This material is based upon work supported under an Integrated University Program Graduate Fellowship (Jessica Bishop).
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The authors declare no conflicts of interest or competing financial interests.
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