Local and Long-Range Structural Response of Swift Heavy Ion Irradiated Iron Oxides

Iron oxides are ubiquitous in Earth and other planetary systems (Liu et al., 2019), and can display a variety of structures and stoichiometries (Ono et al., 2004). Swift heavy ion (SHI) irradiation deposits large amounts of energy (~5 Gev) into nano- to micrometer scale volumes. The energy is dissipated by electronic excitation along a trajectory that forms tracks of damage that typically have diameters of ~5 nm and are tens of micrometers in length. The damage process is complex and spans timescales from femtoseconds to nanoseconds. Furthermore, understanding the physics of ion track formation and annealing has been used to understand the physics of fission track age dating and thermochronology (Li et al., 2021). This work presents examples of the control of structure and stoichiometry on the radiation stability of materials. Three iron oxides, hematite (a-Fe2O3, R-3c), magnetite (Fe3O4, Fd-3m), and wüstite (FeO, Fm3m), were irradiated with 1.7 GeV Au26+ ions at eight fluences ranging from 1011-1013 ions/cm2 at the GSI Accelerator Facility (Darmstadt, Germany). X-ray diffraction measurements showed that all three iron oxides accumulate strain upon irradiation, following a single impact mechanism. Irradiated hematite and wustite undergo partial phase transformation to magnetite and metallic iron, respectively. Raman spectroscopy showed increased bond disordering with increasing irradiation fluence. Finally, Fe K-edge X-ray absorption spectroscopy revealed disordering of the nearest neighbors around the Fe cation in all three irradiated iron oxides and found partial reduction of Fe in irradiated hematite. Works cited Li, W., Cheng, Y., Feng, L., Niu, J., Liu, Y., Skuratov, V. A., Zdorovets, M. V., Boatner, L. A., & Ewing, R. C. (2021). Alpha-decay induced shortening of fission tracks simulated by in situ ion irradiation. Geochimica et Cosmochimica Acta, 299, 114. https://doi.org/10.1016/j.gca.2021.01.022 Liu, J., Hu, Q., Bi, W., Yang, L., Xiao, Y., Chow, P., Meng, Y., Prakapenka, V. B., Mao, H.-K., & Mao, W. L. (2019). Altered chemistry of oxygen and iron under deep Earth conditions. Nature Communications, 10(1), 153. https://doi.org/10.1038/s41467-018-08071-3 Ono, S., Kikegawa, T., & Ohishi, Y. (2004). High-pressure phase transition of hematite, Fe2O3. Journal of Physics and Chemistry of Solids, 65(89), 15271530. https://doi.org/10.1016/j.jpcs.2003.11.042