Structural response of iron oxides to irradiation

Iron oxides are ubiquitous in Earth and planetary systems and can display a variety of structures and stoichiometries. Iron oxides have several industrial applications, some of which function more efficiently when they are irradiated. One form of irradiation, swift heavy ion (SHI) irradiation, deposits large amounts of energy (> 1 MeV/u) into nano- to micrometer scale volumes. The energy is dissipated by electronic excitation along a trajectory that leaves behind tracks of damage that are several nanometers in diameter and tens of micrometers in length. Understanding the physics of ion track formation and annealing has improved our understanding of fission-track age dating and thermochronology. This work presents the effects of iron oxides’ structure and stoichiometry on their radiation stability.
Two iron oxides, hematite (α- Fe2O3, R-3c) and magnetite (Fe3O4, 𝐹𝑑-3𝑚), 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 both iron oxides accumulate strain upon irradiation and that hematite undergoes partial phase transformation to magnetite. Fe K-edge X-ray absorption spectroscopy measurements showed disordering of the nearest neighbors around the Fe cation, along with partial reduction of Fe in both irradiated materials.