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MM: Fachverband Metall- und Materialphysik

MM 15: Phase Transformations I

MM 15.4: Vortrag

Dienstag, 10. März 2026, 14:45–15:00, SCH/A215

Interface structure and migration in phase transformations between Fe₃O₄ and Fe₂O₃ — •Martina Ruffino¹, Baptiste Bienvenu¹, Xuyang Zhou², Guangyi Guo¹, Barak Ratzker¹, Dierk Raabe¹, and Yan Ma³ — ¹Max Planck Institute for Sustainable Materials, Düsseldorf, Germany — ²Xi’an Jiaotong University, Xi’an, China — ³TU Delft, The Netherlands

Although redox phase transformations between hematite (Fe₂O₃) and magnetite (Fe₃O₄) entail long-range diffusion, they are known to occur on well-defined (111)_mag||(0001)_hem habit planes, and to maintain the oxygen sublattice fixed up to a change in stacking sequence (fcc and hcp arrangement for Fe₃O₄ and Fe₂O₃, respectively). Moreover, hematite formations during magnetite oxidation, as well as magnetite formations in hematite during reduction, are often observed to be of lenticular shape. In this study, we propose interfacial disconnections (i. e. steps with dislocation character) suitable for the accomplishment of these phase transformations. Using atomistic simulations with an atomic cluster expansion (ACE) potential developed for iron and its oxides, we calculate the equilibrium structures of the disconnections and we study their motion as a means to transform magnetite into hematite and vice-versa. We then validate theoretical calculations experimentally by investigating i) partially oxidised magnetite and ii) partially reduced polycrystalline hematite. Using transmission electron microscopy, we analyse the hematite/magnetite interfaces, characterising them as faceted interfaces containing steps; we observe good agreement with the simulated disconnection structures.

Keywords: Disconnections; Redox reactions in Fe oxides; Atomic cluster expansion (ACE) potentials; TEM