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O: Fachverband Oberflächenphysik

O 63: Oxides and Insulator Surfaces: Adsorption and Reaction of Small Molecules II

O 63.7: Vortrag

Mittwoch, 19. März 2025, 12:00–12:15, H25

Maghemite (γ-Fe₂O₃): From Bulk Phases to (001) Oriented Surfaces — •Muhammad Munawar^1,2 and Rossitza Pentcheva¹ — ¹Department of Physics and Center for Nanointegration (CENIDE), Universität Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany — ²International Max Planck Research School on Sustainable Metallurgy, Max-Planck-Straße 1, 40237, Düsseldorf, Germany

Maghemite (γ-Fe₂O₃) finds applications across a wide range of fields, including spintronics, magnetic recording, and nano-medicine, to name a few. It can be derived from the magnetite (Fe₃O₄) structure by introducing Fe vacancies in the B layers containing octahedral Fe ions and oxygen. A stoichiometric phase is achieved by tripling the cubic cell along the c-axis, resulting in a charge-transfer insulator with band gap of 1.90 eV. Phonon dispersion indicates that the cubic structure is stable without imaginary frequency modes. Ab initio molecular dynamics (AIMD) simulations confirm the stability at 300 K. Additionally, we explore the stability of the (001) surface within the framework of ab initio thermodynamics. The A and B layer terminations are favored at oxygen-poor and oxygen-rich conditions, whereas at intermediate oxygen chemical potentials, a 0.5A layer termination is stabilized. While the A termination exhibits only a minor band gap change, a significant decrease occurs for the B-layer termination due to reduction of magnetic moments and Fe-O bonds up to 0.21 Å. These surfaces serve as a starting point to explore the mechanism of hydrogen adsorption and reduction of the material in view of green steel production.

Keywords: Iron oxides; maghemite; Surfaces (001); DFT+U; Ab initio study