• Accepted Paper

Si-O network connectivity as a structural signature of self-passivation of β-FeSi2 surfaces

Jun Chai, Hangjia Shen, Mingping He, Yulin Zhou, and Pan Liu

Phys. Rev. B - Accepted 8 October, 2026

DOI: https://doi.org/10.1103/lr3v-61qw

Abstract

β-FeSi2 exhibits exceptional oxidation resistance, commonly attributed to the formation of a dense, protective SiO2 surface layer; however, the atomistic pathway governing the emergence of this layer and the subsequent suppression of oxidation remains elusive. In this work, we develop an active-learning MACE interatomic potential for the reactive Fe–Si–O system and incorporate a Fermi-like potential wall to enable one-sided reactive molecular dynamics simulations of β-FeSi2 surface oxidation. By analyzing 100 statistically independent trajectories, we find that self-limiting oxidation on both Si-terminated and Fe-terminated surfaces is consistently associated with the development of an extended connected Si–O network within the oxidized interfacial region. The Si-terminated surface passivates through direct oxidation of exposed Si atoms, whereas the Fe-terminated surface first undergoes Fe oxidation before oxygen reaches the subsurface Si-rich region and forms an extended connected Si–O network. Statistical analysis shows that Fe–O–Fe connectivity is either negligible or incomplete and does not constitute the primary passivating framework. Species-resolved density profiles ρα(z,t) reveal that oxidation proceeds through coupled oxygen incorporation, substrate-atom migration, and interfacial reconstruction, rather than simple inward oxygen diffusion into a static substrate. These results support a connectivity-based microscopic picture in which the development of an extended Si–O network is consistently associated with self-limiting oxidation of β-FeSi2 surfaces and provide a transferable computational protocol for exploring oxidation mechanisms in transition-metal silicides and related reactive materials.

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