Subsurface Cation Vacancy Stabilization of the Magnetite (001) Surface

TL;DR

This study reveals that the (001) surface of magnetite is stabilized by an ordered array of subsurface iron vacancies and interstitials, which explains its reconstruction and has implications for various applications involving iron oxides.

Contribution

It uncovers a previously unobserved stabilization mechanism involving subsurface cation vacancies in magnetite (001) surfaces using combined experimental and theoretical methods.

Findings

Identified ordered subsurface iron vacancies and interstitials in Fe3O4(001)

Explained the (rt2xrt2)R45° reconstruction of the surface

Suggested this stabilization mechanism is common in metal oxides

Abstract

Iron oxides play an increasingly prominent role in heterogeneous catalysis, hydrogen production, spintronics and drug delivery. The surface or material interface can be performance limiting in these applications, so it is vital to determine accurate atomic-scale structures for iron oxides and understand why they form. Using a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory calculations, we show that an ordered array of subsurface iron vacancies and interstitials underlies the well-known (rt2xrt2)R45{\deg} reconstruction of Fe3O4(001). This hitherto unobserved stabilization mechanism occurs because the iron oxides prefer to redistribute cations in the lattice in response to oxidizing or reducing environments. Many other metal oxides also achieve stoichiometric variation in this way, so such surface structures are likely commonplace.