Surface termination of hematite at environmental oxygen pressures: Experimental surface phase diagram

Abstract

We provide an experimental surface phase diagram (surface termination versus chemical oxygen potential) of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}(0001)$ using a natural single crystal surface. In a partial reduction reoxidation cycle, we observe a sequence from oxygen-, to ferryl-, and again oxygen-terminated surfaces, in better agreement with recent density functional theory in the generalized gradient approximation calculations than with calculations taking into account on-site $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ Coulomb repulsion. The nonreversible change in surface termination is accompanied by the formation of basal twins, which act as a sink for the extra Fe ions during the surface transformation processes.