Ab Initio Study of Magnetic Structure and Chemical Reactivity of Cr₂O₃ and Its (0001) Surface

Abstract

We present the first ab initio density functional theory study of the oxygen-terminated Cr2O3 (0001) surface within the local spin-density approximation (LSDA). We find that spin plays a critical role for even the most basic properties of Cr2O3 such as the structure and mechanical response of the bulk material. The surface exhibits strong relaxations and changes in electronic and magnetic structure with important implications for the chemical reactivity and unusual spin-dependent catalytic activity of the surface. Unlike the bulk, the outermost chromium bilayer is ferromagnetically ordered, and the surface oxygen layer exhibits appreciable net spin polarization in the opposite sense. Surprisingly, despite this ferrimagnetic order, the chemically important states near the Fermi level exhibit ferromagnetic order and thus favor electronic spin alignment of species interacting with the surface. Finally, we also find a high density of unoccupied electronic surface states available to participate in the chemical reactivity of the surface.

Impact of ambient oxygen on the surface structure ofα-Cr2O3(0001)

“…The UHV surface geometry is largely consistent with that derived from previous LEED-IV measurements, 9 although there are some small differences in atomic coordinates and fractional layer occupancies. Ab initio theoretical calculations performed to date [10][11][12][13][14] have not predicted either of the two structures.…”

“…[10][11][12][13][14] Most pertinently, the surface termination as a function of oxygen partial pressure ͑chemical po- FIG. 1.…”

Zinc surface complexes on birnessite: A density functional theory study

“…Magnetic moments were calculated to identify the oxidation states of Mn in chalcophanite and in the Zn-TCS-MnO 2 models through electron population analysis as implemented in CASTEP (Segall et al, 1996). Because unsaturated surface O ions of metal oxides show a large induction effect on spin polarization as compared to saturated O (Cline et al, 2000;Gallego et al, 2005), the spin states of O ions were analyzed to determine the relative bonding saturation of O near a Mn vacancy in Zn IV -TCS vs. Zn VI -TCS.…”

Ab initio LDA+U prediction of the tensile properties of chromia across multiple length scales

“…Most previous theoretical studies of the surfaces of Cr 2 O 3 have focused on the Cr-terminated (0 0 0 1) surface (Mejias et al, 1999;Cline et al, 2000;Rohrbach et al, 2004). However, the morphological features of sintered Cr 2 O 3 crystals studied with high-resolution transmission electron microscopy (HRTEM) suggest that the ð0 11 2Þ, ð1 12 0Þ, and ð1 12 6Þ planes are exposed, and therefore are possible low-energy surfaces (Scarano et al, 1993).…”