Corundum-type surfaces

Corundum-Type Surfaces-AljOj, CrjOj, FejOj.VjOj... 

Corundum-type Magnetic Oxide Surfaces. The substrate hematite with the corundum-type crystal structure is an antiferromagnet below 963 K. In the corundum-type structure of hematite, pairs of ferric ions are in a row spaced by single vacant sites along the <111> direction. The positions of ferric ions in each pair are shifted slightly upward or downward in the <111> direction. We denote these lattice positions as up and down sites (Au and A ), respectively. 

Figure 9. Simplified model of the (111) surface of the corundum-type structure, (a) A view of the surface from a direction slightly shifted from <111>. Only metal ions of the zeroth, first, and second layers are shown, (b) A section of the surface along the arrows depicted in part a. Hexagonally close-packed oxide ion layers are shown with lines. Surface protons are not shown, (c) A divalent Co-57 or pentavalent Sb-119 ion on the zeroth metal ion layer, (d) Aquo or hydroxyl complex of divalent Co-57 or pentavalent Sb-119 hydrogen-bonded to the surface oxide ion layers of hematite.

R.S. (1993) Surface sites on spinel type of corundum type metal oxide powders. Langmuir 9 92-99... 

Fig. 15. Experimental data on the structure of corundum type depolarized (0001) surfaces (side and top views).

The electronic structure of corundum type oxide surfaces have been studied with photoelectron spectroscopy [102, 103] as well as with electron energy loss spectroscopy [104]. Henderson and Chambers [103] have reeently reviewed the photoelectron spectroscopic evidences. Still, there seems to be an ambiguity about the oxidation state of the chromium ions in the immediate surface layer. XPS Cr 2p data may be to a large extent reconciled as being due to Cr(III) in the surface, because there is obviously no change in the spectra as a function of... 

The surface charge density and hence the surface electrical potential are determined by the nature of the surface and solution physicochemistry. As shown in Fig. 1, the surface potential [measured by the zeta potential, (Q, the potential at the slip plane] of corundum (AI2O3) depends on the solution pH and the type and concen-... 

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