Anisotropy of Electrical Properties in Pure and Doped αFe2O3

Interpretation of Electrical Conductance Transition of Hematite in the Spin-Flip Magnetic Transition Temperature Range

“…E g s found in earlier studies, varying from 2.3 to below 1.9 eV as previously noted, lie between the values 2.31 and 1.56 eV, given previously, which as shown above are inaccurate. The strong differences met in the literature for E a , e.g., 2.1 eV 41,42 or 0.735 eV 27 and for E g varying as above or 3.36 eV 46 are thus justified by Eq. 13, the The C UIP must become maximum at a T, which can be considered Ϸ T M , between 260 and 294 K, i.e., around 278 K, which is close to the 265 K in the literature for bulk hematite.…”

“…The radii of Fe 2ϩ and Fe 3ϩ are 0.74 and 0.64 Å, respectively. 40 Fe 4ϩ also can form relatively easily 41,42 ͑see also later͒ the radius of which must be even smaller. The radius of O 2Ϫ is 1.32 Å.…”

“…34 Optical studies supported the process 2Fe 3ϩ ϩ 2.1 eV → Fe 4ϩ ϩ Fe 2ϩ and a twocarrier semiconductance for undoped hematite. 41,42 Fe 4ϩ and Fe 2ϩ concern valence band holes and species enriched with electrons of conduction band. The results agree with this process which justifies both the intrinsic semiconductance and formation of the aforementioned diffusing ions.…”