Abstract
Abstract Values are reported for the d.c. conductivity and Seeback voltage of sintered polycrystalline specimens, prepared from various samples of alpha ferric oxide, in the temperature range 20–1350°C. High-purity samples show a non-linear relationship between the logarithm of the conductivity and the reciprocal of the absolute temperature. This is attributed to the presence of small amounts of ferrous iron (arising from oxygen loss by dissociation), whose influence is suppressed in impure samples. The latter show a linear relation between the logarithm of the conductivity and the reciprocal of the temperature. The Seebeck voltage is very sensitive to the presence of foreign cations in amounts of 100–1000 p.p.m. Manganese and chromium provide trapping sites for negative carriers; magnesium and nickel create positive charge carriers. It is concluded that conduction in ferric oxide is usually dominated either by the effects of impurities or, in highly pure ferric oxide, by deviation from stoichiometry towards metal-excess. An intrinsic process is believed to contribute to conduction above about 800°C.
Published Version
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