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Direct current electrical conductivity of gamma ferric oxide
Authors:A K Nikumbh  K S Rane  A J Mukhedkar
Affiliation:(1) University Department of Chemistry, 411 007 Ganeshkhind, Pune, India
Abstract:The study of the direct current electrical conductivity, sgr, of freshly prepared gamma-Fe2O3 and that of a sample stored for seven days in static air suggests that gamma-Fe2O3 adsorbs oxygen and water from the atmosphere. From infra-red spectra it is deduced that the absorbed water in gamma-Fe2O3 is present as the physically adsorbed water and as lattice water. The adsorbed oxygen and physically adsorbed water are removed by heating to 100Dagger C, while the lattice water remains in gamma-Fe2O3 even up to 280Dagger C. The removal of lattice water is associated with a decomposition during which some of the hydrogen formed occupies the vacancy sites. This suggested formation of the hydrogen ferrite phase is based on the kink in the log sgr against T –1 curve observed at 177Dagger C. This kink is very well resolved for a sample equilibrated at 100Dagger C in normal atmosphere, and the measurements of sgr above 100Dagger C of this sample are done in an N2 atmosphere. The suggestion that the hydrogen ferrite phase is formed has been substantiated by comparison of the X-ray diffraction patterns of gamma-Fe2O3 heated under the different atmospheres. From the log sgr against T –1 plot for a sample heated under a nitrogen atmosphere the activation energy is small (< 0.05 eV) up to 215Dagger C, and it is comparatively large (0.95 eV) above 215Dagger C. These results suggest a hopping mechanism for the direct current electrical conductivity of gamma-Fe2O3. This suggestion has been substantiated by data of the temperature variation of Seebeck voltage.
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