Electrical Conductivity of α-Ferric Oxides

Abstract

It was intended to establish the procedure of electrical conductivity measurement ef fine crystalline materials, uch as metal oxyhydroxides, which decompose at high temperature. The frequency dependence of the conductivity of unfired fine af-Fe20s in different degree of crystallinity was measured in the frequency range of dc to 30 MHz under various pressures of 90N 150kg cm2. The conductivity, 6, increases with increasing frequency, f. The ac conductivity, (=, d d being the dc c nductivity), is proportional to s(0.6 5 0.8)in the 100 7MHz frequency range. The disper ion of a.. is ascribed to the hopping of a d electron from localized ferrous ion to localized ferric ion. The frequency dependence of conductivity aRd dielectric constant is interpreted by regarding the compressed samples as the inhcmogeneous dielectrics consisting of fine crystalline materials with the above frequency dependent conductivity and of the intergranular gaps. Log a showed a linear correlation with the ratio, d, d', where d, is the true density of hematite and d is the apparent density of the compressed specimen. The frequency dependence of oi determined by the extrapolation of the linear log a vs. do d Plot t unity of the do d ratio is similar to that of the c nductivity of the sintered samples. di at 7 MHz increased with the crystallite size determined by X ray diffraction. These results indicate that di at 7 MHz is the electrical conductivity which reflects the inner structure of fine crystalline materials.