JOURNAL OF MATERIALS SCIENCE 24 (1989) 2478 2482 Electrical conduction in -irradiated and unirradiated Fe304, CdFe204 and CoxZnl_xFe204 (0 x 1)ferrites M. A. MOUSA* Chemistry Department, Faculty of Science, Benha University, Benha, Egypt A. M. SUMMAN Chemistry Department, Faculty of Applied Science, Umm AI-Qura University, Mekkah, Saudi Arabia M. A. AHMED Physics Department, Faculty of Science, Cairo University, Cairo, Egypt A. M. BADAWY Centre of Science and Mathematics, Tail, Saudi Arabia The electrical conductivity of 7-irradiated and unirradiated finely divided ferrites of composition Fe304, CdFe204 and CoxFnl_xFe204(0 ~< x ~< 1) was studied in a nitrogen atmosphere as a function of temperature. Fe304, ZnFe204 and CdFe204 showed n-type conduction, whereas CoFe204 showed p-type conduction. For CoxZnl_xFe204 it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe304, and CoxZnl_xFe204(0 < x ~< 1) was explained by a hopping mechanism, whereas the conduction in ZnFe204 and in CdFe204 is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of 7-irradiation on the con- ductivity, activation energy, charge carriers and the conduction mechanism is discussed. 1. Introduction The present investigations are part of a more extensive programme dealing with the effect of both composition and y-irradiation on the electrical conduction of inorganic oxides having spinel crystal structure. These oxides are important in many branches of technology [1-3], e.g. ferrites, ferroelectric, solid state electrolytes, catalyst and nuclear fuels. For a binary oxidic spinel containing divalent, X, and trivalent, Y, cations, two extreme distributions of cations are possible: the "normal" (X)[Y2]O4 and the "inverse" (Y)[XY]O4 distribution [4], where the ions present on the octahedral sites are in square brackets. Between these limiting cases intermediate distributions are possible. The cation distribution in spinels has been found to be an equilibrium function of tempera- ture and pressure [5] as well as other factors con- cerning the ions, such as the ionic charge, ionic radius, anion polarization, etc. [6]. In the present work we investigated the electrical conductivities of y-irradiated and unirradiated Fe304, CoxZn~_xFe204(0 ~< x ~< 1) and CdFe204 ferrites with the aim to investigate the effect of composition on the type of charge carrier and its transport mech- anism. Moreover, the effect of y-irradiation on the conduction in these ferrites was also one of our targets. 2. Experimental details "Analar grade" CdO, CoO, ZnO and Fe203 were used as starting materials to prepare CdFezO4 and CoxZn~_xFe204(O <~ x <~ 1) ferrites under investi- gation. The oxides were mixed intimately in stoichio- metric proportion and preheated under nitrogen at ll00K for 8h and then at 1500K for 10h. Fe304 was prepared by heating tablets of Fe203 at 1700 K in air for 30h. In all cases, the product was quenched in water. The chemical analysis was done using the atomic absorption technique for determining the amounts of zinc, cobalt, cadmium and iron in the prepared samples. X-ray analysis confirmed the spinel phase formation in both v-irradiated and unirradiated samples. The ferrites investigated were irradiated with y-rays using a 6°Co-cell with a dose rate of 3.6 krad h-l for 344 h. Infrared spectra for y-irradiated and unirradiated ferrites were recorded using a Pye Unicam Model SP3-100 spectrophotometer, KBr discs and Nujol oil nulls. The d.c. electrical conductivity, a, was measured on pellets (diameter 7 mm and thickness 2 ram) using a two-probe method with silver electrodes. The conductivity measurements were carried out under a nitrogen atmosphere in the temperature range 300 to 550K. The Seebeck coefficient, 0, measurements *Author to whom all correspondence should be sent. Present address: Chemistry Department, Centre of Science and Mathematics, P.O. Box 1070, Taif, Saudi Arabia. 2478 0022-2461/89 $03.00 + .12 © 1989 Chapman and Hall Ltd.