JOURNAL OF MATERIALS SCIENCE 23 (1988) 3083-3087 Electrical conduction in -irradiated and unirradiated zinc-iron ferrites M. A. MOUSA* Chemistry Department, Faculty of Science, Benha University, Benha, Egypt M. A. AHMED Physics Department, Faculty of Science, Cairo University, Cairo, Egypt The electrical conductivity of 7-irradiated and unirradiated finely-divided spinels of com- position (Znx 2+ 2+ 3+ 2- Fel-xFez )04 was studied in a nitrogen atmosphere as a function of tem- perature. The results of both 7-irradiated and unirradiated ferrites with compositions x ~< 0.79 showed that the electrical conduction occurred by fast electron exchange amongst Fe2§ and Fe3+ ions situated on octahedral sites in the spinel lattice, by a hopping mechanism. For compo- sition x > 0.79 it was found that the transition of the charge carriers through cation vacancies is the predominant mechanism. Some breaks in the conductivity-temperature curves were found near the Curie points. Seebeck voltage measurements showed that y-irradiated and unirradiated spinels behave as n-type semiconductors. The effect of 7-irradiation on the con- ductivity, activation energy, charge carriers and the conduction mechanism is discussed. 1. Introduction Recently several mixed metal oxides having the gen- eral formula XY204 [I-11] have been investigated as they exhibit interesting structural, electrical, mag- netic and catalytic properties. In these oxidic spinels the physical properties were found to be dependent on the nature of the ions involved, their charges and their site distribution amongst 8-tetrahedral (A) and 16-octahedral (B) sites. For these oxidic spinels two extreme distributions of cations are possible: the "normal" ( • )A[Y2]BO4and the "inverse" (Y)A[XY]BO 4 distribution [11], where the ions in the octahedral sites are in square brackets. Several workers [5-10] have studied solid solution by sub- stituting ions at A and B sites. They have obtained a gradual change in the solid state chemistry and in the physical properties of these oxidic spinels by varying the composition of the solution. Magnetite, Fe304, is one of these oxidic spinels. It possesses an inverse spinel structure [12] with the cation distribution 3+ 2+ 3+ 2 (Fe~)A[Fel Fe~ ]~O4 . It has been found [13-19] that for substituted magnetite MxFe3_xO4 a fast electron exchange between ions of different valencies lying on equivalent sites is con- sidered as the reason for the higher electrical conduc- tivity in the case of lower values of x. For higher x values other conduction mechanisms should be considered. The effect of ionizing radiation on the electrical properties of mixed oxides has received limited attention. With a view to investigating the effect of 7-irradiation on the electrical properties of ferrites the system 2+ 3+ 2+ 3+ 2 (Znx Fel_x)A[Fe I xFel+x]BO4 has been investigated. 2. Experimental procedure Analar-grade zinc chloride, ferrous chloride, ferric chloride and sodium hydroxide were used to pre- pare the investigated samples. The hydroxide co- precipitation technique was used in the preparation of ZnxFe3_xO4 spinels, where x lies in the range 0 ~< x ~< 1. Each of the co-precipitated sample was dried at 370K, then calcined in a muffle furnace in an air atmosphere at 600 K for 6 h. The final product appeared as an extremely fine-grained solid. The amounts of zinc and iron in each prepared spinel were analysed using the atomic absorption technique. The Fe 2+ ion content in each spinel was determined by volumetric analysis [20]. X-ray analysis confirmed the spinel phase forma- tion in both y-irradiated and unirradiated samples. The synthesized materials are mixed spinels (Fe 2+ ions are on octahedral sites and Zn 2+ ions on tetrahedral sites) and the lattice parameter varies linearly with x. The lattice parameters recorded in this work coincide well with those reported by Gillot et al. [19]. Electrical conductivity measurements were per- formed on pellets (diameter 7ram and thickness 8 mm) prepared by the compression of powder under a pressure of 1400 kg cm -2. The d.c. conductivity of zinc-iron ferrite was measured between 5 and 900 K with a method already reported [10]. The conductivity measurements were carried out in a nitrogen atmos- phere. Seebeck coefficient measurements were made at temperature intervals of AT ~ 50K (against platinum). The investigated spinels were irradiated with 7-rays using a 6~ cell with a dose rate of 39rdsec -1 (0.39Gysec -1) for 160h. * Present address: Chemistry Department, Centre of Scienceand Mathematics, PO Box 1070, Taif, Saudi Arabia. 0022-2461/88 $03.00 + .12 9 1988 Chapman and Hall Ltd. 3083