The effect of Zn+2 substitution on some structural properties of CuFeCrO4 system

Abstract

The interesting physical and chemical properties of the spinel ferrites are governed by the type of magnetic ions residing on the tetrahedral (A) and octahedral (B) sites and the relative strength of the inter (JAB) and intra sublattice (JBB, JAA) interactions. The distribution of cations among A and B sites and physical parameters such as density, porosity, shrinkage, particle size, etc. can be controlled by preparation parameters like temperature, synthesis technique, pressure and suitable choice of substituent ions. Ferrites containing Cu have shown interesting electrical and magnetic properties [1]. The potential applications of Cu, Ni and Co based soft ferrites are well known, especially where these elements are partially substituted by zinc and cadmium which occupy tetrahedral position in the spinel lattice and strongly affect the magnetic properties of ferro spinels [2, 3]. Such properties are affected and governed by structural parameters. Recently, some work has been reported in the literature on the magnetic properties of slowly cooled [4] and quenched [5] samples of Znx Cu1−x FeCrO4 spinel ferrite system. No systematic study of the concentration dependence of structural properties such as lattice constant, ionic radii, density, porosity, shrinkage, particle size etc. has been reported in the literature. In the present communication we report the effect of Zn+2 substitution for Cu+2 in Znx Cu1−x FeCrO4 (x = 0.0, 0.2, 0.4 and 0.6) on some structural properties with the aim to develop sintered materials whose properties can be tailored to the requirements of the device engineers. The four samples of the spinel series were prepared by usual double sintering ceramic method. The starting materials were AR grade oxides ZnO, CuO, Fe2O3 and Cr2O3 produced from Thomas & Backer. These oxides were mixed in proper proportion and pre-sintered at 950 ◦C for 12 h. In final sintering process, the materials were held at 1100 ◦C for 12 h and slowly cooled to room temperature. The X-ray diffractograms were recorded using Cu Kα radiation in a Philips X-ray diffractometer, model PM 9220. Typical X-ray diffractograms for the samples with x = 0.2, 0.4 and 0.6 are shown in Fig. 1. The diffractograms showed the presence of cubic spinel phase with no extra lines corresponding to any other phase. The X-ray lines were found to be sharp, which makes the detection of any impurity phase easy. The values of lattice constant a were determined with an accuracy of ±0.0002 nm. The variation of lattice constant with zinc concentration, x , is shown in Fig. 2 and the values are tabulated in Table I. The lattice constant increases linearly with increasing x thus obeying the Vegard’s law [6]. Usually in a solid solution of spinels within the miscibility range, a linear change in the lattice constant with the concentration of the components is observed [6]. The slow linear increase in lattice constant is due to the replacement of smaller Cu+2 ions (0.069 nm) by the slightly larger Zn+2 ions(0.070 nm) in the system Znx Cu1−x FeCrO4. The X-ray density (dx) and bulk