Influence of Zn2+ ions on the structural and electrical properties of Mg1-xZnxFeCrO4 spinels

The polycrystalline magnesium-zinc ferrite chromate having the chemical formula Mg1-xZnxFeCrO4 (0.0 <= x <= 1.0) were prepared by conventional solid phase reaction using high purity reagents. The structural and electrical properties at room temperature have been investigated by XRD, TEM, SEM, EDS, TGA, DTA, FT-IR and DC electrical resistivity techniques. The lattice parameters such as the lattice constant, average particle size, bonds length, density, porosity and volume shrinkage were found to vary with increasing Zn2+ content in the sample. The lattice constant a increases from 8.361 angstrom for MgFeCrO4 to 8.382 angstrom for ZnFeCrO4 pinels. The IR spectra confirm the presence of two main absorption bands v(1) and v(2) in the frequency range of 400-1000 cm(-1), arising due to the tetrahedral (A) and octahedral (B) stretching vibrations respectively. Values of v(1) and v(2) decrease with increasing Zn+2 content over the whole composition range. The scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs showed aggregates of stacked large grains. Values of the room temperature DC electrical resistivity decrease as Zn2+ content increases. The low values of the vacancy model parameters indicate that the Mg1 - xZnxFeCrO4 spinels are strongly defective and the participation of the Zn2+ vacancies in the improvement of the electrical conductivity in these spinels. The thermo-gravimetric, TGA and differential thermal analysis, DTA show loss of mass caused by vaporization of the surface and trapped water molecules at higher temperatures. (C) 2015 Elsevier B.V. All rights reserved.