Synthesis, structural and dielectric properties of Cr3+ substituted Fe3O4 nano-particles

FeCrxFe2−xO4 (x==0.1, 0.2, 0.3, 0.4 and 0.5) nano-particles were synthesized by a chemical co precipitation method and the effect of Cr3+ substitution on structural and dielectric properties of Fe3O4 was studied. Structural studies were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. XRD pattern confirmed the single spinel ferrite phase formation. Particle size and crystallite size of the synthesized materials lie in the range of 25-50 nm as calculated from electron microscopy images and X-ray diffraction patterns using Scherrer׳s formula. Dielectric loss (tanδ), real part of dielectric constant (ε′), imaginary part of dielectric constant (ε″), ac conductivity (σac), real (resistive) part of impedance (Z′) and imaginary part of impedance (Z″) were evaluated as a function of frequency, composition and temperature using an impedance analyzer in the frequency range of (1 kHz-5 MHz) and temperature range of (27-250 °C). AC conductivity (σac) was found to decrease with increase in Cr3+ ion doping and can be explained on the basis of hopping mechanism. The variation of dielectric loss (tanδ), dielectric permittivity (ε′), ac conductivity (σac) with temperature and frequency can be explained on the basis of Maxwell-Wagner type of interfacial polarization and hopping mechanism between ferrous and ferric ions at octahedral site. Variation in Cole-Cole plots with temperature shows decrease in resistivity with increase in temperature. The Nyquist impedance plots of the prepared materials reveals the inherent phenomenon involved in conduction mechanism of Cr3+ substituted Fe3O4 ferrites. Behavior of DC electrical resistivity with increasing temperature indicates that the substituted ferrites have semiconductor like behavior. Activation energy was found to increase with increasing Cr3+ ion content.