Structural, electrical and optical properties of sol-gel synthesized cobalt substituted MnFe2O4 nanoparticles

We report the structural, electrical and optical properties of Co substituted manganese ferrite of the composition Mn1-xCoxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) synthesized by sol-gel technique. X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structure. The average crystallite size of these materials is found to be in the range of 20-35 nm and lattice constant is found to decrease as Co2+ concentration is increased. The permittivity (epsilon), dielectric loss (tan delta) and ac conductivity (sigma(ac)) have been determined at room temperature as a function of frequency (42 Hz to 5 MHz). The results of dielectric properties indicate the normal Maxwell-Wagner type dielectric dispersion due to interfacial polarization. DC electrical resistivity has been performed using two probe technique. The decrease of resistivity with temperature confirms the semiconducting nature of the samples. Real and imaginary part of impedance (Z' and Z '') suggest existence of one relaxation mechanism which is attributed to the co-effect of grains and grain boundaries. The energy band gap as determined from the UV-visible spectra decreases gradually with the Co increasing content.