Dielectric studies of nanocrystalline nickel-cobalt oxide

The effects of temperature and frequency on the dielectric behavior and AC electrical conductivity have been studied for nanosized samples of nickel cobalt spinel oxide with grain size 10 +/- 5nm prepared by chemical co-precipitation method. The particle sizes are determined from X-ray diffraction patterns and TEM images. The surface morphologies are revealed by SEM images. The dielectric permittivity of nanosized nickel cobalt spinel oxide samples have been evaluated from the observed capacitance values in the frequency range 100 KHz-5 MHz and temperature range 300-403 K. Space charge polarization and rotation direction polarization play a crucial role in determining the dielectric behavior of this nanosized material. Further, from the permittivity measurements AC conductivity is evaluated. Evaluation of the dispersion parameters, optical dielectric constant, static dielectric constant, relaxation time and spreading factor are carried out following established methods. The dispersion parameters of nickel-cobalt oxide nanoparticles in the temperature range 353-393 K are evaluated using Cole-Cole plots. The results are analyzed and discussed. (c) 2007 Elsevier B.V. All rights reserved.