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Title: Optical, electrical and structural studies of nickel-cobalt oxide nanoparticles
Authors: Tharayil, Nisha J
Raveendran, R
Vaidyan, Alexander Varghese
Chithra, P G
Keywords: Nanoparticles
Arrested precipitation
Calcination temperature
Fourier transform infrared spectrum
Absorption spectra
Optical band gap,
AC conductivity
Dielectric permittivity
Issue Date: Dec-2008
Publisher: CSIR
Abstract: Nanoparticles of nickel-cobalt oxide are prepared by chemical co-precipitation method. The particle size is determined from X-ray diffraction studies and TEM image. The surface morphology is revealed by SEM image. The effect of sintering on the particle size is analyzed. The FTIR studies have been used to confirm the formation of metal oxide. The characteristic stretching and bending frequencies of the sample is analyzed. The absorption spectra of the material in the UV-Vis–NIR range are recorded. An absorption band is observed to occur at 350 nm and another one around 650 nm. From the analysis of absorption spectra, the nickel-cobalt oxide (sintered at 500°C, 700°C and 900°C) are found to have direct band gaps ranging from 1.827 to 1.61 eV. Electrons are highly localized in nanoparticles and interaction between these localized states give rise to the observed band gap. The effect of temperature and frequency on the dielectric behaviour and ac electrical conductivity have been studied for nanosized samples of nickel cobalt spinel oxide prepared by chemical co-precipitation method. The dielectric permittivity of nanosized nickel cobalt spinel oxide sample is evaluated from the observed capacitance values in the frequency range 100 kHz-5 MHz and in the temperature range of 300-403 K. It is seen that with decreasing frequency, the dielectric constant increases much more obviously than that of conventional materials. As the temperature increases more and more dipoles are oriented resulting in an increase in the values of dipole moment. Space charge polarization and rotation direction polarization play a crucial role in the dielectric behaviour of this nanosized material. Further from the permittivity studies ac conductivity is evaluated.
Page(s): 489-496
ISSN: 0971-4588
Source:IJEMS Vol.15(6) [December 2008]

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