Frequency and temperature dependent impedance spectroscopy of cobalt ferrite composite thick films

Abstract

Cobalt ferrite (CoFe2O4) composite thick films consisting of two different sized CoFe2O4 particles were deposited on Pt/Ti/SiO2/Si substrate by a hybridized sol-gel processing and spin coating technique. X-ray diffraction analysis showed a pure spinel phase of CoFe2O4, which was also confirmed by micro-Raman spectra. Scanning electronic microscope indicated a dense microstructure with a thickness above 8 μm. The detailed electrical investigations were conducted in the frequency range of 100 Hz–1 MHz and temperature range between 25 and 200 °C. Real and imaginary parts of impedance (Z′ and Z″) in the above frequency and temperature domain suggested the coexistence of two relaxation regimes: one was induced by electrode polarization; while the other was attributed to the coeffect of grains and grain boundaries, which was totally different from its counterpart of bulks and also not reported in other ferrites. Electrical modulus (M′ and M″) further showed the crossover from grains effect to grain boundaries effect with increasing measured temperature under the suppression of electrode polarization. A non-Debye relaxation behavior and two segments of frequency independent conductivity were observed in dielectric spectra, which was also consistent with the results of ac conductivity spectra. In the conductivity spectra, double power law and single power law were separately applied to the coeffect from grains and grain boundaries and electrode polarization effect. Moreover, the dc conductivity from both effects well obeyed the Arrhenius law and their activation energies were matching to the ones calculated from imaginary impedance peaks, the detailed physical mechanisms on them were finally discussed.