Finite size effects on the electrical properties of sol–gel synthesized CoFe2O4 powders: deviation from Maxwell–Wagner theory and evidence of surface polarization effects

• Published in: Journal of physics. D, Applied physics Vol. 40; no. 6; pp. 1593 - 1602
• Main Authors: George, Mathew, Nair, Swapna S, Malini, K A, Joy, P A, Anantharaman, M R
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 21.03.2007; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity phenomena in semiconductors and insulators; Dielectric properties of solids and liquids; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Electronic transport in condensed matter; Exact sciences and technology; Mobility edges ; hopping transport; Permittivity (dielectric function); Physics; Grain size; Finite size effect; Frequency dependence; Powders; Electrical conductivity; Cobalt oxides; XRD; Heat treatments; Hopping conduction; Surface effect; Fine particle; Iron oxides; Permittivity; Sol-gel process
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/40/6/001

Fine particles of cobalt ferrite were synthesized by the sol-gel method. Subsequent heat treatment at different temperatures yielded cobalt ferrites having different grain sizes. X-ray diffraction studies were carried out to elucidate the structure of all the samples. Dielectric permittivity and ac conductivity of all the samples were evaluated as a function of frequency, temperature and grain size. The variation of permittivity and ac conductivity with frequency reveals that the dispersion is due to Maxwell-Wagner type interfacial polarization in general, with a noted variation from the expected behaviour for the cold synthesized samples. High permittivity and conductivity for small grains were explained on the basis of the correlated barrier-hopping model.