Hopping conduction of localized polarons with scaling behaviour in ceramic composite (YCrO3)1 -x - (CoFe1.6Cr0.4O4)x

Abstract

The percolative (YCrO3)1 -x – (CoFe1.6Cr0.4O4)x (x = 0.3, 0.5, 0.7, 1.0), ceramic composite belongs to a family of materials that exhibit colossal dielectric permittivity. Our fundamental interests lie in the investigation of the conduction mechanism of the composite from both microscopic and macroscopic perspectives. Here, all three ceramic composites have been chosen for a comparative study containing CFCO above fc, near fc, and below fc. The electrical conductivity of the composite follows Mott’s variable range-hopping model in the temperature range of 300 – 500 K, indicating domination of this model in conduction of localized polarons in the electrical behaviour. Parameters, including the dc conductivity, hopping, most probable hopping range, the activation energies involved in the said model, the density of localized states at the Fermi level, and relaxation were obtained and analyzed. Scaling behaviors of conductivity and imaginary part of complex impedance were investigated, showing a temperature-independent distribution of relaxation times. By looking at the impedance data at a variety of temperatures, semiconducting behaviour is demonstrated, which has been modelled by an equivalent circuit model that incorporates grain and grain boundary responses. The ferroelectric nature of the samples resembled lossy characteristics due to the presence of the CFCO phase. The correlation between conductivity and colossal apparent permittivity helps in better understand the conduction mechanism in ceramic composites comprising semiconducting and insulating phases.