Overlapping large polaron tunneling conductivity and giant dielectric constant in Ni0.5Zn0.5Fe1.5Cr0.5O4 nanoparticles (NPs)

We report an orderly study on the structural and dielectric properties of Ni0.5Zn0.5Cr0.5Fe1.5O4 nanoparticles (NPs) synthesized by a polyethylene glycol (PEG)-assisted hydrothermal technique. XRD, FT-IR, FE-SEM and EDX measurements were implemented for the structural, morphological and compositional investigations of the product. Dielectric spectroscopy was used for the dielectric property investigation of the sample. Average particle size of the nanoparticles was estimated using Debye-Scherrer's equation as 34 nm. Electrical properties of the sample have been investigated in the range of 1 Hz to 3 MHz (233-412 K). It is observed that the sample has a giant dielectric constant approaching to 10(6) within the examined temperature range. It is also determined that the sample exhibits a dispersive phase transition around 305 K at which this giant value of dielectric constant has been obtained. This transition has been characterized by Diffuse Phase Transition. Temperature and frequency dependence of dielectric loss function has been attributed to surface charges for the short-time relaxations and to hopping electrons for the long-time relaxations. At low frequencies, dielectric loss function has been supported by the modified Cole-Cole equation. Frequency and temperature dependent conductivity behavior of the sample has been explained by Overlapping Large Polaron Tunneling model. (C) 2011 Elsevier B.V. All rights reserved.