Semiconductor to metallic transition and polaron conduction in nanostructured cobalt ferrite

Abstract

In this paper we report semiconductor to metal transition and polaron conduction in nanostructured cobalt ferrite. The material was prepared by the coprecipitation technique. Average particle size was determined to be ~10 nm by x-ray diffraction and transmission electron microscope analysis. A detailed electrical characterization was performed in the frequency range 20 Hz–2 MHz and temperature range between 300 and 400 K. Nanostructured cobalt ferrite exhibits semiconductor behaviour from 300 to 330 K. From 330 to 400 K it has metallic behaviour. The change at ~330 K is attributed to a change in cation distribution as obtained from Mössbauer spectroscopy. The ac conductivity of cobalt ferrite followed σac ∝ ωs dependence. The observed variation of the exponent 's' with temperature suggests that overlapping large polaron tunnelling is the dominant conduction mechanism from 300 to 400 K and in the frequency range 20 Hz–2 MHz.