Ultrasonic-assisted Co-precipitation synthesis of CoAl2O4 with different capping agents: Determination of electrical and optical features

Abstract

In this study, cobalt aluminate nanoparticles were synthesized by a modified coprecipitation method using different capping agents and ultrasonic treatment. Optical, morphological and structural analyses of the samples were performed and the dielectric behaviour of the samples was investigated using the impedance spectroscopy technique in the frequency range of 10–107 Hz and at room temperature. It was determined that with the use of capping agent for NPs with 30–60 nm grain size, the optical forbidden energy gaps increased from 1.80 eV to 2.15 eV and the Co/Al ratio decreased from 0.534 to 0.362. It has been shown by Williamson Hall analysis that lattice shrinkage occurs with the use of the capping agent in the structural analysis of the materials. It has been determined that the type of capping agent is effective on the grain size, optical absorption and structural content of the final product, and especially lattice shrinkage is an effective mechanism in grain size reduction. The effect seen in the materials produced with the highest OA caused a 50 % decrease in grain size compared to the one without the use of capping agent. AC impedance spectroscopy showed that CoAl2O4 spinel structures have the inhomogeneous distribution of conductive grains with limited conductive grain boundaries and behave in accordance with Koops' model. It was determined that the use of dielectric properties in the high-frequency region improved with the use of capping agents.