Synthesis and dielectric behavior of various novel metal oxide decorated reduced-graphene oxide composites

Abstract

Developing novel dielectric materials has always been an interesting area in material’s research owing to their importance especially in capacitive energy storage. In this context, at the time of problem formulation for this thesis work (i.e., during the year 2012), the dielectric behavior of graphene filled polymers has attracted good attention. However, at that time there were no reported works on “dielectric behavior” of metal oxides (time tested dielectric materials) and graphene containing nanocomposites. Therefore in this thesis work elucidation of various aspects of dielectric behavior of reduced-graphene oxide (r-GO) and metal oxide containing nanocomposites has been taken up. Owing to the presence of residual oxygen functional groups and defects in r-GO, it is hypothesized that it will have a unique influence on the dielectric behavior of metal oxides and r-GO containing nanocomposites. As anticipated, a unique and strong interfacial polarization (Maxwell-Wagner polarization) was observed in metal oxide decorated r-GO nanocomposites synthesized by molecular level mixing technique which resulted in homogenous distribution of metal oxide particles on the surfaces of r-GO sheets. In this thesis work, CuO/r-GO, ZnO/r-GO, MgO/r-GO and NiO/r- GO nanocomposites were synthesized and their dielectric behavior in correlation with their morphology, crystallinity/phase and composition has been elucidated. This thesis also provides a comprehensive treatment to understand the dielectric behavior, especially the dielectric relaxation in metal oxide and r-GO containing nanocomposites. The treatment involves fitting experimental results with suitable theoretical models (for example, Havriliak- Negami relaxation model) that enable the intricate examination of physical mechanisms that controlled the dielectric behavior of the nanocomposites under consideration. Percolation effect on the dielectric permittivity was elucidated in the case of NiO/r-GO nanocomposite which exhibited a giant dielectric permittivity of 3688. This work will pave a way to understand and control the possible physical mechanisms that might take place at a very small length scales and in turn will be useful to control the dielectric behavior of graphene based nanocomposites in particular and nanocomposites, in general