Tailoring frequency/temperature independent colossal dielectric constant in Zn-doped Fe3O4/Fe2O3@C/PANI using phase co-existence approach

Abstract

Introducing doped binary oxides to polymers offers a promising way towards advancement of charge density/energy storage materials with colossal dielectric constant. However, the origin of colossal dielectric constant explored in terms of conduction mechanism with a deeper understanding of the coexistence of phases/interfaces in these materials still requires much attention. In this context, we synthesised Zn-doped Fe3O4/Fe2O3@C/PANI composite that exhibits frequency and temperature independent colossal dielectric constant over a broad range, 1 Hz to 10 MHz and 93 K to 333 K, respectively. We analyzed the impedance data using an equivalent circuit model and Cole-Cole fitting to gain insight into the colossal dielectric response and low dielectric loss. The relaxation phenomenon corresponding to a highly stable electroactive region is validated by the distribution of relaxation time (DRT). Furthermore, the composite exhibited a non-relaxor-like behavior due to diffuse phase transition near semiconductor-to-metallic transition (SMT), observed at 303 K. The charge carriers follow the variable range hopping (VRH) and Arrhenius models yielding localization length of 3 Å and activation energy of 35 meV, which supports the charge transport mechanism between like cation interfaces. This detailed analysis covering the frequency and temperature independent dielectric constant along with the understanding of relaxation and conduction phenomena could provide a viable approach towards producing charge density/energy storage devices for practical applications.