Identification of frequency regimes for short and long range mobility of charge carriers in GO/MnFe₂O₄/PPy nanocomposites

Highlights

• Graphene oxide/manganese ferrite/polypyrrole nanocomposites have been synthesized with varying filler concentrations.

• Wide tenability of dielectric and ferroelectric attributes of nanocomposites is witnessed.

• Conditions are optimized for a favorable composite recipe showing efficient dielectric response.

• Graphene oxide/manganese ferrite/polypyrrole nanocomposites exhibit potential for energy storage devices.

Abstract

The physico-chemical properties of polymer ceramic composites highly depend upon the nature of ceramic, polymer and their interface. Among other interesting features, they have potential for flexible electronics and energy storage devices. Especially, graphene based polymer ceramic composites are unique for their high dielectric characteristics. In this regard, we synthesized a three constituent novel nanocomposite with polymer matrix to check their potential for energy storage applications. Here in, the polypyrrole has been exquisitely decorated with graphene oxide and manganese ferrite nanoparticles with their different concentrations. The development of spherical grains and their transformation into rod like morphology with a significant change in their dimension is noticed. The weight percentage of all elements according to their stoichiometric formula and the finger prints of different constituents in the form of their functional groups are also identified before their dielectric and ferroelectric analyses. The highest value of dielectric constant (121449) has been noticed at 100 Hz frequency, which reduced to 1066 at 1 MHz. The dielectric loss was also quite high at lower frequency which decreased to 1.2 at same high value of frequency (1 MHz). The calculations for recoverable energy density and energy loss density are performed using PE hysteresis loops and the highest value of recoverable energy density is recorded as 4.7 × 10⁻⁸ mJ/cm³. Thus, high values of dielectric constant and low dielectric loss of these nanocomposites make them attractive dielectric material in electrical appliances for capacitive applications.

Introduction

The rapidly increasing trend of miniaturization and development of microelectronic devices, put a high demand for ceramic polymer composites, having profound energy conversion and storing ability so that they could be accommodated in miniaturized devices [1,2]. The dielectric polymers can be prepared by integrating high-k ceramics and conducting nanoparticles into polymer matrix [3,4]. The polymer/ceramic composites are suitable for their use in electronic devices because of their tunable dielectric properties. To achieve a strong dielectric response, a very high filler contents are required which usually make them brittle and heavy weight. On the other hand, the polymer like polypyrrole (PPy) with conducting nanofillers can provide significantly high dielectric constant (ε') values by using small amount of fillers [5]. In contrast with perovskite ceramic capacitors, the dielectric material with polymeric matrix have tremendous properties like high value of ε', low dielectric loss (tanδ), easy handling and low fabrication cost. Therefore, from the last few decades they have attracted much more attention of the researchers worldwide [6,7].

Polymer composites are very captivating because of their broad applications in electronic devices, batteries, sensors and light emitting diodes etc. [[8], [9], [10]]. Among all these, PPy is the most advantageous conducting polymer due to its easy synthesis route and low cost. The mechanical, electrochemical and dielectric properties of PPy may be enhanced by adding small amount of fillers such as barium titanate, titania and reduced graphene oxide (rGO) etc. [[11], [12], [13]]. Manganese ferrite, MnFe₂O₄ (MFO) is a spinel ferrite and has many potential applications in fields like electronic industries, microwave devices and sensors [14]. The dielectric properties of MFO have also been investigated and it is noticed that MSO possessed excellent dielectric properties. This is the reason why we selected MFO as a filler contents in this nanocomposite.

Graphene oxide (GO) is considered as an outclass filler for decoration of polymer composites with excellent dielectric properties. But GO in its pristine form exhibits low electrical conductivity, thus an electrochemically active part must be incorporated into it in order to enhance its dielectric properties. It has been observed that when conducting polymers are decorated with GO they exhibit high dielectric response [15]. From the past few years, the incorporation of two different fillers within same polymer has gained special attention of researchers. Such composites are called hybrid composites where one can simultaneously enhance ε' and suppress tanδ significantly [16,17]. Deshmukh and co-workers synthesized polypyrrole/polyvinyl alcohol (PPy/PVA) composites and they observed a momentous improvement in their dielectric response. The value of ε' was noticed as 27.93, at 50 Hz and 150 °C which increased around 8 times and became 155.18 with the addition of GO at the same value of temperature and frequency. However, tanδ only changed from 2.01–4.71 at same frequency [18]. In another report, He et al., synthesized and discussed the dielectric properties of GO/PPy/polyvinylidene fluoride (PVDF) composites. They observed that the dielectric properties enhanced with the incorporation of GO/PPy into PVDF [19].

In present work, we synthesized a ternary nanocomposite with hybrid fillers i.e. GO and MFO incorporated in PPy. Although PPy is a conducting polymer having almost no capacitance but we have developed and enhanced dielectric performance of PPy by introducing fillers in it. Here, we report a series of nanocomposites with varying concentrations of fillers to tune the dielectric and ferroelectric attributes of these hybrid polymer-ceramic composites for potential applications in energy storage devices.