Identification of frequency regimes for short and long range mobility of charge carriers in GO/MnFe2O4/PPy nanocomposites
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.
Section snippets
Materials
Analytical grade chemicals used for composite synthesis include iron chloride (FeCl3.6H2O), graphite powder, pyrrole 98 % reagent (C4H5N), potassium persulfate (K2S2O8), iron nitrate, (Fe(NO3)3.9H2O), manganese nitrate (Mn(NO3)3.6H2O) and citric acid (C6H8O7) purchased from Sigma-Aldrich. Hydrogen peroxide (H2O2) was purchased from Merck. Commercial sulfuric acid (H2SO4), hydrochloric acid (HCl) and methanol (CH3OH) were also used. Potassium permanganate (KMnO4) was taken from United
Morphological and elemental analysis
Fig. 2 presents the FESEM images of GO/MFO/PPy nanocomposites, depicting a variety in morphology. Fig. 2a shows the micrograph of pure PPy in which well distributed grains having distinct grain boundaries can be observed. Their grain size has been calculated using ImageJ, a Java based software. The average grain size for pure PPy has been recoded as 300 nm. It is witnessed from Fig. 2b that addition of small amounts of GO and MFO in PPy caused an immediate change of its spherical morphology to
Conclusions
A series of GO/MFO/PPy nanocomposites was synthesized using in situ-polymerization method with varying concentrations of fillers i.e. GO and MFO to study the dielectric and ferroelectric response. A variety of morphology has been observed with different filler concentrations and their effect on dielectric properties was noticed. Transformation of spherical morphology of size 300 nm to rod like shape with length of around 100 nm and average diameter of 30 nm was observed. When filler
CRediT authorship contribution statement
Amna Riaz: Methodology, Formal analysis. Qurat ul Ain: Methodology, Formal analysis. Farah Kanwal: Conceptualization, Resources, Supervision. Saira Ishaq: Methodology, Formal analysis. Ali Raza Khan: Formal analysis, Writing - original draft. Ghulam M. Mustafa: Formal analysis, Writing - original draft. S. Kumail Abbas: Software, Formal analysis. Shahzad Naseem: Resources, Supervision. Shahid M. Ramay: Software, Validation. Shahid Atiq: Conceptualization, Resources, Writing - review & editing.
Declaration of Competing Interest
Authors have no competing interests to declare.
Acknowledgements
Shahid M. Ramay would like to acknowledge Researcher’s Supporting Project Number (RSP-2019/71), King Saud University, Riyadh, Saudi Arabia for their partial support in this work.
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