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PVDF and Barium ferrite (~ 10μm) blends are prepared by mechanical mixing of the respective volume ratio of powders and cold pressed in the form of pellets.
High dielectric permittivity in BaFe12O19/polyvinylidene fluoride composites K. Devi Chandrsekhar, S. Karthikeyan, A. K. Das, and A. Venimadhav Citation: AIP Conf. Proc. 1512, 788 (2013); doi: 10.1063/1.4791274 View online: http://dx.doi.org/10.1063/1.4791274 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1512&Issue=1 Published by the AIP Publishing LLC.

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Downloaded 23 Jul 2013 to 140.78.102.177. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://proceedings.aip.org/about/rights_permissions

High Dielectric Permittivity in BaFe12O19/Polyvinylidene fluoride Composites K. Devi Chandrsekhara, b#, S. Karthikeyanc, A. K. Dasa, and A. Venimadhavb a

Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur, Kolkata-721302, India b ,c Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur, Kolkata-721302, India # [email protected]

Abstract. We have prepared BaFe12O19/polyvinylidene fluoride composites and studied their dielectric permittivity of over a wide range of frequency. We have observed a large enhancement of effective dielectric permittivity ~ 23@1KHz for 0.55% volume fraction of BaFe12O19 filler. The effective enhancement of dielectric permittivity with volume fraction follows the Yamada model. Additionally, these composites show the good thermal stability over a wide range of temperature. Keywords: High dielectric permittivity, Inorganic/organic composites. PACS: 77.84.Lf, 32.10.Dk, 81.05.Qk, 77.22.Gm

annealed at ~ 170 °C (which is the melting point of PVDF) for 15min. The electrical and dielectric properties were measured using a precision impedance analyzer (Agilent 4294A) in the frequency range of 40Hz-10MHz. The homogeneity of the samples was confirmed using the field emission scanning electron microscopy (FESEM (JEOL)) in the back scatter electron (BSE) mode.

INTRODUCTION Recently, there has been considerable interest to enhance the dielectric permittivity and reduce the loss in particle filled polymer composites through interfacial polarization. Inorganic/organic composites are mechanically flexible and easy to process with cost effective methods and finds broad range of applications such as embedded passive technology, microelectronics, etc.,.1 In such composites, material selection plays a crucial role to achieve high dielectric permittivity. Most of the literature deals with ferroelectric or conductor fillers in highly insulating polyvinylidene fluoride (PVDF) matrix.1 Even though these composites shows the high dielectric permittivity the potential drawbacks are high loss in the conducting materials and sudden rise of permittivity at the ferroelectric ordering temperature in the ceramic fillers restricts the applicability of these material for a wide range of temperature and frequency. In this present investigation we are reporting the enhanced dielectric properties with good thermal stability in BaFe12O19 (BF)/polyvinylidene fluoride composites.

RESULTS AND DISCUSSIONS

FIGURE 1. (a) & (b): FESEM image of BF/PVDF blends at 0.18 and 0.55% volume fractions.

The FESEM micrographs of BF/PVDF composites with BF volume fraction 0.18 and 0.55% are shown in fig. 1(a) & (b). Inset of the fig. 1(a) shows the micrograph of pure PVDF. From the figures, one can conclude that BaFe12O19 particles are well isolated in the PVDF matrix and fairly distributed even for the higher volume fractions.

EXPERIMENTAL DETAILS PVDF and Barium ferrite (~ 10μm) blends are prepared by mechanical mixing of the respective volume ratio of powders and cold pressed in the form of pellets. For obtaining good flexibility, pellets are

SOLID STATE PHYSICS: Proceedings of the 57th DAE Solid State Physics Symposium 2012 AIP Conf. Proc. 1512, 788-789 (2013); doi: 10.1063/1.4791274 © 2013 American Institute of Physics 978-0-7354-1133-3/$30.00

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relaxation peak at 1 MHz decreases with the increase in barium ferrite volume fraction. The reduction of loss (0.12) and increase of dielectric permittivity (11.46) at 1MHz (fig. 3b) is useful for several high frequency and high dielectric permittivity applications.1 Fig. 2(c) shows the variation of effective conductivity with frequency for different volume fraction. It has been observed that above 10 KHz effective conductivity varies linearly which indicates the high insulating nature of the samples even upto 0.55% volume fraction.

FIGURE 1. shows the variation of (a) εeff (b) Tanδ (c)

σeff (d) Variation of εeff with volume fraction of fillers and the solid line indicates fit to eq. (1). The variations of effective dielectric permittivity with frequency for different volume fraction of BF filler are shown in fig. 2(a). By increase the filler concentration the effective dielectric permittivity increases progressively and reaches a maximum volume fraction of 46 at 40Hz for 0.55% volume fraction. The nature of the effective dielectric permittivity with frequency exactly resembles the conventional ferroelectric-polymer composites such as BaTiO3-PVDF composites.1 The low frequency dispersion in dielectric permittivity and conductivity indicates possibilities of Maxwell-Wagner interfacial polarization. This can be applicable for inhomogeneous systems which satisfies the condition ımİf  ıfİm, where m and f denotes filler and matrix respectively. The variation of effective dielectric permittivity with volume fraction for 1 KHz has been fitted with the expression developed by the Yamada et al. for inhomogeneous medium.1, 2 According to which

H௘௙௙ ൌ Hଵ ሾͳ ൅ ௡H

௡௙ಳಷ ሺHమ ିHభ ሻ



భ ାሺHమ ିHభ ሻሺଵି௙ಳಷ ሻ

FIGURE 3. shows the temperature dependent εeff for 0.55% volume fraction sample.

Fig. 3 shows the temperature dependent of dielectric permittivity for 0.55% volume fraction sample with different frequencies. The dielectric permittivity shows a small decrease with increase in temperature at ~ 75°C again increases for further rise in temperature. The overall variation of dielectric permittivity is about ~ 10% within the measured temperature window which indicates the high thermal stability of the composites. In conclusion, biphasic BF/PVDF composites are fabricated. Large enhancement in effective dielectric permittivity (~ 23@1 KHz) has been noticed upto 0.55% volume fraction. The temperature and frequency dependent of effective dielectric permittivity shows the good thermal stability which is desirable for the high dielectric permittivity applications.

(1)

ACKNOWLEDGMENTS

where fBF is the filler volume fraction, n is the parameter related to the geometry of the ceramic particle, ε1 and ε2 are the dielectric permittivity of matrix and filler respectively. The satisfactory fit (fig. 2(d)) has been obtained with the ‘n’ value of 11.5 which is in good agreement with theoretical model.1 Fig. 2(b) shows the variation of loss tangent with frequency for different volume fractions. The maximum obtained dielectric loss is 0.8 at 40Hz for 0.55% volume fraction sample. Above 1 KHz the dielectric loss is quite low (below 0.4). The PVDF

This work was supported by ISIRD project funded by SRIC, IIT Kharagpur. .

REFERENCES 1. Z. M. Dang, J. K. Yuan, J. W. Zha, T. Zhou, S. T.

Li, G. H. Hu Prog. Mater. Sci. 57, 660 (2012). 2. Y. Bai, Z. Y. Cheng, V. Bharti, H. S. Xu, and Q. M. Zhang , Appl. Phys. Let. 76, 3804 (2000).

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