**2. Experimental details**

*Multifunctional Ferroelectric Materials*

volume is *U KE* <sup>=</sup>

ε <sup>2</sup> 0 max

higher value of εeff [2, 33, 34].

1

To overcome these problems, PF are undergoing development based on ferroelectric polymer as well as ferroelectric ceramics. Among the ceramic fillers, BaTiO3 is a very good ferroelectric material and comparably better as others have harmful lead content [16, 17]. Among the various polymers, very few polymers, such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride trifluoroethylene [PVDF Tr(FE)] and Teflon show ferroelectric/piezoelectric behavior and have high dielectric constants [18, 19]. They are also of high breakdown strength, lightweight, flexible and having permanent dipolar polarization. Among the ferroelectric polymers, PVDF shows high piezo-electric coefficients, good ferroelectric behavior. Due to these advantages, PVDF is used as piezo-electric sensors/actuators/memory devices. But the major problem with PVDF is that, the magnitudes of ferroelectric parameters aren't as good as the parameters, obtained from the

conventional ceramics, which limit them from direct applications. Similarly the PD are having higher flexibility, non-toxicity, bio-compatibility, low cost, higher visco-elastic properties, etc. [20–31]. Due to their higher energy density/lower loss tangent (Tan δ) with higher breakdown field strength, they are going to be the emerging materials of future for electrostatic energy storage applications. The PD composed of polymers with conductor/ceramic nanoparticles are considered recently to be the demanded materials for electrical energy storage applications [20–36]. For energy storage applications, the maximum stored energy per unit

<sup>2</sup> , where *K* is the relative dielectric constant and Emax is the

maximum electric field, which can be applied to the material (proportional to the breakdown field of the material). Over the last 20 years of research, the ferroelectric polymers e.g PVDF matrix also have been preferred due to it's high static dielectric constant (~15)/higher visco-elastic properties/higher insulating nature as compared to other non-polar polymers. The preferred fillers are high dielectric constant ferroelectric ceramics in development of these PD. However, the development of the polymer-ceramic composites (PCC) have been slowed down, as the effective dielectric constant (εeff) for these composites were found be very low i.e. εeff ~ 100 at low frequencies due to the low dielectric constant of the polymers as well as due to the conventional hot molding process conditions. In preparing these PCC, ferroelectric ceramic, such as, PMN-PT, BaTiO3, PbTiO3, etc. with varying particle size are introduced into the PVDF matrix through hot molding and partially the approach becomes effective in order to get better PD [5–10]. For preparing PCC based on PVDF, the traditional mixed technique (solution casting

followed by hot molding) is used, during which the spherulites of PVDF get lost [2, 33, 34], which lowers the value of εeff. Recently Panda et al. [23–30, 32, 33] has shown the importance of spherulites by following the cold pressing technique in preparing the PD based on PVDF, due to which the spherulites of PVDF are retained. The spherulites are responsible in the additional storage of electrical charge due to their additional interfaces, resulting higher interfacial polarization/

With the objective of achieving flexibility with low cost/easy processing and higher value of electrical parameters, for device applications, the traditional process condition (hot molding of the thick films prepared from solution casting) is changed to cold pressing developed by our group in which the spherulites of PVDF will be retained for the case of PCC. Hence, PCC of good ferroelectric/ piezoelectric/dielectric properties, are developed from good ferroelectric ceramics/good ferroelectric polymers. Since in the PZT/PVDF composites, lead is a toxic component, hence the PCC based on PVDF/*n*-BaTiO3, with different volume fraction of *n*-BaTiO3 (*fn*-BaTiO3), were prepared with the help of cold pressing method. The prepared composites have shown the interesting ferroelectric/piezoelectric/ dielectric/conductivity properties and finds suitability for various applications.

**90**

Polymer composite based on PVDF/*n*-BaTiO3 from 0.0 to 0.60 of volume fraction of nano filler *n*-BaTiO3 (*f*BaTiO3) were prepared by mechanical hand mixing with Agate mortar/Pestle for 2 hours. The final pellets under room temperature consolidation at a pressure of 30 MPa with the help of a Hydraulic press [2, 33] were prepared. The microstructure investigation on the samples was carried out with the help of FESEM. The ferroelectric hysteresis, i.e. the polarization versus electric field (P ~ E) measurement, is done with the help of a P ~ E hysteresis loop tracer. The piezoelectric coefficient (d33) for the samples is measured with the help of Piezoelectric measurement instrument. The electrical measurements were made on all the PCC in the frequency range of 50 Hz to 5 MHz and in the temperature range of room temperature to 100 ̊C. The dielectric results of the PCC have been understood by fitting with the help of the software Mathematica.
