**Abstract**

In this chapter, the Ferroelectric, Piezoelectric and Dielectric behavior of novel polymer/ceramic nano-composite (PCC) based on ferroelectric polymer [polyvinyledene fluoride (PVDF)] & nano Barium Titanate (*n*-BaTiO3) with different volume fractions of *n*-BaTiO3 (*f*BaTiO3), prepared through the novel cold pressing method has been discussed. The ferroelectric parameters of PCC are attributed to spherulites of PVDF, the increase of *n*-BaTiO3 and the ordered homogenous structure due to the novel cold pressing. The clustering of ceramic fillers is responsible for randomization of the structures of these composite ferroelectrics for some samples, leading to decrease of electrical polarisations. The piezoelectricity and piezoelectric coefficients of these composites ferroelectrics, increases with increase of ceramic filer content and remains constant beyond a certain ratio. However, the dielectric properties increase linearly as a function of ceramic content due to increase of interfaces/interfacial polarisations. The enhancement of effective dielectric constant (ɛeff) is attributed to the large interfacial polarization arising due to the charge storage at the spherulites of PVDF and at the polymer/filler interfaces of PCC and have been explained on the basis of sum effect with the help of the standard models. The achieved lower loss tangent (Tan δ) for the PCC as compared to the polymer/metal composites (PMC) is attributed to the highly insulating nature of PVDF & semiconducting *n*-BaTiO3. The thermal stability of the composites is also maintained due to the higher melting temperature (170°C) of PVDF. The cold pressed PCC based on PVDF are going to act as better polymer ferroelectric/dielectrics for memory and electrical energy storage applications.

**Keywords:** Polymer ferroelectrics/dielectrics, spherulites, Ferroelectric polymers, Barium titanate, Dielectric constant, Loss Tangent, Polymer nanocomposites

### **1. Introduction**

Polymer ferroelectrics (PF) and polymer dielectrics (PD) are considered recently to be the fascinating materials for their large inherent benefits of nonvolatile memory/sensor/piezoelectric/dielectric/pyroelectric/magneto-electric applications [1–17]. The conventional ferroelectric ceramic materials, e.g. BaTiO3, PZT, PbTiO3, etc. being used as memory elements/piezoelectric sensors/actuators/ transducers, etc. are suffering from a large number of disadvantages, such as; brittleness, high cost and consume higher energy/longer time for their preparation. 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 volume is *U KE* <sup>=</sup> ε <sup>2</sup> 0 max 1 <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/ higher value of εeff [2, 33, 34].

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.

**91**

*Ferroelectric, Piezoelectric and Dielectric Properties of Novel Polymer Nanocomposites*

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

The FESEM micrographs of pure PVDF are given in **Figure 1a** and **b**. **Figure 1a** and **b** shows the presence of spherulites (the spherical semi-crystalline regions of the polymer). The micrographs of PVDF/n-BaTiO3 composites with different *f*BaTiO3 = 0.2 and *f*BaTiO3 = 0.60 are shown (**Figure 1c**–**f**). The ordered homogenous structures are also observable and is attributed to the recent novel method of cold pressing as evident from the sample with *f*BaTiO3 = 0.2 (**Figure 1c** and **d**). The spherulites present in the polymer are of diameter of the order of ~0.1 μm (**Figure 1a** and **b**). The *n*-BaTiO3 are also of the order of diameter of the spherulites as they are of size 100 nm, i.e. 0.1 μm, During cold pressing, the *n*-BaTiO3 clusters (**Figure 1c** and **d**) inside the polymer matrix, may have taken the typical shapes. For the sample with *f*BaTiO3 = 0.6 (**Figure 1e** and **f**), shows high level of heterogeneity, as lot of defects and dislocations has emerged in the structure and is responsible for giving a decrease in the ferroelectric & piezoelectric properties of the PF. **Figure 1** reveal slight agglomeration of BaTiO3 nanoparticles in the nanocomposites. The average filler size in the nanocomposites are of ~100 nm. The nano-dispersion of filler in the polymer matrix is well observed. It is also obvious that a variety of interfaces have occurred into the composites, which will be always useful in the storage of electrical charge at the interfaces The large amount of *n*-BaTiO3 into the PCC will also be responsible for

giving better ferroelectric/piezoelectric/dielectric properties [2, 34–36].

The ferroelectric properties of the PF, prepared from PVDF/*n*- BaTiO3, the polarization versus electric field (P ~ E) of both the pure materials are given (**Figure 2**) at different voltages. **Figure 2a** shows narrow hysteresis loops for pure PVDF due the mixed phases [α, β, γ, δ & ε] as well as the electrical non-poling of

The polarization versus electric field (P-E hysteresis loop) of the PF under different voltages for various *f*BaTiO3 = 0.2 (**Figure 3a**), *f*BaTiO3 = 0.3 (**Figure 3b**) *f*BaTiO3 = 0.4 (**Figure 3c**) and *f*BaTiO3 = 0.5 (**Figure 3d**) are shown. All the samples show symmetrical P-E hysteresis loops. The loop area increases of with increasing

*DOI: http://dx.doi.org/10.5772/intechopen.96593*

by fitting with the help of the software Mathematica.

**2. Experimental details**

**3. Results and discussion**

**3.2 Ferroelectric properties**

*3.2.1 Ferroelectric hysteresis*

the polymer PVDF.

**3.1 Microstructure**
