Synthesis and Characterization of PVDF- CaCu3Ti4O12 Nanocomposite for High Energy Density Capacitors

Abstract

Polymer ceramic nanocompositesare highly in demand due to its prospective applications in electrical and electronics engineering e.g. embedded electronics, varistors, sensors, and high energy density capacitors. Ceramic materials which are usually used as a filler in the polymer matrix such as lead zirconate titanate (PbZrTiO3 ), lead titanate (PbTiO3), barium titanate (BaTiO3), barium strontium titanate ( BaxSr1-xTiO3), etc.possesses a high dielectric constant. But, the dielectric strength of these ceramics is low due to their brittle nature. On the other side, polymers such as polyvinylidene fluoride (PVDF), polyvinyledenedifluoride–trifluoroethylene (PVDF-TrFE), biaxially oriented polypropylene (BOPP) etc shows high dielectric strengthandlow dielectric constants (i.e. < 10). So, incorporationof the ceramic materials inthe polymer matrix could become a promising material for high energy density capacitor and other applications. Among all the polymers, polyvinylidene fluoride (PVDF) is flexible in nature and, has high dielectric breakdown strength but low intrinsic permittivity. Besides this, it is very versatile in nature as it exist in different crystalline phase viz.α, β and γ-phases having different dielectric and polarization behavior.The evolution of these phases are controlled by different ways of processing e.g. quenching, annealing, stretching etc. The β and γ-phases are polar in nature, but the tangent loss of γ-phase is found to be less as compared to β-phase. The γ-phase of PVDF is found to be most suitable for energystorage applications. The dielectric and energy storage behavior of polymer ceramic nanocomposite based on PVDF have been widely investigated. Among all dielectric ceramics, calcium copper titanate (CaCu3Ti4O12) ceramic shows colossal dielectric constant (ε ~ 104 -105) which is constant over a broad frequency (102 Hz -106 Hz) and temperature range (100 K -600 K).The incorporation of the CCTO nanoparticles in the PVDF matrix will be cause less area hysteresis loop by virtue of its non-ferroelectric nature and the composites with less area hysteresis loop have good energy storage properties.Therefore, the composite of calcium copper titanate with PVDF could be an alternative choice of a material for energy storage applications.Earlier studies have confirmed that PVDF-CCTO nanocomposite have moderate dielectric constant, low tangent loss and high mechanical strength. But, the polarization and energy storage behavior of the PVDF-CCTO nanocomposites has not been investigated so far. Therefore, the synthesis and characterization of PVDF-CaCu3Ti4O12nanocomposite for high energy density capacitors has been studied in the present work.The thesis consisting of all these studies has been composed in six chapters. ivThe first chapter gives the brief review of polymers, ceramics and polymer ceramic nanocomposite, which is related with their structural properties, dielectric and energy storage behavior. The aim of thesis is presented in the last section of this chapter. The second chapter describes the details of synthesis and the characterization techniques employed for investigation of materials of interest viz. PVDF thick films, CCTO nanoparticles and PVDF-CCTO nanocomposite thick films. The third chapter describesthe comprehensive study of PVDF polymer thick films and CCTO nanoparticles. The effect of annealing temperature on structural, dielectric and polarization behavior of PVDF thick films has been studied. The annealing temperature in order to have very good dielectric and polarization behavior of PVDF thick film has been optimized CaCu3Ti4O12exhibits high dielectric constant, high breakdown electric field, along withvery good capacitive behavior. Hence the particle size and phase purity of CCTO nanoparticles has also been optimized. The important outcomes of experimental investigation are concluded in the last section of this chapter. The fourth chapter deals with the structural, dielectric and energy storage behaviorof polyvinyline fluroide-CaCu3Ti4O12 nanocomposite films. PVDF-CCTO nanocomposite films have been fabricated by solution casting method, where CaCu3Ti4O12 (CCTO) nanoparticles areincorporated inthe PVDF polymer matrix. Synthesized films have beenstructurally, morphologically, and electrically characterized. Dielectric constant of PVDF-CCTO nanocomposite films are found to increase with increase in loading of CCTO nanoparticles in the frequency range 100 Hz -1 MHz. Obtained dielectric constant of composites has also been fittedin various theoretical models. Unlike dielectric behaviour, polarization does not show the ordered variation with the loading of CCTO nanoparticles. Enhanced energy density and polarization are attributed to increase dipole moment due to ordering of α, β, γ-phases of PVDF in PVDF-CCTO nanocomposite films. The final conclusion of the experimental studies and, its analysis is given in the last section.The fifth chapter describes the effect of functionalization on dielectric and energy storage behavior of PVDF-CCTO nanocomposite thick films. CCTO nanoparticles are functionalized by –NH2functional group by using ethylenediamine. These nanoparticles are incorporated in the PVDF matrix for synthesizing functionalized PVDF-CCTO nanocomposite thick films. The comparative study of functionalized PVDF-CCTO nanocomposite films and normal PVDF –CCTO nanocomposite thick films have been carried out on different parameters viz. structural, dielectric and energy storage behavior. The dielectric constant, electrical displacement, energy density, and efficiency has been found to be increased appreciably in functionalized PVDF-CCTO nanocomposite films as compared to normal PVDF-CCTO nanocomposite films. Improved dielectric and energy storage behavior of functionalized PVDF-CCTO nanocomposite thick films is assigned to modification among the interfaces between PVDF and CCTO vnanoparticles. The chapter ends with important conclusions obtained from the analysis of experimental data.The sixth chapter describes, the summary of all experimental investigation, methodology and, their outcomes of the studies on "Synthesis and characterization of PVDF-CaCu3Ti4O12nanocomposite for high energy density capacitors". Still, there is scope of further investigation on PVDF-CCTO nanocomposites, which wouldbe very important from academic, scientific and technological point of view. The scope of these future investigations have also been suggested.