Correlation of enhancement of β-phase with improved dielectric properties of ferroelectric ceramic polymer composites

Abstract

Ferroelectric ceramics polymer composites have received a significant attention of scientific community due to their wide variety of device applications such as embedded capacitors, multilayer capacitors, high-energy-density capacitors, and gate insulators in organic field effect transistors with reduced weight, size, and cost. Ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers have been mostly utilized owing to their relatively high dielectric permittivity as compared to other polymer matrix. Fabrication of the ferroelectric-ceramics polymer composites by the addition of ferroelectric ceramic filler in to polymer matrix is one of the suitable approach for the enhancement of dielectric and ferroelectric properties. PVDF ([-CH2-CF2]), is a flexible semi-crystalline polymer, which crystalizes into five different phases, viz. α, β, γ, δ and ɛ. The electro active β-phase showed highest dipolar moment per unit cell as compared to the other phases. So there is an urge to enhance the ferroelectric β-phase of the PVDF polymer in the composite systems for device applications. We have prepared ferroelectric ceramic polymer composites using PVDF as polymer host and 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 (BNBT) as ceramic filler. One series of PVDF+ ϕ wt.% of BNBT (ϕ = 0, 5, 10, 15, 20, 25, 30, 35, 40 & 50) composites were prepared using solution casting technique. Structural, morphological, vibrational, dielectric and ferroelectric properties of these composites have been investigated using techniques like SEM, XRD, FTIR, UV-VIS, dielectric and ferroelectric measurement. A homogenous distribution of ceramic fillers has been observed from SEM micrographs. With increasing filler concentration, the electro-active β-phase increases and for 35 wt.% filler concentration it attains the maximum value as observed from both XRD and FTIR results. FTIR and UV-VIS absorbance spectra results, confirms the increasing electro-active β-phase in the composite. The enhancement of β-phase in the composite is explained using ion (negatively charged surface ion of the ferroelectric ceramic filler) -dipole (-CH2 dipole of the polymer matrix) interaction mechanism. The highest value of dielectric constant and ferroelectric polarization has been observed for an optimum filler concentration of ferroelectric ceramic filler (i. e., 35 wt.%).