Dielectric Properties and Phase Stabilization of PVDF Polymer in (1−x)PVDF/xBCZT Composite Films

Abstract

Polyvinylidene fluoride (PVDF) is a semi-crystalline ferroelectric polymer which can be stabilized in its distinct electroactive polymorphs α and γ by selective processing techniques. In this article, to study the effect of processing temperature and barium calcium zirconium titanate (BCZT) ceramic-doping on PVDF phase stabilization, the pure PVDF and PVDF/BCZT composite films were fabricated by solution-casting and melt-pressing. The Fourier-transform infrared spectroscopy and x-ray diffraction studies showed that the pure PVDF and PVDF/BCZT composite films fabricated by solution-casting possessed the characteristic γ-PVDF peaks while melt-pressing stabilized PVDF mostly in the α-phase. The BCZT ceramic particles were found to have no significant effect on PVDF phase stabilization, but it enhanced the overall crystallinity of polymer matrix. The dielectric studies revealed that the relative permittivity (εr) of γ- and α-PVDF phases in pure PVDF film samples was ≈ 10 and 7.5 (at 120 Hz) respectively. The εr of PVDF/BCZT composite films having 50 wt.% BCZT content synthesized by solution-casting and melt-pressing were estimated to be ≈ 31 and 20 (at 120 Hz), respectively, which was about three times that of pure PVDF film synthesized by the respective technique. The value of loss tangent (tanδ) for pure PVDF films synthesized by solution-cast and melt-press technique were ≈ 0.07 and 0.35 (at 120 Hz) respectively. In temperature-dependent dielectric studies, γ-PVDF showed distinct α-relaxation peak at ≈ 120°C and polymer melting at temperature > 130°C. For α-PVDF, the increase in εr and tanδ was observed during α-relaxation transition at higher temperatures. The dielectric studies indicated that the introduction of BCZT ceramic particles in PVDF matrix increased the εr-value by enhancing the dipolar and interfacial polarizations in composites, while the decrease in tanδ-value was observed due to decrease in molecular dipoles with a decrease in wt.% of PVDF content. These phenomena collectively improved the overall electric properties of ceramic/polymer composites which makes them suitable candidates to explore for flexible electroactive material form.