No abstract

The microstructural changes in high-energy electron-irradiated poly(vinylidene fluoridetrifluoroethylene) 68/32 mol % copolymer have been studied by X-ray diffraction, FTIR spectroscopy, and differential scanning calorimetry. The macroscopic polarization response in these materials was investigated by examining the dielectric and polarization behavior in a broad temperature and frequency range. It was found that besides reducing crystallinity in the copolymer film, irradiation produces significant changes in the ferroelectric-to-paraelectric phase transition behavior. The irradiation leads to a reduction in the polar domain size to below a critical size (a few nanometers), resulting in the instability of the macroscopic ferroelectric state and transforming the structure of the crystalline region in the copolymer from a polar all-trans ferroelectric to a nonpolar state represented by a trans-gauche conformation. However, a reentrant polarization hysteresis was observed in the copolymers irradiated with higher doses (>75 Mrad). Therefore, there is an optimized dose that generates a copolymer with a nonpolar structure but relatively high crystallinity whose electromechanical performance is the best. In the copolymers in this optimum dose range, FT-IR data revealed that there is not much change in the molecular conformation with temperature, even as the temperature passes through the dielectric peak, indicating that there is no symmetry breaking in both the macroscale and local level. Although the lattice spacing of the crystalline region along the molecular chain direction discontinuously changes between two special cases, the interchain spacing continuously changes with the irradiation dose, reflecting a strong intrachain coupling between the nonpolar and polar regions. On the other hand, the X-ray data reveal that the crystalline size perpendicular to the polymer chain does not change with irradiation until at doses exceeding 85 Mrad.

The lead-free 0.5((Ba 0.7 Ca 0.3)TiO 3)-0.5(Ba(Zr 0.2 Ti 0.8))O 3 (BCZT) piezoceramics were synthesized using sol-gel method. The Rietveld analysis of X-ray diffraction (XRD) data and differential scanning calorimetry (DSC) studies of as-synthesized BCZT powder suggests the coexistence of ferroelectric orthorhombic (O) and tetragonal (T) phases at room temperature (RT). The value of curie temperature (T T-C) as depicted from DSC and dielectric studies was found to be ≈ 110 C. The BCZT ceramic particles were dispersed in the polyvinylidene fluoride (PVDF) matrix, an electroactive polymer with great ferro/piezoelectric response in its distinct β and γ phases, to form ferroelectric ceramic-polymer composites for their applications in flexible energy storage capacitors. The present work reports the Fourier-transform infrared spectroscopy (FTIR), XRD, dielectric, ferroelectric, and energy density properties of PVDF/BCZT composite films having different wt% of BCZT content fabricated by the solution-cast technique. The FTIR and XRD studies depict the γ-PVDF and pure BCZT phases in composite films. The dielectric studies estimated the relative permittivity (ε r) of a composite film with 50 wt% of BCZT content to be ≈ 31 (at 120 Hz) which was about three times as compared with that of pure PVDF. The dielectric loss (tan δ) was maximum ≈ 0.15 (at 120 Hz) for 50 wt % BCZT composition. The ferroelectric studies and energy storage calculations showed that the value of remnant polarization (P r), coercive field (E c) and energy storage density (W) attain the maximum value of 0.63 μC/cm 2 , 35.22 kV/cm, and 70.46 mJ/cm 3 , respectively for the film sample having 40 wt% BCZT content. The maximum energy storage efficiency, η (%) is calculated to be ≈ 60 for 50 wt% BCZT composition. The results indicated that the incorporation of BCZT particles

The polarization switching transients of spray deposited ferroelectric (NH4)0.39K0.61NO3 (NKN) films has been analyzed with nucleation limited switching (NLS) model by considering domain growth limited process. The experimentally measured microscopic polarization switching curves fitted well with NLS model and the characteristic switching times obeyed the Lorentzian distribution function. The local field variation was found to be minimum at pulse amplitude 15 V, which makes the polarization reversal more probable. The value of spontaneous polarization, Ps and coercive field, Ec was found to be 6.58 μC/cm2 and 4.10 kV/cm, respectively. The value of Ps from the switching and P-E loop is in good agreement with each other. The field emission scanning electron microscopy and atomic force microscopy images of the NKN film reveal the formation of nanoparticles of NKN.

No abstract