Ferroelectric Ceramic-polymer Research Articles

The influence of the chemical structure of selected polymers on the properties of ferroelectric ceramic-polymer composites

The paper presents research on ferroelectric ceramic-polymer composites based on barium-strontium titanate and water-thinnable polymeric dispersions, obtained by using tape casting method. Barium strontium titanate with the assumed stoichiometry Ba0,65Sr0,35TiO3 was synthesized by the high temperature solid-state reaction. Water-thinnable polymeric dispersions were synthesized from butyl acrylate, styrene and tert-butyl acrylate containing different amounts of individual monomers. Then, the ceramic-polymer composites were obtained by tape casting. The influence of the chemical structure of synthesized binders on the rheological properties of the slurries and on physicochemical and electrical properties (characterized by using Broadband Dielectric Spectroscopy, BDS) of ceramic-polymer composites were investigated.

Dielectric/ferroelectric properties of ferroelectric ceramic dispersed poly(vinylidene fluoride) with enhanced β-phase formation

Abstract Free standing and flexible ferroelectric ceramic-polymer composites (PVDF+ ϕ wt.% of BNBT (0.94Na0.5Bi0.5TiO3-0.06BaTiO3)) with 0–3 connectivity were synthesized by solution-casting technique. Composite nature and homogeneous distribution of ceramic filler particles in PVDF were confirmed with x-ray diffraction and scanning electron microscopic analysis. The intensity ratio of β-phase with respect to α–phase i.e., I20.2°/I18.4° (obtained from XRD analysis) and the fraction of electro-active beta phase i.e., F(β)% (obtained from FTIR analysis) are enhanced with increase in filler concentrations and peaked for 35 wt% of the ceramic filler. An enhancement of the % of crystallinity (calculated from XRD analysis) has been observed with increase in the filler concentrations. The increase of the fraction of β-phase has been explained on the basis of ion (negatively charged surface ion of the ferroelectric ceramic filler) -dipole (-CH2 dipole of the polymer matrix) interactions, as evidenced from FTIR and UV-VIS absorbance spectra. Relative dielectric permittivity (dielectric constant) and ferroelectric polarization were found to be highest for the composite with 35 wt% of ferroelectric ceramic filler. Percolation theory has been successfully employed to explain the observed trend in the dielectric properties with the compositional variation. Significant enhancement in the electro active β-phase has been correlated with the improved dielectric and ferroelectric properties of the composite.

Depolarization field effect on dielectric and piezoelectric properties of particulate ferroelectric ceramic-polymer composites

The effects of depolarization field on the dielectric and piezoelectric properties of ferroelectric ceramic particle-filled polymer-matrix composites are investigated at the underlying domain level. Phase field modeling and simulation reveals that the macroscopic properties of the composites are dominated by depolarization field effect, which depends on the arrangement and alignment rather than the size or internal grain structure of the ferroelectric particulates. It is found that 0–3 particulate composites with random dispersion of ferroelectric particles behave essentially like linear dielectric rather than ferroelectric materials, and domain-level analysis reveals the physical mechanism for lack of domain switching or hysteresis as attributed to strong depolarization effect. Thus, without effective reduction or elimination of the depolarization field, the composites cannot benefit from the functional fillers regardless of their superior properties. In order to exhibit the desired ferroelectric behaviors, it necessitates continuous ferroelectric phase connectivity in the composites.

Features of electromechanical properties of piezoactive compositeswith elements of connectivity 1-1

Effective electromechanical properties, figures of merit andrelated parameters are firstly studied within the framework of proposedmodels of piezoactive composites `ferroelectric ceramic-polymer'(connectivity 1-1) and `ferroelectric ceramic-porous polymer'(connectivity 1-0-1). The effect of the shape of the pores on the piezoelectriccoefficients, their anisotropy, electromechanical coupling factors, figures of merit,etc in 1-0-1 composites is analysed. The calculatedconcentration dependences of the piezoelectric coefficients and otherparameters as well as the piezoelectric anisotropy of 1-1 and 1-0-1composites have no analogy to known data on two- and three-componentcomposites on the basis of ferroelectric ceramics.

Effective medium theory of the mechanical, dielectric and piezoelectric properties of ferroelectric ceramic-polymer composite.

Effective medium theory of the mechanical, dielectric and piezoelectric properties of ferroelectric ceramic-polymer composite.

Piezo- and Pyroelectricity in Ferroelectric Ceramic-Polymer Composites

Piezo- and Pyroelectricity in Ferroelectric Ceramic-Polymer Composites

Measurement of the pyroelectric coefficient in composites using a temperature-modulated excitation

Ferroelectric polymers such as PVDF and its copolymer P(VDF/TrFE) as well as ferroelectric ceramic-polymer composites have to be annealed at a high temperature for an extended period of time after polling, before the measurement of the pyroelectric coefficient by the direct method can be performed, in order to eliminate the high depolarization current which hinders the determination of the true pyroelectric current. Here it is suggested that a periodic temperature oscillation of a ceramic-polymer composite sample would permit measurement of its true pyroelectric coefficient without the need to anneal the sample. The temperature distribution inside the composite sample, the magnitude of the pyroelectric current and their variation with the frequency of temperature oscillation have been simulated with the present theory. Pyroelectric measurements using this technique have been made on a poled composite of calcium-modified lead titanate (PbTiO3) and a copolymer of vinylidene fluoride and trifluoroethylene P(VDF/TrFE) and compared with the results of the direct measurements before and after annealing, in order to test the validity of the method.