W.A. Groen

Improving the d33 and g33 properties of 0-3 piezoelectric composites by dielectrophoresis

Composites of piezoelectric particles in a polymer matrix with enhanced properties in the poling direction were prepared by dielectrophoretic alignment of the particles. The effect of processing parameters such as the amplitude and frequency of the applied electric field and the viscosity of the matrix on the dielectric and piezoelectric properties of the cured composite were demonstrated for a composite with a PZT volume fraction of 0.2. The amount of structuring could be correlated to the dielectric and piezoelectric properties of the composite through the order parameter for the average particle chain orientation, which was derived from image analysis of the microstructure. The piezoelectric properties of the aligned composites can be described with a new model for composites containing particles arranged into chains. The model predictions are in good agreement with the experimental results.

Direct strain energy harvesting in automobile tires using piezoelectric PZT–polymer composites

Direct piezoelectric strain energy harvesting can be used to power wireless autonomous sensors in environments where low frequency, high strains are present, such as in automobile tires during operation. However, these high strains place stringent demands on the materials with respect to mechanical failure or depolarization, especially at elevated temperatures. In this work, three kinds of ceramic–polymer composite piezoelectric materials were evaluated and compared against state-of-the-art piezoelectric materials. The new composites are unstructured and structured composites containing granular lead zirconate titanate (PZT) particles or PZT fibers in a polyurethane matrix. The composites were used to build energy harvesting patches which were attached to a tire and tested under simulated rolling conditions. The energy density of the piezoelectric ceramic–polymer composite materials is initially not as high as that of the reference materials (a macro-fiber composite and a polyvinylidene fluoride polymer). However, the area normalized power output of the composites after temperature and strain cycling is comparable to that of the reference devices because the piezoelectric ceramic–polymer composites did not degrade during operation.

Roll-to-roll embedded conductive structures integrated into organic photovoltaic devices

Highly conductive screen printed metallic (silver) structures (current collecting grids) combined with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) are a viable replacement for indium tin oxide (ITO) and inkjet printed silver as transparent electrode materials. To provide successful integration into organic photovoltaic (OPV) devices, screen printed silver current collecting grids should be embedded into a substrate to avoid topology issues. In this study micron-thick conductive structures are embedded and integrated into OPV devices. The embedded structures are produced roll-to-roll with optimized process settings and materials. Topology measurements show that the embedded grids are well suited for integration into OPV devices since the surface is almost without spikes and has low surface roughness. JV measurements of OPV devices with embedded structures on a polyethylene terephthalate/silicon nitride (PET/SiN) substrate show an efficiency of 2.15%, which is significantly higher than identical flexible devices with ITO (1.02%) and inkjet printed silver (1.48%). The use of embedded screen printed silver instead of ITO and inkjet printed silver in OPV devices will allow for higher efficiency devices which can be produced with larger design and process freedom.

Dielectrophoretically structured piezoelectric composites with high aspect ratio piezoelectric particles inclusions

Piezoelectric composites were prepared by dielectrophoretic alignment of high aspect ratio piezoelectric particles in a thermosetting polymer matrix. A high level of alignment was achieved in the cured composite from a resin containing randomly oriented high aspect ratio particles. Upon application of an electric field during curing of the resin, the particles were found to rotate with their long axes in the direction of the electric field, before coalescing to form chains. The dielectric and piezoelectric properties of the structured composites are well described by an analytical model for composites containing particles arranged into chains. The influence of degree of rotation and aspect ratio of the individual particles as well as their spacing is described with this model. The results correlate with the experimental values for both permittivity and piezoelectric constants in the poling direction. Dielectric and piezoelectric properties were significantly improved with respect to randomly dispersed piezoelectric ceramic powder–polymer composites and the maximum g33 was shifted to a lower volume fraction. The results could have implications for development of dielectric and piezoelectric (nano-)fiber composites for dielectrics such as embedded capcitors, as well as piezoelectrics for sensing and energy harvesting applications.

Piezoelectric and mechanical properties of fatigue resistant, self-healing PZT–ionomer composites

Piezoelectric ceramic-polymer composites with 0-3 connectivity were fabricated using lead zirconium titanate (PZT) powder dispersed in an ionomer (Zn ionomer) and its reference ethylene methacrylic acid copolymer (EMAA) polymer matrix. The PZT-Zn ionomer and PZT-EMAA composites were prepared by melt extrusion followed by hot pressing. The effects of poling conditions such as temperature, time and electric field on the piezoelectric properties of the composites were investigated. The experimentally observed piezoelectric charge coefficient and dielectric constant of the composites were compared with theoretical models. The results show that PZT-Zn ionomer composites have better piezoelectric properties compared to PZT-EMAA composites. The static and fatigue properties of the composites were investigated. The PZT-Zn ionomer composites were found to have excellent fatigue resistance even at strain levels of 4%. Due to the self-healing capabilities of the ionomer matrix, the loss of piezoelectric properties after high strain tensile cyclic loading could be partially recovered by thermal healing.

Effect of dielectrophoretic structuring on piezoelectric and pyroelectric properties of lead titanate-epoxy composites

Functional granular composites of lead titanate particles in an epoxy matrix prepared by dielectrophoresis show enhanced dielectric, piezoelectric and pyroelectric properties compared to 0-3 composites for different ceramic volume content from 10% to 50%. Two structuring parameters, the interparticle distance and the percentage of 1-3 connectivity are used based on the Bowen model and the mixed connectivity model respectively. The degree of structuring calculated according to both models correlate well with the increase in piezoelectric and pyroelectric sensitivities of the composites. Higher sensitivity of the electroactive properties are observed at higher ceramic volume fractions. The effect of electrical conductivity of the matrix on the pyroelectric responsivity of the composites has been demonstrated to be a key parameter in governing the pyroelectric properties of the composites.

Structure, dielectric and piezoelectric properties of donor doped PZT ceramics across the phase diagram

ABSTRACT The effects of Zr/Ti ratio on the dielectric and piezoelectric properties of the sintered Pb(ZrxTi(1−x))0.99Nb0.01O3 piezoelectric ceramics across the entire range of phase diagram of the PZT solid solution was studied systematically. The materials were prepared by the conventional mixed oxide process. The phase purity and crystal structure of the calcined powders and sintered ceramics was analysed using X-ray diffraction. The microstructure of the sintered ceramics has been investigated using scanning electron microscopy. It is seen that even though there is a significant increase in dielectric constant (ϵr) and piezoelectric charge coefficient (d33) at the PZT-52 (MPB) composition, the voltage sensitivity (g33) of the PZT-0 (lead titanate) ceramics are higher than that of MPB.

Piezoelectric and pyroelectric properties of conductive polyethylene oxide-lead titanate composites

Polymer-ceramic composites with pyroelectric sensitivity are presented as promising candidates for sensing applications. Selection of the appropriate ceramic filler and the polymer matrix is one of the key parameters in the development of optimized materials for specific applications. In this work lead-titanate (PT) ceramic particulate is incorporated into a polymer matrix, polyethylene oxide (PEO) with a relatively high electrical conductivity to develop sensitive and at the same time flexible composites. PT particles are dispersed in PEO at varying volume fractions, and composite materials are cast in the form of films to measure their dielectric, piezoelectric and pyroelectric properties. From these data the piezoelectric voltage coefficients as well as pyroelctric figures of merit of the composite films have been determined. In order to determine the effect of electrical conductivity of the polymer matrix on the poling efficiency and the final properties, a poling study has been performed. Improving the electrical conductivity of the polymer phase enhances the poling process significantly. It is found that both the piezoelectric and the pyroelectric figures of merit increase with concentration of PT. PT–PEO composites show superior pyroelectric sensitivity compared to other composites with less conductive polymer matrices.

Large Area Photonic Flash Soldering of Thin Chips on Flex Foils for Flexible Electronic Systems: In Situ Temperature Measurements and Thermal Modelling

AbstractIn this work photonic energy from a high power xenon flash lamp is used for soldering thin chips on polyimide and polyester foil substrates using standard Sn-Ag-Cu lead free alloys. The absorption of the xenon light pulse leads to rapid heating of components and tracks up to temperatures above the solder melting temperature, while the temperature in the organic foil substrates remains low. Due to its high transparency the temperature in the delicate polyester foil remains low enough to avoid damage and allows fast soldering with standard lead-free alloys. The technology is fast and could be applied in-line in roll-to-roll fabrication of flexible electronics. In situ temperature measurements were performed and compared to finite element model predictions of the temperature in the chip during and after application of the photonic pulse. The accuracy of the model is within 10°C for the tested samples, which allows it to be used in developing photonic flash soldering compatible circuit designs.

Exploring the piezoelectric performance of PZT particulate-epoxy composites loaded in shear

The active and passive piezoelectric response of lead zirconium titanate (PZT)-epoxy particulate composites loaded in shear is studied using analytical models, a finite element model and by experiments. The response is compared to that of the same composites when loaded in simple tension. Analogously to bulk PZT, particulate PZT-polymer composites loaded in shear show higher piezoelectric charge coefficient (d 15) and energy density figure of merit (FOM15) values compared to simple tension (d 33) and (FOM33). This outcome demonstrates the as-yet barely explored potential of piezoelectric particulate composites for optimal strain energy harvesting when activated in shear.