Piezoelectric polymers are widely used in sensor and actuator applications. Compared to ceramic materials, they have the advantage of mechanical flexibility and an acoustic impedance similar to those of water or air. Their electrical, electromechanical and mechanical properties can be investigated by analyzing piezoelectric resonances in their dielectric spectrum. Apart from its ability to reveal the highfrequency behavior of piezoelectric polymer films, this technique is appealing from a practical point of view because several important parameters can be measured with a single scan that only requires standard dielectric spectroscopy equipment commonly found in many laboratories. This article outlines the theoretical foundations of piezoelectric resonance, examines the experimental aspects, and reviews recent applications in the field of piezoelectric polymers. 1070-9878r r r r r1r r r r r$17.00 ᮊ 2003 IEEE 842 IEEE Transactions on Dielectrics and Electrical Insulation Vol. 10, No. 5; October 2003 1070-9878r r r r r1r r r r r$17.00 ᮊ 2003 IEEE 1070-9878r r r r r1r r r r r$17.00 ᮊ 2003 IEEE 1070-9878r r r r r1r r r r r$17.00 ᮊ 2003 IEEE
Ferroelectrets (i.e., charged cellular polymers) are rendered piezoelectric by means of barrier discharges inside the air-filled voids. The light emission from barrier discharges in cellular polypropylene ferroelectrets was quantitatively studied. Light emission typically occurs above a threshold voltage of 3 kV and then significantly increases with the applied voltage. Time-resolved images reveal discharge processes in individual voids. In addition, a second "back discharge" emission is observed when the voltage is reduced to zero. The buildup of the "effective polarization" in cellular PP ferroelectrets was studied by an acoustic method and dielectric resonance spectroscopy. A polarization-voltage (P-V) hysteresis loop was obtained by analyzing the data with an existing model for the piezoelectric d33 coefficient of ferroelectrets, from which a threshold charging voltage of 3 kV and the back barrier discharges were confirmed and a zero-field "effective polarization" o f 0.5 mC/ m2 was determined. However, charge densities of up to 2 mC/ m2 were measured under an applied bias voltage, leading to the conclusion that the observed back discharges destroy a significant fraction of the effective charge density
Highly uniform polymer-ceramic nanocomposite films with high energy density values were fabricated by exploiting the unique ability of monodomain, nonaggregated BaTiO3 colloidal nanocrystals to function as capacitive building blocks when dispersed into a weakly interacting dielectric matrix. Monodisperse, surface-functionalized ferroelectric 15 nm BaTiO3 nanoparticles have been selectively incorporated with a high packing density into poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) leading to the formation of biphasic BaTiO3-P(VDF-HFP) nanocomposite films. A systematic investigation of the electrical properties of the nanocomposites by electrostatic force microscopy and conventional dielectric measurements reveals that polymer-ceramic film capacitor structures exhibit a ferroelectric relaxor-type behavior with an increased intrinsic energy density. The composite containing 7% BaTiO3 nanocrystals displays a high permittivity (ε = 21) and a relatively high energy density (E = 4.66 J/cm(3)) at 150 MV/m, which is 166% higher than that of the neat polymer and exceeds the values reported in the literature for polymer-ceramic nanocomposites containing a similar amount of nanoparticle fillers. The easy processing and electrical properties of the polymer-ceramic nanocomposites make them suitable for implementation in pulse power capacitors, high power systems and other energy storage applications.
Laserreduced fluorescence study of the carbon monoxide nd triplet Rydberg series: Experimental results and multichannel quantum defect analysis Triplet states of the CO molecule in the region between 86 000 and 94 000 cm -1 have been investigated in a 1 + 1 double-resonance experiment using a detection scheme based on laser-reduced fluorescence (LRF). The strongly predissociated (3pu) j 3I + Rydberg state at 90833 cm -I with an average lifetime of 4.6 ps has been observed spectroscopically at high resolution for the first time, providing a clear identification of this state. Both the accidental predissociation of the J.r= 6 level of CO (E I II, v = 0) and the value of the lambda-doubling constant q of the c 3 II state can be attributed to j 3 I +. In addition, a valence state around 91 960 cm -I has been identified as 3II. Accurate molecular constants have been determined for both states.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.