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Presents information on a study that measured the dielectric properties and positron annihilation lifetime spectra of the ceramics with the nominal composition Sr[sub1-x]La[subx]TiO[sub3]. Methodology of the study; Results and discussion on the study.

Presents a study on the defect structure of the dielectric ceramics using the positron annihilation technique. Experimental details; Results and discussion; Conclusion.

The dielectric and ferroelectric properties of (1-z) (Sr0.7Bi0.2)TiO3–z(Na0.5Bi0.5)TiO3 solid solutions with z=0.65–1 are studied. High remnant polarization of ∼51 μC/cm2 with a coercive field of 50 kV/cm, and a dielectric constant of ∼1000 have been obtained at room temperature in the sample with z=0.9, indicating an application potential as a lead-free ferroelectric material. There are two dielectric anomalies in the temperature range of 150–670 K for all samples; one is the dielectric peak without significant frequency dispersion, and the other is significantly frequency dependent. The result of this work shows that the formula scheme “a ferroelectric relaxor+a ferroelectric” for solid solutions is a promising approach in the search for high performance lead-free ferroelectric materials. [ABSTRACT FROM AUTHOR]

The dielectric behavior and electrical conduction in Bi doped SrTiO3 annealed in both oxidizing (air and oxygen) and reducing atmospheres (nitrogen and “hydrogen+argon”) are studied in this letter. The dielectric constant and electrical conductivity are greatly enhanced in the sample annealed in a reducing atmosphere compared with that annealed in an oxidizing atmosphere. A Mott’s variable range hopping (VRH) conduction mechanism, σ=σ0 exp[-(T0/T)1/4], is observed in a strongly reduced sample, where a significant dielectric relaxation process is present. No direct correlation is found between the VRH conduction and the dielectric relaxation. The underlying physics of these results are briefly discussed. [ABSTRACT FROM AUTHOR]

The dielectric spectra of poly(vinylidene fluoride-trifluoroethylene) copolymers and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymers are studied in a wide temperature and frequency range with electric field. It is found that the dominant relaxation process displays a peculiar characteristic—a “dielectric relaxor” behavior, rather than a “ferroelectric relaxor” behavior reported in the current literature; furthermore, we show the experimental observation that the existence of nanometer scale crystals embedded in an amorphous matrix is the base of the dielectric relaxor behavior and high electroactive performance in these polymers. [ABSTRACT FROM AUTHOR]

The dc electric-field dependence of the dielectric properties of cadmium niobate Cd2Nb2O7 single crystals is studied, and characteristics of the dielectric behavior of Cd2Nb2O7 under dc bias are revealed. The temperature (Tm) where the dielectric relaxation mode occurs is independent of dc bias levels, while its intensity is greatly suppressed and finally eliminated with increasing dc bias from 0 to 15 kV/cm. The observed dielectric relaxation features of Cd2Nb2O7 can be attributed to “dielectric relaxor” behavior, rather than “ferroelectric relaxor” behavior previously designated in literature. The physical nature of the dielectric relaxor behavior is briefly discussed. [ABSTRACT FROM AUTHOR]

The electrostrictive property and dielectric behavior of the stretched poly (vinylidene fluoride–trifluoroethylene) copolymers, denoted as P(VDF–TrFE), have been studied at cryogenic temperatures. Polarization hysteresis loops and high electrostrictive performance (strain ∼1%) are obtained at room temperature. An obvious dielectric relaxation process is observed and the relaxation rate follows the Vogel–Fulcher relation with T[sub VF]=160 K, U=0.18 eV, ν[sub 0]=5.7×10[sup 12] Hz. The dielectric relaxation behavior and high strain level decrease quickly with decreasing temperature, and below 160 K only a small strain level (∼0.1%) and an “intrinsic” dielectric constant sustains. The correlation of dielectric behavior and strain activity and the physical mechanism of the quick suppression of the strain with decreasing temperature are briefly discussed. The results indicate that a high dielectric constant is critical for obtaining high electrostrictive strains in the polymers at a reasonable electric field. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the influence of post-sintering annealing on the dielectric relaxation behavior in La-doped perovskite oxide. Peaking of dielectric permittivity with frequency dispersion; Dielectric polarization behavior; Similarity between La and Bi-doped perovskite oxide.

An innovative morphing scheme, i.e., dynamical chordwise retracting and stretching, has been proposed for flapping wings. Its aerodynamic effects have been investigated based on a plunging two-dimensional flat wing. The conclusive results suggest that the novel morphing scheme can help to enhance the power utilization efficiency of flapping wings in forward motions. Plunging wings equipped with the novel morphing scheme can generate more thrust for a given power consumption or consume less power for a given thrust generation compared with their non-morphing counterparts. Moreover, the morphing scheme tends to function more positively as the defined morphing amplitude increases. In the currently covered parameter spaces, the largest peak propulsive efficiency improvements induced by the morphing scheme are 12.3% at Re = 15 × 104 and 10.8% at Re = 5 × 104, respectively. Examination of the flow structures around the plunging wings reveals that dynamical chordwise retracting and stretching of the wing can ameliorate the vortex distribution, which could account for the propulsive property changes caused by the morphing scheme. The current study may have yielded an inspiring and prospective scheme for enhancing the propulsive capacity of micro-flapping-wing aerial and underwater robots. [ABSTRACT FROM AUTHOR]

The direct-current (dc) electric-field dependence of dielectric constant around paraelectric-ferroelectric transition in Cd[sub 2]Nb[sub 2]O[sub 7] has been studied. The results show significant suppression of the dielectric constant by the application of dc bias. The electric-field dependence of the dielectric constant at the temperature around paraelectric-ferroelectric phase transition can be well described by the modified Devenshire relation including a cluster term, i.e., ε(E)=ε[sub 1]-ε[sub 2]E[sup 2]+ε[sub 3]E[sup 4]+(Px/ε[sub 0])[cosh(Ex)][sup -2]. The fit parameters indicate that the polar-cluster carries polarization P=∼0.5-2.5 mC/m[sup 2] with the cluster size of L=∼11-15 nm. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]