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91.
92.
In this paper, we report on studies of the electrocaloric (EC) effect in lead‐free (1?x)Ba(Zr0.2Ti0.8)O3x(Ba0.7Ca0.3)TiO3 ceramics with compositions range between 0.32 ≤ x ≤ 0.45. The EC effect was measured directly using a modified differential scanning calorimeter. The maximum EC temperature change, ΔTdirect = 0.33 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.32 at ~63°C. We found that the EC effect peaks not only around the Curie temperature but also at the transition between the ferroelectric phases with different symmetries. A strong discrepancy observed between the results of the direct measurements and indirect estimations points out that using Maxwell's equations is invalid for the thermodynamic nonequilibrium conditions that accompany only partial (incomplete) poling of ceramics. We also observe a nonlinearity of the EC effect above the Curie temperature and in the temperature range corresponding to the tetragonal ferroelectric phase.  相似文献   
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The dynamic mechanical properties in terms of the storage modulus G′, loss modulus G″, and loss tangent δ have been studied for polypropylene-sepiolite composites. The effect of surface treatment on the relaxation spectra has been elucidated, and quantitative values indicating the extent of polymer-filler interaction have been given. Analysis of the results show that the addition of sepiolite leads to an increase in the values of the modulus, a value of the glass transition temperature lower than that of unfilled polypropylene, and displacement towards higher temperatures of the αc relaxation associated with the crystalline regions. Surface treatment of the sepiolite, by esterification with organic acids of different chain length, does not have a marked effect on the relaxation spectra of the composites, even though the polymer-filler interaction parameter decreases with respect to untreated sepiolite.  相似文献   
97.
In this work, the electrical characterization of three extrinsic polymeric conducting systems was carried out using complex impedance spectroscopy. These systems were obtained by the incorporation of conducting fillers (carbon black and metallic copper), on the one hand, and, on the other hand, by blending with a superconducting ceramic (YBaCuO). The experimental results prove that the electrical characteristics of these systems vary as a function of the nature of the filler added. In the case of metallic copper, the resulting composites posses a conductivity which is intermediate between insulating materials and semiconductors. When carbon black is incorporated in concentration above 10%, the composites may be considered as metalliclike from the point of view of conductivity. Finally, when the filler is YBaCuO, the low conductivity values obtained are indicative of insulating materials regardless of their composition. © 1996 John Wiley & Sons, Inc.  相似文献   
98.
In this work, the critical temperature (Tc) of a series of polymeric superconducting systems is determined which, sintered or not, are obtained through the incorporation of the superconducting ceramic YBaCuO into two extrinsic conducting polymer systems: PVDF/PS/carbon black and PVDF/PS/copper. In addition, the diamagnetic characteristics of these systems are studied on the basis of susceptibility measurements as a function of temperature. As regards the unsintered systems and according to the experimental results, copper-based composites can be termed as insulating materials and the samples with the highest carbon black content as reaching metalliclike conductivities. In no case, however, is an abrupt leap in conductivity observed as a function of temperature, indicating the superconducting nature of these systems from an electrical point of view. On the contrary, magnetic susceptibility measurements as a function of temperature detect in all cases a superconducting transition, i.e., a shift in the critical temperature range, bringing it close to that of pure YBaCuO (≈100 K). After sintering, the samples retained their original shape as well as reasonable mechanical properties. The electrical conductivity study confirmed the absence of superconductivity as a consequence of polymer combustion during sintering and thereby implying the disappearance of the orthorhombic phase of YBaCuO, which X-ray evidence proved to be accountable for superconductivity in this ceramic material. © 1996 John Wiley & Sons, Inc.  相似文献   
99.
Three new vanadium oxides were synthesized and characterized using an X-ray. Once incorporated into different polymer systems containing either poly(ethylene oxide) or a poly(ethylene oxide)–polyphosphazene (PPz), together with carbon black (CB) as an electronic crosslinker, kinetic isothermal and nonisothermal crystallization studies were conducted, as well as an electrical characterization study through complex impedance spectroscopy for the purpose of examining, on the one hand, the effects exerted by the different vanadium compounds on the microstructure of the systems into which they are incorporated, and, on the other hand, of determining which of the synthesized vanadium compounds possesses the best conducting properties. © 1996 John Wiley & Sons, Inc.  相似文献   
100.
The aim of this work was to obtain films of polypropylene (PP)/polyethylene co‐octene (POE) blends and study the influence of their composition and mixing conditions on final morphology and ultimate properties (thermal, mechanical, oxygen and water vapour transmission rates). Scanning electron microscopy showed segregation of POE domains in the PP matrix. Thermal analysis indicated that the addition of POE modified neither the melting temperature nor the crystallinity of PP in the pressed films. It was found that permeabilities of films were mainly related to POE content rather than morphological features. For the maximum POE concentration used (40%), the oxygen permeability increased up to ∼100% from that of neat PP. A similar trend was found for water vapour permeability. Rigidity of blends dropped significantly with the addition of POE although their ductility slightly increased when compared to pure PP. No significant effect of blend preparation conditions on these properties was found. Mechanical and permeability characteristics of films make them very attractive to be used for MAP of fresh produce such as apple, blueberry and mushroom. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
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