Search results for " COMPOSITES"
showing 10 items of 1620 documents
Broadband dielectric spectroscopy of PSN ceramics
2007
Abstract The complex dielectric permittivity of ordered and disordered PSN ceramics was measured in the frequency range from 20 Hz to 3 GHz. The anomaly of dielectric permittivity is clearly seen in the region of 115 °C for ordered PSN at all measured frequencies. Disordered PSN exhibits typical relaxor behaviour with a huge frequency dispersion below 125 °C. Calculated distribution of relaxation times shows noticeable influence of polar clusters to the total dielectric spectrum of disordered PSN below 80 °C with the longest relaxation times edge diverging according to the Vogel–Fulcher law. In the case of ordered PSN, two almost not overlapping peaks in the distribution of relaxation times…
ELECTRICAL PROPERTIES OF LEAD FERROTANTALATE CERAMICS
2009
ABSTRACT Perovskite structures with high dielectric constants and magnetic properties play an important role in micro- and optoelectronics and have numerous practical applications. Relaxor type ferroelectric ceramics PbFe1/2Ta1/2O3 with perovskite structure was subject of present studies. Pyrochlore free lead ferrotantalate ceramics were produced by solid state technology from oxides. Low- and infra-low frequency studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics have revealed considerable infra-low frequency dispersion at temperatures above the temperature of maximum dielectric permittivity. The observed dispersion described by lemniscates is due to a considerable Maxwell-Wagner r…
Antiferroelectric PbZrO3 thin films: structure, properties and irradiation effects
2004
Abstract Irradiation effects on highly oriented antiferroelectric PbZrO 3 and ferroelectric Pb 0.92 La 0.08 (Zr 0.65 Ti 0.35 )O 3 thin films are investigated being exposed to neutron irradiation up to fluence 2*10 22 m −2 . The higher resistance of antiferroelectric PbZrO 3 thin films as compared to ferroelectric heterostructures to large fluences of neutron irradiation is recognized and discussed. Influence of two factors (structural and charge) was taken into account analysing irradiation effects on materials of different polarization states: ferroelectric PLZT (ceramics and thin films) and antiferroelectric PbZrO 3 films.
Correlating the axial Zero Field Splitting with the slow magnetic relaxation in GdIII SIMs
2021
The field-induced out-of-phase magnetic response of a GdIII complex, selected by its good isolation in the network, has been analyzed and the behaviour of this quasi-isotropic cation has been related to its weak axial zero field splitting ∼0.1 cm-1.
Inhibition of the detrimental double vortex-kink formation in thick YBa2Cu3O7films with BaZrO3nanorods
2013
We investigated the temperature (T) variation of the normalized magnetization relaxation rate S and of the corresponding normalized vortex-creep activation energy U* = T/S for YBa2Cu3O7 films containing BaZrO3 nanorods, with the external magnetic field H oriented perpendicular to the film surface. It was found that by increasing the film thickness and using nanodot decorated substrates the high-T S(T) maximum appearing at low H is substituted by a minimum in S(T). As revealed by the analysis of the current density dependence of U*, this behaviour is due to the inhibition of vortex excitations involving double vortex-kinks and superkinks formation in the investigated thick films, owing to th…
Glass transition of binary mixtures of dipolar particles in two dimensions
2010
We study the glass transition of binary mixtures of dipolar particles in two dimensions within the framework of mode-coupling theory, focusing in particular on the influence of composition changes. In a first step, we demonstrate that the experimental system of K\"onig et al. [Eur. Phys. J. E 18, 287 (2005)] is well described by point dipoles through a comparison between the experimental partial structure factors and those from our Monte Carlo simulation. For such a mixture of point particles we show that there is always a plasticization effect, i.e. a stabilization of the liquid state due to mixing, in contrast to binary hard disks. We demonstrate that the predicted plasticization effect i…
Far-infrared and THz spectroscopy of 0.4PMN–0.3PSN–0.3PZN relaxor ferroelectric ceramics
2007
Abstract Temperature dependence of the optic phonons in 0.4PbMg 1/3 Nb 2/3 O 3 –0.3PbSc 1/2 Nb 1/2 O 3 –0.3PbZn 1/3 Nb 2/3 O 3 (0.4PMN–0.3PSN–0.3PZN) ceramics were studied by means of FTIR reflection and THz transmission spectroscopy in the temperature range of −253.15 to 226.85 °C. On heating from low temperatures, the A 1 component of the strongly split TO 1 mode softens towards the Burns temperature, but the softening ceases near 126.85 °C which could be a signature of polar cluster percolation temperature. Surprisingly, the TO 2 mode also softens on heating and follows the Cochran law with extrapolated critical temperature close to the melting point.
Analytical stress-strain law of FRP confined masonry in compression: Literature review and design provisions
2017
Abstract The use of Fibre Reinforced Polymer (FRP) wraps has become common in practical applications to retrofit existing columns with poor structural features. Wrapping the member with one or more FRP sheets makes it possible to induce confinement action and enhance strength and ductility. This application has been widely studied and adopted in reinforced concrete members for about twenty years, while its suitability to masonry columns and piers has been investigated during the last decade. The results of several studies were summarized in different design expressions for calculating effective confinement pressure, ultimate compressive stress and strain, and the overall trend of the stress…
Finite element analysis of the out-of-plane behavior of FRP strengthened masonry panels
2017
Abstract In the present study a numerical model is proposed for the response of out-of-plane loaded calcarenite masonry walls strengthened with vertical CFRP strips applied on the substrate by means of epoxy resin. A simplified structural scheme is considered consisting in a beam fixed at one end, subjected to constant axial load and out-of-plane lateral force monotonically increasing. Two different constraint conditions are taken into account: in the first one, the panel is assumed free to rotate at the top end while, in the second one, the rotation is restrained. Three-dimensional finite elements are used for the calcarenite parts and an equivalent constitutive law available in the litera…
Biological oxygen apparent transmissibility of hydrogel contact lenses with and without organosilicon moieties.
2003
The instrument oxygen transmissibility (IOT) of organosilicon hydrogels, measured by electrochemical procedures, is 5-10 times larger than that of conventional hydrogels. A method is described that allows the estimation of the oxygen tension at the lens-cornea interface for closed- and open-eyelids situations by combining the IOT of the hydrogels and corneal parameters such as corneal thickness, corneal permeability and oxygen flux across the cornea. From these results the biological oxygen apparent transmissibility (BOAT) is obtained, an important parameter which an multiplication with the pressure of oxygen on the external part of the lens gives the oxygen flux onto the cornea. Contact le…