High frequency diffraction of an electromagnetic plane wave by an imperfectly conducting rectangular cylinder

Copyright @ 2011 IEEEWe shall consider the the problem of determining the scattered far wave field produced when a plane E-polarized wave is incident on an imperfectly conducting rectangular cylinder. By using the the uniform asymptotic solution for the problem of the diffraction of a plane wave by a right-angled impedance wedge, in conjunction with Keller's method, the a high frequency far field solution to the problem is given

Growth and characterization of ZnS and ZnCdS nanoclusters in mordenite zeolite host

The growth of semiconductor nanoclusters of ZnS and the ternary ZnCdS system embedded in synthetic mordenites by ionic exchange using different mixtures of CdCl2 and ZnCl2 as starting sources, followed by treatment in hydrogen sulphide flow, is reported. Compositional, morphological and structural studies were realized by XRD, SEM, TEM and energy dispersive spectroscopy (EDS). XRD shows well-crystallized mordenite and the absence of secondary phase

Dielectric hysteresis and pyroelectricity in the La0.03Sr0.255Ba0.7Nb2-yTiyO(6-y)/2 ferroelectric ceramic system

The dielectric hysteresis and pyroelectric properties of the La0.03Sr0.255Ba0.7Nb2-yTiyO(6-y)/2 (LSBNT) ceramic system were studied for different Nb/Ti concentrations. For dielectric hysteresis measurements at room temperature, the remanent polarization increases and the: coercive field decreases with titanium concentration for an applied electric field of 20 kV/cm. The thermally stimulated current measurements show the pyroelectric peak for all compositions while a second smaller peak at higher temperature, possibly associated with induced vacancy-impurity dipoles, is also observed in all cases. The second peak contribution was mathematically eliminated to determine the remanent polarization and pyroelectric coefficient, both associated only with permanent ferroelectric dipoles. In this case, the remanent polarization decreased with the rise in titanium concentration. The La0.03Sr0.255Ba0.7Nb1.95Ti0.05O5.975 sample, in particular, has excellent pyroelectric response, making this material very suitable for pyroelectricity-derived applications. (C) 2000 Elsevier Science Ltd. All rights reserved

Diffuse phase transition of the Sr0.3-3y/2LayBa0.7Nb2O6 ceramic system

The effect of Lanthanum cation doping in the diffuse phase transition of the Sr0.3-3y/2La yBa0.7Nb2O6 ceramic system is studied for y = 0.01, 0.03 and 0.05. For these compositions, the transition temperature T-c shifts towards higher values with increasing frequency and the temperature dependence of the electrical permittivity presents strongly broadened curves which suggest a non Curie-Weiss behavior near the transition temperature for temperatures far from T-c. The diffuse phase transition coefficient (delta) was also determined and its values lead us to conclude that the degree of disorder in the system increases with the presence of the Lanthanum cation. This result is corroborated by calorimetric measurements, where an increase in entropy with the Lanthanum concentration is also found

Ferroelectric properties of the La0.03Sr0.255Ba0.7Nb2-yTiyO6-y/2 ceramic system

The study of the dielectric properties of the stoichiometric Titanium doped Sr0.255La0.03Ba0.7Nb2O6 ceramics prepared according to the formula Sr0.255La0.03Ba0.7Nb2-yTiyO6-y/2 is reported. A single phase compound is observed for low Ti content (y 0.1), the XRD patterns show, besides the SBN phase reflections, several small peaks associated with an additional phase present in the ceramics. A possible liquid phase sintering is analyzed. Strongly broadened dielectric curves are obtained in dielectric measurements, where the transition temperature decreases with the Titanium content. The diffuse phase transition coefficients are calculated, corroborating that Titanium increases the diffuse character of the transition in the monophasic region

Study by hysteresis measurements of the influence of grain size on the dielectric properties of ceramics of the Sr0.4Ba0.60TiO3 type prepared under different sintering conditions

The ferroelectric properties of the Ba0.6Sr0.4TiO3 system prepared at 1250, 1350 and 1450 degrees C sintering temperatures for up to 4 h, are studied through the measurements of the hysteresis loops at different temperatures and at a constant field of 40 kV/m. Grain size analysis was performed with a scanning electron microscope (SEM) with a statistical method, The dielectric properties of the samples are reported as a function of temperature for the different sintering conditions. The dielectric permittivity and the remanent polarization are correlated to the grain size distributions obtained by SEM. A derivative process of the remanent polarization is used to analyze the phase transitions as the temperature is varied. (C) 1999 Published by Elsevier Science Ltd. All rights reserved

Diffuse phase transition in the (La0.03Sr0.255Ba0.7)(Nb2-yTiy)O-6.y/2 ferroelectric ceramic system

The effect of the titanium cation as a doping element in the diffuse phase transition of the (Sr0.255La0.03Ba0.7)(Nb2-yTiy)O6-y/2 ferroelectric ceramic system is studied. Far from the transition temperature, a Curie-Weiss behavior of the dielectric permittivity with temperature is observed with strongly broadened curves in all cases, however, a non Curie-Weiss behavior above the transition temperature is observed. The diffuseness coefficient (delta) was calculated using Isupov's relation and by a more realistic model assuming a Gaussian distribution for the transition temperatures, in a temperature interval around the maximum permittivity temperature. The conditions under which each expression can be used are discussed

Formation of the La0.03Sr0.255Ba0.7Nb2-yTiyO6-y/2 ferroelectric ceramic system

The study of the formation of the Sr0.255La0.03Ba0.7Nb2 - yTiyO6 - y/2 ferroelectric ceramic system and the influence of the sintering conditions and titanium concentration on the densification process is reported. A single-phase compound is observed for low titanium content (y less than or equal to 0.1) in the XRD spectra, being isostructural with the tetragonal tungsten bronze SBN phase. For high titanium concentrations (y > 0.1) the XRD patterns show, besides the tetragonal phase reflections, several small peaks evidencing an additional phase in the compound. This second phase was identified as isostructural to hexagonal Ba6Nb9Ti7O42. The grain size shows a linear increase with titanium content in the region of monophasic compositions and a possible liquid phase aided sintering process is analyzed. (C) 2000 Kluwer Academic Publishers