Apuntes de electromagnetismo

Apuntes completos de la asignatura Electromagnetisme del grado de Enginyeria Electrònica de Telecomunicació-UPC2022/20232n quadrimestr

Unexpected dielectric response in lead zirconate titanate ceramics: The role of ferroelectric domain wall pinning effects

Temperature dependent dielectric response has been measured in Pb(Zr1-xTix)O-3 ceramics. Samples of different compositions (x=0.40, 0.47, and 0.60), pure and doped with Nb-or Fe, were studied at temperatures between 15 and 700 K and in the frequency range from 100 Hz to 1 MHz. Unexpected dielectric behavior has been found around room temperature. Anomalous temperature dependent permittivity is observed in pure and Fe-doped samples but not in Nb-doped samples. The anomaly appears related to the presence of oxygen vacancies but not on the sample crystallographic phase. The authors suggest that the anomaly may be a manifestation of the domain wall pinning effect. (C) 2007 American Institute of Physics.Peer ReviewedPostprint (published version

Unexpected dielectric response in lead zirconate titanate ceramics: The role of ferroelectric domain wall pinning effects

Temperature dependent dielectric response has been measured in Pb(Zr1-xTix)O-3 ceramics. Samples of different compositions (x=0.40, 0.47, and 0.60), pure and doped with Nb-or Fe, were studied at temperatures between 15 and 700 K and in the frequency range from 100 Hz to 1 MHz. Unexpected dielectric behavior has been found around room temperature. Anomalous temperature dependent permittivity is observed in pure and Fe-doped samples but not in Nb-doped samples. The anomaly appears related to the presence of oxygen vacancies but not on the sample crystallographic phase. The authors suggest that the anomaly may be a manifestation of the domain wall pinning effect. (C) 2007 American Institute of Physics.Peer Reviewe

Preparation of top seeded YBa2Cu3O7 large single-domain tiles

Single domain superconductors with diameters up to 40 mm have been prepared by top seeding growth using Nd123 melt textured ceramics as seeds. We show that the use of these seeds is preferred over MgO single crystals to reduce the multinucleation problem. Large levitation forces and critical currents have been measured which demonstrate the single domain character of the samples.Postprint (author’s final draft

Preparation of top seeded YBa2Cu3O7 large single-domain tiles

Single domain superconductors with diameters up to 40 mm have been prepared by top seeding growth using Nd123 melt textured ceramics as seeds. We show that the use of these seeds is preferred over MgO single crystals to reduce the multinucleation problem. Large levitation forces and critical currents have been measured which demonstrate the single domain character of the samples

Fabrication of melt-textured cylinders and bars of (YBa2Cu3O7-Y2BaCuO5) superconductors

Cylinders and bars of bulk YBa2CuO7-Y2BaCuO5 textured ceramic composites (123-211) have been prepared through different directional solidification processes. Green ceramic preforms for the directional solidification process have been obtained by sintering the starting powders (123) and (211) in ceramic moulds at small pressures and by using a Cold Isostatic Pressing technique (CIP). The bars were melted and solidified in a vertical gradient furnace by the Bridgman technique at different rates up to 5mm/h. Cylinders were melted and solidified at 1-2ºC/h using single crystal seeds of different materials at different vertical gradients. We have studied the influence of (123)/(211) ratios, additions, particle size of the precursors and thermal treatments. The complex microstructure of these ceramic composites has been investigated by SEM, TEM and optical microscope. The directional solidification process allows to obtain quasi-single crystal superconductors with critical currents above 105A/cm2 at 77k and zero field.Postprint (published version

Fabrication of melt-textured cylinders and bars of (YBa2Cu3O7-Y2BaCuO5) superconductors

Cylinders and bars of bulk YBa2CuO7-Y2BaCuO5 textured ceramic composites (123-211) have been prepared through different directional solidification processes. Green ceramic preforms for the directional solidification process have been obtained by sintering the starting powders (123) and (211) in ceramic moulds at small pressures and by using a Cold Isostatic Pressing technique (CIP). The bars were melted and solidified in a vertical gradient furnace by the Bridgman technique at different rates up to 5mm/h. Cylinders were melted and solidified at 1-2ºC/h using single crystal seeds of different materials at different vertical gradients. We have studied the influence of (123)/(211) ratios, additions, particle size of the precursors and thermal treatments. The complex microstructure of these ceramic composites has been investigated by SEM, TEM and optical microscope. The directional solidification process allows to obtain quasi-single crystal superconductors with critical currents above 105A/cm2 at 77k and zero field