FLUX-FLOW DISSIPATION IN GDBA2CU3O7 AT MICROWAVE-FREQUENCIES

We report measurements of the magnetic-field-dependent microwave dissipation in high-purity GdBa2Cu3O7-delta pellets with different grain sizes, by means of a cavity technique with no field modulation. The dissipation is due to the intragranular viscous vortex motion at fields greater than or similar to 0.02 T, and to weak-links at low fields (H 0.02 T) has to be ascribed to the free motion of flux lines

Magnetic penetration depth determination of the high Tc superconductor YBa2Cu3O7 by polarized neutron reflection

The magnetic penetration depth, Λ, is one of the characteristic quantities of a superconductor because it is strictly related to the density of superconducting electrons. The absolute determination of the magnetic penetration depth is possible by using polarized neutron reflection. We have used this technique to determine Λ in the YBa2Cu3O7 high Tc superconductor obtaining a value of 225±75 angstrom at a temperature of 5.0 K

Superconducting compounds in the Bi-Ca-Sr-Cu-O system from citrate polymer precursor: production and preliminary characterization

In this work a procedure followed for the preparation of superconducting compounds in the Bi-Ca-Sr-Cu-O system using the cytrate polymer precursor route is reported. A preliminary characterization of the structure and superconducting properties of the samples so obtained is given through X-ray diffraction analysis, resistivity and a.c. susceptibility measurements. All the samples so obtained showed the presence of superconducting phases at 80 K and 110 K beyond other non superconducting ones

CHARACTERIZATION AND IN-SITU FLUORESCENCE DIAGNOSTIC OF THE DEPOSITION OF YBA2CU3O7-X THIN-FILMS BY PSEUDO-SPARK ELECTRON-BEAM ABLATION

The pseudo-spark electron beam ablation (PSA) technique is a comparatively simple and inexpensive method of depositing thin films of oxide materials. The effects of both the breakdown voltage of the discharge and the oxygen pressure on the power density of a pulsed electron beam and on the efficiency of the PSA process are studied. The PSA technique is applied to the deposition of YBa2Cu3O7-x thin films on single crystal SrTiO3 and MgO substrates. Thin films with zero resistance transition temperature around 87 K have been prepared at breakdown voltages from 18 to 25 kV. The role of the oxygen pressure in the PSA process, which is typically one order of magnitude less than that for a typical laser ablation system, is discussed. In situ spectral analysis of the radiative emission f rom the plasma plume has also been performed at different breakdown voltages of the discharge in an attempt to understand the behaviour of the target constituents in response to intensive pulsed electron beams