L.A. Angurel

Polymer solution processing of (Bi, Pb)SrCaCuO

Abstract A simple polymer processing route to the 110 K phase (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ superconductor has been developed. The influence of the polymer to metal starting ratio, as well as the sintering temperature and time on the quality of the resulting superconducting powders has been studied by XRD, a.c. susceptibility and resistivity measurements. Microstructure of ceramic compacts has been studied by SEM, and qualitatively analysed by EDS for compositional homogeneity. The results indicate that the polymer synthesis route described here may offer a good alternative to the conventional solid state preparation methods towards attaining homogeneous 110 K superconductor powder within a reasonable processing time.

Phase growth and microstructure modifications induced by annealing in highly textured superconducting Bi-2212 thin rods

Bi-2212 cylindrical rods were obtained using a laser-induced directional solidification system. Although as-grown Bi-2212 samples are well textured, they do not exhibit superconducting behavior and, as a result, need further heat treatments. The modifications taking place during annealing were analyzed in the present work, in particular with respect to the evolution of the microstructure with the annealing time and the phase content. Diffusion processes in which the Bi-2212 phase grows along the thickness of the platelets take place during annealing. The presented results show that the physical properties of these samples improve during the initial approximately 60 h of annealing and that they remain constant thereafter.

Pinning by planar high Jc defects and self field limited currents of textured Bi-2212 thin rods

Abstract A self-field limited current model which relates the critical current, I c , and the V–I characteristics with the effective pinning mechanism is introduced in the analysis of the electric behaviour of Bi-2212 textured thin rods. The model generalises previous developments of Kliem et al. on the self-field flux motion due to transport electric currents, taking into account the pinning force of planar high J c boundaries on highly anisotropic Josephson type vortices. Our model describes well the temperature dependence of I c and V–I characteristics of Bi-2212 textured thin rods in the high temperature range (between 65 and 77 K).

Phase formation and microstructure of laser floating zone grown BSCCO fibers: reactivity aspects

Abstract The phase formation and microstructure of Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ fibers are affected by the phase content and morphology of the starting precursor powders which modify reaction pathway and kinetics. A solid state precursor reaction process has been used to prepare (Bi, Pb)-Sr-Ca-Cu-O powders with varying phase composition. These powders were isostatically compacted and the resulting cylinders transformed into textured fibers using a laser floating zone melting apparatus. The results demonstrated that a Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ precursor mixture containing Bi 2 Sr 2 CuO 6 and submicrometer-sized ‘CaCuO 2 ’ particles leads to textured fibers exhibiting high critical current density ( J c ) values.

Annealing evolution of the flux pinning in well-textured Bi-2212 thin rods

Abstract The evolution of the flux pinning energy distribution, irreversibility line shift, critical current and voltage–current characteristics of well-textured Bi-2212 thin rods with annealing is reported. The results confirm an important enhancement of the intergranular pinning with the annealing time, while the intragranular components do not change significantly. Improvement of most superconducting parameters with the annealing time has been found. A self-field limited current model, which includes the flux pinning by planar high- J c (small angle) grain boundaries, has been used to fit the electric transport at high temperatures. The comparisons of the results with the model point out that the energy losses appear before reaching full current penetration of the rods. Moreover, the local J c is almost constant with annealing time and only an external part of the rod cross-section, which increases with annealing time, is used for the current transport.

Inhomogeneous oxygen interchange during annealing and cooling of textured bulk Bi2Sr2CaCu2O8+δ superconductors

The optimized annealing of bulk Bi2Sr2CaCu2O8+δ (Bi-2212) materials textured using the laser floating zone technique requires a two-step process, consisting of a first step at 870 °C and a second step at 801 °C. In this paper, we present an analysis of the changes induced within the samples along this thermal treatment and the subsequent cooling to room temperature. During the initial step the cationic diffusion takes place, while the oxygen content is adjusted during the second step, at lower temperature. The evolution of the superconducting properties reveals that the oxygen diffusion into the sample is not homogeneous and that the different oxygen contents along the annealing are also a consequence of a strong interchange between the central and the external sample regions. It has been shown that, at the different stages of the thermal process, the samples present different degrees of homogeneity in their superconducting properties, this being caused by the improvement of one region to the detriment of the other.

Development of Ag sheathed Bi-2223 multifilamentary tapes with MgO coated filaments

A dip-coating process to obtain controlled, uniform coatings on silver sheathed Bi-2223 wires suitable for the fabrication of multifilamentary tapes is reported. Tapes with continuous fully connected MgO resistive barrier layers 1 to 17 /spl mu/m thick have been produced and characterized. The correlation between their microstructure, electric transport and magnetic properties has been analyzed. An effective reduction of the interfilamentary coupling with a minimum degradation of the tape performance has been obtained for 1 to 3 /spl mu/m thick barrier layers.

Critical state models for inter and intragranular flux pinning in HTS ceramics: universal scaling laws

Abstract Critical state models have been used in the qualitative and quantitative analysis of the ac susceptibility of HTS ceramics. A systematic procedure to derive the characteristic parameters that within a given model define each sample has been established. Good theory-experiment agreements are found.

Inductive and transport simultaneous measurements of the superconducting properties of YBaCuO ceramics: a comparative study

Simultaneous measurements of electric transport Vdc(Idc) and magnetic susceptibility components for different exciting AC field amplitudes and constant temperature on a ceramic YBaCuO sample are reported. The mutual influence of the shielding and transport currents is analyzed and the correlation between these macroscopic magnitudes is clearly established.

Electrical DC characteristics of textured BSCCO-2212 thin rods developed for current leads

Textured Bi-2212 thin rods have been fabricated using a laser floating zone melting technique. Very high critical current densities, J/sub c/(77 K) >5000 A/cm/sup 2/, have been obtained in samples of 1 mm in diameter. Transport properties of these samples at temperatures between 65 and 77 K are reported. The results has been analysed assuming a flux flow mechanism for the appearance of the self field energy losses. A leading pinning mechanism associated with the planar junctions between grains have been considered.