Critical Current Dependence on Deformation Kinetics in Textured YBa₂Cu₃O_xSuperconductor

Abstract

The dependence of critical current on the deformation kinetics has been examined in melt-textured YBa2Cu3O x superconductors that were subjected to uniaxial high temperature deformation. The J c of the deformed superconductors is found to increase with deformation time at all magnetic field orientations with respect to the a-b plane. The rate of increase in J c is found to subside after 12 h of deformation. The deformation time dependence of J c has been analyzed within the framework of high temperature creep, and is found to be very similar to the deformation time dependence of mechanical strain. The rate of J c increase in the secondary creep stage is found to be significantly higher in the orientation of H//c resulting in a lower anisotropy with increasing deformation time. The J c characteristics suggest that an anisotropic defect structure is created after longer periods of deformation, and that the defects responsible for flux pinning are introduced by thermal activation.

Tailoring of microstructure and critical currents in directionally solidified

“…It has been reported that high-temperature uniaxial deformation results in an increase by a factor of twice J c [72,137,138]. Furthermore, the transport J c in the H [001] configuration could be increased in this way to the level of the more favourable H (001) field orientation [138]. Such enhancement of J c was correlated with a concomitant increase of the dislocation density by an order of magnitude [72,138].…”

“…The investigation of the effect of high-temperature deformation on the superconducting behaviour of melttextured 123 has yielded a variety of results. It has been reported that high-temperature uniaxial deformation results in an increase by a factor of twice J c [72,137,138]. Furthermore, the transport J c in the H [001] configuration could be increased in this way to the level of the more favourable H (001) field orientation [138].…”

“…Furthermore, the transport J c in the H [001] configuration could be increased in this way to the level of the more favourable H (001) field orientation [138]. Such enhancement of J c was correlated with a concomitant increase of the dislocation density by an order of magnitude [72,138]. The role of dislocations as pinning centres was subsequently investigated by comparing the J c values of uniaxially deformed samples before and after an annealing process at 900 • C in flowing oxygen of the deformed samples, which resulted in a decrease of the dislocation density [57].…”

Effects of thermomechanical treatments on the critical current density of TSMTG-processed YBa2Cu3O7-δceramics

“…For higher applied pressures (above 2.8 MPa), a decrease in the critical current density is always observed. Vilalta et al [7], using the same experimental conditions as Selvamanickam et al [4] and Zhang et al [5] but higher pressures, observe a decrease in the critical current densities of the samples after experiment. These authors attribute the J c decrease to the formation of large stacking faults that decreases the vortex correlation along the c-axis.…”

“…Most of these authors believe that defects (such as Y-211 inclusions, oxygen vacancies, dislocations, stacking faults, twin boundaries, etc) act as pinning centres for vortices, which then increase the critical current densities. Several authors [4][5][6][7] have already studied the effects of a uniaxial pressure on the critical current densities of different types of Y-123 samples. They applied the pressure along a direction at 30 or 45 • of the (a, b)planes, at high temperatures (near 930 • C); the sample needed annealing under oxygen flow after the experiment to return to the orthorhombic superconducting phase.…”