Effects of thermomechanical treatments on the critical current densityof TSMTG-processed YBa2Cu3O7-δ ceramics

Abstract

TSMTG (top seeding melt texture growth)-processedYBa2Cu3O7-δ ceramics have reached such critical currentdensities (Jc) that it is now possible to envisage technical applicationssuch as magnetic bearings or fault current limiters. Most authors believe thatin this material, defects (such as Y-211 inclusions, oxygen vacancies,dislocations, stacking faults, etc) can act as pinning centres and henceincrease critical current densities. The effects on the critical currentdensity of a uniaxial pressure, applied along a direction perpendicular to thec-axis of Y-123, at 400 °C under an air atmosphere are investigated.These conditions were chosen to avoid oxygen loss in the samples, becauseoxygen content is the most critical parameter for superconducting properties.Thus this allows a sample with the same oxygen content to be compared directlybefore and after experiment. TSMTG-processed Y-123 ceramics exposed tothermomechanical treatment show a complex behaviour. For low pressures (lowerthan 2 MPa) a significant increase in the critical current density (up to 1.37times at H = 0, for a pressure of 1.38 MPa applied for 22 h at 400 °Cunder an air atmosphere) is observed and attributed to an increase in thedislocation density. For higher pressures, the critical current densitiesunder low magnetic fields are always lower but sometimes slightly higher atmoderate magnetic fields (between 1-3 T).