A STUDY OF THE MICROSTRUCTURE AND THE CRITICAL CURRENT-DENSITY OF LA1.85SR0.15CUO4 SUPERCONDUCTOR

The irreversible magnetization, the critical current density and the m icrostructure of the high-temperature superconductor La1.85Sr0.15CuO4 are compared. Direct observations by transmission electron microscopy (TEM) revealed two orthogonal arrays of extended screw-type dislocatio ns (2 to 5 x 10(11) lines per cm2) parallel to the crystallographic di rections [100] and [010], respectively. These dislocations are dissoci ated into partial bound stacking faults. Microanalysis showed that Sr concentration around the dislocation cores is about 10% lower than tha t of the matrix. Measurements of the hysteresis cycle, M(H, T), at var ious angular orientations (theta.phi) of the field H with respect to t he crystalline directions show no detectable correlation between the d irections of the dislocations and the critical current density. This s uggests that the anisotropy of the critical current density is first o f all controlled by the intrinsic properties of the material rather th an by the anisotropy of the dislocation structure.