PEAK EFFECT IN J(C) OF THE CATION-STOICHIOMETRIC SMBA2CU3OY SUPERCONDUCTOR

Cation-stoichometic SmBa2Cu3O7-d samples were prepared by a solid-stal e reaction method and exhibited a peak effect in their J(c) vs H chara cteristics. Oxygen contents of the samples were determined by a coulom etric titration method. A sample annealed at 350 degrees C for 40 h sh owed the largest peak among those studied in this work. The oxygen con tent of this sample was 7-d = 6.84, which was lower than those of othe r samples. Tetragonal regions were revealed in the orthorhombic matrix of this sample by a transmission electron microscope (TEM) observatio n. On the other hand, a sample annealed at the same temperature (350 d egrees C) for a long period (200 h) showed a small peak. The former sa mple was thought to contain some oxygen deficiency which would play a role of pinning centers to cause a peak effect in the J(c) vs H charac teristics. (C) 1998 Elsevier Science Ltd. All rights reserved.