The peak effect observed in the Na substituted melt textured growth YBCO

The effect of Na substitution in melt textured growth (MTG) YB(Na)CO (YBa2- xNaxCu3Oy + 40 mol% Y2BaCuO5) system with x=0.0, 0.1, 0.2 on the critical c urrent characteristics has been investigated. It was observed that with cer tain Na substitution, MTG YB(Na)CO showed an increased critical current den sity and a second peak around 0.8-1.0 T at 77.3 K in the critical current d ensity versus applied field curve. The post-annealing at 900 degreesC in ai r reduced the critical current density and suppressed the second peak. Howe ver, further oxygenation at 400 degreesC raised critical current density an d recovered the second peak partly, but could not completely recover to tho se before the high temperature annealing. The possible source of such a beh avior was supposed to be connected with inhomogeneous distribution of Na (d ifferent x) in MTG YB(Na)CO, which leads to a distribution of different T,c lusters. (C) 2001 Elsevier Science B.V. All rights reserved.