Effect of heat treatment on Jc-H curve for YBa2Cu3O7-δ single crystal

The dependence of critical current density (J(c))-H curves for YBa2Cu3O7-d (Y123) single crystals on heat treatment processes was studied. Several two-step heat treatment processes were performed on the single crystals, which were annealed at 400 degrees C, 500 degrees C, or 600 degrees C for 100 h, followed by an anneal at 500 degrees C for 200 h in a pure oxygen gas flow. The J(c)-H curves with H parallel to c-axis at 70 K and below showed a large dependence on the heat treatment process. These J(c)-H curves also showed a peak effect in a high magnetic field (H > 3 T). The peak effect was significant for the single crystal annealed at 600 degrees C and subsequently at 500 degrees C. Furthermore, the J(c)-H curves with H parallel to c-axis for detwinned single crystals, which were fabricated under a uni-axial compression in (100) direction after the second heat treatment step, were compared with that for the non-detwinned crystal. These results suggested that the dependence of the peak effect on the heat treatment process was due to the difference in the oxygen configuration of the Cu-O basal planes in the single crystals. (C) 1999 Elsevier Science B.V. All rights reserved.