Effect of heat treatment on Jc– H curve for YBa 2Cu 3O 7− δ single crystal

Abstract

The dependence of critical current density ( J c)– H curves for YBa 2Cu 3O 7− δ (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°C, 500°C, or 600°C for 100 h, followed by an anneal at 500°C for 200 h in a pure oxygen gas flow. The J c– H curves with H‖ 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°C and subsequently at 500°C. Furthermore, the J c– H curves with H‖ 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.