Loss of YBCO bulk superconducting ability at high temperatures and its recovery

Single domain yttrium-based (Y-Ba-Cu-O, YBCO) bulk materials exposed to high temperature cycles lose their superconducting ability. This study analyzes the ability of post oxygenation treatment on the recovery of the superconducting ability for joining the YBCO blocks. The superconducting ability, the microstructures, and phase constitution of the original YBCO blocks, post-heat treatment YBCO blocks, and post-oxygenation treatment YBCO blocks and powders. The results show that a top seeded melt-textured growth YBCO block loses its superconducting ability after a welding heat cycle and that the superconducting property recovers completely after heat treatment in flowing oxygen. The texture characteristics of the YBCO block are not obviously changed by the welding heat cycle; however, the block crystal structure is transformed from an orthorhombic structure to a tetragonal structure, which leads to the loss of the superconducting ability. After the post-oxygenation treatment, the block crystal structure changes from the tetragonal structure back to the orthorhombic structure to recover the superconducting ability.