Unusual Enhancement of Normal and Superconducting State Properties of (100-x)YBa 2 Cu 3 O 7-δ + xNi ( x = 1, 2.5, 5, 7.5, 10, and 15 wt%) Composites with Low Level of Ni Additives

Samples of superconducting composite (100-x)YBa 2 Cu 3 O 7-δ + xNi ( x = 1, 2.5, 5, 7.5, 10, and 15 wt%) were synthesized via solid state reaction method. Scanning electron microscope (SEM) images revealed that the grain size of YBCO reduces gradually as Ni content is increased. At the same time, segregation of Ni, primarily as NiO in patches, forms throughout the composite. At low Ni wt%, it was found that the superconducting state properties including the critical current density were improved significantly and then dropped with higher Ni wt%. Segregated patches of NiO on different length scales were observed. The change in the structural and superconducting state parameters of YBCO and the variation of the magnetic moment with Ni additives were investigated in detail in this study.