Flux pinning behaviors of a textured Gd–Ba–Cu–O superconductor mediated by the addition of BaTiO3, TiO2 and BaO2

• The structural effect of the doping of BaTiO3 was studied in Gd123 superconductors.
• Dilute additions are rearranged by crystal growth leading to the prominent peak effect.
• The origin of the peak effect was discussed with respect to weak superconductivity, certain degree of order of defects.

We present a study on the investigation of the proper secondary phases for engineering magnetic flux pinning centers in textured Gd–Ba–Cu–O bulk superconductors. Compared with the joint TiO2 and BaO2 doping methods, the addition of BaTiO3 shows a relevant advantage due to its perovskite structure. Both TiO2 and BaO2 doping tends to enter the crystal lattice of the superconducting matrix by ionic substitution, which leads to the variable peak effect in the Jc–B diagram. The BaTiO3 doping method shows a unique pinning behavior, which is attributed to the distinctive precipitations generated by the additions. The composition of the BaTiO3 doping-related precipitation appears to be controlled under different growth temperatures. The self-field Jc improved by nearly double at 77 K in a sample grown with a low growth temperature. In addition, the second peaks caused by various types of additions are located in a narrow field range of 1.25–1.5 T in the Jc–B diagram, indicating that the dilute doping follows a unique tendency, which is likely relevant to anisotropic crystal growth. The different observed peak heights suggest the existence of several average pinning potentials provided by various types of additions. BaTiO3 doping exhibited a stabilization of the unique onset superconducting transition temperature. Therefore, BaTiO3 can be classified as a useful dopant to control flux pinning behavior in Gd–Ba–Cu–O bulk superconductors.