Effect of Element Substitutions on Flux Pinning in PMP YBCO Superconductors

A series of superconductors with nominal compositions of Y_{1-cursive Greek chi}Lncursive Greek chiBa₂Cu₃O_y(Ln=Ho,Er or Gd) and YBa₂ Cu_{3-cursive Greek chi} Sn_{cursive Greek chi} O_y have been prepared and have been investigated through the differential thermal analysis, superconducting quantum interference device (SQUID) magnetometer, SEM and TEM. It is found that the critical current density and pinning potential can be improved by the partial substitutions of Ho, Er or Gd for Y. The enhancement of J_c may be mainly due to the magnetic pinning and stress -field pinning in addition to the refinement of the size of Y₂ BaCuO₅(211) particles. A lot of collective, stair-like stacking faults, which have been proved to be the pinning centers in YBCO, are observed in PMP YBCO superconductors. Moreover, the experimental results indicate that J_c and flux pinning can be increased and the size of 211 particles can be reduced by the Sn addition.