Flux pinning at high magnetic field in melt-processed SmBa ₂Cu₃O₇ with nanocrystalline Sm211/Nd422 additives

Nano-sized Sm₂BaCuO₅ ('Sm211') and Nd ₄Ba₂Cu₂O₁₀ ('Nd422') non-superconducting particles were prepared by a typical sol-gel process of mixing poly-acrylic acid (PAA) with metal ion solutions. Small amounts (1 to 1 × 10^-2 wt%) of nano-sized Sm211 and Nd422 powders were mixed homogeneously with the precursors of Sm123 + 25 wt% Sm211 followed by the melt-texture processing in air. It is observed that superconducting properties of SmBCO with nano-Sm211 or nano-Nd422 additives were greatly enhanced and a clear secondary peak effect was observed. The scale rule analysis shows that the δT_c pinning mechanism may be responsible for the J_c enhancement at high field. A systematic study of the relationship of J _c(H, T) with different amounts of nm-Sm211 and/or Nd422 additions was performed to determine the optimum nano-particle doping contents and their pinning mechanisms respectively.