Effect of the particle size of micro-scale and nano-scale additions on the formation of compositional fluctuations in Sm-Ba-Cu-O material

Recently, many studies imply that the existence of field induced pinning centers, which include RE-rich clusters and compositional fluctuations, contribute to the flux pinning in high field regions. The mechanisms to introduce field induced pinning centers have been proposed for different single grained high T_c superconductor systems. Our previous studies indicated that the addition of nano-scale RE₂BaCuO₅ (RE211, RE: rare elements) form nano-sized compositional fluctuations during the melt-growth process and thus act as field induced pinning centers. It has been noted that samples with the addition of nano-Nd₄Ba₂Cu₂O₁₀ (Nd422) particles exhibit a higher J_c-H performance than those with nano-Sm211 precursors, which were supposed to be the result of the different solubility, peritectic temperature, and atomic size of Nd compared to Sm. It is therefore believed that the optimum size of compositional fluctuations will be related to the diffusivities of RE elements, solubility, and the precursor particle size. In this study, Nd₄Ba₂Cu₂O₁₀ (Nd422) particles of two different sizes: micro scale and nano scale, were used to reveal the size effect. Different microstructures and J_c-H performance were observed which are related to different reactions between the Nd422 additions and the 123 matrix during the melt-textured growth process.