Effect of nano-scale additions on the enhancement of superconductivity in Y-Ba-Cu-O materials

The coherence length of Y-Ba-Cu-O superconductor is in the nano-meter range, therefore, nano-scale additions can be used to increase the number of effective pinning centers in top-seed melt-growth (TSMG) Y-Ba-Cu-O single grain materials. Different kinds of nano-scale additions: Y₂O₃, and Y₂BaCuO₅ (Y211) were mixed with precursor powders (YBa₂Cu₃O₇ + Y₂BaCuO) followed by TSMG process in air. SEM and TEM were used to investigate the size and morphology of the 211-particles as well as the distribution of defects (e.g. dislocations) in the matrix. It was found that the size of 211-particles was slightly reduced in nm Y₂O₃ doped samples, and sub-micro 211-particles were observed in nmY211 doped samples. In addition, the critical temperature, T _c, for all samples was similar and independent of the type of addition, while the enhancement of critical current density, J _c(H, T), varied with the types of nano-scale addition. Accordingly, the reactions between the superconductive matrix and different nano-scale additions resulted in different pinning properties. These samples with different nano-scale additions were studied using scaling rule analysis to differentiate their pinning mechanisms. For comparison, the results of SmBCO samples with nano-scale additions are also discussed in this study.