Improved magnetic flux pinning in melt processed (Y, Nd)Ba2Cu3O7-δ superconductor

We report the melt processing of Nd-123 precursor pellets enriched with Nd4Ba2Cu2O10 (Nd-422), Y2BaCuO5 (Y-211) and/or nano-sized Y2O3. Microstructural analysis reveals that two different second phase particles of distinct acicular and spherical morphologies form during solidification in the samples containing Y. A large fraction of the volume of the sample prepared with excess Y2O3 contains 300-500 nm sized, spherical-shaped particles. The width and length of the acicular shaped particles in the samples are < 1 mu m and similar to 2-3 mu m, respectively. 90% of second phase particles are of; 500-600 nm size. The transition temperature, T-c, is below the value expected for NdBCO due to the formation of a (Y1-xNdx)Ba2Cu3O7-delta solid solution phase. The superconducting properties, T-c and J(c), are homogeneous within (Y, Nd)BCO single grains compared to that of NdBCO due to suppressed Nd substitution in the Ba site. Significantly improved critical current densities derived from magnetic moment measurements are observed at 77 K in this system compared to both YBCO and NdBCO.