Effect of Pt Addition on Microstructure and Superconducting Properties for Filamentary (Nd,Sm,Gd)-Ba-Cu-O Superconductors

The filamentary (Nd_0.33Sm_0.33Gd_0.33)_1.18-Ba_2.12Cu_3.09O_y (NSG123) superconductors chemically doped with nominal Pt concentrations from 0 to 0.5 at% were fabricated by a solution spinning method. We investigated effects of the amount of Pt addition and cooling rate from partial melting temperature of 1050 degC during OCMG processing on superconducting properties and microstructure of filamentary samples. Pure NSG123 filaments cooled at 20 degC/h-50degC/h showed the J_c vale higher than 2.0 times 10⁴ A / cm² at 77 K and 0 T. Although the sample treated at fast cooling rate of 60 degC/h exhibited the J_c value of about 3.0 times 10³A/cm² at most, the NSG123 doped with 0.05 at% Pt cooled at 60 degC/h showed high J_c value of 2.0 times 10⁴ A / cm² at 77 K and 0 T. The field dependence of transport J_c value was also investigated at 77 K for samples cooled at 60 degC/h. The J_c value of 0.8 times 10⁴ A / cm² was maintained up to magnetic field of 5 T for the 0.05 at% Pt doped sample. The size of (Nd,Sm,Gd)₂BaCuO₅ particles in NSG123 matrix was reduced from about 3 to 0.5 mum with increasing Pt concentration from 0 to 0.5 at%. In addition, the connectivity in microstructure was improved with increasing Pt concentration. It was found that both J_c-B properties and the microstructure for the sample treated at fast cooling were effectively improved by Pt doping.