Fabrication and Superconducting Properties of Aluminum Doped (Nd,Sm,Gd)–Ba–Cu–O Filaments

Abstract

(Nd0.33Sm0.33Gd0.33)1.18Ba2.12Cu3.09Oy (NSG123) precursor filaments doped with Al were prepared by a solution spinning method and partially melted at 1050degC for 30 min in flowing 0.1% O2 + Ar gas. Samples were cooled at various rate of 10-60degC/h, and then oxygenated in pure O2 gas. It was found that the microstructural and superconducting properties were strongly influenced on the cooling rate from partial melting temperature to 900degC during OCMG processing. Although the sample without Al cooled at 20-50degC/h showed Jc value higher than 2.0 times 104 A / cm2 at 77 K and 0 T, the sample treated at fast cooling rate of 60degC/h exhibited the Jc value of about 3.0 times 103 A / cm2 at most. In contrast, the NSG123 doped with 0.05 at%Al even at a rate of 60degC/h cooling showed high Jc value of 1.5 times 104 A / cm2 at 77 K and 0 T, and exhibited a well aligned texture and a dense microstructure. From Jc measurements in applied magnetic fields, a Jc value higher than 103 A / cm2 was maintained up to 9 T for 0.05 at % Al doped filament. It was found that a small amount of Al doping into NSG123 was effective on refinement of the size of the NSG211 particle and reduction pores and cracks in microstructure for sample treated even at fast cooling, and thereby increased Jc values.