The influence of BaCuO2-δ addition in Gd-Ba-Cu-O single-grain superconductors fabricated in air

High quality Gd-Ba-Cu-O single-grain bulks with different BaCuO2-delta adding contents were grown in air via a hot-seeding melt process. At 77 K, all samples show a well-developed secondary peak effect with high J(c) values, which are comparable to that of OCMG-processed Ga-Ba-Cu-O samples. The BaCuO2-delta a addition can effectively suppress the Gd-Ba substitution and therefore enhance the superconducting properties. For the sample with a composition of Gd123:BaCuO2-delta = 1:0.3 in a molar ratio, the J(c)(B = 0) and k(c,peak)(B = 1.3 T) reach 6.45 x 10(4) A cm(-2) and 6.04 x 10(4) A cm(-2), respectively, which are the record high J(c) values at 77 K for Gd-Ba-Cu-O samples melt processed in air.