Enhanced critical current density in Ca-doped Y1Ba2Cu4O8

The Jc of Ca0.1Y0.9Ba2Cu4O8 (Ca-1:2:4) synthesized in elevated oxygen pressure is found to be >106 A/cm2 at low temperatures and fields, two orders of magnitude greater than the Jc of undoped Y1Ba2Cu4O8 (1:2:4). The Jc (determined by magnetic hysteresis measurements) remains high (5x105 A/cm2) up to B=4 T at 5 K, and is still >104 A/cm2 at 40 K and 4 T indicating strong flux pinning. At 77 K, Jc drops to 103 A/cm2 at B=1 T. Ca-1:2:4 was partially converted to 1:2:3+CuO by brief thermal treatment to generate additional flux pinning centers, but Jc did not improve further