Enhanced flux pinning properties of Bi(Pb)2212 single crystals

Abstract

Improvement of flux pinning properties of heavily lead-doped Bi2212 single crystals was attempted by cobalt-doping with low concentrations. T c's of grown crystals with nominal compositions of Bi 1.6Pb 0.6Sr 1.8Ca(Cu 1− x Co x ) 2O y ( x=0, 0.002, 0.005, 0.02) dramatically decreased with an increase of the cobalt-doping level x, however, crystals with x=0.002 and 0.005 showed largely improved flux pinning properties below 50 K. This result suggests that effective point-defect-type pinning sites were successfully introduced by small amount of cobalt-doping. For these crystals, both anisotropic in-plane J c properties and the “temperature induced pinning” effect due to interfaces of the lamella structure were observed, however these characteristic behaviours were suppressed in the crystal with x=0.02.