Effect of Na doping on flux pinning of YBa1.9Na0.1Cu3O7−δ

Abstract We have prepared Na-doped YBa 2 Cu 3 O y (YBa 1.9 Na 0.1 Cu 3 O y +40 mol% Y211) (YBNCO) and Na-free YBa 2 Cu 3 O y (YBCO) samples by the melt-textured growth method to study the effect of doped Na ion on flux pinning. The ac susceptibility curves as well as the hysteresis loops were measured for the samples. Then the effective pinning energy ( U ( T , H dc , J )), irreversibility line ( H irr ( T )) and critical current density ( j c ( H dc )) were determined, where T , H dc and J are temperature, dc magnetic field and current density, respectively. We found that, with Na doping, the H irr ( T ) line shifted to lower temperatures while the J c ( H dc ) and U ( T , H dc , J ) became smaller. Hence Na ions play a negative role in the flux pinning of YBCO. The appearance of the second peak in the J c ( H dc ) curves and the enhancement of anisotropy in YBNCO further support this finding.