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

We have prepared Na-doped YBa2Cu3Oy (YBa1.9Na0.1Cu3Oy + 40 mol% Y211) (YBNCO) and Na-free YBa2Cu3Oy (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, do magnetic field and current density, respectively. We found that, with Na doping, the Hi,, (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,(Hdc) curves and the enhancement of anisotropy in YBNCO further support this finding. (C) 2002 Elsevier Science B.V. All rights reserved.