Clarification of Determining Factors of Irreversibility Fields in High-Tc Superconductors with Short Coherence Length

研究了随机取向的铜酸盐和铁基超导体的合成条件、微观结构和晶界临界电流性能之间的关系。添加还原后退火工艺和实现载流子过掺杂态是显著提高Y123和(Bi，Pb)2223超导体晶间JC的有效方法。这种改善是由控制阳离子组成增加凝聚能和沿c轴方向增加相干长度的影响来解释的。采用上述方法，Y123的不可逆场也得到了很大的改善。对于铁基超导体，晶间JC的改善是通过减少杂质相和添加金属锡来实现的。本研究中实现的晶间临界电流性能对于每种材料都是最高的，作为随机取向的烧结块，致密化可以预期进一步的增强。

Relationships among synthesis conditions, microstructure and critical current properties across the grain boundaries were studies for randomly oriented sintered bulks of cuprate and iron-based superconductors. Addition of reductive post-annealing process and achieving carrier overdoped state were found to be quite effective for dramatic enhancement of intergrain Jc of both Y123 and (Bi,Pb)2223 superconductors. This improvement is explained by the effect of an increase in condensation energy by a control of cation composition and an increase in coherence length along the c-axis direction. Irreversibility field of Y123 was also largely improved by adopting above method. For iron-based superconductors, improvement of intergrain Jc was succeeded by reduction of impurity phases and addition of Sn metal. Intergrain critical current properties achieved in this study are highest for each material as randomly oriented sintered bulks and further enhancement can be expected by densification.