Improvement of Intragrain Critical Current Density in High-TemperatureSuperconductor by Self-Assembled Two-Dimensional Nanoplane Pinning Centers

Sr 2+位点的Al 2 O3-晶种玻璃淬灭片晶法。结果表明，Ca ~（2+）离子占据了25%的Sr ~（2+）位置的Bi系超导晶须具有105 A/cm ~ 2量级的临界电流密度Jc。因此，我们通过每个Ca-2 p3/2，1/2 XPS谱在较高结合能处存在另一个XPS峰来证实Ca 2+离子实际上占据了Sr 2+位点。为了阐明Jc增强的起源，我们通过高分辨率透射电子显微镜观察了Bi基超导晶须的局部结构。因此，我们发现，菌株来自一个较小的离子半径的Ca ~（2+）离子比之一的Sr ~（2+）离子。应变影响Bi系超导体中CuO_2面与SrO面之间的晶格失配，并迫使某些晶胞中的调制长度发生变化。这些应变在Bi系超导晶须中起到了有效的钉扎中心作用。

Sr2+ sites by an Al2O3-seeded glassy quenched platelet method. We found that Bi-based superconducting whiskers whose Sr2+ sites of 25% were occupied by Ca2+ ions showed a high critical current densityJc in the order of 105A/cm2.We clarified chemical bond nature of as-grown Bi-based superconducting whiskers by X-ray photoemission spectroscopy XPS. Therefore, we confirmed that Ca2+ ions actually occupied Sr2+ sites by existence of another XPS peak at higher binding energy of each Ca-2p3/2,1/2 XPS spectrum.To clarify an origin of the Jc enhancement, we observed local structures of Bi-based superconducting whiskers by high-resolution transmission electron microscopy. Therefore, we found that strains which were come from a smaller ion radius of Ca2+ ion compared with one of Sr2+ ion. The strains affected a lattice mismatch between CuO2 plane and SrO plane in Bi-based superconductor and they forced to change modulation lengths in some unit cells. These strains seem to have worked seffective pinning centers in Bi-based superconducting whiskers.