Enhancement of Intragrain Critical Current Density in Bi-Based Superconductor by Substitutional Structural Defects

We synthesized Ca-rich Bi-based superconducting whiskers by an Al₂O₃-seeded glassy quenched platelet method. The grown whiskers were precisely characterized by synchrotron radiation X-ray photoemission spectroscopy and high-resolution transmission electron microscopy. The Ca-rich Bi-based superconducting whiskers show a high critical current density of 2 × 10⁵ A/cm² at 40 K in self-field. We found that excess Ca²⁺ ions substitute for the Sr²⁺ sites and cause nano domains with shorter-period modulation within the conventional 2212 crystal structure. The embedded nano crystalline domains can result in structural distorted defects which work as strong pinning center.