The formation of defects and their influence on inter- and intra-granular current in sintered polycrystalline 122 phase Fe-based superconductors

• Published in: Superconductor science & technology 2019-08, Vol.32 (8), p.84003
• Main Authors: Shimada, Yusuke, Yamamoto, Akiyasu, Hayashi, Yujiro, Kishio, Kohji, Shimoyama, Jun-ichi, Hata, Satoshi, Konno, Toyohiko J
• Format: Article
• Language: English
• Subjects: electromagnetic properties; electron microscopy; Fe-based superconductor; multi-scale grain structure
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/1361-6668/ab0eb6

The evolution of intra- and inter-granular structures in Co-doped BaFe2As2 (Ba-122) has been studied to address key issues associated with limited inter-granular current transport in randomly oriented polycrystalline Fe-based superconducting materials. We found that the following phenomena occur with an increase in reaction temperature: (i) significant grain growth; (ii) formation and evolution of two types of cracks; (iii) enhancement in the intra-granular current loop; (iv) reduction of magnetic shielding volume; and (v) decrease of the inter-granular transport current. A strong correlation between the inverse grain size and the inter-granular current density was observed. These results indicate that the key microstructural feature to achieve high transport current is a small grain size with no inter-granular cracks, and that low temperature synthesis is an effective path to this end. Based on the observed stacking faults and inter-granular amorphous layers, we propose a model for the formation of the two types of cracks in a polycrystalline Ba-122 phase, i.e. intra- and inter-granular cracks.