SEM investigation of outgrowths formation mechanism in Ag-sheathed Bi,Pb(2223) tapes

• Published in: Superconductor science & technology 2002-08, Vol.15 (8), p.1203-1212, Article 1203
• Main Authors: Passerini, Reynald, Dhallé, Marc, Giannini, Enrico, Flükiger, René
• Format: Article
• Language: English
• Subjects: Applied sciences; Electrical engineering. Electrical power engineering; Electronics; Exact sciences and technology; Materials; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Superconducting devices
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/15/8/306

Bi,Pb(2223)/Ag tapes exhibit a strong c-axis texturing but are sometimes perturbed by highly misoriented grains that penetrate the Ag sheath: the so-called Bi,Pb(2223) outgrowths. This study focuses on these outgrowths and on their formation mechanism. Extensive SEM analysis has been performed on samples prepared using different techniques and observed from different points of view. The origin of outgrowths appears to be misoriented Bi,Pb(2212) grains, which remain next to the hard agglomerate particles of secondary phases after the deformation. The subsequent growth of misaligned Bi,Pb(2223) platelets easily perforates the soft Ag sheath, and in most cases outgrowths are not related to Ag grain boundaries. Authors have shown that once these Bi,Pb(2223) grains reach the outer surface of tapes, they melt and crystallize into Bi,Pb(2212) during the cool down. Outgrowth formation can be minimized by using fine-grained precursor powder, which avoids the faults in the Bi,Pb(2212) pre-texture that act as outgrowth nucleation sites. 23 refs.