Speaker
Dr
Fumitake Kametani
(National High Magnetic Field Laboratory)
Description
By utilizing the over pressure technique, Bi2Sr2CaCu2Ox (Bi2212) round wires without macroscopic texture recently achieved Jc of 4000 A/mm2 at 4.2 K, 5T, despite the presence of many universally-assumed obstructing high angle grain boundaries (HAGBs). We sought to understand the nature of more local scale texture, in particular to better understand the apparent disagreement between Bi2212 and its sibling Bi2Sr2Ca2Cu3Ox (Bi2223). In order to understand whether HAGBs in Bi2212 are superior to those in Bi2Sr2Ca2Cu3Ox or REBa2Cu3O7-δ, or whether other mechanisms compensate for obstructing HAGBs, we extensively compared the grain and GB structure in a Bi2212 round wire to those in a uniaxially textured Bi2223 flat tape by using the electron backscatter diffraction orientation image analysis (EBSD-OIM). It turned out that, compared with the Bi2223 tape in which the in-plane orientations of grains are basically random in spite of small out-of-plane GB misorientations, the Bi2212 round wire possesses the quasi-biaxial texture in which large basal-plane-faced GBs are formed as a result of large grain formation in the constraint of narrow filament cavities. It is strongly suggested that the major current paths in the high Jc Bi2212 round wire are ~10-15° basal-plane-faced, c-axis twist GBs which are strongly coupled due to their large area and force-free configuration in current flow and magnetic fields. These unique features of the Bi2212 grain structure may help explain the strong grain-to-grain coupling that we have found and lead to further improvements in performance.
Author
Dr
Fumitake Kametani
(National High Magnetic Field Laboratory)
Co-authors
David Larbalestier
(National High Magnetic Field Laboratory)
Dmytro Abraimov
(National High Magnetic Field Laboratory)
Prof.
Eric Hellstrom
(National High Magnetic Field Laboratory)
Jianyi Jiang
(National High Magnetic Field Laboratory)
Mr
Maxime Matras
(National High Magnetic Field Laboratory)
