Structure of grain boundaries: Correlation to supercurrent transport in textured Bi₂Sr₂Ca_n−1Cu_nO_x bulk material

Abstract

Two kinds of characteristic grain boundaries were observed in textured Bi 2 Sr 2 Ca n21 Cu n O x (n 2 and 3) bulk material: one (P-type) is nearly parallel to the (001) plane, and the other (N-type) is approximately normal to the (001) plane. Low-angle tilt N-type boundaries are composed of arrays of dislocations. However, for a small c-axis misorientation, the regions between the dislocation cores are still well connected, providing "pathways" for supercurrents crossing the boundary plane. The P-type boundaries exhibit compositionally and structurally modulated faceting. Although we see local regions of the low T c (2201) phase at low-angle tilt (, 10 ± ) P-type boundaries, there are also "pathways" crossing the boundary plane made up of the high T c (2212) and (2223) phases. The characteristics of such low-angle tilt grain boundary structures can therefore be modeled to provide general insight into the correlation between high critical current densities and low-texture breadths. On the other hand, a weak link could be formed at high-angle (. 10 ± ) boundaries where there are the low T c (2201) or insulating phases.

A model for texture development in BSCCO high-Tcsuperconductors

“…the c-axis orientation of superconductor nuclei has no preferred direction with respect to the substrate (figure 6). In this fashion, and assuming anisotropic superconductor crystal growth behaviour where growth along the ab direction is preferred, as it has been shown in various investigations [12][13][14], one would predict that after a time interval t two rather different situations should develop from the nucleation event assumed in figure 6. It is assumed that during crystal growth the crystal shape develops into a plate-like configuration.…”

Review: grain boundary faceting–roughening phenomena

“…Below h = 20°, the GB contains the segments of perfect contact of abutting grains forming the high-T c ''pathways'' crossing the boundary plane. They are separated by dislocation cores with low T c [219,[225][226][227][228][229]. One can say to a first approximation, that thereafter a continuous insulating layer of 2-3 nm will lead to a constant attenuation of the supercurrent.…”

Current transport and microstructural development in BSCCO tapes and joints fabricated by groove rolling

“…Analysis of the kink angle indicated that CB1 (in figure 10) is at a 15 • [010] tilt to the grain boundary and CB2 (in figure 10) is at an 18 • [010] tilt to the grain boundary. Colonies with kink angles of 30 • and 18 • have been observed by other investigators [29,30]. At this time, we are not sure what causes these preferred orientations of the platelets and more work needs to be done to estimate their implications on the current transport properties of the tapes.…”