Electrical transport across grain boundaries in bicrystals of YBa2Cu3O7δ

• Published in: Physica. C, Superconductivity Superconductivity, 1991-12, Vol.185-189, p.315-320
• Main Authors: Larbalestier, D.C., Babcock, S.E., Cai, X.Y., Field, M.B., Gao, Y., Heinig, N.F., Kaiser, D.L., Merkle, K., Williams, L.K., Zhang, N.
• Format: Article
• Language: English
• Subjects: 360204 - Ceramics, Cermets, & Refractories- Physical Properties; 656100 - Condensed Matter Physics- Superconductivity; ALKALINE EARTH METAL COMPOUNDS; BARIUM COMPOUNDS; BARIUM OXIDES; BICRYSTALS; CHALCOGENIDES; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COPPER COMPOUNDS; COPPER OXIDES; CRYSTAL STRUCTURE; CRYSTALS; CURRENT DENSITY; ELECTRIC CONDUCTIVITY; ELECTRICAL PROPERTIES; GRAIN BOUNDARIES; HIGH-TC SUPERCONDUCTORS; MATERIALS SCIENCE; MICROSTRUCTURE; OXIDES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; POLYCRYSTALS; SAMPLE PREPARATION; SUPERCONDUCTORS; TRANSITION ELEMENT COMPOUNDS; YTTRIUM COMPOUNDS; YTTRIUM OXIDES
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(91)91992-D

The superconducting properties of about 20 bulk-scale flux-grown bicrystals of YBa2Cu3O7-δ have been measured in order to deduce the nature of the coupling across their grain boundaries. Bicrystals with two types of misorientation relationship were studied: (i) θ [001] (C-type) and (ii) 90° [010] plus an additional rotation about the aI | cII axis (P-type). A general trend for a transition from flux pinning (FP) to Josephson Junction (JJ) to resistive (R) behavior was observed as the misorientation angle increased. However, FP character was observed well into the high-angle regime, in particular, for P-type bicrystals, and JJ behavior was observed at as low as 10° [001]. The Jα values of two bicrystals were increased by a second oxygen anneal. In one case (28° [001] boundary), extended oxygenation produced a change form JJ to mixed JJ/FP behavior, markedly raising the transport critical current density (Jα) at all fields. HRTEM has been performed on two of the same bicrystals which were electromagnetically characterized. A thin second phase layer unobservable by conventional TEM was observed in a resistive boundary, whereas no such phase was detected at a JJ boundary. We conclude that the character of the boundary cannot be predicted either from its misorientation angle or the magnitude of its Jc.