Showing papers by "Zhifeng Ren published in 1992"
TL;DR: In this paper, single crystals of Bi 2 Sr 2 CaCu 2 O y with transition temperature T c =80 K have been reduced in hydrogen at 400°C and showed that the difference in local structure around copper could be a main factor governing the observed changes in superconducting properties.
Abstract: Single crystals of Bi 2 Sr 2 CaCu 2 O y with transition temperature T c =80 K have been reduced in hydrogen at 400°C. After hydrogen reduction, there is no observable change in crystal cell parameters and the modulation wave vector, q , but apparently both the Meissner fraction and the superconducting transition temperature decrease. The copper K-edge X-ray-absorption near-edge spectra (XANES) in the oxidized crystals with higher T c and the reduced crystals with lower T c show that the difference in local structure around copper could be a main factor governing the observed changes in superconducting properties.
17 citations
TL;DR: In this article, the critical current density of bulk ceramic superconductors is often several orders of magnitude lower than that of a single crystal or oriented film of the same material due to the weak links residing at the boundaries between single crystals within the ceramic sample.
Abstract: The critical current density Jc of bulk ceramic superconductors is often several orders of magnitude lower than that of a single crystal or oriented film of the same material due to the weak links residing at the boundaries between single crystals within the ceramic sample. Assuming that the rate of electron transport within each single crystal is much faster than the average rate of electron transport between adjacent single crystals, a working hypothesis of Jc enhancement by granular reorientation is formulated which includes the "brickwall" model and melt-texturing as special cases with long-range granular alignment which usually leads to rigid and brittle bulk samples. Simple geometric considerations show that only short-range local granular alignment is necessary for high Jc. For mis reason, it should be possible to make flexible superconducting wires and tapes for commercial applications at or above 77K.
1 citations