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The superconducting transport characteristics of [HgBA.sub.2][CaCu.sub.2][O.sub.6+δ (Hg-1212) grain-boundary junctions grown on (100)-oriented [SrTiO.sub.3] bicrystal substrates have been investigated. The films exhibit a zero-resistance temperature of 120 kelvin and sustain large critical current densities, with values as high as 106 amperes per square centimeter at around 1 00 kelvin. On the other hand, the grain boundaries behave as weak links, with substantially lower critical currents, as is observed for other cuprate superconductors. A reduction of three orders of magnitude in critical current was observed for transport across a 36.8° grain boundary. The current-voltage characteristics of bridges across such a grain boundary show weak-link behavior qualitatively resembling that of a resistively shunted junction. Single-level direct-current superconducting quantum interference devices SQUIDs) have been fabricated with such bicrystal junctions. These SQUIDs show clear periodic voltage modulations when subjected to applied magnetic fields. The SQUIDs operate at temperatures as high as 11 1.8 kelvin, which makes them attractive for operation in portable sensors and devices that utilize nonconventional cooling methods., Grain boundaries (GBs) of high-transition temperature ([T.sub.c]) cuprates have been extensively studied in recent years. High-angle GBs in these materials are known to form superconducting weak links. In particular, with [...]

The synthesis of high-quality films of the recently discovered mercury-based cuprate films with high transition temperatures has been plagued by problems such as the air sensitivity of the cuprate precursor and the volatility of Hg and HgO. These processing difficulties have been circumvented by a technique of atomic-scale mixing of the HgO and cuprate precursors, use of a protective cap layer, and annealing in an appropriate Hg and [O.sub.2] environment. With this procedure, a zero-resistance transition temperature as high as 124 kelvin in c axis-oriented epitaxial [HgBa.sub.2][CaCu.sub.2][O.sub.6+δfilms has been achieved., The recent discovery of superconductivity in mercury-based cuprates (1, 2) ([HgBa.sub.2][Ca.sub.n-1] [Cu.sub.n][O.sub.2n+2+δ]) has pushed the superconducting transition temperature ([T.sub.c]) to values higher than 130 K. More recently, the [T.sub.c] of [...]

Spatially Resolved Observation of Supercurrents Across Grain Boundaries in YBaCuO Films A DETAILED UNDERSTANDING OF THE electronic properties of the grain boundaries in superconducting [YBa.sub.2.Cu.sub.3.O.sub.7] is important both for fundamental [...]