A sandwich-type all-oxide Josephson junction consisting of an a-axis oriented YBa2Cu3O7−δ/PrBa2Cu3O7−δ′/YBa2Cu3O7−δ structure has been realized and its Josephson characteristics experimentally investigated. Almost all the fabricated junctions showed the Josephson characteristics, including a resistively shunted junction (RSJ)-like current-voltage characteristic and a Fraunhofer-like magnetic-field dependence of the critical current. The obtained maximum values of the critical-current density jc and the IcRn value were 110 A/cm2 and 80 μV, respectively, for a 50-nm-thick PBCO interlayer at 3 K. Besides, the temperature dependencies of the critical current and the normal resistance were measured. Ic was proportional to exp(− aT1/2), where a is a constant.

A variety of armed cyclens were prepared in which ester, amide, nitrile, and pyridine moieties were attached as cation-ligating side arms to a 12-membered ring. Ester-, amide-, and pyridine-armed cyclens nicely accommodated a Na(+) ion in a three-dimensional fashion and clearly discriminated the cation from Li(+) and K(+) ions. They extracted Na(+) ion more efficiently and selectively than common Na(+) ion-selective ligands. X-ray diffraction, FAB-MS, (23)Na NMR binding studies, and computer modeling experiments demonstrated that the cyclens having ester-, amide-, and pyridine-functionalized side arms formed highly selective encapsulated Na(+) complexes via a cooperative action of parent cyclen and side arms.

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