University of Kansas

Midwest Superconductivity, Inc.

Czt Inc.

Kai W Wong

Ying Xin

Yi-Han Kao

Xin Fei

Zhengzhi Sheng

Susana Curatolo

Fui T Chan

Guifu Sun

Wai-Yim Ching

Peter C Fung

A method of operating a superconductor in its superconductivity state at a temperature Tc(i) in the range of T* to T, where T* is greater than the superconductivity temperature Tof the superconductor, includes cooling the superconductor to a temperature of Tor less and applying energy to the superconductor after the superconductor has entered a superconducting state. The energy corresponds to the quantum energy h&#x3bd; in the range of a minimum energy less than Eto less than E, where Eis the ground state of the two-dimensional excitation binding energy of the superconductor The superconductor is then cooled to the selected temperature T(i). The minimum energy is 8/9 of E.

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Improved superconducting oxides are provided having the general formula (Hg.sub.1-x Tl.sub.x)Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2+.alpha. where x is from about 0.05-0.5 and n is 1, 2, 3 or 4, and .alpha. is an oxygen enrichment factor. The Tl-doped oxides exhibit very high T.sub.c and J.sub.c values.

Tl-doped HgBaCaCu superconductors

Composite bulk superconducting materials having desirable physical, measured transport current density and high T.sub.c superconducting characteristics are provided which comprise a first matrix of superconducting ceramic oxide crystalline grains with a second matrix of elemental metal (gold, silver, palladium and tin) situated within the interstices between the crystalline grains. Preferably, each matrix is a continuous phase within the composite material, with the ceramic oxide preferably being present at a level of at least about 80% by weight, whereas the elemental metal is present at a level of up to about 20% by weight. In fabrication procedures, a precursor superconducting ceramic oxide is first prepared and reduced to a fine powder size; this is mixed with powdered elemental metal, and the mixture is compressed using high compaction pressures on the order of 14 tons/cm.sup.2 or greater to form a body, which is then sintered to yield the composite. Particularly preferred composites include a mixed metallic matrix including respective quantities of tin and a noble metal.

Superconductors having continuous ceramic and elemental metal matrices

A selectively controllable, direction-, amplitude- and/or frequency-specific superconducting shield (10) is provided which includes a multiply-connected superconducting shield (12) adapted to shield a zone (13) from external magnetic, electric and/or electromagnetic fields and signals. Controlled gating of the shield (12) is provided by means (16) serving to selectively lower the critical shielding current density of a portion (26) of the shield (12) to a level permitting entrance of external fields through the portion (26), while leaving the critical shielding current densities of other portions of the shield (12) at higher, field-shielding levels. The means (16) preferably includes respective, selectively energizable coil pairs (CP.sub.1, CP.sub.2 . . . CP.sub.n) disposed about the shield (12). A highly sensitive magnetic detector (30) would include the shielding device (10) as well as a SQUID assembly (18) situated within the zone (13) defined by shield (12). The detectors of the invention may be used in passive, gating-controlled arrays in order to improve signal discrimination and signal-to-noise characteristics of conventional arrays.

Selectively switchable superconducting electromagnetic shield

Complex superconducting oxides are fabricated through appropriate selection and use of fundamental superconducting 'building blocks.' In this fashion, the invention provides a rationalized method of fabricating complex oxides having desirably high T.sub.c values. In another aspect of the invention, novel, 112 and 12 superconducting oxides are described.

High T.sub.c superconducting oxides

Vanadium-containing superconducting oxides are disclosed having critical temperature (T.sub.c) values of above about 100.degree. K. and preferably about 110.degree.-150.degree. K., together with predicted current density (J.sub.c) values on the order of 10.sup.4 -10.sup.5 amperes/cm.sup.2. The oxides hereof are moreover relatively ductile and easily bulk sintered to give end products having desirable superconductivity characteristics. Certain preferred oxides of the invention are defined by the general formula:

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Lawrence, KS, United States of America

Kai W Wong