Superconductivity and Superconducting Devices

Titanium alloyed with niobium exhibits superconductivity, and a lack of electrical resistance below 10 K. Composition ranges from 25 to 50 wt % Ti. These alloys are P-phase alloys having superconducting transitional temperatures at ca 10 K. Thek use is of interest for power generation, propulsion devices, fusion research, and electronic devices (52). 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Two-phase flows containing other types of fluids of interest are those of helium and refrigerants. The former fluid is used for cooling different superconductivity devices, while the latter are used in the refrigeration industry. The pressure drop in a two-phase flow of helium in a tube of 1.6 mm (0.06 in.) I.D. under adiabatic conditions and with heat supply were reported by Deev et al. (1978). They indicated that although the actual measured AP (at P = 1.0 to 1.8 X 10s N/m2) differed... 

T.van Duzer, C.W. Turner Principles of Superconducting Devices and Circuits, Edwards Arnold (1981)... 

Research chemists found that they could modify the conducting properties of solids by doping them, a process commonly used to control the properties of semiconductors (see Section 3.13). In 1986, a record-high Ts of 35 K was observed, surprisingly not for a metal, but for a ceramic material (Section 14.24), a lanthanum-copper oxide doped with barium. Then early in 1987, a new record T, of 93 K was set with yttrium-barium-copper and a series of related oxides. In 1988, two more oxide series of bismuth-strontium-calcium-copper and thallium-barium-calcium-copper exhibited transition temperatures of 110 and 125 K, respectively. These temperatures can be reached by cooling the materials with liquid nitrogen, which costs only about 0.20 per liter. Suddenly, superconducting devices became economically viable. 

The new superconducting ceramics offer a way out, if they can be made in some workable form, probably a thin film, and so long as the circuits can be operated at around 80° K or higher. The oxides could then be used on the circuit chips themselves to connect transistors and other devices and to make connections between chips. There is also the possibility that the superconducting properties in the new materials can be manipulated by, say, moving oxygen in and out as needed, or that the ceramics will turn out for some reason to be more suitable than conventional superconducting materials for use in transistors. 

Products closest to commercial production are SQUlDs - " and a microwave passive device. A SQUID is a superconducting device containing one or two... 

The long-term interest, as far as the applied physicist is concerned, lies in the possible uses of supermolecular assemblies for memory storage, molecular switching, and superconducting devices. However, at the present time, potential improvement areas are where monomolecular films show most promise and where the prospects of commercial exploitation seem reasonable in the medium term. A few of these areas are described in this section most of the illustrations are based on work carried out in my research laboratories. These potential improvement areas are grouped into three categories, but most of the emphasis is placed on utilizing the nonlinear properties of LB films. 

Technium was the first synthetic element, although a naturally occurring isotope was discovered in minute quantities in 1962. The metal is silvery grey. It has not been used as a commercial product but may have uses in specialty steel and superconducting devices. 

If a conventional superconductor (S) described by a s-wave order parameter symmetry (OPS) is put together with a non conventional superconductor (D), described by a pure d-wave OPS, to form two junctions in a superconducting loop, as indicated in Fig. 4, a self 7r — frustrated loop is achieved [van Harlingen 1995], Indeed, one of the two SD junctions behaves as a conventional "0" junction, since the Josephson coupling is between the positive lobe of the d-wave superconductor (white color in Fig. 4) and the S electrode on the contrary, the other junction is a V junction, because the coupling is now between the S electrode and the negative lobe. As a consequence, a shift of 7r along the loop is achieved and the device is self-frustrated by a half flux quantum. 

Van Duzer, T., and Turner, C. W. (1981) Principles of Superconductive Devices and Circuits (Elsevier, New York). 

T. Nishino, M. Miyake, Y. Harada, and U. Kawabe, Three-Terminal Superconducting Device using a Silicon Single-Crystal Film, IEEE Electron Dev. Lett., EDL6, 297 (1985). 

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