In this introductory presentation, wide variety of potential applications of superconductivity in space are discussed. They are categorized into such two groups as system applications and device and component applications. Each application of the former utilizes a large superconducting magnet, by which the main feature of the system can be characterized. The second category includes various kinds of applications to devices and components. Among the potential applications, some are in fairly well developed stage and have a great impact upon space technology in the near future, while others are still under development or in the conceptual design phase.
A simple interpolation scheme between insulator and metal limits of the so-called tJ-model of strongly correlated electrons is proposed. The Fermi surface exists in this model, but does not satisfy Luttinger's theorem. D-wave pairing is possible through the super-exchange coupling.
In view of the common features of high Tc superconducting materials, such as very short coherence length and layered perovskite structure, sophiscated ceramics thin film technology is expected to be a powerful tool for fabricating Josephson tunnel junction devices as well as for constructing artificially designed new ceramics layers which may exhibit still higher Tc superconductivity. Studies on the epitaxial growth of ceramics films relating to high Tc superconductors are reported with a focus placed on our recent research using a pulsed laser deposition in ultra-high vacuum system (laser MBE).
Since December 1986, we have been engaged in high Tc oxide superconductor research with emphasis on the synthesis and processing of thin and thick films of cuprate superconductor as well as on the accumulation of some basic data related with the film preparation. This paper reports some of our recent results of film deposition and photochemical processing of the films. 50Hz ac sputtering has been primarily used for preparing a variety of high Tc films by use of its simple and easily modifiable system. A plasma controlled sputtering is applied to the currently interested layer-by-layer deposition of oxide films as a possible approach to new higher Tc materials. Annealing of films under a laser or a UV light irradiation worked effectively to control the oxygen stoichiometry and induced reversible changes in Tc and crystal parameters of the films.
The paper describes two automatic measuring systems for testing high Tc superconductor thin films. In these experimental equipments data translations from measuring devices to personal computer are realised through standard KEITHLEY 570 data acquisition system and through GPIB interface. The measurements of the films resistivity are performed by an AC four probe technique. The contacts are prepared by the method which allows to decrease contact resistance more than 106 times. The measurements of critical current are carried out on the samples in the form of microbridges prepared by photolithography. The experimental results of YBa2Cu3Ox superconductor temperature dependence of electrical resistivity are presented.
In the technological point fo view, the powder-in-tube method is very useful for preparing the superconducting composite. In order to achieve high critical current density (Jc), the thermomechanical treatment by which heat treatment and cold working are repeated several times, has been known to be effective. Here, the changes of Jc by different TMT techniques for Ag sheathed YBaCuO and BiPbSrCaCuO superconducting tapes have been mentioned and the metallurgical factors improving Jc were discussed. The Jc of YBCO tapes increased with decreasing oxide layer thickness. The specimen with 3, 300A/cm2 at 77K consisted of the preferred oriented grain structure of 123 phase with low prosity. The Jc was greatly improved by SnO2 addition. In the BPSCCO tapes, the optimum chemical composition was estimated. The annealing was performed in the temeprature region between 1113 and 1118K. The major superconducting phase 2223 phase was accompanied by minority 2212 and 2201 phases and several impurity phases of CuO, Ca2PbO4 and (Sr, Ca)3Cu5Ox. The specimen with 19, 000A/cm2 at 77K consited of highly laminated grain structure. As BPSCCO tapes exhibited enough Jc for instance, exceed 5×104A/cm2 at 10T at 4.2K, the mechanical property is suggested to be the next research subject for practical applications.
The crystals of high-Tc oxide-superconductors YBCO are grown from the melt at higher temperatures. It is quite disadvantageous that the melt reacts with the crucibles in contact and contaminates the crystals. For the purpose to grow pure crystals a self-sustaining Verneuil method by laser-heating is examined. Unfortunately the oxide superconductors do not grow congruently from the melt. Therefore, further heat treatment is necessary to recover High-Tc phases. As for YBCO crystals the boule is capped with a melt in excess of BaCu2O3 where the target crystals grow. This is a flux method in principle. The finished boule is heated at 910°C to melt away the flux to take out crystals. With an interference contrast microscope, it is confirmed that the crystal has grown by step growth process. The steps are rather heavily bunched. The domain structures have no correlation with the step structures. This suggests that the crystal growth is regular, while the domains are formed at the phase transition from the tetragonal to the orthorhombic phase after the crystal growth.
Recently, laser ablation has been widely used to prepare the films of multicomponent-oxides such as high Tc superconductors, ferroelectric materials, etc. Concerning the superconducting films, the laser ablation is recognized as one of the best deposition techniques. The deposition by laser ablation consists of three processes; a removal of target materials by forcusing the pulsed laser beam, a transport of the ejected atoms and clusters, and a solidification of them onto the substrate. The most significant advantage of this technique is stoichiometric deposition; there is no deviation in the composition between the target and the film. This advantage promotes the research in materials science, saving cost and time for sythesis of advanced thin films. Furthermore, it is possible to utilize excited species of the ejected materials for low temperature deposition. In this paper, the feature of the present technique will be reviewed.
In the water-cooled motorcycle engine, the cooling water heated by the engine is transferred to the radiator in which heat exchange is conducted between the thus heated cooling water and open air. In the motorcycle, due to a restricted size of its body, the radiator to be mounted on such body is also restricted in size, particularly, in width. Therefore, much effort has been directed toward the manufacturing of the motorcycle radiator having a small width. The present invention relates to a method of manufacturing a motorcycle radiator for cooling a motorcycle engine by means of cooling water, and more particularly to a method of manufacturing the motorcycle radiator having an arc-shaped raidator core.
Structures of layered copper oxide compounds and relating high-temperature superconductors are classified by using the concept the block layer which can isolate each CuO2-sheet and control carrier density within the Cu-O plane. Particular emphasis is laid on the Cu-O network dependent physico-c hemical properties which are entirely governed by ordering and combination of constituent block layers. By the new classification method, structures and carrier-doping characteristics are predicted for prospective but hitherto unknown CuO2-layered superconductors. Possible importance of the concept of the block layer is pointed out in epitaxial growth of superconducting structures.