1. Field of the Invention
This invention relates to a substrate for superconductive film fabrication to be employed on the occasion of manufacturing oxide superconductive wires through the deposition of a superconductive film on a substrate. This invention also relates to superconductive wires having a superconductive film fabricated on the substrate and to manufacturing methods of the substrate and the superconductive wires.
2. Description of the Related Art
Conventionally, there have been proposed a many number of ideas for manufacturing oxide superconductive wires through the deposition of a superconductive film on a substrate (see for example, Japanese Patents No. 2614948; No. 3251034; No. 3532253; and No. 3771012; and JP-A 2001-110255 and JP-A 11-3620).
Among them, an oxide superconductive wire utilizing an oxide superconductor represented by a composition formula of REBa2Cu3O7-d (wherein RE means rare earth elements, also referred to as 123-type or yttrium-type superconductor), the oxide superconductor being deposited on a tape-like metal substrate to make the wire flexible, is known to attain excellent current characteristics. For this reason, this oxide superconductive wire is one of the oxide superconductive wires that are intensively studied and developed at present. Under the circumstances, the studies on this oxide superconductive wire have been advanced to such a stage that a large number of prototypes concerning electric power equipments and the like utilizing this oxide superconductive wire have been manufactured.
Therefore, in the art of manufacturing oxide superconductive wires, it is now strongly desired to establish a mass production system aiming at industrialization for the production of superconductive wires, so that we are now faced with a situation where the development of highly reliable and stable process for the production of superconductive wires is urgently needed.
The fact that a thin-film oxide superconductor is capable of exhibiting excellent current characteristics has been already confirmed through experiments on the oxide superconductor deposited as a thin film on the surface of a monocryatalline substrate. When a monocryatalline substrate is to be used however, it is impossible to freely bend it and to work it to obtain an elongated strip having a length of several hundreds meters, thus making it unrealistic.
In any attempt for the practical use or industrialization of the oxide superconductive wires, it is imperative to work the oxide superconductor into a wire-like member having the same degree of flexibility as metals. For this reason, it has been attempted to deposit an oxide superconductor as a thin film on a tape-like metal substrate to thereby enable the resultant substrate to exhibit a function useful as a practical wire. However, it has been found that, in the case of the superconductive thin film which has fundamentally a polycrystalline structure, it is impossible to obtain excellent current characteristics unless a large number of crystal grains constituting the thin film are uniformly arrayed in the same direction.
However, as conducted in the ion beam assist vapor deposition (IBAD) method, inclined substrate deposition (ISD) method, or a method employing an orientated metal, this problem has been already solved by using a substrate where a large number of crystal grains constituting the substrate are orientated in the same direction as a substrate for superconductive film formation.
Further, as a result of considering the matching of lattice constant, reactivity of substrate to the superconductive film, etc. in addition to the orientation of crystal, the development of the superconductive wires is now generally directed to the wires wherein at least one oxide layer called intermediate layer other than a superconductive layer is deposited on a metal substrate and then a superconductive layer is deposited on the intermediate layer, thereby obtaining a wire having a multi-layer structure.
By means of this multi-layer structure, it is now possible to obtain wires which are capable of exhibiting excellent current characteristics even on a metal substrate, e.g., a current density of more than 106 A/cm2 at liquid nitrogen temperature (77K) or a current density of more than 107 A/cm2 at liquid helium temperature (4.2K), the wires moreover being flexible.
However, when the practical use or industrialization of the oxide superconductive wires is taken into consideration, it is imperative to further improve the manufacturing speed of the wires. Thus, it is strongly desired, at present, to improve the manufacturing speed of the wires in the art of manufacturing oxide superconductive wires.