OXIDE SUPERCONDUCTOR SHAPED BODY AND METHOD OF MANUFACTURING THE SAME

Abstract: This invention discloses an oxide superconductor shaped body including a noble metal layer (2) formed on at least one surface of an oxide superconductor layer (3) formed on a substrate (1), and a method of manufac­ turing oxide superconductor shaped body.

Description: The present invention relates to an oxide superconductor shaped body used in electric wires, cables, wiring circuit boards, or electric and electronic components and a method of manufacturing the same. A typical oxide superconductor is a Ba-Pb-Bi oxide which exhibits superconducting properties at a liquid He temperature. In recent years, oxide superconductors (to be referred to simply as superconductors hereinafter) exhibiting superconducting properties at temperatures higher than liquid H₂, N e and N₂ temperatures have been developed. These superconductors are composite oxides such as (La x Sr 1-x )₂CuO₄ and YBa₂Cu₃O x , each of which is constituted by a Group IIIb element, an alkaline earth metal, and Cu. Such a superconductor has a K₂NiF₄ structure or an O₂-deficient laminar perovskite structure. Typical laminar materials having a Cu-O plane structure are a Bi-Sr-Ca-Cu-O material and a Tl-Ba-Ca-Cu-O material, which have higher critical temperatures (Tc). Their examples are Bi₂Sr₂CaCu₂O₈, Bi₂Sr₂Ca₂Cu₃O₁₀, Tl₂Ba₂CaCu₂O₈, Tl₂Ba₂Ca₂Cu₃O₁₀, and TlBa₂Ca₂Cu₃O₁₁. The superconducting mechanism of the above materials is not fully clarified, but it is assumed that a superconducting current is generated along the Cu-O plane. Other superconductor oxides include SrTiO 3-x , A A x WO₃, A x MoO₃, A x ReO₃, Ag₇O₈X, LiTiO₄, and the like. The above oxide superconductors are formed into thick films according to paste printing or the like, or thin films according to physical vapor deposition (to be referred to simply as PVD) and chemical vapor deposition (to be referred to simply as CVD). Alternatively, the oxide superconductors are formed into conductors such as wires and strips and are used in a variety of applications. All epitaxial methods such as PVD are practiced in a vacuum. In order to prepare an oxide such as YBa₂Cu₃Ox, O₂ becomes short due to a side reaction such as a decomposition reaction. In this case, a vacuum atmosphere containing a small amount of O₂ is utilized. However, it is difficult to maintain an optimal composition. For this reason, the resultant film tends to be amorphous and its superconducting properties are degraded. In the worst case, no superconducting properties can be obtained. Under these circumstances, in a conventional method, the resultant film is heated in an oxygen-containing atmosphere at about 900°C to adjust the composition of oxygen and the like and the crystal structure, thereby preparing a superconductor. The superconductor shaped bodies must withstand various types (i.e., mechanical and thermal) of stress and strain in practice and must have flexibility so as to obtain a desired shape. For example, although a superconductor shaped body is cooled in a refrigerant such as liquid nitrogen during use, it is returned to room temperature during nonuse. Therefore, the superconductor shaped bodies are used under severe heat cycle conditions. A method of forming a superconductor film on a substrate with excellent flexibility (e.g., a metal substrate) and using the superconductor shaped body in practice is taken into consideration. However, during heating for controlling the superconducting properties, the substrate metal is diffused in the superconductor to degrade the superconducting properties such as critical current density (Jc), critical temperature (Tc), and critical magnetic field (Hc). In addition, during heating, the constituting components of the superconductor are segregated at an interface between the superconductor and the substrate or at the superconductor surface. In the worst case, volatile components are removed, and desired superconducting properties cannot be obtained. Furthermore, when the superconductor film is brought into contact with outer air, the superconducting properties are immediately degraded by humidity and contamination gas components in air. In order to use oxide superconductors as superconductor shaped bodies which satisfy specific application purposes, at least one of the following conditions must be satisfied as an object of the present invention. Major applications of the present invention are electric wires, cables, wiring circuit boards, various magnets, magnetic and electromagnetic shield bodies, electronics devices, and device wires. (1) A superconductor according to the present invention has Tc and Hc inherent to itself and exhibits a Jc as high as possible. (2) A superconductor satisfies a condition of current capacity Ic according to a specific application. (3) A superconductor satisfies necessary mechanical conditions such as strength and flexibility in addition to the above-mentioned electric conditions. Flexibility is particularly indispensable in electric wires. (4) A superconductor has an excellent thermal property, i.e., a heat stress generated by the superconductor is as small as possible so as to allow it to withstand heat cycles at least at a refrigerant temperature and room temperature. (5) A superconductor has properties and a structure, both of which withstand a high-temperature process during fabrication. This condition is very important in practical applications. (6) A superconductor is stable for a long period of time. In particular, high electromagnetic stability inherent to the superconducting phenomenon and high chemical stability against external substances can be achieved. (7) Electric connection properties are also indispensable. (8) A superconductor is inexpensive, as a matter of course. Patent Abstracts of Japan, Vol. 7, No. 182 (E-192) [1327], 11 Aug 1983 (JP-A-58087884) discloses an oxide superconductor body including a noble metal layer and an oxide superconductor layer formed on a substrate. EP-A-0283313 includes an oxide superconductor body including an oxide superconductor layer and a noble metal layer formed on at least one surface of the oxide superconductor layer formed on a substrate. The present invention has been made in consideration of the above situation, and its object is to provide a highly flexible superconductor shaped body capable of withstanding mechanical and thermal stress and strain and being substantially free from quality deterioration for a long time, and a method of manufacturing the same. According to an aspect of the present invention, there is provided an oxide superconductor shaped body comprising a substrate consisting of a polycrystalline metal or ceramic having a thermal expansion coefficient of 5 x 10⁻⁶/°C to 15 x 10⁻⁶/°C; a noble metal layer directly on and in surface contact with said substrate; an interlayer of an inorganic material directly on and in surface contact with said noble metal layer consisting essentially of a material having a free energy (ΔG°) equal to or lower than that of BaO and selected from the group of materials, comprising cubic, hexagonal, tetragonal or rhombic crystal structures; and an oxide superconductive layer directly on and in surface contact with said interlayer. According to another aspect of the present invention, there is provided a method of manufacturing a superconductor shaped body, comprising the steps of forming, on a substrate, an oxide superconductor layer having a noble metal layer formed on at least one surface of an oxide superconductor layer, with an interlayer formed between the noble metal layer and the oxide superconductor layer; and heat-treating the resultant structure in an oxygen-containing atmosphere. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1 and 2 are sectional views for explaining oxide superconductor shaped bodies according to embodiments of the present invention, respectively. As shown in Fig. 1, an inorganic material layer 5 is interposed between noble metal layer 2 and superconductor layer 3 formed on the substrate 1. As shown in Fig. 2, an inorganic material layer 6 is interposed between superconductor layer 3 and noble metal layer 4. The types of substrate vary according to application purposes. In most cases, a property required as the primary condition for the substrate is mechanical strength, and stability such as electromagnetic stability is also important. In order to prepare electric wires and cable conductors, a metal is most suitable because it is excellent in flexibility and mechanical strength and can be easily elongated at low cost. The properties required for the substrate are minimum heat stress in a cooling/heating cycle and a thermal expansion coefficient of 5 to 15 x 10⁻⁶/°C. Examples of the substrate are Ti, Zr, Ta, Nb, Fe, Ni, Cr, Co, and an alloy of these metals. Typical examples of the alloy are a Monel alloy of Ni-Cr, stainless steel, an Fe-Ni-Cr alloy (e.g. SUS-310® or SUS-410®), an Fe-Cr alloy steel, and Cu-Ni alloy. The above examples may be combined with Cu or Al having a high electric conductivity and more efficient thermal conduction, thereby preparing composite substrates. In addition to the metallic materials described above, a polycrystal of a ceramic such as SrTiO₃, MgO, ZrO2, Aℓ₂O₃, BeO, BN, AlN, or carbon and an amorphous inorganic material such as SiO₂, polycomponent glass, or the like can be used as substrate materials. A ZrO₂ or Aℓ₂O₃ ceramic sintered body is used for, e.g., a wiring circuit board. A single crystal of GaAs, InP, or the like is used for electronics devices. That is, the general shapes of the substrates are a plate-like shape, an elongated tape-like shape, and a wire-like shape. As described above, the polycrystal is an indispensable condition for the substrate with some exceptions to prepare a high-performance film on an industrial basis according to the present invention. Examples of the noble metal layer formed on or above the substrate or the superconductor layer are Ag, Au, Pd, Pt, In, Os, Ru, Rh, and an alloy of these metals. The noble metal layer can be formed by sputtering, vacuum deposition, ion plating, metalorganic chemical vapor deposiiton (to be referred to simply as MOCVD), plasma spraying, and mechanical bonding. The noble metal layer formed on the substrate according to the present invention serves as a barrier for preventing constituting elements of the substrate from entering the superconductor during heating. The noble metal layer formed on the superconductor layer prevents segregation and evaporation of the constituting elements of the superconductor during heating. In addition, the latter layer prevents the superconductor from abrupt deterioration when the superconductor is brought into contact with external moisture or toxic gases such as SO₂, NO x , H₂S, and Cl₂ during use, and at the same time contributes to improve thermal and magnetic stability of the superconductor and to effectively facilitate external electric connections. The thickness of the noble metal layer formed on the substrate preferably falls within the range of 0.01 to 10 µm and most preferably 0.1 to 2 µm so as to maximize the effect as the barrier and the like. Of the noble metals used in the present invention, Ag is more inexpensive but has better workability than gold- and platinum-based metals. Ag does not form a solid solution with a major substrate material such as Fe, Cr, Ni, Ti, Zr, Co, or Mo, thereby providing a better barrier effect. In addition, it is confirmed that Ag is partially mixed in the superconductor to increase a Jc value. The function of Ag can also be found in an Ag alloy such as Ag-Pd, Ag-Au, Ag-Pt, Ag-In, Ag-RE (RE: rare earth elements), Ag-Sn, Ag-Zn, Ag-Cu, and Ag-Ni. The effect can be maximized when the Ag content falls within the range of 99 to 55 wt%. Ag has a high O₂ diffusion rate at high temperatures, and permeates O₂ in the superconductor. This degrades the superconducting property, and in some cases, the substrate is oxidized and peeled from the superconductor layer. However, the above-mentioned alloys have relatively low O₂ diffusion rates, and the above drawback does not occur. These alloys have a better barrier effect for the substrate and the superconductor layer than Ag. In particular, an Ag-Pd alloy is effective. According to the present invention, the noble metal formed on the superconductor layer is preferably Ag which is not oxidized and has good O₂ permeability. Segregation and evaporation of the superconductor components during heating can be prevented. O₂ can be sufficiently supplied to an O₂-deficient superconductor material. The above function is effective when the thickness of the noble metal film falls within the range of 0.05 µm to twice the thickness of the superconductor film. If the thickness is less than 0.05 µm, the above function cannot be sufficiently exhibited. However, the thickness is excessively large, incomplete O₂ permeation, an increase in thermal stress in the cooling/heating cycle, and an economical disadvantage occur. When a third material is interposed between the noble metal and the superconductor according to the present invention, many advantages can be provided. As shown in Fig. 1, a material for interlayer 5 between noble metal layer 2 on the substrate side and superconductor layer 3 includes TiO₂, ZrO₂, HfO₂, BeO, MgO, BaO, SrO, CaO, BaZrO₃, SrZrO₃, SrTiO₃, BaTiO₃, and BaF₂. These materials have free energy (ΔG°) equal to or lower than that of BaO, a crystal structure such as a cubic, hexagonal, tetragonal, or rhombic structure, and is substantially inactive with an oxide superconductor. Therefore, the thickness of the noble metal layer such as an Ag layer can be reduced, and the interlayer serves as a buffer layer for preventing oxidation of the substrate caused by oxygen permeation by the noble metal. It is more important for the interlayer to dominate growth of the superconductor layer and accelerate formation of crystal orientation for maximizing a superconducting current. As described above, most of the oxide superconductors are laminar materials, and a superconducting current flows in a direction parallel to the Cu-O plane perpendicular to the C-axis. Crystal orientation of the substrate in a direction perpendicular to the C-axis is required in most cases. The material for the interlayer having the above functions can be selected in view of both crystal structures and chemical reaction properties. The thickness of the interlayer is 0.01 µm or more, and preferably 0.05 µm to 2 µm in practice. A multi-layered structure according to the present invention is not limited to the above embodiments. For example, a stabilizing metal layer such as a Cu or Aℓ layer may be formed as an uppermost layer. In addition, a heat conduction layer such an AlN, C, or BN layer, or an insulating protective layer consisting of an organic polymer may be formed as the uppermost layer. Typical examples of the superconductor according to the present invention are (LaSr)₂CuO₄, YBa₂Cu₃O x , BiSrCaCuO, and TlBaCaCuO. YSr 0.5 Ba 1.5 Cu₃O x , Y 0.8 Sc 0.2 Ba₂Cu₃O x , ErBa₂Cu₃O x , DyBa₂Cu₃O x , MsBa₂Cu₃O x (Ms: misch metal) (wherein x = 7-δ, and δ = 0 to 0.5) may be used in place of the above examples. These superconductor materials have perovskite structures. The above oxides include an oxide obtained by partially substituting O with an anion such as F, and an oxide obtained by partially substituting Cu with a cation such as Ag, Ni, or Fe. The thickness of the superconductor film can be arbitrarily determined but preferably falls within the range of 0.1 µm to 1 mm, and most preferably 0.1 to 5 µm. The multi-layered structure according to the present invention as described above can be formed by PVD, CVD, plasma spraying, screen printing, spin coating, spraying heat decomposition, or a combination of a plurality of methods as needed. In general, PVD, CVD, and spin coating are used to form thin films on the order of submicrons or microns, and other methods are used to form thick films. The PVD methods include sputtering, vacuum deposition, and ion plating, which are used to form a superconductor layer, a noble metal layer, and an interlayer. In order to form a crystalline superconductor layer, a substrate must be usually heated at a high temperature of about 500°C or more. PVD is performed in the presence of a low-pressure O₂ gas. In general, since a shortage of oxygen produces a deposited product, an oxidation process is inevitable. Oxidation is effectively performed by plasma oxidation or plasma anodic oxidation. However, heating in an O₂ or O₃ atmosphere is generally performed. In particular, in a laminar perovskite structure of YBa₂Cu₃O₇, a rhombic system of a low-temperature stable type is subjected to transition at 500 to 750°C while absorbing O₂. Therefore, heating under this temperature condition must be performed. In this case, heating is performed in the presence of O₂, and a partial pressure of O₂ falls within the range of 1.013 kPa (0.01 atm) or more and, most preferably, 10.13 kPa (0.1 atm) or more. In general, a heat treatment is performed in air or in a flow of pure O₂. The function of O₂ is effectively found in the temperature range of 350 to 980°C. O₂ diffusion, generation and growth of crystal nuclei, and crystal orientation and dislocation occur in this temperature range. As a matter of fact, during heating, heating in another atmosphere may be partially used together with the O₂ atmosphere as needed. If the heating temperature is less than 350°C, the above effect cannot be satisfactorily obtained. However, if the temperature exceeds 980°C, the components are evaporated significantly to degrade the superconducting properties. When a predetermined period of time has elapsed, the heated structure is cooled to at least 200°C at a rate of 50°C/min or less. When the cooling rate is excessively high, the heating effect cannot be satisfactorily obtained. In the worst case, cracks are formed in the superconductor layer, or the superconductor layer may be peeled from the substrate. The above heat treatment can be performed more than once during or after the fabrication as needed. In particular, when the upper noble metal layer is formed, it is very effective to perform oxidation. A noble metal layer is not reacted with an oxide at high temperatures and allows permeation of oxygen. Constituting elements such as an alkaline earth metal and Cu are not segregated or evaporated during heating to optimize the composition of the superconductor material and its crystal structure. Therefore, a superconductor having excellent properties can be obtained. Of the noble metals, Ag has a high O₂ permeability and a high electric conductivity, and is inexpensive, thus resulting in a most useful material. In most practical applications, a Pt element such as Pd or Pt is preferably formed as an underlying thin film under the Ag film. In this case, the thickness of the Pt element layer falls within the range of 0.01 to 0.5 µm and, most preferably 0.03 to 0.3 µm. Then, adhesion strength between the Ag layer and the superconductor layer is not impaired. Durability against thermal stress caused by repeated cooling to a very low temperature of liquid N2 can be increased. In addition, the noble metal film prevents denaturing of the superconductor layer by external moisture and a very small amount of SO₂, NO x , H₂S, and Cl₂. The noble metal film effectively improves thermal and magnetic stability of the superconductor layer and electrical connections with external devices. The above effects can be obtained when the thickness of the noble metal film falls within the range of 0.05 µm and twice the thickness of the superconductor layer. If the thickness is less than 0.05 µm, the above effects cannot be satisfactorily obtained. However, if the film thickness is excessively large, incomplete O₂ permeation, an increase in thermal stress in the cooling/heating cycle, and an economical disadvantage occur. As described above, the substrate must be kept heated at a high temperature to form an oxide superconductor according to any method including PVD and CVD. However, such a temperature condition, in turn, causes a reverse sputtering phenomenon. A sputtering speed is reduced to one of several fractions, thus degrading productivity. In addition, since the substrate is kept heated at a high temperature for a long period of time, a side reaction occurs between the superconductor and the substrate to degrade the superconducting properties. A heating device is required to heat the substrate to a high temperature. In addition, since the substrate is placed in the O₂-containing atmosphere, its surface is excessively oxidized to degrade adhesion strength between the substrate and the superconductor. In some cases, it is more practical to uniformly sputter and form an amorphous oxide film without heating the substrate and to heat the resultant structure in another O₂-containing atmosphere to obtain a superconductor film having excellent crystallinity. When the amorphous oxide superconductor is formed as described above, the shaped body is heated in the oxygen-containing atmosphere to obtain a superconductor. In order to manufacture a tape or a linear superconductor shaped body, the heat-resistive substrate is caused to travel, and a superconductor material, a transition metal, and a noble metal are sequentially formed on the traveling substrate in the form of films. The resultant structure is heated through a furnace. In order to obtain satisfactory electric and mechanical properties of cables and magnetic coil wirings in practical applications, thickness X of the superconductor film falls within the range of 0.1 to 5 µm, and the following inequality defining the relationship between thickness X and diameter or thickness Y of the substrate must be satisfied: 0.5Y ≧ X ≧ 0.001Y wherein X depends on the Jc value. Since the Jc value can be greatly increased according to the present invention, 0.001Y or more is required. In the above case, when the thickness of the superconductor film is less than the minimum value of the above range, sufficient superconducting properties cannot be obtained. However, if the thickness exceeds the maximum value of the above range, the mechanical properties such as flexibility are degraded. In addition, the superconducting properties (especially critical current density Jc) tend to be degraded. If the substrate size in the present invention is large, the space factor of the superconductor is decreased, and the current capacity is decreased accordingly. Otherwise, the mechanical strength is degraded. A plurality of superconductor shaped bodies manufactured by the method of the present invention are bundled to form a multi-core conductor or a multi-layered conductor. Cu or Aℓ as a stabilizing metal is combined with the resultant multi-core or multi-layered conductor, and a polymer is used as an insulator to cover the conductor. When the superconductor shaped body according to the present invention is used for a circuit, a device, and a plate coil, the superconductor shaped body is etched to obtain a desired pattern. The present invention will be described in detail by way of its examples. Example 1 Superconductor shaped bodies were manufactured in the following way. The noble metal layer was sputtered in an Ar-atmosphere following the same film formation and heating procedures 2.66 kPa (20 mTorr) on a Hastelloy® substrate and a SUS 304® substrate, respectively. Layers of Ag, MgO, ZrO₂ and BaZrO₃ were formed by using targets having these compositions. The resultant structure was heated to 670°C by a high frequency magnetron sputtering apparatus using an oxide of composition YBa 2.5 Cu 4.6 O x or Bi₂Sr₂Ca₂Cu₃O₁₀ as a target and applying a load of 250 W in an Ar+O₂ atmosphere (6.66 kPa (50 m Torr); O₂: 25%). Heating was performed at temperatures shown in Table 1 after sputtering was completed. The resultant structures were cooled at a rate of about 2°C/min). X-ray diffraction was performed to evaluate crystallinity of the resultant superconductor shaped bodies. The Tc and Jc values were measured as superconducting properties. Details are summarized in Table 1. The Jc values were measured at 68 K, and the Jc and Tc values were measured with and without an external magnetic field. In this case, the magnetic field of 0.1 Tesla (1,000 gauss) was applied to the substrates in a direction perpendicular to its surfaces. Results are summarized in Table 1 which also lists the respective constituting layers and heating conditions. As is apparent from Table 1, the noble metals have a buffer effect which prevents diffusion of substrate metals. The inorganic material layers have a buffer effect which prevents substrate oxidation caused by oxygen permeation through the noble metal films. Low reactivity with the superconductor layer, and C-axis orientation are obtained. By these effects, the samples of the present invention have large Tc values and high Jc values even in a magnetic field. The samples (comparative products Nos. 3 and 4) have small Jc values adversely affected by the external magnetic field and have poorer properties than those of the samples (Nos. 1 to 8) of Example 1 due to differences in crystal orientation, as can be seen from the results of X-ray diffraction. Classification No. Substrate Nobel Metal Layer Inorganic Material Layer Superconductor Layer Present Invention (Example 1) 1 Hastelloy® 0.1mm Ag 0.9µm MgO 0.2µm Y-Ba-Cu-O 0.3µm 2 " " " " 3 " Ag 1.2µm MgO 0.15µm " 4 " Ag-40Pd 0.5 µm ZrO₂ 0.3µm " 5 " " " " 6 " Ag-25Au 0.8µm BaZrO₃ 0.1 µm " 7 " Ag 0.4µm MgO 0.3µm Bi₂Sr₂Ca₂Cu₃O₁₀ 2.0µm 8 SUS304® 0.1 mm Ag 1.5µm MgO 0.2µm Y-Ba-Cu-O 0.3µm Comparative Product 1 Hastelloy® 0.1 mm Not formed MgO 0.5µm " 2 " Not formed " " 3 " Ag 1.0µm Not formed " 4 " " Not formed " Classification No. Stabilizing Metal Layer Heat Treatment Superconductor crystallinity Tc (K) Present Invention (Example 1) 1 Not formed Not performed C-axis orientation 79 2 " 750°Cx2hrs Po₂=506.5 Pa (0.5atm) " 85 3 Ag 1µm " " 85 4 Not formed Not performed " 80 5 " 800°Cx1hr Atmospheric pressure " 87 6 " " " 88 7 " 890°Cx4hrs Po₂=202.6 Pa (0.2atm) " 100 8 " 750°Cx2hrs Po₂=506.5 Pa (0.5atm) " 85 Comparative Product 1 " Not performed Random orientation 70 2 " 750°Cx2hrs Po₂=506.5 Pa (0.5atm) " 32 3 " Not performed Random orientation 79 4 " 750°Cx2hrs Po₂=506.5 Pa (0.5atm) " 84 Classification No. Jc(A/cm²) at 68K 0 Tesla (O gauss) 0.1 Tesla (1000 gauss) Present Invention (Example 1) 1 165,000 130,000 2 223,000 201,000 3 223,000 190,000 4 209,000 175,000 5 282,000 250,000 6 291,000 260,000 7 302,000 265,000 8 218,000 185,000 Comparative Product 1 900 150 2 --- --- 3 20,500 1,500 4 22,900 1,600 Example 2 Superconductor shaped bodies were manufactured following the same procedures as in Example 1 except that the thickness of a BeO film formed in place of Ag and MgO films was changed in No. 7 of Example 1. The Jc values of the resultant superconductor shaped bodies were measured, and results are summarized in Table 2. As is apparent from Table 2, the thicknesses of the BeO films were checked in Nos. 1 to 6 of Example 2. Samples having small thicknesses (Nos. 1 and 2 of Example 2) have small Jc values which are greatly reduced by a magnetic field. The Jc values of the samples having thicknesses of 1.5 µm and 2.9 µm (Nos. 5 and 6) tend to be reduced. This result coincides with the results of X-ray diffraction. When the thickness of the sample is excessively large, the BeO surface is rough due to its grain size. When the thickness of the sample is small, crystal orientation cannot be effected. The sample containing no Ag (comparative product No. 7) loses superconducting properties at an experiment temperature of 68 K. This is assumed to be attributable to diffusion of the Hastelloy® component. The sample having a very small Ag film thickness (No. 8) has a Jc value half as much as that of the sample (No. 4). No. Thickness of Ag (µ) Thickness of BeO (µ) Crystallinity (Orientation) Jc(A/cm²) at 68K 0 Tesla (0 gauss) 0.1 Tesla (1000 gauss) 1 0.9 0 Random 19,000 1,100 2 " 0.006 Random 38,000 5,000 3 " 0.03 C-axis 195,000 151,000 4 " 0.3 " 311,000 295,000 5 " 1.5 " 296,000 250,000 6 " 2.9 " 190,000 139,000 7 (Comparative Product) 0 0.3 Slightly random 0 0 8 0.1 " C-axis 153,000 109,000 As described above, the present invention provides practical conductors and equipment parts of an oxide superconductor by a multi-layered structure including a noble metal layer. The necessary conditions for industrial applications can be apparently satisfied by the present invention, as is apparent from the contents of detailed description of the invention and the examples. These remarkable effects are obtained with combinations of oxide superconductors and noble metals essentially since an oxide superconductor is an active multi-valent mixture and causes active oxidation and reduction during the fabrication. It is also apparent that a method of improving a structure by using an interlayer is indispensable to maximize the function and effect of the present invention.

Claims: An oxide superconductor shaped body comprising: a substrate (1) consisting of a polycrystalline metal or ceramic having a thermal expansion coefficient of 5 x 10⁻⁶/°C to 15 x 10⁻⁶/°C; a noble metal layer (2) directly on and in surface contact with said substrate (1); an interlayer (5) of an inorganic material directly on and in surface contact with said noble metal layer (2) consisting essentially of a material having a free energy (ΔG°) equal to or lower than that of BaO and selected from the group of materials, comprising cubic, hexagonal, tetragonal or rhombic crystal structures; and an oxide superconductive layer (3) directly on and in surface contact with said interlayer (5). A body according to claim 1, characterized in that a noble metal layer (2,4) is formed on both surfaces of the oxide superconductor layer (3), with an interlayer (5,6) formed between the noble metal layer and the oxide superconductor layer. A body according to claim 1, characterized in that the inorganic material is a material selected from the group consisting of MgO, BeO, BaO, SrO, TiO₂, ZrO₂, HfO₂, BaTiO₃, SrTiO₃, BaZrO₃, SrZrO₃, BaHfO₃ and SrHfO₃. A body according to claim 1, characterized in that the oxide consists of an oxide represented by formula AB₂Cu₃Ox (wherein A represents Y, S, Sc, or a rare earth element, B represents an alkaline earth metal, Cu represents copper, O represents oxygen, and X = 7 - δ where 1 ≧ δ > 0). A body according to claim 1, characterized in that the oxide consists of an oxide represented by Bi₂Sr₂Ca₂Cu₃O₁₀. A body according to claim 1, characterized in that the oxide superconductor consists of a Cu-containing oxide. A body according to claim 1, characterized in that the oxide superconductor layer (3) has a thickness of 0.1 to 5 µm, which is 0.005 to 0.5 times the thickness or diameter of the substrate (1). A body according to claim 2, characterized in that the interlayer (5, 6) has a thickness falling within a range of 0.001 to 0.5 µm, and the noble metal layer (2, 4) has a thickness falling within a range of 0.05 to 3 µm. A body according to claim 1, characterized in that the noble metal is silver or a silver alloy containing 99 to 55 wt% of silver. A body according to claim 1, characterized in that the oxide superconductor shaped body has a wire-, strip-, or plate-like shape. A method of manufacturing an oxide superconductor shaped body, comprising the steps of: forming, on a substrate (1), an oxide superconductor layer (3) having a noble metal layer (2, 4) formed on at least one surface of said oxide superconductor layer (3), with an interlayer (5, 6) formed between said noble metal layer (2, 4) and said oxide superconductor layer (3); and heat-treating the resultant structure in an oxygen-containing atmosphere. A method according to claim 11, characterized in that the step of heat-treating the resultant structure comprises the steps of heating the resultant structure in an oxygen-containing atmosphere having an oxygen partial pressure of not less than 1.013 kPa (0.01 atm) at a temperature of not less than 350°C, and cooling the resultant structure to at least 200°C at a cooling rate of not more than 50°C/min. A method according to claim 11, characterized in that the oxide superconductor layer (3) is formed to satisfy the following inequality under the condition that the substrate (1) comprises a wire and strip: 0.5Y ≧ X ≧ 0.001Y where X is the thickness of the oxide superconductor layer (3), and Y is the diameter or thickness of the wire and strip. A method according to claim 11, characterized in that the layers formed on the substrate (1) are formed by thin-film forming methods including physical vapor deposition, chemical vapor deposition, plasma spraying, screen printing, spin coating and spray heat decomposition.

Inventors: CHANG, TON-CHI, HARADA, NAKAHIRO FURUKAWADENKO-KANAGAWA-RYO, MIMURA, MASANAO FURUKAWADENKO-KANAGAWA-RYO, OZAKI, MASANORI, SHIGA, SHOJI
Applicants: THE FURUKAWA ELECTRIC CO., LTD.
Application year: 1988
Main classification: H01L39
IPC codes: H01L39