JPH0562534A - Superconductive member - Google Patents

Abstract

PURPOSE:To provide a superconductive member which can give a critical current density satisfactory when applied in practical field and which can allow the metal base to function as a stabilizer material. CONSTITUTION:A superconductive member concerned uses a metal base chiefly containing Ag plus alloy additives consisting either of 0.1-10wt.% element or elements soluble solidly with Ag such as Mg, Al, Mn, Cu, Zn, Ga, Ge, Pd, Cd, In, Sn, Sb, Pt, Au or of 0.05-5wt.% element or elements unsoluble solidly with Ag such as Ti, Zr, Hf, V, Nb, Ta, Cr, Fe, Co, Ni, Y, La, Mo, Si, Ca, Ba, Sr. An oxide type superconductive substance layer is formed directly on this metal base by the cluster ion beam method, etc., and thus a superconductive member as object of present invention is achieved. Addition of the mentioned element or elements raises the recrystallizing temp. of Ag, and generation of surface roughness of an Ag base board due to recrystallization at the time of film formation is suppressed. Thereby a flat and smooth film of oxide type superconductive substance is obtained equipped with an enhanced critical current density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting member using an oxide superconductor.

[0002]

2. Description of the Related Art Since it was announced in 1986 that Ba-La-Cu-O-based layered perovskite type oxides had a high critical temperature of 40 K or higher, oxide-based superconductors gained attention, Active research is being carried out in search of new materials. Among them, defect perovskite type oxide superconductors represented by the Y-Ba-Cu-O system, which have a high critical temperature above the liquid nitrogen temperature, and
Bi-Sr-Ca-Cu-O-based, Tl-Ba-Ca-Cu-O-based oxide superconductors can be replaced with expensive liquid helium as a refrigerant, and cheap liquid nitrogen can be used. It also has significant value.

Considering the application of such an oxide superconductor to the energy field, it is first necessary to form a wire rod. Therefore, various attempts have been made to convert the oxide superconductor into a wire rod. For example, (a) an oxide superconductor is enclosed in a metal tube and drawn to form a wire rod.

(B) An oxide superconductor powder and an organic binder are mixed and extruded from a nozzle to form a wire.

(C) An oxide superconductor layer is formed on a metal tape or a metal wire by a sputtering method or a vapor deposition method to form a wire.

Etc. are known.

The critical current density of a superconducting wire using these oxide superconductors tends to gradually increase. In particular,
Although the method of (c) is considered promising, if an oxide superconductor layer is formed directly on a metal substrate by a sputtering method, an evaporation method, or the like, an oriented oxide superconductor layer is difficult to obtain, and There is a problem that a reaction layer is formed at the interface with the oxide superconductor layer depending on the metal substrate used. Therefore, as a practical method for obtaining an alignment layer, a MgO layer or the like having a lattice constant similar to that of an oxide superconductor is formed as a buffer layer on a metal substrate, and the oxide superconductor layer is formed on this buffer layer. The method of doing is being tried.

According to such a method for forming an oxide superconductor layer via a buffer layer, a reaction at the interface can be prevented and an oriented oxide superconductor layer can be obtained to improve the critical current density. On the other hand, there is a drawback in that the oxide superconductor layer and the metal substrate cannot be electrically connected to each other due to the interposition of the insulating layer such as MgO. Therefore, when a part of the oxide superconductor layer is changed to the normal conducting state during use, the current can be biased to the metal base to protect the superconductor, that is, the metal base can function as a so-called stabilizing material. Can not.

On the other hand, according to the cluster ion beam method (ICB method) combined with the oxygen plasma supply method, the oriented oxide superconductor film is formed on a metal substrate such as silver tape by the action of the ion energy of the cluster. Since it can be formed directly, improvement of superconducting properties can be expected, and since it is not necessary to provide a buffer layer at the interface between the oxide superconductor layer and the metal substrate, the metal substrate functions as a stabilizer. The advantage is that

[0010]

By the way, when the oxide superconductor is actually applied as a wire, a critical current density of 10 ⁵ A / cm ² or more is required. However, the critical current density obtained with a wire in which an oxide superconductor layer is directly formed on a silver substrate as described above is not necessarily sufficient at about 10 ⁴ A / cm ^2, and an oxide superconductor is used. In order to put the superconducting wire into practical use, it is necessary to further improve the critical current density.

The present invention has been made to address the above-mentioned problems of the prior art. Superconductivity capable of obtaining a practically sufficient critical current density and allowing a metal substrate to function as a stabilizer. It is intended to provide a member.

[0012]

That is, the superconducting member of the present invention is a superconducting member comprising a metal base and an oxide superconductor layer formed directly on the metal base, wherein the metal base is , An alloy containing silver as a main component, to which an element that is solid-solved in silver is added in the range of 0.1% to 10% by weight, or an element that is not dissolved in silver is added in the range of 0.05% to 5% by weight It is characterized by

The metal substrate used in the present invention contains silver as a main component. When depositing an oxide superconductor on a metal substrate, the substrate temperature is kept at a high temperature of 500 ° C. or higher, and oxygen is supplied in an activated state such as plasma or ozone. Therefore, the metal base is required to be a metal that is difficult to oxidize or react with the oxide superconductor, and therefore a metal base containing silver as a main component is suitable.

Here, the recrystallization temperature of silver alone is low (about
200 ° C), when a metal substrate is heated to the temperature as described above, silver recrystallization and grain growth occur, and grooves with a depth of 1 μm to several μm are formed along the grain boundaries on the substrate surface. Formed. Once such a grain boundary groove is formed, the oxide superconductor layer formed on this groove has a reduced conformity in the c-axis orientation. The present invention was accomplished by discovering that the decrease in the conformity of the oxide superconductor crystal is a factor that hinders the improvement of the critical current density.

Therefore, in the present invention, in order to raise the recrystallization temperature of the silver substrate, a substrate obtained by alloying by adding another element to silver is used. For example, Mg, Al, Mn, Cu,
Elements such as Zn, Ga, Ge, Pd, Cd, In, Sn, Sb, Pt, and Au that are solid-solved in silver prevent the migration of silver within the crystal lattice, and thus increase the recrystallization temperature of silver. You can Also, Ti, Z
r, Hf, V, Nb, Ta, Cr, Fe, Co, Ni, Y, La, Mo, S
Elements such as i, Ca, Ba, and Sr that do not form a solid solution in silver are present in the alloy structure in a dispersed state, and by preventing recrystallization of silver, the recrystallization temperature of silver can be increased. .. One or more of these elements are added to silver and alloyed to be used.

The element that raises the recrystallization temperature of silver is
It is effective to add 0.1% by weight or more for elements that form a solid solution in silver, and 0.05% by weight or more for elements that do not form a solid solution in silver. The recrystallization temperature of silver can be raised to such an extent that the formation of grain boundary grooves can be prevented. However, since the metal substrate needs to function as a stabilizer, it is required to have excellent conductivity. Furthermore, it is required that the characteristics are not deteriorated by reacting with the oxide superconductor during film formation. Therefore, there is an upper limit to the amount of the above-mentioned additional element, and it is necessary to regulate the addition amount to 10% by weight or less for an element that forms a solid solution in silver and 5% by weight or less for an element that does not form a solid solution in silver. When the amount is more than the above, the oxide superconductor formed by lamination reacts with the additional element, and the oxide superconductor layer having desired characteristics cannot be obtained.

As the oxide superconductor used in the present invention, various oxides can be applied as long as they can realize a superconducting state, and examples thereof include a copper-based oxide superconductor. The copper-based oxide superconductor is not particularly limited, but examples thereof include those substantially represented by the following general formula.

La _2−x AE _x Cu O ₄ (wherein AE is at least 1 selected from Ba, Sr and Ca)
X is a number that satisfies 0.02 ≦ x ≦ 0.08) RE Ba ₂ Cu ₃ O _7-δ (where RE is Y, Sc, La, Nd, Sm, Eu, Gd, Dy, Ho, E
At least selected from rare earth elements such as r, Tm, Yb, and Lu
One element, δ represents oxygen deficiency and is usually a number of 1 or less.) Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 + d} Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + d} Bi ₂ Sr ₂ Ca ₃ Cu ₄ O _{12 + d} Tl ₂ Ba ₂ Ca ₁ Cu ₂ O _{8 + d} Tl ₁ Ba ₂ Ca ₁ Cu ₂ O _{7 + d} Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _{10 + d} Tl ₁ Ba ₂ Ca ₂ Cu ₃ O _{9 + d} (In the above equations, d represents a minute fluctuation of oxygen.
Part of Tl and Tl is Pb, and part of Sr, Ca, Ba, etc. can be replaced by RE element) Further, as a method for forming the oxide superconductor layer in the present invention, for example, reactive vapor deposition method, sputtering method, It is possible to apply various thin film forming methods such as the CVD method. Among them, according to the cluster ion beam method, which is one of the reactive vapor deposition methods, it is possible to form an oxide superconducting film having a desired texture at a low substrate temperature by the assist effect of ion energy, and therefore preferable formation It can be called a method.

[0019]

EXAMPLES Examples of the present invention will be described below.

Example 1 First, Mg, Al, Cu, Pd and Sn were selected as typical examples from the group of elements which are solid-soluted in Ag, and 0.1% by weight, 1% by weight, 5% by weight and 10% by weight of these were selected. % Silver-based alloys were prepared.

Next, each of these alloys was processed into a tape having a width of 1 mm and a thickness of 0.3 mm, and then Y was formed on the surface of each silver-based alloy tape by a cluster ion beam film forming method combined with an oxygen plasma supply method. An oxide superconductor layer represented by ₁ Ba ₂ Cu ₃ O _y was formed. The film formation temperature at this time is about 650.
℃ was made. The film thickness is 0.2 μm.

The critical temperature of the obtained short superconducting member is set to 4
As a result of measurement by the terminal method, all superconducting members are 84K ~ 8
It showed a critical temperature in the range of 8K. Further, these superconducting members were immersed in liquid nitrogen to measure the critical current density. As a result, the critical current density was 0.8 to 1.2 × 10 ⁵ A / cm ^2, which was a good value.

As a result of observing the surface of each superconducting member with a scanning electron microscope, it was found that there were few surface irregularities and that the surface was smooth. In addition, when the X-ray diffraction pattern was examined, strong diffraction from the (00l) plane was observed, and it was confirmed that the c-axis orientation was observed.

Example 2 Of the elements that do not form a solid solution in Ag, Si, Ti, Cr, Ni and Zr
Was selected as a representative example, and silver-based alloys containing 0.1% by weight, 1% by weight, 5% by weight and 10% by weight were prepared. After processing these alloys into the same shape as in Example 1, the oxide superconductor was formed under the same conditions as in Example 1.

The critical temperature of the obtained short superconducting member is set to 4
As a result of measurement by the terminal method, all showed critical temperatures in the range of 84K to 86K. As a result of measuring the critical current density of these superconducting members in liquid nitrogen, the critical current density was 0.8 to 1.1 × 10 ⁵ A / cm ^2, which was a good value. Moreover, as a result of observing the surface with a scanning electron microscope, there were few surface irregularities and it showed a smooth morphology. In addition, when the X-ray diffraction pattern was examined, strong diffraction from the (00l) plane was observed, and it was confirmed that the c-axis orientation was observed.

Comparative Example 1 After processing Ag having a purity of 99.99% into the same shape as in Example 1,
The oxide superconductor was formed under the same conditions as in Example 1.
The critical temperature of the five obtained samples was measured and found to be 84K.
It showed a critical temperature in the range of ~ 86K. Next, as a result of measuring the critical current density in liquid nitrogen, 0.7 ~ 1.5 × 10 ⁴ A / cm ²
Only values in the range of were obtained. As a result of observing the surface with a scanning electron microscope, many grain boundary grooves were recognized. In addition, when the X-ray diffraction pattern was examined, strong diffraction from the (00l) plane was observed, and it was confirmed that the c-axis orientation was observed.

In the above-mentioned embodiments, the film formation by the cluster ion beam method has been described as an example, but it is said that the same effect can be obtained in the method of forming a film at a high temperature using a silver base alloy as a substrate. There is no end.

[0028]

As is apparent from the above examples, in the superconducting member of the present invention, the c-plane of the oxide superconductor crystal in which the superconducting current easily flows is oriented to the metal substrate surface, and the grain boundary groove of the metal substrate is formed. Since there is little unevenness due to, high critical current density can be obtained. Further, since the oxide superconductor is directly formed on the metal base, the metal base can function as a stabilizer.

[0029]

Claims (1)

[Claims] 1. A superconducting member comprising a metal base and an oxide superconductor layer directly formed on the metal base, wherein the metal base contains silver as a main component, and an element which forms a solid solution with silver. A superconducting member comprising an alloy containing 0.1% by weight to 10% by weight or an element that does not form a solid solution in silver in the range of 0.05% by weight to 5% by weight.