JP2002150855A - Oxide superconductor wire material, and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide superconductor wire material having stable and excellent crystalline property at its whole lengthened part, with an oxide superconductor film showing high critical current density, and to provide a manufacturing method of the same. SOLUTION: For the oxide superconductor wire material comprising a polycrystalline metal base (1) having an aggregation structure oriented to 100} <001> direction, oxide buffer layers (2, 3) formed on the polycrystalline metal base (1), and an oxide superconductor layer (4) formed on the oxide buffer layer (2, 3), the oxide buffer layer (2, 3) is composed of the first oxide buffer layer (2) with a surface coarseness of Rmax=0.15 μm or less which is a surface oxide layer of the polycrystalline metal base (1), and the second oxide buffer layer (3) formed on the first oxide buffer layer (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting wire and a method for manufacturing the same, and more particularly, to the field of power equipment such as power cables and energy storage, and industrial equipment such as medical MRI and magnets for manufacturing single crystals. The present invention relates to an oxide superconducting wire whose application and development to the field and the like are progressing, and a method for producing the same.

[0002]

2. Description of the Related Art A method for producing a superconducting wire using an oxide superconductor is mainly classified into the following two methods.

In the first method, a metal sheath is filled with an oxide superconducting powder and then processed into a wire, and after further processing or during the processing, a heat treatment is performed to obtain an oxide superconducting wire. This is a method called a powder-in-tube (PIT) method. As a typical example of the oxide superconducting wire obtained by the PIT method, a Bi-based oxide superconductor (Bi22
12, Bi2223) is present as a superconducting tape wire in which a large number of filaments are present in a silver or silver alloy sheath.

However, in the case of Bi2223-based wires, the production speed of the oxide superconducting wires obtained by the PIT method reaches 100 m / h, but the critical current density (J
c) is 77K, 2-6 × 10 ⁴ A / cm ² under a self-magnetic field.
And there is a limit to the use of the device at 77K.
Also, since silver or silver alloy is used as the sheath material,
Tensile stress that does not lower the critical current density is 10
It is as low as about 0 MPa.

The second method is a method in which an intermediate layer is provided on a polycrystalline metal substrate by controlling the crystal orientation, and an oxide superconducting thin film is formed thereon to form a wire. In this method, the intermediate layer suppresses a diffusion reaction between the metal substrate and the oxide superconducting layer,
Further, it is possible to control the orientation of the oxide superconductor layer formed thereon to improve the bonding of crystal grains and to obtain a high critical current density.

As a typical example of the superconducting wire obtained by the second method, an in-plane oriented film of yttrium-stabilized zirconia (YSZ) is formed on a Hastelloy alloy tape by an ion beam assisted deposition (IBAD) method or the like. Layer on which Y is formed by laser ablation.
There is a tape wire obtained by forming a Ba ₂ Cu ₃ O _7-y (Y123) oxide superconducting thin film.

[0007] The Jc of this tape wire material is 77 K and reaches 1 × 10 ⁶ A / cm ² under a self-magnetic field. However, since the film formation speed of the intermediate layer is extremely low, 0.001 to 0.1 m / h,
There is a problem industrially.

As an example of a similar manufacturing method, RABiTS
There is a method called the law. In this method, nickel metal is rolled and heat-treated to give a textured nickel tape, and Pd or the like is deposited thereon by electron beam evaporation,
In this method, eO ₂ or YSZ is formed by sputtering or the like to form an intermediate layer, and a Y123-based superconductor film is formed on the intermediate layer by laser ablation.

[0009] The superconducting tape wire obtained by this method is also
Jc is 77K and reaches 1 × 10 ⁶ A / cm ² under a self-magnetic field. However, since the intermediate layer is formed through a plurality of thin film forming processes, the production speed as a wire is low and the cost is problematic. There is.

[0010]

SUMMARY OF THE INVENTION The present inventors have already
Attempts are being made to form an oxide superconducting thin film with controlled orientation by using the orientation of the metal substrate and the surface oxide layer of the metal substrate to form a wire. From such attempts, Japanese Patent Application No. 9-154410 proposes a method for manufacturing an oxide superconducting wire using a surface oxide layer. This method is based on SOE (Surface Oxida).
This method is referred to as a “tion epitaxy” method, in which a polycrystalline metal tape textured by rolling and heat treatment is oxidized to form a metal oxide layer having excellent orientation directly on a metal substrate, and this is used as an intermediate layer. An oxide superconductor layer is formed thereon by a laser ablation method or a liquid phase epitaxial method.

Although the SOE method can speed up the formation of the intermediate layer and improve the production speed of the superconducting wire, the superconducting properties and its long-term stability are not always sufficient, and a more excellent superconducting wire is obtained. As a result of conducting research with this in mind, the present invention has been reached.

That is, in the SOE method, since a surface oxide layer as an intermediate layer is formed by heat treatment, unevenness of crystal grain boundaries of the oxide layer and heterogeneous growth of oxide crystals cause the Y123-based layer to grow thereon. Various defects occur in the oxide superconductor film, and the number of weakly bonded portions in the oxide superconductor layer increases, so that the critical current density of the superconductor is small, or characteristics are likely to be uneven in a long superconducting wire. There is a problem.

Further, in the vicinity of the crystal grain boundary of the surface oxide layer,
Contamination of the oxide superconductor due to diffusion of the base metal also poses a problem, which also affects the superconducting characteristics of the superconducting wire and its long-term stability.

The present invention has been made in order to further develop the SOE method and effectively solve the above-mentioned problems. The present invention has stable and excellent crystallinity throughout a long superconducting wire and has a high crystallinity. It is an object of the present invention to provide a superconducting wire having an oxide superconducting film exhibiting a critical current density and a method for manufacturing the same.

[0015]

According to the present invention, as a result of various studies to solve the above-mentioned problems, the smoothness (surface roughness: R _max ) of the surface oxide layer formed on the metal substrate is _reduced. The present inventors have found that the superconductivity of the oxide superconducting layer is greatly affected, and have accomplished the present invention.

That is, the present invention provides a polycrystalline metal substrate having a texture oriented in the {100} <001> direction, an oxide buffer layer formed on the surface of the polycrystalline metal substrate, and an oxide buffer A superconducting wire comprising an oxide superconducting layer formed on a layer, wherein the oxide buffer layer is a surface oxide layer of the polycrystalline metal substrate, and has a surface roughness of R _max = 0. .15 .mu.m or less, and a second oxide buffer layer formed on the first oxide buffer layer. I do.

The present invention also provides a step of oxidizing the surface of a polycrystalline metal substrate having a texture oriented in the {100} <001> direction to form a first oxide buffer layer; (1) flattening the surface of the oxide buffer layer by mechanical polishing, chemical polishing, or chemical mechanical polishing to a surface roughness of R _max = 0.15 μm or less; An oxide comprising: a step of forming a second oxide buffer layer on one oxide buffer layer; and a step of forming an oxide superconducting layer on the second oxide buffer layer. Provided is a method for manufacturing a superconducting wire.

Hereinafter, the superconducting wire of the present invention will be described in more detail with reference to the drawings. As shown in FIG. 1, the superconducting wire of the present invention comprises a first oxide buffer layer 2 and a second oxide buffer layer on a polycrystalline metal substrate 1 having a {100} <001> -oriented texture. 3 and an oxide superconductor film 4 are sequentially formed.

Here, the {100} <001> -oriented texture means that most of the crystals constituting the metal tape are
The (100) plane of the crystal is parallel to the tape surface, and the <001> direction of the crystal is oriented parallel to the tape longitudinal direction.

In the superconducting wire of the present invention shown in FIG.
The polycrystalline metal substrate 1 can be made of nickel or a nickel-based alloy containing nickel as a main component. Alternatively, as the polycrystalline metal substrate 1, a composite material of nickel and a nickel-based alloy, nickel and a copper-based alloy, or nickel and an iron-based alloy, whose outermost layer is nickel, can be used.

The first oxide buffer layer 2 is formed by oxidizing the polycrystalline metal substrate 1. Therefore, the first oxide buffer layer 2 is made of nickel oxide (NiO).
It consists of. In this case, by appropriately selecting the oxidation treatment conditions for the polycrystalline metal substrate 1, the (100) plane of nickel oxide can be grown parallel to the substrate surface, and the crystal orientation of the underlying polycrystalline metal substrate 1 Inherited from this property, the crystal orientation of the nickel oxide in the (100) plane can be significantly improved. As a result, a quasi-single crystal nickel oxide layer can be formed as the first oxide buffer layer 2 on the polycrystalline metal substrate 1.

In the present invention, by controlling the surface roughness (R _max ) of the first oxide buffer layer 2, for example, the nickel oxide layer to a certain value, that is, R _max = 0.15 μm or less, The smoothness of the second oxide buffer layer 3 and the oxide superconducting layer 4 formed thereon can be improved. As a result, the number of weakly coupled portions in the four oxide superconductor layers is reduced, and it is possible to improve the critical current density which is practically important.

The surface of the first oxide buffer layer 2 is planarized by mechanical polishing, chemical polishing, or chemical mechanical polishing so that the surface roughness becomes _Rmax = 0.15 μm or less. . The surface roughness of the first oxide buffer layer 2 is preferably 0.02 μm or less. Further, the thickness of the first oxide buffer layer 2 is preferably 1 to 7 μm.

The reason for using the second oxide buffer layer 3 is as follows. That is, by forming the second oxide buffer layer 3 on the first oxide buffer layer 2, the lattice matching with the oxide superconducting layer 4 can be improved, and the crystallinity can be improved. In the case where the oxide superconducting layer 4 is formed directly on the nickel oxide layer as the first oxide buffer layer 2, the nickel superconducting layer 4 However, by using the second oxide buffer layer 3 as the cap layer, the contamination of the oxide superconducting layer 4 with nickel can be completely prevented,
This makes it possible to further improve the critical current density that is practically important.

Used for the second oxide buffer layer 3
A preferred material is SrTiO _Three, BaTiO_Three,
BaZrO_Three, LaGaO_Three, NdGaO_Three, LaAl
O_Three, LaNiO_Three, MgO, YSZ, CeO_Two, Y_Two
O_ThreeAnd the like.

The second oxide buffer layer 3 formed on the first oxide buffer layer 2 whose surface roughness is adjusted to R _max = 0.15 μm or less has a quasi-single crystal oxidation It is necessary to grow epitaxially on the nickel layer. As the formation method, a pulse laser deposition method that has been used in oxide layer formation,
A gas phase method such as a sputtering method, a vapor deposition method, or a CVD method, or a liquid phase method such as a coating thermal decomposition method or a sol-gel method can be used. The thickness of the second oxide buffer layer 2 is 0.02 to 0.4 μm.
Preferably it is m.

As the oxide superconductor constituting the oxide superconducting layer, a rare earth 123-based oxide superconductor represented by YBa ₂ Cu ₃ O _{7 -8} , a Tl-based oxide superconductor, or the like can be used. .

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, various examples as embodiments of the present invention will be shown, and the present invention will be described more specifically.

Example 1 A commercially available nickel rod (99.9% purity) having a diameter of 10 mm was rolled to a thickness of 0.15 mm to obtain a nickel tape. The tape was annealed in vacuum at 800 ° C. for 2 hours. After annealing, the tape surface was examined by X-ray diffraction and X-ray pole figure.
01> Orientation oriented.

Subsequently, the tape was subjected to an oxidation treatment at 1100 ° C. for 1 hour in an oxygen atmosphere to form a first oxide buffer layer having a film thickness of 1 on the surface of the nickel tape.
A 0 μm NiO layer was formed.

Next, N of the formed NiO / Ni tape was
Polishing the surface of the iO layer with diamond abrasive grains,
The surface roughness (R _max ) was 0.07 μm,
Four kinds of samples of 0.15 μm, 0.2 μm and 0.4 μm were prepared. The surface roughness was measured by a contact type surface roughness meter.

On these NiO / Ni tapes, KrF
By a pulse laser deposition (PLD) method using an excimer laser, a YSZ film as a second oxide buffer layer and a YBCO superconducting film were formed. As the YSZ film, two types having a thickness of 0.5 μm and 0.9 μm were prepared. The film forming conditions at this time are as follows.

<YSZ film (second oxide buffer layer)> Laser energy density: ² J / cm ² Substrate temperature: 750 ° C. Repetition frequency: 20 Hz Oxygen gas pressure: 20 Pa Film thickness: 0.5 μm, 0.9 μm <YBCO Superconducting film> Laser energy density: 3 J / cm ² Substrate temperature: 700 ° C. Repetition frequency: 30 Hz Oxygen gas pressure: 26 Pa Film thickness: 1 μm The critical temperature (Tc) of the sample prepared as described above was determined by a DC four-terminal method. It was measured. Critical current density (J
In c), the measurement was performed for 77K and 1 Tesla. The results are shown in Table 1 below.

[0034]

[Table 1]

From the above Table 1, it can be seen that Tc is 87 regardless of the thickness of YSZ for the sample having R _max of 0.15 μm or less.
It is understood that both K and Jc are 70,000 A / cm ² or more, and both exhibit excellent characteristics. In contrast, R
_For samples having _max exceeding 0.15 μm, satisfactory values were not obtained for both Tc and Jc.

Example 2 Nickel-20 wt% in a nickel pipe having a diameter of 20 mm
A nickel / nickel-chromium alloy composite tape having a thickness of 0.2 mm was manufactured by inserting a% chromium alloy rod and performing swaging and rolling. The tape was annealed in vacuum at 800 ° C. for 2 hours. The surface of this tape had a texture oriented in the {100} <001> direction.

Subsequently, the tape was subjected to an oxidation treatment at 1100 ° C. for 1 hour in an oxygen atmosphere to form a 10 μm-thick NiO layer as a first oxide buffer layer on the tape surface.

Next, the surface of the NiO layer of the formed NiO / nickel / nickel-chromium alloy tape is subjected to mechanical polishing using aluminum oxide abrasive grains and chemical polishing using dilute nitric acid to obtain a surface roughness (R _max ). , 0.05 each
Samples of μm, 0.15 μm, 0.18 μm, and 0.3 μm were prepared.

On these NiO / nickel / nickel-chromium alloy tapes, a second laser was formed by pulse laser deposition (PLD) using a KrF excimer laser.
An MgO film as an oxide buffer layer and a YBCO superconducting film were formed. The MgO film has a thickness of 0.1 μm
And 0.3 μm. The film forming conditions at this time are as follows.

<MgO film (second oxide buffer layer)> Laser energy density: ² J / cm ² Substrate temperature: 500 ° C. Repetition frequency: 10 Hz Oxygen gas pressure: 1.3 Pa Film thickness: 0.1 μm, 0.3 μm <YBCO superconducting film> Laser energy density: 2.5 J / cm ² Substrate temperature: 720 ° C. Repetition frequency: 30 Hz Oxygen gas pressure: 26 Pa Film thickness: 1 μm Critical temperature of the sample prepared as described above was measured by a DC four-terminal method. (Tc) was measured. Critical current density (J
In c), the measurement was performed for 77K and 1 Tesla. The results are shown in Table 2 below.

[0041]

[Table 2]

From Table 2 above, for samples with R _max of 0.15 μm or less, Tc was 86 regardless of the thickness of YSZ.
K and Jc are 50,000 A / cm ² or more, and it can be seen that both exhibit excellent characteristics. In contrast, R
_For samples having _max exceeding 0.15 μm, satisfactory values were not obtained for both Tc and Jc.

[0043]

As described above in detail, according to the present invention, the oxide interposed between the polycrystalline metal substrate having the texture oriented in the {100} <001> direction and the oxide superconducting layer As the buffer layer, the surface roughness is R _max =
A first oxide buffer layer that is 0.15 μm or less;
By using the stacked body with the second oxide buffer layer, the crystallinity of the oxide superconducting layer can be improved as compared with the related art, and the number of weakly coupled portions in the superconducting layer can be reduced. Therefore, it is possible to realize a practically important improvement in critical current density.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a superconducting wire of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Polycrystalline metal base 2 ... 1st oxide buffer layer 3 ... 2nd oxide buffer layer 4 ... Oxide superconductor film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Izumi Hirabayashi 1-14-3 Shinonome, Koto-ku, Tokyo Foundation for Superconductivity Engineering, International Superconductivity and Industrial Technology Research Center (72) Inventor Cho Ikeda Marunouchi, Chiyoda-ku, Tokyo 2-6-1 Furukawa Electric Co., Ltd. F-term (reference) 4K029 BA12 BA25 BA50 BB02 BC04 CA01 DB20 FA03 FA06 5G321 AA01 AA04 BA01 BA03 CA04 CA18 CA21 CA24 CA27 CA28 DB37

Claims (7)

[Claims] 1. A polycrystalline metal substrate having a texture oriented in the {100} <001> direction, an oxide buffer layer formed on the surface of the polycrystalline metal substrate, and a polycrystalline metal substrate formed on the oxide buffer layer. A superconducting wire comprising an oxide superconducting layer, wherein the oxide buffer layer is a surface oxide layer of the polycrystalline metal substrate, and has a surface roughness of _Rmax = 0.15 μm or less. An oxide superconducting wire comprising a first oxide buffer layer and a second oxide buffer layer formed on the first oxide buffer layer. 2. The polycrystalline metal substrate is made of nickel or a nickel-based alloy containing nickel as a main component, and the first oxide buffer layer is made of nickel oxide (NiO).
The oxide superconducting wire according to claim 1, comprising: 3. The polycrystalline metal substrate is a composite material of nickel and a nickel-based alloy, nickel and copper, nickel and a copper-based alloy, or nickel and an iron-based alloy, the outermost layer of which is nickel, Wherein the first oxide buffer layer comprises:
The oxide superconducting wire according to claim 1, comprising nickel oxide (NiO). 4. The method according to claim 1, wherein the second oxide buffer layer is formed of SrT
iO_3,BaTiO_3,BaZrO _3,LaGaO_3,
NdGaO_3,LaAlO_3,LaNiO_3,, Mg
O, YSZ, CeO_2,And Y_TwoO_ThreeSelected from the group consisting of
Selected from high melting point oxide crystals
The oxide superconducting wire according to claim 1.
Wood. 5. A method for producing an oxide superconducting wire according to claim 1, wherein {100} <0.
A step of oxidizing the surface of the polycrystalline metal substrate having a texture oriented in the <01> direction to form a first oxide buffer layer; and mechanically polishing the surface of the first oxide buffer layer. Flattening the surface roughness to R _max = 0.15 μm or less by chemical polishing or chemical mechanical polishing, and forming a second oxide on the flattened first oxide buffer layer. A method for producing an oxide superconducting wire, comprising: forming a buffer layer; and forming an oxide superconducting layer on the second oxide buffer layer. 6. The method according to claim 1, wherein the second oxide buffer layer is formed by a pulse laser deposition method, a sputtering method, a vapor deposition method,
The method for producing an oxide superconducting wire according to claim 5, wherein the film is formed by a gas phase method selected from the group consisting of VD methods. 7. The oxide according to claim 5, wherein the second oxide buffer layer is formed by a liquid phase method selected from the group consisting of a coating thermal decomposition method and a sol-gel method. Manufacturing method of superconducting wire.