JP2011238519A - BASE MATERIAL FOR OXIDE SUPERCONDUCTOR AND FILM FORMATION METHOD OF OXIDE SUPERCONDUCTOR AND NiO INTERMEDIATE LAYER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base material for an oxide superconductor which shows good superconductivity and technology useful as an oxide superconductor using the base material.SOLUTION: A base material for an oxide superconductor comprises: a base material; an intermediate layer composed of NiO where a film is formed on the base material by ion beam assist method, crystal orientation is arranged and fourfold symmetry is given; and a cap layer formed on the intermediate layer. An oxide superconducting layer is provided on the cap layer.

Description

  The present invention is a substrate for an oxide superconducting conductor having a NiO intermediate layer that is suitable as an intermediate layer for an oxide superconducting layer and has excellent crystal orientation, and the formation of the oxide superconducting conductor and the NiO intermediate layer. The present invention relates to a membrane method.

An RE-123 series oxide superconductor (REBa ₂ Cu ₃ O _7-X : RE is a rare earth element) is considered as a very promising material for practical use since it exhibits superconductivity at liquid nitrogen temperature. Therefore, it is desired to use it as a conductor for supplying power. Among them, a superconducting wire using a Y-based oxide superconductor (YBa ₂ Cu ₃ O _7-X ) is strong against an external magnetic field and can maintain a high current density even in a strong magnetic field. In addition to its use as a conductor or a power supply cable, research and development as a conductor for a superconducting fault current limiter is underway.
In any of these research and development applications, it is necessary to use an alignment substrate for the production of rare earth oxide superconducting conductors. As an example of a method for preparing an alignment substrate, an ion beam assisted film formation method (IBAD method) is used. : Ion-Beam-Assisted Deposition).

As an example of the structure of the RE-123 oxide superconducting conductor, a tape-shaped metal substrate, an intermediate layer formed thereon by an IBAD method through a bed layer or a diffusion prevention layer, and a film formed thereon are formed. An oxide superconducting wire comprising a cap layer and an oxide superconducting layer is known (see, for example, Patent Document 1).
This type of rare earth oxide superconductor is known to exhibit high superconducting properties by being biaxially oriented on an oriented substrate. The higher the crystal orientation of the rare earth oxide superconductor, the higher the critical current. Further, superconducting properties such as critical magnetic field and critical temperature can be obtained.
Therefore, obtaining a substrate with a high degree of orientation plays an important role in obtaining an excellent rare earth oxide superconductor. In the above structure, when the in-plane orientation of the intermediate layer is higher, the cap layer and the oxide superconducting layer formed thereon are also higher in crystal orientation, and the in-plane orientation of the oxide superconducting layer is higher. The higher the value, the higher the superconducting properties such as the critical current value, the better the oxide superconducting conductor. For example, even if the crystal orientation of the metal substrate 100 is not uniform as shown in FIG. 6, the a-axis of the crystal orientation of each crystal grain 120 in the crystal grain 120 of the intermediate layer 110 formed thereon, Alternatively, when the b-axes are aligned in the same direction within a small grain boundary tilt angle K (see FIG. 7), the crystal orientation of each crystal grain of the oxide superconducting layer formed on the intermediate layer 110 is also aligned. As a result, an excellent oxide superconducting layer can be obtained.

As a material capable of forming a film with a high crystal orientation on a tape-like metal substrate according to the IBAD method, conventionally, an intermediate layer such as YSZ (yttria stabilized zirconium), GZO (Gd ₂ Zr ₂ O ₇ ), MgO or the like In the current technology, MgO that has excellent crystal orientation in a very thin range is considered promising.

By the way, unlike the attempt to manufacture an oxide superconducting conductor by laminating thin films on a long base material by a film forming method, a long superconducting wire is formed by another method without using a thin film forming process. As a part of an attempt to obtain, a method using a polycrystalline metal substrate having a texture oriented in the {100} <001> orientation by rolling and annealing is known.
The texture oriented in the {100} <001> orientation means that the {100} plane is arranged in parallel to the tape surface in the crystal constituting the metal tape, and the <001> direction of the crystal is parallel to the tape longitudinal direction. Shows the oriented structure.
And in order to obtain the base material provided with this texture, using a Ni-based alloy, it is rolled into a tape shape and annealed at a high temperature of about 800 ° C. for several hours in a vacuum. Thus, a technique for obtaining a texture by forming an oxide layer on the surface of a substrate is known. (See Patent Document 2)

JP 2004-71359 A JP 2002-150855 A

  By the way, MgO by the IBAD method (hereinafter abbreviated as IBAD-MgO), which is promising as an intermediate layer for oxide superconductors, can obtain excellent crystal orientation with a film thickness of several nm to several tens of nm. Although the film itself is extremely thin, the film formation time can be shortened and high-speed film formation is possible. However, in recent research, IBAD-MgO has reactivity with moisture, and in a moisture-existing atmosphere. It has been found that when left for a long time, MgO becomes a hydroxide and easily peels off, and the IBAD-MgO layer needs to be handled with care in a moisture atmosphere.

  In the technique of using a polycrystalline metal substrate having a texture oriented in the {100} <001> orientation by the rolling method and the annealing treatment as a substrate of the superconducting conductor, an oxide generated by the rolling and annealing treatment is mainly used. However, it is difficult to increase the production speed when manufacturing a long base material, and it is uniform over the entire surface of the long tape-shaped base material depending on the state of rolling and annealing. There is a problem that the process for generating the texture becomes complicated.

From such a background, the present inventor shows good crystal orientation with a very thin film thickness such as several nm to several tens of nm in a thin film other than the MgO layer by the IBAD method, and is hardly affected by moisture. As a result of research and development of materials and repeated various studies, the present invention was reached.
The present invention is a technique for forming an intermediate layer by an IBAD method, exhibits a good crystal orientation at an extremely thin film thickness, is stable and hardly affected by moisture, and has a novel NiO intermediate layer by an IBAD method. It aims at providing the base material for superconducting conductors.
The present invention also provides a method for producing a substrate for the superconducting conductor, an oxide superconducting conductor capable of exhibiting good superconducting characteristics provided with the substrate for superconducting conductor, and production of a NiO intermediate layer by the IBAD method. The purpose is to provide a method.

The base material for an oxide superconducting conductor of the present invention includes a base body, and an intermediate layer made of NiO formed thereon by an ion beam assist method so that crystal orientation is adjusted and four-fold symmetry is imparted. And a cap layer formed on the intermediate layer, wherein the cap layer is provided with an oxide superconducting layer thereon.
The base material for an oxide superconducting conductor of the present invention is characterized in that the half-value width ΔΦ of crystal axis dispersion of the intermediate layer made of NiO is 16 ° or less.
The base material for an oxide superconducting conductor according to the present invention includes a base body, and an intermediate layer made of NiO formed thereon by an ion beam assist method so that crystal orientation is adjusted and three-fold symmetry is imparted. An intermediate compensation layer formed on the intermediate layer and having a two-layer structure having a three-fold symmetry on the bottom side and a four-fold symmetry on the upper side; and a cap layer formed on the intermediate compensation layer; The cap layer is characterized in that an oxide superconducting layer is provided thereon.

The base material for an oxide superconducting conductor according to the present invention is characterized in that the intermediate compensation layer is made of Gd ₂ Zr ₂ O ₇ .
The base material for an oxide superconducting conductor according to any one of the above, wherein an intermediate layer is formed on the base body through at least one of a diffusion prevention layer and a bed layer. It is.
The base material for oxide superconducting conductors of the present invention is characterized in that an oxide superconducting layer is formed on the cap layer of the base material for oxide superconducting conductors described above.

The film forming method of the 4-fold symmetric NiO intermediate layer according to the present invention is a method of forming a 4-fold symmetric NiO intermediate layer on a substrate by an ion beam assist method. The film is formed at 001 Pa or less.
The film forming method of the four-fold symmetric NiO intermediate layer according to the present invention is characterized in that the back pressure is 0.0002 Pa or less.
The film forming method of the four-fold symmetric NiO intermediate layer according to the present invention has an assist ion beam current density of 75 μA / cm ² or more and 120 μA / cm ² or less when forming the NiO intermediate layer by the ion beam assist method. It is characterized by doing.

  The intermediate layer made of NiO having fourfold symmetry according to the IBAD method of the present invention has high crystal orientation, and has the effect of adjusting the crystal orientation of the thin film laminated thereon, and in a moisture-existing atmosphere. Even when exposed for a long time, it has low reactivity and is difficult to peel off or deteriorate. Therefore, the structure provided with the intermediate layer made of NiO by the IBAD method on the base body is suitable as the base material for the oxide superconducting conductor, and the cap layer and the oxide superconducting layer formed on the intermediate layer are suitable. All of the crystal orientations can be arranged at a high level, which contributes to the provision of superconducting conductors with excellent characteristics.

In addition, the intermediate layer made of NiO having a three-fold symmetry by the IBAD method has a structure in which an intermediate compensation layer for converting the orientation from the three-fold symmetry to the four-fold symmetry is provided on the intermediate layer. Since it has orientation and exhibits fourfold symmetry, it plays the role of adjusting the crystal orientation of the thin film stacked on it, and the intermediate layer made of NiO reacts even when exposed to a moisture-existing atmosphere for a long time. It has low characteristics and is difficult to peel off or deteriorate. Therefore, a structure including an intermediate layer made of NiO having three-fold symmetry by the IBAD method and an intermediate compensation layer capable of converting to four-fold symmetry on the substrate body is suitable as a substrate for an oxide superconducting conductor. In addition, both the cap layer and the oxide superconducting layer formed on the intermediate compensation layer can be aligned at a high level, which contributes to the provision of a superconducting conductor having excellent characteristics.
As the material of the intermediate compensation _layer, Gd 2 _Zr 2 _{O 7} can be _applied, Gd 2 _Zr 2 _{O 7} ensure orientation of the intermediate layer consisting of 3-fold symmetry of NiO underlying the 4-fold symmetry by Can be changed.

When forming the NiO intermediate layer on the metal substrate by the ion beam assist method, forming the NiO intermediate layer with 4-fold symmetry is ensured by forming the film with the back pressure of the film forming atmosphere being 0.001 Pa or less. can do. By setting the back pressure in the film formation atmosphere at this time to 0.0002 Pa or less, a four-fold symmetry NiO intermediate layer having better orientation can be obtained. In addition, by selecting the current density of the assist ion beam used for the ion beam assist method in the range of 75 to 120 μA / cm ² , a highly oriented 4-fold symmetry NiO intermediate layer is formed on the metal substrate. can do.

The block diagram which shows 1st Embodiment of the base material for oxide superconducting conductors which concerns on this invention. The block diagram which shows 2nd Embodiment of the base material for oxide superconductors which concerns on this invention. The block diagram which shows 1st Embodiment of the oxide superconducting conductor which concerns on this invention. The block diagram which shows an example of the film-forming apparatus for implementing IBAD method. The block diagram which shows an example of the ion gun applied to the film-forming apparatus. The schematic diagram of the polycrystalline thin film by IBAD method formed on the metal base-material main body. The schematic diagram which shows the dispersibility of the crystal axis which the crystal grain of the polycrystalline thin film shown in FIG. 6 comprises. The figure which shows the correlation of the electric current density of the assist ion beam used when forming a NiO intermediate layer into a film by the IBAD method in an Example, and (DELTA) (phi) of the obtained NiO intermediate layer. It is a positive electrode point figure of the intermediate | middle layer of 3-fold symmetry NiO obtained in the Example. It is the positive electrode dot diagram of GZO after converting into the 4-fold symmetry obtained in the Example. It is a positive electrode point figure of the intermediate | middle layer of 4-fold symmetry NiO obtained in the Example.

FIG. 1 is a view schematically showing the structure of a first embodiment of a base material for an oxide superconducting conductor according to the present invention.
The base material A for oxide superconducting conductors of the present embodiment is formed on the metal base body 11 through the diffusion prevention layer 9 made of Al ₂ O ₃ and the bed layer 12 made of Y ₂ O _{3 in order.} The intermediate layer 13 made of NiO exhibiting rotational symmetry and the cap layer 14 made of CeO ₂ or the like are laminated.
FIG. 2 is a view schematically showing the structure of the second embodiment of the base material for oxide superconducting conductor according to the present invention.
The base material B for oxide superconducting conductor according to the second embodiment is disposed on the metal base body 21 through a diffusion preventing layer 19 made of Al ₂ O ₃ and a bed layer 22 made of Y ₂ O _{3 in} this order. An intermediate layer 23 made of NiO exhibiting a 3-fold symmetry, an intermediate compensation layer 24 made of GZO (Gd ₂ Zr ₂ O ₇ ) or the like that compensates the 3-fold symmetry with a 4-fold symmetry, and CeO ₂ or the like. A cap layer 25 is laminated.
FIG. 3 is a diagram schematically showing the structure of the first embodiment of the oxide superconducting conductor according to the present invention.
The oxide superconducting conductor C of the present embodiment has four-fold symmetry on the metal base body 31 through a diffusion prevention layer 29 made of Al ₂ O ₃ and a bed layer 32 made of Y ₂ O _{3 in} order. An intermediate layer 33 made of NiO, a cap layer 34 made of CeO ₂ , an oxide superconducting layer 37 such as a rare earth-based material, and a stabilization layer 38 made of a highly conductive metal material such as Ag or Cu are laminated. It is configured.

  The base bodies 11, 21, and 31 applicable to the oxide superconductor bases A and B and the oxide superconductor C can be used as a base body of a normal superconducting wire, as long as it has high strength. In order to obtain a long cable, it is preferably in the form of a tape, and is preferably made of metal from the viewpoint of heat resistance. For example, various metal materials such as silver, platinum, stainless steel, copper, nickel alloys such as Hastelloy, or ceramics arranged on these various metal materials can be used. Among various heat resistant metals, nickel alloys are preferable. Especially, if it is a commercial item, Hastelloy (trade name made by US Haynes Co., Ltd.) is suitable. Any type can be used. The thickness of the substrate body 11 may be appropriately adjusted according to the purpose, and is usually in the range of 10 to 500 μm, more preferably in the range of 20 to 200 μm. When viewed as a superconducting conductor, the strength can be ensured by setting it to the lower limit value or more, and a high critical current density can be easily obtained by setting the upper limit value or less.

The diffusion prevention layers 9, 19, and 29 are formed for the purpose of preventing the diffusion of the constituent elements of the base body bodies 11, 21, and 31, and include silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ , (Also referred to as “alumina”), or GZO (Gd ₂ Zr ₂ O ₇ ) or the like, and the thickness thereof is, for example, 10 to 400 nm.
If the thickness of the diffusion preventing layers 9, 19, 29 is less than 10 nm, there is a possibility that the diffusion of the constituent elements of the substrate bodies 11, 21, 31 cannot be prevented sufficiently. On the other hand, when the thickness of the diffusion preventing layers 9, 19, 29 exceeds 400 nm, the internal stress of the diffusion preventing layers 9, 19, 29 increases, and thus the entire substrate body 11, including other layers, It tends to be easy to peel off from 21 and 31. Further, since the crystallinity of the diffusion preventing layers 9, 19, and 29 is not particularly limited, it may be formed by a film forming method such as a normal sputtering method.

The bed layers 12, 22, and 32 have high heat resistance and are intended to reduce interfacial reactivity, and are used to obtain the orientation of a film disposed thereon. Such bed layers 12, 22, and 32 are, for example, rare earth oxides such as yttria (Y ₂ O ₃ ), and have a composition formula (α ₁ O ₂ ) _2x (β ₂ O ₃ ) _(1-x) . What is shown can be exemplified. More _{specifically, Er 2 O 3, CeO 2} , Dy 2 O 3, Er 2 O 3, Eu 2 O 3, Ho 2 O 3, can be exemplified _La 2 _{O 3} and the like. The bed layers 12, 22, and 32 are formed by a film forming method such as a sputtering method, and the thickness thereof is, for example, 10 to 200 nm.

The intermediate layers 13, 23, and 33 may have either a single layer structure or a multilayer structure, and are formed from a biaxially oriented material for controlling the crystal orientation of the cap layers 14, 25, and 34 stacked on the intermediate layers 13, 23, and 33. Selected. Specifically, NiO can be selected as the intermediate layers 13, 23, and 33.
If the intermediate layers 13, 23 and 33 are formed with a good crystal orientation (for example, a crystal orientation of 16 ° or less) by the IBAD method, the cap layers 14 and 34 or the intermediate compensation layer 24 and the cap formed thereon are formed. The crystal orientation of the layer 25 can be set to a good value (for example, a crystal orientation degree of about 5 ° in the cap layer), whereby the crystal orientation of the oxide superconducting layer formed on the cap layers 14, 25, 34 is obtained. It is possible to obtain an oxide superconducting conductor provided with an oxide superconducting layer capable of exhibiting excellent superconducting properties with good properties.

The thickness of the intermediate layers 13, 23, and 33 made of NiO may be appropriately adjusted according to the purpose, but can usually be in the range of 5 to 300 nm.
The intermediate layers 13, 23, and 33 are stacked by an ion beam assist method (IBAD method). The NiO intermediate layers 13, 23, and 33 formed by the IBAD method are preferable in that they have high crystal orientation and a high effect of controlling the crystal orientation of the oxide superconducting layer 37 and the cap layers 14 and 34. The IBAD method is a method of orienting a crystal axis of a target thin film by assisting irradiation of an ion beam at a predetermined angle with respect to a base film-forming surface during film formation as described above. Usually, an argon (Ar) ion beam is used as the assist ion beam. For example, the intermediate layers 13, 23, and 33 made of NiO are particularly suitable because the value of the half-value width ΔΦ (FWHM: full width at half maximum) of crystal axis dispersion, which is an index representing the degree of crystal orientation in the IBAD method, can be reduced.
In addition, the NiO intermediate layers 13 and 33 shown in FIGS. 1 and 3 formed by the IBAD method show four-fold symmetry, and the intermediate layer 23 shown in FIG. 2 shows three-fold symmetry. Detailed description.

The cap layers 14, 25, and 34 are epitaxially grown on the surfaces of the intermediate layers 13, 23, and 33, and then grow (overgrow) in the lateral direction (plane direction), so that the crystal grains are in the in-plane direction. Those formed through a process of selective growth are preferable. Such a cap layer has a higher in-plane orientation degree than the intermediate layers 13, 23, 33 made of the metal oxide layer.
The material of the cap layer 14,25,34 is not particularly limited as long as it can express the above functions, specifically as _{preferred, CeO 2, Y 2 O 3} , Al 2 O 3, Gd 2 O ₃ , Zr ₂ O ₃ , Ho ₂ O ₃ , Nd ₂ O _{3 and the} like. When the material of the cap layer is CeO ₂ , the cap layer may contain a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.

The CeO ₂ cap layer can be formed by a PLD method (pulse laser deposition method), a sputtering method, or the like, but it is desirable to use the PLD method from the viewpoint of obtaining a high film formation rate. The film formation conditions for the CeO ₂ cap layer by the PLD method can be performed in an oxygen gas atmosphere at a substrate temperature of about 500 to 1000 ° C. and about 0.6 to 100 Pa.
The thickness of the CeO ₂ cap layer may be 50 nm or more, but is preferably 100 nm or more in order to obtain sufficient orientation. However, if it is too thick, the crystal orientation deteriorates, so that it can be in the range of 50 to 5000 nm, more preferably in the range of 100 to 5000 nm.

The oxide superconducting layer 37 may be a known one, and specifically, a material made of REBa ₂ Cu ₃ O _y (RE represents a rare earth element such as Y, La, Nd, Sm, Er, Gd) is exemplified. it can. Examples of the oxide superconducting layer 37 include Y123 (YBa ₂ Cu ₃ O _7-X ) or Gd123 (GdBa ₂ Cu ₃ O _7-X ).
The oxide superconducting layer 37 is laminated by a physical vapor deposition method such as sputtering, vacuum vapor deposition, laser vapor deposition, electron beam vapor deposition, chemical vapor deposition (CVD), or thermal coating decomposition (MOD). In particular, from the viewpoint of productivity, it is preferable to use the TFA-MOD method (organic metal deposition method using trifluoroacetate, coating pyrolysis method), PLD method or CVD method.
This MOD method is a method in which a metal organic acid salt is applied and then thermally decomposed. After a solution in which a metal component organic compound is uniformly dissolved is applied onto a substrate, the substrate is heated and thermally decomposed. This is a method of forming a thin film on top, and is suitable for the production of a long tape-shaped oxide superconducting conductor because it does not require a vacuum process and enables high-speed film formation at low cost.

FIG. 4 shows an example of the structure of a film forming apparatus for carrying out the IBAD method.
As shown in FIG. 4, the ion beam assisted sputtering apparatus 50 in the case of manufacturing the intermediate layer 13 is a state in which the target 52 is supported by the target holder 55 so as to face the film forming region where the tape-like base material is disposed. The sputter ion source source 54 is disposed so as to face the target 52 obliquely with respect to the target 52, and a predetermined amount with respect to the upper surface of the substrate body 11 disposed in the film formation region. The assist ion source source 53 is arranged and configured to face each other at an angle (for example, θ = 45 °) from an oblique direction.
The ion beam assisted sputtering apparatus 50 in this example is a film forming apparatus provided in a form accommodated in a vacuum chamber. When the substrate main bodies 11, 21, and 31 are tape-shaped substrate bodies, the illustration is omitted. For example, a structure in which the first roll and the second roll arranged opposite to each other are reciprocally wound around the film formation region can be exemplified, but in FIG. It was shown as a structure in which the substrate body 11 is installed.
The ion source sources 53 and 54 applied in this embodiment include an extraction electrode 57, a filament 58, and an introduction tube 59 for Ar gas or the like inside the container 49 shown in FIG. Can be irradiated in parallel with a beam.

The vacuum chamber that accommodates the ion beam assisted sputtering apparatus 50 used in the present embodiment is a container that partitions the outside and the film formation space, has airtightness, and has pressure resistance because the inside is in a high vacuum state. It is said. The vacuum chamber is connected to a gas supply means for introducing a carrier gas and a reactive gas into the vacuum chamber and an exhaust means for exhausting the gas in the vacuum chamber. In FIG. 4, these supply means and exhaust means are connected to each other. For brevity, only the arrangement relationship of each device is shown.
The target 52 used here can be a NiO target having a composition commensurate with the formation of the NiO intermediate layer 13 described above.
By using the ion beam assisted sputtering apparatus 50 having the structure shown in FIG. 4, the IBAD method can be performed to form the target intermediate layers 13, 23, and 33.

When the intermediate layer is formed by the IBAD method, a source gas such as Ar gas or oxygen gas is introduced into the vacuum chamber containing the target 52, the ion source sources 53 and 54, and the base body 11 shown in FIG. For example, the inside is adjusted to a desired degree of vacuum and then adjusted to a mixed gas atmosphere (source gas atmosphere) such as Ar: O ₂ = 9: 1.
The vacuum chamber used in the present embodiment can be adjusted to a desired degree of vacuum in the range of 0.008 Pa to 0.00008 Pa in a reduced pressure atmosphere using a vacuum pump, for example, with back pressure. The degree of vacuum in this range can be easily reached by appropriately adjusting the time required for pressure reduction by the vacuum pump.

In order to form the 4-fold symmetrical NiO intermediate layers 13 and 33 on the bed layers 12 and 32 of the substrate bodies 11 and 31, the back pressure of the film formation atmosphere when the pressure is reduced by a vacuum pump is set to 0. After setting to the range of 0.001 to 0.00008 Pa, the target 52 is irradiated with an ion beam from the sputter ion source 54 to eject and eject target particles, and NiO particles are deposited on the bed layers 12 and 32. At the same time, an ion beam assist sputtering method is performed in which film formation is performed while irradiating the ion beam from the assist ion source 53 from an oblique 45 ° direction to the film formation surfaces of the bed layers 12 and 13. The film forming temperature at the time of performing the ion beam assisted sputtering method may be normal temperature. Further, the back pressure may be lower than the above range, but since it takes too much time for evacuation, it is usually preferable to select from the above range.
By performing the ion beam assisted sputtering method with the degree of vacuum in the above range, the four-fold symmetry NiO intermediate layers 13 and 33 can be formed on the bed layers 12 and 32.

  On the other hand, in order to form the 3-fold symmetrical NiO intermediate layer 23 on the bed layer 22 of the base body 21, the back pressure of the film formation atmosphere when the pressure is reduced by a vacuum pump is set to 0.008 to 0.0015 Pa. Then, the target 52 is irradiated with an ion beam from the sputter ion source 54 to eject and eject target particles, and NiO particles are deposited on the bed layers 12 and 32. The ion beam assisted sputtering method is performed in which film formation is performed while irradiating the ion beam from the assist ion source 53 from an oblique 45 ° direction to the 13 film formation surfaces. The film forming temperature at the time of performing the ion beam assisted sputtering method may be normal temperature.

By performing the ion beam assisted sputtering method with the degree of vacuum in the above-mentioned range, the NiO intermediate layer 23 having a three-fold symmetry can be formed on the bed layer 23.
Here, the four-fold symmetry NiO intermediate layers 13 and 33 were obtained by X-ray measurement of the obtained intermediate layer and measuring the NiO (220) positive electrode point as a diffraction test image, and drawing a positive electrode dot diagram. In this case, it means that the symmetry range displayed in a substantially elliptical region is displayed in four places within a 360 ° range, and the three-fold symmetry NiO intermediate layer 23 is the X-ray measurement of the obtained intermediate layer. When NiO (220) positive electrode point measurement, which is a diffraction test image, is performed and a positive electrode point diagram is drawn, it means that the symmetry range displayed in the same figure is displayed in three places within a 360 ° range. . The 4-fold symmetry of NiO means (100) orientation in the vertical direction of the substrate, and the 3-fold symmetry of NiO means (111) orientation in the vertical direction of the substrate. An example of a three-fold symmetry positive point diagram is shown in FIG. 9, and an example of a four-fold symmetry positive point diagram is shown in FIG.

If the four-fold symmetry NiO intermediate layers 13 and 33 are formed, the cap layers 14 and 34 and the oxide superconducting layer 37 formed thereon can be formed epitaxially with a good orientation. This contributes to the production of superconducting conductors. Further, since the NiO intermediate layers 13 and 33 by the IBAD method have low reactivity with moisture, unlike MgO by the IBAD method, even when exposed to a high humidity atmosphere for a long period of time, peeling and deterioration of performance hardly occur.
Further, if the intermediate layer 23 is a three-fold symmetry NiO, it is necessary to convert the three-fold symmetry to the four-fold symmetry, so an intermediate compensation layer 24 is provided, and a cap layer 25 is provided thereon. Let it be the base material B for oxide superconducting conductors.
The intermediate compensation layer 24 is formed on the IBAD-MgO layer having a three-fold symmetry as described in Japanese Patent Application No. 2008-254812, so that the present applicant has formed the three-fold symmetry of the underlying IBAD-MgO layer. It is a layer made of GZO (Gd ₂ Zr ₂ O ₇ ) having a film thickness of about 50 to 300 nm formed by the IBAD method. By passing through the Gd ₂ Zr ₂ O ₇ intermediate compensation layer 24, even if the value of Δφ, which is an index indicating the degree of orientation of the intermediate layer 23 of the three-fold symmetry NiO, is about 20 to 23 °, The Δφ of the compensation layer 24 can be set to about 15 °, and the Δφ of the cap layer 25 can be reduced to about 5 ° or less by further stacking the cap layer 25 thereon.
Further, if the intermediate layer 25 is a three-fold symmetry NiO, an intermediate compensation layer 24 of GZO (Gd ₂ Zr ₂ O ₇ ) is formed thereon, and the bottom side of the intermediate compensation layer 24 is symmetrical three times. Since the upper side of the intermediate compensation layer 24 can be converted into four-fold symmetry, a cap layer 25 and a rare earth oxide superconducting layer are sequentially formed on the GZO intermediate compensation layer 24 to obtain crystal orientation. An oxide superconducting layer having excellent superconducting properties can be obtained.
The intermediate compensation layer 24 of GZO (Gd ₂ Zr ₂ O ₇ ) may be formed to convert the bottom side of the intermediate compensation layer 24 into three-fold symmetry and convert the upper side of the intermediate compensation layer 24 into four-fold symmetry. The technology that can be used corresponds to the technology previously provided by the present applicant in Japanese Patent Application No. 2008-254812.
As an example, by sputtering the GZO (Gd ₂ Zr ₂ O ₇ ) intermediate compensation layer 24 having a thickness of 200 nm while performing ion beam assist with a rare gas ion beam of Ar, the bottom side that is <111> oriented The intermediate compensation layer 24 having a two-layer structure consisting of the initial portion and the upper growth portion of the NiO layer can be formed, whereby the three-fold symmetry of the NiO layer is changed to the four-fold symmetry by the intermediate compensation layer 24 of GZO. Can be converted.

Here, when the oxide superconducting layer 37 is formed on the cap layer 34 having good orientation as in the structure shown in FIG. 3, the oxide superconducting layer 37 laminated on the cap layer 34 is also formed of the cap layer 34. Crystallize to match the orientation. Therefore, the oxide superconducting layer 37 formed on the cap layer 34 is hardly disturbed in crystal orientation, and in each of the crystal grains constituting the oxide superconducting layer 37, The c-axis that hardly allows electricity to flow in the thickness direction is oriented, and the a-axis or the b-axis is oriented in the length direction of the substrate 31. Therefore, the obtained oxide superconducting layer 37 is excellent in quantum connectivity at the crystal grain boundary, and hardly deteriorates in the superconducting characteristics at the crystal grain boundary. High critical current density can be obtained.
The stabilizing layer 38 laminated on the oxide superconducting layer 37 is formed as a layer made of a metal material having good conductivity, such as Ag, and a low contact resistance with the oxide superconducting layer 37, and is suitable for use as needed. Furthermore, a laminated structure in which a stabilizing layer of a highly conductive metal material such as Cu is further combined may be employed.

  In addition, in the oxide superconducting conductor bases A and B shown in FIGS. 1 and 2, if the oxide superconducting layer is laminated on the cap layers 14 and 25, it is excellent as in the structure shown in FIG. In addition, a superconducting conductor having superconducting characteristics can be obtained. Therefore, the oxide superconducting conductor substrates A and B shown in FIGS. 1 and 2 are also useful as excellent oxide superconducting conductor substrates.

  As mentioned above, although each embodiment of base materials A and B for oxide superconductors concerning the present invention and oxide superconductor C was described, in these embodiments, each part which constitutes a superconductor is an example, and this book Modifications can be made as appropriate without departing from the scope of the invention.

Specific examples of the present invention will be described below, but the present invention is not limited to these examples.
An Al ₂ O ₃ diffusion prevention layer (thickness 150 nm) and a Y ₂ O ₃ bed layer (thickness) are formed by sputtering on a substrate body made of tape-shaped Hastelloy C276 (trade name of Haynes, USA) having a width of 10 mm. 20 nm), and an intermediate layer of NiO was formed on this laminate by ion beam assisted sputtering under various back pressures. In carrying out the ion beam assisted sputtering method, a film forming apparatus having the configuration shown in FIG. 4 is used, and the incident direction of the assist ion beam is set to a direction inclined by 45 ° with respect to the normal line of the film forming surface on the upper surface of the laminate. The film temperature was 30 ° C. (room temperature), the source gas in the film formation atmosphere was a mixed gas of Ar gas: O ₂ gas = 9: 1, and an ion beam assisted sputtering method was performed using a NiO target. The acceleration voltage of the assist ion beam is set to 1400 V, the current density is set to 91.5 μA / cm ^2, and the back pressure of the film forming atmosphere is 0.008 Pa, 0.004 Pa, 0.0015 Pa, 0.001 Pa, 0.0008 Pa, 0 Samples were prepared for each of seven cases of .0002 Pa and 0.00008 Pa. Under these conditions, the deposition rate of the NiO intermediate layer is 3.1 Å / s.

  After carrying out ion beam assisted sputtering and forming a NiO intermediate layer with a thickness of about 20 nm, the irradiation of the assisted ion beam is stopped and switched to the ion beam sputtering method. An epitaxial NiO layer (Epi-NiO) was stacked. The epitaxial NiO layer having a thickness of about 400 nm is formed to measure the crystal orientation of the IBAD-NiO intermediate layer by performing X-ray measurement. The NiO intermediate layer having a thickness of 20 nm is too thin. Since X-ray measurement is difficult or impossible, NiO (220) positive electrode point measurement is performed by X-ray measurement after forming an epitaxial NiO layer, and the half-value width Δφ of crystal axis dispersion, which is an index of crystal orientation, is obtained. Asked. Since the epitaxial NiO layer is oriented to follow the orientation of the 20 nm thick NiO intermediate layer formed by the IBAD method, the excellent Δφ of the epitaxial NiO layer is equivalent to the NiO layer by the underlying IBAD method. It means that it has a good orientation. The test results of each sample are shown in Table 1 below.

  From the test results shown in Table 1, the NiO layer formed by the IBAD method has a crystal orientation with three-fold symmetry in the range where the back pressure in the deposition atmosphere is 0.008 to 0.0015 Pa, and the back pressure is 0.001 to 0.001. In the range of 0.00008 Pa, it has been found that the crystal orientation has a 4-fold symmetry. In addition, the value of Δφ of the NiO layer by the IBAD method is in the range of 25.6 ° to 36.2 ° when the back pressure is in the range of 0.008 to 0.0015 Pa, based on the positive electrode point measurement result of the epitaxial NiO layer. It has been found that the back pressure is in the range of 10.9 ° to 15.9 ° in the range of 0.001 to 0.00008 Pa.

Here, if the IBAD-NiO layer has a four-fold symmetry, a CeO ₂ cap layer and a rare earth oxide superconducting layer are sequentially formed thereon, thereby providing excellent crystal orientation and superconducting characteristics. An oxide superconducting layer can be obtained.
On the IBAD-NiO layer of Δφ = 10.9 ° deposited at the back pressure of 0.0008 Pa, a CeO ₂ cap layer having a thickness of 500 nm is deposited at 800 ° C. by a pulse laser deposition method (PLD method). As a result, Δφ of this cap layer was 5 °, indicating good orientation.
Therefore, in order to obtain a four-fold symmetry NiO layer, the back pressure of the film formation atmosphere is preferably set to 0.001 Pa or less, for example, in the range of 0.001 to 0.00008 Pa.

  Next, as a condition for forming the NiO layer by the IBAD method, the back pressure is defined as 0.00008 Pa, the deposition temperature is defined as room temperature (30 ° C.), and the deposition rate of NiO is 3.1 Å / s. The film formation test was conducted with only the current density of the assist ion beam as a different value. Other conditions are the same as in the previous embodiment. The results are shown in Table 2 below and shown in FIG.

From the test results shown in Table 2 and FIG. 8, when the NiO layer is formed by the IBAD method, the current density of the assist ion beam under the above-described film formation conditions is 10 as the value of Δφ which is an index indicating the degree of orientation. A range in which 9 ° to 12.4 ° is obtained and a range of 70 μA / cm ^{2 to} 110 μA / cm ² seems to be preferable.

Next, in order to investigate the moisture resistance of the NiO layer obtained by the IBAD method, the following test was performed.
As the NiO layer obtained by the IBAD method, a sample having Δφ of 10.9 ° was used in the above test example, and an intermediate layer sample of MgO obtained by the IBAD method (back pressure 0.00008 Pa, Δφ = 6.8 °). ) Was used as a comparison, and both were subjected to a moisture resistance test. The test is left in an atmosphere of 80% humidity for 1 to 4 weeks, after which an epitaxial NiO layer is deposited to 400 nm on the NiO layer obtained by the IBAD method, and the epitaxial MgO layer is deposited on the MgO layer obtained by the IBAD method. The half-value width Δφ of crystal axis dispersion was measured after stacking 400 nm and leaving for a predetermined period.
The results are shown in Table 3 below.

  From the results shown in Table 3, the MgO intermediate layer produced by the IBAD method has a Δφ value that deteriorates when the standing time is 1 week, and the Δφ value is measured for peeling when the standing time is 2 weeks or more. I could not. On the other hand, it was found that the NiO intermediate layer produced by the IBAD method had no influence in the moisture resistance test for about one week, and the Δφ value hardly deteriorated even after 2 to 4 weeks. That is, it was found that the NiO intermediate layer produced by the IBAD method is resistant to moisture, specifically, the value of Δφ is hardly deteriorated even when left for about 3 weeks at 80% humidity.

Next, FIG. 9 shows a (220) positive electrode dot diagram of the NiO intermediate layer (Δφ = 25.6 °) having the three-fold symmetry formed at the back pressure (0.008 Pa) described above, and FIG. The (222) positive electrode dot figure of the 200-nm-thick GZO layer formed by the IBAD method on the intermediate layer of NiO is shown. As shown in FIG. 10, it became clear that the orientation of the 3-fold symmetrical NiO intermediate layer of the base can be changed to 4-fold symmetry by the GZO layer.
Further, FIG. 11 shows a (220) positive electrode dot diagram of a NiO intermediate layer (Δφ = 10.9 °) having a four-fold symmetry formed at the back pressure (0.00008 Pa) described above. This four-fold symmetry NiO intermediate layer exhibited an excellent degree of orientation.

  A, B: base material for oxide superconducting conductor, C: oxide superconducting conductor, 11, 21, 31 ... base material body, 9, 19, 29 ... diffusion preventing layer, 12, 22, 32 ... bed layer, 13, 23, 33 ... Intermediate layer, 14, 25, 34 ... Cap layer, 24 ... Intermediate compensation layer, 37 ... Oxide superconducting layer, 38 ... Stabilization layer, 50 ... Ion beam assisted sputtering apparatus, 52 ... Target, 53, 54 ... Ion source,

Claims (9)

  A base material, an intermediate layer made of NiO formed thereon by an ion beam assist method, crystal orientation is adjusted, and 4-fold symmetry is provided; and a cap layer formed on the intermediate layer; A base material for an oxide superconducting conductor, wherein the cap layer is provided with an oxide superconducting layer thereon.   2. The base material for an oxide superconducting conductor according to claim 1, wherein a half-value width Δφ of crystal axis dispersion of the intermediate layer made of NiO is 16 ° or less.   A base material, an intermediate layer made of NiO formed thereon by an ion beam assist method, crystal orientation is adjusted, and three-fold symmetry is provided, and formed on the intermediate layer, the bottom side is 3 An intermediate compensation layer having a two-layer structure having a rotational symmetry and an upper side having a four-fold symmetry, and a cap layer formed on the intermediate compensation layer, the cap layer being formed thereon A substrate for an oxide superconducting conductor, characterized in that an oxide superconducting layer is provided. The base material for an oxide superconducting conductor according to claim 3, wherein the intermediate compensation layer is made of Gd ₂ Zr ₂ O ₇ .   The base material for an oxide superconducting conductor according to any one of claims 1 to 4, wherein an intermediate layer is formed on the base material via at least one of a diffusion prevention layer and a bed layer.   An oxide superconducting conductor comprising an oxide superconducting layer formed on the cap layer of the base material for an oxide superconducting conductor according to any one of claims 1 to 5.   A method of forming a four-fold symmetric NiO intermediate layer on a substrate by an ion beam assist method, wherein the film is formed with a back pressure of 0.001 Pa or less in the atmosphere in which the film is formed. Method for forming an intermediate layer.   The method of forming a four-fold symmetric NiO intermediate layer according to claim 7, wherein the back pressure is 0.0002 Pa or less. The current density of the assist ion beam when forming the NiO intermediate layer by the ion beam assist method is in the range of 75 μA / cm ² or more and 120 μA / cm ² or less. A method of forming a symmetric NiO intermediate layer.