JP2010287475A - Mgb2 superconductor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconductor which has high critical current density and suitable superconductive characteristics by film-depositing while maintaining suitable crystal orientation of MgB<SB>2</SB>, and a method for manufacturing a MgB<SB>2</SB>superconductor which controls stable crystal orientation of the MgB<SB>2</SB>and has high superconductive characteristics. <P>SOLUTION: The superconductor 10 is constituted with a laminated body wherein a metal substrate 11, a three-times symmetry MgO (111) layer 13 formed on the metal substrate 11 by an ion beam assisted deposition (IBAD), and a MgB<SB>2</SB>layer 14 are laminated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a superconducting conductor and a manufacturing method thereof, and more particularly to a superconducting conductor having an MgB ₂ layer in which good crystal orientation is maintained and a manufacturing method thereof.

Magnesium diboride as superconductors discovered in recent years (MgB ₂₎ is the critical temperature Tc is known to exhibit superconductivity at 20K about a temperature higher than 39K and conventional metal superconductors (See Non-Patent Document 1). Unlike conventional superconductors, MgB ₂ is a metal compound that does not contain rare earth or toxic substances and is easy to handle at low cost. Therefore, it is processed into a wire and put into practical use as a power supply conductor. To attract attention.
MgB ₂ has a critical temperature Tc = 39K and can be brought into a superconducting state by a refrigerator that can be cooled to about 20K without using liquid helium. Therefore, if a superconducting wire can be manufactured using MgB ₂ , it can be used without using expensive liquid helium, so it can be used at a lower cost than a metal superconducting wire and can be used for applications such as superconducting magnets. It becomes.

As a method for processing MgB ₂ into a wire rod, a metal tube filled with MgB ₂ powder or mixed powder of Mg and B is drawn or rolled, and further subjected to heat treatment, so that MgB ₂ inside the wire rod is processed. A method of forming an MgB ₂ superconducting wire by sintering powder has been studied (see, for example, Patent Document 1 and Patent Document 2).
Further, as another method, the MgB ₂ film epitaxially deposited by sputtering on the (111) plane of the MgO substrate to form a thin film of MgB ₂ superconductor layer, a superconducting wire using this MgB ₂ superconductor layer A means for forming is also conceivable (see, for example, Patent Document 3).

JP 2005-310600 A JP 2008-226501 A JP 2002-274841 A

Nature, 410 (2001), 63

However, since the conventional MgB ₂ wire is produced by a sintering method, the area where the microcrystals of MgB ₂ produced inside the metal tube are in contact with each other is small, so the critical temperature Tc and critical current density Jc However, there has been a problem that is lower than that of a single crystal superconductor. In addition, a long MgB ₂ superconducting conductor that can exhibit high superconducting properties has not been developed so far.

By the way, the present inventors have been researching and knowing that superconducting properties are influenced by the crystalline orientation of oxide superconductors. For example, in an oxide-based superconductor, the crystal itself has an electric anisotropy such that electricity easily flows in the a-axis direction and the b-axis direction of the crystal axis, but hardly flows in the c-axis direction. ing. Therefore, when a superconductor is formed on a substrate, it is necessary to orient the a-axis or b-axis in the direction in which electricity flows and to orient the c-axis in other directions.
However, since the metal substrate itself is amorphous or polycrystalline, and its crystal structure is also significantly different from that of the superconductor, it is not possible to form a superconductor film with good crystal orientation on the substrate as described above. Have difficulty. In addition, since there is a difference in thermal expansion coefficient and lattice constant between the base material and the superconductor, the superconductor is distorted during the cooling to the superconducting critical temperature, or the oxide superconductor film is removed from the substrate. There is also a problem such as peeling.
In order to solve the above problems, first, MgO, YSZ (yttria stable) in which physical characteristic values such as thermal expansion coefficient and lattice constant are intermediate values between the substrate and the superconductor on the metal substrate. We are studying the formation of an intermediate layer (buffer layer) made of a material such as Zirconia) and SrTiO ₃ and forming a superconductor film on the intermediate layer.
Although this intermediate layer has the c-axis oriented at right angles to the substrate surface, the a-axis (or b-axis) is not oriented in the same direction in the substrate surface, so the superconducting layer formed thereon is also There is a problem that the a-axis (or b-axis) is not in-plane oriented in substantially the same direction, and the critical current density Jc is not improved.

The ion beam assisted method (IBAD method) is a technique for solving this problem, and is generated from an ion gun when depositing constituent particles knocked out of a target by a sputtering method on a substrate. Argon ions and oxygen ions are deposited while simultaneously irradiating from an oblique direction (for example, 45 degrees). According to this method, high c-axis orientation and a-axis with respect to the film formation surface on the substrate are used. An intermediate layer having in-plane orientation is obtained.
5 and 6 show an example in which a polycrystalline thin film forming an intermediate layer is formed on a base material by the IBAD method. In FIG. 5, 100 is a plate-like base material, and 110 is a base material 100. The polycrystalline thin film formed on the upper surface is shown.

  The polycrystalline thin film 110 is formed by joining and integrating a large number of fine crystal grains 120 having a cubic crystal structure via crystal grain boundaries, and the c-axis of the crystal axis of each crystal grain 120 is the base material 100. The a-axis and the b-axis of the crystal axes of each crystal grain 120 are oriented in the same plane and oriented in the same direction. Further, the c-axis of each crystal grain 120 is oriented perpendicular to the (upper surface) film-forming surface of the substrate 100. The a-axis (or b-axis) of each crystal grain 120 is joined and integrated with an angle formed by them (grain boundary inclination angle K shown in FIG. 6) within 30 degrees.

The IBAD method is said to be a highly practical production method, such as excellent mechanical properties of the wire, easy to obtain stable high properties, and the present inventors have proposed various oxide superconductors. We are actively developing research on the application of the IBAD method.
The present invention has been devised in view of such a conventional situation, and a superconducting conductor having a high critical current density and good superconducting characteristics by forming a film of MgB ₂ while maintaining good crystal orientation. The primary purpose is to provide
Further, the present invention is stable by controlling the crystal orientation of MgB _2, and a second object is to provide a method capable of producing the MgB ₂ superconductor having a high superconducting property.

In order to solve the above problems, a superconducting conductor of the present invention includes a metal base, a three-fold symmetric MgO (111) layer formed on the metal base by an ion beam assist (IBAD) method, and an MgB ₂ layer. It consists of the laminated body which laminated | stacked.
In order to solve the above problems, the superconducting conductor of the present invention is characterized in that a diffusion preventing layer is interposed between the metal base and the MgO (111) layer.
In the superconducting conductor of the present invention, the half width (ΔΦ) of crystal axis dispersion in the in-plane direction of the MgB ₂ layer is 16 ° or less.
In the superconducting conductor of the present invention, a three-fold symmetric MgO (formed by epitaxial growth using another film-forming method on the three-fold symmetric MgO (111) layer formed by the ion beam assist method (IBAD) method. 111) layer is preferably formed by laminating the MgB ₂ layer.

In order to solve the above-described problems, a method of manufacturing a superconducting conductor according to the present invention includes forming a three-fold symmetric MgO (111) layer on a metal substrate by an ion beam assist (IBAD) method, and thereafter forming a film forming method. An MgB ₂ layer is formed by the above.
In order to solve the above-described problems, the method of manufacturing a superconducting conductor according to the present invention includes forming a diffusion prevention layer on the metal substrate, and then forming the MgO (111) layer and the MgB ₂ layer on the diffusion prevention layer. It is characterized by forming.
In order to solve the above problems, the method of manufacturing a superconducting conductor of the present invention is characterized in that the MgB ₂ layer is formed so that the half-value width (ΔΦ) of crystal axis dispersion in the in-plane direction is 16 ° or less. To do.

In order to solve the above-mentioned problems, the method of manufacturing a superconducting conductor according to the present invention is to epitaxially grow on the three-fold symmetric MgO (111) layer formed by an ion beam assist method (IBAD) method by another film forming method. To form a three-fold symmetric MgO (111) layer.
In order to solve the above-described problems, the method for producing a superconducting conductor according to the present invention is such that when the three-fold symmetric MgO (111) layer is formed by epitaxial growth by the film forming method, the film forming temperature is 200 to 600 ° C. It is characterized by doing.

In the superconducting conductor of the present invention, MgB ₂ is crystallized with good crystal orientation by forming an MgB ₂ layer on a three-fold symmetric MgO (111) layer in which MgO (111) is oriented in the normal direction of the substrate. And can be laminated. The Mg plane of the three-fold symmetric MgO (111) plane and the Mg plane of the MgB ₂ (001) plane are the same triangular lattice, and the distance between Mg atoms is substantially equal, so that epitaxial film formation is possible. As a result, a superconducting conductor having a high critical current density and good superconducting characteristics can be provided.
According to the present invention, the MgB ₂ layer is formed on the biaxially oriented three-fold symmetric MgO (111) layer having a good crystal orientation state, whereby the crystal axis dispersion in the in-plane direction of the MgB ₂ layer is achieved. The half-value width (ΔΦ) can be 16 ° or less. This makes it possible to provide a superconducting conductor that has a good crystal orientation state of the MgB ₂ layer, which is a superconducting layer, has a high critical current density, and good superconducting characteristics.
Furthermore, in the method for producing a superconducting conductor of the present invention, the MgO (111) layer is formed by the ion beam assist (IBAD) method, and the MgB ₂ layer is formed by the film forming method, so that the crystal orientation is stably maintained. Thus, it is possible to provide a method for manufacturing a MgB ₂ superconducting conductor with good superconducting properties.
According to the present invention, the MgB ₂ layer is provided on the MgO (111) layer by providing the three-fold symmetric MgO (111) layer formed by the ion beam assist (IBAD) method on the metal substrate. Can be formed in a good crystal orientation state. The ion beam assist (IBAD) method is applicable even when the metal substrate is elongated, and the MgB ₂ layer can maintain a stable crystal orientation state on the MgO (111) layer. If a long metal substrate is used as the substrate, a long MgB ₂ superconducting conductor can be provided.

It is a figure which shows typically an example of the superconducting conductor which concerns on this invention. It is a figure which shows typically another example of the superconducting conductor which concerns on this invention. It is a figure which shows typically the film-forming apparatus by IBAD method. It is a figure which shows typically the ion gun with which the film-forming apparatus shown in FIG. 3 is provided. It is a figure which shows typically an example of the conventional polycrystalline thin film. It is a figure which shows typically an example of the conventional polycrystalline thin film. It is a (110) pole figure of a MgO film formed on the Al ₂ O ₃ film on.

<First embodiment>
FIG. 1 is a diagram schematically showing an example of a superconducting conductor 10 according to the present invention.
The superconducting conductor 10 of the present invention has a laminated structure in which a three-fold symmetric MgO (111) layer 13 and an MgB ₂ layer 14 are laminated on a metal substrate 11 with a diffusion preventing layer 12 in order. The rotationally symmetric MgO (111) layer 13 is formed by an ion beam assist (IBAD) method.

In order to produce the MgO (111) layer 13 by the IBAD method, MgO or Mg or the like is used as a target, and an ion gas is incident at an incident angle of 40 to 60 degrees or the like, and oxygen gas is introduced into the deposition atmosphere as necessary. To form a film. Biaxially oriented three-fold symmetry MgO (111) formed by the IBAD method has a half-width (ΔΦ) of crystal axis dispersion in the in-plane direction of 25 ° or less, more preferably 20 ° or less. Thus, the MgB ₂ layer 14 stacked on the MgO (111) layer 13 can be epitaxially grown so as to be aligned with high orientation.
Further, the MgO (111) layer 13 may be formed only by the IBAD method in order to obtain a desired thickness. However, MgO having this structure is characterized in that it is formed while maintaining good crystal orientation. Therefore, after forming an MgO (111) thin film (IBAD-MgO (111)) by IBAD method at an initial stage, MgO is epitaxially grown on the thin film by another film forming method to thereby form a thick MgO (111) layer 13. It is also possible to form The film formation by the IBAD method has a problem that the deposition rate becomes slow because the crystal orientation is controlled by ion beam impact on the non-oriented metal substrate (metal tape). The film formation time can be shortened by combining film formation by other film formation methods.

In order to epitaxially grow MgO on the IBAD-MgO (111) layer, it can be formed by a normal film forming method, for example, ion beam sputtering, electron beam evaporation, other sputtering, PLD, CVD The film can be formed by (chemical vapor deposition) or the like.
The temperature of the metal base 11 when epitaxially growing MgO on the IBAD-MgO (111) layer is such that the half-value width (ΔΦ) of crystal axis dispersion in the in-plane direction of the formed MgO (111) layer is 25 ° or less. Therefore, the temperature range is preferably 200 ° C to 600 ° C, and more preferably 400 ° C to 500 ° C.

The thickness of the MgO (111) layer 13 can be in the range of 5 to 500 nm. If the thickness of the MgO (111) layer is less than 5 nm, it may be difficult to maintain the film thickness stably, and the film thickness may vary.
On the other hand, when the thickness of the MgO (111) layer 13 exceeds 500 nm, the internal stress of the MgO (111) layer 13 increases, thereby increasing the internal stress of the entire superconducting conductor 10, and the diffusion preventing layer 12, MgO ( 111) layer 13 and MgB ₂ layer 14 become easy to peel from the metal substrate 11. On the other hand, if the thickness exceeds 500 nm, the surface roughness increases and the critical current density decreases. The film thickness of the MgO (111) layer 13 can be increased or decreased by adjusting the delivery speed of the metal substrate 11.

The MgB ₂ layer 14 can be formed by a normal film formation method, for example, an ion beam sputtering method, an electron beam evaporation method, other sputtering methods, a PLD method, a CVD method, or the like. As a target for forming the MgB ₂ layer, a material capable of forming the MgB ₂ layer 14 by a film forming method, such as a MgB ₂ powder, a mixed powder of Mg and B, and those formed into pellets or plates. If it is, it will not be specifically limited. The temperature at the time of forming the MgB ₂ layer is not particularly limited, and examples thereof include a range of 200 to 600 ° C.

Here, as described above, when the MgB ₂ layer 14 is formed on the MgO (111) layer 13 having good orientation, the MgB ₂ layer 14 is also crystallized to match the compounding property of the MgO (111) layer 13. To do. Since MgB ₂ has a six-fold symmetry structure of AlB ₂ type crystal structure, the Mg plane of the (111) plane of the MgO (111) layer 13 and the Mg plane of the (001) plane of MgB ₂ are the same triangular lattice. In addition, since the distance between Mg atoms is substantially equal, MgB ₂ can be epitaxially grown in a biaxial orientation. Therefore, by setting the half-value width (ΔΦ) of the crystal axis dispersion in the in-plane direction of the MgO (111) layer 13 to 25 ° or less, the half-value width (ΔΦ) of the crystal axis dispersion in the in-plane direction of the MgB ₂ layer 14. Can be 16 ° or less. Therefore, the obtained MgB ₂ layer 14 is excellent in the quantum connectivity at the crystal grain boundary and has almost no deterioration in the superconducting characteristics at the crystal grain boundary, so that it is easy to flow a current in the length direction of the metal substrate 11. A sufficiently high critical current density is obtained.

Further, as described above, since the MgB ₂ layer 14 is biaxially oriented, the contact area between the fine crystal grains is increased, and a high-performance superconducting layer is obtained. Furthermore, since MgB ₂ has a smaller magnetic anisotropy than conventionally known superconducting materials, it exhibits superconducting characteristics even under conditions where the crystal orientation is low, such as when MgB ₂ powder is heat-treated by a sintering method. However, according to the present invention, since the MgB ₂ layer 14 can be formed with good orientation, the superconducting conductor 10 that can exhibit higher superconducting characteristics can be provided.

The thickness of the MgB ₂ layer 14 is preferably in the range of 0.5 to 5 μm. If the thickness of the MgB ₂ layer 14 is less than 0.5 μm, there is a possibility that the superconducting characteristics cannot be expressed. On the other hand, when the thickness of the MgB ₂ layer 14 exceeds 5 μm, the internal stress of the MgB ₂ layer 14 increases, thereby increasing the internal stress of the superconducting conductor 10 as a whole, and the diffusion preventing layer 12 and the MgO (111) layer 13. and MgB ₂ layer 14 is easily peeled off from the metal substrate 11. The thickness of the MgB ₂ layer 14 can be increased or decreased by adjusting the delivery speed of the metal substrate 11.

In the present embodiment, the metal base material 11 is in the form of a tape. However, the present invention is not limited to this, and various shapes such as a plate material, a wire material, and a strip can be used. For example, silver, Examples include various metal materials such as platinum, stainless steel, copper, nickel alloys such as Hastelloy, or various ceramic materials arranged on various metal materials. Further, as the metal base 11, a long MgB ₂ superconducting conductor is obtained by using a metal that is strong and heat resistant and is processed into a long tape shape from a metal that can be easily processed into a wire. be able to.

The diffusion preventing layer 12 is formed for the purpose of preventing the diffusion of the constituent elements of the metal substrate 11, and silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ , also referred to as “alumina”), or It is comprised from rare earth metal oxide etc., and the thickness is 10-400 nm, for example. When the thickness of the diffusion preventing film 12 is less than 10 nm, there is a possibility that the diffusion of the constituent elements of the metal substrate 11 cannot be sufficiently prevented. On the other hand, when the thickness of the diffusion preventing layer 12 exceeds 400 nm, the internal stress of the diffusion preventing layer 12 increases, thereby increasing the internal stress of the entire superconducting conductor 10, and the diffusion preventing layer 12 and the MgO (111) layer 13. and MgB ₂ layer 14 there is a fear that easily peeled from the metal substrate 11.
Further, a Gd ₂ Zr ₂ O ₇ layer can be used as the rare earth metal oxide layer constituting the diffusion prevention layer 12. In this case, the diffusion preventing layer 12 may be formed by a film forming method such as a normal sputtering method because crystal orientation is not particularly limited. In particular, if a Gd ₂ Zr ₂ O ₇ layer is used as the diffusion preventing layer 12, a diffusion preventing effect close to the two-layer structure of the diffusion preventing layer 12 and the bed layer 9 described later in the second embodiment can be obtained. This is advantageous because the superconducting properties of the MgB ₂ layer 14, which is a superconducting layer formed on the surface, are improved.
If a special film forming method such as the IBAD method is used for adjusting the crystal orientation of the diffusion preventing layer 12, the film forming rate is lowered and it takes time to form the film, but the underlying layer of the MgO (111) layer 13 is used. Since the crystal orientation is not a problem, the diffusion prevention layer 12 can be selected and used by a normal sputtering method having a high film formation rate. There is little risk of making it longer than necessary.

According to the superconducting conductor 10 of the present embodiment, the MgB ₂ layer 14 which is a superconducting layer can be directly deposited on the three-fold symmetric MgO (111) layer 13 with good crystal orientation, and a conventionally known oxide The cap layer that is required when the superconducting layer is laminated can be omitted. As a result, it is possible to reduce the film thickness as compared with the conventional superconducting conductor, and the internal stress is reduced, so that the conventional problem of warping of the substrate can be solved. Further, the manufacturing speed can be increased by thinning the film, and the manufacturing cost can be reduced because MgB ₂ is much cheaper than the conventional superconducting material containing rare earth elements.

<Second Embodiment>
Next, a second embodiment of the superconducting conductor of the present invention will be described. In the following description, portions different from those of the first embodiment described above will be mainly described, and description of similar portions will be omitted.
FIG. 2 is a diagram schematically showing an example of the superconducting conductor 20 according to the present invention. In FIG. 2, the same components as those of the superconducting conductor 10 shown in FIG.

The superconducting conductor 20 of the present embodiment has a laminated structure in which an MgO (111) layer 13 and an MgB ₂ layer 14 are laminated on a metal substrate 11 with a diffusion preventing layer 12 and a bed layer 9 interposed therebetween. Features. The structure of the second embodiment is different from the structure of the first embodiment in the structure in which the bed layer 9 is added.

The bed layer 9 has high heat resistance and is intended to further reduce interfacial reactivity, and functions to obtain the orientation of the coating film disposed thereon. Such a bed layer 9 is arranged as necessary, and for example, a rare earth oxide layer can be used. For example, as the rare earth oxide, a composition formula (α ₁ O ₂ ) _2x (β ₂ O ₃ ) _{(1 -X)} . Here, α and β are rare earth elements belonging to 0 ≦ x ≦ 1. More specifically, Y ₂ O ₃ , CeO ₂ , Dy ₂ O ₃ , Er ₂ O ₃ , Eu ₂ O ₃ , Ho ₂ O ₃ , La ₂ O ₃ , Lu ₂ O ₃ , Nd ₂ O ₃ , Pr Examples include ₆ O ₁₁ , Sc ₂ O ₃ , Sm ₂ O ₃ , Tb ₄ O ₇ , Tm ₂ O ₃ , Yb ₂ O _{3 and the} like.
The bed layer 9 is formed by, for example, a sputtering method and has a thickness of, for example, 10 to 100 nm.
In the case of a two-layer structure of the diffusion prevention layer 12 and the bed layer 9, a structure in which the diffusion prevention layer 12 is made of alumina and the bed layer 9 is formed of Y ₂ O ₃ can be exemplified.

The two-layer structure of the diffusion prevention layer 12 and the bed layer 9 as in the present embodiment is because the MgO (111) layer 13 and the MgB ₂ layer which is a superconducting layer are formed on the bed layer 9 as described in the previous embodiment. 14, when a thermal history is received as a result of inevitably being heated or heat-treated, a part of the constituent elements of the metal substrate 11 is transferred to the superconducting layer side through the diffusion prevention layer 12 and the bed layer 9. This is in order to suppress the diffusion, and the element diffusion from the metal substrate 11 side can be effectively suppressed by adopting a two-layer structure of the diffusion prevention layer 12 and the bed layer 9.
Further, the crystal orientation of the diffusion preventing layer 12 and the bed layer 9 is not particularly limited, and may be formed by a film forming method such as a normal sputtering method.

The superconducting conductor of the present invention has been described above, but the present invention is not limited to this, and can be appropriately changed as necessary. For example, in addition to the MgO (111) layer, the MgB ₂ layer, the diffusion prevention layer, the bed layer, and the like mentioned in the embodiment of the present invention, materials that can be applied to conventionally known superconducting conductors may be appropriately combined. Is possible.

Since the superconducting conductor of the present invention has MgB ₂ laminated with a good crystal orientation, it can exhibit high superconducting characteristics as compared with a MgB ₂ superconducting conductor prepared by a conventional sintering method.
Moreover, the superconducting conductor of the present invention is provided with a three-fold symmetric MgO (111) layer formed by an ion beam assist (IBAD) method on a metal substrate, so that MgB _{2 is formed} on the MgO (111) layer. The layer can be formed with good crystal orientation. The ion beam assist (IBAD) method is applicable even when the metal substrate is elongated, and the MgB ₂ layer can maintain a stable crystal orientation state on the MgO (111) layer. If a long metal base material is used as the base material, it is possible to provide a MgB ₂ superconducting conductor that is long and has good superconducting characteristics.
Furthermore, since the superconducting conductor of the present invention employs the MgB ₂ layer as the superconducting layer, it is possible to provide a superconducting conductor that does not contain rare earth elements or toxic substances and is easy to handle at low cost.
In addition, since the MgB ₂ layer constituting the superconducting conductor of the present invention has a critical temperature Tc of 39 K, there is no need for cooling with liquid helium, and the cost can be reduced. In addition to the superconducting wire, a superconducting magnet, etc. Application to various fields is possible.

First, a film forming apparatus using the IBAD method used in this embodiment will be described.
FIG. 3 shows an example of an apparatus for manufacturing a polycrystalline thin film, and the apparatus of this example has a configuration in which an ion gun for ion beam assist is provided in a sputtering apparatus.
The film forming apparatus includes a substrate holder 51 that holds the substrate A horizontally, a plate-like target 52 that is disposed obliquely above the substrate holder 51 with a predetermined interval, and an obliquely upper portion of the substrate holder 51. Are mainly composed of an ion gun 53 that is opposed to the target 52 and spaced apart from the target 52, and a sputter beam irradiation device 54 that is disposed below the target 52 and toward the lower surface of the target 52. Reference numeral 55 in the drawing denotes a target holder that holds the target 52.
The apparatus is housed in a vacuum container (not shown) so that the periphery of the substrate A can be maintained in a vacuum atmosphere. Further, an atmospheric gas supply source such as a gas cylinder is connected to the vacuum container, the inside of the vacuum container is in a low pressure state such as a vacuum, and an inert gas containing argon gas or other inert gas atmosphere or oxygen The atmosphere can be changed.

When a long metal tape is used as the base material A, a metal tape feeding device and a winding device are provided inside the vacuum container, and the base material A is continuously fed from the feeding device to the base material holder 51. Subsequently, it is preferable that the polycrystalline thin film be continuously formed on the tape-shaped substrate by winding with a winding device.
The base material holder 51 includes a heater inside, and the base material A positioned on the base material holder 51 can be heated to a desired temperature. In addition, an angle adjustment mechanism that can adjust the horizontal angle of the substrate holder 51 is attached to the bottom of the substrate holder 51. An angle adjustment mechanism may be attached to the ion gun 53 to adjust the tilt angle of the ion gun 53 to adjust the ion irradiation angle.

The target 52 is for forming a target MgO layer. Specifically, the target 52 may be formed by using MgO or Mg and supplying oxygen gas in a film forming atmosphere as required.
The ion gun 53 is configured such that a gas to be ionized is introduced into a container and a lead electrode is provided on the front surface. And it is an apparatus which ionizes one part of the atom or molecule | numerator of gas, and irradiates the ionized particle | grain as an ion beam controlled by the electric field generated with the extraction electrode. There are various types of ionization of gas, such as a high frequency excitation method and a filament type. The filament type is a method in which a tungsten filament is energized and heated to generate thermoelectrons and collide with gas molecules in a high vacuum to be ionized. The high-frequency excitation method ionizes gas molecules in a high vacuum by polarization with a high-frequency electric field.
In this embodiment, an ion gun 53 having an internal structure shown in FIG. 4 is used. The ion gun 53 includes an extraction electrode 57, a filament 58, and an introduction tube 59 for Ar gas or the like inside a cylindrical container 56, and can irradiate ions in parallel in a beam shape from the tip of the container 56. It is.

As shown in FIG. 3, the ion gun 53 is opposed to the upper surface (film formation surface) of the substrate A with an inclination angle θ. The inclination angle θ is preferably in the range of 30 to 60 degrees, but in the case of MgO, around 45 degrees is particularly preferable. Accordingly, the ion gun 53 is arranged so as to irradiate ions with an inclination angle θ with respect to the upper surface of the substrate A. The ions irradiated onto the substrate A by the ion gun 53 may be ions of rare gases such as He ⁺ , Ne ⁺ , Ar ⁺ , Xe ⁺ , Kr ⁺ , or mixed ions of these and oxygen ions.
The sputter beam irradiation device 54 has the same configuration as that of the ion gun 53, and can irradiate the target 52 with ions to knock out the constituent particles of the target 52. In the device of the present invention, since it is important that the constituent particles of the target 53 can be knocked out, a voltage is applied to the target 52 with a high-frequency coil or the like so that the constituent particles of the target 52 can be knocked out. The sputter beam irradiation device 54 may be omitted.

Next, the case where a polycrystalline thin film is formed on the base material A using the apparatus having the above configuration will be described.
In order to form a polycrystalline thin film on the substrate A, a predetermined target is used, and the angle adjustment mechanism is adjusted to irradiate the upper surface of the substrate holder 51 with ions irradiated from the ion gun 53 at an angle of about 45 degrees. It can be so. Next, the inside of the container containing the substrate is evacuated to form a reduced pressure atmosphere. Then, the ion gun 53 and the sputter beam irradiation device 54 are operated.

  When the target 52 is irradiated with ions from the sputter beam irradiation device 54, the constituent particles of the target 52 are knocked out and fly onto the substrate A. Then, the constituent particles knocked out from the target 52 are deposited on the substrate A, and at the same time, a mixed ion of Ar ions and oxygen ions is irradiated from the ion gun 53. The irradiation angle θ at the time of ion irradiation is preferably in the range of 40 to 60 degrees, for example, when forming MgO.

"Production Example 1"
As the metal substrate, a 10 mm wide Hastelloy tape whose surface was polished was used. An Al ₂ O ₃ film (200 to 300 nm) was formed as a diffusion preventing layer on this metal substrate by a sputtering method, and then an MgO layer (10 to 30 nm) was formed by an IBAD method. At this time, the MgO layer was produced at a substrate temperature of 300 ° C. while an ion assist beam of a rare gas ion beam of Ar or the like was incident on the substrate at 55 °.
Next, MgO was epitaxially grown on the IBAD-MgO layer by ion beam sputtering to form an MgO layer (about 300 nm). The MgO layer at this time was produced at 200 to 600 ° C. FIG. 7 shows a MgO [110] positive electrode dot diagram of the MgO layer thus fabricated.

Further, MgB ₂ was epitaxially grown at 300 ° C. by the PLD method on the MgO layer to form a MgB ₂ layer (about 1 μm) to obtain a superconducting conductor. With respect to the MgO layer and MgB ₂ layer of the superconducting conductor thus obtained, the half width of crystal axis dispersion in the in-plane direction was measured. The results are shown in Table 1 (Examples 1 to 5).
Further, the critical current density Jc and critical current Ic at 20K of the obtained superconducting conductor were measured. The results are also shown in Table 1.

(Comparative Example 1)
A superconducting conductor was produced in the same manner as in Production Example 1 except that the temperature at which the MgO layer was epitaxially grown by ion beam sputtering was 100 ° C. Table 1 also shows the measurement results of the half width of crystal axis dispersion in the in-plane direction of the MgO layer and MgB ₂ layer of the obtained superconducting conductor, the critical current density Jc at 20 K, and the critical current Ic.

(Comparative Example 2)
After producing the IBAD-MgO layer in the same manner as in Production Example 1, an MgO layer was formed by ion beam sputtering at 700 ° C., but the MgO layer was not epitaxially grown and the three-fold symmetric MgO (111) layer was It was not obtained.

  From the results shown in FIG. 7 and Table 1, under appropriate film forming conditions, the (111) axis is oriented perpendicular to the substrate, the (100) axis is oriented in the ion beam direction, and the crystal axis dispersion in the in-plane direction is A three-fold symmetric MgO (111) layer having a half width within 25 degrees is formed. The thin film having this structure is characterized by being formed with the same structure under a wide range of conditions, and the film thickness can be changed to about 5 to 100 nm. Further, the temperature at which the MgO layer is epitaxially grown is set in the range of 200 to 600 ° C., so that a three-fold symmetric MgO (111) layer having a half-value width of crystal axis dispersion in the in-plane direction within 25 degrees is formed. The Furthermore, the three-fold symmetric MgO (111) layer can be formed only by the IBAD method in order to obtain a desired thickness. Therefore, as shown in this production example, a thin film of three-fold symmetric MgO (111) is first formed by the IBAD method, and then MgO is epitaxially grown on the thin film by the film-forming method. A (111) layer can also be formed. This makes it possible to shorten the film formation time.

Furthermore, in the MgB ₂ layer laminated by the PLD method on the three-fold symmetric MgO (111) layer, the half width of the crystal axis dispersion in the in-plane direction was successfully made 16 degrees or less. This is because MgB ₂ has a six-fold symmetry structure of AlB ₂ type crystal structure, so the Mg surface of MgO (111) face and the Mg face of MgB ₂ (001) face are the same triangular lattice, This is because MgB ₂ can be epitaxially grown in a biaxial orientation because the interatomic distances are substantially equal. As described above, since MgB ₂ is biaxially oriented, the contact area between the fine crystal grains is increased, and a superconducting layer having high characteristics is obtained.
Up to now, there has been no example in which the superconducting layer MgB ₂ has been produced with a good crystal orientation structure matched by a film forming method, and the present invention has opened the way to stably synthesize high-performance films stably.

In addition, all of the superconducting conductors of Examples 1 to 5 had a critical current density Jc of 0.7 MA / cm ² or more and a critical current Ic of 70 A or more at 20 K, and higher superconducting characteristics than the superconducting conductor of Comparative Example 1. It was confirmed that Further, these values exhibit superconducting characteristics superior to those of a superconducting conductor produced by sintering a conventionally known MgB ₂ powder (see, for example, Patent Document 1).

Further, according to the present invention, the MgB ₂ layer, which is a superconducting layer, can be directly deposited on the three-fold symmetric MgO (111) layer with good crystal orientation. Furthermore, the manufacturing speed can be dramatically increased by thinning the film, and the manufacturing cost can be reduced because MgB ₂ is very cheap compared to conventional superconducting materials containing rare earth elements. .

DESCRIPTION OF SYMBOLS 9 ... Bed layer, 10, 20 ... Superconducting conductor, 11 ... Metal base material, 12 ... Diffusion prevention layer, 13 ... MgO (111) layer, 14 ... MgB ₂ layer.

Claims (9)

Superconductivity comprising: a metal substrate, and a laminate in which a three-fold symmetric MgO (111) layer formed on the metal substrate by an ion beam assist (IBAD) method and an MgB ₂ layer are laminated. conductor.   The superconducting conductor according to claim 1, wherein a diffusion preventing layer is interposed between the metal substrate and the MgO (111) layer. The superconducting conductor according to claim 1 or 2, wherein a half-value width (ΔΦ) of crystal axis dispersion in the in-plane direction of the MgB ₂ layer is 16 ° or less. On the three-fold symmetric MgO (111) layer formed by the ion beam assist method (IBAD) method, the three-fold symmetric MgO (111) layer formed by epitaxial growth by another film formation method is used. The superconducting conductor according to any one of claims 1 to 3, wherein MgB ₂ layers are laminated. A method for producing a superconducting conductor, comprising: forming a three-fold symmetric MgO (111) layer on a metal substrate by an ion beam assist (IBAD) method, and thereafter forming an MgB ₂ layer by a film forming method. 6. The superconducting conductor according to claim 5, wherein after the diffusion preventing layer is formed on the metal substrate, the MgO (111) layer and the MgB ₂ layer are formed on the diffusion preventing layer. Method. The method for manufacturing a superconducting conductor according to claim 5 or 6, wherein the MgB ₂ layer is formed so that a half-value width (ΔΦ) of crystal axis dispersion in an in-plane direction is 16 ° or less.   A three-fold symmetric MgO (111) layer is formed by epitaxial growth by another film forming method on the three-fold symmetric MgO (111) layer formed by an ion beam assist method (IBAD) method. Item 8. The method for producing a superconducting conductor according to any one of Items 5 to 7.   The method for producing a superconducting conductor according to claim 8, wherein when the three-fold symmetric MgO (111) layer is formed by epitaxial growth by the film forming method, the film forming temperature is set to 200 to 600 ° C.

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