JP2012212571A - Oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide superconductor including an intermediate thin film of perovskite structure having excellent crystal orientation.SOLUTION: The oxide superconductor comprises a substrate, and an intermediate thin film and an oxide superconducting layer laminated on the substrate directly or with an underlying layer interposed therebetween. The intermediate thin film is an intermediate thin film of perovskite type oxide formed by ion beam assist deposition for irradiating the deposition surface above the substrate with an assist ion beam from oblique direction, when forming the intermediate thin film on the substrate directly or with an underlying layer interposed therebetween by particle deposition. Two axes out of a plurality of crystal axes of the crystal composing the intermediate thin film are oriented, and the intermediate thin film shows the four-fold symmetry in a dot diagram of positive electrode showing the orientation of these crystals.

Description

  The present invention relates to an oxide superconductor.

An RE-123-based oxide superconductor (REBa ₂ Cu ₃ O _7-X : RE is a rare earth element including Y) exhibits superconductivity at a liquid nitrogen temperature and has a low current loss. Therefore, it is an extremely promising material for practical use. It is desired to process this into a wire and use it as a power supply conductor or a magnetic coil. As an example of the structure of this oxide superconducting conductor, an intermediate thin film with good crystal orientation is formed on the surface of a tape-shaped metal substrate with high mechanical strength by ion beam assisted film formation (IBAD method). An oxide superconducting conductor having a structure in which an oxide superconducting layer is formed on the surface of the intermediate thin film by a film forming method and a stabilizing layer made of a highly conductive material such as Ag is formed on the surface is known. (See Patent Document 1)

  In order to further improve the crystal orientation of the oxide superconducting layer, a cap layer is further formed on the intermediate thin film formed while adjusting the crystal orientation by the IBAD method, and the crystal orientation of the cap layer is set to IBAD. A technique for manufacturing an oxide superconducting conductor having excellent superconducting characteristics is provided by further forming an oxide superconducting layer with this cap layer as a base, which is further enhanced than the intermediate thin film obtained by the method. (See Patent Document 2)

As an example of the structure of an oxide superconducting conductor having a laminated structure including this kind of intermediate thin film and cap layer, as shown in FIG. 9, after forming a diffusion prevention layer 101 on a metal tape-like substrate 100, an IBAD An oxide superconducting conductor 107 having a structure in which an intermediate thin film 102 by a method is formed, a cap layer 103 is formed thereon, an oxide superconducting layer 105 is further formed, and an Ag stabilizing layer 106 is formed thereon is known. It has been. The diffusion prevention layer 101 may have a laminated structure of an Al ₂ O ₃ layer and a Y ₂ O ₃ layer or a single layer structure of any one of them, and the intermediate thin film 102 is composed of an MgO layer in this example. The cap layer 103 is composed of a CeO ₂ layer.
Further, the diffusion prevention layer 101 is omitted, and the intermediate thin film 102 by the IBAD method serves as the structure, and after forming a GZO film (Gd ₂ Zr ₂ O ₇ layer) by the IBAD method on the base material 100, the cap layer 103 is formed. A structure in which an oxide superconducting layer 105 is formed and stacked is also provided.
In the oxide superconducting conductor 107 having the above structure, as an example, the diffusion prevention layer 101 is formed to a thickness of about several tens to 100 nm, the MgO layer formed by the IBAD method is formed to a thickness of about 5 nm, and the cap layer 103 is 400 nm. The oxide superconducting layer 105 is formed to a thickness of about several μm. Further, the GZO film formed by the IBAD method is formed with a thickness of about 1 μm.

As an example of a method for forming the intermediate thin film 102 in accordance with the IBAD method, as shown in FIG. 10, a target 110 having a target composition is irradiated with an ion beam from an ion gun 111 to generate sputtered particles 112. The intermediate thin film 102 having excellent crystal orientation is formed by irradiating the ion beam from the ion source 113 arranged at a predetermined angle (θ) with respect to the normal of the substrate surface while being deposited on the substrate 100. Can be membrane.
It should be noted that yttrium-stabilized zirconia (YSZ), MgO, and SrTiO ₃ are disclosed in Patent Document 1 as candidates for the intermediate thin film 102 formed by the IBAD method, and Patent Document 3 discloses YSZ, CeO ₂ , MgO, and SrTiO 3. ₃ , LaMnO ₃ , SrRuO ₃ , Y ₂ O ₃ , Gd ₂ O ₃ , LaSrMnO ₃ are described.

Japanese Patent No. 2721595 JP 2004-71359 A Special table 2007-515053 gazette

Ion Beam Assisted Deposition of Biaxially Aligned Oxide Thin Films: (Kevin Glenn Ressler et al .: Massachusetts Institute of Technology September 1996: Fig 6.3 (110) X-ray φ scan of (h00) biaxially aligned LCMO film on quartz: P132-137

  In the oxide superconducting conductor 107 having the laminated structure, in order to adjust the crystal orientation of the oxide superconducting layer 105, the diffusion of unnecessary elements from the substrate 100 side is suppressed to suppress the deterioration of the film quality, or the whole In order to suppress the film thickness and reduce the thickness as much as possible, the development of materials for each layer, improvement of film quality, specification of manufacturing conditions, and the like have been made for the purpose such as.

For example, the MgO layer has a problem of high reactivity with moisture. If it is used for a long time in the presence of moisture, the MgO may be altered and peeled off from the substrate side. Has been made. Further, the MgO crystal has a relatively large lattice mismatch with the CeO ₂ crystal constituting the cap layer 103 on the MgO crystal, and if a better crystal orientation is desired, an intermediate thin film made of a material with less lattice mismatch can be obtained. Desired. Further, the MgO layer formed by the IBAD method is excellent in crystal orientation at a film thickness of about 5 nm. However, if the MgO layer is formed thicker than this in the film forming method, there is a problem that the crystal orientation deteriorates. In addition, although it is desired that each layer constituting the oxide superconductor 107 is as thin as possible, a thin film having a thickness of about 5 nm is used for a long oxide superconductor in the current film formation technique, for example, several hundred m to 1 km. It is not easy to form a uniform film with a length of 10 mm, and an intermediate thin film having a good crystal orientation at the same level as other layers, for example, a film thickness of several tens of nm or more is desired.

  The GZO film formed by the IBAD method is formed with a thickness of about 1 μm because the crystal orientation cannot be obtained unless the GZO film is formed with a thickness of about 1 μm. However, since the oxide superconducting conductor is a long conductor, there is a demand that each film formed by the film forming method should be as thin as possible. The crystal orientation is improved by the IBAD method and is as thin as possible. It is desired to form an intermediate thin film with a film thickness.

Non-Patent Document 1 discloses a result of performing a film formation experiment by performing an IBAD method using LCMO (La _1-x Ca _x MnO ₃ ) having a perovskite structure. In Non-Patent Document 1, a film was formed at a film formation temperature of 600 ° C., an assist ion beam incident angle of 55 ° (from the direction perpendicular to the substrate), an assist ion beam voltage of 75 V, a film thickness of 380 nm, and a film formation rate of 0.26 Å / s. As a result, it is described that the LCMO (110) positive electrode point measurement result shown in FIG. 11 was obtained.
From the results of the positive electrode point measurement shown in FIG. 11, the degree of orientation (Δφ) of the LCMO thin film disclosed in Non-Patent Document 1 is extremely poor (the spread angle at the base of each diffraction peak is large, and the degree of orientation is very bad. It can be estimated that the film quality cannot be used as a base for the cap layer under the oxide superconducting layer, and an intermediate thin film of LCMO (La _1-x Ca _x MnO ₃ ) having good crystal orientation is obtained. I can understand that this is not done.
Also, as described above, Patent Documents 1 to 3 disclose various materials as candidates for the intermediate thin film for oxide superconducting conductors. Since only YSZ and Gd ₂ Zr ₂ O ₇ are disclosed as examples as substances that can be formed on the material, material selection for obtaining an intermediate thin film with good crystal orientation for oxide superconducting conductors It can be estimated that manufacturing is not easy.

  The present invention has been made in view of the above-described conventional situation, and provides an oxide superconductor comprising an intermediate thin film made of a perovskite oxide, excellent in crystal orientation and hardly affected by moisture. Objective.

The oxide superconducting conductor of the present invention comprises a base material, an intermediate thin film laminated directly or via an underlayer on the base material, and an oxide superconducting layer laminated directly or via a cap layer on the intermediate thin film. When the intermediate thin film forms the intermediate thin film on the base material by particle deposition or through the underlayer on the base material, the direction is oblique with respect to the film formation surface above the base material. An intermediate thin film of a perovskite oxide formed by ion beam assisted film formation that irradiates with an assist ion beam from the crystal, and two of the crystal axes of the plurality of crystals constituting the intermediate thin film are oriented. In the positive electrode diagram showing the degree of orientation of these crystals, it is an intermediate thin film exhibiting fourfold symmetry.
According to the present invention, an oxide superconducting conductor having the world's first intermediate thin film with a perovskite structure excellent in crystal orientation exhibiting 4-fold symmetry in a positive electrode diagram, and having an oxide superconducting layer laminated thereon is provided. Can be provided. An intermediate thin film with a perovskite structure that exhibits four-fold symmetry in the positive pole figure and has an excellent perovskite structure has not been obtained in the research and development of intermediate thin films using the IBAD method so far. This has an extremely great effect on improving the film quality of the oxide superconducting layer laminated thereon.
Further, in the case of an intermediate thin film having a perovskite structure, when a CeO ₂ cap layer is laminated thereon, there are few lattice mismatches with the crystal of the CeO ₂ cap layer, so that a cap layer having excellent orientation can be obtained. When a thin film of an oxide superconducting layer is laminated thereon, an oxide superconducting layer having excellent superconducting characteristics can be obtained because a thin film of an oxide superconducting layer can be formed epitaxially.

In the present invention, the intermediate thin film is an ABO ₃ type perovskite oxide (where A is La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and In the case of one or more selected from Y, B is one or more selected from Al, Ti, Cr, Mn, Fe, Co, Ni, and A is Ca, Sr, In the case of one or more selected from Ba and Pb, B is one or more selected from Ti, Mn, Fe, Sn, Mo, Zr, and Hf, and A is Li In this case, B is Nb.).
ABO ₃ type perovskite type oxide can be realized in the present invention as an intermediate thin film having a perovskite structure, and an oxide superconducting conductor using these perovskite type oxides as an underlayer of an oxide superconducting layer or a cap layer is realized in the present invention. it can.

In the present invention, the intermediate thin film is made of any one of LaNiO ₃ , LaMnO ₃ , PrMnO ₃ , and BaTiO ₃ .
In the present invention, an oxide superconducting conductor using either LaNiO ₃ or LaMnO ₃ as a base layer of an oxide superconducting layer or a cap layer can be realized as an intermediate thin film of a perovskite oxide.

  According to the present invention, it is possible to provide for the first time in the world an intermediate thin film of a perovskite oxide that exhibits a four-fold symmetry in the positive electrode diagram and is excellent in crystal orientation. An intermediate thin film of perovskite oxide with excellent crystal orientation that exhibits four-fold symmetry in the positive dot diagram has not been obtained in research and development of intermediate thin films using the IBAD method so far, and can be provided for the first time this time. As a result, the film quality of the oxide superconducting layer laminated thereon is greatly improved.

1A and 1B show a first embodiment of an oxide superconducting conductor including an intermediate thin film according to the present invention, FIG. 1A is a partial cross-sectional perspective view, and FIG. 1B describes the orientation of crystal grains in the intermediate thin film. FIG. 1C is a schematic plan view showing the orientation of crystal grains in the intermediate thin film. Explanatory drawing which shows an example of the ion beam assist film-forming apparatus used when manufacturing the intermediate | middle thin film with which the same oxide superconductor is equipped. The block diagram which shows an example of the ion source with which the same ion beam assist film-forming apparatus is equipped. The block diagram which shows an example of the ion beam assist film-forming apparatus used when applying an ion beam assist film-forming method to a elongate wire. The graph which shows the relationship of (DELTA) phi which shows the electric current value of an assist ion beam at the time of forming an intermediate thin film by the ion beam assist film-forming method in an Example, and forming the cap layer on it, and the parameter | index of the crystal orientation of a cap layer. Pole figure of CeO ₂ cap layer on the intermediate thin film obtained when the deposition temperature was 500 ° C. in the examples. Pole figure of CeO ₂ cap layer was formed a film forming temperature on the intermediate thin film obtained in the case of a 400 ° C. in the examples. Pole figure of CeO ₂ cap layer formed on the intermediate thin film obtained in the case where the film formation time 2000 seconds in the examples. The block diagram which shows an example of the oxide superconducting conductor of the conventional laminated structure. The block diagram which shows an example of the general ion beam assist film-forming method. Pole figure of an intermediate film described in Non-Patent Document 1 obtained by applying the IBAD method in the production method of the perovskite structure _{LCMO (La 1-x Ca x} MnO 3).

Hereinafter, embodiments of an oxide superconducting conductor according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view schematically showing an oxide superconducting conductor 1 according to a first embodiment of the present invention.
The oxide superconducting conductor 1 of this example has a base layer 3, an orientation layer 4, a cap layer 5, an oxide superconducting layer 6, a first stabilizing layer 7 and a second stabilizing layer above a tape-like substrate 2. The oxide superconducting laminate 9 is formed by laminating the oxide layers 8 in this order, and the peripheral surface of the oxide superconducting laminate 9 is covered with the insulating coating layer 10.

  The base material 2 can be used as a base material for a normal oxide superconducting conductor and has only to have high strength, and is preferably in a tape shape, a sheet shape or a thin plate shape in order to obtain a long cable. Those made of heat-resistant metal are preferred. Examples thereof include various heat-resistant metal materials such as nickel alloys such as stainless steel and hastelloy, or ceramics disposed on these various metal materials. Among various refractory metals, a nickel alloy is preferable. Especially, if it is a commercial item, Hastelloy (trade name made by US Haynes Co., Ltd.) is suitable, and Hastelloy B, C, G, N, W, which have different amounts of components such as molybdenum, chromium, iron, cobalt, etc. Any type can be used. What is necessary is just to adjust the thickness of the base material 3 suitably according to the objective, Usually, it can be set as the range of 10-500 micrometers.

The underlayer 3 can have a multi-layer structure of a diffusion prevention layer and a bed layer, which will be described below, or a structure composed of one of these layers.
When a diffusion prevention layer is provided as the underlayer 3, the diffusion prevention layer is formed for the purpose of preventing the diffusion of constituent elements or for improving the film quality of other layers formed thereon. Silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ , also referred to as “alumina”), GZO (Gd ₂ Zr ₂ O ₇ ), etc. The thickness is, for example, 10 to 400 nm. When the thickness of the diffusion preventing layer is less than 10 nm, there is a possibility that the diffusion of the constituent elements of the substrate 2 cannot be sufficiently prevented only by the diffusion preventing layer. On the other hand, when the thickness of the diffusion preventing layer exceeds 400 nm, the internal stress of the diffusion preventing layer increases, which may cause the whole including the other layers to be easily peeled off from the substrate 2. Further, since the crystallinity of the diffusion preventing layer is not particularly limited, it may be formed by a film forming method such as a normal sputtering method.

When a bed layer is provided as the foundation layer 3, the bed layer has high heat resistance and is used for reducing interfacial reactivity, and is used for obtaining the orientation of a film disposed thereon. Such a bed layer is, for example, a rare earth oxide such as yttria (Y ₂ O ₃ ), and is exemplified by a compositional formula (α ₁ O ₂ ) _2x (β ₂ O ₃ ) _(1-x). it can. More specifically, Er 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 and the} like can be exemplified, and from these materials It may be a single layer structure or a multilayer structure. The bed layer is formed by a film forming method such as a sputtering method, and has a thickness of 10 to 100 nm, for example. Further, since the crystallinity of the bed layer is not particularly limited, it may be formed by a film forming method such as a normal sputtering method.
The underlayer 3 may be a two-layer structure including a diffusion prevention layer and a bed layer, or may be a single layer structure made of either of these layers. In some cases, the underlayer 3 may be omitted. When the base layer 3 is omitted, an alignment layer 4 described below is formed directly on the substrate 2.

The orientation layer 4 may be either a single layer structure or a multilayer structure, and is formed by the IBAD method described below to control the crystal orientation of the cap layer 5 laminated thereon, and is biaxially oriented. It is formed from an intermediate thin film of perovskite oxide.
In this embodiment, as the intermediate thin film, ABO ₃ (where A is selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) In the case of one or more selected, B is one or more selected from Al, Ti, Cr, Mn, Fe, Co, Ni, and A is in Ca, Sr, Ba, Pb In the case of one or more selected from B, B is one or more selected from Ti, Mn, Fe, Sn, Mo, Zr, Hf, and when A is Li, B is Nb The alignment layer 4 is formed from an intermediate thin film of a perovskite type oxide. Among these oxides having a perovskite structure, any one of LaNiO ₃ , LaMnO ₃ , LaAlO ₃ , PrMnO ₃ , SrTiO ₃ , BaTiO ₃ , BaZrO ₃ , and SrHfO ₃ can be selected.
As an example, the orientation layer 4 is configured as a polycrystalline thin film in which a plurality of crystal grains 4a are joined via grain boundaries as shown in an enlarged view in FIG. 1B, and within each crystal grain 4a, the crystal grains The perovskite crystals constituting 4a have their crystal axes c-axis oriented perpendicular to the surface of the substrate 2 (or the surface of the underlayer 3) individually, and the a-axis of the perovskite crystal is almost in one direction. They are arranged so that they are aligned (for example, the angle of dispersion of crystal axes indicated by symbol K in FIG. 1C is aligned within a predetermined range).

If this alignment layer 4 is formed with a good crystal orientation by the IBAD (Ion-Beam-Assisted Deposition) method, the crystal orientation of the cap layer 5 formed thereon can be set to a good value. As a result, the oxide superconducting layer 6 formed on the cap layer 5 can be made to have good crystal orientation, and the oxide superconducting layer 6 that can exhibit more excellent superconducting characteristics can be obtained.
The alignment layer 4 made of a polycrystalline thin film of the above-described perovskite oxide is particularly suitable because the value of the half-value width Δφ (FWHM) of crystal axis dispersion, which is an index representing the degree of crystal orientation in the IBAD method, can be reduced.

The cap layer 5 is epitaxially grown on the surface of the alignment layer 5 and then undergoes a process of grain growth (overgrowth) in the lateral direction (plane direction), and crystal grains are selectively grown in the in-plane direction. Those formed are preferred. Such a cap layer 5 may have a higher in-plane orientation degree than the orientation layer 4.
The material of the cap layer 5 is not particularly limited as long as it can exhibit the above functions, but specific examples of preferable materials include CeO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Gd ₂ O ₃ , and Zr _2. Examples thereof include O ₃ , Ho ₂ O ₃ and Nd ₂ O ₃ . When the material of the cap layer 5 is CeO ₂ , the cap layer may include a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.
The cap layer 5 can be formed by a PLD method (pulse laser deposition method), a sputtering method, or the like, but it is preferable to use the PLD method from the viewpoint of obtaining a high film formation rate. The film formation conditions for the CeO ₂ 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 5 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 6 can be widely applied to an oxide superconductor having a generally known composition, such as REBa ₂ Cu ₃ O _y (RE is Y, La, Nd, Sm, Er, Gd, etc. A material made of a material that represents a rare earth element, specifically, Y123 (YBa ₂ Cu ₃ O _y ) or Gd123 (GdBa ₂ Cu ₃ O _y ) can be exemplified. Further, other oxide superconductors, for _{example, Bi 2 Sr 2 Ca n-} 1 Cu n for _{O 4 + 2n + δ} becomes may be used in compositions such as those made of other oxide superconductors having high critical temperatures representative Of course.
The oxide superconducting layer 6 is laminated by physical vapor deposition such as sputtering, vacuum vapor deposition, laser vapor deposition, or electron beam vapor deposition; chemical vapor deposition (CVD); coating pyrolysis (MOD). Among them, the laser vapor deposition method is preferable. The oxide superconducting layer 6 has a thickness of about 0.5 to 5 μm and preferably a uniform thickness.

The first stabilization layer 7 formed so as to cover the upper surface of the oxide superconducting layer 6 is made of Ag, and is formed by a vapor phase method such as sputtering, and has a thickness of about 1 to 30 μm. It is said.
The second stabilization layer 8 is made of a highly conductive metal material, and when the oxide superconducting layer 6 is about to transition from the superconducting state to the normal conducting state, the oxide stabilizing layer 7 together with the first stabilizing layer 7 6 functions as a bypass to which current of 6 commutates. The metal material constituting the second stabilization layer 8 is not particularly limited as long as it has good conductivity, but copper alloys such as copper, brass (Cu—Zn alloy), Cu—Ni alloy, It is preferable to use a material made of a relatively inexpensive material such as stainless steel. Among them, copper is preferable because it has high conductivity and is inexpensive. When the oxide superconducting conductor 1 is used for a superconducting fault current limiter, the second stabilization layer 8 is made of a high resistance metal material, and a Ni-based alloy such as Ni—Cr can be used.
The thickness of the 2nd stabilization layer 8 is not specifically limited, Although it can adjust suitably, it is preferable to set it as 10-300 micrometers.
The covering layer 10 is made of a resin insulating layer and is formed so as to cover the entire circumference of the oxide superconducting laminate 9 by means such as winding an insulating tape.

The alignment layer 4 by the IBAD method provided on the oxide superconducting conductor 1 having the above structure is formed by, for example, the apparatus shown in FIG.
The apparatus shown in FIG. 2 has a running system (not shown) for running the tape-like substrate 2 provided with the base layer 3 in the longitudinal direction, and the surface thereof is inclined with respect to the surface of the substrate 2. A target 21 opposed to each other, a sputter beam irradiation device 22 that irradiates the target 21 with ions, and an ion source that irradiates ions (mixed ions of rare gas ions and oxygen ions) obliquely with respect to the surface of the substrate 2. These devices are arranged in a vacuum vessel (not shown). In FIG. 2, reference numeral 2A indicates a substrate holder, and reference numeral 21A indicates a target holder.

The vacuum container 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. The vacuum container is connected to a gas supply means for introducing a carrier gas and a reaction gas into the vacuum container and an exhaust means for exhausting the gas in the vacuum container. In FIG. 2, these supply means and exhaust means are connected to each other. For brevity, only the arrangement relationship of each device is shown.
As an example of the configuration of the ion source 23, as shown in FIG. 3, the container 24 includes an extraction electrode 25, a filament 26, and an introduction pipe 27 for Ar gas. A device capable of irradiating ions such as in parallel in a beam shape can be used. In the ion source 23 shown in FIG. 3, the assist ion beam voltage and the assist ion beam current value can be appropriately adjusted to adjust the energy of the assist ion beam.

  In order to form the alignment layer 4 on the base layer 3 of the substrate 2 by the apparatus shown in FIGS. 2 and 3, the inside of the vacuum vessel is set to a reduced pressure atmosphere, and the sputter beam irradiation apparatus 22 and the ion source 23 are operated. Thereby, the target 21 can be irradiated with ions from the sputter beam irradiation apparatus 22, and the constituent particles of the target 21 can be knocked out or evaporated to deposit the target constituent particles on the underlayer 3. At the same time, an assist ion beam of mixed ions of rare gas ions and oxygen ions is radiated from the ion source 23, and a predetermined incident angle (with respect to the surface of the base layer 3 (a film formation surface above the substrate 2)) ( Irradiation is performed at an incident angle θ) with respect to the normal of the film formation surface on the substrate.

When the IBAD method is performed using the apparatus shown in FIGS. 2 and 3, the incident angle θ of the assist ion beam is in the normal line of the film formation surface of the substrate 2 (the upper surface of the underlayer 3 in this embodiment). On the other hand, it is preferably set within a range of 40 to 75 °.
Further, when the ion beam voltage is set to, for example, 300 V as the operating condition of the ion source that radiates the assist ion beam, the ion beam current value can be selected from a range of 300 mA to 650 mA.
The assist ion beam voltage is preferably in the range of 200 to 600V. By setting the assist ion beam voltage within this range, the half width of crystal axis dispersion of the obtained alignment layer 4 can be further reduced.
About the film-forming temperature at the time of forming the alignment layer 4, the range of 300-1000 degreeC can be selected.

  As described above, by irradiating ions at a predetermined incident angle while depositing the constituent particles of the target 21 on the surface of the underlayer 3, the specific crystal axis of the formed sputtered film has an ion incident direction. The c-axis of the perovskite-type oxide crystal is oriented in a direction perpendicular to the surface of the metal substrate, and the a-axes (or b-axis) of the perovskite-type oxide crystals are in a certain direction in the plane. Oriented (biaxially oriented). For this reason, the perovskite-type oxide alignment layer 4 formed on the underlayer 3 by the IBAD method can obtain a high degree of in-plane alignment.

Below, the characteristic in case the orientation layer 4 is comprised from a perovskite type oxide is demonstrated.
Table 1 below shows the substance name and lattice constant (Å) of the material constituting each layer of the oxide superconductor, shows the lattice mismatch between each substance and CeO ₂ constituting the cap layer, and oxidizes each substance. The relationship of lattice mismatch with Gd ₁ Ba ₂ Cu ₃ O _7-x (hereinafter abbreviated as GdBCO), which is an example of a material constituting the material superconducting layer 6, is shown in comparison.

"Table 1"
Substance name Lattice constant (Å) Lattice with CeO ₂ Lattice with GdBCO
Mismatch Mismatch MgO 4.21 28.5 -8.3
GZO 5.25 3.0 3.98
SrTiO ₃ 3.90 -1.9 -1.03
BaTiO ₃ 3.99 -4.1 -3.26
LaMnO ₃ 3.89 -1.75 -0.78
LaNiO ₃ 3.86-0.90 0
LaAlO ₃ 3.78 1.2 2.12
PrMnO ₃ 3.82 0.13 1.05

In Table 1, the lattice constant of CeO ₂ was calculated at 5.41 or 3.825 (45 ° rotation: half the root (in the case of perovskite)). GdBCO lattice constant: 3.86 (To be exact GdBCO is orthorhombic and is the average of the a-axis and b-axis.) Perovskites other than SrTiO ₃ are not cubic but quasi-cubic. The lattice constant was estimated.
The lattice mismatch (lattice mismatch) in Table 1 was calculated according to the equation (ae-as) / as × 100% (ae: the lattice constant of the epitaxial layer (upper layer), as: the lattice constant of the (lower layer) of the substrate). .

As shown in the comparison results in Table 1, the lattice mismatch with CeO ₂ is much less in the perovskite oxides SrTiO ₃ , BaTiO ₃ , LaMnO ₃ , LaNiO ₃ , LaAlO ₃ and PrMnO ₃ than in MgO. If the crystal is grown with good crystal orientation by the method, it can be assumed that the orientation layer 4 having excellent orientation can be formed.

  Here, as described above, when the cap layer 5 is formed on the orientation layer 4 having good orientation, the cap layer 5 can also obtain good orientation, and on the cap layer 5. When the oxide superconducting layer 6 is formed, the oxide superconducting layer 6 is also crystallized so as to match the orientation of the cap layer 5. Therefore, the oxide superconducting layer 6 formed on the cap layer 5 is hardly disturbed in crystal orientation, and in each of the crystal grains constituting the oxide superconducting layer 6, the thickness of the substrate 2 is reduced. The c-axis that hardly allows electricity to flow is oriented in the vertical direction, and the a-axis or the b-axis is oriented in the length direction of the substrate 2 (biaxially oriented). Therefore, the obtained oxide superconducting layer 6 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 can be obtained.

  The oxide superconducting conductor 1 formed as described above includes a perovskite oxide orientation layer 4 having excellent crystal orientation formed by an IBAD method, and has a crystal orientation through a cap layer 5 thereon. Since the oxide superconducting layer 6 is excellent, it exhibits excellent superconducting properties.

FIG. 4 shows an example of an apparatus suitable for use in manufacturing a long oxide superconductor by carrying out the IBAD method.
As shown in FIG. 4, an ion beam assisted sputtering apparatus 30 applied when manufacturing a long oxide superconductor is provided with a target 32 so as to face a film forming region 31 where a tape-like substrate or the like is arranged. The sputter ion source source 33 is disposed so as to face the target 32 in an oblique direction, and faces the normal line of the film forming region 31 at a predetermined angle (for example, 55 °) from the oblique direction. Thus, the assist ion source source 35 is arranged.
The ion beam assisted sputtering apparatus 30 of this example is a film forming apparatus provided in a form accommodated in a vacuum chamber, and includes a first roller group 38 and a second roller group in which a tape-like base material 37 is disposed so as to face each other. For example, a structure in which the film is reciprocally wound around the film 39 and reciprocated in the film formation region 31 can be exemplified.

The ion source sources 33 and 35 applied in this embodiment are configured to include an extraction electrode, a filament, and an introduction tube such as Ar gas inside the container, as in the above-described embodiment, and the tip of the container Can be irradiated in parallel with a beam.
The vacuum chamber 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. 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 the figure, the supply means and the exhaust means are omitted. Only the arrangement relationship of each device is shown.
The target 32 used here can be a target having a composition suitable for forming the intermediate thin film 4 of the above-described material.
The IBAD method is performed by using the ion beam assisted sputtering apparatus 30 having the structure shown in FIG. 4, and the target perovskite oxide intermediate thin film 4 is long, for example, a long base 37 at a level of several tens to several hundreds of meters. This can be applied to the production of a long oxide superconducting conductor by forming a film thereon.

"Example 1"
A tape-like surface-smooth base material having a width of 10 mm, a thickness of 0.1 mm, and a length of 1000 mm made of Hastelloy C276 (trade name of Haynes Corp., USA) is prepared, and the surface is cleaned, and then Al ₂ O ₃ is sputtered. A diffusion prevention layer (thickness 150 nm) and a Y ₂ O ₃ bed layer (thickness 20 nm) were laminated.
Next, an alignment layer of LaNiO ₃ having a thickness of 50 nm was formed on the surface of the bed layer of the tape substrate using a target of LaNiO ₃ by using an ion beam assisted sputtering method described below.
The IBAD method is performed using the ion beam assisted sputtering apparatus having the structure shown in FIG. 2, and the incident angle of the assist ion beam is set to 55 ° with respect to the normal line of the film-form surface of the tape-like substrate. Was set at 500 ° C. and the film formation time was about 400 seconds.

Further, the assist ion beam voltage was fixed at 300 V, and the assist ion beam current value was changed to 300 mA, 350 mA, 400 mA, 450 mA, 500 mA, 550 mA, 600 mA, and 650 mA to prepare a plurality of samples.
Further, a CeO ₂ cap layer having a thickness of 300 nm is laminated on the obtained alignment layer at 800 ° C. by a laser deposition method, and the obtained CeO ₂ cap layer is subjected to X-ray measurement to be a diffraction test image. FIG. 5 shows the results of obtaining a CeO ₂ (220) positive dot diagram and obtaining the half-value width (Δφ) of crystal axis dispersion.

A CeO ₂ (220) positive electrode dot diagram of a sample obtained with an assist ion beam voltage of 300 V, an assist ion beam current value of 500 mA, and a deposition time of 400 seconds is shown in FIG. The values of Δφ obtained were 300 mA: 24.4 °, 350 mA: 23.4 °, 400 mA: 23.1 °, 450 mA: 22.6 °, 500 mA: 21.9 °, 550 mA: 22.2 °, 600 mA: 25 °, 650 mA: 25.2 °.
In addition, since the CeO ₂ cap layer crystal is epitaxially grown on the crystal of the alignment layer, the crystal orientation of the cap layer is excellent, which means that the crystal orientation of the alignment layer as the base is also excellent. Proof. Since the orientation layer is thin as a condition of the present embodiment, a CeO ₂ cap layer is laminated so that positive point measurement data by X-ray diffraction can be easily obtained.

As shown in FIG. 5, the Δφ of the sample manufactured at 300 V, 500 mA, and 500 ° C. is 21.9 °, and the (220) positive pole figure of the cap layer obtained under the conditions is four times symmetrical as shown in FIG. Sex appeared clearly.
Therefore, it was found that an alignment layer having a perovskite structure exhibiting 4-fold symmetry by the IBAD method under the above-described conditions and having excellent crystal orientation can be formed.
In the assist ion beam condition, when the assist ion beam voltage is 300 V, in order to make Δφ smaller, an appropriate range is selected from the relationship shown in FIG. I was able to.

Next, in order to investigate the temperature dependence when forming an alignment layer having a perovskite structure by the IBAD method, the assist ion beam current value is 500 mA, the assist ion beam voltage is 300 V, the deposition time is 400 seconds, and the assist ion beam incident angle. Was fixed at 55 °, and the CeO ₂ (220) positive electrode diagram of the sample obtained when the film formation temperature was 300 ° C., 400 ° C., 500 ° C., and 550 ° C. under these conditions was found to be 300 ° C. At 400 ° C., 4-fold symmetry was not observed, and an unoriented sample was obtained as shown in FIG. On the other hand, in the case of film formation at 500 ° C., four-fold symmetry is seen as shown in FIG. 6, Δφ = 21.9 ° is obtained, and the sample formed at 550 ° C. also has four-fold symmetry. Δφ = 20.4 ° was obtained.
From the results shown in FIGS. 6 and 7, it is desirable that the film formation temperature is 500 ° C. or higher in order to obtain an alignment layer exhibiting 4-fold symmetry in the positive dot diagram, and better alignment can be obtained by further increasing the film formation temperature. It can be assumed that it will be obtained. .

Next, in order to investigate the film formation time dependency in forming an alignment layer having a perovskite structure by the IBAD method, the assist ion beam current value is 500 mA, the assist ion beam voltage is 300 V, the film formation temperature is 500 ° C., the assist ion beam CeO ₂ (220) positive electrode dot diagrams of the samples obtained when the incident angle was fixed at 55 ° and the film formation time was 2000 seconds were obtained and shown in FIG.
Even when the film formation time was set to 2000 seconds, as shown in FIG. 8, an alignment layer having a perovskite structure exhibiting 4-fold symmetry in the positive electrode dot diagram could be obtained. When the film thickness of the obtained alignment layer was measured, in the case of the sample shown in FIG. 6, an alignment layer with a film thickness of 50 nm was obtained at a film formation time of 400 seconds, and an alignment layer with a film thickness of 250 nm at a film formation time of 2000 seconds. A layer was obtained. From the comparison between the result shown in FIG. 8 and the result shown in FIG. 6, the orientation layer of the 250 nm-thickness alignment layer has improved orientation rather than the 50 nm-thickness. Therefore, in the perovskite oxide alignment layer of the present invention, Even if the film thickness is increased to a level of 250 nm, it has a feature that the orientation is excellent.
For this reason, even when an orientation layer is uniformly formed on a long substrate, the orientation layer is excellent in orientation even if the orientation layer is formed to increase the film thickness to a certain extent to ensure uniformity of the film quality over the entire length. It can be seen that can be formed.

Next, in order to investigate the influence of the underlayer in the case of forming a perovskite structure alignment layer by the IBAD method, a test for directly forming a perovskite structure alignment layer (LaNiO ₃ layer) on a Hastelloy substrate, orientation layers having a perovskite structure on the formation of the _{the Al} 2 _{O 3} layer on the manufacturing of the substrate and the test to form the (LaNiO ₃ layers), _{the Al} 2 _{O 3} layer on the Hastelloy substrate and _Y 2 _{O 3} layer Then, a test for forming an orientation layer (LaNiO ₃ layer) having a perovskite structure was performed, and a CeO ₂ (220) positive electrode dot diagram of the sample obtained in each was obtained. The conditions for forming the alignment layer were set to an assist ion beam current value of 400 mA, an assist ion beam voltage of 400 V, a film formation time of 400 seconds, an assist ion beam incident angle of 55 °, and a film formation temperature of 500 ° C.
As a result, in the sample in which the alignment layer is directly formed on the Hastelloy base material, Δφ = 20.1 ° is obtained, and in the sample in which the orientation layer is formed on the Hastelloy base material via the Al ₂ O ₃ layer, Δφ = 17.5 ° was obtained, and Δφ = 19.8 ° was obtained in the sample in which the alignment layer was formed on the base material made of Hastelloy through the Al ₂ O ₃ layer and the Y ₂ O ₃ layer.

Furthermore, an oxide superconducting layer having a composition of GdBa ₂ Cu ₃ O _7-x having a thickness of 1.0 μm is formed on the cap layer by the pulse laser deposition method in each sample in which the four-fold symmetry is obtained in the above positive electrode diagram. Formed.
Next, for each sample, a first stabilizing layer made of Ag having a thickness of 8 μm is formed on the upper surface of the oxide superconducting layer by sputtering, and a Cu stabilizing layer tape having a thickness of 300 μm is further applied thereon. Each oxide superconducting conductor was obtained.
When the plurality of oxide superconducting conductor samples were immersed in liquid nitrogen and subjected to an energization test, a critical current density (Jc) of 1 × 10 ⁵ to 2 × 10 ⁵ A / cm ² was obtained in any sample.

  The present invention provides an oxide superconducting conductor that can be used for, for example, an oxide superconducting power transmission line or a coil winding for a superconducting magnet.

  DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting conductor, 2 ... Base material, 3 ... Underlayer, 4 ... Orientation layer, 4a ... Crystal grain, 5 ... Cap layer, 6 ... Oxide superconducting layer, 7 ... 1st stabilization layer, 8 ... Second stabilization layer, 9 ... oxide superconducting laminate, 10 ... insulating coating layer, 21 ... target, 21A ... target holder, 22 ... ion gun, 23 ... ion source, 24 ... container, 25 ... grid, 26 ... filament 27 ... Gas introduction pipes.

Claims (3)

  An oxide superconducting conductor comprising: a base material; an intermediate thin film laminated on the base material directly or via an underlayer; and an oxide superconducting layer laminated directly or via a cap layer on the intermediate thin film. Thus, when the intermediate thin film is formed on the substrate by particle deposition or on the substrate via an underlayer, the intermediate thin film is formed while irradiating an assist ion beam from an oblique direction on the film formation surface above the substrate. An intermediate thin film of perovskite oxide formed by an ion beam assisted film-forming method, wherein two of the crystal axes of the plurality of crystals constituting the intermediate thin film are oriented, indicating the degree of orientation of these crystals An oxide superconducting conductor, characterized in that it is an intermediate thin film exhibiting 4-fold symmetry in a positive electrode diagram. The intermediate thin film is an ABO ₃ type perovskite oxide (A is selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) In the case of one or more selected, B is one or more selected from Al, Ti, Cr, Mn, Fe, Co, Ni, and A is Ca, Sr, Ba, Pb In the case of one or more selected from among B, B is one or more selected from Ti, Mn, Fe, Sn, Mo, Zr, and Hf, and when A is Li, B is 2. The oxide superconducting conductor according to claim 1, wherein the oxide superconducting conductor is Nb. The oxide superconducting conductor according to claim 1, wherein the intermediate thin film is made of either LaNiO ₃ or LaMnO ₃ .

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