JP2000322951A - Manufacture of oxide-based superconductive structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an oxide-based superconductive structure capable of manufacturing a superconductive layer having a high critical temperature and high critical current density particularly in a magnetic field at a practically possible deposition rate and in a condition that there is no risk of the occurrence of a crack. SOLUTION: This method is used to manufacture an oxide-based superconductive structure by forming a superconductive layer 8 formed of an oxide-based superconductor on a base material 2. The method comprises a pseudo liquid layer forming process for forming a pseudo liquid layer 6 by the use of material having a melting point lower than that of the oxide-based superconductor, and a superconductive layer forming process for depositing the superconductive layer 8 by the use of the oxide-based superconductor after the pseudo liquid layer deposition process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide superconducting structure by forming a superconducting layer made of an oxide superconductor on a substrate. In particular, the liquid nitrogen temperature 77
A method for producing a superconducting structure showing a high critical current density (Jc) even in a magnetic field by compounding an intermediate layer that enables high-speed deposition of a superconducting layer made of a superconducting oxide showing a superconducting state at K or higher. About. The present invention makes a significant contribution in cost to conventional superconducting magnets, superconducting NMR devices, superconducting MRI devices, synchrotron devices, and magnetic separation devices.

[0002]

2. Description of the Related Art In 1986, a copper oxide-based La-Ba-Cu-O perovskite-based superconductor having a high critical temperature was discovered (for example, Japanese Patent Application Laid-Open No. Sho 63-260853).
No., etc.), and the critical temperature for the next year was Y-Ba-Cu-O (YBCO) (MKWu, JRAshbum, CJTorng, YQW
and and CWChu: Phys. Rev. Lett. 58 (1987) 908) were found to be 90K class superconductors for which the application technology of high-temperature superconductors using liquid nitrogen as a refrigerant is expected.
And Bi-Sr-Ca-Cu- having a higher critical temperature
O system (Tc: 110K, H.Maeda, Y.Tanaka, M.Fukutom
i and T. Asano: Jpn. J. Appl. Phys. 27 (1988) L209
), Tl-Ba-Ca-Cu-O system (Tc: 120
K, ZZSheng, and AMHermann: Nature 322 (1988) 5
5) R & D on new superconductors was remarkable.

[0003] A general method for producing these superconductors is as follows.
The raw material powder such as a metal oxide or a carbon salt in the starting composition is repeatedly mixed and pulverized, and heat-treated at a temperature of 800 to 1100 ° C. for several minutes to several hundred hours in air, oxygen, or a reducing atmosphere. Is performed.

However, the above Y-Ba-Cu-O, Bi-
A multi-layered perovskite-type superconductor represented by Sr-Ca-Cu-O, Tl-Ba-Ca-Cu-O, etc.
Each layer has different characteristics.

[0005] One of the characteristics of the above-mentioned multi-layered perovskite type is that it has a large anisotropy in conductivity due to its multi-layered crystal structure. For this reason, in a superconducting film in which the crystal grain direction is disordered, the conductive surface is not connected, and the critical current density in a zero magnetic field is considerably low (for example, 10 ³ A / cm ² or less). Further, when a heterogeneous phase exists between crystal grains, the heterogeneous phase becomes a weak junction, and the critical current density is further reduced, which has been a great obstacle when applied to a superconducting coil or the like.

In order to increase the critical current density, for example, as a method of orientation for growing the intermediate layer in the same crystal direction, Iijima et al. Proposed that an yttria-stabilized zirconia (YSZ) layer be oriented on a Hastelloy substrate. And a superconducting film is grown on the YSZ layer by ion beam assisted deposition (IBAD) (Proceedingof
4th international symposium Superconducting (Spri
nger, Tokyo, 1991).

Further, as a method for producing a crystal on a base material with the crystal direction aligned, Kawashima et al.
ng of 8th international symposium Superconducting
(Springer, Tokyo, 1996) by Ito et al.
₃ materials (Y.Ito, Y.Yoshida, M.Iwata, Y.Takai, I.Hirab
ayashi: Physica C 288 (1997) pp 178), a method of forming a superconducting film on each ceramic single crystal wire has been proposed.

As a process for forming a wire of such a superconducting film, a thin film process such as a physical vapor method called a vacuum evaporation method or a sputtering method, or a chemical vapor method including a metal organic chemical vapor method (MOCVD method). Has been studied a lot.

[0009] However, the thin film process has a limit in the film forming speed, and it is impossible to manufacture a wire of a km class. for that reason,
It has been difficult to produce a superconducting wire of km class or more for producing a superconducting coil used in a system such as a superconducting magnet.

[0010]

As described in the above prior art, when an oxide-based superconductor is used as a superconducting wire and applied to a superconducting magnet, the crystal is grown while aligning the crystal orientations, and a higher speed is obtained. There is a demand for a film forming process capable of forming a film.

As a means for resolving these problems, a liquid phase epitaxial method (LPE method) in which growth proceeds with a liquid phase interposed and high-speed film formation is possible is considered as a promising process.

However, in the LPE method, Kawashima et al. (J. Kawashima, Y. Yamada, I. Hirabayashi: Physica C
306 (1998) p.114) reports that problems such as cracks in the superconducting film occur. As described above, in a thin film process such as a laser vapor deposition method or an MOCVD method, epitaxial growth is performed while aligning crystal orientations with a substrate. Improper.

Further, in a thick film process such as a plasma spraying method, although a film forming rate as a high-speed film forming process such as wire forming is increased, since an epitaxial growth is not performed while aligning crystal orientations, different phases are formed between crystal grains. It is said that there exists a problem that the heterojunction becomes weak junction and the critical current density becomes low.
a, T. Kanai, T. Kamo, S. Matsuda, R. Shiobara: Proceed
ing of 3rd international symposium Superconducting
(Springer, Tokyo, 1990).

In view of the above, the present invention provides a superconducting layer having a high critical temperature and particularly a high critical current density in a magnetic field at a film forming rate that can be practically used, and in a state where there is no possibility of cracking. An object of the present invention is to provide a method for manufacturing an oxide-based superconducting structure that can be manufactured.

[0015]

The present inventors have conducted various studies from various angles to achieve the above object, and as a result, have obtained new knowledge on the growth mechanism of the oxide-based superconducting film. After confirming that the mechanism has a great effect on high-speed film formation in a thin film process, the present inventors have conceived a method for manufacturing an oxide-based superconducting structure having the following structure.

In a method of manufacturing a superconducting structure of an oxide superconductor by forming a superconducting layer made of an oxide superconductor on a substrate, a pseudo liquid layer is formed of a substance having a lower melting point than that of the oxide superconductor. And a superconducting layer forming step of forming a superconducting layer with an oxide superconductor after the pseudo liquid layer forming step and the pseudo liquid layer forming step.

In the above-mentioned manufacturing method, it is preferable that a seed crystal layer forming step of forming a seed crystal layer with the same oxide as the superconducting layer is provided before the pseudo liquid layer forming step.

When the oxide superconductor contains Ba and Cu, the pseudo liquid layer is formed of an oxide containing the constituent elements of Ba and Cu.

[0019]

The operation and effect of the present invention are considered to be as follows.

We have determined that the substrate temperature of the superconductor is 750.
Considering growth at high temperatures of over ℃, Y. Yoshida
Appl. Phys. Lett., Vol. 69 pp. 845-847, (199
6) ". The known example is Ba-Cu-O
Is formed at a temperature of 800 ° C. or less,
In a CO film formation experiment, an excessive amount of Y is required at a substrate temperature of 750 ° C. or more, and a rapid expansion of the terrace width is observed at a substrate temperature of 750 ° C. or more. It is presumed that an extremely thin liquid layer (pseudo liquid layer) exists in the outermost surface layer. The concept of a quasi-liquid layer has been confirmed by T. Kuroda and Y. Furukawa in the crystal growth of ice (for example, T. Kuroda a
nd R. Lacmann: J. Crystal Growth 56 (1982) p189 and Furukawa Yoshizumi: Applied Physics 61 (1992) p776).

On the other hand, some layers of atoms of the structural phase transition occurring at a high temperature close to the melting point leave the lattice points to cause surface melting. This melting layer is a quasi-liquid layer (Quasi-Liquid layer).
). In the roughening transition, when the surface becomes rough, the difference in structure between the low index surface and the high index surface becomes inconspicuous, and the anisotropy of the surface free energy density and the growth rate disappears.

On the other hand, in the pseudo liquid layer, their anisotropy is maintained unless the interface between the layer and the crystal is roughened. The superconducting film can be considered as a quasi-liquid layer also from the viewpoint of maintaining the anisotropy of the film during the crystal growth process at a substrate temperature of 750 ° C. or more.

From the above, the growth of the YBCO film is performed at a substrate temperature of 7
At 50 ° C. or more, solid YBCO on the substrate and
Vapor-Liquid-Solid (VLS) proceeding in a state where each molecule of the gas phase (Vapor) and three phases of a liquid phase (Liquid) presumed to be Ba-Cu-O are mixed. ) It is presumed to be growth.

As described above, on the surface of the superconductor, the solid phase,
It has been confirmed that a liquid phase is generated at the interface of the gas phase. Although this phenomenon is particularly remarkably confirmed by the MOCVD method, such a phenomenon is also confirmed by controlling the film formation atmosphere in other thin film processes, for example, a laser vapor deposition method, a sputtering method, or the like.

The superconducting film grown on the base material cannot be grown by various conventional processes as described above, but is grown by epitaxial growth in which the crystal orientations are aligned, and for increasing the growth rate. The process can be performed by artificially controlling the liquid phase that precipitates at the solid / liquid interface during the growth of the superconducting film.

According to the present invention, it is possible to obtain a superconducting material at a high speed in which the superconducting property between the crystal grains of the oxide superconductor is prevented from deteriorating. Furthermore, the present invention is used for film formation of a large area, and can be applied to energy fields such as magnetic shields and superconducting coils.

That is, a superconducting system manufactured by the conventional superconducting technology, particularly a superconducting magnet, has been operated using liquid helium. By using the present invention, the operation can be performed using liquid nitrogen, so that the cost can be significantly reduced and the present invention is economically advantageous. The superconducting wire using the superconducting material according to the present invention enables operation of a superconducting system such as a superconducting magnet, an NMR apparatus, an MRI apparatus, a synchrotron radiation apparatus, and a magnetic separation apparatus using liquid nitrogen.

[0028]

DETAILED DESCRIPTION OF THE INVENTION A method for manufacturing an oxide-based superconducting structure by forming a superconducting layer comprising an oxide-based superconductor on a substrate is characterized by comprising the following steps (see FIG. 1). ). (1) Seed Crystal Layer Forming Step: This is a step of forming a superconducting seed crystal layer 4 on the base material 2 using an oxide superconductor.

As the substrate 2, a single crystal ceramic or a metal substrate having a lattice constant close to that of the superconductor, such as MgO, S
rTiO ₃ , yttrium stabilized zirconia, Ag base and Ag alloy base are used. Here, the Ag alloy base material includes a material containing Ti, Au, Pt, Pd, Cu, or the like in Ag.

The above-mentioned oxide-based superconductor is desirably in a superconducting state at a liquid nitrogen temperature of 77K or at a temperature of 64K or more which can be cooled by liquid nitrogen. In particular, the chemical composition of the oxide-based superconductor is LnBa ₂ Cu _3. O _7-y (However,
Ln: rare earth element excluding Ce, -0.5 ≦ y ≦ 0.2)
It is desirable that it is shown by. Rare earth element
More preferably, it is Y (yttrium) or Nd (neodymium).

The superconducting seed crystal layer is formed by a physical vapor phase method or a chemical vapor phase method, and has a thickness of 0.01 to
The thickness is 0.5 μm, preferably 0.1 to 0.3 μm. If the film thickness is too thin, it is difficult to secure the film forming rate and film forming orientation in the superconducting layer film forming step as a subsequent step,
The film formation time of the seed crystal layer increases, and the productivity decreases.

The physical vapor phase method includes a vacuum deposition method (resistance heating, arc evaporation, laser heating, high frequency heating, electron beam heating), a sputtering method (two-pole DC glow discharge,
Polar DC glow discharge, bipolar RF glow discharge), ion plating (Matox method, RF excitation method, multi-cathode method, probe method, cluster ion beam method), and the like. Among these, the laser vapor deposition method and the sputtering method are easier to operate than other physical vapor phase methods,
It is also desirable because it has a track record.

As the chemical vapor method, MOCVD is used.
Method enables stable supply of oxide-based superconducting structures,
desirable. In the MOCVD method, the target material is not used, the evaporation flow rate of each composition raw material is stable, and an oxide-based superconducting structure having a uniform composition can be obtained.

For example, the conditions for laser deposition are as follows: substrate temperature: 750 ° C. or higher, preferably 800 to 1000
° C., O ₂ partial pressure: 1.5 Pa or less, preferably 1.0 to 0.
8 Pa, more desirably 0.8 to 0.3 Pa, laser oscillation frequency (RR: Repetition Rate): 200 to 10 Hz, desirably 100 to 10 Hz, and film formation (deposition) time: 10 to 1
min, preferably 5 to 1 min.

The conditions for sputtering (two-pole RF glow discharge) are as follows: substrate (substrate) temperature: 750 ° C. or higher, preferably 800 to 1000 ° C., O ₂ partial pressure: 1.5 Pa or lower, preferably 1.0 ~ 0.8 Pa, more preferably 0.8 ~ 0.
3 Pa, film formation time: 10 to 1 min, preferably 5 to 1 min
And

In the case of MOCVD, the conditions are as follows.
Temperature: 750 ° C. or higher, preferably 800 to 1000 ° C.
O ₂ partial pressure: 1.33 kPa or less, preferably 0.8 kPa or less, more preferably 0.3 kPa or less, film formation time: 90
~ 15 min, preferably 60 ~ 30 min.

In the seed crystal layer forming step, the substrate temperature is usually 750 ° C. or higher (preferably 800 ° C. or higher), but after forming the film at a temperature lower than 750 ° C., for example, 500 ° C. or lower, The heat treatment may be performed at 750 ° C. or more (preferably 800 ° C. or more) at the same time as the pseudo liquid layer film forming step.

(2) Pseudo liquid layer film forming step: After the seed crystal layer forming step, the pseudo liquid layer has some of the constituent elements of the oxide superconductor,
In this step, the pseudo liquid layer 6 is formed of an oxide having a melting point lower than that of the oxide superconductor.

As the oxide, specifically, the chemical composition ratio is BaCu _x O _z (where 1.3 ≦ x ≦ 2.5,
1.65 <z ≦ 3.5, preferably 1.8 ≦ x ≦ 2.
2), and the pseudo liquid layer formed of BaCu _x O _z further contains Ag in an amount of 1 to 20% (preferably 2 to 10%) of the total number of moles of BaCu _x O _z. Or the chemical composition ratio is BaCu _x O _za X _a (where 1.3 ≦ x ≦ 2.5, 1.65−a / 2 ≦ z ≦
3.5-a / 2, 0.01 <a ≦ 0.2, X: F, C
It is preferable that the compound is represented by l, Br or I) because the melting point of the oxide is lowered. In particular, as X (halogen), F is desirable.

Here, even if x is less than 1.3, x is 2.5
Even above this, the melting point increases.

If the content of Ag is less than 1%, it is difficult to expect a decrease in the melting point of the oxide, and if the content of Ag exceeds 20%, no further effect can be expected.

The pseudo liquid layer is formed by a physical vapor phase method or a chemical vapor phase method, and has a thickness of 0.005 to 0.5.
05 μm (50 to 500 A), desirably 0.01 to
It is 0.05 μm. If the film thickness is too small, it is difficult to secure the film forming speed and film forming orientation in the subsequent superconducting layer film forming step, and if it is too thick, the film forming time of the pseudo liquid layer increases, resulting in an increase. Productivity decreases.

In addition, when Ag is added, it is usually performed by another film forming method, and the film forming method is preferably sputtering. The sputtering conditions at this time were as follows:
5 to 1.0 Pa, substrate temperature: room temperature.

As the physical vapor phase method and the chemical vapor phase method, those exemplified above can be used. However, from the viewpoint of productivity, a film forming method similar to that used for forming the seed crystal layer is usually used. It is desirable to adopt it.

The conditions of each of the above-mentioned film forming methods are as follows:
Normally, they are almost the same except for the time.

(3) Superconducting layer forming step: This is a step of forming a superconducting layer with an oxide superconductor after the pseudo liquid layer forming step.

As the oxide-based superconductor, those used in the seed crystal layer forming step can be used, and usually those having the same composition are used.

The pseudo liquid layer is formed by a physical vapor phase method or a chemical vapor phase method, and has a thickness of 0.5 to 3 μm.
Preferably, it is 1-2 μm. If the film thickness is too small, it is difficult to obtain sufficient superconducting properties (particularly, critical current density) for the superconducting structure. Conversely, if the film thickness is too large, the time required for forming the superconducting layer increases, resulting in production. Is reduced.

As the above-mentioned physical vapor phase method and chemical vapor phase method, those exemplified above can be used, but usually from the viewpoint of productivity,
It is desirable to employ the same type of film forming method as used for forming the seed crystal layer.

The conditions of each of the above-mentioned film forming methods are as follows:
Normally, they are almost the same except for the time.

The superconducting structure manufactured by the method of the present invention is
A sectional view as shown in FIG. That is, as shown in FIG. 1, the oxide superconductor projected on the pseudo liquid layer 6 formed on the seed crystal layer 4 formed on the base material 2 diffuses through the pseudo liquid layer 6. As a result, the superconducting layer 8 is formed on the seed crystal layer 4.

FIG. 3 is a model of the film formation rate in the case of a thin film process reported conventionally and the film formation rate of a film obtained by the method of the present invention.

The superconducting structure manufactured by the method of the present invention is
By processing into a superconducting coil shape and combining it with equipment such as a power supply and a refrigerant tank such as liquid nitrogen, it is possible to produce superconducting systems such as superconducting magnets, NMR equipment, MRI equipment, synchrotron radiation equipment, magnetic separation equipment, etc. Becomes

[0054]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.
The film thicknesses described below were measured by inductively coupled plasma emission spectroscopy (ICP method).

<Example 1> (1) Sputtering (two-pole RF glow) on a rolled Ag tape base material
Discharge), YBa _Two Cu_Three O_7-y (-0.5 ≦ y ≦
0.2 (hereinafter the same), a seed crystal layer of oxide superconductor)
A film was formed. The sputtering conditions are as follows: target: YBa_Two Cu
_Three O_7-y , Output: 200W, degree of vacuum: 1.5Pa, target
Cut / substrate distance: 4 mm, substrate temperature: 700 ° C, film formation
Time: 3 hours. The thickness of this seed crystal layer is 0.2 μm.
there were.

(2) A pseudo liquid layer of Ba ₃ Cu ₅ O _z (0 <z ≦ 2, non-conductive metal oxide) was formed on the seed crystal layer by laser vapor deposition. Laser deposition conditions were as follows: target: Ba ₃ Cu ₅ O _z (0 <z ≦ 2, powder mixing method), O ₂ partial pressure: 26.6 Pa (200 mTorr), laser energy density: ² J / cm ² , RR: 100 Hz The distance between the target and the substrate was 40 mm, the substrate temperature was 850 ° C., and the film formation time was 2 minutes. The thickness of this pseudo liquid layer is 0.0
It was 2 μm.

(3) Subsequently, in the laser vapor deposition method,
YBa ₂ C under the same conditions except that the film formation time was 10 min.
A superconducting layer of u ₃ O _7-y was formed. The thickness of the superconducting layer was 1.5 μm (film formation rate: 0.15 μm / mi).
n).

In order to confirm the crystal orientation of the superconducting structure (composite), a pole measurement by an X-ray diffraction method was performed. It is confirmed that the crystal direction of the superconductor grows along the a-axis and the b-axis. In order to measure Tc, terminals were connected to the surface of the superconductor with Au and Ag paste, and current-voltage measurement was performed by a DC method using liquid nitrogen as a refrigerant by a four-terminal method. Jc at the liquid nitrogen temperature was determined from the critical current (Ic) when the voltage between the measurement terminals was 1 μV / cm. As a result, Tc was 87 K and Jc was 2 × 10 ⁵ A / cm ^{2 in} a zero magnetic field at a temperature of 77 K.

Example 2 (1) NdB was deposited on a MgO single crystal substrate by laser evaporation.
A seed crystal layer of a ₂ Cu ₃ O _7-y (oxide-based superconductor) is formed. The film forming conditions are as follows: target: NdBa ₂ Cu ₃ O
_7-y (powder mixing method), O ₂ partial pressure: 2.66 Pa (20 mTo
rr), target / substrate distance: 40 mm, laser energy density: ² J / cm ² , RR: 30 Hz, substrate temperature: 8
00 ° C., film formation conditions: 5 min. The thickness of this seed crystal layer was 0.1 μm.

[0060] (2) by laser evaporation on the seed crystal _{layer, Ba 3 Cu 7 O za F} a (0.2 <z ≦ 2, a =
0.2) is formed. Laser deposition conditions target:
_{Ba 3 Cu 7 O za F a} ( powder mixing method), O ₂ partial pressure: 1
3.3 Pa (100 mTorr), target / substrate distance: 4
0 mm, laser energy density: 3 J / cm ² , RR:
50 Hz, substrate temperature: 850 ° C., and film formation time: 10 min. The thickness of this seed crystal layer was 0.01 μm.

(3) In the laser vapor deposition method, NdBa ₂ Cu ₃ O was used under the same conditions except that the film formation time was 5 minutes.
_{A 7-y} superconducting layer was formed. The thickness of this superconducting layer is 1.
It was 3 μm (film formation rate: 0.26 μm / min).

The crystal orientation of the superconducting structure (composite) was measured at the extreme points by the X-ray diffraction method. As a result, it was confirmed that the crystal direction of the superconductor grew along the a-axis and the b-axis. Is done. In order to measure Tc, terminals were connected to the superconductor surface with Au and Ag pastes, and current-voltage measurement was performed by a DC method using liquid nitrogen as a refrigerant by a four-terminal method. Jc at the liquid nitrogen temperature was determined from the critical current (Ic) when the voltage between the measurement terminals was 1 μV / cm. As a result, Tc
Is 93K and Jc is 5 × 10 in a zero magnetic field at a temperature of 77K.
A characteristic of ⁵ A / cm ² was exhibited.

Example 3 (1) A seed crystal layer of YBa ₂ Cu ₃ O _{7- y} (oxide-based superconductor) was formed on an SrTiO ₃ single crystal substrate by MOCVD. In the MOCVD method, Y (DPM) ₃ , Ba (DPM) ₂ and Cu (DPM) are used as organic metal raw materials.
₂ was used while being kept at 125 ° C, 240 ° C and 120 ° C, respectively. MOCVD conditions were as follows: degree of vacuum (reaction tube pressure): 1.33 kPa (10 Torr), substrate temperature: 800
C. and the film formation time: 1 h. The thickness of this seed crystal layer is 0.1 mm.
It was 2 μm.

(2) On the seed crystal layer, by sputtering, target: Ag, output: 200 W, degree of vacuum: 1.5 Pa, distance between target / substrate: 4 mm, film formation time: 30 s, ambient temperature: room temperature An Ag layer was formed under the conditions described above, and a pseudo liquid layer of Ba ₃ Cu ₇ O _z (oxide) was formed under the same conditions except that the film formation time was 10 minutes in the MOCVD method. The thickness of this pseudo liquid layer is 0.03 μm
Met.

(3) Subsequently, in the MOCVD method,
YBa ₂ Cu _{3 under the} same conditions except that the film formation time was 1 hour.
An O _7-y superconducting layer was formed. The film thickness of this superconducting layer was 1.2 μm (film formation rate: 0.02 μm / min)
).

As a result, it was confirmed that the film was grown at a film formation rate approximately five times as high as the film formation rate obtained under the same conditions of the MOCVD method.

FIG. 2 shows the result of the pole measurement of the crystal orientation of the superconducting structure by the X-ray diffraction method.
In this measurement, the YBCO (103) plane was used as the measurement plane. It is confirmed that the crystal direction of the superconductor grows along the a-axis and the b-axis. To measure Tc,
The terminals are connected to the surface of the superconductor with Au and Ag pastes, and liquid nitrogen is used as a refrigerant in the four-terminal method, and current is applied in the DC method.
A voltage measurement was taken. From the critical current (Ic) when the voltage between the measuring terminals is set to 1 μV / cm, J
c was asked. As a result, Tc exhibited a characteristic of 1 × 10 ⁵ A / cm ^{2 in} a zero magnetic field at a temperature of 87K and Jc of 77K.

Example 4 (1) A seed crystal layer of YBa ₂ Cu ₃ O _{7- y} (oxide-based superconductor) was formed on an SrTiO ₃ single crystal substrate by MOCVD. In this MOCVD method, Y (DPM) ₃ , Ba (TDFND) tetraglyme and Cu (DPM) ₂ were used as organometallic raw materials while keeping them at 125 ° C., 240 ° C. and 120 ° C., respectively. MOCVD conditions were as follows: degree of vacuum (reaction tube pressure): 1.33 kPa (10 Torr), substrate temperature: 800 ° C., and film formation time: 1 hour. The thickness of this seed crystal layer was 0.2 μm.

In the above, DPM is dipivaroylmethan
The TDFND of e is 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetr
adecafluorononane-4,6-dione.

(2) By sputtering, the target: Ag,
Power: 100W, degree of vacuum: 1.5Pa, target / substrate
Between: distance 4 mm, deposition time: 60 s, ambient temperature: room temperature
Ag film is formed under the condition of
Thus, under the conditions for forming the seed crystal layer, the film formation time is
Ba under the same conditions except that_Three Cu₇ O_za F
_a (0.2 <z ≦ 2, oxide)
Was. The thickness of this pseudo liquid layer was 0.02 μm.

(3) Subsequently, a superconducting layer of YBa ₂ Cu ₃ O _7-y was formed by MOCVD under the same conditions except that the film formation time was 1 hour. Filmed. The thickness of this superconducting layer was 2.2 μm (film formation rate: 0.03 μm / min).

As a result, it is confirmed that the film grows at a film formation speed approximately ten times as high as the film formation speed obtained under the same conditions of the MOCVD method.

FIG. 2 shows the result of X-ray diffraction measurement of the orientation of the crystal of the composite. In this measurement, the YBCO (103) plane was used as the measurement plane. It is confirmed that the crystal direction of the superconductor grows along the a-axis and the b-axis. In order to measure Tc, terminals were connected to the surface of the superconductor with Au and Ag pastes, and current-voltage measurement was performed by a DC method using liquid nitrogen as a refrigerant by a four-terminal method. Jc at the liquid nitrogen temperature was determined from the critical current (Ic) when the voltage between the measurement terminals was 1 μV / cm. As a result, Tc exhibited a characteristic of 3 × 10 ⁵ A / cm ^{2 in} a zero magnetic field at a temperature of 88 K and Jc of 77 K.

<Comparative Example 1> (1) NdB was formed on a MgO single crystal substrate by using laser deposition.
An underlying superconducting layer of a ₂ Cu ₃ O _7-y (oxide superconductor) is formed. NdBa ₂ Cu ₃ O prepared by powder mixing method
Laser heating temperature 800 using a target with _7-y composition
° C, O ₂ partial pressure 2.66 Pa (20 mTorr), target /
Substrate distance 40 mm, laser energy density 2 J / cm
² , film thickness 0.1, under conditions of RR 30 Hz and film formation time 5 minutes
A μm underlying superconducting layer was obtained.

(2) Subsequently, the superconducting layer of NdBa ₂ Cu ₃ O _7-y was formed under the same conditions except that the film forming time was 5 minutes under the above-mentioned laser vapor deposition conditions. 2μ
m of the superconducting layer (deposition rate: 0.04 μm / min)
).

It is confirmed that the film formation speed is different from that of Example 2 by a factor of 5 or more.

<Comparative Example 2> (1) In the MOCVD method of Example 3, YBa ₂ Cu ₃ was used under the same MOCVD conditions of the seed crystal layer on the same base material.
An underlying superconducting layer 8 of O _7-y (oxide superconductor) was formed (thickness: 0.05 μm).

(2) Subsequently, a YBa ₂ Cu ₃ O _7-y superconducting layer was formed under the same conditions except that the heating temperature was 830 ° C. and the film forming time was 1 hour in the above MOCVD film forming conditions. A superconducting layer having a thickness of 0.2 μm was formed (film formation rate: 0.0033 μm / min).

It is confirmed that the film forming rate is different from that of Example 2 by a factor of 5 or more.

The Tc of the films obtained in Example 3 and Comparative Example 2
Is 87K and Jc is 1 × 10 in a zero magnetic field at a temperature of 77K.
^Although no difference in characteristics was observed at ⁵ A / cm ² , it was confirmed that the film formation speed of the superconducting layer of Example 3 was 7 times or more that of Comparative Example 2.

[Brief description of the drawings]

FIG. 1 is a conceptual perspective view of a manufacturing process of an oxide superconducting material according to the present invention.

FIG. 2 is a structural sectional view of an oxide-based superconducting material obtained by the present invention.

FIG. 3 is a model diagram showing a relationship between a film forming time and a film thickness of an oxide-based superconducting material obtained by the present invention.

[Explanation of symbols]

 2 base material 4 superconducting seed crystal layer 6 pseudo liquid layer 8 superconducting layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masato Hasegawa 2-4-1 Rokuno, Atsuta-ku, Nagoya-shi, Aichi Japan International Superconducting Technology Research Center Nagoya Laboratory, Superconductivity Engineering Laboratory (72) Inventor Hirabayashi Izumi Aichi Prefecture Nagoya-shi Atsuta-ku 2-4-1 Rokuno International Superconducting Industrial Technology Research Center Nagoya Laboratory, Superconducting Engineering Laboratory F-term (reference)

Claims (18)

[Claims] 1. A method for producing an oxide-based superconducting structure by forming a superconducting layer made of an oxide-based superconductor on a base material, wherein the pseudo-liquid layer is made of a substance having a lower melting point than the oxide-based superconductor. A superconducting layer forming step of forming a superconducting layer with an oxide superconductor after the pseudo liquid layer forming step of forming a superconducting layer. A method for manufacturing a superconducting structure. 2. The method according to claim 1, further comprising a seed crystal layer forming step of forming a seed crystal layer using an oxide of the same type as the superconducting layer before the pseudo liquid layer forming step. A method for producing an oxide-based superconducting structure. 3. The pseudo liquid layer according to claim 1, wherein the oxide-based superconductor contains Ba and Cu, and the pseudo liquid layer is formed of an oxide containing Ba and Cu constituent elements. A method for producing an oxide-based superconducting structure. 4. The method according to claim 3, wherein the pseudo liquid layer is formed by a physical vapor phase method. 5. The physical vapor phase method is a laser vapor deposition method, and the film forming conditions are as follows: substrate temperature: 750 ° C. or higher, O ₂ partial pressure:
The method for producing an oxide-based superconducting structure according to claim 4, wherein the pressure is 10 Torr or less. 6. The physical vapor phase method is a sputtering method,
The film formation conditions are as follows: substrate temperature: 750 ° C. or higher, O ₂ partial pressure: 10
5. The method for producing an oxide-based superconducting structure according to claim 4, wherein the pressure is less than Torr. 7. The method for manufacturing an oxide-based superconducting structure according to claim 3, wherein the pseudo liquid layer is formed by a chemical vapor deposition method. 8. The chemical vapor deposition method is a metal organic chemical vapor deposition (MOCVD) method, and the film forming conditions are as follows: substrate temperature: 7
8. The method for producing an oxide-based superconducting structure according to claim 7, wherein the temperature is 50 ° C. or higher and the O ₂ partial pressure is 10 Torr or lower. 9. The chemical composition ratio of the oxide is BaCu _x O _z (where 1.3 ≦ x ≦ 2.5, 1.6)
The method for producing an oxide-based superconducting structure according to claim 3, 4, 5, 6, 7, or 8, wherein 5 ≦ z ≦ 3.5). 10. The oxide system according to claim 9, wherein the pseudo liquid layer formed of BaCu _x O _z further contains Ag in an amount of 1 to 20% of the total number of moles of BaCu _x O _z. A method for manufacturing a superconducting structure. 11. The oxide has a chemical composition ratio of BaCu _x O _za X _a (where 1.3 ≦ x ≦ 2.5,
1.65−a / 2 ≦ z ≦ 3.5−a / 2, 0.01 <a
The method for producing an oxide-based superconducting structure according to any one of claims 3, 4, 5, 6, 7 and 8, wherein X is represented by ≤ 0.2 and X: F, Cl, Br or I). 12. The superconducting oxide has a chemical composition represented by LnBa ₂ Cu ₃ O _7-y (where Ln is a rare earth element other than Ce, and is −0.5 ≦ y ≦ 0.2). The method for producing an oxide-based superconducting structure according to claim 3, 4, 5, 6, 7, or 8. 13. An oxide-based superconducting structure in which a superconducting layer made of an oxide-based superconductor is formed on a base material, wherein the superconducting layer and the pseudo liquid layer are fused on the base material from the base material side. An oxide-based superconducting structure, characterized in that the pseudo liquid layer has a part of the constituent elements of the oxide-based superconductor and is made of an oxide having a lower melting point than the oxide-based superconductor. . 14. An oxide superconductor comprising Ba and Cu
Wherein the oxide forming the pseudo liquid layer contains constituent elements of Ba and Cu.
4. The oxide superconducting structure according to 3. 15. The oxide has a chemical composition ratio of BaCu _x O _z (where 1.3 ≦ x ≦ 2.5, 1.6)
The oxide superconducting structure according to claim 14, wherein 5 <z ≦ 3.5). 16. The oxide system according to claim 15, wherein the pseudo liquid layer formed of BaCu _x O _z further contains Ag in an amount of 1 to 20% of the total number of moles of BaCu _x O _z. Superconducting structure. 17. The chemical composition ratio of the oxide is BaCu _x O _za X _a (where 1.3 ≦ x ≦ 2.5,
1.65−a / 2 ≦ z ≦ 3.5−a / 2, 0.01 <a
15. The oxide-based superconducting structure according to claim 14, wherein X is F, Cl, Br or I). 18. The chemical composition of the superconducting oxide is represented by LnBa ₂ Cu ₃ O _7-y (where Ln is a rare earth element excluding Ce, −0.5 ≦ y ≦ 0.2). 18. The oxide-based superconducting structure according to claim 14, 15, 16, or 17.