JP2919956B2 - Superconducting member manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a superconducting member using an oxide superconductor.

(Prior Art) Since the oxide-based high-temperature superconductor was discovered in 1986, various studies have been carried out to improve its properties and properties. In particular, the critical temperature exceeds the temperature of liquid nitrogen, the Y-Ba-Cu-O system having an oxygen-deficient provskite structure, Bi-Sr-Ca-
BACKGROUND ART Oxide superconductors such as Cu-O-based and Tl-Ba-Ca-Cu-O-based have been actively studied for application to superconducting wiring, superconducting wires, superconducting devices, and the like.

Considering the application of the oxide superconductor as described above,
It is necessary to reduce the thickness of the oxide superconductor thin film, which has relatively good crystallinity by applying a sputtering method, a CVD method, etc., and using a single crystal substrate such as SrTlO ₃ or MgO. As a result, the critical current density is also exceeding 10 ⁶ A / cm ² .

By the way, in order to actually apply the oxide superconductor as a wire or a wiring material, it is important to enable bending. Therefore, it has been attempted to form an oxide superconductor layer directly on a metal tape by a sputtering method, a vapor deposition method, or the like.

(Problems to be Solved by the Invention) However, the method of forming an oxide superconductor layer directly on a metal tape as described above does not provide practically sufficient superconducting characteristics such as critical current density. There is.

Here, in order to improve the critical current density of the oxide superconductor, a good current path is secured by intentionally controlling the disorder and defects of the crystals constituting the superconductor, and furthermore, the essential magnetic flux It is necessary to disperse the pinning centers. However, in the above-described method, the orientation of the obtained oxide superconductor crystal is reduced, and the critical current density is reduced.

As one of the factors that lower the orientation of the oxide superconductor crystal, the following problems on the metal tape side can be considered.

That is, when an oxide superconductor film is formed on a metal tape by a sputtering method, a vapor deposition method, or the like, it is necessary to maintain the temperature of the metal tape at a high temperature. The orientation of the oxide superconductor crystal is disturbed by the influence of the crystal grains. Therefore, the current path is cut off, and the critical current density is reduced.

The present invention has been made to address such problems of the prior art, and suppresses crystal disorder and orientation deterioration when an oxide superconductor layer is formed on a conductive substrate such as a metal tape. Further, it is an object of the present invention to provide a method for manufacturing a superconducting member capable of improving superconducting characteristics such as a critical temperature and a critical current density by growing an oxide superconducting crystal having good characteristics. .

[Structure of the Invention] (Means for Solving the Problems) That is, in the method for manufacturing a superconducting member of the present invention, when manufacturing a superconducting member having a superconducting material layer formed on a conductive substrate, Performing a heat treatment at a temperature equal to or higher than the formation temperature of the superconducting material layer to recrystallize the conductive substrate, and forming the substrate on the superconducting material layer forming surface of the recrystallized conductive substrate. The method is characterized by comprising a step of forming a conductive material layer of the same kind or a different kind, and a step of forming the superconducting material layer on the conductive material layer.

As the material of the conductive substrate used in the present invention, A
Various metal materials such as g, Au, Cu, Al, W, Mo, Fe, and SUS materials can be used, and the shape thereof is not limited to a tape shape or a long shape, but may be a board shape, a component shape, or the like. It is possible to apply various shapes such as.

Further, as the superconducting material used in the present invention, a perovskite-type oxide superconductor containing a rare earth element, Bi-
Sr-Ca-Cu-O-based oxide superconductor, Tl-Ba-Ca-Cu-O
Various oxide superconductors such as a system oxide superconductor can be used.

The oxide superconductor containing a rare earth element and having a perovskite structure may be any as long as it can realize a superconducting state. For example, REM ₂ Cu ₃ O _7-y (RE is Y, La, Sc, N
d, Sm, Eu, Gd, Dy, Ho, Er, Yb, at least one element selected from rare earth elements such as Lu, M is at least one element selected from Ba, Sr, Ca, y represents an oxygen deficiency and is usually a number of 1 or less, and part of Cu is Ti, V, Cr, Mn, Fe, C
o, Ni, Zn, etc.).

The Bi-Sr-Ca-Co-O-based oxide superconductor has the chemical formula: Bi ₂ (Sr, Ca) ₃ Cu ₂ Ox Bi ₂ Sr ₂ Ca ₂ Cu ₃ Ox Bi ₂ Sr ₂ Ca ₃ Cu ₄ Ox (In the formula, a part of Bi can be substituted with Pb or the like.)
—Ba—Ca—Cu—O-based oxide superconductor has the chemical formula: Tl ₂ (Ba, Ca) ₃ Cu ₂ Ox Tl ₂ Ba ₂ Ca ₂ Cu ₃ Ox Tl ₂ Ba ₂ Ca ₃ Cu ₄ Ox Tl ₂ Ba ₂ It is represented by Ca ₄ Cu ₅ Ox or the like.

In the method for manufacturing a superconducting member according to the present invention, the conductive substrate is first subjected to a temperature higher than the temperature at which the oxide superconductor layer is formed, for example, an air atmosphere, a nitrogen atmosphere, an oxygen atmosphere, or the like. 40 in an atmosphere suitable for the substrate
The conductive substrate is recrystallized in advance by performing a heat treatment at a temperature of about 0 ° C. to about 1000 ° C. for about 1 hour to about 10 hours.

By the heat treatment, the conductive substrate becomes stable with respect to the temperature at which the oxide superconductor layer is formed, and is prevented from disturbing the crystal of the oxide superconductor or deteriorating the orientation during the formation of the oxide superconductor layer. It is possible to grow an oxide superconductor crystal with good characteristics.

Next, in the present invention, a conductive material layer of the same type or different from the conductive substrate is formed on the surface of the recrystallized conductive substrate on which the oxide superconductor layer is formed.

Here, on the surface of the recrystallized conductive substrate, there are relatively sharp irregularities such as irregularities caused by crystal grain boundaries and irregularities directly formed on the crystal grain surfaces, and overall undulations.
Since the irregularities that adversely affect the oxide superconductor crystal are relatively sharp, in the present invention, the conductive material layer may be formed to such an extent that these sharp irregularities are removed,
For example, a thickness of about 0.2 μm to 5 μm is sufficient. Also,
The conductive substance used may be the same kind and material as the base,
It is also possible to use different materials.

In the present invention, an oxide superconductor layer having a thickness of about 100 to 10 μm is formed on a conductive substrate having a smoothed surface as described above, for example, a sputtering method, a CVD method, an ion cluster beam evaporation method, a molecular beam. By forming the thin film by various thin film forming methods such as an epitaxy method, an oxide superconductor layer having good crystallinity can be obtained.

For example, as a target when forming an oxide superconductor layer by a sputtering method, a compound containing a constituent element of each oxide superconductor may be used individually, or a single target containing each constituent element may be used. Good. When a sintered body such as oxide superconductor is used as a target, the composition of the obtained film may not always match the target composition. In the target,
Alternatively, it is desirable to further install a target containing an element that is likely to be insufficient, and to independently control the target.

When the oxide superconductor layer is formed by a sputtering method, heat treatment may be performed while introducing oxygen into the vacuum chamber as necessary, or heat treatment may be performed in an oxygen atmosphere after removing from the vacuum layer. A high-quality oxygenated superconductor film with few defects can be obtained, and the transition temperature can be improved.

Further, the ion cluster beam evaporation method is a method in which a raw material containing each constituent element is individually heated, evaporated and adhered, and the composition can be controlled for each element.
Also, unlike normal evaporation methods, after the evaporated atoms fly out of the nozzle, they are rapidly cooled by adiabatic expansion and condensed to form clusters, which are further ionized and accelerated, resulting in a migration effect on the adherend surface. Is significantly larger than other methods, and has the advantage that an oriented film can be obtained at a comparatively low temperature.

However, in the case of forming an oxide thin film, since the melting point of the oxide is generally high and it is difficult to evaporate itself, each element is evaporated and reacted in an oxygen atmosphere. Therefore, the method of supplying oxygen is an important factor. Oxygen supply is electron cyclotron resonance (ECR)
Supply, or high frequency, microwave,
It is preferable that oxygen plasma is formed and supplied by light or the like, or that oxygen in an activated state is supplied by heating. With these, a greater effect can be obtained than simply blowing oxygen on the adherend surface. It is also effective to ozonize not only oxygen but also oxygen by silent discharge. Further oxygen containing gas, N ₂ O and CO or the like is weak binding energy with other atoms, it is possible to easily form the oxygen radicals by discharge by the high frequency power frequencies body than the molecular state.

(Function) In the method for manufacturing a superconducting member of the present invention, the crystallization of the base is promoted in advance by heat-treating the conductivity, and a conductive material layer of the same or different kind as the conductive gas is formed. Since the smoothness is improved, the oxide superconductor layer formed on this gas does not reflect the crystal defects or the poor surface morphology of the conductive base itself,
The oxide superconductor crystal can always maintain the orientation in a certain direction. Also, by smoothing the surface of the base, favorable crystal growth is promoted from the growth stage of the oxide superconductor crystal,
It is possible to form an oxide superconductor having excellent crystallinity and good orientation. Therefore, by improving these points, the critical temperature and the critical current can be improved.

(Example) Next, an example of the present invention is described.

Example 1 Ag having a thickness of 0.3 mm, a width of 1 mm, and a length of 60 mm was used as a conductive substrate.
First, apply this Ag tape to the Ag tape in air atmosphere.
Heat treatment was performed at 0 ° C. × 8 hours.

Next, the Ag tape was set on a substrate holder having a heating mechanism of the film forming apparatus, the pressure in the vacuum chamber was reduced to 4 × 10 g ^-6 Torr, and then the Ag tape was evaporated to 400 ° C. while heating the Ag tape. As shown in FIG. 1, a 1 μm thick Ag tape 1
An Ag layer 2 was formed.

Thereafter, the pressure in the vacuum chamber was maintained at 4 × 10 ⁻⁶ Torr, and the Ag tape was heated to 600 ° C. and allowed to stand for about 1 hour until it was stabilized. Then, the Y, Ba, and Cu clusters were evaporated from different ion guns, and high-frequency oxygen plasma was directly irradiated on the Ag tape while supplying oxygen at 19 SCCM, whereby a Y-layer having a thickness of 2000 mm was formed on the Ag layer. Ba−Cu−
An O-based oxide superconductor film 2 was formed. The individual conditions of each evaporation source are as follows.

Y: Evaporation rate = 950Å / hour Acceleration voltage = 0.2kV Ionization current = 0.5A Ba: Evaporation rate = 1160Å / hour Acceleration voltage = 0.2kV Ionization current = 0.5A Cu: Evaporation rate = 540Å / hour Acceleration voltage = 0.2kV ionization Current = 0.5 A RF plasma condition Atmospheric pressure = 2 x 10 ^-4 Torr RF power = 50 W Oxygen supply = 19 SCCM → 40 SCCM Also, during the cooling process of the Ag tape, the amount of oxygen introduced was 40
The pressure in the vacuum chamber was increased to 6 × 10 ⁻³ Torr as SCCM, cooled in a stepwise manner, and kept at 400 ° C. for 1 hour to obtain the desired superconducting wire 4.

When the transition temperature and the critical current density at 77 K and OT of the Y-Ba-Cu-O-based oxide superconductor film thus obtained were measured, Tc = 90 K, Jc = 1.1 × 10 ⁵ A / cm ² Good values were obtained.

When X-ray diffraction of the oxide superconductor film was performed,
It was confirmed that the film was a YBa ₂ Cu ₃ O _7-X film having excellent orientation. Further, when the morphology of the surface of the oxide superconductor film was observed using SEM, the influence of the Ag crystal grains hardly occurred, and the crystal of a good oxide conductor was grown from the initial step of crystal growth. It was confirmed that.

In the composition analysis by ICP, a value close to 1: 2: 3, which is the ideal composition of the Y-Ba-Cu-O-based oxide superconductor, was obtained.

In this way, by performing heat treatment and forming a conductive material for surface smoothing on the Ag tape in advance,
An oxide superconductor film excellent in crystal and crystal and orientation system can be obtained.

According to the ion cluster beam evaporation method, a good oxide superconductor film can be obtained at a low substrate temperature. Further, it was confirmed that the obtained Y-Ba-Cu-O-based oxide superconductor film could be further improved in both film quality and isoconductivity by heat treatment in a vacuum chamber or in an oxygen atmosphere using a furnace.

According to the ion cluster beam evaporation method,
Because the composition can be controlled for each single element, Bi-Sr-Ca-Cu-
O- and Tl-Ba-Ca-Cu-o-based oxide superconductor films also had high critical temperatures.

Example 2 A 0.3 mm thick, 1 mm wide, 60 mm long Cu was used as a conductive substrate.
After performing heat treatment and forming an Ag layer on the Cu tape under the same conditions as in Example 1 using a tape, the same conditions as in Example 1 were obtained on the Ag layer of the Cu tape by ion cluster beam evaporation. Thus, a Y-Ba-Cu-O-based oxide superconductor film was formed.

The superconducting tape-like superconductor obtained in this way has the same superconductivity as in Example 1, such as critical temperature = 89K, critical current density = 1.0 × 10 ⁵ A / cm ² (at 77K, OT). The characteristics were shown.

In addition, Fe, SUS, Au, Al, W, Mo
The same effect was obtained when a tape material or a wire material such as that described above was used.

Example 3 Ag having a thickness of 0.3 mm, a width of 1 mm, and a length of 60 mm was used as a conductive substrate.
After setting the Ag tape on the substrate holder in the same manner as in Example 1 using a tape, the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁶ Torr, and the Ag tape was heated to 600 ° C. to form an Ag cluster. By evaporating from an ion gun, an Ag layer having a thickness of 2,000 to 10,000 was formed on the Ag tape. The conditions of the evaporation source are as follows.

Ag: Evaporation rate = 2000 ° -10000 ° / hour Accelerating voltage = 1 kV Ionization current = 0.5 A Thereafter, with the Ag tape temperature maintained at 600 ° C., under the same conditions as in Example 1, Y—Ba—Cu—O A system oxide superconductor film was formed.

The Y—Ba—Cu—O-based oxide superconductor film thus obtained has a critical temperature of 90 K and a critical current density of 1.0 × 10 ⁵ A / cm ² (77
(K, OT), as in Examples 1 and 2.

[Effects of the Invention] As described above, according to the method of manufacturing a superconducting member of the present invention, in order to suppress crystal disorder during formation of a superconductor film, a heat treatment is performed on the conductive substrate in advance, and Since the same or different conductive material is laminated on the conductive substrate to make the surface uniform, the crystal orientation of the oxidized superconductor formed on this conductive material layer is increased and the superconducting properties are improved. It becomes possible to do it. In addition, since breaks in the current path due to the influence of crystal grain boundaries and the like are reduced, it is possible to provide a practical superconducting member capable of flowing a practically sufficient current.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of a superconducting member manufactured in one embodiment of the present invention. 1 ... Ag tape, 2 ... Ag layer, 3 ... Oxide superconductor layer, 4 ... Superconducting member.

Continuing from the front page (72) Inventor Kiyoshi Zhangiwa 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. Toshiba Research Institute, Inc. (56) References JP-A-63-239738 (JP, A) JP-A-2-255505 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C14 / 06

Claims (1)

(57) [Claims] In producing a superconducting member having a superconducting material layer formed on a conductive substrate, a heat treatment is performed on the conductive substrate at a temperature equal to or higher than the temperature at which the superconducting material layer is formed. A step of recrystallizing the substrate; and a step of forming a superconducting material layer on the recrystallized conductive substrate,
A method for manufacturing a superconducting member, comprising: a step of forming a conductive material layer of the same type or a different kind from the substrate; and a step of forming the superconducting material layer on the conductive material layer.