JPH0450103A - Oxide superconducting material and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title superconducting material with improved critical current density by forming an intermediate layer of a compound of specific composition formula on a substrate followed by laminating thereon a thick filmy form of an oxide superconductor and then melting and coagulating said thick film. CONSTITUTION:Using a CVD film-forming equipment, (A) an intermediate layer of a compound of composition formula AxBOy (A is at least one of Mg, Ca, Sr and Ba; B is at least one of Sn, Si, Ce, Ti and Zr; 1<=x<=2; 3<=y<=4) (e.g. BaSnO3) is formed on a substrate consisting of a heat-resistant alloy such as Hastelloy heated to a specified temperature. 0.5-20wt.% of AxBOy fine particles is added to calcined stock oxide powder with a specified atomic ratio capable of forming an oxide superconductor of e.g. RE-Ba-Cu-0 (RE is rare earth element such as Y or La) base followed by mixing a binder and dispersant into a paste. This paste is then made into a green tape using a doctor blade, which is then superposed on the AxBOy layer on the substrate. The system is then calcined in an O2 gas stream and further heated, melted and then coagulated, thus giving the objective oxide superconductor with high critical current density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxide superconducting material having an intermediate layer and a method for manufacturing the same.

[Prior art] Conventionally, RE-Ba-Cu-0 (RE is Y, La, N
d, Sm, Eu, Gd.

one or more selected from the group consisting of Dy, Ho, Er, Tm, Yb, and Lu) based superconductor (hereinafter also referred to as rare earth superconductor), B1-5r-Ca-Cu-0
system superconductor (hereinafter also referred to as Bi system superconductor), Tl-
Oxide superconductors such as Ba-Ca-Cu-0-based superconductors (hereinafter also referred to as Tl-based superconductors) are known.

As a method for producing an oxide superconductor, there is a method in which crystal powder having a predetermined composition is synthesized, and then this is formed and sintered. In addition, it is known to manufacture by a sol-gel method and a melt solidification method.

Superconductors produced by these methods are usually polycrystalline, with individual crystal grains arranged in random directions,
Moreover, the grain boundaries contain an unexpected grain boundary phase exhibiting superconductivity. Further, the grain boundary phase includes a non-superconducting crystalline phase, an amorphous phase, and, in many cases, pores.

However, the above-mentioned oxide superconductor has a drawback in that the direction in which current flows easily within the crystal grains is determined, and therefore current does not flow easily at grain boundaries between crystal grains with different orientations. The grain boundary phase acts as an insulating layer.For this reason, conventional polycrystalline oxide superconductors have not been able to exhibit high critical current densities.

Therefore, in order to solve the above-mentioned problems of polycrystalline superconductors, application of the melt solidification method is being considered. When manufactured by the melt solidification method, the crystal grains become thicker (grow), denser, and the bonds between the grains become stronger, which improves the critical current density.

On the other hand, when applying superconductors to applications such as magnets, it is necessary to process them into a linear or tape-like shape. Therefore, attempts have been made to improve the density and orientation of a molded body of oxide superconductor powder processed into a linear or tape shape by melting and solidifying it. In this case, it is difficult to melt and solidify only the oxide itself in the form of a line or tape due to problems in strength and handling. For this reason, it has been considered to form a polycrystalline superconductor on a linear or tape-shaped substrate and then melt and solidify it.

[Problem to be solved by the invention] Such a substrate may be, for example, silver or gold.

However, when performing melt solidification treatment, RE-Ba-Cu-
Zero oxide superconductors must be melted at a temperature of 1000° C. or higher, and silver and gold cannot be used because they will dissolve. In addition, heat-resistant alloys such as Hastelloy, tape-shaped ZrO
Although it is conceivable to use a 2-polycrystal as a substrate, at this temperature, the constituent elements of the superconductor, not just rare earth elements, react significantly with the substrate, making it impossible to obtain a superconductor crystal with good properties.

B1-5r-Ca-Cu-0 system or Tl-Ba-C
In the case of a-Cu-0-based superconductors, using silver or gold as a substrate has no problems in terms of properties, but it is not practical due to the high price of silver and gold and insufficient mechanical strength. There are problems from a practical standpoint.

[Means for Solving the Problems] Therefore, the inventors of the present invention aimed to form a polycrystalline superconductor on a substrate such as a heat-resistant alloy and then melt and solidify it to obtain an oriented and dense structure. As a result of various studies, it has been found that the above object can be achieved by using a specific compound as the intermediate layer, which has low reactivity with the superconductor constituent elements and is stable at the melting temperature.

In the present invention, AxBOy (A is Mg, Ca
, Sr, and Ba; B is one or more selected from the group consisting of Sn, Si, Ce, Ti, and Zr; 1≦X≦2.3≦y≦4) The present invention provides an oxide superconducting material characterized in that an intermediate layer of a compound represented by the composition formula is formed, and an oxide superconductor layer is further formed.

In the present invention, any combination of the above elements can be suitably used as A and BOy, but when a rare earth superconductor is used as the oxide superconductor, 13a
snoa, BaZr03, BaTiO3, Bace's
, Ba2SiO4 and other elements containing Ba are one of the constituent elements of the superconductor, so even if an element substitution reaction occurs, other alkaline earth elements do not substantially mix into the superconductor, so it does not adversely affect the superconducting properties. It is preferable because there is no.

The superconducting material of the present invention is preferably manufactured by the following method. First, an intermediate layer of a compound represented by the compositional formulas A and BOy is formed on a substrate, and a thick film shaped body of an oxide superconductor is laminated thereon. Next, when the thick film is melted and solidified, the thick film becomes dense and the orientation of the superconductor crystals improves.

As a result, a superconductor with a high critical current density can be obtained.

It is more preferable to perform the melt solidification under a temperature gradient because the compactness and orientation further increase.

The thick film shaped body is obtained by molding raw material powder having a superconducting composition using a doctor blade method or the like. Alternatively, a thick film may be formed directly on the substrate by screen printing or the like.

Alternatively, it can be manufactured by filling a metal tube whose inner surface is coated with AxBOy with superconductor raw material powder and heat-treating this. The orientation of the superconductor can be improved by pressing the metal tube before and/or after heat treatment.

Although various materials can be used for the substrate, it is preferable to use various heat-resistant alloys and ceramics.

Although only the AxBOy layer may be used as the intermediate layer, it is preferable to further provide a second intermediate layer made of a noble metal because this improves the orientation of the superconductor layer when melting and solidifying the superconductor layer.

When a superconductor has a structure containing non-superconductor particles inside a crystalline phase that exhibits superconductivity, these particles act as a center of binding, so it can exhibit a high critical current density even in a magnetic field. It's good to be able to do it. As such non-superconductor particles, A and BOy are preferable, as in the intermediate layer of the present invention, since they have little reactivity with superconductor crystals. The AxBOy particles can be introduced into the superconductor crystal by mixing them into the thick film of the oxide superconductor before the melt-solidification process.

The additive of AxBOy is 0.5 to 20 to the superconductor.
wt% is preferred. If the amount of the additive is less than 0.5 wt%, the effect of the addition will not be apparent, which is not preferable. When the amount added exceeds 20wt%, some of the materials contain A,
This is not preferable because the BOy phase segregates and causes discontinuity in the superconductor. A more preferable addition amount of AxBOy is 2 to 10 wt%.

When a mixture of the superconducting phase and AxBOy is heated above the partial melting temperature of the superconducting phase and then cooled and solidified, the AxBOy crystals are incorporated into the superconducting phase crystals while maintaining the particle size added at the time of preparation. That is, if the above-mentioned A and BO grains selected to have only fine particles are used, a non-superconducting substance of the same size can be dispersed in the superconducting phase crystal, which is desirable from the viewpoint of strengthening the bottle-holding force.

In particular, when only particles of 0.5 μm or less are used, the critical current density increases dramatically and does not decrease much even when a magnetic field is applied.

In the present invention, the oxide superconductor is not particularly limited, and various types such as rare earth-based, bismuth-based, thallium-based, etc. can be suitably applied.

In the case of a rare earth superconductor, when it is melted and solidified, non-superconducting REJaCuOs crystals (hereinafter referred to as 211 phase) are present in the structure of the solidified material and exhibit a bottling effect. It is preferable to employ a composition rich in 211 phase as the composition of the superconductor thick film compared to the composition of crystals exhibiting superconductivity, since this increases the amount of 211 phase in the solidified material and increases the bottling effect. When obtaining a rare earth superconductor from a composition rich in the 211 phase, it is preferable because the orientation of REBaaCusO crystals exhibiting superconductivity is also improved. When the rare earth superconductor contains two or more types of rare earth elements, the particle size of the 211 phase precipitates can be reduced to 0.5 to several μm, which is more preferable since a material with a large critical current density can be obtained. .

[Example] Example 1 Hastelloy with a thickness of 1 mm was cut into a size of 70 mm x 5 mm, and using the CVD film forming apparatus shown in Fig. 2, Hastelloy was produced using dipivaloylmethane complex of Ba and tetraphenyltin as raw materials. A Ba5nOs layer with a thickness of 0.2 μm was formed on the Hastelloy substrate by forming a film while heating to 900° C.

On the other hand, the atomic ratio of Y:Ho:Ba:Cu is 3:4:8:1
A calcined powder of oxide such as No. 1 is prepared, 5 wt% of Ba5nOs with an average particle size of 0.5 μm is added and mixed, and then an acrylic binder, a surfactant (dispersant), and trichlorethylene are added to form a paste. Obtained. Spread the paste onto a polyester film using a doctor blade in a width of 10 mm.
A green tape was obtained by casting into a shape with a thickness of 0 mm and a thickness of 50 μm. The green tape was cut into a size of 70 mm x 5 mm, placed on the surface of the above substrate on which BaSnO3 was formed, and fired at 930° C. for 10 hours in an oxygen stream.

Next, one end of this tape-shaped sintered body was fixed, and the length of the tape was heated at a speed of 2 mm/h in an electric furnace with a temperature gradient of 50 °C/cm and the highest temperature part was 1080 °C under an oxygen stream. I moved it in the opposite direction.

As a result, no reaction between Hastelloy and the superconductor was observed, and the thickness of the obtained superconductor layer was 20 μm. Further, it was heated to 700°C in an oxygen atmosphere, slowly cooled at a rate of 15°C/h, and held at 450°C for 40 hours.

When the sample thus obtained was observed using a scanning electron microscope and an X-ray elemental analyzer, it was found that the crystal grains of the plate-shaped superconductor crystal (123 phase) overlapped in a layered manner as shown in Figure 1. In it, Ba5n with a particle size of about 0.5 μm
It was confirmed that the sample had a structure in which Os particles and 211 phase non-superconductor crystal particles were dispersed in an island shape. The above-mentioned good structure was observed throughout the sample, indicating that Ba5nOs
No precipitation was observed.

A sample with a size of 20 mm x 2 mm was cut from the sample obtained as described above, and the critical temperature and critical current density at 5 Tesla in 1977 were measured using the DC four-terminal method, and the results were 92 K and 6200 A/cm2, respectively. Ta.

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that the green tape was directly layered on Hastelloy without forming an intermediate layer of BaSnO3. When the sample was prepared in the same manner as in Example 1, Hastelloy and the superconductor reacted and a structure as shown in Figure 1 was formed. could not be formed.

Example 2 R1. shown in Table 1. Regarding R2, R1:R2:Ba:
A calcined powder of oxide with a Cu atomic ratio of 3+4:8:11 was prepared, and Ba5nO, which had been selected to have an average particle size of 0.3 μm, was added or not added as shown in Table 1. A green tape was obtained in the same manner as in Example 1. Ba
When adding 5 nOs, the amount added was 5 wt%.

This green tape was stacked on the surface on which the AxBOy intermediate layer having the composition shown in Table 1 was formed in the same manner as in Example 1, and on which the intermediate layer of Hastelloy was formed. Thereafter, the same heat treatment as in Example 1 was performed to obtain a superconductor.

Table 1 shows the critical temperature measured in the same manner as in Example 1 and the critical current density at 775 Tesla.

Table 1 Comparative Example 2 Samples were prepared in the same manner as in Example 2 except that green tape was directly layered on Hastelloy without forming an intermediate layer of AxBOy. It was not possible to form the type of organization shown.

Example 3 Hastelloy with a thickness of 1 mm was cut into a size of 10 mm x 50 mm, and using the CVD film forming apparatus shown in Fig. 2, using tetraphenyltin and Sr dipivaloylmethane complex as raw materials, Hastelloy was heated to 950 ° C. A 0.2 μm thick 5rSn03 layer was formed on the Hastelloy substrate while heating.

A calcined oxide powder with an atomic ratio of Bi:Sr:Ca:Cu of 2+2:1:2 is prepared, and the average particle size is 0.
5 wt % of 5 gm of 5rSnOa was added and mixed.

The powder was mixed with octyl alcohol and then screen printed onto the Hastelloy and dried. This is 89
After melting at 0° C. for 20 minutes and cooling to 870° C. over 3 hours, it was slowly cooled to room temperature, further heated to 500° C., and kept in an atmosphere with an oxygen partial pressure of 0.001 atm for 10 hours for rapid cooling.

When the cross section of the sample thus obtained was observed using a scanning electron microscope and an X-ray elemental analyzer, it was found that the crystal particles of the plate-shaped superconductor crystal (2212 phase) were layered as shown in Figure 1. It was confirmed that the structure had a structure in which non-superconductor (SrSnOa) particles with a particle size of about 0.5 μm were dispersed in an island shape. A good structure as described above was observed throughout the sample.

When measured in the same manner as in Example 1, the critical temperature of this sample was 90 K, and the critical current density S at 77 and 2 Tesla was 4.
It was 500A/cm2.

Example 4 A superconducting material was obtained in the same manner as in Example 3 except that an AxBOy layer as shown in Table 3 was formed on Hastelloy, and the results of measuring the superconducting properties are shown in Table 2.

Table 2 Comparative Example 3 A sample was prepared in the same manner as in Example 3 except that a superconducting layer was directly formed on Hastelloy without forming an intermediate layer, and the critical temperature was 77 or less. Example 5 Hastelloy with a thickness of 1 mm was cut into a size of 10 mm x 50 mm, and using the CVD film forming apparatus shown in Fig. 2, the Hastelloy was heated to 950 °C using tetraphenyltin and Ba dipivaloylmethane complex as raw materials. Meanwhile, a 0.2 μm thick BaSnO3 layer was formed on the Hastelloy substrate.

B such that the atomic ratio of Ba:Ca:Cu is 2:3:4.
aCO3, CaC0a, and CuO were weighed and mixed, and the mixture was fired in air at 880°C for 10 hours using an electric furnace.

Tl□03 is added to this fired powder as Tl:Ba:Ca:C
U was added so that the atomic ratio was 2:2:3:4, and 5 wt % of Ba5nOa powder having an average particle size of 0.5 μm was added and mixed.

The powder was mixed with octyl alcohol, then screen printed on the surface of the Hastelloy on which the BaSnOs layer was formed and dried. This was sealed in an alumina tube with an inner diameter of 16 mmφ, melted at 950° C. for 5 minutes, rapidly cooled to room temperature, and then further heated to 890° C. and held for 8 hours for rapid cooling.

The cross section of the coagulated tape thus obtained was observed using a scanning electron microscope and an X-ray elemental analyzer.
As shown in the figure, crystal grains of plate-shaped superconductor crystals (2223 phase) overlap in a layered manner, and there are particles with a grain size of 0.5 μm in them.
It was confirmed that the non-superconductor (BaSnOs) particles had a structure in which particles of a non-superconductor (BaSnOs) were dispersed in the form of islands. A good structure as described above was observed throughout the sample.

When measured in the same manner as in Example 1, the critical temperature of this superconductor was 123, and the critical current density at 77.2 Tesla was 7200 A/cm2.

Example 6 A superconducting material was obtained in the same manner as in Example 5 except that an AxBOy layer as shown in Table 2 was formed on Hastelloy, and the superconducting properties were measured. Table 3 shows the results.

Table 3 Comparative Example 4 A sample was prepared in the same manner as in Example 4, except that a superconducting layer was directly formed on Hastelloy without forming an intermediate layer, and the critical temperature was 77 or lower.

[Effects of the Invention] The superconducting material of the present invention has a superconductor layer formed on a substrate via an intermediate layer having extremely low reactivity with the superconductor, so that the properties of the superconducting material do not deteriorate even when a substrate other than noble metals is used. do not have.

When the superconductor of the present invention is produced by melt-solidification treatment, reaction between the superconductor and the substrate is prevented, and a dense, highly oriented superconductor with good properties such as critical current density can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the structure of a superconductor obtained in an example.

Claims (1)

[Claims] 1. A_xBO_y (A is Mg, Ca, S
r, one or more selected from the group consisting of Ba, B is Sn
, Si, Ce, Ti, and Zr, forming an intermediate layer of a compound represented by a composition formula of 1≦x≦2, 3≦y≦4), and further comprising an oxide superconductor. An oxide superconducting material characterized by forming a body layer. 2. Claim 1, characterized in that an intermediate layer of a compound represented by the composition formula A_xBO_y is formed on the substrate, a thick film shaped body of an oxide superconductor is laminated, and then the thick film is melted and solidified. A method for producing an oxide superconductor.