JPH0446052A - Oxide superconductor tape - Google Patents

Abstract

PURPOSE:To increase critical current density in an intense magnetic field by laminating an oxide superconducting film contg. granular crystals of a specified multiple oxide insularly dispersed in crystals contg. Tl, Ba, Ca, Cu and O on a metal. CONSTITUTION:Starting materials for a superconductor contg. Tl, Ba, Ca, Cu and O are mixed with 0.5-20wt.% multiple oxide of one or more kinds of metals selected among group IIA elements and one or more kinds of metals selected among groups IVA and IVB elements and rare earth elements. The resulting mixture is heated to the partial melting temp. of the superconducting phase or above and solidified by cooling to obtain an oxide superconductor having a structure contg. granular crystals of the above-mentioned multiple oxide insularly dispersed in crystals contg. Tl, Ba, Ca, Cu and O. This superconductor is pulverized and spread on a metallic sheet to form a film and this film is melted and solidified.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides T1-Ba-Ca-Cu-
This invention relates to a 0-based oxide superconductor tape.

[Prior art] Conventionally, Tl*BatCazCus
Oy (hereinafter also referred to as 2223 phase), TlaBaz
CaCu20y (hereinafter also referred to as 2212 phase),
There are many other phases besides TlBa*CamCu40y (hereinafter also referred to as 1234 phase), and it is known that the critical temperature of most of these phases is higher than the liquid nitrogen temperature (77K). As a method for manufacturing a Tl-based superconductor tape, there is a method in which a crystal powder having the above-mentioned composition is synthesized, and then the crystal powder is sealed in a metal tube and sintered or melted and solidified.

[Problems to be solved by the invention] The cross section of the superconducting tape manufactured by the sintering method is
As shown in Figure 1, it is a porous polycrystalline body. Each crystal grain is arranged in a disordered direction, and the bonds between the grains are weak.

In a Tl-based superconductor, the direction in which current flows easily within the crystal grains is determined, so current has a property that it is difficult for current to flow between crystal grains having different orientations. Furthermore, a small bonding area between grains means that the effective current path is narrow. For this reason, polycrystalline T as shown in Figure 1
1-series superconductors with high critical current density could not be obtained.

When the direction of the crystal grains is controlled by pressing the polycrystalline material, the critical current density is improved because the directions of the crystal grains are aligned. Similarly, when manufactured by the melt solidification method, the crystal grains grow larger, become denser, and the bonds between the grains become stronger, thereby improving the critical current density.

When manufactured using any of these methods, the critical current density at liquid nitrogen temperature significantly decreases in a magnetic field. This is thought to be due to the weak pinning force of the magnetic flux penetrating the crystal in a magnetic field higher than the lower critical magnetic field of the Tl-based superconductor. Application fields of superconductors include:
An electric F that creates a strong magnetic field by processing wire or tape material into a coil shape! It is mainly considered to be used as an iE. Therefore, in order to put Tl-based superconducting tape into practical use, it is necessary to create a structure in which the crystal directions are precisely aligned and to introduce pinning centers into the crystal to further strengthen the pinning force. It is considered necessary to create materials with critical current densities.

Microprecipitates, grain boundaries, and various defects can be considered as pinning centers. For rare earth superconductors, REzBaCu
It is known that the Oa phase (RE is a rare earth element) and other fine particles of the non-superconducting phase (dispersed in the crystal) can become the pinning center. Tl-based superconductors partially melt at temperatures above about 910°C. , when this is cooled, it becomes 2212 in the early stage of solidification.
Phase crystals are formed, and when the mixture is allowed to cool slowly, it easily undergoes a phase transformation to 2223 phase or the like. REJaCuO for T1 superconductor
There is no non-superconducting phase such as the a-phase precipitated in a superconducting crystal, and there are no reports of introducing a non-superconducting substance completely different from a superconductor into a crystal.

[Means for Solving the Problems] The present invention provides T1. In a crystal containing Ba, Ca, Cu, 0 as constituent elements, at least one metal selected from Group 2A elements and at least one metal selected from Group 4A, Group 4B, and rare earth elements. The present invention provides an oxide superconductor tape characterized in that an oxide superconductor film having a structure in which granular crystals of a composite oxide are fractionated into island shapes is laminated with a metal.

In the present invention, a composite oxide of at least one metal selected from Group 2A elements and at least one metal selected from Group 4A, Group 4B, and rare earth elements is ABO.
m (A is 1 selected from Mg, Ca, Sr, Ba
B is preferably one or more selected from Zr, Sn, Ce, and Ti).
In this case, ABOI becomes a crystal with a perovskite structure. All of these crystals are compositionally stable substances up to around 1200°C in the atmosphere, and do not react with the melt of the Tl superconductor at temperatures of 910 to 980°C, which is the partial melting temperature of the T1 superconductor. Almost no grain growth.

The superconductor of the present invention can be suitably produced by mixing the raw material of the Tl-based superconductor with the above composite oxide, heating this above the partial melting temperature of the superconducting phase, and then cooling and solidifying it. When a mixture of the superconducting phase and the composite oxide is heated to a temperature higher than the partial melting temperature of the superconducting phase and then cooled and solidified, the composite oxide crystals form the superconducting phase while maintaining the particle size added at the time of preparation. Incorporated into crystals.

At this time, if the above composite oxide in which only fine particles are selected is used, a non-superconducting substance of the same size as the composite oxide can be dispersed in the superconducting phase crystal, which is desirable from the viewpoint of strengthening the pinning 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.

When using ABOs, the amount added is 0.5wt
% or more and 20 wt% or less. Addition amount is 0.5
If the amount is less than 20 wt%, there is a risk that the effect of the present invention will not be fully expressed, and if the amount added exceeds 20 wt%, the ABO3 phase may segregate in a part of the material, causing discontinuity in the superconductor. I don't like it because it is. More preferably, the amount of ABO added is 1 to 10 wt%.

The superconducting tape of the present invention is preferably manufactured in a metal plate or flat pressed metal tube that does not react with the superconductor melt, so that when crystals grow from the melt, Because the C-axis of the superconductor crystal grows perpendicular to the surface of the metal due to surface tension, a superconducting tape with crystals aligned in the same direction can be obtained.

Preferred metals that do not react with the superconductor melt are gold, silver, or alloys containing these as main components.

The superconducting tape of the present invention can be produced by melting and solidifying a green sheet containing raw material powder obtained by a doctor blade method on a metal plate, by forming a film on a metal plate by screen printing, etc. It is manufactured by filling raw material powder inside, pressing a metal tube, forming it into a tape, and melting and solidifying it.

[Example] Example I B was added so that the atomic ratio of Ba:Ca:Cu was 2:3:4.
aC0m, CaCO5, and CuO were weighed and mixed, and this was calcined in air at 880''C for 10 hours using an electric furnace.TIJs was added to the calcined powder as Tl:Ba:Ca:C.
Add u so that the atomic ratio is 2:2:'3:4 (this is referred to as powder X), and further add ABO and powder (average particle size 0.5 μm ) to 5wt
% and mixed.

After mixing the powder with octyl alcohol, it was mixed with 0.
It was screen printed on a 1mm×10mm×50II1m gold plate and dried. This was sealed in an alumina tube with an inner diameter of 16 mm, melted at 950'C for 5 minutes, rapidly cooled to room temperature, heated further to 89G'C, held for 8 hours, and rapidly cooled.

The cross section of the coagulated tape thus obtained was observed using a scanning electron microscope and an X-ray elemental analyzer.
It was confirmed that the crystal grains of the plate-like 2223 phase overlapped in a layered manner as shown in the figure, and had a structure in which ABO particles with a grain size of about 0.5 μm were dispersed in a layered manner. A good structure as described above was observed throughout the sample.

The measurement results of the superconducting properties are shown in Table 1. For these measurements, a tape cut into a 2I width was used. The critical temperature is the temperature at which zero resistance was measured using the DC four-probe method, and the critical current density was measured using the same DC four-probe method at the temperature of the liquid element with an external magnetic field of 2 Tesla applied. The magnetic field was applied parallel to the C axis of the superconducting crystal.

Table 1 Example 2 5 wt% of ABOa powder (average particle size 0.5 μm) consisting of the combination of ^ and B shown in Table 2 was added to powder X in Example 1.
Add and mix the powder to an outer diameter of 4.6■ψ and an inner diameter of 3 ++v.
After filling a brass tube with a diameter of 100 mm and a wire drawing process to an outer diameter of 1.5 mm, this was pressed to a width of 3 mm.
It was made into a national tape with a thickness of 0.2 m. After sealing both ends of the obtained tape with a welding machine, it was 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.

When the cross section of the coagulated tape thus obtained was observed using a scanning electron microscope and an X-ray elemental analyzer, the third
It was confirmed that the plate-like 2223 phase crystal grains as shown in the figure were layered and had a structure in which ABO particles with a grain size of about 0.5 μm were dispersed in the form of islands. A good structure as described above was observed throughout the sample.

Table 2 shows the superconducting properties measured in the same manner as in Example 1.

Table Example 3 To the powder X in Example 1, 5 wt % of ABO consisting of the combination of A and B shown in Table 3, selected to have an average particle size of 0.15 μm, was added and mixed. After mixing the powder with octyl alcohol, it was divided into 0.1 mm x 50
It was screen printed on a mm gold plate and dried. This inner diameter is 1
6) Enclose in a φ alumina tube, melt at 950°C for 5 minutes, rapidly cool to room temperature, and then further heat to 890°C.
The mixture was held for a period of time and quenched.

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, plate-shaped 2223 phase crystal grains overlap in a layered manner, and ABO with a grain size of about 0.15 μm,
It was confirmed that the particles had a structure in which they were dispersed in the form of islands. A good structure as described above was observed throughout the sample.

Table 3 shows the superconducting properties measured in the same manner as in Example 1.

Table Comparative Example 1 Powder X in Example 1 was mixed with octyl alcohol and then mixed into 0.1 mm
It was screen printed on a gold plate and dried. This inner diameter is 1
It was sealed in an alumina tube with a diameter of 6 mm, melted at 950'C for 5 minutes, rapidly cooled to room temperature, heated further to 890'C, held for 8 hours, and rapidly cooled.

When the cross section of the coagulated tape thus obtained was observed using a scanning electron microscope and an X-element analyzer, it was found that it had a structure in which plate-shaped 2223 phase crystal particles overlapped in a layered manner as shown in Figure 4. It was confirmed that this was the case. A good structure as described above was observed throughout the sample.

When measured in the same manner as in Example 1, the critical temperature was 12
2, the critical current density at liquid nitrogen temperature is 340A.
/am”.

Comparative Example 2 Powder X in Example 1 was mixed with an outer diameter of 4. BT5mφ, inner diameter 3
After filling a brass tube with nunφ and length of 100 mm, wire bowing was performed to obtain an outer diameter of 1.5 mm, and this was pressed into a tape shape with a width of 3 mm and a thickness of 0.2 mm. After sealing both ends of the obtained tape with a welding machine, it was melted at 950°C for 5 minutes, rapidly cooled to room temperature, and then further heated to 890'C and held for 8 hours to be rapidly cooled.

When the cross section of the coagulated tape thus obtained was observed using a scanning electron microscope and an X-ray elemental analyzer, it was found that
It was confirmed that the sample had a structure in which plate-shaped 2223 phase crystal grains overlapped in a layered manner as shown in the figure. The above-mentioned structure was observed throughout the sample.

When measured in the same manner as in Example 1, the critical temperature was 12
0, the critical current density at liquid nitrogen temperature is 300A.
/cm”.

[Effects of the Invention] The superconducting tape of the present invention has very fine non-superconducting phases dispersed therein, and this acts as a center for good binding of magnetic flux, so that the critical current density is high even in a strong magnetic field.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a Tl-based superconducting tape manufactured by a sintering method. FIG. 2 is a schematic diagram showing the structure of the superconducting tapes obtained in Examples 1 and 3. FIG. 3 is a schematic diagram showing the structure of the superconducting tape obtained in Example 2. FIG. 4 is a schematic diagram showing the structure of the superconducting tape obtained in Comparative Example 1. FIG. 5 is a schematic diagram showing the structure of the superconducting tape obtained in Comparative Example 2. '1-' Book 1 (1t1: 2 Figure 2 Bag hammer)

Claims (3)

[Claims] 1. At least one metal selected from Group 2A elements and at least one metal selected from Group 4A, Group 4B, and rare earth elements in a crystal containing TI, Ba, Ca, Cu, and O as constituent elements. An oxide superconductor tape characterized in that an oxide superconductor film having a structure in which granular crystals of a composite oxide with a metal are laminated with a metal. 2. A composite oxide of at least one metal selected from group 2A elements and at least one metal selected from group 4A, group 4B, and rare earth elements is ABO_3 (A is Mg, Ca, Sr, One or more types selected from Ba, B is Z
2. The oxide superconductor tape according to claim 1, wherein the oxide superconductor tape is one or more selected from the group consisting of R, Sn, Ce, and Ti. 3. The oxide superconductor tape according to claim 1 or 2, wherein the crystals containing TI, Ba, Ca, Cu, and O are obtained by solidifying a melt.