JPH0446054A - Superconductor and its production - Google Patents

Abstract

PURPOSE:To improve the critical current density of the superconductor in a strong magnetic field by dispersing a specified multiple oxide in a crystal contg. Tl, Ba, Ca, Cu and O. CONSTITUTION:The superconductor material contg. Tl, Ba, Ca, Cu and O and 0.5-20wt.% of the multiple oxide of >=1 kind of metal selected from group IIb elements such as ABO3 (A is >=1 kind selected from Mg, Ca, Sr and Ba, and B is >=1 kind selected from Zr, Sn, Ce and Ti) and >=1 kind selected from group IVa, group IVb and rare-earth elements are mixed. The mixture is heated above the partial melting temp. (910-980 deg.C) of the superconducting phase, a crystal contg. Tl, Ba, Ca, Cu and O is unidirectionally solidified from the melt at the temp. gradient of >=20 deg.C/cm and at the crystal growth rate of <=20mm/h, and an oxide superconductor in which the granular crystals of the multiple oxide are insularly dispersed in a matrix in which the plate crystals of the oriented superconducting phase are present in layers is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention provides Tl-Ba-'Ca-Cu having a novel structure.
The present invention relates to a -0-based oxide superconductor and a method for producing the same.

[Prior art] Conventionally, T1-Ba-Ca-Cu-0 based superconductor (hereinafter referred to as T
Tl1BaaCaxCusO (also called l-based superconductor)
y (hereinafter also referred to as 2223 phase), ■1tBaaCaC
uzOy (hereinafter also referred to as 2212 phase), TlB
a1CaACu40y (hereinafter also referred to as 1234 phase)
It is known that there are many phases, and the critical temperature of most of these phases is higher than the liquid nitrogen temperature (f77K). T
As a method for manufacturing a bulk body of a type 1 superconductor, there is a method in which a crystal powder having the above composition is synthesized, and then this is formed and sintered. In addition, it is known to manufacture by a melt solidification method.

[Problems to be Solved by the Invention A superconductor produced by a co-sintering method is usually a porous polycrystalline body. Each crystal grain is arranged in a disordered direction, and the bonds between the grains are weak. In T1 superconductors, the direction in which current flows easily within the crystal grains is determined.
There is a property that it is difficult for electric current to flow between crystal grains with different orientations. Furthermore, a small bonding area between grains means that the effective current path is narrow. For this reason, it was not possible to obtain a polycrystalline Tl-based superconductor with a high critical current density. If the direction of the crystal grains is controlled by pressing the polycrystalline material,
Since the crystal grains are oriented in the same direction, the critical current density is improved. Similarly, when manufactured by the melt solidification method, the crystal grains become thicker (grow), denser, and the bonds between the grains become stronger, thereby improving the critical current density.

The critical current density of Tl-based superconductors can be further increased when manufactured by a unidirectional solidification method that combines control of grain direction and melt solidification, but when manufactured by any of these methods, the critical current density at liquid nitrogen temperature is Current density drops significantly in a magnetic field. This is thought to be due to the weak binding force of the magnetic flux penetrating the crystal in a magnetic field higher than the lower critical magnetic field of the Tl-based superconductor. The main field of application for superconductors is considered as electromagnets that create strong magnetic fields by processing wire or tape materials into coils. Therefore, in order to put Tl-based superconductors into practical use, it is necessary to create a structure in which the crystal directions are precisely aligned and to introduce a binding center into the crystal to strengthen the binding force. It is considered necessary to create materials with critical current densities.

T1 superconductors partially melt at temperatures of about 910°C or higher,
When this is cooled, 2212 phase crystals are generated in the early stage of solidification, and when it is slowly cooled as it is, it easily transforms into 2223 phase and the like.

Fine precipitates, grain boundaries, and various defects are considered to be the center of bottle fixation. For rare earth superconductors, REJaCu0
It is known that fine particles of five phases (RE is a rare earth element) and other non-superconducting phases finely dispersed in the crystal can serve as the center of binding. Tl-based superconductors do not have non-superconducting phases such as the RE2BaCuO= phase that precipitate in superconducting crystals, and there are no reports of introducing non-superconducting substances completely different from superconductors into crystals.

However, in the molten state of the D1-based superconductor,
Fine particles of a non-superconducting substance that does not react with any solid phase or liquid phase and do not grow at high temperatures (melting temperature) are homogeneously dispersed in the material before solidification, and are unidirectionally solidified to become homogeneous in the superconducting phase crystal. The method of dispersion is considered to be excellent in strengthening the center of the bottled material.

[Means for Solving the Problems] The present invention includes at least one metal selected from Group 2A elements and Group 4A and 4B elements in a crystal containing TI, Ba, Ca, C, u, and O as constituent elements. The present invention provides an oxide superconductor having a structure in which a composite oxide with at least one metal selected from the group consisting of metals selected from the group consisting of rare earth elements and rare earth elements is dispersed.

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 AB
O3 (^ is one or more selected from Mg, Ca, Sr, and Ba; B is one or more selected from Zr, Sn, Ce, and Ti);
Unfortunately, in this case, ^BO, becomes a perovskite-type transverse crystal. Both of these crystals are 120% in the atmosphere.
It is a substance that is compositionally stable up to around 0°C, and does not react with the melt of the Tl-based superconductor at temperatures of 91.0 to 980°C, which is the partial tolerance temperature of the Tl-based superconductor, and hardly grows grains.

The superconductor of the present invention can be suitably produced by mixing the raw material of the Tl-based superconductor with the above-mentioned composite oxide, heating this to a temperature equal to or higher than the partial melting temperature of the superconducting phase, and then cooling and solidifying.

When a mixture of a superconducting phase and the above composite oxide is heated to a temperature higher than the partial melting temperature of the superconducting phase and then cooled and solidified, the above composite oxide crystals form a superconducting phase while maintaining the particle size added at the time of preparation. Incorporated into crystals. That is, if the above-mentioned 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 bottle-holding force. Especially when using only particles of 0.5 μm or less,
The critical current density increases dramatically and does not decrease much even when a magnetic field is applied.

When ABOS is used, the amount added is 0.5wt%
It is preferably at least 20 wt%. Added amount is 0.5w
If the amount is less than t%, the effect of the present invention may not be fully expressed, and if the amount added exceeds 20 wt%, the ABOs phase will segregate in a part of the material, causing discontinuity in the superconductor. I don't like it because it's scary. More preferably, the amount of ABO added is 1 to 10 wt%.

The superconductor of the present invention has a temperature gradient of 20°C/am or more,
It is preferable to manufacture by unidirectionally solidifying a superconducting phase product from a melt at a crystal growth rate of 20 mm/hLJ under the following conditions. As a result, a solidified product is obtained having a structure in which granular crystals of the composite oxide are dispersed in islands in a matrix in which oriented plate-like crystals of the superconducting phase overlap in a layered manner.

[Example Go Example I
aCO5, CaCO5, and CuO were weighed and mixed, and the mixture was fired in air at 880°C for 10 hours using an electric furnace.

Tl*Oz is added to this fired powder as Tl:Ba:Ca:C
Add u so that the atomic ratio is 2+2:3:4, and further add 5 wt% of ABOs powder (average particle size 0.5 μm) consisting of the combination of A and B shown in Table 1 and mix. 70ml1lX 10mmX2 by mold press
It was molded to +++m.

The obtained molded body was sealed in an alumina tube with an inner diameter of 16 mmφ, and the tube was moved at a speed of 3 mm/h using an electric furnace having a temperature gradient of 50 °C/cm and a maximum temperature of 920 °C. Ta. The resulting coagulum was further
The temperature was increased to °C, held for 8 hours, and then rapidly cooled.

Scanning electron microscope and X
When observed using a line elemental analyzer, the plate-shaped 2223-phase crystal grains as shown in Figure 1 overlapped in a single shape, and among them, ABO1 particles with a grain size of about 0.5 μm were found to be island-like fractions. It was confirmed that the tissue was present. A good structure as described above was observed throughout the sample.

Table 1 shows the III constant results of superconducting properties. For these measurements, the sample size is 1lIlo X O, 1eon
A piece cut to the size of the mouth 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 liquid nitrogen temperature with an external magnetic field of 2 Tesla applied. The magnetic field was applied parallel to the C axis of the superconducting crystal.

Table Example 2 Ba was added so that the atomic ratio of Ba:Ca:Cu was 23.4.
C0m CaCC1m CuO were weighed and mixed, and this was fired in air at 880° C. for 10 hours using an electric furnace. Add 1□O3 to this fired powder.
were added so that the atomic ratio was 2:2:3:4, and further 5 wt% of BO1 powder selected to an average particle size of 0.15 μm consisting of the combination of A and B shown in Table 2 was added and mixed. After that, the powder was molded into a size of 70mm x 10m using a mold press.
It was molded to m x 2 mm.

The obtained molded body was sealed in an alumina tube with an inner diameter of 16 mmφ, and the tube was moved at a speed of 3+ am/h using an electric furnace having a temperature gradient of 50° C/cm and a maximum temperature of 920° C. Ta. The resulting coagulum was further
It was heated to 0°C, held for 8 hours, and then rapidly cooled.

Scanning electron microscope and X
When observed using a line elemental analyzer, as shown in Figure 1, plate-shaped 2223-phase crystal grains overlapped in a layered manner, and ABO particles with a grain size of about 0.15 um were dispersed in islands among them. It was confirmed that the tissue was present. 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 Comparative Example Ba: Ca: Cu so that the atomic ratio is 2:3:4
aC0s, CaC0*, and CuO were weighed and mixed, and this was fired in air at 880"C for 10 hours using an electric furnace. T120m was added to the fired powder at 1:Ba+
After adding and mixing the ca:Cu atomic ratio to be 2:2:3:4, the powder was molded into a 70mm×
It was molded to 10+nm x 2mm.

The obtained molded body was sealed in an alumina tube with an inner diameter of 16n+mφ, and the high temperature part of the layer was heated to 920'C and 50'C/cm.
Using an electric furnace with a temperature gradient of 3 mm/h
moved at a speed of The resulting solidified product was further heated to 890'C, held for 8 hours, and then rapidly cooled.

Scanning electron microscopy M and X of the coagulum obtained in this way
Using a line elemental analyzer, we found that FI! has a structure in which plate-shaped 2223-phase crystal grains overlap in layers as shown in Figure 2. It has been certified. The above-mentioned structure was observed throughout the sample.

Superconducting properties were measured in the same manner as in Example 1. The critical temperature is 122, and the critical current density is 130OA/cm.
"Met.

[Effects of the Invention] The superconductor of the present invention has very fine non-superconductor crystal grains dispersed therein, which act 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 the superconductor obtained in the example. FIG. 2 is a schematic diagram showing the structure of an electromotive conductor obtained in a comparative example.

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 with a structure in which composite oxides are dispersed. 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 according to claim 1, wherein the oxide superconductor is one or more selected from r, Sn, Ce, and Ti. 3. Temperature gradient is 20℃/cm or more, crystal growth rate is 20℃/cm or more
TI, Ba, Ca, Cu from the melt under conditions of less than mm/h
, O. The method for producing an oxide superconductor according to claim 1 or 2, characterized in that the crystal containing O is unidirectionally solidified.