JP2571574B2 - Oxide superconductor and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superconductor, particularly to a high-temperature oxide superconductor.

[Prior art and its problems] La-Ba-Cu-O system, La-Sr-Cu-O system, Y-Ba-Cu-
In a layered perovskite-type oxide ceramic such as an O-based or perovskite-type oxide ceramic, the critical temperature Tc is 40 to 125K.
Such high-temperature superconductors have been discovered, but their conversion into conductors has not yet been sufficiently performed, and the critical current density Jc is naturally at a low level.

As an example of a wire rod, there is a case of the first institute of metallurgy, in which La-Sr-Cu-O-based powder is put into a Cu-Ni tube, drawn, and made into a wire rod. , The critical current is 4.2
1000A / cm ² is emitted in K and 10T. However, this is a property measured after removing the Cu-Ni sheath on the outer periphery after forming the wire and then performing a heat treatment, and is not a property as a clad wire.

As an example of the second wire rod, there is an example of Tohoku University Research Institute of Metals, where only the metal component excluding La-Sr-Cu-O-based oxygen is used.
Amorphous alloy tape was formed by quenching the molten metal, and then heat-treated in an oxygen atmosphere.
It was reported that the tape was used, and showed a critical temperature of 40K, but the critical current value was not specified.

Even in the Y-Ba-Cu-O system with a high critical temperature, it is converted into a conductor and has a critical temperature of 87K and a critical current value of 6A / cm ² (at 77.3K).
However, the conductor structure has not been clarified.

As an example in which the Y—Ba—Cu—O system is not made into a wire material but powder-sintered, there is an ATT case, and the boiling point temperature of liquid nitrogen (7
At 7.3K), a high critical current density of 1100 A / cm ² was reported.

In the case of the participant-based superconducting material shown above, if the powder is sealed in a metal tube and subjected to surface reduction processing by drawing, swaging, etc., it is possible to easily turn it into a wire, but as it is in the superconducting state Current can hardly be passed, and high critical temperature and high critical current density cannot be achieved.

The reason why the properties do not appear in the wire rod state by plastic working is
It is considered that the superconducting connection of the superconducting fine powder with strong anisotropy is impossible only by physical contact due to the deterioration of the characteristics due to the deformation of the superconducting fine powder and the compacting effect of the processing step. It is said that in the case of an oxide-based superconducting material, it is necessary to approach the order of 10 to 20 ° in order to expect a tunnel effect due to proximity, which is considered to be the reason that the properties are not obtained only with the powder compact.

In order to solve this, it is necessary to perform a sintering heat treatment after forming the wire, but in the case of the participant-based superconducting material, it is necessary to perform a high-temperature heat treatment in an oxygen atmosphere, at least in the atmosphere, and Cu
-The superconducting powder contained no oxygen when placed in a Ni or Cu metal tube. Furthermore, the superconducting powder and the metal sheath undergo a diffusion reaction, and the composition changes, etc., so that the superconducting properties are not exhibited.

[Object of the Invention] The object of the present invention is to eliminate the above-mentioned disadvantages of the prior art,
An object of the present invention is to provide a novel oxide superconducting material having a high critical temperature and a high critical current density.

[Summary of the Invention] The gist of the present invention resides in that silver or a silver alloy material is used as a sheath material of the oxide superconducting material, whereby oxygen is sufficiently supplied to the oxide superconducting portion of the core during sintering heat treatment. Thus, even after the sheath is covered, the characteristics after the sintering heat treatment are prevented from deteriorating.

Silver itself has good electrical conductivity and thermal conductivity, whereby an oxide superconducting wire stabilized with silver or a silver alloy can be provided, and the critical temperature and critical current density can be greatly improved.

The melting point of silver or a silver alloy is 960 ° C. or less, which limits the sintering temperature to 920 to 930 ° C. or less.

Taking the Y-Ba-Cu-O system as an example, methods for producing superconducting powder include a powder mixing method and a coprecipitation kneading method, and the optimum sintering temperature differs depending on the powder production method and particle size. In the case of the powder mixing method, the optimum temperature is 950 to 1000 ° C, whereas in the case of the coprecipitation kneading method, the optimum temperature can be lowered by about 50 to 60 ° C, and becomes 900 to 950 ° C. From the relation with the melting point of the silver sheath material, the coprecipitation kneading method is a more suitable powder production method.

The oxide superconducting material here is Y-Ba-Cu-O, Er-Ba
-Cu-O, Yb-Ba-Cu-O, La-Ba-Cu-O, La-Sr-Cu-O
Etc. means a layered perovskite type or an oxide superconducting material containing a perovskite type ceramic.

[Example] Fig. 1 shows an example of a manufacturing process for implementing the present invention.

The high-temperature superconducting oxide fine powder used was (Y _0.33 B
a _0.67 ) ₃ Cu ₃ O ₇ -δ, coprecipitation kneading method and powder mixing method. Coprecipitation kneading method is firing at 900-950 ° C.
What was calcined at 950 to 1000 ° C. was pulverized and pulverized.

The superconducting fine powder is compacted, assembled into a silver sheath tube, subjected to surface-reduction plastic working together with the sheath tube, and further drawn and rolled to form a linear or tape-shaped cross section, and then 850 to 950 ° C. The sintering heat treatment was performed in the O ₂ atmosphere or the air in the above temperature range. Then, if necessary, 500 ~ 800 ℃
In, annealing heat treatment to improve the characteristics,
The required superconducting wires were completed. FIG. 2 shows the cross-sectional shape.

Here, the merits of using a silver or silver alloy tube as the sheath material will be described. The first requirement for the sheath material is that it has ductility, ductility of the sheath tube material is important for protecting and reducing the superconducting powder of the core, and silver or silver alloy material is suitable. ing. Second, during superficial sintering in an oxygen atmosphere, good superconducting properties are exhibited without deteriorating the properties of the superconducting material and the sheath material. There are three factors relating to the second condition, one of which is a characteristic deterioration that changes the composition due to a diffusion reaction between the sheath material and the superconducting powder, and the dotted line is a noble metal, and there is little concern about this. Further, in the case of a La-Ba-Cu-O system, it is known that the addition of an Ag element has an effect of improving the critical temperature.
It can be expected that it will not be bad in the case of -Cu-O system. The second factor is that the sheath material is oxidized in an oxygen atmosphere and can no longer be used. This silver dot is a noble metal and has no problem. Third
This is because oxygen deficiency, which plays an important role in the superconducting mechanism of the oxide superconductor, interrupts the flow of oxygen into and out of the superconducting material during sintering heat treatment and annealing heat treatment due to the presence of the sheath material. This is problematic in that it is not suitable and deteriorates the characteristics. However, compared to other metals, the silver or silver alloy material can easily diffuse oxygen and does not cause a problem of oxygen deficiency. Table 1 shows 900 ° C as a value near the sintering temperature.
Shows the value of the diffusion coefficient of oxygen in the metal in the case of silver. However, silver has an order of magnitude higher diffusion coefficient than other metals. The copper material is also relatively large, but the copper material becomes tattered by heating in oxygen, which changes the copper component ratio in the superconducting material, and the copper material cannot be used.

The third condition required for the sheath material is an effect as a stabilizing material for superconductivity, but it is satisfactory as well as conductivity and heat conductivity, and there is no problem.

Outer diameter 1.6mm, core diameter 1.0 manufactured as shown in Fig.1.
Table 2 shows the low-temperature electrical characteristics of the mm-diameter wire together with the comparative examples. The measurement was performed using a four-terminal method, and the outer sheath material was removed with nitric acid, and the sheath material was determined from the change in resistance of only the superconducting portion of the core. The critical current density value Jc is a measured value at 77.3K and OT.

A superconducting state was achieved in the example using silver as the sheath material and in comparative example 1, and no superconducting state was obtained in the comparative example using another metal. In the case of the embodiment, the superconducting fine powder by the coprecipitation kneading method is used, and the sintering temperature can be lowered.
l) The critical current density at Tc = 89K and the boiling point temperature of liquid nitrogen (77.3K) is Jc = 565A / cm ² .

In the case of Comparative Example 1, the superconducting fine powder by the powder mixing method was used, and the sintering temperature of the wire was 900 ° C and the critical temperature (final) Tc
At 82 K and 77.3 K, the critical current density is as low as Jc = 2 A / cm ² , but the superconducting state is achieved.

Comparative Example 2 is a case where Cu-30% Ni was used as a sheath material using a superconducting fine powder by a coprecipitation kneading method, and a case where no heat treatment was performed only by surface-reduction plastic working. When measured, no superconducting properties were shown. When the characteristics of this sample were separately measured from a change in magnetic susceptibility by an inductance method, it was found that the sample exhibited superconductivity at a critical temperature (onset) of 92K. In other words, this is because the oxide raw material powder that has superconductivity has already been used, so that all has not deteriorated even after surface-reduction plastic working. However, the oxide powders were not connected in a superconducting state, and it can be interpreted that they did not show superconductivity in the four-terminal method.

In Comparative Example 3, the wire rod of Comparative Example 2 was subjected to a sintering heat treatment at 900 ° C., but the oxide powder of the core and the sheath material reacted with each other, and did not show superconductivity.

Comparative Example 4 uses copper as a sheath material.
Again, the core oxide powder reacts with the sheath material and does not exhibit superconducting properties. Further, in this case, the sheath material is oxidized tattered and does not serve as the sheath material.

Comparative Example 5 used platinum as the sheath material. In this case, the appearance was good, but the superconductivity was not exhibited, probably because oxygen deficiency was no longer appropriate.

FIGS. 1 and 2 show examples of Ag / Y-Ba-Cu-O wires having a single core structure, but when assembling the sheath, or by re-bundling the wire with the reduced surface area and assembling it into the sheath. , A multi-core structure as shown in FIG. Specifically, when a wire rod having an outer diameter of 1.4 mm was manufactured in a set of seven wires and subjected to a sintering heat treatment, it was confirmed that the wire exhibited superconductivity at 77.3 K or more. With the use of multiple wires, it is expected that the stability of the wire will increase and the critical current value will increase.

[Effects of the Invention] According to the present invention, an oxide superconductor can be made into a wire, and the problem of stability, which is a disadvantage of the oxide superconductor, can be solved, and a high critical current value can be obtained.

Accordingly, a wire that can be used as a superconducting conductor can be manufactured even under liquid nitrogen.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the manufacturing process of the oxide superconducting conductor of the present invention. FIG. 2 is a cross-sectional view of a single-core wire and ribbon-shaped superconductor according to the present invention. FIG. 3 shows a cross-sectional view of a multi-wire, multi-ribbon superconductor of the present invention. 1: oxide superconducting material, 2: sheath material (silver).

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Shinichi Nishiyama 3550 Kida Yomachi, Tsuchiura City Inside of Metal Research Laboratory, Hitachi Cable Co., Ltd. (72) Inventor Tomokazu Kamo 4026 Kujimachi, Hitachi City Hitachi, Ltd. (56) References JP-A-63-26167 (JP, A) JP-A-63-261616 (JP, A) Appl Phys Lett. vol. 50, No. 9, PP 543-544 Matter hott vol. 4 PP 165-169 Phys Rev B vol. 35, No. 16 PP8705-8708

Claims (2)

(57) [Claims] 1. A core comprising an oxide superconducting material produced by a co-precipitation kneading method, and silver or a silver alloy coated around the core. An oxide superconducting conductor, characterized by being subjected to the following. 2. An oxide superconducting fine powder produced by a coprecipitation kneading method is sealed in a tube made of silver or a silver alloy, and then the surface is reduced by plastic working, followed by sintering heat treatment. A method for producing an oxide superconducting conductor, comprising: