JPH10316421A - Superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bulk material of a structure resistant to electromagnetic force, by forming an electric current passage in a superconducting state of a bulk superconductor inside an oxide-based bulk superconductor out of a nonsuperconductor. SOLUTION: This superconductor is an oxide-based superconductor, in which an electric current passage is formed in a superconducting state inside a bulk superconductor represented by formula I REBa2 Cu3 Ox out of a nonsuperconductor represented by formula II Pry RE'1-y Ba2 Cu3 Ox (RE is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu; RE' is Y, La, Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu). The crystallization starting temperature of the bulk superconductor represented by formula I is the same as or higher than that of the nonsuperconductor represented by formula II. The electric current passage can sufficiently be made long by arranging the nonsuperconductor represented by formula II in the interior of the bulk superconductor represented by formula I so as to provide a meander structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a superconducting / normal-conducting transition resistance type current limiter, a persistent current switch, and a superconducting coil using a superconducting bulk material.

[0002]

2. Description of the Related Art In a superconducting state and a normal conducting state, the ratio of electric resistance becomes close to infinity, and attempts to use this as a switch have been made for a long time. The superconducting / normal-conducting transition resistance type current limiter utilizes the fact that, when a certain overcurrent flows, it makes a normal-conducting transition with a certain finite resistance from a superconducting state with zero electric resistance, and the current flows to another bypass path. Is a device that protects the power transmission system or the electrical equipment at the end by diverting most of the power. On the other hand, the permanent current switch has a heater attached to the superconductor, and mainly controls the superconducting state and the normal conducting state thermally, and is used as a switch.

A material property required for these applications is a high resistivity in a normal conduction state, which is excellent in a switch property. An oxide superconductor, one of which is the YBa ₂ Cu ₃ Ox-based superconductor mentioned in the present invention, generally has a high electric resistivity in a normal conducting state. In addition, the higher the critical current density, the smaller the cross-sectional area of the current path, so that the electric resistance in the normal conducting state can be designed to be relatively large. It is preferable that the critical current density be high as described above. Especially YBa ₂ Cu ₃
The critical current density of the Ox-based superconductor is high and is considered to be suitable for applications such as a current limiter. The position of Y is other La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
y, Ho, Er, Tm, Yb, Lu, it may be replaced with one or more elements selected from the group consisting of
_{It is described as 2} Cu ₃ O _x .

As a method for producing this REBa ₂ Cu ₃ O _x , a QuenchandMeltGrowth method (Patent Registration No. 01869884, and Japanese Patent Application Laid-Open No. H5-1939)
38). By using this manufacturing method, a relatively large superconducting material having a high critical current density can be obtained.

[0005] However, since the shape obtained by this method is bulky, there is a limit to taking a long straight current path. Therefore, in order to increase the electric resistance in the normal conduction state, a zigzag current path (meander structure)
Then, a method of taking a long current path as a whole is adopted. Conventionally, when a meandering structure is formed, the strength of the conductor is reduced as the cross-sectional area is reduced, since the conductor is cut and manufactured. In addition, there is a possibility that the conductors may be destroyed in some cases because an attractive force acts between adjacent conductors due to energization. For this reason, the meander structure and the like have low strength and are fragile. In particular, a structure that is resistant to thermal shock at the time of transition to normal conduction and electromagnetic force caused by flowing a large current has been desired.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a REBa ₂ Cu ₃ Ox-based bulk material having a long current path and having a structure resistant to an electromagnetic force caused by flowing a large current and a thermal shock at the time of normal conduction transition. To provide.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems.
Like a material produced by the Melt Growth method, by partially substituting Pr in the RE composition of the oriented REBa ₂ Cu ₃ O _x -based bulk superconductor, the superconductivity of the portion is lost, and the current of the superconducting current is reduced. In this method, a path is formed, and as a result, means for taking a long current path is taken.

A first feature of the present invention is that the oriented REBa
Inside Pr _y R of ₂ Cu ₃ O _x type bulk superconductor (1)
An oxide superconductor characterized in that a current path in the superconducting state of the bulk superconductor (1) is formed by the E ′ _1-y Ba ₂ Cu ₃ O _x -based non-superconductor (2). Here, RE is Y, La, Ce, Pr, Nd, Pm, Sm, E
u, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
Refers to one or more elements selected from the group consisting of RE ′ is Y, La, Ce, Nd, Pm, Sm, Eu, G
One or more elements selected from the group consisting of d, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

The non-superconductor (2) in the present invention means a temperature (critical temperature) at which the bulk superconductor (1) enters a superconducting state.
Or a non-conductive material at or above the temperature. The fact that the non-superconductor (2) forms a current path in a superconducting state in the present invention means that the current path flowing through the bulk superconductor (1) in the material (2) in the non-superconducting state is used. Limits and lengthens the current path. For example, when the current path of the bulk superconductor (1) has a meander structure, the material (2) in the non-superconducting state is used.
Is arranged in a portion (11) in FIG.
In addition to the two-dimensional meander structure shown in FIG.
The current path may be formed to have a three-dimensional meander structure as disclosed in Japanese Patent Application Laid-Open No. Hei 8-18110.

According to a second feature of the present invention, in the superconductor according to the first aspect, the crystallization onset temperature of the REBa ₂ Cu ₃ Ox-based bulk superconductor (1) is Pr _y RE ′ _{1 -y} Ba ₂ Cu ₃ O _x.
A superconducting conductor characterized by being equal to or higher in crystallization temperature of the non-superconductor (2). A third feature of the present invention is the superconductor according to claim 1 or 2, wherein the ratio y of Pr in the non-superconductor (2) is 0.5 or more and 1.0 or less. . Fourth Embodiment of the Present Invention
The feature of the present invention is a superconducting / normal conducting transition resistance type current limiting device using the superconducting conductor according to any one of claims 1 to 3.

The present invention has a structure that is resistant to electromagnetic force caused by the flow of a large current and thermal shock at the time of transition to normal conduction, and is intended to maintain a long-term stable current limiting operation that is resistant to mechanical destruction. It is a superconducting conductor. Hereinafter, the present invention will be described in detail.

The formation of a current path in the REBa ₂ Cu ₃ Ox-based bulk superconductor (1) by the Pr _y RE ′ _1-y Ba ₂ Cu ₃ O _x -based non-superconductor (2) will be described below. R
The material for forming the current path of the EBa2Cu3Ox-based bulk superconductor (1) has a high electric resistivity and a thermal expansion coefficient similar to that of the bulk superconductor (1) with respect to cooling and temperature rise. Is desired. Pr _y used in the present invention
The RE ′ _1-y Ba ₂ Cu ₃ O _x non-superconductor (2) rapidly loses the superconducting state in accordance with the amount of replacement of RE of the bulk superconductor (1) by Pr, and exhibits a large electric resistivity. In addition, since the crystal structure is almost the same, the thermal expansion coefficient of this non-superconductor (2) is almost the same as that of the bulk superconductor (1). By integrally forming this material, the current path of the bulk superconductor (1) can be lengthened, and the decrease in material strength due to the lengthening of the current path can be reinforced by the non-superconductor (2). .

[0013] The superconductive bulk body (1) said Pr _y R
When a current path is formed by the E ′ _1-y Ba ₂ Cu ₃ O _x non-superconductor (2), the corners of the end portions where (1) and (2) are in contact with each other should not be as sharp as possible and should be as round as possible. Is preferred. This is done, for example, by making the end portion (12) of the non-superconductor (2) not to have a corner as shown in FIG. 2 and by making the corner (13) of the end portion round as shown in FIG. To be placed in If superconducting bulk (1)
If there is a corner at the end portion where the PRE and the PRYRE '1-yBa2Cu3Ox non-superconductor (2) are in contact, the load carrying current tends to concentrate on the corner portion as shown in FIG. Normal conduction transition is likely to occur at this site. However, since this portion is also a portion where the material strength is apt to be weakened, the superconducting bulk body (1) is destroyed by thermal stress generated by heat generation due to normal conduction transition or electromagnetic force due to a sudden change in current. Sometimes. Therefore, the above-described obstacle can be avoided by rounding the corners of the end portion, which is preferable as a limitation on the current path. That is the reason.

Next, the crystallization start temperature of the REBa ₂ Cu ₃ O _x -based bulk superconductor (1) is Pr _y RE ′ _{1 -y} Ba ₂ Cu ₃ O
_The fact that the temperature is the same as or higher than the crystallization start temperature of the non-superconductor (2) will be described. The crystallization onset temperature of the REBa ₂ Cu ₃ O _x -based bulk superconductor (1) is defined as REBa ₂ Cu
_The temperature at which the precipitation of REBa ₂ Cu ₃ O _x starts when the temperature of the ₃ O _x -based bulk superconductor is gradually lowered from a high temperature. That is, in the high temperature, but becomes a semi-molten state of coexistence of RE2BaCuO5 phase and Ba-Cu-O was used as a main component liquid phase, REBa ₂ Cu ₃ O _x by slow cooling
Phase precipitation begins at a certain temperature. The crystallization onset temperature is
Refers to this temperature. Similarly, PryRE '1-yBa2Cu
The crystallization start temperature of the 3Ox non-superconductor (2) is defined as P when the temperature of the RE conductor (1) is gradually lowered from a high temperature.
refers to the temperature at which _{r y RE '1-y Ba} 2 Cu 3 precipitation of O _x (2) is started. If, REBa ₂ Cu ₃ O _{x x} based crystal starting temperature of the bulk superconductor (1) is _{Pr y RE '1-y Ba} 2 Cu 3
If the temperature is lower than the crystallization start temperature of the O _x non-superconductor (2), P
After _{r y RE '1-y Ba} 2 Cu 3 O x non superconductor (2) is crystal-grown, REBa ₂ Cu ₃ O _x type bulk superconductor (1) begins to crystal growth. In this case, REBa ₂ C
Crystal growth of the u ₃ O _x -based bulk superconductor (1) starts from both sides of the current path, and crystal growth surfaces from both sides collide at the center. However, on the surface where the crystal growth surface meets, RE2Ba that could not be incorporated during crystal growth was used.
CuO5 phase precipitates and grain boundaries often occur,
For the REBa ₂ Cu ₃ O _x -based bulk superconductor (1) that functions as a current path, it becomes an undesirable conductor for flowing a large current. However, conversely, REBa ₂ Cu
The crystal onset temperature of the ₃ O _x -based bulk superconductor (1) is Pr _y
When the temperature is higher than the crystallization start temperature of the RE ′ _1-y Ba ₂ Cu ₃ O _x non-superconductor (2), segregation and grain boundaries are caused by Pr _y R
E ′ _1-y Ba ₂ Cu ₃ O _x non-superconductor (2), which is a preferable conductor for flowing a large current. That is the reason.

The fact that the ratio y of Pr in the non-superconductor (2) is 0.5 or more and 1.0 or less will be described. P
_{r y RE '1-y Ba} 2 Cu 3 O x non superconductor it is preferably y is large (2), in particular desirably 0.5 or more.
This is because at a temperature of 100 K at which the REBa ₂ Cu ₃ Ox-based bulk superconductor (1) becomes a normal conductor, the electrical resistivity at y = 0.5 or more is at least 5 times as large as y = 0.0. This is because it has resistivity. Due to this high electric resistivity, the Pr _y RE ′ _1-y Ba ₂ Cu ₃ O _x non-superconductor (2) can effectively form a current path of the REBa ₂ Cu ₃ O _x -based bulk superconductor (1). it can. That is the reason.

Finally, the superconducting / normal conducting transition resistance type current limiting device will be described. The superconducting / normal-conducting transition resistance type current limiting device is, for example, a power transmission system including a superconducting conductor (21), a cooling unit (22), and a current introducing unit (23) as shown in FIG. A device that protects equipment. In addition, in order to stably operate the superconducting conductor, the superconducting conductor is often provided with a shunt part (24) for partially or entirely diverting the current. For example, a current limiting device in which the surface of the superconducting conductor (1) is coated with silver by a sputtering method or the like is also included in the superconducting / normal conducting transition resistance type current limiting device of the present invention. By applying the above-described superconducting conductor to the superconducting conductor portion (21), it has a high electric resistance, is resistant to thermal shock at the time of normal conduction transition and electromagnetic force caused by flowing a large current, and is resistant to mechanical destruction. It is possible to obtain a current limiting device that maintains a strong and stable current limiting operation for a long time. That is the reason.

[0017]

An embodiment will be described below with reference to the drawings. First, Quench and Melt in the following examples
The Growth method will be described. REBa ₂ Cu ₃
A small amount of platinum powder is added to RE ₂ O ₃ , BaO ₂ , and CuO powder, which are raw material powders of Ox, and kneaded. Similarly Pr _y R
RE2O3, Ba, which is a raw material powder of E ' _1-y Ba ₂ Cu ₃ O _x
A very small amount of platinum powder is added to O2 and CuO powders to produce a kneaded powder, and a molded body having a pattern as in each example is produced. This is combined with the RE ₂ BaCuO ₅ phase (or Pr _2y RE ′ _2-2y BaCuO ₅ ) and Ba—Cu—O
The temperature is raised to a semi-molten state in which a liquid phase containing as a main component coexists, and then seeding is performed on the above compact using RE ₂ BaCuO ₅ substituted with an RE element having a high crystal growth start temperature as a seed crystal, and then gradually cooled. Then, a crystal is grown from the seed crystal. The above is Quenchand Melt Growth
It is an explanation of the h method.

(Example 1) Pr _y RE ' _1-y Ba ₂ Cu ₃ O
Pr _y to investigate the change in electrical resistivity due to the change in _x and _y
RE ′ _1-y Ba ₂ Cu ₃ O _x bulk superconductor was prepared, and its electrical resistivity was examined by a four-terminal method. The sample was finally sufficiently annealed at 400 ° C. in an oxygen atmosphere, and the value of x was 6.92.

Table 1 shows that the critical temperature (Tc) for each substitution amount (y) and the electric resistivity of YBa ₂ Cu ₃ Ox at 100 K are 1.0, and Y _{1 -y} Ba ₂ Cu ₃ O is used.
It shows the magnitude of the electrical resistivity of the x-body. From these results, PryY1-y substituted for 0.5 or more with the value of y
It can be said that the Ba2Cu3Ox bulk superconductor has an effective composition as the non-superconductor (2).

[0020]

[Table 1]

(Example 2) As a superconducting conductor of a sample, R
E the Some YBa ₂ Cu ₃ Ox-based bulk superconductor Y ₂ BaCuO ₅ are dispersed 25% charge composition as _{Y (1), Pr 0.7 Y} 0.3 of Pr _0.7 Y _0.3 BaCuO ₅ are dispersed 25% charge composition A precursor having a diameter of 60 mm was prepared by arranging Ba ₂ Cu ₃ Ox non-superconductor (2) as shown in FIG.
Crystals were grown by the Quench and Melt Growth method. 2 mm depth from the seeded surface is polished and shaved off, and 5 m thick with a diamond cutter
m was cut off. This was used as a superconducting conductor. Ag was deposited on both ends and annealed at 400 ° C. in an oxygen atmosphere. Then, it was connected to the current terminal by soldering. The energization was repeated while this was immersed in liquid nitrogen, and stable energization and current limiting were confirmed.

Example 3 As a sample superconducting conductor, R
E is Dy, and Dy ₂ BaCuO5 is 30 in the charged composition.
% Dispersed DyBa ₂ Cu ₃ Ox-based bulk superconductor (1)
Among them, Pr _0.6 Y _0.4 BaCuO ₅ was 2 in the charged composition.
5% dispersed _{Pr 0.6 Y 0.4 Ba 2 Cu 3} Ox non superconductor (2) to create a precursor of the arrangement and diameter 60mm as shown in FIG. 6, Quench and Melt Growt
The crystal was grown by the h method. 2m deep from the seeded surface
m was polished and shaved off, and a 5 mm-thick portion was cut out with a diamond cutter. This was used as a superconducting conductor.
Ag was deposited on both ends and annealed at 400 ° C. in an oxygen atmosphere. Then, it was connected to the current terminal by soldering. This was repeatedly immersed in liquid nitrogen, and the heating and cooling were repeated. However, stable current supply and current limiting were confirmed.

(Embodiment 4) FIG. 7 is a sectional view showing an embodiment of a superconducting / normal conducting transition resistance type current limiting device according to the fourth invention of the present invention. The superconducting conductor produced in Example 3 was applied to the superconducting conductor (21). As a result, it was possible to obtain a current limiting device that maintains a stable current limiting operation for a long time without breaking even at the time of normal conduction transition.

[0024]

According to the present invention, it is possible to obtain an effect of stably limiting current withstanding electromagnetic shock caused by flowing a large current or thermal shock at the transition of normal conduction.

[Brief description of the drawings]

FIG. 1 shows an example in which a current path of a bulk superconductor (1) has a meander structure.

FIG. 2 shows an example in which a corner is formed at an end portion of the non-superconductor (2).

FIG. 3 shows an example in which the end portion of the non-superconductor (2) is rounded

FIG. 4 is a diagram showing a current path when an end portion of a non-superconductor (2) has a corner;

FIG. 5 is a schematic view of a superconducting conductor used in Example 2.

FIG. 6 is a schematic diagram of a superconducting conductor used in Example 3.

FIG. 7 is a sectional view showing one embodiment of a superconducting / normal-conducting transition resistance type current limiting device used in Embodiment 4.

[Explanation of symbols]

Non-superconductive with partial 12-point placing 1 REBa ₂ Cu ₃ O _x type bulk superconductor _{2 Pr y RE '1-y} Ba 2 Cu 3 O x is a bulk superconductor 11 nonsuperconducting state based material (2) End part of body (2) 13 End part of rounded non-superconductor (2) 21 Superconducting conductor part 22 Cooler 23 Current introduction part 24 Shunt part

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 39/20 ZAA H01L 39/20 ZAA // H02H 9/02 ZAA H02H 9/02 ZABB (72) Inventor Mitsuru Morita Nakahara-ku, Kawasaki-shi, Kanagawa 3-35-1, Ida Nippon Steel Corporation Technology Development Division

Claims (4)

[Claims] 1. A current path is formed in a superconducting state by a Pr _y RE ′ _1-y Ba ₂ Cu ₃ O _x -based non-superconductor in an oriented REBa ₂ Cu ₃ O _x -based bulk superconductor. An oxide superconductor characterized by the above-mentioned. Where RE is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, G
at least one element selected from the group consisting of d, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and RE ′ is Y, La, Ce, Nd, Pm, Sm, Eu, Gd, T
At least one element selected from the group consisting of b, Dy, Ho, Er, Tm, Yb, and Lu. 2. The superconducting conductor according to claim 1, wherein
The crystal onset temperature of a ₂ Cu ₃ O _x -based bulk superconductor is Pr
_y RE ′ _1-y Ba ₂ Cu ₃ O _{x A} superconductor characterized by having a crystallization start temperature equal to or higher than that of a non-superconductor. 3. The superconducting conductor according to claim 1, wherein the ratio y of Pr in the non-superconducting conductor is 0.5 or more and 1.0 or less. 4. A superconducting / normal-conducting transition resistance type current limiting device using the superconducting conductor according to claim 1.