JP3123893B2 - Method for producing RE-Ba-Cu-O-based oxide superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an R type having excellent superconducting characteristics, particularly, characteristics of magnetic repulsion with a magnet and characteristics of capturing magnetic flux.
The present invention relates to a method for producing an E-Ba-Cu-O-based oxide superconductor.

[0002]

2. Description of the Related Art After a raw material mixture (precursor) of a RE-Ba-Cu-O-based oxide superconductor (RE is one or more rare earth metal elements) is heated and melted to a temperature equal to or higher than a melting point temperature, a seed is prepared. A crystal is grown from a seed crystal by contacting the crystal, and R
As a method for producing an E-Ba-Cu-O-based oxide superconductor, for example, a method described in JP-A-5-193938 is known. The method described in this publication uses a single crystal having a REBa ₂ Cu ₃ O _7-x phase (123 phase) as a seed crystal. According to this method, the RE element constituting the “123 phase” of the seed crystal and the RE element constituting the “123 phase” of the superconductor to be produced are different from each other, and a combination thereof is selected.
The formation temperature of “three-phase” depends on the “123” of the superconductor to be manufactured.
The temperature is set to be higher than the temperature at which the "phase" is formed, thereby enabling crystal growth by the seed crystal.

[0003]

By the way, the above-mentioned conventional method is so arranged that the formation temperature of the "123 phase" of the seed crystal is higher than the formation temperature of the "123 phase" of the superconductor to be manufactured. Needs to be selected. Therefore, this method is inevitably not applicable when producing a superconductor containing the RE element having the highest formation temperature of the “123 phase” as a constituent element. This is because a seed crystal having a “123 phase” having a higher formation temperature cannot be prepared.

The present invention has been made in view of the above background, and has made it possible to apply a method using a seed crystal even when the formation temperature of the “123 phase” is higher, thereby increasing the size and the size of the seed crystal. RE-Ba-Cu-O that can produce oxide superconductors having high magnetic repulsion characteristics with good yield
An object of the present invention is to provide a method for producing a system oxide superconductor.

[0005]

In order to solve the above-mentioned problems, the present invention provides an RE compound (RE is one or more rare earth metal elements containing Y), a Ba compound, and a Cu compound. mol% (RE, Ba, Cu)
(35, 25, 40), B (35, 35, 30), C
(15, 40, 45) and D (15, 30, 55) are weighed and mixed so as to have a composition in a region surrounded by the points, and then the mixed powder is fired at a temperature of 900 to 1500 ° C. The obtained calcined powder is molded to form a pellet-shaped precursor, and then the precursor is heated at a temperature in the range of 990 to 1300 ° C. to be in a solid-liquid coexistence state, and then brought to a seed crystal contact temperature. Next, this precursor is added to Nd _{1 + Y} Ba _2-Y
In the CU ₃ O _7-x phase (where X and Y are variables that change in the range of X = 0 to 0.5 and Y = 0.1 to 0.5 depending on the oxygen partial pressure during crystallization) Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in composition ratio of Nd _{1 +} YBa _2-y Cu ₃ O _7-x : Nd ₄ Ba
A single crystal dispersed as ₂ Cu ₂ O ₁₀ = 1: 0.1 to 1: 1.5 is contacted as a seed crystal;
The precursor is gradually cooled to room temperature with a temperature gradient of 5 to 50 ° C./cm so that the seed crystal side is on the low temperature side, and has the same orientation as the seed crystal starting from the seed crystal. The structure is characterized in that a large oriented crystal of the RE-Ba-Cu-O-based oxide superconductor is obtained.

[0006]

In the above structure, the precursor having the predetermined composition is subjected to a predetermined treatment and then brought to a seed crystal temperature, and the Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase is used as a seed crystal to be brought into contact with the precursor. (Where X and Y depend on the oxygen partial pressure at the time of crystallization.
0-0.5, Y = 0.1-0.5) Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase contains Nd in composition ratio
_{1 + Y Ba 2-y Cu} 3 O 7-x: Nd 4 Ba 2 Cu 2 O 10 =
By using single crystals dispersed to be in the range of 1: 0.1 to 1: 1.5, for example, “123”
When the formation temperature of the “phase” is relatively high, the RE element is Sm.
In this case, it is possible to obtain a large oriented crystal of the RE—Ba—Cu—O-based oxide superconductor having the same orientation as the seed crystal by performing crystal growth using the seed crystal. RE-Ba-C with excellent superconducting properties, especially the properties of magnetic repulsion with magnets and of capturing magnetic flux
It has become possible to obtain uO-based oxide superconductivity.

[0007] First, as a seed crystal, "123"
Instead of using a single crystal having the “phase” itself, “123”
Nd _{1 + Y} B having a crystal structure similar to that of “phase”
This is because a single crystal having a _2-Y CU ₃ O _7-x phase was used. The Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase functions as a seed crystal and has a function equivalent to “123 phase”.
The fact that the present invention can be used in place of the “123 phase” seed crystal has been found by the present inventors. And this Nd
Nd ₄ Ba ₂ Cu ₂ O in _{1 + Y} Ba _2-Y CU ₃ O _7-x phase
_If it is present in a dispersed form in the ₁₀ phases, its formation temperature depends on the composition ratio of both phases, and by selecting the composition ratio, it is assumed that S is temporarily used as the RE element of the superconductor to be manufactured.
Even if selected m can increase the production temperature of the seed crystal serving _{Nd 1+ Y Ba 2-Y CU} 3 O 7-x phase than generating temperature of the "123 phase".

FIG. 1 shows the composition mol of Nd, Ba and Cu elements in a single crystal in which Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase is dispersed in Nd _{1 +} YBa _{2 -Y} CU ₃ O _{7 -x} phase. The ratio is shown in triangular coordinates.

FIG. 2 is a graph showing a point a where the composition molar ratio {Nd: Ba: Cu} of Nd, Ba and Cu in FIG. 1 is {1.1: 1.9: 3.0}. , $ 4:
When the composition ratio was changed to the point b of 2: 2｝, N
It is a graph showing a change in the formation temperature of the d _{1 + Y} Ba _2-y Cu ₃ O _7-x phase. In addition, this measurement was performed by the suggestive thermal analyzer.

As apparent from FIG. 2, the composition ratio is Δ4:
2: When slightly shifted to the 2 side, Nd _{1+ Y} Ba _2-y Cu ₃ O
The formation temperature of the _7-x phase sharply increased, and NdO _1.5 mol
When the% is 22%, the rapid increase stops and changes to a gradual increase curve. 22% mol% of NdO _1.5
, The formation temperature of the Nd _{1 + Y} Ba _2-y Cu ₃ O _7-x phase is 1130 ° C. or higher, which is sufficiently higher than the formation temperature of the “123 phase” when the RE element is Sm or Nd. . This point corresponds to the point c (in the case of Y = 0.1) and d in FIG.
Nd _{1 + Y} Ba _2-y C
In the form in which the Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase is dispersed in the u ₃ O _7-x phase, the composition ratio of the two is Nd _{1 +} YBa _2-y Cu ₃ O
_7-x : Nd ₄ Ba ₂ Cu ₂ O ₁₀ = 1: 0.1. Therefore, in this case, Nd ₄ Ba ₂
If the composition ratio of Cu ₂ O ₁₀ is 0.1 or more, a sufficiently high formation temperature can be secured.

Meanwhile, when the Nd ₄ Ba ₂ Cu ₂ O composition ratio of ₁₀ to gradually increase in 0.1 above, generation temperature is further increasing, when 1.5 or more, Nd ₄ Ba ₂ Cu ₂ O _Ten
It was found that the number of phases was too large and it was difficult to orient in the same direction as the seed crystal. Therefore, Nd ₄ B
The composition ratio of a ₂ Cu ₂ O ₁₀ must be 1.5 or less. In the case of this composition ratio, the point f (Y = 0.
1) and point e (when Y = 0.5).

Accordingly, the Nd _{1 + Y} Ba _{2 -y} Cu ₃ O _{7 -x} phase contains the Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in the composition ratio of Nd _{1 + Y} Ba 2
_{2-y Cu 3 O 7-} x: Nd 4 Ba 2 Cu 2 O 10 = 1: 0.
By using a single crystal dispersed as a seed crystal in a range of 1-1: 1.5 as a seed crystal, a superconductor having a high temperature at which the “123 phase” is generated because Sm or Nd is used as an RE element However, it can be seen that it is possible to produce a large oriented crystal of an RE-Ba-Cu-O-based oxide superconductor having the same orientation as the seed crystal with the seed crystal as a base point. As shown in FIG. 1, Nd _{1 + Y} B
a _2-y Cu ₃ O _7-x : Nd ₄ Ba ₂ Cu ₂ O ₁₀ = 1
The range of 0.1 to 1: 1.5 is a region surrounded by cdef in FIG.

The composition of the superconductor to be manufactured is such that mol% (RE, Ba, Cu) is A (35, 2).
5, 40), B (35, 35, 30), C (15, 4)
0, 45) and D (15, 30, 55) (see FIG. 3).

This is because when the RE is 35% or more, RE ₂ Ba
_{Since the 1} Cu ₁ O ₅ phase is agglomerated and coarse, the properties are deteriorated.
If the content is 15% or less, an impurity phase of Ba or Cu compound is precipitated. If Ba is smaller than the line of AD, C
This is because a large amount of impurities of the u compound are precipitated, and if the amount of Ba is larger than that of the BC line, a large amount of the impurity phase of the Ba compound is precipitated to significantly deteriorate the characteristics.

The reason why the calcination temperature is set to 900 to 1500 ° C. is that if the temperature is 900 ° C. or lower, unnecessary elements such as carbon remain in the starting material, which deteriorates the properties of the sample after melt crystallization. At a temperature of 1500 ° C. or higher, the reaction with the container becomes violent when the raw materials are charged, and impurities are often mixed.

The reason for setting the melting temperature to 990 to 1300 ° C. is that melting is insufficient at 990 ° C. or lower, crystal grain boundaries remain, and at 1300 ° C. or higher, the RE ₂ Ba ₁ Cu ₁ O ₅ phase is coarsened. That's why.

The reason why the temperature gradient is set to 5 to 50 ° C./cm is as follows.
At 5 ° C. or lower, nucleation of crystals from points other than the contact portion with the seed crystal tends to occur. At 50 ° C. or higher, the sample temperature on the side opposite to the seed crystal becomes too high, and the shape cannot be maintained. That's why. Note that the slow cooling rate is 0.5 to 5 ° C.
/ Hr is desirable. If the temperature is 0.5 ° C. or less, the productivity is poor, and if the temperature is 5 ° C. or more, the crystal growth cannot catch up and impurities are easily precipitated.

[0018]

EXAMPLE 1 In this example, Nd _{1 + Y} Ba _2-y Cu ₃ was used as a seed crystal.
Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in O _{7 -x} phase in composition ratio of 1:
Using a single crystal dispersed to be 0.1, the composition is Y
_This is an example of producing an oriented crystal of an oxide superconductor of _1.8 Ba _2.4 Cu _3.4 O _7-x . In the weighing, Y was assumed to be 0.2.

First, a seed crystal is prepared as follows.

Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase and Nd ₄
The composition ratio of Ba ₂ Cu ₂ O ₁₀ to Nd _{1 + Y} Ba _2-y Cu
_{In order that 3} O _7-x : Nd ₄ Ba ₂ Cu ₂ O ₁₀ = 1: 0.1 (composition: Nd _1.6 Ba ₂ Cu _3.2 O _8.1-x ), N
After weighing each raw material powder of d ₂ O ₃ , BaCO ₃ , and CuO in a molar ratio of Nd: Ba: Cu = 16: 20: 32, only BaCO ₃ and CuO were mixed in a Pt crucible at 95%.
It was calcined at 0 ° C. for 24 hours to obtain a calcined powder of BaCuO ₂ and CuO (BaCuO ₂ : CuO = 20: 3 by molar ratio).
2).

The calcined powder and Nd ₂ O previously weighed are
₃ were mixed and press-formed into a disk having an outer diameter of 50 mm and a thickness of 20 mm to obtain a molded body.

After the molded body is brought into a semi-molten state at 1200 ° C., the temperature is increased to 10 ° C./m until the upper temperature of the sample reaches 1100 ° C.
The temperature was lowered in, and a temperature gradient of 15 ° C./cm was further added above and below the sample, and then gradually cooled to room temperature at a rate of 1 ° C./hr to perform crystallization.

Thus, Nd _{1 + Y} Ba _2-Y CU ₃ O
_The Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in the _7-x phase has a composition ratio of 1:
A polycrystal dispersed to be 0.1 was obtained (composition: Nd _1.6 Ba ₂ Cu _3.2 O _8.1-X ).

A single crystal grain was cut out from the polycrystal to obtain a seed crystal.

Here, Nd _{1 + Y} Ba _2-Y CU ₃ O
_7-x phase in X, Y, and, Y _1.8 Ba _2.4 Cu _3.4 O
X in the _7-x phase depends on the oxygen partial pressure during crystallization, and X =
It changes within the range of 0 to 0.5 and Y = 0.1 to 0.5, and it is difficult to specify the oxygen partial pressure accurately, so it is difficult to specify the exact value. However, even if the average value of X and Y is changed by changing the oxygen partial pressure when forming the seed crystal, the effect remains unchanged.
Within the range of fluctuations, they may be treated as the same substance. The same applies to the following embodiments.

Next, a superconductor is manufactured using the seed crystal as follows.

After weighing each raw material powder of Y ₂ O ₃ , BaCO ₃ , and CuO so that Y: Ba: Cu = 18: 24: 34, only BaCO ₃ and CuO are mixed in a Pt crucible in a Pt crucible.
It was calcined at 50 ° C. for 24 hours to obtain a calcined powder of BaCuO ₂ and CuO (BaCuO ₂ : CuO = 24: 1 by molar ratio).
0).

This calcined powder and Y weighed in advance
₂ O ₃ was mixed and press-molded into a disk shape having an outer diameter of 50 mm and a thickness of 20 mm to make a compact in a semi-molten state at 1150 ° C., and then the temperature was lowered to 1020 ° C. at a rate of 10 ° C./min. The molded body was brought into contact with the upper portion, a temperature gradient of 15 ° C./cm was applied so that the temperature of the seed crystal became low, and the temperature was gradually lowered to room temperature at a rate of 1 ° C./hr to perform crystallization.

The thus obtained YBa ₂ Cu ₃ O _7-x
The crystal in which the Y ₂ Ba ₁ Cu ₁ O ₅ phase was finely dispersed in the phase was a large oriented crystal in which the entire sample reflected the crystal orientation of the seed crystal.

The critical temperature (T
It was 90K when c) was measured.

When the critical current density (Jc) was measured by a vibrating sample magnetometer, the maximum current was 1.5 × 10 ⁴ A / cm ² in a magnetic field of 0.5 T.

Further, this sample was heated to 77K with liquid nitrogen.
And a Nd-based magnet (outside diameter 25 mm, thickness 50 mm) (maximum surface magnetic flux density: 0.53 T) was cooled to 50 mm / mi.
When approaching at a speed of n, the magnetic repulsion was measured and found to be 12 kgf.

Further, an external magnetic field of 5 K Oe was applied to the sample at room temperature, and the sample was cooled to a temperature of 77 K with liquid nitrogen. Then, the application of the external magnetic field was stopped, and the magnetic flux density on the sample surface was measured. The magnetic flux density captured by the sample in the superconducting state was examined. In this measurement, as shown in FIG. 5, a Hall element as a magnetic flux density detector suspended on an XY stage was brought close to the surface of the superconductor sample, and this Hall element was moved in the diameter direction of the sample by the XY stage. The measurement was performed by measuring the magnetic flux density at each point while moving. FIG. 6 is a graph showing the measurement results. In FIG. 6, the vertical axis is the trapped magnetic flux density (unit: KGauss) of the sample of the superconductor, and the horizontal axis is the measurement position (unit: mm), which is represented by the distance from the center of the sample to the measurement point. is there.

Example 2 In this example, Nd _{1 + Y} Ba _2-y Cu ₃ O was used as a seed crystal.
Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in the _7-x phase has a composition ratio of 1:
Using a single crystal dispersed to be 0.2, the composition is S
This is an example of producing an oriented crystal of an oxide superconductor of m _1.8 Ba _2.4 Cu _3.4 O _9-x . In the weighing, Y was assumed to be 0.2.

First, a seed crystal is prepared as follows.

Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase and Nd ₄
The composition ratio of Ba ₂ Cu ₂ O ₁₀ to Nd _{1 + Y} Ba _2-y Cu
₃ O _7-x : Nd ₄ Ba ₂ Cu ₂ O ₁₀ = 1: 0.2 (composition: Nd _2.0 Ba _2.2 Cu _3.4 O _{9.1 X} )
After weighing each raw material powder of Nd ₂ O ₃ , BaCO ₃ , and CuO in a molar ratio of Nd: Ba: Cu = 20: 22: 34, only BaCO ₃ and CuO were mixed in a Pt crucible in 9
It was calcined at 50 ° C. for 24 hours to obtain a calcined powder of BaCuO ₂ and CuO (BaCuO ₂ : CuO = 22: 3 by molar ratio).
4).

The calcined powder and Nd ₂ O weighed in advance
₃ were mixed and press-formed into a disk having an outer diameter of 50 mm and a thickness of 20 mm to obtain a molded body.

After the molded body was made into a semi-molten state at 1200 ° C., the temperature was increased to 10 ° C./m until the upper temperature of the sample reached 1100 ° C.
Then, the temperature was lowered, and a temperature gradient of 15 ° C./cm was applied to the upper and lower portions of the sample, and the temperature was gradually cooled to room temperature at a rate of 1 ° C./hr for crystallization.

Thus, Nd _{1 + Y} Ba _2-Y CU ₃ O
_The Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in the _7-x phase has a composition ratio of 1:
A polycrystal dispersed to be 0.1 was obtained (composition: Nd _1.6 Ba ₂ Cu _3.2 O _8.1-X ).

A single crystal grain was cut out from the polycrystal to obtain a seed crystal.

Next, a superconductor is manufactured using the seed crystal as follows.

First, raw material powders of Sm ₂ O ₃ , BaCO ₃ , and CuO were weighed so that Sm: Ba: Cu = 18: 24: 34, and only BaCO ₃ and CuO were 850.
It was calcined at 30 ° C. for 30 hours to obtain a calcined powder of BaCuO ₂ and CuO (BaCuO ₂ : CuO = 24: 10 in molar ratio).

The calcined powder and S weighed in advance
0.5 wt% of m ₂ O ₃ and Pt powder are added and mixed,
A compact was produced by press molding into a disk having an outer diameter of 50 mm and a thickness of 20 mm.

After the molded body is made into a semi-molten state at 1200 ° C., the temperature is lowered to 1080 ° C. at a rate of 10 ° C./min to reach a seed crystal contact temperature. Crystallization was performed by applying a temperature gradient of 15 ° C./cm so that the temperature on the side became low, and then gradually cooling it to room temperature at a rate of 1 ° C./hr.

The thus obtained SmBa ₂ Cu ₃ O _7-x
In the crystal in which the Sm ₂ Ba ₁ Cu ₁ O ₅ phase was finely dispersed in the phase, a crystal with a different orientation was partially present in the sample. It became.

The thus obtained YBa ₂ Cu ₃ O _7-x
The crystal in which the Y ₂ Ba ₁ Cu ₁ O ₅ phase was finely dispersed in the phase was a large oriented crystal in which the entire sample reflected the crystal orientation of the seed crystal.

The sample has a critical temperature (Tc) of 92 K and a critical current density (Jc) of 1.75 at maximum in a magnetic field of 0.5 T.
× 10 ⁴ A / cm ² .

When the magnetic repulsion was measured in the same manner as in Example 1, it was 11.8 kgf.

Further, when the trapped magnetic flux density distribution was examined in the same manner as in Example 1, the results were as shown in the graph of FIG.

Example 3 This example uses Nd _{1 + Y} Ba _2-y Cu ₃ O as a seed crystal.
Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in the _7-x phase has a composition ratio of 1:
Using a single crystal dispersed to be 1.5, the composition is N
An example of producing an oriented crystal of an oxide superconductor which is d ₁ Ba ₂ Cu ₃ O _7-x will be described. When weighing, set Y to 0.2.
Was assumed.

First, a seed crystal is prepared as follows.

Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase and Nd ₄
The composition ratio of Ba ₂ Cu ₂ O ₁₀ to Nd _{1 + Y} Ba _2-y Cu
₃ O _7-x : Nd ₄ Ba ₂ Cu ₂ O ₁₀ = 1: 1.5 (composition; Nd _7.2 Ba _4.6 Cu ₆ O _22.1-X )
After weighing each raw material powder of Nd ₂ O ₃ , BaCO ₃ , and CuO in a molar ratio of Nd: Ba: Cu = 72: 48: 60, only BaCO ₃ and CuO were mixed in a Pt crucible in 9
It was calcined at 50 ° C. for 24 hours to obtain a calcined powder of BaCuO ₂ and CuO (BaCuO ₂ : CuO = 48: 6 in molar ratio).
0).

The calcined powder and Nd ₂ O previously weighed
₃ were mixed and press-formed into a disk having an outer diameter of 50 mm and a thickness of 20 mm to obtain a molded body.

After the molded body was made into a semi-molten state at 1200 ° C., it was heated at 10 ° C./m until the upper temperature of the sample reached 1100 ° C.
Then, the temperature was lowered, and a temperature gradient of 15 ° C./cm was applied to the upper and lower portions of the sample, and the temperature was gradually cooled to room temperature at a rate of 1 ° C./hr for crystallization.

Thus, Nd _{1 + Y} Ba _2-Y CU ₃ O
_The Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase in the _7-x phase has a composition ratio of 1:
A polycrystal dispersed to 1.5 was obtained (composition: Nd _1.6 Ba ₂ Cu _3.2 O _8.1-X ).

A single crystal grain was cut out from the polycrystal to obtain a seed crystal.

Next, a superconductor is manufactured using the seed crystal as follows.

After weighing each raw material powder of Nd ₂ O ₃ , BaCO ₃ and CuO so that Nd: Ba: Cu = 1: 2: 3, only BaCO ₃ and CuO are calcined at 850 ° C. for 30 hours. A calcined powder of BaCuO ₂ and CuO was obtained. (Molar ratio: BaCuO ₂ : CuO = 2: 1). This calcined powder and Nd ₂ O ₃ and Pt powder weighed in advance were added to 0.1%.
5 wt% was added and mixed, and press-molded into a disk shape having an outer diameter of 50 mm and a thickness of 20 mm to produce a molded body. The molded body was semi-molten at 1200 ° C. in an oxygen partial pressure P O2 = 10 ⁻³ atm, and then cooled to 1080 ° C. at a rate of 10 ° C./min.
The seed crystal prepared above is brought into contact with the upper part of the molded body, and a temperature gradient of 15 ° C./cm is applied so that the temperature of the seed crystal becomes low.
From there, crystallization was performed by slowly cooling to room temperature at a rate of 1 ° C / hr.

The thus obtained Nd ₁ Ba ₂ Cu ₃ O
_{In the} crystal composed of the _7-x phase, some crystals of different orientation existed in the sample, but a relatively large crystal was obtained below the seed crystal reflecting the crystal orientation of the seed crystal.

The sample has a critical temperature (Tc) of 92 K and a critical current density (Jc) of at most 0.94 in a magnetic field of 0.5 T.
× 10 ⁴ A / cm ² , the magnetic repulsion was 6.5 Kg · f, and the trapped magnetic flux density was equivalent to the comparative example described below.

That is, the sample of this example is slightly inferior in characteristics as compared with the above examples 1 and 2, but is superior in magnetic repulsion force to the comparative example, and is superior to the conventional one. is there.

Comparative Example As a comparative example, a single crystal of Sm ₁ Ba ₂ Cu ₃ O _7-x phase (123 phase) was used as a seed crystal, and the composition was Sm _1.8 Ba _2.4.
An example of producing an oriented crystal of an oxide superconductor of Cu _3.4 O _9-x will be described.

After weighing each raw material powder of Sm ₂ O ₃ , BaCO ₃ and CuO so that Sm: Ba: Cu = 18: 24: 34, only BaCO ₃ and CuO were mixed at 950 ° C.
By calcining for 4 hours, a calcined powder of BaCuO ₂ and CuO was obtained (BaCuO ₂ : CuO = 2: 3 in molar ratio). The calcined powder and the previously weighed Sm ₂ O ₃ and Pt powders were added at 0.5 wt% and mixed to form an outer diameter of 50 mm and a thickness of 20 mm.
A molded article was prepared by press molding into a disk having a diameter of 1 mm. After making this molded body semi-molten at 1200 ° C.,
To 10 ° C at 10 ° C / min.
Crystallization was performed by applying a temperature gradient of 5 ° C./cm, and then gradually cooling it to room temperature at a rate of 1 ° C./hr. _{Thus, Sm 1 Ba 2 Cu 3 O} 7-x phase in the Sm ₂ Ba
A polycrystal in which a ₁ Cu ₁ O ₅ phase was dispersed in a trace amount was obtained.

A single crystal grain was cut out from the polycrystal to obtain a seed crystal.

Next, a superconductor is manufactured using the seed crystal as follows.

After weighing each raw material powder of Sm ₂ O ₃ , BaCO ₃ and CuO so that Sm: Ba: Cu = 18: 24: 34, only BaCO ₃ and CuO were mixed at 850 ° C.
By calcining for 0 hour, a calcined powder of BaCuO ₂ and CuO was obtained (BaCuO ₂ : CuO = 24: 10 in molar ratio). This calcined powder and Sm ₂ O ₃ and Pt weighed in advance
0.5 wt% of the powder was added and mixed, and the mixture was press-molded into a disk shape having an outer diameter of 50 mm and a thickness of 20 mm to produce a molded body. After making this molded body semi-molten at 1200 ° C.,
The temperature was lowered to 080 ° C. at a rate of 10 ° C./min. The seed crystal prepared above was brought into contact with the upper part of the molded body, and a temperature gradient of 15 ° C./cm was applied above and below the sample so that the temperature of the seed crystal was low. Crystallization was performed by gradually cooling the mixture to room temperature at a rate of 1 ° C./hr.

The thus obtained Sm ₁ Ba ₂ Cu ₃ O
_{In the} crystal in which the Sm ₂ Ba ₁ Cu ₁ O ₅ phase was finely dispersed in the _7-x phase, the seed crystal was completely melted and became a polycrystal.

The sample has a critical temperature (Tc) of 92 K and a critical current density (Jc) of at most 1.7 × in a magnetic field of 0.5 T.
10 ⁴ A / cm ² , the magnetic repulsion was 5.5 Kg · f, and the distribution of trapped magnetic flux density was as shown in the graph of FIG.

That is, the sample of this comparative example is inferior in magnetic repulsion force and trapped magnetic flux density characteristics as compared with the above Examples 1 and 2, and is superior in critical current density characteristics as compared with Example 3. The magnetic repulsion is inferior.

FIG. 9 is a table summarizing the measurement results of the superconducting characteristics of the example and the comparative example.

[0071]

As described in detail above, the present invention relates to a method of forming an RE compound (RE is one or more rare earth metal elements containing Y), a Ba compound, and a Cu compound by using
1% (RE, Ba, Cu) is A (35, 25, 4)
0), B (35, 35, 30), C (15, 40, 4)
5), weighed and mixed so as to have a composition of a region surrounded by points D (15, 30, 55),
The calcined powder obtained by calcining at a temperature of １1500 ° C. is formed to form a pellet-shaped precursor, which is then heated at a temperature in the range of 990 to 1300 ° C. to form a solid-liquid precursor. After the coexisting state, the seed crystal contact temperature is reached, and then the precursor is added to an Nd _{1 + Y} Ba _{2− Y} CU ₃ O _7-x phase (where X and Y are oxygen partial pressures during crystallization. X =
0-0.5, Y = 0.1-0.5) Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase contains Nd in composition ratio
_{1 + Y Ba 2-y Cu} 3 O 7-x: Nd 4 Ba 2 Cu 2 O 10 =
A single crystal dispersed to be in the range of 1: 0.1 to 1: 1.5 is contacted as a seed crystal, and then the precursor is
5 to 50 ° C./c so that the seed crystal side is the low temperature side
m, a temperature gradient of 1 to 5 ° C./hour is applied to the RE-Ba—Cu—O-based oxide superconductor having the same orientation as the seed crystal as a starting point. It is characterized by obtaining a large oriented crystal, whereby the method using the seed crystal can be applied even when the formation temperature of the “123 phase” is higher, whereby a large and higher critical current can be obtained. This enables an oxide superconductor having a density characteristic to be manufactured with good yield.

[Brief description of the drawings]

FIG. 1. Nd ₄ B in Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase
a Nd element in a single crystal in which a ₂ Cu ₂ O ₁₀ phase is dispersed,
It is the figure which showed the composition mol ratio of Ba element and Cu element by triangular coordinates.

FIG. 2: Nd ₄ B in Nd _{1 + Y} Ba _{2 -Y} CU ₃ O _7-x phase
When a change in the abundance ratio of both phases in a single crystal in which a ₂ Cu ₂ O ₁₀ phase is dispersed is represented by an Nd composition, formation of an Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase with respect to the abundance ratio It is the figure which showed the temperature change with the graph.

FIG. 3 shows the Nd element, Ba element,
FIG. 3 is a diagram showing the composition mol ratio of Cu element in triangular coordinates.

FIG. 4 is a diagram showing a state of crystal growth using a seed crystal.

FIG. 5 is a diagram showing a state of measurement of a trapped magnetic flux density distribution.

FIG. 6 is a graph showing a measurement result of a trapped magnetic flux density distribution of the superconductor manufactured by the method of Example 1.

FIG. 7 is a graph showing a measurement result of a trapped magnetic flux density distribution of a superconductor manufactured by the method of Example 2.

FIG. 8 is a graph showing a measurement result of a trapped magnetic flux density distribution of a superconductor manufactured by a method of a comparative example.

FIG. 9 is a table summarizing the measurement results of the superconducting characteristics of an example and a comparative example.

Continuation of the front page (72) Inventor Shuji Yoshizawa 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-5-279034 (JP, A) JP-A-5-279035 (JP, A) JP-A-5-279032 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 1 / 00,3 / 00 C30B 11 / 14,29 / 22

Claims (1)

(57) [Claims] 1. An RE compound (RE is one or two or more rare earth metal elements containing Y), a Ba compound, and a Cu compound, each of which contains mol% (RE, Ba, Cu) of A
(35, 25, 40), B (35, 35, 30), C
(15, 40, 45) and D (15, 30, 55) are weighed and mixed so as to have a composition in a region surrounded by the points, and then the mixed powder is fired at a temperature of 900 to 1500 ° C. The obtained calcined powder is molded to form a pellet-shaped precursor, and then the precursor is heated at a temperature in the range of 990 to 1300 ° C. to be in a solid-liquid coexistence state, and then to a seed crystal contact temperature. Next, this precursor is added to an Nd _{1 + Y} Ba _2-Y CU ₃ O _7-x phase (where X and Y are X = Y due to the oxygen partial pressure during crystallization).
0-0.5, Y = 0.1-0.5) Nd ₄ Ba ₂ Cu ₂ O ₁₀ phase contains Nd in composition ratio
_{1 + Y Ba 2-y Cu} 3 O 7-x: Nd 4 Ba 2 Cu 2 O 10 =
A single crystal dispersed so as to be in a range of 1: 0.1 to 1: 1.5 is brought into contact with a seed crystal, and then the precursor is placed at 5 to 50 ° C. so that the seed crystal side is at a low temperature side. A large oriented crystal of a RE-Ba-Cu-O-based oxide superconductor having the same orientation as the seed crystal starting from the seed crystal by gradually cooling to room temperature with a temperature gradient of / cm R characterized by
A method for producing an E-Ba-Cu-O-based oxide superconductor.