JPH0597436A - Tl-containing superconductor and its production - Google Patents

Abstract

PURPOSE:To control the evaporation of Tl at the time of firing, to facilitate the control of a compsn. having high homogeneity and nearly free from a foreign phase and to provide a Tl-contg. superconductor having grains easy to orient in the c-axis direction and ensuring high Jc. CONSTITUTION:A compsn. contg. Ba and/or Sr, Ca and Cu as essential components is melted, rapidly cooled, pulverized and mixed with a compd. contg. Tl or Tl and Pb. This mixture is molded and fired to obtain a Tl-contg. superconductor. A compsn. contg. Ba and/or Sr, Ca, Cu and Pb as essential components is melted, rapidly cooled, pulverized and mixed with a compd. contg. Tl or Tl and Pb. This mixture is molded and fired to obtain a Tl-contg. superconductor. Each of the Tl-contg. superconductors has platy grains whose aspect ratio is >=6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Tl superconductor and a method for manufacturing the same.

[0002]

2. Description of the Related Art A Tl-based superconductor is disclosed in JP-A 1-2190.
No. 07, No. 1-242418, No. 2
-133305, JP-A-3-208817, etc., and the Tl-based superconductors disclosed in these publications are, for example, M-Ca-Cu-O and M-Cu-O (where M is Ba. And one or more selected from Sr), Ca-
A compound such as O or Cu-O and a Tl compound are mixed to obtain a raw material for a superconductor, which is molded and fired.

The Tl-based superconductor is a Tl 2-layer system Tl ₂
Ba ₂ Ca ₁ Cu ₂ O ₈ phase (hereinafter referred to as 2212 phase) is 10
5K or more, Tl ₂ Ba ₂ Ca ₂ Cu ₃ O ₁₀ phase (below 2223
Has a high critical temperature of 120 K or more (hereinafter referred to as T _C ) and has a Tl 1 layer system of Tl ₁ Ba ₂ Ca ₁ C.
u ₂ O ₇ (hereinafter referred to as 1212 phase), Tl ₁ Ba ₂ Ca ₂ C
u ₃ O ₉ (hereinafter referred to as 1223 phase) and Tl ₁ Ba ₂ Ca ₃
It is known that the Cu ₄ O ₁₁ phase (hereinafter referred to as the 1224 phase) also has a T _C of 90K or higher. By further substituting a part of Tl in Pb, high T _C shown Tl 1 layer system Tl-based superconductors is that it is easy to obtain, Science (Science, pp Vol.242,249, 198
8 years).

It is also known that an electric current easily flows in the ab plane direction of the crystal grains constituting the Tl superconductor. Therefore, in order to increase the critical current density (hereinafter referred to as J _C ), it is important that the crystal grains are aligned in the ab plane direction and sufficiently oriented in the C axis direction.

[0005]

However, most of the Tl-based superconductors produced by the above method are lumpy,
It is composed of crystal grains of various shapes such as columnar and irregular shapes. Therefore, it is difficult to align the crystal grains in the ab plane direction and to orient in the C-axis direction, which is one of the reasons why it is difficult to obtain a high J _C. Further, since the Tl compound is likely to evaporate during firing, the reaction becomes insufficient, which causes a drawback that a heterogeneous phase other than the superconductor phase is likely to be generated or remain, and the evaporation of Tl makes it difficult to control the composition. Therefore, a non-uniform portion is likely to be formed in the sintered body, and the superconductor volume ratio, J _C, etc. are reduced. Furthermore, since the Tl compound is toxic and expensive, it is important to suppress the evaporation of Tl.

The present invention suppresses evaporation of Tl during firing, facilitates composition control with high homogeneity and few heterogeneous phases, and ab
An object of the present invention is to provide a Tl-based superconductor composed of plate-like crystal grains which are aligned in the plane direction and in which the crystal grains can be easily oriented in the C-axis direction and a high J _C can be easily obtained, and a manufacturing method thereof. It is a thing.

[0007]

DISCLOSURE OF THE INVENTION As a result of various studies to solve the above-mentioned drawbacks, the present inventors have found that in a Tl-based superconductor which has been difficult to be composed of plate-like crystal particles, M ( However, M is one or more elements selected from Ba and Sr), a composition containing Ca and Cu as the main components is rapidly cooled in a molten state, and a powder obtained by crushing this and a compound containing Tl or a compound containing Tl and Pb. After mixing with, the mixture is molded and fired, or a composition containing M (where M is at least one element selected from Ba and Sr), Ca, Cu and Pb as main components is rapidly cooled in a molten state. Then, a powder obtained by pulverizing this and a compound containing Tl or a compound containing Tl and Pb are mixed, and the mixture is molded and fired to grow into plate-shaped superconductor crystal particles having a large aspect ratio. To I began to have. Further, they have found that the evaporation of expensive and toxic Tl is suppressed, a heterogeneous phase other than the superconductor phase is unlikely to be generated or remain, and that it is effective for improving the superconductor volume ratio and the like, and completed the present invention.

The present invention is a Tl-based superconductor having plate-like crystal grains with an aspect ratio of 6 or more, and M (where M is B).
one or more elements selected from a and Sr), Ca and C
A composition containing u as a main component is rapidly cooled in a molten state, pulverized and then mixed with a compound containing Tl or a compound containing Tl and Pb, and then molded and fired. M is one or more elements selected from Ba and Sr), a composition containing Ca, Cu and Pb as main components is rapidly cooled in a molten state, and after crushing this, a compound containing Tl or a compound containing Tl and Pb is added. The present invention relates to a method for producing a Tl-based superconductor in which mixing, molding and firing are performed.

In the present invention, the aspect ratio determined by the following mathematical formula (1) is set to 6 or more, preferably 10 or more. If it is less than 6, the crystal grains can be aligned in the ab plane direction and oriented in the C-axis direction. The drawback is that it is difficult and it is difficult to obtain a high J _C.

[Equation 1]

If the proportion of the plate-like crystal particles is 50% by volume or more, the plate-like crystal particles can be substantially connected to each other, and it is more preferably 60% by volume or more.

The elements constituting the Tl-based superconductor according to the present invention include Tl, M (where M is at least one element selected from Ba and Sr), Ca and Cu or Tl, Pb,
M (where M is one or more elements selected from Ba and Sr), Ca and Cu are used, but other elements may be added if necessary, and some of the above elements may be replaced with other elements. The element may be replaced with, for example, part of Ca may be replaced with Y, Sm, or the like. As the raw material (starting raw material) containing the above-mentioned elements, for example, compounds such as oxides, carbonates, nitrates and oxalates can be used.

M (provided that one or more elements selected from Ba and Sr), a composition containing Ca and Cu as main components or M (provided that at least one element selected from Ba and Sr), Ca, Cu and The temperature at which the composition containing Pb as the main component is melted is appropriately selected depending on the type of starting material and the compounding composition, but the composition should be melted at a temperature about 50 to 500 ° C. higher than the temperature at which the composition begins to melt. Is preferred. When using carbonates, oxalates, etc. as raw materials,
Before melting, it is desirable to sufficiently heat-treat and advance the decomposition of carbon dioxide gas.

The method of quenching the molten composition is not particularly limited, but for example, a method of instantly dropping it on a metallic plate such as stainless steel or copper or twin rolls, a centrifugal spraying method and the like are used. Although it is ideal to obtain an amorphous precursor by rapid cooling, it has been found from the experiments conducted by the inventors of the present invention that the amorphous precursor is 3,0
A favorable result is obtained if the cooling rate is 00 ° C./minute or more.

The crushing method and the mixing method are not particularly limited, and the crushing method is, for example, after coarse crushing in a mortar or the like
There is a method of dry or wet pulverization with a raider (automatic kneader), a ball mill or the like, and as a mixing method, there is a method of dry or wet mixing with a raider or a ball mill similar to the above.

For the firing, it is preferable to use a vessel made of ceramics such as alumina or magnesia, and cover with a lid to perform firing. The firing temperature is appropriately selected according to the mixing ratio of each raw material, etc., but it is preferable to perform firing in the range of 750 to 1,000 ° C., and the firing atmosphere is an oxygen atmosphere.
The firing can be performed in the air, an air stream, a low oxygen atmosphere (oxygen content is 1 to 20% by volume, preferably 2 to 20% by volume), and there is no particular limitation.

The mixing ratio of the mixture forming the Tl-based superconductor according to the present invention is not particularly limited, and the mixing ratio is appropriately adjusted depending on the required crystal phase, for example, 222.
When obtaining a three-phase superconductor, the mixture containing the elements Tl, Ba, Ca, and Cu has an atomic ratio of Tl: Ba: Ca: Cu of 1.3 to 2.1: 1.6 to 2.2: 1.8-2.
6: 2.7-3.6, elements Tl, Ba, Sr, Ca
And a mixture containing Cu is Tl: Ba: Sr: Ca: C
u is an atomic ratio of 1.3-2.1: A: B: 1.8-2.
6: 2.7-3.6 (where A = 1.2-2, B ≦ 1,
It is preferable that (A + B) ≦ 2.4). 2212
When obtaining a phase superconductor, the mixture containing the elements Tl, Ba, Ca and Cu has an atomic ratio of Tl: Ba: Ca: Cu of 1.3 to 2.2: 1.7 to 2.2: 0. .8-1.4:
In the mixture of 1.7 to 2.4, the elements include Tl, Ba, Sr, Ca and Cu, the atomic ratio of Tl: Ba: Sr: Ca: Cu is 1.3 to 2.2: D: E: 0.8-1.4:
1.7-2.4 (where D = 1.2-2, E ≦ 1, (D
It is preferable that + E) ≦ 2.4). See also 1223
To obtain a phase superconductor, a mixture containing Tl, Ba, Sr, Ca and Cu has a Tl: Ba: Sr: Ca: Cu atomic ratio of 0.6 to 1.2: G: H: 1.8. ~ 2.6:
2.7-3.6 (where G ≦ 0.8, H = 1.2-2.
It is preferable that 2 (G + H) ≦ 2.4).

In addition to the above mixture, a part of Tl is added to Pb.
If replaced by, it is easy to obtain a Tl1 layer system Tl-based superconductor having a high Tc. That is, Tl, Pb, Sr, Ca and Cu
The mixture containing is (Tl + Pb) :( Sr + Ca): C
1223 phase superconductor when u or (Tl + Pb) :( Sr + Ba + Ca): Cu is 1: 4: 3 in atomic ratio,
12: 1 phase superconductor at 1: 3: 2 and 1: 5:
When 4, the 1234 phase superconductor is easily obtained.

In the present invention, the compound containing Tl means T
Compounds containing oxides, carbonates, nitrates, sulfates, etc. containing 1 are shown, and compounds containing Pb are compounds containing oxides, carbonates, nitrates, sulfates, etc. containing Pb. T
Examples of the compound containing 1 include Tl ₂ O ₃ , Tl ₂ O, and Tl ₂ C.
Compounds such as O ₃ , TlNO ₃ , Tl ₂ SO ₄ are used, and P
Examples of the compound containing b include PbO, PbO ₂ , Pb
Compounds such as ₃ O ₄ , PbCO ₃ , Pb (NO ₃ ) ₂ and PbSO ₄ are used.

[0019]

EXAMPLES Examples of the present invention will be described below. Example 1 BaO (manufactured by Kojundo Chemical Lab, purity 99% or more), SrO (manufactured by Kojundo Chemical Lab, Purity 99% or more), CaO (manufactured by Kojundo Chemical Laboratory, purity 99.9%) and CuO (manufactured by Kojundo Chemical Laboratory, purity 99.9%) were weighed and used as starting materials.

After that, the starting materials mentioned above are crushed by a smashing machine.
Mix for minutes. 90% of the mixed powder in the atmosphere using an electric furnace
It was pre-baked at 0 ° C. for 10 hours and then crushed for 30 minutes with a clay mill.

The preliminarily fired powder thus obtained is molded into a size having a diameter of 10 mm and a height of 60 mm, and then it is melted at 1,500 ° C. in the atmosphere using an electric furnace, and the melt is then placed on a copper plate. It was dropped instantly and cooled rapidly.

The rapidly cooled composition was roughly crushed in a mortar and then sufficiently crushed in a raker. About this melt-quenched powder,
Quantitative analysis of composition was performed by ICP emission spectroscopy. The results are shown in Table 1.

Next, Tl ₂ O ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 9) was used so that the ratios of thallium, barium, strontium, calcium and copper in the atomic ratio were as shown in Table 2.
9.9%) and weighed and added to the molten quenched powder obtained above,
The mixture was uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture.

The resulting Tl-based superconductor mixture was molded by a die press to obtain a molded body having a diameter of 20 mm and a thickness of 2 mm. Then, this molded body was fired in an alumina container with a lid at the temperature and time shown in Table 2 to obtain a Tl-based superconductor.

As a result of observing the fracture surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), one side is 10-4.
It was confirmed to be composed of plate-like crystal grains having a thickness of 0 μm and a thickness of 0.1 to 3 μm. FIG. 1 (a) shows an SEM photograph of the crystal grains on the fracture surface of sample No. 1. Also, the T obtained above
The aspect ratio of the l-based superconductor was calculated to be 8 to 300.
Met. Furthermore, energy dispersive X-ray spectroscopy (ED
As a result of the quantitative analysis of the composition in X), the plate-like crystal particles had a composition of a superconductor.

On the other hand, the Tl-based superconductor obtained above was crushed in a mortar and powdered, and the following measurements were carried out. 90K obtained by quantitative analysis of composition by ICP emission spectroscopy, identification of crystal phase by powder X-ray diffraction method, and inductance method (trial Nos. 2 and 4)
No.) and 110 K (for trial Nos. 1, 3, 5 and 6), the calculated results of the superconductor volume ratio and the 0.
Table 2 shows the Jc at 5 Tesla and 77K. Further, FIG. 2 shows the temperature change of the AC susceptibility for the trial number 1. From the result of the powder X-ray diffraction method, an X-ray diffraction pattern in which crystal grains were aligned in the ab plane direction and oriented in the C-axis direction was obtained. The peak intensities of the 2223 phase of trial number 2 and trial number 4, the 1234 phase of trial number 5 and the 1223 phase of trial number 6 were slight.

[0027]

[Table 1]

[0028]

[Table 2]

Example 2 The atomic ratio of barium, calcium and copper is 2: 2 :.
BaCO ₃ (manufactured by Wako Pure Chemical Industries,
Purity 99.9%), CaCO ₃ (manufactured by Kojundo Chemical Laboratory,
Purity 99.9%) and CuO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were weighed and used as starting materials.

Thereafter, the above starting materials were filled in a synthetic resin pot together with a steel ball covered with the synthetic resin and methanol, and wet-mixed and pulverized for 60 hours under the condition of 50 rpm. After drying, 900 in air using an electric furnace
It was pre-baked at 10 ° C. for 10 hours, then roughly pulverized in a mortar, then wet pulverized in a ball mill and dried.

The preliminarily fired powder obtained was molded under the same conditions as in Example 1 and then rapidly cooled in a molten state. The rapidly cooled composition was roughly crushed in a mortar and then sufficiently crushed by a raker. The molten quenched powder was quantitatively analyzed for its composition by ICP emission spectroscopy. As a result, the atomic ratio of Ba: Ca: Cu was 2.00: 2.01: 3.00.

Next, Tl ₂ O ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., so that the atomic ratio of thallium, barium, calcium and copper is 1.7: 2.00: 2.01: 3) is obtained. (Purity 99.9%) was weighed and added to the melt-quenched powder obtained above, uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture.

Using the resulting Tl-based superconductor mixture, a Tl-based superconductor was obtained under the same conditions as in Example 1 except that the firing temperature was 850 ° C. and the firing time was 10 hours.

As a result of observing the fracture surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), one side has a thickness of 10 to 40 μm as in the case of the Tl-based superconductor obtained in Example 1. Was confirmed to be composed of plate-like crystal particles of 0.1 to 3 μm. The aspect ratio was determined to be 12 to 300.

Next, the Tl-based superconductor obtained above was crushed in a mortar and powdered, and the following measurements were carried out. As a result of quantitative analysis of the composition by ICP emission spectroscopy, Tl: Ba: Ca:
Cu has an atomic ratio of 1.61: 1.98: 1.99: 3.0.
It was 0.

As a result of identifying the crystal phase by the powder X-ray diffraction method, only the peak of 2223 phase was observed. Example 1
Similar to the result of 1., an X-ray diffraction pattern in which the crystal grains were aligned in the ab plane direction and oriented in the C-axis direction was obtained.

When the change of the AC susceptibility with respect to temperature was measured, the same result as the trial number 1 of Example 1 was shown. The calculated superconductor volume ratio at 110K was 87% by volume.

Comparative Example 1 Barium, strontium, calcium and copper were weighed out using the same raw materials as in Example 1 so that the atomic ratios were as shown in Table 3, and the starting materials were used.

Thereafter, the above starting materials were mixed, pre-baked and pulverized under the same conditions as in Example 1. Next, Tl ₂ O ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) was weighed so that the ratio of thallium, barium, strontium, calcium, and copper was the composition shown in Table 3 in atomic ratio. The mixture was added to the pulverized product, uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture.

Example 1 was repeated, except that the obtained Tl-based superconductor mixture was used and the firing temperature and time shown in Table 3 were used.
By firing under the same conditions as above, a Tl-based superconductor was obtained.

As a result of observing the fractured surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), no growth of plate-like crystals was observed, and crystals of various shapes such as lumps, columns, and irregular shapes were observed. It was confirmed that it was composed of particles. FIG. 1 (b) shows an SEM photograph of the crystal grains on the fracture surface of sample No. 7.
The aspect ratio was not calculated because plate-shaped crystal particles could not be obtained.

On the other hand, the Tl-based superconductor obtained above was crushed in a mortar and made into powder, and the following measurements were carried out. 90K obtained by quantitative analysis of composition by ICP emission spectroscopy, identification of crystal phase by powder X-ray diffraction method, and inductance method (trial numbers 9 and 1
Table 3 shows the calculation results of the superconducting volume ratio at 110 K (in the case of 1) and 110 K (in the case of trial numbers 7, 8, 10 and 12) and Jc at 77 K at 0.5 Tesla obtained by the magnetization method. Further, FIG. 2 shows the temperature change of the AC susceptibility of the sample No. 7. From the results of the powder X-ray diffraction method, the orientation of the crystal grains in the C-axis direction was not recognized, and a crystal phase other than the superconductor phase was observed as in trial number 12.

As described above, in Comparative Example 1, the crystal particles forming the Tl-based superconductor have an indefinite shape, are hard to be oriented, and have a low superconductor volume ratio.

[0044]

[Table 3]

Example 3 SrO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99) was used so that the ratio of strontium, barium, calcium, yttrium, samarium and copper in atomic ratio was as shown in Table 4.
% Or more), BaO (manufactured by Kojundo Chemical Laboratory, purity 99% or more), CaO (manufactured by Kojundo Chemical Laboratory, purity 99.9)
%), Y ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%), S
m ₂ O ₃ (manufactured by Kojundo Chemical Laboratory, purity 99.9%) and C
uO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) was weighed and used as a starting material.

After that, the above starting materials are 30
Mix for minutes. 90% of the mixed powder in the atmosphere using an electric furnace
It was pre-baked at 0 ° C. for 10 hours and then crushed for 30 minutes with a clay mill.

The preliminarily fired powder thus obtained was molded into a size having a diameter of 8 mm and a length of 120 mm, and then melted at 1,600 ° C. (measurement value with a pyrometer) in the atmosphere using an infrared concentrating furnace. Then, the melt was instantly dropped on a copper plate and quenched.

The rapidly cooled composition was roughly crushed in a mortar and then sufficiently crushed in a raider. About this melt-quenched powder,
Quantitative analysis of composition was performed by ICP emission spectroscopy. The results are shown in Table 4.

Next, Tl ₂ O was adjusted so that the ratio of thallium, lead, strontium, barium, calcium, yttrium, samarium, and copper would be the composition shown in Table 5.
₃ (manufactured by Kojundo Chemical Laboratory, purity 99.9%) and PbO
(Manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) was weighed and added to the molten quenched powder obtained above, uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture.

The obtained Tl-based superconductor mixture was molded into a dimension of 20 mm in diameter and 2 mm in thickness by a die press,
Tl after firing in air stream for 10 hours at the temperature shown in Table 5
A superconductor was obtained. About the obtained Tl-based superconductor,
Quantitative analysis of composition was performed by ICP emission spectroscopy. The results are shown in Table 5.

As a result of observing the fracture surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), as in the case of the Tl-based superconductor obtained in Example 1 shown in FIG. It was confirmed that it was composed of plate-like crystal particles having a side of 10 to 40 μm and a thickness of 0.1 to 3 μm. The aspect ratio was determined to be 10 to 280. Further, as a result of quantitative analysis of the composition by energy dispersive X-ray spectroscopy (EDX), the plate crystal particles had a composition of a superconductor.

The temperature at which the electric resistance measured by the four probe method becomes zero (hereinafter referred to as Tc ⁰ ), the crystal phase was identified by the powder X-ray diffraction method, and the Jc at 77 K at 0.5 Tesla was obtained by the magnetization method. 77 obtained from the result and the inductance method
Table 6 shows the calculation results of the superconductor volume ratio in K. Powder X
As a result of the line diffraction method, an X-ray diffraction pattern in which the crystal grains were aligned in the ab plane direction and oriented in the C-axis direction was obtained.

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

[Table 6]

Comparative Example 2 SrO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99) was prepared so that the atomic ratios of strontium, barium, calcium, yttrium, samarium and copper were as shown in Table 7.
% Or more), BaO (manufactured by Kojundo Chemical Laboratory, purity 99% or more), CaO (manufactured by Kojundo Chemical Laboratory, purity 99.9)
%), Y ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%), S
m ₂ O ₃ (manufactured by Kojundo Chemical Laboratory, purity 99.9%) and C
uO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) was weighed and used as a starting material.

Thereafter, the above starting materials were mixed, pre-baked and pulverized under the same conditions as in Example 1, thallium, lead,
The atomic ratio of strontium, barium, calcium, yttrium, samarium and copper is Tl ₂ O ₃ (manufactured by Kojundo Chemical Research Institute, purity 9
9.9%) and PbO (manufactured by Kojundo Chemical Laboratory, purity 9)
9.9%) was weighed and added to the pulverized product, uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture. Using the obtained mixture for Tl-based superconductor, the firing temperature is shown in Table 7.
Molding under the same conditions as in Example 3 except that the temperature shown in
Firing was performed to obtain a Tl-based superconductor. The composition of the obtained Tl-based superconductor was quantitatively analyzed by ICP emission spectroscopy. The results are shown in Table 7.

As a result of observing the fracture surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), a plate similar to the Tl-based superconductor obtained in Comparative Example 1 shown in FIG. It was confirmed that the crystalline crystals did not grow, and were composed of crystal grains of various shapes such as lumps, columns, and irregular shapes. The aspect ratio was not calculated because plate-shaped crystal particles could not be obtained.

Tc ⁰ , the identification of the crystal phase by the powder X-ray diffraction method, the result of Jc at 77 K at 0.5 Tesla by the magnetization method, and the calculation result of the superconductor volume ratio at 77 K obtained by the inductance method. It shows in Table 8. From the results of the powder X-ray diffraction method, the orientation of crystal grains in the C-axis direction was not recognized.

As described above, in Comparative Example 2, the crystal particles constituting the Tl-based superconductor had an indefinite shape, Jc was 0, the orientation was difficult, and the superconductor volume ratio was low.

[0061]

[Table 7]

[0062]

[Table 8]

Example 4 PbO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 9) was used so that the ratios of lead, strontium, barium, calcium, yttrium, samarium and copper in the atomic ratio were as shown in Table 9.
9.9%), SrO (manufactured by Kojundo Chemical Laboratory, purity 99%)
Above), BaO (manufactured by Kojundo Chemical Laboratory, purity 99% or more), CaO (manufactured by Kojundo Chemical Laboratory, purity 99.9)
%), Y ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%), S
m ₂ O ₃ (manufactured by Kojundo Chemical Laboratory, purity 99.9%) and C
uO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) was weighed and used as a starting material.

Thereafter, the above starting materials were mixed, pre-baked and pulverized under the same conditions as in Example 3. Then, the same process as in Example 3 was performed to obtain a melt-quenched powder. The composition of the obtained melt-quenched powder was quantitatively analyzed by ICP emission spectroscopy.
The results are shown in Table 9.

Next, Tl ₂ O ₃ was used so that the ratio of thallium, lead, strontium, barium, calcium, yttrium, samarium, and copper would be the composition shown in Table 10.
(Manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) was weighed and added to the molten quenched powder obtained above, uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture.

Example 3 was repeated except that the firing temperature was changed to that shown in Table 10 by using the obtained Tl-based superconductor mixture.
It was molded and fired under the same conditions as above to obtain a Tl-based superconductor.
The composition of the obtained Tl-based superconductor was quantitatively analyzed by ICP emission spectroscopy. The results are shown in Table 10.

As a result of observing the fracture surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), like the Tl-based superconductor obtained in Example 1 shown in FIG. It was confirmed that it was composed of plate-like crystal particles having a side of 10 to 40 μm and a thickness of 0.1 to 3 μm. The aspect ratio was determined to be 10 to 280. Further, as a result of quantitative analysis of the composition by energy dispersive X-ray spectroscopy (EDX), the plate crystal particles had a composition of a superconductor.

Tc ⁰ , the identification of the crystal phase by the powder X-ray diffraction method, the result of determining Jc at 77 K by 0.5 Tesla by the magnetizing method, and the calculation result of the superconductor volume ratio at 77 K by the inductance method. It shows in Table 11. From the result of the powder X-ray diffraction method, an X-ray diffraction pattern in which crystal grains were aligned in the ab plane direction and oriented in the C-axis direction was obtained.

[0069]

[Table 9]

[0070]

[Table 10]

[0071]

[Table 11]

Comparative Example 3 PbO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) so that the ratio of lead, strontium, barium, calcium, yttrium, samarium and copper in the atomic ratio is as shown in Table 12. , SrO (manufactured by Kojundo Chemical Laboratory, purity 99
% Or more), BaO (manufactured by Kojundo Chemical Laboratory, purity 99% or more), CaO (manufactured by Kojundo Chemical Laboratory, purity 99.9%)
And CuO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were weighed and used as starting materials.

Thereafter, the above-mentioned starting materials were mixed, pre-baked and pulverized under the same conditions as in Example 1, thallium, lead,
The atomic ratio of strontium, calcium, yttrium, samarium, and copper is Tl ₂ O ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%).
Was weighed and added to the pulverized product, uniformly mixed and pulverized in a mortar to obtain a Tl-based superconductor mixture.

Example 3 was repeated except that the firing temperature was changed to that shown in Table 12 using the obtained Tl-based superconductor mixture.
It was molded and fired under the same conditions as above to obtain a Tl-based superconductor.
The composition of the obtained Tl-based superconductor was quantitatively analyzed by ICP emission spectroscopy. The results are shown in Table 13.

As a result of observing the fractured surface of the Tl-based superconductor obtained above with a scanning electron microscope (SEM), it was found that, like the Tl-based superconductor obtained in Comparative Example 1 shown in FIG. No plate-like crystal growth was observed, and it was confirmed to be composed of crystal grains of various shapes such as lumps, columns, and irregular shapes.
The aspect ratio was not calculated because plate-shaped crystal particles could not be obtained.

Table 13 shows Tc ⁰ , the identification of the crystal phase by the powder X-ray diffraction method, the result of determining Jc at 77 K by 0.5 Tesla by the magnetizing method, and the superconductor volume ratio at 77 K determined by the inductance method. Show. From the results of the powder X-ray diffraction method, the orientation of crystal grains in the C-axis direction was not recognized.

As described above, in Comparative Example 3, the crystal particles constituting the Tl-based superconductor had an indefinite shape, Jc was 0, orientation was difficult, and the superconductor volume ratio was low.

[0078]

[Table 12]

[0079]

[Table 13]

From the results of Examples and Comparative Examples, it can be seen that the Tl-based superconductor according to the present invention has less evaporation of Tl and a higher superconductor volume ratio than the Tl-based superconductor of the Comparative Example. .. It is also shown that the Tl-based superconductor according to the present invention has a higher Jc than the Tl-based superconductor of the comparative example.

Further, as shown in FIG. 2, in comparison with the trial number 7 of the comparative example 1, it is clear that the trial number 1 of the example 1 has a large change in AC susceptibility and a high superconductor volume ratio. is there.

[0082]

Since the Tl-based superconductor according to the present invention is composed of plate-shaped superconductor crystal particles having an aspect ratio of 6 or more, the crystal particles are aligned in the ab plane direction in which the superconducting current easily flows, and It is easy to orient in the C-axis direction, Tl is hard to evaporate, and the superconductor volume ratio is high.
It is a Tl-based superconductor that has a very high Jc and is extremely favorable in industry.

[Brief description of drawings]

FIG. 1A is a SEM photograph of a crystal grain on a fracture surface of trial No. 1 in Example 1, and FIG. 1B is a SEM photograph of a crystal grain on a fracture surface of trial No. 7 in Comparative Example 1.

FIG. 2 is a graph showing the relationship between AC magnetic susceptibility and temperature.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location H01L 39/24 ZAA Z 8728-4M (72) Inventor Toshinosuke Ashizawa 4-13 Higashimachi, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi Chemical Co., Ltd. Ibaraki Research Center

Claims (3)

[Claims] 1. A Tl-based superconductor having plate-like crystal grains having an aspect ratio of 6 or more. 2. A composition containing M (where M is at least one element selected from Ba and Sr), Ca and Cu as the main components, is rapidly cooled in a molten state, and after crushing the composition, a compound containing Tl or Tl. And a compound containing Pb, and then molded,
A method for producing a Tl-based superconductor characterized by firing. 3. A compound containing M1 (where M is at least one element selected from Ba and Sr), Ca, Cu and Pb as a main component, is rapidly cooled in a molten state, and is pulverized to contain Tl. Alternatively, a method for producing a Tl-based superconductor, which comprises mixing with a compound containing Tl and Pb, followed by molding and firing.