JPH06321693A - Production of oxide superconducting material - Google Patents

Abstract

PURPOSE:To easily control crystal grow and to obtain a large-sized high quality YBCO single crystal by heating the source material containing Y, Ba, and Cu but containing no crystal of a specified chemical compsn. to prepare the molten material. CONSTITUTION:A mixture of the source materials is prepared by selecting oxides or carbonates of Y, oxides or carbonates of Ba, and oxide or carbonates of Cu in a manner that the molar compsn. of Y:Ba:Cu represented by x:y:w of the start source material satisfies 1.0<=x<=2.5, 20<=y<=40 and x+y+w=100 shown as the dashed area in the figure. The source material containing neither YBa2Cu3Oz (6<=z<=7) nor YBaCuO5 is heated to 980-1000 deg.C by >=100 deg.C/hour heating rate, stirred, and maintained at that temp. for one or more hours to prepare the molten material of a uniform compsn. Then the molten material is cooled to obtain a single crystal of YBa2Cu3Oz. The temp. range from 980 to 1000 deg.C is lower than the reaction temp. of the peritectic decomposition expressed by formula YBa2Cu3OzY2BaCuO5 + liquid phase and is higher than the solid-liquid temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal of oxide superconducting material.
A method for producing crystals, in particular YBa ₂Cu₃O
_ZA method for producing a single crystal of (6 ≦ Z ≦ 7)
It

[0002]

_2. Description of the Related Art YBa ₂ Cu ₃ O _Z (YBCO) which is an oxide superconducting substance
Has a high critical temperature of about 90 K and is expected to be applied in many technical fields.

In order to produce this YBCO single crystal, many methods of gradually cooling a high-temperature melt to precipitate the crystal have been tried, but a flaky crystal can be obtained while a good quality large crystal is obtained. It was difficult.

An object of the present invention is to provide a method in which the growth of crystals can be easily controlled and a large-sized YBCO single crystal of good quality can be produced.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to Y, Ba and
And Cu, while YBa₂Cu₃O_Z(6 ≦ Z ≦ 7)
Crystal and Y₂BaCuO_FiveDeparture without crystals
Raw material is YBa₂Cu ₃O_ZCrystal and Y₂BaCuO
_FivePrepare a molten metal by heating so that crystals do not precipitate, and obtain
Cooling the melt obtained to form a YBCO single crystal
Is characterized by.

In the present invention, Y: B in the starting material
If the molar composition ratio of a: Cu is represented by x: y: w, it is desirable that the following conditions be satisfied.

[0007]

1.0 ≦ x ≦ 2.5 20 ≦ y ≦ 40 and x + y + w = 100 In the present invention, the starting materials are Y oxides and carbonates, Ba oxides and carbonates, and Cu oxidation. It can be preferably prepared from a mixture of raw materials selected from the group consisting of products and carbonates. If it is a mixture of these raw materials, YBCO crystal and Y ₂ BaCu
A raw material containing no O ₅ crystals is easily prepared.

In the present invention, the starting material has a melting temperature which is lower than the reaction temperature of the peritectic decomposition reaction represented by the following formula: YBa ₂ Cu ₃ O _Z → Y ₂ BaCuO ₅ + liquid phase, and is higher than the solid-liquid temperature. It is desirable to heat up. Such melting temperature is 980 ° C or higher and 1000 ° C.
Less than is desirable. The melting temperature in such a temperature range is 1
It is desirable to hold for more than an hour.

Further, it is desirable that the temperature rising rate in heating the raw material until reaching the melting temperature is 100 ° C./hour or more.

Further, in order to keep the composition of the molten metal uniform, in the present invention, it is desirable to stir the molten raw material.

[0011]

[Function] An important feature of the present invention is to precipitate crystals.
In preparing the melt of ₂BaCuO_FiveCrystallization
It has been suppressed. As shown in the examples below, Y
₂BaCuO_FiveBy suppressing the precipitation of crystals,
It is clear that a well-grown YBCO single crystal can be obtained.
It was.

In order to exclude the Y ₂ BaCuO ₅ crystal, the starting material does not initially contain this crystal. In addition, as shown in the following examples, when a raw material containing a YBCO crystal is heated to prepare a molten metal, Y ₂ BaCuO ₅ is precipitated, so that the YBCO crystal was not included in the starting raw material.

From these points, as shown in the embodiment, Y
A mixture of raw materials selected from the group consisting of oxides and carbonates of Ba, oxides and carbonates of Ba, and oxides and carbonates of Cu is particularly preferably used as a starting material. If these raw materials are used, Y ₂ BaCu
It is possible to obtain a uniform molten metal free of O ₅ and BaCuO ₂ .

Further, as shown in the examples, when the molar composition ratio of Y: Ba: Cu in the starting material is x: y: w,
By setting the composition ratio in the range represented by the above [Formula 1], Y ₂ BaCuO ₅ , BaCuO ₂ and C can be obtained.
YB that grows largely in the c-axis direction while suppressing the precipitation of uO
It became clear that a CO single crystal was obtained.

As shown in the examples, it is desirable that the raw materials be completely melted by heating to prepare a uniform molten metal.
When the temperature at the time of melting the raw materials exceeds the reaction temperature of the peritectic decomposition reaction represented by the following chemical formula,

[0016]

## STR1 ## YBa ₂ Cu ₃ O _Z → Y ₂ BaCuO ₅ + Liquid phase Y ₂ BaCuO ₅ phase is precipitated in the molten metal to obtain YB
A CO single crystal grows poorly in the c-axis direction. When Y ₂ BaCuO ₅ was involved in the crystal growth, it was considered that the growth rate of the YBCO single crystal in the c-axis direction was reduced. Therefore, it has been desired to set the dissolution temperature below the peritectic decomposition reaction temperature.

As shown in the examples, it was desired that the melting temperature be 980 ° C. or higher and lower than 1000 ° C.
Further, by setting the holding time in such a temperature range to 1 hour or longer, precipitation of BaCuO _{2 in} the molten metal was further suppressed, and a uniform molten metal could be obtained. This was effective in producing a large YBCO single crystal.

Further, by setting the temperature rising temperature up to the melting temperature to 100 ° C./hour or more, the generation of BaCuO ₂ at the time of temperature rising could be suppressed. BaCu
The preparation of a uniform molten metal free of O ₂ was effective for producing a large YBCO single crystal.

Further, by adding the step of stirring at the melting temperature, it was possible to eliminate the difference in Y concentration between the upper and lower compositions in the molten metal. Obtaining a uniform molten metal in this manner was effective in producing a large YBCO single crystal.

[0020]

【Example】

Example 1 In order to investigate the effect of the presence or absence of YBa ₂ Cu ₃ O _Z crystals in the starting material, the morphology of the starting material was changed and the following experiment was conducted. In the following experiment, the composition ratio of Y: Ba: Cu was set to 2: 3.
An example of 1:67 is shown.

Two pieces of 50 g of the mixed powder placed in an alumina crucible or a magnesia crucible were prepared and heated in an electric furnace at a temperature rising rate of 300 ° C./hour to 900 ° C. and held at that temperature for 20 hours. For one crucible, the melt was rapidly cooled immediately after the holding time and the solidified body was observed. After the holding time, the other crucible was cooled to 950 ° C. at a rate of 0.6 ° C./hour, taken out from the furnace, and crystals precipitated in the solidified body were observed.

As the mixed powder to be heated, Y ₂ O ₃ , B
Mixture of aCO ₃ and CuO (Sample No. 1), YB
a ₂ Cu ₃ O _Z sintered body mixed with BaCO ₃ and CuO (Sample No. 2), Y ₂ O ₃ , BaCO ₃ ,
The above experiment was carried out using CuO mixed and held at 900 ° C. for 50 hours to precipitate YBa ₂ Cu ₃ O _Z crystals in the mixed powder.

The experimental results are shown in Table 1. As can be seen from Table 1, until the melting temperature (990 ° C) is reached, YBCO
In the samples containing a large amount of crystals (Samples 2 and 3), the above-mentioned reaction of [Chemical formula 1] is likely to occur during dissolution, and Y
₂ BaCuO ₅ is generated. Therefore, the starting material is
It can be seen that those not containing YBCO crystals are suitable.

[0024]

[Table 1]

Example 2 To investigate the optimum composition of the starting material, Y ₂ O ₃ , BaCO
_3. Using CuO, the raw materials were mixed so that the molar ratio of Y: Ba: Cu would be the compositions of sample numbers 1 to 9 in Table 2. About 50 g of these mixed powders were placed in an alumina crucible or a magnesia crucible, and heated in an electric furnace up to 990 ° C. at a temperature rising rate of 300 ° C./hour, and then heated at 990 ° C.
After holding for 0 hour, it was cooled to 950 ° C. at a rate of 0.6 ° C./hour.

Then, the crucible was taken out from the electric furnace, the solidified body in the crucible was taken out, and the precipitated crystals were observed.
The type of single crystal obtained from the solidified body and the target YBC
Table 2 shows the crystal size of the O single crystal. In addition, FIG. 1 shows the points having the compositions of sample numbers 1 to 9, respectively. From the results of Table 2, if the composition of the shaded portion shown in FIG. 1, that is, the portion satisfying the condition of [Equation 1] above is used, a large YB
It can be seen that a CO single crystal is obtained.

[0027]

[Table 2]

Example 3 In order to examine the optimum melting and holding temperature for preparing a molten metal which is the basis of YBCO single crystal growth, the following experiment was carried out while changing the holding temperature during melting. In the following experiment, Y ₂ O ₃ , BaCO ₃ , and CuO were mixed so that the composition ratio of Y: Ba: Cu x: y: w satisfies the above-mentioned condition of [Equation 1], and about 50 g of the mixed powder is mixed with alumina. Two pieces placed in a crucible or a magnesia crucible were prepared and heated in an electric furnace.

In one crucible, the molten metal was rapidly cooled immediately after the holding time and the solidified body was observed. After the holding time, the other crucible was cooled to 950 ° C. at a rate of 0.6 ° C./hour, taken out from the furnace, and crystals precipitated in the solidified body were observed.

In Table 3, the composition ratio of Y: Ba: Cu is 2: 3.
The results in the case of 1:67 are shown.

[0031]

[Table 3]

When the holding temperature was 960 ° C. or lower (Sample No. 1), the sample was not completely dissolved. Further, in the samples (Sample Nos. 5 and 6) having a peritectic decomposition reaction temperature of [Chemical Formula 1] above 1000 ° C., the Y ₂ BaCuO ₅ phase was precipitated in the molten metal. A YBCO single crystal was obtained in the sample gradually cooled from these temperatures, but its size in the c-axis direction was small. It was considered that when Y ₂ BaCuO ₅ participated in the crystal growth, the growth rate of the crystal in the c-axis direction decreased.

With respect to the samples having the holding temperatures of 980 and 990 ° C., YBCO single crystals were obtained in which no precipitate was present in the molten metal and which also grew greatly in the c-axis direction. From the above results, when a YBCO single crystal is obtained, in order to obtain a molten metal in which Y ₂ BaCuO ₅ does not precipitate, the melting holding temperature is preferably less than the peritectic decomposition reaction temperature and the solid-liquid temperature or more, particularly 980 ° C. or more and 1000 ° C. or more. It was found that a uniform molten metal having no precipitate was obtained at a temperature of less than and a large YBCO single crystal was obtained.

Example 4 As shown in Table 4, the following experiment was carried out by changing the morphology of the starting material, as shown in Table 4, in order to investigate the optimum morphology of the starting material for producing the molten metal which is the basis of YBCO single crystal growth. In the following experiment Y:
An example in which the composition ratio of Ba: Cu is set to 2:31:67 is shown.
Approximately 50 g of mixed powder was placed in an alumina crucible or a magnesia crucible, and two were prepared.
It was heated to 990 ° C. at 00 ° C./hour and kept at that temperature for 20 hours. In one crucible, the melt was rapidly cooled immediately after the holding time and the solidified body was observed. After the holding time, the other crucible was cooled to 950 ° C. at a rate of 0.6 ° C./hour, taken out from the furnace, and crystals precipitated in the solidified body were observed.

As a mixed powder for heating, Y
_A mixture of ₂ O ₃ , BaCO ₃ and CuO (Sample No. 1), a mixture of Y ₂ O ₃ , BaO and CuO (Sample No. 2), a sintered body of YBa ₂ Cu ₃ O _Z and Ba-Cu −
A mixture of O sintered bodies (Sample No. 3) and Y ₂
O _3, BaCO _3, CuO mixed YBa ₂ Cu ₃ O _Z
A sample (Sample No. 4) was prepared by sintering at 900 ° C. for 10 hours so as to prevent the occurrence of heat.

[0036]

[Table 4]

It can be seen from Example 1 that the sample 3 using the YBCO sintered body is not good. In addition, even in the case of sample 4 in which the raw material was sintered to the extent that YBCO was not generated, a large amount of B
aCuO ₂ was generated, and even if they reached the melting temperature, they were not melted and remained in the melt, and a uniform melt could not be obtained.

Samples 1 and 2 in which oxides or carbonates were simply mixed were mostly BaCuO.
_{No 2} was formed, and it decomposed by holding it at the melting temperature, and a uniform molten metal without precipitates was obtained. From the above results, it is found that a suitable starting material is a mixture of oxides or carbonates of Y, Ba, Cu.

Example 5 Next, the following experiment was conducted in order to know the optimum holding time at the melting temperature. Y is a starting material so that the composition ratio x: y: w of Y: Ba: Cu satisfies the condition of [Equation 1] described above.
₂ O ₃ , BaCO ₃ , CuO are mixed to obtain a mixed powder of about 50
Two pieces of which g was placed in an alumina crucible or a magnesia crucible were prepared. Next, the heating rate is 300 ° C in the electric furnace.
Heated up to 990 ° C./h and at that temperature 0.5, 1, 2
Hold for 0, 100 hours. In one crucible, the melt was rapidly cooled immediately after the holding time and the solidified body was observed. The other crucible is 950 at a rate of 0.6 ° C / hour after the end of the holding time.
The mixture was cooled to 0 ° C., taken out of the furnace, and crystals precipitated in the solidified body were observed. Table 5 shows the results when the mixed powder having the composition ratio x: y: w of 2:31:67 was used.

[0040]

[Table 5]

Comparing these samples, the retention time was 1
If it is shorter than the time (Sample No. 1), B generated at the time of temperature rise
aCuO ₂ remains in the molten metal without being sufficiently decomposed. Therefore, the holding time is preferably 1 hour or more.

Example 6 Next, in order to know the influence of the temperature rising rate until reaching the melting temperature, the composition ratio x: y: w of Y: Ba: Cu should satisfy the condition of [Equation 1] described above. Starting materials Y ₂ O ₃ , BaCO
₃ , CuO were mixed, and about 50 g of the mixed powder was placed in an alumina crucible or a magnesia crucible and heated at various heating rates. Two crucibles containing the mixed powder were prepared for each sample, and the temperature was 99 at the heating rates of 1, 10, 100, and 300 ° C./hour shown in Table 6 in the electric furnace.
Heat to 0 ° C. and hold at that temperature for 20 hours. In one crucible, the molten metal was rapidly cooled immediately after the holding time and the solidified body was observed. The other crucible has a 0.
It was cooled to 950 ° C. at a rate of 6 ° C./hour, taken out from the furnace, and crystals precipitated in the solidified body were observed.

[0043]

[Table 6]

As a result, in the samples (sample numbers 1 and 2) whose temperature rising rate was less than 100 ° C./hour, Y ₂ Ba was contained in the molten metal.
CuO ₅ and BaCuO ₂ remained. Since the rate of temperature rise is slow, YBa ₂ Cu ₃ O _Z , BaCu
This is because a large amount of O ₂ is produced in the sample. In order to prevent this, it can be seen that the temperature rising rate is preferably 100 ° C./hour or more.

Example 7 The following experiment was conducted to examine the effect of stirring. Y: B
a: the composition ratio of Cu x: y: w is to satisfy the condition of Equation 1, was mixed with _{Y 2 O 3, BaCO 3,} CuO.
2 about 50g of mixed powder packed in alumina crucible
I prepared one. They were heated to 990 ° C. at a temperature rising rate of 300 ° C./hour in an electric furnace and kept at that temperature for 20 hours.

[0046]

[Table 7]

Sample No. 1 shown in Table 7 was left to stand during the holding time in the above-mentioned process. On the other hand, Sample No. 2 was stirred with an alumina rod during the holding time. After the end of the holding time, the molten metal was sampled from the upper part of the liquid phase (about 1 mm from the liquid surface) and the lower part of the liquid phase (about 1 mm from the bottom of the crucible), and its composition was investigated. The remaining samples were cooled from 990 ° C. to 950 ° C. at a rate of 0.6 ° C./hour, taken out from the electric furnace, and crystals precipitated in the solidified body were observed. The results are also shown in Table 7.

As can be seen from Table 7, in the sample without stirring, the Y concentration is different between the upper part and the lower part of the liquid phase. On the other hand, in the sample with stirring, there was no difference in Y concentration between the upper part and the lower part of the liquid phase, and the molten metal was uniform. Further, the size of the YBCO single crystal obtained by slow cooling was also larger in the sample with stirring. From this, it can be seen that the stirring step at the melting holding temperature is effective for obtaining a uniform molten metal and is also effective for growing a large YBCO single crystal.

[0049]

As described above, according to the present invention,
By preparing a molten metal while suppressing precipitation of Y ₂ BaCuO ₅ and further precipitation of BaCuO _2, etc., and cooling the obtained homogeneous molten metal, it became possible to produce a large YBCO single crystal of good quality. .

Further, as shown in the examples, the production method of the present invention is easy to control the production conditions, and can be easily prepared by appropriately selecting the conditions such as the raw material, the dissolution temperature, the dissolution holding time, and the heating rate. A large YBCO single crystal can be prepared.

[Brief description of drawings]

FIG. 1 is a diagram showing a molar composition ratio of Y: Ba: Cu in a starting material and a desirable composition range for producing a YBCO single crystal.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01B 13/00 565 D 7244-5G (72) Inventor Shinsuke Fujiwara 1-chome, Shimaya, Konohana-ku, Osaka No. 3 Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Masato Irikura 1-3-3 Shimaya, Konohana-ku, Osaka City Sumitomo Denki Industries Co., Ltd. Osaka Works

Claims (7)

[Claims] 1. Including Y, Ba and Cu, while YBa
₂ Cu ₃ O _Z (6 ≦ Z ≦ 7) crystal and Y ₂ BaCuO
_The starting material which does not contain both ₅ crystals is the above YBa ₂ Cu
Characterized in that the ₃ O _Z crystal and the Y ₂ BaCuO ₅ crystal are heated so as not to precipitate to prepare a molten metal, and the obtained molten metal is cooled to form a YBa ₂ Cu ₃ O _Z single crystal. Manufacturing method of oxide superconducting material. 2. When the molar composition ratio of Y: Ba: Cu in the starting material is represented by x: y: w, 1.0 ≦ x ≦ 2.5, 20 ≦ y ≦ 40 and x + y + w.
= 100 is satisfied, The manufacturing method of the oxide superconducting material of Claim 1 characterized by the above-mentioned. 3. The starting material is a mixture of materials selected from the group consisting of Y oxides and carbonates, Ba oxides and carbonates, and Cu oxides and carbonates. The method for producing an oxide superconducting material according to claim 1. 4. The melting temperature of the starting material is lower than the reaction temperature of the peritectic decomposition reaction represented by the following formula: YBa ₂ Cu ₃ O _Z → Y ₂ BaCuO ₅ + liquid phase, and higher than the solid-liquid temperature. It heats, The manufacturing method of the oxide superconducting material of Claim 1 characterized by the above-mentioned. 5. The melting temperature is 980 ° C. or higher and 1000 ° C.
5. The method for producing an oxide superconducting material according to claim 4, wherein the melting temperature is maintained for 1 hour or more. 6. The method for producing an oxide superconducting material according to claim 5, wherein the temperature rising rate until reaching the melting temperature is 100 ° C./hour or more. 7. The method for producing an oxide superconducting material according to claim 1, further comprising the step of stirring the molten metal.