JPH10120417A - Production of oxide superconductor and precursor for producing oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxide superconductor in a short time by reacting copper hydroxide or a copper alkoxide with a barium alkoxide and a neodymium alkoxide in a nonaqueous solvent and subsequently calcining the obtained precursor. SOLUTION: This method for producing an oxide superconductor comprises reacting copper hydroxide or a copper alkoxide with a barium alkoxide and a neodymium alkoxide in a non-aqueous solvent, drying the obtained precursor, grinding the dried product, molding the ground product in a prescribed shape, calcining the molded product at a temperature of 600-800 deg.C under a pressure of 1×10<-3> Torr, calcining the product at a temperature of 800-1000 deg.C in a mixed gas atmosphere having an oxygen concentration of <=5%, and further thermally treating the product at 300-500 deg.C to obtain the oxide superconductor containing an oxide superconductive compound phase of the formula: NdB2 Cu3 O7-δ .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to NdBa ₂ Cu ₃
The present invention relates to a method for producing an oxide superconductor containing an oxide superconducting compound phase represented by O _7- δ and a precursor for producing an oxide superconductor used as a raw material in the production method.

[0002]

2. Description of the Related Art Conventionally, YBa_Two Cu_Three O_7-δ-type oxide
Oxide superconductor in which the Y site of the conductor is replaced with a rare earth element
Many attempts have been made to synthesize conductors. Among them, NdBa
_Two Cu _Three O_7-The superconducting compound represented by δ has a critical current
It is attracting attention because it is large and chemically stable. This
NdBa_Two Cu_Three O_7-Method for synthesizing δ-based superconducting compound and
The pulling method, solid phase mixing method, etc. have been reported so far.
I have.

For example, it has been reported that a single crystal could be synthesized at 1090 ° C. by the pulling method [M. Nakam
ura et al. Physica C 260 (19
96) 29]. In addition, some reports have been made on polycrystals that could be synthesized at 900 to 950 ° C. by a solid-phase mixing method [for example, J. Am. McHale, J .; Ma
ter. Res. 10 (1995) 1; K. Si
ngh et al. Physica C 224 (19
94) 231 etc.].

[0004]

Although the production of a single crystal by the above-mentioned pulling method is possible at the experimental and research level, there are many problems that must be overcome technically as a production method of practical materials. It is not considered suitable for mass production. On the other hand, in the solid phase mixing method widely used as a method for producing various oxide superconductors, it is necessary to make the reaction uniform in order to improve and stabilize the characteristics of the superconductor. Therefore, in the production of superconductors, it has become common to repeat the mixing, calcining, firing, pulverizing, and mixing of the raw material powders many times, and there is a problem that the production time is long and the process is complicated. Was. Furthermore, in any case, the above-mentioned methods produce an oxide superconductor at a high temperature of 900 ° C. or more, and practically, synthesis at a lower temperature is expected. This is because if the synthesis temperature can be lowered, the range of choices of metals that can be used for the sheath material is widened, and energy consumption can be suppressed.

The present invention has been made in view of the above-mentioned circumstances, and has as its object a shorter and less complicated NdBa ₂ Cu ₃ O _7- δ system as compared with the conventional synthesis method. It is to provide a method for synthesizing a superconducting compound,
An object of the present invention is to provide a method capable of synthesizing an NdBa ₂ Cu ₃ O _7- δ superconducting compound at a lower temperature than before. Still another object is to provide a novel precursor for producing an oxide superconductor used in the synthesis method.

[0006]

The method for producing an oxide superconductor according to the present invention, which has achieved the above objects, uses copper hydroxide or copper alkoxide as a copper source, and includes the copper source, barium alkoxide and neodymium alkoxide. Production of an oxide superconductor mainly containing an NdBa ₂ Cu ₃ O _7- δ-based oxide superconducting compound phase, wherein a precursor derived by reacting a starting material in a non-aqueous solvent is used as a raw material. Is the way.

In the production method of the present invention using this precursor, a step of firing at a temperature of 600 to 800 ° C. under a pressure of less than atmospheric pressure (hereinafter referred to as firing) in a mixed gas having an oxygen concentration lower than that of the atmosphere. 800 to 100
It is intended to include a step of firing in a temperature range of 0 ° C. (hereinafter, referred to as firing) and a step of performing a heat treatment at 300 to 500 ° C. in an oxidizing atmosphere.

It is desirable that the calcination be performed under a pressure of 1 × 10 ⁻³ Torr or less, and that the calcination be performed using a mixed gas having an oxygen concentration of 5% or less.
The step of drying the precursor, calcining the precursor at 400 to 600 ° C., pulverizing the precursor, and shaping the powder into a predetermined shape may be performed before the above steps.

Further, the precursor for producing an oxide superconductor of the present invention is obtained by reacting copper hydroxide or copper alkoxide with a copper source, and reacting the copper source with a starting material containing barium alkoxide and neodymium alkoxide in a non-aqueous solvent. It is a precursor for producing an oxide superconductor that is induced by being caused by this. The reaction in this case is
The reaction can be carried out in a state in which the starting materials are completely dissolved or partially undissolved, that is, in a solution state or a suspended state. However, it is recommended that the reaction be carried out after obtaining a completely dissolved solution state. Therefore, the following description focuses on reacting in a solution state.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have been conducting research on a method for synthesizing various oxide superconductors by applying a sol-gel method, and as a part of the research, NdBa ₂ C
An attempt was made to synthesize an oxide superconductor represented by the chemical formula of u ₃ O _7- δ.

As a result, the sol-gel method is applied using copper hydroxide or copper alkoxide as a copper source, and the copper source and barium alkoxide and neodymium alkoxide as starting materials. By generating a precursor made of an amorphous substance having high reaction activity and using the precursor, even if the baking is performed at a temperature of less than 900 ° C., by appropriately controlling the type and pressure of the atmosphere gas, the reaction can be performed. Progressed uniformly, and a superconducting compound phase represented by NdBa ₂ Cu ₃ O _7- δ was found to be homogeneously formed, thus completing the present invention. As alkoxides of copper, barium and neodymium, lower alkoxides such as methoxide, ethoxide, propoxide and isopropoxide are used, and among them, ethoxide and isopropoxide are most preferred.

As the non-aqueous solvent used in the present invention, alcohol, dialkylamino alcohol, acetone, benzene and the like are arbitrarily used, and the alcohol constituting the alkoxide is most preferably used. Lower alcohols such as methanol, ethanol, propanol, isopropyl alcohol and butanol are exemplified. Further, if necessary, the above solvents can be mixed and used.

According to the present invention, mixing at the molecular level in a solution can be easily performed. Therefore, a complicated and long-time process such as repetition of calcination, firing, pulverization, and mixing as in the conventional solid phase mixing method can be greatly improved.

In the method for producing an oxide superconductor according to the present invention, the above-mentioned precursor is dried, powdered, formed into a predetermined shape, and then subjected to the following steps. Recommended. Firing at a pressure of less than atmospheric pressure in a temperature range of 600 to 800 ° C. 800 to 100 in a mixed gas having an oxygen concentration lower than that of the atmosphere
Step of baking in a temperature range of 0 ° C. Step of performing heat treatment at 300 to 500 ° C. in an oxidizing atmosphere.

First, the condition (1) is utilized in that the decomposition reaction of the fine particle carbonate, which is the rate-determining reaction, proceeds easily under a vacuum lower than atmospheric pressure. The pressure is preferably set to 1 × 10 ⁻³ Torr or less from the viewpoint of easy progress of the reaction. At that time, a preferable firing temperature is 600
８００800 ° C. If the temperature is lower than 600 ° C., there is a disadvantage that decomposition of carbonate is difficult to proceed. At a temperature exceeding 800 ° C., the reduction proceeds too much, and Nd as an impurity phase
The production of ₂ O ₃ is increased. The lower limit of the firing temperature is 650
C. or higher, and more preferably 680.degree. C. or higher. The upper limit of the firing temperature is preferably 750 ° C. or lower, more preferably 720 ° C. or lower.

After that, it is preferable to fire in a mixed gas having an oxygen concentration lower than that of the atmosphere at a temperature of 800 to 1000 ° C.
This firing is a process for growing the crystals of the generated NdBa ₂ Cu ₃ O _7- δ-based superconducting compound and promoting sintering. The baking is performed in an atmosphere having a low oxygen concentration because the valence of copper is reduced and the melting point of the oxide is lowered to promote the reaction. The oxygen concentration at this time is desirably 5% or less. The firing temperature at this time is 800 to 10
The temperature must be set to 00 ° C. If the temperature is lower than 800 ° C., the reaction and sintering do not substantially proceed. At a temperature exceeding 1000 ° C., partial melting proceeds, and liquid phase separation occurs, which tends to cause a heterogeneous reaction.

As understood from the above description, the firing temperature at this time can be lower than 900 ° C., unlike the conventional method. This is because the raw material powder obtained from the precursor of the present invention is finer than the powder used in the ordinary solid-phase mixing method, so that the reaction during firing becomes more uniform,
This is because firing can be performed even at a lower temperature. Sintering is possible even at 900 ° C. or higher, which is equivalent to that of the conventional method, but from the viewpoint of expanding the range of choice of the metal sheath material, 9
It is desirable to employ a firing temperature of less than 00 ° C. Silver is an example of a metal that can be newly selected as a metal sheath material by applying the present invention. The melting point of silver is around 960 ° C., and in the prior art, the sintering temperature and the melting point of silver are close to each other, making it difficult to use as a sheath material. However, in the present invention, as described above, the firing temperature can be reduced, so that it can be used as a sheath material. Conventionally, when silver was used as a sheath material, there was no other choice but to use a silver sheath after forming an oxide superconductor, but according to the present invention, it has become possible to sinter using a silver sheath. This means that a very advantageous method for putting a superconductor into practical use has been provided.

Thereafter, in an oxidizing atmosphere, 300 to 500
It is preferable to carry out a heat treatment at ℃. This is because oxygen is introduced into the crystal by this heat treatment to increase the number of carriers. The heat treatment temperature at this time needs to be 300 to 500 ° C. If the temperature is lower than 300 ° C., it is difficult to introduce oxygen into the crystal. It is more preferable that the temperature be 350 ° C. or higher.
If the temperature exceeds 500 ° C., neodymium and barium are likely to be out of order, and the superconducting properties may be reduced. 450 ° C. or lower is more preferable.

In carrying out the above process, the drying
The dried precursor was calcined in advance at 400 to 600 ° C.
A step of pulverizing the powder and molding the powder into a predetermined shape
May be performed before the above-mentioned steps. This is
In the subsequent firing, NdBa _Two Cu_Three O_7-δ superconductivity
This is because it is effective for producing a compound. Lower limit of calcination temperature
Therefore, 450 ° C. or higher is preferable, and 480 ° C. or higher is more preferable.
preferable. The upper limit is preferably 550 ° C or less.
520 ° C. or lower is more preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention, and all changes and implementations without departing from the spirit of the present invention will be described. Within the technical scope of

[0021]

【Example】

 (Example 1) Copper hydroxide [Cu (OH)] as a copper source_Two ]
Barium isopropoxide [B
a (O-isoC_Three H₇ )_Two ], Neodymium isopropoxy
Sid [Nd (O-isoC_Three H₇ )_Three ]
Has a chemical composition of NdBa_Two Cu _Three O_7-Compound represented by δ
Was prepared according to the following procedure.

First, copper hydroxide and neodymium isopropoxide were mixed in a mixed solvent of dimethylaminoethanol (DMAE) and isopropyl alcohol (IPA) (mixing ratio 1:
Dissolved in 1). In addition, barium isopropoxide was dissolved in IPA.

These solutions were mixed and heated and refluxed at 80 ° C. in an inert gas stream to synthesize a sol in a molecular mixed state.
The sol was subsequently concentrated at 90 ° C. under suction, and then dried in vacuum at 200 ° C. to obtain a powder gel (precursor).

The powder gel was calcined at 500 ° C. in a gas stream of O ₂ : N ₂ = 1: 4 to obtain a raw material powder for firing. After pressure-molding this raw material powder, it was fired in a pattern as shown in FIG. At this time, the degree of vacuum in the step is about 10 ⁻⁵ Torr, the firing temperature is 700 ° C., the oxygen concentration of the mixed gas in the step is 0% (gas pressure is near atmospheric pressure), and the firing temperature is 850 ° C. , The heat treatment temperature was 400 ° C.

The susceptibility of the sample obtained under these conditions was measured by a superconducting quantum interferometer (SQUID).
It exhibited diamagnetism below 0K. FIG. 2 shows the susceptibility-temperature curve of this sample measured in a 100 Oe magnetic field.
When the magnetic susceptibility of the sample which was not subjected to the step but was subjected to only the step separately from the sample was similarly examined, no diamagnetism was shown. FIG. 3 shows a susceptibility-temperature curve measured in a 100 Oe magnetic field of a sample that did not exhibit this diamagnetism. It can be seen that the susceptibility-temperature curve becomes sharper by performing the above steps.

FIG. 4 shows the result of examining the crystal structure of the sample exhibiting diamagnetism by X-ray diffraction. From this X-ray diffraction pattern, it was found that YBa ₂ Cu ₃ O _7- δ
It was inferred that there was a substance having a crystal structure similar to that of. Then, when this sample was further investigated by an energy dispersive X-ray detector (EDX), it was found that a superconducting compound represented by the chemical formula of NdBa ₂ Cu ₃ O _7- δ was present in this sample. Further, this sample has no crystal phase other than NdBa ₂ Cu ₃ O _7- δ,
It was also found that it was almost NdBa ₂ Cu ₃ O _7- δ single phase.

(Example 2) Copper ethoxide [C
u (OC ₂ H ₅ ) ₂ ] and barium isopropoxide [Ba (O-isoC ₃ H ₇ )] as another metal source.
₂ ], neodymium isopropoxide [Nd (O-isoC
₃ H ₇ ) ₃ ] and the apparent chemical composition is NdBa ₂ C
The compound represented by u ₃ O _7- δ was prepared according to the following procedure.

First, copper ethoxide and neodymium isopropoxide were mixed with a mixed solvent of DMAE and IPA (mixing ratio 1: 1).
Dissolved in 1). In addition, barium isopropoxide was dissolved in IPA.

These solutions were mixed and heated and refluxed at 80 ° C. in an inert gas stream to synthesize a sol in a molecular mixed state.
The sol was subsequently concentrated at 90 ° C. under suction, and then dried in vacuum at 200 ° C. to obtain a powder gel (precursor).

The above powder gel is_Two : N_Two = 1: 4 mo
Calcined at 500 ° C in air stream to obtain raw material powder for firing.
Was. After pressure-molding this raw material powder, as in Example 1,
The firing was performed in a pattern as shown in FIG. At this time,
The degree of vacuum in the step is 10 ^-FiveTorr, firing temperature
Is 700 ° C., and the oxygen concentration of the mixed gas in the step is
Degree is 0% (gas pressure is around atmospheric pressure), firing temperature is 900
° C, and the heat treatment temperature in the step is 400 ° C.
Was.

The magnetic susceptibility of the sample obtained under these conditions was measured by a superconducting quantum interferometer (SQUID).
It exhibited diamagnetism below 5K. The magnetic susceptibility-temperature curve of this sample measured in a 100 Oe magnetic field is shown in FIG.

The crystal structure of this sample was determined by X-ray diffraction.
When the structure was examined, the X-ray diffraction pattern almost similar to that of FIG.
was gotten. From these results, it was found that YBa_Two 
Cu _Three O_7-There is a substance with a crystal structure similar to δ
It was speculated that Therefore, this sample was further
Investigated by energy dispersive X-ray detector (EDX)
However, this sample contains NdBa_Two Cu_Three O_7-Chemical formula of δ
It was found that a superconducting compound represented by.

[0033]

The present invention is constituted as described above,
Copper oxide or copper alkoxide is used as a copper source, and the copper source is
Starting with alkoxides and neodymium alkoxides
As a raw material, a precursor obtained through a reaction in a non-aqueous solvent
The use of a solid allows for a shorter time compared to the conventional solid phase mixing method.
And NdBa without complicated steps_Two Cu_Three O
_7-Can produce oxide superconductors containing δ-based superconducting compounds
Was. Furthermore, firing at a lower temperature is possible compared to the conventional method.
Was.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a firing / heat treatment pattern.

FIG. 2 is a graph showing 100 samples of a sample exhibiting diamagnetism in Example 1.
It is a magnetic susceptibility-temperature curve in Oersted.

FIG. 3 shows a sample 1 showing no diamagnetism in Example 1.
It is a magnetic susceptibility-temperature curve in 00 Oersted.

FIG. 4 is an X-ray diffraction pattern of a sample showing diamagnetism in Example 1.

FIG. 5 is a graph showing 100 samples of diamagnetism in Example 2.
It is a magnetic susceptibility-temperature curve in Oersted.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshio Masuda 1-5-5 Takatsukadai, Nishi-ku, Kobe Inside Kobe Research Institute, Kobe Steel Ltd. No. 10-13, Foundation International Superconducting Technology Research Center, Superconductivity Engineering Laboratory (72) Inventor Shinobu Fujiwara 1-10-13, Shinonome, Shintomo, Koto-ku, Tokyo Inside the Institute of Engineering (72) Inventor Kei Tanabe 1-10-13 Shinonome, Koto-ku, Tokyo Foundation International Research Institute of Superconductivity Technology, Superconductivity Engineering Laboratory

Claims (6)

[Claims] 1. Use of a precursor derived by reacting copper hydroxide or copper alkoxide with a copper source and reacting the copper source with a starting material containing barium alkoxide and neodymium alkoxide in a non-aqueous solvent. A method for producing an oxide superconductor mainly including an oxide superconducting compound phase represented by the following chemical formula: Chemical formula: NdBa ₂ Cu ₃ O _7- δ 2. A step of sintering the precursor according to claim 1 at a temperature in the range of 600 to 800 ° C. under a pressure lower than atmospheric pressure, 800 to 100 in a mixed gas having an oxygen concentration lower than the atmosphere.
A method for producing an oxide superconductor, comprising: a step of firing in a temperature range of 0 ° C .; and a step of performing a heat treatment at 300 to 500 ° C. in an oxidizing atmosphere. 3. The calcination performed under a pressure lower than the atmospheric pressure,
3. The method for producing an oxide superconductor according to claim 2, wherein the method is performed under a pressure of 1 × 10 ⁻³ Torr or less. 4. The method for producing an oxide superconductor according to claim 2, wherein the firing performed in the mixed gas having an oxygen concentration lower than that of the atmosphere is performed using a mixed gas having an oxygen concentration of 5% or less. 5. The oxidation according to claim 2, wherein the precursor obtained by calcining the dried precursor at 400 to 600 ° C. is powdered, and the powder is formed into a predetermined shape. Of manufacturing superconductors. 6. A precursor for producing an oxide superconductor derived by reacting copper hydroxide or copper alkoxide with a copper source and reacting the copper source with a starting material containing barium alkoxide and neodymium alkoxide in a non-aqueous solvent. .