JPH0474753A - Production of rare earth-based oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain a uniform rare earth based oxide superconductor having highly superconducting characteristics by subjecting a raw material comprising a mixture of a rare earth element, barium and copper to reaction sintering at a specific temperature and under specific partial pressure of oxygen. CONSTITUTION:A mixed oxide comprising an oxide containing a rare earth element and an oxide containing barium and/or copper is used as a raw mate rial. The raw material is heated to 850-1,200 deg.C in an atmosphere under <=10<-4> atm partial pressure of oxygen and made in an oxygen atmosphere. Then the raw material is maintained at the above-mentioned temperature and/or lowered temperature to form a rare earth-based oxide superconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a rare earth oxide superconductor containing a rare earth element, typified by yttrium.

[Prior Art] In recent years, oxide superconductors have attracted attention due to their high critical temperature, and are expected to be used in various fields such as electric power, nuclear magnetic resonance apparatus, and magnetic shielding.

These oxide superconductors include M-Ba-Cu-0 Kenhokugoite, gates Sc, Y, and La+ Eu, Gd+ E.
There is a rare earth oxide superconductor having a multilayer perovskite structure containing one or more rare earth elements selected from lanthanides such as r, Yb, and Lu.

Among the above-mentioned rare earth-based oxide superconductors, for example, a YBazCu307 crystal phase in which H is typically yttrium (Y) is well known. This YBazCu:+
As a method for producing a rare earth oxide superconductor having a 07 crystal phase, a method is known in which raw material powder having a YBazCu307 phase is sintered under a low oxygen partial pressure. For example, in Japanese Patent Application Laid-Open No. 64-61345, a raw material powder having YBazCu, 07 phase is produced, and the compact is heated to an oxygen partial pressure of 0.
．． less than 2atll1, e.g. 10-” to 100att
A method is shown in which, after sintering in step (a), heat treatment is performed under an oxygen partial pressure of 1ate or more. Furthermore, in Japanese Patent Application Laid-Open No. 1-234353, a material containing LaBazCu30y as a main component is heated at 950° C. or higher at an oxygen partial pressure of 5×10-”ate or lower.
heating at a temperature below the melting point, then at a temperature below 400°C;
Heating in an anhydrous atmosphere with an oxygen partial pressure of 2 x 10-'atrg is indicated.

In addition, conventionally, Ba-
YBa is produced by reacting with CuO-based oxide in the liquid phase by firing.
zCu, 0. Various methods are known for producing and growing crystals. For example, JP-A-2-51468 proposes firing a mixed powder of YzBaCuOs powder and Ba2Cu305 powder in an oxygen atmosphere of 0.01 to Q and 5 atm.

[Secret B to be Solved by the Invention] In the conventional method of producing YBa2Cu,07 by a liquid phase reaction between the above-mentioned YzBaCuOs crystal particles and Ba-Cu~0-based oxide, the calcination temperature, e.g.
A phase of YBa2Cu30 is formed at the temperature during the heating process, and after reaching the calcination temperature, '/9azCu
There was a problem that the crystal growth of 30t was inhibited and excellent superconducting properties could not be obtained. Therefore, the above Y2BaC
Y due to liquid phase reaction between uO5 and Ba-Cu-0 based oxide
In the method for obtaining BazCu, 07, YBazCu30□Ba2Cu305 powder is heated during the heating process, and YzBaCu is heated at a heating rate of 300"C/hour or more.
A method is adopted in which the temperature is raised to 1000° C. or higher, where Os exists stably.

However, it is not only not economical to achieve a rapid heating rate of 300°C/hour to the firing temperature in a large electric furnace, but also because the temperature distribution inside the furnace fluctuates widely. It is difficult to obtain oxide-based superconductors.

Further, when obtaining a sintered body of a large-sized oxide superconducting compact, uneven shrinkage and cracking occur due to temperature rise, making it impossible to obtain a good sintered body.

The present invention solves the various problems of the conventional method described above and prepares a superconductor phase, for example, YBazCu:+0. Obtain rare earth oxide superconductors with excellent superconducting properties from small to large sizes by using oxides containing rare earth elements such as YzBaCu05 and Ba-Cu-0-based oxides as raw materials without forming crystal phases. The purpose is to

[Means for Solving the Problem] According to the present invention, a mixed oxide consisting of an oxide containing a rare earth element and an oxide containing barium and/or copper is used as a raw material, and the oxygen partial pressure is 10 at a temperature of 850 to 1200°C. -“a
After raising the temperature in an atmosphere of t or less, change to an oxygen atmosphere,
A method for producing a rare earth oxide superconductor is provided, which comprises producing a rare earth oxide superconductor by maintaining and/or lowering the temperature.

The present invention will be explained in detail below.

As mentioned above, the rare earth oxide superconductor of the present invention has gates of Sc, Y, and La, Eu, Gd, Er, and Yb.
, one-Ba-Cu having a multilayer perovskite structure containing one or more rare earth elements selected from lanthanides such as Lu.
It is a ~0 type compound.

In the following, an oxide superconductor mainly containing Y as a rare earth element will be representatively explained, but the same applies to those containing other rare earth elements.

In the present invention, oxides containing rare earth elements and barium (
As a mixed oxide consisting of an oxide containing Ba) and/or copper (Cu), Y
Any mixed oxide that produces a Ba2Cu30□ phase can be used without any particular limitation.

For example, YzBaCuOs oxide and BaCuO,,B
aO, CuO1Ba:+Cu50s, BaCuzOx
Examples include one type or a mixture of two or more types of Ba-Cu-0 oxides such as Ba-Cu-0 oxides. In addition, instead of Y2BaCuO5 oxide, YzBaCu0
It is also possible to use a mixed oxide having a composition such that Y2aCuO5 is generated and a Y2aCuO5 phase is generated by a sintering reaction. For example, using a mixed oxide of Y2O3 and the above Ba-Cu-0 oxide as a raw material, YzBaCu
At the same time as Os oxide is generated, the generated YzBaCu
A mixed oxide in which the 05 oxide and the Ba-Cu-0 oxide are uniformly dispersed may also be used.

Y, Ba and Cu in the raw materials of the mixed oxide of the present invention
In order to form a superconductor, the composition ratio is generally mixed so that the molar ratio of Y:Ba:Cu=1:2:3, but the composition ratio is not particularly limited to the above composition ratio. For example, the presence of impurity phases other than the Y3a2Cu307 phase in the sintered body may conversely improve the superconducting properties, and the above molar ratio Y:Ba:Cu-1:2:3
Excellent superconducting properties may be exhibited even when the composition ratio is outside the above, and one or two elements can be increased or decreased by about 50% based on the molar ratio Y: Ba: Cu = 1:2:3. May be used.

The mixed oxide raw material of the present invention may be used in the form of a powder, or the mixed oxide raw material powder may be used to form a molded body. As the molding method, a known molding method such as a doctor blade method, press molding method, cast moldability, etc. can be used.

Further, the molded body may be one in which a molded body layer is formed by spray coating, powder coating, etc. using the mixed oxide raw material powder on a substrate such as metal or ceramics.

In the present invention, an oxide containing a rare earth element such as Y, which is the raw material for the mixed oxide, is mixed with YJaC in a low oxygen partial pressure atmosphere.
Y2O as uOs phase or as above.

Y2BaC such as a mixed oxide of and Ba-Cu-0 oxide
Temperature 850 ~ at which the Ba-Cu-0 oxide is in a liquid phase state while stably existing as a phase that generates the uO5 phase.
The mixed oxide raw material is heated to 1200 DEG C. in an atmosphere with an oxygen partial pressure of 10@-4 atm or less, and then the temperature after the temperature rise and/or the temperature is lowered to maintain the firing temperature while the atmosphere is an oxygen atmosphere. If the oxygen partial pressure in the atmosphere such as inside the firing furnace is made higher than 10-'ate during the temperature raising process to the above prescribed temperature, Y2aCuO5 phase will be generated during the temperature raising process before reaching the prescribed firing temperature. YBa2 with On
As the sintering of the Cu2O7 phase progresses, the final Y
The Ba2Cu3O7 phase oxide superconductor is not homogeneous and has poor superconducting properties. On the other hand, in an atmosphere where the oxygen partial pressure is 10-'at11 or less, YBa2Cu
Since the 2O7 phase is not a stable phase, if YBa2Cu2O
Even if a very small amount of the 7 phase exists, the Y2BaCuO5 phase and Ba
-Cu-0 oxide is decomposed into Y2aCuO5 and phase-free Y2BaCuO5 at a given firing temperature.
A raw material mixture of oxide and Ba-Cu-0 oxide is obtained.

In the present invention, by adopting the step of raising the temperature to reach the firing temperature as described above, there is no need to generate a superconducting phase from the rare earth element oxide and the Ba-Cu-0 oxide in advance. Finally analogy HaYBazCu: +O
An excellent rare earth superconductor having a superconducting phase such as t can be obtained. This is because a uniformly dispersed state of YJaCuOs oxide and Ba-CuO oxide is obtained without including the YBazCu30 phase, and then a sintering reaction is performed in the uniformly dispersed raw material mixed oxide under an oxygen atmosphere. This is thought to be because it is possible to

In the present invention, the heating rate to raise the temperature to 850 to 1200'C is such that the oxygen partial pressure in the atmosphere during the heating process is 1
There is no particular limitation as long as it is less than 0-“atm, and the conventional 30
A rapid temperature increase of 0° C./hour is not necessary.

Therefore, it is possible to appropriately control the temperature distribution in the electric furnace to prevent it from becoming non-uniform, depending on the conditions such as the size of the firing furnace and the type of raw materials. - For boat fishing, the temperature increase rate is preferably 30'C/hour or more in an electric furnace, and preferably 200''C/hour or less for firing large molded bodies, usually 60 to 120℃
/hour range.

In the present invention, the oxygen partial pressure of 10-'at11 or less is
It can be easily obtained by passing an inert gas such as nitrogen gas or argon gas through a firing furnace, such as a conventional electric furnace that is simply airtight. Further, the degree of vacuum may be set to 10 −4 atm or less in an airtight furnace.

The oxygen partial pressure may be extremely low in a reducing gas atmosphere using a reducing gas such as hydrogen gas or carbon dioxide gas. However, even if the oxygen partial pressure is extremely lowered, there is no significant effect, and it is usually 10-4.
~10~4 atm is sufficient.

In the present invention, after the heating process to the above-mentioned predetermined firing temperature is completed, the firing atmosphere is converted to an oxygen atmosphere. After converting to an oxygen atmosphere, maintain the temperature after the temperature increase described above so that Y-containing oxides such as YJaCuOs oxides and Y2o3 oxides and Ba-Cu-0 oxides are uniformly dispersed. to be fired. In this case, an oxide containing Y such as YzBaCu05 oxide and Ba-Cu-0 oxide are Ba-
It is presumed that because the Cu-0 oxide exists in a liquid state at the above temperature, the oxide containing Y is dispersed to form a uniformly dispersed state. The firing time may be appropriately selected depending on the size and amount of the mixed oxide raw material such as a molded body, and there are no particular restrictions. Usually, it is 10 minutes to 3 hours.

After firing, the temperature inside the firing furnace is maintained and/or lowered to a predetermined temperature to complete reaction sintering of the raw mixed oxide in a uniformly dispersed state. For example, Y2BaCuO5 oxide and B
If it is a-Cu-0 oxide, it is about 850 to 1000'
It is preferable to maintain the temperature at C to generate a YBa2Cu2O7 phase and complete the reaction sintering. In this case, the holding may be carried out by slowing down the rate of temperature drop to allow the reaction to proceed so that the reaction is substantially maintained. Further, the temperature decreasing rate is not particularly limited, and may be appropriately selected depending on the firing process so that reaction sintering is completed.

In addition, the heating temperature under the above-mentioned oxygen partial pressure of 10-'at11 or less was set to 850 to 1000°C, and after heating, the atmosphere was replaced with oxygen, and by maintaining the heating temperature, YBa
Alternatively, the 2Cuz07 phase may be generated to start and complete the reaction sintering. In this case, calcination and reactive sintering occur simultaneously, and the holding time is preferably 1 to 6 hours.

After the reaction sintering of the raw material mixed oxide in the present invention is completed, it may be treated in the same manner as the firing of ordinary rare earth oxide superconductors, and may be subjected to slow cooling, heat treatment at a predetermined temperature, etc.

[For production]

In the present invention, an oxide containing a rare earth element as a raw material and B
Oxide containing a or/and Cu is converted into YJaCuOs phase in an atmosphere with extremely low oxygen partial pressure or Y2Ba at high temperature.
MBaz
M of the raw material without producing Cu307 phase during heating.
A mixed oxide of a JaCuOs phase oxide and a Ba-Cu-0 oxide can be obtained stably and in a uniformly dispersed state. Therefore, MzBaCuOs phase oxide and Ba-C
The u~0 oxide is uniformly reacted and sintered to form YBa2Cu3O
A rare earth oxide superconductor having homogeneous superconducting properties can be obtained by homogeneously growing seven phases.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

However, the present invention is not limited to the following examples.

Example 1 Y2O1, BaCO3, CuO powder in a molar ratio of Y:B
They were mixed in a ratio of a:Cu=1:2:3 and calcined at 800° C. for 10 hours in a nitrogen gas atmosphere.

The obtained calcined powder was ground in isopropyl alcohol for 15 hours using a rotary mill using zirconia cobblestones. The average particle size of the obtained powder was 3 μm, and it was confirmed from the results of X-ray diffraction that it was composed of YzBaCuO6 and 50 g of Ba3Cu.

The powder obtained above was molded into 50×50
It was temporarily molded into a flat plate of XIO(x), and then molded using a hydrostatic press at a pressure of 7 tons/i.

The obtained compact was placed in an electric furnace in a nitrogen gas atmosphere with an oxygen partial pressure of 5 X I O-''atm, and heated to 920°C at a temperature increase rate of 120°C/hour.
While maintaining the temperature, dry air was introduced into the furnace from a dry air bomb and replaced with nitrogen gas. After introducing dry air, the temperature was maintained at 920°C for 3 hours. Next, the temperature was lowered to room temperature at a cooling rate of 60° C./hour to obtain a sintered body.

The obtained sintered body was heat treated at 400° C. for 30 hours in an oxygen atmosphere.

The bulk density of the sintered body after the heat treatment was 5.9 g/c+j, and the critical current density at 77°C was measured by the four-terminal method and was 500 A/C11l. Moreover, the obtained sintered body shrunk while maintaining the flat shape of the molded body, and almost no local deformation was observed.

Comparative Example 1 Example 1 except that a dry air atmosphere was used in the furnace during temperature rise.
A sintered body was obtained in the same manner as above.

The bulk density of the obtained sintered body was 5.9 g/ci, 77
The critical current density was 300 A/crA. In addition, deformation in the shape of a flat plate was observed.

Example 2 Y2O3, BaCO3, CuO powder in a molar ratio of Y:B
Mix so that a:Cu=1.5:2:3, Pt(
Platinum) After melting in a crucible for 130 minutes at 1300"C,
It was poured into a stainless steel twin roller and rapidly cooled.

The obtained quenched product was ground in isopropyl alcohol for 3 hours using a vibration mill using zirconia cobblestones. The average particle size of the obtained powder was 2 μm, and X-ray diffraction and EPMA
(Electron beam microanalyzer) results confirmed that Y2O3 was uniformly dispersed in the matrix mainly consisting of BaCuO□ and CuO.

The powder obtained above was temporarily formed into a cylinder having a diameter of 50 mm and a length of 50 plates using an iron mold press, and was further formed using a hydrostatic press at a pressure of 7 tons/cd.

The obtained molded body was placed on a magnesia (MgO) plate,
In an electric furnace in a nitrogen gas atmosphere with an oxygen partial pressure of 5 x 10-4 atm, the temperature was increased to 1100"CQ at a temperature increase rate of 50°C/hour. Thereafter, while holding L I OO"C, it was placed in the furnace. Oxygen gas was introduced to replace nitrogen gas, and the oxygen gas partial pressure was set to 1at+w.

After introducing oxygen gas, the temperature was maintained at 1100° C. for 1 hour. Next, the temperature was lowered to 1,000°C at a cooling rate of 100°C/hour, and the temperature was further lowered from 1,000°C to 900°C at a rate of 1″C/hour.
The temperature was lowered to 500° C. at a rate of 0″C/hour and held at 500° C. for 20 hours. Thereafter, it was left in the furnace and cooled to room temperature to obtain a sintered body.

In the obtained sintered body, YBa2Cu:10 crystal grains have grown to several square degrees, and YJaCu05 is present in the YBazCuJ□ phase.
It had a microstructure with dispersed phases.

The obtained sintered body was immersed in liquid nitrogen with a magnetic field passed through it by an Sm-Co magnet to become a superconductor and trap the magnetic field. After that, the Sm-Co magnet was removed and left for 10 minutes, and the magnetic field of the sintered body was measured with a Gaussmeter, and the result was 1000 Gauss (
It was found that the magnetic field of G) is trapped.

Comparative Example 2 A sintered body was obtained in the same manner as in Example 2, except that the electric furnace was placed in an air atmosphere and the temperature was raised.

In the obtained sintered body, grain growth of YBa2Cu2O7 was observed, but microstructural observation showed that Y2BaCuO5 was aggregated. In addition, in a similar trap magnetic field measurement, 150
C: L was not obtained.

Example 3 BaCOl and CuO powder at a molar ratio of Ba:Cu=2
:3.3, and heated at 900℃ in air for 10
Calcined for an hour.

The obtained powder was found to be mainly BaCuO2 and CuO according to X-ray diffraction.
It consisted of Y2 with an average particle size of 1 μm was added to this calcined powder.
O, powder in molar ratio Y:Ba:Cu=1.3:2:3.
3, add 1% by weight of a dispersant,
The mixture was ground and mixed in isopropyl alcohol using a rotary mill using zirconia cobblestones.

The powder obtained above was molded in the same manner as in Example 2, and then a sintered body was obtained in the same manner as in Example 2.

The trap magnetic field of the obtained sintered body measured in the same manner was 900
It was G.

〔Effect of the invention〕

In the method for producing a rare earth oxide superconductor of the present invention, the raw material mixed oxide is
In an atmosphere of low oxygen gas partial pressure below tm, the mixed oxide is heated to a temperature of 850 to 1000''C at which it stably exists, and the mixed oxide is heated in an oxygen atmosphere without containing the superconducting phase of the target rare earth element. By reaction sintering, a homogeneous rare earth oxide superconductor having high superconducting properties can be obtained.

Claims (1)

[Claims] (1) A mixed oxide consisting of an oxide containing a rare earth element and an oxide containing barium and/or copper was used as a raw material and heated to a temperature of 850 to 1200°C in an atmosphere with an oxygen partial pressure of 10^-^4 atm or less. A method for producing a rare earth oxide superconductor, the method comprising: creating a rare earth oxide superconductor in an oxygen atmosphere and maintaining and/or lowering the temperature at the same temperature.