JP2980650B2 - Method for producing rare earth oxide superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a rare earth-based oxide superconductor containing a rare earth element represented by yttrium.

[Conventional technology]

In recent years, oxide superconductors have attracted attention because of their high critical temperature, and are expected to be used in various fields such as the power field, nuclear magnetic resonance apparatus, and magnetic shield. These oxide superconductors are M-Ba-Cu-O-based compounds, where M is Sc, Y, and L.
There is a rare earth oxide superconductor having a multilayer perovskite structure containing one or more rare earth elements selected from lanthanides such as a, Eu, Gd, Er, Yb, and Lu.

Among the rare earth-based oxide superconductors, for example, those having a YBa ₂ Cu ₃ O ₇ crystal phase in which M is a typical yttrium (Y) are well known. As a method for producing the rare earth-based oxide superconductor having the YBa ₂ Cu ₃ O ₇ crystal phase, YBa ₂ Cu ₃ O
A method of sintering a raw material powder having _seven phases under a low oxygen partial pressure is known. For example, in JP-A-64-61345, Y
Generates a raw material powder having a Ba ₂ Cu ₃ O ₇ phase, the oxygen partial pressure less than 0.2atm the molded product was sintered in example 10 ^-2 to 10 ^-10 atm, the heat treatment at an oxygen partial pressure of more than 1atm How to do is shown. In Japanese Patent Application Laid-Open No. 1-234353, a material containing LaBa ₂ Cu ₃ O ₇ as a main component is 950 ° C. at an oxygen partial pressure of 5 × 10 ⁻² atm or less.
As described above, it is disclosed that heating is performed at a temperature lower than the melting point, and then heating is performed in an anhydrous atmosphere at a temperature of 400 ° C. or less and an oxygen partial pressure of 2 × 10 ⁻¹ atm.

In addition, conventionally, various methods are known in which a Ba-Cu-O-based oxide is reacted with a Ba-Cu-O-based oxide in a liquid phase by sintering to generate YBa ₂ Cu ₃ O ₇ and crystal growth using Y ₂ BaCuO ₅ crystal particles as nuclei. For example,
JP-A-2-51468 discloses that Y ₂ BaCuO ₅ powder and Ba ₂
Firing the mixed powder of Cu ₃ O ₅ powder in an oxygen atmosphere of 0.01~0.5atm have been proposed.

[Problems to be solved by the invention]

In the conventional method of producing YBa ₂ Cu ₃ O ₇ by a liquid phase reaction between the above Y ₂ BaCuO ₅ crystal particles and a Ba-Cu-O-based oxide, a firing temperature, for example, during a heating process up to 1000 ° C. After the YBa ₂ Cu ₃ O ₇ phase is formed at the temperature of and the firing temperature is reached, the crystal growth of YBa ₂ Cu ₃ O _{7 in} the liquid phase reaction is inhibited, and the problem that excellent superconducting properties cannot be obtained there were. Therefore, the above
YBa ₂ by liquid phase reaction between Y ₂ BaCuO ₅ and Ba-Cu-O-based oxide
Cu ₃ In the method of obtaining O _7, for minimizing the YBa ₂ Cu ₃ O ₇ generated in the temperature raising process, the Y ₂ BaCuO ₅ at a heating rate of 300 ° C. / hr or faster remain stable A method of raising the temperature to 1000 ° C. or higher is used.

However, it is not economical to realize a rapid temperature rise of 300 ° C / hour to the firing temperature in a large electric furnace, but also a rare earth element having a large fluctuation range of the temperature distribution in the furnace and uniform superconducting characteristics. It is difficult to obtain a system oxide superconductor.

Further, when obtaining a sintered body of a large oxide superconducting molded body,
Sudden temperature rise causes uneven shrinkage and cracks, and a good sintered body cannot be obtained.

The present invention solves the above-mentioned various problems of the conventional method, and without forming a superconductor phase such as YBa ₂ Cu ₃ O ₇ crystal phase in advance, an oxide containing a rare earth element of Y ₂ BaCuO ₅ and Ba-Cu. It is an object of the present invention to obtain a rare-earth oxide superconductor having excellent superconducting characteristics from a small to a large one by using an -O-based oxide as a raw material.

[Means for solving the problem]

According to the present invention, a mixed oxide containing an oxide containing a rare-earth element and an oxide containing barium and / or copper and containing no desired rare-earth oxide superconducting phase is used as a raw material and has a temperature of 850 to 1200 ° C. A rare-earth-based oxide characterized by raising the temperature in an atmosphere having an oxygen partial pressure of 10 ⁻⁴ atm or less, forming an oxygen atmosphere, and maintaining and / or lowering the temperature to produce a rare-earth-based oxide superconductor A method for manufacturing a superconductor is provided.

 Hereinafter, the present invention will be described in detail.

As described above, the rare earth oxide superconductor of the present invention
Is an M-Ba-Cu-O-based compound having a multilayer perovskite structure containing one or more rare earth elements selected from Sc, Y, and lanthanides such as La, Eu, Gd, Er, Yb, and Lu.

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

In the present invention, as a mixed oxide composed of an oxide containing a rare earth element and an oxide containing barium (Ba) and / or copper (Cu), YBa ₂
There is no particular limitation as long as the mixed oxide produces a Cu ₃ O ₇ phase, and all can be applied. For example, Y ₂ BaCuO ₅ oxide,
BaCuO ₂ , BaO, CuO, Ba ₃ Cu ₅ O ₈ , BaCu ₂ O _3, and a mixture of one or more Ba-Cu—O oxides are exemplified. Further, Y ₂ instead of BaCuO ₅ oxide, to produce a Y ₂ BaCuO ₅ by partial melting during firing, the use of more mixed oxides of the composition as to occur by sintering reaction the YBa ₂ Cu ₃ O ₇ phase Can also. For example, a mixed oxide of Y ₂ O ₃ and the Ba-Cu-O oxide as raw materials, at the same time Y ₂ BaCuO ₅ oxide is generated during firing, Y ₂ BaCuO ₅ oxides generated and Ba-
A mixed oxide in which the Cu-O oxide is uniformly dispersed may be used.

In order to form a superconductor, the composition ratio of Y, Ba and Cu in the raw material of the mixed oxide of the present invention is generally a molar ratio.
The components are mixed so that Y: Ba: Cu = 1: 2: 3, but are not particularly limited to the above composition ratio. For example, YBa ₂ Cu
₃ O ₇ phase other than the phase of impurities is sometimes superconducting properties are improved reversed by mixing, addition, the molar ratio of Y: Ba: Cu
Excellent superconducting properties may be exhibited even outside the composition ratio of 1: 2: 3, and one or two kinds of elements may be expressed based on a molar ratio of Y: Ba: Cu = 1: 2: 3. It may be used by increasing or decreasing about 50%.

The raw material of the mixed oxide of the present invention may be used as it is as a powder, or may be formed into a compact using the mixed oxide raw material powder. As a molding method, a known molding method such as a doctor blade method, a press molding method, and a casting method can be used. Further, the molded body may be one obtained by forming a molded body layer by spray coating, powder coating, or the like with the mixed oxide raw material powder on a substrate of metal, ceramics, or the like.

In the present invention, a lower oxide low oxygen partial pressure atmosphere containing Y or the like rare earth elements of the mixed oxide material for example Y ₂ BaCu
In a state where it is stably present as an O ₅ phase or as a phase for generating a Y ₂ BaCuO ₅ phase such as a mixed oxide of Y ₂ O ₃ and Ba—Cu—O oxide, and Ba—Cu— The temperature of the mixed oxide raw material is raised in an atmosphere having an oxygen partial pressure of 10 ^-4 atm or less until the temperature at which the O oxide becomes a liquid phase temperature of 850 to 1200 ° C. The temperature and / or the temperature is lowered and the firing is maintained. In the temperature raising process up to the predetermined temperature, if the oxygen partial pressure in the atmosphere such as in the firing furnace is higher than 10 ^-4 atm, during the temperature raising process before reaching the predetermined temperature of firing,
Since the YBa ₂ Cu ₃ O ₇ phase is generated and the sintering of the YBa ₂ Cu ₃ O ₇ phase progresses with increasing temperature, the finally obtained YBa ₂ Cu ₃ O ₇ phase oxide superconductor is not homogeneous. Poor superconductivity. On the other hand, in an atmosphere where the oxygen partial pressure is 10 ^-4 atm or less, YB
Since the a ₂ Cu ₃ O ₇ phase is not a stable phase, even if a very small amount of the YBa ₂ Cu ₃ O ₇ phase exists, it is decomposed into the Y ₂ BaCuO ₅ phase and the Ba-Cu-O oxide, At the firing temperature of ₂ , a raw material mixture of a Y ₂ BaCuO ₅ oxide containing no YBa ₂ Cu ₃ O ₇ phase and a Ba—Cu—O oxide is obtained.

In the present invention, it is not necessary to previously generate a superconducting phase from the oxide of the rare earth element and the Ba-Cu-O oxide by adopting a step of reaching the sintering temperature through the above-described heating process. Finally, an excellent rare earth superconductor having a superconducting phase such as YBa ₂ Cu ₃ O ₇ can be obtained. This means that without containing the YBa ₂ Cu ₃ O ₇ phase, a uniform dispersion state of the Y ₂ BaCuO ₅ oxide and the Ba-Cu-O oxide is obtained,
Next, it is considered that the sintering reaction can be performed on the raw material mixed oxide uniformly dispersed in the oxygen atmosphere.

In the present invention, the heating rate for raising the temperature to 850 to 1200 ° C. is not particularly limited as long as the oxygen partial pressure in the atmosphere during the heating process is set to 10 ⁻⁴ atm or less, and the conventional rapid rate of 300 ° C./hour. No need to raise the temperature. Therefore, it is possible to appropriately control the temperature distribution in the electric furnace according to conditions such as the size of the firing furnace and the type of the raw material so that the temperature distribution in the electric furnace does not become uneven. Generally, the heating rate is 30 ° C./hour or more in an electric furnace, and preferably 200 ° C./hour or less for firing a large molded body.
~ 120 ° C / hour.

In the present invention, the oxygen partial pressure of 10 ⁻⁴ atm or less can be easily obtained by flowing an inert gas such as nitrogen gas or argon gas through a baking furnace, for example, an ordinary simple and airtight electric furnace. . In a hermetic furnace, reduce the degree of vacuum to 10 ^-4 at
m or less. The oxygen partial pressure may be extremely reduced in a reducing gas atmosphere by a reducing gas such as hydrogen gas or carbon dioxide gas. However, even if the oxygen partial pressure is extremely lowered, there is not so much effect, and it is usually sufficient to set the oxygen partial pressure to 10 ^-4 to 10 ^-6 atm.

In the present invention, the firing atmosphere is converted to an oxygen atmosphere after the completion of the temperature raising process up to the predetermined firing temperature. After converting to an oxygen atmosphere, the temperature is maintained at the above-mentioned elevated temperature, and for example, an oxide containing Y such as Y ₂ BaCuO ₅ oxide or Y ₂ O ₃ oxide and Ba
-Baking so that the Cu-O oxide is in a uniformly dispersed state. In this case, an oxide containing Y such as Y ₂ BaCuO ₅ oxide and Ba
It is presumed that the -Cu-O oxide is a material in which the Ba-Cu-O oxide exists in the liquid phase at the above-mentioned temperature, whereby the oxide containing Y is dispersed to form a uniform dispersion 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 is not particularly limited. Normally,
10 minutes to 3 hours.

After firing, the temperature in the firing furnace is maintained or / and lowered and maintained at a predetermined temperature to complete the reaction sintering of the raw material mixed oxide in a uniform dispersed state. For example, Y ₂ BaCuO ₅ oxide and Ba-Cu-
If it is an O oxide, the temperature is maintained at about 850 to 1000 ° C. and YBa ₂ Cu ₃ O ₇
Preferably, a phase is formed to complete the reaction sintering. In this case, it is sufficient that the temperature is reduced so that the reaction proceeds and the temperature is substantially maintained. Further, the temperature decreasing rate is not particularly limited, and may be appropriately selected so that the reaction sintering is completed according to the firing process.

Further, the temperature was raised to 850 to 1000 ° C. under an oxygen partial pressure of 10 ⁻⁴ atm or less, and after the temperature was raised, the atmosphere was replaced with an oxygen atmosphere, and the YBa ₂ Cu ₃ O ₇ phase was immediately maintained by maintaining the temperature rising temperature. May occur and reaction sintering starts to complete. In this case, firing and reaction sintering occur simultaneously, and the holding time is 1 to
Six hours is preferred.

After the completion of the reaction sintering of the raw material mixed oxide in the present invention, the treatment may be performed in the same manner as in the usual firing of a rare earth oxide superconductor, and slow cooling, heat treatment at a predetermined temperature, or the like can be performed.

(Operation)

In the present invention, an oxide containing a rare earth element as a raw material
An oxide containing Ba and / or Cu, to the oxygen partial Y ₂ BaCuO ₅ phase or temperature from 850 to 1,200 ° C. for oxide mixed state for generating a Y ₂ BaCuO ₅ phase is stable at high temperatures with very low atmosphere pressure By raising the temperature, the mixed oxide of the raw material M ₂ BaCuO ₅ phase oxide and the Ba-Cu-O oxide is stably formed without generating the MBa ₂ Cu ₃ O ₇ phase during the temperature rise, and It can be obtained in a uniformly dispersed state. Therefore, M ₂ BaCuO ₅ phase oxide and Ba-Cu
-O oxide is uniformly reacted and sintered, and the YBa ₂ Cu ₃ O ₇ phase is uniformly crystal-grown to obtain a rare-earth oxide superconductor having uniform superconducting properties.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples. However,
The present invention is not limited by the following examples.

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

The obtained calcined powder was ground in isopropyl alcohol by a rotary mill using zirconia balls for 15 hours. The average particle size of the obtained powder was 3 μm, and the result of X-ray diffraction confirmed that the powder was composed of Y ₂ BaCuO ₅ and Ba ₃ Cu ₅ O ₈ .

The powder obtained above is 50 × 50 × 10
(Mm), and then formed by isostatic pressing.
Molded at a pressure of ton / cm ² .

The obtained molded body was placed in an electric furnace in a nitrogen gas atmosphere having an oxygen partial pressure of 5 × 10 ⁻⁶ atm, and the temperature was increased to 920 at a heating rate of 120 ° C./hour.
The temperature was raised to ℃. Thereafter, while maintaining the temperature at 920 ° C., dry air was introduced from a dry air cylinder into the furnace to replace the atmosphere with nitrogen gas. After introducing dry air, the temperature was maintained at 920 ° C. for 3 hours.
Next, the temperature is lowered to room temperature at a temperature decreasing rate of 60 ° C./hour,
A sintered body was obtained.

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 / cm ³ , and the critical current density at 77 K was measured by a four-terminal method. As a result, it was 500 A / cm ² . Further, the obtained sintered body contracted while maintaining the flatness of the molded body, and almost no local change was recognized.

Comparative Example 1 A sintered body was obtained in the same manner as in Example 1 except that the inside of the furnace during the heating was changed to a dry air atmosphere.

The bulk density of the obtained sintered body was 5.9 g / cm ³ , and the critical current density at 77 K was 300 A / cm ² . In addition, deformation was observed in a flat plate shape.

Example 2 Y ₂ O ₃ , BaCO ₃ , and CuO powder were mixed at a molar ratio of Y: Ba: Cu = 1.5: 2: 3
And mixed in a Pt (platinum) crucible at 1300 ° C, 30
After melting, the mixture was poured into a stainless steel twin roller and rapidly cooled.

The obtained quenched product was ground in isopropyl alcohol by a vibration mill using zirconia balls for 3 hours. The average particle size of the obtained powder was 2 μm, and the X-ray diffraction and EPMA
(Electron beam microanalyzer) results show that Y ₂ O ₃ is mainly
It was confirmed that they were uniformly dispersed in the matrix composed of BaCuO ₂ and CuO.

The powder obtained above is pressed with an iron mold press to a diameter of 50 mm.
It was provisionally formed into a cylinder having a diameter of 50 mm and formed by a hydrostatic press at a pressure of 7 ton / cm ² .

The obtained molded body is allowed to stand on a magnesia (MgO) plate,
In an electric furnace with a nitrogen gas atmosphere with an oxygen partial pressure of 5 × 10 ^-6 atm,
The temperature was raised to 1100 ° C. at a rate of 0 ° C./hour. Then 1
While maintaining the temperature at 100 ° C., oxygen gas was introduced into the furnace and replaced with nitrogen gas, and the partial pressure of oxygen gas was set at 1 atm.

After the introduction of oxygen gas, the temperature was maintained at 1100 ° C. for 1 hour. Next, the temperature is lowered to 1000 ° C at a temperature decreasing rate of 100 ° C / hour, and 1000 ° C.
The temperature was lowered from 1 to 900 ° C at 1 ° C / hour and further at 60 ° C / hour to 500 ° C, and kept at 500 ° C for 20 hours. Then, it was left as it was in a furnace and cooled to room temperature to obtain a sintered body.

The resulting sintered body, YBa ₂ Cu ₃ grains O ₇ is grown to several mm square, Y ₂ BaCuO ₅ phase had a fine structure dispersed in YBa ₂ Cu ₃ O ₇ phase.

The sintered body was immersed in liquid nitrogen in a state where a magnetic field was penetrated by the Sm-Co magnet in the obtained sintered body, and the magnetic field was trapped in a superconductor state. Thereafter, the Sm-Co magnet was removed, and after leaving it for 10 minutes, the magnetic field of the sintered body was measured with a Gauss meter. As a result, it was found that a magnetic field of 1000 Gauss (G) was trapped.

Comparative Example 2 A sintered body was obtained in the same manner as in Example 2, except that the temperature inside the electric furnace was raised to the atmosphere.

Although grain growth of YBa ₂ Cu ₃ O ₇ was observed in the obtained sintered body, Y ₂ BaCuO ₅ was aggregated in microstructure observation. In the same measurement of the trapping magnetic field, only 150 G was obtained.

Example 3 BaCO ₃ and CuO powder were mixed in a molar ratio of Ba: Cu = 2: 3.3, and calcined in the air at 900 ° C. for 10 hours.

The obtained powder was mainly composed of BaCuO ₂ and CuO from X-ray diffraction. This calcined powder was mixed with a Y ₂ O ₃ powder having an average particle size of 1 μm in a molar ratio of Y: Ba: Cu = 1.3: 2: 3.3, and a dispersant of 1% by weight was added. Inside, it was pulverized and mixed by a rotary mill using zirconia cobblestone.

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

The trap magnetic field of the obtained sintered body measured similarly was 900 G
Met.

〔The invention's effect〕

The method for producing a rare earth-based oxide superconductor of the present invention is a method of producing a raw mixed oxide without forming a superconducting phase in advance at 10 ^-4 atm.
In a low oxygen gas partial pressure atmosphere as described below, the temperature is raised to 850 to 1000 ° C where they are stably present, and the mixed oxide is reacted and fired in an oxygen atmosphere without containing the superconducting phase of the target rare earth element. By sintering, a rare earth oxide superconductor having a uniform and high superconducting property can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 39/24 ZAA H01L 39/24 ZAAZ

Claims (1)

(57) [Claims] An oxide containing a rare earth element and barium and / or
Alternatively, a mixed oxide made of an oxide containing copper and containing no desired rare-earth oxide superconducting phase as a raw material,
After raising the temperature to 850 to 1200 ° C. in an atmosphere having an oxygen partial pressure of 10 ⁻⁴ atm or less, forming an oxygen atmosphere, maintaining the temperature and / or lowering the temperature to produce a rare earth oxide superconductor. Of producing rare earth oxide superconductors.