JPH01261260A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having improved Jc without deteriorating Tc, by adding CuO powder, BaCuO2 powder, etc., as a liquid-phase forming component to Re1Ba2Cu3O7-delta, calcining the mixture and reorienting the crystal. CONSTITUTION:Powder of Re1Ba2Cu3O7-delta (Re is rare-earth element) is added with 0.01-0.4mol, especially 0.05-0.2mol of powder of CuO and/or BaCuO2 as a liquid-phase forming component and the mixture is calcined in an oxidizing atmosphere of 900-1,100 deg.C at a temperature to cause the melting of the liquid- phase forming component, concretely at 960-1,050 deg.C in air or 980-1,100 deg.C in oxygen. The calcined product is cooled at a cooling rate of 50-200 deg.C/hr to obtain the objective oxide superconductor composed of crystals densely lami nated in the same direction. The Re1Ba2Cu3O7-delta oxide superconductor has a Tc of >=77K and Jc of >=1,000A/cm<2>.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an oxide superconductor having a high critical current density, which is used, for example, in superconducting coil parts of magnetic levitation trains, particle accelerators, electronic devices, etc. It is related to.

[Prior art]

Currently, metal-based superconductors such as NbTi and Nb:+Sn are in practical use, but their critical temperature (Tc) is at most about 20°C.

However, in recent years, composite oxide superconductors made of mixtures of rare earth elements, alkaline earth elements, and copper oxide have been developed.
Physical Review Letters 5B (1978) No. 9 shows that c is significantly higher than that of conventional superconductors.
Pages 08 to 910 (Physical Revie
w Letters 5B (1978) pp90B-9
10), etc., as a refrigerant at a relatively high temperature (7.5 K) than the expensive and extremely low temperature (4.2 K) overnight helium.
7K) liquid nitrogen was sufficient for use. therefore,
Significant progress has been made in the practical application of these oxide superconductors in various fields of application. Along with these announcements, research has been conducted to improve the critical current density (Jc) at 77K in bulk or thin film oxide superconductors in the above application fields, in parallel with research to further increase the Tc to room temperature. It is being actively carried out.

[Problem that the invention seeks to solve]

In order to put this oxide superconductor into practical use, it is necessary to consider the performance of the material, especially the critical temperature (Tc) and critical current density (Jc), depending on the application.
improvement is required.

RE+Ba2Cu:+O1-/ (RE: rare earth element)
The oxide superconductor with a system composition belongs to the orthorhombic system, and its unit lattice parameters are approximately a = 3.89, b = 3.82, and c = 11.67, and its physical properties are also It is clear that it has large anisotropy. Therefore, 5rTi
(h, In the case of a thin film epitaxially grown on a single crystal substrate such as MgO and oriented along the C axis, its Jc is I
X 10 hA/cm" (when the magnetic field is OT and at 77 K). However, compared to this, in a sintered body produced by a normal powder-solid reaction,
'^/cm' (when the magnetic field is OT and at 11K)
The extent is quite small. This value is further reduced by applying a magnetic field, and when IT is I
It will be about.

As described above, the current density of conventional oxide superconductors is lower than that of metal-based superconductors, and currently has not reached a practical level.

[Purpose of the invention]

The purpose of the present invention is to improve the critical current density Jc without deteriorating the critical temperature Tc.
-/ system oxide superconductor.

[Means for solving problems]

As a result of research into the above-mentioned problems, the inventors found that R
Add and mix BaCuO, powder and/or CuO powder as a liquid phase forming component to E+BazCuzOt-z (RE□ rare earth element) powder in an amount equivalent to 0.01 to 0.4 mol per 1 mol of RE+BazCuzOt-r. After molding, this is maintained at a firing temperature at which the liquid phase molding components can be eluted in an oxidizing atmosphere, and then cooled to form RE, B
aCu0z powder crystal ′fFJim is formed, which reduces the critical current density J
I x 10'A/cm in a magnetic field where c is 15000e
It was discovered that two or more oxidized superconductors can be obtained. Hereinafter, explanation of RE in the chemical formula will be omitted.

The present invention will be explained in detail below.

REIBa represented by YlBazCu, l0t-/ system
zCuz(1+-/ Production 7 of oxide superconductor includes
A method is used in which a polycrystalline sintered superelectric body is obtained by preparing YlBazCu:+07-/synthetic powder, molding it, and sintering it in an oxidizing atmosphere. According to this method, the crystal structure becomes equiaxed, but RE+BazCu
:+Ot-/ system crystal itself has anisotropy, and it is known that its electrical properties also vary depending on the crystal axis direction.

Therefore, in a polycrystalline body having an equiaxed crystal structure as described above, each crystal has a different orientation, so its electrical characteristics are dominated by the orientation of the crystal with the lowest characteristics. Furthermore, it goes without saying that grain boundaries have an influence on electrical properties.

According to the present invention, in a polycrystalline oxide superconductor, by creating a structure in which the plate-like crystals are densely laminated in the same direction, the influence of anisotropy on electrical properties due to the crystal axis of each crystal grain is reduced. and because of the laminated structure, the grain boundary phase between the crystal grains is thin and the grains are tightly adhered to each other. As the grain boundary phase becomes thinner, the potential of the grain boundary becomes lower than that of conventional RE, BazCu307-l, which has thick grain boundaries. For these reasons, the current density per unit area is greatly improved.

According to the production method of the present invention, CuO and/or BaC are used as liquid phase forming components for RE, Ba2Cu307-Me powder.
After adding u0z powder and molding it, 900-1100
The temperature is maintained in an oxidizing atmosphere of 100% and at a temperature at which the liquid phase-forming components are eluted.

At this time, RE+BazCuxOr-/ is separated into a liquid phase component consisting of the following formula 2, and the liquid phase component surrounds the REJalCu105 crystal.

After that, in the cooling process, REzBalCulOl and B
aCuO□ and CuO are recombined by a peritectic reaction, and RE
+Ba2Cu:1Ot-/ is regenerated. At this time, R
E1Ba2Cu:+Ot-/crystal is REzBa+Cu+
It grows according to the direction of the Os crystal. Therefore, according to the present invention, CuO or Ba added as a liquid phase forming component
After CuO□ forms a liquid phase, by orienting RE2Ba, Cu, and 05 in one direction during the process in which this liquid phase component elutes (flows) out of the system, REIBa2CulOy-/
It becomes possible to orient the crystals in that direction, and as a result, it is possible to obtain an oxide superconductor having a structure in which plate-shaped crystals as described above are laminated densely in the same direction.

As the RE, Ba, Cu, O, powder used in the present invention, any powder synthesized by solid phase reaction method, coprecipitation method, sol-gel method, gas phase synthesis method, etc. can be used, but preferably is an average particle size of 0.5 to 3. One with O11m is used.

BaCuO□, which is one of the liquid phase forming components, is, for example, BaCuO□.
Mix 1 mole each of CO3 and CuO, and heat it to 88% in an oxidizing atmosphere.
Although it can be synthesized by heating to 0 to 1000°C, about 900°C is preferable for pulverization. In addition, BaC
When adding u0z, it is possible to add it not only as BaCuO□ powder but also as a combination of BaC0* powder and CuO powder.

The liquid phase forming components of BaCuOz and CuO are desirably fine powders of 0.5 to 2.0 μm in order to lower the liquid phase formation temperature during firing.

In the present invention, the addition and amount of liquid phase forming components such as Cub and BaCuO
? E.

The amount is set to cause elution (flow) of the liquid phase component that can orient the Ba + Cu + Os crystal. Therefore,
If the amount of this liquid phase forming component is too small, REJatCu+
The Os crystal is not oriented and as a result, R is regenerated.
E.

BaCu0O7-/ Unable to orient crystals,
No improvement in critical current density can be expected. On the other hand, if the amount of the liquid phase forming component is too large, the orientation of REzBa+Cu+Os will occur, but in the end REtBazcusO? -/BaCu0z and CuO at the grain boundaries of the crystal.

Many Y2Ba+Cu105 crystals precipitate, resulting in an extreme decrease in critical current density. For these reasons, Cub,
The amount of liquid phase forming component of BaCub is REIBazCLI
:+Ot-/1 mole of powder per 1 liter of powder, 01 to 0.4 mole L/, specifically set to 0.05 to 0.2 mole.

After the powder blended in this way is uniformly mixed in a mill etc.,
Perform molding.

For molding, known molding means are employed.

Specifically, the doctor blade method, pulling method, extrusion method,
Examples include press forming methods, and in addition, when manufacturing wire drawings,
Of course, it is also possible to insert the wire into a tube such as a pipe and wire-draw it.

The molded body thus obtained is fired in an oxidizing atmosphere. In addition, the temperature at this time is set at a firing temperature at which the liquid phase forming components described above are eluted out of the system, in other words, at a temperature at which the liquid phase flows within the system and allows the REIBa, Cu, and 01 crystals to be oriented. . Specifically, 960 to 1050 in the atmosphere
°C, set at 980-1100 °C in oxygen. The firing temperature is lower than 960°C in air or 960°C in oxygen.
If the temperature is set lower than 80° C., elution and flow of liquid phase forming components will not occur, so crystals cannot be oriented and the critical current density will not improve.

On the other hand, if the temperature is higher than 1050℃ in air or higher than 1100℃ in oxygen, RE1Ba2Cu30t-/
The crystals are not regenerated, remain as REzBa, Cu, and 05, and do not exhibit superconductivity.

The holding time at the maximum temperature during firing is determined by the shape of the sample, but is held for approximately 3 to 30 minutes.

The cooling process after firing is as described above.
RE by peritectic reaction between 05 and BaCuO2, CuO,
Promotes the growth of Ba, Cu5O+-/crystals. The cooling rate at this time affects the size of the crystal grains of RE+BazCusO,t-/, but generally 50~
b The RE+BazCu+Or-Me system oxide superconductor thus obtained exhibits excellent properties as will be clear from the examples described below, with a critical temperature Tc of 77 or higher and a critical current density of 1000A/cm” (15000e
magnetic field, 77 K) or higher is achieved.

In addition, in the chemical formulas described so far in the present invention, RE
is a general rare earth element, specifically Y, Lu, Yb
.

Tm, Er, Ho, Dy, Gd+ Eu, S
Examples include m and Nd.

Furthermore, according to the invention, RElBazCuzOl-/
In the system, for RE, Ba, Cu, O, RE1Ba
It can also be applied to those partially substituted with other elements as long as the superconducting properties of the lCu30y-/ system are not deteriorated.

The invention will now be explained with the following examples.

[Example 1] 9.09 mol χ of ytoi, 36.36 mol χ of BaC0z, and 54.55 mol χ of CuO were mixed, and the mixed powder was
After calcining at 80'C for 5 hours, it was crushed and Y+Ba (Cuz
Ov-/ powder (average particle size 2.0 μm) was obtained. This Y
1Ba2Cu: +Ot-/0.05 per 1 mole of powder
~0.40 mol χ CuO powder (average particle size 1.0 μm)
were mixed. This Y+Ba2Cu30□-d powder and Cu
The mixed powder of O was molded into a pellet having a diameter of 12 mm. This molded body was heated at 960 to 1050°C in air and at 98°C in oxygen.
After firing at 0-1100℃ for 1-2 hours, 100'C/
hr rate, and further annealed in oxygen at 600°C for 5 hours, then slowly cooled to 200°C,
The sample was processed into a size of 4 x 3 Xo, 8 mm.

Note that Samples 1 to 8 were created by changing the amount of CuO added and the firing conditions as shown in Table 1.

The obtained sample was examined for resistance change with respect to temperature by a four-probe method, and temperature (Tco) and offset temperature (Tce) were examined.

Further, in the M-11 hysteresis of the sample measured by a vibrating sample type magnetometer, the magnetization difference Δ between the magnetization curve and the demagnetization curve is expressed by the formula ΔH=μod−Jc. Here, μ0 is the vacuum permeability, d is the width 1/2 of the plate-shaped sample, and Jc is the critical current density. The critical current density Jc was determined from the hysteresis curve using the above equation based on the difference in magnetization. In addition, the crystal structure of each sample was observed using an electron microscope, and Y, Ba2Cu
30. -l The presence or absence of crystal orientation was confirmed.

(Example 2) Tests were conducted in exactly the same manner as in Example 1 except that BaCu0z powder (average particle size 1.0 μm) was used instead of CuO powder, and samples Nos. 12 to 22 in Table 1 were prepared.

For each sample, Y, Ba2Cui
0t-l crystal orientation, onset temperature (Tco),
Offset temperature (Tco), difference in N conversion ΔM (1500
0e), the critical current degree Jc (15000e) was determined.

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As is clear from Table 1, when the firing temperature was lower than the predetermined range (sample numbers 1, 4, 12, 15), no crystal orientation was observed and the critical current density was low. In addition, when the firing temperature is high (sample numbers 3.6, 14.
17), Y1Ba2Cu30+- was not generated and the critical current density could not be measured. On the other hand, when the amount of the additive added was less than 0.01 mol (sample number 7.18), no crystal orientation was observed, and the object of the present invention was not achieved. In addition, when the amount added exceeds 0.4 mol (sample number 11.22), an oriented crystal structure was observed in a part of the structure, but the crystal grain boundaries remained and the critical current density was low. there were.

On the other hand, all the other samples of the present invention exhibited excellent characteristics, achieving an offset l-'tL degree of 88 or more and a critical current density of 1000 A/cm2 or more.

(Effects of the Invention) As detailed above, according to the present invention, REIBa2Cu-
A superconductor having a crystal structure in which 107- crystals are densely stacked in one direction is obtained, and thereby the critical current density Jc can be reduced to I x 10'A/cm under a magnetic field of 15000e without deteriorating the critical temperature Tc. ``It can be made even higher.

Claims (2)

[Claims] (1) RE_1Ba_2Cu_3O_7_-_δ(RE
: rare earth element) powder, as a liquid phase forming component, the RE_
1Ba_2Cu_3O_7_-_δ 1 mole per mole, 0.
01-0.4 mol CuO powder and/or BaCu
An oxide superconductor characterized in that a mixed powder containing O_2 powder is molded, held in an oxidizing atmosphere at a firing temperature at which the liquid phase forming component can be eluted, and then cooled to cause crystal rearrangement. Manufacturing method. (2) The method for producing an oxide superconductor according to claim 1, wherein the firing temperature at which the liquid phase forming component can be eluted is 960 to 1050°C in air and 980 to 1100°C in oxygen.