JPH04104984A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain excellent uniformity and chemical stability of oxide superconductor by sticking a specific substance to the surface of a superconducting parent material and heat-treating in an oxidizing atmosphere. CONSTITUTION:A composition having a composition shown by the formula (M is one or more of K, Rb and Li; x is 0-0.5; N is one or more of Pb and Cu; y is 0-0.8) is sintered to give a superconducting parent material (A). Then one or more substances (B) of simple substance of Cu, Bi, Tl, Mn, Fe, V, Ti, Sb, Cr, Sr, Ca, Ba, Ni, Zn, Li, K, Na, Rb, Cs, Ag, Y or Re (rare earth metal), an oxide (carbonate) thereof and a compound to produce an oxide by thermal decomposition is stuck to the surface of the component A to give an attached substance (C). Then the component C is heat-treated in an oxidizing atmosphere (e.g. O2 gas stream atmosphere) at 300-1,000 deg.C to produce an oxide superconductor.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for producing an oxide superconductor, and more specifically, a method for producing a homogeneous and chemically stable oxide superconductor. The present invention relates to a method for producing oxide superconductors that can be manufactured using oxide superconductors.

[Prior Art] Conventionally, the method for producing oxide superconductors involves mixing a plurality of powders containing elements constituting the oxide superconductor, molding this mixture by compression molding, for example, and then placing it in an oxidizing atmosphere. A method of firing in a sintered container (hereinafter referred to as a sintering method) is known.

However, the oxide superconductor produced by this method has a drawback of poor superconducting properties. Taking critical current density as an example of one of the superconducting properties, a value of 10''^/cm2 or more is required to stably obtain superconducting phenomena, but the oxide superconductivity produced by the conventional method described above The critical current density of a conductor is lower than 1 x 10"A/crn" for boat fishing, and it is very difficult to obtain something on the order of I x 102" = 10'A/crn";'
There were no cases exceeding A/cm.

On the other hand, in order to improve the superconducting properties, for example, Y-Ba-
In the Cu-0 system, a method using the fact that a superconducting phase is generated by a peritectic reaction has been attempted (for example, M,
Murakami et al.: Jpn, J, ^p
p1. Phys, 28.1189 (1989))
. That is, this method is a method of manufacturing a superconductor by rapidly cooling a superconducting material to a melt diameter.

However, this method requires melting the sample at a high temperature, incorporates impurities due to reaction with the crucible, requires remelting, and is non-uniform because a liquid phase is always present during the preparation. It has disadvantages such as the composition.

[fil that invention tries to solve! ! ] The object of the present invention is to develop an oxidation method that allows the easy production of superconductors with excellent superconducting properties (for example, critical current density of I x 10' A/Cd or more) without using methods such as melting. An object of the present invention is to provide a method for manufacturing a physical superconductor.

[Means for Solving the Problem] The gist of the present invention for achieving the above object is (Bad-
xMx) (Bit-yNy) 03 (However, M is one or more selected from KRb, Li,
x=O~0.5, N is one or two selected from Pb and Cu, y=0~0.8), and then CuB1. Ti2. Mn, Fe
, V, Ti, 5bCr, Sr, Ca, Ba, Ni, Zn
, Li.

K, Na, Rb, Cs, Ag, Y, Re (however, R
e is a rare earth metal), one or more substances (hereinafter referred to as adhesion substances) of oxides or carbonates of these or compounds that produce oxides by thermal decomposition are attached to the surface of the superconducting matrix, Then 300-1
A method for producing an oxide superconductor is characterized in that heat treatment is performed at a temperature of 1,000° C. in an oxidizing atmosphere.

Next, the configuration of the present invention will be described in detail.

In the present invention, the superconducting matrix (superconductor before adhering substances and heat treatment) includes, for example, [prior art]
Superconducting sintered bodies obtained by the sintering method, as described in
Or various thin film formation methods (e.g. plasma sputtering method)
One example is the superconducting thin film obtained by Alternatively, a single crystal superconductor may be used.

The superconducting matrix targeted by the present invention is (Bad-xMx) (Bit-yNy) Os.

M is one or more selected from K, Rb, and Li.

N is one or two selected from Pb and Cu.

xwO~0.5.

y=o~0.8.

If x and y are outside this range, excellent superconducting properties cannot be obtained.

Note that the above-mentioned superconducting matrix may be used alone or in combination of two or more.

One feature of the present invention is that an adhesion substance is attached to the superconducting matrix and heat treatment is performed.

Here, the following substances are used as the adhesion substances.

■Cu, Bi, TfL, Mn, Fe, V, Ti.

Sb, Cr, Sr, Ca, Ba, Ni, Zn.

Elements of Li, Na, Rb, Cs, Ag, Y, Re (Re is a rare earth metal) ■■ Metal oxide ■■ Metal carbonate ■ Compound that produces oxides by thermal decomposition Here, ■ The rare earth metal is La.

Nd, Pr, Sm, Eu, Gd, Tb, Dy.

Examples include Ho, Er, Tm, and Tr.

Further, examples of compounds that produce oxides upon thermal decomposition of (2) include K2Cr20y, K, Mn204, and the like.

Note that one type or two or more types of each of these substances can be used.

In the present invention, these substances are attached to the surface of the superconducting matrix, but there are no particular limitations on the method of attaching the substances to the surface of the superconducting matrix. However, in order to uniformly adhere the adhering substance to the surface of the superconducting matrix, the following may be performed, for example. That is, first, if the adhering substance is water-soluble, an aqueous solution is prepared by diluting it with distilled water, and if the adhering substance is insoluble, a suspension is prepared by suspending it in distilled water. Next, the aqueous solution or suspension may be applied to the surface by brush painting, spin cording, or the like.

The temperature of the heat treatment after attaching the adhesion substance is 300~
Although the temperature is 1000°C, it is preferably 500 to 1000°C in order to further improve the superconducting properties.

This heat treatment is performed in an oxidizing atmosphere. Examples of the oxidizing atmosphere include an air atmosphere, an oxygen gas atmosphere, a mixed gas atmosphere of oxygen gas and an inert gas, etc., but an oxygen gas atmosphere is preferable, and an oxygen gas stream atmosphere is more preferable.

[Function] The function of the present invention will be explained below along with the findings obtained in making the present invention.

In developing a method for producing a superconductor with excellent superconducting properties, the present inventor wondered why a superconductor with excellent superconducting properties could not be obtained when produced by a conventional sintering method. We investigated the reason why this is not the case.

The cause of this was not previously clear, but the inventor's investigation revealed the following.

In other words, it has been found that in an oxide superconductor manufactured by a sintering method, a superconducting weak bond state occurs at grain boundaries. The deterioration of superconducting properties is thought to be due to the superconducting weak coupling state occurring in the crystal grains.

As a result, we earnestly searched for ways to reduce the weak bonds that occur at grain boundaries, and came up with the idea of diffusing some kind of substance.

However, it is completely unclear what kind of substance should be diffused, and it is thought that it also depends on the composition of the superconducting matrix. So, as a result of numerous experiments,
The superconducting matrix has the above-mentioned (Bad-xMx) (Bit
-yNy)O5, it has been found that superconducting properties can be improved if diffusion is performed using the adhering substance according to the present invention.

However, even with regard to the heat treatment temperature during diffusion, it is not necessarily the case that improvements in superconducting properties are observed over the entire temperature range, and only when heat treatment in a limited temperature range of 300 to 1000 degrees Celsius improves superconductivity. It was found that the conduction properties were improved.

The present invention has been made based on the above knowledge and idea.

The adhering substance is attached to the surface of the superconducting matrix,
When heat treatment is then performed at a temperature of 300 to 1000°C in an oxidizing atmosphere, the adhered substances diffuse into the superconducting matrix, reducing the superconducting weak bonding characteristics of the grain boundaries and improving the superconducting properties. It is considered that

The superconductor obtained by the present invention has small superconducting weak coupling characteristics at grain boundaries and has excellent superconducting characteristics. Taking the critical current density as an example, conventionally it is 10"A/cm2~10'A
It was also very difficult to obtain something of the order of /cm2,
According to this method, a critical current density of 1×10'A/cm' or more can be easily achieved, and a high current density can also be obtained even when a magnetic field is applied.

[Example] The present invention will be described in detail below, but the scope of the present invention is not limited by this example. (Example 1) In (Bat-xMx) (Bit-yNy)Os, M is The mixture was compounded with a chemical composition in which x = 0.3 and y = 0. The mixture was compression molded, sealed in a silver tube, and then vacuum sealed in a quartz tube to remove oxygen. Firing was performed at 650° C. for 70 hours in an air stream. As a result, a superconducting matrix having the composition shown in Table 1 was obtained.

On the other hand, the substances shown in Table 1 were selected as adherent substances, and these adherent substances were diluted with distilled water to prepare aqueous solutions or suspensions of these substances.

Next, the aqueous solution or suspension thus prepared was applied with a brush to the surface of the superconducting matrix prepared above, thereby causing the adhesion substance to adhere to the surface of the superconducting matrix. The amount of adhesion was 3 mg per unit area (c rn'').

Next, the superconducting base material to which the adhesion substance was attached was heat-treated at 500° C. for 5 hours in an oxygen stream to produce an oxide superconductor.

The critical temperature and critical current density of the oxide superconductor produced as described above were measured.

The critical temperature was measured by a four-terminal method using an alternating current of 73 Hz and a current of 500 μA.

The critical current density is measured using the four-terminal method at a generated voltage of 1 μV.
/cm standard.

Table 1 shows the measurement results.

In either case, it was possible to obtain an oxide superconductor with significantly superior superconducting properties compared to the case without the deposited material.

That is, in all cases in which a superconducting substance was attached to a superconducting matrix and heat treatment was performed, a critical current density of 1 x 10' A/am2 or more was obtained. On the other hand, the best one (bottom row of Table 1) that does not contain any adhesion substances is 1 x 1.
It was only 0' A/cm2.

As is clear from the results, the critical current was significantly improved in Example 1 of the present invention compared to the conventional technology.

In addition, Rb, Li, or a combination of two or more of these other than M crab may be used as a composition, and Cu, Bi, Bi, which is a car body other than Ag shown in Table 1 as an adhesion substance, may also be used.
TI, Mn, Fe, V.

Ti, Sb, Cr, Sr, Ca, Ba, Ni.

Zn, Li, Na, Rb, Cs, Y or La,
Pr, which is a simple substance of Re (rare earth metal) other than Nd,
Sm, Eu, Gd, Tb, DyHo, Er, Tm, Tr
Or these oxides (excluding the oxides shown in Table 1)
Similar results were also obtained for carbonates, and also for combinations of two or more of the above-mentioned car bodies, oxides, and carbonates.

Table 1 (Part 1) Table 1 (Part 2) (Example 2) Among the results of Example 1, Na20°K2O was the most effective in improving the critical current; , K2O was selected and the effect of heat treatment temperature was investigated.

The composition is Baa, . After compression molding the composition to become 3BiOs, it was sealed in a silver tube, then vacuum sealed in a quartz tube, and fired in an oxygen stream at 650 t for 70 hours. As a result, a superconducting matrix having the composition shown in Table 2 was obtained. On the other hand, K2O was diluted with distilled water, and the diluted solution was applied to the surface of the superconducting matrix prepared above with a brush, thereby making 20 adhere to the surface of the superconducting matrix. The amount of adhesion was 3 mg per unit area (Cgo).

Next, the superconducting matrix to which K2O was attached was heat treated in an oxygen stream for 5 hours at varying heat treatment temperatures in the range of 250 to 1200 DEG C. to obtain an oxide superconductor.

The critical temperature and critical current density of the oxide superconductor produced as described above were measured in the same manner as in Example 1.

The results are shown in Table 2.

As shown in Table 2, it can be seen that when the heat treatment temperature was 300 to 1000°C, an oxide superconductor with significantly superior superconducting properties could be obtained compared to when no deposited substance was attached. In particular, it can be seen that the superconducting properties are further improved when the heat treatment temperature is 500 to 1000°C.

As is clear from this result, compared to the conventional technology, the critical current was significantly improved due to the reduction in the weak bonding of the grain anchors.

Regarding the effect of the heat treatment temperature, similar results were obtained when the various materials described in Example 1 were used as M and N as the composition and the attached substances.

Table matrix composition: Baa, tKo, 3BiO5 deposits: 20 (Example 3) (Bat -11Mx) (Bit-yNy) Chemical composition in which N is Pb, x=O, y=o, and 7 After compression-molding the mixture, it was sealed in a silver tube, vacuum-sealed in a quartz tube, and heated to 6 ℃ in an oxygen stream.
Bake at ℃ for 70 hours. As a result, a superconducting matrix having the composition shown in Table 3 was obtained.

On the other hand, the substances shown in Table 3 were selected as adherent substances, and these adherent substances were diluted with distilled water to prepare aqueous solutions or suspensions of these substances.

Next, the aqueous solution or suspension thus prepared was applied with a brush to the surface of the superconducting matrix prepared above, thereby causing the adhesion substance to adhere to the surface of the superconducting matrix. The amount of adhesion was 3 mg per unit area (cm').

Next, the superconducting base material to which the adhesion substance was attached was heat-treated at 500° C. for 5 hours in an oxygen stream to produce an oxide superconductor.

The critical temperature and critical current density of the oxide superconductor produced as described above were measured in the same manner as in Example 1.

Table 3 shows the measurement results.

In either case, it was possible to obtain an oxide superconductor with significantly superior superconducting properties compared to the case without the deposited material.

As is clear from the results, as with Example 1, Example 3 of the present invention significantly improved the critical current compared to the conventional technology.

Note that even when N is Cu as a composition, Cu and Bi, which are simple substances other than Ag shown in Table 3, are added as adhering substances.
, Tl, Mn, Fe, V, Ti.

Sb, Cr, Sr, Ca, Ba, Ni, Zn.

Li, Na, Rb, Cs, Y or La.

Pr, which is a vehicle body made of Re (rare earth metal) other than Nd;
Sm, Eu, Gd, Tb, Dy, Ho.

Similar results were obtained for Er, Tm, Tr, or their oxides (excluding the oxides shown in Table 3) or carbonates, and also for combinations of two or more of the above single substances, oxides, and carbonates. Ta.

Table (Part 1) Table 3 (Part 2) (Example 4) Ba (Bio, 1Pbo, 5cuo, s) O
After compounding with a chemical composition of s and compression molding the compound,
It is sealed in a silver tube and then vacuum sealed in a quartz tube.6
Firing was performed at 50°C for 70 hours. On the other hand, the substances shown in Table 4 were selected as adhering substances, diluted with distilled water, and the diluted liquid was applied to the surface of the superconducting matrix prepared above with a brush to adhere. The amount of adhesion was 3 mg per unit area (cm'').Next, the superconducting matrix to which the adhering substance was attached was heat-treated at 500° C. for 5 hours in an oxygen stream to produce an oxide superconductor.

The critical temperature and critical current density of the oxide superconductor prepared as described above were measured in the same manner as in Example 1.
Table 4 shows the measurement results.

In either case, it was possible to obtain an oxide superconductor with significantly superior superconducting properties compared to the case without the deposited material. As is clear from this result, compared to the conventional technology, Example 4 of the present invention, like Example 1 and Example 3, significantly improved the critical current.

Note that R other than LaNd shown in Table 4 was used as the adherent substance.
e (rare earth metal) Pr.

Sm, Eu, Gd, Tb, Dy, Ho, Er.

Similar results were obtained even when Tm or Tr car bodies or their oxides or carbonates were used.

Table 4 (Part 1) Table 4 (Part 2) (Example 5) (Bal-Xuri (BL-yNy) M in 03
Then, a compound with a chemical composition in which N was set to PB and the values of x and y were changed was compression molded, sealed in a silver tube, and then vacuum sealed in a quartz tube at 650°C for 70 hours. Multiple superconducting matrices were obtained by firing.

On the other hand, CuO was selected as the adhesion substance, diluted with distilled water, and the diluted solution was applied with a brush to the surfaces of the plurality of superconducting matrices prepared above, thereby making CuO adhere to the surfaces of the superconducting matrices. Adhering amount is 3mg per unit area (am”)
And so.

Next, the superconducting matrix to which CuO was attached was heat-treated at 500° C. for 5 hours in an oxygen stream to obtain an oxide superconductor.

The critical temperature and critical current density of the oxide superconductor produced as described above were measured in the same manner as in Example 1.

The results are shown in Table 5.

As shown in Table 5, X is 0.5 or less and y is 0.8
In the case of the following superconducting base materials in the solid solution region, it was possible to obtain oxide superconductors with significantly superior superconducting properties compared to when no adhering substance was attached.

Furthermore, regarding Rb, Li and combinations of two or more of these other than M, N is also applicable to Cu other than Pb or a mixture thereof, and furthermore, C as an adhesion substance.
u, Bi, TI, Mn.

Fe, V, Ti, Cr, Sb, Sr, Ca.

Ba, Ni, Zn, Li, Na, Rb.

Cs, Ag, Y, Re (rare earth metals), C
Oxides or carbonates other than uO, or 2Cr
Results similar to those shown in Table 5 were obtained when using a compound such as 207K2Mn204 that produces oxides through thermal decomposition, and in both cases, the oxides had significantly superior superconducting properties compared to when there was no attached material. We were able to obtain a superconductor.

Moreover, although the case where the superconducting matrix is a sintered body has been described so far, the same results as in Examples 1 to 5 were obtained also for single crystals and thin films.

[Effects of the Invention] As explained above, according to the present invention, it is possible to control the weak superconducting bonds that exist in grain boundaries and defective areas, which are the drawbacks of high-temperature superconductors, and it is possible to control the superconducting weak bonds that exist in grain boundaries and defective areas, which are the drawbacks of high-temperature superconductors. Another advantage is that an oxide superconductor (for example, having a critical current density of 1×10'A/cm" or more) can be obtained.

Oxide superconductors with these improvements have sufficient performance as bulk materials used in superconducting magnets, superconducting motors, etc., and will make a major contribution to the field of superconducting applications.

Claims (1)

[Claims] (Ba_1_-_xM_x) (Bi_1_-_yN_
y) O_3 (M is one or more selected from K, Rb, Li, x = 0 to 0.5, N is one or two selected from Pb, Cu, y = 0 A superconducting matrix with a composition of ~0.8) was prepared, and then Cu, Bi
, Tl, Mn, Fe, V, Ti, Sb, Cr, Sr, C
a, Ba, Ni, Zn, Li, K, Na, Rb, Cs,
One or more substances of Ag, Y, Re (where Re is a rare earth metal), their oxides or carbonates, or compounds that produce oxides through thermal decomposition are attached to the surface of the superconducting matrix. then 300
1. A method for producing an oxide superconductor, which comprises performing heat treatment in an oxidizing atmosphere at a temperature of ~1000°C.