JPH06234527A - Oxide superconducting substance - Google Patents

Abstract

PURPOSE:To obtain a Bi-based oxide superconducting substance having high Jc and hardly reducing the Jc in a magnetic field. CONSTITUTION:This oxide superconducting substance has a compsn. represented by the formula Bi2Sr2Ca1Cu2AxOy (where A is one or more kinds of elements selected among Ru, Rh, Pd, Os, Ir and Pt as Pt group elements and 0.005<=x<=0.5). Since the Pt group elements are added, an impurity phase can finely be dispersed in a partially melted state and an excellent superconducting material having high Jc is obtd. by working it into a wire, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high critical current density (J
The present invention relates to a Bi-based oxide superconducting substance having c) and having a small decrease in Jc due to a magnetic field.

[0002]

2. Description of the Related Art Since the discovery of oxide-based superconducting materials having a high superconducting critical temperature, various studies have been conducted toward their practical application. Among many oxide superconducting materials, the Bi-based superconducting material represented by Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _y is
It has been confirmed that the magnetic field characteristics of the critical current density (Jc) at liquid helium temperature (4.2K) are superior to those of the metallic superconducting materials that have been used conventionally. Applications are expected.

The Bi-based superconducting material can be made into a wire by filling the calcined raw material powder in a silver tube and making it into a wire by die drawing, roll rolling, etc. It is a substance that can Bi
Among the superconducting materials, Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _y , the so-called (221
2) A material with a structure is partially melted at around 890 ℃ and then slowly cooled to obtain a highly oriented texture with uniform texture direction, and a wire with a small decrease in Jc due to a magnetic field is obtained.

For example, Japanese Journal of Applied Ph
ysics, Vol.29, No.7, L1066 contains Bi ₂ O ₃ as raw material powder,
Powders of SrCO ₃ , CaCO ₃ , CuO, and Ag ₂ O were added to Bi: Sr: Ca: C.
The u: Ag atomic ratio was mixed in a ratio of 2: 2: 1: 2: 0.8 and calcined at 880 ° C. The powder obtained was filled into a silver pipe, which was drawn and rolled to form a tape. After being processed into a wire-shaped wire, it is heat-treated by partially melting it in a mixed gas of Ar and O ₂ at 880 ° C and then gradually cooling it to a maximum of 8.88 × 10 ⁴ A / cm ² (temperature 4.2K,
It is reported that the Jc of 1 Tesla of magnetic field) was achieved.

What is common to the heat treatment of Bi (2212) -based wire is that the temperature is raised to 875 ° C. or higher for partial melting, and then gradually cooled for further grain growth. Note that partial melting means that the Bi (2212) phase is wholly melted, but the other C
Impurity phases such as aO and Sr-Ca-Cu-O phases do not melt.

However, if the partial melting temperature is too high or the time is too long, grain growth of the Sr-Ca-Cu-O phase, which is an impurity phase, is promoted and Jc is lowered. So generally 8
After the temperature was raised from 75 ℃ to 895 ℃ and partially melted, the Bi (2212) phase was crystallized, and the temperature around 880 ℃ was maintained at 5 to 20 ℃ / hr so that grain growth would occur. Heat treatment is being performed at a slow cooling rate (eg Japa
nese Journal of Applied Physics, Vol.30, No.12A, pp.
3371-3376).

[0007]

The problems of the above-mentioned heat treatment methods known so far are as follows. That is, as described above, the Bi (2212) phase is melted at the partial melting temperature, but the other impurity phases such as CaO and Sr-Ca-Cu-O phases are present in the wire as solid particles. Therefore Bi
Above the crystallization temperature of the (2212) phase, a solid-liquid coexistence state occurs, and the impurity phase causes grain growth. Especially, the grain growth rate of the Sr-Ca-Cu-O phase is high, and Sr grown even at a low temperature below the crystallization temperature.
-Ca-Cu-O grains remain.

As a result, a deviation from a predetermined composition occurs in the wire, and in addition to the Sr-Ca-Cu-O grains, the normal phase B
i ₂ Sr ₂ Cu ₁ O _{y, that} is, the (2201) phase is generated and deteriorates the Jc characteristics. The (2201) phase disturbs the orientation of the Bi (2212) phase when the Bi (2212) phase is crystallized and grows in grains, which causes a problem that the Jc characteristic is further deteriorated.

An object of the present invention is to provide a superconducting substance having excellent Jc characteristics, in which grain growth of the Sr-Ca-Cu-O phase described above hardly occurs.

[0010]

The subject of the present invention is the following superconducting material. An oxide superconducting substance represented by the composition formula Bi ₂ Sr ₂ Ca ₁ Cu ₂ A _x O _y .

However, A in the above composition formula is a platinum group element (R
u, Rh, Pd, Os, Ir and Pt), and 0.005 ≦ x ≦ 0.5.

[0012]

The inventor of the present invention has made Bi ₂ Sr ₂ Ca by the partial melting method described above.
_The method for producing a ₁ Cu ₂ O _y based oxide-based superconducting material was studied in detail. As a result, the following points became clear.

1. The larger the Sr-Ca-Cu-O grains in the partially molten state, the more the Sr-Ca-Cu remaining in the superconducting material after slow cooling.
-O grains are large.

2. Even if the total amount of remaining Sr-Ca-Cu-O grains is about the same, the smaller the individual grains, the smaller the adverse effect of degrading Jc.

3. Therefore, Sr-Ca-Cu in the partially molten state
-Dispersing O grains as small as possible leads to an improvement in Jc.

4. If the Sr-Ca-Cu-O particles can be dispersed as fine particles of 0.1 μm or less, they can function as pinning sites and further improve Jc.

The present inventor has found that Sr-Ca-Cu in a partially molten state
Searching means for reducing the -O grains, to add specific amounts of a platinum group element _{Bi 2 Sr 2 Ca 1 Cu 2} O y based oxide was confirmed to be effective. That is, Ru (ruthenium) on Bi (2212)
, Rh (rhodium), Pd (palladium), Os (osmium), Ir (iridium), and Pt (platinum), select one or more elements, and add appropriate amount of them in the partially molten state. It becomes possible to finely disperse Sr-Ca-Cu-O, and as a result, it is possible to improve Jc of the oxide superconductor after slow cooling.

The addition amount of the platinum group element is determined by the above composition formula Bi ₂ S.
_{x in} r ₂ Ca ₁ Cu ₂ A _x O _y (however, A in this composition formula is one or a combination of two or more of the above platinum group elements) must be in the range of 0.005 to 0.5. As shown in FIG. 1 described later, when x is smaller than 0.005, the effect of finely dispersing Sr—Ca—Cu—O is not seen. On the other hand, when x exceeds 0.5, fine dispersion is promoted, but the total amount of Sr-Ca-Cu-O increases compared to the case where no platinum group element is added, and the production amount of Bi (2212) after slow cooling is small. Become,
Jc characteristics deteriorate. The preferable range of x is 0.05 to 0.3,
The best Jc is obtained when x = 0.2.

Superconducting material mainly composed of superconducting material of the present invention
The wire (for example, a wire) is manufactured by the partial melting method like the conventional Bi-based superconducting material. That is, the atomic ratio of Bi: Sr: Ca: Cu: A obtained by calcining raw material powder such as oxide is 2: 2:
A powder having a composition of 1: 2: x (x = 0.005 to 0.5) is put into a silver sheath, processed into a predetermined shape by wire drawing, rolling, etc., partially melted and gradually cooled. The temperature of the partial melting treatment is preferably 870 to 910 ° C., as shown in FIG. 3 described later. At temperatures lower than 870 ° C, partial melting does not occur sufficiently and a highly oriented structure cannot be obtained. Also, at temperatures above 910 ° C
The growth of Sr-Ca-Cu-O grains is large and the Jc characteristic is deteriorated.

In addition to oxides, chloride, nitrate, and pure metal powders can be used as the raw material for the platinum group element. Further, the superconducting substance of the present invention can be used as a superconducting material having various shapes other than a wire rod.

[0021]

[Examples] In order to confirm the superconducting properties of a wire using the composition of the present invention, a wire was prepared by the silver sheath method (powder in tube method).

As raw material powders, Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ ,
In addition to CuO, RuO ₂ and Rh ₂ as raw materials for platinum group element (A)
Any one of O ₃ , PdO, Os ₂ O ₃ , Ir ₂ O ₃ and PtO ₂ was used.
These raw material powders have an atomic ratio of Bi: Sr: Ca: Cu: A of 2:
It is mixed and mixed so that it becomes 2: 1: 2: x (x = 0.001 to 0.8), calcined in the air at 800 ° C for 12 hours, then pulverized and mixed, and further in the air at 800 ° C × 12 hours. Calcining,
Raw material powder for wire rod.

The above raw material powder was filled in a silver pipe having an outer diameter of 6 mm and an inner diameter of 4 mm, and the width was 3 mm by die drawing and roll rolling.
It was processed into a tape-shaped wire with a thickness of 0.1 mm.

The tape-shaped wire produced in this way is
The temperature was raised to various partial melting temperatures (Tm, ° C), held for 10 minutes, gradually cooled to 800 ° C at 5 ° C / hr, and further cooled to room temperature.

Table 1 shows the wires treated at Tm = 885 ° C.
The Jc value in 4.2K and 1 Tesla, the amount of the platinum group element added (value of x), and the average particle size and total amount (volume fraction) of Sr-Ca-Cu-O particles are shown. In addition, shown in Table 1 is an example in which only one kind of platinum group element is added by the value of x.

In FIG. 1, Rm is used as the platinum group element, and Tm =
The amount of Rh (x value) of the wire treated at 885 ℃ and 4.2
K shows the relationship with the Jc value in 1 Tesla. As shown in the figure, there is almost no improvement in Jc until x = 0.005, but Jc begins to improve at 0.005 or higher and reaches the maximum value at x = 0.2. After that, Jc starts to decrease again, and when x exceeds 0.5, Jc becomes lower than that without Rh. This is because the growth of Sr-Ca-Cu-O grains is suppressed as x increases, the average grain size decreases, and the Jc value increases, but when x exceeds a certain value, Sr-Ca-Cu- The total amount of O grains increases, and Jc
This is because the value decreases. The same tendency is observed when platinum group elements other than Rh are added.

[0027]

[Table 1]

Similarly, two or more kinds of platinum group elements were added to produce a silver sheath wire. Table 2 shows the relationship between the addition amount of each element and the Jc value in 4.2 Tesla at 4.2K. The value of x shown in Table 2 is the total addition amount of two or more platinum group elements, that is, x = x ₁ + x ₂ + x ₃ + x ₄ + x ₅ + x
_{Is 6} .

It can be seen from Table 2 that even in the case of composite addition of two or more platinum group elements, the Jc value is improved if the total addition amount (value of x) is 0.005 to 0.5.

[0030]

[Table 2]

Table 3 shows the Jc values in the zero magnetic field and the 1 Tesla magnetic field of the sample using Rh as a platinum group element and the sample not adding this (x = 0. 2 and x = 0). As can be seen from this table, the oxide superconductor of the present invention to which the platinum group element is added not only has a large Jc value but also Jc in a magnetic field.
The decrease in value is small. This is a finely dispersed Sr-Ca-
It is considered that this is because the Cu-O grains act as pinning sites.

[0032]

[Table 3]

FIG. 2 shows that Rh is used as a platinum group element at 885 ° C.
FIG. 3 is a copy of a micrograph (500 times) of a cross-sectional structure of a wire rod which has been quenched after performing partial melting treatment for 10 minutes. (a) is x
= 0, that is, Rh is not added, and (b) is x = 0.2. It can be seen that the black Sr-Ca-Cu-O grains are coarse in (a), but are finely dispersed in the Rh-added material in (b). The difference in the particle size of Sr-Ca-Cu-O under the condition of such partial melting treatment is as shown in Table 2
It appears as a difference in value.

In FIG. 3, Rh is added as a platinum group element (x =
0.2) wire (○) and Rh-free (x = 0) wire
Partial melting process temperature (Tm) (marked with △) and 4.2K, 1 Tesla
Shows the relationship with the Jc value in. Tm of all samples
The maximum Jc is shown at around 880 ° C, but the Rh-added material has a much higher Jc, and the Tm range showing a higher Jc is wider.

The same tendency is obtained when a platinum group element other than Rh is added. This means that the Bi-based oxide superconductor to which the platinum group element of the present invention is added has a wide selection range of the partial melting temperature. For example, a large superconducting coil has a uniform temperature throughout. This means that even if a material is difficult to heat, the entire material can be partially melted, so that the target material whose decrease in Jc due to the magnetic field is small can be easily manufactured.

[0036]

The Bi-based oxide superconducting material to which one or more of the platinum group elements of the present invention is added in an appropriate range is obtained by subjecting this material to the partial melting treatment, which is an essential treatment. The impurity phase can be finely dispersed. Therefore, it becomes a superconducting material having a high Jc when processed into a wire or the like and having a small decrease in Jc in a magnetic field.

[Brief description of drawings]

FIG. 1A of Bi ₂ Sr ₂ Ca ₁ Cu ₂ A _x O _y (A is a platinum group element)
X value (Rh addition amount) when Rh is used as 4.2
It is a figure which shows the relationship with the Jc value in K and 1 Tesla.

FIG. 2 is a copy of a micrograph (500 times) of the cross-sectional structure of a Bi ₂ Sr ₂ Ca ₁ Cu ₂ Rh _x O _y wire rod that has been subjected to partial melting treatment at 885 ° C. for 10 minutes and then rapidly cooled. a) is x = 0, that is,
Rh is not added, and (b) is x = 0.2.

FIG. 3 A of Bi ₂ Sr ₂ Ca ₁ Cu ₂ A _x O _y (A is a platinum group element)
As a wire material using Rh (x = 0.2, ○ mark), and a partial melting treatment temperature (Tm) of the wire without Rh additive (x = 0, △ mark)
It is a figure which shows the relationship with the Jc value in 4.2K and 1 Tesla.

Claims (1)

[Claims] 1. An oxide superconducting material represented by the composition formula Bi ₂ Sr ₂ Ca ₁ Cu ₂ A _x O _y . However, A in the above composition formula is at least one element selected from the platinum group elements (Ru, Rh, Pd, Os, Ir and Pt), and 0.005 ≦ x ≦ 0.5.