JPH0672712A - Oxide superconducting material containing rare-earth element and its production - Google Patents

Abstract

PURPOSE:To improve the critical current density by heating a precursor for a specified superconductor to a specified. temp. to form a liq. phase contg. a 211 phase, Ba and Cu, then slowly cooling the precursor to grow a 123 phase and enriching the precursor with oxygen. CONSTITUTION:The RE2O3 (RE is rare-earth element) such as Y2O3 and a Ba and Cu compd. such as BaCuO2 are mixed so that the composition of (RE/Ba/ Cu) is positioned in the area enclosed by the points in atomic % of (10/60/30), (10/20/70) and (50/20/30), and further Pt or PtO2 powder is added to the mixture by 0.05-5wt.% as Pt and kneaded to form a precursor for the oxide superconductor. The precursor us then heated and kept at 900-1300 deg.C to form a liq. phase contg. RE2BaCuO5 (211 phase), Ba and Cu, then slowly cooled from 900-1100 deg.C when the REBa2CU3O7-x (123 phase) begins to be formed at the rate of 5 deg.C/hr to grow a 123 phase and enriched with oxygen to obtain an oxide superconductor in which the 211 phase of <=5mum is finely dispersed and having high critical current density.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide superconducting material and a method for producing the same.

[0002]

_2. Description of the Related Art Superconductor materials having a composition of REBa ₂ Cu ₃ O _7-X (123 phase) are currently mainly manufactured by the melting method in order to increase the critical current density. The manufacturing process called the melting method is MTG (Melt).
Texture Growth method, QMG (Quen)
ch and Melt Growth) method, MPMG
(Melt Power Melt Growth) method and the like. The MPMG method is characterized in that a material containing the RE element that has been melted and cooled is crushed and pressure-molded to prepare a precursor, and the subsequent heat treatment is the same as in the QMG method. Also, as a method for producing a precursor, a QMG method has been reported in which only Ba and Cu oxides are once melt-quenched, and then pulverized, kneaded, and molded together with RE ₂ O ₃ powder to produce a precursor and the same heat treatment. ing. Here, the precursor is 211
It means a compact before heat treatment for growing 123 phase from the liquid phase with the phase (RE ₂ BaCuO ₅ ).

The difference between the MTG method and the QMG, MPMG method is that the finally obtained superconducting material is a unidirectionally oriented polycrystalline body (MTG) and a single crystal material without a large tilt grain boundary (QMG, MPMG). The difference is that the fineness of the 211 phase contained in the 123 phase (MTG is several tens of μm. QMG, M
PMG is about 1 μm).

[0004]

[Problems to be Solved by the Invention] High critical current density (J
c) It is important to disperse the 211 phase finely in order to obtain a superconducting material having (7 K, 10 ⁴ A / square centimeter or more at several T). In order to improve Jc, it is necessary to introduce pinning centers that stop the movement of magnetic flux and prevent the generation of cracks that block current paths. The 211 phase finely dispersed in the QMG material is considered to be effective as a pinning center for magnetic flux and also for preventing cracks. 21
In order to disperse one phase finely, it is necessary to disperse the needle-like 211 phase having a diameter of several μm in the semi-molten state in the liquid BaCu oxide when the precursor is heat-treated. For that purpose, it is necessary to adjust the composition in the precursor.

For example, as in the MTG method, 123 phases and 211
In the precursor mixed with the phase, a large number of block-like 211 phases of several tens of μm can be formed in the semi-molten state, and the 211
The phase will also grow. On the other hand, in the MPMG method, the amount of 2
Since it has a composition in which 11 phases are finely dispersed, a needle-like 211 phase is formed in a semi-molten state, and as a result, a superconducting material in which the 211 phase is finely dispersed can be obtained. However, there is little knowledge about what kind of substance this composition consists of and what kind of action (mechanism) causes the 211 phase to finely disperse, and at present, the precursor is produced through the steps of melting, cooling, and crushing. There is. An object of the present invention is to provide a means for finely dispersing a 211 phase in a 123 phase which is a superconducting phase, and to obtain a superconducting material having a high critical current density.

[0006]

Means for Solving the Problems The present invention is to solve the above problems, and the main metal elements are RE (one kind of rare earth element including Y or a combination thereof), Ba and Cu.
In the oxide superconducting material consisting of R, which is a superconducting phase
EBA ₂ Cu ₃ O _7-X crystal has a structure in which RE ₂ BaCuO _{5 of} 5 μm or less, which is a normal conducting phase, is finely dispersed, and contains 0.05 to 5% by weight of Pt. Is an oxide superconducting material.

In addition, RE ₂ O ₃ and the compounds of Ba and Cu are (10:60:30) and (10: 20: 7) in terms of the atomic ratio of each metal element (RE: Ba: Cu).
0) and (50:20:30) are mixed so as to have a composition in a region surrounded by points, and Pt powder or a compound of Pt is further added as 0.05% by weight to 5% by weight as Pt element in the mixed powder. After adding in a percentage, kneading and pressure molding are carried out to prepare a precursor of an oxide superconductor, and the precursor is heated to 900 ° C. to 1300 ° C. and RE ₂ BaCuO _{5 is} added.
And a liquid phase containing Ba and Cu, 900 ° C.-110
An oxide characterized by performing an oxygen enrichment treatment after growing a REBa ₂ Cu ₃ O _7-X phase by gradually cooling from a temperature range of 0 ° C at a cooling rate of 5 ° C / hour or less. It is a method of manufacturing a superconducting material.

[0008]

The present inventors have discovered that the above problems can be solved by adding a trace amount of platinum (Pt) to an oxide of RE ₂ O ₃ , Ba, and Cu to produce an oxide superconducting material. Was completed.

That is, the final structure (dispersed state of the 211 phase) of the superconducting material produced by the melting method is Y, B in the precursor.
It largely depends on the amounts of a and Cu and the bonding state of these elements, that is, the presence or absence of the starting material and other additional elements. To obtain a structure in which the 211 phase is finely dispersed, a semi-molten state (211
It is necessary that 211 is already finely dispersed in the phase + liquid phase of BaCu oxide). Therefore the precursor is heated 21
The final structure is almost determined by the reaction process in which one phase is formed. For this reason, the starting materials in the precursor (for example, 123, 211, RE ₂ O ₃ , BaCuO ₂ , Ba
Cu ₂ O ₂ ...) and additional elements are important factors that determine the characteristics of the superconducting material.

Specifically, there are two conditions for finely dispersing the 211 phase. (1) RE, Ba, C in the precursor
u substantially consists of RE ₂ O ₃ and Ba and Cu oxides and carbonates. (2) A small amount of Pt is contained in the precursor. It is necessary to satisfy both of these. Under such conditions, the reaction for producing the 211 phase when the precursor is heated is as shown in the following equation. RE ₂ O ₃ + L (liquid phase of BaCu oxide containing Pt) → 211 (needle-shaped with a diameter of 1 μm) + L

On the other hand, when only one of the conditions is satisfied, the following equation is obtained, and a fine 211 phase cannot be obtained in either case. REBa ₂ Cu ₃ O _7-X + Pt → 211 (tens of μm) +
L RE ₂ O ₃ + L ′ (BaCu oxide liquid phase) → 211
(Diameter about 10 μm) + L '

Next, the effect appears when the amount of Pt added is about 0.05% by weight, and a part of the 211 phase begins to become fine. Further, when it is added in an amount of about 5 weight percent or more, a large amount of composite oxide of Pt and Ba of several tens of μm is generated so as to wrap the 211 phase, and a large non-superconducting phase is formed. Pt above 2 weight percent
A considerable amount of Ba composite oxide was found. From the result of elemental analysis of the final structure, Pt is mainly contained in 123 phase instead of 211 phase, and when about 2 wt% or more is added, Pt which cannot be solid-solved forms a complex oxide with Ba. I think that the. Also, Pt seems to be dissolved in the liquid phase in the semi-molten state. For this reason, the amount of Pt added is particularly preferably 0.3 to 2.0 weight percent. The addition of Pt may be Pt alone or a Pt compound such as an oxide.

Further, in the manufacturing method of the present invention, RE ₂
O ₃ and a compound of Ba and Cu have a metal element ratio (RE: Ba: Cu) of 10: 6 in atomic percent.
0:30), (10:20:70), (50: 20: 3)
0) Mix so that the composition is within the area surrounded by points,
Further, Pt powder or a Pt compound is added to the mixed powder as P.
After adding 0.05 wt% to 5 wt% as a t element, kneading and pressure molding are performed to prepare a precursor of an oxide superconductor. Next, this precursor is heated at a temperature rising rate of 10 ° C./hour or more, depending on the RE composition, 900 ° C.
After being kept at 1300 ° C and made into a liquid phase containing RE ₂ BaCuO ₅ and Ba and Cu, REBa ₂ Cu ₃ O _7-X starts to form and the temperature range from 900 ° C to 1100 ° C is 5 ° C / hour. RE by slowly cooling at the following cooling rate
After growing the Ba ₂ Cu ₃ O _7-X phase, an oxygen enrichment treatment is performed to manufacture an oxide superconducting material.

In this case, in order to obtain the single crystal 123 phase in which the 211 phase is finely dispersed, RE, Ba and C in the precursor are obtained.
The u element must be present in a suitable proportion.
(RE: Ba: Cu) is RE from (50:20:30)
If the amount is large, the liquid phase component becomes insufficient and the growth of the 123 phase does not proceed. When the amount of Cu is more than (10:20:70), the 123 phase becomes a foil piece and a bulk material cannot be obtained. Further, when Ba is larger than (10:60:30), the liquid phase component is large and the sample shape cannot be maintained. For this reason, (RE: Ba: Cu) is changed to (50:20:
30), (10:20:70), (10:60:30)
It was limited to the composition range surrounded by. In addition, RE: Ba: C
In the ratio of u metal element, RE is more than (1: 2: 3) ratio.
When the ratio is large, the 211 phase tends to be finer.

The precursor obtained by processing and molding each of the raw material powders is heated to 900 to 1300 ° C., and RE ₂ BaCuO
₅ (211 phase) and a liquid phase containing Ba and Cu. This heating temperature range varies depending on the RE composition, but the lower limit is 9
00 degrees C is a temperature range in which the 123-phase formation temperature is exceeded, that is, the solid phase and the liquid phase, which are 211 phases, coexist. On the other hand, the upper limit of 13
00 ° C. is below the melting temperature of the 211 phase, that is, the temperature at which the precursor cannot retain its shape only in the liquid phase. The heating rate is such that the precursor is not cracked by thermal shock (preferably 200 ° C./hour or less).

Next, the REBa ₂ Cu ₃ O _7-X phase (123 phase) is generated by cooling from the coexisting state of the solid phase and the liquid phase and grown. In this case, the temperature range of 900 ° C. to 1100 ° C. is a 123-phase formation temperature although it varies depending on the RE phase composition. In particular, slow cooling is important from the 123-phase formation temperature to a temperature below 40 ° C. to prevent crystal nucleation due to supercooling. The slow cooling can achieve the same purpose by performing stepwise cooling in which the temperature is gradually maintained at a constant temperature.

The material manufactured as described above is RE
In order to reduce the oxygen deficiency x of Ba ₂ Cu ₃ O _7-X and exert the superconducting property, an oxygen enrichment treatment is performed by heating in an oxygen stream. This may be performed by gradually cooling in an oxygen stream in the manufacturing process, or by once cooling to room temperature and then reheating to 400 ° C. or higher.

[0018]

【Example】

Example 1. A precursor with different starting elements and added elements was prepared, and the structure of the material and the critical current density at 77K and 1T (J
c) was measured.

[0019]

[Table 1]

The following four starting materials were used and compounded so that the metal element ratio (Y: Ba: Cu) was approximately (13:17:23). In addition to Pt, the additive elements are Ag, Cr, Ni, Ti, Pb, Pd, Zn, and Zr as comparative materials.
Was added in the form of an oxide to prepare a precursor so as to have a concentration of 0.5% by weight. The precursor was heated to 1150 ° C. for 1 hour, held for 30 minutes, cooled to 1005 ° C. in 30 minutes, and then gradually cooled to 950 ° C. at 1 ° C./hour to grow 123 phases. In the oxygen enrichment treatment, the mixture was kept at 600 ° C for 5 hours in an oxygen stream, and then gradually cooled to room temperature at 10 ° C / hour. The results are shown in Table 1 below.

From the above results, it has been found that a precursor having a composite oxide of Y ₂ O ₃ and BaCu and a Pt element can produce a material having excellent characteristics.

[0022]

[Table 2]

Next, the amount of Pt added was examined. 6.5
A precursor in which the weight percentage of Pt element was changed was prepared by using PtO ₂ powder with respect to a mixed powder composed of Y ₂ O ₃ + 6BaCu ₂ O ₂ + 11BaCuO _2, and a sample was prepared by the heat treatment method. The results are shown in Table 2.

According to this, below 0.01% by weight, the same structure as that without addition is obtained, and the addition of 0.05% by weight to 5% by weight has an effect.
A structure containing a large amount of 211 phases of less than μm was obtained, and Jc was
Values as high as 15,000 A / square centimeter were obtained. In addition, the sample added with 10 weight percent is several tens of μm.
The amount of PtBa complex oxide was extremely large, and Jc also tended to decrease to 12000 A / square centimeter.

From these experimental results, the Pt element is Y ₂ O.
_In the process of forming the 211 phase from ₃ and BaCu oxide, it has a function of generating a needle-like 211 phase of about 1 μm, exerts its effect even in an extremely small amount, and has a function of greatly improving superconducting properties. I understood.

Example 2. Metal element ratio (Ho: Ba: C
As u) is (13:17:20) Ho ₂ O _3,
Ba ₂ CuO ₃ and BaCu ₂ O ₂ powder were mixed, 0.3 wt% of Pt element was added in the form of PtO ₂ powder, and these mixed powders were pressure-molded to prepare a cylindrical precursor. . This precursor was heated to 1150 ° C for 1 hour, held for 30 minutes, cooled to 1005 ° C in 30 minutes, and then gradually cooled to 950 ° C at 1 ° C / hour.
The phase has grown. In the oxygen enrichment treatment, the temperature was kept at 600 ° C in oxygen air for 5 hours, and then gradually cooled to room temperature at 10 ° C / hour.

As a result, a superconductor containing a large amount of 211 phases having a size of 1 μm or less was obtained. As for the critical current density (Jc) at 1T, a high value of 16000 A / square centimeter was obtained from the result of magnetization measurement.

Example 3. Metal element ratio (Y: Yb: Ba:
Cu) becomes (7: 7: 17: 20) Y ₂ O
₃ , Yb ₂ O ₃ , BaCuO ₂ , and BaCu ₂ O ₂ powders were mixed, 1.0% by weight of Pt element was added in the form of Pt powder, and these mixed powders were pressed to form a cylindrical precursor. The body was made. This precursor was heated to 1150 ° C. for 1 hour, held for 30 minutes, cooled to 1000 ° C., and seeded with Sm-based 123 seed crystals. Further, after cooling to 965 ° C in 30 minutes, it was gradually cooled to 910 ° C at 1 ° C / hour to grow 123 crystals.
In the oxygen enrichment treatment, the mixture was kept at 600 ° C for 5 hours in an oxygen stream, and then gradually cooled to room temperature at 10 ° C / hour.

As a result, a superconductor containing a large amount of 211 phases of 1 μm or less was obtained. As for the critical current density (Jc) at 1T, a high value of 15000 A / square centimeter was obtained from the result of magnetization measurement.

[0030]

As described in detail above, according to the present invention, by adding Pt, it is possible to disperse the fine 211 phase in the 123 phase, thereby facilitating the production of a superconducting material having a high critical current density. It can be applied in various fields and has a great industrial effect. Specific examples include superconducting coils, superconducting bearings, and superconducting magnetic shield materials.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masamoto Tanaka 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Nippon Steel Co., Ltd. Technical Research Institute (72) Inventor Katsuyoshi Miyamoto Ida, Nakahara-ku, Kawasaki-shi, Kanagawa 1618 Nippon Steel Co., Ltd. First Technology Research Laboratory (72) Inventor Kiyoshi Sawano 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Pref.

Claims (2)

[Claims] 1. An oxide superconducting material having a main metal element of RE (one kind of rare earth element including Y or a combination thereof), Ba and Cu, which is a superconducting phase.
a ₂ Cu ₃ O _7-X crystal has a structure in which RE ₂ BaCuO ₅ having a normal conducting phase of 5 μm or less is finely dispersed, and
An oxide superconducting material containing 0.05 to 5 weight percent of Pt. 2. RE ₂ O ₃ and a compound of Ba and Cu having a metal element ratio (RE: Ba: Cu) of (10:60:30), (10:20:70) in atomic percent.
The mixture was mixed so as to have a composition in a region surrounded by points (50:20:30), and Pt powder or a compound of Pt was further added to the mixed powder as a Pt element in an amount of 0.05 to 5 wt%. After that, kneading and pressure molding are performed to prepare a precursor of the oxide superconductor, and the precursor is mixed with 900
It was heated to degrees C~1300 ° C RE ₂ BaCuO ₅ and Ba
And a liquid phase containing Cu, 900 ° C to 1100 ° C
After the REBa ₂ Cu ₃ O _7-X phase is grown by gradually cooling from the temperature range of 5 ° C./hour or less,
A method for producing an oxide superconducting material, which comprises performing an oxygen enrichment treatment.