JPH0818835B2 - Composite oxide superconducting material and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel composite oxide superconducting material and a method for producing the same, and more specifically to a complex oxide superconducting material having a high critical current density (Jc). The present invention relates to a manufacturing method thereof.

2. Description of the Related Art Superconducting materials of complex oxides have been known for a long time, and for example, in U.S. Pat.No. 3,932,315, Ba-Pb-Bi-
O-based complex oxides are disclosed. However, the critical temperature of this system complex oxide is about 11K, and liquid helium must be used as a refrigerant. Last year (April 1986), it was shown by G. Bednorz and KA Muller that the resistance of La-Ba-Cu-O-based composite oxides decreased at 35K or lower. Furthermore, Shoji Tanaka showed that LaBaCuO ₄ with K ₂ NiF ₄ type crystal structure constitutes a superconducting phase with high critical temperature. In February this year, CWChu et al. Superconducting materials have been announced.

This superconducting material has a three-layer orthorhombic perovskite type crystal structure and its composition is Ba ₂ Y _2.
It is represented by Cu ₃ O _7-x . The reason why this material has a high critical temperature Tc is currently unknown, and various theories have been proposed.

It is also known that the critical temperature Tc does not decrease so much even if the above-mentioned Y is replaced with another rare earth element having a large number of localized magnetic moments having the same number of electrons (eg, Jpn. J.Appl.Phys. (26) 4 L
339 (1987)).

In addition, many complex oxides such as a three-element complex oxide such as La-Sr-Cu-O system and a complex oxide in which a part of oxygen is substituted with fluorine may be a superconductor at a high critical temperature. It has been reported that the development of superconducting technology using high temperature superconductors is about to be accelerated. Most of these complex oxides already reported have a crystal structure similar to the perovskite type.

Under the superconducting phenomenon, the substance shows complete diamagnetism, and the potential difference disappears despite the finite steady current flowing inside. The application fields of this superconductivity phenomenon are MHD power generation, power transmission, power storage and other power fields, or maglev trains,
It covers a wide range of fields such as power fields of electromagnetic propulsion vessels, etc., and ultra-high-sensitivity sensors for magnetic fields, high-frequency waves, radiation, etc. In the field of electronics represented by elements, it is expected as a technology that can realize not only a reduction in power consumption but also an element that operates at an extremely high speed.

Problems to be Solved by the Invention In order to actually use the superconducting phenomenon, it is necessary to raise the critical current density Jc in addition to raising the critical temperature Tc. Generally, the critical current density Jc required for practical use is about 10,000 A / cm ² or more at liquid nitrogen temperature (77K), but the critical current density actually obtained by the above complex oxide superconducting material
Jc is only several hundred to several thousand A / cm ² .

As a result of studying a method for improving the critical current density Jc, the applicant has determined that in the case of the above-mentioned oxygen-deficient perovskite-type complex oxide superconducting material, the critical current density Jc can be determined by substituting the Cu atom with another atom. They have found that they can be improved and completed the present invention.

Therefore, an object of the present invention is to provide a complex oxide superconducting material having a high critical current density Jc and a method for producing the same.

Means for Solving the Problems That is, the complex oxide superconducting material provided by the present invention has a general formula: A _U B _V Cu _WX M _X O _Y (where A is an element contained in Group IIa of the periodic table). , B is an element included in Group IIIa of the periodic table, M is the Coulomb potential of the ion Z / r (where Z is the valence of the ion, and r is the ionic radius of the ion). Cu ³⁺ Coulomb potential is an element larger than 5.5 and excluding Ge, and u, v, w, x and y are 0.5 ≦ u ≦ 3, 0.5 ≦ v ≦ 2, 2 <w ≦ 4, 0.1 ≦, respectively. x
(Representing a number in the range of ≦ 3 and 6 ≦ y ≦ 8) and containing an oxygen-deficient perovskite type crystal structure.

The above-mentioned "mainly as" means that the whole superconducting material contains other elements that are inevitably mixed in the production in addition to the complex oxide having the above composition, and the above-mentioned "containing" means This is meant to include not only the case where the entire superconducting material is composed of the complex oxide having the above composition, but also the case where it is contained in part thereof. That is, the superconducting material according to the present invention is not limited to a uniform single crystal or polycrystal represented by the above general formula,
Other compositions and crystal structures may be included.

Examples of the element A include Ca, Sr, Ba and Ra.
Ba and Sr are preferred. Examples of the element B include Sc, Y, actinium series and lanthanum series, and Y, La and lanthanide series elements Gd, Dy, Ho, Er, Yb and Tb are particularly preferable. The element M is Ge, V, Mo, Ta, Nb, Bi, Sb, Mn, Sn
And at least one element selected from the metals represented by W. Examples of the combination of elements for the superconducting material that can be produced by the present invention include Ba
-Y-Cu-M-O, Ba-La-Cu-M-O, Sr-La-Cu-
M-O, Ba-Ho-Cu-M-O, Ba-Er-Cu-M-O, Ba
-Gd-Cu-MO combination (where M is V, Mo, Ta, N
b, Bi, Sb, Mn, Sn and at least one element selected from the metals represented by W),
These composition ratios can be appropriately selected within the range defined above.

The composition ratios (atomic ratios) u, v, w, x and y of the above elements are 0.5 ≦ u ≦ 3, 0.5 ≦ v ≦ 2, 2 <w ≦ 4, respectively.
The range is 0.1 ≦ x ≦ 3 and 6 ≦ y ≦ 8. If the composition ratio is deviated, the oxygen deficient perovskite type crystal structure, which is the composite oxide superconducting material, is largely deviated, and the improvement of the critical temperature Tc and the improvement of the current density Jc cannot be achieved. As a combination of the above elements A and B, Y-Ba, La-Ba, Sr-
When each system of Ba is used, the atomic ratio of each system is preferably 00.6 to 0.94 in the case of Y / (Y + Ba), more preferably 0.1 to 0.4, and Ba / (La
+ Ba) is preferably 0.04 to 0.96, more preferably 0.08 to 0.45, and Sr / (La + Sr) is preferably 0.03 to 0.95, and more preferably 0.05 to 0.95. It is preferably 0.1. When the atomic ratio deviates from the above range, the superconducting critical temperature of the superconductor does not reach the desired value.

The atomic ratios of the element (Cu + M) and oxygen to the above element (A + B) are 1: 0.3 to 3.0 and 1: 1 to 5 respectively.
To the ratio. With such a ratio, the structure of oxide-based superconductors is currently being clarified by analysis of electron microscopes and the like. Perovskite type, oxygen deficient perovskite type, etc. Can be a complex oxide of

A second object of the present invention is to provide a method for producing the above composite oxide superconducting material. This method is II of the periodic table
Element A in group a, element B in group IIIa of the Periodic Table, Cu, Coulomb potential Z / r of ions
(Where Z is the valence of the above ion and r is the ionic radius of the above ion) is the Coulomb potential of Cu ³⁺ :
It is characterized in that the raw material powder which is larger than 5.5 and contains the element M excluding Ge is sintered.

The element M is selected from V, Mo, Ta, Nb, Bi, Sb, Mn, Sn and W, which are metal elements having an ionized Coulomb potential Z / r of more than 5.5 in the ionized state. In the ionized state, these elements are V ⁵⁺ , Mo ⁶⁺ , Ta
^It has an ionic valence of ⁵⁺ , Nb ⁵⁺ , Mn ⁴⁺ , Sn ⁴⁺ , W ⁴⁺ , Bi ⁵⁺ , Sb ^{4+ and the} like.

The raw material powder includes the element A, the element B, the M, and
It can be Cu oxide, hydroxide, carbonate, sulfate or nitrate. This raw material powder is preferably a dried product of a precipitate containing the elements A, B, M and Cu produced by the coprecipitation method. This precipitate can be co-precipitated from a solution of the metal salts of the above elements A, B and Cu, for example nitrates, using a precipitating agent, for example oxalic acid.

Furthermore, before sintering, dry powder of this precipitate 850
It is preferable to perform heat treatment at a temperature of 950 ° C. for 12 hours or more in an oxygen-containing atmosphere.

In practice, sintering is generally carried out at a temperature between about 400 ° C. and about 1100 ° C., preferably at a temperature of 800-950 ° C. for a period of 6 hours or more. The main sintering may be performed after crushing the obtained pre-sintered body. The maximum sintering temperature is preferably about 100 ° C. lower than the melting point of the oxide of each element. As an example, Y
In the case of -Ba-Cu-O system, the temperature is about 800 ° C to about 990 ° C.
It is preferable to sinter for 5 hours. Further, the above-mentioned sintering is preferably performed in an oxygen atmosphere.

Action The reason why the superconducting material according to the present invention has a higher critical current density Jc than the conventional complex oxide superconducting material is considered as follows.

That is, the Coulomb potential of Cu ³⁺ ions, which is directly related to the superconducting properties of the conventionally known complex oxide superconductor: Coulomb potential Z / r of ions larger than 5.5.
By substituting a part of the Cu site with an element M having (wherein Z is the valence of the ion and r is the ionic radius of the ion), the average Coulomb potential of the Cu site is lowered. The electron correlation between metal ions and oxygen ions is weakened, and the critical current density can be improved.

Also, in the region where the Coulomb potential of the Cu ³⁺ ion is larger than the Coulomb potential: 5.5, the electron correlation between the metal ion and the oxygen ion is strong, so that the influence on Tc is reduced, and the conventional composite oxide superconductor Even if the composition deviates, Tc does not decrease, and the critical current density can be improved while maintaining the same critical temperature as in the past.

Hereinafter, the present invention will be specifically described with reference to Examples, but the following disclosure does not limit the technical scope of the present invention.

Example 1 Y ₂ O ₃ having a purity of 99.9%, BaCO ₃ and CuO, and an oxide of each metal element M shown in Table 1 were used in a Y: Ba: Cu: M atomic ratio of 1: 2: 3 (1 −
x): 3x, mixed well. x is 0.033, 0.10
Each sample was prepared for three cases of 0 and 0.167.

After firing this mixture at 100 ° C for 2 hours or more, at 950 ° C
It was sintered in the atmosphere for 24 hours and gradually cooled. After sufficiently crushing this sintered body in a mortar, the pressure is 1.6 tons / cm ² and the diameter is 10φ and the thickness is 2 mm.
Was molded into a circular plate, which was then sintered at 960 ° C. for 6 hours in an oxygen-containing atmosphere and gradually cooled.

A sample of 1 × 2 × 10 mm was cut out from the obtained sintered body, an electrode was attached by gold vapor deposition according to a conventional method, and then the resistance was measured by a 4-point probe method in a cryostat. Temperature was measured using a calibrated Au (Fe) -chromel thermocouple. When the change in resistance was observed while raising the temperature little by little, it was found that the resistance drastically decreased at Tc shown in Table 1 in the case of each sample in which x was 0.167.

For comparison, the results obtained when the sample to which the oxide of the element M outside the scope of the present invention was added was subjected to the same treatment as described above are shown in Table 1 as a comparative example.

In Table 2, the ionic radius of each element M and the Coulomb potential Z / r are also shown for reference.

Example 2 Holmium nitrate, barium nitrate, and copper nitrate were mixed with Ho: Ba: Cu.
Was dissolved in distilled water at a molar ratio of 1: 2: 2.5 in atomic ratio (concentration = 10%). In this case, yttrium nitrate (Y (NO
₃ ) ₃ ], barium nitrate [Ba (NO ₃ ) ₂ ] and copper nitrate [Cu
(NO ₃ ) ₂ ] used were commercial grade reagents in the form of their hexahydrate, anhydrous salt and trihydrate.

On the other hand, oxalic acid was dissolved in ethanol to prepare a 5 wt% ethanol solution of oxalic acid.

When this ethanol solution of oxalic acid was stirred with a magnetic stirrer and the aqueous solution of the above salt was dropped into it, yttrium, barium and copper oxalate were precipitated.

Then, the precipitate obtained as described above was filtered, put in a quartz container, air-dried at room temperature for 5 hours, then put in a furnace and dried at 100 ° C. for 5 hours. Next, the obtained precipitate powder was added with an oxide of each element M shown in Table 2 below in an atomic ratio with respect to Y.
Added at a ratio of 1: 0.3.

After heat-treating (calcining) this mixed powder in the air at 900 ° C for 12 hours, the re-ground powder was press-molded at a pressure of 1 ton / cm ³ and sintered in an oxygen atmosphere at 950 ° C for 12 hours. It was gradually cooled at a cooling rate of 5 ° C / min.

The electrical resistance of the sample cut out from this disk was measured by the four-terminal method according to the conventional method to determine the critical temperature (K). The critical current (Jc) was measured at 77K. The results of these measurements are summarized in Table 2.

Example 3 The same operation as in Example 2 was repeated, but in this Example 3, vanadium nitrate used as a nitrate of the element M was added to distilled water at the same time as the above-mentioned holmium nitrate, barium nitrate and copper nitrate were dissolved. , All co-precipitated at the same time. The atomic ratio of Ho: Ba: Cu: V was 1: 2: 2.7: 0.3. Concentration is 1
0% was used.

In this case, Tc and Jc are 94 ° C and 11,000, respectively.
It was A / cm ² .

FIG. 1 is a graph summarizing the above results, in which the horizontal axis represents the Coulomb potential (Z / r) and the vertical axis represents the zero resistance starting temperature (Tci).

EFFECTS OF THE INVENTION As is clear from the above description, the composite oxide superconducting material of the present invention exhibits high Tc and Jc values.

The composite oxide superconducting material according to the present invention can be used as a bulk or as a wire rod, a tape or a device member, and further, by forming a thin film substrate on the substrate by sputtering or the like, a Josephson device , SQUID, superconducting magnet, various sensors, etc.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the Coulomb potential of ions and the critical temperature Tci (K).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuji Ueshiro 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (56) Reference JP-A-64-111765 (JP, A)

Claims (14)

[Claims] 1. A general formula: A _U B _V Cu _WX M _X O _Y (where A is an element contained in Group IIa of the periodic table,
B is an element included in Group IIIa of the periodic table, M is an ion of Coulomb potential Z / r (where Z is the valence of the above ion, and r is the ionic radius of the above ion).
^Has a Coulomb potential of Cu ³⁺ : greater than 5.5 and Ge
Elements other than, u, v, w, x and y are respectively
0.5 ≦ u ≦ 3, 0.5 ≦ v ≦ 2, 2 <w ≦ 4, 0.1 ≦ x ≦ 3
And represents a number in the range of 6 ≦ y ≦ 8) and containing an oxygen-deficient perovskite type crystal structure. 2. The element M is V, Mo, Ta, Nb, Bi, Sb, M.
The composite oxide superconducting material according to claim 1, which is at least one element selected from the metals represented by n, Sn, and W. 3. The element A is at least one element selected from Sr and Ba, and the element B is Y, La,
Eu Gd Tb is at least one element selected from Dy Ho Er Yb, and the element M is V, Mo, Ta, Nb, Bi, S
The composite oxide superconducting material according to claim 1 or 2, which is at least one element selected from the metals represented by b, Mn, Sn, and W. 4. The composite oxide is mainly Ba ₂ YCu ₃ M _x O _7-p (where p is a number in the range of 0.1 <p ≦ 1, M is V, Mo, Ta, Nb, Bi, 4. At least one element selected from Sb, Mn, Sn, and W) is included), and a composite oxide represented by any one of claims 1 to 3 is included. 7. The composite oxide superconducting material according to. 5. The composite oxide is mainly Ba ₂ HoCu ₃ M _x O _7-p (where p is a number in the range of 0.1 <p ≦ 1 and M is V, Mo, Ta, Nb, Bi, 4. At least one element selected from Sb, Mn, Sn, and W) is included), and a composite oxide represented by any one of claims 1 to 3 is included. 7. The composite oxide superconducting material according to. 6. The composite oxide is mainly composed of Ba ₂ DyCu ₃ M _x O _7-p (where p is a number in the range of 0.1 <p ≦ 1, M is V, Mo, Ta, Nb, Bi, 4. At least one element selected from Sb, Mn, Sn, and W) is included), and a composite oxide represented by any one of claims 1 to 3 is included. 7. The composite oxide superconducting material according to. 7. The complex oxide is mainly Ba ₂ ErCu ₃ M _x O _7-p (where p is a number in the range of 0.1 <p ≦ 1, M is V, Mo, Ta, Nb, Bi, 4. At least one element selected from Sb, Mn, Sn, and W) is included), and a composite oxide represented by any one of claims 1 to 3 is included. 7. The composite oxide superconducting material according to. 8. An element A included in group IIa of the periodic table, an element B included in group IIIa of the periodic table, Cu, and an ion Coulomb potential Z / r (where Z is the valence of the above ion). Is a number, and r is the ionic radius of the above ions), and the Coulomb potential of Cu ³⁺ is larger than 5.5 and the raw material powder containing the element M excluding Ge and the general formula: A _U B _V Cu _WX M _X O _Y (where u, v, w and x are 0.5 ≦ u ≦
3, 0.5 ≤ v ≤ 2, 2 <w ≤ 4 and 6 ≤ x ≤ 7), and a composite oxide superconducting material containing an oxygen-deficient perovskite type crystal structure as a main component Method. 9. The element M is V, Mo, Ta, Nb, Bi, Sb, M.
The method according to claim 8, characterized in that it is at least one element selected from n, Sn and W. 10. The raw material powder comprises the element A and the element B.
10. The method according to claim 8 or 9, wherein the above M and Cu are oxides, hydroxides, carbonates, sulfates or nitrates of Cu. 11. The method according to claim 8, wherein the raw material powder is a dried product of a precipitate containing the elements A, B, M and Cu produced by a coprecipitation method. The method according to any one of 1. 12. The method according to claim 8, wherein the preliminary sintering is performed before the sintering, and the sintering is performed after crushing the obtained preliminary sintered body. The method described in paragraph 1. 13. The method according to claim 8, wherein the sintering is carried out at a temperature of 950 ° C. for a time of 6 hours or more. 14. A dry powder of this precipitate, prior to sintering the precipitate, at a temperature of 850-950 ° C. under an oxygen-containing atmosphere.
The method according to any one of claims 8 to 13, characterized in that the heat treatment is performed for a period of time or longer.