JPH01157454A - Production of oxide superconducting sintered body - Google Patents

Abstract

PURPOSE:To produce the title dense oxide superconducting sintered body having superior orientation characteristic of crystals by molding a powder mixture consisting of oxide superconducting powder having plate structure and oxide superconducting powder having granular structure, and sintering the mixture. CONSTITUTION:A mixture contg. a larger amt. of Cu than a chemical soichiometric ratio (0.1-10mole per 1mole Ln) among each element constituting a perovskite type oxide superconductor expressed by the formula (wherein Ln is at least one kind of rare earth elements; delta is a number of deficient oxygen atom), is heated at a temp. higher than the m.p. of the superconductor and melted, and then crystallized by cooling and pulverized. Thus, oxide superconducting powder (A) having a plate structure having iota5 ratio of particle size in the direction of C face to the thickness of particles in the C axis direction is obtd. Then, a mixture of each starting material consisting of 60-95vol.% (A) and 40-5vol.% granular oxide superconducting powder (B) obtd. by precalcining each starting material of the formula at 800-980 deg.C and pulverizing after crystallization, is molded and sintered at 900-1040 deg.C in O2-contg. atmosphere, then, annealed at 300-700 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for producing an oxide superconducting sintered body that is dense and has excellent crystal orientation.

(Prior Art) In recent years, since it was announced that Ba-La-Cu-0-based layered velorskite oxides may have a high critical temperature, research on oxide superconductors has been conducted in various places. (Z, Phys, B Condensed Mat
ter64, 189-193 (1986)). Among them, defective perovskite type ((LnBa2Cu307-5) with oxygen defects represented by Y-Ba-Cu-0 system)
(δ represents oxygen defect and is usually 1 or less, [n is Y,
La1Sc, Nd15m, Eu, Gd.

At least one element selected from Dy, Ho, ErlTm, Yb and Lu, and a part of 8a can be replaced with sr or the like. The oxide superconductor of
ett.

Vol. 58 No. 9, 908-910).

Since such oxide superconductors are crystalline oxides, in order to create superconducting members of various shapes using this oxide superconductor, it is necessary to contain the constituent elements of the desired oxide superconductor. The starting materials are mixed in a predetermined ratio, this mixed powder is once calcined and crystallized to produce an oxide superconductor powder, and a molded body of the desired shape made using this oxide superconductor powder is fired. This is done by

By the way, in this oxide superconductor, superconducting current flows along the zero plane of the crystal, so simply molding and firing the oxide superconductor powder will cause the crystals to be arranged in random directions, making it difficult to obtain the desired current density. The problem is that it cannot be done.

On the other hand, this oxide superconductor powder has the property that it easily splits from the cleavage plane during pulverization and becomes plate-like powder. Therefore, this plate-like powder is used to orient the zero plane of the crystal during molding. Attempts have been made to improve the current density by increasing the current density.

(Problems to be Solved by the Invention) However, an oxide superconducting sintered body formed and fired using only such a plate-shaped oxide superconducting powder is difficult to form due to the shape of the powder. There is a problem that the density becomes low, and therefore, the effect of improving the critical current density cannot be sufficiently obtained by orienting the C-plane direction of the crystal.

In addition, in the plate-shaped oxide superconductor powder produced by crushing the calcined product of the oxide superconductor obtained by the solid-phase reaction as described above, the thickness of the particle in the C-axis direction is There is also the problem that the ratio of particle diameters is as small as about 2 to 5 on average, making it impossible to obtain a sufficient degree of orientation.

The present invention was made to address these conventional circumstances, and by orienting the zero plane of the crystal and improving the density of the sintered body, superconducting properties such as critical current density were improved. An object of the present invention is to provide a method for manufacturing an oxide superconducting sintered body.

[Structure of the Invention] (Means for Solving the Problems) The method for producing an oxide superconducting sintered body of the present invention comprises: an oxide superconductor powder having a plate-like structure; an oxide superconductor powder having a granular structure; The method is characterized in that the mixed powder is molded into a predetermined shape, and then the obtained molded body is fired at a predetermined temperature.

Many oxide superconductors are known, but
It is practically preferable to use a rare earth element-containing perovskite-type oxide superconductor that has a high critical temperature. The oxide superconductor containing a rare earth element and having a perovskite structure may be one that can realize a superconducting state, and may be LnBa COO (Ln is V lYblTm
, Er, Dy, Ho, 231-δ La, Sc, Nd, Sm, Eu, at least one selected rare earth element such as Gd, δ represents an oxygen defect and usually represents a number of 1 or less, 8a Part of it is Sr, Ca, etc., and part of Cu is D1, V, Cr, HnSFe.
, Ni, Zn, etc. can be substituted. Examples include oxides having a perovskite type in a broad sense, such as a defective velorskite type having oxygen defects such as ), and a layered perovskite type such as a 5r-ta-cu-o type. Rare earth elements are also broadly defined to include sc, y, and ULa elements. In addition to the Y-Ba-Cu-0 system, typical systems include
Y to Yb, T+n, Er.

Systems substituted with rare earth elements such as Dy, No, and Eu, 5
Examples include C-Ba-Cu-0 system, 5r-La-Cu-0 system, and systems in which Sr is replaced with Ba, Ca, etc.

The oxide superconductor powder having a plate-like structure used in the present invention has a ratio of the particle diameter in the C-plane direction to the particle thickness in the C-axis direction (hereinafter referred to as the plate-like ratio in the C-plane direction). But 5
It is preferable to use the above. If the plate ratio in the C-plane direction is less than 5, the crystal orientation during molding will decrease,
The effects of the present invention cannot be sufficiently obtained. Moreover, the average particle diameter in the C-plane direction is preferably 0.2 μm to 500 μm.

An oxide superconductor powder having such a plate-like structure is manufactured, for example, as follows.

First, constituent elements such as Y, 8a, and Cu are thoroughly mixed.

When mixing, oxides and carbonates such as Y203, BaC0, and CuO can be used as raw materials, as well as other compounds such as nitrates and hydroxides that are converted to oxides after firing. . Furthermore, oxalate obtained by a coprecipitation method or the like may be used. Normally, the elements constituting the Y-Ba-Cu-0-based oxide super 1f)9 are mixed so that the composition has a chemical M stoichiometric ratio, but during this mixing, the Cu component is If used in excess, oxide superconductor powder having a plate-like structure is likely to be formed. The amount of this CU acid component added is 0.1 mo1 to 1 mo1 to YllIlol.
A range of 0 mol is preferred.

Next, after thoroughly mixing the aforementioned raw materials, they are heated to a temperature equal to or higher than the melting point of the oxide superconductor to melt it. This melt is then cooled, and the oxide superconductor is crystallized during this cooling process. Note that this melting and cooling is preferably performed in an atmosphere that can supply sufficient oxygen.

Next, this oxide superconductor is pulverized using a ball mill, a sand grinder, or other known means.

At this time, the perovskite-type oxide superconductor produced under these conditions is divided from the cleavage 916 plane,
The result is a fine powder with an excellent plate-like ratio in the C-plane direction.

Further, the oxide superconductor powder having a granular structure used in the present invention preferably has a plate ratio of 3 or less in the C-plane direction. If the plate ratio in the C-plane direction exceeds 3, a sufficient filling effect between the oxide superconductor powders having a plate-like structure due to the granular powder cannot be obtained. Moreover, the average particle diameter in the C-plane direction is preferably 0.2 μm to 100 μm.

Oxide superconductor powder having such a granular structure is produced, for example, as follows.

First, the starting materials for the oxide superconductor as described above are mixed in basically a stoichiometric ratio.

It should be noted that during this mixing, there may be no problem even if there is a slight deviation due to manufacturing conditions and the like. For example, the standard composition is Ba 2 mol and Cu 3 mol for V 1a + ol, but in practice, Ba 2 ± 0.6 m for Y 1 m 0
ol, a deviation of about Cu3±0.4n+ol is not a problem.

Then, this mixture is calcined and crystallized at a temperature of about 800°C to 980°C. After this, if necessary in an oxygen-containing atmosphere, preferably lli! By heat treatment in a two-wire atmosphere or by slow cooling to about 300° C. in a similar atmosphere, oxygen can be introduced into the oxygen defects δ and the superconducting properties can be improved.

This heat treatment is usually performed at about 300°C to 100°C.

Next, this calcined product is pulverized in the same manner as the plate-shaped powder described above so as to satisfy the above conditions.

In the present invention, the mixing ratio of the oxide superconductor powder having a plate-like structure and the oxide superconductor powder having a granular structure is 60% to 60% by volume of the oxide superconductor powder having a plate-like structure in the mixed powder. It is preferable to set it within a range of 95%. If the volume ratio of the plate-shaped powder is less than 60%, the crystal orientation will decrease, and if it exceeds 95%, the density of the sintered body will decrease.

Then, using such mixed powder, a molded body having a desired shape is produced. Various methods such as press molding, slip casting, and injection molding can be used to produce this molded body, but press molding is particularly preferred because it increases the degree of orientation.

Next, this molded body is heated to a sintering temperature, for example, 900° C. to 1040° C., in air or an oxygen atmosphere, and fired to produce an oxide superconducting sintered body.

After sintering in this way, it is possible to slowly cool the material to near room temperature while supplying oxygen, or to perform annealing at a temperature of about 300°C to 100°C in an atmosphere where oxygen can be sufficiently supplied. preferable.

This allows oxygen to be introduced into the oxygen defects δ, improving superconducting properties.

(Function) In the method for manufacturing an oxide superconducting sintered body of the present invention, a mixed powder of plate-like powder and granular powder is used, so that the zero plane of the crystal can be oriented by the plate-like powder. At the same time, the filling effect of the granular powder makes it possible to improve the density of the sintered body, whereas the density of the sintered body decreases when using the plate-like powder alone. Therefore, by passing a current in the C-plane direction of this crystal, the critical current density can be greatly improved.

(Example) Next, examples of the present invention will be described.

Examples 1 to 3, Comparative Examples 1 to 2 First, Y2O3 powder, BaC03 powder and CUO powder with a particle size of 2 to 5 μm were mixed with YOl 513mol1%, 8aC
The mixture was hung for a predetermined test so that O327n+O1% and Cu060mo1% were reached, and after thoroughly mixing it, it was put into a platinum crucible and melted uniformly in an oxygen atmosphere at 1150°C for 48 hours, and then 0.2 After slow cooling at a cooling rate of °C/min, it was pulverized using a ball mill to obtain a particle size of 10 μl to 20 μm in the C-plane direction (average particle size of 12 μm),
A Y-Ba-Cu-0 based oxide superconductor powder having a plate-like structure with a particle thickness in the c-axis direction of 1 μI11 to 3 μm and an average plate-like ratio in the c-plane direction of 7 was obtained.

On the other hand, each starting material used for the oxide superconductor powder having the above-mentioned plate-like structure was 517 mo1% of YOl.

BaC0,33mo! %, CuO50mo1%, and after mixing thoroughly, heated to 900℃ in the atmosphere.
The fired product was further fired in oxygen at 800°C for 24 hours to react, and after introducing oxygen into the oxygen vacancies, it was crushed using a ball mill and classified to obtain an average particle size. A Y-Ba-Cu-0 based oxide superconductor powder having a plate-like structure with a diameter of 8 μm and an average plate-like ratio of 5 in the C-plane direction was obtained.

Next, the oxide superconductor powder having a plate-like structure and the oxide superconductor powder having a granular structure are mixed at the mixing ratio shown in Table 1, and these mixed powders are used for press molding ( A molded body having a shape of 1011111×10ml×2mm in thickness was produced using a press pressure of 200k (1/c), and then this molded body was fired at 950°C for 8 hours while supplying oxygen gas to form an oxide superconductor. A sintered body was produced.

Regarding the oxide superconducting sintered body obtained in this way, the sintered body density, critical temperature, critical current density in the direction perpendicular to the pressing direction at the time of forming the compact, and degree of orientation of the 0-plane of the crystal determined by X-ray diffraction, respectively. Measurements were made. The results are also shown in Table 1.

(Left below) As is clear from the previous table in Table 1, according to this example, a mixed powder of an oxide superconductor powder having a plate-like structure and an oxidizing dynamic Ti conductor powder having a granular structure is used. An oxide superconducting sintered body was obtained which satisfied both the sintered body density and the zero-plane orientation of the crystals, and thus had an excellent critical current density. On the other hand, in the case of only plate-like powder according to the comparative example, the sintered body density decreased, and in the case of only granular powder, C-plane orientation could not be obtained, so the critical current density was low in both cases.

[Effects of the Invention] As is clear from the above examples, the method for producing an oxide superconducting sintered body of the present invention is a method for producing an oxide superconducting sintered body having a plate-like structure and an oxide dynamic powder having a granular structure. Since the mixed powder is used, the obtained oxide superconducting sintered body satisfies both the sintered body density and the orientation of the zero plane of the crystal,
This makes it possible to obtain an excellent critical current density.

Applicant: Toshiba Corporation Agent Patent Attorney Suyama Sa

Claims (9)

[Claims] (1) A mixed powder of an oxide superconductor powder having a plate-like structure and an oxide superconductor powder having a granular structure is molded into a predetermined shape, and then the obtained molded body is fired at a predetermined temperature. A method for producing a featured oxide superconducting sintered body. (2) The ratio of the particle diameter in the c-plane direction to the particle thickness in the c-axis direction of the oxide superconductor powder having a plate-like structure is 5.
A method for producing an oxide superconducting sintered body according to claim 1, which is characterized in that the above is described above. (3) The oxide superconductor powder according to claim 1, wherein the oxide superconductor powder having a plate-like structure in the mixed powder is in a volume ratio of 60% to 90%. Method for producing solids. (4) The method for producing an oxide superconducting sintered body according to claim 1, wherein the molding of the mixed powder is performed by a press molding method. (5) The method for producing an oxide superconducting sintered body according to claim 1, wherein the firing is performed under a temperature condition of 900°C to 1040°C. (6) The method for producing an oxide superconducting sintered body according to claim 1, wherein the oxide superconductor is a perovskite-type oxide superconductor containing a rare earth element. (7) The oxide superconductor according to claim 1, wherein the oxide superconductor contains rare earth elements, Ba and Cu in an atomic ratio of substantially 1:2:3. A method for producing a sintered body. (8) The oxide superconductor is LnBa_2Cu_3O
_7_-_δ (Ln represents at least one element selected from rare earth elements, and δ represents an oxygen defect.) An oxide superconductor with an oxygen-deficient perovskite structure is claimed. A method for producing an oxide superconducting sintered body according to scope 1. (9) The above-mentioned oxide superconductor powder having a plate-like structure contains starting materials of each element constituting the oxide superconductor.
It is characterized in that it is formed by adding a Cu component in a larger amount than the stoichiometric ratio, heating it to a temperature higher than the decomposition temperature of the oxide superconductor to melt it during firing, and then crystallizing it. A method for manufacturing an oxide superconducting sintered body according to claim 7 or 8.