JPH02141420A - Oxide superconductor - Google Patents

Abstract

PURPOSE:To provide an oxide superconductor having high critical current density by mixing an aq. soln. of water-soluble salt of each component corresponding to a compsn. of a rare-earth element-Ba-K-Cu type superconductor, with a soln. of oxalic acid in a lower alcohol and using a precipitate produced from the mixture. CONSTITUTION:An aq. soln. of each water-soluble salt of each component corresponding to a compsn. expressed by the formula I (R is a rare earth element; x is 0.01-0.2) is prepd. Concrete examples for the water-soluble salt are yttrium nitrate, barium nitrate, potassium nitrate, copper nitrate, etc. Then, the aq. soln. is mixed with a soln. of oxalic acid in a lower alcohol (e.g., methanol). Produced precipitate comprising oxalate of each component is used as the starting material powder, which is calcined provisionally, molded and then sintered. Thus, an oxide superconductor consisting of an oxide expressed by the formula II (wherein y is 6.7-6.93), which has a higher critical current density than that of superconductors obtd. by a solid phase process and has a same compsn., is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has the following compositional formula: RBaz-XKXCu, IOy
(However, R is a rare earth element, X is 0.01 to 0.2,
Regarding a superconductor made of an oxide represented by
The present invention relates to a superconductor made of an oxide expressed by the above compositional formula and produced from a precipitate prepared by a specific method (excluding oxygen).

[Conventional technology]

Currently, various oxide-based superconducting materials are known, one of which has the composition formula: RBaz-XKX CL+30y
(However, R is a rare earth element, X is 0.01 to 0.2,
y represents 6.7 to 6.93).

Research into the practical application of this material as a superconductor by forming it into elongated bodies such as wire rods and tapes is actively being conducted. Generally, this shaping process is carried out in the steps of calcination of the raw material powder, pulverization of the calcined body, shaping of the calcined body powder, and sintering of the molded body.

On the other hand, the superconducting phenomenon exhibited by superconductors is a phenomenon in which electrical resistance completely disappears below a certain temperature, but the temperature at which this superconducting phenomenon occurs (critical temperature) differs depending on the material. Materials with high critical temperatures are easy to cool, so
The development of materials with as high a critical temperature as possible has been particularly active recently.

As can be seen in the composition of the oxide represented by the above compositional formula, pure RBaC can be obtained by substituting a part of Ba among the constituent elements of the original RBaCu O system with K.
It has a higher critical temperature than the uO system.

[Problem to be solved by the invention]

In the production of oxide-based superconducting materials, there is a method using the in-phase method to obtain raw material powder for calcination of raw material powder. As is well known, the solid phase method involves mixing and pulverizing raw material powders in a mortar, ball mill, or the like.

Attempts have also been made to manufacture oxide superconductors having the above composition from raw material powder obtained by a solid phase method.

However, in the same phase method, there is a limit to the ability to grind and uniformly mix raw material powders. In addition, the solid phase method has the disadvantage that the particle size of the raw material powder is large and the solid phase reaction proceeds only near the contact area of the particles. Therefore, there is a limit to the critical current of a superconductor manufactured using raw material powder obtained by the solid phase method.

However, in addition to having a high critical temperature, it was also difficult to fabricate a superconductor made of an oxide with a superconducting state class element, where X represents 0101 to 0.2, and y represents 6.7 to 6.93. It was discovered that the critical current was improved by doing so, and the present invention was completed.

The oxide superconductor of the present invention is RBat-*K*Cu
* Mix an aqueous solution of water-soluble salts of each component with a composition of Ov (R, x, y have the same meanings as above) and a lower alcohol solution of oxalic acid, and use the resulting precipitate made of oxalate as a raw material powder. It is characterized in that it is produced by. Since the superconductor of the present invention produces raw material powder by mixing an aqueous solution of water-soluble salts of each component corresponding to the above composition and a lower alcohol solution of oxalic acid, the raw material powder obtained by the solid phase method is compared. In general, a finer powder with a uniform distribution of component elements can be obtained. Therefore, it is possible to fabricate a superconductor in which fine particles of each component are uniformly densely packed.
The critical current is higher than that of a superconductor made of an oxide based on a solid-phase method using raw material powder.

In the present invention, composition: RBaz-x KX Cu3
(However, the upper limit of current that can be passed (critical current) is also an important point in the practical application of ceramic materials. For practical use, it must be made into a wire, for example, but ceramic materials have a small current that can be passed per unit cross-sectional area.) Therefore, the key to practical application is how high a critical current can be obtained.

Therefore, there is still room for improvement in the critical current in RBaz-x KX Cu, Oy-based superconductors.

Therefore, in view of the above points, the object of the present invention is to
The object of the present invention is to provide a KX C1130y superconductor that exhibits a higher critical current than conventional superconductors.

[Means to solve the problem]

In order to achieve the above object, the present inventors made extensive research efforts and found that RBaz-x Kx Cu, (However,
R is a rare earth element, and X is 0. By mixing an aqueous solution of a water-soluble salt of each component corresponding to the composition of OI ~ 0.2) and a lower alcohol solution of oxalic acid, a precipitate consisting of the oxalate of the above component was prepared as a raw material powder. as RB
az-++ Kx Cu, lOy (However, R is rare earth, and R and x have the same meanings as above). Rare earth elements for R include yttrium, lanthanum, neodymium, promethium, samarium, europium, gadolinium, dysprosium, and holmium. Examples include.

Therefore, in the present invention, R1 (az-8KX Cu,
The water-soluble salt of each component corresponding to the composition (where R and x have the same meanings as above) is not particularly limited as long as it is soluble in water. Examples of lanthanum components such as lithium and acid-resistant yttrium include lanthanum nitrate and lanthanum chloride. Examples of the barium component include barium chloride and barium nitrate; examples of the potassium component include potassium chloride and potassium nitrate; and examples of the copper component include cupric chloride and copper nitrate.

In particular, when R is yttrium, the composition excluding oxygen is Y:Ba::Cu, and therefore, for example, yttrium nitrate, barium nitrate, potassium nitrate, or copper nitrate is used.

As the lower alcohol serving as a solvent for the lower alcohol solution of oxalic acid to be mixed with the aqueous solution of the water-soluble salt 2, methanol, ethanol, propatool, etc. may be used. The amount of oxalic acid may be sufficient as long as it can convert each water-soluble salt in the aqueous solution of the water-soluble salt to oxalate.

By mixing an aqueous solution of a water-soluble salt and a lower alcohol solution of oxalic acid, the oxalate of each component is precipitated. For example, in the Y Ba K Cu system described above, oxalate is a precipitate whose raw material powders are yttrium oxalate, barium oxalate, potassium oxalate, and copper oxalate.

There are no particular limitations on the method for producing an oxide superconductor from a raw material powder that is a precipitate of oxalate, and any conventionally known method may be used. For example, the process may be a solid-state process that includes the steps of raw material powder, temporary sintering, molding, and sintering.

Next, an example of the method for manufacturing the oxide superconductor of the present invention will be described.

Therefore, pH adjustment is not necessarily necessary and may be omitted.

After that, the precipitate in the mixture is collected by filtration,
If the formed precipitate is filtered immediately after mixing, there will always be crystals that are too small to be filtered, so it is preferable to leave the precipitate for about 24 hours to grow into crystals large enough to be filtered.

After standing, the resulting precipitate is collected by filtration and dried. Drying may be performed, for example, by applying hot air at about 140° C. for about 2 hours, or by vacuum drying at about 100° C. for about 2 hours.

In this way, a raw material powder with a desired composition is obtained.

Next, the raw material powder is temporarily formed into a pellet shape or the like as it is or under pressure, and then calcined. This calcination is carried out for the purpose of uniformly mixing each component at a molecular level by reaction diffusion at high temperatures, and the temperature is appropriately determined depending on the type and blending ratio of the raw material powder used.
(In the case of , u, and Oy systems, the temperature is usually 850°C or higher, preferably 850 to 950°C, especially around 900°C. The calcination time depends on the temperature, but first, RBa2-XK,
Aqueous solutions of water-soluble metal salts corresponding to each compounding composition are prepared in the composition of Cuz (I, R, and x have the same meanings as above). The molar concentration of each aqueous solution is determined by the rare earth element selected for R, A16 for X, etc., but it is 0.0
01 to 0.1 molar concentration. A lower alcohol solution of oxalic acid is prepared by using a lower alcohol as a solvent, and adding 0.0 ml of oxalic acid to about 200 to 800 ml of the lower alcohol solution.
About 3 to 0.14 mol, preferably about 0.07 mol of the latter dissolved in about 400 ml of the former is used. Each aqueous solution is preferably simultaneously and gradually added to the obtained oxalic acid alcohol solution to precipitate each oxalate.

Here, if the pH of the mixed solution of the water-soluble salt aqueous solution and the oxalic acid alcohol solution is lower than 2, alkaline earth metals such as Ita become soluble. For example, aqueous ammonia or the like is added to a certain alcohol solution, and the pH is adjusted so that the pH of the mixture becomes 2 or more. In fact, for example, barium nitrate and barium oxalate are hardly soluble in lower alcohols, usually for about 2 to 40 hours, preferably about 6 to 15 hours. Further, this calcination causes unnecessary organic components, water vapor, etc. remaining in the raw material powder to disappear.

The calcined body is crushed again. By this pulverization, a fine calcined powder having an average particle size of 0.1 to 2 culms is obtained.

The calcined fine powder thus obtained is molded into a desired shape (for example, a coil shape, a wire shape, a tape shape, etc.), and finally the molded product is sintered. Sintering is preferably performed under the following conditions. That is, the temperature is 900 to 970°C (particularly 920 to 970°C)
°C), and other conditions may be substantially the same as those for the calcination.

By the above procedure, an oxide superconductor in a coil shape, a wire shape, a tape shape, etc. is manufactured.

[Example/Experiment example]

The oxide superconductor of the present invention will be described in detail below using Examples, but the present invention is not limited to the following Examples.

Examples 1 to 4 In the composition of RBa2-XKXCu, 3, the rare earth element of R and the value of , a mixed amount of aqueous solutions are prepared respectively. Next, an aqueous solution of each of the metal salts described above is gradually added to an oxalic acid alcohol solution as shown in Table I to simultaneously precipitate each component of oxalate.

Here, in Example 1, the pH of the precipitation solution at the time of mixing is around 1, and since the solution contains 20% by volume of an aqueous metal solution, ammonia water (28% ) was added dropwise at a rate of 0.35 ml and 175 seconds, and the pH of the resulting solution was adjusted to 4.6.

After the mixed product solution was left to stand for 24 hours, the precipitate was collected by filtration, and the precipitate was dried by applying hot air at 140°C for 2 hours. The raw material powder of each composition ratio obtained by drying was
The calcined product was calcined at 00°C for 6 hours in an oxygen stream, cooled in a furnace, and the resulting calcined product was pulverized to obtain a fine powder with an average particle size of about 1.0 units. Next, shape this fine powder into the desired shape (e.g. coil shape).
Finally, the molded product was sintered at 950°C for 12 hours in an oxygen stream to produce an oxide superconductor. The critical flow density (critical temperature 77K) of the obtained superconductor is as shown in Table 2.

Comparative Examples 1 to 4 In order to make it clearer that the critical current density of the superconductor obtained in the above example is excellent, the solid phase method was performed using the same S1 configuration as described in [Prior Art]. A similar experiment was conducted using the raw material powder obtained using .

That is, the raw material powder is temporarily molded by the solid phase method, and heated to 900°C.
After calcining in an oxygen stream for 6 hours and pulverizing the calcined product, it was molded into the same shape as in the example, and the molded product was heated at 950°C for 12 hours.
Sintered in an oxygen stream for an hour. The critical current density (critical temperature 77K) of the obtained superconductor is as shown in Table I.

As is clear from Table I, the critical current density of the oxide superconductor according to the present invention is much higher than that of the oxide superconductor obtained using the in-phase method with the same composition. .

(The following is a blank space) [Effects of the invention] As explained above, the oxide superconductor of the present invention has RBa
z−x Kx Cu3 (However, R is a rare earth element,
X represents 0.01 to 0.2) A precipitate consisting of the oxalate of the above component produced by mixing an aqueous solution of a water-soluble salt of each component corresponding to the composition and a lower alcohol solution of oxalic acid is used as a raw material. RBaz-x KX prepared as powder
Cu30y (However, R is a rare earth element, X is 0.0
1 to 0.2, and y is 6.7 to 6.93). It exhibits a critical current that is extremely higher than that of superconductors, and exhibits excellent superconducting properties for this type of superconductor.

Claims (2)

[Claims] (1) Mix an aqueous solution of water-soluble salts of each component corresponding to the composition of RBa_2_-_xK_xCu_3 (where R represents a rare earth element and x represents 0.01 to 0.2) and a lower alcohol solution of oxalic acid. RBa_2_-_xK_xCu_3O_y (where R is a rare earth element, x is from 0.01 to 0.2, and y is from 6.7 to
A superconductor comprising an oxide represented by the composition formula (representing 6.93). (2) The superconductor according to claim 1, wherein R in the compositional formula is yttrium (Y).