JPS63252925A - Production of superconductive material - Google Patents

Abstract

PURPOSE:To obtain a superconductive material of compound metallic oxide having excellent stability in good reproducibility, by adding one or more amines not to form a complex with copper to an aqueous solution comprising copper and a specific metallic salt, changing the pH to a basic side and adding a weak acid. CONSTITUTION:One or more amines (e.g. triethylamine) not to form a complex with copper are added to an aqueous solution which is obtained by dissolving nitrates or carbonates of Cu, Ba and one or more rare earth elements selected from Y, Sc, La, Lu, Yb, Tm, Er, Ho, Dy, Cd and Sm and pH of the aqueous solution is changed to a basic side (preferably pH >=8). Then the aqueous solution is mixed with a weak acid such as oxalic acid or carbonic acid to give a starting raw material sufficiently blended in the order of atom. Then the raw material is previously calcined, pressed into pellets, sintered and optionally annealed in O2 to give the titled material having crystal structure of oxygen deficient perovskite type shown by the formula (M is one or more of the above- mentioned rare earth element; x=1-3; y=0.5-1.5; z=0-3).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing superconducting materials. More particularly, the present invention relates to a coprecipitation method for producing composite metal oxide superconducting materials containing copper as a constituent element.

(Prior Art) Recently, many types of composite metal oxide superconducting materials with extremely high critical temperatures have been reported.

For example, C.W., Chu, et al. of Hyuston University in the United States reported that the electrical resistance disappeared in 1994 in a barium-yttrium-copper-oxygen oxide, and it became a superconducting state (Phys, Rev. , Lett, +vo
1.5B, p, 90B-907 (1987)) - also,
Barium-M-copper-oxygen complex metal oxide (M is Sm
5Eu, Gd, Dy, Ho, E r %T m s Y
It has been reported that these become complex metal oxide superconducting materials with critical temperatures around 90°C (for example, in 2013).

1[1tazawa at at, Jap, Jou
rnal of Appl, Phys.

vol, 26. (1987)).

These various superconducting substances with high critical temperatures are produced by weighing the required amount of oxides, carbonates, etc. of each metal component, pulverizing and mixing them using an agate mortar, etc., and then firing them in an electric furnace. It is made by However, this method has the disadvantage that the components cannot be mixed sufficiently and the properties of the produced superconducting material are not very good.

In response, it has been proposed to adopt a coprecipitation method as a starting material preparation method that can improve the mixing of each component element down to the atomic order (for example, J, G, Bed
norz and, A, Muller, Z.
Phys, B.

vol, 64. p, 189-193 (198B)
).

In the production of a barium-lanthanum-copper-oxygen composite metal oxide superconducting material, barium, lanthanum,
Mix the required amounts of aqueous solutions of each nitrate of copper, add an aqueous solution of hesoxalic acid to precipitate barium, lanthanum, and copper in the form of oxalates, and filter to obtain the starting material for firing. That is what it is.

According to this method, a mixed starting material of extremely high quality can be obtained in terms of mixing of component elements, but the disadvantage is that the prepared starting material contains only a considerably small amount of barium compared to the amount charged.

The reason for this is that both the raw element nitrate solution and the oxalic acid aqueous solution are acidic, so the solution after coprecipitation and mixing is also acidic, but barium oxalate has considerable solubility in the acidic range. It is.

Furthermore, since the solubility of barium oxalate is highly dependent on pH, the above method has the disadvantage that it is almost impossible to stably obtain a starting material for calcination with a specific composition.

(Problems to be Solved by the Invention) The above drawbacks can be avoided by controlling the co-precipitation solution to be basic, since the solubility of barium oxalate is considerably low in basicity. However, if a metal hydroxide such as potassium hydroxide or sodium hydroxide is used as a pH 11 adjuster to make the coprecipitate basic, the starting material will contain metal impurities such as Na, which is not preferable. These metal impurities can be removed by washing the precipitate with a large amount of water, but barium oxalate is soluble even in cold water (approximately 1 g/1 cold water).
1) Washing with a large amount of water may reduce barium.

In addition, when ammonia water is used as a pH adjuster to make it basic, the copper contained as a component element is
Ammonia water cannot be used because it generates and dissolves an ammonia complex (Cu (NH3)42+).

As a result of intensive studies to solve the above-mentioned conventional drawbacks, the present inventors have found that when amines are used as a pH 1M adjuster for the coprecipitate, a starting material for firing with a specific composition can be obtained with good reproducibility. The present invention was achieved by discovering that this can be done.

Therefore, a first object of the present invention is to provide a method for producing a superconducting material that can stably obtain the characteristics of a composite metal oxide superconducting material containing copper as a component.

A second object of the present invention is to provide a starting material that is sufficiently mixed on the atomic order before firing to obtain a stable composite metal oxide superconducting material containing copper as a component element. be.

A third object of the present invention is to provide a particularly excellent pH 2 moderation method when preparing a starting material before firing of a composite metal oxide superconducting material containing copper as a component element by a coprecipitation method. It is in.

(Means for Solving the Problems) The above-mentioned aspects of the present invention are such that when producing a composite metal oxide superconducting material containing copper as a component element, each component is added to an aqueous solution in which a salt of each component element is dissolved. In the coprecipitation method, at least one amine selected from the group of amines that do not form a complex with copper is added to an aqueous solution in which the salts of the respective component elements are dissolved, and the aqueous solution is added with a substance that causes the copper to co-precipitate. This was achieved by a method for producing superconducting materials characterized by shifting the pH to the basic side and then adding a weak acid capable of co-precipitating each component element.

In the present invention, the copper-containing composite metal oxide superconducting material has an oxygen-deficient m-perovskite crystal structure represented by the general formula BaXMyCu309Z. Here, M is Y, SC% La, Lu5Yb, Tm, Er,
HO, Dy% At least one or two or more rare earth elements selected from the group of Cd and Sm, and X is 1 to
3. y is 0.5-1°5.2 is 0-3.

The salt of the composite metal oxide is appropriately selected from salts with high solubility in water, and it is particularly preferable to use a nitrate in order to obtain a composite metal oxide with high solubility and purity. In the present invention, a predetermined amount of these highly soluble salts can be dissolved in water and mixed, but oxides and carbonates of various component metals can also be dissolved in nitric acid or the like. The aqueous solution containing each component element cleaved in this way is usually acidic.

Generally, a salt with low solubility is precipitated from the aqueous solution, and in many cases, the salt with low solubility is oxalate. Therefore, it is a conventional method to add oxalic acid to the aqueous solution, but the solubility of Ba oxalate on the acidic side is high, and this is impossible, especially at pH>2.

Therefore, if the aqueous solution is made alkaline by adding Na OH'P K OH, the oxalates (or hydroxides) of each component element will co-precipitate, but it will be contaminated with metals such as Na and K. If you try to avoid this and thoroughly clean the product, barium oxalate and the like will dissolve little by little, and the raw material composition before firing will shift.

On the other hand, since ammonia forms a complex with copper and dissolves in water, the pH of an aqueous solution cannot be adjusted with ammonia.

(Function) However, in the present invention, since an amine that does not form a complex with copper is used, the pH can be adjusted without causing the above-mentioned disadvantages, and the pH of the aqueous solution is moved to the alkaline side by the amine. By adding a weak acid that forms a water-insoluble salt, such as oxalic acid or carbonic acid, it is possible to obtain a starting material for calcination with a specific composition with good reproducibility.

Particularly good results are obtained when the pH is set to 8 or higher.

The amine that can be used in the present invention can be appropriately selected from amines that do not form a complex with copper. Such amines include, for example, triethylamine,
Examples include trimethylamine, dimethylamine, methylamine, ethylamine, triethanolamine, and hydroxytetraethylamine, and among these, triethylamine is particularly preferred.

(Effects of the Invention) Unlike the method of mechanically grinding and mixing, the method of the present invention obtains a mixture by a chemical method, so that the degree of mixing is perfect. Furthermore, since the pH is shifted to the alkaline side using the amine and coprecipitation is carried out, there is no possibility of contamination with insoluble metals. Furthermore, since the solubility of the precipitate can be kept low, it is possible to obtain starting materials having the same composition and being uniformly mixed with good reproducibility. The composite metal oxide obtained by firing such homogeneous raw materials has the desired composition, so it not only has excellent performance as a superconducting material, but also has excellent performance as a superconducting material.
It also has extremely high performance as a target material used as a raw material for manufacturing thin films in electronic devices and the like.

(Example) The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited thereto.

Example 1 A barium-yttrium-copper oxide, Ba2YCu309-δ, was prepared as a composite metal oxide superconductor.

Calculated amount of BaCO3 to obtain 0.1 mole of the target substance
, Y2O3, and CuO were weighed and completely dissolved with a small amount of nitric acid, and then pure water was added to make a total volume of 1°Oml.

On the other hand, the oxalic acid used for coprecipitation is 5a2yCu309-
For δ, Ba is divalent, Y is trivalent, and Cu is mostly precipitated as hydroxide, so the calculated amount (11-0.65 per 1.3 mol)
mole) is not necessary.

Here, 0.5 mol of oxalic acid is dissolved in pure water, and 100 mol of oxalic acid is dissolved in pure water.
ml. Add 250g of triethylamine ((C
2H5)3N) was added. Triethylamine is immiscible with water, but reacts with oxalic acid to form the amine salt of oxalic acid. Into the resulting liquid separated into two layers, Ba, Y
% Cu melt, a blue precipitate immediately formed. The precipitate was aged overnight and then filtered with suction using an aspirator to serve as a starting material for calcination.

The starting materials were placed in a crucible and kept at 500°C for 2 hours to evaporate the oxalic acid, then heated to 900°C and pre-calcined for 6 hours, taken out from the furnace and crushed again to yield approximately 1,000 kg.
The pellets were pressed at a pressure of /cm2 and sintered in a furnace at 950°C for 4 hours.

The taken sample was further annealed for 12 hours in pure oxygen at 700°C.

After partially dissolving the obtained sample in nitric acid, quantitative analysis was performed using plasma emission spectrometry, and it was confirmed that the desired composition had been obtained.

As a comparative example, a calculated amount of 13 a CO3, Y203 to obtain 1 mole of Ba2YCu309-δ 0°
, and CuO powders were weighed and mixed in ethanol in an agate mortar to obtain starting materials for firing.

This pellet was subjected to the same pellet preparation process except for the step of 2 hours at 500°C to evaporate the oxalic acid, and a superconductor was obtained.

Each sintered product was found to have an oxygen-deficient perovskite crystal structure by X-ray diffraction.

For each, superconductivity onset transition temperature Tc (temperature at which electrical resistivity begins to show superconductivity transition) and transition temperature width ΔTc (
Table 1 shows the results of measuring the temperature range when the rate of change in electrical resistivity from a normal value near Tc goes from 90% to 10%.

Table 1 Tc ΔTc Invention 96K 1.2K”
Example 2 in 94K 3: Lanthanum-Storage F as a composite metal oxide superconductor
-umu copper-oxide, (La0.925SrO,075
)2Cu04-1 was produced.

Calculated amount of La2O3 to obtain 0.1 mole of the target substance
, 5rco3, and CuO were weighed and completely dissolved with a small amount of nitric acid, and then pure water was added to make the volume 100 ml.

In this system as well, the amount of oxalic acid is 0.785 molar equivalent (0.3
(925 mol) was necessary for the calculation, but for the above-mentioned reason, 0.3 mol was weighed out and dissolved in pure water to make 100 ml. 150 g of triethylamine was added thereto.

Add La into the liquid separated into two layers obtained above.

As soon as the S r s Cu solution was poured, a blue precipitate formed. The precipitate was aged overnight, filtered with suction using an aspirator, and used as a starting material for calcination.

The starting materials were placed in a crucible, kept at 500°C for 2 hours to remove oxalic acid, and then heated to 900°C and pre-calcined for 6 hours. After taking it out of the furnace, it is crushed again and weighs approximately 1,000 kg.
Press with a pressure of g/cm2 to make pellets 1.050
It was sintered in a furnace at .degree. C. for 24 hours. The taken sample was further annealed for 12 hours in pure oxygen at 700°C.

When the obtained sample was partially dissolved in nitric acid and quantitatively analyzed using plasma emission spectrometry, it was confirmed that the desired composition had been obtained.

As a comparative example, (Lao, 925S, ro, 075)
Calculated amounts of each powder of La 203.5rC03 and CuO were weighed so as to obtain 1 mol of 2Cu04-rO, and mixed in an agate mortar in ethanol to obtain a starting material for firing.

This was subjected to exactly the same pellet manufacturing process except for the 2-hour process at 500°C to evaporate the oxalic acid, and a superconductor was obtained.

It was confirmed by X-ray diffraction that each sintered product had a K2NiF4 type perovskite-like structure.

For each, superconductivity starting transition temperature Tc (temperature at which electrical resistivity begins to show superconducting transition) and transition temperature width ΔTc
Table 2 shows the results of measuring (temperature at which the rate of change of electrical resistivity from a normal value near Tc goes from 90% to 10%).

Table 2 Tc ΔTc Invention 40K 1.5K・-5'
37 K 5 K Although the present invention has been described above in detail based on Examples, the amine is not limited to triethylamine used here, but other amines may be used.

In addition, oxalate ions (Co
Although ol was used, other suitable ions such as carbonate ion (CO32-) can also be used.

Furthermore, in this example, the manufacturing method was described only for two types of composite oxide superconductors, but the present invention can also be applied to other systems, such as
It goes without saying that this technology can be applied to almost all systems, such as barium-ytterbium-copper-oxygen oxides and barium-erbium-copper-oxygen oxides, and its application to these systems is not excluded. stomach.

Claims (1)

[Scope of Claims] 1) Co-precipitation method in which a substance for co-precipitating each component is added to an aqueous solution in which salts of each component element are dissolved in the production of a composite metal oxide superconducting material containing copper as a component element. At least one amine selected from the group of amines that do not form a complex with copper is added to the aqueous solution in which the salts of the respective component elements are dissolved.
A method for producing a superconducting material, which comprises adding a seed amine to shift the pH of the aqueous solution to the basic side, and then adding a weak acid capable of co-precipitating each component element. 2) The method for producing a superconducting material according to claim 1, wherein the amine added to the aqueous solution is a tertiary amine. 3) The method for producing a superconducting material according to claim 2, wherein the tertiary amine is triethylamine. 4) The method for producing a superconducting material according to any one of claims 1 to 3, wherein the weak acid added for coprecipitation is oxalic acid.