JPH0778530A - Oxide superconductor and preparation thereof - Google Patents

Abstract

PURPOSE:To provide an oxide superconductor and new preparation method to prepare the oxide superconductor at pressure close to atmospheric pressure wherein the oxide superconductor has as a main phase a superconductive compound which has a limitless layer relating structure. CONSTITUTION:After prepared by a method selected from sol-gel method, coprecipitation method, and gas deposition method, uniform and highly reactive precursor particles or amorphous substance having a metal composition ratio shown as (A, Ln) aCub or AaCub is presintered at 700-800 deg.C to give a solid solution or a composite material. Continuously, the obtained material is sintered in a temperature range; 850-1200%oC; at pressure near the atmospheric pressure while oxygen concentration in the atmosphere being controlled. In the composition, A stands for one or more metals selected from alkaline earth metal elements, Ln for one or more metals selected from IIIa group metal elements, and a and b have a relation; 0.5<=b/a <=.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconductor having a superconducting compound having an infinite layer-related structure as a main phase, and a novel method for producing such an oxide superconductor.

[0002]

2. Description of the Related Art Oxide superconductors are superior to metal-based superconductors.
It has a higher critical temperature than other
Attempts have been made to develop oxide superconductors. High critical temperature
Perovskite type oxide superconductor having Tc
Crystal structure (RE) Ba₂ Cu ₃ O_x And (RE) Ba₂ 
Cu_Four O_y (However, RE is Y and lanthanoid series rare
One or more elements selected from the group consisting of earth elements) etc.
Of rare earth elements-alkaline earth elements-copper oxide
Known as one. In addition, the rare earth elements of the above oxides
In which Bi is replaced by Bi (or Tl)
Bi₂ Sr₂ Ca _n-1 Cu_n O_{2n + 4}) Also for Tc =
85K (low temperature phase) or Tc = 110K (high temperature phase)
It is regarded as a promising substance having a high critical temperature.
In addition to the above-mentioned copper oxide superconductor, BaPb_1-z Bi_z 
O₃ Compounds are oxide superconductors with perovskite structure
Has been extensively studied.

However, the above oxides have the following drawbacks, respectively, and in reality, new developments of oxide superconductors are desired. That is, (RE) Ba ₂ C
u ₃ O _x , (RE) Ba ₂ Cu ₄ O _y , Bi ₂ Sr ₂ C
Copper oxide-based superconductors such as a _n-1 Cu _n O _{2n + 4} have a complicated multilayer structure, and have a drawback that the process for producing such an oxide superconductor tends to be complicated. . Among the above copper oxide superconductors, (RE) Ba ₂ Cu ₃ O _x is easily deteriorated by moisture and carbon dioxide in the atmosphere, and (RE)
Ba ₂ Cu ₄ O _y is a low temperature stable phase and is said to be easily decomposed at high temperatures. Furthermore, in oxide superconductors containing Tl and Pb, the toxicity of these elements is high and there is a problem in terms of sanitary environment.

On the other hand, (Sr, Ca) CuO₂ And (Sr, L
a) CuO₂ Infinite layer structure such as
(Including the structure having a part) Oxide superconductor has copper oxide
It has the most basic structure of superconductors, and is a copper oxide type.
Special attention as the ultimate crystal structure in superconductors
There is. Research on infinite layer structure is a new development of oxide superconductor
As the basis for the
Various relations with are being studied. Yamane et al.
Is Ca_1-x Sr_x CuO₂poles at (x = 0.14 and 0.09)
Report that an infinite layer structure can be generated with a limited composition
("Journal of the Ceramic Society of Japan, 97
(1989) P143-147). In addition, Takano et al.
Below SrCuO₂ Phase transition to an infinite layer structure, and
And superconducting phase and infinite layer structure are deeply related.
("Powder and powder metallurgy" vol. 39 (199
2), No. 5, P337-340). Furthermore, Yoshikawa et al.
Is SrCuO₂ Doping of rare earth elements into the sample under high pressure
See, infinite layer Sr_1-x La_x CuO ₂ Was successfully synthesized
Reported ("Powder and powder metallurgy" Vol. 39 (19
1992), No. 5, P341-344).

[0005]

However, in the reports so far, there has been a problem that in manufacturing oxide superconductors having an infinite layer structure, ultrahigh pressures of tens of thousands of atmospheric pressure are required, which is not practical. It was According to the report of Yamane et al., An oxide having an infinite layer structure is obtained even under normal pressure, but it is reported that this oxide is a semiconductor and does not have superconductivity. The present invention has been made under these circumstances, and an object thereof is to produce an oxide superconductor having a superconductor compound having an infinite layer structure as a main phase under a pressure near atmospheric pressure. It is to provide a new method and such an oxide superconductor.

[0006]

Means for Solving the Problems The present invention capable of attaining the above-mentioned object means that the metal in the oxide is burned under a pressure near atmospheric pressure and while controlling the oxygen concentration in the atmosphere. It is an oxide superconductor in which the formal ratio of the elements is shown below. (A, L _n ) _a Cu _b or A _a Cu _b, where A: one or more selected from alkaline earth metal elements L _n : one or more selected from Group IIIa metal elements 0.5 ≦ b / a ≦ 3

Further, the method of the present invention which has achieved the above-mentioned object means that when an oxide superconductor composed of the above-mentioned metal element ratio is produced, it is selected from the sol-gel method, the coprecipitation method and the gas deposition method. After preparing homogeneous and highly reactive precursor fine particles or an amorphous substance having the above metal composition ratio by any method selected, 700 to 80
It has a gist in that it is calcined at 0 ° C. to form a solid solution or a mixture, and subsequently, it is baked in a temperature range of 850 to 1200 ° C. while controlling the oxygen concentration in the atmosphere at a pressure near atmospheric pressure. .

[0008]

The method of the present invention is constructed as described above, but in short, it is homogeneous and reactive with the above metal composition ratio by any method selected from the sol-gel method, the coprecipitation method and the gas deposition method. If the precursor fine particles or the amorphous substance having a high temperature are generated, the oxygen concentration in the atmosphere can be controlled at 8
The present invention has been completed by finding that a desired oxide superconductor can be obtained by firing under the condition of a temperature range of 50 to 1200 ° C. The oxide superconductor obtained in the present invention is not a single layer of infinite layer structure. Further, the “formal ratio” means a ratio defined by raw materials.

According to the studies made by the present inventors, it was found that if the firing is performed while controlling the oxygen concentration in the atmosphere, the expected firing effect can be obtained without increasing the oxygen concentration so much. In particular, if the firing is carried out by including at least a part of the atmospheric conditions in which the oxygen concentration is lower than that of the air, then the objective of the present invention can be achieved by firing in an oxidizing atmosphere having an oxygen concentration of 3% or more. I found it. The term "atmosphere conditions in which the oxygen concentration is lower than the atmosphere" includes a non-oxidizing atmosphere, and the non-oxidizing atmosphere is not only a neutral atmosphere but also an extremely small amount that does not contribute to oxidation. It may contain oxygen (for example, oxygen concentration: about 10 ⁻⁴ %). Further, the “oxidizing atmosphere having an oxygen concentration of 3% or more” includes a pure oxygen atmosphere.

The oxide superconductor to which the present invention is directed has a superconducting compound represented by the above metal element ratio as a main phase. The atomic ratio of (A, Ln) or A and Cu (b
/ A) is required to be 0.5 ≦ b / a ≦ 3, and if it is out of this range, the amount of the superconducting compound becomes small and desired superconducting characteristics cannot be obtained. From the viewpoint of the expression of the superconducting compound, the atomic ratio [Ln / (A + Ln)] of Ln to (A + Ln) is preferably 0.1 or less.

On the other hand, the alkaline earth metal represented by A is
Although Ca, Sr, Ba, Ra and the like can be mentioned, and one or more of them can be used in the present invention, but from the viewpoint of the expression of the superconducting compound, A is preferably Sr or Sr and Ca. When A is both Sr and Ca, the atomic ratio (Sr / Ca) of both is preferably 1 or more. Further, the group IIIa metal element represented by Ln includes, in addition to Sc and Y, lanthanoid series rare earth elements and actinoid series rare earth elements. One or more of these elements may be used, but from the viewpoint of expression of a superconducting compound. Particularly preferable element is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements.

In producing the oxide superconductor of the present invention, it is first necessary to prepare precursor fine particles or an amorphous substance which are homogeneous and have high reaction activity. In order to prepare such a precursor, any of the sol-gel method, the coprecipitation method or the gas deposition method may be adopted as described above, but the sol-gel method is particularly preferable, According to this method, a uniform and reactive precursor can be easily obtained.

In the method of the present invention, the calcination temperature range is set to 7
The reason why the temperature is set to 00 to 800 ° C. is that it is effective for generating the superconducting phase in the main firing. Further, in the method of the present invention, firing is then performed at a pressure near atmospheric pressure and while controlling the oxygen concentration in the atmosphere, but the firing temperature must be 850 to 1200 ° C. That is, when the firing temperature is lower than 850 ° C., the oxide having the metal element composition ratio represented by the above does not exhibit superconductivity,
Further, even if it exceeds 1200 ° C, it does not exhibit superconductivity.

If firing is performed while controlling the oxygen concentration, the object of the present invention can be achieved even if firing is performed in an oxidizing atmosphere having an oxygen concentration of 3% or more as the final firing atmosphere. This is because the valence of copper is reduced and the melting point of the oxide is lowered to promote the reaction by previously firing in an atmosphere with a low oxygen concentration. However, in this state, the carrier concentration is insufficient, so oxygen must be added.
The minimum required oxygen concentration at this time is 3%.

In the present invention, it is effective to employ hot isostatic pressing (HIP) treatment in an oxidizing atmosphere after firing. This is because the oxygen concentration for adding the carrier can be increased as compared with the normal pressure firing. The temperature in the case of adopting the HIP treatment is 500 to 500 because the purpose is achieved even if the temperature is lower than the lower limit of the firing temperature due to pressurization, and the decomposition of the infinite layer structure does not occur even if the temperature is higher than the upper limit. A temperature range of 1500 ° C is sufficient. Further, the pressure during the HIP treatment needs to take into consideration the relationship with the above temperature, but the objective is sufficiently achieved at about 100 to 2000 atm, and in any case, ultrahigh pressure is not required as in the conventional case.

The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and any design changes made in view of the spirit of the preceding and the following will not be considered. It is included in the technical scope.

[0017]

【Example】

Example 1 Ca (OC ₂ H ₅ ) ₂ , Sr (OC ₂ H ₅ ) ₂ , Y (OC ₃
A metal alkoxide such as H ₇ ) ₃ and Cu (OCOH ₃ ) ₂ acetate were used as starting materials. Among them, Ca (OC ₂ H ₅ ) ₂ and Sr (OC ₂ H ₅ ) ₂ are mixed solvent of ethoxyethanol and ethylene glycol, and Y (OC ₃ H ₇ ) ₃ and Cu (OC
OH ₃ ) ₂ is N, N-dimethylformamide (DMF)
And dissolved in a mixed solvent of propanol and propanol, respectively. By mixing these solutions, Ca _0.3-x Y _x Sr _0.7 Cu _1.0 O ₂
A mixed solution having a composition (x = 0.1 to 0.3) was prepared. After hydrolyzing the mixed solution under acidic conditions of acetic acid, 60 to 80
Polycondensation was allowed to proceed in the temperature range of ° C to obtain a viscous sol. Subsequently, it was dried at 300 ° C. and calcined at 700 ° C. to obtain a raw material powder for firing. Pellets were prepared using this powder. The pellets were fired in the heat treatment pattern shown in FIG. 1 while changing the firing conditions of Processes I and II as shown in Table 1 below. In the atmosphere gas, the balance when the oxygen concentration is changed is nitrogen gas. As a result, when the oxygen concentration is 3% or more in process II (except when the oxygen concentration is 3% in process I)
, All samples showed diamagnetism.

[0018]

[Table 1]

Comparative Example 1 Using a pellet prepared in the same manner as in Example 1, without using Process I, only Process II was fired in the atmosphere at 1000 ° C. for 600 min to obtain a sample. This sample did not show diamagnetism in the measurement of magnetic susceptibility. Comparative Example 2 Using the pellets produced in the same manner as in Example 1, Process II
No sample was added, but only Process I was fired under a nitrogen gas atmosphere at 950 ° C. for 600 min to obtain a sample, and this sample did not show diamagnetism in the measurement of magnetic susceptibility.

Comparative Example 3 Using the pellets produced in the same manner as in Example 1, the pellets were fired in Process I under a nitrogen gas atmosphere at 950 ° C. for 5 min, and then in Process II under a nitrogen gas atmosphere at 1000 ° C. for 600 min. When a sample was obtained by firing under the conditions described above, this sample did not show diamagnetism in the measurement of magnetic susceptibility.

Example 2 Pellets prepared in the same manner as in Example 1 were used (however,
The composition was Ca _0.2 Y _0.1 Sn _0.7 CuO ₂ ), and the effect was investigated by changing the conditions shown in Table 1 above. First, in the sample obtained by changing the firing temperature, the firing time and the atmosphere gas in Process I, and then firing in Process II in a pure oxygen atmosphere at 1000 ° C. for 600 min, the above-mentioned conditions are the magnetic susceptibility. Was investigated for the effect on.

FIG. 2 is a graph showing the relationship between the firing temperature and the magnetic susceptibility of the sample in Process I. The atmosphere in Process I at this time was pure nitrogen gas, and the firing time was 30 min. As is clear from this result, the susceptibility of the sample increases as the firing temperature in Process I increases.

FIG. 3 is a graph showing the relationship between the firing time and the magnetic susceptibility of the sample in Process I. The firing temperature in Process I at this time was 950 ° C., and the atmosphere was pure nitrogen gas. As is clear from this result, the magnetic susceptibility of the sample depends on the firing time in Process I from 2 min to 5 mi.
It can be seen that it becomes larger as n. However, when the firing time was changed from 5 min to 1 min, the magnetic susceptibility was decreased.

FIG. 4 is a graph showing the relationship between the atmospheric gas and the magnetic susceptibility of the sample in Process I. The firing temperature in Process I at this time was 950 ° C., and the firing time was 5 minutes. As is clear from this result, the magnetic susceptibility of the sample increases as the oxygen concentration in Process I decreases (especially 3% or less).

FIG. 5 shows a sample (a) obtained in the process I under a nitrogen gas atmosphere at a firing temperature of 950 ° C. for a firing time of 5 min, and without performing the process II, and a process II (in a pure oxygen atmosphere). , 1000 ° C, 10 min) is a graph showing the result of powder X-ray diffraction of each sample. In FIG. 5, “ortho” means an orthorhombic compound that is usually formed under atmospheric pressure. The change shown in FIG. 5 is considered to be due to the fact that the atmosphere in Process I is non-oxidizing.

FIG. 6 shows a change in the magnetic susceptibility of the sample obtained in the process I under a nitrogen atmosphere at a firing temperature of 950 ° C. for a firing time of 5 min and then in the process II when the atmosphere gas (oxygen concentration) was changed. It is a graph which shows. As is clear from this result, the susceptibility increases as the oxygen concentration in Process II increases.

FIG. 7 shows that in the process I, the firing temperature was set to 950 ° C. in the nitrogen gas atmosphere and the firing time was set to 5 minutes, and then in the process II, the firing temperature was set to 1 in the pure oxygen atmosphere.
6 is a graph showing the relationship between the electrical resistance ratio and the temperature of a sample obtained at 000 ° C. and a firing time of 600 min. The electrical resistance ratio is the ratio of the electrical resistance R of the sample to the electrical resistance R ₀ (0.28Ω) at room temperature (RT) [R / R ₀ (R.
T)]. As is clear from these results, the electric resistance ratio increased like a semiconductor as the temperature decreased to 80K, and showed a diamagnetic transition at 80K. However, the electric resistance did not suddenly become 0 as it was, and the electric resistance decreased again at around 35K and reached 0 at 20K. The results also showed that the obtained sample contained two superconductor phases.

[0028]

The present invention is constituted as described above, and it becomes possible to produce an oxide superconductor having a formal metal element ratio in the oxide as described above under a pressure near atmospheric pressure. It was

[Brief description of drawings]

FIG. 1 is a graph showing an example of a heat treatment pattern.

FIG. 2 is a graph showing the relationship between the firing temperature and the magnetic susceptibility of the sample in Process I.

FIG. 3 is a graph showing the relationship between the firing time and the magnetic susceptibility of the sample in Process I.

FIG. 4 is a graph showing the relationship between the atmospheric gas and the magnetic susceptibility of the sample in Process I.

FIG. 5 is a powder X-ray diffraction result showing the influence of the presence or absence of Process II on the powder composition.

FIG. 6 is a graph showing the relationship between ambient gas (oxygen concentration) and sample magnetic susceptibility in Process II.

[FIG. 7] In process I, the baking temperature was set to 950 ° C. and the baking time was set to 5 min in a nitrogen gas atmosphere, and then the process
6 is a graph showing the relationship between the electric resistance ratio and the temperature of the sample obtained in II under a firing temperature of 1000 ° C. and a firing time of 600 min in a pure oxygen atmosphere.

Claims (10)

[Claims] 1. An oxide superconductor, which is fired under a pressure near atmospheric pressure while controlling the oxygen concentration in the atmosphere, and the formal ratio of metal elements in the oxide is shown below. (A, Ln) _a Cu _b or A _a Cu _b, where A: one or more selected from alkaline earth metal elements Ln: one or more selected from Group IIIa metal elements 0.5 ≦ b / a ≦ 3 2. The oxide superconductor according to claim 1, wherein A is Sr or Sr and Ca. 3. The oxide superconductor according to claim 2, wherein when A is both Sr and Ca, the atomic ratio (Sr / Ca) of both is 1 or more. 4. The atomic ratio of Ln [Ln / (A + L) in the total (A + Ln) of the alkaline earth metal and the group IIIa metal element.
n)] is 0.1 or less, The oxide superconductor in any one of Claims 1-3. 5. The oxide superconductor according to claim 1, wherein Ln is at least one element selected from the group consisting of Y and a lanthanoid series rare earth element. 6. The method for producing the oxide superconductor according to any one of claims 1 to 5, according to any one method selected from a sol-gel method, a coprecipitation method and a gas deposition method. After preparing homogeneous and highly reactive precursor fine particles or amorphous substance having the metal composition ratio shown in Fig. 3, calcination is performed at 700 to 800 ° C to form a solid solution or a mixture, and then a pressure near atmospheric pressure is applied. And controlling the oxygen concentration in the atmosphere while firing in a temperature range of 850 to 1200 ° C., a method for producing an oxide superconductor. 7. The manufacturing method according to claim 6, wherein the firing is performed by including an atmospheric condition in which the oxygen concentration is lower than that of the atmosphere in at least one step. 8. The manufacturing method according to claim 7, wherein the atmospheric condition in which the oxygen concentration is lower than that in the atmosphere is a non-oxidizing atmosphere. 9. A manufacturing method in which after firing under the atmospheric conditions of claim 7 or 8, firing is performed with an oxygen concentration of 3% or more. 10. After the firing, further in an oxidizing atmosphere, 5
The manufacturing method according to any one of claims 5 to 11, wherein the hot isostatic pressing treatment is performed in a temperature range of 00 to 1500 ° C.