JP2003327498A - Needle-like crystal of oxide superconductor and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a production method for producing a needle-like crystal of R<SB>1</SB>Ba<SB>2</SB>Cu<SB>3</SB>O<SB>7</SB>and to produce the high quality needle-like crystal having a very low defect density. <P>SOLUTION: The needle-like crystal of the oxide superconductor expressed by formula: R<SB>1</SB>Ba<SB>2</SB>Cu<SB>3</SB>O<SB>7</SB>is obtained from a compacted formed body of an oxide powder having an atomic-ratio composition expressed by following formula: R<SB>1</SB>Ba<SB>2</SB>Cu<SB>3</SB>Te<SB>0.2</SB><SB>to</SB><SB>0.8</SB>Ca<SB>0.4</SB><SB>to</SB><SB>2.4</SB>O<SB>x</SB>(wherein, R is a rare earth element) by heat treating the compacted formed body at 900 to 990°C in a 5 to 100% oxygen atmosphere. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconductor needle crystal and a method for producing the same, and in particular, there are almost no defects in an oxide superconductor which are indispensable for realizing superconducting electronic devices. The present invention relates to a needle-like single crystal that does not have a needle-like shape, that is, a needle-like crystal of an oxide superconductor that is extremely close to a perfect crystal, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A single crystal of an oxide superconductor has a crystal structure in which conductive layers and non-conductive layers are alternately laminated, and each layer is formed by intrinsic Josephson coupling. In recent years, a single crystal switching element device using such an intrinsic Josephson effect has been proposed. This new single crystal switching device is almost 1% smaller than the one using the conventional Josephson junction.
/ 100 can be miniaturized, switching speed is about 100 times faster, and operating frequency is THz (terahertz)
High frequencies are expected.

At present, it has been clarified that a superconducting single-electron tunnel phenomenon in which electron pairs pass one by one occurs in a submicron crystal element produced by using needle crystals of an oxide superconductor. There is. Liquid helium temperature (4.2
It is necessary to operate at K), but if the number of laminated unit cells of the crystal is about 1000, the liquid nitrogen temperature (77
It is expected that a superconducting single electron pair device that operates in K) can be realized. In order to realize these devices, a single crystal that is defect-free or has very few defects is required.

From the practical viewpoint, an oxide superconductor has a (BiPb) ₂ Sr ₂ Ca ₂ supercritical temperature of about 110K.
Cu ₃ O ₁₀ , about 80 K Bi ₂ Sr ₂ Ca ₁ Cu ₂ O
₈ and about 90 K of R ₁ Ba ₂ Cu ₃ O ₇ (R represents a rare earth element) crystal structure is known.

The present inventors have found that (BiPb)_TwoSr_TwoCa
_TwoCu_ThreeO₁₀, Bi_TwoSr_TwoCa ₁Cu_TwoO₈composition
Is a compression molded product containing an element that reduces its melting point.
Without a quenching process or an amorphization process,
Very good crystallinity (BiPb)_TwoSr_TwoCa_TwoCu
_ThreeO₁₀And Bi_TwoSr_TwoCa₁Cu_TwoO₈Needle-shaped
He succeeded in growing crystals and had already filed a patent application.
(Japanese Patent Application No. 2001-38170 and Japanese Patent Application No. 2001-22
No. 4741).

On the other hand, R ₁ Ba ₂ Cu ₃ O ₇ (R is Y,
La, Nd, Sm, Eu, Gd, Dy, Ho, Er, T
selected from the group consisting of m, Yb and Lu) is (Bi
Pb) ₂ Sr ₂ Ca ₂ Cu ₃ 0 ₁₀ , Bi ₂ Sr ₂ Ca
Compared with ₁ Cu ₂ O ₈ , the pinning of magnetic flux quantum is stronger,
Since the critical current characteristics at high temperature and magnetic field are good, growth of high-quality needle crystals has been earnestly desired.

However, until now, such oxide superconductors R ₁ Ba ₂ Cu ₃ O ₇ (R is Y, La, Nd, Sm,
The growth of acicular crystals of the system (selected from the group consisting of Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) has not yet been realized because of difficulty in determining the composition of the starting material.

[0008]

Therefore, an object of the present invention is to establish needle-like crystals of R ₁ Ba ₂ Cu ₃ O ₇ and a method for producing the needle-like crystals, and to produce high-quality needle-like crystals with very few defects. , To open the way to the practical application of superconducting electronic devices that have not yet been realized. Specifically, the present invention is
The aim is to provide needle crystals of the oxide superconductor R ₁ Ba ₂ Cu ₃ O ₇ which have extremely few defects which are indispensable for realizing superconducting device elements.

Another object of the present invention is to provide an economical oxide superconductor capable of easily and efficiently producing needle crystals of the above oxide superconductor R ₁ Ba ₂ Cu ₃ O _7. It is an object of the present invention to provide a method for producing needle crystals of a conductor R ₁ Ba ₂ Cu ₃ O ₇ .

[0010]

In order to achieve the above-mentioned object, the present inventors have found that an oxide having an atomic ratio composition represented by R ₁ Ba ₂ Cu ₃ O ₇ (where R represents a rare earth element). Oxide containing a mixture of TeO ₂ and CaO at a constant ratio, that is, R ₁ Ba ₂ Cu ₃ Te containing a mixture of Te and Ca for each element constituting the oxide superconductor.
_{By using} an oxide having an atomic ratio composition of _{0.2 to 0.8} Ca _{0.4 to 2.4} O _x (R: rare earth element) as a starting material, R _{1 having} very few defects directly from the oxide. Ba
The inventors have found that it is possible to produce needle-like crystals of oxide superconductor of ₂ Cu ₃ O ₇ , and have reached the present invention.

The oxide superconductor of the present invention R ₁ Ba ₂ Cu ₃
The needle-like crystal having an O ₇ crystal structure has the following formula (1); R ₁ Ba ₂ Cu ₃ Te _{0.2 to 0.8} Ca _{0.4 to 2.4} O _x (1) (where R is It is obtained in an acicular form from an oxide having an atomic ratio composition represented by (indicating a rare earth element).

Preferably, the above oxide superconductor R₁Ba_Two
Cu_ThreeO₇In the needle crystal having a crystal structure, the above formula (1)
The compression molding of the oxide powder represented by
By heat treatment at 900 to 990 ° C. in an oxygen atmosphere
R from the molded body₁Ba _TwoCu_ThreeO₇Crystal structure needle
It is characterized in that it is obtained in the form of a crystal.

The oxide superconductor R ₁ Ba _{2 of the} present invention is also used.
An acicular crystal having a Cu ₃ O ₇ crystal structure is an oxide having an atomic ratio composition represented by the following formula (2); R ₁ Ba ₂ Cu ₃ O ₇ (2) (wherein R represents a rare earth element). 1 to 1 mol of the product, 0.2 to 0.8 mol of TeO ₂ and CaO in a proportion of 0.4 to 2.4 mol are combined and contained in a compression molded body in an oxygen atmosphere of 5 to 100%, and
By heat treating at 990 ° C., R ₁
It is characterized by being grown and formed into a needle-like crystal having a Ba ₂ Cu ₃ O ₇ crystal structure.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to suitable examples, but the invention is not limited thereto.
The acicular crystals of the oxide superconductor R ₁ Ba ₂ Cu ₃ O ₇ crystal structure of the present invention have the following chemical formula (1); R ₁ Ba ₂ Cu ₃ Te _{0.2 to 0.8} Ca _{0.4 to 2.4} O _x (1) (wherein R represents a rare earth element) is obtained in a needle-like form from an oxide having an atomic ratio composition.

The oxide represented by the above chemical formula (1) has an atomic ratio represented by the following formula (2); R ₁ Ba ₂ Cu ₃ O ₇ (2) (where R represents a rare earth element). It is a compression-molded product in which 1 mol of the oxide having the composition contains TeO _{2 in an amount} of 0.2 to 0.8 mol and CaO in a ratio of 0.4 to 2.4 mol.

The oxide superconductor of the present invention R ₁ Ba ₂ Cu ₃
The above formula (2) is used to produce needle-like crystals having an O ₇ crystal structure.
The combined inclusion of Te and Ca in the oxide having the atomic ratio composition represented by is most important from the viewpoint of effectively growing the acicular crystals.

The acicular crystals are oxide superconductors R₁Ba_TwoC
u_ThreeO₇And compression molded body R₁Ba_TwoCu_ThreeTe
_0.2-0.8Ca_0.4-2.4O_xDifference in melting point from
The larger the size, the faster the growth. Therefore, the melting point of the molded body
TeO to lower_TwoIs an oxide superconductor R₁Ba_TwoCu _Three
O₇It is extremely effective to include it in the composition
R₁Ba_TwoCu_ThreeO ₇TeO to 1 mol_TwoTo
By containing 0.2 to 0.8 mol, needle crystals are formed.
The effect is greatest near 0.5 mol.
Yes.

However, the needle crystals grown when TeO ₂ is contained do not contain Te. This grown needle crystal does not exhibit superconductivity, which means that Ba ₃ Te ₁ O ₆ is generated in the compact during the needle crystal growth process.
As a result, Ba is deficient and needle-like crystals having a R ₂ Cu ₃ O ₆ crystal structure grow.

On the other hand, in the present inventor, the composite body containing Te and Ca was added to the above-mentioned molded body to obtain R ₁ Ba ₂
A needle-like crystal having a Cu ₃ O ₇ crystal structure was grown. That is,
By adding Ca in addition to Te, (BaCa) ₃ Te ₁ O ₆ is generated in the molded body, and Ca partially replaces Ba site to supplement Ba deficiency. It is possible.

The Ca content is 2% of the Te content.
~ 3 times the most effective, R ₁Ba_TwoCu_ThreeO₇
CaO is contained in an amount of 0.4 to 2.4 mol per mol.
Is desirable. In this way, the combination of Te and Ca
Oxide superconductor R₁Ba _TwoCu_ThreeO₇
It is possible to effectively grow acicular crystals with a crystal structure.
It

Further, the oxide superconductor of the present invention R ₁ Ba ₂
When manufacturing a needle crystal having a Cu ₃ O ₇ crystal structure, it is necessary to optimize the heat treatment temperature and atmosphere. Specifically, the acicular crystals of R ₁ Ba ₂ Cu ₃ O ₇ can suitably grow at a heat treatment temperature of 900 to 990 ° C. and an oxygen ratio of 5 to 100% in the atmosphere. Particularly preferable optimum conditions are when the heat treatment temperature is 965 ° C. and the oxygen ratio in the atmosphere is 20%.

[0022]

[Examples] [Examples 1 to 5, Comparative Examples 1 to 6] [Effect of Compounding of Te and Ca] Oxide Superconductor Y₁B
a_TwoCu_ThreeO₇Oxide Y of an element constituting the crystal structure_TwoO
_Three, CuO and carbonate BaCO_ThreeFurther oxidation to each powder of
Thing TeO_TwoAnd carbonate CaCO_ThreePercentage of powder shown in Table 1
Compounded in Y₁Ba_TwoCu_ThreeTe_{0.2 ~ 0.8}
Ca_0.4-2.4O_xA mixed powder with an atomic ratio composition of 82
After calcination at 0 ℃ for 10 hours, diameter φ15mm, thickness 2m
m compression molded body was produced.

Here, the carbonate is used for the alkaline earth element because it is easier to handle than the oxide, and instead of the BaCO ₃ and CaCO ₃ powders, BaO,
CaO powder may be used.

The compression-molded body was subjected to 9% in a 20% oxygen atmosphere.
After heat treatment at 65 ° C. for 5 hours, it was cooled to room temperature over 12 hours to grow needle crystals from the compact. Table 1 shows the structure and length of the grown needle crystals.

[0025]

[Table 1]

It is understood that needle-like crystals grow when the content of Te is 0.2 to 0.8 mol, and the growth is best near 0.5 mol.

However, the needle-shaped crystals obtained in Comparative Examples 1 to 6 have a non-superconducting Y ₂ Cu ₃ O ₆ structure containing no Ba. This is because, as described above, Ba ₃ Te ₁ O ₆ is generated in the compact during the growth process of the needle-like crystals, and Ba is deficient.

On the other hand, in the needle-like crystals obtained in Examples 1 to 5, the needle-like crystals having the Y ₁ Ba ₂ Cu ₃ O ₇ crystal structure were grown by incorporating Te and Ca into the compact. I understand.

That is, by containing Te and Ca in combination, (BaCa) ₃ Te ₁ O ₆ is produced in the molded body, and a part of the Ba site is replaced with Ca to form Ba.
This is because the deficiency of

Therefore, the content of Ca is 2 to 3 of the Te content.
It is preferably about double to 0.4 to 2.4 mol. The needle-like crystals of Y ₁ Ba ₂ Cu ₃ O _{7 with} the best growth and good crystallinity are in the case of a composite content in which the Te content is 0.5 and the Ca content is 1.0.

Here, FIG. 1 shows the relationship between the electric resistance and the temperature of the needle-like crystals having the Y ₂ Cu ₃ O ₆ crystal structure and the needle-like crystals having the Y ₁ Ba ₂ Cu ₃ O ₇ crystal structure. This measurement is DC 4
It is the value measured by the terminal method. The Y ₁ Ba ₂ Cu ₃ O ₇ acicular crystal is a superconductor in which superconducting transition appears at around 90 K, but the Y ₂ Cu ₃ O ₆ acicular crystal does not show superconducting transition and is a normal conductor. Clearly the body.

[Examples 6 to 9] [Substitution of rare earth element] Oxide superconductor R ₁ Ba ₂ Cu ₃
In the O ₇ crystal structure, the rare earth elements R can be mutually substituted. R in the above Examples 1 to 5 is Y
In place of the above case, needle-like crystals were grown by using the rare earth elements shown in Table 2 in the same manner as in Examples 1 to 5 above. The results are shown in Table 2.

[0033]

[Table 2]

From Table 2, it has been clarified that the substitution of rare earth elements has no effect on the structure and growth of needle crystals.

[Examples 10 to 14 and Comparative Examples 7 to 9] [Effect of heat treatment temperature and atmosphere] Y ₁ Ba ₂ Cu ₃ Te
820 mixed powder of _0.5 Ca _1.0 O _x atomic ratio composition
After calcination at 10 ° C. for 10 hours, a compression molded body was produced. The compression molded body was heat-treated for 5 hours while changing the temperature and the oxygen ratio in the atmosphere shown in Table 3, and then cooled to room temperature over 12 hours to grow needle crystals from the molded body. Table 3 shows the length of needle-like crystals grown when the heat treatment temperature and the oxygen ratio in the atmosphere were changed.

[0036]

[Table 3]

From Table 3, the acicular crystals have a heat treatment temperature of 900.
It grows at ˜990 ° C. and grows best at 965 ° C. Further, the acicular crystals have an oxygen ratio of 5 to 5 in the atmosphere.
It grows at 100%, and the best growth occurs at 20%. Furthermore, the optimum conditions for heat treatment are a temperature of 965 ° C.,
It can also be seen that the optimum case is 20% of the acid cord in the atmosphere.

The present invention obtained in Examples 1 to 14 above
The needle crystal is an X-ray diffractometer (Rigaku RINT120
0), electron probe microanalyzer (Shimadzu EPM
A8705), energy dispersive spectrometer (PH
ILIPS EDAX PV9800)
The needle-shaped crystals are oxide superconductor R₁Ba_TwoC
u _ThreeO₇A single crystal structure of a crystal structure,
The element Te, which lowers the melting point of the mother phase, is contained during manufacturing.
It became clear that it did not.

[0039]

The oxide superconductor of the present invention R ₁ Ba ₂ Cu
₃ O ₇ acicular crystals are high-quality acicular crystals with extremely few defects, and by providing such acicular crystals, it is possible to realize a superconducting electronic device which has been theoretically proposed at present but has not yet been realized. You will be able to contribute to the development. In other words, high frequency
It is possible to realize a high-speed switching element, and in particular, it is possible to bring a breakthrough to information related technology.

The oxide superconductor R ₁ Ba _{2 of the} present invention is also used.
Method for producing a needle-like crystals of Cu ₃ O ₇ are those which can be acicular crystals efficiently growing the oxide superconductor R ₁ Ba ₂ Cu ₃ O ₇ of the present invention, superconducting electronics field Can contribute to.

[0041]

[Brief description of drawings]

FIG. 1 shows Y ₁ Ba ₂ Cu ₃ O ₇ needle crystals of the present invention, and Y
₂ is a diagram showing the relationship between temperature and electric resistance, showing the superconductivity of ₂ Cu ₃ O ₆ needle crystals.

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Claims (3)

[Claims] 1. The following formula (1); R ₁ Ba ₂ Cu ₃ Te _{0.2 to 0.8} Ca _{0.4 to 2.4} O _x (1) (wherein R represents a rare earth element). An acicular crystal having an oxide superconductor R ₁ Ba ₂ Cu ₃ O ₇ crystal structure, which is obtained in an acicular form from an oxide having an atomic ratio composition represented by: 2. The oxide superconductor R ₁ Ba _{2 according to} claim 1.
In a needle-like crystal having a Cu ₃ O ₇ crystal structure, a compression molded body of the oxide powder represented by the above formula (1) is used in an amount of 5 to 100%.
Oxide superconductor R ₁ Ba, which is obtained in the form of needle crystals of R ₁ Ba ₂ Cu ₃ O ₇ crystal structure from the compact by heat treatment at 900 to 990 ° C. in an oxygen atmosphere. Needle-like crystals having a ₂ Cu ₃ O ₇ crystal structure. 3. TeO ₂ is added to 1 mol of an oxide having an atomic ratio composition represented by the following formula (2); R ₁ Ba ₂ Cu ₃ O ₇ (2) (wherein R represents a rare earth element). Of 0.2 to 0.8 mol and CaO in a ratio of 0.4 to 2.4 mol in a compression molded body of 900 to 100% in an oxygen atmosphere of 5 to 100%.
By heat treating at 990 ° C., R ₁
Ba ₂ Cu ₃ O ₇ oxide superconductor R ₁ Ba ₂ Cu characterized by being grown and formed into a needle crystal having a crystal structure.
_A method for producing needle-like crystals having a ₃ O ₇ crystal structure.