JP4885001B2 - Compound superconductor and method for producing the same - Google Patents

Description

The present invention relates to a superconductor comprising a compound having a mayenite type crystal structure and a method for producing the same.

Since the discovery of the superconducting phenomenon of mercury in 1911, various compounds exhibiting superconductivity have been found to date and put into practical use as superconducting magnets and magnetic sensors (SQUID). Especially in recent years
A superconducting compound having a superconducting transition temperature Tc exceeding 100 K was found in a group of perovskite-type copper oxide compounds (Non-Patent Document 1), and the possibility of realizing a room-temperature superconductor was increased, and energetic research and development was promoted. (Non-Patent Documents 2 and 3).

As a result, in addition to the perovskite-type copper oxide compound group, MgB ₂ (T _c = 39K) (Non-patent Document 4), Sr ₂ RuO ₄ (T _c = 0.93K) (Non-patent Document 5), Na _0.3 CoO ₂・ 1.3H ₂ O
Although a new superconducting compound such as (T _c = 5K) (Non-Patent Document 6) has been found and a group of compounds exhibiting superconductivity has expanded, a room-temperature superconductor has not yet been discovered.

Realization of room temperature superconductivity requires further discovery of a new group of compounds exhibiting superconductivity. One candidate of such a compound group is an electride compound group, and among them, 12CaO · 7Al ₂ O ₃ (hereinafter referred to as C12A7) electride, which is thermally and chemically stable, is important. The C12A7 crystal having a mayenite type crystal structure is a stable compound found in a two-component phase equilibrium diagram of CaO and Al ₂ O ₃ and is widely put into practical use as a component of alumina cement.

The inventors of the present invention related to a C12A7 compound including a reactive oxygen species and a method for producing the same (Patent Document 1), a C12A7 compound single crystal containing a high concentration of reactive oxygen species, and a C1 free of bubbles.
A patent application has been filed for an invention relating to the FZ method for growing 2A7 single crystals (Patent Document 2).

In addition, as a method for producing a C12A7 compound that includes an active oxygen species, amorphous calcium aluminate is used as a raw material, and an ni partial pressure of 4 × 10 ⁴ Pa or higher is applied in an atmosphere of 1 or more.
A method of heating to 100 ° C. or more and a melting temperature or less (Patent Document 3), a method of spraying using oxygen radical-containing calcium aluminate powder on a substrate having high oxygen ion conductivity at a high temperature (Patent Document 4), calcia A source, an alumina source, and a silica source are mixed, and then heated to produce an inorganic compound having a mayenite structure via a katoite structure (Patent Document 5)
)It has been known.

By heat-treating the pre-treatment substance C12A7 single crystal in Ca metal vapor or Ti metal vapor, it is possible to include electrons in C12A7 at a high concentration. We have C12A
Patent application has been filed for an invention relating to a method of clathrating high-concentration electrons in US Pat.
. From the viewpoint that heat treatment can be performed at a higher temperature, the heat treatment time can be shortened, and TiO _x formed on the sample surface as a result of oxygen / electron substitution is an oxygen ion conductor, and the substitution reaction further proceeds. Steam treatment is superior to Ca metal steam treatment (Patent Document 7).
.

In addition, the inventors of the present invention have high electrical conductivity C12A7 and the same crystalline compound and a method for producing the same (Patent Literature 8) and a method for producing a conductive mayenite type compound (Patent Literatures 9 to 12).
Filed a patent application for the invention.

J.G.Bednorz and K.A.Muller Z. Phys.B64, 189 (1986) Tsuda Ikuo, Nasu Shinichiro, Fujimori Satoshi, Shiratori Kiichi Revised edition "Electrically Conductive Oxides", p350-452, Hanabobo (1993) Maekawa, Y., Applied Physics 75, 17 (2006) J. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani and J. Akimitsu, Nature 410, 63 (2001) Y.Maeo, H.Hashimoto, K.Yoshida, S.Nishizawa, T.Fujita, J.G.Bednorz, F.Lichyenberg, Nature 372, 532 (1994) K.Takada, H.Sakurai, E.Takayama-Muromachi, F.Izumi, R.A.Dilanian, and T.Sasaki, Nature 422, 53 (2003) Japanese Patent Laid-Open No. 2002-3218 Japanese Patent Laying-Open No. 2003-040697 JP 2003-226571 A JP 2005-35858 A JP 2006-83009 A Republished 2005-000741 PCT / JP2006 / 322991 JP 2005-314196 A JP 2006-327894 A WO2005 / 0777859A1 WO2006 / 129674A1 WO2006 / 129675A1

The unit cell of the C12A7 crystal contains two formulas, and the chemical formula is [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2O.
^2- . [] Indicates the composition of the skeletal structure, and the skeleton structure contains 12 polyhedral cages.
(Inner diameter about 0.4 nm) exists. 2O ²⁻ indicates oxygen ions included in the polyhedral cage, and the oxygen ions (O ²⁻ ) are loosely bonded to calcium ions constituting the cage wall. "is called. The free oxygen ions can be replaced with electrons by reduction treatment of C12A7 such as heat treatment in Ca metal vapor or Ti metal vapor.

In addition, a part or all of the free oxygen ions (O ²⁻ ) in C12A7 are replaced with one or more anions selected from OH ⁻ , oxygen ion radicals (O ⁻ ), and super oxygen ion radicals (O ₂ ⁻ ). That is, [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ² + 2yA] (A
Is one or more of OH ⁻ , O ⁻ or O ₂ ^— included in the cage, 0 ≦ x ≦ 1, y =
1-x), these inclusion anions are C12 using Ca metal vapor or Ti metal vapor.
By the reduction treatment of A7, it can be replaced with electrons.

[Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 4e ⁻ , which results from substituting all clathrate anions with electrons, occupies a specific crystal site, serves as an anion, and the skeleton structure and ions It can be regarded as being combined. Such compounds are called “electrides”.

In the C12A7 electride, a state where electrons are confined in the cage is connected to form an electron conduction band (hereinafter referred to as “cage conduction band”), and when two or more electrons per unit lattice are packed in the cage, Shows metallic conduction. The cage conduction band has a relatively narrow bandwidth, electrons exist in high density near the Fermi level, and the electron-lattice interaction is large. It is considered that a superconducting state can be realized by increasing.

In the perovskite-type copper oxide compound group, a high-temperature superconductor compound having a Tc exceeding 100 K has been found, but a room temperature superconductor has not yet been found in spite of much research and development. A powerful strategy for developing room-temperature superconductors is to look at materials from a different perspective, find new superconducting compounds, and expand the system of superconducting compounds.

In the group of perovskite-type copper oxide compounds, two-dimensionally bound copper ions are responsible for electrical conduction, and transition to a superconductor at a superconducting transition temperature or lower. From this fact, superconductivity is expected to appear even in a compound having an electronic conduction band composed of a one-dimensional electronic state. The present inventors have discovered that a superconducting state can be realized with a C12A7 electride having a mayenite type crystal structure, which is one of the compounds satisfying this condition. In a mayenite structure including a nanometer-sized cage structure, when electrons are included in the cage, the electrons have a one-dimensional electronic state.

The present inventors have so far conducted C12A7 single crystals grown by the Choco Lavsky method in a titanium metal vapor so as to include C12A7 electrified by inclusion of electrons exceeding 10 ²¹ cm ^{−3 in the} single crystals. Succeeded in manufacturing the ride. The single crystal showed metallic electrical conductivity and an electrical conductivity of about 1500 S / cm at room temperature. However, since the raw material melting during the crystal growth is performed in the iridium crucible, the single crystal grown from the crucible contains about 5 × 10 ⁻¹ atomic% of iridium which is a magnetic ion. The “Kondo state” was generated by the sd interaction between electrons and magnetic ions, and the superconducting state was not realized. The present inventors have discovered that a superconducting state is manifested in a C12A7 electride that does not contain magnetic ions such as manganese, iron, iridium, and platinum.

That is, the present invention has the chemical formula [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ² + 2yA + 2 {1-
(X + 2y)} e ⁻ ] (A has a mayenite type crystal structure represented by a cage, one or more of OH ⁻ , O ⁻ or O ₂ ⁻ , 0 ≦ x + 2y ≦ 0.5) A compound superconductor characterized by being a compound. In the chemical formula, x and y are O ²⁻ and A ^2, respectively.
Is a numerical value indicating the amount of each component.

In the present invention, the chemical formula is [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ² + 2yA] (A is one or more of OH ⁻ , O ^{− and} O ₂ ^{− included in} a cage. , 0 ≦ x ≦ 1, y = 1−x
The compound having the mayenite type crystal structure represented by the above formula is prepared by a method not containing magnetic ions, and 50 atomic% or more of the total component amount (x + 2y) of O ²⁻ and A included in the cage of the compound is an electron. A method for producing the above-described compound superconductor, wherein

In addition, the present invention is the above method for producing a compound superconductor, wherein the compound is a single crystal prepared by a floating zone method (FZ method).

The present invention provides a superconductor composed of C12A7 electride as one of a group of novel superconducting compounds exhibiting superconductivity, and contributes to expanding the system of superconducting compounds.

In the superconductor of the present invention, [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [] in which 1/2 or more of the entire anion included in the C12A7 electride (x + 2y in the following formula) is substituted with electrons. xO
^2- + 2yA + 2 {1- (x + 2y)} e ⁻ ] (A is one or more of OH ⁻ , O ⁻ or O ₂ ⁻ included in the cage, 0 ≦ x + 2y ≦ 0.5) It is a compound having the mayenite-type crystal structure shown, which exhibits metal conduction at room temperature and has a superconducting transition temperature (Tc = approximately 0.2K).
) The superconductivity is shown below. In this chemical formula, when 0 ≦ x + 2y ≦ 0.5, 2 {1− (
x + 2y)} e ⁻ becomes e ^{− to} 2e ⁻ , and when converted to an electron concentration, about 1.2 ×
It becomes 10 ²¹ cm ⁻³ or more and 2.3 × 10 ²¹ cm ⁻³ or less.

In the C12A7 electride in which electrons of about 1.2 × 10 ²¹ cm ⁻³ or more are included,
Although an anion of about 1.1 × 10 ²¹ cm ⁻³ or less (monovalent conversion) is included, these anions may be O ²⁻ , OH ⁻ , O ^−, or O ₂ ⁻ , and may be C12A7 elect. The electrical conductivity of the ride has no substantial effect and becomes a superconductor below the superconducting transition temperature.
However, since the reaction for replacing OH ⁻ ions with electrons is slow, the pre-treatment substance contains OH
^- It is desirable to be not contained. Such a pre-treatment substance not containing OH ⁻ can be obtained by producing and treating C12A7 in a dry atmosphere containing 1% by volume or more of oxygen.
(1) Preparation of starting material

C12A7 is synthesized, for example, by using a raw material containing calcium and aluminum at an atomic equivalent ratio of 12:14, and performing a solid phase reaction at a firing temperature of 1200 ° C. or higher and lower than 1415 ° C. to obtain a sintered body. A typical raw material is a mixture of calcium carbonate powder and aluminum oxide powder.

The starting material of the superconductor of the present invention is represented by the chemical formula [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2O
It is a C12A7 compound having a mayenite type crystal structure containing free oxygen ions represented by ^2- . [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ² + 2yA] (A is included in a cage, in which free oxygen ions of the C12A7 compound are substituted with monovalent anions such as OH groups and oxygen ion radicals. Any one or more of OH ⁻ , O ^{− and} O ₂ ^— , 0 ≦ x ≦ 1, y = 1−x)
The compound shown by these may be sufficient. Since OH group / electron substitution requires high-temperature reduction treatment at 1200 ° C. or higher, it is desirable that the content of OH groups is low in order to lower the reduction treatment temperature.

C12A7 having a mayenite type crystal structure and a chemical formula represented by [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2O ²⁻ is a dry air having a water vapor dew point of about −40 ° C. It is obtained by quenching from around 900 ° C. to room temperature in the course of cooling from the firing temperature. However, when it is slowly cooled in a dry oxygen atmosphere, a part of free oxygen ions are replaced with active oxygen ion radicals (O ⁻ ) and super oxygen ion radicals (O ₂ ⁻ ), and synthesized in an air atmosphere containing moisture. Includes OH groups. C12A7 containing these anions is [
Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ² + 2yA] (A is a clathrate, OH ⁻ , O
^- or _{O 2} ^- at least one agent, represented by 0 ≦ x ≦ 1, y = 1-x).

The form of the starting material may be any of powder, film, polycrystal, and single crystal. In order to increase the concentration of electrons included in C12A7 by free oxygen / electron substitution treatment or monovalent anion / electron substitution treatment, and to completely remove the oxide film formed on the surface of C12A7, The form of C12A7 (hereinafter referred to as “pre-treatment substance”) before the electron substitution treatment or monovalent anion / electron substitution treatment is preferably a single crystal.

If the pretreatment material contains magnetic ions such as manganese, iron, iridium and platinum, the superconducting state cannot be realized due to the interaction between the conduction electrons and the impurity magnetic ions. In order to remove magnetic ions from the pre-treatment substance, it is necessary to use a high-purity raw material that does not contain magnetic ions as a raw material for the synthesis of C12A7. Further, when growing a C12A7 single crystal, a crucible containing a magnetic material cannot be used. C grown by the chocolate ski method using an iridium crucible
A 12A7 single crystal cannot be used. A C12A7 single crystal containing no magnetic ions grown by the FZ method that does not require a crucible is most suitable.

The C12A7 single crystal, which is a form suitable for the pre-treatment substance, is obtained by the C12 obtained by the solid phase reaction.
Using the A7 sintered body as a precursor, the floating zone method (FZ method) or the chocolate ski method (
CZ method). Since the FZ method does not use a crucible, impurities such as magnetic ions are not mixed during growth, and is particularly preferable as a pre-treatment substance.

In order to obtain a C12A7 single crystal containing no iridium magnetic ions by the CZ method, it is necessary to use a crucible having a composition other than iridium, such as an alumina crucible or a carbon crucible. When these crucibles are used, Crystal growth is very difficult and has never been successful.

(2) ^O, which is inclusion in the reduction treatment process C12A7 2-, ^{OH -,} O - or _{O 2} ^- is any one or more anions, a Ti steaming or Ca steaming, be replaced by an electronic Can do. The following is specifically described for the case of replacing the O ^2-, which is inclusion in C12A7 to electronic, OH ^-, O ^- or O ₂ ^- or one or more anions are inclusion The same applies to the case.

The Ti vapor treatment is the same method as described in PCT / JP2006 / 32991, and the pre-treatment substance C12A7 is used for 1 hour or more and less than 240 hours in an atmosphere containing titanium metal vapor, preferably After holding for more than 10 hours and less than 14 hours, it is cooled to room temperature at a temperature drop rate of about 300 ° C./hour.

The atmosphere containing the titanium metal vapor is sealed in a thermally and chemically durable container such as quartz glass by vacuum sealing the titanium metal pieces and powder and the pre-treatment substance C12A7 to above 600 ° C. and 1450 ° C.
It may be formed by heating to a temperature of less than 1, preferably, more than 1000 ° C. and less than 1450 ° C. to generate vapor of titanium metal. C12A7 does not react directly with gas phase metal vapor, but C12A7
Since it seems to react with the metal Ti deposited on the A7 surface, the vapor pressure of the titanium metal in the container does not need to be strictly controlled. If there are enough titanium metal pieces or powder in the vessel to achieve an equilibrium vapor pressure at a selected heat treatment temperature in the range of more than 600 ° C. and less than 1450 ° C., the heating time is 1
Since it is longer than the time, the equilibrium vapor pressure is obtained. For example, if 5 g of titanium metal is sealed in a quartz glass tube for sealing tube having an internal volume of 10 cm ^3, an equilibrium vapor pressure can be obtained. Alternatively, vapor of titanium metal having an equilibrium vapor pressure may be generated at another place and distributed to C12A7 that is heated to 600 ° C. or higher and lower than 1450 ° C.

In any method, the atmosphere needs to be evacuated in order to remove oxygen in the atmosphere. When a quartz glass tube is used, it is necessary to perform heat treatment at a temperature lower than the softening point of the glass, and the heat treatment temperature is suitably more than 1000 ° C. and less than 1200 ° C. When an alumina tube is used instead of quartz glass, heat treatment can be performed at a temperature higher than 1200 ° C. and lower than 1450 ° C.

The vapor of titanium metal is deposited as titanium metal on the surface of C12A7, and the free oxygen contained in the cage enclosed in C12A7 reacts with the titanium metal to react with titanium oxide (TiO _{x on} the surface of C12A7. ) Form a film. If the temperature for holding C12A7 is kept high, oxygen diffusion in C12A7 will be accelerated, and the reaction rate between titanium metal and free oxygen on the surface of C12A7 will increase, so that free oxygen will be extracted, that is, free oxygen ions in C12A7. The phenomenon of decrease or disappearance due to substitution of electrons with electrons progresses at high speed. When the sintered body and the thin film sample are required to moderate the free oxygen extraction reaction, the heat treatment temperature may be set to a low temperature of about 600 ° C. At a temperature lower than 600 ° C., the vapor pressure of titanium metal is small, the reaction rate for extracting free oxygen is slow, and C12A7 containing a high concentration of electrons is contained.
The compound cannot be created.

However, when the heat treatment temperature exceeds 1450 ° C., C12A7 is decomposed or melted, so that C12A7 electride cannot be obtained. When the heat treatment time exceeds 240 hours, oxygen precipitates from the quartz tube or the like, and the free oxygen drawing reaction is suppressed.
The electron concentration in the 12A7 electride will be saturated. Conversely, when the amount of oxygen precipitated from quartz glass is large, the electron content decreases.

Although the retention time is about 1 hour, free oxygen extraction reaction is observed, but with the length of the retention time, the amount of free oxygen contained in the cage to be extracted increases, and the T on the surface of C12A7 increases.
The iO _x layer becomes thicker. However, completely C12A7 surface be covered with TiO _x, TiO _x
Since the oxygen diffuses inside, the drawing reaction is not hindered, and if the heat treatment time is sufficiently long, the free oxygen of about 95% or more can be replaced with electrons almost completely. The amount of free oxygen extracted, that is, the electron concentration contained in the cage of C12A7 is
It can be determined from the X-ray diffraction spectrum, the thickness of the TiO _x layer, the light absorption band intensity having peaks in the vicinity of 0.4 eV and 2.8 eV, or the electric conductivity.

The Ca vapor treatment is performed in the Japanese Patent Application No. 2005-510971 (republished 2005-000741).
In the atmosphere containing Ca vapor, C12A7, which is a pre-treatment substance, is heated to a temperature of 600 ° C. or higher and lower than 800 ° C., preferably 700 ° C. for 4 hours. After holding for 240 hours, it is cooled to room temperature at a temperature drop rate of about 300 ° C./hour. C
As for the atmosphere containing a vapor, a Ca metal piece or powder and a pre-treatment substance are preferably vacuum-sealed in a thermally and chemically durable container such as quartz glass.

The Ca metal vapor is deposited on the surface of the single crystal and reacts with free oxygen included in the single crystal to form a calcium oxide layer on the surface. When the temperature for holding the single crystal is less than 600 ° C., particularly 500 ° C. or less, the free oxygen drawing reaction is extremely slow. When the temperature is 800 ° C. or more, the drawing of free oxygen proceeds rapidly and the C12A7 compound is decomposed. With the length of the holding time, the amount of free oxygen that is extracted increases, and the surface calcium oxide layer becomes thicker. 700
When held at 240C for 240 hours, almost all of the free oxygen is extracted and replaced with electrons, and an electride C12A7 compound is formed inside the calcium oxide layer. The extracted free oxygen amount can be determined from the X-ray diffraction spectrum, the thickness of the calcium oxide layer, the light absorption band intensity having a peak at 0.4 eV, or the electric conductivity.

The present invention will be described in more detail with reference to examples. High-purity calcium carbonate powder (4N) and aluminum oxide powder (4N) are mixed at an atomic equivalent ratio of 12:14, mixed uniformly in an alumina crucible, and subjected to a solid phase reaction at a firing temperature of 1300 ° C. A sintered body was prepared.

The produced C12A7 sintered body was press-molded into a rod shape. Using this rod, oxygen 1
C12A7 single crystal was grown by FZ method in an argon gas atmosphere containing volume%. The grown single crystal was colorless and transparent, and was electrically insulating (<about 10 ⁻¹¹ Scm ⁻¹ ). Moreover, it turns out that an oxygen ion radical and OH group are not contained from an electron spin resonance absorption measurement and an infrared-light absorption spectrum. Moreover, it turns out that a magnetic ion is not contained from an electron spin resonance absorption spectrum.

That is, in the FZ method, since the grown crystal is rapidly cooled and the atmosphere does not contain moisture, the crystal contains oxygen ion radicals, superoxygen ion radicals, and OH.
A single crystal that does not contain a group and is grown by the FZ method has the chemical formula [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO
² + 2yA] (A is one or more of OH ⁻ , O ⁻ or O ₂ ⁻ included in a cage, y = 1−x), and x = 1.

C12A7 single crystal (2mm × 1mm × 0.1mm) grown by FZ method is put into a silica glass tube (1cmφ) together with 7g of metal Ti powder, and is evacuated to about 10 ⁻² Pa with a rotary pump. The silica glass tube was sealed. The sealed silica glass tube was heated to 1000 ° C. in an electric furnace, Ti metal vapor was generated and held for 12 hours to reduce C12A7.

The atmosphere in the container during the reduction treatment is because the metal Ti in the enclosed silica tube absorbs oxygen,
The degree of vacuum is improved and a strong reducing atmosphere is obtained. Also, a metal Ti film is deposited on the C12A7 single crystal and reacts with free oxygen in the C12A7 single crystal to form a TiO _x film on the surface. TiO
Formation of the _x film was confirmed from an X-ray diffraction spectrum.

The C12A7 single crystal that had undergone the reduction treatment exhibited a blackish brown color, and exhibited an electrical conductivity of about 1500 Scm ⁻¹ at room temperature. Also, the electrical conductivity showed a metallic electrical conductivity that increased with decreasing temperature. There was strong light absorption having a peak in the vicinity of 2.8 eV, and the electron concentration was estimated to be 1.2 × 10 ²³ cm ⁻³ from the value of the absorption coefficient.

The TiO _x film formed on the surface of the obtained sample was mechanically removed using No. 1500 polishing paper, a 4-terminal electrode was attached, and the electrical resistivity was measured to a very low temperature by the 4-terminal method. FIG. 1 shows the temperature dependence of the electrical resistivity of the sample. A sudden drop in electrical resistivity was observed from around 0.2K, and the electrical resistivity became zero at 0.15K. Further, as shown in FIG. 2, when an external magnetic field was applied to the sample, the temperature at which the electrical resistivity dropped shifted to the low temperature side along with the strength of the magnetic field. From the above results, it was shown that C12A7 electride is a superconductor having a Tc of 0.2K.

The superconductor can be used as an electronic device material such as a Josephson element and as a wiring material between the electronic elements.

2 is a graph showing the temperature dependence of the electrical resistivity of the C12A7 electride single crystal obtained in Example 1. FIG. It is a graph which shows the temperature dependence of an electrical resistivity when the magnetic field of the C12A7 electride single crystal obtained in Example 1 is applied.

Claims (3)

Chemical formula [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ^2- + 2yA + 2 {1- (x + 2y)} e ⁻ ] (A
Is one or more of OH ⁻ , O ⁻ or O ₂ ⁻ included in the cage, 0 ≦ x + 2y ≦ 0
. 5) A compound superconductor characterized by being a compound having a mayenite type crystal structure. The chemical formula is [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2 [xO ² + 2yA] (A is the inclusion in the cage, O
A compound having a mayenite type crystal structure represented by any one or more of H ⁻ , O ^{− and} O ₂ ^— , 0 ≦ x ≦ 1, y = 1−x) is prepared by a method not containing magnetic ions, 2. The method for producing a compound superconductor according to claim 1, wherein 50 atomic% or more of the total component amount (x + 2y) of O ²⁻ and A clathrated in the compound cage is substituted with electrons. The method for producing a compound superconductor according to claim 2, wherein the compound is a single crystal prepared by a floating zone method (FZ method).

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