JPH0725700A - Method for manufacturing superconductor and thin film superconductor - Google Patents

Abstract

PURPOSE:To obtain a new mercury-based oxide superconductor having >100K critical temperature and to provide a method for formation of a thin film. CONSTITUTION:This substance is obtained by forming a coating film composed mainly of mercury, an alkaline earth element (Ba or Ca) and copper on a base, subsequently heat-treating the base and the thin film and this substance has a chemical formula of HgBa2CaCu2O6+x (-1<x<1) and a crystal structure in which an oxygen-deficient perovskite layer 14 containing two CuO5 pyramids 12 facing to each other and sandwiching a uniatom layer 11 of Ca element belonging to an alkaline earth element is sandwiched between a pair of uniatom layers 15 each composed mainly of mercury. In addition, the mercury-based thin film superconductor can be produced even in a low vapor pressure Hg system by forming a coating film composed mainly of mercury, an alkaline earth element and copper on a base and heat-treating the base and the coating film in a low-oxidative atmosphere at a low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel copper oxide superconductor having a critical temperature of 100 K or higher, and a thin film manufacturing method.

[0002]

2. Description of the Related Art As a high temperature superconductor, after the discovery of an oxide superconductor having a perovskite type structure by Muller et al., The superconductivity of an oxide system having a perovskite type structure having various chemical compositions was confirmed. Was done.

Thereafter, it was discovered that a HgBa ₂ CuO _{4 + x} compound having a perovskite type structure containing mercury as a main component exhibits superconductivity at a critical temperature of 94 K (Nature 362, 226 (SN Putilin et al. , Nature, Vol.
362, p. 226 (1993)). It is considered that this substance has a crystal structure in which a perovskite layer Ba ₂ CuO ₄ containing a CuO ₆ octahedron is sandwiched between monoatomic layers containing mercury element as a main component.

[0004]

When the superconductor containing mercury is to be used at liquid nitrogen temperature (77K), the temperature margin is taken into consideration, and it is just the critical temperature, and it is stable at liquid nitrogen temperature. Further improvement in critical temperature is required for use.

Conventionally, this type of substance has been obtained only in the form of ceramics, and it is essential to process it into a thin film form for industrial application to electronic devices and the like. A thin film of a superconducting material has not yet been obtained because the vapor pressure of elemental mercury is high.

It is an object of the present invention to provide a superconductor having a critical temperature sufficiently higher than that of liquid nitrogen and a manufacturing method capable of forming a thin film.

[0007]

[Means for Solving the Problems] A book that overcomes the above problems
The superconductor of the invention is mercury, alkaline earth elements, copper oxygen.
Composed of a material, and goes through one atomic layer of alkaline earth element
Two CuO that met each other _FiveOxygen-deficient pero containing pyramids
The skeleton layer is sandwiched by one atomic layer containing mercury as the main component.
Chemical structure of HgA₃Cu₂O_{6 + x}Table with (-1 <x <1)
It is composed of substances that are processed.

Further, another superconductor of the present invention comprises mercury, an alkaline earth element, and an oxygen compound of copper, and a sheet of CuO ₂
A chemical formula HgA having a crystal structure in which an oxygen-deficient perovskite layer containing two CuO ₅ pyramids facing each other with one atomic layer of alkaline earth element on the surface and both sides is sandwiched by one atomic layer containing mercury as a main component. ₄ Cu ₃ O _{8 + x} (-1 <x <1)
It is composed of a substance represented by.

In addition, as a method for producing a thin film of a superconductor in the present invention, a coating containing mercury, an alkaline earth element, and copper as a main component is provided on a substrate, and the substrate and the coating are heat-treated. It is a thing. In particular, the heat treatment is performed at a relatively low temperature and a low oxidizing atmosphere as compared with the conventional oxide superconductor.

[0010]

The reason why the critical temperature of the superconductor of the present invention becomes high is not clear because the superconductivity theory has not been established yet. However, the conventional superconductor containing mercury has one sheet per unit lattice. While having a CuO ₂ surface, the superconductor of the present invention has 2
It is presumed that having three or three sheets is related.

In this case, the critical temperature generally does not necessarily increase as the number of CuO ₂ planes increases, but it can be determined only by actually synthesizing the substance.

However, up to now, in the oxides composed of mercury, alkaline earth elements and copper, a substance having two or more CuO ₂ faces has not been synthesized. Therefore, the present inventors were able to find the superconductor of the present invention by discovering this synthesis method.

Further, the reason why the material having two or more CuO ₂ faces can be synthesized by the manufacturing method of the present invention is that the application of the thin film manufacturing process enables the appearance of a non-thermal equilibrium phase which has not been obtained conventionally. It is thought to be a tame.

At the same time, the present manufacturing method, which contains a mercury element having a high vapor pressure, makes it possible to realize a thin film of this system which has not been obtained in the past.

There are many thin film manufacturing processes, and a substrate is usually heated during film formation to form a crystallized thin film.
The present inventors have found that, in the case of a mercury-containing substance, a thin film can be stably synthesized by adopting a method in which a film is deposited on a substrate and then crystallized during heat treatment.

By analogy with the conventional method of heat-treating an oxide superconducting thin film, it is considered that a mercury-based superconducting thin film can be obtained by heat-treating the coating at about 800 ° C., which is the same as the firing temperature of ceramics. However, in the case of this thin film, surprisingly, a low temperature of 650 or more, which cannot be considered in the past, is 70
It was found that a heat treatment at 0 ° C. or lower is suitable.

Further, it is not necessary to supply mercury vapor by encapsulating it in a capsule as in the case of burning mercury-based ceramics, and it is easy to perform heat treatment in an atmosphere containing 1/500 to 1/10 atmospheric pressure of oxygen. It was also confirmed that a superconducting thin film could be obtained.

Further, it has been said that when a conventional oxide superconducting thin film is produced by heat treatment, it is preferable to promote oxidation, but the mercury-based superconducting thin film of the present invention can be produced only when the oxygen partial pressure is low. I also found it possible.

[0019]

EXAMPLES The present invention will be described in more detail with reference to specific examples.

Example 1 On a magnesium oxide MgO single crystal (100) plane substrate, H was formed by a sputtering method.
A g-Ba-Ca-Cu-O thin film was formed to a thickness of 1 μm. As the sputter target, powders of Ba ₂ CuO ₃ , Ca ₂ CuO ₃ , CuO and HgO were used, and a metal composition of Hg: Ba: Ca: Cu was used.
= 2: 2: 1: 2 and mixed into a disk shape, and sputtering was performed at 50 W under a gas pressure of 3 Pa in an argon atmosphere to form a film.

When the formation temperature is room temperature, the thin film is in an amorphous state and the film composition is Hg: Ba: Ca: Cu = 2.5: 2:
It was 0.7: 1.7.

The film thus formed was heat-treated to evaluate the characteristics of the thin film. However, the heat treatment is 10% by putting the substrate with the coating in a glass capsule and closing the lid.
It was carried out by heating with an infrared lamp in a stream of nitrogen containing oxygen.

When heat treatment is performed at 650 ° C. for 20 minutes,
The film composition is Hg: Ba: Ca: Cu = 0.8: 2: 0.4: 1.5
Thus, an oriented thin film having an axial length of 9.5Å was obtained.

As a result of detailed analysis, this thin film was found to be a known superconductor containing mercury, that is, CuO ₆
HgBa ₂ Cu having a crystal structure in which a perovskite layer containing an octahedron is sandwiched between monoatomic layers containing mercury element as a main component.
It was a c-axis oriented film of an O _{4 + x} (however, -1 <x <1) compound. It has been found that thin films of compounds of this type containing mercury can be produced by this method.

The electrical resistivity of this thin film is 1 mΩcm at room temperature.
The resistance drop due to the superconducting transition was shown at 90 K at a low temperature.

Heat treatment is performed at a slightly low temperature, that is, 620 ° C.
Film composition Hg: Ba: Ca: Cu after 20 minutes
= 1: 2: 0.8: 1.7, an oriented thin film having an axial length of 12.7Å was obtained.

As a result of analysis, the obtained substance has a crystal structure shown in FIG. 1, that is, two CuO ₅ pyramids 12 facing each other through a monoatomic layer 11 of Ca element and an oxygen-deficient perovskite layer 14 composed of Ba element 13. , H having a structure sandwiched between monoatomic layers 15 containing mercury as a main component,
The film was a c-axis alignment film of a gBa ₂ CaCu ₂ O _{6 + x} (where -1 <x <1) compound.

This thin film showed a resistance drop due to the superconducting transition at 102 K, which is higher than the critical temperature of the conventional superconductor containing mercury. That is, HgBa ₂ CaCu ₂ O
It was confirmed that _{6 + x} is a new superconductor.

Although Ba and Ca are used as the combination of alkaline earth elements in this embodiment, it is needless to say that a superconductor can be produced by a combination of other alkaline earth elements.

When a powder of a compound containing mercury or a ceramic pellet is put together with the substrate with the coating during the heat treatment, the evaporation of elemental mercury from the coating is suppressed and the production of the superconductor is reproduced. It was also confirmed to be effective in improving the sex.

Further, cooling after the heat treatment is performed at 500 ° C./hour.
It was also confirmed that the above rapid cooling has better superconducting properties.

(Example 2) On a magnesium oxide MgO single crystal (100) plane substrate, a metal composition Hg: Ba: Ca: C was prepared.
Sputtering was performed using a target of u = 2: 2: 2.2: 3.2. The film composition is Hg: Ba: Ca: C
u = 2.5: 2: 1.8: 3.2.

This coating was put in a glass capsule and covered with a cap, and heat-treated at 620 ° C. for 20 minutes. as a result,
Film composition Hg: Ba: Ca: Cu = 1: 2: 2: 3, axial length 1
A oriented film of 5.9Å was obtained.

As a result of the analysis, the obtained substance had a crystal structure shown in FIG. 2, that is, one CuO ₂ surface 21 and 1 on both sides.
Two Cu facing each other through the Ca element 22 in the atomic layer
The oxygen-deficient perovskite layer 25 composed of the O ₅ pyramid 23 and the Ba element 24 contains mercury as a main component 1.
HgBa ₂ Ca ₂ Cu with a structure sandwiched by atomic layers 26
_The film was a c-axis oriented film of ₃ O _{8 + x} (however, -1 <x <1) compound.

This thin film showed a resistance drop due to the superconducting transition at 105 K, which is higher than the critical temperature of a conventional superconductor containing mercury. That is, HgBa ₂ Ca ₂ Cu ₃ O
It was confirmed that _{8 + x} is a new superconductor.

Even if the composition of the thin film contains other components such as lead as a minor component in addition to the main components such as mercury, alkaline earth elements, and copper, the superconductivity of the thin film production method of the present invention can be improved. Needless to say, a thin film can be produced.

(Example 3) Strontium titanate Sr
An Hg-Ba-Cu-O thin film of 5000 Å was formed on the TiO ₃ single crystal (100) plane substrate by a sputtering method. The metal composition of the sputter target is Hg: Ba: Cu =
Sputtering was carried out at a gas pressure of 0.5 Pa with an argon atmosphere of 2.5: 2: 1. The composition of the film formed at room temperature without heating the substrate varied somewhat depending on the conditions, but about Hg: Ba: Cu = (1-y): 2: (1 + y) (however,
The film was an amorphous film of 0 ≦ y ≦ 0.7).

The characteristics of the thin film superconductor when the heat treatment conditions of the coating were changed were examined. First, heating was performed in a nitrogen atmosphere containing 1% oxygen. It was confirmed that the structure of the mercury-based superconductor HgBa ₂ CuO _{4 + x} was crystallized when the heating temperature was 600 ° C. or higher. However, at 750 ° C. or higher, elemental mercury was released from the film, and the structure could no longer be formed. As a result, in the thin film, good quality HgBa ₂ CuO _{4 + x}
It was found that a low temperature between 650 ° C. and 700 ° C. is suitable for forming the structure, as compared with the conventional heat treatment method for oxide superconductors.

Next, the heating rate of the heat treatment was examined. In conventional heat treatment of oxide superconducting thin film, 100 ℃ / hour
Although it was said that the slow ascending / descending speed described below was good, it was also found that in the case of a mercury-based superconducting thin film, a rapid ascending / descending of 500 ° C. or more per hour is good for crystal structure formation. FIG. 3 shows an X-ray diffraction pattern of a film produced by heating at a heat treatment temperature of 670 ° C. for 45 minutes. It can be seen that a good quality c-axis oriented thin film with an axial length of 9.5Å was obtained.

Next, the effect was investigated by changing the oxygen content in the heat treatment atmosphere. The heat treatment condition was 670 ° C. for 45 minutes, the oxygen content in nitrogen was changed from 0% to 50%, and the 004 diffraction peak intensity of the X-ray diffraction pattern was measured.

FIG. 4 shows the result of the relationship between the relative intensity and the oxygen partial pressure. When a conventional oxide superconducting thin film is prepared by heat treatment, it was said that it is better to have a large amount of oxygen in order to accelerate the oxidation. It was an unexpected result that it became worse.

From FIG. 4, the oxygen partial pressure is 1/500 to
It was found that a thin film having good crystallinity can be obtained in the range of 1/10 atmospheric pressure. A film having a superconducting transition temperature of 90 K or higher was obtained in the film formed by heat treatment with this oxygen content.

This thin film was further exposed to 300 to 500 in oxygen.
It was also confirmed that the low temperature heat treatment at about ℃ improved the reproducibility of superconducting properties.

Although Ba was used as the alkaline earth element in this embodiment, it is a matter of course that the mercury-based superconducting thin film can be formed by a combination of other alkaline earth elements.

Further, in this embodiment, a mixed gas of oxygen and nitrogen was used at the time of heat treatment, but a mixed gas of an inert gas such as argon and oxygen may also be used as long as a predetermined amount of oxygen is contained.

[0046]

INDUSTRIAL APPLICABILITY As described above, the superconductor of the present invention is an oxygen substance composed of mercury (Hg), alkaline earth element (A) and copper (Cu). An oxygen-deficient perovskite layer A ₃ Cu ₂ O ₆ containing two CuO ₅ pyramids facing each other has a crystal structure sandwiched by one atomic layer containing mercury as a main component, and has a chemical formula of HgA ₃ C
u ₂ O _{6 + x} (provided that -1 <x <1) or mercury (H
g), an alkaline earth element (A), and an oxygenate composed of copper (Cu), and two CuO ₅ facing each other through one CuO ₂ surface and one atomic layer of the alkaline earth element on both sides.
Oxygen-deficient perovskite layer containing pyramids A ₄ Cu ₃
O ₈ has a crystal structure in which it is sandwiched by one atomic layer containing mercury as its main component and has a chemical formula of HgA ₄ Cu ₃ O _{8 + x} (however, -1 <x <1). It is a novel mercury-containing oxide superconductor with a critical temperature.

Since the superconductor of the present invention has a temperature exceeding 100K, it is inexpensive and can be supplied in large quantities.
Stable use of K is possible, and as a result, commercialization of an oxide superconductor containing mercury can be expected.

Further, the present invention is a manufacturing method in which a coating containing mercury, an alkaline earth element, and copper as a main component is provided on a substrate, and the substrate and the coating are heat-treated. If possible, the industrial value of the present invention is great.

[Brief description of drawings]

FIG. 1 shows HgBa ₂ Ca produced in one example of the present invention.
Crystal structure diagram of Cu ₂ O _{6 + x} thin film

FIG. 2 HgBa ₂ Ca ₂ produced in one example of the present invention
Crystal structure diagram of Cu ₃ O _{8 + x} thin film

FIG. 3 is a graph showing HgBa ₂ Cu prepared according to an embodiment of the present invention.
X-ray diffraction pattern of O _{4 + x} thin film

FIG. 4 Hg-Ba-C produced in one example of the present invention
System diagram between crystallinity of u-O thin film and oxygen content during heat treatment

[Explanation of symbols] 11 Ca element 1 atomic layer 12 CuO ₅ pyramid 13 Ba element 14 Oxygen-deficient perovskite layer 15 Mercury element 1 atomic layer 21 CuO ₂ surface 22 Ca element 1 atomic layer 23 CuO ₅ pyramid 24 Ba element 25 Oxygen-deficient perovskite Layer 26 1 elemental atomic layer of mercury

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01B 12/00 ZAA 7244-5G H01L 39/24 ZAA B 9276-4M

Claims (11)

[Claims] 1. Mercury (Hg), alkaline earth element (A),
An oxygen deficient perovskite layer A ₃ Cu ₂ O ₆ containing two CuO ₅ pyramids, which are oxygen compounds made of copper (Cu) and face each other through one atomic layer of the alkaline earth element, contains mercury as a main component. Has a crystal structure sandwiched between atomic layers,
A superconductor characterized by being a substance having a chemical formula of HgA ₃ Cu ₂ O _{6 + x} . Here, x is a numerical value in the range of -1 <x <1. 2. The alkaline earth element A is barium (Ba).
And HgBa ₂ composed of calcium and calcium (Ca).
The superconductor according to claim 1, which is a substance having a chemical formula of CaCu ₂ O _{6 + x} . 3. Mercury (Hg), alkaline earth element (A),
An oxygen deficient perovskite layer A ₄ Cu ₃ O ₈ containing oxygen (Cu) containing two CuO ₅ pyramids facing each other through one CuO ₂ plane and one atomic layer of both sides of the alkaline earth element. Has a crystal structure sandwiched by one atomic layer containing mercury as a main component, and has a chemical formula of HgA ₄ Cu ₃ O
A superconductor characterized by being an _{8 + x} substance. Where x
Is a numerical value in the range of -1 <x <1. 4. The alkaline earth element A is barium (Ba).
And HgBa ₂ composed of calcium and calcium (Ca).
The superconductor according to claim 3, which is a substance having a chemical formula of Ca ₂ Cu ₃ O _{8 + x} . 5. A method for producing a thin film superconductor, which comprises providing a coating film containing mercury, an alkaline earth element, and copper as a main component on a substrate and heat treating the substrate and the coating film. 6. The method for producing a thin film superconductor according to claim 5, wherein the temperature of the heat treatment is in the range of 650 to 700 ° C. 7. The method for producing a thin film superconductor according to claim 5, wherein the ascending / descending speed of the heat treatment is 500 ° C. or more per hour. 8. The heat treatment is performed in an oxygen-containing atmosphere in the range of 1/500 atm to 1/10 atm.
A method for producing a thin film superconductor according to claim 5. 9. After heat treatment, further 300 or more 5 in oxygen
The method for producing a thin film superconductor according to claim 5, wherein a low temperature heat treatment at a temperature of 00 ° C. or less is applied. 10. A thin film superconductor having a composition ratio of mercury (H
g), alkaline earth element (A), copper (Cu), Hg
The production of a thin film superconductor according to claim 5, characterized in that when represented by _(1-y) A ₂ Cu _{(1 + y)} , y has a value of 0 ≦ y ≦ 0.7 as a main component. Method. 11. The method for producing a thin film superconductor according to claim 5, wherein the alkaline earth element (A) is a barium element.