JPH06279024A - Superconductor and its production - Google Patents

Abstract

PURPOSE:To obtain a superconductor having many blocking layers by forming a layer of Ca-Sr-Cu-O-based oxide and a layer of a specific oxide having a prescribed distance between cations in a crystalline structure by a piling up method. CONSTITUTION:A layer of oxide of formula I [0<=s<=1; 0.8<=t<=1.1; 1.8<=u<=2.2] and a layer of oxide selected from a substance group of formula II to formula V>=>= and having 0.36-0.41 n m distance between cations in a crystal structure are formed by a piling-up method to produce the objective superconductor [in formulas, alpha is Dy, Sm, Nd, Pr, Ce, etc.; beta is Mn, Co, Al, Ga, Cr, etc.; -0.2<=mu<=0.2; -0.3<=nu<=0.3; gamma is La, Sr or Nd; delta is Li, Ni, Al, etc.; xsi, rho, phi is same range as mu; pi, sigma, tau, chi and omega are same range as nu; epsilon is Pb, Bi or Ba; n is 2-4; eta is Na, Ce, Y, etc.; m is 1-2; q is 1-3; r is 2-3; kappa is Yb, Y, Dy, etc.; lambdais Ta or Nb; -0.1<=psi<=0.1].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion reactor, a magnetohydrodynamic generator, an accelerator, a rotating electrical machine (motor, generator, etc.),
Suitable as a material for magnet coils in magnetic separators, magnetic levitation trains, nuclear magnetic resonance measuring devices, magnetic propulsion vessels, electron beam exposure devices, various experimental devices, and also for power transmission lines, electric energy storage, transformers, rectifiers, Suitable for applications where power loss is a problem, such as phase shifters, as well as Josephson devices and SQUs.
The present invention relates to a superconductor suitable as an element such as an ID element and a superconducting transistor, and further as a functional material such as an infrared detection material and a magnetic shielding material.

[0002]

2. Description of the Related Art A series of copper complex oxide superconductors is called "Zeit
schrift fur Physik B-condensed Matter ", Vol.8
3, pages 7 to 17 (1991), a Cu-O ₂ surface through which a superconducting current flows and this Cu-O.
A media er coating layer to neutralize -2 valence charge of Cu-O _dihedral be between _two faces, the layered structure comprising a these Cu-O ₂ side and media er coating layer and a blocking layer sandwiches the sandwich And Cu-
Depending on the number of O ₂ faces, it is classified into a one-layer system, a two-layer system and a three-layer system.

For example, as a one-layer system, (L
a, Sr) ₂ CuO ₄ , Bi ₂ Sr ₂ CuO ₆ , (N
d, Ce) CuO ₄ , and the two-layer system includes
(La, Sr) ₂ CaCu ₂ O ₆ , YBa ₂ Cu
₃ O ₇ , Bi ₂ Sr ₂ CaCu ₂ O ₈ , Pb ₂ Sr
₂ (Ca, Y) Cu ₃ O ₈ , and as a three-layer system, (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₇ ,
There is Tl ₂ Ba ₂ Ca ₂ Cu ₃ O ₁₀ . In such a copper composite oxide superconductor, the superconducting transition temperature (Tc) depends on the amount of charge carriers doped in the crystal, especially the amount of charge carriers per one layer of Cu—O ₂ surface (carrier concentration). change. The carrier concentration is 0.05 to 0.3
When it is in the range of 2, it exhibits superconducting properties,
The maximum Tc is obtained in the range of 0.23. Also,
In a copper composite oxide superconductor having a carrier concentration in the above range, an empirical rule is established that Tc increases as the number of Cu—O ₂ planes via the mediating layer between blocking layers increases. There is.

By the way, in the copper composite oxide superconductor, the interaction between the Cu—O ₂ planes becomes excessively strong and the electric charge is moderate only when the Cu—O ₂ plane and the mediating layer are stacked. Being harmonized, C
In many cases, it cannot be injected into the uO ₂ plane. Therefore, Cu-
The interaction in the direction perpendicular to the O ₂ plane (c-axis direction) is interrupted to some extent to control the dimensionality of the entire superconductor, and in many cases, carriers are supplied to the Cu—O ₂ plane. Furthermore, when only a stack of mediating layers is unstable in the crystal structure and a stable substance can be obtained only with a limited composition, a layer for firmly forming a skeleton of the crystal structure and making it a stable substance. As a result, the presence of the blocking layer becomes important.

Examples of such a blocking layer include La ₂ O ₂ , BaO / CuO / BaO and BaO /
CuO / CuO / BaO, SrO / Bi ₂ O ₂ / Sr
O, BaO / Tl ₂ O ₂ / BaO, SrO / PbO-C
uO-PbO / SrO, SrO / (Pb, Cu) O / S
rO and Nd ₂ O ₂ are known. However, there are as few as eight types of conventionally known blocking layers, and therefore there is a problem that the production of superconductors that can be applied to various applications is limited.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a superconductor which has many types of blocking layers and can be applied to various applications, and a method for producing the superconductor with good reproducibility.

[0007]

In order to solve the above-mentioned object, the present invention provides a formula (Ca _1-s Sr _s ) _t CuO _u (where 0 ≦ s ≦ 1.0 and 0.8 ≦ t ≦ 1.1, 1.8 ≦
an oxide represented by u ≦ 2.2) and an oxide having a distance between cations of 0.36 nm or more and 0.41 nm or less in the crystal structure, which is selected from the following substance groups a to f. The present invention provides a superconductor characterized by being layered. I~
From the substance group F, one kind may be selected, or two or more kinds may be selected.

A. α _{1 + μ} β _1-μ O _{3 + ν} (where α is Dy, Sm, Nd, Pr, Ce, La,
Eu, Bi, Pb, Gd, Na, Sr, Ca, Ag,
At least one element selected from K and Ba,
β is Mn, Co, Al, Ga, Cr, Ce, Cd, N
i, W, Fe, Ga, Ta, V, Ti, Mo, Sn, R
At least one element selected from h, Nb, and Zr. -0.2≤μ≤0.2, -0.3≤ν≤0.3) b. γ _{2 + ξ} δ _1-ξ O _{4 + π} (where γ is at least one element selected from La, Sr and Nd, and δ is Li, Ni, Al, Co, M
n, Mg, Cr, Ga, Rh, Ti, Fe, Ru, I
At least one element selected from r, Mo and Sn. -0.2≤ξ≤0.2, -0.3≤π≤0.3) c. ε _{n + 1 + ρ} ζ _n-ρ O _{3n + 3 + σ} (where ε is at least one element selected from Pb, Bi and Ba, and ζ is at least 1 selected from Ti, Nb and Ta) Species element, n = 2, 3 or 4.-
0.2 ≦ ρ ≦ 0.2, −0.3 ≦ σ ≦ 0.3) d. η _m O _{q + τ} (where η is Na and m = 2, q = 1, and η is Ce and m =
1, q = 2, or η is Y, Ho, Dy, Tb, G
An element selected from d, Eu, Sm, Pr, Nd and La. m = 2, q = 3. −0.3 ≦ τ ≦ 0.3) E. Sr _{r + 1 + φ} Ti _r-φ O _{3r + 1 + χ} (where r = 2 or 3. −0.2 ≦ φ ≦ 0.2, −
0.3 ≦ χ ≦ 0.3) f. κ _{0.33+ ψ} λ _1-ψ O _{3 + ω} (where κ is Yb, Y, Dy, Gd, Ce, Sm, N
At least one element selected from d, La and Pr, and λ is an element selected from Ta and Nb. −0.1 ≦
ψ ≦ 0.1, -0.3 ≦ ω ≦ 0.3) Further, the present invention is a method for producing a superconductor mentioned above, the formula _{(Ca 1-s Sr s)} t CuO u ( although, 0 ≦
s ≦ 1.0, 0.8 ≦ t ≦ 1.1, 1.8 ≦ u ≦ 2.
2) An oxide layer represented by 2) and an oxide layer selected from the above-mentioned substance groups a to f and having a cation distance of 0.36 nm or more and 0.41 nm or less in the crystal structure. There is provided a method for manufacturing a superconductor, characterized in that and are formed by a stacking method.

The superconducting current in the copper composite oxide superconductor flows in the Cu--O ₂ plane. Superconductor of the present invention also having the formula Cu-O ₂ side _{(Ca 1-s Sr s)} t C
The oxide layer represented by uO _u can be considered as a superconducting layer, is selected from the above-mentioned substance groups a to f, and is 0.36
It is considered that the oxide layer having a cation distance of not less than 0.4 nm and not more than 0.41 nm in the crystal structure is a blocking layer. In the following, the formula (Ca _1-s Sr _s )
A layer of an oxide represented by _t CuO _u is called a superconducting layer,
A layer of oxide having a distance between cations of 0.36 nm or more and 0.41 nm or less in the crystal structure is called a blocking layer.

In the above superconducting layer, (Ca _1-s Sr
_{In the} mediating layer composed of _s ), t = 1 from the viewpoint of not causing Ca or Sr deficiency, but this superconducting layer is formed in a state where t is larger than 1. Then, a defect may occur in the Cu site on the Cu—O ₂ surface. When the Cu deficiency is too large, it may superconducting current does not flow to the Cu-O ₂ surface. Therefore, t has an upper limit value, and the value is 1.1.

Further, when the superconducting layer is formed, (Ca _1-s
The Sr _s ) site may contain some defects. If this amount of deficiency becomes excessive, electrostatic repulsion between oxygen atoms on the Cu—O ₂ planes located above and below the mediating layer becomes strong, and the distance between the Cu—O ₂ planes becomes long. When this distance becomes longer, “Physica C”, Vol.16
7, 515 to 519 (1990), the empirical rule that Tc increases as the distance between the Cu—O ₂ planes closest to each other in the crystal structure becomes shorter, which is not preferable. Therefore, there is a lower limit value for t, and the value is 0.8. After all, the ratio β of the mediating layer in the superconducting layer is 0.8 ≦ for the above reason.
The range is t ≦ 1.1.

On the other hand, the abundance ratio of Ca and Sr in the mediating layer made of (Ca _1-s Sr _s ) has a small ionic radius from the above empirical rule of the distance between the Cu—O ₂ planes and Tc. The above distance should be shortened by adding a large amount of Ca, and only Ca (s
= 0), the superconducting layer can be formed, so the lower limit of s is 0. However, when a SrTiO ₃ single crystal substrate is used during manufacture, the single crystal has a long a-axis length of 0.39 nm. Therefore, when the abundance ratio of Ca is high, the superconducting layer is formed due to the inconsistency with the substrate. There are things you can't do. Therefore, it is necessary to increase the abundance ratio of Sr to grow the crystal of the superconducting layer.
Since the superconducting layer can be formed only by r (s = 1.0), the ratio of Ca to Sr in the mediating layer of the superconducting layer is set to 0 ≦ s ≦ 1.0.

By the way, in the case of a copper composite oxide superconductor,
Oxygen in the crystal is the only anion. Therefore, as in the case of the deficiency of Sr and Ca described above, the amount of oxygen present in the crystal has a great influence on the overall carrier concentration. In the superconducting layer, oxygen in the Cu—O ₂ plane is hard to be lost because the bond with Cu is strong. Even if the superconducting layer is formed under the condition of being deficient, it is considered that oxygen is hardly present in the mediating layers composed of (Ca _{1- s} Sr _s ) located above and below the superconducting layer. Such conditions, i.e., in the oxygen deficiency is large state of Cu-O ₂ plane, not superconducting current flows in the Cu-O ₂ surface. Therefore, by setting the condition that the lower limit value of u is 1.8, excessive oxygen deficiency in the Cu—O ₂ plane is prevented and the superconducting property is secured.

On the other hand, when the superconducting layer is formed under the condition that oxygen is easily taken in, oxygen deficiency hardly occurs in the Cu--O ₂ plane, and oxygen is also introduced into the mediating layer. However, if the amount of oxygen introduced into the mediating layer becomes excessive, the interaction between Cu on the Cu-O ₂ planes located above and below the mediating layer becomes too strong, and eventually the whole becomes a superconductor. Will end up. Therefore, the upper limit of u is 2.2.
To ensure superconducting characteristics. After all,
u must satisfy the condition of 1.8 ≦ u ≦ 2.2.

Next, as described above, the oxide forming the blocking layer interrupts the interaction in the c-axis direction to some extent, controls the dimensionality of the entire superconductor, and firmly forms the framework of the crystal structure. To obtain a stable crystal structure, and in many cases, to be able to supply carriers to the Cu—O ₂ plane. In order to form a framework for achieving a stable crystal structure, the distance between cations in the crystal structure of this oxide and the size of the crystal lattice in the Cu—O _{2 in-} plane direction of the superconducting layer are well matched. There must be. The superconductor according to the present invention has a strong ionic bondability in both the superconducting layer and the blocking layer, and the allowable range of the lattice size matching in crystal formation by those having a strong ionic bondability is 3-5.
It is empirically known to be within%, and the distance between Cu ions in the superconducting layer is 0.38 to 0.39 nm. Therefore, the distance between cations in the crystal structure of the oxide forming the blocking layer is 0. It must be 0.36 nm or more and 0.41 nm or less.

Since the superconducting layer is an oxide,
Considering the electrical neutrality condition of the entire crystal, it is preferable that the material forming the blocking layer is also an oxide, and the size of the structure forming each layer is mainly determined by the arrangement of anions having a large ionic radius. Therefore, considering the compatibility with the size of the crystal lattice in the Cu—O _{2 in-} plane direction of the superconducting layer, the blocking layer is preferably an oxide.

In the blocking layer as well, oxygen is the only anion as in the case of the above-mentioned superconducting layer, and the oxygen content in the blocking layer also greatly affects the amount of carriers supplied to the superconducting layer. The oxygen content in the blocking layer can be introduced in excess of the stoichiometric composition depending on the conditions for forming the superconductor, or can be formed with an oxygen content smaller than the stoichiometric composition. In order to form the structure of the blocking layer, ν, π,
All of σ, τ, χ, and ω need to be −0.3 or more and 0.3 or less.

Further, in the substances of the groups a to c and the group f, α and β, γ and δ, ε and ζ, Sr and Ti, κ and λ are −0.2 ≦ μ ≦ 0.2, respectively. −0.2 ≦ ξ ≦
0.2, -0.2≤ρ≤0.2, -0.2≤φ≤0.
2, complementation is possible within the range of −0.1 ≦ ψ ≦ 0.1, but if it is not within this range, the structure of the blocking layer cannot be formed.

The superconductor of the present invention has a structure in which a blocking layer is inserted between the superconducting layers. The insertion of this blocking layer has regularity in consideration of reproducibility in superconducting characteristics. However, it is preferable to insert them periodically, but they may be inserted randomly.

The layer through which the superconducting current flows is a superconducting layer, and the blocking layer is a layer for controlling the dimensionality of the interaction and, in many cases, supplying carriers, and the number of Cu--O ₂ planes described above is large. From the experience that the higher the number, the higher the Tc, the larger the number of unit cells of the superconducting layer, the more preferable. The unit cell referred to here is c defined by crystallography.
It is the smallest unit in the arrangement of atoms in the axial direction. The unit cell number in the following has the same meaning.

Further, the superconducting layer has n unit lattice numbers (n is 1).
In the case of the structure in which the blocking layer is interposed between the repeating units of the above (integer), if n is increased, the number of Cu—O ₂ planes increases and Tc increases according to the above empirical rule. become. However, if n is made too large, the carrier concentration will decrease, so n is preferably in the range of 1 to 6. In particular, n is preferably 2 to 4 in order to optimize the carrier concentration and to easily form a crystal structure.

Further, m layers (m is 1 or more) of oxide layers selected from the above-mentioned substance groups (a) to (e) and having a cation distance of 0.36 nm or more and 0.41 nm or less in the crystal structure. In the laminated blocking layer, if m is increased, the carrier supply amount to the superconducting layer can be increased, but if the supply amount is too large, the carrier concentration in the superconducting layer becomes too high. Therefore, m is preferably in the range of 1 to 4 because the superconducting transition temperature becomes low and the superconducting transition temperature becomes low, and at the same time, the ratio of the superconducting layer in the superconductor decreases and the critical current density becomes low. More preferred is 1 or 2.

Since the carrier is supplied to the Cu-O ₂ surface, the superconducting layer is made to partially contain alkali metals such as Li, Na and K in addition to the elements Ca, Sr, Cu and O. May be.

The superconductor of the present invention has a tape shape, a wire shape,
It can be used in various shapes such as fiber and sheet. Further, it can be used by being formed on a reinforcing material made of carbon fiber, ceramics such as alumina and zirconia, or metal such as gold and silver. Furthermore, these ceramics, gold, silver, etc. can be coated and used. Furthermore, it can be used as a superconducting wire having a multi-core wire structure using copper or the like as a matrix. Also, S
i, MgO, LaGaO ₃ , LaAlO ₃ , NdGaO
₃ , NdAlO ₃ , LaSrGaO ₄ , Y ₂ O ₃ , Sr
It can be formed as a thin film on a substrate of TiO ₃ , Al ₂ O ₃ , yttrium partially stabilized zirconia, etc., and can be used as various devices and wiring of LSI.

The surface condition of the substrate is important when forming a superconductor on it. Specifically, it is preferable to burn off the surface deposit in a high vacuum in advance so that no impurities are attached and epitaxial growth is possible. In particular, when SrTiO ₃ single crystal is used as a substrate, a large amount of Ti is formed on the surface by heat treatment up to about 1000 ° C. Therefore, when forming a superconductor on this, first stack Sr and then Cu. After that, it is preferable to form a layer of the desired superconductor.

The superconductor of the present invention can be manufactured by various methods, and the formula (Ca _1-s Sr _s )
An oxide layer represented by _t CuO _u and an oxide layer selected from the above-mentioned substance groups a to f and having a cation distance of 0.36 nm or more and 0.41 nm or less in the crystal structure. It is preferable to manufacture by using a stacking method in which and can be controlled in atomic order or one unit lattice order.

As the stacking method, a laser ablation method, a molecular beam epitaxy method, an electron beam vapor deposition method, or a physical vapor deposition method such as various sputtering methods can be used, and a laser ablation method is particularly preferable. . For example, when using the laser ablation method,
Do the following:

First, a CuO target is manufactured. That is, CuO powder is formed into pellets, and the formed body is sintered at a temperature of 700 to 1000 ° C. for 1 to 12 hours to obtain a target (target 1). Similarly,
A target of Sr (target 2), a target of Ca (target 3), and a target of TiO ₂ (target 4) are prepared.

Next, the targets 1, 2, 3 and 4 are separately set in the chamber, and the substrate is set at a position facing these targets and separated by 5 to 300 mm. Adjust the partial pressure of oxidizing substances in the chamber to 1 x 10
After setting the pressure to ^-2 to 1 × 10 ^-4 Pa, the substrate is heated to 400 to 600 ° C.
It is preferably heated to 450 to 550 ° C. Then, the targets 1, 2, 3 and 4 are alternately irradiated with an excimer laser using ArF, KrF, XeCl or the like to deposit the constituent material of each target on the substrate. At this time, by irradiating the substrate and the periphery thereof with a laser, the crystallinity of the obtained thin film can be enhanced and the oxidizing power of the oxidizing gas can be increased. The energy density per laser pulse at the irradiation position on the target needs to be larger than the size at which ablation occurs, but is preferably 1 kJ / cm ² or less. If it is larger than this, the shape of the thin film may be deteriorated. The pulse frequency of the excimer laser used for irradiation varies depending on the type of target used and the type of desired ablation excitation species, but if it is too high, the rearrangement of atoms ablated and flying incompletely occurs on the substrate surface. May cause deterioration of crystallinity. Therefore, the pulse frequency is preferably in the range of 1 to 80 Hz.

If the distance between the target and the substrate is less than 5 mm, the substrate becomes an obstacle to the laser irradiation, and the irradiation angle of the excimer laser with respect to the target cannot help but be extremely small, so that the target is ablated. Less likely to happen. On the other hand, when it exceeds 300 mm, the deposition rate is remarkably slowed, which is not practical.

In order to create an oxidizing atmosphere in the chamber, oxygen or N ₂ O is used in addition to NO ₂ and ozone, or ultraviolet rays or the like are irradiated in the oxygen atmosphere to generate ozone or active oxygen. You may.

When the partial pressure of the oxidizing atmosphere in the chamber is lower than 1 × 10 ^-4 Pa, Cu ₂ O is generated as a stable phase in the obtained crystal structure, and a superconductor cannot be obtained. is there. Also, if it is higher than 1 × 10 ^-2 Pa,
Impurities may be easily mixed in the formed copper complex oxide, or the morphology of the obtained thin film may be deteriorated.

Further, if the substrate temperature is lower than 400 ° C., crystallization of the target material deposited on the substrate becomes difficult to occur, while if it is higher than 600 ° C., a superconductor may not be obtained.

When ablating each target,
Directly change the thickness of the superconducting layer or blocking layer that is formed.
Monitor in advance with a membrane pressure gauge, and obtain the relationship between time and thickness when a standard sample is ablated in advance,
The actual time is measured, the thickness is monitored from the measured value, and when the desired thickness is reached, the irradiation target of the excimer laser is switched to another target.

Regarding the control of the film thickness of each atomic layer, the reflection high-energy electron diffraction method (RHEED) is used, the intensity of the diffraction grating point is monitored on the image obtained by this, and the unit lattice is determined from the vibration pattern. It is advisable to adopt a method in which the irradiation of the excimer laser is switched to another target when the number of points reaches a desired value.

It is preferable to set an interval of about 1 second to 15 minutes after forming each layer because the crystallinity of each layer becomes more reliable. This interval may be changed at any time or sequentially, such that it is made long at first and shortened as the number of unit lattices increases.

In this way, a thin film is formed on the substrate, the laser irradiation is stopped when the thickness reaches a desired value, and the substrate is cooled to about 200 to 450 ° C. at a rate of about 5 to 20 ° C./min. To do. At this time, the partial pressure of the oxidizing gas in the chamber is increased or the temperature range of 200 to 400 ° C. is set to 1 to 6
By holding it for 0 minutes, the uptake of oxygen can be made more complete. Similarly, at a temperature of 200-400 ° C, 1 to make oxygen uptake more complete.
~ 300 minutes, oxygen anneal in 0.1-1 atmosphere,
Under the same temperature condition, it is also preferable to perform the treatment using a hot isotropic pressure treatment method (HIP method) under an oxygen partial pressure higher than 1 atm and 400 atm or less.

In the above, Cu, Sr, Ca, Ti
For each of the above, the case of using one target each has been described, but it is also possible to use one target obtained by mixing and sintering Sr, Ca, and Cu at a desired molar ratio. For example, (Ca _1-s Sr _s ) _t CuO
When forming the _u layer, one pellet having Ca: Sr: Cu in a molar ratio of (1-s) t: st: 1 can be used as a target. Similarly, when forming the blocking layer, one pellet can be used as a target. For example, SrT
One pellet of Sr: Ti 1: 1 can be used to form the layer of i0 ₃ .

[0039]

【Example】

Example 1 A CuO powder was molded into pellets, and the molded body was sintered in air at 900 ° C. for 10 hours and gradually cooled to obtain a target 1. In addition, a Sr pellet was prepared and used as a target 2. Further, each powder of SrCO ₃ and TiO ₂ was weighed so that the molar ratio of Sr: Ti was 1: 1,
Mix, calcine in air at 800 ° C for 5 hours, crush,
It was molded into pellets, sintered in air at 900 ° C. for 10 hours, and gradually cooled to obtain a target 3.

Next, while setting these targets in the chamber, facing these targets,
In addition, a SrTiO ₃ substrate having a plane orientation of (100) is placed at a position 75 mm away from each target, and the partial pressure of the oxidizing atmosphere (NO ₂ ) in the chamber is adjusted to 5 × 10 ⁻⁵ Pa, and the substrate is Heated to 480 ° C.

Next, the RHEED image of the substrate surface is observed,
It was confirmed that the crystallinity and smoothness of the surface were sufficient, and the intensity of the diffraction point was monitored. Below, this monitor was continued during the forming operation, and it was confirmed that one atomic layer or one unit lattice layer could be formed.

Next, each target was irradiated with an ArF excimer laser having a wavelength of 193 nm and a pulse energy density of about 300 mJ / cm ² by switching as follows while monitoring the thickness to be deposited on the substrate by RHEED.

First, the target 2 was irradiated with a laser of 3 Hz, and the time required for the diffraction point intensity of RHEED to surely vibrate once was measured. It was 35 seconds. Next, irradiate the target 1 with a laser of 3 Hz, and similarly perform RHEED.
The time required for the diffraction point intensity to vibrate once surely was measured. It was 40 seconds. In this way, each Sr, C
The time required to form a monolayer thickness of u was determined.

Next, the operation a in which steps 1 to 4 under the conditions shown in Table 1 were performed in this order was repeated three times to form a thin film.

[0045]

[Table 1] Also, when a film was separately formed by the operation a and its composition was examined by the plasma emission spectroscopy (ICP method), it was found to be about Sr _1.0 Cu _1.0 O _u . From this, by repeating the operation a three times, it can be estimated that the thin film of this composition is formed with three unit lattices. This becomes a repeating unit.

Next, on the above-mentioned thin film, the operation b for carrying out the steps 5 and 6 of the conditions shown in Table 2 in this order was performed once.

[0047]

[Table 2] By this operation, it can be estimated that the SrTiO _{3 + ν} layer is formed with one unit lattice number. This becomes the blocking layer.

Next, the following operations 1 and 2 were sequentially performed on the above layer, and these operations were repeated 30 times.

1. Operation a 3 times 2. Operation b 1 time Thus, a thin film was obtained in which a layer of Sr _1.0 Cu _1.0 O _{γ and} a layer of Sr _1.0 Ti _1.0 O _{3 + ν} were alternately stacked 30 times on the substrate 30 times. When the magnetic susceptibility of this thin film was measured by SQUID, it was confirmed that a diamagnetic signal indicating that the film became superconducting started to appear at 94K (Tc (χ) _onset ) and Tc was 94K.

Example 2 A CuO target 1 and a Sr target 2 were prepared in the same manner as in Example 1. In addition, Ca pellets target 3
Prepared as Further, the TiO ₂ powder was molded into pellets, sintered in air at 900 ° C. for 5 hours, and gradually cooled to obtain a target 4.

Next, these targets were set in the chamber and the same procedure as in Example 1 was followed, except that Table 3
The operation a in which steps 1 to 5 under the conditions shown in FIG. 2 are performed in this order is repeated four times to form a thin film.

[0052]

[Table 3] In addition, when a film was separately formed by the operation a and its composition was examined by the ICP method, it was found that Ca _0.3 Sr _0.7 C
It was u _1.0 O _γ . From this, by repeating the operation a four times, it can be estimated that the thin film having this composition has four unit lattice numbers. This becomes a repeating unit.

Next, the operation b for performing steps 6 and 7 under the conditions shown in Table 4 in this order was performed once on the thin film.

[0054]

[Table 4] By this operation, it can be estimated that the SrTiO _{3 + ν} layer is formed with one unit lattice number. This becomes the blocking layer.

Next, the following operations 1 and 2 were sequentially performed on the above layer, and these operations were repeated 20 times.

1. Operation a 4 times 2. Operation b 1 time The substrate was placed 100 mm away from the target. The partial pressure of the oxidizing atmosphere (NO ₂ ) in the chamber was adjusted to 1 × 10 ⁻⁵ Pa. Furthermore, the substrate is 500 ° C
And the oscillation frequency of the laser was 2 Hz.

Thus, Ca _0.3 Sr _0.7 C was formed on the substrate.
The layer of u _1.0 O _γ has 4 unit cells, and Sr _1.0 Ti _1.0 O _{3 + ν}
A thin film was obtained in which the layers of 1 were alternately stacked 20 times for each unit lattice. The Tc (χ) _onset of this thin film was 83K.

Example 3 Each of SrCO ₃ and CuO powders contained 0.95 of Sr: Cu:
Weighed so as to be 1, mixed, calcined in air at 800 ° C. for 5 hours, crushed, molded into pellets, sintered in air at 900 ° C. for 5 hours, and then slowly cooled. Target 1
Got Further, each powder of La ₂ O ₃ and NiO was added to La: N.
Weigh so that i is 2: 1, mix and mix in air for 8
It was calcined at 00 ° C. for 5 hours, crushed, molded into pellets, sintered in air at 950 ° C. for 5 hours, and slowly cooled to obtain a target 2.

Next, these targets were set in the chamber and the same procedure as in Example 1 was followed, except that Table 5
Steps 1 to 4 of the condition shown in 4 are performed in this order.
Sr _0.95 Cu _1.0 O by target 1 was repeated 0 times.
_γ layer is 3 unit cell, La ₂ NiO by target 2
_A thin film in which the _{4 + π} layer is a unit lattice was formed.

[0060]

[Table 5] The substrate was placed 30 mm away from the target. The partial pressure of the oxidizing atmosphere (NO ₂ ) in the chamber was adjusted to 1.5 Pa. Furthermore, the substrate temperature is 650 ° C
And the oscillation frequency of the laser was 4 Hz. A film thickness meter was used to monitor the thickness.

Thus, Sr _0.95 Cu _1.0 O was formed on the substrate.
A thin film was obtained in which a layer of _γ was 3 unit lattices and a layer of La ₂ NiO _{4 + π} was alternately laminated 40 times, one unit lattice each. The Tc (χ) _onset of this thin film was 37K.

Example 4 Each powder of SrCO ₃ , CaCO ₃ and CuO was added to Sr: C.
a: Cu is weighed so as to be 0.2: 0.8: 1, mixed, calcined in air at 800 ° C. for 5 hours, crushed, molded into pellets, and 900 ° C. in air Sintering was performed for 5 hours, and the target 1 was obtained by slow cooling. Also, Bi
₂ O ₃ and TiO ₂ powders were weighed so that Bi: Ti was 4.2: 3, mixed, calcined in air at 600 ° C. for 5 hours, crushed, and molded into pellets, 70 in the air
The target 2 was obtained by sintering at 0 ° C. for 5 hours and gradually cooling.

Next, these targets were set in the chamber and the same procedure as in Example 1 was followed, except that Table 6
Steps 1 to 4 of the condition shown in 4 are performed in this order.
Ca _0.8 Sr _0.2 C with target 1 repeated 0 times
u _1.0 O _γ layer has 3 unit _cells , Bi with target 2
_A thin film in which a layer of ₄ Ti ₃ O _{12+ σ} has one unit lattice was formed.

[0064]

[Table 6] The substrate was placed 30 mm away from the target. The oxidizing atmosphere in the chamber was oxygen gas, and the partial pressure was adjusted to 2 Pa. Furthermore, the substrate temperature is 600
The oscillation frequency of the laser was 6 Hz. A film thickness meter was used to monitor the thickness.

Thus, Ca _0.8 Sr _0.2 C was formed on the substrate.
A thin film was obtained in which a u _1.0 O _γ layer was stacked three times and a Bi ₄ Ti ₃ O _{12+ σ} layer was stacked one by one 40 times alternately. The Tc (χ) _onset of this thin film was 12K.

Example 5 Each of CaCO ₃ and CuO powder contained 0.95 of Ca: Cu.
Weighed so as to be 1, mixed, calcined in air at 700 ° C. for 5 hours, crushed, formed into pellets, sintered in air at 800 ° C. for 5 hours, and then slowly cooled. Target 1
Got Further, CeO ₂ powder was molded into pellets, sintered in air at 1000 ° C. for 5 hours, and gradually cooled to obtain a target 2.

Next, these targets were set in the chamber and the same procedure as in Example 1 was followed, except that Table 7
Steps 1 to 4 of the condition shown in 5 are performed in this order.
Ca _0.95 Cu _1.0 O by target 1 repeated 0 times
_A thin film was formed in which the _γ layer was a 4-unit lattice, and the target 2 CeO _{2 + τ} layer was a 1-unit lattice.

[0068]

[Table 7] The substrate was placed 30 mm away from the target. The oxidizing atmosphere in the chamber was oxygen gas containing 5% ozone, and the partial pressure was adjusted to 10 Pa. further,
Substrate temperature is 600 ℃, laser oscillation frequency is 3Hz
And A film thickness meter was used to monitor the thickness.

Thus, Ca _0.95 Cu _1.0 O was formed on the substrate.
A thin film was obtained in which the _γ layer was stacked alternately with 4 unit lattices and the CeO _{2 + τ} layer was stacked with 1 unit lattice 50 times. T of this thin film
The c (χ) _onset was 8K.

Example 6 Each powder of SrCO ₃ , CaCO ₃ and CuO was mixed with Sr: C.
a: Cu are weighed so as to be 0.5: 0.5: 1, mixed, calcined in air at 700 ° C. for 5 hours, crushed, formed into pellets, and 850 ° C. in air. Sintering was performed for 5 hours, and the target 1 was obtained by slow cooling. In addition, SrC
Each powder of O ₃ and TiO ₂ is weighed so that Sr: Ti becomes 3: 2, mixed, calcined in air at 800 ° C. for 5 hours, crushed, molded into pellets, and put in air. Then, it was sintered at 900 ° C. for 5 hours and gradually cooled to obtain a target 2.

Then, these targets were set in the chamber and the same procedure as in Example 1 was followed, except that Table 8
Steps 1 to 4 of the condition shown in 5 are performed in this order.
Ca _0.5 Sr _0.5 C with target 1 repeated 0 times
u _1.0 O _γ layer is 3 unit cell, Sr by target 2
_A thin film was formed in which a layer of ₃ Ti ₂ O _{7 + χ} has a 2-unit lattice.

[0072]

[Table 8] The substrate was placed 30 mm away from the target. The oxidizing atmosphere in the chamber was oxygen gas, and the partial pressure was adjusted to 1 Pa. Furthermore, the substrate temperature is 650
The laser oscillation frequency was 4 Hz. A film thickness meter was used to monitor the thickness.

Thus, Ca _0.5 Sr _0.5 C was formed on the substrate.
A thin film was obtained in which a layer of u _1.0 O _γ has a 3-unit lattice, and a layer of Sr ₃ Ti ₂ O _{7 + χ} has a 2-unit lattice and is alternately stacked 50 times. The Tc (χ) _onset of this thin film was 4K.

Example 7 SrCO ₃ , CaCO ₃ , and CuO powders were mixed with Sr: C.
a: Cu is weighed so as to be 0.63: 0.27: 1, mixed, calcined in air at 700 ° C. for 5 hours, pulverized, and molded into pellets, and 850 ° C. in air. Sintering was performed for 5 hours, and the target 1 was obtained by slow cooling. Also, Nd
₂ O ₃ and Nb ₂ O ₅ powders were weighed and mixed so that Nd: Nb was 1: 3, mixed, calcined in air at 800 ° C. for 5 hours, crushed, and molded into pellets, 100 in the air
The target 2 was obtained by sintering at 0 ° C. for 5 hours and gradually cooling.

Next, these targets were set in the chamber and the same procedure as in Example 1 was followed, except that Table 9
Steps 1 to 4 of the condition shown in 5 are performed in this order.
Repeated 0 times, with target 1 (Ca _0.3 S
A thin film was formed in which the r _0.7 ) _0.9 Cu _1.0 O _γ layer had a 4-unit lattice, and the target 2 layer of Nd _0.33 NbO _{3 + ω} had a 1-unit lattice.

[0076]

[Table 9] The substrate was placed 30 mm away from the target. The oxidizing atmosphere in the chamber was oxygen gas, and the partial pressure was adjusted to 10 Pa. Furthermore, the substrate temperature is 65
The laser oscillation frequency was 4 Hz. A film thickness meter was used to monitor the thickness.

Thus, (Ca _0.3 S
r _0.7 ) _0.9 Cu _1.0 O _γ layer has 4 unit cells, Nd _0.33
A thin film was obtained in which layers of NbO _{3 + ω} were alternately stacked 50 times in units of 1 unit lattice. The Tc (χ) _onset of this thin film is 48
It was K.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication C01G 53/00 ZAA A C23C 14/08 L 9271-4K H01B 12/06 ZAA 7244-5G 13/00 565 D 7244-5G

Claims (2)

[Claims] 1. The formula (Ca _1-s Sr _s ) _t CuO _u (where 0 ≦ s ≦ 1.0, 0.8 ≦ t ≦ 1.1, 1.8 ≦ u
An oxide represented by ≦ 2.2) and an oxide having a cation distance of 0.36 nm or more and 0.41 nm or less in the crystal structure, which is selected from the following substance groups a to f. A superconductor characterized by being layered. I. α _{1 + μ} β _1-μ O _{3 + ν} (where α is Dy, Sm, Nd, Pr, Ce, La,
Eu, Bi, Pb, Gd, Na, Sr, Ca, Ag,
An element selected from K and Ba, β is Mn, Co,
Al, Ga, Cr, Ce, Cd, Ni, W, Fe, G
a, Ta, V, Ti, Mo, Sn, Rh, Nb and Z
An element selected from r. −0.2 ≦ μ ≦ 0.2, −0.3
≤ν≤0.3) b. γ _{2 + ξ} δ _1-ξ O _{4 + π} (where γ is an element selected from La, Sr and Nd, and δ is Li, Ni, Al, Co, Mn, Mg, Cr,
Ga, Rh, Ti, Fe, Ru, Ir, Mo and Sn
An element selected from. −0.2 ≦ ξ ≦ 0.2, −0.3 ≦
π ≦ 0.3) c. ε _{n + 1 + ρ} ζ _n-ρ O _{3n + 3 + σ} (where ε is an element selected from Pb, Bi and Ba, and ζ is an element selected from Ti, Nb and Ta. n =
2, 3 or 4. −0.2 ≦ ρ ≦ 0.2, −0.3 ≦ σ
≦ 0.3) D. η _m O _{q + τ} (where η is Na and m = 2, q = 1, and η is Ce and m =
1, q = 2, or η is Y, Ho, Dy, Tb, G
An element selected from d, Eu, Sm, Pr, Nd and La. m = 2, q = 3. −0.3 ≦ τ ≦ 0.3) E. Sr _{r + 1 + φ} Ti _r-φ O _{3r + 1 + χ} (where r = 2 or 3. −0.2 ≦ φ ≦ 0.2, −
0.3 ≦ χ ≦ 0.3) f. κ _{0.33+ ψ} λ _1-ψ O _{3 + ω} (where κ is Yb, Y, Dy, Gd, Ce, Sm, N
An element selected from d, La and Pr, and λ is an element selected from Ta and Nb. −0.1 ≦ ψ ≦ 0.1, −
0.3 ≦ ω ≦ 0.3) 2. The formula (Ca _1-s Sr _s ) _t CuO _u (where 0 ≦ s ≦ 1.0, 0.8 ≦ t ≦ 1.1, 1.8 ≦ u)
An oxide layer represented by ≦ 2.2) and an oxide having a cation distance of 0.36 nm or more and 0.41 nm or less selected from the following substance groups a to f in the crystal structure. A method for producing a superconductor, characterized in that the layer and the layer are formed by a stacking method. I. α _{1 + μ} β _1-μ O _{3 + ν} (where α is Dy, Sm, Nd, Pr, Ce, La,
Eu, Bi, Pb, Gd, Na, Sr, Ca, Ag,
An element selected from K and Ba, β is Mn, Co,
Al, Ga, Cr, Ce, Cd, Ni, W, Fe, G
a, Ta, V, Ti, Mo, Sn, Rh, Nb and Z
An element selected from r. −0.2 ≦ μ ≦ 0.2, −0.3
≤ν≤0.3) b. γ _{2 + ξ} δ _1-ξ O _{4 + π} (where γ is an element selected from La, Sr and Nd, and δ is Li, Ni, Al, Co, Mn, Mg, Cr,
Ga, Rh, Ti, Fe, Ru, Ir, Mo and Sn
An element selected from. −0.2 ≦ ξ ≦ 0.2, −0.3 ≦
π ≦ 0.3) c. ε _{n + 1 + ρ} ζ _n-ρ O _{3n + 3 + σ} (where ε is an element selected from Pb, Bi and Ba, and ζ is an element selected from Ti, Nb and Ta. n =
2, 3 or 4. −0.2 ≦ ρ ≦ 0.2, −0.3 ≦ σ
≦ 0.3) D. η _m O _{q + τ} (where η is Na and m = 2, q = 1, and η is Ce and m =
1, q = 2, or η is Y, Ho, Dy, Tb, G
An element selected from d, Eu, Sm, Pr, Nd and La. m = 2, q = 3. −0.3 ≦ τ ≦ 0.3) E. Sr _{r + 1 + φ} Ti _r-φ O _{3r + 1 + χ} (where r = 2 or 3. −0.2 ≦ φ ≦ 0.2, −
0.3 ≦ χ ≦ 0.3) f. κ _{0.33+ ψ} λ _1-ψ O _{3 + ω} (where κ is Yb, Y, Dy, Gd, Ce, Sm, N
An element selected from d, La and Pr, and λ is an element selected from Ta and Nb. −0.1 ≦ ψ ≦ 0.1, −
0.3 ≦ ω ≦ 0.3)