JP2703036B2 - Superconducting material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a new oxide superconductor, and to a stable superconductor having a high critical concentration.

[Conventional technology]

Perovskite-type copper oxide (La _2-x Ba _x CuO _{4 of} K ₂ NiF ₄ type) which shows a superconducting state at a relatively high temperature is formed by Bednorz and Ml
Invented in 1986 by ler. Thereafter, various superconductors were synthesized by substituting A-site ions (La ³⁺ and Ba ^{2+ in the} above example) having a large ionic radius in the basic structure of perovskite, ABO ₃ . As a typical example, La-Sr-Cu-O (critical temperature T _C = 40
K) and Y-Ba-Cu-O (T _C = 90K). Higher T _C
As a substance having, a part of Cu of B site ion is Tl
Or substituted with Bi, Ba-Ca-Tl- Cu-O (T C = 120
K), Sr-Ca-Bi -Cu-O (T C = 105K) and Tl-Sr-Cr-
_{Cu-O (T C = 110K} ) superconductors have been invented.

La-Sr-Cu-O or Y-Ba-Cu-O superconductor is
Although the synthesis method is relatively easy, the _TC is low, and the main research focuses on Tl-Ba-Ca-Cu-O, Tl-Sr-Ca-Cu-O and Bi-.
Moving to Sr-Ca-Cu-O superconductors. But Bi-Sr
-Ca-Cu-O-based superconductors, in one crystal grain, T _C
Phases tend to coexist, and it is very difficult to obtain a single phase. As a result, the critical current density cannot be increased. Tl-Ba-Ca-Cu-O system and Tl-Sr-Ca-Cu
-O-based superconductor, Tl evaporation occurs when firing,
The disadvantage is that it is difficult to control the composition of the final product.

[Problems to be solved by the invention]

Conventional superconducting material described above, relatively easy thing synthesis T _C is not sufficiently high, a high T _C material whose synthesis has been made difficult.

Among the superconductors having a perovskite-like structure discovered so far, La _1-x Ba _x CuO _x has a defect that _TC is as low as 30K. YBa ₂ Cu ₃ O _x is T _C is a 90K,
This degree of T _C, it is difficult to use at liquid nitrogen temperatures and moisture, the disadvantage of degradation readily react with carbon dioxide been filed.

Bi-Sr-Ca-Cu-O-based superconductor has the highest
It is very difficult to synthesize a material consisting only of the crystalline phase Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x that gives T _C and 110 K, and there is a defect that a superconductor material having a high critical current density cannot be produced. Tl-Ba
The -Ca-Cu-O and Tl-Sr-Ca-Cu-O-based superconductors have a defect that the composition of the final product is difficult to control due to evaporation of Tl during firing.

An object of the present invention is to provide a superconducting material having a high critical temperature and various physical and chemical properties to provide a high critical temperature, a high critical current density, and a high critical magnetic field. Another object of the present invention is to provide a superconductive material which is chemically stable and easy to manufacture.

[Means for solving the problem]

The present invention relates to a composite oxide represented by the general formula (A _1-x A ′ _x ) ₂ B ₂ B ′ _n-1 C _un O _{2n + 4 +} δ or (A _1-x A ′ _x ) B ₂ B ′ _n here _{-1 C un O 2n + 3 +} δ, a: B i or Tl a ': ionic radius in the crystal is more than 0.81A 1.05
単 独 One or more of the following elements: B: at least one of Na, K, Rb, Cs, Mg, Ca, Sr and Ba B ': at least one of Na, Ca, Y and lanthanite elements.

Cu: Copper O: Oxygen A compound represented by n = 2,3 or 4-1 <δ <1,0 ≦ x ≦ 1, and in its crystal structure, five oxygen ions are formed around the Cu ions by pyramids. A superconducting material comprising a part coordinated with a mold and having an average valence of copper of more than 2.0 and not more than 2.5.

The crystal structures of the high-temperature superconducting materials discovered so far are summarized in FIG. 1 to FIG. Among these crystal structures, FIG. 1 (2), superconductors having a structure shown in FIG. 2 (2) has a particularly high T _C. The superconductors La _1-x Ba _x CuO _x , La _1-x Sr _x CuO _x and La _1-x Ca having the structure shown in FIG.
_x CuO _x , superconductor YBa ₂ C having the structure shown in FIG. 3 (2)
In the case of u ₃ O _7- δ, the relationship shown in Fig. 3 exists between the T _C and the average valence of Cu in the crystal, and the optimal average valence of Cu exists. Was known. In this study, we also found that an optimal Cu average valence exists for a superconducting material having a crystal structure different from that shown in FIG. It has been found that superconductivity is preserved even if each site is replaced with another element, and the present invention has been reached. In the case of the superconductor having the crystal structure shown in FIGS. 1 and 2 discovered so far, the A and A 'sites are occupied only by Tl or Bi. However, whenever the site was replaced with another atom, the crystal structure did not change and the superconductivity was found to be exhibited if the average valence of Cu was within the range of 2.0 to 2.5. . Similarly, a substance in which another site is replaced with another atom also exhibits superconductivity.

We also performed crystal structure analysis of various materials synthesized by substituting each site with other atoms, and investigated in detail the interatomic distance between Cu ions and O ions forming the pyramid type. In the past, it was said that the bond of Cu-O spreading in the plane direction of the pyramid type was strongly related to superconductivity, but according to our research, the distance between Cu ions and oxygen ions existing in the vertex direction was , A strong correlation with superconductivity was observed. Specifically, it has been found that a material having a distance of 2.10 ° to 2.30 ° is a material having excellent superconductivity.

The superconducting material of the present invention is provided in the form of a powder, a lump, a sintered body, a thick film, or a line. When the starting materials are mixed and reacted by some means to synthesize the substance of the present invention,
Powders, lumps and the like are obtained. After molding, the powder is also obtained as a sintered body. Also, a thick film can be formed by a doctor blade method or the like. If the powder is melted and rolled with a roll or the like, a tape or ribbon-shaped superconductor can be obtained. Filling in a metal pipe or the like and drawing or rolling yields a linear product. In order to obtain the superconductor of the present invention in a thin film, a sputter method, an evaporation method, a thermal spray method, a laser evaporation method, an MBE method (Moleculer Beam Epitaxy), a CVD method (Chemic method).
al Vavor doposition) is used. In order to obtain the powder of the superconducting material of the present invention, methods such as an oxide mixing method, a coprecipitation method, and a sol-gel method can also be used. The temperature at which the raw materials are reacted to synthesize the superconducting substance varies depending on the composition of the substance and the production method, but is suitably in the range of 600 ° C to 1000 ° C. Generally speaking, the larger the number n,
Requires longer reaction times at lower temperatures.

[Action]

T _C high temperature does not exceed 100K superconducting material _{La 1-x Ba x CuO x} , La
_{In 1-x} Sr _x CuO _x and YBa ₂ Cu ₃ O _7- δ, studies on the superconducting mechanism have been actively conducted. La _1-x D _x CuO
Each of the superconducting materials represented by the composition formula of _x (D: Ba, Sr, Ca) has a crystal structure as shown in FIG.
The element in the portion represented by D shows superconductivity regardless of Ba, Sr, or Ca. The superconducting material represented by the composition formula of YBa ₂ Cu ₃ O _7- δ also has a crystal structure shown in FIG. 2 (2), which also has a Y atom part partially substituted with another rare earth element.
Alternatively, it is known that even a completely substituted substance exhibits superconductivity as long as the crystal structure does not significantly change. From these facts, it is thought that the crystal structure of the material, especially the plane of Cu atoms and O atoms extending in the direction perpendicular to the C axis, is the key to the development of superconductivity. Research is also being conducted with a focus on this point. On the other hand, for the La _1-x D _x CuO _x system, the substitution rate of D atoms is determined, and for the YBa ₂ Cu ₃ O _7- δ system,
The Yotsute value from T _C is known to vary. At present, it is said that _TC is strongly dependent on the average valence of Cu in relation to the average valence of Cu (see FIG. 4). Third
Regarding the superconducting material having a T _C of not more than 100 K having the crystal structure shown in the figure, it is considered that the crystal structure and the average valence of Cu have a strong influence on the superconductivity. However, with respect to other crystal structures, such as a group of superconductors having the structures shown in FIGS. 1 and 2, such knowledge has not been obtained at all until now. Therefore, this time, we synthesized many kinds of materials having these crystal structures, studied the crystal structure and hole concentration in detail, and came to find a common feature of the materials showing superconductivity.

The ions occupying the site indicated by (A) in the crystal structure models of FIGS. 1 and 2 do not particularly contribute to the development of superconductivity, and any element as long as the crystal structure is not changed. It turned out that it was OK.

Next, the role of the ions occupying the site shown in FIG. 1B in the model of FIGS. 1 and 2 is explained. It is understood that the nearest oxygen of the cation occupying this portion is deeply involved in superconductivity. We have found. In FIG. 5, a Cu ion to form a Piramitsudo, the distance of the oxygen ions located at the apex of the Piramitsudo the horizontal axis, and the vertical axis shows a graph was convex to T _C. It can be seen that there is a clear correlation between the superconducting critical temperature and this distance. In order to change the interatomic distance in this portion, it is easiest to introduce an element having a different ionic radius into the (B) site.

We have found that for ions occupying the (B ') site, the ionic radius must be greater than or equal to 0.90 ° and less than or equal to 1.0 °. If the size of the ions in this portion is large, oxygen is introduced and pyramids of Cu and O atoms are not formed. If it is too small, the crystal structure will be different.

Although the above results were obtained by synthesizing various superconducting materials and non-superconducting materials and examining them in detail, superconductivity was not exhibited only by satisfying these conditions. Figures 1 and 2
In superconducting material having a structure in which dampening in FIG, T _C be cowpea concentration of holes present in the portion of Piramitsudo structure that forms the Cu atoms and the O atoms to change, we have found. For the various elements A, A ', B, B' and various values of x, a substance having the composition (A _1-x A ' _x ) ₂ B ₂ B' ₂ Cu ₃ O ₁₀₊ δ was synthesized, and the concentration was examined the relationship of T _C. Incidentally, a value obtained by subtracting 2.0 from the average valence of Cu gives a hole concentration approximately. The results are shown in FIG. When the hole concentration is around 0.22, T _C
It can be seen that _TC is less than 60K at 0.08 or less and 0.38 or more.

If a substance that satisfies the above-mentioned conditions regarding the crystal structure and the conditions regarding the hole concentration can be synthesized, it is considered that there is a high possibility that a superconducting substance other than the substance discovered in the present invention can be obtained. However, at present, no clear answer has been obtained regarding the mechanism of superconductivity, and there is no guarantee that a superconducting substance will be obtained if these two conditions are satisfied. However, the principles of the present invention will provide important guidance for the discovery of new superconducting materials.

〔Example〕

Example 1 Tl ₂ O ₃ , Bi ₂ O ₃ , SrO, CaO, CuO were used as starting materials.
First, Bi ₂ O ₃ , SrO, CaO, and CuO were converted to Bi: Sr: Ca: Cu, respectively.
Were mixed at an atomic ratio of 1: 2: 1: 2, and calcined at 880 ° C. for 100 hours in the air. On the way, take it out of the furnace and cool it down,
The pulverizing step was performed three times. Tl is added to the powder thus obtained.
₂ O ₃ is mixed so that the atomic ratio of Tl: Bi: Sr: Ca: Cu becomes 1: 1: 2: 1: 2, sealed with gold foil, and fired at 870 ° C for 50 hours. Natsuta Analyze the X-ray diffraction pattern of the resulting powder to confirm that it has a similar crystal structure to Bi ₂ Sr ₂ CaCu ₂ O _x and that 50% of the Bi sites are a new substance with Tl replaced Was. This powder was sintered at 800 ° C., and the electrical resistance of the obtained sintered body was measured while lowering the temperature. As a result, the resistance began to drop sharply at around 90 K, and became zero at 80 K.

Example 2 According to the method described in Example 1, a substance represented by a composition formula of (Bi _1-x A ′ _x ) ₂ Sr ₂ Ca ₂ Cu ₃ O _x was obtained according to the method described in Example 1.
Performs synthesis was measured T _C of the sample. While results are shown in Table 1, T _C shown here is the temperature at which the resistance begins to drop sharply, i.e. the temperature from T _C Onsetsuto indicated by absolute temperature.

FIG. 7 shows the hole concentration (the value obtained from the measurement of the hole coefficient) of the prepared sample.
Value re of the number of Cu1 per) and shows the relationship of T _C.

EXAMPLE _{-3 Bi 2 (Sr 1-x} B x) 2 Ca 2 Cu 3 O x of composition material oxides such substances can be obtained of the formula are mixed, the T _C by combining the various samples Measurements were made. The results are shown in Table 2.

In Figure 8 shows the relationship between the hole concentration and T _C.

Example-4 Raw materials oxides were mixed and fired to obtain a material represented by a composition formula of Bi ₂ Sr ₂ (Ca _1-x B ′ _x ) ₂ Cu ₃ O _x , and various samples were synthesized. the measurement of the T _C line Natsuta. Third result
It is shown in the table.

Example-5 Raw materials oxides were mixed and fired so that a substance represented by the composition formula of (Tl _1-x A ′ _x ) ₂ Ba ₂ Ca ₂ Cu ₃ O _x was obtained, and various samples were synthesized. the measurement of the T _C line Natsuta. The results are shown in Table 4.

Example -6 The raw material oxides were mixed and calcined so as to obtain the substance represented by the composition formula of Tl (Ba _1-x B _x ) ₂ Ca ₂ Cu ₃ O _x , and various samples were synthesized to obtain the T _C measurements were taken. The results are shown in Table 5.

Also, the relationship between the hole concentration and T _C of the samples No. 9
Shown in the figure.

Comparative Example-1 To prepare a sample having a low hole concentration, Tl (Ba
The _{1-x La x) 2 Co} 2 Cu 3 O x of composition material oxides such substances can be obtained of the formula, mixing and baking, KoTsuta measurement of T _C.

 The results are shown in Table 6.

Also shows hole concentration and T _C of the relationship between these samples in Figure 9.

Example-7 Raw materials oxides were mixed and calcined so as to obtain a material represented by the composition formula of (Tl _1-x A ′ _x ) Sr ₂ Ca ₂ Cu ₃ O _x , and various samples were synthesized. KoTsuta the measurement of T _C. The results are shown in Table 7.

The superconductive material having a crystal structure shown in Example -8 FIG. 1 (3) were synthesized and measured the T _C. Table 8 shows the results.

The superconductive material having a crystal structure shown in FIG. 2 (3) were synthesized and measured the T _C. Table 9 shows the results.

[Effects of the Invention] According to the present invention, it is expected that various characteristics required for a superconducting material such as a critical temperature, a critical magnetic field, a current density, chemical stability, and formability are improved.

[Brief description of the drawings]

1 (1) to (3) show the composition formula A ₂ B ₂ B ′ _n-1 C _n O _{2n + 4 +} δ
Schematic diagrams showing the crystal structure of the superconducting material represented by (n = 2,3,4), and FIGS. 2 (1) to 2 (3) show the composition formula AB ₂ B ′ _n-1 C _n O
Schematic diagrams showing the crystal structure of a superconducting material represented by _{2n + 3 +} δ (n = 2, 3, 4), and FIGS. 3 (1) and (2) show La _1-x D _x CuO
_x (D: Ba, Sr, Ca) and YBa ₂ Cu ₃ On _- δ are schematic diagrams showing the crystal structures, and FIG. 4 is a graph of Cu of La _1-x D _x CuO _x and YBa ₂ Cu ₃ O _7- δ. graph showing the average valence, the relationship between the critical temperature (T _C), the fifth
Figure the length of oxygen atoms located Cu atom and apex portion constituting the Piramitsudo portion of superconducting material according to the present invention, characteristic diagram showing the relationship of T _C, FIG. 6 is a hole concentration of superconducting material according to the present invention characteristic diagram showing the relationship from T _C and, FIG. 7-Fig. 9 is a characteristic diagram showing the number of holes relations per Cu atom critical temperature T _C and Piramitsudo portion.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01B 12/00 ZAA H01L 39/12 ZAAC H01L 39/12 ZAA C04B 35/00 ZAAK (72) Inventor Atsuko Soeda 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Yuichi Kamo 4026 Kuji-machi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Toroshi Takeuchi Ibaraki Prefecture 4026 Kuji-cho, Hitachi City Hitachi, Ltd.Hitachi Laboratory

Claims (15)

(57) [Claims] The general formula (A _1-x A ′ _x ) ₂ B ₂ B ′ _n-1 C _un O _{2n + 4 +} δ (A _1-x A ′ _x ) B ₂ B ′ _n-1 C _un O _{2n + 3 +} δ where A: Bi or Tl A ': An element whose ionic radius in the crystal is 0.81Å or more and 1.05Å or less, B or Na, K, Rb, Cs, One or more selected from La, Ca, Sr, Ba B ': One or more selected from Na, Ca, Y, lanthanoid elements Cu: copper, O: oxygen n = 2, 3 or 4-1 <δ <1,0 <x ≦ 1, wherein the average valence of copper in the crystal is more than 2.0 and not more than 2.5. 2. The superconducting material according to claim 1, wherein the crystal structure of the material includes a portion in which five oxygen atoms are coordinated around Cu in a pyramid form. 3. The substance according to claim 2, wherein the number of holes in the substance is copper 1 in which five oxygen atoms are coordinated in a pyramid form.
A superconducting material characterized by being 0.15 or more and 0.35 or less per piece. 4. The superconducting substance according to claim 2, wherein the crystal structure of the substance is schematically shown in FIG. 1 or FIG. 5. The superconducting material according to claim 2, wherein the element constituting A 'is composed of one or more of Bi, Tl, Ca, Pb, Hg, Y and a lanthanoid element. 6. The superconducting material according to claim 2, wherein the elements constituting B and the elements constituting B ′ are regularly arranged in the crystal. 7. The substance according to claim 4, wherein the A and A 'atoms occupy the portion indicated as (A) site in the schematic diagram of the crystal of FIG. 1 or FIG. A crystal occupied by the atoms constituting B and B 'occupies the site indicated by the sites and (B') site, Cu occupies the portion indicated by (C) site, and oxygen occupies the portion indicated by (D) site Superconductive material characterized by having a structure. 8. The material according to claim 7, wherein Cu occupies a portion indicated by (C-1) in FIG. 1 or FIG.
A superconducting material, wherein a distance between oxygen at sites occupying a portion indicated by (D-1) is not less than 2.10 ° and not more than 2.70 °. 9. A superconducting wire comprising the substance according to any one of claims 1 to 8. 10. A magnet using an element containing the substance according to any one of claims 1 to 8. 11. A device comprising the substance according to claim 1. 12. A measuring device using an element containing the substance according to any one of claims 1 to 8. 13. An arithmetic unit using an element containing the substance according to claim 1. 14. An electric power storage device using an element containing the substance according to any one of claims 1 to 8. 15. A magnetic shield device using the substance according to any one of claims 1 to 8.