JPH09169521A - Oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new oxide superconductor capable of controlling superconducting characteristics over a wide range and capable of controlling the number of CuO2 faces existing in unit lattice by varying the concn. of carriers. SOLUTION: This oxide superconductor contains Hg, Tl, M (M is at least one kind of alkaline earth metal selected from among Ba, Sr and Ca), Cu, O and Ln (Ln is at least one kind of rare earth element selected from among Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) and has a crystal structure formed by alternately superposing parts each based on a rock-salt structure and consisting of two atomic layers each consisting of Hg, Tl and O and parts each having an infinite layer structure while interposing an atomic layer made of at least one of M and Ln. Each of the latter parts are formed by alternately superposing atomic layers each consisting of Cu and O in an atomic ratio of 1:2 and atomic layers each consisting of at least one of M and Ln and O and the number of the parts is 2n-1 [(n) is an integer of >=1].

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide superconductor having a high superconducting transition temperature (Tc).

[0002]

2. Description of the Related Art Oxide superconductors have a zero electric resistance below a superconducting transition temperature (hereinafter abbreviated as Tc), exhibit complete diamagnetism, and have a characteristic that is not present in other substances. Have, cables for power transmission,
A wide range of applications are expected in the fields of generator wires, fusion plasma confinement materials, magnetic levitation train materials, magnetic shield materials, and high-speed computers.

Bednorz and Muller
Has a high Tc of about 30K in 1986 (La
After discovering _1-x Ba _x ) ₂ CuO ₄ , YBa ₂ Cu _{3
O 7 (Tc = 90K),} Bi-Sr-Ca-Cu-O based oxide superconductor (Tc = 110K), Tl- Ba-Ca
-Cu-O-based oxide superconductor (Tc = 125K), Hg
-Ba-Ca-Cu-O-based oxide superconductor (Tc = 13
5 K) and other relatively high temperature oxide superconductors have been reported. Currently, much research is being conducted on the manufacturing methods, physical properties, applications, etc. of these substances.

It is known that in an oxide superconductor containing copper (copper oxide superconductor), Tc is also changed by changing the carrier concentration in the substance, and the maximum T
There is an optimum carrier concentration that gives c. This oxide superconductor becomes a p-type oxide superconductor when the formal average valence of copper forming the CuO ₂ plane in the crystal structure is approximately +2.10 to +2.30. Here, a doped state in which the valence of copper is low and does not reach the maximum Tc is called an underdoped state, and a doped state in which the valence of copper is too high is called an overdoped state.

Considering the electric transport characteristics of the copper oxide superconductor in the normal conducting state, the valence of copper is +
When it is 2.00, it is an insulator, and as the carrier concentration is changed by doping holes, the resistivity gradually decreases, the valence of copper also increases, and the semiconductor changes from a conductor to a conductor. The oxide superconductor is Tc in the middle from the semiconductor to the conductor.
The superconductor state appears when cooled to the temperature below. By changing the carrier concentration in this way, the state of the oxide superconductor (superconductivity, normal conductance) can be controlled.

It is known that the p-type copper oxide superconductor has a layered crystal structure, and various characteristics such as Tc change depending on the number of CuO ₂ planes present in the unit cell. In particular, it has been reported that one having three or more CuO ₂ planes exhibits a high Tc exceeding 100K. Therefore, various characteristics such as Tc can be controlled by controlling the number of CuO ₂ planes during the synthesis of the oxide superconductor. In recent years, it has been proposed that an electronic device composed entirely of an oxide material should be produced by positively utilizing these controllability, and its possibility has been discussed.

[0007]

As described above, the superconducting characteristics and normal conducting characteristics of the p-type copper oxide superconductor can be controlled by changing the carrier concentration.
For application to electronic devices and the like, it is necessary to control the carrier concentration in a wide range. However, most currently known p-type copper oxide superconductors have a narrow range in which the carrier concentration can be changed. Further, there are still few kinds of oxide superconductors having three or more CuO ₂ planes. To realize "all oxide electronic devices", there is an urgent need and an urgent need to increase the types of oxide superconductors that are more flexible in terms of controllability.

The present invention has been made in view of the above point, and it is possible to control the superconducting characteristics in a wide range by changing the carrier concentration and to control the number of CuO ₂ planes existing in the unit cell. The object is to provide a new oxide superconductor.

[0009]

According to the present invention, mercury, thallium, an alkaline earth metal M (M is at least one element of Ba, Sr and Ca), copper, oxygen and a rare earth element L are used.
n (Ln is Y, La, Nd, Sm, Eu, Gd, Dy,
An oxide superconductor containing at least one element of Ho, Er, Tm, Yb, and Lu), which is composed of mercury, thallium, and oxygen, and is based on a rock salt structure composed of two atomic layers. , 2n in which an atomic layer composed of 2 oxygen atoms and an atomic layer composed of at least one element of M and Ln are alternately stacked with respect to 1 copper atom
-1 (n is an integer of 1 or more, but in the case of n = 1, it becomes an atomic layer in which there are two oxygen atoms to one copper atom), and at least one of M and Ln Provided is an oxide superconductor characterized by having a crystal structure in which elements and oxygen atoms are alternately stacked via an atomic layer.

The above oxide superconductor has (Hg _1-x Tl
_{x) 2 M 3-y Ln} y Cu n O 2 + 2 (n + 1) + ( where, n
= 2, 0.15 ≦ x ≦ 0.75, 0 ≦ y ≦ 1.0, −
1.0 ≦ δ ≦ 0.8) or (Hg _1-x Tl _x ) ₂ M
_{n + 1} Cu _n O _{2 + 2 (n + 1) +} (where n = 3 or 4, 0.3 ≦ x ≦ 0.6, −0.7 ≦ δ ≦ 0.4) Is preferred. Further, in the above oxide,
At least part of the thallium may be replaced with bismuth or lead.

[0011]

Embodiments of the present invention will be specifically described below with reference to the drawings. In the oxide superconductor of the present invention, a portion based on a rock salt structure (rock salt structure portion) is a portion where two atomic layers represented by (Hg, Tl) -O are stacked as shown in FIG. is there.

In the oxide superconductor of the present invention, the infinite layer structure portion is, as shown in FIG. 1, composed of an atomic layer having 1 oxygen atom and 2 oxygen atoms and at least one element of M and Ln. 2n- stacked with composed atomic layers
One structure, ie ... CuO _2- (M, Ln) -Cu
It is a (2n-1) atomic layer structure represented by O ₂ . For the alkaline earth metal M, at least one element of Ba, Sr, and Ca is selected.
In this composition formula, n is set to be an integer of 1 or more. However, when n = 1, the atomic layer is composed of 1 copper atom and 2 oxygen atoms. In particular, in the case of an oxide superconductor having an infinite layer structure, as shown by high Tc, n
Is preferably an integer of 2 to 5.

That is, in the oxide superconductor of the present invention, the rock salt structure portion and the infinite layer structure portion are composed of at least one element of M and Ln and an oxygen atom (M,
It has a crystal structure in which Ln) -O layers are alternately stacked.

In particular, (Hg _1-x Tl _x ) ₂ M _3-y Ln _y
Cu _n O _{2 + 2 (n + 1) +} (where n = 2, 0.15 ≦ x
≦ 0.75, 0.0 ≦ y ≦ 1.0, −1.0 ≦ δ ≦ 0.
The oxide superconductor represented by 8) can realize a doped state in a wide range. In addition, (Hg _1-x Tl
_x ) ₂ M _{n + 1} Cu _n O _{2 + 2 (n + 1) +} (where n = 3 or 4, 0.3 ≦ x ≦ 0.6, −0.7 ≦ δ ≦ 0.
The oxide superconductor represented by 4) does not contain a rare earth element whose resource is unevenly distributed and whose refining cost is expensive, and Tc can be controlled in the range of 45 to 113K.

The same effect can be obtained by replacing at least part of thallium with bismuth or lead. By this substitution, the amount of thallium harmful to the human body in the oxide superconductor can be reduced.

Next, examples carried out to clarify the effect of the oxide superconductor of the present invention will be described. (Example 1) BaO ₂ , CaO having a purity of 99.9% or more,
Y ₂ O _3, each raw material powder of _{CuO Ba 2 Y 1-y Ca} y C
u ₂ O _z (z is arbitrary) is mixed in a molar ratio so that y in the composition formula is 0, 0.3, 0.6, and 1.0, and four kinds of mixed powders are mixed. Prepared. This mixed powder is heat-treated at 900 ° C. for 24 hours in an oxygen stream,
It was gradually cooled at a cooling rate of 3 ° C / min. The powder thus obtained was used as a precursor. HgO and Tl ₂ O ₃
(Hg _1-x Tl _x ) ₂ Ba ₂ Y _1-y Ca _y Cu ₂ O _z
And a mixed powder having a molar ratio such that x in the composition formula is 0, 0.15, 0.3, 0.5, 0.75, and 1.0. Prepared. In this way, 20 kinds of mixed powders were produced.

Next, each mixed powder was put into a gold capsule to seal the gold capsule. This gold capsule is installed in the hexagonal cubic anvil type ultra high pressure generator,
The gold capsule was heat-treated at a pressure of 5 GPa and a temperature of 1000 ° C. for 1 hour. The heat treatment was performed by providing a thin NaCl layer on the outer side of the gold capsule, placing the thin NaCl layer in a graphite sleeve as a heater, and applying a current to the graphite while applying pressure.

Then, after heat treatment, the gold capsule was taken out from the apparatus, and further the oxide superconductor was taken out from the gold capsule. The crystal phase in the obtained oxide superconductor (sample) was examined by powder X-ray diffraction. Further, the temperature dependence of magnetic susceptibility (cooling in a 10 Oe magnetic field) and electric resistivity was measured as an evaluation of superconducting properties.

Table 1 below shows Tc calculated from the generation state of 2212 phases and magnetic susceptibility. Here, the 2212 phase means a crystal phase having a cation arrangement similar to that of Tl ₂ Ba ₂ CaCu ₂ O _z . In Table 1, powder X
The proportion of the 2212 phase in the sample determined by line diffraction is ≧ 90%
Those having 90% to 70% were marked with “□”, those having 70 to 50% were marked with “Δ”, and those having ≦ 50% were marked with “X”. The numerical value shown on the right side of the above symbol represents Tc (K). “−” Indicates that it does not exhibit superconducting properties at a temperature of 5K or higher. The values in parentheses are Tc after annealing at 290 ° C in an argon stream.
Represents (K).

[0020]

[Table 1]

As can be seen from Table 1, 0.15≤x≤
Superconducting properties were exhibited under the conditions of 0.75 and 0 ≦ y ≦ 1.0. In addition, by introducing Tl into the Hg site, the Ca solid solution region in the Y site is expanded to 221
It was found that the two phases were stabilized over a fairly wide composition range.

FIG. 2 shows (Hg _1-x Tl _x ) ₂ Ba ₂ Y _1-y
3 shows a powder X-ray diffraction pattern of a sample of Ca _y Cu ₂ O _{z where} x = 0.3 and y = 0.3. This is 221
Two-phase single-phase sample. In addition, the magnetic susceptibility (1
(Oe magnetic field cooling) is shown in FIG. As shown in FIG.
The Meissner signal was observed with sufficient intensity.
It can be seen that the two phases exhibit bulk superconductivity.

In the above composition, x = 0.3, y =
The samples of 0 to 1.0 were further annealed at 290 ° C. in an argon stream in order to remove a small amount of oxygen from the 2212 phase. The sample with y = 0 did not exhibit superconducting properties even after annealing. The samples with y = 0.3 and 0.6 had lower Tc (K). y = 1.0
The sample of No. 1 showed superconducting properties. The result is
It is shown that the 2212 phase of the sample with y ≦ 0.6 is in the underdoped state, and the 2212 phase of the sample with y = 1.0 is in the overdoped state. in this way,
By controlling the carrier concentration in the (Hg, Tl) ₂ Ba ₂ (Y, Ca) Cu ₂ O _z system, the non-conductor on the underdoped side (normal conducting state) passes through the superconductor (superconducting state) and overdoping. It was revealed that even the non-superconductivity on the side could be made differently.

In the above composition, x = 0.15, y = 0-
Composition analysis was performed on eight samples with 1.0 and x = 0.75, y = 0-1.0 using an energy dispersive X-ray microanalyzer attached to a scanning electron microscope. When the surface of the sample was polished and the polished surface was observed with a scanning electron microscope, crystal grains having a grain size of about 2 to 7 μm were confirmed. 10 grains in each sample were analyzed. ± 1 for all samples
It was confirmed that the 2212 phase of the target composition was produced with an accuracy of 5% or less.

In the above composition, x = 0.15, y = 1.
The sample with 0 and x = 0.75, y = 0 is 0.15
It is considered that the samples having the range of ≦ x ≦ 0.75 have the smallest oxygen number and the largest oxygen number, respectively. Then, when the oxygen numbers were measured by the iodometric titration method, they were 7.00 and 8.80, respectively. Therefore, it is considered that the oxygen number of the 2212 phase in the range of 0.15 ≦ x ≦ 0.75 is in the range of 7.00 to 8.80. Note that (Hg, Tl) ₂ Ba ₂ (Y, Ca) Cu ₂
When expressed as O _{2 + 2 (n + 1) +} , n = 2, −1.0 ≦
If δ has a positive value such that δ ≦ 0.8, excess oxygen exists between the lattices. It is considered that this excess oxygen exists between the two atomic layers of the rock salt structure portion.

(Hg, Tl) ₂ Ba ₂ (Y, Ca) Cu
_{In 2} O _z- based oxide superconductors, Ba is used as Sr or Ca.
, Ca to Sr, Y to Ln (Ln is La, N
d, Sm, Eu, Gd, Dy, Ho, Er, Tm, Y
It can be easily inferred from the examples of known copper oxide superconductors that the b or Lu) can be partially or totally substituted. In fact, in the above composition, x = 0.
When 3, y = 0.3, 50% Ba is added to Sr or C
Even if it is replaced with a or 50% of Ca is replaced with Sr, T
A superconducting property of about c = 60K was confirmed. Further, when Y was completely replaced by Ln, the superconducting property of Tc = 58 to 89K was confirmed. (Example 2) BaO ₂ , CaO having a purity of 99.9% or more,
Raw material powders of CuO were mixed in a molar ratio such that a composition of Ba ₂ Ca ₂ Cu ₃ O _z (z is arbitrary) was mixed to prepare a mixed powder. This mixed powder was heat-treated at 900 ° C. for 24 hours in an oxygen stream and gradually cooled at a cooling rate of 3 ° C./min. The powder thus obtained was used as a precursor. Hg to this
O and Tl ₂ O ₃ (Hg _1-x Tl _x ) ₂ Ba ₂ Ca ₂ C
u ₃ O _z is mixed in such a molar ratio that x is 0, 0.1, 0.2, 0.3, 0.
Eleven kinds of mixed powders of 4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 were prepared.

Then, each mixed powder was put into a gold capsule to seal the gold capsule. This gold capsule is installed in the hexagonal cubic anvil type ultra high pressure generator,
The gold capsule was heat-treated at a pressure of 5 GPa and a temperature of 1000 ° C. for 1 hour. The heat treatment was performed by providing a thin NaCl layer on the outer side of the gold capsule, placing the thin NaCl layer in a graphite sleeve as a heater, and applying a current to the graphite while applying pressure.

Then, after heat treatment, the gold capsule was taken out of the apparatus, and the oxide superconductor was taken out from the gold capsule. The crystal phase in the obtained oxide superconductor (sample) was examined by powder X-ray diffraction. In addition, the temperature dependence of magnetic susceptibility and electrical resistivity was measured as an evaluation of superconductivity.

As a result, (Hg _1-x Tl _x ) ₂ Ba ₂ C
In a ₂ Cu ₃ O _z , the sample in which x = 0.3 to 0.6 was a sample in which the 2223 phase was the main phase. 22 here
The 23 phase refers to a crystal phase having a cation arrangement similar to Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _z . FIG. 4 shows a powder X-ray diffraction pattern of a sample in which x = 0.3 in the above composition. As can be seen from FIG. 4, this sample was a sample in which the 2223 phase was the main phase although it contained some impurities.

FIG. 5 shows a for a sample having the above composition.
The lattice constants of the axis and the c-axis are plotted against the Tl content x. The a-axis does not change much depending on the Tl content x, but the c-axis shows the Tl content x.
Becomes smaller as it increases. This is the content x
Means that Tl is replaced by Hg.

FIG. 6 shows the magnetic susceptibility (cooling in a 20 Oe magnetic field) of a sample in which x = 0.3 to 0.6. As shown in FIG. 6, the Meissner signal was observed with sufficient intensity, and it was confirmed that the 2223 phase exhibits bulk superconductivity. Note that Tc is 45K (x = 0.
It increased from 3) to 81K (x = 0.6). Moreover, when the number of oxygen was examined by the iodometric titration method, it was 9.3 for x = 0.3 and 9.8 for x = 0.4.
The value of x = 0.5 was 10.0, and the value of x = 0.6 was 10.2.

In addition, (Hg, Tl) ₂ Ba ₂ Ca ₂ Cu
_When expressed as ₃ O _{2 + 2 (n + 1) +} , n = 3, −0.7
If δ has a positive value such that ≦ δ ≦ 0.2, excess oxygen exists between the lattices. This excess oxygen
It is considered to exist between two atomic layers in the rock salt structure. In this way, (Hg, Tl) can be obtained without using rare earth materials that are unevenly distributed in resources and are expensive to purify.
It has been clarified that the superconducting property can be controlled by the operation of adding CaCuO ₂ to ₂ Ba ₂ CaCu ₂ O _z .

(Hg, Tl) ₂ Ba ₂ Ca ₂ Cu ₃ O ₂
It can be easily inferred from the known examples of copper oxide superconductors that Ba can be partially or totally replaced by Sr or Ca and Ca can be partially replaced by Sr in the oxide superconductors of the system. In fact, in the above composition, x = 0.
In the case of 3, even if 50% of Ba is replaced with Sr or Ca, or if 50% of Ca is replaced with Sr, Tc = 4.
A superconducting property of 1 to 87K was confirmed. (Example 3) BaO ₂ , CaO having a purity of 99.9% or more,
Raw material powders of CuO were mixed at a molar ratio such that a composition of Ba ₂ Ca ₃ Cu ₄ O _z (z is arbitrary) was mixed to prepare a mixed powder. This mixed powder was heat-treated at 900 ° C. for 24 hours in an oxygen stream and gradually cooled at a cooling rate of 3 ° C./min. The powder thus obtained was used as a precursor. Hg to this
O and Tl ₂ O ₃ are (Hg _1-x Tl _x ) ₂ Ba ₂ Ca ₃ C
u ₄ O _z is mixed in such a molar ratio that x is 0, 0.1, 0.2, 0.3, 0.
Eleven kinds of mixed powders of 4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 were prepared.

Next, each mixed powder was put into a gold capsule to seal the gold capsule. This gold capsule is installed in the hexagonal cubic anvil type ultra high pressure generator,
The gold capsule was heat-treated at a pressure of 5 GPa and a temperature of 1000 ° C. for 4 hours. The heat treatment was performed by providing a thin NaCl layer on the outer side of the gold capsule, placing the thin NaCl layer in a graphite sleeve as a heater, and applying a current to the graphite while applying pressure.

Then, after heat treatment, the gold capsule was taken out of the apparatus, and the oxide superconductor was taken out from the gold capsule. The crystal phase in the obtained oxide superconductor (sample) was examined by powder X-ray diffraction. In addition, the temperature dependence of magnetic susceptibility and electrical resistivity was measured as an evaluation of superconductivity.

As a result, (Hg _1-x Tl _x ) ₂ Ba ₂ C
In a ₃ Cu ₄ O _z , the sample in which x = 0.3 to 0.6 was a sample in which the 2234 phase was the main phase. 22 here
The 34 phase means a crystal phase having a cation arrangement similar to that of Tl ₂ Ba ₂ Ca ₃ Cu ₄ O _z . FIG. 7 shows a powder X-ray diffraction pattern of a sample in which x = 0.4 in the above composition. As can be seen from FIG. 7, the 2234 phase was the main phase although it contained some impurities. FIG.
FIG. 8B shows electron diffraction of 2234 phase in FIG.
Shows a high resolution transmission electron micrograph of the above sample.
From these, it can be confirmed that the atomic arrangement in the case of n = 4 shown in FIG. 1 is realized.

FIG. 9 shows the magnetic susceptibility (cooling in a 20 Oe magnetic field) of a sample with x = 0.3 to 0.6. As can be seen from FIG. 9, the Meissner signal is observed with sufficient intensity,
It was confirmed that the 2234 phase exhibits bulk superconductivity.
In addition, Tc showed 113K regardless of the value of x.
FIG. 10 is a diagram showing the temperature dependence of the electrical resistivity of the sample when x = 0.4. As can be seen from FIG.
Zero resistance was shown below 13K. Moreover, when the number of oxygen was examined by the iodometric titration method, it was found that the value of x = 0.3 was 11.
4 and x = 0.4 is 11.9, and x =
0.5 is 12.1 and x = 0.6 is 1
2.3.

FIG. 11 shows a sample having the above composition.
The lattice constants of the a-axis and the c-axis are plotted against the Tl content x. The a-axis does not change much depending on the Tl content x, but the c-axis decreases as the Tl content x increases. This means that Tg is replaced with Hg according to the content x.

Further, (Hg, Tl) ₂ Ba ₂ Ca ₃ Cu
₄ O _{2 + 2 (n + 1) +} , n = 4, -0.6
When δ has a positive value such that ≦ δ ≦ 0.3, excess oxygen exists in the interstitial space. This excess oxygen
It is considered to exist between two atomic layers in the rock salt structure. Thus, as in Example 2, (Hg, T
l) The superconducting property could be controlled by the operation of further adding CaCuO ₂ to ₂ Ba ₂ Ca ₂ Cu ₃ O _z , and Tc could be increased to 113K.

(Hg, Tl) ₂ Ba ₂ Ca ₃ Cu ₄ O _z
It can be easily inferred from the known examples of copper oxide superconductors that Ba can be partially or totally replaced by Sr or Ca and Ca can be partially replaced by Sr in the oxide superconductors of the system. In fact, in the above composition, x = 0.
In the case of 4, even if 50% of Ba is replaced with Sr or Ca or 50% of Ca is replaced with Sr, Tc = 1.
Superconducting characteristics of 10 to 113K were confirmed. (Example 4) For the copper oxide superconductor, Bi ₂ Sr ₂ Ca was used.
_(n-1) Cu _n O _z and HgBa ₂ Ca _(n-1) Cu _n O _z
, Etc., a series of superconductor groups such as n = 1, 2, 3, ... Is formed. From the above Examples 1 to 3, (H
g, Tl) ₂ Ba ₂ Ca _(n-1) Cu _n O _z (n = 1,
It can be easily inferred that there will be a series of superconductors such as 2, 3 ...

In the same manner as in Examples 1 to 3, (Hg _0.5 T
A sample of 1 _0.5 ) ₂ (Ba _0.5 La _0.5 ) ₂ CuO _z was prepared. When the crystal phase of these samples was examined by powder X-ray diffraction, it was found that the 2201 phase was the main phase in these samples. Further, when the temperature dependence of the magnetic susceptibility and the electrical resistivity was measured as an evaluation of the superconducting property, it was confirmed that these samples were oxide superconductors showing Tc = 50K.

In addition, (Hg _0.6 Tl _0.4 ) ₂ Ba ₂ Ca
_{When a 6} Cu ₇ O _z sample was prepared and its crystal phase was examined by powder X-ray diffraction, it was a sample in which both 2234 and 2245 phases were present. The temperature dependence of magnetic susceptibility and electric resistivity of this sample was measured, and it showed two-step superconducting transitions of 113K and 90K. It is considered that the former transition is the transition due to the 2234 phase and the latter transition is due to the 2245 phase. (Example 5) In the same manner as in Example 1, half or all of Tl ₂ O ₃ added to the precursor was replaced with Bi ₂ O ₃ or P.
An oxide superconductor was prepared by substituting bO. For these oxide superconductors, Tc was determined from the generation state of 2212 phase and magnetic susceptibility as in Example 1. The results are shown in Tables 2 to 5 below. Here, 2212 phase means T
A crystalline phase having a cation arrangement similar to that of l ₂ Ba ₂ CaCu ₂ O _z . Further, in Tables 2 to 5, the ratio of the 2212 phase in the sample determined by powder X-ray diffraction is ≧ 90.
%% is the symbol “◯”, 90-70% is the symbol “□”, 70-50% is the symbol “Δ”, and ≦ 50% is the symbol “X”. The numerical value shown on the right side of the above symbol represents Tc (K). “−” Indicates that it does not exhibit superconducting properties at a temperature of 5K or higher. The values in parentheses are Tc after annealing at 290 ° C in an argon stream.
Represents (K).

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

As is clear from Tables 2 to 5, 22
It was found that the same effect can be obtained by replacing Tl with Bi or Pb for the 12th phase. Thus, (Hg,
(Bi or Pb)) ₂ Ba ₂ (Y, Ca) Cu ₂ O _z
By controlling the carrier concentration in the system, it was clarified that the non-conductor on the under-doped side (normal conducting state) to the non-conductor on the over-doped side through the superconductor (superconducting state) can be made separately. (Example 6) In the same manner as in Example ₃ , half or all of Tl ₂ O ₃ added to the precursor was replaced with Bi ₂ O ₃ or P.
An oxide superconductor having 2223 phase and 2234 phase was prepared by substituting bO. In addition, (Hg _0.6 A _0.4 )
₂ Ba ₂ Ca _(n-1) Cu _n O _z (where A = (Tl
An oxide superconductor having a composition of _0.5 Bi _0.5 ), Bi, (Tl _0.5 Pb _0.5 ), or Pb, n = 3 or 4, and z is arbitrary) was prepared.

The crystal phases of these oxide superconductors were examined by powder X-ray diffraction in the same manner as in Example 3. In addition, the temperature dependence of magnetic susceptibility and electrical resistivity was measured as an evaluation of superconductivity. As a result, in any of the oxide superconductors, the 2223 phase and the 2234 phase were the main phases, and bulk superconductivity was confirmed. Further, Tc is shown in Table 6 below.

[0049]

[Table 6] As can be seen from Table 6, all oxide superconductors (particularly those in which n = 4) had a high Tc.

[0050]

Industrial Applicability The oxide superconductor of the present invention comprises mercury, thallium, an alkaline earth metal M (M is at least one element of Ba, Sr and Ca), copper, oxygen and a rare earth element Ln (Ln is Y. , La, Nd, Sm, Eu, Gd, D
At least one of y, Ho, Er, Tm, Yb, Lu
Oxide superconductor containing two elements), which is composed of mercury, thallium, and oxygen, and which is basically composed of a rock salt structure composed of two atomic layers, and one oxygen atom to two copper atoms. 2n-1 (n is an integer of 1 or more, where n = 1 is 1 copper atom for copper atoms) in which the atomic layers and the atomic layers composed of at least one element of M and Ln are alternately stacked. The carrier concentration is changed because the infinite layer structure portion (which is the atomic layer which is oxygen atom 2) and the infinite layer structure portion are alternately stacked via the atomic layer composed of at least one element of M and Ln. By doing so, it is possible to freely control the superconducting characteristics in a wide range and to control the number of CuO ₂ planes existing in the unit cell, and it is a novel material suitable for application to oxide electronic devices.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a crystal structure of an oxide superconductor of the present invention.

FIG. 2 shows (Hg _0.7 Tl in Example 1 of the present invention.
_0.3 ) ₂ Ba ₂ Y _0.7 Ca _0.3 Cu ₂ O _z Sample powder X
The figure which shows a line diffraction pattern.

FIG. 3 is a diagram showing a magnetic susceptibility-temperature characteristic (cooling in a 10 Oe magnetic field) of the sample of Example 1 shown in FIG.

FIG. 4 shows (Hg _0.7 Tl in Example 2 of the present invention.
_{0.3) 2 Ba 2 Ca 2 Cu} 3 O z graph illustrating a powder X-ray diffraction pattern of the sample.

FIG. 5 (Hg _1-x Tl _x ) in Example 2 of the present invention
Shows a _{2 Ba 2 Ca 2 Cu 3 O} z lattice constant of 2223 in the sample.

FIG. 6 shows (Hg _1-x Tl _x ) in Example 2 of the present invention.
_{2 Ba 2 Ca 2 Cu 3 O} z samples of magnetic susceptibility - temperature characteristics (2
The figure which shows 0 Oe magnetic field cooling).

FIG. 7 shows (Hg _0.6 Tl) in Example 3 of the present invention.
_{0.4) 2 Ba 2 Ca 3 Cu} 4 O z graph illustrating a powder X-ray diffraction pattern of the sample.

FIG. 8A shows (Hg _0.6 in Example 3 of the present invention.
Tl _0.4 ) ₂ Ba ₂ Ca ₃ Cu ₄ O _z A photograph showing electron beam diffraction of a sample, (B) is (Hg in Example 3 of the present invention)
High resolution transmission electron micrograph of _{0.6 Tl 0.4) 2 Ba 2 Ca} 3 Cu 4 O z samples.

FIG. 9 shows (Hg _0.6 Tl) in Example 3 of the present invention.
_{0.4) 2 Ba 2 Ca 3 Cu} 4 O z sample susceptibility - diagram showing a temperature characteristic (20 Oe magnetic field cooling).

FIG. 10 shows (Hg _0.6 Tl) in Example 3 of the present invention.
Shows the temperature dependence of _{0.4) 2 Ba 2 Ca 3 Cu} 4 electrical resistivity of the O _z samples.

FIG. 11 shows (Hg _1-x Tl in Example 3 of the present invention.
_x ) ₂ Ba ₂ Ca ₃ Cu ₄ O _z A diagram showing the lattice constant of the 2234 phase in the sample.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H01B 13/00 565 H01B 13/00 565D (72) Inventor Seiji Adachi Shinonome 1-chome, Koto-ku, Tokyo 14-3 International Superconductivity Industrial Technology Research Center Superconductivity Engineering Laboratory (72) Inventor Fumiko Yamamoto 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Industrial Technology Research Center Superconductivity Engineering Laboratory (72) ) Inventor Keiichi Tanabe 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Technology Center Research Institute of Superconductivity Engineering

Claims (4)

[Claims] 1. Mercury, thallium, alkaline earth metal M
(M is at least one element of Ba, Sr, and Ca), copper, oxygen, and a rare earth element Ln (Ln is Y, L
a, Nd, Sm, Eu, Gd, Dy, Ho, Er, T
an oxide superconductor containing at least one element out of m, Yb, and Lu), which is composed of mercury, thallium, and oxygen and is basically composed of a rock salt structure composed of two atomic layers; 2n-1 (n is 1) in which an atomic layer composed of oxygen atoms 2 and an atomic layer composed of at least one element of M and Ln are alternately stacked.
And the above integer, where n = 1, the atomic layer is composed of 1 copper atom and 2 oxygen atoms, and the infinite layer structure portion is composed of at least one element of M and Ln and an oxygen atom. An oxide superconductor having a crystal structure in which alternating atomic layers are stacked. 2. (Hg _1-x Tl _x ) ₂ M _3-y Ln _y Cu
_n O _{2 + 2 (n + 1) +} (where n = 2, 0.15 ≦ x ≦
0.75, 0 ≦ y ≦ 1.0, −1.0 ≦ δ ≦ 0.8), The oxide superconductor according to claim 1. 3. (Hg _1-x Tl _x ) ₂ M _{n + 1} Cu _n O
_{2 + 2 (n + 1) +} (where n = 3 or 4, 0.3 ≦ x
≦ 0.6, −0.7 ≦ δ ≦ 0.4).
The oxide superconductor described. 4. The oxide superconductor according to claim 1, wherein at least part of thallium is replaced with bismuth or lead.