JP2603688B2 - Superconducting material reforming method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a superconducting material having a high superconducting critical temperature and excellent superconducting properties.
More specifically, the present invention relates to a method for modifying a superconducting material.

2. Description of the Related Art The superconductivity phenomenon, which is said to be a phase transition of electrons, is a phenomenon in which the electrical resistance of a conductor becomes zero under a specific condition and shows complete diamagnetism. That is, under the superconductivity, even if a current flows through the superconductor, there is no power loss, and a high-density current continues to flow forever. Therefore, if superconductivity technology is applied to power transmission, about 7
% Transmission loss can be greatly reduced. Further, the application as an electromagnet for generating a high magnetic field, for example, in the field of power generation technology, MH
It is expected to be a technology that advantageously promotes the realization of nuclear fusion reactions, which are said to consume more power than the amount of power generated for development, together with D power generation and electric conductors. In addition, as power for magnetic levitation trains, electromagnetic propulsion ships, etc.
It is expected to be used for NMR, pion therapy, high energy physics experiment equipment, etc.

By the way, despite various efforts, the superconducting critical temperature Tc of the superconducting material could not exceed 23K of Nb ₃ Ge for a long time, but in 1986 Vednauts and Mueller et al. With the discovery of superconducting materials based on materials, the possibility of high-temperature superconductivity has been greatly expanded (Bednorz, Muller, “Z. Phys. B64 (1986) 18)
9 ").

It is known that composite oxide-based ceramic materials exhibit superconducting properties so far.For example, U.S. Pat.No. 3,932,315 states that Ba-Pb-Bi-based composite oxides exhibit superconducting properties. It is stated,
JP-A-60-173,885 describes that a Ba-Bi-based composite oxide exhibits superconducting properties. However, the conventionally known composite oxides have a Tc of 10 K or less, and liquid helium (boiling point of 4.
2K) was unavoidable.

In contrast, the oxide superconductor discovered by Bednotes and Mueller et al. Has a composition of (La, Ba) ₂ CuO ₄ and is considered to have a K ₂ NiF ₄ type perovskite crystal structure. The Tc is about 30K, which is dramatically higher than that of conventional superconducting materials.

Further, in February 1987, Chu and others reported that a Ba-Y-based composite oxide exhibiting a critical temperature of 90K class was discovered in newspapers, and the possibility of realizing a non-low-temperature superconductor was immediately seen. Is growing.

Problems to be Solved by the Invention As a method for producing these oxide superconductors, a solid phase sintering method, or a physical vapor deposition method such as sputtering is general, in order to improve the characteristics in any case, It is general to further heat-treat the obtained composite oxide.

However, the superconducting properties of the oxide superconducting materials obtained so far are very unstable, and the temperature Tc at which the superconducting phenomenon starts and the temperature at which the electric resistance becomes completely zero are reached.
The difference ΔT from Tci was very large.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a novel method for modifying a composite oxide-based superconducting material having high Tc and exhibiting excellent properties with stable superconducting properties. Things.

Means for Solving the Problems That is, according to the present invention, a process of heating the composite oxide-based superconducting material to 500 to 1000 ° C. in oxygen plasma to improve the superconducting characteristics of the composite oxide-based superconducting material There is provided a method for modifying a composite oxide-based superconductor characterized by the following.

The oxygen plasma treatment can be performed at room temperature, but according to a preferred embodiment of the present invention, the treatment is performed at 500
It is carried out at a temperature in the range from 1000C to 1000C. Further, the cooling after the treatment is preferably carried out continuously in an oxygen plasma, and the cooling is advantageously carried out by slow cooling at a cooling rate of 10 ° C./min or less.

The composite oxide superconducting material can be a thin film formed by physical vapor deposition on a substrate, and an element α selected from Group IIa elements of the periodic table and an element β selected from Group IIIa elements of the Periodic Table III. And a composite oxide containing copper (Cu).

By using the method of the present invention, a composite oxide superconductor represented by the following general formula can be obtained from the composite oxide material.

General formula: (α _1−x β _x ) Cu _y O _z [where α and β are elements as defined above, x is an atomic ratio of β to α + β, and 0.1 ≦ x ≦ 0.9, and y and z Is 0.4 ≦ y ≦, where (α _1−x β _x ) is 1.
3.0, 1 ≦ z ≦ 5 atomic ratio] Further, by using the method of the present invention, a composite oxide superconductor represented by the following general formula can also be produced.

General formula: LnBa ₂ Cu ₃ O _7-i (however, 0 <i <1) [However, Ln is Y, La, Gd, Dy, Ho, Er, Tm, Yb, Lu, N
d, Sm, represents at least one element selected from Eu) According to a preferred embodiment of the present invention, the composite oxide superconductor is a perovskite-type or pseudo perovskite-type oxide, the composite oxide superconductor (1) a powder mixture of oxides and / or carbonates of the constituent elements, which is pre-sintered at a temperature of 220 to 1260 ° C., and further main-sintered at a temperature of 650 to 1580 ° C .; (2) Physically vapor-deposited a powder mixture of the oxides and / or carbonates of the constituent elements at a temperature of 220 to 1260 ° C. on a substrate as a deposition source, and (3) Oxidation of the constituent elements The product and / or a powder mixture of carbonates are pre-sintered at a temperature of 220 to 1260 ° C., and further subjected to physical vapor deposition on a substrate as a deposition source by further sintering at a temperature in a range of 650 to 1580 ° C. May be any of

Function The method of the present invention is characterized in that a composite oxide-based superconducting material is treated in oxygen plasma.

The oxygen plasma used for this oxygen plasma processing is
Oxygen can be generated by any means for converting oxygen into a plasma, for example, a high-frequency plasma generator.

According to the findings of the present inventors, a conventional oxide superconductor produced by sintering or physical vapor deposition and then heat-treated in an oxygen-containing atmosphere has a lack of oxygen in the crystal, and thus has a crystal structure, There is a problem with oxygen deficiency and the like, and the Tc is low, and the superconducting properties become unstable. Therefore, in order to improve the superconductivity, it is necessary to supplement oxygen by some method. Therefore, in the present invention, oxygen is supplemented by using oxygen plasma.

In the above oxygen plasma treatment, it is generally preferable to heat the oxide to a high temperature. By this heat treatment, the oxygen taken in by the oxygen plasma treatment is diffused, the uniformity of the oxide is improved, and the oxygen deficiency is optimized. That is, if the heat treatment is performed in an oxygen plasma instead of a mere oxygen-containing atmosphere, oxygen plasma in an extremely high excited state is easily taken into the crystal,
Therefore, it becomes possible to produce an oxide superconductor having superconducting properties superior to those of the conventional production method. At this time, the heating temperature is preferably from 500C to 1000C.

After this heat treatment, it is preferable to gradually cool at a cooling rate of 10 ° C./min or less.

Further, it is preferable that a step of rapidly cooling at a cooling rate of 100 ° C./min or more is included in some cases.

In a preferred embodiment of the present invention, the cooling is performed in oxygen plasma. By doing so, oxygen released during cooling can be fixed in the crystal, and a preferable oxygen-rich crystal can be obtained.

Further, by using the oxygen plasma treatment according to the method of the present invention, oxygen in the crystal is insufficient due to poor conditions at the time of sintering or vapor deposition, that is, oxygen deficiency becomes excessive, and the oxide which does not exhibit superconductivity is reduced to oxygen. Can be transformed into a superconductor.

Examples of the composite oxide material to which the present invention can be applied include Y-Ba-Cu-O-based, La-Ba-Cu-O-based, and La-
Oxide ceramics such as Sr-Cu-O type are exemplified.

More generally, it contains one element α selected from Group IIa elements of the periodic table, one element β selected from Group IIIa elements of the periodic table, and copper (Cu). It is a composite oxide. Some of these constituent elements are Al, Fe, Co, Ni,
It may be replaced with at least one other element selected from the group consisting of Zd, Ag, and Ti.

Ba and Sr are preferable as the group α element of the Periodic Table II group a. In addition, Y, La, G
Lanthanoid elements such as d, Dy, Ho, Er, Tm, Yb, Lu, Nd, Sm, and Eu are preferable, and a plurality of elements from these groups can be used in combination.

According to the method of the present invention, a superconductor made from the above composite oxide material has a general formula: (α _1−x β _x ) Cu _y O _z (where α and β are elements as defined above, and x is α
The atomic ratio of β to + β is 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦ 3 when (α _1−x β _x ) is 1.
0, and the atomic ratio satisfies 1 ≦ z ≦ 5).

The atomic ratio between α and β can be appropriately selected according to the types of α and β. That is, Ba-Y, Ba-La, Sr-
In the case of La system, it is preferable to satisfy the following ratios.

Y / (Y + Ba): 0.06 to 0.94, preferably 0.1 to 0.4 Ba / (La + Ba): 0.04 to 0.96, preferably 0.08 to 0.45 Sr / (La + Sr): 0.03 to 0.95, preferably 0.05 to 0.1 Atomic ratio of oxide Is out of the above range, the oxide crystal structure, oxygen deficiency, etc. are different from desired ones even after the irradiation with oxygen ions, so that Tc becomes low.

Further, a superconductor made of the above-described composite oxide material may be, for example, a general formula: LnBa ₂ Cu ₃ O _7-i (where 0 <i <1) [where Ln is Y, La, Gd, Dy, Ho , Er, Tm, Yb, Lu, N
and represents at least one element selected from d, Sm, and Eu].

Specifically, Y ₁ Ba ₂ Cu ₃ O _7-x , Ho ₁ Ba ₂ Cu ₃ O _7-x , Lu ₁ Ba ₂ Cu ₃ O _7-x , Sm ₁ Ba ₂ Cu ₃ O _7-x , Nd ₁ Ba ₂ Cu ₃ O _7-x , Gd ₁ Ba ₂ Cu ₃ O _7-x , Eu ₁ Ba ₂ Cu ₃ O _7-x , Er ₁ Ba ₂ Cu ₃ O _7-x , Dy ₁ Ba ₂ Cu ₃ O _{7-x, Tm 1 Ba 2} Cu 3 O 7-x Yb 1 Ba 2 Cu 3 O 7-x, La 1 Ba 2 Cu 3 O 7-x, (La, Sr) 2 CuO 4-x, (La, Ba) ₂ CuO _4-x [where x is a number satisfying 0 <x <1].

The oxide is preferably a perovskite oxide or a pseudo perovskite oxide. The pseudo perovskite has a structure similar to the perovskite, and includes, for example, an oxygen-deficient perovskite type, an orthorombic type, and the like.

The composite oxide material in the form of a bulk can generally be produced by sintering a mixed powder of oxides and / or carbonates of the constituent elements with or without a preliminary sintering treatment. . Furthermore, a paste obtained by mixing these mixed powders with a binder can be produced by sintering.

The above preliminary sintering and main sintering temperatures can be appropriately selected from the following ranges according to each system.

Temporary sintering temperature Main sintering temperature Ba-Y system 250-1200 ° C 700-1500 ° C Ba-La system 220-1230 650-1580 Sr-La system 234-1260 680-1530 Next, to carry out the method of the present invention. An apparatus used for the following will be described.

The apparatus shown in FIG. 1 mainly includes a chamber 1, a high-frequency coil 2 attached to the chamber 1, a raw material oxide 3, and a heater 4. The chamber 1 has an exhaust hole 7
To a vacuum pump (not shown) through which a vacuum can be created. The chamber 1 is further provided with an atmosphere gas introduction hole 6.

When actually realizing the method of the present invention using the above-described apparatus, first, the chamber 1 containing the raw material oxide 3 is evacuated and evacuated. Next, O ₂ gas is introduced into the chamber 1, high-frequency power is applied to the high-frequency coil 2 to generate oxygen plasma, and the raw material oxide 3 is subjected to oxygen plasma heat treatment.
At this time, it is preferable to energize the heater 4.

Hereinafter, the present invention will be described with reference to examples, but it is needless to say that the technical scope of the present invention is not limited to these examples.

In each of the following examples, a superconducting material was manufactured using the RF type plasma furnace shown in FIG. The manufacturing conditions are summarized in Table 1.

Example 1 As raw material oxides, Y ₂ O ₃ and BaCO ₃ were mixed at an atomic ratio of Y: Ba of 1: 2.
After mixing CuO in an amount of 10% by weight in excess of that in which the atomic ratio of Y: Ba: Cu is 1: 2: 3, pre-sintering is performed at 880 ° C., and then baked at: 940 ° C. By tying, a Y Ba ₂ Cu ₃ O ₇ sintered block was obtained. The size of the obtained sintered block is 20 × 30 × 3mm
It is.

In the chamber, the oxide sintered body block is mounted,
After evacuating the chamber to a vacuum of 1 × 10 ^-6 Torr or less,
0.1 Torr of O ₂ gas was introduced. High-frequency power of 150 W was applied to the high-frequency coil, heated from room temperature to 900 ° C. at a heating rate of 15 ° C./min, kept at that temperature for 3 hours, and then cooled at a cooling rate of 8 ° C./min [Sample (a)] .

For comparison, a sintered body block was prepared which was completely the same as above except that the heat treatment was performed in an oxygen atmosphere of 760 Torr [sample (b)].

A pair of electrodes was formed by vacuum evaporation on both end portions of the oxide sintered body block prepared for measuring the resistance of each of the obtained oxides, and a lead wire was attached to this electrode.

Heat treatment conditions and obtained Tc and Tci (electrical resistance is completely 0
Table 1 shows the measurement results of the temperature.

Example 2 La ₂ O ₃ and BaCO ₃ were used as raw material oxides when the La: Ba atomic ratio was 9
Mix so that 5: 5, CuO La: Ba: Cu atomic ratio of 95:
A (La, Ba) Cu ₂ O ₃ sintered block obtained by mixing at 5: 200, pre-sintering at 870 ° C., and sintering at 955 ° C. was used.

 The procedure of the oxygen plasma treatment was the same as in Example 1.

For comparison, only heat treatment was performed in an oxygen atmosphere of 760 Torr, and Tc and Tci of each sample were measured.

Table 1 also shows the oxygen plasma heat treatment conditions and the obtained Tc and Tci measurement results.

Example 3 La ₂ O ₃ and SrCO ₃ were used as raw material oxides in an La: Sr atomic ratio of 95:
And mixing so that CuO has an atomic ratio of La: Sr: Cu of 95: 5: 2.
A (La, Sr) Cu ₂ O ₃ sintered body block obtained by mixing and sintering at 850 ° C. and then sintering at 935 ° C. was used.

 The procedure of the oxygen plasma heat treatment is the same as in the first embodiment.

For comparison, only heat treatment was similarly performed in an oxygen atmosphere of 760 Torr, and Tc and Tci of each sample were measured.

Table 1 also shows the oxygen plasma heat treatment conditions and the obtained Tc and Tci measurement results.

Example 4 Using the raw material oxide used in Example 1 as a target,
An oxide thin film was formed on a SrTiO ₃ substrate by sputtering.

The above-mentioned oxide thin film was heat-treated by the method using the oxygen plasma heat treatment of the present invention and the conventional method performed in an oxygen atmosphere of 760 Torr.

Table 1 shows the heat treatment conditions and the measurement results of the obtained Tc and Tci.

Example 5 Using the same material as in Example 1 as the raw material oxide, 84
A sintered block of an oxide superconductor sintered only once at 0 ° C. was used. The raw material oxides, which did not show superconductivity, using the apparatus of Figure 1 introduces a 1 × 10 ^-1 Torr of O ₂ gas, an O ₂ plasma generated by applying a high frequency power 150W The heat treatment shown in Table 1 resulted in a superconductor.

Table 1 shows the heat treatment conditions and the measurement results of the obtained Tc and Tci.

As a result, it was found that the method of the present invention can appropriately control the crystal structure and oxygen concentration of the oxide and produce a superconducting oxide having excellent characteristics. It has also been demonstrated that oxides that did not exhibit superconductivity due to lack of oxygen in the crystals due to inappropriate sintering conditions can be transformed into superconductors.

Effect of the Invention As described in detail above, the superconducting material obtained by the method of the present invention is higher than that produced by the conventional method.
Shows Tc and Tci and has stable superconducting properties.

This is obtained by configuring conditions for generating an oxide having a perovskite-type or pseudo-perovskite-type crystal structure, which is considered to be responsible for superconductivity, according to the characteristic manufacturing method of the present invention. .

In addition, materials which do not have superconductivity due to lack of oxygen due to inappropriate sintering conditions and the like also have superconductivity by the heat treatment according to the method of the present invention. For this reason, the conditions at the time of sintering and physical vapor deposition are relaxed more than before, and the mass productivity of the oxide superconducting material is improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an RF plasma furnace (reactor) used for producing a superconducting oxide material of the present invention. [Main Reference Numbers] 1... Chamber 2... Coil 3... Raw material oxide 4... Heater 5... High-frequency power supply 6.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuji Yazu 1-1-1, Koyokita, Itami City, Hyogo Prefecture, Japan Itami Works, Sumitomo Electric Industries, Ltd. Chome 1-1 Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A 1-282145 (JP, A) JP 1-282122 (JP, A) JP 1-286208 (JP, A A)

Claims (6)

(57) [Claims] (1) A general formula: (α _1-x β _x ) Cu _y O _{z wherein} α is an element selected from Group IIa elements of the periodic table, and β is an element selected from Group IIIa elements of the periodic table. X is the atomic ratio of β to α + β, 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦, where (α _1−x β _x ) is 1.
3.0, where the atomic ratio satisfies 1 ≦ z ≦ 5].
A method for modifying a composite oxide-based superconductor, which comprises performing a heating treatment at 500 to 1000 ° C. to improve the superconductivity of the composite oxide-based superconducting material. 2. The composite oxide-based superconducting material has a general formula: LnBa ₂ Cu ₃ O _7-i (0 <i <1) [where Ln is Y, La, Gd, Dy, Ho, Er, Tm, Yb, Lu,
Represents at least one element selected from Nd, Sm, and Eu]. The method according to claim 1, wherein the oxide superconducting material is represented by the following formula: 3. The method according to claim 1, wherein after the heat treatment in the oxygen plasma, the composite oxide-based superconducting material is cooled in the oxygen plasma. 4. The method according to claim 3, wherein the cooling rate is 10 ° C./min or less. 5. The method according to claim 1, wherein the composite oxide-based superconducting material is a sintered body. 6. The composite oxide superconducting material is a thin film formed by a physical vapor deposition method.
The method according to any one of claims 4 to 4.