JP2532914B2 - Superconducting ceramic laminate and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to bismuth (Bi), strontium (S
r), a calcium (ca) and a copper (Cu) super-copper ceramics laminated body, more specifically, a Bi-oxide film on which a complex oxide crystal film oriented in a specific direction is formed.
The present invention relates to a Sr-Ca-Cu-based superconducting ceramics laminated body laminated body and a manufacturing method thereof.

[Prior Art] A superconducting material is a material exhibiting a property (superconducting state) in which the electric resistance becomes zero under the conditions of critical temperature Tc, critical magnetic field Hc, and critical current density Jc or less.

Y-Ba-Cu-O-based composite oxides are known as oxide ceramics that exhibit superconductivity at a temperature of about 90K. Furthermore, recently, a Bi-Sr-Ca-Cu superconducting ceramic has been discovered as a composite oxide showing a Tc of 80 to 100K. This Bi-Sr-Ca-Cu system is more stable than the Y-Ba-Cu-O system and has a strong resistance to the external environment such as moisture.

Usually, this composite oxide ceramic is obtained by firing a shaped material of ceramic raw material powder by normal pressure sintering, pressure sintering, atmosphere sintering, or the like.

Wires of, as the superconducting material has been put into practical use conventionally been taped and coiling, Nb-Ti alloy and Nb ₃ Sn
Although alloys are known, these materials require cooling to liquid helium temperatures, which is expensive to cool.

Therefore, various proposals have been made for practical use of wire rods and tapes using a high temperature superconductor made of a complex oxide having a high critical temperature.

[Problems to be Solved by the Invention] In order to put a superconductor into practical use, the superconductor is made into a wire rod, a tape, and a coil, and a large critical current density is obtained.
It must be a conductor with Jc. Although the crystal structure of Bi-Sr-Ca-Cu superconducting ceramics has not been established, the characteristic of the proposed one is that the c-axis is remarkably long among the crystal axes and is 5 times as long as the a-axis or the b-axis. The above is that the atoms are arranged in layers on the ab plane. Therefore, in the superconducting state, it is theoretically considered that the crystal structure is such that electrons move along the ab plane (direction perpendicular to the c-axis) and it is difficult for the electrons to move in the c-axis direction.

There are few conventional wire rods, tapes and coils using high temperature superconducting ceramics that take such a crystal structure into consideration, and those that do not take measures to pass a large current in the longitudinal direction of the wire rods and tapes are practically large. Current density cannot be obtained.

In order to obtain a practically large critical current density by applying a large current in the longitudinal direction of wires and tapes, vapor phase methods such as vapor deposition, sputtering, and CVD are proposed as methods for orienting crystals as described above. Has been done. However, in these methods, the film formation speed is small, the manufacturing process is complicated, and the manufacturing cost is extremely high, and it is difficult to increase the length of a wire or tape.

In addition, it is necessary to perform heat treatment at high temperature, and it is necessary to use a heat resistant material such as a heat resistant alloy as a base material, but if a ceramic film is directly formed on the base material of the heat resistant alloy, the lattice constant matching with the ceramic is poor. , It was difficult to obtain an alignment film, and further, a reaction occurred between the ceramic and the substrate during the heat treatment, and the superconducting phase of the ceramic was destroyed.

The present invention has been made based on the above background,
The object is to provide a superconducting ceramics laminated body capable of passing a large current in the longitudinal direction of the wire, tape and coil, exhibiting a practically large critical current density, and using various heat resistant materials as a base material. And
An object of the present invention is to provide a method for easily and inexpensively manufacturing a superconducting ceramics laminate having good crystal orientation.

[Means for Solving the Problems] The above objects are achieved by a superconducting ceramic laminate according to the present invention and a method for producing the same.

That is, the method for producing a superconducting ceramics laminated body of the present invention comprises forming a thick film of a complex oxide composed of bismuth, strontium, calcium and copper on the surface of a base material via an intermediate layer, and subjecting the formed film to heat treatment. A method of forming a ceramics laminate, wherein the composite oxide crystals are oriented by heat treatment such that the c crystal axis is substantially perpendicular to the plane of the intermediate layer, and the intermediate layer promotes the orientation and during the heat treatment. The feature is that it does not impair the superconductivity of ceramics.

In a preferred embodiment of the present invention, the base material can be a tape-shaped heat-resistant material or high-strength material.

In the present invention, it is desirable to use, as the intermediate layer, a noble metal selected from silver, copper, gold and platinum, MgO, SrTiO ₃ , yttrium-stabilized zirconia, and oxides of constituent elements of superconducting ceramics.

In the present invention, the preferable heat treatment conditions for the film are 860
This is performed by heating at a heating temperature of 950 ° C. to melt a part or all of the film, and then gradually cooling.

The superconducting ceramics laminate according to the present invention is bismuth, strontium, a superconducting complex oxide ceramics film composed of calcium and copper, silver, copper, gold, a noble metal selected from platinum, MgO, SrTiO ₃ , yttrium-stabilized zirconia, A laminated body formed on a substrate plane through an intermediate layer made of an oxide of a superconducting ceramics constituent element, wherein the complex oxide crystals in the film are oriented and the c crystal axis is substantially perpendicular to the intermediate plane. It is characterized by being.

In the laminate of the present invention, the base material is preferably tape-shaped, and is preferably a heat-resistant metal, ceramics, or a composite material of metal and ceramics.

 Hereinafter, the present invention will be described in more detail.

Formation of complex oxide film The formation of the complex oxide film on the substrate through the intermediate layer is
It can be carried out by various methods, for example, screen printing method, doctor blade method, solution coating method,
It can be selected appropriately. The thickness of the composite oxide film can be appropriately changed depending on the purpose, and is, for example, several μm to several hundred μm.

It is desirable to appropriately select the kind of the compound of the ceramic raw material by a film forming method or the like.

Usually, as a method for obtaining a ceramic raw material powder, for example, a dry method in which each compound powder of the constituent components of the ceramic is mixed and calcined, and a mixed solution containing the intended ceramic constituent component is prepared, There is a wet method in which a precipitate forming agent such as oxalic acid or potassium carbonate is added in one step or in multiple steps to obtain a coprecipitate, which is dried and calcined.

In the present invention, the complex oxide film is formed on the plane of the intermediate layer on the base material. The shape of the base material may be any shape as long as it has a substantially flat surface that can be oriented and crystallized, but a long material is preferable, for example, a tape shape, a square wire shape, and particularly a tape shape. Is preferred.

The base material used in this invention includes various metals,
There are ceramics and composite materials thereof, and these can be appropriately selected depending on the use and type of the laminate of the present invention. As preferable base materials, there are materials having heat resistance such as metals and ceramics, and materials having mechanical strength. The surface of the base material is appropriately subjected to pretreatment if necessary.

The intermediate layer to be formed on the substrate in the present invention is not limited in kind as long as it promotes the orientation of the ceramics and does not impair the superconductivity of the ceramics during the heat treatment. Noble metals selected from silver, copper, gold, platinum, MgO, SrTiO ₃ , yttrium-stabilized zirconia, oxides of superconducting ceramic constituent elements,
That is, there are Bi ₂ O ₃ , SrO, CaO, CuO and the like. Of these, a noble metal selected from silver, copper, gold, and platinum has a small reaction with the superconducting phase and promotes crystal orientation of the superconducting ceramics, and in MgO and SrTiO ₃ , these react with the superconducting ceramics. This is because the properties are small and the lattice constants are well matched to promote the orientation of the crystals of the superconducting ceramics. Also, in oxides of superconducting ceramic constituent elements such as Bi ₂ O ₃ , SrO, CaO, and CuO, even if a part of this intermediate layer diffuses into the superconducting phase and combines with that phase, the superconducting phase is not destroyed. , Increases the adhesion to the film, and also acts as a barrier for atoms that diffuse from the substrate.

The formation of the intermediate layer on the base material can be appropriately selected depending on the type of the intermediate layer. For example, in the case of precious metals, there are vapor phase methods such as plating, hot dipping, vapor deposition, and in the case of oxides, there are, for example, screen printing, doctor blade method, solution coating method, etc. Dry and bake accordingly.

When the screen printing method is used among the film forming methods, a composite oxide paste is prepared and applied to the intermediate layer surface.

Here, the paste may be prepared by kneading the composite oxide powder obtained by a usual method with a binder such as an acrylic resin, and further adding a solvent, a plasticizer or the like in order to adjust the viscosity of the paste. it can.

To control the sinterability and superconductivity of the superconducting oxide ceramics according to the present invention, trace components can be added. As such component elements, Ti,
Sn, Mn, Al, Cs, Ce, V, Bi, Fe, Cr, Ni, Ir, Rh, Ga
These compounds include hydroxides, oxychlorides, carbonates, bicarbonates, oxynitrates, sulfates, sulfites, nitrates, acetates, formates, oxalates and chlorides. , And fluoride. The addition of the trace components can be carried out in the raw material or in the calcined complex oxide powder.

Heat Treatment of Membrane The composite oxide film formed on the intermediate plane of the substrate is then heat treated. In this invention, by heat treatment,
The c-axis of the complex oxide crystal is oriented substantially perpendicular to the plane of the intermediate layer.

Regarding the heat treatment conditions for the film, pretreatment, heating speed, heating temperature, heating atmosphere, heating time, cooling speed, and the like are selected so that the above-described c-axis oriented film is formed.

100 ° C for complex oxide film formed as paste
Before and after drying, it is desirable to perform a pretreatment by annealing at about 400 ° C. for one hour in order to evaporate a binder such as a resin.

The heating temperature (baking temperature) can be appropriately changed according to the composition of the composite oxide, for example, 860 to 950 ° C,
It is preferably 870 to 910 ° C. If the temperature is lower than 860 ° C., the composite oxide film does not melt, the crystals cannot be oriented along the c-axis, and some of the ceramic particles in the film do not melt. On the other hand, if the temperature exceeds 950 ° C., the composite oxide may be thermally decomposed or partially evaporated.

The heating rate during heating greatly affects the microstructure and superconductivity of ceramics.
It is appropriately set according to the type and content of the constituent components of the composite oxide.

In the present invention, the heating is performed in an oxygen atmosphere or a non-oxygen atmosphere. In addition to oxygen, nitrogen gas, helium,
An inert gas such as argon can also be added.

After heating, it is gradually cooled so that c-axis oriented crystallization occurs. For example, the cooling rate is 500 to 20 ° C / hour, preferably 200
-50 ° C / hour, more preferably around 100 ° C / hour can be adopted.

Complex Oxide Ceramics According to the present invention, the superconducting ceramics laminate is a superconducting complex oxide ceramic film composed of bismuth, strontium, calcium and copper, a noble metal selected from silver, copper, gold and platinum, MgO, SrTiO ₃ , yttrium. Stabilized zirconia, a laminate formed on the flat surface of the base material, which is a heat-resistant metal, ceramics, or a composite material of metal and ceramics, for example, through an intermediate layer made of oxides of constituent elements of superconducting ceramics. The complex oxide crystals in the film are oriented so that the c crystal axis is substantially perpendicular to the plane of the intermediate layer.

In the present invention, the shape, size, and the like of the composite oxide crystal in the film are arbitrary as long as they are c-axis oriented. A schematic partial cross-sectional view of the laminate of the present invention is shown in FIGS. 1A and 1B.
In this aspect, the tape-shaped metal substrate 1 and the complex oxide ceramic film 2 provided on the surface of the tape-shaped metal substrate 1 with the intermediate layer 3 interposed therebetween, and the crystals in the film have the c-axis substantially in the plane of the intermediate layer. It is vertical to. The present invention also includes a mode in which the ab axis directions match (Fig. 1A) and a mode in which they do not match (Fig. 1B).

The produced ceramics can exhibit superconductivity and can be used as various superconducting materials.

[Operation] The mechanism of the method for producing the ceramics of the present invention configured as described above will be described for better understanding of the present invention. Therefore, the following does not limit the scope of the present invention.

In the method of the present invention, in the composite oxide film before treatment, the ceramic particles are randomly arranged, and amorphous and crystalline substances are mixed, and a part or all of the oxide of the film is subjected to heat treatment. By melting and gradually cooling this melt, it is crystallized so as to be c-axis oriented. In particular,
The intermediate layer is one that promotes the orientation of the ceramics and does not impair the superconductivity of the ceramics during the heat treatment.For example, noble metals such as silver have a small reaction with the superconducting phase and the Bi-Sr-Ca-Cu-based ceramics. The crystal lattice matching with and facilitates the c-axis orientation of Bi-based ceramics,
Even in MgO, etc., the reactivity with superconducting ceramics is small and the lattice constant is well matched to promote crystal orientation of superconducting ceramics. Even if it diffuses into a phase and combines with the phase, it does not destroy the superconducting phase, increases the adhesion to the film, and plays a role as a barrier for atoms diffusing from the base material.

[Effects of the Invention] The following effects can be obtained by the present invention.

(B) With this manufacturing method of the present invention, a heat treatment step that is easy to operate and inexpensive is used without using the conventional complicated and expensive vapor deposition method, sputtering method, CVD method, etc. The superconducting ceramics laminated body can be easily manufactured at low cost.

(B) In this production method of the present invention, a flexible material can be used as the base material and the intermediate layer, and the weak point of the ceramics having poor workability can be covered to make the laminate of the present invention flexible. (C) In this production method of the present invention, if a good conductor such as Ag is used as the intermediate layer, even if the superconducting state is broken during use, that is, the quench state occurs, the metal base material bypasses the electric current. And plays the role of stabilizing material.

(D) In the production method of the present invention, the heating conditions are more specified, and by using a specific intermediate layer, it is possible to more reliably achieve c-axis orientation and obtain a good superconducting ceramics laminate.

(E) In the laminated body of the present invention, since the superconducting ceramic film is oriented, a large electric current can be passed in the longitudinal direction of the rectangular wire and tape, and a superconducting ceramic laminated body showing a practically large current density can be obtained. You can

(F) In the production method of the present invention, the heating conditions are more specified, and under these conditions, the film becomes a semi-molten state during heating, and an extremely dense film can be formed.

(G) In the laminate of the present invention, since the superconducting ceramic is in direct contact with the intermediate layer and in contact with the base material, even if the material has a high reactivity with the ceramic and contains an element that destroys the superconducting phase. It can be used as a base material of this laminated body, and metal materials such as heat-resistant alloys and alloys having high mechanical strength, and various ceramic materials and composite materials can be used.

[Examples] The present invention will be specifically described with reference to examples.

Example 1 MgO was dry mixed in a mortar and calcined at 800 ° C. for 10 hours. The calcined powder was pulverized in a mortar to obtain a powder of 280 mesh or less. Next, 3 parts by weight of an acrylic resin was added to 10 parts by weight of the calcined product, and mixed with a kneader for 30 minutes. In order to adjust the viscosity, a few drops of parapinol as a solvent and dibutyl phthalate as a plasticizer were added and mixed well to obtain an MgO paste.

The MgO paste was formed into a thick film on Hastelloy tape (heat resistant Ni alloy) by screen printing. This tape
It was baked at 900 ° C. for 1 hour. The obtained film thickness was 5 to 10 μm.

On the other hand, Bi ₂ O ₃ 0.5 mol, SrCO ₃ 1 mol, CaCO ₃ 1 mol and
Two moles of CuO were dry mixed in a mortar and calcined at 800 ° C for 10 hours. The calcined powder was pulverized in a mortar to obtain a powder of 280 mesh or less. Next, 3 parts by weight of an acrylic resin was added to 10 parts by weight of the calcined product, and mixed with a kneader for 30 minutes. To adjust the viscosity, parapinol as a solvent and a few drops of dibutyl phthalate as a plasticizer were added and mixed well.

The obtained composite oxide paste was formed into a thick film on the tape having the intermediate layer by a screen printing method.
The film thickness was several tens μm to several hundred μm before firing.

The tape was dried at around 100 ° C, pretreated by evaporating the binder at 400 ° C for 1 hour, and heat-treated at 860 ° C for 5 minutes. Thereafter, cooling was performed at a rate of 100 ° C./hour to obtain a superconducting ceramic laminate tape. The resulting film thickness is 5-10
μm to several tens of μm.

In order to test the superconducting properties of the obtained superconducting ceramics laminated body tape, the relationship between temperature and electric resistivity was investigated by the usual 4-terminal method. The results are shown in FIG. As is clear from this figure, from the temperature change of the electrical resistance, 90K
The transition to superconductivity started at Tc of 30K.

In order to examine the crystal orientation, powder X-ray diffraction analysis was performed. As a result, as shown in FIG. 3, the crystal structure has a high and strong (00n) plane peak, is significantly oriented in the c-axis, there is no reaction between the Hastelloy tape and the superconducting ceramics, and the MgO intermediate layer promotes orientation. You can see that it works as a diffusion barrier.

Comparative Example A ceramic laminate was prepared in the same manner as in Example 1 except that the ceramic film was directly formed on the Hastelloy tape without using the intermediate layer, and the superconducting property was examined.

As a result, the heat treatment reacted with the components of the Hastelloy tape to destroy the superconducting phase, and the ceramic film became an electrical insulator.

Example 2 A ceramic laminate was prepared in the same manner as in Example 1 except that the material of the intermediate layer was CuO, the material of the base material was Ag, and the firing temperature of the film was 900 ° C. Examined.

In order to test the superconducting properties of the obtained superconducting ceramics laminate tape, a part of the tape was peeled off, and the relationship between temperature and electric resistivity was investigated by a usual four-terminal method. The results are shown in FIG. As is clear from this figure, Tc
It was 77K.

In order to examine the crystal orientation, powder X-ray diffraction analysis was performed. As a result, it can be seen from FIG. 5 that the crystal structure has a high and strong peak in the (00n) plane and is significantly oriented in the c-axis.

Example 3 A ceramic laminate was prepared in the same manner as in Example 1 except that the material of the intermediate layer formed by plating was Ag and the firing temperature was 880 ° C., and the superconducting property was examined.

In order to test the superconducting properties of the obtained superconducting ceramics laminate tape, a part of the tape was peeled off, and the relationship between temperature and electric resistivity was investigated by a usual four-terminal method. The result is shown in FIG. As is clear from this figure, Tc
It was 78K.

In order to examine the crystal orientation, powder X-ray diffraction analysis was performed. As a result, it can be seen from FIG. 7 that the crystal structure has a high and strong peak in the (00n) plane and is significantly oriented in the c-axis.

[Brief description of drawings]

FIG. 1 is a schematic partial view of a laminated body of the present invention, and FIG.
FIG. 3 is a graph showing the relationship between temperature and electric resistivity of the composite oxide ceramics obtained in Example 1, and FIG. 3 is a graph showing X-ray analysis of the composite oxide ceramics obtained in Example 1. FIG. 4 is a graph showing the relationship between temperature and electrical resistivity of the composite oxide ceramics obtained in Example 2.
FIG. 5 is a graph showing the X-ray analysis of the composite oxide ceramics obtained in Example 2, and FIG. 6 shows the relationship between the temperature and the electrical resistivity of the composite oxide ceramics obtained in Example 3. The graph shown in FIG. 7 is a graph showing the X-ray analysis of the composite oxide ceramics obtained in Example 3.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01B 12/02 ZAA H01B 12/02 ZAA 13/00 HCU 7244-5L 13/00 HCUZ H01L 39/24 ZAA H01L 39/24 ZAAZ (56) Reference JP-A-1-208327 (JP, A)

Claims (5)

(57) [Claims] 1. A thick film of a complex oxide composed of bismuth, strontium, calcium and copper is formed on a substrate surface via an intermediate layer, and the formed film is heat treated to form a ceramics laminate. In the method, the c-axis of the complex oxide crystal is substantially in the plane of the intermediate layer by heat treatment in which a part or the whole of the film is melted by heating to a temperature of 860 to 950 ° C. and then slowly cooled. Orientation crystallized so that it is perpendicular to
A method for producing a superconducting ceramics laminate, wherein the intermediate layer is made of a noble metal selected from silver, copper, gold and platinum, and promotes the orientation and does not impair the superconductivity of the ceramics during heat treatment. 2. The method according to claim 1, wherein the base material is a tape-shaped heat-resistant metal or high-strength alloy. 3. A laminate in which a superconducting composite oxide ceramics film composed of bismuth, strontium, calcium and copper is formed on a flat surface of a substrate through an intermediate layer made of a noble metal selected from silver, copper, gold and platinum. A superconducting ceramics laminate, wherein the composite oxide crystal in the film is oriented and the c crystal axis is substantially perpendicular to the plane of the intermediate layer. 4. The superconducting ceramics laminate according to claim 3, wherein the base material is tape-shaped. 5. The superconducting ceramics laminate according to claim 4, wherein the substrate is a refractory metal, ceramics, or a composite of metal and ceramics.