JPS63303813A - Superconducting compound oxide material - Google Patents

Abstract

PURPOSE:A superconducting compound oxide material constituted of a superconducting compound oxide layer contg. an alkaline earth metal with a moisture preventing protective layer formed on its surface causing scarce change with the lapse of time, and having high stability. CONSTITUTION:A moisture preventing protective layer consisting of a ceramic material, metal, or a semiconducting org. material for inhibiting permeation of steam and contact of water is formed on the surface of a superconducting compound oxide layer contg. at least one kind of alkaline earth metal selected from Ca, Sr, and Ba. Said protective layer is formed by, for example, sputtering or CVD process when a ceramic material is used, by vapor deposition or metal spraying, etc., when a metal is used, and by coating, dipping, or vapor deposi tion, etc., when an org. material is used. The thickness of the protective layer may be in an order of submicron - millimeter. Since the superconducting mate rial provided with the protective layer has the afore-mentioned characteristics, the material may contribute to the field of application of the material for electro magnet, electric or electronic material, and application in electronic devices, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a superconducting composite oxide material which shows little change over time and has excellent stability.

[Prior art] Many materials have been known to exhibit superconductivity, and among alloy systems, Nb-based alloys such as Nb3Ge and NbN exhibit a high superconducting critical temperature (hereinafter referred to as TC), and Nb
It was reported about 10 years ago that xGe has a Tc of 23.6 [ADplied Physic
sLetters, 23480 (1973)] Until recently, no substances with higher TO were known.

On the other hand, in complex oxide systems, 1-iT! Qn is 13.7
It has been reported that it has a Tc of [)Ia
terials Research Bulletin
, 8.

777 (1973)], its T C is low and its practicality as a superconducting material is low.

Superconducting materials have a wide range of applications, and the main area of development is in magnet applications.Superconducting magnets have zero electrical resistance, so they can generate a strong magnetic field with only a small amount of power required for cooling. becomes possible. Therefore, it can be expected to be applied to fields that require a strong magnetic field, such as nuclear fusion, magnetic levitation trains, MHD power generation, accelerators, and motors. In the power field, it has applications in generators, power storage, and power transmission lines.
For the electronics field, computer elements such as logic and memory (Josephson elements),
It has applications in sensors that detect weak magnetic fields (single-child interference devices) and microwave elements that can be used in millimeter-wave mixers and transmitters.

Superconducting materials used in such applications are required to have a high TC, and the search for materials is still ongoing. If a material with high TO is developed, liquid nitrogen (boiling point 4.2K), which is an abundant resource, can be used as a refrigerant instead of expensive and resource-problematic liquid helium (boiling point 4.2K).
boiling point 77.3 K) can now be used,
Its uses are expected to expand dramatically.

It has recently been reported that La-3r (Ba)-Cu-0-based rare earth composite oxides have a TO of as high as 30 [
1eitschrift fur physik.

Phy3iCal ReView
etters, 58, 911 (1987)].

[Problems to be solved by the invention] Superconducting composite oxide, especially La-3r having high Tc
(Ba)-Cu-0-based and Y-5a-cu-o-based rare earth composite oxides may exhibit deterioration in superconducting properties over time due to being left in the air or due to heat cycles between low temperature and room temperature. Understood.

Therefore, superconducting magnets, electric/electronic materials, electronic devices, etc. using the superconducting composite oxide have unstable performance and characteristics, which poses a major problem in practical use.

[Means for Solving the Problem] As a result of extensive research in order to solve the above-mentioned problems, the present inventors have developed a superconducting composite oxide with excellent stability and little change over time even when left in the air. The present invention was achieved by discovering a new material.

That is, the present invention is a superconducting composite oxide material having a moisture-proof protective layer on the surface of a superconducting composite oxide layer containing an alkaline earth metal.

As the superconducting composite oxide containing an alkaline earth metal of the present invention, Ba-(Pb-B i >-〇 system (Te13k
) and copper-based composite oxides. Ba-(Pb-B i
> -0-based composite oxides are expensive due to low TO;
Furthermore, there is the problem that liquid helium, which is a scarce resource, must be used, which limits its practical use.

On the other hand, since some copper-based composite oxides have a TC higher than that of liquid nitrogen, liquid nitrogen, which is a low-cost and abundant resource, can be used for cooling, making it more preferable from an industrial perspective.

The superconducting copper-based composite oxide has the general formula %, where Ml is at least one selected from ca, 3ri, and Ba, and M2 is SC, Y, La, Ce, Pr, Nd,
Pm, Sm, Miu, Gd, Tb, Dy, Ho, Er,
It is at least one selected from Tm, Yb, and Lu.

Roughly speaking, the composition ratio of a and b is 0.5≦a≦3 0.1≦X≦0.9 1, O≦b≦4.0 in a TC superconducting composite oxide. It is preferable because it creates

Next, a method for producing a superconducting composite oxide will be explained.

Complex oxides include, for example, rare earth compounds such as rare earth oxides and rare earth hydroxides, alkaline earth metal compounds such as fermented barium, barium carbonate, strontium oxide, and strontium carbonate, and cupric oxide and cupric carbonate. A method in which an aqueous solution of oxalate is added to a mixture of aqueous solutions of rare earth elements, alkaline earth metals such as strontium and barium, and soluble compounds such as copper chlorides and nitrates. There is a method of adding and co-precipitating and then heating and reacting. Further, a predetermined composite oxide can also be obtained by preparing a precipitate using two of these metal salts by a coprecipitation method and mixing it with other metal compounds.

The heating reaction conditions vary depending on the composition, but 600'
It is preferable to carry out the treatment at a temperature of 1000°C to 1000°C for 0.5 hours to 1 week in a predetermined atmosphere.

The superconducting composite oxide obtained as described above is pulverized to, for example, 5 μm or less using a pulverizing means such as a ball mill or a jet mill, if necessary, and then formed into a predetermined shape and sintered.

The sintering temperature varies depending on the composition, but is between 650 and 1200' (
:, is preferable, and is carried out for 5 hours from 0 minutes.

Then, in the specified atmosphere for 30 minutes to 10 hours, 6
Anneal at a temperature of 00 to io o O'C.

In the present invention, controlling the oxygen content in the composite oxide is also an important factor, and this can be done by changing the atmosphere during annealing. When the oxygen content is desired to be lower than the stoichiometric amount, annealing is performed in an atmosphere of an inert gas such as nitrogen, argon, or helium while adjusting the oxygen partial pressure.

Further, as the shaping or sintering means, a method of shaping the composite oxide by hot pressing, melt solidification, explosive compression, etc. can also be used. In addition, a filler can be added if necessary during molding. As described above, a bulk composite oxide formed into a predetermined shape can be manufactured.

Further, the composite oxide can be produced in the form of a thin film on the substrate. For example, a method of manufacturing by sputtering, CVD, spraying, a binder method, or a method of forming a metal by vapor deposition, MBE, or the like, and then oxidizing it to manufacture a composite oxide can be used. In these methods, any metal, ceramic, organic material, etc. may be used as the substrate.

The present inventors found that the superconducting composite oxide containing the alkaline earth metal cannot obtain stable superconducting properties in air, and the reason for this is that the composite oxide is easily hydrolyzed. It was found that it is unstable in water.

For example, if a sintered body or thin film of the composite oxide is left in the air, the superconducting properties will deteriorate and even structural destruction will occur. Furthermore, when a heat cycle between low temperature and air temperature is performed in air, water vapor in the air condenses and adheres to the material, accelerating the deterioration of superconducting properties. Therefore, it has been found that by providing a moisture-proof protective layer on the surface of the composite oxide, hydrolysis can be prevented and the superconducting properties can be stabilized.

As the material for the moisture-proof protective layer of the present invention, any of ceramics, metals, and semiconductor organic materials can be used as long as it prevents water vapor from passing through and contacting the superconducting composite oxide. For example, SiO2, 5iOX, GeO2, Cr2
O3, Al2O3, TiO2, Z ro2, MgO, cuo, Y203, Si 3N4
．． 5iNX, 5iNXOV, 1'v1gF2, YF3,
Oxides, nitrides, fluorides, borides, sulfides, ceramics, Cu, Ag, Au, Pt such as BN and MO32
, Pd, semiconductors such as Si, GaAs, and InSb, polystyrene, polyethylene, polyvinyl chloride,
Organic substances such as polyvinylidene chloride and silicone oil, and composite materials thereof can be used.

Next, a method for manufacturing the moisture-proof protective layer will be described, but the present invention is not limited thereto.

For example, when the protective layer of the present invention is made of ceramics,
A method of manufacturing by sputtering, CVD, spraying, or a binder method, or a method of manufacturing a ceramic layer by forming a metal layer by evaporation, MBE, or the like, and then oxidizing, nitriding, or the like can be used. When using metal, the metal layer can be manufactured by vapor deposition, thermal spraying, sputtering, CVD, powder sintering, or the like.

When an organic material is used, coating, dipping, vapor deposition, or a method of polymerizing a hexamer on the composite oxide can be used. Further, the protective layer can also be manufactured using a composite material such as a ceramic-polymer composite material in which ceramics are dispersed and coated in a polymer solution, or a ceramic-metal composite material in which metal and ceramic are powder-sintered.

The thickness of the film 1 varies depending on the material used, but it can be on the order of submicron lumi.

It is also possible to produce the composite oxide and the protective layer at the same time by forming the protective layer or a raw material layer for the protective layer on the raw material of the composite oxide and then reacting the mixture.

The superconducting composite oxide material of the present invention provides a superconducting material that shows little change over time and has excellent stability, and the material contributes to applied fields such as electromagnets, electrical/electronic materials, and electronic devices. I have something to do.

The present invention will be explained in more detail with reference to Examples below.

[Example] Example 1 Yttrium oxide 22.6g, barium nitrate 104.5g
i;], cupric oxide 47.7 () were mixed in a ball mill and calcined in air at a temperature of 900'C for 24 hours to obtain a composite oxide.The composite oxide was ground in a whole mill and weighed 1 ton.
After pressing at a pressure of /cm2 to produce pellets of 1 cmφ x 5 mm, the pellets were heated at 900°C in air for 12 hours to produce a sintered body.

After attaching an electrode to the composite oxide sintered body, a 5 μm thick Al2O3 layer was formed on the entire surface by sputtering.

The composite oxide sintered body coated with Al2O3 was heated to 90% RH-
After standing at 30'C for 1 day to 2 weeks, Tc was measured in a cryostat.

Table 1 shows Tc.

Table 1 Tc (zero resistance transition temperature) Example 2 10 g of the composite oxide obtained in Example 1 was dispersed in 8 ml of ethanol to form a slurry, and then applied onto a 4-inch diameter SUS plate to create a powder target. Using this target, sputtering was performed on a sapphire plate (substrate temperature 2
After heating at a temperature of 900'C in an atmosphere of 02C for 1 hour, a composite oxide thin film (thickness 900A>) was obtained.

After attaching an electrode to the composite oxide thin film, 3
i NX sputtering was performed to form a 2 μm thick protective layer.

3i The composite oxide film coated with INx was heated to 90% RH-
After being left at 30°C for 1 day to 2 weeks, Tc was measured in a cryostat.

Table 2 shows the TC.

Table 2 Tc (zero resistance temperature) Example 3 After ball milling the composite oxide obtained in Example 1,
on," After pressing with a pressure of cm2 to create a disc-shaped pellet of 1 cmφ x 5 mm, it was heated at 900°C in air for 1 hour.
A sintered body was created by heating for 2 hours.

After attaching electrodes to the composite oxide sintered body, polystyrene (
A 15% toluene solution with a molecular weight of 100,000) was applied to the surface to form a protective layer with a thickness of 50 μm.

90% RH of composite oxide sintered body covered with polystyrene
After standing for 1-2 weeks at -30°C, Tc was measured in a Taraviostat.

Tc is shown in Table 3.

Table 3 TO (zero resistance temperature) Example 4 The composite oxide powder (average particle size 2 μm) obtained in Example 1 was
．． After pressing with a pressure of 5ton/cm2, 900'
The sintered body (10x
5x5mm) was obtained.

After attaching the electrode to the sintered body, a xylene solution of polystyrene (10% by weight) was applied to the surface (film thickness 200 μm after drying).
I did m. After immersing the polystyrene-coated sintered body in purified water for 8 hours, it was placed in a Taliostat and its electrical conductivity was measured, and it was found to be a superconductor with a TC (zero resistance temperature) of 91k. In addition, when the crystal structure of the sintered body was measured by X-ray analysis, it was found that it had a rhombic island structure (a
: 3.82 mm, b 3.89 L c 11.67 people).

Comparative Example 4 Electrodes were attached in the same manner as in Example 4 except that polystyrene coating was not performed, and the sintered body was immersed in purified water for 8 hours. The electrode attached with carbon paste was peeled off, and the contact resistance of the surface was measured. It turned out that it was an insulator.

As measured by the surface crystal structure using X-ray diffraction method, Y2
It was found that it was a mixture of 03, cuo, and BaCO3, and was hydrolyzed. In addition, the pH of the water in which the sintered body was immersed was 13, and when the white powder obtained after evaporation to dryness was measured for elements contained in it by fluorescent X-ray method, a large amount of Ba was detected, and the sintered body It was found that the surface was hydrolyzed.

1 Effects of the Invention As explained above, the superconducting composite oxide material of the present invention exhibits stable superconductivity even in a high humidity environment.

Claims (1)

[Claims] A superconducting composite oxide material comprising a moisture-proof protective layer on the surface of a superconducting composite oxide layer containing an alkaline earth metal.