JPH0764618B2 - Method for forming superconducting ceramic thick film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a superconducting ceramic thick film. More specifically, the present invention relates to a method for forming a ceramic thick film having a high oxygen content, excellent superconducting properties, and high density.

(Background Art) Conventionally, superconducting materials have been limited to metals such as Nb ₃ Ge and Nb-Al-Ge alloys. Although they are high-density and highly stretchable, they have a low critical temperature (T _c ) of 23 K or less and must use expensive liquid helium as a coolant, so superconducting machines and sensors using them cannot be used. Large and expensive,
There was a problem with the economy. Recently, superconducting ceramics with T _c higher than the liquid nitrogen temperature were discovered, and it is expected that cheaper superconducting machines, devices, sensors, etc. will be developed.

High-temperature superconducting materials are being actively developed for energy saving and high sensitivity sensors. For the former, electric power storage coils, magnetic levitation objects, etc. are important in the field of heavy electric power. On the other hand, in the field of weak electric current, elements for ultra-high speed computers, infrared / millimeter wave detection elements, low heat loss wiring for electronic circuits, etc. have been receiving attention.

However, these superconducting ceramic materials proposed so far have drawbacks such as poor drawability, difficulty in high density, and low current density.

In addition, in recent superconducting ceramics, due to the solid-phase reaction, the porosity is as high as 20-30%, and a high-density sintered body has not been obtained, and it is difficult to obtain a high critical current.

The inventor of the present invention has made extensive studies in order to overcome the problems described above, and has completed a new method for forming a superconducting ceramic thick film having a perovskite structure. That is, looking at the superconducting ceramic material, the requirements for the material are 1) high critical temperature, 2) high critical current, 3) high critical magnetic field, 4) high density, and 5) thick film. / To make the thin film uniform or smooth. In particular, in the field of strong electric current, it is necessary to stack the layers in order to pass a large current, and in the field of weak electric current, it is important to reduce the heat capacity and increase the density. For that purpose, a high density material having a high critical temperature, a high critical current and a high critical magnetic field is required.
Once developed, it can also be used as a device for high speed computers and sensitive sensors.

The inventor of the present invention has found that the superconducting function of the superconducting ceramic material is increased as the oxygen content is increased, and the superconducting function of the orthorhombic c-axis is increased in the high-temperature superconducting ceramic containing copper. The method of the present invention has been completed based on the knowledge that the superconducting current flows in the vertical direction and that it is important to make a thick film as thin as possible to facilitate the oxidation process.

(Object of the Invention) The present invention has been made in view of the above circumstances, overcomes the drawbacks of conventional superconducting ceramic materials, has a high oxygen content and is excellent in superconducting properties, and has a high density. It is an object of the present invention to provide a new thick film forming method capable of forming a large superconducting ceramic thick film.

DISCLOSURE OF THE INVENTION In order to achieve the above object, the present invention provides a superconducting ceramic raw material having a perovskite structure,
A powder or agglomerate having a perovskite phase is used in advance, this raw material is heated and melted above its melting point, and the melt is pressed and rapidly cooled to form a thick film with a thickness of 5 to 300 μm, and then in an oxygen-containing atmosphere or oxygen plasma. The method for forming a superconducting ceramic thick film is characterized in that a perovskite phase is heat-treated at 850 to 950 ° C for 2 to 60 hours, and then oxidized at 200 to 700 ° C for 5 to 24 hours in the same atmosphere. I am trying.

This method forms a superconducting thick film ceramic having a thickness of 5 to 300 μm. More specifically, for example, as an example of a high temperature oxide superconductor having a perovskite type structure, a Y—Ba—Cu—O-based material is used. In this case, the constituent oxides of Y, Ba, Cu, etc., hydroxides, carbonates, nitrates or oxalates are mixed and pulverized at a predetermined ratio, and 500-950
It is heated at 1 ° C for 1 to 12 hours to volatilize and eliminate water, carbonate radicals, nitrate radicals, and oxalate radicals to form a perovskite phase. The use of an oxide raw material having a perovskite phase as a raw material means that when a large amount of oxygen increases due to oxidation in a thermal oxidation treatment in a later step, the thick film expands in volume and a large strain is generated, which easily causes cracking. This is for preventing the above-mentioned phenomenon and for ensuring the uniformity (that is, not containing a different phase) of the finally obtained superconducting perovskite. Then, as shown in FIG. 1 of the accompanying drawings, for example, the powder or lump 1 obtained in this process is put into a platinum nozzle 2 and melted at a temperature of 1250-1450 ° C. for 1-5 minutes, A gas 3 such as air is jetted from above the nozzle 2 and a lump of melt is blown out from a hole 4 below the nozzle, and a thick film (length 10-80 mm, width 5-15 mm, Thickness 5-30
0 μm) is formed. The phase of the material at this point is an amorphous metastable phase or several crystalline phases separated.
This thick film is heat-treated in air, in an oxygen stream or in oxygen plasma at 850-950 ° C for 2-60 hours to form a perovskite phase, and then sufficiently oxidized in the same atmosphere at 200-700 ° C for 5-24 hours. And make it a superconducting phase. If the thickness of the thick film is larger than 300 μm, even if it is squeezed and rapidly quenched, the inside becomes random and the C-plane of the orthorhombic system cannot be made parallel to the surface, and the crystal orientation cannot be obtained. Further, in ABa ₂ Cu ₃ Oy (A: Y, La, Pr, etc.) perovskite phase (so-called 1-2-3 phase) represented by YBa ₂ Cu ₃ Oy, it is a tetragonal phase at y = 6.2, and the superconductivity is high. Does not show sex. This phase can be heat-treated at a relatively low temperature (200 to 700 ° C.) in an oxidizing atmosphere to sufficiently absorb oxygen and transform into the orthorhombic phase, and good superconductivity can be exhibited for the first time. Therefore, since the tetragonal phase of the non-superconducting phase is stable at a temperature higher than 700 ° C from the thermal equilibrium condition,
Invasion of oxygen into thick film is not performed efficiently, while 200
Oxidation cannot be expected at temperatures below ℃.

After that, the electrical resistance is measured by the four-terminal method while the temperature is lowered to a low temperature, and the critical temperature and the critical current are determined.

The basic composition of the superconducting ceramic raw material and thick film having a perovskite structure is YBa ₂ Cu ₃ O _7-δ (A
can be used _x B _y) (compound of Cu _p M _q) O _r.

Where A: Y, Sc, rare earth Ln (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, Lu), B: Ba, Sr, Ca, Mg, M: V, Nb, Zn, Ni, Co,
Fe, Mn, Ag, Cu: copper, O: oxygen, and the range of x, y, p, q is 0.
5 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.5, 2.0 ≦ p ≦ 4.0, 0 ≦ q ≦ 1.5, r
Is determined by the valences of A, B, Cu and M. Each element may be a mixture as long as it does not exceed this range.

In the method of the present invention, when the thick film is formed, the chemical durability and the ductility of the thick film are provided, and the nucleation, growth and orientation of the crystal are controlled, or the thermal expansion coefficient with the substrate is increased. B ₂ O ₃ , SiO ₂ , GeO ₂ , P ₂ O ₅ ,
Glass network forming oxides such as Al ₂ O ₃ or low melting glass (PbO-ZnO-B ₂ O ₃ system, PbO-Tl ₂ O-B ₂ O ₃ system, Bi ₂ O ₃ -Tl ₂ O
System) can be added up to 20 mol%.

The squeeze quencher used in the present invention includes a twin roll melt quenching device, a twin soft roll melt quenching device, a single roll melt quenching device, a piston-anvil device, etc., and about one million degrees / sec. Super quenching rate of At this time, an electric furnace, a high-frequency furnace, an infrared focusing furnace, a laser beam, or the like can be used as a heating method for producing the melt.

The superconducting ceramic thick film that can be produced by the method of the present invention described in detail above has a uniform composition and a high density (95-99.9%), and exhibits high critical temperature and sharp physical properties. From this, a high critical current can be expected. In this method, since a molten state is passed in the manufacturing process, mixing is performed at the atomic level, so that the composition is uniform. It is difficult to obtain a thick film with a two-dimensionally large size and a density close to 100% by ordinary sintering technology.
A thin film having a thickness of m or less can be easily manufactured. A superconducting thick film having good performance can be easily manufactured at low cost.

When the thick film formed by this method is used in the field of high electric current (power storage coil, magnetic levitation object, etc.), it is uniform and has a high density, so that a high current density can be obtained. Further, when applied to the field of weak electric current, a high-sensitivity sensor can be manufactured because of its high density and thin thickness.

In addition, a large number of thick film pieces thus prepared are arranged in a tile shape on a ceramic substrate or a metal plate, and they are brought into close contact with the substrate by heating to form a large-area superconducting film, so that a power storage coil can be produced. . Further, the produced thick films are laminated and brought into close contact with each other by heating to form a superconducting object capable of passing a large amount of current, which can be used as a magnetic levitation device.

Next, the method of the present invention will be described in more detail with reference to examples. Needless to say, the present invention is not limited to the examples below.

Example A production example of a superconducting ceramic thick film having a YBa ₂ Cu ₃ O _7-δ composition is shown below.

As a raw material, reagent grade Y ₂ (CO ₃ ) ₃ , BaCO ₃ and CuO were used, and a predetermined amount of 10 g was weighed so that the desired composition was obtained, and crushed in an agate mortar for 30 minutes and mixed.

This powder was pressed into a disk shape and then calcined at 800 ° C. for 3 hours. Next, the reaction was completed at 950 ° C. for 10 hours to obtain a perovskite phase. 1 piece (0.2g) of the sintered body
In the apparatus shown in the figure, it was placed in a platinum nozzle and melted at 1300 ° C. for 1 minute in a silicon carbide electric furnace. After melting,
From the platinum nozzle upper part, air pressure (1.2 kg / cm ² ) is used to melt 100
By dropping it between twin rolls rotating at 0-3000 rpm, the width is immediately about 10 mm, the length is 30-50 mm, and the average thickness is 30 mm.
A thick film of ˜50 μm was obtained. After this thick film was heat-treated in air or oxygen at 950 ° C for 10 hours, in order to perform sufficient oxidation, it was allowed to pass between 700 and 200 ° C in air for about 6 hours, and then slowly cooled to room temperature. Chilled After that, it is cut into 5 × 10 mm ² with a wire saw, coated with silver paste, and the electrical resistance at low temperature is measured by the four-terminal method. Critical temperature T _c = 87K
A record of (zero resistance temperature) was achieved.

The measured value of the temperature-electrical resistance dependence in Fig. 2 is YBa ₂ Cu ₃ O.
The results are shown when a superconducting ceramic thick film having a thickness of 50 μm and having a composition of _7-δ was subjected to heat treatment and oxidation treatment under the above-mentioned conditions after super-quench cooling.

It is clear from the above examples that the thick film synthesized according to the present invention has sufficient performance as a superconducting wire material or an infrared / millimeter wave detecting element.

[Brief description of drawings]

FIG. 1 shows an example of a twin roll type melt quenching apparatus used in the method of the present invention. Further, FIG. 2 is a correlation diagram showing the dependence of temperature and electric resistance on an example of the superconducting ceramic thick film of the present invention. 1 ... Sample powder, sample agglomerate, 2 ... Platinum nozzle, 3 ... Gas, 4 ... Hole, 5 ... Twin roll ultra-quenching device.

Claims (1)

[Claims] 1. A powder or agglomerate having a perovskite phase is used as a raw material for a superconducting ceramic having a perovskite structure, and the raw material is heated and melted to a temperature equal to or higher than its melting point, and the melt is squeezed and rapidly cooled to a thickness. After forming a thick film of 5 to 300 μm, 85 in an oxygen-containing atmosphere or oxygen plasma
A method for forming a superconducting ceramic thick film, which comprises heat-treating at 0 to 950 ° C for 2 to 60 hours to form a perovskite phase, and then performing oxidation treatment at 200 to 700 ° C at 5 to 24 hours in the same atmosphere.