JPH01298005A - Production of oxide-based superconductor - Google Patents

Abstract

PURPOSE:To obtain the title superconductor wherein the materials of a substrate can be widely selected and having excellent superconductivity by irradiating a superconductor or a superconductor precursor with gaseous oxygen plasma through an electron-rich atmosphere to heat-treat the material. CONSTITUTION:A superconductor layer or a superconductor precursor layer is formed by PVD, etc., on a substrate consisting of an elementary metal, an alloy, ceramics, etc. The obtained superconductor layer or superconductor precursor layer is irradiated by gaseous oxygen plasma through an electron-rich atmosphere, heat-treated, and then annealed. In this case, a DC discharge is used to form the oxygen plasma. Namely, a space between a cathode 1 and an anode 2 is depressurized as shown in the figure, and a DC voltage is impressed between both electrodes to generate an arc discharge. O2 is passed 3 through the discharge region A, heat is exchanged between the O2 and arc, and the O2 is converted to plasma. The superconductor layer or superconductor precursor layer 5 of the substrate 4 is irradiated by the plasma under reduced pressure conditions through an electron-rich atmosphere, and heat-treated to obtain an oxide-based superconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field j] The present invention relates to a method for manufacturing a superconductor used as a superconducting circuit material such as a Josephson element or a superconducting material for various superconducting devices.

“Conventional technology” Is it always the case these days? Various oxide-based superconductors have been discovered that exhibit a transition critical temperature (Tc) from a Tf conducting state to a superconducting state, or a high value higher than the liquid nitrogen temperature.

As a method for manufacturing a superconductor made of such an oxide-based superconducting material, a superconductor layer or a superconducting precursor is deposited on a substrate by, for example, CVD (chemical vapor deposition) or PVD (physical vapor deposition). Methods of forming layers are known.

By the way, in such a method, after forming a superconductor layer or a superconducting precursor layer on a substrate, the entire substrate is heated at about 500 to 900°C for about 5 to 2.1 hours to form the superconductor layer or superconducting precursor layer. It is common to anneal the precursor layer to produce a superconductor with good superconducting properties.

[Problem to be solved by the invention] However, in the above method, the annealing temperature is 50°C.
Since the temperature is as high as 0 to 900°C, there are disadvantages such as the inability to use materials with a low melting point as the substrate material, and there is also the problem that production efficiency is impaired because the annealing time takes about 5 to 24 hours.

Furthermore, in the case of producing a Y-B a-Cu-0 based oxide superconductor, for example, it is desirable to fabricate a layer with an oxygen-deficient IQ type perovskite structure that has excellent superconducting properties. When manufacturing oxide-based superconductors, heat treatment is performed in an atmosphere with as high a concentration of oxygen as possible to ensure that oxygen atoms are sufficiently incorporated into the crystal.
It is considered important to perform heat treatment under temperature conditions that prevent oxygen atoms from escaping to the outside of the crystal. However, in order to perform heat treatment at a temperature that prevents oxygen atoms from escaping to the outside of the crystal, it is necessary to heat the material at a higher temperature and for a longer period of time, resulting in two problems.

This invention was made in view of the above circumstances, and its purpose is to provide a method for manufacturing a superconductor that allows a wide selection of substrate materials, simplifies the annealing process, and has excellent superconducting properties. It is about providing.

"Means for Solving the Problems" In the method for producing an oxide-based superconductor of the present invention, when heat-treating the superconductor or superconducting precursor, the superconductor or superconducting precursor is exposed to oxygen plasma through an electron-rich atmosphere. The solution to the above problem was to perform heat treatment while irradiating with gas.

Hereinafter, an example of the method for manufacturing an oxide-based superconductor of the present invention will be explained in detail with reference to the drawings.

First, prepare a substrate with a layer of superconductor or superconductor precursor formed on its surface. Here, as the weir plate, a single metal, an alloy, a ceramic, etc. are used, but a low melting point metal or alloy with a melting point of about 450°C or higher can also be used, and furthermore, it does not undergo degeneration etc. up to about 450°C. It is also possible to use materials such as synthetic resins that have excellent heat resistance. In addition, a superconductor has the general formula A -0-Cu-0 (where A is Y).

Periodic table items such as Sc, La, Yb, Er, Ho, Dy, etc. [
1] Group A elements, elements of Group Vb of the periodic table such as Bi and Sb, and elements of Group 1IIb of the periodic table such as TI and In.
1 or more, and B represents one or more of the elements in group La of the periodic table, such as Sr, Ba, Ca, etc. ), and a superconducting precursor is an intermediate between the oxide superconductor and a superconductor material.

In addition, specific examples of such superconductors include Y-Ba-Cu-0 system, B i-9r-Ca
-Cu-0 series, Tl-Ba-Ca-5r-Cu-0 series, and Nd-5r-Ce-Cu-0 series.

In addition, in order to produce such a superconductor, for example, compounds containing A, B, and Cu elements are used as gas phase sources, and they are instantaneously pyrolyzed by high heat. The organic matter in the gas phase source is burned out, and the A in the material is
, B, and Cu are excited in high heat to gasify them, and then sublimated and deposited on the substrate 1 in the form of ultrafine powder, thereby forming a thin film superconducting layer or superconducting precursor layer using the CVD method (chemical vapor phase). A bulk oxide superconductor with the same or similar composition to the thin film layer to be formed is used as a target, the target is irradiated with a laser beam, etc. to evaporate a portion of it, and then evaporated onto a substrate. PV to form a superconductor layer or superconductor precursor layer
Method D (physical vapor deposition method) or the like is preferably employed.

Next, the superconductor layer or the superconductor precursor layer of the above-mentioned substrate used is heat-treated while irradiating oxygen plasma gas through an electron-rich atmosphere to perform an annealing treatment. In this case, as a method for producing oxygen plasma gas, a method using direct current arc discharge, a method using high frequency plasma, etc. are adopted.

In the method using DC arc discharge, as shown in Fig. 1, a vacuum is maintained between the cathode 1 and the anode 2, and a DC voltage is applied between them to cause arc discharge. Oxygen is vented through the oxygen tube 3, and the oxygen is heat-exchanged with the arc to turn it into plasma, which is then heated under reduced pressure to the superconductor layer 5 or superconductor precursor of the substrate 4 through an electron-rich atmosphere (described later). This is a method in which the body layer (5) is irradiated.

As shown in FIG. 2, the method using high-frequency plasma involves keeping the inside of the quartz tube 6 under reduced pressure, aerating oxygen into the quartz tube 6, and applying a high-frequency coil 7 (not shown) wound around the quartz tube 6. A high frequency power source is connected, and the oxygen in the quartz tube 6 is made into a plasma state by high frequency electromagnetic induction, and this is heated under reduced pressure through an electric atmosphere as described below.
(This is a method in which one shot is applied to the superconductor layer 5 or superconductor precursor layer (5) of the plate 4.

In addition, in order to create an electron-rich atmosphere, as shown in FIGS. 1 and 2, thermal electrons are generated on the cathode 9 by heating with a heater 8, and these are transferred to the anode 10 facing the By moving toward the 1' Ti element rich 16 atmosphere electron shower 11 is formed [I! 2・
Vru. Then, the above-mentioned oxygen plasma gas is vented into the electron nower 11 and further passed through to be injected into the superconductor layer 5 or the superconductor layer (5) of the weir plate 4. Then, the oxygen plasma gas becomes elect [
Oxygen molecules are ionized by passing through the 1-no-yawer 11 and collide with the superconductor layer 5f) or the superconductor layer 5). In the examples shown in FIGS. 1 and 2, the method of generating the electron shower 11 is to emit thermoelectrons, but a method of emitting photoelectrons may also be adopted.

Furthermore, in the heat treatment of the superconductor layer 5 or the superconducting precursor layer (5) that is carried out simultaneously with the oxygen plasma gas irradiation treatment, the heating temperature is approximately 200 to 450°C. The heating treatment time is expressed as 0.5 to 2 hours. Further, as a heating method, in addition to heat treatment in a heating furnace, heat radiation heating method from the outside using a heater or the like can be adopted.

According to such annealing treatment, oxygen ions ionized and excited by passing through the electron shower 11 are transferred to the conductor layer 5 or the superconducting precursor layer (5).
Because the particles collide with each other, individual atoms in the irradiated oxygen plasma gas become super? 1i conductor layer 5 or superconducting precursor layer (
5) and is incorporated into the crystal thereof, so that the superconductor layer 5 or the superconducting precursor layer (5) becomes a superconductor having an oxygen-deficient perogaskite structure each time it is heat-treated. In addition, since the superconductor becomes a good superconductor with an oxygen-deficient perogaskite structure, the disadvantage that the crystal structure changes and the superconducting properties deteriorate by removing oxygen from the crystal can be prevented. As a result, the critical temperature is higher than that of conventional superconducting properties, resulting in excellent superconducting properties.

Furthermore, by passing through the electron shower 11 and irradiating oxygen plasma, the superconductor 1:'p5
Alternatively, since the reaction and bonding between the M3ITf-conducting precursor layer (5) and the excited oxygen ions is greatly promoted, the heat treatment conditions are lower and shorter than conventional ones.

In addition, by reducing the generation and irradiation of oxygen plasma gas [r: below], it is possible to reduce the production rate of oxygen plasma or oxygen ions. and its flight speed increases,
Oxygen ions are bonded within the crystal of the ultra-1u conductor with a higher probability, and therefore a sufficient amount of oxygen can be co-supplied in a short time.

In addition, in Example 1-1, these thin film layers formed on the weir plate as superconductors or superconducting precursors were heat-treated while irradiating oxygen plasma gas, but the superconductors or superconducting precursors In addition, a superconducting material formed into a desired shape such as a bulk shape may be used, a thin film layer formed on the surface of a tape-like substrate may be used, and a superconducting material formed with a metal coating layer may also be used. The metal coating layer may be removed from the wire and a core wire made of an exposed superconductor or superconducting precursor may be used.

"Effect of the Invention J As explained above, the method for producing an oxide-based superconductor of the present invention involves subjecting a superconductor or a superconducting precursor to heat treatment by irradiating oxygen plasma gas in an electron-rich atmosphere. Therefore, oxygen ions that are ionized and excited by passing through the electron-rich atmosphere collide with the conductor or superconducting precursor, and the oxygen ions are incorporated into the crystal of the superconductor or superconducting precursor. Therefore, the superconductor or superconducting precursor becomes an oxide-based superconductor with a structure in which sufficient oxygen is contained in the crystal, and the resulting oxide-based superconductor exhibits excellent superconducting properties such as a high critical temperature. It becomes the property of the existing Party B.

In addition, by passing through an electron-rich atmosphere and irradiating oxygen plasma, the reaction and bonding between the superconductor or superconducting precursor and excited oxygen ions is greatly promoted, so the heat treatment conditions are better than conventional ones. It can be performed at low temperatures and for a short period of time, and therefore productivity can be improved.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams related to the present invention, with Figure 1 being a schematic configuration diagram for explaining a treatment method using DC arc discharge, and Figure 2 being a diagram showing a treatment method using high-frequency plasma. It is a schematic t11It diagram for explaining the method. DESCRIPTION OF SYMBOLS 1... Cathode, 2... Anode, 4... Substrate, 5... Superconductor layer or superconducting precursor layer, 7...
...High frequency coil, 8...Heater, 9
...Cathode, 10...Anode, II...Electron Yawer.

Claims (1)

[Claims] When heat treating superconductors or superconducting precursors,
A method for producing an oxide-based superconductor, comprising heat-treating a superconductor or a superconducting precursor while irradiating oxygen plasma gas in an electron-rich atmosphere.