JPH0446882B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides rapid and rapid oxidation of oxide superconductors with poor superconducting properties or superconductor raw materials that do not exhibit superconducting properties. and a method for improving its superconducting properties. (Prior Art) In recent years, oxide superconductors have been discovered and their technological development is progressing at a rapid pace. Although it is generally known that the oxygen content of an oxide superconductor greatly affects its superconducting properties, it is extremely difficult to control the oxygen concentration in the superconductor. For example, when creating a Ba ₂ YCu ₃ Ox superconductor, barium carbonate (BaCO ₃ ), yttrium oxide (Y ₂ O ₃ ), and copper oxide (CuO) are mixed in a predetermined ratio and then compression molded. Pellets are made and heated to 930°C in an oxygen atmosphere furnace. However, X may be zero. The pellet exhibits a tetragonal structure at this point. However, this sample has a low oxygen content and does not exhibit superconducting properties. (Hereinafter, what is called a tetragonal substance is
(this type of substance). In order to make the best superconducting material by adjusting the oxygen content to an appropriate value, it is necessary to
It must be cooled in the furnace for a day. The material created in this way is orthorhombic and exhibits superconducting properties at temperatures below around 90K. (Hereinafter, this type of substance will be referred to as an orthorhombic substance). However, in order to obtain good superconducting properties, it is necessary to perform furnace cooling in an oxygen atmosphere for one day as described above, and this is by no means applicable to industrial mass production. BGBagley et al. in their paper (Appl. Phys. Lett.
51 (1987) P.622-P.624), a tetragonal substance that does not exhibit superconducting properties becomes orthorhombic by high-frequency discharge treatment in an oxygen atmosphere.
This indicates that it begins to exhibit superconducting properties. However, in this case as well, 285 hours of treatment is required to obtain 90K-class superconducting properties, and as with the above, this is also not industrially applicable. S. Minomo et al. in their paper (Jpn.J.Appl.Phys.
27 (1988) P.L411-P.L413), when ECR discharge treatment is performed, 60K class superconducting material is heated to 400℃,
This shows that 30 minutes of treatment can improve the temperature to 90K. However, this only improves the superconducting properties by applying a treatment to a sample that originally had superconducting properties, and the superconducting properties are produced by changing the crystal structure of a tetragonal substance that does not produce superconducting properties. It's not something. This is important; in order to change from a tetragonal system to an orthorhombic system, there is no change even after long-term high-temperature oxygen treatment (2 hours at 300°C).
It was not possible to rapidly cool a substance (tetragonal system) from a high temperature to orthorhombic system and obtain superconducting properties. Also, the 35th Applied Physics Related Lecture 29a in 1988
In -X-5, Eryu et al. locally changed a tetragonal material into an orthorhombic material by oxygen ion implantation and laser annealing, but this was a very localized process over a large area. It cannot be applied to mass production. (Problems to be Solved by the Invention) As described above, in order to obtain an orthorhombic substance that exhibits good superconducting properties, it is necessary to process it for a long time in an oxygen atmosphere in a furnace or to All conventional methods have problems with mass production, as it requires processing for more than an hour. In addition, the ECR discharge treatment method only modifies orthorhombic substances, but cannot change tetragonal substances to orthorhombic substances, and therefore requires a long treatment time. There has been no improvement at all. (Objective of the invention) The present invention solves this problem, and uses a short-time oxidation treatment to produce tetragonal substances obtained by rapid cooling without slow cooling from high temperatures, or substances with poor superconducting properties. The purpose of the present invention is to provide a novel oxidation improvement method that can produce a material that exhibits good superconducting properties. (Means for Solving the Problems) In order to achieve the above object, the present invention uses oxygen-based active species created by high-temperature non-equilibrium plasma or high-temperature equilibrium plasma to conduct oxide superconductors or superconducting oxide superconductors. A method of irradiating the body material and improving its superconducting properties through oxidation is adopted. (Operation) High-temperature non-equilibrium plasma or high-temperature equilibrium plasma generates a large amount of atomic active species within the plasma. This active species has a large diffusion coefficient in solids and has the property of rapidly diffusing at low temperatures. Superconducting properties can be greatly improved by irradiating an oxide superconductor or its superconductor raw material with such oxygen-based active species. Therefore, there is no need to slowly cool the sample, and even tetragonal samples obtained by rapid cooling can be effectively oxidized at low temperatures, completing the oxidation in a short time and obtaining good superconducting properties. be able to. (Example) The present invention was filed in the patent application filed in 1983 by the applicant of the present application.
-069646 (Japanese Unexamined Patent Publication No. 62-227089) ``Surface Treatment Method and Apparatus'', and by utilizing this in the oxidation process of oxide superconductors, which was not generally known at the time of the application, a new invention was created. We were able to obtain a useful invention. "LTE plasma" in the specification of the above-mentioned patent application corresponds to "high-temperature non-equilibrium plasma or high-temperature equilibrium plasma" in the specification of the present application. FIG. 1 shows a front sectional view of an apparatus utilizing the method of the present invention. Reference numeral 11 denotes a processing chamber made of stainless steel, which has a structure that allows it to be evacuated or kept airtight as required. 12 is a substrate holder for holding the substrate 15 and controlling the temperature; 13 is a heater; and 14 is a thermocouple. The substrate holder 12 has a diameter of 10 cm and can be heated to about 450°C. Measuring the temperature of the substrate holder 12 with a thermocouple 14,
By using a temperature controller and a thyristor unit (not shown), power is applied to the heater 13 and the temperature of the substrate holder 12 is adjusted by P, PI, PID control or ON/OFF control using a simple relay. When necessary, use a cooling mechanism such as water cooling for this part. Reference numeral 21 denotes a discharge tube, which is a double tube made of quartz glass, and has a structure in which water can be cooled by flowing water between the double tubes. In this example, the inner diameter of the quartz glass tube is 3 cm in diameter and 53 cm in length. 26, 26'
indicates the direction of cooling water flow. 22 is a coil made of copper pipe, and the inside of the pipe is water-cooled. One end of the coil 22 is grounded, and the other end is connected to a high frequency power source 24 through a matching circuit 23. In this embodiment, a separately excited high frequency power source with a frequency of 13.56 MHz and an output of 5 kW was used as the high frequency power source 24. In addition, a predetermined gas (oxygen was used in this example)
is introduced from a cylinder (not shown) in the direction of arrow 25 via a pressure reducing valve and a flow controller, and is exhausted in the direction of arrow 29. Although not shown, a Roots pump and an oil rotary pump are used as exhaust pumps. The processing chamber 11 made of stainless steel and the discharge tube 21 made of quartz glass are joined by a rubber O-ring. Reference numeral 17 denotes a pressure gauge, which measures the pressure within the processing chamber 11, and adjusts the pressure to a constant level by adjusting the conductance of a valve (not shown) installed at the tip of the arrow 29. As described in Japanese Patent Application No. 61-069646,
When power is injected into the coil 22 from the high-frequency power source 24, a high-frequency glow discharge that spreads widely within the discharge tube 21 initially occurs. When a larger power is injected, a locally pinched high-temperature nonequilibrium plasma or high-temperature equilibrium plasma 27 is generated inside the coil 22. (This high-temperature non-equilibrium plasma or high-temperature equilibrium plasma is discussed in “Vacuum” by Hideo Mito et al.
It is described in detail in Volume 31, No. 4 (1988), P271-P278, and its cited references. ) This high-temperature non-equilibrium plasma or high-temperature equilibrium plasma has a much higher emission intensity than high-frequency glow discharge, generates a large amount of active species, especially atomic active species, and has a low discharge impedance electrically. It is characterized by a low value. 28 is an active species created by high temperature non-equilibrium plasma or high temperature equilibrium plasma 27. Some active species 28 are released by pressure (often 10 Torr).
It is assumed that active species of glow-like discharge plasma observed around the high-temperature non-equilibrium plasma or the high-temperature equilibrium plasma 27 (on the lower pressure side than the front and back) are also included. Regarding the lifespan of oxygen-based active species when they are transported to the processing chamber 11, see JMCook's paper Solid State
I am familiar with Technology/Japanese Edition May (1987) P.28-P.33 and this cited document. They discussed the downstream lifetime of oxygen atoms generated by microwave discharge, and found that even 50 cm behind the plasma, the lifetime is 90%.
This shows that it has a long lifespan. However, there is no description of its application to superconducting materials. In this example, we used a tetragonal substrate that did not exhibit superconducting properties and was produced by rapidly cooling a Ba ₂ YCu ₃ Ox pellet with a diameter of 1 cm and a thickness of 2 mm from 930°C without cooling in a furnace. Processing was carried out at a flow rate of 200 sccm, a pressure of 0.7 Torr, an electric power of 3 kW, and a substrate holder temperature of 300°C and 400°C. FIG. 2 shows the results of observation by X-ray diffraction of the substrate treated as described above. Figure 2 a is untreated, b is treated for 1 minute at 300℃, c
is the pattern obtained when treated at 300°C for 5 minutes. The X-ray diffraction patterns of Ba ₂ YCu ₃ Ox superconductors are widely known, and the relationship between the tetragonal system and the orthorhombic system that exhibits superconducting properties, and the intracrystalline oxygen concentration and superconducting properties was reported by S. Nakanishi et al. Paper Jpn.J.Appl.Phys.
27 (1988) P.L329-P.L332 and papers by Y. Kubo et al.
Jpn.J.Appl.Phys. 26 (1987) P.L768-P.L770 and these cited documents are detailed. a is a normal typical tetragonal pattern, and as will be described later, it does not have a crystal structure exhibiting superconducting properties. Sample b was treated at 300°C for 1 minute using high-temperature non-equilibrium plasma, and has a structure in which tetragonal and orthorhombic systems are mixed. Sample c was treated at the same temperature for 5 minutes and has a typical orthorhombic crystal structure. Orthorhombic substances can exhibit superconducting properties, and the method of the present invention was able to change the crystal structure in a short time of 5 minutes. FIG. 3 shows the temperature change of the resistance of this substrate. Figure 3a is untreated. b is treatment at 300℃ for 30 minutes, c
is the characteristic of the substrate treated at 400°C for 30 minutes. a
has semiconductor properties, and as mentioned above, it has a tetragonal system and does not exhibit superconductivity. Superconducting properties have occurred in b and c, especially c
It shows good superconducting properties of 90K class. b, c
Diamagnetism was confirmed in both cases at liquid nitrogen temperature (77K). As described above, when the method of the present invention is used, it is possible to transform a tetragonal substance that does not exhibit superconducting properties into an orthorhombic substance that exhibits superconducting properties in an extremely short period of time, and also to change that property. The properties can be improved to 90K class. Similarly, even when treating a substrate with poor superconducting properties, it was possible to improve the properties to good properties. In this example, the treatment was performed under a vacuum of 0.7 Torr, but high-temperature nonequilibrium plasma or high-temperature equilibrium plasma treatment under a pressure of 1 atmosphere or more is also effective. In this case, the plasma often changes from non-equilibrium to equilibrium plasma. Further, the processing chamber 11 shown in FIG. 1 is unnecessary. Furthermore, although the present example uses a bulk sample, the method of the present invention was also effective for thin film and thick film samples produced by sputtering, vapor deposition, etc., as well as powder samples. Furthermore, the method of the present invention can also be used for simultaneous oxidation treatment during film formation when a superconducting film is formed by the CVD method, and the same remarkable effects as described above could be obtained. When forming a film by vapor deposition, MBE, etc., it was possible to carry out oxidation treatment during film formation by using working exhaust in combination. In addition, not only Ba ₂ YCu ₃ Ox but also other Y and Ln-based elements are used as raw materials for superconductors.
That is, MBa ₂ Cu ₃ Ox where M=Y, Ln (=La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Tm,
Yb, Lu), compounds with the same elemental composition and other stoichiometry, or Bi-based - _{Bi 2} Ca ₂ Sr ₂ Cu ₃ Ox Tl-based - Tl ₂ Ba ₂ Ca ₂ Cu ₃ Ox, or compounds with the same element The method of the present invention was also effective for compounds having other stoichiometry in composition and compounds having other stoichiometry in various other elemental compositions. The apparatus for carrying out the method of the present invention is not limited to the structure shown in FIG. Said patent application 1986-069646
Devices with various structures described in the issue, documents written by the inventor of the present application, "Vacuum" Vol. 31, No. 4 (1988) P.271-P.278, and the documents cited therein The present invention was also able to obtain similar effects by using the above device. Further, in the above description, oxygen was used as the oxidizing gas, that is, the "predetermined gas", but the same effect could be obtained using gases such as ozone and nitrous oxide. Further, the processing conditions are not limited to the above-mentioned pressure of 0.7 Torr, oxygen flow rate of 200 sccm, etc. Furthermore, when utilizing the effect of plasma as an active species of oxygen, the substrate holder 12 is provided with DC, AC,
A bias such as RF may be applied. As described above, the method of the present invention uses active species created by high-temperature non-equilibrium plasma or high-temperature equilibrium plasma to form an oxide superconductor (which already exhibits a certain degree of superconducting properties) or its superconductor raw material (as a composition). It is characterized by the fact that it improves the superconducting properties by irradiating a material (which has the potential of becoming a superconductor but has not yet shown superconducting properties), and it can be used in various devices with various structures. This can be done under the following conditions. (Effects of the Invention) As described above, the method of the present invention achieves good superconductivity from an oxide superconductor or its superconductor raw material in an extremely short time by performing oxidation using high-temperature non-equilibrium plasma or high-temperature equilibrium plasma. characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of an apparatus for carrying out the method of the present invention. Figure 2 shows the X-ray diffraction results of the substrate to be treated.
Process for 5 minutes. Figure 3 shows the temperature change in the resistance of the substrate.
Treated for 30 minutes at °C. DESCRIPTION OF SYMBOLS 11... Processing chamber, 12... Substrate holder, 15... Substrate, 21... Discharge tube, 27... High temperature nonequilibrium plasma or high temperature equilibrium plasma, 28... Active species.

Claims (1)

[Claims] 1. Oxidation characterized by irradiating an oxide superconductor or its superconductor raw material with oxygen-based active species created by high-temperature non-equilibrium plasma or high-temperature equilibrium plasma to improve superconducting properties by oxidation. Methods for improving physical superconductors. 2. The method for improving an oxide superconductor according to claim 1, wherein the oxide superconductor or its superconductor raw material has a composition of Ba ₂ YCu ₃ Ox.