JPH0214801A - How to improve oxide superconductors - Google Patents

Abstract

PURPOSE:To make it possible to improve even a tetragonal substance obtained by quenching thereof from a high temperature into excellent superconducting characteristics through oxidation treatment in a short time by irradiating an oxide superconductor or a raw material therefor with an O2-based active species prepared by a high-temperature (non)equilibrium plasma. CONSTITUTION:An oxide superconductor having preferably a composition of Ba2YCu3Ox or a raw material therefor is irradiated with an O2-based active species prepared by a high-temperature (non)equilibrium plasma.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention quickly and efficiently oxidizes oxide superconductors with poor superconducting properties or superconductor raw materials that do not exhibit superconducting properties. This article relates to a method for dramatically improving its superconducting properties.

(Prior Art) In recent years, oxide superconductors have been discovered and their technological development is progressing at a rapid pace. - It is known that the oxygen content of an oxide superconductor greatly affects its superconducting properties, but it is extremely difficult to control the oxygen concentration in the superconductor.

For example, when creating a superconductor of Ba2YCu3O, barium carbonate (BaCOs), yttrium oxide (
After mixing Y2O2) and copper oxide (Cu2O) in a predetermined ratio, compression molding is performed to make pellets, and the pellets are 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, this type of material will be referred to as a tetragonal material).

In order to adjust the oxygen content to an appropriate value and make the best superconducting material, it is necessary to cool the material in an oxygen atmosphere from 930° C. over a period of one day. The material thus prepared is orthorhombic and exhibits superconducting properties at temperatures around 90°C or lower. (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 over a day as described above, and this cannot be applied to industrial mass production of the bottom.

B. G. Bagley et al. in their paper (Appl. Ph.
ys, Lett.

(1987) P, 822-P, 624), by high-frequency discharge treatment in an oxygen atmosphere, a tetragonal substance that does not exhibit superconducting properties becomes orthorhombic, and exhibits superconducting properties. It shows that it will become as shown.

However, in this case as well, in order to obtain superconducting properties of 90-degree
This method requires 85 hours of treatment, and similarly to the above, it cannot be applied industrially.

S. Minomo et al. in their paper (Jpn, J. App.
l, Phys, 2ヱ(198B) P, L411-P, L
413) shows that when ECR discharge treatment is performed, a 60 grade superconducting material is improved to 90 grade by treatment at 400° C. for 30 minutes.

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, long-term high-temperature oxygen treatment (at 300°C, there is no change even after 2 hours) is necessary, and the material is rapidly cooled from a high temperature. It has not been possible to convert a (tetragonal system) to an orthorhombic system in a short time and obtain superconducting properties.

In addition, the 35th Applied Physics Related Lecture 29a-
In X-5, Nakamura et al. used oxygen ion implantation and laser annealing to locally transform a tetragonal material into an orthorhombic material, but this is a very localized process and is not suitable for large-area mass production. It cannot be applied to

(Problems to be Solved by the Invention) As described above, in order to obtain an orthorhombic substance exhibiting good superconducting properties, it is necessary to process it for a long time in an oxygen atmosphere in a furnace,
Alternatively, it is necessary to process in oxygen plasma for more than 200 hours, and all conventional methods have problems in mass productivity.

In addition, the ECR discharge treatment method only modifies orthorhombic substances and 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 improves the properties of tetragonal materials obtained by rapid cooling without slow cooling from high temperatures, or materials with poor superconducting properties, by short-term oxidation treatment. The purpose of the present invention is to provide a new method for improving oxidation, which can produce materials that exhibit excellent 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. The method employs a method of irradiating the body material and improving its superconducting properties through oxidation.

(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 a tetragonal sample 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 is disclosed in the patent application filed in 1986-06 filed by the applicant of the present application.
Based on No. 9646 "Surface Treatment Method and Apparatus", a new and useful invention was obtained by utilizing this in the oxidation process of oxide superconductors, which was not generally known at the time of the application. . "LTE plasma" in the specification of the above 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. 1
2 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 an IC diameter of 1 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 (not shown) and a thyristor unit in combination, power is applied to the heater 13 to adjust the temperature of the substrate holder 12 through 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 flow of cooling water.

22 is a coil made of a steel vibrator, 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, the high frequency power source 24 has a frequency of 13. e
A high frequency separately excited power supply with a frequency of 56 MHz and an output of 5 kW was used.

Further, a predetermined gas (oxygen was used in this embodiment) 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.

Processing chamber 11 made of stainless steel and 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,
Initially, a widely spread high-frequency glow discharge occurs within the discharge tube 21. 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. (About this high-temperature non-equilibrium plasma or high-temperature equilibrium plasma, please refer to Hideo Mito et al.'s "Vacuum" Vol. 31 No. 4 (1988) P27!-P278
and are described in detail in the cited literature. ) 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 high temperature nonequilibrium plasma or high temperature equilibrium plasma 27
It is an active species created by Among the active species 28,
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 depending on the pressure (often on the lower pressure side than around 10 Tor) are also included.

Regarding the lifespan of oxygen-based active species when they are transported to the processing chamber 11, see J. M. Cook's paper 5solid 5ta.
te Technology / Japanese version May (19
87) P, 28-P, 33 and this cited document are detailed. They discussed the downstream lifetime of oxygen atoms generated by microwave discharge, and
This shows that the life span is more than 90% even after m backwards. However, there is no description of its application to superconducting materials.

In this example, Ba2YC1130x type, diameter 10m1
Using a tetragonal substrate that does not exhibit superconducting properties, which was produced by rapidly cooling a 2 mm thick pellet from 930°C without furnace cooling, an oxygen flow rate of 200 sccrn and a pressure of 0.7 Torr were used.
r, power 3kW, substrate holder temperature 300℃ and 400℃
It was processed with.

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, C is 30
This is a pattern when processed at 0°C for 5 minutes.

The X-ray diffraction pattern of Ba2YCu30x superconductors is widely known, and the relationship between the tetragonal system and the orthorhombic system exhibiting superconducting properties, and the intracrystalline oxygen concentration and superconducting properties is S,N.
Paper by akan ish i et al. Jpn, J, Appl
-Phys, 27 (1988) P, L329-P, L3
32, Y, Kubo et al. Jpn, J-App1
．． Phys, 26 (1987) P, L768-P, L7
70 and these cited references.

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.

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 the characteristic of the substrate treated at 300°C for 30 minutes, and C is the characteristic of the substrate treated at 400°C for 30 minutes. A has semiconducting properties and is tetragonal as described above, and does not exhibit superconductivity.

Superconducting properties have occurred in samples b and c, and in particular, C shows good superconducting properties of grade 90. Diamagnetism could be confirmed in both samples b and c 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 up to 90 degrees.

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 carried out under a vacuum of 0.7 Torr, but it is also effective to carry out high-temperature non-equilibrium plasma or high-temperature equilibrium plasma treatment under a pressure of 1 atmosphere or more. In this case, the plasma often changes from non-equilibrium to equilibrium plasma. Also, the processing chamber 11 in FIG.
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 be used for simultaneous oxidation treatment during film formation of a superconducting film by the CVD method, and remarkable effects similar to those described above could be obtained.

When forming a film by evaporation, MBE, etc., oxidation treatment can be performed during film formation by using working exhaust in combination.

In addition, the raw materials for superconductors include Ba2YC, u30. < but also those using other Y and Ln-based elements, i.e. MBa2Cu30X where M=Y, Ln(=LaS ce, Pr.

Nd, Pm, Sm.

Eu, Gd, Tb.

DV, Ho, Tm.

Yb, Lu), other compounds with the same elemental composition and other stoichiometry, or Bi-based - Bi2Ca2S r2Cu30xTll-
The method of the present invention is also effective for 12B a2Ca2Cu 3ox, compounds with the same elemental composition and other stoichiometry, and compounds with various other elemental compositions and other stoichiometry. there were.

The apparatus for carrying out the method of the present invention is not limited to the structure shown in FIG. Devices with various structures described in the above-mentioned Japanese Patent Application No. 61-069646, documents written by the inventor of the present application, "Vacuum" - Vol. 31, No. 4 (1988) P,
271-P, 278, and the devices cited therein, the present invention was able to obtain similar effects.

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.

Moreover, the processing conditions are the above-mentioned pressure of 0.7 Torr and oxygen flow of f! It is not a matter of sticking to t200sec or the like.

Furthermore, when utilizing the effect of plasma as an active species of oxygen, the substrate holder 12 is provided with DC and AC power.

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 materials (which have the potential to become superconductors but have not yet shown superconducting properties), and can be used with devices of various structures and under various conditions. You can do this with

(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 results of X-ray diffraction of the substrate to be treated, a: untreated, b: treated at 300°C for 1 minute, treated at 0300°C for 5 minutes. Figure 3 is a diagram showing the temperature change in the resistance of the substrate; a: untreated; b: treated at 300°C for 30 minutes; c: treated at 400°C for 30 minutes. 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 (2)

[Claims] (1) An oxide superconductor characterized in that the oxide superconductor or its superconductor raw material is irradiated with oxygen-based active species created by high-temperature non-equilibrium plasma or high-temperature equilibrium plasma to improve superconducting properties through oxidation. How to improve. (2) The oxide superconductor or its superconductor raw material is B
The method for improving an oxide superconductor according to claim 1, wherein the oxide superconductor has a composition of a_2YCu_3O_x.