JPH01183494A - High temperature superconductor bulk single crystal fabrication method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

D) Technical Field The present invention relates to a method for growing bulk single crystals of high temperature superconductors.

A high-temperature superconductor has a critical temperature of liquid nitrogen temperature (7
7K) or more. A wide range of applied research is being conducted in various engineering fields. Various compositions have been published.

(1) La-Ba-Cu-0 (if) LaSr-Cu-0 (fit) Y-Ba-Cu-0, etc. Among these, the critical temperature for (iii) is said to be 93 or 125.

The superconducting material is a thin film, a wire, or in the case of a bulk O 2 thin film, a superconducting ceramic thin film is formed on a substrate by sputtering, electron beam evaporation, or printing. After this, it is necessary to perform heat treatment at 900° C. or higher in an oxygen atmosphere.

In the case of wire rods, the fired hepteramic is powdered, packed into a steel pipe, and rolled through rollers and dies.

Superconductors made into thin films or wires have a wide variety of uses.

However, large single crystals are required to develop applications and elucidate the physical properties of high-temperature superconductors. For this reason, attempts have been made to produce bulk single crystals.

(a) Prior Art Bulk single crystals are produced, for example, by the 7-lux method. Y-Ba-cu- was created by the Institute for Solid State Physics.

The single crystal is obtained by adding extra Cu-0 to Y-B, -cu-o powder, melting it at about 1050°C, and recrystallizing it. This is a crystal of approximately 2ff x 111f x 0.3ff.

H, Takei et al”Growth of Y
Ba2Cu30x single crystalsw
ith superconducting Trans
ition above 90 K', J, J
, Appl.

phys, vol, 26, Jf, 9, 5ep
t, (1987) pp, L1425-1427Y203
, BaCO3, and CuO were mixed (1:2:3) and heat-treated at 900°C for 12 hours. Now powder Y-B
, -cu-.

The material is ready. Grind this into fine powder.

Add CuO at a ratio of 1/3 to V1 and mix.

This powder is 10m11φ×15 under a pressure of 130kg/-.
Form into a Wx rod. Place this in the crucible for 50
Heating is carried out while flowing 0 ml of oxygen. The temperature increase rate is 100°C/h. Once a temperature between 1200°C and 1050°C is reached, hold at that temperature for 5 hours. Furthermore, the temperature is lowered at a rate of -15°C/h. The rod broke,
It becomes small particles. This is a single crystal of several d.

Although the single crystals obtained by this method are useful for research on physical properties, they are too small and insufficient for practical applications.

It is an object of the present invention to provide a method for growing bulk single crystals of high-temperature superconductors with large dimensions and high purity.

B) Method of the Invention The method of growing a bulk single crystal of a high-temperature superconductor of the present invention is different from previously attempted single crystal manufacturing methods.

The high temperature superconductor bulk single crystal growth method of the present invention uses polycrystals produced by sintering as a starting material.

Since it is sintered, oxides y, o3, B, CO3, CuO
It is made by mixing powders such as, in an appropriate mixing ratio, shaping and baking. Of course, it can be made into any shape.

Here, it is formed into a rod shape. The use of sintered powder as a raw material is the same as in other methods. The Pro Sevens from now on will be different.

The sintered body is placed in a reaction tube, for example, a quartz ampoule, at a concentration of 0.1 to 1
Enclosed with oxygen at 00 Torr, the maximum temperature is 70 Torr.
0°C to 900°C, 0.05 sow/day in a triangular temperature distribution with a temperature gradient of 50°C/cIn to 200°C/a
Annealing is performed at a rate of ~5 wz/day.

The method of the present invention thus obtains a single crystal.

This will be explained below with reference to the drawings.

Figure 1 shows YBa2Cu30 made by sintering. The polycrystal is cut out into a prismatic shape (5m×5iv×50ff) or a cylindrical shape (8Hφ×5ON).

The size and shape are arbitrary, but it must be in the shape of an elongated rod and can be sealed in a quartz ampoule or the like.

After this, the rod-shaped YBB2Cu30x polycrystal was placed in a reaction tube.
For example, it is sealed in a quartz capsule along with oxygen gas. The pressure of oxygen gas is 0.1 to 100 Torr.

At this time, the YBa2Cu3Ox polycrystal does not fill the inside of the quartz capsule. The volume of a quartz capsule is larger than that of a polycrystalline capsule, leaving a space inside the quartz capsule.

The YBa2Cu3Ox polycrystal contained in this quartz capsule is zone-annealed.

Figure 2 hints at this situation.

YBa, Cu30. A polycrystal 1 is housed inside a quartz capsule 2, and the inside of the capsule 2 contains 0.1 to 100
The oxygen atmosphere is 4 Torr. A suspension device 3 suspends the quartz capsule 2 from above.

The YBa2Cu1Ox polycrystal 1 is heated by the heater 5 from the bottom end.

The heater 5 locally generates heat and locally heats the polycrystal 1.

A temperature distribution as shown in FIG. 2 is formed by the heater 5.

In Figure 2, the horizontal axis represents temperature and the vertical axis represents the position in the vertical direction. From above, the trap is such that the room temperature is T1 at AB, and the temperature rapidly rises at BC.

The temperature gradient of BC is as steep as 50°C/side to 200°C/cIn.

If the temperature gradient is lower than 50°C, single crystallization will not occur.

It is difficult to create a temperature gradient greater than the shoulder at 200℃2. This also depends on the length of BC. A resistance heating heater, the BC
When is short, it is difficult to create a particularly steep temperature gradient.

In the case of induction heating, it is easy to create a temperature gradient. Therefore, it is limited to 50°C/cIn to 200°C/cIn. Among these, 100°C/σ is the best.

In CD, high temperature T2 is maintained. T2 is 700℃~900
It is ℃. In particular, about 860° is good.

The shorter the length of the flat temperature region CD, the better.

However, if it is too short, a steep temperature gradient cannot be maintained in BC%DI. Therefore, the length of the CD is 5
ff~20jff. For example, about 1011111 is optimal.

In the present invention, the YB a2 Cu30x polycrystal is locally heated between the CDs, and the crystal grains in the locally heated portion are moved so as to align with the single crystallized portion below. For this reason, the narrower the CD, the better. When the CD is 20n or more, the grain boundary growth movement does not necessarily occur from the side closer to the single crystallized portion. In this case, single crystallization is hindered.

The explanation will be based on the temperature T2 of the CD.

If T2 is set to 900° C. or higher, local evaporation or decomposition occurs, resulting in material loss. In addition, contamination of materials by impurities and quartz contained in quartz capsules and the like becomes a problem. Therefore, T2 is set to 900°C or less.

If T2 is lower than 700°C, recrystallization will not occur at a sufficient rate. For this reason, polycrystals never become single crystals.

Of course, evaporation and decomposition occur even at 700°C to 900°C, but the amount is small and the presence of oxygen pressure makes it possible to suppress evaporation loss to a sufficiently low level.

In DE, on the other hand, the temperature drops rapidly. As with the BC part, the temperature gradient is from 0℃/cIn to -200℃/cI.
It is n. The best temperature is around -100°C/cm.

EF is maintained at room temperature T1.

In the end, the following conditions are imposed in each region regarding the temperature T. Let h be the downward position coordinate.

Between AB T-room temperature T1 dT/dh=0 Between BC 50
Shoulder to ℃2≦(dT/dh)≦200℃/cInCD
T=700℃～900℃ Between DE -200℃/cIn≦'(dT/dh)≦-5
Between 0℃/aEF T=room temperature Tl dT/dh=0 When the sample moves from top to bottom, that is, from A to F, AB
can be called a low temperature section, BC a temperature rising section, CD a high temperature section, DE a temperature falling section, and EF a low temperature section.

Although AB and EF are at room temperature T1, they are not actively heated. Since there is a sample, there is heat conduction from both the shell and the heater, so the temperature ranges from room temperature to 100℃.
It will be about.

Although CDs are illustrated as being flat, they cannot actually be made to be flat. The temperature distribution curves slightly upward.

The quartz capsule 2 moves from top to bottom or from bottom to top in a temperature distribution with such a steep temperature gradient.

It may be in either direction.

The moving speed V is o, os m/day ~ 5 ax/d
It is about ay.

In particular, about 2ynx/day is good. If the sample is 50 fl in length, it will take 25 days just to pass through the CD section, assuming 23/day. In reality, it takes even longer.

In this method, the sample is heat-treated, but only a narrow portion corresponding to the CD is heated to high temperature T2 (700°C to 900°C), so zone annealing zone
It can be called ealing.

(6) Effect In this method, the heater is moved up or down relative to the sample, so the traveling heater method (
traveling heater method
, T HM ) category.

The THM method is one of the crystal growth techniques that has been known for a long time.

However, it is new that the superconducting material YBa2Cu3Ox polycrystal is encapsulated with oxygen gas at 0.1 to 100 Torr and passed through the above temperature distribution.

After passing through an area with such a steep temperature gradient,
Break the quartz capsule 2 and take out YBa, C, 30. The entire sample is monocrystalline except for the edges that were heated first.

The first heated end means the lower end K when the quartz capsule is lowered, and the upper end when the quartz capsule is raised.

The area between these end fins is polycrystalline, and grain growth is observed to occur. It is a single crystal except for such ends.

Since most of the polycrystalline YBalCu30x has become a single crystal, a large single crystal can be obtained.

The reason why the first heated portion is polycrystalline is considered to be due to the following reason. When the polycrystal in this area is heated, the crystal grains grow, and since there are grains with various orientations, each grain grows and becomes larger.

Among them, the one in the direction that grew the fastest becomes dominant. From then on, crystals with this orientation will preferentially grow.

Since a seed crystal is not used, in the case of the present invention, which orientation will the single crystal be? This cannot be specified in advance.

The fact that it has become a single crystal can be confirmed by the clear appearance of the cleavage plane ((100) plane) and by X-ray diffraction.

The present invention has been described in detail above.

(9) Methods of using high-temperature superconductor polycrystals by sintering starting materials are known, and there are several methods. For example, mix powdered raw materials in an appropriate ratio, stir well to obtain a mixed material, and in air,
Preliminary firing is performed by heating to 00°C to 900°C. When this is cooled, a lump is obtained. This is crushed into powder, further mixed and molded, and then sintered again at 900°C for several tens of hours.

In this way, a rod-shaped sintered body is obtained.

(e) Although a quartz capsule is illustrated in FIG. 2 as a reaction tube for containing the expanded polycrystal of the present invention, tubes made of materials other than quartz such as graphite, alumina, BH, etc. can also be used.

In the above example, the reaction tube is sealed, but it may be open instead of being sealed. In this case, it is an open tube with a gas inlet, a gas outlet, etc. on both sides. The pressure of oxygen gas needs to be maintained at 0.1 to 100 Torr even if the tube is open.

Further, in the above example, a temperature distribution is formed in the vertical direction, and the polycrystalline sample is moved in the vertical direction.

However, the present invention is not limited to this, and the temperature distribution may be formed in the horizontal direction, and the heater and the reaction tube may be moved relative to each other in the horizontal direction.

In addition to oxygen, the atmospheric gas may include an inert gas such as hydrogen, He, or He, or a mixed gas of nitrogen gas N2 and oxygen.

Furthermore, in addition to performing zone annealing once,
This may be repeated two or more times.

If zone annealing is performed more than once, it will take twice as long or more, but a single crystal of better quality can be obtained.

When zone annealing is performed a plurality of times, a plurality of heaters may be arranged in order and the heat may be passed through these heaters in sequence.

The method of the present invention uses YBa and Cu5O made by a sintering method.

Put the polycrystal into a reaction tube and set the temperature to 0. I Torr ~100
It passes through a local high temperature part T2 in an oxygen atmosphere of Torr.

During this treatment, the sample remains solid without changing its shape or dimensions.

(b) Example made by sintering method? A YBa2Cu3Ox polycrystal of ffX7jflX50111 was placed in a quartz capsule with oxygen gas and sealed. The oxygen gas pressure at room temperature is I T
I made one with orr and one with 5 Torr.

This was set in the zone annealing apparatus shown in FIG. TI=room temperature, T2=860°C. B.C.

DE temperature gradient is +100℃/c11, -100℃/a
It is.

The movement speed was 2III/day.

The annealed sample was taken out by breaking the quartz capsule. The upper half of each sample was single crystallized.

It was confirmed by interfold analysis and X-ray diffraction that it was a single crystal.

Cut out the polycrystalline part, 7H x 7ff x 2011
A single crystal of 11M was obtained.

(g) Effects (1) A large YB32Cu30x single crystal can be manufactured.

(2) High purity single crystals containing almost no residual impurities can be obtained. This is because unlike the flux method, no solvent is used.

(3) It is a stable method with high reproducibility.

(4) It can be used as a substrate for superconducting devices. If this is used as a substrate, a high quality epitaxial growth layer can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating a polycrystalline sample used as a starting material in the manufacturing method of the present invention. FIG. 2 is a configuration diagram showing zone annealing of the present invention. 1......YBa2Cu3Ox polycrystalline 2......Quartz capsule 3...
......Suspension system 4...Oxygen atmosphere 5...
...Heater No. 1, No. 2, Figure 700 Heta 0σC Procedural Amendment Old Issue) Director General of the Japan Patent Office Kunio Ogawa 1. Indication of the case Japanese Patent Application No. 1983-6598 2. Title of the invention High temperature Superconductor bulk single crystal production method 3, person making amendment, case and relationship Patent applicant Residence 5-15 Kitahama, Higashi-ku, Osaka Name (213) Representative President of Sumitomo Electric Industries, Ltd.
Tetsu Kawakami Department 4, Agent No. 1 Fig. 2 Fig. 1...r Seven Risushi

Claims (1)

[Claims] A rod-shaped polycrystalline high-temperature superconductor made by a sintering method is placed in a reaction tube, and the atmosphere is set at 0.1 Torr to 100 Torr of oxygen gas or an inert gas, or a mixed gas of nitrogen gas and oxygen gas, and heated to room temperature to 100°C. The low temperature part AB and the temperature gradient are 50
The temperature rising part BC is between ℃/cm and 200℃/cm, and the temperature T
A high temperature section CD where _2 is 700°C to 900°C, and a low temperature section D where the temperature gradient is from -200°C/cm to -50°C/cm.
By moving the high temperature superconductor polycrystal at a speed of 0.05 mm/day to 5 mm/day at a speed of 0.05 mm/day to 5 mm/day, the high temperature superconductor polycrystal becomes a high temperature superconductor. A method for producing bulk single crystals of high-temperature superconductors, which is characterized by converting them into solid single crystals.