JPH01167912A - Sheathing material of superconducting material and manufacture thereof - Google Patents

Abstract

PURPOSE:To increase critical current density and enable manufacture with good repeatability by inclining the crystal direction of an MgO substrate from a perpendicular direction to some extent and depositing an oxide therein for growth. CONSTITUTION:In an MgO substrate, a plane inclined, for example, 0.2 to 2.0 deg. from a plane <100> about a <010> axis, is used, thereby introducing a step parallel to a <010> direction to the substrate. An oxide superconductor of RBa2Cu3O7-delta type is deposited on the substrate via sputtering and an amorphous state film is thereby formed. When the substrate is heated, an amorphous crystal growth progresses and the orientation thereof aligns in a constant direction, the (a) axis is oriented in parallel to the step and the (c) axis is oriented to a direction perpendicular to the plane. And even in the case of transformation from a tetoragonal system to a rhombic system appearing at the time of annealing by inclining the substrate to one direction by a micro angle, the step becomes a nucleus for the progress of the transformation, a crystal grain becomes large and a grain boundary is reduced. Consequently, superconducting critical current density becomes high. In the formula, R stands for any one of Y, Eu, Gd, Tb, Dy, Er and Yb.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a coating material of an R-Ba-Cu-0 based oxide superconducting material, which can be used, for example, in a Josephson device, or a 5QtlID or The present invention relates to a superconducting material covering material used in computer devices and the like, and a method for manufacturing the same.

(Prior art and its problems) A typical superconducting material that is currently expected to be put into practical use is an R-Ba-Cu-0-based oxide superconducting material (for example, YBazCuzOl-/). Conventionally, these oxide superconducting thin films have been created by sputtering using sapphire as a substrate.

For example, a sapphire substrate heated to 580°C (110
2) Y1BaaCu+ in a total of +50% O2 gas on the surface
Spunter deposition method of a target with a composition of oO9-/ (Japanese Journal of
Applied Physics, Vol. 26 (
1987), L1199), or Ar on the same substrate.
Y + Ba 2 Cu 30 when the substrate temperature is 550 to 650°C in +70%○2 gas? −♂Targent and Cu
Y1Ba2Cu30.The target was simultaneously sputtered and the a-axis was preferentially oriented perpendicular to the substrate surface. -/How to make crystalline films (Japanese Journal o
f Applied Physics, Vol. 26 (
1987).

LL221).

In the conventional method as described above, a difference in composition between the sputtered target and the growing thin film tends to occur, making it difficult to obtain a thin film having a desired composition ratio with good reproducibility. In addition, oxide superconductors undergo a phase transformation from tetragonal (high sum) to orthorhombic (low sum) at 500 to 600°C, but at this time, there are two orientations of the orthorhombic a-axis. Therefore, many orthorhombic crystals are formed from one tetragonal crystal, which deteriorates superconducting properties.

An object of the present invention is to provide a superconducting material coating material having a certain composition ratio R+BazCu30t-/, a desirable crystal orientation, and a high critical current density, and to provide a method for manufacturing the same with good reproducibility. .

(Means for solving the problem) Who is the inventor? Using IgO as a substrate, the crystal < 1
00 > direction is tilted to some extent with respect to the vertical direction,
It was confirmed that if RBatCu30t-/ type oxide is grown by vapor deposition here, a superconducting thin film can be obtained with good reproducibility and in which the desired crystal axis direction of R1BazCu307-/ is aligned in a certain direction.

The gist of the present invention is the following superconducting coating material and method for manufacturing the same.

(1) A substrate of MgO crystal whose <100> direction is inclined with respect to the vertical direction of the substrate surface, and R Ba2CusO? whose a-axis is grown preferentially in the <100> direction of the substrate MgO crystal on this substrate. A superconducting material covering material comprising a -/type oxide super Tj and a conducting material covering layer.

(2) heating a MgO crystal substrate whose <100> direction is inclined with respect to the direction perpendicular to the substrate surface at a temperature of 500° C. or less in an inert gas or an inert gas containing oxygen;
depositing an RBa2CusOq-type oxide superconducting material on the substrate to form an amorphous compound film;
1. A method for producing a superconducting material coating material, characterized in that the superconducting material is then heated to a temperature of 800 to 950° C. to crystallize, and further heated to a temperature of 400 to 550° C. to form a superconducting material.

R in the above RBa2Cus 07- is Y, Eu
, Gd, Tb, DyEr, or Yb.

FIG. 1 is a conceptual diagram of the surface of a substrate MgO for explaining the present invention. As shown in the figure, a step parallel to the <010> direction is introduced into the substrate by using a plane that is inclined, for example, 0.2 to 2.0'' with respect to the <010> axis from the (100) plane of MgO. This substrate is kept at a low temperature of 500° C. or less and an oxide superconductor is deposited by sputtering to form an amorphous film.

The substrate on which the oxide superconductor film is formed as described above is heated to a temperature of 800 to 950°C. By this heating, amorphous crystal growth progresses using the step of the substrate as a core, and the orientation thereof is aligned in a certain direction. That is,
The a-axis is oriented parallel to the step, and the a-axis is oriented perpendicular to the plane. Moreover, by tilting the substrate at a small angle in one direction, the steps become the nucleus for the transformation from tetragonal to orthorhombic crystals that occur during annealing at 400 to 550°C, resulting in larger crystal grains. As a result, grain boundaries are reduced.

Therefore, the superconducting H field current density becomes significantly large.

Hereinafter, the present invention will be explained in detail along with its effects using examples.

(Example) The (100) plane and (10) plane of the MgO substrate were prepared under the following conditions.
YBazCu*○1. , t were sputter-deposited, and the X-ray scattering intensity was measured as shown in Table 1.

(Sample preparation conditions) Sputtering conditions Ar gas pressure is 1 x 10 Torr, electric rod area is 20 cm
”, the distance between the electrodes was 5 cm, and the applied voltage was DCIKV.

The substrate used was a monocrystalline Go single crystal that had been polished at an angle of 1° from the (100) plane, and the surface was thinly etched with dilute sulfuric acid. The thickness of the deposited film is 5000.

Annealing conditions After sputter deposition, annealing was performed at 900°C for 10 hours in the air, and further annealing at 450°C for 2 hours.

Table 1 Table 1 shows the scattering intensities of several other planes when the scattering intensity of the (103) plane is taken as 100. As is clear from this result, when an oxide superconductor is deposited on a polished surface tilted from the (100) plane of the MgO crystal and annealed, the scattering intensity from the plane perpendicular to the C-axis increases. and
This indicates that the C axis is oriented in a direction perpendicular to the substrate surface.

next,? RBa2Cu30 when changing the inclination angle from the (100) plane of the IgO substrate. Changes in the superconducting critical current density of the J-deposited film were measured. The sample preparation conditions were the same as above.

FIG. 2 shows the measurement results for each type of RBazCux○ and J. As shown in the figure, any oxide (10
0) When the inclination from the plane is in the range of 0.2 to 2.0'', the critical current density is larger than when the inclination angle is 0°.

From the above results, it can be seen that the C axis of the crystal of the RBazCu30 q-(type oxide superconducting material is <1
A superconducting material coating material grown preferentially in the <100> direction on the substrate, the 00> direction being slightly inclined (preferably 0.26 to 2.0') with respect to the direction perpendicular to the substrate surface. However, it is clear that it has extremely superior characteristics compared to conventional ones.

The manufacturing conditions for the superconducting material coating material of the present invention are as follows:
The substrate temperature during deposition by sputtering and the annealing temperature of the deposited film are important.

First, when the substrate temperature during vapor deposition exceeds 500° C., the composition of the vapor deposited film deviates significantly from the composition of the target, and Cu in particular tends to escape, making it impossible to obtain the desired perovskite structure. Even when vapor deposition is performed without heating the substrate (at room temperature), no particular deterioration in characteristics is observed. Therefore, the lower limit of the substrate temperature is set to room temperature.

Further, as the atmosphere for sputtering, an inert gas such as Ar or a gas containing an appropriate amount of oxygen is used.

Next, the obtained vapor deposited film is annealed in a temperature range of 800 to 950°C. The purpose of this annealing is to crystallize the amorphous deposited film, and at temperatures below 800°C, the phase transition progresses slowly, and at temperatures above 950°C, the deposited film melts and solidifies again. Sometimes the components break down.

The deposited film crystallized (tetragonal) by the above annealing is further annealed in a temperature range of 400 to 550°C to transform from tetragonal to orthorhombic. Since this transition temperature is approximately 550°C, it is sufficient to maintain the temperature below 550°C for an appropriate period of time. However, if this temperature is lower than 400'C, the progress of the transition will be extremely slow and this cannot be said to be a practical condition.

(Effect of the invention) The superconducting oxide coating material of the present invention manufactured under the above-mentioned conditions has the prescribed composition and the crystal axis C
Since the axis is preferentially oriented perpendicular to the substrate, it has a high critical current density, and is expected to be put to practical use in the various applications mentioned above.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a substrate surface for explaining the present invention, and FIG. 2 is a diagram showing measurement results of critical current densities of various oxide superconducting materials including examples of the present invention.

Claims (2)

[Claims] (1) A substrate of MgO crystal whose <100> direction is inclined with respect to the perpendicular direction of the substrate surface, and an RBa whose C axis is preferentially grown in the <100> direction of the substrate MgO crystal on this substrate.
A superconducting material coating material comprising a _2Cu_3O_7_-_δ type oxide superconducting material coating layer. However, R is Y, Eu, Gd, Tb, Dy, Er, Yb
Either. (2) A substrate of MgO crystal whose <100> direction is inclined with respect to the perpendicular direction of the substrate surface is heated to a temperature of 500°C or less in an inert gas or an inert gas containing oxygen, and the RBa_2Cu_3O_7_-_δ type oxide superconducting material is vapor-deposited to form an amorphous compound film, then heated to a temperature of 800 to 950°C to crystallize, and further heated to a temperature of 400 to 550°C to form a superconducting material. A method for manufacturing a superconducting material coating material, characterized by: However, R is Y, Eu, Gd, Tb, Dy, Er, Yb
Either.