JP2595261B2 - Manufacturing method of oxide superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an oxide superconductor that can be used as a superconducting device such as a Josephson element or a superconducting storage element, a coil for a superconducting magnet, or the like.

[Conventional technology]

Recently, various oxide-based superconductors exhibiting a high critical temperature (Tc) at which a transition from a normal conducting state to a superconducting state is higher than the temperature of liquid nitrogen are being discovered. Such oxide superconductors can be used under significantly more advantageous cooling conditions than alloy or intermetallic compound superconductors that require the use of liquid helium for cooling. It has been.

Incidentally, as a method of manufacturing such an oxide superconductor, for example, chemical vapor deposition (hereinafter, referred to as CVD) is used.
A chemical vapor deposition method such as a method tends to be frequently used because an oxide superconductor having relatively good superconducting properties can be obtained in a thin film form. In such a chemical vapor deposition method, for example, thermal CV
When a Y-Ba-Cu-O-based oxide superconductor is obtained by the method D, the constituent elements of the oxide superconductor such as Y (yttrium), Ba (barium), and Cu (copper) are used as a reaction atmosphere in the vapor deposition. A mixed gas containing a gas of a starting compound such as an alkoxide compound, an oxyketone compound, a cyclopentadienyl compound, an acetylacetone compound, or a halide, and an oxygen gas is preferably used.

[Problems to be solved by the invention]

However, in such a chemical vapor deposition method, since the vapor pressure of each of the above raw material compounds is as low as several to several tens mmHg,
The reaction atmosphere needs to be under reduced pressure. For this reason, when the deposition is performed under reduced pressure, the amount of oxygen gas contained in the reaction atmosphere is relatively reduced, so that the oxygen element introduced into the composition of the oxide superconductor tends to be insufficient. There is a problem that it is difficult to obtain an oxide superconductor having excellent superconducting characteristics.

Therefore, at present, there is an urgent need to develop a method for producing an oxide superconductor that can improve the superconducting properties by introducing a required amount of oxygen element into the composition of the oxide superconductor.

The present invention has been made in view of the above circumstances, and it is possible to perform a heat treatment on an oxide superconductor generated in a chamber by a chemical vapor deposition method while efficiently supplying oxygen in the same chamber. To provide a method for manufacturing an oxide superconductor, which can reduce the amount of heat, can save thermal energy, can eliminate the work of replacing the base, and can shorten the manufacturing time. Aim.

[Means for solving the problem]

In the present invention, the solution is to subject the oxide superconductor generated by the chemical vapor deposition method to heat treatment in an oxygen atmosphere having a specific oxygen partial pressure.

 Hereinafter, the present invention will be described in detail.

In the present invention, as shown in FIG. 1, first, a base 1 is prepared. As the base 1, various shapes such as a plate material, a wire material, a tape material, a cylindrical body, and a columnar body are used. Examples of the material for forming the substrate 1 include metal materials such as silver, gold, platinum, stainless steel, aluminum, and copper, alloy materials thereof, nitrides and carbides of the above metals or alloys, and SrTiO ₃ (titanium). Strontium acid), Al ₂ O ₃ (alumina), Si (silicon), SiO ₂
Crystal materials such as (silica), LiNbO ₃ (lithium niobate), sapphire, and ruby are preferably used.

Next, a thin film 2 made of an oxide superconductor described later is formed on the surface of the substrate 1 by a chemical vapor deposition method. Here, as the above-mentioned chemical vapor deposition method, a plasma CVD method, a photo CVD method, an MO-CVD (metal organic chemical vapor deposition) method, etc. are used in addition to a normal thermal CVD method. This chemical vapor deposition step is performed under reduced pressure, and includes an alkoxide compound containing a constituent element of an oxide superconductor described later, an oxyketone compound, a cyclopentadienyl compound, an acetylacetone compound,
The reaction is performed in an atmosphere of a mixed gas composed of a gas of a raw material compound such as a halide and oxygen gas. As the carrier gas, a common inert gas such as an argon gas or a mixture of the inert gas and the periodic table VI such as O, S, Se, etc.
A gas of a group b element or a mixed gas obtained by mixing a gas of a group VII b element of the Periodic Table VII such as F, Cl, or Br is appropriately selected and used.

An oxide superconductor as a material for forming such a thin film 2 is an ABCD-based (where A is Y, Sc, La, Yb, Er,
One or two elements from Group IIIa of the Periodic Table, such as Ho and Dy
B represents one or more of Group IIa elements of the Periodic Table such as Sr, Ba, Ca, etc., and C represents a Group Ib element of the Periodic Table of Cu, Ag, Au. Among them, Cu or two or more kinds containing Cu are represented, and D is a group VIb element of the periodic table such as O, S, Se and F,
O or two or more elements containing O among elements of Group VIIb of the periodic table such as Cl and Br. ) Is used. And
The composition of each constituent element of this oxide superconductor is, for example, Y-Ba
In the case of -Cu-O-based oxide superconductor, Y1, Ba2, Cu3, O (7-
δ) and 0 ≦ δ ≦ 5.

Since the thin film 2 thus formed by the chemical vapor deposition method is formed under a reduced pressure, particularly in a reaction atmosphere having a low oxygen gas concentration, the thin film 2 is introduced into the composition of the oxide superconductor forming the thin film 2. Insufficient amount of oxygen has been obtained, and the superconducting properties have not yet been shown.

Therefore, in the present invention, the above thin film 2 is subjected to a heat treatment in an oxygen atmosphere. In this heat treatment, the oxygen partial pressure in the heat treatment atmosphere was set to 0.1 to 1 atm, and the treatment temperature was set to 300 ° C.
10001000 ° C., the treatment time is several to several tens of hours.
By such a heat treatment, a necessary amount of oxygen element can be surely and easily introduced into the composition of the oxide superconductor forming the thin film 2, so that the superconducting properties can be improved and good superconducting properties can be obtained. The oxide superconductor shown can be obtained.

It is desirable that this heat treatment step be performed in the same chamber as the previous chemical vapor deposition step, and that both steps be performed continuously. In other words, if one chamber is shared by both processes, it is not necessary to provide a dedicated chamber for each process, so that equipment costs can be reduced. Further, if both steps are performed in succession, the heat of the previous step can be reused, so that heat energy can be saved and the replacement work of the base 1 due to the change of the chamber can be omitted.
It is possible to obtain effects such as shortening the manufacturing time.

Next, the thin film 2 thus improved in superconductivity is cooled. This cooling operation is performed in two ways according to the processing temperature of the heat treatment in the preceding step. First, the first is that the processing temperature of the heat treatment in the previous step is the crystal transformation temperature (400
When the temperature is not lower than 600 ° C.) and lower than 1000 ° C., the thin film 2 is gradually cooled to the crystal transformation temperature. The slow cooling rate at this time is determined according to the characteristics required for the oxide superconductor, the type and shape of the oxide superconductor, and for example, it is desirable that the temperature drop per hour is about 200 ° C. The reason for performing such slow cooling is that the oxide superconductor that has been heat-treated at a temperature equal to or higher than the crystal transformation temperature is tetragonal, whereas the oxide superconductor that exhibits good superconductivity is orthorhombic. This is because it is necessary to gradually cool and transition from tetragonal to orthorhombic over time. Second, when the treatment temperature of the heat treatment is equal to or higher than 300 ° C. and equal to or lower than the crystal transformation temperature, the oxide superconductor forming the thin film 2 is already orthorhombic and does not need to be gradually cooled. There is a method of rapidly cooling to room temperature.

According to such a manufacturing method, the thin film 2 made of an oxide superconductor formed by a chemical vapor deposition method is subjected to a heat treatment in a specific oxygen atmosphere.
Since the required amount of oxygen element can be reliably and easily introduced into the composition of the oxide superconductor forming the oxide superconductor, the oxygen deficiency in the composition of the oxide superconductor can be eliminated and the superconductivity can be improved. As a result, a layered perovskite-type oxide superconductor exhibiting good superconducting properties can be obtained.

In this example, the oxide superconductor formed by the chemical vapor deposition method is formed into a thin film, but may be formed into a powder, for example. In this case, by making the oxide superconductor powdery, a larger surface area can be obtained compared to a thin-film oxide superconductor. Can be introduced in a short time.

(Production example)

An attempt was made to produce a Y-Ba-Cu-O-based oxide superconductor using the CVD apparatus shown in FIG.

The chamber 10 of the CVD apparatus is capable of continuously performing a thin film forming step by a CVD method and a heat treatment step. As the substrate 11 provided on the inner bottom of the chamber 10, a plate material made of strontium titanate having a perovskite structure was used.

Further, to the chamber 10, three raw material vaporization chambers 13, 14 and 15 are connected via a supply pipe 12, and an oxygen cylinder 17 is connected via a supply pipe 16. Then, in the raw material vaporization chamber 13, tris / cyclopentadienyl / yttrium Y (C ₅ H ₅ ) ₃ which is a cyclopentadienyl compound of yttrium element is accommodated, and in the raw material vaporization chamber 14, a barium element Bis (cyclopentadienyl) barium Ba (C ₅ H ₅ ) ₂ which is a cyclopentadienyl compound of the formula, and acetylacetone copper Cu (C ₅ H ₇ O ₂ ) ₂ was contained. One carrier gas supply cylinder 21 is connected to these three raw material vaporization chambers 13 to 15 via supply pipes 18, 19, and 20, respectively. That is, the raw material vaporization chambers 13, 14, 15
The raw material gas supply means is constituted by the gas supply cylinder 21 and the carrier gas supply cylinder 21. In this example, argon gas was used as a carrier gas. Further, the chamber 10 includes:
An exhaust pump 23 is connected via an exhaust pipe 22.

Then, the surface temperature of the substrate 11 in the chamber 10 becomes approximately
While controlling the temperature to 800 ° C., the pressure was reduced by the exhaust pump 23 until the pressure in the chamber 10 became about 0.2 Torr. Next, each of the raw material compounds contained in the raw material vaporization chambers 13 to 15 was vaporized, and each of these raw material gases was supplied into the chamber 10 together with the argon gas from the carrier gas supply cylinder 21. Further, oxygen gas was supplied from the oxygen cylinder (oxygen gas supply means) 17 into the chamber 10. In this way, CVD is performed in an atmosphere of a mixed gas composed of each raw material gas sent into the chamber 10, and YBa
A thin film 24 having a composition of ₂ Cu ₃ O ₇ was produced. By the way, this thin film
After gradually cooling 24, the critical temperature (Tc) was measured.
It was 31K.

Next, while gradually changing the internal atmosphere of the chamber 10 from the above-described source gas atmosphere to an oxygen atmosphere, the internal temperature was increased and the thin film 24 was heat-treated under the following conditions.

300 ° C, 10 hours 500 ° C, 5 hours, 1000 ° C, 2 hours In this heat treatment, in addition to the above conditions 1 to 3, the oxygen partial pressure in the processing atmosphere is changed in the range of 0 to 1 atm. The Tc of the thin film 24 after the heat treatment at the partial pressure was measured, and the results are shown in Table 1. In the case of the heat treatment under the condition, the measurement of Tc is performed after the quenching of the thin film 24, and in the case of the heat treatment under the condition, the temperature of the thin film 24 is increased per hour.
This was performed after gradually cooling by a method of decreasing the temperature by 200 ° C.

It should be noted that the mark x in the column of Tc in Table 1 means that no superconductivity is exhibited. This is presumably because the heat treatment of the thin film 24 was performed in an oxygen-free state, so that the oxygen element once introduced by the CVD method in the composition of the oxide superconductor forming the thin film 24 was released.

Further, as is clear from Table 1 above, in each of the examples in which the oxygen partial pressure was 0.1 atm or more, the Tc before the heat treatment was lower than in each of the comparative examples in which the oxygen partial pressure was less than 0.1 atm.
It can be seen that can be significantly improved.

[Effects of the Invention] As described above, according to the present invention, an oxide superconductor generated by a chemical vapor deposition method is subjected to an oxygen atmosphere having an oxygen partial pressure of at least 0.1 atm in the same chamber. Since the heat treatment is performed, the necessary amount of oxygen element can be reliably and easily introduced into the composition of the oxide superconductor generated by the chemical vapor deposition method, thereby improving the superconducting properties of the oxide superconductor. As a result, an oxide superconductor exhibiting good superconducting properties can be obtained. Further, if one chamber is shared by both the chemical vapor deposition process and the heat treatment process, it is not necessary to provide a dedicated chamber for each process, so that equipment costs can be reduced. In addition, if both steps are performed continuously, the heat of the previous step can be reused, so that heat energy can be saved, and the work of replacing the substrate due to the change of the chamber can be omitted, thereby shortening the manufacturing time. And the like can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an oxide superconductor manufactured by the present invention, and FIG. 2 is a schematic configuration diagram showing an example of a CVD apparatus suitably used in the present invention. 2,24 …… A thin film made of oxide superconductor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Nobuyuki Sadakata, Inventor 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd. (72) Nobuya Aoki 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Inside Wire Co., Ltd. (72) Inventor Yu Sugimoto 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Inside Wire Co., Ltd. (56) References JP-A-64-27131 (JP, A)

Claims (1)

(57) [Claims] An AB-Cu-O system (where A is Y, Sc, La, Yb, Er, Ho, Dy, etc., Periodic Table IIIa)
Represents one or more than one group element, and B represents Sr, Ba,
Represents one or more of Ca. ), Wherein the oxide superconductor is generated by a chemical vapor deposition method using a chamber provided with a raw material gas supply means and an oxygen gas supply means, and then the oxide superconductor in the chamber is produced. A method for producing an oxide superconductor, comprising subjecting a body to a heat treatment in an oxygen atmosphere in which a partial pressure of oxygen in a chamber is at least 0.1 atm.