JPH0393620A - Production of oxide superconductor thin film - Google Patents

Abstract

PURPOSE:To obtain the subject thin film having a superconducting transition temperature sufficiently higher than liquid nitrogen temperature by forming a specific amorphous oxide thin film for the production of an oxide superconductor on a substrate in vacuum and hot-pressing the thin film under hydraulic pressure in a mixed gas atmosphere comprising an inert gas and O2 gas. CONSTITUTION:A surface of a substrate such as SrTiO3 plate or LaAlO3 plate is mirror-polished and an amorphous oxide thin film for the production of an oxide superconductor is deposited on the surface in vacuum. The amorphous oxide is composed of R (R is one or more elements selected from Y and lanthanide rare-earth elements), Ca, Ba, Cu and O. The substrate is hot-pressed with hydraulic pressure at 850-110 deg.C for 20-40min in a mixed gas atmosphere comprising an inert gas and O2 gas under a pressure of >=400atm to obtain an oxide superconductor thin film containing the oxide of formula (x is 0.001-0.5).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a novel oxide superconductor thin film, and in particular, the present invention relates to a method for producing a novel oxide superconductor thin film, and in particular, the superconducting transition temperature Tc sufficiently exceeds the liquid nitrogen temperature, and the method is performed during high-temperature processing. The present invention relates to a method for producing an oxide superconductor thin film that is free from the problem of fluctuations in Tc due to oxygen escape during the process.

[Prior art] As a typical oxide superconductor with Tc exceeding the liquid nitrogen temperature (for example, 90 K), three-layered berovskite RB
az Cu,07 (where R is Y or one or more elements selected from the group consisting of lanthanide series rare earth elements) has been discovered [^ppl. phys. Le
tt. Vol. 51 (19+17)P57]. However, the above-mentioned oxide superconductor has the property that the constituent oxygen atoms easily escape due to the thermal influence during processing, and therefore the oxygen content changes depending on the heat treatment conditions during processing, and accordingly, the oxygen content changes due to the heat treatment conditions during processing. Causes orthorhombic monotetragonal transition,
It is known that Tc varies greatly in the range from OK to 90K due to this phase transition [Phys. Re
v. 836 (1987) P5719], for example, a molded body made of RBa2 Cu3 07 powder as a superconducting material had the disadvantage that oxygen atoms were removed during sintering heat treatment, resulting in deterioration of superconducting properties. On the other hand, RBa2Cu40a type oxide has RBa
2 (U3 0t-type oxide, which has a double chain of Cu-0 and is stable with no oxygen escape even when heated to around 850℃.Moreover, Tc is 8
Although the temperature is around 0 K, which is higher than the liquid nitrogen temperature, from a practical point of view there is a need to develop an oxide superconductor with a slightly higher Tc. By the way, the following two methods have been proposed so far as methods for manufacturing RBa2 Cu406 type oxide superconductors.

(1) A method of heat-treating calcined powder in a high-pressure atmosphere of pure oxygen (for example, 930°C x 8 hours. Oxygen pressure 100 atm) [
Hyperbaric oxygen method; Tcsw81K. Nature 336
(1988) P66G-662 or Phys.
Rev. B39 (19H) P7347-7350
1. (2) A method of mixing calcined powder with a catalyst such as sodium carbonate and heat-treating it in an oxygen stream for a long time [normal pressure method;
T c sw 7 7 K; Nature 33
8 (19H) P328-330]. However, the inventors have confirmed through experiments that (1) above. Method (2) had the following drawbacks. In method (1), depending on the temperature and pressure conditions, RBa2
Cus O,-, phase, R2 Ba4 Cuy o, phase, etc. appear, and the amount of RBaa Cu40a produced becomes extremely small, and the characteristics of the RBa2Cua 06 phase cannot be expected. In addition, method (2) tends to leave impurities in the product and requires a long time for heat treatment, making it unsuitable for practical application. In addition, RBa2 Cu4 0a type oxide is attracting attention because its Tc exceeds the liquid nitrogen temperature, but as mentioned above, since it is close to the liquid nitrogen temperature, there are various obstacles in practical use. The development of oxide superconductors exhibiting Tc is expected. On the other hand, methods for producing thin film oxide superconductors can be broadly classified into the following two types. One is the sputtering method.
This is a method in which an amorphous oxide film of an appropriate composition is formed on a substrate by a vacuum evaporation method such as EB evaporation method or co-evaporation method, and then crystallized by heat treatment to obtain a superconducting phase. In this case, the substrate temperature rises only from room temperature to about 350°C during the film formation process, making it possible to form films at relatively low temperatures. Another method is to lower the substrate temperature to 60
The temperature is raised to 0 to 800°C, and an amorphous oxide thin film of an appropriate composition is formed on the substrate by the same vacuum evaporation method as above, and the oxide constituting the thin film is crystallized using the substrate temperature. This is a method of converting the superconducting phase into a superconducting phase. Of the above two methods, the former has the advantage of being able to control the crystal structure by controlling the heat treatment conditions after film formation, although it is difficult to synthesize a single crystal film. So, as long as it is thermally stable, for example, RBat Cu3 of-6
It has the advantage that single crystal films such as can be obtained. [Problem to be solved by the invention] However, with the current technology, R B a 2C u 40
It is not possible to obtain a single-phase crystalline film from an amorphous oxide thin film having a composition of 6. That is, for example, in the case of an amorphous oxide thin film having a composition of RBa Minoh Cu 307-6, it is heated at 0.5 to 1 atm in a pure oxygen atmosphere at 800 to 950°C for 20
Heat for about 60 minutes and further heat at 400-600℃ for 120-
It is possible to turn the film into a single crystal thin film by performing heat treatment for about 600 minutes, but such heat treatment conditions are not suitable for RB.
When an amorphous oxide thin film having a composition of atCu40@ is crystallized, RBa. Cu. Ov
BaCuO. , one δ°RBaCuOs . ..., etc., resulting in a multiphase film containing many crystals, and the resulting film has a multiphase structure containing many insulating phases, making it impossible to obtain the intended superconducting properties. The present invention has been made to solve these technical problems, and is an oxide superconductor that has a substantially single-phase structure and a Tc sufficiently higher than the temperature of liquid nitrogen. The aim is to establish a method that can produce body thin films.

[ll! Means for Solving the Problems] The configuration of the present invention that can solve the above problems is as follows: R(
However, R has the same meaning as before). Ca. Ba, Cu. After forming an amorphous oxide thin film composed of O for producing an oxide superconductor on a substrate by a vacuum film-forming method, hot isostatic pressing is performed in a temperature range of 850 to 1100°C in a mixed atmosphere of inert gas and oxygen gas. By pressure treatment, (Rt-x Ca, ) Ba2C ua Oa(
However, X is 0.001 to 0.5, R has the same meaning as before)
The gist of this is that it is an oxide superconductor thin film containing the oxide shown in . [Function] The present inventors conducted studies from various angles in order to realize a thin film superconductor that has Tc sufficiently higher than the temperature of liquid nitrogen and does not allow oxygen to escape even at high temperatures. Ta. As a result, a three-layer perovskite RBazCu30y
In the type crystal structure, a single Cu O chain is replaced by a double Cu O chain.
RBa2 Cu40 as O chain. In the type oxide, R
0.1 to 50 atom% of was substituted with Ca (RI-.Ca
．． ) Ba, Cu. It has been found that o-type oxides can exhibit stable superconducting properties with Tc sufficiently higher than the liquid nitrogen temperature and no oxygen loss even under high-temperature conditions.
As a result of repeated studies on specific manufacturing conditions for obtaining a thin film with such characteristics, we found that R, Ca, Ba. C
A uniform amorphous oxide thin film for producing oxide superconductors is formed on a substrate by a vacuum deposition method using raw materials containing u and O (R oxide, Ca and Ba oxides and carbonates, Cu oxide, etc.). After forming , the desired (
Rl -X C ax ) B at C ua Oa
They discovered that a type oxide superconductor thin film could be obtained, and completed the present invention.

In the present invention, first, a vacuum deposition method is adopted as a means for forming a uniform amorphous oxide thin film for producing an oxide superconductor. As the vacuum film forming method itself, conventionally known methods including, for example, sputtering method, CVD method, EB evaporation method, co-evaporation method, etc. or improved methods thereof can be applied.
As a result, an amorphous oxide thin film with a uniform composition can be easily obtained. In vacuum deposition, the composition of the amorphous oxide thin film produced is not necessarily (R+Ca):Ba:Cuml:
It does not necessarily have to be 2:4, and even if the composition is slightly different from this, it can be converted to (Rl-X C ax ) B a2 C u4 by subsequent HIP processing.
Any material that generates the 0B phase is sufficient. However, in order to stably generate this phase, the composition of the amorphous oxide thin film must be (R+Ca): Ba: Cu=1.
: 2 : 4 is preferable, so when performing vacuum evaporation, it is desirable to adjust the evaporation raw material composition, vacuum evaporation conditions, etc. with these points in mind. There are no particular restrictions on the type of substrate used at this time, but SrTiO is preferable in order to obtain an oxide thin film with excellent superconducting properties through the subsequent HIPIA process.
, plate, LaA10. , MgO plate (more preferably S r
T i O. plate, LaA103 plate), etc., and these are usually used with a mirror-polished finish. Also, as a substrate, N
SrTiO. ．． It is also possible to use a composite substrate on which a sputtering film of LaA10 or the like is formed. In the present invention, the uniform amorphous oxide thin film obtained in this manner is crystallized by HIP treatment at a predetermined temperature range in a mixed gas atmosphere of inert gas and oxygen gas. ) Convert to Ba,Cu4oa type oxide superconductor thin film. In this case, HIP processing is performed in a mixed gas atmosphere of inert gas and oxygen gas, so if you try to achieve the same pressure (for example, 200 atm) with oxygen partial pressure as in the case of pure oxygen, it will be treated as a mixed gas atmosphere. can significantly increase the total pressure. For example, when the mixing molar ratio of inert gas and oxygen is 1=1, the total pressure can be made 400 atm, and when it is 4:1, the pressure can be made 1000 atm. The diffusion is further enhanced and (Rl-w Ca.) Ba2 Cu4 04
This is thought to facilitate the formation of type 1 oxide superconductors. This can also be said to be a major advantage from the standpoint of operational safety compared to increasing the total pressure using pure oxygen. The temperature at H I P,l C is RBa2CllsO
Suppresses y-type oxide, (R,IICa,I)Ba2Cu
From the viewpoint of promoting the production of 40, type oxides, it is necessary that the temperature is at least 850 °C or higher, but 110
When it exceeds 0℃, R 2 B a 4 C u t O
The upper limit of the treatment temperature needs to be 1100°C because z is likely to be generated and a mixed phase is likely to occur. On the other hand, in the present invention. (Rl-XCJIyo) Ba2
Cu. The Ca substitution amount (i.e. the range of X) in the 06 type oxide was set to o. The reason for setting ooi to 0.5 is as follows. In other words, the effect of Ca substitution (increase in Tc, improvement in thermal stability) appears when X is 0.001 or more, and under the production conditions of the present invention, X is not formed when it exceeds 0.5. This is because there are hardly any. The preferred range of X is 0
．． It is 001-0.2. The HIP processing conditions employed in the present invention are as described above, but it should be noted that these HIP processing conditions vary depending on the type of substrate used. For example, when using SrTiOs as a substrate, HIP! During A process, the oxygen partial pressure of the atmospheric gas is 40 atmospheres or more, and the temperature is 880 degrees.
If the temperature is set at ~930°C, a high-performance superconducting oxide thin film with a high Tc can be stably obtained in a processing time of about 20 to 40 minutes, but if the processing time exceeds 40 minutes, S in the substrate will increase.
As r and Ti diffuse into the oxide thin film, the superconducting properties deteriorate. On the other hand, as a substrate, L a A 1 0
When using S, it is possible to obtain an oxide thin film with stable K superconducting properties even over a wide processing time range of 0 to 600 minutes under the same atmospheric gas and temperature conditions as above. From this point of view, it is desirable to appropriately select and determine HIP processing conditions in consideration of the type of substrate (accompanying diffusion of constituent elements, etc.) during HIP processing.Hereinafter, the present invention will be implemented. Although explained in detail by way of example, the following examples are not intended to limit the present invention, and any design changes in accordance with the spirit of the preceding and following are included within the technical scope of the present invention. [Example] Adopts two-pole RF spatter method to achieve mirror finish (R@a
ll<0-. LaA10.08p tn).
Y, Ca, Ba. Cu,
An amorphous oxide thin film containing O was formed. At this time, the chamber pressure, spatter gas mixture ratio, etc. are adjusted so that the thin film composition is Y. 1Ca. ,,Ba2±21tCu4±2κ, and the film formation time was adjusted so that the film thickness was approximately 1 μm. (Sbatter conditions) Target composition: (Yo.a Cao.2 8as Cus Oy) Champer pressure: 3Pa Spatter gas: 02/Ar-50/
50 substrate Temperature: 200°C RF power density: 3 W/cm” Distance between electrode and substrate 11i:31)+m Thus, the substrate on which the amorphous oxide thin film was formed was
Ar-80%. Under a mixed gas atmosphere of Ox-20%, 10
00at-X was held at 900°C for 130 minutes and subjected to HIP treatment for crystallization. When the obtained oxide thin film of the HIP-treated product was irradiated with X-rays and the X-ray diffraction pattern of the thin film was measured, a peak of < (002n) as shown in Fig. 1 was clearly observed. Superconducting Y06Cao. a
It was confirmed that it consists of a Ba2Cu4o6 phase structure. For comparison, Y06C a0 obtained in the same manner as above
．． 2 B am 2% C ul ± 2% oa The substrate on which the amorphous oxide thin film was formed was 100%
The X-ray diffraction pattern of the resulting oxide thin film, which was heat-treated at 80°C for 25 minutes in an oxygen atmosphere and then further heat-treated at 550°C for 120 minutes for crystallization, is shown in Figure 2. As is clear from the pattern, the oxide thin film contains Y2 B a C u OS and B a C
Numerous peaks including u O 2 etc. were observed, and Yo
．． a C ao. Almost no peak indicating the single crystal of z B a4C u40B was observed, and excellent superconducting properties could not be expected. [Effects of the Invention] The present invention is configured as described above, and the superconducting transition temperature is sufficiently higher than the liquid nitrogen temperature, and the oxidation process is free from the problem that the transition temperature fluctuates due to the escape of oxygen during high-temperature processing. It became possible to produce superconducting thin films.

[Brief explanation of drawings]

Figure 1 shows the X-ray diffraction pattern of the superconducting thin film obtained by the present invention, and Figure 2 shows the X-ray diffraction pattern of the oxide thin film crystallized by heat treatment under conventional conditions after vacuum deposition. It is.

Claims (1)

[Claims] R (wherein R is one or more elements selected from the group consisting of Y and lanthanide series rare earth elements), Ca, Ba, C
After forming an amorphous oxide thin film for producing an oxide superconductor consisting of u and O on a substrate by a vacuum film forming method, the film was heated to 850 to 110 mL in a mixed gas atmosphere of inert gas and oxygen gas.
By hot isostatic pressing in the temperature range of 0℃, (R_1_-_xCa_x)Ba_2Cu_4O_8(
A method for producing an oxide superconductor thin film, characterized in that the oxide superconductor thin film contains an oxide represented by x = 0.001 to 0.5 and R the same meaning as above.