JPH02152109A - Y-ba-cu-o group superconductor film formed onto alumina base material and forming method thereof - Google Patents

Abstract

PURPOSE: To provide a film showing a superconduction critical temperature of about 90 deg.K by repeating the process of forming a film of paste on an alumina base and drying it until the thickness of the film becomes 20μm or more. CONSTITUTION: Yttrium oxide, barium carbonate, and copper oxide are weighed and mixed in a mole ratio of 1:2:3, absolute alcohol is added, and they are stirred until becoming a uniform paste. Next, pulverization milling using a vibrating mill and then filtering are performed, and after drying the filtered substances are heated at 900 deg.C for about 15 hours and then furnace cooled. The milling and heating and furnace cooling are repeated a number of times until the mixture completely becomes a Y1 Ba2 Cu2 O7-s phase, and then the mixture is injected and mixed in Y1 Ba2 Cu2 O7-s mixed powders in a weight ratio of 2 to about 3 using an organic caking agent in which about 10wt.% ethyl cellulose is dissolved in butyl carbitol acetate, and milling using a roll mill is performed until the mixture becomes a uniform paste. The mixture is printed on an alumina base in the form of a film using screen printing method and dried, printing is repeated until the thickness of the film becomes 20μm or more, and heating at 900 deg.C is performed for about one hour.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to yttrium-barium-copper oxide based superconductor powder (hereinafter referred to as Y-Ba
-Cu-0 based superconductor)
The present invention relates to a method for forming a -0-based superconductor film and its products.

[Prior art]

The applicant and his co-researchers have proposed a method for more economically mass producing Y-Ba-Cu-0 superconductors with a superconducting critical temperature exceeding 90'K, as disclosed in Japanese Patent Application No. 130484/1984. (filed on May 30, 1988).

In addition, the critical current density of superconductors is 10 in the bulk state.
'Compared to A/crM, in the case of a thin film, Teha, 106A/
In order to reach ci, the applicant and others focused on development, and as a result, at the Autumn Meeting of the Materials Research Society (MR3) on August 4, 1987, Y- Ba-Cu-
We reported a method for forming 0-based superconductor films.

In the method proposed in the above report, Y-Ba-Cu-0 based superconductor powder is mixed with an organic binder (for example, a binder made by dissolving ethyl cellulose in butyl calpitol acetate) in a weight ratio of 3=2. This paste is mixed to form a uniform paste, and then this paste is printed on the surface of the alumina substrate using a mesh screen printing method, and the printed alumina substrate is repeatedly dried naturally and heated to increase the film thickness and form a desired film. After reaching a thickness and drying, it is sintered at a temperature of 900 to 950°C, further annealed in an oxidizing atmosphere with oxygen or air, and slowly cooled, so that the superconducting critical temperature is approximately 90χ. A stable Y-Ba-Cu-0 based superconductor has been obtained.

The background for proposing the above-mentioned mesh screen printing method is that in the conventional method for forming this type of superconductor film, the base substrate on which the superconductor film is formed is made of single-crystal magnesia or strontium titanate. However, the price of this kind of base material is too high, whereas alumina is much cheaper and is available commercially at around 96% purity, and is widely used in microelectronic hybrid circuit technology. It is in the fact that However, alumina substrates still have other problems. First, Y-Ba-C
In order for the u-0 series superconductor to exhibit a high superconducting critical temperature, its composition must be Y+BazC+u+07-s and the δ value must be 0.1.
Although it should be about 0.2, the printed film and the alumina substrate react at the contact surface during the isothermal heat treatment, resulting in a deviation from the composition of Y1BazCuJt-s and loss of superconducting properties. As a countermeasure for this, Y2O with a weight ratio of 0.6:1.5:1 is used as a buffer layer.
No. 3, Vol. 27. Itomineo et al. reported that a mixture of 3, BaC0, and CuO was made into a paste with ethylene glycol and applied to the substrate surface. J.

proposed by J.A.P. (March 1088).
This also means an extra step. Furthermore, the bonding force between the formed film and the alumina substrate is extremely weak and the film easily peels off, which is a major drawback in terms of practicality.

On the other hand, in terms of technology for forming superconductor films, conventional methods include the plasma spray method in which superconductor powder is made into a solution and sprayed onto a substrate in the form of a plasma agent, and the method in which superconductor powder is made into a paste and then applied onto a substrate using a knife or the like. There is a tape casting method that involves painting, but in the former, the plasma equipment is extremely expensive and it is difficult to match the assembly of other electronic parts to the work, and in the latter, because it is done by hand, it cannot be used with curved fabrics or shapes. Depending on the complexity of the product, there may be restrictions that prevent it from being produced in large quantities.

[Problem to be solved by the invention]

In view of the above, the present invention solves these problems,
A method for forming a Y-Ba-Cu-0 based superconductor film exhibiting a superconducting critical temperature of about 90' directly on an inexpensive commercially available alumina substrate without requiring an expensive plasma spray device, and a method for forming a Y-Ba-Cu-0 based superconductor film that exhibits a superconducting critical temperature of approximately 90'; 90% without peeling easily.
The present invention aims to provide a Y--Ba--Cu--0 based superconductor film that exhibits a superconducting critical temperature on the order of .

[Means to solve the problem]

In order to achieve the above object, the present invention... Yttrium
A barium-copper oxide superconductor and an organic binder are mixed to form a paste, and this paste mixture is printed on an alumina substrate using a screen printing method and dried, followed by high-temperature sintering. In a method for forming a yttrium-barium copper oxide superconductor film on an alumina substrate by thermal annealing in an oxidizing atmosphere and slow cooling,
The process of printing the pasty mixture on an alumina base material and drying it is repeated until the thickness of the film becomes 20 mm or more.

[For production]

According to the features of the above means taken by the present invention, between the conventionally known alumina phase and the Y-Ba-Cu-0 phase,
An interdiffusion phenomenon occurs in the thickness range of about 16 to 20 μm, and a so-called buffer layer consisting of a transition phase with no superconducting properties is generated, and the superconducting composition is maintained in the part of the formed film with a thickness of 20 μm or more. 90′ without mutual diffusion with alumina.
The superconducting critical temperature is maintained at about .

[Experiment example]

The present invention will be explained in detail below.

Sample preparation: Weigh and mix yttrium oxide, barium carbonate, and copper oxide in a molar ratio of 1:2:3, add anhydrous alcohol, and stir to form a uniform paste. After milling into fine powder using a vibrating mill, the mixture was filtered, dried, heated at 900° C. for about 15 hours, and cooled in a furnace. This was repeated many times until the −δ phase was reached.

Next, the above Y+B
The azCU:+0t-5 mixed powder is injected and mixed in a weight ratio of about 3 to 2, and milled using a roll mill to form a uniform paste.

At this time, a small amount of silver oxide was added to enhance the adhesive strength between the paste mixture and the alumina base material.

The above paste-like mixture is printed onto a commercially available 96% alumina substrate, usually formed into a plate, in the form of a film using a screen printing method using a stainless steel screen of about 200 mesh, so that the film surface is uniform and flat. The substrate was allowed to stand for a while in the air at room temperature, and then dried at a temperature of 100° C. This procedure of printing, standing, and drying was repeated until the film formed on the surface of the substrate reached a predetermined thickness.

Here, the alumina substrate was ultrasonically cleaned in methanol for 10 minutes and then dried.

In addition, the screen printing equipment used in this experiment was
It was a 1202 automatic screen printer in UK DE.

Y obtained above, Ba2Cu, 0. The alumina substrate on which the -δ film has been formed is then heated in the atmosphere at a temperature of 900 to 950°C for about 1 hour, and then the inside of the furnace is made into an oxidizing atmosphere with oxygen or other gas, and the temperature is gradually raised to room temperature. The temperature was lowered or annealed for about 20 hours in the temperature range of 800 to 400°C.

By annealing in the above oxidizing atmosphere, the higher the annealing temperature within the above range (i.e., preferably in the range of 700 to 800°C), the more stable the superconducting critical temperature near 90'' can be obtained. It is already known that it is easy.

For each sample of different thickness prepared by the above procedure,
I did some tests:

(1) Measure the film thickness using an alpha step thickness meter, observe the microstructure using a scanning electron microscope (SEM), and perform energy dispersion X in the thickness direction.
Linear analysis (EDXA) was performed.

(2) X-ray diffraction measurement (XRDA) was performed to confirm the crystal structure of the substance forming the film.

(3) Measure the resistance at each temperature using the four-point probe method, and
at+Tz. ,. I asked for

However, T On I Q t: Unit 'K (same below), temperature at which resistance decreases.

Tzero: The temperature at which the resistance becomes 0.

The data obtained in this experiment are shown in Tables 1 to 1 below.

In Table 1, sample 1.2゜3 of the group of Example 1 is
This shows the influence of differences in annealing conditions; the higher the temperature, the higher the T z
*r. is obtained. Sample 4 of the group of example 2,
5.6, the total value is almost 9.
0 to 95'K, and it can be said that the film thickness does not significantly affect the superconducting critical temperature, but the thinner sample 6 has a significantly higher T2°. It is understood that this is because the composition of the film near the interface deviates from the Y:Ba:Cu molar ratio of 1:2:3:(7-δ), which exhibits superconducting properties. Samples 7-1 of the group of Example 3
0 changes the range of film thickness significantly and increases the annealing temperature to 9
The results are shown at 25°C, and sample 7 with a film thickness of 16 μm is not superconducting (it shows semiconductivity, but the analysis results indicate that a reaction occurs between the alumina substrate and the film components, resulting in superconductivity). Y, B
This indicates that the composition of a, Cu, O, and -δ phases is IQ, and sample 8°9 has a higher T than samples 5 and 6. n5eL is 90
~936, T z e r of sample IO
The fact that o was 85° C., which was lower than that of the groups of Examples 1 and 2, seems to be due to the influence of diffusion with the substrate due to the high annealing temperature. Samples 11-1 of the following Example 4 group
3 had the same processing conditions as the Example 3 group, except that the sintering temperature was 950°C, and as a result, T z tt
r o increases, and samples 12 and 13 have a liquid nitrogen temperature of 7.
The temperature is 7°.

Regarding the structure analysis of each group of Examples 1-4, according to X-ray diffraction, Y1Ba2Cu30 of the membranes in Samples 4-6
Deterioration of the t-δ phase due to decomposition or conversion to a non-superconducting phase was observed, and in test Nemi 17, the intensity ratio of the crystal planes (013)/(110) of the main superconducting phase was 60/10.
0 is reversed to 100/60 and the non-superconducting phase Y2BaCuO
5 was formed, indicating that the crystal structure had changed from orthorhombic to tetragonal. In sample 8.9, such phase conversion did not occur, and in sample 13, in which the film thickness and annealing temperature were increased, Y1BatC+g07 ．． Only y-phase orthorhombic crystals appear, and Y, Ba, and C are formed orthogonally to the interface between the film and the substrate.
EDX8 for u and A1 shows that the superconductor-semiconductor transition occurs over a thickness range of about 20 μm on the interface side film.

Table 1 [Effects of the invention] As is clear from the above, the present invention provides Y-Ba-Cu-0
A superconductor mixture is mixed with an organic binder to form a paste, and a film of the mixture is formed on the surface of the alumina base material by directly printing it on the alumina base material using a screen printing method, followed by drying. A Y-Ba-Cu-0 based superconductor film can be formed on an alumina base material simply by performing sintering and annealing treatment, and unlike the plasma spray method, a plasma spray device is not required.

In addition, by forming a Y-Ba-Cu-0 based superconductor film with an I7 of 20 IM or more directly on the alumina base material surface, an interdiffusion layer with a thickness of 20 μl or less is formed. The Y-Ba-Cu-0 superconductor layer on the surface is protected, and a separate process for forming a protective layer is not required.

Margin below

Claims (2)

[Claims] 1. A paste of yttrium-barium-copper oxide superconductor is formed into a film on an alumina base material, and after drying, sintering, thermal annealing in an oxidizing atmosphere, and slow cooling are performed to form yttrium on the alumina base material. - In a method for forming a barium-copper oxide superconductor film, the step of forming the paste onto an alumina base material and drying the paste until the film has a thickness of 20 μm.
A method for forming a Y--Ba--Cu--O based superconductor film using alumina as a base material, the method comprising repeating the steps until the above is achieved. 2. Yttrium-barium-copper based oxide film with a thickness of 20 μm or more is formed on an alumina base material, and at least the surface layer of the film is a superconductor layer. -Ba-Cu-O superconductor film.