DE20315783U1 - Oxide superconductor thick film has a defined composition which can be applied to a surface of a substrate or a base - Google Patents

Abstract

Oxide superconductor thick film which contains Bi, Pb, Sr, Ca and Cu and essentially has the composition (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ CusO _Z (in which: 0 <a <0.5), which is to be applied to a surface of a substrate or a base, wherein there is no fracture area in the vicinity of an interface between the substrate or the base and the oxide superconductor thick film in the oxide superconductor thick film.

Description

Background of the Invention

1. Field of the Invention

The present invention relates on an oxide superconductor thick film, the Bi, Pb, Sr, Ca and Contains Cu, a high critical current density and a high adhesive strength an oxide substrate or on an oxide base.

2. Description of the related State of the art

An oxide substrate or base, such as. MgO, aluminum oxide or YSZ, or a metal substrate or a metal base such as Ag, Au, Pt or Ni is made together with an oxide superconductor in the form of a thick film (thick film) to develop a variety of application products.

As a method of forming this Oxide superconductor in the form of a film, a method is used where an oxide superconductor powder, which is a suitable organic Binder is added, is formed into a paste, which is then applied the substrate or base is applied using a Screen printing process, a doctor blade coating process, a spray process or The like, and is fired to thereby form a polycrystalline oxide superconductor thick film to build.

This method of forming the oxide superconductor thick film using an oxide superconductor paste exhibits very low Manufacturing costs, i.e. it has the advantage that it is not expensive Single crystal substrate and not a large and expensive device that requires a high vacuum system, e.g. PVD, CVD or the like, and therefore it is regarded as a method which is described in is the easiest to apply in practice.

When considering the application of this oxide superconductor thick film to a practical product, the use of a thick film is (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z (generally 0 <a <0 , 5) (hereinafter referred to as Bi2223-based thick film) as an oxide superconductor thick film material, promisingly viewed from the two perspectives of the required superconducting properties and the manufacturing cost including the raw materials and the manufacturing processes.

A method of making the Thick films on Bi2223 bases are explained below.

First, a bi-based superconductive paste is applied to an oxide base such as MgO, alumina or YSZ using a screen printing method, a doctor blade coating method, a spraying method or the like. At this stage, an oxide superconductor powder in the Bi-based superconductive paste which has been applied to the base has a (Bi, Pb) ₂ Sr ₂ Ca ₁ Cu ₂ O _z phase (hereinafter referred to as Bi2212 phase ), whose critical temperature is between Tc and about 80 K, as the main phase and does not have the (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z phase (hereinafter referred to as Bi2223 phase), whose critical temperature is between Tc and about 110 K. This oxide superconductor powder is a multiphase which also comprises a phase which has been formed in the meantime (as an intermediate), such as, for example, Ca ₂ PbO ₄ , CaCuO ₂ or CuO.

Then the Bi-based superconductive paste is heat-treated so that a reaction between the (Bi, Pb) ₂ Sr ₂ Ca ₁ Cu ₂ O _z - and the intermediate phase occurs to form the (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z phase and in this way the Bi2223 phase is formed from the Bi2212 phase and the phase formed in the meantime. As a result, an oxide superconductor thick film containing the Bi2223 phase with a high critical temperature is formed on the oxide base.

Although it is important to have a high critical temperature when the oxide superconductor thick film is applied to a practical product, it is also necessary to have a high critical current density (hereinafter referred to as Jc). In addition, when the oxide superconductor thick film is applied to a practical product, a Jc of more than 5,000 A / cm ^{2 is} required.

In order to achieve a Jc of more than 5000 A / cm ² using a thick film containing the above-mentioned Bi2223 phase (hereinafter referred to as Bi2223 thick film), platelet-shaped crystals with large ab-areas and short c- Axes that are typical of the bi-based oxide superconductor are appropriately oriented to align their ab-surfaces on which a superconductor current flows easily in the direction of conduction. As a result, a compression operation using a CIP (cold isostatic press) or a HIP (hot isostatic press) is used to align the platelet-shaped crystals in the direction of conduction.

But even with the high Jc that can be achieved by using this compression operation then when a substantial cross-sectional area of the thick film on which the superconducting current flows, is small, no sufficient total value for the superconductor current is achieved and is therefore for the practical use is not suitable. It is therefore necessary to design a Bi2223 thick film so that the cross-sectional area for one suitable critical current value (Ic) is ensured.

The following procedures are therefore usually done to form an oxide superconductor thick film with a high Jc value and a high critical current value on a basis.

Patent Document 1 is here called given an example.

• 1. A bi-based oxide superconductor paste is applied to a appropriately selected Oxide base applied so that it has a greater thickness than a predetermined Film thickness.
• 2. The oxide base with the oxide superconductor paste applied to it is based on bi subjected to a first burning.
• 3. After the first firing, the oxide base is placed in a CIP and pressed into it.
• 4. Burning in the stage 2 and pressing in the stage 3 are repeated with a sufficient frequency. After the last firing is finished, an oxide base with a Bi2223 thick film applied is obtained.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-358 298.

In the method for Production of a Bi2223 thick film occurs according to the prior art frequently a replacement the thick film from an oxide base in the middle of a film forming process on, which lowers the process yield and thus reduces productivity becomes.

This detachment phenomenon usually occurs while burning or after a CIP, especially during the first burning or after the first CIP. The inventors of the present Invention have studies on this detachment phenomenon of Thick film is carried out from the oxide base and then found the following.

First is the detachment during the Burning attributed to:

• 1. a difference in the coefficient of thermal expansion (linear expansion) between an oxide base and a superconductor,
• 2. a spatial Volume change as a result of an expansion of the entire thick film that coincides with transformation of a crystal structure occurs to form a High Tc phase from a low Tc phase and an intermediate phase,

In particular the influence of the factor 2 is dominant during the first burn and is therefore considered a major cause of the frequent occurrence of peeling during the burn.

Next is the replacement after attributed to a CIP:

• 3. a force phenomenon in such a direction that a thick film separates from an oxide base. This force arises as a result of a residual tension inside the thick film when the thick film and the oxide base, which has the thick film applied thereon, are compressed with a predetermined isostatic pressure (0.5 to 3.0 t / cm ² ) and then the residual voltage is released, the above-mentioned effect occurring when the thick film and the oxide are decompressed. In addition, this force phenomenon mainly affects an oxide base with a cylindrical shape.

The inventors of the present invention have carried out an analysis of the Bi2223 thick film applied on a prior art basis. The results of this analysis are described below with reference to the 7 explained. The 7 shows an optical microphotograph of a cross section of the MgO-based Bi2223 thick film according to the prior art.

In the 7 denotes the reference number 51 the cross section of the MgO base, the reference number 59 denotes the cross section of the Bi2223 thick film according to the prior art and the reference number 53 denotes an interface between the MgO base 51 and the Bi2223 thick film 59 , Looking at the 7 it can be seen that a fractured surface 58 in a range of about 2 to 10 μm from the interface 53 in the Bi2223 thick film 59 arose. The inventors of the present invention have also performed similar analyzes on a large number of prior art Bi2223 thick films and found that a fracture surface in an oxide superconductor thick film is not only present when an oxide superconductor thick film differs from one Oxide base in the middle of a manufacturing process, but also when the thick film does not separate from the oxide base.

If a fracture area is relatively large, an oxide superconductor thick film dissolves during the Burning or during a CIP compression in the middle of a manufacturing process of an oxide base. If the fracture area is small, it will come loose the oxide superconductor thick film in the middle of a manufacturing process does not depend on the oxide base. However, the fracture surface develops every time a thermal or mechanical shock applied to the oxide superconductor thick film who finally acts for replacement of the oxide superconductor thick film.

Summary the invention

From the results given above The investigation poses the problem of the present invention solves, namely the Providing a Bi2223 thick film that does not peel off when a thermal or mechanical shock on a base or one Oxide superconductor thick film in the middle of a manufacturing process and acts in a process for producing the same.

A first means of solving the above problem is an oxide superconductor thick film which contains Bi, Pb, Sr, Ca and Cu and essentially has the composition (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z ( where 0 <a <0.5) to be applied to a surface of a substrate or a base, with no fracture surface near an interface between the substrate or the base and the Oxide superconductor thick film is present in the oxide superconductor thick film.

The existence of the fracture surface can for example confirmed are made by cutting a base that has one attached to it Oxide superconductor thick film has, in several arbitrary places using a Diamond cutting device or the like. In such a way that cross-sections the base and thick film are exposed and then these cross sections can be viewed using an optical microscope. If no broken surface in these cross sections can generally be determined from this that no fracture surface is derived over the entire oxide superconductor thick film exist. In a Bi2223 thick film with the above composition there is no fracture surface over the entire thick film, so that a detachment of the thick film from the Substrate or from the base can be prevented if heating, a cooling, compression or mechanical shock on the substrate, the base or the oxide superconductor thick film in the middle of a manufacturing process or after the manufacturing process is left to act.

An oxide superconductor thick film can be manufactured by forming an oxide superconductor thick film containing Bi, Pb, Sr, Ca and Cu on a surface of a substrate or a base, the method comprising Formation of a first thick film, which essentially has the composition Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _z , on the surface of the substrate or the base and the subsequent formation of an oxide superconductor thick film, which essentially has the composition (Bi, Pb ) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z (where significant 0 <a <0.5) on the first thick film.

In the manufacturing process of the Bi2223 thick film with the above composition a Bi2223 thick film can easily be formed in which there is no fracture surface is.

Short description of the drawings

1 Fig. 4 is a process flow diagram showing the steps of forming an oxide superconductor thick film according to the invention;

2 Fig. 3 is a process flow diagram showing examples of the steps for producing an oxide superconductor paste according to the present invention;

3 shows an optical microphotograph of a cross section of an oxide superconductor thick film according to the invention;

4 shows an optical microphotograph of another cross section of the oxide superconductor thick film according to the invention;

5A to 5F are diagrams showing the analysis results when an EPMA is applied to the oxide superconductor thick film of the present invention;

6A to 6D are diagrams showing the analysis results when an XRD is applied to the oxide superconductor thick film of the present invention; and

7 shows an optical microphotograph of a cross section of an oxide superconductor thick film according to the prior art.

detailed Description of the preferred embodiments

An embodiment is as follows of the present invention with reference to the drawings explained in more detail.

1 Fig. 11 is a flowchart showing the steps of forming an oxide superconductor thick film of the present invention on a substrate or a base, using, for example, a cylindrical MgO base as the base. First, the steps of manufacturing the oxide superconductor thick film according to an embodiment of the present invention will be described with reference to FIG 1 explained.

For example, a substrate or a base (hereinafter referred to as a base) 3 is made of ceramics and the like. An oxide superconductor paste having a mixing ratio of the Bi2212 composition (hereinafter referred to as Bi2212 paste) 1 is made on the base 3 applied and dried (a preferred manufacturing process for this Bi2212 paste 1 is described below). After drying is complete, the base 3 with the Bi2212 paste applied to it 1 in the atmosphere 10 heated to 880 to 885 ° C for up to 30 min and the Bi2212 paste 1 is fired at a temperature near its melting point. The Bi2212 paste fired at a temperature close to its melting point 1 is then partially in the molten state. As a result, the basis lies 3 in a state where a partially melted Bi2212 layer 4 , which essentially has the composition Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _z , is formed as the first thick film.

Then, an oxide superconductor paste having a mixing ratio of the Bi2223 composition (hereinafter referred to as Bi2223 paste) 2 is made on this basis 3 applied, on which the partially melted Bi2212 layer 4 and dried (a preferred method of making this Bi2223 paste 2 is described below). After drying is complete, the base 3 with the Bi2223 paste applied to it 2 in the atmosphere 50 heated to 830 to 860 ° C for up to 100 h and the Bi2223 paste 2 is burned. The base 3 which the fired Bi2223 paste 2 on it is compressed using a CIP (a cold isostatic press) at a pressure of 2 to 3 c / cm ^2, and then the burning and compressing repeated for a predetermined frequency. After the last firing, the oxide base 3 that have a Bi2223 thick film formed on it 5 has received.

Next are the above steps for making the base 3 with the desired oxide superconductor thick film formed thereon 5 explained in detail.

First, a cylindrical base or a plate-shaped substrate made of a ceramic material such as MgO, alumina or YSZ, or a material such as Ag, Au, Pt or Ni, as a base 3 be used so that a material of sufficient quality, shape and size can be selected depending on the end use of the manufacturer. However, from the standpoint of low reactivity and high adhesiveness (high bond strength), MgO is a preferred material for the base 3 ,

For applying the Bi2212 paste 1 to the base 3 For example, a method such as brushing, dipping, or spraying can be used. Spraying is a preferred method of effectively applying to a large area.

If the Bi2212 paste 1 to the base 3 the preferred film thickness is applied 10 up to 100 μm. A film thickness of more than 10 μm is preferred because it can prevent partial non-uniformity, so that a uniform bond strength can be obtained as shown below. On the other hand, a film thickness of less than 100 μm is preferred because a Bi2212 film with the Bi2223 paste reacts satisfactorily in a post-process as described below.

After the Bi2212 paste 1 to the base 3 applied and sufficiently dried, it is heated in the atmosphere to 880 to 885 ° C, baked for 10 to 30 minutes and then allowed to come back to room temperature. Since the temperature in the atmosphere is near the melting point of the Bi2212 film, the applied Bi2212 film is partially melted, so that the base 3 is in a state in which a partially melted layer 4 from Bi2212 is present on it. The film thickness of the partially melted Bi2212 layer is approximately 40 μm.

Then the Bi2223 paste 2 on the partially melted Bi2212 layer 4 that are based 3 is present, applied. The application process can be the same as that for the above Bi2212 paste 1 applied order process. This time the film thickness is preferably the better the thicker it is, preferably it is more than 200 μm.

After the Bi2223 paste 2 on the partially melted Bi2212 layer 4 applied and sufficiently dried, it is heated in the atmosphere to 830 to 860 ° C, preferably 835 to 850 ° C, baked for 50 to 100 hours and allowed to come back to room temperature. Then the entire base is inserted into the CIP and compressed at a pressure of 2 to 3 t / cm ² . This compression increases the density of the plate-shaped crystals of (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z , which was formed during firing, from less than 3 to more than 4. The Jc is also increased from about 100 A / cm ² to about 5000 A / cm ² because the plate-shaped crystals are appropriately oriented so that their ab-faces are aligned with the direction of conduction in which a superconductor current flows easily.

After compression is complete, the entire base is removed from the CIP, reheated in the atmosphere to 830 to 860 ° C, preferably 835 to 850 ° C, baked for 50 to 100 hours and allowed to come back to room temperature. As a result, a sintered film 5 made of Bi2223, applied to the base 3 , receive. In addition, the Bi2223 sintered film obtained in the above-mentioned process steps did not detach from the base 3 from.

Structural studies have been carried out in relation to the sintered film made of Bi2223 and the like, which is from the base 3 undetected, and the results obtained are explained below with reference to the drawings.

The 3 shows an optical microphotograph of a cross-sectional structure of a partially melted Bi2212 layer 54 that in the 1 with the reference number 4 is provided on an MgO basis 51 on an interface 55 had been formed.

The 4 shows an optical microphotograph of a cross-sectional structure of a sintered Bi2223 film 52 , the Indian 1 with the reference number 5 is provided, which is based on 51 on the interface 55 and the partially melted Bi2212 layer 54 had formed.

The 5A to 5F show the results of a line analysis of each structural element in the direction of film thickness using an EPMA that matches that in 4 The sintered Bi2223 film shown was carried out from the surface to the base.

The 6A to 6D are graphs showing the results of X-ray diffraction measurements made with the one in 4 Sintered Bi2223 film were performed from the surface to the base.

Looking at the partially melted Bi2212 layer 54 in the 3 It can be seen that crystal grains have partially melted and penetrated into the pores between the crystal grains because the firing temperature is near the melting point of Bi2212 in the atmosphere, thereby strengthening the bond between the crystal grains to form a dense film. It is also at the interface 55 between the partially melted Bi2212 layer 54 and the MgO base 51 notice that the partially melted Bi2212 layer 54 is firmly anchored in the imperceptible gaps and irregularities on the surface of the MgO base 51 ,

It is also conceivable that at the interface between the partially melted Bi2212 layer 54 and the MgO base 51 interactive element diffusion occurs between a molten liquid phase and the MgO base 51 when the Bi2212 layer partially melts. As a result, it can be assumed that the partially melted Bi2212 layer 54 and the MgO base 51 are firmly connected in both the structural and chemical states (a part above the partially melted Bi2212 layer 54 , is with the reference number 60 provided, which indicates an epoxy resin for the preparation of this optical microscope sample).

When looking at the 4 is the partially melted Bi2212 layer as in 3 is not clearly recognizable, as if the sintered Bi2223 film 52 through the MgO base 51 and the interface 55 would be formed through it.

Hence the structures of the layer and the film in this part closer analyzed in detail.

As a result of the analysis of Mg as in 5A shown, it was found that the interface was at a distance of about 150 μm from a reference point (a point at which the horizontal axis was zero), and here the Mg rapidly decreased with an inclination. This indicates a phenomenon of Mg element diffusion that builds the base.

From the results of the analysis of the elements Sr, Pb, Bi, Cu and Ca as described in the 5B to 5F are shown, there is a film thickness of the with the reference number 52 in the 4 designated film of 350 microns. This proves that the film thickness, which is the partially melted Bi2212 layer, which is 640 μm when the Bi2223 film is applied and dried, decreases to about 350 μm after firing and compression.

Below are the results of the analysis of the elements Sr, Pb, Bi, Cu and Ca as shown in the 5B to 5F are examined.

It turns out that the elements Sr, Bi, Cu and Ca are present in the film in approximately the same concentration, except Pb. Usually have in the Bi2212 and Bi2223 layers Ca and Cu different composition ratios and the corresponding Line analysis should therefore make changes in terms of their strengths near the interface between the partial reflect the melted Bi2212 layer and the Bi2223 film. However, there are practically no changes in terms of Strengths of Ca and Cu were determined and their concentrations are essentially even across the entire thick film.

The 5C shows that a Pb concentration in the thick film gradually decreases from the base interface toward the surface of the film. The decrease in Pb concentration can be attributed to evaporation of Pb that occurs during the sintering of Bi2223 in such a way that the smaller the distance to the surface of the film, the more Pb evaporates into the atmosphere.

On the other hand, the 5C that the Pb concentration in the thick film hardly decreases to the interface with the base. Taking into account the fact that the partially melted Bi2212 layer did not contain Pb when it was formed into a film, it can be deduced that diffusion of Pb into the original partially melted Bi2212 layer took place.

The analysis results also include the 6A to 6D no peak for Bi2212 was detected in the XRD analysis of the thick film at a position 20 µm from the base which was the partially melted Bi2212 layer before firing, and at positions between 20 and 200 µm, and so on proves that all peaks have diffraction peaks for Bi2223.

All of the above results show that a diffusion of the elements Pb, Ca and Cu from the Bi2223 film, the has been applied to the partially melted Bi2212 layer burning occurred in the partially melted Bi2212 layer is so that the composition of the overall film is standardized and therefore most of it the partially melted Bi2212 layer including the Crystal structure has been converted into Bi2223.

The importance of converting the Mostly the partially melted Bi2212 layer in Bi2223 is shown below discussed.

First, as stated above, the partially melted Bi2212 layer over the interface with the base firmly bound to the base. The state of attachment is maintained if the biggest part of the partially melted Bi2212 layer converted into Bi2223 and thus the solid state of attachment is maintained.

Second, it follows that spatial expansion of Bi2223 that occurs when the Bi2223 paste is baked to form Bi2223 results in an expansion of the entire thick film that prevents the thick film from detaching from the base. In other words, in the event that the Bi2223 paste is applied directly to a base, such as, for example, made of MgO, and then a spatial expansion of this Bi2223 paste occurs, the Bi2223 formed detaches from the base. However, when the partially melted Bi2212 layer is between the Bi2223 paste and the base, this partially melted Bi2212 layer maintains the solid state of bonding with the Base upright, absorbs Pb, Ca and Cu, which come from the paste layer with the Bi2223 composition in which crystals are formed, and gradually transforms itself into Bi2223. As a result, the conversion of the crystal structure in the film creates a continuity like a gradient material that softens the expansion like a cushion at the interface with the base, preventing it from peeling off.

Below is a preferred manufacturing process for both the Bi2212 paste 1 as well as for the Bi2223 paste 2 which are used in the embodiment according to the invention, with reference to the 2 explained, which is a fleece diagram in which examples of preferred production stages of an oxide superconductor paste are given.

In the 2 become the powder 11 Weighed out of Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ and CuO so that they have the molar ratio of Bi2212, and mixed together to produce a powder mixture 12 , In this case the CaCO _{3 can be} replaced by CaO or Ca (OH) ₂ . Instead of the powder mixture mentioned above, the powder mixture 12 are also obtained by producing the elements Bi, Sr, Ca and Cu in such a manner that they have the desired molar ratio, by a wet coprecipitation method or the like.

Then the powder mixture 12 calcined to produce a calcined powder 13 , The calcining conditions are a temperature of 600 to 1000 ° C, preferably 750 to 850 ° C, in the atmosphere for a period of 3 to 50 hours. The calcined powder obtained 13 is placed together with Zr balls and an organic solvent such as toluene or the like in a ceramic pot, placed on a rotating platform and subjected to ball milling. The purpose of this operation is the calcined powder 13 finely ground to improve its uniformity so as to increase its thermal response in the subsequent firing step. The calcined powder 13 in the form of a slurry, the treatment of which has been finished in a ball mill, is dried in a dryer. Then this calcined powder 13 calcined again under the same calcination conditions. After this calcination, the calcined powder 13 again ground in a ball mill and fired using a powder mixture 14 with a Bi2212 composition. This powder mix 14 is divided into two equal portions.

A serving of the divided powder mixture 14 with the Bi2212 composition with a suitable organic binder and an organic vehicle 15 mixed and kneaded using a triple roller or the like, whereby the superconducting paste 1 with the mixing ratio of the Bi2212 composition.

The other part of the divided powder mixture 14 with the Bi2212 composition powder 16 from Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO added, weighed so that they have the molar ratio of Bi2223, and mixed together to produce the powder mixture 17 , In this case the CaCO _{3 can be} replaced by CaO or Ca (OH) ₂ . Instead of the powder mixture mentioned above, the powder mixture 17 can also be obtained by producing the elements Bi, Sr, Ca and Cu in such a way that they have the desired molar ratio, by using a wet coprecipitation method or the like, or another material can also be used in which the elements Bi, Pb, Sr, Ca and Cu were made to have the desired molar ratio by using a wet coprecipitation method or the like.

Then the powder mixture 17 calcined, being a calcined powder 18 with a mixing ratio according to the Bi2223 composition. The calcining conditions are a temperature of 600 to 1000 ° C, preferably 750 and 850 ° C, in the atmosphere for a period of 3 to 50 hours. The calcined powder obtained 18 , which has the mixing ratio of the Bi2223 composition, contains a total of a Bi2212 phase and an intermediate phase, for example made of Ca ₂ PbO ₄ , CaCuO ₂ , CuO or the like.

The calcined powder 18 with the mixing ratio of the Bi2223 composition is introduced together with Zr balls and an organic solvent such as toluene or the like into a ceramic pot, placed on a rotating platform, and subjected to ball mill milling. The purpose of this operation is the calcined powder 13 finely ground to improve its uniformity and thus increase its thermal reaction in the subsequent firing stage. The calcined powder 18 in the form of a slurry with the mixing ratio of the Bi2223 composition, the ball mill grinding of which has been completed, is dried in a dryer and calcined again. After this calcination, the calcined powder 18 again ground in a ball mill and fired using a powder mixture 19 with the mixing ratio of the Bi2223 composition.

The powder mixture obtained 19 with the Bi2223 composition with a suitable organic binder and an organic vehicle 20 mixed and kneaded using a triple roller or the like, whereby the superconducting paste 2 with the mixing ratio of the Bi2223 composition.

Practical example

As the basis on which a superconducting thick To be applied film, an MgO polycrystal was produced in a cylindrical shape with an outer diameter of 50 50 mm, and an inner diameter of 40 Φ mm and a length of 100 mm. A superconductor paste having a mixing ratio corresponding to a Bi2212 composition was applied to the MgO base using a spray method, and dried, and then baked in the atmosphere at a baking temperature of 880 to 885 ° C for 30 minutes. This temperature is close to the melting temperature of Bi2212 in the atmosphere, so that a partially melted Bi2212 layer was obtained in a partially melted state. The thickness of the partially melted Bi2212 layer was 40 μm.

Then a superconductor paste was used a mixing ratio according to the Bi2223 composition on the partially melted Bi2212 layer, which had been applied to the MgO base, under Application of a spraying process applied and dried. The film thickness of the superconductor paste with the mixing ratio the Bi2223 composition was 600 μm. Then the superconductor paste in the atmosphere Baked at a firing temperature of 850 ° C for 50 h.

The MgO base with the oxide superconductor thick film applied thereon was introduced into a CIP (a cold isostatic press) and compressed with a pressure of 2 to 3 t / cm ² . Thereafter, the base was baked, compressed in a CIP, and baked again under the same conditions, whereby a thick film sample was obtained.

The above steps were with 10 MgO bases carried out under the same conditions. None of these samples however, a replacement of the Thick film on.

Comparative Examples

An MgO base was made which was identical to that in the practical example was used. An oxide superconductor paste was applied to the MgO base with the mixing ratio the Bi2223 composition, which was identical to that used in the practical example was applied and dried. The film thickness of the superconductor paste with the mixing ratio the Bi2223 composition was 600 μm. Then the superconductor paste into the atmosphere Baked at a firing temperature of 850 ° C for 50 h.

This time 10 MgO bases were made and then the application and burning of them were among the same Conditions carried out. At five Bases came a detachment of the thick films. Subsequently became the other five MgO bases, the superconducting thick film applied thereon had compressed in a CIP and then occurred in four of them a replacement of the thick film. As a result, only one sample was obtained in which the levels of CIP compression, burning, CIP compression and the last burning were carried out in a similar way Way as with the samples in the practical example.

As described in detail above, the present invention provides an oxide superconductor thick film containing Bi, Pb, Sr, Ca and Cu and essentially the composition (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ Cu ₃ O _z (in which means 0 <a <0.5) to be applied to the surface of a substrate or a base with no fracture surface near an interface between the substrate or the base and the oxide superconductor thick film in the oxide superconductor thick film occurs. In the Bi2223 thick film having the above-mentioned composition, detachment of the thick film from the substrate or from the base can be prevented by heating, cooling, compressing or mechanical shock treatment on the substrate, the base or the oxide superconductor thick film is applied in the middle of the manufacturing process or after the manufacturing process.

Claims (1)

Oxide superconductor thick film which contains Bi, Pb, Sr, Ca and Cu and essentially has the composition (Bi, Pb) _{2 + a} Sr ₂ Ca ₂ CusO _Z (in which: 0 <a <0.5), which is to be applied to a surface of a substrate or a base, wherein there is no fracture area in the vicinity of an interface between the substrate or the base and the oxide superconductor thick film in the oxide superconductor thick film.