JPH0816025B2 - Superconducting thick film manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a superconducting thick film,
More specifically, the present invention relates to a method for producing a thick film made of a novel superconducting material having a high superconducting critical temperature and a phase transition end temperature having a small difference from the critical temperature.

In the following description, the superconducting critical temperature is Tc, and the end temperature of the phase transition at which the electric resistance of the superconductor becomes zero is Tc.
The difference between f, Tc and Tcf is expressed as ΔT.

Conventional technology Under the superconducting phenomenon, a substance shows complete diamagnetism, and the potential difference disappears even though a finite steady current flows inside. Therefore, various applications have been proposed in which a superconductor is used as a transmission medium having no power loss.

That is, MHD power generation, power transmission, power storage, etc. in the electric power field, power field such as magnetic levitation train, electromagnetic propulsion ship in the power field, and ultra high magnetic field, microwave, radiation, etc. in the medical or measurement field. As a sensitive sensor, it can be applied to an extremely large number of applications such as NMR, pion therapy, and high energy physics experimental device.

Also, in the field of electronic devices represented by Josephson devices, not only mere reduction of power consumption,
It is expected as a technology that can realize extremely high-speed operation.

By the way, conventionally, the superconducting phenomenon has been observed only under an extremely low temperature. Even in Nb ₃ Ge, which was said to have the highest superconducting critical temperature Tc as a conventional superconducting material, it was about 23.2K.

Therefore, conventionally, in order to realize the superconducting phenomenon, liquid helium having a boiling point of 4.2K was used to cool the superconducting material to Tc or lower. However, the use of liquid helium has
The technical burden and cost burden of the cooling equipment including the liquefaction equipment were extremely large, which hindered the practical application of the superconducting technology.

However, with the discovery of superconducting oxides with high Tc in the fall of 1986, the possibility of high-temperature superconductivity opened up greatly (Bednorz, Muller, “Phys.B64 (1986) 18
9). This oxide superconductor is [La, Ba] ₂ CuO ₄ or [La,
Sr] ₂ CuO ₄ , which is called K ₂ NiF ₄ type oxide,
It has a similar crystal structure to the conventionally known perovskite type superconducting oxide. The Tc of these substances is 30-50K,
The value is dramatically higher than the conventional value, and at present, the achievement of a higher critical temperature is being sought in various fields.

As described above, when the Tc of the superconducting material is improved, liquid nitrogen that is easily available and inexpensive can be used as the cooling medium, and the superconducting phenomenon can be industrially used.

However, since the perovskite type or pseudo perovskite type oxide as described above is obtained as a so-called fired body, it is inconvenient to handle. Because, the fired body is generally brittle and easily breaks even under a slight mechanical load. In particular, since the superconducting material is often used as a power transmission medium, it is necessary to use it in a thin linear shape, and as described above, the superconducting material vulnerable to mechanical load cannot be practically used. .

Therefore, the present invention solves the above-mentioned problems of the conventional technology,
The purpose of the present invention is to enable mechanically stable use of superconducting materials having high Tc and Tcf.

Means for Solving the Problems That is, according to the present invention, an element α which is Ba, Ba, Y,
Average particle size of each oxide or carbonate of one element β selected from Yb, Eu, La, Nd, Gd, Dy, Ho, Er, Tm, and Lu and an element γ that is Cu Powders having a particle size of 5 μm or less are mixed so as to have an atomic ratio of α: β: γ = w: x: y (where w, x, and y are positive numbers of 1 or less) to obtain a raw material powder, A fired body obtained by pre-firing the raw material powder in the range of 700 to 950 ° C. is pulverized to an average particle size of 10 μm or less to obtain a powder fired body, and the powder fired body is mixed with an organic vehicle to form a paste, The paste is applied on a substrate by a screen printing method in a thickness of 10 to 50 μm and dried, and then main-baked in a range of 800 to 1000 ° C. under an O ₂ partial pressure of 5 to 10 atm. General formula: α with an average crystal grain size of 15 μm or less
_w β _x γ _y δ _z [where α, β, γ and w, x, y are as defined above, δ is O (oxygen),
z is a number of 1 or more and 5 or less], and a thick film of a perovskite-type or pseudo-perovskite-type complex oxide superconducting material having a composition represented by the following formula is formed on the substrate: Will be provided.

Here, according to one embodiment of the present invention, the main firing is 800 to 1
It is preferably carried out in the range of 000 ° C. Moreover, it is preferable to carry out the pre-baking in the range of 700 to 950 ° C.

According to a preferred embodiment of the present invention, it is advantageous to repeat a series of steps including pre-firing, pulverization and molding of the raw material powder at least 3 times, and the fired body after the final pre-firing has an average particle size of 8 μm. It is preferable to grind below.

In the method of the present invention, the pulverization can be performed by, for example, a pole mill, a jet mill or the like. Further, the organic vehicle can be composed of a resin and a solvent, for example, the resin can be an ethyl cellulose resin or an acrylic resin, and the solvent can be terpionel or butyl carbitol acetate Q Here, according to a preferred embodiment of the present invention, the viscosity of the paste is preferably 100 to 1000 poise. The screen printing can be performed with a stainless mesh of 100 to 325 mesh, and the paste is preferably applied to a thickness of 10 to 50 μm. The applied paste can be dried at 100 to 200 ° C.

Further, in the method of the present invention, the O ₂ partial pressure is from 0.1 atm to
It is advantageous to perform the main calcination in an atmosphere of 0.5 atm, but not limited to this, it is also preferable to perform the main calcination in the air or perform the main calcination in an O ₂ atmosphere. Here, as one embodiment, the main firing may be performed in an O ₂ atmosphere of 5 atm to 10 atm.

Furthermore, according to one embodiment of the present invention, the fired body after the main firing is heat-treated in the range of 400 to 700 ° C., and / or immediately after the main firing or in the range of 500 to 800 ° C. after the firing. It is also preferable to carry out a heat treatment including a quenching treatment after reheating to 1.

The thick film manufacturing method according to the present invention comprises the steps of pre-firing oxide or carbonate powder having an average particle size of 5 μm or less, and then pulverizing the powder to an average particle size of 10 μm or less and mixing the powdered product with an organic vehicle. Its main feature is to use a paste formed by

The thick film formed as described above is formed of a perovskite type or pseudo perovskite type oxide, and this substance becomes a superconductor at an extremely high critical temperature.

Further, a superconductor made of a perovskite type or pseudo perovskite type oxide is a superconducting thick film formed according to the method of the present invention, in which a substance having a high superconducting critical temperature is particularly likely to be formed at a grain boundary, that is, an interface between crystal grains. Is formed as a superconducting material having a crystallized fine structure due to its characteristic production method and having an extremely high critical temperature.

That is, first, the average particle size of the raw material powder to be pre-baked is 5 μm.
It is limited to m or less. This is because if the average grain size exceeds 5 μm, the grain size of the crystal grain is not sufficiently refined even after the crushing step after firing, and specifically, it exceeds 6 μm. Therefore, in order to reduce the crystal grain size, it is essential that the grain size of the raw material powder is 5 μm or less.

Further, the crushing step after the preliminary firing has a direct effect on the crystal grain size after the main firing, and when it exceeds 10 μm, the crystal grain size of the fired body after the main firing becomes large and the crystal grain boundary area becomes large. Decrease. As described above, the reduction of grain boundaries is not preferable for achieving a high Tc.

In addition, the above-mentioned process of [pre-baking → pulverization → molding] is repeated a plurality of times to further promote the solid solution reaction of the raw material powder or the fired body. It is also preferable to make the crystal grain size of the powder to be subjected to the main firing fine. From these viewpoints, the above [pre-baking → crushing → molding]
It is preferable to repeat the above series of steps at least three times or more.

Further, the main firing temperature is an extremely important control factor,
It is necessary to control the progress of calcination in the solid-state reaction and the crystal growth of the calcined perovskite type or pseudo-perovskite type oxide not to be excessive.

As a result of repeating the experiment based on these findings, when the main firing temperature is less than 800 ° C, sufficient strength cannot be obtained in the final fired body, while when it exceeds 1000 ° C, the solid solution phase in the fired body is increased. Occurs, or coarse crystal grains are generated. Therefore, in the present invention, the main firing temperature is limited to the range of 800 to 1000 ° C.

Further, for the same reason as in the control of the main calcination described above, when the pre-calcination temperature is also lower than 700 ° C., the solid solution reaction does not proceed sufficiently and a perovskite type or pseudo perovskite type oxide cannot be obtained. On the other hand, if the pre-baking temperature exceeds 950 ° C, as in the case of the main baking, a love-melting phase occurs in the fired body or coarsening of crystal grains occurs, and it becomes difficult to reduce the size by pulverization in the subsequent steps. .

Furthermore, according to the knowledge of the present inventors, a superconductor made of a perovskite type or pseudo perovskite type oxide is
Particularly, excellent properties are exhibited near the surface of the fired body.
This is considered to be because the reaction with the atmosphere during the firing or heat treatment favorably progressed to the superconducting properties near the surface of the material.

Therefore, in the method of the present invention, it is necessary to carefully control the viscosity of the paste forming the thick film and the thickness of the coating film on the substrate.

That is, when the thickness of the applied paste is less than 10 μm, it becomes difficult to form a continuous film having a uniform thickness. If the thickness exceeds 50 μm, the pattern is likely to be deformed due to so-called sag, and the characteristics of the formed thick film near the substrate and the surface of the thick film tend to be different.

Further according to a preferred embodiment of the present invention, the obtained fired body is further heat-treated to obtain a substantially uniform pseudo-perovskite type oxide. This heat treatment remarkably raises the superconducting critical temperature at which the electric resistance becomes completely zero. This heat treatment is preferably carried out at a temperature in the range of 500 to 800 ° C.

If the heating temperature is less than 500 ° C., the fired body does not become the desired perovskite type or pseudo-perovskite type oxide and the desired superconducting critical temperature cannot be obtained, or long-term heat treatment is required. . On the other hand, at a processing temperature of more than 800 ° C, the perovskite type crystal structure having a superconducting effect disappears and the critical temperature drops significantly. By the heat treatment after these firings, ΔT is further improved by 3 to 5 ° C. Q According to a preferred embodiment of the present invention, immediately after the above firing, it is immediately cooled, or after reheating to a range of 500 to 800 ° C. after firing. The rapid cooling can further improve the superconducting critical temperature.

Further, according to these preferred embodiments of the present invention, the composition of the superconducting material is made uniform and stable,
As will be specifically described later, it was also found that the deterioration of the characteristics over time was small.

The perovskite-type or pseudo-perovskite-type oxide thick film obtained by the method of the present invention has the general formula: α _w
β _x γ _y δ _z [where element α is Ba, element β is Ba,
One element selected from Y, Yb, Eu, La, Nd, Gd, Dy, Ho, Er, Tm, and Lu, element γ is Cu, and element δ is O (oxygen). In addition, w, x, and y are each a positive number of 1 or less.] Is a perovskite-type or pseudo-perovskite-type oxide superconducting material having a composition represented by Therefore, it is desirable that the powder of the oxide or carbonate of the material is mixed in such a ratio that the fired body is in the above range.

As the organic vehicle, many organic vehicles conventionally used for forming a thick film paste can be applied. That is, representative ones include, but are not limited to, one obtained by dissolving ethyl cellulose resin with terpionel, one obtained by dissolving acrylic resin with butyl carbitol acetate, and the like.

As described above in detail, the thick film produced according to the present invention exhibits extremely good superconducting properties, and its excellent properties are stable for a long period of time.

This is because, according to the characteristic manufacturing method of the present invention, the increase of the crystal interface length due to the refinement of the crystal grains and the uniformity of the oxygen defect concentration were achieved, and a high Tcf and a small ΔT were obtained.

The superconductor formed as a thick film on the substrate is mechanically stable because it is supported by the substrate, and is therefore easy to handle. Further, it is economical because it is not necessary to use the superconducting material more than necessary in order to have strength.

As described above, according to the present invention, a superconducting material having a high and stable Tc can be obtained in an easy-to-use form, so that economical superconducting ceramics using liquid nitrogen as a cooling medium can be obtained, and the superconducting technology can be put into practical use. Is possible.

Hereinafter, the present invention will be specifically described with reference to Examples, but the technical scope of the present invention is not limited by the following disclosure.

Example When powders of BaCO ₃ , Y ₂ O ₃ , and CuO having a purity of 3 N or more and an average particle size of 3 μ or less were each Ba _1-x Y _x Cu ₁ O ₃ after firing, x = 0.2. , 0.4 and 0.8 were mixed to prepare three kinds of materials.

These powders were fired at 900 ° C. for 12 hours in the air, and the cake-solidified powder was pulverized for 8 hours by a ball mill made of alumina to obtain a powder having an average particle diameter of 4 μm. This operation was repeated three times, and particularly in the last step, the powder fired body was pulverized to have a particle size of 2 to 3 μm.

The fired powder thus obtained was mixed with ethyl cellulose dissolved in terpineol as an organic vehicle and roughly mixed in a mortar. Further, this mixture was made into a uniform mixed paste by using a Raiki machine and three rolls made of high-purity alumina. At this time, the viscosity of the paste was measured with a viscometer and adjusted so that the viscosity would be 500 poise.

This paste is printed on an alumina substrate using a 200-mesh stainless screen so that the thickness is about 30 μm, and the paste is printed using a mesh belt dryer for 150
It was dried at ℃ for 15 minutes. The thickness of the paste film after this drying step was about 25 μm. Further, the substrate on which the dried paste was mounted was baked in O ₂ at 930 ° C. for 24 hours.

The critical temperatures Tc and Tcf of the thick film thus obtained were measured by a direct current four-point probe method in a cryostat with electrodes attached with Ag conductive paste on both ends of the sample according to a standard method. Temperature is calibrated Au (Fe)-
This was done using an Ag thermocouple. The change in resistance was measured while gradually increasing the temperature. Table 1 shows the measured Tc and Tcf. The difference ΔT between Tc and Tcf is also shown in Table 1. In addition, Table 1 also shows the results of measuring the Tc and Tcf of each sample by thickening the other elements of Group IIa and Group IIIa of the periodic table under the same conditions as those described above, and by the above method. There is.

Furthermore, when Tc was measured again under the same conditions three weeks after the production of these superconducting thick films, the change in Tc of any of the superconducting thick films was in the range of ± 1 K, and no significant change was observed. This was also confirmed by the measurement result of the AC susceptibility measured by using the L meter.

EFFECTS OF THE INVENTION As described above in detail, the thick film produced according to the present invention exhibits extremely good superconducting properties, and its excellent properties are stable for a long period of time.

This is because, according to the characteristic manufacturing method of the present invention, the increase of the crystal interface length due to the refinement of the crystal grains and the uniformity of the oxygen defect concentration were achieved, and a high Tcf and a small ΔT were obtained.

The superconductor formed as a thick film on the substrate is mechanically stable because it is supported by the substrate, and is therefore easy to handle. Further, it is economical because it is not necessary to use the superconducting material more than necessary in order to have strength.

As described above, according to the present invention, a superconducting material having a high and stable Tc can be obtained in an easy-to-use form, so that economical superconducting ceramics using liquid nitrogen as a cooling medium can be obtained, and the superconducting technology can be put into practical use. Is possible.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01L 39/24 ZAA Z // H01B 12/06 ZAA (72) Inventor Tetsuji Kamishiro Kuniyo, Itami City, Hyogo Prefecture North 1-1-1 Sumitomo Electric Industries, Ltd. Itami Works (56) Reference JP 61-207576 (JP, A) JP 63-233070 (JP, A) Physical Review Letters Vol. 58 p. 405 to 407 Physical Review Letters Vol. 58 p. 908-912

Claims (1)

[Claims] 1. An element α which is Ba, Ba, Y, Yb, Eu, La,
A powder having an average particle size of 5 μm or less of each oxide or carbonate of one element β selected from Nd, Gd, Dy, Ho, Er, Tm, and Lu and an element γ that is Cu, Atomic ratio of α: β: γ = w: x: y (where w, x, and y are positive numbers of 1 or less) are mixed to obtain a raw material powder, and the raw material powder is The fired body obtained by preliminary firing in the range of 950 ° C. is pulverized to an average particle size of 10 μm or less to obtain a powder fired body, which is mixed with an organic vehicle to form a paste, and the paste is screen-printed. On the substrate by the method,
After being applied in a thickness range of 10 to 50 μm and dried, it is main-baked in a range of 800 to 1000 ° C. under an O ₂ partial pressure of 5 to 10 atm, and has an average crystal grain size of 15 μm or less. α _w β _x γ _y δ
_z [wherein α, β, γ and w, x, y are as defined above, δ is O (oxygen), and z is 1 or more and 5
The following number] is used to form a thick film of a perovskite-type or pseudo-perovskite-type complex oxide-based superconducting material on the substrate.