JP2593917B2 - Superconducting material having high critical temperature and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel superconducting material and a method for producing the same, and in particular, a novel fluorine-containing composite oxide superconducting material containing titanium and fluorine, which exhibits a superconducting phenomenon at a high temperature. And its manufacturing method.

2. Description of the Related Art Under superconducting phenomena, a material shows perfect diamagnetism, and no potential difference appears even though a finite steady current flows inside. The application fields of this superconductivity phenomenon are MHD power generation, power transmission, power storage and other power fields, or maglev trains,
It covers a very wide range of fields, such as power fields such as electromagnetic propulsion ships, and fields of measurement such as NMR, pion therapy, and high energy physics experimental equipment as ultra-sensitive sensors for magnetic fields, high frequencies, and radiation. In the field of electronics typified by Josephson devices, it is expected to be a technology capable of realizing not only a reduction in power consumption but also an extremely high-speed device.

By the way, superconductivity was a phenomenon observed only at very low temperatures. That is, even in Nb ₃ GE, which is said to have the highest superconducting critical temperature Tc as a conventional superconducting material, an extremely low temperature of 23.2 K has been the limit of the superconducting critical temperature for a long period of time. Therefore, conventionally, in order to realize the superconductivity phenomenon, the superconducting material has been cooled to Tc or less using liquid helium having a boiling point of 4.2K. However, the use of liquid helium imposes a very large technical and cost burden on the cooling equipment including the liquefaction equipment, which hinders the practical application of superconducting technology.

However, recently, it has been reported that a composite oxide sintered body can become a superconductor at a high critical temperature, and practical application of superconducting technology using a non-low-temperature superconductor is being rapidly promoted. Examples already reported include yttrium-barium-copper, lanthanum-barium-copper, and lanthanum-copper.
A composite oxide having a crystal structure similar to a perovskite type, such as a strontium-copper system, may be mentioned as one exhibiting a superconducting phenomenon at liquid nitrogen temperature or higher.

Considering the stability of the superconducting state, the critical temperature of the superconducting material is required to be sufficiently higher than the temperature of the cooling medium. Therefore, in order to put the superconducting technology into practical use, it is preferable that the critical temperature of the superconducting material be higher. Considering the use of liquid nitrogen as a typical inexpensive cooling medium, even a composite oxide-based superconducting material can be used. Realization of a critical temperature is strongly desired.

SUMMARY OF THE INVENTION The object of the present invention is to provide a novel superconducting material exhibiting superconducting properties at higher temperatures, which reduces the limitation on the use of superconducting technology caused by cooling technology and enables stable use of superconducting phenomena. And a method of manufacturing the same.

Means for Solving the Problems The present invention provides the following general formula: _Mw Ba _x (Cu _1-y Ti _y ) (O _1-q F _q ) _z [where M represents a group IIIa element in the periodic table. , Q, w, x, y, and z are 0.3 ≦ w ≦ 1.95, 0.05 ≦ x ≦ 1.8, 2.0 ≦ z ≦ 5.0, 0.01 ≦ y ≦ 0.6, where (Cu _1-y Ti _y ) is 1, A superconducting material having a high critical temperature, characterized by being a fluorine-containing composite oxide represented by the following formula: 0.01 ≦ q ≦ 0.5.

This superconducting material is new. This superconducting material is considered to have a perovskite type or a similar crystal structure.

Embodiment Examples of the element M include, but are not limited to, Y, La, Sc, Er, Yb, Eu, Ho, and Dy.

The superconducting material of the present invention has M (where M is the periodic table IIIa).
Group element), a compound powder selected from oxides, carbonates, sulfates, nitrates and oxalates of each of Ba, Cu and Ti, and a fluoride selected from each of the elements M, Ba, Cu and Ti From the group consisting of fluoride powder, the elements M, Ba,
A powder mixture prepared so as to contain all of Cu and Ti, or a powder of a sintered body obtained by sintering the powder mixture is used as a raw material powder to have the above general formula: M _w Ba _x (Cu _1-y Ti _y ) (O _1-q F _q ) _z (where M, q, w, x, y and z represent the above definitions) Can be.

Further, the superconducting material of the present invention comprises a compound powder selected from M (where M is an element of Group IIIa of the periodic table), oxides, carbonates, sulfates, nitrates and oxalates of Ba, Cu and Ti. And a fluoride powder selected from the fluorides of the elements M, Ba, Cu and Ti.
Using a powder mixture prepared so as to contain all of Ba, Cu and Ti or a sintered body obtained by sintering the powder mixture as an evaporation source, the above general formula: M _w Ba _x (Cu _{1− y} Ti _y ) (O _1-q F _q ) _z [where M, q, w, x, y and z represent the above definitions] Can be formed on.

In a preferred embodiment of the present invention, as the compound powder used in the above method, an oxide, carbonate, sulfate, nitrate or oxalate powder of each element can be used, each having a particle size of 0.1 to 10 μm. Advantageously, it is a powder.

In another embodiment of the present invention, it is preferable to pre-fire the raw material powder before the sintering process. 700 ° C
It is preferable to carry out in a temperature range of not less than 1000 ° C.
After the preliminary firing, the fired body is pulverized to a particle size of 0.1 to 10 μm.
It is advantageous to sinter the powder after firing into a fired body powder of m.

The sintering treatment is preferably performed in a temperature range of 850 ° C. or more and 1050 ° C. or less, and after sintering, it is preferable to gradually cool at a cooling rate of 100 ° C./min or less. Further, the calcination and / or sintering treatment is preferably performed in an oxygen-containing atmosphere in the range of 10 ⁻³ to 10 ³ Torr, for example, in the air, and more preferably in a fluorine gas-containing atmosphere.

When producing a thin film of a superconducting material by physical vapor deposition,
It is preferable to use a sapphire, strontium titanate or magnesium oxide substrate as the substrate.

In one embodiment of the present invention, the composite oxide superconducting material prepared as a sintered body or a thin film as described above is used in a range of 300 to 900.
Reheat to a temperature range of ° C., hold for 1-50 hours, then
It is advantageous to carry out a heat treatment at a cooling rate of 100 ° C./min or less. Note that this heat treatment is also preferably performed in an oxygen-containing atmosphere in the range of 10 ⁻³ to 10 ³ Torr, for example, in the air, and more preferably in a fluorine gas-containing atmosphere.

The superconducting material according to the present invention has a more stabilized superconducting property by adding a specific element to a composite oxide known to have a perovskite structure on a layer of Y-Ba-Cu or the like. It is characterized by:

That is, the material on which the composite oxide-based superconducting material provided by the present invention is based is a conventional perovskite-type composite oxide.
Ti is added, and can be represented by the following general formula.

Ba ₂ M _p Cu _q Ti _r O _x [where M represents an element of Group IIIa of the periodic table, and p, q, r and x are numbers in the following ranges, respectively.

0.1 ≦ p ≦ 1.2, 2.0 ≦ q ≦ 3.0, 0.1 ≦ r ≦ 0.8, 6.0 ≦ x ≦ 7.0].

The present inventors consider that this composite oxide is actually a Ba-Y-Cu-based composite oxide superconducting material having a perovskite-type crystal structure, in which a part of Cu is replaced by Ti,
Its composition is represented as follows: Formula: M _w Ba _x (Cu _1-y Ti _y ) O _z [where M represents the above definition, w, x, y and z are (Cu _1-y When Ti _y ) is 1, each represents a number in the following range: 0.3 ≦ w ≦ 1.8, 0.5 ≦ x ≦ 1.8, 2.0 ≦ z ≦ 5.0, 0.01 ≦ y ≦ 0.6] This composite oxide is a superconducting material. Can be manufactured as a sintered body by sintering a mixture of compound powders of the respective elements that form the above. Further, it can be formed into a thin film by physical vapor deposition using an evaporation source comprising a compound powder of each element or a mixture thereof, a fired body, a fired body powder, a sintered body or a sintered body powder. As the compound of each element, powder of an oxide, carbonate, sulfate, nitrate or oxalate of each element can be used.

The superconducting material provided by the present invention is a fluorine-containing composite oxide in which the above-mentioned composite oxide containing Ti further contains fluorine.
It is considered that the fluorine-containing composite oxide of the present invention has a structure in which a part of the metal of the conventional complex oxide having a perovskite structure on the layer is replaced with Ti and a part of the oxygen atom is replaced with a fluorine atom. Therefore, this fluorine-containing composite oxide can be represented by the following general formula: _Mw Ba _x (Cu _1-y Ti _y ) (O _1-q F _q ) _z [where M is group IIIa of the periodic table Represents an element, and q, w, x, y, and z are: 0.3 ≦ w ≦ 1.95, 0.05 ≦ x ≦ 1.8, 2.0 ≦ z ≦ 5.0, 0.01 ≦ y when (Cu _1-y Ti _y ) is 1 ≦ 0.6, 0.01 ≦ q ≦ 0.5.] This fluorine-containing composite oxide can be produced as a sintered body by sintering a mixture of compound powders of the respective elements forming the same. .

The addition of fluorine can be easily realized by adding a fluoride of each element to the raw material powder. Generally, a fluoride of a metal element can be obtained by reacting a hydroxide, oxide, carbonate, or the like of the corresponding metal element with hydrofluoric acid.
In the case of sintering fluoride powder which is easily decomposed, it is preferable that the sintering be performed in a sealed state or in a fluorine-containing atmosphere.

The superconducting material of the present invention can be formed into a thin film by physical vapor deposition using a compound powder of each element or a mixture thereof, a fired body, a fired body powder, a sintered body, or an evaporation source composed of a sintered body powder. .

The compound of each element is preferably selected from the group consisting of fluoride, oxide, carbonate, sulfate, nitrate and oxalate of each element. In particular, powders of at least one metal compound selected from the group consisting of oxides, carbonates, sulfates, nitrates and oxalates of the elements M, Ba, Cu and Ti, and powders of M, Ba, Cu and Ti It is preferable to use a mixture of at least one metal fluoride selected from the group consisting of fluorides such that each constituent metal is within the composition range of the superconducting complex oxyfluoride. Thus, the composition ratio of the constituent metals is adjusted by the mixing ratio of the compound used as a raw material, and the ratio of oxygen and fluorine can be controlled by changing the mixing ratio of the compound, firing conditions and sintering conditions. .

In the production of the superconducting material of the present invention, if the average particle diameter of the powder before the sintering or sintering treatment is large, an oxide having a uniform composition cannot be obtained in the sintering reaction. Therefore, in order to reduce the crystal grain size, the particle size of the raw material powder is preferably 0.1 μm or more and 10 μm or less. The reason why the thickness is set to 0.1 μm or more is that if it is less than 0.1 μm, it becomes difficult to handle the raw material, and if it is a fired body, it takes too much time to pulverize it to less than 0.1 μm. This is industrially disadvantageous in that the yield is reduced.

It is also advantageous to repeat the [firing-to-pulverization] process a plurality of times to homogenize the sintered body.

The sintering temperature is preferably set to a temperature range in which the sintering reaction is sufficiently performed and at the same time, the appearance of a solid solution phase is prevented.
It is advantageous to carry out at a temperature in the range of 050 ° C., especially 850 ° C. and 1000 ° C. That is, when the sintering temperature does not reach the above temperature range, the sintering reaction is not sufficiently performed, and the composition of the obtained sintered body is not uniform. If the sintering temperature exceeds the above range, a solid solution phase is formed in the raw material powder, and the probability of forming a crystal structure having the desired superconducting properties is reduced. The body may be contaminated. Further, in order to allow the reaction to spread over the entire raw material powder, the firing time is preferably set to 1 hour or more.

An important management item that is expected to greatly affect the superconducting properties of the superconducting material according to the present invention is cooling immediately after firing or sintering. That is, it is necessary to control the cooling rate after sintering in order to preferably form the superconducting material. According to the knowledge of the present inventors, the cooling from the sintering temperature or the sintering temperature to room temperature is 100 ° C./min or less. It is preferably carried out at a cooling rate of

The superconducting material of the present invention can be formed into a thin film by various physical vapor deposition methods such as a sputtering method and an ion plating method using a mixture of the above raw materials, a fired body, a fired body powder or a sintered body as an evaporation source. When a thin film of the superconducting material of the present invention is formed, a mixture of each element constituting the superconducting material or a compound thereof can be used as an evaporation source. In this case, it is advantageous to use a substrate having a perovskite crystal structure such as sapphire, strontium titanate, or magnesium oxide on the surface as a substrate on which a thin film is grown.

The bulb-shaped or thin-film superconducting material thus obtained is reheated to a temperature in the range of 300 to 900 ° C., held for 1 hour to 50 hours, and then cooled at a cooling rate of 100 ° C./min or less to homogenize the superconducting material. And stabilization can be realized,
A longer life of the superconducting material is realized.

It is considered that the fluorine-containing composite oxide superconducting material of the present invention still contains a perovskite-type or pseudo-perovskite-type crystal structure, but it seems that a substance having another crystal structure is also included.

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

Example 1 An oxide M ₂ O ₃ powder of a group IIIa element M shown in Table 1 and BaCO ₃
Powder, CuO powder, and TiO ₂ powder (each having a particle size of 10
μm or less and a purity of 99.9% or more).

First, when M: Ba: (Cu _1-y Ti _y ) is expressed as w: x: 1 in atomic ratio, each powder is weighed so that w, x and y have the values shown in Table 1. Then, they were mixed to prepare an oxide raw material powder (A).

Next, an oxyfluoride raw material powder (B) was prepared by the same operation as the above-described method for preparing the composite oxide raw material powder (A) using BaF ₂ powder instead of BaCO ₃ powder.

Next, the composite oxide raw material powder (A) and the composite oxyfluoride raw material powder (B) are mixed and mixed so that the O: F atomic ratio (1-q): q becomes the value shown in Table 1. Raw material powder was prepared.

Each mixed raw material powder was filled in a mold and preformed into a disk having a diameter of about 10 mm at a load of 100 kg per 10 mm in diameter of the formed body.

The preform was heated to 900 ° C. by an electric furnace in the atmosphere and kept at that temperature for 6 hours to perform a firing treatment. After the completion of the baking treatment, the mixture was air-cooled.

Each fired body thus obtained is ground in a mortar, and the particle size is 10 μm.
m and then filled in the mold again, the diameter of the molded body 7mm
It was formed into a disk having a diameter of about 7 mm at a pressure of 50 kg per unit.

The obtained molded body is again heated in an atmosphere by an electric furnace.
After heating to 0 ° C. and maintaining this temperature for 6 hours, it was cooled to room temperature over 12 hours.

An electrode was attached to the disc-shaped sample prepared as described above according to a standard method, and a change in resistance value with respect to temperature was measured by a DC four-terminal method.

In the measurement results, the temperature at which the electrical resistance of the sample was completely zero (10 ⁻⁶ Ω or less) was indicated as Tc.

Example 2 Commercially available Y ₂ O _{3 having a} particle size of 10 μm or less and a purity of 99.9% or more
Powder, BaCO ₃ powder, CuO powder, and TiO ₂ powder were prepared.

When the target oxyfluoride composition is expressed as YBa ₂ (Cu _1-x Ti _x ) ₃ (O _1-y F _y ) _z , the values of x and z are as shown in Table 2. The powders were weighed at appropriate ratios and mixed to prepare an oxide raw material powder (A).

Next, using BaF ₂ powder instead of the above BaCO ₃ powder,
An oxyfluoride raw material powder (B) was prepared by the same operation.

Next, the composite oxide raw material powder (A) is adjusted so that the value of y that determines the atomic ratio (1-y): y of O: F becomes the value shown in Table 2.
And the composite oxyfluoride raw material powder (B) were mixed to prepare a mixed raw material powder.

Each mixed raw material powder was filled in a mold and preformed into a disk having a diameter of about 10 mm at a load of 100 kg per 10 mm in diameter of the formed body.

This preformed body was heated to 900 ° C. in an air atmosphere in an electric furnace, and calcined by maintaining this temperature for 6 hours. After the completion of the baking treatment, the mixture was air-cooled.

Each fired body thus obtained is ground in a mortar, and the particle size is 10 μm.
m or less, and then re-filled in the mold, and the molded body diameter 7mm
It was formed into a disk having a diameter of about 7 mm at a pressure of 50 kg per unit.

The obtained molded body was also heated to 950 ° C. in an electric furnace in the air, maintained at this temperature for 6 hours, and then cooled to room temperature over 12 hours.

An electrode was attached to the disc-shaped sample prepared as described above according to a standard method, and a change in resistance value with respect to temperature was measured by a DC four-terminal method.

In Table 2, the temperature at which the electrical resistance of the sample is completely zero (10 ⁻⁶ Ω or less) is shown as Tc.

Effect of the Invention As described above, the composite oxide superconducting material of the present invention is a novel superconducting material that exhibits a higher and higher critical temperature than conventional superconducting materials. By using the superconducting material of the present invention, the superconducting phenomenon can be used economically and economically.

The superconducting material of the present invention can be directly used as a thin plate, a thin wire, or a small part, and can be formed into a thin film by sputtering or the like, so that it can be applied to various electronic technologies.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 39/12 ZAA H01L 39/12 ZAAC (72) Inventor Kazuya Omatsu Shimaya Konohana-ku, Osaka-shi, Osaka 1-3-1, Sumitomo Electric Industries, Ltd., Osaka Works (72) Inventor Kazuo Sawada 1-3-1, Shimaya, Konohana-ku, Osaka, Osaka Prefecture, Japan Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor: Hajime Ichiyanagi Osaka 1-3-3 Shimaya, Konohana-ku, Osaka-shi, Japan Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Yoshihiro Nakai 1-3-1, Shimaya, Konohana-ku, Osaka-shi, Osaka Sumitomo Electric Industries, Ltd. References JP-A-63-236748 (JP, A) JP-A-63-291855 (JP, A) JP-A-63-291817 (JP, A) Physica l Reuiew B Vol. 35, p. 8782-8784 Japaneous Journal of Applied Phgsics Vol. 26, p. L337-338

Claims (3)

(57) [Claims] 1. The following general formula: M _w Ba _x (Cu _{1 -y} Ti _y ) (O _{1 -q} F _q ) _z [where M represents an element of Group IIIa of the periodic table, q, w, x , Y and z are defined as 0.3 ≦ w ≦ 1.95, 0.05 ≦ x ≦ 1.8, 2.0 ≦ z ≦ 5.0, 0.01 ≦ y ≦ 0.6, 0.01 ≦ q ≦ 0.5 when (Cu _1-y Ti _y ) is set to 1. A superconducting material having a high critical temperature, which is a fluorine-containing composite oxide represented by the following formula: 2. M (where M is an element of Group IIIa of the periodic table), B
a, each oxide of Cu and Ti, a carbonate powder, a sulfate powder, a compound powder selected from nitrate and oxalate, and the element M, Ba, a fluoride powder selected from each fluoride of Cu and Ti, From the group consisting of the elements M, Ba, Cu and Ti
Or a powder of a sintered body obtained by sintering the powder mixture as a raw material powder, the following general formula: M _w Ba _x (Cu _1-y Ti _y ) ( O _1-q F _q ) _z [where, M represents an element of Group IIIa of the periodic table, and q, w, x, y, and z are 0.3 ≦ when (Cu _1-y Ti _y ) is 1 w ≦ 1.95, 0.05 ≦ x ≦ 1.8, 2.0 ≦ z ≦ 5.0, 0.01 ≦ y ≦ 0.6, and 0.01 ≦ q ≦ 0.5, respectively.] A method for producing a sintered body of a superconducting material having a high critical temperature. 3. M (where M is an element of Group IIIa of the periodic table), B
a, each oxide of Cu and Ti, a carbonate powder, a sulfate powder, a compound powder selected from nitrate and oxalate, and the element M, Ba, a fluoride powder selected from each fluoride of Cu and Ti, From the group consisting of the elements M, Ba, Cu and Ti
And a sintered body obtained by sintering the powder mixture prepared so as to contain all of the following, by physical vapor deposition, using the following general formula: M _w Ba _x (Cu _1-y Ti _y ) ( O _1-q F _q ) _z [where, M represents an element of Group IIIa of the periodic table, and q, w, x, y, and z are 0.3 ≦ when (Cu _1-y Ti _y ) is 1 w ≦ 1.95, 0.05 ≦ x ≦ 1.8, 2.0 ≦ z ≦ 5.0, 0.01 ≦ y ≦ 0.6, and 0.01 ≦ q ≦ 0.5, respectively.] A thin film of a fluorine-containing composite oxide represented by A method for producing a thin film of a superconducting material having a high critical temperature, characterized by being formed on a substrate.