JPH01215722A - Superconducting material and compound thereof - Google Patents

Abstract

PURPOSE:To obtain a high-temperature superconductor material capable of reducing restriction concerning utilization of superconductor technique by cooling equipment and stably utilizing superconducting phenomenon, by forming a complex oxide having specific composition of Bi-(Ca and Sr)-Cu system. CONSTITUTION:The aimed superconducting material mainly contains a complex oxide having composition expressed by the formula Bi2-x(Ca and Sr)1-xCu2O7-y (ratio of Sr to Ca is 10-90atom.% and x and y are numbers each satisfying the equations 0<=x<=1, 0<=y<=1). The superconducting material is obtained according to the following method: Process sintering a blend obtained by blending raw material powders selected from each element of Sr, Ca, Bi, and Cu and compounds containing at least one among these element so as to contain all of these elements or calcined powder obtained by calcining the above-mentioned blend and then pulverizing the calcined product at least once.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting materials and methods for producing the same. More particularly, the present invention relates to a novel superconducting material that exhibits superconducting phenomena at extremely high temperatures, and a method for producing the same.

BACKGROUND OF THE INVENTION Certain materials exhibit diamagnetic properties under superconducting phenomena, and no potential difference appears even though a finite steady current flows inside them.

The fields of application of this superconducting phenomenon are MHD power generation, power transmission,
It can be used in the power field such as power storage, or in the power field such as magnetic levitation trains and electromagnetic propulsion ships.It is also used as an ultra-sensitive sensor for magnetic fields, high frequencies, radiation, etc. for measurements such as NMR, pi-meson therapy, and high-energy physical experiment equipment. Furthermore, in the field of electronics such as Josephson devices, it is expected that this technology will not only reduce power consumption but also realize devices that operate at extremely high speeds. There is.

By the way, superconductivity was once a phenomenon observed only at extremely low temperatures. That is, Nb and G, which are said to have the highest superconducting critical temperature Tc among conventional superconducting materials,
For a long time, an extremely low temperature of 23.2 K was considered to be the limit of superconducting critical temperature.

Therefore, conventionally, in order to realize the superconducting phenomenon, superconducting materials have been cooled to below Tc using liquid helium with a boiling point of 4.2. However, the use of liquid helium imposes an extremely large technical burden and cost burden due to cooling equipment including liquefaction equipment, which has hindered the practical application of superconducting technology.

However, in recent years, it has been reported that composite oxide sintered bodies can become superconductors at high critical temperatures, and the practical application of superconducting technology using non-low temperature superconductors is rapidly gaining momentum. In already reported examples, three-element complex oxides such as Y-Ba-C1 that have a crystal structure similar to a perovskite type exhibit superconducting phenomena at temperatures above liquid nitrogen temperature. .

Problems to be Solved by the Invention Since liquid nitrogen is relatively easy to use and inexpensive, it is true that the discovery of superconducting materials that operate at liquid nitrogen temperatures has made great progress in the practical application of superconducting technology. However, the very basic configuration of the cooling equipment has not changed, and the cost reduction of superconducting technology has only been realized by lowering the cost of the cooling medium.

In addition, considering the stability of the superconducting state, it is desirable that there is a sufficient difference between the temperature of the cooling medium (especially the boiling point) and the superconducting critical temperature Tc of the material. We need to improve further.

Therefore, an object of the present invention is to provide a new superconducting material that exhibits superconducting properties at high temperatures and a method for manufacturing the same, which can alleviate the restrictions on the use of superconducting technology due to cooling equipment and stably utilize the superconducting phenomenon. It is said that

Means for solving the problem, namely according to the present invention, Formula: Bi2-M (Ca, Sr) l-X Cu
2Ch-y [However, the ratio of element Sr to Ca is 10
~90 atomic%, and xly is 0≦X≦1.0, respectively
y≦1] A superconducting material is provided that is characterized by mainly containing a composite oxide having a composition represented by the following formula.

According to a preferred embodiment of the present invention, in the above formula, y
preferably satisfies y■x/2, and furthermore, X satisfies x■x/2.
It is preferable that the number satisfies 1. Further, according to a preferred embodiment of the present invention, in the above formula, it is advantageous that the ratio of element Sr to Ca is 1:1 in atomic ratio.

Further, as a method for manufacturing the above-mentioned superconducting material, according to the present invention, raw material powders selected from the above-mentioned individual Sr, Ca5Bi, and Cu, and compounds containing at least one of the elements are mixed so as to contain all of the elements. blend,
Alternatively, there is provided a method for producing a superconducting material, which includes at least one step of sintering a sintered body powder obtained by pulverizing the mixture after firing.

Here, as the raw material powder, in addition to each element alone, powders of oxides, carbonates, sulfates, nitrates, or oxalates of at least one element selected from the above element groups may be used. However, from the viewpoint of product quality, oxides are preferred, and from the viewpoint of ease of preparation of raw material powder, carbonates are preferred. Further, it is desirable that the material to be subjected to final sintering is formed into a desired shape and sintered.

In the method for producing a superconducting material according to the present invention, according to a preferred embodiment of the present invention, the steps of pulverizing the sintered body, shaping and sintering the sintered body powder can be repeated two or more times. In addition, the particle size of the powder containing the composite oxide that forms the compact that is subjected to firing or sintering is 10 μm.
It is advantageous that the thickness is less than m, more preferably in the range of I to 5 μm.

The sintering temperature in the firing and sintering process is preferably 700°C or higher, with the upper limit being the melting point of the compound with the lowest melting point among the raw material powders used, and the sintering time is , preferably for 1 hour to 50 hours.

Now, the superconducting material provided according to the present invention is further characterized in that a thin film is grown on a predetermined substrate by a physical vapor deposition method using the fired body or sintered body provided according to the present invention as a target. It can also be obtained as a thin film using the manufacturing method described above.

However, the composition of the target is preferably adjusted according to the evaporation rate of each element constituting the target, etc. so that the composition of the thin film to be formed is the composition of the superconducting material. In addition, in the method according to the present invention, according to one embodiment of the present invention, any one of sputtering method, electron beam method, and ion plating method can be selected as the physical vapor deposition method. Further, as a substrate on which a thin film is grown, MgO1SrTiO3,5iCh, sapphire, YSZ, etc. can be exemplified as preferable substrates.

Function: The superconducting material obtained by the method of the present invention has the formula:
B12-X (Ca, Sr) 1ull Cu20
t-Y [However, the ratio of element Sr to Ca is 10 to 9
0 atomic %, and xly is 0≦X≦1.0×y, respectively.
A number that satisfies ≦1.

Here, the superconducting material according to the present invention mainly contains a composite oxide represented by the above formula, but is not necessarily strictly limited to this ratio, and ±5 from these ratios.
Even those having a composition within a range of 0%, more preferably within a range of ±20%, may exhibit effective superconducting properties.

That is, in the claims, the expression "mainly contains a complex oxide represented by the above formula" means that the superconducting thin film produced by the method of the present invention may have an atomic ratio other than that defined by the above formula. It means including.

As will be specifically described below, the superconducting material according to the present invention exhibits extremely excellent superconducting properties and is also excellent in stability, exhibiting effective superconducting properties over a long period of time even during standby.

Note that the superconducting material according to the present invention contains elements other than the above composition,
That is, it may contain unavoidable impurities mixed in on the order of ppm or a third component added for the purpose of improving other properties of the obtained sintered body or thin film. Specific examples of the third component include Group IIA elements of the periodic table, ]]Ja
Examples include group elements.

Superconducting materials mainly containing composite oxides as described above are
It can be obtained as a sintered body or as a thin film.

When manufacturing a composite oxide material as a sintered body, according to research by the present inventors, in order to manufacture a sintered body that exhibits high characteristics as a superconducting material, the following points must be strictly controlled. is necessary.

■ Particle size of raw material powder ■ Firing temperature ■ Particle size of fired body powder after firing treatment and crushing ■ Sintering temperature, that is, if the average particle size of raw material powder before firing treatment exceeds 10 pm, crushing after sintering Even after the process, crystal grains cannot be sufficiently refined. Therefore, in order to reduce the crystal grain size, the particle size of the raw material powder should be 10 μm or less, preferably l
The thickness is preferably in the range of 5 μm to 5 μm. In addition, 1 to 5
The reason for choosing µm is that while grinding to 5 µm or less will significantly reduce the fineness of the powder, grinding to 1 µm or less is industrially disadvantageous in terms of working time and contamination with impurities. This is because. In addition, particular attention should be paid to the refinement of the powder to be subjected to final sintering, as this has a direct effect on the crystal grain size of the product. Furthermore, by repeating these series of steps (firing → crushing → molding) multiple times, the raw material powder or the fired body can be homogenized and a high quality product can be obtained.

The sintering temperature is an important controlling factor when producing superconducting materials, and it is important that sintering proceeds only by solid-phase reaction without melting of the material during sintering, and that the material is formed by sintering. It is necessary to control the crystal growth of the composite oxide so that it does not become excessive. Therefore, the sintering must be carried out at a temperature that does not exceed the melting point of the sintered powder. However, if the sintering temperature is too low, sufficient sintering reaction will not be obtained, so at least
It is necessary to heat it to 00°C or higher. In addition, the sintering time is
- The longer the time is numerically, the more preferable the composition can be obtained, but in practice, about 1 hour to 50 hours is preferable.

Furthermore, for the same reason as the control of the sintering process described above, the management of the firing process should also be strictly controlled.

That is, if the firing temperature does not reach 500°C, the firing reaction will not proceed sufficiently and the desired composition will not be obtained.

On the other hand, as mentioned above, it is not preferable for the heating temperature to exceed the melting point of the raw material powder.

The multi-element complex oxide superconducting material as described above can also be grown as a thin film on a substrate by physical vapor deposition. In this case, the evaporation source may include each element forming the superconducting material itself, a powder mixture of each compound of these elements, a fired body obtained by mixing and firing these elements, or its powder, This sintered body powder or a sintered body obtained by sintering each of the above compound powders or a powder thereof can be used. Specific examples of physical vapor deposition include sputtering, electron beam, and ion plating.

In addition, the composition ratio of each element and/or oxygen partial pressure of the evaporation source may be adjusted and wiped according to the vapor deposition efficiency of each element so that the composition ratio of the composite oxide to be formed has an appropriate composition ratio. preferable. Furthermore, it is advantageous to use a substrate used for film formation that has a similar crystal structure to the composite oxide to be formed.

The present invention will be specifically explained below with reference to examples, but the following disclosure is only one example of the present invention, and does not limit the technical scope of the present invention.

Example: Commercially available Bi2O, powder, 5rC03 powder, CaCO3 powder, and CuO powder were mixed in the proportions shown in Table 1 below, ground/mixed to a particle size of 4 μm or less using a ball mill, and then press-molded at a pressure of 1000 kg/ci. did. The obtained molded body was sintered at 850° C. for 8 hours to obtain a bulk sample.

When the superconducting critical temperature of the sample prepared as shown in Table 1 was measured, the resistance of the sample began to decrease rapidly at 115.
Electrical resistance could no longer be detected at 100K. still,
The measurement of this critical temperature is carried out using Ag at both ends of the sample according to the standard method.
Electrodes were attached using conductive paste, and the test was carried out using a four-terminal method in a Taraviostat. Temperature was monitored using a calibrated Au(Fe)-Ag thermocouple. Further, although this sample was left in the air for 20 days after its preparation, no significant difference in superconducting properties was found in subsequent remeasurements.

Effects of the Invention As detailed above, the multi-element composite oxide superconducting material according to the present invention becomes a superconductor at a significantly higher critical temperature than conventional superconducting materials. Furthermore, this superconducting material is superior to conventional composite oxide-based superconducting materials in that its properties are maintained over a long period of time.

Thus, according to the present invention, a novel superconducting material having a stable and high critical temperature is obtained, so that the superconducting phenomenon can be utilized with economical cooling equipment. These superconducting materials according to the present invention can be formed into Josephson elements, 5QUI
D, can be applied to a wide range of fields such as superconducting magnets and various sensors.

Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (9)

[Claims] (1) Formula: Bi_2_−_x(Ca,Sr)_1_+_
xCu_2O_7_-_y [However, the ratio of Sr to Ca is 10 to 90 at%, and x and y are each 0≦
x≦1, 0<y≦1] A superconducting material characterized by mainly containing a composite oxide having a composition represented by the following. (2) The superconducting material according to the first claim, which has the formula: B
i_2_−_x(Ca,Sr)_1_+_xCu_2O
A superconducting material characterized by mainly containing a composite oxide having a composition represented by _7_-_y [where y is a number satisfying yx/2]. (3) The superconducting material according to the first claim or the second claim, which has the following formula: Bi_2_−_x(Ca,Sr)_1_+_xCu
_2O_7_-_y [However, the number satisfies x■1] A superconducting material characterized by mainly containing a composite oxide having the composition shown in the following. (4) The superconducting material according to any one of the first to third claims, wherein the formula: Bi_2_−_x(Ca,Sr)_1_+_xCu
_2O_7_-_y [However, the ratio of element Sr to Ca is 1:1 in atomic ratio] A superconducting material characterized by mainly containing a composite oxide having a composition shown in the following. (5) A method for manufacturing the superconducting material according to any one of claims 1 to 4, comprising:
a, a mixture of raw material powders selected from each element of Bi and Cu, and a compound containing at least one of the elements so as to contain all of the elements, or a fired mixture obtained by pulverizing the mixture after firing. 1. A method for producing a superconducting material, comprising at least one step of sintering body powder. (6) A method for manufacturing a superconducting material according to claim 5, characterized in that final sintering is performed after forming the raw material powder, sintered body, or sintered body powder. . (7) The method for producing a superconducting material according to claim 5 or 6, in which the raw material powder contains the Sr, Ca,
, Bi, and Cu oxide or carbonate. (8) The fired body or sintered body containing the composite oxide obtained by the method according to any one of claims 5 to 7 is used as a target and deposited on a predetermined substrate by physical vapor deposition. 1. A method for producing a superconducting thin film, which comprises growing a thin film. (9) The method of manufacturing a superconducting thin film according to claim 8, wherein the physical vapor deposition method includes a sputtering method or an ion plating method.