JPH0226831A - Production of superconducting material - Google Patents

Abstract

PURPOSE:To obtain a superconducting material of Bi-Sr-Ca-Cu-O, etc., type consisting only of a single phase exhibiting superconductivity at about 105K by sintering powder of oxide as raw material by heating under an extremely high pressure, and reheating the sintered product at below melting temp. CONSTITUTION:A superconducting material cansisting of a compound superconductor having a compsn. expressed by the formula is prepd. under conditions described hereunder. Namely, when the superconductor is a Bi-Sr-Ca-Cu-O type supercondutor, powder of Bi2O3, SrCO3, CaCO3 and Cu are mixed in a proportion so as to obtain a compsn. expressed by the formula. Said mixture is mixed in a ball mill, then calcined in O2-stream to obtain thus a Bi-Sr-Ca-Cu-O type compound oxide, which is pulverized again to obtain thus the raw material powder. Then, obtd. raw material powder is formed with a simple press and encapsulated in capsules. After sintering the capsules by heating at 600-1200 deg.C under 10b-100Kb, and reheated at 350 deg.C-blow m.p. Thus, an above-described superconductor is obtd. A Ti-Ba-Ca-Cu-O type compound oxide superconductor may be prepd. by a similar method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing superconducting materials. More specifically, Bi-5r-Ca-Cu-0 system and Tl
- Temperature Tc at which a superconducting material composed of a Ba-Ca-Cu-0 based composite oxide superconductor exhibits perfect superconductivity
This invention relates to a new manufacturing method that dramatically increases (R=O).

Background of the Invention Superconductivity is a phenomenon in which an object exhibits complete diamagnetic properties under certain conditions, and no potential difference appears even though a finite steady current is flowing inside the object. Substances in this state are called superconductors, and various applications have been proposed for them as transmission media with no power loss.

For example, if superconducting technology is applied to power transmission, it will be possible to significantly reduce the approximately 7% unavoidable transmission loss that currently occurs with power transmission. Furthermore, superconducting power storage is said to be the most efficient power storage method known today.

Furthermore, its application to electromagnets for generating high magnetic fields was realized at the earliest, and the field of use is extremely wide. In the field of power generation technology, along with MHD power generation and electric motors, it is expected to be a technology that advantageously promotes the realization of nuclear fusion reactions, which are said to consume more power than a power generator. Furthermore, in the field of transportation equipment, it is expected to be used as a power source for magnetic levitation trains, electromagnetically propelled ships, etc., and in the field of measurement and medicine, it is expected to be used in NMR, pi-meson therapy, high-energy physical experiment equipment, etc.

Furthermore, when multiple superconductors are weakly bonded, the Josephson effect, which is a macroscopic manifestation of a quantum effect, can be observed. A tunnel junction type Josephson device that utilizes this effect is expected to be an extremely high-speed and low-power switching device because the energy gap of the superconductor is small. Furthermore, since the Josephson effect on electromagnetic waves and magnetic fields appears as a sharp quantum decrease, it has been proposed and suggested that this element be used as an ultra-sensitive sensor for magnetic fields, microwaves, radiation, etc.

In this way, superconducting technology is said to be an important technology, along with the practical application of nuclear fusion, as a technology that responds to the social need to improve power efficiency in all fields.

By the way, in conventional technology, superconducting phenomena have been observed only at extremely low temperatures. In other words, among conventionally developed superconducting materials, it has been confirmed that a group of substances with an A-15 type crystal structure exhibit a relatively high Tc (superconducting critical temperature), but Nb, which is said to have the highest Tc,
Even in 3Ge, Tc remained at 23.2 K.

On the other hand, despite various efforts, the superconducting critical temperature Tc of superconducting materials could not exceed 23K of Nb3Ge for a long period of time, but in 1986, Bednautz and Muller et al. With the discovery of physical superconducting materials, the possibility of high-temperature superconductivity has greatly opened up (Bednorz, Mull
er,”Z, Phys, B64 (1986) 189
”).

The oxide superconductor discovered by Bednotes and Muller et al. is (La, Ba), CuO4. Although its crystal structure is similar to that of superconducting materials, its Tc is significantly higher than that of conventional superconducting materials, at about 30.

Furthermore, in February 1987, 9
Y lBa2Cus O1 showing the critical temperature of the class at 0
- It was reported in the newspaper that an x-based complex oxide had been discovered.
The possibility of realizing non-low temperature superconductors is rapidly increasing.

Recently, since rare earths are not used, the raw materials are relatively cheap, and i-3r-Ca-Cu-0 and Tl-Ba
-Ca-Cu-0 complex oxide has Tc of 100K
Although it has been reported that the electrical resistance may exceed 100, conventional manufacturing methods have not yielded a material whose electrical resistance becomes completely zero when the resistance exceeds 100.

Problems to be Solved by the Invention Conventionally, Bi-3r-Ca-Cu-0 system and Tl
-Ba -Ca-Cu-〇-based superconducting materials are generally sintered and produced under atmospheric pressure, but B
The i-3r-Ca-Cu-0 based superconducting material is approximately 10
Both phases, a phase showing superconductivity at about 5 and a phase showing superconductivity at about 80, were mixed. In addition, the Tl-Ba-Ca-Cu-0-based superconducting material produced by the conventional method contains both a phase that exhibits superconductivity at about 120 and a phase that exhibits superconductivity at about 90. was.

Therefore, the temperature at which the electric resistance of the entire superconducting material produced by the conventional method becomes zero is 70 to 80 and 80 to 90, respectively, and when comparing YBa and Cu30 systems, the temperature Tco at which superconductivity is exhibited is Although high, the temperature Tc (R=O), which indicates perfect superconductivity, remained almost the same or was even lower.

Accordingly, the present invention provides a Bi-3r-Ca-Cu-0 system consisting of a single phase of only a phase exhibiting superconductivity at about 105 and a Tl-3r-Ca-Cu-0 system consisting of a single phase of only a phase exhibiting superconductivity at about 120. The object of the present invention is to provide a method for manufacturing a Ba-Ca-Cu-〇-based superconductor.

Means for Solving the Problems According to the present invention, the formula: α4(βI−X+ Ca,)+aCuw Opay
(Here, α is Di or Tl, β is Sr when α is Bi, and Ba when α is Tl, m satisfies 6≦m≦10, and n is 4≦n≦ 8, p=6+m+n, X satisfies 0.2<x<0.8, and y represents a number satisfying -2≦y≦2). In the method of manufacturing a superconducting material, raw material oxide powder is heated to 600 to 1 under ultra-high pressure of 10 b or more and 100 kb or less.
A method for producing a superconducting material is provided, which comprises heating to a temperature of 200° C. or lower for sintering, and then reheating at a temperature of 350° C. or higher and lower than the melting point temperature.

Effect: The method of the present invention has the following formula: α4(βI-)1. Ca, 1) Jurl o, +
y (where α is B1 or Tl, β is α is Bi
When α is Tl, it is Sr, when α is Tl, it is Da, m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=6+m+n, and X is 0.2<x <0.8, and y represents a number satisfying -2≦y≦2) A superconducting material consisting of a composite oxide superconductor with a composition expressed as follows is obtained by sintering raw material oxide powder under ultra-high pressure. Its main feature is that it is manufactured using

In the 81-3r -Ca-Cu -0-based superconductor, there are two phases: a phase that exhibits superconductivity at about 80 K and a phase that exhibits superconductivity at about 105 K.
It is known that in the -Cu -0-based superconductor, two types of phases coexist: a phase that exhibits superconductivity at about 90 and a phase that exhibits superconductivity at about 120. Conventionally, when sintering is performed in a normal atmospheric atmosphere or an oxygen atmosphere at about atmospheric pressure, Bi-Sr-Ca-Cu-0-based superconductors are used for 105, Tl-Ba-Ca-Cu-
In 0-series superconductors, a phase exhibiting superelectric properties at 120,
Superconducting materials consisting of a single phase have not been created.

As a result of various studies, the present inventors found that B1-3r-Ca
-Cu-○ superconductor phase showing superconductivity at 105 and Tl -Ba-Ca-Cu -0 system superconductor phase 12
It was discovered that the phase structure exhibiting superelectric properties at zero is more stable under high temperature and high pressure.

In the method of the present invention, in the process of proceeding with the sintering reaction of the raw material oxide powder for each of the above-mentioned superconductors, the above-mentioned substances are placed in an environment of high temperature and high pressure, thereby achieving superconductivity at 105 or 120. By creating a material consisting only of the phases shown and subjecting this material to heat treatment again,
The critical temperature TC (R=0) indicating perfect superconductivity is 100 to 1
A superconductor having a higher superconducting critical temperature Tc (R=0) than conventional superconductors, such as 0.05 or 100 to 111, is produced.

In the present invention, in order to synthesize the above superconductor, it is necessary to heat it to 600° C. or higher under ultra-high pressure of 10 b or higher. If the pressure during sintering is less than 10b, the effect of sintering under ultra-high pressure will not be apparent, and Tc (R=0) will decrease.

Although a higher pressure is preferable, the practical pressure range is up to 100 kb even if an ultra-high pressure apparatus used for diamond synthesis is used. Therefore, the pressure range for sintering should be set to 10b or more, 100
KB or less. Preferred pressure range is 10kb to 60k
It is b. The sintering temperature is 600°C to 1200°C, preferably 870°C to 950°C, more preferably 900°C. At sintering temperatures below 600° C., a completely single-phase material cannot be obtained and Tc (R=O) decreases.

Materials sintered under ultrahigh pressure have distortions and defects in their crystals, so they do not exhibit superconducting properties as they are. By reheating this material at a temperature of 350° C. or higher and lower than its melting point, a material that exhibits superconductivity can be obtained without distortions and defects in the crystal. Reheating temperature is 35
If the temperature is below 0°C, distortions and defects in the crystal cannot be removed sufficiently, and if reheated at a temperature above the melting point, a phase exhibiting superconducting properties will precipitate at 80°C, making it impossible to obtain a completely single-phase material. First, Tc (R=O) decreases.

EXAMPLES The present invention will be specifically explained below using examples, but these examples are merely illustrative of the present invention and do not limit the technical scope of the present invention in any way.

When producing a superconducting material by the method of the present invention, the raw material oxide powder is sintered under an ultra-high pressure of 10 b to 100 kt), but in this example, sintering in a low pressure range of about 100 b A belt-type ultra-high pressure device shown in FIG. 1 was used for sintering under an ultra-high pressure exceeding that of a general hot press.

FIG. 1 shows that when producing superconducting materials by the method of the present invention,
FIG. 1 is a schematic diagram of a belt-type ultra-high pressure device used to produce a composite oxide sintered body. This ultra-high-pressure cell is a cell normally used when synthesizing diamond, and the raw material oxide powder contained in a ceramic capsule 9 is compressed with a carbide piston 1 in a carbide die 2 while a carbon heater It is heated at 7. Electric power is supplied to the carbon heater 7 from the energizing ring 4 via the Mo plate 5. Further, the pressure between the carbide piston 1 and the carbide die 2 is sealed by a pyro gasket 3, and the heat of the carbon heater 7 is insulated by NaC 16 and ZrO□8. Furthermore, NaC16 also functions as a pressure medium.

FIG. 2 is an enlarged view of the sample portion of FIG. 1.

The capsule 9 is made of ceramic that does not react with the sample, and is surrounded by a carbon heater 7. In this example, the raw material oxide powder 10 was formed by molding a composite oxide powder as described later.

Example 1 B1-3r-Ca
-Cu-0 composite oxide was produced. This composite oxide was finely crushed in a mortar to obtain a raw material powder. Next, this powder was
g, molded with a simple press, and stored in a capsule 9.

Capsule 9 was pressurized to 10 kb using an ultra-high pressure device and subsequently heated at 900° C. for 30 minutes. The obtained sintered body was black in color and had a dense structure. This sintered body was reheated at 820° C. for 12 hours under atmospheric pressure. As a result of compositional analysis, it was confirmed that this sintered body was a composite oxide superconductor corresponding to Bi25r2Ca2Cu30)l.

The composite oxide superconductor obtained in this way is cut,
Create a sample of 3 mm x 1 mm x 15 mm,
The resistance-temperature characteristics were measured in liquid N2 using the usual four-terminal method. The measurement current is 20 mA.

As a result, a sudden decrease in resistance was observed at 110, and at 105
Full superconducting properties were observed in the Figure 3 shows the resistance-temperature characteristics of this material.

Next, using the above raw material powder, the superconducting critical temperature Tco of a composite oxide sintered body produced by changing the sintering pressure/temperature and reheating temperature, and the temperature Tc at which the resistance becomes completely zero (R=O
) was measured. Table 1 shows the manufacturing conditions and each Tco
, Tc (R=0).

Table 1 Example 2 Purity 3 N (DBa 20 g and 24 g of CuO powder were blended, mixed in a ball mill, and fired at 900° C. for 8 hours in an oxygen stream to obtain Ba
-Cu-0 composite oxide was produced. Add 23g of Tl2O3 powder and 17g of CaO powder to this composite oxide, and add acid!
Calcination was performed at 910°C for 10 hours in an air stream to obtain Tl-C
An a-Ba-Cu-0 composite oxide was produced. This composite oxide was finely crushed in a mortar to obtain a raw material powder. Next, 10 g of this powder was taken, molded using a simple press, and housed in a capsule 9.

Capsule 9 was pressurized to IQkb using an ultra-high pressure device and subsequently heated at 950° C. for 30 minutes. The obtained sintered body was black in color and had a dense structure. This sintered body was reheated at 920° C. for 10 hours under atmospheric pressure. As a result of compositional analysis, it was confirmed that this sintered body was a composite oxide superconductor corresponding to T1□Da, Ca2Cu, and OX.

The composite oxide superconductor obtained in this way is cut,
Create a sample of 3 mm x 1 mm x 15 mm, and
The resistance-temperature characteristics were measured in liquid N2 by the @son method. The measurement current is 20 mA.

As a result, a rapid decrease in resistance was observed at 120, and at 110
Full superconducting properties were observed in the Figure 4 shows the resistance-temperature characteristics of this material.

As a result, the method of the present invention provides high Tco and Tc(R
=O) was confirmed to be effective for producing superconducting materials.

As described in detail, when the method of the present invention is followed, the formula showing a high perfect superconducting critical temperature: C4(βI-1+1 CaX)+aCuB Opa
y (where α is Bi or Tl, β is α is Bi
When , it is Sr, when α is Tl, it is Ba, m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=5+m×n, and X is 0.2. <x<0.8, and y represents a number satisfying -2≦y≦2) It becomes possible to manufacture a superconducting material composed of a composite oxide superconductor having a composition expressed by the following.

Because such a high and stable superconducting critical temperature can be obtained,
The superconducting material obtained by the method of the present invention includes a Josephson element, a 5QUID (magnetometer), a superconducting magnet,
It can be suitably applied to a wide range of application fields such as infrared sensor elements and motors.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an example of an ultra-high pressure device and cell configuration used in carrying out the method of the present invention, and FIG. 2 is an enlarged view of the portion near the sample in FIG. 1. , FIG. 3 and FIG. 4 are diagrams showing the resistance-temperature characteristics of the superconducting material produced by the method of the present invention. [Main reference numbers] 1... Carbide piston, 2... Carbide die, 3...
・Pyro gasket, 4...Electricity ring, 5...Mo plate, 5---
NaC1゜7...Carbon heater 8...2rO2 9...Ceramic force pressenope 10...Composite oxide powder compact

Claims (1)

[Claims] Formula: α_4(β_1_−_x, Ca_x)_mCu_n
O_p_+_y (where α is Bi or Tl, β is Sr when α is Bi, and B when α is Tl)
a, m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=6+m+n, x satisfies 0.2<x<0.8, y satisfies -2≦y In a method for manufacturing a superconducting material made of a composite oxide superconductor having a composition represented by ≦2, raw material oxide powder is heated at 600° C. or higher under an ultra-high pressure of 10 b or more and 100 kb or less, 12
A method for producing a superconducting material, the method comprising heating to a temperature of 00°C or lower to sinter, and then reheating at a temperature of 350°C or higher and lower than the melting point temperature.