JPH0226832A - Production of superconducting material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing superconducting materials. More specifically, a novel manufacturing method that dramatically increases the temperature Tc (R=O) at which a superconducting material composed of a Di-Sr-Ca-Cu-0-based composite oxide superconductor exhibits perfect superconductivity. Regarding the method.

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 the amount of power generated. Furthermore, in the field of transportation equipment, it is expected to be used as a power source for maglev trains, electromagnetically propelled ships, etc., and in the fields of measurement and medicine, it is expected to be used in NMR 1π 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 also been proposed to use this element 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,
, Tc still remained at 23.2 K even in Ge.

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 possibilities for high-temperature superconductivity have widened (Bednorz, Mull).
er,” 2. Phys, B64 (1986) 189
”).

The oxide superconductor discovered by Bednotes and Muller et al. is (La, Ba) 2Cu 04. This oxide superconductor is called a K2NiF4 type oxide, and is different from the previously known perovskite type superconducting oxide. Although their crystal structures are similar, their TC is approximately 30, which is significantly higher than that of conventional superconducting materials.

Furthermore, in February 1987, 9
Y+Ba2CusOt-x showing the critical temperature of the class at 0
The discovery of a complex oxide has been reported in the newspapers, and the possibility of realizing non-low-temperature superconductors has suddenly increased.

Recently, raw materials are relatively cheap because rare earths are not used, and i -3r -Ca-Cu -0-based composite oxides,
Although it has been reported that Tc may exceed 100K, conventional manufacturing methods have not yielded a material whose electrical resistance becomes completely zero at Tc of 100K or more.

Problems to be Solved by the Invention Conventionally, Bi-3r-Ca-Cu-0-based superconducting materials have been generally sintered and produced under atmospheric pressure. The -Cu -0 based superconducting material had both phases, a phase exhibiting superconductivity at about 105 and a phase exhibiting superconductivity at about 80.

Therefore, the temperature at which the electric resistance of the entire superconducting material produced by the conventional method becomes zero is between 70 and 80℃, and YBa
Comparing 2Cu30 with the system, the temperature Tco at which superconductivity is exhibited is high, but the temperature Tc at which zero resistance is achieved (R=0) is low.

Therefore, an object of the present invention is to provide a method for manufacturing a Di-3r-Ca-Cu-0 based superconductor material consisting of a single phase that exhibits superconductivity at about 105%.

Means for Solving the Problems According to the present invention, the formula: (Bt+-x, Pt1J, (Srl-y, Cay
) JunOp-z (where m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=5+m+n, X satisfies Q<x<Q, 5, and y is 0.2 <y<0.8, and 2 represents a number satisfying -2≦Z≦2. above, 600℃ or above under ultra-high pressure of 100kb or less, 12
Provided is a method for producing a superconducting material, which comprises heating and sintering the material to a temperature of 00° C. or lower, and then reheating the superconducting material at a temperature of 350° C. or higher and lower than the melting point temperature.

Effect The method of the present invention is based on the formula: (B1+-x, Pbx)*(Sr+-y, Cay
)+*Cu+, Op+z (where m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=5+m+n, X satisfies Q<x<9.5, and y is 0 A superconducting material made of a composite oxide superconductor with a composition expressed as follows (2<y<0.8, and 2 represents a number satisfying -2≦2≦2) is produced by heating raw material oxide powder under ultra-high pressure. Its main feature is that it is manufactured by sintering.

That is, the main points of the present invention are: ■Replace a part of B1 with pb.

■Heating and sintering under ultra-high pressure It is 02 points.

It is known that in Bi-3r-Ca-Cu-0 superconductors, two types of phases coexist: a phase that exhibits superconductivity at about 80 and a phase that exhibits superconductivity at about 105. . Conventionally, Bi-8r-Ca-Cu-
A superconducting material consisting of a single phase of 0 series superconductor and 105 phase exhibiting superelectric properties has not been produced.

As a result of various studies, the present inventors found that 1. Bi-3r-Ca-Cu-0 based superconductor 8
By substituting a part of 1 with pb, the phase that exhibits superconductivity at about 110 K becomes stable. 2. The structure of the phase that exhibits superconductivity at about 110 K is stable under high temperature and high pressure. We discovered two facts:

In the method of the present invention, Pb, Bi, 5rSCa
By sintering raw material oxide powder containing Cu in a predetermined proportion under high pressure, a material consisting only of a phase that exhibits superconductivity at about 110 nm was created, and this material was further heat-treated again. By applying this method, a superconductor having a critical temperature Tc (R=0) indicating perfect superconductivity of 105 to 109, which is higher than that of conventional superconductors, is produced.

In the method of the present invention, under ultra-high pressure of 10b or more,
The above superconductor is sintered by heating to a temperature above .degree. 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 sintering pressure range was set to 10 kb or more and 100 kb or less. The preferred pressure range is 10-60 kb. The sintering temperature is 6
00 to 1200°C, preferably 900 to 1000°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 lower than 0° C., reheating has little effect and the desired superconductor cannot be obtained. Furthermore, when reheating is performed at a temperature higher than the melting point temperature, a phase exhibiting superconducting properties precipitates at 80°C.
A material consisting of a complete single phase cannot be obtained, and 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 ultra-high pressure of 10b to 100kb, but in this example, sintering in a low pressure range of about 1oOb requires - A belt-type ultra-high-pressure device shown in FIG. 1 was used for sintering under ultra-high pressure exceeding this using a boat-type 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. Raw material oxide powder 10. In this example, composite oxide powder was molded as described later.

Purity 3N PbO1B1□03.5rCO8, CaCO
3 and CuO powder, 47g and 185g, respectively.
150g, 100g and 120g were blended and mixed in a ball mill, followed by firing in the air at 800°C for 10 hours to produce a B1-Pb-5r-Ca-Ct, +-0 composite oxide. This composite oxide was finely crushed in a mortar to obtain a raw material powder. Next, 10 g of this raw material powder was taken, molded using a simple press, and housed 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 845° C. for 10 days under atmospheric pressure. As a result of compositional analysis, this sintered body has the following properties: (BIo, 8. Pbo, 2) 2 (Sro, S
, Cao, S) was confirmed to be a composite oxide superconductor corresponding to 4CU30x.

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 lOmA.

As a result, Tco is 115 and 108.8 K
It became zero resistance. 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=0
) was measured. Table 1 shows the manufacturing conditions and each Tco
, 'I'c (R=O).

Table 1 The results show that the method of the present invention provides high Tco and Tc(R
= 0) was confirmed to be effective for producing a superconducting material.

As described in the detailed description of the invention, according to the method of the present invention, the formula showing a high perfect superconducting critical temperature: (B++->l, PbII)4(Srl-y, C
ayLC11nOp+z, (where m is 6≦m≦10
, n satisfies 4≦n≦8, p=5+m+n, X satisfies Q<x<0.5, y satisfies 0.2<y<0.8, 2 satisfies -2≦ (representing a number satisfying 2≦2) It becomes possible to manufacture a superconducting material composed of a composite oxide superconductor having a composition represented 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 can be suitably applied to a wide range of fields such as Josephson elements, 5QUIDs (magnetometers), superconducting magnets, 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. , Figure 3 shows the resistance of the material produced by the method of the present invention.
FIG. 3 is a diagram showing temperature characteristics. [Main reference numbers] 1... Carbide piston, 2... Carbide die, 3...
・Pyro gasket, 4...Electricity ring, 5...MO plate, 6 ・-
-Na[l:1゜7...Carbon heater 8...Zr0z 9...Ceramics capsule, 10...Composite oxide powder compact

Claims (1)

[Claims] Formula: (Bi_1_-_x, Pb_x)_4(Sr_1_
−_y, Ca_y)_mCu_nO_p_+_z (where m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=6+m+n, x satisfies 0<x<0.5, y is 0 .2<y<0.8, and z represents a number satisfying -2≦z≦2. under ultra-high pressure of 10b or more and 100kb or less at 600℃ or more, 12
A method for producing a superconducting material, which comprises heating and sintering the superconducting material to a temperature of 00° C. or lower, and then reheating the superconducting material at a temperature of 350° C. or higher and lower than its melting point.