JPH0226827A - Method for manufacturing superconducting materials - Google Patents

Abstract

PURPOSE:To obtain a Ti-Ba-Ca-Cu-O type superconducting material consisting of a specified compsn. comprising a single phase exhibiting superconductivity at about 120K by sintering powdery oxide as raw material by heating under extremely high pressure, then reheating at a specified temp. or above and below melting temp. CONSTITUTION:Powder of oxide as raw material contg. Pb, Ti, Ba, Ca and Cu in specified proportions is sintered by heating at 600-1200 deg.C under an extremely high pressure of 10b-100kb. The sintered product is then reheated at >=350 deg.C and below m.p., thus, strains and defects in the crystal are eliminated and a superconducting material constituted of a compound oxide supercondutor having superconductivity and expressed by the formula is obtd. In the above-described superconducting material, a phase exhibiting superconductivity at about 120K is stabilized by replacing a part of Ti of the Ti-Ba-Ca-Cu-O type superconductor with Pb and heating and sintering the material under an extremely high pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing superconducting materials. More specifically, a new manufacturing method that dramatically increases the temperature Tc (R=O) at which a superconducting material composed of a TI-Ba-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 power generation. 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 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 is believed that a group of substances with an A-15 type crystal structure exhibit a relatively high Tc (superconducting critical temperature); Become N
Even in b3Ge, 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 for Nb and Ge for a long period of time, but in 1986 Bednautz and Mueller et al. With the discovery of composite oxide-based 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 Mueller is (La, 5r)2Cu04, and this oxide superconductor is called a KJiF4 type oxide.
Although its crystal structure is similar to that of previously known perovskite-type superconducting oxides, its Tc is approximately 30, which is significantly higher than that of conventional superconducting materials.

Furthermore, in February 1987, 9
Y, Ba2CuaOt-χ, which shows 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, TI-Ba-Ca-Cu-0-based composite oxides, which do not use rare earth elements and are relatively inexpensive as raw materials, have been developed.
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, TI-Ba-Ca-Cu-0 based superconducting materials are generally sintered and produced under atmospheric pressure. The Cu-0-based superconducting material contained a mixture of both a phase exhibiting superconductivity at about 120 and a phase exhibiting superconductivity at about 90.

Therefore, the temperature at which the electric resistance of the entire superconducting material produced by the conventional method becomes zero is between 80 and 90 degrees, and YBa
Compared to the 2Cu30□ system, the temperature Tco at which superconductivity was exhibited was higher, but the temperature Tc at which zero resistance was achieved (R=O) was lower.

Therefore, an object of the present invention is to provide a method for producing a TI-Ba-Ca-Cu-0 based superconducting material consisting of a single phase showing superconductivity at about 120 nm.

According to the invention, the formula: (T1+-X,PbX)4(Bal-y+cay
Lcunop+z (where m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=6+m+n, X satisfies Q<x<0.5, y satisfies 0.2<y< 0.8, and 2 represents a number satisfying -2≦2≦2) In a method for manufacturing a superconducting material made of a composite oxide superconductor having a composition expressed by 600℃ or more under ultra-high pressures below, 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 uses the formula: (Tll-+++PbX)i(Bat-y, Ca
y)+aCunOp+g (where m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=5+m+n, X satisfies Q<x<9.5, and y satisfies 0.2< A superconducting material made of a composite oxide superconductor with a composition represented by Its main feature is that it is manufactured by

That is, the main points of the present invention are: ■Replacing part of TI with pb.

■Heating and sintering under ultra-high pressure There are two points.

It is known that in TI-Ba-Ca-Cu-0 superconductors, two types of phases coexist: a phase that exhibits superconductivity at about 90 and a phase that exhibits superconductivity at about 120. . Conventionally, sintering in a normal atmospheric atmosphere or an oxygen atmosphere at about atmospheric pressure
A superconducting material consisting of a single phase of a u-0 based superconductor exhibiting superelectric properties at 120 nm has not been produced.

As a result of various studies, the present inventors have found the following: 1. T1 of TI-Ha-Ca-Cu-0 based superconductor
By substituting part of the phase with pb, the phase that exhibits superconductivity at about 120 K becomes stable. 2. The structure of the phase that exhibits superconductivity at about 120 is stable under high temperature and high pressure. The following two facts were discovered.

In the method of the present invention, PbSTl, Ba, Ca
By sintering raw material oxide powder containing a predetermined proportion of 5Cu under high pressure, a material consisting only of a phase that exhibits superconductivity at about 120 nm is created, and this material is further heat-treated again. By doing so, a superconductor having a critical temperature Tc (R=O) indicating perfect superconductivity is 117, which is higher than conventional superconductors.

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=0) 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. In addition, when reheating is performed at a temperature higher than the melting point temperature, a phase exhibiting superconducting properties at 90°C precipitates,
A substance consisting of a complete single phase cannot be obtained and Tc (R=0) 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 using the method of the present invention, the raw material oxide powder is sintered under an ultra-high pressure of 10 kb to 100 kb, but in this example, sintering in a low pressure range of about 100 kb A belt-type ultra-high pressure device shown in FIG. 1 was used for sintering under 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. Moreover, 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 NaC16 and ZrOH8. 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.

BaCO3 and CuO powder with a purity of 3N at 19.7
After mixing in a ball mill and baking at 900°C for 8 hours in an oxygen stream, Ba
-Cu-0 composite oxide was produced. T in this composite oxide
l2O3 powder 18.3x, PbO powder 4.5x, CaO
Add 16.8 g of powder and heat at 910°C in an oxygen stream for 10
TI-Pb-Ba-Ca-Cu
-0 composite oxide was produced. This composite oxide was finely crushed in a mortar to obtain a raw material powder. Next, add this raw powder to 10
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 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, this sintered body has (TIo, 8+ pbo, 2) 2 (Bao, s
, l:'ao, S) It was confirmed that it is a composite oxide superconductor corresponding to 4Cu30x.

The composite oxide superconductor obtained in this way is cut,
A sample measuring 3 mm x 1 mm x 15 m was prepared, and its resistance-temperature characteristics were measured in liquid N2 by a normal four-terminal method. The measurement current is 10 mA.

As a result, Tco was 125 and zero resistance at 117. 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 The results show that 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 is: (Tll-M, PbX)4(Bat-y, Cay
)acunop, z (where m satisfies 6≦m≦10, n satisfies 4≦n≦8, p=6+m×n, X satisfies Q<x<Q, 5, y is 0 .2< y <Q, satisfies 3, 2 is -2≦2
It is possible to manufacture a superconducting material composed of a composite oxide superconductor having a composition expressed by the following (representing a number satisfying ≦2).

In this way, a high (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... energizing ring, 5... MO board, 6...
NaC11 7... Carbon heater 8... ZrO□ 9... Ceramic capsule, 10... Composite oxide powder compact

Claims (1)

[Claims] Formula: (Tl_1_-_x, Pb_x)_4(Ba_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 it at a temperature of 350°C or higher and lower than the melting point.