JPH02248319A - Production of oxide superconducting material - Google Patents

Abstract

PURPOSE:To obtain an oxide superconducting material having a high superconductivity transition temp. with high reproducibility by using Sr2CuO3, Ca2CuO3 and the oxides of Tl, Pb and Cu as starting materials. CONSTITUTION:SrCO3 is mixed with CuO and calcined in the air to obtain Sr2CuO3. CaCO3 is mixed with CuO and calcined in the air to obtain Ca2CuO3. The obtd. Sr2CuO3 and Ca2CuO3 are mixed with PbO and CuO into an org. solvent, dried, calcined in the air, pulverized and dried to obtain calcined powder. This calcined powder is dry-mixed with Tl2O3, molded and sintered in vacuum to obtain an oxide superconducting material having >=120K superconductivity transition temp. The oxide is represented by a formula Tl9.6Pb9.6Sr2Ca2Cu2 Oy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing oxide superconducting materials with a high superconducting transition temperature (T).

Conventional technology Superconducting materials have properties not found in other materials, such as 1) zero electrical resistance, 2) complete diamagnetism, and 3) the Dia-Sefson effect, and have already become superconducting. It is used in magnets, 5QUID, etc. Also in the future,
It is expected to have a wide range of applications, including power transportation, power generators, fusion plasma confinement, magnetic levitation trains, magnetic shielding, and high-speed computers. Conventionally, the material is Nb5G
Metal-based superconductors such as e were used. However, in metallic superconductors, the highest To is 23
In actual use, it had to be cooled using expensive liquid helium and a large-scale insulation device, which was a major industrial problem. For this reason, research has been underway to find materials that become superconductors at higher temperatures.

In 1986, a high T of about 40 was developed by Badnorz and Muller. An oxide-based superconducting material (L a +−zs
r z) Nitrogen Cu Oll was discovered, and since then YB
a*Cu5Ox, B i-8r-Ca-Cu-0, T
Superconducting transitions at higher temperatures have been reported in I-B a-Ca-Cu-0 and the like.

It is expected that the higher To is, the easier the cooling will be, and the critical current density and critical magnetic field will be larger when used at the same temperature, and the range of applications will be expanded.

The present invention covers 100 of these new oxide superconductors.
T 1Pb-, which is one of those with To greater than or equal to
The present invention relates to a method for producing 8r-Ca-Cu-0.

Problem 122 to be solved by the invention T, la, sP bs, ss
rac&mCu5Ov is produced by using oxides of the respective elements as starting materials, enclosing a molded body in a closed container such as a quartz tube, and firing it at about 900°C.
(1, Mu, S@1) pHanian, C, IC, Torardl, Gopolakrlshnan.
Lachryceton), P, L, 0il (j”i)
, J, (j, Calabrese).

T, R, MU5kev (as ex-), R, B,
Fllppen and Tom, Cao,
Sleight, 5science (
(1918) vol, 24LL249 (1918
)). However, Sr and Ca oxides easily react with carbon dioxide gas to form carbonates, which not only inhibits the reaction during compound formation, but also increases the internal pressure inside the sealed container during firing, causing rupture in containers as simple as quartz. It's possible. Therefore, during production, contact with carbon dioxide gas had to be avoided as much as possible.

Means for solving the problem Sr*Cu0s1 Ca*Cu0ss and Ti,
Using Pb1 cu oxide as a raw material, Ti, Pb
Producing an oxide superconducting material consisting of xsr% Ca and Cu.

According to the present invention, even if the mixing, granulation, and molding steps are performed in an atmosphere containing carbon dioxide gas, the reproducibility is <120%.
It is possible to manufacture a material having a To of more than .

Example Using 5rCOs and CuO with a purity of 99% or more as raw materials, they were weighed and weighed so that the molar ratio of Sr:Cu was 2=1.
Mixed and baked in air at 900°C for 20 hours, S r *
We synthesized CuOs. In addition, CaC with a purity of 99% or more
Ca*CuOs was synthesized in the same manner using O5 and CuO by firing at 950°C for 20 hours. It was confirmed by X-ray diffraction that single-phase powders were obtained in each case. Next, the obtained Sr snow Cu0ss Caucus
s and each powder of PbO1CuO with a purity of 99% or more, p
b: Sr: Ca: CU molar ratio is 0.5: 2:
Weigh the powder so that the ratio is 2:3, and add 20% ethanol to the powder using a vibration mill using a Zr09 pole with a diameter of 2mm.
The mixture was pulverized and mixed for 1 hour using m1 as a dispersion medium. After mixing,
The entire amount including the dispersion medium was dried in a dryer at 120°C. After calcining the obtained powder in air at 750°C for 5 hours,
Grind for 30 minutes using a vibrating mill in the same manner as described above.
℃ and then add purity 99 to the resulting calcined powder.
% or more of Tl5On, TI:Pb: Sr: Ca:
The molar ratio of Cu is 0. 7: 0゜5: 2: 2:
3 and dry mixed. 0 of this powder
．． 6g in a 18mm x 4mm mold to 500kg/
The molded body was uniaxially pressed at a pressure of 1.5 cm. This molded body was wrapped in gold foil and vacuum sealed in a quartz tube, and then heated to 890°C in an electric furnace.
The mixture was baked for 5 hours and cooled. The temperature increase/decrease rate is 30 in both cases.
The temperature was set at 0°C/h. A silver electrode was attached to the sample, and the temperature change in electrical resistance was measured using the usual 4-terminal method.
Measured from K to 77K. Resistance decreases metallically, 1
It started to drop sharply at 24 and reached zero at 121. In addition, when we measured the temperature change in magnetic susceptibility when cooled under an external magnetic field of 100 e using a superconducting quantum interference magnetometer (SQUID), it showed diamagnetic properties from 123 K, and the magnetic susceptibility at 4 K was 0.014 emu/ It was g.

Comparative example 1 1g degree 99% or more +7) T l * Os, P
b OlS r 0ssCabs, CuO powder,
Tl: pb: Sr:Ca:Cu composition ratio (molar ratio)
is 0. 7: o.

They were weighed and dry mixed in a ratio of 5:2:2:3. This powder was press-molded in the same manner as in the above example.

Note that all of the above steps were performed in a glow box dripping with argon. This molded body was fired under the same conditions. The resistance of the obtained sample decreased metallically, starting to drop sharply at 123 and reaching zero at 118. Further, the magnetic susceptibility was 122 or less, indicating diamagnetic properties, and the magnetic susceptibility at 4K was 0.010 emu/g. The reason why both the critical temperature and the magnetic susceptibility were not smaller than that of the sample produced according to the present invention is that the homogeneity was not improved through the mixing/pulverizing process.

Comparative Example 2 Tlll0a, PbO1Sr's, C with purity of 99% or more
A sample was prepared in the same manner as in the example using aOa and CuO as raw materials. After firing, cracks had appeared in the quartz tube. The resistance of the obtained sample decreased metallically, starting to drop sharply at 118 and reaching zero at 105. Further, the magnetic susceptibility was 120 or less, indicating diamagnetic properties, and the magnetic susceptibility at 4K was 0.00 Elemu/g. The reason why only smaller values of critical temperature and magnetic susceptibility were obtained than the samples of Examples of the present invention and Comparative Example 1 is that SrO* and Cafe react with carbon dioxide gas in the air due to the treatment in air. This is thought to be due to inhibition of the reaction during compound production.

Effects of the Invention According to the present invention, S r2c u 0s1Carc u
By using oxides of Oa and T Is P bs Cu as raw materials, even if the mixing, granulation, and molding steps are performed in an atmosphere where carbon dioxide gas exists, the product has a To of 120 or more with good reproducibility. Ti, Pb.

Oxide superconducting materials consisting of 5rzCa and Cu can be produced.

Claims (1)

[Claims] Sr_2CuO_3, Ca_2CuO_3, and Ti
, Pb, and Cu oxides as raw materials.