JPH04170316A - Production of oxide superconducting material - Google Patents

Abstract

PURPOSE:To effectively improve the critical temp., superconductor integration rate, etc., at the time of producing an oxide superconducting material having a crystal structure in which the first, second and third layers of specified composition are successively laminated by quenching or heat-treating the material in an inert gas. CONSTITUTION:The first layer consisting of an octahedron with copper atom at the center and oxygen atom at the apex and the second layer consisting of an octahedron with lead atom or copper atom at the center and oxygen atom at the apex are laminated so that the oxygen atom at the apex is used in common. The third layer consisting of the oxygen atom in common between the second layers, an alkaline-earth element (e.g. Sr) and a rare-earth element (e.g. La) is laminated on the second layer to produce an oxide superconducting material. In this case, quenching or heat treatment in an inert gas is applied to obtain an oxide superconducting material excellent in superconductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an oxide superconducting material having a high superconducting transition temperature.

[Prior Art] Superconducting materials have the following properties: 1) They have zero electrical resistance, 2) They are completely diamagnetic, and 3) They have the Josephson effect.
It has properties not found in other materials, and is used in power transportation, generators, etc.
It is expected to have a wide range of applications, including fusion plasma confinement, magnetic levitation trains, magnetic shielding, and high-speed computers.

NbXP is currently used as a practical material.
There are metal-based materials such as Nb, NbTi, and NbaSn.

However, in metallic superconductors, the zero resistance temperature (Tc)
At its highest, the temperature was around 23, and 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, efforts have been made to find materials that become superconductors at higher temperatures.

In 1986, Bednorx and Müller discovered an oxide-based superconducting material (LaBa2CUO) with a high zero resistance temperature (Tc) of about 30 (J, G, Bednorx and K,
A, Muller, 2゜Phys, B64 (
1986) 189), thereafter YBa2Cu30
, B1-8r-Ca-Cu-0, Tl-Ba-Ca-
Superconducting transitions at higher temperatures have been reported in Cu-0 and the like.

The higher the zero resistance temperature (Tc), the easier the cooling becomes.
Furthermore, the critical current density and critical magnetic field are expected to increase when used at the same temperature, and the range of applications is expected to expand. For this reason, much research is currently being conducted on the manufacturing methods, physical properties, applications, etc. of these materials.

[Problem to be solved by the invention] As one of the oxide-based superconducting materials, there is a first layer consisting of an octahedron with a copper atom at the center and an oxygen atom at the apex, and a lead or copper atom at the center at the apex. a second layer consisting of an octahedron in which oxygen atoms are arranged on the vertices, and the oxygen atoms shared by the second layer and the alkaline earth element and the rare earth element. An oxide superconducting material (Pb/Cu) having a crystal structure in which the third layer is formed by sequentially stacking the third layer, the second layer, and the third layer.
rLaCuO was discovered, but its critical temperature is zero resistance temperature (Tc) (onset) = 28, which exceeds the highest value (23 K) of zero resistance temperature (Tc) of metallic superconductors. (S, Aaachi.

K, 5etsune an+I K, Wasa,
Jpn, J, Appl, Phys, 29
(1990) 890).

In order to solve the problems of the prior art described above, the present invention aims to solve the problems of the prior art described above.
b/Cu) 5rLaCuO and (Pb/Cu)
(Ba/Sr/Ca) (Ln/Y) Cub, (where Ln is a rare earth) Oxide superconductor that can improve the superconducting properties such as the critical temperature and superconducting volume fraction of oxide superconducting materials. The purpose is to provide a method for manufacturing materials.

[Means for Solving the Problems] In order to achieve the above object, the method for producing an oxide superconducting material of the present invention includes: A second layer consisting of an octahedron with a lead atom or a copper atom at the center and an oxygen atom at the apex is stacked so as to share the oxygen atom at the apex, and the oxygen atom is shared by the first layer and the second layer. In the production of an oxide superconducting material having a crystal structure in which the third layer is composed of an alkaline earth element and a rare earth element, and the third layer, second layer, and third layer are sequentially laminated, quenching or inert It is characterized by including a step of heat treatment in a gas.

[Function] According to the configuration of the method of the present invention described above, when producing an oxide superconducting material having a crystal structure in which a first layer, a second layer, and a third layer are sequentially laminated, the material is rapidly cooled or in an inert gas. Since heat treatment is performed, superconducting properties such as critical temperature and superconducting volume fraction can be effectively improved.

[Example] The present invention will be explained in more detail below using an example.

The inventors have proposed (Pb/Cu) 5rLaCu, O and (Pb/Cu) (Ba/Sr/Ca) (Ln/Y)
As a result of studying the manufacturing method of Cub, (Ln being a rare earth element), it was found that its critical temperature could be improved by rapid cooling operation or heat treatment in an inert gas.

In the method of the present invention, the rapid cooling is preferably performed at a cooling rate of 50° C./min or more. The heat treatment in an inert gas is preferably performed at 350 to 900'C in a gas such as helium gas, argon gas, or nitrogen gas. The heat treatment time varies depending on the size of the sample, but is preferably about 1 minute for thin films and about several hours for molded products.

Next, an experimental example will be explained.

Example 1 As starting materials, PbQ, La2 with a purity of 99.5% or more
03, S rco3 and CuO powders were used.

The blending composition is (PbQ, 6 CuO, 5) S r La
CuOy and 2mm diameter zirconia (
1 using ZrO2) balls and using ethanol as a dispersion medium.
Mixed for an hour.

After the mixing was completed, the entire amount including the dispersion medium was dried in a dryer at 120°C, and the obtained powder was calcined in air at 800°C for 5 hours. The mixture was ground and mixed for 1 hour using a vibrating mill in the same manner as described above, and then dried at 120°C. 0.4 of this powder
g to 600kg/cnf in a 15+nm x 5mm mold
Uniaxial pressure molding was carried out at a pressure of .

This molded body was heated in an electric furnace at 1000'C in an oxygen atmosphere for 2 hours.
Baked for an hour. Two types of cooling were performed: slow cooling at 100° C./h in an oxygen atmosphere and rapid cooling in which the material was instantly taken out of the firing furnace into the air, and the respective samples were designated as sample (a) and sample (b).

The crystal structure of the obtained sintered body was investigated by powder X-ray diffraction, and the temperature change in magnetic susceptibility was measured as a superconducting property.
) was sought.

FIG. 1 shows the powder X-ray diffraction patterns of sample (a) and sample (b). The black circles in the figure are peaks due to impurities. All other peaks are (Pb/Cu) 5rLa Cu
It was possible to index the samples based on Oy, and it was confirmed that all the samples had almost a single phase.

Figure 2 shows the temperature characteristics of magnetic susceptibility. At 4.2K, both exhibited demagnetization at the same volume fraction.

Sample (a) showed a zero resistance temperature (Tc) of 35 at TcM, which was higher than the above-mentioned literature value, but sample (b), which underwent rapid cooling, showed an even higher value of 38, indicating that the zero resistance temperature due to rapid cooling was (Tc) Improvement was observed.

Example 2 Next, sample (a) was annealed in nitrogen with the aim of improving its superconducting properties through post-treatment.

Sample (a) was heated in nitrogen at 500.650.720°C for 24 hours.
The samples were heat-treated and designated as sample (C), sample (d), and sample (e), respectively. Sample (C) and sample (
It was confirmed that sample (d) was a single phase and sample (e) was decomposed.

Figure 2 shows the temperature characteristics of magnetic susceptibility. TcM is the sample (C
) and sample (d) both increased to 27K, and it was confirmed that the volume fraction of demagnetization at 4.2K also increased.

Similar results were also obtained using argon or helium instead of nitrogen.

Furthermore, in a system in which Sr and La of (Pb/Cu)5rLaCuO were partially replaced with Ba, Ca, Y, and other rare earth elements, the superconducting properties were similarly improved by rapid cooling and annealing in an inert gas.

As explained above, according to this embodiment, the second layer consists of an octahedron with a copper atom at its center and an oxygen atom at its apex, and an octahedron with a lead or copper atom at its center and an oxygen atom at its apex. The second layer is stacked by sharing the oxygen atom at the apex, and the third layer is composed of the oxygen atom shared by the second layer and the alkaline earth element and the rare earth element. In the production of an oxide superconducting material having a crystal structure in which a first layer, a second layer, and a third layer are sequentially laminated,
By employing a rapid cooling operation or a heat treatment step in an inert gas, the superconducting properties such as the critical temperature and superconducting volume fraction of the above-mentioned oxide superconducting material can be improved.

[Effects of the Invention] As explained above, according to the method of the present invention, when producing an oxide superconducting material having a crystal structure in which a first layer, a second layer, and a third layer are sequentially laminated, quenching or non-cooling is not necessary. Since the heat treatment is performed in an active gas, superconducting properties such as critical temperature and superconducting volume fraction can be effectively improved.

[Brief explanation of drawings]

FIG. 1 shows powder X-ray diffraction patterns of sample (a) and sample (b). FIG. 2 shows the temperature characteristics of magnetic susceptibility for samples (a) to (d). 2θC) Fig. 1 0 10 20 30
1i050 temperature (K)

Claims (1)

[Claims] (1) A first layer consisting of an octahedron with a copper atom at the center and an oxygen atom at the apex, and a second layer consisting of an octahedron with a lead or copper atom at the center and an oxygen atom at the apex. The second layer is composed of the oxygen atoms, the alkaline earth element, and the rare earth element, which are stacked together sharing oxygen atoms, and which are shared by the first layer and the second layer, and the first layer, the second layer, and A method for producing an oxide superconducting material, which comprises a step of rapid cooling or heat treatment in an inert gas in producing an oxide superconducting material having a crystal structure in which a third layer is sequentially laminated.