JPH09255332A - Manufacturing method of oxide superconductor - Google Patents

Abstract

(57) Abstract: A method for producing a mercury-containing copper oxide superconductor having a high Tc by a simplified process with good reproducibility is provided. The present invention relates to mercury, M (M is Ba, Sr,
In a method for producing an oxide superconductor containing at least one element of Ca), copper and oxygen as main components, a mixture of metallic copper powder and oxide powder forming another oxide superconductor is heat treated. It is a method of manufacturing an oxide superconductor including steps. Particularly, a mixture of HgO, BaO ₂ , CaO, CuO and metallic copper powder is used. It is possible to carry out the production by a simple direct method using a commercially available raw material without requiring a complicated step of producing the precursor. No special equipment such as a glove box is required, and the powder process in the atmosphere can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconductor having a high transition temperature by a simple process with good reproducibility.

[0002]

2. Description of the Related Art Superconductors have characteristics that other substances do not have, such as 1) zero electric resistance, 2) perfect diamagnetism, and 3) Josephson effect. Machine, fusion plasma confinement, magnetic levitation train,
A wide range of applications such as magnetic shields and high-speed computers are expected.

In 1986, according to Bednorz and Muller, a copper oxide superconductor (La _1-x Ba _x ) ₂ having a high superconducting transition temperature Tc of about 30K.
CuO ₄ was found. After that, YBa ₂ Cu ₃ O ₇ (T
c = 90 K), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y (Tc = 11)
0K), Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _y (Tc = 125
K), HgBa ₂ Ca ₂ Cu ₃ O _y (Tc = 135K) and the like have been reported to have superconducting transitions at successively higher temperatures.
Currently, much research is being done on the preparation methods, physical properties, and applications of these substances. Among them, a copper oxide superconductor containing mercury has a high superconducting transition temperature Tc and is a substance that is considered as a promising material for practical use.

A method for synthesizing a copper oxide superconductor containing mercury is as follows:
The method can be roughly classified into (1) direct method and (2) precursor method.

(1) The direct method is a method in which oxides of the respective constituent elements are mixed and molded, placed in a closed container, and fired. Generally, active BaO is used as a Ba source, but it is necessary to perform the powder process in a system in which the atmosphere is strictly controlled using a glove box or the like.

(2) In the precursor method, HgO is added to a precursor obtained by previously firing an oxide (or carbonate, nitrate, etc.) of a constituent element other than mercury, and the mixture is mixed and molded.
It is a method of baking in a closed container. Due to the high volatility of mercury, in each case the firing is carried out in a closed vessel.

In the case of heat treatment under normal pressure (normal pressure method), a quartz tube is used as the closed container. In the case of heat treatment using an ultrahigh pressure generator (high pressure method), gold or platinum capsules are used. At present, copper oxide superconductors containing mercury are synthesized by any one of the following three methods: (a) normal pressure direct method, (b) normal pressure precursor method, and (c) high pressure precursor method. It is being appreciated. There are no reports of high-pressure direct methods.

[0008]

SUMMARY OF THE INVENTION The present inventor has found the following problems as a result of studying the above conventional technology.

The conditions for synthesizing a copper oxide superconductor containing mercury depend on many factors such as raw materials (precursors), mixing ratio, and heat treatment conditions. In order to produce a high quality sample, the synthesis conditions such as the raw material (precursor), the mixing ratio and the heat treatment condition must be precisely controlled. However, since too strict control is required, most of the reports have a problem that only samples containing impurities are obtained.

An object of the present invention is to provide a method for producing an oxide superconductor which allows a copper oxide superconductor containing mercury to be produced with good reproducibility by a simplified process.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0012]

The following is a brief description of an outline of a typical invention among the inventions disclosed by the present application.

As a result of earnest research on a method for producing a copper oxide superconductor containing mercury, the inventors have found the following means for solving the above problems. That is, (1) In a method for producing an oxide superconductor containing mercury, M (M is at least one element of Ba, Sr, and Ca), copper, and oxygen as main components, metallic copper powder and other oxides are used. The heat treatment is performed on the mixture of the oxide powders forming the superconductor.

(2) In the method for producing an oxide superconductor according to (1), a mixture of HgO, BaO ₂ , CaO, CuO and metallic copper powder is heat treated.

According to the above-mentioned means, metallic copper (Cu) powder is present in the mixture to be heat-treated, and during the heat treatment, mercury (Hg) forms amalgam with copper (Cu), and mercury (H)
By suppressing the reaction between g) and calcium (Ca), it is possible to suppress the production of CaHgO _{2 which} is most likely to remain as an impurity. It also reduces the dissipation of mercury (Hg) due to evaporation. The amalgam formed at the same time promotes the mutual movement between the substances in the mixture and accelerates the formation of the target superconductor.

As a result, a copper oxide superconductor containing mercury can be produced with good reproducibility by heat treatment for a short time. It is possible to carry out the production by a simple direct method without requiring a complicated step of producing the precursor. A commercially available raw material can be used without requiring strict quality control of the raw material or re-purification of the raw material before use. It does not require equipment such as a glove box and can use powder processes in the atmosphere.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below along with its embodiments (examples).

(Embodiment 1) An attempt was made to synthesize by the high pressure direct method according to the present invention, which has not been reported so far.

HgO with a purity of 99.9% or more (average particle size 2
μm or less), BaO ₂ (2 μm or less), CaO (2 μm or less)
Below), CuO (2 μm or less), Cu (15 μm or less)
Each powder of (1) was weighed in a molar ratio of 1: 2: 2: 1: 2, and mixed in an agate mortar for about 3 minutes. This mixed powder is molded into pellets, put into a gold capsule, and 5 GPa, 1000
Heat treatment was performed at ℃ for 1 hour. All the steps of weighing, mixing and molding were performed in the atmosphere. A hexagonal cubic anvil type ultrahigh pressure generator was used to generate ultrahigh pressure. The gold capsule was placed into the heater graphite sleeve through a thin NaCl layer. Heat treatment was performed by applying a current to graphite while applying pressure.

FIG. 1 shows a powder X-ray diffraction pattern of a sample obtained by the method for producing an oxide superconductor according to the first embodiment. In FIG. 1, almost single-phase HgBa ₂ Ca ₂ C
u ₃ O _y is obtained. Magnetic susceptibility of the sample (external magnetic field: 2
The temperature dependence of 0 Oe) is shown in FIG. In FIG. 2, 1
A large Meissner signal was observed below 33K. From these results, it can be seen that the HgBa ₂ Ca ₂ Cu ₃ O _y single-phase sample showing bulk superconductivity was synthesized for the first time by the high-pressure direct method.

Under high pressure, the diffusion path between substances is obstructed,
Since mass transfer slows down, when synthesizing materials under high pressure, a mixture in which the constituent elements are distributed as uniformly as possible is desirable.

However, the particle size of the metallic copper used in this embodiment is very large. Also, the mixing method is very simple and the uniformity is extremely low. Metal copper powder with a coarser average particle size of 74
When the same synthesis was performed using the one with μm, FIG.
A sample having a powder X-ray diffraction pattern shown in was obtained. HgBa ₂ Ca ₂ Cu ₃ O _y single-phase samples having the same degree as in the case of the average particle size of 15 μm were obtained. The sample showed a large Meissner signal below 134K.

In order to investigate the reason why the HgBa ₂ Ca ₂ Cu ₃ O _y single-phase sample was obtained from the heterogeneous mixture by heat treatment for a relatively short time of 1 hour, a sample during the reaction was prepared. 5 GP using metallic copper powder with an average particle size of 74 μm
a, heat treatment was performed at 1000 ° C. for 3 minutes only. The powder X-ray diffraction pattern is shown in FIG. Peaks due to Cu ₂ O, CaO and other phases are observed.

FIG. 5 is a scanning electron micrograph (SEM) of the fracture surface of the sample and its trace diagram. You can see three types of organizations in the picture. A is a rounded and coarse grain, B is a rough surface portion without roundness, and C is a liquid phase portion that fills the gap. The composition of each cation was analyzed with an X-ray microanalyzer, and the main component was A: C.
u, B: Ba, Ca, Cu, C: Hg, Cu.
The presence of the characteristic C portion indicates that mercury (Hg) forms amalgam with copper (Cu) during the heat treatment of the metallic copper powder. This suppresses the reaction between mercury (Hg) and calcium (Ca). That is, it is possible to suppress the production of CaHgO ₂ that is most likely to remain as an impurity.

Generally, the solid-solid reaction is remarkably promoted through the liquid phase. The liquid phase component of the C part facilitates the mutual movement of substances, resulting in the desired HgBa
_It can be seen that the formation of the ₂ Ca ₂ Cu ₃ O _y superconductor was accelerated.

(Comparative Embodiment) As a comparative embodiment, a synthesis by a high pressure method was attempted without using metallic copper powder.

As a raw material, HgO having a purity of 99.9% or more
(Average particle size 2 μm or less), BaO ₂ (2 μm or less), B
aO (2 μm or less), BaCuO ₂ (5 μm or less), C
aO (2 μm or less), CuO (2 μm or less), Cu ₂ O
Each powder (2 μm or less) was used. However, BaCuO
No. ₂ was prepared by mixing BaCO ₃ and CuO in a molar ratio of 1: 1 and firing in an oxygen stream at 960 ° C. for 48 hours, followed by rapid cooling. BaO and CaO are respectively in a vacuum and an oxygen stream 10
The product was purified by heat treatment at 00 ° C. for 12 hours. The raw materials were mixed in the proportions shown in Table 1 and heat treated at 5 GPa at 1000 ° C. for 1 hour in the same manner as in the first embodiment.

[0028]

[Table 1]

The product phase in each of the obtained samples was examined by powder X-ray diffraction.
Although Ba ₂ Ca ₂ Cu ₃ O _y was produced, a strong peak indicating the presence of impurities was also observed. FIG. 6 shows the powder X of the # 5 sample with the fewest impurities among the six types shown in Table 1.
It is a line diffraction pattern. Compared with FIGS. 1 and 3 in the case of using the metallic copper powder, the peak of impurities is strong and the quality is inferior.

(Embodiment 2) An attempt was made to synthesize another mercury-containing copper oxide superconductor by the high pressure direct method using metallic copper powder. Similar to the first embodiment, HgO, BaO ₂ , C
The mixing ratio of aO, CuO, and Cu (15 μm) is 1: 2 :.
A sample was prepared as (n-1) :( n-2): 2.
(However, n = 1, 2, 4, 5) When the produced phases were examined by powder X-ray diffraction, HgBa ₂ C was obtained.
uO _y , HgBa ₂ CaCu ₂ O _y , HgBa ₂ Ca ₃ Cu ₄
It was almost a single phase of O _y and HgBa ₂ Ca ₃ Cu ₄ O _y .
When the temperature characteristics of magnetic susceptibility were measured, it was confirmed that these samples exhibited the Meissner effect at 93 K, 127 K, 120 K, and 108 K or less, respectively, and exhibited superconductivity.
The reaction was almost completed in a short time of 1 hour, and the desired single-phase superconductor sample could be synthesized.

Besides, the following mercury-containing copper oxide superconductors, (Hg _0.8 Pb _0.2 ) Ba ₂ Ca ₂ Cu ₃ O _y , (Hg
_0.8 Pb _0.2 ) Ba ₂ Ca ₃ Cu ₄ O _y , (Hg _0.5 Pb _0.5 )
Sr ₂ Ca ₂ Cu ₃ O _y , (Hg _0.8 Bi _0.2 ) Ba ₂ Ca ₂ C
u ₃ O _y , (Hg _0.8 Tl _0.2 ) Ba ₂ Ca ₂ Cu ₃ O _y , (H
g _0.8 Re _0.2 ) Ba ₂ Ca ₂ Cu ₃ O _y , (Hg _0.8 R
_{e 0. 2) Sr 2 Ca 2} Cu 3 O y, (Hg 0.75 Mo 0.25) S
r ₂ Ca ₂ Cu ₃ O _y , (Hg _0.6 Cr _0.4 ) Sr ₂ CuO _y ,
Hg ₂ Ba ₂ Y _0.6 Ca _0.4 Cu ₂ O _y was synthesized by a high-pressure direct method using metallic copper powder, and a sample having a quality equal to or higher than the reported example could be synthesized in a short time.

(Embodiment 3) Attempts were made to synthesize by the atmospheric pressure direct method.

Similar to the first embodiment, HgO, Ba
Powders of O ₂ , CaO, CuO and Cu (15 μm) were weighed in a molar ratio of 1: 2: 2: 1: 2, mixed and molded. All the above steps were performed in the atmosphere. The molded body is vacuum-sealed in a quartz tube and kept at 665 ° C. for 1 to 100 hours (1, 3,
6, 9, 12, 20, 30, 50, 70, 90, 120
Heat treatment).

HgBa ₂ Ca ₂ Cu ₃ O _y in the obtained sample
Ratio of (HgBa ₂ Ca ₂ Cu _{3 in the} powder X-ray diffraction pattern)
It was evaluated by the ratio of the strongest peak intensity of O _y and that of impurities. Was the largest when heat-treated for 12 to 30 hours, and could be synthesized with a purity of 90% or more. K. Isawa et al. (Physica C) 222 (1994)
33. ) Is Hg by the normal atmospheric direct method without using metallic copper.
A high quality sample of Ba ₂ Ca ₂ Cu ₃ O _y is being prepared.
It requires a long firing time of 48 hours or more at 65 ° C. We were able to prepare HgBa ₂ Ca ₂ Cu ₃ O _y by heat treatment for a short time without refining the raw material and using a glove box. By using metallic copper, it was possible to produce high quality samples by the atmospheric powder process of commercial raw materials.

Although the invention made by the present inventor has been specifically described based on the embodiments (examples), the present invention is not limited to the above-mentioned embodiments (examples), and the gist thereof is not limited. It goes without saying that various changes can be made without departing from the scope.

[0036]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) It can be produced by a simple direct method using a commercially available raw material without requiring a complicated step of producing a precursor.

(2) No special equipment such as a glove box is required, and the powder process in the atmosphere can be used.

(3) A copper oxide superconductor containing mercury can be produced with good reproducibility by a simplified process.

[Brief description of drawings]

FIG. 1 shows a sample (HgBa ₂ Ca ₂ C) of Embodiment 1 of the present invention.
is a graph illustrating a powder X-ray diffraction pattern of u ₃ O _y).

FIG. 2 shows a sample of the first embodiment (HgBa ₂ Ca ₂ Cu
₃ susceptibility of O _y) (external magnetic field: is a diagram showing temperature dependence of 20 Oe).

FIG. 3 is a view showing a powder X-ray diffraction pattern of another sample of Embodiment 1.

FIG. 4 is a view showing a powder X-ray diffraction pattern of another sample of Embodiment 1.

5 is a scanning electron microscope photograph of a fracture surface of the sample shown in FIG. 4 and its trace diagram.

FIG. 6 is a diagram showing a powder X-ray diffraction pattern of a sample (# 5) produced by a high pressure direct method (5 GPa, 1000 ° C., 1 hour) using the oxide raw material of Comparative Example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 000005290 Furukawa Electric Co., Ltd. 2-6-1, Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Yoshiyuki Moriwaki 1-14-3, Shinonome, Koto-ku, Tokyo International Superconductivity Foundation Industrial Technology Research Center Superconductivity Engineering Laboratory (72) Inventor Tadashi Tadashi 1-14-3 Shinonome, Koto-ku, Tokyo Tokyo Superconductivity Industrial Technology Center Superconductivity Engineering Laboratory (72) Inventor Fumiko Yamamoto Tokyo 1-14-3 Shinonome, Koto-ku International Superconductivity Industrial Technology Research Center Superconductivity Research Institute (72) Inventor Toshiyuki Tamura 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Industry Technology Research Center Superconductivity Inside Institute of Engineering (72) Inventor Seiji Adachi 1-14-3 Shinonome, Koto-ku, Tokyo Dan Japan International Superconductivity Technology Center, more than conductivity engineering the laboratory (72) inventor Keiichi Tanabe Koto-ku, Tokyo Shinonome chome 14 No. 3 Foundation International Superconductivity Technology Center, more than conductivity engineering in the Institute

Claims (2)

[Claims] 1. A method for producing an oxide superconductor containing mercury, M (M is at least one element of Ba, Sr, and Ca), copper and oxygen as main components, and metallic copper powder and other oxides are used. A method for producing an oxide superconductor, comprising a step of heat-treating a mixture of oxide powders constituting the superconductor. 2. The method for producing an oxide superconductor according to claim 1, wherein a mixture of HgO, BaO ₂ , CaO, CuO and metallic copper powder is heat-treated.