JPH0733437A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To produce an HgBa2CuO4+z superconductor having a superconductivity transition temp. Tc above 94 K with high reproducibility. CONSTITUTION:Powdery starting material is compacted and fired at 620-780 deg.C in a hermetically sealed vessel and the resulting oxide superconductor is annealed at 250-450 deg.C in a reducing atmosphere to produce the objective oxide superconductor represented by a chemical formula HgM2CuO4+z (where M is one or more kinds of elements among Ba, Sr and Ca and 3.5<=(4+z)<=4.5].

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, and more particularly to a method for producing an oxide superconductor having a high superconducting transition temperature (Tc ≧ 77K) above the liquid nitrogen temperature. Is.

[0002]

2. Description of the Related Art Superconductors have characteristics such as zero electric resistance, complete diamagnetism, and Josephson effect, which are not found in other materials, and they are used for power transport, generators, and fusion plasma confinement. , Magnetic levitation train, magnetic shield,
A wide range of applications such as high-speed computers are expected.

In 1986, an oxide superconductor (La _1-X Ba _X ) ₂ having a high superconducting transition temperature Tc of about 30 K was obtained by Bednorz and Muller.
CuO ₄ was found and thereafter YBa ₂ Cu ₃ O
₇ (Tc = 90K), Bi-Sr-Ca-Cu-O (T
c = 110K), Tl-Ba-Ca-Cu-O (Tc =
125 K) and other oxide superconductors having successively higher superconducting transition temperatures have been reported. At present, much research has been conducted on the production method, physical properties, application and the like of these substances.

In these studies, a new superconductor HgBa ₂ CuO _{4 + Z} having a superconducting transition temperature Tc of 94 K was recently discovered (N. Putilin et al., Nature).
t al., Nature) 362 (1993) 226. ). As a method of manufacturing this new superconductor, first, Ba ₂ CuO
_{3 + Z} , HgO and CuO are mixed and vacuum sealed in a silica tube. Next, this is further placed in a steel container and baked at a temperature of up to 800 ° C. for 5 hours to manufacture.

The new superconductor Hg manufactured in this way
Ba ₂ CuO _{4 + Z} has an alternate layer structure of a part having a perovskite structure composed of barium, copper and oxygen and a part composed of one atomic layer of mercury. Then, it is reported that Z oxygen atoms are present in the latter atomic layer of mercury.

[0006]

[Problems to be Solved by the Invention] This new superconductor HgB
At present, the only experimental report on a ₂ CuO _{4 + Z} is that of Petitline et al. According to their susceptibility-temperature dependence data, the superconducting transition temperature Tc is 94K.
Met.

An object of the present invention is that the superconducting transition temperature Tc is
HgBa higher than 94K₂CuO _{4 + Z}The superconductor
It is to provide a method that can be manufactured with good physical properties.

[0008]

The method for producing an oxide superconductor according to the present invention is provided with a chemical formula HgM ₂ CuO _{4 + Z} (M is at least one element of Ba, Sr and Ca,
3.5 ≦ 4 + Z ≦ 4.5), which is a method of manufacturing an oxide superconductor, the step of molding a raw material powder,
A step of firing the shaped raw material powder in a closed container at a temperature of 620 to 780 ° C. to produce an oxide superconductor, and the oxide superconductor produced by firing in a reducing atmosphere.
Annealing at a temperature of 450 ° C.

[0009]

According to the present invention, HgBa ₂ CuO having a superconducting transition temperature Tc higher than that reported in the past has been reported.
_{4 + Z} superconductor can be manufactured with good reproducibility. Further, the obtained oxide superconductor has a steep superconducting transition and exhibits a good Meissner effect.

[0010]

EXAMPLES HgO, BaO and Cu having a purity of 99% or more
Each powder of O was weighed and mixed with a charge composition of HgBa ₂ CuO ₄ . Pellets were prepared at a pressure of 800 kg / cm ² , put into a gold tube and crushed at both ends to be closed. This was fired under various conditions shown in Table 1 for 1 hour, and the produced crystal phase was examined by powder X-ray diffraction (using CuKα ray). The results are shown in Table 1.

[0011]

[Table 1]

As is clear from Table 1, HgBa ₂ C is contained in a quartz tube and calcined at 620 to 780 ° C.
A sample having uO ₄ as the main phase was obtained. It is generally known that HgO starts to evaporate at 500 ° C. or higher, but since HgO was suppressed from being evaporated by enclosing it in a closed container, 5
It is considered that HgBa ₂ CuO ₄ could be produced despite the heating above 00 ° C.

FIG. 1 is a diagram showing powder X-ray diffraction patterns of samples before and after annealing. In FIG. 1, the horizontal axis represents the X-ray intensity in arbitrary units, and the vertical axis represents the diffraction angle 2θ (degrees).

In FIG. 1, (a) relates to the sample before the annealing treatment, and among the above various conditions, the powder X-ray diffraction pattern of the sample obtained by firing in a quartz tube at 700 ° C. for 1 hour. Is. Note that (b) relates to the sample after annealing described later.

Referring to FIG. 1 (a), it can be seen that the sample powder before the annealing treatment has a substantially single phase, but it also contains some impurity phase.

FIG. 2 is a diagram showing the magnetic susceptibility-temperature dependence of the sample before and after annealing. SQUID was used for the measurement, and the measurement was performed under the condition of cooling the magnetic field of the external magnetic field of 10 oersted. In FIG. 2, the horizontal axis represents temperature (K) and the vertical axis represents magnetic susceptibility (10 ⁻³ emu / g.
Oe) is shown.

In FIG. 2, (a) relates to the sample before the annealing treatment, and is a diagram showing the magnetic susceptibility-temperature dependence of the sample obtained by firing in a quartz tube at 700 ° C. for 1 hour as described above. is there. Note that (b) relates to the sample after the annealing treatment described later.

FIG. 3 is a partially enlarged view in the vicinity of the superconducting transition temperature in the graph showing the magnetic susceptibility-temperature dependence shown in FIG. 3, the horizontal axis represents temperature (K) and the vertical axis represents magnetic susceptibility (10 ⁻⁴ emu / g.Oe).

Referring to FIGS. 2 (a) and 3 (a),
The sample before annealing shows diamagnetism below 90K,
The superconductor integration rate at 5K can be estimated to be about 5%.

Next, for the purpose of improving the quality of the sample obtained by firing in a quartz tube at 700 ° C. for 1 hour, annealing in a high pressure oxygen atmosphere (270 atmospheric pressure oxygen) and a reducing atmosphere (argon stream) is performed. Tried to process.

The powder X-ray diffraction, the superconducting transition temperature Tc, and the superconductor integration rate M of the sample thus obtained were obtained.
/ M (f) was measured. The results are shown in Table 2.
In Table 2, ⊚, ∘, and × marks in the powder X-ray diffraction results indicate single phase, almost single phase, and decomposition, respectively. Further, the superconducting transition temperature Tc is a value obtained by measuring the magnetic susceptibility, and M / M
(F) represents the superconductor integration rate at 5K. In addition,
M is the actually measured magnetic susceptibility (emu / g), and M (f) is (-1 /
4π) / ρ (emu / g). (However, ρ is Hg
The theoretical density of Ba ₂ CuO _{4 + Z} was set to about 7 g / cm ³ for calculation. )

[0022]

[Table 2]

As is clear from Table 2, deterioration of the sample was observed after annealing in the annealing treatment in high-pressure oxygen. On the other hand, in the annealing treatment in Ar flow, 250 to
The improvement in properties was observed under the processing conditions of 450 ° C.

FIG. 1 (b) shows a powder X-ray diffraction pattern of a sample obtained by annealing at 300 ° C. for 6 hours in an Ar stream. Pattern of sample before annealing (a)
It can be seen that the peak of the impurity phase disappeared and the sample became a complete single-phase sample.

2 (b) and 3 (b) show the magnetic susceptibility-temperature dependence of the sample. Superconducting transition temperature Tc
Increased to 96K, and the superconductor integration rate at 5K was 10
It can be seen that it has increased to over%. In addition, the superconducting transition near the superconducting transition temperature Tc is also very steep, 3% at 94K,
A volume fraction of 10% was observed at 90K.

HgBa₂CuO_{4 + Z}Ba is Sr
It could be partially replaced with Ca or Ca,
It can be easily inferred from research reports on superconductors. Actually, Hg
Ba ₂CuO_{4 + Z}Part of Ba with Sr or Ca (each
Superconductivity with similar crystals even after substitution (up to about 50%)
I got a body. In addition, with or without partial replacement
The superconducting transition temperature T due to the annealing treatment in the original atmosphere
The effect of improving c and crystallinity was recognized. Reproducibility
Very good and effective on all samples
It was

[Brief description of drawings]

FIG. 1 is a diagram showing powder X-ray diffraction patterns of a sample before and after annealing.

FIG. 2 is a diagram showing the magnetic susceptibility-temperature dependence of a sample before and after annealing.

FIG. 3 is a diagram showing the magnetic susceptibility-temperature dependence of a sample before and after annealing.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location // H01B 12/00 ZAA 7244-5G (72) Inventor Mu Ito 1-10 Shinonome, Koto-ku, Tokyo No. 13 Foundation Superhuman Industrial Technology Research Center Superconductivity Engineering Laboratory (72) Inventor Fumiko Yamamoto 1-10-13 Shinonome, Koto-ku, Tokyo Foundation Supernatural Engineering Research Center Superconductivity Engineering Research In-house (72) Inventor Seiji Adachi 1-10-13 Shinonome, Koto-ku, Tokyo Foundation Hojin International Superconducting Industrial Technology Research Center Superconducting Engineering Research Laboratory (72) Inventor Nao Yamauchi 1-10 Shinonome, Koto-ku, Tokyo No. 13 Foundation Hojin International Superconductivity Industrial Technology Research Center Superconductivity Research Institute

Claims (1)

[Claims] 1. The chemical formula HgM ₂ CuO _{4 + Z} (M is Ba,
At least one element of Sr and Ca, 3.5 ≦
4 + Z ≦ 4.5), which is a method for producing an oxide superconductor, the method comprising: forming a raw material powder; and forming the raw material powder in a closed container at 620 to 780.
An oxide comprising: a step of firing at a temperature of ℃ to produce an oxide superconductor; and a step of annealing the oxide superconductor produced by the firing at a temperature of 250 to 450 ° C. in a reducing atmosphere. Superconductor manufacturing method.