JP2732809B2 - Superconducting material composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic superconducting material.

[0002]

_2. Description of the Related Art As a porcelain composition having a high superconducting transition temperature, YBa ₂ Cu ₃ O _7-d is known. Y ₂ O ₃ constituting this superconductor is scarce in mineral resources and expensive. Lanthanide barium cuprate LnBa containing Y
_{In the case of} 2Cu ₃ O _7-d- based superconductor, Ln from Lu to Nd
Of the superconducting transition temperature T as the ionic radius of
_C is known to be high. La has the largest ionic radius in this series, and Tc of 95 K or more is expected from the relationship between the ionic radius and the superconducting transition temperature.
Moreover, LaBa ₂ Cu ₃ O _7-d in which Y is replaced by La
Since La ₂ O ₃ is less expensive than Y ₂ O _3, superconductors have great industrial value if they can be put to practical use.

However, the recently announced superconducting transition temperature of 92
K LaBa ₂ Cu ₃ O _7-d superconductor (Applied Physics
Letters, 52 ( 23), P. 1989, 1988) requires two calcinations at 900 ° C. and 950 ° C. and a further 980 ° C. × 4.
300 ° C x 4 for 0 hour sintering and superconducting phase formation
This requires a long-time heat treatment of 0 hour annealing. Therefore, there is a problem that productivity is low and energy efficiency is low.

[0004] Furthermore, the critical current density of LaBa ₂ Cu ₃ O _7-d superconducting oxide has not been reported so far, nor has the optimum firing condition been clarified. There remains a problem that needs to be solved.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to improve the properties of a superconducting material composition. An object of the present invention is to provide a superconducting material composition containing LaBa ₂ Cu ₃ O _7-d as a main component and capable of realizing a high superconducting transition temperature and a large critical current density in a short baking time.

[0006]

According to the present invention, there is provided LaBa ₂ Cu ₃ O _7-d
Ag ₂ O is added in a proportion of from 0.1% by weight to 70% by weight with respect to 1 mole, and the majority of Ag is characterized in that it is present in the form of precipitate as metallic silver.

[0007]

According to the present invention, the superconducting material LaBa ₂ Cu ₃ O is used.
_Since Ag ₂ O is added to _7-d , the critical current density can be improved despite the short baking time.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings.

La ₂ O ₃ , Ba (OH) ₂ .8H ₂ O and CuO were weighed so that the ratio of La: Ba: Cu was 1: 2: 3, mixed in a dry system, and pulverized. The mixed powder was heat-treated at 800 to 900 ° C. for 10 hours. The heat treatment atmosphere may be any of air, oxygen and nitrogen. After the heat treatment, the powder was re-ground and passed through a 30 μm sieve to obtain LaBa ₂ Cu ₃ O _7-d powder.

[0010] BaCO ₃ is usually used as a Ba raw material. However, if BaCO ₃ is used as a starting material, 90
Even if the heat treatment is performed at 0 to 950 ° C., a trace of carbonic acid remains, resulting in a composition shift. In the present invention, highly reactive, and having no _{Ba (OH) 2 · 8H 2} O carbonate mark was used as a Ba feed. For comparison, some samples using BaCO ₃ as a starting material were prepared.

A predetermined amount of Ag ₂ O powder (purity: 99.99) is added to 1 mol of the powder in a range of 0 to 70 wt%.
%) And a pressure of 1-2 ton / cm ² ,
A pellet having a diameter of 15 mm and a thickness of 1.5 mm was prepared.
The pellets were placed in a crucible and fired while controlling the temperature and the heating atmosphere, that is, the total pressure and the oxygen partial pressure.

FIG. 1 shows an example of a time-temperature curve during firing. As shown in the figure, the sintering process includes four steps: a heating step to a sintering temperature, a sintering step at a constant temperature, a cooling step to an annealing temperature, and a superconducting phase generation step by annealing at a constant temperature. .

In the following examples, the temperature raising and cooling rates were kept constant at 200 ° C./hr and 60 ° C./hr, respectively.
The sintering temperature was appropriately selected in the range of 900 ° C. to 980 ° C., and the sintering time was fixed at 5 hours. The annealing temperature was fixed at 300 ° C., and the holding time was 5 hours or 10 hours.

Further, as shown in FIG. 1, the baking process was divided into four segments a, b, c and d to control the atmosphere during the baking. Segment a focuses on the temperature rise process up to 700 ° C, segment b focuses on the sintering process, 700 ° C
It includes the above-mentioned temperature raising process and the temperature lowering process up to 900 ° C.
Segment c is a cooling process under 900 ° C, segment d
Corresponds to annealing, that is, a superconducting phase generation process. At the time of firing, simultaneously controlling the total pressure in the furnace, detecting the oxygen partial pressure in the vicinity of the object to be fired, and firing each sample having a different amount of Ag ₂ O added while controlling the oxygen partial pressure in each segment unit. Was.

FIG. 2 schematically shows an apparatus for performing the above-described firing. First, the inside of the firing furnace 1 is rotated by a rotary pump 2A,
Evacuation is performed to a predetermined degree of vacuum by an exhaust system 2 including a vacuum solenoid valve 2B, an exhaust filter 2C, a leak valve 2D, and a vacuum gauge 2E. Next, a mixed gas of oxygen and nitrogen (or argon) is supplied to the firing furnace 1. Oxygen passes from cylinder 3A through stop valve 3B, needle valve 3C, mass flow controller 3D, check valve 3E, and control valve 3F, and nitrogen (or argon) similarly travels from cylinder 4A to stop valve 4B, needle valve 4C, mass flow controller 4D. , Check valve 4E and control valve 4F
, And enter the gas mixer 5 to be mixed. The mixed gas (or a single gas) is led to the firing furnace 1 through the gas introduction valve 6. 3G and 4G are primary pressure gauges, respectively. An oxygen sensor 7 is placed near the object to be fired in the firing furnace 1 and detects the amount of oxygen near the object to be fired.
This detection signal is input to the oximeter 8, and an oxygen concentration signal is input from the oximeter 8 to the oxygen partial pressure controller 9.
On the other hand, the temperature controller 10 for controlling the temperature of the firing furnace 1 includes:
The oxygen partial pressure determined for each segment described above is stored, and the predetermined oxygen partial pressure is compared with the oxygen concentration signal from the oximeter 8 by the oxygen partial pressure controller 9, and the oxygen partial pressure is determined. The controller controls the opening and closing of the control valves 3F and 4F so that the oxygen partial pressure near the object to be fired becomes a predetermined value.

On the other hand, the pressure signal of the gas introduced into the firing furnace 1 is input to the compound meter 11. The compound meter 11 operates the exhaust valve 12 so that the pressure in the furnace is maintained at a predetermined value.
13 is a safety valve. The furnace body of the firing furnace 1 is water-coolable and has a pressure resistance of 1.5 kg / cm ² .

The superconducting transition temperature and the critical current density of each of the samples prepared using the apparatus shown in FIG. 2 were measured, and the crystal structure was analyzed by X-ray diffraction. As for the superconducting transition temperature, DC resistance was measured by a four-terminal method to measure _Tcend at which the electric resistance became 0, and further, using a Hertz-horn bridge, the superconducting transition temperature _TCI was measured from the temperature change of the AC susceptibility. The critical current density J _C was determined by applying a large current pulse to the sample under liquid nitrogen and obtaining the maximum current value at which the superconducting state was maintained.

Tables 1 to 5 show the superconducting transition temperatures T _cend and T _CI and the critical current density J _C of each sample prepared by changing the Ag ₂ O concentration and the firing conditions. Samples marked with * in the table are samples using BaCO ₃ as a starting material.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

[Table 4]

[0023]

[Table 5]

FIGS. 3 and 4 show sample Nos. 7 shows an electrical resistance-temperature characteristic and an AC susceptibility-temperature characteristic of FIG.

Referring to Tables 1 to 5, the critical current density J _C can be reduced, for example, by the addition of Ag ₂ O. 9 of 390
A / cm ² , sample No. Twelve 280 A / cm ² . Samples of this value Ag ₂ O-free additive that conventional BaCO ₃ as a starting material No. Ag is 20 times or more as large as 42, and is obtained by using Ba (OH) ₂ .8H ₂ O as a starting material.
Of ₂ O no addition sample, the sample with the highest J _C No. 3
5 is several times or 10 times or more of 25 A / cm ² . A
The superconducting transition temperature of the sample whose _JC was improved by the addition of g ₂ O was about 90 K, and no remarkable decrease in the superconducting transition temperature due to the addition of Ag ₂ O was observed. Ag ₂ O is 0.1%
Can be sintered at a low temperature with the addition of J. At that time, there is no difference in _{JC from} that without addition. On the other hand, if it exceeds 70%, it is difficult to prepare a sample because metallic silver precipitates on the porcelain surface and fuses with the crucible. Become. Further, addition of Ag ₂ O exceeding 70% is not preferable in terms of cost. A small amount of Ag ₂ O is LaBa ₂ Cu ₃
Although it is supposed that it forms a solid solution with O _7-d , most of them are precipitated as metallic silver. FIG. 5 shows the sample No. to which 70% of Ag ₂ O was added. 19 is an X-ray diffraction diagram of FIG. Orthogonal LaBa ₂
As shown in the figure, a strong peak of metallic silver appears together with a peak corresponding to Cu ₃ O _7-d .

Returning to Tables 1 to 5, Sample No. 1 containing Ag ₂ O at the same amount (10%) was added. 7, 17, 20, and 3
Comparing Sample No. 2, the critical current density J _C depends on the firing conditions. Sample No. 17 from 70 A / Cm ² . It can be seen that there is a large change up to 32, 201 A / cm ² . Sample No. 7 and no. In FIG. 20, since the total pressure in the furnace is equal, it is understood that the oxygen partial pressure in each segment greatly affects the value of the critical current J _C. Furthermore, from the comparison of _JC of these four samples, it is better that the oxygen partial pressure in the sintering process (segment b) is lower and the oxygen partial pressure in the annealing process (segment d) is higher. The superconducting transition temperatures T _cend and T _CI are not significantly affected by the oxygen partial pressure. This tendency is the same for sample N with the same 20% Ag ₂ O addition.
o. 9, 18, 21, 27 and 32 are also found. That is, by controlling the oxygen partial pressure in the vicinity of the object to be fired according to the segment of the firing process, the value of the critical current density J _C can be improved while shortening the firing time.

As in the conventional method, BaC is used as a starting material.
Sample No. using O ₃ Sample No. 42 under the same firing conditions as in Sample No. 42, but using Ba (OH) ₂ .8H ₂ O as a starting material. 35, the former annealing time is 40.
Despite the long time, the sample No. No. 35 has better superconducting transition temperature and critical current density. This indicates the superiority of using _{Ba (OH) 2 · 8H 2} O as the starting material.

[0028] As shown in the above embodiments, the present invention, the superconducting transition temperature T _C was obtained La system 123 superconductivity 93K. Although this value does not reach the above-mentioned T _{C of} 95 K or more, it is the first step in realizing the expected T _C by improving the manufacturing method.

[0029]

As described above, according to the present invention, since the superconducting material LaBa ₂ Cu ₃ O _7-d is added with Ag ₂ O, the critical current density is improved despite the short firing time. can do.

The composition of the present invention is applicable to superconducting magnets, various superconducting devices, and power storage using superconductivity.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a firing method used for carrying out the present invention.

FIG. 2 is a schematic view of a firing apparatus used in the present invention.

FIG. 3 is an electric resistance-temperature characteristic diagram of the example of the present invention.

FIG. 4 is an AC susceptibility-temperature characteristic diagram of the example of the present invention.

FIG. 5 is an X-ray diffraction diagram of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Firing furnace 7 Oxygen sensor 8 Oxygen concentration meter 9 Oxygen partial pressure controller 10 Temperature controller

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Izumi Hirabayashi Nagoya Laboratory, International Superconducting Technology Research Center, 2-4-1 Rokuno, Atsuta-ku, Nagoya, Aichi, Japan (56) References 192760 (JP, A) Japanese Journal of Applied Physics Vol. 26 (3) P.E. L223-L224 Japanese Journal of Applied Physics Vol. 26 (5) P.E. L834-L835

Claims (1)

(57) [Claims] (1) Ag ₂ O is present in an amount of 0.1 mol per mol of LaBa ₂ Cu ₃ O _7-d .
A superconducting material composition, characterized in that it is added in a proportion of from 1% to 70% by weight, the majority of the Ag being present in the form of precipitates as metallic silver.