JPH0840767A - Superconducting material composition - Google Patents

Abstract

PURPOSE:To obtain the superconducting material composition comprising LaBa2 Cu3O7-d and Ag2O in a specific ratio, capable of realizing a high superconducting transition temperature and a large critical electric current density in a short sintering time. CONSTITUTION:The superconducting material composition comprises 100wt.% of LaBa2Cu3O7-d and 0.1-70wt.% of Ag2O. Since the Ag2O is added to the superconducting material: LaBa2Cu3O7-d, the critical electric current density of the composition can be improved in spite of a short sintering time. A La 123 superconductor having a superconducting transition temperature Tc of 93K is obtained from the superconducting composition. The value gives the first step for realizing a Tc predicted by the improvement of the production method. The superconducting material composition can improve the critical electric current density in spite of a short sintering time, and can be applied to superconducting magnets, various superconducting devices, and electric power storage using the superconductor.

Description

Detailed Description of the Invention

[0001]

This invention relates to ceramic superconducting materials.

[0002]

_2. Description of the Related Art YBa ₂ Cu ₃ O _7-d is known as a ceramic composition having a high superconducting transition temperature. Y ₂ O ₃ which constitutes this superconductor is scarce in mineral resources and is expensive. Lanthanide barium copper oxide containing Yn LnBa
_{In the case of 2} Cu ₃ O _7-d superconductor, Ln from Lu to Nd
As the ionic radius of T increases, the superconducting transition temperature T
It is known that _C becomes high. La has the largest ionic radius in this series, and Tc of 95 K or higher 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 cheaper than Y ₂ O _{3 in a} superconductor, it has great industrial value if it 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 980 ° C x 4
300 ° C x 4 for 0 hour sintering and superconducting phase formation
It requires a long heat treatment of 0 hour annealing. Therefore, there is a problem that productivity is low and energy efficiency is low.

Further, the critical current density of LaBa ₂ Cu ₃ O _7-d superconducting oxide has not been reported so far, and the optimum firing conditions have not been clarified. , There remains a problem that needs to be solved.

[0005]

The present invention has been made to improve the properties of superconducting material compositions. 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 firing time.

[0006]

The present invention is based on LaBa ₂ C
It is characterized by containing Ag ₂ O in a proportion of 0.1% by weight to 70% by weight with respect to 1 mol of u ₃ O _7-d .

[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 firing 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 dry and pulverized. The mixed powder was heat-treated at 800 to 900 ° C. for 10 hours. The heat treatment atmosphere may be air, oxygen or nitrogen. After the heat treatment, the powder was re-ground and passed through a 30 μm sieve to obtain a LaBa ₂ Cu ₃ O _7-d powder.

BaCO ₃ is usually used as the Ba raw material. However, if BaCO ₃ is used as the starting material, 90
Even if it heat-processes at 0-950 degreeC, since a carbonic acid trace remains, composition gap arises. In the present invention, Ba (OH) ₂ .8H ₂ O, which is highly reactive and has no carbonic acid trace, was used as the Ba raw material. For comparison, a part of a sample using BaCO ₃ as a starting material was prepared.

With respect to 1 mol of this powder, a predetermined amount of Ag ₂ O powder (purity 99.99) is used in the range of 0 to 70 wt%.
%), And a pressure of 1-2 ton / cm ² is added,
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 temperature and heating atmosphere, that is, total pressure and oxygen partial pressure.

FIG. 1 shows an example of a time-temperature curve during firing. As shown in the figure, the firing process includes four processes including a temperature raising process up to a sintering temperature, a sintering process at a constant temperature, a temperature decreasing process to an annealing temperature, and a superconducting phase generation process by annealing at a constant temperature. .

In the following examples, the temperature raising and lowering 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 kept constant for 5 hours. The annealing temperature was constant at 300 ° C., and the holding time was 5 hours or 10 hours.

Further, as shown in FIG. 1, the firing process was divided into four segments a, b, c and d to control the atmosphere during firing. The temperature of segment a is 700 ℃ and the temperature of segment b is 700 ℃.
It includes the above temperature raising process and the temperature lowering process up to 900 ° C.
Segment c is the temperature decreasing process below 900 ° C, segment d
Corresponds to annealing, that is, a superconducting phase generation process. At the time of firing, while controlling the total pressure in the furnace, at the same time detecting the oxygen partial pressure in the vicinity of the object to be fired and controlling the oxygen partial pressure in each segment unit, each sample with a different Ag ₂ O addition amount was fired. It was

FIG. 2 schematically shows an apparatus for performing the above-mentioned firing. First, in the firing furnace 1, the rotary pump 2A,
The exhaust system 2 including the vacuum solenoid valve 2B, the exhaust filter 2C, the leak valve 2D and the vacuum gauge 2E exhausts to a predetermined vacuum degree. Next, a mixed gas of oxygen and nitrogen (or argon) is supplied to the firing furnace 1. Oxygen passes from the cylinder 3A through the stop valve 3B, needle valve 3C, mass flow controller 3D, check valve 3E and control valve 3F, and nitrogen (or argon) similarly from the cylinder 4A to stop valve 4B, needle valve 4C, mass flow controller 4D. , Check valve 4E and control valve 4F
Via the gas mixer 5 and mixed. The mixed gas (or a single gas) is introduced into the firing furnace 1 through the gas introduction valve 6. 3G and 4G are primary pressure gauges, respectively. An oxygen sensor 7 is placed in the firing furnace 1 near the article to be fired to detect the amount of oxygen near the article to be fired.
This detection signal is input to the oxygen concentration meter 8, and the oxygen concentration signal from the concentration meter 8 is input to the oxygen partial pressure controller 9.
On the other hand, in the temperature controller 10 that controls the temperature of the firing furnace 1,
The oxygen partial pressure determined for each segment described above is stored, and this predetermined oxygen partial pressure is compared with the oxygen concentration signal from the oxygen concentration meter 8 by the oxygen partial pressure controller 9 to obtain the oxygen partial pressure. The controller controls opening / 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 gauge 11. The compound gauge 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 was water-coolable and had a pressure resistance of 1.5 kg / cm ² .

Superconducting transition temperatures and critical current densities of various samples produced by using the apparatus shown in FIG. 2 were measured, and crystal structure analysis by X-ray diffraction was performed. The superconducting transition temperature was measured by measuring the direct current resistance by the four-terminal method to measure T _cend at which the electric resistance became 0, and further measuring the superconducting transition temperature T _CI from the temperature change of the alternating magnetic susceptibility using a Hertzhorn bridge. The critical current density J _C was determined by applying a large current pulse to the sample under liquid nitrogen and determining 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 densities J _C of the samples prepared by changing the Ag ₂ O concentration and the firing conditions. The 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]

As an example, FIG. 3 and FIG. 7 shows the electric resistance-temperature characteristic and the AC magnetic susceptibility-temperature characteristic of No. 7.

Referring to Tables 1 to 5, the critical current density J _C can be determined by adding Ag ₂ O, for example, in the sample No. 9 of 390
A / cm ² , sample No. 12 rises as 280 A / cm ² . This value is the same as sample No. 1 containing no conventional Ag ₂ O and using BaCO ₃ as a starting material. The value is more than 20 times that of 42 and Ag using Ba (OH) ₂ .8H ₂ O as a starting material
_{Of the 2} O-free samples, the sample No. with the highest J _C. Three
5 times 25 A / cm ² or 10 times or more. A
The superconducting transition temperature of the sample whose J _C was improved by the addition of g ₂ O was around 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%
Addition, the sintering can be carried out at a low temperature. At that time, there is no difference in J _{C from} the one without addition. On the other hand, when it exceeds 70%, metallic silver is deposited on the porcelain surface and fused to the crucible, making sample preparation difficult. Become. Furthermore, addition of Ag ₂ O exceeding 70% is not preferable in terms of price. A small amount of Ag ₂ O is LaBa ₂ Cu ₃
It is supposed that it forms a solid solution in O _7-d , but most of it precipitates as metallic silver. FIG. 5 shows the sample No. added with 70% Ag ₂ O. 19 is an X-ray diffraction pattern of 19. Orthorhombic LaBa ₂
A peak corresponding to Cu ₃ O _7-d and a peak of metallic silver strongly appear as shown in the figure.

Returning to Tables 1 to 5, sample No. 1 having the same addition amount of Ag ₂ O (10%) was used. 7, 17, 20 and 3
Comparing No. 2 with each other, 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 to 32 of 201 A / cm ² . Sample No. 7 and No. At 20, the total pressure in the furnace is equal, so it can be seen that the oxygen partial pressure in each segment greatly affects the value of the critical current J _C. Furthermore, from the comparison of J _C 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 20% addition of Ag ₂ O.
o. It is also seen for 9, 18, 21, 27 and 32. 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, it is possible to shorten the firing time and improve the value of the critical current density J _C.

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

As shown in the above examples, according to the present invention, La-based 123 superconductivity having a superconducting transition temperature T _C of 93 K was obtained. Although this value does not reach the above-mentioned T _{C of} 95 K or more, it is the first step to realize the T _C expected 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 can be applied to superconducting magnets, various superconducting devices, and electric power storage using superconductivity.

[Brief description of drawings]

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

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

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

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

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

[Explanation of symbols]

 1 Baking Furnace 7 Oxygen Sensor 8 Oxygen Concentration Meter 9 Oxygen Partial Pressure Controller 10 Temperature Controller

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01L 39/12 ZAA C 39/24 ZAA Z (72) Inventor Hirabayashi Izumi 6 Atsuta-ku, Nagoya-shi, Aichi 2-4-1 No. International Superconducting Industrial Technology Research Center Nagoya Laboratory

Claims (1)

[Claims] 1. A superconducting material composition characterized by containing Ag ₂ O in an amount of 0.1 wt% to 70 wt% relative to 1 mol of LaBa ₂ Cu ₃ O _7-d .