JPH02225319A - Method for manufacturing oxide superconducting materials - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to
The present invention relates to a method for producing a 1-3r-Ca-Cu-0 based oxide superconducting material.

[Conventional technology and its issues]

Since the discovery of rare earth superconducting materials that exhibit superconductivity above the liquefaction temperature of nitrogen (77 K), numerous studies have been conducted on rare earth superconducting materials.
Although the superconducting transition temperature of perovskite-type compounds represented by 0t-x (R; rare earth element) is higher than 77, it is around 90, and as long as cheap liquefied nitrogen is used as a refrigerant, they are close in temperature. This is a cause for concern, and in order to put it to practical use as an industrial material, it has been desired to develop a superconducting material with a high Tc of 120 or higher, which is at least 1.5 times the liquefaction temperature of nitrogen. However, even if the perovskite type compound, which is a 90 class superconducting material, were subjected to composition changes and element substitutions around the material, a high Tc superconducting material exceeding 90 class could not be obtained.

On the other hand, B1-5r-Ca-Cu-0-based oxide superconducting materials were developed by H. Maeda et al. (Jap, J. Appl.
Phys, Lett, 27L209 (19
88)), and the system contains at least three compounds with different critical temperatures (TC~20, 80, and 120).
It has become clear that K) exists. Among these three types of compounds, the compound Tc-120 (hereinafter referred to as phase I), which is a practically promising substance due to its high critical temperature, can be obtained in a certain amount by increasing the firing time. However, it is industrially disadvantageous that the firing takes a long time, and B containing a large amount of H phase
In order to obtain i-based oxide superconducting materials, it was necessary to optimize manufacturing conditions.

[Means to solve the problem]

An object of the present invention is to provide an advantageous method for producing a Bl-based oxide superconducting material having a high Tc of about 120,
The above object of the present invention is as follows: Compositional formula: Sr, Caz air Cu50° (in the formula,
α, β, γ, δ and X represent the number of moles of each element, 0, I≦α/β≦1.5 0.8≦α/T≦2.0 0.25≦δ/(α+β+γ+δ) ≦0.65.

), a mixture of a strontium compound, a calcium compound, a bismuth compound, and a copper compound is mixed in an oxygen-containing gas atmosphere.
After primary firing at 600-820℃, 830-8℃
When performing secondary firing at 95°C, if the average temperature (TI°C) of secondary firing is 600°C or more and 700°C or less, 0
．． 0157+ + 12°36≦t,≦40 (however, t
, indicates the next firing time (hours), -0,015TI + 1 if the average temperature (T1°C) of the next firing is higher than 700°C and lower than 820°C.
2.36≦t1≦-0,2TI + 165 (however, t
This is achieved by performing time-second firing that satisfies the following conditions: 1 represents the primary firing time (hours).

The present invention will be explained in detail below.

The oxide superconducting material produced by the present invention is an oxide of strontium, calcium, bismuth and copper, and has the following compositional formula (%) (where α, β, T, δ and X are the respective elements. Represents the number of moles, 0.1≦α/β≦1.5.0.8≦α/
γ≦2.0.0.25≦δ/(α+β+γ+δ)≦0.
It is 65. ), which can be produced using carbonates, hydroxides, nitrates, sulfates, oxalates, chlorides, alkoxides, etc. of strontium, calcium, bismuth, and copper as raw materials.

By appropriately selecting from these raw material compounds, Sr+ Car
Bi and Cu are weighed so that the atomic ratio is the above composition, and mixed by a conventionally known method for uniform mixing, such as a powder mixing method, wet coprecipitation method, evaporation drying method, or alkoxide method. Ru. The resulting mixture is dried and then fired.

At this time, in order to ensure a sufficient solid phase reaction, it is preferable to pressure-form the powder and sinter it in the form of a pellet.The sintering is carried out in an oxygen-containing gas atmosphere in order to decompose each salt. In the invention, firing occurs in two stages.

The primary firing is usually performed at a temperature range of 600 to 820°C. Although it depends on the temperature, if the secondary firing time is too short or too long, the proportion of H phase produced tends to decrease.

In the present invention, when the mixture is under a temperature range of 600°C to 820°C, it is regarded as primary firing, and empirically, if the average temperature (T1°C) of primary firing is 600°C or more and 700°C or less, - 0,0157, + 12.36≦11≦40 (however,
t indicates the second firing time (hours). If the average temperature (T°C) of the second firing is higher than 700°C and lower than 820°C, -O,015T, +12
．． 36≦t, ≦-0, 2TI + 165 (however, t,
is carried out for a time that satisfies the conditions of - indicates the next firing time (hours).

- In the next firing, the temperature may be held at a certain constant level or the temperature may be gradually raised, and the firing pattern can be selected as appropriate.

Since the H phase is thermodynamically stable in an oxygen-containing gas atmosphere at high temperatures similar to the secondary firing temperature, the secondary firing time can be shortened by generating as much H phase as possible in the secondary firing. be able to.

Next, secondary firing is performed at a temperature range of 830 to 895°C.The secondary firing requires at least 1 hour, preferably 24 hours or more, and more preferably 120 hours or more. The more the properties of the obtained superconductor are improved. Although the firing pattern for the secondary firing can be appropriately selected as in the case of the primary firing, it is usually preferable to carry out the firing by maintaining the temperature at a certain constant temperature.

In addition, in order to increase the generation rate of the H phase, it is preferable to change the temperature of the secondary firing ('r z °C) depending on the oxygen partial pressure in the atmosphere, and when firing at normal pressure, empirically, 830≦T8≦32.5 X logPot+ 895
Preferably, 20.3 X log P ot + 860≦T! ≦
32.5 X log P ox + 895 (however,
It has been found that it is effective to carry out the secondary firing at a temperature of 100% (Po), which represents the oxygen partial pressure (atmospheric pressure) during firing.

By analyzing the superconducting properties of the thus obtained composite oxide, it can be confirmed that it is an oxide superconducting material having Tc-120K. A common method for confirming that a material is a superconducting material is to examine the temperature characteristics of electrical resistance, and Tc can be determined from the rapid decrease in electrical resistance. However, in this case, care must be taken as even if the amount is extremely small as in the thin-skin model of superconducting materials, information may be given that appears to be entirely superconducting material. be.

In order to evaluate superconducting materials as materials, it is not always sufficient to examine the temperature characteristics of electrical resistance, so in the present invention, powder X-ray analysis is used as an indicator of the content of superconducting materials. did.

That is, powder X by CuKa radiation (1,5418 people)
When 41 diffraction is performed, a Tc- peak similar to that appearing in the diffraction pattern of known oxide superconducting materials containing bismuth, strontium, calcium, and copper as essential components.
Superconductor in 80's! (hereinafter referred to as L phase) and a diffraction peak due to H phase appear. In addition, peaks of impurities such as Cub and CazCu03 appear.

In the sintered body, the volume fraction of the H phase is determined by 2θ=23.3±0. which specifically appears in the L phase in powder X-ray diffraction.
Comparison can be made by determining the ratio of the intensity (H) of the diffraction peak at 2θ-24,0±0.2°, which specifically appears in the H phase, to the intensity (L) of the diffraction peak at 2°.

The larger the volume fraction of the H phase in the sintered body, the better the superconducting properties.When H/L exceeds 0.4, the H phase increases, so from the AC magnetic susceptibility, the entire sample is almost H. measured as forming a phase.

Therefore, a value of H/L of 0.4 is used as a guideline, and if it is higher than this value, it can be said that it is a good superconductor.

〔Example〕

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Examples 1-11. Comparative Examples 1 to 10 Bismuth oxide (I[I) 1.165 g, charcoal full
Strontium 0.738g, Calcium carbonate 1.50
Put 1g of copper oxide (It) and 1.591g of copper oxide (It) (both made by Kojundo Kagaku Co., Ltd., powder with a purity of 99.9% or higher) into an agate mortar, add several milliliters and liters of ethanol, and make a slurry to eliminate the ethanol smell. The operation of thoroughly stirring and mixing was repeated two or more times. The atomic ratio of Bi, 5rCa and Cu in the mixture was 1:1:3:4.

0.2 g of the obtained mixed powder was press-molded (1
A beret of 10 tons of sushi and a diameter of 10 cranes was prepared.

The pellets were heated in air according to the firing pattern shown in Figure 3, taking one hour to raise the temperature from room temperature to the temperature shown in Table 1, and held at that temperature for the time shown in Table 1. and fired.

Here, when the temperature of the pellets is in the range of 600° C. to 820° C., it is regarded as primary firing, and the time required for secondary firing and the average temperature of secondary firing are shown in Table 1.

Next, this pellet was heated to 875° C. over 1 hour and fired at this temperature for 24 hours. After that, let it cool and
After an hour, the pellet was returned to room temperature.

As a result of measuring the temperature dependence of the electrical resistance and AC complex magnetic susceptibility of the obtained fired product, it was found that the critical temperature was reached around 120°C, indicating that this material is a 120th grade superconducting material! It has been certified.

In order to compare the volume fraction of the superconducting material in Tc-120, 2θ = 23.3±, which specifically appears in the L phase,
2θ that appears specifically in the H phase for the intensity of the 0.2° diffraction peak (L in Figure 2) = 24.0±0.2
The ratio of the intensity of the diffraction peak of 6 (H in Figure 2) (H
/L) was determined and shown in Table 1. Moreover, FIG. 1 shows the change in H/L with respect to the average temperature (T° C.) of the primary firing and the secondary firing time (1+ hours). In FIG. 1, white circles indicate examples (H/L is 0.4 or more), and black circles indicate comparative examples (H/L is 0.4 or more).
is less than 0.4).

Further, FIG. 3 shows firing patterns in Examples and Comparative Examples.

Table 1 [Effects of the Invention] According to the present invention, a B1-5r-Ca-Cu-D-based oxide superconducting material having a high critical temperature (Tc) of 120 degrees can be advantageously produced. useful.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in H/L with respect to the average temperature and secondary firing time of the superconducting material of the present invention. In FIG. 1, white circles represent Examples 1 to 11 (H/L is 0.4 or more), and black circles represent Comparative Examples 1 to 10 (H/L is less than 0.4). Figure 2 shows the CuKa line (1,54
This is an enlarged view of the diffraction angle (2θ) in the vicinity of 23 to 24° in powder X-ray diffraction by 18 people, and H is 2θ-24,0
The intensity of the diffraction peak at ±0.2°, L is 2θ=23.
It represents the intensity of the diffraction peak of 3±0.2". Figure 3 is a diagram showing the firing patterns in Examples and Comparative Examples. Mamoru J('c>Kou2
Concave 2θ

Claims (1)

[Claims] (1) Compositional formula Sr_αCa_βBi_γCu_δO_x (wherein α, β, γ, δ and x represent the number of moles of each element, 0.1≦α/β≦1.5 0.8≦ α/γ≦2.0 0.25≦δ/(α+β+γ+δ)≦0.65 , under an oxygen-containing gas atmosphere, 6
After primary firing at 00-820℃, 830-89℃
When performing secondary firing at 5℃, if the average temperature of primary firing (T_1℃) is 600℃ or more and 700℃ or less, -0.015T_1+12.36≦t_1≦40 (however, t_1 is the primary baking time (hours) ).The average temperature of primary firing (T_1℃) is 700℃.
-0.015T_1 if higher than ℃ and below 820℃
A method for producing an oxide superconducting material, characterized in that primary firing is performed for a time that satisfies the following condition: +12.36≦t_1≦−0.2T_1+165 (where t_1 indicates primary firing time (hour)). (2) The temperature of secondary firing (T_2℃) is 830≦T_2≦32.5×logPo_2+895(
However, Po_2 indicates the oxygen partial pressure (atmospheric pressure) during firing. )
The manufacturing method according to claim 1. (3) The temperature of secondary firing (T_2℃) is 20.3×logPo_2+860≦T_2≦32.5
×logPo_2+895 (However, Po_2 indicates the oxygen partial pressure (atmospheric pressure) at the time of firing.)
Manufacturing method described in section.