JPH03112815A - Oxide superconducting substance and its production - Google Patents

Abstract

PURPOSE:To obtain a Bi-Sr-Ca-Cu-O-based oxide superconducting substance having high critical temperature by blending a Sr compound with Ca compound, Bi compound and copper compound in a given ratio and calcining the blend in an oxygen-containing atmosphere at specific two stages. CONSTITUTION:A strontium compound (e.g. strontium carbonate) is blended with a calcium compound (e.g. CaCO3), a bismuth compound (e.g. bismuth oxide) and a copper compound (e.g. CuO) to give a compound shown by the formula [alpha/beta<=1.5;0.8<= alpha/gamma<=2; 0.25<=delta/(alpha+beta+gamma+delta)<=0.8; 0.5<=beta/delta<=0.85; 0.57<=(alpha+delta)/(alpha+ beta+gamma+delta)<=0.65]. Then the blend is calcined in an oxygen-containing atmosphere at 600-820 deg.C as first stage and then further burnt at 830-895 deg.C as a second stage to give a superconducting substance having high critical temperature of about 120K class and a small amount of impurity phase.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a Bi-Sr-Ca-Cu-0 based oxide superconducting material having a high critical temperature (Tc-12OK) and a method for producing the same. be.

[Prior art 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 the perovskite compound represented by 07-x (R; rare earth element) is higher than that of 77,
As long as cheap liquefied nitrogen is used as a refrigerant, it is a concern that the temperatures are close to each other. It has been desired to develop a superconducting material with a high Tc of 120 or higher, which is five times that of the previous one. 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, Bi-Sr-Ca-Cu-0-based oxide superconducting materials have been proposed by H., Maeda et al. (Jap, J., A.
ppl, Phys, Lett, 27L209 (
(1988)), and the system contains at least three compounds with different critical temperatures (Tc-2OK, 80
K.

120 K) was found to exist. Among these three types of compounds, it is known that a certain amount of the Tc-120 compound (hereinafter referred to as H phase), which is a promising material for practical use due to its high critical temperature, can be obtained by increasing the firing time. It is being However, if the charged composition does not match the composition of the H phase, the excessively charged elements will form another impurity phase that is not a superconducting material. Therefore, in order to obtain a Bi-based oxide superconducting material containing a large amount of H phase, it was necessary to optimize the composition and manufacturing conditions.

[Means for Solving the Problems 1] An object of the present invention is to provide an optimal composition of a Bi-based oxide superconducting material having a high Tc of about 120, and a method for producing the same.

That is, the gist of the present invention is as follows: Compositional formula: Sr a Cap Bi 7 CuδOx (
In the formula, αeDtγ, δ and X represent the number of moles of each element, α/p≦1.5 0.8≦αlγ≦2.0 0.25≦δ/(α+β+γ+δ)≦0.800.50
≦131δ≦0.85 0.57≦(β+δ)/(α+β+γ+δ)≦0.65
It is. ) and a mixture of a strontium compound, a calcium compound, a bismuth compound, and a copper compound in an oxygen-containing gas atmosphere at 60°C.
After firing at 0 to 820°C, further 830 to 89°C
The method for producing the oxide superconducting material described above is characterized in that firing is performed at 5°C.

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 α1p2γ, δ, and X represent the number of moles of each element. , α/p≦1.5.0.8≦α/γ≦2.0
．． 0.25≦δ/(α+p+γ+δ)≦0.80.0.
50≦43/δ≦0.85.0.57≦(p+δ)/(
α1p1γ+δ)≦0.65. ) of carbonates, hydroxides, nitrates, sulfates, chlorides of strontium, calcium, bismuth and steel;
It can be produced using alkoxides and the like as raw materials.

Sr, Ca, etc. are suitably selected from these raw material compounds.

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 that the powder is pressure-molded and fired in the form of pellets. The calcination is performed in an oxygen-containing gas atmosphere in order to decompose each salt, and in the present invention, the calcination is performed in two stages.

First, a first stage firing is performed at 600 to 820°C. Although it depends on the firing temperature, if the firing time is too short or too long, the proportion of H phase produced tends to decrease. Further, the firing may be performed by keeping the temperature at a certain constant level or gradually increasing the temperature, and the firing pattern can be selected as appropriate.

Since the H phase is thermodynamically stable even at considerably high temperatures in an oxygen-containing gas atmosphere, by generating as much H phase as possible in the -th stage firing, the second stage firing time can be shortened. be able to.

Next, a second stage of firing is performed at 830 to 895°C. The firing time is required to be at least 1 hour, preferably 24 hours or more, more preferably 120 hours or more, and the longer the firing time, the better the properties of the obtained superconductor will be.

Although the second stage firing pattern can be selected as appropriate in the same manner as the first stage, 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 (T2°C) of the secondary firing depending on the oxygen partial pressure in the atmosphere, and when firing at normal pressure, empirically, 830≦ T2≦32.5 X 1θgP02+ 895
Preferably, 20.3X1θgP02+860≦T2≦32.5X
It has been found that it is effective to perform the secondary firing at log PO2+ 895 (where PO2 indicates the oxygen partial pressure (atmospheric pressure) at the time of 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 wire (1,5418 pieces)
When line diffraction is performed, Tc-8, which is similar to the peak that appears in the diffraction pattern of known oxide superconducting materials containing bismuth, strontium, calcium, and copper as essential components, is found.
0, a diffraction peak due to the superconducting material (hereinafter referred to as L phase) and a diffraction peak due to the H phase appear. In addition, Cub is an impurity.

Peaks such as Ca2CuO3 appear.

The volume fraction of the H phase in a superconducting material is determined by 2θ = 23.3, 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 appears specifically in the H phase, to the intensity (L) of the diffraction peak at ±0.2°. .

In the superconducting material of the present invention, Ca is the main impurity.
2CuO3 generally exists between grains of superconducting materials and prevents conduction of superconducting current.

2θ which characteristically appears in Ca2CuO3 = 36.2±
The intensity of the diffraction peak at 0.2° (A) and the ratio of H (A/H
), the amount of impurity phase produced can be compared.

The larger the volume fraction of the H phase, the better the superconducting properties.

When H/L exceeds 0.4, the 120K phase increases, so it can be determined from the AC magnetic susceptibility that the entire sample forms almost the 120K phase. Therefore, in practice H/
A value of L of 0.4 is used as a guideline, and if it is greater than this value, it can be said that it is a good superconductor.

Further, the smaller A/H is, the better the superconducting properties are. A
If /H is 0.4 or less, the amount of impurities decreases, and from the DC resistivity, a drop in resistance due to superconductivity near Tc-120 becomes noticeable. Therefore, if the value of A/H is less than 0.4, it can be said to be a good superconductor.

[Example 1] Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 0.932 g of bismuth oxide (III), 0.591 g of strontium carbonate, 0.601 g of calcium carbonate, and 0.636 g of steel oxide (II) (all manufactured by Kojundo Kagaku Co., Ltd., powder with a purity of 99.9% or more) into an agate mortar,
The operation of adding several meters of ethanol (to form a slurry) and thoroughly stirring and mixing until the ethanol odor disappeared was repeated two or more times.

The atomic ratio of Bi, Sr, Ca and Cu in the mixture is:
The ratio is 2:2:3:4.

0.2 g of the obtained mixture powder was pressure-molded (1 t
on/cm2) L, a pellet with a diameter of 10 mm was prepared. This pellet was fired in air at 630°C for 100 hours and then at 875°C for 200 hours.

As a result of measuring the temperature dependence of the electrical resistance and AC magnetic susceptibility of the obtained fired product, the critical temperature was found around 120, and it was confirmed that this material contains an originating conductive material at 120.

In order to compare the size of the volume fraction of the superconducting material in Tc-120, 2 which appears specifically in the superconducting material in Tc-80
The intensity of the diffraction peak at 2θ = 24.0 ± 0.2° (L in Figure 1) that appears specifically in the superconducting material at Tc-120 is The ratio (H/L) of intensity (H in FIG. 1) was determined.

In addition, in order to compare the volume fraction of Ca2CuO3, which is the main impurity, the intensity of the diffraction peak at 2θ = 36.2 ± 0.2° (A in Figure 1), which characteristically appears in Ca2CuO3 with respect to H, is The ratio (A/H) was determined.

The results are shown in Table 1.

Examples 2 to 13, Comparative Examples 1 to 2 Superden 4 substances were produced and evaluated in the same manner as in Example 1, except that the raw material powder was weighed and used so as to have the chemical composition shown in Table 1. I did this. The results are shown in Table 1.

Table 1 4゜ [Effect of the invention] According to the present invention, a critical temperature (Tc) as high as 120
Bi-Sr-Ca-C with few impurity phases
It is industrially useful because u-0-based oxide superconducting materials can be produced.

[Brief explanation of drawings]

FIG. 1 shows the CuKa line (wavelength 1.
Diffraction angle (
2θ) is an enlarged view of around 23 to 24° and around 36°. In FIG. 1, H represents the intensity of the diffraction peak at 2θ: 24.0±0.2°, and L represents the intensity of the diffraction peak at 2θ=23.3±0.2°. Furthermore, A is 2θ=36.2±0.2
It represents the intensity of the diffraction peak due to C, a2cu03 at °C.

Claims (4)

[Claims] (1) Composition formula SrαCaβBiγCuδOx (In the formula, α, β, γ, δ and x represent the number of moles of each element, α/β≦1.5 0.8≦α/γ≦2.0 0.25 ≦δ/(α+β+γ+δ)≦0.800.50
≦β/δ≦0.85 0.57≦(β+δ)/(α+β+γ+δ)≦0.65
It is. ) is an oxide superconducting material. (2) A mixture of a strontium compound, a calcium compound, a bismuth compound, and a copper compound is fired in the first stage at 600 to 820°C in an oxygen-containing gas atmosphere, and then the second stage is fired at 830 to 895°C. A method for producing an oxide superconducting material according to claim 1, characterized in that the method is carried out. (3) In the second stage firing, the firing temperature (T°C) is 8
The manufacturing method according to claim 2, wherein 30≦T≦32.5×logP_O_2+895 (where P_O_2 indicates the oxygen partial pressure (atmospheric pressure) at the time of firing). (4) In the second stage firing, the firing temperature (T°C) is 2
0.3×logP_O_2+860≦T≦32.5×l
ogP_O_2+895 (however, P_O_2 indicates oxygen partial pressure (atmospheric pressure) at the time of firing)
Manufacturing method described in section.