JPH0269321A - Oxide superconducting material and its production - Google Patents

Abstract

PURPOSE:To obtain an oxide superconducting material having high critical temp. as high as 120K level by calcining a mixture consisting of an Sr compd., Ca compd., Bi compd., Cu compd., and Cr compd. under a specified condition. CONSTITUTION:A mixture consisting of an Sr compd., Ca compd, Bi compd., Cu compd. and Cr compd. is calcined primarily at 750-820 deg.C in O2-contg. atmosphere until Bi oxide becomes unrecognizable. Then, the product is calcined secondarily at 830-860 deg.C to obtain thus a target oxide superconducting material, which is expressed by the formula wherein each alpha, beta, gamma, delta, epsilon, and x is number of mole of each element; alpha/beta is <=1.0; 0<epsilon/beta<=0.6; gamma>0.; 0.5<=alpha/(gamma+epsilon) <=1.2; 0.25>=delta/(alpha+beta+gamma+delta+epsilon)<=0.65; pref. 1.8<=alpha<=2.2; 1.8<=beta<=2.2) 2.7<=delta<=3.3) 0.1<=epsilon<1.0; 1.0<=gamma<=2.2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxide superconducting material and a method for producing the same.

In particular, the present invention relates to high temperature oxide superconducting materials with high critical temperatures (Tc).

[Prior art and its challenges] Since the discovery of rare earth superconducting materials (Tc = 90Klr&) that exhibit superconductivity above the liquefaction temperature of nitrogen (77K),
Superconducting fever has occurred on a global scale, and this fever has been supported by the public's expectations for technological innovation, and in industry, it has increased in the fields of power storage, transportation, and power generation in power electronics, and in the field of low-power electronics. ,
It is expected to be used in a wide range of fields, including science and technology that utilize high magnetic fields and medical fields.

As a conventional superconducting material with high Tc, RBa 2
A perovskite type compound represented by Cu 30°-X (R; rare earth element) is known. Research on this material has been carried out all over the world, and the reason for this is that it has been found that of all the previously known superconducting materials, it is the only one that exhibits superconductivity at temperatures above the liquefaction temperature of nitrogen.

However, although the superconducting transition temperature of this substance is higher than 77, it is around 90, and as long as cheap liquefied nitrogen is used as a refrigerant, the close temperature is a cause for concern, and industrial In order to put it into practical use as a 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, the Bi-Sr-Cu-0-based oxide superconducting material was developed by C. Michel et al. (Z, Phys, B-
Condensed Matter 68.

421-423 (1987)). Although this Bi-Sr-Cu-0 type material exhibited superconductivity, it was unfortunately as low as Tc-22.

[Means for Solving the Problems 1] An object of the present invention is to exhibit superconductivity above the liquefaction temperature of nitrogen,
In particular, it is an object of the present invention to provide an oxide superconducting material having a high Tc of about 120, and a method for producing the same.

The above object of the present invention is achieved by an oxide superconducting material containing strontium, calcium, bismuth, copper and chromium in specific proportions.

The present invention will be explained in detail below.

The oxide superconducting material according to the present invention is an oxide of strontium, calcium, bismuth, copper and chromium,
The following composition formula % formula % (In the formula, αI D lγ, δ, ε and X represent the number of moles of each element, α/p≦1.0, O<ε/
p≦0.6゜γ>0.0.5≦α/(γ+ε)≦1,2
゜0.25≦δl (α10+γ+δ+8)≦0.65, preferably 1.8≦α≦2.2, 1.8≦p≦2.2
゜2.7≦δ≦3.3, 0.1≦ε≦1.0, 1.
0≦γ≦2.2. ).

The oxide superconducting material according to the present invention can be produced using carbonates, hydroxides, nitrates, sulfates, oxalates, chlorides, alkoxides, etc. of strontium, calcium, bismuth, steel, and chromium as raw materials. By appropriately selecting from these raw material compounds, Sr, Ca, Bi,
The atomic ratio of Cu and Cr is weighed so as to have the above composition, and mixed by a conventionally known method aiming at uniform mixing such as a powder mixing method, a wet coprecipitation method, an evaporation drying method, an alkoxide method, etc. 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 be pressure-molded and fired in the form of pellets. Generally, the firing temperature is preferably 500° C. or higher in order to decompose each salt. Bismuth oxide is preferably used as the bismuth compound, but since the melting point of bismuth oxide is 825°C, the second firing is performed at 750 to 8200°C.
After this is carried out sufficiently and bismuth oxide becomes virtually incomparable due to the formation of a composite oxide, secondary firing is carried out at 830 to 860°C. Disappearance of bismuth oxide can be detected by X-ray diffraction. By analyzing the superconducting properties of the composite oxide thus obtained, Tc-12
It can be confirmed that the material is an oxide superconducting material with 0K.

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,
Even if the amount is extremely small, as is the case with the thin-skinned model of superconducting materials, care must be taken because it may give information that appears to be entirely superconducting material.

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, when powder X-ray diffraction is performed using Cu Ka rays (1,5418 people), a Tc-
Diffraction peak due to superconducting material at 80 and Tc-12
0, a diffraction peak due to the superconducting material appears. Also,
In addition, peaks of impurities such as CuO and Ca2CuO3 appear.

The volume fraction of the substance having a diffraction peak group at Tc-120 in the sintered body is determined by powder X-ray diffraction.
2θ which appears specifically in superconducting materials at 80 = 23.
Tc- for the intensity (L) of the diffraction peak at 3±0.2°
2θ that appears specifically in superconducting materials at 120:24.
Comparison can be made by determining the ratio of the intensities (H) of the diffraction peaks at 0±0.2°.

The larger the volume fraction of the substance having a diffraction peak group at Tc-120 in the sintered body, the higher the Tc< and the H/L of 1.
A superconductor with a molecular weight of 5 or more, preferably 3.0 or more exhibits extremely good superconducting properties.

[Example J] 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 the gist thereof is exceeded.

Example 1 Strontium carbonate 0.7789 g, calcium carbonate 0.5281 g, bismuth (III) oxide 0
．． 9833 g, oxidized steel (II) 0.6295
g and 0.0802 g of chromium oxide (all manufactured by Kojundo Kagaku Co., Ltd., powders with a purity of 99.9% or higher) are placed in an agate mortar, and approximately 1 m of ethanol is added (to form a slurry, stir until the ethanol smell disappears). The mixture was stirred and mixed.The atomic ratio of Sr, Ca, Bi, Cu, and Cr in the mixture was 2:2:1.6:3:0.4.

0.4 g of the obtained mixed powder was press-molded (1
ton/cm2) L, a pellet with a diameter of 10 mm was created. This pellet is soo'c in the air for 5
A time-second firing was performed, followed by a 24-hour method firing at 850°C.

As a result of measuring the temperature dependence of the electrical resistance and AC complex magnetic susceptibility of the obtained fired product, the critical temperature was reached at 120°,
It was confirmed that this material is a 120 class superconducting material.

In order to compare the volume fraction of the superconducting material in Tc-120, the intensity of the diffraction peak at 2θ = 23.3 ± 0.2° that appears specifically in the superconducting material in Tc-80 (Fig. Find the ratio (H/L) of the intensity of the diffraction peak at 2θ:24.0±0.2° (H in Figure 1) that appears specifically in the superconducting material in Tc-120 to L) in Figure 1,
Table 1 shows the atomic ratio of the fired product.

Examples 2 to 6 and Comparative Examples 1 to 2 Superconducting materials were produced in the same manner as in Example 1 by changing the atomic ratios of Sr, Ca, Bi, Cu, and Cr, and (H/L) was determined. . The results obtained are shown in Table-1.

Table-1

[Brief explanation of the drawing]

Figure 1 shows the CuKa line (1,541
Powder X by 8 people)! This is an enlarged view where the diffraction angle (2θ) in 8 diffraction is around 23 to 24°, and H is 2θ=24.
The intensity of the diffraction peak at 0±0.2°, L is 2θ:23.
It represents the intensity of the diffraction peak at 3±0.2°.

Claims (1)

[Claims] (1) Compositional formula SrαCaβBiγCuδCrεOx (wherein α, β, γ, δ, ε and x represent the number of moles of each element, α/β≦1.0 0<ε/β≦ 0.6 γ>0 0.5≦α/(γ+ε)≦1.2 0.25≦δ/(α+β+γ+δ+ε)≦0.65). (2) Composition formula SrαCaβBiγCuδCrεOx (in the formula, α, β, γ, δ, ε and x represent the number of moles of each element, 1.8≦α≦2.2 1.8≦β≦2.2 2 .7≦δ≦3.3 0.1≦ε≦1.0 1.0≦γ≦2.2). (3) A mixture of strontium compounds, calcium compounds, bismuth compounds, copper compounds and chromium compounds,
After primary firing in an oxygen-containing gas atmosphere at 750 to 820°C until bismuth oxide is virtually no longer observed, 83
3. A method for producing an oxide superconducting material according to claim 1 or 2, characterized in that secondary firing is performed at 0 to 860°C.