JPH0214826A - Oxide superconductor and its manufacturing method - 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 Field of Application 1] The present invention relates to an oxide superconductor and a method for producing the same.

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

[Conventional technology and its problems 1 Conventionally, Ba (Pb Bi ) was used as an oxide superconductor.
03 was known, but this material had a Tc of 12 and required the use of liquid helium as a refrigerant.

Recently, among substances represented by RBa2Cu307x (R; rare earth element), a substance with Tc exceeding 90K has been found, and liquid nitrogen has become usable as a refrigerant.

However, in order to put it into practical use as a superconducting material, it is desirable to have a material with an even higher critical temperature.

[Means for Solving the Problems 1] An object of the present invention is to provide an oxide superconductor that exhibits superconductivity above the liquefaction temperature of nitrogen. This is achieved with copper-containing oxide superconductors.

The present invention will be explained in detail below.

The oxide superconductor according to the present invention is an oxide of bismuth, vanadium, strontium, calcium, and copper, and has the following compositional formula: BiaV13SrγCaδCueOx (where α, I3.γ, δ, ε, and X are each Represents the number of moles of the element, α = 2.0-13 0.2≦p≦0,8 1.8≦γ≦2.2 1.8≦δ≦2.2 2.7≦8≦3.3 Preferably, α=2.0-13 0.4≦p≦0.6 γ=2.0 δ=2.0 ε=3.0.

The oxide superconductor according to the present invention can be produced using oxides, carbonates, hydroxides, nitrates, sulfates, oxalates, chlorides, alkoxides, etc. of bismuth, vanadium, strontium, calcium, and copper as raw materials. I can do it. By appropriately selecting from these raw material compounds, Bi, V,
Weigh so that the atomic ratios of Sr, Ca and Cu become the above composition, and aim for homogeneous mixing using conventionally known methods such as powder mixing method, wet coprecipitation method, evaporation to dryness method, sol-gel method using alkoxide, etc. Mixed by method. The resulting mixture is dried and then fired.

At this time, in order to allow the solid phase reaction to proceed sufficiently, it is preferable that the powder is press-molded and fired in the form of pellets. Generally, the firing temperature is preferably 500° C. or higher in order to decompose each salt. Vanadium oxide is preferably used as the vanadium compound, but since the melting point of vanadium oxide is 690°C, it is not sufficient to perform the second firing at 680°C or lower. ℃1 Preferably 850-8
Secondary firing is performed at 60°C. Vanadium oxide disappeared by X-ray diffraction (the main diffraction angle of vanadium pentoxide is 2θ:20
．． 3°) can be detected. The secondary firing is
At least one hour is required, preferably 24 hours or more, more preferably 120 hours or more, and the longer the firing time, the better the superconducting properties of the superconductor obtained.

By analyzing the superconducting properties of the composite oxide thus obtained, it can be confirmed that it is an oxide superconductor having Tc-ll0K. That is, when powder X-ray diffraction is performed using CuKa radiation (1,5418A), bismuth, strontium, calcium,
A diffraction peak due to the substance at Tc-80 and a diffraction peak due to the substance at Tc-110 similar to those appearing in the diffraction pattern of a known oxide superconductor containing copper as an essential component appear. In addition, impurities Cub, C
Peaks such as a2CuO3 and some unknown peaks appear. In the sintered body of the present invention, the larger the volume fraction of the substance having the diffraction peak group at 110, the higher the Tc. The size of the volume fraction of a substance having a diffraction peak group at 110 in a sintered body is determined by powder X-ray diffraction at 2θ = 23.3 ± 0.2°, which appears specifically for a substance at Tc-80. 2<3 = 24.0±0. which appears specifically in a substance having a diffraction peak group at Tc-110 with respect to the intensity (L) of the diffraction peak.
By determining the ratio of the intensities (H) of the 2° diffraction peak, it is possible to conveniently compare, and H/L≧0.
1. In particular, oxide superconductors with H/L≧1.0 exhibit extremely good superconducting properties.

[Examples] 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 Bismuth (III) oxide 0.8777g, vanadium (V) oxide 0.1468g, strontium carbonate 0.7946g, calcium carbonate 0.5387g
, 0.6421 g of copper (II) oxide (all powders with a purity of 99.9% or higher) were placed in a Mehan mortar, and approximately 1 me of ethanol was added to form a slurry and thoroughly stirred and mixed. The atomic ratio of Bi, V, Sr, Ca and Cu in the mixture is 1.4:0.6+2.0+2.0:3
．． It is 0.

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 was heated to 600'C in air for 2 hours.
After 4-hour secondary firing and then 24-hour firing at 860°C, it was slowly cooled to room temperature at a cooling rate of 50°C/hr.

As a result of measuring the temperature dependence of the electrical resistance and AC complex magnetic susceptibility of the obtained fired product, the critical gain was reached at 110,
It was confirmed that this material is a class 110 superconductor.

Powder X of this substance by CuKa ray (1,5418A)
As a result of line diffraction, 2θ = 4.8°, 2θ = 24, mixed with the diffraction peaks due to impurities and Tc-80
．． At 0°, 2θ: 26.2° and other angles, Tc
A diffraction peak due to the substance at -110 was obtained. The obtained X-ray diffraction pattern is shown in Figure 1.

In addition, in order to compare the volume fractions of lloK-class superconducting materials, 2e, which specifically appears in Tc-80 materials, was
2e: Intensity of the diffraction peak at 24.0±0.2° (L in Figure 2) that appears specifically in the substance having the above diffraction peak group for the intensity of the diffraction peak at 23.3±0.2° (L) When we calculated the ratio of H) in Figure 2, we found that H
/L=2.7, and it was recognized that Tc-110 contained a large amount of superconducting material.

Examples 2 to 5, Comparative Examples 1 to 6 Oxide superconductors were produced in the same manner as in Example 1, except that the atomic ratios of bismuth, vanadium, strontium, calcium, and copper were changed as shown in Table 1. was manufactured and H/L was measured. The results obtained are shown in Table-1.

Table-1 It will be done.

[Brief explanation of the drawing]

Figure 1 shows the superconductor manufactured in Example 1 with C
Powder X obtained using uKa radiation (1,5418A)
This is a line diffraction pattern. In Figure 1, the peaks marked ([) indicate the phase of TC~110, the peaks marked Δ indicate the phase of TC~80, and the peaks marked 0 indicate the phase of CuO The peaks marked with ・ are Ca2
Indicates CuO3. In Figure 2, the diffraction angle (20) in Figure 1 is 23 to 24.
This is an enlarged view around °, H and L are each 2 E3
:24.04° and 2 (3 = represents the intensity of the diffraction peak at 23.29°. Diffraction intensity diagram-2 Diffraction angle 2θ (degrees)

Claims (2)

[Claims] (1) Composition formula BiαVβSrγCaδCuεOx (In the formula, α, β, γ, δ, ε and x represent the number of moles of each element, α=2.0−β 0.2≦β≦0.8 1.8 ≦γ≦2.2 1.8≦δ≦2.2 2.7≦ε≦3.3. ) oxide superconductor. (2) A mixture of a bismuth compound, a vanadium compound, a strontium compound, a calcium compound, and a copper compound is primarily fired in an oxygen-containing gas atmosphere at a temperature of 680°C or lower until vanadium oxide is virtually no longer observed, and then 2. The method for producing an oxide superconductor according to claim 1, wherein the secondary firing is carried out at a temperature of .degree.