JP2831755B2 - Oxide superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide high-temperature superconductor, and more particularly to an oxide high-temperature superconductor having an extremely high superconducting transition critical temperature (hereinafter, referred to as Tc). Things.

[Prior art] As a superconducting oxide, La _2-x Ba _x CuO _4-y (x ≦ 0.3, y ≦ 0.5) having a Tc of 30 K class was developed by Bednorz Müller of IBM et al. −190712), since it has received attention as a material that dramatically increases the Tc of intermetallic compound superconductors represented by Nb ₃ Sn.
YBa ₂ Cu ₃ O of _7-δ Tc90K class represented by Y-based oxide superconductor (WO88 / 05029), Bi-based oxide of Tc110K class represented by _{Bi 2 Sr 2 Ca 2 Cu 3} O 10-δ Superconductor (JP-A-1-188456)
And Tl _- based oxide superconductors represented by Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _10-δ (JP-A-1-219007) are known. In addition, as a Bi-based oxide superconductor, a system in which a part of Bi is substituted by Pb is known as an improvement in the difficulty in the production.

As seen in the above oxide superconductor, when Tc exceeds 77 K, it becomes possible to use inexpensive and easily available liquid nitrogen as a refrigerant for the superconductor, and expectations for practical use are increasing. .

However, superconductors have the danger of suddenly becoming superconductors when used at temperatures near Tc, and may become normal conductors. A material having a higher Tc than a material superconductor or a Bi-based oxide superconductor is desired. On the other hand, T1-based oxide superconductors have the highest Tc among the above-mentioned oxide superconductors, but simple substances and compounds of Tl are toxic and dangerous when touching or inhaling the skin. However, there is a problem in terms of safety in industrial production and use.

[Problem to be Solved by the Invention] The present invention has been made by focusing on the above circumstances,
An object of the present invention is to provide a superconducting material which has stable Tc even when used at the temperature of liquid nitrogen and is safe in industrial production and use.

[Means for Solving the Problems] The oxide superconductor of the present invention that has achieved the above objects is an oxide containing Bi and Pb and Sr, La, Ca, Cu, The gist is that the composition ratio of the element is an oxide represented by the following formula.

(Bi _1-x Pb _x ) _a (Sr _1-y La _y ) _b Ca _c Cu _d … where 0 <x ≦ 0.5,0.01 ≦ y ≦ 0.3, and b, c, d is a =
Assuming that 1, 0.7 ≦ b ≦ 1.2, 0.3 ≦ c ≦ 3, 0.8 ≦ d ≦ 5 In order to obtain a still higher Tc, particularly in the above composition formula, 0.1
When ≦ x ≦ 0.4, 0.05 ≦ y ≦ 0.2, a = 1, 0.8 ≦ b ≦
1.1,0.8 ≦ c ≦ 2,1.3 ≦ d ≦ 3 or 0.8 ≦
It is effective that b ≦ 1.1, 0.3 ≦ c ≦ 0.6, 0.8 ≦ d ≦ 1.2.

[Operation] The present inventors repeatedly performed substitution experiments on the Bi-based oxide superconductor with various elements and composition ratios of the oxide constituent elements. As a result, it was found that by effectively introducing La into the Bi-Sr-Ca-Cu-based oxide, Tc can be greatly improved. From the analysis by X-ray diffraction and the like, it can be estimated that La in the present invention replaces part of the Sr site in the conventional Bi—Sr—Ca—Cu crystal structure.

The superconductor of the present invention may be any one having a composition as set forth in the claims, and is not limited by the manufacturing method. However, the above-mentioned La introduction is the same as the conventional Bi-based superconductor manufacturing method. If it is adopted, it may not be performed effectively, and it is necessary to pay particular attention to the firing conditions.
A typical method for producing the superconductor of the present invention will be described below.

The compounds of Bi, Pb, Sr, La, Ca, and Cu are weighed so as to have the atomic ratio of the above formula, and are uniformly mixed. The present invention is not limited by the type of the compound used. The compound may be an oxide, an inorganic acid salt such as a carbonate, a nitrate or a sulfate, or an organic acid such as an acetate or an oxalate. Salts, alkoxide compounds, various complex compounds and the like are applicable. The mixing method is also not particularly limited, and may be appropriately selected from known methods such as, for example, mechanical mixing, uniform solution, coprecipitation, and the like, depending on the type and physical properties of the compound.

Next, after drying the above mixture as necessary, 750 to 8
Perform calcination at 50 ° C. Although the calcining time and the number of times are not particularly limited, it is usually only 2 to 20 hours, but it is sufficient that the calcined product has a more stable Tc when the calcined product is pulverized once, remixed, and calcined repeatedly. can get. Pressing the powder after calcination into a disk-shaped molded article, under an oxygen atmosphere or an inert gas atmosphere, from the melting lower limit temperature of the calcination mixture in that atmosphere
The firing is performed in a temperature range having a lower limit of 20 ° C. Preferably, the calcination is carried out at a temperature within the range of the lower limit of melting temperature or 30 ° C. higher than the lower limit. The firing time is preferably 10 hours or more. The lower limit of the melting temperature of the calcined mixture in the present invention is a temperature at which the endothermic peak of the phase change rises in the differential thermal analysis, and the molded product is deformed even if it is fired at a temperature about 20 ° C. higher than this temperature. Such melting does not occur.

Since the lower limit of the melting temperature is shifted to a higher temperature by adding La, the firing temperature may be set accordingly. Although the oxygen partial pressure in the firing atmosphere is not particularly limited, a low oxygen partial pressure is preferable in relation to the firing temperature because the lower limit of melting temperature is in the direction of lowering and the optimum firing temperature can be lowered. It is also possible to adopt an atmosphere containing no oxygen at all, but in this case, it is recommended to perform an oxygen treatment in a post-process.

The oxide superconductor manufactured through the above steps has an extremely high Tc and has a higher density and strength than conventional oxide superconductors containing Bi, which is advantageous for forming wires.

[Example] Example _{1 Bi (NO 3) 3 ·} 5H 2 O, Pb (NO 3) 2, Sr (NO 3) 2, La (N
_{O 3) 3 · 6H 2 O} , Ca a _{(NO 3) 2 · 4H 2} O, Cu (NO 3) 2 · 3H 2 O commercial reagent (manufactured by Wako Pure Chemical Industries, Ltd., purity: 99.9%), metal atoms in the formula When the ratio is x = 0.2, y = 0.1, a = 1, b = 0.9, c = 1.0,
Weigh so that d = 1.5, mix and stir to heat,
The nitrate was gradually melted to make a homogeneous liquid. This is 230
It was dried for 20 hours in a dryer at ℃. This at 800 ° C in air
The calcining / crushing / remixing for 0 hour was repeated three times. When the powder obtained at the end was subjected to differential thermal analysis, the lower limit melting point was 845 ° C.
Met. This powder was pressed to form a disk having a diameter of about 15 mm and a thickness of about 2 mm, and calcined at 865 ° C for 150 hours at an oxygen partial pressure of 0.1 atm to obtain a test piece. Was measured Tc by an ordinary four-terminal method the test piece, superconducting transition beginning temperature (hereinafter referred to as Tc onset) is 133K, zero resistance temperature (hereinafter referred to as Tc ₀₎ showed 121K.

Example 2 Commercially available reagents of Bi ₂ O ₃ , PbO, SrCO ₃ , La ₂ O ₃ , CaCO ₃ , and CuO (purity: 99.9%, manufactured by Wako Pure Chemical Industries, Ltd.) were used with the metal atom ratio x = 0.35, y = 0.15, a = 1, b = 0.9, c = 1.0, d = 1.5 were weighed and thoroughly mixed in a mortar. 800 ° C
After calcination for 10 hours, a disk was formed by pressurizing to form a disk having a diameter of about 15 mm and a thickness of about 2 mm, and baked at 870 ° C for 200 hours at an oxygen partial pressure of 0.1 atm to obtain a test piece. Was measured Tc by an ordinary four-terminal method the test piece, Tc onset 132K, Tc ₀ showed 120K.

Examples 3 to 5 Test pieces were obtained in the same manner as in Example 1 except for the metal atomic ratio, the oxygen partial pressure, and the firing temperature shown in Table 1, and Tc was measured by a usual four-terminal method. The results are shown in Table 1.

Thus, the oxide superconductor of the present invention has a Tc of at least 77.
In Examples 1 and 2, a superconductor having a Tc of 120 K or more was obtained.

[Effects of the Invention] Since the present invention is configured as described above, a Tc120K-class oxide superconducting material that exhibits stable superconductivity even when liquid nitrogen is used as a refrigerant and that is safe during production and use is also provided. It can be provided.

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Claims (3)

(57) [Claims] An oxide comprising Bi and Pb and Sr, La, Ca, Cu, wherein the composition ratio of each metal element is represented by the following formula: Oxide superconductor. (Bi _1-x Pb _x ) _a (Sr _1-y La _y ) _b Ca _c Cu _d where 0x ≦ 0.5,0.01 ≦ y ≦ 0.3 and b, c, d is a = 1
0.7 ≦ b ≦ 1.2, 0.3 ≦ c ≦ 3, 0.8 ≦ d ≦ 5 (2) 0.1 ≦ x ≦ 0.4, 0.05 ≦ y ≦ 0.2, and a =
The oxide superconductor according to claim 1, wherein when 1 is satisfied, 0.8 ≦ b ≦ 1.1, 0.8 ≦ c ≦ 2, 1.3 ≦ d ≦ 3. 3. The condition of 0.1 ≦ x ≦ 0.4, 0.05 ≦ y ≦ 0.2, and a =
The oxide superconductor according to claim 1, wherein, when 1, 1, 0.8 ≦ b ≦ 1.1, 0.3 ≦ c ≦ 0.6, 0.8 ≦ d ≦ 1.2.