JP2761722B2 - Oxide superconductor and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide superconductor used for a magnetic coil portion such as a magnetic levitation train and a particle accelerator, an electronic device, a circuit board of a Josephson computer, and the like. It is. [Prior Art] At present, metallic superconductors represented by Nb ₃ Ge and Nb ₃ Sn have been put to practical use, but their critical temperature (Tc) is at most about 23.2K. However, recently, it has been announced that an oxide superconductor composed of a mixture of a rare earth element, an alkaline earth element, and copper oxide has a significantly higher critical temperature than a metal superconductor (for example, the University of Tokyo group of engineering). The American Physical Society of Japan announced that it had achieved 90K), and it was possible to use inexpensive liquid nitrogen instead of expensive, extremely low temperature (4.2K = 268.8 ° C) liquid helium as a refrigerant. Therefore, great progress has been made in the prospect of practical use of this oxide-based superconductor in various application fields. With these announcements, in bulk or thin film oxide superconductors in the above application fields,
Research is being actively conducted to further increase the critical temperature (Tc) to room temperature. [Problems to be Solved by the Invention] In accordance with the demand for such an oxide superconductor, an improvement in its performance is required. In particular, high critical temperature (Tc) and high critical current density (Jc) are required in electronics applications and transport systems. However, the current density of current oxide superconductors is lower than the current density required for electronics applications and transport systems because the critical current density is lower than that of metallic superconductors.
Therefore, there is a problem that the critical current density of the oxide superconductor must be improved in order to use the oxide superconductor for electronics, transportation systems, and the like. [Object of the Invention] An object of the present invention is to improve the critical current density (Jc) without deteriorating the critical temperature of a RE ₁ Ba ₂ Cu ₃ O _{7- δ-} based oxide superconductor. [Means for Solving the Problems] According to the present invention, RE ₁ Ba ₂ Cu ₃ O _{7- δ} (RE = rare earth element)
Oxidation with a crystal structure in which Ba ₂ SiO ₄ is precipitated in a polycrystalline body of an oxide superconductor having a critical current density (Jc) of 1.1 × 10 ³ A / cm ² or more in a magnetic field of 0.15 T A superconductor is provided. According to the present invention, RE: Ba: Cu: Si = 1: 2 (x
+1): y: x (RE = rare earth element) (0.05 ≦ x ≦ 0.80,3 ≦ y
≦ 3.3) RE ₁ Ba _{2 (x + 1)} Cu _y O _{7- δ} (0.05 ≦ x ≦
0.80,3 ≦ y ≦ 3.3) A powder obtained by mixing at least one of SiC, SiO ₂ and Si ₃ N _{4 with} the calcined powder at 920 ° C. to 980 ° C. for about 1 hour
There is provided a method for producing an oxide superconductor, which is characterized in that the oxide superconductor is cooled after baking for 5 to 5 hours. Also according to the invention, RE ₁ B
a ₂ Cu ₃ O _{7- δ} · nBa ₂ SiO _{4 The} composition is characterized in that n is 0.05 ≦ n ≦ 0.80 and the mixed powder is calcined at 920 ° C. to 980 ° C. for about 1 to 5 hours and then cooled. A method for manufacturing an oxide superconductor is provided. That is, by depositing Ba ₂ SiO ₄ in a polycrystalline oxide superconductor of RE ₁ Ba ₂ Cu ₃ O _{7- δ} (RE = rare earth element), general Y ₁ Ba ₂ Cu ₃ O _{7- From} the grain boundary layer of the _δ oxide superconductor, it is possible to generate a grain boundary layer that does not become a barrier to the flow of current, and it is possible to generate a general Y ₁ Ba ₂ Cu ₃ O _{7- δ} oxide superconductor (bulk). A current density higher than the current density is obtained. In normal of Y ₁ Ba ₂ Cu ₃ grain boundaries of O _{7- [delta],} the cooling process in the firing, especially on the low temperature side, a solid solution of crystal and perfect crystal with oxygen defects of Y ₁ Ba ₂ Cu ₃ O _{7- [delta]} Phase separation occurs, and this phase separation is a barrier to current flow. However, when Ba ₂ SiO ₄ is precipitated in the polycrystal of oxide superconductor of RE ₁ Ba ₂ Cu ₃ O _{7- δ} (RE = rare earth element), the crystal with oxygen vacancies at the grain boundary is completely The phenomenon of phase separation of the solid solution with the crystal hardly occurs. Therefore, in the superconductor of the present invention, a grain boundary through which current flows more easily than a general Y ₁ Ba ₂ Cu ₃ O _{7- δ} grain boundary is generated by the precipitation of Ba ₂ SiO ₄ . A manufacturing method for obtaining such a superconductor (bulk) is, for example, using RE ₂ O ₃ , BaCO ₃ , and CuO as raw material powders and using RE ₁ Ba
_{2 (x + 1)} Cu _y O _{7- δ} (0.05 ≦ x ≦ 0.80, 3 ≦ y ≦ 3.3) are mixed and calcined at 850 ° C. to 950 ° C. Then R
E: Ba: Cu: Si = 1: 2 (x + 1): y: x (0.05 ≦ x ≦ 0.80,3 ≦
The oxide superconductor calcined powder of RE ₁ Ba _{2 (x + 1)} Cu _y O _{7- δ} is mixed with SiO _2, SiC or Si ₃ N ₄ so that y ≦ 3.3), mixed and molded. This compact is placed in an oxygen gas stream 920
After calcination at a temperature of from ℃ to 980 ° C for a relatively short time, that is, about 1 to 5 hours, cooling is performed. By such an operation, an oxide superconductor having a critical current density of 1.1 × 10 ³ A / cm ² or more in which Ba ₂ SiO ₄ is deposited is generated. If the calcination temperature is lower than 850 ° C, RE ₁ Ba _{2 (x ≠ 1)} Cu _y O
_{The 7- δ} composition cannot be formed, and the calcined powder does not become a superconductor.
When the temperature is higher than 950 ° C, solid solution advances and the raw material elutes, and RE ₁ Ba
The crystal structure of only the _{2 (x + 1)} Cu _y O _{7- δ} composition mixture is not obtained. If the main firing temperature is lower than 920 ° C. in the main firing in an oxygen stream, the crystal of Y ₁ Ba ₂ Cu ₃ O _{7- δ} causes oxygen defects, and the critical temperature does not increase. If the temperature is higher than 980 ° C., the solution is completely dissolved and eluted, so that the RE ₁ Ba ₂ Cu ₃ O _{7- δ} composition cannot be formed, and the superconductor having a critical temperature of 95 K or more is not obtained. further,
By cooling after the main firing, the superconductor phase can be stabilized. Another production method for obtaining this superconductor is, for example, to use RE ₂ O ₃ , BaCO ₃ , CuO as a raw material powder in RE ₁ Ba ₂ Cu _y O _{7- δ.}
Mix, mix and calcine at 850 ° C to 950 ° C
A calcined product of RE ₁ Ba ₂ Cu _y O _{7- δ} was obtained, and then RE ₁ Ba ₂ Cu ₃ O _{7- δ}
・ RE ₁ Ba ₂ C so that 0.05 ≦ n ≦ 0.80 in the composition of nBa ₂ SiO ₄
Ba ₂ SiO ₄ is mixed with u ₃ O _{7- δ} oxide superconductor calcined powder, mixed and molded. This compact is placed in an oxygen gas stream at 920 ° C to 980
After calcination at a temperature of for a relatively short time, that is, for 1 to 5 hours, the mixture is cooled. By such an operation, an oxide superconductor in which the critical current density at which Ba ₂ SiO ₄ is deposited is 1.1 × 10 ³ A / cm ² or more is generated. The present invention will be described with the following examples. Example 1 Y ₂ O ₃ 8.475mol% and BaCO ₃ 40.678mol% and CuO 50.847Mo
After mixing and mixing at a ratio of ₁ % to Y ₁ Ba _2.4 Cu ₃ O _{7- δ} , the mixture was calcined in air at 880 ° C. for 5 hours. This calcined body is pulverized, and S: S: Y: Ba: Cu: Si = 1: 2.4: 3: 0.2
i ₃ N ₄ was mixed with the calcined powder. This mixed powder is molded into a 12 mmφ pellet, and the molded body is heated to 920 ° C. to 9 ° C. in an oxygen stream.
After firing at 80 ° C. for 1 to 5 hours, the sample was cooled to obtain a sample. As a result of examining the resistance change with respect to temperature of this sample by a four-terminal method, the onset temperature (Tco) was 94K and the offset temperature (Tce) was 92K. The density (Archimedes method) was 6.0 g / cm ² . Further, the MH hysteresis curve of the sample was determined using a vibrating sample magnetometer. These results are shown in FIG. In FIG. 1, in the MH hysteresis curve, the difference (ΔM) in magnetization between the elevation curve 1 and the demagnetization curve 2 is expressed by the following equation:
It is expressed as _{Δ M (Be) = μ o} · d · Jc. Here, mu _o is 1/2, Jc vacuum permeability, d is the plate-like sample width represents the critical current density. From the hysteresis curve of FIG. 1, the critical current density Jc was determined from the magnetization difference ΔM using the above equation. As a result, the magnetization difference ΔM (0.15
T) is 3.40 (mT) and the critical current density Jc (0.15T) is 1.12 ×
It was 10 ³ (A / cm ² ). Example 2 Y ₂ O ₃ 8.475mol% and BaCO ₃ 40.678mol% and CuO 50.847Mo
After mixing and mixing at a ratio of ₁ % to Y ₁ Ba _2.4 Cu ₃ O _{7- δ} , the mixture was calcined in air at 880 ° C. for 5 hours. This calcined body was pulverized, and SiO ₂ was mixed with the calcined powder in a ratio of Y: Ba: Cu: Si = 1: 2.4: 3: 0.2. 12mmφ this mixed powder
Into a pellet shape of
After calcining at 1 to 5 hours at 1 to 5 hours, the sample was cooled to obtain a sample. As a result of examining the resistance change with respect to temperature of this sample by a four-terminal method, the onset temperature (Tco) was 93.5K and the offset temperature (Tce) was 91K. The density (Archimedes method) was 6.0 g / cm ² . Further, the MH hysteresis curve of the sample was determined using a vibrating sample magnetometer. These results are shown in FIG. The critical current density Jc was obtained from the magnetization difference ΔM from the hysteresis curve of FIG.
M (0.15T) is 3.40 (mT) and critical current density Jc (0.15T)
Was 1.15 × 10 ³ (A / cm ² ). Example 3 Y ₂ O ₃ 8.457mol% and BaCO ₃ 40.678mol% and CuO 50.847Mo
After mixing and mixing at a ratio of ₁ % to Y ₁ Ba _2.4 Cu ₃ O _{7- δ} , the mixture was calcined in air at 880 ° C. for 5 hours. This calcined body is pulverized, and S: S: Y: Ba: Cu: Si = 1: 2.4: 3: 0.2
iC was mixed with the calcined powder. This mixed powder is molded into a pellet shape of 12 mmφ, and the molded body is 920 ° C. to 980 in an oxygen stream.
After firing at 1 ° C. for 1 to 5 hours, the sample was cooled to obtain a sample. As a result of examining the resistance change with respect to temperature of this sample by a four-terminal method, the onset temperature (Tco) was 93.0K and the offset temperature (Tce) was 90K. The density (Archimedes method) was 6.0 g / cm ² . Further, the MH hysteresis curve of the sample was determined using a vibrating sample magnetometer. These results are shown in FIG. The critical current density Jc was determined from the magnetization difference ΔM from the hysteresis curve of FIG.
M (0.15T) is 3.40 (mT) and critical current density Jc (0.15T)
Was 1.20 × 10 ³ (A / cm ² ). Example 4 Y ₂ O ₃ 9.09mol% and BaCO ₃ 36.36mol% and CuO 54.55mol%
After mixing and mixing to obtain Y ₁ Ba ₃ Cu ₃ O _{7- δ} , the mixture was calcined in air at 880 ° C. for 5 hours. Crush the calcined body, Y ₁ B
As it will be _{a 2 Cu 3 O 7- δ ·} 0.2Ba 2 SiO 4, the Ba ₂ SiO _4, and mixed to the calcined body. Y ₁ Ba ₂ Cu ₃ O _{7- δ} mixed with this Ba ₂ SiO ₄
Into a 12mmφ pellet, which is then heated to 920 ° C in oxygen.
After firing at 〜980 ° C. for 1 to 5 hours, the sample was cooled to obtain a sample. As a result of examining the resistance change of this sample with respect to temperature by the four-terminal method, the onset temperature (Tco) was 93.5K and the offset temperature (Tce) was 90K. The density (Archimedes method) was 6.0 g / cm ² . Further, the MH hysteresis curve of the sample was determined using a vibrating sample magnetometer. These results are shown in FIG. The critical current density Jc was obtained from the magnetization difference ΔM from the hysteresis curve of FIG.
M (0.15T) is 3.40 (mT) and critical current density Jc (0.15T)
Was 1.15 × 10 ³ (A / cm ² ). [Comparative Example] Y ₁ Ba ₂ Cu ₃ O _{7- δ1} having the same molar ratio as that of the above example was pulverized, then put in alumina or mullite board, and calcined, pulverized, molded and fired under the same conditions as in the above example. 11 × 11 × 1.
A 3 mm sample was obtained. This sample was similarly examined for resistance change with respect to temperature by the four-terminal method. As a result, the onset temperature (Tco) was 91.5K and the offset temperature (Tce) was 89K. Further, the density was 4.5 g / cm ² . Further, the M of the sample was measured by a vibrating sample magnetometer.
The -H hysteresis curve was determined. These results are
Shown in the figure. From the hysteresis curve of FIG. 5, the difference ΔM in magnetization and the critical current Jc were determined using the equation of the above embodiment.
As a result, the difference ΔM (0.15T) in magnetization is 1.83 (mT).
It is understood that the critical current density Jc (0.15T) is 2.2 × 10 ² (A / cm ² ), which is significantly smaller than that of the embodiment of the present invention. [Effects of the Invention] As described above, the oxide superconductor of the present invention has a RE
_The critical density (Jc) can be improved without deteriorating the high critical temperature of ₁ Ba ₂ Cu ₃ O _{7- δ-} based oxide superconductor.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 show oxide superconductors according to the present invention (Example 1).
5 to 5) show MH hysteresis curves, and FIG. 5 shows MH hysteresis curves of comparative examples.

Claims (1)

(57) [Claims] RE ₁ Ba ₂ Cu ₃ O _7- δ (RE = rare earth element) oxide superconductor is a crystal structure in which Ba ₂ SiO ₄ is precipitated in a polycrystal. The critical current density (Jc) is 0.15T in a magnetic field. At 1.1 × 10 ³ A / c
An oxide superconductor having an m of ³ or more. 2. RE: Ba: Cu: Si = 1: 2 (x + 1): y: x (RE = rare earth element) (0.05 ≦ x ≦ 0.80, 3 ≦ y ≦ 3.3)
E ₁ Ba _{2 (x + 1)} Cu _y O _7- δ (RE = rare earth element) (0.05 ≦ x ≦ 0.
80, 3 ≦ y ≦ 3.3) A powder obtained by mixing at least one of Si ₃ N ₄ , SiC, and SiO ₂ with the calcined powder at 920 to 980 ° C.
After calcination for 5 hours, cooling is performed, and Ba ₂ SiO ₄ is precipitated in polycrystalline oxide superconductor of RE ₁ Ba ₂ Cu ₃ O _7- δ (RE = rare earth element). Manufacturing method of superconductor. 3. RE ₁ Ba ₂ Cu ₃ O _7- δ · nBa ₂ SiO ₄ composition, where n is 0.05 ≦ x ≦
After sintering the mixed powder which can be 0.80 at 920 ° C. to 980 ° C. for 1 to 5 hours, it is cooled and mixed in a polycrystalline oxide superconductor of RE ₁ Ba ₂ Cu ₃ O _7- δ (RE = rare earth element). A method for producing an oxide superconductor, comprising depositing Ba ₂ SiO ₄ on a substrate.