JP3411048B2 - Manufacturing method of oxide superconductor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide superconductor having a large magnetic repulsion and a magnetic attraction, and more particularly
The present invention relates to a method for producing a single-crystal oxide superconductor having a large pinning force. [0002] Conventionally, a method for producing an oxide superconductor utilizing a peritectic reaction has been known. For example, Y-Ba-
In the case of a Cu-based oxide superconductor, Y: Ba: Cu = 1:
The raw material mixed at a mixing molar ratio of 2: 3 is separated into Y ₂ BaCuO ₅ and a Ba—Cu liquid phase under a high temperature condition of 1,200 ° C. or more, and Y ₂ BaCuO ₅ and a Ba—Cu liquid phase are separated. Is cooled to 1,050 ° C. or less to form a superconducting crystal of YBa ₂ Cu ₃ OX, the so-called MTG method is known (S. Jin et al., Appl.
phys.lett.52 (1988) 2074). After that, the molar ratio of Y, Ba, and Cu is shifted from 1: 2: 3, and the molar ratio of Y, Ba, and Cu is set to 1 + 2α: 2 + α: 3 + α. α, 0.1 to 0.4), Y, Ba, Cu
A so-called QMG method has been proposed in which a heat treatment such as heating, quenching, molding, heating and slow cooling is mixed to leave a fine Y ₂ BaCuO ₅ phase in the superconducting phase. As a result, the pinning force of the magnetic flux has been improved to more than 10 times that of the conventional MTG method (M. Murakami et al., Jpn. J. Appl. Phys.
28 (1989) 1189). Further, a so-called MPMG method has been proposed in which a powder / homogenization step of pulverizing and mixing the raw material solidified by heating and quenching is inserted between the heating and quenching step and the molding step. This facilitates the manufacture of oxide superconductors of any size and any shape (M. Murakami et al., Jp.
nJAppl.phys.29 (1990) L1991.). [0005] However, the MTG method and the MPMG method employ a Ba-Cu liquid phase and a Ba-Cu liquid phase.
Dispersed crystals fine Y ₂ BaCuO ₅ in -Cu liquid phase (2
This method is intended to obtain a superconductor YBa ₂ Cu ₃ OX (also referred to as 123 phase) by a peritectic reaction with 11 phases), and thus has the following problems. [0006] (a) The initial phase serving as a nucleus of the peritectic reaction (in the case of yttrium, the 211 phase is the initial phase) has a diameter of 0.1 mm.
The distribution ranges from a fine substance of about 1 micron to a slightly large substance of about 1 micron. When the Ba-Cu liquid phase and its primary phase are allowed to react for a sufficient time at the peritectic reaction temperature, the fine primary phase of about 0.1 micron disappears upon completion of the peritectic reaction and has a pinning effect. It almost disappears. (B) Conversely, when the Ba-Cu liquid phase and its initial phase are allowed to react at a peritectic reaction temperature in a short time without taking much time, a slightly larger 211 phase of about 1 micron is formed in the peritectic reaction. And the size remains almost without causing the pinning effect. In addition, since the reaction part at the end of the Ba-Cu liquid phase remains, the superconducting phase is divided, and it is difficult to obtain a large-sized oxide superconducting single crystal. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to disperse a fine and dense normal conducting phase serving as a pinning point. An object of the present invention is to provide a method for manufacturing an oxide superconductor capable of manufacturing a large-sized superconductor. In order to achieve the above object, a manufacturing method according to the present invention comprises a method for manufacturing yttrium (Y)
The elements of lithium (Ba) and copper (Cu) are calculated based on the following formula.
Yttrium (Y) element mixed according to the molar ratio
To the copper and barium in the liquid phase
Element ratio (Cu / Ba) for manufacturing superconductors
Deviates from stoichiometrically normal molar ratio resulting in liquid phase
The composition ratio (Cu / Ba) of both elements in
And increase with decreasing liquid phase temperature.
The peritectic reaction temperature in the early stage of cooling and the
And the peritectic reaction rate at the beginning of slow cooling
With the increase in the above composition ratio, the
It is characterized by manufacturing a conductor, Y: Ba: Cu = β (1 + 2α): 2 + α: 3 + α , where α = 0.1 to 0.4 and β = 1.1 to 1.5 . According to the method for manufacturing an oxide superconductor according to the present invention , yttrium Y is added so that the value of β exceeds 1.
By increasing it compared to the conventional method, copper and burr
The elemental molar ratio with Cu ( Cu / Ba ) is shifted from the stoichiometrically normal molar ratio for producing a superconductor ,
Peritectic the composition ratio (Cu / Ba) of copper and barium in the liquid phase
Increase as the reaction progresses and the temperature of the liquid phase decreases.
Can be. Thus, it is possible to vary the annealing initial peritectic reaction temperature and annealing late peritectic reaction temperature, also the composition with slow cooling initial peritectic reaction rate peritectic reaction
Can be decelerated based on the increase in the ratio
The peritectic reaction was properly carried out so that the 211 phase remained.
Can be made. That is, at the beginning of slow cooling,
The disappearance of the fine primary phase of about 0.1 μm , that is, the 211 phase , is prevented, and the slightly larger 211 μm of the about 211 μm peritectic reaction proceeds from the initial stage of the slow cooling to the latter stage of the slow cooling. The portion is prevented from remaining unreacted. In the peritectic reaction at the later stage of slow cooling, 211 phases were collected.
Since crystals grown 123 phase is floating manner Komu Ri, the direction of the crystal is easily aligned. Therefore, slow cooling first
Reaction at each peritectic reaction temperature in the
Therefore, the initial phase of 211 phase is properly dispersed and the
Large superconductor pellet with uniform magnetic orientation and large magnetic repulsion
Good superconductivity due to stable growth of
The body is manufactured. FIG. 1 shows an example of an electric furnace used in a method for manufacturing an oxide superconductor according to the present invention. In FIG. 1, 1 is an electric furnace, 2 is a heater, 3
Denotes a mounting jig, and 4 denotes a molded body. In this case, the compact 4 has a compounding molar ratio of each element of yttrium Y, barium Ba, copper Cu, and silver Ag of 2.34: 2.4: 3.4: 0.
The raw material powders of Y ₂ O ₃ , BaCO ₃ , CuO, and Ag ₂ O were mixed so as to be 1 (corresponding to the case of α = 0.4, β = 1.3). That is, the amount of yttrium Y was increased as compared with the mixing molar ratio of the conventional MTG method and MPMG method. FIG. 7 is a table showing the preparation of the raw materials in the embodiment of the present invention in comparison with the conventional one. The molded body 4 is, as indicated by reference numeral M in FIG.
It is formed by quenching after heating to 1400 ° C. or higher, followed by pulverization, mixing and molding (see symbol P in FIG. 2). This compact 4 is made of fine powder of Y ₂ O ₃ and Ba-Cu.
It is composed of amorphous fine powder. Thereafter, heat is applied to the molded body 4 from its upper part and side parts by the heater 2, and the molded body 4 is once heated to about 1200 ° C. (refer to the symbol M ′ in FIG. 2), and thereafter , And slowly cooled at a cooling rate of about 1 ° C. per minute (FIG. 2)
G). The compact 4 is partially melted during the slow cooling process. In this state, the Y ₂ CO ₃ particles take in equivalent amounts of Ba and Cu to form a 211 phase, and the remaining substance becomes a liquid phase. Ba is reduced most by the formation of the 211 phase, and the Cu / Ba ratio increases from 1.67, for example, 1.81. At the start of slow cooling of the molded body 4 (t =
(0 min) is 1025 ° C. The temperature of the molded body 4 is higher in the upper part than in the lower part.
As shown in (1), there is a temperature difference of about 20 ° C. between the lower part and the upper part. As shown in (1) of FIG. 4, the crystal state inside the compact 4 is, for example, at the initial stage of slow cooling (t = 0 minutes), for example, the side length is 0.1,
0.5, 1.0 micron 211 phases a, b, c are Cu-
It is floating in the Ba liquid phase d. Here, the peritectic reaction of the Y-based superconductor is 21
It is reported that the peritectic reaction temperature occurs between one phase and the Ba-Cu liquid phase, and the peritectic reaction temperature changes as follows depending on the Cu / Ba ratio in the liquid phase (T. Aselage and K. Kecer: J. .Mater.Res.
3 (1988) 1279). According to T. Aselage et al., Cu and Ba in the liquid phase
It is stated that when the element ratio of is 1.67, a peritectic reaction with respect to the 211 phase occurs at 1015 ° C., and a 123 phase of the superconducting phase precipitates. On the other hand, when the element ratio of Cu and Ba in the liquid phase is 2.33, the peritectic reaction occurs at 940 ° C., and superconducting phase 123 and CuO are precipitated. [0017] That is, when the Cu / Ba ratio in the liquid phase is 1.67, the peritectic reaction temperature is about 1015 ° C., and the Cu / Ba ratio is 2.33.
At this time, the peritectic reaction temperature is about 940 ° C., and the peritectic reaction temperature changes with a change in the composition. First, after 10 minutes have passed from the initial stage of slow cooling (t
= 10 minutes), the temperature of the lower half of the molded body 4 is 1015 ° C
It is as follows. The liquid phase has a Cu-Ba molar ratio of 1.81, which is slightly higher than the normal molar ratio (5/3). Therefore, in the lower half of the compact 4, 123 phase e starts to be generated at this temperature of 1015 ° C., and 211 phases a, b, and c start to be consumed. FIG. 4B shows the crystal growth state of the lower half of the compact 4 after t = 10 minutes from the start of slow cooling. Here, the crystal fragments of the 123 phase generated so as to surround the 211 phase are floating in the Cu-Ba liquid phase. From the start of slow cooling t =
After elapse of 20 minutes, the temperature of the upper half of the compact 4 becomes 1015 ° C. or lower as shown in FIG. 3C, and the upper half of the compact 4 as shown in FIG. Then, a crystal fragment of the 123 phase e is formed so as to surround the 211 phases a, b and c. When t = 25 minutes from the start of slow cooling, (4) in FIG.
As shown in (1), the temperature of the lower part of the compact 4 is 990 ° C. and the temperature of the upper part thereof is 1010 ° C., and the crystal growth proceeds while the peritectic reaction rate of the compact 4 is suppressed. When t = 35 minutes from the start of the slow cooling, the temperature of the lower part of the compact 4 is 980 ° C. and the temperature of the upper part thereof is 1000 ° C., as shown in FIG. Crystal growth proceeds while the crystal reaction rate is similarly suppressed. (4) in FIG.
Shows the growth state of the crystal after a lapse of t = 25 minutes from the start of the slow cooling, and FIG. 4 (5) shows the growth state of the crystal after a lapse of t = 35 minutes from the start of the slow cooling. This peritectic reaction is C
Proceeding at a u / Ba ratio of 1.67, a residual amount of copper Cu is generated, and the total amount of the matrix is reduced. Therefore, the Cu / Ba ratio increases from the initial value of 1.81 with the reaction, and the concentration of Cu in the liquid phase is increased. And its concentration approaches 2.33. T from the start of slow cooling
= 85 minutes have passed, the temperature of the lower half of the compact 4 has dropped to 940 ° C. or lower, as shown in FIG. The second reaction starts. Since the crystal fragments of the 123 phase e generated in the first reaction are in a floating state, they can be grown while being aligned so that the crystal orientations are aligned with each other. Further, in the peritectic reaction, the remaining Cu-Ba liquid phase is repelled upward, thereby preventing the liquid phase components BaO and CuO from being entangled and remaining when the cooling is completed. FIG. 4 (6) shows the crystal growth state of the compact 4 after t = 85 minutes from the start of the slow cooling. That is, in this embodiment, the raw materials are mixed and melted so that the element ratio of Cu and Ba in the liquid phase is slightly larger than 1.67, and then cooled at 1015 ° C.
As in 1.67, the peritectic reaction occurred, and the superconducting 12
Although three phases are precipitated, the elements of Cu and Ba are consumed at a ratio of 1.67, so that the ratio of unreacted elements increases. As a result, the peritectic reaction is suppressed, but the element ratio approaches 2.33, so that the peritectic reaction starts at the lower peritectic reaction temperature. In the present invention, Cu and Ba in the liquid phase are used.
The raw materials were blended such that the element ratio of 1.7 to 1.8 was obtained, and the mixture was melted and gradually cooled.
At around 015 ° C., fine crystals of superconductivity can be partially deposited. Since they are suspended in the surrounding liquid phase, they will move, rotate and align with one another. As described above, the suppression of the peritectic reaction prevents the 211 phases a, b, and c from being consumed, prevents the Cu—Ba liquid phase d from remaining in two reactions, and allows the crystal fragments to float. Since the peritectic reaction is performed in a state where the crystal pieces are aligned, alignment of crystal pieces is promoted. After passing through this slow cooling step, the compact 4 is cooled to room temperature (reference H in FIG. 2). FIG. 5A is a view showing the lower surface of the pellet 5 as an oxide superconductor manufactured in this manner, and FIG. 5B is a longitudinal sectional view of the pellet 5.
The pellet 5 is made of a relatively large crystal having a diameter of, for example, 10 to 20 mm, and has a crystal size of 2 to 2 as compared with the pellet 6 as an oxide superconductor made at a conventional molar ratio of β = 1. It has tripled. FIG. 6 (1) is a view showing the lower surface of a pellet 6 made with a conventional molar ratio, and FIG. 6 (2) is a longitudinal sectional view of the pellet 6. When the crystalline material constituting the pellets 5 produced according to the present invention was analyzed by x-ray diffraction, it was found that YBa ₂ Cu
_It was mainly composed of ₃ Ox and Y ₂ BaCuO ₅ , and contained trace amounts of CuO. However, BaO was not detected, and it was confirmed that almost 100% of the raw material had undergone peritectic reaction. The magnetization range of the pellet 5 measured from the DC susceptibility was 0.5.
emu / cm ³ , which was 15,000 A / cm ³ in terms of critical current. These corresponded to the highest values measured for pellets 6 made at conventional compounding molar ratios with β = 1. As described above, according to the present invention, as the peritectic reaction progresses, the element ratio of the liquid phase surrounding the initially deposited phase slightly deviates from the stoichiometrically normal value. Thus, the crystallization proceeds in a wavy manner during the cooling step. Since the crystal fragments of the 123 phase generated by the peritectic reaction at a higher temperature are floating until the next reaction starts, they can grow while being aligned so that the crystal orientations are aligned with each other. Therefore, a superconducting pellet having a large magnetic repulsion can be stably manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of an electric furnace used for a method for manufacturing an oxide superconductor according to the present invention. FIG. 2 is a graph for explaining a heating / cooling pattern of the oxide superconductor according to the present invention. FIG. 3 is a schematic explanatory diagram showing a temperature distribution of a molded body in a slow cooling step of the oxide superconductor according to the present invention with time. FIG. 4 is an explanatory view showing a crystal growth state corresponding to the temperature distribution in FIG. 3; FIG. 5 is a bottom view of an oxide superconductor pellet obtained by the method for manufacturing an oxide superconductor according to the present invention. FIG. 6 is a longitudinal sectional view of an oxide superconductor pellet obtained by the method for manufacturing an oxide superconductor according to the present invention. FIG. 7 is a table showing the preparation of raw materials in an example of the present invention according to the present invention as compared with a conventional example. [Description of Signs] Y Yttrium Ba Barium Cu Copper 4 Molded products a, b, c 211 phases d Liquid phase e 123 phases

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenki Tada 2109-8 Yashimanishimachi, Takamatsu City, Kagawa Prefecture Inside Shikoku Research Institute, Inc. (56) References JP-A-4-193714 (JP, A) JP-A-Hei. JP-A-2-153803 (JP, A) JP-A-2-204358 (JP, A) JP-A-3-65509 (JP, A) JP-A-4-175296 (JP, A) JP-A-5-17205 (JP, A A) JP-A-5-238731 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 C01G 1/00 C01G 3/00

Claims (1)

(57) [Claims] [Claim 1] Yttrium (Y) and barium (Ba)
And the element of copper (Cu) are mixed in accordance with the mixing molar ratio based on the following formula, and the element of yttrium (Y) is made larger than the remaining elements, and the element mixing ratio of copper and barium in the liquid phase
(Cu / Ba) is deviated from the stoichiometrically normal molar ratio for producing a superconductor, and consequently the two elements in the liquid phase
The composition ratio (Cu / Ba) is determined by the progress of the peritectic reaction and the temperature of the liquid phase.
By increasing with the degree reduction, it causes different from the annealing initial peritectic reaction temperature and annealing late peritectic reaction temperature, the composition with the slow cooling initial peritectic reaction rate peritectic reaction
A method for producing an oxide superconductor, comprising: producing an oxide superconductor at a reduced speed based on an increase in the ratio . Y: Ba: Cu = β (1 + 2α): 2 + α: 3 + α where α = 0.1 to 0.4, β = 1.1 to 1.5