JP4190914B2 - Method for producing oxide superconductor and oxide superconductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an oxide superconductor based on a semi-molten solidification method and an oxide superconductor manufactured thereby, and relates to a technique capable of easily obtaining a large oxide superconductor.
[0002]
[Prior art]
As an example of a method for producing a large bulk oxide superconductor, there are known melting methods disclosed in Japanese Patent No. 1869884 and Japanese Patent No. 2555640. The melting methods described in these patents are RE₁Ba₂Cu₃O_7-XIn manufacturing an oxide superconductor having a composition (RE represents a rare earth element), RE₂Ba₁Cu₁O₅Phase or RE₄Ba₂Cu₂O₁₀After heating to a temperature range in which the phase and the liquid phase mainly composed of Ba—Cu—O coexist, RE₁Ba₂Cu₃O_7-XThis is a manufacturing method in which an oxide superconductor is obtained by cooling to a temperature just above the peritectic temperature where a phase is formed and gradually cooling from that temperature to grow crystals and control nucleation and crystal orientation.
[0003]
In addition, a semi-melt solidification method is known in which an oxide superconductor is manufactured by using one seed crystal and sequentially combining materials having different crystal growth start temperatures to control nucleation, crystal orientation, and crystal growth direction. . (See Patent Document 1)
[0004]
In this semi-molten solidification method, a raw material powder obtained by mixing compound powders of elements constituting an oxide superconductor is consolidated to obtain a precursor, and then this precursor is used to make a RE.₁Ba₂Cu₃O_7-XIn manufacturing an oxide superconductor having a composition (RE represents a rare earth element), RE₂Ba₁Cu₁O₅Phase or RE₄Ba₂Cu₂O₁₀The precursor is heated to a temperature range in which a phase and a liquid phase mainly composed of Ba-Cu-O coexist to be in a semi-molten state, then a seed crystal is placed on the semi-molten precursor, and RE₁Ba₂Cu₃O_7-XA manufacturing method in which a crystal is gradually grown inside a semi-molten precursor by cooling to a temperature just above the peritectic temperature where a phase is formed, and gradually cooling from that temperature, and the precursor is the oxide superconductor. It is. It is also known to perform heat treatment in an oxygen atmosphere in order to adjust the crystal structure by adding oxygen to the oxide superconductor crystal by the semi-melt solidification method as necessary.
[0005]
Next, as a technique for stacking and manufacturing bulk bodies of different rare earth oxide superconductors, different types of rare earth elements,₁Ba₂Cu₃O_7-XA method is known in which a precursor is formed by laminating a plurality of raw material layers so that the temperature at which a phase is generated is continuous from the high temperature side or the low temperature side, and then a semi-melt solidification method is performed. (See Patent Document 2)
[0006]
[Patent Document 1]
JP-A-5-170598
[Patent Document 2]
Japanese Patent No. 2556401 (Japanese Patent Laid-Open No. 5-1993938)
[0007]
[Problems to be solved by the invention]
However, the oxide superconductor manufacturing method described above has a limit on the size of a precursor that can be crystal-grown. That is, when the semi-melt solidification method is performed inside the precursor, 2REBa₂Cu₃O_7-X(R123 phase) = RE₂Ba₁Cu₁O₅(R211 phase) + L (liquid phase; 3BaCuO₂Based on the reaction represented by the formula + 2CuO), the R211 phase and the liquid phase generate the R123 phase while the R211 phase moves inside the semi-molten precursor, When the R123 phase is generated while moving, the progress speed is very slow, and if there is an impurity or reaction inhibiting factor inside the semi-molten precursor, the reaction stops immediately or an oxide superconductor with a poor crystalline state is generated. Therefore, the Nd-based or Sm-based oxide superconductor has a diameter of about 2 cm and a thickness of about several millimeters to 1 cm, and the Y-based oxide superconductor has a diameter of a little over 10 cm and a thickness of several millimeters to 1 cm. The degree is the limit of the current technology. That is, even when a large precursor larger than these sizes is used, the semi-molten solidification reaction stops halfway or the crystal growth partially proceeds in an arbitrary direction, and the oxide superconductor having a good orientation as a whole. Have problems that you can't get.
[0008]
In addition, the precursor used in the semi-melt solidification method is obtained by mixing and compacting the raw material powder of the oxide superconductor, and therefore usually by a consolidation method using a CIP device (cold isostatic pressure device) or the like. It is generally used as a dense state having almost no voids. However, for that purpose, it is necessary to use a CIP device that is tens of millions of equipment, and it is not easy to manufacture at low cost, and it is even larger than the size of a precursor that can be solidified with a normal CIP device. There was a problem that an oxide superconductor could not be manufactured. In order to obtain a larger precursor, the precursor cannot be produced if a larger CIP apparatus is used. However, as the CIP apparatus becomes larger, the equipment cost will increase significantly, and the production cost will increase. May increase significantly.
[0009]
The present invention has been made in view of the above-described problems, and an oxide superconductor capable of easily producing a larger oxide superconductor than the conventional one when producing an oxide superconductor by a semi-melt solidification method. It is an object of the present invention to provide an oxide superconductor obtained thereby.
Another object of the present invention is to provide a production method that can be carried out without requiring a special CIP device for producing a large precursor and an oxide superconductor obtained thereby.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the present inventionRE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more rare earth elements) When producing an oxide superconductor having a composition of ₁ Ba ₂ Cu ₃ O _7-X A compact of a raw material in which a compound of an element constituting an oxide superconductor having the following composition is mixed: ₁ Ba ₂ Cu ₃ O _7-X Ingredient 1.1 (5 mol% RE ₂ Ba ₁ Cu ₁ O ₅ Phase component) or more, 1.8 (40 mol% RE) ₂ Ba ₁ Cu ₁ O ₅ Phase component) Consists of a compacted raw material with a blending ratio in the following rangeThe precursor is heated to a semi-molten state and then cooled, and the semi-molten precursor is crystallized into an oxide superconductor based on the crystal structure of the seed crystal placed on the precursor. A method for producing an oxide superconductor by a semi-molten solidification method, and in carrying out the semi-melt solidification method, a plurality of the precursors are stacked, a seed crystal is placed on the uppermost stacked precursor, The uppermost precursor is crystallized based on the seed crystal by the melt solidification method, and the other precursors stacked are sequentially crystallized by propagating the crystallization to the lower precursor.In carrying out the semi-molten solidification method, preheated to heat the stacked precursors into a semi-molten state, hold isothermally, then cool down and keep isothermally in a temperature range higher than the crystallization start temperature After performing the above, the temperature is lowered to the crystallization start temperature lower than the preheating temperature, the crystallization is performed while maintaining the isothermal temperature at the crystallization start temperature, and then the temperature is lowered.It is characterized by that.
[0011]
  By simply stacking multiple precursors and growing a crystal based on a seed crystal for the uppermost precursor, the uppermost precursor can be made into an oxide superconductor, and the lower side of the precursor Oxide superconductors can be sequentially formed by propagating crystallization with respect to other precursors provided in the substrate. At this time, the stacked precursors do not need to be pressure-contacted with each other, and may be in a state where they are naturally in contact by their own weight. As a result, an oxide superconductor having a thickness several times that of an oxide superconductor obtained by using a conventional precursor can be easily manufactured by simply adding the precursors.
  Here, the semi-molten solidification method refers to obtaining a raw material mixed molded body (precursor) formed by mixing a plurality of elemental compounds constituting an oxide superconductor and then placing a seed crystal on the precursor. After this, the precursor is heated and melted at a temperature equal to or higher than the melting point to a temperature in which the liquid phase and the solid phase coexist to form a semi-molten state, and then cooled, using the previous seed crystal and starting from the seed crystal. In this method, a single crystal of the desired oxide superconductor is grown to obtain an oxide superconductor having a good crystal structure and excellent superconducting characteristics.
  In carrying out the semi-molten solidification method, the temperature in the semi-molten stateKeep it isothermal to itKeep isothermal at lower temperaturesAfter performing the preheating, the temperature is lowered to a crystallization start temperature lower than the preheating temperature,If the crystallization is performed while maintaining the isothermal temperature at the crystallization start temperature, the progress of the crystallization can be promoted, compared with the case where the crystal is grown by applying a temperature gradient while gradually cooling.FarCrystallization can proceed in a short time.
[0012]
  In order to achieve the above object, the present invention provides the oxide superconductor as RE.₁Ba₂Cu₃O_7-XThe present invention is characterized by being applied to an oxide superconductor having a composition (RE represents one or more rare earth elements).
  As a specific oxide superconductor applicable, RE₁Ba₂Cu₃O_7-XA composition having a composition (RE represents one or more rare earth elements) can be exemplified. More specifically, as RE, one or more of rare earth elements including Y (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) are included. Show. When an oxide superconductor represented by these composition formulas is to be manufactured, if it is in a semi-molten state, RE₂Ba₁Cu₁O₅Phase or RE₄Ba₂Cu₂O₁₀It can be made into a semi-molten state by heating to a temperature region where a phase and a liquid phase mainly composed of Ba-Cu-O coexist,After isothermal holding at a temperature lower than that of the semi-molten state,RE₁Ba₂Cu₃O_7-XCool to the crystallization temperature just above the peritectic temperature where the phase forms, Keep it isothermal at its crystallization temperature and grow the crystalBy slowly cooling fromObtaining the desired stacked oxide superconductorbe able to.
[0013]
In order to achieve the above-mentioned object, the present invention is characterized in that a plurality of stacked upper and lower precursors are not placed in a completely close contact state but in a natural placement state having a gap.
The stacked precursors do not need to be consolidated with each other by a consolidation method or the like, and may be in an installed state where they are in contact by their own weight. That is, even if the stacked precursors are not completely in close contact with each other, even if they are simply stacked with some gaps between them, the precursors on the lower side are based on the crystals of the upper oxide superconductor. The body can be an oxide superconductor.
In order to achieve the above-mentioned object, the present invention provides a target RE as the precursor.₁Ba₂Cu₃O_7-X(RE represents one or more rare earth elements) A compact of a raw material in which a compound of an element constituting an oxide superconductor having a composition of₁Ba₂Cu₃O_7-XThe phase component is 1.1 (5 mol% RE₂Ba₁Cu₁O₅Phase component) 1.8 or more (40 mol% RE)₂Ba₁Cu₁O₅Phase component) It is characterized by using a compacted material having a blending ratio in the following range.
RE inside the precursor when in a semi-molten state₂Ba₁Cu₁O₅Phase (R211 phase) and liquid phase (3BaCuO)₂When it is decomposed to + 2CuO), the formation of the R123 phase is promoted, and crystallization is facilitated.
[0014]
In order to achieve the above-mentioned object, the present invention, when sequentially crystallizing a plurality of stacked precursors from the upper stage side to the lower stage side, only the precursor that is in the process of crystallization is maintained at the crystallization temperature. The precursor on the side is maintained at a temperature in a semi-molten state, and crystallization is performed while giving a temperature gradient in which the precursors in the semi-molten state are sequentially set to a crystallization temperature as crystallization progresses.
By controlling the temperature in this way, only the precursor to be crystallized can be crystallized, and by preventing the crystallization from occurring in the semi-molten precursor, it is continuous from the upper stage side to the lower stage side. Thus, uniform crystallization can proceed.
[0015]
  In order to achieve the above object, the present inventionRE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more rare earth elements) When producing an oxide superconductor having a composition of ₁ Ba ₂ Cu ₃ O _7-X A compact of a raw material in which a compound of an element constituting an oxide superconductor having the following composition is mixed: ₁ Ba ₂ Cu ₃ O _7-X Ingredient 1.1 (5 mol% RE ₂ Ba ₁ Cu ₁ O ₅ Phase component) or more, 1.8 (40 mol% RE) ₂ Ba ₁ Cu ₁ O ₅ Phase component) Using a precursor consisting of a compacted raw material with a blending ratio in the following range,The oxide superconductor precursor is heated to form a semi-molten state.And keep isothermalAfterAfter preheating to lower the temperature and hold isothermally in a temperature range higher than the crystallization start temperature, the temperature is lowered to a crystallization start temperature lower than the preheating temperature, and crystallization is performed while maintaining the isothermal temperature at the crystallization start temperature. Do, then cool downAn oxide superconductor manufactured by a semi-melt solidification method based on a crystal structure of a seed crystal placed on the precursor to crystallize the precursor in a semi-molten state to form an oxide superconductor. In addition, a plurality of the precursors are stacked, and the plurality of stacked precursors are crystallized into oxide superconductors by crystallization based on a seed crystal placed in the uppermost precursor. Is.
  If it is an oxide superconductor manufactured based on multiple stacked precursors, even if the stacked individual precursors themselves are the same size as the conventional precursors, it will ultimately depend on the number of stacks. An oxide superconductor several times thicker can be obtained.
  On the other hand, if it is going to obtain the precursor several times thick from the beginning, a large sized manufacturing apparatus will be needed with pressurization apparatuses, such as CIP, and an installation cost will improve significantly. Therefore, the oxide superconductor obtained by the present invention can produce an oxide superconductor having a thickness corresponding to a precursor having a thickness not conventionally obtained by a normal press device, even if a normal press device is used. It is an oxide superconductor that can be obtained without increasing the equipment cost.
[0016]
In order to achieve the above-mentioned object, the present invention is characterized in that, among the stacked oxide superconductors, the oxide superconductors which are in contact with each other are welded and integrated at the portions where they are in contact with each other.
Since the stacked precursors are crystal-grown based on the semi-melt solidification method, the precursors that are in contact with the top and bottom are melted at the time of melt solidification to form a welded integrated part that is integrally joined.
In order to achieve the above-mentioned object, the present invention specifically provides an oxide superconductor as RE.₁Ba₂Cu₃O_7-X(RE represents one or more rare earth elements) and can be applied to those having a composition
[0017]
When the semi-molten solidification method is performed, crystallization of a plurality of precursors stacked on the basis of the seed crystal proceeds sequentially, but from the region decomposed into the R211 phase and the liquid phase inside the semi-molten precursor. Instead of the liquid phase pushing out the R211 phase, crystallization proceeds throughout the precursor in a manner that produces the R123 phase. Then, the R211 phase existing in the semi-molten state is pushed out to the bottom of the uppermost precursor and then moves to the lower precursor side, and into the lower-half-molten precursor R123. It moves to the bottom side of the next lower precursor while forming a phase. As a result of the sequential movement of the R211 phase to the lower precursor in this way, the R211 phase accumulates at the center of the bottom of the oxide superconductor finally crystallized.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 and FIG. 2 are side views for explaining a state in which the manufacturing method according to the present invention is carried out. FIG. 1 shows disk-shaped oxide superconductor precursors 1 and 2 in their thickness direction. FIG. 2 shows a state in which the seed crystal 3 is placed in the center of the upper portion of the precursor 1 on the upper side (upper side), and FIG. 2 performs the manufacturing method described below on the precursors 1 and 2 shown in FIG. The oxide superconductor 5 obtained by this is shown.
The oxide superconductor precursors 1 and 2 used in the present invention are compacts of a raw material mixture having the same composition as the target oxide superconductor or an approximate composition, and the present invention can be applied to the precursors. As an oxide superconductor, for example, RE-Ba-Cu-O system (RE is a rare earth element containing Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. 1 type | mold or 2 types or more are shown.) Can be illustrated.
[0019]
Here, when the target oxide superconductor is a RE-Ba-Cu-O-based oxide superconductor, for example, as the precursors 1 and 2, RE compound powder, Ba compound powder, and Cu compound powder are RE. : Ba: Cu = 1: 2: 3, or a compacted raw material mixed powder mixed with a composition close to that can be used.
When the above compound powder is mixed with a composition approximate to RE: Ba: Cu = 1: 2: 3, RE₁Ba₂Cu₃O_7-XRE for phase component (R123 phase component)₂Ba₁Cu₁O₅The ratio of the phase component (R211 phase component) is preferably 1.1 or more and 1.8 or less, and the molar ratio is preferably 5 mol% or more and 40 mol% or less. Note that the value of the critical current density of the obtained bulk body tends to saturate in the vicinity of 1.4. Further, when the ratio of the R211 phase to the R123 phase is less than 1.1, a normal crystallization reaction is difficult to proceed during melt solidification.
[0020]
As specific values of the molar ratio, for example, the ratio of the R123 phase component to the R211 phase component is 1.1 (5 mol% R211 phase component), 1.2 (10 mol% R211 phase component), 1.4 (20 Mol% R211 phase component) and 1.8 (40 mol% R211 phase component). Here, for example, a ratio of 1.8 means that the number of Sm moles of Sm211 is 8 moles with respect to 10 moles of Sm123.
That is, 10 (RE₁Ba₂Cu₃O_7-X) +4 (RE₂Ba₁Cu₁O₅) = 100 (RE₁Ba₂Cu₃O_7-X) +40 (RE₂Ba₁Cu₁O₅) Is considered as a percentage. Accordingly, the ratio 1.1 used in this specification means 5 mol% R211 phase component, the ratio 1.2 means 10 mol% R211 phase component, and the ratio 1.4 means 20 mol%. R211 phase component is meant, and a ratio of 1.8 means 40 mol% R211 phase component.
[0021]
In this embodiment, the precursors 1 and 2 are obtained by forming the raw material mixed powder having the above composition into a disk shape by a pressing device such as a press device or a CIP device (hydrostatic pressure device). Of course, if the CIP device is expensive, the manufacturing cost is lower when the precursors 1 and 2 are manufactured by the press device. Moreover, the magnitude | sizes of the precursors 1 and 2 may be arbitrary, and should just be a precursor of the magnitude | size which can be manufactured with the press apparatus and CIP apparatus to be used.
In addition, when the precursors 1 and 2 are manufactured, after obtaining the raw material mixed powder, the calcining and grinding operation is performed as many times as necessary by calcining at about 800 to 1000 ° C. and then remixing the material pulverized by the pulverizer. You may shape | mold. Examples of the conditions for powder mixing and calcination include calcining conditions such as an agate mortar or an attritor or ball mill for about 1 hour and then calcining at about 900 ° C. for about 15 hours.
Further, when repeatedly calcining a plurality of times and finally pulverizing and mixing, Ag is used for the purpose of lowering the melting temperature and improving the mechanical strength in the subsequent semi-melt solidification method.₂A precursor may be formed by adding O, or by mixing Pt as a re211 refining catalyst as an additive substance into a molded body. In addition, Au may be mixed as an additive substance as another element.
These additive substances may be those that improve the superconducting properties of the finally obtained oxide superconductor or that do not impair the superconducting properties. For example, if the additive substance is Ag, it is known that it can be added to the oxide superconductor in a range of about 5 to 20 wt%, and therefore silver may be added.
[0022]
When manufacturing a precursor through such a process, when grind | pulverizing after calcining and mixing a ground material again, it is desirable to make the particle size of a ground material as small as possible, and to arrange those particle sizes. For example, the pulverized product may be pulverized such that the maximum particle size is 300 μm or less, preferably an average particle size in the range of about 50 to 100 μm so that there are almost no large particles exceeding 300 μm, It may be pulverized and mixed so as to have an average particle size finer than this range. The particle size of the pulverized product is sufficient for the practice of the present invention to be in the range of about 50 to 100 μm as described in the examples described later.
[0023]
When these precursors 1 and 2 are stacked, they are simply stacked by aligning their centers at the coaxial position and aligning their upper and lower surfaces, and placing the precursor 1 on the precursor 2 by its own weight; To do. Of course, the upper and lower precursors 1 and 2 may be stacked while being shifted in the center. In this state, the overlapping surfaces of the precursors 1 and 2 are in close contact with each other as shown in FIG. 1, but when the close contact portion is enlarged, the surfaces of the precursors 1 and 2 are completely in contact with each other. Since it cannot be a flat surface, it necessarily has a slight gap. Of course, when forming the precursors 1 and 2, the formation accuracy of the upper surface and the lower surface may be strictly formed to improve the adhesion between the surfaces, but only a slight gap can be confirmed visually. Even when the precursors 1 and 2 formed of the molded body formed with the above surface accuracy are stacked, it is sufficient for use in the present invention.
Although not shown in FIG. 1, a YSZ (yttrium stabilized zirconia) film or plate (sheet having a thickness of 0.1 to 0.2 mm) is laid under the stacked precursors 1 and 2. Further, a base made of a heat-resistant material such as a plate shape, a boat shape, or a crucible shape for supporting them may be installed and charged into the heating furnace together with these bases during heating.
The YSZ film or plate previously prevents impurities from entering the precursors 1 and 2, and the lower precursor 2 is in contact with other substances unless the film or plate is placed underneath. Thus, crystallization occurs and the finally obtained crystal becomes a polycrystal or a crystal with poor orientation.
In addition, for the purpose of suppressing the reaction between the heat-resistant base and the precursor 2, a heat-resistant layer, an intermediate layer made of a heat-resistant material, a base material, or the like may be appropriately laid on the base.
[0024]
  If the stacked state shown in FIG. 1 is obtained, the seed crystal 3 is placed on the precursor 1 on the upper stage, and these are placed in a heating furnace and heat-treated based on a semi-melt solidification method.
  The semi-molten solidification method performed here is a method in which a seed crystal is placed on a precursor of an oxide superconductor in advance, and the precursor is heated and melted at a temperature equal to or higher than the melting point to a temperature where a liquid phase and a solid phase coexist. After making it into a molten state, a cooling process is performed, and a seed crystal is used to grow a single crystal of the target oxide superconductor in the precursor starting from the seed crystal. This is a known method for producing an oxide superconductor. Further, in the case of crystal growth, in this embodiment, as described later, it is carried out by maintaining isothermal at a specified crystallization start temperature.. NaIn this embodiment, a cold seeding method in which a seed crystal is placed on a precursor and then heated is used. However, a hot seeding method in which a seed crystal is placed after being in a semi-molten state is used. Of course, there is no problem.
[0025]
As the seed crystal 3 used in this embodiment, a single crystal or thin film of an oxide superconductor of a kind using a rare earth different from the target rare earth oxide superconductor is used.
For example, when the target oxide superconductor is Sm-based, a single crystal or thin film of an Nd-based oxide superconductor having a peritectic temperature higher than that of the Sm-based can be used. That is, since the seed crystal 3 needs to maintain a crystal state at the semi-melting temperature of the precursor, a seed crystal 3 having a peritectic temperature higher than that of the precursor to be used is used.
An oxide superconducting thin film having a single crystal film of an Nd-based oxide superconductor formed on a heat resistant substrate such as MgO by a film forming method can be applied. Of course, in addition to these, single crystals or superconducting thin films of various systems applicable to the semi-melt solidification method such as Gd, Dy, Ho, and Y can be used as seed crystals.
[0026]
That is, first, the whole is heated to the highest ultimate temperature (Tmax) slightly higher than the melting points of the precursors 1 and 2 to bring the precursors 1 and 2 into a semi-molten state. The heating atmosphere may be air or an oxygen atmosphere in which a small amount of oxygen is supplied in an inert gas. For example, 1% O as an example₂A concentration Ar gas atmosphere can be selected.
The heating temperature at this time is slightly different depending on the composition of the target oxide superconductor or depending on the components of the atmospheric gas when the heat treatment is performed, but is approximately 1% O₂If it is an Nd-based oxide superconductor in an inert gas atmosphere, it is in the range of 1000 to 1200 ° C, and other oxide superconductors are generally in the range of 950 to 1200 ° C. Further, when the precursors 1 and 2 are suddenly heated when the temperature is raised, there is a risk of introducing a defective portion such as a crack. Therefore, it is preferable to gradually raise the temperature. In addition, the temperature gradient from heating the precursor to the semi-molten state can be any temperature gradient, but if the temperature gradient is not moderated near the maximum temperature, the temperature adjustment function of the heating furnace can be achieved. Depending on this, there is a possibility that the temperature will be far beyond the maximum temperature, so it is preferable to make the temperature gradient gentle in the vicinity of the maximum temperature.
[0027]
If the precursors 1 and 2 are brought into a semi-molten state at the highest attained temperature, the temperature of the precursors 1 and 2 is lowered from the previous temperature by several tens of degrees C. After the preheating to be held, the temperature is lowered to a crystallization start temperature lowered by several tens of degrees centigrade, for example, about 20 to 40 degrees centigrade from the previous temperature, and the crystals are grown by maintaining the crystallization start temperature for several hours. Then cool in the furnace. Thereby, the two-layered oxide superconductor 5 as shown in FIG. 2 can be obtained.
More specifically, when producing an Sm-based oxide superconductor, the temperature is raised from room temperature to 900 ° C. over about 1 hour, and then gradually increased from the half-melting temperature to 1080 ± 20 ° C. over 1 hour. Warm, hold at semi-melting temperature for about 40 minutes, drop to 1050 ° C. over about 5 minutes, and then crystallize for about 5 hours at the target crystallization temperature of 1020 ° C. for about 5 hours. An example of the heat treatment condition is that the temperature is lowered to 900 ° C. over about 1 hour, and then the furnace is cooled to room temperature. The temperature may be increased to 1080 ± 20 ° C. at a stretch, but if the temperature gradient at the time of temperature increase is too high, the precursor will be heated over the 1100 ° C. defined as the upper limit of the half-melting temperature, Since it may be dissolved, the temperature gradient at the time of temperature rise needs to be set so as not to exceed the defined 1080 ± 20 ° C. Of course, if the heating device can precisely control the precursors 1 and 2 to a specified temperature, the heating temperature is not restricted by the above-mentioned temperature rising conditions, and the target half-melting temperature determined according to the composition It goes without saying that the temperature is raised at an appropriate rate in accordance with the above range.
[0028]
  The crystal generation temperatures of other oxide superconductors are 1000 ° C. for the Y system, 1060 ° C. for the Nd system, 1050 ° C. for the Eu system, 1030 ° C. for the Gd system, 1010 ° C. for the Dy system, and 990 ° C. for the Ho system. Since the Er system is known as 970 ° C. and the Yb system is known as 900 ° C., the crystallization start temperature condition required for these systems is set.
  by the wayHalfFor example, in the case of a precursor having a diameter of about 30 mm, the above-described conditions are desirable for the maximum temperature that is the melting temperature and the subsequent isothermal holding time. However, when the precursor is applied to a precursor having a larger diameter, Since the temperature tends to be non-uniform in the part, the temperature and time can be changed as appropriate.
  In addition, it is important to keep isothermal at the crystallization start temperature, and by this isothermal keeping, about one hundred hours in the conventional crystal growth time performed while gradually cooling one seed crystal with a temperature gradient. In the present embodiment, what is necessary can be reduced to a crystal growth time of about 5 hours even when two are stacked. This is because the crystal can be grown by isothermal treatment in this embodiment.
  In general, in the semi-molten solidification method, crystal growth is performed by setting a crystallization temperature for one precursor and then gradually cooling it with a temperature gradient. It takes about 100 hours to grow crystals having a body diameter of 20 to 30 mm. However, a precursor having a diameter of 20 to 30 mm can be crystallized in about 5 hours as in the examples described later by growing the crystal while maintaining isothermal temperature at the crystallization temperature as described above. Of course, the maintenance temperature and the maintenance time in the case of crystallization at the isothermal temperature may be appropriately adjusted according to the size of the precursor.
  Furthermore, the cooling time and cooling conditions for furnace cooling at the final stage vary depending on the size of the furnace used, so they are the same as natural cooling and cooling conditions that do not apply heat shock to the resulting oxide superconductor. Good.
[0029]
The seed crystal 3 is placed on the semi-molten precursor 1 and kept at the crystallization temperature.₂Ba₁Cu₁O₅Phase (R211 phase) and L phase (liquid phase: 3BaCuO)₂+ 2CuO), starting from the seed crystal, the liquid phase moves to extrude the R211 phase downward (toward the side away from the seed crystal) and the seed crystal as the starting point.₁Ba₂Cu₃O_7-XIt is possible to grow an oxide superconductor crystal having a composition ratio of (R123 phase). As a result, the entire precursor 1 is finally crystallized to form RE.₁Ba₂Cu₃O_7-XPhase (R123 phase) oxide superconductor.
[0030]
Next, RE₁Ba₂Cu₃O_7-XWhen the crystal growth is transmitted to the bottom of the precursor 1 in the process of growing the oxide superconductor crystal having the composition ratio as described above, this crystal growth is transmitted to the precursor 2 side, and also in the precursor 2 from the upper side to the lower side. The crystal growth progresses toward the end, and finally the whole of the precursor 2 is also RE.₁Ba₂Cu₃O_7-XAn oxide superconductor having a composition ratio of The crystal growth here proceeds simply by placing the precursor 1 on the precursor 2. It is not necessary to integrate the precursors 1 and 2 in advance by a pressurizing method using a press device or a CIP device.
[0031]
Although the oxide superconductor 5 manufactured as described above has a visible boundary 6 at the boundary between the precursors 1 and 2, it becomes an integrated oxide superconductor having a crystal structure and crystallized. . The semi-molten precursors 1 and 2 are placed on the center of the bottom of the oxide superconductor 5 (on the center of the bottom of the precursor 2) while being discharged from the liquid phase by a reaction during melting and solidification. Remaining RE as a result of moving from side to bottom₂Ba₁Cu₁O₅A residual layer 7 mainly composed of a phase (R211 phase) is formed. Further, a welded portion 8 formed when the slight gap portion of the boundary between the precursors 1 and 2 is welded and integrated so as to occupy a part of the boundary line 6 in the oxide superconductor 5 is formed. The
In addition, when the R211 phase moves to the bottom side of the precursor 1 with the crystal growth of the precursor 1 on the upper stage side, and then the crystal growth moves to the precursor 2 on the lower stage side, the precursor 1 and the precursor 2 It seems that there is an area where a part of the R211 phase remains around the boundary line 6.
[0032]
Next, FIG. 3 shows an example of the shape of the upper surface of the oxide superconductor 5 obtained as described above. According to the melt solidification method used in the present invention, the single crystal region grows radially based on the seed crystal 3 (see FIG. 3 omits the seed crystal) installed in the center of the upper surface, and the rectangular single crystal region A single crystal region 15 having a cross-shaped facet line as shown in FIG. 3 is generated when the corner portion of the disk reaches the periphery of the disk, and a polycrystalline region 16 having a arch shape in plan view is generated outside the region. . However, the single crystal region shown in FIG. 3 is an example, and when the single crystal region is completely spread over the entire area of the disk-shaped precursors 1 and 2, the single crystal region is the disk-shaped precursors 1 and 2. In this case, it may be any case such as a case where it stops before the peripheral edge of the substrate and becomes a rectangular single crystal region smaller than the single crystal region 16 shown in FIG.
[0033]
The oxide superconductor 5 in this form has a thickness corresponding to the precursors 1 and 2, and if the precursors 1 and 2 have the same thickness, the thickness is twice that of the original precursor. The oxide superconductor 5 is obtained. In this regard, in the conventional manufacturing method, if an oxide superconductor having a thickness twice as large as that of the precursor having the specified thickness is to be obtained, the precursor itself is compacted to a thickness twice that of the precursor. A semi-melt solidification method must be applied.
That is, in order to obtain a double-thickness precursor, a special pressure device such as a CIP device capable of compacting a double-thickness precursor must be introduced. Therefore, in the conventional method, it is necessary to purchase an expensive CIP device corresponding to the double thickness, and it is necessary to expect a significant increase in equipment cost. However, in the method of the present invention, the pressure device currently used is used as it is. However, since an oxide superconductor having a double thickness can be easily obtained, it is extremely economical, and an oxide superconductor thicker than the conventional one can be realized without increasing the equipment cost.
In addition, according to this method, although the boundary line 6 is present at the boundary portion between the precursors 1 and 2, the single crystal region 15 is substantially continuously formed from the upper part to the lower part of the oxide superconductor 5. It becomes an oxide superconductor having an integrated crystal structure.
[0034]
FIG. 4 shows an embodiment of an oxide superconductor obtained when the second example of the production method according to the present invention is carried out. The oxide superconductor 9 of this form is obtained by applying the semi-melting solidification method to the precursors of the three-stage stack with respect to the precursors 1 and 2 of the two-stage stack.
As shown in FIG. 4, the precursors may be stacked in three stages. Even if the precursors are stacked in three stages, the crystallization of the uppermost precursor 1 can be transmitted to the second precursor 2 by applying a semi-melt solidification method substantially equivalent to the previous conditions. The crystallization of the second-stage precursor 2 can be transmitted to the third-stage precursor, and as a result, all the three-stage precursors can be crystallized in the same manner to form an oxide superconductor. .
[0035]
As shown in FIG. 4, boundary lines 6 and 10 are generated at positions corresponding to the boundary positions of the three precursors, and the oxide superconductor 9 is visually divided into three parts by the boundary lines 6 and 10. Although it appears to be divided into an upper oxide superconductor 9a, a central oxide superconductor 9b, and a bottom oxide superconductor 9c, it has a single crystal region that is single-crystallized from the top to the bottom. . The planar shape of the single crystal region is equivalent to the single crystal region 15 described above with reference to FIG.
Further, a residual layer 11 mainly composed of the R211 phase is formed in the center of the bottom surface of the bottom portion 9c of the oxide superconductor 9 of this form, as in the case of the first embodiment.
[0036]
If the structure shown in FIG. 4 is used, an oxide superconductor 9 having a thickness three times that of the conventional precursor can be obtained, and the thickness of the oxide superconductor 9 is larger than that in the case of the first embodiment. The physical superconductor 9 can be obtained.
In addition, as an example of the single crystal region formed in each of the precursors stacked in three stages, a case where a rectangular single crystal region is generated as in the case described above with reference to FIG. In any case where is a single crystal region, it is the same as in the previous embodiment.
[0037]
  In the embodiments described so far, the whole of the stacked precursors is heated or cooled to a uniform temperature to achieve the object. However, a temperature gradient may be given according to the stacked precursors. For example, when cooling from a semi-molten state and lowering the temperature below the crystallization temperature, crystal growth starts from that portion. Therefore, only the uppermost precursor 1 is first set to a temperature lower than the crystallization start temperature and lower than that The second precursor is heated to the crystallization start temperature when crystallization of the first-stage precursor 1 is completed, and the third-stage precursor is Even if the oxide superconductor is manufactured by setting the semi-melting temperature and proceeding with crystallization while giving a temperature gradient such that the precursor on the lower stage is sequentially brought to the crystallization start temperature as the crystallization progresses. Of course it is good.
[0038]
【Example】
"Example 1"
Sm₁Ba₂Cu₃O_7-XSamarium oxide (Sm₂O₃) Powder and barium carbonate (BaCO)₃) Powder and copper oxide (CuO) powder into R123 phase components (Sm₁Ba₂Cu₃O_7-XPhase component) and R211 phase component (Sm)₂Ba₁Cu₁O₅The ratio of the phase component) is 1.1 (5 mol% R211 phase component), 1.2 (10 mol% R211 phase component), 1.4 (20 mol% R211 phase component), 1.8 (40 mol% R211 phase component). Were individually weighed so as to be each of the phase components) and individually mixed using an agate mortar to prepare four kinds of raw material mixed powders for testing.
[0039]
Then, each raw material mixed powder was calcined at 900 ° C. for 15 hours, further pulverized, and then calcined at 900 ° C. for 15 hours. To this calcined powder, silver oxide (Ag₂O) 20 wt% powder and 0.5 wt% platinum (Pt) powder were added and further mixed for 1 hour to obtain four kinds of raw material mixed powder. These raw material mixed powders were molded into a plurality of pellets having a diameter of 20 mm and a thickness of 5 mm by a uniaxial pressure press to obtain a plurality of precursors.
Of these pellets, those having the same outer diameter are stacked in two or three layers to form test specimens, and Nd is used as a seed crystal.₁Ba₂Cu₃O_7-XA thin film of the composition was placed and heat-treated in the air according to the following heating pattern. This thin film is formed on a MgO substrate with a composition ratio of 10 × 10 mm.²An oxide superconducting thin film having a thickness of 700 nm was formed and used by dividing it into a size of about 1 mm square.
[0040]
In the heat treatment, each specimen is heated in the atmosphere from room temperature to 900 ° C. over 1 hour, heated from 900 ° C. to 1080 ° C. over 1 hour, held at this temperature for 40 minutes, and then 5 The temperature is lowered to 1050 ° C. over 1 minute and held at 1050 ° C. for 1 hour, then the temperature is lowered to 1020 ° C. over 5 minutes, this temperature is maintained for 10 to 20 hours, and then the temperature is lowered to 900 ° C. over 1 hour. Thereafter, the temperature was lowered to room temperature over 1 hour.
Among the samples obtained by the above steps, the cross section of the junction boundary portion of the upper and lower oxide superconductors in the portion between the single crystal regions of the sample in which the Sm211 phase component is 40 mol% with respect to the Sm123 phase component An enlarged photograph of is shown in FIG.
As shown in FIG. 5, black dots are formed in a beaded manner in the lateral direction at the boundary between the upper and lower oxide superconductors. Further, in FIG. 5, a plurality of large black circles indicate pores, a white irregular-shaped portion indicates a portion where silver particles are present, and most of other gray plain portions are R123 phase. This corresponds to the portion where the single crystal has grown. Further, in the photograph taken at a higher magnification than the photograph of FIG. 5, the presence of a large number of irregular R211 phases can be confirmed in the portion where the single crystal has grown, and the structure in which the R211 phase is dispersed in the R123 phase It can be confirmed that the presence of the R211 phase cannot be confirmed with the magnification shown in the photograph shown in FIG.
[0041]
FIG. 6 shows the result of elemental analysis of one of the black dots connected in a bead shape shown in FIG. 5 by energy dispersive X-ray spectroscopy. As a result of the analysis of the black spot portion of the boundary portion, Sm, Ba, Cu, and O are present at a ratio of approximately 1: 2: 3: (about 7).₁Ba₂Cu₃O_7-XIt can be presumed that this is an oxide superconductor having the following composition.
From the analysis results shown in FIG. 6, it can be estimated that the oxide superconductor obtained by the present invention is a single crystal integrated with good crystal matching at the upper and lower precursor portions.
[0042]
Next, for each oxide superconductor sample obtained in the previous step, when each sample is in a non-superconducting state, a magnetic field of 200 to 5000 G is applied by a Helmholtz type coil, and then the liquid nitrogen temperature (77.3 K) is applied. Each sample was cooled by cooling in a magnetic field to be cooled, and after cooling, the magnetic field on each sample surface was detected using a Hall element, and the magnetic field distribution was measured.
As a representative example, FIG. 7 shows the result of measuring the trapped magnetic field distribution in each applied magnetic field (0 to 5000 G) for a sample having an outer diameter of 17 mm manufactured using a raw material mixed powder having a ratio of 1.8 (40 mol%). Show. This sample had an outer diameter of 20 mm in the pellet state, but became an oxide superconductor having an outer diameter of 17 mm after the melt solidification reaction.
[0043]
FIG. 7 is a three-dimensional representation of the captured magnetic field distribution of a sample prepared from a raw material mixed powder added with 40 mol% of Sm211 phase component, and FIG. 8 is a sample manufactured from the raw material mixed powder added with 40 mol% of Sm211 phase component. FIG. 9 is a diagram in which the captured magnetic field distribution of a sample manufactured from a raw material mixed powder added with 40 mol% of the Sm211 phase component is displayed in three dimensions. All samples show excellent single peak values.
From the above test results, an oxide superconductor having a single peak can be obtained in a case where two precursors are crystallized and integrated by a semi-melt solidification method to form an oxide superconductor. At the same time, when an oxide superconductor having an improved trapping magnetic field is to be manufactured, it seems preferable to disperse the Sm211 phase component in a large amount as finely and uniformly as possible.
[0044]
FIG. 10 shows the particle size distribution measurement result of the powder obtained after calcining in the step of producing the precursor. Looking at the particle size distribution in each step of the first and second calcinations, it can be seen from the ratio of those of 53 μm or less, the ratio of 53 to 106 μm, the ratio of 106 to 300 μm, and the ratio of 300 to 500 μm. Since the first one is mostly 53 to 300 μm and the second calcining is mostly 53 to 106 μm in particle size, it can be used for molding the precursor of the present invention without making the calcined material very fine. Then, it became clear that an excellent oxide superconductor could be manufactured without making the calcined material very fine. Of course, the calcined material may be further refined and processed into a powder with a fine particle diameter, and then molded, but it takes time and effort to grind.
[0045]
【The invention's effect】
  As detailed above, according to the present invention,RE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more rare earth elements) When producing an oxide superconductor having a composition of ₁ Ba ₂ Cu ₃ O _7-X A compact of a raw material in which a compound of an element constituting an oxide superconductor having the following composition is mixed: ₁ Ba ₂ Cu ₃ O _7-X Ingredient 1.1 (5 mol% RE ₂ Ba ₁ Cu ₁ O ₅ Phase component) or more, 1.8 (40 mol% RE) ₂ Ba ₁ Cu ₁ O ₅ Phase component) As a consolidated body of raw materials with a blending ratio in the following rangeStacking multiple precursors, based on the seed crystal for the uppermost precursor,After the semi-molten state is maintained isothermally, the temperature is decreased and preheating is performed so that the temperature is higher than the crystallization start temperature.After that, the temperature is decreased to a crystallization start temperature lower than the preheating temperature, and the Crystallize while maintaining isothermal temperature at the starting temperature, and then cool down the precursor.Semi-molten solidification method by crystallizing oxide superconductorByCrystal growth allows the precursor to become an oxide superconductor, and can also propagate crystallization to other precursors on the lower side of the precursor. The whole can be made into an oxide superconductor by sequentially crystallizing based on the crystal structure of the physical superconductor. At this time, the stacked precursors do not need to be pressure-contacted with each other, and may be in a state where they are naturally in contact by their own weight. This produces an effect that an oxide superconductor having a thickness several times that of an oxide superconductor obtained by using a conventional precursor can be manufactured by simply stacking the precursors. In addition, the oxide superconductor has excellent superconducting characteristics in which the trapped magnetic field distribution has a single peak.
  Next, when crystallizing the stacked precursors,After the semi-molten state is maintained isothermally, the temperature is decreased and preheating is performed so that the temperature is higher than the crystallization start temperature.After that, the temperature is decreased to a crystallization start temperature lower than the preheating temperature, and the Crystallization while keeping isothermal at the starting temperatureBy carrying out, the whole can be crystallized in a much shorter time than the method of crystallization by slow cooling. In addition, an oxide superconductor several times thicker than the conventional one can be easily obtained in a shorter time than the prior art by propagating the crystallization of the upper precursor to the crystallization of the lower precursor.Specifically, a precursor having a diameter of 20 to 30 mm can be crystal-grown by the above-described manufacturing method.
[0046]
The present invention provides an RE superconductor as an RE superconductor.₁Ba₂Cu₃O_7-X(RE represents one or more rare earth elements) The present invention can be applied to an oxide superconductor having a composition. Furthermore, since the present invention can be realized in a naturally mounted state between the plurality of stacked upper and lower precursors instead of being in a completely close contact state, it is possible to manufacture a large oxide superconductor without increasing the manufacturing cost. There is.
[0047]
  The present invention provides a target RE₁Ba₂Cu₃O_7-XA compact of a raw material in which a compound of an element constituting an oxide superconductor having the following composition is mixed:₁Ba₂Cu₃O_7-XRE for phase components₂Ba₁Cu₁O₅Since the raw material compact is used in such a ratio that the phase component ratio is in the range of 1.1 or more and 1.8 or less, the crystal growth is smoothly transmitted to all of the accumulated precursors, so that Can be obtained as an oxide superconductor.
  In addition, the present invention uses a pulverized product having an average particle size in the range of 50 to 100 μm when a precursor obtained by mixing and compacting and calcining the raw materials and then pulverizing and re-compacting the pulverized product is used. The target oxide superconductor can be manufactured.
[0048]
If it is an oxide superconductor according to the present invention, an oxide superconductor having a thickness corresponding to a thickness that cannot be obtained by a conventional method for producing a precursor is easier than in the past, and a special pressurizing apparatus is used. Can be obtained at low cost. Furthermore, the obtained oxide superconductor has excellent superconducting properties in which the trapped magnetic field distribution has a single peak.
[Brief description of the drawings]
FIG. 1 is a side view showing a state in which the method of the present invention is being carried out, and shows a state in which a seed crystal is placed on a stack of two precursors.
FIG. 2 is a side view of the first embodiment of the oxide superconductor according to the present invention obtained by carrying out the method of the present invention.
FIG. 3 is a diagram showing an example of a planar shape of an oxide superconductor obtained by the method of the present invention.
FIG. 4 is a side view of a second embodiment of the oxide superconductor according to the present invention.
FIG. 5 is a cross-sectional structure photograph of the boundary portion of the crystallization region of the oxide superconductor obtained in the example.
FIG. 6 is a diagram showing an analysis result of a black spot portion at a boundary portion of the sample shown in FIG.
FIG. 7 is a diagram showing the trapped magnetic field distribution of the oxide superconductor obtained in the example.
FIG. 8 is a three-dimensional distribution diagram of the trapping magnetic field of the oxide superconductor sample of the first example obtained in the example.
FIG. 9 is a three-dimensional distribution diagram of the trapping magnetic field of the oxide superconductor sample of the second example obtained in the example.
FIG. 10 is a diagram showing the particle size distribution of the pulverized material for forming precursors applied in the examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 2 ... Precursor, 3 ... Seed crystal, 5, 9 ... Oxide superconductor, 6, 10 ... Borderline, 15 ... Single-crystal region, 16 ... Polycrystalline region.

Claims (9)

When manufacturing an oxide superconductor having a composition of RE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more rare earth elements), the target RE ₁ Ba ₂ Cu ₃ O _7-X A raw material compacted with a compound of an element constituting an oxide superconductor having the composition as shown above, wherein the RE ₁ Ba ₂ Cu ₃ O _7-X component is 1.1 (5 mol% RE ₂ Ba ₁ Cu ₁ O ₅ phase component) to 1.8 (40 mol% RE ₂ Ba ₁ Cu ₁ O ₅ phase component), the precursor composed of a compacted raw material having a blending ratio so as to be in the range of not more than 1.8 (40 mol% RE ₂ Ba ₁ Cu ₁ O ₅ phase component) Then, the oxide superconductor is cooled, and the oxide superconductor is formed by a semi-melting solidification method by crystallizing the precursor in the semi-molten state based on the crystal structure of the seed crystal placed on the precursor. A method of manufacturing
In carrying out the semi-molten solidification method, a plurality of the precursors are stacked, a seed crystal is placed on the stacked uppermost precursor, and the uppermost precursor is formed based on the seed crystal by the semi-melt solidification method. In addition to crystallization, the crystallization is propagated to the lower precursor, and the other precursors stacked are sequentially crystallized. In carrying out the semi-melt solidification method, the stacked precursors are heated. The semi-molten state is maintained isothermally, and then the temperature is lowered and preheating is performed so that the temperature is higher than the crystallization start temperature, and then the crystallization start temperature is lowered to a temperature lower than the preheat temperature. A method for producing an oxide superconductor , wherein crystallization is performed while maintaining isothermal temperature at a crystallization start temperature, and then the temperature is lowered . The method for producing an oxide superconductor according to claim 1, wherein a cold seeding method in which the seed crystal is placed on the precursor and then heated to be in a semi-molten state is used . A single crystal film of an oxide superconductor formed as a seed crystal on a heat-resistant substrate by a film forming method, and has a peritectic temperature higher than that of the oxide superconductor to be manufactured. The method for producing an oxide superconductor according to claim 1 or 2, wherein a single crystal film of the oxide superconductor is used. The method for producing an oxide superconductor according to any one of claims 1 to 3, wherein the plurality of stacked precursors are placed in a natural placement state having a gap instead of a completely close contact state. 2. A pulverized product having an average particle diameter in the range of 50 to 100 μm is used when a precursor obtained by mixing and compacting and calcining the raw materials and then pulverizing and then re-compacting the pulverized product is used. The manufacturing method of the oxide superconductor in any one of -3. When the plurality of stacked precursors are sequentially crystallized from the upper stage side to the lower stage side, only the precursor that is in the process of crystallization is kept at the crystallization temperature, and the precursor on the lower stage side is kept at a temperature in a semi-molten state. The oxide superconductivity according to any one of claims 1 to 5, wherein the oxide superconductivity is maintained and crystallized while giving a temperature gradient in which the precursors in a semi-molten state are sequentially set to a crystallization temperature as crystallization progresses. Body manufacturing method. When manufacturing an oxide superconductor having a composition of RE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more rare earth elements), the target RE ₁ Ba ₂ Cu ₃ O _7-X A raw material compacted with a compound of an element constituting an oxide superconductor having the composition as shown above, wherein the RE ₁ Ba ₂ Cu ₃ O _7-X component is 1.1 (5 mol% RE ₂ Ba ₁ Cu ₁ O ₅ phase component) to 1.8 (40 mol% RE ₂ Ba ₁ Cu ₁ O ₅ phase component), the precursor composed of a compacted raw material having a blending ratio so as to be in the range of not more than 1.8 (40 mol% RE ₂ Ba ₁ Cu ₁ O ₅ phase component) After that, it was manufactured by a semi-melting solidification method by crystallizing the precursor in a semi-molten state from the crystal structure of a seed crystal placed on the precursor after being gradually cooled to form an oxide superconductor. An oxide superconductor,
A plurality of the precursors are stacked, and the plurality of stacked precursors are crystallized into an oxide superconductor by crystallization by a semi-melt solidification method based on a seed crystal placed on the uppermost precursor. In carrying out the semi-molten solidification method, the stacked precursors are heated to a semi-molten state, held isothermally, and then cooled and pre-heated to be kept isothermal in a temperature range higher than the crystallization start temperature. The oxide superconductor is characterized in that it is cooled to a crystallization start temperature lower than the preheating temperature, crystallized while being kept isothermally at the crystallization start temperature, and then cooled . 8. The oxide superconductor according to claim 7, wherein, among the stacked oxide superconductors, the oxide superconductors that are in contact with each other are welded and integrated at portions where they are in contact with each other. The oxide superconductor according to claim 7 or 8, wherein any one of Ag, Pt, and Au is added .

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