SUPERCONDUCTOR AND METHOD OF MANUFACTURING THE SAME

Abstract: A method of manufacturing a superconductor is carried out by first preparing a material composed of Y₁Ba₂Cu₃O₇. This material is heated/molten in a platinum crucible. A melt thus obtained is drawn out from a high-temperature frame provided above the platinum crucible and heated to a temperature exceeding the melting point of the material. The melt thus drawn out is cooled by natural standing, to be solidified. As the result, an elongated superconductor composed of Y₁Ba₂Cu₃O₇ can be obtained. This superconductor enters a superconductive state at 90 K.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a superconductor of ceramics, and more particularly, it relates to a method of manufacturing a superconductor, which comprises steps of melting a raw material and thereafter solidifying the same. Description of the Prior Art A superconductive material of ceramics is recently being watched as that superconducts at a higher critical temperature. A superconductor of such a ceramics superconductive material is formed by press-forming a raw material of ceramics powder and sintering the same. The sintered body may be temporarily fired in advance to glost firing after press forming, as the case may be. In the conventional method employing powder sintering, length of the superconductor has been restricted to that of a mold for press forming. Thus, it has been extremely difficult to elongate the conventional superconductor in order to apply the same to a conductor for forming a coil for a high current density magnet or a long-distance transmission line for making the best use of its superconductivity. In the conventional method, further, complicated steps have been required for manufacturing an elongated body, leading to difficulty in productivity. In the aforementioned conventional sintering method, the superconductor has been restricted in manufacturable configuration. Further, it has been difficult to obtain a dense superconductor because of voids remaining after sintering. Thus, it has been impossible to attain high critical current density in a superconductor obtained by the sintering method. In addition, it has been difficult to control crystal structure of the superconductor in the sintering method. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of efficiently manufacturing an elongated superconductor according to claim 1 which is composed in design by a ceramics superconductive material. The present invention provides a method of manufacturing a superconductor made of a ceramics superconductive material, preferably a material which comprises a layer structure compound containing oxygen and at least two sorts of metal elements. The present invention provides a method of manufacturing a ceramics superconductor being in composition generally expressed in a formula AaBbCc. In this general formula, A represents at least a single sort of element, preferably at least two sorts of elements selected from a group of those belonging to the groups Ia, IIa and IIIa of the periodic table. The elements belonging to the group Ia of the periodic table are H, Li, Na, K, Rb, Cs and Fr. The elements belonging to the group IIa of the periodic table are Be, Mg, Ca, Sr, Ba and Ra. The elements belonging to the group IIIa of the periodic table are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Ly, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No and Lr. On the other hand, B in the general formula represents at least a single sort of element selected from a group of those belonging to the groups Ib, IIb and IIIb of the periodic table. The elements belonging to the group Ib of the periodic table are Cu, Ag and Au and those belonging to the group IIb of the periodic table are Zn, Cd and Hg, while those belonging to the group IIIb of the periodic table are B, Al, Ga, In and Tl. C represents at least a single sort of element selected from a group of oxygen, carbon, nitrogen, fluorine and sulfur. The general a , b and c represent numbers showing the composition ratio of A , B and C respectively. While relation of a x (average valence of A) + b x (average valence of B) = c x (average valence of C) generally holds for a , b and c , satisfaction of such relation is not necessarily required. Preferably at least copper is contained as B and at least oxygen is contained as C in the aforementioned final composition, for the possibility of superconduction at a higher critical temperature. In the method of manufacturing a superconductor according to the present invention, first prepared is a raw material of layer structure compound containing oxygen and at least two sorts of metal elements, or a raw material being in composition generally expressed in the formula AaBbCc. This raw material is molten in a vessel having an opening portion. A melt of AaBbCc obtained by such melting is drawn out from a frame provided in the opening portion and heated to a temperature exceeding the melting point of the raw material. The melt thus drawn out is solidified. Such solidification may be performed through forced cooling or natural standing. According to the inventive manufacturing method, the melt of the aforementioned material is drawn out from the frame of a high temperature to be solidified, thereby to form a conductor. Thus, an elongated superconductor can be stably obtained with small drawing force, requiring no complicated mold or steps for obtaining an elongated body. Further, elongated conductors can be continuously manufactured. A deformed or tape-like conductor can be easily obtained in addition to a conductor having a circular sectional configuration, by selecting the configuration of a portion of the high-temperature frame for passing the melt. The melt can be cooled with an abrupt temperature gradient to increase the speed for drawing out the same, thereby to efficiently manufacture an elongated superconductor. Further, an elongated superconductor of a unidirectionally solidified member or a monocrystal body can be manufactured. If the superconductive material such as an oxide being in layer structure has a high melting point and requires protection against contamination in manufacturing, a crucible for melting the raw material and the high-temperature frame are preferably formed by an appropriate material selected from a group of platinum, rhodium, iridium, platinum alloy, rhodium alloy, iridium alloy and boride ceramics, in order to obtain a superconductor in desired composition. According to the present invention, the raw material is molten and drawn out from the high-temperature frame to be solidified thereby to obtain a superconductor. Thus, an elongated superconductor can be stably and efficiently manufactured at a low cost. Further, the material is drawn out from the frame of a high temperature, so that elongated superconductors of various sectional configurations such as those in the form of fine wires including deformed ones and a tape-like superconductor can be easily obtained by devising the sectional configuration of the high-temperature frame. Thus, enabled is industrial mass production of superconductors, which are optimum for forming a long-distance transmission line and a coil for a high current density magnet, in order to make the most effective use of characteristics of a superconductor. It is pointed out that the inventive manufacturing method is also applicable to manufacturing of a superconductor other than an elongated one. In the aforementioned melting-solidifying method according to the present invention, it is difficult to obtain a ceramics superconductor being composed in design even if the raw material is correctly prepared in composition. The composition is easily fluctuated particularly by dissociation or coupling of elements contained in the raw material being in a molten state. In consideration of this, the inventors have found out that a ceramics superconductor being composed in design can be reliably obtained by adjusting an atmosphere in at least one of the entire steps including melting, cooling and solidifying steps. According to the inventive method of manufacturing a superconductor based on the aforementioned point of view, prepared is a raw material which is generally expressed in a formula AaBbC x c x , in order to manufacture a ceramics superconductor of the aforementioned composition. In this general formula, C x represents at least a single sort of element selected from a group of oxygen, carbon, nitrogen, fluorine and sulfur, which may be identical to the aforementioned C . If C consists of two or more sorts of elements, C x may be prepared by a part thereof. In this general formula, c x represents a number showing the composition ratio of C x . In the inventive manufacturing method, the material expressed as AaBbC x c x is first prepared to be molten. The inventive method further comprises at least a step of drawing out a melt of AaBbC x c x obtained by such melting through a frame provided in an outlet for the melt and heated to a temperature exceeding the melting point of the raw material and a step of solidifying the melt of AaBbC x c x thus drawn out. The present invention may comprise at least the melting step, the drawout step and the solidifying step, while some steps may be freely performed after the solidifying step. The solidifying step may be performed by natural standing or forced cooling. In case of forced cooling, the melt can be drawn out at a higher speed, to more efficiently produce an elongated superconductor. The inventive manufacturing method is further characterized in that at least one of steps including the aforementioned melting step, drawout step and solidifying step is performed under an atmosphere containing a C y component of partial pressure being higher than C y partial pressure in the atmospheric air. The C y component is prepared by a gas containing at least a single sort of element selected from a group of oxygen, nitrogen, carbon, fluorine and sulfur, which may be identical to C in the aforementioned general formula expressing the final composition. If C consists of two or more sorts of elements, C y contains at least difference between C and C x , i.e., that left by eliminating C x from C . This C y gas may be prepared by oxygen, nitrogen, carbon monoxide, carbon dioxide, hydrogen fluoride or hydrogen sulfide, for example. The aforementioned atmosphere in which the C y partial pressure is higher than that in the atmospheric air may be introduced into "at least" one of the entire steps, and hence only the melting step may be performed under the said atmosphere, while only the drawout step or the solidifying step may alternatively be performed under the said atmosphere. The melting, drawout or solidifying step is carried out under the said atmosphere in order to perform melting, drawout or solidification in the atmosphere which is rich in C y . Therefore, if C x is smaller in sort or amount of element than C in the final composition, C y can be added to the material being in a molten, drawn-out or cooled state from the C y atmosphere. Thus, Cc in the final composition can be reliably implemented. If C x contained in the material is identical to C in the final composition, on the other hand, dissociation of the C component in the material can be suppressed in the molten state or a state directed to solidification by preparing C y to be identical in element to C x and C . Even if the C component is dissociated, the same can be recombined in a desired state. After the solidifying step, the material can be re-heated under an atmosphere in which C y partial pressure is higher than that in the atmospheric air. In this case, the C component in the final composition can be attained by supplying the C y component through the re-heating step. The superconductor obtained according to the present invention is drawn out from the high-temperature frame to be solidified, whereby a superconductor being in structure of a monocrystal body or a unidirectionally solidified body can be easily obtained. It is pointed out that the material expressed as AaBbC x c x can be prepared not only by a mixed body or a compact, but also by a partially fabricated item, which is in incomplete superconduction. Thus, according to the inventive manufacturing method, dissociation or change of elements in a molten state can be effectively prevented by partially adjusting an atmosphere in the steps, while a component not contained in the raw material can be supplied from the atmosphere, as the case may be. Thus, a ceramics superconductor can be reliably composed in design. The aforementioned melting-solidifying method according to the present invention may include a step of passing an elongated base material through a melt in a frame portion heated to a temperature exceeding the melting point of a raw material, to apply the melt to the base material. Thus, a superconductor of a base material coated with a solidified body of a ceramics superconductive material can be manufactured by drawing out the base material applied with the melt and solidifying the melt. In this manufacturing method, the step of passing the base material through the melt in the frame portion may be performed by moving the melt in a passage portion provided between an opening portion of a vessel and the frame portion for supplying the melt into the frame. According to the inventive manufacturing method, a superconductor can be obtained by simply passing the base material through the melt of the superconductive material, whereby an elongated superconductor can be efficiently and stably manufactured. As hereinafter described with reference to Example, the superconductive material can be provided in desired thickness around the base material by controlling the speed for passing the base material through the melt or passing the same through the melt by a plurality of times. Further, the sectional configuration of the superconductor as obtained is controlled by the sectional configuration of the frame portion or the like, whereby a superconductor of a desired sectional configuration such as a circular one or a flat one can be obtained. The superconductive material can be molten in an atmosphere containing a large amount of oxygen, carbon, nitrogen, fluorine or sulfur, which is an element forming the superconductive material, to compensate for shortage of such an element caused by the melting, thereby to obtain a superconductor of excellent superconductivity. The present invention is first characterized in that the conventional sintering method is not employed but steps of melting a raw material and thereafter solidifying the same are employed. While it is known that a superconductor composed of Y₁Ba₂Cu₃O x , for example, has a high superconductivity transition temperature of 90 K, for example, it has been experimentally found out that the raw material employed in the melting and solidifying steps must be within a specific composition range in order to obtain such a superconductor having a relatively high superconductivity transition temperature. Thus, the present invention is secondly characterized in that a raw material to be molten and solidified is a composite oxide of YO 1.5 , BaO and CuO in a composition region enclosed by three points of CuO, A (50at.%YO 1.5 -25at.%BaO - 25at.%CuO) and B (50at.%BaO - 50at.%CuO), excluding the line CuO - B, in a three-component composition diagram of respective oxides of yttrium, barium and copper as shown in Fig. 1. In the present invention, the said composite oxide is preferably selected so that composition of YO 1.5 , BaO and CuO is in a region enclosed by three points of C (10at.%YO 1.5 - 20at.%BaO - 70at.%CuO), D (30at.%YO 1.5 -30at.%BaO - 40at.%CuO) and E (5at.%YO 1.5 - 45at.%BaO - 50at.%CuO) in the three-component composition diagram as shown in Fig. 1. In a preferred embodiment of the present invention, a raw material of composition shown in the aforementioned three-component composition diagram is molten in a platinum crucible, to be solidified by a crucible solidifying process, casting, a quenching method, a unidirectional solidifying method, a "spinning method" of extruding or drawing out a melt from a hole communicating with the interior of a crucible to cool and solidify the same, "hot mold casting" of drawing out a melt through a frame of a high temperature exceeding the melting point provided in an outlet for the melt and solidifying the same, a "pipe suction method" of filling a melt in a pipe and solidifying the same, a "dipping method" of passing a core member through a molten solution to solidify the same around the core member or "movable mold casting" of casting a melt in a mold which is movable with respect to a casting position for the melt thereby to cast the same. Preferably a solidified body thus obtained is held in a temperature range of 800 to 1000°C for at least two hours, to be thereafter cooled at a speed not more than 200°C/h. The aforementioned melting and solidifying steps and/or the steps of holding the solidified body in a prescribed temperature range for at least a prescribed time and thereafter cooling the same at a prescribed speed are preferably performed in an oxygen atmosphere of at least 0.2 atm. In the present invention, it has been found out that a solidified body obtained by solidifying a melt of a composite oxide within the composition range enclosed by CuO - A - B in Fig. 1 has a high volume ratio of a Y₁Ba₂Cu₃O x superconductive phase, to be in excellent superconductivity. It has also been found out that a superconductivity transition temperature of the solidified body exceeds the temperature of liquid nitrogen if the composition thereof is in a range enclosed by the points C, D and E in Fig. 1. It has been experimentally confirmed that, although the composition of a raw material can be simply selected so that Y, Ba and Cu are in the ratio 1:2:3 in order to obtain a superconductor composed of Y₁Ba₂Cu₃O x by the conventional sintering method, the composition of the raw material cannot be so much simply selected in the present invention including the melting and solidifying steps. In other words, it has been recognized that a melt being composed of Y₁Ba₂Cu₃O x is separated in solidification into a plurality of phases being different in composition, whereby the volume ratio of the composition of Y₁Ba₂Cu₃O x is rather reduced. It has been also confirmed that, if a melt being composed of Y₁Ba₂Cu₃O x is simply solidified in order to obtain a superconductor having a high superconductivity transition temperature, a superconductive state may not be attained even at a temperature of 4.2 K (liquid helium temperature). According to the present invention, a melt of prescribed configuration is solidified in various technique, thereby to obtain a dense superconductor of high critical current density having an arbitrary configuration. Thus, the manufacturing method according to the present invention can be advantageously applied to a method of manufacturing a Y-Ba-Cu oxide superconductor, which is generally applicable to a superconductor for a high current density magnet or a long-distance transmission line. In a preferred embodiment of the present invention, a platinum crucible is employed to perform the melting step, in order to minimize reaction of the melt with the crucible within a range causing no problem in practice. In other words, no bad influence is exerted on superconductivity even if platinum is contaminated in the superconductor thus obtained. While the step of solidifying the melt in the present invention may be performed by any method being well known in the art, the melt is held in a temperature range of 800 to 1000°C for at least two hours upon solidification and thereafter cooled at a speed of not more than 200°C/h. in the preferred embodiment, as hereinabove described. Such process is adapted to compensate for shortage of oxygen being dissociated in melting, as well as to perfect phase transformation of a Y₁Ba₂CuO₃O x phase, i.e., phase transformation from a tetragonal system into a rhombic system, which is effective for superconductivity. In the preferred embodiment of the present invention, the melting and solidifying steps and/or the aforementioned steps after solidification are performed in an oxygen atmosphere exceeding prescribed atmospheric pressure, as hereinabove described. Thus, tendency to shortage of oxygen in the obtained superconductor can be prevented. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a three-component composition diagram showing composition of a Y-Ba-Cu-O raw material which is employed to be molten in a method of manufacturing a superconductor according to the present invention; Fig. 2 is a schematic process diagram showing steps of a method of manufacturing a superconductor according to the present invention; Fig. 3 is a sectional view schematically showing an apparatus employed for carrying out first Example of the present invention; Fig. 4 is a sectional view schematically showing an apparatus employed for carrying out second Example of the present invention; Fig. 5 is a sectional view schematically showing an apparatus employed for carrying out third Example of the present invention; Fig. 6 is a sectional view schematically showing an apparatus employed for carrying out fourth Example of the present invention; Fig. 7 is a sectional view schematically showing an apparatus employed for carrying out fifth Example of the present invention; and Fig. 8 is a sectional view schematically showing an apparatus employed for carrying out sixth Example of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 2 is a process diagram schematically showing a method of manufacturing a superconductor according to the present invention. Referring to Fig. 2, a raw material of prescribed composition is first prepared in the form of powder or a compact. This raw material is molten in a vessel having an opening portion. A melt thus obtained is drawn out through a frame which is provided in the opening portion and heated to a temperature exceeding the melting point of the raw material. The melt thus drawn out is thereafter cooled to be solidified. Thus, a superconductor of prescribed composition is obtained in the form of a solidified body. The inventive method of manufacturing a superconductor is now described with reference to Examples. Example 1 An apparatus as shown in Fig. 3 was employed to form an elongated ceramics superconductor. Referring to Fig. 3, numeral 1 indicates a heater and numeral 2 indicates a crucible, while numeral 3 indicates a melt and numeral 4 indicates a high-temperature frame which is provided on the melt 3. Numerals 5 and 6 indicate rolls, which are rotated along arrows in the figure, in order to draw out a solidified ceramics material. First, a material being composed of (Y,Ba)₃Cu₂O₇ was heated/molten by the crucible 2 of platinum, and a melt 3 thus obtained was drawn out from the high-temperature frame 4 of platinum having a portion of 1.0 mm in diameter for passing the melt 3 at a speed of 11 mm/min. Such drawout operation was stopped upon drawing out 100 mm of a (Y,Ba)₃Cu₂O₇ wire 10 of 1.0 mm in diameter, to examine its superconductivity. It has been confirmed that this wire superconducted at 50 K. Example 2 An apparatus as shown in Fig. 4 was employed to obtain an elongated superconductor. The apparatus as shown in Fig. 4 comprises a crucible 12 having a heater 11 on its outer side, a high-temperature frame 14 provided on the side wall of the crucible 12 and rolls 15 and 16 for drawing out a solidified melt 13. A material being composed of (La 0.925 Sr 0.075 )₂CuO₄ was heated/molten by the crucible 12 of PBN, to drawn out the melt 13 thus obtained from the high-temperature frame 14 of PBN having a portion of 0.5 mm in thickness and 10 mm in width for drawing out the melt 13, at a speed of 9 mm/min. Such drawout operation was stopped upon drawing out 50 m of the melt 13, to obtain a tape-like body 20 of (La 0.925 Sr 0.075 )₂CuO₄ which was 0.5 mm in thickness and 10 mm in width. This tape-like body 20 superconducted at 41 K. Example 3 An apparatus as shown in Fig. 5 was employed to obtain an elongated superconductor. Referring to Fig. 5, numeral 21 indicates a heater and numeral 22 indicates a crucible, while numeral 23 indicates a melt and numeral 24 indicates a high-temperature frame provided on the melt 23. This apparatus is so controlled that a C y atmosphere is present above the melt 23. A pair of rolls 26 and 27 are provided further above the melt 23, to be rotated along arrows in the figure, in order to draw out a solidified ceramics material. A mixture of Y₂O₃, BaCO₃ and CuO was first molded and previously subjected to heat treatment. A compact thus obtained was heated/molten in the crucible 22 as shown in Fig. 5 under the C y atmosphere containing oxygen of 26 660 Pa (200 Torr). A melt 23 thus obtained was drawn out from the high-temperature frame 24 having a hole of 1 mm in diameter for passing the melt 23, to be solidified in the form of a fine wire 30. It has been confirmed that the fine wire 30 thus obtained was a monocrystal body. This fine wire 30 was made of a ceramics superconductive material being composed of (Y,Ba)₃Cu₂O₇, and superconducted at 60 K. Example 4 An apparatus as shown in Fig. 6 was employed to obtain a ceramics superconductor. The apparatus as shown in Fig. 6 comprises a crucible 32 having a heater 31 on its outer side, a high-temperature frame 34 provided on the side wall of the crucible 32, an atmosphere furnace 35 externally adjacent to the high-temperature frame 34 and rolls 36 and 37 for drawing out a solidified melt. A heater 38 is also provided around the atmosphere furnace 35. A material being in average composition of La 1.1 Sr 0.34 CuO x containing 0.01 wt.% of fluorine was first molten in the crucible 32 of the apparatus as shown in Fig. 6. A melt thus obtained was drawn out from the high-temperature frame 34 having a rectangular outlet hole of 0.3 mm in thickness and 10 mm in width and passed through the atmosphere furnace 35 under an atmosphere containing SF₆ gas of 13 330 Pa (100 Torr)., to obtain a tape-like body 40 of 0.3 mm in thickness and 10 mm in width. This tape-like body 40 was recognized to be a unidirectionally solidified body, which superconducted at 42 K. Example 5 The fine wire obtained in Example 3 was heated under an atmosphere containing oxygen of 26 660 Pa (200 Torr). at a temperature of 950°C for three hours. A ceramics superconductor thus obtained superconducted at 65 K. Example 6 Fig. 7 is a sectional view showing an apparatus for illustrating Example 6. Referring to Fig. 7, a frame portion 43 is provided on a vessel 41 through a communicating portion 42. A heater 44 is provided around the vessel 41, the communicating portion 42 and the frame portion 43. The vessel 41 stores a molten solution 46 of a superconductive material, which is guided into the frame portion 43 through the communicating portion 42. In order to continuously guide the molten solution 46 into the frame portion 43, it is necessary to regularly maintain the level of the molten solution 46 contained in the vessel 41 higher than the communicating portion 42. Thus, a level adjusting rod 45 is provided in the vessel 41 in order to adjust the level of the molten solution 46. The level adjusting rod 45 is so vertically movable that the same is increased in volume in the molten solution 46 through downward movement, thereby to raise up the level of the molten solution 46. An opening 43a is formed in the bottom of the frame portion 43, to receive a core member 47. A die 48 and rollers 49 are provided above the frame portion 43, to pass the core member 47 through inner central portions thereof. The core member 47 is upwardly fed to be passed through the molten solution 46 in the frame portion 43 from the opening 43a, so that the molten solution 46 is applied around the core member 47. The molten solution 46 is raised up with the core member 47 and passed through the die 48, to be shaped into a prescribed sectional configuration, while being cooled and solidified. Thus, the core member 47 is coated by the superconductive material to provide a superconductor 50, which is raised up by the roller 49. The amount of the molten solution 46 is gradually decreased during thus coating the core member 47, and hence the level adjusting rod 45 is downwardly moved to regularly adjust the level thereof. A ceramics superconductive material being composed of (La 0.925 Sr 0.075 )₂CuO₄ was employed to manufacture a superconductor by the apparatus as shown in Fig. 7. The core member 47 was prepared by a platinum wire of 1.0 mm in diameter, and passed through the molten solution 46 in the frame portion 43 by three times in total. Inner diameters of the opening 43a of the frame portion 43 and the die 48 were gradually increased every passage to increase thickness of the superconductive material to be coated, thereby to finally obtain a superconductor 50 of 1.6 mm in diameter. The superconductor 50 thus obtained superconducted at 40 K. Example 7 Fig. 8 is a sectional view showing an apparatus for illustrating Example 7. Referring to Fig. 8, a vessel 51 contains a molten solution 56 of a superconductive material, and a frame portion 53 is provided under the vessel 51 through a communicating portion 52. A flow rate adjusting rod 55 is provided above the communicating portion 52, in order to adjust the flow rate of the molten solution 56 toward the frame portion 53. The forward end of the flow rate adjusting rod 55 is so tapered that a clearance between the tapered portion and an upper inlet of the communicating portion 52 is changed by vertical movement of the flow rate adjusting rod 55, thereby to adjust the flow rate of the molten solution 56 to be supplied to the frame portion 53. The frame portion 53 has a hole horizontally passing through the same to define openings 53a and 53b. The core member 57 is guided into the opening 53a, to be drawn out from the opening 53b. A heater 54 is provided in the frame portion 53. Another heater 58 is provided around the vessel 51 provided above the communicating portion 52. The molten solution 56 heated by the heater 58 is passed through the clearance between the forward tapered portion of the flow rate adjusting rod 55 and the upper inlet of the communicating portion 52, to be guided into the frame portion 53 from the communicating portion 52. The core member 57 is passed through the horizontal hole of the frame portion 53 from the opening 53a toward the opening 53b, so that the molten solution 56 guided into the frame portion 53 is applied to the surface of the core member 57 in the vicinity of the opening 53b and drawn out from the frame portion 53. A melt thus coated on the surface of the core member 57 is cooled by the outside air or the like and solidified to form a superconductor 60. The frame portion 53 is heated by the heater 54 to a temperature exceeding the melting point of the superconductive material so that the molten solution 56 is not solidified in the frame portion 53. A lid 59 is provided on the vessel 51 to closely seal the vessel 51 against the outside air, so that the superconductive material can be molten under a desired atmosphere. A superconductive material of YBa₂Cu₃O₇ was employed to manufacture a superconductor by the apparatus as shown in Fig. 8. The vessel 51 was provided in an atmosphere containing oxygen of 26 660 Pa (200 Torr)., to melt the superconductive material. The core member 57 was prepared by a platinum wire of 0.8 mm in diameter. The core member 57 was fed at a speed of 40 mm/min. to finally obtain a superconductor 60 of 1.2 mm in diameter. The superconductor 60 thus obtained superconducted at 90 K. In each of Examples 6 and 7, thickness of the coated superconductive material can be adjusted by changing the inner diameter of the die 48 as shown in Fig. 7 or sectional size of the opening 53b as shown in Fig. 8, or controlling the speed for feeding the core member, that for supplying the molten solution into the frame portion and the like. Further, the sectional configuration of the coated superconductive material can be arbitrarily controlled by the sectional configuration of an inner hole of the die 48 as shown in Fig. 7 or the sectional configuration of the opening 53b as shown in Fig. 8. Although the core member is formed by a platinum wire in each of Examples 6 and 7, such a core member may be prepared by any material in the present invention, so far as the same is higher in melting point than the superconductive material as employed. Further, the core member can also be adapted to stabilize superconductivity, by preparing the same by a normal conduction material. Example 8 Powder materials of Y₂O₃, BaCO₃ and CuO were weighed to be in composition ratios of Y, Ba and Cu as listed up in Table 1 and mixed with each other to be temporarily fired in the atmospheric air at 900°C for 12 hours, thereby to provide raw materials to be molten. Such powder materials were introduced into a platinum crucible to be molten in an oxygen atmosphere of 1 atm. at 1350°C, and thereafter directly solidified. Then the materials were held at 950°C for 12 hours during temperature drop, and thereafter cooled to the room temperature at a speed of 150°C/h. Samples of 2 mm x 2 mm x 30 mm in size were cut by a wire saw from solidified bodies thus obtained, and superconductivity transition temperatures (T C ) were decided through measurement of electric resistance by a general four-terminal method. The values T C were decided as temperatures at which the materials lost all resistance to electric current. Table 1 also shows the result of such measurement of electric resistance. Sample No. Composition Tc(K) Example 8 1 Y 0.3 Ba 0.2 Cu 0.5 O x 50 2 Y 0.2 Ba 0.2 Cu 0.6 O x 62 3 Y 0.3 Ba 0.3 Cu 0.4 O x 80 4 Y 0.2 Ba 0.3 Cu 0.5 O x 93 5 Y 0.1 Ba 0.4 Cu 0.5 O x 88 6 Y 0.1 Ba 0.3 Cu 0.6 O x 85 Reference Example 7 Y 0.3 Ba 0.1 Cu 0.6 O x - 8 Y 0.5 Ba 0.3 Cu 0.2 O x - 9 Y 0.1 Ba 0.5 Cu 0.4 O x - Table 1 shows no superconductivity transition temperatures T C as to samples 7 to 9, being reference examples, since superconductive states were not yet attained even at 2 K in these samples. Example 9 A composite oxide being composed of Y 0.15 Ba 0.3 Cu 0.55 O x was unidirectionally solidified in a platinum crucible under the atmosphere with oxygen partial pressure of 20 265 Pa (0.2 atm). by the Bridgeman method, at a speed of 2 mm/h. A solidified body thus obtained was held in an oxygen atmosphere of 1 atm. at 900°C for three hours, and thereafter cooled to the room temperature at a speed of 200°C/h. The solidified body thus obtained caused transition into a superconductor at 90 K, and critical current density in flowing of current in the direction of solidification was 1000 A/cm² at 77 K. Example 10 Powder materials of Bi₂O₃, SrCO₃, CaCo₃ and CuO were weighed to be in composition ratio of Bi : Sr : Ca : Cu = 1 : 1 : 1 : 2 and mixed with each other to be temporarily fired in the atmospheric air at 800°C for 8 hours, thereby to provide raw materials to be molten. Such powder materials were introduced into a platinum crucible to be molten in the atmosphere at 1050°C, and thereafter drawn out and solidified by employing an apparatus as shown in Fig. 3. A fine wire of 1 mm in diameter was thus obtained. The fine wire was annealed at 830°C for 8 hours and thereafter slow cooled. The superconductivity transition temperature (T C ) of the fine wire was decided through measurement of electric resistance by a general four-terminal method. The value T C was decided as temperature at which the materials lost all resistance to electric current, and 100 K.

Claims: A method of manufacturing a superconductor made of a ceramic superconductive material, comprising: a step of preparing a raw material of said ceramics superconductive material; a step of melting said raw material in a vessel having an opening portion to obtain a melt; a step of drawing out said melt through a frame provided in said opening portion and heated to a temperature exceeding the melting temperature of said raw material; a step of solidifying said drawn out melt to obtain a solidified body; and a step of adjusting an atmosphere in at least one of the entire steps including melting, cooling and solidifying steps. A method of manufacturing a superconductor in accordance with claim 1, wherein said ceramics superconductive material comprises a layer structure compound containing oxygen and at least two sorts of metal elements. A method of manufacturing a superconductor in accordance with claim 1, wherein said ceramics superconductive material being in composition generally expressed in a formula AaBbCc, where A includes two elements being Y and Ba, or La and Sr, or three elements being Bi, Sr and Ca, B is Cu, C is oxygen and a, b and c represent numbers showing the composition ratio of A, B and C respectively, said method comprising: a step of preparing a raw material being in composition generally expressed by said formula AaBbCc; a step of melting said raw material in a vessel having an opening portion to obtain a melt; a step of drawing out said melt through a frame provided in said opening portion and heated to a temperature exceeding the melting point of said raw material; and a step of solidifying said drawn-out melt to obtain a solidified body, at least one of said steps of melting said raw material, drawing out said melt and solidifying said melt being performed in an atmosphere containing said oxygen as said C component of partial pressure being higher than partial pressure of oxygen in the atmospheric air. A method of manufacturing a superconductor in accordance with claim 3, wherein said melting step comprises a step of adding said C being oxygen to said melt. A method of manufacturing a superconductor in accordance with claim 3, wherein said solidifying step comprises a step of adding said oxygen to said solidified body. A method of manufacturing a superconductor in accordance with claim 3, further comprising a step of reheating said solidified body in said atmosphere containing said oxygen as said C component of partial pressure being higher than partial pressure of oxygen in the atmospheric air after said solidifying step to add said oxygen to said solidified body. A method of manufacturing a superconductor in accordance with any of the preceding claims, wherein said solidified body is formed by either a undirectionally solidified member or a monocrystal body. A method of manufacturing a superconductor in accordance with any of the preceding claims, wherein said vessel and said frame are made of a material selected from a group of platinum, rhodium, iridium, platinum alloy, rhodium alloy, iridium alloy and boride ceramics. A method of manufacturing a superconductor in accordance with any of the preceding claims, wherein said superconductor is formed by a base material coated with a ceramics superconductive material being in composition generally expressed in a formula AaBbCc, where A includes two elements being Y and Ba, or La and Sr, or three elements being Bi, Sr and Ca, B is Cu, C is oxygen and a, b and c represent numbers showing the composition ratio of A, B and C respectively. A method of manufacturing a superconductor in accordance with claim 9, wherein said step of passing said base material through said melt in said frame portion comprises a step of moving said melt to a passage portion provided between said opening portion and said frame portion and heated to a temperature exceeding the melting point of said raw material through said opening portion. A method according to any of the preceding claims, wherein said superconductor is made of a superconductive material of Y-Ba-Cu-O, comprising: a step of preparing a composite oxide of YO 1.5 , BaO and CuO being in a composition region enclosed by a first point showing 100 at.% CuO, a second point showing 50 at.% YO 1.5 - 25 at.% BaO -25 at.% CuO and a third point showing 50 at.% BaO - 50 at.% CuO, excluding a line connecting said first and third points so that said first and said third points are being exlcuded, in a three-component composition diagram of respective oxides of yttrium, barium and copper; a step of melting said composite oxide to obtain a melt; and a step of solidifying said melt to obtain a solidified body. A method of manufacturing a superconductor in accordance with claim 11, wherein said composition of YO 1.5 , BaO and CuO is in a region enclosed by a fourth point showing 10 at.% YO 1.5 - 20 at.% BaO - 70 at.% CuO, a fifth point showing 30 at.% YO 1.5 - 30 at.% BaO - 40 at.% CuO and a sixth point showing 5 at.% YO 1.5 - 45 at.% BaO - 50 at.% CuO. A method of manufacturing a superconductor in accordance with claim 12, wherein said melting step comprises a step of melting said composite oxide in a vessel of platinum. A method of manufacturing a superconductor in accordance with one of the preceding claims, further comprising steps of holding said solidified body in a temperature range of 800 to 1000° C for at least two hours after said solidifying step and cooling the same at a cooling speed of not more than 200° C/h. A method of manufacturing a superconductor in accordance with claim 14, wherein said steps of holding said solidified body and cooling the same comprise steps performed in an oxygen atmosphere of at least 0.2 atm. A method of manufacturing a superconductor in accordance with claim 11, wherein said melting step and said solidifying step comprise steps being performed in an oxygen atmosphere of at least 0.2 atm. A method of manufacturing a superconductor in accordance with claim 11, wherein said melting step and said solidifying step comprise a step of melting said composite oxide in a vessel having an opening portion to obtain a melt, a step of drawing out said melt through a frame provided in said opening portion and heated to a temperature exceeding the melting point of said composite oxide and a step of solidifying said drawn-out melt to obtain a solidified body.

Inventors: HAYASHI, KAZUHIKO C/O OSAKA WORKS, NAKAI, YOSHIHIRO C/O OSAKA WORKS, NISHIO, MASANOBU C/O OSAKA WORKS, SAWADA, KAZUO C/O OSAKA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1988
Main classification: C04B35
IPC codes: H01B12, C01G3, H01B13, C04B35, C01G1, C01G29, H01L39