Patent Grant
9096440
The invention relates to a method of producing a superconductive material for use in the fields of power transmission, power equipment, and information equipment, and in particular, to a method of producing a superconductive film (such as a fault current limiter, a microwave filter, wires and tapes).
In the past, a substrate has been coated with a solution of an organic compound containing metal elements of which a superconductive material is formed to be subsequently dried (1), and thereafter, a process step (2) (provisional baking) for executing decomposition of the organic components, and a process step (3) (main baking) for forming the superconductive material have all been executed by the agency of thermal energy (refer to Patent Document 1).
Further, there has been known a method of producing metal oxides, and metal oxide thin films by use of an excimer laser (refer to Patent Document 2), characterized in that when preparing metal oxides (exhibiting no superconductivity), metal salts of organic acids, or metalorganic compounds MmRn (provided that M=Si, Ge, Pb, Sn among the group 4b elements, Cr, Mo, W among the group 6a elements, and Mn, Tc, Re among the group 7a elements; R=an alkyl group such as CH3, C2H5, C3H7, C4H9, etc., a carboxyl group such as CH3COO., C2H5COO., C3H7COO., C4H9COO., etc., or a carbonyl group of CO; m, n: integers) are dissolved in a soluble solvent (or if those are in liquid form, as they are), and a solution thus obtained is dispersed and applied over a substrate before the substrate is irradiated in an oxygen atmosphere with an excimer laser light.
Still further, there has been known a method of producing metal oxides, which is a method of producing metal oxides (exhibiting no superconductivity) on a substrate without applying heat treatment at a high temperature unlike a conventional case known as the coating thermal decomposition method, characterized in that metalorganic compounds (metal salts of organic acids, metal-acetylacetonate, metal-alkoxides containing an organic group having 6 or more carbon atoms) are dissolved in a solvent to be turned into a solution, and the substrate is coated with the solution to be subsequently dried, thereby forming metal oxides on the substrate by irradiating the substrate with laser light at a wavelength not more than 400 nm (Patent Document 3). Herein, there has been described the method of producing metal oxides, characterized in that the metalorganic compounds are dissolved in a solvent to be turned into a solution, and the substrate is coated with the solution to be subsequently dried, thereby forming metal oxides on the substrate by irradiating the substrate with the laser light at a wavelength not more than 400 nm such as, for example, an excimer laser beam selected from the group consisting of excimer laser beams ArF, KrF, XeCl, XeF, and F2, and further, it has been described therein that irradiation with the laser light at the wavelength not more than 400 nm is executed in a plurality of stages, and weaker irradiation on the order of not causing complete decomposition of the metalorganic compounds is executed in the initial stage of the irradiation while executing stronger irradiation capable of converting the metalorganic compounds into the metal oxides in the next stage. Further, it is also known that the metalorganic compounds are not less than two kinds of compounds, each containing a different metal, the metal oxides obtained are composite oxides containing various metals, and respective metal constituents of the metal salts of the organic acids are elements selected from the group consisting of iron, indium, tin, zirconium, cobalt, nickel, and lead.
Still further, with a method of producing composite oxide films, whereby a precursor coating liquid containing raw material constituents of respective oxides of La, Mn, and any of Ca, Sr, and Ba is applied to a surface of a material to be coated to thereby form a film, and subsequently, a thin film formed on the surface of the material to be coated is caused to undergo crystallization to thereby form composite oxide films (exhibiting no superconductivity) having the perovskite structure expressed by a composition formula (Ls1-x Mx) MnO3-δ(M: Ca, Sr, Ba, 0.09≦x≦0.50), there has been known a method of producing composite oxide films (refer to Patent Document 4) characterized in that the precursor coating liquid is applied to the surface of the material to be coated to thereby form a film, and subsequently, a thin film formed on the surface of the material to be coated is irradiated with light at a wavelength not more than 360 nm to thereby crystallize the thin film. Herein, it is further described that as a light source for irradiating the thin film formed on the surface of the material to be coated with light, use is made of a third harmonic light of an ArF excimer laser, KrF excimer laser, XeCl excimer laser, XeF excimer laser, and YAG laser, or a fourth harmonic light of the YAG laser, and the precursor coating liquid to be applied to the surface of the material to be coated is prepared by mixing an alkanolamine coordination compound of La, Mn carboxylate, and metal M or M alkoxide together in a first alcohol having carbon atoms in a range of 1 to 4.
The inventor has been faced with the fact that with the conventional method of producing a superconductive material, a long time was required, orientation was difficult to control and, further, uniformity underwent deterioration due to the occurrence of a reaction with a support body in practical use when carrying out the thermal decomposition of metalorganic compounds, and formation of a superconductive material by means of heat treatment, and in order to overcome problems, the inventor has succeeded in finding a method of efficiently producing a superconductive material excellent in performance upon execution of the thermal decomposition of the metalorganic compounds, and the formation of the superconductive material by means of the heat treatment, and has already submitted a Japanese Patent Application (refer to Patent Document 5). More specifically, such a method is a method of producing a superconductive material, characterized in that laser light is irradiated between the step of applying a solution of an organic compound containing metals, oxides of the metals forming a superconductive material, onto a support body to be subsequently dried (1), and the provisional baking step of causing organic components of the organic compound containing the metals to undergo thermal decomposition (2). The superconductive material obtained by the method according to this invention is superior in production efficiency, suitable for mass production, and excellent in superconductivity, however, in the case of a YBa2Cu3O7 (YBCO) film about 100 nm in film thickness, the upper limit of the critical current density has been found to be on the order of Jc=2.0 MA/cm2 at most. Furthermore, with this invention, only a surface of a substrate, coated with the solution of the organic compound containing the metals for forming the superconductive material on the substrate, is simply irradiated with laser light.
With the conventional method of producing a superconductive material, when carrying out the thermal decomposition of a metalorganic compound and formation of a superconductive material with heat treatment, a long time was required, orientation was difficult to control, and uniformity underwent deterioration due to the occurrence of a reaction with a support body in practical use. It is an object of the present invention to provide a method of efficiently producing a superconductive material more excellent in properties and larger in area when executing thermal decomposition of a metalorganic compound, and formation of a superconductive material with heat treatment.
In order to attain the described object, with the method of producing a superconductive material according to the present invention, a part of a heat treatment process of a coating thermal decomposition method is replaced with irradiation with laser light. More specifically, in accordance with a first aspect of the invention, there is provided a method of producing a superconductive material comprising the step (1) of applying a solution of an organic compound of metals, oxides of the metals forming a superconductive material, onto a support body to be subsequently dried, a provisional baking step (2) of causing the organic components of the organic compound of the metals to undergo thermal decomposition and a main baking process step (3) of causing transformation of the oxides of the metals into the superconductive material, as shown in
Still further, the total energy ranging from a condition where a change in color appears on the surface to a condition where cracks occur on the surface is preferably irradiated with the laser light.
Yet further, upon irradiation with the laser light, a laser beam is preferably set to an intensity in a range of 10 to 100 mJ/cm2 to thereby execute irradiation by scanning the laser light.
Further, in accordance with a second aspect of the invention, there is provided a method of producing a superconductive material comprising the step (1) of applying a solution of an organic compound of metals and oxides of the metals forming a superconductive material onto a support body to be subsequently dried, a provisional baking step (2) of causing the organic components of the organic compound of the metals to undergo thermal decomposition, and a main baking process step (3) of causing transformation of the oxides of the metals into the superconductive material, subsequently producing a superconductive coating material having undergone epitaxial growth, wherein upon irradiation of a surface of the support body coated with the solution of the organic compound of metals, forming the superconductive material, with laser light during a period between the steps (1) and (2), the laser light being set to an intensity in a range of 0.5 to 20 mJ/cm2, the irradiation being started with laser light of a low intensity to be followed by irradiation with laser light of a high intensity.
Yet further, in accordance with a third aspect of the invention, there is provided a method of producing a superconductive material comprising the step (1) of applying a solution of an organic compound of metals, oxides of the metals forming a superconductive material onto a support body to be subsequently dried, a provisional baking step (2) of causing organic components of the organic compound of the metals to undergo thermal decomposition, and a main baking process step (3) of causing transformation of the oxides of the metals into the superconductive material, subsequently producing a superconductive coating material having undergone epitaxial growth, wherein upon irradiation of a surface of the support body, coated with the solution of the organic compound of metals forming the superconductive material, with laser light during a period between the steps (1) and (2), the laser light is set to an intensity in a range of 10 to 20 mJ/cm2 to thereby execute irradiation by scanning the laser light. In this case, use may be made of a laser light of no less than 30000 in the number of pulses.
Since the method of producing a superconductive material according to the present invention is provided with a prerequisite for the invention described, it is possible to implement high-speed production (significant reduction in heat treatment time) of a film made of a superconductive material having excellent properties and a large area, and to concurrently execute patterning necessary for manufacturing devices of a microwave filter, a fault current limiter, and so forth, by use of a mask and accurate control of a position to be irradiated with laser light.
Further, with the present invention, as metals, oxides thereof for forming a superconductive material, selection can be made of at least one element selected from the group consisting of RE (RE refers to Y, and rare earth element), and AE (AE refers to alkaline earth metals), respectively, and Cu. Still further, with the present invention, as the support body, selection may be made of one single crystal substrate selected from the group consisting of lanthanum aluminate substrate, strontium titanate substrate, lanthanum-strontium-tantalum-aluminum oxide substrate, neodymium gallate substrate, and yttrium aluminate substrate.
Yet further, with the present invention, as the support body, selection may be made of one single crystal substrate selected from the group consisting of an aluminum oxide substrate, a yttria-stabilized zirconia substrate, a magnesium oxide substrate, the lanthanum aluminate substrate, strontium titanate substrate, lanthanum-strontium-tantalum-aluminum oxide substrate, neodymium gallate substrate, and yttrium aluminate substrate, each with a cerium oxide buffer layer formed thereon (by means of vapor deposition, sputtering, pulsed laser deposition, a coating thermal decomposition method, coating photodecomposition method, sol-gel method, and so forth).
Further, with the present invention, as the organic compound of metals, use may be made of at least one organic compound selected from the group consisting of β-diketonate, metal-alkoxides, and metal salts of organic acids that can include a halogen.
With those features, the method of producing a superconductive material according to the invention is excellent in production efficiency, suitable for mass production and capable of providing a superconductive material of superconductivity significantly improved, having a large area.
In the case of fabricating, for example, a YBCO film by scanning and irradiating a film coated with a metalorganic compound, and dried with a laser light, and further, by applying an adequate heat treatment to a film irradiated with the laser light, the following effect has been confirmed. More specifically, it has turned out that if unidirectional scanning and irradiation is executed with laser light in a front-end stage of the provisional baking step (2) for causing the organic components of the organic compound of the metal to undergo thermal decomposition after the step of applying a solution of the metalorganic compound for generating YBCO onto a support body to be subsequently dried (1), this will promote decomposition of the organic components at a low temperature.
In the case of a conventional coating thermal decomposition method, it has been known that it takes a long time to cause a thermal decomposition reaction of the metalorganic compounds as a raw material for YBCO, however, it has been confirmed that with a method of producing a superconductive material, according to the present invention, the time required in a thermal decomposition reaction process can be shortened. A variation with time of the decomposition reaction occurring in a film coated with a solution of the raw material for YBCO, caused by an excimer laser, was measured by Fourier transform infrared spectroscopy. Results of such a measurement are shown in
Now, embodiments of the present invention are described in more detail hereinafter, however, it is to be pointed out that the present invention not be not limited to those embodiments. Substrates and solutions for the raw material, used in carrying out the embodiments of the present invention, are described as follows.
(1) a substrate (K1); a commercially available substrate of lanthanum aluminate (LaAlO3) (100), a substrate (K2); a commercially available substrate of strontium titanate (SrTiO3) (100), a substrate (K3); a commercially available substrate of lanthanum-strontium-tantalum-aluminum oxide {(LaxSr1-x) (AlxTa1-x) O3} (100), a substrate (K4); a commercially available substrate of neodymium gallate (NdGaO3) (110), a substrate (K5); a commercially available substrate of yttrium aluminate (YAlO3) (110), a substrate (KC1); a substrate with a cerium oxide (CeO2) buffer layer formed on a commercially available substrate of the R-plane of an aluminum oxide (Al2O3) single crystal (sapphire), a substrate (KC2); a substrate with a cerium oxide (CeO2) buffer layer formed on a commercially available substrate of yttria-stabilized zirconia {(Zr,Y) O2, YSZ} (100), a substrate (KC3); a substrate with a cerium oxide (CeO2) buffer layer formed on a commercially available substrate of magnesium oxide (MgO) (100), a substrate (KC4); a substrate with a cerium oxide (CeO2) buffer layer formed on a commercially available substrate of LaAlO3 (100), a substrate (KC5); a substrate with a cerium oxide (CeO2) buffer layer formed on a commercially available substrate of SrTiO3 (100), a substrate (KC6); a substrate with a cerium oxide (CeO2) buffer layer formed on the commercially available substrate of {(LaxSr1-x) (AlxTa1-x) O3} (100), a substrate (KC7): a substrate with a cerium oxide (CeO2) buffer layer formed on the commercially available substrate of (NdGaO3) (110), and a substrate (KC8): a substrate with a cerium oxide (CeO2) buffer layer formed on the commercially available substrate of YAlO3 (110). The buffer layer can be formed by the use of any of layer-forming means including, for example, vapor deposition, sputtering, pulsed laser deposition, a coating thermal decomposition method, coating photodecomposition method, sol-gel method, and so forth.
(2) a raw material solution:
(Y1); a solution obtained by dissolving an acetylacetonate containing Y:Ba:Cu at ample ratio of 1:2:3 into a mixed liquid of pyridine and propionic acid, and removing most of the solvent at about 80° C. by use of a vacuum evaporator before re-dissolution into methanol, (YC1); a solution prepared by substituting an acetylacetonate containing Y:Ca:Ba:Cu at the mole ratio of 0.95:0.05:2:3 for the acetylacetonate in the solution (Y1) containing Y:Ba:Cu at the mole ratio of 1:2:3, (Y2); a solution obtained by mixing a toluene solution of salts of Y, Ba, Cu of naphthenic acid such that Y:Ba:Cu will be at the mole ratio of 1:2:3, (Y3); a solution obtained by mixing a toluene solution of 2-ethylhexanoates of Y, Ba, Cu such that Y:Ba:Cu will be at the mole ratio of 1:2:3, (Y4); a solution prepared by substituting trifluoroacetic acid for propionic acid in the solution (Y1), (Y5) a solution obtained by mixing a methanol solution of trifluoroacetates of Y, Ba, Cu such that Y:Ba:Cu will be at the mole ratio of 1:2:3, (D1) a solution prepared by substituting Dy-acetylacetonate for Y-acetylacetonate in the solution Y1, (E1) a solution prepared by substituting Er-acetylacetonate for Y-acetylacetonate in the solution Y1
(3) laser light
(H1) KrF excimer laser light, (H2) XeCl eximer laser light, (H3) ArF eximer laser light
A surface of the substrate KC1 was spin-coated at 4000 rpm with the coating solution Y1 for 10 seconds, and was dried at 130° C. in a constant-temperature oven for the removal of a solvent to be subsequently irradiated at room temperature by causing the laser light H1 to scan in the longitudinal direction. Provided, however, that the substrate KC1 was irradiated with the laser light H1 from a surface thereof, opposite to the surface coated with a solution of a metal-organic compound of metals for constituting a superconductive material. Irradiation conditions were as follows: room temperature; in the ambient atmosphere; irradiated with the laser light H1 from the surface thereof, on the opposite side of the coated surface; fluence at 74 mJ/cm2; frequency at 100 Hz; an overlapping ratio at 99%; the number of pulses=30,000
Subsequently, a specimen of the substrate KC1, subjected to the irradiation with the laser light, was inserted into a muffle oven kept at 500° C. beforehand, and was kept at that temperature for 30 minutes before being taken out. Thereafter, main baking was applied thereto in a quartz furnace tubular in shape under the following condition. First, the specimen in a flow of a mixed gas of argon and oxygen with a partial pressure of oxygen adjusted at 100 ppm was heated up to 770° C. at a heating rate of about 16° C./min, and that temperature was kept for 45 minutes before the gas was changed over to pure oxygen to be then held further for 30 minutes, after which the specimen was slowly cooled.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 1 except that the irradiation with the laser light was not applied, the critical current density Jc by the inductive method was found at a measurement limit (0.1 MA/cm2) or lower.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 1 except that use was made of the substrate K1, which was not scanned with laser light, the critical current density Jc=1.2 MA/cm2 by the inductive method was obtained.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 1 except that use was made of the substrate K5, there was obtained an a-axis oriented film with in-plane orientation.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 2 except that use was made of the substrate KC3, there was obtained a critical current density Jc=0.6 MA/cm2 by the inductive method.
With a Y0.95Ca0.05Ba2Cu3O7 film about 100 nm in film thickness produced in the same way as in the case of Example 1 except that use was made of the coating solution YC1, there was obtained a critical current density Jc=1.2 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 1 except that use was made of the coating solution Y2, and the main baking was applied at 740° C., there was obtained a critical temperature Tc=80 K by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 6 except that use was made of the coating solution Y3, there was obtained a critical current temperature Tc=80 K by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 7 except that use was made of the coating solution Y4, there was obtained a critical current density Jc=0.6 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 7 except that use was made of the coating solution Y5, there was obtained a critical current density Jc=0.6 MA/cm2 by the inductive method.
With a DyBa2Cu3O7 film about 100 nm in film thickness produced in the same way as in the case of Example 7 except that use was made of the coating solution D1, there was obtained a critical current density Jc=1.2 MA/cm2 by the inductive method.
With a ErBa2Cu3O7 film about 100 nm in film thickness produced in the same way as in the case of Example 6 except that use was made of the coating solution E1, there was obtained a critical current density Jc=1.0 MA/cm2 by the inductive method.
A surface of the substrate KC1 was spin-coated at 4000 rpm with the coating solution Y1 for 10 seconds, was dried at 130° C. in a constant-temperature oven for removal of a solvent and subsequently irradiated at room temperature with the laser light H1, the irradiation being executed such that the fluence is varied in five stages from a low value of 1 mJ/cm2 to a high value of 15 mJ/cm2, and the number of pulses at respective fluences will total 30,000, as shown in Table 1. The irradiation conditions in other respects were as follows: room temperature; in the ambient atmosphere; frequency at 100 Hz; an overlapping ratio at 99%
Subsequently, a specimen of the substrate KC1, subjected to the irradiation with the laser light, was inserted into a muffle oven kept at 500° C. beforehand, and was kept at that temperature for 30 minutes before being taken out. Thereafter, main baking was applied thereto in a quartz furnace tubular in shape under the following condition. First, the specimen in a flow of a mixed gas of argon and oxygen with a partial pressure of oxygen adjusted at 100 ppm was heated up to 770° C. at a heating rate of about 16° C./min, and that temperature was maintained for 45 minutes before the gas was changed over to pure oxygen to be then held for a further 30 minutes, after which the specimen was slowly cooled.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 12 except that irradiation was executed at respective pulses 10000, 20000, 30000, and 40000 by scanning a specimen in one direction with the laser light at fluence of 16.4 mJ/cm2, there was obtained Jc as shown in Table 2.
In the case of the number of pulses being at 30000, in particular, excellent characteristics of Jc=6.4 MA/cm2 by the inductive method were exhibited. This represented a value considerably in excess of 2.0 to 3.0 MA/cm2, regarded as the level in practical use. This is presumably attributable to the fact that following progress in scanning with the laser beam (as indicated by dotted lines in
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 13 except that irradiation with the laser beam was not executed, Jc by the inductive method was found at the measurement limit (0.1 MA/cm2) or lower.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 12 except that use was made of the substrate K1, and the laser Hght (fluence of 16.4 mJ/cm2) with the number of pulses, at 30000, there was obtained Jc=1 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the substrate K2, there was obtained Jc=1.5 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the substrate K3, there was obtained Jc=1.5 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the substrate K4, there was obtained an a-axis oriented film with in-plane orientation.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the substrate K5, there was obtained an a-axis oriented film with in-plane orientation.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the substrate K7, there was obtained Jc=2 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the substrate K8, there was obtained Jc=0.5 MA/cm2 by the inductive method.
With a Y0.95Ca0.05Ba2Cu3O7 film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the coating solution YC1, there was obtained Jc=1 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the coating solution Y2, and the main baking was executed at 740° C., there was obtained Tc=80 K by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 22 except that use was made of the coating solution Y3, there was obtained Tc=80 K by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 22 except that use was made of the coating solution Y4, there was obtained Jc=0.5 MA/cm2 by the inductive method.
With a YBCO film about 100 nm in film thickness produced in the same way as in the case of Example 22 except that use was made of the coating solution Y5, there was obtained Jc=0.5 MA/cm2 by the inductive method.
With a DyBa2Cu3O7 film about 100 nm in film thickness produced in the same way as in the case of Example 22 except that use was made of the coating solution D1, there was obtained Jc=1 MA/cm2 by the inductive method.
With a ErBa2Cu3O7 film about 100 nm in film thickness produced in the same way as in the case of Example 14 except that use was made of the coating solution E1, there was obtained Jc=0.8 MA/cm2 by the inductive method.
Since the method of producing a superconductive material according to the invention is superior in production efficiency, suitable for mass production and is capable of providing a superconductive material having an excellent superconductivity and large area, the method has technical significance important for commercialization of the superconductive material, so that it has a high industrial applicability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-217678 | Aug 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/064922 | 7/31/2007 | WO | 00 | 4/15/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2008/018314 | 2/14/2008 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4997809 | Gupta | Mar 1991 | A |
| 5310990 | Russell et al. | May 1994 | A |
| 6576302 | Yamaguchi et al. | Jun 2003 | B1 |
| 6887770 | Ueda et al. | May 2005 | B2 |
| Number | Date | Country |
|---|---|---|
| 2527572 | Dec 2002 | CN |
| 64-035806 | Feb 1989 | JP |
| 64-35806 | Feb 1989 | JP |
| 01-115823 | May 1989 | JP |
| 01-294506 | Nov 1989 | JP |
| 05-147941 | Jun 1993 | JP |
| 05-262597 | Oct 1993 | JP |
| 07-106905 | Nov 1995 | JP |
| 2759125 | Mar 1998 | JP |
| 2000-256862 | Sep 2000 | JP |
| 2001-031417 | Feb 2001 | JP |
| 2007-070216 | Mar 2007 | JP |
| Entry |
|---|
| “Excimer Laser Assist MOD-ho ni yoru YBCO no Kosoku-Teion Seimaku”, by Mitsugu SOMA, Extended abstracts; the Japan Society of Applied Physics, 67th, Aug. 2006, p. 252. |
| Number | Date | Country | |
|---|---|---|---|
| 20090156411 A1 | Jun 2009 | US |
