Patent Application
20090149330
The present invention relates to a method of manufacturing a superconducting thin film material, a superconducting device and a superconducting thin film material. More specifically, the invention relates to a method of manufacturing a superconducting thin film material having an RE123 composition, a superconducting device and a superconducting thin film material.
Two types of superconducting wires: a superconducting wire using a bismuth-based superconductor and a superconducting wire using an RE123-based superconductor are now being particularly developed. Of these wires, the RE123-based superconducting wire has the advantage that the critical current density at the liquid nitrogen temperature (77.3 K) is higher than that of the bismuth-based superconducting wire. Additionally, it has the advantage of a high critical current value under a low temperature condition and under a constant magnetic field condition. Therefore, the RE123-based superconducting wire is expected as a next generation high-temperature superconducting wire.
Unlike the bismuth-based superconductor, the RE123-based superconductor cannot be covered with a silver sheath. Therefore, the RE123-based superconductor is manufactured by depositing a film of a superconductor (superconducting thin film material) on a textured metal substrate by a vapor phase method for example.
Japanese Patent Laying-Open No. 2003-323822 (Patent Document 1) for example discloses a method of manufacturing a conventional RE123-based superconducting thin film material. Patent Document 1 discloses the technique of forming an intermediate layer on a metal tape substrate using the pulsed laser deposition (PLD) method, forming a first superconducting layer having an RE123 composition on the intermediate layer using the pulsed laser deposition method, and forming a second superconducting layer having an RE123 composition on the first superconducting layer using the pulsed laser deposition method. The method of manufacturing the superconducting thin film material of Patent Document 1 can increase the film thickness of the superconducting thin film material by depositing multiple superconducting layers. Therefore, the cross-sectional area where current flows is increased and the critical current value of the superconducting wire can be increased.
The superconducting wire obtained using the conventional manufacturing method, however, has the following property. As the thickness of the superconducting thin film material increases, the critical current density decreases and the critical current value becomes gradually slow to increase. The resultant problem is therefore that the critical current value cannot be improved.
An object of the present invention is therefore to provide a method of manufacturing a superconducting thin film material, a superconducting device and a superconducting thin film material for which the critical current value can be improved.
According to an aspect of the present invention, a method of manufacturing a superconducting thin film material includes an underlying layer step of forming an underlying layer and a superconducting layer step of forming a superconducting layer by a vapor phase method such that the superconducting layer is in contact with the underlying layer. Between the underlying layer step and the superconducting layer step, the underlying layer is kept in a reduced water vapor ambient or reduced carbon dioxide ambient.
According to another aspect of the present invention, a method of manufacturing a superconducting thin film material includes an underlying layer step of forming an underlying layer and a superconducting layer step of forming a superconducting layer by a vapor phase method such that the superconducting layer is in contact with the underlying layer. Between the underlying layer step and the superconducting layer step, the underlying layer is kept without exposed to atmosphere.
The inventors of the present application found that the moisture in the atmosphere and any impurity such as carbon dioxide in the atmosphere attach to the underlying layer of the superconducting layer to deteriorate the quality of the superconducting layer, which is a cause of hindrance to increase of the critical current value. The method of manufacturing the superconducting thin film material in Patent Document 1 removes the metal tape substrate from the vacuum chamber for replacing the windings of the wire for example and leaves the metal tape substrate in the atmosphere between the formation of the intermediate layer and the formation of the first superconducting layer and between the formation of the first superconducting layer and the formation of the second superconducting layer. Therefore, the moisture and any impurities such as carbon dioxide in the atmosphere attach to the underlying layer (such as intermediate layer and underlying superconducting layer) of the superconducting layer. The impurities react with the superconducting layer to deteriorate the superconducting property of the superconducting thin film material, resulting in decrease of the critical current value.
Accordingly, the method of manufacturing the superconducting thin film material of the present invention keeps the underlying layer in the reduced water vapor ambient or reduced carbon dioxide ambient, or keeps the underlying layer without exposing it to the atmosphere between the underlying layer step and the superconducting layer step. Therefore, the moisture or carbon dioxide in the atmosphere can be prevented from attaching to the underlying layer of the superconducting layer. As a result, deterioration of the superconducting property of the superconducting thin film material can be prevented and the critical current value can be improved while increasing the thickness of the superconducting thin film material.
Here, “reduced water vapor ambient” refers to an ambient containing moisture equal to or lower than a moisture content of the atmosphere dried at a room temperature (20 to 25° C.). Namely, the reduced water vapor ambient refers to a water vapor ambient having a moisture content lower than that of the atmosphere having a humidity of 10% at the room temperature, and specifically corresponds to, for example, an ambient having a pressure lower than the atmospheric pressure or an ambient filled with an inert gas such as nitrogen or argon. Further, “reduced carbon dioxide ambient” refers to an ambient having a carbon dioxide content lower than that of the air. The reduced water vapor ambient and the reduced carbon dioxide ambient include, in addition to the ambient having a pressure lower than the atmospheric pressure (reduced pressure ambient), an ambient filled with a noble gas such as nitrogen.
Preferably, according to the method of manufacturing the superconducting thin film material of the present invention, an underlying superconducting layer is formed as the underlying layer in the underlying layer step.
Accordingly, any impurity is less prone to attach to the surface of the underlying superconducting layer. Therefore, in the case where multiple superconducting layers are deposited to form a superconducting layer of a large thickness, deterioration of the superconducting property of the superconducting layer formed on the underlying superconducting layer can be prevented.
Preferably, according to the method of manufacturing the superconducting thin film material of the present invention, an intermediate layer is formed as the underlying layer in the underlying layer step.
Accordingly, any impurity is less prone to attach to the surface of the intermediate layer. Therefore, deterioration of the superconducting property of the superconducting layer formed on the intermediate layer can be prevented.
Preferably, according to the method of manufacturing the superconducting thin film material of the present invention, an underlying layer is formed on a substrate in the underlying layer step. The substrate is made of a metal, the underlying layer is made of an oxide having a crystal structure of any of rock type, perovskite type and pyrochlore type, and the superconducting layer has an RE123 composition.
In this way, the superconducting thin film material excellent in crystal orientation and surface smoothness can be obtained and the critical current density and the critical current value can be improved.
Preferably, according to the method of manufacturing the superconducting thin film material of the present invention, in the underlying layer step, the underlying layer is formed on a tape-shaped substrate, and the underlying layer is formed while a position where the underlying layer is formed at the substrate is shifted in one direction along longitudinal direction of the substrate. In the superconducting layer step, the superconducting layer is formed while a position where the superconducting layer is formed at the underlying layer is shifted in a direction opposite to the aforementioned one direction.
Accordingly, the underlying layer and the superconducting layer can be successively formed without replacing the windings of the wire for example. Therefore, between the underlying layer step and the superconducting layer step, the underlying layer can be easily kept in the reduced pressure ambient.
Regarding the method of manufacturing the superconducting thin film material of the present invention, preferably the vapor phase method is any of laser deposition method, sputtering method and electron beam evaporation method.
In this way, the superconducting thin film material excellent in crystal orientation and surface smoothness can be obtained and the critical current density and the critical current value can be improved.
A superconducting device according to the present invention uses a superconducting thin film material manufactured by the method of manufacturing a superconducting thin film material as described above.
With the superconducting device of the present invention, the critical current density and the critical current value can be improved.
A superconducting device of the present invention is preferably a superconducting device using a superconducting thin film material including a first superconducting layer, a second superconducting layer formed to be in contact with the first superconducting layer and a third superconducting layer formed to be in contact with the second superconducting layer, and having a critical current value larger than 70 (A/cm-width).
It should be noted that “RE123” herein refers to RExBayCuzO7-d where 0.7≦x≦1.3, 1.7≦y≦2.3, 2.7≦z≦3.3. RE of “RE123” refers to a material including at least any of a rare earth element and an yttrium element. The rare earth element includes for example neodymium (Nd), gadolinium (Gd), holmium (Ho) and samarium (Sm).
With a method of manufacturing a superconducting thin film material, a superconducting device and a superconducting thin film material of the present invention, the critical current value can be improved.
1 metal substrate, 2 intermediate layer, 3-5 superconducting layer, 10 superconducting thin film material, 11, 12 rotational shaft, 13 vapor deposition source, 14 platform, 20 chamber
In the following, an embodiment of the present invention will be described based on the drawings.
Metal substrate 1 is made of a metal such as stainless, nickel alloy (Hastelloy for example) or silver alloy for example.
Intermediate layer 2 is formed on metal substrate 1 and functions as a diffusion preventing layer. Intermediate layer 2 is made of an oxide having a crystal structure which is any of rock type, perovskite type and pyrochlore type for example. Specifically, intermediate layer 2 is made of a material such as ceric oxide, yttria stabilized zirconia (YSZ), magnesium oxide, yttrium oxide, ytterbium oxide or barium zirconia, for example.
Superconducting layer 3 and superconducting layer 4 are layered on intermediate layer 2. Superconducting layer 3 and superconducting layer 4 are made of substantially the same material and have an RE123 composition for example.
Although the structure including intermediate layer 2 is described in connection with
A method of manufacturing a superconducting thin film material in the present embodiment will now be described.
Referring to
Referring to
In this way, while metal substrate 1 is wound up on rotational shafts 11 and 12 by turns, intermediate layer 2, superconducting layer 3 and superconducting layer 4 are each formed on each other. Thus, without the need to remove metal substrate 1 from chamber 20, these layers can be formed in the reduced pressure ambient. Through the above-described process steps, superconducting thin film material 10 is completed.
In the case where intermediate layer 2 is not formed, the above-described step of forming intermediate layer 2 (step S2) is not performed and, in the step of forming superconducting layer 3 (step S3), superconducting layer 3 is formed such that superconducting layer 3 is in contact with metal substrate 1.
Referring to
The method of manufacturing the superconducting thin film material in the present embodiment keeps intermediate layer 2 in the reduced pressure ambient between the formation of intermediate layer 2 and the formation of superconducting layer 3. Therefore, any impurity in the atmosphere can be prevented from attaching to intermediate layer 2. Similarly, between the formation of superconducting layer 3 and the formation of superconducting layer 4, superconducting layer 3 is kept in the reduced pressure ambient. Therefore, any impurity in the atmosphere can be prevented from attaching to superconducting layer 3. As a result, deterioration of the superconducting property of superconducting layers 3 and 4 each can be prevented, and the critical current value can be improved while the film thickness of the superconducting thin film material is increased.
Since intermediate layer 2 made of an oxide having a crystal structure that is any of rock type, perovskite type and pyrochlore type is formed on metal substrate 1 and superconducting layer 3 and superconducting layer 4 both have an RE 123 composition, the superconducting thin film material excellent in surface smoothness and compactness of the crystal can be obtained and the critical current density and the critical current value can be improved.
Further, since the vapor phase method is any of the laser deposition method, sputtering method and electron beam evaporation method, the superconducting thin film material excellent in surface smoothness and compactness of the crystal can be obtained and the critical current density and the critical current value can be improved.
While the present embodiment shows the case where the two layers that are superconducting layer 3 (first superconducting layer) and superconducting layer 4 (second superconducting layer) are formed, a superconducting layer 5 (third superconducting layer) may further be formed on superconducting layer 4 as shown in
Further, the present embodiment shows the case where intermediate layer 2, superconducting layer 3 and superconducting layer 4 are formed in the reduced pressure ambient by the successive deposition. Alternatively, the present invention may form intermediate layer 2, superconducting layer 3 and superconducting layer 4 each by the fixed deposition fixing metal substrate 1 to a platform 14 and fixing vapor deposition source 13 to chamber 20 as shown in
In the present example, respective superconducting thin film materials of Present Invention's Examples A to D and Comparative Examples E to H were manufactured and the critical current value thereof was measured.
As to Present Invention's Examples A to D, on an Ni alloy substrate, an intermediate layer made of a metal-based oxide was deposited using a vapor phase deposition method. Subsequently, the laser deposition method was used to deposit multiple superconducting layers made of HoBa2Cu3Ox (HoBCO) on the intermediate layer. Each superconducting layer had a thickness of 0.3 μm, and the number of deposited superconducting layers was changed so that three superconducting layers, five superconducting layers, seven superconducting layers and nine superconducting layers were formed, thereby changing the total thickness of the superconducting layers. The superconducting layers were formed by the successive deposition and, between one formation step and the subsequent formation step for the intermediate layer and the superconducting layers, the sample was kept in the reduced pressure ambient without exposed to the atmosphere.
As to Comparative Examples E to H, on an Ni alloy substrate, an intermediate layer made of a metal-based oxide was deposited using a vapor phase deposition method. Subsequently, the laser deposition method was used to deposit multiple superconducting layers made of HoBa2Cu3Ox (HoBCO) on the intermediate layer. Each superconducting layer had a thickness of 0.3 μm, and the number of deposited superconducting layers was changed so that three superconducting layers, five superconducting layers, seven superconducting layers and nine superconducting layers were formed, thereby changing the total thickness of the superconducting layers. The superconducting layers were formed by the successive deposition and, between one formation step and the subsequent formation step for the intermediate layer and the superconducting layers, the sample was exposed to the atmosphere.
The critical current value per cm width measured for each of Present Invention's Examples A to D and Comparative Examples E to H is shown in Table 1 and
Referring to Table 1 and
It should be construed that embodiments disclosed above are by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present invention is defined by claims, not by the embodiments and examples above, and includes all modifications and variations equivalent in meaning and scope to the claims.
The present invention is appropriate for a superconducting device including, for example, superconducting fault current limiter, magnetic field generating device, superconducting cable, superconducting busbar and superconducting coil and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-039396 | Feb 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/050593 | 1/17/2007 | WO | 00 | 8/5/2008 |
