WO2003034448A1 - Superconducting composite structures - Google Patents
Superconducting composite structures Download PDFInfo
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- WO2003034448A1 WO2003034448A1 PCT/US2001/046876 US0146876W WO03034448A1 WO 2003034448 A1 WO2003034448 A1 WO 2003034448A1 US 0146876 W US0146876 W US 0146876W WO 03034448 A1 WO03034448 A1 WO 03034448A1
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- Prior art keywords
- oxide
- layer
- buffer layer
- angstroms
- superconductive structure
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- 239000002131 composite material Substances 0.000 title description 10
- 239000000463 material Substances 0.000 claims abstract description 28
- 239000000758 substrate Substances 0.000 claims abstract description 26
- 229910001233 yttria-stabilized zirconia Inorganic materials 0.000 claims description 17
- 229910021521 yttrium barium copper oxide Inorganic materials 0.000 claims description 16
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 12
- 239000000395 magnesium oxide Substances 0.000 claims description 12
- 229910000420 cerium oxide Inorganic materials 0.000 claims description 11
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims description 11
- 239000013078 crystal Substances 0.000 claims description 10
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 10
- 229910052751 metal Inorganic materials 0.000 claims description 8
- 239000002184 metal Substances 0.000 claims description 8
- VQCBHWLJZDBHOS-UHFFFAOYSA-N erbium(iii) oxide Chemical compound O=[Er]O[Er]=O VQCBHWLJZDBHOS-UHFFFAOYSA-N 0.000 claims description 6
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims description 6
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 5
- VEALVRVVWBQVSL-UHFFFAOYSA-N strontium titanate Chemical group [Sr+2].[O-][Ti]([O-])=O VEALVRVVWBQVSL-UHFFFAOYSA-N 0.000 claims description 5
- -1 rare earth copper oxides Chemical class 0.000 claims description 4
- 229910002113 barium titanate Inorganic materials 0.000 claims description 3
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 claims description 3
- 229910001940 europium oxide Inorganic materials 0.000 claims description 3
- AEBZCFFCDTZXHP-UHFFFAOYSA-N europium(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Eu+3].[Eu+3] AEBZCFFCDTZXHP-UHFFFAOYSA-N 0.000 claims description 3
- 229910001938 gadolinium oxide Inorganic materials 0.000 claims description 3
- 229940075613 gadolinium oxide Drugs 0.000 claims description 3
- CMIHHWBVHJVIGI-UHFFFAOYSA-N gadolinium(iii) oxide Chemical compound [O-2].[O-2].[O-2].[Gd+3].[Gd+3] CMIHHWBVHJVIGI-UHFFFAOYSA-N 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- UZLYXNNZYFBAQO-UHFFFAOYSA-N oxygen(2-);ytterbium(3+) Chemical compound [O-2].[O-2].[O-2].[Yb+3].[Yb+3] UZLYXNNZYFBAQO-UHFFFAOYSA-N 0.000 claims description 3
- 229910003454 ytterbium oxide Inorganic materials 0.000 claims description 3
- 229940075624 ytterbium oxide Drugs 0.000 claims description 3
- KJXBRHIPHIVJCS-UHFFFAOYSA-N oxo(oxoalumanyloxy)lanthanum Chemical compound O=[Al]O[La]=O KJXBRHIPHIVJCS-UHFFFAOYSA-N 0.000 claims description 2
- 229910052594 sapphire Inorganic materials 0.000 claims description 2
- 239000010980 sapphire Substances 0.000 claims description 2
- 238000000151 deposition Methods 0.000 description 9
- 230000008021 deposition Effects 0.000 description 9
- 238000000034 method Methods 0.000 description 8
- 239000004020 conductor Substances 0.000 description 6
- 238000004549 pulsed laser deposition Methods 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 239000002887 superconductor Substances 0.000 description 5
- 239000010949 copper Substances 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 239000008188 pellet Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- RKMSYLGAZSHVGJ-UHFFFAOYSA-N barium(2+) cerium(3+) oxygen(2-) Chemical compound [O-2].[Ba+2].[Ce+3] RKMSYLGAZSHVGJ-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 238000010884 ion-beam technique Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- 206010067484 Adverse reaction Diseases 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- CPKNPEXMGALOSZ-UHFFFAOYSA-N [Cu]=O.[Y] Chemical compound [Cu]=O.[Y] CPKNPEXMGALOSZ-UHFFFAOYSA-N 0.000 description 1
- YIJOXVSKEMKZHR-UHFFFAOYSA-N [O--].[O--].[O--].[Gd+3].[Yb+3] Chemical compound [O--].[O--].[O--].[Gd+3].[Yb+3] YIJOXVSKEMKZHR-UHFFFAOYSA-N 0.000 description 1
- BYEDQPGWBSIRBS-UHFFFAOYSA-N [O--].[O--].[O--].[Y+3].[Sm+3] Chemical compound [O--].[O--].[O--].[Y+3].[Sm+3] BYEDQPGWBSIRBS-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000006838 adverse reaction Effects 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910021523 barium zirconate Inorganic materials 0.000 description 1
- DQBAOWPVHRWLJC-UHFFFAOYSA-N barium(2+);dioxido(oxo)zirconium Chemical compound [Ba+2].[O-][Zr]([O-])=O DQBAOWPVHRWLJC-UHFFFAOYSA-N 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 238000000541 cathodic arc deposition Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- IQOFRWVYCUFBHP-UHFFFAOYSA-N europium oxocopper Chemical compound [Cu]=O.[Eu] IQOFRWVYCUFBHP-UHFFFAOYSA-N 0.000 description 1
- 229910000856 hastalloy Inorganic materials 0.000 description 1
- 229910001026 inconel Inorganic materials 0.000 description 1
- 229910001119 inconels 625 Inorganic materials 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000000869 ion-assisted deposition Methods 0.000 description 1
- 238000001659 ion-beam spectroscopy Methods 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 238000004943 liquid phase epitaxy Methods 0.000 description 1
- 238000001755 magnetron sputter deposition Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000001451 molecular beam epitaxy Methods 0.000 description 1
- AVHJXXPOKDPHIL-UHFFFAOYSA-N neodymium oxocopper Chemical compound [Cu]=O.[Nd] AVHJXXPOKDPHIL-UHFFFAOYSA-N 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 125000002524 organometallic group Chemical group 0.000 description 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000000623 plasma-assisted chemical vapour deposition Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- 239000013077 target material Substances 0.000 description 1
- 229910052716 thallium Inorganic materials 0.000 description 1
- BKVIYDNLLOSFOA-UHFFFAOYSA-N thallium Chemical compound [Tl] BKVIYDNLLOSFOA-UHFFFAOYSA-N 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/01—Manufacture or treatment
- H10N60/0268—Manufacture or treatment of devices comprising copper oxide
- H10N60/0296—Processes for depositing or forming copper oxide superconductor layers
- H10N60/0576—Processes for depositing or forming copper oxide superconductor layers characterised by the substrate
- H10N60/0632—Intermediate layers, e.g. for growth control
Definitions
- the present invention relates to improvements in high temperature superconducting composite structures and in particular to the use of ultra-thin buffer layers in high temperature superconducting composite structures. This invention is the result of a contract with the United States Department of Energy (Contract No. W-7405-ENG-36).
- the present invention provides an improvement to a superconductive structure including a layer of a high temperature superconducting oxide and a buffer layer adjacent to the layer of a high temperature superconducting oxide, where the improvement is the buffer layer having a thickness of from about 25 Angstroms to about 180 Angstroms.
- the present invention provides a superconductive structure including a substrate, a layer of material selected from the group consisting of MgO and YSZ upon the substrate, at least one buffer layer upon the layer of MgO or YSZ, wherein the topmost buffer layer furthest from the layer of MgO or YSZ is characterized as being from about 25 Angstroms to about 180 Angstroms in thickness, and, a layer of a high temperature superconducting material upon the topmost buffer layer.
- the present invention is concerned with buffer layers adjacent to a high temperature superconducting material in high temperature superconducting wire or tape formed in a thick film process upon a flexible substrate.
- the present invention is further concerned with buffer layers adjacent to a high temperature superconducting material formed upon a single crystal substrate.
- the high temperature superconducting (HTS) material is generally YBCO, e.g., YBa 2 Cu 3 O 7 _ ⁇ , Y 2 Ba 4 Cu 7 O ⁇ 4+x , or YBa 2 Cu 4 O 8 , although other minor variations of this basic superconducting material, such as use of other rare earth metals as a substitute for some or all of the yttrium as is well known, may also be used. Other superconducting materials such as bismuth and thallium based superconductor materials may also be employed. YBa 2 Cu O . ⁇ is preferred as the superconducting material.
- the initial or base substrate can be, e.g., any polycrystalline material such as a metal or a ceramic such as polycrystalline aluminum oxide or polycrystalline yttria-stabilized zirconia (YSZ). Alloys including nickel such as various Hastelloy metals, Haynes metals and Inconel metals are also useful as the substrate.
- the metal substrate on which the superconducting material is eventually deposited should preferably allow for the resultant article to be flexible whereby superconducting articles (e.g., coils, motors or magnets) can be shaped.
- the initial or base substrate can be a single crystal substrate.
- One class of suitable single crystal substrates may generally include perovskite single crystals, e.g., an oxide having the formula ABO wherein A represents an element selected from alkaline earth metals and lanthanoid elements and B represents a metal selected from those belonging to IVB and HIA of the Periodic Table.
- suitable elements A are Sr, La and Nd
- suitable elements B are Ti, Ga and Al.
- particularly suitable single crystal substrates are included lanthanum aluminum oxide, magnesium oxide, strontium titanate, sapphire, and yttria-stabilized zirconium oxide (YSZ).
- One embodiment of the present invention involves the preparation of a coated conductor as is generally described in U.S. Patent No. 5,872,080 by Arendt et al.
- a coated conductor including a flexible polycrystalline metal and an ion beam assist deposited (IBAD) nucleation layer of, e.g., yttria-stabilized zirconia (YSZ), magnesium oxide (MgO) or the like
- IBAD ion beam assist deposited
- YSZ yttria-stabilized zirconia
- MgO magnesium oxide
- one or more intermediate buffer layers are deposited onto the fBAD-deposited layer so that they are between the IBAD-deposited layer and the subsequently deposited superconducting YBCO layer.
- the one or more intermediate layers serve as buffer layers between the IBAD-deposited layer and the YBCO and assist in lattice matching.
- a so-called “buffer layer” should have good "structural compatibility" between the IBAD-deposited material, typically an oriented cubic oxide material, and the YBCO and should have good chemical compatibility with both adjacent layers.
- chemical compatibility is meant that the intermediate layer does not undergo property-degrading chemical interactions with the adjacent layers.
- structural compatibility is meant that the intermediate layer has a substantially similar lattice structure with the superconductive material.
- yttria-stabilized zirconia strontium titanate, barium titanate, magnesium oxide, rare earth oxides such as, e.g., cerium oxide, yttrium oxide, gadolinium oxide, ytterbium oxide, erbium oxide, europium oxide and mixtures of rare earth oxides containing two or more rare earth metals such as, e.g., yttrium samarium oxide ((Y ⁇ . x Sm x ) 2 O ), gadolinium ytterbium oxide ((Gd ⁇ . x Yb x ) 2 O ) and the like, and other cubic oxide materials such as those described in U.S. Patent No.
- the buffer layer may also be of europium copper oxide (Eu 2 CuO 4 ), neodymium copper oxide (Nd 2 CuO 4 ), yttrium copper oxide (Y 2 CuO 4 ), and other rare earth copper oxides (RE 2 CuO 4 ).
- the thickness of the buffer layer adjacent to the superconducting layer should be from about 25 Angstroms to about 180 Angstroms in thickness, preferably from about 50 Angstroms to about 125 Angstroms in thickness for best results. Though careful examination, it has now been confirmed that in the absense of any buffer layer between the superconducting layer and the IBAD-deposited layer that reaction between the layers results in a continuous interfacial layer of barium zirconate along the interface between the layers.
- the topmost buffer layer e.g., cerium oxide
- the superconducting YBCO layer has a thickness of from about 250 Angstroms up to about 11,000 Angstroms (1.1 microns)
- reaction between the layers results in detrimental effects including generation of porosity within the YBCO layer, formation of some barium cerium oxide phases near the interface, tilting of the buffer layer crystal structure, and lower critical cu ⁇ ent densities.
- a thinner topmost buffer layer of generally less than about 250 Angstroms, preferably from about 50 Angstroms to about 180 Angstroms, more preferably from about 75 Angstroms to about 125 Angstroms, reaction between the layers is minimal and the critical cu ⁇ ent densities are increased.
- Such a buffer layer can be considered as an ultra-thin buffer layer.
- the intermediate or buffer layers are generally deposited at temperatures of greater than about 750°C, preferably at temperatures of from about 750°C to about 950°C.
- the HTS layer e.g., the YBCO layer
- the HTS layer can be deposited, e.g., by pulsed laser deposition or by methods such as evaporation including coevaporation, e-beam evaporation and activated reactive evaporation, sputtering including magnetron sputtering, ion beam sputtering and ion assisted sputtering, cathodic arc deposition, chemical vapor deposition, organometallic chemical vapor deposition, plasma enhanced chemical vapor deposition, molecular beam epitaxy, a sol-gel process, liquid phase epitaxy and the like.
- powder of the material to be deposited can be initially pressed into a disk or pellet under high pressure, generally above about 1000 pounds per square inch (PSI) and the pressed disk then sintered in an oxygen atmosphere or an oxygen-containing atmosphere at temperatures of about 900°C to about 950°C for at least about 1 hour, preferably from about 12 to about 24 hours.
- PSI pounds per square inch
- An apparatus suitable for pulsed laser deposition is shown in Appl. Phys. Lett. 56, 578 (1990), "Effects of Beam Parameters on Excimer Laser Deposition of YBa 2 Cu 3 O - ⁇ ", such description hereby incorporated by reference.
- Suitable conditions for pulsed laser deposition include, e.g., the laser, such as an excimer laser (20 nanoseconds (ns), 248 or 308 nanometers (nm)), targeted upon a rotating pellet of the target material at an incident angle of about 45°.
- the substrate can be mounted upon a heated holder rotated at about 0.5 rpm to minimize thickness variations in the resultant film or coating,
- the substrate can be heated during deposition at temperatures from about 600°C to about 950°C, preferably from about 700°C to about 850°C.
- An oxygen atmosphere of from about 0.1 millito ⁇ (mTorr) to about 10 Ton, preferably from about 100 to about 250 mTorc, can be maintained within the deposition chamber during the deposition.
- Distance between the substrate and the pellet can be from about 4 centimeters (cm) to about 10 cm.
- the deposition rate of the film can be varied from about 0.1 Angstroms per second
- the laser beam can have dimensions of about 3 millimeters (mm) by 4 mm with an average energy density of from about 1 to 4 joules per square centimeter (J/cm 2 ).
- the films After deposition, the films generally are cooled within an oxygen atmosphere of greater than about 100 Ton to room temperature.
- EXAMPLE 1 Highly textured YSZ films were prepared on polished Inconel 625 substrates by the method of U.S. Patent No. 5,872,080.
- YSZ layer thin cerium oxide buffer layers were deposited by pulsed laser deposition.
- the substrate temperature during deposition was held at 775°C and the oxygen pressure was held at 0.2 ton, i.e., optimum deposition conditions for YBCO.
- Each deposition included two samples: one for measurement of critical cunent density and one for examination by TEM.
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Superconductors And Manufacturing Methods Therefor (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
Abstract
A superconducting article is disclosed including a substrate, a layer of material selected from the group consisting of MgO and YSZ upon the substrate, at least one buffer layer upon the layer of MgO or YSZ, and, a layer of a high temperature superconducting material upon a topmost buffer layer wherein the topmost buffer layer adjacent to the high temperature superconducting material is characterized as being from about 25 Angstroms to about 180 Angstroms in thickness.
Description
SUPERCONDUCTING COMPOSITE STRUCTURES
FIELD OF THE INVENTION The present invention relates to improvements in high temperature superconducting composite structures and in particular to the use of ultra-thin buffer layers in high temperature superconducting composite structures. This invention is the result of a contract with the United States Department of Energy (Contract No. W-7405-ENG-36).
BACKGROUND OF THE INVENTION One process in the production of coated conductors (superconductive tapes or films) has been referred to as a thick film process where the thickness of the superconductive layer is generally at least one micron in thickness. In the thick film process, YBCO films on single crystal substrates and on polycrystalline or amorphous substrates with selected intermediate buffer layers have achieved critical current density (Jc) values of over 106 amperes per square centimeter (A/cm ) at 77 K. Despite the successes in achieving these critical current values, continued improvements in the critical current densities and reproducibility of high Jc values of coated conductors are sought.
It has been found generally by investigators that high temperature superconductor materials react with most other materials during normal methods of manufacture leading to adverse results. Hence, the construction and processing of a practical high temperature superconducting composite conductor must account for such adverse reactions. A common method for accommodating the high temperature superconductor has been to place a buffer material between the high temperature superconductor and the base material used to form the composite. Such buffer layers have typically been on the order of around one micron or less. For example, in U.S. Patent No. 5,873,080, a buffer layer of yttrium oxide with a thickness of 30 nm (300 Angstroms) separated an ion-beam assist deposited YSZ layer from a high temperature superconductor layer of YBCO.
After extensive and careful investigation, further improvements have been found in the composite structure of superconducting coated conductors. In particular, it has been found that controlling the thickness of intermediate buffer layers in the composite structure and more particularly in the thickness of the buffer layer adjacent to the
superconducting layer, the critical current density can be enhanced and the reproducibility improved.
It is an object of the present invention to provide superconducting composite structures, especially YBCO superconducting composite structures, wherein the buffer layer adjacent to the superconducting layer is from about 25 Angstroms to about 180 Angstroms in thickness.
SUMMARY OF THE INVENTION To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides an improvement to a superconductive structure including a layer of a high temperature superconducting oxide and a buffer layer adjacent to the layer of a high temperature superconducting oxide, where the improvement is the buffer layer having a thickness of from about 25 Angstroms to about 180 Angstroms.
In one embodiment the present invention provides a superconductive structure including a substrate, a layer of material selected from the group consisting of MgO and YSZ upon the substrate, at least one buffer layer upon the layer of MgO or YSZ, wherein the topmost buffer layer furthest from the layer of MgO or YSZ is characterized as being from about 25 Angstroms to about 180 Angstroms in thickness, and, a layer of a high temperature superconducting material upon the topmost buffer layer. DETAILED DESCRIPTION
The present invention is concerned with buffer layers adjacent to a high temperature superconducting material in high temperature superconducting wire or tape formed in a thick film process upon a flexible substrate. The present invention is further concerned with buffer layers adjacent to a high temperature superconducting material formed upon a single crystal substrate.
In the present invention, the high temperature superconducting (HTS) material is generally YBCO, e.g., YBa2Cu3O7_δ, Y2Ba4Cu7Oι4+x, or YBa2Cu4O8, although other minor variations of this basic superconducting material, such as use of other rare earth metals as a substitute for some or all of the yttrium as is well known, may also be used. Other superconducting materials such as bismuth and thallium based superconductor
materials may also be employed. YBa2Cu O .δ is preferred as the superconducting material.
In one embodiment of the present invention, the initial or base substrate can be, e.g., any polycrystalline material such as a metal or a ceramic such as polycrystalline aluminum oxide or polycrystalline yttria-stabilized zirconia (YSZ). Alloys including nickel such as various Hastelloy metals, Haynes metals and Inconel metals are also useful as the substrate. The metal substrate on which the superconducting material is eventually deposited should preferably allow for the resultant article to be flexible whereby superconducting articles (e.g., coils, motors or magnets) can be shaped. In another embodiment of the present invention, the initial or base substrate can be a single crystal substrate. One class of suitable single crystal substrates may generally include perovskite single crystals, e.g., an oxide having the formula ABO wherein A represents an element selected from alkaline earth metals and lanthanoid elements and B represents a metal selected from those belonging to IVB and HIA of the Periodic Table. Illustrative of suitable elements A are Sr, La and Nd, while illustrative of suitable elements B are Ti, Ga and Al. Among particularly suitable single crystal substrates are included lanthanum aluminum oxide, magnesium oxide, strontium titanate, sapphire, and yttria-stabilized zirconium oxide (YSZ).
One embodiment of the present invention involves the preparation of a coated conductor as is generally described in U.S. Patent No. 5,872,080 by Arendt et al. In the preparation of such a coated conductor including a flexible polycrystalline metal and an ion beam assist deposited (IBAD) nucleation layer of, e.g., yttria-stabilized zirconia (YSZ), magnesium oxide (MgO) or the like, one or more intermediate buffer layers are deposited onto the fBAD-deposited layer so that they are between the IBAD-deposited layer and the subsequently deposited superconducting YBCO layer. The one or more intermediate layers serve as buffer layers between the IBAD-deposited layer and the YBCO and assist in lattice matching. A so-called "buffer layer" should have good "structural compatibility" between the IBAD-deposited material, typically an oriented cubic oxide material, and the YBCO and should have good chemical compatibility with both adjacent layers. By "chemical compatibility" is meant that the intermediate layer
does not undergo property-degrading chemical interactions with the adjacent layers. By "structural compatibility" is meant that the intermediate layer has a substantially similar lattice structure with the superconductive material. Among the materials suitable as an intermediate buffer layer are included yttria-stabilized zirconia, strontium titanate, barium titanate, magnesium oxide, rare earth oxides such as, e.g., cerium oxide, yttrium oxide, gadolinium oxide, ytterbium oxide, erbium oxide, europium oxide and mixtures of rare earth oxides containing two or more rare earth metals such as, e.g., yttrium samarium oxide ((Yι.xSmx)2O ), gadolinium ytterbium oxide ((Gdι.xYbx)2O ) and the like, and other cubic oxide materials such as those described in U.S. Patent No. 5,262,394, by Wu et al. for "Superconductive Articles Including Cerium Oxide Layer" such description hereby incorporated by reference. The buffer layer may also be of europium copper oxide (Eu2CuO4), neodymium copper oxide (Nd2CuO4), yttrium copper oxide (Y2CuO4), and other rare earth copper oxides (RE2CuO4).
It has now been discovered that the thickness of the buffer layer adjacent to the superconducting layer should be from about 25 Angstroms to about 180 Angstroms in thickness, preferably from about 50 Angstroms to about 125 Angstroms in thickness for best results. Though careful examination, it has now been confirmed that in the absense of any buffer layer between the superconducting layer and the IBAD-deposited layer that reaction between the layers results in a continuous interfacial layer of barium zirconate along the interface between the layers. Further, it has been found that when the topmost buffer layer, e.g., cerium oxide, adjacent to the superconducting YBCO layer (about 1.5 microns in thickness), has a thickness of from about 250 Angstroms up to about 11,000 Angstroms (1.1 microns), that reaction between the layers results in detrimental effects including generation of porosity within the YBCO layer, formation of some barium cerium oxide phases near the interface, tilting of the buffer layer crystal structure, and lower critical cuπent densities. In contrast, with a thinner topmost buffer layer of generally less than about 250 Angstroms, preferably from about 50 Angstroms to about 180 Angstroms, more preferably from about 75 Angstroms to about 125 Angstroms, reaction between the layers is minimal and the critical cuπent densities are increased. Such a buffer layer can be considered as an ultra-thin buffer layer.
The intermediate or buffer layers are generally deposited at temperatures of greater than about 750°C, preferably at temperatures of from about 750°C to about 950°C.
The HTS layer, e.g., the YBCO layer, can be deposited, e.g., by pulsed laser deposition or by methods such as evaporation including coevaporation, e-beam evaporation and activated reactive evaporation, sputtering including magnetron sputtering, ion beam sputtering and ion assisted sputtering, cathodic arc deposition, chemical vapor deposition, organometallic chemical vapor deposition, plasma enhanced chemical vapor deposition, molecular beam epitaxy, a sol-gel process, liquid phase epitaxy and the like. In pulsed laser deposition, powder of the material to be deposited can be initially pressed into a disk or pellet under high pressure, generally above about 1000 pounds per square inch (PSI) and the pressed disk then sintered in an oxygen atmosphere or an oxygen-containing atmosphere at temperatures of about 900°C to about 950°C for at least about 1 hour, preferably from about 12 to about 24 hours. An apparatus suitable for pulsed laser deposition is shown in Appl. Phys. Lett. 56, 578 (1990), "Effects of Beam Parameters on Excimer Laser Deposition of YBa2Cu3O -δ ", such description hereby incorporated by reference.
Suitable conditions for pulsed laser deposition include, e.g., the laser, such as an excimer laser (20 nanoseconds (ns), 248 or 308 nanometers (nm)), targeted upon a rotating pellet of the target material at an incident angle of about 45°. The substrate can be mounted upon a heated holder rotated at about 0.5 rpm to minimize thickness variations in the resultant film or coating, The substrate can be heated during deposition at temperatures from about 600°C to about 950°C, preferably from about 700°C to about 850°C. An oxygen atmosphere of from about 0.1 millitoπ (mTorr) to about 10 Ton, preferably from about 100 to about 250 mTorc, can be maintained within the deposition chamber during the deposition. Distance between the substrate and the pellet can be from about 4 centimeters (cm) to about 10 cm.
The deposition rate of the film can be varied from about 0.1 Angstroms per second
(A/s) to about 100 A/s by changing the laser repetition rate from about 0.1 hertz (Hz) to
about 200 Hz. Generally, the laser beam can have dimensions of about 3 millimeters (mm) by 4 mm with an average energy density of from about 1 to 4 joules per square centimeter (J/cm2). After deposition, the films generally are cooled within an oxygen atmosphere of greater than about 100 Ton to room temperature. The present invention is more particularly described in the following examples which are intended as illustrative only, since numerous modifications and variations will be apparent to those skilled in the art.
EXAMPLE 1 Highly textured YSZ films were prepared on polished Inconel 625 substrates by the method of U.S. Patent No. 5,872,080. On top of the YSZ layer, thin cerium oxide buffer layers were deposited by pulsed laser deposition. A layer of YBCO, approximately 1.5 microns, was then deposited by pulsed laser deposition upon the cerium oxide layer. For both the ceriun oxide and YBCO layers, the substrate temperature during deposition was held at 775°C and the oxygen pressure was held at 0.2 ton, i.e., optimum deposition conditions for YBCO. Each deposition included two samples: one for measurement of critical cunent density and one for examination by TEM.
Samples were made with measured cerium oxide thicknesses of 11,000 Angstroms, 1300 Angstroms, 250 Angstroms, and 90 Angstroms. An additional sample was made with no cerium oxide layer. Critical cunent densities were measured for each sample and x-ray analysis of the in-plane and out-of-plane texture was conducted. The results of analysis are shown in Table 1. It can be seen from the results presented in Table 1 that having a buffer layer is clearly better than no buffer layer, but that in addition, a thinner (ultra-thin) buffer layer provides improved critical cunent density. Additonal examination of the different samples by TEM showed additonal problems including generation of porosity within the YBCO layer, formation of some barium cerium oxide phases near the interface, and tilting of the buffer layer crystal structure, whenh the buffer layer was 250 Angstroms, 1300 Angstroms, or 11,000 Angstroms.
TABLE 1
Although the present invention has been described with reference to specific details, it is not intended that such details should be regarded as limitations upon the scope of the invention, except as and to the extent that they are included in the accompanying claims.
Claims
1. In a superconductive structure including a layer of a high temperature superconducting oxide and a topmost buffer layer adjacent to the layer of a high temperature superconducting oxide, the improvement comprising the topmost buffer layer is from about 25 Angstroms to about 180 Angstroms in thickness.
2. The superconductive structure of claim 1 wherein the topmost buffer layer is selected from the group consisting of strontium titanate, barium titanate, yttria- stabilized zirconia, magnesium oxide, rare earth copper oxides, and rare earth oxides.
3. The superconductive structure of claim 2 wherein the rare earth oxides include cerium oxide, gadolinium oxide, ytterbium oxide, erbium oxide, europium oxide, and mixtures thereof.
4. The superconductive structure of claim 1 wherein the topmost buffer layer is cerium oxide.
5. The superconductive structure of claim 4 wherein the topmost buffer layer is from about 50 to 125 Angstroms in thickness.
6. A superconductive structure comprising: a substrate; a layer of material selected from the group consisting of MgO and YSZ upon the substrate; at least one buffer layer upon the layer of MgO or YSZ; and, a layer of a high temperature superconducting material upon a topmost buffer layer, wherein the topmost buffer layer is characterized as being from about 25 Angstroms to about 180 Angstroms in thickness.
7. The superconductive structure of claim 6 wherein the topmost buffer layer is selected from the group consisting of strontium titanate, barium titanate, yttria- stabilized zirconia, magnesium oxide, rare earth copper oxides, and rare earth oxides.
8. The superconductive structure of claim 7 wherein the rare earth oxides include cerium oxide, gadolinium oxide, ytterbium oxide, erbium oxide, europium oxide, and mixtures thereof.
9. The superconductive structure of claim 6 wherein the topmost buffer layer is cerium oxide.
10. The superconductive structure of claim 9 wherein the topmost buffer layer is from about 50 to 125 Angstroms in thickness.
11. The superconductive structure of claim 6 wherein the high temperature superconducting material is YBCO.
12. The superconductive structure of claim 10 wherein the high temperature superconducting material is YBCO.
13. The superconductive structure of claim 6 wherein the substrate is a flexible polycrystalline metal.
14. The superconductive structure of claim 6 wherein the substrate is a single crystal substrate.
15. The superconductive structure of claim 14 wherein the single crystal substrate is selected from the group consisting of lanthanum aluminum oxide, magnesium oxide, strontium titanate, sapphire and yttria-stabilized zirconia.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US73164600A | 2000-12-06 | 2000-12-06 | |
| US09/731,646 | 2000-12-06 |
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| Publication Number | Publication Date |
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| WO2003034448A1 true WO2003034448A1 (en) | 2003-04-24 |
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| Application Number | Title | Priority Date | Filing Date |
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| PCT/US2001/046876 WO2003034448A1 (en) | 2000-12-06 | 2001-12-04 | Superconducting composite structures |
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| US5130294A (en) * | 1990-08-13 | 1992-07-14 | Kookrin Char | High temperature superconductor-calcium titanate structures |
| US5132282A (en) * | 1990-03-16 | 1992-07-21 | Nathan Newman | High temperature superconductor-strontium titanate sapphire structures |
| US5135906A (en) * | 1989-07-24 | 1992-08-04 | Sumitomo Electric Industries, Ltd. | Superconducting thin film of compound oxide and process for preparing the same |
| US5162294A (en) * | 1991-02-28 | 1992-11-10 | Westinghouse Electric Corp. | Buffer layer for copper oxide based superconductor growth on sapphire |
| US5179070A (en) * | 1988-04-30 | 1993-01-12 | Sumitomo Electric Industries, Ltd. | Semiconductor substrate having a superconducting thin film with a buffer layer in between |
| US5252553A (en) * | 1991-05-20 | 1993-10-12 | Sumitomo Electric Industries, Ltd. | Process for preparing a superconducting thin film of compound oxide |
| US5260267A (en) * | 1989-07-24 | 1993-11-09 | Sumitomo Electric Industries, Ltd. | Method for forming a Bi-containing superconducting oxide film on a substrate with a buffer layer of Bi2 O3 |
| US5372992A (en) * | 1989-11-07 | 1994-12-13 | Sumitomo Electric Industries, Ltd. | Superconducting thin film |
| US5420102A (en) * | 1993-03-12 | 1995-05-30 | Neocera, Inc. | Superconducting films on alkaline earth fluoride substrate with multiple buffer layers |
| US5712227A (en) * | 1989-06-30 | 1998-01-27 | Sumitomo Electric Industries, Ltd. | Substrate having a superconductor layer |
| US6226538B1 (en) * | 1997-12-25 | 2001-05-01 | Sumitomo Electric Industries, Ltd. | Magnetic sensor with squid and having superconducting coils formed on sapphire substrate |
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2001
- 2001-12-04 WO PCT/US2001/046876 patent/WO2003034448A1/en not_active Application Discontinuation
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5179070A (en) * | 1988-04-30 | 1993-01-12 | Sumitomo Electric Industries, Ltd. | Semiconductor substrate having a superconducting thin film with a buffer layer in between |
| US5712227A (en) * | 1989-06-30 | 1998-01-27 | Sumitomo Electric Industries, Ltd. | Substrate having a superconductor layer |
| US5135906A (en) * | 1989-07-24 | 1992-08-04 | Sumitomo Electric Industries, Ltd. | Superconducting thin film of compound oxide and process for preparing the same |
| US5260267A (en) * | 1989-07-24 | 1993-11-09 | Sumitomo Electric Industries, Ltd. | Method for forming a Bi-containing superconducting oxide film on a substrate with a buffer layer of Bi2 O3 |
| US5372992A (en) * | 1989-11-07 | 1994-12-13 | Sumitomo Electric Industries, Ltd. | Superconducting thin film |
| US5132282A (en) * | 1990-03-16 | 1992-07-21 | Nathan Newman | High temperature superconductor-strontium titanate sapphire structures |
| US5130294A (en) * | 1990-08-13 | 1992-07-14 | Kookrin Char | High temperature superconductor-calcium titanate structures |
| US5162294A (en) * | 1991-02-28 | 1992-11-10 | Westinghouse Electric Corp. | Buffer layer for copper oxide based superconductor growth on sapphire |
| US5252553A (en) * | 1991-05-20 | 1993-10-12 | Sumitomo Electric Industries, Ltd. | Process for preparing a superconducting thin film of compound oxide |
| US5420102A (en) * | 1993-03-12 | 1995-05-30 | Neocera, Inc. | Superconducting films on alkaline earth fluoride substrate with multiple buffer layers |
| US6226538B1 (en) * | 1997-12-25 | 2001-05-01 | Sumitomo Electric Industries, Ltd. | Magnetic sensor with squid and having superconducting coils formed on sapphire substrate |
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