RU2696182C1 - High-temperature superconducting tape manufacturing method and tape - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to production of high-temperature superconducting tape. Buffer layers are deposited on the substrate in the following sequence: an aluminum oxide layer, an yttrium oxide layer, a magnesium oxide layer, a homoepitaxial magnesium oxide layer and a lanthanum manganite layer, depositing high-temperature superconductor layer on buffer layers and applying at least one protective layer. Layers of magnesium oxide and homoepitaxial magnesium oxide are deposited by electron-beam evaporation. Magnesium oxide layer is deposited with simultaneous irradiation of the deposition zone with argon ion flow, a layer of homoepitaxial magnesium oxide is deposited while heating the substrate to temperature of 400–800 °C. Application of high-temperature superconductor layer to buffer layers is carried out by pulse laser deposition with substrate heating to 500–900 °C and subsequent annealing at temperature of 300–500 °C in an oxygen atmosphere.

EFFECT: high stability of properties of the obtained high-temperature superconducting tape.

11 cl, 1 dwg

Description

The field of technology.

The invention relates to the manufacturing technology of second-generation high-temperature superconducting conductors (HTSC) in the form of multilayer thin-film tapes and can be used in the industrial production of long HTSC to create conductive cables, current limiters, motor windings, etc.

The prior art.

Second-generation HTSC tapes are multilayer thin-film structures on flexible metal substrates.

A chemical compound such as ReBa ₂ Cu ₃ O ₇ (ReBCO), where Re is a rare-earth element, is used as a superconducting layer in HTSC.

For substrates of HTSC tapes, metal tapes from alloys based on nickel or iron are traditionally used. Substrates can have a biaxial texture, the so-called RABiTS (Rolling-Assisted Biaxially Textured Substrate) or not to have this texture. In the latter case, the texture is created on additional layers located between the substrate and the HTSC layer. Such layers are called buffer.

During the deposition of buffer layers, either the texture of the HTSC substrate is transferred to the layer due to epitaxial growth (if the substrate itself has a texture), or the texture is created directly on the buffer layers and the HTSC texture is transferred to the layer due to epitaxial growth.

By transferring the texture from the substrate or from each previous buffer layer to the next and further to the superconducting layer, high performance characteristics of the entire superconducting tape are ensured.

Epitaxy is easy to implement if the difference between the constant lattices between the layers does not exceed 5-7%. Otherwise, epitaxial growth is very difficult or impossible.

In this sense, the sequence of arrangement of buffer layers is important for transferring the texture of an HTSC layer due to epitaxial growth.

So, in the patent RU 2481673 the layers are applied to the substrate in the following sequence: substrate, biaxially textured layers of magnesium oxide, strontium bifluoride and cerium oxide or yttrium oxide, HTSC layer, after which the resulting material is annealed at 780-850 ° C to facilitate and accelerate the process dissolution of the fluoride sublayer in cerium oxide.

Such a HTSC conductor, as reported in the cited patent, has the simplest architecture possible, moreover, the deposition of each subsequent buffer layer does not lead to a significant increase in the surface roughness of the HTSC.

The deposition of layers can occur by various methods. And application methods can also play a negative or positive role.

In patent RU 2481673, the deposition of all the buffer and superconducting layers is carried out by chemical vapor deposition (MOCVD - Metal-Organic Chemical Vapor Deposition). The pressure in all cases is maintained at the level of 3-30 mbar, argon acts as the carrier gas for the precursor vapors.

The patent notes that the proposed approach to the creation of superconducting materials can be successfully implemented using other methods of deposition of layers, such as pulsed laser deposition, electron beam or thermal evaporation, molecular beam epitaxy, etc.

However, it is difficult to agree with this, since often the technology of applying one of the layers strongly depends on the composition of the applied layer and not everything is as obvious as it seems at first glance. In addition, their properties strongly depend on the use of a particular technology for applying layers.

The closest technical solution is described in the article “Progress in High Throughput Processing of Long-Length, High quality and Low Cost IBAD MgO and Buffer Tapes at SuperPower”, Xuming Xiong et al. IEEE Transactions on Applied Superconductivity (Volume: 19, Issue: 3 , June 2009), pp. 3319-3322).

The article reveals a high-temperature superconductor with the following architecture:

Hastelloy nickel alloy substrate with a thickness of 50 microns;

buffer layers, deposited in the following sequence, an Al ₂ O ₃ layer with a thickness of 75 nm and a Y ₂ O ₃ layer with a thickness of 7 nm, obtained by reactive magnetron sputtering;

MgO layer obtained by reactive ion beam sputtering technology with simultaneous irradiation of the deposition zone by a stream of argon ions (deposition by ion assisting: IBAD - Ion Beam Assisted Deposition) with a thickness of 10 nm;

a 30 nm thick homoepitaxial MgO layer obtained by magnetron sputtering in a DC chamber and

30 nm thick LaMnO ₃ layer obtained by radio frequency magnetron sputtering.

Next, a layer of a high-temperature superconductor was deposited on a LaMnO ₃ layer by the 1 μm MOCVD method, after which protective layers of silver 2 μm thick and copper 20 μm thick were applied.

The use of all of the above technologies, tied to the specific chemical composition of the deposited layer, has significantly increased the productivity of the process of applying layers. So, the authors of the article argue that the production capacity of HTSC tapes has increased to 500 km per year.

However, independent studies of the tape obtained using this technology (see L Rossi, X Hu, F Kametani, D Abraimov, A Polyanskii, J Jaroszynski and D With Larbalestier, Sample and length-dependent variability of 77 and 4.2K properties in nominally identical RE123 coated conductors, Supercond. Sci. Technol. 29 (2016) 054006 and D. Abraimov, HW Weijers, WD Markiewicz, M. Santos, J. McCallister, J. Jaroszynski, J. Jiang, J. Lu, V. Toplosky, B. Jarvis, YL Viouchkov, and DC Larbalestier, Characterization of (Re) BCO conductor for development of 32 T all superconducting magnet, presented at ICEC / ICMC 2014, 7-11 July 2014, Twente, the Netherlands, available online at https: // indico.cern.ch/event/244641/contributions/1563095/attachments/418145/580797/O3-2_Dmytro_Abraimov-Tue-Mo-O1.pdf showed that the superconducting properties of the resulting tape in an external magnetic field are not reproducible and correlate very weakly with superconducting properties at a temperature of 77 K in the absence of an external magnetic field. So, the ratio of the critical current of the tape obtained by the described technology, measured at 77 K in the absence of an external magnetic field to the critical current of the same tape at 4.2 K in a magnetic field of 17 T for different samples ranged from 1.4-4.6 , that is, the maximum value is more than 3 times the minimum value.

In the patent EP 1042820 B1, the importance of having an electrical connection between the HTSC layer and the metal substrate is indicated and a method for creating such a connection by the special removal of insulating oxide buffer layers is described. In our invention, due to the small thickness of the oxide buffer layers, an electrical connection between the substrate tape and the HTSC layer exists without the introduction of additional technological processes.

The aforementioned unsatisfactory properties of HTSC tapes obtained by known technologies present a certain technical problem, which we eliminate by our invention.

Disclosure of the invention.

The objective of the invention is to increase the stability of the properties of the obtained high-temperature superconducting tape, as well as reducing the complexity of obtaining HTSC tape by providing electrical connection between the HTSC layer and the metal substrate without introducing additional technological processes. The problem is solved by a method of manufacturing a high-temperature superconducting tape, including the deposition of buffer layers on a substrate in the following sequence: an alumina layer, a yttrium oxide layer, a magnesium oxide layer, a homoepitaxial magnesium oxide layer and a lanthanum manganite layer, deposition of a high-temperature superconductor layer on the buffer layers and deposition, at least one protective layer, characterized in that the layers of magnesium oxide and homoepitaxial magnesium oxide are deposited by electron beam and vaporization, while the magnesium oxide layer is deposited while the deposition zone is irradiated with a stream of argon ions, the homoepitaxial magnesium oxide layer is deposited when the substrate is heated to a temperature of 400-800 ° C, the layer of a high-temperature superconductor is deposited on the buffer layers by pulsed laser deposition when the substrate is heated to 500 -900 ° C and subsequent annealing at a temperature of 300-500 ° C in an oxygen atmosphere.

In particular embodiments of the invention, a GdBa ₂ Cu ₃ O ₇ layer is applied as a high temperature superconducting layer.

In the most desirable embodiments of the invention, the yttrium oxide layer and the lanthanum manganite oxide layer are precipitated by pulsed magnetron sputtering.

In this case, a layer of lanthanum manganite oxide in particular embodiments of the invention is precipitated by heating the substrate to 500-850 ° C.

A layer of alumina is applied to the substrate with a roughness of not more than 1.0 nm.

It is desirable to deposit an alumina layer by high-frequency magnetron sputtering.

The protective layer is most desirably deposited by direct current magnetron sputtering.

As a protective layer, a silver layer is preferably applied.

The problem is also solved by a high-temperature superconducting tape, which is obtained in accordance with the described method, and contains a substrate, buffer layers, a high-temperature superconducting layer and at least one protective layer located in the following sequence: alumina layer, yttrium oxide layer, layer magnesium oxide, a layer of homoepitaxial magnesium oxide, a layer of lanthanum manganite oxide, a layer of high temperature superconductor and at least one protective layer.

In private embodiments of the invention, the tape as a high-temperature superconducting layer contains a layer of GdBa ₂ Cu ₃ O ₇ .

The tape as a protective layer may contain a silver layer.

In FIG. 1 diagram of the layered structure of a thin-film superconducting tape. The invention consists in the following.

The layer-by-layer structure of HTSC tapes (the architecture of HTSC tapes) related to HTSC conductors of the second generation consists of several buffer oxide layers (films) placed on a metal substrate, a HTSC layer and a protective coating, for example, based on silver.

High critical current density in HTSC films is realized only in the presence of an acute biaxial layer texture.

An increase in the misorientation angles of neighboring grains of the superconductor relative to each other leads to a decrease in the critical current density.

The location of the buffer layers, in particular as shown in FIG. 1, is selected in such a way as to reduce the disorientation of neighboring grains.

To transfer the texture, an important factor is the method of deposition of both the buffer layers and the HTSC layer.

The method in accordance with the invention provides for the replacement of some technologies for applying layers of the known method, without changing the architecture of the HTSC tape.

In particular, during the deposition of magnesium oxide layers according to the IBAD process, i.e. with simultaneous irradiation of the deposition zone by a stream of argon ions, reactive ion evaporation (a known method) is replaced by electron-beam evaporation of magnesium oxide, when precipitating a homoepitaxial magnesium oxide, magnetron sputtering (a known method) is replaced by electron-beam evaporation of magnesium oxide, carried out by heating the substrate to temperature 400-800 ° C, and when applying HTSC layer on the buffer layers instead of applying the method of MOCVD (known method) use the method of pulsed laser deposition when heating the substrate up to 500–900 ° C (pulsed laser deposition refers to the production of films and coatings by condensation on the surface of a substrate of the products of interaction in a vacuum of pulsed laser radiation with the target material).

These technologies not only improve the current carrying capacity of HTSC tape, but also significantly improve the reproducibility of the superconducting properties of HTSC tape in an external magnetic field and provide electrical coupling between the HTSC layer and the metal substrate.

On the one hand, such an improvement may be due to the fact that, using these technologies, layer growth occurs at very high rates and the coating material is not contaminated, the composition of the layers remains stable due to congruent transfer of the target material.

However, it is important that only with all of these operations in the claimed technology provides this technical result, while not only the sequence and type of technological operations are important, but also the parameters of these operations.

The deposition of homoepitaxial magnesium oxide occurs when the substrate is heated to 400-800 ° C, and the deposition of HTSC layer - when the substrate is heated to 500-900 ° C and when beyond the stated limits - the technical result is not achieved. These temperatures provide good adhesion of the applied layers.

The annealing temperature is 300-500 ° C. In this interval, the chemical compound obtained by pulsed laser deposition is stable enough to accept oxygen and create a chemical compound with a stoichiometric composition corresponding to ReBa ₂ Cu ₃ O _7-x or with small deviations from it, usually corresponding to the homogeneity region of this composition.

At a temperature of less than 300 ° C, reactions with oxygen practically do not proceed; at a temperature of more than 500 ° C, stoichiometry is violated.

The deposition of a preliminary layer of magnesium oxide is carried out while irradiating the deposition zone with a stream of argon ions (IBAD technology). Such irradiation is carried out, as a rule, from a high-frequency ion source with an ion energy of 500-1200 eV. Irradiation with a stream of argon ions allows one to obtain a layer of magnesium oxide with a biaxial texture, which, due to the epitaxial growth of subsequent buffer layers, is transferred to the HTSC layer to ensure maximum superconducting properties.

Particular embodiments of the invention relate to the refinement of certain parameters of the method.

Thus, it is most desirable that a GdBa ₂ Cu ₃ O _7-x layer be applied as a high-temperature superconducting layer, which does not limit the method of producing HTSC ribbons with other HTSC layers.

As already indicated, in the most desirable embodiments of the invention, the yttrium oxide layer and the lanthanum manganite layer are precipitated by pulsed magnetron sputtering, which provides the claimed technology with additional advantages in the form of an increase in process performance. The layer of lanthanum manganite is deposited on a substrate heated to 500–850 ° С, and the yttrium oxide layer is deposited without heating the substrate.

The alumina layer acts as a barrier layer - it prevents the diffusion of the metal components of the substrate into the HTSC layer. The layer is characterized by an amorphous structure. It is desirable that the deposition of this layer is carried out using high-frequency magnetron sputtering without heating the substrate. The alumina layer can be deposited by other methods, such as, for example, in the known method — reactive magnetron sputtering. Despite the fact that in the known method, the alumina layer is deposited faster than in the proposed one, high-frequency magnetron sputtering provides a more uniform distribution of alumina and ensures the absence of incompletely oxidized aluminum inclusions.

To obtain a high-quality insulating layer of aluminum oxide, the substrate should be with a roughness of not more than 1.0 nm. Such a roughness can be achieved by pre-polishing the surface of the substrate.

The function of the yttrium oxide layer is the formation of a “seed” surface, which favors the formation of a biaxial texture when applying the IBAD MgO layer, which improves at the next stage of applying the homoepitaxial MgO layer and is transferred to the HTSC layer through the buffer layer of lanthanum manganite.

The lanthanum manganite layer in particular embodiments of the invention is precipitated by pulsed magnetron sputtering when the substrate is heated to 500-850 ° C. As a protective layer, layers of silver and, if necessary, copper are traditionally applied, although the choice is not limited to these two elements. The protective layer of silver in the examples of specific performance was besieged by direct current magnetron sputtering, although the invention is not limited to the use of this method for applying a silver layer.

The claimed invention was carried out as follows.

The substrate used was a tape made of an alloy based on nickel, for example, Hastelloy C-276 or stainless steel, for example, grade 310S.

The thickness of the substrate ranged from 25 to 200 μm.

The substrate was pre-polished to an average roughness level of not more than 1.0 nm (when analyzing from an area of 5 × 5 μm).

Buffer layers (layers between the metal substrate and the superconductor), a superconductor layer, and a silver protective layer were applied to the substrate. All layers were applied in vacuo.

A layer of alumina (Al ₂ O ₃ ) was deposited on a metal strip by high-frequency magnetron sputtering of a ceramic target from Al2O3. The layer thickness ranged from 15 to 150 nm (mainly 50 nm). The process took place without heating the substrate.

A yttrium oxide layer (Y2O3) was deposited onto an alumina layer by pulsed magnetron sputtering from a yttrium metal target. As a result of reaction with oxygen in a vacuum chamber, yttrium oxide was deposited on the substrate. The layer thickness ranged from 1 to 40 nm (mainly 3 nm). The process took place without heating the substrate.

A layer of magnesium oxide (MgO)) was applied by two different sequential processes. In the first process, magnesium oxide was deposited on a yttrium oxide layer by electron beam evaporation from ceramic or single-crystal granules of magnesium oxide, the deposition zone was simultaneously irradiated with a stream of argon ions from a high-frequency ion source with an ion energy of 500-1200 eV (the so-called deposition by ion assisting = IBAD ) The thickness of the layer obtained in this process was 2-30 nm. The process took place without heating the substrate. The resulting MgO layer is biaxially textured (has a predominant orientation of the crystal structure).

In the second magnesium oxide deposition process, the deposition was carried out on a magnesium oxide layer obtained by IBAD. Homoepitaxial growth occurred (i.e., the MgO layer grows epitaxially on the MgO layer). The process of homoepitaxial growth was carried out by electron beam evaporation. Magnesium oxide was deposited from ceramic or single-crystal granules of magnesium oxide by heating the tape (up to 400-800 ° C). The layer thickness ranged from 5 to 300 nm (mainly 45 nm). The resulting MgO layer was biaxially textured, repeating and sharpening the texture of the previous layer.

A layer of lanthanum manganite oxide (LaMnO3) was deposited on a magnesium oxide layer by pulsed magnetron sputtering from a ceramic target of lanthanum manganite. The layer thickness varies from 10 to 300 nm (mainly 50 nm). The process took place when the substrate was heated to 500-850 ° C. The resulting LaMnO3 layer was biaxially textured, repeating the texture of the previous layer.

A superconductor layer (GdBa2Cu3O7-x) is deposited onto a lanthanum manganite layer by pulsed laser deposition from a Gd-Ba-Cu-O ceramic target.

The composition of the superconductor could deviate from the stoichiometry of GdBa ₂ Cu ₃ O _7-x , and also have inclusions of other compositions up to 30%. The layer thickness ranged from 200 to 6000 nm (mainly 1700 nm). The process took place when the substrate was heated to 500-900 ° C. The resulting GdBa2Cu3O7-x layer was biaxially textured, repeating and sharpening the texture of the previous layer.

A protective layer (metallic silver) was deposited on a superconductor layer by magnetron sputtering of a metal target from silver in direct current. The layer thickness ranged from 200 to 8000 nm (mainly 2000 nm). The process took place without heating the tape.

After applying a layer of silver, the tape was annealed in an oxygen atmosphere at a temperature of 300-500 ° C.

After annealing, the tape was certified according to the criterion of current-carrying capacity (critical current was measured).

An example implementation of the method.

In accordance with the foregoing, received a tape with the following parameters:

Hastelloy Alloy Substrate Thickness - 60 μm

Aluminum oxide layer thickness - 50 nm

Yttrium oxide layer thickness - 3 nm

MgO IBAD Layer Thickness - 5 nm

Homo epi MgO layer thickness - 50 nm

The layer thickness of LaMnO ₃ - 50 nm

Gd-Ba-Cu-O layer thickness - 1600 nm

Ag layer thickness - 2000 nm

The layers were applied in accordance with the following:

Polishing the substrate in an electrolyte of the composition H ₃ PO ₄ 50%, H ₂ SO ₄ 25%, H ₂ O 25%, modes: current density 70 A / dm ² , polishing time 35 s, to the level of average roughness no more than 1.0 nm (at analysis with an area of 5 × 5 μm).

A layer of alumina (Al2O3) was deposited onto a metal strip by high-frequency magnetron sputtering of a ceramic target from Al2O3 without heating the substrate. Modes: spray power 2800 W, pressure 1 mTorr.

The yttrium oxide (Y2O3) layer was deposited onto the alumina layer by pulsed magnetron sputtering from a yttrium metal target in a vacuum chamber with a mixture of argon and oxygen. The process took place without heating the substrate. The spraying modes are as follows: power 750 W, frequency 150 kHz, pressure 1.8 mTorr.

A layer of magnesium oxide (MgO) was deposited on a yttrium oxide layer by electron beam evaporation from ceramic granules of magnesium oxide, and the deposition zone was simultaneously irradiated with a stream of argon ions from a high-frequency ion source with an ion energy of 1000 eV without heating the substrate. Electron beam evaporation modes: power 1 kW, deposition rate on the substrate 0.5 nm / s.

The second layer of magnesium oxide (MgO Homo epi) was deposited on the magnesium oxide layer obtained by the IBAD method, by electron beam evaporation from ceramic or single crystal granules of magnesium oxide by heating the tape 600 ° C. The deposition modes are as follows: power 1 kW, the deposition rate on the substrate of 0.6 nm / s.

A layer of lanthanum manganite (LaMnO3) was deposited on a magnesium oxide layer by pulsed magnetron sputtering from a ceramic target of lanthanum manganite when the substrate was heated to 650 ° C. The application modes are as follows: power 1100 W, frequency 150 kHz, pressure 2.1 mTorr.

A superconductor layer (GdBa2Cu3O7) is applied to the lanthanum manganite layer by pulsed laser deposition from a Gd-Ba-Cu-O ceramic target in the following mode: heater temperature 950-1050 ° C, oxygen partial pressure 50-80 Pa, ribbon drawing speed through the deposition zone 50 m / h, the evaporation of the substrate is carried out by focused laser radiation with a wavelength of 308 nm (excimer laser) and a frequency of 200 Hz.

The material of this layer (GdBa2Cu3O7) repeated the texture of the previous layer.

A protective layer (metallic silver) was deposited on a superconductor layer by magnetron sputtering of a metal target from silver in direct current. The process took place without heating the tape in the following mode: pressure 3 mTorr, magnetron power 2300 W and 1150 W, belt speed 60 m / h.

After applying a layer of silver, the tape was annealed in an oxygen atmosphere at a temperature of 480 ° C.

The resulting tape had the following characteristics: critical current 600-650 A at 12 mm width, standard deviation <10 A.

The electrical resistance between the HTSC layer and the metal strip substrate was <1 Ω.

As follows from the above data, HTSC tapes are characterized by high critical current values.

In addition, upon receipt of the tape using the claimed invention, the superconducting properties of the tape in an external magnetic field are much more reproducible than in the known method: the spread between the ratio of the critical current measured at 77 K in the absence of an external magnetic field to the critical current of the same tape at 4, 2 K in a magnetic field of 17 T of the tape in accordance with the invention does not exceed 1.7 times, while by the known method such a spread can reach 4.6.

Also, the invention allows to reduce the complexity of obtaining the tape, since for the formation of an electrical connection between the substrate and the HTSC layer, it is not provided for the removal of insulating buffer layers, as is done in known solutions.

Claims (11)

1. A method of manufacturing a high-temperature superconducting tape, including the deposition of buffer layers on a substrate in the following sequence: an alumina layer, a yttrium oxide layer, a magnesium oxide layer, a homoepitaxial magnesium oxide layer and a lanthanum manganite layer, deposition of a high-temperature superconductor layer on the buffer layers and applying at least at least one protective layer, characterized in that the layers of magnesium oxide and homoepitaxial magnesium oxide are deposited by electron beam evaporation, while the oxide layer m rotting is deposited by simultaneously irradiating the deposition zone with a stream of argon ions, and a layer of homoepitaxial magnesium oxide is precipitated by heating the substrate to a temperature of 400-800 ° С, while the deposition of a high-temperature superconductor on the buffer layers is carried out by pulsed laser deposition when the substrate is heated to 500-900 ° C and subsequent annealing at a temperature of 300-500 ° C in an oxygen atmosphere. 2. The method according to p. 1, characterized in that a layer of GdBa ₂ Cu ₃ O _7-x is applied as a high-temperature superconductor. 3. The method according to p. 1, characterized in that the yttrium oxide layer and the lanthanum manganite oxide layer are precipitated by pulsed magnetron sputtering. 4. The method according to p. 3, characterized in that the layer of lanthanum manganite oxide is precipitated by heating the substrate to 500-850 ° C. 5. The method according to p. 1, characterized in that the layer of alumina is applied to the substrate with a roughness of not more than 1.0 nm. 6. The method according to p. 1, characterized in that the alumina layer is deposited by high-frequency magnetron sputtering. 7. The method according to p. 1, characterized in that the protective layer is precipitated by direct current magnetron sputtering. 8. The method according to p. 1, characterized in that a silver layer is applied as a protective layer. 9. A high temperature superconducting tape obtained by the method according to one of claims 1 to 8, comprising a substrate, buffer layers, a high temperature superconducting layer and at least one protective layer located in the following sequence: alumina layer, yttrium oxide layer, magnesium oxide layer , a homoepitaxial magnesium oxide layer, a lanthanum manganite oxide layer, a high-temperature superconductor layer, and at least one protective layer. 10. The tape according to claim 9, characterized in that as a high-temperature superconductor, it contains a layer of GdBa ₂ Cu ₃ O _7-x . 11. The tape under item 10, characterized in that as a protective layer it contains a layer of silver.

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