RU2477900C1 - Method to treat high-temperature superconductor - Google Patents

Abstract

FIELD: nanotechnologies.

SUBSTANCE: invention relates to the field of superconductivity and nanotechnologies, namely, to the method for production and processing of composite materials on the basis of high-temperature superconductors (HTSC), which may be used in devices of energy transmission, for development of current limiters, transformers, powerful magnetic systems. The method to process a high-temperature superconductor representing a composite structure made of a substrate material with applied buffer layers of metal oxides, a layer of a superconducting material of metal oxides, above which a protective layer of silver is applied, consists in radiation of the specified structure with an ion beam of heavy noble gases with energy from 48 to 107 MeV with a flux of 2×10¹⁰ - 5×10¹⁰ ion/cm² and density of ion flux of 2.6×10^-8 - 6.5×10^-8 A/cm² maintaining temperature from 30°C to 100°C, with provision of relief of internal elastic stresses in the composite structure.

EFFECT: improved characteristics.

3 dwg, 1 tbl

Description

The invention relates to the field of superconductivity and nanotechnology, and in particular to a technology for producing and processing composite materials based on high-temperature superconductors (HTSC), which in the future can be used to transfer electricity, to create current limiters, transformers, and powerful magnetic systems.

The technology for the generation of HTSCs of the 2nd generation involves layer-by-layer epitaxial deposition of buffer layers of nanometer thickness to match the lattice parameters of the HTSC material with the substrate, which determines the mechanical strength of the composite.

However, it is impossible to achieve complete coordination of the parameters, especially in the manufacture of a long composite. Therefore, it turns out that the superconductor layer has local elastic stresses, which can gradually lead to the destruction of the HTSC film layer. The larger the mismatch of the parameters of the crystal lattices, the lower the film thickness its morphological stability is lost. This is especially evident in the manufacture of long composite superconductors.

In the case of thick films and bulk samples, elastic stresses are usually removed by long-term thermal annealing, but thermal annealing is not applied at nanometer-scale layers due to diffusion smearing, which leads to a sharp decrease in functional parameters.

A known method of processing superconductors (Wu Ming Chen, SSJiang, YCGuo, JRJin, X / S.Wu, XHWang, X.Jin, XNXu, XXYao, SXDou. Effects of low-energy neutron irradiation on Bi- based superconductors. Physica C 299 (1998, pp. 77-82 [1]), which consists in irradiating a superconductor composition with bismuth Bi (2223) with low energy neutrons. As a result of such irradiation, the critical current of the superconductor increases by 30%, and the critical temperature increases by 2.5-5.0 K.

A known method of processing superconductors (DHGalvan, Shi Li, WMYuhasz, JunHo Kim, MB Maple, E. Adem. Superconductivite of N0802 samples obtained to electron irradiation. Physica C 398 (2003), P.147-151 [2]), which consists in irradiation NbSe ₂ superconductor by electrons at the Van de Graaff accelerator with various radiation doses of 100, 200 and 500 Mrad. As a result of such irradiation, the critical current doubled in comparison with unirradiated samples.

There is also known a method for processing superconducting materials (RF patent No. 2404470, IPC НВВ 12/00 dated December 16, 2009 [3]), based on the formation of a plasma stream in a gas medium and its impact on a solid-state target, in which a cumulative plasma jet focused by a magnetic field is formed in a pulsed mode with a jet expiration velocity of (4-10) · 10 ⁵ m / s with providing a pulse of a jet pressure on a solid-state target of 10 ⁵ -10 ⁶ atmospheres, a temperature of more than 10 ⁶ ° С and an energy flux density in a plasma jet of 10 ⁸ - 10 ¹⁰ W / cm ² , and when exposed and a plasma flow to a solid-state target creates a shock wave in it and transfers the energy of the shock wave through a layer of a viscous medium to a superconducting material.

The disadvantages of the known methods of processing superconductors [1, 2, 3] are the presence of local elastic stresses in the layers of the superconductor, which gradually lead to the destruction of the HTSC film layer.

Closest to the technical nature of the present invention is a known method for the synthesis of a superconductor with ion assist (Kidszun M., Huehne R., Holzapfel B., Schultz L. Ion-beam-assisted deposition oftextured NbN thin films. // Supercond. Sci. Technol . 2010. V.23. 025010 6pp.). This synthesis method involves the simultaneous deposition of niobium and ion implantation of nitrogen.

There are various modifications to the application of ion assisted treatment methods, depending on the purpose: in some cases, the synthesis of several components occurs, in others, the film is densified. In the known method of processing a superconductor, low-energy ions — tens of keV — are used, which does not provide the desired result — the complete elimination of local elastic stresses in the layers and increase the mechanical strength and durability of a long composite superconductor. For low-energy ions, as in the prototype, the mean free path is less than the thickness of the silver layer, so heavy high-energy ions are required.

The technical result, which consists in eliminating the noted drawback, in the proposed method of processing a high-temperature superconductor, which is a composite structure consisting of a substrate material with buffer layers of metal oxides deposited on it, a layer of a superconducting material based on barium cuprates and rare-earth elements, on top of which a protective a layer of silver is achieved by irradiating the composite structure with an ion beam of heavy noble gases with an energy of 48 to 107 MeV and a fluence of 2 × 10 ¹⁰ -5 × 10 ¹⁰ ions / cm ² and an ion current density of 2.6 × 10 ^-8 -6,5 × 10 ^-8 A / cm ² while maintaining the temperature from 30 ° C to 100 ° C to ensure the removal of internal elastic stresses in the composite structure.

The invention is illustrated by drawings, where:

- figure 1 shows an isometric section of a composite HTSC in an enlarged scale;

- figure 2 shows a micrograph of the structure of the composite HTSC obtained using a scanning electron microscope;

- figure 3 shows a micrograph of a composite HTSC obtained using a scanning electron microscope: a) before processing; b) after processing;

The proposed method is as follows.

To implement the method, a high-temperature superconductor (HTSC) is used, which is a composite structure (Fig. 1): silver layer 1 (δ = 2 μm); layer 2 YB ₂ C ₃ O _7-x (δ = 1 μm) - (hereinafter, we use the notation YBCO); layer 3 of La oxide ₃ O ₃ (δ = 37 nm); MgO oxide layer 4 (δ = 58 nm); layer 5 of oxide Y ₂ About ₃ (δ = 10 nm); layer 6 of Al ₂ O ₃ oxide (δ = 93 nm); and a Hastelloy alloy substrate 7 (δ = 50-100 μm).

HTSC processing consists in irradiating the indicated structure with an energy stream - an ion beam of heavy noble gases (Ar ⁸⁺ , Kr ¹⁷⁺ with an energy of 48 to 107 MeV with a fluence of 2 × 10 ¹⁰ -5 × 10 ¹⁰ ions / cm ² and an ion current density of 2 , 6 × 10 ^-8 -6.5 × 10 ^-8 A / cm ² while maintaining the temperature from 30 ° C to 100 ° C to ensure the removal of internal elastic stresses in the composite structure.

Elastic stresses were detected in the initial samples of the superconductor. In FIG. 3a is a photomicrograph of the initial HTSC ribbon, in which the dark region is a superconducting layer of YBCO 2, and the oblique lines 8 are structural defects — cracks resulting from internal elastic stresses.

A sample of the same series was irradiated with ⁸⁴ Kr ¹⁷⁺ krypton ions with an energy of 107 MeV and a fluence of 1 × 10 ¹⁰ ions / cm ² . Then it was studied using electron microscopy. On micrograph no structural defects such as cracks were detected (figb).

Thus, as a result of processing the composite HTSC according to the proposed method, the internal stresses in the superconductor film are relieved - see Fig. 3b.

Confirmation of the described results was obtained by X-ray diffraction studies of samples irradiated with ions. Three other samples of the same series were studied after irradiation with argon ions of ⁴⁰ Ar ⁸⁺ with energies from 48 MeV to 107 MeV using x-ray diffraction. A series of diffraction patterns of these YBCO samples was obtained. The width of the diffraction reflection peaks at half their height was measured under irradiation with argon ions at various fluences.

It is known that by the width of the reflection peaks, one can judge the presence of stresses in the crystal lattice. The results obtained in the proposed method are presented in the table.

№№ Fluence (F) of ions ⁴⁰ Ar ⁸⁺ The density of ion current, A / cm ² Temperature ° C Width at half height, degrees one 2 3 four 5 one 0 (no exposure) - - 0.108 2 2.0 × 10 ¹⁰ ion / cm ² 2.6 × 10 ^-8 thirty 0.096 3 5.0 × 10 ¹⁰ ion / cm ² 6.5 × 10 ^-8 40 0.098 four 1.0 × 10 ¹¹ ion / cm ² 1.3 × 10 ^-7 80 0.107 5 5.0 × 10 ¹¹ ion / cm ² 6.5 × 10 ^-7 one hundred 0.107

As can be seen from the data presented (see column 4 of the table), the minimum width of the peak of diffraction reflection does not correspond to the initial (unirradiated) sample (row 1 of the table), but to the sample after irradiation with fluences (2-5) × 10 ¹⁰ ion / cm ² ( rows 2 and 3 of the table).

Note that at such fluences, an increase in the critical current was also associated with the generation of additional pinning centers, the so-called columnar defects. If the fluence and the density of the ion current are outside the specified range, no improvement in the quality of the structure is observed - this is proved by the width at half the height of the diffraction reflection (see column 5, 4, and 5 of the table). Thus, the proposed method for processing a high-temperature superconductor eliminates the disadvantages of the prototype, since it provides the removal of internal elastic stresses of composite multilayer HTSCs and at the same time leads to an increase in the critical current. The proposed method meets the criterion of industrial applicability, since it was tested on real, industrially manufactured HTSCs and was repeatedly reproduced with obtaining stable results on an ion accelerator of the type IC-100.

Claims (1)

A method of processing a high-temperature superconductor, which is a composite structure consisting of a substrate material with buffer layers of metal oxides deposited on it, a layer of a superconducting material of metal oxide, on top of which a protective layer of silver is deposited, which consists in irradiating this structure with an energy flow, characterized in that that irradiation of the composite structure is carried out by an ion beam of heavy noble gases with an energy of 48 to 107 MeV with a fluence of 2 · 10 ¹⁰ -5 · 10 ¹⁰ ions / cm ² and density an ion current of 2.6 · 10 ^-8 -6.5 · 10 ^-8 A / cm ² while maintaining the temperature from 30 ° C to 100 ° C to ensure the removal of internal elastic stresses in the composite structure.

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