WO2006082164A1 - High-temperature layered superconductor structure and method for the production thereof - Google Patents

Abstract

The invention relates to the field of material sciences, more particularly a high-temperature layered superconductor structure that can be used in devices transporting current, for example. The aim of the invention is to create a high-temperature layered superconductor structure that is provided with a comparatively thin buffer layer and a secure diffusion barrier. Said aim is achieved by a high-temperature layered superconductor comprising a supporting material, at least one buffer layer, and a high-temperature superconducting layer, the buffer layer containing cerium oxide(s) that is/are doped with cations. Said aim is also achieved by a method for producing a high-temperature layered superconductor structure, in which at least one buffer layer containing cerium oxide(s) and/or the precursor substances thereof is applied to a supporting material, the cerium oxides or the precursor substances thereof already containing cations as dopants and/or at least one layer of cation-containing doping elements being applied onto or between the buffer layer(s), and at least one high-temperature superconductor layer is applied thereto following a thermal treatment at 700 to 1000 °C in a reduced atmosphere.

Description

High-temperature layer superconductor structure and method for its production

The invention relates to the field of materials science and high-temperature superconducting technology and relates to a high-temperature layer superconductor structure, such as can be used in devices for transport, storage or conversion of electrical energy and a method for its preparation.

Coatings made of high-temperature superconductors are frequently used for applications in energy technology. The disappearance of the electrical resistance below the transition temperature allows an increase in the efficiency of various devices, as well as more compact designs.

Such layer constructions usually consist of a carrier material, which in many cases is a thin metal strip with a layer of nonconductive material applied thereto, or it is a carrier of a non-conductive material, such as ceramic. Then there is the high-temperature superconducting layer. Such so-called band conductors can replace copper lines in established applications, which are loaded with high currents. The existing high copper losses high losses can be significantly reduced by the use of this band conductor and high current densities are feasible. For technical applications, the current carrying capacity of a superconductor is still of great importance. Investigations have shown that in order to maintain the current carrying capacity of superconductor layers either a monocrystalline or textured substrate and an epitaxially grown buffer layer must be present between superconductor layer and substrate. For this purpose, according to DE 102 48 025 A1, a polycrystalline or amorphous substrate is provided with a biaxially textured buffer layer by means of coating under oblique deposit direction (ISD). The superconductor layer is then applied to this buffer layer.

Buffer layers also serve to prevent the diffusion of metal atoms of the carrier material into the superconducting material (diffusion barrier). At the same time, such a buffer layer can prevent the uncontrolled oxidation of the metallic substrate material during superconductor coating and specific temperature treatment in an oxygen-rich atmosphere, adjust the lattice parameters of the various materials, smooth the surface of the substrate to be coated and improve the adhesion of the superconducting material. Such buffer layers consist in particular of oxides of metals, such as zirconium, cerium, yttrium, aluminum, strontium or magnesium or their mixed oxides and are generally electrically insulating (DE 299 23 162 U1).

Also known is an elongated superconductor structure with high-T _c - superconducting material and metallic carrier, wherein the carrier is biaxially textured and on the support an intermediate layer system with at least two intermediate layers of different oxidic materials is present (DE 299 23 162 U1). The superconducting material is then located on the intermediate layers, the intermediate layer facing the carrier consisting of an yttrium oxide and a comparatively thin intermediate layer facing the superconductor layer consisting of a cerium oxide. Advantageously used is yttrium oxide Y ₂ O ₃ and cerium oxide as CeO _2. The disadvantage is that pure Ceθ2 layers are known to tend to form cracks from a layer thickness of> 30 nm because of the oxygen deficit. Also, very high process temperatures of up to 1100 ⁰ C are required for the preparation of such biaxially textured Ceθ ₂ layers, making the manufacturing process technologically difficult and expensive. Overall, pure Ceθ ₂ layers could not reliably avoid metal atom diffusion and metal oxidation, so that such layers are only rarely used as individual buffers in practice. The only exception here form vapor-deposited ceria layers, which would be unprofitable because of high process costs, especially in elongated superconductor structures. As is known, the preparation of ceria-based buffer layers is problematic for CSD technologies, since toxic substances such as methanol and methoxyethanol must be used, or organic acids such as concentrated acetic acid are used which lead to oxidation of the metallic substrate (Supercond. Technol.16 (2003) 1305-1309).

Even with other metal oxide layers, no satisfactory results could be achieved by chemical solution deposition (CSD), metal-organic deposition (MOD) or sol-gel processes, since the phase formation of the metal oxides deposited one above the other as a material for the buffer layers is high Reaction temperatures is connected, which leads to high process costs and problems with the buffer effect. Furthermore, it can be assumed that, with each buffer layer, metal atoms diffuse out of the substrate into the buffer layer due to the concentration gradient and high process temperatures with long service lives. Therefore, as is known, the buffer layers are used with comparatively high layer thicknesses.

With high layer thickness distributions, however, the danger again increases that internal stresses exceed a critical value and cracks form in the buffer layer or even the buffer layer chips off the substrate. Furthermore, the surface roughness increases with the layer thickness, which hampers the textured growth of further coatings.

Also known is the production of YiBa ₂ Cu ₃ O ₇ (YBCOJ layer superconductors on Ni substrates, between which a CeGd-O buffer layer (CGO) is applied (Takahashi, Y. et al., I Physica C 412-414 (2004) 905-909). Such CGO layers have low chemical reactivity with the YBCO superconductor and lead to crack-free buffer layers. However, they also have increased Ni diffusion into the YBCO superconductor layer through the CGO layer, which is undesirable. This increased diffusion is attributed to the increase in oxygen vacancies in the CGO layer at elevated Gd content.

A disadvantage of the known solutions is that the buffer layers must be used from several layers of different materials and with relatively large thicknesses.

The object of the invention is to specify a high-temperature layer superconductor structure which has a reliable diffusion barrier with a comparatively thin buffer layer and to specify a simple process for its production.

The object is achieved by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims.

The high-temperature layer superconductor structure according to the invention consists of a carrier material, at least one buffer layer and a high-temperature superconductor layer, in which the buffer layer contains cerium oxides doped with cations.

Advantageously, the carrier material has a textured surface and is still advantageously a metal having a textured surface.

Also advantageously, the support material is Ni or Hastalloy + IBAD.

Also advantageously, only one buffer layer is realized.

It is also advantageous if the buffer layer contains CeO 2. It is furthermore advantageous if the buffer layers contain cations of calcium, magnesium, manganese, zinc, potassium, lanthanum, samarium and / or zirconium as doping.

And it is also advantageous if 2 to 49 mol% of cations of calcium, magnesium, manganese zinc, potassium and / or zirconium, lanthanum, samarium are included as doping.

In the method according to the invention for producing a high-temperature layer superconductor structure, at least one buffer layer containing cerium oxides and / or their precursor substances is applied to a carrier material, the cerium oxides or their precursor substances may already contain cations as dopants, and / or at least one layer of cation-containing doping elements applied on or between the buffer layer (s) and then after the temperature treatment, at 700 to 1000 ⁰ C in a reducing atmosphere, at least one high-temperature superconductor layer is applied.

Advantageously, as cerium, CeO 2, _Cei-x Ca _x θ2, _Cei-x Sm _x θ2, Ce2Zr ₂ + δ _{θ6> Cei-x} Zr _x O _{2, Cei-x} Nd _x O _{2, Cei-x} La _x O ₂ , _Cei-x Zn _x O _{2, Cei-x} Mn _x O _{2, Cei-x} Mg _x O _{2, Cei-x} K _x O _2, where x = 0.02 - 0.49 used.

Likewise advantageously used as precursor substances of the cerium oxides are cerium (III) acetate, cerium (III) nitrate, cerium (IV) nitrate, cerium (IV) ammonium nitrate, cerium (IV) isopropoxide.

Further advantageously, the precursors of the doping elements are calcium acetate, calcium acetylacetonate, calcium nitrate, calcium nitrides, calcium peroxides, calcium hydrides, zinc acetate, zinc acetylacetonate, zinc 2-ethylhexonate, zinc nitrate, samarium (IM) acetylacetonate, samarium (III) isopropoxide, neodymium acetylacetonate, neodymium (IM ) isopropoxide, neodymium (III) nitrate,

Lanthanum (IM) acetate, lanthanum (IM) acetylacetonate, zirconium (IM) acetylacetonate, zirconium acetate, potassium acetate, potassium acetylacetonate, potassium benzoates, potassium tert-butoxide, potassium cabonate, potassium ethoxide, potassium ethylhexanoate, potassium hydroxide, Magnesium acetate, magnesium acetylacetonate, manganese acetate, manganese acetylacetonate, manganese nitrate, manganese oxalate, used.

It is also advantageous if the buffer layer (s), the cation-containing dopant element layers and the high-temperature superconductor layers by MOD / CSD or sol-gel technologies, as solutions by dipping, spin coating, spin coating, pouring, knife coating, spraying, printing or by CVD or MOCVD or PLD or vapor deposition or sputtering.

It is also advantageous if a solution is prepared from precursor substances of the cerium oxides with a solvent and precursors of the cation-containing doping elements, this solution is applied to the substrate, dried and synthesized in a reducing atmosphere at 700 ⁰ C to 1000 ⁰ C, a buffer layer and subsequently a High-temperature superconducting layer is applied and subjected to a temperature treatment, being advantageously used as the solvent carboxylic acids and alkanols or mixtures thereof or short-chain organic acids, short-chain alcohols and acetylacetone or propionic acid, isopropanol or acetylacetone.

It is likewise advantageous if a very thin buffer layer of cerium oxides is applied to the carrier material, then a likewise very thin layer of cation-containing doping elements is applied and then a further buffer layer of cerium oxides can be applied, which in turn is followed by a layer of cation-containing doping elements can be applied, wherein advantageously after the layer of cation-containing doping elements either another layer of cerium oxides or at least one further layer of other buffer layer materials is applied.

It is also advantageous if at least one buffer layer of cerium oxides, which either contains cations as dopants or is applied to at least one layer of cation-containing doping elements, is applied to the substrate at least one layer below After cooling, at least one further buffer layer without cations is applied as doping and the composite is synthesized under an oxidizing atmosphere.

By means of the solution according to the invention, thinner (<250 nm) and reliable buffer layers between the support material and the high-temperature superconductor layer can be realized. It is also particularly advantageous that a sufficient barrier effect can be achieved here by a single buffer layer according to the invention.

The use of only one buffer layer (<250 nm) or lower layer thicknesses of several buffer layers using at least one buffer layer according to the invention on the carrier material improves the mechanical properties of the high-temperature layer superconductor structure according to the invention. In particular, for example, a smaller bending radius in bands from the high-temperature layer superconductor construction according to the invention becomes possible, and flaking of the buffer layer and / or the high-temperature superconductor layer can be reduced or avoided altogether. Likewise, crack-free buffer layers according to the invention can be produced.

By incorporating the cations according to the invention as dopants in a buffer layer containing cerium oxides, the barrier effect is ensured by partially replacing cerium in its lattice with a cation of the doping elements. This stabilizes oxygen vacancies and causes an increase in the binding energies within the cerium oxide lattice. It is likewise advantageous in the case of the high-temperature layer superconductor structure according to the invention that, in the case of production, a concentration gradient is achieved by using one or more layers with cation-containing doping elements, via the location of the layers in the layer structure of the entire buffer layer and via the thickness and the content of cations can be achieved in the synthesized buffer layer. This grading affects the lattice parameters of the cerium oxides and allows the possibility of minimizing lattice mismatch of the various materials. In this way stresses within the layers are reduced and heteroepitaxial growth of comparatively thick and crack-free cerium oxide layers possible.

A further advantage is that the doping of the cerium oxide buffer layer with cations, in particular with cations of calcium, has a positive effect on the grain boundaries of the high-temperature superconductor and thus the critical current carrying capacity of the high-temperature layer superconductor structure according to the invention is improved.

For example, YBCO can be used as the superconducting material for the high-temperature layer superconductor structure according to the invention.

In the inventive production of high-temperature layer superconductor structure according to the invention is also advantageous that can be dispensed in the case of production on the application of solutions to the use of toxic substances. Also, the stability of various solutions over several weeks is stable, with consistently good coating properties. This makes a large-scale process easier to handle, cheaper and safer.

Furthermore, the invention will be explained in more detail using an exemplary embodiment. Show

Fig. 1: XRD diagram of crystallized Cei-χCa _x θ ₂ buffer layers with x = 0.1

Fig. 2: Pole figures and results of the RHEED measurements on Cei _-x Ca _x θ2 buffer layers with x = 0.1 on a Ni5% W substrate

Example:

On a textured metal strip (Ni - 5% W) a Cei _-x Ca _x O _{2 is applied} as a buffer layer with x = 0.1.

ii) The coating is carried out on the textured nickel tape with the dimensions 10 x 10 x 0.08 mm ³ by means of a dipping apparatus. The sample is drawn from the coating solution at a speed of 0.2 cm / s at a 90 ° angle to the solution surface. After drying at 140 ^° C. in the course of 5 minutes under air, the sample is introduced into the oven preheated to 600 ^° C. under a reducing atmosphere (Ar / 5% H ₂ ) and, after reaching the temperature, a holding time of 0.5 h takes place. Thereafter, a temperature treatment includes at peak temperature (600 ° C / h to 1000 ⁰ C, holding time 1 h). The X-ray diffraction patterns (Figure 1), pole figure measurements, and RHEED measurements (Figure 2) show good texture. After coating with the high-temperature superconductor YBCO by TFA process, inductive measurements at 77 K allowed critical current densities of Jc = 1.5 * 10 ⁶ A * cm ^{2 to be} recorded.

Claims

claims 1. High-temperature layer superconductor structure, consisting of a support material, at least one buffer layer and a high-temperature superconductor layer, wherein the buffer layer contains cerium oxides, which is doped with cations. 2. High-temperature layer superconductor structure according to claim 1, wherein the carrier material has a textured surface. 3. A high temperature layered superconductor structure according to claim 2, wherein the support material is a metal having a textured surface. 4. High-temperature layer superconductor structure according to claim 1, wherein the support material is Ni or Hastalloy + IBAD. 5. High-temperature layer superconductor structure according to claim 1, wherein only one buffer layer is realized. 6. High-temperature layer superconductor structure according to claim 1, wherein the buffer layer contains Ceθ2. 7. High-temperature layer superconductor structure according to claim 1, wherein the buffer layers contain cations of calcium, magnesium, manganese, zinc, potassium, lanthanum, samarium and / or the zirconium, as doping. 8. high-temperature layer superconductor structure according to claim 1, wherein 2 to 49 mol% of cations of calcium, magnesium, manganese zinc, potassium and / or zirconium, lanthanum, samarium are included as doping. 9. A method for producing a high-temperature layer superconductor structure according to at least one of claims 1 to 8, wherein at least one buffer layer is applied to a carrier material containing cerium oxides and / or their precursor substances, wherein the cerium oxides or their precursor substances may already contain cations as dopants . and / or at least one layer of cation-containing doping elements applied to or between the buffer layer (s) and then after the temperature treatment, at 700 to 1000 ⁰ C in a reducing atmosphere, at least one high-temperature superconductor layer is applied. 10. The method of claim 9, wherein as cerium oxides, CeO ₂ , Cei _-x CaχO ₂ , Cei. Xsm _x O _2, Ce ₂ Zr ₂ O _{6 + 5, Cei-x} Zr _x O _{2, Cei-x} Nd _x O _{2, Cei-x} La _x O _{2, Cei-x} Zn _x O _{2, Cei-x} Mn _x O _{2, Cei-x} Mg _x O _{2, Cei-x} K _x O _2, where x = 0.02 - 0.49 are used. 11.A method according to claim 9, in which are used as precursor substances of cerium cerium (III) acetate, cerium (III) nitrate, cerium (IV) nitrate, cerium (IV) ammonium nitrate, cerium (IV) - isopropoxide. 12. The method of claim 9, wherein as precursors of the doping elements calcium acetate, calcium acetylacetonate, calcium nitrate, calcium nitrides, calcium peroxides, calcium hydrides, zinc acetate, Zinkacethylacetonat, zinc 2-ethylhexonat, zinc nitrate, Samarium (IM) acetylacetonate, samarium (Ml) - isopropoxide, Neodymium acetylacetonate, neodymium (IM) isopropoxide, neodymium (III) nitrate, lanthanum (IM) acetate, lanthanum (IM) acetylacetonate, zirconium (IM) acetylacetonate, zirconium acetate, potassium acetate, potassium acetylacetonate, potassium benzoates, potassium tert-butoxide, potassium cabonate , Potassium ethoxide, potassium ethylhexanoate, potassium hydroxide, magnesium acetate, magnesium acetylacetonate, manganese acetate, manganese acetylacetonate, manganese nitrate, manganese oxalate, are used. 13. The method of claim 9, wherein the buffer layer (s), the cation-containing dopant element layers and the high-temperature superconductor layers by MOD / CSD or sol-gel technologies, as solutions by dipping, spin-coating, spin-coating, pouring, knife coating, Spraying, printing or by CVD or MOCVD or PLD process or vapor deposition or by sputtering applied. 14. The method of claim 9, wherein from precursor substances of the cerium oxides with a solvent and precursors of the cation-containing Doping a solution is prepared, this solution applied to the substrate, dried and synthesized in a reducing atmosphere at 700 ⁰ C to 1000 ⁰ C, a buffer layer and then applied a high temperature superconducting layer and subjected to a temperature treatment. 15. The method of claim 14, wherein as the solvent carboxylic acids and alkanols or mixtures thereof are used. 16. The method of claim 14, wherein the solvent used are short-chain organic acids, short-chain alcohols and acetylacetone. 17. The method of claim 14, wherein the solvent used are propionic acid, isopropanol or acetylacetone. 18. The method of claim 9, wherein a very thin buffer layer of cerium oxides is applied to the carrier material, subsequently a likewise very thin layer of cation-containing doping elements is applied and then a further buffer layer of cerium oxides can be applied, which in turn of a layer of cation-containing Doping elements can be followed. 19. The method according to claim 18, wherein after the layer of cation-containing doping elements, either a further layer of cerium oxides or at least one further layer of other buffer layer materials is applied. 20. Method according to claim 9, wherein at least one buffer layer of cerium oxides, which either contains cations as dopants or on which at least one layer of cation-containing doping elements is applied, is subjected to at least one layer under reducing atmosphere of a temperature treatment, after cooling, at least one further buffer layer without Cations is applied as dopants and the layer composite is synthesized under an oxidizing atmosphere.