WO2011029976A2

WO2011029976A2 - Superconducting strips formed from metalorganic solutions that contain two transition metals

Info

Publication number: WO2011029976A2
Application number: PCT/ES2010/070577
Authority: WO
Inventors: Xavier Obradors Berenguer; Teresa Puig Molina; Susana RICART MIRÓ; Alberto Pomar Barbeito; Anna Palau Masoliver; Fernando Javier MARTÍNEZ JULIÁN
Original assignee: Consejo Superior De Investigaciones Científicas (Csic)
Priority date: 2009-09-11
Filing date: 2010-09-02
Publication date: 2011-03-17
Also published as: WO2011029976A3; ES2355222B1; ES2355222A1

Abstract

The invention relates to a method for producing a superconducting material that comprises the deposition of a solution that comprises at least one rare-earth or yttrium salt, at least one alkaline-earth metal salt, at least one transition-metal salt and at least one Ag(I) salt. Furthermore, the invention relates to the superconducting material that can be produced by means of said method and, more preferably, a superconducting material of formula YBa₂Cu₃O_7.

Description

SUPERCONDUCTOR TAPES FORMED FROM

METALLORGANIC SOLUTIONS CONTAINING TWO TRANSITIONAL METALS The present invention relates to obtaining a new solution of metalorganic precursors using as a starting point the solution previously described in patent ES2259919 B1. This modification allows to obtain improvements in the heat treatment of the superconducting layers, such as absence of defects (cracks and folding) and the possibility of working at different final growth temperatures (from 720 to 810 ° C). This also allows controlling the tensions in the final layer and consequently modulating their properties. The use of the modified solution in the present invention also allows obtaining extremely flat superconducting layers with steps of the order of the YBCO unit cell.

STATE OF THE PREVIOUS TECHNIQUE

High temperature superconducting materials have great potential to be used in very diverse technologies but for this it is an indispensable requirement to develop methodologies for obtaining conductors with high performance, in particular that they can transport high electrical currents without losses, even under high magnetic fields . The first high temperature drivers that were developed were based on phases type BiSrCaCuO and these were called conductors 1 generation (1 G). The development of these materials was deeply revolutionized with the discovery of a new methodology for the preparation of a second generation (2G) of conductors, based on REBa ₂ Cu ₃ 0 ₇ type materials (REBCO, where RE = Rare Earth or Yttrium), called epitaxial superconductive conductors (CSE or "coated conductors"). In recent years, various methodologies for obtaining CSEs have been developed based on various multilayer architectures with high potential for high field, high temperature and high current applications. Several strategies have been followed for the preparation of these 2G conductors based primarily on vacuum deposition methodologies of epitaxial layers on metal substrates. These substrates can have either a textured oxide template deposited by Ion Beam Deposition (IBAD) on a polycrystalline substrate or they can be composed of textured buffer layers that replicate the texture achieved in the substrates via Rolling Assisted Biaxial Texturing (RABiTs) obtained by means of thermomechanical processes Other interesting approaches are also those where the textured buffer layer is achieved by Epitaxial Surface Oxidation (Surface Oxidation Epitaxy, SOE) or by inclined evaporation (Inclined Surface Deposition, ISD).

Once these textured substrates have been obtained, the deposition of epitaxial oxides in the form of multilayer that act as a buffer for atomic diffusion and oxidation of the REBCO superconducting layer which carries the electric current is carried out. Vacuum deposition techniques (evaporation, laser ablation, sputtering) or deposition techniques based on metallurgical chemical solutions (CSD) can be used to prepare such multilayer structures. These second ones are particularly interesting due to their possibilities to develop CSE with a low cost.

The demonstration of the possibility of using trifluoroacetate (TFA) precursors to grow the YBCO superconductor has been widely described as a very important step forward (A. Gupta, R. Jagannathan, E. I. Cooper, EA Giess, J. I. Landman, BW Hussey, "Superconducting oxide films with high transition temperature prepared from metal trifluoroacetate precursors" Appl. Phys. Lett. 52, 1988, 2077; PC Mclntyre, MJ Cima, and MF Ng, "Metalorganic deposition of high-J Ba YCu O thin films from trifluoroacetate precursors onto (100) SrTiO" J. Appl. Phys. 68, 1990, 4183). These precursors have BaF2, Y203 and CuO as final products after the decomposition of the metalorganic precursors, a process also called pyrolysis by those skilled in the art, and thus avoid the formation of BaCO3, which allows thin films to grow of YBCO at lower temperatures. Recently, a new methodology for obtaining anhydrous TFA precursors that allow obtaining high quality sheets has been described, while reducing the time required for processing the sheets and increasing the stability of the precursor solution ( X. Obradors, T. Puig, S. Ricart, N. Romá, JM Moretó, A. Pomar, K. Zalamova, J. Gázquez and F. Sandiumenge, "Preparation of anhydrous metalorganic precursors and use for deposition and growth of layers and superconducting tapes "2005, patent ES2259919 B1; N. Roma, S. Morlens, S. Ricart, K. Zalamova, JM Moreto, A. Pomar, T. Puig and X Obradors," Acid anhydrides: a simple route to highly puree organometallic solutions for superconducting films "Supercond. Sci. Technol. 2006, 19, 521-527). These precursors have been widely used to obtain sheets and multilayers of high crystalline quality and good superconducting properties (X. Obradors, T. Puig, A. Pomar, F. Sandiumenge, N. Mestres, M. Coll, A. Cavallaro, Romá, J. Gázquez, JC González, O. Castaño, J. Gutiérrez, A. Palau, K. Zalamova, S. Morlens, A. Hassini, M. Gibert, S. Ricart, JM Moretó, S. Piñol, D. Isfort, J. Bock. "Progress towards all chemical superconducting YBCO coated conductors" Supercond. Sci. Technol. 2006, 19 S13-S26).

There are other metal-organic solutions that give rise to superconducting belts with good properties. They are usually solutions of yttrium, barium and copper trifluoroacetates in a 1: 2: 3 ratio in solutions with concentrations between 1, 5 and 2 M in methanol as solvent Specifically, it is possible to cite patents ES2259919 B1 of the same group to which the present invention belongs and US7326434 of the American Superconductor Corporation, the content of which is incorporated in the present application by reference.

DESCRIPTION OF THE INVENTION

The present invention provides a process for obtaining superconducting materials through the use of a new solution of metalorganic precursors comprising salts of Ag (1). The new process makes it possible to obtain higher quality superconducting materials easily. For example, improvements in the heat treatment of the superconducting layers are obtained, such as absence of defects (cracks and folding) and the possibility of working at different final growth temperatures (from 720 to 810 ° C). This also allows controlling the tensions in the final layer and consequently modulating their properties. The use of the modified solution in the present invention also allows obtaining extremely flat superconducting layers with steps of the order of the YBCO unit cell. The present invention is also useful for the preparation of superconducting tapes.

Therefore, in a first aspect the present invention relates to a process for obtaining a superconducting material (hereinafter method of the invention), which comprises the deposition of a solution comprising at least one salt of a rare earth or yttrium , at least one salt of an alkaline earth metal, at least one salt of a transition metal and at least one salt of Ag (1).

The invention shows that in the formation of layers of certain mixed oxides in the preparation of the superconducting material, such as YBCO compounds (YBa2Cu3O7 _-x ), the formation of defects and improved process conditions by adding salts of Ag (l) in the solutions of the precursors of said oxides. Said modified precursor solutions can be used to form the intermediate oxide and oxyfluoride layers with a high quality (absence of cracks and folds) and relatively thick (about 700 nm) under the same conditions previously used, as for example in the international application WO 2006/103303 A1. Through this procedure, an intermediate layer is also obtained that allows the final growth to form the superconducting oxide, such as YBCO

in a greater range of temperatures (720-810 ° C) resulting in good performance in critical currents throughout the range (Je of 2-4 106 A cm ^"2 ). Moreover, the final result on the surface of the surfaces is improved layers significantly increasing the planarity thereof with steps of the order of the unit cell of the mixed oxide formed.This allows, for example, the formation of multilayers of different compositions.

In a preferred embodiment of the process of the invention, the proportion of Ag (1) salt is between 0.5% and 25% by weight of the total solution. Preferably, the proportion of Ag (1) salt is between 1% and 15% by weight of the total solution. More preferably, the proportion of Ag (1) salt is between 1% and 10% by weight of the total solution, and even more preferably it is between 2.5% and 10%. Weight ratios of 5 to 10% give the best results in final properties of the layers.

The suitability lies mainly in the solubility of the silver salts in the medium. For example, useful Ag (l) salts may be selected from the list comprising trifluoroacetate, nitrate, acetylacetonate, benzoate, carboxylates, acetylacetonates, nitrates, amines, sulfocyanides, cyanides or salts complexed with polyaminocarboxylic acids (EDTA, EGTA, DTPA, etc.), polyimines or other complexers to use; and any of its combinations. Preferably, the Ag (1) salt is selected from the list comprising trifluoroacetate, nitrate, acetylacetonate and any combination thereof. Salts with higher solubility products in the desired medium are the most suitable because they can be easily solubilized and in greater concentration.

The materials with greater efficiency are obtained when the solution is anhydrous, anhydrous being understood as a water content of less than 1.0%. Larger contents of water lead to uneven layers.

In addition, in another preferred embodiment, the total metal ion concentration of the solution is between 0.1 and 4.0 M, preferably it is between 0.5 and 3.0 M, more preferably it is between 1.5 and 2.5 M, and even more preferably it is less than 2.0 M. The concentrations used condition the thickness of the final layer so that for layers of thicknesses of the order of 300-400 nm the total concentrations of metal ions must be of the order of 1 .5 to 1 .7M.

In another preferred embodiment of the process, the concentration of Ag (1) is between 0.01 and 1 M, preferably it is between 0.1 and 0.2 M.

In another preferred embodiment of the process of the invention, the solution comprises at least one solvent selected from acetic acid, acetone, acetonitrile, benzene, 1-butanol, 2-butanol, 2-butanone, pentanone, t-butyl alcohol, tetrachloride carbon, chlorobenzene, chloroform, cyclohexane, 1,2-dichloroethane, diethyl ether, diethylene glycol, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethyl ether, dimethyl formamide, dimethylsulfoxide, dioxane, ethanol, ethyl acetate, ethylene glycol , heptane, triamide, hexane, methanol, methyl t-butyl ether, dichloromethane, N- methyl-2-pyrrolidinone, N-methylpyrrolidine, nitromethane, pentane, petroleum ether, 1-propanol, 2-propanol, pyridine, tetrahydrofuran, toluene, triethylamine, o-xylene, m-xylene, p-xylene and any combination thereof . Preferably, the solution comprises at least one solvent that is selected from methanol, ethanol, isopropanol and any combination thereof, more preferably the solution comprises methanol. Methanol turns out to be the most suitable solvent due to its polarity (polarity index 6.6), which allows the dissolution of the suitable amounts of the metalorganic salts having a boiling point sufficiently low (65 ° C) so that the initial drying of the deposited solution be quick.

Another preferred embodiment of said method comprises at least one element that is selected from Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu and any combination thereof. Preferably it comprises a salt that is selected from salts of Y, Gd, Eu, Dy and any combination thereof.

In another preferred embodiment of the process, the rare earth or yttrium salt is selected from trifluoroacetate, acetate, acetylacetonate, naphthenates, trifluoroacetylacetonate, ethylhexanoate; nitrates, complex salts such as amine, cyanide, sulfocyanide, polyaminocarboxylates, polyimines or other complexing agents; and any of its combinations.

Preferably trifluoroacetate is used. Trifluoroacetates are soluble in the solvent usually used (methanol) and are also necessary in the pyrolysis process for the generation of barium fluoride.

In another preferred embodiment of the process, the alkaline earth metal is selected from Ba, Sr, Ca and any combination thereof. Preferably, the alkaline earth metal is Ba. In another preferred embodiment of said process, the alkaline earth metal salt is selected from trifluoroacetate, acetate, acetylacetonate, naphthenates, trifluoroacetylacetonate, ethylhexanoate, nitrates, amine complexed salts, cyanide, sulfocyanide, polyaminocarboxylates, polyimines or other complexers to use; and any of its combinations, preferably trifluoroacetate.

In another preferred embodiment of the process, the transition metal is Cu.

In another preferred embodiment of the process, the Cu salt is selected from trifluoroacetate, acetate, acetylacetonate, naphthenates, trifluoroacetylacetonate, ethylhexanoate; nitrates, complex salts such as amine, cyanide, sulfocyanide, polyaminocarboxylates, polyimines or other complexing agents; and any of its combinations, preferably trifluoroacetate.

Another preferred embodiment of the process comprises the decomposition of the deposited product. Preferably, the decomposition takes place between 100 and 500 ° C, and more preferably between 250 and 400 ° C. The usual decomposition temperatures of metalorganic salts usually range between these two values. Particularly the yttrium, barium and copper trifluoroacetates used in the process have a combined decomposition temperature, controlled by thermogravimetric analysis (weight loss measurement by heat treatment) that starts at 250 ° C and ends at 320 ° C.

In another preferred embodiment of the process, the decomposition is carried out in a controlled atmosphere of oxygen, nitrogen or any combination thereof at a pressure of 1 bar, using a controlled gas flow with a velocity between 0.80 and 24 mm / s, at the same time as a temperature rise from 250 ° C to a temperature between 300 and 350 ° C, with a heating ramp between 30 and 600 ° C / h, remaining at this temperature for a period of time between 10 and 90 min.

Another preferred embodiment of the process comprises the crystalline growth of the deposited product.

In another preferred embodiment of the process, the crystalline growth takes place at a temperature between 400 and 1000 ° C, preferably between 600 and 900 ° C, and more preferably between 700 and 820 ° C.

An advantage of the process of the following invention is the improvement in the result of the pyrolysis, which is much less dependent on the environmental conditions, also giving pyrolized layers with few defects, which will facilitate multideposition and consequently, the obtaining of final layers thicker.

In another preferred embodiment of the process, the crystalline growth is carried out in an oven in a controlled atmosphere and comprises: a first heating which is carried out in an atmosphere comprising nitrogen, with a water vapor pressure between 7 and 100 mbar and an oxygen pressure between 0.1 and 1 mbar, up to a temperature between 700 and 820 ° C; and a second heating at a temperature between 300 and 500 ° C at an oxygen pressure of 1 bar for a period of time less than 8 h, followed by cooling to room temperature.

For example, it has been proven that for the growth of the YBCO thin film the use of the conditions previously described (atmosphere of N ₂ with 200 ppm of 02 and ramps of 25 ° C / min up to temperatures of the order of 810 ° C typically) , layers are obtained superconductors with good properties and high planarity (Figure 2 and 4). It is also found that the use of the process of the present invention allows to expand the range of maximum growth temperatures, allowing to obtain layers with good performance at much lower temperatures (from 720 ° C to 810 ° C, Figure 3) which decreases the problem of its reactivity with the buffer sheets and the degradation of the metal substrates.

In another preferred embodiment of the process, the superconducting material has a composition AA ' ₂ Cu307 + _x , where A is a rare earth or Y, A' is an alkaline earth metal and x is between -1 and 0.

Preferably, A is selected from Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu and any combination thereof. And more preferably, A is Y.

Preferably, A 'is selected from Ba, Sr, Ca and any of its combinations. And more preferably, A 'is Ba.

In another preferred embodiment of the process, the superconducting material has a formula YBa ₂ Cu ₃ 0 ₇ .

In another preferred embodiment of the process, the solution further comprises at least one salt that is selected from various salts of Zr, Ce, Sn, Ru, La, Mn, Sr, Ca and any combination thereof. These salts form a secondary phase distributed randomly within the matrix so that the structure of the superconductor is profoundly modified, improving its characteristics. These phases can be BaZr0 ₃ , Ce0 ₂ , BaSn0 ₃ , BaCe0 ₃ , SrRu0 ₃ , Lai- _x M _x Mn0 ₃ , Re ₂ 0 ₃ , or Re ₂ Cu ₂ 0 ₅ , where Re is a rare earth or Y. salts that are capable of forming this secondary phase are described in WO / 2008/071829, which is incorporated in its entirety by reference. In another preferred embodiment of the process, the material that is deposited has a composition (Lai-yZy) 2Cu04 _-z , where Z is an alkaline earth, and is a number between 0 and 0.2 and z is a number between 0 and 1. In another preferred embodiment of the process, the solution is deposited on a monocrystalline or biaxial textured substrate. The substrates are usually very diverse oxides (LaAI03, SrTi03, NdTi03, AI2O3), being essential that they have a good crystallographic orientation, that is, little deviation in the orientation of the crystals inside and outside the plane of the layer (monocrystals or textured materials biaxial). Said substrates may be previously coated by YSZ oxide barrier layers (yttrium stabilized zirconia), (Ce, M) 0 _2-x (M = Rare Earth), AT1O3 (A = Ca, Sr, Ba), TR ₂ 0 ₃ (TR = Rare Earth), AB1O3 (A = Ca, Sr, Ba), MgO, Al ₂ 03, TiN (titanium nitride) and combinations thereof.

Preferably, said substrate is selected from: a salt or oxide of a rare earth; a salt or oxide of an alkaline earth metal; a salt or oxide of a transition metal; and any of its combinations. More preferably, the substrate is selected from the list comprising single crystals of SrTi03, LaAI03, YSZ and biaxially textured metal tapes. And even more preferably, said substrates may be previously coated by layers of YSZ (yttrium stabilized zirconia), (Ce, M) 0 _2-x (M = Rare Earth), AT0 ₃ (A = Ca, Sr, Ba ), TR ₂ 0 ₃ (TR = Rare Earth), AB1O3 (A = Ca, Sr, Ba), MgO, AI ₂ O ₃ , TiN (titanium nitride) and any combination thereof. The substrates can be single layer or multilayer.

In a particular embodiment of the present invention the precursor solutions are used for obtaining superconducting layers of YBCO. This solution is deposited on monocrystalline LaAIO ₃ or on metal tape protected by some type of buffer layer. The heat treatments to which they undergo consist of a calcination up to 350 ° C in a reduced time, such as 1.5 h, for obtaining intermediate oxides and oxyfluorides. The pyrolized layers thus obtained have the characteristic of being free of cracks and presenting much less folding than those achieved using the unmodified solution due to the lower sensitivity of the present solution to environmental conditions. On the other hand, the SEM image shows that they have a lower porosity in the structure (Figure 2). The presence of the second transition metal (Ag) in the solution competing with copper could decrease its cross-coordination with oxygen or fluorine molecules and, consequently, decrease the presence of defects that in some cases have been attributed to excessive coordination cross of copper.

In another embodiment of the present invention with respect to the preparation of the anhydrous solution of yttrium, barium and copper trifluoroacetates prepared according to the procedure described in the invention of international patent application WO 2006/103303 A1, the modification consisting of the addition is introduced in variable amounts as described in the preferred embodiments already mentioned (from 2.5% to 20% by weight) of silver salts (trifluoroacetates, nitrates, acetylacetonates, etc.) preferably soluble in the medium. This results in homogeneous solutions of metalorganic salts consisting of salts from a rare earth, an alkaline earth metal and at least two transition metals with a global concentration expressed as a sum of metals of up to 2 M.

Therefore, in a second aspect the present invention relates to the superconducting material that is obtained by the process of the invention (hereinafter material of the invention). In addition, in a third aspect the present invention relates to multilayer epitaxial superconducting conductors and ceramic wafers coated with superconducting layers comprising the material of the invention.

In a fourth aspect the present invention relates to the solution (hereinafter solution of the invention) comprising at least one salt of a rare earth or yttrium, at least one salt of an alkaline earth metal, at least one salt of a metal of transition and at least one salt of Ag (l).

In a fifth aspect the present invention relates to the use of the solution of the invention for obtaining a superconducting material.

And in a final aspect the present invention relates to the superconducting material of the formula YBa ₂ Cu ₃ 0 _7. , which has a roughness of between 0.5 and 3.0 nm rms. Said roughness is obtained by obtaining the topography of the layer by microscopy of atomic forces on a square surface not less than 5 microns per side and calculating the average deviation of the heights on said surface from an average value by the method of the Least Squares. Preferably, said superconducting material has a critical current density greater than 1 MA / cm ² and, more preferably, between 1 and 4 MA / cm ² at 77 K and autofield). Said critical current density is obtained from the magnetization curves with respect to the magnetic field at a temperature of 77 K and applying magnetic field penetration models in the superconducting sample known to those skilled in the art, such as the model of Bean

The sheets of superconducting material with high performance provided by the present invention are of particular relevance for example in the following sectors: - Chemical sector: soluble complex metalorganic chemical precursors.

- Ceramic-metallurgical sector: deposition and growth of ceramic coatings on metal or ceramic substrates.

- Energy, electromechanical and transport sector: improvement of the efficiency of the existing electrical system for the generation, transport, distribution and use of electrical energy, development of new power electrical equipment, powerful magnets for various applications (including nuclear fusion) , powerful and light electric motors for aeronautics or nautical.

- Biomedicine and pharmaceutical sector: new equipment, more powerful and capable of operating at higher temperatures, magnetic resonance imaging, new NMR spectrometers for molecular design.

- Electronic sector: new devices, passive or active, that work in the microwave range and are of interest in the field of telecommunications.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention.

DESCRIPTION OF THE FIGURES

FIG. 1.- Optical microscopy images of the layers after pyrolysis from the modified solution a) on monocrystalline LaAI0 ₃ ; b) on textured metal tape. FIG. 2.- SEM image of a YBCO layer grown from the modified solution in which a considerable decrease in porosity and high surface planarity can be seen. FIG. 3. Comparison of the current densities at different temperatures between the unmodified and the modified solution according to the present invention.

FIG. 4.- Measurement of AFM that shows the high planarity of a layer of YBCO grown from the modified solution. It is seen in the lower profile that steps corresponding to the YBCO unit cell are achieved.

EXAMPLES

The invention will now be illustrated by tests carried out by the inventors, which demonstrates the specificity and effectiveness of superconducting belts formed from metal-organic solutions containing two transition metals.

Example 1

A solution of 50 ml of Y, Ba and Cu trifluoroacetates was prepared with a total metal concentration of 1.5 M (Y: Ba: Cu ratio of 1: 2: 3). For this, 8.334 g (0.0125 mol) of commercial YBa2Cu ₃ 0 ₇ were weighed in a 250 ml spherical flask, coupled to a Dimroth refrigerant and provided with magnetic stirring. In addition, 25 ml of freshly distilled dry acetone, 22 ml of trifluoroacetic anhydride (0.000156 mol) (slow addition to avoid overheating) and 5 ml of trifluoroacetic acid were added. The mixture was heated at 50 ° C for 72 h under an inert atmosphere (Ar). It was then cooled to room temperature and filtered at

REPLACEMENT SHEET (Rule 26) through a 0.45 μηι filter. The resulting solution was then evaporated under reduced pressure using a rotary evaporator, first at room temperature (2 h) and then progressively heating to 80 ° C, obtaining the trifluoroacetates of Y, Ba and Cu. A part of the solid obtained was dissolved in acetone and another in methanol, both solutions being kept in closed vials and in an inert atmosphere.

This solution was deposited by the spin coating technique on a square monocrystalline substrate of SrTi03 of dimensions 5 mm * 5 mm, thickness 0.5 mm and orientation (100). Then the pyrolysis was performed, consisting of the decomposition of organic matter. For this, an alumina crucible was used, where the substrate that was placed in a 23 mm diameter quartz tube was placed, which was placed inside an oven. The program followed by the oven consists of a ramp of 300 ° C / h up to a maximum temperature of 310 ° C, which was maintained for 30 min. The use of a controlled atmosphere inside the furnace is needed, for this purpose an oxygen pressure of 1 bar, a flow of 0.05 l / min and a water pressure of 24 mbar were worked on. Said humidity is achieved by passing the gas through some washing jars provided with a porous plate in its inner lower part, to divide the gas into small drops, thus increasing the surface of contact with the water. At the end of the process, the sample was stored in a desiccator.

The heat treatment was carried out from the pyrolized layer to achieve the formation of the YBa ₂ Cu ₃ 0 ₇ phase. It worked with an oven, which was applied a rapid rise in temperature (25 ° C / min) until reaching temperatures in the range 790-815 ° C. This temperature was maintained for 180 min (the last 30 min dry) and then a ramp was applied at a speed of 2.5 ° C / min to room temperature. In this case 0.2 mbar of 0 ₂ and 7 mbar of water pressure was used. The gas flow was what allows the mass flow controller used (Bronkhorst High-Tech) to mix with a range of 0.012 to 0.6 l / min for N ₂ and between 0.006 and 0.03 l / min for 02.

Without removing the sample from the oven, oxygenation of said sample was performed using the same dry atmosphere. It was raised to 450 ° C, the carrier gas was changed to dry O ₂ at 1 bar pressure and maintained at this temperature for a time of 90 min. Then a ramp was made at 300 ° C / h to room temperature. The resulting layer is approximately 300 nm thick.

The sample was characterized by X-ray diffraction, SEM images, and measurements of the critical current at 77 K (Je = 3.5 ^■ 10 ⁶ A cm2). As reference values, the dependence of the critical current was characterized as a function of the magnetic field applied perpendicular to the substrate at 65 K. It was found that Je = 0.45-10 ⁶ A / cm2 at 65 K and H = 1 T.

Example 2 In a vial with septum cap, 27.6 mg of Ag (TFA) (12.5 ^■ 10 ^{~ 5} mol) was weighed and 10 ml of the methanolic YBCO solution prepared as in Example 1 was added thereto, the mixture was stirred at room temperature and filtered through a 0.45 μηπ filter. The mixture thus prepared was preserved under Ar.

ICP analyzes were performed in order to verify that the initial stoichiometric ratio had changed to contain the expected excess% (5%) of silver salt. From this solution trifluoroacetates of Y, Ba and Cu, which contained 5% of Ag salt, were deposited on a LaAIO3 substrate in the same conditions as indicated in Example 1. The deposited sample was decomposed following a pyrolysis process as described in Example 1. The sample thus pyrolized was characterized by optical microscopy to verify that it is homogeneous and free of cracks and roughness (Figure 1).

From the pyrolized sample, the heat treatment described in Example 1 was carried out but within a higher temperature range, between 700 and 810 ° C to achieve the formation of the YBa ₂ Cu ₃ 0 ₇ phase. The resulting layer is 300 nm thick. The sample was characterized by scanning electron microscopy (Figure 2) and by X-ray diffraction.

Claims

one . A method for obtaining a superconducting material, comprising the deposition of a solution comprising at least one salt of a rare earth or yttrium, at least one salt of an alkaline earth metal, at least one salt of a transition metal and at minus one salt of Ag (l).

2. The process according to the preceding claim, characterized in that the proportion of Ag (1) salt is between 0.5% and 25% by weight of the total solution.

3. The process according to the preceding claim, characterized in that the proportion of Ag (1) salt is between 1% and 15% by weight of the total solution.

4. The process according to the preceding claim, characterized in that the proportion of Ag (1) salt is between 1% and 10% by weight of the total solution.

5. The method according to any of the preceding claims, wherein the salt of Ag (1) is selected from the list comprising trifluoroacetate, nitrate, acetylacetonate, benzoate, carboxylates, acetylacetonates, nitrates, amines, sulfocyanides, cyanides or salts complexed with acids polyaminocarboxylic, polyimines or other complexers to use; and any of its combinations.

6. The method according to the preceding claim, wherein the Ag (1) salt is selected from the list comprising trifluoroacetate, nitrate, acetylacetonate and any combination thereof.

7. The method according to any of the preceding claims, characterized in that the water content of the solution is less than 1.0%. 8. The method according to the preceding claim, characterized in that the total metal ion concentration of the solution is between 0.1 and 4.0 M.

9. The method according to any of the preceding claims, characterized in that the concentration of Ag (1) is between 0.01 and 1 M.

10. The process according to any of the preceding claims, characterized in that the solution comprises at least one solvent selected from acetic acid, acetone, acetonitrile, benzene, 1-butanol, 2-butanol, 2-butanone, pentanone, t-alcohol butyl, carbon tetrachloride, chlorobenzene, chloroform, cyclohexane, 1, 2- dichloroethane, diethyl ether, diethylene glycol, diethylene glycol dimethyl ether, 1, 2- dimethoxyethane, dimethyl ether, dimethylformamide, dimethylsulfoxide, dioxane, ethanol, ethyl acetate, ethylene glycol, glycerin, heptane, triamide, hexane, methanol, methyl t-butyl ether, dichloromethane, N-methyl-2-pyrrolidinone, N-methylpyrrolidine, nitromethane, pentane, petroleum ether, 1-propanol, 2-propanol, pyridine, tetrahydrofuran , toluene, triethylamine, o-xylene, m-xylene, p-xylene and any combination thereof. eleven . The process according to the preceding claim, characterized in that the solution comprises at least one solvent selected from methanol, ethanol, isopropanol and any combination thereof.

The method according to any of the preceding claims, characterized in that it comprises at least one element that is select between Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu and any of their combinations.

13. The method according to the preceding claim, characterized in that it comprises a salt that is selected from salts of Y, Gd, Eu, Dy and any combination thereof.

14. The method according to any of the two preceding claims, wherein the rare earth or yttrium salt is selected from trifluoroacetate, acetate, acetylacetonate, naphthenates, trifluoroacetylacetonate, ethylhexanoate; nitrates, complex salts such as amine, cyanide, sulfocyanide, polyaminocarboxylates, polyimines or other complexing agents; and any of its combinations. 15. The method according to any of the preceding claims, characterized in that the alkaline earth metal is selected from Ba, Sr, Ca and any combination thereof.

16. The method according to the preceding claim, wherein the alkaline earth metal is Ba.

17. The process according to any of the two preceding claims, wherein the salt of the alkaline earth metal is selected from trifluoroacetate, acetate, acetylacetonate, naphthenates, trifluoroacetylacetonate, ethylhexanoate; nitrates, complex salts such as amine, cyanide, sulfocyanide, polyaminocarboxylates, polyimines or other complexing agents; and any of its combinations.

18. The method according to any of the preceding claims, characterized in that the transition metal is Cu.

19. The process according to the preceding claim, wherein the Cu salt is selected from trifluoroacetate, acetate, acetylacetonate, naphthenates, trifluoroacetylacetonate, ethylhexanoate; nitrates, complex salts such as amine, cyanide, sulfocyanide, polyaminocarboxylates, polyimines or other complexing agents; and any of its combinations.

20. The method according to any of the preceding claims, characterized in that it comprises the decomposition of the deposited product.

twenty-one . The process according to the preceding claim, wherein the decomposition takes place between 100 and 500 ° C. 22. The process according to any of the two preceding claims, characterized in that the decomposition is carried out in a controlled atmosphere of oxygen, nitrogen or any combination thereof at a pressure of 1 bar, using a controlled gas flow with a velocity between 0.80 and 24 mm / s, while a temperature increase is made from 250 ° C to a temperature between 300 and 350 ° C, with a heating ramp between 30 and 600 ° C / h, remaining at this temperature for a period of time between 10 and 90 min. 23. The method according to any of the preceding claims, characterized in that it comprises the crystalline growth of the deposited product.

24. The process according to the preceding claim, wherein the crystalline growth takes place at a temperature between 400 and 1000 ° C.

25. The method according to any of the two preceding claims, characterized in that the crystalline growth is carried out in an oven in a controlled atmosphere and comprises: a first heating which is carried out in an atmosphere comprising nitrogen, with a vapor pressure of water between 7 and 100 mbar and an oxygen pressure between 0.1 and 1 mbar, up to a temperature between 700 and 820 ° C; and a second heating at a temperature between 300 and 500 ° C at an oxygen pressure of 1 bar for a period of time less than 8 h, followed by cooling to room temperature.

26. The method according to any of the preceding claims, characterized in that the superconducting material has a composition AA ' ₂ Cu30 _{7 + x} , where A is a rare earth or Y, A' is an alkaline earth and x is between -1 and 0.

27. The method according to any of the preceding claims, characterized in that A is selected from Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu and any combination thereof.

28. The method according to the preceding claim, wherein A is Y.

29. The method according to any of the three preceding claims, characterized in that A 'is selected from Ba, Sr, Ca and any of its combinations.

30. The method according to the preceding claim, wherein A 'is Ba.

31. The method according to any of the five preceding claims, characterized in that the superconducting material has a formula YBa ₂ Cu3Ü ₇ .

32. The method according to any of the six preceding claims, characterized in that the solution comprises a salt that is selected from various salts of Zr, Ce, Sn, Ru, La, Mn, Sr, Ca and any combination thereof.

33. The method according to any one of claims 1 to 17, characterized in that the material that is deposited has a composition (Lai-yZy) 2Cu04 _-z , where Z is an alkaline earth, and is a number between 0 and 0.2 and z is a number between 0 and 1.

34. The method according to any of the preceding claims, characterized in that the solution is deposited on a monocrystalline or biaxial textured substrate. 35. The method according to the preceding claim, characterized in that the substrate is selected from: a salt or oxide of a rare earth; a salt or oxide of an alkaline earth; a salt or oxide of a transition metal; and any of its combinations. 36. The method according to the preceding claim, characterized in that the substrate is selected from the list comprising single crystals of SrTi03, LaAI03, YSZ and biaxially textured metal tapes.

37. A superconducting material obtainable as described in any of the preceding claims.

38. A multilayer product comprising the material of the preceding claim.

39. A solution comprising at least one salt of a rare earth or yttrium, at least one salt of an alkaline earth metal, at least one salt of a transition metal and at least one salt of Ag (1). 40. Use of the solution according to any of the preceding claims for obtaining a superconducting material.

41. A superconducting material of formula YBa ₂ Cu307., Characterized by having a roughness of between 0.5 and 3.0 nm rms.

42. The superconducting material according to the preceding claim characterized by having a critical current density greater than 1 MA / cm ² .