WO2006103303A1

WO2006103303A1 - Preparation of anhydrous metal-organic precursors and use thereof for the deposition and growth of superconducting tapes and layers

Info

Publication number: WO2006103303A1
Application number: PCT/ES2005/070056
Authority: WO
Inventors: Xavier Obradors Berenguer; Teresa Puig Molina; Susagna Ricart; Neus Roma; Josep Maria MORETÓ; Alberto Pomar Barbeito; Katerina Zalamova; Stephanie Morlens; Jaume Gazquez Alabart; Felip Sandiumenge
Original assignee: Consejo Superior De Investigaciones Científicas
Priority date: 2005-04-01
Filing date: 2005-04-28
Publication date: 2006-10-05
Also published as: ES2259919B1; ES2259919A1

Abstract

The invention relates to a novel method of producing metal-organic precursors of oxides by reaction with anhydrides of said starting oxides. The inventive method has a very wide area of application and can be used to prepare all types of oxide films (ferroelectric, ferromagnetic, piezoelectric, etc.). The invention also relates to a method of producing anhydrous metal-organic YBCO precursors and to the use thereof in the production of layers of said superconducting material. Intermediate purification steps can be eliminated owing to the low water content of precursors prepared in accordance with the invention. Said novel precursors enable the pyrolysis time required for the decomposition thereof to be reduced, such that productivity in relation to the production of superconducting tapes and layers is significantly increased while the quality and performance thereof are maintained.

Description

TITLE

PREPARATION OF ANHYDING METALORGANIC PRECURSORS AND THEIR USE FOR THE DEPOSITION AND GROWTH OF LAYERS AND SUPERCONDUCTOR RIBBONS.

SECTOR OF THE TECHNIQUE

The present invention relates to a new method of producing metalorganic oxide precursors by means of anhydride attack of those same starting oxides. Its use is very general and valid for preparing oxide sheets of all types (ferroelectric, ferromagnetic, piezoelectric, etc.), although in the present invention it is applied to the manufacture of superconducting oxides.

The objects of the present invention are of special relevance in the following sectors:

Chemical Sector: Metalorganic precursors. - Ceramic-metallurgical sector: Deposition and growth of ceramic coatings on metal substrates.

Energy Sector: Improvement of the efficiency of existing electrical equipment and development of new power electrical equipment.

Biomedicine and Pharmaceutical Sector: New diagnostic equipment and new NMR spectrometers for molecular design.

STATE OF THE TECHNIQUE

Metal oxides are compounds of great interest due to their wide range of application ranging from superconductivity at high temperatures, ferromagnetism, piezoelectricity to semiconductivity. The preparation of them by a low cost method such as the deposition of chemical precursor solutions has led to a large number of them being studied for possible application in obtaining oxides. Depending on the final objective to be achieved, chemical precursors such as organometallic molecules (trifluoroacetate acetates, acetylacetonates, ethylhexanoates, alkoxides), metal salts (nitrates, iodides) and polymers. Mixed oxides can be obtained by mixing similar precursors in a common solvent before pyrolysis.

The preparation of superconducting oxides is a field of great interest due to the wide variety of applications thereof, ranging from diagnostic imaging in Medicine (Nuclear Magnetic Resonance) to its numerous applications in the Energy sector (eg magnets superconductors for energy storage).

There are two types of superconducting oxides, those based on Bismuth

(BÍ2Ca2Sr2Cu ₃ O ₁₀ ) and those of Ytrio (YBa ₂ Cu ₃ O ₇ ), however due to their better properties, from the point of view of stability and critical current density, even under a magnetic field, the latter are the They have aroused more interest.

Currently, work is already underway to obtain superconducting tapes called second generation which typically consist of a metallic substrate, one or several epitaxial thin sheets that chemically protect the substrate, and a thin superconductive epitaxial sheet of YBa ₂ Cu ₃ or ₇ (YBCO).

There are different methods for the preparation of superconductors based on Ytrium oxides, among them we can mention laser deposition (PLD), radiofrequency spraying, liquid phase epitaxy or electron beam evaporation. Among all of them, the deposition of thin sheets using chemical solutions has recently deserved special attention since it avoids the use of expensive vacuum techniques and allows the preparation of superconducting oxides with low cost.

The use as metalorganic precursors of the corresponding Ytrium, Copper and Barium acetates results in low-performance superconducting oxides, normally due to the formation of barium carbonate during pyrolysis. As an alternative, mostly metal trifluoroacetates have been used as starting products, mainly due to the simplicity of their preparation methods, however there are some published studies that start from other precursors such as halides or some fluorine-free precursors that they are normally pivalates of the corresponding metals. For the preparation of the precursor mixture, the commercial acetates are normally used which, in aqueous solution and in the presence of trifluoroacetic acid, generate the corresponding trifluoroacetates (T. Araki, K. Yamagiwa, I. Hirabayashi. US Pat. No. 6,586,042 ( 2003), "Method of preparing oxide superconductor with purified mixed metal trifluoroacetate"). Under these conditions the compounds formed require subsequent purifications in order to remove water (reaction solvent) and possible secondary products (acetic acid) to give rise to the mixture of metal trifluoroacetates with sufficient purity for, after pyrolysis and growth, give rise to superconducting material with good performance. Among the methods of preparation based on acetates we can also mention those used by Gupta et al. (A. Gupta, R. Jagannathan, EICooper, EAGiess, JILandman, BWHussey, "Superconducting oxide films with high transition temperature prepared from metal trifluoroacetate precursors" Appl. Phys. Let. 52, 1988, 2077) or the Mclntyre and Cima group (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).

Likewise, the YBCO thin film deposition methodology using TFA salts in the form of a chemical solution has been used by other authors on monocrystalline substrates (J. Smith, MJ. Cima, International Patent Classification HOlL 39/24, International Publication Number WO 98/58415, "Controlled Conversion Of Metal Oxyfluorides Into Superconducting Oxides") or on metal substrates with buffer sheets deposited by vacuum techniques.

An aspect of the use of said Technique that is also of great relevance, from the point of manufacture of large lengths of tapes, is to minimize the time required to perform pyrolysis, that is, the decomposition of metalorganic precursors. In a continuous manufacturing process this time will determine the productivity (meters per hour) of tape that can be achieved.

The precursors used to date require very long pyrolysis times if good superconductive performance is to be maintained. In order to reduce said pyrolysis time, other authors have used additives in the dissolution of trifluoroacetates that allow reducing said time, for example diethanolamine

(DEA) (JT Dawley, PG Clem, TJ. Boyle, LM Ottley, DL Overmyer, MP Siegal, "Rapid processing method for solution deposited YBa ₂ Cu ₃ O _7-S thin film", Physica C, 402, 2004, 143), These additives, however modify the properties that control crystallization and superconducting performance. It is therefore desirable to reduce the pyrolysis time without thereby introducing limitations in the performance of the manufactured superconductors.

DESCRIPTION OF THE INVENTION - Brief Description

An object of the present invention relates to the production of metalorganic oxide precursors by means of anhydride attack of those same starting oxides.

Another object of the present invention relates to the production of anhydrous metalorganic material consisting of Y, Ba and Cu trifluoroacetates from the attack with YBCO trifluoroacetic anhydride. Another object of the present invention relates to the materials obtained by the production processes of metalorganic precursors claimed therein.

Finally, another object of the present invention is to provide a new improved process for obtaining superconducting oxide sheets using deposition and decomposition of metal trifluoroacetates prepared under anhydrous conditions, according to the procedure claimed above.

To date, the preparation of metalorganic precursors for the production of oxides implies the realization of numerous intermediate purification processes that are necessary to achieve good performance. The use of anhydrous solutions avoids a large part of these intermediate steps, achieving very good results in the final oxides in a simplified way. The process for obtaining anhydrous metallurgical material from its oxides of the present invention comprises the following steps: a) dissolution of the oxide powder in: i) an anhydride corresponding to an organic acid capable of dissolving said oxide, ii) a small amount of the organic acid of point i) acting as a reaction catalyst and iii) acetone as a solvent, b) heating the mixture in atmosphere inert, c) filtration of the resulting suspension at room temperature, d) evaporation of the resulting mixture with a rotary evaporator under reduced pressure, e) redisolution of the solid residue thus obtained, and f) optionally, storage of the trifluoroacetates thus obtained in vials in inert atmosphere

In particular, step a) may consist of the powder dissolution of the oxide in trifluoroacetic anhydride ((CF3CO) 2O), a small amount of trifluoroacetic acid (CF3COOH) as the reaction catalyst and acetone as the solvent.

The use of anhydrous solutions for the preparation of metalorganic precursors for obtaining superconducting oxides avoids a large part of the intermediate purification processes currently required, giving rise to final oxides with very good performance (thicknesses of several hundreds of nanometers and current densities of 1 -5 MA / cm ² ) in a simplified way.

The properties of the sheets and tapes obtained with the new anhydrous metalorganic precursors are improved compared to the methods used previously because they have a higher purity, in particular the water content of the solution is practically nil (below the limit of detection using the Karl-Fischer method (lppm). On the other hand, a great practical advantage of the new methodology developed is that this level of purity is achieved directly, that is, without the need to carry out long and expensive purification processes of the solutions. An additional advantage of the new precursors obtained refers to the possibility of considerably reducing the time required in the process of decomposition of the deposited precursors, with respect to those They have been used before, while maintaining high layer quality. The advantage of such a reduction in the decomposition time is that it allows the production speed of superconducting tapes to be increased in continuous processes.

The method used to produce epitaxial superconducting sheets in monocrystalline ceramic substrates or metal tapes containing epitaxial buffer sheets allows to obtain critical current densities J ₀ to 4,000,000 A / cm ² at 77K in a null magnetic field.

- Detailed description An object of the present invention relates to the production of anhydrous metalorganic precursors from their oxides by means of anhydride attack of those same starting oxides. The flowchart of the processes to be followed for the synthesis of the precursor solution of a generic oxide is shown in Figure 1. These steps are as follows: a) dissolution of the oxide powder in: i) an anhydride corresponding to an organic acid capable of dissolving said oxide, ii) a small amount of the organic acid of point i) which acts as a catalyst for the reaction , and iii) acetone as solvent, b) heating the mixture in an inert atmosphere, c) filtration of the resulting suspension at room temperature, d) evaporation of the resulting mixture with a rotary evaporator under reduced pressure, e) redisolution of the solid residue thus obtained, and f) optionally, storage of the trifluoroacetates thus obtained in vials in an inert atmosphere. In particular, step a) may consist of the powder dissolution of the oxide in trifluoroacetic anhydride ((CF3CO) 2O), a small amount of trifluoroacetic acid (CF3COOH) as the reaction catalyst and acetone as the solvent.

There are different chemical precursors that can be used for the preparation of metallurgical solutions that can be deposited in the substrate for the subsequent growth of a crystalline phase. These precursors are those that are usually used in the so-called sol-gel or metallurgical decomposition methodologies.

In the first case these precursors are normally alkoxides, soluble in alcohols and sensitive to environmental humidity, therefore they must be handled throughout the process in an inert atmosphere. In the second case, carboxylates (acetates, hexanoates) or pentadionates (acetylacetones) soluble in different organic solvents and less sensitive to environmental humidity are used. Hybrid solutions with precursors belonging to both groups can also be used.

In the present invention, trifluoroacetates prepared under anhydrous conditions have been used using trifluoroacetic anhydride ((CF ₃ CO) 2θ) as the starting reagent instead of trifluoroacetic acid (CF ₃ COOH). The lower reactivity of the anhydrides necessitates the use of a small amount of trifluoroacetic acid (5% by volume) as the reaction catalyst. Although the use of anhydride and trifluoroacetic acid has been particularized in the embodiments of the present invention, in general any anhydride corresponding to another organic acid that dissolves the oxide powders can be used.

In a spherical flask provided with a Dimroth refrigerant and stirring, MM'O oxide powder, excess trifluoroacetic anhydride and trifuoroacetic acid (5% by volume) are introduced as catalyst, using acetone as solvent. The mixture is heated to a temperature between 45 ° C and 50 ⁰ C for a period of time between 50 and 80 hours under inert. The resulting suspension is then filtered and evaporated in a vacuum of between 0.6 and 2 mbar, heating to 75 ° C or 80 ⁰ C. The solid residue thus obtained is redissolved in acetone or methanol to the desired concentration. The resulting anhydrous M and M 'trifuoroacetate solution is stored in vials in an inert atmosphere.

These materials, with a low water content in the solution, prepared according to the procedure just described, constitute another object of the present invention. It is also the object of the present invention to use said materials for the deposition and growth of layers and bands of oxides, such as ferroelectric, ferromagnetic and piezoelectric oxides.

Another object of the present invention relates to the production of anhydrous metalorganic precursors consisting of trifluoroacetates of Y, Ba and Cu from

YBCO by way of attack with anhydride of that same starting oxide. The flowchart of the processes that must be followed for the synthesis of said precursor solution is shown in Figure 2. The steps are as follows: a) dissolution of YBCO powder in trifluoroacetic anhydride ((CF ₃ CO) 2θ), a small amount of trifluoroacetic acid (CF ₃ COOH) as reaction catalyst and acetone as solvent, b) heating of the mixture in an inert atmosphere, c) filtration of the resulting suspension at room temperature, d) evaporation of the resulting mixture with a rotary evaporator under reduced pressure, e) redisolution of the solid residue thus obtained, and f) optionally, storage of the trifluoroacetates thus obtained in vials in an inert atmosphere.

In the present invention, trifluoroacetates prepared under anhydrous conditions have been used using trifluoroacetic anhydride ((CF ₃ CO) 2θ) as the starting reagent instead of trifluoroacetic acid (CF ₃ COOH). The lower reactivity of the anhydrides necessitates the use of a small amount of trifluoroacetic acid (5% by volume) as the reaction catalyst. Although the use of anhydride and trifluoroacetic acid has been particularized in the embodiments of the present invention, in general any anhydride corresponding to another organic acid that dissolves YBCO powders can be used.

For the preparation of the chemical solution it is introduced into a spherical flask provided with a Dimroth refrigerant and magnetic stirring powder of YBCO oxide, excess trifluoroacetic anhydride and trifuoroacetic acid as catalyst, using acetone as solvent. 5% by volume of the catalyst substance gives results optimal, although this amount could be varied. The mixture is heated to a temperature between 45 ° C and 50 ⁰ C for a period of time between 50 and 80 hours under inert. Heating at 50 ⁰ C for 72 hours under argon provides optimum results. The resulting suspension is then filtered with 0.45 μm filters and evaporated in vacuo (0.6 to 2 mbar) by heating to a temperature range of 75 ° C to 80 ⁰ C. The solid residue thus obtained is redissolved in acetone or methanol until desired concentration The solution of anhydrous Ytrio, Barium and Copper trifuoroacetates is stored in vials in an inert atmosphere.

Such materials, prepared according to the procedure described above, which results in solutions with a very low water content (less than lppm), constitute another object of the present invention. It is also an object of the present invention to use these materials as anhydrous metalorganic precursors for the deposition and growth of superconducting layers and tapes.

Another object of the present invention is the process for obtaining superconducting material in the form of a layer characterized by the use of anhydrous chemical solutions type Trifluoroacetate described above, for the deposition of the superconducting sheet, which comprises the following steps.

Deposition of chemical solutions

The deposition of the solution in the metallic substrate can be carried out by any method that allows to control the thickness of the sheet obtained while allowing to obtain a homogeneous thickness. Preferred methods, for their simplicity, are

"spin coating" and "dip coating" in which parameters such as rotation speed and acceleration (spin coating) and travel speed must be controlled

(dip coating). The first method is better suited to tests on substrates of small dimensions while the second case is better suited to continuous tape manufacturing.

The concentration of the solutions can vary between 0.3 M and 1.5 M. The thickness of the sheet obtained must not exceed values of up to 600 nm, if you want to preserve the quality of the material. Pyrolysis

Once the precursor has been synthesized and deposited on the LaAlO ₃ substrate, the layer is pyrolyzed in an oven controlling the atmosphere. Ascent ramps can vary over a wide range, starting at 300 ° C / h and reaching up to 1,500 ° C / h between 5O ⁰ C and 25O ⁰ C and up to 600 ° C / h between 25O ⁰ C and a temperature between 300 ⁰ C and 350 ⁰ C. The maximum temperature is maintained between 10 and 60 minutes. The flow is pure O ₂ varying between 0.02 1 / min and 0.6 1 / min in a quartz tube 23mm in diameter, at a pressure of 1 bar and a pressure of H ₂ O of 24 mbar.

Heat treatment The heat treatment is carried out in an oven that controls the temperature, as well as the ramps for changes. The substrate must be kept inside a 23mm diameter quartz tube in a controlled atmosphere throughout the process. Normally a mixture of N ₂ and O ₂ gases is used, with a range of 0.012 to 0.6 1 / min for N ₂ and between 0.006 to 0.03 1 / min for O ₂ . This results in linear speeds between 0.80mm / s and 24mm / s. The maximum temperature at which the heat treatment is carried out can be varied over a wide range, usually between 750 ⁰ C and 820 ⁰ C, while the ramps Up and down can also be variable. The choice of the maximum temperature at which the heat treatment is carried out will basically determine two morphological characteristics of the thin sheets: the grain size of the oxide and its roughness. The total time the sample will remain at the maximum temperature will normally be 90 minutes, although it can be varied over a wider range. Optimized characteristics are obtained when the procedure described above is carried out in a temperature range between 250 ⁰ C and a temperature between 300 ⁰ C and 350 ⁰ C with a ramp between 30 ° C / h and 600 ° C / h and remaining finally at the maximum temperature for a time that can be between 10 minutes and 90 minutes.

This process is followed by another heat treatment at high temperature for the crystallization of the superconducting sheet that is carried out in an oven in a controlled atmosphere and comprising the following two phases. A first stage of heating carried out in an atmosphere formed mainly by nitrogen (with a water vapor pressure between 7 mbar and 100 mbar and an oxygen pressure between 0.1 mbar and 1 mbar) until a temperature between 750 ⁰ C and 820 ⁰ C and staying at this temperature between 30 and 120 minutes and a second heating stage at a temperature between 500 ⁰ C and 300 ⁰ C in an oxygen bar for a time less than about 8 hours finally followed by a cooling process to room temperature. Once the thermal process to which the samples are submitted has been described, the structure and morphological characteristics generated by the thin epitaxial sheets must be recorded. These determinations were made from X-ray diffraction diagrams, Scanning Electron Microscopy and Atomic Force Microscopy. The description of these analyzes to the deposits made on a single crystal of LaAlO ₃ , are described in the examples that are detailed below, although any metal tape conveniently protected with a layer of epitaxially grown oxide could also be used as a substrate.

DESCRIPTION OF THE FIGURES

Figure 1 - Flow chart illustrating the different stages of the synthesis process of anhydrous metalorganic precursors from a generic MM'O oxide via anhydride attack of that same starting oxide. Figure 2- Flow chart illustrating the different stages of the synthesis process of the YBCO precursor solution.

Figure 3- IR spectrum of the TFA precursor solution where the characteristic carboxylate band is observed around lóδOcm ^"1 .

Figure 4- Intensity of the carboxylate peak in the IR spectra as a function of the heat treatment time at 250 ⁰ C (figure 4b) and 300 ⁰ C (figure 4a).

Figure 5- Optical Microscopy images of pyrolized sheets in optimal conditions (figure 5a) and unacceptable conditions (with cracks (figure 5b) or with undulations (figure 5c)).

Figure 6- General scheme of the heat treatments used for pyrolysis. The temperature rise ramps, the isothermal treatment temperature and the time can be modified in the ranges indicated.

Figure 7- Image obtained by TEM of a thin sheet of YBCO on a substrate of LaAlO ₃ , after the pyrolysis process where nanometric particles can be seen. Figure 8- SEM images after optimal growth of a thin YBCO sheet on a LaAlO ₃ substrate. Figures 8a and 8b correspond to the same sample at different magnifications. In them you can see that there are few pores and the size of these is very small, resulting in a good critical current.

Figure 9- Graph of the critical current as a function of temperature for a YBCO sheet grown under optimal conditions.

Figure 10- X-ray diagram type Θ-2Θ in which the Bragg peaks (001) of the YBCO phase and (hOO) of the LaAlO ₃ substrate can be seen. EXAMPLES OF EMBODIMENT OF THE INVENTION

Example I

A solution of 50 mL of Y, Ba and Cu trifluroacetates was prepared with a concentration of 1.5M (Y: Ba: Cu ratio of 1: 2: 3). For this, 8.334 g (0.0125moles) of commercial YBa ₂ Cu ₃ O 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 mmol) (slow addition to avoid overheating) and 5 mL of trifluoroacetic acid were added. The mixture was heated at 50 ⁰ C for 72 hours in inert atmosphere (Ar). It was then cooled to room temperature and filtered through a 0.45 μm filter. He then proceeded to evaporating the resulting solution under reduced pressure using a rotary evaporator, first at room temperature (2 hours) and heating then progressively to 80 ⁰ C, obtaining the trifluoroacetates of Y, Ba and Cu (characterized by its IR spectrum ( Figure 3)). 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.

ICP analysis (1: 1.98: 2.97) was performed in both the ketone and methanolic solution in order to verify that the initial stoichiometric relationship had been maintained. An evaluation of the water content of the powder sample was also carried out and it was found that it was below the detection limits using the Karl-Fischer technique (below lppm). The IR spectrum of the mixture evidenced the existence of the bands at 1650-1720 cm ^"1 corresponding to the trifluoroacetates formed.

Example II

From the trifluoroacetates of Y, Ba and Cu, their deposition (14μl) was carried out on a LaAlO ₃ substrate (of dimensions 5mm * 5mm, thickness 0.5mm and orientation (100)) using the Spin-coating technique (6000rpm for 2.02 minutes). It is necessary to carry out the experiment in a controlled atmosphere room because a high humidity in the medium can deteriorate the fat solution. Then the pyrolysis was performed, consisting of the decomposition of organic matter. For this, an alumina crucible (where the substrate is placed) was used, which was placed in a 23mm diameter quartz tube, which was placed inside an oven. The program followed by the oven is the one described in figure 6 with a ramp of 300 ° C / h up to a maximum temperature of 309 ⁰ C, which was maintained for 30 minutes. The use of a controlled atmosphere inside the furnace is needed, for this purpose an oxygen pressure of 1 bar, a flow of 0.051 / 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 sheet obtained was characterized by Optical Microscopy (Figure 5a), where a homogeneous distribution can be seen, without cracks or roughness and by Transmission Electron Microscopy to confirm that the layer retains its homogeneity on a nanometric scale (Figure 7). A series of IR spectra obtained from treated sheets during different times and at two different temperatures were also made (Figure 4a and 4b). These experiments allowed confirming the total decomposition of organic matter (the disappearance of the carboxylate group). In this way it is possible to determine the minimum duration of the pyrolysis process of the layer.

In other cases, when the concentration of the solution of the trifluoroacetates of Y, Ba and Cu is increased, the samples show cracks due to the tensions generated (when the concentration increases, the resulting sheet has a greater thickness and that generates greater tensions giving place to crack formation (figure 5b)). When the precursor solution was not homogeneous, precipitates may appear, forming sheets showing different thicknesses and roughnesses (Figure 5c) that subsequently reduce their quality.

Example III From a pyrolized layer, heat treatment was performed to achieve the formation of the YBa ₂ Cu ₃ O ₇ phase. It worked with an oven, which was applied a rapid rise in temperature (25 ° C / min) until reaching 795 ° C. This temperature was maintained for 180 minutes (the last 30 minutes 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 O ₂ and 7 mbar of water pressure was used. The gas flow was the one that allows the mass flow controller used (Bronkhorst High-Tech) to mix with a range of 0.012 to 0.6 1 / min for N ₂ and between 0.006 and 0.03 1 / min for O ₂ . Without taking out the oven sample, 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 minutes. Then a ramp was made at 300 ° C / h to room temperature.

Sample characterization was performed using SEM images (Figure 8), critical current measurements at 5K (J _c = 3.3 * 10 ⁷ A / cm ² ) and 77K (J _c = 4.3 * 10 ⁶ A / cm ² ) (figure 9) and DRX analysis (figure 10).

Claims

1. Procedure for obtaining anhydrous metalorganic material from its oxides comprising the following steps: a) dissolution of the oxide powder in: i) an anhydride corresponding to an organic acid capable of dissolving said oxide, ii) a small amount of the organic acid of item i) acting as the reaction catalyst, and iii) acetone as solvent, b) heating the mixture in an inert atmosphere, c) filtration of the resulting suspension at room temperature, d) evaporation of the mixture resulting with a rotary evaporator under reduced pressure, e) redisolution of the solid residue thus obtained, and f) optionally, storage of the trifluoroacetates thus obtained in vials in an inert atmosphere.

2. Method for obtaining anhydrous metalorganic material according to claim 1 wherein step a) is carried out using trifluoroacetic anhydride ((CF ₃ CO) 2θ), a small amount of trifluoroacetic acid (CF ₃ COOH) as the reaction catalyst and acetone as solvent.

3. Method for obtaining anhydrous metalorganic material according to claims 1 and 2, characterized in that the amount of trifluoroacetic acid used as a catalyst in step a) is 5% by volume.

4. Method for obtaining anhydrous metalorganic material according to claims 1 to 3, characterized in that the dissolution of step a) is carried out in a flask coupled to a Dimroth refrigerant and provided with magnetic stirring.

5. Process for obtaining metallo anhydrous material according to claims 1 to 4 wherein step b) is conducted at a temperature between 45 ° C and 50 ⁰ C in an Ar atmosphere for 50-80 hours, 6. Method for obtaining anhydrous metalorganic material according to claims 1 to 5, characterized in that step d) is carried out at a temperature between 75 ° C and 85 ° C, and at a pressure between 0.

6 mbar and 2 mbar

7. Method for obtaining anhydrous metalorganic material according to claims 1 to 6, characterized in that the redisolution of step e) uses acetone as solvent.

8. Method for obtaining anhydrous metalorganic material according to claims 1 to 6, characterized in that the redisolution of step e) uses methanol as a solvent.

9.- Method of obtaining anhydrous metallurgical material consisting of Y, Ba and Cu trifluoroacetates from YBCO comprising the following steps: a) dissolution of YBCO powder in trifluoroacetic anhydride ((CF ₃ CO) 2θ), a small amount of trifluoroacetic acid (CF ₃ COOH) as reaction catalyst and acetone as solvent, b) heating the mixture in an inert atmosphere during c) filtration of the resulting suspension at room temperature, d) evaporation of the resulting mixture with an evaporator rotary under reduced pressure, and e) redisolution of the solid residue thus obtained.

10. Process for obtaining anhydrous metalorganic material according to claim 9 to which the storage of the trifluoroacetates obtained in vials in an inert atmosphere is added as a last step.

11. Method for obtaining anhydrous metalorganic material according to claims 9 and 10, characterized in that the amount of trifluoroacetic acid used as catalyst in step a) is 5% by volume.

12. Method for obtaining anhydrous metalorganic material according to claims 9 to 11, characterized in that the dissolution of step a) is carried out in a flask coupled to a Dimroth refrigerant and provided with magnetic stirring.

13.- A process for obtaining anhydrous material metallo according to claims 9 to 12 wherein step b) is conducted at a temperature between 45 ° C and 50 ⁰ C in an Ar atmosphere for 50-80 hours,

14. Method for obtaining anhydrous metalorganic material according to claims 9 to 13, characterized in that step d) is carried out at a temperature between 75 ° C and 85 ° C, and at a pressure between 0.6 mbar and 2 mbar

15. Process for obtaining anhydrous metalorganic material according to claims 9 to 14, characterized in that the redisolution of step e) uses acetone as solvent.

16. Process for obtaining anhydrous metalorganic material according to claims 9 to 15, characterized in that the redisolution of step e) uses methanol as a solvent.

17. Trifluoroacetate obtained according to the procedures of claims 1 to 9 characterized in that its water content is less than 1 pmm.

18. Trifluoroacetate obtained according to the procedures of claims 9 to 16 characterized in that it is a trifluoroacetate of Y and that its water content is less than 1 pmm.

19. Trifluoroacetate obtained according to the procedures of claims 9 to 16 characterized in that it is a Ba trifluoroacetate and that its water content is less than 1 pmm.

20. Trifluoroacetate obtained according to the procedures of claims 9 to 16 characterized in that it is a Cu trifluoroacetate and that its water content is less than 1 pmm.

21. Use of the trifluoroacetate of claim 17 as anhydrous metalorganic precursor for the deposition and growth of layers and ribbons of oxides.

22. Use of the trifluoroacetate of claims 18 to 20 as anhydrous metalorganic precursor for the deposition and growth of superconducting layers and tapes.

23.- Procedure for obtaining superconducting material in the form of a layer characterized by the use of anhydrous Trifluoroacetate chemical solutions of the claims 18 to 20 for the deposition of the superconducting sheet, and in that it comprises the following steps: a) cleaning of the surface of the substrate, b) deposition of the chemical solution by any method that allows obtaining a homogeneous thickness and controlling the thickness of the sheet obtained, in a controlled atmosphere with low humidity, c) rapid drying of the chemical solution of b), at temperatures below 250 ⁰ C using a temperature rise ramp between 300 ° C / h and 1,500 ° C / h in a oxygen flow at a pressure of 1 bar and a pressure of H ₂ O of 24mbar, and maintaining the maximum temperature between 10 and 60 minutes. d) decomposition of the metalorganic precursors by means of a heat treatment in a controlled atmosphere of oxygen, nitrogen or a mixture of both using a controlled gas flow corresponding to a linear velocity between 0.80 mm / s and 24 mm / s, while a temperature increase is made between 250 ⁰ C and a temperature between 300 ⁰ C and 350 ⁰ C with a ramp between 30 ° C / h and 600 ° C / h and finally remaining at the maximum temperature for a time that can be found between 10 minutes and 90 minutes, and e) high temperature heat treatment for the crystallization of the superconducting sheet which is carried out in an oven in a controlled atmosphere and comprising the following phases: i) a first stage of heating carried out in a formed atmosphere mainly by nitrogen (with a vapor pressure of water between 7 mbar and

100 mbar and an oxygen pressure between 0.1 mbar and 1 mbar) up to a temperature between 750 ⁰ C and 820 ⁰ C and remaining at this temperature between 30 and 120 minutes and ii) a second heating stage at a temperature between 500 ⁰ C and 300 ⁰ C in an oxygen bar for less than 8 hours, finally followed by a cooling process to room temperature.

24. Method for obtaining superconducting material in the form of a layer of claim 23, characterized in that the deposition of the chemical solution in step b) is carried out by "spin-coating".

25. Method for obtaining superconducting material in the form of a layer of claim 23, characterized in that the deposition of the chemical solution in step b) is carried out by dip-coating.