Tl-series superconducting thin film and preparation method thereof

Abstract

The invention provides a Tl-series superconducting thin film and a preparation method thereof, and belongs to the field of superconducting thin film materials. The preparation method of the Tl-series superconducting thin film provided by the invention comprises the following steps: mixing nitrate or acetate of metal, ethylenediaminetetraacetic acid, a water-soluble high-molecular polymer and water to obtain precursor sol; the metals are thallium, barium, calcium and copper; the molar ratio of thallium to barium to calcium to copper to ethylenediamine tetraacetic acid is (2-3): 2: 1: 2: (7-8); coating a substrate with the precursor sol to obtain a precursor film; and carrying out heat treatment on the precursor thin film in an oxygen atmosphere under a closed condition to obtain the Tl-series superconducting thin film. The Tl-series superconducting thin film obtained by the preparation method provided by the invention presents a Tl-2212 phase, no impurity phase is generated, and the critical transition temperature can reach 100K and is close to the Tl-2212 theoretical superconducting transition temperature.

Description

Technical Field

[0001] This invention relates to the field of superconducting thin film materials, and more particularly to a Tl-based superconducting thin film and its preparation method. Background Technology

[0002] Tl-based superconducting thin films, such as Tl2Ba2CaCu2O8 (Tl-2212), possess excellent electromagnetic properties, including a high critical transition temperature (Tc greater than 105K), high critical current density, and extremely low microwave surface resistance, as well as strong structural stability in atmospheric environments. They exhibit unique advantages in fields such as superconducting microwave devices and superconducting quantum interference devices.

[0003] The fabrication of Tl-2212 superconducting thin films primarily employs physical methods such as magnetron sputtering and laser pulse deposition. These methods require complex and expensive vacuum equipment, resulting in high production costs and low efficiency, making large-scale industrial production difficult. When using chemical deposition (sol-gel method) to prepare Tl-2212 superconducting thin films, one of the key steps is the hydrolysis of the ester. However, once hydrolysis begins in the presence of water and alcohols, it is difficult to stop, leading to gel aging effects. This makes it difficult to control the stability of the film structure and properties, resulting in limited improvement in the performance (critical transition temperature) of the Tl-2212 superconducting thin film. Furthermore, the complexing agent used in the sol preparation of existing chemical deposition methods is a composite complexing agent, requiring the use of thallium-containing palladium calcination to replenish the thallium volatilized during heat treatment, further complicating the preparation process. Summary of the Invention

[0004] The purpose of this invention is to provide a Tl-based superconducting thin film and its preparation method. The preparation method provided by this invention is simple, and the prepared Tl-based (Tl-2212) superconducting thin film has good crystal structure and a critical transition temperature of up to 100K, which is close to the theoretical superconducting transition temperature of Tl-2212.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a Tl-based superconducting thin film, comprising the following steps: (1) A precursor sol is obtained by mixing a metal nitrate or acetate, ethylenediaminetetraacetic acid, a water-soluble polymer and water; the metal is thallium, barium, calcium and copper; the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is (2~3):2:1:2:(7~8); (2) The precursor sol obtained in step (1) is coated onto the substrate to obtain a precursor film; (3) The precursor film obtained in step (2) is heat-treated in an oxygen atmosphere under sealed conditions to obtain a Tl-based superconducting film.

[0006] Preferably, the water-soluble polymer in step (1) is polyethyleneimine or polyvinyl alcohol.

[0007] Preferably, in step (1), the mass ratio of the water-soluble polymer to ethylenediaminetetraacetic acid is 1:(0.8~1.2).

[0008] Preferably, the mixture in step (1) is: A first solution is obtained by mixing a metal nitrate or acetate with a portion of water. The water-soluble polymer and ethylenediaminetetraacetic acid were dissolved in the remaining water in sequence for a second mixing to obtain a second solution; The first solution and the second solution are then mixed in a third way.

[0009] Preferably, the concentration of calcium ions in the first solution is 0.2~0.3 mol / L.

[0010] Preferably, the concentration of ethylenediaminetetraacetic acid in the second solution is 0.3~0.35 mol / L.

[0011] Preferably, the thickness of the precursor film in step (2) is 0.1~1μm.

[0012] Preferably, the heat treatment in step (3) is a segmented heat treatment.

[0013] Preferably, the segmented heat treatment is as follows: first, the temperature is raised to a first heat treatment temperature at a first heating rate and held for a first time, and then the temperature is raised to a second heat treatment temperature at a second heating rate and held for a second time. The first heating rate is 2~3℃ / min; The first heat treatment temperature is 500~550℃; The first heat preservation time is 30~90 minutes; The second heating rate is 6~8℃ / min; The second heat treatment temperature is 760~800℃; The second heat preservation time is 20~60 minutes.

[0014] The present invention also provides a Tl-based superconducting thin film prepared by the preparation method described in the above technical solution.

[0015] This invention provides a method for preparing a Tl-based superconducting thin film, comprising the following steps: (1) mixing a metal nitrate or acetate, ethylenediaminetetraacetic acid, a water-soluble polymer and water to obtain a precursor sol; wherein the metal is thallium, barium, calcium and copper; wherein the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is (2~3):2:1:2:(7~8); (2) coating the precursor sol obtained in step (1) onto a substrate to obtain a precursor thin film; (3) subjecting the precursor thin film obtained in step (2) to heat treatment under sealed conditions in an oxygen atmosphere to obtain a Tl-based superconducting thin film. This invention uses ethylenediaminetetraacetic acid (EDTA) as a complexing agent, while avoiding the use of metal alkoxides, thus preventing the introduction of alcohols during hydrolysis. It also limits the molar ratio of metal to EDTA, ensuring sufficient EDTA to continuously chelate metal cations during precursor sol preparation, forming small chelating groups. The water-soluble polymer utilizes its own molecular chains and active groups to uniformly and stably bind these small chelating groups through hydrogen bonds and potential electrostatic adsorption, resulting in a uniform distribution of metal cations in the precursor sol. This effectively prevents the hydrolysis of metal cations, yielding a stable precursor sol. Heat treatment of the precursor film under sealed conditions significantly reduces Tl evaporation, ensuring sufficient film crystallization and stable preparation of well-crystalline Tl-based (Tl-2212) superconducting films, thereby increasing the critical transition temperature of the Tl-based (Tl-2212) superconducting film. The results of the examples show that the Tl-based (Tl-2212) superconducting thin films obtained by the preparation method provided by the present invention exhibit the Tl-2212 phase without the formation of impurity phases, and the critical transition temperature can reach 100K, which is close to the theoretical superconducting transition temperature of Tl-2212. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the sealed alumina crucible of the present invention; Figure 2 The image shows the XRD pattern of the Tl-based superconducting thin film prepared in Example 2 of this invention. Figure 3 The resistance-temperature curve of the Tl-based superconducting thin film prepared in Example 2 of this invention is shown. Figure 4 The resistance-temperature curve is shown for the Tl-based superconducting thin film prepared in Comparative Example 2 of this invention. Detailed Implementation

[0017] This invention provides a method for preparing a Tl-based superconducting thin film, comprising the following steps: (1) A precursor sol is obtained by mixing a metal nitrate or acetate, ethylenediaminetetraacetic acid, a water-soluble polymer and water; the metal is thallium, barium, calcium and copper; the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is (2~3):2:1:2:(7~8); (2) The precursor sol obtained in step (1) is coated onto the substrate to obtain a precursor film; (3) The precursor film obtained in step (2) is heat-treated in an oxygen atmosphere under sealed conditions to obtain a Tl-based superconducting film.

[0018] This invention involves mixing a metal nitrate or acetate, ethylenediaminetetraacetic acid, a water-soluble polymer, and water to obtain a precursor sol.

[0019] In this invention, the metal is thallium, barium, calcium, and copper.

[0020] In this invention, the molar ratio of thallium, barium, calcium, copper, and ethylenediaminetetraacetic acid is (2~3):2:1:2:(7~8), preferably (2.2~2.6):2:1:2:(7.2~7.6), and more preferably (2.4~2.6):2:1:2:(7.4~7.6). Limiting the molar ratio of thallium, barium, calcium, copper, and ethylenediaminetetraacetic acid to the above range ensures sufficient ethylenediaminetetraacetic acid to continuously chelate metal cations during the precursor sol preparation process, forming small chelating groups, promoting uniform dispersion of metal cations, and ensuring sufficient thallium to participate in crystallization during subsequent heat treatment under sealed conditions, forming a good crystal structure.

[0021] In one embodiment of the present invention, the water-soluble polymer may be polyethyleneimine or polyvinyl alcohol; the degree of polymerization of polyethyleneimine may be 1200~20000; and the degree of polymerization of polyvinyl alcohol may be 1000~5000.

[0022] In one embodiment of the present invention, the mass ratio of the water-soluble polymer to ethylenediaminetetraacetic acid (EDTA) can be 1:(0.8~1.2), 1:(0.9~1.1), or 1:1. The present invention uses a water-soluble polymer and limits the mass ratio of the water-soluble polymer to EDTA to the above range. This allows the active groups on the molecular chain of the water-soluble polymer to uniformly and stably bind small chelating groups through hydrogen bonds and possible electrostatic adsorption (polyethyleneimine has electrostatic adsorption properties), resulting in a more uniform distribution of metal cations in the precursor sol.

[0023] As one embodiment of the present invention, the mixing can be: A first solution is obtained by mixing a metal nitrate or acetate with a portion of water. The water-soluble polymer and ethylenediaminetetraacetic acid were dissolved in the remaining water in sequence for a second mixing to obtain a second solution; The first solution and the second solution are then mixed in a third way.

[0024] In one embodiment of the present invention, the temperature of the first mixing can be 65~75℃, or even 70℃; the time of the first mixing can be 1~2h, or even 1~1.5h. Limiting the temperature and time of the first mixing to the above ranges ensures that the metal nitrates or acetates are completely dissolved in water.

[0025] In one embodiment of the present invention, the concentration of calcium ions in the first solution can be 0.2~0.3 mol / L, 0.22~0.28 mol / L, or 0.24~0.26 mol / L. Limiting the concentration of calcium ions in the first solution to the above range provides a good foundation for subsequent uniform mixing.

[0026] In one embodiment of the present invention, the temperature and time selection ranges for the second mixing are the same as those for the first mixing, and will not be repeated here. Limiting the temperature and time of the second mixing to the above-mentioned ranges ensures that the water-soluble polymer and ethylenediaminetetraacetic acid are completely dissolved in water.

[0027] In this invention, since ethylenediaminetetraacetic acid (EDTA) has poor water solubility, it is necessary to add highly water-soluble polyethyleneimine to water to assist in the dissolution of EDTA and obtain a clear second solution.

[0028] In one embodiment of the present invention, the concentration of ethylenediaminetetraacetic acid (EDTA) in the second solution can be 0.3~0.35 mol / L, 0.32~0.34 mol / L, or 0.32~0.33 mol / L. Limiting the concentration of EDTA in the second solution to the above range provides a good basis for subsequent uniform mixing.

[0029] In one embodiment of the present invention, the first mixing, the second mixing, and the third mixing can be carried out by stirring. The present invention does not impose any particular limitation on the stirring speed of the first mixing, the second mixing, and the third mixing; stirring speeds commonly used by those skilled in the art to mix the raw materials uniformly are sufficient.

[0030] The present invention does not have a special limitation on the amount of water / remaining water added in the first solution / second solution. As long as the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is within the above-mentioned limited range, the concentration of calcium ions in the first solution / concentration of ethylenediaminetetraacetic acid in the second solution is within the above-mentioned limited range.

[0031] After obtaining the precursor sol, the present invention coats the precursor sol onto the substrate to obtain a precursor film.

[0032] In one embodiment of the present invention, the substrate material can be LaAlO3; the crystal orientation of the LaAlO3 is (001). In this invention, LaAlO3 has a good lattice ratio with the Tl-based superconducting thin film (Tl-2212) to be prepared, making it a high-quality substrate for preparing Tl-based superconducting thin films. In an embodiment of the present invention, the size of the substrate is 10×10 mm.

[0033] In one embodiment of the present invention, the coating method can be spin coating; the number of coatings can be 1 to 3 times, or 1 to 2 times; the coating amount for each coating can be independently 0.1 to 0.2 mL / cm³. 2 The spin coating speed can be independently set to 4000~8000 r / min or 4000~6000 r / min; the spin coating time for each coat can be independently set to 40~60 s or 40~50 s. By limiting the number of coats and the parameters for each spin coating to the above ranges, this invention can obtain a precursor film with both high thickness and high quality.

[0034] In one embodiment of the present invention, drying can be performed after each coating; the drying can be carried out in a flat plate heater; the drying temperature can be 90~120℃ or 100~110℃; the drying time can be 20~30 min or 25~30 min. By limiting the drying temperature and time to the above ranges, the present invention can better obtain the precursor film.

[0035] In one embodiment of the present invention, the thickness of the first film layer obtained after drying following the first coating can be 50-500 nm, 100-400 nm, 150-300 nm, or 200 nm. In this invention, the thickness of the second film layer obtained after further coating and drying on the first film layer is less than the thickness of the first film layer, even with the same spin-coating parameters, because the precursor sol fills the pores in the first film layer.

[0036] In one embodiment of the present invention, the thickness of the precursor film can be 0.1~1μm, 0.2~0.8μm, or 0.3~0.5μm. Limiting the thickness of the precursor film to the above range ensures that subsequent heat treatment yields a Tl-based superconducting film with better performance.

[0037] After obtaining the precursor film, the present invention heat-treats the precursor film in an oxygen atmosphere under sealed conditions to obtain a Ti-based superconducting film.

[0038] The present invention does not have a specific limitation on the pressure of the oxygen atmosphere, as long as it is an oxygen atmosphere. In an embodiment of the present invention, the pressure of the oxygen in the oxygen atmosphere is 101 kPa.

[0039] In one embodiment of the present invention, the sealing condition can be a sealed alumina crucible; a schematic diagram of the structure of the sealed alumina crucible is shown below. Figure 1 As shown, the crucible includes a grooved top cover and a bottom plate; the contact surfaces of the top cover and the bottom plate of the alumina crucible are polished; the precursor film is placed in the groove of the top cover of the alumina crucible. This invention heat-treats the precursor film within a sealed alumina crucible, utilizing the excellent high-temperature resistance and chemical stability of the alumina crucible to effectively avoid chemical reactions between the crucible and the precursor film during high-temperature processes, ensuring the purity of the film composition and the integrity of its structure. The sealed space of the alumina crucible during heat treatment significantly reduces the evaporation of Ti, thereby ensuring sufficient crystallization of the film, stably preparing well-crystalline Ti-based (Tl-2212) superconducting films, and increasing the critical transition temperature of the Ti-based (Tl-2212) superconducting films.

[0040] In an embodiment of the present invention, the roughness R of the top cover and the bottom plate of the alumina crucible is... a The size is 1~2nm; the size of the groove on the top cover is 15~20mm in diameter and 2~10mm in depth.

[0041] In one embodiment of the present invention, the heat treatment can be performed in a tube furnace; the heat treatment can be a segmented heat treatment; the segmented heat treatment can be: first, heating to a first heat treatment temperature at a first heating rate and holding for a first time, then heating to a second heat treatment temperature at a second heating rate and holding for a second time; the first heating rate can be 2~3℃ / min, or 2.5℃ / min; the first heat treatment temperature can be 500~550℃, or 525℃; the first holding time can be 50~70min, or 60min; the second heating rate can be 6~8℃ / min, or 7℃ / min; the second heat treatment temperature can be 760~800℃, or 780℃; the second holding time can be 20~60min, or 40min. In this invention, holding at a first heat treatment temperature (500~550℃) decomposes and removes the organic polymers contained in the precursor film, at which point the metal cations bound to ethylenediaminetetraacetic acid are gradually released to the substrate surface. Holding at a second heat treatment temperature (760~800℃) controls the crystallization and phase formation of the film, ultimately forming a single-crystal epitaxial Tl-based (Tl-2212) superconducting film. Limiting the heat treatment parameters to the above range ensures the acquisition of a high-performance Tl-based (Tl-2212) superconducting film.

[0042] In one embodiment of the present invention, after the second heat preservation is completed, the furnace can be cooled to room temperature; the cooling method can be furnace-side cooling.

[0043] This invention uses ethylenediaminetetraacetic acid (EDTA) as a complexing agent, while avoiding the use of metal alkoxides, thus preventing the introduction of alcohols during hydrolysis. It also limits the molar ratio of metal to EDTA, ensuring sufficient EDTA to continuously chelate metal cations during precursor sol preparation, forming small chelating groups. The water-soluble polymer utilizes its own molecular chains and active groups to uniformly and stably bind these small chelating groups through hydrogen bonds and potential electrostatic adsorption, resulting in a uniform distribution of metal cations in the precursor sol. This effectively prevents the hydrolysis of metal cations, yielding a stable precursor sol. Heat treatment of the precursor film under sealed conditions significantly reduces Tl evaporation, ensuring sufficient film crystallization and stable preparation of well-crystalline Tl-based (Tl-2212) superconducting films, thereby increasing the critical transition temperature of the Tl-based (Tl-2212) superconducting film.

[0044] The present invention also provides a Tl-based superconducting thin film prepared by the preparation method described in the above technical solution.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] Example 1 A method for preparing a Ti-based superconducting thin film comprises the following steps: (1) The nitrates of metals (thallium, barium, calcium and copper) are mixed with a portion of water at 70°C for 1 hour to obtain a first solution (the concentration of calcium ions in the first solution is 0.2 mol / L); the water-soluble polymer (polyethyleneimine, degree of polymerization 10000) and ethylenediaminetetraacetic acid are dissolved in the remaining water and stirred at 70°C for 1 hour to obtain a second solution (the concentration of ethylenediaminetetraacetic acid in the second solution is 0.3 mol / L); the first solution and the second solution are mixed for a third time to obtain a precursor sol; the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is 2.6:2:1:2:7.6; the mass ratio of the water-soluble polymer and ethylenediaminetetraacetic acid is 1:1; (2) Dissolve the precursor sol obtained in step (1) at 0.1 mL / cm 2 The coating amount was spin-coated (spin-coating speed was 6000 r / min, spin-coating time was 40 s) onto the substrate (LaAlO3, the crystal orientation of LaAlO3 was (001)) and then dried in a flat plate heater at 100 °C for 20 min to obtain the first film layer (150 nm). Then the above spin-coating and drying operations were repeated (i.e., the number of spin-coatings was 2, and the spin-coating operation was the same each time) to obtain the precursor film (200 nm). (3) In an oxygen atmosphere (oxygen pressure is 101 kPa), the precursor film obtained in step (2) is placed in a sealed alumina crucible. In a tube furnace, the temperature is first raised to the first heat treatment temperature (500°C) at the first heating rate (2°C / min) and held for the first time (60 min). Then, the temperature is raised to the second heat treatment temperature (760°C) at the second heating rate (6°C / min) and held for the second time (60 min). Then, the furnace is cooled to room temperature to obtain a Tl-based superconducting film.

[0047] Example 2 A method for preparing a Ti-based superconducting thin film comprises the following steps: (1) The nitrates of metals (thallium, barium, calcium and copper) are mixed with a portion of water at 70°C for 1 hour to obtain a first solution (the concentration of calcium ions in the first solution is 0.3 mol / L); the water-soluble polymer (polyethyleneimine, degree of polymerization 20000) and ethylenediaminetetraacetic acid are dissolved in the remaining water and stirred at 70°C for 1 hour to obtain a second solution (the concentration of ethylenediaminetetraacetic acid in the second solution is 0.35 mol / L); the first solution and the second solution are mixed for a third time to obtain a precursor sol; the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is 2.4:2:1:2:7.4; the mass ratio of the water-soluble polymer and ethylenediaminetetraacetic acid is 1:0.9; (2) The precursor sol obtained in step (1) is prepared at a concentration of 0.15 mL / cm³. 2 The coating amount was spin-coated (spin-coating speed was 4000 r / min, spin-coating time was 60 s) onto the substrate (LaAlO3, the crystal orientation of LaAlO3 was (001)) and then dried in a flat plate heater at 110 °C for 30 min to obtain the first film layer (300 nm). Then the above spin-coating and drying operations were repeated (i.e., the number of spin-coatings was 3, and the spin-coating operation was the same each time) to obtain the precursor film (500 nm). (3) In an oxygen atmosphere (oxygen pressure is 101 kPa), the precursor film obtained in step (2) is placed in a sealed alumina crucible. In a tube furnace, the temperature is first raised to the first heat treatment temperature (550°C) at the first heating rate (3°C / min) and held for the first time (60 min). Then, the temperature is raised to the second heat treatment temperature (800°C) at the second heating rate (8°C / min) and held for the second time (20 min). Then, the furnace is cooled to room temperature to obtain a Tl-based superconducting film.

[0048] Comparative Example 1 The only difference between Comparative Example 1 and Example 2 is that ethylenediaminetetraacetic acid (complexing agent) is replaced with tartaric acid; otherwise, they are the same as in Example 2.

[0049] The sol prepared in Comparative Example 1 will show a white precipitate after 1 to 6 hours. The sol composition is unstable and cannot be used to prepare Tl-based superconducting thin films.

[0050] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is the content of thallium. The molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is 1.5:2:1:2:7.4. All other aspects are the same as in Example 2.

[0051] The Tl-based superconducting thin film prepared in Example 2 was tested using an X-ray diffractometer, and the obtained XRD pattern is shown below. Figure 2 As shown. By Figure 2It can be seen that the XRD pattern shows the characteristic (00l) diffraction peak of Tl-2212, indicating that the superconducting thin film mainly exhibits the Tl-2212 phase, without the formation of impurity phases, and its growth orientation is epitaxial growth along the c-axis.

[0052] The superconducting properties of the Tl-based superconducting thin films prepared in Example 2 and Comparative Example 2 were tested using a low-temperature resistance testing device.

[0053] The resistance-temperature curve of the Tl-based superconducting thin film prepared in Example 2 is shown in the figure below. Figure 3 As shown. From Figure 3 It can be seen that the critical transition temperature of the Tl-2212 superconducting thin film is 100K, which is close to the theoretical superconducting transition temperature of Tl-2212.

[0054] The resistance-temperature curve of the Tl-based superconducting thin film prepared in Comparative Example 2 is shown in the figure. Figure 4 As shown. From Figure 4 As can be seen, the critical transition temperature of the superconducting thin film in Comparative Example 2 is 90.2K, which is lower than 100K in Example 2.

[0055] The Tl-based (Tl-2212) superconducting thin film obtained by the preparation method provided by the present invention exhibits the Tl-2212 phase without the formation of impurity phases, and the critical transition temperature can reach 100K, which is close to the theoretical superconducting transition temperature of Tl-2212.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Tl-based superconducting thin film, comprising the following steps: (1) A precursor sol is obtained by mixing a metal nitrate or acetate, ethylenediaminetetraacetic acid, a water-soluble polymer and water; the metal is thallium, barium, calcium and copper; the molar ratio of thallium, barium, calcium, copper and ethylenediaminetetraacetic acid is (2~3):2:1:2:(7~8); (2) The precursor sol obtained in step (1) is coated onto the substrate to obtain a precursor film; (3) The precursor film obtained in step (2) is heat-treated in an oxygen atmosphere under sealed conditions to obtain a Tl-based superconducting film.

2. The preparation method according to claim 1, characterized in that, In step (1), the water-soluble polymer is polyethyleneimine or polyvinyl alcohol.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of water-soluble polymer to ethylenediaminetetraacetic acid is 1:(0.8~1.2).

4. The preparation method according to claim 3, characterized in that, The mixture in step (1) is: A first solution is obtained by mixing a metal nitrate or acetate with a portion of water. The water-soluble polymer and ethylenediaminetetraacetic acid were dissolved in the remaining water in sequence for a second mixing to obtain a second solution; The first solution and the second solution are then mixed in a third way.

5. The preparation method according to claim 4, characterized in that, The concentration of calcium ions in the first solution is 0.2~0.3 mol / L.

6. The preparation method according to claim 4, characterized in that, The concentration of ethylenediaminetetraacetic acid in the second solution is 0.3~0.35 mol / L.

7. The preparation method according to claim 1, characterized in that, The thickness of the precursor film in step (2) is 0.1~1μm.

8. The preparation method according to claim 1, characterized in that, The heat treatment in step (3) is a segmented heat treatment.

9. The preparation method according to claim 8, characterized in that, The segmented heat treatment is as follows: first, the temperature is raised to a first heat treatment temperature at a first heating rate and held for a first time; then, the temperature is raised to a second heat treatment temperature at a second heating rate and held for a second time. The first heating rate is 2~3℃ / min; The first heat treatment temperature is 500~550℃; The first heat preservation time is 30~90 minutes; The second heating rate is 6~8℃ / min; The second heat treatment temperature is 760~800℃; The second heat preservation time is 20~60 minutes.

10. The Tl-based superconducting thin film prepared by the preparation method according to any one of claims 1 to 9.

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