A method for preparing (Cu,C)Ba2Ca n-1 Cu n O 2n+3 Method for superconducting thin films

Abstract

This invention discloses the preparation of (Cu,C)Ba2Ca on a metal soft substrate. n‑1 Cu n O 2n+3 (n=3,4) Method for superconducting thin films. A target material is obtained by weighing a certain amount of barium, calcium, and copper oxides or carbonates according to chemical proportions, followed by multiple grinding, pressing, and sintering processes. A suitable metal substrate with a buffer layer is selected, and (Cu,C)Ba2Ca is prepared using the prepared target material via PLD deposition technology. n‑1 Cu n O 2n+3 (n=3,4) Thin film; High-purity oxygen and carbon dioxide are introduced into the PLD coating cavity at a certain flow rate to maintain a constant gas pressure in the cavity; The distance between the target and the soft baseband is adjusted to make the distance between the feather tip and the soft baseband appropriate; After the temperature stabilizes, the thin film is deposited and grown; Under appropriate laser energy, pulse frequency and baseband temperature, a superconducting thin film with high critical temperature, high irreversible magnetic field and high critical current density is obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing practical (Cu,C)Ba2Ca on a metal soft substrate. n-1 Cu n O 2n+3 (n=3,4) The technology of superconducting thin films is applied to the preparation technology and application fields of superconducting materials. Background Technology

[0002] Superconducting materials possess properties such as zero resistance and perfect diamagnetism. Using superconducting materials, lossless, high-capacity current transmission can be achieved, a feat impossible with conventional techniques. The resulting strong magnetic field magnets have significant, even revolutionary, applications in magnetic resonance imaging, magnetic confinement fusion, high-speed rail transportation, and large-scale scientific engineering projects. Before the discovery of high-temperature superconducting materials, the use of conventional superconducting materials at extremely low temperatures required expensive liquid helium to maintain their cryogenic environment, placing high demands on cooling technology, which greatly limited the applications of superconducting materials.

[0003] Since the discovery of copper oxides, many high-temperature superconductors with superconducting transition temperatures higher than the boiling point of liquid nitrogen (77K, approximately -194℃) have been discovered, and large-scale application of copper oxide high-temperature superconductors has been anticipated. Copper oxide superconductors are further classified into Y-series, Bi-series, Hg-series, and Tl-series, among others. However, Bi-series high-temperature superconducting materials exhibit extremely strong anisotropy and intense magnetic flux movement in the high-temperature region, making them unsuitable for high-magnetic-field applications in the liquid nitrogen temperature range. Currently, they are mainly used in high-field environments at liquid helium temperatures or in power transmission cables at liquid nitrogen temperatures. Hg-series and Tl-series copper oxide high-temperature superconductors have limited applications due to the presence of highly toxic elements, and their magnetic flux movement is also very strong. Although the Y-series (YBa2Cu3O7, abbreviated as YBCO) has a critical temperature of 91K, its irreversible magnetic field in the liquid nitrogen temperature range (65K-77K) is only about 10 Tesla, and even if it is made into a wire and wound into a magnet, the usable magnetic field is not high. Choosing copper oxide superconductors, which have higher critical temperatures and irreversible fields, as the focus for future high-temperature superconducting applications is more in line with people's expectations.

[0004] In 2018, the applicant's research group synthesized (Cu,C)Ba2Ca3Cu4O using high temperature and high pressure technology. 11 The polycrystalline material was systematically measured and found to have a superconducting transition temperature of 116 K and the highest irreversible magnetic field H to date. irr(Yue Zhang, Wenhao Liu, Xiyu Zhu, Haonan Zhao, Zheng Hu, Chengping He, and Hai-Hu Wen. Sci. Adv., 4(9): eaau0192, 2018). This is very exciting. Its irreversible magnetic field is the highest among all known superconductors, reaching 15T at 86K and 5T even at 98K. Such properties mean it has great application potential. However, (Cu,C)Ba2Ca3Cu4O 11 Currently, bulk materials can only be prepared under high temperature and high pressure (30,000 atmospheres), resulting in samples with too small a volume for large-scale applications. If it were possible to utilize the fabrication process of metal soft substrates to grow (Cu,C)Ba2Ca3Cu4O... 11 Thin films and their long conductive lines will have great application value. However, the (Cu,C)Ba2Ca3Cu4O films grown using pulsed laser deposition (PLD) technology have been previously limited to this method. 11 The highest transition temperature of the thin film is only 78K, and it is grown on a polished crystal substrate with limited size; the highest transition temperature of the thin film grown using MBE technology is only 55K. Until 2020, the applicant's research group grew this film on a LaAlO3 substrate using laser pulse deposition technology, and its zero-resistance transition temperature reached 96K (Tianfeng Duan, Jiahao Hao, Haifeng Chu and Hai-Hu Wen, Supercond. Sci. Technol. 33 (2020) 025009). If this film can be grown on a metal soft substrate, it will be a major step towards practical application and could bring huge market applications.

[0005] After high-pressure synthesis and annealing, the (Cu,C)Ba2Ca2Cu3O9 superconducting material achieves a superconducting critical temperature of approximately 120K, exhibiting advantages such as high critical temperature and non-toxicity. However, currently, bulk synthesis of this material can only be achieved through high-temperature, high-pressure processes, preventing its industrial application. There are also no reports of successful growth on soft substrates. Successful growth on soft substrates would lead to large-scale applications.

[0006] CN1082231 discloses the preparation of YBa2Cu3O 7－δ The high-temperature superconducting epitaxial thin film scheme mainly employs an inverted-cylinder DC sputtering apparatus with in-situ substrate rotation, adjustable speed, radiation heating, and simultaneous double-sided film deposition, along with an optimized self-epitaxy preparation method. This improves the film quality and yields higher quality YBa2Cu3O. 7－δ High-temperature superconducting epitaxial films exhibit excellent performance; their T c0All are greater than 90k, and ΔTc is less than 0.3k; the properties of the double-sided films on both sides of the substrate are consistent; their T c0 The phase difference is less than 0.5 K, and the ΔTc phase difference is less than 0.5 K, but practical methods for preparing these on soft metallic substrates remain an important research topic. However, the highest critical temperature of this system is limited to below 95 K. The application of strong magnetic fields in the liquid nitrogen temperature range is also limited. Summary of the Invention

[0007] To address the existing technical problems, the present invention aims to provide a method for preparing (Cu,C)Ba2Ca on a metal soft substrate using pulsed laser deposition technology. n-1 Cu n O 2n+3 (n=3,4) Thin film method. Using oxides or carbonates of barium, calcium, and copper in chemical proportions to sinter into a target material, and then using pulsed laser deposition technology, oxygen and carbon dioxide are introduced during the deposition process to prepare superconducting thin films with high critical temperatures, which have broad application prospects.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: preparing (Cu,C)Ba2Ca n-1 Cu n O 2n+3 The method for (n=3,4) thin films includes the following steps:

[0009] (1) Weigh out a certain mass of barium, calcium, and copper oxides or carbonates according to the ratio, mix them, and then crush and grind them in a mortar, preferably for more than two hours to obtain a uniform powder; the preferred raw materials are BaCO3, CaCO3, and CuO; for (Cu,C)Ba2Ca3Cu4O 11 The optimal Cu ratio for the target material used in preparation is 4.2-4.8; for the target material used in the preparation of (Cu,C)Ba2Ca2Cu3O9, the optimal Cu ratio is 3.2-3.8; or the target material used in the preparation of (Cu,C)Ba2Ca3Cu4O9... 11 The target material used for thin films can be adjusted, and the conditions during film growth can also be adjusted to prepare (Cu,C)Ba2Ca2Cu3O9;

[0010] The conditions for thin film growth include laser energy, frequency, gas pressure, substrate composition and buffer layer, and temperature. After weighing the raw materials according to the specified amounts, mix them and grind them thoroughly to ensure uniform composition.

[0011] (2) Place the uniform powder prepared in step (1) into a clean crucible or onto a corundum sheet. Place the crucible or corundum sheet into a heating furnace and heat-treat the powder in air; control the heat treatment temperature to be 750-950℃, the heat treatment heating rate to be 1-10℃ / min, the heat treatment holding time to be 12-72h, and the cooling rate to be 1-10℃ / min; preferably control the heat treatment temperature to be 800-860℃, the heat treatment heating rate to be 2-5℃ / min, the heat treatment holding time to be 24-48h, and the cooling rate to be 2-5℃ / min.

[0012] (3) Crush the mixture after firing in the above steps (placed in a mortar or other container) and grind it for more than two hours to obtain a uniform powder. Place the powder in a mold (cylindrical or other) and press it into a sheet under a pressure of 5-20 MPa. Then remove the block from the mold and place it in a crucible with a stable bottom or on a corundum sheet. Place the crucible or corundum sheet in a heating furnace and heat treat the block in air (or oxygen-enriched air) to obtain a mixture block; control the heat treatment temperature at 750-950℃, the heat treatment heating rate at 1-10℃ / min, the heat treatment holding time at 12-72h, and the cooling rate at 1-10℃ / min; preferably, the heat treatment temperature is 800-860℃, the heat treatment heating rate is 2-5℃ / min, the heat treatment holding time is 24-48h, and the cooling rate is 2-5℃ / min;

[0013] (4) Repeat step (3) 2-8 times.

[0014] (5) Place the block obtained in step (4) in a mortar and crush and grind it into a uniform powder.

[0015] (6) Place the uniform powder prepared in step (5) into a mold (cylindrical, etc.) and apply a pressure of 5-20 MPa to the mold to press it into a block or sheet. Then remove the block from the mold and place it in a sealed bag for more than one layer of (vacuum or airtight) sealing. Place the sealed block together with the sealed bag in a hydraulic press for pressing, preferably with a pressure of 40-100 MPa.

[0016] (7) Take the pressed block from the sealed bag in step (6) and place it in a crucible or on a corundum sheet with a stable bottom. Place the crucible or corundum sheet in a heating furnace and heat-treat the block in air to obtain the target material required for PLD coating; control the heat treatment temperature to 750-950℃, the heat treatment heating rate to 1-10℃ / min, the heat treatment isothermal time to 12-72h, and the cooling rate to 1-10℃ / min; preferably control the heat treatment temperature to 800-860℃, the heat treatment heating rate to 2-5℃ / min, the heat treatment isothermal time to 24-60h, and the cooling rate to 2-5℃ / min.

[0017] (8) Polish the target material prepared in step (7) and then install it in the PLD coating vacuum chamber.

[0018] (9) The cap layer material is mixed with (Cu,C)Ba2Ca n-1 Cu n O 2n+3 (n=3,4) A metal soft substrate with a lattice constant matching the material is fixed in a suitable position on a polished substrate and then installed in a PLD coating vacuum chamber; the preferred cap layer is CeO2, LaAlO3, SrTiO3, YAlO3, LaMnO3, YSZ, LaSrAlO4, LSAT, NdGaO3, etc.; the soft substrate is positioned on the substrate at the position directly opposite the center of the plume.

[0019] The soft substrate used has a film structure of CeO2 / Epi-MgO / IBAD-MgO / Y2O3 / Al2O3 / metal alloy substrate; the metal alloy substrate includes NiW alloy and Hastelloy alloy; its cap layer is CeO2, LaAlO3, SrTiO3, YAlO3, LaMnO3, YSZ, LSAO, NGO, etc., which match the lattice constant of the film; other buffer layers below the cap layer can be changed according to the actual application requirements. The soft substrate is deposited at the center of the plume tip.

[0020] (10) Heat the stage to 600-800°C. The preferred temperature is 600-700°C. Maintain a vacuum environment inside the PLD coating chamber during this process.

[0021] (11) High-purity oxygen and carbon dioxide are introduced into the PLD coating chamber at a certain rate to maintain a constant pressure between 5-50 Pa. The ventilation scheme is as follows: oxygen and carbon dioxide are introduced separately; oxygen enters the coating chamber from the far port, and carbon dioxide enters the coating chamber from the near port (see...). Figure 1The preferred oxygen flow rate is 20-30 sccm; the preferred carbon dioxide flow rate is 3-10 sccm; and the preferred internal pressure is 10-30 Pa.

[0022] (12) Block the baseband with a baffle, turn on the laser, set the optical frequency to 2-10Hz, and control the laser energy density to 1-8J / cm². 2 Pre-deposition is performed for 2-15 minutes; the preferred laser energy density is 1.5-3.5 J / cm². 2 The preferred frequency is 5Hz. During this period, the distance between the target and the baseband is adjusted so that the distance between the tip of the plume and the baseband is 0.5-2.5cm; preferably, the distance between the tip of the plume and the baseband is about 1cm.

[0023] (13) After the pre-deposition is completed, open the baffle to allow the baseband to dissipate heat for 2-10 minutes.

[0024] (14) Turn on the laser, set the energy to be the same as the laser energy used during pre-deposition in step (12), and the frequency to be 2-6 Hz; perform deposition. Preferably, the laser frequency is 5 Hz; preferably, the deposition time is 20-40 mins.

[0025] (15) After deposition, if in-situ annealing is performed, oxygen or nitrogen needs to be introduced into the PLD coating chamber to maintain the pressure in the chamber at 10. 1 -10 5 Pa; the cooling rate from the deposition temperature to the in-situ annealing temperature is 1-10℃ / min; the in-situ annealing temperature is 450-650℃; the in-situ annealing time is 0-3h; the cooling rate from the in-situ annealing temperature to room temperature is 1-10℃ / min; the preferred annealing method is in-situ annealing. The preferred annealing residence temperature is 500-600℃, the preferred annealing gas is oxygen, and the preferred annealing gas pressure is 1×10⁻⁶. 4 -8×10 4 Pa, preferably a heating / cooling rate of 5-8℃ / min.

[0026] (16) If ex-situ annealing is adopted, the substrate temperature is reduced from the deposition temperature to room temperature at a rate of 1-10℃ / min; the prepared film is placed in an oxygen-filled heating furnace for oxygen or nitrogen annealing. The annealing temperature is 450-650℃; the annealing time is 0-3h; and the heating and cooling rates are 1-10℃ / min.

[0027] This invention prepares (Cu,C)Ba2Ca3Cu4O with a zero resistance transition temperature of approximately 97K. 11 The thin film has an onset transition temperature of 116 K. It possesses a high irreversible magnetic field. The irreversible magnetic field line H... irrThe term (T) is defined as the magnetic field line with zero resistance at a fixed temperature; the higher the value, the better the superconductor's performance in high-voltage applications. Improving preparation and post-processing conditions is expected to narrow the transition width.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following obvious and prominent substantive features and significant advantages:

[0029] 1. The method of this invention utilizes pulsed laser deposition technology to optimize thin film preparation conditions, allowing for further adjustment of the position and angle of carbon dioxide and oxygen inlet gas, thereby preparing (Cu,C)Ba2Ca3Cu4O with a zero-resistivity transition temperature higher than 97K. 11 The thin film exhibits an onset transition temperature of 116 K. It possesses a high critical temperature and a high irreversible magnetic field. With optimized conditions, the zero-resistance temperature and irreversible magnetic field can be further increased.

[0030] 2. The method of this invention, by optimizing the thin film preparation conditions and adjusting the position and angle of carbon dioxide and oxygen inlet, prepares c-axis oriented (Cu,C)Ba2Ca2Cu3O9 thin films on soft substrates, a previously unreported technique. Its zero-resistivity transition temperature is 97K, higher than that of the second-generation high-temperature superconducting tape YBCO. However, based on the understanding of the phase properties of bulk (Cu,C)Ba2Ca2Cu3O9, the critical temperature and irreversible magnetic field can be further increased.

[0031] 3.(Cu,C)Ba2Ca n-1 Cu n O 2n+3 (n=3,4) Superconducting materials possess characteristics such as non-toxicity, high critical temperature, and high irreversible field. The successful fabrication of thin film materials on soft metallic substrates allows for convenient practical application and holds great promise for future applications. Attached Figure Description

[0032] Figure 1 This is a schematic diagram showing the positions of the carbon dioxide and oxygen inlets relative to the baseband and target material in this invention.

[0033] Figure 2 This is (Cu,C)Ba2Ca3Cu4O prepared in Example 1 of the present invention. 11 RT relationship diagram of thin film.

[0034] Figure 3 This is the RT relationship diagram of the (Cu,C)Ba2Ca2Cu3O9 thin film prepared in Example 2 of the present invention.

[0035] Figure 4 This is the XRD diffraction pattern of the (Cu,C)Ba2Ca2Cu3O9 thin film prepared in Example 2 of this invention.

[0036] Figure 5 This is the RT relationship diagram of the (Cu,C)Ba2Ca2Cu3O9 thin film prepared in Example 3 of this invention. Detailed Implementation

[0037] The above solution will be further described below with reference to specific embodiments. The preferred embodiments of the present invention are described in detail below:

[0038] Example 1: A method for growing (Cu,C)Ba2Ca3Cu4O on a YAlO3 substrate 11 The method for preparing thin films includes the following steps:

[0039] (1) According to Ba2Ca3Cu 4.6 O y A certain mass of high-purity BaCO3, CaCO3 and CuO were weighed and mixed, and then ground in a mortar for more than two hours to obtain a uniform powder; the uniform powder particles were less than 10 micrometers; the uniformly ground powder was placed in a crucible or on a corundum sheet and placed in a heating furnace for heat treatment in air; the heat treatment temperature was 800℃ and the heat treatment time was 24h; BaO and CaO were selected to replace BaCO3 respectively, and there was no difference in CaCO3.

[0040] (2) Place the product obtained in the above steps into a mortar and grind it for more than two hours to obtain a uniform powder. Press the powder into a sheet using a mold with a pressure of 10 MPa, and place it in a heating furnace for heat treatment; the heat treatment temperature is 830℃, and the heat treatment holding time is 24 hours. Repeat this step three times. This time, the pressure can be 5 MPa or 15 MPa.

[0041] (3) The block obtained in step (2) is crushed and ground into a uniform powder in a mortar, and then pressed into a sheet using a mold with a pressure of 10 MPa. After being sealed in a vacuum bag, it is placed in a hydraulic press and pressed under a pressure of 66 MPa (50 or 100 MPa is also acceptable). The block is then removed and placed in a heating furnace for heat treatment. The heat treatment temperature is 860℃, and the heat treatment holding time is 48 h; the heating and cooling rates for the above heat treatments are all 5℃ / min.

[0042] The heat treatment temperature can be 800℃-900℃; the heat treatment holding time can be 24-48h, or 72h; the heat treatment heating rate can be 2-5℃ / min, and the cooling rate can be 2-5℃ / min, all of which can yield basically the same results.

[0043] (4) Polish the target material prepared in step (3) and then install it in the PLD coating vacuum chamber; fix the substrate in the position of the base facing the laser feather and then install it in the PLD coating vacuum chamber;

[0044] (5) Heat the substrate to 650℃. Maintain a vacuum environment within the PLD coating chamber during this process. After the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber. Figure 1 Oxygen is introduced at a rate of 30 sccm from the distal end, and carbon dioxide is introduced at a rate of 5 sccm from the proximal end, maintaining a pressure of 20 Pa within the chamber. The volume of carbon dioxide is typically 10%-25% of that of oxygen.

[0045] (6) Block the substrate with a baffle, turn on the laser, and set the laser energy density to 1.5–3.5 J / cm². 2 The laser was set at a frequency of 5 Hz, allowing for a 5-minute pre-deposition. The distance between the target and the substrate was adjusted to 4 cm. After pre-deposition and temperature stabilization, the thin film was deposited for 20 minutes, while maintaining constant laser energy and frequency.

[0046] (7) After deposition, oxygen or nitrogen is introduced into the PLD coating chamber to maintain the chamber pressure at 5 × 10⁻⁶. 4 Approximately Pa. The temperature is lowered to 450-550℃ at a rate of 5℃ / min, and held for 1 hour for in-situ annealing; then the temperature is lowered to room temperature at a rate of 5℃ / min.

[0047] Experimental test analysis in this embodiment:

[0048] The (Cu,C)Ba2Ca3Cu4O prepared in this embodiment 11 The thin film was characterized by measurements. The RT curves of the thin film were measured using a Power Proportional Measurement System (PPMS). Figure 2 This shows the relationship between the resistivity of the thin film and temperature, revealing that the zero-resistance temperature of the film is approximately 97 K. Using 90% of the normal-state resistance as a standard, its initial transition temperature... It is around 116K.

[0049] In the target preparation process of this embodiment, multiple grinding and sintering steps are performed to ensure the uniformity of the target composition. The (Cu,C)Ba2Ca3Cu4O prepared by this method... 11 The thin film transition temperature exceeds the reported maximum value.

[0050] Example 2: A method for preparing a (Cu,C)Ba2Ca2Cu3O9 thin film on a soft substrate with a CeO2 cap layer, comprising the following steps:

[0051] (1) The target preparation method is the same as in Example 1.

[0052] (2) The soft baseband is glued to the position of the cavity stage facing the laser feather with silver paste, dried with a heating stage, and then placed into the PLD coating vacuum cavity; the baseband is deposited on the stage, and in batches, the baseband can be deposited in a continuous motion manner.

[0053] (3) Heat the substrate to 640℃. After the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber, such as... Figure 1 Oxygen is introduced from the distal port at a rate of 30 sccm, and carbon dioxide is introduced from the proximal port at a rate of 5 sccm, maintaining the gas pressure in the cavity at 20 Pa.

[0054] (4) Adjust the distance between the target and the baseband to 4 cm. Adjust the laser energy density to 1.5–3.5 J / cm². 2 The laser was pre-deposited at a frequency of 5 Hz for 5 mins. After the pre-deposition was completed and the temperature stabilized, the thin film was deposited for 20 mins, while the laser energy and frequency remained constant.

[0055] (5) After deposition, high-purity oxygen is introduced into the PLD coating chamber to maintain the pressure in the chamber at 5×10⁻⁶. 4 Approximately Pa. The temperature was lowered to 500℃ at a rate of 5℃ / min, and held for 1 hour for in-situ annealing; then the temperature was lowered to room temperature at a rate of 5℃ / min.

[0056] The raw material ratio is: (Cu,C)Ba2Ca2Cu 3.5 O y (Cu,C)Ba2Ca2Cu3O9 can also be prepared.

[0057] Stainless steel, copper-based, or silver-plated strips can also be used as the substrate. Selecting a suitable buffer layer and the cap layer (material) chosen in this invention is also within the scope of protection of this invention. For example, if a soft metal substrate is used: the film structure is CeO2 / Epi-MgO / IBAD-MgO / Y2O3 / Al2O3 / metal alloy substrate. The metal alloy substrate is not limited to NiW alloy and Hastelloy alloy.

[0058] Experimental test analysis in this embodiment:

[0059] The (Cu,C)Ba2Ca2Cu3O9 thin film prepared in this embodiment was characterized by measuring the RT curve of the thin film using a Power Proportional Measurement System (PPMS). Figure 3 This is a curve showing the relationship between the resistivity of the thin film and temperature. As indicated in the figure, the zero-resistance temperature of the thin film is approximately 91 K. Using 90% of the normal-state resistance as a standard, its initial transition temperature is... It is 105K. Figure 4The X-ray diffraction pattern of the thin film shows the (00L) diffraction peak, indicating that the film is c-oriented. A (Cu,C)Ba2Ca2Cu3O9 thin film was grown on a soft substrate using laser pulse deposition. The soft substrate cap layer is CeO2, whose in-plane lattice constant is close to that of the thin film. The smaller lattice size allows for a better fit, resulting in a higher quality film. After growth, the film is heat-treated in high-purity oxygen to reduce potential defects and oxygen loss during growth.

[0060] Example 3: A method for preparing a (Cu,C)Ba2Ca2Cu3O9 thin film on a soft substrate with a LaMnO3 cap layer, comprising the following steps:

[0061] (1) The target preparation method is the same as in Example 1. A mixture with a ratio of (Cu,C)Ba₂Ca₂Cu was used. 3.5 O y The same raw materials and targets prepared using the same method can also yield the same results.

[0062] (2) The soft base tape is glued to the position of the cavity base directly opposite the laser feather with silver glue, dried with a heating stage, and then installed in the PLD coating vacuum cavity.

[0063] (3) Heat the substrate to 645℃. After the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber, such as... Figure 1 Oxygen is introduced from the distal port at a rate of 30 sccm, and carbon dioxide is introduced from the proximal port at a rate of 5 sccm, maintaining the gas pressure in the cavity at 20 Pa.

[0064] (4) Adjust the distance between the target and the baseband to 4 cm. Adjust the laser energy density to 1.5–3.5 J / cm². 2 The laser was pre-deposited at a frequency of 5 Hz for 5 mins. After the pre-deposition was completed and the temperature stabilized, the thin film was deposited for 20 mins, while the laser energy and frequency remained constant.

[0065] (5) After deposition, high-purity oxygen is introduced into the PLD coating chamber to maintain the pressure in the chamber at about 20 Pa. The temperature is then reduced to room temperature at a rate of 5 °C / min.

[0066] Experimental test analysis in this embodiment:

[0067] The (Cu,C)Ba2Ca2Cu3O9 thin film prepared in this embodiment was characterized by measuring the RT curve of the thin film using a Power Proportional Measurement System (PPMS). Figure 5 This is a curve showing the relationship between the resistivity of the thin film and temperature. As indicated in the figure, the zero-resistance temperature of the thin film is approximately 97 K. Using 90% of the normal-state resistance as a standard, its initial transition temperature is... The superconducting transition temperature is 113 K. This is higher than that of films grown on a soft substrate with a CeO2 cap layer. The film is c-oriented. By adjusting the doping levels under different annealing conditions, the superconducting transition temperature can be increased.

[0068] The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Without departing from the purpose and spirit of the claims, any method for preparing (Cu,C)Ba2Ca on a metal soft substrate... n-1 Cu n O 2n+3 Any changes or modifications made to the method of superconducting thin films (n=3,4) are within the scope of protection of this invention.

Claims

1. A method for growing a (Cu,C)Ba2Ca2Cu3O9 thin film on a soft substrate with a cap layer of CeO2 or LaMnO3, characterized in that, Includes the following steps: (1) According to Ba2Ca2Cu 3.5 O y Weigh out a certain mass of high-purity BaCO3 or BaO, CaCO3 or CaO and CuO, mix them, and grind them in a mortar for more than two hours to obtain a uniform powder; the uniform powder particles are less than 10 micrometers; place the uniformly ground powder in a crucible or on a corundum sheet, put it in a heating furnace, and perform heat treatment in air; the heat treatment temperature is 800~900℃, and the heat treatment is constant for 24~48h; (2) Place the product obtained in the above steps in a mortar and grind it for more than two hours to obtain a uniform powder; press the powder into a sheet with a pressure of 5MPa, 10MPa or 15MPa using a mold, and place it in a heating furnace for heat treatment; the heat treatment temperature is 800~900℃, and the heat treatment holding time is 24~48h; repeat this step three times. (3) Place the block obtained in step (2) in a mortar and grind it into a uniform powder. Press it into a sheet with a pressure of 10 MPa using a mold. Then seal it with a vacuum bag and place it in a hydraulic press. Press it with a pressure of 50 MPa, 66 MPa or 100 MPa. Take out the block and place it in a heating furnace for heat treatment. The heat treatment temperature is 800~900℃ and the heat treatment holding time is 24~48h. The heating and cooling rate of the above heat treatment is 2~5℃ / min. (4) Polish the target material prepared in step (3) and then install it in the PLD coating vacuum cavity; use silver glue to stick the soft base tape to the position of the base in the cavity facing the laser feather, dry it with a heating stage, and then install it in the PLD coating vacuum cavity. (5) Heat the base to 640°C or 645°C. After the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber. Introduce oxygen at a rate of 30 sccm from the far end and carbon dioxide at a rate of 5 sccm from the near end to maintain the pressure in the chamber at 20 Pa. (6) Adjust the distance between the target and the baseband to 4 cm; adjust the laser energy density to 1.5~3.5 J / cm. 2 Pre-deposition was performed at a frequency of 5 Hz for 5 mins; after pre-deposition and temperature stabilization, thin film deposition was carried out for 20 mins, while the laser energy and frequency remained constant. (7) After deposition, high-purity oxygen is introduced into the PLD coating chamber to maintain the pressure in the chamber at 5×10⁻⁶. 4 Pa; reduce the temperature to 500℃ at a rate of 5℃ / min, hold for 1 hour for in-situ annealing; then reduce the temperature to room temperature at a rate of 5℃ / min. The (Cu,C)Ba2Ca2Cu3O9 thin film prepared by the above method is C-axis oriented.

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