A (Cu,C)Ba2Ca alloy for high-temperature superconducting filter applications n-1 Cu n O 2n+3 Superconducting thin film preparation method

Abstract

A (Cu,C)Ba2Ca n‑1 Cu n O 2n+3 Method for preparing superconducting thin film. Barium, calcium and copper oxides or carbonates are weighed according to the chemical proportion, and after multiple grinding, tabletting and sintering, target material is obtained; the obtained block is put in a mortar and crushed and ground into uniform powder; the powder is put in a mold and pressed into a tablet; then after vacuum packaging with a sealed bag, it is put into a hydraulic press for further pressing; after pressing, it is put into a heating furnace for heat treatment to obtain a PLD target; the prepared target is polished and installed in a PLD coating cavity; a single crystal substrate with matching lattice constant is selected; it is fixed on the appropriate position of the base, and then installed in the PLD coating cavity, and a (Cu,C)Ba2Ca n‑1 Cu n O 2n+3 thin film is prepared by laser pulse deposition technology; under appropriate laser energy, gas pressure and substrate temperature, a superconducting thin film with high critical temperature and low surface microwave impedance is obtained.

Description

Technical Field

[0001] This invention relates to (Cu,C)Ba2Ca for high-temperature superconducting filters. n-1 Cu n O 2n+3 (n=3,4) Superconducting thin film preparation method, applied to the field of high-temperature superconducting weak current application. Background Technology

[0002] With the development of modern information technology, humanity is becoming increasingly reliant on electromagnetic wave transmission. From everyday mobile communications to military, aerospace, and radio astronomy, electromagnetic wave transmission is indispensable. With the advent of 6G mobile communication and the development of low-altitude satellites, more new microwave spectrum will be used. This also means that the radio spectrum will become increasingly crowded, with less and less unused spectrum. Simultaneously, mutual interference between mobile communications, satellite communications, and deep space exploration will become more severe. These factors will lead to more stringent requirements for microwave filter performance. Due to the limitations of microwave surface impedance, filters made from ordinary materials are insufficient to meet the demands of the rapidly evolving communication environment.

[0003] Within the microwave frequency range, below their critical temperature, superconducting materials exhibit surface microwave impedance less than one-thousandth that of normal metals. This results in filters fabricated from superconducting thin films possessing advantages such as low loss, low noise, and high resonator Q-factor. Superconducting filters offer significant advantages in detecting weak signals, enhancing the anti-interference capability of wireless transmission and meeting current communication demands. For mobile communications, high-temperature superconducting filters enable mobile base stations to achieve wider coverage with the same power consumption while improving communication quality. Currently, ReBCO is primarily used to fabricate superconducting filters, with a critical temperature of approximately 90K. The use of high-temperature superconducting filters necessitates expensive mechanical cryogenic systems, significantly limiting their commercial application. Increasing the operating temperature of superconducting filters and reducing their operating costs will drive their application and address current challenges in the communication environment.

[0004] Conventional superconducting materials, due to their low critical temperatures, require liquid helium to maintain their cryogenic environment. Since liquid helium is a non-renewable resource and expensive, its application is significantly limited. In 1986, scientists discovered copper oxide superconductors and subsequently discovered many high-temperature superconductors with superconducting transition temperatures higher than the boiling point of liquid nitrogen (77K, approximately -194°C). Because of their high critical temperatures, they only require liquid nitrogen to maintain their cryogenic environment to achieve a superconducting state, making large-scale industrial applications possible. Copper oxide superconductors with superconducting transition temperatures higher than liquid nitrogen temperatures mainly include Y-based, Bi-based, Hg-based, and Tl-based superconductors. Bi is currently mainly used in high-field environments within the liquid helium temperature range. The application of Hg-based and Tl-based copper oxide high-temperature superconductors is limited due to the presence of highly toxic elements. Y-based superconductors (YBa₂Cu₃O₇, abbreviated as YBCO) have a critical temperature of around 90K and are currently the main materials used in superconducting filters, but their cost remains too high.

[0005] In 1994, scientists discovered (Cu,C)Ba₂Ca₃Cu₄O 11 Its superconducting transition temperature is approximately 118 K. Subsequently, (Cu,C)Ba₂Ca₂Cu₃O₉, belonging to the same system, was discovered, and its superconducting transition temperature can reach 120 K after annealing. Both materials have high superconducting transition temperatures and are non-toxic and environmentally friendly. If high-performance thin-film materials can be fabricated and applied to microwave filters, their performance will be significantly superior to YBCO because its superconducting transition temperature is much higher. These materials are metastable in bulk and can currently only be synthesized under high temperature and high pressure. Due to lattice mismatch between the crystal lattice and the thin film, similar to the effect of physical pressure, this metastable material can be grown in thin film form. However, after more than thirty years of development, the preparation of (Cu,C)Ba₂Ca₂Cu₃O₉ with a high superconducting transition temperature has become increasingly difficult. n-1 Cu n O 2n+3 Thin films remain challenging. The preparation of (Cu,C)Ba₂Ca films with higher critical temperatures is a further challenge. n-1 Cu n O 2n+3 Superconducting thin films could become a new type of material for high-temperature superconducting filters, reducing their cost and enabling wider commercial applications, thus solving current problems in the communication environment.

[0006] The applicant's research group has applied for a method to prepare (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. Application No. 2024104149184. Summary of the Invention

[0007] To address the existing technical problems, the present invention aims to provide a method for fabricating (Cu,C)Ba2Ca on a single-crystal substrate for high-temperature superconducting filters 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 the target material, and then using pulsed laser deposition technology, oxygen and carbon dioxide are introduced during the film growth 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 formula, mix them, and grind them thoroughly, 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; the target material used in the preparation of (Cu,C)Ba2Ca3Cu4O9... 11 The target material used for thin films, and the conditions during thin film growth, can also be adjusted to prepare (Cu,C)Ba2Ca2Cu3O9; the thin film growth conditions refer to laser energy, frequency, gas pressure, substrate, temperature, etc.

[0010] (2) Place the uniform powder ground in step (1) in a crucible or on a corundum sheet, and place it in a heating furnace to heat treat the powder; 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;

[0011] (3) Grind the product after firing in the above steps into a uniform powder. Press the powder into a sheet using a mold with a pressure of 5-20 MPa. Then remove the sheet from the mold and place it in a crucible with a stable bottom or on a corundum sheet. Place it in a heating furnace for heat treatment. 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, the heat treatment temperature is 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] (4) Repeat step (3) 2-8 times.

[0013] (5) Grind the block obtained in step (4) thoroughly to obtain a uniform powder. Press the powder into a sheet using a circular mold, vacuum seal it in a sealed bag, and place it in a hydraulic press to apply a pressure of 40-100 Mba for pressing.

[0014] (6) Take the pressed block from the sealed bag in step (5) 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 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.

[0015] (7) Polish the target material prepared in step (6) and then install it in the PLD coating vacuum chamber.

[0016] (8) Combine with (Cu,C)Ba2Ca n-1 Cu n O 2n+3 A single-crystal substrate with a lattice constant matching that of the materials (n=3,4) is fixed in a suitable position on a polished abutment and then placed in a PLD coating vacuum chamber; the single-crystal substrate is LaAlO3, SrTiO3, YAlO3, LaMnO3, MgO, YSZ, NdCaAlO4, LaSrAlO4, LSAT, CeO2, NdGaO3, etc.; the substrate is positioned on the abutment directly opposite the center of the plume.

[0017] (9) 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.

[0018] (10) High-purity oxygen and carbon dioxide are introduced into the PLD coating chamber at a certain rate to maintain a constant gas pressure between 5-50 Pa. The ventilation scheme is that oxygen and carbon dioxide are introduced separately, with carbon dioxide flowing towards the substrate; preferably, the oxygen introduction rate is 20-30 sccm; preferably, the carbon dioxide introduction rate is 3-10 sccm; preferably, the gas pressure in the chamber is 10-30 Pa.

[0019] (11) Block the substrate with a baffle, turn on the laser, set the laser frequency to 2-10Hz, and control the laser energy density to 0.5-8J / cm². 2 Pre-deposition is performed for 2-15 minutes; the preferred laser energy density is 1.0-3.5 J / cm². 2 The preferred frequency is 5Hz. During this period, the distance between the target and the substrate is adjusted so that the distance between the tip of the plume and the substrate is 0.5-2.5cm; preferably, the distance between the tip of the plume and the substrate is about 1cm.

[0020] (12) After the pre-deposition is completed, open the baffle to allow the substrate to dissipate heat for 2-10 minutes.

[0021] (13) 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 2-10 Hz; perform deposition. Preferably, the laser frequency is 5 Hz; preferably, the deposition time is 20-40 mins.

[0022] (14) 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 300-650℃; 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 450-550℃, the preferred annealing gas is oxygen, and the preferred heating / cooling rate is 5-8℃ / min.

[0023] (15) If ex-situ annealing is adopted, the substrate temperature is reduced from the deposition temperature to room temperature at a rate of 1-10 °C / min; the prepared film is placed in an atmosphere heating furnace for oxygen or nitrogen annealing. The preferred annealing temperature is 450-550 °C; the heating and cooling rate is 5-8 °C / min. Under suitable laser energy, gas pressure and substrate temperature, a superconducting film with high critical temperature and low surface microwave impedance is obtained.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following obvious and prominent substantive features and significant advantages:

[0025] 1. 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 single-crystal substrates, a previously unreported method. Its zero-resistivity transition temperature is 98K, higher than the superconducting transition temperature of YBCO. Based on the understanding of the bulk properties of (Cu,C)Ba2Ca2Cu3O9, the critical temperature can be further increased.

[0026] 2. The method of this invention utilizes pulsed laser deposition technology to optimize thin film preparation conditions and adjust the position and angle of carbon dioxide and oxygen inlet gas, thereby preparing (Cu,C)Ba2Ca3Cu4O with a zero resistance transition temperature higher than 96K on a single-crystal substrate. 11 The thin film achieved an initial transition temperature of 117 K. With optimized conditions, the zero-resistance transition temperature can be further increased.

[0027] 3.(Cu,C)Ba2Ca n-1 Cu n O 2n+3 (n=3,4) Superconducting materials possess advantages such as non-toxicity and high critical temperature. Successfully fabricating thin film materials of these materials on single-crystal substrates and then using them to create microwave filters will reduce their usage costs and promote their commercial application, offering broad prospects for future applications. Attached Figure Description

[0028] Figure 1 This is the RT relationship diagram of the (Cu,C)Ba2Ca2Cu3O9 thin film prepared in Example 1 of the present invention.

[0029] Figure 2 This is the RT relationship diagram of the (Cu,C)Ba2Ca2Cu3O9 thin film prepared in Example 2 of the present invention.

[0030] Figure 3 This refers to (Cu,C)Ba2Ca3Cu4O prepared in Example 3 of this invention. 11 RT relationship diagram of thin film.

[0031] Figure 4 This refers to (Cu,C)Ba2Ca3Cu4O prepared in Example 3 of this invention. 11 XRD diffraction pattern of the thin film. Detailed Implementation

[0032] 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:

[0033] Example 1: A method for preparing (Cu,C)Ba2Ca2Cu3O9 thin films on SrTiO3 single crystal substrates, comprising the following steps:

[0034] (1) According to Ba2Ca3Cu 4.6 O y Weigh out a certain mass of high-purity BaCO3, CaCO3 and CuO powders according to the chemical ratio, mix them and grind them into a uniform powder in a mortar with powder particles smaller than 10 micrometers; place the uniformly ground powder in a crucible or on a corundum sheet, put it in a heating furnace and heat treat it in air; the heat treatment temperature is 800℃ and the heat treatment is constant for 24 hours; BaO and CaO can also be selected to replace BaCO3 and CaCO3 respectively.

[0035] (2) Grind the product obtained in the above steps again to obtain a uniform powder. Press the powder into sheets using a mold with a pressure of 10 MPa, and place them in a heating furnace for heat treatment; the heat treatment temperature is within the above heating range of 830℃, and the heat treatment holding time is 24 hours. Repeat this step 2-8 times. The pressure can be 5 MPa or 15 MPa.

[0036] (3) Grind the block obtained in step (2) into a uniform powder, and press it into a sheet using a mold with a pressure of 10 MPa. Then seal it with a vacuum bag, place it in a hydraulic press, and press it with a pressure of 66 MPa (50 or 100 MPa is also acceptable). Remove the block and place it in a heating furnace for heat treatment. The heat treatment temperature is 860℃, and the heat treatment holding time is 48h; the heating and cooling rates for the above heat treatment are all 5℃ / min.

[0037] 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 1-10℃ / min, and the cooling rate can be 1-10℃ / min, all of which can yield basically the same results.

[0038] (4) Polish the target material prepared in step (3) and then install it in the PLD coating vacuum chamber; fix the single crystal substrate at the position of the base facing the laser feather and then install it in the PLD coating vacuum chamber;

[0039] (5) Heat the substrate to 640℃. 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 through different inlets. Introduce oxygen at a rate of 30 sccm and carbon dioxide at a rate of 5 sccm, maintaining a pressure of 20 Pa within the coating chamber. The volume of carbon dioxide is generally 5%-25% of that of oxygen.

[0040] (6) Block the substrate with a baffle, turn on the laser, and the laser energy density is 1-3 J / cm². 2 The laser frequency was 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, thin film deposition was performed for 20 minutes, with the laser energy and frequency remaining constant. Single-crystal substrates such as LaAlO3, SrTiO3, YAlO3, LaMnO3, NdCaAlO4, LaSrAlO4, LSAT, CeO2, and NdGaO3 have all been used to grow superconducting films. Superconducting films can also be grown on substrates with LaMnO2 and CeO2 cap layers.

[0041] (7) After deposition, maintain the gas pressure in the PLD coating chamber during film deposition and reduce the temperature to room temperature at a rate of 5°C / min. Alternatively, oxygen or nitrogen can be introduced for in-situ annealing to adjust the oxygen content.

[0042] Experimental test analysis in this embodiment:

[0043] The (Cu,C)Ba2Ca2Cu3O9 thin film prepared in this embodiment was characterized by measurements. The resistance-temperature relationship curve of the thin film was measured using a Power Proof-of-Material Measurement System (PPMS). Figure 1 This shows the relationship between the resistivity of the thin film and temperature, revealing that the zero-resistance temperature of the film is approximately 98K. Using 90% of the normal-state resistance as a standard, its initial transition temperature... It is around 110K.

[0044] This study successfully prepared a C-oriented (Cu,C)Ba₂Ca₂Cu₃O₉ thin film for the first time, with a superconducting transition temperature higher than the previously reported maximum value for (Cu,C)Ba₂Cu₃O₉ thin films. It also exceeds the highest transition temperature of YBCO, indicating a promising future for this material. Based on reports of bulk material studies, the oxygen content can be adjusted through different annealing conditions, thereby further increasing its superconducting transition temperature.

[0045] Example 2: A method for preparing (Cu,C)Ba2Ca2Cu3O9 thin films on LSAT single-crystal substrates, comprising the following steps:

[0046] (1) The target preparation method is the same as in Example 1.

[0047] (2) Fix the substrate in the position of the base directly facing the laser feather, dry it, and then put it into the PLD coating vacuum chamber;

[0048] (3) Heat the substrate to 620℃. After the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber. The oxygen is introduced at a rate of 30 sccm, and the carbon dioxide flows to the substrate at a rate of 5 sccm, maintaining the gas pressure in the coating chamber at 20 Pa.

[0049] (4) Adjust the laser energy density to 1-2 J / cm² 2 The laser energy and frequency were kept constant. A 5-minute pre-deposition washing was performed to remove contaminants adhering to the surface. After the pre-deposition was completed and the temperature stabilized, the thin film was deposited for 20 minutes.

[0050] (5) After deposition, high-purity oxygen is introduced into the PLD coating chamber to maintain the pressure in the chamber at 7×10⁻⁶. 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.

[0051] Experimental testing and analysis in this embodiment: The (Cu,C)Ba2Ca2Cu3O9 thin film prepared in this embodiment was characterized, and the resistance of the thin film was measured using a comprehensive physical property measurement system (PPMS). Figure 2 This is a curve showing the resistivity of the thin film as a function of temperature. As shown in the figure, the zero-resistance temperature of the thin film is approximately 92K. Using 90% of the normal-state resistance as a standard, its initial transition temperature is... The temperature was 103 K. X-ray diffraction analysis showed that the film was c-oriented. This example is the first to fabricate a (Cu,C)Ba2Ca2Cu3O9 film on an LSAT substrate, with a critical temperature close to that of materials currently used in filters. Changing the annealing conditions or further optimizing the fabrication conditions could further increase its superconducting transition temperature.

[0052] Example 3: A method for preparing (Cu,C)Ba2Ca3Cu4O on a YAlO3 single crystal substrate 11 The method for preparing thin films includes the following steps:

[0053] (1) The target preparation method is the same as in Example 1.

[0054] (2) Fix the substrate on the stage directly opposite the laser feather, dry it with a heating stage, and then put it into the PLD coating vacuum chamber.

[0055] (3) Heat the substrate to 665℃. After the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber. The oxygen is introduced at a rate of 30 sccm, and the carbon dioxide flows to the substrate at a rate of 5 sccm, maintaining the gas pressure in the coating chamber at 20 Pa.

[0056] (4) Adjust the laser energy density to 1-3 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.

[0057] (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.

[0058] Experimental test analysis in this embodiment:

[0059] The (Cu,C)Ba2Ca3Cu4O prepared in this embodiment 11 The thin film was characterized by measuring its RT curve using a comprehensive physical property measurement system (PPMS). Figure 3 This is a curve showing the resistivity of the thin film as a function of temperature. As shown in the figure, the zero-resistance temperature of the thin film is approximately 96 K. Using 90% of the normal-state resistance as a standard, its initial transition temperature is... It is 117K. Figure 4 The X-ray diffraction pattern of the thin film shows the (h00) diffraction peak, indicating that the film is α-oriented. This example is the first to prepare (Cu,C)Ba2Ca3Cu4O on a YAO substrate. 11 The thin film has a critical temperature higher than that of the materials currently used in filters. After growth, the thin film is annealed in high-purity oxygen to reduce potential defects and oxygen loss during growth.

[0060] 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 application of this invention to the fabrication of (Cu,C)Ba2Ca on a single-crystal substrate for superconducting filters is permitted. 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 preparing a c-axis oriented (Cu,C)Ba2Ca2Cu3O9 superconducting thin film, characterized in that, Includes the following steps: (1) Weigh a certain amount of high-purity BaCO3 or BaO, CaCO3 or CaO and CuO powder according to the ratio, mix them and grind them into uniform powder. The ratio of copper is 3.2-3.8 and the powder particles are less than 10 micrometers. Place the uniformly ground powder in a crucible or on a corundum sheet and put it in a heating furnace for heat treatment in air. The heat treatment temperature is 800℃ and the heat treatment isothermal time is 24h. (2) Grind the product obtained in the above steps again to obtain a uniform powder; press the powder into a sheet using a mold with a pressure of 5MPa, 10MPa or 15MPa, and place it in a heating furnace for heat treatment; heat treatment temperature 830℃, heat treatment time 24h; repeat this step 2-8 times. (3) Grind the block obtained in step (2) 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, place it in a hydraulic press, and press it with a pressure of 50, 66 or 100 MPa; take out the block and place it in a heating furnace for heat treatment; the heat treatment temperature is 860℃, and the heat treatment constant temperature time is 48h; the heating and cooling rates of the above heat treatment are all 5℃ / min; (4) Polish the target material prepared in step (3) and then install it in the PLD coating vacuum chamber; fix the SrTiO3 single crystal substrate on the stage facing the laser plume and then install it in the PLD coating vacuum chamber. (5) Heat the substrate to 640℃, and maintain the vacuum environment in the PLD coating chamber during this period; after the temperature stabilizes, introduce high-purity oxygen and carbon dioxide into the PLD coating chamber through different air inlets; oxygen is introduced at a rate of 30 sccm and carbon dioxide at a rate of 5 sccm, and the gas pressure in the coating chamber is maintained at 20 Pa; the volume of carbon dioxide is 5%-25% of that of oxygen; (6) Block the substrate with a baffle, turn on the laser, and the laser energy density is 1-3 J / cm². 2 The laser was pre-deposited at a frequency of 5 Hz for 5 mins; the distance between the target and the substrate was adjusted to 4 cm; 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. (7) After deposition, maintain the gas pressure in the PLD coating chamber during film deposition and reduce the temperature to room temperature at a rate of 5℃ / min; or introduce oxygen or nitrogen and perform in-situ annealing to adjust its oxygen content.

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