Composite buffer layer structure for high-temperature superconducting tape, preparation method of composite buffer layer structure and superconducting tape

Abstract

The invention relates to a composite buffer layer structure for a high-temperature superconducting tape, a preparation method of the composite buffer layer structure and the superconducting tape, and belongs to the technical field of high-temperature superconducting materials. The composite buffer layer structure comprises a first buffer layer and a flattened cap layer which is formed by epitaxial growth of lanthanum strontium manganese oxide (LSMO) on the first buffer layer through a pulse laser deposition technology. By introducing the LSMO flattening cap layer, the interface roughness is reduced to the atomic level while the excellent texture quality is maintained, and an almost ideal growth template is provided for the superconducting layer. According to the design, the problem that the quality of the superconducting layer is reduced due to the fact that the surface appearance of a traditional buffer layer is rough is effectively solved, the current-carrying performance of the superconducting tape is remarkably improved, and the high-temperature superconducting tape is a breakthrough solution for promoting the second-generation high-temperature superconducting technology to develop to higher performance.

Description

Technical Field

[0001] This invention relates to a composite buffer layer structure for high-temperature superconducting tapes, its preparation method, and the superconducting tape itself, belonging to the field of high-temperature superconducting materials technology. Background Technology

[0002] High-temperature superconducting materials refer to oxide ceramic materials with critical temperatures significantly higher than those of traditional low-temperature superconductors. Their discovery paved the way for superconducting applications in the liquid nitrogen temperature range. These materials, especially the rare-earth barium copper oxide (REBCO) system, have shown great potential in the power and energy sectors. However, the key to their commercial application lies in how to fabricate brittle superconducting ceramics into flexible long strips with high current-carrying capacity, which has spurred the development of coated conductor technology based on flexible metal substrates.

[0003] For example, the invention patent with authorization announcement number CN 100550453C discloses a resistive current limiting device with a strip-shaped high critical temperature superconductor. The strip-shaped superconductor of this resistive current limiting device includes: at least one normally conductive substrate strip, a buffer layer, and a layer made of AB2Cu3O. X A high-Tc superconducting layer and a protective layer composed of oxides; wherein a buffer layer with a maximum Tc between the substrate and the superconducting layer is formed. -3 Ωcm 2 The transition resistance is specified; A is a rare earth metal including 100 million, and B is a rare alkaline earth metal. Specifically, the buffer layer is one of lanthanum manganese oxide, strontium ruthenium oxide, lanthanum nickel oxide, and indium tin oxide. The early second-generation high-temperature superconducting (2G-HTS) technology represented by this patent adopts the basic architecture of "metal substrate strip + buffer layer + REBCO superconducting layer", but its buffer layer design has clear limitations. This device aims to solve the core problem that traditional insulating buffer layers (such as CeO2) are easily broken down by high voltage when the current limiting device fails. The solution is to use a buffer layer material with specific conductivity (such as lanthanum manganese oxide) to form a lower transition resistance between the superconducting layer and the metal substrate strip, so as to achieve potential balance and avoid breakdown.

[0004] However, while pursuing improvements in electrical performance, this technical solution neglects the crucial structural function of the buffer layer as a template for epitaxial growth. The aforementioned buffer layer primarily serves electrical bypass requirements and falls short in meeting the demands of modern high-performance superconducting tapes for high-quality biaxial texture, ultra-smooth surface morphology, and excellent lattice matching with the superconducting layer. This early second-generation tape buffer layer technology may not meet the current requirements for the fabrication of ultra-high critical current density superconducting layers (especially novel copper-carbon superconductors that are extremely sensitive to growth conditions) in terms of texture quality, surface smoothness, and ability to induce epitaxial growth.

[0005] To systematically overcome the shortcomings of early second-generation tapes in terms of texture quality and epitaxial growth quality of the superconducting layer, a more advanced multilayer structure system has been developed. Second-generation high-temperature superconducting (2G-HTS) tapes typically employ a more precise layered structure: a barrier layer (e.g., Al2O3), a textured template layer (e.g., IBAD-MgO), a buffer layer (e.g., LaMnO3, CeO2), and a superconducting layer (e.g., REBCO) are sequentially deposited on a flexible metal substrate (e.g., Hastelloy). This system, by introducing a specialized textured template layer (e.g., IBAD-MgO) and an optimized buffer layer, aims to precisely control crystal orientation, providing a near-perfect epitaxial growth template for the superconducting layer, thereby significantly improving current-carrying performance.

[0006] In recent years, novel copper-carbon based high-temperature superconductors (Cu,C)Ba2Ca2Cu3O have been developed. y Or (Cu,C)Ba2Ca3Cu4O y It has attracted attention due to its excellent current-carrying performance under high magnetic fields. However, its high-quality epitaxial growth is highly dependent on the surface quality and lattice size matching of the strip buffer layer.

[0007] Currently, the buffer layers of commercially available tapes (such as CeO2 or LaMnO3) typically exhibit nanoscale roughness, grain boundary trenches, or protrusions caused by island-like growth patterns, as well as in-plane lattice sizes that differ significantly from those of copper-carbon high-temperature superconductors. In other words, traditional buffer layers are incompatible with novel copper-carbon high-temperature superconductors. These surface defects are replicated in subsequent superconducting layers, leading to: 1) localized uneven thickness in the superconducting layer, which can easily form weak connections or become bottlenecks for current transport in thin regions; 2) the formation of amorphous regions or lattice distortions, disrupting the continuity of the superconducting phase and reducing intergranular current; and 3) during subsequent superconducting layer deposition and growth, uneven surfaces can lead to cracks or uneven coating, and large differences in in-plane lattice sizes are detrimental to the epitaxial growth of the superconducting layer. Summary of the Invention

[0008] To solve the above problems, the present invention provides, in a first aspect, a composite buffer layer structure for high-temperature superconducting tapes.

[0009] The technical solution of the present invention to solve the above problems is as follows:

[0010] A composite buffer layer structure for high-temperature superconducting tapes, comprising:

[0011] a) A first buffer layer formed on the template layer; and

[0012] b) A planarization cap layer formed on the first buffer layer, wherein the planarization cap layer is formed by epitaxial growth of lanthanum strontium manganese oxide (LSMO) material using pulsed laser deposition technology, and the thickness of the planarization cap layer is 20~100 nanometers.

[0013] In the above technical solution of this invention, the template layer is a biaxial texture layer formed on the barrier layer, which provides high-quality crystallographic texture and lays a perfect foundation for the epitaxial growth of the subsequent buffer layer; the barrier layer is formed on the metal substrate, and its function is to form a chemical barrier to prevent element interdiffusion; the flexible metal substrate is preferably Hastelloy to balance mechanical strength and high-temperature stability. The composite buffer layer structure introduces a planarization cap layer (LSMO) specifically used to modify the surface morphology of the original buffer layer (such as CeO2 or LaMnO3), providing an atomically flat interface for the epitaxial growth of the subsequent superconducting layer.

[0014] This approach is not a simple replacement or stacking of traditional buffer layer materials, but rather an interface engineering solution proposed based on a profound understanding of the epitaxial growth mechanism of superconducting layers, the intrinsic relationship between interface effects and current-carrying performance. It aims to overcome the current bottlenecks in the fabrication of high-performance superconducting tapes (especially novel copper-carbon superconductors that are extremely sensitive to growth interfaces). Its goal is to address the core issues of poor texture quality, rough surface morphology, and lack of epitaxial growth induction ability in traditional and existing buffer layers, thereby improving the critical current density of superconducting tapes.

[0015] Existing technologies reveal that buffer layers need to possess good biaxial texture, chemical inertness, smooth surface morphology, and in-plane lattice size similar to copper-carbon high-temperature superconducting materials. The composite buffer layer structure of this invention is specifically proposed to address the aforementioned issue of "buffer layer interface restricting epitaxial growth quality."

[0016] This invention decouples and reconstructs the traditional buffer layer's integrated functions of "providing texture templates" and "chemical barrier / interface smoothing"; and on this basis, it expands and refines the interface function from the basic "chemical barrier" to a synergistic optimization of "chemical barrier and atomic-level smoothing interface".

[0017] Firstly, the professional decoupling and independent realization of the texture template function. This invention introduces a specialized biaxial texture template layer (such as an IBAD-MgO or RABiTS substrate) to separate the core function of "providing high-quality crystallographic texture" from the traditional buffer layer and realize it independently. The technical logic lies in allowing the template layer to focus solely on inducing the formation of highly oriented crystal structures through advanced processes such as IBAD or RABiTS, laying a perfect epitaxial growth foundation for the entire multilayer film system and providing a reliable crystallographic guarantee for obtaining high critical current density from the source.

[0018] Secondly, the introduction of interface smoothing function and the source control of growth defects. The core innovation of this invention lies in introducing an additional LSMO cap layer with a dedicated "smoothing" function on a substrate with good texture. The technical logic is to utilize the excellent two-dimensional layered growth characteristics of LSMO materials, and grow it on an underlying layer (such as IBAD-MgO / CeO2) with intrinsic roughness using pulsed laser deposition (PLD) technology in a "peak-shaving and valley-filling" mode. The direct technical effect is a significant reduction in the root mean square roughness (RMS) of the surface to below 1 nanometer, providing a near-atomic-level smooth substrate surface. This eliminates the randomness of heterogeneous nucleation in the superconducting layer at its source, creating prerequisites for achieving uniform, dense, and defect-free high-quality epitaxial growth, directly overcoming the problems of "local thickness non-uniformity" and "coating non-uniformity leading to cracks" described in the background technology.

[0019] Thirdly, there is the synergistic optimization of texture inheritance and lattice matching. The planarized cap layer (LSMO) has a good lattice match with common oxide buffer layers (such as CeO2 or LaMnO3), perfectly replicating their high-quality biaxial texture and ensuring that the superconducting layer obtains an excellent crystallographic template. At the same time, its in-plane lattice constant is more compatible with novel copper-carbon superconductors (such as CuC-1223 / 1234). This design achieves dual optimization of texture quality and interface lattice matching. Its technical effect is to promote the epitaxial growth of the superconducting layer with a lower defect density, effectively reduce lattice distortion, enhance the continuity of the superconducting phase, and thus significantly improve the intercrystalline current transport capability.

[0020] Fourthly, process compatibility and functional layered design. This invention employs a composite structure of "template layer + first buffer layer + planarization cap layer," a typical functional layered design. Its technical logic lies in allowing each sublayer to perform its specific function: the template layer provides texture; the first buffer layer (such as CeO2 or LaMnO3) primarily undertakes lattice bonding and basic chemical barrier functions; while the planarization cap layer (LSMO) specializes in surface morphology optimization. The effect of this design is that it can be seamlessly integrated as a standard module into existing commercial tape fabrication processes such as IBAD-MgO or RABiTS, requiring only an additional PLD deposition step of the LSMO cap layer before the superconducting layer deposition. This eliminates the need for major modifications to existing production lines, demonstrating significant potential for industrial application.

[0021] As a preferred embodiment of the above technical solution, the thickness of the smoothing cap layer is 20-50 nanometers.

[0022] This thickness range is sufficient to smooth out the surface undulations of the original buffer layer, achieving excellent smoothing, while avoiding excessive thickness that could lead to stress accumulation or unnecessary increases in manufacturing costs.

[0023] As a preferred embodiment of the above technical solution, the root mean square surface roughness of the smoothed cap layer is less than 1 nanometer.

[0024] Atomic-level smooth surfaces are key indicators for inducing high-quality epitaxial growth and minimizing weak grain boundary connections, which are directly related to improving the critical current density of superconducting tapes.

[0025] As a preferred embodiment of the above technical solution, the planarization cap layer is formed by epitaxial growth using pulsed laser deposition (PLD) technology at a temperature of 600~800℃ and an oxygen partial pressure of 10~200 mTorr.

[0026] This PLD process window ensures that LSMO films are epitaxially grown in a two-dimensional layered mode to obtain the required crystal quality and surface morphology, which is a key process guarantee for realizing its planarization function.

[0027] As a preferred embodiment of the above technical solution, the template layer is an MgO layer prepared by ion beam assisted deposition (IBAD).

[0028] IBAD-MgO is a mature and reliable technology that provides high-quality biaxial texture in currently commercial 2G-HTS tapes, providing an excellent texture foundation for this composite buffer layer structure.

[0029] As another preferred embodiment of the above technical solution, the template layer is a NiW alloy layer and an oxide layer thereon prepared by rolling-assisted biaxial texturing technology (RABiTS).

[0030] As a preferred embodiment of the above technical solution, the first buffer layer is CeO2.

[0031] As another preferred embodiment of the above technical solution, the first buffer layer is LaMnO3.

[0032] CeO2 is a classic buffer layer material with a lattice match to the MgO template layer; LaMnO3, on the other hand, is inherently conductive and can be selected based on the electrical performance requirements of the final tape. The planarization cap layer of this invention is compatible with various first buffer layers, demonstrating its wide applicability.

[0033] Secondly, the present invention provides a method for preparing the above-mentioned composite buffer layer structure for high-temperature superconducting tapes.

[0034] The technical solution is as follows:

[0035] A method for preparing a composite buffer layer structure for high-temperature superconducting tapes includes the following steps:

[0036] 1) Provide a metal base strip with a barrier layer, a biaxial textured template layer, and a first buffer layer;

[0037] 2) Place the baseband in the PLD vacuum chamber and heat it to 600~800℃;

[0038] 3) Introduce oxygen into the chamber and control the oxygen partial pressure to 10~200 mTorr;

[0039] 4) Use a pulsed laser to ablate the LMO or LSMO ceramic target, and epitaxially grow an LSMO thin film with a thickness of 20~100 nanometers on the first buffer layer to form the planarization cap layer.

[0040] Thirdly, the present invention provides a superconducting tape.

[0041] The technical solution is as follows:

[0042] A superconducting tape comprising the composite buffer layer structure described above and (Cu,C)Ba2Ca2Cu3O epitaxially grown on the planarized cap layer. y Or (Cu,C)Ba2Ca3Cu4O y Superconducting layer.

[0043] In summary, the present invention has the following beneficial effects:

[0044] 1. Fundamental improvement in crystal quality and current-carrying capacity of superconducting layer: By providing an atomically flat growth interface, lattice defects and weak connections in the superconducting layer are fundamentally reduced, significantly improving the intercrystalline current transport capacity and laying the material foundation for the preparation of high-performance superconducting tapes;

[0045] 2. Strong compatibility with novel superconducting materials: It is especially suitable for new-generation high-temperature superconducting materials such as copper-carbon (CuC) materials, which are extremely sensitive to the growth interface, solving the key bottleneck of their high-quality epitaxial growth and broadening the selection range of high-performance superconducting materials.

[0046] 3. Strong process inheritance and bright industrialization prospects: It can be directly embedded into existing commercial production lines, added as only as an optimization process, without the need for disruptive transformation. The cost of technology upgrade is low, and it is easy to promote and implement, which accelerates the industrialization process of high-performance superconducting tapes.

[0047] 4. In summary, the composite buffer layer structure of this invention, starting from the intrinsic requirements of epitaxial growth of superconducting materials, achieves precise control of the growth interface through an innovative "flattened cap layer" design. This solution surpasses the basic requirements of traditional buffer layers that only meet the requirements of texture and chemical stability, elevating the interface quality to a new level of atomic-level flatness. It is a breakthrough solution for the key bottlenecks currently restricting the performance of high-temperature superconducting tapes, and is of great significance for promoting the development of second-generation high-temperature superconducting technology towards higher performance. Attached Figure Description

[0048] Figure 1 Atomic force microscopy (AFM) images of the comparative surface and the surface of Embodiment 1 of the present invention;

[0049] Figure 2 This is an XRD pattern of Embodiment 1 of the present invention;

[0050] Figure 3 This is the resistance-temperature curve of Embodiment 1 of the present invention. Detailed Implementation

[0051] The present invention will be further explained and described below with reference to the accompanying drawings.

[0052] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. Any changes made by those skilled in the art after reading this specification, as long as they fall within the scope of the claims, will be protected by patent law.

[0053] Example 1

[0054] A high-temperature superconducting tape with a composite buffer layer structure, comprising, from bottom to top:

[0055] a) Flexible metal substrate;

[0056] b) A barrier layer formed on the metal substrate;

[0057] c) A template layer with a biaxial texture formed on the barrier layer;

[0058] d) A first buffer layer formed on the template layer;

[0059] e) A planarization cap layer formed on top of the first buffer layer;

[0060] f) A superconducting layer formed on the planarized cap layer.

[0061] The metal substrate, barrier layer, template layer, and first buffer layer are a commercially available whole, which is an IBAD-MgO template strip. Its specific structure is Hastelloy substrate / Al2O3 barrier layer / IBAD-MgO texture layer / sputter-deposited LaMnO3 first buffer layer.

[0062] The planarization cap layer is formed by epitaxial growth of lanthanum strontium manganese oxide (LSMO) material using pulsed laser deposition technology; in this embodiment, the thickness of the planarization cap layer is approximately 30 nanometers.

[0063] The superconducting layer is CuC-Ba2Ca2Cu3O y The thickness is approximately 300 nanometers.

[0064] Specifically, the preparation method of the high-temperature superconducting tape includes the following steps:

[0065] 1) Provide a commercially available IBAD-MgO template tape, the structure of which is / Al2O3 barrier layer / IBAD-MgO texture layer / sputtered LaMnO3 first buffer layer;

[0066] 2) Load the strip into a continuous multi-chamber PLD equipment;

[0067] 3) In the deposition chamber, the strip is locally heated to 700°C and high-purity oxygen is introduced to maintain the chamber pressure at 100mTorr;

[0068] 4) Ablation of La using a KrF excimer laser (248nm) 0.7 Sr 0.3 MnO3 (LSMO) target material, laser energy density of 1.5 J / cm², repetition frequency of 10 Hz;

[0069] 5) Control the tape movement speed and deposit an LSMO planarization cap layer with a thickness of approximately 30 nm on the first buffer layer;

[0070] 6) Subsequently, in an adjacent deposition chamber or the same chamber, without interrupting the vacuum and temperature, switch to CuC-BaCaCuO target material to deposit a superconducting layer of about 300 nm thickness on the LSMO cap layer.

[0071] 7) The final superconducting tape is then produced through standardized silver plating and annealing processes.

[0072] Example 2

[0073] It is basically the same as Example 1, except that the thickness of the smoothing cap layer is about 20 nanometers.

[0074] Example 3

[0075] It is basically the same as Example 1, except that the thickness of the smoothing cap layer is about 50 nanometers.

[0076] Example 4

[0077] It is basically the same as Example 1, except that the thickness of the planarization cap layer is about 80 nanometers.

[0078] Example 5

[0079] It is basically the same as Example 1, except that the thickness of the planarization cap layer is about 100 nanometers.

[0080] Comparative Example

[0081] A high-temperature superconducting tape with a buffer layer structure, comprising, from bottom to top:

[0082] a) Flexible metal substrate;

[0083] b) A barrier layer formed on the metal substrate;

[0084] c) A template layer with a biaxial texture formed on the barrier layer;

[0085] d) A buffer layer formed on the template layer;

[0086] e) A superconducting layer formed on the buffer layer.

[0087] The metal substrate, barrier layer, template layer, and buffer layer are a commercially available whole, consisting of an IBAD-MgO template strip. Its specific structure is a Hastelloy substrate / Al2O3 barrier layer / IBAD-MgO texture layer / sputter-deposited LaMnO3 buffer layer.

[0088] The superconducting layer is CuC-Ba2Ca2Cu3O y The thickness is approximately 300 nanometers.

[0089] Specifically, the preparation method of the high-temperature superconducting tape includes the following steps:

[0090] 1) Provide a commercially available IBAD-MgO template tape, the structure of which is / Al2O3 barrier layer / IBAD-MgO texture layer / sputtered LaMnO3 first buffer layer;

[0091] 2) Load the strip into the PLD equipment;

[0092] 3) In the deposition chamber, the strip is locally heated to 700°C and high-purity oxygen is introduced to maintain the chamber pressure at 100mTorr;

[0093] 4) Ablate the CuC-BaCaCuO target using a KrF excimer laser (248nm) with a laser energy density of 1.5 J / cm² and a repetition frequency of 10 Hz.

[0094] 5) Control the tape moving speed and deposit a superconducting layer about 300 nm thick on the buffer layer;

[0095] 6) The final superconducting tape is then produced through standardized silver plating and annealing processes.

[0096] The samples from Example 1 and the comparative example are characterized below.

[0097] 1. Atomic Force Microscopy (AFM) – Surface Topography Characterization

[0098] Experimental methods:

[0099] AFM scanning of the sample surface detects the interatomic forces between the needle tip and the surface, generating a three-dimensional topographic map.

[0100] Data analysis: Root mean square roughness (RMS) was calculated to compare the change in surface smoothness before and after LSMO deposition. RMS < 1 nm is considered "atomic-level smoothness" and is suitable for high-quality epitaxial growth.

[0101] 2. X-ray diffraction (XRD) – Characterization of crystal structure and texture

[0102] Experimental methods:

[0103] θ-2θ scan: detect c-axis orientation (e.g., the (001) diffraction peak of CuC-1223).

[0104] 3. Resistance-Temperature Curve (RT Curve) – Characterization of Superconducting Properties

[0105] Experimental methods:

[0106] Four-probe method: Electrodes are arranged on the sample surface, a direct current is passed through, and the voltage changes with temperature is measured.

[0107] Temperature control range: typically from room temperature (300 K) down to liquid nitrogen temperature.

[0108] Key parameters:

[0109] Superconducting transition temperature: The high point of the superconducting transition temperature range, the temperature at which the electrical resistance is about to change abruptly from the normal state;

[0110] Zero resistance temperature: the lowest point in the superconducting transition temperature range, also called the final transition temperature, the temperature at which the resistance drops to 0.

[0111] Representation order and correlation:

[0112] First, the morphology and texture quality of the LSMO cap layer were verified using AFM. Figure 1 );

[0113] The epitaxial growth of the superconducting layer was then verified using XRD. Figure 2 );

[0114] Finally, the electrical properties of the superconducting layer were verified using RT curves. Figure 3 This establishes a complete chain of "flat interface → high-quality epitaxy → high-performance superconductivity".

[0115] Characterization results:

[0116] like Figure 1As shown, atomic force microscopy (AFM) images are of the surface of the comparative example (only the conventional LaMnO3 buffer layer) and the surface of Example 1 of the present invention (LaMnO3 + PLD-LSMO cap layer). AFM tests show that after depositing the LSMO cap layer, the surface morphology is effectively optimized, and the RMS roughness of the surface is reduced from ~1.2 nm of the original LaMnO3 layer to <0.9 nm; an atomically smooth surface is achieved.

[0117] like Figure 2 As shown, this is Example 1 (LaMnO3 + LSMO planarization cap layer + CuC-Ba2Ca2Cu3O) y XRD pattern of the superconducting layer, showing the LSMO planarized cap layer + CuC-Ba2Ca2Cu3O y Epitaxial growth on a LaMnO3 buffer layer resulted in a film with high crystallinity. This indicates that the LSMO planarization cap layer fully inherited the strong biaxial texture of IBAD-MgO and LaMnO3, and induced a c-axis preferred orientation of CuC-Ba2Ca2Cu3O. y Epitaxial growth of (CuC-1223) superconducting thin films.

[0118] Figure 3 Example 1 (LaMnO3 + LSMO planarization cap layer + CuC-Ba2Ca2Cu3O) y The resistance-temperature curve of the superconducting layer; as shown in the figure, the initial transition temperature of the superconducting thin film is 115K, and the zero resistance temperature of the superconducting thin film is 94K.

[0119] Figures 1-3 Together, these findings indicate that the LSMO smoothing cap layer, while maintaining excellent texture quality, significantly improves the smoothness of the growth interface, thus facilitating the formation of CuC-Ba2Ca2Cu3O. y The high-quality epitaxial growth of the (CuC-1223) superconducting layer provides an ideal crystallographic and morphological basis, and ultimately a high-performance superconducting thin film with a high onset transition temperature (about 115 K) and a steep superconducting transition is successfully realized, verifying the effectiveness and advantages of the composite buffer layer structure of the present invention in improving the performance of second-generation high-temperature superconducting tapes.

Claims

1. A composite buffer layer structure for high-temperature superconducting tapes, comprising: a) A first buffer layer formed on the template layer; Its characteristic is that it further includes: b) A planarization cap layer formed on the first buffer layer, wherein the planarization cap layer is formed by epitaxial growth of lanthanum strontium manganese oxide material using pulsed laser deposition technology, and the thickness of the planarization cap layer is 20~100 nanometers.

2. The composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The thickness of the smoothing cap layer is 20-50 nanometers.

3. The composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The root mean square surface roughness of the smoothed cap layer is less than 1 nanometer.

4. The composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The smoothed cap layer is formed by epitaxial growth using pulsed laser deposition technology at a temperature of 600~800℃ and an oxygen partial pressure of 10~200 mTorr.

5. A composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The template layer is a MgO layer prepared by ion beam assisted deposition technology.

6. The composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The template layer consists of a NiW alloy layer and an oxide layer thereon, prepared by rolling-assisted biaxial texturing technology.

7. A composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The first buffer layer is CeO2.

8. The composite buffer layer structure for high-temperature superconducting tapes according to claim 1, characterized in that: The first buffer layer is LaMnO3.

9. A method for preparing a composite buffer layer structure for high-temperature superconducting tapes according to any one of claims 1 to 8, comprising the following steps: 1) Provide a metal base strip with a barrier layer, a biaxial textured template layer and a first buffer layer; 2) Place the baseband in the PLD vacuum chamber and heat it to 600~800℃; 3) Introduce oxygen into the chamber and control the oxygen partial pressure to 10~200 mTorr; 4) Use a pulsed laser to ablate the LMO or LSMO ceramic target, and epitaxially grow an LSMO thin film with a thickness of 20~100 nanometers on the first buffer layer to form the planarization cap layer.

10. A superconducting tape, characterized in that: Includes the composite buffer layer structure as described in any one of claims 1 to 8 and (Cu,C)Ba2Ca2Cu3O epitaxially grown on the planarized cap layer. y Or (Cu,C)Ba2Ca3Cu4O y Superconducting layer.

Images