CN102723141B - Gd1-xCaxBiO3 buffering layer of high temperature superconducting coated conductor and preparation method thereof - Google Patents

Abstract

The invention discloses a high-temperature superconducting coating conductor Gd _1-x Ca _x BiO ₃ buffer layer, which is characterized in that the high-temperature superconducting coating conductor GdBiO ₃ buffer layer is replaced by Ca of Gd and then epitaxial phase forming heat treatment Generate oxide Gd _1-x Ca _x BiO ₃ solid solution, where 0.1≤x≤0.4. The Gd _1-x Ca _{x BiO} buffer layer of the high-temperature superconducting coating conductor of the present invention, after it is to replace the Ca of Gd to the _GdBiO buffer layer of the high-temperature superconducting coating conductor, will make the _GdBiO buffer layer element The environment and lattice parameters are fine-tuned to adjust the lattice mismatch between the GdBiO ₃ buffer layer and the REBCO superconducting layer. The buffer layer can be grown epitaxially in the air at about 810 ° C. Its structure is dense and the surface is flat, and in the subsequent High-temperature superconducting coated conductors maintain structural stability during the preparation of the superconducting layer. The preparation method of the Gd _1-x Ca _x BiO ₃ buffer layer described in the present invention adopts the chemical solution deposition method using nitrate as the precursor to prepare in the air, has the advantages of low cost, easy operation and control, and is suitable for large-scale deposition and other advantages.

Description

A high-temperature superconducting coating conductor Gd1-xCaxBiO3 buffer layer and its preparation method

technical field

The invention relates to the technical field of preparation of high-temperature superconducting materials, in particular to a high-temperature superconducting coating conductor Gd _1-x Ca _x BiO ₃ buffer layer and its preparation technology.

Background technique

In recent years, the second-generation high-temperature superconducting tape, that is, rare-earth barium-copper-oxide-coated conductors, has attracted worldwide attention due to its potential application prospects. Because the second-generation high-temperature superconducting tape has better current-carrying performance than the first-generation bismuth-based superconductor in the liquid nitrogen temperature zone and external magnetic field, it is used in superconducting cables, generators, motors, magnetic energy storage and magnetic resonance imaging. etc. have important applications. Starting from the technological innovation and long-term interests of their own electric energy, the developed countries are vigorously promoting the research and practical application of the second-generation high-temperature superconductors, and the international competition is becoming more and more fierce. the

The composition of the high temperature superconducting layer of the coated conductor is REBa ₂ Cu ₃ O _x (referred to as REBCO, RE is yttrium or lanthanide). For practical applications such as superconducting wires and superconducting magnets, brittle REBCO high-temperature oxide superconducting materials must be coated on metal substrates with excellent mechanical properties (strength, toughness) to reduce or avoid mechanical damage during processing or use. damage. In addition, this substrate material also needs to have good electrical and thermal conductivity to avoid system failure and collapse caused by local quenching during use.

In addition, REBCO high-temperature superconducting layer material has extremely strong anisotropy due to its own layered structure, and the carrying current capacity of the ab plane of the crystal lattice is much higher than that of the c-axis direction. The current-carrying performance of REBCO high-temperature superconducting materials is extremely sensitive to the lattice mismatch in the a and b directions. To ensure the current-carrying capacity of REBCO, epitaxial weaving constitutes an indispensable process in its preparation technology. So far, the best substrate material recognized at home and abroad is Ni-based alloy material. However, there is a certain lattice mismatch between the ab plane of Ni-based alloy and REBCO high-temperature superconducting material, and the epitaxial growth of REBCO high-temperature superconducting material directly on the Ni-based alloy substrate has extremely poor superconductivity, so a layer must be added to the alloy substrate. The buffer layer. On the one hand, it prevents the interdiffusion and chemical reaction between Ni-based alloy and REBCO, and on the other hand, it acts as an intermediate template for epitaxial growth from Ni-based alloy to REBCO. Only in this way can we ensure the preparation of REBCO high temperature superconducting coated conductors with excellent performance. Therefore, all high-temperature superconducting coated conductors have a three-layer structure of substrate, buffer layer (at least one layer) and REBCO superconducting coating.

At present, various developed countries have invested heavily and developed a series of buffer layer materials with practical level after more than 20 years of development. Such as SrTiO ₃ , La ₂ Zr ₂ O ₇ , CeO ₂ , YSZ, RE ₂ O ₃ and so on. However, most of these materials have a high melting point, and they need to be epitaxially grown at about 1000°C to form a buffer layer with good performance, and they need to be prepared under low oxygen partial pressure. The high preparation cost seriously affects the practical application of high-temperature coated conductors. progress. More importantly, most of these buffer layer materials are under the protection of intellectual property rights in Europe, the United States, Japan and other countries, which will seriously affect and restrict my country's research and development and industrial production of second-generation high-temperature superconducting coated conductors. .

In addition, methods for preparing high-temperature superconducting coated conductors include physical vapor deposition (PVD), metal-organic chemical vapor deposition (MOCVD), and chemical solution deposition (CSD). Compared with other methods, the CSD method has unique advantages such as low cost, relatively simple operation, precise composition control and suitable for large-area deposition. It is conducive to accelerating the large-scale industrial application of the second-generation high-temperature superconducting coated conductors, and has gradually become the main process method and research hotspot for preparing buffer layers and REBCO layers.

Contents of the invention

The object of the present invention is to provide a buffer layer (Gd _1-x Ca _x BiO ₃ ) of a high-temperature superconducting coated conductor, which can be epitaxially grown in air at about 810°C, and has a dense structure and a flat surface. And the structure is kept stable during the subsequent preparation process of the superconducting layer of the high-temperature superconducting coated conductor.

The present invention is achieved by constructing a high-temperature superconducting coating conductor Gd _1-x Ca _x BiO ₃ buffer layer, which replaces Ca of Gd on the high-temperature superconducting coating conductor GdBiO ₃ buffer layer and then epitaxially forms a phase The oxide Gd _1-x Ca _x BiO ₃ solid solution formed by heat treatment, where 0.1≤x≤0.4.

REBiO ₃ series buffer layer materials are new buffer layer materials independently developed by the Superconducting and New Energy Center of Southwest Jiaotong University, and their crystal structure, phase formation temperature, electrical and magnetic properties, and stability during the preparation of REBCO were studied. The results show that REBiO ₃ series buffer layer materials match REBCO in crystal structure, and the lower phase formation temperature becomes the highlight of this type of material; in addition, during the preparation process of REBCO thin film, REBiO ₃ also maintains a high stability. GdBiO ₃ is one of REBiO ₃ series buffer layer materials, and the Gd element in its chemical formula has an ionic radius close to that of Ca element. After replacing Ca with Gd in the GdBiO ₃ buffer layer, the element environment and lattice parameters of the GdBiO ₃ buffer layer will be fine-tuned, thereby adjusting the lattice mismatch between the GdBiO ₃ buffer layer and the REBCO superconducting layer. And obtained a series of buffer layer Gd _1-x Ca _x BiO ₃ of new high-temperature superconducting coated conductors, where 0.1≤x≤0.4.

In addition, the Gd _1-x Ca _x BiO ₃ buffer layer is made by epitaxial phase formation heat treatment of Gd ₂ O ₃ , CaO, Bi ₂ O ₃ , and the lattice parameters of Gd ₂ O ₃ , CaO, Bi ₂ O ₃ are mostly cubic structure. Or tetragonal structure, and has a good match with the REBCO superconducting layer lattice, and the Gd _1-x Ca _x BiO ₃ formed by their solid solution should also have a good lattice match with the REBCO superconducting layer. The melting point of CaO is about 2580°C, which is much higher than the melting point of the REBCO superconducting layer (about 1050°C). The Gd _1-x Ca _x BiO ₃ buffer layer prepared by replacing the Gd element of the GdBiO ₃ buffer layer with Ca element is subsequently The superconducting layer of the HTS coated conductor will maintain structural stability during the preparation process.

The performance of the Gd _1-x Ca _x BiO ₃ buffer layer of the present invention will be verified by the experiments provided by the present invention.

The present invention also provides a method for preparing the high-temperature superconducting coating conductor Gd _1-x Ca _x BiO ₃ buffer layer, which is prepared in air by chemical solution deposition using nitrate as a precursor, and has the advantages of low cost , suitable for large-scale deposition and other advantages. Substituting Ca of Gd for the high-temperature superconducting coating conductor GdBiO ₃ buffer layer and then epitaxially forming a phase-forming heat treatment to generate an oxide Gd _1-x Ca _x BiO ₃ solid solution, wherein 0.1≤x≤0.4, and the preparation method includes the following steps:

a. Colloid preparation: dissolve the precursors Gd, Ca, and Bi nitrate in an appropriate amount of polyacrylic acid according to the metal cation ratio Gd:Ca:Bi=1-x:x:1, where 0.1≤x≤0.4, The total molar concentration of the final solution is 0.2mol/L;

b. Colloid coating and drying and thermal decomposition treatment: coat the colloid prepared in step a on the substrate, and then dry; after drying, perform thermal decomposition treatment in the air before sintering, that is, the substrate coated with colloid The piece is placed in the sintering furnace, and the furnace temperature is slowly raised from room temperature to 180°C-230°C, and then raised to 300°C-340°C at a speed of 0.1-2°C/min, and then at a speed of 0.1-1°C/min Raise to 540°C-560°C and keep it warm for 0.5 hours to make the coating formed by sintering smoother and denser;

c. Sintering to form a phase: After drying and decomposing the colloid-coated substrate, put it into a sintering furnace to sinter to form a phase, and finally obtain a Gd _1-x Ca _x BiO ₃ buffer layer; the specific method is: in the air Rapidly raise the furnace temperature to 800°C -820°C at a rate of 10-100°C/min, and keep it warm for 40-60 minutes; then let the furnace temperature slowly drop to room temperature.

According to the preparation method of the high-temperature superconducting coating conductor Gd _1-x Ca _{x BiO} buffer layer of the present invention, it is characterized in that: in the b step, the specific way of coating the colloid on the substrate is: drop the colloid On the substrate, use a glue leveler to rotate, so that the colloid is evenly coated on the substrate.

According to the preparation method of the high-temperature superconducting coated conductor Gd _1-x Ca _x BiO ₃ buffer layer of the present invention, it is characterized in that: the drying temperature in the b step is 100°C-150°C.

According to the preparation method of the high-temperature superconducting coating conductor Gd _1-x Ca _{x BiO} buffer layer of the present invention, it is characterized in that: after the drying of the above-mentioned b step, before the sintering of the c step to form a phase, also carry out the sintering before the sintering Thermal decomposition treatment in the air, that is, place the colloid-coated substrate in a sintering furnace, and slowly increase the temperature of the furnace from room temperature to 180°C-230°C, and rise to 300°C at a speed of 0.1-2°C/min. -340°C, then rise to 540°C-560°C at a speed of 0.1-1°C/min, and hold for 0.5 hours. After such thermal decomposition treatment before sintering, the coating formed by sintering can be made smoother and denser.

The beneficial effect of the present invention is: the Gd _1-x Ca _{x BiO} buffer layer of the high-temperature superconducting coating conductor of the present invention, it is after the replacement of Ca of Gd to the high-temperature superconducting coating conductor GdBiO ₃ buffer layer, The element environment and lattice parameters of the GdBiO ₃ buffer layer will be fine-tuned, thereby adjusting the lattice mismatch between the GdBiO ₃ buffer layer and the REBCO superconducting layer, and a series of new high-temperature superconducting coated conductor buffer layers Gd ₁ will be obtained. _-x Ca _x BiO ₃ , where 0.1≤x≤0.4. In addition, the buffer layer can be epitaxially grown in air at about 810°C, and its structure is dense and its surface is flat. And the structure is kept stable during the subsequent preparation process of the superconducting layer of the high-temperature superconducting coated conductor. The preparation method of the Gd _1-x Ca _x BiO ₃ buffer layer described in the present invention adopts the chemical solution deposition method using nitrate as the precursor to prepare in the air, has the advantages of low cost, easy operation and control, and is suitable for large-scale deposition and other advantages.

Description of drawings

Fig. 1 is the X-ray diffraction pattern of the Gd _0.9 Ca _0.1 BiO ₃ buffer layer in Example 1.

Fig. 2 is a 10000 times scanning electron microscope (SEM) photo of the Gd _0.9 Ca _0.1 BiO ₃ buffer layer in Example 1.

Fig. 3 is the X-ray diffraction pattern of the Gd _0.7 Ca _0.3 BiO ₃ buffer layer in Example 2.

Fig. 4 is a 10000 times scanning electron microscope (SEM) photo of the Gd _0.7 Ca _0.3 BiO ₃ buffer layer in Example 2.

Fig. 5 is the X-ray diffraction pattern of the Gd _0.6 Ca _0.4 BiO ₃ buffer layer in Example 3.

Fig. 6 is a 10000 times scanning electron microscope (SEM) photo of the Gd _0.6 Ca _0.4 BiO ₃ buffer layer in Example 3.

The vertical coordinates of Figures 1, 3 and 5 are diffraction intensity (Intensity), arbitrary unit (a.u.); the horizontal coordinate is diffraction angle 2θ, and the unit is degree (deg). the

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention will be described in further detail:

Embodiment one

The invention provides a buffer layer Gd _0.9 Ca _0.1 BiO ₃ of a high-temperature superconducting coated conductor. And a kind of method for preparing high-temperature superconducting coating conductor Gd _0.9 Ca _{0.1 BiO} buffer layer film, its steps are:

a. Gd _0.9 Ca _0.1 BiO ₃ buffer layer colloid preparation: the precursors Gd, Ca, and Bi nitrate were dissolved in an appropriate amount of polyacrylic acid (PAA) at a cation concentration of 0.9:0.1:1 to obtain an organic system. The total molar concentration of the final solution is 0.2mol/L.

b. Coating of Gd _0.9 Ca _0.1 BiO ₃ buffer layer, drying and decomposition: Coating the colloid prepared in step a on the LaAlO ₃ single crystal substrate, and then drying at 100°C; then placing it in a sintering furnace, In the air, the furnace temperature was slowly raised from room temperature to 180°C, and then raised to 300°C at a speed of 0.1°C/min, and then raised to 540°C at a speed of 0.1°C/min, and kept for 30 minutes.

c. Sintering phase formation: Put the substrate obtained after the above drying and heat treatment decomposition into a sintering furnace, rapidly raise the furnace temperature to 800°C at a rate of 10°C/min in the air, and keep it warm for 50 minutes; The furnace temperature was slowly lowered to room temperature, and finally a Gd _0.9 Ca _0.1 BiO ₃ buffer layer was obtained.

Fig. 1 is the X-ray diffraction pattern of the Gd _0.9 Ca _0.1 BiO ₃ buffer layer in Example 1 of the present invention. It can be seen from the figure that except for the diffraction peak _of the Gd _0.9 Ca _0.1 BiO ₃ buffer layer (002) and the diffraction peak of the substrate LaAlO ₃ , there are no other impurity peaks of Gd _0.9 Ca 0.1 BiO ₃ , implying that the Gd _0.9 Ca _0.1 BiO ₃ buffer layer The film has a strong out-of-plane texture.

Fig. 2 is a scanning electron microscope (SEM) photograph at 10,000 times of a Gd _0.9 Ca _0.1 BiO ₃ buffer layer according to Example 1 of the present invention. It can be seen from Figure 2 that the surface of the thin film sample is smooth and dense, without holes and seamless. From this, it can be seen that in Example 1, a Gd _0.9 Ca _0.1 BiO ₃ buffer layer film with a good texture and a dense and flat surface was prepared.

Example two

The invention provides a buffer layer Gd _0.7 Ca _0.3 BiO ₃ of a high-temperature superconducting coated conductor. And a kind of method for preparing high temperature superconducting coating conductor Gd _0.7 Ca _{0.3 BiO} buffer layer film, its steps are:

a. Gd _0.7 Ca _0.3 BiO ₃ buffer layer colloid preparation: the precursors Gd, Ca, and Bi nitrate were dissolved in an appropriate amount of polyacrylic acid (PAA) at a cation concentration of 0.7:0.3:1 to obtain an organic system. The total molar concentration of the final solution is 0.2mol/L.

b. Gd _0.7 Ca _0.3 BiO ₃ buffer layer coating, drying and decomposition: coat the colloid prepared in step a on the LaAlO ₃ single crystal substrate, and then dry it at 120°C; then place it in a sintering furnace, In the air, the furnace temperature was slowly raised from room temperature to 200°C, and then raised to 320°C at a speed of 2°C/min, and then raised to 550°C at a speed of 0.5°C/min, and kept for 30 minutes.

c. Sintering phase formation: Put the substrate obtained after the above drying and heat treatment decomposition into a sintering furnace, rapidly raise the furnace temperature to 810°C at a rate of 70°C/min in the air, and keep it warm for 40 minutes; The furnace temperature was slowly lowered to room temperature, and finally a Gd _0.7 Ca _0.3 BiO ₃ buffer layer was obtained.

Fig. 3 is an X-ray diffraction pattern of the Gd _0.7 Ca _0.3 BiO ₃ buffer layer in Example 2 of the present invention. It can be seen from the figure that except for the diffraction peak of the Gd _0.7 Ca _0.3 BiO ₃ buffer layer (002) and the diffraction peak of the substrate LaAlO ₃ , there are no other impurity peaks of Gd _{0.7 Ca} 0.3 BiO ₃ , implying that the Gd _0.7 Ca _0.3 BiO ₃ buffer layer The film has a strong out-of-plane texture.

Fig. 4 is a scanning electron microscope (SEM) photograph at 10,000 times the Gd _0.7 Ca _0.3 BiO ₃ buffer layer of Example 2 of the present invention. It can be seen from Figure 4 that the surface of the thin film sample is smooth and dense, without holes and seamless. From this, it can be seen that in Example 1, a Gd _0.7 Ca _0.3 BiO ₃ buffer layer film with a good texture and a dense and flat surface was prepared.

Embodiment three

The invention provides a buffer layer Gd _0.6 Ca _0.4 BiO ₃ for a high-temperature superconducting coated conductor. And a kind of method for preparing high-temperature superconducting coating conductor Gd _0.6 Ca _{0.4 BiO} buffer layer film, its steps are:

a. Gd _0.6 Ca _0.4 BiO ₃ buffer layer colloid preparation: the precursors Gd, Ca, and Bi nitrate were dissolved in an appropriate amount of polyacrylic acid (PAA) at a cation concentration of 0.6:0.4:1 to obtain an organic system. The total molar concentration of the final solution is 0.2mol/L.

b. Coating of Gd _0.6 Ca _0.4 BiO ₃ buffer layer, drying and decomposition: Coating the colloid prepared in step a on the LaAlO ₃ single crystal substrate, and then drying at 150°C; then placing it in a sintering furnace, In the air, the furnace temperature was slowly raised from room temperature to 230°C, and then raised to 340°C at a speed of 1°C/min, and then raised to 560°C at a speed of 1°C/min, and kept for 30 minutes.

c. Sintering phase formation: Put the substrate obtained after the above drying and heat treatment decomposition into a sintering furnace, rapidly raise the furnace temperature to 820°C at a rate of 100°C/min in the air, and keep it warm for 60 minutes; The furnace temperature was slowly lowered to room temperature, and finally a Gd _0.6 Ca _0.4 BiO ₃ buffer layer was obtained.

Fig. 5 is an X-ray diffraction pattern of the Gd _0.6 Ca _0.4 BiO ₃ buffer layer in Example 3 of the present invention. It can be seen from the figure that except for the diffraction peak of the Gd _0.6 Ca _0.4 BiO ₃ buffer layer (002) and the diffraction peak of the substrate LaAlO ₃ , there are no other impurity peaks _of Gd _0.6 Ca 0.4 BiO ₃ , implying that the Gd _0.6 Ca _0.4 BiO ₃ buffer layer The film has a strong out-of-plane texture.

Fig. 6 is a scanning electron microscope (SEM) photo at 10,000 times the Gd _0.6 Ca _0.4 BiO ₃ buffer layer of Example 3 of the present invention. It can be seen from Figure 6 that the surface of the film sample is flat and compact, without holes and seamless. From this, it can be seen that in Example 1, a Gd _0.6 Ca _0.4 BiO ₃ buffer layer film with a good texture and a dense and smooth surface was prepared.

The present invention relates to a high-temperature superconducting coating conductor buffer layer Gd _1-x Ca _x BiO ₃ and a preparation method thereof. The Gd, Ca, and Bi nitrates used in the preparation process are analytically pure. In the polyacrylic acid (PAA) organic solvent system of the present invention, acrylic acid monomer is added into N,N-dimethylformamide (DMF) to polymerize polyacrylic acid, thereby forming an organic solvent system.

Claims (3)

1. a conductor of high-temperature superconductor coat Gd _1-xca _xbiO ₃the preparation method of resilient coating, is characterized in that, for to conductor of high-temperature superconductor coat GdBiO ₃alternative and then the extension that resilient coating carries out the Ca of Gd becomes phase heat treatment to generate oxide Gd _1-xca _xbiO ₃solid solution, wherein 0.1≤x≤0.4; shouldresilient coating is prepared as follows; Comprise the following steps:

The preparation of a, colloid: by predecessor Gd, Ca, the nitrate of Bi is dissolved in appropriate polyacrylic acid in the ratio of metal cation ratio Gd:Ca:Bi=1-x:x:1,0.1≤x≤0.4 wherein, the total molar concentration of final solution is 0.2mol/L;

B, colloid coating and dry and thermal decomposition process: the colloid that a step is made is coated on substrate, then is dried; After dry, carry out the front aerial thermal decomposition process of sintering, the substrate that is about to be coated with colloid is placed in sintering furnace, make furnace temperature slowly rise to 180 ℃-230 ℃ from room temperature, and rise to 300 ℃-340 ℃ with the speed of 0.1-2 ℃/min, speed with 0.1-1 ℃/min rises to 540 ℃-560 ℃ again, is incubated 0.5 hour;

C, sinter phase into: after dry and heat treatment is decomposed by the substrate that is coated with colloid, then put into sintering furnace and sinter phase into, finally obtain Gd _1-xca _xbiO ₃resilient coating; The concrete practice is: in air, furnace temperature is risen to 800 ℃-820 ℃ with the speed of 10-100 ℃/min fast, insulation 40-60 minute; Allow again furnace temperature slowly be down to room temperature.

2. conductor of high-temperature superconductor coat Gd according to claim 1 _1-xca _xbiO ₃the preparation method of resilient coating, is characterized in that: in described b step, colloid is coated in the on-chip concrete practice and is: on substrate, with sol evenning machine rotation, colloid is evenly coated on substrate colloid drops.

3. conductor of high-temperature superconductor coat Gd according to claim 1 _1-xca _xbiO ₃the preparation method of resilient coating, is characterized in that: temperature when dry in described b step is 100 ℃-150 ℃.