Method for improving critical current density of Cu1234 superconducting polycrystalline bulk material

Abstract

The present invention relates to a method for improving the critical current density of a Cu1234 superconductor, belonging to the technical field of superconducting materials, and is used to solve the problem that the actual critical current density of the polycrystalline bulk material of the Cu1234 superconductor synthesized by the existing technical method is lower than the intrinsic critical current density of the crystal grains. The method of the present invention heat-treats the prepared polycrystalline bulk material of the Cu1234 superconductor in a specific temperature and oxygen atmosphere. By setting specific heat-treatment temperature and heat-treatment time, the sample can fully release internal stress, continuously regulate the oxygen content in the crystal lattice, improve the problems such as weak intergranular connection and lattice distortion that cause the reduction of the actual current density of the polycrystalline bulk material, and effectively improve the critical current density J of the polycrystalline bulk material of the Cu1234 superconductor c .

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting materials, and particularly relates to a method for enhancing the critical current density of a polycrystalline bulk material of a Cu1234 superconductor. Background Art

[0002] Superconducting materials have three important performance parameters: superconducting transition temperature T c , critical magnetic field strength H c , and critical current density J c . These three parameters affect the practical applications of superconducting materials. Higher performance parameters mean a broader application prospect for superconducting materials. Cuprate high-temperature superconducting materials (referred to as copper-based superconductors for short) are currently the only materials that can achieve superconductivity in the liquid nitrogen temperature range under normal pressure conditions and have great application prospects. Copper-based superconducting materials include multiple systems, such as: "yttrium-based", "bismuth-based", "thallium-based", "mercury-based", "copper-based", etc. Due to various reasons, currently only two types of copper-based superconducting materials, "yttrium-based" and "bismuth-based", have been initially applied. Among them, the critical current density of the "bismuth-based" rapidly decays with the increase in temperature and is only suitable for low-temperature scenarios; although the "yttrium-based" has a relatively high critical current density in the liquid nitrogen temperature range, its superconducting transition temperature is only 93K, which is significantly lower than that of superconducting material systems such as "bismuth-based", "thallium-based", and "mercury-based", and is also restricted in some application scenarios.

[0003] In recent years, people have carried out systematic research on the "copper-based" copper-based superconductor CuBa2Ca n-1 Cu n O 2n+2+δ (n = 2, 3, 4...). This system is one of the important systems in the copper-based high-temperature superconducting family and can be abbreviated as Cu12(n - 1)n according to the naming rules of copper-based superconductors. Compared with other systems, the "copper-based" copper-based high-temperature superconductor only contains copper, oxygen, and alkaline earth elements, and does not contain toxic, volatile, rare earth metals, etc. It has simple components, is environmentally friendly, and has low costs. Among them, CuBa2Ca3Cu4O 10+δ (abbreviated as Cu1234) in the "copper-based" copper-based superconductor family has four [CuO2] planes. It has been found that the superconducting transition temperature T c of Cu1234 can reach up to 120K at most; it has a relatively high critical current density J c in the liquid nitrogen temperature range, which is better than that of the "bismuth-based" and comparable to that of the "yttrium-based" with the best comprehensive performance. Since the Cu1234 superconductor combines the characteristics of high T c of the "bismuth-based" and high J c of the "yttrium-based", it is a candidate for the next-generation commercial copper-based superconducting materials.

[0004] Although the Cu1234 superconductor has intrinsic high T c and high Jc However, during the process of practical application, some problems still exist. Especially, the actual critical current density of polycrystalline bulk materials strongly depends on the microstructure of the materials. For example, the random orientation of grains results in the existence of weak connection effects between grain boundaries, leading to a significant decrease in the critical current density of the material at grain boundaries. Currently, Cu1234 superconductors need to be synthesized through high-temperature and high-pressure methods. The Cu1234 superconductors synthesized under high pressure belong to polycrystalline bulk materials. The random orientation of grains within the bulk causes weak connection effects between grain boundaries. This effect causes the actual critical current density of the material to be lower than the intrinsic critical current density. Therefore, the actual critical current density J c of the directly synthesized polycrystalline bulk Cu1234 superconducting material is generally low, less than its intrinsic critical current density, which limits the application of Cu1234 superconductors. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a method for improving the critical current density of polycrystalline bulk Cu1234 superconducting materials, so as to solve the problem that the actual critical current density of polycrystalline bulk Cu1234 superconducting materials synthesized by existing technical methods is much lower than the intrinsic critical current density of grains.

[0006] In a first aspect, the present invention provides a method for improving the critical current density of polycrystalline bulk Cu1234 superconducting materials, including heat-treating the polycrystalline bulk Cu1234 superconducting materials in an oxygen atmosphere at a temperature of 200 - 500 °C for 6 - 20 h.

[0007] Furthermore, the critical current density of the heat-treated polycrystalline bulk Cu1234 superconducting materials is 6862 - 14872 A / cm 2 at 5 K, 0 T.

[0008] Furthermore, the polycrystalline bulk Cu1234 superconducting materials are prepared by the following method:

[0009] (1) Mix BaO2 powder and CuO powder, grind and synthesize to obtain BaCuO2 compound powder;

[0010] (2) Mix CaO powder and CuO powder, grind and synthesize to obtain Ca2CuO3 compound powder;

[0011] (3) Mix BaCuO2 powder, Ca2CuO3 powder, CaO powder, CuO powder and BaO2 powder, grind to obtain a superconducting phase starting reaction mixture;

[0012] (4) Press the superconducting phase starting reaction mixture into a cylindrical sample, and then seal and wrap it with gold foil to obtain a sealed sample;

[0013] (5) Place the sealed sample into a cubic anvil press for high-pressure and high-temperature synthesis to obtain a polycrystalline bulk material of Cu1234 superconductor.

[0014] Further, in step (1), the molar ratio of BaO2 powder to CuO powder is 1:1, the synthesis temperature is 300 - 1200 °C, and the synthesis time is 1 - 80 h.

[0015] Further, in step (2), the molar ratio of CaO powder to CuO powder is 2:1, the synthesis temperature is 300 - 1200 °C, and the synthesis time is 1 - 80 h.

[0016] Further, in step (3), the molar ratio of BaCuO2 compound powder, Ca2CuO3 compound powder, CaO powder, CuO powder, and BaO2 powder is 2:1:1:2:δ, where δ ranges from 0 to 1.

[0017] Further, in step (4), under a pressure of 10 - 15 MPa, press the superconducting phase starting reaction mixture into a cylindrical shape.

[0018] Further, in step (5), the synthesis pressure is 2 - 10 GPa, the synthesis temperature is 800 - 1400 °C, and the synthesis time is 0.1 - 5 h.

[0019] Further, the chemical formula of the Cu1234 superconductor is CuBa2Ca3Cu4O 10+2δ .

[0020] In a second aspect, the present invention provides a polycrystalline bulk material of Cu1234 superconductor with a high critical current density prepared by the above method.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The method of the present invention performs heat treatment on the prepared polycrystalline bulk material of Cu1234 superconductor in a specific temperature and oxygen atmosphere. By setting specific temperature and heat treatment time, the sample can fully release internal stress, continuously regulate the oxygen content in the lattice, improve the weak connection at grain boundaries and lattice distortion, etc., which cause a decrease in the actual current density, and effectively improve the critical current density J of the polycrystalline bulk material of Cu1234 superconductor; c ;

[0023] (2) The method of the present invention is simple and feasible, with low manufacturing cost, and has a significant effect on improving the performance of the polycrystalline bulk material of Cu1234 superconductor, laying a good foundation for the large-scale application of the subsequent polycrystalline bulk material of Cu1234 superconductor.

[0024] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combined solutions. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the specification and the drawings. Description of the Drawings

[0025] The drawings are only for the purpose of showing specific embodiments and are not considered as a limitation to the present invention. Throughout the drawings, the same reference signs denote the same components.

[0026] Figure 1 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method of Example 1;

[0027] Figure 2 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method of Example 2;

[0028] Figure 3 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method of Example 3;

[0029] Figure 4 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method of Example 4;

[0030] Figure 5 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method of Example 5;

[0031] Figure 6 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method of Comparative Example 1;

[0032] Figure 7 Critical current density diagram of the as-received Cu1234 superconducting polycrystalline bulk material without heat treatment in Comparative Example 2;

[0033] Figure 8 Critical current density diagram of the Cu1234 superconducting polycrystalline bulk material processed by the method in Comparative Example 3;

[0034] Figure 9 X-ray diffraction pattern of the Cu1234 superconductor prepared in Example 1 of the present invention;

[0035] Figure 10 Crystal structure diagram of the Cu1234 superconductor prepared in Example 1 of the present invention. Detailed Description of the Invention

[0036] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings, in which the drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0037] A specific embodiment of the present invention discloses a method for improving the critical current density of a Cu1234 superconducting polycrystalline bulk material, which includes heat-treating the Cu1234 superconducting polycrystalline bulk material at a temperature of 200 - 500 °C, for example, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, in an appropriate oxygen atmosphere for 6 - 20 h, for example, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h.

[0038] The method of the present invention heat-treats the prepared Cu1234 superconducting polycrystalline bulk material in a specific temperature and oxygen atmosphere. By setting specific temperature and heat-treatment time, the sample can fully release internal stress, continuously regulate the oxygen content in the lattice, improve the weak connection at grain boundaries and lattice distortion, etc., which cause the reduction of the actual current density, and effectively improve the critical current density J of the Cu1234 superconducting polycrystalline bulk material. c The present invention significantly improves the superconducting critical current density by optimizing the carrier concentration and oxygen vacancy order through heat-treatment technology.

[0039] In a specific embodiment, the critical current density of the heat-treated Cu1234 superconducting polycrystalline bulk material is 6862 - 14872 A / cm 2 @5K, 0T.

[0040] In a specific embodiment, the Cu1234 superconducting polycrystalline bulk material is prepared by the following method:

[0041] (1) Mix BaO2 powder and CuO powder, grind and synthesize to obtain BaCuO2 compound powder;

[0042] (2) Mix CaO powder and CuO powder, grind and synthesize to obtain Ca2CuO3 compound powder;

[0043] (3) Mix BaCuO2 powder, Ca2CuO3 powder, CaO powder, CuO powder and BaO2 powder, grind to obtain a superconducting phase starting reaction mixture;

[0044] (4) Press the superconducting phase starting reaction mixture into a cylindrical sample, and then seal and wrap it with gold foil to obtain a sealed sample;

[0045] (5) Place the sealed sample into a cubic anvil press for high-pressure and high-temperature synthesis to obtain a polycrystalline bulk material of Cu1234 superconductor.

[0046] In a specific embodiment, in step (1), the molar ratio of BaO2 powder to CuO powder is 1:1, the synthesis temperature is 300 - 1200 °C, and the synthesis time is 1 - 80 h.

[0047] In a preferred embodiment, in step (1), the synthesis temperature is 600 - 900 °C, and the synthesis time is 20 - 28 h.

[0048] Exemplarily, in step (1), the synthesis temperatures are 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, and the synthesis times are 1 h, 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h, 48 h, 52 h, 56 h, 60 h, 64 h, 68 h, 72 h, 76 h, 80 h.

[0049] In a specific embodiment, in step (1), the heating rate of synthesis is 0.1 - 100 °C / min. Exemplarily, the heating rates are 1 °C / min, 5 °C / min, 10 °C / min, 15 °C / min, 20 °C / min, 25 °C / min, 30 °C / min, 35 °C / min, 40 °C / min, 45 °C / min, 50 °C / min, 55 °C / min, 60 °C / min, 65 °C / min, 70 °C / min, 75 °C / min, 80 °C / min, 85 °C / min, 90 °C / min, 95 °C / min, 100 °C / min. Preferably, the heating rate is 2 - 6 °C / min.

[0050] In a specific embodiment, in step (2), the molar ratio of CaO powder to CuO powder is 2:1, the synthesis temperature is 300 - 1200 °C, and the synthesis time is 1 - 80 h.

[0051] In a preferred embodiment, in step (2), the synthesis temperature is 900 - 1100 °C, and the synthesis time is 20 - 28 h.

[0052] Exemplarily, in step (2), the synthesis temperatures are 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, and the synthesis times are 1 h, 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h, 48 h, 52 h, 56 h, 60 h, 64 h, 68 h, 72 h, 76 h, 80 h.

[0053] In a specific embodiment, in step (2), the heating rate of the synthesis is 0.1 - 100 °C / min. Exemplarily, the heating rates are 1 °C / min, 5 °C / min, 10 °C / min, 15 °C / min, 20 °C / min, 25 °C / min, 30 °C / min, 35 °C / min, 40 °C / min, 45 °C / min, 50 °C / min, 55 °C / min, 60 °C / min, 65 °C / min, 70 °C / min, 75 °C / min, 80 °C / min, 85 °C / min, 90 °C / min, 95 °C / min, 100 °C / min. Preferably, the heating rate is 2 - 6 °C / min.

[0054] In a specific embodiment, in step (3), the molar ratio of the BaCuO2 compound powder, Ca2CuO3 compound powder, CaO powder, CuO powder, and BaO2 powder is 2:1:1:2:δ, where δ ranges from 0 to 1.

[0055] In a specific embodiment, in step (4), under a pressure of 10 - 15 MPa, the superconducting phase starting reaction mixture is pressed into a cylindrical shape.

[0056] In a specific embodiment, in step (5), the synthesis pressure is 2 - 10 GPa, for example, 2 GPa, 3 GPa, 4 GPa, 5 GPa, 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, the temperature is 800 - 1400 °C, for example, 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, and the synthesis time is 0.1 - 5 h, for example, 0.1 h, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h.

[0057] In a specific embodiment, the chemical formula of the Cu1234 superconductor is CuBa2Ca3Cu4O 10+2δ .

[0058] In another specific embodiment of the present invention, a Cu1234 superconductor polycrystalline bulk material with a high critical current density prepared by the above method is disclosed. The critical current density of the Cu1234 superconductor polycrystalline bulk material is 6862-14872A / cm 2 @5K, 0T.

[0059] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0060] Example 1

[0061] A method for improving the critical current density of a Cu1234 superconductor polycrystalline bulk material comprises the following steps:

[0062] (1) In an inert gas argon atmosphere glove box, high-purity BaO2 powder and high-purity CuO powder were mixed in a molar ratio of 1:1, fully ground and poured into a corundum crucible, placed in a tube furnace, and oxygen was introduced, and the temperature was increased from room temperature to 750°C at a heating rate of 4°C / min, and synthesized at 750°C for 24 hours. After synthesis, the mixture was taken out and transferred into a glove box, and the synthesized block was ground into powder to obtain BaCuO2 compound powder;

[0063] (2) in an inert gas argon atmosphere glove box, high-purity CaO powder and high-purity CuO powder were mixed in a molar ratio of 2:1, fully ground and poured into a corundum crucible, placed in a tube furnace, introduced with oxygen, and heated from room temperature to 1000° C. at a heating rate of 4° C. / min, synthesized at 1000° C. for 24 h, and after synthesis, taken out and transferred into a glove box, and the synthesized block was ground into powder to obtain Ca2CuO3 compound powder;

[0064] (3) in an inert gas argon atmosphere glove box, the BaCuO2 compound powder, the Ca2CuO3 compound powder, high-purity CaO powder, high-purity CuO powder and high-purity BaO2 powder are mixed in a molar ratio of 2:1:1:2:1 to obtain a superconducting phase starting reaction mixture;

[0065] (4) using a tablet press to press the superconducting phase starting reaction mixture into a dense cylindrical shape at a pressure of 10 MPa, and sealing and wrapping it with gold foil to obtain a sealed sample;

[0066] (5) placing the sealed sample in a six-sided top press for high pressure and high temperature synthesis, the synthesis pressure is 5 GPa, the temperature is 1000° C., and the synthesis time is 0.5 h to obtain a Cu1234 superconductor polycrystalline bulk material;

[0067] (6) The Cu1234 superconductor polycrystalline bulk material is heat treated at a temperature of 200° C. in an oxygen atmosphere for 12 hours.

[0068] The chemical formula of the polycrystalline bulk material of Cu1234 superconductor prepared in this example is CuBa2Ca3Cu4O 12.0 The polycrystalline bulk material of Cu1234 superconductor prepared in this example was ground into powder, and X-ray diffraction was tested. The X-ray diffraction pattern is as Figure 9 shown. The crystal structure of the sample was obtained, as Figure 10 shown, and the unit cell parameters and atomic position information obtained are shown in Table 1.

[0069] Table 1

[0070]

[0071] Space group P4 / mmm (No.123), lattice parameters: Unit cell volume:

[0072] Example 2

[0073] A method for improving the critical current density of a polycrystalline bulk material of Cu1234 superconductor, comprising the following steps:

[0074] (1) In a glove box under an inert gas argon atmosphere, high-purity BaO2 powder and high-purity CuO powder were mixed in a molar ratio of 1:1, thoroughly ground and then poured into a corundum crucible. Oxygen was introduced into a tube furnace, and the temperature was raised from room temperature to 300 °C at a heating rate of 0.1 °C / min. It was synthesized at 300 °C for 1 h. After synthesis, it was taken out and transferred into the glove box, and the synthesized block was ground into powder to obtain BaCuO2 compound powder;

[0075] (2) In a glove box under an inert gas argon atmosphere, high-purity CaO powder and high-purity CuO powder were mixed in a molar ratio of 2:1, thoroughly ground and then poured into a corundum crucible. Oxygen was introduced into a tube furnace, and the temperature was raised from room temperature to 300 °C at a heating rate of 0.1 °C / min. It was synthesized at 300 °C for 1 h. After synthesis, it was taken out and transferred into the glove box, and the synthesized block was ground into powder to obtain Ca2CuO3 compound powder;

[0076] (3) In a glove box under an inert gas argon atmosphere, the BaCuO2 compound powder, the Ca2CuO3 compound powder, high-purity CaO powder, high-purity CuO powder and high-purity BaO2 powder were mixed in a molar ratio of 2:1:1:2:0.7 to obtain a superconducting phase starting reaction mixture;

[0077] (4) Using a tablet press, the superconducting phase starting reaction mixture was pressed into a dense cylindrical shape at a pressure of 13 Mpa and sealed with gold foil to obtain a sealed sample;

[0078] (5) placing the sealed sample in a six-sided press for high pressure and high temperature synthesis, the synthesis pressure is 2 GPa, the temperature is 1000° C., and the synthesis time is 0.5 h to obtain a Cu1234 superconductor polycrystalline bulk material;

[0079] (6) The Cu1234 superconductor polycrystalline bulk material is heat treated at a temperature of 300° C. in an oxygen atmosphere for 15 hours.

[0080] The chemical formula of the Cu1234 superconductor polycrystalline bulk material prepared in this embodiment is CuBa2Ca3Cu4O 11.4 The X-ray diffraction pattern and crystal structure of the Cu1234 superconductor prepared in this embodiment are basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0081] Example 3

[0082] A method for improving the critical current density of a Cu1234 superconductor polycrystalline bulk material comprises the following steps:

[0083] (1) In an inert gas argon atmosphere glove box, high-purity BaO2 powder and high-purity CuO powder are mixed in a molar ratio of 1:1, fully ground and poured into a corundum crucible, placed in a tube furnace, and oxygen is introduced, and the temperature is increased from room temperature to 500°C at a heating rate of 10°C / min, and synthesized at 500°C for 10 hours. After synthesis, the mixture is taken out and transferred into a glove box, and the synthesized block is ground into powder to obtain BaCuO2 compound powder;

[0084] (2) in an inert gas argon atmosphere glove box, high-purity CaO powder and high-purity CuO powder were mixed in a molar ratio of 2:1, fully ground and poured into a corundum crucible, placed in a tube furnace, introduced with oxygen, and heated from room temperature to 500° C. at a heating rate of 10° C. / min, and synthesized at 500° C. for 10 h. After synthesis, the mixture was taken out and transferred into a glove box, and the synthesized block was ground into powder to obtain a Ca2CuO3 compound powder;

[0085] (3) in an inert gas argon atmosphere glove box, the BaCuO2 compound powder, the Ca2CuO3 compound powder, high-purity CaO powder, high-purity CuO powder and high-purity BaO2 powder are mixed in a molar ratio of 2:1:1:2:0.5 to obtain a superconducting phase starting reaction mixture;

[0086] (4) using a tablet press machine to press the superconducting phase starting reaction mixture into a dense cylindrical shape at a pressure of 15 MPa, and sealing and wrapping it with gold foil to obtain a sealed sample;

[0087] (5) Put the sealed sample into a cubic press for high-pressure and high-temperature synthesis. The synthesis pressure is 10 GPa, the temperature is 1000 °C, and the synthesis time is 0.5 h to obtain a polycrystalline bulk material of Cu1234 superconductor.

[0088] (6) Heat-treat the polycrystalline bulk material of Cu1234 superconductor in an oxygen atmosphere at a temperature of 350 °C for 12 h.

[0089] The chemical formula of the polycrystalline bulk material of Cu1234 superconductor prepared in this example is CuBa2Ca3Cu4O 11.0 , and the X-ray diffraction pattern and crystal structure of the Cu1234 superconductor prepared in this example are basically the same as those in Example 1. Due to limited space, they will not be listed one by one.

[0090] Example 4

[0091] A method for improving the critical current density of a polycrystalline bulk material of Cu1234 superconductor, comprising the following steps:

[0092] (1) In a glove box under an inert gas argon atmosphere, mix high-purity BaO2 powder and high-purity CuO powder according to a molar ratio of 1:1, fully grind them and pour them into a corundum crucible, put them into a tube furnace, introduce oxygen, and heat from room temperature to 1000 °C at a heating rate of 50 °C / min, synthesize at 1000 °C for 50 h, take out and transfer to the glove box after synthesis, grind the synthesized block into powder to obtain BaCuO2 compound powder;

[0093] (2) In a glove box under an inert gas argon atmosphere, mix high-purity CaO powder and high-purity CuO powder according to a molar ratio of 2:1, fully grind them and pour them into a corundum crucible, put them into a tube furnace, introduce oxygen, and heat from room temperature to 1000 °C at a heating rate of 50 °C / min, synthesize at 1000 °C for 50 h, take out and transfer to the glove box after synthesis, grind the synthesized block into powder to obtain Ca2CuO3 compound powder;

[0094] (3) In a glove box under an inert gas argon atmosphere, mix the BaCuO2 compound powder, the Ca2CuO3 compound powder, high-purity CaO powder, high-purity CuO powder and high-purity BaO2 powder according to a molar ratio of 2:1:1:2:0.3 to obtain a starting reaction mixture of the superconducting phase;

[0095] (4) Use a tablet press to press the starting reaction mixture of the superconducting phase into a dense cylindrical shape at a pressure of 10 Mpa, and seal and wrap it with gold foil to obtain a sealed sample;

[0096] (5) placing the sealed sample in a six-sided top press for high pressure and high temperature synthesis, the synthesis pressure is 5 GPa, the temperature is 800° C., and the synthesis time is 5 h to obtain a Cu1234 superconductor polycrystalline bulk material;

[0097] (6) The Cu1234 superconductor polycrystalline bulk material is heat treated at a temperature of 400° C. in an oxygen atmosphere for 6 hours.

[0098] The chemical formula of the Cu1234 superconductor polycrystalline bulk material prepared in this embodiment is CuBa2Ca3Cu4O 10.6 The X-ray diffraction pattern and crystal structure of the Cu1234 superconductor prepared in this embodiment are basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0099] Example 5

[0100] A method for improving the critical current density of a Cu1234 superconductor polycrystalline bulk material comprises the following steps:

[0101] (1) In an inert gas argon atmosphere glove box, high-purity BaO2 powder and high-purity CuO powder are mixed in a molar ratio of 1:1, and after being fully ground, the mixture is poured into a corundum crucible, and then placed in a tube furnace and oxygen is introduced, and the temperature is increased from room temperature to 1200° C. at a heating rate of 100° C. / min, and synthesized at 1200° C. for 80 h. After the synthesis, the mixture is taken out and transferred into a glove box, and the synthesized block is ground into powder to obtain a BaCuO2 compound powder;

[0102] (2) in an inert gas argon atmosphere glove box, high-purity CaO powder and high-purity CuO powder were mixed in a molar ratio of 2:1, fully ground and poured into a corundum crucible, placed in a tube furnace, introduced with oxygen, and heated from room temperature to 1200° C. at a heating rate of 100° C. / min, synthesized at 1200° C. for 80 h, taken out after synthesis and transferred into a glove box, and the synthesized block was ground into powder to obtain Ca2CuO3 compound powder;

[0103] (3) in an inert gas argon atmosphere glove box, the BaCuO2 compound powder, the Ca2CuO3 compound powder, high-purity CaO powder, high-purity CuO powder and high-purity BaO2 powder are mixed in a molar ratio of 2:1:1:2:0 to obtain a superconducting phase starting reaction mixture;

[0104] (4) using a tablet press machine to press the superconducting phase starting reaction mixture into a dense cylindrical shape at a pressure of 15 MPa, and sealing and wrapping it with gold foil to obtain a sealed sample;

[0105] (5) Put the sealed sample into a cubic press for high-pressure and high-temperature synthesis. The synthesis pressure is 5 GPa, the temperature is 1400 °C, and the synthesis time is 0.1 h to obtain a polycrystalline bulk material of Cu1234 superconductor;

[0106] (6) Heat-treat the polycrystalline bulk material of Cu1234 superconductor in an oxygen atmosphere at a temperature of 500 °C for 20 h.

[0107] The chemical formula of the polycrystalline bulk material of Cu1234 superconductor prepared in this example is CuBa2Ca3Cu4O 10.0 , and the X-ray diffraction pattern and crystal structure of the Cu1234 superconductor prepared in this example are basically the same as those in Example 1. Due to limited space, they are not listed one by one.

[0108] Comparative Example 1

[0109] The method of this comparative example is the same as that of Example 1, except that in step (6), the polycrystalline bulk material of Cu1234 superconductor is heat-treated in an oxygen atmosphere at 600 °C for 12 h.

[0110] Comparative Example 2

[0111] The method of this comparative example is the same as that of Example 1, except that step (6) is removed.

[0112] Comparative Example 3

[0113] The method of this comparative example is the same as that of Example 1, except that in step (6), the polycrystalline bulk material of Cu1234 superconductor is heat-treated in an oxygen atmosphere at 200 °C for 5 h.

[0114] Test Example 1

[0115] Use the general magnetic measurement method to measure the critical current density J of the polycrystalline bulk material of Cu1234 superconductor after heat treatment in Examples 1-5 and Comparative Examples 1-3 respectively c . The principle of the magnetic measurement method is to measure the magnetization intensity by generating an electromotive force according to the change of magnetic flux in the detection coil. At a fixed temperature, measure the magnetization intensity at different magnetic fields to determine the hysteresis loop (M-H). Based on the Bean critical state model, the magnetization J c can be calculated based on the hysteresis loop. This method is safe and reliable for measurement and can measure the current characteristics in the measurable region. According to the above method, the test results are shown in Figures 1-8 and Table 1 respectively.

[0116] Table 1

[0117]

[0118] As can be seen from Table 1, the critical current density of the as-prepared polycrystalline bulk Cu1234 superconductor synthesized under high pressure and high temperature is relatively low, and the critical current density at 5K in zero field is 6808 A / cm 2 . After heat treatment of the initial sample of the polycrystalline bulk Cu1234 superconductor at different temperatures in an oxygen atmosphere, the critical current density is improved. After heat treatment at 400 °C for 6 hours, the critical current density is maximally increased to 14872 A / cm 2 @5K, 0T. As the heat treatment temperature is further increased, the critical current density begins to gradually decrease. After heat treatment at 600 °C for 12 hours, the critical current density decreases to 5569 A / cm 2 @5K, 0T. In addition, the critical current density of the polycrystalline bulk Cu1234 superconductor obtained under heat treatment times not within the scope of the present invention is also relatively low.

[0119] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for improving the critical current density of a Cu1234 superconducting polycrystalline bulk material, characterized in that, Including heat-treating the polycrystalline bulk material of Cu1234 superconductor at a temperature of 200 - 450 °C in an oxygen atmosphere for 6 - 20 h; The critical current density of the heat-treated polycrystalline bulk Cu1234 superconductor material is 6862 - 14872 A / cm 2 @5K, 0T; The polycrystalline bulk material of Cu1234 superconductor described above is prepared by the following method: (1) Mix BaO2 powder and CuO powder, grind and synthesize to obtain BaCuO2 compound powder; (2) Mix CaO powder and CuO powder, grind and synthesize to obtain Ca2CuO3 compound powder; (3) Mix BaCuO2 powder, Ca2CuO3 powder, CaO powder, CuO powder and BaO2 powder, grind to obtain a superconducting phase starting reaction mixture; (4) Press the superconducting phase starting reaction mixture into a cylindrical sample, and then seal and wrap it with gold foil to obtain a sealed sample; (5) Put the sealed sample into a cubic press for high-pressure and high-temperature synthesis to obtain the polycrystalline bulk material of Cu1234 superconductor; The heat treatment enables the Cu1234 superconducting polycrystalline bulk material to fully release internal stress, continuously regulate the oxygen content in the lattice, improve the reduction of the actual current density caused by weak grain boundaries and lattice distortion, optimize the carrier concentration and oxygen vacancy order, and effectively increase the critical current density of the Cu1234 superconducting polycrystalline bulk material J c 。 2. The method according to claim 1, characterized in that, In step (1), the molar ratio of BaO2 powder to CuO powder is 1:1, the synthesis temperature is 300 - 1200 °C, and the synthesis time is 1 - 80 h.

3. The method according to claim 1, wherein In step (2), the molar ratio of CaO powder to CuO powder is 2:1, the synthesis temperature is 300 - 1200 °C, and the synthesis time is 1 - 80 h.

4. The method according to claim 1, wherein In step (3), the molar ratio of BaCuO2 compound powder, Ca2CuO3 compound powder, CaO powder, CuO powder and BaO2 powder is 2:1:1:2:δ, where δ ranges from 0 to 1.

5. The method according to claim 1, characterized in that In step (4), under a pressure of 10 - 15 MPa, press the superconducting phase starting reaction mixture into a cylinder.

6. The method according to claim 1, wherein In step (5), the synthesis pressure is 2 - 10 GPa, the synthesis temperature is 800 - 1400 °C, and the synthesis time is 0.1 - 5 h.

7. The method according to any one of claims 1-6, characterized in that, The chemical formula of the described Cu1234 superconductor is CuBa2Ca3Cu4O 10+2δ , where δ ranges from 0 to 1.

8. A polycrystalline bulk material of Cu1234 superconductor with high critical current density prepared by the method according to any one of claims 1 - 7.

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