Method for preparing iron-based superconducting material single crystal in microgravity environment

Abstract

The invention provides a method for preparing an iron-based superconducting material single crystal in a microgravity environment, and belongs to the field of superconducting materials. The method specifically comprises the following steps: carrying out a microgravity crystal growth experiment in a high-temperature experiment cabinet of a space station, putting a solid-phase sintered or pre-melted rod-like raw material into a furnace body, heating and melting, then slowly solidifying, and finally growing the iron-based superconducting material single crystal with large size and extremely low defect density.

Description

Technical Field

[0001] This invention belongs to the field of superconducting materials technology, specifically relating to a method for preparing iron-based superconducting single crystals under microgravity conditions. Background Technology

[0002] The novel iron-based superconducting materials discovered in 2008 possess advantages such as high superconducting transition temperature, low anisotropy, high upper critical field, and inexpensive raw materials. They hold significant scientific importance and enormous potential market benefits, and are expected to find wide applications in high-field magnets, high-field nuclear magnetic resonance (NMR), controlled nuclear fusion, and next-generation high-energy accelerators. However, current research on the application of iron-based superconducting materials faces significant challenges, with many problems remaining unresolved and failing to meet practical application requirements. Among these challenges, the small size and high defect density of iron-based superconducting single crystals grown under gravity on Earth severely restrict the study of the iron-based superconducting mechanism and its applications in low-voltage systems.

[0003] Currently, several countries internationally have conducted systematic experiments on the growth of copper-based superconducting single crystals and polycrystalline bulk materials under microgravity conditions in space, achieving fruitful results. Microgravity conditions can effectively weaken the container wall effect, reduce the tendency for non-uniform nucleation, and increase the final crystal size of the material. In addition, natural convection disappears under microgravity conditions, and crystal growth is dominated by a pure diffusion mechanism, which can effectively eliminate internal defects in the crystal, ultimately resulting in large-size crystals with low defect density.

[0004] Although my country's space materials science has developed rapidly, research on the preparation of superconducting materials under microgravity conditions has not yet been conducted. Since the discovery of iron-based superconducting materials, Chinese scientists have carried out extensive work on their preparation, mechanisms, and applications, enabling my country to maintain a leading position in the field. This invention aims to utilize the microgravity conditions of the space station to obtain stable, uniform, and high-performance iron-based superconducting single crystals, and to control the crystal structure and defects of iron-based superconducting materials. Summary of the Invention

[0005] To address the technical problems in the background art, this invention provides a large-size iron-based superconducting single crystal with extremely low defect density, wherein the diagonal length of the ab face of the single crystal is greater than 1.5 cm. This invention also provides a method for preparing the aforementioned iron-based superconducting single crystal.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing iron-based superconducting single crystals under microgravity conditions includes the following steps:

[0008] (1) Place the solid-state sintered or pre-melted rod-shaped raw material in the high-temperature experimental chamber of the space station;

[0009] (2) At microgravity levels less than Under g conditions, heat to 900-1450 ℃ to completely melt the raw materials, and hold at that temperature for 0.5-2 hours;

[0010] (3) Cool down to 750 °C at a rate not exceeding 3 °C / h, and then freely cool to room temperature to obtain an iron-based superconducting single crystal with an ab face diagonal length greater than 1.5 cm and a defect density less than 10 pieces / μm².

[0011] In the above technical solution, the composition of the iron-based superconducting material is as follows: , where 0.2 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.2.

[0012] In the above technical solution, the composition of the iron-based superconducting material is as follows: , where 0.2 ≤ z ≤ 0.8.

[0013] In the above technical solution, the preparation method of the rod-shaped raw material includes: solid-state sintering or pre-melting molding.

[0014] In the above technical solution, during the cooling process, when the temperature is higher than 750 ℃, the cooling rate is 1-3 ℃ / h.

[0015] In the above technical solution, the microgravity environment is provided by the high-temperature experimental chamber on the space station, and its vacuum degree is ≤ Pa.

[0016] In the above technical solution, the length of the ab face diagonal of the single crystal is 1.8-2.0 cm.

[0017] In the above technical solution, the defect density of the single crystal is 3-8 pieces / μm².

[0018] In the above technical solution, the melting and holding time is 0.5-1.5 hours.

[0019] In the above technical solution, the average cooling rate of free cooling is 100-150 ℃ / h.

[0020] Beneficial effects:

[0021] (1) This invention utilizes microgravity conditions to significantly weaken the wall effect, reduce the non-uniform nucleation effect caused by the wall, and ultimately grow large-sized crystals.

[0022] (2) The present invention utilizes microgravity conditions to significantly weaken natural convection, and the solid-liquid interface shift during solidification is dominated by a pure diffusion mechanism, thus basically eliminating crystal defects. Attached Figure Description

[0023] Figure 1The images are TEM images of the samples in Example 4, where (a): ground and (b): space. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0025] Example 1

[0026] by Using rods as raw materials, the samples were heated to 1450℃ in a high-temperature experimental chamber on the space station. After forming a melt and holding at that temperature for 2 hours, cooling began. The cooling rate was 3℃ / h when the temperature was between 1450-750℃. Once the temperature dropped below 750℃, the heating power was turned off, with an average cooling rate of approximately 150℃ / h. After the sample descended, it dissociated into single crystals. The ab-face diagonal dimension of the single crystal reached 1.8 cm, and the defect density was 5 pieces / μm. 2 .

[0027] Example 2

[0028] by Using rods as raw materials, the samples were heated to 1300℃ in a high-temperature experimental chamber on the space station. After forming a melt and holding at that temperature for 1 hour, cooling began. The cooling rate was 2℃ / h when the temperature was between 1300-750℃. Once the temperature dropped below 750℃, the heating power was turned off, with an average cooling rate of approximately 150℃ / h. After the sample descended, it dissociated into single crystals. The diagonal dimension of the ab face of the single crystal reached 2.0 cm, and the defect density was 3 pieces / μm. 2 .

[0029] Example 3

[0030] by Using rods as raw materials, the samples were placed in a high-temperature experimental chamber on the space station and heated to 1000 °C. After forming a melt, the samples were held at this temperature for 1.5 h before cooling began. The cooling rate was 2.5 °C / h when the temperature was between 1000 and 750 °C. Once the temperature dropped below 750 °C, the heating power was turned off, with an average cooling rate of approximately 150 °C / h. After the samples descended, they dissociated into single crystals. The ab-face diagonal dimension of the single crystal reached 1.8 cm, and the defect density was 8 pieces / μm. 2 .

[0031] Example 4

[0032] by Using rods as raw materials, the samples were placed in a high-temperature experimental chamber on the space station and heated to 1050 °C. After forming a melt and holding at that temperature for 0.5 h, cooling began. The cooling rate was 1 °C / h when the temperature was between 1050 and 750 °C. Once the temperature dropped below 750 °C, the heating power was turned off, with an average cooling rate of approximately 150 °C / h. After the sample descended, it dissociated into single crystals. The diagonal dimension of the ab face of the single crystal reached 2.0 cm, and the defect density was 4 pieces / μm. 2 .

[0033] Example 5

[0034] This embodiment describes the comparative experiments of the performance of each iron-based superconducting single crystal sample in space and on the ground in Examples 1-4 above.

[0035] Experimental procedure:

[0036] 1. Sample preparation

[0037] Space samples: Following the methods in Examples 1-4, microgravity crystal growth was completed in the high-temperature experimental chamber of the space station (microgravity level < g, vacuum degree ≤ Pa).

[0038] Ground samples: composed of the same raw materials ( , , , Both the melting temperature and the rod shape are used in the same temperature control program under the gravity environment of the ground (melting temperature 900-1450℃, cooling rate 1-3℃ / h to 750℃ and then free cooling), but due to the influence of gravity, natural convection and the wall effect cannot be eliminated.

[0039] 2. Performance Testing:

[0040] The superconducting transition temperature (Tc) and transition width (ΔTc) were determined using the PPMS integrated physical property measurement system.

[0041] The critical current density (Jc) was measured using the four-wire method under both 4.2K self-field and 5T magnetic field conditions. The test results are shown in Table 1 below.

[0042] Table 1 Comparison of superconductivity of samples

[0043]

[0044] Experimental Results and Analysis:

[0045] 1. Improved superconducting conversion performance

[0046] Tc significantly increased: the superconducting transition temperature of space samples was higher than that of ground samples (e.g., ...). Space sample Tc=24.2K vs. Ground 22.8K).

[0047] ΔTc narrowing: The spatial sample transition width is narrower (e.g., The spatial ΔTc = 1.5K vs. ground level 3.2K indicates a significant improvement in crystal uniformity.

[0048] 2. Critical current density leap

[0049] Self-field Jc enhancement: The self-field Jc of space samples is 1.5-2.8 times that of ground samples (e.g., Space Jc = 2.0 × A / cm² vs. ground 1.2× A / cm²).

[0050] The advantage of Jc is more significant in high-field environments: the Jc of space samples under a 5T magnetic field is 1.5-4.2 times that of ground samples (e.g., Space Jc = 7.2 × A / cm² vs. ground 1.7× A / cm²).

[0051] Figure 1 The TEM comparison charts reveal the microscopic reasons for the performance improvement: Figure 1 The ground sample in (a) shows that high-density dislocations (>20 pieces / μm²) and grain boundaries lead to strong magnetic flux pinning, but excessive defects impede the superconducting current path. Figure 1 (b) The space sample has a defect density of only 3-8 pieces / μm², and the dislocations are arranged in an orderly manner to form a highly efficient magnetic flux pinning center. At the same time, the large-size single crystal (ab plane > 1.5cm) provides a continuous superconducting channel, which together achieves a breakthrough improvement in Jc under high field.

[0052] in conclusion:

[0053] By suppressing gravity-driven convection and the wall effect, the microgravity environment allowed crystal growth to be dominated by pure diffusion, successfully preparing large-size (1.8-2.0 cm), low-defect (3-8 pieces / μm²) iron-based superconducting single crystals. Its core advantages are: a sharper superconducting transition (ΔTc ↓ by more than 50%) reflecting highly uniform composition; and a 2-4 fold increase in high-field Jc, breaking through the bottleneck of terrestrial preparation and providing a material basis for strong-field applications such as nuclear magnetic resonance and fusion devices.

[0054] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing iron-based superconducting single crystals under microgravity conditions, characterized in that, Includes the following steps: (1) Place the solid-state sintered or pre-melted rod-shaped raw material in the high-temperature experimental chamber of the space station; (2) At microgravity levels less than Under g conditions, heat to 900-1450 ℃ to completely melt the raw materials, and hold at that temperature for 0.5-2 hours; (3) Cool down to 750 °C at a rate not exceeding 3 °C / h, and then freely cool to room temperature to obtain an iron-based superconducting single crystal with an ab face diagonal length greater than 1.5 cm and a defect density less than 10 pieces / μm².

2. The method according to claim 1, characterized in that, The composition of the iron-based superconducting material is: Where 0.2 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.

2.

3. The method according to claim 1, characterized in that, The composition of the iron-based superconducting material is: , where 0.2 ≤ z ≤ 0.

8.

4. The method according to claim 1, characterized in that, The preparation method of the rod-shaped raw material includes: solid-state sintering or pre-melting molding.

5. The method according to claim 1, characterized in that, During the cooling process, when the temperature is above 750 ℃, the cooling rate is 1-3 ℃ / h.

6. The method according to claim 1, characterized in that, The microgravity environment was provided by the high-temperature experimental chamber on the space station, and its vacuum level was ≤ Pa.

7. The method according to claim 1, characterized in that, The length of the ab face diagonal of the single crystal is 1.8-2.0 cm.

8. The method according to claim 1, characterized in that, The defect density of the single crystal is 3-8 pieces / μm².

9. The method according to claim 1, characterized in that, The melting and holding time is 0.5-1.5 hours.

10. The method according to claim 1, characterized in that, The average cooling rate of the free cooling is 100-150℃ / h.

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