A method for preparing iron-based superconducting materials

Abstract

This invention discloses a method for preparing iron-based superconducting materials, comprising: according to the chemical formula Ae 1‑x A x+a Fe 2‑b As 2+c The mixture is prepared and thoroughly mixed to obtain unreacted raw starch. Ae is an alkaline earth metal element, A is an alkali metal element, 0.15 ≤ x ≤ 0.8, 0

Description

Technical Field

[0001] This invention relates to a method for preparing iron-based superconducting materials, which is a method for preparing high-purity, highly uniform iron-based superconducting materials, and belongs to the field of materials preparation technology. Background Technology

[0002] Iron-based superconducting materials possess excellent high-field performance. However, due to the presence of volatile alkali metals and arsenic in these materials, elemental loss is prone to occur during high-temperature sintering. Currently, the elemental content matching in the nominal compositions widely used internationally is poor, leading to problems such as elemental segregation, significant deviation from the target chemical composition, and high impurity phase content in the final products, thus hindering the improvement of iron-based superconducting material performance. Therefore, it is necessary to develop a novel preparation process for iron-based superconducting materials to suppress elemental segregation and impurity phase formation, thereby improving the purity and uniformity of the materials.

[0003] Traditional iron-based superconducting material preparation processes generally employ a nominal composition with excess K and no excess As, without adjusting the iron content (e.g., iScience 25, 103992, 2022). The final product prepared according to this nominal composition is prone to elemental segregation and contains a large amount of residual second phases such as iron-arsenic impurities, iron particles, barium arsenide, and potassium arsenide, severely limiting performance improvement. Furthermore, traditional processes typically employ only a single sintering method (e.g., Supercond. Sci. Technol. 33, 065001, 2020), leaving impurities in the sample. Some processes employ a second sintering process using hot isostatic pressing (HIP), with pressures reaching up to 190 MPa, resulting in a bulk material (e.g., Scientific Reports 11, 3143, 2021). Such high pressure conditions are unfavorable for impurity removal, and this process heavily relies on expensive high-pressure equipment, resulting in high preparation costs and hindering large-scale production. Summary of the Invention

[0004] To overcome the problems existing in the prior art, the present invention provides a method for preparing iron-based superconducting materials.

[0005] The present invention adopts the following technical solution:

[0006] A method for preparing an iron-based superconducting material, the method comprising the following process steps:

[0007] (1) In an inert atmosphere, the raw materials are reacted according to the chemical formula Ae 1-x A x+a Fe 2-b As 2+cThe mixture is proportioned and thoroughly mixed to obtain unreacted raw starch, wherein Ae is an alkaline earth metal element, A is an alkali metal, 0.15≤x≤0.8, and 0 <c<a≤0.4x,0≤b≤0.1;

[0008] (2) Press the raw starch from step (1) into shape in an inert atmosphere;

[0009] (3) At a pressure of 10 -3 The raw powder pressed in step (2) is sintered at high temperature in an inert atmosphere or vacuum environment of Pa-0.1MPa to prepare a block material;

[0010] (4) In an inert atmosphere, the sintered blocks are further processed into powder, and the powder is placed in a container with a packing density of 0.1 g / cm³. 3 -3 g / cm 3 ;

[0011] (5) At a pressure of 10 -3 The powder in step (4) is annealed in an inert atmosphere or vacuum environment of Pa-0.1MPa or in a flowing inert atmosphere.

[0012] Furthermore, in step (1), 0.15 ≤ x ≤ 0.8, for example, x is 0.15, 0.17, 0.19, 0.21, 0.23, 0.25, 0.27, 0.29, 0.3, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0. 54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, or 0.8. 0 ≤ b ≤ 0.1, for example, b is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1.

[0013] Furthermore, in step (1), Ae is Ca, Sr or Ba, and A is Na, K, Rb or Cs.

[0014] Furthermore, the raw materials mentioned in step (1) are: alkaline earth metal elements or compounds, alkali metal elements or compounds, iron elements or compounds, and arsenic elements.

[0015] Furthermore, in step (1), 0.001 ≤ b ≤ 0.1.

[0016] Furthermore, the pressure used for pressing in step (2) is 0.1MPa-1 GPa. For example, the pressure used for pressing is 0.1MPa, 10MPa, 30MPa, 500MPa or 1GPa, and the shape of the formed sample includes cylindrical, cuboid or spherical.

[0017] Further, the sintering procedure in step (3) is as follows: the temperature is increased to 400-700℃ (e.g., 400℃, 450℃, 500℃, 550℃, 600℃, 700℃, 800℃, 900℃, or 1000℃ / h) at a rate of 100-1000℃ / h (e.g., at a rate of 100℃ / h, 200℃ / h, 300℃ / h, 400℃ / h, 500℃, 600℃, 650℃, or 700℃) and held for 1-12 hours, then... Heat to 800-1200℃ (e.g., at rates of 100-600℃ / h, 150℃ / h, 200℃ / h, 250℃ / h, 300℃ / h, 350℃ / h, 400℃ / h, 450℃ / h, 500℃ / h, 550℃ / h or 600℃ / h) and hold for 1-100 hours.

[0018] Furthermore, in step (4), the powder packing density is 0.1 g / cm³. 3 0.5g / cm 3 1g / cm 3 1.5g / cm 3 2g / cm 3 2.5g / cm 3 Or 3g / cm 3 .

[0019] Further, in step (5), the annealing temperature is 40℃-400℃, and the annealing time is 0.01 hours-24 hours. For example, the annealing temperature is 40℃, 90℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, or 400℃, and the annealing time is 0.01 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 20 hours, or 24 hours.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Optimized chemical composition: Ae 1-x A x+a Fe 2-b As2+c , the excess value of alkali metal is defined as a, and the excess value of As element is defined as c. It is stipulated that the two meet the relationship: 0 < c < a ≤ 0.4x. This nominal component can supplement the loss of alkali metal elements and As elements during the high-temperature sintering process. The upper limit of the content of the excess alkali metal is limited to a ≤ 0.4x to prevent the residue of excessive alkali metal phases or alkali metal arsenide phases. Since alkali metal A is more likely to volatilize and be lost during the high-temperature sintering process, the content of the excess As element c < a is set, so that the excess alkali metal A element reacts with the excess As element, reducing the consumption of As element in the main phase, thereby preventing the segregation of Fe element and suppressing the formation of impurity phases such as barium arsenide. The content of iron element is moderately reduced, and the reduction value is 0.001 ≤ b ≤ 0.1, achieving the purpose of eliminating excessive iron.

[0022] (2) After the first sintering, the superconducting bulk material contains a superconducting main phase and impurity phases, and the impurity phases exist between the main phase grains. The bulk material after the first sintering is crushed into powder to expose the alkali metal, alkaline earth metal or arsenide impurity phases between the superconducting grains; the second annealing uses a flowing inert atmosphere or a low-pressure inert atmosphere, which is beneficial to the volatilization of some impurity phases, thereby further reducing the arsenide impurity phases.

[0023] (3) The method of the present invention is only sintered in vacuum or normal pressure, without the assistance of high-pressure equipment, greatly reducing the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is the X-ray diffraction pattern and fitting result of the iron-based superconducting material prepared by the method of the present invention. The difference between the two is small and there is no impurity phase peak, indicating that the superconducting material has high purity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the protection scope 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.

[0026] Example 1:

[0027] (1) In an argon atmosphere, barium arsenide, potassium arsenide, iron arsenide and arsenic单质 are proportioned and mixed evenly to obtain unreacted raw powder; 0.6 K 0.5 Fe 1.95 As 2.03 and mixed evenly to obtain unreacted raw powder;

[0028] (2) In an argon atmosphere, the raw powder in step (1) is pressed into a cuboid shape under a pressure of 30 MPa;

[0029] (3) The raw powder pressed in step (2) is sintered into blocks in a vacuum atmosphere with a pressure of 1 Pa at high temperature. The sintering procedure is as follows: the temperature is raised to 500℃ at a rate of 200℃ / h and held for 10 hours, and then raised to 900℃ at a rate of 200℃ / h and held for 50 hours.

[0030] (4) In an argon atmosphere, the sintered bulk material is further processed into powder and placed in a container with a powder packing density of 1 g / cm³. 3 ;

[0031] (5) The powder from step (4) was annealed at 40°C for 24 hours in a vacuum environment with a pressure of 1 Pa.

[0032] The obtained iron-based superconducting material, after X-ray diffraction testing, was found to contain no impurities and had a purity of up to 99.5%. Figure 1 As shown; scanning electron probe microanalysis revealed that the elements in the sample were uniformly distributed without segregation, and the actual chemical composition was determined to be Ba. 0.593 K 0.407 Fe 2.003 As 2.013 .

[0033] Example 2:

[0034] (1) In a nitrogen atmosphere, strontium, sodium, iron, and arsenic elements are reacted according to the chemical formula Sr 0.85 Na 0.21 Fe 1.999 As 2.04 The proportions are adjusted and mixed evenly to obtain unreacted raw starch;

[0035] (2) In a nitrogen atmosphere, the raw powder from step (1) is pressed into a cylindrical shape using a pressure of 0.1 MPa;

[0036] (3) At a pressure of 10 -3 The raw powder pressed in step (2) was sintered into a block in a vacuum of MPa at high temperature. The sintering procedure was as follows: the temperature was raised to 400℃ at a rate of 100℃ / h and held for 12 hours, and then raised to 800℃ at a rate of 100℃ / h and held for 100 hours.

[0037] (4) In a nitrogen atmosphere, the sintered blocks are further processed into powder and placed in a container with a powder packing density of 0.1 g / cm³. 3 ;

[0038] (5) Anneal the powder from step (4) at 100°C for 10 hours in flowing argon gas.

[0039] The obtained iron-based superconducting material was analyzed by synchrotron X-ray diffraction, revealing a superconducting phase purity of 99.8%. Scanning electron probe microanalysis showed no segregation in the sample, and the actual chemical composition was determined to be Sr. 0.853 Na 0.147 Fe 2.021 As 2.013 .

[0040] Example 3:

[0041] (1) In an argon atmosphere, strontium, potassium arsenide, iron, and arsenic are reacted according to the chemical formula Sr 0.5 K 0.7 Fe 1.9 As 2.12 The proportions are adjusted and mixed evenly to obtain unreacted raw starch;

[0042] (2) In an argon atmosphere, the raw powder from step (1) is pressed into a cylindrical shape using a pressure of 500 MPa.

[0043] (3) The raw powder pressed in step (2) is sintered into blocks in a nitrogen atmosphere with a pressure of 0.1 MPa at high temperature. The sintering procedure is as follows: the temperature is raised to 600℃ at a rate of 500℃ / h and held for 8 hours, and then raised to 1000℃ at a rate of 300℃ / h and held for 24 hours.

[0044] (4) In an argon atmosphere, the sintered bulk material is further processed into powder and placed in a container with a powder packing density of 2 g / cm³. 3 ;

[0045] (5) The powder from step (4) was annealed at 300°C for 1 hour in a nitrogen atmosphere of 0.1 MPa.

[0046] X-ray diffraction analysis of the obtained iron-based superconducting material revealed a superconducting phase purity of 99.3%. Scanning electron probe microanalysis showed no segregation in the sample, and the actual chemical composition was determined to be Sr. 0.503 K 0.497 Fe 1.995 As 2.003 .

[0047] Example 4:

[0048] (1) Barium, rubidium, iron, and arsenic elements are introduced into a nitrogen atmosphere according to the chemical formula Ba. 0.2 Rb 0.9 Fe 1.99 As 2.08 The proportions are adjusted and mixed evenly to obtain unreacted raw starch;

[0049] (2) In a nitrogen atmosphere, the raw powder from step (1) is pressed into a spherical shape using a pressure of 1 GPa.

[0050] (3) The raw powder pressed in step (2) is sintered into a block in an argon atmosphere with a pressure of 0.05 MPa. The sintering procedure is as follows: the temperature is raised to 700℃ at a rate of 1000℃ / h and held for 1 hour, and then raised to 1200℃ at a rate of 600℃ / h and held for 1 hour.

[0051] (4) In a nitrogen atmosphere, the sintered blocks are further processed into powder and placed in a container with a powder packing density of 3 g / cm³. 3 ;

[0052] (5) The powder from step (4) was annealed at 400°C for 0.01 hours in an argon atmosphere of 0.1 MPa.

[0053] X-ray diffraction analysis of the obtained iron-based superconducting material revealed a superconducting phase purity of 99.5%. Scanning electron probe microanalysis showed a uniform elemental distribution without segregation, and the actual chemical composition was determined to be Ba. 0.211 Rb 0.789 Fe 2.013 As 2.016 .

[0054] Example 5:

[0055] (1) Barium arsenide, potassium arsenide, iron, and arsenic are reacted in an argon atmosphere according to the chemical formula Ba 0.7 K 0.4 Fe 1.999 As 2.01 The proportions are adjusted and mixed evenly to obtain unreacted raw starch;

[0056] (2) In an argon atmosphere, the raw powder from step (1) is pressed into a cylindrical shape using a pressure of 10 MPa.

[0057] (3) The raw powder pressed in step (2) is sintered into a block in an argon atmosphere with a pressure of 0.1 MPa. The sintering procedure is as follows: the temperature is raised to 500℃ at a rate of 700℃ / h and held for 9 hours, and then raised to 880℃ at a rate of 400℃ / h and held for 48 hours.

[0058] (4) In an argon atmosphere, the sintered bulk material is further processed into powder and placed in a container with a powder packing density of 0.5 g / cm³. 3 ;

[0059] (5) In 10 -2 In a vacuum environment of Pa, the powder in step (4) was annealed at 120°C for 0.03 hours.

[0060] Neutron diffraction analysis of the obtained iron-based superconducting material revealed a superconducting phase purity of 99.9%. Scanning electron probe microanalysis showed that the elements in the sample were uniformly distributed without segregation, and the actual chemical composition was determined to be Ba. 0.691 K 0.309 Fe 1.993 As 2.011 .

[0061] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the present invention, and do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for preparing an iron-based superconducting material, characterized in that, The preparation method includes the following process steps: (1) In an inert atmosphere, the raw materials are reacted according to the chemical formula Ae 1-x A x+a Fe 2-b As 2+c The mixture is prepared and thoroughly mixed to obtain unreacted raw starch, wherein Ae is an alkaline earth metal element, A is an alkali metal element, 0.15≤x≤0.8, and 0 <c<a≤0.4x,0≤b≤0.1; (2) Press the raw starch from step (1) into shape in an inert atmosphere; (3) At a pressure of 10 -3 The raw powder pressed in step (2) is sintered at high temperature in an inert atmosphere or vacuum environment of Pa-0.1MPa to prepare a block material; (4) In an inert atmosphere, the sintered blocks are further processed into powder, and the powder is placed in a container with a packing density of 0.1 g / cm³. 3 -3g / cm 3 ; (5) The powder in step (4) is annealed in an inert atmosphere or vacuum environment with a pressure of 10-3 Pa-0.1 MPa, or in a flowing inert atmosphere.

2. The method for preparing an iron-based superconducting material according to claim 1, characterized in that: In step (1), Ae is Ca, Sr or Ba, and A is Na, K, Rb or Cs.

3. The method for preparing an iron-based superconducting material according to claim 1, characterized in that: The raw materials mentioned in step (1) are: alkaline earth metal elements or compounds, alkali metal elements or compounds, iron elements or compounds, and arsenic elements.

4. The method for preparing an iron-based superconducting material according to claim 1, characterized in that: In step (1), 0.001 ≤ b ≤ 0.

1.

5. The method for preparing an iron-based superconducting material according to claim 1, characterized in that: The pressure used in step (2) is 0.1 MPa-1 GPa, and the shape of the molded sample includes cylindrical, cuboid or spherical.

6. The method for preparing an iron-based superconducting material according to claim 1, characterized in that: The sintering procedure in step (3) is as follows: heat up to 400-700°C at a rate of 100-1000°C / h and hold for 1-12 hours, then heat up to 800-1200°C at a rate of 100-600°C / h and hold for 1-100 hours.

7. The method for preparing an iron-based superconducting material according to claim 1, characterized in that: In step (5), the annealing temperature is 40°C-400°C and the annealing time is 0.01 hours-24 hours.

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