Fe < 1-x > CrxS superconducting single crystal and preparation method thereof

Abstract

The invention provides a Fe < 1-x > CrxS superconducting single crystal and a preparation method thereof, and the method comprises the following steps: taking iron powder, chromium powder and sulfur powder as simple substance raw materials, firstly preparing a (Fe < 1-x > Crx) < 0.8 > S precursor, preparing a K0.4 (Fe < 1-x > Crx) < 0.8 > S matrix from the precursor and a potassium block through high-temperature sintering by a solid-phase sintering method, then deintercalating interlayer K in the K0.4 (Fe < 1-x > Crx) < 0.8 > S in an alkaline environment through a hydrothermal reaction, and supplementing missing iron and chromium elements to obtain the Fe < 1-x > CrxS superconducting single crystal. And finally, the tetragonal Fe < 1-x > CrxS superconducting single crystal is obtained. The superconductivity of the iron-based superconductor is closely related to the Fe site, and 3d metal Fe site doping becomes an important way for improving the superconductivity of the iron-based superconductor and exploring the superconducting mechanism. The Cr atoms with the radius similar to that of the Fe atoms are used for conducting electron doping on the iron sites of FeS, and the superconducting performance of the FeS can be adjusted so as to adapt to different electronic devices. The preparation method is simple, and the safety of experimenters is guaranteed; and on the other hand, the transition temperature of each component superconducting single crystal is relatively high, the superconducting broadening is relatively small, and the quality of the single crystal is relatively good.

Description

Technical Field

[0001] The present invention belongs to the technical field of FeS superconducting single crystal preparation, and specifically relates to a Fe 1-x Cr x S superconducting single crystal and preparation method thereof. Background Art

[0002] Layered chalcogenide FeS is a two-dimensional van der Waals material, and is a 11-series iron-based superconductor like FeSe and FeTe. Compared with copper-based superconductors, which are also high-temperature superconductors, iron-based superconductors have the advantages of larger critical current and critical field, and simpler superconducting layer structure. Many interesting physical properties have been obtained based on Fe-site doping of FeSe. It is believed that FeS, an 11-series iron-based superconductor like FeSe, also has great potential in superconductivity and obtains rich physical properties. FeS, similar to FeSe, also has a different phase structure. Traditional preparation and synthesis methods cannot obtain tetragonal superconducting FeS and can only obtain non-superconducting hexagonal FeS. People are more interested in tetragonal FeS with superconducting properties. The superconducting transition temperature of tetragonal FeS is 4.5K, the space group is P4 / nmm, and the lattice constant is It is generally believed that the superconducting mechanism of iron-based superconductors is closely related to the Fe site. Therefore, research on iron-site doping helps to understand the superconducting mechanism of tetragonal FeS. Summary of the invention

[0003] Invention purpose, in view of this, the present invention provides a Fe 1-x Cr x S superconducting single crystal.

[0004] Technical solution, in order to achieve the above technical solution, the present invention provides a Fe 1-x Cr x S superconducting single crystal, Cr replaces the Fe position of FeS to form Fe 1-x Cr x S superconducting single crystal, where 0 <x≤0.05。

[0005] In addition, the present invention also proposes a Fe 1-x Cr x A method for preparing an S superconducting single crystal, the method comprising the following steps:

[0006] S1: grinding single powders of iron powder, chromium powder and sulfur powder and mixing them thoroughly to obtain an alloy powder mixture;

[0007] S2: Under argon protection, placing the alloy powder mixture into a first quartz tube and sealing it with a first quartz column;

[0008] S3: vacuum-seal the first quartz tube, and the water and oxygen contents in the first quartz tube are below a predetermined content;

[0009] S4: heating the first quartz tube to a first predetermined temperature and maintaining it for a first predetermined time to obtain a first precursor;

[0010] S5: placing the first precursor powder and the potassium block in an alumina crucible, placing the alumina crucible into a second quartz tube with a cover, and covering it with a second quartz column;

[0011] S6: vacuum-seal the second quartz tube, and when the water and oxygen contents in the second quartz tube are below a predetermined content, place the second quartz tube into a third quartz tube;

[0012] S7: vacuum-seal the third quartz tube, and the water and oxygen contents in the third quartz tube are below predetermined contents, thereby obtaining a first double-layer quartz tube to be heated;

[0013] S8: heating the first double-layer quartz tube to be heated to a second predetermined temperature and maintaining the temperature for a second predetermined time to obtain a second precursor.

[0014] S9: Put the second precursor and a certain amount of sodium hydroxide, thiourea, iron powder, chromium powder and ultrapure water into a polytetrafluoroethylene liner, then put the polytetrafluoroethylene liner into a stainless steel hydrothermal kettle, heat to a third predetermined temperature, and maintain for a third predetermined time to obtain Fe 1-x Cr x S superconducting single crystal, in which Fe 1-x Cr x S-doped superconducting single crystal is composed of Cr replacing the Fe position of FeS. <x≤0.05。

[0015] Preferably, in S3, S6 and S7, the predetermined content is less than 0.1 ppm.

[0016] Preferably, in S4, the first predetermined temperature is 400° C., and the first predetermined time is 24 hours.

[0017] Preferably, in S8, the second predetermined temperature is 1030° C., and the second predetermined time is 12 hours.

[0018] Preferably, in S1, the molar ratio of the iron powder, chromium powder and sulfur powder is (0.744-0.792):(0.008-0.056):1.

[0019] Preferably, in S1, grinding is required for 0.5 to 1 h.

[0020] Preferably, in S1, the purity of the iron powder, chromium powder and sulfur powder is above 99.99%.

[0021] Preferably, in S8, after maintaining the second predetermined time, the temperature is lowered to 730°C at a rate of 0.05°C / min, and then lowered to room temperature to obtain a second precursor.

[0022] Preferably, in S9, the mass of the second precursor is 0.24 g, the mass of sodium hydroxide is 0.12 g, the mass of thiourea is 0.2284 g, the room temperature resistivity of ultrapure water is 18 MΩ·cm, the volume of ultrapure water is 10 mL, and the molar ratio of iron powder, chromium powder and the second precursor is (0.115-0.120):(0.001-0.006):1.

[0023] Preferably, in S9, the third predetermined temperature is 120° C., and the third predetermined time is 72 hours.

[0024] As mentioned above, Fe 1-x Cr x The application of S superconducting single crystals in the preparation of superconducting materials.

[0025] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0026] (1) The present invention provides a Fe 1-x Cr x S superconducting single crystal and preparation method thereof, using iron powder, chromium powder and sulfur powder as single material raw materials, first preparing (Fe 1-x Cr x ) 0.8 S precursor, and then the precursor and potassium block are solid-phase sintered to prepare K 0.4( Fe 1- x Cr x ) 0.8 S matrix, and finally K 0.4( Fe 1-x Cr x ) 0.8 Interlayer K deintercalation in S, replenishment of K 0.4( Fe 1-x Cr x ) 0.8 The Fe vacancy in the S matrix finally gives the tetragonal Fe 1-x Cr x S superconducting single crystal. The traditional preparation method can only prepare hexagonal non-superconducting FeS doped single crystals, while the present invention successfully prepares tetragonal superconducting FeS doped single crystals by combining a solid-phase reaction method and a hydrothermal method. The superconductivity of iron-based superconductors is closely related to the Fe position. Doping the iron position of FeS with 3d metal Cr is helpful for further exploration and understanding of the superconducting mechanism of iron-based superconductors. The present invention successfully prepared Cr-doped tetragonal superconducting FeS single crystals, the single crystal quality is good, and the sample composition is correct.

[0027] (2) The superconductivity of iron-based superconductors is closely related to the Fe site. 3d metal Fe site doping has become an important way to improve the superconductivity of iron-based superconductors and explore the superconductivity mechanism. By using Cr atoms with a radius close to that of Fe atoms to electron-dope the iron site of FeS, its superconducting properties can be adjusted to adapt to different electronic devices. The above preparation method is simple and ensures the safety of the experimenters; on the other hand, the superconducting single crystals of each component of the present invention have a high transition temperature, a small superconducting broadening, and a good quality of the single crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the EDS energy spectrum of the Fe0.99Cr0.01S superconducting single crystal prepared in Example 1 of the present invention.

[0029] Figure 2 This is the EDS energy spectrum of the Fe0.98Cr0.02S superconducting single crystal prepared in Example 2 of the present invention.

[0030] Figure 3 This is the EDS energy spectrum of the Fe0.97Cr0.03S superconducting single crystal prepared in Example 3 of the present invention.

[0031] Figure 4 This is the EDS energy spectrum of the Fe0.96Cr0.04S superconducting single crystal prepared in Example 4 of the present invention.

[0032] Figure 5 This is the EDS energy spectrum of the Fe0.95Cr0.05S superconducting single crystal prepared in Example 5 of the present invention.

[0033] Figure 6 This is the EDS energy spectrum of the Fe0.99Cr0.01S superconducting single crystal prepared in Comparative Example 1 of the present invention.

[0034] Figure 7 This is the EDS energy spectrum of the Fe0.99Cr0.01S superconducting single crystal prepared in Comparative Example 2 of the present invention.

[0035] Figure 8 It is a flow chart of sample preparation of the present invention. DETAILED DESCRIPTION

[0036] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0037] The present invention proposes a Fe 1-x Cr x S superconducting single crystal, Cr replaces the Fe position of FeS to form Fe 1-x Cr x S superconducting single crystal, where 0 <x≤0.05。

[0038] like Figure 8 As shown, the present invention also proposes a Fe 1-x Cr x A method for preparing an S superconducting single crystal, the method comprising the following steps:

[0039] S1, grinding single powders of iron powder, chromium powder and sulfur powder and mixing them thoroughly to obtain an alloy powder mixture;

[0040] S2, under the protection of argon gas, placing the alloy powder mixture into a first quartz tube and sealing it with a first quartz column;

[0041] S3, vacuum-sealing the first quartz tube, and ensuring that the water and oxygen contents in the first quartz tube are below a predetermined content;

[0042] S4, heating the first quartz tube to a first predetermined temperature and maintaining it for a first predetermined time to obtain a first precursor;

[0043] S5, placing the first precursor powder and the potassium block in an alumina crucible, placing the alumina crucible into a second quartz tube with a cover, and covering it with a second quartz column;

[0044] S6, vacuum-seal the second quartz tube, and when the water and oxygen contents in the second quartz tube are below a predetermined content, place the second quartz tube into a third quartz tube;

[0045] S7, vacuum-seal the third quartz tube, and the water and oxygen contents in the third quartz tube are below predetermined contents, thereby obtaining a first double-layer quartz tube to be heated;

[0046] S8, heating the first double-layer quartz tube to be heated to a second predetermined temperature, and maintaining the temperature for a second predetermined time to obtain a second precursor.

[0047] S9, placing the second precursor and a certain amount of sodium hydroxide, thiourea, iron powder, chromium powder and ultrapure water into a polytetrafluoroethylene liner, then placing the polytetrafluoroethylene into a stainless steel hydrothermal kettle, heating to a third predetermined temperature, and maintaining the temperature for a third predetermined time to obtain Fe 1-x Cr x S superconducting single crystal, in which Fe 1-x Cr x S-doped superconducting single crystal is composed of Cr replacing the Fe position of FeS. <x≤0.05。

[0048] Furthermore, in S3, S6 and S7, the predetermined content is less than 0.1 ppm.

[0049] Furthermore, in S4, the first predetermined temperature is 400° C., and the first predetermined time is 24 hours.

[0050] Furthermore, in S8, the second predetermined temperature is 1030° C., and the second predetermined time is 12 hours.

[0051] Furthermore, in S1, the molar ratio of the iron powder, chromium powder and sulfur powder is (0.744-0.792):(0.008-0.056):1.

[0052] Furthermore, in S1, grinding is required for 0.5 to 1 h.

[0053] Furthermore, in S1, the purity of the iron powder, chromium powder and sulfur powder is above 99.99%.

[0054] Furthermore, in S8, after maintaining the second predetermined time, the temperature is lowered to 730° C. at a rate of 0.05° C. / min, and then lowered to room temperature to obtain a second precursor.

[0055] Furthermore, in S9, the mass of the second precursor is 0.24 g, the mass of sodium hydroxide is 0.12 g, the mass of thiourea is 0.2284 g, the room temperature resistivity of ultrapure water is 18 MΩ·cm, the volume of ultrapure water is 10 mL, and the molar ratio of iron powder, chromium powder and the second precursor is (0.115-0.120):(0.001-0.006):1.

[0056] Preferably, in S9, the third predetermined temperature is 120° C., and the third predetermined time is 72 hours.

[0057] As mentioned above, Fe 1-x Cr x The application of S superconducting single crystals in the preparation of superconducting materials and single-photon detection devices.

[0058] The present invention is described by the following examples and comparative examples.

[0059] The devices used in the following examples and comparative examples are as follows:

[0060] The glove box was purchased from Mikrouna; the hydrogen and oxygen tube sealing machine was purchased from BALAB, model MRVS-1003; and the box furnace model was KSL-1200X.

[0061] Example 1

[0062] In a glove box filled with argon, weigh the prepared (Fe 0.99 Cr 0.01 ) 0.8 The metal powder raw materials of S, iron, chromium, and sulfur, have masses of 0.8828 g, 0.0083 g, and 0.6400 g, respectively; they are placed in a pre-cleaned agate mortar and ground for 0.5 to 1 h;

[0063] The ground powder raw materials were placed in small quartz tubes that had been ultrasonically cleaned and dried with deionized water in advance. The small quartz tube had an inner diameter of 17 mm and a length of 150 mm. It was sealed with a quartz column with a diameter of 16 mm and a height of 10 mm. The above operation process maintained H2O and O2 < 0.1 ppm.

[0064] The device containing the reaction powder was sealed with a vacuum valve to ensure that the reaction powder was not exposed to the air atmosphere, and then the device was removed from the glove box and vacuum sealed with a hydrogen-oxygen tube sealing machine. During this process, the quartz tube was washed three times to ensure the vacuum degree. Finally, the device was heat treated in a box furnace, slowly heated to 400°C and kept warm for 24h, and then slowly cooled to 300°C at a rate of 4°C / min. When the temperature dropped to room temperature, the device was taken out to obtain the (Fe) prepared superconducting single crystal. 0.99 Cr 0.01 ) 0.8 S precursor powder.

[0065] Will (Fe 0.99 Cr 0.01 ) 0.8 The S precursor powder was taken out and put into a glove box and ground in an agate crucible for 0.5 to 1 h. 0.3200 g of potassium block and the ground (Fe 0.99 Cr 0.01 ) 0.8 The S powder is placed in an alumina crucible in a medium-sized quartz tube. The medium-sized quartz tube has an inner diameter of 21 mm and a length of 150 mm. It is sealed with a quartz column with a diameter of 20 mm and a height of 10 mm. The above operation process always keeps H2O and O2 < 0.1 ppm. It is sealed with a vacuum valve to ensure that the powder and potassium block are not exposed to the air atmosphere. It is removed from the glove box and vacuum sealed with a hydrogen and oxygen tube sealing machine. During this process, the quartz tube must be washed three times to ensure the vacuum degree. Then the sealed tube containing (Fe 0.99 Cr 0.01 ) 0.8 The quartz tube containing S powder and potassium block is placed in a large quartz tube. The inner diameter of the large quartz tube is 26mm and the length is 200mm. It is sealed with a quartz column with a diameter of 25mm and a height of 10mm. The above operation process always keeps H2O and O2 < 0.1ppm. The double-layer quartz tube is used to prevent the potassium vapor from corroding the single-layer quartz tube during the growth process and causing the quartz tube to rupture. Similarly, the large quartz tube is vacuum-sealed using a hydrogen and oxygen tube sealing machine. During this process, the quartz tube must be washed three times to ensure the vacuum degree. Finally, heat treatment is carried out in a box furnace, slowly heating up to 1030℃ and keeping warm for 12h. The temperature is slowly reduced to 730℃ at a rate of 0.05℃ / min. When it drops to room temperature, it is taken out to obtain the K for preparing superconducting single crystals. 0.4 (Fe 0.99 Cr 0.01 ) 0.8 S mother.

[0066] The sintered K 0.4 (Fe 0.99 Cr 0.01 ) 0.8 The S matrix was taken out and placed in a glove box for dissociation. 0.2400 g of single crystal, 0.1200 g of sodium hydroxide, 0.2284 g of thiourea, 0.0287 g of iron powder and 0.0003 g of chromium powder were weighed and placed in a polytetrafluoroethylene liner. Sodium hydroxide was used to provide an alkaline reducing environment, thiourea was used to replenish the sulfur lost during the reaction, and iron powder and chromium powder were used to replenish K. 0.4 (Fe 0.99 Cr 0.01 ) 0.8 Iron vacancies in S single crystals. 10 mL of ultrapure water was added to the polytetrafluoroethylene liner to form a solution, and then the polytetrafluoroethylene liner was placed in a stainless steel hydrothermal kettle. The stainless steel hydrothermal kettle was then placed in a hydrothermal oven and kept at 120°C for 72 hours. After the heating is completed, Fe 0.99 Cr 0.01 S superconducting single crystal sample.

[0067] Example 2

[0068] In a glove box filled with argon, weigh the prepared (Fe 0.98 Cr 0.02 ) 0.8 The masses of the raw materials of the alloy powder of S, iron, chromium, and sulfur, are 0.8739 g, 0.0166 g, and 0.6400 g, respectively; the mass of the potassium block is 0.3200 g, and 0.2400 g of single crystal, 0.1200 g of sodium hydroxide, 0.2284 g of thiourea, 0.0285 g of iron powder, and 0.0005 g of chromium powder are added during hydrothermal treatment. The other steps are the same as those in Example 1 to obtain Fe 0.98 Cr 0.02 S superconducting single crystal.

[0069] Example 3

[0070] In a glove box filled with argon, weigh the prepared (Fe 0.97 Cr 0.03 ) 0.8 The masses of iron, chromium and sulfur of the alloy powder raw materials of S are 0.8650g, 0.02491g and 0.6400g respectively; the mass of potassium block is 0.3200g, and 0.2400g single crystal, 0.1200g sodium hydroxide, 0.2284g thiourea, 0.0282g iron powder and 0.0008g chromium powder are added during hydrothermal treatment. The other steps are the same as those in Example 1 to obtain Fe 0.97 Cr 0.03 S superconducting single crystal.

[0071] Example 4

[0072] In a glove box filled with argon, weigh the prepared (Fe 0.96 Cr 0.04 ) 0.8 The masses of the raw materials of the alloy powder of S, iron, chromium, and sulfur, are 0.8560g, 0.0332g, and 0.6400g, respectively; the mass of the potassium block is 0.3200g, and 0.2400g of single crystal, 0.1200g of sodium hydroxide, 0.2284g of thiourea, 0.02789g of iron powder, and 0.0011g of chromium powder are added during hydrothermal treatment. The other steps are the same as those in Example 1 to obtain Fe 0.96 Cr 0.04 S superconducting single crystal.

[0073] Example 5

[0074] In a glove box filled with argon, weigh the prepared (Fe 0.95 Cr 0.05 ) 0.8 The masses of the raw materials of the alloy powder of S, iron, chromium, and sulfur, are 0.8471 g, 0.0415 g, and 0.6400 g, respectively; the mass of the potassium block is 0.3200 g, and 0.2400 g of single crystal, 0.1200 g of sodium hydroxide, 0.2284 g of thiourea, 0.02761 g of iron powder, and 0.0014 g of chromium powder are added during hydrothermal treatment. The other steps are the same as those in Example 1 to obtain Fe 0.95 Cr 0.05 S superconducting single crystal.

[0075] Figure 1-5 These are the EDS spectra of the five superconducting single crystals prepared in Examples 1-5. In the figures, the peaks of the three elements of the target product can all be observed, proving that the obtained single crystals are the target products.

[0076] Comparative Example 1

[0077] In a glove box filled with argon, weigh the prepared (Fe 0.99 Cr 0.01 ) 0.8 The masses of the raw materials of the alloy powder of S, iron, chromium, and sulfur, are 0.8828 g, 0.0083 g, and 0.6400 g, respectively; they are placed in a pre-cleaned agate mortar and ground for 0.5 to 1 hour.

[0078] The ground powder raw materials were placed in small quartz tubes that were ultrasonically cleaned and dried with deionized water in advance. The small quartz tubes had an inner diameter of 17 mm and a length of 150 mm. They were sealed with a quartz column with a diameter of 16 mm and a height of 10 mm. The above operation process maintained H2O and O2 < 0.1 ppm.

[0079] The device containing the reaction powder was sealed with a vacuum valve to ensure that the reaction powder was not exposed to the air atmosphere, and then the glove box was removed and vacuum sealed with a hydrogen-oxygen tube sealing machine. During this process, the quartz tube was purged three times to ensure the vacuum degree. Finally, a heat treatment was performed in a box furnace, and the temperature was slowly raised to 300°C, which was 100°C lower than that in Example 1, and the temperature was kept for 24 hours. The temperature was slowly lowered to 300°C at a rate of 4°C / min, and the superconducting single crystal (Fe) was obtained after it was cooled to room temperature. 0.99 Cr 0.01 ) 0.8 S precursor powder.

[0080] Will (Fe 0.99 Cr 0.01 ) 0.8 The S precursor powder was taken out and put into a glove box and ground in an agate crucible for 0.5 to 1 h. 0.3200 g of potassium block and the ground (Fe 0.99 Cr 0.01 ) 0.8 The S powder is placed in an alumina crucible in a medium-sized quartz tube. The medium-sized quartz tube has an inner diameter of 21 mm and a length of 150 mm. It is sealed with a quartz column with a diameter of 20 mm and a height of 10 mm. The above operation process always keeps H2O and O2 < 0.1 ppm. It is sealed with a vacuum valve to ensure that the powder and potassium block are not exposed to the air atmosphere. It is removed from the glove box and vacuum sealed with a hydrogen and oxygen tube sealing machine. During this process, the quartz tube must be washed three times to ensure the vacuum degree. Then the sealed tube containing (Fe 0.99 Cr 0.01 ) 0.8 The quartz tube containing S powder and potassium block is placed in a large quartz tube. The inner diameter of the large quartz tube is 26mm and the length is 200mm. It is sealed with a quartz column with a diameter of 25mm and a height of 10mm. The above operation process always keeps H2O and O2 < 0.1ppm. The double-layer quartz tube is used to prevent the potassium vapor from corroding the single-layer quartz tube during the growth process and causing the quartz tube to rupture. Similarly, the large quartz tube is vacuum-sealed using a hydrogen and oxygen tube sealing machine. During this process, the quartz tube must be washed three times to ensure the vacuum degree. Finally, heat treatment is carried out in a box furnace, slowly heating up to 1030℃ and keeping warm for 12h. The temperature is slowly reduced to 730℃ at a rate of 0.05℃ / min. When it drops to room temperature, it is taken out to obtain the K for preparing superconducting single crystals. 0.4 (Fe 0.99 Cr 0.01 ) 0.8 S mother.

[0081] The sintered K 0.4 (Fe 0.99 Cr 0.01 ) 0.8The S matrix was taken out and placed in a glove box for dissociation. 0.2400 g of single crystal, 0.1200 g of sodium hydroxide, 0.2284 g of thiourea, 0.0287 g of iron powder and 0.0003 g of chromium powder were weighed and placed in a polytetrafluoroethylene liner. Sodium hydroxide was used to provide an alkaline reducing environment, thiourea was used to replenish the sulfur lost during the reaction, and iron powder and chromium powder were used to replenish K. 0.4 (Fe 0.99 Cr 0.01 ) 0.8 Iron vacancies in S single crystal. 10 mL of ultrapure water was added to the polytetrafluoroethylene liner to form a solution, and then the polytetrafluoroethylene liner was placed in a stainless steel hydrothermal kettle. The stainless steel hydrothermal kettle was then placed in a hydrothermal oven and kept at 120°C for 72 hours. After the heating was completed, the prepared sample was taken out.

[0082] Comparative Example 2

[0083] In a glove box filled with argon, weigh the prepared (Fe 0.99 Cr 0.01 ) 0.8 The masses of the raw materials of the alloy powder of S, iron, chromium, and sulfur, are 0.8828 g, 0.0083 g, and 0.6400 g, respectively; they are placed in a pre-cleaned agate mortar and ground for 0.5 to 1 hour.

[0084] The ground powder raw materials were placed in small quartz tubes that had been ultrasonically cleaned and dried with deionized water in advance. The small quartz tube had an inner diameter of 17 mm and a length of 150 mm. It was sealed with a quartz column with a diameter of 16 mm and a height of 10 mm. The above operation process maintained H2O and O2 < 0.1 ppm.

[0085] The device containing the reaction powder was sealed with a vacuum valve to ensure that the reaction powder was not exposed to the air atmosphere. The device was removed from the glove box and vacuum sealed with a hydrogen-oxygen tube sealing machine. During this process, the quartz tube was washed three times to ensure the vacuum degree. Finally, it was heat treated in a box furnace, slowly heated to 400°C and kept warm for 24h. The temperature was slowly lowered to 400°C at a rate of 4°C / min. When it was cooled to room temperature, it was taken out to obtain the (Fe) prepared superconducting single crystal. 0.99 Cr 0.01 ) 0.8 S precursor powder.

[0086] Will (Fe 0.99 Cr 0.01 ) 0.8 The S precursor powder was taken out and put into a glove box and ground in an agate crucible for 0.5 to 1 h. 0.3200 g of potassium block and the ground (Fe 0.99 Cr 0.01 ) 0.8The S powder is placed in an alumina crucible in a medium-sized quartz tube. The medium-sized quartz tube has an inner diameter of 21 mm and a length of 150 mm. It is sealed with a quartz column with a diameter of 20 mm and a height of 10 mm. The above operation process always keeps H2O and O2 < 0.1 ppm. It is sealed with a vacuum valve to ensure that the powder and potassium block are not exposed to the air atmosphere. It is removed from the glove box and vacuum sealed with a hydrogen and oxygen tube sealing machine. During this process, the quartz tube must be washed three times to ensure the vacuum degree. Then the sealed tube containing (Fe 0.99 Cr 0.01 ) 0.8 The quartz tube containing S powder and potassium block is placed in a large quartz tube. The inner diameter of the large quartz tube is 26mm and the length is 200mm. It is covered with a quartz column with a diameter of 25mm and a height of 10mm. The above operation process always keeps H2O and O2 < 0.1ppm. The double-layer quartz tube is used to prevent the potassium vapor from corroding the single-layer quartz tube during the growth process and causing the quartz tube to rupture. Similarly, the large quartz tube is vacuum-sealed using a hydrogen and oxygen tube sealing machine. In this process, the quartz tube must be washed three times to ensure the vacuum degree. Finally, it is heat treated in a box furnace, slowly heated to 1000℃, which is 30℃ lower than the embodiment, and kept warm for 12h. The temperature is slowly lowered to 730℃ at a rate of 0.05℃ / min. When it drops to room temperature, it is taken out to obtain K for preparing superconducting single crystals. 0.4 (Fe 0.99 Cr 0.01 ) 0.8 S mother.

[0087] The sintered K 0.4 (Fe 0.99 Cr 0.01 ) 0.8 The S matrix was taken out and placed in a glove box for dissociation. 0.2400 g of single crystal, 0.1200 g of sodium hydroxide, 0.2284 g of thiourea, 0.0287 g of iron powder and 0.0003 g of chromium powder were weighed and placed in a polytetrafluoroethylene liner. Sodium hydroxide was used to provide an alkaline reducing environment, thiourea was used to replenish the sulfur lost during the reaction, and iron powder and chromium powder were used to replenish K. 0.4 (Fe 0.99 Cr 0.01 ) 0.8 Iron vacancies in S single crystal. 10 mL of ultrapure water was added to the polytetrafluoroethylene liner to form a solution, and then the polytetrafluoroethylene liner was placed in a stainless steel hydrothermal kettle. The stainless steel hydrothermal kettle was then placed in a hydrothermal oven and kept at 120°C for 72 hours. After the heating was completed, the prepared sample was taken out.

[0088] Figure 6 This is the EDS spectrum of the product prepared in Comparative Example 1. Figure 7 This is the EDS spectrum of the product prepared in Comparative Example 2. Figure 6 , 7Only the peaks of Fe and S elements of the target product can be observed, and the peak of Cr element is not observed, which proves that the obtained single crystal is not the target product. Therefore, the temperature in the single crystal preparation process is crucial. Figure 1-Figure 5 The peaks of Fe, Cr, and S can be seen in the EDS spectrum of the embodiment, indicating that the prepared sample is Fe 1-x Cr x S is correct. Figure 6-Figure 7 In the EDS spectrum of the comparative example, only the peaks of Fe and S elements can be seen, and the peak of Cr element cannot be seen, indicating that the process of the comparative example cannot produce Fe 1-x Cr x S sample.

[0089] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A kind of Fe 1-x Cr x S superconducting single crystal, characterized in that Cr replaces the Fe site of FeS to form a tetragonal Fe 1-x Cr x S superconducting single crystal; where 0 <x≤0.05。 2. A kind of Fe 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: The method comprises the following steps: S1, grinding single powders of iron powder, chromium powder and sulfur powder and mixing them thoroughly to obtain an alloy powder mixture; S2, under the protection of argon gas, placing the alloy powder mixture into a first quartz tube and sealing it with a first quartz column; S3, vacuum-sealing the first quartz tube, and ensuring that the water and oxygen contents in the first quartz tube are below a predetermined content; S4, heating the first quartz tube to a first predetermined temperature and maintaining it for a first predetermined time to obtain a first precursor; S5, placing the first precursor powder and the potassium block in an alumina crucible, placing the alumina crucible into a second quartz tube with a cover, and covering it with a second quartz column; S6, vacuum-seal the second quartz tube, and when the water and oxygen contents in the second quartz tube are below a predetermined content, place the second quartz tube into a third quartz tube; S7, vacuum-seal the third quartz tube, and the water and oxygen contents in the third quartz tube are below predetermined contents, thereby obtaining a first double-layer quartz tube to be heated; S8, heating the first double-layer quartz tube to be heated to a second predetermined temperature and maintaining the temperature for a second predetermined time to obtain a second precursor; S9, placing the second precursor and a certain amount of sodium hydroxide, thiourea, iron powder, chromium powder and ultrapure water into a polytetrafluoroethylene liner, then placing the polytetrafluoroethylene liner into a stainless steel hydrothermal kettle, heating to a third predetermined temperature, and maintaining the temperature for a third predetermined time to obtain Fe 1-x Cr x S superconducting single crystal, in which Fe 1-x Cr x S-doped superconducting single crystal is composed of Cr replacing the Fe position of FeS. <x≤0.05。 3. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S3, S6 and S7, the predetermined content is less than 0.1 ppm.

4. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S4, the first predetermined temperature is 400° C., and the first predetermined time is 24 hours.

5. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S8, the second predetermined temperature is 1030° C., and the second predetermined time is 12 hours.

6. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S1, the molar ratio of the iron powder, chromium powder and sulfur powder is (0.744-0.792):(0.008-0.056):

1.

7. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S1, the grinding time is 0.5-1h.

8. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S1, the purity of the iron powder, chromium powder and sulfur powder is above 99.99%.

9. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S8, after maintaining the second predetermined time for 12 hours, the temperature is lowered to 730°C at a rate of 0.05°C / min, and then to room temperature to obtain Fe 1-x Cr x S superconducting single crystal; in said S9, the third predetermined temperature is 120°C, and the third predetermined time is 72h.

10. Fe as claimed in claim 2 1-x Cr x The method for preparing S superconducting single crystal is characterized in that: In S9, the mass of the second precursor is 0.24 g, the mass of sodium hydroxide is 0.12 g, the mass of thiourea is 0.2284 g, the room temperature resistivity of ultrapure water is 18 MΩ·cm, the volume of ultrapure water is 10 mL, and the molar ratio of iron powder, chromium powder and the second precursor is (0.115-0.120):(0.001-0.006):1.

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