Preparation method for regulating and controlling superconducting performance of Fe (Se, Te) single crystal by doping boron

Abstract

The invention discloses a preparation method for regulating and controlling the superconducting performance of a Fe (Se, Te) single crystal by doping boron, which mainly comprises the following steps of: mixing Fe, Se, Te and B powder according to Fe (1-y) Se (1-x) TexBy (x = 0.1-1); y = 0.02-0.1, weighing powder, carrying out ball milling mixing on the powder, packaging the powder in a vacuum quartz tube, and carrying out presintering to obtain FBST superconductor precursor powder; and sintering the FBST superconductor powder through a self-service solvent method to obtain a single crystal, and quenching by adopting a liquid nitrogen cooling method to obtain the FBST superconductor single crystal block with uniform components and high preferred orientation. According to the method, the Fe < 1-y > Se < 1-x > TexBy powder subjected to low-temperature pretreatment is adopted as precursor powder, the single crystal Fe < 1-y > Se < 1-x > TexBy is obtained through a self-service solvent method, then liquid nitrogen quenching is adopted, the phenomenon that impurity phases exist in a single crystal sample is improved, and therefore the doping effect is remarkably improved. The method is simple, is suitable for preparing the element-doped superconducting single crystal, is beneficial to large-scale popularization and application, and has huge commercial value.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature superconducting material preparation methods, and in particular relates to a preparation method for regulating the superconducting properties of Fe(Se, Te) single crystals by doping with boron. Background Art

[0002] The "11" series superconductors in the iron-based superconducting family have a typical layered structure, which can accommodate foreign elements very well. By replacing the Se element with the Te element, its superconducting transition temperature is increased to about 14 K. At the same time, the superconducting transition temperature is effectively increased to about 37 K by applying pressure, indicating that adjusting the stress or strain in the crystal is expected to increase the superconducting transition temperature and superconducting properties, further unraveling the mechanism of high-temperature superconductivity.

[0003] FeSe 1-x Te x (abbreviation: FST) superconductor is a typical iron-based superconductor, which has attracted much attention due to its simple structure and non-toxicity. The current method for preparing FST single crystal superconductors is the solid phase reaction method, which controls the cost to a certain extent and has a certain process improvement space. It can produce a large number of single crystal materials on a large scale, which is convenient for the research of superconducting properties and is also expected to be applied to high-field materials.

[0004] As we all know, FeSe 1-x Te x Superconductors are very sensitive to the Se / Te ratio, and even slight changes will affect their superconducting properties. At the same time, the typical layered structure gives elements a certain amount of space to adjust their superconducting properties. At present, most doping is mainly concentrated on 3d metal elements, and the superconducting properties are improved by regulating the content of Fe elements. However, transition elements are easy to introduce magnetism, thereby inhibiting superconductivity. Light elements have a small element radius, doping advantages, and are non-magnetic, so they are expected to improve superconductivity. However, whether light elements can enter the crystal has always been a difficult problem in process preparation, so seeking the best process for FeSe 1-x Te x Doping superconductor materials is critical to improving crystal quality. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method for regulating the superconducting properties of Fe(Se,Te) single crystal by doping boron element. The preparation method is simple and easy to promote, and can obtain single-phase high-quality single crystal superconducting materials.

[0006] The technical solution adopted by the present invention is: using Fe, Se, Te and B (boron) powder as raw materials, according to the stoichiometric ratio of Fe 1- y Se 1-x Tex B y (x=0.1~1; y=0.02~0.1) The powder is weighed, the powder is mixed by ball milling and then packaged in a vacuum quartz tube for pre-sintering, wherein the mixed powder is named FBST, and the FBST superconductor precursor powder is obtained; the FBST superconductor precursor powder is then ball milled to obtain uniform FBST powder, which is then loaded into a double-layer quartz tube and sintered in a box furnace under vacuum conditions. Finally, after quenching heat treatment, high-quality FBST superconducting single crystal blocks are obtained.

[0007] The present invention is also characterized in that the FBST superconducting powder pretreated at low temperature is used as raw material, a single-phase crystal is prepared by a high-temperature self-solvent method, and then quenched at low temperature to improve the problem of multi-phase production in single-crystal superconductor materials. The preparation cost is low, the process is simple and the preparation cycle is short. Specifically, the following steps are included: Step 1: FBST powder pre-sintering With Fe, Se, Te and B powder, according to Fe 1-y Se 1-x Te x B y The powders were weighed in a stoichiometric ratio of x = 0.1~1; y = 0.02~0.1, mixed evenly, and sealed in a vacuum quartz tube and heated to 500 o C ~1100 o C, keep warm for 2 h~36 h to obtain FBST superconductor precursor powder; Step 2: Preparation of single-phase FBST single crystal superconducting bulk The FBST superconductor precursor powder obtained in step 1 was mixed evenly for 30 min and then sealed in a double-layer quartz tube again. The powder was ground by planetary milling for 1 h to 10 h under Ar atmosphere protection at a ball-to-weight ratio of 10:1 and then placed in a box furnace for 3 to 10 min. o C / min heating up to 700 o C ~1100 o C, then 1~5 o C / min cooling down to 650 o C, that is, to establish a crystallization temperature gradient in the double-layer quartz tube and sinter at this temperature for 2 to 5 days; Step 3: Single-phase FBST single crystal superconducting bulk quenching The FBST single crystal superconducting block obtained in step 2 was heated at 650 o C for 12 h and then annealed with liquid nitrogen.

[0008] In the above step 1, the purity of Fe powder among Fe, Se, Te and B powder cannot be less than 99.9%, the purity of Te powder and Se powder cannot be less than 99.0%, and the purity of B powder cannot be less than 99.9% and it is an extremely fine nano powder; The single-phase FBST superconducting block obtained in step 2 above must have a vacuum degree of 1Í10 -4 about; In step 3 above, the quenching of the FBST superconducting single crystal block needs to be carried out at 650 o C and quenched in liquid nitrogen.

[0009] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing Fe(Se,Te) single crystal superconducting properties by doping with boron, using low-temperature pretreated FBST superconducting powder as raw material, preparing single-phase crystals by a high-temperature self-solvent method, and then quenching at low temperature to obtain high-quality FBST single crystal blocks. This method solves the problems of difficulty in doping B elements, uneven phase reaction, many residual impurities, and difficulty in doping in traditional methods, and significantly improves and shortens the process cycle of doping preparation of FST superconductors. The method is simple, suitable for the preparation of superconducting single crystal doped samples, conducive to large-scale promotion and application, and has great commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 XRD patterns of B-doped and undoped samples of the present invention; Figure 2 It is the SEM-Mapping spectrum of the B-doped and undoped samples of the present invention. DETAILED DESCRIPTION

[0011] The present invention is described in detail below in conjunction with specific implementation modes. Example 1

[0012] Step 1: FST powder sintering Take Fe powder, Se powder and Te powder with a particle size of 300 mesh and a purity of 99.9%, and mix them according to the stoichiometric ratio of FeSe 0.5 Te 0.5 Weigh and mix, seal the mixed powder in a vacuum quartz tube, and heat to 500 o C and keep warm for 36 h to obtain FST superconductor powder.

[0013] Step 2: Preparation of single-phase FBST single crystal superconducting bulk The powders in step 1 were mixed for 30 min, sealed in a double-layer quartz tube again, and the powders were ground by planetary milling for 2 h under Ar atmosphere protection at a ball weight ratio of 10:1. o C / min heating up to 1090o C, then 4 o C / min cooling down to 650 o C, that is, a crystallization temperature gradient is established in the double-layer quartz tube and sintered at this temperature for 5 days; Step 3: Single-phase FBST single crystal superconducting bulk quenching The FBST single crystal superconducting block obtained in step 2 was heated at 650 o C for 12 h and then annealed with liquid nitrogen.

[0014] The crystal structure and composition of the obtained FBST superconducting single crystal were tested. Figure 1 It can be seen that the prepared sample only shows the typical diffraction peak of the tetragonal phase, and no impurity phase appears, indicating that the prepared single crystal sample has a high preferred orientation and a pure phase. Figure 2 This is a mapping diagram, from which we can see that the composition of the obtained samples is very uniform. Example 2

[0015] Step 1: FBST powder sintering Take Fe powder, Se powder, Te powder and B powder with a particle size of 300 mesh and a purity of 99.9%, and mix them according to the stoichiometric ratio of Fe 0.097 B 0.03 Se 0.5 Te 0.5 Weigh the mixture (called 0.03 B), seal the mixed powder in a vacuum quartz tube, and heat it to 600 o C and keep warm for 36 h to obtain FBST superconductor precursor powder.

[0016] Step 2: Preparation of single-phase FBST single crystal superconducting bulk The powders in step 1 were mixed for 30 min, sealed in a double-layer quartz tube again, and the powders were ground by planetary milling for 2 h under Ar atmosphere protection at a ball weight ratio of 10:1. o C / min heating up to 1000 o C, then 3 o C / min cooling down to 650 o C, that is, a crystallization temperature gradient is established in the double-layer quartz tube and sintered at this temperature for 5 days; Step 3: Single-phase FBST single crystal superconducting bulk quenching The FBST single crystal superconducting block obtained in step 2 was heated at 650 o C for 12 h and then annealed with liquid nitrogen.

[0017] The crystal structure and composition of the obtained FBST superconducting single crystal were tested. Figure 1It can be seen that the prepared sample only shows the typical diffraction peak of the tetragonal phase, and no impurity phase appears, indicating that the introduction of small component boron will not change the parent structure of the single crystal sample, and it has a high preferred orientation and pure phase. Figure 2 This is a mapping diagram. From the figure, we can see that the obtained sample has uniform composition, typical layered structure and surface defects, proving that the boron element has entered the crystal. Example 3

[0018] Step 1: FBST powder sintering Take Fe powder, Se powder, Te powder and B powder with a particle size of 300 mesh and a purity of 99.9%, and mix them according to the stoichiometric ratio of Fe 0.093 B 0.07 Se 0.5 Te 0.5 Weigh the mixture (called 0.07 B), seal the mixed powder in a vacuum quartz tube, and heat it to 680 o C and keep warm for 36 h to obtain FBST superconductor precursor powder.

[0019] Step 2: Preparation of single-phase FBST single crystal superconducting bulk The powders in step 1 were mixed for 30 min, sealed in a double-layer quartz tube again, and the powders were ground by planetary milling for 2 h under Ar atmosphere protection at a ball weight ratio of 10:1. o C / min heating up to 980 o C, then 2 o C / min cooling down to 650 o C, that is, a crystallization temperature gradient is established in the double-layer quartz tube and sintered at this temperature for 5 days; Step 3: Single-phase FBST single crystal superconducting bulk quenching The FBST single crystal superconducting block obtained in step 2 was heated at 650 o C for 12 h and then annealed with liquid nitrogen.

[0020] The crystal structure and composition of the obtained FBST superconducting single crystal were tested. Figure 1 From the XRD patterns of boron-doped and undoped samples, we can see that the prepared samples only show typical diffraction peaks of tetragonal phase, and no impurity phase appears, indicating that doping B element will not change the crystal structure of the matrix. Figure 2SEM images of boron-doped and undoped samples: (a) undoped; (b) 0.03 B; (c) 0.07 B; Mapping images of boron-doped and undoped samples: (a) undoped; (b) 0.03B; (c) 0.07 B; It can be seen from the figure that the obtained samples have uniform composition, and the amount of Fe precipitation increases with the increase of B doping amount, indicating that the B element may adjust the content of excess iron in Fe(Se,Te) superconductors and further improve the superconducting properties.

Claims

1. A method for preparing Fe(Se,Te) single crystal superconducting properties by doping with boron, characterized in that: It specifically includes the following steps: Step 1: FBST powder sintering With Fe, Se, Te and B powder, according to Fe 1-y Se 1-x Te x B y The powders were weighed in a stoichiometric ratio of x = 0.1~1; y = 0.02~0.1, mixed evenly, and sealed in a vacuum quartz tube and heated to 500 o C ~1100 o C, keep warm for 2 h~36 h to obtain FBST superconductor precursor powder; Step 2: Preparation of single-phase FBST single crystal superconducting bulk The FBST superconductor precursor powder obtained in step 1 was mixed evenly for 30 min and then sealed in a double-layer quartz tube again. The powder was ground by planetary milling for 1 h to 10 h under Ar atmosphere protection at a ball-to-weight ratio of 10:1 and then placed in a box furnace for 3 to 10 min. o C / min heating up to 700 o C ~1100 o C, then 1~5 o C / min cooling down to 650 o C, that is, to establish a crystallization temperature gradient in the double-layer quartz tube and sinter at this temperature for 2 to 5 days; Step 3: Single-phase FBST single crystal superconducting bulk quenching The FBST single crystal superconducting block obtained in step 2 was heated at 650 o C for 12 h and then annealed with liquid nitrogen.

2. The method for preparing Fe(Se,Te) single crystal by doping with boron to control superconducting properties as claimed in claim 1, characterized in that: In the step 1, the purity of Fe powder among Fe, Se, Te and B powder cannot be lower than 99.9%, the purity of Te powder and Se powder cannot be lower than 99.0%, and the purity of B powder cannot be lower than 99.9% and is extremely fine nano powder.

3. The method for preparing Fe(Se,Te) single crystal superconducting properties by doping with boron as claimed in claim 1, characterized in that: The single-phase FBST superconducting bulk obtained in step 2 is prepared by adopting a self-solvent method to obtain a single-phase single crystal bulk.

4. The method for preparing Fe(Se,Te) single crystal superconducting properties by doping with boron as claimed in claim 1, characterized in that: The step 3 adopts a low-temperature liquid nitrogen quenching method, which performs rapid cooling at an instantaneous low temperature to retain the phase structure, thereby improving the phenomenon of the presence of impurity phases in the single crystal.

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