A method for growing superconducting RCoC2 single crystals

Abstract

This invention discloses a method for growing superconducting RCoC2 single crystals. The method includes: S1, preparing materials according to the stoichiometric ratio of R, Co, and C elements, with the total carbon input compensating for 3%-5% relative to the stoichiometric ratio of RCoC2. The carbon source consists of C blocks and C powder, with the C powder accounting for 7%-15% of the total carbon source and having a particle size of 53-150 μm; S2, placing the raw materials in an arc melting furnace in the order of Co, C, and R, and adding an oxygen absorber; S3, evacuating and then filling with a protective atmosphere; S4, melting the raw materials under the protective atmosphere, flipping them over, and repeating the melting process; S5, cooling to obtain superconducting RCoC2 single crystals. This method can stably obtain millimeter-scale, non-centrosymmetric superconducting RCoC2 single crystals with an Amm² space group. When R is Y, the YCoC2 single crystal exhibits a superconducting transition at low temperatures, with a maximum superconducting transition temperature of 3.7 K. This single crystal can be used to prepare superconducting materials, samples for low-temperature transport research, or samples for topological superconductivity research.

Description

Technical Field

[0001] This invention relates to the field of low-temperature superconductivity and topological quantum materials technology, and in particular to a method for growing superconducting RCoC2 single crystals. Background Technology

[0002] RCoC2 is a class of ternary rare-earth cobalt carbide materials composed of rare-earth element R, transition metal Co, and C, where R can be one of rare-earth elements such as Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. This class of materials is of significant research value in the study of low-temperature transport, magnetism, superconductivity, and potential topological quantum states. In the RCoC2 system, YCoC2, as a representative member without a 4f local magnetic moment, can be used to study low-temperature transport behavior and superconductivity in non-centrosymmetric structures; members containing magnetic rare-earth elements, such as GdCoC2, can be used to study the regulatory effect of the introduction of R-site magnetic moments on crystal structure, magnetic response, and transport properties. Therefore, obtaining RCoC2 single-crystal samples with different R-site compositions is of great significance for systematically comparing rare-earth element substitution effects, studying the structure-property relationships of this type of material, and conducting low-temperature quantum property tests.

[0003] However, RCoC2 is a multi-component carbide material, and its single crystal growth process is affected by various factors such as raw material ratio, carbon volatilization, rare earth element oxidation, melting power, melting atmosphere, cooling process, and the number of repeated melting cycles. Especially during arc melting, carbon is easily lost at high temperatures, rare earth elements are sensitive to oxygen, and the degree of reaction between Co, C, and R elements, as well as the local compositional uniformity, directly affect the formation of the target phase. Therefore, improper process control can easily lead to problems such as impurity phase formation, compositional deviation, small crystal size, low single crystal yield, unstable crystal quality, or poor batch repeatability. For subsequent XRD structural characterization, EDS compositional analysis, low-temperature electrical transport, magnetic susceptibility, and superconductivity or magnetic-related tests, the phase purity, compositional uniformity, crystal integrity, and size of the sample will significantly affect the accuracy and repeatability of the test results. In the existing technology, there are still limited publicly available methods for obtaining high-quality single crystals of the RCoC2 system, especially for obtaining millimeter-scale single crystal samples stably through a simple and repeatable process. For this type of material, how to effectively compensate for carbon loss, improve the uniformity of raw material reaction, reduce oxygen pollution, promote the formation of the target phase, and improve the stability of single crystal under electric arc melting conditions remains an urgent technical problem to be solved. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for growing millimeter-scale, high-quality, and compositionally accurate superconductor RCoC2 single crystals in a stable and repeatable manner, in order to solve the problems of insufficient repeatability of RCoC2 single crystal growth, unstable crystal quality, difficulty in obtaining millimeter-scale single crystal samples, difficulty in controlling impurity phases, and insufficient process scalability among different R-site members in the prior art.

[0005] Technical solution: The method for growing superconductor RCoC2 single crystals according to the present invention, where R is a rare earth element, includes the following steps: S1, the ingredients are prepared according to the stoichiometric ratio of R, Co and C elements, wherein the total carbon input is compensated by 3%-5% relative to the stoichiometric ratio of RCoC2, and the carbon source is composed of C blocks and C powder, wherein the C powder accounts for 7%-15% of the total carbon source and the particle size of the C powder is 53-150 μm; S2, place the raw materials from step S1 into an electric arc melting furnace, with the order of raw material placement being Co, C, R, and an oxygen absorber is placed inside the furnace; S3, after evacuating the electric arc melting furnace, a protective atmosphere is introduced; S4, the raw material is melted under a protective atmosphere, then flipped over and melted again to obtain a smelted ingot with uniform composition; S5, after cooling, yields a superconductor RCoC2 single crystal.

[0006] Preferably, R includes Y, Gd, Tb, Er, Ho, or Dy.

[0007] Preferably, the total carbon feed amount in step S1 is prepared according to a molar ratio of R:Co:C = 1:1:2.06-2.10.

[0008] More preferably, the total carbon feed amount in step S1 is prepared according to a molar ratio of R:Co:C = 1:1:2.06.

[0009] Preferably, the oxygen absorber in step S2 is titanium foam.

[0010] Preferably, the protective atmosphere in step S3 is argon, and the argon pressure inside the furnace is 0.028~0.032 MPa.

[0011] Further preferably, the argon pressure inside the furnace is 0.03 MPa.

[0012] Preferably, the number of repeated meltings in step S4 is 4-8 times to improve the uniformity of sample composition.

[0013] More preferably, the melting process involves maintaining the power at which R begins melting for a period of time to effectively reduce the volatilization of C, followed by a slow increase in power. After melting, the ingot is flipped over and the melting process is repeated to obtain a smelted ingot with uniform composition.

[0014] Preferably, the superconducting RCoC2 single crystal obtained in step S5 is located on the surface or edge region of the smelted ingot.

[0015] The superconductor RCoC2 single crystal of the present invention is obtained by the growth method described above. The superconductor RCoC2 single crystal is rod-shaped or plate-shaped, has a metallic luster, and is millimeter-sized. Its crystal structure belongs to the non-centrosymmetric structure of the Amm2 space group.

[0016] Preferably, when R is Y, the single crystal is YCoC2, which exhibits a superconducting transition at low temperatures, with a superconducting transition temperature of up to 3.7 K, and has characteristics of a type II superconductor.

[0017] The application of the superconducting RCoC2 single crystal described in this invention in the preparation of superconducting materials, low-temperature transport research samples, or topological superconducting research samples.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. By employing a total carbon compensation and partial C powder substitution strategy, the formation conditions of the RCoC2 target phase were improved, thereby enhancing the stability and repeatability of single crystal acquisition. 2. The arc melting method, which combines argon protection and oxygen absorption of foamed titanium, has a simple process flow and is easy to operate, making it suitable for rapid screening and preparation of superconductor RCoC2 single crystals; 3. The obtained single crystals are in the form of plates or rods, with metallic luster and millimeter-sized dimensions, which can meet the sample quality requirements of subsequent XRD, EDS, low-temperature transport and magnetic tests; 4. The obtained YCoC2 single crystals exhibit a superconducting transition at low temperatures, possessing both non-centrosymmetric structure and topological electronic state research value, and have application prospects in superconductivity and potential topological superconductivity research. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the YCoC2 single crystal obtained in Example 1.

[0020] Figure 2 The image shows the EDS spectrum of the YCoC2 single crystal obtained in Example 1.

[0021] Figure 3 The ρ-T curves of the YCoC2 single crystal prepared in Example 1 are shown in the range of 2 K-300 K.

[0022] Figure 4 The image shows the MR test results of the YCoC2 single crystal prepared in Example 1 at 2 K.

[0023] Figure 5The image shows the XRD pattern of the GdCoC2 single crystal obtained in Example 4. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. The Y block, Co block, C block, and C powder used in the present invention can all be commercially available high-purity raw materials, preferably with a purity of not less than 99.9%. Foamed titanium is used as an oxygen absorber. Unless otherwise specified, the percentage contents mentioned in the following embodiments are all proportions relative to the total carbon source.

[0025] Example 1

[0026] A method for growing superconducting YCoC2 single crystals specifically includes the following steps: (1) The ingredients are prepared according to the molar ratio of Y:Co:C = 1:1:2.06, wherein the total carbon feed is compensated by 3%-5% relative to the stoichiometric ratio of YCoC2, wherein the total carbon source is composed of C blocks and C powder, wherein the C powder accounts for 10% of the total carbon source and has a particle size of 53-150 μm; (2) Place the Co block, C block, C powder and Y block in the copper crucible or water-cooled copper platform of the electric arc melting furnace in sequence, and place foamed titanium near the reaction area as an oxygen absorber. (3) Evacuate the electric arc melting furnace and fill it with argon. Repeat the evacuation-argon filling process to keep the argon pressure in the furnace at 0.03 MPa. (4) Melt the raw material by arc under argon protection. After forming a molten ingot, take it out, turn it over, and melt it again. Repeat this process 4-8 times to improve the uniformity of the sample. (5) After melting, cool to room temperature and select the obtained superconductor YCoC2 single crystals from the surface or edge area of ​​the molten ingot.

[0027] The obtained crystals are plate-like or rod-like, with a metallic luster, and are on the order of millimeters in size. XRD analysis shows that the obtained samples are dominated by the target YCoC2 phase, and EDS analysis shows that the ratio of Y and Co elements is close to the target stoichiometry. Low-temperature resistivity and magnetization tests show that the obtained single crystals exhibit a significant superconducting transition at low temperatures, with the highest superconducting transition temperature reaching 3.7 K.

[0028] Figure 1 and 2 The XRD and EDS spectra of YCoC2 single crystals are shown, indicating that high-quality target component single crystals were obtained. Figure 3 The ρ-T curves of the single-crystal sample at temperatures ranging from 2 K to 300 K show obvious superconducting behavior, with a superconducting transition temperature of approximately 3.7 K. Figure 4 The image shows the MR test results of the sample at 2 K, illustrating the field-induced superconductivity to normal state transition of the sample at 2 K.

[0029] Example 2

[0030] Unlike Example 1, the total carbon feed amount was compensated by 5% relative to the stoichiometry of YCoC2, the replacement ratio of C powder in the total carbon source was adjusted to 7%, and the feed was prepared according to a molar ratio of Y:Co:C = 1:1:2.10, while the other process conditions remained unchanged. YCoC2 single crystals can also be obtained using the above method, but the number and size distribution of single crystals differ from those in Example 1.

[0031] The applicant's experiments show that when the total carbon feed is compensated by 3%-5% relative to the stoichiometry of YCoC2, the C powder replacement ratio is in the range of 7%-15%, and the feed is prepared according to the molar ratio of Y:Co:C = 1:1:2.06~2.10, the growth of YCoC2 single crystals can be achieved, and the ratio around 10% shows good reproducibility.

[0032] Example 3

[0033] Unlike Example 1, the replacement ratio of C powder in the total carbon source was adjusted to 15%, while the other process conditions remained unchanged. YCoC2 single crystals can still be obtained using the above method.

[0034] Experiments show that replacing some C blocks with C powder and compensating with 3% total carbon is beneficial for the formation of the YCoC2 target phase and the precipitation of single crystals.

[0035] Example 4

[0036] Unlike Example 1, the Y block in Example 1 was replaced with a Gd block, while the other process conditions remained unchanged, and GdCoC2 single crystals were prepared.

[0037] Specifically, the ingredients are prepared according to a molar ratio of Gd:Co:C = 1:1:2.06, wherein the total carbon input is compensated by 3%-5% relative to the stoichiometric ratio of GdCoC2; the total carbon source consists of C blocks and C powder, wherein the C powder accounts for 10% of the total carbon source and has a particle size of 53-150 μm.

[0038] Co blocks, C blocks, C powder, and Gd blocks were placed on a water-cooled copper crucible in the electric arc melting furnace in the order of Co, C, and Gd. Simultaneously, foamed titanium was placed near the reaction zone as an oxygen absorber. The electric arc melting furnace was evacuated and then filled with argon gas. This evacuation-argon filling process was repeated three times to maintain the argon pressure inside the furnace at 0.03 MPa.

[0039] Under an argon protective atmosphere, the raw materials are melted by electric arc. After arc ignition, the current of the TIG-200P inverter DC pulse tungsten inert gas (TIG) welding machine is slowly increased. A current of 30 A is maintained for at least 15 minutes until Gd begins to melt, to reduce C volatilization. Subsequently, a current of 50 A is maintained until all C within the field of view is melted. Then, a current of 60 A is maintained for at least 10 minutes to ensure complete melting of all materials and the formation of a molten ingot. After the molten ingot cools, it is flipped and melted again. This process requires repeating the front-side melting steps, increasing the current by 5 A in 2-minute increments until the current reaches approximately 100 A. The process is stopped once the actively moving C spheres on the melt surface are observed to be completely melted. This flipping and melting process is repeated 4-8 times to improve sample composition homogeneity and the stability of the target phase formation.

[0040] After melting, the ingot is cooled to room temperature, and the resulting GdCoC2 single crystals are selected from the surface or edge areas. The resulting crystals are plate-like or rod-like, have a metallic luster, and are in the millimeter range in size.

[0041] XRD analysis was performed on the obtained GdCoC2 single crystal. The test results are as follows: Figure 5 As shown, the main diffraction peaks of the obtained sample can be attributed to the GdCoC2 target phase, indicating that the method described in this embodiment can obtain GdCoC2 single crystals. Compared with Example 1, this embodiment shows that, while keeping the arc melting growth process, carbon compensation strategy, partial C powder substitution strategy, and oxygen absorption protection conditions basically unchanged, replacing the R-site element with Gd can still yield RCoC2 type single crystal materials, proving that the method described in this invention is applicable to the substitution of R-site rare earth elements.

[0042] Comparative Example 1 Unlike Example 1, the total carbon feed amount was not compensated in any way, while the other process conditions remained unchanged.

[0043] The results show that without carbon compensation, the stability of the target phase formation in the obtained product decreases and the single crystal yield decreases.

[0044] Comparative Example 2 Unlike Example 1, the total carbon source was entirely C blocks, without using C powder with a particle size of 53-150 μm, while the other process conditions remained unchanged.

[0045] The results show that without a partial C powder replacement strategy, it is difficult to stably obtain YCoC2 single crystals, and the reproducibility of the obtained products is poor.

[0046] Comparative Example 3 Unlike Example 1, no foamed titanium oxygen absorber was used, while the other process conditions remained unchanged.

[0047] The results show that without the use of foamed titanium oxygen absorber, oxygen contamination is more easily introduced during the smelting process, affecting the formation of the YCoC2 target phase and the quality of single crystals.

Claims

1. A method for growing a single crystal of superconductor RCoC2, where R is a rare earth element, characterized in that... Includes the following steps: S1, the ingredients are prepared according to the stoichiometric ratio of R, Co and C elements, wherein the total carbon input is compensated by 3%-5% relative to the stoichiometric ratio of RCoC2, and the carbon source is composed of C blocks and C powder, wherein the C powder accounts for 7%-15% of the total carbon source and the particle size of the C powder is 53-150 μm; S2, place the raw materials from step S1 into an electric arc melting furnace, with the order of raw material placement being Co, C, R, and an oxygen absorber is placed inside the furnace; S3, after evacuating the electric arc melting furnace, a protective atmosphere is introduced; S4, the raw material is melted under a protective atmosphere, then flipped over and melted again to obtain a smelted ingot with uniform composition; S5, after cooling, yields a superconductor RCoC2 single crystal.

2. The growth method according to claim 1, characterized in that, The R includes Y, Gd, Tb, Er, Ho, or Dy.

3. The growth method according to claim 1, characterized in that, The total carbon feed amount in step S1 is prepared according to a molar ratio of R:Co:C = 1:1:2.06-2.

10.

4. The growth method according to claim 1, characterized in that, The oxygen absorber mentioned in step S2 is titanium foam.

5. The growth method according to claim 1, characterized in that, The protective atmosphere described in step S3 is argon, and the argon pressure inside the furnace is 0.028~0.032 MPa.

6. The growth method according to claim 1, characterized in that, The number of times the melting process is repeated in step S4 is 4-8 times.

7. The growth method according to claim 1, characterized in that, The superconductor RCoC2 single crystal obtained in step S5 is located on the surface or edge region of the smelted ingot.

8. A superconductor RCoC2 single crystal, characterized in that, The superconductor RCoC2 single crystal, prepared by the growth method described in claim 1, is rod-shaped or plate-shaped, has a metallic luster, is millimeter-sized, and has a non-centrosymmetric structure belonging to the Amm2 space group.

9. The superconducting RCoC2 single crystal according to claim 8, characterized in that, When R is Y, the single crystal is YCoC2, and the YCoC2 single crystal exhibits a superconducting transition at low temperatures, with a superconducting transition temperature of 3.2~3.7 K.

10. The application of the superconducting RCoC2 single crystal according to claim 8 or 9 in the preparation of superconducting materials, low-temperature transport research samples, or topological superconducting research samples.

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