High-temperature superconductor

Abstract

To provide a high-temperature superconductor that can improve the critical current density without a change in the critical temperature by substituting some of Gd constituting a ReBCO-based superconductor with Ho.SOLUTION: A high-temperature superconductor according to an embodiment is a ReBCO-based high-temperature superconductor, represented by ReBa2Cu3O7-δ, where the Re refers to Gd and Ho.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a high-temperature superconductor, and more particularly to a high-temperature superconductor in which a part of Gd constituting a ReBCO-based superconductor is replaced with Ho, thereby enabling the critical current density to be improved without changing the critical temperature. [Background technology]

[0002] In 1911, Heike Kamerlingh-Onnes of Leiden University in the Netherlands discovered that mercury's electrical resistance suddenly disappeared at an absolute temperature of 4.2K (-268.8°C) while conducting an experiment to measure its electrical resistance. This marked the beginning of the use of low-temperature superconductors such as NbTi and SnTi in applications requiring high magnetic fields.

[0003] High-temperature superconductors were discovered by Johannes Bednorz and Karl Muller of Switzerland in 1987. Since then, active research has been conducted to improve the critical temperature and critical current density of high-temperature superconductors.

[0004] Representative compositions of high-temperature superconductors include BSCCO and ReBCO.

[0005] In both compositions, the oxygen content in the copper oxide (Cu Oxide) is chemically unstable (non-stoihiometric compound), so it is important to control the oxygen atmosphere during production and use.

[0006] The chemical composition of BSCCO is Bi 2 Sr 2 CuO 6+x / Bi 2 Sr 2 CuO 8+x / Bi 2 Sr 2 CuO 10+xThe higher the oxygen content in the copper oxide (Cu-Oxide), the higher the critical temperature (Tc). BSCCO is made into wire rods through an extrusion process, and research and development is underway to replace NbTi and SnTi, but there is a problem that Ag is used to control the texturing to increase the critical current of BSCCO, and the price must be overcome.

[0007] On the other hand, the chemical composition of ReBCO is ReBa 2 Cu 3 O 7-δ and has a lower critical temperature than BSCCO, but a higher critical current.

[0008] However, unlike BSCCO, ReBCO has a rapid decrease in critical current depending on the texture, so wires are generally manufactured using a thin film process. Re in ReBCO is a rare earth, and representative examples include Y and Gd.

[0009] The applicant has therefore been conducting research into improving the critical current density of GdBCO, a ReBCO-based alloy, and has conducted research into substituting rare earth elements, noting that the critical current density can be improved without changing the critical temperature when rare earth elements are replaced with specific elements.

[0010] The contents described above as the background art are intended only to facilitate understanding of the background to the present invention, and should not be construed as an admission that they constitute prior art already known to those of ordinary skill in the art. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent No. 10-2152927 (September 1, 2020) Summary of the Invention

Problems to be Solved by the Invention

[0012] The present invention provides a high-temperature superconductor capable of improving the critical current density without changing the critical temperature by substituting a part of Gd constituting the ReBCO-based superconductor with Ho.

[0013] The technical problems to be solved by the present invention are not limited to the above-described technical problems, and other technical problems not described above will be clearly understood by those having ordinary knowledge in the technical field from the description of the present invention.

Means for Solving the Problems

[0014] The high-temperature superconductor according to an embodiment of the present invention is a ReBCO-based high-temperature superconductor,

[0015] ReBa 2 Cu 3 O 7-δ represented by, wherein Re is Gd and Ho.

[0016] At this time, the superconductor is Ho x Gd 1-x Ba 2 Cu 3 O 7-δ represented by, wherein x satisfies 0 < x < 1, and δ satisfies δ < 7.

[0017] In particular, it is preferable that x satisfies 0.4 ≤ x ≤ 0.6.

[0018] On the other hand, the high-temperature superconductor according to an embodiment of the present invention is a (Gd, Ho)BCO-based high-temperature superconductor, characterized in that a part of Gd is substituted with Ho.

[0019] At this time, the substitution amount of Ho is preferably 40 to 60% with respect to the molar amount of Gd before substitution.

[0020] Meanwhile, a method for producing a high temperature superconductor according to one embodiment of the present invention is a method for producing a (Gd,Ho)BCO-based high temperature superconductor, and includes a powder preparation step of preparing Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder, respectively; a mixing step of mixing the prepared Gd oxide powder, Ba oxide powder, and Cu oxide powder according to the chemical composition amount to prepare a mixed powder, and replacing a part of the Gd oxide powder with Ho oxide powder and mixing it; a molding step of molding the prepared mixed powder into a compact; a first heat treatment step of controlling the carbon (C) content of the compact; a second heat treatment step of synthesizing the compact into a (Gd,Ho)BCO-based compact; a third heat treatment step of growing crystal grains of the compact; and an oxygen heat treatment step of controlling the oxygen (O) content of the compact.

[0021] In the mixing step, the amount of Ho in the Ho oxide powder that substitutes for the Gd sites of the Gd oxide powder is preferably 40 to 60% relative to the molar amount of Gd.

[0022] The molding step is characterized by compressing and molding the mixed powder.

[0023] At this time, it is preferable that the molding step is performed by pressing the mixed powder at 5 to 20 MPa.

[0024] The first heat treatment step includes a first heating process of heating the molded body at a heating rate of 10°C / min or less, a first maintaining process of maintaining the molded body at 880°C for 20 hours or more, and a first cooling process of cooling the molded body at a cooling rate of 10°C / min or less.

[0025] The second heat treatment step includes a second heating process of heating the molded body at a heating rate of 10°C / min or less, a second maintaining process of maintaining the molded body at 900°C for 20 hours or more, and a second cooling process of cooling the molded body at a cooling rate of 10°C / min or less.

[0026] The third heat treatment step includes a third heating process of heating the molded body at a heating rate of 10°C / min or less, a third maintaining process of maintaining the molded body at 925°C for 15 hours or more, and a third cooling process of cooling the molded body at a cooling rate of 10°C / min or less.

[0027] The oxygen heat treatment step preferably involves heat treating the compact in an oxygen atmosphere at 500° C. for 12 hours or more. Effect of the Invention

[0028] According to the embodiment of the present invention, the following effects can be expected by substituting a part of Gd constituting the ReBCO-based superconductor with Ho.

[0029] First, when using superconducting materials as wire, it is possible to increase the critical current density of the wire used in drive motors. This makes it possible to increase the magnetic field of the superconducting coil (racetrack) more than that of wire at the level of GdBCO-based superconductors, thereby maximizing the output density.

[0030] Secondly, when used as a superconducting bulk magnet, the critical current density of the magnetized bulk magnet can be increased to maximize the output density of the motor. [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of the crystal structure of a high-temperature superconductor according to one embodiment of the present invention; [Figure 2a] 1 is a graph showing a change in crystal structure due to the addition of Ho. [Figure 2b] 1 is a graph showing a change in crystal structure due to the addition of Ho. [Diagram 3] 1 is a graph showing the change in magnetic susceptibility depending on the amount of Ho added at 10K. [Figure 4] 1 is a graph showing the change in critical current density depending on the amount of Ho added at 10 K, utilizing the Bean model. [Diagram 5]1 is a graph showing the change in magnetic susceptibility depending on the amount of Ho added at 77K. [Figure 6] 1 is a graph showing the change in critical current density depending on the amount of Ho added at 77 K, utilizing the Bean model. [Figure 7] 1 is a graph showing the change in critical current value depending on the amount of Ho added at 10K. [Figure 8] 1 is a graph showing the change in critical current value depending on the amount of Ho added at 77K. [Figure 9] 1 is a graph showing the change in critical current value depending on the type and amount of rare earth element added to substitute for Gd. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, the embodiments disclosed in this specification will be described in detail with reference to the accompanying drawings. Regardless of the drawing numbers, the same or similar components will be given the same reference numbers and duplicate descriptions thereof will be omitted.

[0033] In describing the embodiments disclosed herein, if it is determined that a detailed description of related known technologies may distract from the gist of the embodiments disclosed herein, the detailed description will be omitted. In addition, the attached drawings are merely for the purpose of making it easier to understand the embodiments disclosed herein, and the technical ideas disclosed herein are not limited by the attached drawings, and should be understood to include all modifications, equivalents, or alternatives included in the ideas and technical scope of the present invention.

[0034] Terms including ordinal numbers such as "first," "second," etc. may be used to describe various components, but these components are not limited by these terms. These terms are used only to distinguish one component from another.

[0035] A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0036] In this specification, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preclude in advance the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0037] FIG. 1 is a schematic diagram of the crystal structure of a high-temperature superconductor according to an embodiment of the present invention.

[0038] As shown in FIG. 1, the high-temperature superconductor according to an embodiment of the present invention is a ReBCO-based high-temperature superconductor, and ReBa 2 Cu 3 O 7-δ is represented by. At this time, Re is Gd and Ho.

[0039] More precisely, the high-temperature superconductor according to an embodiment of the present invention is a (Gd, Ho) BCO-based high-temperature superconductor, which is formed by substituting a part of Gd with Ho.

[0040] For example, the high-temperature superconductor is Ho x Gd 1-x Ba 2 Cu 3 O 7-δ is represented by.

[0041] At this time, it is preferable that x satisfies 0 < x < 1 and δ satisfies δ < 7.

[0042] In particular, it is preferable that x satisfies 0.4 ≤ x ≤ 0.6.

[0043] In addition, the substitution amount of Ho is preferably 40 to 60% with respect to the molar amount of Gd before substitution. For example, when the content of Gd before a part of Gd is substituted with Ho is 1 mol%, 40 to 60% of Gd is substituted with Ho, so that the content of Gd after substitution is 0.4 to 0.6 mol%, and the content of Ho is 0.4 to 0.6 mol%.

[0044] Meanwhile, in this embodiment, the rare earth element substituted for Gd has an ionic radius similar to that of Gd in the lanthanide group, and changes in magnetic moment (μB / h) and critical current density (A) were considered. It was confirmed that the critical current density can be significantly improved when Ho is substituted.

[0045] In addition, part of Gd is replaced by Ho in the crystal structure of the unit cell of the superconductor. x Gd 1-x Ba 2 Cu 3 O 7-δ In the unit cell of Ho 3+ Ion is Gd 3+ Replaces.

[0046] At this time, the crystal structure of the unit cell and Ho x Gd 1-x Ba 2 Cu 3 O 7-δ It can be seen from Figures 2a and 2b that the superconductivity of the material is not affected.

[0047] Next, a method for producing a high temperature superconductor according to one embodiment of the present invention will be examined.

[0048] A method for producing a high temperature superconductor according to one embodiment of the present invention is a method for producing a (Gd,Ho)BCO-based high temperature superconductor, and includes the steps of: a powder preparation step of preparing Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder, respectively; a mixing step of mixing the prepared Gd oxide powder, Ba oxide powder, and Cu oxide powder according to the chemical composition amounts to prepare a mixed powder, with part of the Gd oxide powder being replaced with Ho oxide powder and mixed; a molding step of molding the prepared mixed powder into a compact; a first heat treatment step of controlling the carbon (C) content of the compact; a second heat treatment step of synthesizing the compact into a (Gd,Ho)BCO-based compact; a third heat treatment step of growing crystal grains of the compact; and an oxygen heat treatment step of controlling the oxygen (O) content of the compact.

[0049] The powder preparation step is a step of preparing Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder respectively.

[0050] At this time, the Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder are respectively Gd 2 O 3 、BaCO 3 、CuO and Ho 2 O 3 and can be prepared in the form of.

[0051] The mixing step is to determine the mixing amount of the Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder according to the molar ratio of Gd, Ba, Cu, and Ho in order to produce a high-temperature superconductor represented by Ho x Gd 1-x Ba 2 Cu 3 O 7-δ O. At this time, it is preferable that x satisfies 0 < x < 1 and δ satisfies δ < 7. In particular, it is preferable that x satisfies 0.4 ≦ x ≦ 0.6.

[0052] For example, the mixing amount of each of the Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder is preferably weighed so that the molar ratio of Gd, Ba, Cu, and Ho is 0.5:2:3:0.5.

[0053] At this time, the molar ratio of Gd to Ho is preferably maintained at 40 - 60%:40 - 60%.

[0054] The forming step is a step of determining the mixing amount according to the set molar ratio and pressing the mixed powder of Gd oxide powder, Ba oxide powder, Cu oxide powder, and Ho oxide powder into a formed body of a predetermined shape.

[0055] The mixed powder in the forming process is preferably pressed at 5 - 20 MPa.

[0056] On the other hand, the first heat treatment step is a heat treatment for controlling the carbon (C) content in the compact.

[0057] For this purpose, the first heat treatment step includes a first heating process for heating the compact, a first maintaining process for maintaining the compact at 880°C for 20 hours or more, and a first cooling process for cooling the compact.

[0058] In this case, the heating rate during the first heating step is preferably maintained at 10° C. / min or less in order to minimize the thermal shock to the molded body, and is preferably 120° C. / hr.

[0059] Similarly, the cooling rate during the first cooling step should be kept at 10°C / min or less to minimize the thermal impact on the compact, preferably at 120°C / hr.

[0060] In the first maintenance process, if the heat treatment is performed at a lower temperature and for a shorter time than the temperature and time suggested as the minimum conditions for controlling the carbon (C) content in the compact, a problem may occur in which the heat treatment effect is not fully exerted.

[0061] The second heat treatment step is to heat the ZnO, which is a high-temperature superconductor, x Gd 1-x Ba 2 Cu 3 O 7-δ This is a heat treatment to ensure that

[0062] For this purpose, the second heat treatment step includes a second heating process for heating the compact, a second maintaining process for maintaining the compact at 900°C for 20 hours or more, and a second cooling process for cooling the compact at 120°C / hr.

[0063] In this case, the heating rate and cooling rate when heating and cooling the molded body in the second heating process and the second cooling process should be maintained at 10° C. / min or less in order to minimize the thermal shock of the molded body, and preferably at 120° C. / hr.

[0064] Similarly, in the second sustaining step, the compact is heated to 1000° C., and the high-temperature superconductor Ho x Gd 1-x Ba 2 Cu 3 O 7-δ If the heat treatment is performed at a temperature lower than the minimum temperature and for a shorter period of time than the temperature and time specified as the minimum conditions for ensuring the above, a problem may occur in which the effect of the heat treatment is not fully exerted.

[0065] The third heat treatment step is Ho x Gd 1-x Ba 2 Cu 3 O 7-δ This is a heat treatment for increasing the crystal grain size and ensuring stable crystallinity.

[0066] For this purpose, the third heat treatment step includes a third heating process for heating the compact, a third maintaining process for maintaining the compact at 925°C for 15 hours or more, and a third cooling process for cooling the compact.

[0067] Similarly, the heating and cooling rates of the molded body in the third heating process and the third cooling process should be maintained at 10° C. / min or less in order to minimize the thermal shock of the molded body, and preferably at 120° C. / hr.

[0068] In the third maintenance process, the compact is made of high-temperature superconductor Ho x Gd 1-x Ba 2 Cu 3 O 7-δIf the heat treatment is performed at a lower temperature and for a shorter time than the temperature and time suggested as the minimum conditions for increasing the crystal grain size and ensuring stable crystallinity, a problem may occur in which the heat treatment effect is not fully exerted.

[0069] On the other hand, the oxygen heat treatment step is a heat treatment for stabilizing the oxygen (O) content in the compact.

[0070] For this reason, the oxygen heat treatment step preferably involves heat treating the compact in an oxygen atmosphere at 500° C. for 12 hours or more.

[0071] Next, the reasons for limiting the content of Ho which substitutes for the Gd site in the unit cell crystal structure of the high-temperature superconductor and for selecting Ho will be explained.

[0072] FIG. 3 is a graph showing the change in magnetic susceptibility depending on the amount of Ho added at 10 K, FIG. 4 is a graph showing the change in critical current density depending on the amount of Ho added at 10 K using the Bean model, FIG. 5 is a graph showing the change in magnetic susceptibility depending on the amount of Ho added at 77 K, FIG. 6 is a graph showing the change in critical current density depending on the amount of Ho added at 77 K using the Bean model, FIG. 7 is a graph showing the change in critical current value depending on the amount of Ho added at 10 K, FIG. 8 is a graph showing the change in critical current value depending on the amount of Ho added at 77 K, and FIG. 9 is a graph showing the change in critical current value depending on the type and amount of rare earth element substituted for Gd.

[0073] First, in order to confirm the magnetic properties depending on the amount of Ho added to substitute for Gd in the superconductor, the magnetic susceptibility due to an external magnetic field was measured at 10 K and 77 K using an MPMS (mechanical properties measurement system). The results are shown in Figures 3 and 5.

[0074] As can be seen from FIG. 3 and FIG. 5, as the amount of Ho added increases, the magnetic susceptibility increases, and when the amount of Ho exceeds 50%, the magnetic susceptibility decreases again.

[0075] In particular, it was confirmed that the magnetic susceptibility was significantly improved when the amount of Ho added was at the level of 40 to 60 mol %.

[0076] In order to confirm how the critical current value changes depending on the amount of Ho added to substitute for Gd in the superconductor, the critical current density was calculated under 10K and 77K conditions using the Extended Beans critical current model.

[0077] At this time, the critical current density was calculated by substituting it into the following formula, and the results are shown in FIGS.

[0078] <Critical current density calculation formula>

[0079]

number

[0080] As can be seen from FIGS. 4 and 6, as the amount of Ho added increases, the magnetic susceptibility increases, and when the amount of Ho exceeds 50%, the critical current density value decreases again.

[0081] In particular, it was confirmed that when the amount of Ho added was at a level of 40 to 60 mol %, the critical current density value was significantly improved.

[0082] In order to confirm the change in the critical current density value depending on the amount of Ho added to substitute for Gd in the superconductor, actual test pieces were fabricated and the critical current density was measured under conditions of 10K and 77K. The results are shown in Table 1, Figures 7 and 8.

[0083] [Table 1]

[0084] As can be seen from Table 1, FIGS. 7 and 8, it was confirmed that the critical current density increases / decreases depending on the addition of Ho, and that the critical current density increases as the amount of Ho added increases.

[0085] In particular, a rapid increase was observed when the amount of Ho added was between 40 and 50%, and a rapid decrease was observed when the amount of Ho added exceeded 50%.

[0086] Therefore, it was confirmed that the critical current density value can be controlled according to the addition of Ho. Preferably, it is 1000 kA / cm at 10 K. 2 Higher, 50kA / cm at 77K 2 It can be seen that a higher value, around the inflection point of 40 to 60%, is better.

[0087] Next, the reason why Ho was selected as the rare earth element to substitute for Gd will be explained.

[0088] FIG. 9 is a graph showing the change in critical current value depending on the type and amount of rare earth element substituted for Gd.

[0089] In this embodiment, the rare earth element substituted at the Gd position has an ionic radius similar to that of Gd in the lanthanide group, while taking into consideration the change in magnetic moment (μB / h) and critical current density (A), and it was confirmed that the critical current density can be significantly improved when substituting Ho, so Ho, Tb, Y, and Lu, which have an ionic radius similar to that of Gd in the lanthanide group, were substituted at the Gd position in the crystal structure of the unit lattice of the superconductor in the same proportion. At this time, the changes in magnetic moment and critical density were measured and are shown in Table 1 below.

[0090] The amounts of Ho and Y added were changed, and the critical current density was measured. The results are shown in Table 2 and FIG.

[0091] [Table 2]

[0092] As can be seen from Table 2 and FIG. 9, it was confirmed that Ho, one of the lanthanide elements substituted at the Gd site, can improve the magnetic moment and critical current density of the high temperature superconductor.

[0093] Although the present invention has been described with reference to the accompanying drawings and the above-mentioned preferred embodiment, the present invention is not limited thereto, but is limited by the following claims. Therefore, those skilled in the art can make various modifications and changes to the present invention without departing from the technical spirit of the following claims.

Claims

1. A ReBCO-based high-temperature superconductor, ReBa ２ Cu ３ O ７－δ It is expressed as A high-temperature superconductor, wherein Re is Gd and Ho.

2. The superconductor is Ho ｘ G.D. １－ｘ Ba ２ Cu ３ O ７－δ It is expressed as The x satisfies 0<x<1, 2. The high temperature superconductor according to claim 1, wherein δ satisfies δ<7.

3. 3. The high temperature superconductor according to claim 2, wherein x satisfies 0.4≦x≦0.

6.

4. A (Gd,Ho)BCO-based high-temperature superconductor, A high-temperature superconductor, characterized in that a portion of Gd is replaced by Ho.

5. 5. The high temperature superconductor according to claim 4, wherein the amount of Ho substituted is 40 to 60% of the molar amount of Gd before substitution.

6. A method for producing a (Gd,Ho)BCO-based high temperature superconductor, comprising the steps of: A powder preparation step of preparing a Gd oxide powder, a Ba oxide powder, a Cu oxide powder, and a Ho oxide powder, respectively; A mixing step of mixing the prepared Gd oxide powder, Ba oxide powder, and Cu oxide powder according to the chemical composition to obtain a mixed powder, and replacing a part of the Gd oxide powder with Ho oxide powder and mixing the resulting mixture; A molding step of molding the prepared mixed powder into a molded body; A first heat treatment step for controlling the carbon (C) content of the molded body; a second heat treatment step for synthesizing the compact into a (Gd,Ho)BCO-based compact; A third heat treatment step for growing crystal grains of the compact; and an oxygen heat treatment step for controlling the oxygen (O) content of the compact.

7. In the mixing step, 7. The method for producing a high temperature superconductor according to claim 6, wherein the amount of Ho substituted at the Gd site of the Gd oxide powder in the Ho oxide powder is 40 to 60% with respect to the molar amount of Gd.

8. 7. The method for producing a high temperature superconductor according to claim 6, wherein the molding step comprises compressing and molding the mixed powder.

9. 9. The method for producing a high temperature superconductor according to claim 8, wherein the molding step comprises compressing the mixed powder at 5 to 20 MPa to mold it.

10. The first heat treatment step includes: a first heating step of heating the molded body at a heating rate of 10° C. / min or less; a first maintaining step of maintaining the compact at 880° C. for 20 hours or more; 7. The method for producing a high temperature superconductor according to claim 6, further comprising a first cooling step of cooling the compact at a cooling rate of 10° C. / min or less.

11. The second heat treatment step includes: a second heating step of heating the molded body at a heating rate of 10° C. / min or less; a second maintaining step of maintaining the compact at 900° C. for 20 hours or more; 7. The method for producing a high temperature superconductor according to claim 6, further comprising a second cooling step of cooling the compact at a cooling rate of 10° C. / min or less.

12. The third heat treatment step includes: a third heating step of heating the molded body at a heating rate of 10° C. / min or less; a third maintaining step of maintaining the compact at 925° C. for 15 hours or more; 7. The method for producing a high temperature superconductor according to claim 6, further comprising a third cooling step of cooling the compact at a cooling rate of 10° C. / min or less.

13. 7. The method for producing a high temperature superconductor according to claim 6, wherein said oxygen heat treatment step comprises heat treating said compact in an oxygen atmosphere at 500[deg.] C. for 12 hours or more.

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