CN102747416B - Method of oriented induced growth of REBCO superconductive block from multiple seed crystals in asymmetric(110)/(110) manner - Google Patents

Abstract

The invention discloses a method for inducing the growth of REBCO superconducting bulk with multi-seed crystals, which comprises the steps of: preparing powders of RE123 phase and RE211 phase; preparing a precursor; placing multiple seed crystals on the precursor at non-equidistant intervals On the surface, these seed crystals are c-axis oriented NdBCO/MgO films, and the surface of the film that is in contact with the upper surface of the precursor is its ab plane; the precursor and multiple seed crystals are placed in a growth furnace for melting structure growth REBCO Superconducting bulk, these seed crystals induce the growth of REBCO crystals on the precursor, and these REBCO crystals meet in pairs at the opposite corners of their growth fronts and grow into a whole. The invention realizes effectively eliminating the residual melt at the grain boundary during the growth process of the REBCO superconducting bulk by properly arranging the directions and distances of each seed crystal, thereby improving the overall performance of the superconducting bulk.

Description

Method for Induced Growth of REBCO High Temperature Superconducting Bulk with Multi-seed Asymmetric (110)/(110) Orientation

technical field

The invention relates to a preparation method of a high-temperature superconducting material, in particular to a method for growing a REBCO high-temperature superconducting bulk body through induction of multi-seed crystal asymmetric (110)/(110) orientation.

Background technique

First discovered in 1911, superconductors have two main properties: zero electrical resistance and complete diamagnetism. These peculiar properties make it have application potential in many fields, for example, in the power industry, superconducting cables can be used to realize lossless power transmission, superconducting motors can break through the limit capacity of conventional generators; superconducting coils made of superconducting The magnet is not only small in size and light in weight, but also has low loss, requires low excitation power, and can obtain a strong magnetic field. However, its extremely low temperature greatly limits its application, so the development of superconductors with higher critical temperatures has become a hot spot.

A superconductor whose critical temperature is above the liquid nitrogen temperature (77K) is called a high-temperature superconductor. The discovery of superconductors above the temperature of liquid nitrogen has enabled ordinary physics laboratories to conduct superconducting experiments. At present, high-temperature superconductors include four categories: 90K rare earth system, 110K bismuth system, 125K thallium system and 135K mercury system.

Among them, due to the characteristics of complete diamagnetism and high freezing magnetic field of REBa ₂ Cu ₃ O _x (referred to as REBCO, RE123, rare earth barium copper oxide, where RE represents rare earth element) superconductors, REBCO superconducting bulk materials can be used in such fields as magnetic levitation force, magnetic bearing , flywheel energy storage, and permanent magnets have many potential applications. As an inevitable prerequisite for application, the preparation of REBCO blocks with large size and high performance is a problem that must be solved. At present, the top-seed melt-textured method (TSMTG) is generally considered to be a very promising method for the preparation of REBCO high-temperature superconducting bulk materials. In this growth process, a single seed crystal is placed in the center of the upper surface of the REBCO precursor, which serves as the only nucleation point to induce the REBCO block to solidify and grow according to the seed crystal orientation, and finally form a single-domain superconducting block with a single c-axis orientation. material. However, due to the low growth rate of RE123, it takes a long time to obtain large-sized superconducting bulk materials; and too long growth time will lead to problems such as spontaneous nucleation and grain coarsening of the second phase RE211. Therefore, it is very important to shorten the preparation time.

The multi-seed melt texture method is an extremely effective method to solve the long growth time of superconducting bulk materials, that is, to place multiple seed crystals in a certain orientation on the upper surface of the sample and induce the directional solidification of the REBCO block according to the orientation of the seed crystals. grow. Since multiple seed crystals are induced to grow at the same time, the time required for the entire preparation process is greatly shortened. However, the study found that, using the traditional multi-seed crystal method, the sample has a large amount of residual non-superconducting phase melt at the grain boundary, which makes the freezing magnetic field of the REBCO bulk material attenuate to a certain extent at the grain boundary, and finally leads to the block decrease in the overall performance of the material. On the other hand, in the traditional multi-seed crystal equidistant placement induced bulk preparation process, as the number of seed crystals used increases, the weak link of the grain boundary inside the bulk material will be further reduced, thereby reducing the superconducting performance of the bulk material.

Therefore, those skilled in the art are devoting themselves to developing a method for the induced growth of REBCO superconducting bulk with multi-seed crystals, so as to realize the induced growth of complete REBCO single-domain crystals with clean grain boundaries.

Contents of the invention

In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a method for inducing the growth of REBCO superconducting bulk with multi-seed crystals, by asymmetrically placing multiple seed crystals on the upper surface of the precursor to realize Induced growth of complete REBCO monodomain crystals with clean grain boundaries.

In order to achieve the above object, the present invention provides a method for multi-seed induced growth REBCO superconducting bulk, characterized in that, comprising the steps:

The first step, preparing powders of RE123 phase and RE211 phase;

The second step is to prepare the precursor;

In the third step, a plurality of seed crystals are placed on the upper surface of the precursor, the seed crystal is a c-axis oriented NdBCO/MgO square film, the film has a first pair of sides and a second pair of sides, the The first pair of edges is in the <100> or <010> crystal direction, the second pair of edges is in the <100> or <010> crystal direction, and the surface of the thin film in contact with the upper surface of the precursor is the The ab surface of the seed crystal, the first pair of sides of the plurality of seed crystals placed on the upper surface of the precursor are parallel to each other, and the second pair of sides of the plurality of seed crystals are parallel to each other;

The fourth step is to place the precursor and the plurality of seed crystals in a growth furnace to grow a REBCO superconducting block in a molten structure. During the growth of the molten structure, the plurality of seed crystals are placed in the growth furnace. The REBCO crystals are induced to grow on the precursor, and the plurality of REBCO crystals meet each other at the opposite corners of their growth fronts and grow into a whole.

Further, the first step includes:

According to the ratio of RE:Ba:Cu=1:2:3 and RE:Ba:Cu=2:1:1, RE ₂ O ₃ , BaCO ₃ and CuO powder were mixed to obtain the RE123 phase and the RE211 phase Powder;

The powders of the RE123 phase and the RE211 phase are ground and sintered three times to obtain the powders of the RE123 phase and the RE211 phase.

Further, the sintering process conditions are: under an air atmosphere, a sintering temperature of 900° C. and a sintering time of 48 hours.

Further, the second step includes: grinding and mixing the powders of the RE123 phase and the RE211 phase according to the composition of RE123+30mol%RE211+1 wt%CeO ₂ , and pressing them into a cylindrical precursor .

Further, the temperature sequence for the growth of the molten structure is: room temperature for 5 hours, heating up to 950°C, holding for 4 hours, heating up to the highest temperature T _max , holding for 1-2 hours, cooling down to the initial growth temperature at the first cooling rate T _s , cooling at the second cooling rate within the growth temperature range, and cooling with the furnace; the first cooling rate is in the range of 60-150°C/h, and the second cooling rate is in the range of 0.2-0.4°C/h within range.

Further, the RE is Gd.

Further, the maximum temperature T _max is 1095°C.

Further, the initial growth temperature T _s is 1052°C.

Further, the cooling rate is 0.3°C per hour.

In a preferred embodiment of the present invention, four seed crystals are used to induce the growth of a GdBCO superconducting bulk. The powders of Gd123 phase and Gd211 phase were first prepared, and then the precursors were prepared using the powders of Gd123 phase and Gd211 phase according to the composition of Gd123+30mol%Gd211+1wt% _CeO2 . The precursor is cylindrical with a diameter of 50 mm and a height of 15 mm. Then take four c-axis oriented NdBCO/MgO square films (<100> or <010> crystal orientation on the four edges of the square) with dimensions of 1.5 mm in length, 1.5 mm in width and 0.5 mm in thickness as seeds, and place them on the precursor The upper surface of the body, the surface where the seed crystal is in contact with the upper surface of the precursor is the plane (ab plane) determined by the a and b axes of the seed crystal. The four seed crystals constitute four vertices of a rectangle (length 14 mm, width 2 mm), and the four sides of the four seed crystals are opposed to and parallel to each other. Finally, the precursor and the seed crystal are placed in a growth furnace for molten structure growth to obtain a GdBCO superconducting bulk. During the growth of the molten structure, the REBCO crystals induced to grow by each seed crystal on the precursor meet at the opposite corners of their growth fronts, so that the residual melt (non-superconducting phase melt) will Expelled outward from the meeting, thereby inducing the growth of a complete single-domain crystal.

It can be seen that the multi-seed crystal induced growth method of REBCO superconducting bulk in the present invention adopts the c-axis oriented NdBCO/MgO thin film as the seed crystal, and uses its superheating characteristics to induce homoepitaxial growth. The method is simple, easy to operate, and repeatable. Controllable; and the c-axis oriented NdBCO/MgO film is easy to cut to obtain a single-oriented seed crystal. In addition, compared with the single-seed method, the multi-seed method of the present invention induces the growth of REBCO superconducting bulk at the same time, which can effectively shorten the time for growing REBCO superconducting bulk; Compared with the seed crystal method, the multi-seed crystal induced growth method of REBCO superconducting bulk in the present invention can effectively eliminate the residual melting at the grain boundary during the growth process of REBCO superconducting bulk through the arrangement of suitable seed crystal direction and spacing. Body, improve the overall performance of the superconducting bulk.

The idea, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings, so as to fully understand the purpose, features and effects of the present invention.

Description of drawings

Fig. 1 is a schematic diagram of the distribution of seeds on the upper surface of the precursor when four seed crystals are used to induce the growth of a GdBCO superconducting bulk in one embodiment of the present invention.

Fig. 2 is a schematic diagram of the growth process of four seed crystal induced growth GdBCO superconducting bulks as shown in Fig. 1 .

FIG. 3 is a diagram of the crystallographic morphology of the GdBCO superconducting bulk obtained by inducing the growth of the GdBCO superconducting bulk from four seed crystals as shown in FIG. 1 .

Fig. 4 is a schematic diagram of the distribution of seeds on the upper surface of the precursor when three seed crystals are used to induce the growth of a REBCO superconducting bulk.

FIG. 5 is a schematic diagram of the growth process of the REBCO superconducting bulk induced by three seed crystals as shown in FIG. 4 .

Fig. 6 is a schematic diagram of the distribution of seeds on the upper surface of the precursor when five seed crystals are used to induce the growth of a REBCO superconducting bulk.

FIG. 7 is a schematic diagram of the growth process of the REBCO superconducting bulk induced by five seed crystals as shown in FIG. 5 .

Detailed ways

In one embodiment of the present invention, four seed crystals are used to induce the growth of REBCO superconducting bulk. Wherein, the rare earth element RE selects Gd, and the specific steps are as follows:

In the first step, powders of Gd123 phase and Gd211 phase are prepared.

In the first step, three kinds of powders of BaCO ₃ , CuO and Gd ₂ O ₃ are firstly taken, and these three powders are mixed according to the ratio of Gd:Ba:Cu=1:2:3 to prepare the powder of Gd123 phase, according to The ratio of Gd:Ba:Cu=2:1:1 was mixed to prepare the powder of Gd211 phase by mixing these three powders.

Fully grind the powder of Gd123 phase evenly, sinter the powder of Gd123 phase under air atmosphere at a sintering temperature of 900°C for 48 hours, repeat the above grinding and sintering process three times to obtain powder of Gd123 phase.

Fully grind the powder of Gd211 phase evenly, sinter the powder of Gd211 phase under air atmosphere at a sintering temperature of 900°C for 48 hours, repeat the above grinding and sintering process three times to obtain powder of Gd211 phase.

The second step is to prepare the precursor.

In the second step, the powder of the Gd123 phase and the powder of the Gd211 phase obtained in the first step are batched, milled, and mixed according to the composition of Gd123+30mol%Gd211+1wt% _CeO2 , and pressed into a cylindrical precursor body. Among them, 120 g of the above-mentioned ingredients were mixed, and the mixture was obtained after being sufficiently ground and pressed to form a cylindrical precursor 100 with a diameter of 50 mm and a height of 15 mm (see FIG. 1 ).

The third step is to place the seed crystal.

As shown in FIG. 1 , four seed crystals 101 , 102 , 103 and 104 are placed on the upper surface of the precursor 100 . The used seed crystals 101, 102, 103 and 104 are all c-axis oriented NdBCO/MgO films, and the surface where the film is in contact with the upper surface of the precursor 100 is the ab plane of the seed crystals 101, 102, 103 and 104 (that is, the The plane defined by the a-axis and b-axis of the seed crystal).

In this embodiment, the seed crystals 101, 102, 103 and 104 are all square flakes with a length of 1.5 mm, a width of 1.5 mm, and a thickness of 0.5 mm. get everything. Among them, the surface of the film is the plane (ab plane) determined by its a and b axes, and the shearing is carried out along its <100> and <010> crystal directions, so that the four edges of the obtained square sheet are <100> or <010 >Crystal orientation. That is, the seed crystals 101 , 102 , 103 and 104 all have a first pair of sides and a second pair of sides, the first pair of sides is along the <100> or <010> crystal orientation, and the second pair of sides is along the <100> or <010> crystal orientation. When placing these four seeds, make them form a rectangle, each seed crystal occupies a vertex of the rectangle, and make the square slices of two seeds crystals on any side of the rectangle diagonal to each other, and make these seeds crystals The first pair of sides are parallel to each other and the second pair of sides are parallel to each other. That is, the first pair of sides of the seed crystals 101 , 102 , 103 and 104 are parallel to each other, and the second pair of sides of the seed crystals 101 , 102 , 103 and 104 are parallel to each other. Wherein, the length l ₁ of one side of the rectangle formed by the four seed crystals is 2 mm, and the length l ₂ of the other side is 14 mm. That is: the distance between the seed crystal 101 and the seed crystal 102 is 2 mm and diagonal to each other, the distance between the seed crystal 103 and the seed crystal 104 is 2 mm and diagonal to each other, the distance between the seed crystal 101 and the seed crystal 103 is 14 mm and diagonal to each other, and the distance between the seed crystal 102 and the seed crystal 102 is 2 mm and diagonal to each other. The distance from the seed crystal 104 is 14 mm and they are diagonal to each other. The arrangement of the seed crystals is to ensure that when the seed crystals induce the growth of the GdBCO superconducting bulk, the (110)/(110) grain boundaries of the GdBCO superconducting bulk can be formed between these seed crystals. It should be noted that, for a pair of seed crystals 101 and 102 and another pair of seed crystals 103 and 104 with a distance l ₁ =2 mm, the distance l ₂ between these two pairs of seed crystals can also be selected to be greater than 14 mm, namely The minimum distance between the two pairs of seeds is 14mm.

The fourth step is to grow the GdBCO superconducting bulk.

In the fourth step, the precursor 100 and the seed crystals 101 , 102 , 103 and 104 are placed in the growth furnace according to the arrangement in the third step, and the GdBCO superconducting block is subjected to molten structure growth (MTG). The temperature program of MTG can be realized by setting the temperature control program of the growth furnace, which is: room temperature for 5 hours, temperature rise to 950°C, heat preservation for 4 hours, temperature rise to the highest temperature T _max , heat preservation for 1 to 2 hours, the first The cooling rate is to lower the temperature to the initial growth temperature T _s , to lower the temperature at the second cooling rate within the growth temperature range, and to cool with the furnace. Wherein, the range of the first cooling rate is 60-150°C/h, and the range of the second cooling rate is 0.2-0.4°C/h. In this example, the temperature program of the MTG used is: room temperature for 5 hours, temperature rise to 950°C, heat preservation for 4 hours, heating for 2 hours, temperature rise to 1095°C, heat preservation for 2 hours, cooling to 1052°C (within 15 minutes), cooling 36 hours (cooling rate is 0.3°C/h), cooling with the furnace.

The growth process of the GdBCO superconducting bulk is shown in FIG. 2 . After a period of growth, the seed crystals 101 , 102 , 103 and 104 respectively induce monodomain growth to obtain crystals 111 , 112 , 113 and 114 . The growth fronts of crystal 111 and crystal 112 meet at their diagonals and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point to induce a complete single-domain crystal 121 and continue to grow. The growth fronts of crystal 113 and crystal 114 meet at their diagonals and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point, induce a complete single-domain crystal 122, and continue to grow. After a period of growth, the growth fronts of the crystals 121 and 122 meet at their diagonals and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point, inducing a complete single-domain crystal.

Figure 3 shows the crystal morphology of the upper surface of the GdBCO superconducting bulk material prepared by the above process steps. In the figure, the distribution of the four seed crystals can be seen, and the four seed crystals are opposite to each other. (110)/(110) grain boundaries of the GdBCO superconducting bulk formed between the boundaries. It can be seen that, through the method for growing REBCO superconducting bulk induced by multi-seed crystals of the present invention, it is possible to prepare a complete single-domain GdBCO superconducting bulk with clean grain boundaries.

The method for the multi-seed induced growth REBCO superconducting bulk of the present invention is not only applicable to the GdBCO superconducting bulk of rare earth element Gd, but also suitable for preparing REBCO superconducting bulk of other rare earth elements, such as YBCO, GdBCO, SmBCO and NdBCO and other superconducting bulk materials, the specific process steps are similar to those in this embodiment, and will not be repeated here.

In addition, the multi-seed crystal induction growth method of the REBCO superconducting bulk in the present invention can also use 3 seed crystals, 5 seed crystals or more seed crystals for induced growth. Figures 4 and 5 show the distribution diagrams of the seed crystals and the growth process of the REBCO superconducting bulk when three seed crystals are used to induce the growth of the REBCO superconducting bulk. As shown in FIG. 4 , the seed crystals 201 , 202 and 203 are distributed on the upper surface of the precursor 200 . As shown in FIG. 5 , after a period of growth, the seed crystals 201 and 202 respectively induce monodomain growth to obtain crystals 211 and 212 . The growth fronts of crystal 211 and crystal 212 meet at their diagonals and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point to induce a complete single-domain crystal 221 and continue to grow. After a period of growth time, the crystal 221 and the seed crystal 203 induce monodomain growth so that the growth fronts of the crystal 222 meet at its diagonal and the residual melt (non-superconducting phase melt) is discharged along the direction of the arrow at the meeting point, inducing into a complete monodomain crystal.

Figures 6 and 7 show the distribution diagram of the seed crystals and the growth process of the REBCO superconducting bulk when five seed crystals are used to induce the growth of the REBCO superconducting bulk. As shown in FIG. 6 , seed crystals 301 , 302 , 303 , 304 and 305 are distributed on the upper surface of the precursor 300 . As shown in FIG. 7 , after a period of growth time, the seed crystals 301 and 302 respectively induce monodomain growth to obtain crystals 311 and 312 . The growth fronts of the crystal 311 and the crystal 312 meet at their diagonals and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point to induce a complete single-domain crystal 321 and continue to grow. Seed crystals 304 and 305 induce monodomain growth to yield crystals 314 and 315, respectively. The growth fronts of the crystal 314 and the crystal 315 meet at their diagonals and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point to induce a complete single-domain crystal 323 and continue to grow. After a period of growth time, crystal 321 and seed crystal 303 induce monodomain growth to obtain that the growth fronts of crystal 322 meet at its diagonal and discharge the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point, and at the same time Crystal 323 also meets the growth front of crystal 322 at its diagonal and discharges the residual melt (non-superconducting phase melt) along the direction of the arrow at the meeting point, thereby inducing a complete single-domain crystal.

The above details describe preferred embodiments of the invention. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (9)

1. A method for multi-seed induced growth REBCO superconducting bulk, characterized in that, comprising the steps: The first step, preparing powders of RE123 phase and RE211 phase; The second step is to prepare the precursor; In the third step, a plurality of seed crystals are asymmetrically placed on the upper surface of the precursor, the seed crystals are c-axis oriented NdBCO/MgO square films, and the films have a first pair of sides and a second pair of sides , the first pair of edges is along the <100> or <010> crystal orientation, the second pair of edges is along the <100> or <010> crystal orientation, the surface of the thin film in contact with the upper surface of the precursor is the ab surface of the seed crystal, the first pair of sides of the plurality of seed crystals placed on the upper surface of the precursor are parallel to each other, and the second pair of sides of the plurality of seed crystals parallel to each other; The fourth step is to place the precursor and the plurality of seed crystals in a growth furnace to grow a REBCO superconducting block in a molten structure. During the growth of the molten structure, the plurality of seed crystals are placed in the growth furnace. The REBCO crystals are induced to grow on the precursor, and the plurality of REBCO crystals meet each other at the opposite corners of their growth fronts and grow into a whole. 2. the method for multi-seed induced growth REBCO superconducting block as claimed in claim 1, wherein said first step comprises: According to the ratio of RE:Ba:Cu=1:2:3 and RE:Ba:Cu=2:1:1, RE ₂ O ₃ , BaCO ₃ and CuO powder were mixed to obtain the RE123 phase and the RE211 phase Powder; The powders of the RE123 phase and the RE211 phase are ground and sintered three times to obtain the powders of the RE123 phase and the RE211 phase. 3. The method for growing a REBCO superconducting bulk with multi-seed induction as claimed in claim 2, wherein the sintering process conditions are: under an air atmosphere, a sintering temperature of 900° C. and a sintering time of 48 hours. 4. The method for multi-seed induced growth of REBCO superconducting bulk as claimed in any one of claims 1 to 3, wherein said second step comprises: powders of said RE123 phase and said RE211 phase according to RE123+ The components of 30mol% RE211 + 1wt% CeO ₂ were ground, mixed, and pressed into a cylindrical precursor. 5. The method for multi-seed induced growth of REBCO superconducting bulk as claimed in claim 4, wherein the temperature program for the growth of the molten structure is: room temperature for 5 hours, heating up to 950°C, holding for 4 hours, heating up to the highest temperature (T _max ), keep warm for 1 to 2 hours, cool down to the initial growth temperature (T _s ) at the first cooling rate, cool at the second cooling rate within the growth temperature range, and cool with the furnace; the first cooling rate is at In the range of 60-150° C./h, the second cooling rate is in the range of 0.2-0.4° C./h. 6. The method for multi-seed induced growth of REBCO superconducting bulk as claimed in claim 5, wherein said RE is Gd. 7. The method for multi-seed induced growth of REBCO superconducting bulk as claimed in claim 6, wherein the maximum temperature (T _max ) is 1095°C. 8. The method for multi-seed induced growth of REBCO superconducting bulk as claimed in claim 7, wherein the initial growth temperature (T _s ) is 1052°C. 9. The method for induced growth of REBCO superconducting bulk with multi-seed crystals according to claim 8, wherein the second cooling rate is 0.3° C./h.