CN109082708B - Method for preparing c-axis YBCO high-temperature superconducting thick film with two a-axis grains - Google Patents

Abstract

The invention discloses a method for preparing a _c -axis YBCO high-temperature superconducting thick film with two kinds of a-axis crystal grains. powder; 2) adding the Ba-Cu-O powder into the Y ₂ O ₃ crucible and heating it to a high temperature until it is fully melted, then adding the Ba-Cu-O powder with a fixed weight to it and maintaining a constant initial state for a long time 3) Add Ba-Cu-O powder with a fixed weight to the high-temperature solution, and adjust the intermediate state of undersaturation by changing the melting time Δt _m of the Ba-Cu-O powder U _int , making the state of the solution reach U _int2 ; 4) cooling the solution to the second temperature; 5) inserting the seed crystal material fixed on the connecting rod into step 4) for 5-15 s growth. By finely adjusting the supersaturation of the solution, the invention makes the Y-Ba-Cu-O solution reach the state of the specified supersaturation accurately in the metastable region, and grows to obtain a c-axis YBCO high-temperature ultra-high temperature with two kinds of a-axis crystal grains. Thick film, simple process and convenient operation.

Description

A method for preparing c-axis YBCO high-temperature superconducting thick films with two types of a-axis grains

technical field

The present invention relates to a preparation method of high-temperature superconducting material, in particular to a method for preparing c-axis YBCO high-temperature superconducting thick film, and more particularly to a method for preparing c-axis YBCO high-temperature superconducting film with two kinds of a-axis grains thick film method.

Background technique

Since the discovery of high-temperature superconductors, a large number of crystallographers have devoted themselves to the basic research and preparation of high-quality films. Because YBa ₂ Cu ₃ O _x (referred to as YBCO, Y123, yttrium barium copper oxide) has a superconducting transition temperature Tc higher than the temperature of liquid nitrogen, it exhibits Meissner effect and zero resistance effect in a temperature environment lower than Tc characteristic. It is precisely because of these important properties of YBCO high-temperature superconducting materials that YBCO superconducting thick films have many potential applications in superconducting devices such as current limiters and filters.

The application of the material depends on the properties of the material, and the structure of the material determines the properties of the material, which in turn affects the application of the material in practice. In general, since the lattice constants of YBCO superconducting crystals are approximately equal in two directions, a-axis and b-axis, YBCO superconducting thick films have two orientations, ie, a-axis orientation and c-axis orientation. The c-axis oriented REBCO high-temperature superconducting thick film has a high critical current density, so it has important applications in power transportation, while the a-axis oriented REBCO high-temperature superconducting thick film has a crucial role in Josephson junction devices. application.

Liquid Phase Epitaxy (LPE) is generally regarded as a promising method for the preparation of YBCO superconducting thick films. In the process of liquid-phase epitaxy growth of YBCO superconducting thick film, the seed crystal was fixed on the connecting rod and slowly approached the surface of the saturated solution as the only nucleation point to induce the growth of YBCO superconducting thick film. Since the growth conditions of LPE are close to the equilibrium state, the thick film obtained by using the thin film material as the seed crystal induced growth has the characteristics of low defect, high flatness, and high crystallinity. In addition, since LPE is carried out under non-vacuum conditions, this method has the advantages of low preparation cost. And compared with the general film-forming technology, LPE has a faster growth rate.

Therefore, it is of great significance for the development of Josephson junction devices and the basic research of superconducting mechanism to be able to prepare a specific c-axis oriented YBCO high-temperature superconducting thick film by using LPE.

SUMMARY 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 convenient and efficient method for growing a c-axis YBCO high-temperature superconducting thick film embedded with two kinds of a-axis grains on an NGO substrate, It overcomes the difficulties that the initial state of the solution cannot be fixed and the supersaturation state of the solution cannot be adjusted to σ _int2 .

The idea of the present invention is: when YBCO crystal is grown by liquid phase epitaxy on a NdGaO ₃ (NGO, neodymium gallate) substrate, two kinds of nucleation directions with different nucleation directions will be obtained on the c-axis film according to the state of the supersaturation of the solution. a-axis grains a ₁ and a ₂ . Typically, the _two solution supersaturation states (σ _int1 and σ int1 and σ _int1 and σ _int1 and σ int1 and σ int1 and σ int1 and σ int1 and σ int1 and σ _int2 ), between very large and very small supersaturation. In the past, when using NGO single crystal substrates to prepare liquid phase epitaxial YBCO films, the supersaturation state of the solution was generally adjusted by controlling the weight of fresh Ba-Cu-O powder and the length of the holding time, but this method ignored the solution. It is usually difficult to adjust the supersaturation of the solution to an intermediate state, and it can only be adjusted to two extreme supersaturation states, the maximum and the minimum. The technical features of the present invention are as follows: firstly, a relatively constant initial state U ₀ of the solution is obtained through a long-term heat preservation at a high temperature; secondly, a fixed weight of Ba-Cu-O powder is added, and the underflow is adjusted by changing and adjusting the melting time Δt _m Intermediate state of supersaturation U _int . Unlike previously reported techniques, U _int can be easily subdivided into U _int1 and U _int2 under this condition. Finally, the corresponding intermediate supersaturation states σ _int1 and σ _int2 are obtained at the growth temperature. Under the condition of σ _int2 , the c-axis YBCO high-temperature superconducting thick film with two kinds of a-axis grains can be reliably prepared on the substrate material.

In order to achieve the above object, the present invention provides a method for preparing a c-axis YBCO high temperature superconducting thick film with two kinds of a-axis grains, comprising the following steps:

a) Preparation of the precursor powder of Ba-Cu-O phase;

b) adding the Ba-Cu _- O precursor powder to the crucible of the _Y2O3 material in the crystal growth furnace;

c) heating the crucible of the Ba-Cu-O precursor powder and the Y ₂ O ₃ material in the step b) to the first temperature for heat preservation to obtain a Y-Ba-Cu-O solution;

d) liquid phase epitaxy growth of YBCO superconducting thick film by top seed crystal pulling method in the crystal growth furnace; wherein, the liquid phase epitaxy growth in step d) comprises the following steps:

e) the Ba-Cu-O precursor powder added to the Y-Ba-Cu-O solution in step c), and the first temperature is kept for a long time;

f) reducing the Y-Ba-Cu-O solution in step e) to the second temperature at the first cooling rate;

g) adding Ba-Cu-O precursor powder to the Y-Ba-Cu-O solution in step f), and warming up to the first temperature at the first heating rate for insulation;

h) reducing the Y-Ba-Cu-O solution in step g) to the second temperature at the first cooling rate;

i) Insert the seed crystal material fixed on the connecting rod into the Y-Ba-Cu-O solution obtained in step h), and take it out after epitaxial growth for a period of time to obtain a c-axis YBCO high-temperature superconducting thickness with two kinds of a-axis grains membrane.

Further, process a) comprises:

Mix BaCO3 and _CuO powder according to the ratio of Ba:Cu=0.3～0.8, put it into the ball mill, add absolute ethanol or water for wet grinding to obtain the mixed slurry of BaCO3 and _CuO , the wet grinding time is 2～4 Hour;

The mixed slurry of BaCO ₃ and CuO is heated and dried at a temperature of 90 ℃ to 120 ℃ to obtain a mixed powder of BaCO ₃ and CuO;

The mixed powder of BaCO ₃ and CuO is sintered in air at 890° C. to 910° C. for 40 to 50 hours to obtain the precursor powder of Ba-Cu-O phase.

Further, the first temperature in step c) is 5 to 35°C higher than the peritectic temperature of YBCO, and the holding time is 20 to 24 hours.

Further, the addition amount of the Ba-Cu-O precursor powder in step e) is 15-20 grams, and the holding time is 11-13 hours. Among them, in the process of invention, the inventor found that a short holding time in step e) is not conducive to obtaining a Y-Ba-Cu-O solution with a constant initial state. In fact, when a short holding time is used, it is often easy to obtain a Y-Ba-Cu-O solution whose initial state is not fixed, so that only a very large or very small degree of supersaturation can be obtained when the solution state is adjusted in the next step. state, it is difficult to get an intermediate supersaturation state. Based on this, the inventor innovatively proposed an optimized process of "the addition amount of the Ba-Cu-O precursor powder is 15-20 grams, and the holding time is 11-13 hours" through repeated experiments.

Further, the first cooling rate in step f) is 1.5-3°C/min, and the second temperature is 3-30°C below the peritectic temperature of YBCO.

Further, the addition amount of the Ba-Cu-O precursor powder in step g) is 15-20 grams, and the holding time is 2-4 hours. The inventors found that, in step g), two different intermediate supersaturation states σ _int1 and σ _int2 are obtained correspondingly due to the difference in the holding time. Among them, when the holding time is short, a lower intermediate supersaturation state σ _int1 will be obtained, and when the holding time is long, a higher intermediate supersaturation state σ _int2 will be obtained. Under the condition of the intermediate supersaturation state σ _int1 , it is easy to obtain a c-axis YBCO high-temperature superconducting thick film with a kind of a-axis grains. The c-axis YBCO high-temperature superconducting thick film with two kinds of a-axis grains is obtained only under the condition of the intermediate supersaturation state σ _int2 . In the process of invention, the inventor innovatively concluded that the addition amount of Ba-Cu-O precursor powder is 15-20 grams and the holding time is 2-4 hours, the solution can be obtained by finely adjusting the supersaturation degree of the solution. The intermediate supersaturation state of σ _int2 is favorable for the preparation and growth of c-axis YBCO high-temperature superconducting thick films with two types of a-axis grains.

Further, the first heating rate in step g) is 1.5˜3° C./min.

Further, the seed crystal material in the step i) is an NdGaO ₃ single crystal substrate with a size of 10mm×3mm.

Further, the rotation speed of the epitaxial growth in step i) is 10-20 rpm, and the growth time is 5-15 s.

To sum up, the present invention discloses a method for preparing a c-axis YBCO high-temperature superconducting thick film with two kinds of a-axis grains, comprising the steps of: 1) batching BaCO powder and _CuO powder and sintering to obtain Ba-Cu-O powder; 2) Add Ba-Cu-O powder into a Y ₂ O ₃ crucible and heat it to a high temperature, and through long-term heat preservation, a Y-Ba-Cu-O solution with a constant initial state is obtained; 3) Add a fixed weight of Ba-Cu-O powder to the high temperature solution, adjust the intermediate state U _int of under-saturation by changing the melting time Δt _m of the Ba-Cu-O powder, so that the state of the solution reaches U _int2 ; 4) Cool the solution to the second temperature; 5) insert the seed crystal material fixed on the connecting rod into step 4) to grow for 5-15 s. The invention innovatively introduces a long-term heat preservation procedure in the initial stage of the solution, solves the problem that the initial state of the solution is not fixed, and lays a foundation for the fine adjustment of the solution state in the later stage, so that the solution finally reaches the specified state accurately and grows out A c-axis YBCO high temperature superconducting thick film with two types of a-axis grains.

Technical effect:

1. In the present invention, Ba-Cu-O powder is added for the first time in the high temperature stage of the liquid phase epitaxy method, and the temperature is kept for 11-13 hours, in order to obtain a solution with a constant initial state. Add Ba-Cu-O powder again in the high temperature stage of liquid phase epitaxy, and keep it for 2 to 4 hours. By controlling the weight of Ba-Cu-O powder added and the length of holding time, the supersaturation of the solution is finely adjusted to make the solution supersaturated. The Y-Ba-Cu-O solution accurately reaches the specified supersaturation state in the metastable region, and a c-axis YBCO high-temperature superconducting thick film with two types of a-axis grains is grown. The process is simple and the operation is convenient.

2. The present invention can artificially regulate the growth time of liquid phase epitaxy, thereby controlling the required thickness of the YBCO epitaxial film with mixed grain boundary structure.

3. The liquid phase epitaxy method of the present invention grows a YBCO superconducting thick film with a specific mixed orientation, so that the a-axis YBCO grains of two different orientations are widely distributed in the YBCO thick film with a c-axis orientation, which is used to obtain two kinds of a-axis crystals The grain boundary where the grain meets the c-axis YBCO film is of great significance for the development of Josephson junction devices and basic research on the superconducting mechanism.

Detailed ways

The invention adopts the NGO single crystal substrate as the seed crystal to grow the c-axis YBCO high-temperature superconducting thick film with two kinds of a-axis grains by liquid phase epitaxy. By fixing the initial state of the solution and controlling the supersaturation of the solution, the liquid phase epitaxy growth has C-axis YBCO high-temperature superconducting thick films of two types of a-axis grains.

Example 1

This embodiment provides a method for preparing a c-axis YBCO high-temperature superconducting thick film with two types of a-axis grains, including the following steps:

1. Mix BaCO3 powder and _CuO powder according to the ratio of Ba:Cu=0.6, put it into a ball milling jar, add absolute ethanol or water for wet milling to obtain a mixed slurry of BaCO3 and _CuO , the wet milling time is 3 hours .

2. The mixed slurry of BaCO ₃ and CuO obtained in step 1 is heated and dried at a temperature of 105° C. to obtain a mixed powder of BaCO ₃ and CuO.

3. The mixed powder of BaCO ₃ and CuO obtained in step 2 was sintered in air at 900° C. for 48 hours to obtain the precursor powder of Ba-Cu-O phase.

4. Add the Ba-Cu-O precursor powder into the crucible of the Y ₂ O ₃ material in the crystal growth furnace, and add the Ba-Cu-O precursor powder to be flush with the top edge of the crucible.

5. Heat the Ba-Cu-O precursor powder and the crucible of the _Y2O3 material in step ₄ to 1030°C (that is, 25°C above the peritectic temperature of YBCO), and keep the temperature for 24 hours to obtain Y-Ba-Cu -O solution;

6. Add 20 g of Ba-Cu-O precursor powder to the Y-Ba-Cu-O solution obtained in step 5, and continue to keep the temperature at 1030° C. for 12 hours.

7. Cool the Y-Ba-Cu-O solution obtained in step 6 to 985°C (ie, 20°C below the peritectic temperature of YBCO) at a cooling rate of 2.25°C/min.

8. 15g of Ba-Cu-O precursor powder was added to the Y-Ba-Cu-O solution obtained in step 7, and then heated to 1030°C at a heating rate of 2.25°C/min for 3 hours.

9. Cool the Y-Ba-Cu-O solution obtained in step 8 to 985°C at a cooling rate of 2.25°C/min.

10. The NGO single crystal substrate with a size of 3mm×10mm was used as the seed crystal and fixed on the connecting rod. The surface of the NGO substrate was inserted into the Y-Ba-Cu-O solution, and the top seed crystal pulling method was used for liquid phase epitaxy growth. YBCO superconducting thick film. The specific process parameters in the growth process are: the rotation speed of the seed crystal is 16 rpm, and the growth time is 10 s.

Embodiment 2

This embodiment provides a method for preparing a c-axis YBCO high-temperature superconducting thick film with two types of a-axis grains, including the following steps:

1. Mix BaCO3 powder and _CuO powder according to the ratio of Ba:Cu=0.6, put it into a ball milling jar, add absolute ethanol or water for wet milling to obtain a mixed slurry of BaCO3 and _CuO , the wet milling time is 4 hours .

2. Heat and dry the mixed slurry of BaCO ₃ and CuO obtained in step 1 at a temperature of 120° C. to obtain a mixed powder of BaCO ₃ and CuO.

3. Sinter the mixed powder of BaCO ₃ and CuO obtained in step 2 at 910° C. for 50 hours in air to obtain the precursor powder of Ba-Cu-O phase.

4. Add the Ba-Cu-O precursor powder into the crucible of the Y ₂ O ₃ material in the crystal growth furnace, and add the Ba-Cu-O precursor powder to be flush with the top edge of the crucible.

5. Heat the Ba-Cu-O precursor powder and the crucible of the _Y2O3 material in step ₄ to 1020°C (i.e. 15°C above the peritectic temperature of YBCO), and keep the temperature for 24 hours to obtain Y-Ba-Cu -O solution;

6. Add 15 g of Ba-Cu-O precursor powder to the Y-Ba-Cu-O solution obtained in step 5, and continue to keep the temperature at 1030° C. for 10 hours.

7. Cool the Y-Ba-Cu-O solution obtained in step 6 to 985°C (ie, 20°C below the peritectic temperature of YBCO) at a cooling rate of 1.75°C/min.

8. 16g of Ba-Cu-O precursor powder was added to the Y-Ba-Cu-O solution obtained in step 7, and then heated to 1020°C at a heating rate of 1.75°C/min for 3 hours.

9. Cool the Y-Ba-Cu-O solution obtained in step 8 to 985°C at a cooling rate of 1.75°C/min.

10. The NGO single crystal substrate with a size of 3mm×10mm was used as the seed crystal and fixed on the connecting rod. The surface of the NGO substrate was inserted into the Y-Ba-Cu-O solution, and the top seed crystal pulling method was used for liquid phase epitaxy growth. YBCO superconducting thick film. The specific process parameters in the growth process are: the rotation speed of the seed crystal is 20 rpm, and the growth time is 8 s.

The preferred embodiments of the present invention have been described in detail above. It should be understood that many modifications and changes can be made according to the concept of the present invention by those skilled in the art without creative efforts. Therefore, any technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the prior art according to the concept of the present invention shall fall within the protection scope determined by the claims.

Claims (4)

1. A method for preparing a c-axis YBCO high-temperature superconducting thick film with two kinds of a-axis grains, comprising the following steps: a) Preparation of the precursor powder of Ba-Cu-O phase; b) adding the Ba-Cu-O precursor powder to the Y ₂ O ₃ crucible in the crystal growth furnace; c) heating the crucible of the Ba-Cu-O precursor powder and the Y ₂ O ₃ material in the step b) to a first temperature for heat preservation to obtain a Y-Ba-Cu-O solution; wherein the first temperature is the The above-mentioned peritectic reaction temperature of YBCO is 5~35°C, and the holding time is 20~24 hours; d) Liquid phase epitaxy growth of YBCO superconducting thick film by top seed pulling method in a crystal growth furnace; It is characterized in that, the liquid phase epitaxial growth in step d) includes the following steps: e) adding the Ba-Cu-O precursor powder to the Y-Ba-Cu-O solution in step c), and keeping it at the first temperature for a long time to obtain a solution with a constant initial state; the Ba-Cu-O The amount of O precursor powder added is 15-20 grams, and the holding time is 11-13 hours; f) reducing the Y-Ba-Cu-O solution obtained in the step e) to a second temperature at a first cooling rate; wherein, the first cooling rate is 1.5~3°C/min, and the second cooling rate The temperature is 3~30°C below the peritectic temperature of the YBCO; g) adding Ba-Cu-O precursor powder to the Y-Ba-Cu-O solution obtained in the step f), and heating up to a first temperature at a first heating rate for heat preservation; wherein, the Ba-Cu-O The add-on of -O pioneer powder is 15～20 grams, the described first heating rate is 1.5～3 ℃/min, and the holding time is 2～4 hours; h) reducing the Y-Ba-Cu-O solution obtained in step g) to the second temperature at the first cooling rate; i) Insert the seed material fixed on the connecting rod into the Y-Ba-Cu-O solution obtained in step h), and take it out after epitaxial growth for a period of time to obtain a c-axis YBCO high-temperature superconducting thickness with two kinds of a-axis grains membrane. 2. The method of claim 1, wherein the process a) comprises: Mix BaCO3 and _CuO powder according to the ratio of Ba:Cu=0.3~0.8, put it into the ball mill, add absolute ethanol or water for wet milling to obtain the mixed slurry of BaCO3 and _CuO , the wet milling time is 2~4 Hour; heating and drying the mixed slurry of BaCO ₃ and CuO at a temperature of 90° C. to 120° C. to obtain a mixed powder of BaCO ₃ and CuO; The mixed powder of BaCO ₃ and CuO is sintered in air at 890° C. to 910° C. for 40 to 50 hours to obtain a Ba-Cu-O phase precursor powder. 3. The method of claim 1, wherein the seed crystal material in step i) is a NdGaO ₃ single crystal substrate with a size of 10 mm×3 mm. 4. The method according to claim 1, wherein the rotational speed of the epitaxial growth in step i) is 10-20 rpm, and the growth time is 5-15 s.