CN101901646B - A kind of Y1-xYbxBCO high temperature superconducting film and its preparation method - Google Patents

Abstract

The invention discloses a Y _1-x Yb _x BCO high-temperature superconducting thin film and a preparation method thereof, where 0<X≤1, and belongs to the technical field of high-temperature superconducting material preparation. The thickness of the Y _1-x Yb _x BCO high-temperature superconducting film is about 200nm. The preparation method is: first prepare the precursor solution of Y _1-x Yb _x BCO, apply the precursor solution on the single crystal substrate, and then heat it under 400℃ The precursor amorphous film was pre-fired in wet oxygen, and then the precursor amorphous film was sintered at 800-850°C for 1-4 hours, and wet Ar/O ₂ mixed gas was passed in the first 3/4 of the time period, and then In 1/4 of the time period, dry Ar/ _O mixed gas is introduced; the method of the present invention has simple equipment, low cost, no need for vacuum, and fast deposition speed. The most important thing is that the composition of the film is easy to control, and the dopant and Its ratio is more suitable for the development of practical high-temperature superconducting long tapes.

Description

A kind of Y1-xYbxBCO high temperature superconducting film and its preparation method

technical field

The invention belongs to the technical field of preparation of high-temperature superconducting materials, and in particular relates to the preparation technology of second-generation coating superconducting high-temperature superconducting thin films of rare earth barium copper oxides. the

Background technique

The second-generation coated superconductor of rare earth barium copper oxide mainly based on YBCO, due to its high irreversible field, high current-carrying capacity, low AC loss, and potential price advantage, has been popular since it was discovered in the late 1980s. has been widely concerned. With the progress of research, YBCO coated conductor technology is becoming more and more mature, and the realization of practical application is getting closer and closer. So far, people have prepared YBCO films with a critical current value (I _c ) as high as 1400A/cm at 77K by using pulsed laser deposition (PLD), and YBCO films prepared by metal-organic deposition (MOD) have the highest I _c The value has also reached 795A/cm; in terms of long strips, the US SuperPower company has used metal organic salt chemical vapor deposition (MOCVD) technology to prepare more than 1000 meters of strips, and the overall _Ic value of the strips is 220A/cm, completely A practical standard can be achieved.

However, since the Ic value of the YBCO film under the applied magnetic field decreases rapidly with the increase of the applied magnetic field, some nanoscale defects must be artificially introduced into the YBCO film as pinning centers to suppress the decrease of the Ic value of the YBCO film. The Y _1-x RE _x BCO film prepared by using other rare earth elements to partially replace the Y element in YBCO, the lattice distortion inside the film is caused by the different radii of Y ³⁺ and rare earth element ions. These defects can serve as effective pinning centers to increase the Ic value of YBCO films under magnetic field. In addition, compared with the PLD method and MOCVD method, the Y _1-x RE _x BCO film prepared by the MOD method is not only low in cost, but also can flexibly control the stoichiometric ratio of Y elements and rare earth elements, which has a broader application prospect .

Contents of the invention

The object of the present invention is to provide a Y _1-x Yb _x BCO thin film prepared by chemical solution method and its preparation method. The method has simple equipment and low cost, and the prepared Y _1-x Yb _x BCO thin film has a compact and smooth surface, and the superconducting performance under an external magnetic field is well improved.

A Y _1-x Yb _x BCO thin film provided by the present invention, wherein 0<X≤1, has a thickness of about 200-250 nm. Since Y ³⁺ and Yb ³⁺ ions can be exchanged in any ratio in the Y _1-x Yb _x BCO film, the ratio of Y ³⁺ and Yb ³⁺ ions can be adjusted according to different requirements.

The present invention adopts a low-cost MOD chemical method to prepare Y _1-x Yb _x BCO film, firstly obtain the precursor solution of Y _1-x Yb _x BCO, and then obtain Y _1-x Yb _x BCO through coating, low temperature and high temperature sintering film, the specific steps are as follows:

1) Preparation of Y _1-x Yb _x BCO precursor solution: Yttrium trifluoroacetate, ytterbium trifluoroacetate, barium trifluoroacetate and copper trifluoroacetate or copper acrylate in the ratio of 1-x:x:2: 3 is completely dissolved in anhydrous methanol, 0<X≤1, and a Y _1-x Yb _x BCO precursor solution of 1.0-2.0 mol/L is obtained;

2) Coating of the thin film: coating the Y _1-x Yb _x BCO precursor solution on the single crystal substrate by spin coating or dip coating to obtain the precursor film;

3) Low-temperature pre-firing: Pre-fire the coated precursor film in wet oxygen below 400°C to obtain a precursor amorphous film;

4) High temperature sintering: sinter the precursor amorphous film at 800-850°C for 1-4 hours, during the sintering process, in the first 3/4 of the time period, pass wet Ar/O ₂ mixed with oxygen content of 100-1000ppm Gas, in the last 1/4 period of time, pass dry Ar/O ₂ mixed gas with oxygen content of 100-1000ppm, after sintering, continue to pass dry Ar/O ₂ mixed gas with oxygen content of 100-1000ppm to lower the temperature , when the temperature drops to 500°C, replace it with pure oxygen, keep it warm for 2-4 hours, and cool down with the furnace to obtain a Y _1-x Yb _x BCO film.

Wherein, the trifluoroacetate used in step 1) is obtained by the reaction of corresponding acetate and trifluoroacetic acid, and copper acrylate is obtained by the reaction of copper acetate and acrylic acid;

In step 2), the Y _1-x Yb _x BCO precursor solution is coated on the lanthanum aluminate (LAO) or strontium titanate (STO) substrate by spin coating, and the rotation speed of the coating film is 3000-6000 rpm. The film time is 1-2 minutes; when dip coating is used, the film pulling speed is 5-80 mm/min;

The wet oxygen described in step 3) is realized by feeding oxygen into a container of distilled water heated by a water bath. The range is between 150～400℃;

The sintering process used in step 3) varies depending on the copper salt used: when copper trifluoroacetate is used, the sintering process is as follows: the heating rate from room temperature to 200 °C is 135 °C/hour, between 200 °C and 250 °C The temperature rise rate is 5-7°C/hour, the temperature rise rate between 250°C-300°C is 30°C/hour, and the temperature rise rate between 300°C-400°C is 300°C/hour; when using acrylic pain, the sintering process As follows: the temperature rise rate from room temperature to 150°C is 400-600°C/hour, and the temperature rise rate from 150-400°C is 100-300°C/hour;

The wet Ar/ _O2 gas mixture described in step 4) is achieved by passing the Ar/ _O2 gas mixture into a vessel heated by a water bath with distilled water. The temperature of the water bath is 30-50° C. 1.5 l/min.

Compared with the prior art, the present invention has the following beneficial effects:

1) Compared with the widely used PLD method doping technology at present, the equipment used in the method of the present invention is simple, the cost is low, no vacuum is needed, and the deposition speed is fast. The most important thing is that the film composition is easy to control, and the dopant and Its ratio is more suitable for the development of practical high-temperature superconducting long tapes. the

2) Compared with the pure YBCO film, the surface of the Y _1-x Yb _x BCO film is well improved and becomes smoother and denser; in addition, the interior of the Y _1-x Yb _x BCO film is due to the Y ³⁺ and Yb ³⁺ Different ionic radii will lead to lattice distortion. This lattice distortion can be used as a pinning center to reduce the magnetic field creep under the magnetic field and increase the critical current density of the YBCO film under the magnetic field. At the same temperature, the higher the magnetic field, the higher the J _c of the doped sample than that of the pure YBCO film. Y _1-x Yb _x BCO films have higher superconducting properties at high temperature and high field, and have more application prospects than pure YBCO films.

Description of drawings

Figure 1: SEM image of the surface of the film obtained in Comparative Example 1. the

Figure 2: XRD pattern of the thin film obtained in Example 1. the

Fig. 3: The (103) plane Φ scanning result of the thin film obtained in Example 1. the

Fig. 4: The results of the critical transition temperature _Tc of the film obtained in Example 2.

Fig. 5: The _Jc value of the thin film obtained in Example 2 as a function of the external field.

Figure 6: XRD pattern of the thin film obtained in Example 3. the

Figure 7: SEM image of the thin film obtained in Example 3. the

Fig. 8: SEM picture of the section of gained film in embodiment 4

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. the

Detailed ways

Comparative example 1

1) Dissolve 0.01mol yttrium trifluoroacetate, 0.02mol barium trifluoroacetate and 0.03mol copper trifluoroacetate in anhydrous methanol to obtain a 1.5mol/L YBCO precursor solution;

2) Apply the YBCO precursor solution to the LAO substrate by spin coating method to obtain a wet film, the coating rotation speed is 4000 rpm, and the coating time is 1 minute;

3) Pre-fire the wet film in wet oxygen below 400°C at low temperature to obtain the precursor amorphous film, wherein the temperature rise rate from room temperature to 200°C is 135°C/hour, and the temperature rise rate between 200°C and 250°C is 5°C/hour Hours, the temperature rise rate between 250°C-300°C is 30°C/hour, and the temperature rise rate between 300°C-400°C is 300°C/hour; wet oxygen is a container filled with distilled water heated by passing oxygen into a 30°C water bath Realized, starting from 150°C (inconsistent with the content of the invention), the oxygen flow rate is 0.2 liters/minute;

4) Precursor amorphous film was kept at 820°C for 2 hours, among which, wet Ar/O ₂ mixed gas (oxygen content was 200ppm was passed through for the first 1.5 hours, and Ar/O ₂ mixed gas was passed into a water bath at 50°C to heat Realized by a container equipped with distilled water, the flow rate of the mixed gas is 0.5 liters/minute), after 0.5 hours, the dry Ar/O ₂ mixed gas is introduced, and after the sintering is completed, the temperature is lowered under the condition of continuing to feed the dry Ar/O ₂ mixed gas , when the temperature drops to 500°C, replace it with pure oxygen, keep it warm for 2 hours, and then cool down with the furnace to get a YBCO film.

The SEM of the surface of the film is shown in Figure 1, and it can be found that there are tiny holes and spherical particles. the

Example 1

1) Dissolve 0.0075 mol of yttrium trifluoroacetate, 0.0025 mol of ytterbium trifluoroacetate, 0.02 mol of barium trifluoroacetate and 0.03 mol of copper acrylate in anhydrous methanol to obtain a 1.5 mol/L Y _0.75 Yb _0.25 BCO precursor solution;

2) Coating the Y _0.75 Yb _0.25 BCO precursor solution onto the LAO substrate by spin coating method to obtain a wet film, the coating rotation speed is 4000 rpm, and the coating time is 2 minutes;

3) The wet film is pre-fired at a low temperature in wet oxygen below 400°C to obtain a precursor amorphous film, wherein the temperature rise rate from room temperature to 150°C is 500°C/hour, and the temperature rise rate between 150°C and 400°C is 200°C/hour Hour; The wet oxygen condition of feeding is identical with comparative example 1;

4) Precursor amorphous film was kept at 830°C for 2.0 hours, and wet Ar/O ₂ mixed gas (oxygen content was 500ppm, Ar/O ₂ mixed gas was passed into a water bath at 50°C for heating in the first 1.5 hours) The container that is equipped with distilled water is realized, and the mixed gas flow rate is 0.35 liters/min), and after 0.5 hour, pass dry Ar/O ₂ mixed gas, after sintering finishes, continue to pass into dry Ar/O ₂ mixed gas condition to lower the temperature , when the temperature dropped to 500°C, it was replaced with pure oxygen, and kept at this temperature for 4 hours, and then cooled with the furnace to obtain a Y _0.75 Yb _0.25 BCO film.

The XRD of the film is shown in Figure 2. Only the diffraction peaks of the (00l) plane appear in the figure, indicating that the film has a good orientation. In addition, only one peak appears on each (00l) plane diffraction peak , indicating that the prepared film is pure Y _0.75 Yb _0.25 BCO, not a mixture of YBCO and YbBCO. From the Phi scanning of the (103) surface of the film, it can be seen that the film has a good in-plane texture, as shown in FIG. 3 .

Example 2

1) Dissolve 0.005 mol of yttrium trifluoroacetate, 0.005 mol of ytterbium trifluoroacetate, 0.02 mol of barium trifluoroacetate and 0.03 mol of copper trifluoroacetate in anhydrous methanol to obtain a 1.0 mol/L Y _0.5 Yb _0.5 BCO precursor solution;

2) Coating the Y _0.5 Yb _0.5 BCO precursor solution onto the STO substrate by spin coating method to obtain a wet film, the coating rotation speed is 4500 rpm, and the coating time is 2 minutes;

3) the sintering process is the same as step 3) of comparative example 1;

4) sintering process is identical with the step 4) of comparative example 1;

The critical transition temperature _Tc of the film is shown in Figure 4, and its initial critical transition temperature is 86.5K; the relationship between its Jc value and the external magnetic field is shown in Figure 5.

Example 3

1) Dissolve 0.0025mol of yttrium trifluoroacetate, 0.0075mol of ytterbium trifluoroacetate, 0.02mol of barium acetate and 0.03mol of copper acrylate in anhydrous methanol to obtain a 1.3mol/L Y _0.25 Yb _0.75 BCO precursor solution;

2) Coating the Y _0.25 Yb _0.75 BCO precursor solution onto the LAO substrate by dip coating method to obtain a wet film at a pulling speed of 20 mm/min;

3) Pre-fire the wet film in wet oxygen below 400°C to obtain the precursor amorphous film, wherein the heating rate from room temperature to 150°C is 600°C/hour, and the heating rate between 150°C and 400°C is 300°C/hour Hours; wet oxygen is achieved by passing oxygen into a container filled with distilled water heated by a water bath at 50°C, starting from 150°C, and the oxygen flow rate is 0.3 liters/minute;

4) Precursor amorphous film was kept at 780°C for 2 hours, among which, wet Ar/O ₂ mixed gas (oxygen content was 200ppm, Ar/O ₂ mixed gas was passed into a water bath at 50°C for heating in the first 1.5 hours) The container that distilled water is housed is realized, and the flow rate of mixed gas is 0.5 liters/minute), after 0.5 hours, feed dry Ar/O ₂ mixed gas, after sintering finishes, continue to feed dry Ar/O ₂ mixed gas, lower the temperature , when the temperature dropped to 500°C, it was replaced with pure oxygen, and kept for 2 hours, and then cooled with the furnace to obtain Y _0.25 Yb _0.75 BCO film.

The XRD of the film is shown in Figure 6. Only the diffraction peak of the (00l) plane appears in the figure, indicating that the film has a good orientation, and the prepared film is pure Y _0.25 Yb _0.75 BCO. FIG. 7 is a SEM image of the surface of the film, and it can be seen that the film has a very smooth surface.

Example 4

1) Dissolve 0.005mol ytterbium trifluoroacetate, 0.01mol barium trifluoroacetate and 0.015mol copper trifluoroacetate in anhydrous methanol to obtain a 1.0mol/L YbBCO precursor solution;

2) Apply the YbBCO precursor solution to the LAO substrate to obtain a wet film by dip coating, and the pulling speed is 50 mm/min;

3) Pre-fire the wet film in wet oxygen below 400°C at low temperature to obtain the precursor amorphous film. The temperature rise rate from room temperature to 200°C is 135°C/hour, and the temperature rise rate between 200°C and 250°C is 4°C/hour , the heating rate between 250°C-300°C is 30°C/hour, and the heating rate between 300°C-400°C is 300°C/hour;

4) Precursor amorphous film was kept at 820°C for 2.5 hours, wherein, the first 2 hours was fed with wet Ar/O ₂ mixed gas (the oxygen content was 500ppm, and the Ar/O ₂ mixed gas was passed into a 50°C water bath to heat The container that is equipped with distilled water is realized, and the mixed gas flow rate is 0.8 liters/min), and the dry Ar/O ₂ mixed gas is passed into after 0.5 hours, and after the sintering is completed, the temperature is lowered under the condition of continuing to pass into the dry Ar/O ₂ mixed gas , when the temperature dropped to 500 ° C, it was replaced with pure oxygen, and kept for 2 hours, and then cooled with the furnace to obtain a YbBCO film.

FIG. 8 is a SEM image of a cross-section of the thin film. It can be seen that the thickness of the film is about 200nm. the

Claims (7)

1. a kind of Y of claim ₁ The preparation method of Yb _x BCO thin film is characterized in that, comprises the following steps: (1) Preparation of Y _1-x Yb _x BCO precursor solution: Dissolve yttrium trifluoroacetate, ytterbium trifluoroacetate, barium trifluoroacetate and copper acrylate completely in In anhydrous methanol, 0<X≤1, a Y _1-x Yb _x BCO precursor solution of 1.0-2.0 mol/L is obtained; (2) Coating of thin films: Coating the Y _1-x Yb _x BCO precursor solution onto a single crystal substrate by spin coating or dip coating to obtain a precursor film; (3) Low-temperature pre-firing: pre-fire the coated precursor film in wet oxygen below 400°C to obtain a precursor amorphous film; (4) High temperature sintering: sinter the precursor amorphous film at 800-850°C for 1-4 hours, during the sintering process, in the first 3/4 of the time period, pass wet Ar/O ₂ with an oxygen content of 100-1000ppm Mixed gas, in the last 1/4 period of time, feed dry Ar/O ₂ mixed gas with oxygen content of 100-1000ppm, and continue to feed dry Ar/O ₂ mixed gas with oxygen content of 100-1000ppm after sintering Lower the temperature, and replace it with pure oxygen when the temperature drops to 500°C, keep it warm for 2-4 hours, and cool down with the furnace to obtain a Y _1-x Yb _x BCO film. 2. the preparation method of a kind of Y _1-x Yb _x BCO thin film of claim 1 is characterized in that, yttrium trifluoroacetate, ytterbium trifluoroacetate, barium trifluoroacetate used in step (1) are by corresponding vinegar It is obtained by the reaction of acid salt and trifluoroacetic acid, and copper acrylate is obtained by the reaction of copper acetate and acrylic acid. 3. the preparation method of a kind of Y _1-x Yb _x BCO thin film of claim 1 is characterized in that, in step (2), adopts spin-coating mode with Y _1-x Yb _x BCO precursor solution is coated on lanthanum aluminate ( LAO) or strontium titanate (STO) substrates, the number of rotations of the coating film is 3000-6000 rpm, and the coating time is 1-2 minutes; when dip coating is used, the coating film pulling speed is 5-80 mm /minute. 4. the preparation method of a kind of Y _1-x Yb _x BCO thin film of claim 1 is characterized in that, the wet oxygen described in step (3) is to pass oxygen into the container that the distilled water of water bath heating is housed and realize , the temperature of the water bath is 20-50°C, the oxygen flow rate is 0.2-1.0 liters/min, and the temperature range of the wet oxygen is 150-400°C. 5. The preparation method of a Y _1-x Yb _x BCO film according to claim 1, characterized in that, when copper acrylate is used, the sintering process is as follows: the heating rate from room temperature to 150°C is 400-600°C/hour, 150°C The rate of temperature rise to 400°C is 100°C to 300°C/hour. 6. a kind of Y _1-x Yb _x BCO film preparation method of claim 1 is characterized in that, the wet Ar/O described in step (4) _mixed gas is by Ar/ _O mixed gas is passed into It is realized by a container filled with distilled water heated by a water bath, the temperature of the water bath is 30-50° C., and the flow rate of the mixed gas is 0.2-1.5 liters/minute. 7. A Y _1-x Yb _x BCO thin film prepared according to the method of claim 1, 0<X≤1.

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