CN115974548B - A lead-free high-entropy ferroelectric film and its preparation method and application - Google Patents

Abstract

The application belongs to the technical field of film materials, and discloses a lead-free high-entropy ferroelectric film, a preparation method and application thereof. The application prepares the lead-free high-entropy ferroelectric film with controllable thickness by using a sol-gel method, and the sol-gel method has the advantages of simple process, low equipment requirement, low production cost and good film forming efficiency and uniformity, and is applicable to large-area film making; the proportion of the material prepared by the sol-gel method to the chemical components is easy to control, and the material can be designed by molecular structure engineering, so that the method is particularly suitable for preparing lead-free high-entropy ferroelectric film multicomponent materials. The lead-free high-entropy ferroelectric film prepared by the application has ultrahigh breakdown field strength and good temperature stability, the breakdown field strength which can be born by the film can be more than 8MV/cm, and the energy storage density can reach 5.88J/cm ³ The energy storage efficiency can reach 93%, can work normally under the condition of-55-200 ℃, and has larger dielectric constant and smaller dielectric loss.

Description

A lead-free high-entropy ferroelectric film and its preparation method and application

Technical field

The invention belongs to the technical field of thin film materials, and particularly relates to a lead-free high-entropy ferroelectric thin film and its preparation method and application.

Background technique

At present, there are research reports that the breakdown electric field strength of ordinary ferroelectric thin films is generally 1-2MV/cm (Reference 1: Xie, Yanjiang, et al. "Ultra-high energy storage density and enhanced dielectric properties in BNT-BT based thin film."Ceramics International 47.16(2021):23259-23266; Reference 2: Peng, Biaolin, et al."Low-temperature-poling awakenedhigh dielectric breakdown strength and outstanding improvement of dischargeenergy density of(Pb,La)(Zr, Sn,Ti)O3 relaxor thin film." Nano Energy 77(2020):105132), the breakdown electric field strength of commercial polymer films is 0.2-0.6MV/cm (Reference 3: Pei, Jia-Yao, et al. al. "Enhancement of breakdown strength of multilayer polymer film through electric field redistribution and defect modification." AppliedPhysics Letters 114.10(2019):103702; Reference 4: Samant, Saumil P., et al. "Directed self-assembly of block copolymers for high breakdown strength polymer film capacitors." ACS applied materials&interfaces 8.12(2016):7966-7976), the breakdown electric field strength of ceramic particle/polymer composite film is 2.3-4.1MV/cm (Reference 5: Beier, Christopher W. , Jason M. Sanders, and Richard L. Brutchey. "Improved breakdown strength and energy density in thin-film polyimide nanocomposites with small barium strontium titanate nanocrystal fillers." The Journal of Physical Chemistry C 117.14 (2013): 6958-6965; Reference 6: Wang, Yifei, et al. "Compositional tailoring effect on electric field distribution for significantly enhanced breakdown strength and restrained conductive loss insandwich-structured ceramic/polymer nanocomposites." Journal of MaterialsChemistry A 5.9 (2017): 4710-4718). The breakdown electric field strength of these thin film materials is low and cannot meet the market demand for higher breakdown electric field strength (above 5MV/cm).

High-entropy ferroelectric materials refer to a solid solution compound formed by more than four metal elements in an equimolar or approximately equimolar ratio at a certain site in the crystal structure of the material. Its characteristic is that the enhanced chemical disorder makes the composition The state entropy is maximized, resulting in a more stable system. Compared with traditional ferroelectric materials, high-entropy ferroelectric materials have inherent characteristics such as stable thermodynamic phases, significant lattice distortion, and composition complexity. These properties give high-entropy ferroelectric materials good thermal stability, strong mechanical properties, outstanding piezoelectric properties and dielectric properties.

Traditional high-entropy ferroelectric materials are generally prepared by physical solid-state reaction methods, but this method is suitable for preparing corresponding bulk materials and is not suitable for preparing high-entropy ferroelectric thin films. The preparation methods of ferroelectric thin film materials generally include physical vapor deposition (PVD) and chemical vapor deposition (CVD). Among them, PVD vaporizes metal and deposits it on the substrate through inter-atomic collision in a vacuum high-temperature environment to form a thin film, but this method requires a high degree of vacuum. For multi-component compounds, the melting point and gas phase vapor pressure between elements are stringent. At the same time, the control of the component ratio is small, the film formation is uneven and the quality is poor. CVD uses a variety of gas phase substances to react chemically at high temperatures and deposit them on a substrate to form a thin film. However, this method has great limitations. For example, toxic reaction gases are generated during the preparation process, some reaction products (impurities) may remain in the coating, the substrate must have good high temperature resistance (>1000°C) and the preparation High cost etc.

Therefore, how to overcome the problems of high equipment requirements and high cost in the preparation method of high-entropy ferroelectric thin films, and the development of high-entropy ferroelectric thin films with higher breakdown electric field strength has become an urgent need in the current electronics industry.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for preparing lead-free high-entropy ferroelectric films. The sol-gel method is used to prepare lead-free high-entropy ferroelectric films with controllable thickness. The equipment requirements are low, the cost is low, and the lead-free high-entropy ferroelectric films produced are Entropy ferroelectric films have ultra-high breakdown electric field strength, and the breakdown electric field strength of lead-free high-entropy ferroelectric films is greater than 8MV/cm.

A first aspect of the invention provides a method for preparing a lead-free high-entropy ferroelectric film, which includes the following steps:

1) Prepare a BNKLST precursor solution. The general chemical formula of BNKLST is ( _Bix Na _x K _{y Lay} Sr _y )TiO ₃ , where x>0, y>0, 2x+3y=1;

2) Spin-coat the BNKLST precursor solution obtained in step 1) on the conductive substrate to obtain a wet film;

3) Dry the wet film obtained in step 2) at 200-250°C for 3-5 minutes, and then pyrolyze it at 400-450°C for 3-5 minutes to obtain an amorphous film;

4) The amorphous film obtained in step 3) is subjected to rapid heating treatment; the rapid heating treatment is: heating to 650-700°C at a heating rate of 50-100°C/s, and keeping the temperature for 3-5 minutes;

5) Perform annealing treatment on the amorphous film that has been rapidly heated in step 4) to obtain the lead-free high-entropy ferroelectric film.

Preferably, the BNKLST precursor solution is prepared as described in step 1), specifically by following the following steps:

According to the stoichiometric ratio of the general chemical formula, weigh bismuth salt, sodium salt, potassium salt, strontium salt, lanthanum salt and titanium salt;

Dissolve the bismuth salt in a solvent, then add the sodium salt, the potassium salt, the strontium salt and the lanthanum salt, and dissolve to obtain solution A;

Mix the titanium salt with a solvent and a chelating agent to obtain solution B;

Add the B solution to the A solution, then add formamide with a volume ratio of 0.5-1%, stir for 24-36 hours, and then let it stand for 72-84 hours, and react to obtain the BNKLST precursor solution.

Preferably, the bismuth salt includes at least one of bismuth acetate, bismuth nitrate and bismuth sulfate; the sodium salt includes at least one of sodium acetate trihydrate, sodium nitrate and sodium sulfate; the potassium salt includes potassium acetate , at least one of potassium nitrate and potassium sulfate; the strontium salt includes at least one of strontium acetate, strontium nitrate and strontium sulfate; the lanthanum salt includes at least one of lanthanum nitrate hexahydrate, lanthanum nitrate and lanthanum sulfate species; the titanium salt is tetrabutyl titanate.

Preferably, the solvent includes at least one of glacial acetic acid, ethylene glycol methyl ether, ethanol, and isopropyl alcohol; the chelating agent includes at least one of acetylacetone, EDTA, potassium sodium tartrate, and ammonium citrate.

Preferably, the ratio of x and y is 0.5-2:1.

Preferably, the conditions of the annealing treatment include: the annealing temperature is 650-700°C, and the annealing time is 10-15 minutes.

Preferably, before performing step 5), repeat steps 2), step 3) and step 4) multiple times to obtain a multi-layer amorphous film.

Preferably, the number of layers of the lead-free high-entropy ferroelectric film is 4-10, and the thickness of each layer of the lead-free high-entropy ferroelectric film is 40-50 nm.

A second aspect of the present invention provides a lead-free high-entropy ferroelectric film, which is produced by the preparation method of the present invention. The breakdown electric field strength of the lead-free high-entropy ferroelectric film is greater than 8MV/cm.

Preferably, the lead-free high-entropy ferroelectric film has a single-phase crystal structure.

A third aspect of the present invention provides a dielectric energy storage device, in which the dielectric energy storage device includes the lead-free high-entropy ferroelectric film of the present invention.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) The preparation method of the lead-free high-entropy ferroelectric film of the present invention uses the sol-gel method to prepare the lead-free high-entropy ferroelectric film with controllable thickness. The sol-gel method has the advantages of simple process, low equipment requirements and low production cost. , with the advantages of good film-forming efficiency and uniformity, it can be applied to large-area film-making; and the proportion of chemical components of materials prepared by the sol-gel method is easy to control, and the materials can be designed through molecular structure engineering, which is especially suitable for the preparation of lead-free High-entropy ferroelectric thin film multi-component materials.

(2) The lead-free high-entropy ferroelectric film produced by the present invention has ultra-high breakdown field strength and good temperature stability. The breakdown electric field strength it can withstand is greater than 8MV/cm, and the energy storage density can reach 5.88 J/cm ³ , the energy storage efficiency can reach 93%, it can work normally at -55-200℃, and has a large dielectric constant and small dielectric loss.

(3) The lead-free high-entropy ferroelectric film prepared by the present invention does not contain toxic elements such as lead, and is more environmentally friendly than the lead-containing ferroelectric film; dielectric energy storage prepared by using the lead-free high-entropy ferroelectric film of the present invention The device has excellent energy storage density and energy storage efficiency.

Description of the drawings

Figure 1 is an XRD pattern of the lead-free high-entropy ferroelectric film obtained in Example 1;

Figure 2 is an SEM image of a cross-section of the lead-free high-entropy ferroelectric film obtained in Example 1;

Figure 3 is a graph showing changes in dielectric constant and dielectric loss with frequency of the dielectric energy storage device assembled in Embodiment 1;

Figure 4 is a graph showing the relationship between conductivity and temperature of the dielectric energy storage device assembled in Example 1;

Figure 5 is a Weber distribution curve diagram of the breakdown electric field of the dielectric energy storage device assembled in Embodiment 1;

Figure 6 is an electrical hysteresis loop diagram of the dielectric energy storage device assembled in Embodiment 1;

Figure 7 is an SEM image of a cross-section of the lead-free high-entropy ferroelectric film obtained in Comparative Example 1;

Figure 8 is an electrical hysteresis loop diagram of the dielectric energy storage device assembled in Comparative Example 1.

Detailed ways

In order to allow those skilled in the art to understand the technical solution of the present invention more clearly, the following examples are listed for description. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

Unless otherwise specified, the raw materials, reagents, and devices used in the following examples can be obtained from conventional commercial sources, or can be obtained by existing known methods.

The room temperature in the present invention refers to 25±5°C; the slow dripping refers to the dropping acceleration rate of 5-10 seconds/drop; the slow stirring refers to the stirring rate of 10-20rpm; the amorphous film refers to the amorphous state that has not yet crystallized. membrane.

Example 1

A method for preparing a lead-free high-entropy ferroelectric film, including the following steps:

1) Prepare (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 )TiO ₃ precursor solution:

Weigh bismuth acetate, sodium acetate trihydrate, potassium acetate, strontium acetate, lanthanum nitrate hexahydrate and tetrabutyl titanate as raw materials according to the stoichiometric ratio of (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 ) TiO ₃ , and add acetic acid to Add bismuth to an appropriate amount of glacial acetic acid, heat and stir for 30 minutes at 70°C, then add a small amount of deionized water and stir for 30 minutes, then add sodium acetate trihydrate, potassium acetate, strontium acetate and lanthanum nitrate hexahydrate in sequence, and stir for 2.5 hours. Dissolve to obtain solution A;

Mix the three solutions of tetrabutyl titanate, ethylene glycol methyl ether, and acetylacetone at room temperature according to a volume ratio of 1:3:2, and stir for 1 hour to obtain solution B;

Heat solution A to 80°C and slowly drop solution B into solution A. After solution B is completely added, in order to avoid the hydrolysis reaction of tetrabutyl titanate, add an appropriate amount of 0.2M glacial acetic acid and stir for 3 hours. Then add formamide with a volume ratio of 0.5%, stir slowly at room temperature for 24h, and then let it stand for 72h. The reaction yields (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 ) TiO ₃ precursor solution;

2) Add 5 drops of (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 ) TiO ₃ precursor solution on the 1cm×1cm Pt(111)/Ti/SiO ₂ /Si(100) conductive substrate, and use a homogenizer First, spin coating at a rotation speed of 600r/min for 9 seconds, and then at a rotation speed of 3000r/min for 30 seconds to obtain a wet film;

3) Place the wet film on an electric heating plate, dry it at 200°C for 5 minutes, and then pyrolyze it at 400°C for 5 minutes to obtain an amorphous film;

4) Rapidly heat the amorphous film; the rapid heating treatment is: use a rapid annealing furnace to heat the amorphous film to 650°C at a heating rate of 80°C/s and keep it warm for 5 minutes;

5) Repeat steps 2), 3) and 4) three times, and then perform annealing treatment at 650°C for 15 minutes to obtain 4 layers of lead-free high-entropy ferroelectric films.

Product Characterization:

1. The lead-free high-entropy ferroelectric thin film obtained in Example 1 was subjected to X-ray diffraction, and its XRD pattern is shown in Figure 1. It can be seen from Figure 1 that the lead-free high-entropy ferroelectric film of the present invention exhibits a perovskite crystal structure without impurities and impurities.

2. Scan the cross section of the lead-free high-entropy ferroelectric thin film obtained in Example 1 with an SEM electron microscope. The SEM image is shown in Figure 2. From top to bottom in Figure 2, “1” represents the background of the SEM sample stage, “2” represents (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 )TiO ₃ , “3” represents the Pt/Ti electrode layer of the conductive base, "4" represents the SiO ₂ /Si layer of the conductive substrate. It can be seen from Figure 2 that the lead-free high-entropy ferroelectric film of the present invention has a higher crystallinity and a denser structure.

Product performance test:

The lead-free high-entropy ferroelectric film obtained in Example 1 was used as a dielectric material to assemble a dielectric energy storage device. Among them, the conductive substrate of the lead-free high-entropy ferroelectric film serves as one electrode of the dielectric energy storage device, and the other electrode of the dielectric energy storage device deposits gold on the other surface of the lead-free high-entropy ferroelectric film through magnetron sputtering. The diameter of the gold electrode is 0.4mm and the thickness is 0.25μm. Conduct relevant electrical performance tests on the assembled dielectric energy storage devices;

As shown in Figure 3, the test frequency range is 1-10 ⁵ kHz. At the test frequency of 10kHz, the dielectric constant of the dielectric energy storage device is higher than 100, while the dielectric loss is lower than 0.05.

As shown in Figure 4, the test voltage is 150V, the conductivity of the dielectric energy storage device at room temperature is 5.13×10 ^-4 S/m, and the leakage current is about 10 ^-7 A. At the same time, the conductivity can be stably maintained at 3.3×10 ^-3 S/m in the range of 60-140°C.

As shown in Figure 5, the breakdown electric field strength Eb of the dielectric energy storage device is measured according to the Weber distribution and is Eb=10.99MV/cm. Dielectric energy storage devices achieve high energy storage effects with ultra-high breakdown electric field strength.

As shown in Figure 6, under the conditions of a periodic triangular wave signal with a frequency of 1000Hz and a maximum voltage of 95V, the electrical hysteresis loop test of the dielectric energy storage device can obtain an energy storage density of 5.88J/ ^cm3 and an energy storage density of 93%. Excellent energy storage efficiency.

Comparative Example 1 (the difference from Example 1 is that the amorphous film adopts conventional heat treatment)

A method for preparing a lead-free high-entropy ferroelectric film, including the following steps:

1) Prepare (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 )TiO ₃ precursor solution:

Weigh bismuth acetate, sodium acetate trihydrate, potassium acetate, strontium acetate, lanthanum nitrate hexahydrate and tetrabutyl titanate as raw materials according to the stoichiometric ratio of (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 ) TiO ₃ , and add acetic acid to Add bismuth to an appropriate amount of glacial acetic acid, heat and stir for 30 minutes at 70°C, then add a small amount of deionized water and stir for 30 minutes, then add sodium acetate trihydrate, potassium acetate, strontium acetate and lanthanum nitrate hexahydrate in sequence, and stir for 2.5 hours. Dissolve to obtain solution A;

Mix the three solutions of tetrabutyl titanate, ethylene glycol methyl ether, and acetylacetone at room temperature according to a volume ratio of 1:3:2, and stir for 1 hour to obtain solution B;

Heat solution A to 80°C and slowly drop solution B into solution A. After solution B is completely added, in order to avoid the hydrolysis reaction of tetrabutyl titanate, add an appropriate amount of 0.2M glacial acetic acid and stir for 3 hours. Then add formamide with a volume ratio of 0.5%, stir slowly at room temperature for 24h, and then let it stand for 72h. The reaction yields (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 ) TiO ₃ precursor solution;

2) Add 5 drops of (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 ) TiO ₃ precursor solution on the 1cm×1cm Pt(111)/Ti/SiO ₂ /Si(100) conductive substrate, and use a homogenizer First, spin coating at a rotation speed of 600r/min for 9 seconds, and then at a rotation speed of 3000r/min for 30 seconds to obtain a wet film;

3) Place the wet film on an electric heating plate, dry it at 200°C for 5 minutes, and then pyrolyze it at 400°C for 5 minutes to obtain an amorphous film;

4) The amorphous film is subjected to conventional heat treatment; the conventional heat treatment is: use a muffle furnace to heat the amorphous film to 650°C at a heating rate of 30°C/min, and keep it warm for 5 minutes;

5) Repeat steps 2), 3) and 4) three times, and then perform annealing treatment at 650°C for 15 minutes to obtain 4 layers of lead-free high-entropy ferroelectric films.

The cross-section of the lead-free high-entropy ferroelectric film obtained in Example 1 was scanned by an electron microscope, and the SEM image is shown in Figure 7. From top to bottom in Figure 7, “1” represents the background of the SEM sample stage, “2” represents (Bi _0.2 Na _0.2 K _0.2 La _0.2 Sr _0.2 )TiO ₃ , “3” represents the Pt/Ti electrode layer of the conductive base, "4" represents the SiO ₂ /Si layer of the conductive substrate. It can be seen from Figure 7 that the lead-free high-entropy ferroelectric film of Comparative Example 1 has poor crystallinity and a loose structure.

The lead-free high-entropy ferroelectric film obtained in Example 1 was used as a dielectric material to assemble a dielectric energy storage device. Among them, the conductive substrate of the lead-free high-entropy ferroelectric film serves as one electrode of the dielectric energy storage device, and the other electrode of the dielectric energy storage device deposits gold on the other surface of the lead-free high-entropy ferroelectric film through magnetron sputtering. The diameter of the gold electrode is 0.4mm and the thickness is 0.25μm. The assembled dielectric energy storage device is subjected to relevant electrical performance tests (the test conditions are the same as those in Example 1). As shown in Figure 8, under the same test conditions, the highest energy storage density of the dielectric energy storage device was measured to be 0.61J/cm ³ , which was significantly lower than the energy storage density of the dielectric energy storage device assembled in Example 1. .

Example 2

A method for preparing a lead-free high-entropy ferroelectric film, including the following steps:

1) Prepare (Bi _0.26 Na _0.26 K _0.16 La _0.16 Sr _0.16 ) TiO ₃ precursor solution:

Weigh bismuth acetate, sodium acetate trihydrate, potassium acetate, strontium acetate, lanthanum nitrate hexahydrate and tetrabutyl titanate as raw materials according to the stoichiometric ratio of (Bi _0.26 Na _0.26 K _0.16 La _0.16 Sr _0.16 ) TiO ₃ , and add acetic acid Add bismuth to an appropriate amount of glacial acetic acid, heat and stir at 70°C for 30 minutes, then add a small amount of deionized water and stir for 30 minutes, then add sodium acetate trihydrate, potassium acetate, strontium acetate and lanthanum nitrate hexahydrate in sequence, stir for 3 hours, and dissolve Obtain solution A;

Mix the three solutions of tetrabutyl titanate, ethylene glycol methyl ether, and acetylacetone at room temperature according to a volume ratio of 1:3:2, and stir for 1 hour to obtain solution B;

Heat solution A to 80°C and slowly drop solution B into solution A. After solution B is completely added, in order to avoid the hydrolysis reaction of tetrabutyl titanate, add an appropriate amount of 0.2M glacial acetic acid and stir for 3 hours. Then add formamide with a volume ratio of 0.5%, stir slowly at room temperature for 24h, and then let it stand for 72h. The reaction yields (Bi _0.26 Na _0.26 K _0.16 La _0.16 Sr _0.16 ) TiO ₃ precursor solution;

2) Add 5 drops of (Bi _0.26 Na _0.26 K _0.16 La _0.16 Sr _0.16 ) TiO ₃ precursor solution on the 1cm×1cm Pt(111)/Ti/SiO ₂ /Si(100) conductive substrate, and use a glue homogenizer First, spin coating at a rotation speed of 600r/min for 9 seconds, and then at a rotation speed of 3000r/min for 30 seconds to obtain a wet film;

3) Place the wet film on an electric heating plate, dry it at 200°C for 5 minutes, and then pyrolyze it at 400°C for 5 minutes to obtain an amorphous film;

4) Rapidly heat the amorphous film; the rapid heating treatment is: use a rapid annealing furnace to heat the amorphous film to 650°C at a heating rate of 80°C/s and keep it warm for 5 minutes;

5) Repeat steps 2), 3) and 4) three times, and then perform annealing treatment at 650°C for 15 minutes to obtain 4 layers of lead-free high-entropy ferroelectric films.

The lead-free high-entropy ferroelectric thin film obtained in Example 2 was used as a dielectric material to assemble a dielectric energy storage device. Among them, the conductive substrate of the lead-free high-entropy ferroelectric film serves as one electrode of the dielectric energy storage device, and the other electrode of the dielectric energy storage device deposits gold on the other surface of the lead-free high-entropy ferroelectric film through magnetron sputtering. The diameter of the gold electrode is 0.4mm and the thickness is 0.25μm. The assembled dielectric energy storage device was subjected to a dielectric energy storage performance test (the test conditions were the same as those in Example 1), and the energy storage density and energy storage efficiency of the dielectric energy storage device were measured to be 5.6 J/cm ³ 90%.

Example 3

A method for preparing a lead-free high-entropy ferroelectric film, including the following steps:

1) Prepare (Bi _1/4 Na _1/4 K _1/6 La _1/6 Sr _1/6 )TiO ₃ precursor solution:

Weigh bismuth nitrate, sodium nitrate, potassium nitrate, strontium nitrate, lanthanum nitrate and tetrabutyl titanate according to the stoichiometric ratio of (Bi _1/4 Na _1/4 K _1/6 La _1/6 Sr _1/6 ) TiO ₃ Using ester as raw material, add bismuth nitrate to an appropriate amount of glacial acetic acid, heat and stir at 60°C for 30 minutes, then add a small amount of deionized water and stir for 30 minutes, then add sodium nitrate, potassium nitrate, strontium nitrate and lanthanum nitrate in sequence, and stir for 2 hours , dissolve to obtain solution A;

Mix the three solutions of tetrabutyl titanate, ethylene glycol methyl ether, and acetylacetone at room temperature according to a volume ratio of 1:3:2, and stir for 1 hour to obtain solution B;

Heat solution A to 80°C and slowly drop solution B into solution A. After solution B is completely added, in order to avoid the hydrolysis reaction of tetrabutyl titanate, add an appropriate amount of 0.2M glacial acetic acid and stir for 3 hours. Then add formamide with a volume ratio of 0.5%, stir slowly at room temperature for 24h, and then let it stand for 72h. The reaction yields (Bi _1/4 Na _1/4 K _1/6 La _1/6 Sr _1/6 ) TiO ₃ precursor body solution;

2) Add 5 drops (Bi _1/4 Na _1/4 K _{1/ 6} La _1/6 Sr _1/6 ) on the 1cm×1cm Pt(111)/Ti/SiO ₂ /Si(100) conductive substrate. For the TiO ₃ precursor solution, use a glue leveler to spin-coat at a speed of 600r/min for 9s, and then spin-coat at a speed of 3000r/min for 30s to obtain a wet film;

3) Place the wet film on an electric heating plate, dry it at 200°C for 5 minutes, and then pyrolyze it at 400°C for 5 minutes to obtain an amorphous film;

4) Perform rapid heating treatment on the amorphous film; the rapid heating treatment is: use a rapid annealing furnace to heat the amorphous film to 650°C at a heating rate of 50°C/s and keep it warm for 3 minutes;

5) Repeat steps 2), 3) and 4) 5 times, and then perform annealing treatment at 650°C for 15 minutes to obtain 6 layers of lead-free high-entropy ferroelectric films.

The lead-free high-entropy ferroelectric thin film obtained in Example 3 was used as a dielectric material to assemble a dielectric energy storage device. Among them, the conductive substrate of the lead-free high-entropy ferroelectric film serves as one electrode of the dielectric energy storage device, and the other electrode of the dielectric energy storage device deposits gold on the other surface of the lead-free high-entropy ferroelectric film through magnetron sputtering. The diameter of the gold electrode is 0.4mm and the thickness is 0.25μm. The assembled dielectric energy storage device was subjected to a dielectric energy storage performance test (the test conditions were the same as those in Example 1), and the energy storage density and energy storage efficiency of the dielectric energy storage device were measured to be 5.63 J/cm ³ 91%.

Example 4

A method for preparing a lead-free high-entropy ferroelectric film, including the following steps:

1) Prepare (Bi _2/7 Na _2/7 K _1/7 La _1/7 Sr _1/7 )TiO ₃ precursor solution:

Weigh bismuth sulfate, sodium sulfate, potassium sulfate, strontium sulfate, lanthanum sulfate and tetrabutyl titanate according to the stoichiometric ratio of (Bi _2/7 Na _2/7 K _1/7 La _1/7 Sr _1/7 ) TiO ₃ Using ester as raw material, add bismuth sulfate to an appropriate amount of glacial acetic acid, heat and stir at 80°C for 30 minutes, then add a small amount of deionized water and stir for 30 minutes, then add sodium sulfate, potassium sulfate, strontium sulfate and lanthanum sulfate in sequence, and stir for 3 hours , dissolve to obtain solution A;

Mix the three solutions of tetrabutyl titanate, ethylene glycol methyl ether, and acetylacetone at room temperature according to a volume ratio of 1:3:2, and stir for 1 hour to obtain solution B;

Heat solution A to 80°C and slowly drop solution B into solution A. After solution B is completely added, in order to avoid the hydrolysis reaction of tetrabutyl titanate, add an appropriate amount of 0.2M glacial acetic acid and stir for 3 hours. Then add formamide with a volume ratio of 1%, stir slowly at room temperature for 24h, and then let it stand for 72h. The reaction yields (Bi _2/7 Na _2/7 K _1/7 La _1/7 Sr _1/7 ) TiO ₃ precursor body solution;

2) Add 4 drops (Bi _2/7 Na _2/7 K _{1/ 7} La _1/7 Sr _1/7 ) on the 1cm×1cm Pt(111)/Ti/SiO ₂ /Si(100) conductive substrate. For the TiO ₃ precursor solution, use a glue leveler to spin-coat at a speed of 600r/min for 9s, and then spin-coat at a speed of 3000r/min for 30s to obtain a wet film;

3) Place the wet film on an electric heating plate, dry it at 250°C for 3 minutes, and then pyrolyze it at 450°C for 3 minutes to obtain an amorphous film;

4) Rapidly heat the amorphous film; the rapid heating treatment is: use a rapid annealing furnace to heat the amorphous film to 700°C at a heating rate of 100°C/s, and keep it warm for 4 minutes;

5) Repeat step 2), step 3) and step 4) 9 times, and then perform annealing treatment at 700°C for 10 minutes to obtain 10 layers of lead-free high-entropy ferroelectric films.

The lead-free high-entropy ferroelectric thin film obtained in Example 4 was used as a dielectric material to assemble a dielectric energy storage device. Among them, the conductive substrate of the lead-free high-entropy ferroelectric film serves as one electrode of the dielectric energy storage device, and the other electrode of the dielectric energy storage device deposits gold on the other surface of the lead-free high-entropy ferroelectric film through magnetron sputtering. The diameter of the gold electrode is 0.4mm and the thickness is 0.25μm. The assembled dielectric energy storage device was subjected to a dielectric energy storage performance test (the test conditions were the same as those in Example 1), and the energy storage density and energy storage efficiency of the dielectric energy storage device were measured to be 5.87J/ ^cm3 . 90%.

The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the embodiments. Those skilled in the art can also make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims (7)

1. A method for preparing a lead-free high-entropy ferroelectric film, which is characterized by comprising the following steps: 1) Prepare a BNKLST precursor solution. The general chemical formula of BNKLST is ( _Bix Na _x K _{y Lay} Sr _y )TiO ₃ , where x>0, y>0, 2x+3y=1; 2) Spin-coat the BNKLST precursor solution obtained in step 1) on the conductive substrate to obtain a wet film; 3) Dry the wet film obtained in step 2) at 200-250°C for 3-5 minutes, and then pyrolyze it at 400-450°C for 3-5 minutes to obtain an amorphous film; 4) The amorphous film obtained in step 3) is subjected to rapid heating treatment; the rapid heating treatment is: heating to 650-700°C at a heating rate of 50-100°C/s, and keeping the temperature for 3-5 minutes; 5) annealing the amorphous film after rapid heating treatment in step 4) to obtain the lead-free high-entropy ferroelectric film; Prepare the BNKLST precursor solution as described in step 1), specifically according to the following steps: According to the stoichiometric ratio of the general chemical formula, weigh bismuth salt, sodium salt, potassium salt, strontium salt, lanthanum salt and titanium salt; Dissolve the bismuth salt in a solvent, then add the sodium salt, the potassium salt, the strontium salt and the lanthanum salt, and dissolve to obtain solution A; Mix the titanium salt with a solvent and a chelating agent to obtain solution B; Add the B solution to the A solution, then add formamide with a volume ratio of 0.5-1%, stir for 24-36h, and then let it stand for 72-84h, and react to obtain the BNKLST precursor solution; The bismuth salt includes at least one of bismuth acetate, bismuth nitrate and bismuth sulfate; the sodium salt includes at least one of sodium acetate trihydrate, sodium nitrate and sodium sulfate; the potassium salt includes potassium acetate, potassium nitrate and at least one of potassium sulfate; the strontium salt includes at least one of strontium acetate, strontium nitrate and strontium sulfate; the lanthanum salt includes at least one of lanthanum nitrate hexahydrate, lanthanum nitrate and lanthanum sulfate; The titanium salt is tetrabutyl titanate; The solvent includes at least one of glacial acetic acid, ethylene glycol methyl ether, ethanol, and isopropyl alcohol; the chelating agent includes at least one of acetylacetone, EDTA, potassium sodium tartrate, and ammonium citrate. 2. The preparation method according to claim 1, characterized in that the ratio of x and y is 0.5-2:1. 3. The preparation method according to claim 1, characterized in that the conditions of the annealing treatment include: the annealing temperature is 650-700°C, and the annealing time is 10-15 minutes. 4. The preparation method according to claim 1, characterized in that, before performing step 5), repeat steps 2), step 3) and step 4) multiple times to obtain a multi-layer amorphous film. 5. The preparation method according to claim 4, characterized in that the number of layers of the lead-free high-entropy ferroelectric film is 4-10 layers, and the thickness of each layer of the lead-free high-entropy ferroelectric film is 40-10 layers. 50nm. 6. A lead-free high-entropy ferroelectric film, characterized in that it is prepared by the preparation method described in any one of claims 1-5, and the breakdown electric field strength of the lead-free high-entropy ferroelectric film is greater than 8MV/ cm. 7. A dielectric energy storage device, characterized by comprising the lead-free high-entropy ferroelectric film according to claim 6.