High-entropy ferroelectric film material with high energy storage density as well as preparation method and application of high-entropy ferroelectric film material

Abstract

The invention discloses a high-entropy ferroelectric film material with high energy storage density and a preparation method and application thereof, the chemical formula of the high-entropy ferroelectric film material is (1-x) (0.96 Bi < 0.5 > Na < 0.5 > TiO < 3-0.04 > BaTiO < 3 >)-x (Bi < 0.2 > Na < 0.2 > K < 0.2 > La < 0.2 > Sr < 0.2 >) TiO < 3 >, the high-entropy ferroelectric film material is simple in preparation process, low in cost and adjustable in material component, when x is equal to 0.5, the recoverable energy storage density reaches up to 16.92 J / cm < 3 >, and the high-entropy ferroelectric film material can be applied to integrated and miniaturized film dielectric capacitors.

Description

Technical Field

[0001] The present invention relates to the technical field of functional thin film materials, and particularly relates to a high-entropy ferroelectric thin film material with a high energy storage density, a preparation method thereof, and an application thereof. Background Art

[0002] Renewable clean energy sources such as solar energy, tidal energy, and wind energy have been vigorously developed globally to reduce carbon emissions brought by traditional energy sources. However, current electronic devices can no longer meet the storage and conversion requirements of these renewable energy sources. Dielectric capacitors are ubiquitous electronic components. Due to their ultra-high power density and fast charge and discharge capabilities, they can be applied to fields such as medical devices, laser weapons, and hybrid electric vehicles. With the continuous development of miniaturization and integration technologies, thin film capacitors have gradually attracted attention in energy storage and conversion. However, currently commercially available thin film capacitor materials are mainly polymers with low dielectric constants (such as polypropylene). Although polymer thin films exhibit a high breakdown electric field, the obtained energy storage density is only 2 J / cm 3 , so it is necessary to develop new dielectric thin film materials with high energy storage performance to meet the high demand for energy storage in the future market.

[0003] Sodium bismuth titanate Bi 0.5 Na 0.5 TiO3 (BNT) has strong ferroelectricity and a large saturation polarization intensity. However, at the same time, it has a large remanent polarization intensity and a low breakdown electric field strength, resulting in a low energy storage density. To improve the energy storage performance of BNT, a large number of studies on BNT-based thin films have been carried out by scientific researchers. For example, introducing SrTiO3 into Bi 0.5 Na 0.5 TiO3-BaTiO3 was found to improve both the polarization intensity and dielectric constant of the thin film, and the maximum recoverable energy storage density can reach 22.5 J / cm 3 . At the same time, it exhibits excellent dielectric temperature stability in the temperature range of 25 - 200 °C.

[0004] The concept of high-entropy ceramics was proposed by Professor Rost in 2015. Due to more than five elements occupying the same crystal lattice in an equimolar ratio or approximately equimolar ratio, a high degree of chemical disorder and severe lattice distortion will be formed inside the high-entropy ceramic material. At the same time, the large configurational entropy will make it have single-phase thermal stability and slow kinetic diffusion. These characteristics indicate that high-entropy ceramics have great application potential in energy storage. However, currently, the high-entropy concept is rarely used in BNT-based ferroelectric thin film materials. Therefore, developing new high-entropy ferroelectric thin film materials is of great significance and value for the design of dielectric energy storage materials and the miniaturization and integration applications of energy storage devices. Summary of the Invention

[0005] The object of the present invention is to provide a high-entropy ferroelectric thin film material with high energy storage density, and its preparation method and application. By introducing high-entropy components (Bi 0.5 Na 0.5 TiO3-0.04BaTiO3) into the ferroelectric 0.96Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3, it is found that the grains of the thin film material become finer, the surface becomes smoother, the dielectric loss is reduced, and the maximum recoverable energy storage density can reach 16.92 J / cm 3 under an electric field of 1500 kV / cm.

[0006] The present invention solves the problems of poor densification, large dielectric loss and low energy storage density of ferroelectric thin film materials.

[0007] The technical solution of the present invention is as follows:

[0008] A high-entropy ferroelectric thin film material, the chemical formula of which is:

[0009] (1-x)(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3

[0010] wherein, x represents the molar fraction, 0 < x < 1; preferably x = 0.3 or 0.5.

[0011] The preparation method of the high-entropy ferroelectric thin film material of the present invention includes the following steps:

[0012] (a) At room temperature, tetrabutyl titanate, ethylene glycol methyl ether and acetylacetone are mixed to form solution A;

[0013] Preferably, the volume ratio of tetrabutyl titanate, ethylene glycol methyl ether and acetylacetone is 1:3:2;

[0014] (b) NaCH3COO·3H2O, KNO3, Sr(CH3COO)2, La(NO3)3·6H2O, Bi(NO3)3·5H2O, Ba(CH3COO)2 are added to a mixed solution of glacial acetic acid and deionized water, and dissolved thoroughly at 60-80 °C to obtain solution B;

[0015] Weigh NaCH3COO·3H2O, KNO3, Sr(CH3COO)2, La(NO3)3·6H2O, Bi(NO3)3·5H2O, and Ba(CH3COO)2 according to the corresponding stoichiometric ratios in the target chemical formula;

[0016] (c) At 60 °C, while stirring, slowly add solution B dropwise to solution A. After mixing evenly, add formamide and stir at room temperature for 24 h. Then let it stand for 24 - 48 h to obtain a transparent precursor solution;

[0017] It should be noted that solution B should be slowly added dropwise to solution A to prevent the formation of white precipitates;

[0018] The volume of formamide used accounts for 0.5 - 1% of the total volume of the precursor solution. The purpose of adding formamide is to prevent the subsequent wet film from cracking during the heat treatment process;

[0019] (d) Spin - coat the precursor solution onto a conductive substrate to obtain a wet film;

[0020] The specific operation is as follows: Load the precursor solution into a syringe with a filter, drop the precursor solution onto a clean 1 cm × 1 cm conductive substrate, and then prepare the wet film under the set spin - coating parameters;

[0021] The specification of the filter: 0.22 μm;

[0022] The material of the conductive substrate: Pt(111) / Ti / SiO2 / Si(100);

[0023] The spin - coating parameter settings: First, maintain at a rotation speed of 600 r / min for 9 s, and then maintain at a rotation speed of 3000 r / min for 30 s;

[0024] (e) Heat - treat the obtained wet film. First, keep it at 200 °C and 450 °C for 5 min in sequence (decompose the organic matter in the precursor to form an amorphous film), and then anneal it at 650 - 700 °C for 5 min in an oxygen atmosphere to form a single - layer high - entropy ferroelectric thin - film material (with a certain crystal structure);

[0025] (f) Repeat steps (d) and (e) for the lamination process, and finally sinter it at 650 - 700 °C for 15 min to obtain the high - entropy ferroelectric thin - film material;

[0026] Preferably, after the lamination process, there are a total of 8 layers.

[0027] In the above - mentioned preparation method, "solution A" and "solution B" have no special meaning. Marking them as "A" and "B" is only used to distinguish different solution systems.

[0028] Cover the obtained high-entropy ferroelectric thin film material with a mask plate having an electrode array structure, and place it in an ion sputtering device for electrode sputtering, which can be used for subsequent electrical performance testing;

[0029] Mask plate specifications: 2 cm × 2 cm;

[0030] Electrode array: 8×8 and the hole diameter is 200 μm;

[0031] The sputtering target used is Au.

[0032] The high-entropy ferroelectric thin film material described in the present invention can be used to prepare miniaturized and integrated thin film dielectric capacitors.

[0033] The technical principle of the present invention includes:

[0034] The present invention provides a nano-thin film material containing high-entropy ceramics:

[0035] (1-x)(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3

[0036] Among them, 0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3 crystal structure is a simple R3c trigonal phase and is not at the morphotropic phase boundary in the BNT-BT system. Therefore, this material has a large saturation polarization intensity and remanent polarization intensity. This is because for the trigonal phase, it shows a - a - a - anti-phase oxygen octahedron tilt and polarization along the

[111] direction. This structural distortion is beneficial to obtaining a higher polarization intensity and a larger dielectric constant. By adding a high-entropy ceramic component (Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3 with a pseudo-cubic phase Pm-3m, the overall structure changes from a trigonal phase to a coexistence of a trigonal phase and a pseudo-cubic phase. Since the oxygen octahedron tilt of the pseudo-cubic phase is not obvious, although it causes the polarization intensity of the material to slightly decrease, the energy storage density of the overall material increases and the piezoelectric performance is enhanced. The specific reasons are as follows:

[0037] Explanation of the principle of the increase in energy storage density: On the one hand, due to the chemical disorder of the high-entropy ceramic component, it disrupts the original 0.96Bi 0.5Na 0.5 The ferroelectricity with long-chain order in NaTiO3-0.04BaTiO3 generates more nano-polarization regions. These nano-polarization regions can respond quickly to the change of the applied electric field, resulting in a decrease in the remanent polarization intensity and a reduction in the dielectric loss of the material. On the other hand, the slow dynamic diffusion effect at the grain boundaries brought about by the high-entropy ceramic components makes the grains refined, the obtained material structure denser, and the film surface smoother, reducing the leakage current density of the material while increasing the electric field breakdown strength. Therefore, the energy storage density of the material is increased.

[0038] Explanation of the principle for enhanced piezoelectric performance: Due to the addition of (Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3, the overall structure becomes a coexistence of rhombohedral phase and pseudo-cubic phase. Under the action of an electric field or external force, domain wall motion is likely to occur. At the same time, the high-entropy ceramic components generate more short-range disordered nano-domains with lower energy barriers, reducing the average energy barrier of the polar domains, which is beneficial to the occurrence of spontaneous polarization, thus improving the piezoelectric performance of the thin film. (Piezoelectric coefficient increase: 34 pm / V (x = 0), 40.5 pm / V (x = 0.3), 46.9 pm / V (x = 0.5), 78 pm / V (x = 1))

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) Compared with thin film growth technologies such as magnetron sputtering and epitaxial growth, the present invention uses the sol-gel method to prepare high-entropy ferroelectric thin film materials, which has the advantages of a wide selection range of raw material components, controllable preparation conditions, simple process flow, and low cost, and can realize the simultaneous preparation and sintering of multiple samples.

[0041] (2) The high-entropy ferroelectric thin film materials prepared by the present invention have the advantages of uniform chemical composition, small grains, and smooth film surface. Due to the addition of high-entropy components, the component diffusion effect of the material is slow, which hinders the growth of the second phase, makes it difficult for the grains to coarsen, and forms a relatively dense ferroelectric thin film structure.

[0042] (3) The high-entropy ferroelectric thin film materials prepared by the present invention have good piezoelectric and ferroelectric properties. When x = 0.5, the maximum piezoelectric coefficient is 46.9 pm / V, the dielectric loss is only 0.01827 at 100 MHz, and the saturation polarization intensity can reach 39.38 μC / cm 2 , and the maximum recoverable energy storage density can reach 16.92 J / cm under an electric field of 1500 kV / cm 3 . Description of the Drawings

[0043] Figure 1 : XRD patterns of the high-entropy ferroelectric thin film materials (1-x)(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3 (x = 0, 0.3, 0.5, 1) prepared by the present invention.

[0044] Figure 2 : SEM micrographs of the microstructure and thickness profile of the cross-section of the high-entropy ferroelectric thin film material 0.5(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-0.5(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3 prepared by the present invention.

[0045] Figure 3 : Surface roughness of the high-entropy ferroelectric thin film materials (1-x)(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3; where (a) x = 0, (b) x = 0.3, (c) x = 0.5, (d) x = 1.

[0046] Figure 4 : PFM images of the high-entropy ferroelectric thin film material 0.5(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-0.5(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3, including height, amplitude, and phase (a); PFM images of the high-entropy ferroelectric thin film material 0.5(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-0.5(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2)Piezoelectric response of TiO3 at 20 V voltage, including amplitude butterfly curve and phase lag loop (b).

[0047] Figure 5 : The dielectric and energy storage properties of the 0.5(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-0.5(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3 high-entropy ferroelectric thin film material; (a): Dielectric spectrum at 40 - 100 MHz and static dielectric constant fitting for x = 0.5; (b): Polarization-electric field hysteresis curve measured at different electric fields at room temperature for x = 0.5. Detailed implementation manners

[0048] The present invention will be further described below with reference to the accompanying drawings through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0049] Embodiment 1

[0050] The chemical formula of the thin film material in this embodiment is (1 - x)(0.96(Bi 0.5 Na 0.5 )TiO3 - 0.04BaTiO3)-x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3, where x = 0.5.

[0051] The preparation method of this thin film material includes the following steps:

[0052] a. Chelate 2.55 mL of tetrabutyl titanate, 7.65 mL of ethylene glycol methyl ether and 5.1 mL of acetylacetone at room temperature to form a transparent yellow solution A;

[0053] b. Add NaCH3COO·3(H2O) (0.3470 g, 2.55 mmol), KNO3 (0.0758 g, 0.75 mmol), Sr(CH3COO)2 (0.1610 g, 0.75 mmol), La(NO3)3·6H2O (0.3248 g, 0.75 mmol), Bi(NO3)3·5H2O (1.2369 g, 2.55 mmol), Ba(CH3COO)2 (0.0383 g, 0.15 mmol) into a mixed solution of 10 mL of glacial acetic acid and 5 mL of deionized water in sequence for dissolution. After fully mixing at 80 °C, solution B is obtained;

[0054] c. While stirring at 60 °C, slowly add solution B to solution A dropwise with a dropper to allow it to slowly absorb moisture and prevent the formation of white precipitates. After mixing evenly, add formamide (final volume concentration 0.5%) to prevent the film from cracking. Stir for 24 hours, and then let it stand for 24 hours to obtain a transparent precursor solution;

[0055] d. Clean the 1 cm × 1 cm conductive substrate Pt(111) / Ti / SiO2 / Si(100) successively with acetone and ethanol and then dry it for standby. After the precursor solution is filtered through a 0.22 μm filter, 4 - 5 drops are dropped on the conductive substrate for spin coating; the spin coating parameters are set as follows: maintain at a rotation speed of 600 r / min for 9 s, and then maintain at a rotation speed of 3000 r / min for 30 s to prepare a wet film;

[0056] e. Heat - treat the prepared wet film. First, heat it on a heating plate at 200 °C and 450 °C successively for 5 minutes to decompose the organic matter in the precursor and form an amorphous film. Then, anneal it in a rapid annealing furnace in an oxygen atmosphere at 700 °C for 5 minutes to sinter and form a single - layer high - entropy ferroelectric thin - film material with a certain crystal structure;

[0057] f. Repeat steps (d) and (e) a total of 8 times for lamination treatment. Finally, sinter it fully at 700 °C for 15 minutes in a rapid annealing furnace to obtain a high - entropy ferroelectric thin - film material with a thickness of ∼200 nm;

[0058] g. Cover the high - entropy ferroelectric thin - film material with a mask template of an array structure with an electrode diameter of 200 μm, and then put it into an ion sputtering device to sputter the electrode at a current of 10 mA for 45 s to obtain an Au electrode for convenient subsequent electrical property testing.

[0059] Characterize the structure and properties of the thin - film material prepared in this example:

[0060] Figure 1 In which x = 0.5 is the XRD pattern of the high - entropy ferroelectric thin - film material prepared in Example 1. As can be seen from the figure, after sintering at 700 °C, the thin - film material as a whole presents a perovskite structure, but there is a second phase. After refinement, it is confirmed to be the pyrochlore phase Bi2Ti2O7. This is because the sample was prepared under annealing conditions at a relatively low temperature (below 800 °C), so the excess Bi element could not be completely pyrolyzed.

[0061] Figure 2 This is the microscopic SEM characterization of the high - entropy ferroelectric thin - film material prepared in Example 1. As can be seen from the figure, the surface of the high - entropy ferroelectric thin - film material prepared in Example 1 is dense and the grains are relatively fine. At the same time, the thickness of the thin film can be estimated by measuring the height of the film cross - section, which is about 200 nm.

[0062] Figure 3 The surface roughness of the high-entropy ferroelectric thin film material (1-x)(0.96Bi 0.5 Na 0.5 TiO3-0.04BaTiO3)-x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3 (x = 0, 0.3, 0.5, 1) prepared according to the present invention. As can be seen from the figure, with the increase of the high-entropy component, the film surface becomes smoother, and the surface roughness decreases, changing from ±20 nm at x = 0 to ±5 nm at x = 1.

[0063] Figure 4 Among them, (a) is the PFM diagram of the high-entropy ferroelectric thin film material prepared in Example 1. It can be seen that the addition of the high-entropy component makes the material grains smaller, the piezoelectric amplitude larger, and the phase shows an obvious chromaticity contrast. This is because the original long-range ferroelectric order in 0.96(Bi 0.5 Na 0.5 )TiO3-0.04BaTiO3 is destroyed by the chemical disorder of Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 , thus generating nano-domains with different polarization fluctuations. At the same time, it is found that for the film with x = 0.5, coexisting domain structures are found in its phase signal, including long-range ordered domains and short-range disordered nano-domains. (b) is the piezoelectric response diagram of the high-entropy ferroelectric thin film material prepared in Example 1, where the amplitude butterfly curve shows an asymmetric phenomenon, which is caused by the lattice distortion brought by the high-entropy component. The maximum piezoelectric coefficient measured from it is 46.9 pm / V, and the coercive electric field is 2.76 V. At the same time, it is observed that the phase hysteresis loop is related to the 180-degree domain change, indicating that the film has ferroelectric properties.

[0064] Figure 5 Among them, (a) is the dielectric spectrum diagram of the high-entropy ferroelectric thin film material prepared in Example 1. It can be seen that the dielectric constant decreases as the frequency increases from 40 Hz to 100 MHz. According to the fitting, the static dielectric constant of this material is 144.6, and the dielectric loss at 100 MHz is only 0.01827. Figure 5 Among them, (b) is the polarization-electric field hysteresis curve of the high-entropy ferroelectric thin film material prepared in Example 1 measured at room temperature under different electric fields. It can be seen that the polarization intensity of the thin film material in Example 1 increases with the increase of the electric field, and its maximum saturation polarization intensity can reach 39.38 μC / cm 2 , and the maximum recoverable energy storage density can reach 16.92 J / cm 3, the energy storage efficiency is 59.4%. Compared with the currently commercial thin-film dielectric material, biaxially oriented polypropylene (BOPP) (energy storage density is ~2 J / cm 3 ), the energy storage density is increased by about 8 times.

Claims

1. A high-entropy ferroelectric thin film material with the chemical formula: (1 - x)(0.96Bi 0.5 Na 0.5 TiO3 - 0.04BaTiO3) - x(Bi 0.2 Na 0.2 K 0.2 La 0.2 Sr 0.2 )TiO3 Among them, x represents the molar fraction, where 0 < x < 1.

2. The high-entropy ferroelectric thin film material according to claim 1, wherein x = 0.3 or 0.

5.

3. The preparation method of the high-entropy ferroelectric thin film material according to claim 1, characterized in that, It includes the following steps: (a) At room temperature, mix tetrabutyl titanate, ethylene glycol monomethyl ether, and acetylacetone to form solution A; (b) Add NaCH3COO·3H2O, KNO3, Sr(CH3COO)2, La(NO3)3·6H2O, Bi(NO3)3·5H2O, and Ba(CH3COO)2 into a mixed solution of glacial acetic acid and deionized water, and fully dissolve it at 60 - 80 °C to obtain solution B; (c) At 60 °C, while stirring, add solution B dropwise to solution A. After mixing evenly, add formamide, stir at room temperature for 24 h, and then let it stand for 24 - 48 h to obtain a transparent precursor solution; (d) Spin-coat the precursor solution onto a conductive substrate to obtain a wet film; (e) Heat-treat the obtained wet film. First, keep it at 200 °C and 450 °C for 5 min in sequence, and then anneal it at 650 - 700 °C for 5 min in an oxygen atmosphere to form a single-layer high-entropy ferroelectric thin film material; (f) Repeat steps (d) and (e) for lamination treatment, and finally sinter it at 650 - 700 °C for 15 min to obtain the high-entropy ferroelectric thin film material.

4. The preparation method according to claim 3, characterized in that, In step (a), the volume ratio of tetrabutyl titanate, ethylene glycol monomethyl ether, and acetylacetone is 1:3:2; in step (b), NaCH3COO·3H2O, KNO3, Sr(CH3COO)2, La(NO3)3·6H2O, Bi(NO3)3·5H2O, and Ba(CH3COO)2 are weighed according to the corresponding stoichiometric ratios in the target chemical formula.

5. The preparation method according to claim 3, characterized in that, In step (c), the volume dosage of formamide accounts for 0.5 - 1% of the total volume of the precursor solution.

6. The preparation method according to claim 3, characterized in that, The operation of step (d) is as follows: Load the precursor solution into a syringe with a filter, drop the precursor solution onto a clean 1 cm × 1 cm conductive substrate, and then prepare a wet film under the set spin-coating parameters; the specification of the filter: 0.22 μm; the material of the conductive substrate: Pt(111) / Ti / SiO2 / Si(100); the spin-coating parameter settings: first maintain at a rotation speed of 600 r / min for 9 s, and then maintain at a rotation speed of 3000 r / min for 30 s.

7. The preparation method according to claim 3, characterized in that, After the lamination treatment in step (f), there are a total of 8 layers.

8. The application of the high-entropy ferroelectric thin film material according to claim 1 in the preparation of miniaturized and integrated thin film dielectric capacitors.

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