High-entropy relaxor ferroelectric ceramic material and preparation method thereof

Abstract

The invention belongs to the technical field of ceramic materials, and particularly relates to a high-entropy relaxor ferroelectric ceramic material and a preparation method thereof.The chemical general formula of the high-entropy relaxor ferroelectric ceramic material is (1-x) (Pb0. 25Ba0. 25Sr0. 25Ca0. 25) TiO3-xNaNbO3, x is the mole fraction, x is larger than or equal to 0.1 and smaller than or equal to 0.3, and x is larger than or equal to 0.1 and smaller than or equal to 0.3. The high-entropy relaxor ferroelectric ceramic material disclosed by the invention has relatively high energy storage density, energy storage efficiency, breakdown field energy and stability at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic materials, and in particular relates to a high-entropy relaxor ferroelectric ceramic material and a preparation method thereof. Background Art

[0002] Ferroelectric ceramic materials have excellent dielectric properties such as low dielectric loss and high dielectric constant. They are one of the ideal materials for realizing high energy storage density ceramic capacitors. They have good application prospects in the fields of pulse power equipment and energy storage equipment. Compared with ordinary ferroelectric ceramics, relaxor ferroelectric materials in ferroelectric ceramics have better performance and can achieve higher energy storage efficiency.

[0003] Preparation and Photoelectric Properties of Relaxor Ferroelectric Ceramics, Hou Jie, Master's thesis of Xi'an University of Technology, which discloses that relaxor ferroelectric ceramic materials are generally prepared by solid phase reaction method. Common energy storage ceramic material systems include BT (BaTiO3) system, BST (Ba 0.5 Sr 0.5 TiO3) system, NN (NaNbO3) system, KNN (K 0.5 Na 0.5 NbO3) system, BNT (Bi 0.5 Na 0.5 TiO3) system, AN (AgNbO3) system, the core preparation steps include: first ball milling, first screening, pre-sintering, second ball milling, second screening, granulation, tableting, debinding and sintering. 0.5 Na 0.5 NbO3-0.15Bi(Mg 0.5 (Zr 0.95 Hf 0.05 ) 0.5 )O3(0.85KNN-0.15BMZH) ceramic has 1.73J / cm 3 The recoverable energy storage density value (W rec ), and also has an energy storage efficiency value of 83.2% under a high applied electric field of 250 kV / cm. As the requirements for material performance become higher and higher, there is a need to further improve the energy storage density, efficiency and breakdown field energy at the same time. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a high-entropy relaxor ferroelectric ceramic material and a preparation method thereof, wherein the high-entropy relaxor ferroelectric ceramic material has high energy storage density, energy storage efficiency, breakdown field energy and stability.

[0005] The embodiment of the present invention provides a high entropy relaxor ferroelectric ceramic material, the chemical formula of the high entropy relaxor ferroelectric ceramic material is (1-x) (Pb 0.25 Ba 0.25Sr 0.25 Ca 0.25 )TiO3-xNaNbO3, x is the molar fraction, 0.1≤x≤0.3, preferably 0.2-0.3.

[0006] The embodiment of the present invention provides a method for preparing the high entropy relaxor ferroelectric ceramic material, comprising the following steps: PbO, BaCO3, SrCO3, CaCO3, TiO2, Na2CO3 and Nb2O5 powders are proportioned according to the chemical formula, mixed, ball-milled for the first time, dried, and sintered at 800-900° C. to obtain calcined powder; The calcined powder is ball-milled again, dried, mixed with a binder, granulated, and tableted to obtain a sheet material; The sheet material is covered with the calcined powder, the binder is removed at 600-650° C., and then sintered at 1200-1250° C. to obtain the high entropy relaxor ferroelectric ceramic material.

[0007] Preferably, the method of the first ball milling and the second ball milling is to wet-mill the powder, anhydrous ethanol and zirconium balls (diameter of the zirconium balls is 2-5 mm) at 200-300 rpm (12-24 h), and the mass ratio of the powder, anhydrous ethanol and zirconium balls is 1:1-1.5:3-4.

[0008] Preferably, the drying temperature is 75-85° C., preferably 80° C., and the drying time is 10 h.

[0009] Preferably, the sintering time at 800-900° C. is 4-6 hours.

[0010] Preferably, the binder is polyvinyl alcohol.

[0011] Preferably, after granulation, the granules are sieved (preferably through a 200-mesh sieve), and then pressed into sheet-like materials at 200-250 MPa (preferably 225 MPa).

[0012] Preferably, the time for removing the binder at 600-650° C. is 4-6 hours.

[0013] Preferably, the sintering time at 1200-1250° C. is 3-5 h.

[0014] The beneficial effects of the present invention are that the present invention controls the proportion of each element and the value of x, so that it has a high resistance to breakdown electric field and a high polarization strength to enhance the energy storage density of the system, and utilizes the polar nanodomain structure of the high entropy relaxor ferroelectric ceramic to enhance the energy storage efficiency of the system, so that the prepared material obtains a high energy storage density (1.3~2.4 J / cm 3), high energy storage efficiency (85~91%), high breakdown field energy, and high stability and other excellent comprehensive performance.

[0015] The stability of the organizational performance of the present invention is enhanced. Experimental measurements show that as the entropy value (S) of the system increases (x=0.1, S=1.43; x=0.2, S=1.61; x=0.3, S=1.39), the energy storage density and energy storage efficiency of the material maintain good stability in the frequency range of 1-120 Hz and the temperature range of 40-120°C, and the stability gradually increases. The optimal situation is at the maximum entropy value component, and the energy storage density and energy storage efficiency only decrease by 18.4% and 4.48% at 1-120 Hz, and only decrease by 8.67% and 4.23% at 40-120°C. Therefore, the high entropy relaxor ferroelectric ceramic component has an additional effect on enhancing the stability of the material performance. In addition, the slow diffusion of elements under the high entropy effect makes the grain refinement higher. Experimental measurements show that at the maximum entropy value component of x=0.2, the grain is the finest (1.30±0.7μm), which has an additional effect on enhancing the anti-breakthrough field strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a key process flow chart for preparing the high entropy relaxor ferroelectric ceramic material.

[0017] Figure 2 The room temperature PE curves of the ceramic materials of Examples 1-3. (a) is the bipolar curve of the material with x=0.1, (b) is the bipolar curve of the material with x=0.2, (c) is the bipolar curve of the material with x=0.3, and (d) is the single-stage hysteresis loop of the ceramic materials of Examples 1-3 at room temperature.

[0018] Figure 3 The stability of the ceramic materials of Examples 1-3 at a frequency of 1-120 Hz. Among them, (a), (b), and (c) are the variable frequency unipolar hysteresis loops of Examples 1-3, and (d), (e), and (f) are the energy storage density (W) at different frequencies. rec ) and energy storage efficiency (η) change curve.

[0019] Figure 4 The stability of the ceramic materials of Examples 1-3 at 40-120°C. Among them, (a), (b), and (c) are the temperature-variable unipolar hysteresis loops of Examples 1-3, and (d), (e), and (f) are the energy storage density (W) at different temperatures. rec ) and energy storage efficiency (η) change curve.

[0020] Figure 5 This is the room temperature PE curve of the ceramic material of Comparative Example 1.

[0021] Figure 6The room temperature energy storage performance of the ceramic material of Comparative Example 2, where (a) is the room temperature PE curve of BNTBT-xNN; and (b) is the energy storage density and energy storage efficiency that vary with composition. DETAILED DESCRIPTION

[0022] The object of the present invention is to provide a high entropy relaxor ferroelectric ceramic material and a preparation method thereof, comprising a ratio (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-xNaNbO3 composition-wet ball milling-calcination-secondary ball milling-pressing-sintering to prepare materials by solid phase synthesis method. The key process flow is as follows Figure 1 As shown, the present invention will be further described in detail below with reference to specific examples: Example 1 The object of the embodiment of the present invention is (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.2NaNbO3 high entropy relaxor ferroelectric ceramic material. The preparation method comprises the following steps: 1. According to the chemical formula (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.2NaNbO3 PbO, BaCO3, SrCO3, CaCO3, TiO2, Na2CO3 and Nb2O5 powders were weighed, the powders, anhydrous ethanol and 5 mm zirconium balls were mixed in a ball mill at a mass ratio of 1:1.2:3.5, and the mixture was ball milled at 250 rpm for 12 hours using a planetary ball mill. The resulting mixture was dried in an oven at 80°C for 10 hours, loaded into an alumina crucible, and calcined in a muffle furnace at 850°C for 6 hours to obtain a calcined powder.

[0023] 2. The calcined powder was ball-milled for a second time at 280 rpm for 12 hours and dried, and about 0.1 mL of 5 wt% PVA solution was dropped into the mixture for mixing and granulation. After being sieved through a 200-mesh sieve, the mixture was placed in a 10 mm diameter mold and pressed into a disc at a pressure of 225 MPa.

[0024] 3. Place the disc in an alumina crucible and cover it with calcined powder. Move the crucible into a muffle furnace and heat it to 650°C for 4 hours to remove the binder. Then heat it to 1250°C for 4 hours to sinter it to obtain (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.2NaNbO3 high entropy relaxor ferroelectric ceramic materials.

[0025] The above specific process steps are as follows Figure 1 shown.

[0026] Example 2 The object of the embodiment of the present invention is (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.1NaNbO3 high entropy relaxor ferroelectric ceramic material. According to the chemical formula (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.1NaNbO3 Weigh PbO, BaCO3, SrCO3, CaCO3, TiO2, Na2CO3 and Nb2O5 powders, and the remaining steps are the same as Example 1.

[0027] Example 3 The object of the embodiment of the present invention is (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.3NaNbO3 high entropy relaxor ferroelectric ceramic material. According to the chemical formula (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-0.3NaNbO3 Weigh PbO, BaCO3, SrCO3, CaCO3, TiO2, Na2CO3 and Nb2O5 powders, and the remaining steps are the same as Example 1.

[0028] Comparative Example 1 This comparative example 1 is not doped with NaNbO3 (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3, the preparation method is the same as that in Example 1.

[0029] Comparative Example 2 The object of the embodiment of the present invention is (1-x) (0.94Bi 0.5 Na 0.5 TiO3-0.06BaTiO3)-xNaNbO3. The preparation method is the same as that in Example 1.

[0030] The breakdown field strength and room temperature energy storage performance of the ceramic materials obtained in Examples 1, 2, and 3 were measured using the polarization-electric field hysteresis loop (PE) method. Figure 2As shown in the figure, the breakdown field strength under the double-stage PE test is above 125 kV / cm, and the maximum breakdown field strength under the single-pole test is about 160, 180 and 230 kV / cm respectively. When the NaNbO3 component is 0.3, its energy storage density and energy storage efficiency reach 2.4 J / cm 3 and 85.4%, showing excellent energy storage performance. When the NaNbO3 component is 0.2, its energy storage density drops to 1.8 J / cm 3 , but the energy storage efficiency increased to 91.6%, and its energy storage density dropped to 1.32 J / cm when the NaNbO3 component was 0.1. 3 , its energy storage efficiency remains at 91.4%.

[0031] The energy storage performance stability of the ceramic materials obtained in Examples 1, 2, and 3 in a low electric field in a frequency range of 1 to 120 Hz and a temperature range of 40 to 120° C. was measured using variable temperature / variable frequency PE. The results are as follows: Figure 3 , 4 As shown, it can be found that the fluctuations of its various performances with temperature and frequency are not large (standard deviation).

[0032] The room temperature energy storage performance of the material obtained in Comparative Example 1 was measured by PE method. The results are as follows: Figure 5 As shown in the figure, it can be seen that its breakdown field strength is not high (60 kV / cm) and its energy storage density is low (<1 J / cm 3 ), the energy storage efficiency is low (<80%), and the performance is inferior to that of this embodiment.

[0033] The room temperature energy storage performance of the material obtained in Comparative Example 2 was measured by PE method. The results are as follows: Figure 6 As shown in Figure 2, the breakdown field strength of each component is 70 kV / cm, and the energy storage density is about 0.1~0.6 J / cm 3 , the energy storage efficiency is between 5% and 90%, and the performance is inferior to that of the present embodiment.

[0034] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0035] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A high entropy relaxor ferroelectric ceramic material, characterized in that: The chemical formula of the high entropy relaxor ferroelectric ceramic material is (1-x) (Pb 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )TiO3-xNaNbO3, x is the molar fraction, 0.1≤x≤0.

3.

2. The high entropy relaxor ferroelectric ceramic material according to claim 1, characterized in that: x is 0.2~0.

3.

3. A method for preparing a high entropy relaxor ferroelectric ceramic material as claimed in claim 1 or 2, characterized in that: The steps include: PbO, BaCO3, SrCO3, CaCO3, TiO2, Na2CO3 and Nb2O5 powders are proportioned according to the chemical formula, mixed, ball-milled for the first time, dried, and sintered at 800-900° C. to obtain calcined powder; The calcined powder is ball-milled again, dried, mixed with a binder, granulated, and tableted to obtain a sheet material; The sheet material is covered with the calcined powder, the binder is removed at 600-650° C., and then sintered at 1200-1250° C. to obtain the high entropy relaxor ferroelectric ceramic material.

4. The preparation method according to claim 3, characterized in that: The method of the first ball milling and the second ball milling is to wet-mill the powder, anhydrous ethanol and zirconium balls at 200-300 rpm, and the mass ratio of the powder, anhydrous ethanol and zirconium balls is 1:1-1.5:3-4.

5. The preparation method according to claim 3, characterized in that: The drying temperature is 75~85℃.

6. The preparation method according to claim 3, characterized in that: The sintering time at 800~900℃ is 4~6h.

7. The preparation method according to claim 3, characterized in that: The binder is polyvinyl alcohol.

8. The preparation method according to claim 3, characterized in that: After granulation, it is sieved and then pressed into sheet material at 200~250MPa.

9. The preparation method according to claim 3, characterized in that: The time for removing the binder at 600~650℃ is 4~6h.

10. The preparation method according to claim 3, characterized in that: The sintering time at 1200~1250℃ is 3~5h.

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