Sodium bismuth titanate-based relaxor ferroelectric ceramics with excellent energy storage performance under high electric fields and a preparation method thereof

Abstract

The present invention provides a sodium bismuth titanate-based relaxor ferroelectric ceramic with excellent energy storage performance under high electric fields and a preparation method thereof, belonging to the field of dielectric energy storage materials; its chemical composition is (1-x)Bi 0.375 Na 0.375 Ba 0.25 TiO3-xNaNbO3, where 0.09 ≤ x ≤ 0.15. The sodium bismuth titanate-based energy storage ceramic material provided by the present invention can exhibit excellent energy storage performance with W rec = 15.2 J / cm 3 , η = 91% under a high electric field of 73 kV / mm, and also has good frequency stability, temperature stability and anti-fatigue characteristics, and it also shows an ultra-fast charge-discharge rate in the over-damped charge-discharge test. The present invention is expected to be practically developed in the fields of electric vehicles, microelectronics, etc.

Description

Technical Field

[0001] The present invention relates to the field of dielectric energy storage materials, and particularly to a sodium bismuth titanate-based relaxor ferroelectric ceramic having excellent energy storage performance under high electric fields and a preparation method thereof. Background Art

[0002] In recent years, the world energy problem has become increasingly severe. How to store energy with high efficiency and low loss has become a hot research topic. Compared with other energy storage materials, energy storage ceramic capacitors have the characteristics of large power density, long cycle life, good environmental stability, low production cost, etc., and play an irreplaceable role in fields such as electric vehicles, microelectronics, and pulsed power devices. Currently, the most widely used energy storage ceramics are lead-based energy storage ceramics. With the advancement of environmental protection and the sustainable development strategy, the development of lead-free energy storage ceramics has become an inevitable trend.

[0003] Among the currently widely studied lead-free energy storage ceramics, relaxor ferroelectric ceramics have become the focus of research in this field due to their high dielectric constant, good temperature stability, and slender electric hysteresis loops. In current research, the energy storage performance of relaxor ferroelectric ceramics has been greatly improved. However, a common problem still faced by most current relaxor ferroelectric energy storage ceramics is that as the applied electric field increases, the waist property of the electric hysteresis loop deteriorates and the energy loss increases. Therefore, solving the problem of low energy storage efficiency under high electric fields still has important research significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the energy storage efficiency of lead-free relaxor ferroelectric ceramics is relatively low under high electric fields. Therefore, a sodium bismuth titanate-based relaxor ferroelectric ceramic having excellent energy storage performance under high electric fields and a preparation method thereof are provided.

[0005] To solve the above technical problem, the present invention provides the following technical solutions:

[0006] In the first aspect, a sodium bismuth titanate-based relaxor ferroelectric ceramic having excellent energy storage performance under high electric fields is provided, and its chemical composition is (1 - x)Bi 0.375 Na 0.375 Ba 0.25 TiO3 - xNaNbO3.

[0007] For the present invention, 0.09 ≤ x ≤ 0.15, and x can specifically be, for example, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15.

[0008] Preferably, 0.11 ≤ x ≤ 0.13.

[0009] More preferably, x = 0.12.

[0010] Under the above preferred x scheme, its energy storage efficiency can be stabilized above 82%, and under an electric field of 73 kV / mm, the energy storage density can reach 15.2 J / cm 3 , and the energy storage efficiency can reach 91%.

[0011] The phase of the sodium bismuth titanate-based relaxor ferroelectric ceramic described in the present invention is a cubic phase, which is beneficial to improving the energy storage performance under high electric fields.

[0012] In a second aspect, a preparation method of the sodium bismuth titanate-based relaxor ferroelectric ceramic described in the first aspect is provided.

[0013] Specifically, it includes the following steps:

[0014] S1. Weigh Bi2O3, Na2CO3, BaCO3, Nb2O5, and TiO2 according to the stoichiometric ratio of (1-x)Bi 0.375 Na 0.375 Ba 0.25 TiO3-xNaNbO3 and pour them into a ball milling tank, and add ethanol for ball milling;

[0015] S2. Dry, grind the ball-milled mixture, and calcine it in a muffle furnace;

[0016] S3. Weigh the calcined powder in a mortar, add a binder for grinding, granulation, and sieving, and press it into a green body;

[0017] S4. Place the green body in a crucible, put it in a muffle furnace for debinding and sintering to obtain a sodium bismuth titanate-based relaxor ferroelectric ceramic with excellent energy storage performance under high electric fields.

[0018] Preferably, the conditions for the ball milling in S1 include: the time is 20-24 h, and the rotation speed is 300-500 rpm.

[0019] The amount of ethanol used in S1 of the present invention is 100-200 mL.

[0020] Preferably, the conditions for the calcination in S2 include: the temperature is 800-900 °C, and the time is 2-3 h.

[0021] Preferably, the sieving in S3 uses a sieve mesh of 300-400 meshes, preferably 400 meshes.

[0022] Preferably, the binder is an aqueous solution of polyvinyl alcohol with a mass fraction of 3%-5%, and the mass ratio of the binder to the sample obtained after calcination in S2 is 1:5-15.

[0023] Among them, preferably, the debinding conditions described in S4 include: temperature of 500 - 600 °C, time of 2 - 3 h, and heating rate of 3 - 5 °C / min.

[0024] Among them, preferably, the sintering conditions described in S4 include: temperature of 1100 - 1300 °C, time of 2 - 3 h, and heating rate of 3 - 5 °C / min.

[0025] The beneficial effects of the above technical solutions of the present invention are as follows:

[0026] In the present invention, an appropriate proportion of Ba with a relatively large ionic radius is introduced into the sodium bismuth titanate matrix, 2+ resulting in obvious local lattice distortion, making the matrix generate a relatively large spontaneous polarization intensity; an appropriate amount of NaNbO3 is introduced to construct a ternary solid solution, forming nano-scale atomic clusters inside the ceramic, increasing local chemical disorder, destroying the long-range ordered macroscopic ferroelectric domains, forming polar nano-domains, accelerating the electric field response and effectively reducing the energy loss generated by the electric domain flipping;

[0027] More importantly, by controlling the content of Ba to remain at a relatively high 25% in the present invention and coordinating the regulation of the chemical ratios of other components, the lattice undergoes obvious expansion, which provides a structural basis for the reversible elongation of polarization clusters with the electric field. Macroscopically, it is manifested that the energy storage efficiency is significantly improved under a high electric field; at the same time, the phase is transformed into a cubic phase, which is beneficial to improving the relaxation degree of the material, reducing the energy loss during the removal of the electric field and improving the environmental stability.

[0028] Benefiting from the reasonable chemical composition, the ferroelectric hysteresis loop of the sodium bismuth titanate-based energy storage ceramic of the present invention shows two regions with different electric field-induced polarization behaviors: at low electric fields, the polar nano-domains are relatively easily flipped with the electric field, and the ferroelectric hysteresis loop shows a large ΔP / ΔE, accompanied by a relatively large energy loss; at high electric fields, the fully oriented polar domains can reversibly elongate with the increase of the electric field, showing a lower energy loss. This polarization behavior caused by this structure shows a unique trend that the energy storage efficiency increases with the increase of the electric field. Finally, the energy storage efficiency can be stabilized above 82%, and at an electric field of 73 kV / mm, the energy storage density can reach 15.2 J / cm 3 , and the energy storage efficiency can reach 91%, achieving excellent effects. Description of the Drawings

[0029] Figure 1 SEM picture of the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared in Example 1;

[0030] Figure 2 Ferroelectric hysteresis loop of the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared in Example 1;

[0031] Figure 3 Variation curve of the energy storage performance of the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared in Example 1 with the applied electric field.

[0032] Figure 4 Overdamped discharge energy density curve of the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared in Example 1. Detailed implementation manners

[0033] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0034] Example 1:

[0035] Using the method of the present invention to prepare 0.88Bi 0.375 Na 0.375 Ba 0.25 TiO3 - 0.12NaNbO3. Weigh 3.8442 g of Bi2O3, 1.1924 g of Na2CO3, 2.1707 g of BaCO3, 0.7974 g of Nb2O5, and 3.5143 g of TiO2 according to the chemical dosage ratio, pour them into a ball milling tank, add 150 ml of ethanol and ball mill for 20 h, and set the rotation speed to 400 rpm. The ball milled sample is dried and ground in sequence, and then put into a muffle furnace for calcination. The calcination temperature is 850 °C and the time is 2 h. Pour the calcined powder into a mortar, add an appropriate amount of 5wt% polyvinyl alcohol aqueous solution binder (the mass ratio of the binder to the sample is 1:10), grind and granulate, and pour it into a 400-mesh sieve for sieving. Use a mold with φ = 10 mm to press the sieved powder into a green body and put it into a muffle furnace for debinding. The heating rate is 4 °C / min, the debinding temperature is 550 °C, and the time is 2 h. Subsequently, heat up for sintering. The heating rate is 4 °C / min, the sintering temperature is 1150 °C, and the time is 2 h. After cooling, a sodium bismuth titanate-based relaxor ferroelectric ceramic with excellent energy storage performance under high electric fields can be obtained.

[0036] For energy storage performance testing, grind the ceramic sheet to a thickness of 50 μm. Use an ion sputtering instrument to deposit gold electrodes on the upper and lower surfaces of the ceramic. The conditions for ion sputtering include: using a gold target as the target material, the current is 10 mA, and the time is 300 s.

[0037] Figure 1 SEM picture of the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared in this example. It can be seen from the figure that the grain size of this ceramic is about 1 μm, and it has a high density, making it have good breakdown electric field strength.

[0038] Figure 2The single - polar hysteresis loop of the sodium bismuth titanate - based relaxor ferroelectric ceramic prepared in this example at room temperature. As can be seen from the figure, due to the influence of polar atomic clusters, the hysteresis loop shows two regions with different characteristics. The first half corresponds to a larger ΔP / ΔE and has a large energy loss, which is a typical behavior of relaxor ferroelectrics under high electric fields. The second half shows a relatively smaller ΔP / ΔE and lower energy loss. The unique polarization characteristics enable the sodium bismuth titanate - based energy - storage ceramic described in the present invention to exhibit the characteristic that the energy - storage efficiency increases with the increase of the applied electric field.

[0039] Figure 3 The curve of the energy - storage performance of the sodium bismuth titanate - based relaxor ferroelectric ceramic prepared in this example with respect to the applied electric field. As can be seen from the figure, the sodium bismuth titanate - based energy - storage ceramic described in this application shows a trend that the energy - storage efficiency increases with the increase of the electric field. Its energy - storage efficiency can be stabilized above 82%, and at an electric field of 73 kV / mm, the energy - storage density can reach 15.2 J / cm 3 , and the energy - storage efficiency can reach 91%.

[0040] Figure 4 The over - damped discharge energy - density curve of the sodium bismuth titanate - based relaxor ferroelectric ceramic prepared in this example. Usually, the discharge time (t 0.9 ) when the discharge energy density reaches 90% is used as an important evaluation criterion for the practical application of energy - storage ceramics. As can be seen from the figure, during the discharge process with a charging electric field of 35 kV / mm, 4.5 J / cm 3 of energy is rapidly released within 39 ns. The ultra - fast charge - discharge rate provides great development potential for the application of the sodium bismuth titanate - based energy - storage ceramic described in the present invention in pulsed - power devices.

[0041] Example 2:

[0042] The method of Example 1 was referred to. The difference is that the ceramic material composition is: 0.85Bi 0.375 Na 0.375 Ba 0.25 TiO3 - 0.15NaNbO3. Accordingly, 3.7131 g of Bi2O3, 1.2421 g of Na2CO3, 2.0967 g of BaCO3, 0.9968 g of Nb2O5, and 3.3945 g of TiO2 were weighed according to the stoichiometric ratio.

[0043] After testing, the sodium bismuth titanate - based relaxor ferroelectric ceramic prepared in this example has an energy - storage density of 10.3 J / cm 3 at an electric field of 65 kV / mm, and the energy - storage efficiency reaches 87.8%.

[0044] Example 3:

[0045] It is carried out according to the method of Example 1, with the difference that the ceramic material composition is: 0.91Bi 0.375 Na 0.375 Ba 0.25 TiO3 - 0.09NaNbO3. Accordingly, 3.9752 g of Bi2O3, 1.1427 g of Na2CO3, 2.2447 g of BaCO3, 0.5981 g of Nb2O5, and 3.6341 g of TiO2 are weighed according to the stoichiometric ratio.

[0046] After testing, the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared from this composition has an energy storage density of 8.4 J / cm 3 under an electric field of 57 kV / mm, and the energy storage efficiency reaches 82.3%.

[0047] Comparative Example 1:

[0048] It is carried out according to the method of Example 1, with the difference that the ceramic material composition is: 0.88Bi 0.425 Na 0.425 Ba 0.15 TiO3 - 0.12NaNbO3.

[0049] After testing, the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared from this composition has an energy storage density of 7.3 J / cm 3 under an electric field of 50 kV / mm, and the energy storage efficiency reaches 68.4%.

[0050] Comparative Example 2:

[0051] It is carried out according to the method of Example 1, with the difference that the ceramic material composition is: 0.83Bi 0.375 Na 0.375 Ba 0.25 TiO3 - 0.17NaNbO3.

[0052] After testing, the sodium bismuth titanate-based relaxor ferroelectric ceramic prepared from this composition has an energy storage density of 5.9 J / cm 3 under an electric field of 53 kV / mm, and the energy storage efficiency reaches 74.6%.

[0053] It can be seen from the above examples and comparative examples that only the ceramic material with the specific composition of the present invention can obtain excellent energy storage performance under a high electric field.

[0054] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A sodium bismuth titanate-based relaxor ferroelectric ceramic with excellent energy storage performance under high electric fields, characterized in that, Its chemical composition is (1-x)Bi 0.375 Na 0.375 Ba 0.25 TiO3-xNaNbO3, where 0.11 ≤ x ≤ 0.13; The preparation method of the sodium bismuth titanate-based relaxor ferroelectric ceramic includes the following steps: S1. Weigh Bi2O3, Na2CO3, BaCO3, Nb2O5, and TiO2 according to the stoichiometric ratio of (1 - x)Bi 0.375 Na 0.375 Ba 0.25 TiO3 - xNaNbO3, pour them into a ball - milling tank, and add ethanol for ball - milling; S2. Dry, grind the ball-milled mixture, and calcine it in a muffle furnace. S3. Weigh the calcined powder into a mortar, add a binder, grind, granulate, and screen it, and then press it into a green body. S4. Place the green body in a crucible and put it into a muffle furnace for debinding and sintering.

2. The sodium bismuth titanate-based relaxor ferroelectric ceramic according to claim 1, characterized in that The phase of the sodium bismuth titanate-based relaxor ferroelectric ceramic is a cubic phase.

3. A preparation method of a sodium bismuth titanate-based relaxor ferroelectric ceramic as described in claim 1, characterized in that, It includes the following steps: S1. Weigh Bi2O3, Na2CO3, BaCO3, Nb2O5, and TiO2 according to the stoichiometric ratio of (1 - x)Bi 0.375 Na 0.375 Ba 0.25 TiO3 - xNaNbO3, pour them into a ball - milling tank, and add ethanol for ball - milling; S2. Dry, grind the ball-milled mixture, and calcine it in a muffle furnace. S3. Weigh the calcined powder into a mortar, add a binder, grind, granulate, and screen it, and then press it into a green body. S4. Place the green body in a crucible and put it into a muffle furnace for debinding and sintering.

4. The preparation method according to claim 3, characterized in that, The conditions of the ball milling in S1 include: the time is 20 - 24 h, and the rotation speed is 300 - 500 rpm.

5. The preparation method according to claim 3, characterized in that, The conditions of the calcination in S2 include: the temperature is 800 - 900 °C, and the time is 2 - 3 h.

6. The preparation method according to claim 3, characterized in that, The binder in S3 is an aqueous solution of polyvinyl alcohol with a mass fraction of 3% - 5%, and the mass ratio of the binder to the powder calcined in S2 is 1:5 - 15.

7. The preparation method according to claim 3, characterized in that, The screen used for screening in S3 is a 300 - 400 mesh screen.

8. The preparation method according to claim 3, characterized in that, The conditions of the debinding in S4 include: the temperature is 500 - 600 °C, the time is 2 - 3 h, and the heating rate is 3 - 5 °C / min.

9. The preparation method according to claim 3, characterized in that, The conditions of the sintering in S4 include: the temperature is 1100 - 1300 °C, the time is 2 - 3 h, and the heating rate is 3 - 5 °C / min.

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