Lead-free ceramic materials with nanograin size for local structure strengthening design and preparation

Abstract

The present invention aims to provide a lead-free ceramic material with a nanocrystalline grain size and a locally structure-strengthened design, and its preparation method, belonging to the field of dielectric energy storage ceramic materials. Its chemical composition is: (0.7 - x)BaTiO<subgt;3< / subgt> - 0.3Bi<subgt;0.5< / subgt>Na<subgt;0.5< / subgt>TiO<subgt;3< / subgt> - xBa(Zn<subgt;1 / 3< / subgt;Nb<subgt;2 / 3< / subgt;)O<subgt;3< / subgt>, where 0.04 ≤ x ≤ 0.16. The breakdown field strength of the barium titanate-based ceramic designed in this invention patent is as high as 90 kV mm<supgt; - 1< / supgt>. Its energy storage performance stands out among all barium titanate-based ceramics, not only achieving an efficiency of 85% and an energy storage density of 15.1 J cm<supgt; - 3< / supgt>, but also having excellent frequency, thermal, and cycling stabilities in charge and discharge capabilities. The average grain size corresponding to the best energy storage performance component is approximately 630 nm.

Description

Technical Field

[0001] The present invention relates to the field of dielectric energy storage ceramic materials, and particularly to a lead-free ceramic material with a nanograin size designed by local structure strengthening and its preparation. Background Art

[0002] The increasing material needs of humanity and the incomplete and insufficient development of energy are important contradictions in the current energy industry. The concept of sustainable development urges scientists to use advanced energy storage technologies to achieve efficient storage and utilization of these energy resources. Among them, dielectric energy storage capacitors play a key role in pulsed power systems and high-voltage application fields. As a core component, the energy storage performance limitations of lead-free perovskite ferroelectric energy storage ceramics hinder the development of devices towards miniaturization, intelligence, and integration. Therefore, it is particularly urgent to develop new environmentally friendly and high-performance dielectric energy storage materials.

[0003] However, the existing barium titanate-based lead-free relaxor ferroelectric ceramics have a conflict between energy storage density and efficiency under high electric fields, and it is necessary to further improve both the energy storage density and efficiency. Summary of the Invention

[0004] The technical problem to be solved by the present invention is the conflict between the energy storage density and efficiency of lead-free relaxor ferroelectric ceramics under high electric fields. Therefore, a lead-free ceramic material with a nanograin size designed by local structure strengthening and its preparation are proposed, which can simultaneously improve the energy storage density and efficiency at a relatively high level.

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

[0006] In the first aspect, a lead-free ceramic material with a nanograin size designed by local structure strengthening is provided, and its chemical composition is (0.7 - x)BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - xBa(Zn 1 / 3 Nb 2 / 3 )O3.

[0007] In the present invention, 0.04 ≤ x ≤ 0.16, and x can be specifically, for example, 0.04, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.16.

[0008] Preferably, 0.10 < x ≤ 0.14, and more 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 at 90 kV mm -1Under the electric field, the energy storage density can reach 15.1 J cm -3 , and the energy storage efficiency can reach 85%.

[0011] Preferably, the lead-free ceramic material has a nanoscale grain size.

[0012] More preferably, the grain size of the lead-free ceramic material is 500 - 700 nm, which is more conducive to the formation of polar nano-domains; the grains are dense, the grain boundary density increases, and the potential distribution is more uniform, thereby increasing the breakdown field strength; the polarization reorientation stress is reduced, and thus the relative remanent polarization intensity increases, ultimately achieving high efficiency.

[0013] In a second aspect, a method for preparing a lead-free ceramic material with a nanograin size by local structure strengthening design as described in the first aspect is provided, including the following steps:

[0014] S1. Weigh Bi2O3, Na2CO3, BaCO3, TiO2, ZnO, and Nb2O5 powders according to the stoichiometric ratio of (0.7 - x)BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - xBa(Zn 1 / 3 Nb 2 / 3 )O3, soak them in an organic solvent for primary ball milling, obtain a filtered slurry, dry it and then grind it into powder, and then perform primary calcination;

[0015] S2. After the powder obtained from the primary calcination in S1 is cooled to room temperature, drop in a binder, grind it into powder, and then press it into a shape;

[0016] S3. Place the sample obtained in S2 in a muffle furnace, heat it to 500 - 600 °C for low-temperature sintering to react off the binder; then heat it to 1100 - 1300 °C for high-temperature sintering;

[0017] S4. Polish the ceramic sheet obtained from the high-temperature sintering in S3, and then perform ion sputtering to deposit a gold electrode.

[0018] Preferably, in S1, the conditions for the primary ball milling include: the rotation speed is 300 - 400 rpm, and the time is not less than 8 h. This preferred scheme is more conducive to ensuring the full mixing of raw materials, sufficient solid-phase reaction; the particles are more refined, which helps to form a more uniform microstructure during the subsequent sintering process; the powder after ball milling is more likely to form a dense structure during pressing and sintering, which is beneficial to improving the mechanical strength of the ceramic material.

[0019] Preferably, the drying time is 2 - 3 h.

[0020] Preferably, the conditions for the first calcination include: a temperature of 800 - 900 °C and a time of 2 - 3 h. This preferred solution is more conducive to improving the ceramic density and helps to maintain the single-phase structure of the material.

[0021] Preferably, in S1, the organic solvent is anhydrous ethanol. The amount of ethanol in S1 can be freely selected according to the volume of the container used and the evenness of grinding, as long as it is conducive to even grinding, and the ethanol will evaporate during the subsequent drying process.

[0022] Preferably, in S2, the binder is an aqueous solution of polyvinyl alcohol with a mass fraction of 3% - 5%.

[0023] Preferably, the mass ratio of the binder to the powder after the first calcination in S1 is 1:5 - 15. This preferred solution is more conducive to reducing the cracking of the pressed ceramic sheet during sintering and improving the density of the material.

[0024] Preferably, in S3, the time for low-temperature sintering is 2 - 3 h, and the time for high-temperature sintering is 2 - 3 h.

[0025] Preferably, the heating rate in both the low-temperature sintering and high-temperature sintering stages is independently 4 - 6 °C / min. This preferred solution is more conducive to controlling the grain growth rate, thereby obtaining a uniform grain size distribution; reducing the internal thermal stress of the material, avoiding stress concentration and crack formation inside the material caused by rapid heating, and reducing the porosity.

[0026] Preferably, the temperature of the high-temperature sintering in S3 satisfies: when 0.04 ≤ x < 0.08, the high-temperature sintering temperature is 1160 °C, and when 0.08 ≤ x ≤ 0.16, the high-temperature sintering temperature is 1140 °C. This preferred solution is more conducive to optimizing grain growth and forming a uniform microstructure.

[0027] Preferably, in S4, the polishing process includes: polishing on sandpaper to a thickness of 0.05 - 0.3 mm. This preferred solution is more conducive to improving breakdown. A sufficiently high electric field needs to be applied to conduct subsequent ferroelectric instrument tests and energy storage tests.

[0028] Further preferably, the grit size of the sandpaper is 400 - 800 Cw.

[0029] Preferably, in S4, the ion sputtering process includes: using a gold target as the target material, when the vacuum is pumped to less than 10 Pa, a current of 9 - 11 mA is passed, and the time is 200 - 400 s. This preferred solution can make the electrodes on the ceramic surface more uniform, thus being more conducive to the stability and improvement of the breakdown electric field strength.

[0030] In a specific embodiment of the present invention, the preparation method includes the following steps:

[0031] S1. Weigh Bi2O3, Na2CO3, BaCO3, TiO2, ZnO and Nb2O5 powders according to the stoichiometric ratio of (0.7 - x)BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - xBa(Zn 1 / 3 Nb 2 / 3 )O3, soak them in anhydrous ethanol and ball - mill with a planetary ball mill. Filter the slurry, place it in a drying oven to dry, then pour it out and grind it into powder. Then put it into a crucible and heat it in a muffle furnace for the first calcination;

[0032] S2. After the powder obtained by calcination in S1 is cooled to room temperature, pour the powder into a mortar, drip the binder, wait until the sample becomes a block and then grind it into powder. Then pour it into a special mold and press it into a disc;

[0033] S3. Place the sample obtained in S2 in a muffle furnace, heat it to 550°C and keep it warm for two hours to react away the binder. Then heat it to 1100 - 1300°C and keep it warm for two hours (all heating processes are at a rate of 5°C / min);

[0034] S4. Polish the sintered ceramic disc obtained in S3 on sandpaper, coat both sides with gold electrodes by magnetron sputtering and grind off the gold coated on the side. In summary, a lead - free ceramic material with nanoscale grain size and both high energy storage density and efficiency based on local structure strengthening design can be obtained.

[0035] The beneficial effects of the above - mentioned technical solutions of the present invention are as follows:

[0036] Through local structure design, the present invention successfully develops a novel lead - free energy - storage ceramic material based on BaTiO3 (BT). This material exhibits excellent energy - storage performance, including extremely high polarization change (ΔP = 49μC cm -2 ), high breakdown electric field (E B = 90kV mm -1 ), as well as excellent thermal stability, frequency stability and cycling stability. The energy - storage density of this material reaches 15.1 J cm -3 ), showing a significant improvement in the field of BT - based lead - free bulk ceramics.

[0037] Specifically, the present invention adds appropriate amounts of Bi 0.5 Na 0.5 TiO3 and Ba(Zn 1 / 3 Nb 2 / 3 )O3 to the BT matrix, and cooperates with appropriate ratios of BaTiO3 and Ba(Zn 1 / 3 Nb 2 / 3)O3, can introduce a variety of different valence ions at the atomic scale through the local structure to enhance the random field, and coordinately design the local polymorphic distortion structure by regulating the polycrystalline phase transition temperature, realizing the gradual evolution of ceramics from nanodomains to microdomains and then to PNRs, significantly improving the breakdown field strength and energy storage performance of the material. The polarization displacement size and angular distribution were analyzed using spherical aberration electron microscopy, revealing the mechanism by which local diverse polarization configurations enhance polarization and thus optimize energy storage. This achievement clarifies the advantages of local structure design for the development of new lead-free ceramic materials with both high energy storage capacity and high efficiency. Among them, under the same conditions, if Ba(Zn) is not added, 1 / 3 Nb 2 / 3 )O3, will lead to the Curie temperature Tm not dropping to the room temperature, the relative residual polarization intensity is reduced, and the energy storage efficiency is reduced; if BaTiO3 and Ba(Zn 1 / 3 Nb 2 / 3 ) Different O3 ratios will lead to large differences in grain size, which in turn leads to low maximum energy storage density. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a grain picture of the barium titanate-based relaxor ferroelectric ceramic prepared in Example 1, taken by SEM.

[0039] Figure 2 1 is a diagram of hysteresis loops of the barium titanate-based relaxor ferroelectric ceramic prepared in Example 1 under different applied electric fields.

[0040] Figure 3 The barium titanate-based ceramics prepared in Example 1 were subjected to a 10 kV mm -1 to 90kV mm -1 The dotted line graph below shows the changes in energy storage density and efficiency.

[0041] Figure 4 3 is a curve showing the change of the unipolar hysteresis loop of the barium titanate-based relaxor ferroelectric ceramic prepared in Example 1 with frequency.

[0042] Figure 5 3 is a curve showing the change of the unipolar hysteresis loop of the barium titanate-based relaxor ferroelectric ceramic prepared in Example 1 with temperature.

[0043] Figure 6 3 is a curve showing the change of the unipolar hysteresis loop of the barium titanate-based relaxor ferroelectric ceramic prepared in Example 1 with the number of cycles. DETAILED DESCRIPTION

[0044] The present invention aims to propose a lead-free ceramic material with nano-scale grain size and high energy storage density and efficiency based on a localized structural strengthening design and its preparation process. It belongs to the field of dielectric energy storage ceramic materials; its chemical composition is: (0.7-x)BaTiO3-0.3Bi 0.5 Na0.5 TiO3-xBa(Zn 1 / 3 Nb 2 / 3 )O3, 0.04 ≤ x ≤ 0.16. The breakdown field strength of the barium titanate-based ceramic of the present invention is as high as 90 kV / mm -1 , and the relative remanent polarization intensity is as high as 49 μC / cm -2 . In terms of energy storage performance, not only does it achieve an efficiency of 85% and an energy storage density of 15.1 J / cm -3 , but also its charge-discharge ability has excellent frequency, thermal, and cycling stabilities. The average grain size corresponding to the best component in terms of energy storage performance is about 630 nm, standing out among all barium titanate-based energy storage ceramics.

[0045] 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.

[0046] Example 1:

[0047] Using the method of the present invention, prepare the best component in terms of energy storage performance in this composition, 0.58BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - 0.12Ba(Zn 1 / 3 Nb 2 / 3 )O3. Weigh 1.7474 grams of Bi2O3, 0.3975 grams of Na2CO3, 6.9069 grams of BaCO3, 3.5143 grams of TiO2, 0.1628 grams of ZnO, and 0.5316 grams of Nb2O5 according to the chemical dosage ratio and pour them into a nylon ball milling jar. Add 150 - 200 ml of anhydrous ethanol and ball mill for no less than 8 hours. Set the rotation speed of the planetary ball mill to 400 rpm, and let the instrument cool for 5 minutes every 15 minutes. Filter the slurry, place it in a drying oven to dry for three hours, then pour it out and grind it into powder. Then put it into a crucible and heat it to 850°C in a muffle furnace, and keep it warm for two hours. After cooling to room temperature, pour the powder into a mortar, drop in the PVA binder (i.e., an aqueous solution of polyvinyl alcohol with a mass fraction of 3%, and the mass ratio of the binder to the calcined powder is 1:10). Wait until the sample becomes a block, then grind it into powder. Then pour it into a special mold and press it into a 10-mm-diameter disc under a pressure of about 300 MPa. Then place it in a muffle furnace, heat it to 550°C and keep it warm for two hours to react away the binder. Then heat it up to 1140°C for high-temperature sintering and keep it warm for two hours (all heating processes are at a rate of 5°C / min). Polish the sintered ceramic disc on sandpaper with a grit size of 400 Cw to a thickness of 0.3 mm, then grind it with 800 Cw sandpaper to 0.2 mm. Finally, use magnetron sputtering to coat gold electrodes on both sides in a chamber with the air pressure pumped below 10 Pa. Coat a dot electrode on one side, and apply 10 A of current to each side for 300 s, and grind off the gold coated on the side.

[0048] Figure 1 is the grain morphology of the barium titanate-based ceramic obtained in this example under a scanning electron microscope. After statistics, the average grain sizes of 0.12 are 630 nm respectively;

[0049] Figure 2 is the single-polar ferroelectric hysteresis loop of the barium titanate-based ceramic obtained in this example from 10 kV / mm -1 to 90 kV / mm -1 Under this condition, the maximum recoverable energy storage density can be calculated to be 15.1 J / cm -3 , the energy storage efficiency is 85%, and the relative remanent polarization intensity is 49 μC / cm -2 ;

[0050] Figure 3 is the dot-line graph of the change in energy storage density and efficiency of the barium titanate-based ceramic obtained in this example from 10 kV / mm -1 to 90 kV / mm -1 Under this condition, the stability of the efficiency and the linear growth of the energy storage density can be seen;

[0051] Figure 4 is the change curve of the single-polar ferroelectric hysteresis loop of the barium titanate-based relaxor ferroelectric ceramic obtained in Example 1 with frequency, indicating the temperature stability of the barium titanate-based ceramic obtained in this example from room temperature of 30 °C to 160 °C at 45 kV / mm -1 ;

[0052] Figure 5 is the change curve of the single-polar ferroelectric hysteresis loop of the barium titanate-based relaxor ferroelectric ceramic obtained in Example 1 with temperature, indicating the cycle number stability from 10 0 times to 10 6 times of cycles;

[0053] Figure 6 is the change curve of the single-polar ferroelectric hysteresis loop of the barium titanate-based relaxor ferroelectric ceramic obtained in Example 1 with the number of cycles, indicating the single-polar ferroelectric hysteresis measured from the frequency stability of 1 - 200 Hz. It can be seen from Figures 4 - 6 that its stability is quite excellent.

[0054] Example 2:

[0055] Refer to the method of Example 1. The difference is that the ceramic material composition is: 0.6BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - 0.1Ba(Zn 1 / 3 Nb 2 / 3)O3, weigh 1.7474 g of Bi2O3, 0.3975 g of Na2CO3, 6.9069 g of BaCO3, 3.5942 g of TiO2, 0.1357 g of ZnO, and 0.4430 g of Nb2O5 according to the chemical dosage ratio accordingly.

[0056] After testing, the barium titanate-based relaxor ferroelectric ceramic prepared in this example has an energy storage density of 12.9 J / cm -1 under an electric field of 79 kV / mm -3 , and the energy storage efficiency reaches 86.8%.

[0057] Example 3:

[0058] Carry out according to the method of Example 1, the difference is that the ceramic material composition is: 0.56BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - 0.14Ba(Zn 1 / 3 Nb 2 / 3 )O3, weigh 1.7474 g of Bi2O3, 0.3975 g of Na2CO3, 6.9069 g of BaCO3, 3.4344 g of TiO2, 0.1899 g of ZnO, and 0.6202 g of Nb2O5 according to the chemical dosage ratio accordingly.

[0059] After testing, the barium titanate-based relaxor ferroelectric ceramic prepared with this composition has an energy storage density of 11.2 J / cm -1 under an electric field of 72 kV / mm -3 , and the energy storage efficiency reaches 85.7%.

[0060] Example 4:

[0061] Carry out according to the method of Example 1, the difference is that the high-temperature sintering temperature is 1160 °C.

[0062] After testing, the barium titanate-based relaxor ferroelectric ceramic prepared with this composition has an energy storage density of 14.1 J / cm -1 under an electric field of 85 kV / mm -3 , and the energy storage efficiency reaches 85.7%.

[0063] Comparative Example 1:

[0064] Carry out according to the method of Example 1, the difference is that the ceramic material composition is: 0.7BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 (i.e., x = 0).

[0065] After testing, the barium titanate-based relaxor ferroelectric ceramic prepared with this composition has an electric field of 10 kV / mm -1Under the electric field of, the energy storage density reaches 1.29 J cm -3 , and the energy storage efficiency reaches 16.6%.

[0066] Comparative Example 2:

[0067] It was carried out by referring to the method of Example 1, except that the ceramic material composition was: 0.90BaTiO3 - 0.10Ba(Zn 1 / 3 Nb 2 / 3 )O3.

[0068] After testing, the barium titanate-based relaxor ferroelectric ceramic prepared from this component has an energy storage density of 0.32 J cm -1 under the electric field of 10 kV mm -3 , and the energy storage efficiency reaches 55.5%.

[0069] 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 lead-free ceramic material with a nanograin size featuring a locally structured enhanced design, characterized in that Its chemical composition is (0.7 - x)BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - x Ba(Zn 1 / 3 Nb 2 / 3 )O3, 0.04 ≤ x ≤ 0.16 2. The lead-free ceramic material according to claim 1, characterized in that, 0.10≤ x ≤0.14。 3. A method for preparing a lead-free ceramic material with a nanocrystalline grain size and a locally structure-strengthened design as described in claim 1 or 2, characterized in that, It includes the following steps: S1. Weigh Bi2O3, Na2CO3, BaCO3, TiO2, ZnO and Nb2O5 powders according to the chemical stoichiometry of (0.7 - x)BaTiO3 - 0.3Bi 0.5 Na 0.5 TiO3 - x Ba(Zn 1 / 3 Nb 2 / 3 )O3, soak them in an organic solvent for primary ball milling, obtain the filtered slurry, grind it into powder after drying, and then conduct primary calcination; S2. After the powder obtained from the first calcination in S1 is cooled to room temperature, a binder is dropped in, ground into powder, and then pressed into shape; S3. The sample obtained in S2 is placed in a muffle furnace, heated to 500 - 600 °C for low-temperature sintering to react away the binder; then heated to 1100 - 1300 °C for high-temperature sintering; S4. The ceramic sheet obtained after high-temperature sintering in S3 is polished, and then a gold electrode is deposited by ion sputtering.

4. The preparation method according to claim 3, wherein In S1, the conditions for the first ball milling include: the rotation speed is 300 - 400 rpm, the time is not less than 8 h; the drying time is 2 - 3 h; the conditions for the first calcination include: the temperature is 800 - 900 °C, and the time is 2 - 3 h.

5. The preparation method according to claim 3, characterized in that, In S1, the organic solvent is absolute ethanol; In S2, 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 powder after the first calcination in S1 is 1:5 - 15.

6. The preparation method according to claim 3, wherein In S3, the time for low-temperature sintering is 2 - 3 h, and the time for high-temperature sintering is 2 - 3 h.

7. The preparation method according to claim 3 or 6, characterized in that, In S3, the heating rate in both the low-temperature sintering and high-temperature sintering stages is independently 4 - 6 °C / min.

8. The preparation method according to claim 3, characterized in that, The temperature of the high-temperature sintering described in S3 satisfies: when 0.04 ≤ x < 0.08, the temperature of the high-temperature sintering is 1160 °C, and when 0.08 ≤ x ≤ 0.16, the temperature of the high-temperature sintering is 1140 °C.

9. The preparation method according to claim 3, wherein The process of ion sputtering in S4 includes: the target is a gold target, when the vacuum is pumped to below 10 Pa, a current of 9 - 11 mA is passed, and the time is 200 - 400 s.

Images