A lead-free ceramic and a method for manufacturing the same, and a capacitor

Abstract

The application relates to a lead-free ceramic and a preparation method and a capacitor thereof, and belongs to the technical field of ceramics; BKT ceramic is solid-solved into ST ceramic, the paraelectric phase in the ST ceramic is broken by introducing the BKT ceramic, and the relaxation characteristic is improved. Meanwhile, BZT ceramic is introduced, the sintering temperature of the whole body is reduced, and then the probability of forming a liquid phase of the ceramic during sintering is reduced. The introduction of the BZT ceramic can make the micro-ordering of the ceramic become disordered, finally forming a bicrystal site disordered relaxor ferroelectric, and then being beneficial to the power density of the lead-free ceramic. In addition, the grain size of the BKT ceramic is small, the reduction of the grain size reduces the number of oxygen vacancies, the oxygen vacancies are oxidized again in the sintering process, the oxygen vacancies are further reduced, the grain growth is inhibited by the fewer oxygen vacancies, finally leading to the reduction of the grain size, more grain boundaries can be formed, so that the lead-free ceramic has a higher breakdown field strength and is beneficial to the improvement of the energy storage performance of the material.

Description

Technical Field

[0001] This application relates to the field of ceramic technology, and in particular to a lead-free ceramic and its preparation method, and a capacitor. Background Technology

[0002] With the continuous growth of global energy demand and the increasing severity of environmental problems, the search for efficient and environmentally friendly energy storage and conversion technologies has become an important issue in the field of science and technology. In power systems, capacitors, as key energy storage components, directly affect the efficiency and stability of the entire system. Therefore, developing capacitor materials with high power density and excellent energy storage characteristics has become a research hotspot.

[0003] Traditional capacitor materials, such as polymer energy storage materials, while exhibiting good performance in some aspects, still have significant room for improvement in power density and energy storage efficiency. In contrast, ceramic energy storage materials, due to their high dielectric constant, low dielectric loss, good mechanical properties, and temperature stability, show a broader application prospect. However, most lead-free ceramic energy storage materials still struggle to meet the demands of further technological development in terms of power density and energy storage efficiency, especially in applications where high energy density and high power density coexist. Power density is an indicator that measures the maximum power output per unit volume or unit weight of a capacitor, and is crucial for improving energy conversion efficiency and system compactness. Energy storage characteristics focus on the energy storage and release capabilities of a capacitor during charging and discharging, directly affecting its lifespan and stability. Therefore, developing a lead-free ceramic material that combines high power density and excellent energy storage characteristics is of great significance for promoting the development of power systems and related electronic equipment. Summary of the Invention

[0004] This application provides a lead-free ceramic, a method for preparing the same, and a capacitor, to improve the energy conversion efficiency and energy storage characteristics of lead-free ceramics.

[0005] In a first aspect, this application provides a lead-free ceramic, said lead-free ceramic comprising materials with the chemical formula xSrTiO3-yBi a K b TiO3-zBi(Zn c Ti d The main components represented by O3 are x+y+z=1, a+b=1, and c+d=1.

[0006] As an optional implementation, the main component satisfies at least one of the following conditions (1) to (7):

[0007] (1) 0.78 ≤ x ≤ 0.98;

[0008] (2) 0.01 ≤ y ≤ 0.13;

[0009] (3) 0.01≤z≤0.09;

[0010] (4) 0.4 ≤ a ≤ 0.6;

[0011] (5) 0.4 ≤ b ≤ 0.6;

[0012] (6) 0.4 ≤ c ≤ 0.6;

[0013] (7) 0.4≤d≤0.6.

[0014] As an optional implementation, the main component satisfies at least one of the following conditions (8) to (14):

[0015] (8) 0.84 ≤ x ≤ 0.92;

[0016] (9) 0.05 ≤ y ≤ 0.09;

[0017] (10) 0.03 ≤ z ≤ 0.07;

[0018] (11) 0.45 ≤ a ≤ 0.55;

[0019] (12) 0.45 ≤ b ≤ 0.55;

[0020] (13) 0.45 ≤ c ≤ 0.55;

[0021] (14) 0.45≤d≤0.55.

[0022] As an optional implementation, the lead-free ceramic comprises 0.88SrTiO3-0.07Bi. 0.5 K 0.5 TiO3-0.05Bi(Zn 0.5 Ti 0.5 O3 represents the main component.

[0023] As an optional implementation, the main component accounts for ≥90% by mass in the lead-free ceramic.

[0024] As an optional implementation, the main component accounts for 95% to 100% of the mass of the lead-free ceramic.

[0025] Secondly, this application provides a method for preparing lead-free ceramics according to the first aspect, the method comprising:

[0026] The raw materials are mixed and subjected to a first ball milling process to obtain a first mixture;

[0027] The first mixture is pre-sintered to obtain pre-sintered powder.

[0028] The pre-sintered powder is subjected to a second ball milling process to obtain a second mixture;

[0029] The second mixture is then molded to obtain a ceramic component;

[0030] The ceramic component is sintered to obtain lead-free ceramic.

[0031] As an optional implementation, the raw materials include Sr source, K source, Bi source, Ti source and Zn source.

[0032] As an optional implementation, the sintering temperature is 1000℃~1300℃; and / or

[0033] The sintering treatment time is 1 hour to 3 hours; and / or

[0034] The heating rate of the sintering process is 3℃ / min to 7℃ / min.

[0035] Thirdly, this application provides a capacitor made of the lead-free ceramic provided in the first aspect.

[0036] The technical solutions provided in this application have the following advantages compared with the prior art:

[0037] The lead-free ceramic provided in this application embodiment is a BKT ceramic (Bi a K b TiO3 is dissolved into ST ceramic (SrTiO3), making Bi at the A crystal site. 3+ K + 、Sr 2+ By introducing BKT ceramics, the paraelectric phase in ST ceramics is broken, and Bi 3+ and Sr 2+ The composite material causes lattice distortion, increases the ionic disorder at the A-site, and improves its relaxation properties. Simultaneously, the introduction of BZT ceramics (Bi(Zn)) c Ti d BZT ceramics are low-melting-point materials that can lower the overall sintering temperature, thereby reducing the probability of liquid phase formation during sintering. Furthermore, the introduction of BZT ceramics allows for the addition of Zn at the boron crystal sites. 2+ This allows it to simultaneously possess Ti at the B crystal site. 4+ Zn 2+This process disrupts the microscopic arrangement of the ceramic grains, ultimately forming bicrystalline disordered relaxor ferroelectrics, which is beneficial to the power density of lead-free ceramics. Furthermore, the smaller grain size of BKT ceramics reduces the number of oxygen vacancies. These vacancies are then oxidized again during sintering, further reducing the number of oxygen vacancies. The fewer oxygen vacancies inhibit grain growth, ultimately leading to a smaller grain size and the formation of more grain boundaries. The presence of grain boundaries results in the formation of a space charge depletion layer, hindering carrier transport. This results in higher resistivity at the grain boundaries. Therefore, ceramics with small grain sizes have more grain boundaries but smaller areas, resulting in lower leakage current and higher breakdown field strength, which is beneficial for improving the material's energy storage performance. Attached Figure Description

[0038] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0039] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A flowchart illustrating the method provided in the embodiments of this application;

[0041] Figure 2 This is a unipolar hysteresis loop diagram of the lead-free ceramic provided in Embodiment 1 of this application at 10Hz;

[0042] Figure 3 This is a charge-discharge diagram of lead-free ceramic overdamped ceramic provided in Embodiment 1 of this application. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0045] Most lead-free ceramic energy storage materials still fall short of the requirements for further development of new technologies in terms of power density and energy storage efficiency, especially in situations where high energy density and high power density coexist.

[0046] This application aims to achieve a dual improvement in power density and energy storage characteristics through optimization of material composition and improvement of preparation process. By conducting in-depth research on the relationship between the microstructure, phase composition and properties of ceramic materials, lead-free ceramic materials with high power density and excellent energy storage characteristics are prepared.

[0047] This application provides a lead-free ceramic, the lead-free ceramic comprising, in the form of, having the chemical formula,

[0048] xSrTiO3-yBi a K b TiO3-zBi(Zn c Ti d The main components represented by O3 are x+y+z=1, a+b=1, and c+d=1.

[0049] This lead-free ceramic will incorporate BKT ceramic (Bi a K b TiO3 is dissolved into ST ceramic (SrTiO3), making Bi at the A crystal site. 3+ K + 、Sr 2+ By introducing BKT ceramics, the paraelectric phase in ST ceramics is broken, and Bi 3+ and Sr 2+ The composite material causes lattice distortion, increases the ionic disorder at the A-site, and improves its relaxation properties. Simultaneously, the introduction of BZT ceramics (Bi(Zn)) c Ti d BZT ceramics are low-melting-point materials that can lower the overall sintering temperature, thereby reducing the probability of liquid phase formation during sintering. Furthermore, the introduction of BZT ceramics allows for the addition of Zn at the boron crystal sites. 2+ This allows it to simultaneously possess Ti at the B crystal site. 4+ Zn 2+ This process disrupts the microscopic arrangement of the ceramic grains, ultimately forming bicrystalline disordered relaxor ferroelectrics, which is beneficial to the power density of lead-free ceramics. Furthermore, the smaller grain size of BKT ceramics reduces the number of oxygen vacancies. These vacancies are then oxidized again during sintering, further reducing the number of oxygen vacancies. The fewer oxygen vacancies inhibit grain growth, ultimately leading to a smaller grain size and the formation of more grain boundaries. The presence of grain boundaries results in the formation of a space charge depletion layer, hindering carrier transport. This results in higher resistivity at the grain boundaries. Therefore, ceramics with small grain sizes have more grain boundaries but smaller areas, resulting in lower leakage current and higher breakdown field strength, which is beneficial for improving the material's energy storage performance.

[0050] In some embodiments, 0.78 ≤ x ≤ 0.98, and further, 0.84 ≤ x ≤ 0.92. For example, the value of x can be 0.78, 0.79, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, etc., or it can be any value within the range of 0.78 ≤ x ≤ 0.98.

[0051] In some embodiments, 0.01 ≤ y ≤ 0.13, and further, 0.05 ≤ y ≤ 0.09. For example, the value of y can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, etc., or it can be any value within the range of 0.01 ≤ y ≤ 0.13.

[0052] In some embodiments, 0.01 ≤ z ≤ 0.09, and further, 0.03 ≤ z ≤ 0.07. For example, the value of z can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, etc., or it can be any value within the range of 0.01 ≤ z ≤ 0.09.

[0053] In some embodiments, 0.4 ≤ a ≤ 0.6, and further, 0.45 ≤ a ≤ 0.55. For example, the value of a can be 0.4, 0.42, 0.45, 0.47, 0.5, 0.52, 0.55, 0.57, 0.6, etc., or it can be any value within the range of 0.4 ≤ a ≤ 0.6.

[0054] In some embodiments, 0.4 ≤ b ≤ 0.6, and further, 0.45 ≤ b ≤ 0.55. For example, the value of b can be 0.4, 0.42, 0.45, 0.47, 0.5, 0.52, 0.55, 0.57, 0.6, etc., or it can be any value within the range of 0.4 ≤ b ≤ 0.6.

[0055] In some embodiments, 0.4 ≤ c ≤ 0.6, and further, 0.45 ≤ c ≤ 0.55. For example, the value of c can be 0.4, 0.42, 0.45, 0.47, 0.5, 0.52, 0.55, 0.57, 0.6, etc., or it can be any value within the range of 0.4 ≤ c ≤ 0.6.

[0056] In some embodiments, 0.4 ≤ d ≤ 0.6, and further, 0.45 ≤ d ≤ 0.55. For example, the value of d can be 0.4, 0.42, 0.45, 0.47, 0.5, 0.52, 0.55, 0.57, 0.6, etc., or it can be any value within the range of 0.4 ≤ d ≤ 0.6.

[0057] In some embodiments, the lead-free ceramic comprises ceramics with the chemical formula 0.88SrTiO3-0.07Bi. 0.5 K 0.5 TiO3-0.05Bi(Zn 0.5 Ti 0.5 O3 represents the main component.

[0058] In some embodiments, the main component accounts for ≥90% of the mass of the lead-free ceramic. Further, the main component accounts for 95% to 100% of the mass of the lead-free ceramic. A higher mass percentage of the main component is more conducive to fully realizing its energy conversion efficiency and energy storage characteristics.

[0059] Figure 1 A flowchart illustrating the method provided in the embodiments of this application, as shown below. Figure 1 As shown, based on a general inventive concept, this application also provides a method for preparing lead-free ceramics.

[0060] This method is used for the preparation of the lead-free ceramics described above. The specific details of the lead-free ceramics can be found in the above embodiments. Since this method adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0061] In some embodiments, the method includes:

[0062] S1. Mix the raw materials and perform a first ball milling process to obtain a first mixture;

[0063] In some embodiments, the raw materials include an Sr source, a K source, a Bi source, a Ti source, and a Zn source. Specifically, the Sr source can be selected from SrCO3, the K source from K2CO3, the Bi source from Bi2O3, the Ti source from TiO2, and the Zn source from ZnO.

[0064] In some embodiments, the first ball milling process includes: mixing anhydrous ethanol, the mixed raw material, and milling beads in a certain ratio for the first ball milling process, i.e., methanol:raw material:milling beads = 1:1:1.2. The ball milling time is 24 hours, and the ball milling speed is 5 rad / s. The slurry after the first ball milling process is placed in a rotary dryer for drying, with the dimethyl silicone oil at the bottom heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0065] S2. The first mixture is pre-sintered to obtain pre-sintered powder;

[0066] In some embodiments, pre-sintering involves placing the powder in an 800°C furnace and holding it at that temperature for 3 hours, then cooling it to room temperature with the furnace before removing it.

[0067] S3. The pre-sintered powder is subjected to a second ball milling process to obtain a second mixture;

[0068] In some embodiments, the second ball milling process includes a second ball milling of the pre-sintered powder, with process control the same as the first ball milling process, and ball milling for 12 hours. After ball milling, the slurry is placed in a rotary dryer for drying, with the bottom dimethyl silicone oil heated to 120°C, and the dried sample is passed through a 60-mesh sieve.

[0069] S4. The second mixture is subjected to molding processing to obtain a ceramic component;

[0070] In some embodiments, the molding process can be dry pressing with added PVA. The template for the molding process is a circular ceramic blank, which is a circular piece with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0071] S5. The ceramic component is sintered to obtain lead-free ceramic.

[0072] In some embodiments, the sintering temperature is 1000℃~1300℃; the sintering time is 1h~3h; and the heating rate of the sintering process is 3℃ / min~7℃ / min.

[0073] Specifically, in this embodiment, the ceramic blank with ceramic components is placed in a heating furnace and sintered at 1150°C for 2 hours at a heating rate of 5°C / min. Afterward, it is cooled to room temperature in the furnace and removed. Both sides of the sample are polished clean, washed, and dried to obtain lead-free ceramic.

[0074] Based on a general inventive concept, embodiments of this application also provide a capacitor, the material of which includes the lead-free ceramic provided above.

[0075] The capacitor is based on the aforementioned lead-free ceramic. The specific details of the lead-free ceramic can be found in the above embodiments. Since the capacitor adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0076] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0077] Example 1

[0078] A lead-free ceramic, the preparation process of which includes:

[0079] (1) The raw materials SrCO3 (99% purity), K2CO3 (99.98% purity), Bi2O3 (99.9% purity), TiO2 (99.8% purity), and ZnO (99% purity) are mixed according to the chemical composition 0.88SrTiO3-0.07Bi 1 / 2K 1 / 2 TiO3-0.05Bi(Zn 1 / 2 Ti 1 / 2 After the O3 is evenly mixed, it is placed into the ball mill jar.

[0080] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0081] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0082] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0083] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0084] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0085] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0086] Example 2

[0087] A lead-free ceramic, the preparation process of which includes:

[0088] (1) The raw materials SrCO3 (99% purity), K2CO3 (99.98% purity), Bi2O3 (99.9% purity), TiO2 (99.8% purity), and ZnO (99% purity) are prepared according to their chemical composition.

[0089] 0.78SrTiO3-0.13Bi 1 / 2 K 1 / 2 TiO3-0.09Bi(Zn 1 / 2 Ti 1 / 2 After the O3 is evenly mixed, it is placed into the ball mill jar.

[0090] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0091] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0092] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0093] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0094] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0095] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0096] Example 3

[0097] A lead-free ceramic, the preparation process of which includes:

[0098] (1) The raw materials SrCO3 (99% purity), K2CO3 (99.98% purity), Bi2O3 (99.9% purity), TiO2 (99.8% purity), and ZnO (99% purity) are prepared according to their chemical composition.

[0099] 0.98SrTiO3-0.01Bi 1 / 2 K 1 / 2 TiO3-0.01Bi(Zn 1 / 2 Ti 1 / 2 After the O3 is evenly mixed, it is placed into the ball mill jar.

[0100] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0101] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0102] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0103] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0104] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0105] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0106] Example 4

[0107] A lead-free ceramic, the preparation process of which includes:

[0108] (1) The raw materials SrCO3 (99% purity), K2CO3 (99.98% purity), Bi2O3 (99.9% purity), TiO2 (99.8% purity), and ZnO (99% purity) are prepared according to their chemical composition.

[0109] 0.84SrTiO3-0.09Bi 1 / 2 K 1 / 2 TiO3-0.07Bi(Zn 1 / 2 Ti 1 / 2 After the O3 is evenly mixed, it is placed into the ball mill jar.

[0110] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0111] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0112] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0113] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0114] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0115] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0116] Example 5

[0117] A lead-free ceramic, the preparation process of which includes:

[0118] (1) The raw materials SrCO3 (99% purity), K2CO3 (99.98% purity), Bi2O3 (99.9% purity), TiO2 (99.8% purity), and ZnO (99% purity) are prepared according to their chemical composition.

[0119] 0.92SrTiO3-0.05Bi 1 / 2 K 1 / 2 TiO3-0.03Bi(Zn 1 / 2 Ti 1 / 2 After the O3 is evenly mixed, it is placed into the ball mill jar.

[0120] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0121] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0122] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0123] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0124] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0125] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0126] Comparative Example 1

[0127] A lead-free ceramic, the preparation process of which includes:

[0128] (1) The raw materials SrCO3 (99% purity), K2CO3 (99.98% purity), Bi2O3 (99.9% purity), and TiO2 (99.8% purity) are mixed according to the chemical composition 0.93SrTiO3-0.07Bi 1 / 2 K 1 / 2 After the TiO3 is evenly mixed, it is placed into a ball mill jar.

[0129] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0130] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0131] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0132] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0133] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0134] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0135] Comparative Example 2

[0136] A lead-free ceramic, the preparation process of which includes:

[0137] (1) The raw materials SrCO3 (99% purity), Bi2O3 (99.9% purity), TiO2 (99.8% purity), and ZnO (99% purity) are mixed according to the chemical composition 0.95SrTiO3-0.05Bi(ZnO) 1 / 2 Ti 1 / 2 After the O3 is evenly mixed, it is placed into the ball mill jar.

[0138] (2) Anhydrous ethanol, the mixed raw materials, and milling beads were mixed in a certain ratio and subjected to a first ball milling treatment, namely methanol: raw materials: milling beads = 1:1:1.2. The ball milling time was 24 hours and the ball milling speed was 5 rad / s to obtain the first mixture.

[0139] (3) The first mixture after ball milling is placed in a rotary dryer for drying. The bottom dimethyl silicone oil is heated to 120°C. After drying, the sample is passed through a 60-mesh sieve.

[0140] (4) The dried first mixture is placed in an 800℃ furnace and kept at the temperature for 3 hours for pre-sintering. Then it is cooled to room temperature with the furnace and taken out to obtain pre-sintered powder.

[0141] (5) The pre-sintered powder is subjected to a second ball milling process. The parameters for the second ball milling process are the same as those for the first ball milling process. The ball milling is carried out for 12 hours. After ball milling, the rotary drying step is repeated and the mixture is sieved again to obtain the second mixture.

[0142] (6) PVA is added to the second mixture for dry pressing. The template for the molding process is a circular ceramic blank with a diameter of 10 mm and a thickness of 1 mm, to obtain a ceramic component.

[0143] (7) Place the ceramic blank with ceramic components in a heating furnace, heat it to 1150°C at a heating rate of 5°C / min, sinter and hold for 2 hours, then cool it to room temperature and take it out; polish and grind both sides clean, clean and dry to obtain lead-free ceramic.

[0144] Electrical performance tests were performed on the lead-free ceramics provided in Examples 1 to 5 and Comparative Examples 1 to 2. The tests included:

[0145] Energy storage density and energy storage efficiency testing: The lead-free ceramics to be tested were all polished to a thickness of 0.2 mm, and the electrodes were coated with gold electrodes. The size of the gold electrodes on both sides was 0.0314 cm. 2 During testing, the lead-free ceramic to be tested is immersed in silicone oil. By obtaining the PE curve from the test, the maximum polarization intensity, remanent polarization intensity, and coercive field magnitude can be obtained, and then the effective energy storage density and energy storage efficiency of the material can be calculated.

[0146] Charge-discharge test: Apply voltage to both ends of the lead-free ceramic under test, then suddenly remove the voltage and observe the relationship between its discharge waveform and discharge time. The test mainly examines two states: overdamped and underdamped. The results are calculated using the following formula.

[0147]

[0148] In the formula I max S is the peak current (A), and S is the electrode area (cm²). 2 E is the applied electric field strength (kV / cm), and h is the sample thickness (mm).

[0149] The results are shown in the table below:

[0150]

[0151] As can be seen from the table above, the lead-free ceramics provided in the embodiments of this application have good energy conversion efficiency and energy storage characteristics.

[0152] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0153] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b or c" or "at least one of a, b and c" can both mean: a, b, c, ab (i.e. a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0154] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A lead-free ceramic, characterized in that, The lead-free ceramic comprises materials with the chemical formula xSrTiO3-yBi a K b TiO3-zBi(Zn c Ti d The main components represented by O3 are: x+y+z=1, a+b=1, c+d=1; 0.78≤x≤0.92; 0.05≤y≤0.13; 0.03≤z≤0.

09. 0.4≤a≤0.6； 0.4≤b≤0.6； 0.4≤c≤0.6； 0.4≤d≤0.6。 2. The lead-free ceramic according to claim 1, characterized in that, The main component satisfies at least one of the following conditions (1) to (4): （1）0.45≤a≤0.55； （2）0.45≤b≤0.55； （3）0.45≤c≤0.55； （4）0.45≤d≤0.55。 3. The lead-free ceramic according to claim 2, characterized in that, The lead-free ceramic comprises materials with the chemical formula 0.88SrTiO3-0.07Bi. 0.5 K 0.5 TiO3-0.05Bi(Zn 0.5 Ti 0.5 O3 represents the main component.

4. The lead-free ceramic according to any one of claims 1 to 3, characterized in that, The main component accounts for ≥90% of the mass of the lead-free ceramic.

5. The lead-free ceramic according to claim 4, characterized in that, The main component accounts for 95% to 100% of the mass of the lead-free ceramic.

6. A method for preparing lead-free ceramic according to any one of claims 1 to 5, characterized in that, The method includes: The raw materials are mixed and subjected to a first ball milling process to obtain a first mixture; The first mixture is pre-sintered to obtain pre-sintered powder; The pre-sintered powder is subjected to a second ball milling process to obtain a second mixture; The second mixture is then molded to obtain a ceramic component; The ceramic component is sintered to obtain lead-free ceramic.

7. The method for preparing lead-free ceramics according to claim 6, characterized in that, The raw materials include Sr source, K source, Bi source, Ti source and Zn source.

8. The method for preparing lead-free ceramics according to any one of claims 6 to 7, characterized in that, The sintering temperature is 1000℃~1300℃; and / or The sintering treatment time is 1 hour to 3 hours; and / or The heating rate of the sintering process is 3℃ / min to 7℃ / min.

9. A capacitor, characterized in that, The capacitor is made of lead-free ceramic as described in any one of claims 1 to 5.

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