Sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields and preparation methods thereof

Abstract

The sodium bismuth titanate-based ceramic material with high energy storage density under low electric field disclosed by the present invention has a chemical composition general formula of (1-x)(Bi 0.5 Na 0.5 Ti03-BaTiO3)-xCa 0.5 TaO3, where x is 0.01 to 0.15; the preparation method of the sodium bismuth titanate-based ceramic material with high energy storage density under low electric field of the present invention comprises the following steps: proportioning according to the stoichiometric ratio of the chemical composition general formula, and successively performing primary ball milling, primary drying, pre-sintering, secondary ball milling, secondary drying, sieving, tabletting, cold isostatic pressing and sintering to obtain the sodium bismuth titanate-based ceramic material with high energy storage density under low electric field. The sodium bismuth titanate-based ceramic material and the preparation method thereof of the present invention introduce a third component into the matrix, have small grain size, low remanent polarization intensity, and extremely high energy storage density under low electric field; adopt the cold isostatic pressing technology, save costs, have high and uniform green body density, and small internal stress in the green body; and are environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium bismuth titanate-based ceramic materials, and particularly relates to sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields, and also relates to a preparation method of the above-mentioned sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields. Background Art

[0002] Ceramic materials have the advantages of high dielectric constant, wide working temperature range, corrosion resistance, long cycle life, high mechanical strength, simple preparation, etc. According to the type of P-E curve of ceramics, they can be divided into four categories: linear materials, ferroelectrics, relaxor ferroelectrics, and antiferroelectrics. Among them, ferroelectrics have a relatively high remanent polarization intensity and a relatively low breakdown electric field. Therefore, people pay more attention to their piezoelectric properties and less to their energy storage properties. While linear materials, relaxor ferroelectrics, and antiferroelectrics have a large polarization difference (ΔP = P m -P r ), and have received extensive attention and research.

[0003] Sodium bismuth titanate Bi 0.5 Na 0.5 TiO3-based ceramics usually have a higher effective energy storage density W rec under low electric fields. This is mainly because the hybridization of the 6p orbit of Bi atoms and the 2p orbit of O atoms in their structure leads to a high polarization intensity. However, their relatively low breakdown electric field E b limits the further improvement of the effective energy storage density W rec . At present, the development of lead-free energy storage ceramics faces two major challenges. One is that it is difficult to obtain both high energy storage density and high energy storage efficiency in the same energy storage ceramic material; the other is that high energy storage density often needs to be obtained at a very high electric field strength, which limits the practical application of ceramic materials. Summary of the Invention

[0004] The purpose of the present invention is to provide sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields, which have the characteristic of high energy storage performance under low electric fields.

[0005] Another purpose of the present invention is to provide a preparation method of the above-mentioned sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields, which has the characteristics of simple process, good repeatability, and low cost.

[0006] The technical solution adopted by the present invention is that the sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields have a chemical composition general formula of (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3) - xCa 0.5 TaO3, where the value of x ranges from 0.01 to 0.15.

[0007] The characteristics of the present invention also lie in:

[0008] x is 0.12.

[0009] Another technical solution adopted by the present invention is a preparation method of a sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field. The specific steps are as follows:

[0010] According to the chemical composition general formula (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5 TaO3, where x is 0.01 - 0.15. Weigh the following raw materials respectively: Bi2O3 powder, Na2CO3 powder, BaCO3 powder, TiO2 powder, CaCO3 powder, Ta2O5 powder. After mixing all the weighed raw materials, perform primary ball milling, primary drying, pre-sintering, secondary ball milling, secondary drying, sieving, tabletting, cold isostatic pressing and sintering in sequence to obtain a sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field.

[0011] The characteristics of another technical solution of the present invention also lie in that

[0012] The purity of each weighed raw material is ≥99.00%.

[0013] The time of both primary ball milling and secondary ball milling is 20h - 28h, and the ball milling medium is anhydrous ethanol; both primary drying and secondary drying are carried out at 60°C - 100°C for 20h - 28h.

[0014] Pre-sintering is carried out by heating at a heating rate of 3°C / min to 700°C - 900°C for 2h - 4h.

[0015] Pre-sintering is carried out by heating at a heating rate of 3°C / min to 850°C for 3h.

[0016] Sieving is carried out using a 120 - mesh to 300 - mesh sieve to obtain the pre-sintered powder.

[0017] Tabletting is carried out by using a powder tabletting machine to press into a cylindrical green body; the conditions of cold isostatic pressing are: cold isostatic pressing at a pressure of 200MPa - 240MPa for 4min - 8min; the sintering conditions are heating at a heating rate of 3°C / min to 1100°C - 1200°C for 2h - 4h.

[0018] The conditions of cold isostatic pressing are: cold isostatic pressing at a pressure of 200MPa for 6min; the sintering conditions are heating at a heating rate of 3°C / min to 1150°C for 3h.

[0019] The beneficial effects of the present invention are:

[0020] The sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field of the present invention, in (Bi0.5 Na 0.5 Introduce the third component Ca into the (Bi 0.5 TaO3 matrix, thereby inhibiting grain growth, gradually reducing the grain size, and decreasing its remanent polarization intensity, which helps to obtain an elongated hysteresis loop and has an extremely high energy storage density under low electric fields;

[0021] The preparation method of the sodium bismuth titanate-based ceramic material with high energy storage density under low electric fields of the present invention adopts cold isostatic pressing forming technology, which avoids waste of samples, eliminates binders and subsequent debinding processes, saves costs, and shortens the preparation cycle; at the same time, the green body formed by cold isostatic pressing has a high density, uniform density, and small internal stress in the green body, reducing the occurrence of green body cracking, delamination, etc., improving the quality; the raw materials selected do not contain lead heavy metals and are environmentally friendly. Description of the Drawings

[0022] Figure 1 XRD patterns of Examples 1 to 4 of the sodium bismuth titanate-based ceramic material with high energy storage density under low electric fields of the present invention;

[0023] Figure 2 Tungsten filament scanning electron microscope image of Example 3 of the present invention;

[0024] Figure 3 Unipolar hysteresis loop diagrams of Examples 1 to 4 of the present invention;

[0025] Figure 4 Unipolar hysteresis loop diagrams of Example 3 of the present invention under different electric fields;

[0026] Figure 5 Variation diagrams of the saturation polarization intensity, remanent polarization intensity, and polarization intensity difference of Examples 1 to 4 of the present invention;

[0027] Figure 6 Variation diagrams of the energy storage density and energy storage efficiency of Examples 1 to 4 of the present invention. Detailed Embodiments

[0028] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0029] The sodium bismuth titanate-based ceramic material with high energy storage density under low electric fields of the present invention has a chemical composition general formula of (1-x)(Bi 0.5 Na 0.5 TiO3-BaTiO3)-xCa 0.5TaO3, where the value of x ranges from 0.01 to 0.15. In this value range, it is a relaxor ferroelectric with a high energy storage density, which can meet the requirements of capacitors for achieving a high energy storage density under a low electric field. If outside this range, it becomes a linear ferroelectric, and the saturation polarization intensity of the ceramic will also decrease sharply, and the effective energy storage density will also decrease.

[0030] x is preferably 0.12, and its general composition formula is 0.88(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-0.12Ca 0.5 TaO3. Under an electric field of 250 KV / cm, the effective energy storage density is 5.10 J / cm 3 ~5.30 J / cm 3 The total energy storage density is 6.30 J / cm 3 ~6.60 J / cm 3 The energy storage efficiency is 80% - 84%, and the average grain size is 0.6 μm - 0.8 μm. When the electric field is 250 kV / cm, its saturation polarization intensity reaches 58.30 - 58.60 μC / cm 3 .

[0031] For the sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field of the present invention, in order to adjust the relaxor ferroelectric phase of the sodium bismuth titanate BNT ceramic at high temperature to near room temperature and obtain an energy storage ceramic with an elongated P-E curve, due to the nearly zero remanent polarization intensity P of the linear dielectric material r , an appropriate amount is introduced to effectively reduce the total remanent polarization intensity P of the system r , so the sodium bismuth titanate - barium titanate BNT - BT is selected as the basic material system for research; the third component calcium tantalate Ca 0.5 TaO3 is introduced. In the (Bi 0.5 Na 0.5 Ti03 - BaTiO3) matrix, the third component Ca 0.5 TaO3 is introduced, thereby inhibiting grain growth, gradually reducing the grain size, and reducing its remanent polarization intensity, which helps to obtain an elongated hysteresis loop and has an extremely high energy storage density under a low electric field.

[0032] The preparation method of the sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field of the present invention is specifically implemented according to the following steps:

[0033] According to the general chemical composition formula (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5TaO3, where x ranges from 0.01 to 0.15. Weigh the following raw materials respectively: Bi2O3 powder, Na2CO3 powder, BaCO3 powder, TiO2 powder, CaCO3 powder, Ta2O5 powder, and the purity of each raw material is above 99.00%; after mixing all the weighed raw materials evenly, put them into a nylon tank, mix well and perform primary ball milling for 20 h to 28 h, and perform primary drying at 60 °C to 100 °C for 20 h to 28 h to obtain a raw material mixture; heat the raw material mixture to 700 °C to 900 °C at a heating rate of 3 °C / min and pre-sinter for 2 h to 4 h. After secondary ball milling for 20 h to 28 h and drying at 60 °C to 100 °C for 20 h to 28 h, sieve with a 120-300 mesh sieve to obtain pre-sintered powder; press the pre-sintered powder into tablets, perform cold isostatic pressing at a pressure of 200 MPa to 240 MPa for 4 min to 8 min, and finally heat to 1100 °C to 1200 °C at a heating rate of 3 °C / min and sinter for 2 h to 4 h to obtain a sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field.

[0034] The ball milling media for both primary ball milling and secondary ball milling are anhydrous ethanol.

[0035] The preferred pre-sintering conditions are: pre-sinter the raw material mixture at 850 °C for 3 h;

[0036] Preferably, a powder press is used to press the tablets into cylindrical green bodies.

[0037] The preferred cold isostatic pressing conditions are: perform cold isostatic pressing at a pressure of 200 MPa for 6 min.

[0038] The preferred sintering conditions are: sinter at 1150 °C for 3 h.

[0039] In the preparation method of the sodium bismuth titanate-based ceramic material with a high energy storage density under a low electric field of the present invention, during the preparation process of the ceramic material, an advanced cold isostatic pressing forming technology is adopted, which avoids waste of samples, eliminates the binder and subsequent debinding process, saves costs, and shortens the preparation cycle of the ceramic; at the same time, the green body formed by cold isostatic pressing has a high density, uniform density, and small internal stress in the green body, reducing defects such as cracking and delamination of the green body, which guarantees the quality of the ceramic, and the raw materials selected in the present invention do not contain lead heavy metals and are environmentally friendly.

[0040] Example 1

[0041] 1. Batching

[0042] According to (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5For the stoichiometric ratio of x = 0.01 in TaO3, 9.5992 g of Bi2O3 powder with a purity of 99%, 2.1660 g of Na2CO3 powder with a purity of 99.8%, 1.0281 g of BaCO3 powder with a purity of 99.95%, 6.9691 g of TiO2 powder with a purity of 99.5%, 0.1937 g of Ta2O5 powder with a purity of 99.99%, and 0.0439 g of CaCO3 powder with a purity of 99.99% were weighed respectively. After mixing them evenly, they were put into a nylon pot. Then, using zirconia balls as grinding balls and absolute ethanol as the ball-milling medium, they were fully mixed and ball-milled for 24 hours at a time. The zirconia balls were separated, and they were dried at 80 °C for 24 hours at a time, and then ground with a mortar to obtain a raw material mixture;

[0043] 2. The raw material mixture was placed in an alumina crucible, compacted with an agate rod, covered, and placed in an electric resistance furnace. It was heated to 850 °C at a heating rate of 3 °C / min, pre-sintered for 3 hours, naturally cooled to room temperature in the furnace, taken out of the furnace, ground with a mortar for 30 minutes, and then subjected to secondary ball-milling. The grinding balls were zirconia balls, and the ball-milling medium was absolute ethanol. It was ball-milled for 24 hours, placed in a drying oven and dried at 80 °C for 24 hours at a time, ground with a mortar for another 10 minutes, and sieved through a 180-mesh sieve to obtain a pre-sintered powder;

[0044] 3. The pre-sintered powder was put into a stainless-steel mold with a diameter of 11.5 mm, and it was pressed into a cylindrical green body with a thickness of 1.5 mm by a powder press without applying pressure. The cylindrical green body was put into a cold isostatic press and cold isostatically pressed at a pressure of 200 MPa for 6 minutes. The cylindrical green body was placed on a zirconia zirconium plate, and the zirconia zirconium plate was placed in an alumina sealed crucible. It was heated to 1150 °C at a heating rate of 3 °C / min, held for 3 hours, and naturally cooled to room temperature in the furnace to obtain a sodium bismuth titanate-based ceramic material sample with a high energy storage density under low electric fields. The chemical composition general formula is: 0.99(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-0.01Ca 0.5 TaO3.

[0045] Example 2

[0046] According to (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5For the stoichiometric ratio of x = 0.08 in TaO3, 8.8035 g of Bi2O3 powder with a purity of 99%, 1.9864 g of Na2CO3 powder with a purity of 99.8%, 0.9429 g of BaCO3 powder with a purity of 99.95%, 6.3914 g of TiO2 powder with a purity of 99.5%, 1.5293 g of Ta2O5 powder with a purity of 99.99%, and 0.3464 g of CaCO3 powder with a purity of 99.99% were weighed respectively;

[0047] Other steps were the same as in Example 1, and a sodium bismuth titanate-based ceramic material sample with a high energy storage density under low electric fields was obtained. The general chemical composition formula was: 0.92(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-0.08Ca 0.5 TaO3.

[0048] Example 3

[0049] According to the stoichiometric ratio of x = 0.12 in (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5 TaO3, 8.3581 g of Bi2O3 powder with a purity of 99%, 1.8859 g of Na2CO3 powder with a purity of 99.8%, 0.8952 g of BaCO3 powder with a purity of 99.95%, 6.0681 g of TiO2 powder with a purity of 99.5%, 2.2769 g of Ta2O5 powder with a purity of 99.99%, and 0.5157 g of CaCO3 powder with a purity of 99.99% were weighed respectively;

[0050] Other steps were the same as in Example 1, and a sodium bismuth titanate-based ceramic material sample with a high energy storage density under low electric fields was obtained. The general chemical composition formula was: 0.88(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-0.12Ca 0.5 TaO3.

[0051] Example 4

[0052] In step 1 of this example, according to (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5The stoichiometric ratio of x=0.15 in TaO3 was 8.0284g of Bi2O3 powder with a purity of 99%, 1.8115g of Na2CO3 powder with a purity of 99.8%, 0.8599g of BaCO3 powder with a purity of 99.95%, 5.8287g of TiO2 powder with a purity of 99.5%, 2.8304g of Ta2O5 powder with a purity of 99.99%, and 0.6411g of CaCO3 powder with a purity of 99.99% respectively.

[0053] The other steps are the same as those in Example 1, and a sodium bismuth titanate-based ceramic material sample with high energy storage density under low electric field is obtained, and the general chemical composition formula is: 0.85 (Bi 0.5 Na 0.5 Ti03-BaTiO3)-0.15Ca 0.5 TaO3.

[0054] Example 5

[0055] 1. Ingredients

[0056] According to (1-x)(Bi 0.5 Na 0.5 Ti03-BaTiO3)-xCa 0.5 The stoichiometric ratio of x=0.12 in TaO3 was respectively weighed: 8.3581 g of Bi2O3 powder with a purity of 99%, 1.8859 g of Na2CO3 powder with a purity of 99.8%, 0.8952 g of BaCO3 powder with a purity of 99.95%, 6.0681 g of TiO2 powder with a purity of 99.5%, 2.2769 g of Ta2O5 powder with a purity of 99.99%, and 0.5157 g of CaCO3 powder with a purity of 99.99%;

[0057] After being mixed evenly, the mixture is put into a nylon jar, and then zirconium balls are used as grinding balls and anhydrous ethanol is used as ball milling medium, the mixture is fully mixed and ball milled for 20 hours, the zirconium balls are separated, the mixture is dried at 100° C. for 20 hours, and the mixture is ground with a mortar to obtain a raw material mixture;

[0058] 2. Place the raw material mixture in an alumina crucible, compact it with an agate rod, cover it, place it in a resistance furnace, heat it to 800°C at a heating rate of 3°C / min, pre-sinter for 3 hours, cool it naturally to room temperature with the furnace, take it out of the furnace, grind it with a mortar for 30 minutes, and then perform secondary ball milling. The grinding balls are zirconium balls and the ball milling medium is anhydrous ethanol. Ball milling for 20 hours, place it in a drying oven at 100°C for secondary drying for 20 hours, grind it with a mortar for another 10 minutes, and sieve it with a 210-mesh screen to obtain pre-sintered powder;

[0059] 3. Place the pre-sintered powder into a stainless-steel mold with a diameter of 11.5 mm, and use a powder press to press it into a cylindrical green body with a thickness of 1.5 mm without applying pressure. Put the cylindrical green body into a cold isostatic press and perform cold isostatic pressing at a pressure of 220 MPa for 8 minutes. Place the cylindrical green body on a zirconia plate, and place the zirconia plate in an alumina sealed crucible. Heat it to 1200 °C at a heating rate of 3 °C / min, hold for 2 hours, and then cool it naturally in the furnace to room temperature to obtain a sodium bismuth titanate-based ceramic material sample with a high energy storage density under low electric fields;

[0060] The general chemical composition formula is: 0.88(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-0.12Ca 0.5 TaO3.

[0061] Example 6

[0062] 1. Batching

[0063] According to the stoichiometric ratio of x = 0.12 in (1 - x)(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-xCa 0.5 TaO3, weigh 8.3581 g of Bi2O3 powder with a purity of 99%, weigh 1.8859 g of Na2CO3 powder with a purity of 99.8%, weigh 0.8952 g of BaCO3 powder with a purity of 99.95%, weigh 6.0681 g of TiO2 powder with a purity of 99.5%, weigh 2.2769 g of Ta2O5 powder with a purity of 99.99%, and weigh 0.5157 g of CaCO3 powder with a purity of 99.99%;

[0064] After mixing evenly, put it into a nylon jar, then use zirconia balls as grinding balls and anhydrous ethanol as the ball-milling medium, mix well and perform primary ball-milling for 28 hours, separate the zirconia balls, dry at 60 °C for 28 hours for the first time, grind with a mortar to obtain a raw material mixture;

[0065] 2. Place the raw material mixture in an alumina crucible, compact it with an agate rod, cover it, place it in a resistance furnace, heat it to 900 °C at a heating rate of 3 °C / min, pre-sinter for 2 hours, cool it naturally in the furnace to room temperature, take it out of the furnace, grind with a mortar for 30 minutes and then perform secondary ball-milling. The grinding balls are zirconia balls and the ball-milling medium is anhydrous ethanol. Ball-mill for 28 hours, place it in a drying oven and dry at 60 °C for 28 hours for the second time, grind with a mortar for another 10 minutes, and sieve it through a 300-mesh sieve to obtain the pre-sintered powder;

[0066] 3. Place the pre-sintered powder into a stainless steel mold with a diameter of 11.5 mm, and use a powder tablet press to press it into a cylindrical body with a thickness of 1.5 mm without pressure. Place the cylindrical body in a cold isostatic press and cold isostatic press for 4 minutes at a pressure of 240 MPa. Place the cylindrical body on a zirconia plate, which is placed in an alumina sealed sagger, and heat it to 1100°C at a heating rate of 3°C / min, keep it warm for 4 hours, and cool it naturally to room temperature with the furnace to obtain a sodium bismuth titanate-based ceramic material sample with high energy storage density under low electric field;

[0067] The general chemical formula is: 0.88(Bi 0.5 Na 0.5 Ti03-BaTiO3)-0.12Ca 0.5 TaO3.

[0068] Example 7

[0069] 1. Ingredients

[0070] According to (1-x)(Bi 0.5 Na 0.5 Ti03-BaTiO3)-xCa 0.5 The stoichiometric ratio of x=0.12 in TaO3 was respectively weighed: 8.3581 g of Bi2O3 powder with a purity of 99%, 1.8859 g of Na2CO3 powder with a purity of 99.8%, 0.8952 g of BaCO3 powder with a purity of 99.95%, 6.0681 g of TiO2 powder with a purity of 99.5%, 2.2769 g of Ta2O5 powder with a purity of 99.99%, and 0.5157 g of CaCO3 powder with a purity of 99.99%;

[0071] After being mixed evenly, the mixture is put into a nylon jar, and then zirconium balls are used as grinding balls and anhydrous ethanol is used as ball milling medium, the mixture is fully mixed and ball milled for 20 hours, the zirconium balls are separated, the mixture is dried at 100° C. for 20 hours, and the mixture is ground with a mortar to obtain a raw material mixture;

[0072] 2. Place the raw material mixture in an alumina crucible, compact it with an agate rod, cover it, place it in a resistance furnace, heat it to 700°C at a heating rate of 3°C / min, pre-sinter it for 4 hours, cool it naturally to room temperature with the furnace, take it out of the furnace, grind it with a mortar for 30 minutes, and then perform secondary ball milling. The grinding balls are zirconium balls and the ball milling medium is anhydrous ethanol. Ball milling for 20 hours, place it in a drying oven at 100°C for secondary drying for 20 hours, grind it with a mortar for another 10 minutes, and sieve it with a 120-mesh screen to obtain pre-sintered powder;

[0073] 3. Put the pre-sintered powder into a stainless-steel mold with a diameter of 11.5 mm, and use a powder press to press it into a cylindrical green body with a thickness of 1.5 mm without applying pressure. Then put the cylindrical green body into a cold isostatic press and perform cold isostatic pressing at a pressure of 220 MPa for 8 minutes. Place the cylindrical green body on a zirconia zirconium plate, and the zirconia zirconium plate is placed in an alumina sealed crucible. Heat it to 1200 °C at a heating rate of 3 °C / min, hold for 2 hours, and then cool it naturally to room temperature in the furnace to obtain a sodium bismuth titanate-based ceramic material sample with a high energy storage density under a low electric field;

[0074] The general chemical composition formula is: 0.88(Bi 0.5 Na 0.5 Ti03 - BaTiO3)-0.12Ca 0.5 TaO3.

[0075] Grind, ultrasonically clean, and sputter gold on the surfaces of the sodium bismuth titanate-based ceramic materials with high energy storage density prepared in Examples 1 to 4 above. Characterize their properties using a ferroelectric tester produced by Radiant Corporation of the United States.

[0076] The XRD patterns of Examples 1 to 4 are as Figure 1 shown. It can be seen that there is the strongest single diffraction peak at about 2θ angle of 32°. By comparing with the BNT standard PDF card (PDF#97 - 004 - 3769), it can be known that the main crystal phase of these four groups of ceramic samples is the rhombohedral perovskite structure. Thus, it can be seen that CT has been solid-solved into the main lattice of BNT - BT. Figure 2 This is the scanning electron microscope image of the ceramic material prepared in Example 3. It can be calculated that its average grain size is only 0.7 μm, which can effectively increase its breakdown electric field.

[0077] Figure 3 This is the single-pole ferroelectric hysteresis loop diagram of the ceramic materials prepared in Examples 1 to 4. As the doping amount of the third component Ca 0.5 TaO3 increases, the ferroelectric hysteresis loop becomes gradually slender. When x = 0.12, that is, in Example 3, its ferroelectric hysteresis loop is the most excellent.

[0078] Figure 4 This is the single-pole ferroelectric hysteresis loop of the ceramic material prepared in Example 3 under different electric fields. It can be seen from the figure that as the electric field increases, its ferroelectric hysteresis loop gradually becomes slender, and the saturation polarization intensity also gradually increases, so that its effective energy storage density is also increased.

[0079] Figure 5 This is the diagram of the polarization intensity and the change in polarization intensity difference of the ceramic materials prepared in Examples 1 to 4. It can be seen from the figure that as the third element Ca 0.5With the increase of the doping amount of TaO3, the maximum polarization intensity of the ceramic material is improved. Under the critical breakdown electric field, its saturation polarization intensity reaches 58.46 μC / cm 3 , the remanent polarization intensity decreases, and the polarization intensity difference gradually increases, with the maximum polarization intensity difference at x = 0.12.

[0080] Figure 6 Figure shows the changes in the effective energy storage density, total energy storage density, and energy storage efficiency of the ceramic materials prepared in Examples 1 to 4. It can be seen from the figure that the ceramic materials have good ferroelectric energy storage characteristics. At x = 0.12, the effective energy storage density of the ceramic material prepared in Example 3 can reach 5.18 J / cm 3 , and the total energy storage density can reach 6.45 J / cm 3 , and the energy storage efficiency is 80%, achieving high energy storage characteristics at low electric fields.

[0081] The sodium bismuth titanate-based ceramic material with high energy storage density at low electric fields of the present invention realizes high energy storage density at low electric fields, which can further broaden the application range of electronic functional materials.

Claims

1. Sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields, characterized in that, The general chemical formula is (1-x)(Bi 0.5 Na 0.5 Ti03-BaTiO3)-xCa 0.5 TaO3, where the value of x ranges from 0.01 to 0.

15.

2. The sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 1, characterized in that, The x is 0.

12.

3. A preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields, characterized in that, The specific steps are as follows: According to the chemical composition general formula (1 - x)(Bi 0.5 Na 0.5 TiO3 - BaTiO3)-xCa 0.5 TaO3, where x is 0.01 - 0.15, respectively weigh the following raw materials: Bi2O3 powder, Na2CO3 powder, BaCO3 powder, TiO2 powder, CaCO3 powder, Ta2O5 powder. After mixing all the weighed raw materials, perform primary ball milling, primary drying, pre - sintering, secondary ball milling, secondary drying, sieving, tabletting, cold isostatic pressing and sintering in sequence to obtain a sodium bismuth titanate - based ceramic material with a high energy storage density under low electric fields.

4. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 3, characterized in that, The purity of each of the weighed raw materials is ≥99.00%.

5. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 3, characterized in that, The time of both the primary ball milling and the secondary ball milling is 20 h to 28 h, and the ball milling medium is anhydrous ethanol; both the primary drying and the secondary drying are carried out at 60 °C to 100 °C for 20 h to 28 h.

6. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 3, characterized in that, The pre-sintering is carried out by heating to 700 °C to 900 °C at a heating rate of 3 °C / min and pre-sintering for 2 h to 4 h.

7. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 6, characterized in that, The pre-sintering is carried out by heating to 850 °C at a heating rate of 3 °C / min and pre-sintering for 3 h.

8. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 3, characterized in that, The sieving is carried out by filtering with a 120-mesh to 300-mesh sieve to obtain the pre-sintered powder.

9. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 3, characterized in that, The tabletting is carried out by using a powder tabletting machine to press into a cylindrical green body; the cold isostatic pressing conditions are: cold isostatic pressing at a pressure of 200 MPa to 240 MPa for 4 min to 8 min; the sintering conditions are heating to 1100 °C to 1200 °C at a heating rate of 3 °C / min and sintering for 2 h to 4 h.

10. The preparation method of sodium bismuth titanate-based ceramic materials with high energy storage density under low electric fields according to claim 9, characterized in that, The cold isostatic pressing conditions are: cold isostatic pressing at a pressure of 200 MPa for 6 min; the sintering conditions are heating to 1150 °C at a heating rate of 3 °C / min and sintering for 3 h.

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