Lead-free relaxor ferroelectric ceramic material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of energy storage ceramic materials, in particular to a lead-free relaxor ferroelectric ceramic material and a preparation method and application thereof. The composition of the ceramic material has the following chemical formula: (SrxCayBiz) TiO3 + nM, in the formula, x, y, z and n are atomic numbers, x + y + 3z / 2 = 1, and n is greater than 0 and less than or equal to 0.5; m is a metal oxide. According to the ceramic material, through the multi-scale collaborative design of'ion doping-defect regulation and control-domain structure engineering ', the ceramic material has the characteristics of ultralow loss and quick response while keeping a high dielectric constant, and can have the cycle service life of more than 100 thousand times.

Description

Technical Field

[0001] This application relates to the technical field of energy storage ceramic materials, and particularly relates to a lead-free relaxor ferroelectric ceramic material, a preparation method thereof, and an application thereof. Background Art

[0002] Pulse energy storage ceramic capacitors have characteristics such as good temperature stability, high energy storage efficiency, and high power density, and have broad application prospects in fields such as high-power pulse systems, new energy vehicles, communication, and electronic devices. Traditional pulse energy storage ceramics are mainly lead-based ceramic materials. However, lead-based ceramic materials have a greater impact on the environment, and the recycling and treatment of lead-based ceramic materials are relatively complex. Therefore, using lead-free ceramic materials to replace lead-based ceramic materials has become an existing trend.

[0003] In order to maintain the high energy storage density requirement of pulse energy storage ceramic capacitors, lead-free ceramic materials usually use antiferroelectrics as dielectrics. However, using traditional antiferroelectrics will greatly affect the function and energy consumption of lead-free ceramic materials, and ultimately reduce the service life of pulse energy storage ceramic capacitors. Summary of the Invention

[0004] This application provides a lead-free relaxor ferroelectric ceramic material, a preparation method thereof, and an application thereof to solve the following technical problem: how to improve the service life of lead-free ceramic materials.

[0005] In a first aspect, an embodiment of this application provides a lead-free relaxor ferroelectric ceramic material. The composition of the ceramic material has the following chemical formula: (Sr x Ca y Bi z )TiO3 + nM, where x, y, z, and n are the number of atoms, x + y + 3z / 2 = 1, and 0 < n ≤ 0.5; M is a metal oxide.

[0006] Optionally, the number of atoms x, y, and z satisfy the relationship: 0 < x < 1, 0.1 ≤ y ≤ 0.5, and 0 < z ≤ 0.5.

[0007] Optionally, the metal oxide is selected from one of the following: La2O3, Sm2O3, Nb2O5, MgO, ZrO2, and Al2O3.

[0008] In a second aspect, an embodiment of this application provides a method for preparing the lead-free relaxor ferroelectric ceramic material described in the first aspect. The method includes:

[0009] Pre-treat the metal oxide powder and titanate powder of the ceramic material to obtain a mixed powder;

[0010] Heat-treat the mixed powder so that the mixed powder forms a single perovskite phase to obtain perovskite powder;

[0011] Perform sand grinding on the perovskite powder to obtain a sintering raw material;

[0012] Mix the binder and the sintering raw material to obtain a green body of the sintering raw material;

[0013] Perform sintering treatment on the green body of the sintering raw material to obtain a ceramic material.

[0014] Optionally, the temperature of the heat treatment is 900°C to 1100°C, and the time of the heat treatment is 2h to 4h.

[0015] Optionally, the sintering treatment includes a heating sintering section, a first heat preservation section, a cooling section, and a second heat preservation section. The end temperature of the heating sintering section is 1200°C to 1300°C, the time of the first heat preservation section is 10min to 30min, the temperature of the cooling section is 1100°C to 1150°C, and the time of the second heat preservation section is 3h to 6h.

[0016] Optionally, the mass m1 of the binder and the mass m2 of the sintering raw material satisfy the relational expression: m1:m2 = (0.5 to 2.0):100.

[0017] Optionally, the grain size of the ceramic material is 0.5μm to 1.2μm.

[0018] In a third aspect, an embodiment of the present application provides a lead-free relaxor ferroelectric ceramic capacitor. The ceramic capacitor includes the lead-free relaxor ferroelectric ceramic material described in the first aspect, and a conductive paste covering the surface of the ceramic material.

[0019] In a fourth aspect, an embodiment of the present application provides a method for manufacturing the ceramic capacitor described in the third aspect. The method includes:

[0020] Print the conductive paste on the surface of the ceramic material to obtain a rough blank of the ceramic capacitor;

[0021] Perform co-heat treatment on the rough blank of the ceramic capacitor to obtain a ceramic single-chip capacitor; wherein, the temperature of the co-heat treatment is 600°C to 700°C, and the time of the co-heat treatment is 20min to 30min;

[0022] Assemble a plurality of the ceramic single-chip capacitors to obtain an electric ceramic capacitor.

[0023] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0024] An embodiment of the present application provides a lead-free relaxor ferroelectric ceramic material. The ceramic material is based on a Sr-Ca-Bi-based ceramic material that satisfies the condition of x + y + 2z / 3 = 1. By adding metal oxides, the macroscopic ferroelectric domains of the ceramic material can be decoupled into dynamic nano-domains, significantly improving the relaxation characteristics of the ceramic material. At the same time, the metal oxides can also inhibit the leakage current of the ceramic material, reduce the dielectric loss of the ceramic material, and increase the dielectric constant of the ceramic material. In addition, the metal ions of the metal oxides can partially replace titanium. This substitution process will generate oxygen vacancies and form a defect dipole group. Under the action of an external electric field, the defect dipole group will cooperate with the main lattice dipoles of the ceramic material to respond. On the one hand, it will reduce the hysteresis effect of the dipole response during the polarization and depolarization processes of the ceramic material. On the other hand, it will reduce the dipole flipping activation energy and increase the speed of the dipole response. In addition, the lone pair electrons of Bi in the ceramic material will form a local electric field with the oxygen vacancies to stabilize the domain wall movement path, inhibit irreversible domain flipping, and reduce the remanent polarization intensity of the ceramic material. When charging and discharging are carried out under the condition of an externally applied repetitive pulse electric field, the ceramic material with a low remanent polarization intensity, a high dipole response speed, and a high dielectric constant can effectively reduce the stress accumulation and heat generation of the ceramic material, so as to effectively extend the service life of the ceramic material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 It is a schematic diagram of the product of a lead-free relaxor ferroelectric ceramic material provided by an embodiment of the present application;

[0028] Figure 2 It is a schematic diagram of the process flow of a method for preparing a lead-free relaxor ferroelectric ceramic material provided by an embodiment of the present application;

[0029] Figure 3 It is a schematic diagram of the structure of a lead-free relaxor ferroelectric ceramic capacitor provided by an embodiment of the present application;

[0030] Figure 4 It is a schematic diagram of the process flow of a method for preparing a ceramic capacitor provided by an embodiment of the present application;

[0031] Figure 5The figure showing the dependence characteristics of the dielectric constant and loss frequency of a lead-free relaxor ferroelectric ceramic material provided in Embodiment 1 of the present application;

[0032] Figure 6 The figure showing the ferroelectric hysteresis loop result of a lead-free relaxor ferroelectric ceramic capacitor provided in Embodiment 1 of the present application;

[0033] Figure 7 The figure showing the discharge performance of the ceramic capacitor provided in Embodiment 1 of the present application before and after cyclic use under a DC pulsed voltage, where Figure 7 A is the figure showing the discharge performance of the ceramic capacitor before cyclic use under a DC pulsed voltage, Figure 7 B is the figure showing the discharge performance of the ceramic capacitor after cyclic use under a DC pulsed voltage. Detailed implementation manners

[0034] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0035] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and single values within that range; for example, it should be considered that the description of the range 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 that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0036] In this text, terms such as "including" mean "including but not limited to". Relative terms such as "first" and "second" are only used 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. "And / or", which describes the association relationship of associated objects, indicates that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, "multiple" means two or more; "at least one kind", "at least one of the following items" or similar expressions refer to any combination of these items, including any combination of single item 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, a-b (that is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively. "Part representation methods" such as parts by weight and parts by mass represent the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by the ratio should be understood as the antecedents of the ratio formula in the order of description, and the ratio numbers should be understood as the consequents of the ratio formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the ratio numbers in the ratio formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0037] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in this text can be obtained through market purchases or can be prepared by existing methods.

[0038] It should be noted that the antiferroelectrics used in traditional lead-free ceramic materials have a domain structure with antiparallel arrangements. When the pulsed energy storage ceramic capacitor is subjected to an electric field with a repetitive frequency, these domain structures will undergo strong inter-domain friction, resulting in high energy consumption losses and even causing the pulsed energy storage ceramic capacitor to overheat severely; in addition, after cyclic discharge for a period of time, the lead-free ceramic material will cause the remanent polarization intensity to increase irreversibly and sharply due to the pinning effect. These defects will greatly reduce the service life of the pulsed energy storage ceramic capacitor.

[0039] Therefore, a ceramic material with relaxor properties can be used for this lead-free ceramic material to mitigate the damage to the antiferroelectrics.

[0040] Figure 1 Exemplarily shown is a schematic diagram of a lead-free relaxor ferroelectric ceramic material product provided by an embodiment of the present application;

[0041] AsFigure 1 As shown, an embodiment of the present application provides a lead-free relaxor ferroelectric ceramic material, and the composition of the ceramic material has the following chemical formula: (Sr x Ca y Bi z )TiO3 + nM, where x, y, z, and n are the number of atoms, x + y + 2z / 3 = 1, and 0 < n ≤ 0.5; M is a metal oxide.

[0042] It should be noted that the number of atoms x, y, z, and n are all obtained by proportioning according to the way of valence balance, and to a certain extent, they can represent the molar ratio of these elements in the ceramic material.

[0043] It should be noted that an embodiment of the present application provides a lead-free relaxor ferroelectric ceramic material. Through the multi-scale collaborative design of "ion doping - defect regulation - domain structure engineering", the ceramic material has ultra-low dielectric loss and fast response speed while maintaining a high dielectric constant, effectively improving the service life of the ceramic material. The specific principle is as follows:

[0044] 1. Structure regulation and enhancement of relaxor characteristics:

[0045] Introducing metal oxides (such as La2O3, ZrO2, etc.) into the Sr-Ca-Bi-based ceramic material can cause lattice distortion through ion doping. Taking La2O3 as an example, La 3 +(the ionic radius is ) can partially replace Sr 2+ (the ionic radius is ) or Ca 2+ (the ionic radius is ), which will cause the non-uniform distortion of TiO6 octahedrons, destroy the long-range ferroelectric ordered structure, and form a large number of nano-domains with short dynamic polar micro-regions. These nano-domains can flip independently under the action of an external electric field, significantly enhancing the relaxor characteristics of the ceramic material and simultaneously suppressing the energy loss caused by macroscopic domain wall friction.

[0046] 2. Defect engineering and conductance suppression:

[0047] When high-valence ions (such as Nb 5+ , Al 3+ ) in the metal oxide replace Ti 4+ , oxygen vacancies will be generated in the ceramic material due to the influence of charge compensation. These oxygen vacancies and surrounding cations (such as Bi 3(+) Local defect dipole groups will be formed, whose directions cooperate with the external electric field to reduce the hysteresis effect of the main lattice dipole flipping. In addition, wide-bandgap oxides (such as Al2O3, Eg = 8.8 eV) will form electron traps at grain boundaries, which will reduce the leakage conduction current density and dielectric loss at the same time.

[0048] 3. Dynamic response optimization and polarization regulation:

[0049] Bi 3+ 's 6s 2 The lone pair electrons can act together with oxygen vacancies to form a local electric field in the lattice of the ceramic material and guide the 90° domain walls to move along a specific path, inhibiting the irreversible 180° domain flipping. This effect can reduce the remanent polarization intensity (Pr). In addition, ZrO2 doping will reduce the recovery potential barrier of TiO6 octahedra, and the dipole response speed is increased to the sub-microsecond level, improving the charge-discharge efficiency of the ceramic material.

[0050] 4. Fatigue resistance and thermal stability improvement:

[0051] Under the action of the repetitive pulsed electric field, the cooperative flipping of dynamic nano-domains will disperse the mechanical stress of the ceramic material. In addition, La2O3 nanoparticles at grain boundaries will form an elastic buffer layer, and after multiple charge-discharge cycles, the growth of the remanent polarization intensity is low; in addition, the ceramic material with low dielectric loss can control the temperature rise value at a low level, avoiding the risk of thermal runaway of the ceramic material.

[0052] In summary, a lead-free relaxor ferroelectric ceramic material provided by an embodiment of the present application, through the multi-scale collaborative design of "ion doping - defect regulation - domain structure engineering", while maintaining a high dielectric constant, enables the ceramic material to have the characteristics of ultra-low loss and fast response. In addition, based on the lead-free characteristics and excellent cycle stability of the ceramic material, a solution for the core dielectric material with both high performance and low cost is provided for the next generation of pulsed power devices.

[0053] In some alternative embodiments, the atomic numbers x, y, and z satisfy the relationship: 0 < x < 1, 0.1 ≤ y ≤ 0.5, and 0 < z ≤ 0.5.

[0054] In these embodiments, x, y, and z satisfy the relationship: 0 < x < 1, 0.1 ≤ y ≤ 0.5, and 0 < z ≤ 0.5, enabling the ceramic material to form a Sr-Ca-Bi-based ceramic material crystal that meets expectations, facilitating the subsequent incorporation of metal oxides.

[0055] In some alternative embodiments, the metal oxide is selected from one of the following: La2O3, Sm2O3, Nb2O5, MgO, ZrO2, and Al2O3.

[0056] In these embodiments, a metal oxide selected from one of La2O3, Sm2O3, Nb2O5, MgO, ZrO2 and Al2O3 can be effectively doped into the Sr-Ca-Bi-based ceramic material to improve the dielectric constant, dielectric loss and response speed of the ceramic material, thereby effectively increasing the service life of the ceramic material.

[0057] Figure 2 Exemplarily, a schematic flow chart of a method for preparing a lead-free relaxor ferroelectric ceramic material provided by an embodiment of the present application is shown;

[0058] Based on a general inventive concept, as Figure 2 shown, an embodiment of the present application provides a method for preparing the lead-free relaxor ferroelectric ceramic material, and the method includes:

[0059] S1. Pretreat the metal oxide powder and titanate powder of the ceramic material to obtain a mixed powder;

[0060] S2. Heat-treat the mixed powder so that the mixed powder forms a single perovskite phase to obtain a perovskite powder;

[0061] S3. Grind the perovskite powder to obtain a sintering raw material;

[0062] S4. Mix the binder and the sintering raw material to obtain a sintering raw material blank;

[0063] S5. Sinter the sintering raw material blank to obtain a ceramic material.

[0064] This method is for the preparation method of the above-mentioned ceramic material. The specific composition and structure of the ceramic material can refer to the above embodiments. Since this method adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0065] It should be noted that by first pretreating the metal oxide powder and titanate powder of the ceramic material, these metal raw materials can be distributed in a specific molar ratio (0 < x < 1, 0.1 ≤ y ≤ 0.5, 0 < z ≤ 0.5, 0 < n ≤ 0.5); then through heat treatment, the metal phase of the mixed powder is transformed into a single perovskite phase to obtain a perovskite powder with a sufficient perovskite phase; then through grinding, the perovskite powder can be further finely ground into a sintering raw material with a small particle size; then the binder is added to the sintering raw material, and through the binding action of the binder, the sintering raw material forms a sintering raw material blank; finally, through the sintering treatment of the sintering raw material blank, not only can the sintering raw material blank form a ceramic material, but also the binder of the sintering raw material blank can be removed to obtain a pure ceramic material.

[0066] It should be noted that the particle size of the sintering raw material finally obtained by this sand grinding is 400 nm.

[0067] It should be noted that this pretreatment may include a mixed grinding process of ball milling and wet milling, as well as a 60-mesh screening process. Before screening, the powder obtained by the mixed grinding process can also be dried.

[0068] In some alternative embodiments, the temperature of the heat treatment is 900 °C to 1100 °C, and the time of the heat treatment is 2 h to 4 h.

[0069] In these embodiments, the heat treatment at a temperature of 900 °C to 1100 °C and a time of 2 h to 4 h can cause the metal phase of the mixed powder to be fully transformed into the perovskite phase, obtaining perovskite powder with an abundant perovskite phase.

[0070] The temperature of this heat treatment can be 900 °C, 950 °C, 1000 °C, 1050 °C or 1100 °C.

[0071] The time of this heat treatment can be 2 h, 2.5 h, 3.0 h, 3.5 h or 4.0 h.

[0072] In some alternative embodiments, the sintering treatment includes a heating sintering section, a first heat preservation section, a cooling and temperature reduction section, and a second heat preservation section. The end temperature of the heating sintering section is 1200 °C to 1300 °C, the time of the first heat preservation section is 10 min to 30 min, the temperature of the cooling and temperature reduction section is 1100 °C to 1150 °C, and the time of the second heat preservation section is 3 h to 6 h.

[0073] In these embodiments, through the sintering treatment including a heating sintering section, a first heat preservation section, a cooling and temperature reduction section, and a second heat preservation section, the sintering raw material blank is fully heated in the heating sintering section, and then the phase transformation of the sintering raw material blank is promoted to fully proceed through the first heat preservation section to eliminate the pore structure of the sintering raw material blank, and then the abnormal growth of grains in the sintering raw material blank is inhibited through the cooling and temperature reduction section, so that the grains of the ceramic material are evenly distributed.

[0074] The end temperature of this heating sintering section can be 1200 °C, 1210 °C, 1220 °C, 1230 °C, 1240 °C, 1250 °C, 1260 °C, 1270 °C, 1280 °C, 1290 °C or 1300 °C.

[0075] The time of this first heat preservation section can be 10 min, 15 min, 20 min, 25 min or 30 min.

[0076] The temperature of this cooling and temperature reduction section can be 1100 °C, 1110 °C, 1120 °C, 1130 °C, 1140 °C or 1150 °C.

[0077] The time of the second heat preservation stage can be 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, 5.5 h or 6.0 h.

[0078] In some alternative embodiments, the mass m1 of the binder and the mass m2 of the sintering raw material satisfy the relational expression: m1:m2 = (0.5 - 2.0):100.

[0079] In these embodiments, the mass m1 of the binder and the mass m2 of the sintering raw material can satisfy the relational expression: m1:m2 = (0.5 - 2.0):100, so that sufficient binder can be added to the sintering raw material, and the sufficient binder can effectively bond the sintering raw material to facilitate the subsequent sintering process.

[0080] The value of the mass m1 of the binder can be 0.5, 1.0, 1.5 or 2.0.

[0081] In some alternative embodiments, the grain size of the ceramic material is 0.5 μm - 1.2 μm.

[0082] In these embodiments, the ceramic material with a grain size of 0.5 μm - 1.2 μm makes the grain distribution more uniform, and the grains are in the sub-micron state. These ceramic materials with sub-micron grains can facilitate the subsequent preparation and shaping of the ceramic material.

[0083] The grain size of the ceramic material can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm or 1.2 μm.

[0084] Figure 3 Exemplarily shown is a schematic structural diagram of a lead-free relaxor ferroelectric ceramic capacitor provided by an embodiment of the present application;

[0085] As Figure 3 shown, based on a general inventive concept, an embodiment of the present application provides a lead-free relaxor ferroelectric ceramic capacitor, and the ceramic capacitor includes the lead-free relaxor ferroelectric ceramic material and a conductive paste covering the surface of the ceramic material.

[0086] The lead-free relaxor ferroelectric ceramic capacitor is realized based on the above ceramic material. The specific composition of the ceramic material can refer to the above embodiments. Since the lead-free relaxor ferroelectric ceramic capacitor adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0087] Figure 4A schematic flow chart of a method for preparing a ceramic capacitor provided by an embodiment of the present application is exemplarily shown;

[0088] As Figure 4 shown, based on a general inventive concept, an embodiment of the present application provides a method for preparing the ceramic capacitor, and the method includes:

[0089] S1. Printing a conductive paste on the surface of the ceramic material to obtain a rough blank of the ceramic capacitor;

[0090] S2. Co-annealing the rough blank of the ceramic capacitor to obtain a ceramic single-chip capacitor; wherein, the temperature of the co-annealing is 600°C to 700°C, and the time of the co-annealing is 20 min to 30 min;

[0091] S3. Assembling a plurality of the ceramic single-chip capacitors to obtain an electric ceramic capacitor.

[0092] This method is for the preparation method of the above-mentioned ceramic capacitor. The specific composition of the ceramic capacitor can refer to the above embodiment. Since this method adopts some or all of the technical solutions of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment, and will not be elaborated one by one here.

[0093] It should be noted that the conductive paste can be silver or a mixed conductive paste of silver and palladium.

[0094] It should be noted that the printing method can be screen printing.

[0095] The following further elaborates the present application in conjunction with specific embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0096] Example 1

[0097] As Figure 1 shown, a lead-free relaxor ferroelectric ceramic material, the composition of the ceramic material has the following chemical formula:

[0098] (Sr 0.49 Ca 0.21 Bi 0.2 )TiO3 + 0.01ZrO2.

[0099] As Figure 2 shown, a method for preparing a lead-free relaxor ferroelectric ceramic material includes:

[0100] S1. Pretreating the oxide powder of the ceramic material and the titanate powder to obtain a mixed powder;

[0101] S2. Heat-treat the mixed powder so that the mixed powder forms a single perovskite phase, obtaining perovskite powder material;

[0102] S3. Grind the perovskite powder material to obtain sintering raw material;

[0103] S4. Mix the binder and the sintering raw material to obtain a sintering raw material blank;

[0104] S5. Subject the sintering raw material blank to a sintering treatment to obtain a ceramic material.

[0105] The temperature of the heat treatment is 1000 °C, and the time of the heat treatment is 4 h.

[0106] The sintering treatment includes a heating and sintering section, a first heat preservation section, a cooling and temperature reduction section, and a second heat preservation section. The end temperature of the heating and sintering section is 1260 °C, the time of the first heat preservation section is 120 min, the temperature of the cooling and temperature reduction section is 1000 °C, and the time of the second heat preservation section is 60 min.

[0107] The mass m1 of the binder and the mass m2 of the sintering raw material satisfy the relation: m1:m2 = 0.5:100.

[0108] The grain size of the ceramic material is 0.5 μm to 1.2 μm.

[0109] As Figure 3 shown, a lead-free relaxor ferroelectric ceramic capacitor, the ceramic capacitor includes a lead-free relaxor ferroelectric ceramic material, and a conductive paste covering the surface of the ceramic material.

[0110] As Figure 4 shown, a method for preparing a ceramic capacitor includes:

[0111] S1. Print the conductive paste on the surface of the ceramic material to obtain a rough blank of the ceramic capacitor;

[0112] S2. Subject the rough blank of the ceramic capacitor to a co-heat treatment to obtain a single-piece ceramic capacitor; wherein, the temperature of the co-heat treatment is 600 °C, and the time of the co-heat treatment is 20 min;

[0113] S3. Assemble a plurality of single-piece ceramic capacitors to obtain an electric ceramic capacitor.

[0114] Example 2

[0115] Compared with Example 1, this example has the following differences, and the rest are the same:

[0116] The composition of the ceramic material has the following chemical formula: (Sr 0.36 Ca 0.4 Bi 0.16)TiO3 + 0.05La2O3。

[0117] Example 3

[0118] Compared with Example 1, this example has the following differences, and the rest are the same:

[0119] The composition of the ceramic material has the following chemical formula: (Sr 0.4 Ca 0.33 Bi 0.18 )TiO3 + 0.10MgO。

[0120] Example 4

[0121] Compared with Example 1, this example has the following differences, and the rest are the same:

[0122] The end temperature of the thermal sintering section is 1200 °C, the time of the first heat preservation section is 30 min, the temperature of the cooling section is 1100 °C, and the time of the second heat preservation section is 6 h.

[0123] Example 5

[0124] Compared with Example 1, this example has the following differences, and the rest are the same:

[0125] The end temperature of the thermal sintering section is 1300 °C, the time of the first heat preservation section is 10 min, the temperature of the cooling section is 1150 °C, and the time of the second heat preservation section is 3 h.

[0126] Comparative Example 1

[0127] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0128] Use traditional commercial capacitor products, such as Huoju Electronics chip multi-layer ceramic capacitors.

[0129] Comparative Example 2

[0130] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0131] The composition of the ceramic material has the following chemical formula: (Sr 0.49 Ca 0.21 Bi 0.2 )TiO3。

[0132] Comparative Example 3

[0133] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0134] The composition of the ceramic material has the following chemical formula: (Sr 0.49 Ca 0.21 Bi 0.2)TiO3 + 0.6ZrO2。

[0135] Comparative Example 4

[0136] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0137] The end temperature of the thermal sintering section is 1100 °C, and the temperature of the cooling section is 1000 °C.

[0138] Comparative Example 5

[0139] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0140] The end temperature of the thermal sintering section is 1400 °C, and the temperature of the cooling section is 1200 °C.

[0141] Relevant experiments and effect data:

[0142] 1. Measure the dielectric loss (tanδ) of the ceramic material obtained in Example 1. Under the condition that the loss frequency is 1 kHz, the dielectric loss is as Figure 5 shown, and the tanδ of this ceramic material is <0.005.

[0143] 2. Measure the hysteresis loop of the ceramic capacitor obtained in Example 1 at room temperature, as Figure 6 shown. The remanent polarization (Pr) of this ceramic capacitor is below 0.5 μC / cm 2 .

[0144] 3. Under the action of a DC pulsed voltage with a working voltage of 3 kV and a repetition frequency of 10 Hz, measure the charge and discharge cycle times of the ceramic capacitor in Example 1. As a result, the charge and discharge cycle times of the ceramic capacitor in Example 1 are more than 100,000 times. In addition, before and after the action of the DC pulsed voltage, the discharge diagrams of this ceramic capacitor are statistically analyzed. The results show that after 100,000 cycles of processing, the discharge capabilities of the ceramic capacitors are not very different.

[0145] 4. Under the action of a DC pulsed voltage with a working voltage of 3 kV and a repetition frequency of 10 Hz, measure the service lives of the capacitors in each example and comparative example respectively. The results are shown in Table 1.

[0146] Table 1 Service Lives of Capacitors in Each Example and Comparative Example

[0147]

[0148] As can be seen from Table 1, compared with Example 1, for the existing mature Huoju Electronics multilayer ceramic chip capacitor used in Comparative Example 1, its cyclic service life is only 3000 times, while the cycle times of the ceramic capacitor in Example 1 are more than 100,000 times, which is more than 30 times that of the capacitor in Comparative Example 1.

[0149] Compared with Example 1, in Comparative Example 2, metal oxide is not added, and in Comparative Example 3, an excessive amount of metal oxide is added, both of which will affect the cycle service life of the ceramic capacitor. Excessive addition of metal oxide may cause the lattice of the ceramic capacitor to be overly filled with metal oxide ions, affecting the activity of the dynamic nano-domains of the ceramic capacitor, and will also lead to the degradation of the electrical properties of the ceramic capacitor, affecting the mechanical properties and reliability of the ceramic capacitor.

[0150] Compared with Example 1, using lower temperatures in the thermal sintering section and the cooling section in Comparative Example 4 will affect the performance of the final ceramic capacitor; in addition, using higher temperatures in the thermal sintering section and the cooling section in Comparative Example 5 will also affect the performance of the final ceramic capacitor, resulting in a decrease in the service life of these ceramic capacitors.

[0151] In summary, an unleaded relaxor ferroelectric ceramic material provided by an embodiment of the present application, through multi-scale collaborative design of "ion doping - defect regulation - domain structure engineering", while maintaining a high dielectric constant, enables the ceramic material to have the characteristics of ultra-low loss and fast response, and can have a cycle service life of more than 100,000 times.

[0152] In addition, an unleaded relaxor ferroelectric ceramic material provided by an embodiment of the present application, based on the lead-free property and excellent cycle stability of the ceramic material, provides a solution for the core dielectric material with both high performance and low cost for the next generation of pulse power devices.

[0153] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A lead-free relaxor ferroelectric ceramic material, the composition of the ceramic material having the following chemical formula: (Sr x Ca y Bi z )TiO3 + nM, where x, y, z, and n are the number of atoms, x + y + 3z / 2 = 1, and 0 < n ≤ 0.5; M is a metal oxide.

2. The ceramic material according to claim 1, characterized in that, The atomic numbers x, y, and z satisfy the relationship: 0 < x < 1, 0.1 ≤ y ≤ 0.5, and 0 < z ≤ 0.

5.

3. The ceramic material according to claim 1, characterized in that, The metal oxide is selected from one of the following: La2O3, Sm2O3, Nb2O5, MgO, ZrO2, and Al2O3.

4. A method for preparing the lead-free relaxor ferroelectric ceramic material according to any one of claims 1 to 3, the method comprising: Pre-treating the metal oxide powder and the titanate powder of the ceramic material to obtain a mixed powder; Performing heat treatment on the mixed powder so that the mixed powder forms a single perovskite phase to obtain a perovskite powder; Performing sand grinding on the perovskite powder to obtain a sintering raw material; Mixing a binder and the sintering raw material to obtain a sintering raw material blank; Performing sintering treatment on the sintering raw material blank to obtain a ceramic material.

5. The method according to claim 4, wherein The temperature of the heat treatment is 900 °C to 1100 °C, and the time of the heat treatment is 2 h to 4 h.

6. The method according to claim 4, characterized in that The sintering treatment includes a heating sintering section, a first heat preservation section, a cooling section, and a second heat preservation section. The end temperature of the heating sintering section is 1200 °C to 1300 °C, the time of the first heat preservation section is 10 min to 30 min, the temperature of the cooling section is 1100 °C to 1150 °C, and the time of the second heat preservation section is 3 h to 6 h.

7. The method according to claim 6, wherein The mass m1 of the binder and the mass m2 of the sintering raw material satisfy the relationship: m1:m2 = (0.5 to 2.0):

100.

8. The method according to claim 6, wherein The grain size of the ceramic material is 0.5 μm to 1.2 μm.

9. A lead-free relaxor ferroelectric ceramic capacitor, the ceramic capacitor comprising the lead-free relaxor ferroelectric ceramic material according to any one of claims 1 to 3, and a conductive paste covering the surface of the ceramic material.

10. A method for preparing the ceramic capacitor according to claim 9, the method comprising: Printing the conductive paste on the surface of the ceramic material to obtain a rough ceramic capacitor blank; Performing co-heat treatment on the rough ceramic capacitor blank to obtain a ceramic single-chip capacitor; wherein, the temperature of the co-heat treatment is 600 °C to 700 °C, and the time of the co-heat treatment is 20 min to 30 min; Assembling a plurality of the ceramic single-chip capacitors to obtain an electric ceramic capacitor.

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