CN112479705A

CN112479705A - Barium titanate-based X8R dielectric material for multilayer ceramic capacitor and preparation method thereof

Info

Publication number: CN112479705A
Application number: CN202011207796.XA
Authority: CN
Inventors: 陈志武; 胡婉兵; 王歆; 卢振亚; 符小芝
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2020-11-03
Filing date: 2020-11-03
Publication date: 2021-03-12

Abstract

The invention discloses a dielectric material for barium titanate-based X8R type multilayer ceramic capacitor and a preparation method thereof, wherein the chemical formula of the material is BaTiO₃‑0.01A‑0.005Nd₂O₃‑x Bi₂O₃‑y Ho₂O₃+0.5 wt% of B, wherein x ═ y ═ 0.75 to 1.5 mol%. The preparation method comprises the following steps: 1) by Nb₂O₅And Co₂O₃Preparation of Nb-Co composite oxide dopant powder materialA; 2) with Zn (CH)₃COO)₂·2H₂O and H₃BO₃Preparing boron-zinc sintering aid powder B as a raw material; 3) mixing the materials according to the chemical formula, putting the raw materials into a ball mill, mixing and ball-milling the raw materials by a wet ball-milling method, and drying the raw materials to obtain ceramic powder; 4) grinding, granulating, sieving and dry-pressing the ceramic powder to obtain a ceramic green body; 5) and (4) removing the glue from the ceramic green body and sintering. The dielectric ceramic material prepared by the invention meets the temperature change rate DeltaC/C within the temperature range of-55-150 DEG C_25℃Less than or equal to 15 percent, dielectric constant of over 2400 at room temperature, and dielectric loss of not more than 2.0 percent at room temperature.

Description

Barium titanate-based X8R dielectric material for multilayer ceramic capacitor and preparation method thereof

Technical Field

The invention relates to a dielectric material for a ceramic capacitor, in particular to a barium titanate-based X8R type dielectric material for a multilayer ceramic capacitor with high-temperature stability and a preparation method thereof; belongs to the technical field of dielectric ceramics.

Background

A multilayer ceramic capacitor (MLCC) is a parallel chip electronic component formed by alternately arranging dielectric ceramic diaphragms and internal electrodes. Compared with other capacitors, the MLCC has the advantages of small volume, low price, small equivalent series resistance, good high-frequency characteristic, multiple product types and the like, is the most mainstream product in the capacitor market at present, and is widely applied to various electronic circuits and electronic equipment. With the expansion of the application range, the application requirement of the temperature-stable high-temperature capacitor device in special fields such as aerospace, automobile engines, national defense and military industry and the like is more and more urgent. Satisfying American Electronic Industries Association (Electronic Industries Association) X7R type (X represents the lowest temperature service temperature of-55 ℃; 7 represents the highest temperature of 125 ℃; R represents the maximum deviation of the allowable capacitance along with the temperature change and the capacitance value at the room temperature of 25 ℃ is not more than 15%, namely delta C/C₂₅The temperature is less than or equal to +/-15 percent). The multilayer ceramic capacitor of the X7R standard has not been able to meet the use requirements. Therefore, multilayer ceramic capacitors of the X8R type (8 stands for a maximum use temperature of 150 ℃) are becoming more and more the focus of research.

The current large-capacity lead-free temperature stable MLCC mainly consists of barium titanate (BaTiO)₃) Is typically of perovskite (ABO)₃) A structural room temperature ferroelectric material. The dielectric constant of the product is high and can reach 200 at room temperature0 to 3000, the dielectric loss is small, and meanwhile, the environment is not polluted in the production and use processes of the composite material, so that the composite material is particularly suitable for manufacturing high-performance dielectric materials. However, pure barium titanate has a curie temperature of about 120 ℃, a large dielectric constant, and a dielectric constant rapidly decreases after the temperature is higher or lower than the curie temperature, so that the temperature-holding characteristic requirements cannot be met.

The Chinese patent application CN103204677A discloses a high dielectric property X8R type ceramic capacitor dielectric material and a preparation method thereof, and the chemical composition general formula of the ceramic dielectric material satisfies: ba_1-xBi_xTiO₃+aNb₂O₅+bCo₂O₃+cNd₂O₃+dMnO₂+eZrO₂Wherein x is more than 0.010 and less than or equal to 0.045, a is 0.6 to 0.9 wt%, b is 0.1 to 0.2 wt%, c is 0.3 to 0.6 wt%, d is 0.01 to 0.03 wt%, e is 0.5 to 2.0 wt%, and the balance is Ba_1-xBi_xTiO₃. The performance of the ceramic dielectric material prepared by the invention reaches the following indexes: the ceramic wafer has sintering temperature of 1100-1200 deg.c, grain size of 0.1-0.5 micron and room temperature dielectric loss<1.0 percent. The technical raw material contains MnO₂+ZrO₂，MnO₂And ZrO₂Two main roles are played throughout the doped ceramic system, the first: zr⁴⁺Or Mn⁴⁺Equivalently substituted Ti⁴⁺Formation of BaTi_1-x(Zr,Mn)_xO₃The chemical uniformity of (2) doping the non-ferroelectric phase, and simultaneously slightly expanding the unit cell volume, so that the dielectric peak is widened and the Curie point is slightly raised integrally. Secondly, the method comprises the following steps: zr substituting for Ti site to make redundant TiO₂The liquid phase is formed by segregation at the grain boundary. Experiments have shown that excess TiO₂Can reduce BaTiO₃The starting temperature of the sintering shrinkage of the base ceramic. But Zr⁴⁺Or Mn⁴⁺Are all equivalent substitutions of Ti⁴⁺Are not acceptor doped (low valence doping replaces Ti)⁴⁺Is acceptor doped) or the problem of semiconducting of barium titanate ceramics during sintering in reducing atmosphere cannot be completely solved because of barium titanate ceramicsSintering the ceramic material in a reducing atmosphere to obtain Ti⁴⁺Is reduced to Ti³ ⁺And meanwhile, weak bound electrons and oxygen vacancies which can move freely are generated, so that n-type semi-conduction occurs in the dielectric material, the insulation resistance is greatly reduced, and the performance is degraded. The acceptor doping is a deep potential well of conductive electrons, and can play a role in binding free electrons, increasing insulation resistance and reducing conductivity. Namely, the doping element replaces Ti position to form acceptor doping, so as to obtain the anti-reduction dielectric material. Meanwhile, with the increasing number of MLCC lamination layers, the dosage of electrode materials is increased continuously, for example, the traditional noble metal electrode material palladium and silver are adopted, so that the preparation cost of the MLCC is higher, and the research and development of BME-MLCC using relatively cheap base metals such as nickel (Ni) and copper (Cu) as inner electrodes are promoted. Since Ni and Cu electrodes are easily oxidized when sintered in air, a green BEM-MLCC using Ni and Cu electrodes needs to be sintered in a reducing atmosphere (usually a nitrogen-hydrogen mixture) to ensure the electrical conductivity of the electrodes. However, sintering of barium titanate ceramic materials in a reducing atmosphere results in Ti⁴⁺Is reduced to Ti³⁺And meanwhile, weak bound electrons and oxygen vacancies which can move freely are generated, so that n-type semi-conduction occurs in the dielectric material, the insulation resistance is greatly reduced, and the performance is degraded. The acceptor doping is a deep potential well of conductive electrons, and can play a role in binding free electrons, increasing insulation resistance and reducing conductivity. Namely, the doping element replaces Ti position to form acceptor doping, so as to obtain the anti-reduction dielectric material. Whereas the CN1032046677A patent application does not add an acceptor doping element. In addition, this technique MnO₂Mn during sintering in a reducing atmosphere⁴⁺Is also easily reduced to Mn³⁺Or Mn²⁺And meanwhile, weakly bound electrons and oxygen vacancies which can move freely are generated, so that the dielectric material is further semiconductive.

Chinese invention patent CN102718477A discloses a high dielectric constant X8R type MLCC dielectric material and a preparation method thereof, wherein 100 parts by weight of barium titanate is taken as a base material, and the following components in parts by weight are added: 1.6-2.5 parts of niobium-cobalt compound; 0.722-1.805 parts of a sodium titanium bismuth compound; 1.25-2.0 parts of zirconium calcium compound; 1-3 parts of glass powder; 0.369-1.2 parts of one or more oxides of Ce, Yb, Dy and Ho; 0.1-0.25 parts of manganese carbonate. The technology is an MLCC system, namely barium titanate and titanium bismuth sodium compound are solid-dissolved. Bi participates in the formation of a titanium bismuth sodium compound, the Curie temperature of the compound is about 320 ℃, and the compound and BaTiO3 are compounded into a solid solution with a perovskite structure by utilizing the high Curie point of the compound, so that the Curie temperature can be improved, and the temperature stability of the dielectric constant at a high temperature end can be realized. However, the sintering temperature of the technology is required to be 1270-1310 ℃, so that the ceramic crystal grains are easy to be overlarge, and the technology is not suitable for preparing the miniaturized, thinned and large-capacity MLCC element.

Disclosure of Invention

The invention aims to solve the technical problem of developing a lead-free environment-friendly novel high-performance dielectric material for a multilayer ceramic capacitor, which meets the requirements of EIAX8R standard on wide working temperature range and high temperature stability, and has the advantages of low sintering temperature, high reduction resistance and suitability for using base metal nickel and copper as internal electrodes.

The purpose of the invention is realized by the following technical scheme:

a dielectric material for a high dielectric constant X8R type multilayer ceramic capacitor: it is prepared from tetragonal submicron barium titanate BaTiO₃Nb-Co composite oxide dopant A, Nd₂O₃、Bi₂O₃、Ho₂O₃And boron-zinc sintering aid B with the chemical formula of BaTiO₃-0.01A-0.005Nd₂O₃-xBi₂O₃-yHo₂O₃+0.5 wt% B, wherein x ═ y ═ 0.75 to 1.5 mol%; the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor meets the temperature change rate DeltaC/C within the temperature range of-55-150 DEG C₂₅The dielectric constant at room temperature is more than 2400 ℃, and the dielectric loss at room temperature is not more than 2.0 percent;

the Nb-Co composite oxide dopant A is Nb₂O₅And Co₂O₃Controlling Nb as raw material₂O₅And Co₂O₃The molar ratio is 1.5: 1-2.5: 1, ball milling, drying and pre-treating the raw materialsAnd (4) firing to obtain the product.

In order to further achieve the object of the present invention, preferably, the ball milling is to put the raw materials into a ball mill and mix and ball mill the raw materials by a wet ball milling method; the pre-sintering process comprises the steps of heating to 900-950 ℃ at a heating rate of 10 ℃/min at room temperature, preserving heat for 1.5-3 h, and then naturally cooling along with a furnace; and the drying is carried out for 12-24 hours at the temperature of 100-120 ℃.

Preferably, the wet ball milling method is to perform mixed ball milling for 22-26 hours by taking zirconia balls and deionized water as media.

The preparation method of the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor comprises the following steps:

1) preparing Nb-Co composite oxide dopant A powder;

2) with Zn (CH)₃COOH)₂And H₃BO₃Controlling Zn (CH) as raw material₃COOH)₂And H₃BO₃The molar ratio of 11: 14-13: 14, putting the prepared raw materials into a ball mill, mixing and ball-milling by a wet ball-milling method, drying and presintering to obtain boron-zinc sintering aid B powder;

3) with BaTiO₃、Nd₂O₃、Bi₂O₃、Ho₂O₃The Nb-Co composite oxide dopant A powder obtained in the step 1) and the boron-zinc sintering aid B obtained in the step 2) are used as raw materials according to the chemical formula BaTiO₃-0.01A-0.005 Nd₂O₃-x Bi₂O₃-yHo₂O₃+0.5 wt% of B ingredient, putting the prepared raw materials into a ball mill, mixing and ball-milling by a wet ball-milling method, and drying to obtain ceramic powder;

4) grinding, granulating and sieving the ceramic powder obtained in the step 3), and then performing dry pressing to obtain a ceramic green body;

5) and (3) placing the ceramic green body obtained in the step 4) in a high-temperature furnace for sintering after glue discharging to obtain the dielectric material with the high dielectric constant of X8R type for the multilayer ceramic capacitor, wherein the sintering temperature is 1160-1210 ℃, and the sintering time is 2-4 hours.

Preferably, in the step 2) and the step 3), the wet ball milling method is to perform mixing ball milling for 22-26 hours by using zirconia balls and deionized water as media.

Preferably, in the step 2), the pre-sintering is carried out by heating to 550-600 ℃ at a heating rate of 3 ℃/min at room temperature, preserving heat for 1-2 h, and then naturally cooling along with the furnace;

preferably, in the step 5), the rubber discharging is carried out by heating to 600 ℃ at room temperature at a heating rate of 2 ℃/min, then keeping the temperature for 2 hours, and then naturally cooling along with the furnace.

Preferably, the temperature rise mode of the sintering is that the temperature is raised to 1160-1210 ℃ from room temperature at the temperature rise rate of 10 ℃/min.

Preferably, in the step 2) and the step 3), the drying is carried out for 12-24 hours at the temperature of 100-120 ℃.

Preferably, in the step 4), the granulation is carried out after polyvinyl alcohol (PVB) accounting for 5-10% of the mass of the ceramic powder is added; and the sieving is to sieve the mixture by a sieve of 60-100 meshes.

In the invention, BaTiO is mixed with₃And Nb-Co composite oxide dopant A, Nd₂O₃Boron-zinc sintering aid B and Bi₂O₃And Ho₂O₃And the raw materials are sintered together to form the ceramic. Bi₂O₃And Ho₂O₃Is diffused into BaTiO in the sintering process₃The shell part of (1), namely the shell, is doped and modified (comprising doping elements such as Bi, Ho and the like) paraelectric phase BaTiO₃The "core" is essentially the pure ferroelectric phase BaTiO₃。

Proper amount of Bi in the invention₂O₃And Ho₂O₃Mixing the raw materials in a ratio of 1: the ratio of 1 codopants is based on the following mechanism. Bi₂O₃And Ho₂O₃(1: 1 may be abbreviated as BiHoO)₃) When co-doped, Nb⁵⁺、Co³⁺Ion introduction into BaTiO₃Lattice substitution of Ti⁴⁺Forming a core-shell structure, which can make the dielectric constant-temperature curve flat, and the concrete process is as follows: nb₂O₅And Co₂O₃First rapidly neutralize BaTiO₃React to form various intermediate phases, and then Nb and Co are diffused from the intermediate phases to the perovskite latticeScattered, but slowly diffused. Nb and Co are both the sites for Ti substitution, but Nb⁵⁺Is donor doped and Co³⁺It is the acceptor doping. Additive Nb₂O₅And Co₂O₃Shows strong Co-solubility, and Co enrichment can be observed in the Nb-enriched area, so that the donor defect Nb_TiAnd acceptor defect Co_TiNot independently present in BaTiO₃In the crystal lattice, but tends to be in the form of [2 Nb. ]_TiCo″_Ti]X such a form of defect association enters the perovskite lattice.

And Nb⁵⁺、Co³⁺Ion introduction into BaTiO₃Lattice substitution of Ti⁴⁺Helping to form a "core-shell" structure. While the rare earth element Ho has a partial effect in that it can occupy the Ti sites of the grain shell portion and cause lattice expansion, causing lattice mismatch between the formed "core" and "shell" to cause internal stress. The internal stress plays a role in stabilizing the core tetragonal phase, increasing the curie temperature and raising the curie peak. By reasonably adjusting Nb⁵⁺、Co³⁺、Ho³⁺The proportion can reasonably construct internal stress between the core and the shell, and the effect of lifting the Curie peak is realized. Ho replaces Ti position to form acceptor doping, and the acceptor is deep potential well of conductive electron, which can play the role of restricting free electron and reducing conductivity, so the anti-reduction performance of the ceramic can be improved. In addition, Ho has an ionic radius of 0.0901nm, shows an amphoteric characteristic, can occupy the A position to replace Ba to play a role in donor doping, can occupy the B position to replace Ti to play a role in acceptor doping, and Ho & ltr & gt generated by donor doping_BaAnd Ho 'produced by acceptor doping'_TiAttract each other, and cause defect association [ Ho ]_BaHo′_Ti]The defect has poor mobility under the action of an electric field and can be an obstacle to oxygen vacancy migration, so that the insulation resistivity, the service life, the reliability and the reduction resistance of the dielectric material can be improved. And the diffusivity of Bi is lower than that of Ho, so that the deep diffusion of Ho to the core part can be inhibited, and the stability of the core-shell structure is ensured. The ionic radius of Bi is smaller than that of Ba, so that the substitution of Bi for Ba can enlarge the adjacent oxygen octahedral voids, thereby increasing the substitution of Ho for TiThe probability, the solid solubility of Ho in barium titanate matrix is improved, the formation of pyrochlore phase is reduced, and the peak shift effect is enhanced. In addition, Bi₂O₃Because of low melting point, it also has a certain liquid-phase sintering-aid action, and can reduce sintering temp., reduce grain size, raise density of medium ceramic body and reduce loss.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the addition of appropriate niobium-cobalt composite oxide can help to form a core-shell structure, and the structure can play a role in suppressing and widening a dielectric peak and is beneficial to reducing the temperature change rate of the material. With simultaneous addition of Nd₂O₃The volume ratio of the core to the shell can be effectively changed, the dielectric constant of the low-temperature section of the material is improved, and the dielectric constant of the high-temperature section is depressed. In the sintering process, the added boron-zinc sintering aid forms a liquid phase on a crystal boundary, promotes material transmission, can obviously reduce the sintering temperature, reduces the grain size, improves the density of a dielectric ceramic body and reduces the loss.

(2) The invention is a proper amount of Bi₂O₃And Ho₂O₃Mixing the raw materials in a ratio of 1:1, doping Ho alone may cause the metastable "core-shell" structure of barium titanate-based ceramics to be destroyed by excessive diffusion of Ho, losing the temperature stability of dielectric constant. And the diffusivity of Bi is lower than that of Ho, and the introduction of Bi obviously helps to inhibit the diffusion of Ho and maintain the stability of a core-shell structure. In addition, Bi₂O₃Because of low melting point, it also has a certain liquid-phase sintering-aid action, and can reduce sintering temp., reduce grain size, raise density of medium ceramic body and reduce loss. Therefore, the sintering temperature of the invention is obviously lower than that of the Chinese patent application CN 102718477A.

(3) The ceramic dielectric material prepared by the invention has low sintering temperature of 1160-1210 ℃, meets the EIA X8R standard requirement, has good dielectric property and lower dielectric loss (less than or equal to 2.35%), wherein the room-temperature dielectric constant is more than 2400, and the room-temperature (25 ℃) dielectric loss is only 1.64%. The anti-reduction performance is strong, and the method is suitable for the production and application of the base metal nickel and copper as the inner electrode MLCC, and the cost of the material is obviously reduced.

(4) The dielectric material of the invention does not contain lead and is harmless to the environment. The ceramic preparation process adopts a solid phase method, and the process flow is simple and easy to operate.

Drawings

FIG. 1 is a graph of dielectric constant versus temperature for examples 1-4;

FIG. 2 is a graph of dielectric loss as a function of temperature for examples 1-4;

FIG. 3 is a graph showing the temperature change rate of examples 1 to 4 as a function of temperature;

FIG. 4 is a SEM of crystal grains of a sample obtained in example 1

FIG. 5 is an SEM image of the crystal grains of a sample obtained from the Chinese patent application CN 102718477A.

Detailed Description

For better understanding of the present invention, the present invention is further illustrated by the following figures and examples, but the embodiments of the present invention are not limited to the following examples, and the purity of the raw materials used in the present invention is analytical.

Example 1

By Nb₂O₅And Co₂O₃As a raw material, according to Nb₂O₅And Co₂O₃The molar ratio is 2: 1, mixing materials, putting the prepared raw materials into a ball mill, and mixing and ball-milling by a wet ball-milling method. The ball milling medium is zirconia balls and deionized water, and the mixture is ball milled for 24 hours. And then drying the mixture at 100 ℃ for 12h, and putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is raised to 950 ℃ at the room temperature at the heating rate of 10 ℃/min, the temperature is kept for 2 hours, and the Nb-Co composite oxide dopant A powder is obtained after the mixture is naturally cooled along with the furnace;

with Zn (CH)₃COOH)₂And H₃BO₃As starting material, according to Zn (CH)₃COOH)₂And H₃BO₃The molar ratio is 13: 14, mixing and ball-milling the prepared raw materials in a ball mill by a wet ball-milling method, wherein ball-milling media are zirconia balls and deionized water, and mixing and ball-milling for 24 hours. And then drying the mixture at 100 ℃ for 12h, and putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is raised to 550 ℃ at the temperature raising rate of 3 ℃/min at room temperature, the temperature is preserved for 1h,then naturally cooling along with the furnace to obtain boron-zinc sintering aid B powder;

with BaTiO₃、Nd₂O₃、Bi₂O₃、Ho₂O₃The Nb-Co composite oxide dopant A powder obtained in the step (3) and the boron-zinc sintering aid B obtained in the step (3) are used as raw materials according to the chemical formula BaTiO₃-0.01A-0.005 Nd₂O₃-x Bi₂O₃-yHo₂O₃+0.5 wt% of B, wherein x is y is 0.75 mol%, the prepared raw materials are put into a ball mill and mixed and ball-milled by a wet ball milling method, the ball milling media are zirconia balls and absolute ethyl alcohol, the mixture is ball-milled for 24 hours, and then the mixture is dried for 24 hours at 100 ℃. Grinding the dried ceramic powder, adding PVB accounting for 10% of the mass of the ceramic powder, granulating, sieving with a 80-mesh sieve, and dry-pressing into a ceramic green body with the diameter of 10 mm and the thickness of 1.2 mm. Heating the obtained ceramic green body to 600 ℃ at room temperature at the heating rate of 2 ℃/min, then preserving heat for 2 hours, then naturally cooling along with the furnace to carry out binder removal, then sintering in a high-temperature furnace, wherein the sintering process is heating to 1210 ℃ at the heating rate of 10 ℃/min at room temperature, preserving heat for 3 hours, and then naturally cooling along with the furnace to obtain the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor.

Grinding and polishing two ends of the dielectric material prepared in the embodiment, coating electrodes, drying and burning silver to obtain a dielectric ceramic element, and then testing and calculating the relative dielectric constant epsilon of the dielectric ceramic element_rDielectric loss tan delta and capacity temperature change rate delta C/C₂₅DEG C. FIG. 1, FIG. 2 and FIG. 3 show the dielectric constant ε of example 1_rDielectric loss tan delta and capacity temperature change rate DeltaC/C₂₅The temperature is changed along with the temperature. Specific dielectric property parameters are listed in Table 1, and the temperature change rate of the ceramic, | Delta C/C₂₅The temperature of | is not more than 15% in the temperature range of-55-150 ℃, and the EI X8R standard is met. The dielectric constant can reach 2668 at room temperature, the loss is only 1.35%, and the insulation resistivity reaches 2.58 multiplied by 10¹²Ω·cm。

As can be seen from Table 1, the dielectric ceramic element obtained in the present example had an insulation resistivity of 2 to 3X 10¹²Omega cm order of magnitude, and the same method tests Chinese hairThe insulation resistivity of the sample obtained in example 1 of the patent application CN1032046677A is only 2-3 x 10¹⁰In the order of Ω · cm. The product has the insulation resistivity far larger than CN1032046677A, has strong anti-reduction performance, is suitable for the production and application of the internal electrode MLCC made of base metal nickel and copper, and obviously reduces the cost of materials. The main reason is that the use amount of electrode materials is increasing with the increasing number of MLCC stacked layers, for example, the traditional noble metal electrode material palladium and silver are adopted to make the MLCC preparation cost higher, which promotes the research and development of BME-MLCC using relatively cheap base metals such as nickel (Ni), copper (Cu) and the like as internal electrodes. Since Ni and Cu electrodes are easily oxidized when sintered in air, a green BEM-MLCC using Ni and Cu electrodes needs to be sintered in a reducing atmosphere (usually a nitrogen-hydrogen mixture) to ensure the electrical conductivity of the electrodes. However, sintering of barium titanate ceramic materials in a reducing atmosphere results in Ti⁴⁺Is reduced to Ti³⁺And meanwhile, weak bound electrons and oxygen vacancies which can move freely are generated, so that n-type semi-conduction occurs in the dielectric material, the insulation resistance is greatly reduced, and the performance is degraded. The acceptor doping is a deep potential well of conductive electrons, and can play a role in binding free electrons, increasing insulation resistance and reducing conductivity. Namely, the doping element replaces Ti position to form acceptor doping, so as to obtain the anti-reduction dielectric material. Whereas the CN1032046677A patent does not add an acceptor doping element.

TABLE 1 dielectric Properties of ceramic media of different formulations

The invention is a proper amount of Bi₂O₃And Ho₂O₃Mixing the raw materials in a ratio of 1:1 co-doping, Bi₂O₃Because the melting point is low and the sintering aid has a liquid phase sintering effect, the sintering temperature of the invention is greatly reduced compared with the Chinese patent application CN 102718477A. The sintering temperature is lowered, the preparation cost can be reduced, and the grain size can be reduced (SEM pictures of the crystal grains of the sample obtained in the example 1 of the present example and the Chinese patent application CN1032046677A are shown in FIGS. 4 and 5, under the same magnificationThe crystal grains of the sample of the embodiment are obviously smaller than the Chinese patent application CN1032046677A), and the density of the dielectric ceramic body is improved. The Chinese patent application CN102718477A actually uses another MLCC system, namely barium titanate and titanium bismuth sodium compound solid solution. Bi₂O₃Firstly, the titanium bismuth sodium compound is formed, the Curie temperature of said compound is about 320 deg.C, and it and BaTiO are mixed by utilizing its high Curie point₃The solid solution having perovskite structure is compounded to increase Curie temperature and realize temperature stability of dielectric constant at high temperature, so that Bi is used in the application₂O₃It cannot play a role of reducing the sintering temperature in the present invention.

Invention H₂O₃Is an amphoteric rare earth oxide, Ho³⁺The ionic radius is 0.0901nm and is between Ba²⁺And Ti⁴⁺In place of Ba²⁺And may be substituted for Ti⁴⁺. Incorporation of BaTiO₃Ti in place of B⁴⁺And the doped silicon nitride is doped with an acceptor, and the acceptor can play a role in binding conductive electrons, increasing insulation resistance and reducing conductivity. When Ho³⁺Ba substituted for A position²⁺And then belongs to donor doping. Ho. produced by doping of donors_BaAnd Ho 'produced by acceptor doping'_TiAttract each other, and cause defect association [ Ho ]_BaHo′_Ti]The defect has poor mobility under the action of an electric field and can be used as an obstacle for oxygen vacancy migration, so that the insulation resistivity of the dielectric material can be improved, namely the effect of improving the reduction resistance of the ceramic is achieved.

Invention Ho³⁺In BaTiO₃Low solid solubility in (C), excessive Ho³⁺Optionally substituted Ti⁴⁺Reaction to form Ho₂Ti₂O₇The generated second phase with lower dielectric constant can play a part of the role of broadening dielectric peak and can play a role of pinning to limit BaTiO₃The average grain size is kept small at 300 nm. The theory of fine crystals states that: BaTiO with average grain size of 100nm-700nm₃Natural has better temperature stability and slightly higher CurieAnd (3) temperature. However, the content of the second phase should not be too large, which may cause BaTiO₃Becomes small and even destroys BaTiO₃Core-shell structure of (a).

Bi of the invention₂O₃And Ho₂O₃(1: 1 may be abbreviated as BiHoO)₃) Upon co-doping, a portion of the rare earth element Ho occupies the Ti site of the crystal shell portion and causes lattice expansion, and lattice mismatch of the "core" and "shell" causes internal stress. The internal stress plays a role in stabilizing the core tetragonal phase, increasing the curie temperature and raising the curie peak. Ho doping is the root cause of the Curie temperature increase, and Bi doping alone does not have a peak shift effect. In addition, doping Ho alone can result in the destruction of the metastable "core-shell" structure of the barium titanate-based ceramic due to excessive diffusion of Ho, which can lose the temperature stability of the dielectric constant. And the diffusivity of Bi is lower than that of Ho, and the introduction of Bi obviously helps to inhibit the diffusion of Ho and maintain the stability of a core-shell structure. In fact, when the atomic ratio of Bi/Ho is too small, the barium titanate-based ceramic also undergoes a solid solution phenomenon, and only when the atomic ratio of Bi/Ho is greater than 1:1 has a significant effect of increasing the Curie temperature. Because of Bi³⁺Has an ionic radius of 0.134nm less than Ba²⁺Has an ionic radius of 0.161nm, so that Bi³⁺Substituted Ba²⁺Then the adjacent oxygen octahedron gaps are enlarged, thereby increasing Ho³⁺Substituted Ti⁴⁺The probability of (c). When Ho₂O₃Bi with a constant content and high content₂O₃The doping amount is beneficial to more Ho³⁺Ground access BaTiO₃Lattice, thereby reducing the generation of pyrochlore phases. In conclusion, the ratio of the two is determined as 1: 1. the invention uses 1: molar ratio of 1 Bi₂O₃，Ho₂O₃The co-doping of BaTiO3 can not only properly reduce the sintering temperature, but also broaden the dielectric peak, increase the Curie temperature and improve the dielectric temperature characteristic and the anti-reduction performance of the barium titanate ceramic. In addition, Bi₂O₃Because of low melting point, it also has a certain liquid-phase sintering-aid action, and can reduce sintering temp., reduce grain size, raise density of medium ceramic body and reduce loss.

Example 2

By Nb₂O₅And Co₂O₃As a raw material, according to Nb₂O₅And Co₂O₃The molar ratio is 1.5: 1, mixing materials, putting the prepared raw materials into a ball mill, and mixing and ball-milling by a wet ball-milling method. The ball milling medium is zirconia balls and deionized water, and the mixture is ball milled for 24 hours. And then drying the mixture at 100 ℃ for 16h, and putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is increased to 900 ℃ at the room temperature at the heating rate of 10 ℃/min, the temperature is kept for 3 hours, and the Nb-Co composite oxide dopant A powder is obtained after the mixture is naturally cooled along with the furnace;

with Zn (CH)₃COOH)₂And H₃BO₃As starting material, according to Zn (CH)₃COOH)₂And H₃BO₃The molar ratio of 12: 14, mixing and ball-milling the prepared raw materials in a ball mill by a wet ball-milling method, wherein ball-milling media are zirconia balls and deionized water, and mixing and ball-milling for 26 hours. And then drying the mixture at 120 ℃ for 20 hours, and putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is raised to 600 ℃ at room temperature at the heating rate of 3 ℃/min, the temperature is kept for 1h, and then the boron-zinc sintering aid B powder is obtained after the boron-zinc sintering aid B powder is naturally cooled along with the furnace;

with BaTiO₃、Nd₂O₃、Bi₂O₃、Ho₂O₃The Nb-Co composite oxide dopant A powder obtained in the step (3) and the boron-zinc sintering aid B obtained in the step (3) are used as raw materials according to the chemical formula BaTiO₃-0.01A-0.005 Nd₂O₃-x Bi₂O₃-yHo₂O₃+0.5 wt% of B, wherein x is y is 1.0 mol%, the prepared raw materials are put into a ball mill and mixed and ball-milled by a wet ball milling method, the ball milling media are zirconia balls and absolute ethyl alcohol, the mixture is ball-milled for 26 hours, and then the mixture is dried for 24 hours at 120 ℃. Grinding the dried ceramic powder, adding PVB accounting for 8% of the mass of the ceramic powder, granulating, sieving by a 60-mesh sieve, and dry-pressing into a ceramic green body with the diameter of 10 mm and the thickness of 1.2 mm. Heating the obtained ceramic green body to 600 ℃ at room temperature at a heating rate of 2 ℃/min, then preserving heat for 2 hours, then naturally cooling along with the furnace to discharge glue, and then sintering in a high-temperature furnace, wherein the sintering process is that the temperature is increased to 1180 ℃ at room temperature at a heating rate of 10 ℃/min andkeeping the temperature for 2 hours, and then naturally cooling along with the furnace to obtain the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor.

Grinding and polishing two ends of the dielectric material prepared in the embodiment, coating electrodes, drying and burning silver to obtain a dielectric ceramic element, and then testing and calculating the relative dielectric constant epsilon, the dielectric loss tan delta and the temperature change rate delta C/C of the dielectric ceramic element₂₅DEG C. FIG. 1, FIG. 2 and FIG. 3 show the dielectric constant ε of example 2_rDielectric loss tan delta and capacity temperature change rate DeltaC/C₂₅The temperature is changed along with the temperature. Specific dielectric property parameters are listed in Table 1, and the temperature change rate of the ceramic, | Delta C/C₂₅The temperature of | is not more than 15% in the temperature range of-55-150 ℃, and the EI X8R standard is met. The dielectric constant can reach 2567 at room temperature, the loss is only 1.41 percent, and the insulation resistivity reaches 3.46 multiplied by 10¹²Ω·cm。

Example 3

By Nb₂O₅And Co₂O₃As a raw material, according to Nb₂O₅And Co₂O₃The molar ratio is 2.5: 1, mixing materials, putting the prepared raw materials into a ball mill, and mixing and ball-milling by a wet ball-milling method. The ball milling medium is zirconia balls and deionized water, and the mixture is ball milled for 26 hours. And then drying the mixture for 24 hours at 100 ℃, and then putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is raised to 950 ℃ at the room temperature at the heating rate of 10 ℃/min, the temperature is kept for 3 hours, and the Nb-Co composite oxide dopant A powder is obtained after the mixture is naturally cooled along with the furnace; with Zn (CH)₃COOH)₂And H₃BO₃As starting material, according to Zn (CH)₃COOH)₂And H₃BO₃The molar ratio of 11: 14, mixing and ball-milling the prepared raw materials in a ball mill by a wet ball-milling method, wherein ball-milling media are zirconia balls and deionized water, and mixing and ball-milling for 22 hours. And then drying the mixture for 24 hours at 100 ℃, and then putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is raised to 550 ℃ at the temperature raising rate of 3 ℃/min at room temperature, the temperature is preserved for 2 hours, and then the boron-zinc sintering aid B powder is obtained after the boron-zinc sintering aid B powder is naturally cooled along with the furnace;

with BaTiO₃、Nd₂O₃、Bi₂O₃、Ho₂O₃The Nb-Co composite oxide dopant A powder obtained in the step (3) and the boron-zinc sintering aid B obtained in the step (3) are used as raw materials according to the chemical formula BaTiO₃-0.01A-0.005 Nd₂O₃-x Bi₂O₃-yHo₂O₃+0.5 wt% of B, wherein x ═ y ═ 1.25 mol%, the prepared raw materials were put into a ball mill and mixed and ball milled by a wet ball milling method with zirconia balls and absolute ethyl alcohol as the milling media, mixed and ball milled for 22 hours, and then dried by baking at 120 ℃ for 20 hours. Grinding the dried ceramic powder, adding PVB accounting for 5% of the mass of the ceramic powder, granulating, sieving with a 100-mesh sieve, and dry-pressing into a ceramic green body with the diameter of 10 mm and the thickness of 1.2 mm. Heating the obtained ceramic green body to 600 ℃ at room temperature at the heating rate of 2 ℃/min, then preserving heat for 2 hours, then naturally cooling along with the furnace to carry out binder removal, then sintering in a high-temperature furnace, wherein the sintering process is heating to 1200 ℃ at the heating rate of 10 ℃/min at room temperature, preserving heat for 4 hours, and then naturally cooling along with the furnace to obtain the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor.

Grinding and polishing two ends of the dielectric material prepared in the embodiment, coating electrodes, drying and burning silver to obtain a dielectric ceramic element, and then testing and calculating the relative dielectric constant epsilon, the dielectric loss tan delta and the temperature change rate delta C/C of the dielectric ceramic element₂₅DEG C. FIG. 1, FIG. 2 and FIG. 3 show the dielectric constant ε of example 3_rDielectric loss tan delta and capacity temperature change rate DeltaC/C₂₅The temperature is changed along with the temperature. Specific dielectric property parameters are listed in Table 1, and the temperature change rate of the ceramic, | Delta C/C₂₅The temperature is not more than 15% in the temperature range of-55-150 ℃. And the standard EI X8R is met. The dielectric constant can reach 2515 at room temperature, the loss is only 1.99%, and the insulation resistivity reaches 2.44 multiplied by 10¹²Omega cm. Example 4

By Nb₂O₅And Co₂O₃As a raw material, according to Nb₂O₅And Co₂O₃The molar ratio is 2.5: 1, mixing materials, putting the prepared raw materials into a ball mill, and mixing and ball-milling by a wet ball-milling method. The ball milling medium is zirconia balls and deionized water, and the mixture is ball milled for 23 hours. Then dried for 22h at 120 ℃ and then put intoAnd (4) pre-burning in a high-temperature furnace. The pre-sintering process is that the temperature is increased to 920 ℃ at room temperature at the heating rate of 10 ℃/min, the temperature is kept for 2.5 hours, and the Nb-Co composite oxide dopant A powder is obtained after the mixture is naturally cooled along with the furnace; with Zn (CH)₃COOH)₂And H₃BO₃As starting material, according to Zn (CH)₃COOH)₂And H₃BO₃The molar ratio of 12: 14, mixing and ball-milling the prepared raw materials in a ball mill by a wet ball-milling method, wherein ball-milling media are zirconia balls and deionized water, and mixing and ball-milling for 25 hours. And then drying the mixture at 100 ℃ for 20 hours, and putting the dried mixture into a high-temperature furnace for presintering. The pre-sintering process is that the temperature is raised to 600 ℃ at room temperature at the heating rate of 3 ℃/min, the temperature is kept for 1h, and then the boron-zinc sintering aid B powder is obtained after the boron-zinc sintering aid B powder is naturally cooled along with the furnace;

with BaTiO₃、Nd₂O₃、Bi₂O₃、Ho₂O₃The Nb-Co composite oxide dopant A powder obtained in the step (3) and the boron-zinc sintering aid B obtained in the step (3) are used as raw materials according to the chemical formula BaTiO₃-0.01A-0.005 Nd₂O₃-x Bi₂O₃-yHo₂O₃+0.5 wt% of B, wherein x ═ y ═ 1.5 mol%, the prepared raw materials were put into a ball mill and mixed and ball milled by a wet ball milling method with zirconia balls and absolute ethyl alcohol as the milling media, mixed and ball milled for 24 hours, and then dried by baking at 100 ℃ for 24 hours. Grinding the dried ceramic powder, adding PVB accounting for 5% of the mass of the ceramic powder, granulating, sieving with a 100-mesh sieve, and dry-pressing into a ceramic green body with the diameter of 10 mm and the thickness of 1.2 mm. Heating the obtained ceramic green body to 580 ℃ at room temperature at the heating rate of 2 ℃/min, then preserving heat for 2 hours, naturally cooling along with the furnace to carry out binder removal, then sintering in a high-temperature furnace, wherein the sintering process is heating to 1180 ℃ at room temperature at the heating rate of 10 ℃/min, preserving heat for 3 hours, and naturally cooling along with the furnace to obtain the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor.

Grinding and polishing two ends of the dielectric material prepared in the embodiment, coating electrodes, drying and burning silver to obtain a dielectric ceramic element, and then testing and calculating the relative dielectric constant epsilon, the dielectric loss tan delta and the temperature change rate delta C/C of the dielectric ceramic element₂₅DEG C. FIG. 1, FIG. 2 and FIG. 2FIG. 3 shows the dielectric constants ε of example 4_rDielectric loss tan delta and capacity temperature change rate DeltaC/C₂₅The temperature is changed along with the temperature. Specific dielectric property parameters are listed in Table 1, and the temperature change rate of the ceramic, | Delta C/C₂₅The temperature of | is not more than 15% in the temperature range of-55-150 ℃, and the EI X8R standard is met. The dielectric constant can reach 2472 at room temperature, the loss is only 1.82%, and the insulation resistivity reaches 2.78 multiplied by 10¹²Ω·cm。

It should be noted that the embodiments of the present invention are not limited by the above-mentioned examples, and any other changes, modifications, substitutions, combinations, and simplifications which are made without departing from the spirit and principle of the present invention should be regarded as equivalent substitutions, and are included in the scope of the present invention.

Claims

1. A dielectric material for a high dielectric constant X8R type multilayer ceramic capacitor is characterized in that: it is prepared from tetragonal submicron barium titanate BaTiO₃Nb-Co composite oxide dopant A, Nd₂O₃、Bi₂O₃、Ho₂O₃And boron-zinc sintering aid B with the chemical formula of BaTiO₃-0.01A-0.005Nd₂O₃-xBi₂O₃-yHo₂O₃+0.5 wt% B, wherein x ═ y ═ 0.75 to 1.5 mol%; the dielectric material for the high-dielectric-constant X8R type multilayer ceramic capacitor meets the temperature change rate DeltaC/C within the temperature range of-55-150 DEG C_25℃Less than or equal to 15 percent, dielectric constant of over 2400 at room temperature, and dielectric loss of less than or equal to 2.0 percent at room temperature;

the Nb-Co composite oxide dopant A is Nb₂O₅And Co₂O₃Controlling Nb as raw material₂O₅And Co₂O₃The molar ratio is 1.5: 1-2.5: 1, ball-milling the raw materials, drying and presintering to obtain the product.

2. The dielectric material for high dielectric constant X8R type multilayer ceramic capacitor as claimed in claim 1, wherein: the ball milling is to put the raw materials into a ball mill and mix and ball mill the raw materials by a wet ball milling method; the pre-sintering process comprises the steps of heating to 900-950 ℃ at a heating rate of 10 ℃/min at room temperature, preserving heat for 1.5-3 h, and then naturally cooling along with a furnace; and the drying is carried out for 12-24 hours at the temperature of 100-120 ℃.

3. The dielectric material for high dielectric constant X8R type multilayer ceramic capacitor as claimed in claim 2, wherein: the wet ball milling method adopts zirconia balls and deionized water as media, and the mixing and ball milling is carried out for 22-26 hours.

4. The method for producing a dielectric material for a high dielectric constant X8R type multilayer ceramic capacitor as claimed in any one of claims 1 to 3, characterized by the steps of:

1) preparing Nb-Co composite oxide dopant A powder;

3) with BaTiO₃、Nd₂O₃、Bi₂O₃、Ho₂O₃The Nb-Co composite oxide dopant A powder obtained in the step 1) and the boron-zinc sintering aid B obtained in the step 2) are used as raw materials according to the chemical formula BaTiO₃-0.01A-0.005Nd₂O₃-x Bi₂O₃-y Ho₂O₃+0.5 wt% of B ingredient, putting the prepared raw materials into a ball mill, mixing and ball-milling by a wet ball-milling method, and drying to obtain ceramic powder;

5. The method of claim 4, wherein: in the step 2) and the step 3), the wet ball milling method is to perform mixed ball milling for 22-26 hours by taking zirconia balls and deionized water as media.

6. The method of claim 4, wherein: in the step 2), the pre-sintering is carried out by heating to 550-600 ℃ at a heating rate of 3 ℃/min at room temperature, preserving heat for 1-2 h, and then naturally cooling along with the furnace.

7. The method of claim 4, wherein: in the step 5), the binder removal is carried out by heating to 600 ℃ at room temperature at a heating rate of 2 ℃/min, then carrying out heat preservation for 2 hours, and then carrying out natural cooling along with the furnace.

8. The method of claim 4, wherein: the temperature rise mode of the sintering is that the temperature is raised to 1160-1210 ℃ from room temperature at the temperature rise rate of 10 ℃/min.

9. The method of claim 4, wherein: in the step 2) and the step 3), the drying is carried out for 12-24 hours at the temperature of 100-120 ℃.

10. The method of claim 4, wherein: in the step 4), the granulation is carried out after polyvinyl alcohol accounting for 5-10% of the mass of the ceramic powder is added; the sieving is to sieve the mixture by a sieve of 60-100 meshes.