CN111377734A

CN111377734A - X9R type multilayer ceramic capacitor dielectric material and preparation method thereof

Info

Publication number: CN111377734A
Application number: CN202010190750.5A
Authority: CN
Inventors: 张蕾; 庄后荣; 曾俊; 于洪宇; 王宏兆
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology; Southern University of Science and Technology
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2020-07-07

Abstract

The invention belongs to the technical field of ceramic capacitor dielectric materials, and particularly relates to an X9R type multilayer ceramic capacitor dielectric material and a preparation method thereof. The X9R type multilayer ceramic capacitor dielectric material of the invention is of a 'core-shell' structure, wherein 0.9BT-0.1BNT is used as a 'core', and a surface cladding layer formed by cobalt element and neodymium element is used as a 'shell'. In the X9R type multilayer ceramic capacitor dielectric material, cobalt element can react with neodymium element to form a compound or replace the position of the neodymium element, thereby reducing the diffusion rate of the neodymium element, hindering the diffusion of doping elements to a core, enabling more doping elements to stay in a shell part, further reducing the proportion of the shell in a core-shell structure, enabling the low-temperature dielectric peak of the obtained multilayer ceramic capacitor dielectric material to be more moderate, improving the overall temperature stability, and meeting the X9R standard.

Description

X9R type multilayer ceramic capacitor dielectric material and preparation method thereof

Technical Field

The invention belongs to the technical field of capacitor dielectric materials, and particularly relates to an X9R type multilayer ceramic capacitor dielectric material and a preparation method thereof.

Background

With the development of multilayer ceramic capacitors (MLCC) in the extreme fields of automotive electronics, oil drilling, aerospace, defense industry and the like, the popularization of hybrid electric vehicles and fuel cell vehicles in particular will increase the demand for high-temperature power devices, and the development of research on X9R MLCC devices which can normally work in a wide temperature spectrum has been slow. The International Electronic Industry Association (EIA) makes special provisions on the temperature tolerance characteristics of a medium material for a common type of MLCC, wherein the X9R type MLCC is an MLCC device with the temperature tolerance change rate of less than or equal to +/-15% within the range of-55-200 ℃.

The dielectric constant of the pure BT ceramic is often suddenly changed at the Curie point, and the temperature stability of the pure BT ceramic in an actual circuit is not enough. The curie point of BT ceramics is mainly influenced by several factors: intrinsic properties (e.g., grain size, tetragonal, Ba/Ti ratio, etc.), external environment (e.g., applied electric field and stress, and external doping elements), wherein doping is the most common and effective way to change the curie point. Therefore, in order to meet the requirement of X9R type MLCC on high service temperature, the temperature stability is improved by doping elements. When the same-order doped oxide is introduced into a matrix through a traditional ball milling doping process, the doping effect is greatly reduced, and mixed powder which is uniformly mixed and has good dispersibility is difficult to form, so that the dopant is difficult to fully play a role after sintering, ceramic grains with more core-shell structures cannot be formed, and the low reliability of the MLCC is caused. Doping elements are introduced by means of dopant nanocrystallization, isopropanol dispersion and coating, and the like, so that an ultrathin MLCC dielectric material with excellent performance is successfully obtained, however, the ultrathin MLCC dielectric material is not suitable for doping of particles below 100nm, and the defects of high isopropanol cost, flammability and the like still hinder application of the methods.

Disclosure of Invention

The invention aims to provide an X9R type multilayer ceramic capacitor dielectric material and a preparation method thereof, and aims to solve the technical problems that the existing multilayer ceramic capacitor dielectric material has poor doping effect in the preparation process, and the temperature-tolerant characteristic of the obtained multilayer ceramic capacitor dielectric material does not meet the requirement of X9R.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

the invention provides a preparation method of an X9R type multilayer ceramic capacitor dielectric material, which comprises the following steps:

providing 0.9BT-0.1 BNT;

in a water system, carrying out coprecipitation reaction on the 0.9BT-0.1BNT and a solution containing cobalt ions and neodymium ions to obtain 0.9BT-0.1BNT with the surface coated with cobalt elements and neodymium elements;

and sintering the 0.9BT-0.1BNT coated with the cobalt element and the neodymium element on the surface to obtain the X9R type multilayer ceramic capacitor dielectric material.

In a preferred embodiment of the present invention, the total molar concentration of the cobalt ions and the neodymium ions in the solution containing cobalt ions and neodymium ions is 4% based on the molar concentration of 0.9BT-0.1 BNT.

In a preferred embodiment of the present invention, the solution containing cobalt ions and neodymium ions has a total molar concentration of 4% and a molar concentration ratio of (0.5:1) - (2:1) of the cobalt ions to the neodymium ions, based on the molar concentration of 0.9BT-0.1 BNT.

In a preferred embodiment of the present invention, an auxiliary dispersant is further added to the water system.

In a further preferred embodiment of the present invention, an auxiliary dispersant is further added to the aqueous system, and the auxiliary dispersant is an acidic dispersant.

In a further preferred embodiment of the present invention, an auxiliary dispersant selected from at least one of glycine, polyacrylic acid, an anionic dispersant I-7, and an anionic dispersant Lomar PWA-40K is further added to the aqueous system.

In a further preferred embodiment of the present invention, an auxiliary dispersant is further added to the aqueous system, and the mass of the auxiliary dispersant accounts for 3% of the mass of the 0.9BT-0.1 BNT.

In a preferred embodiment of the present invention, the reaction system has a pH of >6 during the coprecipitation reaction.

As a preferred technical scheme of the invention, the temperature of the sintering treatment is 1100-1200 ℃.

As a preferred technical scheme of the invention, the synthesis method of the 0.9BT-0.1BNT comprises the following steps:

providing bismuth oxide, sodium carbonate, titanium dioxide and barium titanate;

calcining the ball-milled mixture of the bismuth oxide, the sodium carbonate and the titanium dioxide for the first time to obtain bismuth sodium titanate;

and calcining the ball-milled mixture of the barium titanate and the sodium bismuth titanate for the second time to obtain 0.9BT-0.1 BNT.

In a more preferred embodiment of the present invention, the particle size of the barium titanate is 60nm to 200 nm.

As a further preferable technical scheme of the invention, the temperature of the first calcination is 800-1000 ℃.

As a further preferable technical scheme of the invention, the temperature of the second calcination is 900-1100 ℃.

The invention also provides an X9R type multilayer ceramic capacitor dielectric material, which is prepared by the preparation method of the X9R type multilayer ceramic capacitor dielectric material.

In a preferred embodiment of the present invention, the X9R type multilayer ceramic capacitor dielectric material has a "core-shell" structure in which 0.9BT-0.1BNT is used as a "core" and a surface cladding layer made of a cobalt element and a neodymium element is used as a "shell".

Because the dielectric constant of pure BT ceramic is frequently changed suddenly at the Curie point, the temperature stability in an actual circuit is insufficient, and the X9R type multilayer ceramic capacitor dielectric material is required to be in the range of-55-200 ℃, the capacity temperature change rate is less than or equal to +/-15%, and the temperature stability to the material is higher, therefore, in order to improve the temperature stability of the multilayer ceramic capacitor dielectric material, the invention takes 0.9BT-0.1BNT as a substrate, and forms a doped element coating layer on the surface of 0.9BT-0.1BNT in a mode of composite doping of cobalt element and neodymium element, so that the obtained multilayer ceramic capacitor dielectric material meets the requirements of the X9R type multilayer ceramic capacitor dielectric material. On one hand, the invention firstly synthesizes the 0.9BT-0.1BNT with the perovskite structure substrate, and then introduces the doping elements through water-based coating, thereby avoiding the reaction between the sodium bismuth titanate and the doping elements; on the other hand, cobalt may react with neodymium to form a complex or substitute for the neodymium to reduce the diffusion rate of neodymium, so as to further avoid the diffusion of the doping element. The preparation method of the X9R type multilayer ceramic capacitor dielectric material is simple, and has the advantages of easy implementation and safe and controllable reaction process.

The X9R type multilayer ceramic capacitor dielectric material of the invention is of a 'core-shell' structure, wherein 0.9BT-0.1BNT is used as a 'core', and a surface cladding layer formed by cobalt element and neodymium element is used as a 'shell'. Because the invention uses the mode of cobalt element and neodymium element composite doping, cobalt element can react with neodymium element to form a composite or replace the position of neodymium element, thereby reducing the diffusion rate of neodymium element, hindering the diffusion of doping element to 'core', making more doping element stay in 'shell' part, further reducing the proportion of 'shell' in 'core-shell' structure, and the proportion of 'shell' is reduced to make the low-temperature dielectric peak of the dielectric material moderate, so the multilayer ceramic capacitor dielectric material of the invention has the advantages of more moderate low-temperature dielectric peak and high integral temperature stability, and accords with the X9R standard.

Drawings

FIG. 1 is an SEM photograph of the starting material used in step (1) of an example of the present invention, wherein (a) is sodium carbonate, (b) is bismuth oxide, and (c) is titanium dioxide;

FIG. 2 is a graph showing the relationship between different doping elements, different sintering temperatures and the density of the dielectric material of the resulting multilayer ceramic capacitor in examples 1 to 30 of the present invention;

FIG. 3 is a graph of the dielectric temperature spectrum and TCC of a multilayer ceramic capacitor dielectric material;

FIG. 4 is a TEM image of dielectric materials of multilayer ceramic capacitors obtained in examples 1 and 5;

FIG. 5 shows HAADF diagram (a) and the composition distribution (b) of selected EDS regions of the dielectric material of multilayer ceramic capacitor obtained in example 5;

FIG. 6 is a diagram showing the morphology of the powder obtained in step (4) of example 1 after removal of the organic substances by pre-sintering at 550 ℃;

FIG. 7 is a graph showing the effect of adding different auxiliary dispersants to the particle size distribution of the solution system in example 1 and examples 31-33;

FIG. 8 is a Fourier transform infrared spectrum (FTIR) of a commercial anionic dispersant LomarPWA-40K;

FIG. 9 is an SEM image and an XRD image of barium titanate powders with different particle sizes;

FIG. 10 is a diagram showing the relationship between XRD and unit cell parameters after compounding barium titanate powder with different particle sizes and bismuth sodium titanate;

FIG. 11 is SEM, XRD and Raman images of sodium bismuth titanate synthesized at different calcination temperatures;

FIG. 12 is a graph showing the relationship between XRD and unit cell parameters of 0.9BT-0.1BNT obtained by calcining and compounding barium titanate and sodium bismuth titanate with different particle sizes at different calcining temperatures;

FIG. 13 is an SEM image of 0.9BT-0.1BNT obtained by calcining and compounding barium titanate and sodium bismuth titanate with different particle sizes at different calcining temperatures.

Detailed Description

In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and the embodiments described below are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the description of the present invention, it should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight described in the embodiments of the present invention may be a unit of mass known in the chemical field such as μ g, mg, g, kg, etc.

In the description of the invention, an expression of a word in the singular should be understood to include the plural of the word, unless the context clearly dictates otherwise. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.

The embodiment of the invention provides a preparation method of an X9R type multilayer ceramic capacitor dielectric material, which comprises the following steps:

s1, providing 0.9BT-0.1 BNT;

s2, in a water system, carrying out coprecipitation reaction on 0.9BT-0.1BNT and a solution containing cobalt ions and neodymium ions to obtain 0.9BT-0.1BNT with the surface coated with cobalt elements and neodymium elements;

s3, sintering the 0.9BT-0.1BNT coated with the cobalt element and the neodymium element on the surface to obtain the X9R type multilayer ceramic capacitor dielectric material.

In order to improve the temperature stability of the dielectric material of the multilayer ceramic capacitor, 0.9BT-0.1BNT is used as a substrate, and a doping element coating layer is formed on the surface of the 0.9BT-0.1BNT in a mode of composite doping of cobalt element and neodymium element, so that the obtained dielectric material of the multilayer ceramic capacitor meets the requirement of the dielectric material of the X9R type multilayer ceramic capacitor. On one hand, the invention firstly synthesizes the 0.9BT-0.1BNT with the perovskite structure substrate, and then introduces the doping elements through water-based coating, thereby avoiding the reaction between the sodium bismuth titanate and the doping elements; on the other hand, cobalt may react with neodymium to form a complex or substitute for the neodymium to reduce the diffusion rate of neodymium, so as to further avoid the diffusion of the doping element. The preparation method of the X9R type multilayer ceramic capacitor dielectric material is simple, and has the advantages of easy implementation and safe and controllable reaction process.

In S1, barium titanate has a sharp phase transition peak at about 130 ℃, and the dielectric constant change at the temperature is large, so in order to obtain the dielectric material with a mild low-temperature dielectric peak, the invention adopts sodium bismuth titanate and barium titanate which have a perovskite structure and a Curie temperature of about 320 ℃ to form a solid solution 0.9BT-0.1BNT with the perovskite structure as a base material for preparing the dielectric material of the multilayer ceramic capacitor by subsequent doping element coating.

In some embodiments, in order to further improve the performance of the obtained dielectric material of the multilayer ceramic capacitor, the 0.9BT-0.1BNT is prepared by the following steps:

s11, providing bismuth oxide, sodium carbonate, titanium dioxide and barium titanate;

s12, calcining the ball-milled mixture of bismuth oxide, sodium carbonate and titanium dioxide for the first time to obtain sodium bismuth titanate;

s13, calcining the ball-milled mixture of barium titanate and sodium bismuth titanate for the second time to obtain 0.9BT-0.1 BNT.

In S11, since the target product X9R type multilayer ceramic capacitor dielectric material should have the characteristic of being ultra-thin, in some embodiments, barium titanate powder with the particle size of 60nm-200nm, preferably 60nm, is selected to enable sodium bismuth titanate to be dissolved in barium titanate to form a solid solution with moderate particles, which is beneficial to preparing the ultra-thin X9R type multilayer ceramic capacitor dielectric material.

In S12, bismuth oxide, sodium carbonate and titanium dioxide are used as initial raw materials, and the initial raw materials, the bismuth oxide, the sodium carbonate and the titanium dioxide are fully mixed through ball milling to obtain a solid phase mixture with uniform size. In some embodiments, ethanol is preferred as the ball milling medium for achieving better ball milling effect, and the ball milling time is preferably 24 h.

The solid phase mixture formed by bismuth oxide, sodium carbonate and titanium dioxide is calcined for the first time, so that the sodium bismuth titanate can be synthesized and used for compounding with barium titanate. Along with the rise of the calcination temperature, the particle size of the obtained sodium bismuth titanate is gradually increased, and by optimizing the temperature of the first calcination, the bismuth oxide, the sodium carbonate and the titanium dioxide can be ensured to react completely, and the problems that the particle size of the sodium bismuth titanate material is too large and the like caused by overhigh calcination temperature can be avoided. Thus, in some embodiments, the first calcination temperature is preferably from 800 ℃ to 1000 ℃; when the first calcination temperature is 900 ℃, the particle size of the obtained sodium bismuth titanate is moderate, and the reactants are completely reacted at the time, so the temperature value is the most preferable temperature value. Specifically, typical, but not limiting, first calcination temperatures are 800 deg.C, 850 deg.C, 900 deg.C, 950 deg.C, 1000 deg.C.

S13, it is understood that, since the present invention uses 0.9BT-0.1BNT as the matrix material, when barium titanate and sodium bismuth titanate are compounded, they are mixed according to the molar ratio of 9:1, then the barium titanate and sodium bismuth titanate are fully mixed by ball milling to obtain a solid phase mixture with uniform size, and then the solid phase mixture is calcined for the second time, so that sodium bismuth titanate can be dissolved in barium titanate to form a disordered solid solution with the perovskite structure as the framework. As the calcination temperature increased, the tetragonality of 0.9BT-0.1BNT gradually decreased, since more sodium bismuth titanate was dissolved into barium titanate, deteriorating the tetragonality of 0.9BT-0.1 BNT; meanwhile, with the increase of the calcination temperature, the main peak of 0.9BT-0.1BNT near 30 degrees gradually shifts to a large angle, namely is biased to the position of the main peak of the sodium bismuth titanate. Therefore, the calcining temperature is too low, the solid solution amount of the sodium bismuth titanate is limited, and the required solid solution is difficult to form; too high calcination temperature in turn leads to too coarse particles of 0.9BT-0.1BNT, which is not favorable for preparing ultrathin X9R type multilayer ceramic capacitor dielectric material. Thus, in some embodiments, the second calcination temperature is preferably from 900 ℃ to 1100 ℃; when the second calcination temperature is 1000 ℃, the solid solution amount of the sodium bismuth titanate is increased, and the obtained 0.9BT-0.1BNT has moderate particle size, which is the most preferable temperature value. Specifically, typical, but not limiting, second calcination temperatures are 900 deg.C, 950 deg.C, 1000 deg.C, 1050 deg.C, 1100 deg.C.

In S2, the formation of the doped element coating layer on the surface of the substrate should be performed in an aqueous system. This is because when the same level of doped oxide is introduced into the matrix by the conventional ball-milling doping process, the doping effect will be greatly reduced because it is difficult to form a mixed powder with uniform mixing and good dispersibility. The water-based chemical coating method has the advantages of convenience in regulating and controlling the pH value of the system and uniform coating of the doping elements.

The invention takes solution containing cobalt ions and neodymium ions as a composite doping agent for coating 0.9BT-0.1BNT matrix material. The solution containing cobalt ions and neodymium ions is obtained by mixing cobalt ions and neodymium ions, and in some embodiments, Co (NO) is preferred for simplicity of the process₃)₂·6H₂O and C₁₀H₅NbO₂₀·xH₂O is obtained after being dissolved in water with the temperature of 45 ℃ by stirring.

When the dopant is introduced through cladding, the doping amount is determined by the concentration of the solution containing cobalt ions and neodymium ions, the doping amount is related to the proportion of a core/shell in a core-shell structure, and improper doping amount can cause the core-shell structure to be out of order, so that the dielectric property of the MLCC cannot meet the requirement of X9R. In some embodiments, the solution comprising cobalt and neodymium ions has a total of 4 mole percent cobalt and neodymium ions, based on a 0.9BT-0.1BNT mole concentration.

Further, neodymium is easier to promote the sintering of 0.9BT-0.1BNT than cobalt, and associated defects or Co is formed during Co/Nb composite doping²⁺Nb₂O₆The composite inhibits the diffusion of the doping elements inwards, so that the proportion of the shell part of the core-shell structure is smaller, the low-temperature dielectric peak is flattened, and the overall temperature stability is improved, therefore, in some embodiments, the sum of the molar concentrations of the cobalt ions and the neodymium ions in the solution containing the cobalt ions and the neodymium ions is 4% based on the molar concentration of 0.9BT-0.1BNT, and the molar concentration ratio of the cobalt ions to the neodymium ions is (0.5:1) - (2: 1). It was found experimentally that when the molar concentration ratio of cobalt ions to neodymium ions was 1:1, the ratio of the "shell" was lower than that of the other molar concentration ratios, i.e., the optimum value was found when the molar concentrations of cobalt ions and neodymium ions were both 2%.

The coprecipitation reaction of 0.9BT-0.1BNT and the solution containing cobalt ions and neodymium ions is a liquid phase chemical coating process, which is essentially a nucleation process containing both non-uniformity and uniformity. Wherein, the heterogeneity means that the dopant is precipitated on the surface of the dispersoid in a metastable liquid phase dispersion system; the uniformity refers to that the deposition on the surface of the dispersoid is uniform in thickness and regular in appearance. Therefore, to achieve uniform coating, the matrix must first be well dispersed. In some embodiments, in order to sufficiently disperse the matrix in the aqueous system, it is preferable to add an auxiliary dispersant to the aqueous system to promote the dispersion effect of the matrix.

Further, since the doping ion to be added later belongs to a cation of a weak base or a medium-strength base, the selected auxiliary dispersant is preferably an acidic dispersant.

Further, at least one of glycine, polyacrylic acid, an anionic dispersant I-7, and an anionic dispersant Lomar PWA-40K is selected as the acidic dispersant. Among them, LomarPWA-40K has a long carbon chain and a carboxyl group directly bonded to the carbon chain, and thus has the best effect of auxiliary dispersion, and is the most preferable auxiliary dispersant.

By optimizing the addition amount of the auxiliary dispersing agent, the problems of overlarge system viscosity, performance change and the like caused by excessive dispersing agent can be avoided while a good dispersing effect is ensured. Thus, in some embodiments, the mass of the secondary dispersant comprises 3% of the mass of the 0.9BT-0.1BNT matrix material.

In some embodiments, the pH of the reaction system is lower during the coprecipitation reaction of 0.9BT-0.1BNT with the solution containing cobalt ions and neodymium ions, and the precipitate can be more rapidly and completely formed by adjusting the pH of the reaction system to be greater than 6. Wherein, the solution for adjusting the pH value is preferably ammonia water, and has the advantages of low cost and difficult introduction of impurities.

Further, in order to make the precipitation more complete, it is preferable to adjust the pH of the reaction system to 10.

In S3, organic impurities in the surface coated with cobalt and neodymium 0.9BT-0.1BNT are removed by sintering, and simultaneously, the doping element neodymium and cobalt form a completely crystallized doping element coating layer, thus obtaining the X9R type multilayer ceramic capacitor dielectric material. In some embodiments, the densification of the obtained X9R type multilayer ceramic capacitor dielectric material can be optimized by optimizing the sintering temperature. Therefore, the temperature of the sintering treatment is preferably 1100 ℃ to 1200 ℃. Specifically, typical, but not limiting, sintering temperatures are 1100 deg.C, 1120 deg.C, 1140 deg.C, 1160 deg.C, 1180 deg.C, 1200 deg.C.

Correspondingly, the embodiment of the invention also provides the X9R type multilayer ceramic capacitor dielectric material prepared by the preparation method of the X9R type multilayer ceramic capacitor dielectric material.

In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art and to make the advanced performance of the dielectric material of the multilayer ceramic capacitor of the embodiment X9R type and the method for preparing the same of the present invention obviously manifest, the above technical solution is exemplified by a plurality of embodiments.

Example 1

A preparation method of a dielectric material of a multilayer ceramic capacitor comprises the following steps:

(1) with bismuth (Bi) oxide₂O₃Analytical pure, Shanghai test), sodium carbonate (Na)₂CO₃Analytical grade, Shanghai test), titanium dioxide (TiO)₂Analytically pure, alatin) as a starting material, taking ethanol as a ball milling medium, performing ball milling for 24 hours, drying, and calcining the solid phase mixture at 900 ℃ to obtain bismuth sodium titanate;

(2) mixing barium titanate (HBT006P, particle size 60nm, Shandong China porcelain) and sodium bismuth titanate by ball milling, drying, calcining at 1000 deg.C, and synthesizing 0.9BT-0.1 BNT;

(3) c is to be₁₀H₅NbO₂₀·xH₂O and Co (NO)₃)₂·6H₂Dissolving O in water at 45 ℃ by magnetic stirring to obtain an aqueous solution containing cobalt ions and neodymium ions, wherein the molar concentrations of the cobalt ions and the neodymium ions are both 2% based on the molar concentration of 0.9BT-0.1 BNT;

(4) adding synthesized 0.9BT-0.1BNT into 3 wt% of auxiliary dispersant Lomar PWA-40K to disperse in water solvent, pouring aqueous solution containing cobalt ions and neodymium ions into the solution dispersed with 0.9BT-0.1BNT, magnetically stirring for 2h to uniformly mix, slowly dropping dilute ammonia water until the pH value is more than 6, precipitating at the moment, then continuing dropping ammonia water until the pH value of the solution is 10 to ensure that the solution is completely precipitated, drying the solution, and presintering at 550 ℃ to remove organic matters; and then, sieving, granulating and tabletting the pre-sintered powder, and sintering at the sintering temperature of 1160 ℃ to obtain the dielectric material of the multilayer ceramic capacitor.

Example 2

This example is substantially the same as example 1 except that the molar concentration of cobalt ions is 4% and the molar concentration of neodymium ions is 0, i.e., a single doping of cobalt element, based on the molar concentration of 0.9BT-0.1 BNT.

Example 3

This example is essentially the same as example 1 except that the molar concentration of cobalt ions is 2.66% and the molar concentration of neodymium ions is 1.33% based on the molar concentration of 0.9BT-0.1 BNT.

Example 4

This example is essentially the same as example 1 except that the molar concentration of cobalt ions is 1.33% and the molar concentration of neodymium ions is 2.66% based on the molar concentration of 0.9BT-0.1 BNT.

Example 5

This example is substantially the same as example 1 except that the molar concentration of cobalt ions is 0 and the molar concentration of neodymium ions is 4%, based on the molar concentration of 0.9BT-0.1BNT, i.e., neodymium is doped singly.

Examples 6 to 10

Examples 6 to 10 were substantially the same as example 1 except that the sintering temperatures were 1100 ℃, 1120 ℃, 1140 ℃, 1180 ℃ and 1200 ℃, respectively.

Examples 11 to 15

Examples 11-15 are substantially the same as example 2 except that the sintering temperatures were 1100 deg.C, 1120 deg.C, 1140 deg.C, 1180 deg.C and 1200 deg.C, respectively.

Examples 16 to 20

Examples 16 to 20 were substantially the same as example 3 except that the sintering temperatures were 1100 ℃, 1120 ℃, 1140 ℃, 1180 ℃ and 1200 ℃, respectively.

Examples 21 to 25

Examples 21-25 are essentially the same as example 4, except that the sintering temperatures were 1100 deg.C, 1120 deg.C, 1140 deg.C, 1180 deg.C, and 1200 deg.C, respectively.

Examples 26 to 30

Examples 26 to 30 were substantially the same as example 5 except that the sintering temperatures were 1100 ℃, 1120 ℃, 1140 ℃, 1180 ℃ and 1200 ℃, respectively.

Example 31

This example is essentially the same as example 1 except that the auxiliary dispersant is glycine.

Example 32

This example is essentially the same as example 1, except that the auxiliary dispersant is polyacrylic acid.

Example 33

This example is essentially the same as example 1, except that the auxiliary dispersant is commercial anionic dispersant I-7.

Example 34

This example is substantially the same as example 1 except that barium titanate is HBT010, has a particle size of 100nm, and is available from Shandong China.

Example 35

This example is substantially the same as example 1 except that barium titanate is HBT020 with a particle size of 200nm, which is commercially available from Shandong China.

Example 36

This example is substantially the same as example 1 except that in step (1), the calcination temperature was 800 ℃.

Example 37

This example is substantially the same as example 1 except that in step (1), the calcination temperature was 1000 ℃.

Example 38

This example is substantially the same as example 1 except that in step (2), the calcination temperature was 900 ℃.

Example 39

This example is substantially the same as example 1 except that in step (2), the calcination temperature was 1100 ℃.

Example 40

This example is substantially the same as example 1 except that barium titanate is HBT010, has a particle size of 100nm, is commercially available from Shandong China and that in step (2), the calcination temperature is 900 ℃.

EXAMPLE 41

This example is substantially the same as example 1 except that barium titanate is HBT010, has a particle size of 100nm, is commercially available from Shandong China and that in step (2), the calcination temperature is 1100 ℃.

Example 42

This example is substantially the same as example 1 except that barium titanate is HBT020 with a particle size of 200nm, which is commercially available from Shandong China and the calcination temperature in step (2) is 900 ℃.

Example 43

This example is substantially the same as example 1 except that barium titanate is HBT020 with a particle size of 200nm, which is commercially available from Shandong China and the calcination temperature in step (2) is 1100 ℃.

Performance testing and characterization method

1. Structural analysis

The powder to be subjected to structural analysis according to the present invention was subjected to structural analysis using a 9KW multifunction X-Ray diffractometer manufactured by Rigaku, japan. When preparing a sample to be detected by XRD, about 3g of powder to be detected is placed in the center of a glass slide. And applying pressure to the glass slide by using another glass slide to flatten the top layer of the stacked powder. And (5) placing the sample into an XRD testing device for measurement and analysis.

2. Topography analysis

For the calcined powder, a Gemini SEM300 model field emission scanning electron microscope from ZEISS, Germany was used for testing.

When preparing the powder sample, firstly, absolute ethyl alcohol is poured into the sample tube, and about 0.2g of the sample to be detected is taken out by tweezers and dissolved in the absolute ethyl alcohol. After the sample tube is shaken, the sample tube is subjected to ultrasonic dispersion for about 40 minutes, a dropper is used for taking out 5-6 drops of sample solution from the sample tube to be dropped on the surface of a glass slide, and then the glass slide is placed into a 100 ℃ oven to be dried, so that the absolute ethyl alcohol is evaporated. After about 2-3 min, the absolute ethyl alcohol dissolving the powder is completely evaporated. And taking out the glass slide, using conductive adhesive to pick the powder on the surface of the glass slide, selecting a place where the powder is uniform and smooth when sampling, and then fixing the conductive adhesive with the powder on a special sample table of the scanning electron microscope. Since the ceramic sample is not conductive, the surface of the sample needs to be treated by spraying gold by using a gold spraying instrument.

When the surface morphology of a sample is observed by using a scanning electron microscope, the voltage is 10kV, the 10000 times, 20000 times, 30000 times, 40000 times and 50000 times of the surface morphology are respectively subjected to screenshot analysis, and particle size statistics is performed by using particle size statistics software.

Performance test and characterization results

SEM scans of the sodium carbonate, bismuth oxide and titanium dioxide used in step (1) of examples 1-43 are shown in FIG. 1. As can be seen from FIG. 1, the uniformity of the three raw material powders is good, and meets the requirements of the dielectric material for preparing the multilayer ceramic capacitor.

As a result of measuring the densities of the dielectric materials for multilayer ceramic capacitors obtained in examples 1 to 30, it was found that the sintering temperatures of the various doping elements were different from the densities of the dielectric materials for multilayer ceramic capacitors obtained, and the results are shown in FIG. 2, in which the folding line 1 corresponds to example 2 and examples 11 to 15, the folding line 2 corresponds to example 3 and examples 16 to 20, the folding line 3 corresponds to example 1 and examples 6 to 10, the folding line 4 corresponds to example 4 and examples 21 to 25, and the folding line 5 corresponds to example 5 and examples 26 to 30. It can be seen that when the molar concentration of cobalt in the doping element is less than 2%, the optimum sintering temperature is 1180 ℃, and when the doping element is more than 2%, the optimum sintering temperature is 1160 ℃, indicating that neodymium is easier to promote sintering of 0.9BT-0.1BNT than cobalt.

The resulting multilayer ceramic capacitor dielectric materials having the best respective densities in the folding lines 1 to 5 were subjected to dielectric temperature spectrum and TCC map, as shown in FIG. 3, wherein (a) is the dielectric temperature spectrum and (b) is the TCC map. It can be seen that when only cobalt element is doped, the curie peak is too high to meet the requirement of X9R type; when only neodymium is doped, the effect of pressing the Curie peak is better than that of only cobalt doping; when the cobalt and the neodymium are doped compositely, the Curie peak inhibition effect is obviously better than that of single doping, and the low-temperature dielectric peak also has a more gentle trend. This may be due to Co/Nb formation of association defects or Co formation²⁺Nb₂O₆The compound hinders the inward diffusion of the doping elements, so that the proportion of the shell part of the core-shell structure is smaller, the low-temperature dielectric peak is leveled, and the overall temperature stability is improved. To verify this conclusion, TEM images of the multilayer ceramic capacitor dielectric materials obtained in examples 1 and 5 were made as shown in FIG. 4, wherein (a) is the multilayer ceramic capacitor dielectric material obtained in example 5, and (b) is the multilayer ceramic capacitor dielectric material obtained in example 1. It can be seen that both form a "core-shell" structure, but the proportion of the "shell" portion of (b) is significantly lower than that of (a).

In order to determine the distribution of the doping elements, fig. 5 shows the HAADF graph (a) and the composition distribution (b) of the EDS selected region of the multilayer ceramic capacitor dielectric material obtained in example 5. It can be seen that the material has formed a "core-shell" structure which is clearly visible, and that the distribution of neodymium from the "shell" portion to the "core" portion is a straight descending trend, mainly in the region of the "shell" portion.

In example 1, after removing the organic substances by pre-firing at 550 ℃ in step (4), the morphology of the obtained powder was examined, as shown in fig. 6, wherein (a) is a TEM image, (b) is an STEM image, and (c) is an EDS distribution chart. As can be seen from the TEM image, a layer of small particles with slightly poor crystallinity is coated on the periphery of the matrix with the particle diameter of less than 100 nm; from the EDS distribution chart, it was confirmed that these small particles were liquid-phase-coated and then pre-sintered with the doping elements of cobalt and neodymium attached to the surface of the base particles, and thus it was confirmed that the liquid-phase coating according to the present invention allows the doping elements of cobalt and neodymium to be deposited on the surface of the base particles and form a crystallized doping element coating layer.

The particle size distribution of example 1 and examples 31 to 33 was measured by adding different auxiliary dispersants, and the results are shown in FIG. 7 and Table 1, in which samples 1 to 3 correspond to examples 31 to 33, respectively, and sample 4 corresponds to example 1.

TABLE 1 results of particle size distribution in solution systems after dispersion of different auxiliary dispersants

As can be seen from the particle size distribution data in FIG. 7 and Table 1, the commercial anionic dispersant I-7 has the worst dispersion effect and the commercial anionic dispersant LomarPWA-40K has the best dispersion effect, and from the Fourier transform infrared spectroscopy (FTIR) (FIG. 8), it is found that the commercial anionic dispersant LomarPWA-40K has a long carbon chain and a carboxyl group directly connected to the carbon chain, and therefore, the use of LomarPWA-40K as an auxiliary dispersant is most suitable for obtaining a 0.9BT-0.1BNT matrix uniformly dispersed in an aqueous system.

In example 1 and examples 34 and 35, barium titanate powders having different particle diameters were used, and the SEM chart and the XRD chart are shown in fig. 9, in which (a) is HBT006P used in example 1, (b) is HBT010 used in example 35, and (c) is HBT020 used in example 35.

Fig. 10 shows the XRD and cell parameter relationship diagrams after the barium titanate powder with different particle sizes and the sodium bismuth titanate were combined, where (a) is HBT006P used in example 1, (b) is HBT010 used in example 35, and (c) is HBT020 used in example 35.

In example 1 and examples 36 and 37, different calcination temperatures were used in the synthesis of sodium bismuth titanate, and FIG. 11 shows SEM, XRD and Raman diagrams of sodium bismuth titanate obtained in example 1 and examples 36 and 37, wherein (a) is the implementationBismuth sodium titanate obtained in example 36, (b) is bismuth sodium titanate obtained in example 1, and (c) is bismuth sodium titanate obtained in example 37. It can be seen that the particle size of the sodium bismuth titanate gradually increased with the increase of the calcination temperature, and the sodium bismuth titanate was synthesized after calcination at 800 ℃, but some bismuth oxide did not react completely at this time, corresponding to 300cm^-1The cleavage peak of (a); on the other hand, when the calcination temperature is 1000 ℃, the particle size of the obtained sodium bismuth titanate is about 350nm and is too coarse, so 900 ℃ is the optimum calcination temperature.

In examples 1 and 38 to 43, barium titanate with different particle sizes and sodium bismuth titanate were calcined and compounded at different calcination temperatures, and the XRD and cell parameter relationship diagrams of the obtained 0.9BT-0.1BNT are shown in fig. 12, in which the barium titanate used in (a)/(a1) was HBT006P, the barium titanate used in (b)/(b1) was HBT010, and the barium titanate used in (c)/(c1) was HBT 020. As can be seen from FIG. 12, the 0.9BT-0.1BNT synthesized at the three calcination temperatures are all perovskite phases, indicating that the sodium bismuth titanate has been complexed with barium titanate to form a disordered solid solution framed by a perovskite structure. As the calcination temperature increases, the tetragonality of 0.9BT-0.1BNT gradually decreases, since more sodium bismuth titanate is dissolved into barium titanate, deteriorating its tetragonality; further, as the calcination temperature was increased, the main peak located in the vicinity of 30 ° was gradually shifted toward a large angle, i.e., toward the position of the main peak of sodium bismuth titanate.

Barium titanate and sodium bismuth titanate with different particle sizes are calcined and compounded at different calcination temperatures, and the SEM images of the obtained 0.9BT-0.1BNT are shown in figure 13, wherein (a1) - (a3) are products obtained by calcining and compounding HBT006P and sodium bismuth titanate at 900 ℃, 1000 ℃ and 1100 ℃, respectively, (b1) - (b3) are products obtained by calcining and compounding HBT010 and sodium bismuth titanate at 900 ℃, 1000 ℃ and 1100 ℃, respectively, and (c1) - (c3) are products obtained by calcining and compounding HBT020 and sodium bismuth titanate at 900 ℃, 1000 ℃ and 1100 ℃, respectively. As can be seen from fig. 13, after the calcination at 900 ℃, the morphology of barium titanate is substantially maintained, and it can be seen that the solid solution amount of sodium bismuth titanate is limited at the calcination temperature; when the calcination temperature is 1000 ℃, the particles begin to grow larger along with the increase of the solid solution amount of the sodium bismuth titanate; when the calcination temperature is raised to 1100 ℃, the particles are too coarse, and therefore, 1000 ℃ is the preferred calcination temperature.

It can be seen from the above embodiments and performance test results that, in the core-shell structure of the present invention, 0.9BT-0.1BNT is used as a substrate, and in a manner of composite doping of cobalt and neodymium, cobalt can react with neodymium to form a composite or substitute for the position of neodymium, thereby reducing the diffusion rate of neodymium, and hindering the diffusion of doping elements to the core, so that more doping elements stay in the shell, thereby reducing the proportion of the shell in the core-shell structure, and the reduction of the proportion of the shell can alleviate the low-temperature dielectric peak of the dielectric material, so that the multilayer ceramic capacitor dielectric material of the present invention has the advantages of more moderate low-temperature dielectric peak and high overall temperature stability.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of an X9R type multilayer ceramic capacitor dielectric material is characterized by comprising the following steps:

providing 0.9BT-0.1 BNT;

2. The method of claim 1 wherein the total molar concentration of cobalt ions and neodymium ions in said solution containing cobalt ions and neodymium ions is 4% based on the molar concentration of 0.9BT-0.1 BNT; and/or;

in the solution containing cobalt ions and neodymium ions, the sum of the molar concentrations of the cobalt ions and the neodymium ions is 4% based on the molar concentration of 0.9BT-0.1BNT, and the molar concentration ratio of the cobalt ions to the neodymium ions is (0.5:1) - (2: 1).

3. The method for preparing a dielectric material of a multilayer ceramic capacitor of X9R type according to claim 1, wherein an auxiliary dispersant is further added to the water system; and/or

An auxiliary dispersant is also added into the water system, and the auxiliary dispersant is an acidic dispersant; and/or

An auxiliary dispersant is also added into the water system, and the auxiliary dispersant is at least one selected from glycine, polyacrylic acid, an anionic dispersant I-7 and an anionic dispersant Lomar PWA-40K; and/or

An auxiliary dispersant is also added into the water system, and the mass of the auxiliary dispersant accounts for 3% of the mass of the 0.9BT-0.1 BNT.

4. The method for preparing a dielectric material of a multilayer ceramic capacitor of X9R type according to claim 1, wherein the pH of the reaction system is greater than 6 during the coprecipitation reaction.

5. The method for preparing a dielectric material of a multilayer ceramic capacitor of X9R type according to claim 1, wherein the sintering temperature is 1100-1200 ℃.

6. The method for preparing X9R-type multi-layer ceramic capacitor dielectric material according to any one of claims 1-5, wherein the method for synthesizing 0.9BT-0.1BNT comprises the following steps:

7. The method for preparing a dielectric material of a multilayer ceramic capacitor of X9R type according to claim 6, wherein the particle size of the barium titanate is 60nm-200 nm.

8. The method for preparing the X9R-type multilayer ceramic capacitor dielectric material as claimed in claim 6, wherein the temperature of the first calcination is 800-1000 ℃; and/or

The temperature of the second calcination is 900-1100 ℃.

9. An X9R type multilayer ceramic capacitor dielectric material, which is prepared by the method for preparing the X9R type multilayer ceramic capacitor dielectric material according to any one of claims 1 to 8.

10. The X9R-type multilayer ceramic capacitor dielectric material as claimed in claim 9, wherein the X9R-type multilayer ceramic capacitor dielectric material has a "core-shell" structure in which 0.9BT-0.1BNT is used as a "core" and a surface clad layer formed of cobalt element and neodymium element is used as a "shell".