JP6517012B2 - Method of manufacturing dielectric ceramic particles and dielectric ceramic - Google Patents

Description

  The present invention relates to a method of manufacturing dielectric ceramic particles and dielectric ceramics.

  With the spread of smartphones, tablets, etc., miniaturization and high performance of electronic components used for these are being promoted, and as a matter of course, MLCC (Multi Layer Ceramic Capacitor) used as a multilayer capacitor is also natural. Small size and large capacity are required.

At present, in order to miniaturize and increase the capacity of MLCCs, it is the mainstream to thin the dielectric layer to increase the number of stacked layers. For this purpose, a technology capable of micronizing (reducing the particle diameter) of dielectric ceramics such as barium titanate (BaTiO ₃ : BT) used as dielectric materials is required.

  However, barium titanate is known to decrease in relative dielectric constant as the particle size decreases (size effect), and as long as barium titanate is used, further miniaturization and capacity increase of future MLCCs A difficult situation is coming to Therefore, development of a new material that exhibits a dielectric constant higher than that of barium titanate has been made.

  As one type of such materials, dielectric ceramic particles in the form of a core-shell structure are known, in which core particles and a shell phase are respectively formed by different types of complex oxides. The dielectric ceramic particles having such a core-shell structure are expected to exhibit not only the relative dielectric constant but also an improvement effect on other physical properties such as DC bias characteristics.

As an example of a dielectric ceramic particle having a core-shell structure, barium titanate is used as a core particle, and the core particle is covered with strontium titanate (SrTiO ₃ : ST) to form a shell phase, thereby forming BT / ST. A technique for producing a composite nanoparticle (core-shell structure) of the above has been proposed (for example, Patent Document 1).

Such core - a method for manufacturing a shell structure, Patent Document 1, the barium titanate particles as the core particles, strontium hydroxide and titanium diisopropoxy blunder acetylacetonate _{^{(Ti (i PrO) 2 (}} AcAc) ₂ discloses a method using TPA) as a raw material for shell phase formation. In the above method, the core-shell structure can be produced by performing a solvothermal synthesis process using barium titanate particles, strontium hydroxide and TPA.

JP, 2010-208923, A

  According to the technique of Patent Document 1, barium titanate / strontium titanate composite nanoparticles can be manufactured. However, since TPA used as a raw material is a chelate complex and is an expensive compound, from the viewpoint of industrialization, a technique capable of using a cheaper raw material is required.

  Therefore, an object of the present invention is to provide a method for producing dielectric ceramic particles having a core-shell structure using cheaper raw materials. Another object of the present invention is to provide a dielectric ceramic containing dielectric ceramic particles obtained by the above method.

  The present inventors diligently studied to solve the above problems. As a result, in the method for producing dielectric ceramic particles having core particles and shell phase, the core particles and the raw material compound for shell phase are dry mixed by a mechanical rotator having a mechanism rotating at a specific angular velocity or more. It has been found that it is possible to manufacture the above-mentioned dielectric ceramic particles using inexpensive raw materials, and the present invention has been completed.

  That is, the above object of the present invention is achieved by the following constitution.

A core particle mainly composed of a first complex oxide having a perovskite structure at 1.25 ° C., and a second complex oxide formed on the surface of the core particle and different from the first complex oxide A method of manufacturing dielectric ceramic particles having a shell phase mainly composed of
Dry-mixing the core particle and the material compound of the second composite oxide to coat the material particle of the second composite oxide on the core particle to obtain a material mixture;
Performing a hydrothermal synthesis process or a solvothermal synthesis process on the raw material mixture,
The method for producing dielectric ceramic particles, wherein the dry mixing is performed by a mechanical rotating body having a mechanism rotating at an angular velocity of 6 × 10 ³ rad / s or higher;
2. The dry mixing is carried out by a mechanofusion apparatus. A method of producing dielectric ceramic particles described in
3. The raw material compound of the second composite oxide includes at least one selected from the group consisting of zirconium oxide, titanium oxide and niobium oxide. Or 2. A method of producing dielectric ceramic particles described in
4. The second composite oxide is barium zirconate, barium titanate, strontium titanate, calcium titanate, potassium niobate or sodium niobate. ~ 3. A method of producing dielectric ceramic particles according to any one of the above;
5. The first composite oxide is barium titanate, barium zirconate, strontium titanate, calcium titanate, potassium niobate or sodium niobate. ~ 4. A method of producing dielectric ceramic particles according to any one of the above;
6. Above 1. To 5. A dielectric ceramic comprising dielectric ceramic particles produced by the method according to any one of the above.

  According to the present invention, there is provided a method of producing dielectric ceramic particles having a core-shell structure using a cheaper raw material. Furthermore, according to the present invention, there is provided a dielectric ceramic containing dielectric ceramic particles obtained by the above method.

7 is a STEM image of dielectric ceramic particles according to Example 1. FIG. It is the mapping data of Ba measured in the same visual field as FIG. 1A. It is the mapping data of Ti measured by the same visual field as FIG. 1A. It is mapping data of Zr measured by the same visual field as FIG. 1A. It is the mapping data of Ba + Ti + Zr measured by the same visual field as FIG. 1A. 5 is a SEM image of core particles before the mixing step according to Example 1. FIG. 5 is a SEM image of dielectric ceramic particles (1) according to Example 1. FIG. 7 is a SEM image of core particles before the mixing step according to Example 2. FIG. 7 is a SEM image of dielectric ceramic particles (2) according to Example 2. FIG. 16 is a SEM image of core particles before the mixing step according to Example 3. FIG. 10 is a SEM image of dielectric ceramic particles (3) according to Example 3. FIG. FIG. 16 is a SEM image of core particles before the mixing step according to Example 4. FIG. 7 is a SEM image of dielectric ceramic particles (4) according to Example 4. 15 is a SEM image of core particles before the mixing step according to Example 5. FIG. 15 is a SEM image of dielectric ceramic particles (5) according to Example 5. FIG. 15 is a SEM image of core particles before the mixing step according to Example 6. FIG. FIG. 18 is a SEM image of dielectric ceramic particles (6) according to Example 6. FIG. FIG. 18 is a SEM image of core particles before the mixing step according to Example 7. FIG. FIG. 16 is a SEM image of dielectric ceramic particles (7) according to Example 7. FIG. 21 is a SEM image of core particles before the mixing step according to Example 8. FIG. FIG. 16 is a SEM image of dielectric ceramic particles (8) according to Example 8. FIG. 21 is a SEM image of core particles before the mixing step according to Example 9. FIG. FIG. 18 is a SEM image of dielectric ceramic particles (9) according to Example 9. FIG. 21 is a SEM image of core particles before the mixing step according to Example 10. FIG. FIG. 16 is a SEM image of dielectric ceramic particles (10) according to Example 10. FIG. 15 is a SEM image of core particles before the mixing step according to Example 11. FIG. FIG. 16 is a SEM image of dielectric ceramic particles (11) according to Example 11. FIG. It is a SEM image of comparative dielectric ceramic particles (1) concerning comparative example 1. FIG. It is a SEM image of comparative dielectric ceramic particles (2) concerning comparative example 2. It is a XRD spectrum of dielectric material ceramic particles (1) and (2) concerning Examples 1 and 2. It is a XRD spectrum of dielectric material ceramic particles (3) and (4) concerning Examples 3 and 4. It is a XRD spectrum of dielectric material ceramic particles (5) and (6) concerning Examples 5 and 6. It is a XRD spectrum of dielectric material ceramic particles (7) and (8) concerning Examples 7 and 8. It is a XRD spectrum of dielectric material ceramic particles (9) and (10) concerning Examples 9 and 10. FIG. 18 is an XRD spectrum of dielectric ceramic particles (11) according to Example 11. FIG. It is a XRD spectrum of comparative dielectric ceramic particles (1) and (2) concerning comparative examples 1 and 2.

  Hereinafter, embodiments of the present invention will be described.

According to a first aspect of the present invention, a core particle mainly composed of a first complex oxide having a perovskite structure at 25 ° C., and a core particle formed on the surface of the core particle, What is claimed is: 1. A method of manufacturing dielectric ceramic particles having a shell phase mainly composed of different second composite oxides, comprising:
Dry-mixing the core particle and the material compound of the second composite oxide to coat the material particle of the second composite oxide on the core particle to obtain a material mixture;
Performing a hydrothermal synthesis process or a solvothermal synthesis process on the raw material mixture,
The dry mixing is a method of manufacturing dielectric ceramic particles, which is performed by a mechanical rotator having a mechanism that rotates at an angular velocity of 6 × 10 ³ rad / s or more.

  In the process of examining the core-shell structure as disclosed in Patent Document 1, the present inventors focused on the production method, and examined a method that can be manufactured at lower cost. At that time, attention was paid to the method disclosed in Japanese Patent Application Laid-Open No. 2013-129560, in which barium titanate as a main component and a metal oxide as a minor component are mixed and fired. However, the sintered body obtained by the technique disclosed in the above-mentioned document becomes a solid solution, and the target core-shell structure can not be obtained.

  Next, the present inventors examined using a material of the above-mentioned literature, performing mixing processing by a general mixing method using a mortar and a pestle, and then performing hydrothermal synthesis processing or solvothermal synthesis processing, Even with this method, the coating of the shell phase on the core particles was insufficient, and it was not possible to obtain the intended core-shell structure.

  Therefore, the present inventors repeatedly conducted intensive studies, and surprisingly, using a mechanical rotator having a mechanism rotating at a specific angular velocity, the core particles and the raw material compound of the shell phase were mixed, and this mixture was used. It has been found that, by carrying out hydrothermal synthesis treatment or solvothermal synthesis treatment, dielectric ceramic particles having a target core-shell structure can be obtained.

  As described above, in the method of producing dielectric ceramic particles according to the present invention, when dry-mixing the core particles and the raw material compound of the shell phase, the mechanical rotation body having a mechanism rotating at a specific angular velocity or more is used. A mechanical rotator having such a mechanism can apply large mechanical energy such as shear stress and centrifugal force to the core particle and the raw material compound of the shell phase. And when this mechanical energy is added to the core particle and shell phase raw material compounds, the action such as friction and compression is added, the structure and bonding state of these raw materials are changed and activated, and it is easy to interact with other substances (Mechanochemical interaction). Therefore, due to this interaction, the raw material compound of the shell phase can be attached substantially uniformly to the surface of the core particle. As a result, the core particle surface is sufficiently coated with the raw material compound of the shell phase. At this time, it is not necessary to use an expensive chelate complex such as TPA as a raw material compound for the shell phase, and a relatively inexpensive compound such as a metal oxide can be applied. In addition, since processing can be performed in the form of powder, steps such as pellet molding can be omitted, and the manufacturing process is simplified, and there is also an advantage that it is easy to scale up.

  And, by performing the hydrothermal synthesis process or the solvothermal synthesis process in a state where the core particle is coated with the raw material compound of the shell phase as described above, production of dielectric ceramic particles having the above-mentioned core-shell structure is possible. Become. The present invention is not limited to the above mechanism.

  Hereinafter, components of the dielectric ceramic particles of the present invention, and modes and modes for carrying out the present invention will be described in detail. In addition, "-" shown in the following description uses the numerical value described before and after that in the meaning included as a lower limit and an upper limit. Moreover, unless otherwise indicated, measurement of operation, a physical property, etc. is measured on the conditions of room temperature (25 degreeC) / 40 to 50% relative humidity.

  Furthermore, in the present specification, “particle size” is obtained by imaging with an electron microscope, randomly extracting 50 particles, measuring the particle size, and averaging the particle sizes. Moreover, when the shape of particle | grains is not spherical, it defines as what measured and calculated the major axis.

«Method of manufacturing dielectric ceramic particles (dielectric ceramic)»
The process for producing dielectric ceramic particles according to the present invention comprises (1) mixing core particles with a raw material compound for forming a shell phase (mixing process) and (2) hydrothermal synthesis or solvothermal synthesis Are roughly divided into the steps of carrying out (synthesis steps). Moreover, you may perform (3) washing | cleaning / drying process as needed other than these. Each step will be described in detail below.

(1) Mixing Step In this step, core particles mainly composed of a first composite oxide having a perovskite structure at 25 ° C. and second composite oxides different from the first composite oxide as a main component A raw material compound for forming a shell phase is dry mixed, and the raw material compound is coated on core particles to obtain a raw material mixture.

  In the present specification, "having the first composite oxide as a main component" means that the first composite oxide is contained in an amount of 90% by mass or more based on the total amount of core particles. Further, "having the second composite oxide as a main component" means that the second composite oxide is contained in an amount of 90% by mass or more based on the total amount of the shell phase. Therefore, a slight amount of impurities which may be contained in the production may be contained in the core particles or in the shell phase. In addition, that a core particle contains 90 mass% or more of 1st complex oxides, and a shell phase contains 90 mass% or more of 2nd complex oxides is confirmed by the analysis by a fluorescent X ray.

  In this step, a core particle and a raw material compound of a second composite oxide for forming a shell phase (which may be simply referred to herein as "raw material compound" or "raw material compound for shell phase") The mixing is performed using a mechanical rotator having a mechanism that rotates at a specific angular velocity or more. Here, by using a mechanical rotator having a mechanism that rotates at a specific angular velocity or more, it is possible to use as a raw material compound for core particles and shell phase (herein, these may be simply referred to as “raw material mixture”). Suitable shear stress can be given to it. As a result, the surface of the core particle can be almost uniformly coated with the above-mentioned raw material compound by the above-mentioned mechanochemical interaction.

In the present invention, the specific angular velocity or more is 6 × 10 ³ rad / s or more. By using a mechanical rotator having a mechanism that rotates at an angular velocity equal to or greater than the value, it is possible to uniformly mix the core particle and shell phase raw material compounds while suppressing the uneven distribution of shell phase raw material compounds. The core particle can be coated with the raw material compound of the shell phase. Therefore, dielectric ceramic particles with few structural defects can be obtained. On the other hand, if it is less than the above value, the core particle can not be coated with the raw material compound of shell phase sufficiently, and it is difficult to obtain a dielectric ceramic particle having a core-shell structure.

  In addition, in this process, although it is preferable that the whole surface of core particle is coat | covered with the raw material compound of a shell phase with "coating | cover", a part of surface may be exposed. In detail, if 50% or more of the surface area of the core particle is occupied by the shell phase starting compound, it indicates that the core particle is "covered" by the shell phase starting compound. In addition, the specific measuring method of a coverage is based on the method as described in an Example.

  In a preferred embodiment, it is preferable that 50 area% or more of the surface of the core particle is covered with the shell phase starting compound, more preferably 60 area% or more, still more preferably 70 area% or more, particularly preferably 80 area% The above, most preferably 90% by area or more is preferably covered with the shell phase starting compound.

Thus, from the viewpoint of sufficiently covering the core particle surface with the raw material compound of the shell phase, the angular velocity is preferably 6.2 × 10 ³ rad / s or more, and 1.0 × 10 ⁴ rad / s. It is more preferable that it is the above, and it is especially preferable that it is 1.5 * 10 < ⁴ > rad / s or more.

On the other hand, the upper limit of the angular velocity is not particularly limited, but is 3.2 × 10 ⁴ rad / s or less in consideration of mechanical limit values.

  In this step, the core particles and the raw material compound of the shell phase are dry mixed. By dry mixing in this way, when using a mechanical rotating body as described above, shear stress is sufficiently applied to the raw material mixture, and the coating of the shell phase raw material compound is performed by mechanochemical interaction. Facilitate. In addition, it is industrially advantageous because it is not necessary to add or remove the solvent.

  In the present step, the mixing time is not particularly limited, but preferably 1 to 10 minutes. From the viewpoint of sufficient mixing and coating, the mixing time is preferably 2 to 8 minutes, and more preferably 3 to 6 minutes.

  Examples of mechanical rotating bodies (that is, mixing devices) used to perform mixing based on the above conditions include, for example, a hybridization device, a mechanofusion device, a theta composer and a mechano mill, but are not particularly limited.

  Specific examples of the mechanical rotator include hybridization devices such as Hybridizer NHS-1 (manufactured by Nara Machinery Co., Ltd.); mechanofusion system (manufactured by Hosokawa Micron Corporation), Nobilta (registered trademark) (manufactured by Hosokawa Micron Corporation) Etc .; Theta composer (made by Dekushou Seisakusho Co., Ltd.); Mechano mill (made by Okada Seiko Co., Ltd.); Henschel mixer (eg made by Nippon Coke Kogyo Co., Ltd.); Multipurpose mixer (eg A composite (manufactured by Japan Coke Industry Co., Ltd.) and the like.

  As described above, it is desirable that the diameter of the dielectric ceramic particles be reduced (the particle diameter be reduced) as a recent trend, and therefore the core particles preferably have a small particle diameter. Therefore, in order to coat core particles having a particle size of 1 μm or less for this purpose, it is preferable to use Mechanofusion system or Nobilta (registered trademark) (both Hosokawa Micron Corporation) among the above mixing devices. is there. Therefore, dry mixing in this step is particularly preferably performed by a mechanofusion system or a mechanofusion apparatus such as Nobilta (registered trademark).

  Here, the mechanofusion device is outlined. The mechanofusion device includes a rotating container and an inner piece (press head) that rotates in the rotating container. Here, the surface on the side close to the inner wall of the rotary container of the inner piece has a radius of curvature different from that of the inner wall of the rotary container. Therefore, the core particles and the raw material compound of the shell phase (that is, the raw material mixture) charged into the rotary vessel are pressed against and fixed to the inner wall of the rotary vessel by centrifugal force, and the inner piece having different curvature radius It receives shear stress between As a result, the core particle surface is coated with the raw material compound of the shell phase.

  By using the mechanofusion device, the core particle having a particle diameter of 100 nm to 1 μm can be sufficiently coated with the raw material compound of the shell phase, and the distance between the inner piece and the inner wall of the rotary vessel By adjusting the above, it is possible to coat the shell phase starting compound even on core particles having a smaller particle size. Specifically, the distance between the inner piece and the inner wall of the rotary container is preferably more than 0 mm and 3 mm or less.

  The atmosphere in this step is not particularly limited, and may be performed in the air or in an inert gas atmosphere such as nitrogen gas or argon gas. Also, the temperature at the time of mixing is not particularly limited, but it is preferable to carry out at a temperature at which the core particles and the raw material of the shell phase do not undergo modification to an extent that is unsuitable for preparation of the core-shell structure. Therefore, it is preferable to carry out at about 5 to 40 ° C.

  In addition, in order to prevent the shell phase from being separated on the core particle, the raw material compound of the core particle and the shell phase may be pre-mixed using a mortar and a pestle before mixing by the mechanical rotator. .

  Hereafter, the raw material compound of the core particle and shell phase used in this process is demonstrated.

(Core particle)
The core particle as a raw material of the dielectric ceramic particle is not particularly limited as long as it is a particle having a first composite oxide having a perovskite structure at 25 ° C. as a main component.

  The definition of the term “based on the first composite oxide” is as described above, and a slight amount of impurity components that may be contained in the production may be contained in the core particle. As the impure component, elements other than the elements constituting the first complex oxide, that is, components derived from metals such as potassium, sodium, aluminum, calcium, niobium, iron, lead, etc., glass components and organic components of hydrocarbon type, Surface adsorption water etc. are mentioned.

  The core particles preferably contain 93% by mass or more of the first composite oxide, more preferably 95% by mass or more, and particularly preferably 98% by mass or more based on the total amount of the core particles. . On the other hand, the upper limit thereof is not particularly limited, but is substantially 100% by mass. As the content of the first complex oxide increases, the interaction with the second complex oxide constituting the shell phase becomes easy, and contributes to the improvement of various physical property values such as the relative dielectric constant and the DC bias characteristic. preferable.

Here, as the first composite oxide having a perovskite structure at 25 ° C., barium titanate (BaTiO ₃ ), barium zirconate (BaZrO ₃ ), strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ) And potassium niobate (KNbO ₃ ) and sodium niobate (NaNbO ₃ ). As core particles containing the first composite oxide as a main component, a commercially available product may be used, and synthesis may be performed as appropriate.

  Among them, barium titanate is preferably used from the viewpoint of obtaining dielectric ceramic particles having a high relative dielectric constant. From the viewpoint of obtaining dielectric ceramic particles excellent in DC bias characteristics, it is preferable to use barium titanate, barium zirconate, strontium titanate, calcium titanate or potassium niobate.

  The particles containing the first composite oxide as a main component may be used alone or in combination of two or more.

  The particle size (average particle size) of the core particle is not particularly limited, and depends on the type of the first composite oxide constituting the core particle, but from the tendency of the particle size reduction of dielectric ceramic particles in recent years And 1 μm or less. On the other hand, it is preferable that the particle diameter of the core particle is 50 nm or more from the viewpoint of suppressing the size effect (reduction of the relative dielectric constant accompanied by the reduction of the particle diameter) and the aggregation.

  Also, from the viewpoint of forming a good core-shell structure, the particle diameter of the core particle is preferably 500 nm or less. Furthermore, from the practical viewpoint of reducing the particle diameter of the dielectric ceramic particles while suppressing the influence of the size effect, the particle diameter of the core particles is more preferably 80 to 450 nm, and 100 to 400 nm. And particularly preferred.

(Source compounds for shell phase)
In this step, the raw material compound of the shell phase is used in combination with the core particles to form a shell phase composed mainly of the second composite oxide. Here, the second composite oxide has a composition different from that of the first composite oxide, and is appropriately selected in consideration of the physical properties of the first composite oxide.

  Here, the second composite oxide constituting the shell phase is not particularly limited as long as the composition is different from the first composite oxide, but similar to the first composite oxide, it is a perovskite at 25 ° C. It is preferable that it has a structure. In addition, the second composite oxide can improve the physical properties (specific dielectric constant, DC bias characteristics, etc.) of the first composite oxide by interaction with the first composite oxide. And more preferred. Specifically, it is preferable that the first complex oxide and the second complex oxide be a combination in which lattice constants in the coaxial direction are different from each other. Thus, by using a combination of lattice constants different in the coaxial direction in the first composite oxide and the second composite oxide, the first core particle contained in the core particle at the core particle-shell phase interface is obtained. The unit cell of the complex oxide can be distorted. As a result, the dielectric constant and the DC bias characteristics can be improved.

Therefore, it is preferable that the second composite oxide satisfies the above conditions, and barium zirconate (BaZrO ₃ ), barium titanate (BaTiO ₃ ), and the like in consideration of the relationship with the first composite oxide. It is preferable to select from strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ), potassium niobate (KNbO ₃ ), and sodium niobate (NaNbO ₃ ).

In order to form a shell phase constituted by the second complex oxide, the raw material compound of the shell phase is preferably a compound containing an element contained in the second complex oxide. Here, the “element contained in the second complex oxide” is an element contained in the complex oxide having the perovskite structure (ABO ₃ type), which is the second complex oxide, that is, A site and B In this specification, a raw material compound containing an element occupying the B site of the second composite oxide is referred to as a “first raw material compound” and a raw material containing an element occupying the A site The compound may be referred to as a “second raw material compound.” A raw material compound containing both an element occupying the A site and an element occupying the B site is included in the “first raw material compound”.

  It is more preferable that it is an oxide or carbonate of the element contained in 2nd complex oxide as a raw material compound of the shell phase added at this process. By using such a compound as a raw material compound for the shell phase, the core-shell structure can be obtained by a relatively inexpensive method without using an expensive chelate complex such as TPA disclosed in Patent Document 1, for example. You can get it.

  In this step, it is not necessary to add both of the first raw material compound and the second raw material compound. Therefore, in this step, any one of the first raw material compound and the second raw material compound may be added. That is, in this step, the core particles and at least one of the raw material compounds of the shell phase may be mixed.

Here, the raw material compound of the shell phase added in this step is preferably the first raw material compound. Furthermore, among the first raw material compounds, oxides or carbonates of elements (metals) occupying the B site in the perovskite structure (ABO ₃ type) of the second complex oxide are more preferable. At this time, it is preferable that the raw material compound (second raw material compound) containing an element occupying the A site be added in (2) synthesis step described in detail below. In addition, the description regarding a 2nd raw material compound is explained in full detail in the section of the following (2) synthetic | combination process.

  Considering the elements contained in the second composite oxide, the first raw material compound added in this step is an oxide or carbonate of any one metal selected from the group consisting of zirconium, titanium and niobium Preferably it is a salt. These starting compounds are industrially advantageous because they are relatively inexpensive. In addition, it is said that the second complex oxide derived from the above-mentioned raw material compound can easily improve various physical properties such as relative dielectric constant and DC bias characteristics by the interaction with the first complex oxide constituting the core particle. There is also an advantage.

When a carbonate is used, (2) in the synthesis step, in order to accelerate the reaction to form a shell phase, an alkali source (OH ^- source) such as sodium hydroxide or potassium hydroxide may be further added. preferable.

  Among the first raw material compounds, in consideration of the ease of handling of the raw material compound in dry mixing and the simplicity of the post-treatment step, the raw material compound of the shell phase added in this step is a metal oxide It is preferable that it is a thing.

Therefore, if the raw material compound for the shell phase (first raw material compound) contains at least one selected from the group consisting of zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ) and niobium oxide (Nb ₂ O ₅ ) preferable. The first raw material compound may be used singly or in combination of two or more depending on the composition of the second composite oxide constituting the shell phase.

  The amount of the raw material compound for the shell phase (first raw material compound) to be added in this step is not particularly limited, and may be appropriately changed depending on the content ratio of the core particles and shell phase in the target dielectric ceramic particles.

  Here, the content ratio (molar ratio) of the second composite oxide constituting the shell phase is as long as the shell phase can coat the surface of the core particle containing the first composite oxide as a main component. There is no particular limitation, but as described in detail below, the second composite oxide constituting the shell phase is equimolar to the first composite oxide constituting the core particle, or It is preferable to be contained in a small molar ratio. Therefore, the molar ratio of the raw material compound of the shell phase (preferably, the first raw material compound) added in this step to the first composite oxide contained in the core particle is 0.1 to 1: 1 (shell The ratio of the raw material compound of the phase: the first composite compound) is preferable, and the ratio of 0.25 to 0.5: 1 is more preferable. In addition, when using 2 or more types of raw material compounds of a shell phase, the sum of B site element (element which occupies B site of 2nd complex oxide) contained in all the raw material compounds becomes 1st complex oxide. On the other hand, it is preferable to be within the above range.

  On the other hand, the shape of the raw material compound for the shell phase is not particularly limited, and any structure such as powdery, spherical, rod-like, needle-like, plate-like, columnar, indeterminate, scaly and spindle-like can be adopted. Among them, the spherical or irregular shape is preferable from the viewpoint of the availability of the raw material compound and the ease of coating the core particles. When the raw material compound of the shell phase is spherical, the particle size thereof is not particularly limited, but preferably smaller than the particle size of the core particle. More specifically, the particle diameter of the spherical shell phase starting compound is preferably 1.0 to 40% of the particle diameter of the core particles.

(2) Synthesis Step In this step, a shell phase is formed on the surface of the core particle by subjecting the raw material mixture obtained in the above step to a hydrothermal synthesis treatment or a solvothermal synthesis treatment.

  Hydrothermal synthesis treatment and solvothermal synthesis treatment are reactions performed under moderate to high pressure (usually 0.10 to 1,000 MPa) and moderate to high temperature (usually 100 ° C. to 1000 ° C.) The treatment is carried out using a solvent, which is differentiated according to the solvent used. The "hydrothermal synthesis process" is a case where only water (pure water, ion-exchanged water, ultrapure water, etc.) is used as a solvent, and other organic solvents are not contained as a solvent. On the other hand, "solvothermal synthesis treatment" is a form using an organic solvent, but if it contains an organic solvent, it is called "solvothermal synthesis treatment" even if it contains water.

  In this step, a raw material compound for forming a shell phase may be further added to the raw material mixture prepared in the above (1) mixing step. In the (1) mixing step described above, a mode in which only the first raw material compound (the raw material compound containing the element occupying the B site of the second composite oxide) is added as the shell phase raw material compound is described as a preferable form In this case, it is preferable to add a second raw material compound (a raw material compound containing an element occupying the A site of the second composite oxide) in this step.

The second raw material compound depends on the composition of the second composite oxide constituting the shell phase, but in the perovskite structure (ABO ₃ type) of the second composite oxide, hydroxylation of the element occupying the A site Substances, carbonates, acetates or alkoxide compounds are preferred.

  By adding the second raw material compound, elements necessary for forming the shell phase can be further added and supplemented.

  Considering the elements contained in the second composite oxide described in the section (1) of the mixing step, the second raw material compound is any one selected from the group consisting of barium, potassium, sodium, strontium and calcium Preference is given to the hydroxides, carbonates, acetates or alkoxides of one element. These starting compounds are industrially advantageous because they are relatively inexpensive. In addition, the second composite oxide derived from the first raw material compound and the second raw material compound has a relative dielectric constant or a DC bias due to an interaction with the first complex oxide constituting the core particle. There is also an advantage that it is easy to improve various physical properties such as properties.

In the case of using a carbonate, in order to promote the reaction to form the shell phase, sodium hydroxide, an alkali source such as potassium hydroxide ^- further adding what can be a (OH source) preferred.

  Among the second starting compound, the second starting compound is a hydroxide or a carbonate of the above element from the viewpoint of ease of handling of the starting compound and that the starting compound is relatively inexpensive. Preferably, the hydroxide is particularly preferred.

Therefore, the raw material compound for the shell phase (second raw material compound) is barium hydroxide such as barium hydroxide octahydrate (Ba (OH) ₂ .8H ₂ O), sodium hydroxide (NaOH), potassium hydroxide It is preferable to be selected from the group consisting of (KOH), strontium hydroxide (Sr (OH) ₂ ) and calcium hydroxide (Ca (OH) ₂ ). The above-mentioned second raw material compounds may be used singly or in combination of two or more depending on the composition of the second composite oxide constituting the shell phase.

  The addition amount of the second raw material compound is not particularly limited, and may be appropriately changed depending on the composition of the shell phase in the target dielectric ceramic particles. As an example, it is preferable that the molar ratio of the first raw material compound to the second raw material compound is a ratio of 1: 1.0-0. 0 (first raw material compound: second raw material compound). By setting the ratio as such, it is possible to convert into the target second complex oxide without remaining the first raw material compound, and to suppress the formation of an unreacted material which can be an impurity.

  As the solvent used in this step, water (pure water, ion-exchanged water, ultrapure water, etc.) and an organic solvent can be appropriately selected according to the material constituting the shell phase. That is, in this step, the hydrothermal synthesis process and the solvothermal synthesis process may be appropriately selected according to the material constituting the shell phase.

  Although it does not restrict | limit especially as a solvent which can be used at this process, The following are illustrated.

  As described above, the solvent used in the hydrothermal synthesis treatment is water (pure water, ion-exchanged water, ultrapure water, etc.).

  The solvent used in the solvothermal synthesis process is not particularly limited, and various organic solvents can be used. For example, alcohols such as methanol, ethanol, benzyl alcohol, methoxyethanol, etc .; ethylene glycol, diethylene glycol, etc. Glycols; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; esters such as butyl acetate, ethyl acetate, carbitol acetate and butyl carbitol acetate; ethers such as methyl cellosolve, ethyl cellosolve, butyl ether and tetrahydrofuran; Examples thereof include amines such as methyl ethanolamine and diethanolamine; and aromatics such as benzene, toluene and xylene. In addition, the said solvent may be used individually by 1 type, and may be used combining 2 or more types. Moreover, it is good also as a mixed solvent which mixed water with the said organic solvent.

  The solvent used in this step is preferably a non-acidic (that is, neutral or basic) mixture (reaction mixture) from the viewpoint of corrosion of the container and the like.

  Among the above solvents, water which is a strong polar solvent, alcohols, and a mixed solvent thereof are used as a particularly suitable solvent. Thus, by using a highly polar solvent, the reactivity becomes high, and the shell phase compound can be synthesized at a lower temperature. When a mixed solvent is used, it is preferable to mix water: alcohol in a mixing ratio (volume ratio) of 1: 9 to 9: 1. Furthermore, it is particularly preferable to use water as a solvent (that is, to carry out a hydrothermal synthesis treatment) in that it is a more polar solvent in addition to being inexpensive.

  The temperature during the hydrothermal synthesis reaction and the solvothermal reaction is not particularly limited, but is preferably 120 ° C. to 400 ° C., and more preferably 150 ° C. to 300 ° C.

  The time for carrying out the hydrothermal synthesis reaction or the solvothermal reaction is also not particularly limited, but preferably 1 to 72 hours, more preferably 5 to 50 hours, and still more preferably 10 to 30 hours.

  Although the pressure at the time of performing a hydrothermal synthesis reaction or a solvothermal reaction is not specifically limited, It is preferable to carry out by about 0.10-4.0 MPa. The reaction under such pressure can be carried out in a pressure container such as an autoclave.

(3) Washing / Drying Step After the dielectric ceramic particles having a core-shell structure are formed by the above (1) mixing step and (2) synthesis step, a washing / drying step may be carried out as required. This step is mainly performed to remove impurities and unreacted substances generated in the above (2) synthesis step. Therefore, as the washing solvent, a solvent which can dissolve them and which does not affect the produced dielectric ceramic particles is used. For example, washing with an aqueous solution of acetic acid, water or the like is preferable. The temperature of the cleaning solvent at this time is preferably 10 to 80 ° C. in order to efficiently remove impurities and unreacted substances and to prevent the physical properties of the purified dielectric ceramic particles from being damaged.

  Also, the drying conditions are not particularly limited, but drying at 100 to 150 ° C. is preferable. The drying apparatus used at this time is not particularly limited, and for example, a commonly used apparatus such as an oven or a hot air dryer can be used. These drying devices may be used in combination.

  The atmosphere at the time of drying is not particularly limited, and may be performed in the air or in an inert gas atmosphere such as nitrogen gas or argon gas.

«Dielectric ceramic particles»
The dielectric ceramic particle obtained by the manufacturing method of the present invention is formed on the surface of the core particle having a first composite oxide having a perovskite structure at 25 ° C. as a main component, and the first core particle. And a shell phase mainly composed of a second complex oxide different from the complex oxide. That is, the dielectric ceramic particle obtained by the production method of the present invention is a core-shell structure having a core particle and a shell phase covering the surface of the core particle. Here, the core-shell structure can be confirmed by STEM-EDS analysis or SEM observation. In particular, it can confirm more clearly by measuring elemental distribution by STEM-EDS analysis.

  The core particles are preferably coated on the entire surface with the shell phase, but part of the surface may be exposed. Specifically, if 50% or more of the surface of the core particle is occupied by the shell phase, it indicates that the core particle is "covered" by the shell phase. In addition, the specific measuring method of a coverage is based on the method as described in an Example.

  In a preferred embodiment, 50 area% or more of the surface of the core particle is preferably covered with the shell phase, more preferably 60 area% or more, still more preferably 70 area% or more, particularly preferably 80 area% or more Preferably, 90% by area or more is covered with the shell phase.

  The particle size of the dielectric ceramic particles (the particle size of the state in which the shell phase is formed on the core particles) is not particularly limited, but is preferably 50 nm to 1 μm, more preferably 80 to 450 nm, and 100 It is especially preferable that it is -400 nm.

(Core particle)
The core particles contained in the dielectric ceramic particles are as described in the section of (1) mixing step in the above-mentioned << Method of manufacturing dielectric ceramic particles (dielectric ceramic) >>, and thus detailed description will be omitted.

(Shell phase)
The shell phase is formed to have the second composite oxide as a main component and to cover the surface of the core particle.

  The definition of the term “based on the second composite oxide” is as described above, and a slight amount of impure components that may be contained in production may be contained in the shell phase. As the impure component, elements other than the elements constituting the second complex oxide, that is, components derived from metals such as potassium, sodium, aluminum, calcium, niobium, iron and lead, glass components and organic components of hydrocarbon type, Surface adsorption water etc. are mentioned.

  The shell phase preferably contains 93% by mass or more of the second composite oxide, more preferably 95% by mass or more, and particularly preferably 98% by mass or more based on the total amount of the shell phase. . On the other hand, the upper limit thereof is not particularly limited, but is substantially 100% by mass. The larger the content of the second composite oxide, the more easily it interacts with the first composite oxide constituting the core particle, which is preferable because it contributes to the improvement of various physical property values.

  As described above, the second composite oxide constituting the shell phase preferably has a perovskite-type crystal structure at 25 ° C. Since the first complex oxide constituting the core particle has a perovskite structure, the first complex oxide and the second complex oxide form an interface by forming the core particle and the shell phase having the same crystal structure. In the above, it is easy to interact with each other and to improve various physical properties of the obtained dielectric ceramic particles.

Here, the content ratio (molar ratio) of the second composite oxide constituting the shell phase is not particularly limited as long as it can coat the core particle containing the first composite oxide as a main component. However, it is preferable that the second composite oxide constituting the shell phase is contained in an equimolar amount or a small molar ratio with respect to the first composite oxide constituting the core particle. That is, the molar ratio (M ₂ / M ₁ ) of the second composite oxide (M ₂ ) constituting the shell phase to the first composite oxide (M ₁ ) constituting the core particle is 1 or less Is preferable. More preferably, it is 0.75 or less, and particularly preferably 0.5 or less.

  The second composite oxide constituting the shell phase can improve various physical properties such as relative dielectric constant and DC bias characteristics by interacting with the first composite oxide. However, on the other hand, the composite oxide itself has relatively low values of various physical properties such as relative dielectric constant, so if the amount of the second composite oxide is increased, the physical properties of the dielectric ceramic particles as a whole become It may decrease. Therefore, by reducing the content of the second composite oxide with respect to the content of the first composite oxide to set the content in the above range, it is possible to suppress a decrease in the physical property value of the entire dielectric ceramic particle.

On the other hand, the lower limit of the molar ratio (M ₂ / M ₁ ) of the content molar ratio (M ₂ / M ₁ ) of the second composite oxide constituting the shell phase to the first composite oxide constituting the core particle is not particularly limited. In order to sufficiently obtain the effect of improving various physical properties, M ₂ / M ₁ is preferably 0.005 or more, more preferably 0.1 or more, and particularly preferably 0.2 or more.

  When two or more complex oxides are used as the second complex oxide constituting the shell phase, the sum of all the complex oxides is within the above range with respect to the first complex oxide. preferable.

(Combination of core particle and shell phase)
The combination of the core particle (first complex oxide) and the shell phase (second complex oxide) constituting the dielectric ceramic particles obtained by the production method according to the present invention is a combination of the first complex oxide and the second complex oxide. There is no particular limitation as long as the complex oxides of the present invention have mutually different compositions. According to the production method of the present invention, a core-shell structure containing complex oxides different in composition from each other can be obtained inexpensively and easily.

  In view of the physical properties of the obtained dielectric ceramic particles, core particles such that at least one of various physical properties (dielectric constant, DC bias characteristics, etc.) exhibited by the dielectric ceramic particles is improved as compared with the core particle alone. It is preferable that it is a combination of (first complex oxide) and shell phase (second complex oxide). Specifically, it is preferable that the first complex oxide and the second complex oxide be a combination in which lattice constants in the coaxial direction are different from each other.

  Examples of such a combination include, but are not limited to, the combinations shown in Table 1 below. In addition, in Table 1, the raw material compound (The raw material compound of a core particle and a shell phase) used in order to manufacture the core-shell structure of a preferable combination is also shown collectively.

«Dielectric ceramics»
A second aspect of the present invention provides a dielectric ceramic comprising dielectric ceramic particles produced by the above method.

  The form of the dielectric ceramic is not limited as long as it contains dielectric ceramic particles produced by the above method, but is preferably an aggregate of dielectric ceramic particles produced by the above method. For example, it may be in the form of spheres, platelets, pellets, sheets or mixtures thereof. The method for producing the above aggregate is not particularly limited, and any known method can be used. For example, the assembly can be produced by press-molding the dielectric ceramic particles obtained by the method of the present invention using a suitable binder.

  As an example of the binder which can be used at this time, PVA (polyvinyl alcohol), PVB (polyvinyl butyral), and acrylic resin are mentioned. The amount of the binder to be added is not particularly limited, and is preferably 0.01% by mass to 20% by mass with respect to the mass of the dielectric ceramic particles, from the viewpoint of improving the density of the molded body 0.5 It is more preferable that it is mass%-15 mass%.

  After molding using the above-mentioned binder, debinding treatment is performed. The debinding treatment is preferably performed by heating the molded body to 300 to 800 ° C, more preferably 400 to 600 ° C.

  As described above, according to the manufacturing method according to the present invention, since dielectric ceramic particles in the form of powder can be manufactured, a dielectric which is widely applicable to various aggregates and is excellent in processability Ceramic particles can be obtained.

«Applications of dielectric ceramics»
The application of the dielectric ceramic is not particularly limited, but since it is possible to manufacture ones excellent in relative dielectric constant (ε) and DC bias characteristics, it is suitably used for capacitors for power device substrates, capacitors for power substrate, etc. Can.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples.

«Production of dielectric ceramics»
Example 1
(Mixing process)
Barium titanate having a particle diameter 100nm as a raw material of the core particle (BT: BaTiO ₃ Name T-BTO-100RK: Toda Kogyo Co., Ltd.) and, with respect to the particle size of a particle size of about 10 nm (core particles as a raw material of the shell phase 10% size) of zirconium oxide (ZrO ₂ product name UEP-100: Daiichi Kigenso Kagaku Kogyo Co., Ltd.) in a molar ratio so as to be ZrO ₂ : BT = 0.25: 1.00 The mixture was mixed at 25 ° C. for 5 minutes using a mortar and pestle to obtain a mixed powder. This mixed powder was subjected to 3000 rpm (1.88 × 10 ⁴ rad) using a mechanofusion apparatus (product name: Nobilta NOB-MINI, manufactured by Hosokawa Micron Corporation, distance between the inner piece and the inner wall of the rotating container: 1 mm, the same applies hereinafter). Dry mixing was performed for 3 minutes at 25 ° C./s).

(Synthesis process: Hydrothermal synthesis process process)
24.5 g of the powder after dry mixing treatment (mixing step) is placed in a 100 mL autoclave vessel (manufactured by Sanai Scientific Co., Ltd .: HU-100), and 9.4 g of barium hydroxide octahydrate (Ba (OH) _2. Add 8H ₂ O: Kishida Chemical Co., Ltd.) (1.2 times the molar ratio to ZrO ₂ in the mixed powder), add 40 mL of pure water, and then, in a drying oven, heat to 230 ° C x 18 The hydrothermal synthesis process was performed under the conditions of time.

(Post-processing process)
After the hydrothermal reaction (synthesis step: hydrothermal synthesis treatment step), in order to separate the solution and the powder, it is filtered to remove barium carbonate generated by the reaction of barium ion contained in the raw material and carbon dioxide in the atmosphere. Therefore, it was rinsed in hot water at about 80 ° C. Thereafter, the powder was dried overnight in an air atmosphere with a dryer set at 100 ° C. The dried powder was crushed with a mortar and a pestle to obtain dielectric ceramic particles (1).

Example 2
A dielectric was prepared in the same manner as in Example 1, except that barium titanate particles used in the mixing step were changed to barium titanate having a particle diameter of 150 nm (BT: BaTiO ₃ product name T-BTO-155RK: Toda Kogyo Co., Ltd.). Body ceramic particles (2) were obtained. At this time, the size of the zirconium oxide particle is 6.7% with respect to the particle diameter of the core particle.

[Example 3]
A dielectric was prepared in the same manner as in Example 1 except that barium titanate particles used in the mixing step were changed to barium titanate having a particle diameter of 200 nm (BT: BaTiO ₃ product name T-BTO-200: Toda Kogyo Co., Ltd.) Body ceramic particles (3) were obtained. At this time, the size of the zirconium oxide particles is 5% with respect to the particle diameter of the core particles.

Example 4
A dielectric is prepared in the same manner as in Example 1 except that barium titanate used in the mixing step is changed to barium titanate having a particle diameter of 300 nm (BT: BaTiO ₃ product name T-BTO-300: Toda Kogyo Co., Ltd.) Ceramic particles (4) were obtained. At this time, the size of the zirconium oxide particles is 3.3% of the particle diameter of the core particles.

[Example 5]
The synthesis step is the same as Example 3 except that in place of the hydrothermal synthesis treatment, solvothermal synthesis treatment using ethanol is used (in place of pure water, a mixed solvent of ethanol and pure water is used as a solvent). To obtain dielectric ceramic particles (5). In the solvothermal synthesis process, a mixed solvent in which 4 mL of pure water and 36 mL of ethanol were mixed was used, and the heating temperature and the heating time were the same as in Example 1.

[Example 6]
Dielectric ceramic particles (6) were obtained in the same manner as in Example 5, except that in the solvothermal synthesis process, the mixing ratio of the mixed solvent was changed as follows. The mixed solvent was used by mixing 20 mL of pure water and 20 mL of ethanol.

[Example 7]
Example 3 except that dry mixing was performed using a mechanofusion apparatus (NOB-MIN manufactured by Hosokawa Micron Corporation) for 3 minutes under the conditions of 2000 rpm (1.26 × 10 ⁴ rad / s). In the same manner as in the above, dielectric ceramic particles (7) were obtained.

[Example 8]
Example 3 except that dry mixing was performed using a mechanofusion apparatus (NOB-MIN manufactured by Hosokawa Micron Corporation) for 3 minutes under the conditions of 1000 rpm (6.28 × 10 ³ rad / s). In the same manner as in the above, dielectric ceramic particles (8) were obtained.

[Example 9]
A dielectric is prepared in the same manner as in Example 1, except that barium titanate particles used in the mixing step are changed to strontium titanate having a particle diameter of 300 nm (ST: SrTiO ₃ product name ST-03: Sakai Chemical Industry Co., Ltd.) Ceramic particles (9) were obtained. At this time, the size of the zirconium oxide particles is 3.3% of the particle diameter of the core particles.

[Example 10]
(Mixing process)
Barium zirconate with a particle size of 300 nm (BZ: BaZrO ₃ product name BZ-03: Sakai Chemical Industry Co., Ltd.) as a raw material for core particles, and a particle size of about 70 nm (for the particle size of core particles) as a raw material for shell phase 23% size) of titanium oxide (TiO ₂ product name PT-401M: Ishihara Sangyo Co., Ltd.) in a molar ratio of TiO ₂ : BZ = 0.25: 1.00, mortar and pestle The mixture was mixed at 25 ° C. for 5 minutes to obtain a mixed powder. The mixed powder was subjected to dry mixing treatment at 3000 rpm (1.88 × 10 ⁴ rad / s) at 25 ° C. for 3 minutes using a mechanofusion apparatus (NOB-MIN manufactured by Hosokawa Micron Corporation).

(Synthesis process: Hydrothermal synthesis process process)
27.7 g of powder after dry mixing treatment (mixing step) is placed in a 100 mL autoclave container (manufactured by Sanai Scientific Co., Ltd .: HU-100), and 5.7 g of barium hydroxide octahydrate (Ba (OH) _2. Add 8H ₂ O: Kishida Chemical Co., Ltd.) (1.2 times the molar ratio with respect to TiO ₂ in the mixed powder), add 40 mL of pure water, and then add 180 ° C × 18 in the drying oven. The hydrothermal synthesis process was performed under the conditions of time.

(Post-processing process)
The post-treatment step was carried out in the same manner as in Example 1 to obtain dielectric ceramic particles (10).

[Example 11]
(Mixing process)
Strontium titanate having a particle diameter of 300 nm (ST: SrTiO ₃ product name ST-03: Sakai Chemical Industry Co., Ltd.) as a raw material for core particles, and titanium oxide (particle diameter of core particles about 70 nm as a raw material for shell phase 23% of the size) (TiO ₂ product name PT-401M respect: Ishihara Sangyo Kaisha, Ltd.) and _TiO 2 in a molar ratio: ST = 0.25: weighed so that 1.00, and the mortar and pestle The mixture was mixed at 25 ° C. for 5 minutes to obtain a mixed powder. The mixed powder was subjected to dry mixing treatment at 3000 rpm (1.88 × 10 ⁴ rad / s) at 25 ° C. for 3 minutes using a mechanofusion apparatus (NOB-MIN manufactured by Hosokawa Micron Corporation).

(Synthesis process: Hydrothermal synthesis process process)
16.3 g of the powder after dry mixing treatment (mixing step) is placed in a 100 mL autoclave vessel (manufactured by Sanai Scientific Co., Ltd .: HU-100), and 7.6 g of barium hydroxide octahydrate (Ba (OH) _2. Add 8H ₂ O: Kishida Chemical Co., Ltd.) (1.2 times the molar ratio with respect to TiO ₂ in the mixed powder), add 40 mL of pure water, and then add 180 ° C × 18 in the drying oven. The hydrothermal synthesis process was performed under the conditions of time.

(Post-processing process)
The post-treatment step was carried out in the same manner as in Example 1 to obtain dielectric ceramic particles (11).

Comparative Example 1
Comparative dielectric ceramic particles (1) were obtained in the same manner as in Example 3 except that mixing by the mechanofusion device was not performed in the mixing step.

Comparative Example 2
Comparative dielectric ceramic particles (2) were obtained in the same manner as in Example 4 except that mixing by the mechanofusion device was not performed in the mixing step.

  The formulations and the like of the above Examples and Comparative Examples are shown in Table 2 below. In addition, "-" in a table | surface shows that the shell phase did not form.

«Evaluation»
The dielectric ceramics obtained in the above Examples and Comparative Examples were evaluated as follows.

[STEM-EDS analysis]
FE-STEM-EDS analysis was performed on the dielectric ceramic particles obtained in the above examples. In addition, the measurement was performed using Nippon Denshi Co., Ltd. JM2800. As an example, with respect to the dielectric ceramic particles (1) according to Example 1, the obtained STEM image is shown in FIG. 1A. 1B to 1E show mapping data of Ba, Ti, Zr, and Ba + Ti + Zr measured in the same field of view as FIG. 1A.

  As a result, it was confirmed that in the dielectric ceramic particle (1), a shell phase consisting of barium zirconate was uniformly formed (coated) on the surface of the barium titanate particle (core particle).

  Moreover, also in the dielectric ceramic particles according to the other examples, it was confirmed by STEM-EDS analysis that the above-mentioned core-shell structure is formed similarly.

[SEM observation]
SEM analysis was performed on particles (barium titanate, barium zirconate, strontium titanate) which constitute core particles used as raw materials in the above-described Examples and Comparative Examples. In addition, SEM analysis was performed on the dielectric ceramic particles (1) to (11) and the comparative dielectric ceramic particles (1) to (2) obtained in the above-described Examples and Comparative Examples. In addition, the measurement was performed using Nippon Denshi Co., Ltd. JSM-7800F. The obtained SEM images are shown in FIGS. 2A to 14. In the figure, “before reaction” indicates before dry mixing treatment, and “after reaction” indicates after hydrothermal synthesis treatment or after solvothermal synthesis treatment.

As a result, in the dielectric ceramic particles (1) to (11) according to the examples, it was confirmed that a shell phase was uniformly formed on the surface of the core particle. In the SEM images, in the dielectric ceramic particles (1) to (11) obtained in the examples, very fine particles (complex oxide particles constituting the shell phase) are uniformly distributed on the core particles. It is shown that the surface of the core particle is almost completely covered by the shell phase. On the other hand, in the comparative dielectric ceramic particles (1) to (2), the barium zirconate particles are segregated (localized) on the surface of the core particles (barium titanate particles), and the core-shell structure is not confirmed The This is because, in the dry mixing treatment under the conditions of the comparative example, the zirconium oxide as the raw material of the shell phase could not sufficiently cover the core particles, so BaZrO ₃ (barium zirconate) was filtered and washed with water. It is considered to have fallen out.

[XRD measurement]
The XRD measurement was performed on the dielectric ceramic particles (1) to (11) and the comparative dielectric ceramic particles (1) to (2) obtained in the above examples and comparative examples. The measurement was performed using an X-ray diffractometer (PANAlytical, RAYON S X, a radiation source of Cu-Kα, a voltage of 45 kV, and a current of 40 mA. From the obtained results, 2θ was observed in the region of 20-80 °. The peaks are shown in FIGS.

As a result, in the dielectric ceramic particles (1) to (11) obtained in the examples, not only core particles (barium titanate, barium zirconate, strontium titanate) but also shell phases (barium zirconate, titanate) A peak was observed indicating the formation of barium). As for the comparative dielectric ceramic particles (1) and (2) obtained in the comparative example, since the BaZrO ₃ (barium zirconate) peak is extremely small as compared with the example, as described above, the shell It was considered that BaZrO ₃ (barium zirconate) was removed by filtration and washing with water because the core particles could not be sufficiently coated by the phase.

[Measurement of coverage rate]
The coverage was calculated as follows. First, the SEM photograph of the dielectric ceramic particles was enlarged, and the particles covered with the shell phase and the particles not covered with the particles in the field of view were counted, and the ratio was calculated. Then, for the particles being coated, the area was calculated from the SEM image and the coverage was calculated. At this time, the magnification of the SEM may be appropriately determined depending on the size (particle diameter) of the core particle (For reference, Examples 1 and 2 are 70,000 times, Examples 3 to 8 are 50,000 times, Examples 9 to 11 were 30,000 times, and Comparative Examples 1 and 2 were 50,000 times). The results are shown in Table 2. The coverage of the core particle by the shell phase shows substantially the same value as the coverage by the above-mentioned raw material compound when the core particle and the raw material compound of the second composite oxide constituting the shell phase are mixed. Therefore, the coverage of the core particle by the above-mentioned raw material compound can be calculated by measuring the coverage by the shell phase in dielectric ceramic particles.

Claims (5)

A core particle mainly composed of a first complex oxide having a perovskite structure at 25 ° C., and a second complex oxide formed on the surface of the core particle and different from the first complex oxide A method for producing dielectric ceramic particles having a shell phase as a component,
Dry-mixing the core particle and the material compound of the second composite oxide to coat the material particle of the second composite oxide on the core particle to obtain a material mixture;
Performing a hydrothermal synthesis process or a solvothermal synthesis process on the raw material mixture,
The method for producing dielectric ceramic particles, wherein the dry mixing is performed by a mechanical rotating body having a mechanism that rotates at an angular velocity of 6 × 10 ³ rad / s or more.   The method for producing dielectric ceramic particles according to claim 1, wherein the dry mixing is performed by a mechanofusion apparatus.   The method of manufacturing dielectric ceramic particles according to claim 1, wherein the raw material compound of the second composite oxide contains at least one selected from the group consisting of zirconium oxide, titanium oxide and niobium oxide.   The dielectric according to any one of claims 1 to 3, wherein the second composite oxide is barium zirconate, barium titanate, strontium titanate, calcium titanate, potassium niobate or sodium niobate. Method for producing ceramic particles.   The dielectric according to any one of claims 1 to 4, wherein the first composite oxide is barium titanate, barium zirconate, strontium titanate, calcium titanate, potassium niobate or sodium niobate. Method for producing ceramic particles.