JP2015187969A - Dielectric ceramic particles and dielectric ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide dielectric ceramic particles capable of forming a dielectric ceramic exhibiting a high dielectric constant and having a high relative density.SOLUTION: The dielectric ceramic particles have core particles containing barium titanate as a main component and a shell phase containing a metal oxide as a main component formed on the surface of the core particles. The core particle has a particle diameter of more than 50 nm and 500 nm or less, and the metal oxide has a lattice constant (a) in an axis direction larger than a lattice constant (a) in an axis direction of the barium titanate by 0.5% or more.

Description

  The present invention relates to dielectric ceramic particles and dielectric ceramics.

  With the spread of smartphones, tablets, etc., electronic components used in these devices are becoming smaller and higher performance, and MLCCs (Multi Layer Ceramic Capacitors) used as multilayer capacitors are natural, There is a demand for a smaller and larger capacity.

At present, in order to increase the size and capacity of MLCCs, the mainstream is to reduce the number of dielectric layers and increase the number of layers. For this purpose, there is a need for a technique that can make the dielectric ceramics such as barium titanate (BaTiO ₃ : BT) used as a dielectric material fine (small particle size).

For example, in Patent Document 1, barium titanate is deposited on the surface of fine strontium titanate (SrTiO ₃ : ST) nanocubes having a particle size distribution of about 5 to 50 nm as a technique for making fine particles of dielectric ceramics containing barium titanate. Techniques for making them disclosed are disclosed. According to the technique disclosed in Patent Document 1, barium titanate-containing fine particles having a very small particle size are produced, including strontium titanate as a so-called core particle and barium titanate as a shell phase covering the core particle. can do.

JP 2012-240860 A

  On the other hand, in order to increase the size and capacity of MLCCs, in addition to reducing the size of dielectric ceramic particles, when producing dielectric ceramics (particle aggregates) in which the particles are integrated, a high relative density is achieved. A dielectric ceramic having a high dielectric constant is required.

  Accordingly, an object of the present invention is to provide dielectric ceramic particles that can form a dielectric ceramic having a high dielectric constant and a high relative density. Another object of the present invention is to provide a dielectric ceramic having a high dielectric constant and a high relative density.

  The present inventors have intensively studied to solve the above problems. As a result, the particle size of the core particles mainly composed of barium titanate is within a predetermined range, and a shell phase mainly composed of a metal oxide having a specific lattice constant is formed on the surface of the core particles. As a result, it was found that dielectric ceramic particles exhibiting a high dielectric constant and capable of forming dielectric ceramics having a high relative density were obtained, and the present invention was completed.

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

1. A core particle mainly composed of barium titanate and a shell phase mainly composed of a metal oxide formed on the surface of the core particle, and the particle diameter of the core particle is more than 50 nm and 500 nm. Dielectric ceramic particles, wherein the lattice constant (a _M ) of the metal oxide in the a-axis direction is 0.5% or more larger than the lattice constant (a _BT ) of the barium titanate in the a-axis direction ;
2. 1. The crystal structure of the metal oxide at room temperature is a perovskite type. Dielectric ceramic particles according to claim 1;
3. The metal oxide is barium zirconate. Or 2. Dielectric ceramic particles according to claim 1;
4). 2. The molar ratio (M _BZ / M _BT ) of the barium zirconate to the barium titanate is 1 or less. Dielectric ceramic particles according to claim 1;
5. Above 1. ~ 4. A dielectric ceramic comprising the dielectric ceramic particles according to any one of the above.

  ADVANTAGE OF THE INVENTION According to this invention, the dielectric ceramic particle which can form the dielectric ceramic which shows a high dielectric constant and has a high relative density is provided. In addition, according to the present invention, a dielectric ceramic having a high dielectric constant and a high relative density is provided.

3 is a STEM image of dielectric ceramic particles according to Example 2. It is the mapping data of Ti measured in the same visual field as FIG. 1A. It is the mapping data of Zr measured in the same visual field as FIG. 1A. It is the mapping data of Ba measured in the same visual field as FIG. 1A. 10 is an SEM image of a dielectric ceramic according to Comparative Example 3. 2 is an XRD spectrum of a dielectric ceramic according to Example 1. FIG. 3 is an XRD spectrum of a dielectric ceramic according to Example 2. 3 is an XRD spectrum of a dielectric ceramic according to Example 3. 7 is an XRD spectrum of a dielectric ceramic according to Example 4. 7 is an XRD spectrum of a dielectric ceramic according to Example 5. 7 is an XRD spectrum of a dielectric ceramic according to Example 6. 7 is an XRD spectrum of a dielectric ceramic according to Example 7. 7 is an XRD spectrum of a dielectric ceramic according to Example 8. It is a graph showing the relationship between the relative dielectric constant of the dielectric ceramic which concerns on an Example, and the content molar ratio (M _BZ / M _BT ) of barium zirconate to barium titanate.

  Embodiments of the present invention will be described below.

A first aspect of the present invention includes a core particle mainly composed of barium titanate and a shell phase mainly composed of a metal oxide formed on a surface of the core particle, and the core particle particle size is at 500nm or less beyond 50 nm, the a-axis direction of the lattice constant of barium titanate _{(a BT)} (hereinafter, simply referred to as "the lattice constant _{(a BT)")} to the metal oxide A dielectric ceramic particle having a lattice constant (a _M ) in the a-axis direction (hereinafter also simply referred to as “lattice constant (a _M )”) of 0.5% or more is provided.

  In the present specification, “core particles mainly composed of barium titanate” means that 90% by mass or more of barium titanate is contained with respect to the total amount of the core particles. In addition, it is confirmed by the analysis by a fluorescent X ray that a core particle contains 90 mass% or more of barium titanates. Further, the “shell phase containing a metal oxide as a main component” means that 90% by mass or more of the metal oxide is included with respect to the total amount of the shell phase. Accordingly, an impure component that is included in the production may be contained in a trace amount in the core particle or the shell phase. In addition, it is confirmed by the analysis by a fluorescent X ray that a shell phase contains 90 mass% or more of metal oxides.

  Furthermore, in this specification, “particle size” is obtained by taking an image with a transmission electron microscope, extracting 50 particles at random, measuring the particle size, and averaging the results. Moreover, when the shape of particle | grains is not spherical, it defines as what was calculated by measuring a major axis.

Further, the lattice constants “a _BT ” and “a _M ” indicate the a-axis lengths (lattice constants in the a-axis direction) of barium titanate (BT) and metal oxide (M) at room temperature (25 ° C.), respectively. Shall. Further, for these lattice constants, values calculated by the Rietveld method from the diffraction intensity obtained by X-ray diffraction shall be adopted.

  The dielectric ceramic particles of the present invention have core particles whose main component is barium titanate and whose particle diameter exceeds 50 nm and is 500 nm or less, and a shell phase that coats the core particles.

  As described above, in order to reduce the size and increase the capacity of MLCC, conventionally, a technique for making dielectric ceramics into fine particles (smaller particle size) has been studied. However, when the present inventors proceeded to reduce the particle size of the particles having a core-shell structure as in Patent Document 1, a sufficient relative density and dielectric constant could not be obtained when dielectric ceramics were produced. Found that there is a case. Therefore, when the above problems were studied, the particle diameter of the core particle was set within a specific range, and further, the core particle was coated with a specific metal oxide, thereby showing a high dielectric constant and a high relative density. The present inventors have found that dielectric ceramic particles capable of forming the dielectric ceramics can be obtained and have reached the present invention.

  The mechanism for exerting the operational effects of the above-described configuration of the present invention is presumed as follows.

  As described in detail below, when producing dielectric ceramic particles having a core-shell structure, a method of preparing the core particles in advance and coating the core particles with a metal oxide constituting the shell phase is preferably used. Here, in order to reduce the particle size of the dielectric ceramics, it is preferable to reduce the particle size of the core particles. However, in such a manufacturing process, it has been found that if the particle size of the core particles is too small, the core particles may aggregate. Furthermore, as a result of the core particles aggregating during the manufacturing process as described above, it was found that dielectric ceramics having a high relative density could not be formed, and it was difficult to obtain a high dielectric constant. . And it became clear that such a tendency becomes especially remarkable when barium titanate is used as a core particle.

  In addition, when the fine particles of barium titanate are made fine (small particle size), a phenomenon called a “size effect” in which the dielectric constant is reduced occurs. Therefore, if the particle size is too small while reducing the particle size, it is difficult to obtain a sufficient dielectric constant.

  On the other hand, the present inventors can eliminate the above inconveniences by setting the particle diameter of the core particles mainly composed of barium titanate in the core-shell structure to more than 50 nm and not more than 500 nm. I thought it was possible. That is, by making the particle size of the core particles contained in the dielectric ceramic particles of the present invention within the above range, aggregation of the core particles in the production process can be suppressed and the influence of the size effect can be reduced. As a result, a dielectric ceramic having a high relative density and a high dielectric constant can be produced.

Furthermore, the dielectric ceramic particles of the present invention are formed by forming a shell phase mainly composed of a metal oxide satisfying a specific lattice constant relationship on the surface of core particles mainly composed of barium titanate. Specifically, the metal oxide constituting the shell phase is characterized in that its lattice constant (a _M ) is 0.5% or more larger than that of barium titanate (a _BT ).

  As described above, by using a metal oxide constituting the shell phase having a lattice constant larger than that of barium titanate constituting the core particle, the metal oxide of the shell phase is formed at the interface between the core particle and the shell phase. The unit cell of barium titanate is distorted by interaction so as to be pulled by the unit cell. As a result, it is considered that the titanium atom located at the center of the barium titanate lattice, which is the core particle, easily moves, thereby improving the spontaneous polarization and improving the dielectric constant of the core-shell structure. Therefore, according to the present invention, it is possible to obtain a dielectric ceramic having a high dielectric constant having core particles mainly composed of barium titanate by having a shell phase mainly composed of a specific metal oxide. .

  The present invention is not limited to the above mechanism.

  Hereinafter, constituent elements 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 is used in the meaning which contains the numerical value described before and behind that as a lower limit and an upper limit. Unless otherwise specified, measurement of operation and physical properties is performed under conditions of room temperature (25 ° C.) / Relative humidity 40 to 50%.

≪Dielectric ceramic particles≫
The dielectric ceramic particle 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 be confirmed more clearly by measuring the element distribution by STEM-EDS analysis.

  The entire surface of the core particle is preferably coated with a shell phase, but a part of the surface may be exposed as long as the effects of the present invention are not impaired. In a preferred embodiment, 50 area% or more of the surface of the core particle is preferably coated with a shell phase, more preferably 60 area% or more, further preferably 70 area% or more, particularly preferably 80 area% or more, most preferably 90% by area or more is preferably covered with a shell phase.

  The particle size of the dielectric ceramic particles (the particle size in a state where a shell phase is formed on the core particles) is not particularly limited, but is preferably 50 to 500 nm, and more preferably 60 to 400 nm.

(Core particles)
The core particle is a particle mainly composed of barium titanate. The definition of the term “consisting of the main component” is as described above, and the impure component that is included in the production may be contained in a small amount in the core particle. Examples of the impure component include metal-derived components such as potassium, sodium, aluminum, calcium, niobium, iron and lead, glass components and hydrocarbon organic components.

  The core particles preferably contain 93% by mass or more of barium titanate, more preferably 95% by mass or more, and particularly preferably 98% by mass or more with respect to the total amount of the core particles. On the other hand, the upper limit is not particularly limited, but is substantially 100% by mass. The higher the barium titanate content, the easier it is to interact with the metal oxide constituting the shell phase, which contributes to the improvement of the dielectric constant.

  The core particle has a particle size of more than 50 nm and 500 nm or less. When the particle diameter of the core particles is 50 nm or less, the dielectric constant is lowered due to the size effect, and it becomes difficult to obtain dielectric ceramic particles having a high dielectric constant. In addition, as described above, when the particle size is too small, the core particles aggregate in the manufacturing stage, and the surface of the core particles cannot be sufficiently covered with the shell phase, and the dielectric ceramic has a high relative density. Difficult to form. On the other hand, if the particle size is increased, the dielectric constant can be improved, but if it exceeds 500 nm, it is difficult not only to form a good core-shell structure, but also from the practical viewpoint in MLCC.

  Therefore, from the practical viewpoint of suppressing the influence of the size effect, improving the dielectric constant by forming a good core-shell structure, and reducing the particle size of the dielectric ceramic particles, The particle size is more preferably 80 to 400 nm, even more preferably 100 to 450 nm, and particularly preferably 200 to 400 nm.

(Shell phase)
The shell phase has a specific metal oxide as a main component and is formed so as to cover the surface of the core particle. The definition of the term “main component” is as described above, but the shell phase preferably contains 93% by mass or more, and 95% by mass or more of the metal oxide based on the total amount of the shell phase. It is more preferable if it is contained, and it is particularly preferable if it contains 98% by mass or more. On the other hand, the upper limit is not particularly limited, but is substantially 100% by mass. The higher the content of the metal oxide, the easier it is to interact with barium titanate contained in the core particles, which contributes to the improvement of the dielectric constant.

The metal oxide constituting the shell phase has a lattice constant (a _M ) in the a-axis direction at room temperature that is 0.5% or more larger than the lattice constant (a _BT ) of barium titanate. That is, the ratio (a _M / a _BT ) of the lattice constant (a _M ) in the a-axis direction of the metal oxide to the lattice constant (a _BT ) of barium titanate is 1.005 or more.

When the proportion of the lattice constant (a _M ) is less than 0.5%, it is difficult to distort the unit lattice of barium titanate in the core particles to such an extent that the dielectric constant can be improved. On the other hand, as the lattice constant (a _M ) of the metal oxide constituting the shell phase is larger than the lattice constant (a _BT ) of barium titanate, the unit lattice of barium titanate at the interface may be greatly distorted. This is preferable because the dielectric constant can be improved as a result. Therefore, the upper limit of the ratio of the lattice constant (a _M ) to the lattice constant (a _BT ) of barium titanate is not particularly limited, but considering the metal oxide species that can be substantially used. About 45%.

In other words, since the lattice constant (a _BT ) of barium titanate at room temperature is 3.992Å, the lattice constant (a _M ) of the metal oxide constituting the shell phase is 3.992 × (100 + 0.5) /100=4.012 mm or more. On the other hand, the upper limit of the lattice constant (a _M ) is about 3.992 × (100 + 45) /100=5.79Å.

The lattice constant (a _M ) of the metal oxide constituting the shell phase in the present invention is as described above, but the lattice constant (a _M ) is preferably larger than the lattice constant (a _BT ). . This is because by using a metal oxide having a large lattice constant (a _M ), the unit lattice of barium titanate at the interface between the core particle and the shell phase is more distorted and the dielectric constant can be further increased. Therefore, the lattice constant (a _M ) is preferably 0.6 to 8% larger, more preferably 1 to 7% larger, and particularly preferably 3 to 6% larger than the lattice constant (a _BT ). That is, the ratio (a _M / a _BT ) of the lattice constant (a _M ) in the a-axis direction of the metal oxide to the lattice constant (a _BT ) of barium titanate is preferably 1.006 to 1.08. More preferably, it is 0.01 to 1.07, and particularly preferably 1.03 to 1.06.

The metal oxide constituting the shell phase may be any metal oxide as long as it has the lattice constant (a _M ). For example, barium zirconate (BaZrO ₃ : BZ a _BZ = 4). 193Å), strontium zirconate (SrZrO ₃ : SZ a _SZ = 4.103Å), potassium niobate (KNbO ₃ : KN a _KN = 4.016Å), lithium niobate (LiNbO ₃ : LN a _LN = 5.148１) ), Calcium titanate (CaTiO ₃ : CT a _CT = 5.381Å), bismuth ferrite (BiFeO ₃ : BF a _BF = 5.631Å). In addition, the said metal oxide may be individual, or 2 or more types may be used together.

  The metal oxide preferably has a perovskite crystal structure at room temperature (25 ° C.). Since barium titanate constituting the core particle has a perovskite structure, the metal oxide constituting the shell phase is also preferably a perovskite structure. By using such a metal oxide, the barium titanate and the metal oxide easily interact with each other, and the unit lattice of the barium titanate is easily distorted at the interface. As a result, a high dielectric constant can be obtained. .

  Therefore, from the viewpoint of easily forming a core-shell structure together with barium titanate, which is a metal oxide satisfying the above-mentioned definition of the lattice constant, the metal oxides constituting the shell phase include barium zirconate and potassium niobate. Is preferable, and barium zirconate is more preferably used.

The content (molar amount) of the metal oxide constituting the shell phase is not particularly limited as long as the effects of the present invention can be obtained, but the metal oxide is based on barium titanate constituting the core particles. It is preferable that they are contained in equimolar amounts or in a small molar ratio. That is, the content molar ratio (M _M / M _BT ) of the metal oxide constituting the shell phase to the barium titanate constituting the core particle is preferably 1 or less. More preferably, it is 0.9 or less, and particularly preferably 0.65 or less.

  As described above, the predetermined metal oxide constituting the shell phase of the present invention interacts with barium titanate, thereby distorting the unit cell of barium titanate and improving the dielectric constant. However, on the other hand, some metal oxides themselves have a relatively low dielectric constant, so if the amount of metal oxide is increased, the dielectric constant of the dielectric ceramic particles as a whole may decrease. Therefore, by reducing the content of the metal oxide with respect to the content of barium titanate within the above range, it is possible to suppress a decrease in the dielectric constant of the dielectric ceramic particles as a whole.

On the other hand, the lower limit of the molar ratio (M _M / M _BT ) of the metal oxide constituting the shell phase to the barium titanate constituting the core particle is not particularly limited, but in order to sufficiently obtain the effects of the present invention, M _M / _MBT is preferably 0.005 or more, more preferably 0.1 or more, and particularly preferably 0.2 or more.

  In addition, when using 2 or more types of metal oxides, it is preferable that the sum of all the metal oxides exists in the said range with respect to barium titanate.

In particular, when the metal oxide is barium zirconate, the molar ratio (M _BZ / M _BT ) of barium zirconate to barium titanate is preferably 1 or less. At this time, M _BZ / M _BT is more preferably 0.85 or less, even more preferably 0.7 or less, and particularly preferably 0.6 or less. On the other hand, the lower limit is not particularly limited, but M _BZ / M _BT is preferably 0.01 or more and more preferably 0.15 or more in order to sufficiently obtain the effects of the present invention.

  Thus, by making barium zirconate relative to barium titanate in the above range, the dielectric constant improvement effect due to the distortion of the barium titanate unit cell can be maximized, and the dielectric constant itself is The content of low barium zirconate can be minimized.

  The shell phase is preferably coated on the core particle with a substantially uniform thickness in order to suppress structural defects.

≪Dielectric ceramics≫
A second aspect of the present invention provides a dielectric ceramic including the dielectric ceramic particles.

  The form of the dielectric ceramic is not limited as long as it includes the dielectric ceramic particles. However, the dielectric ceramic is preferably an aggregate of the dielectric ceramic particles, for example, a spherical object, a plate-like object, It can take the form of pellets, or mixtures thereof.

  The dielectric ceramic of the present invention has a relative dielectric constant (ε) of preferably 89 or more, more preferably 100 or more, still more preferably 150 or more, and particularly preferably 200 or more.

  Further, the dielectric ceramic of the present invention preferably has a relative density of 90% or more. When the relative density is 90% or more, sufficient dielectric properties and mechanical strength can be obtained. Furthermore, the relative density is more preferably 95% or more, even more preferably 96% or more, and particularly preferably 97% or more. The upper limit is not particularly limited, but is substantially 100%. In addition, the value measured by the method as described in an Example shall be employ | adopted for a relative density.

  Since the dielectric ceramic of the present invention contains the dielectric ceramic particles, it exhibits a high dielectric constant. Moreover, since it has a high relative density, not only has a high dielectric constant, but also strength (particularly mechanical strength) is improved.

≪Method for producing dielectric ceramic particles (dielectric ceramics) ≫
The method for producing dielectric ceramic particles (dielectric ceramics) of the present invention is roughly divided into (1) a step of preparing core particles and (2) a step of forming a shell phase. In addition to these, (3) a cleaning / drying step may be performed as necessary. Hereinafter, each step will be described in detail.

(1) Core particle preparation step (step (1))
In this step, core particles mainly composed of barium titanate are prepared, and the core particles are mixed with other materials as necessary. Furthermore, you may shape | mold using a binder as needed.

  The core particle as a raw material may be a commercially available barium titanate powder or may be produced by a conventionally known method. At this time, the particle diameter of the core particle as a raw material is more than 50 nm and 500 nm or less. When the particle size of the core particles used is 50 nm or less, the core particles are aggregated during the shell phase forming step described in detail below, and the shell phase cannot be formed uniformly, and the relative density and dielectric constant It becomes difficult to obtain the improvement effect.

In this step, other than the barium titanate powder used as the core particles, another material for forming the shell phase, that is, a metal oxide raw material, may be added in advance. At this time, other materials that can be added are determined by the metal oxide species constituting the shell phase. For example, zirconium oxide (ZrO ₂ ), zirconium carbonate, zirconium acetate, zirconium alkoxide, niobium oxide (Nb ₂ O) ₅ ) and the like. Among these, it is preferable to add zirconium oxide, which is easy to handle and relatively inexpensive.

Here, the above-mentioned M _M / M _BT can be controlled by other materials (metal oxide raw materials) that can be added in addition to the barium titanate powder and the addition amount of the barium titanate particles.
More specifically, M _M / M _BT can be controlled by the content of titanium in barium titanate and the content of metal contained in the metal oxide raw material.

For example, when a shell phase mainly composed of barium zirconate (BaZrO ₃ ), which is one of the most preferable forms, is formed, the total amount of titanium (Ti) and zirconium (Zr) is used for forming dielectric ceramic particles. Therefore, when zirconium oxide (ZrO ₂ ) / barium titanate (BaTiO ₃ ) is mixed at a molar ratio of 0.25 / 1, dielectric ceramic particles having M _BZ / M _BT = 0.25 can be obtained. it can.

  Furthermore, when mixing the barium titanate powder and the metal oxide raw material as described above, a solvent may be added. Although the solvent used at this time is not specifically limited, For example, an aqueous solvent and an organic solvent can be selected suitably. Usable solvents include, for example, water (pure water); alcohol solvents such as ethanol, methanol, benzyl alcohol, and methoxyethanol; glycol solvents such as ethylene glycol and diethylene glycol; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like. Ketone solvents; ester solvents such as butyl acetate, ethyl acetate, carbitol acetate, and butyl carbitol acetate; ether solvents such as methyl cellosolve, ethyl cellosolve, butyl ether, and tetrahydrofuran; amine solvents such as methylethanolamine and diethanolamine; Aromatic solvents such as benzene, toluene, xylene and the like can be mentioned. Of these, water or an alcohol solvent is preferably used in consideration of the operability of the shell phase forming step performed later.

  When the barium titanate powder and the metal oxide raw material are wet mixed using the solvent, it is preferably carried out by a wet ball mill or a stirring mill. In the case of using zirconia balls in a wet ball mill, it is preferable to perform wet mixing for 8 to 24 hours, preferably 10 to 20 hours using a large number of zirconia balls having a diameter of 1 to 10 mm.

  The barium titanate powder as a raw material or a mixture with the metal oxide raw material obtained as described above may be further dried and press-molded using a suitable binder.

  Examples of binders that can be used at this time include PVA (polyvinyl alcohol), PVB (polyvinyl butyral), and acrylic resins. The amount of the binder to be added is preferably 0.01% by mass to 10% by mass with respect to the total mass (total mass) of the barium titanate powder and the metal oxide raw material, and the viewpoint of improving the density of the molded body From 0.5 mass% to 5 mass%, it is more preferable.

  After molding using the binder, a binder removal treatment is performed. The binder removal treatment is preferably performed by heating the molded body to 300 to 800 ° C, and more preferably 400 to 600 ° C.

(2) Shell phase forming step (step (2))
In this step, the shell phase is coated on the core particles prepared in the above step. At this time, the method is not limited as long as the core-shell structure can be formed, and a conventionally known method can be adopted. For example, various methods such as a solid phase method, a liquid phase method, and a spray pyrolysis method can be applied. In particular, in order to obtain fine particles having a uniform particle size, spray pyrolysis method, crystallization A method of synthesis by a method, a sol-gel method, a solvothermal method or the like is preferable, and a solvothermal method is particularly preferably used among them.

  Hereinafter, an example of a method for producing the dielectric ceramic particles (and dielectric ceramics) of the present invention by the solvothermal method will be described.

  The solvothermal reaction is a reaction performed under a medium to high pressure (usually 0.10 to 1,000 MPa) and a medium to high temperature (usually 100 ° C. to 1000 ° C.). Especially when used as “hydrothermal reaction”. The dielectric ceramic particles (and dielectric ceramics) of the present invention can form a shell phase covering the core particles through this step.

  At this time, a material for forming a shell phase is further added to the core particles (or a molded body thereof) prepared in the step (1). That is, in addition to the metal oxide raw material added in the core particle preparation step, a material containing an element necessary for forming a shell phase is added. Examples of the material added here include a compound containing an element that depends on the metal oxide species constituting the shell phase but cannot be supplemented by the metal oxide raw material added in the step (1). Examples of the compound include a compound serving as a barium source, a compound serving as a potassium source, and a compound serving as a lithium source.

Examples of compounds serving as the barium source is not particularly limited, barium hydroxide, such as barium hydroxide octahydrate (Ba (OH) 2 · 8H 2 O), various barium alkoxides, barium carbonate, barium acetate , Etc. Among these, it is preferable to add barium hydroxide octahydrate, which is easy to handle and relatively inexpensive.

  Although it does not restrict | limit especially as an example of the compound used as the said potassium source, Potassium hydroxide etc. are mentioned. Moreover, although it does not restrict | limit especially as an example of the compound used as the said lithium source, Lithium hydroxide etc. are mentioned.

The addition amount of the material for forming the shell phase is not particularly limited, but depends on the metal oxide species constituting the shell phase and the type (composition) of the metal oxide raw material added in the step (1). To be determined. For example, when a shell phase mainly composed of barium zirconate (BaZrO ₃ ), which is one of the most preferable forms, is formed and zirconium oxide is added in the above step (1), this step (2 In this case, it is preferable to add 1.0 to 2.0 equivalents (molar ratio) of barium hydroxide octahydrate, which is one of the most preferable materials as a barium source compound, with respect to the zirconium oxide. By setting it as the said range, it can convert into barium zirconate, without a zirconium oxide remaining, and can suppress the production | generation of the unreacted substance which can become an impurity.

  As the solvent used at this time, an aqueous solvent or an organic solvent can be appropriately selected according to the material constituting the shell phase. Usable solvents include, for example, water (hydrothermal synthesis); alcohol solvents such as ethanol, methanol, benzyl alcohol and methoxyethanol; glycol solvents such as ethylene glycol and diethylene glycol; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and the like Ketone solvents; ester solvents such as butyl acetate, ethyl acetate, carbitol acetate and butyl carbitol acetate; ether solvents such as methyl cellosolve, ethyl cellosolve, butyl ether and tetrahydrofuran; amine solvents such as methylethanolamine and diethanolamine An aromatic solvent such as benzene, toluene, xylene and the like. In addition, the said solvent may be used individually by 1 type, and may be used in combination of 2 or more type. The solvent is preferably a non-acidic (that is, neutral or basic) mixed solution (reaction mixed solution) from the viewpoint of corrosion of the container.

  Among the above solvents, water and alcohol solvents are preferable because they are strong polar solvents. Furthermore, it is particularly preferable to use water as a solvent in that it is a solvent having higher polarity in addition to being inexpensive. During the solvothermal synthesis, by using a highly polar solvent, the core particles and the shell phase adhere more firmly, and the crystal distortion of the core particles at the interface increases.

  Although the temperature at the time of solvothermal reaction is not specifically limited, It is preferable in it being 150 to 400 degreeC, and it is more preferable in it being 200 to 300 degreeC.

  Moreover, it is although it does not specifically limit about the time which performs solvothermal reaction, Preferably it is 1 to 72 hours, More preferably, it is 5 to 50 hours, More preferably, it is 10 to 30 hours.

  Although the pressure at the time of performing solvothermal reaction is not specifically limited, It is preferable when it carries out at about 0.10-4.0 Mpa. The reaction under such pressure can be performed in a pressure-resistant vessel such as an autoclave.

(3) Washing / drying step After the shell phase is formed by the above steps, a washing / drying step may be performed as necessary. This step is mainly performed to remove impurities and unreacted substances generated in the step (2). Therefore, as the cleaning solvent, a solvent that can dissolve them and does not affect the generated dielectric ceramic particles is used. For example, it is preferable to wash using an acetic acid aqueous solution, water (pure water) or the like.

  The drying conditions are not particularly limited, but it is preferable to dry at 100 to 150 ° C.

  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 only to the following examples.

≪Manufacture of dielectric ceramics≫
(Example 1)
Barium titanate having a particle size of 300 nm (BT: BaTiO ₃ product name T-BTO-300: Toda Kogyo Co., Ltd.) and zirconium oxide (ZrO ₂ product name UEP-100: Daiichi Rare Element Chemical Co., Ltd.) in a molar ratio of ZrO ₂ : The mixture was mixed for 16 hours in a wet ball mill (zirconia balls, φ3 mm) so that BT = 0.25: 1.00 (solvent: pure water, solid content concentration 30 wt%). The obtained slurry was dried and pulverized with a mortar and pestle to obtain a powder. A PVA binder was added to the powder so as to have a ratio of 1% by mass.

  Using a 1 cm square mold, the powder was press-molded at a pressure of 2 t, and the resulting molded body (pellet) was treated at 500 ° C. for 3 hours to remove the binder.

The molded body produced as described above is put into a 25 ml autoclave container (manufactured by Sanai Kagaku Co., Ltd .: HU-25), and barium hydroxide octahydrate (Ba (OH) ₂ .8H ₂ O: Kishida Chemical Co., Ltd.) is added. After 1.2 times the same molar amount as ZrO ₂ contained in the molded body and 5 ml of pure water were added, hydrothermal synthesis treatment was performed in a drying oven at 230 ° C. for 18 hours.

In order to remove unreacted Ba (becomes BaCO ₃ ), the sample taken out was washed with an acetic acid aqueous solution (acetic acid: water = 1: 1), further washed with pure water, and then dried. By this series of operations, a dielectric ceramic (1) having a BZ / BT core-shell structure was obtained. In the dielectric ceramic (1), BZ / BT = 0.25 / 1.00 molar ratio.

(Example 2)
A dielectric ceramic (2) was obtained in the same manner as in Example 1 except that the molar ratio of barium titanate and zirconium oxide was changed to ZrO ₂ : BT = 0.5: 1.00. In the dielectric ceramic (2), BZ / BT = 0.5 / 1.00 molar ratio.

(Example 3)
A dielectric ceramic (3) was obtained in the same manner as in Example 1 except that the molar ratio of barium titanate and zirconium oxide was changed to ZrO ₂ : BT = 0.75: 1.00. In the dielectric ceramic (3), BZ / BT = 0.75 / 1.00 molar ratio.

Example 4
A dielectric ceramic (4) was obtained in the same manner as in Example 1 except that the molar ratio of barium titanate and zirconium oxide was changed to ZrO ₂ : BT = 1.0: 1.00. In the dielectric ceramic (4), BZ / BT = 1.0 / 1.00 molar ratio.

(Example 5)
Dielectric ceramics (5) was obtained in the same manner as in Example 1 except that ethanol was used instead of hydrothermal synthesis treatment (ethanol was used instead of water as a solvent). In the dielectric ceramic (5), BZ / BT = 0.25 / 1.00 molar ratio.

(Example 6)
Dielectric ceramics (6) were obtained in the same manner as in Example 2 except that ethanol was used instead of hydrothermal synthesis treatment (ethanol was used instead of water as a solvent). In the dielectric ceramic (6), BZ / BT = 0.5 / 1.00 molar ratio.

(Example 7)
Dielectric ceramics (7) was obtained in the same manner as in Example 3 except that ethanol was used instead of hydrothermal synthesis, and ethanol was used instead of water (ethanol was used instead of water). In the dielectric ceramic (7), BZ / BT = 0.75 / 1.00 molar ratio.

(Example 8)
A dielectric ceramic (8) was obtained in the same manner as in Example 4 except that instead of the hydrothermal synthesis treatment, a solvothermal synthesis treatment using ethanol was used (ethanol was used instead of water as a solvent). In the dielectric ceramic (8), BZ / BT = 1.0 / 1.00 molar ratio.

(Comparative Example 1)
A PVA binder was added to a barium titanate having a particle size of 300 nm (BT: BaTiO ₃ product name T-BTO-300: Toda Kogyo Co., Ltd.) at a ratio of 1% by mass.

  Using a 1 cm square mold, the powder was press-molded at a pressure of 2 t, and the resulting molded body (pellet) was treated at 500 ° C. for 3 hours to remove the binder. By this series of operations, a comparative dielectric ceramic (1) made of BT particles (also referred to as comparative dielectric ceramic (1)) was obtained.

(Comparative Example 2)
Barium titanate having a particle size of 300 nm (BT: BaTiO ₃ product name T-BTO-300: Toda Kogyo Co., Ltd.) and BaZrO ₃ having a particle size of 100 nm synthesized by a hydrothermal synthesis method in a molar ratio of 1: 1. The mixture was mixed with a wet ball mill (zirconia balls, φ3 mm) (solvent: pure water, solid content concentration 30 wt%). The obtained slurry was dried and pulverized with a mortar and pestle to obtain a powder. A PVA binder was added to the powder so as to have a ratio of 1% by mass.

  Using a 1 cm square mold, the powder was press-molded at a pressure of 2 t, and the resulting molded body (pellet) was treated at 500 ° C. for 3 hours to remove the binder. By this series of operations, a comparative dielectric ceramic (2) (also referred to as a comparative dielectric ceramic (2)) composed of BT particles and BZ particles was obtained.

(Comparative Example 3)
Barium titanate having a particle size of 50 nm synthesized by hydrothermal synthesis and zirconium oxide (ZrO ₂ product name UEP-100: Daiichi Rare Element Chemical Co., Ltd.) in a molar ratio of ZrO ₂ : BT = 0.25: 1.00 The mixture was mixed with a wet ball mill (zirconia balls, φ3 mm) for 16 hours (solvent: pure water, solid content concentration 30 wt%). The obtained slurry was dried and pulverized with a mortar and pestle to obtain a powder. After that, a PVA binder was added to the powder so as to have a ratio of 1% by mass.

  Using a 1 cm square mold, the powder was press-molded at a pressure of 2 t, and the resulting molded body (pellet) was treated at 500 ° C. for 3 hours to remove the binder.

The molded body produced as described above is put into a 25 ml autoclave container (manufactured by Sanai Kagaku Co., Ltd .: HU-25), and barium hydroxide octahydrate (Ba (OH) ₂ .8H ₂ O: Kishida Chemical Co., Ltd.) is added. After 1.2 times the same molar amount as ZrO ₂ contained in the molded body and 5 ml of pure water were added, hydrothermal synthesis treatment was performed in a drying oven at 230 ° C. for 18 hours.

In order to remove unreacted Ba (becomes BaCO ₃ ), the sample taken out was washed with an acetic acid aqueous solution (acetic acid: water = 1: 1), further washed with pure water, and then dried. By this series of operations, a comparative dielectric ceramic (3) (also referred to as comparative dielectric ceramic (3)) was obtained.

≪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 about the dielectric ceramic obtained in the said Example. In addition, the measurement was performed using JEOL Ltd. JM2800. As an example, the obtained STEM image of the dielectric ceramic (2) according to Example 2 is shown in FIG. 1A. 1B to 1D show Ti, Zr, and Ba mapping data measured in the same field of view as FIG. 1A.

  As a result, it was confirmed that a shell phase composed of barium zirconate was formed (coated) on the surface of the barium titanate particles (core particles) in the dielectric ceramic (2). Further, it was confirmed by STEM-EDS analysis that such a core-shell structure was similarly formed in dielectric ceramics according to other examples.

(SEM observation)
The comparative dielectric ceramic (3) obtained in Comparative Example 3 was subjected to SEM analysis. In addition, the measurement was performed using JEOL Co., Ltd. JSM-7800F. The obtained SEM image is shown in FIG.

  As a result, in the comparative dielectric ceramic (3), barium zirconate particles were observed on the surface of the molded body (pellet), and a good core-shell structure was not confirmed. This is because the barium titanate particles used as the core particles are small in size, and as a result of aggregation of the barium titanate particles, barium zirconate is not synthesized inside the pellet, and barium zirconate is formed on the surface of the core particles. It is considered that a shell phase was not formed.

(XRD measurement)
The structural change of barium titanate before and after hydrothermal synthesis or solvothermal synthesis was observed by XRD measurement. The measurement was performed using an X-ray diffractometer (PANalytical, RAYONS X, and the radiation source was Cu-Kα, voltage 45 kV, current 40 mA. From the obtained results, 2θ was observed in the region of 44 to 46 °. About a peak, it shows in FIGS.

  In the XRD spectrum of the figure, “before reaction” means before hydrothermal synthesis reaction or before solvothermal synthesis treatment, and after debinding treatment, and “after reaction” means after hydrothermal synthesis reaction or solvothermal synthesis treatment. Shown later. As a result, in all the samples of the examples, the peak width of the spectrum after the reaction is expanded, so that the crystal of barium titanate is formed at the interface between the barium titanate core particle and the shell phase of barium zirconate. This suggests that the structure has changed. More specifically, the XRD spectrum suggests that the surface of barium titanate core particles is coated with a shell phase of barium zirconate, and the crystal structure of barium titanate at the interface with the shell phase is distorted.

(Specific permittivity measurement)
About the dielectric ceramics obtained in the above examples and comparative examples, the conductive paste DOTITE (registered trademark) TYPE D550 (Fujikura Kasei Co., Ltd.) was applied, and the electrodes were baked under conditions of 300 ° C. × 15 minutes, The relative dielectric constant was measured using an LCR meter (Agilent 4284A measurement conditions: 1 KHz, 1.0 V). The obtained results are shown in Table 1 and FIG. In addition, "-" in a table | surface shows that it was not able to measure.

(Density measurement)
About the dielectric ceramics obtained by the said Example and the comparative example, the density was measured using the Archimedes method. The obtained results are shown in Table 1. The relative density was calculated by dividing the measured density of the sample by the theoretical density. At this time, the density of barium titanate was determined to be 6.06 g / cm ³ and the density of barium zirconate was determined to be 5.52 g / cm ³ . . In addition, "-" in a table | surface shows that it was not measuring or was not able to measure.

  From Table 1 above, in all of the examples, the result that the dielectric constant was improved as compared with the normal barium titanate particles (Comparative Example 1) was obtained. Even when compared with a sample obtained by simply mixing barium titanate particles and barium zirconate particles (Comparative Example 2), the sample obtained in the example according to the present invention has a dielectric constant. it was high. In consideration of the result of XRD measurement, such a result is due to the fact that barium titanate particles are coated with barium zirconate to form a core-shell structure, and as a result, the barium titanate crystal at the interface is distorted. This is probably because the dielectric constant has been improved.

  Furthermore, at the time of solvothermal synthesis, a sample having a higher dielectric constant was obtained when the solvent was water (Examples 1 to 4) than when the solvent was ethanol (Examples 5 to 8). . The reason for this is that water is a solvent that is more polar than ethanol, so the reactivity in the synthesis reaction is higher, and the barium zirconate shell phase is more strongly adhered to the barium titanate, which causes distortion of the barium titanate crystals. This is probably because the ratio has increased.

In addition, the results showed that the relative permittivity tends to improve as the molar ratio of barium zirconate to barium titanate (M _BZ / M _BT ) decreases.

Furthermore, when the relative density was evaluated, the examples show that dielectric ceramics having a high relative density were obtained. Thus, it is considered that the high relative density also contributes to the improvement of the dielectric constant.

Claims (5)

Core particles mainly composed of barium titanate;
A shell phase mainly composed of a metal oxide formed on the surface of the core particles,
The core particle has a particle size of more than 50 nm and not more than 500 nm,
Dielectric ceramic particles in which the lattice constant (a _M ) in the a-axis direction of the metal oxide is 0.5% or more larger than the lattice constant (a _BT ) in the a-axis direction of the barium titanate.   The dielectric ceramic particle according to claim 1, wherein a crystal structure of the metal oxide at room temperature is a perovskite type.   The dielectric ceramic particle according to claim 1, wherein the metal oxide is barium zirconate. The dielectric ceramic particles according to claim 3, wherein a content molar ratio (M _BZ / M _BT ) of the barium zirconate to the barium titanate is 1 or less. Dielectric ceramics including the dielectric ceramic particles according to claim 1.