JP6508766B2 - Dielectric ceramic particles and dielectric ceramics - Google Patents

Description

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

  With the spread of smartphones and tablets, 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 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.

For example, in Patent Document 1, barium titanate is deposited on the surface of a fine strontium titanate (SrTiO ₃ : ST) nanocube having a particle size distribution of about 5 to 50 nm as a technique for micronizing dielectric ceramics containing barium titanate. Technology is disclosed. According to the technology disclosed in Patent Document 1, a barium titanate-containing fine particle having a very small particle diameter is prepared, which includes strontium titanate as so-called core particles and barium titanate as a shell phase covering the core particles. can do.

JP 2012-240860 A

  On the other hand, in order to reduce the size and increase the capacity of MLCC, in addition to the reduction of the diameter of the dielectric ceramic particles, high relative density can be obtained when producing dielectric ceramics (aggregates of particles) in which the particles are accumulated. It is necessary to be able to form the dielectric ceramic having the dielectric ceramic and to have a high dielectric constant.

  Therefore, an object of the present invention is to provide dielectric ceramic particles capable of forming a dielectric ceramic exhibiting a high dielectric constant and a high relative density. Another object of the present invention is to provide a dielectric ceramic which exhibits a high dielectric constant and a high relative density.

  The present inventors diligently studied to solve the above problems. As a result, the particle diameter of the core particle containing barium titanate as a main component is within the predetermined range, and further, a shell phase containing a metal oxide having a specific lattice constant as a main component is formed on the surface of the core particle. As a result, the inventors have found that dielectric ceramic particles capable of forming a dielectric ceramic exhibiting a high dielectric constant and a high relative density can be obtained, and the present invention has been completed.

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

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

  According to the present invention, dielectric ceramic particles capable of forming a dielectric ceramic exhibiting a high dielectric constant and a high relative density are provided. Also, according to the present invention, a dielectric ceramic exhibiting a high dielectric constant and a high relative density is provided.

7 is a STEM image of dielectric ceramic particles according to Example 2. FIG. 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 measured in the same visual field as FIG. 1A. 7 is a SEM image of dielectric ceramic according to Comparative Example 3; 1 is an XRD spectrum of a dielectric ceramic according to Example 1. FIG. FIG. 6 is an XRD spectrum of a dielectric ceramic according to Example 2. FIG. FIG. 7 is an XRD spectrum of a dielectric ceramic according to Example 3. FIG. FIG. 18 is an XRD spectrum of a dielectric ceramic according to Example 4. FIG. FIG. 16 is an XRD spectrum of a dielectric ceramic according to Example 5. FIG. FIG. 18 is an XRD spectrum of a dielectric ceramic according to Example 6. FIG. FIG. 18 is an XRD spectrum of a dielectric ceramic according to Example 7. FIG. FIG. 18 is an XRD spectrum of a dielectric ceramic according to Example 8. FIG. It is a graph showing the relationship between the dielectric constant of the dielectric ceramics which concerns on an Example, and the content molar ratio of barium zirconate with respect to barium titanate (M _BZ / M _BT ).

  Hereinafter, embodiments of the present invention will be described.

According to a first aspect of the present invention, there is provided a core particle comprising barium titanate as a main component, and a shell phase mainly comprising a metal oxide formed on the surface of the core particle, wherein the core particle is The particle diameter of the metal oxide is more than 50 nm and not more than 500 nm, and the metal oxide relative to the lattice constant ( _a.sub.BT ) of the barium titanate in the a-axis direction (hereinafter also simply referred to as "lattice constant ( _a.sub.BT )") The present invention provides dielectric ceramic particles in which the lattice constant (a _M ) in the a-axis direction of (hereinafter, also simply referred to as “lattice constant (a _M )”) is 0.5% or more.

  In the present specification, “core particles containing barium titanate as a main component” means that 90 mass% or more of barium titanate is contained with respect to the total amount of core particles. In addition, it is confirmed by the analysis by a fluorescent X ray that core particles contain 90 mass% or more of barium titanate. Moreover, "the shell phase which has a metal oxide as a main component" means that 90 mass% or more of metal oxides are included with respect to the whole quantity of a 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, 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 the present specification, “particle size” is obtained by imaging with a transmission 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.

The lattice constants "a _BT " and "a _M " refer to 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. It shall be. Further, as these lattice constants, values calculated by the Rietveld method from diffraction intensities obtained by X-ray diffraction are adopted.

  The dielectric ceramic particle of the present invention is mainly composed of barium titanate, and has a core particle having a particle size of more than 50 nm and 500 nm or less, and a shell phase for coating the core particle.

  As described above, in the past, in order to miniaturize and increase the capacity of MLCC, a technology for micronizing (reducing the particle size) of dielectric ceramics has been studied. However, when the present inventors proceeded to reduce the particle size of particles having a core-shell structure as disclosed in Patent Document 1, sufficient relative density and dielectric constant can not be obtained when producing dielectric ceramics. I found that there is a case. Therefore, when the above problems were examined, the particle diameter of the core particle was made to be in a specific range, and further, by coating the core particle with a specific metal oxide, a high dielectric constant was exhibited and a high relative density was obtained. It has been found that it is possible to obtain dielectric ceramic particles capable of forming the dielectric ceramic having the dielectric ceramic particles, and it is possible to arrive at the present invention.

  The mechanism of exerting the effect by the above-mentioned composition of the present invention is presumed as follows.

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

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

  On the other hand, in the core-shell structure, the present inventors can eliminate the above-mentioned inconvenience by setting the particle diameter of the core particle containing barium titanate as the main component to more than 50 nm and 500 nm or less. I thought I could. That is, by setting the particle size of the core particles contained in the dielectric ceramic particles of the present invention in the above range, the aggregation of the core particles in the manufacturing process can be suppressed and the influence of the size effect can be reduced. As a result, dielectric ceramics having a high relative density and a high dielectric constant can be produced.

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

  Thus, the metal oxide of the shell phase is formed at the interface between the core particle and the shell phase by using, as the metal oxide constituting the shell phase, one having a lattice constant larger than that of barium titanate constituting the core particle. The barium titanate unit cell distorts by interaction with the unit cell to be pulled to the unit cell. As a result, titanium atoms located at the center of the barium titanate lattice core, which is a core particle, are likely to move, thereby improving 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 and having core particles containing barium titanate as a main component by having a shell phase containing a specific metal oxide as a main component. .

  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% of relative humidity.

«Dielectric ceramic particles»
The dielectric ceramic particle of the present invention is a core-shell structure having a core particle and a shell phase coating 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 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 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 diameter of the dielectric ceramic particles (the particle diameter of the state in which the 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 particle)
Core particles are particles containing barium titanate as a main component. The definition of the term "main component" is as described above, and a slight amount of impure components which may be contained in production may be contained in the core particles. Examples of the impure components include metal-derived components such as potassium, sodium, aluminum, calcium, niobium, iron and lead, glass components, and hydrocarbon-based 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 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. The higher the content of barium titanate, the more easily it interacts with the metal oxide constituting the shell phase, which is preferable because it contributes to the improvement of the dielectric constant.

  In addition, the core particle has a particle size of more than 50 nm and not more than 500 nm. When the particle size of the core particles is 50 nm or less, the dielectric constant is reduced due to the size effect, and it becomes difficult to obtain dielectric ceramic particles having a high dielectric constant. Also, as described above, when the particle size is too small, the core particles aggregate in the production stage, and the surface of the core particle can not be sufficiently covered with the shell phase, and dielectric ceramics having 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 not only difficult to form a good core-shell structure, but it is not preferable from the practical viewpoint in MLCC.

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

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

The metal oxide constituting the shell phase is such that the lattice constant (a _M ) in the a-axis direction at room temperature 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 ratio of the size of the lattice constant (a _M ) is less than 0.5%, it is difficult to distort the barium titanate unit cell in the core particle 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 largely distorted. It is preferable because the dielectric constant can be improved as a result. Therefore, the upper limit of the ratio of the size of the lattice constant (a _M ) to the lattice constant (a _BT ) of barium titanate is not particularly limited, but considering the usable metal oxide species substantially , About 45%.

In other words, since the lattice constant (a _BT ) of barium titanate at room temperature is 3.992 Å, the lattice constant (a _M ) of the metal oxide constituting the shell phase is 3.992 × (100 + 0.5). /100=4.012 Å or more. On the other hand, the upper limit of the lattice constant (a _M ) is about 3.929 × (100 + 45) /100=5.79 Å.

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 ) . By using a metal oxide having a large lattice constant (a _M ), the unit cell of barium titanate at the interface between the core particle and the shell phase can be distorted more largely, and the dielectric constant can be further increased. Therefore, the lattice constant (a _M ) is preferably as large as 0.6 to 8%, more preferably as large as 1 to 7%, and particularly preferably as large as 3 to 6% with respect to 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 metal oxide to the lattice constant (a _BT ) of barium titanate is preferably 1.006 to 1.08, and 1 It is more preferably 0.11 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 above 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 =} 5.148Å And calcium titanate (CaTiO ₃ : CT a _CT = 5.381 Å) bismuth ferrite (BiFeO ₃ : BF a _BF = 5.631 Å). The metal oxides may be used alone or in combination of two or more.

  The metal oxide is preferably one having a perovskite crystal structure at room temperature (25 ° C.). Since the barium titanate constituting the core particle has a perovskite structure, it is preferable that the metal oxide constituting the shell phase also have a perovskite type structure. By using such a metal oxide, the barium titanate and the metal oxide easily interact, and the barium titanate unit cell is easily distorted at the interface, and as a result, a high dielectric constant can be obtained. .

  Therefore, from the viewpoint of easy formation of a core-shell structure with barium titanate, which is a metal oxide satisfying the definition of the above lattice constant, barium zirconate and potassium niobate can be used as the metal oxide constituting the shell phase. Is preferred, 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 used relative to barium titanate constituting the core particle. It is preferable to be 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 can distort the barium titanate unit cell and improve the dielectric constant by interacting with barium titanate. However, on the other hand, some metal oxides themselves have relatively small dielectric constants, so if the amount of metal oxides is increased, the dielectric constant of the dielectric ceramic particles as a whole may decrease. Therefore, the decrease in the dielectric constant of the dielectric ceramic particles as a whole can be suppressed by reducing the content of the metal oxide relative to the content of barium titanate and setting the content in the above range.

On the other hand, the lower limit of the content molar ratio (M _M / M _BT ) of the metal oxide constituting the shell phase to barium titanate constituting the core particle is not particularly limited, but the effect of the present invention can be sufficiently obtained. _{M 2} / M _BT is preferably 0.005 or more, more preferably 0.1 or more, and particularly preferably 0.2 or more.

  When two or more types of metal oxides are used, the sum of all the metal oxides is preferably within the above range with respect to barium titanate.

In particular, when the metal oxide is barium zirconate, the molar ratio of barium zirconate to barium titanate (M _BZ / M _BT ) is preferably 1 or less. At this time, M _BZ / M _BT is more preferably 0.85 or less, still 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 in order to sufficiently obtain the effects of the present invention, M _BZ / M _BT is preferably 0.01 or more, and more preferably 0.15 or more.

  As described above, by setting barium zirconate in the above range to barium titanate, the dielectric constant improvement effect due to distortion of the unit cell of barium titanate can be maximized, and the dielectric constant itself is The content of barium zirconate of low 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 containing the above dielectric ceramic particles.

  The form of the dielectric ceramic is not limited as long as it contains the dielectric ceramic particles, but is preferably an aggregate of the dielectric ceramic particles, for example, a spherical material, a plate-like material, It can be in the form of pellets, or a mixture of these.

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

  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, still more preferably 96% or more, and particularly preferably 97% or more. Also, the upper limit thereof is not particularly limited, but is substantially 100%. In addition, the relative density shall employ | adopt the value measured by the method as described in an Example.

  Since the dielectric ceramic of the present invention contains the above-mentioned dielectric ceramic particles, it exhibits a high dielectric constant. Also, having a high relative density not only has a high dielectric constant but also improves the strength (especially mechanical strength).

«Method of manufacturing dielectric ceramic particles (dielectric ceramic)»
The method for producing dielectric ceramic particles (dielectric ceramic) of the present invention is roughly classified into (1) a step of preparing core particles and (2) a step of forming a shell phase. Moreover, you may perform (3) washing | cleaning / drying process as needed other than these. Each step will be described in detail below.

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

  The core particle as a raw material may use a commercially available barium titanate powder, and may be manufactured by a conventionally well-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. If the particle size of the core particle to be 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 can not be formed uniformly, and the relative density and dielectric constant It is difficult to obtain the improvement effect of

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

Here, it is possible to control the above-mentioned M _M / M _BT by the other materials (metal oxide raw materials) which may be added other than the barium titanate powder and the addition amount of the barium titanate particles.
More specifically, it is possible to control M _M / M _BT by the content of titanium in barium titanate and the content of metal contained in the metal oxide raw material.

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

  Furthermore, when the barium titanate powder and the metal oxide raw material are mixed as described above, a solvent may be added. Although the solvent used at this time is not particularly limited, for example, an aqueous solvent and an organic solvent can be appropriately selected. Examples of usable solvents include 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 methyl ethanolamine and diethanolamine; Aromatic solvents such as benzene, toluene, xylene and the like can be mentioned. Among them, water or an alcohol solvent is preferably used in consideration of the operability of the shell phase forming step to be performed later.

  When the barium titanate powder and the metal oxide raw material are wet-mixed using the above-mentioned solvent, it is preferable to carry out by a wet ball mill or a stirring mill. When 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 the mixture with the metal oxide raw material obtained as described above may be further dried and press molded 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 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, from the viewpoint of improving the density of the molded body Therefore, it is more preferable that it is 0.5 mass%-5 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.

(2) Shell phase forming step (step (2))
In this step, a 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 conventionally known methods can be adopted. For example, various methods such as solid phase method, liquid phase method, spray thermal decomposition method, etc. can be applied, but in particular, to obtain fine particles with uniform particle diameter, spray thermal decomposition method, crystallization The method of synthesizing by a method, a sol-gel method, a solvothermal method or the like is preferable, and in particular, the solvothermal method is particularly preferably used.

  Hereinafter, an example of the manufacturing method of the dielectric ceramic particle (and dielectric ceramic) of this invention by the solvothermal method is demonstrated.

  The solvothermal reaction is a reaction carried out under moderate to high pressure (usually 0.10 to 1,000 MPa) and moderate to high temperature (usually 100 ° C. to 1000 ° C.), and the solvent is water Especially when used as "hydrothermal reaction". The dielectric ceramic particles (and dielectric ceramic) of the present invention can form a shell phase that covers the core particles through this process.

  At this time, a material for forming a shell phase is further added to the core particles (or a molded product thereof) prepared in the above 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 to form a shell phase is added. Examples of the material to be added here include compounds containing elements that depend on the metal oxide species constituting the shell phase, but can not be compensated by the metal oxide raw material added in the above 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 the compound serving as the barium source include, but are not particularly limited to, 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 a compound used as the said potassium source, Potassium hydroxide etc. are mentioned. In addition, examples of the compound serving as the lithium source include, but not particularly limited to, lithium hydroxide and the like.

The addition amount of the material for forming the shell phase is not particularly limited, but it depends on the metal oxide species constituting the shell phase and the kind (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 the above, 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 compound to be a barium source to the zirconium oxide. By setting it as the said range, it can convert into barium zirconate, without zirconium oxide remaining, and can suppress generation | occurrence | production of the unreacted substance which can become an impurity.

  As a solvent used at this time, an aqueous solvent and an organic solvent can be suitably selected according to the material which constitutes shell phase. Examples of usable solvents include 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 methyl ethanolamine and diethanolamine And aromatic solvents such as benzene, toluene and xylene. 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 (i.e., neutral or basic) mixture (reaction mixture) from the viewpoint of corrosion of the container and the like.

  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 more polar solvent in addition to the point of being inexpensive. At the time of solvothermal synthesis, by using a solvent having high polarity, the core particle and the shell phase are more firmly adhered, and the crystal distortion of the core particle at the interface becomes large.

  The temperature at the time of the solvothermal reaction is not particularly limited, but is preferably 150 ° C to 400 ° C, and more preferably 200 ° C to 300 ° C.

  Moreover, it does not specifically limit also about time to perform a solvothermal reaction, However, 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 a solvothermal reaction is not particularly limited, it is preferable to carry out at about 0.10 to 4.0 MPa. The reaction under such pressure can be carried out in a pressure container such as an autoclave.

(3) Washing and Drying Step After forming the shell phase in the above steps, if necessary, a washing and drying step may be performed. This step is mainly performed to remove impurities and unreacted substances generated in the above step (2). 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 (pure water) or the like is preferable.

  Also, the drying conditions are not particularly limited, but drying at 100 to 150 ° C. is preferable.

  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
Barium titanate having a particle diameter of 300 nm (BT: BaTiO ₃ Name T-BTO-300: Toda Kogyo Co., Ltd.) and zirconium oxide: _ZrO 2 in (ZrO ₂ Name UEP-100 Daiichi Kigenso Kagaku Co., Ltd.) molar ratio: It mixed by the wet ball mill (zirconia ball, (phi) 3 mm) for 16 hours so that it might become BT = 0.25: 1.00 (solvent: pure water, solid content concentration 30 wt%). The resulting slurry was dried and ground with a mortar and pestle to obtain a powder. A PVA binder was added to the powder to a ratio of 1% by mass.

  The powder was press-molded at a pressure of 2 t using a 1 cm square mold, and the obtained molded body (pellet) was treated at 500 ° C. for 3 hours for debinding treatment.

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

In order to remove unreacted Ba (which has become BaCO ₃ ), the sample taken out was washed with an aqueous acetic acid solution (acetic acid: water = 1: 1), further washed with pure water, and then dried. This series of operations yielded a dielectric ceramic (1) having a BZ / BT core-shell structure. 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 to 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 to 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 to 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)
A dielectric ceramic (5) was obtained in the same manner as in Example 1 except that solvothermal synthesis was performed using ethanol instead of the hydrothermal synthesis (ethanol was used as a solvent instead of water). In the dielectric ceramic (5), BZ / BT = 0.25 / 1.00 molar ratio.

(Example 6)
A dielectric ceramic (6) was obtained in the same manner as in Example 2, except that solvothermal synthesis was performed using ethanol (in place of water, ethanol was used as the solvent) instead of the hydrothermal synthesis. In the dielectric ceramic (6), BZ / BT = 0.5 / 1.00 molar ratio.

(Example 7)
A dielectric ceramic (7) was obtained in the same manner as in Example 3, except that solvothermal synthesis was performed using ethanol (in place of water, ethanol was used as the solvent) instead of the hydrothermal synthesis. 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 solvothermal synthesis was performed using ethanol (in place of water, ethanol was used as a solvent) instead of the hydrothermal synthesis. In the dielectric ceramic (8), BZ / BT = 1.0 / 1.00 molar ratio.

(Comparative example 1)
Barium titanate having a particle diameter of 300nm (BT: BaTiO ₃ Name T-BTO-300: Toda Kogyo Co., Ltd.) with respect to, the addition of PVA binder so that the proportion of 1 wt%.

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

(Comparative example 2)
Barium titanate with a particle size of 300 nm (BT: BaTiO ₃ product name T-BTO-300: Toda Kogyo Co., Ltd.) and BaZrO ₃ with a particle size of 100 nm synthesized by a hydrothermal synthesis method, at a molar ratio of 1: 1 It mixed with the wet ball mill (zirconia ball, (phi) 3 mm) so that it might become (Solvent: pure water, solid content density | concentration 30 wt%). The resulting slurry was dried and ground with a mortar and pestle to obtain a powder. A PVA binder was added to the powder to a ratio of 1% by mass.

  The powder was press-molded at a pressure of 2 t using a 1 cm square mold, and the obtained molded body (pellet) was treated at 500 ° C. for 3 hours for debinding treatment. 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 diameter of 50 nm synthesized by a hydrothermal synthesis method and zirconium oxide (ZrO ₂ product name UEP-100: First Rare Element Chemical Co., Ltd.) in molar ratio ZrO ₂ : BT = 0.25: 1.00 The mixture was mixed by a wet ball mill (zirconia ball, φ 3 mm) for 16 hours (solvent: pure water, solid content concentration 30 wt%). The resulting slurry was dried and ground with a mortar and pestle to obtain a powder. After that, a PVA binder was added to the powder to a proportion of 1% by mass.

  The powder was press-molded at a pressure of 2 t using a 1 cm square mold, and the obtained molded body (pellet) was treated at 500 ° C. for 3 hours for debinding treatment.

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

In order to remove unreacted Ba (which has become BaCO ₃ ), the sample taken out was washed with an aqueous acetic acid 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 a 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 on the dielectric ceramic obtained in the above example. In addition, the measurement was performed using Nippon Denshi Co., 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 mapping data of Ti, Zr, and Ba measured in the same field of view as that of FIG. 1A.

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

(SEM observation)
SEM analysis was performed on the comparative dielectric ceramic (3) obtained in Comparative Example 3 above. In addition, the measurement was performed using Nippon Denshi 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 particle size of the barium titanate particles to be core particles is small, and as a result of aggregation of the barium titanate particles, barium zirconate is not synthesized inside the pellet and is made of barium zirconate on the surface of the core particles It is considered that the shell phase was not formed.

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

  In the XRD spectrum in the figure, "before reaction" means before hydrothermal synthesis reaction or before solvothermal synthesis treatment, and after debinding treatment, "after reaction" means after hydrothermal synthesis reaction or solvothermal synthesis treatment Show after. As a result, since the peak width of the spectrum after reaction is expanded in all the samples of the examples, crystals of barium titanate at the interface between the barium titanate core particle and the barium zirconate shell phase It is suggested that the structure has changed. More specifically, the XRD spectrum suggests that the barium titanate core particle surface is coated with the barium zirconate shell phase, and that the barium titanate crystal structure at the interface with the shell phase is distorted.

(Specific dielectric constant measurement)
About the dielectric ceramics obtained in the above-mentioned example and comparative example, DOTITE (registered trademark) TYPE D550 (Fujikura Kasei Co., Ltd.) which is a conductive paste is applied, and an electrode is baked on conditions of 300 ° C x 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 could not measure.

(Determination of density)
The density was measured using the Archimedes method about the dielectric ceramics obtained by the said Example and comparative example. 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 as 6.06 g / cm ³ and the density of barium zirconate as 5.52 g / cm ³ . . In addition, "-" in a table | surface shows not having measured or having not been able to measure.

  From the above-mentioned Table 1, in all the examples, the result that the dielectric constant is improved as compared to the normal barium titanate particles (comparative example 1) was obtained. Moreover, compared with the sample (comparative example 2) obtained by only mixing barium titanate particles and barium zirconate particles, the dielectric constant of the sample obtained in the example according to the present invention is it was high. Such results are attributed to the fact that barium titanate particles are coated with barium zirconate to form a core-shell structure, as a result of distortion of barium titanate crystals at the interface, also in consideration of the results of XRD measurement. It is considered that the dielectric constant is improved.

  Furthermore, in the case of solvothermal synthesis, when the solvent was water (Examples 1 to 4), a sample having a higher dielectric constant was obtained than when the solvent was ethanol (Examples 5 to 8). . The reason for this is that since water is a more polar solvent than ethanol, the reactivity in the synthesis reaction is higher and the barium zirconate shell phase is more tightly attached to the barium titanate, which causes distortion of the barium titanate crystal. It is thought that this is because the ratio has increased.

The results also show that the relative dielectric constant 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, it is shown in Examples that dielectric ceramics having a high relative density were obtained. Thus, the high relative density is also considered to contribute to the improvement of the dielectric constant.

Claims (5)

Core particles containing barium titanate as a main component,
A metal oxide-based shell phase formed on the surface of the core particle;
The particle diameter of the core particle is more than 50 nm and not more than 500 nm,
The contrast barium titanate in the a-axis direction of the grating constant _{(a BT),} the a-axis direction of the lattice constant of the metal oxide _{(a M)} is rather large 0.5% or more,
The crystal structure of the metal oxide at room temperature is a perovskite type,
The molar ratio of the metal oxide to the barium titanate (M _M / M _BT ) is 1 or less.
Dielectric ceramic particles. The molar ratio of the metal oxide to the barium titanate (M _M / M _BT ) is 0.65 or less .
The dielectric ceramic particle according to claim 1.   The dielectric ceramic particle according to claim 1, wherein the metal oxide is barium zirconate. A dielectric ceramic comprising the dielectric ceramic particle according to any one of claims 1 to 3 . The dielectric ceramic according to claim 4, wherein the relative density is 90% or more.