JP5475415B2 - Novel dielectric nanopore material and its production method - Google Patents

Description

  The present invention relates to a novel dielectric nanopore material and a method for producing the same.

  In recent years, research and development of nanomaterials, that is, bulk bodies in which a large number of nano-sized closed pores are present are being conducted. For example, Non-Patent Document 1 discloses that a ceramic coating layer formed by an EB-PVD method is composed of columnar particles, and nanopores are formed therein. Such nanopores are said to greatly affect the low thermal conductivity characteristics of ceramic films. Non-Patent Document 1 also discloses an example in which cross-sectional observation and planar observation of a ceramic film on which nanopores are formed are performed using a transmission electron microscope (TEM).

“Microstructure of zirconia film formed by electron beam (EB-PVD) method”, [online], JFCC (Fine Ceramics Center), [November 12, 2008 search], Internet <URL: http: //www.jfcc.or.jp/23_develop_2/09res_04a.html>

  However, as far as the present inventors know, no nanopore material that has been researched and developed so far has been reported as a suitable dielectric.

  The present invention has been made in view of such problems, and has as its main object to provide a dielectric nanopore material having a high relative dielectric constant.

  In order to achieve the above-mentioned object, the inventors added nano-sized organic fine particles to a barium titanate ferroelectric ceramic powder, mixed, molded, and then formed in an inert atmosphere or an air atmosphere. It has been found that the nanopore material obtained by firing at a very high relative dielectric constant has completed the present invention.

That is, the dielectric nanopore material of the present invention has a structure in which many closed pores having an average pore diameter of 1 μm or less are introduced into a ferroelectric ceramic dense body.

  In addition, the dielectric nanopore material of the present invention is produced by adding organic fine particles having an average particle size of 1 μm or less to a ferroelectric ceramic powder, mixing, molding, and firing in an inert atmosphere or an air atmosphere. By doing so, a nanopore material is obtained.

The dielectric nanopore material of the present invention has a relative dielectric constant several times higher than that of a ceramic dense body having the same component and having no closed pores. The reason is not clear, but it is presumed as follows. That is, it is known that a ferroelectric such as barium titanate particles has a so-called size effect in which the dielectric constant changes depending on the particle diameter. Wada et al. Of Yamanashi University obtained and obtained barium titanate particles with few defects and impurities in the particle size range of 10-1000 nm in the SPring-8 Research Results Report (2006), Ministry of Education, Culture, Sports, Science and Technology. As a result of measuring the relative permittivity of the particles, it was reported that the relative permittivity increased as the particle size decreased, showed a maximum value at 140 nm, and then rapidly decreased as the particle size decreased. In order to elucidate this result, structural analysis using synchrotron radiation was carried out. As a result, in the ferroelectric nanoparticles represented by barium titanate, (1) the surface is a surface cubic that is a paraelectric material. A three-layer structure comprising a crystal layer, (2) an internal tetragonal layer that is a ferroelectric substance inside the particle, and (3) a gradient structure in which the crystal structure gradually changes from tetragonal to cubic between the two layers. The existence of a particle structure consisting of (see FIG. 1). On the other hand, when the inner peripheral surface of the closed pores of the dielectric nanopore material of the present invention was observed with a TEM, the crystal phase of the inner peripheral surface of the closed pores was different from the crystal phase outside the inner peripheral surface. Considering the above reports and experimental results, this dielectric nanopore material has a closed cubic inner surface with a surface cubic layer and a structure gradient layer and an internal tetragonal layer on the outside. There is a possibility (see FIG. 2). In other words, there is a possibility that the bulk body has a large amount of the structure gradient layer. And, as the relative permittivity of barium titanate particles increases with decreasing particle size and shows the maximum value at 140 nm, this dielectric nanopore material also has an average pore diameter between the closed pores and the relative permittivity. It is presumed that the dielectric constant was very large when the average pore diameter was 1 μm or less. The structural gradient layer is assumed to increase as the average pore diameter of closed pores is small and the porosity is large, so that the relative dielectric constant can be further increased by further reducing the average pore diameter from 200 nm.

It is explanatory drawing which shows the structure of a barium titanate particle, and the graph of a particle size-specific dielectric constant characteristic. It is a schematic diagram which shows the structure of the dielectric nanopore material of this invention. It is a graph which shows the relationship between an average pore diameter and the dielectric constant characteristic with respect to a porosity.

The dielectric nanopore material of the present invention has a structure in which a large number of closed pores having an average pore diameter of 1 μm or less are introduced into a ferroelectric ceramic dense body.

  Here, examples of the ferroelectric ceramic dense body include, for example, barium titanate, lead zirconate titanate (PZT), lead titanate, bismuth titanate, potassium sodium niobate (KNN), and bismuth sodium titanate (BNT). Among them, barium titanate is preferable.

The average pore diameter of the closed pores is preferably 1 μm or less, and more preferably 200 nm or less. This is because the dielectric constant of such a dielectric nanopore material changes depending on the average pore diameter of the closed pores, but the relative dielectric constant increases as the average pore diameter decreases. The reason for this is not clear, but it is thought that the smaller the average pore diameter, the greater the number of structurally inclined layers having a higher relative dielectric constant. The average pore diameter is preferably 100 nm or more, which is because closed pores can be formed stably.

  The porosity of the closed pores is preferably 50 to 80%. The dielectric constant of such a dielectric nanopore material changes depending on the porosity of the closed pores, but when the porosity is 50 to 80%, the relative dielectric constant takes a maximum value or a value in the vicinity thereof.

  The method for producing the dielectric nanopore material of the present invention is to add and mix organic fine particles having an average particle size of 1 μm or less into a ferroelectric ceramic powder, and after molding, firing in an inert atmosphere or an air atmosphere. Thus, a nanopore material is obtained.

According to this manufacturing method, a dielectric nanopore material having a structure in which a large number of closed pores having an average pore diameter of 1 μm or less are introduced into a ferroelectric ceramic dense body can be easily produced.

Here, examples of the organic fine particles include polymethacrylate fine particles, polyacrylic ester fine particles, and melamine fine particles . If added to and mixed with organic particles in ceramics powder may be wet-mixed in a solvent (e.g., water). When performing wet mixing, a mixing and grinding machine such as a pot mill, a trommel, an attrition mill, or the like may be used. Further, dry mixing may be performed instead of wet mixing. In order to pelletize the mixed powder, pressure molding is generally employed, and uniaxial press molding is particularly preferably employed. The molding pressure is preferably 100 MPa or more, but is not particularly limited as long as the shape can be retained. The atmosphere when firing the pellet is not particularly limited, and examples thereof include an inert atmosphere and an air atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere. The firing temperature may be appropriately set according to the composition of the calcined ceramic powder. For example, in the case of barium titanate, the firing temperature may be set to 1250 to 1350 ° C.

[Example 1]
Barium titanyl oxalate (manufactured by Fuji Titanium Industry) was fired at 1000 ° C. in an atmospheric furnace to obtain a calcined powder of barium titanate. 10 wt% of polymethyl methacrylate fine particles (manufactured by Soken Chemical Co., Ltd., MP) having an average particle diameter of 150 nm were added to the obtained calcined barium titanate powder, and the mixture was mixed for 3 minutes in a planetary pot mill using water as a solvent. After drying, it was pelletized by uniaxial press molding (100 MPa) and then fired at 1300 ° C. in a nitrogen atmosphere to obtain a sintered body of barium titanate having nano-closed pores. When the porosity of the sintered body of Example 1 was measured by the Archimedes method (based on JIS R 1634), the porosity was 10%. Further, when the microstructure of the cross section of the sintered body of Example 1 was observed with a field emission scanning electron microscope (manufactured by ZEIS, ULTRA55), closed pores having a pore diameter of 100 to 200 nm (average pore diameter of 150 nm) were found. Observed.

[Comparative Example 1]
A barium titanate sintered body was obtained under the same conditions as in Example 1 except that the polymethyl methacrylate fine particles were not added.

[Comparison of relative permittivity]
When the relative dielectric constants of the sintered body of Example 1 and the sintered body of Comparative Example 1 were measured with an LCR meter (manufactured by Hewlett-Packard Japan, 4194A), the relative dielectric constant of the sintered body of Example 1 was measured. The dielectric constant of the sintered body of Comparative Example 1 was 1600. Therefore, the specific permittivity of Example 1 was about twice as high as that of Comparative Example 1. In Example 1, firing was performed in an air atmosphere or an argon atmosphere instead of the nitrogen atmosphere, and the same results as in Example 1 were obtained.

[Example 2]
The experiment of Example 1 was carried out by changing the particle diameter and addition amount of the polymethyl methacrylate fine particles. Specifically, polymethyl methacrylate fine particles having average particle diameters of 100 nm, 200 nm, and 1 μm were used. Here, the average particle diameter is an arithmetic average value obtained by dividing the sum of the diameters of 10 fine particles randomly selected by 10 by observing the fine particles with an SEM. For each average particle size, the amount of addition was set to 10 wt%, 30 wt%, 60 wt%, and 80 wt%, and experiments were performed. As a result, the larger the average particle size of the polymethyl methacrylate fine particles, the larger the closed pores formed in the sintered body. Specifically, when the average particle diameter was 100 nm, 200 nm, and 1 μm, the average pore diameters obtained in the same manner as in Example 1 were 100 nm, 200 nm, and 1 μm, respectively. In addition, the porosity of the sintered body increased as the amount of polymethyl methacrylate fine particles added increased. Specifically, when the addition amount was 10 wt%, 30 wt%, 60 wt%, and 80 wt%, the porosity determined in the same manner as in Example 1 was 10%, 30%, 60%, and 80%, respectively. .

[ Average pore diameter, porosity-relative dielectric constant characteristics]
Regarding the sintered bodies of Example 1 and Example 2, the relationship between the average pore diameter and the relative dielectric constant with respect to the porosity is shown in FIG. As is clear from FIG. 3, the relative dielectric constant was higher as the average pore diameter was smaller. Further, as the porosity increased, the relative dielectric constant increased and reached a maximum at a porosity of about 60%. However, the relative dielectric constant decreased when the porosity exceeded 60%. The reason for this is not clear, but as the porosity increases, the number of structurally inclined layers having a high relative dielectric constant increases. On the other hand, the number of voids having a low relative dielectric constant also increases. It is thought that the trend has declined. From FIG. 3, it can be said that the preferable numerical range of the porosity at a certain average pore diameter is 50 to 80%. If it is this range, a relative dielectric constant will become a very big value. From FIG. 3, the relative dielectric constant of the sintered body having an average pore diameter of about 100 nm, 150 nm, and 200 nm was about twice or more that of the relative dielectric constant 1600 of the sintered body of Comparative Example 1. When the average pore diameter was about 100 nm and the porosity was about 60%, the relative dielectric constant was 18000 at the maximum, which was about 11 times higher than the relative dielectric constant of the sintered body of Comparative Example 1.

  When the inner peripheral surface of the closed pores of the sintered body of Example 1 was observed with a TEM (transmission electron microscope), the crystal phase thereof was a phase different from the outside of the inner peripheral surface of the closed pores.

Claims (5)

Chi lifting ferroelectric average pore diameter 1μm or less closed pores in the ceramic dense body of was introduced many structures,
The closed pores have an average pore diameter of 200 nm or less and a porosity of 50 to 80%.
Dielectric nanopore material. The ceramic dense body is barium titanate.
The dielectric nanopore material according to claim 1. The crystal phase of the inner peripheral surface of the closed pores is different from the crystal phase outside the inner peripheral surface,
The dielectric nanopore material according to claim 1 or 2. A method for producing the dielectric nanopore material according to claim 1, comprising:
Adding and mixing organic fine particles with an average particle size of 200 nm or less to ferroelectric ceramic powder, forming, and then forming a nanopore material by firing in an inert atmosphere or air atmosphere,
Dielectric nanopore material manufacturing method. The ceramic powder is barium titanate.
The manufacturing method of the dielectric nanopore material of Claim 4 .

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