JP2014005200A - Artificial superlattice particle, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel-structured artificial superlattice nano particle that is expected to have relative dielectric constant one order or more higher than the ceramic particle of general film capacitors, unlike the general film capacitor consisting of the ceramic particles having high dielectric constant, of which relative dielectric constant has limit and cannot provide necessary capacity density, and polymers having low dielectric constant.SOLUTION: A novel-structured spherical type artificial superlattice nano particle is formed by alternatively laminating two or more types of oxides having different chemical compositions concentrically on a spherical core.

Description

  The present invention relates to a method for producing artificial superlattice dielectric nanoparticles, and can be used as dielectric nanoparticles used in a film capacitor having a large capacity density.

  Artificial superlattices in which two or more types of unit cells with different chemical compositions are stacked in a periodic structure that does not exist in nature are currently manufactured as superlattice thin films under ultrahigh vacuum using a single crystal as a substrate. However, in a thin film, the modulation structure exists only in the film thickness direction, and therefore the giant physical properties that can be expected from the modulation structure are limited to one dimension. In addition, the production of the artificial superlattice thin film requires a high temperature of 500 ° C. or higher, and as a result, it has been difficult to maintain an interface having a steep chemical composition. Patent Document 1 discloses an oxide artificial superlattice thin film and a method for producing the same, but it is the production of a thin film, and there is no description or suggestion regarding the production of spherical particles according to the present invention. Patent Document 2 discloses a method for producing tetragonal barium titanate particles, but does not describe or suggest the lamination of the nanoparticles of the present invention. Patent Document 3 discloses a method for producing calcium-doped barium titanate, but neither describes nor suggests the lamination of nanoparticles.

JP 2000-154100 A JP 2005-272295 A JP 2005-281092 A

For example, as a high-frequency circuit element for realizing future ultra-high-speed and large-capacity communication, it is expected to realize a system-in-package (SIP) in which L, C, and R elements are three-dimensionally mounted on an electronic board. However, the problem is C (capacitor), and a film capacitor having a capacity density of 10 nF / mm ² or more is required. However, at present, its capacity density is an order of magnitude smaller and its improvement is required. If artificial superlattice nanoparticles with a three-dimensional modulation structure can be fabricated at a low temperature of 300 ° C or lower, a new material with a modulation structure in all directions and huge physical properties in all directions can be created. I can live. In general, a film capacitor is composed of ceramic particles having a high dielectric constant and a polymer having a low dielectric constant. However, the relative dielectric constant of ceramic particles is limited, and a necessary capacity density cannot be achieved. However, if artificial superlattice nanoparticles with a novel structure that can be predicted to have a relative dielectric constant higher by an order of magnitude or more can be used in place of the ceramic particles, it is possible to provide a film capacitor that exceeds the above capacity density. .

  The method for producing artificial superlattice particles according to the present invention includes a step of placing a core particle and a compound material having a different chemical composition from the core particle into a sealed container, and heating and holding the core particle. And a step of stacking the compound on the surface by heteroepitaxial growth.

  Artificial superlattices in which two or more types of unit cells with different chemical compositions are stacked with a periodic structure that does not exist in nature are currently manufactured as a thin film under ultrahigh vacuum using a single crystal as a substrate. Therefore, the giant physical properties that can be expected from the modulation structure remain only in one dimension, and as a result of film formation at a high temperature, it is difficult to maintain an interface having a sharp chemical composition. Therefore, if artificial superlattice nanoparticles with a three-dimensional modulation structure can be fabricated at 300 ° C or lower, new materials with huge physical properties in all directions can be created. Therefore, if a three-dimensional artificial superlattice nanoparticle can be created, a new material of a dream that has unprecedented physical properties and multiple functions can be created, and the present invention forms the basis thereof.

  In the present invention, attention has been paid to dielectric nanoparticles, but a giant characteristic due to a strain modulation structure can be expected even in a magnetic substance or a semiconductor other than a dielectric substance.

Conceptual diagram of artificial superlattice nanoparticles Autoclave equipment BT XRD water / ethanol ratio dependence BT XRD reaction temperature dependence BT XRD Ba / Ti ratio dependence BT generation area ST / XRD dependence of water / ethanol ratio Dependence of BT XRD on reaction temperature ratio ST XRD dependence of Sr / Ti ratio ST generation area First stage XRD results of ST / BT composite particles One-stage SEM photograph of ST / BT composite particles First stage TEM photograph of ST / BT composite particles Second stage XRD results of ST / BT composite particles Second stage SEM photograph of ST / BT composite particles

FIG. 1 shows a conceptual diagram of the structure of the present invention. Shows the condition examination results for BaTiO _3, SrTiO ₃ is an oxide which constitutes the artificial superlattice nanoparticles of the present invention, as the oxide, other _{CaTiO 3, PbTiO 3, PbZrO 3} , CaZrO 3, SrZrO 3, BaZrO ₃ can also be used, but is not limited thereto.

(1) Selection of starting material As a starting material in the present invention, a raw material containing four kinds of elements of Ba source, Sr source, Ti source and O source is required. Of these, O (oxygen) can be obtained from OH such as alcohol and water, and is therefore excluded from the study. In addition, Ba and Sr have various raw material forms from high to low solubility. In the present invention, BaTiO ₃ (BT) and SrTiO ₃ (ST) are synthesized independently, so that Ba and Sr raw materials are general raw materials such as anhydrous barium hydroxide (Ba (OH) ₂ ) and anhydrous hydroxide. Instead of using strontium (Sr (OH) ₂ ), we tried to control the overall reaction by controlling the Ti source common to both synthesis reactions.

In general, Ti is unstable in a solution and exists in a form like titanium hydroxide (gel). In addition, use in a form such as titanium oxide nanoparticles has been reported, and in this case, it is known that when the basicity is high, it dissolves as Ti ions. However, it is ideally desirable from the uniformity of reaction that it exists stably in the form of a complex dissolved in a solution. In general, titanium tetraisopropoxide (Ti (iPrO) ₄ , TP), which is an alkoxide, is used with alcohol as a solvent, but because of its high reactivity, it reacts and decomposes with a little moisture even at room temperature, and finally titanium hydroxide gel Is generated. There are two processes in the synthesis of ceramic particles: nucleation and subsequent nucleation. Both the nucleation rate and each growth rate show a normal distribution with respect to temperature. In addition, it is known that the temperature at which each maximum speed is shown is generally lower in nucleation than in nucleation. Therefore, nucleation does not occur if there is a Ti source that is stable in the form of a complex in solution but does not react to high temperatures and becomes unstable at a temperature at which nucleation becomes more dominant. It can be an optimal Ti source for causing only nuclear growth.

Therefore, a part of the TP isoproxil group was replaced with a chelate ligand, and a compound that was stably coordinated to high temperatures was studied. Two of the TP isoproxyl groups of TP were chelated with acetylacetone. It was decided to use titanium diisopropoxide diacetylacetonate (Ti (iPrO) ₂ (AcAc) ₂ , TPA) substituted with ligand as the Ti source. The generation mechanism of BT and ST using TPA is shown below.

(2) Conditions where only heteronuclear growth occurs without BT nucleation using TPA (a) Dependence of water-ethanol solvent mixing ratio First, BT synthesis by solvothermal method, solvent mixing ratio of 0 Changed to ~ 1.0. Ba / Ti charge ratio is 1.5, Ba (OH) ₂ 2.570 g (0.015 mol) and TPA 4.820 ml (0.010 mol) are put into water-ethanol mixed solution (250 ml) with different mixing ratio and stirred for about 5 minutes. Went. The resulting solution was transferred into a 500 ml autoclave. It was attached to a device as shown in (FIG. 2), kept in a sealed state at 260 ° C. for 18 hours, and the heating rate was 120 ° C./h. The inside of the autoclave was constantly stirred at 300 rpm during sealing. Thereafter, the container was air-cooled until it cooled to room temperature, the reaction product was taken out, collected by filtration using a high-speed centrifuge, and the collected precipitate was dried for about 20 hours. The obtained sample was lightly pulverized with a mortar and observed with an X-ray diffraction measurement (XRD), or a 56 scanning electron microscope (FE-SEM) and a transmission electron microscope (TEM). The sample for electron microscope observation was mixed with ethanol and subjected to dispersion treatment by ultrasonic waves. In addition, powder containing a large amount of impurities such as barium carbonate (BaCO ₃ ) and strontium carbonate (SrCO ₃ ) is washed with a thin acetic acid solution for about 10 minutes, collected by filtration with a high-speed centrifuge, and then dried. Dried in-flight.

The water-ethanol solvent mixing ratio was determined by combining ethanol ratios of 0-100% (hereinafter Et0-Et1.0) to Et0, Et0.3, Et0.5, Et0.7, Et1.0. XRD measurement was performed. (Fig. 3) From this result, the formation of BT was confirmed at three points of Et0.3, Et0.5, and Et0.7. In Et0 and Et1.0, no BT was formed, and Et0 contains Ti-rich barium titanium oxides such as Ba ₄ Ti ₁₂ O ₂₇ and Ba ₆ Ti ₁₇ O ₄₀ from the XRD profile. The other four points contained barium carbonate (BaCO ₃ ) as an impurity.

(B) Reaction temperature dependence The experiment was carried out with the solvent mixture ratio fixed at 0.5 water: 0.5 ethanol, the Ba / Ti feed ratio fixed at 1.5, the Ti concentration fixed at 0.04 mol / l, and the reaction temperature varied from 170 to 260 ° C. . As a result of XRD measurement of seven points synthesized at a reaction temperature of 170 to 260 ° C., BT was generated at a reaction temperature of 180 ° C. or higher, and formation of BT could not be confirmed at 175 ° C. or lower. (Fig. 4) Also, at the five points where BT was generated, the X-ray diffraction intensity increased as the temperature increased.

(C) Ba / Ti charge ratio dependency The solvent mixing ratio is 0.5 water: 0.5 ethanol, the reaction temperature is 240 ° C., the Ba concentration is fixed at 0.06 mol / l, and the Ba / Ti charge ratio is changed from 0.75 to 15. The experiment was conducted. As a result of XRD measurement of four points synthesized by changing the Ba / Ti charge ratio from 0.75 to 15, formation of BT was confirmed at Ba / Ti = 1.5 to 15. (FIG. 5) It can be seen that the main peak of Ba / Ti = 3 is the highest, and the main peak of BaCO _{3 as} an impurity is about one _third of that of Ba / Ti = 15. When Ba / Ti = 0.75, BT was not generated and almost amorphous.

(D) Summary of BT generation reaction Fig. 6 is a three-dimensional diagram showing the region where BT is generated, with the three axes as water-ethanol ratio, Ba / Ti ratio, and reaction temperature. BT generation means that BT nucleation and growth actually occurred. This suggests that BT nucleation did not occur in areas where BT did not form.

(3) Conditions where only heteronuclear growth occurs without ST nucleation using TPA (a) Dependence on water-ethanol solvent mixture ratio
In ST, the same experiment as BT was conducted. The reaction temperature is 240 ° C, the Sr / Ti feed ratio is fixed at 1.5, and Sr (OH) ₂ 1.825 g (0.015 mol) and TPA 4.820 ml (0.010 mol)
The water-ethanol solvent mixing ratio was varied from 0 to 1.0. In ST, synthesis of three points of Et0, Et0.5, and Et1.0 was performed. The XRD measurement results are shown in FIG. From this result, unlike BT, synthesis of ST was confirmed not only at Et0.5 but also at Et0 and Et1.0. It was also found that the X-ray diffraction intensity was much stronger overall than BT.

(A) The reaction temperature-dependent solvent mixing ratio was fixed at 0.5 water: 0.5 ethanol, the Sr / Ti feed ratio was fixed at 1.5, the Ti concentration was fixed at 0.04 mol / l, and the reaction temperature was changed at 180 to 260 ° C. FIG. 8 shows the XRD measurement results of the synthesis changed at 7 points of the reaction temperature of 180 to 260 ° C. From this result, it was found that ST was produced at a temperature of 190 ° C. or higher, and that only the impurity SrCO 3 was produced at a temperature of 185 ° C. or lower.

(C) Ba / Ti charge ratio dependency The solvent mixing ratio was fixed at 0.5 water: 0.5 ethanol, the reaction temperature was fixed at 240 ° C., the Sr concentration was fixed at 0.06 mol / l, and the Sr / Ti charge ratio was varied between 0.75 and 3. . FIG. 9 shows the XRD measurement results of four points synthesized by changing the Sr / Ti feed ratio from 0.75 to 3. From this measurement result, it was confirmed that ST was produced at Sr / Ti = 1.5 and 3, and titanium oxide (TiO ₂ (Anatase)) was produced at Sr / Ti = 0.75. Furthermore, when an experiment was conducted at Sr / Ti = 1.0 between the ST formation point and that of TiO ₂ , most of them were amorphous and a small amount of SrCO ₃ was formed.

(D) Summary of ST Generation Reaction FIG. 10 is a three-dimensional view showing the region where ST is generated, with each of the three axes being water-ethanol ratio, Sr / Ti ratio, and reaction temperature. ST generation means that ST nucleation and growth have actually occurred. Therefore, the region where ST was not generated suggests that ST nucleation did not occur.

(4) BT and ST formation mechanism In experiments in which the reaction temperature was changed, formation was confirmed at 180 ° C or higher for BT and 190 ° C or higher for ST. Considering the solubility of Ba (OH) ₂ and Sr (OH) ₂ , both are well dissolved in water and are considered to be dissolved before the temperature in the sealed container reaches 180 ° C. This is considered to be almost the same as the temperature at which Ti begins to dissolve. Also, it is clear from the experimental results that the temperature at which BT and ST begin to form is within 5 ° C, so the Ti concentration is between 175-180 ° C for BT and 185-190 ° C for ST. It is thought that it has increased rapidly.

This difference in the melting start temperature of Ti between BT and ST is considered to be related to the difference in solubility between Ba (OH) ₂ and Sr (OH) ₂ . The solubility of Ba (OH) ₂ is more than 5 times different at 80 ° C. compared to that of Sr (OH) ₂ . In the experiment for changing the reaction temperature, since the 0.5 water-0.5 ethanol mixed solution is used as the solvent, the solubility of both Ba (OH) ₂ and Sr (OH) ₂ decreases. As a result, the solubility becomes higher in temperature dependency than the condition using only water as a solvent, and accordingly, the difference in solubility between Ba (OH) ₂ and Sr (OH) ₂ appears as a difference in pH in the solvent. Therefore, it is considered that due to this difference in pH, dissolution of Ti which is usually difficult to dissolve is assisted, and the solution containing Ba (OH) ₂ having a high pH value has slightly produced BT on the low temperature side. The dissolution reaction of Ti is shown below.

Ti (i-PrO) ₂ (AcAc) ₂ + 4H ₂ O → Ti (OH) ₄ +
2i-PrOH + 2AcAc… (*)
As a reaction below this, the reaction when TiO ₂ is produced is
Ti (OH) ₄ → TiO ₂ + 2H ₂ O
Therefore, the reaction of BT generation is considered as follows.

Ti (OH) ₄ + Ba (OH) ₂ → BaTiO ₃
+ 3H ₂ O
TiO ₂ + Ba (OH) ₂ → BaTiO ₃ + H ₂ O
Except for changing the Ti charging ratio, Ba / Ti = 1.5 was used as the basis, and ST was synthesized in the same way with Sr / Ti = 1.5 in the synthesis of ST, but it was very large when comparing the diffraction intensities of BT and ST. You can see that there is a difference. When the solvent mixing ratio is also compared between Et0 and Et1.0, BT was not produced in the BT experiment, whereas ST was produced at both points in the synthesis of ST. As a result, the Ti preparation ratio suitable for the generation differs between BT and ST. From the experimental results, it is considered that Ba / Ti = 3 and Sr / Ti = 1.5 is generated efficiently in ST. Here, the BT and ST were considered as follows with respect to the fact that the raw material ratio was not 1 in the production of BT and ST.

nAcAc + Ba (OH) ₂ → Ba (OH) ₂ (AcAc) n
Assuming that such a reaction occurred together with the reaction shown in the formula (*), Ba ions attacked by AcAc (acetylacetone) become inactive and cannot be used for the BT formation reaction. In addition, in the reaction of ST formation, the same thing can be said for the formation of BT by 3-4 coordination of AcAc to one Sr ion.

  A method for producing BT / ST composite nanoparticles for the purpose of epitaxially growing an ST layer on commercially available BT spherical nanoparticles will be described below.

First, in the first stage (low temperature), the Sr / Ti feed ratio was 1.1, Sr (OH) ₂ 1.338 g (0.011 mol) and TPA 4.820 ml (0.010 mol) were mixed with 0.5 water-0.5 ethanol mixed solution (250 ml ) In a solution stirred for about 5 minutes, a commercial BT spherical nanoparticle BT-01 (Sakai Chemical Industry Co., Ltd., 100 nm) 2.33 g (0.010 mol: the same as the theoretical amount of ST) and 500 ml sealed Transferred into the container. It was put in an autoclave apparatus and kept heated at 190 ° C. for 18 hours in a sealed state. The heating rate was 120 ° C./h. The inside of the autoclave was constantly stirred at 300 rpm. Thereafter, the vessel was allowed to cool to room temperature, the reaction product was taken out, collected by filtration using a high-speed centrifuge, and the collected precipitate was dried for about 20 hours. The obtained sample was lightly pulverized with a mortar and observed with an X-ray diffraction measurement (XRD), or a scanning electron microscope (FE-SEM) and a transmission electron microscope (TEM).

  Next, as the second stage, without cooling from 190 ° C. in the same apparatus state, the heating temperature was raised to 240 ° C. at 120 ° C./h, held for 18 hours, and then cooled to room temperature by air cooling. .

  The XRD measurement results and SEM and TEM observation photographs of the composite particles synthesized at low temperature are shown in (FIGS. 11, 12, and 13). First, SEM observation shows that the layer covers BT-01. (FIG. 12) From the layer covering the periphery of BT-01, there were also particles in which cube-shaped particles of 30 to 40 nm were partially generated. These cube-shaped particles were confirmed to be ST from the XRD measurement results (FIG. 11). Furthermore, observation by TEM (FIG. 13) was performed. From the results of this TEM observation, the spherical particles of about 100 nm seen on the inside were confirmed to be BT-01 because the Ba element and the Ti element existed at the same coordinates, but the layered layer seen on the surface Since only the Sr element exists, it was confirmed that the substance is an amorphous substance containing Sr such as strontium oxide, that is, a precursor of ST.

  14 and 15 show the XRD measurement results and SEM observation photographs of the composite particles synthesized at high temperature. Since it was synthesized at high temperature, the XRD profile detected the same X-ray diffraction intensity as ST BT-01, and it was found that ST with high crystallinity was included. In addition, in the observation by the SEM photograph, some ST particles adhere to BT-01, but ST crystals cover the periphery of BT-01 at the same frequency to form a multilayer. As a result, it was confirmed that the composite particles had a BT-ST multilayer structure.

Claims (15)

A step of putting a core particle and a compound material having a chemical composition different from the core particle into a sealed container;
A step of laminating the compound by heteroepitaxial growth on the surface of the core particles by heating and holding;
A method for producing artificial superlattice particles, comprising:   2. The method for producing artificial superlattice particles according to claim 1, wherein the compound contains barium titanate or strontium titanate, and the titanium source is diisopropoxide diacetylacetonate.   3. The artificial material according to claim 1, wherein the compound contains strontium titanate, and a solvent of a solution for laminating the compound containing strontium titanate is a mixed solution of water and ethanol. A method for producing superlattice particles.   The artificial superlattice particle according to any one of claims 1 to 3, wherein the compound contains strontium titanate, and a temperature at which the compound containing the strontium titanate is stacked is 190 ° C or higher. Production method.   5. The Sr / Ti molar ratio of an Sr raw material and a Ti source for laminating the compound containing the strontium titanate, the compound containing strontium titanate, is 1.0 or more. A method for producing the artificial superlattice particles according to claim 1.   The compound contains barium titanate, the solvent of the solution for laminating the compound containing barium titanate is a mixed solution of water and ethanol, and the solvent ratio of water to ethanol in the mixed solution is 0.3 or more, 0.7 3. The method for producing artificial superlattice particles according to claim 1, wherein:   7. The artificial superlattice according to claim 1, wherein the compound contains barium titanate, and a temperature at which the compound containing the barium titanate is stacked is 180 ° C. or higher. Particle production method.   The said compound contains barium titanate, and a Ba / Ti molar ratio of a Ba raw material and a Ti source for stacking the compound containing said barium titanate is 1.5 or more, characterized in that: Or the manufacturing method of the artificial superlattice particle | grains in any one of 7. The core particles,
Layered by heteroepitaxial growth on the surface of the core particle, the compound layer having a different chemical composition from the core particle;
An artificial superlattice particle characterized by comprising:   10. The artificial superlattice particle according to claim 9, wherein the core particle and the compound are compounds having dielectric properties.   11. The artificial superlattice particle according to claim 9, wherein each of the core particle and the compound is a metal oxide.   The core particle and the compound are each at least one first metal selected from Ba, Sr, Ca, and Pb, and at least one second selected from Ti and Zr. 12. The artificial superlattice particle according to claim 9, wherein the artificial superlattice particle is a metal oxide containing any of the above metals.   13. The artificial superlattice particle according to claim 9, wherein one of the core particle and the compound contains barium titanate and the other contains strontium titanate.   14. The artificial superlattice particle according to claim 9, wherein the core particle is barium titanate.   15. A film capacitor comprising the artificial superlattice particles according to claim 9.