JP7724112B2 - Alkaline earth metal titanate particles and method for producing same - Google Patents

Description

The present invention relates to alkaline earth metal titanate particles having a perovskite structure.

Alkaline earth metal titanates are used in electronic components such as multilayer ceramic capacitors, thermoelectric elements, and piezoelectric elements. For example, it is known that thin films formed from coating solutions containing alkaline earth metal titanate precursors are used in thermoelectric elements (see, for example, Patent Document 1). Thin films obtained by coating precursors generally have a dense crystalline structure, which is thought to result in little energy loss when electrons flow.

Furthermore, in order to miniaturize electronic components, dense and thin films are required. By reducing the particle size, dense and thin films can be formed. A known method for producing small particles is to add titanium alkoxide to a mixed solution of alkaline earth metal hydroxide and alkyl cellosolve, and then hydrolyze the titanium alkoxide (see, for example, Patent Document 2). Particles obtained by this method have a particle size of 50 nm or less and are highly dispersible in solvents. Therefore, they can be used in small electronic components. Such small particles easily enter the gaps between other compounds in thin films. This makes it possible to make films thin and dense.

JP 2011-037661 A JP 2012-240904 A

The alkaline earth metal titanate precursor described in Patent Document 1 is suitable for forming a single-phase thin film consisting only of alkaline earth metal titanate. However, when forming a thin film using a coating liquid that mixes this precursor with solid components other than the precursor, there is a possibility that crystals other than the perovskite structure will also be formed during firing. When multiple types of crystals are formed, localized non-uniform thermal shrinkage is likely to occur, making the thin film more susceptible to cracking.

The particles described in Patent Document 2 have a small particle size of 50 nm or less, enabling the miniaturization of electronic components. However, it is believed that the presence of fine compounds is due to suboptimal alkaline earth metal concentrations when adding titanium alkoxide and suboptimal amounts of water added during hydrolysis. When such fine compounds are fired at high temperatures of 500°C or higher, they grow and form crystals other than perovskite structures that can be detected by X-ray structural analysis. If crystals other than perovskite structures are formed when a coating film is fired, localized non-uniform thermal shrinkage is likely to occur, making the thin film prone to cracking. In particular, if particles are present in the gaps between other compounds that make up the thin film, the film is likely to crack due to its dense structure.

The object of the present invention is to provide alkaline earth metal titanate particles that are less likely to produce crystals other than perovskite structures during firing and have small crystallite sizes.

To solve the above problem, the crystallite diameter D of the alkaline earth metal titanate particles with a perovskite structure is set to 5 to 30 nm, and after the particles are fired at 500°C for 3 hours, the particles do not contain any crystals other than the perovskite structure. Placing particles with a crystallite diameter D of 30 nm or less in the gaps between other compounds that make up the thin film allows for the formation of a dense, thin film. However, if crystals other than the perovskite structure are formed after firing, localized stress is generated, making the dense film prone to cracking. Even if the crystallite diameter D is 30 nm or less, the absence of crystals other than the perovskite structure after firing makes the film less susceptible to cracking.

Here, the atomic ratio (E/Ti) of alkaline earth metal (E) to titanium (Ti) was set to 0.95 to 1.02. The lattice constant ratio (c/a) was set to 0.95 to 1.05.

Furthermore, the ratio (D50/D) of the median diameter (D50) to the crystallite diameter D is preferably 1.3 or less. If this value is large, there will be more crystallites in the particles, and the crystallites will be more likely to sinter during firing. This makes the particles more susceptible to thermal shrinkage, and cracks are more likely to occur in the thin film.

Furthermore, the crystallite diameter increase rate "(D ₁ -D)/D" calculated from the crystallite diameter D ₁ and the crystallite diameter D after the particles are fired at 500°C is preferably 0.32 or less. The smaller this value, the less likely the crystallite diameter is to change during firing, and the less likely cracks are to occur when forming a dense thin film. When the alkaline earth metal is strontium, the crystallite diameter D is preferably 15 to 25 nm and the crystallite diameter increase rate is preferably 0.05 or less. When the alkaline earth metal is barium, the crystallite diameter D is preferably less than 11 nm and the median diameter (D50) is preferably 14 nm or less.

Alkaline earth metal particles can also be produced by performing the following steps in order: Prepare a mixed solution of alkaline earth metal hydroxide and alkyl cellosolve (step 1). Separate undissolved compounds from the mixed solution (step 2). Add titanium alkoxide to the mixed solution when the alkaline earth metal concentration in the mixed solution is 10% by weight or higher (step 3). Add a solvent containing water to the mixed solution (step 4). Heat the mixed solution to 70°C or higher (step 5). Note that the molar ratio of water added in step 4 to titanium alkoxide in the mixed solution (molar amount of water/molar amount of titanium alkoxide) is set to a range of 6 to 15.

The alkaline earth metal titanate particles with a perovskite structure according to the present invention have a crystallite diameter of 5 to 30 nm, and even after calcining the particles at 500°C for 3 hours, the particles contain no crystals other than the perovskite structure. If the particles contain fine compounds (such as alkaline earth metal carbonates, alkaline earth metal hydroxides, barium oxide, or titanium oxide) before calcination, the fine compounds will grow into crystals other than the perovskite structure upon calcination. While it is difficult to detect the fine compounds contained in the particles before calcination using measurements such as X-ray structural analysis, it is possible to detect crystals other than the perovskite structure after calcination using X-ray structural analysis. In other words, by analyzing the crystal structure of the particles after calcination using an X-ray structural analysis device, it is possible to estimate whether the fine compounds were present before calcination. Furthermore, particles that do not contain crystals other than the perovskite structure after calcination can be considered to have contained no impurities such as fine compounds before calcination. The presence of such impurities depends on the raw materials and manufacturing method of the alkaline earth metal titanate particles.

When a thin film is formed using particles that do not contain fine compounds, uneven thermal shrinkage is less likely to occur during firing. As a result, cracks are less likely to occur in the thin film. Furthermore, particles with a crystallite diameter of 30 nm or less can easily enter the gaps between other compounds that make up the thin film, allowing for the formation of a dense film (a dense film). However, if crystals other than the perovskite structure are formed after firing, localized stress is generated, making dense films more susceptible to cracking. Therefore, by using particles that do not contain fine compounds, a dense thin film that is less likely to crack can be formed, even with a crystallite diameter of 30 nm or less. Using such a thin film allows for the production of high-performance, compact electronic components. Note that if the crystallite diameter D is less than 5 nm, it is difficult to identify the crystal structure using an X-ray structure analyzer.

Here, the alkaline earth metal titanate particles preferably have an atomic ratio (E/Ti) of alkaline earth metal (E) to titanium (Ti) in the range of 0.95 to 1.02. The closer the atomic ratio (E/Ti) is to 1, the less likely it is that crystals other than perovskite structures will form. When the atomic ratio (E/Ti) is greater than 1.02, alkaline earth metal compounds other than perovskite structures are likely to be present in the particles. When the atomic ratio (E/Ti) is less than 0.95, titanium compounds other than perovskite structures are likely to be present in the particles. The atomic ratio (E/Ti) is more preferably 0.98 to 1.02, and even more preferably 0.985 to 1.015. If the particles are free of impurities, there is no risk of crystals other than perovskite structures forming, even if the atomic ratio (E/Ti) is 0.95 to 1.05 or 0.9 to 1.1.

The lattice constant ratio (c/a) of the perovskite structure is preferably 0.95 to 1.05. The closer this ratio (c/a) is to 1, the closer the particles are to cubic crystals. Cubic crystal particles have a small crystallite diameter and tend to be spherical. This makes them more likely to enter the gaps in the compounds that make up the thin film, making the film more dense. The ratio (c/a) is more preferably 0.99 to 1.01.

When dispersing particles in a solvent, the smaller the crystallite size, the smaller the particle size after dispersion. The smaller the particle size, the easier it is to miniaturize electronic components. On the other hand, the larger the particle size, the more crystallites there are in the particle, and the more likely the particle is to become polycrystalline. The particle size (median size) is preferably 40 nm or less. The median size (D50) is preferably 20 nm or less, 10 nm or less, or even 7 nm or less. If the median size (D50) is too small, the dispersion stability of the particles in the solvent decreases, so the median size (D50) is preferably 3 nm or more. Note that, because crystallites are the smallest particle units (i.e., primary particles), they are typically smaller than the particle size when dispersed in a solvent. However, because the median size (D50) is measured using light scattering, small particles may be detected as smaller than the actual particle size. Therefore, the median size (D50) may be detected as smaller than the crystallite size D.

The lower the ratio (D50/D) of the median diameter (D50) to the crystallite diameter D, the fewer crystallites there are in the particles dispersed in the solvent. Therefore, this ratio is preferably 1.3 or less. This ratio is more preferably 1.1 or less, 0.9 or less, or 0.8 or less. On the other hand, it is difficult to obtain particles with a ratio of less than 0.3.

The crystallite diameter increase rate "(D ₁ -D)/D" is calculated from the crystallite diameter D ₁ after the particles are fired at 500 ° C. and the crystallite diameter D. The lower this increase rate, the more difficult it is for the crystallites to sinter during firing. This increase rate is preferably 0.32 or less, more preferably 0.27 or less, and even more preferably 0.22 or less.

When the alkaline earth metal is strontium, the crystallite size tends to be large (15 to 25 nm), but the crystallite size increase rate and ratio (D50/D) tend to be low. This increase rate is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.005 or less. Furthermore, the ratio (D50/D) is more preferably 0.6 or less, and even more preferably 0.5 or less.

Furthermore, when the alkaline earth metal is barium, it is preferable that the crystallite diameter D is 11 nm or less and the median diameter (D50) is 14 nm or less. With such barium titanate particles, the crystallite diameter and particle diameter are small, and the difference between them is also small, making it difficult for fine compounds to form. It is more preferable that the crystallite diameter D is 10 nm or less and the median diameter (D50) is 10 nm or less, and even more preferable that the crystallite diameter D is 9 nm or less and the median diameter (D50) is 8 nm or less.

Alkaline earth metals include beryllium, magnesium, calcium, strontium, barium, and radium. Barium and strontium titanates have high dielectric constants and are therefore suitable for MLCCs. Particles may contain multiple types of alkaline earth metals.

The particles may contain at least one element selected from Group 3, lanthanides, actinides, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13, and Group 14.

Alkaline earth metal particles can also be produced by performing the following steps in order. A mixed solution of alkaline earth metal hydroxide and alkyl cellosolve is prepared (step 1). Next, undissolved compounds are separated from the mixed solution (step 2). Titanium alkoxide is added to the mixed solution when the alkaline earth metal concentration in the mixed solution is 10% by weight or higher (step 3). A water-containing solvent is added to the mixed solution (step 4). The molar ratio of the added water to the titanium alkoxide in the mixed solution (molar amount of water/molar amount of titanium alkoxide) is 6 to 15. The addition of water hydrolyzes the titanium alkoxide, which undergoes a condensation reaction with the hydroxide to form a hydrate gel. Next, the mixed solution is heated to 70°C or higher (step 5). This heats the hydrate gel to 70°C or higher, allowing it to mature, resulting in perovskite-structured particles.

Each process is explained in detail below.

<First step>
First, a mixed solution of an alkaline earth metal hydroxide (hereinafter simply referred to as hydroxide) and an alkyl cellosolve is prepared. Multiple types of alkaline earth metals may be used. By using hydroxide as the alkaline earth metal source for the particles, counterions do not diffuse to other layers when the coating film is baked. This improves performance during lamination. The interaction between the alkyl cellosolve and the hydroxide facilitates a smaller particle size. Furthermore, this interaction also dissolves the hydroxide. The fewer the carbon atoms in the hydrocarbon group of the alkyl cellosolve, the more easily the alkyl cellosolve and the hydroxide interact. The carbon number is preferably 4 or less, more preferably 2 or less. Methyl cellosolve is preferred as the alkyl cellosolve. Furthermore, irradiating the mixed solution with ultrasound facilitates dissolution of the hydroxide.

When hydroxide and alkyl cellosolve interact, water is generated. Water inhibits the interaction. Removing water from the mixed solution (i.e., dehydrating the mixed solution) promotes the interaction. Furthermore, dehydration at 40°C or higher makes it easier for hydroxide to interact with alkyl cellosolve. A temperature of 50°C or higher during dehydration is more preferable, and 60°C or higher is even more preferable. A higher temperature is better, but if it is too high, bumping occurs easily and sufficient safety cannot be ensured. If the temperature is 90°C or lower, bumping is less likely to occur.

The longer the dehydration time, the more water can be removed, promoting interaction. Therefore, a dehydration time of 10 minutes or more is preferable, and 30 minutes or more is even more preferable. On the other hand, if the dehydration time is too long, production efficiency will decrease. The shorter the dehydration time, such as 10 hours or less, 5 hours or less, or 3 hours or less, the better the efficiency. Furthermore, the longer the dehydration time, the less residual hydroxide will remain. The dehydration time can be adjusted taking the residual amount into consideration. For example, if dehydration is performed so that the residual amount is less than 40% of the raw material, the particle yield will be 60% or more. The smaller the residual amount, such as less than 30% or less than 2.5%, the higher the particle yield.

Methods for dehydrating the mixed solution include (reduced pressure) distillation and methods using adsorbents such as silica gel or zeolite. When (reduced pressure) distillation is performed for a longer time, the amount of hydroxide that dissolves increases. For example, distillation for 30 minutes or more reduces the amount of residual hydroxide.

The lower the water content of the mixed solution after dehydration, the easier it is for the hydroxide and alkyl cellosolve to interact. Furthermore, gel formation is less likely when titanium alkoxide is added. Therefore, the water content is preferably less than 1% by weight, more preferably 0.8% by weight or less, and even more preferably 0.55% by weight or less.

When the alkaline earth metal is strontium, leaving the mixed solution standing promotes dissolution of the hydroxide. The hydroxide dissolves easily when the standing temperature is below 30°C. In particular, a temperature range of 2 to 15°C is preferable in terms of solubility and cost, as the mixed solution can be cooled using a refrigerator, etc.

<Second process>
In this step, undissolved compounds are separated from the mixed solution. These undissolved compounds include undissolved hydroxides and alkaline earth metal salts (such as carbonates) produced by the reaction of alkaline earth metals with substances in the air (such as _CO2 ). If separation is not performed, these compounds will remain within the particles. These undissolved compounds will produce crystals other than perovskite structures upon firing. Separation methods include filtration and decantation. The mixed solution may be centrifuged before decantation. Even if gel is generated before this step, it will be separated in this step. Gel can cause impurities to form. The yield can be increased by promoting the dissolution of hydroxides in the first step and reducing the amount of undissolved compounds before performing this step.

<Third step>
Next, titanium alkoxide is added to the mixed solution. During the addition, the alkaline earth metal concentration in the mixed solution must be 10% by weight or higher. If the concentration is less than 10% by weight, it is difficult for the alkaline earth metal and titanium to react uniformly in the mixed solution, which can easily result in the formation of compounds other than perovskite structures (alkaline earth metal compounds and titanium compounds) after aging. If the concentration is too high, gel formation is likely. Therefore, the concentration is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less. When multiple types of alkaline earth metals are present in the mixed solution, this concentration refers to the total concentration of these alkaline earth metals. The alkaline earth metal concentration may be adjusted at any step before this step. That is, it may be adjusted at any time between steps 1 and 3, and may be before or after the separation step. Selecting (reduced pressure) distillation as the concentration method allows for simultaneous heating, dehydration, and concentration, resulting in fewer steps and higher production efficiency. If the (reduced pressure) distillation time is too long, the alkaline earth metal concentration in the mixed solution will become too high, so 5 hours or less is preferable. The (reduced pressure) distillation time can be adjusted taking into consideration the distillation temperature, the alkaline earth metal concentration, the amount of mixed solution, etc. When the alkaline earth metal is strontium and the concentration of the mixed solution is adjusted by heating, it is preferable to dissolve the hydroxide by leaving it to stand and then heat and concentrate it. If the mixed solution is heated and concentrated before dissolving the strontium hydroxide, the temperature of the mixed solution will increase, making it difficult for the strontium hydroxide to dissolve.

The closer the atomic ratio (E/Ti) of alkaline earth metal to titanium in the mixed solution is to 1, the less likely impurities are to be generated. Therefore, it is preferable to add titanium alkoxide so that the atomic ratio is in the range of 0.95 to 1.02. By using titanium alkoxide with a structure of Ti(OR) ₄ (where R is a hydrocarbon group having 1 to 4 carbon atoms and may be the same or different), impurities are less likely to be generated. Tetraisopropoxytitanium is easily available and is suitable for mass production.

<Fourth step>
Next, a water-containing solvent is added to the mixed solution to hydrolyze the titanium alkoxide. The hydrolyzed titanium alkoxide undergoes a condensation reaction with the hydroxide to form a hydrate gel. The molar ratio of the added water to the titanium alkoxide in the mixed solution is 6 to 15. Outside this range, fine compounds are produced. The closer the molar ratio is to 12, the lower the crystallite size increase rate. Therefore, if a lower crystallite size increase rate is desired, a molar ratio of 9 to 14 is preferred, with 10 to 13 being even more preferred. Furthermore, by adding a mixed solvent of alcohol and water as the water-containing solvent, the hydrolysis rate and thus the particle size can be adjusted. To reduce the particle size, the weight ratio of alcohol to water (alcohol/water) is preferably in the range of 0.5 to 4.0, more preferably 1.5 to 3.5. In particular, when the molar ratio of the added water to the titanium alkoxide in the mixed solution is close to 8, i.e., when the molar ratio is 7 to 9 and the weight ratio of alcohol to water is in the range of 1.5 to 3.5, the particle size tends to be small. On the other hand, the lower the ratio of alcohol in the mixed solvent, the lower the crystallite size increase rate. Therefore, when it is desired to reduce the crystallite size increase rate, the weight ratio of alcohol to water (alcohol/water) is preferably 4.0 or less, more preferably 1.5 or less, and even more preferably 0.5 or less. It is more preferable to add only water without using a mixed solvent. As alcohol, ethanol and methanol are easily mixed with water, so they are easy to handle. Methanol is particularly easy to handle.

<Fifth process>
Next, the mixed solution is heated to 70°C or higher. This causes the hydrated gel to reach a temperature of 70°C or higher (i.e., it is aged), resulting in the production of particles with a perovskite structure. This method allows the production of particles free of fine compounds without calcination. Furthermore, aging allows the particles to crystallize while still dispersed in the solvent, eliminating the need to remove the particles from the solvent as in calcination. Therefore, there is no need to redisperse the particles in the solvent when liquefying the particles for coating, reducing the number of manufacturing steps. Furthermore, aging tends to result in a uniform particle size. If the aging temperature is too high, production efficiency decreases. For example, aging at 120°C or below is efficient. A relatively long aging time tends to result in a uniform particle size, so a time of 2 hours or more is preferable, and 5 hours or more is more preferable. On the other hand, if the aging time is too long, production efficiency decreases. For example, a time of 200 hours or less or 100 hours or less is efficient.

When adding a metal salt containing at least one element selected from Group 3, lanthanides, actinides, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13, and Group 14, it is preferable to add the metal salt before the fourth step. This timing makes it less likely that impurities will be generated.

Below, we will specifically explain alkaline earth metal titanate particles with a perovskite structure and a crystallite diameter D of 5 to 30 nm.

[Example 1]
<First step>
First, a mixed solution of alkaline earth metal hydroxide and alkyl cellosolve was prepared. Specifically, 100 g of barium hydroxide octahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 630 g of 2-methoxyethanol (methyl cellosolve) were placed in a 1 L beaker and mixed. After mixing, a portion of the barium hydroxide was dissolved over 30 minutes at 40 °C while irradiating with ultrasound. This mixed solution was placed in a 2 L eggplant-shaped flask and subjected to reduced pressure distillation using an evaporator. In other words, dehydration and concentration were performed simultaneously. The distillation was performed for 1 hour at 70 °C and 15 hPa.

<Second process>
Next, the mixed solution after distillation was centrifuged to precipitate undissolved compounds. Thereafter, the supernatant (mixed solution) was decanted to separate the sediment (undissolved compounds). The sediment was white. The centrifugation conditions were 3000 rpm and 15 minutes. The alkaline earth metal concentration (barium concentration) of the supernatant (mixed solution immediately before adding titanium alkoxide) measured by ICP-OES was 16.35 wt %, and the water content was 0.5 wt %.

<Third step>
Titanium alkoxide was added to this supernatant so that the atomic ratio (E/Ti) was 1.00. That is, in a glove box under a nitrogen gas atmosphere, 50.5 g of tetraisopropoxytitanium (Orgatix (registered trademark) TA-10, manufactured by Matsumoto Fine Chemical Co., Ltd.; Ti concentration 16.85 wt%) was added to 150 g of the supernatant to prepare a mixture.

<Fourth step>
While stirring the mixture at 25°C, a mixed solvent of 125 g of methanol and 25 g of water (weight ratio of methanol to water: 5.0, molar ratio of water to titanium alkoxide: 8.0) was added over 1 minute, and the mixture was then stirred at 25°C for 2 hours.

<Fifth process>
The resulting hydrate gel was heated to 80°C and aged for 48 hours to obtain a particle dispersion. 20 g of this dispersion was dried at 130°C for 1 hour to obtain a particle powder. The powder had a white appearance. 5 g of this particle powder was placed in a crucible and heated to 500°C over 2.5 hours, and then fired at 500°C for 3 hours. After cooling to 400°C, the powder was placed in a desiccator and cooled to room temperature to obtain a 500°C-fired product.

The particle preparation conditions are shown in Table 1. The physical properties of the obtained particles (powders) were measured by the following methods. The measurement results are shown in Table 2. The column for 130°C dried product in Table 2 lists the measured values of the powder after drying in the fifth step. The column for 500°C fired product lists the measured values of the powder after firing at 500°C in the fifth step. The crystallite size increase rate was calculated by taking the crystallite size of the 130°C dried product as D and the crystallite size of the 500°C fired product as _D1 .

(1) Particle size After filling a measurement cell with 1 g of 2-methoxyethanol, two drops of particle dispersion were added using a dropper (5 ml poly dropper manufactured by AS ONE Corporation) while maintaining the temperature at approximately 23 to 26°C. After that, the dropper was used to suck up the liquid in the cell to make it uniform inside the cell, and then the liquid was returned to the cell. This operation was repeated twice to prepare a sample for measurement. The particle size distribution was measured by dynamic light scattering using a particle size distribution analyzer (Nanotrac UPA-UT151 manufactured by Nikkiso Co., Ltd.). The particle size (median diameter (D50)) was determined from the particle size distribution.

(2) Crystal structure The target powder was pulverized and used as a measurement sample. The crystal structure was measured using an X-ray diffraction measurement device, MiniFlex (registered trademark) 600 manufactured by Rigaku Corporation. The crystal structure can be identified using analysis software PDXL2. The crystallite diameter was measured by measuring the half-width β of the perovskite structure around 2θ = 31.5 ° (if the crystal structure is cubic, the half-width of the Miller index (110); if the crystal structure is tetragonal, the half-width of the Miller index (101)). The half-width β (rad) was calculated using Scherrer's formula "D = Kλ / β cos θ". Here, D is the crystallite diameter (Å), K is the Scherrer constant, λ is the X-ray wavelength (1.7889 Å), and θ is the reflection angle. The presence or absence of impurities was determined by performing a peak search (hybrid search match) using the analysis software PDXL2 (version 2.0.3.0) and determining whether or not peaks other than those of the perovskite structure were detected. In the powder of the particles of this example and the product fired at 500°C, no peaks other than those of the perovskite structure were detected. Therefore, it was determined that the particles did not contain impurities such as fine compounds.

[Example 2]
A particle powder was prepared in the same manner as in Example 1, except that in the third step, the amount of titanium alkoxide added was 49.8 g (added so that the atomic ratio (E/Ti) was 1.015), and in the fourth step, the weight of methanol in the mixed solvent was 50 g so that the weight ratio of alcohol to water was 2.0.

[Example 3]
A particle powder was prepared in the same manner as in Example 1, except that in the first step, the mixed solution was distilled so that the barium concentration of the mixed solution before adding titanium alkoxide was 10.09% by weight, and in the fourth step, the weight of water in the mixed solvent was 37 g and the weight of methanol was 37 g (so that the weight ratio of alcohol to water was 1.0).

[Example 4]
In the fourth step, a powder of particles was prepared in the same manner as in Example 1, except that the weight of methanol in the mixed solvent was 75 g so that the weight ratio of alcohol to water was 3.0.

[Example 5]
In the fourth step, a powder of particles was prepared in the same manner as in Example 1, except that the weight of methanol in the mixed solvent was 50 g so that the weight ratio of alcohol to water was 2.0.

[Example 6]
In the fourth step, a powder of particles was prepared in the same manner as in Example 1, except that the weight of methanol in the mixed solvent was 0.0 g so that the weight ratio of alcohol to water was 0.0.

[Example 7]
In the fourth step, a particle powder was prepared in the same manner as in Example 1, except that the weight of water in the mixed solvent was 37 g and the weight of methanol was 37 g (so that the molar ratio of water to titanium alkoxide was 12.0 and the weight ratio of alcohol to water was 1.0).

[Example 8]
In this example, strontium was used as the alkaline earth metal. 218 g of strontium hydroxide octahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 1,610 g of methyl cellosolve were placed in a beaker, stirred for 1 hour, and then allowed to stand at 23 to 25°C for 6 hours. The mixture was then allowed to stand in a refrigerator at 5 to 10°C for 15 hours.

Next, the distilled mixed solution was centrifuged to settle any undissolved compounds. The supernatant (mixed solution) was then decanted to separate the sediment (undissolved compounds). The centrifugation conditions were 3000 rpm and 15 minutes. The supernatant was concentrated using an evaporator, and the alkaline earth metal concentration (strontium concentration) of the mixed solution (supernatant) was 10.60 wt%. The water content was 1.85 wt%. Concentration was carried out for 1 hour at 60°C and 40 hPa.

In the third step, titanium alkoxide was added to the mixed solution after concentration in this example so that the atomic ratio (E/Ti) was 1.00. In the fourth step, water and methanol were added so that the weight ratio of water to methanol was 3.0 and the molar ratio of water to titanium alkoxide was 8. Other than this, a particle powder was prepared in the same manner as in Example 1.

[Comparative Example 1]
The second step was omitted, and titanium alkoxide was added to the mixed solution obtained in the first step. Furthermore, in the fourth step, the weight of water in the mixed solvent was changed to 37 g, and the weight of methanol was changed to 37 g (so that the molar ratio of water to titanium alkoxide was 12.0, and the weight ratio of alcohol to water was 1.0). A particle powder was prepared in the same manner as in Example 7, except for this.

[Comparative Example 2]
In the first step, the mixed solution was distilled so that the barium concentration of the mixed solution was 5.14 wt%. In the fourth step, the weight of water in the mixed solvent was 37 g and the weight of methanol was 37 g (so that the molar ratio of water to titanium alkoxide was 12.0 and the weight ratio of alcohol to water was 1.0). Except for this, a particle powder was prepared in the same manner as in Example 1.

[Comparative Example 3]
A particle powder was prepared in the same manner as in Example 1, except that in the third step, the amount of titanium alkoxide added was 49.1 g (added so that the atomic ratio (E/Ti) was 1.03), and in the fourth step, the weight of methanol in the mixed solvent was 50 g so that the weight ratio of alcohol to water was 2.0.

[Comparative Example 4]
In the fourth step, a particle powder was prepared in the same manner as in Example 1, except that the weight of water in the mixed solvent was 12 g so that the molar ratio of water to titanium alkoxide was 4.0, and the weight of methanol in the mixed solvent was 62 g.

[Comparative Example 5]
In the fourth step, a particle powder was prepared in the same manner as in Example 1, except that the weight of water in the mixed solvent was 50 g so that the molar ratio of water to titanium alkoxide was 16.0, and the weight of methanol in the mixed solvent was 25 g.

[Comparative Example 6]
In the fifth step, a powder of particles was prepared in the same manner as in Example 1, except that aging was carried out at 60°C.

Claims (7)

Alkaline earth metal titanate particles having a perovskite structure,
The atomic ratio (E/Ti) of alkaline earth metal (E) to titanium (Ti) is 0.95 to 1.02
and
The crystallite diameter D is 5 to 30 nm,
the ratio of the lattice constant c to the lattice constant a (c/a) obtained by analyzing the crystal structure of the alkaline earth metal titanate particles measured using an X-ray diffraction measurement device is 0.95 to 1.05;
The particles are characterized in that, after being fired at 500°C for 3 hours, they do not contain crystals other than the perovskite structure. 2. The particles according to claim 1, wherein the ratio (D50/D) of the median diameter (D50) to the crystallite diameter D is 1.3 or less. The particles according to claim 1, characterized in that the crystallite diameter increase rate "(D1-D)/D" calculated from the crystallite diameter D1 after firing the particles at 500 ° C. for 3 hours and the crystallite diameter D is 0.32 or less. the alkaline earth metal is strontium;
The crystallite diameter D is 15 to 25 nm,
4. The particle according to claim 3, wherein the crystallite size increase rate is 0.05 or less. the alkaline earth metal is barium;
The crystallite diameter D is less than 11 nm,
2. The particles according to claim 1, characterized in that the median diameter (D50) is 14 nm or less. A first step of preparing a mixed solution of an alkaline earth metal hydroxide and an alkyl cellosolve;
a second step of separating undissolved compounds from the mixed solution;
a third step of adding titanium alkoxide to the mixed solution in a state where the alkaline earth metal concentration in the mixed solution is 10% by weight or more;
a fourth step of adding a solvent containing water to the mixed solution; and a fifth step of heating the mixed solution to a temperature of 70°C or higher,
A method for producing barium titanate particles, characterized in that the molar ratio of water added in the fourth step to titanium alkoxide in the mixed solution (molar amount of water/molar amount of titanium alkoxide) is 6 to 15. 7. The method according to claim 6, wherein in the fourth step, the solvent is a mixed solvent of alcohol and water, and the weight ratio of alcohol to water in the mixed solvent is 4.0 or less.