JP5149929B2 - Tetragonal barium titanate particles, method for producing the same, and ceramic capacitor - Google Patents

Description

  The present invention relates to barium titanate particles used for multilayer ceramic capacitors and the like, a method for producing the same, and a ceramic capacitor.

  In recent years, the progress of miniaturization and high performance of mobile phones, personal computers and peripheral devices has been remarkable. Development of electronic components used therein, for example, multilayer ceramic capacitors, is being promoted from the viewpoint of miniaturization and large capacity, and the dielectric layers in the capacitors are being made thinner and higher in thickness. As a raw material for this dielectric layer, particles of barium titanate, which is a high dielectric material, are mainly used.

  On the other hand, as a method for producing particles of barium titanate, a solid phase method, an oxalate method, a sol-gel method, and a hydrothermal synthesis method are known. The solid phase method is a method in which barium titanate is produced by solid phase synthesis of a mixed powder of titanium oxide and barium carbonate at a high temperature (see, for example, Non-Patent Document 1).

In the oxalate method, an aqueous solution of barium chloride and an aqueous solution of titanium tetrachloride are mixed, and this mixture is dropped into an aqueous oxalic acid solution and stirred to produce barium titanyl oxalate. After removing chlorine by washing, barium titanyl oxalate is dehydrated. It is a method of drying and calcining it to produce barium titanate (see, for example, Non-Patent Document 2).

  The sol-gel method is a method in which a composite alkoxide is generated from a mixed liquid of titanium alkoxide and barium hydroxide, and then the composite alkoxide is calcined to generate barium titanate.

  The hydrothermal synthesis method is a method of generating barium titanate by hydrothermally treating titanium chloride and barium chloride in an alkaline solution (see, for example, Patent Documents 1 and 2 and Non-Patent Document 3).

Occupational Chemistry Magazine Volume 70 Issue 6 (1967) Journal of the Ceramic Industry Association 92 (1) 1984 Occupational Chemistry Magazine Vol. 59, No. 8 (1956)

JP 61-031345 JP Japanese Patent Laid-Open No. 2002-211926

The barium titanate particles are mixed with a binder, a solvent, and an additive to form a slurry. After being formed into a green sheet by a sheet forming machine, the dielectric layer is formed, and the dielectric layer is laminated to form a multilayer ceramic capacitor. In accordance with the demand for thinner and higher-layer dielectric layers in capacitors, it can be filled uniformly in both the barium titanate particles and in the thinned green sheets. There is a demand for low variation in mechanical characteristics. However, with the barium titanate particles according to the prior art, when the green sheet is thinned, it is difficult to uniformly fill, the electrical characteristics vary greatly, and the reliability is low.

  Therefore, the problem to be solved by the invention is, for example, sufficient reliability even if the green sheet filled with barium titanate particles is made thin, as the dielectric layer in the capacitor is thinned and highly laminated. An object of the present invention is to provide barium titanate particles capable of maintaining electrical characteristics, a method for producing the same, and a ceramic capacitor using the barium titanate particles.

  As a result of studies conducted by the present inventors in order to solve the above-mentioned problems, the average particle size, particle size distribution, uniformity, roundness, crystal axis ratio c / a measured with an electron microscope of barium titanate particles It has been thought that it is important to satisfy the predetermined conditions. Furthermore, the present inventors have come up with an easy and inexpensive production method of barium titanate particles satisfying the various conditions.

That is, the first means for solving the above-described problem is:
When the average particle size measured from an electron microscope image was D _TEM, D _TEM is 0.3μm or less, the particle size distribution is 0.5 or less, uniformity is 0.90 or more, 0.80 or more roundness, crystal axis ratio c / a is D ₅₀ / D _TEM when 1.050 or more, and the molar ratio Ba / Ti between barium and titanium is 0.99 or more and 1.01 or less, and the value of 50% of the cumulative diameter in the particle size distribution measured by the dynamic light scattering method is D ₅₀ Is a tetragonal barium titanate particle, characterized in that it is 3.0 or less.

The second means is
A method for producing barium titanate particles by a hydrothermal synthesis method,
Titanium salt and barium hydroxide aqueous solution are mixed so that the molar ratio Ba / Ti of barium and titanium is 1.5 to 10.0,
This is a method for producing tetragonal barium titanate particles, wherein the mixed solution is hydrothermally treated in a temperature range of 150 ° C. or more and 250 ° C. or less for 24 hours or more.

The third means is
A ceramic comprising the tetragonal barium titanate particles described in the first means or the tetragonal barium titanate particles produced by the method for producing tetragonal barium titanate particles described in the second means. It is a capacitor.

The tetragonal barium titanate particles according to the first means have an average particle diameter _DTEM measured from an electron microscope image of 0.3 μm or less, a particle size distribution of 0.5 or less, a uniformity of 0.90 or more, a roundness of 0.80 or more, The crystal axis ratio c / a is 1.005 or more, the molar ratio Ba / Ti of barium and titanium is 0.99 or more, 1.01 or less,
When the average particle diameter obtained from the particle size distribution measured by the dynamic light scattering method is D ₅₀ , D ₅₀ / D _TEM is 3.0 or less, so even if the green sheet is thinned, sufficient reliability, It was possible to keep the target characteristics.

According to the method for producing tetragonal barium titanate particles according to the second means, the average particle diameter _DTEM measured from an electron microscope image is 0.3 μm or less, the particle diameter distribution is 0.5 or less, the uniformity is 0.90 or more,
Roundness is 0.80 or more, crystal axis ratio c / a is 1.005 or more, molar ratio of barium to titanium Ba / Ti is 0.99
Above, 1.01 or less, and easy and inexpensive production of tetragonal barium titanate particles having a D ₅₀ / D _TEM of 3.0 or less when the average particle size obtained from the particle size distribution measured by the dynamic light scattering method is D ₅₀ It was possible to manufacture at a cost.

  The ceramic capacitor according to the third means can reduce the thickness of the green sheet, which is a dielectric layer, to avoid destabilization of electrical characteristics, new equipment investment, increase in production cost, etc. it can.

4 is a transmission electron micrograph (20,000 magnifications) of barium titanate fine particles according to Example 3. 6 is a transmission electron micrograph (20,000 magnifications) of barium titanate fine particles according to Example 6. FIG. 2 is a transmission electron micrograph (magnification 20,000 times) of barium titanate fine particles according to Comparative Example 1. 4 is an X-ray diffraction pattern of barium titanate fine particles according to Example 3. FIG. 2 is an X-ray diffraction pattern of barium titanate fine particles according to Comparative Example 1. FIG. It is a table | surface of the fine particle characteristic measurement result of Examples 1-7 and Comparative Examples 1-6.

In order to produce tetragonal barium titanate particles having desired particle characteristics, the present inventors have intensively studied a production method based on a hydrothermal synthesis method. As a result, a titanium salt and a barium hydroxide aqueous solution are selected as production raw materials, and mixed so that the molar ratio Ba / Ti of barium and titanium is 1.5 to 10.0 in the charged amount of the titanium salt and barium hydroxide, By subjecting the mixed solution to hydrothermal treatment at a temperature range of 150 ° C. or higher and 250 ° C. or lower for 24 hours or longer, the average particle size D _TEM measured from an electron microscope image is 0.3 μm or less, the particle size distribution is 0.5 or less, and homogeneous. 0.90 or more, roundness is 0.80 or more, crystal axis ratio c / a is 1.005 or more, molar ratio of barium and titanium Ba / Ti is 0.99 or more, 1.01 or less, by dynamic light scattering method using microtrack Tetragonal barium titanate particles having a D ₅₀ / D _TEM of 3.0 or less when the average particle size obtained from the measured particle size distribution is D ₅₀ can be produced.

Hereinafter, first, an embodiment of the present invention will be described while describing a method for producing barium titanate particles according to the present invention.
First, after adding a titanium tetrachloride aqueous solution as a titanium salt to pure water with stirring, an alkali solution is added to hydrolyze the titanium tetrachloride, followed by washing and filtration to obtain a titanium hydroxide gel. To this titanium hydroxide gel, an aqueous barium hydroxide solution is added under a nitrogen atmosphere so that the molar ratio of Ba / Ti is 1.5 to 10.0, and water is added to obtain a slurry. The slurry is stirred and aged at 40 to 100 ° C. for 0.5 to 5 hours, then charged into an autoclave and subjected to hydrothermal synthesis at 150 to 250 ° C. for 24 hours or longer, preferably 48 to 100 hours. After the reaction, after cooling to room temperature, the product is washed and filtered under a nitrogen atmosphere and dried at 105 to 150 ° C. for 12 hours to obtain barium titanate particles.

Here, the barium titanate according to the present invention can be obtained by using titanium tetrachloride and an aqueous barium hydroxide solution instead of the titanium hydroxide gel and the aqueous barium hydroxide solution as raw materials. In this case, an alkaline solution such as sodium hydroxide or ammonia water is added to the barium hydroxide aqueous solution under a nitrogen atmosphere, and the titanium tetrachloride aqueous solution is added so that the molar ratio Ba / Ti of barium and titanium is 1.5 to 10.0. And water to obtain a slurry. The slurry is stirred and aged at 40 to 100 ° C. for 0.5 to 5 hours, then charged into an autoclave and subjected to hydrothermal synthesis at 150 to 250 ° C. for 24 hours or more, preferably 48 to 100 hours. After the reaction, after cooling to room temperature, the product was washed and filtered under a nitrogen atmosphere and dried at 105 to 150 ° C. for 12 hours to obtain barium titanate particles.
Furthermore, in any of the above cases, titanium tetrachloride can be substituted for titanium sulfate as the titanium salt.

Next, an example of a method for evaluating the particle characteristics of the barium titanate particles will be described.
The average particle size, particle size distribution, uniformity, roundness, and particle shape were determined from an electron microscope image such as an electron micrograph (for example, a 20,000-fold transmission electron micrograph). First, 300 non-overlapping particles were selected from an electron micrograph of barium titanate particles, the major axis and minor axis of the particles were measured, and the average value of the major axis was determined as the average particle diameter _DTEM . The particle size distribution is obtained by dividing the standard deviation of the particle size distribution of the particles by the average particle size _DTEM , and is an index of the sharpness of the particle size distribution. The particle shape was judged from an electron microscope image such as the electron micrograph. The uniformity was determined as an average value of the ratio of the measured major axis to minor axis. The circularity is the based on the mean particle diameter D _TEM, in which the particle shape specific surface area assuming that a sphere, divided by the specific surface area measured by the BET method. Next, the particle size distribution of the barium titanate particles was measured by a dynamic light scattering method using a microtrack. In the measurement, as a pretreatment, the barium titanate particles are sufficiently dispersed in an appropriate dispersion medium, the particle size distribution is measured with a microtrack, and a value that gives a cumulative diameter of 50% is determined from the particle size distribution. the value was defined as _{D 50.} Then, to determine the value of _D 50 _{/ D TEM} by dividing the _{D 50} in the _{D TEM.} The value of D ₅₀ / D _TEM is an index of particle dispersibility.

The crystal structure and crystal system of the barium titanate particles were judged from the diffraction pattern measured by X-ray diffraction. The crystal axis ratio c / a was calculated from the ratio of the lattice constants of the a axis and the c axis by obtaining the lattice constant from the X-ray diffraction pattern.

Next, the evaluation results of the particle characteristics of the barium titanate particles will be described.
First, the average particle diameter of the barium titanate particles is 0.3 μm or less, more preferably 0.2 μm or less, and most preferably 0.1 μm or less. Even when the thickness of the dielectric layer is within several μm, the dielectric layer The packing density is increased and the reliability is improved. If it exceeds 0.3 μm, the packing density of the dielectric layer is low, and the reliability may be lowered. If the particle size distribution is 0.5 or less, more preferably 0.3 or less, the characteristic variation among the barium titanate particles can be suppressed, so that the variation in electric capacity of the dielectric layer can be reduced. When the uniformity is 0.90 or more and the roundness is 0.80 or more, voids between particles when the barium titanate particles or the like are made into a green sheet can be reduced, so that the packing density is increased and the reliability is improved. If the uniformity is less than 0.90 and the roundness is less than 0.80, the gap between the particles becomes large when the green sheet is formed, and the packing density may be low and the reliability may be lowered. The value of D ₅₀ / D _TEM of the barium titanate particles indicates the dispersibility of the particles, and when the value of D ₅₀ / D _TEM is 3.0 or less, preferably 2.5 or less, It can be easily dispersed, and the packing density when it is made into a green sheet increases and the reliability is improved. If the value of D ₅₀ / D _TEM exceeds 3.0, it is difficult to disperse in a solvent, the packing density when it is made into a green sheet is low, and there is a risk that the reliability may be lowered, such as defects caused by the formation of aggregated particles. is there.
In addition, since the particle shape of the barium titanate particles according to the present invention is almost spherical and has not undergone a heat treatment step, there is no interparticle sintering and the viscosity during dispersion does not increase. Since it can be increased, a high-density capacitor can be manufactured in combination with the filling property of the barium titanate particles themselves.

When the crystal axis ratio c / a of the barium titanate particle crystal is 1.005 or more, preferably 1.008 or more, more preferably 1.09 or more, since the tetragonal ratio of the barium titanate particle crystal exhibiting ferroelectric characteristics is high, the dielectric constant is high. Characteristics can be shown. When the crystal axis ratio c / a is less than 1.005, the proportion of pseudo cubic crystals increases and the dielectric properties decrease. When the molar ratio Ba / Ti between barium and titanium is between 0.99 and 1.01, there are few impurities such as hydroxide ions and lattice defects, resulting in ferroelectric properties.
The percentage of tetragonal crystals shown is high. If Ba / Ti of the barium titanate particle crystal is less than 0.99, there are many impurities such as hydroxide ions and lattice defects, and the ratio of pseudo cubic crystals may be increased, leading to a decrease in dielectric properties. On the other hand, when Ba / Ti exceeds 1.01, impurities such as Ba carbonate and Ba-rich compound may be present and the dielectric characteristics may be deteriorated.

By the production method according to the present invention described above, the average particle size is 0.3 μm or less, the particle size distribution is 0.5 or less, the uniformity is 0.90 or more, the roundness is 0.80 or more, and the D ₅₀ / D _TEM value is 3.0. Below, it is unclear why spherical tetragonal barium titanate particles can be directly synthesized, characterized in that the crystal structure is perovskite, the crystal axis ratio c / a is 1.005 or more, and Ba / Ti is 0.99 to 1.01. However, in a reaction environment where an excess amount of barium ions and hydroxide ions is present, dissolution / reprecipitation becomes active by reacting with the titanium compound at 150 ° C. or higher, and this dissolution / reprecipitation state is maintained for 24 hours or longer. By continuing, it is presumed that the grains could be grown without containing hydroxide ions or water as impurities.

The spherical tetragonal barium titanate particles according to the present invention have a small particle size, a narrow particle size distribution, a high degree of uniformity, a spherical particle shape and a high dispersibility, and with respect to dielectric properties, Ba / Ti has a composition. Uniform and highly tetragonal. As a result, for example, it is possible to cope with the reduction in the thickness of the dielectric layer in the ceramic capacitor and the reduction in the thickness of the green sheet accompanying the increase in the number of layers without increasing new capital investment and production cost. As a result, a small and high performance ceramic capacitor can be manufactured without causing an increase in production cost.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
To pure water maintained at 25 ° C, 0.077 mol of titanium tetrachloride aqueous solution with Ti equivalent is added with stirring to make approximately 5 wt% aqueous solution, and then 114 g of 5% aqueous ammonia solution is slowly added to hydrolyze titanium tetrachloride. Then, the produced precipitate is washed and filtered to obtain a titanium hydroxide gel. To this titanium hydroxide gel, 0.154 mol of a barium hydroxide aqueous solution is added in an equivalent amount of Ba in a nitrogen atmosphere, and water is added to obtain a slurry of 0.3 mol / kg in terms of BaTiO3. The slurry is aged by stirring at 60 ° C. for 30 minutes, and then charged in an autoclave and subjected to hydrothermal synthesis at 200 ° C. for 96 hours. After the reaction, the reaction mixture was cooled to room temperature, washed and filtered under a nitrogen atmosphere, and dried at 105 ° C. for 12 hours to obtain barium titanate fine particles.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.20 μm
A spherical shape with a particle size distribution of 0.21, uniformity of 0.91, roundness of 0.83, D ₅₀ / D _TEM of 1.3, crystal structure of perovskite, crystal axis ratio c / a of 1.008 and Ba / Ti of 0.99 It was highly dispersible tetragonal barium titanate fine particles.
Incidentally, for obtaining the D _50, determined by dynamic light scattering method using a micro-track, in the preprocessing, using pure water as a dispersion medium for the barium titanate fine particles, ultrasonic output using an ultrasonic homogenizer After carrying out a dispersion treatment at 150 W for 3 minutes, the particle size distribution was measured using a Microtrac UPA150 manufactured by Nikkiso Co., Ltd. And it obtains the granularity value of 50% cumulative diameter of distribution and its value as D _50. Hereinafter, Examples 2-7, in Comparative Examples 1 to 6 were obtained the values of _{D 50} in the same manner.

(Example 2)
Barium titanate fine particles were obtained in the same manner as in Example 1 except that hydrothermal synthesis was performed at 250 ° C. for 96 hours.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.23 μm
A spherical shape with a particle size distribution of 0.20, uniformity of 0.92, roundness of 0.84, D ₅₀ / D _TEM of 1.3, crystal structure of perovskite, crystal axis ratio c / a of 1.010, and Ba / Ti of 0.99. It was highly dispersible tetragonal barium titanate fine particles.

(Example 3)
Barium titanate fine particles were obtained in the same manner as in Example 1 except that the addition amount of titanium tetrachloride aqueous solution was 0.077 mol in terms of Ti, and the addition amount of aqueous barium hydroxide solution was 0.230 mol in terms of Ba equivalent.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.17 μm
A spherical shape with a particle size distribution of 0.19, uniformity of 0.93, roundness of 0.85, D ₅₀ / D _TEM of 1.4, crystal structure of perovskite, crystal axis ratio c / a of 1.010, and Ba / Ti of 0.99 It was highly dispersible tetragonal barium titanate fine particles.
A transmission electron micrograph (20,000 times) of the barium titanate fine particles according to this example is shown in FIG. 1, and an X-ray diffraction pattern is shown in FIG.

Example 4
In the same manner as in Example 1 except that the addition amount of titanium tetrachloride aqueous solution was 0.077 mol in terms of Ti, the addition amount of barium hydroxide aqueous solution was 0.230 mol in terms of Ba, and hydrothermal synthesis was conducted at 250 ° C. for 96 hours. Barium titanate fine particles were obtained.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.24 μm
A spherical shape with a particle size distribution of 0.18, uniformity of 0.94, roundness of 0.86, D ₅₀ / D _TEM of 1.3, crystal structure of perovskite, crystal axis ratio c / a of 1.010, and Ba / Ti of 1.00. It was highly dispersible tetragonal barium titanate fine particles.

(Example 5)
Obtain titanium hydroxide gel from titanium tetrachloride aqueous solution, and instead of reacting this titanium hydroxide gel and barium hydroxide aqueous solution, an alkaline solution such as sodium hydroxide or ammonia water is added to the barium hydroxide aqueous solution under a nitrogen atmosphere, Barium titanate fine particles were obtained in the same manner as in Example 1 except that a titanium tetrachloride aqueous solution was added so that the molar ratio of Ba / Ti was 3, and the slurry was obtained by adding water.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.15 μm
Dispersion in a spherical shape with a particle size distribution of 0.22, uniformity of 0.91, roundness of 0.83, D ₅₀ / D _TEM of 1.5, crystal structure of perovskite, crystal axis ratio c / a of 1.009 and Ba / Ti of 0.99 It was highly tetragonal barium titanate fine particles.

(Example 6)
Obtain titanium hydroxide gel from titanium tetrachloride aqueous solution, and instead of reacting this titanium hydroxide gel and barium hydroxide aqueous solution, an alkaline solution such as sodium hydroxide or ammonia water is added to the barium hydroxide aqueous solution under a nitrogen atmosphere, Titanium tetrachloride aqueous solution was added so that the molar ratio of Ba / Ti was 1.5, water was added to obtain a slurry, and hydrothermal synthesis was performed at 240 ° C. for 24 hours,
In the same manner as in Example 1, barium titanate fine particles were obtained.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.08 μm
Spherical dispersion with particle size distribution of 0.18, homogeneity of 0.92, roundness of 0.97, D ₅₀ / D _TEM of 2.5, crystal structure of perovskite, crystal axis ratio c / a of 1.006, Ba / Ti of 0.99 It was highly tetragonal barium titanate fine particles.
Incidentally, a transmission electron micrograph (20,000 times) of the barium titanate fine particles according to this example is shown in FIG.

(Example 7)
In the same manner as in Example 1 except that the addition amount of titanium tetrachloride aqueous solution was 0.077 mol in terms of Ti, the addition amount of barium hydroxide aqueous solution was 0.116 mol in terms of Ba, and hydrothermal synthesis was carried out at 200 ° C. for 24 hours. Barium titanate fine particles were obtained.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.10 μm
A spherical shape with a particle size distribution of 0.14, uniformity of 0.91, roundness of 0.92, D ₅₀ / D _TEM of 2.1, crystal structure of perovskite, crystal axis ratio c / a of 1.007, and Ba / Ti of 0.99 It was highly dispersible tetragonal barium titanate fine particles.

(Comparative Example 1)
In the same manner as in Example 1, except that the addition amount of titanium tetrachloride aqueous solution was 0.077 mol in terms of Ti, the addition amount of barium hydroxide aqueous solution was 0.077 mol in terms of Ba, and hydrothermal synthesis was carried out at 150 ° C. for 96 hours. Barium titanate fine particles were obtained.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.25 μm
The particle size distribution is 0.23, the uniformity is 0.86, the roundness is as low as 0.73, D ₅₀ / D _TEM is 1.2,
It was a pseudo cubic cubic barium titanate fine particle with a spherical structure and high dispersibility, with a perovskite crystal structure, a crystal axis ratio c / a as low as 1.000 and Ba / Ti as low as 0.92.
A transmission electron micrograph (20,000 times) of the barium titanate fine particles according to this comparative example is shown in FIG. 3, and an X-ray diffraction pattern is shown in FIG.

(Comparative Example 2)
Except that the addition amount of titanium tetrachloride aqueous solution was 0.077 mol in terms of Ti, the addition amount of aqueous barium hydroxide solution was 0.077 mol in terms of Ba equivalent, and hydrothermal synthesis was performed at 300 ° C. for 96 hours, the same as in Example 1, Barium titanate fine particles were obtained.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.28 μm
The particle size distribution is 0.21, the uniformity is as low as 0.89, the roundness is 0.82, the D ₅₀ / D _TEM is 1.3,
Pseudocubic barium titanate fine particles with a spherical structure and high dispersibility, with a perovskite crystal structure, a crystal axis ratio c / a as low as 1.000 and Ba / Ti as low as 0.95.

(Comparative Example 3)
In the same manner as in Example 1 except that the addition amount of titanium tetrachloride aqueous solution was 0.077 mol in terms of Ti, the addition amount of aqueous barium hydroxide solution was 0.230 mol in terms of Ba, and hydrothermal synthesis was performed at 300 ° C. for 24 hours. Barium titanate fine particles were obtained.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.34 μm
The particle size distribution is 0.21, the uniformity is as low as 0.89, the roundness is 0.86, the D ₅₀ / D _TEM is 1.2, the crystal structure is perovskite, the crystal axis ratio c / a is 1.009, and Ba / Ti is 0.99. They were spherical and highly dispersible tetragonal barium titanate fine particles.

(Comparative Example 4)
Add 1250 ml of water to 139.3 g (Ti = 0.48 mol) of titanium chloride aqueous solution kept at 40 ° C., and add 483 ml of 5.0 wt% ammonia water over 30 minutes to obtain a titanium hydroxide slurry, which is separated by washing with water. . Under a nitrogen atmosphere, 151.4 g (Ba = 0.48 mol) of barium hydroxide is added to the titanium hydroxide, and water is added to obtain a 0.8 mol / kg slurry in terms of BaTiO3. The slurry is aged by stirring at 60 ° C. for 30 minutes, and then put into an autoclave and subjected to hydrothermal synthesis at 150 ° C. for 5 hours. After the reaction, the reaction mixture was cooled to room temperature, washed and filtered under a nitrogen atmosphere, and dried at 105 ° C. for 12 hours to obtain barium titanate fine particles. The barium titanate fine particles were calcined at 1020 ° C. for 3 hours to obtain calcined barium titanate fine particles.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.68 μm
With a large particle size distribution of 0.62, a low uniformity of 0.78, a high D ₅₀ / D _TEM of 7.7, a crystal structure of perovskite, a crystal axis ratio c / a of 1.009, and Ba / Ti of 0.97 The shape was tetragonal barium titanate fine particles with low dispersibility.

(Comparative Example 5)
In a nitrogen atmosphere, add 175.2 g of titanium tetrachloride aqueous solution (Ti equivalent 0.600 mol) to 250 ml of pure water, and add 557 ml of 6.1 N sodium hydroxide aqueous solution containing 11.6 g of sodium propionate to add titanium tetrachloride to water. The resulting precipitate is washed and filtered to obtain titanium hydroxide colloid. Under a nitrogen atmosphere, 1000 ml of an aqueous barium hydroxide solution containing 197.1 g of barium hydroxide (0.606 mol in terms of Ba) is added to the titanium hydroxide colloid, and the mixture is further added to a total volume of 2000 ml to obtain a slurry. The slurry is aged by stirring at 70 ° C. for 2 hours, and then charged in an autoclave to carry out hydrothermal synthesis at 150 ° C. for 16 hours. After the reaction, the reaction mixture was cooled to room temperature, washed and filtered under a nitrogen atmosphere, and dried at 105 ° C. for 12 hours to obtain barium titanate fine particles. The barium titanate fine particles were calcined at 1020 ° C. for 3 hours to obtain calcined barium titanate fine particles.
As a result of measuring the fine particle characteristics of the obtained calcined barium titanate fine particles, the average particle size was
Large as 0.37 .mu.m, broad particle size distribution 0.58, uniformity is 0.90, D _{50 /} D _TEM is as high as 9.5, the crystal axis ratio c / a crystal structure in perovskite 1.007, Ba / Ti is as small as 0.98, It was a tetragonal barium titanate fine particle with a polygonal shape and low dispersibility.

(Comparative Example 6)
To pure water maintained at 25 ° C, 0.077 mol of titanium tetraisopropoxide aqueous solution with Ti equivalent was added with stirring to make a 5 wt% aqueous solution, then 114 g of 5% ammonia aqueous solution was slowly added to add titanium tetrachloride. Hydrolysis, and the resulting precipitate is washed and filtered to obtain a titanium hydroxide gel. To this titanium hydroxide gel, 0.154 mol of a barium hydroxide aqueous solution is added at a Ba equivalent in a nitrogen atmosphere, and water is added to obtain a slurry of 0.3 mol / kg in terms of BaTiO3. The slurry is aged by stirring at 60 ° C. for 30 minutes, and then charged into an autoclave and hydrothermal synthesis is performed at 150 ° C. for 16 hours. After the reaction, the reaction mixture was cooled to room temperature, washed and filtered under a nitrogen atmosphere, and dried at 105 ° C. for 12 hours to obtain barium titanate fine particles.
As a result of measuring the fine particle characteristics of the obtained barium titanate fine particles, the average particle size was 0.22 μm.
The particle size distribution is 0.22, the homogeneity is as low as 0.86, the D ₅₀ / D _TEM is 1.3, the crystal structure is perovskite, the crystal axis ratio c / a is 1.09, and Ba / Ti is 0.98, which is a low cubic shape and dispersible High tetragonal barium titanate fine particles.

(Summary)
The barium titanate fine particles obtained in Examples 1 to 7 have an average particle size of 0.3 μm or less, a particle size distribution of 0.5 or less, a uniformity of 0.90 or more, and a roundness of 0.80 or more, and D ₅₀ / D _TEM Is 3.0 or less, the crystal structure is perovskite, the crystal axis ratio c / a is 1.005 or more, and Ba / Ti is 0.99 to 1.01.
It was a spherical and highly dispersible tetragonal barium titanate fine particle characterized by
On the other hand, in Comparative Examples 1 and 2, when Ba / Ti was 1, the crystal system was pseudo cubic. In Comparative Example 3, the crystal system was tetragonal with fine particles at a reaction temperature of 300 ° C., but the particle size increased. In both Comparative Example 4 and Comparative Example 5, the crystal system became tetragonal by heat treatment, but the particle size increased due to grain growth, and the D ₅₀ / D _TEM value was high due to sintering between the grains. Also, when the heat treatment temperature was lowered, the grain growth could be suppressed, but the D ₅₀ / D _TEM value increased due to inter-particle sintering, and the crystallinity was low. In Comparative Example 6, the crystal system was tetragonal with fine particles, but the particle shape was not spherical but cubic.
In addition, the list of the fine particle characteristic measurement results of Examples 1 to 7 and Comparative Examples 1 to 6 is shown in FIG.

Claims (6)

When the average particle size measured from an electron microscope image was D _TEM, D _TEM is 0.3μm or less, the particle size distribution is 0.5 or less, uniformity is 0.90 or more, 0.80 or more roundness, crystal axis ratio c / a is D ₅₀ / D _TEM when 1.050 or more, the molar ratio Ba / Ti between barium and titanium is 0.99 or more and 1.01 or less, and the value that gives 50% cumulative diameter in the particle size distribution measured by the dynamic light scattering method is D ₅₀ Tetragonal barium titanate particles, wherein the particle size is 3.0 or less. When the average particle size measured from an electron microscope image was D _TEM, D _TEM is 0.1μm or less, the particle size distribution is 0.5 or less, uniformity is 0.90 or more, 0.80 or more roundness, crystal axis ratio c / a is D ₅₀ / D _TEM when 1.050 or more, and the molar ratio Ba / Ti between barium and titanium is 0.99 or more and 1.01 or less, and the value of 50% of the cumulative diameter in the particle size distribution measured by the dynamic light scattering method is D ₅₀ Tetragonal barium titanate particles, wherein the particle size is 3.0 or less. A method for producing barium titanate particles by a hydrothermal synthesis method,
Titanium hydroxide gel and barium hydroxide aqueous solution are mixed so that the molar ratio Ba / Ti of barium and titanium is 1.5 to 10.0, and the mixed solution is at a temperature range of 150 ° C or higher and 250 ° C or lower for 24 hours or longer. The method for producing tetragonal barium titanate particles according to claim 1, wherein hydrothermal treatment is performed. Adding titanium tetrachloride aqueous solution and ammonia aqueous solution to pure water, hydrolyzing titanium tetrachloride, washing and filtering the produced precipitate to obtain titanium hydroxide gel;
Adding a barium hydroxide aqueous solution to the obtained titanium hydroxide gel under a nitrogen atmosphere and adding water to obtain a slurry; and
The method according to claim 1, further comprising: subjecting the obtained slurry to hydrothermal synthesis treatment, washing and filtering in a nitrogen atmosphere, and drying to obtain barium titanate fine particles. Method for producing crystal barium titanate particles. Under a nitrogen atmosphere, adding an alkali solution and an aqueous titanium tetrachloride solution to an aqueous barium hydroxide solution and adding water to obtain a slurry;
And a step of performing hydrothermal synthesis treatment on the obtained slurry, washing and filtering in a nitrogen atmosphere, and drying to obtain barium titanate fine particles. Method for producing crystal barium titanate particles.   A ceramic capacitor comprising the tetragonal barium titanate particles according to claim 1.