Strontium titanate particles

Abstract

The present invention provides strontium titanate fine particles having a small average particle size, excellent crystallinity and dispersibility. The strontium titanate fine particles are spherical and have an average particle size (D50) measured by a laser diffraction / scattering type particle size distribution measuring machine of 10 nm to 30 nm.

Description

Technical Field

[0001] The present invention relates to strontium titanate fine particles. Background Art

[0002] Since strontium titanate (SrTiO3) has dielectric properties, thermoelectric properties, photocatalytic ability, high refractive index property, etc., it is expected to be popularized as a functional material in various applications.

[0003] For example, Patent Document 1 discloses that strontium titanate having an average particle diameter of 50 nm or less, an average aspect ratio of 1.0 to 1.2, and a refractive index of 1.8 to 2.6 has a high refractive index property. In addition, Patent Document 1 discloses that when using strontium titanate as a component for imparting a high refractive index property, high dispersibility in which no aggregation occurs in the coating film is required.

[0004] In addition, when used as such a functional material, it is necessary to have crystallinity capable of obtaining highly pure crystals.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2011 / 004750 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] An object of the present invention is to provide strontium titanate fine particles having a small average particle diameter and excellent crystallinity and dispersibility.

[0010] The present inventors conducted in-depth research on strontium titanate fine particles and found that strontium titanate fine particles that can be produced by reacting an organic titanate with a strontium compound in the presence of a specific amount of hydrazine or hydrazide compound under specified conditions (temperature and reaction time) have a small average particle diameter and excellent dispersibility.

[0011] Means for Solving the Problems

[0012] The present invention relates to strontium titanate fine particles that are spherical and have an average particle diameter (D50) measured by a laser diffraction / scattering type particle size distribution measuring machine of 10 nm to 30 nm.

[0013] When 50 mg of the above strontium titanate is dissolved in 50 mL of methanol, the strontium titanate fine particles of the present invention do not cause turbidity.

[0014] In addition, in the strontium titanate fine particles of the present invention, the ratio of the crystal grain diameter calculated by an X-ray diffractometer to the particle diameter observed by a transmission electron microscope (particle diameter observed by transmission electron microscope / crystal grain diameter calculated by X-ray diffractometer) is preferably 0.9 to 1.0.

[0015] In addition, for the strontium titanate fine particles of the present invention, the content of hydrazine or hydrazide compound is preferably 0.1% by mass to 60% by mass relative to the above-mentioned strontium titanate fine particles.

[0016] In addition, the strontium titanate fine particles of the present invention preferably contain an aminosilane compound, and the molar ratio of the content of the above-mentioned aminosilane compound to the above-mentioned hydrazine or hydrazide compound is 0.003 to 0.025.

[0017] In addition, the roundness of the strontium titanate fine particles of the present invention is preferably 0.900 to 1.000.

[0018] Advantages of the Invention

[0019] Based on the present invention, it is possible to provide strontium titanate fine particles having a small average particle diameter, excellent crystallinity and dispersibility. Detailed Embodiments

[0020] (Strontium Titanate Fine Particles)

[0021] The strontium titanate fine particles of the present invention are spherical, and the average particle diameter (D50) measured by a laser diffraction / scattering type particle size distribution measuring machine is 10 nm to 30 nm.

[0022] The strontium titanate fine particles of the present invention have a small average particle diameter (D50), excellent crystallinity and dispersibility.

[0023] The particle shape of the strontium titanate fine particles of the present invention is spherical.

[0024] Here, the so-called spherical shape includes not only a spherical ball but also an ellipsoid, a cylinder, a straw bag shape (a shape in which the corners of a cylinder are rounded), etc.

[0025] Specifically, the roundness of the above-mentioned strontium titanate fine particles is 0.900 to 1.000.

[0026] In addition, if the area of the particles in the image taken by a transmission electron microscope is set as S and the perimeter is set as L, the roundness can be calculated by roundness = 4πS / L 2 for calculation.

[0027] In addition, the shape of the above-mentioned strontium titanate fine particles can be confirmed, for example, by observing with a transmission electron microscope ("JEM-1011" manufactured by JEOL Ltd.) at an observation magnification of 300,000 times.

[0028] In addition, the above-mentioned roundness is the average value of the fine particles appearing in the image taken by a transmission electron microscope after removing the fine particles having a special shape significantly different from the above-mentioned spherical shape.

[0029] The average particle diameter of the strontium titanate fine particles of the present invention is 10 nm to 30 nm.

[0030] The above average particle size is preferably 14 nm to 25 nm.

[0031] By having such an average particle size, it can have excellent dispersibility.

[0032] In addition, the above average particle size is the average particle size (D50) measured by dissolving strontium titanate fine particles in methanol to obtain a dispersion liquid, putting the obtained dispersion liquid into a measuring element (measurement cell), and using a laser diffraction / scattering type particle size distribution measuring machine (manufactured by Nikkiso Co., Ltd., "Microtrack MT 3300EXII").

[0033] The strontium titanate fine particles of the present invention have excellent dispersibility.

[0034] Here, the dispersibility can be judged as follows: After dissolving 50 mg of strontium titanate fine particles in 50 mL of methanol to obtain a dispersion liquid, putting the obtained dispersion liquid into a screw tube bottle and setting black paper on the back, when visually confirming the state of the dispersion liquid, the dispersibility is judged according to whether white turbidity occurs. In the case where no white turbidity occurs, it can be evaluated as having excellent dispersibility, and for example, it can be applied to high refractive index materials and the like.

[0035] The strontium titanate fine particles of the present invention preferably have good crystallinity.

[0036] In addition, for the crystallinity of the above strontium titanate fine particles, if the crystallite size calculated by an X-ray diffraction apparatus is the same as the particle size observed by a transmission electron microscope [the ratio of particle sizes (the particle size observed by a transmission electron microscope / the crystallite size calculated by an X-ray diffraction apparatus) is 0.9 to 1.0], it is judged that the crystallinity is good, and in the case where the ratio is small or no crystallization is confirmed, it is judged as poor.

[0037] In the strontium titanate fine particles of the present invention, the content of hydrazine or hydrazide compound is preferably 0.1% by mass to 60% by mass, more preferably 1% by mass to 30% by mass, relative to the above strontium titanate fine particles.

[0038] Based on such a content, the dispersibility becomes good.

[0039] The strontium titanate fine particles of the present invention contain an aminosilane compound, and the content of the above hydrazine or hydrazide compound is preferably 0.003 to 0.025 in terms of molar ratio (aminosilane compound / hydrazine or hydrazide compound) relative to the above strontium titanate fine particles.

[0040] By including the above aminosilane compound within the above range, the average particle size of the strontium titanate fine particles can be appropriately controlled.

[0041] The content of the above-mentioned amino-silane compound is more preferably in a molar ratio of 0.004 to 0.019, further preferably 0.007 to 0.015, relative to the above-mentioned hydrazine or hydrazide compound.

[0042] (Method for manufacturing strontium titanate fine particles)

[0043] The strontium titanate fine particles of the present invention can be manufactured, for example, by the following method.

[0044] The method includes a reaction step of reacting an organic titanate with a strontium compound in the presence of a hydrazine or hydrazide compound under the conditions that the pH is 12 or more, the reaction temperature is 150°C or more and 250°C or less, and the reaction time is 0.5 hour or more and 2 hours or less, and the molar ratio of the above-mentioned hydrazine or hydrazide compound to the above-mentioned organic titanate (hydrazine or hydrazide compound / organic titanate) is 10 to 75.

[0045] (Organic titanate)

[0046] Examples of the above-mentioned organic titanate include: tetraethyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, and their polymers, titanium acetyl titanate, poly(titanium acetylacetonate), titanium glycine octylate, titanium lactate, titanium lactate ethyl ester, titanium triethanolaminate, titanium chelates such as titanium phosphate ester complex, etc.

[0047] Among them, from the viewpoint of hydrophilicity, titanium lactate is preferred.

[0048] (Hydrazine or hydrazide compound)

[0049] Examples of the above-mentioned hydrazide compound include: 1-monomethylhydrazine, 1,1-dimethylhydrazine, 1-ethyl-2-methylhydrazine, adipic dihydrazide, oxalic dihydrazide, malonic dihydrazide, succinic dihydrazide, glutaric dihydrazide, isophthalic dihydrazide, sebacic dihydrazide, maleic dihydrazide, fumaric dihydrazide, itaconic dihydrazide, etc.

[0050] Among them, from the viewpoint of easy operation and excellent effect of controlling the shape of the obtained strontium titanate fine particles, hydrazine is preferred.

[0051] The above-mentioned hydrazine or hydrazide compound can be in a hydrogenated state.

[0052] As the content of the above-mentioned hydrazine or hydrazide compound, the molar ratio to the above-mentioned organic titanate (hydrazine or hydrazide compound / organic titanate) is 10 to 75, preferably 30 to 65.

[0053] By setting it within the above range, the shape of the obtained strontium titanate fine particles can be appropriately controlled.

[0054] (Strontium compound)

[0055] As the above-mentioned strontium compound, examples include strontium nitrate, strontium hydroxide, strontium carbonate, strontium peroxide, strontium formate, strontium acetate, strontium lactate, strontium oxalate, strontium chloride, strontium fluoride, strontium iodide, strontium bromide, strontium chlorate, strontium iodate, strontium perchlorate, etc. They can also be used as hydrates.

[0056] Among them, from the viewpoint of hydrophilicity, at least one selected from strontium acetate and strontium formate is preferred, and strontium acetate is more preferred.

[0057] As the content of the above-mentioned strontium compound, the molar ratio (strontium compound / organotitanate) relative to the above-mentioned organotitanate is preferably 1.0 or more.

[0058] By setting it within the above range, the progress of crystallization can be appropriately controlled.

[0059] In addition, from the viewpoint of suppressing raw material costs, the above molar ratio (strontium compound / organotitanate) is more preferably 2.0 or less.

[0060] (Aminosilane compound)

[0061] As the aminosilane compound, examples include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, etc.

[0062] Among them, 3-aminopropyltriethoxysilane is preferred.

[0063] (Solvent)

[0064] As the solvent used in the method for producing the above-mentioned strontium titanate fine particles, water is preferably used.

[0065] In addition, the above solvent preferably contains a polyol.

[0066] As the above polyol, examples include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, butylene glycol, pentylene glycol, hexylene glycol, heptylene glycol, nonylene glycol, decylene glycol, and neopentyl glycol, and polyhydric alcohols having three or more hydroxyl groups such as glycerol, trimethylolpropane, and pentaerythritol.

[0067] Among them, from the viewpoint of adjusting the particle size of the obtained strontium titanate fine particles and maintaining appropriate dispersibility in the reaction system, at least one selected from ethylene glycol, propylene glycol, diethylene glycol, and 1,3-propanediol is preferred, and ethylene glycol is more preferred.

[0068] The content of the above polyol is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and further preferably 7 to 12% by mass relative to the total amount of the above solvent.

[0069] (pH regulator)

[0070] In the method for manufacturing the above strontium titanate fine particles, it is preferable to use a pH regulator to adjust the pH.

[0071] Examples of the above pH regulator include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, etc.

[0072] Among them, potassium hydroxide is preferable from the viewpoint of solubility in the above solvent.

[0073] When adjusting the pH, from the viewpoints of controlling the reaction rate and the shape of the obtained strontium titanate fine particles, it is preferable to set the pH to 12 or more.

[0074] For the pH, it is more preferably 12.5 or more, further preferably 13 or more, and particularly preferably 13.5 or more.

[0075] The content of the above pH regulator is not limited and can be appropriately added according to the target pH.

[0076] (Others)

[0077] In the method for manufacturing the above strontium titanate fine particles, an amphiphilic compound may not be added.

[0078] In the conventional method for manufacturing strontium titanate fine particles, by carrying out the reaction in the presence of an amphiphilic compound, the particle size and shape were highly controlled, and particle dispersibility was imparted.

[0079] On the other hand, in the method for manufacturing the above strontium titanate fine particles, if the above amphiphilic compound is added, it will be unevenly dispersed in the system, and as a result, the average particle diameter of the obtained strontium titanate fine particles will become larger.

[0080] Examples of the above amphiphilic compound include saturated fatty acids such as propionic acid, butyric acid, valeric acid, hexanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid; unsaturated fatty acids such as α-linolenic acid, stearidonic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, γ-linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, oleic acid, elaidic acid, erucic acid, and nervonic acid.

[0081] In the method for manufacturing the above strontium titanate fine particles, for example, it preferably includes a mixing step of mixing an organic titanate and a hydrazine or hydrazide compound in a solvent to obtain a mixed solution, a pH adjusting step of adjusting the pH of the above mixed solution to 12 or more, and the above reaction step.

[0082] The above mixing process is a process of adding an organic titanate and a hydrazine or hydrazide compound to a solvent.

[0083] It is speculated that through the above mixing process, hydrazine coordinates with the organic titanate.

[0084] In the above mixing process, there is no particular limitation on the method of adding various materials, and addition, stirring, etc. can be carried out by known methods.

[0085] In the above adjustment process, the pH is adjusted. Thereby, the reaction rate and the shape of the obtained strontium titanate fine particles can be appropriately controlled.

[0086] In addition, through the above mixing process, the increase in the average particle size of the organic titanate coordinated with hydrazine is controlled. As a result, the average particle size of the obtained strontium titanate fine particles can be controlled within an appropriate range.

[0087] In addition, the adjustment of the pH is preferably carried out using the above pH adjuster.

[0088] In addition, when adding the above amino-silane compound, it is preferably added to the above adjustment process together with the above pH adjuster.

[0089] For strontium titanate fine particles, on the one hand, if there is a large amount of water, crystal growth becomes faster; on the other hand, if the hydrophobicity of the solvent becomes higher, since the surface of the strontium titanate fine particles is hydrophilic, aggregation is promoted.

[0090] On the other hand, since the above polyol has hydrophilicity and has an effect of inhibiting crystal growth, it is preferably added in the above preparation process.

[0091] In the above adjustment process, there is no particular limitation on the method of adding various materials, and addition, stirring, etc. can be carried out by known methods.

[0092] In the above reaction process, it is preferred to react the above organic titanate with the above strontium compound under the conditions that the pH is 12 or more, the reaction temperature is 150 °C or more and 250 °C or less, and the reaction time is 0.5 hour or more and 2 hours or less.

[0093] The above reaction temperature is preferably 150 °C or more and 250 °C or less.

[0094] If the above reaction temperature is less than 150 °C, the reaction does not proceed, and sometimes the target strontium titanate fine particles cannot be obtained; if it exceeds 250 °C, the reaction efficiency decreases, and at the same time, the obtained strontium titanate particles become larger and the dispersibility decreases.

[0095] The above reaction temperature is preferably 180 - 250 °C, more preferably 200 - 240 °C.

[0096] The above reaction time is preferably more than 0.5 hours and less than 2 hours.

[0097] If the above reaction time is less than 0.5 hours, the reaction does not proceed, and sometimes strontium titanate fine particles as the target cannot be obtained; if it exceeds 2 hours, the reaction efficiency decreases, and at the same time, the obtained strontium titanate particles become larger and the dispersibility decreases.

[0098] The above reaction time is preferably 1 to 2 hours.

[0099] As the pressure during the reaction, for example, it can be about 2 to 5 MPa, and there is no need to apply a pressure exceeding 10 MPa.

[0100] As the method for performing the above reaction process, there is no particular limitation as long as it is a method that satisfies the above conditions.

[0101] For example, a pressure reaction vessel or the like can be used.

[0102] Embodiment

[0103] Hereinafter, the present invention will be further described in detail by giving examples, but the present invention is not limited to these examples. In addition, unless otherwise specified, "%" means "mass %" and "parts" means "mass parts".

[0104] The materials used in the examples and comparative examples are as follows.

[0105] (Organic titanate)

[0106] Titanium lactate (ORGATIX TC-310, component concentration 44 wt%, manufactured by Matmoto Fine Chemical Co., Ltd.)

[0107] Titanium phosphate complex (ORGATIX TC-1040, component concentration 75 wt%, manufactured by Matmoto Fine Chemical Co., Ltd.)

[0108] (Hydrazine or hydrazide compound)

[0109] Hydrazine hydrate (manufactured by NIPPON CARBIDE INDUSTRIES CO., INC.)

[0110] (Strontium compound)

[0111] Strontium acetate hemihydrate (manufactured by Fujifilm Wako Pure Chemical Corporation)

[0112] Strontium formate dihydrate

[0113] (Solvent)

[0114] Ethylene glycol

[0115] Propylene glycol

[0116] Purified water (ion-exchanged water)

[0117] (pH regulator)

[0118] Potassium hydroxide

[0119] (Aminosilane compound)

[0120] 3-Aminopropyltriethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0121] (Example 1)

[0122] 3 g of purified water and 3.0 g of hydrazine hydrate (manufactured by Nippon Carbide Industries Co., Ltd.) were added to 0.584 g of titanium lactate (ORGATIX TC-310, component concentration 44 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.) to obtain a yellow transparent solution.

[0123] Next, a solution prepared with 0.48 g of potassium hydroxide, 0.432 g of ethylene glycol, and 5.088 g of purified water was added to the above yellow transparent solution to obtain a turbid white solution.

[0124] Then, 0.429 g of strontium acetate hemihydrate (manufactured by Fujifilm Wako Pure Chemical Corporation) was added to the obtained turbid white solution, and it was stirred at room temperature for 30 minutes to obtain a transparent solution. The obtained transparent solution was placed in a pressure reaction vessel and reacted under the conditions of 230 °C for 1 hour. Additionally, the pressure was about 2.8 MPa.

[0125] The solution containing the reactants was subjected to centrifugation (model SIGMA 3-30KS, conditions 15000 rpm, 5 minutes) to cause the fine particles to settle, thereby performing separation and purification (refined production) from the unreacted substances. A redispersion solution of the fine particles was prepared with purified water, and the operation of centrifugation to cause the fine particles to settle was repeated 3 times to complete the separation and purification.

[0126] The obtained fine particles were recovered and observed with an X-ray diffractometer (manufactured by Rigaku Corporation, "MiniFlex600-C"). As a result, it was confirmed that the fine particles were strontium titanate.

[0127] (Examples 2 - 8, Comparative Examples 1 - 6)

[0128] Strontium titanate particles were produced in the same manner as in the examples, except that the compounding amounts of the various materials and the reaction conditions were changed as shown in Table 1. In addition, in Examples 5 and 6, 3-aminopropyltriethoxysilane was added together with the pH regulator (potassium hydroxide).

[0129] The obtained particles were recovered and observed with an X-ray diffractometer (manufactured by Rigaku Corporation, "MiniFlex600-C"). As a result, it was confirmed that strontium titanate particles were obtained in Examples 2 to 8 and Comparative Example 4. On the other hand, in Comparative Examples 1 to 3, 5, and 6, the reaction did not proceed and strontium titanate was not obtained.

[0130] <Evaluation method>

[0131] (Particle shape)

[0132] The strontium titanate particles obtained in the examples and comparative examples were recovered and observed with a transmission electron microscope ("H-800" manufactured by Hitachi High-Technologies Corporation) at an observation magnification of 300,000 times, and the particle shape was confirmed.

[0133] Particles with a circularity of 0.900 to 1.000 were evaluated as spherical.

[0134] (Crystallinity)

[0135] The particles obtained in the examples and comparative examples were observed with a transmission electron microscope ("JEM-1011" manufactured by JEOL Ltd.) and an X-ray diffractometer ("MiniFlex600-C" manufactured by Rigaku Corporation), and evaluated according to the following criteria.

[0136] 〇: The ratio of the crystallite size calculated by the X-ray diffractometer to the particle size observed by the transmission electron microscope is 0.9 to 1.0;

[0137] △: The ratio of the crystallite size calculated by the X-ray diffractometer to the particle size observed by the transmission electron microscope is less than 0.9;

[0138] ×: No crystal was formed.

[0139] (Average particle size)

[0140] 50 mg of the strontium titanate particles obtained in the examples and comparative examples was dissolved in 50 mL of methanol to obtain a dispersion.

[0141] The obtained dispersion was placed in a measuring element (measurement cell), and the average particle diameter (D50) was measured using a laser diffraction / scattering type particle size distribution measuring machine ("microtrack MT 3300EXII" manufactured by Nikkiso Co., Ltd.).

[0142] (Dispersibility)

[0143] 50 mg of strontium titanate fine particles obtained in the examples and comparative examples were dissolved in 50 mL of methanol to obtain a dispersion.

[0144] The obtained dispersion was placed in a screw tube bottle, black paper was set on the back, the state of the dispersion was visually confirmed, and evaluation was carried out according to the following criteria.

[0145] 〇: The obtained dispersion is a transparent solution.

[0146] ×: The obtained dispersion is a turbid solution.

[0147]

[0148] The particle shape of the strontium titanate fine particles obtained in the examples was spherical, the average particle diameter was 14 nm to 30 nm, and excellent crystallinity and dispersibility were confirmed.

[0149] In particular, in Examples 5 and 6 containing 3-aminopropyltriethoxysilane, strontium titanate fine particles with a small average particle diameter and excellent dispersibility can be obtained.

[0150] In addition, in Example 7 using a phosphate titanate complex and Example 8 using propylene glycol as a solvent, the transparency of the dispersion was slightly lower and the dispersibility was slightly lower compared to other examples.

[0151] On the other hand, in Comparative Examples 1 to 3, 5, and 6, the reaction did not proceed and strontium titanate fine particles were not obtained.

[0152] In addition, the fine particles obtained in Comparative Examples 1 to 3 (which do not contain hydrazine or hydrazide compounds or the addition amount is not within the specified range) have a large average particle diameter and poor dispersibility (the dispersion is turbid).

[0153] In addition, the crystallinity of the strontium titanate fine particles obtained in Comparative Example 4 with a reaction temperature outside the specified range was insufficient.

[0154] In addition, the fine particles obtained in Comparative Example 5 with an excessively long reaction time have a large average particle diameter and poor dispersibility (the dispersion is turbid).

[0155] In addition, in Comparative Example 6 with a long reaction time and a low pH, the reaction did not proceed and no fine particles were obtained.

[0156] Industrial Applicability

[0157] The strontium titanate fine particles of the present invention can be used as functional materials such as, for example, high refractive index agents, thermoelectric conversion materials, photocatalysts, ion conductive materials, ferroelectric materials, magnetic materials, catalyst materials, oxygen electrode materials, piezoelectric materials, thermoelectric materials, non-linear optical materials, fillers, etc., and are useful in this regard.

Claims

1. A strontium titanate fine particle, which is spherical and has an average particle diameter D50 measured by a laser diffraction / scattering type particle size distribution measuring machine of 10 nm to 30 nm, with respect to the strontium titanate fine particle, the content of hydrazine or hydrazide compound is 0.1% by mass to 60% by mass, the ratio of the particle diameter observed by a transmission electron microscope to the crystallite particle diameter calculated by an X-ray diffractometer is 0.9 to 1.0, and this ratio is the particle diameter observed by the transmission electron microscope / the crystallite particle diameter calculated by the X-ray diffractometer; the strontium titanate fine particle is obtained by a reaction step of reacting an organic titanate with a strontium compound in the presence of a hydrazine or hydrazide compound and under the conditions that the pH is 12 or more, the reaction temperature is 150 or more and 250 or less, and the reaction time is 0.5 hour or more and 2 hours or less.

2. The strontium titanate fine particle according to claim 1, wherein, When 50 mg of the strontium titanate is dissolved in 50 mL of methanol, no turbidity occurs.

3. The strontium titanate fine particle according to claim 1 or 2, which contains an aminosilane compound, and the content of the aminosilane compound is 0.003 to 0.025 in terms of the molar ratio with respect to the hydrazine or hydrazide compound.

4. The strontium titanate fine particle according to claim 1 or 2, which has a circularity of 0.900 to 1.000.

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