JP6993058B2 - Rectangular parallelepiped single crystal sodium niobate particles and their production method - Google Patents

Description

The present invention relates to rectangular parallelepiped single crystal NaNbO ₃ particles and a method for producing the same, and a dielectric porcelain composition using rectangular parallelepiped single crystal NaNbO ₃ particles and a method for producing the same.

Since lead zirconate titanate (Pb (Zr _x , Ti _1-X ) O ₃ ) currently used as a piezoelectric material contains lead, which is a substance subject to the RoHS Directive, it is necessary to search for lead-free piezoelectric materials. There is an urgent need. In recent years, Nb-based ceramic materials such as NaNbO ₃ , KNbO ₃ and K _0.5 Na _0.5 NbO ₃ have been actively studied as lead-free piezoelectric materials, and are attracting attention as alternative materials to lead zirconate titanate. ..

A feature of Nb-based ceramics is that they generally have a higher Curie temperature than barium titanate (BaTIO ₃ ), which is known as a dielectric material. From this, two-component materials of barium titanate and Nb-based ceramics, or three-component materials with other components added, have been actively studied in recent years as candidate materials for high-temperature dielectrics of 200 ° C. or higher. ..

On the other hand, in the study of dielectric materials, it is considered to utilize the crystal interface strain effect, and as a configuration for this, the formation of a nanocube aggregate in which barium titanate nanocubes are arranged is examined. There is. In such a configuration, the barium titanate nanocubes are arranged and heat-treated to bond the interface between the barium titanate nanocubes, and the crystal lattice is distorted at the interface, so that a huge dielectric constant is developed. It is speculated that it will be done.

It is expected that the application of Nb-based ceramics to nanocube aggregates will enable further improvement of the properties of dielectric materials. For example, it is predicted that a structure in which barium titanate nanocubes and NaNbO3 _nanocubes are arranged and the crystal lattice is distorted at the interface can be a dielectric material having excellent various properties such as high temperature characteristics and DC bias characteristics. Will be done.

As a technique relating to this Nb-based ceramic nanocube, Patent Document 1 describes NaK _(1-x) NbO ₃ (1-x) NbO 3 having a maximum particle diameter of 0.05 to 20 μm and an aspect ratio of 1 to 1.5. Sodium niobate / potassium salt particles represented by 0.05 ≦ x ≦ 0.8) are disclosed. Further, Patent Document 2 describes a step of preparing a mixture containing niobium oxide, a sodium hydroxide aqueous solution and sodium niobate produced in a separate step, and a step of subjecting the obtained mixture to hydrothermal treatment. A method for producing sodium niobate fine particles including the above is disclosed.

Japanese Unexamined Patent Publication No. 2014-88314 Japanese Unexamined Patent Publication No. 2013-224228

The particles according to Patent Document 1 are polycrystalline particles to which fine single crystal particles are bonded and are not single crystal particles, but the particle size D50 having a diameter of 50% in the cumulative fraction based on the number in the particle size distribution is It is several μm or more. Further, the particles produced by the method according to Patent Document 2 have a wide particle size distribution, and the average particle size is 200 nm or more.

In the formation of nanocube aggregates, it is required that the Nb-based ceramic nanocubes are single crystal particles, the shape of the particles is rectangular parallelepiped (preferably cubic), the average particle size is small, and the particle size distribution is narrow. Will be done. Therefore, the particles described in the above prior art document have a problem that it is difficult to arrange different nanocubes and apply them to a nanocube aggregate from the viewpoint of particle type, particle size, and particle size distribution. was there.

The present inventors have made this in view of the above problems, and an object of the present invention is to provide rectangular parallelepiped single crystal _NaNbO3 particles having a small average particle size and a narrow particle size distribution.

The above-mentioned problems of the present invention are solved by the following means;
To prepare an Nb ₂ O ₅ sol solution containing an Nb ₂ O ₅ sol and a sodium-containing compound, and
Solvothermal synthesis using the solution A and
A method for producing ₃ rectangular parallelepiped NaNbO particles, which comprises.
The rectangular single crystal NaNbO ₃ particles have a particle size D50 of 5 nm or more and 100 nm or less, which is a 50% diameter in the number-based integrated fraction in the particle size distribution, and have a particle size distribution in the number-based integrated fraction. D90 / D50, which is the ratio of the particle size D90 having a diameter of 90% to D50, is 1.01 or more and 1.4 or less.
A method for producing ₃ rectangular parallelepiped single crystal NaNbO particles.

The above-mentioned problems of the present invention are also solved by the following means;
The particle size D90 having a particle size D50 which is 50% diameter in the number-based integrated fraction in the particle size distribution is 5 nm or more and 100 nm or less, and has a particle size D90 which is 90% diameter in the number-based integrated fraction in the particle size distribution. D90 / D50, which is the ratio to the particle size D50, is 1.01 or more and 1.4 or less.
Rectangular parallelepiped single crystal NaNbO ₃ particles.

According to the present invention, it is possible to provide rectangular parallelepiped single crystal _NaNbO3 particles having a small average particle size and a narrow particle size distribution.

6 is an XRD spectrum of cubic single crystal NaNbO ₃ particles according to Example 3. 3 is an SEM photograph of ₃ cubic single crystal NaNbO particles according to Example 3, in which (a) represents a single crystal particle and (b) represents an enlarged one of the single crystal particles. It is a schematic diagram which shows the structure of the preferred form of the dielectric porcelain composition which is manufactured by the manufacturing method which concerns on the 3rd aspect of this invention, or which concerns on 4th aspect of this invention.

One embodiment of the present invention comprises forming an Nb ₂ O ₅ sol solution containing an Nb ₂ O ₅ sol and a sodium-containing compound, and performing sorbothermal synthesis using the Nb ₂ O ₅ sol solution. A method for producing _{3 rectangular single-crystal NaNbO particles including, the rectangular single-crystal NaNbO 3 particles} have a particle size D50 which is 50% of the integrated fraction based on the number of particles in the particle size distribution. D90 / D50, which is the ratio of the particle size D90 having a particle size of 5 nm or more and 100 nm or less and 90% of the particle size-based integrated fraction in the particle size distribution to the D50, is 1.01 or more and 1.4 or less. This is a method for producing _three rectangular single crystal NaNbO particles.

In the present specification, the "particle size" is obtained by imaging a particle with a scanning electron microscope (SEM) and measuring the particle size. The average particle size is obtained by randomly extracting 50 particles, measuring the particle size, and averaging the particles. Here, when the shape of the particle is not spherical, it is defined as the one calculated by measuring the major axis.

Further, in the present specification, "particle size D50, which is a 50% diameter in the number-based integrated fraction in the particle size distribution" is the number-based integration in the particle size distribution of 50 particles obtained by the above SEM measurement. It can be calculated from the fraction. Similarly, "particle size D90 having a diameter of 90% in the number-based integrated fraction in the particle size distribution" is calculated from the number-based integrated fraction in the particle size distribution of 50 particles obtained by the above SEM measurement. can.

Here, in the present specification, "cuboidal shape" and "cubic shape" mean that the shapes of the particles determined by checking the photograph obtained by imaging the particles by the above SEM are the rectangular parallelepiped shape and the cubic shape, respectively. say. Here, the "cuboidal shape" and the "cubic shape" may be any as long as they are visually determined to be a rectangular parallelepiped shape or a cube shape, and are not required to be strictly a rectangular parallelepiped shape or a cube shape.

In the present specification, the term "single crystal" refers to an electron diffraction pattern of a particle imaged by a transmission electron microscope (TEM) using an electron diffraction (ED) method. It is assumed that the diffraction spots are regularly arranged. The "polycrystal" is a state in which the electron diffraction pattern of the particle is a concentric ring, and the "acrystal" is a state in which the electron diffraction pattern of the particle is a broad annular shape. Suppose there is.

The fact that the synthesized particles are crystalline NaNbO ₃ can be confirmed by identifying the product by X-ray diffraction (XRD).

The mechanism of exerting the action and effect by the above-mentioned constitution of the present invention is presumed as follows.

In the synthesis of NaNbO ₃ particles, by performing solvothermal synthesis using Nb ₂ O ₅ and a sodium-containing compound, the reaction proceeds from the surface of Nb ₂ O ₅ and crystalline NaNbO ₃ is gradually produced. .. Here, the produced crystalline NaNbO ₃ particles change depending on the dispersed state of Nb ₂ O ₅ . Then, when Nb ₂ O ₅ is reacted in a sol state, that is, in a highly dispersed state under suitable conditions in relation to the nucleation rate and each growth rate, the crystalline NaNbO ₃ produced is produced. , Square-shaped single crystal NaNbO ₃ particles. It is presumed that the reason for this is that it is extremely unlikely that the crystalline NaNbO ₃ will come into contact with other crystalline NaNbO ₃ until the crystal growth is completed. On the other hand, when Nb ₂ O ₅ is in an aggregated state such as powder, the produced crystalline NaNbO ₃ becomes polycrystalline particles to which fine single crystal particles are bonded. It is presumed that the reason for this is that until the crystalline NaNbO ₃ finishes growing, it comes into contact with other crystalline NaNbO ₃ and the crystalline NaNbO ₃ bind to each other.

Here, when a crystalline substance grows as a single crystal, the shape of the single crystal particles is usually determined by the crystal system, so that it is possible to produce rectangular single crystal NaNbO ₃ particles. Further, since the Nb ₂ O ₅ sol is in a highly dispersed state, the uniformity as a raw material at the start of the reaction is high, and when the crystalline NaNbO ₃ grows as a single crystal, the crystal growth rate and the reaction time. By controlling with, the particle size can be easily controlled. As a result, it becomes possible to produce rectangular parallelepiped single crystal NaNbO ₃ particles having a smaller average particle size and a narrower particle size distribution than in the past.

The present invention is not limited to the above mechanism.

Hereinafter, the rectangular parallelepiped single crystal NaNbO ₃ particles according to the present invention and the forms and embodiments for carrying out the present invention will be described in detail. Unless otherwise specified, the operation and physical properties are measured under the conditions of room temperature (25 ° C.) / relative humidity of 40 to 50% RH.

Further, in the present specification, "solution" means a solution or a dispersion liquid, and "solvent" means a solvent or a dispersion medium.

<Square-shaped single crystal NaNbO ₃ particles and their production method>
(1) Square single crystal NaNbO ₃ particles In the first embodiment of the present invention, the particle size D50, which is 50% of the cumulative fraction based on the number of particles in the particle size distribution, is 5 nm or more and 100 nm or less, and the particle size is 100 nm or less. A method for producing rectangular single crystal NaNbO ₃ particles in which the ratio of the particle size D90, which is 90% in the integrated fraction based on the number of particles, to D50 is 1.01 or more and 1.4 or less. Regarding.

Further, in the second embodiment of the present invention, the particle size D50, which is a 50% diameter in the number-based integrated fraction in the particle size distribution, is 5 nm or more and 100 nm or less, and the particle size distribution is in the number-based integrated fraction. It is also a rectangular single crystal _NaNbO3 particle having a D90 / D50 ratio of a particle size D90 having a diameter of 90% to a particle size D50 of 1.01 or more and 1.4 or less.

The particle size D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles is 5 nm or more. When D50 is less than 5 nm, it is difficult to form a rectangular parallelepiped shape, and the proportion of spherical shapes increases. From this, from the viewpoint of obtaining rectangular parallelepiped-shaped particles, the particle size D50 is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 70 nm or more. The particle size D50 is 100 nm or less. If the particle size D50 is more than 100 nm, it becomes difficult to apply it to a nanocube integrated body, and it becomes difficult to increase the size and capacity of a laminated chip capacitor or the like. From this point of view, from the viewpoint of application to nanocube integrated bodies and miniaturization and large capacity of laminated chip capacitors and the like, 98 nm or less is preferable, and 95 nm or less is more preferable.

D90 / D50 is 1.40 or less. If D90 / D50 is more than 1.40, it becomes difficult to form a uniform nanocube aggregate. From this, from the viewpoint of forming a uniform nanocube aggregate, D90 / D50 is preferably 1.38 or less, and more preferably 1.35 or less. The smaller the D90 / D50, the more preferable, but from the viewpoint of ease of manufacture, it is usually 1.01 or more, preferably 1.10 or more, more preferably 1.20 or more, and further preferably 1.25 or more. preferable.

The rectangular parallelepiped single crystal NaNbO ₃ particles are preferably cubic single crystal NaNbO ₃ particles.

(2) Preparation of Nb ₂ O ₅ Sol Solution The production method according to one embodiment of the present invention comprises forming an Nb ₂ O ₅ sol solution containing an Nb ₂ O ₅ sol and a sodium-containing compound. In addition, in this specification, the said Nb ₂ O ₅ sol solution is also simply referred to as "solution A". Further, the solvothermal synthesis treatment using the solution A is also simply referred to as "solvothermal synthesis treatment A".

In the preparation of the solution A, the mixing method and the mixing order of each component are not particularly limited.

[Nb ₂ O ₅ sol]
Solution A contains an Nb ₂ O ₅ sol. The Nb ₂ O ₅ sol is used as an Nb source in the synthesis of rectangular parallelepiped single crystal NaNbO ₃ particles.

The particle size D50 of Nb ₂ O ₅ in the Nb ₂ O ₅ sol is not particularly limited as long as Nb ₂ O ₅ forms a sol state, but is preferably 0.1 nm or more and 30 nm or less. Here, the particle size D50 of Nb ₂ O ₅ in the sol can be measured by SEM in the same manner as the rectangular parallelepiped single crystal NaNbO ₃ particles. Within this range, it becomes easier to control the particle sizes D50 and D90 / D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles within the range of the present invention. From the same viewpoint, the particle size D50 of Nb ₂ O ₅ in the Nb ₂ O ₅ sol is preferably 1 nm or more and 20 nm or less. Here, as the particle size D50 of Nb ₂ O ₅ in the sol increases, the particle size D50 and the particle size distribution of the rectangular parallelepiped single crystal NaNbO ₃ particles tend to increase.

The solvent for forming the Nb ₂ O ₅ sol is not particularly limited as long as the Nb ₂ O ₅ forms a sol state, and water (pure water, ion-exchanged water, ultrapure water, etc.) or a known organic solvent is used. be able to. Examples of the organic solvent include alcohols such as methanol, ethanol, benzyl alcohol and methoxyethanol; glycols such as ethylene glycol and diethylene glycol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; butyl acetate and ethyl acetate. Esters such as carbitol acetate and butyl carbitol acetate; ethers such as methyl cellosolve, ethyl cellosolve, butyl ether and tetrahydrofuran; amines such as methylethanolamine and diethanolamine; aromatics such as benzene, toluene and xylene. Be done. The solvent may be used alone or in combination of two or more. Further, it may be a mixed solvent in which water is mixed with the above organic solvent. Among these, water is the solvent for forming the Nb ₂ O ₅ sol from the viewpoint of reducing the possibility of inhibiting the later synthesis of rectangular parallelepiped single crystal NaNbO ₃ particles (solvothermal synthesis treatment A). preferable.

The content of the Nb ₂ O ₅ sol in the solution A is preferably 3 × 10 ^-3 mol / l or more and 12.5 × 10 ^-3 mol / l or less in terms of the molar amount of the Nb element with respect to the total volume of the solution A. It is more preferably 4 × 10 ^-3 mol / l or more and 10 × 10 ^-3 mol / l or less, and further preferably 5 × 10 ^-3 mol / l or more and 8 × 10 ^-3 mol / l or less.

[Preparation of Nb ₂ O ₅ sol]
The method for preparing the Nb ₂ O ₅ sol is not particularly limited, and a known method can be used. The production method according to one embodiment of the present invention is a Nb ₂ O ₅ sol by a sorbothermal synthesis treatment using a solution containing Nb ₂ O ₅ hydrate (Nb ₂ O ₅ · nH ₂ O) or a hydroxide. It is preferable to further include synthesizing. This is because the purity of the Nb ₂ O ₅ sol can be further increased, and as a result, the purity of the rectangular parallelepiped single crystal NaNbO ₃ particles can be further increased. In addition, by controlling the formulation of the solution containing the hydrate or hydroxide of Nb ₂ O ₅ used in the solvothermal synthesis treatment and the applied conditions, the particle size D50 of the rectangular single crystal NaNbO ₃ particles and This is because the D90 / D50 can be more easily controlled within the scope of the present invention.

In the present specification, the solution containing the hydrate or hydroxide of Nb ₂ O ₅ is also simply referred to as “solution B”. Further, the solvothermal synthesis treatment using the solution B is also simply referred to as “solvothermal synthesis treatment B”.

The hydrate or hydroxide of Nb ₂ O ₅ which is the raw material of the Nb ₂ O ₅ sol is not particularly limited, and a commercially available product may be used, or a product synthesized by a known method may be used. The hydrate or hydroxide of Nb ₂ O ₅ may be used alone or in combination of two or more. Among these, it is more preferable to use the hydrate of Nb ₂ O ₅ .

As a method for synthesizing the hydrate of Nb ₂ O ₅ , for example, ethanol is added to a niobium-containing compound to prepare a solution, and ammonia water is added dropwise while stirring this solution to obtain Nb ₂ O ₅ · nH ₂ O. Examples include a method of producing a precipitate. Here, as the niobium-containing compound, a known compound can be used without particular limitation as long as a hydrate of Nb ₂ O ₅ can be synthesized. Among these, the niobium-containing compound is preferably niobium chloride (V) (NbCl ₅ ) or niobium nitrate. The above niobium-containing compound may be used alone or in combination of two or more. Here, the hydrate of Nb ₂ O ₅ can be taken out by centrifuging the solution containing the obtained precipitate to remove the supernatant. However, the method for synthesizing the hydrate of Nb ₂ O ₅ is not limited to this method.

The solvent of the solution B is not particularly limited as long as the Nb ₂ O ₅ sol can be synthesized by the sorbothermal synthesis treatment B, and water (pure water, ion-exchanged water, ultrapure water, etc.) or a known organic solvent is used. be able to. Examples of the organic solvent include alcohols such as methanol, ethanol, benzyl alcohol and methoxyethanol; glycols such as ethylene glycol and diethylene glycol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; butyl acetate and ethyl acetate. Esters such as carbitol acetate and butyl carbitol acetate; ethers such as methyl cellosolve, ethyl cellosolve, butyl ether and tetrahydrofuran; amines such as methylethanolamine and diethanolamine; aromatics such as benzene, toluene and xylene. Be done. The solvent may be used alone or in combination of two or more. Further, it may be a mixed solvent in which water is mixed with the above organic solvent. Among these, water is preferable as the solvent of the solution B from the viewpoint of reducing the impurities of the obtained Nb ₂ O ₅ sol.

Solution B preferably further contains an oxidizing agent. The oxidant acts to convert Nb elements other than Nb ⁵⁺ into Nb ⁵⁺ in solution B. As a result, the purity of the Nb ₂ O ₅ sol obtained by containing the oxide can be increased, and the obtained rectangular parallelepiped single crystal NaNbO ₃ particles have a particle size D50 or D90 / D50 outside the range of the present invention. The amount of particles having a sol and other impurities can be further reduced.

The oxidizing agent is not particularly limited as long as the Nb element existing other than Nb ⁵⁺ can be Nb ⁵⁺ , and a known oxidizing agent can be used. Examples of the oxidizing agent include hydrogen peroxide, hypochloric acid, chloric acid, perchloric acid, potassium nitrate, potassium permanganate and the like. The above-mentioned oxidizing agent may be used alone or in combination of two or more. Among these, nitric acid or hydrogen peroxide is more preferable as the oxidizing agent, and the oxidizing agent is decomposed from the viewpoint of dissolving in water, which is a preferable solvent of the solution B, and further reducing the impurities generated in the Nb ₂ O ₅ sol. Hydrogen peroxide is further preferred from the viewpoint of providing water, which is a preferred solvent for forming the Nb ₂ O ₅ sol.

The method of adding the oxidizing agent is not particularly limited, and may be a method of directly adding the oxidizing agent to the hydrate of Nb ₂ O ₅ or the mixture of the hydroxide and the solvent. The method of adding the oxidant is as follows: the oxidant is prepared by forming an oxidant solution in advance, and then using a hydrate of niobium (V) (Nb ₂ O ₅ ) or a mixed solution of a hydroxide and a solvent. It may be mixed with an oxidizing agent solution. At this time, the solvent of the oxidant solution is not particularly limited as long as it can form the oxidant solution, and water or a known organic solvent can be used, but solutions B and Nb ₂ O ₅ are used. Water, which is the preferred solvent for the sol, is preferred. Here, a hydrogen peroxide solution is mentioned as a preferable example of the oxidizing agent solution.

The content of the oxidizing agent in the solution B can be appropriately set according to the type of the oxidizing agent used, or the amount and type of the raw material of the remaining Nb ₂ O ₅ hydrate or hydroxide.

Solution B may contain other additives as long as it does not interfere with the effects of the present invention.

In the present specification, the solvothermal synthesis treatment is a reaction carried out under a medium to high pressure (usually 0.20 to 1,000 MPa) and a medium to high temperature (usually 50 ° C. to 1000 ° C.). Is defined as processing using. Here, the "hydrothermal synthesis treatment" is a sorbothermal synthesis treatment in which only water (pure water, ion-exchanged water, ultrapure water, etc.) is used as a solvent, and other organic solvents are used as solvents. It is defined as a form not included as.

In the solvothermal synthesis treatment B, the holding temperature during the solvothermal synthesis treatment is not particularly limited, but is preferably 60 ° C. or higher. Within this range, the reaction is preferably carried out, the particle size D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles is set to a value equal to or higher than a certain value satisfying the range of the present invention, and D90 / D50 is within the range of the present invention. It becomes easier to control. From the same viewpoint, the holding temperature during the solvothermal synthesis treatment is preferably 70 ° C. or higher, more preferably 75 ° C. or higher. Further, in the solvothermal synthesis treatment B, the holding temperature during the solvothermal synthesis treatment is preferably 200 ° C. or lower. Within this range, the reaction is preferably carried out, the particle size D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles is set to a value below a certain value satisfying the range of the present invention, and D90 / D50 is within the range of the present invention. It becomes easier to control. From the same viewpoint, the holding temperature during the solvothermal synthesis treatment is preferably 150 ° C. or lower, preferably 95 ° C. or lower. Further, in the solvothermal synthesis treatment B, it is preferable that the holding temperature is a constant temperature.

Further, in the solvothermal synthesis treatment B, the holding time during the solvothermal synthesis treatment is not particularly limited, but is preferably 1 hour or more and 500 hours or less, more preferably 5 hours or more and 200 hours or less, and further preferably 24 hours or more and 168 hours or less. It's less than an hour. Within this range, the reaction is preferably carried out, and it becomes easier to control the particle sizes D50 and D90 / D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles within the range of the present invention.

In the solvothermal synthesis treatment B, the pressure during the solvothermal synthesis treatment is not particularly limited, but is preferably 0.2 MPa or more and 4.0 MPa or less. The reaction under such pressure is preferably carried out in a pressure-resistant container such as an autoclave.

Therefore, in the production method according to one embodiment of the present invention, the solvothermal synthesis treatment B is preferably carried out by holding at 60 ° C. or higher and 200 ° C. or lower for 1 hour or longer and 500 hours or lower.

The Nb ₂ O ₅ sol synthesized by the solvothermal synthesis treatment B is preferably used for the preparation of the solution A while maintaining the sol state. By maintaining the sol state from the formation of the Nb ₂ O ₅ sol to the formation of the solution A and avoiding aggregation due to drying, the suitable particle size D50 of Nb ₂ O ₅ in the sol realized by the solvothermal synthesis treatment B and Good dispersibility can be better maintained. As a result, the particle sizes D50 and D90 / D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles can be better controlled within the range of the present invention.

[Sodium-containing compound]
Solution A contains a sodium-containing compound. The sodium-containing compound is used as a Na source in the synthesis of rectangular parallelepiped single crystal NaNbO ₃ particles.

The sodium-containing compound is not particularly limited as long as it can synthesize rectangular parallelepiped single crystal _NaNbO3 particles by the solvothermal synthesis treatment A, and known sodium-containing compounds can be used. As the sodium-containing compound, sodium hydroxide or a sodium salt is preferable. The sodium salt is not particularly limited, and is, for example, a sodium salt of an inorganic acid such as sulfuric acid, carbonic acid, nitrate, boric acid, carbonic acid, hypophosphite, phobic acid and phosphoric acid, formic acid, acetic acid, propionic acid, etc. Buty acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2 -Ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid and lactic acid, etc. Examples thereof include carboxylic acids of the above, and sodium salts of organic acids such as methanesulfonic acid, ethanesulfonic acid and isethionic acid. The sodium-containing compound may be used alone or in combination of two or more. Among these, sodium hydroxide or a sodium salt of an inorganic acid is more preferable as the sodium-containing compound from the viewpoint of further reducing impurities in the rectangular single crystal NaNbO ₃ particles, and sodium hydroxide, sodium nitrate, and sodium hydrogen carbonate. Alternatively, sodium carbonate is more preferred, and sodium hydroxide or sodium carbonate is particularly preferred. Here, the sodium hydroxide is most preferably sodium hydroxide, which is both a sodium-containing compound and an alkali, from the viewpoint that the addition of another alkali is not essential in order to make the solution A alkaline.

The content of the sodium-containing compound in the solution A is preferably 5 or more and 20 or less, more preferably 7 or more and 15 or less, as the ratio of the molar amount of the Na element to the molar amount of the Nb element contained in the solution A, Na / Nb. 8 or more and 12 or less are more preferable.

[Surfactant]
Solution A may further contain a surfactant. Surfactants are used to narrow the particle size distribution of rectangular parallelepiped single crystal NaNbO ₃ particles and facilitate shape control in synthesis.

The surfactant is not particularly limited as long as it is possible to synthesize rectangular parallelepiped single crystal NaNbO ₃ particles by the solvothermal synthesis treatment A in the presence thereof, and a known surfactant can be used. The surfactant is not particularly limited, and examples thereof include an amine-based surfactant, a phosphine-based surfactant, and a thiol-based surfactant. Examples of the amine-based surfactant include oleylamine, tri-n-octylamine, dodecylamine, n-octylamine, butylamine, hexylamine and the like. Examples of the phosphine-based surfactant include tri-n-octylphosphine, tri-n-hexylphosphine, and tri-n-hebutylphosphine. Examples of the thiol-based surfactant include 1-dodecanethiol and the like. The above-mentioned surfactant may be used alone or in combination of two or more. Among these, as the surfactant, an amine-based surfactant is preferable, and oleylamine is more preferable.

The content of the surfactant in the solution A is preferably 20% by mass or less with respect to the total mass of the solution A. Within this range, as a nanocube aggregate produced by the production method according to the third aspect of the present invention described later, or as an example of the dielectric porcelain composition according to the fourth aspect of the present invention, dielectric. The characteristics are further improved. The reason for this is presumed to be that epitaxial growth is promoted at the interface between the rectangular parallelepiped single crystal NaNbO ₃ particles and the nanocubes arranged adjacent to each other. From the same viewpoint, the content of the surfactant in the solution A is preferably 10% by mass or less, more preferably 1% by mass or less, and particularly preferably the solution A does not substantially contain the surfactant (lower limit 0%). ). In addition, in this specification, "substantially not contained" means that it is 0.1 mass% or less with respect to the total mass of a system.

[Other additives]
Solution A may contain other additives as long as it does not interfere with the effects of the present invention.

[solvent]
The solution A preferably further contains a solvent. The solvent that forms the Nb ₂ O ₅ sol is not included in the solvent described here.

The solvent of the solution A is not particularly limited as long as it is possible to synthesize rectangular single crystal NaNbO ₃ particles by the solvothermal synthesis treatment A in the presence thereof, and water (pure water, ion-exchanged water, ultrapure water, etc.) or A known organic solvent can be used. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, benzyl alcohol and methoxyethanol; glycols such as ethylene glycol and diethylene glycol; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; esters such as butyl acetate, ethyl acetate, carbitol acetate and butyl carbitol acetate; ethers such as methyl cellosolve, ethyl cellosolve, butyl ether and tetrahydrofuran; methyl ethanolamine , Amines such as diethanolamine; aromatics such as benzene, toluene, xylene and the like. The solvent may be used alone or in combination of two or more. Further, it may be a mixed solvent in which water is mixed with the above organic solvent.

Among these, the solvent of the solution A preferably contains alcohol, and more preferably contains two or more kinds of alcohol. When the solvent of the solution A contains two or more kinds of alcohols, the reaction is preferably carried out, and the particle sizes D50 and D90 / D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles are controlled within the range of the present invention. Will be easier. From the same viewpoint, the two or more alcohols are preferably two or more selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol, and methanol is preferable. And at least one selected from the group consisting of ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol are more preferred, and methanol and ethanol are even more preferred.

When the solvent of the solution A contains methanol and other alcohol (preferably ethanol), the content of methanol is not particularly limited, but is preferably 25% by volume or more based on the total volume of the alcohol. Within this range, it becomes easier to control the particle sizes D50 and D90 / D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles within the range of the present invention. From the same viewpoint, the content of methanol is more preferably 50% by volume or more, still more preferably 75% by volume or more, based on the total volume of alcohol. The content of methanol is not particularly limited, but is preferably 99% by volume or less with respect to the total volume of alcohol. Within this range, the formation of rectangular parallelepiped single crystal NaNbO ₃ particles is further promoted. From the same viewpoint, the content of methanol is more preferably 95% by volume or less, still more preferably 90% by volume or less, based on the total volume of alcohol.

The ratio of alcohol in the solvent of the solution A is preferably 50% by volume or more, more preferably 75% by volume or more, still more preferably 100% by volume, based on the total volume of the solvent of the solution A.

[Characteristics of solution A]
The solution A preferably contains water. In order for the solution A to contain water, water may be used as a solvent in forming the Nb ₂ O ₅ sol, water may be used as the solvent of the solution A, or both. May be good. Further, at this time, the solution A is more preferably alkaline. In the present specification, alkaline means that the pH is 7 or more. When the solution A is alkaline, the synthesis of rectangular parallelepiped single crystal NaNbO ₃ particles by the solvothermal synthesis treatment A is further promoted. From the same viewpoint, the pH of the solution A is more preferably 7 or more and 14 or less, particularly preferably 9 or more and 13 or less, and most preferably 10 or more and 13 or less.

In order to make the solution A alkaline, it is preferable that the solution A further contains an alkali. Alkali refers to a compound that dissolves in water to generate hydroxide ions (OH- ⁾ . The alkali is not particularly limited as long as it is possible to synthesize rectangular parallelepiped single crystal _NaNbO3 particles by the solvothermal synthesis treatment A in the presence thereof, and a known alkali can be used.

Here, the alkali other than sodium hydroxide, which is also a sodium-containing compound and is also an alkali, described in the above description of the sodium-containing compound is not particularly limited, but for example, ammonia or the like can be preferably used. The above alkali may be used alone or in combination of two or more.

From this, it is preferable that the production method according to one embodiment of the present invention comprises preparing a solution A containing an Nb ₂ O ₅ sol, a sodium-containing compound, and an alkali.

The amount of alkali added may be appropriately set so that the solution A becomes alkaline or has a desired pH value.

(3) Solvothermal synthesis process A
The production method according to one embodiment of the present invention includes performing a solvothermal synthesis treatment (solvothermal synthesis treatment A) using the solution A.

The definitions of the solvothermal synthesis treatment and the hydrothermal synthesis treatment are the same as the definitions in the synthesis of the Nb ₂ O ₅ sol by the solvothermal synthesis treatment B described above.

In the solvothermal synthesis treatment A, the temperature of the solution A is raised from a state of less than 50 ° C. (preferably 25 ° C.) to a temperature higher than the holding temperature at the time of the solvothermal synthesis treatment at a heating rate of 40 ° C./min or more. It is preferable to include it. Within this range, a large number of crystal nuclei will be generated due to the rapid increase in NaNbO ₃ concentration, and the particle sizes D50 and D90 / D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles will be controlled within the range of the present invention. It will be easier to do. From the same viewpoint, the heating rate is more preferably 50 ° C./min or higher, and even more preferably 60 ° C./min or higher. Further, from the viewpoint of easiness of realizing the target temperature rise rate, the solvothermal synthesis treatment A prepares the solution A from a state of less than 50 ° C. (preferably room temperature) to a temperature higher than the holding temperature at the time of the solvothermal synthesis treatment. It is preferable to include the temperature rising at a heating rate of 200 ° C./min or less. From the same viewpoint, the heating rate is more preferably 120 ° C./min or less, and further preferably 100 ° C./min or less. However, the rate of temperature rise of the solution A in the solvothermal synthesis treatment A is not limited to this.

From this, it is preferable that the production method according to one embodiment of the present invention includes the solvothermal synthesis treatment A in which the solution A is heated at a heating rate of 40 ° C./min or more and 200 ° C./min or less.

In the solvothermal synthesis treatment A, the holding temperature during the solvothermal synthesis treatment is not particularly limited, but is preferably 60 ° C. or higher and 300 ° C. or lower, more preferably 140 ° C. or higher and 260 ° C. or lower, and 180 ° C. or higher and 230 ° C. The following is more preferable. Further, in the solvothermal synthesis treatment A, the holding temperature is preferably a constant temperature.

Further, in the solvothermal synthesis treatment A, the holding time during the solvothermal synthesis treatment is not particularly limited, but is preferably 1 minute or more. Within this range, the amount of unreacted material can be further reduced when forming rectangular parallelepiped single crystal NaNbO ₃ particles. From the same viewpoint, the holding time during the solvothermal synthesis treatment is more preferably 2 minutes or more, further preferably 3 minutes or more, and particularly preferably 5 minutes or more. Further, in the solvothermal synthesis treatment A, the holding time during the solvothermal synthesis treatment is preferably 20 hours or less. Within this range, it becomes easier to suppress the formation of polycrystalline particles and to control the particle size D50 of the rectangular parallelepiped single crystal NaNbO ₃ particles to a value below a certain level. From the same viewpoint, the holding time during the solvothermal synthesis treatment is more preferably 60 minutes or less, further preferably 10 minutes or less, and particularly preferably 7 minutes or less.

In the solvothermal synthesis treatment A, the pressure during the solvothermal synthesis treatment is not particularly limited, but is preferably 0.2 MPa or more and 4.0 MPa or less. The reaction under such pressure may be carried out in a pressure-resistant container such as an autoclave, depending on the pressure required for the reaction.

The method for achieving such a temperature rise rate or reaction temperature (holding temperature) is not particularly limited, but a method of irradiating with microwaves is preferable. As the microwave irradiation device, a commercially available device may be used, and for example, a microwave synthesizer (manufactured by Milestone General Co., Ltd .: Start SYNTH) or the like can be used. The microwave output is not particularly limited, but is preferably 500 W or more and 1000 W or less. That is, it is preferable that the sorbothermal synthesis process A is realized by a method in which both the temperature rising rate and the reaction temperature (holding temperature) are irradiated with microwaves, that is, it is performed under microwave irradiation.

In the solvothermal synthesis treatment A, it is preferable that stirring is performed. The stirring method is not particularly limited, and a known method can be used. A preferable example of the stirring method is a method using a stirrer. The rotation speed at the time of stirring is not particularly limited as long as the solution A is sufficiently stirred during the solvothermal reaction, but is preferably 20 rpm or more and 2000 rpm or less, for example.

(4) Washing / Drying Treatment After synthesizing ₃ rectangular parallelepiped single crystal NaNbO particles by the above solvothermal synthesis treatment A, washing / drying may be performed as necessary. These are mainly performed to remove impurities and unreacted substances generated by synthesis. Therefore, as the cleaning solvent, a solvent that can dissolve these and does not affect the produced rectangular parallelepiped single crystal NaNbO ₃ particles is used. For example, it is preferable to use ethanol, an aqueous acetic acid solution, water or the like. The temperature of the washing solvent at this time is 10 ° C. or higher and 80 ° C. or lower in order to efficiently remove impurities and unreacted substances and to suppress the deterioration of the physical properties of the purified rectangular single crystal NaNbO ₃ particles. It is preferable to have it.

Further, the drying conditions are not particularly limited, but it is preferable to dry at 100 ° C. or higher and 150 ° C. or lower. The drying device used at this time is not particularly limited, and for example, a commonly used device such as an oven or a hot air dryer can be used. A plurality of these drying devices may be used in combination.

The atmosphere at the time of drying is not particularly limited, and the atmosphere may be the atmosphere or an atmosphere of an inert gas such as nitrogen gas or argon gas.

<Dielectric porcelain composition and its manufacturing method>
The third aspect of the present invention is to synthesize rectangular single crystal NaNbO ₃ particles by the production method according to the first aspect of the present invention, and to form a dielectric porcelain containing the rectangular single crystal NaNbO ₃ particles. The present invention relates to a method for producing a dielectric porcelain composition, which comprises molding a material forming material.

From this, the fourth aspect of the present invention is also a dielectric porcelain composition containing the single crystal NaNbO ₃ particles according to the second aspect of the present invention.

The material for forming the dielectric porcelain composition may contain other components (other components) other than NaNbO ₃ , and the other components are preferably metal oxides other than NaNbO ₃ , and include titanium. It is more preferably a metal oxide, and even more preferably barium titanate (BaTIO ₃ ). Further, as the other components, single crystal particles are preferable, rectangular parallelepiped single crystal particles are more preferable, and cubic single crystal particles are further preferable.

The method for producing the dielectric porcelain composition is not particularly limited, and for example, the rectangular single crystal NaNbO ₃ particles synthesized by the production method according to the first embodiment of the present invention, or the second embodiment of the present invention. A step (adjustment step) of preparing a dielectric porcelain composition forming material by mixing the square-shaped single crystal NaNbO ₃ particles according to the above and other components, and using the obtained dielectric porcelain composition forming material. A manufacturing method including a step of producing a molded body (green sheet) by molding (green sheet) and a step of firing the molded body (green sheet) can be mentioned. Further, for example, the rectangular single crystal NaNbO _{3 particles synthesized by the production method according to the first embodiment of the present invention, or the rectangular single crystal NaNbO 3 particles} according to the second embodiment of the present invention, and other A step of preparing a dielectric porcelain composition forming material by mixing the components (adjustment step), a step of slurry-dispersing the obtained dielectric porcelain composition-forming material (slurry dispersion step), and a slurry dispersion. Examples thereof include a manufacturing method including a step of coating a dielectric porcelain composition forming material on a substrate by dip coating using a capillary force (coating step). The method may further include a step of firing the obtained molded product after the coating step. In the manufacturing method, the adjustment step and the slurry dispersion step may be performed as the same step.

The dielectric porcelain composition is not particularly limited, but an aggregate having a three-dimensional junction structure in which single crystal particles including rectangular parallelepiped single crystal NaNbO ₃ particles are arranged is preferable. As such an aggregate, a nanocube aggregate is preferable, and a particularly preferable example of the nanocube aggregate is shown in FIG. FIG. 3 has a three-dimensional heterojunction structure in which barium titanate nanocubes and sodium niobate nanocubes (cubic single crystal NaNbO ₃ particles) are arranged and the crystal lattice is distorted at the interface thereof. , Represents a heterogeneous ferroelectric nanocube aggregate.

In FIG. 3, 1 is a heterogeneous ferroelectric nanocube aggregate, 2 is a barium titanate nanocube (that is, cubic single crystal BaTiO ₃ particles: tetragonal structure), and 3 is a sodium niobate nanocube (that is, that is). , Cube-shaped single crystal NaNbO ₃ particles: tetragonal structure). Here, 4 represents the interface between the barium titanate nanocube and the sodium niobate nanocube. Distortion of the crystal lattice occurs at such an interface, and as a result, the heterogeneous ferroelectric nanocube aggregate exhibits excellent dielectric properties.

In FIG. 3, the barium nanocube titanate and the cubic single crystal NaNbO ₃ particles are both cubic, but the configuration of the aggregate which is the dielectric porcelain composition according to the present invention is limited to this. Instead of a cube, rectangular parallelepiped single crystals having a shape other than a cube may be arranged, or a rectangular parallelepiped single crystal particle having a shape other than a cube and a cubic single crystal particle may be arranged. ..

<Use>
The rectangular parallelepiped single crystal NaNbO ₃ particles or the dielectric porcelain composition produced by the production method according to the present invention or according to the present invention are preferably used for miniaturization and large capacity of laminated chip capacitors and the like. .. These are preferably used as electronic component materials such as dielectric ceramics and dielectric ceramic compositions, particularly as electronic component materials having temperature characteristics suitable for automobiles, and in the future, electronic components for electric vehicles. It is also expected to be used as a material.

The effects of the present invention will be described with reference to the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples.

(Example 1)
<Preparation of Nb ₂ O ₅ sol>
[Preparation of solution B]
5 g of NbCl ₅ (manufactured by High Purity Chemical Laboratory Co., Ltd.) was weighed, and 10 ml of ethanol was added thereto to prepare a solution. While stirring this solution, this solution was added dropwise to 200 ml of 0.3 mol / L ammonia water to form a precipitate of Nb ₂ O ₅ · nH ₂ O. Then, the solution containing this precipitate was centrifuged at 10000 rpm for 5 minutes to remove the supernatant to obtain a precipitate Nb ₂ O ₅ · nH ₂ O. A solution B was prepared by adding 20 ml of hydrogen peroxide solution having a concentration of 30% by mass to the obtained precipitate Nb ₂ O ₅ · nH ₂ O in a state of being cooled by ice water while stirring. Here, hydrogen peroxide solution was added so that the molar ratio of Nb element and H ₂ O ₂ was Nb element: H ₂ O ₂ = 1:10.

[Solvothermal synthesis process B]
The obtained solution B is placed in an autoclave container (manufactured by San-ai Kagaku Co., Ltd.) and reacted at 75 ° C. for 24 hours to perform solvothermal synthesis treatment _B (hydrothermal synthesis treatment). ₅ sol was prepared. Here, in the solvothermal synthesis treatment B, the pressure in the reaction system during holding was 0.2 MPa or more.

<Synthesis of ₃ rectangular parallelepiped single crystal NaNbO particles>
[Preparation of solution A]
The above-mentioned Nb ₂ O ₅ sol: 0.25 mmol in terms of Nb element, NaOH: 5 mmol, methanol: 30 ml, ethanol: 10 ml are weighed, and the solution A is placed in a 100 ml microwave synthesizer container. Prepared.

[Solvothermal synthesis process A]
The obtained solution A is heated to 200 ° C. in 3 minutes under a microwave irradiation environment with an output of 800 W while stirring at 200 rpm using a microwave synthesizer (manufactured by Milestone General Co., Ltd .: Start SYNTH). After a rate of 66.7 ° C./min), solvothermal synthesis treatment A was performed under the conditions of holding at 200 ° C. for 5 minutes to prepare a product solution. Here, in the solvothermal synthesis treatment A, the pressure in the reaction system at the time of raising the temperature after a certain period of time from the start of the temperature rise and the pressure in the reaction system at the time of holding were 0.2 MPa or more.

[Washing / drying process]
The obtained product solution was centrifuged at 10000 rpm for 5 minutes, and the supernatant was removed to remove the product. After adding this product to ethanol to prepare an ethanol solution, the ethanol solution is centrifuged at 10000 rpm for 5 minutes, and the supernatant is removed to wash the particles and dry at 80 ° C. The product was obtained.

[evaluation]
The obtained product was identified by performing XRD (X-ray diffraction) measurement under the conditions of a voltage of 40 kV and a current of 30 mA using a sample horizontal multipurpose X-ray diffractometer Ultra IV manufactured by RIGAKU Co., Ltd., and FEI. It was confirmed that the crystal was a single crystal by performing TEM (Transmission Electron Microscope) electron diffraction under the condition of an acceleration voltage of 200 kV using Tecnai Osiris manufactured by company.

Furthermore, the shape of the particles of the obtained product is confirmed by observing the SEM (Scanning Electron Microscope) using JSM-6500 manufactured by JEOL Ltd. under the condition of an acceleration voltage of 15 kV. The individual particle sizes were measured, and the particle sizes D50 and D90 were calculated from the measurement results.

Here, in the TEM electron diffraction, it was confirmed that the particles of the obtained product were single crystals because the diffraction spots (spots) were regularly arranged in the electron diffraction pattern.

(Example 2)
In the solvothermal synthesis treatment B, an Nb ₂ O ₅ sol was prepared in the same manner as in Example 1 except that the hydrothermal synthesis treatment using an autoclave container was carried out under the conditions of 75 ° C. and 168 hours to obtain a product. Then, the particles obtained in the same manner as in Example 1 were evaluated.

(Example 3)
In the solvothermal synthesis treatment B, an Nb ₂ O ₅ sol was prepared in the same manner as in Example 1 except that the hydrothermal synthesis treatment using an autoclave container was carried out at 95 ° C. for 24 hours, and a product was obtained. Then, the particles obtained in the same manner as in Example 1 were evaluated.

(Example 4)
In the solvothermal synthesis treatment B, an Nb ₂ O ₅ sol was prepared in the same manner as in Example 1 except that the hydrothermal synthesis treatment using an autoclave container was carried out under the conditions of 95 ° C. and 168 hours to obtain a product. Then, the particles obtained in the same manner as in Example 1 were evaluated.

(Comparative Example 1)
Nb ₂ O ₅ powder: 0.25 mmol (manufactured by Kishida Chemical Co., Ltd.) in terms of Nb element, NaOH: 5 mmol, methanol: 30 ml, ethanol: 10 ml, respectively, weighed and placed in a 100 ml microwave synthesizer container to prepare the solution. Prepared. Here, the Nb ₂ O ₅ powder was precipitated in the solution and did not form a sol.

While stirring this solution at 200 rpm using a microwave synthesizer (manufactured by Milestone General Co., Ltd .: Start SYNTH), the temperature rises to 200 ° C. in 3 minutes under a microwave irradiation environment with an output of 800 W (heating rate 66. After 7 ° C./min), a solvothermal synthesis treatment was carried out under the conditions of holding at 200 ° C. for 60 minutes to prepare a product-containing solution.

The obtained product-containing liquid was taken out in the same manner as in Example 1, washed and dried, and evaluated in the same manner as in Example 1.

(Comparative Example 2)
Nb (C ₂ H ₅ O) ₅ : 0.25 mmol (manufactured by Wako Pure Chemical Industries, Ltd.) in terms of Nb element, NaOH: 5 mmol, methanol: 30 ml, ethanol: 10 ml, respectively, weighed and used for a 100 ml microwave synthesizer. The solution was prepared in a container.

While stirring this solution at 200 rpm using a microwave synthesizer (manufactured by Milestone General Co., Ltd .: Start SYNTH), the temperature rises to 200 ° C. in 3 minutes under a microwave irradiation environment with an output of 800 W (heating rate 66. After 7 ° C./min), a solvothermal synthesis treatment was carried out under the conditions of holding at 200 ° C. for 60 minutes to prepare a product-containing solution.

The obtained product-containing liquid was taken out in the same manner as in Example 1, washed and dried, and evaluated in the same manner as in Example 1.

Here, for the product of Example 3, the XRD results are shown in FIG. 1, and the SEM observation results are shown in FIG. 2, respectively.

From the results of FIG. 1, it was confirmed that the product was crystalline NaNbO ₃ from the obtained peak position. In the XRD spectrum of FIG. 1, "before reaction" means before solvothermal synthesis treatment A, and "after reaction" means after solvothermal synthesis treatment A.

In FIG. 2, (a) is an imaged SEM photograph, and (b) is an enlarged SEM photograph for one particle. From this, it can be confirmed that the obtained particles are cubic.

Similar results to those of Example 3 were confirmed for the products of Examples 1, 2 and 4, although the average particle size and D90 / D50 were different.

The conditions of the reaction temperature and reaction time of the solvothermal synthesis treatment B in each example and each comparative example, the Nb source in the solvothermal synthesis treatment A, and the characteristics of the obtained particles are summarized in Table 1 and Table 2 below, respectively. In Table 2 below, particles with an average particle size of 5 nm or more and 100 nm or less and D90 / D50 of 1.01 or more and 1.40 or less are judged as ◯, and particles that do not meet this average particle size or the range of D90 / D50 are defined as ×. Judged.

From the above results, according to the production methods of Examples 1 to 4 according to the present invention, the particle size D50, which is a 50% diameter in the integrated fraction based on the number of particles in the particle size distribution, is 5 nm or more and 100 nm or less, and the number of particles in the particle size distribution. A rectangular parallelepiped (cubic in the above example) single crystal NaNbO having a particle size D90 having a diameter of 90% in the standard integrated fraction and a ratio of D90 / D50 to D50 of 1.01 or more and 1.4 or less. It was confirmed that ₃ particles were produced.

Due to their small average particle size and narrow particle size distribution, these particles are nanocube aggregates having a three-dimensional junction structure in which nanocubes containing rectangular parallelepiped single crystal NaNbO ₃ particles are arranged, especially in FIG. It is expected to be applied to nanocube aggregates as shown.

On the other hand, unlike the production method according to the present invention, it was confirmed that the target particles were not formed in the production methods of Comparative Example 1 and Comparative Example ₂ in which the _Nb2O5 sol was not used as the Nb source.

1 Heterogeneous ferroelectric nanocube aggregate,
2 Barium titanate nanocubes,
3 Sodium niobate nanocubes,
4 Interface.

Claims (9)

To prepare an Nb ₂ O ₅ sol solution containing an Nb ₂ O ₅ sol and a sodium-containing compound, and
Solvothermal synthesis treatment using the Nb ₂ O ₅ sol solution and
A method for producing ₃ rectangular parallelepiped NaNbO particles, which comprises.
In the particle size distribution of the rectangular single crystal NaNbO ₃ particles, the particle size D50, which is 50% of the number-based integrated fraction, is 5 nm or more and 100 nm or less, and the particle size distribution is 90 in the number-based integrated fraction. The ratio of the particle size D90, which is the% diameter, to the D50, D90 / D50, is 1.01 or more and 1.4 or less.
The Nb ₂ O ₅ sol solution further contains two or more alcohols.
The two or more alcohols include methanol and ethanol.
The solvothermal synthesis treatment using the Nb ₂ O ₅ sol solution includes raising the temperature of the Nb ₂ O ₅ sol solution at a heating rate of 40 ° C./min or more and 200 ° C./min or less.
A method for producing ₃ rectangular parallelepiped single crystal NaNbO particles. The method for producing rectangular parallelepiped single crystal NaNbO ₃ particles according to claim 1, wherein the Nb ₂ O ₅ sol solution does not substantially contain a surfactant. The method for producing rectangular parallelepiped single crystal NaNbO ₃ particles according to claim 1 or 2, wherein the Nb ₂ O ₅ sol solution is alkaline. The method for producing rectangular parallelepiped single crystal NaNbO ₃ particles according to any one of claims 1 to 3, wherein the solvothermal synthesis treatment is performed under microwave irradiation. Prior to the preparation of the Nb ₂ O ₅ sol solution, further comprising synthesizing the Nb ₂ O ₅ sol by a sorbothermal synthesis treatment using a solution containing Nb ₂ O ₅ hydrate or hydroxide. The method for producing ₃ rectangular single crystal NaNbO particles according to any one of claims 1 to 4. In the synthesis of the Nb ₂ O ₅ sol, the solvothermal synthesis treatment using the solution containing the hydrate or hydroxide of the Nb ₂ O ₅ is maintained at 60 ° C. or higher and 200 ° C. or lower for 1 hour or more and 500 hours or less. The method for producing ₃ square-shaped single crystal NaNbO particles according to claim 5. The particle size D90 having a particle size D50 which is 50% diameter in the number-based integrated fraction in the particle size distribution is 5 nm or more and 100 nm or less, and has a particle size D90 which is 90% diameter in the number-based integrated fraction in the particle size distribution. D90 / D50, which is the ratio to the particle size D50, is 1.01 or more and 1.4 or less.
Rectangular parallelepiped single crystal NaNbO ₃ particles. The production method according to any one of claims 1 to 6 is used to synthesize rectangular single crystal NaNbO ₃ particles, and to form a dielectric porcelain composition-forming material containing the rectangular single crystal NaNbO ₃ particles. A method for producing a dielectric porcelain composition, including. A dielectric porcelain composition comprising the rectangular parallelepiped single crystal NaNbO ₃ particles according to claim 7.

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