KR100627632B1 - Wet- chemical synthesis of highly dispersible crystalline barium titanate into organic solvents - Google Patents

Abstract

The present invention relates to a method for preparing crystalline barium titanate (BaTiO ₃ ) nanoparticles having excellent organic solvent dispersibility, and more specifically, (a) after dissolving titanium alkoxide in a solvent, β-diketone compound or organic carbohydrate. Adding carbonyl acid dropwise to form a chelated titanium compound; (b) slowly adding the solution (a) to the aqueous barium hydroxide solution and then stirring to form a barium titanate; And (c) separating the barium titanate; Characterized in that it comprises a.

The crystalline barium titanate prepared by the production method according to the present invention has an average particle diameter of 100 nm or less, which has a small particle size and uniformity and high dispersibility in an organic solvent, requiring high dielectric constant and flexibility. It is suitable for the manufacture of organic hybrid type high dielectric nanocomposite, and its application is expected to be applied to the advanced electronic industry such as embedded capacitor for printed circuit board (PCB) or gate insulator film such as organic semiconductor (OTFT). do.

 Barium titanate, wet-chemical process, organic solvent dispersibility

Description

Method for producing crystalline barium titanate having high dispersibility in organic solvents {Wet- chemical synthesis of highly dispersible crystalline barium titanate into organic solvents}

1 is an X-ray diffraction analysis of the barium titanate prepared in Example 1,

2 is an X-ray diffraction analysis of the barium titanate prepared in Example 2,

3 is an X-ray diffraction analysis of the barium titanate prepared in Example 3,

4 is a transmission electron microscope (TEM) photograph of the barium titanate prepared in Example 1,

5 is a scanning electron microscope (SEM) photograph of the barium titanate prepared in Example 1,

6 is a view showing the dispersibility test results of barium titanate prepared in Example 1 and Comparative Examples.

The present invention relates to a method of preparing crystalline barium titanate (BaTiO ₃ ) nanoparticles having excellent dispersibility in an organic solvent in a low temperature solution, and more specifically, chelated with β-diketone compound or organic carbonyl acid. The present invention relates to a method for preparing nanocrystalline barium titanate by chemical decomposition / bonding method in a low temperature solvent using titanium alkoxide and barium hydroxide [Ba (OH) ₂ )] solution.

Perovskite phase mixed oxides such as barium titanate (BaTiO ₃ ) have excellent properties in terms of ferroelectricity, piezoelectricity, chemical and physical properties such as catalysts and oxygen carriers. These good properties are mainly dependent on the size, structure, shape, stoichiometry, homogeneity, and surface and interface properties of the crystal. Since barium titanate has a very high dielectric constant due to the nature of crystals, barium titanate has been used for a long time in various materials for electronic components such as capacitors and capacitors. The high dielectric constant is due to the high polarizability of the relatively simple lattice structure, which is consistent with the TiO ₆ -octahedral structure. Barium titanate has a high degree of polarization because small Ti (IV) ions have a relatively large space in the octahedron of oxygen. The stability of the structure is very closely related to the Curie temperature (130 ° C), and at temperatures below the Curie temperature, Ti (IV) ions occupy a position off-center. Therefore, the crystal structure is changed, and the structure is changed from cubic to tetragonal at 5 ° C. to 130 ° C., and is orthohombic at -90 ° C. to 5 ° C., below -90 ° C. Is transformed into a rhombohedral structure. Therefore, the dielectric constant of barium titanate also changes depending on the stability of the crystal structure. The stability between the cubic and tetragonal, two phases also depends on the size of the barium titanate nanocrystals (Y. Kobayashi, A. Nishikata, T. Tanase and M. Konno, J. Sol-Gel Sci. Technol ., 2004 , 29 , 49), and the critical size is reported to be 50 nm (K. Ishikawa, K. Yoshikawa and N. Okada, Phys. Rev. , 1998, B 37 , 5852; S. Schlag and H. F. Eicke, Solid State Commun ., 1994, 91 , 883). Dependence of the dielectric constant of barium titanate on particle size has been reported in other reports (G. Arlt, D. Hennings and G. de With, J. Appl. Phys. , 1985, 58 , 1619; PK Dutta, R. Asiaie, SK Akbar and W. Zhu, Chem. Mater. , 1994, 6 , 1542; PR Arya, P. Jha and AK Ganguli, J. Mater. Chem. , 2003, 13 , 415)

Recently, various attempts have been made to prepare barium titanate-polymer nanocomposite compositions for electronic applications such as embedded capacitors, multilayer ceramic capacitors (MLCC), and printed circuit boards (PCBs). The preparation of the composite has been of major concern because of its ease of process and flexibility by the polymer medium and the improvement of electrical properties by the inorganic components. However, very few reports have been made of barium titanate with polymers because organic polymers have relatively low thermal stability and inorganic materials require high thermal energy to crystallize. Therefore, attempts have been made to produce inorganic / organic hybrid materials by preparing barium titanate nanoparticles and then mixing crystalline nanoparticles with an organic polymer medium to prevent thermal decomposition of the composition (H. Hsiang, K.-Y. Lin). , F.-S. Yen, C.-Y. Hwang, J. Mater. Sci ., 2001, 36 , 3809; Y. Rao and CP Wong, J. Appl. Polym. Sci ., 2004, 92 , 2228) . However, a mixture which simply mixes crystalline barium titanate prepared by conventional methods such as homogeneous co-precipitation, hydrothermal synthesis and sol-gel method with an organic medium has a high degree of dispersibility of agglomeration of nanoparticles and dispersibility of inorganic particles into an organic medium. As it becomes worse, there is a difficulty in producing a hybrid organic / organic hybrid material having excellent uniformity.

Given the increasing technical demands of electronic components and the demand for nanoparticles based on barium titanate, the high dispersibility of crystal grains into the organic medium must be considered very important. Several attempts have been made to overcome this problem. For example, a method of denaturing the surface of nanoparticles prepared in advance using oleic acid or acetic acid has been known for a long time, but due to the difficulty of removing agglomeration of nanoparticles having a high specific surface area, There is a limit to the high concentration dispersion into the medium. In addition, Brieten et al. Synthesized a monodisperse barium titanate using a Ba-Ti-alkoxide precursor, but the prepared barium titanate has low crystallinity and low dielectric properties are expected (S. O'Brien, L. Brus and CB Murray, J. Am. Chem. Soc ., 2001, 123 , 1208).

In order to solve the above problems, the present inventors have proposed a method of allowing organic functional groups having good affinity to organic materials to still exist on the surface of crystalline barium titanate, that is, β-diketone in titanium alkoxide, which is an important starting material for barium titanate production. Chelated titanium compound is prepared by dropwise addition of a compound or organic carbonyl acid, and a barium hydroxide solution dissolved in an aqueous solution is added dropwise to prepare crystalline barium titanate nanoparticles in solution by chemical decomposition / synthesis at low temperature. It was successful. The crystalline barium titanate thus prepared has excellent crystallinity as compared to barium titanate reported by Brieten et al. Without using expensive Ba-Ti-alkoxide precursors, and is essential in the process of barium titanate-polymer systems. Dispersibility in organic solvents, which can be a property, has been greatly improved.

Accordingly, an object of the present invention is to provide a method for preparing nanocrystalline barium titanate in solution using a specially designed starting material for barium titanate, which is expected to have high dielectric constant due to high crystallinity without a separate heat treatment process at a high temperature. It is.

In addition, another object of the present invention is crystalline barium titanate nanoparticles having excellent crystallinity and high dispersibility in an organic solvent, compared to conventional barium titanate without using an expensive Ba-Ti-alkoxide precursor. It is to provide an economical and effective method for producing the particles.

The present invention adds a [beta (d-diketonate) ₃ ] ⁺ or [Ti derived from a β-diketone compound such as acetylacetone or an organic carbonyl acid such as acrylic acid to titanium alkoxide. (Carbonate) ₃ ] ⁺ Crystalline barium titanate of uniform particle size with high dispersibility in an organic solvent by a method for producing crystalline barium titanate nanoparticles by chemical decomposition / synthesis using an aqueous solution of barium hydroxide and ⁺ To provide.

Nanocrystalline barium titanate production method according to the present invention

(a) Titanium alkoxide is dissolved in a solvent, and then a beta -diketone compound such as acetylacetone or an organic carbonyl acid such as acrylic acid is added dropwise to [Ti (β-diketonate) ₃ ] ⁺ or [Ti ( Carbonate) ₃ ] ⁺ forming a compound;

(b) slowly adding the solution (a) to the aqueous barium hydroxide solution and then stirring to form a barium titanate; And

(c) separating the barium titanate;

It includes, all the above steps are characterized in that the production under N ₂ atmosphere.

The step of forming [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ is a β-diketone compound such as titanium alkoxide and acetylacetone or an acrylic acid such as The Ti precursor [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ complex is prepared by reaction with an organocarbonyl acid.

The titanium alkoxide may include titanium methoxide [titanium (IV) methoxide], titanium butoxide [titanium (IV) butoxide], titanium isopropoxide [titanium (IV) isopropoxide] and the like regardless of the type of starting material. Although it can be used, it is preferable to use titanium alkoxide which is easy to obtain and inexpensive.

The β-diketone compound coordinates with Ti (IV) ions as a chelate to form [Ti (β-diketonate) ₃ ] ⁺ complex. Β-diketone compounds that can be used are represented by the following formula (1).

[Formula 1]

In the above formula, R and R 'are independently C ₁ ~ C ₁₀ linear or branched alkyl group or aryl group. Examples of the alkyl group include methyl group, ethyl group, propyl group or t-butyl group and the like, and specific compounds include 2,4-pentandione (acetylacetone), 2,2,6,6-tetramethyl -3,5-heptanedione (2,2,6,6-tetramethyl -3,5-heptanedione). The aryl group includes, for example, a phenyl group and a benzyl group.

The process of forming a Ti complex will be described using, for example, acetylacetone, which is one of diketone compounds. Β-diketone, such as acetylacetone, has a keto-enol tautomer form, as shown in Scheme 1 below, and the enol form easily forms a metal ion (Ti ⁴⁺ ) and Coordination results in the formation of a triconfiguration complex, [Ti (acac) ₃ ] ⁺ (Scheme 2).

In addition, as the organic carbonyl acid, acrylic acid (acryl acid), lactic acid (lactic acid), etc. may be used to form Ti (carbonate) ₃ ] ⁺ complex in a similar manner to β-diketone. do.

Scheme 1

Scheme 2

The solvent used in the production method according to the present invention may be any solvent as long as it can dissolve all of the reacted titanium alkoxide and β-diketone compound and the resulting Ti complex, ethanol and isopropanol, Solvents of alcohols such as propanol are preferred because they can be mixed well with the aqueous solution.

[Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ complex prepared in step (a) was found to be very stable in aqueous solution, and the prepared Ti complex was added to the aqueous solution of barium hydroxide. When a chemical reaction occurs between [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ complex and Ba (OH) ₂ , a crystalline barium titanate is produced in an aqueous solution.

The barium hydroxide is preferably used in an amount of 2.5 to 5 molar ratio with respect to titanium alkoxide. The formation of barium titanate crystals in solution is highly dependent on the concentration of Ba (OH) ₂ (molar ratio of Ba / Ti). Experimental results of varying the molar ratio of Ba / Ti to determine the effect of Ba ion concentration showed that the crystalline barium titanate appeared only in the region where the molar ratio of Ba / Ti was 2.5 or more, whereas the Ba / Ti molar ratio was 2.5 If less, no crystalline phase was observed. This means that the Ba / Ti molar ratio plays an important role in producing barium titanate crystals in solution. From the XRD results, at high Ba (OH) ₂ concentrations (Ba / Ti molar ratio of 2.5 or more and pH of 13 or more), the Ti complex was first decomposed by Ba (OH) ₂ , and thus Ba [OH ( ₆ ) ^2- than Ba [ After the formation of Ti (OH) ₆ ], it is presumed to form crystalline barium titanate in solution as shown in Schemes 3 to 5 below.

Scheme 3

2 [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ + 5Ba (OH) ₂ + 2OH ⁻

= 3Ba (β-diketonate) ₂ + 2Ba [Ti (OH) ₆ ]

Scheme 4

2 [Ti ^{_{(carbonate) 3] + + 5Ba (OH}} ) 2 + 2OH - = 3Ba ( carbonate) ₂₊

2Ba [Ti (OH) ₆ ]

Scheme 5

Ba [Ti (OH) ₆ ] = BaTiO ₃ + 3 H ₂ O

Hexahydroxy titanate (IV), [Ti (OH) ₆ ] ^2- formation under strong alkaline conditions was reported by Kiss et al. Intermediate Ba [Ti (OH) ₆ ] cannot be produced under relatively low Ba ²⁺ ion concentrations (Ba / Ti molar ratio of less than 2.5), in which case it is decomposed directly to Ti (OH) ₄ , which is amorphous TiO. Becomes ₂ (Scheme 6 ~ 8)

Scheme 6

2 [Ti (β-diketonate) ₃ ] ⁺ or 2 [Ti (carbonate) ₃ ] ⁺ + 3Ba (OH) ₂ + 2OH ⁻

= 3Ba (β-diketonate) ₂ + ₂ Ti (OH) ₄

Scheme 7

2 [Ti ^{_{(carbonate) 3] + + 3Ba (OH}} ) 2 + 2OH - = 3Ba ( carbonate) ₂ + 2Ti (OH) ₄

Scheme 8

Ti (OH) ₄ = TiO ₂ + 2 H ₂ O

The reason why the Ba / Ti molar ratio should be high initially is that 1.5 mol of Ba (OH) ₂ is used to form barium (β-diketonate) ₂ or barium (carbonate) ₂ . Ba (β-diketonate) ₂ or barium (carbonate) ₂ is a stable compound in alkaline media. At low Ba concentrations, Ba [Ti (OH) ₆ ] intermediates cannot be produced and thermally stable Ti (OH) ₄ is produced and eventually converted to amorphous TiO ₂ by condensation polymerization of Ti (OH) ₄ . Samples having a Ba / Ti molar ratio of 1.0 to 1.5 were heat treated at 800 ° C. for 2 hours to form TiO ₂ crystals, which were confirmed by the reaction schemes 5-6.

The formation of barium titanate crystals in solution is highly dependent on temperature. The reaction temperature at which a chemical reaction takes place between [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ complex and Ba (OH) ₂ is preferably 70 ° C. to 95 ° C. In order to confirm the influence of temperature related to the formation of barium titanate in the solution, the Ba / Ti molar ratio was fixed at 2.5, and the experiment was performed for 1 hour while changing from 50 ° C to 95 ° C. As a result, barium titanate crystals were formed in all cases except those below 70 ° C. When the chelate was not used, crystals were formed even below 50 ° C, but in this case using a chelate such as β-diketone compound, crystals were formed only at a relatively high temperature, that is, above 70 ° C. This means that the titanium alkoxide directly produces Ba [Ti (OH) ₆ ] under strong alkali such as Ba (OH) ₂ (pH ≧ 13). However, in the present invention, [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ is considerably more stable than Ti (OPr ⁱ ) _{4 and} thus [Ti (β-diketonate) ₃ ] ⁺ Or it is interpreted that more activation energy is required to decompose [Ti (carbonate) ₃ ] ⁺ to form Ba [Ti (OH) ₆ ].

The reaction time for forming the barium titanate is related to the Ba / Ti molar ratio and temperature, the reaction time is selected in the range of 30 minutes to 5 hours. When the reaction temperature is high and the Ba / Ti molar ratio is high, the reaction time is relatively low, and when the reaction temperature is low and the Ba / Ti molar ratio is low, the reaction time is relatively long.

The barium titanate prepared in step (b) is separated through a centrifuge, washed with deionized water and dried in air to prepare a nanocrystalline barium titanate in solid state.

As a result of analyzing the diffraction pattern of the solid crystalline barium titanate obtained after drying at room temperature using an X-ray powder diffractometer, the diffraction peaks characteristic of barium titanate were well observed as shown in FIGS. 1 to 3. The lattice parameters for the cubic cells calculated from the XRD results were found to have a range of 4.043 to 4.047 ± 0.0012, which is slightly larger than the standard value (a = 4.031). The grain size of the nanocrystalline barium titanate is the Scherer equation [D = kλ / h _1/2 cosθ, where k is a constant 0.9, λ is 1.5418 으로 in the wavelength of the X-ray, h _1/2 is the angle θ XRD peak mean the height of the interval.] It was observed to have a range of 33 ~ 50 nm depending on the reaction temperature. The crystal size decreased slowly with increasing reaction temperature and increased very slowly with increasing reaction time. The slight decrease in crystal size over time is due to the very low growth rate of the nanocrystals present in solution due to the loss of small particles over time called Oswald ripening. The decrease in crystal size with temperature can be explained by considering the process of nucleation and growth during nanocrystal formation. The rate of crystal growth with temperature in solution phase is much smaller than in the reaction in the solid state. In the precipitation process, the growth rate is k · a · s, where k is a specific system constant, a is the area of the solid being grown, and s is the degree of supersaturation. It has been reported that a large number of nuclei are produced at high supersaturation and crystal growth may be slowed down during competitive crystal growth (SD Sathaye, KR Patil, DV Paranjape, A. Mitra, SV Awate and AB Mandale, Langmuir , 2000, 16 , 3487). In the present case, the decrease in crystal size of barium titanate according to temperature can be explained by the fact that the number of nuclei generated as the temperature increases as the above phenomenon decreases the crystal size.

The microstructure of the barium titanate nanoparticles prepared above was confirmed by transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively, and are shown in FIGS. 4 and 5, respectively. The polycrystalline nature of the particles was observed on the TEM micrographs and the SEM pictures showed that the particles were almost spherical in shape. The particle size obtained from the TEM and SEM photographs ranged from 50 to 80 nm, which was found to be slightly larger than the value calculated from Scherer's equation (33-50 nm). This is because the particles aggregate when the solvent is removed from the nanoparticles.

In the present invention, the barium titanate separated in the step (c) is added to an organic solvent selected from NMP (N-methyl-2-pyrollidone) or DMF (N, N-dimethyl formamide), and the liquid is monodispersed in the organic solvent. It includes a method for producing barium titanate, and as a method of dispersing, a physical method commonly used such as ultrasonication can be used.

Analysis using the Dynamic Light Scattering (DLS) technique, which provides the particle size and distribution as a function of time, has shown that barium titanate dispersed in an organic solvent has an average particle diameter of 70 to 100 nm. The particle distribution initially had a larger value of about 10 nm, but after 6 to 8 hours, on average, about 70 to 100 nm, it remained stable and almost unchanged for several days. This means that relatively larger particles are produced through the reaction of smaller particles (Ostwald repining), and the larger particles initially settle very quickly, resulting in a stable sol.

FIG. 6 shows the weight of barium titanate particles retained per 1 g of NMP solvent over time. The barium titanate prepared without using the β-diketone compound as in Comparative Example is precipitated within 24 hours after dispersing in an organic solvent, and the weight remaining in the solvent rapidly decreases, and gradually decreases thereafter. Barium titanate prepared by chemical decomposition of [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ^{+ according} to the present invention was confirmed to maintain the remaining weight after 7 days. It was. This means that the presence of β-diketone groups or alkylcarbonate groups in the production method of the present invention helps to prevent the aggregation of particles, and the aggregation of particles not containing β-diketone or alkylcarbonate groups Means that it runs at a high speed and continues over time. Coordination with β-diketone or alkylcarbonate groups on the surface of the oxide powder particles prevents the particles from agglomerating and serves to improve dispersibility in an organic solvent. However, adding acetylacetone to the barium titanate sol prepared in the comparative example had no effect on the aggregation of the particles. This means that large particles have already been formed during the reaction, and cannot be redispersed with an organic solvent by a post-treatment method with β-diketone groups or alkylcarbonate groups on the surface of the already formed large particles. Therefore, it can be seen that the method for producing the crystalline barium titanate particles plays an important role in the dispersibility in an organic solvent, and [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ Through chemical decomposition by the aqueous solution of barium hydroxide of barium titanate which is well dispersed in the solution and good crystallinity can be provided, and the β-diketone group or alkylcarbonate group present in the manufacturing process NMP of barium titanate It can be seen that it improves the dispersibility in an organic solvent such as (M-methyl-2-pyrollidone) or N, N-dimethylformamide (DMF).

Hereinafter, the present invention will be described in detail with reference to the following Examples, the following examples are merely illustrative of the present invention, the present invention is not limited by the examples.

Example 1

Titanium isopropoxide (Ti (OPr ⁱ ) 4 or TTIP, 97% Aldrich) and barium hydroxide octahydrate (98 +%, Aldrich) used in the present invention were used without further purification. . All other chemicals and solvents were reagent grades sold by Sigma-Aldrich and used as purchased without further purification. Deionized water was used to purge dry nitrogen (N ₂ ) to remove CO ₂ .

Titanium isopropoxide (2.5 g, 8.8 mmol) was dissolved in 2-propanol (10 g) and then acetylacetone (Hacac, 2.64 g, 26.4 mmol) was added dropwise. After stirring the reaction mixture at room temperature for 30 minutes, the solution turns yellowish yellow as [Ti (acac) ₃ ] ⁺ is produced. Deionized water (10 g) was then added to the solution and stirring continued for 30 minutes. This solution was used as Ti precursor.

In a two-necked round flask containing 50 g of deionized water without CO ₂ , Ba (OH) ₂ .8H ₂ O (6.94 g, 22.0 mmol) was dissolved at 50 ° C.

[Ti (acac) ₃ ] ⁺ solution was added slowly to the barium hydroxide solution while blowing N ₂ to prevent BaCO ₃ from being generated by CO ₂ in air at 50 ° C., and then stirred at 95 ° C. for 3 hours. . The solid particles were separated at 17,000 rpm in a high speed centrifuge and washed with deionized water without CO ₂ to obtain barium titanate powder.

Example 2

Titanium isopropoxide (Ti (OPr ⁱ ) 4 or TTIP, 97% Aldrich) and barium hydroxide octahydrate (98 +%, Aldrich) used in the present invention were used without further purification. . All other chemicals and solvents were reagent grades sold by Sigma-Aldrich and used as purchased without further purification. Deionized water was used to purge dry nitrogen (N ₂ ) to remove CO ₂ .

Titanium isopropoxide (2.5 g, 8.8 mmol) was dissolved in 2-propanol (10 g) and acrylic acid (HAcr, 1.91 g, 26.5 mmol) was added dropwise. After stirring the reaction mixture at room temperature for 30 minutes, the solution turns yellowish yellow as [Ti (Acr) ₃ ] ⁺ is produced. Deionized water (10 g) was then added to the solution and stirring continued for 30 minutes. This solution was used as Ti precursor.

In a two-necked round flask containing 50 g of deionized water without CO ₂ , Ba (OH) ₂ .8H ₂ O (6.94 g, 22.0 mmol) was dissolved at 50 ° C.

[Ti (Acr) ₃ ] ⁺ solution was added slowly to the barium hydroxide solution while blowing N ₂ to prevent BaCO ₃ from being generated by CO ₂ in air at 50 ° C., and then stirred at 70 ° C. for 5 hours. . The solid particles were separated at 17,000 rpm in a high speed centrifuge and washed with deionized water without CO ₂ to obtain barium titanate powder.

Example 3

Titanium isopropoxide (Ti (OPr ⁱ ) 4 or TTIP, 97% Aldrich) and barium hydroxide octahydrate (98 +%, Aldrich) used in the present invention were used without further purification. . All other chemicals and solvents were reagent grades sold by Sigma-Aldrich and used as purchased without further purification. Deionized water was used to purge dry nitrogen (N ₂ ) to remove CO ₂ .

Titanium isopropoxide (2.5 g, 8.8 mmol) was dissolved in 2-propanol (10 g) followed by the dropwise addition of lactic acid (HLa, 2.38 g, 26.42 mmol). After stirring the reaction mixture for 30 minutes at room temperature the solution turns yellowish yellow as [Ti (La) ₃ ] ⁺ is produced. Deionized water (10 g) was then added to the solution and stirring continued for 30 minutes. This solution was used as Ti precursor.

In a two-necked round flask containing 50 g of deionized water without CO ₂ , Ba (OH) ₂ .8H ₂ O (6.94 g, 22.0 mmol) was dissolved at 50 ° C.

[Ti (La) ₃ ] ⁺ solution prepared above is slowly added to the barium hydroxide solution while blowing N ₂ such that BaCO ₃ is not produced by CO ₂ in air at 50 ° C., and then stirred at 80 ° C. for 4 hours. . The solid particles were separated at 17,000 rpm in a high speed centrifuge and washed with deionized water without CO ₂ to obtain barium titanate powder.

[Comparative Example]

Titanium isopropoxide (Ti (OPr ⁱ ) 4 or TTIP, 97% Aldrich) and barium hydroxide octahydrate (98 +%, Aldrich) used in the present invention were used without further purification. . All other chemicals and solvents were reagent grades sold by Sigma-Aldrich and used as purchased without further purification. Deionized water was used to purge dry nitrogen (N ₂ ) to remove CO ₂ .

Titanium isopropoxide (2.5 g, 8.8 mmol) is dissolved in 2-propanol (10 g). In a two-necked round flask containing 50 g of deionized water without CO ₂ , Ba (OH) ₂ · 8H ₂ O (3.3 g, 10.56 mmol) was dissolved at 50 ° C.

The titanium isopropoxide solution prepared above was slowly added to the barium hydroxide solution while blowing N ₂ to prevent BaCO ₃ from being generated by CO ₂ in air at 50 ° C., and then stirred at 95 ° C. for 3 hours. The solid particles were separated at 17,000 rpm in a high speed centrifuge and washed with deionized water without CO ₂ to obtain barium titanate powder.

Example 4

In order to analyze the crystallinity and structure of the solid barium titanate prepared in Examples 1 to 3 by X-ray powder diffraction analysis (XRD, Rigaku D / Max-2200V) using CuKα (1.5418 Å) 1 to 3 are shown. It was confirmed that the crystalline barium titanate had a Ba / Ti molar ratio of 2.5 or more.

Example 5

The shape and microstructure of the solid barium titanate prepared in Example 1 were analyzed using a scanning electron microscope (SEM, Jeol JSM 6700 F) and a transmission electron microscope (TEM, Tecnai GII, FEI, operating voltage 200kV). , Results are shown in FIGS. 4 and 5. The shape of the crystal grains was almost spherical, and the average particle size was 50 to 80 nm.

The method for producing nanocrystalline barium titanate according to the present invention is a method of chemically decomposing / synthesizing [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ using an aqueous solution of barium hydroxide, Barium titanate produced by the production method according to the present invention has an average particle diameter of 100 nm or less, the particle size is small and uniform, and the dispersibility in an organic solvent is high, such as a dielectric or piezoelectric element composited with an organic polymer It is expected to have high applicability in various industrial fields such as electronic materials.

Claims (7)

(a) dissolving titanium alkoxide in a solvent, followed by the dropwise addition of β-diketone compound or organic carboxylic acid to form [Ti (β-diketonate) ₃ ] ⁺ or [Ti (carbonate) ₃ ] ⁺ . ; (b) slowly adding the solution (a) to the aqueous barium hydroxide solution and then stirring to form a barium titanate; And (c) separating the barium titanate; Method for producing a nano-crystalline barium titanate excellent dispersibility comprising a. The method of claim 1, The method for producing nanocrystalline barium titanate having excellent dispersibility, wherein the molar ratio of titanium alkoxide to barium hydroxide is 1: 2.5 to 5. The method of claim 1, The reaction temperature of the step (c) is 70 to 95 ℃, the reaction time is a method for producing nanocrystalline barium titanate excellent in dispersibility, characterized in that 0.5 to 5 hours. The method of claim 1, Separating the barium titanate is a method for producing nanocrystalline barium titanate having excellent dispersibility, comprising the step of dispersing in an organic solvent selected from NMP or DMF. The method of claim 1, The β-diketone compound is a compound represented by the following formula (1), characterized in that the nanocrystalline barium titanate excellent dispersibility. [Formula 1]

(Wherein R and R 'are independently C ₁ -C ₁₀ linear or branched alkyl or aryl groups.) The method of claim 5, The β-diketone compound is 2,4-pentanedione or 2,2,6,6-tetramethyl-3,5-heptanedone is a method for producing nanocrystalline barium titanate excellent in dispersibility. The method of claim 1, The organic carbonyl acid is acrylic acid or lactic acid, characterized in that the nanocrystalline barium titanate excellent dispersibility.

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