JPH10298769A - Production of metal oxide precursor sol, and production of metal oxide compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a homogeneous metal oxide precursor sol contg. a small amt. of a residual org. material and capable of forming a homogeneous gel film by adding water at a specified temp. or below to a metal alkoxide. SOLUTION: Water is added at <=-20 deg.C to one or more metal alkoxides as starting material and the alkoxides are hydrolyzed and polymerized to obtain the objective high concn. metal oxide precursor sol not contg. an unnecessary org. material such as a multidentate coordination compd. When this sol is used, a gel film, gel, fibers, bulky gel, etc., having a low org. material content are obtd. When the org. material is removed from the gel by heating or other method, the breaking of the fine texture of a formed compact is suppressed and the volume of residual pores in the compact is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal oxide thin film such as a transparent conductive thin film such as In ₂ O ₃ —SnO ₂ (ITO) or Pb (Zr, Ti) on a surface of glass, ceramics, plastics or the like. A) a method for producing a metal oxide precursor sol used for forming a thin film of a functional metal oxide such as a dielectric thin film such as O ₃ , and a metal oxidation using the metal oxide precursor sol. The present invention relates to a method for producing a metal oxide molded article such as a thin film of an object.

[0002]

2. Description of the Related Art In order to form a metal oxide thin film on a substrate surface using a sol-gel method, a metal alkoxide is used as a raw material, which is hydrolyzed and polymerized to form a substrate oxide precursor sol. After preparing and applying the obtained sol to the surface of a substrate, forming a thin film of a metal oxide gel on the surface of the substrate, the gel film is heated at an appropriate temperature. However, in general, the hydrolysis rate of metal alkoxides excluding silicon alkoxides is extremely high, so that it is difficult to prepare a uniform sol capable of forming a uniform film. Therefore, several methods for suppressing the rate of hydrolysis of metal alkoxide have been studied.

As a method of suppressing the hydrolysis rate of a metal alkoxide, for example, there is a method of extremely lowering the concentration of the metal alkoxide. In this case, a uniform sol film can be formed. However, this method is not effective from an industrial point of view because the thickness of a film obtained in one film forming step is extremely small. Further, as a method of obtaining a sol capable of forming a film by increasing the concentration of the metal alkoxide and suppressing the hydrolysis rate, a method of adding a polydentate organic compound to stabilize the metal alkoxide is known. Some have been proposed. For example, aluminum-s-
In the formation of an alumina thin film using butoxide as a starting material,
β-diketone is effective (Academic Journal of the Ceramic Society of Japan, 97, 396 (1989)), and in forming a titania thin film using titanium isopropoxide as a starting material,
1,3-butanediol is effective (Toshio Koshiba, Ph.D. dissertation at Toyohashi University of Technology, March 1993), and β-diketone is effective (Academic Journal of the Ceramic Society of Japan,
97, 213 (1989)). Also, it has been reported that the use of diethylene glycol is effective in forming a zirconia thin film using zirconium-n-butoxide as a starting material (Ceramic Industry Association, 95, 942 (1987)). Furthermore, the use of β-diketones and alkanolamines has led to PbTiO ₃ and Pb
It has been reported that it is also effective for the synthesis of complex oxides such as (Zr, Ti) O ₃ , but it is reported in the Journal of American Ceramic Society
eric Ceramics Society),
74, 1407 (1991) and Japanese Ceramics Association Scientific Transactions, 98, 745 (1990).

Further, Physics of TinFilm, 5, p.
87 (1969), Academic Press (Acade)
mic Press) includes chloride, sulfate, nitrate,
There are reports on the hydrolysis of various inorganic salts such as ammonium salts and the production of oxide films using aqua complexes. In addition, in order to prepare a sol of In ₂ O ₃ —SnO ₂ as a composite oxide, indium nitrate and tin chloride are used in place of metal alkoxide in the Journal of the Ceramic Society of Japan, 102, 200 (1994). Shown to use.

[0005]

However, as described above, according to the method of stabilizing a metal alkoxide by adding a polydentate compound to suppress the rate of hydrolysis of the metal alkoxide, a uniform sol for film formation is obtained. Can be easily prepared, but many organic substances having a high boiling point and difficult to decompose coexist in the sol or gel film. As a result, it is necessary to heat-treat the gel film at a high temperature of about 500 ° C. in order to remove the organic substances. In addition, since many organic substances remain in the gel film, the heat treatment of the gel film greatly reduces the weight of the film. In other words, the removal of organic matter from the gel film generates many pores in the film, which causes defects in the obtained metal oxide thin film. On the other hand, in order to remove pores in the film, extra energy is required for densification of the thin film.

The method using a metal salt as described above is basically a thermal decomposition method, and causes many problems in the quality of a film after heat treatment.

[0007] The present invention has been made in view of the above circumstances, and can prepare a homogeneous metal oxide precursor sol capable of forming a uniform film, and
Providing a method capable of producing a metal oxide precursor sol having a small amount of organic substances remaining in a sol or a gel film after film formation, and using a metal oxide precursor sol to form a film, for example, The amount of organic matter remaining in the gel film is small when the gel film is removed.Therefore, it is not necessary to heat the gel film at a high temperature to remove the organic matter. To provide a method for producing a metal oxide molded body that can form a homogeneous metal oxide thin film without defects and does not require extra energy for densification of the thin film. And

[0008]

The invention according to claim 1 is
In a method for producing a metal oxide precursor sol by hydrolyzing and polymerizing one or more metal alkoxides, the addition of water to the metal alkoxide is at −20 ° C.
It is performed at the following temperature.

The invention according to a second aspect is characterized in that, in the production method according to the first aspect, a metal oxide precursor sol is produced without using a polydentate compound.

According to the manufacturing method of the first aspect of the present invention,
Since the rate of hydrolysis of the metal alkoxide is suppressed by adding the water to the metal alkoxide at a low temperature of −20 ° C. or less, a homogeneous metal oxide precursor sol capable of forming a uniform film is prepared. can do. And, as in the production method of the invention according to claim 2, since a polydentate coordination compound may not be used, when a film is formed using the obtained metal oxide precursor sol, a gel film is formed. The amount of remaining organic matter is small.

According to a third aspect of the present invention, in the manufacturing method according to the first or second aspect, the metal alkoxide is an alkali metal element or an alkaline earth metal element from the second period to the sixth period of the periodic table. And one element selected from the group consisting of a Group 3B element, a Group 4B element and a Group 5B element from the third to sixth periods of the periodic table, a transition metal element, and a lanthanoid element An alkoxide, a combination of two or more metal alkoxides, a composite alkoxide obtained by a reaction between two or more metal alkoxides, or one or two or more metal alkoxides and one or two or more metal salts Characterized by using a composite alkoxide obtained by the reaction of

According to a fourth aspect of the present invention, in the manufacturing method according to any one of the first to third aspects, the metal oxide is In ₂ O ₃ , SnO ₂ or In ₂ O ₃ -SnO _2. It is characterized by.

According to a fifth aspect of the present invention, in the method according to any one of the first to third aspects, the metal oxide is a composite oxide having a perovskite structure.

According to a sixth aspect of the present invention, in the method according to any one of the first to fifth aspects, the water is added to the metal alkoxide in a temperature range of -50 ° C to -80 ° C. Features.

According to a seventh aspect of the present invention, a metal oxide molded body is manufactured using the metal oxide precursor sol obtained by the manufacturing method according to any one of the first to sixth aspects. And

According to an eighth aspect of the present invention, in the manufacturing method of the seventh aspect, the metal oxide precursor sol is applied to the surface of the object to form a thin film of a metal oxide gel on the surface of the object. After that, the metal oxide gel forming the thin film is crystallized to form a metal oxide thin film on the surface of the object to be coated.

According to the manufacturing method of the invention according to claim 7,
The homogeneous metal oxide precursor sol obtained by the production method of the invention according to claim 1 is applied to the surface of an object to be coated, for example, as in the production method of the invention according to claim 8, and the metal oxide gel is applied. , The amount of residual organic matter in the gel film is small. Therefore, it is not necessary to perform a heat treatment of the gel film at a high temperature for removing organic substances, and a uniform metal oxide thin film without bubbles can be obtained by crystallizing the metal oxide gel.

According to a ninth aspect of the present invention, in the method of the seventh aspect, the solvent of the metal oxide precursor sol is removed under reduced pressure to prepare a high-viscosity sol, and the sol is spun. After forming the metal oxide gel fiber, crystallize the metal oxide gel forming the fiber,
It is characterized by forming a metal oxide fiber.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In the method for producing a metal oxide precursor sol according to the present invention, one or more metal alkoxides are used as starting materials, and water is added to the metal alkoxides.
The metal alkoxide is hydrolyzed and polymerized by adding at a temperature of 20 ° C. or less.

The temperature at which water is added to the metal alkoxide depends on the stability of the metal alkoxide.
Although it may be a temperature of not more than ℃, depending on the type of metal alkoxide, the addition of water to the metal alkoxide is -50 ℃
It is more preferable to carry out in a temperature range of -80C. -2
By adding water at a low temperature such as 0 ° C. or less, the metal alkoxide performs a hydrolysis / polymerization reaction at a high concentration without adding a polydentate compound to the metal alkoxide to stabilize the metal alkoxide. This makes it possible to obtain a high-concentration metal oxide precursor sol containing no unnecessary organic substances such as a polydentate compound. As a result, when the metal oxide precursor sol is used, a gel film, a gel fiber, a bulk gel, and the like having a low organic substance content are obtained, and the organic substance is obtained when the organic substance is desorbed from the gel by a heat treatment or the like. It is possible to reduce the destruction of the microstructure and the amount of residual porosity in the formed compact.

Examples of usable metal alkoxides include alkali metal elements, alkaline earth metal elements and Group 3B elements in the second to sixth periods of the periodic table, and third to sixth periods in the periodic table. A single metal alkoxide or a combination of two or more metal alkoxides of elements selected from the group consisting of Group 4B and Group 5B elements, transition metal elements, and lanthanoid elements, There is no particular limitation. A complex alkoxide obtained by a reaction between two or more metal alkoxides of the above-mentioned elements;
It may be a complex alkoxide obtained by reacting at least one kind of metal alkoxide with one or more kinds of metal salts. Furthermore, these can be used in combination.

The complex alkoxide obtained by the reaction between two or more metal alkoxides includes a complex alkoxide obtained by reacting an alkoxide of an alkali metal or an alkaline earth metal with an alkoxide of a transition metal, a Group 3B element The complex alkoxide as a complex salt obtained by the combination of is used. For example, BaTi (O
R) ₆ , SrTi (OR) ₆ , BaZr (OR) ₆ , Sr
Zr (OR) ₆ , LiNb (OR) ₆ , LiTa (OR)
₆ and combinations thereof, LiVO (OR) ₄ , Mg
Al ₂ (OR) ₈ and the like. Also, (RO) ₃ SiOA
l (OR ') ₂ , (RO) ₃ SiOTi (OR') ₃ ,
(RO) ₃ SiOZr (OR ') ₃ , (RO) ₃ SiOB
(OR ') ₂ , (RO) ₃ SiONb (OR') ₄ , (R
A reaction product with a silicon alkoxide such as O) ₃ SiOTa (OR ′) ₄ or a condensation polymer thereof is also used. Where R
And R ′ represent an alkyl group. Complex alkoxides obtained by reacting one or more metal alkoxides with one or more metal salts include chlorides, nitrates, sulfates, acetates, formates, oxalates and the like. A compound obtained by reacting a metal salt of the above with an alkoxide is used.

In particular, the metal oxide finally obtained is In ₂ O ₃ , SnO ₂ or In ₂ O ₃ -SnO ₂ (ITO)
The production method according to the present invention is effective when producing a precursor sol of a transparent conductive material such as described above or a dielectric material such as a composite oxide having a perovskite structure.

The number of carbon atoms of the alkoxyl group of the metal alkoxide is not particularly limited, but is preferably 1 to 4 carbon atoms from the viewpoint of the concentration of the contained oxide, the ease of desorption of organic substances, the availability, and the like.

The solvent used may be a single solvent or a mixed solvent as long as the metal alkoxide raw material and the water used for the hydrolysis are each soluble and do not solidify at the temperature at which the water is added. Is not particularly limited. For example, a combination of a polar solvent and a non-polar solvent may be used. From the viscosity in the temperature range in which water is added, ease of removal, etc., methanol, which is an alcohol having 1 to 3 carbon atoms,
Ethanol and propanol are particularly preferred.

In order to facilitate the elimination of the solvent after gelation, it is preferable to reduce the amount of the polydentate compound directly bonded to the metal alkoxide as much as possible. On the contrary, according to the method of the present invention, it is also possible to prepare a metal oxide precursor sol without using a polydentate compound. On the other hand, RCONR 'having a plurality of coordinable functional groups (R and R' are hydrogen or alkyl groups)
Does not form a bond by substitution with an alkoxyl group, does not solidify at the temperature of addition of water,
If removal by volatilization is easy, it can be used.

The amount of water to be added cannot be specified because it differs depending on the type of metal element and the type of alkoxyl group in the metal alkoxide. Further, since the optimum stable pH value of the sol varies depending on the type of the metal element, an acid or a base is appropriately used as a catalyst. The catalyst to be used is not particularly limited, but in order to obtain a high-purity material, a compound containing no metal component is preferable. For example, as an acid,
Mineral acids such as hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, and organic acids such as carbonic acid, boric acid, formic acid, acetic acid and oxalic acid are used. Also,
As the base, ammonia, amines and the like are used.

The obtained metal oxide precursor sol can be used in bulk, fiber, thin film, etc. depending on the molding method.
Various forms of gel are possible. In particular, the production method according to the present invention is effective when forming a thin film of a functional metal oxide by forming a thin film of a metal oxide gel.

The method for forming the gel is not particularly limited, and any method may be used as long as it can be generally used as a forming method using a sol liquid. For example, a bulk body can be obtained by adding an amount of water necessary for gelation to a metal alkoxide, casting it in a container, and allowing it to stand at room temperature or at a temperature lower than the boiling point of the solvent used. After adding water to the metal alkoxide, the solvent is partially removed to adjust the viscosity, and then the high-viscosity sol is leaked (spun).
It is obtained by doing. A thin film can be obtained by applying a sol solution on a substrate on which a film is to be formed. As a coating method, a generally practiced method such as dip coating, spin coating, and flow coating can be used.

The molded product of the metal oxide gel obtained from the sol of the metal oxide precursor is subjected to a treatment such as heat treatment or irradiation with light such as ultraviolet light according to the purpose to obtain a functional oxide molded product. Become.

In a method for producing a metal oxide molded body using a metal alkoxide as a starting material and utilizing a sol-gel method, the stability of the precursor sol and the moldability such as film formability are very important. . In general, in order to improve the stability of the sol, the degree of polymerization of the metal alkoxide is increased (at the stage of sol formation, M-O-M (metal-oxygen-metal) bonds are formed instead of the association of metal alkoxide molecules. Or the method of adding a polydentate compound is effective. However, since the stability of water to metal alkoxides excluding silicon alkoxides is very low, it has been very difficult to obtain a homogeneous sol by the conventional method. On the other hand, if a polydentate compound is added, a stable sol can be easily obtained, but the sol and the gel will contain a large amount of residual organic substances, and the gel will be formed in the final mineralization process. It is necessary to remove residual organic matter from inside. With the removal of the residual organic matter, the microstructure is deteriorated due to the destruction of the structure and the generation of pores in the molded body, and in order to improve the fine structure, heat treatment or the like requires more energy than necessary. On the other hand, according to the method of the present invention described above, the hydrolysis / polymerization reaction of the metal alkoxide after the addition of water can be suppressed without adding an extra polydentate coordination compound. It is possible to obtain a stable metal oxide precursor sol. Then, the amount of residual organic matter in the obtained gel is small, and the target functional material can be obtained by low-energy post-treatment.

[0032]

Next, a more specific embodiment of the present invention will be described. [Preparation of metal oxide precursor sol] a <Example 1-14> indium alkoxide, an In ₂
O ₃ was added to ethanol so that the solid content concentration became 15% by weight. A mixed solution of distilled water and ethanol was prepared such that the solid content of In ₂ O ₃ was 10% by weight when added to the indium alkoxide solution. After cooling the indium alkoxide solution and the distilled water-ethanol mixture to a predetermined temperature in a refrigerant, the two solutions are mixed,
Thereafter, the liquid was returned to room temperature. Thereby, homogeneous In ₂
An O ₃ precursor sol was obtained. Table 1 shows the mixing ratio and the synthesis conditions.
In addition, Comparative Examples 1 to 3 described later are also shown together. Table 1
In the column of “addition amount” of “water”, the molar ratio of H ₂ O / In is shown, and “pH” of “water” is hydrochloric acid (HCl).
Adjusted by Further, “〇” in the column of “sol state” in Table 1 indicates that a transparent homogeneous sol was prepared.

[0033]

[Table 1]

Comparative Example 1 Tri-s-butoxyindium was added to ethanol so that the solid concentration of In ₂ O ₃ was 5% by weight. Further, when added to the tri-s-butoxyindium solution, the solid content concentration of In ₂ O ₃ is 2.
A 1N hydrochloric acid-ethanol mixture (H ₂ O / In molar ratio was 0.6) was prepared so as to have a concentration of 5% by weight. 1N hydrochloric acid-ethanol mixture was added to the indium alkoxide solution at room temperature.

Comparative Example 2 Tri-t-butoxyindium was mixed with In ₂ O _{3 so that} the solid content concentration was 5% by weight.
-Added to butanol. Also, a 1N hydrochloric acid-2-butanol mixed solution (molar ratio of H ₂ O / In) was adjusted so that the solid content of In ₂ O ₃ was 2.5% by weight when added to the tri-t-butoxyindium solution. 0.6) was prepared.
A 1N hydrochloric acid-2-butanol mixture was added to the indium alkoxide solution at room temperature.

In each of Comparative Examples 1 and 2, cloudiness and gelation were locally observed from the portion where water was added, and a homogeneous sol could not be obtained.

[0037] The <Comparative Example 3> tri -t- butoxy indium was added to 2-butanol, furthermore, by adding acetylacetone to a equimolar indium, an In ₂
An indium alkoxide solution having a solid content of O ₃ of 5% by weight was prepared. Also, a 1N hydrochloric acid-2-butanol mixed solution (H) was added so that when added to the indium alkoxide solution, the solid concentration of In ₂ O ₃ was 2.5% by weight.
The molar ratio of ₂ O / In was 1). 1N hydrochloric acid-2-
The butanol mixture was added to the indium alkoxide solution at room temperature. When the solid content concentration of In ₂ O ₃ was up to 2.5% by weight, a homogeneous solution was obtained, but when it was 3% by weight or more, the solution became partially cloudy.

Example 15 Tetra-s-butoxytin was added to ethanol so that the solid content of tin oxide became 20% by weight. Further, when added to the tetra-s-butoxytin solution, the solid content concentration of SnO ₂ was 10% by weight.
Thus, a 1N hydrochloric acid-ethanol mixture was prepared. After cooling the tin alkoxide solution and the 1N hydrochloric acid-ethanol mixed solution to −25 ° C. in a refrigerant, the two solutions were mixed, and then the solution was returned to room temperature. As a result, a homogeneous S
An nO ₂ precursor sol was obtained.

Comparative Example 4 Tetra-s-butoxytin was added to ethanol, and a 1N hydrochloric acid-ethanol mixture was added to the tin alkoxide solution at room temperature. As a result, Sn
When the solid content concentration of O ₂ is 2.5% by weight or more, homogeneous Sn
O ₂ could not be obtained a precursor sol.

Examples 16 to 32 Indium alkoxide and tin alkoxide were added to ethanol such that the solid content of the metal oxide became 15% by weight to prepare a mixed solution of the metal alkoxide. A mixed solution of distilled water and ethanol was prepared such that the solid content of the metal oxide was 10% by weight when added to the mixed solution of the metal alkoxide. After cooling the mixed solution of the metal alkoxide and the distilled water-ethanol mixed solution to a predetermined temperature in a refrigerant, the two solutions were mixed, and then the solution was returned to room temperature. Thus, a homogeneous In ₂ O ₃ —SnO ₂ (ITO) precursor sol was obtained. Table 2 summarizes the mixing ratios and the synthesis conditions. In Table 2, in the column of “addition amount” of “water”, H ₂ O /
It shows the molar ratio of (In + Sn), and the “p” of “water”
"H" was adjusted with hydrochloric acid (HCl). Further, “〇” in the column of “sol state” in Table 1 indicates that a transparent homogeneous sol was prepared.

[0040]

[Table 2]

Comparative Example 5 Tri-t-butoxyindium and tetra-s-butoxytin were added to 2-butanol such that the metal oxide had a solid content of 5% by weight.
A mixed solution of the metal alkoxide was prepared. Also, 1N hydrochloric acid-2-hydrochloride was added so that when added to the mixed solution of the metal alkoxide, the solid content concentration of the metal oxide was 2.5% by weight.
A butanol mixture (H ₂ O / In molar ratio was 0.6) was prepared, and the mixture was added to a mixed solution of metal alkoxide. From the place where water (1N hydrochloric acid-2-butanol mixture) was added, local turbidity and gelation occurred locally, and a homogeneous sol could not be obtained. The mixing ratio and the synthesis conditions at this time are shown in Table 3 together with Comparative Examples 6 and 7 described later. In Table 3, in the column of "addition amount" of "water", H
₂ indicates the molar ratio of O / In, and indicates the “pH” of “water”.
Was adjusted with hydrochloric acid (HCl). Further, “〇” in the column of “sol state” in Table 3 indicates that a transparent homogeneous sol was prepared.

[0042]

[Table 3]

Comparative Example 6 Tri-t-butoxyindium and tetra-s-butoxytin were added to N, N-dimethylformamide (DMF) such that the solid concentration of the metal oxide was 5% by weight. Then, a mixed solution of the metal alkoxide was prepared. Further, a 1N hydrochloric acid-DMF mixed solution (H ₂ O / (In +) was added so that the solid content concentration of the metal oxide was 2.5% by weight when added to the mixed solution of the metal alkoxide.
The molar ratio of Sn) was adjusted to 0.6), and the mixed solution was added to the mixed solution of the metal alkoxide. As in Comparative Example 5, locally cloudy and gelled from the location where water was added,
A homogeneous sol could not be obtained.

Comparative Example 7 Tri-t-butoxyindium and tetra-s-butoxytin were added to 2-butanol such that the metal oxide had a solid content of 5% by weight.
A mixed solution of the metal alkoxide was prepared. Also, 1N hydrochloric acid-2-hydrochloride was added so that when added to the mixed solution of metal alkoxide, the solid content concentration of the metal oxide was 2.5% by weight.
A butanol mixture (H ₂ O / (In + Sn) molar ratio was 1) was prepared. After adding an equimolar amount of acetylacetone to the indium alkoxide and the tin alkoxide to the mixed solution, a 1N hydrochloric acid-2-butanol mixed solution was added to the mixed solution of the metal alkoxide at room temperature. When the solid content concentration of the metal oxide was up to 2.5% by weight, a homogeneous solution was obtained, but when the concentration was 3% by weight or more, the solution became partially cloudy.

Examples 33 to 43 Metallic barium was added in an equimolar amount to titanium to an ethanol solution of titanium alkoxide, and the solid content of metal oxide was 20% by weight.
An ethanol solution of the a-Ti composite alkoxide was obtained. A mixed solution of distilled water and ethanol was prepared such that the solid content of the metal oxide was 1.0% by weight when added to the composite alkoxide solution. After cooling the Ba-Ti composite alkoxide solution and the distilled water-ethanol mixed solution to a predetermined temperature in a refrigerant, the two solutions were mixed, and then the solution was returned to room temperature. As a result, a homogeneous BaTiO ₃ precursor sol was obtained. Table 4 also shows the mixing ratios and the synthesis conditions, together with Comparative Examples 8 to 9 described later. In Table 4, the column of "amount" of "water" indicates the molar ratio of H ₂ O / Ti, "pH" of the "water" was adjusted by hydrochloric acid (HCl). Further, “〇” in the column of “sol state” in Table 4 indicates that a transparent homogeneous sol was prepared.

[0046]

[Table 4]

(Ba, Sr) (Zr, T) wherein titanium alkoxide is partially replaced by zirconium alkoxide or metal barium is partially replaced by metal strontium.
i) O ₃ sol was obtained in the same manner as above.

Comparative Example 8 Barium metal was added in an equimolar amount to titanium to an ethanol solution of tetraethoxytitanium to obtain an ethanol solution of a Ba-Ti composite alkoxide. 1N hydrochloric acid was diluted with ethanol (molar ratio of H ₂ O / Ti is 1) was added to the Ba-Ti composite alkoxide solution, but even if a metal oxide concentration of 0.5% by weight, to produce a white precipitate.

Comparative Example 9 Metallic barium was added to a 2-methoxyethanol solution of tetramethoxyethoxytitanium in an equimolar amount with titanium to obtain a 2-methoxyethanol solution of a Ba-Ti composite alkoxide. Also, a 1N hydrochloric acid-2-methoxyethanol mixed solution (H ₂ O / Ti molar ratio is 1) was prepared so that the solid content concentration of BaTiO ₃ when added to the composite alkoxide solution was 1% by weight.
The mixture was added to the Ba-Ti composite alkoxide solution at room temperature. When the solid concentration of BaTiO ₃ was 1% by weight, a homogeneous sol was obtained. However, when the oxide concentration was more than 1% by weight, gelation and precipitation partially occurred, and a homogeneous sol could not be obtained. Was.

Comparative Example 10 Metallic barium was added to an ethanol solution of tetraethoxytitanium in an equimolar amount with titanium to obtain an ethanol solution of a Ba-Ti composite alkoxide. When added to the composite alkoxide solution, Ba
A 1N hydrochloric acid-ethanol mixture (H ₂ O / Ti molar ratio is 1) is prepared so that the solid content concentration of TiO ₃ is 1% by weight, and acetyl acetone of twice the molar amount of titanium alkoxide is added to the composite alkoxide solution. After addition, 1N hydrochloric acid-
An ethanol mixture was added. Thereby, a homogeneous Ba
Although TiO ₃ was obtained, when the oxide concentration was more than 1% by weight, gelation and precipitation partially occurred, and a homogeneous sol could not be obtained.

<Examples 44 to 53> Anhydrous lead acetate was added to an ethanol solution of titanium alkoxide and / or zirconium alkoxide in an equimolar amount to the amount of Ti + Zr, and reacted at the reflux temperature of ethanol for 24 hours. % Of a Pb-Zr-Ti composite alkoxide in ethanol solution was obtained. Further, a mixed solution of distilled water and ethanol was prepared such that the solid content of the metal oxide was 10% by weight when added to the composite alkoxide solution. P
After cooling the b-Zr-Ti composite alkoxide solution and the distilled water-ethanol mixture to a predetermined temperature in a refrigerant,
The two solutions were mixed and returned to room temperature. This allows a homogeneous P
A b (Zr, Ti) O ₃ precursor sol was obtained. Table 5 shows the compounding ratios and the synthesis conditions, together with Comparative Example 11 described later. In Table 5, the column of “addition amount” of “water” shows H ₂ O
/ (Ti + Zr) molar ratio, and “p” of “water”
“H” was adjusted with hydrochloric acid (HCl) or ammonia (NH ₃ ). Further, “〇” in the column of “sol state” in Table 1 indicates that a transparent homogeneous sol was prepared.

[0052]

[Table 5]

Even when the titanium alkoxide and / or zirconium alkoxide was partially or entirely replaced with tin alkoxide or germanium alkoxide, a homogeneous sol could be obtained in the same manner as described above.

Comparative Example 11 Tetraethoxytitanium and tetra-n-butoxyzirconium (Zr / Ti = 53 /
Anhydrous lead acetate in Ti + Z
r, and reacted at the reflux temperature of ethanol for 24 hours to obtain Pb-Zr- having an oxide concentration of 10% by weight.
An ethanol solution of the Ti composite alkoxide was obtained. 1N hydrochloric acid was diluted with ethanol (molar ratio of _{H 2 O / (Ti + Zr} ) is 1) a was added to the Pb-Zr-Ti composite alkoxide solution, generating a white precipitate even when the oxide concentration of 0.5% by weight did.

As is apparent from the above results, according to the production method of the present invention, the metal oxide concentration is 10% by weight or more without adding an extra organic substance such as a polydentate compound. A homogeneous transparent sol is obtained. In contrast,
In the conventional method, it is possible to prepare a partially stable sol by adding a polydentate compound, but the metal oxide concentration is lower than that of the sol obtained by the method according to the present invention. Quite low.

In the above embodiment, In ₂ O ₃ -SnO
_Although only the method for preparing the _binary oxide and some perovskite-based composite oxide sols has been shown, the production method according to the present invention is widely applicable to the preparation of metal oxide sols starting from metal alkoxides. Needless to say.

[Shape-Providing Property] Next, according to the method of the present invention, it is possible to obtain metal oxide precursor sols of various shapes.

By setting the amount of water to be 1 or more under the sol preparation conditions described in the above Example 6, the transparent In ₂ O ₃
A transparent ITO gel (Example 54) was obtained from the gel (Example 53) and the addition amount of water was 1 or more under the sol preparation conditions described in Example 23 above. In BaTiO ₃ and Pb (Zr, Ti) O ₃ ,
When the amount of water added was 2 or more, a homogeneous gel was obtained.

By removing the solvent from the sol obtained in Example 6 under reduced pressure, a high-viscosity sol was obtained.
By spinning this high-viscosity sol, an In ₂ O ₃ fiber could be produced (Example 55). In a similar manner, ITO, BaTiO ₃ and Pb (Zr,
The production of Ti) O ₃ fibers is also possible.

[Thinning and Physical Properties of Thin Film] The In ₂ O ₃ sol and the ITO sol obtained in each of the above Examples were diluted so that the oxide concentration was 5% by weight, and the diluted sol was used. Was spin-coated at 1,000 rpm to form a film on a silica substrate. As a result, a gel film having a homogeneous appearance was obtained. After the obtained gel film was subjected to a heat treatment, the thickness and resistance of the In ₂ O ₃ film and the ITO film were measured and evaluated. The film thickness was measured using a step meter. The resistance value was obtained as a sheet resistance by a four-terminal method. For comparison, the sols obtained in Comparative Examples 3 and 7 were formed in the same manner. Table 6 summarizes the properties of the obtained films.

[0060]

[Table 6]

The I manufactured by the method according to the present invention
The n ₂ O ₃ film and the ITO film tend to be thicker, have lower sheet resistance, and have lower specific resistance than those of the comparative example. This is presumably because the film formed by the method according to the present invention has a small amount of residual organic components, so that defects such as pores inside the film are reduced.

In addition, the IT obtained in Example 21
Dilute the O sol to an oxide concentration of 5% by weight,
The diluted sol was formed into a film by dip coating, and the same evaluation as above was performed. The obtained gel film is baked at 400 ° C. to give a film thickness of 85 nm and a sheet resistance of 2.6.
A × 10 ³ Ω / □ ITO film was obtained. Example 2
The ITO sol obtained in 1 was diluted so that the oxide concentration became 1% by weight, and the diluted sol was formed on a 50 mm square glass plate by flow coating. was gotten.

Next, the perovskite-type oxide precursor sol obtained in each of the above examples was diluted so that the oxide concentration became 5% by weight, and the diluted sol was rotated at 1,000 rpm. A film was formed on Pyrex glass by spin coating with a number. As a result, a gel film having a homogeneous appearance was obtained. For comparison, the sols obtained in Comparative Examples 8 and 9 described above were formed in the same manner. After heat treatment of the obtained gel film, the crystallization behavior of the film and the film thickness at the crystallization temperature were evaluated. Table 7 summarizes the properties of the obtained film.

[0063]

[Table 7]

The thin film obtained by using the sol produced by the method according to the present invention has a thickness at the time of crystallization about four times as thick as that of the comparative example. In the method of the comparative example, since the oxide concentration cannot be increased in order to prepare a stable sol, the thickness of the film formed by one coating operation is small, and the desired thickness is obtained. For this purpose, a multilayer coating is required. The thin film obtained by the method according to the present invention has a crystallization temperature of 300 ° C. to 500 ° C. depending on the sol preparation method using BaTiO ₃ , and 400 ° C. using PZT.
From 500 ° C to 500 ° C.

As described above, according to the method of the present invention, it is possible to prepare a precursor sol having a high oxide concentration, and it is possible to apply the precursor sol to metal oxide compacts of various shapes. In particular, in forming a thin film, a thick coating film can be easily obtained as compared with the conventional method. In addition, the crystallization temperature is lowered because the amount of residual organic matter in the gel is small.

It is needless to say that the present invention is not limited to the above-described embodiments, but is applicable to the production of precursor sols and molded articles of various metal oxides.

[0067]

According to the manufacturing method of the first aspect of the present invention, the amount of organic substances remaining in the gel film after high-density and homogenous film formation so that high-concentration and uniform film formation is possible. To obtain a metal oxide precursor sol having a low content. The obtained precursor sol can be formed into various shapes, and is particularly suitable for forming a metal oxide thin film, and a high quality metal oxide thin film can be obtained from this precursor sol. .

Further, according to the manufacturing method of the present invention, when the metal oxide precursor sol is gelled, the amount of organic substances remaining in the gel is small. It is not necessary to perform the heat treatment of the metal oxide gel described above, so that the treatment can be performed at a relatively low temperature, and a uniform metal oxide thin film without bubbles can be formed. Further, the obtained metal oxide molded body does not require extra energy for densification of a thin film or the like. In particular, the method of the present invention is most suitable for forming a metal oxide thin film, and a high quality metal oxide thin film can be obtained.

Claims (9)

[Claims] 1. A method for producing a metal oxide precursor sol by hydrolyzing and polymerizing one or more metal alkoxides, wherein water is added to the metal alkoxide at a temperature of -20 ° C. or lower. A method for producing a metal oxide precursor sol, comprising: 2. The method for producing a metal oxide precursor sol according to claim 1, wherein the metal oxide precursor sol is produced without using a polydentate compound. 3. The metal alkoxide comprises an alkali metal element, an alkaline earth metal element and a Group 3B element in the second to sixth periods of the periodic table, and a third to sixth period in the periodic table. An element selected from the group consisting of a Group 4B element and a Group 5B element, a transition metal element, and a lanthanoid element, one metal alkoxide, a combination of two or more metal alkoxides, and a mixture of two or more metal alkoxides. Or a composite alkoxide obtained by a reaction of one or more metal alkoxides with one or two or more metal salts.
The method for producing a metal oxide precursor sol according to the above. 4. The method for producing a metal oxide precursor sol according to claim 1, wherein the metal oxide is In ₂ O ₃ , SnO ₂ or In ₂ O ₃ —SnO ₂ . 5. The method for producing a metal oxide precursor sol according to claim 1, wherein the metal oxide is a composite oxide having a perovskite structure. 6. The method according to claim 1, wherein the addition of water to the metal alkoxide is -50.
6. The method according to claim 1, wherein the heat treatment is performed at a temperature in a range of from .degree.
The method for producing a metal oxide precursor sol according to any one of the above. 7. A method for producing a metal oxide molded body, comprising using the metal oxide precursor sol obtained by the production method according to claim 1. 8. A metal oxide precursor sol is applied to the surface of an object to be coated, a metal oxide gel thin film is formed on the surface of the object, and the metal oxide gel forming the thin film is removed. The method for producing a metal oxide molded body according to claim 7, wherein the metal oxide thin film is formed on the surface of the object by crystallizing. 9. A high-viscosity sol is prepared by removing the solvent of the metal oxide precursor sol under reduced pressure, and the sol is spun to form a metal oxide gel fiber, and then the fiber is formed. The method for producing a metal oxide molded article according to claim 7, wherein the metal oxide gel is crystallized to form metal oxide fibers.