TWI568676B - ITO powder and its manufacturing method - Google Patents

Description

ITO powder and method of producing the same

The present invention relates to an ITO powder which exhibits a low volume resistivity when it is a green compact, and a method for producing the same. In the present specification, ITO means Indium Tin Oxide.

ITO is a compound doped with tin (Sn) in In ₂ O ₃ , and has a high carrier concentration of 10 ²⁰ to 10 ²¹ cm ^-3 and can be formed by a vapor phase method such as sputtering. Obtain 1 × 10 ^-4 Ω. Low resistivity around cm. However, in the state of ITO powder, its resistance value is usually high resistance at 10 Ω. In the range of cm or more (for example, refer to Patent Documents 1 and 2). In order to reduce the electric resistance value of the ITO powder, in the method described in Patent Document 1 or 2, the ITO powder prepared by the alkoxide method is in an inert gas atmosphere containing an alcohol gas or a hydrazine hydrate gas at 200 to 450 ° C. The temperature is heated to perform deoxidation, thereby generating lattice defects of oxygen. According to these methods, when a pressure of 100 kgf/cm ² (9.80 MPa) is applied, a low resistance of 0.01 to 0.50 Ω can be obtained. ITO powder in the range of cm.

Further, as another method for reducing the resistance of the ITO powder, a method is disclosed in which a mixed aqueous solution of indium chloride and tin chloride is mixed with a final pH of 2 to 8 at a temperature of 5 to 95 ° C. The mixing is carried out to coprecipitate the indium and the hydroxide of tin, and the obtained precipitate is hydrolyzed at 400 ° C to 950 ° C for 30 to 8 hours (for example, refer to Patent Document 3). According to this manufacturing method, it is possible to obtain a specific resistance of 70 Ω when a pressure of 50 kgf/cm ² (4.90 MPa) is applied. Below cm or 15Ω. ITO powder below cm. Further, in this method, a tetravalent tin compound, that is, an aqueous solution of SnCl _{4 is} used as the tin chloride.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-024837 (Application No. [0005], [0010], [0011])

[Patent Document 2] Japanese Patent Laid-Open No. Hei 5-139940 (Patent Application, [0005], [0010], [0011])

[Patent Document 3] Japanese Patent Laid-Open No. Hei 5-201731 (Application No. [0012] to [0015]

In order to reduce the resistance of the ITO powder, in the methods of Patent Documents 1 and 2, it is necessary to post-treat the ITO powder in an inert gas atmosphere containing an alcohol gas or a hydrazine hydrate gas. Further, in the conventional method, a tetravalent tin compound, SnCl ₄ or SnCl _{2 , is} used as the tin chloride. In other words, since a raw material having a single valence is used, the precursor (for example, a hydroxide) becomes unstable depending on the difference in ionic radius between the In ion and the Sn ion, and the Sn compound is easily precipitated, and Sn cannot be sufficiently doped.

An object of the present invention is to provide an ITO powder which can obtain a volume resistivity lower than a conventional one in a green compact of ITO powder without post-treatment in a powder state, and a method for producing the same.

The first aspect of the present invention is an ITO powder obtained by filling the sample holders attached to the apparatus with the X-ray diffraction apparatus D8 Advance manufactured by Bruker AXS Co., Ltd. in Examples 1 to 5 and Comparative Examples 1 and 2. Each of the ITO powders was irradiated with X-rays in a range of 2θ=15 to 90 deg, and the obtained diffraction line was analyzed by the Pawley method using FP as a contour function using TOPAS (manufactured by Bruker AXS), a software for Rietveld analysis. The half-width of the Lorentz function component calculates the crystallite size and lattice strain, and the lattice strain at this time is in the range of 0.2-0.8.

Further, a second aspect of the present invention is the invention according to the first aspect, which is an improvement of a method for producing an ITO powder comprising the steps of: mixing an aqueous alkali solution with a mixed aqueous solution of a trivalent indium compound and a tin compound to form indium and tin; a step of coprecipitating a hydroxide; a step of washing the coprecipitated hydroxide with pure water or ion-exchanged water; removing a supernatant of the coprecipitated hydroxide to prepare a slurry in which indium tin hydroxide particles are dispersed a step of drying the slurry; and a step of firing the dried indium tin hydroxide to obtain indium tin oxide. The tin compound is a mixture of a tetravalent tin compound and a divalent tin compound, and the tin ion ratio of Sn ⁴⁺ :S ²⁺ is in the range of 90:10 to 10:90.

According to a third aspect of the invention, the tetravalent tin compound is an aqueous solution of SnCl ₄ and the divalent tin compound is SnCl ₂ . A method for producing an ITO powder of 2H ₂ O powder.

Further, a fourth aspect of the present invention is a method for producing a dispersion by dispersing ITO powder of the first aspect or ITO powder produced by the second or third viewpoint in a solvent.

Further, a fifth aspect of the present invention is a method for producing an ITO film from the dispersion liquid of the fourth aspect.

The ITO powder according to the first aspect of the present invention is irradiated with X-rays under predetermined conditions by a predetermined X-ray diffraction apparatus, and a predetermined analysis software is used from the obtained diffraction line to perform Pawley method using FP as a contour function. Analysis, and the crystallite size and lattice strain are calculated from the half-width of the Lorentz function component, and the lattice strain at this time is in the range of 0.2-0.8. The larger the lattice strain, the lower the volume resistivity that can be obtained when the compact is formed. Specifically, the ITO powder having a lattice strain in the range of 0.2 to 0.8 can have a volume resistivity of 0.20 Ω when a pressure of 4.9 MPa (50 kgf/cm ² ) is applied to the compact. Below cm.

Further, in the method for producing an ITO powder according to the second aspect of the present invention, in the step of forming a coprecipitated hydroxide of indium and tin, the tin compound is a mixture of a tetravalent tin compound and a divalent tin compound, and Sn ⁴⁺ : The tin ion ratio of Sn ^{2+ is} in the range of 90:10 to 10:90. It is considered that by setting this range, the structure of the precursor of indium tin hydroxide is stabilized, whereby the amount of Sn entering the precursor increases, and the lattice strain of In ₂ O ₃ can be increased to obtain an ITO powder. The low volume resistivity of the compact.

Further, in the method for producing an ITO powder according to the third aspect of the present invention, an aqueous SnCl ₄ solution and SnCl _{2 are} mixed. A 2H ₂ O powder was used to prepare an aqueous tin-containing solution. The combination of the tetravalent tin compound and the divalent tin compound has advantages in terms of versatility and low cost.

1‧‧‧Cylinder

2‧‧‧Precast of ITO powder

Fig. 1 is a schematic view of an apparatus for measuring the electrical resistivity of a green compact of ITO powder.

Fig. 2 is a graph showing the relationship between the reciprocal of the lattice strain of ITO and its resistivity.

Modes for carrying out the invention are described below. The electrical resistivity of the ITO powder is an important index when evaluating the characteristics of the ITO film made of the ITO powder. In particular, when an ITO film is used as a conductive sheet or an electrode, high conductivity, that is, low resistivity is required.

This ITO is a solid solution in which tin (Sn) is dissolved in In ₂ O ₃ , and one carrier electron is replaced with one Sn atom which has been solid-dissolved at the In position, whereby high conductivity can be exhibited. Further, the ionic radius (Shannon radius) of In ³⁺ is 0.80 Å, and the ionic radius (Shannon radius) of Sn ⁴⁺ is 0.69 Å smaller than this, so that it is considered that if Sn is dissolved in the In position of In ₂ O ₃ , the lattice of In ₂ O ₃ will produce strain. Therefore, by combining the two, it can be considered that the more Sn is replaced, that is, the more carrier electrons generated by Sn, the larger the lattice strain of the In ₂ O ₃ lattice.

As shown in Fig. 2, the reciprocal of the lattice strain of the In ₂ O ₃ lattice and the volume resistivity of the compact of the ITO powder can be linearly obtained, so the larger the lattice strain, the lower the volume of the compact can be obtained. Resistivity. In order to produce the high lattice strain, it is necessary to increase the amount of solid solution of tin (Sn) to In ₂ O ₃ by setting the precursor, that is, indium tin hydroxide, to a more stable structure.

Regarding the solid solution of tin (Sn) to In ₂ O ₃ , focusing on the ionic radii of In ³⁺ , Sn ^{4+ ,} and Sn ²⁺ , the ionic radius (Shannon radius) of In ³⁺ is 0.80 Å as described above. The ionic radius (Shannon radius) of Sn ⁴⁺ is less than 0.69 Å of 0.80 Å. On the other hand, the ionic radius (Shannon radius) of Sn ²⁺ is 1.18 Å greater than 0.80 Å. From the difference in the ionic radii of the In ³⁺ , Sn ^{4+ ,} and Sn ²⁺ , it is presumed that when the tin compound is a mixture of a tetravalent tin compound and a divalent tin compound, Sn ^{2 having} an ionic radius larger than In ^{3+ is used} . ⁺ to alleviate the strain caused by the Sn ⁴⁺ solid solution having an ionic radius smaller than In ³⁺ , whereby the structure of the indium tin hydroxide is stable. When the structure of the precursor becomes stable, the amount of Sn entering the precursor increases, and the lattice strain of the In ₂ O ₃ lattice can be increased to obtain a low volume resistivity of the green compact composed of the ITO powder.

The lattice strain of the ITO powder of the present invention is in the range of 0.2 to 0.8. When it is less than 0.2, the amount of solid solution of tin (Sn) to In ₂ O ₃ is small, and low volume resistivity cannot be obtained. Further, a value exceeding 0.8 was not obtained by the production method of the present invention.

The ITO powder of the present invention is produced by the following method. First, a mixed aqueous solution is prepared by mixing a mixture of a tetravalent tin compound and a divalent tin compound in a trivalent indium compound. The aqueous alkali solution is mixed in the mixed aqueous solution to form a coprecipitated hydroxide of indium and tin, dried and fired to form the precipitate, and then obtained by pulverizing the obtained indium tin oxide. Examples of the trivalent indium compound include indium trichloride (InCl ₃ ), indium nitrate (In(NO ₃ ) ₃ ), and indium acetate (In(CH ₃ COO) ₃ ). An aqueous solution of tin tetrachloride (SnCl ₄ ), or a tin bromide (SnBr ₄ ), and the like, and examples of the divalent tin compound include tin dichloride (SnCl ₂ .2H ₂ O), tin sulfate (SnSO ₄ ), and bromine. Tin (SrBr ₂ ) and the like. As a combination of the tetravalent tin compound and the divalent tin compound, it is preferred to mix the SnCl ₄ aqueous solution and SnCl ₂ from the viewpoints of versatility and low cost. 2H ₂ O. Examples of the aqueous alkali solution include ammonium (NH ₃ ) water, ammonium hydrogencarbonate (NH ₄ HCO ₃ ) water, and the like which do not require the alkali metal to remain.

The mixing ratio of the mixture of the tetravalent tin compound and the divalent tin compound mixed in the trivalent indium compound is in the range of 90:10 to ^10:90 in terms of the tin ion ratio of Sn ⁴⁺ :S ²⁺ . When there is too much Sn ⁴⁺ and too little Sn ²⁺ in this range, the hydroxide of Sn is easily precipitated, and Sn is not doped, so there is a problem that conductivity is low, and when Sn ^{4+ is} too small, Sn ²⁺ When there is too much, SnO is easily precipitated, and Sn is not doped, so there is a problem that conductivity is low. It is preferably in the range of 15:85 to 85:15. In other words, when the tin compound mixed in the trivalent indium compound has only a tetravalent tin compound or only a divalent tin compound, there is a problem that Sn is hardly doped.

The final pH of the reaction solution when the indium and tin hydroxide are coprecipitated is adjusted to 3.5 to 9.3, preferably adjusted to pH 5.0 to 8.0, and the solution temperature is adjusted to 5 ° C or higher, preferably adjusted to a solution temperature of 10 °C~80 °C, so that the coprecipitated hydroxide of indium tin can be precipitated. The mixing of the aqueous alkali solution may be carried out by dropping the aqueous alkali solution into the mixed aqueous solution to adjust the pH range, or may be carried out by simultaneously dropping the mixed aqueous solution and the aqueous alkali solution in water to adjust the pH range.

After the coprecipitated indium tin hydroxide is formed, the precipitate is washed with pure water or ion-exchanged water, and the resistivity of the supernatant is at least 5000 Ω. Cm, preferably at least 50,000 Ω. Cm. If the supernatant has a resistivity of less than 5000 Ω. When cm is used, impurities such as chlorine cannot be sufficiently removed, and high-purity indium tin oxide powder cannot be obtained. Remove the resistivity to 5000Ω. The supernatant of the above precipitate of cm or more was obtained as a slurry having a high viscosity in which indium tin hydroxide particles were dispersed.

In the atmosphere, the slurry is preferably dried in a range of 100 to 200 ° C for 2 to 24 hours in an inert gas atmosphere such as nitrogen or argon, and then fired in a firing furnace at a temperature of 250 to 800 ° C in the atmosphere. 0.5~6 hours. The ITO powder is obtained by pulverizing and decomposing the aggregate formed by the firing using a hammer mill or a ball mill or the like. The ITO powder is placed in a surface treatment liquid in which 50 to 95 parts by mass of absolute ethanol and 5 to 50 parts by mass of distilled water are mixed, and then immersed in a glass petri dish. When heated in the range of 200 to 400 ° C for 0.5 to 5 hours in a nitrogen atmosphere, an ITO powder subjected to surface modification treatment can be obtained.

[Examples]

Next, an embodiment of the present invention will be described in detail together with a comparative example.

<Example 1> [Method of Manufacturing Surface-Modified ITO Powder]

In an aqueous solution of indium chloride (InCl ₃ ) having a concentration of In metal of 24% by mass, an aqueous solution of tin tetrachloride (SnCl ₄ ) mixed with a concentration of 55% by mass and tin dichloride (SnCl ₂ .2H ₂ O) were added. A powdered tin-containing aqueous solution was stirred and prepared to prepare a raw material solution. At this time, a tin-containing aqueous solution was prepared by mixing tin tetrachloride and tin dichloride with a tin ion of Sn ⁴⁺ :S ^{2+ in} a ratio shown in Table 1. Further, the mass of the raw material solution mixed with tin (Sn):indium (In) was as shown in Table 1.

In the pure water heated to 45 ° C, the above raw material solution and a 25% by mass aqueous solution of ammonium (NH ₃ ) were added dropwise while adjusting the pH. The reaction temperature at this time was adjusted to 45 ° C, and the pH of the final reaction solution was adjusted to 8.0. The formed indium tin coprecipitated hydroxide, that is, the precipitate, was repeatedly subjected to oblique washing by ion-exchanged water. The resistivity in the supernatant becomes 5000 Ω. When it is cm or more, the supernatant of the above precipitate is removed to obtain a slurry having a high viscosity in which indium tin hydroxide particles are dispersed.

After the slurry was dried at 110 ° C for 10 hours in the atmosphere, It was baked at 600 ° C for 3 hours in the atmosphere, and the aggregate was pulverized and decomposed to obtain an ITO powder. The ITO powder was placed in a surface treatment liquid (mixing ratio of 95 parts by mass of ethanol and 5 parts by mass of distilled water) mixed with anhydrous ethanol and distilled water, and then immersed in a glass petri dish under nitrogen. The ITO powder subjected to the surface modification treatment was obtained by heating at 400 ° C for 2 hours under an atmosphere.

[Manufacture of ITO film]

20 g of the surface-modified ITO powder was placed in distilled water (0.020 g), triethylene glycol-bis-2-hexanoic acid ethyl ester [3G] (23.8 g), absolute ethanol (2.1 g), and phosphoric acid polyester ( 1.0 g), a mixture of 2-ethylhexanoic acid (2.0 g) and 2,4-pentanedione (0.5 g) was dispersed. The prepared dispersion was diluted with absolute ethanol to a solid content, that is, the content of the ITO powder was 10% by mass. The diluted dispersion was applied onto a quartz glass plate by spin coating to form a film, thereby obtaining an ITO film having a thickness of 0.2 μm.

<Examples 2 to 5>

Using the same indium chloride, tin tetrachloride and tin dichloride as in Example 1, a tin-containing aqueous solution was prepared by mixing tin tetrachloride and tin dichloride with the tin ion ratio shown in Table 1, and Table 1 The tin-containing aqueous solution and the raw material solution are mixed in a mass ratio as shown. The surface-modified ITO powder was obtained in the same manner as in Example 1 except that the above tin ion ratio was changed to the above mass ratio.

<Comparative Example 1>

A mixed solution of tin tetrachloride (SnCl ₄ ) having a concentration of 55% by mass was added to an aqueous solution of indium chloride (InCl ₃ ) having an In metal concentration of 24% by mass to prepare a mixed solution of InCl ₃ -SnCl ₄ . At this time, the mixed solution was mixed into tin (Sn): the mass of indium (In) is as shown in Table 1. The surface-modified ITO powder was obtained in the same manner as in Example 1 below.

<Comparative Example 2>

A mixed solution of indium chloride (SnCl ₂ .2H ₂ O) was added to an aqueous solution of indium chloride (InCl ₃ ) having an In metal concentration of 24% by mass to prepare a mixed solution of InCl ₃ —SnCl ₂ . At this time, the mixed solution was mixed into tin (Sn): the mass of indium (In) is as shown in Table 1. The surface-modified ITO powder was obtained in the same manner as in Example 1 below.

<Comparative test> [Glass strain of ITO powder]

Each of the ITO powders obtained in Examples 1 to 5 and Comparative Examples 1 and 2 was filled in a sample holder attached to the apparatus by an X-ray diffraction apparatus D8 Advance manufactured by Bruker AXS Co., Ltd., and irradiated in a range of 2θ=15 to 90 deg. X-ray, from the obtained diffraction line, using the Rietveld analysis software, TOPAS (manufactured by Bruker AXS), to analyze the Pawley method using FP as a contour function, and calculate the crystallite size from the half-width of the Lorentz function component. Lattice strain. In the measurement, CuKa was used as a bulb, and it was set to 40 kV and 40 mA, and X-ray (wavelength 1.54 Å) was designated, and the step interval was set to 0.05 deg. The results are shown in Table 1.

[Volume resistivity of ITO powder]

The volume resistivity of each of the ITO powders obtained in Examples 1 to 5 and Comparative Examples 1 and 2 was measured by a measuring apparatus (MCP-PD51 manufactured by Mitsubishi Chemical Analytical Co., Ltd.) shown in Fig. 1 . The results are shown in Table 1. Specifically, the measurement of the volume resistivity of each ITO powder was carried out as follows: the inner diameter shown in FIG. The cylinder 1 of 25 mm was filled with 2.00 g of ITO powder, and a pressure of 4.9 MPa (50 kgf/cm ² ) was applied to measure the electric resistance of the ITO powder obtained in Examples 1 to 5 and Comparative Examples 1 and 2, respectively. rate. The pressure was measured by a pressure sensor (not shown), and the specific resistance was measured by a DC four-terminal method. In Fig. 1, 2 is a green compact of ITO powder.

<evaluation>

As can be seen from Table 1, in Comparative Example 1 in which only the tetravalent tin compound was present and Comparative Example 2 in which only the divalent tin compound was present, the lattice strain of the ITO powder was 0.075 and 0.155, respectively, and the volume resistivity at this time was 0.239 Ω. Cm, 0.201 Ω. In contrast, in Examples 1 to 5 in which the tin ion ratio of Sn ⁴⁺ :S ²⁺ is in the range of 90:10 to 10:90, the lattice strain of the ITO powder is in the range of 0.2 to 0.8. At this time, the volume resistivity is 0.20 Ω. The range below cm. From this, it was confirmed that the volume resistivity of the ITO powder having a lattice strain of 0.2 to 0.8 was low.

Claims (4)

A method for producing an ITO powder, comprising the steps of: mixing an aqueous alkali solution in a mixed aqueous solution of a trivalent indium compound and a tin compound to form a coprecipitated hydroxide of indium and tin; and washing the foregoing with pure water or ion-exchanged water a step of coprecipitating a hydroxide; a step of removing the supernatant of the coprecipitated hydroxide to prepare a slurry in which indium tin hydroxide particles are dispersed; a step of drying the slurry; and firing the dried indium tin The step of obtaining a indium tin oxide by a hydroxide, wherein in the cleaning step, the resistivity of the supernatant to the supernatant is at least 5000 Ω. In the calcination step, the dried indium tin hydroxide is fired in the air at a temperature of 250 to 800 ° C for 0.5 to 6 hours, and the tin compound is a mixture of a tetravalent tin compound and a divalent tin compound. The tin ion ratio of Sn ⁴⁺ :S ²⁺ is in the range of 90:10 to 80:20. The method of claim 1, wherein the tetravalent tin compound is an aqueous solution of SnCl ₄ and the divalent tin compound is SnCl ₂ . 2H ₂ O powder. A method of producing a dispersion in which an ITO powder produced by the method of claim 1 or 2 is dispersed in a solvent to produce a dispersion. A method of producing an ITO film, wherein an ITO film is produced from the dispersion liquid of claim 3.