JP4750491B2 - Plate-like metal titanate compound and method for producing the same - Google Patents

Description

  The present invention relates to a plate-like metal titanate compound which is a dielectric material for electronic parts and a method for producing the same.

Patent Documents 1 to 3 describe a method for producing a titanate having a plate shape or a flake shape.
Patent Document 1 describes a method for preparing a plate-like titanate having a layered structure by a heat melting method using a flux raw material. However, the obtained plate-like titanate has a large shape having a width of 2 to 3 mm, a length of 5 mm, and a thickness of 0.1 to 0.5 mm. In Patent Document 2, flaky titanate is prepared by limiting flux raw materials and processing conditions. The obtained crystal has a major axis of 30 μm, a minor axis of 15 μm, and a thickness of 2 μm. In patent document 3, plate-like titanate is prepared by baking the raw material of a target composition, without using a flux raw material. The obtained crystals have an average diameter of 4 to 15 μm and an aspect ratio of about 10.
Japanese Patent Application Laid-Open No. H5-222195 JP 2000-344520 A JP 2003-335519 A

Patent Documents 4 to 6 disclose a method for producing a metal titanate compound having a specific shape such as a fiber shape, a flake shape, a plate shape, or a spherical shape. As a method, a metal titanate compound having a specific shape is obtained by heat-reacting an alkali metal halide such as a metal sulfate using a titanate having a shape such as a fiber, flake, plate, or sphere as a raw material. It is prepared.
JP 2003-81634 A JP 2003-81635 A JP 2003-81636 A

Patent Document 7 describes that acicular barium titanate can be obtained by treating fibrous potassium titanate fibers with acid and reacting them with barium hydroxide at 80 to 95 ° C. Patent Document 8 describes that fibrous barium titanate having a length of 10 to 30 μm and an aspect ratio of 50 to 150 can be prepared by hydrothermal synthesis of barium and a titanium raw material under an excessive alkali concentration condition. In Patent Document 9, a metal titanate compound that is a precursor of plate-like barium titanate is prepared by a flux method, and titanic acid is converted to titanic acid by acid treatment and hydrothermal reaction with barium hydroxide is performed at 10 × 60 × 100 μm. There is a description that a plate-like barium titanate of a certain degree can be prepared.
JP-A-6-135720 JP-A-7-172833 JP 2000-281340 A

Patent Document 10 describes a production method for a calcium titanate compound having a plate shape by a flux method. The resulting compound has a shape of 15 to 25 μm and an aspect ratio of about 15 to 25.
JP-A-11-92144

  With the miniaturization and high integration of electronic devices, the required characteristics for dielectric materials used for multilayer chip capacitors, which are constituent parts, have become more prominent. These dielectric materials are polycrystalline, and the dielectric properties have anisotropy depending on the direction of the crystal axis. Therefore, in order to improve the dielectric properties, it is necessary to increase the orientation and align the crystal axes. In order to increase the capacity of the multilayer capacitor, it is necessary to make the dielectric thin. Accordingly, there is a demand for a metal titanate compound such as barium titanate having a high degree of orientation and a small amount.

An object of the present invention is to provide a metal titanate compound having a high degree of orientation and a small particle size.
Another object of the present invention is to provide a method for producing a metal titanate compound that can prepare a metal titanate compound having a high degree of orientation and a small particle size by hydrothermal synthesis or the like at a relatively low temperature without using a flux. .

In the present invention, the average particle diameter in the radial direction is 0.5 to 5 μm, the average particle diameter in the width direction is 0.1 to 3 μm, the average particle diameter in the thickness direction is 0.05 to 0.5 μm, and the composition formula is BTiO 3. (B is an element of at least one member of the group consisting of Mg, Ca, Sr, and Ba) and is in plate-like barium titanate titanate.

In the plate-like barium titanate of the present invention, the orientation degree i specified by the following formula (1) is 10 or more, or the orientation degree ii specified by the formula (2) is 4 or more.
Orientation degree i = I (110) / I (111) (1)
Orientation degree ii = I (110) / (I (100) + I (111)) (2)
(Where I (110), I (111), and I (100) are peak intensities obtained from X-ray diffraction spectra)

In the present invention, titanium oxide, an oxide, hydroxide or salt of element A and an oxide, hydroxide or salt of element M are hydrothermally treated in an aqueous medium at a reaction temperature of 120 to 300 ° C. By
A layered titanate represented by the general formula AxMy □ zTi (2- (x / 4 + ky / 4 + z)) O4 was prepared,
(Where A is an element of at least one member of the group consisting of Na, K, Rb, Cs, and M is at least one member of the group consisting of Li, Mg, Co, Ni, Zn, Mn (III), Fe (III)). Is an element, k represents the valence of the M element, and □ represents a defect site of Ti:
(x is a positive number of 0 <x <1.0, y is a positive number, z is 0 or a positive number, and 0 <y + z <1.0 and x> y)
The obtained layered titanate is reacted with an acid to convert it into plate-like titanate hydrate,
Further, the plate-like titanic acid hydrate is mixed with at least one member of the group consisting of Mg, Ca, Sr, Ba, and Pb (where Pb is divalent), an oxide, or a salt, and an aqueous medium under heating. By reacting in
The average particle diameter in the radial direction is 0.5 to 5 μm, the average particle diameter in the width direction is 0.1 to 3 μm, the average particle diameter in the thickness direction is 0.05 to 0.5 μm, and the composition formula is BTiO 3 (B is Mg , Ca, Sr, Ba, Pb), a plate-like metal titanate compound.
Preferably, the A element is K and the M element is Li.

  Z representing the number of Ti defect sites is generally a small number, for example, 0 or more and 0.01 or less. The element A is particularly preferably K which is inexpensive and has an appropriate ionic radius, and the element M is particularly preferably Li which can be easily removed by an acid and has a small amount of impurities. The value of x is, for example, 0.5 to 1.0, the value of y is, for example, 0.2 to 0.5, and x> y. Particularly preferably, x is 0.6 to 1.0, and y is 0. .2 to 0.4. Conversion to titanic acid hydrate with an acid is performed at room temperature to 100 ° C., particularly preferably at room temperature to 60 ° C., and reaction with a divalent element compound such as Ba (OH) 2 is performed at 60 ° C. to 200 ° C., for example. The divalent element compound is prepared in a molar ratio with the titanic acid hydrate, for example, about 1 to 1.5 times.

  The average particle diameter of the plate-like metal titanate compound is obtained from an electron microscope image obtained by providing a thin layer of the metal titanate compound on the substrate by spin coating, for example. Since the metal titanate compound particles are polygonal, the diagonal of the maximum length is the diameter, and the maximum length in the direction perpendicular to the diameter on the surface of the polygon is the width. The substrate and the thin layer are embedded in an adhesive or the like and cut at right angles to the substrate, and the thickness of the metal titanate compound particles on the cut surface is defined as the thickness.

  As shown in FIG. 3, the plate-like particles of the metal titanate compound maintain the shape of the layered titanate of FIG. 1, and there are a number of particles such as barium titanate inside one plate-like particle, The average particle size and the crystallite size are different. As shown in FIG. 3, some metal titanate particles are not plate-like, which are derived from non-plate-like particles that existed even in the original layered titanate, and plate-like titanate. This is thought to be generated by missing the corners of the particles. If the particles that are not plate-like are called granular particles, the number of granular particles is about 1/5 to 10 times the number of plate-like particles, and the size of each particle is small, so it is ignored in calculating the average particle size. It should be noted that the granular particles having a volume ratio of 20% or more of the plate-like particles are not included in the present invention.

Preferably, B is Ba,
The orientation degree i specified by the following formula (1) is 10 or more, or the orientation degree ii specified by the formula (2) is 4 or more.
Orientation degree i = I (110) / I (111) (1)
Orientation degree ii = I (110) / (I (100) + I (111)) (2)
(Where I (110), I (111), and I (100) are peak intensities obtained from X-ray diffraction spectra)

  The plate-like metal titanate compound of the present invention is used for, for example, a multilayer capacitor material.

  According to the present invention, a plate-like metal titanate compound having a small average particle diameter and a high degree of orientation can be obtained, so that a thin layer of a thin and well-oriented dielectric material can be obtained. Therefore, a multilayer capacitor having excellent characteristics can be obtained.

  In this invention, a layered titanate represented by the general formula AxMy □ zTi (2- (x / 4 + ky / 4 + z)) O4 is reacted with an acid such as nitric acid or hydrochloric acid to convert it into plate-like titanate hydrate. And reacted with Mg, Ca, Sr, Ba or Pb hydroxide, oxide, or salt in an aqueous medium under heating. In the process of converting the layered titanate to barium titanate, the initial shape is kept as a shape particle, and the crystals in one shape particle are considered to be aligned, and materials such as highly oriented multilayer capacitors Is obtained. Shape particles are particles whose diameter (the longest diagonal of the polygon) and width (the maximum width in the direction perpendicular to the diameter) are sufficiently large compared to the thickness, all of which are small in diameter, width, and thickness. Therefore, it is easy to make a thin layer.

  In this invention, the layered titanate is synthesized hydrothermally, so there is no contamination by flux and there is no need to react at 1000 ° C. or higher. The A element of the layered titanate is an element having an ionic radius larger than that of the M element, and K is optimal because it is an inexpensive element with an appropriate ionic radius. The element M is easy to remove with an acid, Li does not become an impurity source of the final metal titanate compound, and Li that can easily perform hydrothermal synthesis of the layered titanate is optimal.

  The conversion with an acid can be easily performed by replacing an A element or an M element with an H element, for example, using an excess amount of acid at room temperature. In the reaction with hydroxylated Ba or the like, hydroxylated Ba or the like is required in a molar ratio with titanic acid hydrate to be 1 or more. For example, when added twice or more, the product contains a ratio of particles other than plate-like particles. Since it increases, 1.5 times or less is preferable.

  In the following, an optimum embodiment for carrying out the present invention will be shown.

Example 1
Titanium oxide, potassium hydroxide, and lithium hydroxide were added to an autoclave with a capacity of 30 ML so that the atomic ratio of Ti: K: Li was 5: 4: 1, and the reaction was carried out at 250 ° C. for 20 hours with stirring under hydrothermal conditions. Layered particles of K0.80Li0.27 □ <0.01Ti1.73O4 were obtained. Note that □ indicating a defective portion of Ti is generally a small positive number less than 0.01. The composition of the layered particles was determined by atomic absorption analysis and confirmed to be potassium lithium titanate by X-ray diffraction. An electron micrograph of the obtained layered particles is shown in FIG. The layered particles were treated with a 1M-HNO3 aqueous solution (20 mol of HNO3 per mol of layered particles) at room temperature to obtain plate-like H2Ti2O5.H2O. An electron micrograph of the particles is shown in FIG. This was reacted in an aqueous solution of 0.3M-Ba (OH) 2 (1.1 mol of barium hydroxide per mol of titanate hydrate) at 150 ° C. for 24 hours under hydrothermal conditions. After the reaction, the filtered and washed product was dried at 105 ° C. for 5 hours to obtain barium titanate. It was confirmed that the composition was BaTiO3 and there was no segregation of Ba atoms and Ti atoms, and the crystal structure was confirmed by X-ray diffraction. An electron micrograph of the obtained barium titanate is shown in FIG.

  The hydrothermal synthesis temperature of the layered titanic acid compound is 120 to 300 ° C, preferably 140 to 270 ° C. Although the medium is water, it may contain a small amount of medium other than water such as ethanol, and the reaction time is, for example, 5 hours to 50 hours. As the element A, Na may be used, but since the ionic radius is smaller than that of K, preparation of the layered titanate compound is somewhat difficult, and Rb and Cs are expensive, so K is preferable. Mg, Co, Ni, Zn, or trivalent Mn or Fe may be used instead of Li, but Li is preferable because the layered titanate compound can be easily prepared and removed with an acid. Even when elements other than K and Li are used, the layered titanate compound can be prepared under the same conditions. Since it is hydrothermal synthesis, the layered titanate compound can be prepared in the same manner even if the A element and the M element are not limited to hydroxides, but are added as oxides, halides, nitrates, and other salts. The alkaline earth such as Ba and the Pb source may be salts such as chlorides and nitrates, but oxides and hydroxides are preferable for easy cleaning, and hydroxides are particularly preferable for easy reaction. .

  The product, barium titanate, was added to 2 ml of ethanol per 0.1 g of sample, dispersed with an ultrasonic disperser for 30 minutes, spin-coated onto a 76 × 26 mm glass substrate at 4000 rpm to form a thin layer, and a scanning electron microscope Observed at. The plate-like barium titanate particles are polygonal, and the maximum diagonal line is the diameter, and the maximum width in the direction perpendicular to the diameter is the width. The substrate was fixed to an adhesive, cut at right angles to the substrate, and the cut surface was similarly observed with a scanning electron microscope, and the average thickness of the barium titanate particles was determined. The diameter, width, and thickness are simple averages that do not consider the size of the particles, but they are not included in the calculation of the average particle size in view of the fact that non-plate-like particles are negligibly small in volume ratio. In Example 1, the average particle diameter in the radial direction was 4.8 μm, the average particle diameter in the width direction was 2.8 μm, and the thickness direction was 0.3 μm.

  In the same manner as described above, a thin layer of barium titanate was prepared on a glass substrate and measured by X-ray diffraction. As a result, the degree of orientation i according to Equation 1 was 31, and the degree of orientation ii according to Equation 2 was 10. 1 In addition, the average particle diameter and orientation degree of the barium titanate particles in the following are values measured according to the above. A plate-like barium titanate having a small diameter, width and thickness, particularly a small thickness and strongly oriented in the (110) plane was obtained.

Example 2
Titanium oxide, potassium hydroxide, and lithium hydroxide were added to a 30 ML autoclave so that the ratio of Ti: K: Li was 5: 4: 1, and the mixture was reacted at 150 ° C. for 20 hours under hydrothermal conditions with stirring. (2-0.25 (x + y)) O4 was obtained. Note that z indicating the amount of Ti defect sites was 0.01 or less, x was about 0.8, and y was about 0.3. The obtained layered titanate was treated with an excess amount of 1M-HNO3 aqueous solution at room temperature to obtain plate-like H2Ti2O5.H2O, and further in an aqueous solution of 0.3M-Ba (OH) 2 (1.3 equivalents). The reaction was carried out at 100 ° C. for 24 hours under hydrothermal conditions. After the reaction, the filtered and washed product was dried at 105 ° C. for 5 hours.

  As a result of X-ray diffraction of the obtained product, it was found that the product was only barium titanate, the average particle size in the radial direction was 3.0 μm, the average particle size in the width direction was 1.0 μm, and the thickness direction was 0.0 μm. The plate-like particles were 2 μm. Further, the degree of orientation i according to the formula 1 was 20, and the degree of orientation ii according to the formula 2 was 5.67. The average particle diameter could be reduced by lowering the hydrothermal synthesis temperature of the layered titanate. When the hydrothermal reaction temperature in the autoclave was lowered from 250 ° C. to 110 ° C. and the reaction time was 60 hours (others were the same as in Example 1), the layered titanate could not be synthesized.

  As described above, barium titanate or the like having a small plate shape suitable for a multilayer capacitor material, a particularly small thickness, and highly oriented was obtained.

Comparative Example: A commercially available reagent BaTiO 3 -powder-nanosize (manufactured by Wako Pure Chemical Industries, Ltd.) was applied thinly on a glass substrate under the same conditions as in Example 1 to form a thin film, and the result of measurement by X-ray diffraction The degree of orientation i according to formula 1 was 5, and the degree of orientation ii according to formula 2 was 2.03. In addition, in the commercially available reagent BaTiO3 (manufactured by Wako Pure Chemical Industries, Ltd.), the degree of orientation i according to formula 1 was 4, and the degree of orientation ii according to formula 2 was 1.86.

Scanning electron micrograph showing the ceramic particle structure of the layered titanate prepared in the examples Scanning electron micrograph showing the ceramic particle structure of titanic acid hydrate produced by reaction of the layered titanate of FIG. 1 with an acid Scanning electron micrograph showing the ceramic particle structure of plate-like barium titanate obtained by reacting the titanate hydrate of FIG. 2 with barium hydroxide

Claims (5)

The average particle diameter in the radial direction is 0.5 to 5 μm, the average particle diameter in the width direction is 0.1 to 3 μm, the average particle diameter in the thickness direction is 0.05 to 0.5 μm, and the composition formula is BaTiO 3. A plate-like barium titanate having an orientation degree i defined by the formula (1) of 10 or more or an orientation degree ii defined by the formula (2) of 4 or more.
Orientation degree i = I (110) / I (111) (1)
Orientation degree ii = I (110) / (I (100) + I (111)) (2)
(Where I (110), I (111), and I (100) are peak intensities obtained from X-ray diffraction spectra) Titanium oxide and oxides, hydroxides or salts of element A and oxides, hydroxides or salts of element M are hydrothermally treated in an aqueous medium at a reaction temperature of 120 to 300 ° C.
A layered titanate represented by the general formula AxMy □ zTi (2- (x / 4 + ky / 4 + z)) O4 was prepared,
(Where A is an element of at least one member of the group consisting of Na, K, Rb, Cs, and M is at least one member of the group consisting of Li, Mg, Co, Ni, Zn, Mn (III), Fe (III)). Is an element, k represents the valence of the M element, and □ represents a defect site of Ti:
(x is a positive number of 0 <x <1.0, y is a positive number, z is 0 or a positive number, and 0 <y + z <1.0 and x> y)
The obtained layered titanate is reacted with an acid to convert it into plate-like titanate hydrate,
Further, the plate-like titanic acid hydrate is mixed with at least one member of the group consisting of Mg, Ca, Sr, Ba, and Pb (where Pb is divalent), an oxide, or a salt, and an aqueous medium under heating. By reacting in
The average particle diameter in the radial direction is 0.5 to 5 μm, the average particle diameter in the width direction is 0.1 to 3 μm, the average particle diameter in the thickness direction is 0.05 to 0.5 μm, and the composition formula is BTiO 3 (B is Mg , Ca, Sr, Ba, Pb), a plate-like metal titanate compound. B is Ba,
3. The plate-like metal titanate compound according to claim 2 , wherein the orientation degree i defined by the following formula (1) is 10 or more, or the orientation degree ii defined by the formula (2) is 4 or more. Method.
Orientation degree i = I (110) / I (111) (1)
Orientation degree ii = I (110) / (I (100) + I (111)) (2)
(Where I (110), I (111), and I (100) are peak intensities obtained from X-ray diffraction spectra) 4. The method for producing a plate-like metal titanate compound according to claim 2 , wherein the A element is K and the M element is Li. The plate-like metal titanate compound according to claim 1 for a multilayer capacitor.