JP4096152B2 - Dielectric composition - Google Patents

Description

【００９０】
【表２】

【００９１】
【表３】

【００９２】
比較例２〜４で得られたチタン酸バリウム粒子粉末のＸ線回折パターンを図５〜７に示す。Ｘ線回折パターンからＢａＴｉＯ_３以外のピークも見られることから、単一結晶ではないことが確認された。
【００９３】
また、比較例５及び６で得られた誘電体組成物を前記発明の実施の形態と同様にして誘電体単板を作製し、誘電体単板の誘電率を測定した。比較例５の誘電体組成物を用いて作製した誘電体単板では誘電率が高いものの粒子径が大きいため粒子界面が減少し耐電圧が低下して信頼性が低下するものである。比較例６の誘電体組成物を用いて作製した誘電体単板では誘電率が低いものであった。
【００９４】
【発明の効果】
本発明に係る誘電体組成物は、平均粒子径が０．０５〜０．５μｍであり、結晶構造が正方晶であって結晶性が高い球状チタン酸バリウム粒子粉末からなるので、誘電率が高く、温度依存性が低い積層コンデンサ用として好適である。
【図面の簡単な説明】
【図１】発明の実施の形態で得られた誘電体組成物の粒子形状を示す透過型電子顕微鏡写真（２０，０００倍）
【図２】発明の実施の形態で得られた誘電体組成物のＸ線回折パターン
【図３】発明の実施の形態で得られた誘電体組成物、参考例及び比較例１の各誘電体単板の誘電率の温度依存性を示すグラフである。
【図４】比較例１で得られた誘電体組成物の粒子形状を示す透過型電子顕微鏡写真（２０，０００倍）
【図５】比較例２で得られたチタン酸バリウム粒子粉末のＸ線回折パターン
【図６】比較例３で得られたチタン酸バリウム粒子粉末のＸ線回折パターン
【図７】比較例４で得られたチタン酸バリウム粒子粉末のＸ線回折パターン[0001]
[Industrial application fields]
The present invention relates to a spherical dielectric having an average particle diameter of 0.05 to 0.5 μm used for a multilayer capacitor having a high dielectric constant, a tetragonal crystal structure and high crystallinity.Particle powderIt is about.
[0002]
[Prior art]
In recent years, with the reduction in size, performance, and weight of various electronic devices, further improvement in characteristics is desired for electronic device parts, such as multilayer capacitors.
[0003]
That is, multilayer capacitors are required to have a high dielectric constant and low temperature dependency in accordance with demands for miniaturization and high performance.
[0004]
As is well known, a multilayer capacitor uses a barium titanate particle powder, which is a perovskite compound and has a high dielectric constant, and the barium titanate particle powder used for the multilayer capacitor has no agglomeration, excellent dispersibility, and is dense. Therefore, there is a strong demand for high purity and excellent dielectric properties.
[0005]
As the barium titanate particle powder satisfying the above-mentioned properties, the particle shape must be spherical and have an excellent particle size distribution, and Ba / Ti is as much as possible in consideration of dielectric properties. Therefore, it is necessary that the crystal system is tetragonal.
[0006]
Known methods for producing barium titanate particles include a solid phase reaction in which a titanium compound and a barium compound are mixed and baked at a high temperature of 1000 ° C. or higher, and a wet reaction in which barium and titanium are reacted in a solution.
[0007]
Since the barium titanate particle powder obtained by the solid phase reaction has a large average particle size, it is difficult to say that the particle size distribution is bad and the shape is also suitable for dispersion because the fired powder is pulverized and used. It was. Therefore, production of barium titanate particles by the wet reaction has been performed.
[0008]
In the wet reaction, in order to obtain a barium titanate particle powder having Ba / Ti as close to 1.0 as possible, “BaTiO of Ba / Ti = 1” is used.₃A relatively large amount of Ba to synthesize²⁺Need. In this study, it was found that Ba / Ti = 8 was required for mixing in order to obtain a Ba / Ti ratio of 1 in the composite. In the case of Ba / Ti below that, barium-deficient barium titanate is obtained ”(Journal of the Chemical Society of Japan, No. 7, 1155 (1974)), and it is necessary to add excess Ba to Ti. is there.
[0009]
In order to obtain tetragonal barium titanate particles, it is necessary to transform the crystal system from cubic to tetragonal at a high temperature of 800 ° C. or higher. The resulting barium titanate particle powder has a polygonal shape, and it is difficult to say that the particle size distribution is sufficient.
[0010]
Conventionally, as a method for producing barium titanate particles by wet reaction, JP-A-61-31345, JP-A-62-72525, JP-A-2998211, JP-A-5-330824, JP-A-5-330824 Each method described in Japanese Patent Application Laid-Open No. 8-119745 is known. Further, coating the surface of barium titanate particles with silica or the like is described in JP-A Nos. 61-111957, 7-330427, 2000-509703, and the like.
[0011]
[Problems to be solved by the invention]
Barium titanate that satisfies the above-mentioned properties is currently most demanded, but has not yet been obtained.
[0012]
That is, in the method described in JP-A-61-31345, barium titanate having a Ba / Ti ratio of 1.00 is obtained by synthesizing barium titanate particles and then insolubilizing unreacted barium. Although it is a particle powder, it is a mixture of cubic barium titanate and Ba compound, and in order to make tetragonal barium titanate alone, the same high temperature as in the solid phase reaction is required, and the generated tetragonal crystal It is difficult to say that the particle size distribution of the barium titanate particles is sufficient.
[0013]
In addition, the above-mentioned JP-A-62-72525 describes a method of hydrothermal synthesis by dissolving a barium compound in an aqueous solution of titanium tetrachloride and adding an alkaline aqueous solution. When the particle powder is calcined, it is difficult to say that it has high dielectric properties because it is not a single crystal as shown in a comparative example.
[0014]
In addition, the above-mentioned Japanese Patent No. 2999821 describes a method of reacting excess barium and titanium to obtain barium titanate particles and calcining, and then pickling excess barium. The particle shape is a rectangular parallelepiped, and in pickling, Ba in the barium titanate crystal is likely to be eluted, and it is difficult to control the Ba / Ti ratio. At the same time, pickling is not preferable because the crystallinity of the particle surface of the barium titanate particle powder also decreases.
[0015]
In addition, the above-mentioned JP-A-5-330824 describes a method in which a titanium compound and a barium compound are wet-reacted by adding hydrogen peroxide water. The resulting barium titanate particle powder is cubic. In order to obtain tetragonal barium titanate, calcination is required. In addition, the publication discloses that [[0071] tetragonal barium titanate is obtained when calcined at 900 to 1300 ° C. In this case, when the temperature is low and the particle size is large, it becomes spherical. Or, when calcined at a high temperature, a cuboidal single crystal powder is obtained. ”As described, the particles having a small average particle diameter, particularly, a tetragonal crystal in a fine barium titanate particle powder having an average particle diameter of 0.5 μm or less. It is difficult to obtain spherical barium titanate particles.
[0016]
Further, as shown in the comparative example, a wet reaction is carried out according to Example 5 described in JP-A-5-330824, the product is washed with water, filtered and dried, and cubic titanic acid having a Ba / Ti ratio of 1.002. Barium was obtained, and this product was calcined at 1020 ° C. and measured by X-ray diffraction.₃Other peaks appear (BaTi₃O₇It is difficult to say that the particle powder after calcining is not a single crystal and therefore has excellent dielectric properties.
[0017]
In addition, the above-mentioned JP-A-8-119745 describes a method for obtaining barium titanate particle powder by hydrothermal reaction of a mixture of barium hydroxide and titanium hydroxide. The particle powder is a cubic crystal, and as shown in the following comparative examples, when this particle powder is calcined, it is difficult to say that it is not a single crystal and has excellent dielectric properties.
[0018]
Further, the above-mentioned Japanese Patent Application Laid-Open No. 61-11957 discloses a technique for mixing and firing a low melting point material composed of an oxide of an element selected from Bi, B, Pb and W and cubic barium titanate. However, since firing is performed using cubic barium titanate, a low-boiling substance and barium titanate react to form a part of a solid solution, so that it is difficult to say that the dielectric has a high dielectric constant.
[0019]
In addition, the above-mentioned Japanese Patent Application Laid-Open No. 7-330427 describes a technique in which the surface of the barium titanate particles is coated with alumina and is baked by adding a glass component. However, it is described that voids are generated due to the reaction and that the dielectric constant is reduced, and the addition of a small amount of silica does not improve the dielectric properties of the barium titanate particles.
[0020]
In addition, in the above-mentioned special table 2000-509703, barium titanate particles whose particle surfaces are coated with a metal oxide, a metal hydrated oxide, a metal hydroxide or an organic acid salt are described. The invention described in the publication is intended to improve dispersibility by controlling the surface coating and the particle size distribution, and is not intended to prevent sintering, and the crystal system and crystallinity are considered. Not.
[0021]
In addition, the above-mentioned Japanese Patent No. 3146961 describes that the Si component is contained in the barium titanate particles, but the crystal system is not considered, and the Si component and barium titanate are dissolved. As a result, the ratio of contribution to dielectricity decreases, so the dielectric constant tends to decrease.
[0022]
Accordingly, the present invention provides a spherical dielectric that has no aggregation, excellent dispersibility, is dense, has high purity, and has excellent dielectric properties.Particle powderIt is a technical challenge to provide
[0023]
[Means for solving the problems]
The technical problem can be achieved by the present invention as follows.
[0024]
That is, the present invention provides one or two kinds selected from Si, Y, and Nd on the surface of spherical barium titanate particles having a Ba / Ti ratio of 0.99 to 1.01 and a crystal system of tetragonal crystal. The sintering inhibitor comprising the oxides of the above elements was coated on the spherical barium titanate particle powder in an amount of 0.01 to 3.0% by weight, and the average particle size was 0.05 to 0.5 μm. And a dielectric having a particle size distribution σg of 0.70 or moreParticle powderAnd the dielectricParticle powderWhen adding barium salt aqueous solution to titanium hydroxide colloid to produce barium titanate core particles, 1 to 60 mol% of carboxylic acid is present with respect to the number of moles of barium in the barium salt aqueous solution, In addition, the ratio of titanium to barium (Ba / Ti) is set to 1.00 to 1.10, and then the reaction solution containing the barium titanate core particles is hydrothermally treated in a temperature range of 100 to 350 ° C. to form cubic crystals. After the spherical barium titanate particles were obtained and washed with water, the particle surface of the spherical barium titanate particles was coated with a sintering inhibitor comprising a compound of one or more elements selected from Si, Y, and Nd. It can be obtained by calcining in the temperature range of 800 to 1200 ° C. to make the crystal system of barium titanate particles tetragonal.
[0025]
The configuration of the present invention will be described in more detail as follows.Hereinafter, the “dielectric particle powder” according to the present invention is expressed as “dielectric composition”.
[0026]
The dielectric composition according to the present invention has an average particle size of 0.05 to 0.5 μm and a particle size distribution σg of 0.70 or more.
[0027]
When the average particle diameter is less than 0.05 μm, the packing density is low and the shrinkage during sintering is large when molding is performed. When the thickness exceeds 0.5 μm, it is difficult to reduce the thickness of the dielectric layer of the multilayer capacitor. Preferably it is 0.05-0.4 micrometer.
[0028]
When the particle size distribution σg of the particle diameter is less than 0.7, the thickness of the dielectric layer of the multilayer capacitor becomes nonuniform due to the coarse particles present. Preferably it is 0.75 or more. The upper limit is preferably 0.9.
[0029]
The sphericity (longest diameter / shortest diameter) of the dielectric composition according to the present invention is preferably 1.0 or more and less than 2.0, more preferably 1.0 to 1.4, and most preferably 1.0 to 1. 3.
[0030]
The BET specific surface area value of the dielectric composition according to the present invention is 2 to 20 m.²/ G is preferred. 2m²If it is less than / g, the particles are coarse or particles are sintered between the particles, and the dispersibility tends to be impaired. BET specific surface area value is 20m²When the amount exceeds / g, aggregation is likely to occur due to an increase in surface adsorption force due to particle miniaturization, and thus dispersibility decreases.
[0031]
The composition ratio (Ba / Ti) of barium and titanium of the spherical barium titanate particles in the present invention is 0.99 to 1.01, preferably 0.99 to 1.008. When the Ba / Ti ratio is out of the above range, it is difficult to obtain a multilayer capacitor having high dielectric properties when the multilayer capacitor is used.
[0032]
The crystal system of the spherical barium titanate particles in the present invention is tetragonal. When the crystal system is a cubic crystal, the crystallinity is insufficient, so that when a multilayer capacitor is used, the physical characteristics and electrical characteristics of the capacitor are deteriorated.
[0033]
The crystallinity of the spherical barium titanate particles in the present invention is ((c / a) -1) × 10 using the a-axis length and c-axis length of the lattice constant.³Is preferably 5 or more, more preferably 7 or more. It is not preferable that the crystallinity is close to 0 because the crystal system is close to cubic. The upper limit is 16.
[0034]
In the dielectric composition according to the present invention, the surface of the spherical barium titanate particles is coated with a sintering inhibitor comprising an oxide of one or more elements selected from Si, Y, and Nd.
[0035]
When the particle surface of the barium titanate particles is not coated with a sintering inhibitor, sintering between particles and particle enlargement cannot be suppressed during calcination, so the calcination temperature may be increased. Therefore, it is difficult to obtain a dielectric having a high dielectric constant. As the sintering inhibitor, Si oxide and Y oxide are preferable.
[0036]
The coating amount of the sintering inhibitor on the spherical barium titanate particle powder is 0.01 to 3.0% by weight, preferably 0.01 to 1.5% by weight, more preferably, to the barium titanate particle powder. 0.02 to 0.5% by weight.
[0037]
When the coating amount by the sintering inhibitor is less than 0.01% by weight, it is difficult to say that the intended sintering preventing effect is sufficient. When it exceeds 3.0% by weight, not only the effect is saturated, but also the capacity is lowered when the final capacitor is obtained, so there is no point in adding more than necessary.
[0038]
In the present invention, since the coating amount of the sintering inhibitor is small, the particle size of the spherical barium titanate particles used is approximately the same as the particle size of the target dielectric composition, and the barium titanate particles The average particle diameter is preferably 0.05 to 0.5 μm, and the particle size distribution σg is preferably 0.70 or more.
[0039]
Next, a method for producing the dielectric composition according to the present invention will be described.
[0040]
The dielectric composition according to the present invention is obtained by adding an aqueous barium salt solution to a titanium hydroxide colloid in the presence of 1 to 60 mol% of carboxylic acid based on the number of moles of barium in the aqueous barium salt solution. Barium core particles are generated, and then the reaction solution containing the barium titanate core particles is hydrothermally treated in a temperature range of 100 to 350 ° C. to obtain cubic spherical barium titanate particles. After washing with water, the spherical titanate The surface of the barium particles is coated with a predetermined amount of a sintering inhibitor comprising a compound of one or more elements selected from Si, Y and Nd, and then calcined at a temperature range of 800 to 1200 ° C. It is obtained by making the system tetragonal.
[0041]
The titanium hydroxide colloid in the present invention can be obtained by neutralizing a titanium salt aqueous solution with an alkaline aqueous solution. As the titanium salt aqueous solution, titanium tetrachloride, titanium sulfate and the like can be used.
[0042]
As the alkaline aqueous solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, aqueous ammonia, or the like can be used.
[0043]
The addition amount of the alkaline aqueous solution is preferably 1.0 to 1.5 with respect to the number of moles of titanium.
[0044]
As the barium salt aqueous solution, barium hydroxide, barium chloride, barium nitrate and the like can be used. Other than barium hydroxide, it is preferable to neutralize with an alkaline aqueous solution and use as basic.
[0045]
As the carboxylic acid, propionic acid, acetic acid and salts thereof can be used.
[0046]
The amount of carboxylic acid added is 1 to 60 mol% with respect to the number of moles of barium in the barium salt aqueous solution. When the amount is less than 1 mol%, the effect is insufficient, and when it exceeds 60 mol%, the effect is saturated, so there is no meaning to add more than necessary. Preferably it is 3-50 mol%.
[0047]
Carboxylic acid may be added to an alkaline aqueous solution, or may be added to a reaction solution containing a titanium hydroxide colloid obtained by reacting a titanium salt aqueous solution and an alkaline aqueous solution.
[0048]
The charge composition (Ba / Ti) of titanium and barium is preferably 1.00 to 1.10, and more preferably 1.00 to 1.08. When it is less than 1.00, the production yield of barium titanate core particles is lowered. When it exceeds 1.10, different phases other than barium titanate are liable to occur.
[0049]
In this invention, it is preferable to age | cure | ripen after adding barium salt aqueous solution. By aging, the effect of adding carboxylic acid is improved. The aging temperature is 40 to 100 ° C, preferably 60 to 100 ° C. The aging time is preferably 0.5 to 5 hours. If it is less than 0.5 hours, sufficient effects cannot be obtained. When it exceeds 5 hours, it is hard to say that it is industrial.
[0050]
It is necessary to flow nitrogen during the reaction so that the barium compound does not react with carbon dioxide in the air.
[0051]
The barium titanate core particles are preferably spherical particles having an average particle diameter of 0.01 to 0.50 μm.
[0052]
Next, the reaction solution containing the barium titanate core particles is hydrothermally treated. The reaction temperature of the hydrothermal treatment is preferably 100 to 350 ° C. When the temperature is lower than 100 ° C., it is difficult to obtain dense spherical barium titanate particles. It is difficult to say that the treatment exceeding 350 ° C. is industrial. Preferably it is 120-300 degreeC.
[0053]
The particles after hydrothermal treatment are washed with water. Excess barium can be washed away by washing with water. Further, impurities such as sodium and Cl can be removed at the same time.
[0054]
After hydrothermal synthesis, the washed particles are cubic spherical barium titanate particles having an average diameter of 0.01 to 0.50 μm and Ba / Ti of 0.99 to 1.01.
[0055]
The cubic spherical barium titanate particles are surface-coated with a sintering inhibitor. Each element of Si, Y and Nd used as a sintering inhibitor may be coated in any state of oxide, hydroxide and hydrated oxide. In the case of hydroxide and hydrated oxide, it will be described later. It becomes an oxide by calcination.
[0056]
The coating process may be either a dry process or a wet process, but a wet process is preferred.
[0057]
The wet treatment may be performed by a conventional method. For example, a compound containing an anion is added to a suspension containing spherical barium titanate particles to form a hardly soluble precipitate of Si, Y, and Nd to form spherical titanate. These include a method of precipitation on the surface of barium particles and a method of hydrolysis of organic silicic acids such as 3-aminopropyltriethoxysilane.
[0058]
The dry treatment may be performed by a conventional method, for example, a method of adsorbing the silane coupling agent on the surface of the spherical barium titanate particles using a mechanochemical reaction with a dry mixing and grinding machine.
[0059]
As the Si compound used for the coating treatment, No. 3 water glass, sodium orthosilicate, sodium metasilicate and the like, and organic silicates such as ethyl silicate and 3-aminopropyltriethoxysilane are preferable. As the Y compound, yttrium nitrate, yttrium chloride and the like are preferable. As the Nd compound, neodymium nitrate and neodymium chloride are preferable.
[0060]
The processing amount of the sintering inhibitor is preferably 0.01 to 3.0% by weight with respect to the spherical barium titanate particles.
[0061]
Spherical barium titanate particles that have been surface-treated with a sintering inhibitor are calcined in a temperature range of 800 to 1200 ° C. to transform the crystal system into tetragonal crystals. Although it can be transformed into a tetragonal crystal even in a temperature range of 500 to 800 ° C., it is difficult to sufficiently increase the crystallinity. Since it can be transformed into tetragonal crystals with high crystallinity by calcining at 800 to 1200 ° C., the temperature does not have to be higher than necessary. Preferably it is 900-1150 degreeC.
[0062]
The multilayer capacitor can be produced by a conventional method. For example, the dielectric composition and various additives are mixed, and a solvent / binder is added to form a slurry, which is then formed into a green sheet. The internal electrode is printed by using it, cut out, and then laminated and pressed using a press. The green chip can be fired to form an external electrode.
[0063]
DETAILED DESCRIPTION OF THE INVENTION
A typical embodiment of the present invention is as follows.
[0064]
The average particle size of the dielectric composition was determined by measuring the particle size of about 350 particles shown in a photograph obtained by enlarging the electron micrograph (× 20,000) four times in the vertical direction and the horizontal direction. Indicated by value.
[0065]
The particle shape of the dielectric composition was judged from the electron micrograph.
[0066]
The particle size distribution of the dielectric composition was indicated by the geometric standard deviation value σg obtained by the following method.
[0067]
That is, the major axis diameter of 350 particles shown in the above enlarged photograph is measured, and the actual major axis diameter and the number of particles obtained by calculation from the measured values are used on a log-normal probability paper according to a statistical method. The horizontal axis of the graph plots the major axis diameter, and the vertical axis plots the cumulative number of particles belonging to each of the predetermined major axis diameter sections (under integrated sieve) as a percentage. Then, the value of the major axis diameter corresponding to the number of particles of 50% and 84.13% is read from this graph, the major axis diameter (μm) at the number of 50% is the major axis diameter at the number of 84.13% ( It was shown by the value divided by μm). The closer the geometric standard deviation value is to 1, the better the particle size distribution of the major axis diameter of the particles.
[0068]
The Ba / Ti ratio and the coating amount of the sintering inhibitor were measured using a “fluorescence X-ray analyzer Simultix 12” (manufactured by Rigaku Corporation).
[0069]
The specific surface area value was indicated by a value measured by the BET method.
[0070]
The crystal structure of the barium titanate particle powder is obtained by using “X-ray diffractometer RINT-II00K” (manufactured by Rigaku Corporation) (tube: Cu) and measuring 2θ in the range of 10 to 90 °. It was judged from the obtained diffraction peak.
[0071]
<Production of barium titanate particle powder>
175.2 g (Ti = 0.600 mol) of a titanium tetrachloride aqueous solution (manufactured by Sumitomo Sitix Kashiwazaki Co., Ltd., Ti = 3.43 mol / kg) was added to 250 ml of pure water in a nitrogen atmosphere, and 11.6 g of sodium propionate was further added. 557 ml of a sodium hydroxide aqueous solution (6.1 N) containing (0.121 mol) was added to obtain a titanium hydroxide colloid.
[0072]
Next, Ba (OH)₂・ 8H₂A barium salt aqueous solution obtained by heating and dissolving 197.1 g (Ba = 0.006 mol) of O (manufactured by Kanto Chemical Co., Ltd.) in 1000 ml of pure water was added to the solution containing the titanium hydroxide colloid, Further, pure water was added to make the total amount 2000 ml (Ba / Ti atomic ratio = 1.01, propionic acid / Ba = 20 ml%). The solution was aged at 70 ° C. for 2 hours to obtain barium titanate core particles. Next, hydrothermal treatment was performed at 150 ° C. for 16 hours. After cooling to room temperature, it was washed with Nutsche until no Ba ions were observed in the filtrate, filtered and dried to obtain barium titanate particle powder.
[0073]
The obtained barium titanate particle powder is a spherical particle having an average particle diameter of 0.2 μm and a sphericity of 1.01, the crystal system is cubic, and the Ba / Ti atomic ratio is 1.001. there were.
[0074]
65 g of the spherical barium titanate particle powder obtained here was slurried by grinding with 100 g of water for 24 hours using 1 mm zirconia beads having a diameter of 260 g in a ball mill. 0.325 g of sodium silicate (No. 3 water glass) was added to the slurry (on the basis of barium titanate particle powder, SiO 2₂As 0.143% by weight). After that, it is washed with Nutsche, filtered and dried to obtain SiO.₂Coated barium titanate particle powder was obtained. The obtained spherical barium titanate particle powder was calcined at 1100 ° C. for 3 hours in an electric furnace to obtain a dielectric composition.
[0075]
As shown in FIG. 1, the obtained dielectric composition was spherical particles having an average particle size of 0.22 μm, a particle size distribution σg of 0.81, and a sphericity of 1.04. Ba / Ti atomic ratio is 1.001, SiO₂/ BaTiO₃Is 0.10% by weight, and the BET specific surface area is 3.8 m.²/ G. The result of X-ray diffraction of the dielectric composition is shown in FIG. As is apparent from FIG. 2, BaTiO₃Since no diffraction peak other than that is seen, BaTiO₃It was confirmed to be a single crystal, a perovskite structure, and a tetragonal crystal. The crystallinity was 10. In addition, SiO₂Was not confirmed by X-ray diffraction.
[0076]
<Preparation of single plate for dielectric property measurement>
The dielectric composition obtained here was mixed with 98 mol% BaTiO of niobium oxide and cobalt oxide.₃-1.5 mol% Nb₂O₅-0.5 mol% Co₃O₄Then, the mixture was pulverized for 5 minutes using a Reika machine equipped with an agate mortar. A PVA solution (Kuraray RS2117 dissolved in a concentration of 4 wt%) is mixed with the pulverized product (dielectric composition), pulverized for 10 minutes using a raikai machine in which an agate mortar is set, and then a 500 μm stainless steel sieve is used. The resulting mixture was sized and dried with a dryer at 100 ° C. for 60 minutes.
After drying, the sized product obtained here is filled in a 21.2 mmφ mold, and 2 g is 1 t / cm for 3 seconds with a pressurizer.²Press molding with the molding pressure of
The molded body was placed on an alumina plate, heated to 1150-1300 ° C. at a heating rate of 100 ° C./hr in an electric furnace, and fired at that temperature for 4 hours.
Ag paste was applied to the fired product and held in an electric furnace at 700 ° C. for 2 hours, and the Ag electrode was baked to obtain a dielectric single plate.
[0077]
The dielectric constant ε and dielectric loss tan δ of the obtained dielectric single plate are temperature characteristics at −55 to 150 ° C. with an input signal level of 1 Vrms and a frequency of 1 kHz using an LCR meter (Hewlett Packard, 1 kHz / 1 MHz Capacitance Meter). Was measured.
[0078]
FIG. 3 shows the temperature dependence of the measured dielectric constant ε. Since the dielectric constant is high and there is no projecting peak between −20 and 120 ° C., it can be seen that the dielectric constant does not depend on temperature and the temperature dependence is low. The result in the reference example is shown in FIG. It can be seen that the dielectric constant is lower than that of the present invention.
[0079]
[Action]
The most important point in the present invention is that the dielectric composition according to the present invention is spherical and has an excellent particle size distribution, and since the crystal system is tetragonal and has high crystallinity, it has excellent dispersibility and high The fact is that it has a dielectric constant.
[0080]
The reason why the dielectric composition according to the present invention is spherical and has an excellent particle size distribution is that a carboxylic acid is added to the titanium hydroxide colloid in advance to effectively adsorb barium on the titanium hydroxide colloid, thereby producing a balanced titanic acid. Barium core particles are generated, and then the crystallinity is enhanced by hydrothermal treatment. Furthermore, the surface of the particle surface is coated with a sintering inhibitor, so that there is less sintering between particles, and the particle shape before calcination It is presumed that the crystal system could be transformed while maintaining the spherical shape.
[0081]
The high crystallinity of the dielectric composition according to the present invention is that the surface of cubic barium titanate particles is coated with an anti-sintering agent, thereby suppressing sintering even when calcined at a higher temperature. It is estimated that it was possible to do.
[0082]
Usually, when making a multilayer capacitor, a barium titanate particle powder and a glass component are mixed and subjected to main firing, and a glass component or the like is formed so as to cover the core of the barium titanate particle and the particle surface of the barium titanate particle. A core-shell structure is formed in which a shell is formed. When the dielectric composition according to the present invention is used, since the particle surface of the barium titanate particles is coated with the sintering inhibitor, unnecessary components are not dissolved in the barium titanate core. Therefore, it is possible to obtain a multilayer capacitor having a high dielectric constant and a low temperature dependence of the capacitance while maintaining the characteristics of barium titanate.
[0083]
【Example】
Next, examples and comparative examples are given.
[0084]
Examples 1-4, reference examples, comparative examples 1, 5 and 6:
Titanium salt type and reaction concentration, alkaline aqueous solution type and addition ratio, barium salt type and addition ratio, carboxylic acid type and addition amount, hydrothermal treatment temperature and time, sintering inhibitor type and coating amount, temporary A dielectric composition was obtained in the same manner as in the above embodiment except that the baking temperature and time were variously changed.
[0085]
In the dielectric composition obtained in each example, the crystal system of barium titanate is tetragonal. As a result of X-ray diffraction, BaTiO₃No other peaks were observed, and it was confirmed to be a barium titanate single crystal. When the dielectric constant of the dielectric single plate produced using the obtained dielectric composition was measured, it showed a high dielectric constant as in the embodiment of the invention.
[0086]
A dielectric single plate was produced from the dielectric composition obtained in Reference Example and Comparative Example 1 in the same manner as in the above-described embodiment, and the dielectric constant of the dielectric single plate was measured. The measurement results of the dielectric constant are shown in FIG. It is clear that the dielectric single plate produced using the dielectric composition of the reference example and the comparative example has a low dielectric constant.
[0087]
Comparative Examples 2-4
Comparative Example 2 is Example 1 of JP-A-62-72525, Comparative Example 3 is Example 5 of JP-A-5-330824, and Comparative Example 4 is Example of JP-A-8-119745. It is the particle powder obtained by calcining the barium titanate particle powder produced based on the material number 4 at 1020 ° C. for 3 hours.
[0088]
The production conditions at this time are shown in Tables 1 and 2, and the characteristics of the obtained dielectric composition are shown in Table 3.
[0089]
[Table 1]

[0090]
[Table 2]

[0091]
[Table 3]

[0092]
The X-ray diffraction patterns of the barium titanate particle powders obtained in Comparative Examples 2 to 4 are shown in FIGS. BaTiO from X-ray diffraction pattern₃Since other peaks were also observed, it was confirmed that the crystals were not single crystals.
[0093]
A dielectric single plate was produced from the dielectric compositions obtained in Comparative Examples 5 and 6 in the same manner as in the above-described embodiment, and the dielectric constant of the dielectric single plate was measured. In the dielectric single plate produced using the dielectric composition of Comparative Example 5, although the dielectric constant is high, the particle diameter is large, so the particle interface is reduced, the withstand voltage is lowered, and the reliability is lowered. A dielectric single plate produced using the dielectric composition of Comparative Example 6 had a low dielectric constant.
[0094]
【The invention's effect】
Since the dielectric composition according to the present invention is composed of spherical barium titanate particles having an average particle diameter of 0.05 to 0.5 μm, a tetragonal crystal structure and high crystallinity, the dielectric constant is high. It is suitable for a multilayer capacitor having low temperature dependency.
[Brief description of the drawings]
FIG. 1 is a transmission electron micrograph (magnification of 20,000) showing the particle shape of a dielectric composition obtained in an embodiment of the invention.
FIG. 2 shows an X-ray diffraction pattern of the dielectric composition obtained in the embodiment of the invention.
FIG. 3 is a graph showing the temperature dependence of the dielectric constant of each dielectric single plate of the dielectric composition, reference example and comparative example 1 obtained in the embodiment of the invention.
4 is a transmission electron micrograph (magnification of 20,000) showing the particle shape of the dielectric composition obtained in Comparative Example 1. FIG.
5 is an X-ray diffraction pattern of the barium titanate particle powder obtained in Comparative Example 2. FIG.
6 is an X-ray diffraction pattern of the barium titanate particle powder obtained in Comparative Example 3. FIG.
7 is an X-ray diffraction pattern of the barium titanate particle powder obtained in Comparative Example 4. FIG.

Claims (2)

An oxide of one or more elements selected from Si, Y and Nd on the surface of spherical barium titanate particles having a Ba / Ti ratio of 0.99 to 1.01 and a crystal system of tetragonal crystal Is coated with 0.01 to 3.0% by weight of the spherical barium titanate particle powder, the average particle size is 0.05 to 0.5 μm, and the particle size distribution σg is 0. A dielectric particle powder characterized by being 70 or more. When adding barium salt aqueous solution to titanium hydroxide colloid to produce barium titanate core particles, 1 to 60 mol% of carboxylic acid is present with respect to the number of moles of barium in the barium salt aqueous solution, and The ratio of titanium to barium (Ba / Ti) was set to 1.00 to 1.10, and then the reaction solution containing the barium titanate core particles was hydrothermally treated in a temperature range of 100 to 350 ° C. to form a cubic sphere. After obtaining barium titanate particles and washing with water, the particle surface of the spherical barium titanate particles was coated with a sintering inhibitor comprising a compound of one or more elements selected from Si, Y, Nd, and then 800 to The method for producing a dielectric particle powder according to claim 1, wherein the crystal system of the barium titanate particles is converted to tetragonal crystals at a temperature range of 1200 ° C.

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