JPH11147716A - Barium titanate powder, ceramic composition by using the same and laminated ceramic capacitor by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a barium titanate powder having improved reduction resistance, sintering properties and dielectric constant by coating the surface of barium titanate particles having a specific average particle diameter with titanium oxide. SOLUTION: This barium titanate powder coated with titanium oxide is obtained by adding barium titanate particles having 0.1-1 μm average particle diameters and 0.997-1.003 molar ratios of Ba/Ti to a solution obtained by dissolving 0.0001-0.1 mol titanium alkoxide expressed in terms of titanium atom based on 1 mol barium titanate in an organic solvent and mixing the added product, drying the organic solvent of the obtained mixture, heat-treating the dried material to provide the barium titanate coated with the titanium oxide in a ratio of 0.0001-0.1 mol of titanium oxide per mol of the barium titanate. The reduction resistant ceramic composition is obtained by adding 0.1-3 mol magnesium oxide based on 100 mol barium titanate to the barium titanate coated with the titanium oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a barium titanate powder, a reduction-resistant porcelain composition containing barium titanate powder as a main raw material, and a base metal internal electrode type multilayer ceramic containing barium titanate as a main raw material. Related to capacitors.

[0002]

2. Description of the Related Art A firing process for manufacturing a nickel internal electrode type multilayer ceramic capacitor is performed in a reducing atmosphere.
This is to prevent oxidation of the internal electrodes due to firing.
At this time, there is a problem if the insulation resistance of the dielectric layer is excessively reduced by the reduction. It is known to add manganese or chromium as one of the methods for maintaining the insulation resistance of the dielectric layer. However, when the amount of manganese or chromium added is large, the stability over time deteriorates. In order to minimize the amount of addition, there is a method of using a powder having high resistance to reduction as barium titanate powder which is a main raw material of the dielectric layer. Specifically, high crystallinity,
The height of Ba / Ti (molar ratio) contributes to the reduction resistance. However, such barium titanate powder having high reduction resistance has poor sinterability, and more sintering aids are required for dense sintering. Silicon dioxide or silicate is widely used as a sintering aid, but at this time, a decrease in dielectric constant and a decrease in insulation resistance occur.

[0003]

The barium titanate powder has a lower sintering property as the reduction resistance is higher, and in order to obtain a dense porcelain without grain growth, more silicon dioxide and silicate are required. Is required. However, silicon dioxide and silicates have a detrimental effect on properties other than sinterability. For this reason, it is an issue to obtain sufficient sintering even with a small amount of silicon dioxide or silicate. In order to utilize titanium oxide as a substitute for silicon dioxide or silicate, the dispersibility of titanium becomes an issue. If it is simply added as titanium oxide powder, uneven distribution of titanium occurs, and abnormal grain growth of barium titanate particles and local deterioration of insulation resistance during firing become problems. This is a disadvantage in a material system characterized in that barium titanate does not grow much, for example, a material system for a multilayer ceramic capacitor in which the temperature characteristic of capacitance satisfies X7R or B.

A low-cost nickel internal electrode type multilayer ceramic capacitor, which has recently been demanded with good temperature characteristics and good bias characteristics and is inexpensive, is characterized in that barium titanate particles as a main material hardly grow during firing. For this reason, titanium oxide powder is not used as a sintering aid for the above reasons, and silicon dioxide and silicate are added by a few percent by weight. As the amount of addition of silicon dioxide or silicate increases, the dielectric constant and the insulation resistance decrease. In recent years, a capacitor having a larger capacity has been demanded, and therefore, a higher dielectric constant has been demanded. Titanium oxide addition can be a sintering aid that does not adversely affect properties as much as silicon dioxide or silicate addition, if abnormal grain growth and local decrease in insulation resistance can be prevented. By using this material, a material having a higher dielectric constant than before can be obtained, which can contribute to the recent demand for large-capacity capacitors.

[0005]

According to the present invention, there is provided a titanium-coated barium titanate powder in which the surface of barium titanate particles is coated with titanium oxide.

Another object of the present invention is to provide a reduction-resistant porcelain composition using the titanium-coated barium titanate.

Further, there is provided a base metal internal electrode type multilayer ceramic capacitor using the above-mentioned reduction-resistant ceramic composition as a dielectric layer.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) A titanium-coated barium titanate powder of the present invention will be described.

The titanium-coated barium titanate powder of the present invention is obtained by coating a barium titanate powder particle with a coating of titanium oxide. At this time, the average particle size of the barium titanate to be coated is 0.1 to 1 μm.
When the thickness is 0.1 μm or less, handling as a powder becomes difficult due to problems such as aggregation. In addition, the dielectric constant of the sintered body decreases. If it is 1 μm or more, sufficient sintering cannot be obtained. Ba / Ti (molar ratio) is 0.997 to 1.00.
Use three. When it is 0.997 or less, the grains grow easily and the reduction resistance is reduced. On the other hand, if it is 1.003 or more, the sinterability is reduced. In addition, the crystallinity can be selected according to the intended characteristics of the reduction-resistant porcelain composition. For example, when obtaining a porcelain having a flat temperature characteristic, a highly crystalline material such as barium titanate powder produced by a hydrothermal synthesis method is desirable. In this case, if the crystallinity is low, the barium titanate particles are likely to grow and have poor temperature characteristics, and also have low reduction resistance and low insulation resistance after sintering.

Next, a process for forming a film of titanium oxide on the barium titanate will be described. First, an alkoxide of titanium is dissolved in an organic solvent. This alkoxide can be freely selected according to the conditions of the film forming process. Next, this solution is mixed with the barium titanate powder. At this time, the alkoxide is decomposed. Thereafter, the organic solvent is dried to obtain a titanium-coated barium titanate powder. The added amount of the alkoxide is 0.0001 to 0.1 mol in terms of titanium atom per 1 mol of barium titanate. 0.0001
If the amount is less than the mole, the effect of the present invention cannot be sufficiently obtained. On the other hand, if it exceeds 0.1 mol, remarkable grain growth and reduction occur during firing.

Heat treatment may be applied to strengthen the bond between the titanium oxide film and barium titanate. The temperature at this time is 500 ° C to 1200 ° C, preferably 700 ° C to 11 ° C.
Set to 00 ° C. If the temperature is lower than 500 ° C., the effect of the heat treatment is not obtained. If the temperature is higher than 1200 ° C., the barium titanate particles are considerably sintered, and a fine powder cannot be obtained. The titanium-coated barium titanate powder satisfying the above requirements can have both sinterability and resistance to reduction inside crystal grains.

(Embodiment 2) A reduction resistant porcelain composition of the present invention will be described.

Embodiment 1 As a main raw material of dielectric porcelain,
The titanium-coated barium titanate described in the above section is prepared. A magnesium-containing substance such as magnesium oxide, magnesium carbonate, or magnesium hydroxide is mixed with the mixture. The compounding ratio is 0.1 to 3 mol in terms of magnesium atom per 100 mol of barium titanate. If it is less than 0.1 mol, the insulation resistance at the crystal grain boundaries of the porcelain will be low. On the other hand, when the amount is 3 mol or more, the insulation resistance is reduced, and the sinterability and the dielectric constant are lowered. In addition to the above two raw materials, if necessary, silicon dioxide or silicate for improving sinterability may be added. This amount can be smaller than the conventional amount by utilizing the titanium-coated barium titanate of the present invention. In addition, manganese or chromium may be added to increase the insulation resistance of the whole porcelain.
Further, rare earth or calcium may be added to suppress the grain growth of barium titanate. The mixed powder of the above raw material powders becomes the raw material powder for the dielectric porcelain. Thereafter, the raw material powder is formed into a disk shape and fired at 1100 to 1350 ° C, preferably 1200 to 1325 ° C in a reducing atmosphere having an oxygen partial pressure of 10 ^-7 to 10 ^-12 atm. Oxygen partial pressure is 10 ^-7
When the pressure is higher than the atmospheric pressure, the advantage of the reduction resistance of the product of the present invention is not particularly required. If the pressure is lower than 10 ^-12 atm, the reduction is too strong and the insulation resistance is deteriorated. Also,
If the firing temperature is 1100 ° C or lower, sufficient sintering cannot be obtained, and if the firing temperature is 1350 ° C or higher, barium titanate grain growth occurs.

In the above description, an embodiment in which a powder in which a titanium coating is formed on barium titanate powder is prepared and then mixed with other additives such as magnesium is shown.
The formation time of the titanium coating is not limited to this. The effects of the present invention can be obtained even after mixing the barium titanate powder, which is the main raw material, with an additive such as magnesium or forming a titanium film simultaneously with the mixing.

(Embodiment 3) A method for manufacturing a base metal internal electrode type multilayer ceramic capacitor of the present invention will be outlined. Embodiment 2 is the same as Embodiment 2 up to the production of the mixed powder of the raw material powder. Subsequently, a sheet comprising the mixed powder and an organic binder is prepared. On the other hand, a sheet composed of a base metal powder and an organic binder is also prepared. These two types of sheets are alternately laminated to have a cross-sectional structure as shown in FIG. Next, the organic binder in this structure is removed by heat treatment in an appropriate atmosphere and temperature. Subsequently, firing is performed under the same conditions as in the second embodiment. Thereafter, external electrodes are attached to both end portions in FIG.

The multilayer ceramic capacitor manufactured as described above has a higher dielectric constant since it is densely sintered even if the amount of silicon dioxide or silicate is small, as compared with conventional products.

In the above description, a method has been described in which barium titanate powder coated with titanium as described in the second embodiment is first prepared and then the subsequent manufacturing steps are performed.
The timing for applying the titanium coating is not limited to this. The effect of the present invention can be obtained even if titanium coating is applied at the time of mixing the raw materials or during the mixing step of the raw materials and the organic binder.

[0019]

The present invention will be described below in detail with reference to examples.

(Example 1) The following liquids are mixed.

Titanium tetraisopropoxide (manufactured by Kanto Kagaku): 1.42 g Butyl acetate (manufactured by Kanto Kagaku): 98.5 g Note that titanium tetraisopropoxide is decomposed in the air, so mixing is performed in a nitrogen atmosphere. Do it. Thus, about 100 g of a solution containing 0.005 mol of titanium atoms is obtained.

The average particle diameter is 0.5 μm, and Ba / Ti
(Molar ratio) is 1.000 and barium titanate (BT-0 manufactured by Sakai Chemical Industry Co., Ltd.) produced by a hydrothermal synthesis method.
5) is mixed with barium titanate: 117 g and butyl acetate 170 g.

To the mixture of the barium titanate powder and butyl acetate, 30 g of the titanium tetraisopropoxide butyl acetate solution prepared above is added. Thereby, 0.003 to 1 mol of barium titanate was obtained.
This means that moles of titanium atoms have been added. The above mixture was placed in a polypot having a diameter of 10 cm and a volume of 500 ml together with 200 g of a stabilized zirconia ball having a diameter of 5 mm and mixed at 100 rpm for 1 hour. Thereafter, the zirconia balls are removed by a sieve, and further dried at 200 ° C 5 ° C.
After drying for an hour, the butyl acetate was completely evaporated. continue,
Heat treatment was performed at 900 ° C. for 4 hours. Temperature rise / fall 2 per hour
00 ° C./hour.

Thus, barium titanate powder coated with titanium oxide was obtained. (Example 2) A, B, C and D four types of weighing were performed as follows.

Weighing of mixed powder A Barium titanate treated according to Example 1 above: 10
0 g MgO: 0.115 g CaCO3: 0.573 g SiO2: 0.172 g Weighing of mixed powder B Ordinary barium titanate (Ba / Ti ratio: 1.000):
100 g TiO2: 0.103 g MgO: 0.115 g CaCO3: 0.573 g SiO2: 0.172 g Weighing of mixed powder C Normal barium titanate (Ba / Ti ratio: 1.000):
100 g MgO: 0.115 g CaCO3: 0.573 g SiO2: 0.172 g Weighing of mixed powder D Normal barium titanate (Ba / Ti ratio 0.997):
100 g MgO: 0.115 g CaCO3: 0.573 g SiO2: 0.172 g For each of the weighed dielectric materials A, B, C, and D, 200 g of stabilized zirconia balls having a diameter of 5 mm.
And 500 ml of distilled water together with 200 ml of distilled water in a polypot having a diameter of 10 cm, and rotationally mixed at 100 rotations per minute for 20 hours. Thereafter, the zirconia balls were removed, and the mixture was placed in a stainless steel container, kept at 200 ° C. for about 15 hours, and dried to obtain a mixed powder.

The mixed powders A, B, and D have exactly the same weight in terms of the ratio of atoms. The difference is that the surplus titanium atoms are uniformly present in the barium titanate powder particles, A is present on the surface of the barium titanate powder, B is present as an independent powder from the beginning. C is a state in which no excess titanium exists.

Ceramo P is used as a binder in this mixed powder.
About 15 ml of B15 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) diluted twice with pure water was added and mixed for 10 minutes with a raikai machine, and then granulated through a 32 mesh nylon sieve. Next, the granulated powder was packed in a mold having a diameter of 13 mm and pressed. The press load was 1 ton. Next, the binder was removed from the molded body. The binder was removed in air at 700 ° C. for 2 hours (temperature rise / fall 100 ° C./hour). Next, baking was performed at 1325 ° C. for 6 hours (200 ° C./hour) using a box-type atmosphere electric furnace. The firing atmosphere was such that a nitrogen gas as a carrier gas was flowed at a rate of 5 liters per minute, and a 10% green gas (1% hydrogen was ^added) so that the oxygen partial pressure was 10 ^-9 atm.
The flow rate of nitrogen gas containing 0% was controlled and adjusted. Incidentally, the reason why the oxygen partial pressure exists even when the oxygen gas is not particularly supplied is that a trace amount of oxygen exists as an impurity in the carrier gas and the green gas. Subsequently, gold was deposited on the surface of the obtained sintered body using chromium as a base, and the cylindrical curved surface was polished with sandpaper (roughness # 320) to leave only a circular counter electrode. The dielectric constant, dielectric loss, insulation resistance, and temperature characteristics of the single-layer capacitor thus prepared were measured. The dielectric constant and the dielectric loss were measured at 1 kHz, 1 V and room temperature using an LCR meter (manufactured by Hewlett Packard). The insulation resistance was measured using an insulation resistance meter (manufactured by Hewlett-Packard Company). Further, the temperature change of the dielectric constant was measured from -55 ° C to + 130 ° C. Further, the diameter of the sintered body was measured with a vernier caliper, and the sintering shrinkage was measured. They are shown in Table 1 together. As for the dielectric constant, only the value at room temperature is described, but A, B, C, and D all satisfy the temperature characteristics X7R and B of the capacitance.

[0028]

[Table 1]

As is clear from Table 1, the porcelain composition using the titanium-coated barium titanate of the present invention has a dielectric constant, a dielectric loss, a CR product (a product of capacitance and insulation resistance),
It can be seen that all aspects of sintering are superior to those using ordinary barium titanate. In particular, the three types of porcelains A, B and D have the same ratio of barium atoms to titanium atoms, but differ only in their physical and chemical structures. From this, it can be said that barium titanate powder having a structure unique to the present invention in which barium titanate is coated with titanium contributes to the characteristics of porcelain using the barium titanate powder.

Example 3 Next, using the same dielectric material compositions A, B, C, and D as in Example 2, a nickel internal electrode type multilayer ceramic capacitor was manufactured. Hereinafter, the manufacturing method will be described in detail. As the raw material mixed powder, one prepared in the same manner as in Example 2 was used. Using them as inorganic components, polyvinyl butyral resin as an organic binder, DBP (dibutyl phthalate) as a plasticizer,
As a solvent, 1.1.1. Trichloroethane and butyl acetate were added and mixed by a ball mill to prepare a slurry.
The conditions for slurrying were as follows: 100 g of the inorganic component, 8 g of polyvinyl butyral resin, 4 g of DBP, 1.
1.1. The amount was 50 g of trichloroethane and 35 g of butyl acetate. The slurry thus prepared was subjected to vacuum defoaming and then formed into a film by a doctor blade method to produce a green sheet. The blade gap was 200 μm. The thickness of the green sheet after drying was about 35 μm. Next, as the base metal paste for the internal electrode, a commercially available nickel paste (manufactured by Sumitomo Metal Mining) was used. Next, a desired pattern was screen-printed (about 5 μm after printing and drying) on the green sheet using the nickel paste. The green sheet on which the electrode pattern has been formed in this manner is placed on an 11
The sheets were laminated (that is, the effective layer was 10 layers), and were integrated by thermocompression bonding. And it cut | disconnected further to the dimension of 3.8 mm x 1.9 mm, and the unsintered laminated body was prepared. The thickness of this green laminate is 3 mm on each side of the effective layer so as to be about 1 mm.
An invalid layer of 00 μm was provided. FIG. 1 shows a cross-sectional view thereof.
In FIG. 1, 1 indicates a dielectric layer (ineffective layer), 2 indicates a dielectric layer (effective layer), and 3 indicates an internal electrode layer. Next, the binder is removed from the unsintered laminate. A box-type electric furnace was used for debinding in nitrogen. After heating at a rate of 15 ° C / hour and a maximum temperature of 400 ° C for 2 hours,
The temperature was lowered at 100 ° C./hour. The purpose of the binder removal is to remove the organic binder, and it is not limited to this method as long as they can be sufficiently removed. The binder-free sample thus prepared was fired. The firing temperature and the firing atmosphere were the same as in Example 2. Subsequently, a commercially available copper paste for sintering in a nitrogen atmosphere at 900 ° C. was applied as an external electrode to the end face of the sintered body obtained by sintering, and baked in a continuous belt furnace to obtain a sample for property evaluation. The evaluation results are shown in (Table 2).

[0031]

[Table 2]

As is clear from Table 2, similarly to the case of the porcelain composition of Example 2, even in the case of the multilayer ceramic capacitor, when the titanium-coated barium titanate was used, the dielectric constant, the dielectric loss, It can be seen that the product is excellent in all aspects of CR product (product of capacitance and insulation resistance).

In the above embodiment, nickel is used as the internal electrode of the multilayer ceramic capacitor. However, copper or an alloy containing nickel and copper as main components may be used.

[0034]

According to the dielectric ceramic composition and the multilayer ceramic capacitor of the present invention, a method for achieving both reduction resistance, sinterability and high dielectric constant is provided. This method is particularly effective as a nickel internal electrode type multilayer ceramic capacitor having a temperature characteristic of X7R or B, which does not allow barium titanate to grow too much in a firing atmosphere in a reducing atmosphere and requires a high dielectric constant. It is.

[Brief description of the drawings]

FIG. 1 is a sectional view of a laminate according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 dielectric layer (ineffective layer) 2 dielectric layer (effective layer) 3 internal electrode layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideaki Omura 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] An average particle size of 0.1 to 1 μm, Ba / Ti
(Mole ratio) Barium titanate particles having a molar ratio of 0.997 to 1.003 are coated with titanium oxide in an amount of 0.0001 to 0.1 mol per 1 mol of the barium titanate. Coated barium titanate powder. 2. An average particle diameter of 0.1 to 1 μm, Ba / Ti
The alkoxide of titanium dissolved in an organic solvent with respect to 1 mol of the barium titanate is added to the barium titanate particles having a molar ratio of 0.997 to 1.003 in terms of titanium atom in an amount of 0.0001 to 0.1 in terms of titanium atom. A titanium-coated barium titanate powder obtained after adding, mixing and drying an organic solvent in an amount of only moles. 3. Titanium-coated barium titanate obtained by heat-treating the titanium-coated barium titanate according to claim 2 at a temperature of 500 ° C. to 1200 ° C. 4. A titanium-containing barium titanate powder according to claim 1, 2 or 3 as a main raw material powder, and at least magnesium oxide as one of the trace additive components. A reduction-resistant porcelain composition, wherein the amount of magnesium oxide is 0.1 to 3 mol per 100 mol of barium. 5. A base metal internal electrode type multilayer ceramic capacitor using the reduction resistant porcelain composition according to claim 4 as a dielectric layer.