JPH0778511A - Dielectrid porcelain composition and manufacture of composition powder thereof - Google Patents

Abstract

PURPOSE:To provide a highly reliable dielectric porcelain composition having less characteristic dispersion, a small grain size, a large dielectric constant, a small change of the dielectric constant to temperature change, small voltage dependency, and moreover in which relatively indexpensive Ag-Pd alloy can be used for the internal electrode of a laminated ceramic capacitor by using this composition. CONSTITUTION:Ce of 2.0-4.8mol calculated in terms of CeO2, Ti and Sn of 1.0-7.0mol calculated in terms of (Ti1-aSna)O2 (0<a<=1.0), and Mn of 0.88-0.5mol calculated in terms of MnO2 are contained to a barium titanate of 100mol containing an alkaline metal oxide, as an impurity, of 0.03wt.% or less and halogen of 0.03wt.% or less. The following formula is to be satisfied; 0.97<=(BaO +CeO2)/(TiO2+SnO2)<=1.02 (mol ratio).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic composition and a method for producing a powder of the composition, and particularly to a dielectric ceramic composition mainly composed of barium titanate and used for, for example, a laminated ceramic capacitor and its composition. The present invention relates to a method for producing powder.

[0002]

2. Description of the Related Art Heretofore, a large number of dielectric ceramic compositions mainly composed of barium titanate have been known for use in ceramic capacitors. 1 barium titanate
It has a Curie point near 20 ° C. and a dielectric constant of close to 10,000, but it alone cannot provide a high dielectric constant at room temperature. Therefore, what is called a shifter material is added, and the Curie point is moved to room temperature to have a high dielectric constant at room temperature. A composition to which tin oxide, zirconium oxide or the like is added as the shifter material is known as a high dielectric constant dielectric ceramic composition.

However, the porcelain using this high dielectric constant dielectric ceramic composition has a large crystal grain size of 10 μm to 20 μm. Therefore, when a laminated ceramic capacitor is formed using this dielectric ceramic composition, the breakdown voltage value is low,
Further, there is a drawback that the mechanical strength is low.

Further, recent porcelain capacitors have tended to be miniaturized, and in particular, in multilayer capacitors, dielectric capacitors having a thickness of 5 μm to 15 μm are being put to practical use.
As the dielectric layer becomes thinner, the structural defects of the porcelain are more likely to be reflected in the characteristics. Therefore, the dielectric porcelain composition not only has a high dielectric constant but also has a large crystal grain size (grain size). It is desired to be uniform and fine, and to have few and small pores. Further, since the strength of the electric field applied to the dielectric layer increases as the dielectric layer becomes thinner, it is required that the voltage dependency is small.

A dielectric ceramic mainly composed of barium titanate having a small grain size is disclosed in, for example, Japanese Patent Laid-Open No. 58-1.
35507, JP-A-58-223669, JP-A-5-
No. 9-86103 and the like. In these dielectric porcelains, cerium oxide is added to barium titanate, cerium oxide and barium zirconate are added, or neodymium oxide is added to reduce the grain size of barium titanate. Also,
In an attempt to reduce the grain size, fine barium titanate has been used.

As a method for producing barium titanate powder, a mixture of barium carbonate and titanium oxide is conventionally used.
A method is used in which a raw material powder is obtained by calcining at a temperature of 00 ° C. or higher and then pulverizing. However, in this method, since sintering proceeds during calcination and a large amount of coarse particles are contained, it is difficult to obtain a powder having a fine and uniform particle size. As an attempt to solve this problem, coprecipitation method, alkoxide method,
Raw material powders are synthesized by a hydrolysis method, a hydrothermal synthesis method, or the like. Among them, the powder synthesized by the hydrothermal reaction has not only fine particles but also a uniform composition,
It is known that a crystal grain size is small and a large dielectric constant can be obtained as compared with a dielectric ceramic sintered body using a raw material powder manufactured by a conventional manufacturing method.

[0007]

However, a dielectric ceramic mainly composed of barium titanate having a small grain size has a maximum dielectric constant of about 10,000 at room temperature, which is higher than that of a large grain size. Is small, and it is difficult to obtain a large capacitance when the multilayer capacitor is downsized. Another problem is that the temperature change curve of the dielectric constant is steep. In addition, the dielectric ceramic with a small grain size has a high sintering temperature,
Since firing must be performed at a temperature of 0 ° C. or higher, it was necessary to use an expensive Pd electrode as an internal electrode when forming a laminated ceramic capacitor. Therefore, the cost ratio of the internal electrode material to the production cost is high, and the number of internal electrodes is large especially in the case of large capacitance, resulting in higher cost and a major obstacle in terms of price despite high reliability. Was there.

In addition, in the conventional dielectric composition powder, sub-component raw materials other than the main raw material are added as oxide powder or carbonate. Generally, the dispersion state of the main raw material and the sub-component raw material affects the cause of the characteristic variation and the reliability. In order to improve the dispersion state, it is necessary to make the auxiliary component raw material finer, like the main raw material, and rather a finer powder than the main raw material is required. However, since conventional auxiliary ingredient raw material powder cannot be made very fine,
In the dielectric composition powder, the dispersion state of the main raw material and the subcomponent raw material was very poor. Therefore, in particular, in the dielectric ceramic composition powder mainly composed of barium titanate having a small grain size and a small amount of addition of the auxiliary component raw material to the main component raw material, it has been a cause of variations in characteristics.

Therefore, the main object of the present invention is to have a small grain size, a large dielectric constant, a small change in the dielectric constant with respect to a temperature change, and a small voltage dependence.
Moreover, by using this, a relatively inexpensive Ag-Pd alloy can be used for the internal electrodes of a monolithic ceramic capacitor, and a highly reliable dielectric ceramic composition with little variation in properties and a method for producing the composition powder are provided. It is to be.

[0010]

The present invention relates to 100 mol of barium titanate having an alkali metal oxide content of 0.03% by weight or less and a halogen content of 0.03% by weight or less as impurities. On the other hand, Ce is 2.0 to 4.8 mol in terms of CeO ₂ and Ti and Sn are (Ti _1-a S
n _a ) O ₂ (where 0 <a ≦ 1.0) conversion is 1.0 to
7.0 mol, 0.08 to 0.5 mol of Mn in terms of MnO ₂ , and 0.97 ≦ (BaO + CeO ₂ ) / (T
The dielectric ceramic composition is iO ₂ + SnO ₂ ) ≦ 1.02 (molar ratio). Barium titanate having a specific surface area of 4.0 m ² / g or less and an unreacted BaO content of 2.0%
The following powders are preferably used to produce the composition powder of the dielectric ceramic composition. Further, as the barium titanate, it is preferable to use a powder produced by utilizing a hydrothermal reaction to produce the composition powder of the dielectric ceramic composition. Furthermore, it is preferable to produce a composition powder of the above dielectric ceramic composition by using an organic solvent-soluble organometallic compound as Ce, Ti, Sn, and Mn.

[0011]

In the barium titanate powder synthesized by the hydrothermal synthesis method, chloride is often used as a starting material, and in order to promote crystallization, NaOH as a mineralizer is added.
It is common to use various alkali metal solutions such as KOH. Therefore, alkali metal oxides such as Na ₂ O and K ₂ O and halogens such as Cl are incorporated as impurities.

As a result of various studies on the cause of the dielectric constant of less than 10000 when the particle diameter of the dielectric ceramic mainly composed of barium titanate is as small as 3 μm or less, the present inventors have found that barium titanate as a main raw material. It was found that the dielectric constant does not increase when the types of impurities and their contents are large. It was also found that the dielectric constant does not increase even with the specific surface area of the barium titanate powder, which is the main raw material, and the amount of unreacted BaO. That is, Na ₂ O, K ₂
In barium titanate having a small amount of unreacted BaO with a small content of alkali metal oxide such as O and a small amount of unreacted BaO, by adding cerium oxide thereto, the grain size is reduced and the dielectric constant is large. Found to show. It was also found that by adding tin oxide, a dielectric ceramic with a small rate of change in dielectric constant with temperature can be obtained. Further, it was also found that reliability is greatly affected when a monolithic ceramic capacitor is manufactured by using barium titanate containing a certain amount of halogen such as Cl as an impurity as a main material.

[0013]

By using the dielectric ceramic composition according to the present invention, a dielectric material having a dielectric constant of 11,000 or more and a small crystal grain size of 2 μm or less despite its high dielectric constant is obtained. Porcelain is obtained. Therefore, when a multilayer ceramic capacitor is manufactured, even if the dielectric layer is thinned, the amount of crystal grains existing in the layer does not decrease unlike the conventional multilayer ceramic capacitor. For this reason,
It is possible to obtain a monolithic ceramic capacitor that has high reliability, is small, and has a large capacity. Furthermore, since this dielectric porcelain composition can be fired at a relatively low temperature of 1300 ° C. or lower, it is possible to use an Ag—Pd alloy as an internal electrode, and an inexpensive monolithic ceramic capacitor can be obtained.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0015]

【Example】

(Example 1) First, 0.10 mol of titanium isopropoxide (Ti (OC ₃ H ₇ ) ₄ ) was weighed and about 300 ml.
Several kinds of isopropyl alcohol (IPA) dissolved in were prepared. After thoroughly stirring these solutions,
120 cc of an aqueous solution containing 0.2 mol to 0.6 mol of NaOH was added to each solution for hydrolysis. Next, 0.10 mol of BaCl ₂ .2H ₂ O was added to and mixed with each of these hydrolyzed solutions while blowing nitrogen gas to obtain a mixed solution. After that, each of these mixed solutions was put into a 500 ml autoclave and hydrothermally treated at 200 ° C. for 10 hours. After hydrothermal treatment,
The slurry obtained by cooling was separated by filtration, washed and filtered several times by a usual method, and then dried at 110 ° C. After drying, heat treatment was performed in the air at a temperature of 700 ° C. to 1150 ° C. for 1 hour, and seven types of BaTiOs A to G having different Na amounts, CI amounts and powder characteristics shown in Table 1 were used.
A white powder of ₃ was obtained. Ba / T of these 7 types of white powder
The i ratio was 1.00.

[0016]

[Table 1]

Then, the above six kinds of BaTiOs A to F are used.
₃ and Ce octylate, Sn octylate, Ti acetylacetonate, and Mn acetylacetonate were prepared. After blending these raw materials in the proportions shown in Table 2, a mixed organic solvent of ethanol and toluene was added and mixed and dispersed by a ball mill for 16 hours. Then, after drying and granulation by spray drying, heat treatment was performed in air at a temperature of 600 ° C. to remove organic substances. After that, it is crushed by a dry crusher and BaTiO ₃
A raw material powder in which and other components were uniformly dispersed was obtained.

[0018]

[Table 2]

A vinyl acetate binder and pure water were added to this raw material powder and wet mixed for 16 hours to obtain a mixture. After the mixture was dried and granulated, a disc having a diameter of 10 mm and a thickness of 0.5 mm was fired at a pressure of 2000 kg / cm ² for 2 hours at a temperature shown in Table 3 to obtain a disc-shaped porcelain. . Then, the surface of the obtained porcelain was observed with a scanning electron microscope at a magnification of 1500 times to measure the grain size.

[0020]

[Table 3]

A silver electrode was baked on the main surface of the obtained porcelain to obtain a measurement sample (capacitor), and the dielectric constant at room temperature,
The rate of change of capacitance with respect to dielectric loss and temperature change was measured. Further, an AC voltage of 200 V / mm and 1 KHz was applied, and the dielectric loss (tan δ) was measured. Furthermore, the insulation resistance value was measured after applying a DC voltage of 500 V for 2 minutes with an insulation resistance meter. The insulation resistance was measured at 25 ° C. and 85 ° C., and the logarithm (logρ) of each volume resistivity was calculated.

The dielectric constant (ε) and the dielectric loss (ta
nδ) is measured at a temperature of 25 ° C., 1 KHz, 1 Vrms,
The rate of change in capacitance with temperature changes is 20 ° C
The rate of change in capacitance (ΔC / C ₂₀ ) at −25 ° C. and 85 ° C. based on the capacitance in FIG.

The results of each of the above tests are also shown in Table 3.

(Embodiment 2) A dielectric material prepared by using the dielectric ceramic raw material powder of sample No. 10 of Example 1 and barium titanate of G of Table 1 in the same mixing ratio as in Sample No. 10 by the same method. A porcelain raw material powder was prepared (Sample No. 21). A polyvinyl butyral binder and an organic solvent such as ethanol were added to the dielectric ceramic raw material powder, and the mixture was wet-mixed by a ball mill to prepare a slurry. after that,
The slurry was formed into a sheet by a doctor blade method to obtain a rectangular green sheet having a thickness of 14 μm.

Next, a conductive paste containing Pd as a main component was printed on the ceramic green sheet to form a conductive paste layer for forming internal electrodes. A plurality of ceramic green sheets on which the conductive paste layers were formed were laminated so that the sides from which the conductive paste was drawn out were staggered to obtain a laminate. The obtained laminate was fired in air at the temperature shown in Table 4 for 2 hours. After firing
Silver paste was applied to both end faces of the obtained ceramic sintered body and baked at a temperature of 750 ° C. in the atmosphere to form an external electrode electrically connected to the internal electrode.

[0026]

[Table 4]

The external dimensions of the multilayer capacitor obtained as described above are: width: 1.6 mm, length: 3.2 mm, thickness: 1.2 mm, and the dielectric ceramic interposed between the internal electrodes. The layer thickness is 9 μm. The total number of effective dielectric ceramic layers is 19, and the area of the counter electrode per layer is 2.1 mm ² .

Capacitance (C) and dielectric loss (tan)
δ) is a frequency of 1KH using an automatic bridge type measuring instrument
The measurement was performed under the conditions of z, 1 Vrms, and temperature of 25 ° C., and the dielectric constant (ε) was calculated from the capacitance. Next, in order to measure the insulation resistance (R), a DC voltage of 16 V was applied for 2 minutes using an insulation resistance meter to measure the insulation resistance (R) at 25 ° C. and 85 ° C.
Was measured, and the product of the electrostatic capacitance (C) and the insulation resistance (R), that is, the CR product was obtained. In addition, the rate of change in capacitance (ΔC / C ₂₀ ) with respect to temperature changes at −25 ° C. and 85 ° C. based on the capacitance at 20 ° C. was measured. Further, the DC breakdown voltage value B. D. V (V) and bending strength were measured, and the average value and the minimum value were shown.

The bending strength was measured using a bending strength measuring device 10 shown in FIG. The bending strength measuring device 10 includes a sample holder 12. On the sample holder 12, a monolithic ceramic capacitor under test 14 is placed. The test multilayer ceramic capacitor 14 is pressed by the pressing pin 16. Then, the applied pressure is displayed by the tension gauge 18 with a stationary needle. In this test, the span of the jig of the sample holder 12 was 2 mm.

As a high temperature load test, 10
A DC voltage of 32 V was applied to each of them at a temperature of 85 ° C., and the insulation resistance after 1000 hours was measured. In the wet / medium load test, 100 samples of each sample were applied with a DC voltage of 16 V at a humidity of 95% and a temperature of 70 ° C., and the insulation resistance after 1000 hours was measured. In both the high temperature load test and the humidity and humidity load test, the product of the insulation resistance value (R) and the capacitance (C) after 1000 hours, and the CR product were 50 MΩ ·
The number of samples was shown as being unsatisfactory for samples of μF or less.

As Comparative Example 1, barium titanate of A in Table 1 and CeO ₂ , SnO ₂ , Ti having a purity of 99% or more are used.
O ₂ and MnO ₂ were prepared, weighed so that the compounding ratio was the same as that of sample No. 10 of Example 1, and a laminated ceramic capacitor was manufactured by the same method as described above. Further, as Comparative Example 2, BaTiO ₃ , Ba having a purity of 99.8% or more was used.
ZrO ₃ and CaZrO ₃ are prepared, and BaTiO ₃ 100
18.5 mol of BaZrO ₃ and CaZrO based on mol
₃ Weighed so as to be 8.9 mol, and a monolithic ceramic capacitor was produced by the same method as described above. The above-mentioned respective characteristics were measured for Comparative Examples 1 and 2. The surface of each monolithic ceramic capacitor was observed with a scanning electron microscope at a magnification of 1500 to measure the grain size.

The results of each of the above tests are also shown in Table 4.

As is clear from Table 3, the dielectric ceramic composition according to the present invention has a large permittivity ε of 11,000 or more, and has a dielectric loss of 5. when an alternating voltage of 200 V / mm is applied. It is as small as 0% or less. Moreover, the rate of change in capacitance ΔC / C ₂₀ ) with respect to temperature is -25 ° C to 85 ° C.
The F characteristic standard defined in the JIS standard is satisfied within the range of. Further, the insulation resistance at 25 ° C. and 85 ° C. is 13 when expressed by the logarithm (log ρ) of the volume resistivity.
As described above, the value is as high as 11 or more. Furthermore, the firing temperature is 1
It can be sintered at a relatively low temperature of 300 ° C. or less, and has a small particle size of 2 μm or less.

Further, as is clear from Table 4, the monolithic ceramic capacitor made of the dielectric ceramic composition according to the present invention has higher breakdown voltage and bending strength as compared with the comparative example, and its variation is also large. small. Furthermore, this monolithic ceramic capacitor has a long life of insulation resistance under a load in the wet and shows excellent reliability.

From the above, the monolithic ceramic capacitor manufactured by the dielectric ceramic composition according to the present invention can be sufficiently applied even when the dielectric layer is thinned to 10 μm or less, and can be expected as a small-sized and high-capacity monolithic ceramic capacitor. . Further, since the firing temperature is as low as 1300 ° C. or lower, Ag-such as 30Ag-70Pb (wt%) is used as an internal electrode.
It is possible to use Pb alloys.

Here, the reason for limiting the composition in the present invention will be explained.

As sample No. 1, BaTiO ₃ 100
When CeO ₂ is less than 2.0 mol per mol, the dielectric constant is less than 11,000, the dielectric loss when an AC voltage of 200 V / mm is applied exceeds 5.0%, and the temperature characteristic is F. Does not meet the characteristic standards. On the other hand, as in Sample No. 15, when CeO ₂ exceeds 4.8 mol, the dielectric constant becomes 1
It becomes less than 1,000, and the temperature characteristic does not satisfy the F characteristic standard.

In addition, as in sample No. 2, BaTiO ₃
When (Ti _1-a Sn _a ) O ₂ is less than 1.0 mol with respect to 100 mol, the dielectric constant is less than 11,000 and 20
The dielectric loss becomes large when an AC voltage of 0 V / mm is applied, which is not preferable. On the other hand, like sample number 16,
When (Ti _1-a Sn _a ) O ₂ exceeds 7.0 mol, the dielectric constant becomes less than 11,000 and the temperature characteristics do not satisfy the F characteristics standard.

As sample No. 3, BaTiO ₃ 100
When MnO ₂ is less than 0.08 mol based on mol, the insulation resistance at room temperature and high temperature becomes low, which is not preferable. When MnO ₂ exceeds 0.50 mol as in Sample No. 17, the dielectric loss when an AC voltage of 200 V / mm is applied exceeds 5.0% and the insulation resistance at 25 ° C and 85 ° C is increased. Will be significantly reduced.

Further, as in sample No. 4, (BaO + C
The molar ratio of eO ₂ ) / (TiO ₂ + SnO ₂ ) is 0.97.
When it is less than 1.0%, the dielectric loss when an AC voltage of 200 V / mm is applied exceeds 5.0%, the insulation resistance at room temperature and high temperature becomes low, and the grain size becomes larger than 2 μm. On the other hand, like sample number 18, (Ba
When the molar ratio of O + CeO ₂ ) / (TiO ₂ + SnO ₂ ) exceeds 1.02, the sinterability becomes extremely poor.

When the SnO ₂ amount a is 0 as in sample No. 5, the dielectric loss when an AC voltage of 200 V / mm is applied exceeds 5.0%, and the temperature characteristic does not satisfy the F characteristic standard. .

As in Sample No. 19, the specific surface area is 4.0.
When barium titanate E exceeding m ² / g and having an unreacted BaO amount of over 2.0% is used, the rate of change in capacitance with temperature is small, but the dielectric constant is significantly reduced. Also,
When barium titanate F produced by utilizing a hydrothermal reaction having a large content of alkali metal oxide is used as in Sample No. 20, the dielectric constant becomes small. When a multilayer capacitor was manufactured by using barium titanate G prepared by utilizing a hydrothermal reaction having a large halogen content as in Sample No. 21, the number of defects in the high temperature load test and the humidity and medium load test was high. It is not preferable because it increases.

When the additive is added in the form of powder as in Comparative Example 1, the breakdown voltage value and the mean value of the bending strength are
Although it is larger than that of Comparative Example 2, the min value is significantly smaller than the average value, which is not preferable.

As the organic solvent-soluble organometallic compound according to the present invention, octyl acid Ce and octyl acid S are used.
Although n, Ti acetylacetonate and Mn acetylacetonate were used, the present invention is not limited to this, and similar effects can be obtained with alkoxides, other fatty acid salts and acetylacetonate.

[Brief description of drawings]

FIG. 1 is an illustrative view showing a bending strength measuring device for measuring a bending strength of a sample.

[Explanation of symbols]

 10 Bending strength measuring device 12 Sample holder 14 Multilayer ceramic capacitor under test 16 Pressure pin 18 Tension gauge with needle

Claims (4)

[Claims] 1. Ce based on CeO ₂ with respect to 100 mol of barium titanate having an alkali metal oxide content of 0.03% by weight or less and a halogen content of 0.03% by weight or less contained as impurities. 2.0 to 4.8 mol of Ti, Sn to (Ti _1-a Sn _a ) O ₂ (where 0 <a
≦ 1.0) 1.0-7.0 mol Mn 0.08-0.5 mol MnO ₂ conversion, and 0.97 ≦ (BaO + CeO ₂ ) / (TiO ₂ + SnO)
₂ ) Dielectric porcelain composition, wherein ≦ 1.02 (molar ratio). 2. The composition of the dielectric ceramic composition according to claim 1, wherein a powder having a specific surface area of 4.0 m ² / g or less and an unreacted BaO content of 2.0% or less is used as the barium titanate. Powder manufacturing method. 3. The method for producing a composition powder of a dielectric ceramic composition according to claim 1, wherein a powder produced by utilizing a hydrothermal reaction is used as the barium titanate. 4. The method for producing a composition powder of a dielectric ceramic composition according to claim 1, wherein an organic solvent-soluble organometallic compound is used as the Ce, Ti, Sn, and Mn.