JPH0118522B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates primarily to high dielectric constant ceramic compositions useful as dielectrics for ceramic capacitors. Conventionally, this type of composition has barium titanate (BaTiO ₃ ) as the main component, and Bi ₂ O ₃ −
Bismuth compounds such as TiO ₂ , Bi ₂ O ₃ −SnO ₂ , Bi ₂ O ₃ −ZrO ₂ with rare earth added as a subcomponent;
Alternatively, materials to which MgO, SiO ₂ , etc. are added as subcomponents are widely used because they have a high dielectric constant and can provide large capacitance. however,
A composition containing the above components has a large dielectric loss (tan δ) at high frequencies. In addition, when the dielectric constant is increased, the temperature change rate of capacitance increases, and conversely, when the temperature change rate is decreased, the dielectric constant decreases, which is a contradictory tendency.For this reason, the above composition is applied to capacitors. In this case, there was a limit to miniaturization and large capacity. In addition, among the above compositions, those containing bismuth compounds as subcomponents may cause Bi ₂ O ₃ to evaporate during sintering, causing distortion in the porcelain, or changing the composition ratio, resulting in poor electrical properties. There are problems such as variations. Furthermore, when this is applied to a multilayer capacitor, if Pd or Ag-Pd alloy is used as the internal electrode, this Pd
Reacts with Bi ₂ O ₃ and impairs the properties of the electrode. For this reason, there is also the problem that expensive Pt that does not react with Bi ₂ O ₃ must be used. The present invention has been made in view of the above problems, and has a high dielectric constant of 2400 or more, yet has a small temperature change rate of capacitance over a wide temperature range, and has a dielectric material. It is an object of the present invention to provide a high dielectric ceramic composition with low loss. The present inventors discovered that alkaline earth metal oxides such as SrO and CaO, alkali metal oxides such as Na ₂ O and K ₂ O, and other alkaline metal oxides such as Al ₂ O ₃ and SiO ₂ that exist as impurities in barium titanate. Among oxides, especially Na ₂ O,
It has been found that the content of alkali metal oxides such as K ₂ O greatly affects the electrical characteristics. Therefore,
In order to achieve the above object, the present invention limits the content of alkali metal oxide as an impurity present in barium titanate to a low level, and does not contain a conventional bismuth compound as a subcomponent. Therefore, Nb ₂ O ₅ , Co ₂ O ₃ and SiO ₂ are added. That is, the high dielectric constant ceramic composition of the present invention contains barium titanate containing 0.04% by weight or less of alkali metal oxide as an impurity.
1.0 to 4.0 parts by weight of Nb ₂ O ₅ to 100 parts by weight,
It contains 0.1 to 0.8 parts by weight of Co ₂ O ₃ and 0.1 to 2.0 parts by weight of SiO ₂ . The reason for limiting the above component ranges is as follows. First, regarding alkali metal oxides such as Na ₂ O and K ₂ O, when they exceed 0.04% by weight as impurities relative to BaTiO ₃ , the dielectric constant decreases, and the dielectric constant decreases to 2400.
This is because the values are as follows. In addition, if Nb ₂ O ₅ is less than 1.0 part by weight based on 100 parts by weight of BaTiO ₃ containing the above impurities, sinterability will deteriorate and the temperature change rate of capacitance will also increase, making it impossible to satisfy the X7R characteristics specified by EIA. I won't. On the other hand, if it exceeds 4.0 parts by weight, the dielectric constant decreases to a value of 2400 or less. _{Co2O3 is}
If it is less than 0.1 part by weight based on 100 parts by weight of BaTiO ₃ , the effect of reducing the temperature change rate of capacitance is poor;
Moreover, if it exceeds 0.8 parts by weight, the dielectric constant decreases and the temperature change rate of capacitance deteriorates. _SiO2 is
This is because if it is less than 0.1 part by weight based on 100 parts by weight of BaTiO ₃ , the effect of improving sinterability is poor, and if it exceeds 2.0 parts by weight, the dielectric constant value will decrease below 2400. Hereinafter, the present invention will be explained in more detail based on examples. Example In this example, the procedure for manufacturing a high dielectric constant ceramic composition according to the present invention will be explained along the manufacturing process shown in FIG. The results of investigating the characteristics will also be explained. First, prepare BaCO ₃ and TiO ₂ of various purity,
These were weighed so that the molar ratio of BaCO ₃ and TiO ₂ was 1000, and mixed in a ball mill using agate for 50 minutes.
Wet mixed for ~20 hours (step). After the moisture in this mixture was evaporated, it was calcined by holding at a temperature of 1150° C. for 2 hours (step), and then ground again in a ball mill until the average particle size was 3 microns or less (step). In this way, five types of barium titanate having different purities, A to E shown in Table 1, were obtained. In addition, in the same table, the alkali metal oxide content of A to D is within the range according to the present invention, and that of E is outside the range.

[Table] Next, Nb ₂ O ₅ , Co ₂ O ₃ and SiO ₂ were weighed and mixed with the above various barium titanates so as to have the composition ratios shown in Table 2, and agate was mixed in the same manner as above. Wet mixing was carried out for 5 to 20 hours using the ball mill used, and the mixture was evaporated and dried (step). Each of the powders thus obtained was kneaded with 3% by weight of polyvinyl alcohol as a binder, and after granulation, 2000Kg/cm ²
It was molded into a disk with a diameter of 15 mm and a thickness of 1 mm using a pressure of 1.5 mm (process). Next, these molded discs were fired in an electric furnace at (1200 to 1350)°C for 2 hours to obtain porcelain (step). In order to investigate the electrical properties of each of the porcelain compositions obtained in this way, silver electrodes were baked on both sides of each porcelain disk using a conventional method to form a capacitor.
The dielectric constant (ε), dielectric loss (tanδ), and temperature change rate of capacitance (ΔC/
_C25 ) was measured. The results are also shown in Table 2.

[Table] Each electrical property in the table is a value measured under the following conditions. Dielectric constant (ε), dielectric loss (tanδ): Temperature 25℃,
Measured at a frequency of 1KHz. Temperature change rate of capacitance (ΔC/C ₂₅ ): Temperature 25℃
-55°C and +125°C, respectively, based on the capacitance at
The rate of change in °C and the value at which the rate of change is maximum as an absolute value within the range of -55°C to +125°C (|
ΔC/C ₂₅ |). Furthermore, those marked with * in Table 2 are outside the scope of this invention, and the others are within the scope of the invention. As is clear from Table 2, the ceramic compositions according to the present invention all have a high dielectric constant (ε) of 2400 or more, and in spite of this high dielectric constant, the temperature change rate of capacitance ( ΔC/C ₂₅ ) also -55℃~＋
It is flat within ±15% within the temperature range of 125℃,
The X7R characteristics specified by EIA are also satisfied. Also,
It is understood that the dielectric loss (tan δ) is also low at 1.1% or less, and has excellent electrical characteristics. As described above, according to the present invention, the dielectric constant value is
High at over 2400, yet -55℃~+
The capacitance temperature change rate is flat at ±15% over a wide temperature range of 125°C. Furthermore, dielectric loss is also small. Therefore, when the high dielectric constant ceramic composition of the present invention is applied to a multilayer ceramic capacitor, relatively inexpensive Pd or Ag-Pd alloy can be used for the internal electrode, and a small and large capacitor with a high dielectric constant can be used. The excellent effect of obtaining a large capacity is exhibited. In addition, trace amounts of MnCO ₃ and
Addition of a reduction inhibitor such as Fe ₂ O ₃ does not impair the properties of the composition according to the invention.

[Brief explanation of drawings]

The drawings are manufacturing process diagrams showing the procedure for manufacturing the high dielectric constant ceramic composition according to the present invention.

Claims (1)

[Claims] 1. 1.0 to 4.0 parts by weight of Nb ₂ O _{5 and} 0.1 to 0.1 to 4.0 parts by weight of Co ₂ O 3 to 100 parts by weight of barium titanate with an alkali metal oxide content of 0.04% by weight or _less as an impurity.
A high dielectric constant ceramic composition containing 0.8 parts by weight and 0.1 to 2.0 parts by weight of _SiO2 .