JPH0680564B2 - High dielectric constant dielectric ceramic composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a high dielectric constant dielectric ceramic composition of a ceramic capacitor, particularly a laminated ceramic capacitor capable of low temperature firing.

[Conventional technology]

Conventionally, generally, a laminated porcelain capacitor is formed by laminating a plurality of sheet-like dielectrics containing BaTiO ₃ (barium titanate) as a main component with internal electrodes coated on the surface and alternately pairing the internal electrodes of each sheet in parallel. It is formed by connecting it to the external connection electrode and sintering and integrating it.
Such multilayer ceramic capacitors have been rapidly used in a wide variety of electronic circuits due to rapid miniaturization of electronic parts with the recent progress of electronics.

However, this conventional BaTiO ₃ -based dielectric material must be fired at a high temperature of 1250 ° C to 1350 ° C, and when this material is used as the dielectric of a laminated ceramic capacitor, the internal electrodes are Since expensive precious metal palladium (melting point 1555 ° C) or its alloy that does not melt at the firing temperature of the body and does not oxidize is used, the number of internal electrodes is particularly large for those with large capacitance. Since the cost is large and the cost is high, the conventional multilayer ceramic capacitor has high capacity efficiency, excellent dielectric properties, and high reliability, but the price is a major obstacle to its progress. Therefore, silver (melting point 960 ℃), copper (melting point 1
In order to use an inexpensive metal such as (083 ° C.) as an internal electrode, a dielectric material having a high dielectric constant that is sintered at a low temperature, particularly at 950 ° C. or lower, has been strongly desired.

In recent years, several proposals have been made as a porcelain composition which can be sintered at a low temperature of 1000 ° C. or less in a high dielectric constant type dielectric. They are Pb (F
e _1/2 Nb _1/2 ) O ₃ , Pb (Fe _2/3 W _1/3 ) O ₃ , Pb (Mg _1/2 W _1/2 ) O ₃ , Pb
(Zn _1/3 Nb _2/3 ) O ₃ , Pb (Mg _1/3 Nb _2/3 ) O ₃ , Pb (Ni _1/3 Nb _2/3 )
A combination of two or three components of O ₃ and PbTiO ₃ ,
It is intended to obtain desired dielectric properties at room temperature. However, when the relative dielectric constant is large,
It has drawbacks such as large dielectric loss and small insulation resistance. Furthermore, since the synthetic components are all ferroelectrics, the theoretical defect that the dielectric loss is extremely large in the Curie temperature and a low temperature region near the Curie temperature cannot be avoided.

Incidentally, it was disclosed in Japanese Patent Laid-Open No. 52-21699 [Sr _x Pb _1-x Ti
O ₃ ] _A [Pb (Mg _1/2 W _1/2 ) O ₃ ] _1-A × = 0 to 0.10, A
= 0.35-0.50 has been put into practical use, and dielectric powders of the above composition are commercially available. However, this composition system has the advantages that it can be sintered at a low temperature of 1000 ° C or less and that it has excellent insulation resistance, but the dielectric loss is 1.5%.
However, when applied as a laminated ceramic capacitor, the condition that the dielectric loss is at least 1% or less is not satisfied.

[Object of the Invention]

The present invention has been devised as a result of various experiments in view of the above-mentioned drawbacks, and for Pb (Fe _1/2 Nb _1/2 ) O ₃ which is a ferroelectric substance, a perovskite having the same crystal structure as that of Pb (Fe _1/2 Nb _1/2 ) O ₃ . Dielectric property of Pb (Fe _1/2 Nb _1/2 ) O ₃ originally obtained by solid solution of Ba (Cr _1/2 Nb _1/2 ) O ₃ which is a paraelectric material with a structure that can be sintered at low temperature An object of the present invention is to provide an excellent high-dielectric-constant dielectric porcelain composition that has improved characteristics and has a small dielectric loss, a large insulation resistance, and a good temperature dependence of the relative dielectric constant.

[Means for solving problems]

The high dielectric constant dielectric ceramic composition of the present invention has a composition formula of Pb (Fe
_{In the} composition represented by _{1 / 2-x} Sm _x Nb _1/2 ) O ₃ , x is 0.02
It is characterized by being in the range of 1 ≦ × ≦ 0.070.

The reason why the range of X is limited to the above range is that the dielectric characteristics required for a porcelain capacitor, particularly a laminated porcelain capacitor, that is, the relative dielectric constant is 7500 or more and the dielectric loss is 1.00.
%, The insulation resistance is 3.0 × 10 ¹¹ Ω · cm or more, and the temperature dependence of the relative permittivity must be good. Either of the dielectric properties must be satisfied. If 0.021> X, the relative permittivity is This is because the dielectric properties are less than 7500 and the temperature dependence of the relative permittivity is large, and when X> 0.070, the relative permittivity is less than 7500 and the insulation resistance is less than 3.0 × 10 ¹¹ Ω · cm, which do not satisfy the dielectric properties.

〔Example〕

 Next, the present invention will be described based on examples.

PbO ₂ , Fe ₂ O ₃ , Nb ₂ O ₅ , and Sm ₂ O ₃ were the first starting materials.
Each was weighed so as to have the composition ratio shown in the table, wet-mixed with a dispersant and a dispersion medium in a ball mill, and then this raw material slurry was dried and calcined at a temperature of 950 ° C. for 3 hours. Then, this calcined product was roughly crushed and then finely crushed with a vibration mill, and about 1% by weight of polyvinyl alcohol was added to the obtained fine powder having an average particle size of 0.7 to 0.8 μm to form granules. About 90
It was formed into a disk shape having a diameter of about 12 mm and a thickness of 1.0 mm at a pressure of 0 Kg / cm ² . Polyvinyl alcohol of this disk-shaped molded body is 500
After burning out at ℃, 2 hours at a temperature of 900 ℃ ~ 950 ℃,
It was fired in an atmosphere containing oxygen.

Finally, 80 silver electrodes were formed on the upper and lower surfaces of the obtained disc-shaped fired body.
It was baked at 0 ° C. Similarly, the ferroelectric substance Pb (Fe _2/3 W
_The composition formula of Pb (Fe _1/2 Nb _1/2 ) O ₃ which is the same ferroelectric substance in _1/3 ) O ₃ as a solid solution is Pb (Fe _2/3 W _1/3 ) x (Fe ₁ A dielectric ceramic composition represented by _{/ 2} Nb _1/2 ) _1-x O ₃ and having X = 0.5 was used as a comparative example. Various characteristics of the disk-shaped capacitor sample thus obtained are shown in Table 1.

However, the relative permittivity in the table shows the value calculated from the capacitance value at room temperature measured by the capacitance bridge using the input signal of 1.0 KHz and 1.0 Vrms and the sample size, and the dielectric loss (tan δ) is Measured value at input signal of 1.0KHx1.0Vrms at room temperature. The insulation resistance is a value obtained by applying a DC voltage of 250 V with an insulation resistance tester after 1 minute and the volume resistivity (Ω · cm) calculated from the dimensions of the sample. The temperature characteristic of the relative permittivity is Measure the capacitance under the same conditions as above at each temperature of -30 ℃, + 25 ℃, and + 85 ℃, and calculate the rate of change of the capacitance at each temperature with respect to the capacitance at + 25 ℃. _-30 /
It is shown as ε ₂₅ and ε ₈₅ / ε ₂₅ .

As is clear from Table 1, Sample No. 1 has a small relative permittivity and extremely large temperature dependence of the relative permittivity, and Sample No. 12 has a small relative permittivity and a low insulation resistance. Further, in the comparative examples, the dielectric loss is extremely large and the insulation resistance is extremely low, and practical dielectric characteristics are not obtained in any of the examples.

On the other hand, the dielectric ceramic composition within the scope of the claims of the present invention has a sufficiently high relative dielectric constant of 8250 to 16760, and thus the dielectric loss (Tan
δ) is as small as 0.13 to 0.57, and the insulation resistance (Ω · cm) is 5.8.
It is very large as × 10 ^{11 to} 3.3 × 10 ¹² and the temperature characteristics of the above-mentioned relative permittivity are good, and all have excellent dielectric characteristics, but it is understood that sample numbers 5 to 8 are more preferable. It

〔The invention's effect〕

The dielectric ceramic composition within the scope of the present invention has a relative permittivity,
All of the dielectric loss (Tanδ), insulation resistance (Ω · cm), and relative dielectric constant temperature characteristics are satisfactory.

Further, in the present invention, since the firing temperature can be fired in the range of 900 ° C to 950 ° C, and all the dielectric characteristics of the sintered porcelain are satisfied, inexpensive metals such as silver and copper can be used internally. It is understood that it is sufficiently practical as a dielectric porcelain of a laminated porcelain capacitor used as an electrode.

Claims (1)

[Claims] 1. A composition represented by Pb (Fe _{1 / 2-x} Sm _x Nb _1/2 ) O ₃ wherein x is in the range of 0.021 ≦ × ≦ 0.070. High dielectric constant dielectric ceramic composition.