JPH075364B2 - 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.

[Prior art]

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.
With the progress of electronics in recent years, miniaturization of electronic parts of such multilayer ceramic capacitors has rapidly progressed, and they have come to be used in a wide range of electronic circuits.

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 108
In order to use an inexpensive metal such as (3 ° C) as an internal electrode, a dielectric material having a high dielectric constant which is sintered at a low temperature, particularly at 950 ° C or less, 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 as a ferroelectric that can be sintered at low temperature.
(Fe _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 , P
It is intended to obtain desired dielectric properties at room temperature by combining two or three components of b (Ni _1/3 Nb _2/3 ) O ₃ and PbTiO ₃ . However, these have drawbacks such as a large dielectric loss and a small insulation resistance when the relative dielectric constant is large. Furthermore, since the synthetic components are all ferroelectrics, the theoretical disadvantage 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 is disclosed in Japanese Patent Laid-Open No. 52-21699 [Sr _x Pb
_1-x TiO ₃ ] _A [Pb (Mg _1/2 W _1/2 ) O ₃ ] _1-A , a composition in which x = 0 to 0.10, A = 0.35 to 0.50 is put to practical use,
Dielectric powders of the above composition are commercially available. However, this composition system has the advantage that it can be sintered at a low temperature of 1000 ° C or lower and has excellent insulation resistance, etc., but its dielectric loss is about 1.5%. Does not satisfy the condition that is at least 1%.

[Object of the Invention]

The present invention has been devised as a result of various experiments in view of the above-mentioned drawbacks, and has a perovskite structure of the same crystal structure as that of Pb (Fe _1/2 Nb _1/2 ) O ₃ which is a ferroelectric substance. the paraelectric a is Ba (Cr _1/2 Nb _1/2) Pb by solid solution O ₃ (Fe _1/2 Nb _1/2) dielectric properties O ₃ has inherently capable sintered at a low temperature with An object of the present invention is to provide an excellent high-dielectric-constant dielectric ceramic composition which has been modified to have 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 [Pb
(Fe _1/2 Nb _1/2 ) O ₃ ] _1-x [Ba (Cr _1/2 Nb _1/2 ) O ₃ ] _{x In} the composition represented by _x , x is in the range of 0.028 ≦ x ≦ 0.070. It is characterized by being.

The reason for limiting the range of x to the above range is 0.028>
When x or x> 0.070, the relative dielectric constant must be 7500 or more, the dielectric loss must be 1.00% or less, the insulation resistance must be 3.0 × 10 ¹¹ Ω · cm or more, and the temperature dependence of the dielectric constant must be good. This is because either one is not satisfied.

〔Example〕

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

As starting materials, PbO ₂ , Fe ₂ O ₃ , Nb ₂ O ₅ , BaCO ₃ and Cr ₂ O ₃ were weighed so as to have the composition ratios shown in Table 1 and wet-mixed with a dispersant and a dispersion medium in a ball mill. Then, the 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. A disk having a diameter of about 12 mm and a thickness of 1.0 mm was formed at a pressure of about 900 kg / cm ² . After the polyvinyl alcohol of this disk-shaped molded body was burnt out at 500 ° C., it was baked at a temperature of 900 ° C. to 950 ° C. for 2 hours in an atmosphere containing oxygen. Finally, silver electrodes were baked at 800 ° C. on both upper and lower surfaces of the obtained disc-shaped fired body. Similarly, for Pb (Fe _2/3 W _1/3 ) O ₃ which is a ferroelectric substance,
The composition formula of Pb (Fe _1/2 Nb _1/2 ) O ₃ , which is the same ferroelectric substance, as a solid solution is Pb (Fe _2/3 W _1/3 ) _x (Fe _1/2 Nb _1/2 ) ₁ A dielectric porcelain composition represented by _−x O ₃ and having x = 0.5 was used for comparison. 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 dimension of the sample, and the dielectric loss (Tanδ) is The following shows the measured values with an input signal of 1.0 KHz and 1.0 Vrms 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 size of the sample. -30 ° C., + at 25 ° C. + 85 each temperature of ° C. to measure the capacitance at the same conditions as described above, to calculate a change rate of the capacitance at each temperature for the electrostatic capacity at + 25 ° C., epsilon _{- 30} /
It is shown as ε ₂₅ and ε ₈₅ / ε ₂₅ .

As is clear from Table 1, Sample No. 1 has a large dielectric loss and extremely large temperature dependence of the relative dielectric constant, and Sample No. 12 has a small relative dielectric constant 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 permittivity of 8270 to 12900, and thus the dielectric loss (Tan
ε) is as small as 0.54 to 1.00, and the insulation resistance (Ω · cm) is 7.9.
It is very large as × 10 ^{11 to} 3.1 × 10 ¹² and has good relative dielectric constant temperature characteristics as described above, and all have excellent dielectric characteristics, but it is understood that sample numbers 4 to 8 are more preferable. .

〔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. The composition formula is [Pb (Fe _1/2 Nb _1/2 ) O ₃ ] _1-x [Ba (Cr _1/2 Nb _1/2 ) O ₃ ].
A composition represented by _x , wherein x is in a range of 0.028 ≦ x ≦ 0.070, a high dielectric constant type dielectric ceramic composition.