JPH08198675A - Lead-containing combined perovskite type dielectric porcelain - Google Patents

Abstract

PURPOSE: To obtain dielectric porcelain having a high dielectric constant and high mechanical strength even by sintering at <=1,000 deg.C. CONSTITUTION: This dielectric porcelain has 2-5μm average grain diameter and the ratio of the max. grain diameter to the min. grain diameter is 4-6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-based composite perovskite type dielectric ceramic used as a dielectric of a laminated ceramic capacitor.

[0002]

2. Description of the Related Art Conventionally, dielectric ceramics containing barium titanate (BaTiO ₃ ) as a main component have been widely put into practical use. However, dielectric ceramics containing barium titanate as a main component are usually 1300 to 1400 ° C. High sintering temperature was required. Therefore, when this is used as a dielectric of a multilayer capacitor, a material that can withstand this sintering temperature, for example, an expensive noble metal such as platinum or palladium must be used as an internal electrode, which increases the manufacturing cost. There was a drawback.

Therefore, in order to reduce the manufacturing cost of the multilayer capacitor, it is possible to use an inexpensive metal containing silver or the like as a main component for the internal electrode at a temperature as low as possible.
In particular, there was a need for porcelain compositions that could be sintered below 1000 ° C. Further, as the electrical characteristics of the dielectric ceramic, it is basically required that the dielectric constant is high, the dielectric loss is small, and the insulation resistance is high.

To meet such demands, 1000
As a porcelain composition that can be sintered at a temperature of ℃ or less, Pb (F
e_2/3W_1/3) O₃-PbZrO₃System (JP-A-55-2
1850), Pb (Fe_2/3W_1/3) O₃-Pb
ZrO₃-Pb (Mn_2/3W _1/3) O₃System (JP-A-55
-23058), Pb (Mn_1/3Nb_2/3) O₃
-Pb (Mg_1/2W_1/2) O₃-PbTiO₃System
58-60670) and other lead-based composite perovskers
Ito-type dielectric ceramic compositions have been proposed.

[0005]

However, in recent years,
As the composite perovskite-type dielectric ceramic composition is used as a dielectric for a chip-type multilayer ceramic capacitor, in addition to the conventional high dielectric constant, low dielectric loss, and high insulation resistance, the mechanical strength of porcelain is increased. Has become especially necessary.

That is, when a chip-type monolithic ceramic capacitor is mounted on a circuit board, the monolithic ceramic capacitor is mechanically affected by a difference in coefficient of thermal expansion between the circuit board and the monolithic ceramic capacitor or due to bending of the circuit board. It is necessary to increase the mechanical strength of the dielectric porcelain that composes the monolithic ceramic capacitor so that it will not be damaged even if strain is applied.

However, the conventional lead-based composite perovskite-type dielectric ceramic has a relatively small mechanical strength and may be cracked and damaged.

Therefore, an object of the present invention is to solve the above problems and to sinter at a temperature of 1000 ° C. or lower, which has a high dielectric constant and a large mechanical strength, and is a lead-based composite perovskite type dielectric ceramic. To provide.

[0009]

In order to achieve the above object, the lead-based composite perovskite type dielectric ceramic of the present invention comprises:
The average crystal grain size is in the range of 2 μm to 5 μm, and
The ratio of the maximum crystal grain size to the minimum crystal grain size is in the range of 4 to 6.

[0010]

EXAMPLES Examples of lead-based composite perovskite type dielectric ceramics of the present invention will be described below.

First, as a starting material, industrial Pb ₃ O is used.
₄ , Fe ₂ O ₃ , WO ₃ , ZnO, Nb ₂ O ₅ , Mg
O and NiO were prepared, weighed so as to have the composition shown in Table 1, and mixed with a ball mill for 16 hours using ion-exchanged water as a solvent. 750 the obtained mixed powder in the air
It was calcined at ℃ for 2 hours and pulverized to obtain a calcined powder.

Thereafter, a binder such as polyvinyl butyral, a plasticizer such as DOP and an organic solvent such as toluene were added to the obtained calcined powder and mixed to obtain a slurry. Then, using this slurry, a thickness of 50 to 60
A green sheet of μm was prepared by the doctor blade method. After that, the green sheets are stacked and pressure-bonded, and then punched or cut to obtain a disk sample having a diameter of 10 mm and a thickness of 1.0 mm, and a rectangular parallelepiped sample having a size of 45 mm × 5 mm × 1.5 mm. It was

Next, these samples were heated in the air to remove the binder, and then fired in the air at the temperatures shown in Table 1 for 2 hours to obtain porcelain samples. Further, with respect to the disk-shaped porcelain sample, silver paste was applied to both surfaces of the sample, and the sample was exposed to 800
The disc-shaped capacitor was baked at ℃.

[0014]

[Table 1]

After that, the relative permittivity was determined using a disk-shaped capacitor. In this case, the relative dielectric constant was calculated from the capacitance measured under the conditions of a temperature of 25 ° C., a frequency of 1 KHz, and a measurement voltage of 1 Vrms, and the dimensions of the disk-shaped capacitor.

Further, using a rectangular parallelepiped porcelain sample, the bending strength by three-point bending was determined. Specifically, the sample was set with an autograph with the distance between fulcrums set to 30 mm, and 0.5
The breaking load (P) when the crosshead is advanced at a speed of mm / min is calculated, and the bending strength (σ) = 3PL / 2WT
² (where L is the distance between fulcrums, T is the thickness of the sample, and W is the width of the sample). And
As the value of the bending strength, an average value obtained by Weibull plotting 20 values and performing Weibull statistical analysis was adopted.

Further, the sample surface of which the bending strength was measured was observed by a scanning electron microscope, and the average crystal grain size, the maximum crystal grain size and the minimum crystal grain size of 100 arbitrarily sampled crystal grains were analyzed by image analysis. I asked.
Then, the ratio between the maximum crystal grain size and the minimum crystal grain size was calculated. Table 2 shows the above results.

[0018]

[Table 2]

As is clear from the results shown in Table 2, within the range of the present invention, the average crystal grain size is 2 μm to 5 μm, and the ratio of the maximum crystal grain size to the minimum crystal grain size is 4 to 6. In (Sample Nos. 2, 3, 4, 7, 8), the relative dielectric constant is 12000 or more and the bending strength is 115MP.
A lead-based composite perovskite-type dielectric ceramic of a or higher is obtained.

On the other hand, when the average crystal grain size is less than 2 μm, the relative dielectric constant is 30 as shown in sample number 1.
It is as low as 00 and the bending strength is also as low as 103 MPa.
On the other hand, when the average crystal grain size exceeds 5 μm, the bending strength is as low as 80 MPa as shown in Sample No. 5.

When the ratio of the maximum crystal grain size to the minimum crystal grain size is less than 4, as shown in sample No. 6, the bending strength is as low as 95 MPa. Even when the ratio of the maximum crystal grain size to the minimum crystal grain size exceeds 6, the sample number 9
As shown in, the bending strength is as low as 80 MPa.

The present invention is not limited to the dielectric ceramics shown in the above embodiments. That is, for example, Pb
(Fe _2/3 W _1/3 ) O ₃ -PbZrO ₃ system, Pb (Fe
_{2/3 W 1/3) O 3 -PbZrO 3} -Pb (Mn 2/3 W
_1/3 ) O ₃ system, Pb (Mn _1/3 Nb _2/3 ) O ₃ -Pb
Similar results can be obtained with a lead-based composite perovskite type dielectric ceramic such as (Mg _1/2 W _1/2 ) O ₃ -PbTiO ₃ system.

[0023]

As is apparent from the above description, the average particle size of the porcelain is kept within the range of 2 μm to 5 μm, and the ratio of the maximum crystal grain size to the minimum crystal grain size is kept within the range of 4-6. To obtain a lead-based composite perovskite-type dielectric ceramic having a high dielectric constant of 12,000 or more and a mechanical strength of 115 MPa or more, which is sintered at a temperature of 1000 ° C. or less. You can

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Claims (1)

[Claims] 1. A lead-based composite perovskite having an average crystal grain size in the range of 2 μm to 5 μm and a ratio of the maximum crystal grain size to the minimum crystal grain size in the range of 4 to 6. Type dielectric porcelain.