JPH02255553A - Composition of dielectric ceramics - Google Patents

Abstract

PURPOSE:To allow calcination at a relatively low temp. and to improve the change of an insulation resistance and dielectric constant with temp. by mixing PbO, CaCO3, SrCO3, BaCO3, MgO, Nb2O5, WO3, TiO2, and CuO and calcining the mixture. CONSTITUTION:The PbO, CaCO3, SrCO3, BaCO3, MgO, Nb2O5, WO3, TiO2, and CuO having chemically high purity are mixed and are ground by a wet process and thereafter, the mixture is dried and calcined to obtain the calcined powder. An org. binder is added to the powder obtd. by grinding the calcined powder by a wet process then drying the powder and after the powder is molded under pressurization, the molding is calcined. The compsn. of the dielectric ceramics which can be calcined at <=1000 deg.C, >=8000 dielectric constant, has >=800kg/cm<2> deflective strength by a 3-point bending method and in which X, Y in formula (Me is >=1 kinds of the elements selected from Ca, Sr and Ba) are in a range enclosed by A, B, C, D, E of the table and (a) and aZ are 0.03<=a<1.0, 0.002<=aZ<=0.04 is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high dielectric constant dielectric ceramic composition that can be fired at a relatively low temperature of 1000° C. or lower.

BACKGROUND OF THE INVENTION Due to the demand for smaller devices and larger capacitances as electronic devices become smaller, multilayer capacitors have become mainstream in the ceramic capacitor market in recent years.

Multilayer ceramic capacitors are usually obtained by co-firing internal electrodes and dielectric ceramics. BACKGROUND ART Barium titanate-based ceramic compositions have been widely used as dielectric materials for high-permittivity ceramic capacitors. However, the firing temperature for barium titanate porcelain is 1800℃.
Since the temperature is as high as approximately .degree. C., it is necessary to use an expensive metal such as Pd or Pt for the internal electrodes when manufacturing a multilayer capacitor.

Therefore, many lead-based perovskite dielectric ceramic compositions have been proposed that can be fired at a temperature of 1000° C. or lower and can use inexpensive materials mainly composed of Ags or Cu for the internal electrodes.

Problems to be Solved by the Invention However, the mechanical strength of the above-mentioned porcelain is generally lower than that of barium titanate-based porcelain, which may cause chips and cracks to occur in the porcelain during various treatments after firing. It had become.

For example, when measuring the cutting strength, barium titanate porcelain has a strength of 1000 kg/cm2 or more, whereas the above porcelain has a strength of only about 700 kg/cm2.

An object of the present invention is to provide a dielectric ceramic composition that solves the above problems.

Means for Solving the Problems The present invention is based on the compositional formula % formula % T at-a) z) Oav (where Me is C
a1 one or more elements selected from Sr or Ba), where X and Y are the following A181 C1D
and E, and X Y A O,00,15 B O,00,01 G O,10,01 D O,340,45 E O,340,73 and a and aZ are the following formulas The dielectric ceramic composition should be made within the range of .

0.03 ≦ a<1.0 0.002 ≦ aZ ≦ 0.04 Furthermore, the dielectric ceramic composition contains 9 mol parts or less of Pb in terms of Pbo with respect to 100 mol parts of the above composition. .

According to the dielectric ceramic composition of the first aspect of the present invention, within a limited range of composition, it can be fired at a temperature of 1000°C or less, has a dielectric constant of 8000 or more, and has a cutting strength of 800 kg by the three-point bending method. /cm2 or more.

According to the dielectric ceramic composition of the second aspect of the present invention, the sintering temperature can be further lowered by the action of the additive.

Examples Examples of the present invention will be described below with reference to the drawings.

Example 1 This example corresponds to the invention described in claim 1,
The problem was solved by selecting the main composition and limiting the range of the composition.

Chemically pure PbO5CaCO5 as starting material,
5rCOs, BaCO5, MgO, Nb*Os, WOa
, T i Os, and CuO were used. After correcting the purity, a predetermined amount of these was weighed and mixed in a ball mill for 15 hours. The solvent is pure water and the ball is 4m in diameter.
A zirconia sphere of m was used. After drying the mixture, it was placed in an alumina crucible, covered with a homogeneous lid, and calcined at 750°C to 900°C. Roughly crush the calcined material in an alumina mortar,
The mixture was ground in a ball mill for 15 hours. The same solvent and ball as used for mixing were used. A 6 wt % aqueous solution of polyvinyl alcohol was added to the powder obtained by sufficient drying in an amount of 10 wt % based on the powder amount, and the mixture was mixed and passed through a 32 mesh sieve to granulate it. The granules were pressure-molded into a disk shape at a pressure of 1000 kg/cm2. The organic components in the molded product were dispersed by heat treatment in air at 650° C. for 2 hours. For firing, place the sample in a magnesia porcelain container.
A homogeneous lid was placed, and the temperature was raised to a predetermined temperature at a rate of 400°C/hr, held for 2 hours, and then lowered at a rate of 400°C/hr. The density of the sintered bodies fired at various temperatures was measured by the Archimedes method, and the temperature giving the maximum density was determined as the optimum firing temperature, and the following electrical properties were measured.

Au was vacuum-deposited on both sides of the sintered body using Cr as a base to form electrodes. dielectric constant and tanδ to 1 kHz
Measurements were made under an electric field of IV/mm. resistivity to 1kV
It was determined from the value 1 minute after applying a voltage of /mm. Also,
Length 15mm1 Width 3mm1 Thickness 0.7mm from the sintered body
A rectangular parallelepiped was cut out, and the cutting strength was measured using the three-point bending method. Results represent the average of 10 samples.

Table 1 shows the results. xlylzl and a in the composition column are the composition formula % formula % (W+--) -) Os, (where Me is Ca, S
(one or more elements selected from r or Ba) corresponds to X1y, z, and a, respectively.

(Left below) From Table 1, it can be seen that the composition within the claimed range can be fired at a temperature of 1000°C or less, has a dielectric constant of 8000 or more at room temperature, and has a cutting strength of 800 kg/cm” or more by the three-point bending method. becomes.

Example 2 This example corresponds to the invention described in claim 2.
The problem was solved by adding a specific amount in terms of P bt-P bO.

By the same method as in Example 1, Pb is converted to PbO and becomes b mole parts with respect to 100 mole parts of the composition represented by the compositional formula % (Cu+/aW+/a) i, s+s) Os. The properties of the sintered body were evaluated.

Table 2 shows the results.

(The following is a margin) Table 2 No. marked with a # is a comparative example number outside the scope of claims.
, No. 19 is within the scope of claim 1. From Table 2, the firing temperature decreased as the amount of added PbO increased. However, when b is more than 9 mol%,
Since the mechanical strength was less than 800 kg/cm'', it was excluded from the scope of claims.

Note that elements that do not significantly affect the effects of the present invention, such as AIN SIN Crx Mn, Fe
, Co5N+1Zn, Zr1Ta1Sbs, lanthanide elements, etc. may be contained up to approximately Iwt%.

Effects of the Invention The dielectric ceramic composition of the present invention can be fired at a temperature of 1000°C or less, has a dielectric constant of 8000 or more at room temperature, and has a cutting strength of 800 kg/cm” or more by the three-point bending method. In addition, the insulation resistance value was high, and although it was not shown as data, the temperature change in dielectric constant was also good, and within the claimed range, J
It satisfies the YmF characteristics of IS.

Therefore, it can be used as a dielectric material for multilayer ceramic capacitors that use inexpensive materials as internal electrodes.

[Brief explanation of drawings]

The figure shows the composition formula, P b+ -xMex ((Mg+, -3Nb2]a)
l-++-zT' Iy (Cu5W+--)-
) Os, (where Me is Ca1Sr or B
X and Y in one or more elements selected from a)
FIG.

Claims (2)

[Claims] (1) Composition formula Pb_1_-_xMe_x{(Mg_1_/_3Nb_
2_/_3)_1_-_y_-_zTi_y(Cu_a
W_1_-_a)_z}O_3, (Me is Ca
, Sr, or Ba), X and Y are in the range surrounded by A, B, C, D, and E below, and there are ▲mathematical formulas, chemical formulas, tables, etc.▼ A dielectric ceramic composition characterized in that a and aZ are in the following ranges: 0.03≦a<1.0 0.002≦aZ≦0.04. (2) The dielectric ceramic composition according to claim 1, wherein the dielectric ceramic composition contains at least 9 mole parts or less of Pb in terms of PbO, based on 100 mole parts of the dielectric ceramic composition.