JP2538440B2 - Method for producing lead-based dielectric ceramic composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lead-based dielectric ceramic composition used for a dielectric layer of a ceramic capacitor.

[0002]

2. Description of the Related Art In general, a lead-based dielectric ceramic composition is prepared by thoroughly mixing a raw material compound containing lead oxide with a ball mill or the like and then calcining the mixture to cause a solid phase reaction between the raw material compounds. It is made by molding and sintering this reaction product.

Here, as lead oxide, Pb ₃ O ₄ and Pb are used.
O or the like is used, and Mg is used as a raw material compound other than lead oxide.
O, Nb ₂ O ₅ , ZnO, NiO, TiO ₂ , W, Ag
Etc. are used. Further, since impurities have a great influence on various electrical characteristics of the obtained dielectric ceramic composition, high-purity compounds containing few impurities are used as these raw material compounds. Moreover, calcination is, for example, 800 ° C., 3
The sintering is performed under the condition of about Hr, for example, 1200
It is carried out under the conditions of ° C and about 2 hours.

[0004]

By the way, when a lead-based dielectric ceramic composition is manufactured by a conventional method, lead oxide is often used as a raw material of lead. In most cases, the lead oxide used at this time is an oxide represented by Pb ₃ O ₄ or PbO in the molecular formula, but conventionally, no attention was paid to such a crystal form, and Pb contained in the molecule was used. I used it paying attention only to the atomic weight.

However, as is generally well known, PbO has two types of crystal forms, a high temperature type and a low temperature type, and each shows different reactivity. In addition, Pb ₃ O ₄
In many cases, the oxides said to actually contain PbO in a certain ratio. Conventionally, the crystal forms are not the same as described above, but the crystal forms with different reactivity are contained in different ratios.
The desired electrical characteristics
It may not be possible to obtain a dielectric porcelain composition with
Cormorants there was a problem.

Further, in order to prevent compositional variation due to evaporation of lead during firing, it is often practiced in actual production to add an excessive amount of lead oxide which is expected to be reduced by evaporation. In this case, since the evaporation amount of lead is affected by the manufacturing conditions, it was very difficult to obtain an accurate value. For this reason, lead may be insufficient and may not sinter, or the excess may change the dielectric constant, resulting in lack of stability as a material.

It is an object of the present invention to provide a method for producing a lead-based dielectric ceramic composition, which makes it possible to obtain a lead-based dielectric ceramic composition that always has desired electrical characteristics. .

[0008]

Means for Solving the Problems A method for producing a lead-based dielectric ceramic composition according to the present invention is one obtained by calcining a raw material compound containing lead oxide in excess of the target composition, and performing the calcining. In the method for producing a lead-based dielectric ceramic composition obtained by molding, and baking the product obtained by this molding,
Pb containing 75 mol% or more of litharge phase as the lead oxide
It is characterized by using O.

Here, as the raw material compound, lead oxide
Outside, it is possible to use those containing Mg, Nb, Zn, Ni, Ti, W, an oxide of one or more elements selected from Ag or the like.

PbO containing 75 mol% or more of litharge phase as lead oxide is used because it has a desired relative permittivity when the litharge phase contained in lead oxide is 75 mol% or more. This is because a dielectric ceramic composition can be obtained, but if the litharge phase contained in lead oxide is less than 75 mol%, a dielectric ceramic composition having a desired relative dielectric constant cannot be obtained.

Further, the calcination can be carried out under the conditions of a temperature of 700 to 850 ° C. and a time of about 1 to 10 hr, and a calcination of a temperature of 1000 to 1300 ° C. and a time of 0.5 to 10 hr.
It can be performed under moderate conditions.

The present invention is not limited to the examples described later, but can be similarly applied to other dielectric ceramic compositions.

[0013]

When PbO (litharge phase) reacts with B site atom (eg MgO, Nb ₂ O ₅ ) in a solid state, it produces a perovskite phase which is a target reactant, and at the same time, it is a by-product in a certain proportion. It produces a pyrochlore phase, which exists in the sintered body as particles and has little effect on the overall electrical properties. This pyrochlore phase is hardly generated unless excess lead atoms are present, is generated when excess lead atoms are present, and since the content of lead atoms is higher than that in the perovskite phase, a large amount of lead atoms are trapped and absorbed. The lead atomic weight.

[0014]

Example 1 First, PbO (litharge phase: 100 mol%), MgO and Nb ₂ O ₅ raw material powders were mixed with Pb (Mg _1/3 Nb).
_2/3 ) Weighed at a ratio to produce O ₃ . Further, PbO (litharge phase: 100 mol%) is added to the amount of 0.5, 1.0, 2.0, 4.0, 6. 0, 8.0,
An amount of 10.0 mol% was weighed.

Next, these raw material powders and excess PbO are placed in a resin pot containing alumina balls, ethanol is further added, and this resin pot is rotated for 20 hours, and these raw material powders and excess PbO are sufficiently wet. Mixed in.

Next, the mixture obtained by this mixing was dried and calcined at 800 ° C. for 5 hours to cause a solid-phase reaction between the mixtures. By this reaction, a perovskite phase {Pb (Mg _1/3 Nb _2/3 ) O ₃ } and a small amount of pyrochlore phase (Pb ₂ Nb ₂ O ₇ ) were produced.

Next, the product obtained by this calcination is crushed by a ball mill, an organic binder is added, and granulated,
This granulated product was pressure-molded at a pressure of 1 t / cm ² to have a diameter of 1
A disk-shaped molded product having a cmφ and a thickness of 1 mm was obtained. And
The disk-shaped moldings were lined up on a zirconia setter and placed in a dense alumina sheath at 1200 ° C. for 3 hours.
It baked and the sintered compact was obtained.

Next, the abundance ratio of the perovskite phase and the pyrochlore phase in this sintered body was determined by the X-ray diffraction method.
Further, Ag baked electrodes were formed on both surfaces of this sintered body, and the relative dielectric constant of this sintered body was measured. The results are shown in Sample No. 1 of Table 1.
It became as shown in 2-8.

In order to confirm the effect of excess PbO, the same experiment was carried out without PbO being excessively added. The results are shown in Sample No. 1 of Table 1. It became as shown in 1.

Comparative Example 1 Pb ₃ O ₄ was used as lead oxide, a sintered body was formed in the same manner as in Example 1, and the abundance ratio of the perovskite phase and the pyrochlore phase in this sintered body was measured by the X-ray diffraction method. I asked.
Further, Ag baked electrodes were formed on both surfaces of this sintered body, and the relative dielectric constant of this sintered body was measured. The results are shown in Sample No. 1 of Table 1.
It became as shown in 25-32.

Example 2 As lead oxide, a litharge phase of 75 mol% and a lead oxide other than the litharge phase of 25 mol% were used, and a sintered body was formed in the same manner as in Example 1 and subjected to X-ray diffraction. The abundance ratio of the perovskite phase and the pyrochlore phase in this sintered body was determined by the method. Further, Ag baked electrodes were formed on both surfaces of this sintered body, and the relative dielectric constant of this sintered body was measured. The results are shown in Sample No. 1 of Table 1. It became as shown in 9-16.

Comparative Example 2 A lead oxide having a litharge phase of 70 mol% and a lead oxide other than the litharge phase of 30 mol% was used, and a sintered body was formed in the same manner as in Example 1 and subjected to X-ray diffraction. The abundance ratio of the perovskite phase and the pyrochlore phase in this sintered body was determined by the method. Further, Ag baked electrodes were formed on both surfaces of this sintered body, and the relative dielectric constant of this sintered body was measured. The results are shown in Sample No. 1 of Table 1. It became as shown in 17-24.

[0023]

[Table 1]

[0024]

According to the present invention, the litharge phase is set to 7
Since PbO containing 5 mol% or more was used as a raw material, it is possible to prepare a material having an optimum composition ratio without strictly adjusting the amount of lead oxide to be added excessively.
There is an effect that it is possible to obtain a lead-based dielectric ceramic composition that always has desired electrical characteristics.

Further, in the present invention, the litharge phase PbO is a low temperature phase, and heat treatment at a high temperature (up to 800 ° C.) is not required for producing PbO, so that the particles are not coarsened, There is an effect that a small and uniform raw material powder can be easily obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Mizuno 6-16-20 Ueno, Taito-ku, Tokyo Within Taiyo Yuden Co., Ltd. (56) Reference JP 48-79215 (JP, A) JP 54 -25909 (JP, A) JP-A-63-225404 (JP, A)

Claims (2)

(57) [Claims] 1. A method in which a raw material compound containing lead oxide in excess of the stoichiometry of a target composition is calcined, a product obtained by this calcining is molded, and a product obtained by this molding is calcined. A method for producing a lead-based dielectric ceramic composition, wherein PbO containing 75 mol% or more of a litharge phase is used as the lead oxide. 2. A raw material compound is lead oxide, Mg, Nb,
2. The method for producing a lead-based dielectric ceramic composition according to claim 1, comprising an oxide of one or more elements selected from Zn, Ni, Ti, W, and Ag. .