JP2594465B2 - Method for producing dielectric porcelain composition - Google Patents

Description

The present invention relates to a method for producing a Ba (Zn _1/3 Ta _2/3 ) O ₃ -based dielectric ceramic composition for microwaves, and more particularly to barium. The present invention relates to a method for producing a dielectric ceramic composition in which the composition ratio is slightly insufficient based on stoichiometry, and a calcined product is fired without performing wet pulverization.

[Prior Art] Various material series have been developed for dielectric ceramic compositions used in the microwave region. One of them is Ba (Zn _1/3).
Ta _2/3 ) O ₃ -based compositions are available. In addition to this type of material series, ceramic materials are generally manufactured through the following steps. First, the raw materials are weighed and mixed so as to have a predetermined composition, mixed, pre-fired, wet finely pulverized by a ball mill or the like, and then dried. Next, the dried powder is kneaded with a binder, granulated, molded, and then fired under appropriate conditions.

A pure Ba (Zn _1/3 Ta _2/3 ) O ₃ composition (stoichiometric composition) containing no additive has poor sinterability even when fired at a high temperature of 1600 to 1700 ° C. In the case of firing for a longer time, abnormal grain growth occurs and the density is significantly reduced.
Difficult to control.

However, it has been reported that by firing at a temperature of 1350 to 1600 ° C. for several tens to hundreds of hours, the no-load Q at 12 GHz can be improved up to about 14000 (“Electronic Ceramics” '86) March issue, pages 41-45: Published by Gakudensha. In this case, the relative dielectric constant is about 29 to 30, but it is reported that the relative permittivity can be improved to about 30.2 by using a powder obtained by a coprecipitation method or a hot press method. The resonance frequency temperature characteristic is 0 ± 0.
It is about 5 ppm / ° C.

The relative permittivity and the temperature coefficient of the resonance frequency are Ba (Zn _1/3 Nb
_2/3 ) O ₃ , BaZrO ₃ , Ba (Ni _1/3 Ta _2/3 ) O _{3 and} other additives can be controlled to some extent by strictly weighing and mixing them.

[Problems to be Solved by the Invention] As a microwave dielectric material, it is required that the unloaded Q is high in a high frequency band and the relative dielectric constant εr and the temperature characteristic τf can be controlled.

However, to improve the no-load Q with the conventional technology, 13
Since firing must be performed at 50 to 1600 ° C. for as long as 120 hours, energy loss is large, and costs such as consumption of the firing furnace are increased. The dielectric properties are improved by employing a coprecipitation method or a hot press method, but these methods are not suitable for industrial production and are not practical.

Further, the relative permittivity and the temperature coefficient of resonance frequency can be controlled by strictly weighing and adding the additives, but the amount is often very small and the number of weighed substances increases, which makes production management difficult.

In addition, when firing at a high temperature of 1600 ° C. or more, the sinterability is poor as described above, and when the firing time is prolonged, zinc evaporates and the characteristics deteriorate.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to achieve extremely high no-load Q by firing at high temperature for a short time.
It is another object of the present invention to provide a method for producing a dielectric ceramic composition which can control the relative dielectric constant and the temperature coefficient of resonance frequency with good reproducibility.

[Means for Solving the Problems] The present invention, which can achieve the above object, has the general formula Ba
_A calcined product weighed and calcined to have a composition expressed as _1-X (Zn _1/3 Ta _2/3 ) O ₃ and within the range of 0.004 ≦ X ≦ 0.01 is obtained by a dry method without performing wet grinding. Only by grinding and after molding
This is a method for producing a dielectric ceramic composition which is fired at 1600 to 1700 ° C. for 1 to 10 hours.

Normally, the production process of ceramics is performed in the order of mixing, calcination, pulverization, molding, and firing. The grinding of the calcined product
Wet pulverization for ten to several tens of hours is common. After performing wet fine pulverization, granulation is performed using the dried powder, and molding is performed.

The features of the present invention are that only the dry pulverization is performed without such a wet pulverization step, and that the barium composition is produced at a compounding ratio slightly inadequate from the stoichiometric composition.

[Function] In the Ba (Zn _1/3 Ta _2/3 ) O ₃ derivative ceramic composition, when the calcined product is wet-milled for a long time, the interface of the powder becomes very unstable and the powder Barium reacts with water to form a hydroxide (mechanochemical reaction). The hydroxide absorbs carbon dioxide in the air in the subsequent drying step and becomes barium carbonate. This step is the same as recrystallization, and giant columnar crystals appear. When such a giant crystal appears, the sinterability deteriorates extremely. In other words, it decomposes during the sintering process, carbon dioxide gas jumps out and barium remains,
If it contains such a decomposition product, it is difficult to densify it,
It does not become a uniform fired product. It is believed that one hundred hours of firing was required in the prior art for one reason.

However, it was found that this kind of material was very soft even if calcined, and even if it was crushed by hand and roughly crushed, the particle size was small enough and both sinterability and dielectric properties were hardly affected. . In the present invention, since only dry pulverization is required without using a wet pulverization step, good sinterability can be obtained without the appearance of giant crystals of barium carbonate.

By the way, as described in connection with the prior art, in this series of porcelain compositions, stoichiometric compositions do not sinter even when fired at a high temperature of 1600 ° C. or higher. It does not sinter even when the wet pulverization step is not performed. Zn and Ta, which are B-site ions of ABO ₃ type perovskite ceramics represented by Ba (Zn _1/3 Ta _2/3 ) O ₃ , are regularly arranged by prolonged firing, and super lattice reflection appears. This is one of the reasons that the prior art requires firing for a long time as described above. However, it has been found that this arrangement occurs in a shorter time than the reduction of the amount of Ba, which is the A-site ion, and that the degree of arrangement increases in accordance with the amount of reduction of Ba. That is, by making the amount of Ba insufficient from the stoichiometric composition, sintering can be performed by firing at a high temperature for a short time to improve the dielectric characteristics.

Increasing the firing temperature improves the Q value in a short time. This is the reason for firing at a high temperature of 1600 to 1700 ° C. in the present invention. However, sintering does not occur simply by firing at a high temperature. In the present invention, therefore, Ba is set to be smaller than the stoichiometric composition. The value is 0.004 ≦ x ≦ 0.01. The lower limit of this value, 0.004, was set so as to obtain sufficient characteristics when fired at 1600 ° C. for 1 hour. If the firing time is less than 1 hour, sufficient sintering cannot be obtained.
Conversely, if the time exceeds 10 hours, the Q value and the like are not significantly affected, and it is not preferable that the time is long from the viewpoint of energy loss or the like, and it is not preferable because the evaporation of Zn proceeds to deteriorate the characteristics. The reason why the upper limit value of the insufficient amount X of Ba is set to 0.01 is that if it exceeds that value, the dielectric properties deteriorate.

Further, by adjusting the amount of Ba deficiency, it becomes possible to control the relative dielectric constant and the resonance frequency temperature coefficient without adding an additive and keeping the unloaded Q at an extremely high value.

[Example] BaCO _{3 having} a purity of 99.7% and Zn having a purity of 99.9% as starting materials
O, also using 99.9% pure Ta ₂ O ₅ , the general formula Ba _1-X (Zn
_1/3 Ta _2/3 ) O ₃ , weighed so as to fall within the composition range of 0.004 ≦ X ≦ 0.01, and wet-mixed with pure water in a polyethylene ball mill equipped with zirconia balls for 20 hours.
After taking out this mixture from the ball mill and drying, it was molded at a molding pressure of 500 kg / cm ² using a mold and a hydraulic press,
Calcination was performed in air at 1300 ° C. for 10 hours.

The calcined product was crushed lightly in a mortar, and the obtained powder was homogenized by adding 10% by weight of a polyvinyl alcohol solution as a binder, and then granulated through a 60 mesh sieve. This granulated powder is formed using a mold and a hydraulic press at a molding pressure of 3000 kg / cm ²
Into a 14 mm diameter disc.

This molded product was fired at a temperature of 1600 ° C. or more and 1700 ° C. or less for 10 hours or less to obtain a dielectric porcelain. Both the upper and lower surfaces and the side surfaces were scraped off, and the unloaded Q and relative permittivity were measured at a frequency of about 7 GHz by the dielectric cylinder resonator method. Temperature coefficient of resonance frequency is -30
It was measured and determined in the range of ° C to 80 ° C.

FIG. 1 shows the unloaded Q, the relative permittivity εr, and the resonance frequency temperature coefficient τ with respect to the Ba deficiency X when baked at 1600 ° C. for 4 hours.
It is a graph which shows the relationship of f. As shown in the figure, it can be seen that good dielectric properties can be obtained by making Ba less than the stoichiometric composition and eliminating the wet pulverization step. In addition, it can be seen that by changing the Ba deficiency X, the no-load Q remains at an extremely high value, but the relative permittivity εr and the resonance frequency temperature coefficient τr change. Therefore, by controlling the Ba deficiency X, the relative dielectric constant ε can be maintained at a high Q value.
r and the resonance frequency temperature coefficient τf can be controlled.

The reason that the relative permittivity εr changes depending on the amount of Ba deficiency may be because the crystal structure is significantly different. This is shown in FIG. This is the result of measuring the superlattice reflection of Zn and Ta by X-ray diffraction. Even when the firing conditions are the same, the degree of regular arrangement and the dielectric properties are completely different due to the change in the composition ratio of Ba.

FIG. 3 shows the dielectric characteristics under the firing conditions of 1600 ° C. for one hour. From FIG. 3, the worst firing conditions 1600
In the region satisfying the practical characteristics in 1 ° C.-1 hour, the shortage X of Ba is 0.004 to 0.01. The numerical range of the present invention is determined from such experimental results. Under these firing conditions, the unloaded Q is the largest when the shortage X of Ba is 0.006, and X = 0.0
When it is near 05, the relative permittivity εr becomes the largest.

FIG. 4 shows the dielectric characteristics when firing at 1600 ° C. when the shortage X of Ba is 0.005, and the horizontal axis shows the firing time. The no-load Q rises sharply for one hour of firing, and then gradually increases. The relative dielectric constant εr is highest when the firing time is one hour, and then gradually decreases.

For these reasons, the firing time must be at least one hour. The reason why the upper limit of the firing time is set to 10 hours is that the characteristics are not significantly improved even if firing is performed longer, and only the amount of time required for firing for a long time is sufficient.
This is because the evaporation of the Zn component causes the characteristics to deteriorate, and baking for a long time leads to energy loss, which is not preferable.

[Effects of the Invention] In the present invention, a calcined product weighed and calcined so that Ba has a compounding ratio slightly smaller than the stoichiometric composition is pulverized by a dry method without wet pulverization, and after molding, 1600 to 1 at 1700 ° C
Because it is a method of firing for up to 10 hours, the firing time ranging from several tens of hours to one hundred and several tens of hours as in the conventional technology can be significantly reduced, and a significant reduction in manufacturing costs including reduction in energy cost etc. is possible Becomes In the present invention, a high relative dielectric constant of about 30 or more, which had to use a coprecipitation method or a hot press method in the prior art, can be arbitrarily selected by ordinary normal pressure firing in the present invention.

Further, in the present invention, additives are not required for controlling the resonance frequency temperature coefficient and the relative dielectric constant, and their characteristics can be easily controlled with good reproducibility only by changing the mixing ratio of the basic raw materials.

In the present invention, the wet fine pulverizing step is not required, and the accompanying drying step is also unnecessary, so that the possibility of weighing error due to tool loss is reduced, and there is no appearance of a substance that causes difficulty in sintering. Can be simplified and a dielectric ceramic composition having good characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing the dielectric characteristics under the firing conditions of 1600 ° C. for 4 hours, FIG. 2 is a diagram showing the X-ray diffraction pattern for the Ba deficiency, and FIG. FIG. 4 is a graph showing the dielectric characteristics with respect to the sintering time when the composition temperature is 1600 ° C. in the composition where X = 0.005.

Claims (1)

(57) [Claims] (1) The compound represented by the general formula Ba _1-X (Zn _1/3 Ta _2/3 ) O ₃ .
The calcined product weighed and calcined so as to have a composition within the range of 004 ≦ X ≦ 0.01 is pulverized only by a dry method, and after molding.
A method for producing a dielectric ceramic composition, comprising firing at 1600 to 1700 ° C for 1 to 10 hours.