JPH07282625A - Dielectric ceramic and its manufacture - Google Patents

Abstract

PURPOSE:To provide dielectric ceramic and its manufacture capable of forming in accuracy by improving sintering difficulty without worsening an essentially excellent dielectric characteristic. CONSTITUTION:Composition is formed of barium, magnesium, tantalum, titanium and oxygen. When represented by wBaO, xMgO, yTa2O5, zTiO2, w, x, y, z are in a range of respectively 0.95<=w<=1.05, 0.30<=x<=0.35, 0.30<=y<=0.35, 0.005<=<=S0.04.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic having a high dielectric constant, a low dielectric loss and good temperature stability, which is used for a dielectric resonator, a filter and the like, and a method for producing the same.

[0002]

2. Description of the Related Art With the remarkable development of communication technology utilizing microwave band such as mobile communication and satellite broadcasting, dielectric ceramics for high frequency devices such as dielectric resonators and filters. The demand for is increasing more and more. The dielectric ceramics are roughly classified into two types. One is dielectric ceramics for high frequency filters installed in automobile phones, mobile phones and second generation cordless phones, and the other is microwave dielectric ceramics for dielectric resonators used in base stations and the like. . These dielectric ceramics are
First, high dielectric constant, low dielectric loss (large unloaded Q value), and small temperature coefficient are required. By the way, among these dielectric ceramics, the microwave dielectric ceramics for a dielectric resonator used in a base station or the like, in particular, have been given particular importance to the dielectric loss among the above-mentioned characteristics because of the demand for energy saving.

Conventional low dielectric loss (large unloaded Q
BaTi ₄ as the dielectric ceramics having
O ₉ , (Zr, Sn) TiO ₄ and Ba (Zn _1/3 Ta)
_2/3 ) O _{3 and the} like, but none of them can reduce the dielectric loss to the extent that they can be applied to microwave dielectric ceramics for dielectric resonators. On the other hand, Ba (Mg _1/3 Ta
_2/3 ) O ₃ (hereinafter referred to as BMT) has a temperature coefficient close to zero and a sufficiently low dielectric loss as a dielectric, and is expected as an excellent microwave dielectric ceramic for a dielectric resonator. However, when this BMT is produced by the solid-phase reaction method, the difficulty of sintering is a fatal problem, and the practical application of this material is delayed. So this B
Various attempts have been made to improve the difficulty of sintering in the solid phase reaction method of MT. For example, Japanese Patent Publication No. 2-23310
In Japanese Patent No. 3 publication, BMT is added by adding P to the calcined powder.
We are trying to improve the difficulty of sintering in the solid-state reaction method. However, although the sintering resistance of BMT is improved to some extent, the addition of P to the calcined powder causes the BMT to have the excellent characteristics (temperature coefficient close to zero and sufficiently low dielectric loss) inherent to BMT. Impairment has become a new issue.

The present invention has been made as a result of intensive studies in view of the above problems of the prior art, and has excellent characteristics (a temperature coefficient close to zero and a sufficiently low dielectric loss) and can be densified. An object of the present invention is to provide ceramics and a method for manufacturing the same.

[0005]

Means and Actions for Solving the Problems In the present invention,
Consists of barium, magnesium, tantalum, titanium, oxygen, wBaO, xMgO, yTa ₂ O ₅ , zTiO ₂
When expressed by, w, x, y, and z are 0.95 ≦ w, respectively.
≦ 1.05, 0.30 ≦ x ≦ 0.35, 0.30 ≦ y ≦
The dielectric ceramics in the range of 0.35 and 0.005 ≦ z ≦ 0.04 is defined as the first invention, and the general formula

[Chemical 3] The second invention is a dielectric ceramic in which titanium oxide is added as a subcomponent to the basic composition represented by
General formula

[Chemical 4] As a third invention, a method for producing a dielectric ceramic in which titanium oxide is added to a basic composition represented by (hereinafter referred to as BMT), mixed, and fired is aimed to solve the above problems.

The blending ratio of titanium oxide to BMT in the present invention is preferably 0.3 to 2.0 mol%. This is because when the compounding amount of titanium oxide is within the above range, it is possible to obtain a dielectric ceramic that can be sufficiently densified and that has excellent characteristics.

[0007]

EXAMPLES The present invention will be described in detail below based on examples. (Examples 1-6) 99.9% pure BaCO _3, MgO
And a fine powder of Ta ₂ O ₃ is weighed in a 3: 1: 1 molar ratio to formulate the premix. This premix was then added to 0.
3 mol% (Example 1), 0.5 mol% (Example 2), 1.0 mol% (Example 3), 2.0 mol%
(Example 4), 0.1 mol% (Example 5), 2.2 m
TiO ₂ powder was added so as to have an ol% (Example 6) to obtain a raw material powder. Here, mol% is the BaC
O ₃ , MgO, Ta ₂ O ₅ to Ba (Mg _1/3 T
Assuming that only a _2/3 ) O ₃ is generated, this Ba (Mg
The mol% of TiO ₂ with respect to _1/3 Ta _2/3 ) O ₃ is displayed. Next, BaCO ₃ , MgO, Ta ₂ O ₃
The raw material powder to which TiO ₂ was added was wet-mixed for 16 hours in ethanol with U-2M (ball mill manufactured by Irie Shokai, trade name). After the mixed raw material powders were dried, each was calcined in the atmosphere for 5 to 10 hours to prepare a calcined powder. The calcination temperature at this time is preferably 1250 ° C to 1300 ° C. This is because if it is within this range, the raw material powder sufficiently reacts with almost no generation of secondary particles. Then, the calcined powder was divided into 6 equal parts, and each was mixed and pulverized in a ball mill for 16 hours to obtain a mixed powder. Then, an organic binder was added to these mixed powders and dry pressing (pressure: 98 to 196) was performed.
(MPa) to form a cylindrical molded body having an outer diameter of 12 mm and a length of 10 mm. Then, these molded bodies are
Six types of sintered bodies were obtained by firing in air at 1600 ° C. for 3 to 5 hours.

The bulk density of each of the obtained sintered bodies was measured, and the densification rate of the sintered body was calculated from the ratio of the measured bulk density to the theoretical density. The results are shown in Table 1 in percentage. Further, the dielectric properties of the sintered body of the example were measured at a frequency of 10 G using the both-end short-circuit type dielectric resonator method described below.
It was measured at Hz. The results are shown in Table 1. In addition, the rate of temperature change of the resonance frequency of the sintered body is also shown in Table 1 as a temperature coefficient.

(Short-Ended Short-Circuit Dielectric Resonator Method) The measurement procedure of the both-end short-circuited dielectric resonator method is shown below. (1) Assemble a measurement circuit for measuring dielectric properties as shown in FIG. 1 is a network analyzer (manufactured by Hewlett-Packard Co.,
Product name 8757A), 2 is a sweep oscillator (Hewlett
Packard Co., Ltd., trade name 8340A, 3 is a directional coupler (manufactured by Hewlett-Packard Co., Ltd., trade name 19025B), 4 is a controller (manufactured by Hewlett-Packard Co., Ltd., trade name model 300) ) 5 is a short-circuit type dielectric resonator (manufactured by Micro Device Co., Ltd., trade name MSC-12CEV), 6 is 150 mm long
Is the coaxial reference line.

(2) A cylindrical sintered body is inserted into the dielectric resonator 5 of which both ends are short-circuited. (3) Connect the coaxial reference line 6 to the measurement circuit to determine the 0 dB line. (4) The coaxial reference line 6 is removed from the measuring circuit, and the both-end short-circuited dielectric resonator 5 in which the sintered body is inserted is connected to the measuring circuit. (5) From the sweep oscillator 2, a microwave is supplied to the sintered body by a 2.2 mm diameter coaxial wire having a loop-shaped tip. (6) The mode (T
The peak of E ₀₁₁ or TE ₀₁₄ ) is displayed on the network analyzer 1. (7) Peak resonance frequency f ₀ displayed on the network analyzer 1, 3 dB bandwidth Δf, insertion loss IL
(DB) is measured.

The resonance frequency f ₀ measured as described above
From this, the relative permittivity ε of the sintered body is obtained by the following equation (1).

## EQU1 ## ε = (λ ₀ / πD) ² × (u ² + v ² ) +1 (1) where v ² = (πD / λ ₀ ) ² × [(λ ₀ / λ _g ) ² -1] λ _g : Guide wavelength D: Diameter of sintered body λ ₀ = c / f ₀ : Resonance wavelength c: Speed of light u is obtained from the characteristic equation of the following equation (2).

## EQU00002 ## u = (J ₀ (u) / J ₁ (u)) = − v × (K ₀ (v) / K ₁ (v)) (2) where J _n (x) is the first The seed Bessel function, K _n (x), is the modified Bessel function of the second kind.

The unloaded Q value was calculated from the following equation (3).

Q = (f ₀ / Δf) / (1-10 ^{−IL / 20} ) (3)

Comparative Example 1 A sintered body was obtained in the same manner as in Example 1 except that TiO ₂ was not added. Comparative example 1 obtained
The bulk density and the dielectric properties of the sintered body were measured in the same manner as in the example. The results are shown in Table 1.

[0014]

[Table 1]

(Results) From Table 1, the sintered bodies of Examples 1 to 6 have a densification rate of 90% or more, a relative dielectric constant of 22 to 25, an unloaded Q value of 6000 to 53000, and a temperature coefficient of 4. .0 to
It was 12.0. Particularly, TiO ₂ is 0.3 to 2.0 mo
Examples 1 to 4 added with 1% show a high densification rate of 98% or more, a large unloaded Q value of 25000 or more, and a small temperature coefficient of 6.0 or less, and may have more excellent characteristics as a dielectric. all right. On the other hand, the sintered body of Comparative Example 1 had a densification rate of 80%, which was hardly densified, and therefore the measurement of the dielectric properties was impossible. From the above, it can be seen that the sintered bodies of the examples have achieved densification and also have more excellent dielectric properties as compared with the comparative examples.

[0016]

As described above, according to the invention of claim 1, there is provided a dielectric ceramic having excellent characteristics (a temperature coefficient close to zero and a sufficiently low dielectric loss) and capable of being densified. can do. In the inventions of claims 2 and 4, by adding titanium oxide as a sub-component to BMT, it is possible to prevent the original excellent characteristics (temperature coefficient close to zero and sufficiently low dielectric loss) from being impaired. It is possible to provide a dielectric ceramic capable of improving sinterability and densification, and a method for producing the same. In the inventions of claims 3 and 5, the mixing ratio of titanium oxide is B
Since it is 0.3 to 2.0 mol% with respect to MT, it is possible to improve sinter resistance and to densify without impairing the original excellent characteristics (temperature coefficient close to zero and sufficiently low dielectric loss). The effect of being able to do is more remarkable.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a measuring circuit for measuring the dielectric properties of a sintered body.

[Explanation of symbols]

 1 Network Analyzer 2 Sweep Oscillator 3 Directional Coupler 4 Controller 5 Short-Circuit Dielectric Resonator 6 Coaxial Reference Line

Claims (5)

[Claims] 1. Barium, magnesium, tantalum, titanium, oxygen, wBaO, xMgO, yTa ₂ O
₅ , w, x, y and z when expressed by zTiO ₂ are 0.95 ≦ w ≦ 1.05, 0.30 ≦ x ≦ 0.35, 0.30 ≦ y ≦ 0.35, 0. A dielectric ceramic having a range of 005 ≦ z ≦ 0.04. 2. A general formula: Dielectric ceramics characterized in that titanium oxide is added as an auxiliary component to the basic composition represented by. 3. The dielectric ceramics according to claim 2, wherein the mixing ratio of the subcomponent is 0.3 to 2.0 mol% with respect to the basic composition. 4. A general formula: A method for producing a dielectric ceramics, characterized in that titanium oxide is added to the basic composition represented by, mixed, and then fired. 5. The method for producing a dielectric ceramics according to claim 4, wherein the mixing ratio of the titanium oxide is 0.3 to 2.0 mol% with respect to the basic composition.