JPH02129065A - Dielectric ceramic composition and its production - Google Patents

Abstract

PURPOSE:To reduce the dispersion of the permittivity and temperature coefficient and enable fine control of them by containing MgO, CaO and TiO2 as essential components and having a crystalline structure composed of the perovskite phase and the ilmenite phase. CONSTITUTION:The subject dielectric magnetic composition contains MgO, CaO and TiO2 and is composed of 2 phases: the ilmenite phase of MgTiO3 and the perovskite phase of CaTiO3. The composition is produced by calcinating individual raw materials separately for individual phases to effect uniform reaction, formulating them in a prescribed proportion, crushing, granulating, forming and calcinating. In addition to the above-stated 3 components, ZnO, Nd2O, La2O3 and PbO are added, to form complex perovskite phase consisting of CaO, TiO2, PbO, Nd2O3 and La2O3 and ilmenite phase of MgO, TiO2 and ZnO whereby another dielectric magnetic composition is obtained from the seven components in a similar way.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to dielectric materials used in microwave circuit elements, microwave circuit boards, etc. The present invention relates to a dielectric ceramic composition with low dielectric loss and low temperature coefficient of dielectric constant.

(Prior Art) In recent years, with advances in microwave circuit technology, circuits have been made smaller.

Conventionally, this microwave frequency band (300MHz to 3
Cavity resonators, antennas, and the like have been used in circuits of 0 GHz), but these are not suitable for miniaturizing circuits because their size is about the same as the wavelength of microwaves. In contrast, in recent years, microwave filters using dielectric resonators used in the microwave frequency band, small dielectric resonators for stabilizing the frequency of oscillators, and microwave ICs have been developed.
Dielectric porcelain is used in microwave circuits, such as dielectric porcelain used in capacitors and substrates, to reduce the size of the circuit. The characteristics required of these ceramics are that they have low dielectric loss in the microwave frequency band, a high dielectric constant suitable for the frequency band used, and a small temperature coefficient of dielectric constant.

Ti has traditionally been used as a porcelain material that satisfies these characteristics.
e, type is often used, especially Ba0-Ti
In order to adjust the temperature coefficient of dielectric constant, Tie, which has a negative temperature coefficient, and dielectric porcelain and glass, which have a positive temperature coefficient, are available. Many combinations have been devised and applied.

(Problems to be Solved by the Invention) In conventional dielectric materials, another phase with a crystal structure other than the main phase is a factor that increases dielectric loss.

There was a tendency to structure the structure so as to not include it as much as possible.

For this reason, the temperature coefficient (τf) of conventional dielectric materials is almost determined by the unique temperature coefficient of its main phase, making it difficult to obtain a free temperature coefficient.

Additionally, in the manufacturing process, all raw materials are processed at the same time from mixing to firing, resulting in crystal structures that do not dissolve into each other, resulting in variations in properties due to subtle process factors. .

In view of the above, an object of the present invention is to provide a dielectric ceramic composition with less variation in properties and a method for manufacturing the same.

(Means for Solving the Problems) As a result of studying various composition systems, the inventors found that a dielectric ceramic composition containing at least MgO, CaO, and TiO2 has a crystal structure consisting of a perovskite phase and an ilmenite phase. A dielectric ceramic composition consisting of two phases is dielectric 1! rate,
The composition must have little variation in temperature coefficients and its absolute value can be finely controlled, and M g O, C
a 0 , 71' i 0, , ZnO, Nd, 03. L
a20. , a dielectric ceramic composition consisting of a seven-component system of PbO, the dielectric ceramic composition having a two-phase crystal structure of a perovskite phase and an ilmenite phase, which has small variations in dielectric constant and temperature coefficient, and It is a composition that allows fine control of the absolute value of

It has been found that a manufacturing method that involves blending, pulverizing, granulating, molding, and firing in a predetermined ratio is a manufacturing method that has little variation in dielectric constant and temperature coefficient, and allows fine control of their absolute values.

(Function) In a composition system containing MgO, CaO, and TiO2, due to the difference in ionic radius, the ilmenite phase of MgTiO3 and the C
It is a well-known fact that the perovskite phase of a T i O3 is a mixed crystal phase. However.

In actual compositions, each crystalline phase does not form a solid solution with each other and is not separated from each other, but may vary depending on the powder characteristics of the raw materials and the mixing, calcination, pulverization, and firing conditions during the manufacturing process. Insoluble elements, such as Ca ions, are present in the crystal lattice of MgTi-O, and Mg ions are present in the crystal lattice of MgTi-O.

It enters the crystal lattice of CaT i O, and becomes a lattice defect. This lattice defect affects material properties, especially dielectric loss (1
/janδ6) is one of the causes of variation.

Therefore, in the present invention, we actively create a mixed crystal phase, eliminate lattice defects as much as possible, reduce the variation in dielectric loss, and further improve Ca
Since the Ti○3 system has a positive temperature coefficient and the MgTie system has a negative temperature coefficient, by appropriately selecting the mixing ratio of both, a dielectric ceramic composition having a desired temperature coefficient can be constructed.

Also, MgO, CaO, TiO2, ZnO, Nd2O3
, La, O, , PbO, in the seven-component system, Ca OHT
l 02. P b Og N d203+ L a20
．． forms a composite perovskite phase, and MgO,I' i
0, ZnO forms an ilmenite phase, and the same thing as above can be said.

In addition, unnecessary lattice defects can be easily reduced by calcining the raw materials for each phase separately, allowing them to react uniformly, and then blending and pulverizing them.

It is possible to reduce the dielectric loss by 1W.

(Example) The present invention will be explained below according to examples.

The starting materials for preparing the samples are MgO, CaC0, Tie, Nd, with a high purity of 95 to 99.9% or more.
O,, ZnO.

Shia203+ pbo powder was used. Of course, the raw materials are not limited to oxides, and may also be nitrates, carbonates, organic acid salts, etc. that become oxides during firing. The above-mentioned starting materials were weighed so as to have each predetermined composition, and put into a ball mill together with pure water for wet mixing.

After drying this mixture in a hot air dryer, an air width of about 10
The powder was calcined at 00°C for 4 hours, and the resulting calcined powder was again put into a ball mill together with pure water at a predetermined ratio for wet pulverization. This pulverized material was dried, an aqueous binder solution was added and kneaded, and the particles were sized using a sieve, then molded at a pressure of 1 ton/ci+2, and fired in air at 1200 DEG C. to 1450 DEG C. for 2 hours. Then the diameter is 10mm.

It is processed into a cylinder with a height of 5 m @ to configure a cylindrical dielectric resonator, and from the resonance frequency (about 6 GHz), the dielectric constant (εr),
Dielectric loss (janδE) was determined.

Also, from the change in resonance frequency between -20℃ and +60℃,
The temperature coefficient (τf[ρpm/'C)) was determined.

Table 1 shows the characteristic results of the samples obtained by the present invention. In this table, the samples marked with an umbrella mark are samples obtained by the conventional manufacturing process. In addition, Fig. 1 shows a free firing surface of a sample obtained by the present invention, and Fig. 2 shows an SEM observation photograph of its lapping surface. In Fig. 2, what appears black is the ilmenite phase, and the white What you can see is the perovskite phase.

Samples 1'-1 to 1-5 and samples 6-1 to 6- of this Table 1
Sample 1-5, which is an example of the present invention, is compared with Sample 1-5.
It can be seen that samples 1 to 1-5 have less variation in dielectric constant, dielectric loss, and temperature coefficient.

(Effects of the Invention) As described above, the present invention provides a dielectric ceramic composition with little variation in properties (permittivity 1, dielectric loss, temperature coefficient, etc.) and whose absolute values can be precisely controlled, and a method for producing the same. This is what I was able to obtain.

[Brief explanation of drawings]

Figure 1 is an SEM of the free firing surface of the sample obtained by the present invention.
This is an observation photograph, and Figure 2 is an SEM of the wrapping surface.
This is an observation photo.

Claims (3)

[Claims] 1. A dielectric ceramic composition containing at least MgO, CaO, and TiO_2, characterized in that its crystal structure consists of two phases: a perovskite phase and an ilmenite phase. 2. MgO, CaO, TiO_2, ZnO, Nd_2O
A dielectric ceramic composition comprising a seven-component system of _3, La_2O_3, and PbO, the dielectric ceramic composition having a crystal structure consisting of two phases: a perovskite phase and an ilmenite phase. 3. In claim 1 or 2, during manufacturing, components constituting phases with different crystal structures are separately weighed, mixed, and calcined, and then blended in a predetermined ratio, pulverized, granulated, molded, A method for producing a dielectric ceramic composition, characterized in that it is fired.