JPS62170102A - Dielectric ceramic and making thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to dielectric ceramics, and particularly to dielectric ceramics that have a high no-load Q and are suitable for low-loss high-frequency applications.

[Conventional technology]

In general, dielectric ceramics used as materials for resonators used in signal circuits in high frequency ranges such as microwaves and millimeter waves have a high relative permittivity, a small temperature coefficient at the resonant frequency, and a high no-load resistance. It is desirable to have Q. By the way, in recent years, the frequency used for communication has rapidly increased, and satellite broadcasting using the SHF band is entering the stage of practical use, so there is a strong demand for the development of low-loss dielectric ceramics with even higher no-load Q. It has been demanded.

Conventionally, the unloaded Q of the materials used as low-loss dielectric porcelain for high frequency applications was around 3,000 to 7,000, but only in recent years have more than 10,000 been manufactured. However, it is expected that communication frequencies will further advance in the future, and resonator materials with an even higher no-load Q and extremely low loss are required.

Currently, as a low-loss dielectric porcelain with such a very high no-load Q, AQ203 has a price of 30,000 (9 GH).
z), 22,000 (5 GHz) for MgTiO3 is known.

[Problem that the invention seeks to solve]

However, these materials with high unloaded Q have low dielectric constants of 9.8 and 17, respectively, and
Temperature coefficient of resonance frequency is 155 ppm/”C and -
It has a disadvantage of being as low as 45 ρpm/'C, making it difficult to put it into practical use.

Therefore, an object of the present invention is to provide a low-loss dielectric ceramic suitable for high frequency use, which has a very high no-load Q of 18,000 or more, a large relative dielectric constant, and a good temperature coefficient of resonance frequency. It's about doing.

[Means for solving problems]

The present invention provides such dielectric ceramic having a composition of the general formula:
xBaO・yMgO・zTa205 − (
1) [However, 0.5≦x≦0.7.0.15≦y≦0
．． 25.0.15≦z≦0.25, and x+y+z=1]
The object of the present invention is to provide a dielectric ceramic having a sintered density of 90% or more of the theoretical density and a regularity of 0.8 or more as a composite perovskite structure.

In the general formula (I) representing the above composition, X, y, z
If any one of these is not within the above range, the resulting porcelain will not be dense, have low mechanical strength, and have low dielectric constant and low unloaded Q. x, y and Z are
Preferably, each 0.56≦x≦0.64.0.1
The range is 8≦y≦0.22 and 0.18≦z≦0.22.

In this specification, the regularity of a composite perovskite structure has the following meaning. It is known that the complex perovskite type oxide site ions, ie, B1 and B2 in the above formula, take a periodic arrangement (long period arrangement) in which three layers are repeated in the order BI B2 B2 over a wide range as one period. In this specification, the degree of regularity means that the manufactured porcelain has a composite perovsky 1
It represents the degree of regularity of such a long-period arrangement as ~, and is defined by the following formula S.

Here, Lea is (100) of a superlattice based on a long-period array.
The intensity of the X-ray diffraction line of the plane, 111°, 1°2, is (110
) plane and the intensity of the strongest peak of the (102) plane fold line. Also, the numerator is the actual observed value, and the denominator is the intensity calculated using the hexagonal atomic coordinates assuming that the B site ion is completely ordered (Engineering, .o/■, □).

toz)calc, = 0.083.

When a complex perovskite-type regular long-period array structure exists in manufactured porcelain, superlattice X-ray diffraction lines (I,...) based on this are observed, and if the regularity is perfect, S = 1, and conversely, if it is completely disordered, S = O.

In the dielectric ceramic of the present invention, the regularity of the composite perovskite structure is required to be 0.8 or more, preferably 0.9 or more. This regularity is 0
．． If it is less than 8, the no-load Q will not improve even if it is made of dense porcelain.

Although the porcelain of the present invention is substantially entirely composed of perovskite-type phases, trace amounts of other phases may be produced. However, there is no problem with the characteristics of porcelain.

Furthermore, the dielectric ceramic of the present invention has a sintered density of 90% of the theoretical density.
% or more, preferably 95% or more.

If the sintered density is less than 90% of the theoretical density, no improvement in the no-load Q can be expected, and the dielectric constant and mechanical strength are also low, making it difficult to put into practical use.

The production of the dielectric ceramic of the present invention can be carried out, for example, by the general formula (I
) A press-molded product having the required composition represented by 150
Heating at a temperature rate of 100 to 150℃ to a temperature of 0℃ or higher,
Hold at a temperature of 0℃ or higher for 1 minute or more, then 1200℃
This can be done by maintaining the above temperature for 3 hours or more.

The press-molded product used in this manufacturing method is prepared by mixing, for example, barium carbonate, magnesium oxide, and ditantalum pentoxide in proportions such that IlaO-MgO-Ta205 porcelain of the required composition is obtained according to a conventional method. It is made by pressing and molding the oxide that has been converted into an oxide by sintering.

There are no particular limitations on the pressure molding method, but a method using one isostatic pressure is preferred. Moreover, the pressure for pressure molding is not particularly limited, but is preferably 1,000 kg/cJ or more.

The temperature increase rate in the temperature increase process is 100° to 1.60°.
0°C/min, preferably 200-1.600807 min. If the heating rate is less than 100°C/min, sintering will be insufficient and the unloaded Q of the porcelain will decrease.
It has a low dielectric constant, a low dielectric constant, and a low mechanical strength, making it suitable for practical use. In addition, the rapid temperature increase can be carried out by various methods, since if the temperature exceeds 1,600° C./min, the porcelain will crack.

For example, a method in which a press-formed product is suspended from above into a heated furnace core tube of a vertical furnace using a platinum support (e.g., a cage) having thermal shock resistance.

Similarly, examples include a method of pushing the material into the furnace core tube from below by placing it on a support made of platinum, and a method of rapidly heating with an image furnace using infrared rays, a xenon lamp, or sunlight.

Among these, the first method of suspending and lowering into the heated furnace core tube is a simple and preferable method.

In addition, the first stage heat treatment temperature in this method is 1
, 500°C or higher, preferably 1,550-1, 6
Must be between 50°C. This temperature is 1,5
If the temperature is less than 00°C, sintering will be insufficient, so the mechanical strength of the resulting porcelain will be low and the no-load Q will also be low. If the firing temperature exceeds 1,700°C, if the porcelain holding container is a platinum container, which is often used in the firing process because of its high temperature stability, the porcelain will react with the container and the resulting product will be damaged. The properties of the porcelain may deteriorate.

In this first stage heat treatment, it is necessary to hold the molded product for at least 1 minute, and more specifically, for example, at a temperature of 1500°C, for at least 4 hours, at 1650°C, for at least 3 minutes, at 1700°C. It is appropriate to hold the temperature at ℃ for 1 minute or more. If the heat treatment time at this stage is too short,
Sintering becomes insufficient and the dielectric properties and mechanical strength of the porcelain are poor. This heat treatment is performed in an inert atmosphere such as nitrogen or argon, or an oxidizing atmosphere such as oxygen or air.

Next, the second stage heat treatment needs to be carried out at a temperature of 1200°C or higher, preferably 1]00 to 1650°C for 3 hours or more. When the temperature is less than 1200°C,
The degree of regularity is insufficient, making it difficult to obtain dielectric ceramics with a high no-load Q.

Note that when the temperature exceeds 1700° C., the above-mentioned problem occurs when the holding container is made of platinum. More specifically, it is appropriate that the heating time is, for example, 200 hours or more when the temperature is 1200°C, 12 hours or more when the temperature is 1500°C, and 3 hours or more when the temperature is 1650°C. If this heating time is too short, the regularity will be insufficient and it will be difficult to obtain a dielectric ceramic with a high no-load Q. This second stage heat treatment is performed in an atmosphere of oxygen, air, argon, nitrogen, etc., and oxygen is particularly preferred.

In addition, when carrying out the above manufacturing method, it is preferable to wrap the press-molded object, which is the object to be treated, in refractory powder throughout the entire process, and the degree of firing of each part of the individual porcelain obtained thereby also depends on the A highly uniform degree of firing can be obtained between each product, and variations in dielectric properties, etc., can be reduced, and the yield of products can also be improved. As the refractory powder that can be used, any powder that does not react with the press-molded product having the above composition at the firing temperature can be used. Examples of such non-reactive refractory powders include ceramic powders such as alumina, zirconia, magnesia, hafnia, and ittria. The particle size of these refractory powders is not particularly limited, but is preferably about 10 μm to
Those having an average particle size of about 1 mm are used.

〔Example〕

Next, the present invention will be specifically explained using examples.

Powders of barium carbonate, magnesium oxide, and ditantalum pentoxide, each having a purity of 99.9% by weight, were used as raw materials, and these three substances were first mixed at a predetermined ratio. That is, x, y and 2 in general formula (I)
The samples were weighed so as to have the values shown in Table 1, and mixed together with pure water in a polyethylene pot for 16 hours using a pole whose surface was coated with resin. This mixture was removed from the pot and dried at 150°C for 5 hours.

It was pressed into a lump at a pressure of 700 kg/cnf, and calcined on a platinum plate in air at 900-1]00°C for 2 hours in order to convert the carbonate in the mixture into an oxide. After calcining, the lump was crushed in an alumina mortar and passed through a 42-mesh sieve to make the particle size uniform. The obtained powder was heated to a pressure of 500 kg/cA.
The material was first formed into a disk shape with a diameter of 10 mm and a thickness of approximately 5 mm, and then compressed with isostatic pressure of 2000 kg/cJ to obtain a molded product.

This molded product was wrapped in magnesia powder in a platinum boat and subjected to firing.

The first stage heat treatment is performed at a heating rate of 100℃ in air.
It was heated to the firing temperature within the range of 1600° C./min, the firing temperature was set within the range of 1500 to 1700° C., and the holding time at this temperature was within the range of 3 minutes to 12 hours. Next, a second heat treatment was performed at a temperature of 1200 to 1650° C. in an oxygen, air, nitrogen, or argon atmosphere. The relative dielectric constant (Er) and unloaded Q (Q
u) was measured at a frequency around llG11z by the dielectric cylindrical resonator method.

Further, the superlattice diffraction line intensity of the perovskite structure oxide was measured by using a pulverized ceramic sample, using a copper target, and determining the integrated intensity by step scanning at 30 kV - 15 mA.

As shown in Table 1, when the degree of regularity S exceeds 0.8, the unloaded Q becomes 18,000 or more, reaching a maximum of 30, 600 and 36,000 at 9 GIIz. This is an unprecedented value. If the rule JfS does not exceed 0.8, the no-load Q will not reach such a high value. Comparative Example Experiment Nα16.
17 and 18 are cases in which the dielectric properties are poor due to insufficient sintering and a low relative density of 90% or less, and experiments N (119 to 24 are cases in which the relative density is dense and has a relative density of about 95% or more), which is a comparative example. Even though it is made of porcelain, the regularity is 0.
This is a case where the no-load Q is not high because it is less than 8.

In experiments Nα1 to Nα15 of the example, the degree of regularity is 0.8 or more, which indicates that the no-load Q becomes very high. Also, these are enough! ! & Since it is a dense porcelain, its mechanical strength is sufficiently high, and the temperature coefficient of the resonance frequency is as small as 4 ppm/'C as shown in Table 2, so it is stable against temperature changes and is good as a resonator material. It can be seen that it has excellent characteristics and is extremely practical.

In addition, when the porcelain obtained in Experiment Na 6 of Examples was crushed and subjected to X-ray diffraction, the diffraction pattern shown in FIG. 1 (,) was obtained. Superlattice diffraction lines (umbrellas) due to long-period alignment were observed (in the figure, indexing is done using hexagonal crystals). On the other hand, in experiment Nα6 of the example, porcelain obtained by the same treatment except that the second heat treatment (1450°C x 100 hours) was not performed was crushed and subjected to X-ray diffraction as a sample. A diffraction pattern shown in FIG. 1(b) was obtained.

This diffraction diagram shows a cubic crystal, with almost no superlattice diffraction lines seen.

Table 2 [Effects of the Invention] The dielectric ceramic of the present invention has a large no-load Q and a large relative dielectric constant.
It also has a low loss with a small temperature coefficient of resonance frequency, and has the characteristics required for high frequency applications.

In particular, the no-load Q is extremely large, over 18,000, and 3
It is possible to manufacture more than 5,000 pieces of dielectric porcelain, and it is an excellent dielectric porcelain that can fully cope with the higher frequencies of communication in the future.

[Brief explanation of drawings]

FIG. 1(a) shows the X of dielectric ceramic which is an embodiment of the present invention.
FIG. 1(b) is an X-ray diffraction diagram of a comparative example.

Claims (1)

[Claims] 1) The composition has the general formula: xBaO・yMgO・zTa_2O
_5 [However, 0.5≦x≦0.7, 0.15≦y≦0
．． 25, 0.15≦z≦0.25, x+y+z=1]
A dielectric porcelain represented by , having a sintered density of 90% or more of the theoretical density and a degree of order as a composite perovskite structure of 0.8 or more. 2) General formula: xBaO・yMgO・zTa_2O_5 [
However, 0.5≦x≦0.7, 0.15≦y≦0.25
.
Hold at a temperature of 500°C or higher for 1 minute or more, then 120°C
A method for manufacturing dielectric porcelain, which comprises maintaining the temperature at 0°C or higher for 3 hours or more.