JPH0542762B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of 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. [Prior Art] Generally, dielectric ceramics used as materials for resonators used in signal circuits in high frequency ranges such as microwaves and millimeter waves have a large relative dielectric constant and a small temperature coefficient of the resonant frequency. At the same time, it is desirable to have a high no-load Q. By the way, in recent years, the frequencies used for communication have been rapidly increasing, 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 is around 3,000 to 7,000, and only in recent years have more than 10,000 products been manufactured. It is expected that this trend will further advance, and there is a need for extremely low loss resonator materials with even higher no-load Q.
Currently, low-loss dielectric porcelain with such a very high no-load Q is 30,000 (9 GHz) for Al ₂ O ₃ ,
22000 (5GHz) is known for MgTiO ₃ . [Problems to be solved by the invention] However, these materials with high unloaded Q have low dielectric constants of 9.8 and 17, respectively, and temperature coefficients of resonant frequencies of −55 ppm/
℃ and -45 ppm/℃, which is a drawback that makes 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 is in. [Means for Solving the Problems] The present invention provides such dielectric ceramics having the general composition formula: xBaO・yMgO・zTa ₂ O ₅ ... () [However, 0.5≦x≦0.7, 0.15≦y≦0.25 , 0.15≦
z≦0.25, x+y+z=1], the sintered density is 90% or more of the theoretical density, and the degree of order as a composite perovskite structure is 0.8 or more. In the general formula () representing the above composition,
If any one of x, y, and z is not within the above range, the resulting porcelain will not be dense, have low mechanical strength, and will have a low dielectric constant and low unloaded Q. x, y and z are preferably 0.56≦x≦0.64, 0.18≦y≦0.22 and 0.18≦, respectively
The range is z≦0.22. In this specification, the regularity of a composite perovskite structure has the following meaning. Mating perovskite oxide (A(B ¹ _1/3
B ² _2/3 ) O ₃ ) is a hexagonal crystal, the B site ion, that is, B ¹ and B ² in the above formula are B ¹
It is known to take a periodic arrangement (long period arrangement) in which three layers are repeated over a wide range in the order -B ² -B ² as one period. In this specification, the degree of regularity refers to the degree to which the manufactured porcelain has such long-period arrangement regularity as a composite perovskite, and is defined by the following formula S. Here, ₁₀₀ is 1 of the superlattice based on the long-period array.
The intensity of the X-ray diffraction line of the 00 plane, I ₁₁₀ , ₁₀₂ , is 110
This is the intensity of the strongest peak of the plane and 102 plane diffraction lines. 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 (I ₁₀₀ /I ₁₁₀ , ₁₀₂ ) calc. =0.083. When a complex perovskite-type regular long-period array structure exists in manufactured porcelain, a superlattice X-ray diffraction line (I ₁₀₀ ) based on this is observed, and if the regulation is perfect, S = 1. On the other hand, if it is completely disordered, S=0. 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.
If this degree of regularity is less than 0.8, no-load Q will not improve even if the device is dense. 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. Further, the dielectric ceramic of the present invention has a sintered density of 90% or more of the theoretical density, 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 low, making it difficult to put it into practical use. The dielectric ceramic of the present invention can be produced by, for example, heating a press-molded product having the required composition represented by the above general formula () to a temperature of 1500°C or higher at a heating rate of 100 to 1600°C/min. This can be carried out by holding at a temperature of 1500°C or higher for 1 minute or more, and then holding at a temperature of 1200°C or higher for 3 hours or more. The press-molded product used in this manufacturing method is prepared by adding, for example, barium carbonate, magnesium oxide, and ditantalum pentoxide in proportions such that BaO-MgO-Ta ₂ O ₅ porcelain of the required composition is obtained according to a standard method. It is a product that is blended, completely converted to oxide through calcination, and then pressure molded. Although there are no particular limitations on the pressure molding method, a method using isostatic pressure is preferred. In addition, the pressure for pressure molding is not particularly limited, but
1000Kg/cm ² or more is preferable. The temperature increase rate in the temperature increase process is 100° to 1600°
C/min, preferably 200 to 1600 C/min. If the heating rate is less than 100℃/min,
Due to insufficient sintering, the resulting porcelain has a low no-load Q, a low dielectric constant, and a low mechanical strength, making it difficult to put it into practical use. Also, if the temperature exceeds 1600℃/min, the porcelain will crack. This rapid temperature increase can be carried out by various methods. For example, a platinum support (e.g. cage) with thermal shock resistance is placed inside the heated furnace core tube of a vertical furnace.
A method of suspending and lowering the press-formed product from above using a furnace, a method of pushing it into the furnace core tube from below by placing it on a platinum support, and a method of rapidly heating it with an image furnace using infrared rays, xenon lamps, or sunlight. This can be mentioned in terms of methods, etc. Among these, the method mentioned first, in which it is suspended into a heated furnace core tube, is simple and suitable. Further, the temperature of the first heat treatment in this method must be 1500°C or higher, preferably between 1550 and 1650°C. If this temperature is less than 1500°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. Note that the firing temperature is
If the temperature exceeds 1700°C, if the porcelain holding container is a platinum container often used in the firing process due to its high temperature stability, the porcelain will react with the container and the properties of the resulting porcelain will deteriorate. Sometimes. This first
For the heat treatment in the third stage, it is necessary to hold the molded product for 1 minute or more, and more specifically, for example,
It is appropriate to hold the temperature at 1500°C for at least 4 hours, at 1650°C for at least 3 minutes, and at 1700°C for at least 1 minute. If the heat treatment time at this stage is too short, sintering will be insufficient and the dielectric properties and mechanical strength of the porcelain will be 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 1300 to 1650°C for 3 hours or more. If the temperature is less than 1200°C, the degree of regularity will be insufficient and it will be difficult to obtain dielectric porcelain 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, the heating time is, for example, when the temperature is 1200℃
Appropriately, the heating time is 200 hours or more, 12 hours or more at 1500°C, and 3 hours or more at 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 can be used as long as it does not react with the press-molded product having the above composition at the firing temperature. Examples of such non-reactive refractory powder include alumina, zirconia, magnesia, hafnia,
Ceramic powders such as Ittria can be mentioned. The particle size of these refractory powders is not particularly limited, but those having an average particle size of approximately 10 μm to 1 mm are preferably used. [Example] Next, the present invention will be specifically explained with reference to 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, the general formula ()
The samples were weighed so that x, y, and z were the values shown in Table 1, and placed in a polyethylene pot along with the pure sample, and wet mixed for 16 hours using a pole whose surface was coated with resin. After taking out this mixture from the pot and drying it at 150℃ for 5 hours,
The mixture was pressure-molded into a lump at a pressure of 700 kg/cm ² , and calcined on a platinum plate in air at 900 to 1300° C. for 2 hours in order to convert the carbonate in the mixture into an oxide. After calcining, the mass 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/
After ^primary molding into a disc shape with a diameter of 10 mm and a thickness of about 5 mm, the material was compressed under isostatic pressure of 2000 kg/cm ² to obtain a molded product. This molded product was wrapped in obtained magnesia powder in a platinum boat and subjected to firing. The first stage of heat treatment is the temperature increase rate in air.
The material was heated to a firing temperature within a range of 100°C to 1600°C/min, and the firing temperature was set within a range of 1500°C to 1700°C, and the holding time at this temperature was within a range of 3 minutes to 12 hours. Next, the second stage heat treatment is performed at 1200 to 1650
The experiments were carried out in an oxygen, air, nitrogen, or argon atmosphere at a temperature of .degree. The relative dielectric constant (Er) and unloaded Q (Qu) of the obtained ceramic were measured at a frequency around 11 GHz using the dielectric cylindrical resonator method. In addition, the superlattice diffraction line intensity of the perovskite structure oxide was measured by using a crushed porcelain sample, using a copper target, and determining the integrated intensity by step scan at 30 kV and 15 mA. As shown in Table 1, when the degree of regularity S exceeds 0.8, the no-load Q becomes 18,000 or more, reaching a maximum of 30,600 at 11 GHz and 36,000 at 9 GHz. This is an unprecedented value. Regularity S
If does not exceed 0.8, the unloaded Q will not reach such a high value. Comparative Example Experiments No. 16, 17, and 18 are cases in which dielectric properties are poor due to insufficient sintering and a low relative density of 90% or less, and Comparative Example Experiments No. 19 to 24 are cases in which the relative density is low due to insufficient sintering. Although the porcelain has a fineness of over 95%, the degree of regularity is still low.
This is a case where the no-load Q is not high because it is less than 0.8. Experiment Nos. 1 to 15 of the example have a regularity of 0.8 or more, which indicates that the no-load Q is extremely high. In addition, since these are sufficiently dense porcelains, their mechanical strength is sufficiently high, and the temperature coefficient of the resonant frequency is as small as 4 ppm/℃ as shown in Table 2, so they are stable against temperature changes and do not resonate. It can be seen that it has good properties as a container material and is extremely practical. When the porcelain obtained in Experiment No. 6 of the Examples was crushed and subjected to X-ray diffraction, the diffraction pattern shown in FIG. 1a was obtained. Superlattice diffraction lines (*) due to long-period alignment were observed (in the figure, indexing is done using hexagonal crystals). On the other hand, Example Experiment No. 6
When the 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, the diffraction pattern shown in Figure 1b was obtained. Obtained with. This diffraction diagram shows a cubic crystal, with almost no superlattice diffraction lines seen.

【table】

〔Effect of the invention〕

The dielectric ceramic of the present invention has a high no-load Q, a large dielectric constant, and a low loss with a small temperature coefficient of resonance frequency, and has the characteristics required for high frequency use. In particular, it has a very high no-load Q of over 18,000, and it is possible to manufacture products with Q over 35,000, making it an excellent dielectric porcelain that can fully support future high-frequency communications.

[Brief explanation of the drawing]

1A is an X-ray diffraction diagram of a dielectric ceramic according to an example of the present invention, and FIG. 1B is an X-ray diffraction diagram of a comparative example.

Claims (1)

[Claims] 1 Composition is general formula: xBaO・yMgO・zTa ₂ O ₅ [However, 0.5≦x≦0.7, 0.15≦y≦0.25, 0.15≦z≦
0.25, x+y+z=1], the sintered density is 90% or more of the theoretical density, and the degree of order as a composite perovskite structure is 0.8 or more. 2 General formula: xBaO・yMgO・zTa ₂ O ₅ [However,
0.5≦x≦0.7, 0.15≦y≦0.25, 0.15≦z≦0.25
x + y + z = 1] is heated to a temperature of 1500℃ or higher for 100 to 1600℃.
Heating at a temperature increase rate of 1500°C or more for 1 minute or more, then heating at a temperature of 1200°C or more for 3 minutes.
A method of manufacturing dielectric porcelain that consists of holding it for more than an hour.