JPH0458412B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to dielectric ceramic materials that are dense and have few defects, such as dielectric resonators and duplexers for microwave communication equipment, substrates for microstrip circuits, etc. The present invention relates to a method for manufacturing body materials. [Prior Art] For example, by using only several metal alkoxides and fine powder obtained by hydrolysis of these metal alkoxides as raw materials, dense dielectric ceramics can be obtained, and these BaTiO ₃ and SrTiO ₃ The synthesis of is known in Japanese Patent Publication No. 59-39724, Japanese Patent Publication No. 59-39725, and various other documents. And the composition formula,
The porcelain material represented by SrZr _1-x Ti _x O ₃ (0≦x≦1) has been widely known as a dielectric material used in capacitors, etc., and has a particularly high dielectric constant and is sensitive to temperature changes in the dielectric constant. If the above formula is small, 0≦x≦0.1
A range of porcelain materials are known as dielectrics for microwave communications. For example, Journal of the American Ceramics Society, Volume 7, 56
pp. 352-354, “High-permittivity”
Temperature−Stable Ceramic Dielectrics
withLow Microwave Loss”
According to Kell, General Electric Company Central Research Laboratory), the composition where the temperature coefficient of dielectric constant is 0 is:
0.043 for average from −50 to +100℃ at 1.6KHz
<x<0.048, and 0.060<x<0.063 for the average from 0 to 60° C. at 4 GHz.
Further, the dielectric constants of SrZr _0.955 Ti _0.045 O ₃ at 1.6 KHz and 4 GHz are 34.2 and 33.9, respectively. In addition, as a manufacturing method for the above-mentioned Sr-Zr-Ti-O dielectric ceramic material, a dry method is generally used that uses raw material powder obtained by solid-phase reaction, and after the solid-phase reaction, it is ground in a ball mill. The average particle size of the obtained raw material powder was about 0.5 μm. [Problem to be solved by the invention] The compositional formula of SrZr _1-x Ti _x O ₃ (0≦x≦0.15) is expressed as Sr _1- 〓Zr _1-x Ti _x O _3- 〓 By the way,
It has a property that as the value of δ approaches 0 from a positive value, the sinterability deteriorates significantly. Furthermore, the present inventors have discovered that unless the value of δ is sufficiently close to 0, the microwave loss is large. Furthermore, the present inventors have discovered through experiments using a dry method that a porcelain material whose δ is sufficiently close to 0 cannot produce a dense sintered body even when fired at a temperature of 1600°C. Conventionally, sintering aids have been added to improve sinterability, but as the amount of sintering aids added increases, the loss increases, and no benefits are obtained. Furthermore, when looking microscopically at the dielectric porcelain made by the conventional dry process mentioned above, it is found that the composition is non-uniform and the porosity becomes relatively high due to the large particle size, resulting in a decrease in dielectric constant. Characteristics such as microwave loss may vary and these characteristics may not be fully demonstrated. [Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the loss in the microwave high frequency band by firing at 1600°C or lower, and to reduce the variation in composition. The purpose of the present invention is to provide a method for producing a dielectric material that makes it possible to obtain a small, dense sintered body, that is, is easily sinterable and has a uniform composition. That is, the present invention has a compositional formula, SrZr _1-x Ti _x O ₃ (0≦x
≦0.15), metal strontium and titanium tetraalkoxides that react with alcohol to form metal alkoxides, and alcohol-soluble inorganic zirconium compounds are
A step of dissolving and stirring in an alcohol solution maintained at a temperature range of ℃ or above and below the boiling point of the alcohol, a step of hydrolyzing and coprecipitating the alcohol solution in the above temperature range, and a step of dissolving the resulting precipitate into a water-alcohol mixture solution. After separating and drying, 500° ~
This is a method for producing a dielectric material, which includes a step of performing heat treatment within a temperature range of 1000° C. to form a fine powder. In the present invention, an inorganic metal compound is dissolved and mixed in alcohol together with a metal that reacts with alcohol to form a metal alkoxide as described above, and is simultaneously hydrolyzed, which is equivalent to the case where only the metal alkoxide is used. A fine powder material with a uniform particle size is obtained. In addition, since it is a fine powder material, its surface activity increases, resulting in improved sinterability, which was previously thought to be difficult to sinter.
With a composition of SrZr _1-x Ti _x O ₃ (0≦x≦0.15), a dense sintered body can be obtained by specifically firing at 1600° C. or lower. The above range of x has good sinterability,
Moreover, it is limited to 0.15 or less, which provides good microwave characteristics. By the way, SrZr _1-x Ti _x O ₃ (0≦x
≦0.15) It is known that the temperature coefficient of the dielectric constant changes significantly to the negative side as x increases, and the dielectric constant increases.
Therefore, in order to make the dielectric constant relatively large and the temperature coefficient small, it is effective to add an additive having a positive temperature coefficient, such as Y ₂ O ₃ .
However, on the other hand, the addition of Y ₂ O ₃ lowers the sinterability, and when fired at temperatures below 1600°C, it is common that a dense sintered body cannot be obtained and sufficient properties cannot be brought out. In the present invention, the above-mentioned problems can also be solved because of the ease of sintering as described above. Furthermore, uniformity of the precipitate composition due to the fact that the starting materials in the present invention have similar hydrolysis rates is also effective for the above purpose. Next, the present invention is advantageous in terms of cost because it does not use expensive strontium alkoxide, but instead uses relatively inexpensive metal strontium, which easily reacts directly with alcohol to form metal alkoxide. Furthermore, the titanium alkoxide in the present invention is inexpensive and, since it is a liquid, has good solubility in alcohol and the like and is easy to use. Next, when metal alkoxides are expensive and the synthesis of metal alkoxides is complicated such that substitution reactions must be carried out, that is, especially in the case of zirconium and yttrium, it is effective to use their cheap nitrates and halides. [Function] In the present invention, an inorganic metal compound is dissolved and mixed in alcohol together with a metal that reacts with alcohol to form metal alkoxide as described above, and is simultaneously hydrolyzed to form fine particles with uniform particle size. A powder material is obtained, and being a fine powder material increases its surface activity and, as a result, improves its sinterability.Furthermore, the starting materials in the present invention have a similar rate of hydrolysis. It is presumed that these factors increase the uniformity of the precipitate composition, and that these factors work together to solve the above-mentioned problems. [Example] Example 1 and Comparative Example 1 Metal Sr, ZrO (NO ₃ ) ₂・2H ₂ O and Ti
Three types of starting materials (OC ₃ H ₇ ) ₄ were used as shown in the composition shown in Table 1 below, and the amount of Ti substitution was varied from 3 to 14 mol% to give SrZr _1-x Ti _x O ₃ . Each was weighed. Fine powders were synthesized in exactly the same manner for each of the following examples. First, the metals Sr and Ti(OC ₃ H ₇ ) ₄ are dissolved in isopropyl alcohol with a weight more than 20 times their total weight.
The mixture was kept at 75°C and stirred for 2 hours under reflux in an Ar gas atmosphere. Next, add isopropyl alcohol solution in which ZrO(NO ₃ ) ₂ 2H ₂ O was dissolved, and heat again at 75℃ Ar.
Stirring was performed for about 2 hours under reflux in a gas atmosphere. Furthermore, under the same environment, an appropriate amount of dilute ammonia water was added to carry out hydrolysis, and the mixture was stirred for 5 hours to ripen.
It was washed with alcohol, separated into solid and liquid using filtration or a centrifugal separator, and dried. 500~
It was confirmed by X-ray diffraction that the precipitate had a perovskite structure after heat treatment at 1000℃, and the results of electron microscopy showed that it was a fine particle with a particle size of several Å to 1,000 Å. Ta. Next, we examined the synthesis conditions for the fine powder and found that the temperature of the alcohol or alcohol-water mixed solution in the process from dissolving the starting material to hydrolysis must be at least 40°C and below the boiling point of the alcohol. I found out. If the temperature is below 40°C, the dissolution rate of the starting material will be slow and the temperature of the alcohol will not rise above its boiling point, but if more heat is added than necessary, the alcohol will boil violently, which is undesirable. Even during the above hydrolysis, if the temperature is within this range, a precipitate with a uniform composition can be obtained. Further, the weight of isopropyl alcohol in which the starting material is dissolved is preferably about 30 times the weight of the starting material, and if it is reduced to a certain extent, it has been found that the composition during hydrolysis becomes non-uniform. Furthermore, if the heat treatment temperature of the precipitated and dried powder is below 500°C, occluded alcohols will remain and the porosity will increase during subsequent firing, and if it exceeds 1000°C, the particles will Growth in diameter significantly reduces reactivity, which defeats the purpose of forming microparticles by wet methods. Each of the fine powders synthesized as described above is
It was pressed into a cylindrical shape with a diameter of 12 mm and a height of 18 mm at a pressure of 700 Kg/cm ² . The obtained molded body was fired at about 1570° C. for 3 hours in an oxygen atmosphere. The obtained sintered body was ground to 6.0mmψ×40
1MHz and 9G with dimensions of mm and 5.8mmψ×2.3mmH
It was processed into a sample for measuring electrical properties at Hz. 1MHz,
Average temperature coefficient at relative permittivity (0-60℃) and
The Q (reciprocal of microwave loss) at 9 GHz was measured, and the density of the sintered body, which is an important factor regarding electrode attachment, moisture resistance, dielectric constant, etc., was measured, and the results are shown in the same table. For comparison, a dielectric ceramic having the same composition as in Example 1 was prepared using a conventional dry method using SrCO ₃ , TiO ₂ and ZrO ₂ powders as starting materials. At this time, the starting materials were thoroughly mixed and pulverized using a ball mill, and then calcined at 1150° C. for 2 hours and pulverized. The particle size of this powder was found to be 0.5 μm by SEM observation. then 700
It was press-molded into a molded body similar to that in Example 1 by applying a pressure of Kg/cm ² and fired at 1600° C. for 5 hours, and its properties were examined in the same manner. FIG. 1 shows changes in the temperature coefficient of permittivity due to differences in the amount of Ti substitution for porcelains obtained by sintering the powders of Example 1 and Comparative Example 1, respectively.
According to the same figure, it was found that differences in particle size and uniformity of composition of the raw materials do not have much influence on the temperature coefficient. Next, FIG. 2 shows the change in relative dielectric constant due to the difference in the amount of Ti substitution in the porcelains obtained using the raw materials according to Example 1 and Comparative Example 1. Straight line a in the diagram
(the present invention) is superior to the comparative example (straight line b),
Furthermore, when the density of _the composition whose temperature coefficient was ₀ in _FIG .
cm ³ , and Comparative Example 1 had 5.00 g/cm ³ , as can be seen from the fact that Example 1 had
It was found that even when fired at 1570°C, the material was sintered extremely densely, and the dielectric constant was improved. Example 2 and Comparative Example 2 Regarding dielectric ceramics with a non-stoichiometric composition of Sr _1- 〓Zr _0.94 Ti _0.06 O _3- 〓, an example was carried out under the range of 10×10 ^-3 ≦δ≦30×10 ^-3 It was produced using the same starting materials as in No. 1 under exactly the same conditions and method, and processed into a material for measuring properties. Note that δ=0 is the composition of Example 1.
For comparison, an attempt was made to obtain a sintered body with the same composition using the conventional method, but as described in Example 1, sufficient sintering was not achieved and the Q (reciprocal of microwave loss) was significantly reduced due to moisture in the air. It was not suitable for material evaluation due to changes. Therefore, 0.05 mol of Y ₂ O ₃ was added to the composition of Sr _1- 〓Zr _0.94 Ti _0.06 O _3- 〓 to correct the temperature coefficient, and 0.05 mol of Mn ₂ O ₃ was added as a sintering agent to the main component composition. A dielectric ceramic was obtained in the same manner as in Example 1 and processed in the same manner as Comparative Example 2. FIG. 3 shows the change in Q as the value of δ changes. In FIG. 3, curve c is Example 2, curve d
is Comparative Example 2, and in Comparative Example, Q was small overall due to the influence of additives, but as δ became smaller, Q increased, but sinterability tended to deteriorate. When δ<15×10 ^-3 , sintering became difficult and a sufficient sintered body could not be obtained. On the other hand, in Example 2, δ
Even when δ=0, a good crystal with high Q, that is, low microwave loss, can be obtained, especially when δ=10×10 ^-3
In this case, a good sintered body was obtained even after firing at 1550°C for 4 hours. Although not shown here, the relative permittivity and the temperature coefficient of the permittivity did not change significantly depending on the value of δ.

〔Effect of the invention〕

As is clear from the above explanation, the above-mentioned SrZr _1-x
In a wet manufacturing method of a raw material for dielectric porcelain represented by Ti _x O ₃ (0≦x≦0.15), in short, dielectric powder is precipitated by hydrolysis of the metal, metal alkoxide, and inorganic metal compound. For example, the obtained product is heated at 1600℃
By the following firing process, it is possible to provide a dielectric ceramic which is extremely densified and has low microwave loss, and its industrial use effect is very large.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the temperature coefficient of permittivity of dielectric ceramics obtained by the present invention and the conventional method and the mole percent of Ti, and Figure 2 is a graph showing the relationship between the relative permittivity of the same dielectric ceramics and the mole % of Ti. Figure 3 is a graph showing the relationship between mole% and Q (microwave loss) of the same dielectric ceramic and Sr _1- 〓
It is a graph showing the relationship with δ in Zr _0.94 Ti _0.06 O _3- 〓.

Claims (1)

[Claims] 1. In a method for producing dielectric powder for obtaining dielectric ceramic represented by the compositional formula SrZr _1-x Ti _x O ₃ (0≦x≦0.15), metal alkoxide is formed by reacting with alcohol. A process of dissolving and stirring the metal strontium and titanium tetraalkoxides that form strontium and an inorganic zirconium compound soluble in alcohol in an alcohol solution maintained at a temperature range of 40°C or higher and below the boiling point of the alcohol; It is characterized by having a step of hydrolyzing and coprecipitating within a range of 100 to 100°C, and a step of separating the resulting precipitate from the water-alcohol mixture solution, drying it, and then heat-treating it within a temperature range of 500 to 1000°C to pulverize it. A method for manufacturing a dielectric material. 2. The method for producing a dielectric material according to claim 1, wherein the steps of dissolving and stirring and hydrolyzing and co-precipitating in the above item 1 are carried out in an inert gas atmosphere. 3. An inorganic yttrium compound containing an appropriate amount of yttrium as a subcomponent is present in the alcohol solution, or the water after the hydrolysis is
Claim 1, characterized in that an alcohol solution in which the inorganic yttrium compound is dissolved is mixed dropwise into an alcohol mixture solution, and a precipitate of the subcomponent is uniformly dispersed in the precipitate.
A method for producing a dielectric material as described in Section 1. 4. The method for producing a dielectric material according to claim 1, wherein titanium tetrapropoxide or titanium tetrabutoxide is used as the titanium tetraalkoxide. 5. The method for producing a dielectric material according to claim 1, wherein a nitrate or a halide is used as the inorganic zirconium compound. 6. The method for producing a dielectric material according to claim 3, wherein the inorganic yttrium compound added as a subcomponent is used as a nitrate or a halide. 7. The method for producing a dielectric material according to claim 1, wherein the alcohol solution as a solvent is methyl alcohol, ethyl alcohol, iso-propyl alcohol, or n-propyl alcohol. 8. Part of the above main component or subcomponent is replaced with a commonly used raw material powder and added to a solution of other components before hydrolysis, or added to and mixed in a solid-liquid mixed solution after hydrolysis. A method for manufacturing a dielectric material according to claim 1 or 3.