JPH0323500B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to perovskite ceramics having a high dielectric constant and low temperature dependence and electric field dependence, and a method for producing the same, and in particular perovskite ceramics having small crystal grain size and small variations thereof. Concerning porcelain and its manufacturing method.

[Prior Art] Dielectric materials for ceramic capacitors are required to have a high dielectric constant and low dependence on temperature and electric field. However, a high dielectric constant and a reduction in dependence on these are contradictory demands, and it has been difficult to satisfy them at the same time in the past. As a solution to this problem, the present inventors have proposed a mixed sintered porcelain in which two or more types of perovskite ceramic materials exhibiting high dielectric constants and having different Curie temperatures are mixed, and a method for manufacturing the same (Japanese Patent Application Laid-open No. 63565/1983). This porcelain is made by the process shown in FIG. That is, for example, Pb(Fe _2/3
W _1/3 ) _0.1 (Fe _1/2 Nb _1/2 ) _0.9 O ₃ and Pb (Fe _2/3 W _1/3 ) _0.5
(Fe _1/2 Nb _1/2 ) _0.5 O ₃ are weighed independently, mixed, pre-fired, crushed, mixed, and then main fired so that the two types of perovskite do not completely form a solid solution. It is something. The porcelain obtained in this way does not require subcomponents to improve the above-mentioned dependence like conventional porcelain, and has a high dielectric constant of 10,000 or more, while its temperature dependence and electric field dependence are about 1 /
It can be reduced to 2. The dependence can be freely controlled by the combination of porcelain materials to be mixed and their mixing ratio. It has the following characteristics. However, the perovskite-based porcelain materials to be mixed have different grain growth rates during main firing, making it difficult to obtain uniform crystal grains, and those with fast grain growth rates have grain sizes of up to 10 μm, leaving room for improvement. It was hot.

[Problems to be Solved by the Invention] An object of the present invention is to improve the above-mentioned conventional method and provide a perovskite porcelain having a small crystal grain size and small variation in grain size, and a method for manufacturing the same.

[Means for Solving the Problems] Perovskite is a complex oxide represented by the chemical formula ABO ₃ , in which A forms a simple square lattice, B is located at its body-centered position, and O is located at its face-centered position.

In order to achieve the above object, in the present invention, two types of perovskite porcelain materials having different Curie temperatures are mixed and fired without completely forming a solid solution.
It is an oxide of an element that does not occupy the B position of ABO ₃ , has a higher melting point than the perovskite ceramic, and is characterized by the addition of a chemically stable metal oxide.

[Function] The above-mentioned oxides are hardly dissolved as a solid solution in the perovskite ceramic material during firing, and are mostly present at the grain boundaries, suppressing the growth of perovskite grains, and causing almost no change in dielectric properties. I won't give it.

[Example] As an example of the present invention, two types of perovskite ceramic materials are Pb (Fe _2/3 W _1/3 ) _X (Fe _1/2
Nb _1/2 ) _1-X O ₃ (0≦X≦1), when materials with X = 0.1 and materials with X = 0.5 are used, and Dy ₂ O ₃ is used as a metal oxide to suppress grain growth. We will explain the results.

Figure 1 shows the manufacturing process. Raw material powder PbO,
Fe ₂ O ₃ , WO ₃ , Nb ₂ O ₃ with each of the above X being 0.1
and 0.5, and mixed with pure water in a ball mill. After dehydration and drying, they were pre-calcined in air at 1050℃ and 850℃ for 1 hour, respectively.
It was further ground in a ball mill. The X-ray diffraction pattern of the pre-fired composition in the range of 2θ=20 to 90° was measured using CuKα rays, and it was confirmed that it was a predetermined perovskite ceramic material. These two types of perovskite-based porcelain materials are mixed in equimolar amounts,
Dy ₂ O ₃ was added and the pellets were pressure-molded using a polyvinyl alcohol solution binder into pellets with a diameter of about 12 mm and a thickness of about 0.7 mm, and main firing was performed in air at 1000° C. for 1 hour. The fired surface of the fired porcelain was examined under an electron microscope (magnification
The average grain size (Martin
diameter) was measured. Also, Ag on both sides of the fired porcelain
Bake the electrode and measure the dielectric properties with a dielectric constant εr of 1k.
The temperature range was from −40 to 120°C at Hz.

FIG. 2 shows the relationship between the amount of Dy ₂ O ₃ added and the average particle size and particle size deviation of porcelain. The amount of Dy ₂ O ₃ added is shown in mol% relative to the mixture of the material with X=0.1 and the material with X=0.5. Furthermore, the number of crystals measured was 20. From the figure, when the amount of Dy ₂ O ₃ added increases to 0.1 mol%, the crystal grain size decreases to 2.6 μm, which is about half of the 5.0 μm without addition.
Furthermore, the particle size deviation is considerably smaller, 1 to 4 μm, compared to 1.5 to 10 μm in the case without additives. However, when the content exceeds 0.2 mol%, the average particle size and particle size deviation become larger. Accordingly
It can be seen that when Dy ₂ O ₃ is added at 0.1 mol % to 0.2 mol %, the effect of inhibiting grain growth becomes remarkable.

When another metal ion is substituted at the B position of the perovskite ceramic material (ABO ₃ ), the Curie temperature changes and the peak of the dielectric constant seen in the temperature dependence shifts. However, when comparing the temperature dependence of the dielectric constant of perovskite ceramics shown in Figure 3, with no addition of Dy ₂ O ₃ (a in the figure) and with 0.1 mol% of Dy 2 O 3 added (b in the figure), it is found that Dy ₂ O Even when 0.1 mol% of ₃ is added, weak dielectric constant peaks occur at 20°C and 80°C, similar to the case without addition, and no peak shift is observed. Moreover, even if Dy ₂ O ₃ is added, the dielectric constant and its flattening of its temperature dependence are not impaired. Therefore, added
It is thought that Dy ₂ O ₃ is not diffused into the crystal grains of X = 0.1 and .

In this example, the square porcelain materials to be mixed are pre-fired,
After pulverization, a method was explained in which a metal oxide (for example, Dy ₂ O ₃ ) that inhibits grain growth is added at the same time when mixed to a desired molar ratio, and then fired.
As shown in the figure, when weighing the raw material powder, a metal oxide (for example, Dy ₂ O ₃ ) that suppresses grain growth is added at the same time, pre-calcined and pulverized, mixed to the desired molar ratio, and fired. The effect remains the same. Furthermore, in this case, the same effect can be obtained by simply adding a metal oxide that suppresses grain growth to only the perovskite whose grain growth rate is faster during main firing (X=0.5 in this example).

The oxide to be added must not form a solid solution in the perovskite porcelain during firing, and in particular must be an oxide of a metal element that does not replace the atom at the B position (body _center position) in the general formula represented by ABO 3. This is necessary in order not to damage the dielectric properties of the porcelain material. Also,
It is effective for the oxide to be hardly dissolved in the perovskite and to be present at the grain boundaries for suppressing grain growth. For this purpose, chemically stable oxides that have a higher melting point than perovskite ceramics are effective. An example of such an oxide is
An example of Dy ₂ O ₃ (melting point 2375°C) is shown, Dd ₂ O ₃ (melting point
2395°C) and Sm ₂ O ₃ (melting point 2250°C) also show similar effects.

The method shown in Fig. 1 differs from the conventional method shown in Fig. 5 in that a metal oxide (for example, Dy ₂ O ₃ ) is added to suppress the growth of crystal grains when mixing the pre-fired porcelain material. In addition, in the method shown in Figure 4, metal oxides (for example,
The only difference is that Dy ₂ O ₃ ) is added, but the method is basically the same as the conventional method. It goes without saying that these methods can also be applied to the case where three or more different types of perovskite ceramic materials are mixed and sintered.

[Effects of the Invention] As explained above, the addition of metal oxides such as Dy ₂ O ₃ that suppress grain growth can improve crystallization without impairing the dielectric properties of porcelain in which two or more types of perovskite ceramic materials are mixed. It has the advantage that the grains can be made smaller and the grain size deviation can also be made smaller. Therefore, when used as a material for a multilayer ceramic capacitor, it has the advantage that the dielectric ceramic layer can be made thinner and defects such as pinholes can be reduced.

[Brief explanation of drawings]

Figure 1 is a diagram showing the steps of an embodiment of the method for manufacturing perovskite ceramics of the present invention, Figure 2 is a diagram showing the relationship between the amount of Dy ₂ O ₃ added and the average grain system, and Figure 3 is a diagram showing the relationship between the amount of Dy 2 O 3 added and the average grain system.
Figure 4 shows the temperature dependence of the dielectric constant of perovskite ceramics with and without the addition of Dy ₂ O _3. Figure 4 is a diagram showing the manufacturing process of another example of the present invention. Figure 5
The figure shows a conventional manufacturing process for perovskite ceramics.

Claims (1)

[Claims] 1. Two or more chemical formulas with different Kyrie temperatures
In perovskite porcelain in which perovskite porcelain materials represented by ABO ₃ are mixed, metal oxides that do not occupy the B position of ABO ₃ and have a melting point higher than the melting points of the two types of perovskite porcelain materials are included. Characteristic perovskite porcelain. 2 Two or more chemical formulas with different Kyrie temperatures
The raw material powder of the perovskite porcelain material represented by ABO ₃ is calcined separately in advance to produce two or more types of perovskite porcelain materials with different Curie temperatures, and then these materials are pulverized and each is mixed in an appropriate non-zero ratio. When mixing, an oxide of a metal element that does not occupy the B position in the ABO ₃ and has a melting point higher than the melting point of the two or more types of perovskite ceramic materials is added, and the two or more types of perovskite ceramic materials are mixed. A method for producing perovskite mixed sintered porcelain characterized by sintering perovskite porcelain materials without completely forming a solid solution. 3 Two or more chemical formulas with different Curie temperatures
At least one of the raw material powders of the perovskite ceramic material represented by ABO ₃ is an oxide of a metal element that does not occupy the B position of ABO ₃ , and said 2
After adding a metal oxide with a melting point higher than the melting point of more than one type of perovskite-based porcelain material, they are pre-fired separately to form two or more types of perovskite-based porcelain materials with different Curie temperatures, and then these are pulverized to separate them. A method for producing perovskite porcelain, which is characterized by mixing the following in an appropriate non-zero ratio and sintering without forming a complete solid solution.