JP2508373B2 - Dielectric ceramic composition and method for producing dielectric ceramic - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic composition and a method for manufacturing a dielectric ceramic, and particularly to a dielectric ceramic composition mainly containing barium titanate and used for a ceramic capacitor or the like. The present invention relates to a method of manufacturing an object and a dielectric ceramic.

(Prior Art) As a dielectric ceramic composition used for a ceramic capacitor, there have been known many conventional dielectric ceramic compositions mainly containing barium titanate. Barium titanate has a Curie point near 120 ° C. and a dielectric constant of close to 10,000, but that alone cannot provide a high dielectric constant at room temperature. Therefore, a material called a shifter material is added, and the Curie point is moved to room temperature to have a high dielectric constant at room temperature. As the shifter material, tin oxide, zirconia oxide, rare earth element, etc. are known.

As a ceramic capacitor mainly composed of barium titanate using such a shifter material, a single plate type lead wire type capacitor has been manufactured. However, in recent years, the lamination technology has advanced, and it has become easy to obtain a dielectric green sheet of about 30 to 80 μm. Then, so-called multilayer ceramic capacitors in which a plurality of layers are laminated by sandwiching a dielectric thin film between internal electrodes have entered the electronics industry, and conventional dielectric ceramic compositions are also used as materials for such multilayer ceramic capacitors. became.

On the other hand, recent porcelain capacitors tend to be smaller,
Especially in multilayer capacitors, the thickness of the porcelain dielectric layer is
There is a tendency for the layer to become thinner, such as 10 to 20 μm. In this case, as compared with a single plate type capacitor having a thickness of 100 to 10,000 μm, it receives electric field strength ten times or more. Therefore, there is a demand for a composition having a smaller voltage dependency than a single plate capacitor.

Further, as the dielectric layer becomes thinner, structural defects of ceramics are more likely to be reflected in the characteristics, so that the crystal grain size (grain size) is uniform and fine, and the number of pores is small and small. Is desired.

Derivative porcelain mainly composed of barium titanate having a small grain size is disclosed, for example, in Japanese Patent Application Nos. 56-18059 and Sho.
No. 7-16809, Japanese Patent Application No. 57-105919, Japanese Patent Application No. 57-196469 and the like. These dielectric porcelains mainly composed of barium titanate are added with cerium oxide, barium titanate, cerium oxide and barium zirconate, or neodymium oxide, and fired in an atmosphere in which air flows. This reduces the grain size.

(Problems to be solved by the invention) In these dielectric porcelains having a small grain size, the dielectric constant is as small as around 10,000 at maximum at room temperature, and the dielectric constant is smaller than that of a large grain size. In that case, it was difficult to obtain a large capacitance. Another problem is that the temperature change curve of the dielectric constant is steep.

Therefore, a main object of the present invention is to provide a dielectric ceramic composition having a small grain size, a large dielectric constant, a small change in the dielectric constant with respect to temperature changes, and a small voltage dependence. It is to provide things.

Another object of the present invention is to provide a method for manufacturing a dielectric ceramic which can obtain a dielectric ceramic having a larger dielectric constant despite having a smaller grain size.

The present inventor has found that the grain size of the dielectric ceramic is 1 to 3 μm.
As a result of various studies on the cause that the dielectric constant is less than 10,000 when m is small, it has been found that the dielectric constant does not increase when the type and content of impurities of barium titanate, which is the main raw material, are large.

Furthermore, in barium titanate containing a small amount of alkali metal oxides, the grain size can be reduced by adding at least one selected from lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide and samarium oxide. Moreover, they have found that they have a large dielectric constant.

It was also found that by adding tin oxide and, if necessary, at least one of zirconium oxide and titanium oxide, it is possible to obtain a dielectric porcelain having a small change in dielectric constant with temperature and a small voltage dependence.

(Means for Solving the Problems) The dielectric ceramic composition according to the present invention is based on 100% by mol of barium titanate containing 0.03% by weight or less of an alkali metal oxide as an impurity, and lanthanum oxide or oxide is used. 2.5 to 5.0 of at least one selected from cerium, neodymium oxide, praseodymium oxide, and samarium oxide
Mol% and zirconium oxide, tin oxide, titanium oxide (Zr _1-ab Sn _a Ti _b ) O ₂ (where a> 0, b ≧ 0,0 <a +
It is a dielectric ceramic composition containing 0.5 to 8.5 mol% in terms of b ≦ 1.0).

The method for manufacturing a dielectric ceramic according to the present invention is based on 100 mol% of barium titanate and at least one oxide selected from lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, and samarium oxide.
2.5 to 5.0 mol%, and zirconium oxide, tin oxide, and titanium oxide (Zr _1-ab Sn _a Ti _b ) O ₂ (where a> 0, b ≧ 0,
A method for producing a dielectric ceramic containing 0.5 to 8.5 mol% as converted to 0 <a + b ≦ 1.0, wherein a lanthanum compound, a cerium compound, a neodymium compound, a praseodymium compound, and samarium are added to a barium titanate raw material. This is a method for producing a dielectric ceramic in which a molded body made of a composition to which at least one selected from compounds and a zirconium compound, a tin compound and a titanium compound is added is fired in an atmosphere having an oxygen concentration of 60% or more.

Next, the reason for limiting the composition range of the dielectric ceramic composition according to the present invention will be described.

Conventionally, barium titanate, which is industrially used in large quantities,
It has a purity of about 98.5-99.5% and contains impurities such as SrO, CaO, and
It is common to contain alkaline earth metals such as MgO, alkali metal oxides such as Na ₂ O and K ₂ O, and contaminants such as Al ₂ O ₃ and SiO ₂ that accompany the grinding and mixing operation.

The present invention was conceived by discovering that, of the impurities in barium titanate, the characteristics deteriorate particularly when the content of alkali metal oxides such as Na ₂ O and K ₂ O exceeds a certain limit. It was done.

That is, in the dielectric ceramic composition according to the present invention,
Of the impurities in barium titanate, the content of alkali metal oxides is set to 0.03% by weight or less. This is because when the content exceeds 0.03% by weight, the dielectric constant becomes as low as 10,000 or less.

Further, in the dielectric ceramic composition according to the present invention, lanthanum oxide, cerium oxide, neodymium oxide, and oxide are mixed with 100 mol% of barium titanate in which the content of alkali metal oxides as impurities is 0.03% by weight or less. At least 1 selected from praseodymium and samarium oxide
Contains 2.5 to 5.0 mol% of types. The content of these is 2.
If it is less than 5 mol%, the grain size of the obtained porcelain will not be sufficiently small. On the other hand, if the content of these exceeds 5.0 mol%, the Curie point moves to a temperature lower than room temperature, and the dielectric constant at room temperature decreases or the sinterability deteriorates.

Thus, with respect to 100 mol% of barium titanate having an alkali metal oxide content of 0.03% by weight or less, at least one selected from lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, and samarium oxide is selected. If one type is contained in an amount of 2.5 to 5.0 mol%, it is possible to obtain a dielectric porcelain having a small grain size and a large dielectric constant of 11,000 or more.

However, in such a composition, the change of the dielectric constant with respect to the temperature change becomes large, and the JIS standard F characteristics and the like are not satisfied. Further, the voltage dependency becomes large, which is not preferable for thinning the ceramic dielectric layer in the laminated ceramic capacitor.

In order to solve such a problem, zirconium oxide, tin oxide, and titanium oxide are converted into (Zr _1-ab Sn _a Ti _b ) O ₃ (where a> 0, b ≧ 0,0 <a + b ≦ 1.0) Then 0.5 to 8.5
It is added in the range of mol%. When the content of zirconium oxide, tin oxide or titanium oxide is less than 0.5 mol%, the temperature characteristics of the dielectric constant are not improved and the voltage dependence is large. On the other hand, when the content of zirconium oxide, tin oxide or titanium oxide exceeds 8.5 mol%, the temperature characteristic of the dielectric constant is improved, but the dielectric constant is lowered.

In obtaining a dielectric ceramic from the dielectric ceramic composition according to the present invention, a small amount of MnCO ₃ ,
The addition of Fe ₂ O ₃ or the like does not impair the characteristics of the obtained porcelain.

(Effect of the Invention) According to the present invention, it is possible to obtain a dielectric porcelain having a small grain size, a large dielectric constant, a small change in the dielectric constant with respect to a temperature change, and a small voltage dependence.

Further, according to the present invention, it is possible to obtain a dielectric porcelain having a larger permittivity even though the grain size is small.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

(Example) Example 1 BaCO ₃ and TiO ₂ of various purities were used as raw materials, these were weighed so that the molar ratio of BaCO ₃ and TiO ₂ was 1.000, and a ball mill using zirconia cobblestone was used. Wet mixing was performed for 16 hours to obtain a mixture.

After evaporating the water content in the obtained mixture, the mixture was kept at 1150 ° C. for 2 hours for calcination, and the average particle size was 2 μm again with a ball mill.
Grind until the following: In this way, A, B, and
Four types of barium titanate having different purities shown in C and D were obtained.

And, for this barium titanate 100 mol%,
As shown in Table 2, lanthanum oxide (La ₂ O ₃ ), cerium oxide (CeO ₂ ), neodymium oxide (Nd ₂ O ₃ ), protheodium oxide (Pr ₆ O ₁₁ ), samarium oxide (Sm ₂ O ₃ ), Zirconium oxide (ZrO ₂ ), tin oxide (SnO ₂ ), titanium oxide (TiO ₂ ), etc. are weighed and added with vinyl acetate binder.
The mixture was wet-mixed for an hour to obtain a mixture. After this mixture was dried and granulated, it was molded into a disk having a diameter of 10 mm and a thickness of 0.5 mm at a pressure of 2000 kg / cm ² . The disc was fired at the temperature shown in Table 3 for 2 hours,
A disk-shaped porcelain was obtained.

Observe this porcelain surface at 2000 times using an electron microscope,
The grain size was measured.

A silver electrode is baked on both main surfaces of the obtained porcelain to make a measurement sample (capacitor), and its dielectric constant ε and dielectric loss at room temperature are measured.
The change rate of capacitance with respect to tan δ (%) and temperature change was measured. In addition, applying an AC voltage of 100V / mm, 1kHz,
The dielectric loss tan δ (%) was measured.

The dielectric constant ε and the dielectric loss tan δ are as follows:
It was measured at a frequency of 1 kHz. Regarding the rate of change of capacitance with respect to temperature change, the rate of change (ΔC / C ₂₀ ) of capacitance at −25 ° C. and 85 ° C. based on the capacitance at 20 ° C. was shown.

 The results of these measurements are shown in Table 3.

Next, the reason for limiting the composition range of the dielectric ceramic composition according to the present invention will be described based on the results shown in Table 1, Table 2 and Table 3.

When the content of lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, samarium oxide, etc. is less than 2.5 mol% as in Sample Nos. 1 and 2, the dielectric constant becomes smaller or the grain size becomes larger than 3 μm. I will end up. On the other hand, when the content of these is more than 5 mol% as in Sample Nos. 13 and 14, the dielectric constant becomes small and the firing temperature becomes high.

When the content of zirconium oxide, tin oxide and titanium oxide is less than 0.5 mol% as in Sample No. 15, the rate of change in capacitance exceeds -80%, which is not preferable.
On the other hand, when the content of zirconium oxide, tin oxide and titanium oxide is more than 8.5 mol% as in Sample No. 16,
The rate of change in capacitance is small, but the dielectric constant is greatly reduced. In addition, as in Sample No. 17, the content of zirconium oxide, tin oxide and titanium oxide is 0.5 to 8.5 mol%.
100 V / mm when tin oxide and titanium oxide are not contained at all, that is, when a + b = 0
When the AC voltage is applied, the dielectric loss increases, which is not preferable.

When using barium titanate raw materials C and D having a large content of alkali metal oxides as in sample numbers 18 and 19,
Dielectric constant decreases.

On the other hand, in the samples using the dielectric ceramic composition within the scope of the present invention (see Sample Nos. 3 to 12),
The grain size of the sintered porcelain is as small as 1-3 μm,
It has a large dielectric constant of 11,000 or more and a small dielectric loss of 3.0% or less when an AC voltage of 100 V / mm is applied. Moreover, the rate of change in capacitance at −25 ° C. and 85 ° C. based on 20 ° C. is within −80%, which satisfies the JIS standard F characteristics.

Example 2 15% by weight of a mixed aqueous solution of an organic binder, a dispersant and an antifoaming agent was added to a raw material which was weighed so as to have the composition of sample No. 8 in Table 2, and pulverized with a ball mill together with 50% by weight of water,
A raw material slurry was obtained by mixing. Using this raw material slurry,
A 22 μm ceramic green sheet was produced by the doctor blade method. A palladium paste for internal electrodes was printed on this ceramic green sheet by a screen printing method. A plurality of ceramic green sheets were laminated so that the printed palladium paste faces each other, and thermocompression bonded to obtain a laminated body.

The obtained laminate was fired at 1320 ° C. for 2 hours to obtain a sintered body. Silver paste was applied to both end surfaces of the obtained sintered body and baked in air at 800 ° C. to form external electrodes electrically connected to the internal electrodes. Thus, a monolithic ceramic capacitor was obtained. The dimensions of this laminated ceramic capacitor are as follows.

External dimensions Width: 1.6 mm Length: 3.2 mm Thickness: 1.2 mm Ceramic thickness: 13 μm Number of effective dielectric layers: 19 Counter electrode area per layer: 2.0 mm ^{2 About the} obtained multilayer ceramic capacitor sample,
The capacitance C (nF) and dielectric loss tan δ (%) at 1 kHz and 1 V _rms at a temperature of 25 ° C were measured. Further, a DC voltage of 25 V was applied for 2 minutes, and the insulation resistance IR (Ω) was measured. In addition, the rate of change in capacitance ΔC / C ₂₀ (%) at −25 ° C. and 85 ° C. with reference to the capacitance at 20 ° C. was measured. further,
The DC breakdown voltage value BDV (V) and the bending strength were measured.

The bending strength is the bending strength measuring device 10 shown in FIG.
It measured using. In FIG. 1, reference numeral 12 is a sample multilayer ceramic capacitor to be tested, and 14 is a sample holder. The capacitor 12 placed on the sample holder 14 is pressurized by the pressure pin 16. Then, the applied pressure is displayed by the tension gauge 18 with a stationary needle.
During this test, the jig span of the sample holder 14 is 2 mm.
And

As a comparative example, with respect to BaTiO ₃ 100 mol%, BaZrO ₃ 18.
5 mol% and CaZrO ₃ 8.9 mol% were added, and a multilayer ceramic capacitor was manufactured by the same method as described above. Then, the above-mentioned respective characteristics were measured for this comparative example.

The surface of each monolithic ceramic capacitor was observed with an electron microscope at a magnification of 2000 to measure the grain size. The above results are shown in Table 4.

As can be seen from Table 4, the monolithic ceramic capacitor made of the material having the composition of the present invention has a smaller grain size and a smaller dielectric loss than the comparative example. Also,
The monolithic ceramic capacitor made of the material of the present invention has about twice the dielectric breakdown voltage and bending strength as compared with the comparative example.

Example 3 First, barium carbonate and titanium oxide were mixed at a molar ratio of 1:
The mixture was weighed to be 1 and wet-mixed for 16 hours in a ball mill using zirconia boulders to obtain a mixture. And
After evaporating the water in the resulting mixture,
Hold for a time to calcinate, then use a ball mill again to obtain an average particle size of 2
The powder was pulverized to a size of not more than μm to obtain barium titanate fine powder.

Next, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, zirconium oxide, tin oxide, and titanium oxide were selectively added to the obtained fine powder of barium titanate in the proportions shown in Table 5. Was weighed and added to, and vinyl acetate binder was added and wet mixed for 16 hours.

Next, this was dried and granulated, and then press-molded at a pressure of 2000 kg / cm ² to obtain a disk-shaped molded body having a diameter of 10 mm and a thickness of 0.5 mm. Then, the obtained molded body was fired under the firing conditions shown in Table 5 to obtain a dielectric ceramic. The firing patterns A, B and C under the firing conditions are as follows.

As shown in FIG. 2 (A), the firing pattern A was heated to the firing temperature shown in Table 5 at a rate of 200 ° C./1 hour in the air, and kept at the firing temperature for 2 hours, and then at room temperature. Up to 200
It is cooled at a rate of ℃ / 1 hour.

The firing pattern B is shown in Table 5 as shown in FIG.
In an oxygen atmosphere with the oxygen concentration shown in Table 5, the temperature was raised to the firing temperature shown in Table 5 at a rate of 200 ° C / 1 hour, held at that firing temperature for 2 hours, and then kept at room temperature at a rate of 200 ° C / 1 hour. It is what is cooled in.

The firing pattern C is, as shown in FIG. 2 (C), heated to 800 ° C. in the atmosphere at a rate of 200 ° C./hour, and further changed the firing atmosphere from the atmosphere to the oxygen concentration of oxygen shown in Table 5. The atmosphere is changed, and the temperature is raised from 800 ° C. to the firing temperature shown in Table 5 at the same rate. Then, after keeping the firing temperature for 2 hours in an oxygen atmosphere, it is cooled to 800 ° C. at a rate of 200 ° C./hour, the firing atmosphere is returned to the atmosphere again, and it is cooled to room temperature at the same rate. .

The surface of the porcelain thus obtained was observed with an electron microscope at a magnification of 2000 to measure the grain size.

Next, silver electrodes were baked on both main surfaces of the porcelain to make a measurement sample (capacitor), and its dielectric constant ε and dielectric loss at room temperature were measured.
The change rate of capacitance with respect to tan δ (%) and temperature change was measured. In addition, applying an AC voltage of 100V / mm, 1kHz,
The dielectric loss tan δ (%) was measured.

The dielectric constant ε and the dielectric loss tan δ are as follows:
It was measured at a frequency of 1 kHz. As for the rate of change of capacitance with respect to temperature change, the rate of change ΔC / C ₂₀ (%) at −25 ° C. and 85 ° C. based on the capacitance at 20 ° C. was shown.

 Table 6 shows the above measurement results.

As is clear from Table 5 and Table 6, the sample (Sample No. 24) manufactured by the method for manufacturing a dielectric ceramic of the present invention.
~ 33), the grain size of the sintered body is 1-3 μm.
It was small and had a high dielectric constant of 13,000 or more. Moreover, the temperature change rate of the capacitance at 85 ° C is within -80%, and the F characteristic that is the temperature characteristic of the JIS standard (based on the capacitance at 20 ° C, the capacitance at -25 ° C to + 85 ° C) The rate of change in capacity is within the range of -80% to + 30%.).

Moreover, the dielectric loss tan δ when an AC voltage of 100 V / mm is applied is as small as 3.0% or less.

In addition, samples (sample numbers 21 to 23) that are outside the scope of the present invention
And 34-38), the following can be understood.

In sample numbers 21 and 22, the added amounts of lanthanum oxide, cerium oxide, neodymium oxide, and samarium oxide were small, and the dielectric constant at room temperature was small.

In Sample No. 23, the amount of zirconium oxide, tin oxide, and titanium oxide added was small, and the temperature change rate of capacitance was -80%.
Therefore, the F characteristic, which is the JIS standard temperature characteristic, cannot be satisfied.

In sample No. 34, since the added amounts of cerium oxide, neodymium oxide, and samarium oxide are large, the Curie point moves to a low temperature and the dielectric constant at room temperature becomes small.

In sample No. 35, the Curie point moves to a low temperature and the dielectric constant at room temperature decreases because the amounts of zirconium oxide, tin oxide, and titanium oxide added are large.

In Sample No. 36, since tin oxide and titanium oxide were not added (a + b = 0), the dielectric loss tan δ when an AC voltage of 100 V / mm was applied was large.

In sample numbers 37 and 38, the oxygen concentration during firing was low,
Dielectric constant decreases.

On the other hand, according to the method for manufacturing a dielectric ceramic according to the present invention, although the grain size is small,
A dielectric ceramic having a large dielectric constant can be obtained.

Further, by using such a dielectric ceramic, it is possible to obtain a laminated ceramic capacitor that is smaller and has a larger capacity than the conventional laminated ceramic capacitor.

In addition, although an oxide was used as the compound added to barium titanate in the above-mentioned examples, the compound is not limited to the oxide and the following compounds may be used.

Lanthanum compound _{... La 2 CO 3, La (} NO 3) 2, La (C 2 O 4) 3 cerium compound _{... CeCO 3, Ce (NO 3} ) 3, Ce (OH) 4 neodymium compound ... Nd (OH) _3, Nd (NO ₃ ) ₃ , Nd ₂ (C
_{O 3) 3, Nd 2 (} C 2 O 4) 3 praseodymium compound _{... Pr 2 (CO 3) 3} , Pr (NO 3) 3 Semariumu compound _{... Sm 2 (C 2 O 4} ) 3, Sm (NO 3) 3 Zirconium compound: BaZrO ₃ , CaZrO ₃ , ZrCl ₄ , ZrO (NO ₃ )
₂ , ZrO (CH ₃ COO) ₂ tin compound ... BaSnO ₃ , CaSnO ₃ , Sn (OCH ₃ ) ₄ titanium compound ... BaTiO ₃ , CaTiO ₃ , TiCl ₄ , Ti (OCH ₃ ) ₄

[Brief description of drawings]

FIG. 1 is an illustrative view showing a bending strength measuring device for measuring the bending strength of a sample. 2 (A), (B) and (C) are graphs showing firing patterns (relationship between firing atmosphere and temperature and time), respectively. In the figure, 10 is a bending strength measuring device, 12 is a multilayer ceramic capacitor to be tested, 14 is a sample holder, 16 is a pressure pin,
18 is a tension gauge with a stationary needle.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Sakabe 2-26-10 Tenjin, Nagaokakyo City, Kyoto Prefecture Murata Manufacturing Co., Ltd. (56) Reference JP-A-59-154703 (JP, A)

Claims (2)

(57) [Claims] 1. Alkali metal oxide as an impurity is selected from lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, and samarium oxide with respect to 100 mol% of barium titanate having a content of 0.03% by weight or less. 2.5 to 5.0 mol% of at least one kind, and zirconium oxide, tin oxide, and titanium oxide (Zr _1-ab Sn _a
Ti _b ) O ₂ (provided that a> 0, b ≧ 0,0 <a + b ≦ 1.0) is contained in an amount of 0.5 to 8.5 mol%, which is a dielectric ceramic composition. 2. 2.5 to 5.0 mol% of at least one oxide selected from lanthanum oxide, cerium oxide, neodymium oxide, praseodymium oxide, and samarium oxide based on 100 mol% of barium titanate, and oxidized. Zirconium, tin oxide, titanium oxide (Zr _1-ab Sn _a Ti _b ) O ₂
(However, 0.5 when converted to a> 0, b ≧ 0,0 <a + b ≦ 1.0)
A method for producing a dielectric porcelain containing ˜8.5 mol%, wherein at least one selected from a lanthanum compound, a cerium compound, a neodymium compound, a praseodymium compound and a samarium compound is used for a barium titanate raw material, and a zirconium compound. A method for producing a dielectric ceramic, comprising firing a molded body made of a composition containing a tin compound and a titanium compound in an atmosphere having an oxygen concentration of 60% or more.