JPH04357608A - Dielectric porcelain composition - Google Patents

Abstract

PURPOSE:To provide a porcelain composition having a high dielectric constant, a low dielectric loss, a large dielectric voltage, large insulating resistance, and a small diameter of a crystalline particle by using a compound having a specific composition including oxides of Ba, Sr, Ti and Nd. CONSTITUTION:A composition expressed by Formula (x)>>(Ba0)(1-m).(SrO)S].yTiO2 zNdO3/2 is used, wherein (m) ranges from 0.005 to 0.100. (x), (y) and (z) represent a mol ratio: (x)+(y)+(z)=1; and (x), (y) and (z) are within a range of mol ratios surrounded by a point (a) of (x)=0.430, (y)=0.525, and (z)=0.045, a point (b) of (x)=0.475, (y)=-0.490, and (z)=0.035, a point (c) of (x)=0.490, (y)=0.505, and (z)=0.005, and a point (d) of (x)=0.450, (y)=0.545, and (z)=0.005. Consequently, it is possible to obtain a porcelain composition having a high dielectric constant, a low dielectric loss, a large dielectric voltage, large insulating resistance, and a small diameter of a crystalline particle, and further, a dielectric can be formed thin, thus achieving miniaturization and a large capacitance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic composition having a high dielectric constant, low dielectric loss, high dielectric breakdown voltage and high insulation resistance, and small crystal grain size.

0002

[Prior Art] Conventionally, as a dielectric ceramic composition having a high dielectric constant, BaO, CaO, and Ti are used in BaTiO3.
It is known that suitable amounts of O2, ZrO2, etc. are added.

0003

[Problems to be Solved by the Invention] However, these dielectric ceramic compositions have large crystal grain sizes of 10 to 20 μm and high porosity, so they cannot be applied to products with thin dielectric materials such as multilayer ceramic capacitors. However, there were problems such as increased dielectric loss, low dielectric breakdown voltage, and decreased dielectric breakdown voltage and insulation resistance during the plating process for forming the external electrodes.

0004

[Means for Solving the Problems] In order to solve these problems, the dielectric ceramic composition of the present invention has the general formula xB
It is expressed as aO・yTiO2・zNdO3/2, and barium oxide (BaO) in the formula is replaced with strontium oxide (Sr
O) or calcium oxide (CaO), and the substitution rate m is 0.00 with strontium oxide (SrO).
5≦m≦0.100, 0 for calcium oxide (CaO)
．． 005≦m≦0.200, and x, y and z represent molar ratios, and x+y+z=1 and x
,y,z values are: a is x=0.430, y=0.525, z=0.045
, b is x=0.475, y=0.490, z=0.035
, c is x=0.490, y=0.505, z=0.005
, d is x=0.450, y=0.545, z=0.005
, has a composition within the molar ratio range surrounded by a, b, c, and d.

[0005] Furthermore, there is provided a dielectric ceramic composition characterized in that the above composition is the main component, and 0.3 to 3.0 parts by weight of niobium (calculated in the form of Nb2O5) is added as a subcomponent. It is something.

[0006]

[Operation] With this configuration, by replacing BaO with SrO, dielectric loss is reduced and the product of capacitance and insulation resistance (CR product) is increased. Furthermore, by replacing BaO with CaO, dielectric loss can be reduced. Furthermore, by adding niobium as a subcomponent, the CR product and dielectric breakdown voltage will be increased. Furthermore, these configurations reduce the crystal grain size.

[0007]

【Example】

(Example 1) Chemically high purity BaCO3 was used as the starting material.
, SrCO3, TiO2, Nd2O3, and MnO2 powder as a sintering aid were weighed so as to have the composition ratio shown in Table 1 below, and placed in a rubber-lined ball mill equipped with an agate ball with pure water, and wet mixed. After that, it was dehydrated and dried. This dry powder was placed in a high alumina crucible and calcined in air at 1100°C for 2 hours. This calcined powder,
The mixture was placed in a rubber-lined ball mill equipped with agate balls together with pure water, wet-milled, and then dehydrated and dried. After adding an organic binder to this pulverized powder and making it homogeneous, it was sized through a 32-mesh sieve, and molded using a mold and hydraulic press at a molding pressure of 1 t/cm2 to a diameter of 15 mm and a thickness of 0.4 mm.
It was molded into. Next, the obtained molded disk was placed in an alumina pod covered with zirconia powder and heated in air (
Firing was carried out for 2 hours at the firing temperature shown in Table 1) to obtain a dielectric porcelain assembly disc having the composition ratio shown in Table 1.

[0008]

[Table 1]

The thickness and diameter of the dielectric ceramic disk thus obtained were measured, and the samples for measuring the dielectric constant, dielectric loss, and capacitance temperature characteristics were coated with silver on both sides of the dielectric ceramic disk. A sample for measuring dielectric breakdown voltage and insulation resistance was prepared by baking a dielectric ceramic disk with a 1 mm wide portion without a silver electrode inside the outer periphery, and baking a silver electrode thereon. The dielectric constant, dielectric loss, and capacitance temperature characteristics were measured using a Yokogawa-Hewlett-Packard digital LCR meter model 4274A at a measurement temperature of 20°C and a measurement voltage of 1V.
rms, and was determined by measurement at a measurement frequency of 1 kHz.

[0010] The temperature change rate of capacitance is expressed as the rate of change in capacitance at a measurement temperature appropriately selected within the temperature range of -25°C to +85°C, with 20°C as a reference temperature. The rate of change was calculated using the following formula.

dC=(CT-CO)/CO×100dC
: Capacitance temperature change rate CT: Capacitance at T°C (pF) CO: Capacitance at 20°C (pF)
Then, the dielectric constant was determined from the following formula.

K=143.8×C0×t×D2K: Dielectric constant C0: Capacitance at 20°C (pF) D: Diameter of dielectric ceramic disk (mm) t: Thickness of dielectric ceramic disk (mm) The dielectric breakdown voltage was measured using a high-voltage DC power supply PHS35K-3 manufactured by Kikusui Electronics Co., Ltd. by placing the sample in silicone oil and increasing the voltage at a voltage increase rate of 50 V/s. It was determined as dielectric breakdown strength per 1 mm.

B1=B0/t B1: Dielectric breakdown strength (kV/mm) B0: Dielectric breakdown voltage (kV) Furthermore, insulation resistance was measured using a high resistance meter manufactured by Takeda Riken Co., Ltd. at a measurement voltage of 50 V. It was determined by measurement using DC and a measurement time of 1 minute, and the CR product was determined from the following formula.

CR=C0×R0/1012CR: CR product (MΩ・μF) C0: Capacitance at 20°C (F) R0: Insulation resistance (Ω) Furthermore, the crystal grain size is the optical Obtained from microscopic observation.

The above measurement results are shown in Table 2 for sample numbers 1 to 10.

[0016]

[Table 2]

FIG. 1 is a ternary diagram showing the composition range of the main components according to the present invention, and the reason for limiting the composition range of the main components will be explained with reference to FIG. That is, in region A, the dielectric constant is small, making it impractical. Further, in region B, the Curie point becomes too large on the negative side, and the capacitance temperature change rate of the temperature characteristic deviates too much on the positive side, making it impractical. Furthermore, sintering is extremely difficult in the C region. Furthermore, the dielectric constant is small in the D region, making it impractical.

[0018] Furthermore, by replacing BaO with SrO, the dielectric loss can be reduced without significantly changing the dielectric constant and dielectric breakdown voltage, and the product of capacitance and insulation resistance (CR side) can be reduced.
However, when the substitution rate m is 0.
If it is less than 0.005, there will be no effect, while if it exceeds 0.100, the dielectric constant will decrease and become impractical.

Furthermore, the crystal grain size can be reduced to 5 to 10 μm. (Practical example 2) High purity SrCO3 among the raw materials of Example 1
In place of the powder, high-purity CaCO3 powder was used and weighed to have the composition ratio shown in Table 3 below, and the subsequent steps were performed in the same manner as in Example 1 to obtain the sample number of (Table 3). 11~
Dielectric ceramic disks having the composition ratio shown in Example 20 were obtained, treated in the same manner as in Example 1, and the electrical properties and crystal grain sizes were measured. The results are shown in Table 4 for sample numbers 11 to 20.

[0020]

[Table 3]

[0021]

[Table 4]

FIG. 2 is a ternary diagram showing the composition range of the main component according to the present invention, and the reason for limiting the composition range of the main component will be explained with reference to FIG. That is, in region A, the dielectric constant is small, making it impractical. Further, in region B, the Curie point becomes too large on the negative side, and the capacitance temperature change rate of the temperature characteristic deviates too much on the positive side, making it impractical. Furthermore, sintering is extremely difficult in the C region. Furthermore, the dielectric constant is small in the D region, making it impractical.

[0023] Also, by replacing BaO with CaO, it has the effect of reducing dielectric loss without significantly changing the dielectric constant, dielectric breakdown voltage, and CR product.
If the substitution rate m is less than 0.005, there is no effect; on the other hand, 0
．． When it exceeds 200, sintering properties deteriorate and the dielectric constant decreases, making it impractical.

Furthermore, the crystal grain size can be reduced to 5 to 10 μm. (Example 3) High purity Nb2O5 was used as the raw material shown in Example 1.
Powder was added and weighed to obtain the composition ratio shown in Table 5 below, and the subsequent steps were performed in the same manner as in Example 1 to obtain the composition ratio shown in sample numbers 21 to 30 in Table 5. Dielectric ceramic disks were obtained, treated in the same manner as in Example 1, and the electrical properties and crystal grain sizes were measured. The results are shown for each sample number 21 to 30 (Table 6)
Shown below.

[0025]

[Table 5]

[0026]

[Table 6]

Here, the reason for limiting the composition range of the main components is the same as in Example 1, so the explanation will be omitted.

[0028] Then, with respect to the main component, N as a subcomponent
Containing b2O5 has the effect of improving the product of capacitance and insulation resistance (CR product) and dielectric breakdown voltage, but the content is 0.3 parts by weight per 100 parts by weight of the main component.
If the content is less than 3.0 parts by weight, there will be no effect, while if it exceeds 3.0 parts by weight, the Curie point will shift to the negative side, lowering the dielectric constant and making it impractical.

Furthermore, the crystal grain size can be reduced to 3 to 8 μm. (Example 4) High purity Nb2O5 was used as the raw material shown in Example 2.
Powder was added and weighed to obtain the composition ratio shown in Table 7 below, and the subsequent steps were carried out in the same manner as in Example 1 to obtain the composition ratio shown in sample numbers 31 to 40 in Table 7. Dielectric ceramic discs were obtained, treated in the same manner as in Example 1, and the electrical properties and crystal grain sizes were measured. The results are shown for each sample number 31 to 40 (Table 8)
Shown below.

[0030]

[Table 7]

[0031]

[Table 8]

Here, the reason for limiting the composition range of the main components is the same as in Example 2, so the explanation will be omitted.

[0033] Then, with respect to the main component, N as a subcomponent
By containing b2O5, it has the effect of improving the product of capacitance and insulation resistance (CR product) and dielectric breakdown voltage, but the content is 0.00% per 100 parts by weight of the main component.
If the content is less than 3 parts by weight, there will be no effect, while if it exceeds 3.0 parts by weight, the Curie point will shift to the negative side, lowering the dielectric constant and making it impractical.

Furthermore, the crystal grain size can be reduced to 3 to 8 μm. In addition, in the method for producing the dielectric ceramic composition in the above example, BaCO3, SrCO3, CaC
O3, TiO2, Nd2O3, Nb2O5 and MnO
2 was used, but it is not limited to this method,
Compounds such as BaTiO3 to achieve the desired composition ratio,
Or by heating carbonates, hydroxides, etc. in the air.
BaO, SrO, CaO, TiO2, Nd2O3, Nb
Characteristics comparable to those of the examples can be obtained even when compounds forming 2O5 and MnO2 are used.

[0035] Also, commonly used industrial BaT
The Ba/Ti ratio of iO3 is 0.98 or more, and BaTi
When O3 is used as a starting material, properties comparable to those of the examples can be obtained even if BaO or TiO2 is added to compensate for the shortage.

Furthermore, even if the main component is calcined in advance and subcomponents are added, properties comparable to those of the examples can be obtained.

Furthermore, titanium dioxide, an industrial raw material commonly used for dielectric ceramics, such as titanium dioxide KA-10 manufactured by Titan Kogyo Co., Ltd. and titanium dioxide FA-55W manufactured by Furukawa Mining Co., Ltd., has a maximum of 0. .45% by weight Nb
2O5 is included, but even if these titanium dioxides are used to create dielectric porcelain as the main component, the content of Nb2O5 is at most 0.17% by weight relative to 100% by weight of the main component. Although it is outside the scope of the invention, properties comparable to those of the examples can be obtained by taking into consideration the amount of Nb2O5 in titanium oxide, which is an industrial raw material, and adding the insufficient amount of Nb2O5.

In addition to the above basic composition, MnO
2. Salts, oxides, etc., which are generally considered to be fluxes, such as ZnO, SiO2, and Fe2O3, can also be added within a range that does not impair the properties.

[0039]

As described above, according to the present invention, a dielectric ceramic having a high dielectric constant, low dielectric loss, high dielectric breakdown voltage, high insulation resistance, and small crystal grain size can be obtained. The body thickness can be reduced, making it possible to downsize the product and increase capacity.

[Brief explanation of drawings]

FIG. 1 is a ternary diagram showing the composition range of the main components of a dielectric ceramic composition in one embodiment of the present invention

FIG. 2 is a ternary diagram showing the composition range of the main components of a dielectric ceramic composition in another embodiment of the present invention.

Claims (4)

[Claims] Claim 1: In general, x[(BaO)(1-m)(S
rO)m]・yTiO2・zNdO3/2, m
has a composition in which the value of is in the range of 0.005≦m≦0.100, and x, y and z represent the molar ratio, and x+y+z
= 1 and the values of x, y, z are: a is x = 0.430, y = 0.525, z = 0.045
, b is x=0.475, y=0.490, z=0.035
, c is x=0.490, y=0.505, z=0.005
, d is x=0.450, y=0.545, z=0.005
, A dielectric ceramic composition having a composition having a molar ratio range surrounded by a, b, c, and d. Claim 2: Instead of strontium oxide, calcium oxide has a value of m of 0.005≦ in terms of CaO form.
The dielectric ceramic composition according to claim 1, having a composition in the range of m≦0.200. 3. The dielectric ceramic composition according to claim 1, wherein 0.3 to 3.0 parts by weight of niobium in the form of Nb2O5 is added as a subcomponent. 4. The dielectric ceramic composition according to claim 2, wherein 0.3 to 3.0 parts by weight of niobium in the form of Nb2O5 is added as a subcomponent.