JPH0676247B2 - Dielectric porcelain composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high dielectric constant type dielectric ceramic composition which is fired at 1100 ° C. or less, and particularly, a composition which can be fired in a low oxygen partial pressure atmosphere to obtain a high resistivity. Regarding

2. Description of the Related Art In recent years, in ceramic capacitors, multilayer ceramic capacitors are rapidly becoming popular due to the demand for smaller size and larger capacity of elements. Multilayer ceramic capacitors are usually manufactured by a process of integrally firing internal electrodes and ceramics. Conventionally, barium titanate-based materials have been used for high dielectric constant ceramic capacitor materials.
Since the firing temperature is as high as about 1300 ° C, it was necessary to use expensive metals such as Pt and Pd as the internal electrode material.

On the other hand, lead composite perovskite-based materials that can be fired in air at 1000 ° C or lower and inexpensive Ag-based materials can be used as internal electrodes, or base metal materials such as Ni that can be fired in a low oxygen partial pressure atmosphere can be used as internal electrodes. Barium titanate-based materials have been developed. For the former, for example, Pb
TiO ₃ -Pb (Mg _1/3 Nb _2/3 ) O ₃ -Pb (Mg _1/2 W _1/2 ) O ₃ is disclosed in JP-A-55-1.
It is described in Japanese Patent No. 11011. Regarding the latter, Japanese Patent Publication 5
The materials and the like described in JP-A 6-46641 are known. PbTi
O ₃ -Pb (Mg _1/3 Nb _2/3 ) O ₃ -Pb (Mg _1/2 W _1/2 ) O ₃ -based solid solution can be fired at low temperature, and titanic acid with similar dielectric constant temperature change rate can be obtained. Higher permittivity than that of barium materials can be obtained. Therefore, the multilayer capacitor including the dielectric ceramic composition and the Ag-based internal electrode has the advantages that the device can have a large capacity, a small size, and a low cost. However, in recent years, it has been required to use a base metal such as Cu, which can further reduce the cost of the internal electrode material, as the internal electrode.Therefore, in a low oxygen partial pressure atmosphere in which the metal such as Cu does not oxidize when co-fired. There is a need for materials that can be fired and have high resistivity.

Problems to be Solved by the Invention PbTiO ₃ -Pb (Mg _1/3 Nb _2/3 ) O ₃ -Pb (Mg _1/2 W _1/2 ) O ₃ based solid solution is fired in a low oxygen partial pressure atmosphere. D. It does not sinter densely and the resistivity tends to decrease.

The present invention relates to PbTiO ₃ -Pb (Mg _1/3 Nb _2/3 ) O ₃ -Pb (Mg _1/2 W _1/2 ) O ₃
An object of the present invention is to provide a dielectric ceramic composition which does not impair the high dielectric constant and low-temperature sinterability of the system and has a high resistance value when fired in a low oxygen partial pressure atmosphere.

Means for Solving Problems In the composition formula represented by Pba (Mg _1/3 Nb _2/3 ) xTiy (Mg _1/2 W _1/2 ) zO _{2 + a} (where x + y + z = 1), 1.001 ≦ a ≦
1.110, and for each value of a within this range, Pb _a (Mg _1/3 Nb _2/3 ) O _{2 + a} , Pb _a TiO _{2 + a} , and Pb _a (Mg _1/2 W _{1 / 2} ) In triangular coordinates with O _{2 + a} as the apex, the composition is within the rectangular area with the following composition points A, B, C, D as apexes.

A; x = 0.950 y = 0.025 z = 0.025 B; x = 0.850 y = 0.125 z = 0.025 C; x = 0.100 y = 0.600 z = 0.300 D; x = 0.100 y = 0.400 z = 0.500 Action Composition of the present invention In the case of (1), by making the A site component excessive, a dense fired product can be obtained at a low oxygen partial pressure atmosphere at 1100 ° C. or less, and a highly reliable device having a high resistivity can be obtained.

Example Starting materials were chemically high-purity PbO, MgO, Nb ₂ O ₅ , TiO ₂ , WO ₃
Was used. These were corrected for purity and weighed a predetermined amount, and wet-mixed for 17 hours in a ball mill using agate stones and pure water as a solvent. This is suction-filtered to separate most of the water content, then dried, then charged and decomposed with a Lykai machine, and then added with 5 wt% of the powder amount of water, and the diameter is 60 mm and the height is 50 mm.
Was molded into a cylindrical shape with a molding pressure of 500 kg / cm ² . Put this in an alumina crucible and cover with the same material.
I calcined for an hour. Next, the calcined product is roughly crushed in an alumina mortar, and then agate stones are used and pure water is used as a solvent in a ball mill.
It was crushed for 17 hours, suction filtered to separate most of the water content, and then dried. After repeating the above calcination, crushing, and drying several times, add 6 wt% of polyvinyl alcohol 6 wt% aqueous solution to this powder, granulate through a 32 mesh sieve, and increase the diameter 13 mm at a molding pressure of 1000 kg / cm ^2. It was formed into a cylindrical shape with a size of about 5 mm. The molded product was heated to 700 ° C. in the air and held for 1 hour to burn out the polyvinyl alcohol content. Place this on top of about 1/3 of the volume of the above calcined powder and apply 200
Move the mesh ZrO ₂ powder to a magnesia porcelain container laid about 1 mm, put a lid of the same quality, and insert it in the core tube of the tubular electric furnace,
After degassing the inside of the core tube with a rotary pump and replacing it with N ₂ -H ₂ mixed gas, while adjusting the mixing ratio of N ₂ and H ₂ gas so that the oxygen partial pressure (Po ₂ ) becomes 1.0x10 ^-8 atm. Flowing mixed gas,
After raising the temperature to 400 ° C / hr to the specified temperature and holding for 2 hours, 400 ° C / hr
The temperature dropped at. Po ₂ in the core tube was measured by a stabilized zirconia oxygen sensor inserted. FIG. 2 shows the structure of the magnesium porcelain container at the time of firing, and FIG. 3 shows a cross-sectional view of the inside of the core tube.

In FIG. 2, reference numeral 1 is a magnesia container, and the upper part thereof is sealed with a magnesia container lid 2. A calcined powder 3 was placed in the lower part of the magnesia container 1, and a zirconia powder 24 was placed thereon. Furthermore, the sample 5 was arranged on it.

The magnesia container 1 prepared as shown in FIG. 2 was placed in the core tube 6 as shown in FIG. 7 is a stabilized zirconia oxygen sensor.

The fired product was cut into a disc with a thickness of 1 mm, Cr-Au was vapor-deposited on both sides, and the dielectric constant and tan δ were measured under an electric field of 1 kHz and 1 V / mm.
The resistivity was calculated from the value of 1 minute after applying a voltage of 1 kV / mm.

The firing temperature was the temperature at which the density of the fired product was the highest.

Table 1 shows the components (a, x,
y and z are values expressed as Pb _a (Mg _1/2 Nb _2/3 ) xTiy (Mg _1/2 W _1/2 ) zO _{2 + a} ), and when firing in a low oxygen partial pressure atmosphere. Firing temperature, firing temperature when fired in a low oxygen partial pressure atmosphere, permittivity, temperature change rate of permittivity (relative to 20 ° C), tanδ,
The resistivity and density are shown.

Figure 1 shows the samples shown in Table 1 for Pb _a TiO _{2 + a} and Pb _a (Mg _1/3 Nb
_2/3 ) O _{2 + a} and Pb _a (Mg _1/2 W _1/2 ) O _{2 + a} are shown in the triangular composition diagram, and the shaded area is the scope of the invention. .

Compositions outside the scope of the invention have the problem that if a is less than 1.001, a dense sintered product cannot be obtained or the resistivity becomes low when fired in a low oxygen partial pressure atmosphere.
When it is larger than 0, there is a problem that the dielectric constant and the resistivity decrease. Further, a composition in which x, y, z is out of the limited range has a problem that the Curie point is largely deviated from room temperature and the dielectric constant is lowered, or the temperature change rate of the dielectric constant is increased. Compositions within the scope of the claims overcome all of the above problems.

The low oxygen partial pressure atmosphere selected as the firing atmosphere Po ₂ ; 1.
0x10 ^-8 atm is lower than the equilibrium oxygen partial pressure of copper at the firing temperature, and it is considered that the metal is hardly oxidized.

EFFECTS OF THE INVENTION According to the present invention, a dense, high-resistivity sintered body for obtaining high reliability as a multilayer capacitor element can be obtained by firing in a low oxygen partial pressure atmosphere at 1100 ° C. or lower, and Cu etc. as internal electrodes It is possible to obtain an excellent dielectric ceramic composition that makes it possible to use a base metal material.

[Brief description of drawings]

FIG. 1 is a triangular composition diagram showing the component composition of a porcelain composition according to the present invention, FIG. 2 is a sectional view of a magnesia container in which porcelain is put in during firing, and FIG. 1 ... Magnesia container, 2 ... Magnesia container lid, 3 ...
… Calcined powder, 4 …… Zirconia powder, 5 ……; Sample, 6 ……
Core tube, 7 ... Stabilized zirconia oxygen sensor.

Claims (1)

[Claims] 1. In the composition formula represented by Pba (Mg _1/3 Nb _2/3 ) xTiy (Mg _1/2 W _1/2 ) zO _{2 + a} (where x + y + z = 1),
1.001 ≦ a ≦ 1.110, and for each value of a within this range, Pb _a (Mg _1/3 Nb _2/3 ) O _{2 + a} , Pb _a TiO _{2 + a} , and Pb _a (Mg _1/2 W _1/2 ) O _{2 + a} in a triangular coordinate, the dielectric ceramics characterized by being composed of a composition within a rectangular region having the following composition points A, B, C, D as apexes. Composition. A; x = 0.950 y = 0.025 z = 0.025 B; x = 0.850 y = 0.125 z = 0.025 C; x = 0.100 y = 0.600 z = 0.300 D; x = 0.100 y = 0.400 z = 0.500