JPH0676249B2 - Dielectric porcelain composition - Google Patents

Description

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

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 materials that can be fired in air at 1000 ° C or less and can use inexpensive Ag-based materials as internal electrodes, and base metal materials such as Ni that can be fired in a low oxygen partial pressure atmosphere as internal electrodes can be used. Barium titanate-based materials that can be used have been developed. Regarding the former,
58-176175, Pb (Ni _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ -Pb (Mg
Dielectric porcelain compositions containing _1/2 W _1/2 ) O ₃ are described.
For the latter, the materials described in JP-B-56-46641 are known.

Pb (Ni _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ -Pb (Mg _1/2 W _1/2 ) O ₃ -based solid solution can be fired at low temperature, and titanic acid with similar temperature change rate of dielectric constant can be obtained. Higher permittivity than that of barium materials can be obtained. Therefore, the multilayer capacitor composed of this 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 base metals such as Cu, which can further reduce the cost of internal electrode materials, as internal electrodes.
There is a need for a material that can be fired in a low oxygen partial pressure atmosphere in which the metal does not oxidize and that can obtain a high resistivity.

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

The present invention provides Pb (Ni _1/3 Nb _2/3 ) O ₃ -PbTiO 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 Pba (Ni _1/3 Nb _2/3 ) xTiy (Mg _1/2 W _1/2 ) zO _{2 + a In} the composition formula (where x + y + z = 1), 1.001 ≦ a ≦
1.110, and for each value of a within this range, Pb _a (Ni _1/3 Nb _2/3 ) O _{2 + a} , Pb _a TiO _{2 + a} , and Pb _a (Mg _{1 / When 2} W _1/2 ) O _{2 + a} is the apex, the composition is within the rectangular region with the following composition points A, B, C, D in the angular coordinates.

A; x = 0.700 y = 0.275 z = 0.025 B; x = 0.500 y = 0.475 z = 0.025 C; x = 0.100 y = 0.450 z = 0.450 D; x = 0.100 y = 0.300 z = 0.600 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 lower, and a highly reliable device having a high resistivity can be obtained.

Example The starting materials were chemically high-purity PbO, NiO, MgO, Nb ₂ O ₅ , and Ti.
O ₂ and WO ₃ were used. These were subjected to purity correction, weighed a predetermined amount, and wet-mixed in a ball mill for 17 hours using agate stones and pure water as a solvent. This is suction filtered to separate most of the water content, then dried, and then lyophilized with a Lykai machine, and then added with 5 wt% of the powder amount of water, and a diameter of 60 mm and height of 5
It was molded into a 0 mm column at a molding pressure of 500 kg / cm ² . This was put in an alumina crucible, covered with the same material, and calcined at 750 ° C to 880 ° C for 2 hours. Next, the calcined product is crushed in an alumina mortar,
Further, agate stones were used and crushed for 17 hours in a ball mill using pure water as a solvent, and this was 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 with a molding pressure of 1000 kg / cm ² , a diameter of 13 mm It was molded into a cylindrical shape with a height 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-mentioned calcined powder, and then add 2
Transfer 00 mesh ZrO ₂ powder to a magnesia porcelain container laid with about 1 mm, put a lid of the same quality, insert it into the core tube of a tubular electric furnace, degas the core tube with a rotary pump, then N ₂ -H
₂ Replace with mixed gas, flow the mixed gas while adjusting the mixing ratio of N ₂ and H ₂ gas so that the oxygen partial pressure (Po ₂ ) becomes 1.0 × 10 ⁻⁸ atm, and raise the temperature to 400 ° C / hr. After warming and holding for 2 hours, 40
The temperature was lowered at 0 ° C / hr. 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 4 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,
z is the value expressed as Pb _a (Ni _1/3 Nb _2/3 ) xTiy (Mg _1/2 W _1/2 ) zO _{2 + a} ), the firing temperature when firing in a low oxygen partial pressure atmosphere , Permittivity, rate of change of permittivity with temperature (at 20 ℃), ta
nδ, resistivity and density are shown.

Figure 1 shows the samples shown in Table 1 for Pb _a TiO _{2 + a} , Pb _a (Ni _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 large.
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 cross-sectional view of a magnesia container in which porcelain is put in during firing, and FIG. 3 is a cross-sectional view of a core tube during firing. 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 a composition formula represented by Pba (Ni _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 (Ni _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 triangular coordinates, the dielectric composition characterized by being composed of a composition within a rectangular area having the following composition points A, B, C, D as vertices. Porcelain composition. A; x = 0.700 y = 0.275 z = 0.025 B; x = 0.500 y = 0.475 z = 0.025 C; x = 0.100 y = 0.450 z = 0.450 D; x = 0.100 y = 0.300 z = 0.600