JPH0324426B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a high dielectric constant dielectric ceramic composition that is fired at a firing temperature of 1100° C. or less, and particularly to a composition that can be fired in a low oxygen partial pressure atmosphere and has a high resistivity. BACKGROUND OF THE INVENTION In recent years, multilayer ceramic capacitors are rapidly becoming popular due to the demand for smaller devices and larger capacitances. Multilayer ceramic capacitors are usually manufactured by a process in which internal electrodes and ceramic are fired together. Barium titanate-based materials have traditionally been used for high-permittivity ceramic capacitor materials, but because the firing temperature is as high as 1300°C, expensive metals such as Pt and Pd are used as internal electrode materials. The need arose. On the other hand, there are lead composite perovskite materials that can be fired in air at temperatures below 1000℃ and inexpensive Ag-based materials can be used for the internal electrodes, and lead composite perovskite materials that can be fired in a low oxygen partial pressure atmosphere and base metal materials such as Ni can be used as the internal electrodes. Barium titanate-based materials have been developed that can be used as Regarding the former, the inventors have already identified PbTiO ₃ −Pb (Mg _1/3 Nb _2/3 ) O ₃ −Pb (Ni _1/2 W _1/2 )
A dielectric ceramic composition containing O ₃ is proposed. Regarding the latter, materials such as those described in Japanese Patent Publication No. 56-46641 are known. _PbTiO3 −Pb(Mg _1/3 Nb _2/3 ) _O3 −Pb(Ni _1/2 W _1/2 )
O ₃ -based solid solutions can be fired at low temperatures and have a higher dielectric constant than barium titanate-based materials, which have a similar rate of change in dielectric constant with temperature. Therefore, a multilayer capacitor consisting of this dielectric ceramic composition and Ag-based internal electrodes,
It has the advantage that the device can be made larger in capacity, smaller in size, and lower in cost. However, in recent years, there has been a demand for using base metals such as Cu as internal electrodes, which can further reduce the cost of internal electrode materials. For this reason,
There is a need for a material that does not reduce the resistivity of dielectric ceramics even when fired in a low oxygen partial pressure atmosphere that does not oxidize metals such as Cu when fired simultaneously. Problems to be solved by the invention PbTiO ₃ −Pb (Mg _1/3 Nb _2/3 ) O ₃ −Pb (Ni _1/2 W _1/2 )
When O ₃ -based solid solutions are fired in a low oxygen partial pressure atmosphere, they do not sinter tightly and tend to have low resistivity. The present invention provides _PbTiO3 -Pb(Mg1 _/ 3Nb2 _/3 ) _O3 -Pb
To provide a dielectric ceramic composition that does not impair the high dielectric constant and low-temperature sinterability of the (Ni _1/2 W _1/2 ) O ₃ system and has a high resistance value when fired in a low oxygen partial pressure atmosphere. It is an object. Means to solve the problem (Pb _a Sr _b ) (Mg _1/3 Nb _2/3 ) _x Ti _z (Ni _1/2 W _1/2 )
A porcelain composition represented by O _2+a+b (where x+y+z
=1), 0.001≦b≦0.225, 1.000≦a+b
The range shall be ≦1.250. Effect The composition of the present invention can be used in a low oxygen partial pressure atmosphere at 1100°C.
A dense fired product can be obtained at the firing temperature below, and a highly reliable element with high resistivity can be obtained. Example The starting materials are chemically highly pure PbO, SrCO ₃ ,
MgO, Nb ₂ O ₅ , TiO ₂ , NiO, and WO ₃ were used. After correcting the purity of these, a predetermined amount was weighed, and wet-mixed for 17 hours in a ball mill using agate cobblestones and pure water as a solvent. This is suction filtered to separate most of the water, then dried, and then thoroughly crushed in a Raikai machine, after which 5wt% of water is added to the powder amount.
Molding pressure 500Kg/ into a cylindrical shape with a diameter of 60mm and a height of approximately 50mm.
Molded in cm ² . This was placed in an aluminum crucible, covered with a homogeneous lid, and calcined at 750°C to 880°C for 2 hours.
Next, the calcined product was roughly crushed in an alumina mortar, and further crushed in a ball mill using agate boulders and pure water as a solvent.
The mixture was pulverized for several hours, filtered under suction to remove most of the moisture, and then dried. After repeating the above calcining, crushing, and drying several times, 6wt% of polyvinyl alcohol aqueous solution was added to the powder, and the powder was granulated through a 32-mesh sieve to a diameter of 13mm in height at a compacting pressure of 1000Kg/ ^cm2. Approximately 5
It was formed into a cylindrical shape of mm. The molded product is heated to 700℃ in air.
The temperature was raised to 100% and maintained for 1 hour to burn out the polyvinyl alcohol. This was transferred to a magnesia porcelain container in which about 1/3 of the volume of the above-mentioned calcined powder was spread and 200 mesh ZrO ₂ powder was spread about 1 mm, covered with a homogeneous lid, and inserted into the core tube of a tubular electric furnace. After degassing the inside of the reactor core tube with a rotary pump, N ₂ −H ₂
The oxygen partial pressure (Po ₂ ) is
Flow the mixed gas while adjusting the mixture ratio of N ₂ and H ₂ gas to 1.0x10 ^-8 atm until the specified temperature is 400 ℃.
The temperature was raised at a rate of 400°C/hr, held for 2 hours, and then lowered at a rate of 400°C/hr. Po ₂ in the reactor core tube was measured by an inserted stabilized zirconia oxygen sensor. FIG. 2 shows the structure of the magnesia porcelain container during firing, and FIG. 3 shows a cross-sectional view of the inside of the furnace tube. In FIG. 2, 1 is a magnesia container, the upper part of which is sealed with a magnesia container lid 2.
Calcined powder 3 was placed at the bottom of magnesia container 1, and zirconia powder 24 was placed on top of it. Furthermore, material 5 was placed on top of it. The magnesia container 1 prepared as shown in FIG. 2 was placed in the furnace core tube 6 as shown in FIG. 7 is a stabilized zirconia oxygen sensor. The fired product is cut into discs with a thickness of 1 mm, and cut on both sides.
Cr-Au was deposited, and the dielectric constant and tan δ were measured under an electric field of 1 kHz and 1 V/mm. Further, the resistivity was determined from the value 1 minute after applying a voltage of 1 kV/mm. The firing temperature was set at a temperature at which the density of the fired product increased. Table 1 shows the composition range and peripheral composition components of the present invention, (a, b, x, y, z are (Pb _a Sr _b ) (Mg _1/3
Nb _2/3 ) _x Ti _y (Ni _1/2 W _1/2 ) _z O _2+a+b )
Firing temperature, dielectric constant, temperature change rate of dielectric constant (relative to 20℃) when firing in a low oxygen partial pressure atmosphere,
Tanδ, resistivity, and density are shown. Figure 1 shows each sample shown in Table 1 (Pb _a Sr _b )
TiO _2+a+b , (Pb _a Sr _b ) (Mg _1/3 Nb _2/3 ) O _2+a+b (Pb _a
Sr _b )(Ni _1/2 W _1/2 )O _2+a+b is shown in a triangular composition diagram as an end member, and the shaded area is the scope of the invention.

[Table] * Comparative examples outside the scope of the invention For compositions outside the scope of the invention, if a + b is smaller than 1.000, a dense sintered product cannot be obtained when fired in a low oxygen partial pressure atmosphere, or the resistivity will be low. It has the disadvantage that the dielectric constant and resistivity decrease when it becomes larger than 1.250. Moreover, when b is larger than 0.225, the dielectric constant decreases. x,
Compositions in which y and z are outside the specified ranges have the disadvantage that the Curie point greatly deviates from room temperature, resulting in a low dielectric constant, or that the rate of change in dielectric constant with temperature is large. Both of the aforementioned problems are overcome in the claimed compositions. Note that the low oxygen partial pressure atmosphere Po ₂ ; 1.0x10 ^-8 atm selected as the firing atmosphere is lower than the equilibrium oxygen partial pressure of copper at the firing temperature, and it is considered that the metal hardly oxidizes. Effects of the Invention According to the present invention, a dense and highly resistive sintered body for obtaining high reliability as a multilayer capacitor element can be obtained by firing at a temperature of 1100°C or lower in a low oxygen partial pressure atmosphere. This is an excellent dielectric ceramic composition that allows the use of base metal materials.

[Brief explanation of the drawing]

Fig. 1 is a triangular composition diagram showing the composition of the porcelain composition according to the present invention, Fig. 2 is a cross-sectional view of a magnesia container in which the porcelain is placed during firing, and Fig. 3 is a cross-sectional view of the inside of the furnace tube during firing. show. 1; Magnesia container, 2; Magnesia container lid,
3; Calcined powder, 4; Zirconia powder, 5; Sample, 6;
Furnace tube, 7; stabilized zirconia oxygen sensor.

Claims (1)

[Claims] 1 (Pb _a Sr _b ) {(Mg _1/3 Nb _2/3 ) _x Ti _y (Ni _1/2 W _1/2 ) _z }
When expressed as O _2+a+b (x+y+z=1), it is in the range of 0.001≦b≦0.225 1.000≦a+b≦1.250, and for each value of a and b within this range, (Pb _a Sr _b ) (Mg _1/3 Nb _2/3 ) O _2+a+b , (Pb _a Sr _b )
TiO _2+a+b , (Pb _a Sr _b ) (Ni _1/2 W _1/2 ) O _2+a+b The following composition points A, B,
A dielectric ceramic composition characterized by comprising a composition within a rectangular region with vertices C and D. A: x=0.950 y=0.049 z=0.001 B: x=0.400 y=0.591 z=0.001 C: x=0.001 y=0.900 z=0.099 D: x=0.001 y=0.600 z=0.399