JPH05262556A - Production of dielectric porcelain - Google Patents

Abstract

PURPOSE:To obtain a PT-PMT dielectric porcelain holding a high dielectric constant, capable of being calcined at a lower temperature than the melting point of an inner electrode and capable of employing inexpensive electrode materials without lowering the resistivity. CONSTITUTION:The raw materials of formula: (PbaMeb) {(Mg2/3Nb2/3)xTiy02+a+b (Me is Ca, Sr, Ba; x+y=1.00; 0.650<=5x<=0.950; 0.001<=b<=0.225; 1.010<=a+b<=1.255) are preliminarily weighed, mixed, ground, repeatedly calcined and pulverized to sufficiently convert the raw materials into fine particles. The fine particles are mixed with a binder (e.g. polyvinyl alcohol) formed into a green sheet and subsequently heated at approximately 700 deg.C in air to burn out the binder. The product is placed in a tubular electric oven, etc., subjected to a degasification, to a gas substitution with a N2-H2 gas mixture to give oxygen partial pressure below the equilibrium oxygen partial pressure between copper and copper oxide, and subsequently calcined at a temperature below the melting point (1083 deg.C) of the copper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high dielectric constant type dielectric ceramic, and more particularly to a method for manufacturing a dielectric ceramic which is fired in a low oxygen partial pressure atmosphere.

[0002]

2. Description of the Related Art In recent years, in ceramic capacitors, multilayer ceramic capacitors are rapidly becoming popular due to demands for miniaturization and large capacity of elements. A multilayer ceramic capacitor is usually manufactured by a process of integrally firing internal electrodes and ceramics.

Conventionally, a barium titanate-based material has been used as a high dielectric constant type ceramic capacitor material, but since the firing temperature is as high as about 1300 ° C., an expensive internal electrode material such as Pt or Pd is used. It was necessary to use metal.

On the other hand, a lead composite perovskite material which can be fired in air at about 1150 ° C. and can be used as an internal electrode by partially mixing Pd with an inexpensive Ag material, or in a low oxygen partial pressure atmosphere. Barium titanate-based materials have been developed that can be fired and can use a base metal material such as Ni as an internal electrode. For the former, PbTiO ₃ -Pb
A dielectric ceramic composition comprising (Mg _1/3 Nb _2/3 ) O ₃ has been proposed in, for example, Japanese Patent Application Laid-Open No. 55-51758,
Regarding the latter, for example, the materials described in Japanese Patent Publication No. 56-46641 are known.

In particular, PbTiO ₃ --Pb (Mg _1/3 Nb
_{The 2/3} ) O ₃ -based solid solution can be fired at a relatively low temperature, and has a higher dielectric constant than barium titanate-based materials having the same rate of change in dielectric constant with temperature. Therefore, this dielectric ceramic composition and P
With a multilayer capacitor composed of d-Ag system internal electrodes,
It has an advantage that an element capable of achieving large capacity, miniaturization, and cost reduction can be provided.

[0006]

Problems to be Solved by the Invention PbTiO ₃ -Pb
The (Mg _1/3 Nb _2/3 ) O ₃ solid solution has the advantage that it can be fired at a relatively low temperature, but when fired in a low oxygen partial pressure atmosphere, it does not sinter densely and the resistivity decreases. There is.

Further, in order to reduce the cost of the element by applying an inexpensive internal electrode material in recent years, for example, Cu or Cu is used.
It is required to use a base metal such as a system as an internal electrode. In response to this demand, in the conventional lead composite perovskite-based material, the melting point of Cu is exceeded, and when a layered internal electrode is formed without forming a layered internal electrode, a capacitor and a dielectric ceramic composition are formed. There was also a problem that the resistivity decreased.

The present invention relates to PbTiO ₃ --Pb (Mg _1/3 N
b _2/3 ) It can be fired at a temperature lower than the melting point of the internal electrode without impairing the high dielectric constant of the O ₃ system, and can be fired in a low oxygen partial pressure atmosphere that does not cause a decrease in resistivity. It is an object of the present invention to provide a method for manufacturing a dielectric porcelain which can apply various internal electrode materials and can reduce the cost of the multilayer capacitor element.

[0009]

[Means for Solving the Problems]

(Pb _a Me _b ) {(Mg _1/3 Nb _2/3 ) _x Ti _y } O _{2 + a + b} (where Me is at least one element selected from the group consisting of Ca, Sr, and Ba, x + y = 1.00, 0.650 ≤ x ≤ 0.950 0.001 ≤ b ≤ 0.225 1.010 ≤ a + b ≤ 1.255). The conventional problems have been overcome by the method for manufacturing a dielectric ceramic in which the firing is performed in an oxygen partial pressure atmosphere below the equilibrium oxygen partial pressure between the copper oxide and the copper oxide.

[0010]

The method of manufacturing a dielectric ceramic according to the present invention is characterized by firing in an oxygen partial pressure atmosphere lower than the equilibrium oxygen partial pressure between copper and copper oxide.

Although the reason is not clear,
Is supposed to be. Obtained by the production method of the present invention (Pb
_aMe_b) {(Mg_1/3Nb_2/3)_xTi_y} O _{2 + a + b}Represented by
Dielectric porcelain is Pb on A site_aMe_b, B site
To (Mg_1/3Nb_2/3)_xTi_yWith perovskite structure
It is made of P and is selected from Ca, Sr, and Ba at the A site.
Add Me, which has a smaller atomic radius than b and is easily oxidized
To do. Therefore, the excess A-site PbO component
Evaporates during firing and PbO vapor forms a film as if it were
Cover the area around the fired product as if. Therefore, the low oxygen partial pressure
Even in the firing atmosphere, the presence of PbO vapor covering the surroundings
The oxygen partial pressure at the time of baking the baked product is substantially determined, and the low oxygen partial pressure is
The so-called self-made atmosphere where the firing conditions of
It is thought to be due to the dielectric porcelain produced.

Further, in a manufacturing method in which an electrode layer is formed on a calcined dielectric ceramic composition and the electrode material and the dielectric ceramic composition are simultaneously fired, for example, in a method for manufacturing a laminated ceramic capacitor or the like, In the present invention, which has a drawback that the electrode material is oxidized and the resistivity is improved to deteriorate or impair the function as an electrode when the oxygen partial pressure is high, these problems are solved by firing at a low oxygen partial pressure. is there. Furthermore, if the oxygen partial pressure during firing is equal to or lower than the equilibrium oxygen partial pressure between the electrode material and the oxide of the electrode material, even if an oxide of the electrode material is used as the electrode material, this low oxygen partial pressure is obtained. The electrode material oxide is reduced in the atmosphere, and an electrode having a low resistivity can be formed.

As described above, in the production method of the present invention, the oxygen partial pressure during firing is more important than the firing temperature.

[0014]

EXAMPLE Obtained by the production method of the present invention (Pb_aMe_b)
{(Mg_1/3Nb_2/3)_xTi_y} O _{2 + a + b}Invitation represented by
The number of moles (a and b) of the A site of the electric porcelain is 0.00
1 ≦ b ≦ 0.225, 1.010 ≦ a + b ≦ 1.25
A range of 5 is suitable.

The total number of moles of A site (a + b) is 1.01
When it is less than 0, a dense sintered product cannot be obtained or the resistivity becomes low when firing in a low oxygen partial pressure atmosphere. Furthermore, when the total number of moles of A site is larger than 1.255, the dielectric constant and the resistivity decrease. Also, b is 0.2
Even if it is larger than 25, the dielectric constant is lowered. Therefore, the range of the specified A site is preferable.

The number of moles of B site (x and y) is
0.650 ≦ x ≦ 0.950, and x + y = 1.00.

In a composition in which the number of moles x of B site is outside this range, the Curie point deviates greatly from room temperature and the dielectric constant decreases, or the rate of change in dielectric constant with temperature increases, so the specified range is preferred. ..

The raw material of the dielectric porcelain of the manufacturing method of the present invention is
For example, oxides, metal carbonates, metal nitrates, etc. of the constituent metal materials are provided.

Further, in weighing the raw material, it is necessary to correct the purity of the raw material and accurately weigh a predetermined amount.

It is preferable that the weighed raw materials are mixed and pulverized, and calcination and pulverization are repeated to sufficiently mix the raw materials to form fine particles. The fine particles thus obtained are molded under a desired pressure or so-called green sheet. In order to form a compact, a usual method of adding a small amount of a binder that does not deteriorate the dielectric properties and the like even if it remains during sintering is applied. The mixing method may be either wet mixing such as a ball mill or dry mixing. As a crushing method, for example, a raikai machine,
A usual method such as a ball mill can be applied. The binder may be any material as long as it is a material that volatilizes or burns out under the conditions of calcination, and examples of such a material include polyvinyl alcohol and volatile wax. The material of the binder is selected in consideration of the ease of molding and the dispersibility of the raw material powder, and the amount of the binder added to the raw material is determined in consideration of the density of the sintered body and the ease of molding. You can select it.

When the dielectric porcelain produced by the manufacturing method of the present invention is applied to an element such as a capacitor, particularly a laminated capacitor, in which electrodes are directly provided on the porcelain, the binder is removed after forming to form an electrode layer. To do. As a method for forming the electrode layer, a usual method such as vapor deposition or printing can be applied. As the electrode material, for example, Pt, Pd, Ag, Cu, etc. are simple substances, alloys, oxides, or complex oxides. However, when an inexpensive electrode material such as Cu or a material containing Cu is used, The invention is particularly effective.

The firing in the oxygen partial pressure atmosphere in which the oxygen partial pressure during firing is lower than the equilibrium oxygen partial pressure between the electrode material and the oxide of the electrode material as in the manufacturing method of the present invention It is necessary because the conductivity is not deteriorated by oxidation.

Further, it can be obtained by the manufacturing method of the present invention (Pb
_The dielectric ceramic represented by _a Me _b ) {(Mg _1/3 Nb _2/3 ) _x Ti _y } O _{2 + a + b} has Pb _a Me _{b at} the A site and (Mg _1/3 Nb at the B site). _2/3 ) _x Ti _y is a perovskite structure, and P at the A site is selected from Ca, Sr, and Ba.
Me having an atomic radius smaller than that of b and being easily oxidized is added. Therefore, the equilibrium oxygen partial pressure between the electrode material and the oxide of the electrode material is higher than the equilibrium oxygen partial pressure between Pb and PbO so that the excess PbO component of the A site is not reduced to metal Pb. It is preferable to select a high electrode material.

The oxygen partial pressure during firing can be detected by using a sensor, such as a stabilized zirconia oxygen sensor, which can operate at the firing temperature in the firing furnace. The method for controlling the oxygen partial pressure during firing is, for example, degassing to a desired oxygen partial pressure, and then the mixed gas while adjusting the mixing ratio of the neutral gas and the reducing gas or a plurality of reducing gases. It can be carried out by a usual means such as pouring.

It is preferable that the firing temperature is lower than the melting point of the electrode material because the electrode layer can be prevented from flowing out during firing, but in the production method of the present invention, the melting point of copper (10
Since it can be fired at an extremely low temperature of 83 ° C or less,
In particular, it can exert its power in the manufacture of multilayer capacitors using copper as an internal electrode.

However, when the dielectric porcelain produced by the manufacturing method of the present invention is used for a purpose other than the element in which the above-mentioned electrodes are directly provided on the porcelain, the binder is removed after molding and then fired. However, since the characteristics of the dielectric porcelain produced by the production method of the present invention are excellent even in such an application, the production method of the present invention is not limited only to the application of simultaneous firing with the electrode layer.

The present invention will be described in more detail with reference to specific examples. (Specific example) As a starting material, chemically pure Pb is used.
O, MgO, Nb ₂ O ₅ , TiO ₂ , CaCO ₃ , SrCO
₃ and BaCO ₃ were used. These were subjected to purity correction and then weighed in predetermined amounts, and pure water was used as a dispersion medium using agate boulders, and wet mixing was performed in a ball mill for 17 hours. This is suction-filtered to separate most of the water content, then dried, and then lyophilized and crushed with a liquor machine to add 5 wt% of the powder amount of water, and a molding pressure of 500 k is formed into a column having a diameter of 60 mm and a height of 50 mm.
Molded at g / cm ² . This was put into an alumina crucible, covered with a homogenous lid, and calcined at 750 to 880 ° C. for 2 hours. The calcined product thus obtained was roughly crushed in a mortar, and further crushed for 17 hours by a ball mill using pure agate cobblestone as a dispersion medium, and this was suction-filtered to separate most of the water content and then dried.

After the above calcination, pulverization and drying were repeated several times, 6 wt% aqueous solution of polyvinyl alcohol was added to this powder in an amount of 6 wt% of the amount of the powder, and the mixture was granulated using a 32 mesh sieve and the molding pressure was applied. Diameter 13m at 1000kg / cm ²
It was formed into a cylindrical shape having a height of about 5 mm. The molded product was heated to 700 ° C. in air and kept for 1 hour to burn out polyvinyl alcohol. About 1/3 of the volume of the molded product thus obtained is spread with the above-mentioned calcined powder, and further 200
The mesh ZrO ₂ powder was transferred to a magnesia porcelain container laid with about 1 mm, covered with the same quality, and inserted into the core tube of a tubular electric furnace, and the inside of the core tube was degassed with a rotary pump, followed by N ₂ -H _2.
It is replaced with a mixed gas, and Po ₂ is 1.0 × 10 as an oxygen partial pressure (Po ₂ ) equal to or lower than the equilibrium oxygen partial pressure between copper and copper oxide.
Adjusting the mixing ratio of N ₂ gas and H ₂ gas so that it becomes ⁻⁸ atm, and letting the mixed gas flow up to a predetermined temperature 400 ° C./hr.
The temperature was raised at 400 ° C./hr and the temperature was lowered at 400 ° C./hr. Po ₂ in the core was measured by a stabilized zirconia oxygen sensor inserted.

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

The firing temperature was the temperature at which the density of the fired product was the highest. The components (a, b, x, y) of the composition range and the peripheral composition of the present invention are (Pb _a Me _b ) {(Mg
_1/3 Nb _2/3 ) _x Ti _y } O _{2 + a + b} ),
Firing temperature when firing in a low oxygen partial pressure atmosphere, dielectric constant,
The rate of change in permittivity with temperature (with respect to 20 ° C.), tan δ, resistivity, and density are shown in (Table 1).

[0031]

[Table 1]

As is clear from (Table 1), the dielectric ceramics produced by the manufacturing method of the present invention and within the composition range of the present invention exhibit excellent characteristics in all evaluation items. When the composition is out of the composition range defined by the production method of the present invention, if a + b is less than 1.010, a dense sintered product cannot be obtained when fired in a low oxygen partial pressure atmosphere, or the resistivity is low. It has a problem that it becomes low, and when it is larger than 1.255, it has a problem that the dielectric constant and the resistivity decrease. If b is larger than 0.225, the dielectric constant will decrease. The composition in which x is out of the limited range has a problem that the Curie point largely deviates from room temperature and the dielectric constant decreases, or the temperature change rate of the dielectric constant increases. Compositions within the scope of the invention overcome all of the above problems.

It should be noted that the selection made in this embodiment (Po ₂ = 1.
In a low oxygen partial pressure atmosphere such as 0 × 10 ⁻⁸ atm), the electrode metal material is lower than the equilibrium oxygen partial pressure of Cu. Therefore, even when co-firing with the electrode metal material used for a multilayer capacitor, the electrode metal material is It is thought that it hardly oxidizes.

Although the present embodiment has been described only with respect to the pressure-molded body, for example, a green sheet is formed in place of the pressure-molded body, and the green sheet has an electrode conforming to the idea of the present invention. It is apparent that the manufacturing method of the present invention is also suitable for a manufacturing method of a so-called laminated capacitor in which a green sheet is stacked and green sheets are stacked.

[0035]

According to the present invention, (Pb _a Me _b ) {(Mg _1/3
Nb _2/3 ) _x Ti _y } O _{2 + a + b} (where Me is Ca, Sr,
At least one element selected from the group consisting of Ba, x + y = 1.00, 0.650 ≦ x ≦ 0.950,
0.001 ≦ b ≦ 0.225, 1.010 ≦ a + b ≦
1.255), a predetermined amount of the raw material of the dielectric ceramic is weighed in advance and baked in an oxygen partial pressure atmosphere equal to or lower than the equilibrium oxygen partial pressure between copper and copper oxide. Therefore, PbTiO ₃ —Pb (M
g _1/3 Nb _2/3 ) O ₃ can be fired at a temperature lower than the melting point of the internal electrode without impairing the high dielectric constant of the system, and can be fired in a low oxygen partial pressure atmosphere that does not cause a decrease in resistivity. When applied as a dielectric of a capacitor, especially a multilayer capacitor, there is an effect that an inexpensive internal electrode material such as Cu can be applied and the cost of the capacitor element can be reduced.

Claims (3)

[Claims] 1. (Pb _a Me _b ) {(Mg _1/3 Nb _2/3 ) _x T
i _y } O _{2 + a + b} (where Me is at least one element selected from the group consisting of Ca, Sr, and Ba, x + y = 1.00, 0.650 ≦ x ≦ 0.950, 0. 001 ≤ b ≤ 0.225, 1.010 ≤ a + b ≤ 1.255), the raw material of the dielectric porcelain is weighed in advance by a predetermined amount, and low oxygen having an equilibrium oxygen partial pressure or less between copper and copper oxide is A method for manufacturing a dielectric ceramic, comprising firing in a partial pressure atmosphere. 2. The method for producing a dielectric ceramic according to claim 1, wherein the firing is performed at a temperature lower than the melting point of copper. 3. The method for producing a dielectric ceramic according to claim 1, wherein a material having an equilibrium oxygen partial pressure equal to or higher than the equilibrium oxygen partial pressure between Pb and PbO is used as an electrode material.