JPH029753A - Ceramic composition having high dielectric constant - Google Patents

Abstract

PURPOSE:To enable the maintenance of high resistance even by calcining in an atmosphere under a low partial pressure of oxygen by substituting Mg for part of Nb or Ti in compound perovskite represented by a formula Pb(Ni1/3 Nb2/3)O3-PbTiO3-Pb(Zn1/3Nb2/3)O3 so as to obtain a specified compsn. CONSTITUTION:This ceramic compsn. having a high dielectric constant is represented by the general formula (where 0.95<=a<=1.2 and x+y+z=1) and consists of components within a tetragonal range having compsn. points A-D as vertexes corresponding to variables a, b in the triangular coordinates having Pba(Ni1/3-Nb2/3)Oa+2, PbaTiOa+2 and Pba(Zn1/3Nb2/3)Oa+2 as vertexes. The points A-D (x, y, z) are A (0.000, 0.600, 0.400), B (0.005, 0.005, 0.990), C (0.600, 0.000, 0.400) and D (0.600, 0.150, 0.250).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high dielectric constant ceramic composition with good reducibility and useful as a capacitor material.

Conventional technology lead-based composite perovskite, for example, pb(Nj+zYNb273)03-PbTiO*-P
The sintered body of b(Z,,+,'Jbt,'z)0U is used as a capacitor material because it has excellent bias characteristics, high dielectric properties, etc.

By the way, in order to manufacture sub-components using this lead-based composite perovskite, the ceramic material and the electrode are usually fired together, or in this case, W is used as the rod material to prevent oxidation. Therefore, it is necessary to use noble metals such as platinum and palladium, which inevitably increases the cost.In order to avoid the high cost due to the use of such noble metal electrodes, an inexpensive silver-palladium alloy is used instead. However, it has been proposed that using this material will significantly increase the resistivity and degrade high frequency characteristics and other electrical properties, and that increasing the proportion of silver will cause migration and impair reliability. produce defects.

On the other hand, attempts have also been made to use base metals such as nickel and copper as electrode materials. In this case, in order to prevent oxidation of nickel and copper during firing, it is necessary to fire in a low oxygen partial pressure atmosphere, but when lead-based composite perovskite is fired in a low oxygen partial pressure atmosphere, the lattice changes. Oxygen is lost, and as a result, excess electrons are generated, resulting in an n-type semiconductor and a decrease in resistance.

In order to overcome these drawbacks, Ca is added to a part of pb located at the A site in the crystal lattice of lead-based composite perovskite.
A method has been proposed in which semiconductors are suppressed by introducing (Japanese Unexamined Patent Publication No. 62-87455).

Problems to be Solved by the Invention In the conventional reduction-resistant lead-based composite perovskite sintered body, divalent Ca atoms are further introduced into some of the divalent Pb atoms at the A site of the crystal lattice, and the A site elements are By making the total amount in excess of the total amount of B site elements, electrons generated due to the release of oxygen atoms are captured, but if a new component such as CaO is not added to introduce this Ca atom, It won't happen. However, in this case, the pb located at site A
Since the atom and the newly introduced Ca atom have different ionic radii, it is difficult to replace them, and there is an undesirable tendency that the dielectric constant decreases as the amount of CaO added increases.

In the present invention, instead of replacing the components of the A site, Mg and Nb, which are components of the B site, or part of Nb and Ti in Ti are replaced with the axis, thereby replacing the components of the A site. The aim is to generate an electron trapping effect equivalent to that of substitution, and to overcome problems caused by the introduction of different components and differences in ionic radius between substituted metals.

Means for Solving the Problems As a result of extensive research to improve the reduction resistance of lead-based composite perovskites, the present inventors found that PbO, MgO,
Nb, Us, TiO2, ZnO, NiO and MnO2
are mixed in a predetermined ratio and fired in a non-oxidizing atmosphere to obtain a composition expressed by Ichiro's formula %, with part of the A site replaced with at least one of Ba and Sr, and Mg added to the B site. In the composition of excessive addition, we found that the purpose could be achieved by forming a sintered body that satisfies the following conditions: 0.95≦a≦1.2 x+y+z=1 0.001≦MgO≦0.1 This led to an invention.

That is, the present invention provides the general formula %formula% Part of A site Ba, Sr 0.01≦Ba.

Sr≦0.2 Part of substituted B site MgO 0.001≦MgO≦0.
02 (in the formula, a, x, and y have the same meanings as above), a high dielectric constant ceramic composition is provided.

Among the ceramic compositions of the present invention, particularly preferred are ceramic compositions represented by the general formula % Excessive addition of MgO at the B site: 0.0 Old≦MgO≦0.1.

In the ceramic composition of the present invention, some of the pentavalent Nb atoms or tetravalent Ti atoms in the B site component are 2
It replaces the valent Mg atom, and due to the difference in valence,
It is thought that the excess electrons generated by the release of oxygen during firing are captured and the formation of an n-type semiconductor is suppressed.

In the general formula (I), if the number of pb atoms of the A-site component in the composition is less than 0.95 or more than 1.20, the crystal structure of the lead-based composite perovskite becomes incomplete.

Further, if the Mg atoms in the B site component are 0.001F or less, reduction resistance cannot be obtained, and if the number is more than 0.1, the dielectric constant decreases.

The ceramic composition of the general formula (I) contains PbO, Mg
O, Nb2O5, NiO, Tie, , ZnO and Mn
O□ or a compound that produces a stiff oxide upon firing is mixed in an atomic ratio corresponding to the final desired composition and calcined, and this calcined product is crushed and formed into a desired shape.
Manufactured by firing in a non-oxidizing atmosphere. At this time, an inert atmosphere such as nitrogen or argon or a reducing atmosphere such as -carbon oxide or hydrogen is used as the non-oxidizing atmosphere, and the oxygen partial pressure is 10-4 to 10-12 atm, preferably 10- It is best to set the pressure to ~1040 atmospheres. The firing temperature is 700 to 1300°C, preferably 800°C.
A range of ˜1000° C. is used.

The thus obtained ceramic composition of the present invention can be produced under conditions in which copper is not oxidized, for example, at 970°C and an oxygen partial pressure of 1.
101 for those fired under the conditions of 0-7 atm.
It exhibits a high specific resistance value of 2 Ωcm or more.

Next, in order to manufacture a multilayer capacitor using the ceramic composition of the present invention, for example, a binder and a solvent are added to raw material powder to make a slurry, formed into a sheet of about 15 μm, and then laminated after printing a copper electrode paste. disconnect. Next, the binder was removed by heat treatment, followed by firing while controlling the oxygen partial pressure. It is also possible to coat the fired body with a commercially available steel paste as the external two electrodes and bake it in nitrogen, or to simultaneously fire the external electrodes.

Effects of the Invention The lead-based composite perovskite ceramic composition of the present invention can maintain a high resistance value even when fired in a low oxygen partial pressure atmosphere, making it possible to use base metal electrodes and reducing costs. Compared to conventional barium titanate-nickel capacitors, it is smaller with the same capacity, has better bias characteristics, and also requires lower firing temperatures, making it possible to use electrodes with low resistivity such as copper, making it possible to use high-frequency This has the remarkable effect of not only improving properties but also reducing firing costs.

The lead-based composite perovskite ceramic composition of the present invention is useful as a capacitor material.

Example Next, the present invention will be explained in more detail with reference to Examples.

Example 1 High purity PbO, MgO, Nb2O, NiO, TiO
2,7,nO.

A predetermined amount of MnO2 was weighed, mixed for 15 hours in a ball mill using zirconia balls and pure water as a solvent, dried through suction filtration, and then calcined at 800° C. for 2 hours. The obtained calcined product was coarsely crushed, pulverized in a ball mill using zirconia balls and pure water as a solvent for 15 hours, and then dried through suction filtration. The above calcination, pulverization, and drying were repeated several times to obtain a raw material powder. Adding 6% by weight aqueous solution of polyvinyl alcohol as a binder to this powder, 6% by weight of the powder amount,
Granulated through a 32 mesh sieve and molded under a pressure of 1000
It was molded by dry pressing at 100Ox2. This molded product was heated in air at 700°C for 2 hours to burn out the binder, and then heated in an electric furnace with a co-co2 gas mixture so that the oxygen partial pressure became 10 x 1 O-7 atm. The temperature was raised at 400°C/hr to 970°C while
After holding for a period of time, the temperature was lowered at a rate of 400° C./hr to obtain a lead-based composite perovskite ceramic composition.

The following Table 1 shows the proportions (a, x) of the components of the composition.

y, z are Pba (Ni1/ffNb2/3) Jiy (Z mouth r/3
Nb2/3) ff1Oa4-Madashi 0.
001≦MgO≦0.2), resistivity, and dielectric constant.

It should be noted that those marked with water in Table 1 are outside the scope of this invention (1).

:jt, the figure shows each sample shown in Table 1 as Pba(Ni+
z:+Nb2/*)0□. 2. PbaTiOa, etc.

PbaCZnly, JNb2/3)Oa*z is shown in a triangular composition diagram as an end member, so the shaded area is the scope of the invention.

Numbers in brackets in the figure indicate sample defects.

In FIG. 1, A to D are the vertices of a quadrangle that is the scope of the present invention, and the composition of each vertex is as follows.

D O, 6000, 1500, 150 (margin below)

[Brief explanation of the drawing]

FIG. 1 is a triangular composition diagram showing the composition range according to the present invention.

Claims (1)

[Claims] (1) General formula Pb_a(Ni_1_/_3Nb_2_/_3)_xT
i_y(Zn_1_/_3Nb_2_/_3)_zO_
It is within the range of a_+_2 (0.95≦a≦1.2 x+y+z=1), and Pb_a(Ni_1_/_3Nb_2_/_3)O_a for the values of a and b
___+_2, Pb_aTiO_a_+_2, Pb_a(Z
n_1_/_3Nb_2_/_3) A high dielectric constant ceramic composition comprising a composition within a rectangular region having the following composition points A, B, C, and D as vertices in triangular coordinates with O_a_+_2 as the apex. x y z A 0.000 0.600 0.400 B 0.005 0.005 0.990 C 0.600 0.000 0.400 D 0.600 0.150 0.150 (2) Claim 1 Part of the Pb in the composition is 1 to 20 mol%
A high dielectric constant ceramic composition, characterized in that the above is substituted with at least one of Ba and Sr, and further MgO is present at the B site at a molar ratio within the following range. 0.001≦MgO≦0.1 (3) A high dielectric constant ceramic composition containing MnO_2 in a molar ratio of 0.001≦MnO_2≦0.02 with respect to the composition of claim 1 or 2. thing.