Manganese-containing complex oxide, and process for preparing complex perovskite compound composition by use of this complex oxide

There are herein disclosed a raw material for a complex perovskite ceramic composition which is intended to uniformly disperse a trace amount of an addition component (manganese) therein, and a process for preparing the ceramic composition. A manganese-containing composite oxide is represented by the general formula (Mn.sub.a MeI.sub.1-a)MeII.sub.b O.sub.c wherein a is a value in the range of 0<a.ltoreq.0.3; MeI is at least one of Mg, Ni and Zn; MeII is one of Nb, Ta and W; when MeII is Nb or Ta, b is 2 and c is 6, or when MeII is W, b is 1 and c is 4. By the use of a raw material containing this manganese-containing complex oxide, there can be prepared an Mn-containing complex perovskite compound composition which contains Mn and at least one of complex perovskite compounds represented by the general formula Pb(BIBII)O.sub.3 wherein BI is one of Mg, Ni and Zn; and BII is one of Nb, Ta and W.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a raw material for a complex perovskite 
ceramic composition for use in electronic materials and a process for 
preparing the ceramic composition. 
2. Description of the Prior Art 
Complex perovskite compounds containing lead (Pb) have been widely used in 
dielectric materials and piezo-electric materials. The dielectric 
materials have been mainly used in multilayer ceramic capacitors. For 
example, in Japanese Patent Application Laid-Open No. 42167/1982, a 
ceramic composition comprising Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 
--PbTiO.sub.3 --Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 has been disclosed, and 
in Japanese Patent Application Laid-Open No. 74569/1983, a ceramic 
composition comprising Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 --Pb(Mg.sub.1/2 
W.sub.1/2)O.sub.3 --PbTiO.sub.3 has been disclosed. 
As the composite perovskite compounds for use in the piezo-electric 
materials, Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 --PbTiO.sub.3, Pb(Zn.sub.1/3 
Nb.sub.2/3)O.sub.3 --PbTiO.sub.3 and the like are known. To the complex 
perovskite compounds containing lead, manganese has often been added. 
For example, the dielectric materials have been used for the prevention of 
the deterioration of insulation resistance or for the improvement of 
temperature characteristics of dielectric constant On the other hand, as 
the piezo-electric materials, there have been reported characteristic 
compositions of composite perovskite compounds containing Mn. For example, 
in Japanese Patent Application Laid-Open No. 103486/1981, (Pb, 
Sr)TiO.sub.3 --(Mn1/3Sb.sub.2/3)O.sub.3 and the like have been disclosed. 
In the case that a trace amount of Mn is added to the ceramic composition, 
manganese carbonate (MnCO.sub.3) or MnO.sub.2 has often been used as a raw 
material which is insoluble in water and which has a small particle 
diameter, if water is used as a dispersant. 
On the other hand, there has been reported an example where a composite 
oxide as a raw material is used as one means for increasing a ratio of a 
product phase of a perovskite phase and for improving dielectric 
properties. For example, in Mat. Res. Bull., No. 17, p. 1245 (1982), 
Swartz et al. have reported that the employment of MgNb.sub.2 O.sub.6 in a 
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 system is effective to improve the 
dielectric properties, and on the other hand, Japanese Patent Application 
Laid-Open No. 94649/1989 has disclosed that it is effective for the 
improvement of the dielectric properties to use MgWO.sub.4 in a 
Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 system. 
Since the amount of Mn to be added or to be replaced is usually several mol 
% or less in terms of MnO, it is difficult to uniformly mix the same. As a 
means for uniformly mixing the trace amount of the component in the 
complex perovskite compound containing Mn, for example, Japanese Patent 
Application Laid-Open No. 54122/1991 has disclosed a technique for 
improving the characteristics by doing, in a solution, a synthesis with an 
organic metal compound such as a metal alkoxide as a raw material. 
However, when the synthesis is done by this technique, it is required to 
use a more expensive organic metal oxide as the raw material than a usual 
oxide, which is industrially disadvantageous. 
SUMMARY OF THE INVENTION 
Under such circumstances, one technical object of the present invention is 
to provide a novel manganese (Mn) containing complex oxide. 
In addition, another technical object of the present invention is to 
provide a process for preparing a complex perovskite compound composition 
using an Mn-containing complex oxide which can be used in multilayer 
ceramic capacitors and in which insulation resistance is less uneven and 
scarcely deteriorates. 
In order to achieve the above objects, the present inventors have 
intensively investigated, and as a result, it has been found that a novel 
complex oxide which can be used as a raw material is effective, and the 
use of this complex oxide as the raw material is also effective in 
preparing a complex perovskite compound containing lead. In consequence, 
the present invention has now been attained. 
That is to say, a first aspect of the present invention is directed to a 
manganese-containing complex oxide represented by the general formula 
(Mn.sub.a MeI.sub.1-a)MeII.sub.b O.sub.c wherein MeI is one of Mg, Ni and 
Zn; a is a value in the range of 0&lt;a.ltoreq.0.3; MeII is one of Nb, Ta and 
W; when MeII is Nb or Ta, b is 2 and c is 6, or when MeII is W, b is 1 and 
c is 4. Here, in the present invention, a is preferably a value in the 
range of 0.05.ltoreq.a.ltoreq.0.3. 
Furthermore, a second aspect of the present invention is directed to a 
process for preparing a ceramic composition comprising a complex 
perovskite compound which contains Mn and at least one of complex 
perovskite compounds represented by the general formula Pb(BIBII)O.sub.3 
wherein BI is one of Mg, Ni and Zn; and BII is one of Nb, Ta and W, 
wherein the complex oxide of the above first aspect is used. 
In addition, a third aspect of the present invention is directed to a 
process for preparing a complex perovskite compound composition wherein 2 
to 5 kinds of the complex perovskite compounds of the second aspect are 
used. 
In the preparation of the manganese-containing complex oxide of the present 
invention, a high temperature of 1,100 to 1,300.degree. C. is necessary 
and this temperature is much higher than a perovskite production 
temperature. Therefore, even if this complex oxide is used as a raw 
material of the complex perovskite compound, it does not decompose during 
the preparation process, and the trace component can be uniformly 
dispersed.

EXAMPLE 1 
In order to inspect a solid solubility limit of a complex oxide used as a 
raw material, (Mn.sub.x Ni.sub.1-X)Nb.sub.2 O.sub.6 and (Mn.sub.x 
Mg.sub.1-X)WO.sub.4 were used as raw materials of complex perovskite 
compounds, and X ray diffraction patterns in the case of 
0.ltoreq.x.ltoreq.0.40 were measured and then shown in FIGS. 1 and 2. 
Incidentally, a preparation process of this complex oxide will be 
described in undermentioned Example 2. 
It is apparent from FIGS. 1 and 2 that even when Mg, Ni and Zn of 
MgNb.sub.2 O.sub.6, NiNb.sub.2 O.sub.6 and ZnNb.sub.2 O.sub.6 having a 
columbite structure as well as MgWO.sub.4 having a wolframite structure 
(another name=a nickel tungstate type structure) were partially replaced 
with Mn, their crystalline structures did not change, and complex oxides 
having single structures were obtained in which a manganese oxide 
(Mn.sub.2 O.sub.3) was not observed on an X ray diffraction chart. In the 
respective cases, a replacement ratio is limited to 30%, and if the 
replacement ratio is higher than this level, Mn.sub.2 O.sub.3 appears on 
the X ray diffraction chart. In consequence, the obtained oxides cannot be 
considered any more to be the complex oxides having the single structures. 
These complex oxides containing Mn have not been referred to even in 
Inorganic Alphabetical Index (International Centre for Diffraction Data, 
1995) which is a compilation of X ray diffraction patterns of inorganic 
compounds synthesized until now. Therefore, these oxides can be judged to 
be novel substances. 
Here, a replacement ratio x of Mn is effective in the range of 
0&lt;x.ltoreq.0.30, but from the viewpoint of a ratio between an amount of 
MnO (conversion) to be added to the ceramic composition and a main 
component composition, the replacement ratio x is suitably in the range of 
0.05&lt;x.ltoreq.0.2. For example, when 0.5 mol % of MnO is added to a 
composition containing 30 mol % of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3, the 
replacement ratio of x.gtoreq.0.05 is required. If not so, it is necessary 
to add another manganese oxide such as MnCO.sub.3. On the contrary, if the 
replacement ratio x is too high, large amounts of MgO and Nb.sub.2 O.sub.5 
are supplementally required. In consequence, an uniform dispersion effect 
of manganese can be obtained, but there is a fear that reactions of the 
other oxides are not sufficiently carried out. 
Therefore, it is not preferable to heighten the replacement ratio x of Mn 
prior to the precipitation of the manganese oxide (Mn.sub.2 O.sub.3). 
EXAMPLE 2 
A composition comprising 4 kinds of complex perovskite compounds was used 
as a ceramic composition, and its composition ratio was 30 Pb(Mg.sub.1/3 
Nb.sub.2/3)O.sub.3 -50 Pb(Ni.sub.1/3 Nb.sub.2/3 O.sub.3 -20 PbTiO.sub.3 
+1.5 mol % of Pb(Mn.sub.1/3 Nb.sub.2/3 O.sub.3. As raw materials, PbO and 
(Mn.sub.0.3 Ni.sub.0.7)Nb.sub.2 O.sub.6 were used, and (Mn.sub.0.3 
Ni.sub.0.7)Nb.sub.2 O.sub.6 was obtained by weighing predetermined amounts 
of MnCO.sub.3, NiO and Nb.sub.2 O.sub.5, wet-mixing them together with 
lead core resin balls as a medium in a resin pot for 72 hours, calcining 
the mixture at 950 to 1000.degree. C. for 8 hours, wet-grinding the 
calcined mixture for 72 hours, further calcining it at 1,150 to 
1,200.degree. C. again, and then wet-grinding it for 72 hours again. The 
weighed materials were similarly wet-mixed together with the lead core 
resin balls as the medium in the resin pot for 72 hours, followed by 
filtration and drying. After calcination at 800 to 900.degree. C., the 
calcined material was mixed again in a wet state in the same manner for 72 
hours, followed by filtration. The resulting cake was dried and then 
ground to obtain a powder of the ceramic composition. The thus obtained 
dielectric powder was mixed with an organic solvent and a binder to 
prepare a slurry, and from this slurry, ceramic green sheets having 
thicknesses of 15.+-.2 .mu.m and 10.+-.1 .mu.m were formed in accordance 
with a doctor blade method. Next, printing was done with a silver 
palladium paste on the green sheets by a screen printing method to form 
internal electrodes thereon, and they were cut into a predetermined shape. 
After lamination and thermocompression bonding, they were cut into chips. 
The number of the laminated green sheets was in the range of 70 to 100. The 
respective cut chips were put side by side on a setter, and the binder was 
then removed at 400 to 500.degree. C. Afterward, the chips were fired in a 
predetermined profile in a rectangular shaped crusible. At this times a 
firing temperature was in the range of 1,000 to 1,100.degree. C. Next, a 
silver paste was applied onto the fired chips to form external electrodes, 
thereby obtaining a multilayer ceramic capacitor. 
An insulation resistance of the obtained multilayer ceramic capacitor was 
measured. This measurement was carried out by applying DC of 25 V to the 
sample, and then measuring a leak current after 60 seconds from the 
voltage application. An insulation resistance distribution at this time is 
shown as a sample 2 of the present invention in FIG. 3. 
For comparison, a ceramic composition having the same composition ratio as 
in the sample 2 of the present invention was prepared from raw materials 
of PbO, MgO, MnCO.sub.3, NiO, Nb.sub.2 O.sub.5 and TiO.sub.2 by the same 
procedure as in Example 2. By the use of this ceramic composition, a 
multilayer ceramic capacitor having the same structure as mentioned above 
was formed, and an insulation resistance of the sample was then measured. 
The thus measured insulation resistance is shown as a comparative sample 1 
together with the results of the sample 2 of the present invention in FIG. 
3. 
EXAMPLE 3 
A composition comprising 4 kinds of complex perovskite compounds was used 
as a ceramic in composition, and its composition ratio was 30 
Pb(Mg.sub.1/3 W.sub.1/2)O.sub.3 -30 Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -40 
PbTiO.sub.3 +1.5 mol % of Pb(Mn1/3Nb.sub.2/3)O.sub.3. As raw materials, 
PbO, (Mn.sub.0.3 Ni.sub.0.7)Nb.sub.2 O.sub.6, MgO, WO.sub.3, NiO, Nb.sub.2 
O.sub.5 and TiO.sub.2 were used, and (Mn.sub.0.3 Ni.sub.0.7)Nb.sub.2 
O.sub.6 which was one of these materials was obtained by weighing 
predetermined amounts of MnCO.sub.3, NiO and Nb.sub.2 O.sub.5, wet-mixing 
them together with lead core resin balls as a medium in a resin pot for 72 
hours, calcining the mixture at 950 to 1,000.degree. C. for 8 hours, 
wet-grinding the calcined mixture for 72 hours, further firing it at 1,150 
to 1,200.degree. C. again, and then wet-grinding it for 72 hours again. 
Afterward, a powder of the ceramic composition was prepared by the same 
procedure as in Example 2, and through the same process as in Example 2, a 
multilayer ceramic capacitor was obtained as a sample 3 of the present 
invention (however, the thickness of a green sheet was only 15.+-.2 
.mu.m). 
An insulation resistance of the obtained multilayer ceramic capacitor 
sample was measured in the same manner as in Example 2, and the thus 
measured insulation resistance is shown in FIG. 4. 
For comparison, a ceramic composition having the same composition ratio as 
in the sample 3 of the present invention was prepared from raw materials 
of PbO, MgO, WO.sub.3, MnCO.sub.3, NiO, Nb.sub.2 O.sub.5 and TiO.sub.2 by 
the same procedure as in Example 3. By the use of this ceramic 
composition, a multilayer ceramic capacitor having the same structure as 
mentioned above was formed as a comparative sample 2, and an insulation 
resistance of the sample was then measured. The thus measured insulation 
resistance is shown together with the results of the sample 3 of the 
present invention in FIG. 4. However, the thickness of a green sheet was 
only 15.+-.2 .mu.m. 
EXAMPLE 4 
A composition comprising 4 kinds of complex perovskite compounds was used 
as a ceramic composition, and its composition ratio was 30 Pb(Mg.sub.1/3 
W.sub.1/2)O.sub.3 -30 Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -40 PbTiO.sub.3 
+1.0 mol % of Pb(Mn.sub.1/2 W.sub.1/2)O.sub.3 as in Example 3. As raw 
materials, PbO, (Mn.sub.0.2 Mg.sub.0.8)WO.sub.4, MgO WO.sub.3, NiO, 
Nb.sub.2 O.sub.5 and TiO.sub.2 were used, and (Mn.sub.0.2 
Mg.sub.0.8)WO.sub.4 which was one of these materials was obtained by 
weighing predetermined amounts of MnCO.sub.3, MgO and WO.sub.3, wet-mixing 
them together with lead core resin balls as a medium in a resin pot for 72 
hours, calcining the mixture at 1,150 to 1,200.degree. C. for 8 hours, 
wet-grinding the calcined mixture for 72 hours, further firing it at 1,200 
to 1,250.degree. C. again, and then wet-grinding it for 72 hours again. 
Afterward, a powder of the ceramic composition was prepared by the same 
procedure as in Example 2, and through the same process as in Example 2, a 
multilayer ceramic capacitor was obtained as a sample 4 of the present 
invention. However, the thickness of a green sheet was only 15.+-.2 .mu.m. 
An insulation resistance of the obtained multilayer ceramic capacitor 
sample was measured in the same manner as in Example 2, and the thus 
measured insulation resistance is shown in FIG. 5. 
Usual oxides of all the raw materials in the sample 4 of the present 
invention were the same as in comparative sample 2 of the multilayer 
ceramic capacitor. Therefore, for comparison, the measured insulation 
resistance of the comparative sample 2 is shown together with the results 
of the sample 4 of the present invention in FIG. 5. 
EXAMPLE 5 
A composition comprising 4 kinds of complex perovskite compounds was used 
as a ceramic composition, and its composition ratio was 45 Pb(Mg.sub.1/2 
W.sub.1/2)O.sub.3 -25 Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 -30 PbTiO.sub.3 
+1.5 mol % of Pb(Mn.sub.1/3 Nb.sub.2/3)O.sub.3. As raw materials, PbO, 
(Mn.sub.0.1 Zn.sub.0.9)Nb.sub.2 O.sub.6, MgO, WO.sub.3, ZnO, Nb.sub.2 
O.sub.5 and TiO.sub.2 were used, and (Mn.sub.0.1 Zn.sub.0.9)Nb.sub.2 
O.sub.6 which was one of these materials was obtained by weighing 
predetermined amounts of MnCO.sub.3, ZnO and Nb.sub.2 O.sub.5, wet-mixing 
them together with lead core resin balls as a medium in a resin pot for 72 
hours, calcining the mixture at 1,200 to 1,250.degree. C. for 8 hours, 
wet-grinding the calcined mixture for 72 hours, further firing it at 1,300 
to 1,350.degree. C. again, and then wet-grinding it for 72 hours again. 
Afterward, a powder of the ceramic composition was prepared by the same 
procedure as in Example 2, and through the same process as in Example 2, a 
multilayer ceramic capacitor was obtained as a sample 5 of the present 
invention. However, the thickness of a green sheet was only 15.+-.2 .mu.m. 
An insulation resistance of the obtained multilayer ceramic capacitor 
sample was measured in the same manner as in Example 2, and the thus 
measured insulation resistance is shown in FIG. 6. 
For comparison, a ceramic composition having the same composition ratio as 
in the sample 5 of the present invention was prepared from raw materials 
of PbO, MgO, WO.sub.3, MnCO.sub.3, ZnO, Nb.sub.2 O.sub.5 and TiO.sub.2 by 
the same procedure as in Example 5. By the use of this ceramic 
composition, a multilayer ceramic capacitor having the same structure as 
mentioned above was formed as a comparative sample 3, and an insulation 
resistance of the sample was then measured. The thus measured insulation 
resistance is shown together with the results of the sample 5 of the 
present invention in FIG. 6. However, the thickness of a green sheet was 
only 15.+-.2 .mu.m. 
As described in Examples 2 to 5, when an insulation resistance of a 
multilayer ceramic capacitor sample made of a powder of a complex 
perovskite compound obtained in the case that a complex oxide containing 
Mn regarding the present invention is used as a raw material is compared 
with that of a multilayer ceramic capacitor sample made of a powder of a 
complex perovskite compound obtained in the case that a usual oxide is 
used as a raw material, it is apparent from FIGS. 3 to 6 that the 
unevenness of the insulation resistance is smaller and the deterioration 
of the insulation resistance is also smaller in the case that the complex 
oxide in Example 1 regarding the present invention is used as the raw 
material As described above, according to the present invention, there can 
be provided an Mn-containing complex oxide which can be used in a 
multilayer ceramic capacitor and in which insulation resistance is less 
uneven and scarcely deteriorates, and a process for preparing a complex 
perovskite compound composition by the use of the Mn-containing complex 
oxide.