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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to high dielectric constant type ceramic
compositions, and, in particular, to high dielectric constant type ceramic
compositions which are capable of sintering at low temperatures, which
have excellent electrical characteristics such as high insulation
resistance and which are suitable for producing multilayer ceramic
capacitors or the like. And this invention relates to multilayer ceramic
capacitors produced by using such compositions as dielectrics.
Electrical characteristics which must be considered for dielectric
materials include dielectric constant, temperature coefficient of
dielectric constant (T.C.C.), dielectric loss, bias electric field
dependence of dielectric constant, capacitance-resistance product and the
like.
In particular, it is required that the capacitance-resistance product (CR
product) be amply high. For example, Standards of Electronic Industries
Association of Japan (EIAJ) stipulates, in the standards RC-3698B,
entitled "Multilayer ceramic capacitors (chip-type) for electronic
equipment", that the CR product be at least 500 M.OMEGA..multidot..mu.F at
room temperature. Further it is required to maintain the high CR product
even at higher temperatures so that capacitors can be used under even more
severe conditions. (For example, Military Specification MIL-C-55681B
stipulates a CR product at 125.degree. C.)
In the case of multilayer type elements, it is necessary to use internal
electrode materials which can withstand even at the sintering temperatures
of dielectric materials, because the electrode layers and the dielectric
layers are co-fired. Accordingly, if the sintering temperatures of the
ceramic dielectric materials are high, expensive precious metals such as
platinum (Pt) or palladium (Pd) must be used as internal electrodes not to
react mutually. Therefore, a requirement is that sintering be possible at
lower temperatures of the order of 1100.degree. C. or below so that
inexpensive metal such as silver (Ag) based alloy can be used.
A conventional high dielectric constant type ceramic composition is a solid
solution containing barium titanates (BaTiO.sub.3) as the base materials
and stannates, zirconates, titanates, etc. as additives. It is certainly
possible to obtain a composition having a high dielectric constant, but
such a composition has problems. If the dielectric constant becomes high,
then T.C.C. becomes large. Further, the bias electric field dependence
becomes large. Furthermore, since the sintering temperatures of the
BaTiO.sub.3 -based materials are as high as 1,300.degree. to 1,400.degree.
C., high-temperature resistant expensive precious metals such as platinum
or palladium should be used for the internal electrode materials, thus
resulting in cost augmentation.
In order to overcome the above mentioned problems of the BaTiO.sub.3 -based
materials, extensive studies are being carried out on a variety of
low-firing type compositions. For example, Japanese Patent Laid-Open Pub.
No. 57204/1980 discloses a Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 -based
composition; Japanese Patent Laid-Open Pub. No. 51758/1980 discloses a
Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 -based composition; and Japanese Patent
Laid-Open Pub. No. 21662/1977 discloses a Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3
-based composition.
The Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 -based composition is accompanied by
the following problems. The sintering temperature dependence of the CR
product is quite large. Particularly, the decrease of the CR product at a
higher temperature such as at 85.degree. C. is large. The Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3 -based composition requires a relatively high sintering
temperature. Further, the Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 -based
composition is accompanied by the following problems. If the CR product is
large, then the dielectric constant is small. If the dielectric constant
is large, then the CR product is small. Furthermore, the T.C.C. of these
materials is superior to that of the barium titanate, but it is
insufficient.
Further, Japanese Patent Laid-Open Pub. No. 121959/1980 discloses a
composition comprising a solid solution of Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3 and lead titanate wherein if necessary a portion of Pb,
less than 10 mole %, is substituted by barium, strontium or calcium.
However, the T.C.C. of this composition cannot be said to be sufficient,
the T.C.C. of the best composition being -59.8% at a temperature range of
from -25.degree. to 85.degree. C. Further, Japanese Patent Laid-Open Pub.
No. 121959/1980 mentioned above does not describe the CR product which is
the most important property of a capacitor material, whereby the
usefulness of this composition as a capacitor material is uncertain.
Still further, Japanese Patent Laid-Open Pub. No. 25607/1982 discloses a
solid solution of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 and Pb(Zn.sub.1/3
Nb.sub.2/3)O.sub.3. However, this publication describes neither the CR
product nor the T.C.C. Thus, the usefulness of this material as a
capacitor material is also uncertain.
An object of the present invention is therefore to provide a high
dielectric constant type ceramic composition wherein the following
problems of the prior art are overcome:
(1) the sintering temperature is high;
(2) when the dielectric constant is large, the CR product is small; and
(3) the CR product (insulation resistance) at high temperatures is small;
wherein the dielectric constant and insulation resistance are high;
wherein such a composition can be sintered at low temperatures; and
wherein it has excellent electrical characteristics.
Another object of the present invention is to provide a multilayer ceramic
capacitor produced through the use of such a composition.
SUMMARY OF THE INVENTION
The present invention is directed to a ceramic composition wherein a
portion of Pb of a ternary diagram of lead zinc niobate (Pb(Zn.sub.1/3
Nb.sub.2/3)O.sub.3), lead magnesium niobate (Pb(Mg.sub.1/3
Nb.sub.2/3)O.sub.3) and lead titanate (PbTiO.sub.3) is substituted by
calcium, and more particularly to a high dielectric constant type ceramic
composition, characterized in that when said composition is represented by
the general formula:
xPb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 --
yPb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 --zPbTiO.sub.3,
a portion of Pb of the composition within lines connecting the following
points of the ternary composition diagram shown in the accompanying FIG. 1
having apexes of respective components, is substituted by from 2 to 30
mole % of calcium:
______________________________________
a: (x = 0.60, y = 0.40, z = 0.00)
b: (x = 0.60, y = 0.05, z = 0.35)
c: (x = 0.45, y = 0.05, z = 0.50)
d: (x = 0.01, y = 0.49, z = 0.50)
e: (x = 0.01, y = 0.85, z = 0.14)
f: (x = 0.15, y = 0.85, z = 0.00)
______________________________________
The present invention is directed to a high dielectric constant type
ceramic composition wherein, when lead and calcium elements are
represented by A, further, zinc, magnesium, niobium and titanium elements
are represented by B, and the chemical formula of the complex compound is
represented by ABO.sub.3, the molar ratio of A to B is in the range shown
in the following formula:
1.00 .ltoreq.A/B <1.10
The present invention is directed to a high dielectric constant type
ceramic composition which optionally further comprises at least one of
manganese, cobalt, nickel and chromium additionally included therein in an
amount of up to 1.0 mole % on the basis of MnO, CoO, NiO and Cr.sub.2
O.sub.3.
The present invention is directed to a multilayer ceramic capacitor having
at least a pair of internal electrodes and produced through the use of
such compositions as dielectrics.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is a ternary composition diagram indicating the compositional ranges
of ceramic compositions according to this invention.
DETAILED DESCRIPTION OF THE INVENTION
The compositional ranges of the composition according to the present
invention will now be described.
A ceramic composition according to the present invention is a high
dielectric constant type ceramic composition, characterized in that when
said composition is represented by the general formula
xPb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 --
yPb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 --zPbTiO.sub.3,
a portion of Pb of the composition within lines connecting the following
points of the ternary composition diagram shown in the accompanying FIG. 1
having apexes of respective components, is substituted by from 2 to 30
mole % of calcium:
______________________________________
a: (x = 0.60, y = 0.40, z = 0.00)
b: (x = 0.60, y = 0.05, z = 0.35)
c: (x = 0.45, y = 0.05, z = 0.50)
d: (x = 0.01, y = 0.49, z = 0.50)
e: (x = 0.01, y = 0.85, z = 0.14)
f: (x = 0.15, y = 0.85, z = 0.00)
______________________________________
In a region (1) wherein the content of Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 is
more than line a-b, the dielectric constant is small (no more than 3,000)
and the insulation resistance is small (no more than 10.sup.10
.OMEGA..multidot.cm at 25.degree. C.).
In a region (2) wherein the content of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 is
less than line b-c, the dielectric constant is small (no more than 3,000)
and the CR product at room temperature is no more than
1000.OMEGA..multidot.F.
In a region (3) wherein the content of PbTiO.sub.3 is more than line c-d,
many pores are formed in the sintered bodies, satisfactory ceramics are
not obtained, the insulation resistance is no more than 10.sup.10
.OMEGA..multidot.cm and the CR product is extremely small.
In a region (4) wherein the content of Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 is
less than line d-e, the sintering temperature exceeds 1,100.degree. C.,
and the insulation resistance is low.
In a region (5) wherein the content of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 is
more than line e-f, the sintering temperature is high and the CR product
is no more than 1,000 .OMEGA..multidot.F.
When b is b'(x=0.6, y=0.2, z=0.2) and c is c'(x=0.3, y=0.2, and z=0.5), a
region wherein the content of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 is more
than line b'-c' is more preferable, and a ceramic composition having a
dielectric constant of at least 5,000 is obtained.
When e is e'(x=0.01, y=0.8, and z=0.19) and f is f'(x=0.5, y=0.5, and z=0),
a region wherein the content of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 is less
than line e'-f' is more preferable, and there is obtained a ceramic
composition wherein the CR product is at least 1,000 even at high
temperatures.
The temperature dependence of dielectric constant is largely influenced by
the Curie temperature (Tc). However, when a portion of Pb of a composition
within the a-b-c-d-e-f region is substituted by Ca, the variation is
inhibited within the range of from +22% to -56% at a temperature range of
from -30.degree. C. to +85.degree. as compared with that at room
temperature. Thus, characteristics satisfying the U.S. Specification
EIAY5U can be obtained.
The amount of Ca by which Pb is substituted is from 2 mole% to 30 mole%. If
the amount of Ca is less than 2 mole%, the sintering temperature will
exceed 1,100.degree. C., and the CR product will be less than 1,000
.OMEGA..multidot.F. If the amount of Ca is more than 30 mole%, many pores
will be formed in sintered bodies, the insulation resistance will be less
than 10.sup.10 .OMEGA..multidot.cm and the CR product will be extremely
reduced. Accordingly, the amount of Ca by which Pb is substituted is to be
from 2 to 30 mole%.
In a preferred ceramic composition of the present invention, when Pb and Ca
elements are represented by A, further, Zn, Mg, Nb and Ti elements are
represented by B, and the chemical formula of the complex compound is
represented by ABO.sub.3, the molar ratio of A to B is
1.00.ltoreq.A/B<1.10. If the molar ratio is less than 1.00, the dielectric
constant will be reduced and the dielectric loss will exceed 1.5%. Thus,
the molar ratio of less than 1.00 is impractical.
The molar ratio of more than 1.10 is undesirable because the insulation
resistance begins to decrease. Accordingly, the molar ratio of A to B is
to be in the range of 1.00.ltoreq.A/B<1.10. When Pb is substituted by Ba
or Sr rather than Ca, the molar ratio of A to B of more than 1.00 reduces
the dielectric constant as opposed to Ca substitution. It is believed that
this shows that the substitution of Pb by Ca cannot be dealt in the same
manner as in the case of Ba or Sr substitution. However, the reasons why
Ca substitution is different from Ba or Sr substitution are not entirely
apparent.
The ceramic composition of the present invention is based on the complex
compound represented by the general formula described above. This
composition is shown on the basis of oxides as follows:
______________________________________
PbO 55.15-72.27
wt %
ZnO 0.08- 5.91
wt %
MgO 0.20- 4.20
wt %
Nb.sub.2 O.sub.5 13.60-31.27
wt %
TiO.sub.2 0.00-15.12
wt %
CaO 0.34-6.57 wt %
______________________________________
Impurities, additives, substituents and the like may be contained without
impairing the effects of the present invention. For example, in addition
to MnO, CoO, NiO and Cr.sub.2 O.sub.3 already stated, Sb.sub.2 O.sub.3,
ZrO.sub.2, La.sub.2 O.sub.3 or the like can be used. The content of such
additives is about 1% by weight at most.
Processes for producing the present composition will be described
hereinafter.
Oxides of Pb, Ca, Zn, Nb, Ti and Mg, or precursors which are converted into
oxides during the sintering step, for example salts such as carbonates and
oxalates, hydroxides, and organic compounds are used as starting materials
and weighed in a predetermined proportion. They are thoroughly mixed and
then calcined. This calcination is carried out at a temperature of from
about 700.degree. to about 850.degree. C. If the calcination temperature
is too low, the density of sintered bodies will be reduced. If the
calcination temperature is too high, the density of the sintered bodies
will be reduced and the insulation resistance will decrease. The calcined
material is then pulverized to produce powder. It is preferable that the
average grain size of the powder be from about 0.8 to 2 micrometers. If
the average grain size is too large, pores present in the sintered bodies
will be increased. If the average grain size is too small, then easiness
of forming will be reduced. Such a calcined and pulverized powder is used
and formed into a desired shape. Thereafter, the formed product is
sintered to obtain high dielectric constant type ceramics. The sintering
can be carried out at a relatively low temperature of 1,100.degree. C. or
below, preferably from about 900.degree. to about 1,050.degree. C. by
using the composition of the present invention.
When elements of multilayer type are produced, the following procedure can
be used. A binder, a solvent and the like are added to the powder
described above to prepare a slurry. The slurry is formed into green
sheets, and internal electrodes are printed on the green sheets.
Thereafter, the predetermined number of green sheets are laminated,
pressed and sintered to produce the elements. Since the dielectric
material of the present invention can be sintered at a low temperature,
inexpensive metals such as Ag-based materials can be used as the internal
electrodes.
The present compositions can be sintered at a relatively low temperature of
1,100.degree. C. or below, preferably from 900.degree. to 1,050.degree. C.
The present compositions have stable and excellent electrical
characteristics as follows:
______________________________________
Dielectric constant
3,000 (25.degree. C.) or above
Dielectric loss 2.0% or below
CR product 2,000 .OMEGA. .multidot. F (25.degree. C.) or above
CR product 500 .OMEGA. .multidot. F (125.degree. C.) or above
Insulation resistance
10.sup.12 .OMEGA. .multidot. cm or above
Temperature dependence
+22% through -56%
of dielectric constant
(at -30.degree. C. through +85.degree. C.)
______________________________________
The present compositions have an excellent direct-current bias voltage
dependence, for example, of within 45% under 1 KV/mm, and excellent
mechanical strength. Further, the present compositions are effective as
materials for multilayer capacitor wherein internal electrodes and
dielectric layers are laminated and cofired, because the present
compositions can be sintered at a temperature as low as
900.degree.-1,050.degree. C. In this case, low melting metals such as Ag,
Cu, Ni or Al, which are relatively inexpensive as compared with Pd or Pt,
can be used as materials from which internal electrodes are produced. The
use of such materials contributes to reduction in cost. Further, even if
the present compositions are used in infinitesimal displacement elements
which utilize piezoelectric/electrostrictive effects, the change of
characteristics due to temperatures is little.
Since the present compositions can be sintered at a low temperature as
described above, they are also effective as paste materials for thick film
dielectrics which are to be printed on circuit substrates or the like and
sintered. In this case, even if the partial pressure of oxygen is lowered,
the fundamental characteristics are not reduced and therefore the present
compositions are useful. The incorporation of at least one of manganese,
cobalt, nickel and chromium into such compositions at a level of up to 1
mole % on the basis of their oxides can reduce the dielectric loss and
improve their sinterability, and thus good characteristics can be
obtained. If the amount of such metals is more than 1 mole %, the
insulation resistance will be reduced and the dielectric loss will be
increased. Thus, the maximum content of such metals is 1 mole %.
As stated hereinbefore, according to the present invention, high dielectric
constant type ceramic compositions which have high dielectric constant and
insulation resistances, can be sintered at low temperatures, and have
excellent electrical characteristics can be obtained. Further, according
to the present invention, excellent multilayer ceramic capacitors produced
by using such ceramic compositions can be obtained.
The following non-limiting examples are set forth to illustrate the present
invention more fully.
EXAMPLES 1 to 12
Starting materials such as oxides of Pb, Ca, Zn, Nb, Ti and Mg were mixed
by means of a ball mill or the like. The mixtures were calcined at a
temperature of from 700.degree. to 850.degree. C. The calcined materials
were then milled by means of the ball mill or the like and dried to
prepare powder. A binder was added to the powder. The mixtures were
granulated and pressed to form disk-like specimens each having a diameter
of 17 mm and a thickness of about 2 mm. In order to prevent contamination
of impurities, it is preferable that balls having high values of hardness
and toughness such as partially stabilized zirconia balls be used as the
balls for mixing/milling.
These formed specimens were sintered for 2 hours in air at a temperature of
from 900.degree. to 1,050.degree. C., and silver electrodes were printed
on the main surfaces of the sintered specimens to measure dielectric
electrical properties. Their dielectric loss and capacitance were measured
by using a digital LCR meter under 1 KHz and 1 Vrms at 25.degree. C. Their
dielectric constant was calculated from the data of size of the specimen
and capacitance measured. Further, their insulation resistance values were
calculated from the data measured by applying a voltage of 100 V for 2
minutes by using an insulation resistance meter. The temperature
coefficient of capacitance was determined by using a value at 25.degree.
C. as a standard and examining the percent change at -30.degree. C. and
standard and examining the percent change at -30.degree. C. and 85.degree.
C., respectively. Capacitance-resistance product was determined from
(dielectric constant) x (insulation resistance) x (dielectric constant in
vacuo) at 25.degree. C. and 125.degree. C., respectively. The measurement
of insulation resistance was carried out in silicone oil in order to
exclude the effect of moisture in air. The results are shown in Table 1.
TABLE 1
Temperature Insulation CR CR Coefficient of
Dielectric Dielectric Resistance Product Product Capacitance Composition
(mole) PbO CaO ZnO MgO Nb.sub.2
O.sub.5 TiO.sub.2 Constant Loss .rho.25.degree. C. 25.degree. C.
125.degree. C. (%) x y z a (wt %) (wt %) (wt %)(wt %) (wt %) (wt
%)K25.degree. C. DF (%) (.OMEGA. .multidot. cm) (.OMEGA. .multidot. F)
(.OMEGA. .multidot. F) -30.degree. C. +85.degree.
C. Exam. 1 0.54 0.44 0.02 0.075
64.59 1.32 4.58 1.85 27.16 0.50 5,400 0.8 8.0 .times. 10.sup.12 3,800
1,060 -53 -41 2 0.5 0.3 0.2 0.16 62.30 2.98 4.51 1.34 23.56 5.31 5,600
0.7 1.7 .times. 10.sup.13 8,400 2,400 -52 -39 3 0.5 0.1 0.4 0.26 59.03
5.21 4.85 0.48 19.00 11.42 3,100 0.7 1.6 .times. 10.sup.13 4,400 1,300
-52 -36 4 0.34 0.33 0.33 0.20 61.75 3.88 3.19 1.53 20.53 9.12 7,700 0.8
1.8 .times. 10.sup.13 12,300 3,400 -54 -45 5 0.1 0.4 0.5 0.245 61.37
5.00 0.99 1.96 16.13 14.55 14,600 0.9 1.0 .times. 10.sup.13 12,900 3,700
-53 -47 6 0.1 0.5 0.4 0.195 63.01 3.83 0.95 2.36 18.64 11.21 15,300 0.9
1.4 .times. 10.sup.13 19,000 5,700 -55 -48 7 0.01 0.7 0.29 0.125 65.52
2.35 0.09 3.16 21.11 7.77 19,200 0.9 8.2 .times. 10.sup.12 13,900 3,900
-55 -47 8 0.1 0.7 0.2 0.09 66.13 1.64 0.88 3.06 23.08 5.20 16,300 0.9
1.1 .times. 10.sup.13 15,900 4,100 -53 -48 9 0.3 0.5 0.2 0.125 64.24
2.31 2.68 2.21 23.32 5.26 9,700 0.8 1.9 .times. 10.sup.13 16,300 4,900
-55 -47 10 0.3 0.6 0.1 0.075 65.63 1.34 2.59 2.56 25.35 2.54 10,300 0.8
1.7 .times. 10.sup.13 15,500 5,300 -54 -48 11 0.3 0.7 0 0.025 66.92 0.43
2.50 2.89 27.25 0.00 10,800 0.8 6.5 .times. 10.sup.12 6,200 980 -52 -45
12 0.1 0.8 0.1 0.04 67.44 0.71 0.85 3.38 25.10 2.51 17,000 0.9 1.6
.times. 10.sup.12 2,400 920 -54 -53 Ref. Exam. 1 0.8 0.1 0.1 0.155 61.22
2.82 7.04 0.44 25.89 2.59 200 0.6 3 .times. 10.sup.9 0.05 0.002 +10 -8
2 0.05 0.9 0.05 0 68.71 0.00 0.42 3.72 25.91 1.23 21,000 3.4 3.3 .times.
10.sup.11 620 170 -57 -48 3 0.1 0.1 0.8 0.4 55.33 9.27 1.12 0.56 7.32
26.41 650 0.8 2 .times.
10.sup.9 0.12 0.03 -30 +68
As can be seen from Table 1, the ceramic compositions having a dielectric
constant of from 3,000 to 19,000 or above and a dielectric loss of no more
than 2.0% according to the present invention can be sintered at low
temperature of no more than 1,100.degree. C., for example, from
900.degree. C. to 1,050.degree. C. Further, the insulation resistance is
large (at least 10.sup.12 .OMEGA..multidot.cm) and the reduction in
insulation resistance is extremely small even at elevated temperatures.
This is apparent from the fact that the CR product is large (from 800 to
5,000 .OMEGA..multidot.F at 125.degree. C.). Furthermore, the temperature
characteristics of the dielectric constant are good (within -56% at a
temperature of from -30.degree. to +85.degree. C.).
For comparison, Reference Examples will be described.
Reference Example 1 is a comparative example belonging to the region (1)
described above. The dielectric constant is small, and thus the
composition described in Reference Example 1 is impractical.
Reference Example 2 is a comparative example belonging to the region (5)
described above. The CR product is reduced, sintering is insufficient at a
temperature of from 900.degree. C. to 1,050.degree. C., and the mechanical
strength is weakened.
Reference Example 3 is a comparative example belonging to the region (3)
described above. Both the dielectric constant and the CR product are
reduced, and thus the composition described in Reference Example 3 is
impractical.
EXAMPLES 13 and 14
The ceramic compositions were prepared as in Examples 1 to 12 except that
the molar ratio of A to B was varied (Examples 13 and 14 and Reference
Example 4). The results are shown in Table 2. Reference Examples wherein
Pb was substituted by Ba or Sr rather than Ca are shown in Table 2 as
Reference Examples 5 to 8.
TABLE 2
Insula- Dielec- tion CR Temperature tric
Dielec- Resist- CR Pro- Coefficient of Cons- tric ance Product
duct Capacitance Composition (mole) PbO CaO ZnO MgO Nb.sub.2 O.sub.5
TiO.sub.2 tant Loss .rho.25.degree. C. 25.degree. C 125.degree. C. (%) x y
z a A/B (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) K25.degree. DF (%)
(.OMEGA. .multidot. cm) (.OMEGA. .multidot. F) (.OMEGA. .multidot. F)
-30.degree. C. +85.degree.
C. Exam.
13 0.3 0.5 0.2 (Ca) 0.1 1.03 65.81 1.84 2.59 2.14 22.55 5.08 13,300 1.2
2.0 .times. 10.sup.13 23,600 6,600 -51 -38 14 0.3 0.5 0.2 (Ca) 0.1 1.00
65.18 1.82 2.64 2.18 23.00 5.18 10,800 1.5 1.3 .times. 10.sup.13 12,400
3,500 -53 -35 Ref. Exam. 4 0.3 0.5 0.2 (Ca) 0.1 0.97 64.52 1.80 2.69
2.22 23.47 5.29 7,400 3.3 7.2 .times. 10.sup.12 4,700 1,300 -64 -29 5
0.3 0.5 0.2 (Ba) 0.125 1.03 62.35 (BaO) 6.12 2.52 2.08 21.97 4.95 7,200
0.7 2.0 .times. 10.sup.13 12,700 3,600 -25 -25 6 0.3 0.5 0.2 (Ba) 0.125
1.00 61.77 (BaO) 6.06 2.57 2.12 22.42 5.05 9,300 0.8 1.9 .times.
10.sup.13 15,600 4,500 -32 -30 7 0.3 0.5 0.2 (Sr) 0.1 1.03 64.81 (SrO)
3.34 2.55 2.10 22.20 5.00 7,900 0.5 2.1 .times. 10.sup.13 14,700 4,400
-28 -35 8 0.3 0.5 0.2 (Sr) 0.1 1.00 64.19 (SrO) 3.31 2.60 1.15 22.65
5.11 10,500 0.6 2.0 .times.
10.sup.13 18,600 5,600 -33 -38
As can be seen from Table 2, when the molar ratio of A to B was
1.0.ltoreq.A/B <1.10, good results were obtained wherein the dielectric
constant was particularly high and the insulation resistance was high.
Reference Example 4 was one wherein the molar ratio of A to B was 0.97. It
is apparent that the dielectric constant is reduced and the dielectric
loss is increased.
Further, Reference Examples 5 to 8 show those wherein Pb was substituted by
Ba or Sr in place of Ca and the molar ratio of A to B was varied. When the
molar ratio of A to B is more than 1, the dielectric constant is reduced.
This is a tendency contrary to Ca substitution and is a new discovery
which suggests that Ba and Sr cannot be put in the same category with Ca.
EXAMPLES 15 to 26
Examples wherein at least one of MnO, CoO, NiO and Cr.sub.2 O.sub.3 was
incorporated in the composition described in Example 4 are shown in Table
3 as Examples 15 to 26.
Comparative example wherein 2 mole % of MnO was incorporated in the
composition described in Example 4 is shown in Table 3 as Reference
Example 9.
TABLE 3
Dielec- Temperature tric Dielec- Insulation CR CR Coefficient
of Cons- tric Resistance Product Product Capacitance Composition
(mole) Fundamental Composition (wt %) Additive tant Loss .rho.25.degree.
C. 25.degree. C. 125.degree. C. (%) x y z a PbO CaO ZnO MgO Nb.sub.2
O.sub.5 TiO.sub.2 (mole %) K25.degree. DF (%) (.OMEGA. .multidot. cm)
(.OMEGA. .multidot. F) (.OMEGA. .multidot. F) -30.degree. C. +85.degree.
C.
Exam. 4 0.34 0.33 0.33 0.20 61.75 3.88 3.19 1.53
20.53 9.12 0 7,700 0.8 1.8 .times. 10.sup.12 12,300 3,400 -54 -45 15 " "
" " " " " " " " (MnO) 0.05 7,600 0.7 1.7 .times. 10.sup.13 11,000 3,000
-51 -45 16 " " " " " " " " " " 0.1 7,500 0.7 1.6 .times. 10.sup.12
10,600 2,700 -54 -44 17 " " " " " " " " " " 0.2 6,800 0.5 1.4 .times.
10.sup.13 8,200 1,900 -55 -42 18 " " " " " " " " " " 0.5 6,100 0.3 1.2
.times. 10.sup.13 6,500 1,400 -51 -39 19 " " " " " " " " " " 1.0 5,200
0.5 1.0 .times. 10.sup.13 4,600 1,010 -45 -37 Ref. 0.34 0.33 0.33 0.20
61.75 3.88 3.19 1.53 20.53 9.12 2.0 3,900 1.1 5.1 .times. 10.sup.12
1,700 340 -31 -33 Exam. 9 Exam. 20 0.34 0.33 0.33 0.20 61.75 3.88 3.19
1.53 20.53 9.12 (CoO) 0.2 7,600 0.5 1.3 .times. 10.sup.13 8,700 2,200
-55 -42 21 " """""""""0.5 6,300 0.3 1.3 .times. 10.sup.13 7,300 1,500
-53 -40 22 " """""""""(NiO) 0.5 6,200 0.5 1.2 .times. 10.sup.13 6,600
1,300 -54 -40 23 " """""""""(Cr.sub.2 O.sub.3) 0.5 6,200 0.4 1.3 .times.
10.sup.13 7,100 1,400 -54 -39 24 " """""""""(MnO) 0.25 6,100 0.3 1.1
.times. 10.sup.13 5,900 1,200 -52 -41 (CoO) 0.25 25 "
"""""""""(MnO) 0.25 6,200 0.3 1.2 .times. 10.sup.13 6,600 1,300 -51 -40
(NiO) 0.25 26 " """"""""" (MnO) 0.25 6,000 0.4 1.3 .times.
10.sup.13 6,900 1,500 -50 -39 (Cr.sub.2
O.sub.3) 0.25
As can be seen from Table 3, the incorporation of at least one of
manganese, cobalt, nickel and chromium in an amount of up to 1 mole % (on
the basis of their oxides) in the ceramic compositions of the present
invention can reduce the dielectric loss, improve sinterability and
provide good characteristics. However, it is apparent from Reference
Example 9 that the addition of more than 1% of such an additive is
undesirable because this leads to an extreme reduction in dielectric
constant and reduction in insulation resistance particularly at elevated
temperatures.
EXAMPLE 27
A disk-like formed specimen having a diameter of 17 mm and a thickness of
about 2 mm was formed as in Example 1-12. This disk was heated to a
temperature of 500.degree. C. to burn out the binder and sintered for 15
minutes in a nitrogen atmosphere having a partial pressure of oxygen of
1.0.times.10.sup.-5 atm at a temperature of 900.degree. C. Gold electrodes
were deposited on the main surfaces of the sintered specimen. Its
characteristics were measured as in Examples 1 to 12.
For the composition wherein x=0.3, y=0.5, z=0.2, a=0.1, A/B=1.03 and
MnO=0.1 mole %, the following characteristics were obtained.
______________________________________
Dielectric Constant K 25.degree. C.
6,200
Dielectric Loss 1.9%
Insulation Resistance
.rho..sub.25.degree. C. 1.1 .times. 10.sup.13 .OMEGA.
.multidot. cm
CR Product at 25.degree. C.
6,000 .OMEGA. .multidot. F
Temperature Coefficient
at -30.degree. C. -39%
of capacitance at +85.degree. C. -31%
______________________________________
Further, Cu powder was simultaneously placed on the alumina substrate
during the sintering step and placed in a furnace. The resulting product
had a gloss of Cu metal powder after sintering.
Thus, according to the present invention, it is possible to satisfactorily
sinter in an atmosphere having a low partial pressure of oxygen.
EXAMPLES 28 to 39
Starting materials such as oxides of Pb, Ca, Zn, Nb, Ti and Mg were mixed
by means of a ball mill or the like. The mixtures were calcined at a
temperature of from 700.degree. C. to 850.degree. C. in ordinary air. The
calcined materials were then milled by means of the ball mill or the like
to prepare powder. A binder was added to the powder. The mixtures were
granulated and pressed to form disk-like specimens each having a diameter
of 17 mm and a thickness of about 2 mm.
The binder was burnt for 4 hours in air at a temperature of 500.degree. C.
and thereafter the disk specimen was sintered for one hour in a nitrogen
atmosphere having a partial pressure of oxygen of about 10.sup.-8 to
10.sup.-9 atm at a temperature of 950.degree. C. Aluminum electrodes were
formed on the main surfaces of the sintered specimens by vacuum evaportion
to measure dielectric and electrical properties. Their dielectric loss and
capacitance were measured by using a digital LCR meter under 1 KHz and 1
Vrms at 25.degree. C. Their dielectric constant was calculated from the
data of the size of the specimen and the capacitance measured. Further,
their insulation resistance values were calculated from the data measured
by applying a voltage of 100 V for 2 minutes by using an insulation
resistance meter. The temperature coefficient of capacitance was
determined by using a value at 25.degree. C. as a standard and examining
the percent change at -30.degree. C. and 85.degree. C., respectively.
Capacitance-resistance product was determined from (dielectric constant) x
(insulation resistance) x (dielectric constant in vacuo) at 25.degree. C.
and 125.degree. C., respectively. The measurement of insulation resistance
was carried out in silicone oil in order to exclude the effect of moisture
in air. The results are shown in Table 4.
TABLE 4
Temperature Insulation CR CR Coefficient of
Dielectric Dielectric Resistance Product Product Capacitance Composition
(mole) PbO CaO ZnO MgO Nb.sub.2
O.sub.5 TiO.sub.2 Constant Loss .rho.25.degree. C. 25.degree. C.
125.degree. C. (%) x y z a (wt %) (wt %) (wt %) (wt %) (wt %) (wt %)
K25.degree. C. DF (%) (.OMEGA. .multidot. cm) (.OMEGA. .multidot. F)
(.OMEGA. .multidot. F) -30.degree. C. +85.degree.
C. Exam. 28 0.54 0.44 0.02 0.075
64.59 1.32 4.58 1.85 27.16 0.50 5,200 0.9 7.5 .times. 10.sup.12 3,500
1,040 -53 -40 29 0.5 0.3 0.2 0.16 62.30 2.98 4.51 1.34 23.56 5.31 5,500
0.8 9.9 .times. 10.sup.12 4,800 2,200 -51 -38 30 0.5 0.1 0.4 0.26 59.03
5.21 4.85 0.48 19.00 11.42 3,050 0.8 1.3 .times. 10.sup.13 3,500 1,200
-51 -38 31 0.34 0.33 0.33 0.20 61.75 3.88 3.19 1.53 20.53 9.12 7,500 0.9
1.5 .times. 10.sup.13 10,000 3,300 -54 -44 32 0.1 0.4 0.5 0.245 61.37
5.00 0.99 1.96 16.13 14.55 13,800 1.0 8.5 .times. 10.sup.12 10,400 3,600
-53 -46 33 0.1 0.5 0.4 0.195 63.01 3.83 0.95 2.36 18.64 11.21 15,100 1.0
1.2 .times. 10.sup.13 16,000 5,400 -54 -46 34 0.01 0.7 0.29 0.125 65.52
2.35 0.09 3.16 21.11 7.77 18,900 1.0 8.0 .times. 10.sup.12 13,400 3,800
-55 -45 35 0.1 0.7 0.2 0.09 66.13 1.64 0.88 3.06 23.08 5.20 16,000 1.1
9.5 .times. 10.sup.12 13,500 4,000 -52 -47 36 0.3 0.5 0.2 0.125 64.24
2.31 2.68 2.21 23.32 5.26 9,500 0.9 1.5 .times. 10.sup.13 12,600 4,700
-54 -46 37 0.3 0.6 0.1 0.075 65.63 1.34 2.59 2.56 25.35 2.54 10,000 0.9
1.3 .times. 10.sup.13 11,500 5,200 -53 -47 38 0.3 0.7 0 0.025 66.92 0.43
2.50 2.89 27.25 0.00 10,500 0.9 4.8 .times. 10.sup.12 4,500 960 -51 -44
39 0.1 0.8 0.1 0.04 67.44 0.71 0.85 3.38 25.10 2.51 16,700 1.1 1.4
.times. 10.sup.12 2,100 910 -54 -52 Ref. Exam. 10 0.8 0.1 0.1 0.155
61.22 2.82 7.04 0.44 25.89 2.59 190 0.8 1.7 .times. 10.sup.9 0.03 0.002
+9 -10 11 0.05 0.9 0.05 0 68.71 0.00 0.42 3.72 25.91 1.23 20,000 4.2 1.5
.times. 10.sup.11 270 150 -57 -49 12 0.1 0.1 0.8 0.4 55.33 9.27 1.12
0.56 7.32 26.41 620 0.9 2 .times.
10.sup.9 0.11 0.03 -30 +65
As can be seen from Table 4, the ceramic compositions of the present
invention can be satisfactorily sintered in an atmosphere having a low
partial pressure of oxygen, and characteristics as good as those obtained
by sintering in air (Table 1) can be obtained. Reference Examples 10, 11
and 12 correspond to Reference Examples 1, 2 and 3 in which sintering was
carried out in air. All of the ceramic compositions described in Reference
Examples 10, 11 and 12 are impractical for the same reasons as given in
Reference Examples 1, 2 and 3.
EXAMPLES 40 and 41
The ceramic compositions of Reference Examples 40 and 41 and Reference
Example 13 were prepared as in Examples 28 to 39 except that the molar
ratio of A to B was varied. The results are shown in Table 5. Reference
Examples wherein Pb was substituted by Ba or Sr rather than Ca are shown
in Table 5 as Reference Examples 14 to 17.
TABLE 5
CR Temperature Dielec- Dielec- Insulation CR Pro-
Coefficient of tric tric Resistance Product duct Capacitance
Composition (mole) PbO CaO ZnO MgO Nb.sub.2 O.sub.5 TiO.sub.2 Constant
Loss .rho.25.degree. C. 25.degree. C. 125.degree. C. (%) x y z a A/B (wt
%) (wt %) (wt %) (wt %) (wt %) (wt %) K25.degree. C. DF (%) (.OMEGA.
.multidot. cm) (.OMEGA. .multidot. F) (.OMEGA. .multidot. F) -30.degree.
C. +85.degree.
C. Exam.
40 0.3 0.5 0.2 (Ca) 0.1 1.03 65.81 1.84 2.59 2.14 22.55 5.08
13,300 1.2 1.8 .times. 10.sup.13 21,200 6,400 -51 -37 41 0.3 0.5 0.2
(Ca) 0.1 1.00 65.18 1.82 2.64 2.18 23.00 5.18 10,400 1.6 1.2 .times.
10.sup.13 11,000 3,200 -52 -33 Ref. Exam. 13 0.3 0.5 0.2 (Ca) 0.1 0.97
64.52 1.80 2.69 2.22 23.47 5.29 6,500 3.5 3.8 .times. 10.sup.12 2,190
1,100 -63 -28 14 0.3 0.5 0.2 (Ba) 0.125 1.03 62.35 (BaO) 6.12 2.52 2.08
21.97 4.95 2,300 3.1 6.1 .times. 10.sup.10 12 -- -19 -19 15 0.3 0.5 0.2
(Ba) 0.125 1.00 61.77 (BaO) 6.06 2.57 2.12 22.42 5.05 4,200 4.2 5.8
.times. 10.sup.10 22 -- -22 -21 16 0.3 0.5 0.2 (Sr) 0.1 1.03 64.81 (SrO)
3.34 2.55 2.10 22.20 5.00 3,500 3.0 8.3 .times. 10.sup.10 26 -- -21 -24
17 0.3 0.5 0.2 (Sr) 0.1 1.00 64.19 (SrO) 3.31 2.60 2.15 22.65 5.11 5,100
3.5 7.9 .times.
10.sup.10 36 -- -23 -27
As can be seen from Table 5, when the molar ratio of A to B was
1.00.ltoreq.A/B<1.10, good results were obtained wherein the dielectric
constant was particularly high and the insulation resistance was high.
Reference Example 13 was one wherein the molar ratio of A to B was 0.97. It
is apparent that the dielectric constant is reduced and the dielectric
loss is increased.
Further, Reference Examples 14 to 17 show those wherein Pb was substituted
by Ba or Sr in place of Ca. It is apparent that the dielectric constants
and insulation resistances of the compositions substituted by Ba or Sr are
remarkably reduced as compared with those of the compositions substituted
by Ca.
EXAMPLES 42 to 53
Examples wherein at least one of MnO, CoO, NiO and Cr.sub.2 O.sub.3 was
incorporated in the composition described in Example 31 are shown in Table
6 as Examples 42 to 53.
Comparative example wherein 2 mole % of MnO was incorporated in the
composition described in Example 31 is shown in Table 6 as Reference
Example 18.
TABLE 6
Dielec- Temperature tric Dielec- Insulation CR CR Coefficient
of Cons- tric Resistance Product Product Capacitance Composition
(mole) Fundamental Composition (wt %) Additive tant Loss .rho.25.degree.
C. 25.degree. C. 125.degree. C. (%) x y z a PbO CaO ZnO MgO Nb.sub.2
O.sub.5 TiO.sub.2 (mole %) K25.degree. DF (%) (.OMEGA. .multidot. cm)
(.OMEGA. .multidot. F.) (.OMEGA. .multidot. F.) -30.degree.
C. +85.degree.
C. Exam.
31 0.34 0.33 0.33 0.20 61.75 3.88 3.19 1.53 20.53 9.12 0
7,500 0.9 1.5 .times. 10.sup.13 10,000 3,300 -54 -44 42 " " " " " " " "
" " (MnO) 0.05 7,400 0.8 1.5 .times. 10.sup.13 9,800 2,900 -50 -44 43 "
" " " " " " " " " 0.1 7,300 0.8 1.4 .times. 10.sup.13 9,050 2,600 -54
-43 44 " " " " " " " " " " 0.2 6,600 0.6 1.3 .times. 10.sup.13 7,600
1,800 -54 -41 45 " " " " " " " " " " 0.5 6,000 0.4 1.1 .times. 10.sup.13
5,800 1,300 -51 -40 46 " " " " " " " " " " 1.0 5,100 0.7 9.8 .times.
10.sup.12 4,400 980 -45 -38 Ref. 0.34 0.33 0.33 0.20 61.75 3.88 3.19
1.53 20.53 9.12 2.0 3,800 1.3 5.0 .times. 10.sup.11 170 120 -31 -34
Exam. 18 Exam. 47 0.34 0.33 0.33 0.20 61.75 3.88 3.19 1.53 20.53 9.12
(CoO) 0.2 6,600 0.6 1.4 .times. 10.sup.13 8,200 2,100 -54 -41 48 " " " "
" " " " " " 0.5 6,100 0.4 1.3 .times. 10.sup.13 7,000 1,400 -53 -39 49 "
" " " " " " " " " (NiO) 0.5 6,100 0.6 1.2 .times. 10.sup.13 6,500 1,200
-53 -39 50 " " " " " " " " " " (Cr.sub.2 O.sub.3) 0.5 6,000 0.5 1.2
.times. 10.sup.13 6,400 1,20 | | |
