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Description  |
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BACKGROUND OF THE INVENTION
1. (Field of the Invention)
The present invention relates to a dielectric ceramic composition. More
specifically, the invention relates to a dielectric ceramic composition
which contains BaTiO.sub.3 as a chief component, as well as Nb.sub.2
O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and
MnO, and which can be preferably used as a material of ceramic capacitors
and resonators.
2. (Description of the Related Art)
Dielectric ceramic compositions have heretofore been used as materials for
multi-layer ceramic capacitors. Such a multi-layer ceramic capacitor is
fabricated by stacking plural pieces of a green sheet of a dielectric
ceramic composition having an internal electrode formed therein such that
a predetermined capacitance is obtained followed by firing as a unitary
structure. For instance, a dielectric ceramic composition used for a
multi-layer ceramic capacitor of X7R (EIA Standards: change of capacitance
is within .+-.15% over a temperature range of from -55.degree. C. to
+125.degree. C.) has a dielectric constant of as high as not smaller than
2500 at +25.degree. C., and has a thickness of not larger than 15 .mu.m
per a piece of green sheet. It is important here that the firing
temperature is not higher than, for example, 1300.degree. C.
That is, by employing a green sheet having a dielectric constant of not
smaller than 2500 at 25.degree. C. and a thickness of not larger than 15
.mu.m, it is allowed to minimize the thickness of the raw green between
the internal electrodes and to minimize the opposing areas and, hence, to
realize a multi-layer ceramic capacitor in a small size. By selecting the
firing temperature to be not higher than 1300.degree. C., furthermore, it
is allowed to choose the internal electrodes from an increased variety of
materials such as from an expensive material consisting of 100% of
palladium through up to cheap Pd-Ag. In addition to the above, sufficient
degree of attention must be given to properties of the dielectric ceramic
composition such as dielectric loss tan .delta. and insulation resistance,
and it is further desired that the dielectric loss is little dependent
upon the AC voltage.
So far, dielectric ceramic compositions containing BaTiO.sub.3, Nb.sub.2
O.sub.5 and ZnO have been proposed already featuring improved dielectric
constants (see Japanese Laid-Open Patent Publications Nos. 18162/1984,
18159/1984, etc.). Dielectric constants of from 2000 to 3000 can be
obtained by using such dielectric ceramic compositions. Despite of their
high dielectric constants, however, such dielectric ceramic compositions
have large dielectric losses tan .delta. making it difficult to decrease
the thickness of the green sheet. When used for the multi-layer
capacitors, therefore, a large capacitance is not obtained.
In order to decrease the dielectric loss tan .delta., a dielectric ceramic
composition containing BaTiO.sub.3, Nb.sub.2 O.sub.5, MgO and La.sub.2
O.sub.3 has been developed already (see Japanese Patent Publication No.
10766/1993). There has further been proposed a composition comprising
BaTiO.sub.3 to which are added Nb.sub.2 O.sub.5 and MgO in such amounts
that the molar ratio of Nb.sub.2 O.sub.5 /MgO is from 2.3 to 4 as well as
rare earth oxides in amounts of from 0.1 to 0.5% by weight (see Japanese
Patent Publication No. 19007/1980).
In fact, however, the above-mentioned dielectric ceramics all have
dielectric constants of not larger than 2200, with which it is difficult
to obtain a capacitor having a large capacitance in a small size. Besides,
these dielectric ceramics still have such large dielectric losses that it
is difficult to decrease the thickness of the green sheet.
Moreover, the above-mentioned dielectric ceramics all have AC voltage
dependence of dielectric loss of not smaller than 3.0% under the
application of a voltage of 2000 V/cm, making it difficult to decrease the
thickness of the dielectric layer and, hence, making it difficult to
obtain a capacitor having a large capacitance in a small size.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems, the present inventors have
conducted keen study and have accomplished the present invention after
having discovered the fact that a ceramic composition containing barium
titanate (BaTiO.sub.3) as a chief component as well as Nb.sub.2 O.sub.5
and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and MnO at a
predetermined composition ratio, the molar ratio of MgO to Nb.sub.2
O.sub.5 and/or Ta.sub.2 O.sub.5 lying within a particular range, exhibits
a dielectric constant of as large as not smaller than 2500, has a
temperature chararistics of capacitance that satisfies X7R of the EIA
Standards, has a dielectric loss of as small as 2.5% or less, and has an
AC voltage dependence of as small as 3.0% or less even under the
application of an AC voltage of 2000 V/cm.
It is therefore an object of the present invention to provide a dielectric
ceramic composition having a dielectric constant of not smaller than 2500,
a temperature chararistics of capacitance satisfying X7R of the EIA
Standards, a dielectric loss of as small as 2.5% or less, and such a small
AC voltage dependence that the dielectric loss is not larger than 3.0%
even under the application of an AC voltage of 2000 V/cm.
Another object of the present invention is to provide a dielectric ceramic
composition which is obtained in the form of a layer of a decreased
thickness, and is suited as a material for producing a multi-layer ceramic
capacitor of a small size having a large capacitance.
A further object of the present invention is to provide a dielectric
ceramic composition that can be fired at a temperature of not higher than
1300.degree. C. and can be easily produced industrially.
According to the present invention, there is provided a dielectric ceramic
composition containing, per 100 parts by weight of BaTiO.sub.3, at least
either one of Nb.sub.2 O.sub.5 or Ta.sub.2 O.sub.5 in an amount of from
0.8 to 3.5 parts by weight, MgO in an amount of from 0.06 to 0.7 parts by
weight, oxides of rare earth elements in an amount of from 0.005 to 0.520
parts by weight, and MnO in an amount of from 0.01 to 0.30 parts by weight
in the form of MnCO.sub.3, the molar ratio of MgO to Nb.sub.2 O.sub.5 or
Ta.sub.2 O.sub.5 being from 0.5 to 2.2.
According to the present invention, furthermore, there is provided a
dielectric ceramic composition which comprises the above-mentioned
composition and further containing at least either one of SiO.sub.2 or
Al.sub.2 O.sub.3 in an amount of from 0.05 to 0.50 parts by weight per 100
parts by weight of BaTiO.sub.3.
According to the present invention, there is further provided a dielectric
ceramic composition which comprises the above-mentioned composition and
further containing ZnO in an amount of not larger than 0.5 parts by weight
per 100 parts by weight of BaTiO.sub.3.
DETAILED DESCRIPTION OF THE INVENTION
A dielectric ceramic composition of the present invention contains
BaTiO.sub.3 as a chief component as well as Nb.sub.2 O.sub.5 and/or
Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and MnO in
predetermined amounts. Here, in the composition of the present invention,
Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 are contained in amounts over a
range of from 0.8 to 3.5 parts by weight per 100 parts by weight of
BaTiO.sub.3.
When the contents of the above components are smaller than 0.8 parts by
weight, the ceramic composition exhibits large dielectric loss, poor
temperature characteristics and poor sintering property. When the contents
of the above components exceed 3.5 parts by weight, the dielectric
constant decreases and the temperature characteristics are greatly
deteriorated.
It is desired that Nb.sub.2 O.sub.5 is contained in an amount within a
range of from 1.3 to 3.0 parts by weight per 100 parts by weight of
BaTiO.sub.3.
MgO is contained in an amount within a range of from 0.06 to 0.7 parts by
weight per 100 parts by weight of BaTiO.sub.3. When the content of this
component is smaller than 0.06 parts by weight, the dielectric constant
and insulation resistance decrease, the temperature characteristics are
deteriorated, and the voltage dependence of dielectric loss increases.
When the content of this component exceeds 0.70 parts by weight, the
dielectric constant drops and the insulation resistance decreases, either.
It is desired that the amount of MgO lies within a range of from 0.1 to
0.4 parts by weight.
According to the present invention, the oxides of rare earth elements are
contained in amounts of from 0.005 to 0.520 parts by weight. Examples of
the oxides of rare earth elements used in the present invention include
those oxides of, for example, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb and Lu. Among them, La.sub.2 O.sub.3, Nd.sub.2 O.sub.3,
Pr.sub.6 O.sub.11, Sm.sub.2 O.sub.3, Gd.sub.2 O.sub.3, and Tb.sub.4
O.sub.7 are desirably used.
When the contents of the oxides of rare earth elements are smaller than
0.005 parts by weight, the dielectric constant drops and the sintering
property is deteriorated. When their contents exceed 0.520 parts by
weight, the temperature characteristics are deteriorated. It is desired
that the oxides of rare earth elements are contained in amounts of from
0.005 to 0.2 parts by weight.
In the present invention, furthermore, MnO is contained in an amount of
from 0.01 to 0.30 parts by weight in the form of MnCO.sub.3.
When the content of this component is smaller than 0.01 part by weight, the
insulation resistance decreases, dielectric loss increases and sintering
property is deteriorated. When the content of this component exceeds 0.30
parts by weight, the dielectric constant drops. It is desired that MnO is
contained in an amount of from 0.04 to 0.10 part by weight in the form of
MnCO.sub.3.
In the present invention, furthermore, it is important that the molar ratio
of MgO to Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 is over a range of from
0.5 to 2.2. When this molar ratio is smaller than 0.5, the dielectric
constant drops, and the temperature characteristics and sintering property
are deteriorated. When the molar ratio is larger than 2.2, on the other
hand, the temperature characteristics are deteriorated and the dielectric
constant drops.
More preferably, it is desired that the molar ratio lies over a range of
from 0.6 to 1.4.
According to a preferred embodiment of the present invention, a dielectric
ceramic composition contains 0.8 to 2.5 parts by weight of Nb.sub.2
O.sub.5, 0.06 to 0.70 parts by weight of MgO, 0.005 to 0.520 parts by
weight of at least one oxide of a rare earth element selected from
La.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Gd.sub.2 O.sub.3,
Tb.sub.4 O.sub.7 and Sm.sub.2 O.sub.3, and 0.01 to 0.30 parts by weight of
MnO reckoned as MnCO.sub.3 per 100 parts by weight of BaTiO.sub.3, the
molar ratio of MgO to Nb.sub.2 O.sub.5 lying within a range of from 0.5 to
2.2.
From the standpoint of dielectric properties contemplated by the present
invention, it is more desired that, in the above-mentioned composition,
the content of Nb.sub.2 O.sub.5 lies within a range of from 1.3 to 2.0
parts by weight, the content of MgO lies within a range of from 0.1 to 0.4
parts by weight, the contents of the oxides of rare earth elements lie
within a range of from 0.005 to 0.2 parts by weight, and the content of
MnO lies within a range of from 0.04 to 0.10 reckoned as MnCO.sub.3, the
above-mentioned molar ratio lying within a range of from 0.6 to 1.4.
According to a second preferred embodiment of the present invention, the
dielectric ceramic composition contains 1.3 to 3.5 parts by weight of
Ta.sub.2 O.sub.5, 0.06 to 0.6 parts by weight of MgO, 0.005 to 0.5 parts
by weight of oxides of rare earth elements, and 0.01 to 0.30 parts by
weight of MnO reckoned as MnCO.sub.3 per 100 parts by weight of
BaTiO.sub.3, the molar ratio of MgO to Ta.sub.2 O.sub.5 lying within a
range of from 0.5 to 2.0.
In the composition of the second embodiment, it is more desired that the
content of Ta.sub.2 O.sub.5 is from 2.0 to 3.0 parts by weight, the
content of MgO is from 0.1 to 0.4 parts by weight, the contents of the
oxides of rare earth elements are from 0.005 to 0.2 parts by weight, and
the content of MnO is from 0.04 to 0.10 part by weight reckoned as
MnCO.sub.3.
Moreover, it is desired that the molar ratio of MgO to Ta.sub.2 O.sub.5 is
within a range of from 0.6 to 1.4.
It is further desired that the dielectric ceramic composition of either
embodiment of the present invention containing BaTiO.sub.3, Nb.sub.2
O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and
MnO which are the essential components, further contains at least either
one of SiO.sub.2 or Al.sub.2 O.sub.3 in an amount of from 0.05 to 0.50
parts by weight per 100 parts by weight of BaTiO.sub.3 from the standpoint
of further increasing capacitance and dielectric constant, and lowering
the firing temperature depending upon the composition. The above-mentioned
action is not so much exhibited when the content of SiO.sub.2 or Al.sub.2
O.sub.3 is not greater than 0.05 parts by weight. When the content of
SiO.sub.2 or Al.sub.2 O.sub.3 is larger than 0.50 parts by weight, on the
other hand, the dielectric constant drops. More desirably, at least either
SiO.sub.2 or Al.sub.2 O.sub.3 is contained in an amount of from 0.1 to 0.2
parts by weight per 100 parts by weight of BaTiO.sub.3.
According to the present invention, it is further desired that the
dielectric ceramic composition comprising the essential components such as
BaTiO.sub.3, etc. further contains ZnO alone or in addition to the
above-mentioned SiO.sub.2 or Al.sub.2 O.sub.3 in an amount of not larger
than 0.5 parts by weight and, particularly, from 0.0001 to 0.3 parts by
weight per 100 parts by weight of BaTiO.sub.3, in order to further improve
insulation resistance, dielectric loss, sintering property, dielectric
constant and temperature characteristics of the ceramic composition. When
the content of ZnO is larger than 0.5 parts by weight, the temperature
characteristics are rather deteriorated and the dielectric loss increases,
which are not desirable.
In the dielectric ceramic composition that contains ZnO, it is particularly
desired that ZnO is contained in an amount over a range of from 0.1 to 0.5
parts by weight per 100 parts by weight of BaTiO.sub.3, and the molar
ratio of the total amount of MgO and ZnO to Nb.sub.2 O.sub.5 or Ta.sub.2
O.sub.5 is from 0.5 to 2.2 from the standpoint of dielectric constant and
temperature characteristics.
According to the present invention, BaTiO.sub.3 particles used for
preparing the dielectric ceramic composition are those having an average
particle diameter of not larger than 1.0 .mu.m and formed by, for example,
calcination synthesizing method, sol-gel method, oxalic acid method or
hydrothermal synthesizing method.
The dielectric ceramic composition of the present invention is prepared by
weighing powders of Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides
of rare earth elements and, as required, powders of SiO.sub.2, Al.sub.2
O.sub.3 and ZnO in predetermined amounts with respect to 100 parts by
weight of BaTiO.sub.3, wet-grinding the powders using a ball mill or the
like for 20 to 48 hours followed by drying, adding a binder in a
predetermined amount thereto to mold the mixture into a predetermined
shape, and firing the molded article in an open air at 1200.degree. to
1300.degree. C. for 1 to 2 hours.
To obtain a multi-layer ceramic capacitor, a slurry of the above-mentioned
powders is prepared and is formed into a sheet relying upon a doctor blade
method, and a suitable internal electrode such as of Ag-Pd is applied onto
the sheet. The sheets are then stacked in a plural number one upon the
other and are fired under the above-mentioned firing conditions.
Instead of the powders of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, MgO, oxides
of rare earth elements, MnCO.sub.3, SiO.sub.2, Al.sub.2 O.sub.3 and ZnO
that are used in the present invention, there can be used hydroxides,
carbonates, nitrates, oxalates or alkoxides of Nb, Ta, Mg, rare earth
metal elements, Mn, Si, Al and Zn, that decompose at a temperature lower
than the sintering temperature to form oxides.
In order to improve AC voltage dependence of the dielectric ceramic
composition of the present invention, it is desired to control the average
particle diameter d of the sintered product to be d<1.0 .mu.m. To control
the average particle diameter d of the sintered product to be d<1.0 .mu.m,
it is necessary to use a powder of barium titanate having an average
particle diameter of not larger than 1.0 .mu.m as a starting material, or
to decrease the particle diameter of the powder to be not larger than 0.8
.mu.m through wet-type milling executed for a long period of time, and to
set the firing temperature to be as low as possible and to execute the
firing for only a short period of time.
The dielectric ceramic composition of the present invention exhibits a
temperature characteristics of capacitance of within .+-.15% over a range
of from -55.degree. C. to 125.degree. C., a dielectric constant at
+25.degree. C. of not smaller than 2500, a dielectric loss of as small as
2.5% or less despite a green sheet thereof has a thickness of 15 .mu.m,
and a dielectric loss of as small as 3% or less under the application of
an AC voltage of 2000 V/cm. It is therefore allowed to obtain a
multi-layer capacitor which is small in size but having a large
capacitance. Moreover, since the firing temperature is not higher than
1300.degree. C., the dielectric ceramic composition can be easily produced
industrially permitting an internal electrode composed of cheaply
available silver-palladium (Ag/Pd=20/80 to 40/60) to be incorporated
therein, lending the composition itself to be well suited for producing
multi-layer capacitors. Furthermore, there is obtained a dielectric
ceramic composition having a dielectric loss of not larger than 2.5% and
an insulation resistance (IR) of not smaller than 10.sup.4 M.OMEGA. which
are sufficiently satisfactory fundamental properties.
EXAMPLES
Examples of the present invention will now be described in detail.
Example 1
A BaTiO.sub.3 powder having an average particle diameter of not larger than
1.0 .mu.m formed by the hydrothermal synthesizing method was used as a
chief component. Powders of Nb.sub.2 O.sub.5 MgO, La.sub.2 O.sub.3 and
MnCO.sub.3 were weighed as shown in Table 1 with respect to 100 parts by
Weight of BaTiO.sub.3, and were wetgrinded in a ball mill for 20 to 48
hours. Then, an organic binder agent was added thereto followed by
milling, and the mixture was formed into a tape having a thickness of 15
.mu.m by the doctor blade method. The tape was cut into 130 mm.times.100
mm, overlapped in a number of 20 pieces one upon the other and was
hot-pressed at 80.degree. C. to prepare a laminate thereof.
TABLE 1
__________________________________________________________________________
BaTiO.sub.3
Nb.sub.2 O.sub.5
MgO La.sub.2 O.sub.5
MnCO.sub.3
Nb.sub.2 O.sub.5 /MgO
Firing
Sample
pts. by
pts. by
pts. by
pts. by
pts. by
molar temp.
No. wt wt. wt. wt. wt. ratio (.degree.C.)
__________________________________________________________________________
1-*1
100 0.7 0.2 0.2 0.1 0.5 1320
1-2 100 0.8 0.2 0.2 0.1 0.6 1300
1-3 100 1.6 0.2 0.2 0.1 1.2 1280
1-4 100 2.5 0.2 0.2 0.1 2.0 1250
1-*5
100 0.8 0.05
0.2 0.1 2.5 1280
1-6 100 0.8 0.06
0.2 0.1 2.1 1280
1-7 100 2.3 0.3 0.2 0.1 1.2 1260
1-8 100 2.5 0.7 0.2 0.1 0.6 1250
1-*9
100 2.5 0.75
0.2 0.1 0.5 1250
1-*10
100 1.8 0.3 0.004
0.1 0.9 1330
1-11
100 1.8 0.3 0.005
0.1 0.9 1300
1-12
100 1.8 0.3 0.2 0.1 0.9 1270
1-13
100 1.8 0.3 0.52
0.1 0.9 1250
1-*14
100 1.8 0.3 0.53
0.1 0.9 1250
1-*15
100 1.8 0.3 0.2 0.005
0.9 1320
1-16
100 1.8 0.3 0.2 0.01 0.9 1300
1-17
100 1.8 0.3 0.2 0.05 0.9 1280
1-18
100 1.8 0.3 0.2 0.3 0.9 1260
1-*19
100 1.8 0.3 0.2 0.31 0.9 1260
1-*20
100 0.9 0.3 0.2 0.1 0.4 1280
1-*21
100 2.3 0.15
0.2 0.1 2.3 1250
1-22
100 2.0 0.4 0.2 0.1 0.8 1250
1-23
100 2.2 0.6 0.2 0.1 0.8 1260
1-24
100 1.8 0.3 0.1 0.1 0.9 1280
1-25
100 1.8 0.3 0.3 0.1 0.9 1260
1-26
100 1.8 0.3 0.4 0.1 0.9 1250
1-27
100 1.8 0.3 0.2 0.2 0.9 1280
1-28
100 1.4 0.1 0.2 0.1 2.2 1260
__________________________________________________________________________
Samples marked with * lie outside the scope of the invention.
An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The
laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at
1250.degree. to 1320.degree. C. for two hours. Then, the electrodes of the
silver paste were glazed on both end surfaces at 800.degree. C. for 10
minutes to obtain samples for measurement.
The thus obtained samples were measured for their capacitances and
dielectric losses at a reference temperature of 25.degree. C., a frequency
of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending
upon the temperature was measured over a range of from -55.degree. to
+125.degree. C., and the capacitance at +25.degree. C. was used as a
reference. The insulation resistance was measured at a moment after a DC
voltage of 25 V was applied for one minute.
The dielectric constant was calculated from the capacitance.
As for the average particle diameter of the sintered product, the surface
of the sintered product was observed using a scanning-type electron
microscope at a magnification of 15000 times, and particles of more than
500 were measured and calculated by the line intercept method.
Furthermore, the dielectric loss was measured by applying a voltage of
2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table
2.
TABLE 2
__________________________________________________________________________
Di- Di- Insulating
Temp. Particle
Tan .delta.
Capaci-
electric
electric
resist-
character-
di- at 2000
Sample
tance
const.
loss ance IR
istics
ameter
V/cm
No. nF .epsilon.r
tan .delta. (%)
(M.OMEGA.)
(%) (.mu.m)
(%)
__________________________________________________________________________
1-*1
170.5
3500
3.3 2 .times. 10.sup.4
-27.about.+3
0.4 4.5
1-2 180.2
3700
2.5 3 .times. 10.sup.4
-14.about.+3
0.3 2.8
1-3 145.1
3000
1.6 8 .times. 10.sup.4
-5.about.+5
0.4 2.4
1-4 130.8
2700
2.0 9 .times. 10.sup.4
-12.about.+8
0.4 2.8
1-*5
110.9
2300
2.5 4 .times. 10.sup.3
-19.about.+8
1.5 4.0
1-6 131.0
2700
2.0 2 .times. 10.sup.4
-13.about.+7
0.5 2.8
1-7 140.3
2900
1.8 8 .times. 10.sup.4
-6.about.+5
0.4 2.6
1-8 149.9
3100
1.6 3 .times. 10.sup.4
-5.about.+3
0.3 2.6
1-*9
116.0
2100
1.7 7 .times. 10.sup.3
-6.about.+2
0.4 2.6
1-*10
112.8
2350
2.5 2 .times. 10.sup.4
-3.about.+6
0.5 3.2
1-11
136.7
2800
2.0 3 .times. 10.sup.4
-3.about.+6
0.4 2.8
1-12
140.6
2900
1.6 7 .times. 10.sup.4
-5.about.+6
0.4 2.4
1-13
174.1
3600
1.8 7 .times. 10.sup.4
-11.about.+6
0.4 2.7
1-*14
185.2
3800
1.8 7 .times. 10.sup.4
-20.about.+7
0.4 2.7
1-*15
144.7
3000
2.6 9 .times. 10.sup.3
-5.about.+6
0.4 3.2
1-16
145.2
3000
2.2 2 .times. 10.sup.4
-5.about.+6
0.4 3.0
1-17
141.0
2900
1.8 9 .times. 10.sup.4
-5.about.+5
0.5 2.7
1-18
136.1
2800
1.4 2 .times. 10.sup.5
-4.about.+3
0.9 2.2
1-*19
102.0
2100
1.4 9 .times. 10.sup.4
-4.about.+3
0.9 2.2
1-*20
111.2
2300
2.7 3 .times. 10.sup.3
-30.about.+4
0.5 3.8
1-*21
97.1 2000
2.3 7 .times. 10.sup.4
-18.about.+11
0.6 2.9
1-22
141.5
2900
1.8 6 .times. 10.sup.4
-5.about.+5
0.3 2.5
1-23
140.6
2900
1.6 5 .times. 10.sup.4
-5.about.+4
0.3 2.6
1-24
140.9
2900
1.8 4 .times. 10.sup.4
-3.about.+6
0.4 2.7
1-25
156.1
3200
1.8 5 .times. 10.sup.3
-7.about.+7
0.3 2.7
1-26
164.8
3400
1.8 5 .times. 10.sup.4
-9.about.+8
0.4 2.8
1-27
141.2
2900
1.5 7 .times. 10.sup.4
-5.about.+4
0.4 2.3
1-28
127.1
2600
1.9 7 .times. 10.sup.4
-13.about.+9
0.5 2.8
__________________________________________________________________________
Samples marked with * lie outside the scope of the invention.
The dielectric ceramic compositions lying within the scope of the present
invention all have dielectric constants which are as large as 2500 or more
and satisfy X7R characteristics (change of the capacitance is within
.+-.15% over a temperature range of from -55.degree. C. to +125.degree.
C.) stipulated under the EIA Standards. Moreover, the compositions have
dielectric losses tan .delta. which are as small as 2.5% or less and
exhibit losses of not larger than 3.0% even under the application of an AC
voltage of 2000 Vrms/cm. The compositions further have insulation
resistances (IR) of more than 10.sup.4 M.OMEGA..
In Table 1, samples Nos. 1-1 to 1-4 are those in which Nb.sub.2 O.sub.5 was
added in an amount of from 0.7 to 2.5 parts by weight to BaTiO.sub.3 that
is the chief component of the dielectric ceramic compositions. In these
cases, MgO, La.sub.2 O.sub.3 and MnCO.sub.3 were added in amounts of 0.2
parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.
In the sample No. 1-1 (Nb.sub.2 O.sub.5 is added in an amount of 0.7 parts
by weight), the dielectric constant .epsilon.r is as good as 3500 but the
dielectric loss tan .delta. becomes as large as 3.3%. Besides, the
temperature characteristics become -27%. In the samples Nos. 1-2 to 1-4
(Nb.sub.2 O.sub.5 is added in an amount of from 0.8 to 2.5 parts by
weight), the dielectric constants .epsilon.r are from 2700 to 3700,
dielectric losses tan .delta. are not larger than 2.5%, temperature
characteristics are within .+-.14%, tan .delta. are not larger than 2.8%
when an AC voltage of 2000 V/cm is applied, and insulation resistances
(IR) are from 3 to 9.times.10.sup.4 M.OMEGA., which are within favorable
ranges. That is, the dielectric ceramic compositions have large dielectric
constants .epsilon.r, excellent temperature characteristics, small
dielectric losses tan .delta. and small AC voltage dependence of
dielectric loss.
In the samples Nos. 1-5 to 1-9, the amount of MgO to be added to
BaTiO.sub.3 which is the chief component of the dielectric ceramic
compositions was changed to be from 0.05 to 0.75 parts by weight. In these
cases, the amounts of Nb.sub.2 O.sub.5, La.sub.2 O.sub.5 and MnCO.sub.3
were selected to be 0.8 to 2.5 parts by weight, 0.2 parts by weight and
0.1 part by weight, respectively.
In the sample No. 1-5 (MgO is contained in an amount of 0.05 parts by
weight), tan .delta. becomes 4.0% when an AC voltage of 2000 V/cm is
applied. In the samples Nos. 1-6 to 1-8 (MgO is added in an amount of from
0.06 to 0.70 parts by weight), the dielectric constants .epsilon.r are
from 2700 to 3100, dielectric losses tan .delta. are not larger than 2.0%,
temperature characteristics are within .+-.13%, tan .delta. are not larger
than 2.8% when an AC voltage of 2000 V/cm is applied, and insulation
resistances (IR) are from 3 to 8.times.10.sup.4 M.OMEGA., which are within
favorable ranges. That is, the dielectric ceramic compositions exhibit
high dielectric constants .epsilon.r, excellent temperature
characteristics, small dielectric losses tan .delta. and small AC voltage
dependence of dielectric loss. In the sample No. 1-9 (MgO is added in an
amount of 0.75 parts by weight), the dielectric loss tan .delta. is as
good as 1.7% but the dielectric constant .epsilon.r is 2100. In the
present invention, therefore, the amount of MgO to be added to the barium
titanate BaTiO.sub.3 is selected to be from 0.06 to 0.70 parts by weight
per 100 parts by weight of the barium titanate BaTiO.sub.3.
In the samples Nos. 1-10 to 1-14, the amount of La.sub.2 O.sub.3 to be
added to BaTiO.sub.3 that is the chief component of the dielectric ceramic
compositions was changed to be from 0.004 to 0.53 parts by weight. In
these cases, the amounts of Nb.sub.2 O.sub.5, MgO and MnCO.sub.3 were
selected to be 1.8 parts by weight, 0.3 parts by weight and 0.1 part by
weight, respectively.
In the sample No. 1-10 (La.sub.2 O.sub.3 is added in an amount of 0.004
parts by weight), the dielectric loss tan .delta. is 2.5% but the
dielectric constant .epsilon.r is as low as 2350. In the samples Nos. 1-11
to 1-13 (La.sub.2 O.sub.3 is added in an amount of from 0.005 to 0.52
parts by weight), the dielectric constants .epsilon.r are from 2800 to
3600, dielectric losses tan .delta. are not larger than 2.0%, temperature
characteristics are within .+-.11%, tan .delta. are not larger than | | |
