A dielectric ceramic composition is disclosed which consists principally of: barium oxide, titanium oxide, neodymium oxide and samarium oxide as major components which are represented by the following formula xBaO - yTiO.sub.2 - z[(1 - a)Nd.sub.2 O.sub.3 - aSm.sub.2 O.sub.3 ], where 0.10.ltoreq.x.ltoreq.0.20, 0.60.ltoreq.y.ltoreq.0.75, 0.10.ltoreq.z.ltoreq.0.25, x+y+z=1, and 0<a.ltoreq.0.50; and not larger than 2.5 parts by weight of alumina per 100 parts by weight of a total amount of the major components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a dielectric ceramic 
composition, particularly to a dielectric ceramic composition suitable for 
forming dielectric resonators, for example, which are used with microwave 
(high-frequency) devices. 
2. Discussion of the Prior Art 
Keeping pace with recent developments of various microwave devices such as 
pocket or portable telephones, there has been a growing demand for 
small-sized high-performance dielectric resonators used in such devices. 
In particular, a dielectric ceramic used to form such dielectric 
resonators is required to have the following physical and structural 
features; 
(1) The dielectric ceramic should have a sufficiently high specific 
dielectric constant (.epsilon.r), to reduce the size of a resonator when 
the resonator is operated at a given frequency. 
(2) The dielectric ceramic should have a sufficiently high Q value, to 
reduce the transmission loss of the resonator formed of the dielectric 
ceramic. 
(3) The temperature coefficient (.tau.f) of the resonance frequency of the 
resonator formed of the dielectric ceramic should be sufficiently low, to 
minimize changes of the operating characteristics of the resonator with 
respect to temperature. 
There have been known various dielectric ceramic compositions used for 
forming such dielectric resonators. For example, laid-open Publication No. 
58-20905 of examined Japanese Patent Application discloses a dielectric 
ceramic composition whose major components consist of BaO and TiO.sub.2, a 
portion of which may be substituted by another element or other elements. 
A dielectric ceramic formed of the disclosed composition has a relatively 
low dielectric constant of around 30 .about. 40, and a relatively low Q 
value. Another example of dielectric ceramic composition is disclosed in 
laid-open Publication No. 59-23048 of examined Japanese Patent 
Application, which has a composite perovskite structure such as 
Ba(Mg.sub.1/3 Ta.sub.2/3)O.sub.3. The dielectric ceramic formed of this 
composition has a relatively high Q value, but suffers from a relatively 
low dielectric constant of around 30 .about. 40. 
There is also known a dielectric ceramic composition as disclosed in 
laid-open Publication 56-102003 of unexamined Japanese Patent Application, 
whose major components consist of BaO, TiO.sub.2, Nd.sub.2 O.sub.3 and 
Bi.sub.2 O.sub.3. While this dielectric ceramic composition has a 
relatively high dielectric constant, the temperature coefficient of the 
resonance frequency of the resonator formed of this ceramic composition is 
undesirably high, making it difficult for the resonator to provide 
satisfactory operating characteristics. A further example of dielectric 
ceramic composition as disclosed in laid-open Publication No. 57-21010 of 
unexamined Japanese Patent Application, whose major components consist of 
BaO, TiO.sub.2, Nd.sub.2 O.sub.3 and Sm.sub.2 O.sub.3, has a relatively 
high temperature coefficient of the resonance frequency, which causes some 
problems in practical use. Still another example of dielectric ceramic 
composition is disclosed in laid-open Publication No. 1-227303 of 
unexamined Japanese Patent Application, which contains BaO, TiO.sub.2, 
Nd.sub.2 O.sub.3 and Al.sub.2 O.sub.3 as major components. The dielectric 
ceramic formed of this composition has a relatively low Q value resulting 
in an increase in the transmission loss of the obtained resonator, owing 
to the presence of Al.sub.2 O.sub.3 in the composition. 
SUMMARY OF THE INVENTION 
The present invention was developed in the light of the prior art 
situations described above. It is accordingly an object of the present 
invention to provide a dielectric ceramic composition which has a 
sufficiently high dielectric constant and a sufficiently high Q value, and 
whose resonance frequency has a sufficiently low temperature coefficient. 
The above object may be attained according to the principle of the present 
invention, which provides a dielectric ceramic composition which consists 
principally of: barium oxide, titanium oxide, neodymium oxide and samarium 
oxide as major components which are represented by the following formula 
xBaO - yTiO.sub.2 - z[(1 - a)Nd.sub.2 O.sub.3 - aSm.sub.2 O.sub.3 ], where 
0.10.ltoreq.x.ltoreq.b 0.20, 0.60.ltoreq.y.ltoreq.0.75, 
0.10.ltoreq.z.ltoreq.0.25, x+y+z=1, and 0&lt;a.ltoreq.0.50; and not more than 
2.5 parts by weight of alumina per 100 parts by weight of a total amount 
of the major components. 
The dielectric ceramic composition according to the present invention 
consists principally of barium oxide (BaO), titanium oxide (TiO.sub.2), 
neodymium oxide (Nd.sub.2 O.sub.3) and samarium oxide (Sm.sub.2 O.sub.3), 
in respective specific amounts as indicated by the above formula. A 
dielectric ceramic body formed of the present composition exhibits 
excellent microwave dielectric properties as described below. Since the 
ceramic composition of this invention further comprises alumina (Al.sub.2 
O.sub.3) in a given suitable amount, the dielectric ceramic formed of the 
present composition is given a further increased Q value, and a 
sufficiently reduced temperature coefficient. 
If the BaO content of the dielectric ceramic composition is smaller than 10 
mole % (x&lt;0.10), the dielectric constant of the obtained dielectric 
ceramic is undesirably lowered. If the BaO content exceeds 20 mole % (x 
&gt;0.20), the dielectric ceramic suffers from an excessively high 
temperature coefficient of the resonance frequency. If the TiO.sub.2 
content of the dielectric ceramic composition is smaller than 60 mole % 
(y&lt;0.60), the Q value of the dielectric ceramic obtained is considerably 
deteriorated. If the TiO.sub.2 content exceeds 75 mole % (y&gt;0.75), the 
temperature coefficient of the resonance frequency of the dielectric 
ceramic becomes excessively high. 
If the total content of Nd.sub.2 O.sub.3 and Sm.sub.2 O.sub.3, i.e., the 
above-indicated term [(1-a)Nd.sub.2 O.sub.3 - aSm.sub.2 O.sub.3 ] is 
smaller than 10 mole % (z&lt;0.10), the resonance frequency of the dielectric 
ceramic has a comparatively high temperature coefficient. If the total 
content of Nd.sub.2 O.sub.3 and Sm.sub.2 O.sub.3 exceeds 25 mole % 
(z&gt;0.25), the sinterability of the dielectric ceramic is unfavorably 
deteriorated. 
According to the present invention, Sm.sub.2 O.sub.3 is used with Nd.sub.2 
O.sub.3 so as to substitute for a portion of Nd.sub.2 O.sub.3, to thereby 
increase the Q value of the dielectric ceramic and lower the temperature 
coefficient of the same. It is particularly desirable to substitute at 
least 3 mole % (a.gtoreq.0.03) of Sm.sub.2 O.sub.3 for a portion of 
Nd.sub.2 O.sub.3 so that the use of the samarium oxide gives sufficient 
effects as described above. However, if the amount of substitution of 
Sm.sub.2 O.sub.3 for Nd.sub.2 O.sub.3 exceeds 50 mole % (a&gt;0.50), the 
dielectric constant of the dielectric ceramic is lowered. Further, since 
the cost of samarium oxide is comparatively high, the substituting amount 
of Sm.sub.2 O.sub.3 should be practically kept lower than 50 mole % from 
an economical point of view. 
The addition of Al.sub.2 O.sub.3 to the present ceramic composition results 
in the increased Q value and lowered temperature coefficient of the 
dielectric ceramic formed of this composition. If the amount of addition 
of Al.sub.2 O.sub.3 exceeds 2.5 parts by weight per 100 parts by weight of 
the major components described above, the Q value and dielectric constant 
of the dielectric ceramic are deteriorated or excessively lowered, whereby 
the ceramic body obtained is rendered unsuitable for practical use.

EXAMPLE 
To further clarify the concept of the present invention, an example of the 
invention will be described. It is to be understood that the invention is 
not limited to the details of the illustrated example, but may be embodied 
with various alterations, modifications and improvements, which may occur 
to those skilled in the art, without departing from the scope of the 
invention defined in the appended claims. 
Initially, the amounts of highly pure barium oxide, titanium oxide, 
neodymium oxide and samarium oxide were measured so as to give various 
mole proportions (x, y, z and a) as indicated in TABLES 1-A, 1-B and 2 
below. The measured materials having each mole proportion were then 
wet-mixed with some pure water in a polyethylene pot mill using alumina 
balls. The thus obtained mixture was taken out of the pot mill, dried, and 
calcined in the air for two hours at 1000.degree. C. Then, the calcined 
mixture was thrown back into the polyethylene pot mill using alumina 
balls, and wet-ground with some pure water added to the calcined mixture. 
Before the addition of the water, the weight of the calcined mixture was 
measured, and alumina was introduced into the pot mill along with the 
calcined mixture such that the alumina provides a given number of parts by 
weight as indicated in TABLES 1-A, 1-B and 2, per 100 parts by weight of 
the mixture. At the same time, 1% by weight of polyvinyl alcohol (PVA) was 
added as a binder, which was uniformly mixed with the calcined mixture in 
the form of a powder. The thus obtained mixture was then dried and passed 
through a 400 mesh sieve, whereby dielectric ceramic mixture powders Nos. 
1-40 as indicated in TABLE 1-A, 1-B and 2 were prepared. 
The thus prepared dielectric ceramic mixture powders were subjected to a 
press-forming operation under surface pressure of 1 ton/cm.sup.2, to 
prepare respective samples of circular discs, each of which has a diameter 
of 20 mm and a thickness of 15mm. The samples were fired in air for two 
hours at a temperature of 1300.degree.-1400.degree. C. The fired samples 
were ground to a final size of 14mm diameter and 7 mm thickness. 
The thus prepared samples (Nos. 1-40) of dielectric ceramic body in the 
form of discs were tested to measure the dielectric constant and the 
non-load Q value, according to Hakki & Coleman method. Also, the 
temperature coefficients (.tau.f) of the resonance frequency of the 
samples over a range of -25.degree. C. to 75.degree. C. were measured. The 
measured values are indicated in TABLE 1-A, 1-B and 2. The measurements 
were made over the frequency range of 2-5 GHz. The Q values indicated in 
the tables are converted equivalents at 3 GHz. 
While alumina was added to the calcined mixture of the major components 
BaO, TiO.sub.2, Nd.sub.2 O.sub.3 and Sm.sub.2 O.sub.3 in the illustrated 
example, alumina may be mixed with the major components so that all of 
these components are wet-mixed prior to calcination. 
It will be understood from TABLES 1-A, 1-B and 2 that the dielectric 
ceramic bodies made of the compositions Nos. 1-23 and 27-34 according to 
the present invention had sufficiently high dielectric constants and Q 
values, and significantly lowered temperature coefficients (.tau.f) of the 
resonance frequency. On the other hand, the comparative samples made of 
the compositions Nos. 24-26 and 35-38 were unsatisfactory in terms of at 
least one of the dielectric constant, Q value and temperature coefficient 
(.tau.f). The comparative samples Nos. 39 and 40 could not be sintered. 
It will be understood from the above description that the dielectric 
ceramic made of the dielectric ceramic composition according to the 
present invention has a sufficiently high dielectric constant, a 
sufficiently high Q value and a sufficiently low temperature coefficient 
of the resonance frequency. The present dielectric ceramic composition 
contains alumina in a predetermined suitable amount, whereby the Q value 
can be significantly increased while the temperature coefficient can be 
sufficiently lowered. 
TABLE 1 - A 
__________________________________________________________________________ 
Dielectric 
.tau.f 
No. x y z a Al.sub.2 O.sub.3 * 
Constant 
Q (ppm/.degree.C.) 
__________________________________________________________________________ 
PRESENT INVENTION 
1 0.135 
0.680 
0.185 
0.150 
0.5 73 3960 
16 
2 0.135 
0.680 
0.185 
0.150 
1.0 70 3970 
12 
3 0.135 
0.680 
0.185 
0.150 
1.25 
67 4030 
7 
4 0.135 
0.680 
0.185 
0.150 
1.5 66 4210 
7 
5 0.135 
0.680 
0.185 
0.150 
2.0 64 3090 
11 
6 0.135 
0.675 
0.190 
0.150 
0.5 71 3010 
9 
7 0.135 
0.675 
0.190 
0.150 
1.0 68 3930 
4 
8 0.135 
0.675 
0.190 
0.150 
1.25 
67 4000 
4 
9 0.135 
0.675 
0.190 
0.150 
1.5 66 3750 
7 
10 0.135 
0.675 
0.190 
0.150 
2.0 63 2120 
-4 
11 0.140 
0.675 
0.185 
0.150 
0.5 75 3540 
14 
12 0.140 
0.675 
0.185 
0.150 
1.0 71 3960 
12 
13 0.140 
0.675 
0.185 
0.150 
1.25 
69 3970 
9 
14 0.140 
0.675 
0.185 
0.150 
1.5 68 4090 
8 
15 0.140 
0.675 
0.185 
0.150 
2.0 67 2280 
7 
__________________________________________________________________________ 
*parts by weight 
TABLE 1 - B 
__________________________________________________________________________ 
Dielectric 
.tau.f 
No. x y z a Al.sub.2 O.sub.3 * 
Constant 
Q (ppm/.degree.C.) 
__________________________________________________________________________ 
PRESENT INVENTION 
16 0.145 
0.675 
0.180 
0.150 
0.5 79 3660 
23 
17 0.145 
0.675 
0.180 
0.150 
1.0 74 3820 
17 
18 0.145 
0.675 
0.180 
0.150 
1.25 
73 3990 
14 
19 0.145 
0.675 
0.180 
0.150 
1.5 70 3950 
12 
20 0.145 
0.675 
0.180 
0.150 
2.0 68 3020 
5 
21 0.145 
0.675 
0.180 
0.100 
1.5 70 3740 
16 
22 0.145 
0.675 
0.180 
0.100 
1.7 67 3270 
13 
23 0.145 
0.675 
0.180 
0.100 
1.9 68 3790 
12 
COMATIVE 
24 0.140 
0.675 
0.185 
0.150 
0.0 78 2810 
32 
25 0.140 
0.675 
0.185 
0.150 
3.0 64 1700 
6 
26 0.150 
0.750 
0.100 
0.000 
1.5 58 3900 
60 
__________________________________________________________________________ 
*parts by weight 
TABLE 2 
__________________________________________________________________________ 
Dielectric 
.tau.f 
No. x y z a Al.sub.2 O.sub.3 * 
Constant 
Q (ppm/.degree.C.) 
__________________________________________________________________________ 
PRESENT INVENTION 
27 0.150 
0.750 
0.100 
0.200 
1.5 56 4120 
38 
28 0.100 
0.750 
0.150 
0.200 
1.5 60 4480 
52 
29 0.170 
0.700 
0.130 
0.150 
2.0 61 3200 
49 
30 0.150 
0.710 
0.140 
0.200 
2.0 62 3600 
36 
31 0.200 
0.700 
0.100 
0.150 
1.0 54 3750 
42 
32 0.125 
0.750 
0.125 
0.200 
1.5 61 4880 
49 
33 0.115 
0.670 
0.215 
0.200 
1.0 57 2710 
3 
34 0.125 
0.695 
0.180 
0.200 
1.0 63 4360 
12 
COMATIVE 
35 0.220 
0.650 
0.150 
0.200 
1.0 71 2400 
74 
36 0.125 
0.775 
0.100 
0.200 
1.0 66 3900 
162 
37 0.175 
0.740 
0.085 
0.200 
1.0 52 3120 
90 
38 0.075 
0.700 
0.225 
0.200 
1.0 44 1760 
93 
39 0.120 
0.620 
0.260 
0.100 
1.0 not sinterable 
40 0.190 
0.590 
0.220 
0.200 
1.0 not sinterable 
__________________________________________________________________________ 
*parts by weight