Piezoelectric ceramic composition and piezoelectric element using the piezoelectric ceramic composition

Provided is a piezoelectric ceramic composition containing a lead titanate which has excellent temperature stability of the resonance frequency, and is suitable for application in a filter, a vibrator or the like, and a piezoelectric element using the piezoelectric ceramic composition. A piezoelectric substrate comprising a ceramic material containing PbTiO.sub.3 is provided with vibrating electrodes on the front and rear surfaces. The ceramic material containing PbTiO.sub.3 contains not less than about 0.1% by weight or more than about 3.0% by weight of Mn based on MnCO.sub.3 as the subcomponent in the main component having a composition satisfying 0.02.ltoreq.x.ltoreq.0.16 and 0.15.ltoreq.y.ltoreq.0.50 of the general formula Pb.sub.1-1.5x Nd.sub.x [(In.sub.1/2 Nb.sub.1/2).sub.y Ti.sub.1-y ]O.sub.3.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a piezoelectric ceramic composition and a 
piezoelectric element using the piezoelectric ceramic composition. 
2. Description of the Related Art 
Conventional piezoelectric ceramic composition containing a lead titanate 
(PbTiO.sub.3) are known. Since a piezoelectric ceramic composition 
containing a lead titanate has a low dielectric constant and small 
particle size, it is suitable for the use in the high frequency range. 
Moreover, it has excellent characteristics such as ability in restraining 
sub-resonance due to large piezoelectric anisotropy, durability in use at 
a high temperature due to a high Curie point, and the like. Therefore, use 
of a piezoelectric ceramic containing lead titanate is indicated in the 
field of filters, vibrators, or the like, intended to be used in a high 
frequency range. However, the piezoelectric ceramic containing a lead 
titanate has disadvantages such as difficulty in obtaining a dense 
sintered compact having a large mechanical strength due to difficulty in 
sintering, and difficulty in polarization. In order to solve these 
problems, for example, a piezoelectric ceramic composition containing a 
lead titanate obtained by partially substituting the Pb of PbTiO.sub.3 by 
La and adding a Mn compound such as MnCO.sub.3 or the like has been used. 
Such piezoelectric ceramic has characteristics such as a good sintering 
property and capability of a polarization treatment at a high temperature 
in a high electric field. However, a problem is involved in that the 
piezoelectric ceramic has a poor temperature coefficient of the resonance 
frequency and thus when it is used in a filter or a vibrator, the passing 
frequency or the oscillating frequency changes drastically according to 
temperature. Therefore, it has been difficult to use a ceramic containing 
lead titanate in a filter or a vibrator, which are required to have a high 
accuracy. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a 
piezoelectric ceramic composition containing a lead titanate having 
excellent temperature stability of the resonance frequency, suitability 
for application in a filter, a vibrator or the like, and a piezoelectric 
element using the piezoelectric ceramic composition. 
In order to achieve the above-mentioned object, a piezoelectric ceramic 
composition according to the present invention is represented by the 
general formula Pb.sub.1-1.5x Nd.sub.x [(In.sub.1/2 Nb.sub.1/2).sub.y 
Ti.sub.1-y ]O.sub.3, wherein not less than about 0.1% by weight but not 
more than about 3.0% by weight of Mn based on MnCO.sub.3 is contained as a 
subcomponent in a main component having a composition satisfying 
0.02.ltoreq.x.ltoreq.0.16 and 0.15.ltoreq.y.ltoreq.0.50. According to the 
above-mentioned configuration, a piezoelectric ceramic composition having 
a good temperature coefficient of the resonance frequency can be obtained. 
Moreover, a piezoelectric element using the piezoelectric ceramic 
composition with the above-mentioned configuration can restrain the change 
of the passing frequency, the oscillating frequency or the like, derived 
from the temperature. 
The amount x (substituting Nd by Pd) is set to be 0.02.ltoreq.x.ltoreq.0.16 
because the sintering property of the ceramic cannot be good and the 
improving effect of the temperature coefficient of the resonance frequency 
is small if x&lt;0.02, and the Curie temperature is drastically deteriorated 
so as not to be durable at high temperature if 0.16&lt;x. The range of y is 
set to be 0.15.ltoreq.y=0.50 because the temperature coefficient of the 
resonance frequency is poor if y&lt;0.15, and the Curie temperature is 
drastically deteriorated so as not to be durable at high temperature if 
0.50&lt;y. The amount of Mn as the subcomponent is preferably not less than 
about 0.1% by weight and not more than about 3.0% by weight as MnCO.sub.3. 
This is because the mechanical quality coefficient Qm is small so that it 
is not suitable for the application in a vibrator, a filter or the like, 
with less than about 0.1% by weight, and the insulating property of the 
ceramic is deteriorated so that it cannot be applied with a polarization 
treatment and thus it cannot be used as a piezoelectric ceramic with more 
than about 3.0% by weight.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of a piezoelectric ceramic composition and a piezoelectric 
element using the piezoelectric ceramic composition according to the 
present invention will hereinafter be explained with reference to the 
accompanied drawing. 
As shown in FIG. 1, a piezoelectric element to be used as a piezoelectric 
filter comprises a piezoelectric substrate 1, an insulating container 10 
accommodating the piezoelectric substrate 1, and a sealing lid 20. The 
piezoelectric substrate 1 has a substantially rectangular shape. The 
piezoelectric substrate 1 is provided with vibrating electrodes 2a, 2b, 
vibrating electrodes 3a, 3b on the front surface, and vibrating electrodes 
2c, 3c on the rear surface. The vibrating electrodes 2a, 3b are connected 
electrically with lead electrodes 4a, 4b provided on the end parts of the 
front surface of the piezoelectric substrate 1, respectively. The 
vibrating electrodes 2b, 3a are connected electrically therewith via a 
conductor path. The lead electrodes 4a, 4b are arranged on both end parts 
of the substrate 1, respectively. Furthermore, the vibrating electrodes 2c 
and 3c are connected electrically via a conductor path provided at the 
rear center part of the substrate 1. The piezoelectric substrate 1 
comprises a ceramic material containing PbTiO.sub.3. The vibrating 
electrodes 2a to 3c and the lead electrodes 4a, 4b comprise Ag, Ag--Pd, 
Ni, Cu or the like. The piezoelectric substrate 1 generates the thickness 
longitudinal vibration by the vibrating electrodes 2a, 2b, 2c and the 
vibrating electrodes 3a, 3b, 3c. 
The insulating container 10 has a concave part 10a, with notches 11 
provided at both end parts of the concave part 10a. A base 12 is provided 
at the bottom surface center part of the concave part 10a. The 
piezoelectric substrate 1 is guided by the notches 11 so as to be 
accommodated horizontally long sideways for being supported by the notches 
11 and the base 12 without contacting with the bottom surface of the 
concave part 10a. 
The three parts, that is, the parts of the notches 11 and the base 12 of 
the container 10 are applied with a conductive adhesive paste so that the 
piezoelectric substrate 1 and the container 10 are fixed and connected 
electrically via the conductive adhesive. That is, lead electrodes 16, 17, 
18 are formed at both end parts and the center part of the container 10 by 
sputtering, deposition or the like. The lead electrodes 16, 17 elongate 
from the notch 11 parts, respectively, and the lead electrode 18 elongates 
from the base 12 part. The vibrating electrode 2a is connected 
electrically with the lead electrode 16 of the container 10 via the lead 
electrode 4a and the conductive adhesive. The vibrating electrode 3b is 
connected electrically with the lead electrode 17 of the container 10 via 
the lead electrode 4b and the conductive adhesive. The vibrating 
electrodes 2c, 3c are connected electrically with the lead electrode 18 of 
the container 10 via the conductive adhesive. 
The sealing lid 20 is provided with conductors 21, 22, 23 at both end parts 
and the center part by sputtering, deposition or the like. The sealing lid 
20 is fixed to the open end face of the container 10 with an adhesive. 
Accordingly, the piezoelectric substrate 1 is accommodated in the sealed 
vibrating space provided by the container 10 and the sealing lid 20. 
The composition of the piezoelectric substrate 1 will be explained. As the 
materials of the piezoelectric substrate 1, Pb.sub.3 O.sub.4, Nd.sub.2 
O.sub.3, In.sub.2 O.sub.3, Nb.sub.2 O.sub.5, TiO.sub.2 and MnCO.sub.3 were 
used. Other oxides of Pb, Nd, In, Nb, Ti, Mn, or a compound convertible to 
an oxide can also be used. 
The above-mentioned materials measured so as to have the compositions shown 
in Tables 1 to 3 were mixed and pulverized by the wet process, and 
calcined at 750.degree. C. to 950.degree. C. for 1 to 4 hours. The 
obtained calcined powders were pulverized with an organic binder, and 
press-molded with a 1 ton/cm.sup.2 pressure. The molded products were 
baked at 1,050.degree. C. to 1,250.degree. C. for 1 to 4 hours so as to 
obtain sintered compacts. After forming an electrode, the sintered 
compacts were polarized by applying a 3 to 5 kV/mm electric field for 10 
to 30 minutes in a silicone oil of 100.degree. C., and evaluated. The 
electric mechanical coupling coefficient k.sub.t (%) at the time of the 
thickness longitudinal vibration, the mechanical quality coefficient Qm, 
the Curie temperature Tc (.degree. C.), and the temperature coefficient of 
the resonance frequency F-TC (ppm/.degree. C.) are shown in Tables 1 to 3. 
Those marked with * at the specimen number are comparative examples 
outside the range of the present invention. 
TABLE 1 
__________________________________________________________________________ 
Specimen 
Nd substitution 
In.sub.1/2 Nb.sub.1/2 substitution 
MnCO.sub.3 content 
k.sub.t 
T.sub.c 
F-TC 
number 
x amount 
y amount (% by weight) 
(%) 
Q.sub.m 
(.degree. C.) 
(ppm/.degree. C.) 
__________________________________________________________________________ 
*1 0.10 0.20 0.0 41 110 
350 
10 
*2 0.10 0.00 0.1 37 650 
380 
-55 
*3 0.02 0.01 0.1 38 610 
400 
-49 
*4 0.10 0.01 0.1 39 600 
370 
-46 
*5 0.16 0.01 0.1 39 590 
340 
-38 
*6 0.00 0.15 0.1 29 230 
390 
-62 
7 0.02 0.15 0.1 38 540 
380 
-34 
8 0.10 0.15 0.1 40 550 
360 
-9 
9 0.16 0.15 0.1 42 610 
300 
-5 
*10 0.18 0.15 0.1 41 590 
280 
12 
*11 0.00 0.20 0.1 30 290 
380 
-59 
12 0.02 0.20 0.1 39 550 
370 
-33 
13 0.10 0.20 0.1 41 540 
350 
5 
14 0.16 0.20 0.1 43 560 
290 
9 
*15 0.18 0.20 0.1 42 560 
280 
15 
*16 0.00 0.35 0.1 31 210 
360 
-44 
17 0.02 0.35 0.1 42 590 
350 
-30 
18 0.10 0.35 0.1 41 540 
320 
10 
19 0.16 0.35 0.1 44 550 
290 
10 
*20 0.18 0.35 0.1 44 520 
260 
40 
21 0.02 0.50 0.1 42 500 
330 
-10 
22 0.10 0.50 0.1 43 480 
290 
11 
23 0.16 0.50 0.1 44 510 
290 
14 
*24 0.10 0.60 0.1 45 450 
280 
45 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Specimen 
Nd substitution 
In.sub.1/2 Nb.sub.1/2 substitution 
MnCO.sub.3 content 
k.sub.t 
T.sub.c 
F-TC 
number 
x amount 
y amount (% by weight) 
(%) 
Q.sub.m 
(.degree. C.) 
(ppm/.degree. C.) 
__________________________________________________________________________ 
*25 0.10 0.00 1.0 36 2010 
380 
-55 
*26 0.02 0.01 1.0 38 2030 
400 
-50 
*27 0.10 0.01 1.0 38 1980 
370 
-45 
*28 0.16 0.01 1.0 41 2000 
370 
-40 
*29 0.00 0.15 3.0 36 1810 
400 
-66 
30 0.02 0.15 3.0 40 2010 
380 
-33 
31 0.10 0.15 3.0 41 1910 
360 
-12 
32 0.16 0.15 3.0 40 1920 
300 
-10 
*33 0.18 0.15 3.0 39 2000 
280 
10 
*34 0.00 0.20 1.0 39 1820 
390 
-60 
35 0.02 0.20 1.0 40 2030 
370 
-30 
36 0.10 0.20 1.0 42 1990 
350 
2 
37 0.16 0.20 1.0 42 2040 
290 
10 
*38 0.18 0.20 1.0 42 2100 
280 
14 
*39 0.00 0.35 3.0 39 1870 
370 
-50 
40 0.02 0.35 3.0 41 1990 
350 
-22 
41 0.10 0.35 3.0 43 2000 
320 
8 
42 0.16 0.35 3.0 43 1920 
290 
13 
*43 0.18 0.35 3.0 44 1940 
260 
20 
44 0.02 0.50 1.0 41 1940 
330 
-21 
45 0.10 0.50 1.0 43 1960 
290 
9 
46 0.16 0.50 1.0 45 1960 
290 
14 
*47 0.10 0.60 1.0 44 1900 
260 
8 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Specimen 
Nd substitution 
In.sub.1/2 Nb.sub.1/2 substitution 
MnCO.sub.3 content 
k.sub.t 
T.sub.c 
F-TC 
number 
x amount 
y amount (% by weight) 
(%) 
Q.sub.m 
(.degree. C.) 
(ppm/.degree. C.) 
__________________________________________________________________________ 
*48 0.10 0.00 3.0 37 2110 
380 
-52 
49 0.02 0.01 3.0 38 2040 
400 
-49 
*50 0.10 0.01 3.0 39 2060 
370 
-45 
*51 0.16 0.01 3.0 39 2010 
340 
-39 
*52 0.00 0.15 3.0 27 1980 
390 
-66 
53 0.02 0.15 3.0 40 2020 
380 
-36 
54 0.10 0.15 3.0 41 2060 
360 
-10 
55 0.16 0.15 3.0 42 2010 
300 
-8 
*56 0.18 0.15 3.0 44 2050 
280 
10 
*57 0.00 0.20 3.0 28 2000 
380 
-62 
58 0.02 0.20 3.0 40 1980 
370 
-35 
59 0.10 0.20 3.0 42 1950 
350 
7 
60 0.16 0.20 3.0 43 1980 
290 
8 
*61 0.18 0.20 3.0 42 2060 
270 
12 
*62 0.00 0.35 3.0 39 2060 
360 
-50 
63 0.02 0.35 3.0 40 2080 
350 
-35 
64 0.10 0.35 3.0 41 2110 
370 
10 
65 0.16 0.35 3.0 41 2000 
290 
11 
*66 0.18 0.35 3.0 40 2050 
260 
16 
67 0.02 0.50 3.0 41 2050 
330 
-25 
68 0.10 0.50 3.0 45 2100 
290 
12 
69 0.16 0.50 3.0 44 1980 
290 
14 
*70 0.10 0.60 3.0 44 1990 
260 
15 
__________________________________________________________________________ 
Since the specimen 1 not containing the subcomponent MnCO.sub.3, which is 
outside the range of the present invention, has a mechanical quality 
coefficient Qm of 200 or less, it is not suitable for the application in a 
filter, a vibrator or the like. Moreover, if the subcomponent MnCO.sub.3 
content is increased to 5% by weight, the insulating property of the 
sintered compact is deteriorated so that the polarization cannot be 
achieved. Therefore, in the present invention, the content of the 
subcomponent MnCO.sub.3 is defined to be not less than about 0.1% by 
weight and not more than about 3.0% by weight, wherein a preferable 
mechanical quality coefficient Qm can be obtained as well as the 
polarization operation can be conducted easily. 
Moreover, as in the specimens 10, 15, 20, 33, 38, 43, 56, 61 and 66, if the 
amount x of substituting Pb by Nd is increased to 0.18, which is outside 
the range of the present invention, the Curie temperature is lowered to 
280.degree. C. or less. When the Curie temperature is 280.degree. C. or 
less, the piezoelectric property of the ceramic is drastically 
deteriorated by reflow at the time of mounting an element utilizing a 
piezoelectric ceramic, such as a filer, a vibrator or the like, and thus 
it is not preferable. On the other hand, if the amount x of substituting 
Pb by Nd is 0.00 (specimens 6, 11, 16, 21, 34, 39, 52, 57, and 62), the 
temperature coefficient of the resonance frequency F-TC is deteriorated 
beyond -37 ppm/.degree. C., and it is not suitable for the application in 
a filter, a vibrator or the like. With the amount x of substituting Pb by 
Nd in the range of the present invention, 0.02.ltoreq.x.ltoreq.0.16, a 
piezoelectric ceramic having a temperature coefficient of the resonance 
frequency within .+-.37 ppm/.degree. C. and a 290.degree. C. or more Curie 
temperature, advantageous in the application in a filter, a vibrator or 
the like, can be obtained. 
Furthermore, as in the specimens 24, 47 and 70, if the amount y of 
substituting Ti by (In.sub.1/2 Nb.sub.1/2) is 0.6, which is outside the 
range of the present invention, the Curie temperature is lowered to 
280.degree. C. or less, and thus it is not preferable for the reason 
mentioned above. However, if the substitution amount by (In.sub.1/2 
Nb.sub.1/2) y is less than 0.15 (specimens 2 to 5, 25 to 28, and 48 to 
51), the temperature coefficient of the resonance frequency F-TC is 
deteriorated beyond -37 ppm/.degree. C., and thus the amount y of 
substituting Ti by (In.sub.1/2 Nb.sub.1/2) needs to be in the range of the 
present invention, 0.15.ltoreq.y.ltoreq.0.50 in order to obtain a ceramic 
having both temperature stability of the resonance frequency and heat 
durability. 
A piezoelectric ceramic composition and a piezoelectric element using the 
piezoelectric ceramic composition according to the present invention are 
not limited to the above-mentioned embodiment, but can be modified 
variously within the gist hereof. In particular, the piezoelectric element 
is not limited to the above-mentioned embodiment, but can be a vibrator, a 
trap element or the like. Moreover, the vibration mode of the 
piezoelectric substrate can be a thickness sliding vibration mode. 
As apparent from the explanation provided above, a piezoelectric ceramic 
composition having a good temperature coefficient of the resonance 
frequency and an excellent heat durability can be obtained according to 
the present invention. Accordingly, a piezoelectric element, such as a 
ceramic vibrator, a ceramic filter or the like, having an excellent 
temperature stability can be realized without the risk of deteriorating 
properties at the time of reflow soldering.