Compositions – Piezoelectric
Reexamination Certificate
2001-02-26
2002-07-30
Koslow, C. Melissa (Department: 1755)
Compositions
Piezoelectric
C501S136000, C501S137000, C501S138000, C310S365000
Reexamination Certificate
active
06426017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition and a piezoelectric element using the same.
2. Description of the Related Art
As a piezoelectric ceramic composition used for a piezoelectric ceramic element such as a piezoelectric ceramic resonator, in general, a ceramic composition containing lead zirconate titanate (PZT) or lead titanate (PT) as a main component has been used.
In recent years, as alternatives to the above-mentioned ceramic composition, those containing no lead have been developed. More specifically, as ceramics for a sensor actuator usable at high temperatures, a piezoelectric ceramic composition containing a layered bismuth compound as a main component has been considered.
However, the conventionally reported piezoelectric ceramic composition containing a layered bismuth compound as a main component has a problem in that an electromechanical coupling factor is not large enough. Thus, such a composition has not been put into practical use.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a piezoelectric ceramic composition having an electromechanical coupling factor larger than that of the conventional composition containing a layered bismuth compound by conventional ceramics processing and a piezoelectric element using the same.
In order to achieve the above-mentioned object, a first piezoelectric ceramic composition of the present invention contains, as a main component, a material having a composition represented by Formula: CaM
X
Bi
4−X
Ti
4−X
(Nb
1−A
Ta
A
)
X
O
15
, where M is at least one element selected from the group consisting of Ca, Sr, and Ba; 0.0≦A≦1.0; and 0.0≦X≦0.6. The first piezoelectric ceramic composition is composed of a main component alone, or composed of a main component and a subsidiary component. According to the first piezoelectric ceramic composition, a piezoelectric ceramic composition having an electromechanical coupling factor larger than that of a conventional layered bismuth compound and containing no lead is obtained.
The above-mentioned first piezoelectric ceramic composition further may contain MnO
2
as a subsidiary component. According to this constitution, a piezoelectric ceramic composition having satisfactory characteristics such as a mechanical quality factor is obtained.
In the above-mentioned first piezoelectric ceramic composition, a content of the MnO
2
may be 0.6% by mass or less.
Furthermore, a second piezoelectric ceramic composition of the present invention contains, as a main component, a material having a composition represented by Formula: CaM
Y
Bi
4−Y
Ti
4−Y
(Nb
1−B
Ta
B
)
Y
O
15
, where M is at least one element selected from the group consisting of Ca, Sr, and Ba; 0.0≦B≦1.0; and 0.0≦Y≦0.6, and contains WO
3
as a subsidiary component. According to the second piezoelectric ceramic composition, a piezoelectric ceramic composition having an electromechanical coupling factor larger than that of a conventional layered bismuth compound and containing no lead is obtained.
In the above-mentioned second piezoelectric ceramic composition, a content of the WO
3
may be 0.5% by mass or less. According to this constitution, polarization will not be difficult.
The above-mentioned second piezoelectric ceramic composition further may contain MnO
2
as a subsidiary component. According to this constitution, a piezoelectric ceramic composition having satisfactory characteristics such as a mechanical quality factor is obtained.
Furthermore, a first piezoelectric element of the present invention includes a piezoelectric substance made of a piezoelectric ceramic composition, wherein the piezoelectric ceramic composition contains, as a main component, a material having a composition represented by Formula: CaM
X
Bi
4−X
Ti
4−X
(Nb
1−A
Ta
A
)
X
O
15
, where M is at least one element selected from the group consisting of Ca, Sr, and Ba; 0.0≦A≦1.0; and 0.0≦X≦0.6. According to the first piezoelectric element, a piezoelectric element having satisfactory electrical characteristics and containing no lead is obtained.
In the above-mentioned first piezoelectric element, the piezoelectric ceramic composition further may contain MnO
2
as a subsidiary component.
In the above-mentioned first piezoelectric element, a content of the MnO
2
in the piezoelectric ceramic composition may be 0.6% by mass or less.
The above-mentioned first piezoelectric element further may include two vibrating electrodes formed on the piezoelectric substance so as to be opposed to each other with the piezoelectric substance interposed therebetween, wherein a thickness t of the piezoelectric substance and an area S of the vibrating electrode satisfy a relationship: 22≦S/t
2
. According to this constitution, a piezoelectric resonator that is designed and produced easily is obtained.
In the above-mentioned first piezoelectric element, the vibrating electrodes may have a circular shape.
Furthermore, a second piezoelectric element of the present invention includes a piezoelectric substance made of a piezoelectric ceramic composition, wherein the piezoelectric ceramic composition contains, as a main component, a material having a composition represented by Formula: CaM
Y
Bi
4−Y
Ti
4−Y
(Nb
1−B
Ta
B
)
Y
O
15
, where M is at least one element selected from the group consisting of Ca, Sr, and Ba; 0.0≦B≦1.0; and 0.0≦Y≦0.6, and contains WO
3
as a subsidiary component. According to the second piezoelectric element, a piezoelectric element having satisfactory electrical characteristics and containing no lead is obtained.
In the above-mentioned second piezoelectric element, a content of the WO
3
in the piezoelectric ceramic composition may be 0.5% by mass or less.
In the above-mentioned second piezoelectric element, the piezoelectric ceramic composition further may contain MnO
2
as a subsidiary component.
The above-mentioned second piezoelectric element further may include two vibrating electrodes formed on the piezoelectric substance so as to be opposed to each other with the piezoelectric substance interposed therebetween, wherein a thickness t of the piezoelectric substance and an area S of the vibrating electrode satisfy a relationship: 22≦S/t
2
.
In the above-mentioned second piezoelectric element, the vibrating electrodes may have a circular shape.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.
REFERENCES:
patent: 982 782 (2000-03-01), None
patent: 2000-313662 (2000-11-01), None
“Energy Trapping Characteristics of Bismuth Layer Structured Compound Ca Bi4Ti4O15”; Kimura, M.; Sawada, T.; Ando, A.; Sakabe, Y.; Japanese Journal Of Applied Physics; vol. 38; 1999; pp. 5557-5560.
Nishida Masamitsu
Sogou Hiroshi
Takahashi Keiichi
Koslow C. Melissa
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P,C,
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