Compositions – Piezoelectric
Reexamination Certificate
2000-02-07
2001-07-10
Koslow, C. Melissa (Department: 1755)
Compositions
Piezoelectric
C501S135000
Reexamination Certificate
active
06258291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric ceramic compositions and piezoelectric ceramic devices using the same. In particular, the present invention relates to piezoelectric ceramic compositions, which are useful as materials for piezoelectric ceramic filters, piezoclectric ceramic oscillators and piezoelectric ceramic vibrators, and relates to piezoelectric ceramic devices using the same.
2. Description of the Related Art
Piezoelectric ceramic compositions comprising lead titanate zirconate (Pb(Ti
x
Zr
1−x
)O
3
) or lead titanate (PbTiO
3
) as main components are extensively used in piezoclectric ceramic filters, piezoelectric ceramic oscillators, and piezoelectric ceramic vibrators. In piezoelectric ceramic compositions comprising lead titanate zirconate or lead titanate as the main components, lead oxide is generally used. Lead oxide, however, requires facilities such as filters for removing powdered lead oxide, which is scattered by vaporization during the production steps. Such facilities incur increased production costs. In addition, the vaporization of the lead oxide causes deterioration of the uniformity of product quality.
On the other hand, piezoelectric ceramic compositions comprising bismuth layered compounds such as (Sr
1−x
M
x
)Bi
2
Nb
2
O
9
as main components and Mn as an optional component do not contain lead oxide and do not cause the above problems. These piezoelectric ceramic compositions, however, must be sintered at high temperatures of at least 1,250° C. in order to obtain piezoelectric ceramics having electromechanical coupling coefficients kt of at least 10%, which are at practical levels. Thus, these piezoelectric ceramic compositions require sintering furnaces which withstand such high-temperature sintering. Moreover, setters and the like for containing the piezoelectric ceramic compositions during sintering have short service lives in high-temperature operation, resulting in increased production costs.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a piezoelectric ceramic composition which can be sintered at a temperature of 1,100° C. or less, does not contains lead or lead compounds, and exhibits a practical level of electromechanical coupling coefficient kt at such a low sintering temperature. The piezoelectric ceramic composition is useful as materials for piezoelectric ceramic filters, piezoelectric ceramic oscillators and piezoelectric ceramic vibrators.
It is another object of the present invention to provide a piezoelectric ceramic device using the piezoelectric ceramic composition.
According to a first aspect of the present invention, a piezoelectric ceramic composition comprises a main component represented by the general formula SrBi
2
(Nb
1−x
W
y
)
2
O
9
, wherein 0<y≦0.3.
According to second aspect of the present invention, a piezoelectric ceramic composition comprises a main component represented by the general formula (Sr
1−x
M1
x
)Bi
2
)Nb
1−y
W
y
)
2
O
9
, wherein M1 is one of divalent metals other than Sr and trivalent metals other than Bi, 0<x ≦0.3, and 0<y ≦0.3. The M1 in the general formula may be at least one element selected from the group consisting of Ca, Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
According to a third aspect of the present invention, a piezoelectric ceramic composition comprises a main component represented by the general formula (Sr
1−x
M2
2x/3
)Bi
2
(Nb
1−y
W
y
)
2
O
9
, wherein M2 is a trivalent metal other than Bi, 0<x ≦0.45, and 0<y ≦0.3. The M2 in the general formula may be at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
According to a fourth aspect of the present invention, a piezoelectric ceramic composition comprises a main component represented by the general formula SrBi
2
Nb
2
O
9
and more than 0 to about 0.3 mole of W with respect to 1 mole of Bi in the main component. This piezoelectric ceramic composition may further comprise one of divalent metals other than Sr and trivalent metals other than Bi in an amount of more than 0 to about 0.15 mole with respect to 1 mole of Bi in the main component. The divalent metal or the trivalent metal may be at least one element selected from the group consisting of Ca, Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
The piezoelectric ceramic compositions according to the first to fourth aspects may further comprise manganese as an auxiliary component in an amount of more than 0 to about 1.0 percent by weight calculated as MnCO
3
.
According to a fifth aspect of the present invention, a piezoelectric ceramic device comprises a piezoelectric ceramic comprising the piezoelectric ceramic composition according to one of the first to fourth aspects, and electrodes.
The above objects, other objects, features and advantages of the present invention will be further apparent from the following preferred embodiments.
REFERENCES:
patent: 4978646 (1990-12-01), Bardhan et al.
patent: 6117354 (2000-09-01), Kimura et al.
Database WPI, Section Ch, Week 199703; Derwent Publications, Ltd., London GB; Class L03, An 1997-029376; XP002143528 & JP 08 290964 A (Sumitomo Chem. Co., Ltd.) Nov. 5, 1996; Abstract.
Ando Akira
Hayashi Koichi
Kimura Masahiko
Sawada Takuya
Koslow C. Melissa
Murata Manufacturing Co. Ltd
Ostrolenk Faber Gerb & Soffen, LLP
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