Compositions – Piezoelectric – Lead – zirconium – titanium or compound thereof containing
Reexamination Certificate
2000-05-22
2001-10-09
Koslow, C. Melissa (Department: 1755)
Compositions
Piezoelectric
Lead, zirconium, titanium or compound thereof containing
C501S134000, C501S135000, C501S136000
Reexamination Certificate
active
06299791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectrie ceramic material and a piezoelectric ceramic sintered body obtained using the same. The present invention particularly relates to a piezoelectric ceramic material that can be advantageously used for piezoelectricity application devices that are required to have a relatively small electromechanical coupling coefficient and a small resonant resistance, and a piezoelectric ceramic sintered body obtained using the same.
2. Description of the Related Art
Pb[(Mn
⅓
Nb
⅔
), Zr, Ti]O
3
based piezoelectric ceramic materials have been widely used for materials for constituting piezoelectric ceramic parts provided in piezoelectricity application devices including filters, oscillators and trap elements making use of bulk wave or surface wave because these materials have good resonance characteristics.
For example, Japanese Laid-open Patent Application No. 5-327397 discloses that a surface wave device having good resonance characteristics, temperature dependency of the resonance characteristics and heat resistance can be practically obtained by using a piezoelectric ceramic material represented by a general formula of (Pb
1−x
Me
x
){(Mn
⅓
Nb
⅔
)
a
Ti
b
Zr
c
}O
3
, wherein Me represents at least one of the element selected from Ca, Ba and Sr, and x, a and b satisfy the following relations:
0.005≦×≦0.10
0.0≦a≦0.14
0.40≦b≦0.60
0.26≦c≦0.59 and
a+b+c=1.00
Japanese Laid-open Patent Application No. 5-24916 discloses {PbSr}{(TiZr)(MnNb)}O
3
based materials containing at least one of 0.005 to 0.040% by weight of SiO
2
and 0.005 to 0.040% by weight of Al
2
O
3
in which irregularity of electric characteristics has been improved.
Narrow-band filters of conventional Pb[(Mn
⅓
Nb
⅔
), Zr, Ti]O
3
based piezoelectric ceramic materials that are required to have a small electromechanical coupling coefficient cannot be designed in a saturation polarization state because the materials have a large electromechanical coupling coefficient in that saturation polarization state. Another problem is that filter insertion loss is increased due to increased resonant resistance when the degree of polarization is made to be in a saturated state for decreasing the electromechanical coupling coefficient.
Narrow-band filters are desired to be superior to wide-band filters in temperature stability of resonant frequencies. It is not possible for the conventional Pb[(Mn
⅓
Nb
⅔
), Zr, Ti]O
3
based piezoelectric ceramic materials to exhibit such excellent temperature stability as required for the narrow-band filters.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a piezoclectric ceramic material that can satisfy such characteristics as required for designing the narrow-band filters, and more practically, a piezoelectric material that can satisfy such characteristics as a small electromechanical coupling coefficient, a small resonant resistance and a small temperature dependency of the resonant frequency, and to provide a piezoelectric ceramic sintered body obtained by firing the piezoelectric ceramic material.
In one aspect, the present invention provides a piezoelectric ceramic material containing at least Pb, Sr, Zr, Ti, Mn, Nb, Si and Al, comprising a principal component represented by a general formula of (Pb
a
Sr
b
)(Zr
c
Ti
d
Mn
e
Nb
f
)O
3
and having a composition satisfying the following relations: 0.93≦a≦1.01, 0.01≦b≦0.04, 0.37≦c≦0.47, 0.48≦d≦0.58, 0.0105≦e≦0.06, 0.02≦f≦0.06; preferrably 0.96≦a≦0.99, 0.01 <b<0.04, 0.39<c<0.43, 0.5<d<0.54, 0.02≦e≦0.04 and 0.02<f<0.06; and 1.05≦2e/f≦2, wherein about 0.003% by weight or more and about 0.1% by weight or less, preferrably about 0.02% to 0.1% by weight of SiO
2
and about 0.003% by weight or more and about 0. 1% by weight or less, preferrably about 0.02% to 0.1% by weight of Al
2
O
3
as sub-components are contained relative to the principal component.
The piezoelectric ceramic material according to the present invention is preferably destined to be fired in an oxygen atmosphere. Accordingly, the present invention is also directed toward a piezoelectric ceramic sintered body obtained by firing the piezoelectric ceramic material in an oxygen atmosphere.
Preferably, the piezoelectric ceramic sintered body is used in an unsaturated polarization state having an electromechanical coupling coefficient of 80% or less of that in the saturated polarization state.
A piezoelectric ceramic sintered body having a small electromechanical coupling coefficient, a small resonant resistance and small temperature dependency of the resonant frequency can be obtained according to the present invention as hitherto described. A filter having a small insertion loss at narrow-bands and being excellent in temperature stability in a pass-band frequency is obtainable by using such piezoelectric ceramic sintered body for the filter.
The content of Pb (a) in the principal component is preferably within a range of 0.93≦a≦1.01 because when a is smaller than 0.93, sintering property is decreased, failing obtaining a sufficiently dense sintered body, while the sintered body may be deformed when a is larger than 1.01.
The content of Sr (b) is preferably within a range of 0.01≦b≦0.04 because when b is smaller than 0.01, electric characteristics turn out to be uneven in the sintered body due to decreased degree of polarization while when b is larger than 0.04, the electromechanical coupling coefficient is so extremely increased that the sintered body cannot be used for the piezoelectric ceramic materials for use in the narrow-band filters that are required to have a small electromechanical coupling coefficient.
When the content of Zr (c) and the content of Ti (d) are out of the ranges of 0.37≦c≦0.47 and 0.48≦d≦0.58, respectively, the temperature range where temperature dependency of the resonant frequency is small varies from the ambient temperature range of−20° C. to 80° C. where the filter is usually used. Consequently, the content of Zr (c) and the content of Ti (d) preferably fall within the ranges of 0.37≦c≦0.47 and 0.48≦d≦0.58, respectively, in order to prepare a piezoelectric ceramic material for obtaining a highly practical piezoelectric ceramic sintered body having an excellent temperature stability at ambient temperatures.
The content of Mn (e) is preferably within a range of 0.0105≦e≦0.06 because when e is smaller than 0.0105, the resonant resistance Z
r
is increased to enhance the filter insertion loss while, when e is larger than 0.06, the insulation resistance of the sintered body is decreased to make polarization treatment difficult.
The content of Nb (f) is preferably within a range of 0.02≦f≦0.06 because when f is smaller than 0.02, abnormal grain growth occurs while when f is larger than 0.06, the sintering temperature is increased over 1250° C. to remarkably facilitate evaporation of PbO, causing deformation of the sintered body.
With respect to the relation between the content of Mn (e) and the content of Nb (f), the ratio of 2e/f was limited within a range of 1.05≦2e/f≦2 because, when the ratio of 2e/f is smaller than 1.05, temperature dependency of the resonant frequency is increased while insulation resistance is decreased to make polarization treatment impossible when the ratio of 2e/f is larger then 2.
Concerning SiO
2
and Al
2
O
3
as sub-components, both of the content of SiO
2
, and the content of Al
2
O
3
are preferably to be about 0.003% or more and about 0.1% by weight or less because when the content of SiO
2
or Al
2
O
3
is below the range as described above, mechanical strength of the sintered body becomes insufficient to give rise to damage in subsequent machining of the sintered body while, when the content is over the rang
Horikawa Katsuhiro
Yoshizawa Isamu
Koslow C. Melissa
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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