High-power piezoelectric ceramics

Details High-power piezoelectric ceramics High-power piezoelectric ceramics

2002-04-16

2004-11-02

Koslow, C. Melissa (Department: 1755)

Compositions

Piezoelectric

Lead, zirconium, titanium or compound thereof containing

C501S134000, C501S152000, C310S311000

Reexamination Certificate

active

06811719

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to high power piezoelectric ceramics, more particularly, to piezoelectric ceramic compositions for use in ultrasonic motors, ultrasonic vibrators, piezoelectric actuators, and the like.
BACKGROUND OF THE INVENTION
The art has explored the high-power characteristics of piezoelectric materials for use in devices such as ultrasonic motors, piezoelectric actuators and piezoelectric transformers. It is preferred in the art that the piezoelectric materials used in these types of devices have a high mechanical quality factor, low heat generation, a high piezoelectric constant, as well as high vibrational velocities (v
o
) when subjected to low AC electric fields. The art has found it difficult, however, to achieve a piezoelectric material which has both a high mechanical quality factor and a high piezoelectric constant, as well as high vibrational velocity.
It is known in the art that the v
0
in lead-zirconate-titanate (PZT) compounds which have the ABO
3
perovskite structure can be increased by introducing lower valent dopants such as Fe on the B-site, and that v
0
can be decreased by introducing higher valent dopants such as Nb on the B-site. The lower valent dopants tend to produce “hardening” effects on the base PZT type compounds by increasing the mechanical quality factor (Q
m
) while decreasing the electromechanical coupling factor (k). In contrast, higher valent substituents tend to decrease the Q
m
while increasing the (k) value.
It also is known in the art that the vibrational velocity (v
0
)of a piezoelectric material is restricted by heat generation within the piezoelectric material when subjected to an electric field (E
ac
). Heat generation under an electric field is known to be a function of vibrational velocity (v
o
). The value of v
o
is directly proportional to Q
m
and to the electromechanical coupling factor (k) under constant E
ac
. Development of a piezoelectric material with significantly higher v
o
, however, has not been successful in the art since each of Q
m
and k are increased at the expense of the other.
A need therefore exists for a piezoelectric material which has both increased Q
m
and increased k values, as well as increased vibrational velocity for high-power applications.
SUMMARY OF THE INVENTION
This invention relates to piezoelectric compositions for manufacture of rare earth (“RE”) doped Pb(Zr,Ti)O
3
—Pb(Mn,Sb)O
3
compounds which have increased vibrational velocity as well as increased Q
m
and (k) values. The invention further relates to piezoelectric compounds corresponding to the formula (zPb(Zr
w
Ti
(1−w)
)O
3
—(1−z)Pb(Mn
1/3
Sb
2/3
)O
3
+RE
x
) where z is ≦0.95, preferably about 0.90, 0.4≦w≦0.6, preferably 0.50≦w≦0.54, more preferably about 0.52, and where RE is a rare earth cation dopant, and 0<x<5%, preferably 0<x<2%.
The RE dopants employed advantageously generate both “hardening” and “softening” effects in the doped Pb(Zr,Ti)O
3
—Pb(Mn,Sb)O
3
compounds. Examples of RE dopants which may be employed include Eu
+3
, Yb
+3
, Ce
3+
, Er
3+
, Tm
3+
, Ho
3+
and Dy
3+
, and mixtures thereof, preferably Eu
+3
, and Yb
+3
, most preferably Yb
+3
. The Eu and Yb dopants advantageously produce both “hardening” and “softening” effects in Pb(Zr,Ti)O
3
—Pb(Mn,Sb)O
3
compounds such as 0.90Pb(Zr
0.52
Ti
0.48
)0
3
−0.10Pb(Mn
1/3
Sb
2/3
)O
3
. Doping of 0.90Pb(Zr
0.52
Ti
0.48
)0
3
−0.10Pb(Mn
1/3
Sb
2/3
)O
3
with any of Eu and Yb produces increased Q
m
, d
31
, and k
31
relative to undoped 0.90Pb(Zr
0.52
Ti
0.48
)0
3
−0.10Pb(Mn
1/3
Sb
2/3
)O
3
. Under high E
ac
conditions, Eu and Yb doping of Pb(Zr,Ti)O
3
—Pb(Mn,Sb)O
3
type compounds such as 0.90Pb(Zr
0.52
Ti
0.48
)0
3
−0.10Pb(Mn
1/3
Sb
2/3
)O
3
advantageously produces an increased v
0
relative to undoped 0.90 Pb(Zr
0.52
Ti
0.48
)0
3
−0.10Pb(Mn
1/3
Sb
2/3
)O
3
. These doped compounds include compounds of formula (zPb(Zr
w
Ti
(1−w)
)O
3
−(1−z)Pb(Mn
1/3
Sb
2/3
)O
3
+RE
x
) where z is 0.90, w is 0.52, RE is Yb and x is about 0.1 to about 0.3%. Advantageously, Pb(Zr,Ti)O
3
—Pb(Mn,Sb)O
3
type compounds such as 0.90Pb(Zr
0.52
Ti
0.48
)O
3
−0.10Pb(Mn
1/3
Sb
2/3
)O
3
, when doped with about 0.1 to about 2.0 wt. % Yb, preferably about 0.1% to about 0.2% Yb, produces a high-power piezoelectric material.
In another aspect, the invention relates to piezoelectric devices such as ultrasonic motors, ultrasonic vibrators, and piezoelectric actuators which include a piezoelectric ceramic compound represented by formula (zPb(Zr
w
Ti
(1−w)
)O
3
−(1−z)Pb(Mn
1/3
Sb
2/3
)O
3
+RE
x
) where z≦0.95, preferably about 0.90, 0.4≦w≦0.6, preferably 0.50≦w≦0.54, more preferably about 0.52, RE is a rare earth cation such as Yb, Eu and Ce, and 0<x<5%, preferably 0<x<2%.
In yet another aspect, the invention relates to piezoelectric ceramic compounds represented by formula (zPb(Zr
w
Ti
(1−w)
)O
3
−(1−z)Pb(Mn
1/3
Sb
2/3
)O
3
+RE
x
) where z is 0.9, w is 0.52, RE is a rare earth cation selected from the group consisting of Eu, Lu, Nd and La and x is 0.1%.


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