Piezoelectric ceramic composition for use in an ultrasonic...

Details Piezoelectric ceramic composition for use in an ultrasonic... Piezoelectric ceramic composition for use in an ultrasonic...

2000-07-27

2001-08-21

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

Reexamination Certificate

active

06278225

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition for use in an ultrasonic wave motor, a piezoelectric transducer, etc.
2. Description of Related Art
As piezoelectric ceramic compositions used for an ultrasonic wave motor, an ultrasonic oscillator, a piezoelectric transducer, an igniter and the like, compositions comprised mainly of lead titanate zirconcite, as disclosed in Japanese Examined Patent Publication (Kokoku) No. 39-6277 and Japanese Unexamined Patent Publication (Kokai) No. 8-119733, for example, are known.
Japanese Examined Patent Publication (Kokoku) No. 39-6277 discloses a composition in which Sb
2
O
3
and MnO
2
are externally added to a stoichiometric lead titanate zirconate represented by Pb(Zr
x
Ti
y
)O
3
where x+y=1 and Sr partially substitutes for Pb.
Japanese Unexamined Patent Publication (Kokai) No. 8-119733 discloses a composition of Pb((Mn
1
/
3
Sb
2
/
3
)
x
Zr
y
Ti
2
)O
3
where x+y+z=1, Sr partially substitutes for Pb, and the total mole of Sr and Pb is less than 1.
It is known that these compositions provide an excellent initial electric property when they are applied to a ultrasonic wave motor, etc.
However, the above known piezoelectric ceramic compositions have the following problems.
The piezoelectric ceramic compositions, although they have an excellent initial electric property, have a low fatigue resistance and therefore lack reliability. The reason therefor is thought to be that since a temperature of about 1200° C. or higher is required to sinter the above known piezoelectric ceramic compositions for densification, the crystal grain size of the sintered body becomes relatively large and a microstructure, including fine ZrO
2
particles deposited in grain boundaries, is formed. Also, stable commercial manufacture of the piezoelectric ceramic compositions is not easy due to a high sintering temperature, resulting in non-uniform quality of the products.
Thus, development of a piezoelectric ceramic composition which has an excellent electric property and excellent reliability and can be easily manufactured, has been demanded.
The present invention responds to the above demand and aims to provide a piezoelectric ceramic composition which can be manufactured at a temperature lower than the conventional temperature, has a small crystal grain size and is excellent in fatigue resistance.
SUMMARY OF THE INVENTION
The present invention attains the above object by providing a piezoelectric ceramic composition, having a tetragonal perovskite structure and represented by a general formula (Pb
a
Sr
b
)(Zr
c
Ti
d
Sb
e
Mn
f
)O
3
wherein Pb and Sr are assumed to occupy an A site, Zr, Ti, Sb and Mn are assumed to occupy a B site, and a molar ratio M of A site/B site atoms of (a+b)/(c+d+e+f) is in a range of more than 1.00 to 1.03 (1.00<M23 1.03), preferably in a range of 1.01 to 1.03 (1.01≦M≦1.03).
In a preferred embodiment, the piezoelectric ceramic composition of the present invention has an average crystal particle size of 1 to 3 &mgr;m and an average flexural strength of not less than 100 MPa.
In another preferred embodiment, the piezoelectric ceramic composition of the present invention has a piezoelectric constant −d
31
of not less than 140 pm/V and a mechanical quality Q
m
of not less than 500.


REFERENCES:
patent: 4751209 (1988-06-01), Yokotani et al.
patent: 40 41 993 A1 (1992-07-01), None
patent: 43 27 993 C 1 (1994-11-01), None
patent: 39-6277 (1964-05-01), None
patent: 1-111725 (1989-04-01), None
patent: 8-119733 (1992-07-01), None
patent: 8-119733 (1996-05-01), None
patent: 8-325058 (1996-12-01), None
patent: 11-191968 (1999-07-01), None

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