Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-02-07
2004-05-04
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C252S06290R
Reexamination Certificate
active
06731049
ABSTRACT:
BACKGROUND OF INVENTION AND RELATED ART
The present invention relates to a piezoelectric element. More particularly, the present invention relates to a piezoelectric portion which has very high piezoelectric properties, and which has a high rate of increase of displacement as an actuator in the case of applying a large electric field and a high decomposability as a sensor in the case that a great force is applied.
In recent years, piezoelectric elements have been used in ink jet printer heads, speakers, microphones, etc.
As the piezoelectric elements, there are generally known those comprising a ceramic substrate, a piezoelectric portion made of a piezoelectric ceramic composition, formed on the substrate, and electrodes electrically connected to the piezoelectric portion. As to the piezoelectric ceramic composition constituting the piezoelectric portion, various improved compositions have been disclosed.
For example, a Pb(Mg
1/3
Nb
2/3
)O
3
—PbTiO
3
—PbZrO
3
ternary system solid solution composition and a piezoelectric ceramic composition wherein part of Pb in the above composition is replaced by Sr, La, etc., were disclosed [Japanese Patent Publication S44-17103, Japanese Patent Publication S45-8145]. With regard to a piezoelectric portion itself which are the most important factor determining the piezoelectric element properties of the piezoelectric element, a piezoelectric element having excellent piezoelectric properties (e.g. piezoelectric d constant is expected.
When a piezoelectric element is produced actually by superposing a piezoelectric material made of the above piezoelectric ceramic composition on a ceramic substrate and then subjecting the piezoelectric material to heat treatment, the obtained piezoelectric portion has a low density, and therefore, there have been pointed out such a problem that the piezoelectric element has a low flexural displacement or, when a voltage is applied thereto, it causes dielectric breakdown at the low density area. In particular, this problem is remarkable in the case of a piezoelectric element having a structure that a negative electrode and a positive electrode are disposed between piezoelectric portions alternatively, and its improvement has been strongly demanded.
In addition, sufficient piezoelectric properties cannot always be obtained with a piezoelectric portion made of the aforementioned piezoelectric ceramic composition, and there have been such a problem that when a voltage is raised to increase a flexural displacement, an increase of the flexural displacement obtained is very small relative to an increase of voltage on a side of a high electric field of 4 kV/mm or more.
Hence, there has been proposed a piezoelectric element produced by previously heat-treating a piezoelectric material made of the above piezoelectric ceramic composition to produce a piezoelectric portion, and then attaching this piezoelectric portion onto a ceramic substrate (Japanese Patent Application H11-29357).
In this piezoelectric element, attention was paid to a fact that use of a ceramic substrate impairs the densification of a piezoelectric portion. Thus, the piezoelectric element was accordingly improved in piezoelectric properties by means of obtaining a dense piezoelectric portion where a piezoelectric material made of a piezoelectric ceramic composition was previously heartbeat.
In this piezoelectric element, however, it is necessary to use an inorganic or organic adhesive at the time of attaching the piezoelectric onto the ceramic substrate. Therefore, there have been such problems that the adhesive impairs the vibration transmitability between the ceramic substrate and the piezoelectric or the adhesive components infiltrate into the piezoelectric or the ceramic substrate, deteriorating their properties.
In addition, in this piezoelectric element, no consideration is given to a piezoelectric ceramic composition itself constituting a piezoelectric portion. Therefore, there has been a problem that sufficient piezoelectric properties cannot always be obtained like the aforementioned piezoelectric element, and further, an increase of the flexural displacement obtained is very small relative to an increase of voltage in a region of a high electric field.
SUMMARY OF THE INVENTION
The present invention has been completed in view of the aforementioned problems and aims at providing a piezoelectric element which has very high piezoelectric properties, which is excellent in vibration transmittability between a substrate and a piezoelectric portion, and where linearity of a flexural displacement to voltage is ensured till a high electric region, and a method for production thereof.
Incidentally, in a piezoelectric element of the present invention, the aforementioned effect is great in a structure of laminating piezoelectric portions and electrodes alternatively to give a plurality of layers. The piezoelectric element can be suitably used for an actuator, a sensor, etc.
The present inventor made a study in order to solve the aforementioned problems. As a result, the present inventor found out that when there is used, as a piezoelectric material, a piezoelectric ceramic composition composed mainly of a PbMg
1/3
Nb
2/3
O
3
—PbZrO
3
—PbTiO
3
ternary system solid solution composition of particular formulation and containing NiO in a particular proportion, the densified piezoelectric portion can be obtained even when a piezoelectric material is superposed on a substrate and then heat-treated, whereby the aforementioned problems can be solved. The present invention has been completed based on the above finding.
That is, according to the present invention, there is provided a piezoelectric element including a ceramic substrate, and piezoelectric portion made of a piezoelectric ceramic composition containing a PbMg
1/3
Nb
2/3
O
3
—PbZrO
3
—PbTiO
3
ternary system solid solution composition having an average particle diameter of 1-10 &mgr;m with a maximum particle diameter being 5 times as large as the average particle diameter or less and being represented by the chemical formula discussed below as a main component. The piezoelectric portion contains 0.05 to 10.0 mass % of NiO
2
.
An electrode is electrically connected to said the piezoelectric portion, and the piezoelectric portion is solidly attached to the ceramic substrate directly or via the electrode.
The piezoelectric ceramic compositions represented by the following general formula: Pb
3
(Mg
y/3
Nb
2/3
)
a
Ti
b
Zr
c
O
3
.
In the above general chemical formula the following are satisfied: 0.95≦x≦1.05; 0.8≦y≦1.0; a, b and c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425) arid (0.375, 0.425, 0.200) in the coordinates with coordinate axes of said a, b and c, and a−b+c=1.00.
According to the present invention, there is further provided a piezoelectric element including a ceramic substrate, and a plurality of piezoelectric portions made of a piezoelectric ceramic composition containing a PbMg
1/3
Nb
3/3
O
3
—PbZrO
3
—PbTiO
3
ternary system solid solution composition represented by the chemical formula discussed below as a main component. The plurality of piezoelectric portions 0.05 to 10.0 mass % of NiO, and include a plurality of electrodes thereon.
The plurality of piezoelectric portions are laminated with interposing negative electrodes and positive electrodes of the plurality of electrodes alternately in each gap between the piezoelectric portions provided in stories and a lowermost piezoelectric portion is solidly attached to the ceramic substrate directly or via said electrode.
The piezoelectric ceramic composition is represented by the following general formula: Pb
x
(Mg
y/3
Nb
2/3
)
a
Ti
b
Zr
c
O
3
.
In the above general chemical formula the following are satisfied 0.95≦x≦1.05; 0.8≦y≦1.0; a, b and c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425. 0.025), (0.550, 0.325, 0.125), (0.375. 0.325, 0.
Kashiwaya Toshikatsu
Kitagawa Mutsumi
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