JPS61222186A - Piezoelectric ceramic for electromechanical transduction element - Google Patents

Abstract

PURPOSE:To increase the quantity of displacement extremely by using a substance capable of taking either phase of a ferroelectric phase, a non-ferroelectric phase or the coexistent phase of the ferroelectric phase and the non-ferroelectric phase when applied voltage is brought to 0. CONSTITUTION:The titled piezoelectric ceramics consist of a substance having properties in which phase transformation is generated by applying voltage within the range of a working temperature and the length of a crystallographic axis and/or the unit cell volume of a crystal changes while either phase of a ferroelectric phase, a non- ferroelectric phase or the coexistent phase of the ferroelectric phase and the non- ferroelectric phase can be taken. Ceramics composed of (Pb0.85Sr0.15)(Zr0.51Ti0.34Zn0.0125 Ni-0.0378Nb0.20)O3 are processed in 10mm length and 0.35mm thickness, chromium-gold are evaporated onto both upper and lower surfaces and an electrode is shaped, the ceramics are polarized are treated, and the result of the measurement of P-E characteristics at a time when voltage is applied to the ceramics is displayed in the graph 5 and the result of the measurement of strain (DELTAl/l) in the longitudinal direction in the graph 6. According to the result, it is recognized that extremely large displacement is displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric ceramic for an electromechanical transducer, and particularly to a piezoelectric ceramic for an electromechanical transducer whose displacement is extremely large.

[Conventional technology]

Electrical/mechanical conversion elements include high frequency filters, ultrasonic delay lines,
In addition to being widely used in various elements for information processing devices such as optical modulation elements, they are also widely used in power devices such as gas igniters, ultrasonic oscillators, piezoelectric transformers, and piezoelectric motors.

Conventional electrical/mechanical transducers use ferroelectric ceramics/ceramics and take advantage of their piezoelectric effects, but when used as power devices, they are expected to have even larger displacements. ing.

In addition, in recent years, an electrical +11a mechanical conversion element using an antiferroelectric material and an electrical/mechanical conversion element using a paraelectric material have been proposed (JP-A-54-78993 (JP-A-59-3643).
9), Japanese Patent Publication No. 54-78994 (Japanese Patent Publication No. 59-3644)
0)) These electrical/mechanical conversion elements are made by bonding an antiferroelectric ceramic plate or a paraelectric ceramic plate to a substrate or the like.

The residual polarization is small or zero when the external electric field is reduced to zero.

[Problems to be Solved by the Invention] All of the dielectrics used in the above-mentioned conventional electromechanical conversion elements have a small amount of displacement, and have a larger amount of displacement and are suitable for use as a dynamic device. There is expected.

For example, the electro-mechanical conversion element disclosed in Japanese Patent Publication No. 59-36439 is as follows:
As described in the fourth line of the column, the amount of displacement is smaller and the sensitivity is smaller than in the case of conventional ferroelectric ceramics.

Furthermore, the electromechanical transducer disclosed in Japanese Patent Publication No. 59-36440 also has a smaller amount of displacement than that made of ferroelectric material.
Its sensitivity is low (page 4, column 7, lines 15 to 19 of the same publication).

That is, all of the methods disclosed in Japanese Patent Publication No. 59-36439.36440 attempt to minimize the residual displacement of the dielectric when the applied electric field is O.
This is intended to provide a small electromechanical coupling coefficient icp. Therefore, if the strain when an electric field E is applied to the piezoelectric material is S, then the piezoelectric constant d is expressed as dmi=asi/aEm (where isl~6.Otori-1~3), and this piezoelectric constant dmi is , which in many cases has a linear relationship with the electromechanical coupling coefficient. Therefore, the special public
As in No. 9-36439.36440, when k is made small, the piezoelectric constant becomes small, and therefore the displacement when the same electric field is applied must also become small.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides the following.

By applying a voltage within the operating temperature range, a phase transformation occurs and the length of the crystal axis and/or the unit cell volume of the crystal changes, and when the applied voltage is O, a ferroelectric phase and a non-ferroelectric phase change. and a piezoelectric ceramic for an electrical/mechanical transducer element, characterized in that it is made of a material that has the property of having either of the coexisting phases of a ferroelectric phase and a non-ferroelectric phase.

The present invention will be explained in more detail below.

The piezoelectric ceramic for electromechanical conversion elements of the present invention exhibits any of the following phases: a ferroelectric phase, a non-ferroelectric phase, and a coexistence phase of a ferroelectric phase and a non-ferroelectric phase when the applied voltage is 0. You can get it.

As is well known, a ferroelectric material is one in which the direction of spontaneous polarization is reversed by the reversal of the polarity of an external electric field, and it has a hysteresis loop type P (polarization) as schematically shown in Figure 2.
E C electric field) characteristics.

As shown in the figure, in a ferroelectric material, E+ or more or -E I
By applying the following electric field, the spontaneous polarization is reversed and the state changes from 21 to 23 or from 23 to 21. Even if E=0 after applying an arbitrary electric field E, the dielectric exists in state 22 or 24, that is, as a ferroelectric having spontaneous polarization.

Furthermore, an antiferroelectric material is composed of two sublattices whose crystal lattices are antiparallel to each other and have spontaneous polarizations of equal absolute value, and these two spontaneous polarizations can be made parallel by an external electric field. The P-E characteristic of the antiferroelectric material is a double hysteresis loop as schematically shown in FIG.

As shown in the figure, in a single antiferroelectric material, by applying an electric field with an absolute value of 83 or more, the state becomes s31 or 33,
Polarization appears, but no polarization appears in an applied electric field whose absolute value is less than E2, and depending on the history, either state 31, 32 or 33 will result. If E=Q with an arbitrary electric field E being applied, the dielectric will be in a state of P=0 and will not exhibit spontaneous polarization.

Furthermore, a paraelectric substance has a cubic crystal lattice, and as shown schematically in Figure 4, phase transformation does not occur due to changes in the applied electric field, and since it does not originally have spontaneous polarization, its orientation is also variable. I don't get it.

Therefore, even if an electric field is applied, polarization is extremely small.

The term "nonferroelectric material" as used herein is a general term for the above-mentioned antiferroelectric material and paraelectric material.

FIG. 1 is a hysteresis loop showing the P-E characteristics of the dielectric of the present invention.

The piezoelectric ceramic for electromechanical transducer of the present invention exhibits any phase among the ferroelectric phase, the non-ferroelectric phase, and the coexistence phase of the ferroelectric phase and the non-ferroelectric phase when the applied voltage is O. You can get it. That is, by applying an electric field with an absolute value of E5 or higher, the ceramic composition according to the present invention assumes a ferroelectric phase of state 1 or 14 and exhibits polarization.If E=0 in this state, state 1 is obtained.
2 or 15, the spontaneous polarization remains and the ferroelectric phase is maintained. When an electric field of -E4 to -E5 is applied in state 12 or an electric field of E4 to E5 is applied in state 15, P=0 and no polarization is shown in state 13.16, that is,
It becomes a non-ferroelectric phase. Moreover, in state 13 or 16, E
=O, the state of P=0 is maintained and the origin 0 is reached, maintaining the non-ferroelectric phase.

Furthermore, when an electric field slightly smaller than E4 (E4-ΔE) or an electric field slightly larger than E5 (E5+ΔE) is applied at state s14 or s15, and then E=0.

Alternatively, in state 11 or 12, an electric field slightly larger than -E4 (-E4+ΔE) or slightly smaller than -E5 (-E5-ΔE) is applied.

Next, when E=0, E=0 follows a path as shown by the broken line arrow in FIG. 1, and a phase in which a ferroelectric phase and a non-ferroelectric phase coexist is assumed.

Generally, when an electric field is applied to a dielectric, the displacement of the dielectric is caused by electrostriction or phase transformation.

It can be classified into four elements: deformation due to the orientation of spontaneous polarization and deformation due to the dE (d: piezoelectric constant) term, and displacement is caused by one or more of these elements. (Electrostriction occurs in all dielectric materials.) In the piezoelectric ceramic according to the present invention, large deformation occurs due to the combination of deformation due to phase transformation and deformation due to the orientation of spontaneous polarization.

That is, as detailed in the explanation of FIG. 1, in the piezoelectric ceramic according to the present invention, the ferroelectric phase, the non-ferroelectric phase, the coexistence of the ferroelectric phase and the non-ferroelectric phase; There is a mutual transformation between them, which causes displacement. Due to phase transformation, the length of one or more of the a-axis, b-axis, and a-axis changes, or the axis crossing angles α, β, and γ change, even though the axial length does not change, resulting in a change in the unit cell of the crystal. The volume changes and this causes a displacement.

Further, according to the inventors' research, in the ceramic composition according to the present invention, for example, in the case of a tetragonal system, the ratio C/a of the a-axis to the a-axis of the crystal lattice often has a degree of deviation from 1. , it was recognized that the degree of delamination from 1 of the crystals constituting the normal antiferroelectric phase was greater. In this way, a crystal with a large deviation of C/a from 1 has a larger deformation due to phase transformation or a larger displacement due to the orientation of spontaneous polarization than one with a C/a close to 1.

On the other hand, in a ferroelectric material, although spontaneous polarization reversal or orientation may occur due to changes in the applied electric field, phase transformation does not occur, so the displacement is correspondingly smaller.

Furthermore, in antiferroelectric materials, changes in the applied electric field cause reversal or orientation of spontaneous polarization and phase transformation between the antiferroelectric phase and the ferroelectric phase. However, the antiferroelectric phase and the ferroelectric phase resulting from this phase transformation are usually C
/a is close to 1, and the displacement is that much smaller.

In the ordinary lightning body, no phase transformation occurs due to the I- of the I+ applied to the lightning, and since there is no spontaneous polarization in the first place, its orientation is impossible, and therefore the displacement is extremely small.

By applying a voltage within the operating temperature range, a phase transformation occurs and the length of the crystal axis and/or the unit cell volume of the crystal changes, and when the applied voltage is 0, the ferroelectric phase and non-ferroelectric phase change. Examples of substances that have the property of having either phase or a coexisting phase of a ferroelectric phase and a non-ferroelectric phase include the following.

(PbO, 924LaO, 07B) (Zro, 7oT
io, ao) o, 5szoa (PbO, 91BLa0.
084) (Zr0.85Ti0.35)0.97903
(Pbo, 5sSro, ts) (Zro, 5tTio,
34Zno, ot25 old 0.0375NbO, 1G) 0
3 (Pb0.85SrO, 15) (ZrO, 50TiO,
35 old 0.05Nb0.10)03(”)0.85Sr
0.15) (ZrO,55TiO03ONiO,05N
b0.10) 03 (Pbo, esSro, ts) (Zr
o, 5tTio, atZno, ot2s old 0.0375
Nb0.1G)3 ('bO,85srO,15) (ZrQ,5QTiQ
, 35 old 0.05NbO, 1G) 03ko (7), (Pbo, 52aLao, o7e) (ZrO07
0Tio, 3o)o, and 5st03 have particularly large solenoid displacements and are suitable.

[Function] The piezoelectric ceramic for an electro-mechanical transducer of the present invention is capable of producing both large displacements due to phase transformation and displacements due to spontaneous polarization upon application of an electric field, and an extremely large displacement can be obtained by the synergistic effect of these displacements. .

[Example] Example 1 (PbO, 85SrO, 15) (Zr0.51TiO0
34Z! 10.0125NiQ, 03?5NbO, 1G
)03 is processed to a length of 10 mm and a thickness of 0.35 mm, and after 0 polarization treatment in which electrodes are formed by vapor depositing chromium-gold on both the upper and lower surfaces, P when a voltage is applied to this porcelain.
The measurement results of -E characteristics are shown in Figure 5.
Figure 6 shows the measurement results of the strain (ΔfL/fL) of the transverse vibration motor.

From the above results, it is recognized that the piezoelectric ceramic for electromechanical conversion elements of the present invention exhibits extremely large displacement.

[Effect] As described above, the piezoelectric ceramic for electromechanical transducer of the present invention undergoes phase transformation by applying a voltage within the operating temperature range, and the length of the crystal axis and/or the unit cell volume of the crystal changes. In addition, when the applied voltage is O, it is made of a substance that has the property of taking any of the following phases: ferroelectric phase, non-ferroelectric phase, and coexistence phase of ferroelectric phase and non-ferroelectric phase, and has an extremely large Therefore, it can be used in various dynamic devices such as VTR head positioning devices, mask alignment devices during IC manufacturing, piezoelectric motors, dot printer wire dot drive devices, ultrasonic oscillators, and piezoelectric transformers. suitable.

[Brief explanation of the drawing]

Fig. 1 is a P-E characteristic diagram of a dielectric material according to the present invention, Fig. 2 is a P-E characteristic diagram of a ferroelectric material, and Fig. 3 is a P-E characteristic diagram of an antiferroelectric material.
FIG. 4 is a p-E characteristic diagram of a paraelectric material. In addition, each figure in FIGS. 5 and 6 is a P-
FIG. 3 is a characteristic diagram showing measurement results of E characteristics and longitudinal strain characteristics.

Claims (1)

[Claims] (1) By applying a voltage within the operating temperature range, a phase transformation occurs and the length of the crystal axis and/or the unit cell volume of the crystal changes, and when the applied voltage is 0, the ferroelectric phase changes to the non-ferroelectric phase. 1. A piezoelectric ceramic for an electric/mechanical transducer, characterized in that it is made of a substance that has the property of having either a body phase or a coexisting phase of a ferroelectric phase and a non-ferroelectric phase.