JP2820000B2 - Piezoelectric material composition for actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric material composition, and more particularly, to a piezoelectric material composition that can be advantageously used in a piezoelectric element such as an actuator. The piezoelectric material composition according to the present invention has very little deterioration in displacement characteristics after repeated use under a high load as compared with the conventional piezoelectric material composition.

[0002]

2. Description of the Related Art Research on piezoelectric material compositions has been conducted for a long time, and products utilizing such piezoelectric material compositions are widely used in various fields. Products using such a piezoelectric material composition include, for example, ceramic filters, glass delay lines, ultrasonic transducers, piezoelectric buzzers, piezoelectric ignition units, ultrasonic motors, piezoelectric fans, piezoelectric sensors, and piezoelectric actuators. Can be mentioned. here,
2. Description of the Related Art Piezoelectric actuators utilize displacement and force generated through a piezoelectric phenomenon as a mechanical drive source, and are one of the things that have recently attracted attention in the field of mechatronics. Since this piezoelectric actuator is a solid-state element utilizing the piezoelectric effect, it consumes less power, has a faster response speed, and has a larger displacement compared to a conventional electromagnetic actuator having a configuration in which a coil is wound around a magnetic material. It has excellent features such as low heat generation, small size and weight.

[0003] Various types of piezoelectric material compositions are known for use in such piezoelectric elements. For example, many piezoelectric material compositions have been known, starting from a technique of adding a simple oxide to a PZT-based ceramic described in Japanese Patent No. 275421 issued in 1960. U.S. Pat. No. 2,911,370 discloses that PZT-based ceramics may be added with elements such as niobium (Nb), tantalum (Ta), and rare earth metals, or a part of Pb may be made of strontium (S).
It teaches to increase the piezoelectric constant and dielectric constant of the resulting composition by substituting it with an element of an alkaline earth metal such as r) or calcium (Ca). JP-A-62-298192 teaches a piezoelectric material composition having a basic composition of Pb (Zr _x Ti _y ) O ₃ as a piezoelectric material composition used for an actuator element, and this composition is used as a material for an actuator. It reports that it has a usable piezoelectric strain constant and extremely low dielectric loss.

Further, Japanese Patent Application Laid-Open No. 4-260662 discloses a Pb
_0.89-x Sr _0.11 Ba _x (Zr _a Ti _b Sc _c ) O ₃ (where 0.01 ≦ x
≤0.04, 0.545 ≤a≤0.555, 0.435 ≤b≤0.445, 0.
005 ≦ c ≦ 0.015, a + b + c = 1), and teaches a piezoelectric material composition having high piezoelectric characteristics, particularly high Curie temperature, which is suitable for a piezoelectric actuator of an automobile.

[0005]

[Problems to be Solved by the Invention] (PbZrO ₃ ) _x (
PZT represented by PbTiO ₃ ) _1-x is classified into two crystal systems according to its composition ratio. That is, the phase boundary (M
In PB), a tetragonal system of rhombohedral and PbZrO ₃ less composition of excess composition PbZrO ₃ than the MPB composition. Conventionally, when a piezoelectric material is used for an actuator of a laminated type or the like, evaluation and judgment have been made by measuring its piezoelectric characteristics. The measurement of the piezoelectric characteristics is performed without applying a load. In such a case, for example, the displacement of the piezoelectric material is better in the tetragonal system than in the rhombohedral system, and therefore, conventionally, the tetragonal system is used. The system was selected.

However, in actual use of the actuator, a displacement amount when a load is applied is required, and the displacement amount in this case does not always correspond to the piezoelectric characteristics. For example, when a load is applied to the piezoelectric material composition disclosed in Japanese Patent Application Laid-Open No. 4-260662, the amount of displacement is reduced to 1/2 to 1/4 of that when no load is applied, and is greatly reduced. . In addition, there is a problem that the displacement characteristic is greatly deteriorated when repeatedly used for durability.

An object of the present invention is to provide a piezoelectric material composition which has excellent electric characteristics under a load and has little deterioration in displacement characteristics when used for a long time.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, in a PZT-based composition, by making the composition slightly rhombohedral from the phase boundary, It has been found that it has excellent characteristics under a load, and that the displacement characteristics are less deteriorated when used durably.

[0009] That is, the actuator piezoelectric material composition of the present invention is characterized by having a composition of rhombohedral crystal side from the MPB composition is a phase boundary,, 5 MPa or more under pressure
Used to produce an actuator operated by
You . Specifically, the present invention is operated under a pressure of 5 MPa or more.
That the piezoelectric material composition for actuators, the formula _{Pb (Zr a Ti 1-a} ) O 3 ( In the above formula, 0.52 <a _{a ≦ 0.54) Pb 1-x} Sr x (Zr a Ti 1-ab Nb b in) O ₃ (the above formula, 0.08 ≦ x ≦ 0.14, 0.555 <a ≦ 0.565, 0.005 ≦ b ≦ a _{0.06) Pb 1-xy Sr x} Ba y (Zr a Ti 1-ab Sb b) O 3 ( upper in the formula, 0.09 ≦ x ≦ 0.13, 0.01 ≦ y ≦ 0.04 0.555 <a ≦ 0.565, 0.005 ≦ b ≦ a _{0.15) Pb 1-xy Sr x} La y (Zr a Ti 1-ab M b) O 3 ( upper in the formula, 0.09 ≦ x ≦ 0.13, 0 <y ≦ 0.01 0.555 <a ≦ 0.565, M is 0.005 ≦ b ≦ 0.03 is Sb or _{Nb) Pb 1-xy Sr x} Ba y La z (Zr a Ti 1 _-ab M _b ) O ₃ , and (in the above formula, 0.09 ≦ x ≦ 0.13, 0 ≦ y ≦ 0.04 0 <z ≦ 0.01 0.555 <a ≦ 0.565, 0.005 ≦ b ≦ 0.03, and M is Sb or Nb. ) The composition represented by It is characterized by having.

The piezoelectric material composition of the present invention can be used particularly for a piezoelectric actuator of an automobile and for other piezoelectric elements. For example, a piezoelectric actuator may be formed by using a known method, for example, by bonding two thin plates of a piezoelectric material to form a bimorph structure, or by stacking tens to hundreds of thin plates of a piezoelectric material, and using one of them. It can be manufactured by alternately laminating and fixing one sheet so that the polarization in the thickness direction is reversed to form a laminated structure.

[0011]

As described above, conventionally, when a piezoelectric material is used for a laminated actuator or the like, its piezoelectric characteristics are measured and evaluated in a state where no load is applied. The tetragonal system was superior to the tetragonal system, and therefore the tetragonal system was selected. However, when an actual actuator is used, displacement under a load of several hundred kgf is a problem. The present inventor has found that when a load is applied, the rhombohedral system exhibits a displacement almost equal to that of the tetragonal system.

On the other hand, durability is important for an actuator for an automobile, and therefore, a piezoelectric material composition that has a small change in displacement by a durability test is desired. The present inventor has found that the rhombohedral system has less change in displacement and higher durability than the tetragonal system. It is considered that the reason for this is that crystal distortion due to voltage application is larger in the tetragonal system than in the rhombohedral system. If the strain of the crystal is large, the stress concentration at the point where the directionality between the crystals does not match increases, and the crystal is broken.
Damage will of course lead to element breakage,
This is because there is an effect on the displacement amount.

Thus, the rhombohedral system is different from the tetragonal system in that
The displacement characteristics under a load are almost comparable, and the durability is clearly excellent. Therefore, rhombohedral is suitable as a piezoelectric material for a high-load actuator for an automobile or the like.

[0014]

The present invention will be described below with reference to examples and comparative examples. In represented by the composition formula in Example 1 and Comparative Example _{1 Pb (Zr a Ti 1-} a) O 3, the raw material such that a = 0.53 PbO, ZrO ₂ and T
A predetermined amount of iO ₂ was weighed and wet mixed in a ball mill for 48 hours. Next, after calcining at 800 ° C. for 2 hours, the mixture was again ground in a ball mill for 48 hours and dried. As a comparative example, compositions represented by the above formula and in which a = 0.51 and 0.52 were produced in the same manner.

To the powder thus produced, 1% by weight of PVA (polyvinyl alcohol) was added, and the diameter was measured at 98 MPa.
It was formed into a disk having a thickness of 18 mm and a thickness of 2 mm, and sintered at 1250 ° C. for 2 hours under a lead atmosphere control. The obtained sintered body has a diameter
Processed to 15mm, 0.5mm thickness, baking silver electrodes on both planes,
At an applied voltage of 40 kV, 30
A polarization treatment was performed for a minute to obtain a piezoelectric pellet. Next, 50 piezoelectric pellets were laminated, and external electrodes were alternately taken out from the outer periphery to obtain a laminated actuator.

When a mechanical load is applied to the laminated actuator
After applying ~ 35 MPa, a sine wave was applied at a voltage of 0 to 800 V and 10 Hz, and the displacement was measured by a laser displacement meter.
These results are expressed as the displacement per pellet in FIG.
Shown in

On the other hand, it was processed to a thickness of 1 mm, silver electrodes were baked on both planes, and the electrical characteristics of the similarly polarized piezoelectric pellet were measured with an impedance analyzer. The result is shown in FIG. In addition, both end faces of the above-mentioned laminated actuator
The displacement was repeated at an applied voltage of ± 400 V in the atmosphere by applying a pressure of 30 MPa, and the displacement was measured by a laser displacement meter, and the dependence of the displacement on the number of repetitions, that is, the durability was measured. The result is shown in FIG.

In this composition, the composition ratio, Zr / (Z
It has been found by X-ray diffraction that tetragonal crystal is obtained when (r + Ti) is up to 52.0 and rhombohedral when r + Ti is larger than 52.0. Therefore, it is considered that the phase boundary exists between 52.0 and 53.0.

As shown in FIG. 1, at a load of 0 MPa, the displacement of tetragonal crystals having the above-mentioned ratios of 51.0 and 52.0 is more advantageous than that of rhombohedral crystals having the ratio of 53.0. . However, when a load was applied, the significant difference disappeared, and at a load of 5 MPa or more, there was almost no effect of the composition.
Above MPa, the rhombohedral was rather larger.

As shown in FIG. 2, the electromechanical coupling constant Kp
Has a maximum at a composition ratio of 52.0 to 53.0, while a relative permittivity ε _r has a maximum at a composition ratio of 52.0. Thus, the electrical properties are slightly better on the tetragonal side,
This tendency is also indicated by the amount of displacement under no load.

As shown in FIG. 3, the durability of the composition of the present invention (rhombohedral) is clearly superior to that of the conventional composition (tetragonal). That is, the displacement amount after ¹⁰⁸ times endurance test, in the compositions of the present invention, but remains the reduction of 25% compared to before the durability, whereas in the conventional composition of about 85
% Has fallen.

[0022] In the composition formula represented by Example 2 and Comparative Example _{2 Pb 1-x Sr x (} Zr a Ti 1-ab Nb b) O 3, x = 0.11, b = 0.01, and a = 0.
Raw material powder PbO, SrCO ₃ , Zr
O ₂ , TiO ₂ and Nb ₂ O ₅ were weighed in predetermined amounts, and a laminated actuator was manufactured in the same manner as in Example 1. Also,
As comparative examples, those having a = 0.55 and 0.555 were similarly manufactured. The MPB in this system had a composition ratio, Zr / (Zr + Ti + Nb) of 55.0, as a result of X-ray diffraction measurement.
It turns out to be between 56.0. The characteristics were measured in the same manner as in Example 1. FIG. 4 shows the measurement results of the displacement amount, FIG. 5 shows the electrical characteristics, and FIG. 6 and FIG. 7 show the durability characteristics.

As in the case of Example 1, the electrical characteristics were as follows:
It becomes maximum at 5.0, and this tendency reflects the tendency of the displacement characteristic under no load shown in FIG. However, as the load increases, the difference between the displacements decreases.
The difference was only about%, and became almost equal at 34 MPa. For durability, as shown in FIG. 6, in the load 30 MPa, the actuator of the composition ratio 55.0 (tetragonal) significantly decrease the amount of displacement, but also 30% of the initial displacement amount was decreased at 10 ⁸ times On the other hand, in the actuator having the composition ratio of 56.0 (rhombohedral), the decrease is only 5% at the same number of times, which indicates that the durability is high. Further, as shown in FIG. 7, the actuator of the composition ratio 55.0 compared to an actuator composition ratio 56.0, the initial amount of displacement is large, in association with the displacement times, the amount of displacement decreases significantly, the composition ratio is 10 ⁸ times 56.0 It is understood that the composition of the present invention is suitable for an actuator which is repeatedly used under a high load for an automobile or the like.

[0024] Example 3 and Comparative Example _{3 Pb 1-xy Sr x Ba} y (Zr a Ti 1-ab Sb b) O
_{In the} composition formula represented by ₃ , x = 0.11, y = 0.03, b
= 0.01 and a = 0.56 so that the raw material powders PbO, Sr
CO ₃ , ZrO ₂ , TiO ₂ , BaCO ₃ and Sb ₂ O
₅ was weighed in a predetermined amount, and a laminated actuator was manufactured in the same manner as in Example 1. As comparative examples, a = 0.55 and
The one with 0.555 was similarly prepared. As a result of X-ray diffraction measurement, the MPB in this system was found to have a composition ratio of Zr / (Z
r + Ti + Sb) has been found to be between 55.5 and 56.0. The characteristics were measured in the same manner as in Example 1. FIG. 8 shows the measurement results of the displacement amount, FIG. 9 shows the electrical characteristics, and FIG. 10 shows the durability characteristics.

As in Example 1, the electric characteristics were slightly larger on the tetragonal side than MPB. This tendency is indicated by the amount of displacement under no load. However, the load increases, 15 ~
The displacement was equivalent under a load of 35MPa. Next, when a durability test similar to that in Example 1 was performed, the displacement amount of the sample having a composition ratio of 55.0 after 10 ⁸ times of durability was 25% of the initial value.
Has decreased, whereas the displacement amount after ¹⁰⁸ times endurance of samples having a composition ratio 56.0 is remained 4%, it was found that high durability.

[0026]Example 4 and Comparative Example 4 Pb_1-xySr_xLa_y(Zr_aTi_1-abM_b) O_Three
In the composition formula represented by the formula, M is Nb, and x = 0.1
1, Raw materials such that y = 0.05, b = 0.01 and a = 0.56
Powder PbO, SrCO_Three, ZrO_Two, TiO_Two, La_Two
O_ThreeAnd Nb_TwoO _FiveIs weighed in a predetermined amount, and
Thus, a laminated actuator was manufactured. Also, as a comparative example
And a = 0.55 and 0.555 are similarly manufactured.
Was. The characteristics are measured in the same manner as in Example 1, and the displacement is measured.
The results are shown in FIG. 11 and the durability characteristics are shown in FIG.

Under a load of 15 to 38 MPa, the composition ratio, Z
The sample (rhombic) in which r / (Zr + Ti + Nb) was 56.0 had a larger displacement than the sample (tetragonal) in which the composition ratio was 55.0 and 55.5. If subjected to the same durability test as in Example 1, the amount of displacement of 10 ⁸ times after the durability of the sample composition ratio of 55.0 is reduced by 22%, whereas the composition ratio of 56.0
Displacement amount after ¹⁰⁸ times endurance sample is is remained decreased 5%, it was found that high durability.

[0028] Example 5 and Comparative Example _{5 Pb 1-xy Sr x Ba} y La z (Zr a Ti
_1-ab M _b ) In the composition formula represented by O ₃ , M is Sb
And the raw material powders PbO, SrCO ₃ , x = 0.11, y = 0.16, z = 0.005, b = 0.02 and a = 0.56.
BaCO ₃ , ZrO ₂ , TiO ₂ , La ₂ O ₃ and Sb
_A predetermined amount of ₂ O ₅ was measured, and a laminated actuator was manufactured in the same manner as in Example 1. As a comparative example, a = 0.54
5, 0.55, and 0.555 were similarly prepared. The characteristics were measured in the same manner as in Example 1. FIG. 13 shows the measurement results of the displacement amount, and FIG. 14 shows the durability characteristics.

Under a load of 15 to 35 MPa, the composition ratio, Z
The sample (rhombic) in which r / (Zr + Ti + Sb) was 56.0 had a larger displacement than the sample (tetragonal) in which the composition ratio was 54.5, 55.0 and 55.5. When a durability test similar to that in Example 1 was performed, a sample having a composition ratio of 55.0 was obtained.
Displacement after 10 ⁸ endurance decreases by 23%, while displacement after 10 ⁸ endurance of the sample whose composition ratio is 56.0 is 3%.
, And it was found that the durability was high.

[0030]

The environment in which a piezoelectric body is used as an actuator for an automobile is high temperature and high load. Under such a high load condition, a composition having a rhombohedral composition which has not been conventionally used is more likely to be a piezoelectric material than a composition having a tetragonal crystal system which has been conventionally used. As excellent. Further, the composition having such a rhombohedral composition has higher durability than a composition having a conventionally used tetragonal crystal composition. Further, the composition having a rhombohedral composition can reduce power consumption by about 40% as compared with a conventional composition, and can reduce the capacity of a driving power supply. This makes it possible to reduce the size and cost of the power supply system.

[Brief description of the drawings]

FIG. 1 is a graph showing the measurement results of the amount of displacement of the compositions of Example 1 and Comparative Example 1 with respect to load.

FIG. 2 is a graph showing the measurement results of electrical characteristics of the compositions of Example 1 and Comparative Example 1.

FIG. 3 is a graph showing the measurement results of the durability of the compositions of Example 2 and Comparative Example 2.

FIG. 4 is a graph showing measurement results of displacement amounts of the compositions of Example 2 and Comparative Example 2 with respect to load.

FIG. 5 is a graph showing the measurement results of electrical characteristics of the compositions of Example 2 and Comparative Example 2.

FIG. 6 is a graph showing the measurement results of the durability of the compositions of Example 2 and Comparative Example 2 under a load of 30 MPa.

FIG. 7 is a graph showing the measurement results of the durability of the compositions of Example 2 and Comparative Example 2 under a load of 10 MPa.

FIG. 8 is a graph showing measurement results of displacement amounts of the compositions of Example 3 and Comparative Example 3 with respect to load.

FIG. 9 is a graph showing the measurement results of electrical properties of the compositions of Example 3 and Comparative Example 3.

FIG. 10 is a graph showing the measurement results of the durability of the compositions of Example 3 and Comparative Example 3.

FIG. 11 is a graph showing the results of measuring the amount of displacement of the compositions of Example 4 and Comparative Example 4 with respect to load.

FIG. 12 is a graph showing the measurement results of the durability of the compositions of Example 4 and Comparative Example 4.

FIG. 13 is a graph showing the results of measuring the amount of displacement of the compositions of Example 5 and Comparative Example 5 with respect to load.

FIG. 14 is a graph showing the measurement results of the durability of the compositions of Example 5 and Comparative Example 5.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-24846 (JP, A) JP-A-4-262581 (JP, A) JP-A-5-163063 (JP, A) JP-A-4-164 260662 (JP, A) JP-A-47-44000 (JP, A) JP-A-52-64700 (JP, A) JP-A-62-274502 (JP, A) JP-A-61-53119 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C04B 35/42-35/49 H01L 41/00-41/26 CA (STN) CAOLD (STN) REGISTRY (STN)

Claims (5)

(57) [Claims] 1. A composition represented by the following formula: (In the above formula, 0.52 <a is _{a ≦ 0.54) Pb (Zr a} Ti 1-a) O 3 and having a, 5 MPa or more under pressure Works with
And a piezoelectric material composition for an actuator. 2. A composition represented by the following formula: Operates under pressure of 5MPa or more, characterized by having
And a piezoelectric material composition for an actuator. 3. A composition represented by the following formula: Operates under pressure of 5MPa or more, characterized by having
And a piezoelectric material composition for an actuator. 4. A composition represented by the following formula: Operates under pressure of 5MPa or more, characterized by having
And a piezoelectric material composition for an actuator. 5. A composition represented by the following _{formula: Pb 1-xy Sr x Ba} y La z (Zr a Ti 1-ab M b) O 3 Operates under pressure of 5MPa or more, characterized by having
And a piezoelectric material composition for an actuator.