JPH07240546A - Piezoelectric ceramic for large displacement and polarization treatment method of piezoelectric ceramic - Google Patents

Abstract

PURPOSE:To enhance the voltage-to-displacement conversion efficiency of a piezoelectric ceramic by a method wherein the piezoelectric ceramic is domain-oriented ha a direc tion perpendicular to a direction in which an electric field is applied. CONSTITUTION:Silver electrodes, 13 are attached, by a screen printing operation, to both worked surfaces of a ceramic sintered body 12, this assembly is fired in an electric furnace, and a ceramic piezoelectric body 11 is manufactured. The ceramic piezoelectric body 11 is sandwiched between pressurization plates 14, it is immersed in silicone oil at 100 deg.C, compressive stresses 15 are applied via the pressurization plates 14 from both surfaces to which the silver electrodes 13 have been attached, the compressive stresses are held, and, while the compressive stresses are being applied, the ceramic piezoelectric body is then cooled down to room temperature. Thereby, the polarization of a piezoelectric ceramic is oriented a direction perpendicular to a direction in which the compressive stresses have been applied, i.e. to a direction in which an electric field has been applied, and it turns table Consequently, it is possible to obtain the piezoelectric ceramic, for large displacement, whose voltage-to- displacement conversion efficiency is excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic which is a ferroelectric substance and a method for manufacturing the piezoelectric ceramic, and more particularly to a piezoelectric ceramic for large displacement and a method for polarization treatment of the piezoelectric ceramic as the manufacturing method. .

[0002]

2. Description of the Related Art It is well known that a piezoelectric ceramic is displaced (electric field induced displacement) when an electric field is applied. Utilizing this displacement, piezoelectric ceramics are applied to actuators, ultrasonic motors, buzzers and the like. That is, piezoelectric ceramics convert electrical input energy into mechanical energy such as displacement and force. Typical examples of the piezoelectric ceramics include lead zirconate titanate (PZT: solid solution of PbZrO ₃ and PbTiO ₃ ) and barium titanate. These piezoelectric ceramics are usually produced by molding, sintering, processing, electrode baking, and polarization treatment of a raw material mixture.

Piezoelectric ceramics, which are ferroelectrics such as PZT-based ceramics and barium titanate-based ceramics, are aggregates of crystal grains made of single crystals, and in the as-fired state, the polarization direction of each crystal grain is disordered. Therefore, it does not exhibit piezoelectric characteristics. Therefore, in order to use these sintered bodies as piezoelectric bodies, normally, as shown in FIG. 6, a polarization electric field is applied after firing to apply a DC electric field in a fixed direction to align the domains in the direction of the electric field. .

[0004]

Both the piezoelectric property and the domain inversion contribute to the electric field-induced displacement of the piezoelectric ceramic, which is a ferroelectric substance. However, domain inversion has a property that it is difficult to invert when the electric field width applied to the piezoelectric ceramic is small. Therefore, the conventional piezoelectric ceramics that have been subjected to the polarization treatment as described above mainly use displacement due to piezoelectricity, and thus have a problem of small displacement.

Therefore, in the case of manufacturing an actuator using the above-mentioned piezoelectric ceramics, in order to secure the amount of displacement, it has a laminated structure in which a plurality of piezoelectric ceramics are laminated. However, in the conventional technique, in order to further increase the displacement amount, the applied electric field must be increased or
Or / and there was a problem that it was necessary to considerably increase the number of laminated layers and to increase the thickness.

Therefore, the inventors of the present invention have earnestly studied to solve the above-mentioned problems of the prior art, and as a result of various systematic experiments, the present invention has been accomplished.

(Object of the Invention) An object of the present invention is to provide a piezoelectric ceramic for large displacement which is excellent in conversion efficiency of electric field-displacement (strain) and a method for manufacturing the same.

The present inventors have focused on the following points with respect to the above-mentioned problems of the prior art. That is, in the conventional method,
Since the displacement of the piezoelectric ceramics in the electric field application direction is small, the applied electric field is increased or the number of laminated piezoelectric ceramics is increased to secure the displacement amount. That is,
Instead of improving the displacement characteristics of the piezoelectric ceramic itself, the displacement amount was secured by external means. The present inventors have focused on improving the displacement characteristics of the piezoelectric ceramic itself, as compared with such a conventional technique. As a result of repeating various systematic experiments, in the piezoelectric ceramics in which the domain orientation direction during the polarization operation in which a conventional DC electric field is applied and the electric field application direction (displacement extraction direction) during driving are the same, the polarization orientation direction and the electric field It was found that the electric field-displacement (strain) conversion efficiency was poor because the application directions (displacement extraction directions) were the same. Then, the domain is preliminarily oriented perpendicularly to the displacement direction by a polarization operation different from the conventional one, and the domain is inverted in the direction of the electric field application by the application of the electric field during driving. They have found the present invention and completed the present invention.

[0009]

[Means for Solving the Problems]

(Structure of First Invention) The large displacement piezoelectric ceramics of the first invention comprises a piezoelectric ceramics which is a ferroelectric substance and electrodes formed in the thickness direction of the piezoelectric ceramics, and an electric field is applied in the thickness direction. In a piezoelectric ceramic that can be displaced in the direction of applying an electric field, the piezoelectric ceramic is domain-oriented in a direction perpendicular to the direction of applying the electric field.

The method for polarization treatment of piezoelectric ceramics according to the second aspect of the present invention is characterized in that, in the polarization treatment step of piezoelectric ceramics, polarization treatment is performed such that the domain orientation direction is perpendicular to the electric field application direction. And

[0011]

The mechanism by which the large displacement piezoelectric ceramics of the present invention and the method of polarization treatment of the piezoelectric ceramics exhibit excellent effects is not always clear, but
It can be considered as follows.

(Operation of the First Invention) The large displacement piezoelectric ceramics of the present invention comprises a piezoelectric ceramics which is a ferroelectric substance and an electrode formed in the thickness direction of the piezoelectric ceramics, and an electric field is applied in the thickness direction. In the piezoelectric ceramic that obtains displacement in the electric field application direction, the domains are oriented perpendicular to the electric field application direction. When an electric field is applied to this piezoelectric ceramic, the domains are oriented in the direction of the applied electric field. At this time, the inversion amount of the domain becomes larger than the inversion amount of the piezoelectric ceramic that has been subjected to the conventional polarization treatment (orientation of the domain in the direction of applying the electric field), so that the displacement amount becomes large and the electric field-displacement conversion efficiency is increased. Can be improved.

(Operation of the Second Invention) In the polarization treatment method for piezoelectric ceramics of the present invention, in the polarization treatment step for the piezoelectric ceramics, the polarization treatment is performed so that the domain orientation direction is perpendicular to the electric field application direction. It becomes. As a result, it is possible to manufacture a piezoelectric ceramic that is domain-oriented in a direction perpendicular to the direction of applying an electric field. When an electric field is applied to this piezoelectric ceramic, the domains are oriented in the direction of the applied electric field. At this time, the inversion amount of the domain becomes larger than the inversion amount of the piezoelectric ceramic that has been subjected to the conventional polarization treatment (orientation of the domain in the direction of applying the electric field), so that the displacement amount becomes large and the electric field-displacement conversion efficiency is increased. Can be improved.

[0014]

【The invention's effect】

(Effect of the first invention) The large displacement piezoelectric ceramics of the present invention is excellent in electric field-displacement (strain) conversion efficiency.

(Effect of the Second Invention) By the method of polarization treatment of piezoelectric ceramics of the present invention, piezoelectric ceramics excellent in electric field-displacement (strain) conversion efficiency can be manufactured.

[0016]

EXAMPLES Specific examples (other inventions) of the piezoelectric ceramic for large displacement and the method of polarization treatment of piezoelectric ceramics of the present invention will be described below.

The present invention (specific examples) can be applied to all of what are called piezoelectric ceramics which are ferroelectrics. Specifically, PZT (lead zirconate titanate) and P
P such as LZT (lanthanum-substituted lead zirconate titanate)
Examples include ZT-based ceramics, barium titanate-based ceramics, and other component-based ceramics of three or more components.

The electrode is an electrode formed in the direction in which the electric field of the piezoelectric ceramic is applied, and all substances generally used as the electrode of the piezoelectric ceramic can be applied. Specific examples thereof include metals such as Ag, Cu, Au, and Al, alloys thereof, In, Sn, Pb, Ni, and alloys thereof. As a method of forming the electrode, a known method such as a baking method, a vapor deposition method, a plating method or the like can be applied.

The piezoelectric ceramic for large displacement of the present invention is manufactured by performing polarization treatment in the polarization treatment step of the piezoelectric ceramic so that the domain orientation direction is perpendicular to the electric field application direction.

[0020] In the polarization step, the compressive stress polarization temperature is added to the inter-range a and the electrode of the Curie temperature _{(T C) ~ (T C} -300 ℃) is 10~100MPa
It is preferable that the method is a polarization treatment method in which the temperature is maintained for a predetermined time within the range of (4) and then cooled to room temperature with the compressive stress applied or unloaded.

In this polarization treatment method, both sides (both sides of the electrode) in the displacement direction (electric field application direction) at a temperature lower than the Curie temperature at which the domain is easily inverted with respect to the piezoelectric ceramics.
By applying a compressive stress to the domain, the domain is oriented by the compressive stress in a direction perpendicular to the compressive stress applying direction, that is, the electric field applying direction. By cooling from that state to room temperature, the domains are oriented in the compressive stress application direction, that is, perpendicular to the electric field application direction, and become stable. As a result, it is possible to obtain a piezoelectric ceramic for large displacement that is polarized and oriented in a direction perpendicular to the direction of applying an electric field.

According to this polarization treatment method, the domains are oriented perpendicular to the direction of the electric field application. Therefore, when an electric field is applied to drive the domains, the domains are inverted in the direction of the electric field application and a large amount of displacement is obtained.

In the above polarization treatment step, the polarization treatment temperature is set within the range of Curie temperature ( _Tc ) to ( _Tc- 300 ° C) when the temperature is lower than ( _Tc- 300 ° C). Has a problem that the domain is difficult to invert even if a compressive stress is applied, and when the Curie temperature is exceeded, the domain disappears due to the phase transition to the paraelectric material, and the effect of domain inversion that contributes to displacement disappears. Because there is a problem. Further, the reason why the compressive stress applied between the electrodes is 10 to 100 MPa is
If the stress is less than 10 MPa, there is a problem that the domains cannot be oriented, and the stress is 100 MPa.
This is because if a is exceeded, there is a problem that cracks will occur in the piezoelectric ceramics.

The holding time is preferably 1 second to 60 minutes. The reason is that if the holding time is less than 1 second, the domains are not sufficiently oriented, and if the holding time is more than 60 minutes, the domains are not further oriented and the working efficiency is deteriorated.

The cooling rate is 0.1 ° C./sec to 5 ° C. /
It is preferably sec. The reason is that when the cooling rate is high, thermal shock causes cracks in the piezoelectric ceramics, and when the cooling rate is low, work efficiency is poor.

The polarization treatment by the compressive stress is effective not only for piezoelectric ceramics but also for an actuator in which a plurality of pellets composed of piezoelectric ceramics and electrodes and metal electrodes are alternately laminated. That is,
By holding the stack at a predetermined temperature and then applying a predetermined compressive stress, the domains of each pellet constituting the actuator are oriented in the direction perpendicular to the direction of applying the compressive stress. This makes it possible to obtain an actuator having excellent electric field-displacement characteristics.

On the other hand, when the polarization treatment is performed by an electric field instead of compressive stress, the polarization treatment temperature is in the range of Curie temperature ( _Tc ) to ( _Tc- 300 ° C.) and in the driving electric field direction (displacement direction). On the other hand, an electric field of 1 to 4 kV / mm is applied between the vertically arranged polarization electrodes for a predetermined time, and then cooled to room temperature with the electric field applied or with the electric field removed. A polarization treatment method is suitable.

In this polarization treatment method, the piezoelectric ceramic has a high temperature for orienting the domains in a direction close to the Curie temperature at which the domains easily move and in a direction perpendicular to the displacement direction (driving electric field application direction). Apply an electric field. Due to this high electric field, the domains are oriented in the direction of applying the high electric field. By cooling from that state to room temperature, the domains are oriented and fixed in the direction perpendicular to the displacement direction (driving electric field application direction). As a result, it is possible to obtain a piezoelectric ceramic for large displacement in which domains are oriented in a direction perpendicular to the driving electric field application direction (displacement direction).

By this polarization treatment method, the domains are oriented perpendicularly to the displacement direction (driving electric field applying direction). Therefore, when an electric field is applied in the displacement direction (driving electric field applying direction), the domains are oriented in the electric field applying direction. It reverses and a large displacement is obtained.

In the above polarization treatment step, the polarization treatment temperature is set within the range of Curie temperature ( _Tc ) to ( _Tc- 300 ° C) when the temperature is lower than ( _Tc- 300 ° C). This is because the domain has a problem that it is difficult to move, and when the Curie temperature is exceeded, the domain disappears and the effect of domain inversion that contributes to displacement disappears. The applied electric field of 1 to 4 kV / mm has a problem that the domain cannot be inverted when the electric field is less than 1 kV / mm, and the dielectric breakdown of the piezoelectric ceramics occurs when the electric field exceeds 4 kV / mm. Because there is a problem of doing.

The holding time is preferably 1 second to 60 minutes. The reason is that if the holding time is less than 1 second, the domains are not sufficiently oriented, and if the holding time is more than 60 minutes, the domains are not further oriented and the working efficiency is deteriorated.

The cooling rate is 0.1 ° C./sec to 5 ° C. /
It is preferably sec. The reason is that when the cooling rate is high, thermal shock causes cracks in the piezoelectric ceramics, and when the cooling rate is low, work efficiency is poor.

The large displacement piezoelectric ceramics of the present invention have excellent electric field-displacement (strain) conversion efficiency. That is,
Compared with the conventional piezoelectric ceramics, a large amount of displacement can be taken out with the same applied electric field, so that if the amount of displacement is constant, the applied electric field can be made small and defects such as cracks can be eliminated. Also, the number of layers to be laminated can be reduced, and the device to which the piezoelectric ceramic is applied can be made compact.

The large displacement piezoelectric ceramics of the present invention can be applied to all uses to which conventional piezoelectric ceramics are applied. Specifically, various actuators, fine movement devices, motors, pumps and the like can be mentioned. Among them, it is particularly suitable for applications in which large displacement is required such as actuators that require responsiveness such as hydraulic control valves and fuel injection valves.

First Example A fine powder of lead zirconate titanate (PZT) was prepared as a raw material for piezoelectric ceramics, subjected to press molding, CIP (cold isostatic pressing), degreasing, and further 120 in an electric furnace.
A ceramic sintered body was obtained by firing at 0 ° C. for 4 hours. Next, this sintered body is processed into an outer diameter of 12 mm and a thickness of 0.5 mm,
The surface was finished with a # 600 grindstone. Next, silver electrodes 13 were attached to both processed surfaces of the ceramic sintered body 12 by screen printing and then fired in an electric furnace to produce a ceramic piezoelectric body 11. The Curie temperature of this PZT is 170 ° C.

Next, the obtained ceramic piezoelectric material was polarized. That is, as shown in the schematic explanatory view of the polarization treatment method of FIG. 1, the ceramic piezoelectric body 11 is sandwiched between the pressure plates 14 and immersed in silicon oil at 100 ° C.
60MP via a pressure plate 14 from both surfaces to which the silver electrodes 13 are attached by a hydraulic cylinder or the like (not shown)
A compressive stress 15 of a is applied, and the state is maintained for 20 minutes,
Then, the piezoelectric ceramics of this example according to the present invention was obtained by gradually cooling to room temperature while applying compressive stress.

(Comparative Example 1) A comparative piezoelectric ceramic was obtained in the same manner as in the first example except that the polarization treatment was not performed.

(Performance Evaluation Test) The performance evaluation test of the piezoelectric ceramics obtained in this example was conducted by an electric field-displacement characteristic measurement test. As shown in the schematic diagram of the electric field-displacement characteristic measurement test of FIG. 2, an electric field of 0 to 1200 V / mm is applied in the thickness direction by a sine wave, and a compressive stress is applied by a displacement meter (not shown) using laser light. The amount of displacement in the thickness direction (electric field application direction) was measured below. Among the obtained results, the results obtained under the conditions of applied electric field: 0 to 1200 V / mm, compressive stress: 20 MPa, temperature: room temperature are shown in FIG. It should be noted that FIG. 2 is also a diagram showing an example of use of the piezoelectric ceramics obtained in the first embodiment.

The results of the performance evaluation test of the comparative piezoelectric ceramics performed in the same manner are also shown in FIG.
A schematic explanatory view of the test is shown in FIG.

As is apparent from FIG. 3, the compressive stress is 20M.
The displacement amount at Pa is 0.51 μm in the case of the present embodiment, and it can be seen that the displacement amount is improved by about 50% compared to the displacement amount of 0.34 μm in the comparative example. Further, it was confirmed that the same effect was obtained in the piezoelectric ceramics of the present example even within the other compressive stress range, and it was found that the piezoelectric ceramic had excellent electric field-displacement characteristics.

Further, the temperature of the silicone oil in the polarization treatment is from the Curie temperature (T _c ) of the piezoelectric ceramics to
Any temperature may be used within the range of (T _c −300 ° C.), the compressive stress may be 10 to 100 MPa, the holding time may be 1 second to 60 minutes, and the cooling rate to room temperature may be It was confirmed that a similar effect could be obtained at 0.1 ° C / sec to 5 ° C / sec.

Second Example First, a ceramic sintered body prepared by the same method as in the first example was prepared. The ceramics sintered body is processed into a length of 5 mm, a width of 5 mm and a thickness of 2 mm, the surface is finished with a # 600 grindstone, and silver electrodes are screen-printed on both processed surfaces A, A'and B, B '. And then fired in an electric furnace to produce a ceramics piezoelectric body. here,
Make sure that the silver electrodes on the AA 'side and the BB' side do not touch B
The electrode on the −B ′ surface was attached to be slightly smaller than the AA ′ surface.

Next, the obtained piezoelectric ceramic was subjected to polarization treatment. That is, first 100
Immerse in silicon oil at ℃, apply an electric field of 2 kV / mm to B and B'sides for 20 minutes as shown in the schematic explanatory view of the polarization treatment method in FIG. 4, and then gradually increase to room temperature with the electric field applied. After cooling, the piezoelectric ceramic of this example according to the present invention was obtained. B of the piezoelectric ceramics polarized in this way
After the silver electrode on the −B ′ surface was removed by processing, an electric field was applied to the A and A ′ surfaces in the same manner as in the first example, and the displacement amount in the electric field application direction was measured. FIG. 5 shows a schematic explanatory diagram of the performance evaluation test. The measurement conditions are the same as in the first embodiment. In addition,
FIG. 5 is also a diagram showing an example of use of the piezoelectric ceramics obtained in the second embodiment.

The obtained results are shown in FIG. The amount of displacement of the compressive stress at 20 MPa was 0.50 μm, which was improved by 47% compared to 0.34 μm of the comparative example (prior art). Also, the same effect was confirmed within other compressive stress ranges.
Also, in the present embodiment, the temperature of the silicone oil in the polarization treatment is the Curie temperature (T _c ) of the piezoelectric ceramics.
~ ( _Tc- 300 ° C), applied electric field is 2.0 to 4 kV / m
m, holding time 1 second to 60 minutes, cooling rate 0.1 ° C / sec
It was confirmed that a similar effect can be obtained at a temperature of up to 5 ° C / sec.

Third Example First, 20 ceramic piezoelectric bodies prepared by the same method as in the first example were prepared. Next, thickness 20 μm
21 sheets of SUS electrodes were prepared, and the electrodes and the ceramic piezoelectric material were alternately laminated to prepare a stack (the uppermost surface and the lowermost surface serve as electrodes).

Next, the obtained stack was polarized. That is, first, the stack is immersed in silicon oil at 150 ° C., and a compressive stress of 30 MPa is applied from both upper and lower surfaces of the stack by a hydraulic cylinder (not shown) via a pressure plate, and in that state. Hold for 30 minutes, then slowly cool to room temperature with compressive stress applied,
The stack of this example according to the present invention was obtained.

Electric field of stack polarized in this way
A displacement characteristic measurement test was performed. The test was carried out by the same method and conditions as in the first embodiment. Of the results obtained, applied electric field: 0 to 1200 V / mm, compressive stress: 20 M
The results obtained under the conditions of Pa and temperature: room temperature are shown in FIG. 7.

Comparative Example 2 Twenty comparative piezoelectric ceramics obtained in the same manner as in Comparative Example 1 were prepared, and the comparative piezoelectric ceramics were laminated to form a comparative stack. The results of the performance evaluation test of this comparative stack performed in the same manner as in the third embodiment are also shown in FIG.

As is apparent from FIG. 7, the compressive stress is 20M.
The displacement amount at Pa is 11 μm in the case of the present embodiment,
It can be seen that the displacement amount is improved by about 57% as compared with the displacement amount of 7.0 μm of the comparative example. Further, it was confirmed that the same effect was obtained in the stack of this example even within the other compressive stress range, and it was found that the stack had excellent electric field-displacement characteristics.

Further, the temperature of the silicone oil in the polarization treatment may be any temperature within the range of Curie temperature ( _Tc ) to ( _Tc- 300 ° C.) of the ceramic piezoelectric material forming the stack, and the compression is performed. Stress is 10-100M
During Pa, the holding time may be between 1 second and 60 minutes,
It was confirmed that the same effect could be obtained if the cooling rate to room temperature was between 0.1 ° C / sec and 5 ° C / sec.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a polarization treatment process of piezoelectric ceramics in a first embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a performance evaluation test of the piezoelectric ceramics obtained in the first example of the present invention.

FIG. 3 is a diagram showing performance evaluation test results of the piezoelectric ceramics obtained in the first example, the second example, and the comparative example 1 of the present invention.

FIG. 4 is a schematic explanatory diagram of a polarization treatment process of the piezoelectric ceramics in the second embodiment of the present invention.

FIG. 5 is a schematic explanatory view showing a performance evaluation test of the piezoelectric ceramics obtained in the second embodiment of the present invention.

FIG. 6 is a schematic explanatory diagram showing a performance evaluation test of the piezoelectric ceramics obtained in a comparative example.

FIG. 7 is a diagram showing performance evaluation test results of piezoelectric ceramics obtained in a third example of the present invention and a comparative example 2.

[Explanation of symbols]

 11, 21 ・ ・ ・ Piezoelectric ceramics 12, 22 ・ ・ ・ Ceramics sintered body 13, 23 ・ ・ ・ Electrodes 14, 24 ・ ・ ・ Pressurizing plate 15, 25 ・ ・ ・ Compressive stress 16, 26 ・ ・ ・ Polarization direction

Claims (4)

[Claims] 1. A piezoelectric ceramic comprising a piezoelectric ceramic which is a ferroelectric substance and an electrode formed in the thickness direction of the piezoelectric ceramic, wherein an electric field is applied in the thickness direction to cause displacement in the electric field application direction. Is a piezoelectric ceramic for large displacement characterized by being polarized and oriented in a direction perpendicular to an electric field application direction. 2. A method for polarization treatment of piezoelectric ceramics, characterized in that in the polarization treatment step of piezoelectric ceramics, polarization treatment is carried out so that the polarization orientation direction is perpendicular to the electric field application direction. 3. The polarization treatment step, wherein the polarization treatment temperature is in the range of Curie temperature (T _C ) to (T _c -300 ° C.) and the compressive stress applied between the electrodes is in the range of 10 to 100 MPa. 3. The method for polarization treatment of piezoelectric ceramics according to claim 2, wherein the polarization treatment is performed for a predetermined time and then cooled to room temperature in a state where the compressive stress is applied or a state where the load is unloaded. 4. The polarization treatment step is arranged such that the polarization treatment temperature is in the range of Curie temperature (T _C ) to (T _c −300 ° C.) and is perpendicular to the electric field application direction (displacement direction). An electric field of 1 to 4 kV / mm is applied to the polarization electrode for a predetermined period of time, and then cooled to room temperature with or without the electric field applied. 3. The method for polarization treatment of piezoelectric ceramic according to 2.