JPH04239187A - Piezoelectric of gradient functional type - Google Patents

Abstract

PURPOSE:To prevent inside breakdown during driving by changing ratio of elements constituting dielectric porcelain composition successively in the thickness direction of a piezoelectric and by changing piezoelectric characteristics successively in the thickness direction of the piezoelectric in accordance with the change of element ratio. CONSTITUTION:A piezoelectric is constituted of dielectric porcelain composition. Ratio of elements constituting dielectric porcelain composition changes successively in the thickness direction of the piezoelectric, and one or more kinds of Curie temperatures, resistance to electric field and piezoelectric constant (d31) change successively. Thereby, a piezoelectric having gradient functional structure regarding piezoelectric characteristics can be obtained in this way.

Description

Detailed Description of the Invention [0001] The present invention relates to a piezoelectric body used, for example, in a piezoelectric actuator, and more specifically,
The present invention relates to a functionally graded piezoelectric material whose piezoelectric properties change continuously in the thickness direction of the piezoelectric material. 2. Description of the Related Art A piezoelectric actuator is a typical device constructed using a piezoelectric material. FIG. 2 is a perspective view of a conventional piezoelectric actuator. The piezoelectric actuator 1 has a structure in which external electrodes 6a and 6b are formed on the upper and lower surfaces of a piezoelectric body 5 made up of piezoelectric layers 3 and 4 stacked with an internal electrode 2 in between. Piezoelectric body 5
is obtained by laminating ceramic green sheets made of piezoelectric material with internal electrode material interposed therebetween, pressing them in the thickness direction, and then firing them together. Also, as an alternative,
The piezoelectric body 5 can also be constructed by bonding two piezoelectric plates fired in advance with an electrode interposed therebetween. The piezoelectric layers 3 and 4 are polarized in the directions of arrows Pa and Pb in FIG. 2, respectively. As schematically shown in FIG. 3, a DC electric field is applied between the external electrode 6a and the internal electrode 2, and the piezoelectric layer 3 is first polarized in the direction of arrow Pa, and then as shown in FIG. As shown, this is performed by applying a DC electric field between the internal electrode 2 and the external electrode 6b and polarizing the piezoelectric layer 4 in the direction of arrow Pb. As described above, in the piezoelectric actuator 1, the polarization directions of both the piezoelectric layers 3 and 4 are opposite to each other with the internal electrode 2 as a boundary, so that the piezoelectric actuator 1 can be driven as a bimorph type piezoelectric actuator. It is considered possible. On the other hand, as shown in FIG. 5, a DC electric field is applied between the external electrode 6a and the internal electrode 2, and the piezoelectric layer 3 is
If the piezoelectric layer 4 is polarized in the direction and the piezoelectric layer 4 is not polarized, the piezoelectric actuator 8 with a monomorph structure
It is also possible to configure [0005] In the conventional piezoelectric actuators 1 and 8, the piezoelectric layer 3 is connected with the internal electrode 2 in between.
, 4 are stacked. On the other hand, since the piezoelectric ceramic and the internal electrode are different materials, the adhesive strength between them is not very high. Therefore, when the piezoelectric actuators 1 and 8 are driven, if a large shear stress is applied between the piezoelectric layers 3 and 4 and the internal electrode 2, layer peeling occurs between the internal electrode 2 and the piezoelectric layers 3 and 4. As a result, even if the piezoelectric actuators 1 and 8 have sufficient initial performance, there is a problem in that the characteristics deteriorate during use. The above-mentioned problems have been observed not only in piezoelectric actuators but also in general laminated piezoelectric devices in which piezoelectric layers are laminated with internal electrodes interposed therebetween. Therefore, an object of the present invention is to provide a piezoelectric body that makes it possible to obtain a piezoelectric device that is less likely to suffer internal breakdown during driving and, therefore, less likely to suffer from characteristic deterioration. Means for Solving the Problems The piezoelectric body of the present invention is characterized by having a functionally graded structure. That is, the present invention provides a piezoelectric body composed of a dielectric ceramic composition, in which the ratio of elements constituting the dielectric ceramic composition is continuously changed in the thickness direction of the piezoelectric body, and Curie temperature, coercive electric field and piezoelectric constant d31 as the ratio changes
characterized in that at least one of the above is continuously changed. [0008] A functionally graded material is one in which the material composition is changed as a function of position within the material, and thereby the material properties are changed as a function of position within the material. The present invention provides a piezoelectric body made of a dielectric ceramic composition,
There are multiple elements that make up the dielectric ceramic composition, and focusing on the fact that the piezoelectric properties change depending on the ratio of the multiple elements, the content ratio of the multiple elements is continuously changed in the thickness direction of the piezoelectric material, The piezoelectric property is thereby changed continuously in the thickness direction of the piezoelectric body. The operation of the present invention will be specifically explained below by explaining a structural example applied to a piezoelectric actuator. FIG. 6 is a perspective view showing a piezoelectric actuator constructed using the piezoelectric body of the present invention. The piezoelectric body 12 is made of a rectangular flat piezoelectric ceramic, and external electrodes 13a and 13b are formed on both main surfaces thereof. The piezoelectric body 12 of the present invention is made of a dielectric ceramic composition in which the ratio of contained elements is continuously changed in the thickness direction, that is, in the direction of the arrow x. That is, whereas the piezoelectric body used in the conventional piezoelectric actuator was composed of a dielectric ceramic composition having a uniform composition, in the present invention, the composition of the dielectric ceramic composition varies depending on the thickness of the piezoelectric body. The direction is varied as a function of position. In the piezoelectric body 12, the piezoelectric constant d31 is changed so as to gradually increase in the thickness direction, that is, in the x direction, as shown in FIG. 1, in accordance with the change in the composition. Therefore, if voltage is applied from the external electrodes 13a, 13b to drive the piezoelectric actuator 11, the side with a relatively large piezoelectric constant, that is, the external electrode 13a side, will be largely displaced, while the side with a relatively small piezoelectric constant will be displaced largely. The portion, ie, the portion near the external electrode 13b, is slightly changed and bending occurs. That is, a piezoelectric actuator can be realized without forming the internal electrode 2 in the conventional piezoelectric actuator 1. [0011] Therefore, it can be seen that a piezoelectric actuator can be obtained in which internal damage such as separation between piezoelectric layers due to the provision of internal electrodes is less likely to occur. In the above explanation, the piezoelectric body 1
Although the piezoelectric constant was configured to change continuously in the thickness direction of No. 2, the Curie temperature or the coercive electric field may be changed continuously in the thickness direction. for example,
As shown in FIGS. 7 and 8, the Curie temperature is
That is, the piezoelectric body 14 is continuously changed in the x direction.
Prepare. External electrodes are formed on both principal surfaces of this piezoelectric body 14, similarly to the piezoelectric actuator 11 shown in FIG. 6, to constitute a piezoelectric actuator. In this piezoelectric actuator, a certain temperature T (T2 > T >
When the piezoelectric material 14 is held at a temperature T1), the upper piezoelectric layer portion 14a becomes a ferroelectric portion, and the lower piezoelectric layer portion 14a becomes a ferroelectric portion in the thickness direction of the piezoelectric material 14, as shown in FIG. The piezoelectric layer portion 14b becomes a paraelectric portion. Therefore, if polarization treatment is performed in this state, only the ferroelectric piezoelectric layer portion 14a will be polarized and will have piezoelectricity. Therefore, a piezoelectric body 14 having a monomorph structure in which only the upper piezoelectric layer portion 14a is polarized (FIG. 10)
can be obtained. Furthermore, as shown in FIG.
A piezoelectric material whose coercive electric field changes continuously from V1 to V2 in the direction, that is, the thickness direction, may be used. First of all,
A voltage V having a relationship of V2 <V is applied to the piezoelectric body to polarize the entire piezoelectric body in the thickness direction so that the polarization direction is directed from the bottom surface to the top surface. Next, in the opposite direction to the voltage V, a voltage Va
(However, when V2 > Va > V1), as shown in FIG. 12, the polarization of the piezoelectric layer portion 15a whose coercive electric field is smaller than that of the portion v of Va is reversed, and the piezoelectric layer having a bimorph structure body 15 can be obtained. As mentioned above, the piezoelectric constant d31 in the thickness direction
By configuring the piezoelectric body to have a functionally graded structure in which Curie temperature, coercive electric field, etc. are continuously changed, a bimorph or monomorph piezoelectric actuator can be obtained without providing internal electrodes. Therefore, it is possible to provide a piezoelectric actuator that is less prone to internal breakdown during driving. [0013] Although each of the above-mentioned structural examples has been explained using a piezoelectric actuator as an example, the functionally graded piezoelectric material of the present invention can also be used in other laminated piezoelectric elements other than piezoelectric actuators. , thereby effectively preventing internal destruction or the like due to the presence of internal electrodes. Furthermore, in the explanation of the above structural example, the piezoelectric constant d31, the Curie temperature, or the coercive electric field were continuously changed in the thickness direction, but it is also possible to continuously change the piezoelectric properties of two or more of these. . Furthermore, in order to continuously change the piezoelectric constant d31, Curie temperature, and coercive electric field described above in the thickness direction, in the present invention, the element ratio in the dielectric ceramic composition constituting the piezoelectric body is changed in the thickness direction. However, by changing the ratio of multiple elements that make up the dielectric ceramic composition, the piezoelectric properties can be changed continuously in the thickness direction as described above. The thing is,
As is clear from the examples described below, this can be easily implemented using conventionally known piezoelectric material manufacturing techniques. [Example] As raw materials, Pb3 O4, TiO2, ZrO2 with an average particle size of 2 μm or less and a purity of 99% or more
, Nb2O5, and NiO powders were prepared. Next, each of the above powders is converted into x, y and z in the following compositional formula.
were weighed so as to have the proportions shown in Table 1 below, and five types of mixed powders were obtained. xPb(Ni1/3 Nb2/3)O3 +yP
bZrO3 +zPbTiO3 [Table 1] [0018] The above composition is PNN-PZT-PT
Although a composition on the morphotropic phase boundary of a ternary system is used, the composition that can be used in the present invention is not limited to the composition on the morphotropic phase boundary and its vicinity. In addition, piezoelectric materials having a functionally graded structure with respect to the Curie temperature, coercive electric field, and piezoelectric constant are not limited to the above-mentioned material systems.
It can also be constructed using other dielectric ceramic compositions,
For example, in the (Ba,Sr)TiO3 system, Ba/S
This can also be achieved by changing the r ratio. 200 g of each of the above-mentioned mixed powders was milled for 24 hours using a wet ball mill method using ethanol and PSZ balls.
The mixture was uniformly mixed for a period of time to form a slurry. Each of the obtained slurries was dried using a rotary evaporator to obtain respective mixed raw materials. Next, each mixed raw material was calcined in air at a temperature of 700 to 1000° C. for about 3 hours to obtain each calcined product. Next, each calcined product was mixed with an ethanol/toluene mixture (the mixing ratio was 7 ethanol to toluene by weight).
:3) and PSZ balls, the powder was pulverized for about 24 hours by a wet ball mill method. Next, for each of the pulverized calcined raw materials, 6 to 12% by weight of a polyvinyl butyral binder and 0.5 to 2% of a sorbitan fatty acid ester dispersant were added.
．． 0% by weight and 1 to 5% by weight of a dioctyl butarate plasticizer were added and mixed uniformly for about 24 hours, respectively.
It turned into slurry. Each of the obtained slurries was formed into a green sheet with a thickness of 100 μm by the doctor blade method. Next, the five types of ceramic green sheets obtained were laminated as shown in FIG. 13. In FIG. 13, the ceramic green sheets 21 to 25 include ceramic green sheets 21 to 2.
The ceramic green sheets were selected from the above five types so that the ratios of Ti, Zr, Nb, and Ni changed continuously as they reached the 5th side. That is, each ceramic green sheet 2 consisting of mixed powder numbers 1 to 5 in Table 1
Ceramic green sheets 21 one by one, starting from the top.
~25 was assigned and used. Next, the laminate was thermocompressed in the thickness direction, and then cut into a predetermined size to obtain a strip-shaped laminate with external dimensions of 30 x 5 x 0.9 mm. Next, the obtained laminate was heated in air at 400°C.
The organic material components were burned for about 10 hours, and the sintered body 27 shown in FIG. 14 was obtained by baking in air at a temperature of 900 to 1200° C. for 3 hours. In the thickness direction of the obtained sintered body 27, Ni, Nb, Ti,
and Zr concentration was analyzed using an X-ray microanalyzer. As a result, the compositional discontinuity caused by using multiple green sheets was resolved by thermal diffusion during sintering, and as shown in FIGS. 15 to 18, Ti,
It was found that the element ratios of Zr, Nb, and Ni changed continuously in the thickness direction. Actuators of Examples 1 to 3 below were manufactured using the sintered body 27 having a functionally graded structure obtained as described above. Example 1 In the same manner as in the above example, sintered bodies of each mixed powder composition prepared in the example were prepared, and the Curie temperature of each was measured, and the results shown in Table 2 below were obtained. [Table 2] Therefore, from the Curie temperature of the sintered body made only of the above mixed powder materials, Ti, Zr, Nb and Ni
It can be seen that the Curie temperature changes as the element ratio changes. Therefore, in the sintered body produced in the example, Ti,
It can be seen that since Zr, Nb, and Ni change continuously in the thickness direction, a functionally graded structure is given to the Curie temperature. As shown in FIG. 19, the obtained sintered body 27
External electrodes 28a and 28b were formed by baking Ag onto both main surfaces. Next, place it in an oil bath at a temperature of 200℃,
The ferroelectric part and the paraelectric part were separated, and only the ferroelectric part was subjected to polarization treatment under the conditions of an applied voltage of 3 KV/mm x 30 minutes to obtain a monomorph actuator. Example 2 A sintered body made of a single mixed powder material of each mixed powder number was prepared in the same manner as in Example, and the coercive electric field at room temperature was evaluated, and the results shown in Table 3 were obtained. [Table 3] [0028] Therefore, it can be seen that the sintered body 27 obtained in the example has a functionally graded structure with respect to the coercive electric field. Therefore, in the same manner as in Example 1, external electrodes 28a and 28b were formed by baking Ag onto both main surfaces of the sintered body, and polarization treatment was performed at room temperature under the conditions of an applied voltage of 3 KV/mm x 30 minutes. Furthermore, the voltage application direction was reversed, and the voltage was 0.5KV.
By performing the polarization treatment again under the conditions of /mm x 30 minutes, the polarization of the weak coercive electric field portion was reversed, and a bimorph type actuator was obtained. Example 3 External electrodes were formed by baking Ag on both main surfaces of the sintered body of each mixed sample prepared by the same method as in Example, and polarization treatment was performed at room temperature under the conditions of applied voltage 3 KV/mm x 30 minutes. did. When the piezoelectric constant d31 of each sintered body was measured at room temperature, the results shown in Table 4 below were obtained. [Table 4] As is clear from Table 4, it can be seen that the d31 of the sintered bodies obtained by firing each mixed powder sample individually is different as described above. Therefore, it can be seen that the sintered body obtained in the example has a functionally graded structure with respect to the piezoelectric constant d31 in the thickness direction. Therefore, Ag was baked on both main surfaces of the sintered body of the example to form external electrodes 28a and 28b, and a polarization treatment was performed at room temperature under the conditions of an applied voltage of 3 KV/mm x 30 minutes. As a result, it was possible to obtain an actuator having a bending mode based on the difference in the piezoelectric constant d31 in the thickness direction. Each of the actuators of Examples 1 to 3 obtained as described above was heated at a driving voltage of 20°C in a constant temperature bath at 60°C.
Driving was continued at 0 V/mm, and changes in tip displacement were monitored. As a result, the results shown in FIG. 20 were obtained. Also,
For comparison, a similar reliability test was conducted on the conventional piezoelectric actuator shown in FIG. 2, and the results shown by the dashed-dotted line in FIG. 20 were obtained. As is clear from FIG. 20, in the piezoelectric actuators of Examples 1 to 3 constructed using the piezoelectric material of the present invention, the amount of tip displacement hardly changes even after 1000 hours have passed. It can be seen that in the conventional piezoelectric actuator, the amount of tip displacement gradually decreases after several tens of hours have passed. Note that the ceramic green sheets each composed of mixed powder material numbers 1 to 5 may be laminated in a different order from the above example. For example, as shown in FIG. 21, ceramic green sheets 31 to 35 each made of mixed powder materials 1 to 5 are arranged as follows: ceramic green sheet 31 - ceramic green sheet 32 - ceramic green sheet 33 - ceramic green sheet 34 - ceramic green sheet. 35 - ceramic green sheet 34 - ceramic green sheet 33 - ceramic green sheet 32 - ceramic green sheet 31 may be laminated in this order. In addition, ceramic green sheet 35 - ceramic green sheet 34 - ceramic green sheet 33 - ceramic green sheet 32
- Ceramic green sheet 31 - Ceramic green sheet 32 - Ceramic green sheet 33 - Ceramic green sheet 34 - Ceramic green sheet 35
They may be stacked in this order. In this way, the continuous change in the element ratio in the thickness direction can be varied in various patterns. As described above, according to the present invention, the ratio of a plurality of elements constituting the dielectric ceramic composition is continuously changed in the thickness direction of the piezoelectric material. Since the piezoelectric properties such as the Curie temperature, coercive electric field, and piezoelectric constant d31 in the thickness direction of the piezoelectric body are changed,
A piezoelectric body having a functionally graded structure with respect to these piezoelectric properties can be realized. Therefore, by utilizing these functionally graded structures with respect to piezoelectric properties, it is possible to obtain a laminated piezoelectric component having a structure in which internal electrodes are omitted. Therefore, it is possible to provide a highly reliable piezoelectric component in which problems such as peeling at the interface between the internal electrode and the piezoelectric layer are unlikely to occur.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the thickness direction of a piezoelectric body and a piezoelectric constant.

FIG. 2 is a perspective view showing a conventional piezoelectric actuator.

FIG. 3 is a schematic diagram for explaining a polarization method for obtaining a conventional bimorph piezoelectric actuator.

FIG. 4 is a schematic diagram for explaining a polarization method for obtaining a conventional bimorph piezoelectric actuator.

FIG. 5 is a schematic diagram for explaining a polarization method for obtaining a conventional monomorph piezoelectric actuator.

FIG. 6 is a perspective view showing an example of a piezoelectric actuator constructed using the piezoelectric body of the present invention.

FIG. 7 is a diagram showing the relationship between the position in the thickness direction and the Curie temperature of a piezoelectric body constructed according to the present invention.

FIG. 8 is a perspective view showing a piezoelectric body constructed according to the present invention.

FIG. 9 is a schematic diagram showing a piezoelectric body in which a ferroelectric part and a paraelectric part are configured in the thickness direction.

FIG. 10 is a schematic diagram for explaining a monomorph piezoelectric actuator configured by polarizing only a ferroelectric portion.

FIG. 11 is a diagram showing the relationship between the position in the thickness direction and the coercive electric field.

FIG. 12 is a schematic diagram for explaining a bimorph piezoelectric actuator having two piezoelectric layer portions with different polarization directions based on a difference in coercive electric field.

FIG. 13 is an exploded perspective view for explaining a plurality of ceramic green sheets prepared in an example.

FIG. 14 is a perspective view showing a laminate prepared in an example.

FIG. 15 is a diagram showing the relationship between the position in the thickness direction and the element ratio in the piezoelectric body obtained in the example.

FIG. 16 is a diagram showing the relationship between the position in the thickness direction and the element ratio in the piezoelectric body obtained in the example.

FIG. 17 is a diagram showing the relationship between the position in the thickness direction and the element ratio in the piezoelectric body obtained in the example.

FIG. 18 is a diagram showing the relationship between the position in the thickness direction and the element ratio in the piezoelectric body obtained in the example.

FIG. 19 is a diagram showing a piezoelectric actuator prepared in an example.

FIG. 20 is a diagram showing reliability test results of the piezoelectric actuators configured in Examples 1 to 3 and a conventional piezoelectric actuator.

FIG. 21 is a perspective view for explaining another example of a method of laminating ceramic green sheets having different element ratios.

[Explanation of symbols]

11… Piezoelectric actuator 12...Piezoelectric body 13a, 13b...External electrode x...Thickness direction.

Claims (1)

[Claims] 1. A piezoelectric body made of a dielectric ceramic composition, wherein the ratio of elements constituting the dielectric ceramic composition is continuously changed in the thickness direction of the piezoelectric body, and the ratio of the elements constituting the dielectric ceramic composition is A functionally graded piezoelectric material, characterized in that at least one of Curie temperature, coercive electric field, and piezoelectric constant d31 is continuously changed in the thickness direction of the piezoelectric material according to a change in ratio.