JP2015222780A - Piezoelectric ceramic, method for manufacturing the same, and piezoelectric material device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a piezoelectric ceramic including A1B1Obased material and BaMOadded thereto, by which a high piezoelectric constant d33 can be ensured even with a simple step.SOLUTION: A method for manufacturing a piezoelectric ceramic having a composition expressed by the general formula: (1-s)A1B1O-sBaMO. The method comprises the steps of: preparing a ceramic raw material powder having an average particle size of 0.05-0.3 μm; molding the ceramic raw material powder into a compact; and reducing and firing the compact at a temperature of 900-1300°C under an atmosphere of which the oxygen partial pressure is 1×10to 1×10kPa.

Description

  The present invention relates to a perovskite-type piezoelectric ceramic containing alkali metal and Nb, a manufacturing method thereof, and a piezoelectric element.

In recent years, the tendency to eliminate heavy metal harmful elements such as Pb, Hg, Cd, Cr ^{6+ has} increased due to the heightened awareness of environmental protection, and a ban on use (RoHS directive) has been issued and enforced mainly in Europe. Lead oxide (PbO), which is a raw material that plays an important role in enhancing the functionality of electronic materials, is also subject to environmental concerns regarding disposal issues.

By the way, a wide variety of materials have been developed for piezoelectric materials constituting piezoelectric elements that have been widely put into practical use in fields such as electronics, mechatronics, and automobiles, mainly piezoelectric ceramics. Conventional piezoelectric ceramics are Pb-based perovskite ferroelectric ceramics, and the mainstream is PbZrO ₃ —PbTiO ₃ (PZT). A piezoelectric ceramic having this composition contains a large amount of lead oxide as a main component, and thus has a problem with respect to disposal.

  In view of this situation, research into environment-friendly lead-free piezoelectric ceramics is considered urgent and indispensable. The performance of high-performance lead-free piezoelectric ceramics comparable to that of conventional PZT piezoelectric ceramics R & D is attracting interest. In many cases, the piezoelectric constant d33 (ratio of mechanical displacement per electric field in 33 directions) is used as a performance index of piezoelectric ceramics.

As a lead-free piezoelectric ceramic, a composition of A1B1O ₃ (where A1 is at least one element selected from alkali metals and B1 is at least one element of transition metal elements and contains Nb) is known. ing.

For example, Patent Document 1, the main component is represented by the general formula {(1-x) (K 1-ab Na a Li b) m (Nb 1-cd Ta c Sb d) O 3 -xM1 n M2O 3} ( however M1 represents at least one metal element selected from Ca, Sr, and Ba, and M2 represents at least one metal element selected from Ti, Zr, and Sn. And x, a, b, c, d, m, and n are 0.005 ≦ x ≦ 0.1, 0 ≦ a ≦ 0.9, 0 ≦ b ≦ 0.3, and 0 ≦ a + b ≦, respectively. Piezoelectric ceramic compositions in the ranges of 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.1, 0.9 ≦ m ≦ 1.1, and 0.9 ≦ n ≦ 1.1 Have been described.

The Patent Document 1, the average particle diameter D ₅₀ is equal to or less than 0.60 .mu.m, specific surface area of 7.0 m ² / g or more 20.0 m ² / g describes the use of the following ceramic raw material powder (claim 6) Yes. Moreover, in patent document 1, baking is performed in air | atmosphere.
In Patent Document 1, the effect of adjusting the ceramic raw material powder is that the ceramic raw material powder is an ultrafine powder and has good dispersibility, so that the firing temperature is lowered and the alkali metal that easily evaporates during firing is lower than the evaporation temperature. It is a solid solution in the crystal grains at the temperature, and as a result, the polarization failure rate is remarkably reduced. Moreover, it is described that a piezoelectric ceramic composition having an even higher piezoelectric constant can be produced with high efficiency (paragraph 0044).

International Publication No. 2006/117990

In the case of using the above A1B1O ₃ series piezoelectric ceramics, it is known that the piezoelectric characteristics are enhanced by sufficiently oxidizing the ceramic raw material powder during firing to suppress the generation of oxygen defects. As described, calcination is generally performed in air.

On the other hand, the present inventors examined a composition in which BaMO ₃ (wherein M is at least one element of group 4A and containing Zr) was added to an A1B1O ₃ based material. It has been found that ceramics can obtain a higher piezoelectric constant d33 by adopting a two-step heating process in which re-oxidation treatment is performed after reduction firing rather than firing in the air.
However, there is a problem that the number of steps increases when reoxidation is performed.

In view of the above problems, the present invention provides a piezoelectric ceramic manufacturing method in which BaMO ₃ is added to an A1B1O ₃ based material, and a high piezoelectric constant d33 can be ensured even in a simple process. The purpose is to provide.
Another object of the present invention is to provide a piezoelectric ceramic having a high piezoelectric constant d33 and a piezoelectric element that can be obtained by this simple manufacturing method.

The present invention is a manufacturing method of the piezoelectric ceramic, the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 is a transition metal element At least one element that includes Nb, M is at least one element of Group 4A, includes Zr, has a composition represented by 0.05 <s ≦ 0.15), and has an average particle size of A step of preparing a ceramic raw material powder of 0.05 μm to 0.3 μm, a step of using the ceramic raw material powder as a molded body, and an atmosphere having an oxygen partial pressure of 1 × 10 ⁻¹² kPa to 1 × 10 ⁻⁴ kPa And a step of reducing and firing the molded body at 900 ° C. or higher and 1300 ° C. or lower. The firing is preferably performed at an oxygen partial pressure of 8 × 10 ⁻¹¹ kPa to 1 × 10 ⁻⁶ kPa, and 900 ° C. to 1150 ° C. The present invention, the composition of the ceramic, the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 is at least one transition metal element Element is Nb, M is at least one element of Group 4A and includes Zr, 0.05 <s ≦ 0.15), and the average crystal grain size is 2.0 μm or less. The piezoelectric ceramic is characterized in that the standard deviation of the particle diameter is 1.0 μm or less and the piezoelectric constant d33 is 200 pC / N or more. A base metal electrode can be formed on this piezoelectric ceramic to form a piezoelectric element.

According to the present invention, a piezoelectric ceramic manufacturing method in which BaMO ₃ is added to an A1B1O ₃ -based material can have a high piezoelectric constant d33 without performing a two-step heating process in which re-oxidation is performed after reduction firing. A simple manufacturing method can be provided. Since the manufacturing process is reduced, the cost can be reduced.
In addition, this manufacturing method can provide piezoelectric ceramics and piezoelectric elements having a piezoelectric constant d33 of 200 pC / N or more at low cost.

(A) SEM observation photograph (5000 times visual field) of ceramics in the piezoelectric element of the present invention, and (b) a schematic diagram thereof. It is a figure which shows the particle size distribution of the crystal grain of the ceramic of FIG. (A) SEM observation photograph (viewing field 5000 times) of ceramics in a piezoelectric element of a comparative example, and (b) a schematic diagram thereof. It is a figure which shows the particle size distribution of the crystal grain of the ceramics of FIG.

Method of manufacturing a piezoelectric ceramic of the present invention, first, the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 is at least a transition metal element A step of preparing a ceramic raw material powder having a composition represented by 0.05 <s ≦ 0.15) which is a kind of element and contains Nb, and M is at least one kind of element of group 4A and contains Zr. Have.

As described above, in order to obtain a high piezoelectric constant d33 with the composition of the above general formula, the present inventors perform a re-oxidation treatment after heating in an oxidizing atmosphere in the case of reduction firing, and then a high piezoelectric constant d33. It was found that can be obtained. On that basis, it was studied to obtain a high piezoelectric constant by a simpler process. As a result, it has been found that it is effective to pulverize the ceramic raw material powder to be used to an average particle size of 0.05 μm to 0.3 μm. Thus, it has been newly found that a high piezoelectric constant d33 can be obtained by firing within a specific oxygen partial pressure and firing temperature range. The reason why the piezoelectric characteristics are enhanced by using such a finely divided ceramic raw material powder is considered that excess oxygen adsorbed on the surface is reduced to an appropriate crystal state at the time of firing together with a reducing atmosphere. In addition, since the variation in the crystal grain size of the ceramics to be obtained becomes small, it is considered that the deformation amount of each crystal grain at the time of polarization becomes almost the same, so that the generation of strain between the crystal grains can be suppressed.

In addition, by using the manufacturing method of the present invention, the following effects are secondary. In the production method of the present invention, since specific reduction firing conditions are applied, even if the base metal electrode paste and the ceramic raw material powder are fired at the same time, the base metal electrode can be baked while suppressing oxidation, and oxygen defects in the ceramic raw material powder can be obtained. Can be sufficiently suppressed. Thereby, for example, a piezoelectric element composed of a piezoelectric ceramic layer and a base metal electrode layer and having a piezoelectric constant d33 of 200 pC / N or more can be provided.

The production method of the present invention is described in detail below. Ceramic raw material powder used in the production method of the present invention have the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 is at least a transition metal element A kind of element that contains Nb, M is at least one kind of element of Group 4A, contains Zr, and is represented by 0.05 <s ≦ 0.15). In the general formula, the composition of oxygen is a stoichiometric value. In the actual composition, deviation from the stoichiometric composition of oxygen is allowed.

Just Unlike A1B1O ₃ based piezoelectric ceramic compositions of ceramics of the general formula to be applied to the present invention is becomes ceramic piezoelectric constant d33 is small when fired in the air, the production method of the present invention When a prescribed condition is applied, it has a special property of developing a high piezoelectric constant d33.
The reason for this is presumed, however, since Ba and M have the property of hardly dissolving in the perovskite main phase, a sufficiently homogeneous fired body cannot be obtained by firing by a normal solid phase method. In contrast, by pulverizing the raw materials as described above and firing within the range of oxygen partial pressure, a small amount of oxygen defects are generated in the main phase, and the diffusion is promoted to homogenize the components. It is thought to do.

The composition of the above general formula will be described.
In the composition represented by A1B1O _3, A1 is at least one selected from alkali metal (Li, Na, K). Preferably A1 contains Li, K and Na.
More specifically, A1B1O ₃ is an alkali metal-containing niobate oxide-based composition _formula: it is a composition represented by _{K 1-x-y Na x} Li y (Nb 1-z Q z) O 3 Is preferred. Here, Q is at least one of transition metal elements other than Nb, and x, y, and z satisfy 0 <x <1, 0 <y <1, and 0 ≦ z ≦ 0.3.
By including both K and Na as the alkali metal, it is possible to exhibit higher piezoelectric properties than when K or Na is included alone.
Moreover, Li can obtain the effect of increasing the Curie temperature and the effect of enhancing the piezoelectric characteristics by enhancing the firing property, and also exhibits the effect of improving the mechanical strength. However, when the Li content y exceeds 0.3, the piezoelectric characteristics tend to be lowered. For this reason, the content y of Li in the alkali metal is preferably 0 <y ≦ 0.3.
When z exceeds 0.3, it is difficult to obtain high piezoelectric characteristics.
The ranges of x, y, and z are more preferably 0.3 ≦ x ≦ 0.7, 0.05 ≦ y ≦ 0.2, and 0 ≦ z ≦ 0.2.

A1B1O ₃ and BAMO ₃ are contained in the piezoelectric ceramic at a ratio represented by the following general formula (1).
_{(1-s) A1B1O 3 -sBaMO} 3 (0.05 <s ≦ 0.15) ··· (1)
When the content ratio of BaMO ₃ is in the range of 0.05 <s ≦ 0.15, a piezoelectric ceramic having a high piezoelectric constant d33 and a high Curie temperature can be obtained. On the other hand, if s is 0.05 or less, or if s exceeds 0.15, the obtained piezoelectric constant becomes too low, and it becomes difficult to obtain a practical piezoelectric ceramic. A preferable range of s is 0.065 ≦ s ≦ 0.10.
M is preferably a composition containing 80 at% or more of Zr as Group 4A.

The ceramic raw material powder is obtained by preparing, mixing, and calcining raw materials composed of A1, B1, Ba, and M so as to have the composition described by the above general formula. The calcination temperature is preferably 900 ° C. or higher and 1200 ° C. or lower. If the temperature is lower than 900 ° C., the raw materials do not react and it is difficult for the composition uniformity to be sufficient. On the other hand, when the temperature exceeds 1200 ° C., the reaction of the raw material proceeds so much that the densification in the subsequent firing is deteriorated, or it is fired into a lump and difficult to grind, so that molding becomes difficult.

In the present invention, ceramic raw material powder having an average particle size of 0.05 μm or more and 0.3 μm or less is used. When the average particle size of the ceramic raw material powder is less than 0.05 μm, the raw material powder aggregates and it is difficult to perform the molding step described later. On the other hand, if the average particle size exceeds 0.3 μm, the variation in the crystal particle size of the sintered ceramic becomes large, and the effect of enhancing the piezoelectric characteristics cannot be sufficiently obtained.

Moreover, the temperature at which densification starts as ceramics can be reduced by making the raw material powder fine. Therefore, oxidation can be suppressed when a base metal electrode is used. Specifically, firing is possible even at a firing temperature of 1000 ° C. or lower, and further 950 ° C. or lower.

It is preferable that the ceramic raw material powder has a composition of the above general formula as 100 mol% and further contains a Mn compound in an amount of 0.5 to 5 mol%. MnO ₂ can be used as the Mn compound. The addition of the Mn compound has an effect that a high piezoelectric constant d33 can be obtained only by reduction firing without re-oxidation treatment. Further, the resistance of the piezoelectric ceramic is increased, and a higher voltage can be applied during the polarization process. Moreover, the firing temperature of the ceramic can be further lowered. Since firing can be performed at a low firing temperature, oxidation of the electrode is suppressed when a base metal electrode is formed. Since the conductivity of the base metal electrode can be ensured, the polarization process can be performed reliably.

Known means can be used as means for forming the ceramic raw material powder into a molded body. For example, it can be formed into a sheet-like molded body with a bar coder or the like.

An electrode paste such as a base metal can be applied to the molded body. As means for applying the electrode paste, known means such as screen printing and bar coders can be used. A molded body for a piezoelectric element composed of a laminated body of a ceramic layer and an electrode layer can be obtained by laminating a molded body to which an electrode paste is applied. As the electrode paste, the cost of the electrode can be reduced by using the base metal electrode paste, and in particular, the cost can be further reduced by using the base metal electrode paste mainly composed of at least one element of Cu, Ni, and Al.

The firing process will be described. Firing is performed in an atmosphere having an oxygen partial pressure of 1 × 10 ⁻¹² kPa to 1 × 10 ⁻⁴ kPa. When the pressure is less than 1 × 10 ⁻¹² kPa, the reducing power of the atmosphere is too strong, and oxygen defects are generated in the fired ceramic, and a piezoelectric ceramic having a high piezoelectric constant d33 cannot be obtained. On the other hand, if it exceeds 1 × 10 ⁻⁴ kPa or less, a high piezoelectric constant cannot be obtained. Further, when the base metal electrode paste is used, the base metal electrode is oxidized and is not energized, so that it does not function as a piezoelectric element. The oxygen partial pressure is preferably 8 × 10 ⁻¹¹ kPa to 1 × 10 ⁻⁶ kPa, more preferably 1 × 10 ⁻¹⁰ kPa to 1 × 10 ⁻⁸ kPa.

The firing temperature is 900 ° C. or higher and 1300 ° C. or lower. If the temperature is lower than 900 ° C., the ceramic is not sufficiently fired and is not densified, and a piezoelectric element having a piezoelectric constant d33 of less than 200 pC / N is obtained. On the other hand, when the temperature exceeds 1300 ° C., over-baking occurs, and in this case, the density and the piezoelectric characteristics are lowered. By using the finely divided ceramic raw material powder, the firing temperature can be set to 1150 ° C. or lower. If it is 1150 degrees C or less, when a base metal electrode is used, the oxidation can further be suppressed and the piezoelectric element which has further the piezoelectric characteristic of a piezoelectric ceramic layer and the electroconductivity of an electrode layer can be manufactured. A more preferable firing temperature is 920 ° C. or higher and 1000 ° C. or lower.

The resulting piezoelectric ceramic by the above production method, the composition of the ceramic, the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 transition It is at least one element of a metal element and includes Nb, M is at least one element of Group 4A and includes Zr, and is represented by 0.05 <s ≦ 0.15), and the average crystal grain size is 2.0 μm or less, the standard deviation of crystal grain size is 1.0 μm or less, and the piezoelectric constant d33 is 200 pC / N or more. As a result of using the finely divided ceramic raw material powder, the average crystal grain size of the ceramic is 2.0 μm or less, the standard deviation of the crystal grain size is 1.0 μm or less, and the piezoelectric constant d33 is used in order to use the above firing conditions. Large piezoelectric ceramics can be obtained.

In addition, since a high piezoelectric constant d33 can be maintained even if simultaneously fired using a base metal electrode paste, a piezoelectric element having a piezoelectric constant d33 in which a piezoelectric ceramic layer and a non-metal electrode layer are laminated and having a value of 200 pC / N or more can be obtained. it can.

The measurement method of the composition, the piezoelectric constant d33, the average crystal grain size, and the standard deviation of the crystal grain size described in the present invention will be described below. [Composition] The composition was measured by SEM-EDX (Energy Dispersive X-ray spectroscopy). As measurement conditions, the acceleration voltage was 15 kV, the current was 100 nA, and the beam diameter was 1 μm.

[Piezoelectric constant d33] After the polarization treatment, the piezoelectric constant d33 is measured. In the polarization treatment, an Ag electrode was formed on the laminate by sputtering, a DC electric field was applied until a current of 1 mA flowed at 373 K (100 ° C.), and a DC electric field of maximum 2.0 kV / mm was applied for 10 minutes. The piezoelectric constant d33 was measured with a d33 meter (manufactured by the Institute of Speech, Chinese Academy of Sciences).

[Average crystal grain size]
The average crystal grain size was observed with a back-scattered electron image (5000 times) by a scanning electron microscope (SEM), and after describing the grain boundary of each crystal grain in an image, the number average was calculated using image analysis software: ImageJ. It is obtained by the diameter (= Σ (maximum diameter of crystal) / (number of evaluated oriented crystals)).

[Standard Deviation of Crystal Grain Size] For the maximum diameter r and average crystal grain size R of each crystal, the standard deviation σ is an equation of σ = {Σ (rR) ² / (number of evaluated oriented crystals)} ^0.5 Calculated from

The invention is further described in detail on the basis of examples.
(Examples 1-1 to 1-3, Comparative Example 1-4)
_{Formula: 0.92 (K 0.414 Na 0.46 Li} 0.046) Nb 0.92 O 3 + 0.08BaZrO to be a composition represented by _{3, K, Na, Li,} Nb, Ba, Zr Raw materials were prepared. These raw materials were ball-milled for 16 hours in an ethanol solvent. The media used for the ball mill was a zirconia ball having a diameter of 5 mm, and the rotation speed was 100 rpm. After the mixed raw material was separated from the media, it was dried in the atmosphere at 130 ° C. The dried raw material was passed through a 500 mesh sieve, then placed in a zirconia mortar and calcined at 1050 ° C. for 3 hours in the air. In the present invention also to the composition 100 mol% of the above formula, was added MnO ₂ of 1 mol%. Then, it grind | pulverized for 1 hour with the bead mill, and produced the ceramic raw material powder whose average particle diameter is 0.15 micrometer. For comparison, a ceramic raw material powder having an average particle size of 0.8 μm was prepared by pulverizing with a ball mill for 16 hours.

Next, this ceramic raw material powder was used as a sheet-like molded body.
First, in order to make the mixture into a slurry, the obtained ceramic raw material powder was taken as 100% by mass, and 200 to 300% by mass of ethanol and 50 to 100% by mass of butanol were added. A plasticizer was also added. In this example, 5 to 15% by mass of dioctyl phthalate was added as a plasticizer to 100% by mass of the mixture. A binder was also added. In this example, 5 to 15% by mass of polyvinyl butyral was added as a binder to 100% by mass of the mixture. The slurry thus obtained was formed into a sheet.

  Next, a base metal electrode paste was applied to the molded body. As a raw material for the base metal component, a spherical commercial Ni particle paste having an average particle diameter of 0.6 μm was used. The Ni paste was mixed with 30 mass% of the above ceramic composition powder in order to adjust the shrinkage ratio with the ceramic. The electrode paste was applied to one side of the sheet-like molded body by screen printing and then dried.

  A sheet-like formed body coated with the electrode paste was stacked for 10 layers to obtain a laminated body in which the formed body and the electrode paste were alternately formed. The laminate was densified by cold isostatic pressing (CIP), and then a binder removal treatment was performed.

Next, these laminates were fired under different conditions.
The oxygen partial pressure and the firing temperature are shown in Table 1. The oxygen partial pressure and the firing temperature (No. 1-1: 1 × 10 ⁻¹⁰ kPa at 925 ° C., No. 1-2: 3 × 10 ⁻¹⁰ kPa at 950 ° C. No. 1-3: 2 × 10 ⁻⁹ kPa and 1000 ° C.), the compact and the base metal electrode paste were fired simultaneously. The firing time was 4 hours.
As a comparative example, a ceramic raw material powder having an average particle diameter of 0.8 μm was fired at 1180 ° C. with an oxygen partial pressure and a firing temperature of 7 × 10 ⁻¹¹ kPa.
Manufacturing conditions of the obtained piezoelectric element (oxygen partial pressure in firing atmosphere, firing temperature, average grain size of ceramic raw material powder, MnO ₂ addition amount), piezoelectric constant d33, average crystal grain size, standard of crystal grain size Deviations are listed in Table 1.

Example No. using a ceramic raw material powder having an average particle size of 0.15 μm. Samples 1-1 to 1-3 were obtained with a piezoelectric constant d33 of 200 pC / N or higher without re-oxidation treatment. The average crystal grain size of the ceramics was 1.5 μm to 1.6 μm, which was 2.0 μm or less, and the standard deviation of the crystal grain size was 1.0 μm or less.
Comparative Example No. Since 1-4 could not be polarized, the piezoelectric constant was substantially zero.

(A) of FIG. SEM observation photograph of 1-2 ceramics, (b) is a diagram describing the grain boundaries of the crystal grains. It can be seen that the crystal grain size is fine and almost uniform. As shown in FIG. 2, this ceramic had a very small standard deviation of the crystal grain size of 0.7 μm. The average crystal grain size was 1.5 μm.
On the other hand, FIG. The SEM observation photograph of 1-4 ceramics, (b) is the figure which described the grain boundary of a crystal grain. As shown in FIG. 4, this ceramic had a large standard deviation of the crystal grain size of 1.2 μm. The average crystal grain size was 2.1 μm.

Claims (4)

A method of manufacturing a piezoelectric ceramic, the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 is at least one element of the transition metal element Nb is included, M is at least one element of Group 4A, includes Zr, has a composition represented by 0.05 <s ≦ 0.15), and has an average particle size of 0.05 μm or more A step of preparing a ceramic raw material powder of 0.3 μm or less, a step of using the ceramic raw material powder as a molded body, an oxygen partial pressure of 1 × 10 ⁻¹² kPa to 1 × 10 ⁻⁴ kPa in an atmosphere of 900 And a step of reducing and firing the molded body at a temperature of not lower than 1 ° C and not higher than 1300 ° C. 2. The method for producing a piezoelectric ceramic according to claim 1, wherein the firing is performed at an oxygen partial pressure of 8 × 10 ⁻¹¹ kPa to 1 × 10 ⁻⁶ kPa and 900 ° C. to 1150 ° C. 3. The composition of the ceramic, the general _{formula: (1-s) A1B1O 3} -sBaMO 3 ( where, A1 is at least one element selected from alkali metals, B1 is an element of at least one transition metal element Nb M is at least one element of Group 4A and includes Zr, and is expressed by 0.05 <s ≦ 0.15), the average crystal grain size is 2.0 μm or less, and the standard deviation of crystal grain size Is a piezoelectric ceramic, characterized by having a piezoelectric constant d33 of 200 pC / N or more. A piezoelectric element, wherein a base metal electrode is formed on the piezoelectric ceramic according to claim 3.

Images