JP2023060517A - Piezoelectric element, ultrasonic transducer and ultrasonic motor having the same - Google Patents

Abstract

To provide a piezoelectric element with small mechanical loss and large displacement when driven at high speed and large amplitude.SOLUTION: A piezoelectric element consists of first and second electrodes provided opposite each other, and a piezoelectric ceramics disposed between the first electrode and the second electrode and in contact therewith, mainly composed of a compound having a perovskite-type structure containing Pb, Zr, Ti and O as constituent elements, wherein the average domain width in the sintered particles 11 observed in the cross section perpendicular to the first and second electrodes is between 100 nm and 500 nm and the area percentage of sintered particles with observed domain 12 in the cross section is 60% or more.SELECTED DRAWING: Figure 4

Description

The present invention relates to a piezoelectric element, and an ultrasonic vibrator and an ultrasonic motor having the same.

Piezoelectric elements are used in sensor elements, power generating elements, and the like by utilizing the positive piezoelectric effect that converts mechanical energy into electrical energy. Piezoelectric elements are also used in vibrators, sound generators, actuators, ultrasonic motors, pumps, etc., by utilizing the inverse piezoelectric effect of converting electrical energy into mechanical energy. Furthermore, piezoelectric elements are also used in circuit elements, vibration control elements, etc., due to the combination of the positive piezoelectric effect and the inverse piezoelectric effect.

Among piezoelectric elements, vibrators, ultrasonic motors, and the like are continuously driven under conditions such as a resonance point where large amplitude occurs, so the elements themselves tend to generate heat. Since the heat generation of the piezoelectric element leads to deterioration or loss of piezoelectric characteristics, it is necessary to suppress this. The heat generated by the piezoelectric element is caused by mechanical loss and electrical loss that occur during driving. For this reason, the above-described piezoelectric element is made of a material called a hard piezoelectric material or a hard material, which has a small loss in both cases. In hardware piezoelectric materials, a high mechanical quality factor Qm is important as an index of small mechanical loss, and a small dielectric loss tangent tan δ is important as an index of small electrical loss.

As such a low-loss hard piezoelectric material, lead zirconate titanate (Pb(Zr, Ti)O ₃ : PZT) having a perovskite structure is used as a basic composition, and various elements are dissolved therein. A low-loss type has been proposed.

For example, as a piezoelectric ceramic composition having a high mechanical quality factor Qm, a compound containing Pb, Zn, Nb, Ti, Zr and O as constituent elements and having a perovskite structure with Mn added thereto is known. (Patent Documents 1 and 2).

In addition, as a means of increasing the mechanical quality factor Qm of PZT-based piezoelectric ceramics, it is also known to increase the area ratio of crystal grains having a domain size of 100 nm or less to 30% or more (Patent Document 3).

Japanese Patent Publication No. 54-18400 Japanese Patent Application Laid-Open No. 2001-181037 JP 2017-92280 A

Piezoelectric elements used in ultrasonic vibrators and ultrasonic motors are required to generate little heat when driven and to have a large displacement. The displacement amount of the piezoelectric element increases as the piezoelectric d constant increases. However, since the mechanical quality factor Qm and the piezoelectric d-constant of a piezoelectric element generally have a trade-off relationship, it has been difficult to obtain a piezoelectric element with both high values. In fact, according to the piezoelectric ceramic compositions described in Patent Documents 1 to 3, although a piezoelectric element having a high mechanical quality factor Qm is obtained, the element often has a low piezoelectric d-constant.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a piezoelectric element having a small mechanical loss and a large amount of displacement when driven at high speed and large amplitude.

The present inventor focused on the domain structure in the sintered particles in the PZT-based piezoelectric ceramics in the course of investigation for solving the above problems. Then, the inventors found that the problem can be solved by increasing the width of the domain, and completed the present invention.

That is, one aspect of the present invention for solving the above-mentioned problems is to provide first and second electrodes that are provided facing each other, and between and in contact with the first and second electrodes. The main component is a compound having a perovskite structure containing Pb, Zr, Ti and O as elements, and the average domain width in the sintered particles observed in the cross section perpendicular to the first and second electrodes is 100 nm. The piezoelectric element comprises piezoelectric ceramics having a size of 500 nm or more and having an area percentage of 60% or more of the sintered particles in which the domains are observed occupying the cross section.

Another aspect of the present invention is an ultrasonic transducer comprising the piezoelectric element described above and a pair of block bodies sandwiching the piezoelectric element from one axial direction.

Furthermore, another aspect of the present invention is an ultrasonic motor comprising the piezoelectric element described above and a sliding member adhered to the piezoelectric element.

According to the present invention, it is possible to provide a piezoelectric element with small mechanical loss and large displacement when driven at high speed and large amplitude.

1 is a schematic perspective view showing the structure of a laminated piezoelectric element according to one aspect of the present invention; FIG. A-A' cross-sectional view of the laminated piezoelectric element shown in FIG. Explanatory drawing showing a method of measuring a domain width in a piezoelectric element according to one aspect of the present invention. Explanatory drawing showing a method for measuring the area of sintered particles in which domains are observed in the piezoelectric element according to one aspect of the present invention.

Hereinafter, with reference to the drawings, the configuration and effects of the present invention will be described along with technical ideas. However, the mechanism of action is presumed, and whether it is correct or not does not limit the present invention.

In this specification, "driving at high speed and large amplitude" of the piezoelectric element means driving at the resonance frequency, or driving under the condition that the vibration velocity measured with a laser Doppler vibrometer is 0.62 m / s or more. Say.

[Piezoelectric element]
A piezoelectric element according to one aspect of the present invention (hereinafter sometimes simply referred to as "first aspect") includes first and second electrodes provided to face each other, and the first and second electrodes. A compound having a perovskite structure containing Pb, Zr, Ti and O as constituent elements is placed between and in contact with the electrodes as a main component, and is observed in a cross section perpendicular to the first and second electrodes. wherein the average domain width in the sintered particles is 100 nm or more and 500 nm or less, and the area percentage of the sintered particles in which the domains are observed in the cross section is 60% or more.

The first and second electrodes are provided facing each other so as to sandwich piezoelectric ceramics, which will be described later, and are applied with voltages having different polarities ("+" or "-") when driven. The material, shape and arrangement of the electrodes are not particularly limited as long as a desired voltage can be applied to the piezoelectric ceramics. Examples of electrode materials include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof. Examples of the shape and arrangement of the electrodes include those that cover substantially the entire specific surface of the piezoelectric ceramic. Further, the electrodes may be formed only on the surface of the piezoelectric element, or may be formed inside the piezoelectric element like internal electrodes in a laminated piezoelectric element to be described later.

When the first side surface is the laminated piezoelectric element 100 having the structure shown in FIGS. They are provided with connecting conductors 30a and 30b for electrical connection, respectively. Examples of the material of the connection conductor include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof, as with the electrodes described above. be. The connection conductors may be arranged on the surface of the laminated piezoelectric element 100 as shown in FIGS. good too. In the laminated piezoelectric element 100 shown in FIGS. 1 and 2, the first electrode 20a and the second electrode 20b are arranged inside the piezoelectric element, so they are collectively called internal electrodes 20. As shown in FIG.

In addition, when the first side surface is the laminated piezoelectric element 100, as shown in FIGS. A pair of external electrodes 40a and 40b for applying voltage to the piezoelectric ceramics may be provided. As the material of the external electrode, the same material as that of the connection conductor described above can be used.

The first side comprises a piezoelectric ceramic disposed between and in contact with the first and second electrodes.

This piezoelectric ceramic is mainly composed of a compound having a perovskite structure containing Pb, Zr, Ti and O as constituent elements. Thereby, a large displacement can be obtained when a voltage is applied to the piezoelectric element.

Here, it is confirmed by the following procedure that the piezoelectric ceramics is mainly composed of a compound having a perovskite structure.
First, a piezoelectric ceramic is pulverized to prepare a powdery sample. In this case, it is preferable to pulverize after removing portions other than the piezoelectric ceramics such as electrodes and coatings, but it is difficult to separate the piezoelectric ceramics portion from other portions such as the laminated piezoelectric element described above. In addition, for a piezoelectric element having a higher percentage of piezoelectric ceramics than other parts, the entire element may be pulverized to obtain a powdery sample.
Next, for the obtained powdery sample, the diffraction line profile is measured with an X-ray diffraction (XRD) apparatus using Cu-Kα rays, and the diffraction line derived from other structures is compared with the strongest diffraction line intensity in the profile derived from the perovskite structure. When the ratio of the strongest diffraction line intensity in the profile is 10% or less, it is determined that the piezoelectric ceramic is mainly composed of a compound having a perovskite structure. In addition, when the piezoelectric element is pulverized into a powder sample without separating the piezoelectric ceramic portion from other portions, a peak clearly derived from a portion other than the piezoelectric ceramic, such as the electrode, in the diffraction line profile is observed, the peak is excluded and the strongest line intensity is compared as described above.

In addition, it is confirmed by the following procedure that the compound having the perovskite structure contains Pb, Zr, Ti and O as constituent elements.
First, a powdery sample determined to be mainly composed of a compound having a perovskite structure by the above-described method is subjected to an inductively coupled plasma (ICP) emission spectrometer, an ion chromatography device, or an X-ray fluorescence (XRF) analysis. A compositional analysis is performed by the instrument.
Then, the presence of Pb, Zr, and Ti was confirmed as a result of composition analysis, and it was determined that the compound having the perovskite structure contained each of the above elements and O. In addition, when the presence of Zn, Nb and Mn is also confirmed by this composition analysis, it is determined that the compound having the perovskite structure further contains Zn, Nb and Mn as constituent elements, as will be described later. .

The compound having the perovskite structure preferably further contains Zn, Nb and Mn as constituent elements. As a result, the compound mainly contains Pb(Zr, Ti)O ₃ —Pb(Zn, Nb)O ₃ —Pb(Mn, Nb)O ₃ , and when a voltage is applied to the piezoelectric element, Larger displacement can be obtained, and mechanical loss during driving is reduced.

More preferably, the compound having a perovskite structure is represented by the following general formula (1). This makes it possible to achieve larger displacements and smaller mechanical losses.

xPb(Zr1 _{-aTia )} O3 _- yPb(Zn1 _/ 3Nb2 _/3 ) _O3
-zPb(Mn1 _{/3Nb2 /3} ) _O3 (1)

provided that a, x, y and z in the formula are respectively 0.45≤a≤0.60, 0<x≤0.85, 0≤y<0.99, 0.01<z<0.10 and x+y+z=1.0.

In the following description, the compound represented by the general formula (1) may be referred to as "PZT-PZN-PMnN", and in the general formula (1), each connected by a hyphen (-) When referring to the parts individually, they may be denoted as "PZT," "PZN," and "PMnN," respectively.

Here, it is confirmed by the following procedure that the compound having the perovskite structure is represented by the general formula (1).
First, the contents of Zr, Ti, Zn, Nb and Mn are calculated in terms of atomic % to mol % from the results of the composition analysis described above.
Next, the ratio of the content of Ti to the total amount of Zr and Ti is defined as "a".
Next, the contents of Zn, Nb and Mn in the perovskite structure are determined so that the ratio of the Nb content to the Zn content and the ratio of the Nb content to the Mn content are both 2. At that time, when the ratio of the content of Nb to the total amount of Zn and Mn exceeds 2, the excess Nb is not included in the perovskite structure. On the other hand, when the ratio of the Nb content to the total amount of Zn and Mn is less than 2, in other words, when the ratio of the total amount of Zn and Mn to the Nb content exceeds 1/2, the total amount of Nb is proportionally divided according to the content ratio of Zn and Mn to determine the amount of Nb contained in PZN and PMnN, respectively, and then Zn and Mn corresponding to 1/2 of the amount of each Nb are added in the perovskite structure Zn and Mn in excess of this are not included in the perovskite structure.
Next, the determined contents of Zn, Nb and Mn in the perovskite structure, and the ratio of the total amount of Zr and Ti to the total amount of Zr and Ti (hereinafter simply referred to as "the total amount of B sites") is "x", the ratio of the total amount of Zn and Nb in PZN to the total amount of B sites is "y", and the ratio of the total amount of Mn and Nb in PMnN to the total amount of B sites is "z".
Then, when the obtained values of "a", "x", "y" and "z" all satisfy the general formula (1), the compound having the perovskite structure is represented by the general formula (1) determined to be represented.

The piezoelectric ceramics may contain other additive elements or compounds as long as it contains the above elements as constituent elements and is mainly composed of a compound having a perovskite structure. Examples of additive elements include Ca, Sr, Ba, Ag, La, Ce, Bi, etc., which form a solid solution at the A site, Mg, Fe, Co, which form a solid solution at the B site, in the perovskite structure represented by _ABO3 . , Ni, Ta and W, and the like. Examples of the compound include a glassy grain boundary phase derived from a component added to lower the sintering temperature.

In the first aspect, when observing the cross section perpendicular to the first and second electrodes in the piezoelectric ceramic, the average value of the widths of the domains present in the sintered particles, that is, the average domain width is 100 nm or more and 500 nm or less. Become. As a result, the piezoelectric element has a large mechanical quality factor Qm and a large piezoelectric d constant. Although the reason for this is not clear, the large average domain width of 100 nm or more suppresses the movement of the domain wall, which is the boundary between the domains, when the piezoelectric element is driven, and reduces the mechanical loss caused by the movement. and that the average domain width is not too large, ie, 500 nm or less, so that the sintered particles contain a certain amount of domain walls, and the displacement capability is improved due to the excellent electric field responsiveness of the domain walls. , is presumed to have an effect. From the viewpoint of obtaining a larger mechanical quality factor Qm, the average domain width is preferably 105 nm or more, more preferably 110 nm or more. On the other hand, in terms of obtaining a larger piezoelectric d constant, the average domain width is preferably 450 nm or less, more preferably 400 nm or less. For the reason described above, the average domain width is preferably 105 nm or more and 450 nm or less, more preferably 110 nm or more and 400 nm or less.

In the first aspect, when a section perpendicular to the first and second electrodes in the piezoelectric ceramic is observed, the area percentage of sintered particles in which a domain is observed in the section is 60% or more. As a result, the piezoelectric element has a large mechanical quality factor Qm. Although the reason for this is not clear, it is presumed that the domain wall that appears in the cross section is less likely to move when the piezoelectric element is driven than the domain wall that does not appear in the cross section. From the point of obtaining a larger mechanical quality factor Qm, the area percentage is preferably 65% or more, preferably 70% or more. On the other hand, the higher the area percentage, the better, so the upper limit is not limited and may be 100%.

In the first aspect, it is preferable that the density of domain walls existing in the sintered particles is 2.5 lines/μm ² or less when a cross section perpendicular to the first and second electrodes in the piezoelectric ceramic is observed. . As a result, the piezoelectric element has a large mechanical quality factor Qm. Although the reason for this is not clear, in sintered particles having domains of the same width, the domain wall density is lower when the dimension of the domain wall in the longitudinal direction is larger, that is, when the domain wall length is longer. Considering that the density of the domain walls in the sintered particles is low and the length of the domain walls contained is long, the energy required to move the domain walls increases, and the domain walls are less likely to move when the piezoelectric element is driven. It is presumed that

Here, the average domain width in the cross section perpendicular to the first and second electrodes of the piezoelectric ceramic, the area percentage of the sintered particles in which the domains are observed occupying the cross section, and the domain wall density in the sintered particles are , determined by the following procedure.
First, the piezoelectric element is cut along a plane perpendicular to the first and second electrodes. A cutting means is not particularly limited, and a dicing saw, a cutter, or the like can be used.
Next, the cut piezoelectric ceramic is embedded in epoxy resin so that the cut surface is exposed, and then the cut surface is mirror-polished using colloidal silica.
Next, in order to impart electrical conductivity to the cut surface of the piezoelectric ceramic, the polished surface is coated with osmium (Os) to obtain a sample for measurement.
Next, a Schottky scanning electron microscope is used to obtain a backscattered electron (BSE) image of the piezoelectric ceramic portion of the mirror-finished cut surface. At this time, the acceleration voltage is 7.00 kV, the working distance (WD), which is the distance between the lower surface of the objective lens and the sample, is 4 mm, and the magnification is 10000 times.
Next, after saving the image file of the obtained BSE image in PDF format, the PDF file is opened with Acrobat (manufactured by Adobe).
Next, among the sintered particles observed in the BSE image, three particles in which striped domains are clearly confirmed from end to end are arbitrarily selected, and these are used as particles to be measured. Then, for each particle to be measured, as shown in FIG. 3, the widths of the striped domains 12 existing inside are measured for the domains 12 at five different locations. The measurement is performed by selecting the "distance tool" as the measurement type in the "measurer tool" function of Acrobat, setting one end of the domain 12 as the starting point (see FIG. 3(a)), and then measuring the other end of the domain 12. (see (b) of FIG. 3), and the line segment displayed on the other end sets the position along the boundary of the domain (domain wall 13) as the end point (see (c) of FIG. 3). ), by reading the displayed distance.
Next, the average value of a total of 15 domain width data obtained from each particle to be measured is calculated, and the average domain width of the piezoelectric ceramic is defined as 1/10000.
Next, in the Acrobat function "measure tool", select "area tool" as the measurement type, and among the sintered particles observed in the BSE image, the striped domain inside is the width direction of the domain Next, as shown in FIG. 4, trace the contours of all grains that are clearly identified from one end to the other, draw a polygon, and display the area of the polygon. In FIG. 4, sintered particles 11 in which stripe-shaped domains 12 are clearly observed from one end to the other in the width direction of the domains 12 are displayed with dots. Then, the sum of the displayed areas divided by the area of the entire BSE image and multiplied by 100 is taken as the area percentage of the sintered particles in which the domain is observed, which occupies the cross section of the piezoelectric ceramic.
Next, arbitrarily select three sintered particles 11 from which the domains 12 are clearly observed from end to end, and count and total the domain boundaries (domain walls 13) present in each selected particle. . The domain wall density in the sintered particles is obtained by dividing the total value by the total area (μm ² ) of the selected particles.

[Manufacturing method of piezoelectric element]
The piezoelectric element according to the first aspect includes, for example, mixing powder of a compound containing one or more elements selected from Pb, Zr and Ti to obtain a mixed powder containing each of the elements; calcining to obtain a calcined powder, molding the calcined powder into a predetermined shape to obtain a molded body, firing the molded body to obtain a sintered body, and on the surface of the sintered body It is manufactured through forming electrodes and/or connecting conductors and applying a high voltage between the electrodes or connecting conductors to perform a polarization treatment. This manufacturing method will be described below.

The composition and particle size of the powder of the compound used as the raw material are not limited as long as the predetermined piezoelectric ceramics can be obtained by sintering. The compound constituting the powder may contain additional elements other than the elements described above. Examples of usable compounds include PbO and Pb ₃ O ₄ as Pb-containing compounds, ZrO ₂ as Zr-containing compounds, and TiO ₂ as Ti-containing compounds. When Zn, Nb and Mn are contained in the perovskite structure in order to obtain a higher mechanical quality factor Qm and piezoelectric d constant, ZnO or the like is used as the Zn-containing compound, and Nb ₂ O as the Nb-containing compound. ₅ and the like, and MnCO ₃ and the like as the Mn-containing compound may be used, respectively.

The method of mixing the raw material powders is not particularly limited as long as the powders are uniformly mixed while preventing contamination of impurities, and either dry mixing or wet mixing may be employed. When wet mixing using a ball mill is employed, mixing may be performed for, for example, about 8 to 24 hours.

The calcination conditions are not limited as long as each raw material reacts to form a compound with a perovskite structure having a predetermined composition. Just do it. If the firing temperature is too low or the firing time is too short, unreacted raw materials and intermediate products may remain. On the other hand, if the firing temperature is too high or the firing time is too long, there is a possibility that the compound with the desired composition may not be obtained due to volatilization of Pb or Zn, or the product may solidify and become difficult to crush. There is a risk that the productivity will decrease.

The calcined powder may be mixed with a component that will be incorporated into the perovskite structure during firing, which will be described later, or a component that will form a precipitate between the sintered particles of the piezoelectric ceramic before molding. In this case, a mixing method similar to the method for mixing raw material powders can be employed.

When ZnO powder is added to the calcined powder, the above-described average domain width is expanded, making it easier to obtain the piezoelectric element relating to the first side surface. In order to keep the average domain width of the piezoelectric element within a predetermined range, the amount of ZnO powder added is preferably 0.1% by mass or more and 1.0% by mass or less relative to the calcined powder. More preferably, the content is 3% by mass or more and 0.5% by mass or less.

As a method for molding the calcined powder, methods commonly used for molding ceramic powder, such as uniaxial pressure molding of powder, extrusion molding of clay containing powder, and cast molding of slurry in which powder is dispersed, are employed. be able to.

Here, when the piezoelectric element is the laminated piezoelectric element 100 shown in FIGS. 1 and 2, the following molding method can be employed.

First, the calcined powder is mixed with a binder or the like to form a slurry or clay, which is formed into a sheet to obtain a green sheet containing the calcined powder. As a method for forming the sheet, commonly used methods such as a doctor blade method and an extrusion molding method can be employed.

Next, an electrode pattern that will become the internal electrode 20 after firing is formed on the green sheet containing the calcined powder. The electrode pattern may be formed by a commonly used method, and a method of printing or applying a paste containing an electrode material is preferable in terms of cost. When forming an electrode pattern by printing or coating, powder (common material) or glass frit having the same composition and crystal structure as the fired piezoelectric ceramics is used in order to improve the adhesion strength to the fired piezoelectric ceramics. It may be contained in the paste.

As a multilayer piezoelectric element having a structure different from that shown in FIGS. 1 and 2, connection conductors for electrically connecting internal electrodes are arranged in through holes (vias) penetrating through the piezoelectric ceramic layers. things are also mentioned. When manufacturing a laminated piezoelectric element having such a structure, prior to the formation of the electrode pattern, through holes are formed in the obtained green sheet by punching or irradiation with a laser beam. to fill the through holes with an electrode material. The filling method is not particularly limited, but a method of printing a paste containing an electrode material is preferable in terms of cost.

Next, a predetermined number of green sheets having electrode patterns formed thereon are laminated, and the sheets are adhered to each other to obtain a compact. Lamination and bonding may be performed by a commonly used method, and a method in which the green sheets are thermocompressed by the action of a binder is preferable from the viewpoint of cost.

The compact obtained by the above procedure is fired after the binder is removed as necessary. The sintering conditions may be appropriately set in consideration of the sinterability of the calcined powder and the durability of the electrode material in the case where the compact is contained. When firing a compact containing copper (Cu) or nickel (Ni) as an internal electrode material, the firing atmosphere is preferably a reducing or inert atmosphere in order to prevent oxidation. An example of firing conditions for a compact containing neither copper (Cu) nor nickel (Ni) as an internal electrode material is 900° C. to 1200° C. for 1 hour to 5 hours in an air atmosphere. If the sintering temperature is too low or the sintering time is too short, the densification will be insufficient, and there is a risk that a piezoelectric ceramic with desired characteristics will not be obtained. On the other hand, if the firing temperature is too high or the firing time is too long, there is a risk that Pb or Zn will volatilize, resulting in a compositional deviation, or that coarse particles will be formed, resulting in deterioration of properties. Moreover, when the compact contains an internal electrode material, there is a possibility that the electrode material will melt or diffuse, making it impossible to obtain piezoelectric ceramics or piezoelectric elements having desired characteristics. It is preferable to set the firing temperature to 1100° C. or lower in order to avoid such inconveniences due to an excessively high firing temperature and to reduce the material cost by using a material with a low melting point for the internal electrode material. When obtaining a plurality of piezoelectric ceramics or piezoelectric elements from one compact, the compact may be divided into several blocks prior to firing.

In the first aspect, when firing is performed in the atmosphere during the manufacturing process, increasing the temperature tends to increase the average domain width. As a firing temperature for obtaining a piezoelectric element having a large average domain width, 1050° C. or higher is exemplified. On the other hand, when the firing temperature is not too high, the area percentage of sintered particles in which domains are observed tends to increase. As a firing temperature at which a piezoelectric element having a large area percentage of sintered particles in which domains can be observed is obtained, 1100° C. or less is exemplified. From these points, an example of the firing temperature in the air at which a piezoelectric element having a large average domain width and a large area percentage of sintered particles in which domains are observed is obtained is 1050° C. or more and 1100° C. or less. .

Next, electrodes and/or connection conductors are formed on the surface of the obtained sintered body. If the sintered body does not contain internal electrodes, a pair of electrodes is formed on its surface. These electrodes become the first and second electrodes of the piezoelectric element, respectively. On the other hand, when the sintered body includes internal electrodes, a pair of connecting conductors are formed on the surfaces thereof. In this case, a pair of external electrodes electrically connected to each connection conductor may be further formed on the surface of the sintered body as a first electrode and a second electrode. For the formation of electrodes and/or connecting conductors, commonly used methods such as applying or printing a paste containing electrode materials to the surface of the piezoelectric ceramics and baking the paste, or vapor-depositing the electrode material on the surface of the piezoelectric ceramics are employed. can.

Next, a high voltage is applied between the formed electrodes or connection conductors to polarize the piezoelectric ceramics. Conditions for the polarization treatment are not particularly limited as long as the direction of spontaneous polarization can be aligned without causing damage such as cracks in the piezoelectric ceramics. An example is applying an electric field of 1 kV/mm to 5 kV/mm at a temperature of 100.degree. C. to 180.degree.

[Ultrasonic transducer]
An ultrasonic transducer according to another aspect of the present invention (hereinafter sometimes simply referred to as "second aspect") comprises a piezoelectric element according to the first aspect and a pair of piezoelectric elements sandwiching the piezoelectric element from one axial direction. and a block body. This ultrasonic transducer is known as a Langevin transducer. The Langevin vibrator may be a so-called bolt-tightened Langevin vibrator in which a block body is sandwiched between and integrated with a piezoelectric element by bolting. The Langevin vibrator operates to generate ultrasonic vibrations by supplying electric energy to a piezoelectric element and to transmit the ultrasonic vibrations to the outside through the block body. Since the second side includes the piezoelectric element related to the first side, the vibrator generates little heat when driven at high speed and large amplitude, and can be stably driven for a long period of time. Further, the second side surface is provided with the piezoelectric element related to the first side surface, so that it becomes a vibrator capable of vibrating with a large amplitude.

The material of the block used in the second side is not particularly limited as long as it can efficiently transmit the ultrasonic vibration generated from the piezoelectric element, and for example, titanium alloy, aluminum alloy, SUS, or the like can be used.

[Ultrasonic motor]
An ultrasonic motor according to another aspect of the present invention (hereinafter sometimes simply referred to as a "third aspect") includes a piezoelectric element according to the first aspect and a sliding body adhered to the piezoelectric element. Prepare. The ultrasonic motor operates such that the vibration of the piezoelectric element causes the sliding body adhered to the piezoelectric element to draw a predetermined trajectory, and the driven body moves when the sliding body comes into contact with the driven body. Since the third side includes the piezoelectric element related to the first side, the motor generates little heat when driven at high speed and large amplitude, and can be stably driven for a long period of time. In addition, since the third side includes a piezoelectric element related to the first side, the trajectory drawn by the sliding body becomes large, and the amount of movement of the driven body per vibration increases. It becomes a motor that can move the body at a higher speed.

The material of the sliding body used in the third side is not particularly limited as long as it can be displaced following the vibration of the piezoelectric element and has excellent wear resistance. Ceramic materials such as alumina and silicon nitride are suitable. can be used for

In the third aspect, the means for bonding the piezoelectric element and the sliding body is not particularly limited as long as they can be displaced integrally without peeling off during driving. One example is bonding with an adhesive.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples.

(Example 1)
As starting materials, high-purity Pb ₃ O ₄ , ZrO ₂ , TiO ₂ , ZnO, Nb ₂ O ₅ and MnCO ₃ powders were prepared, and each of the powders was prepared according to the general formula 0.79Pb (Zr _1/2 Ti _{1/ 2} ) A calcined powder having a perovskite structure represented by O ₃ -0.16Pb(Zn _1/3 Nb _2/3 )O ₃ -0.05Pb(Mn _1/3 Nb _2/3 )O ₃ It was weighed as obtained and wet-mixed in a ball mill using zirconia balls. After mixing, the mixed powder from which the dispersion medium was removed was calcined in the atmosphere at 820° C. for 3 hours to obtain calcined powder. After adding 0.3% by mass of ZnO powder to the obtained calcined powder and pulverizing it, an acrylic binder is mixed and uniaxially press-molded with a load of 2 tf to form a disk with a diameter of 10 mm. A compact was obtained. The obtained disk-shaped molded body was fired at 1100° C. for 2 hours in the atmosphere to obtain a sintered body (piezoelectric ceramics). After applying Ag paste to both surfaces of the obtained sintered body, the temperature was raised to 600° C. and baked to form a pair of connecting conductors and external electrodes. After forming the electrodes, the sintered body was subjected to a polarization treatment in silicon oil at 150° C. for 15 minutes at an electric field strength of 2.2 kV/mm to obtain a piezoelectric element according to Example 1.

(Example 2)
The blending amount of the starting raw material powder was calculated according to the general formula 0.79Pb(Zr _1/2 Ti _1/2 )O ₃ -0.13Pb(Zn _1/3 Nb _2/3 )O ₃ -0.08Pb(Mn _1/ A piezoelectric element according to Example 2 was obtained in the same manner as in Example 1, except that a calcined powder represented by ₃ Nb _2/3 )O ₃ was obtained.

(Comparative example 1)
It is assumed that a calcined powder represented by the general formula 0.79Pb(Zr _0.51 Ti _0.49 )O ₃ -0.21Pb(Zn _1/3 Nb _2/3 )O ₃ is obtained. A piezoelectric element according to Comparative Example 1 was produced in the same manner as in Example 1 except that ZnO was not added to the calcined content, and the firing temperature of the disk-shaped compact was set to 1000 ° C. got

(Comparative example 2)
The blending amount of the starting raw material powder was calculated according to the general formula 0.79Pb(Zr _0.51 Ti _0.49 )O ₃ -0.18Pb(Zn _1/3 Nb _2/3 )O ₃ -0.03Pb(Mn _1/3 Nb _{2/ 3} ) A piezoelectric element according to Comparative Example 2 was obtained in the same manner as in Example 1, except that calcined powder represented by O ₃ was obtained.

(Comparative Example 3)
The blending amount of the starting raw material powder was calculated according to the general formula 0.79Pb(Zr _1/2 Ti _1/2 )O ₃ -0.17Pb(Zn _1/3 Nb _2/3 )O ₃ -0.04Pb(Mn _1/ A piezoelectric element according to Comparative Example 3 was obtained in the same manner as in Example 1, except that a calcined powder represented by ₃ Nb _2/3 )O ₃ was obtained.

<Evaluation>
[Average domain width, area percentage of sintered particles where domains are observed, and domain wall density in sintered particles]
For each piezoelectric element obtained, the average domain width, the area percentage of the sintered particles where the domains are observed, and the domain wall density in the sintered particles were measured and calculated by the methods described above. Table 1 shows the results.

[Mechanical quality factor Qm]
For each piezoelectric element obtained, the relationship between frequency and impedance was measured using an impedance analyzer, and the mechanical quality factor Qm was calculated by the resonance-antiresonance method. Table 1 shows the results.

[Piezoelectric constant d ₃₃ ]
For each piezoelectric element obtained, the piezoelectric constant _d33 was measured using a _d33 meter. Table 1 shows the results.

When comparing the example and the comparative example, the average domain width in the sintered particles observed in the cross section perpendicular to the first and second electrodes is 100 nm or more and 500 nm or less, and occupies the cross section. The piezoelectric element according to the example in which the area percentage of the sintered particles where the domains are observed is 60% or more has a high mechanical quality factor Qm and the piezoelectric d-constant. From this result, in the piezoelectric ceramics containing Pb, Zr, Ti and O as constituent elements and mainly composed of a compound having a perovskite structure, the sintering observed in the cross section perpendicular to the first and second electrodes The average domain width in the sintered grains is 100 nm or more and 500 nm or less, and the area percentage of the sintered grains in which the domains are observed, which occupies the cross section, is 60% or more. It can be said that a piezoelectric element having both high constants can be obtained.

According to the present invention, it is possible to provide a piezoelectric element with small mechanical loss and large displacement when driven at high speed and large amplitude. When such a piezoelectric element is driven at high speed and with large amplitude, the amount of heat generated during driving is suppressed more than the conventional one, and a larger amplitude can be obtained. Therefore, the piezoelectric element according to the present invention can be suitably used for ultrasonic vibrators, ultrasonic motors, etc., which are driven at high speed and large amplitude.

100 Laminated piezoelectric element 10 Piezoelectric ceramic layer 11 Sintered particles 12 Domain 13 Domain wall 20 Internal electrode 20a First electrode 20b Second electrode 30a, 30b Connection conductor 40a, 40b External electrode

Claims (6)

first and second electrodes provided to face each other, and disposed between and in contact with the first and second electrodes,
The main component is a compound having a perovskite structure containing Pb, Zr, Ti and O as constituent elements,
An average domain width in the sintered particle observed in a cross section perpendicular to the first and second electrodes is 100 nm or more and 500 nm or less, and the sintered particle in which the domain is observed occupying the cross section A piezoelectric element comprising piezoelectric ceramics having an area percentage of 60% or more. 2. The piezoelectric element according to claim 1, wherein the domain wall density in said sintered particles is 2.5 lines/[mu]m ^<2> or less. 3. The piezoelectric element according to claim 1, wherein said compound having a perovskite structure further contains Zn, Nb and Mn as constituent elements. 4. The piezoelectric element according to any one of claims 1 to 3, wherein the compound having a perovskite structure is represented by the following general formula (1).

xPb(Zr1 _{-aTia )} O3 _- yPb(Zn1 _/ 3Nb2 _/3 ) _O3
-zPb(Mn1 _{/3Nb2 /3} ) _O3 (1)

provided that a, x, y and z in the formula are respectively 0.45≤a≤0.60, 0<x≤0.85, 0≤y<0.99, 0.01<z<0.10 and x+y+z=1.0. An ultrasonic transducer comprising: the piezoelectric element according to any one of claims 1 to 4; and a pair of block bodies uniaxially sandwiching the piezoelectric element. An ultrasonic motor comprising the piezoelectric element according to any one of claims 1 to 4, and a sliding member adhered to the piezoelectric element.

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