Piezoelectric element

Abstract

This piezoelectric element 10 comprises: a piezoelectric electromagnetic device 1 containing, as the main component, a composite oxide having a perovskite-type crystal structure; a first electrode 2a provided on a first surface 1a of the piezoelectric electromagnetic device 1; and a second electrode 2b provided on a second surface 1b facing the first surface 1a. The piezoelectric electromagnetic device 1 mainly has a rhombohedral crystal structure. A crystal axis of the piezoelectric electromagnetic device 1 is [100] oriented, and the direction of the [100] orientation is perpendicular to the direction in which the first electrode 2a and the second electrode 2b face each other.

Description

[Technical field]

[0001] The present invention relates to a piezoelectric element. [Background technology]

[0002] 2. Description of the Related Art Piezoelectric elements capable of converting electrical energy into mechanical energy and converting mechanical energy into electrical energy are known.

[0003] Patent Document 1 describes a piezoelectric element that includes PZT and electrodes, the PZT having a perovskite structure with a composition ratio in which Zr and Ti contained therein are rhombohedral at room temperature, and the crystal orientation of the PZT is such that the

[0100] direction, the

[0010] direction, or the

[0001] direction is approximately perpendicular to the electrode surface, and a piezoelectric element in which the PZT has a perovskite structure with a composition ratio in which Zr and Ti contained therein are tetragonal at room temperature, and the crystal orientation of the PZT is such that the

[0001] direction is approximately perpendicular to the electrode surface. Patent Document 1 describes that this piezoelectric element has a large piezoelectric constant in the electric field direction, and can improve characteristics, compared to conventional piezoelectric elements in which the

[0111] direction is perpendicular to the electrode surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-233844 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in order to further improve the characteristics of piezoelectric elements, there is a demand for the development of piezoelectric elements having a larger piezoelectric constant.

[0006] The present invention is devised to solve the above problems, and has an object to provide a piezoelectric element having a large piezoelectric constant. [Means for solving the problem]

[0007] The piezoelectric element of the present invention is a piezoelectric ceramic containing as a main component a composite oxide having a perovskite crystal structure; a first electrode provided on a first surface of the piezoelectric ceramic, and a second electrode provided on a second surface opposite to the first surface; Equipped with The piezoelectric ceramic has a predominantly rhombohedral crystal structure, The crystal axis of the piezoelectric ceramic is oriented in {100}; The direction of the {100} orientation is characterized by being perpendicular to the direction in which the first electrode and the second electrode face each other.

[0008] In another aspect of the present invention, a piezoelectric element includes: a piezoelectric ceramic containing as a main component a composite oxide having a perovskite crystal structure; a first electrode provided on a first surface of the piezoelectric ceramic, and a second electrode provided on a second surface opposite to the first surface; Equipped with The crystal axis of the piezoelectric ceramic is oriented in {100}; the direction of the {100} orientation is perpendicular to the direction in which the first electrode and the second electrode face each other, The piezoelectric ceramic is characterized in that the half-width of a composite peak consisting of diffractions from the (002) and (200) planes in an X-ray diffraction pattern viewed from the {100} oriented plane is 0.5° or more. Effect of the Invention

[0009] The piezoelectric element of the present invention has a higher piezoelectric constant and can provide superior piezoelectric characteristics compared to a non-oriented piezoelectric element and a piezoelectric element in which the crystal axes are oriented in the direction in which a pair of electrodes face each other. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a piezoelectric element of the present invention. [Diagram 2]FIG. 1(a) shows X-ray diffraction patterns from the {100} oriented plane of six types of piezoelectric ceramics with different compositions, and FIG. 1(b) shows an enlarged view of the diffraction peaks at an X-ray diffraction angle of about 45°. [Diagram 3] FIG. 2 is a diagram showing the relationship between the polarization axis and the orientation direction of the crystal axis of a plate-shaped ceramic that is a piezoelectric ceramic. [Figure 4] 3 is a diagram showing a schematic diagram of the relationship between the electric field direction, the orientation direction of the plate-shaped ceramic, the polarization direction, and the vibration direction of the piezoelectric element. FIG. [Diagram 5] FIG. 13 is a diagram showing the relationship between the angle of the orientation direction and the piezoelectric constant. [Figure 6] FIG. 13 is a diagram showing the relationship between the angle of the orientation direction and the coupling coefficient. [Figure 7] 1 is a diagram for explaining vibration modes of 31 mode, 32 mode, and t mode. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The features of the present invention will be described in detail below with reference to embodiments of the present invention.

[0012] The piezoelectric element of the present invention comprises a piezoelectric ceramic containing as its main component a complex oxide having a perovskite crystal structure, a first electrode provided on a first surface of the piezoelectric ceramic, and a second electrode provided on a second surface opposite the first surface, wherein the piezoelectric ceramic has a mainly rhombohedral crystal structure, and the crystal axes of the piezoelectric ceramic are {100} oriented, and the direction of the {100} orientation is perpendicular to the direction in which the first electrode and the second electrode face each other.

[0013] The piezoelectric element of the present invention can also be expressed as comprising a piezoelectric ceramic containing as a main component a complex oxide having a perovskite crystal structure, a first electrode provided on a first surface of the piezoelectric ceramic, and a second electrode provided on a second surface opposite the first surface, the crystal axis of the piezoelectric ceramic is {100} oriented, the direction of the {100} orientation is perpendicular to the direction in which the first electrode and the second electrode face each other, and the half-width of a complex peak formed by diffraction of the (002) plane and the (200) plane in an X-ray diffraction pattern viewed from the {100} oriented surface of the piezoelectric ceramic is 0.5° or more.

[0014] 1 is a cross-sectional view showing a schematic configuration of a piezoelectric element 10 of the present invention. The piezoelectric element 10 of the present invention includes a piezoelectric ceramic 1, a first electrode 2a provided on a first surface 1a of the piezoelectric ceramic 1, and a second electrode 2b provided on a second surface 1b opposite to the first surface 1a.

[0015] The piezoelectric ceramic 1 contains a complex oxide having a perovskite crystal structure as a main component. The main component means a component that accounts for 50% or more of the contained components by weight. Examples of the complex oxide having a perovskite crystal structure include PZT (lead zirconate titanate), PNN-PZT (lead nickelate niobate (PNN)-lead titanate (PT)-lead zirconate (PZ)), PMN-PZT (lead magnesium niobate (PMN)-lead titanate (PT)-lead zirconate (PZ)), etc.

[0016] The crystal axis of the piezoelectric ceramic 1 is oriented in the {100} direction, i.e., in the

[0100] direction, the

[0010] direction, or the

[0001] direction. The {100} orientation is a direction perpendicular to the direction in which the first electrode 2a and the second electrode 2b face each other (the direction of the arrow Y1 in FIG. 1), i.e., a direction parallel to the first face 1a and the second face 1b of the piezoelectric ceramic 1. However, in the present invention, the "direction perpendicular to the direction in which the first electrode 2a and the second electrode 2b face each other" includes a direction within a range of ±10° based on the perpendicular direction. Here, the crystal axis of the piezoelectric ceramic 1 is considered to be oriented in the {100} direction when the degree of orientation of the combined

[0100] axis,

[0010] axis, or

[0001] axis is 0.30 or more according to the Lotgering Method. The piezoelectric ceramic 1 may have a laminated structure in which a plurality of layers are laminated.

[0017] The direction of the {100} orientation can be determined as follows: the main surface, side surface, end surface, or cross section of the element is measured by an XRD analyzer using the θ-2θ method, and the plane showing the highest value by the Lotgering method is the orientation direction.

[0018] Piezoelectric ceramic 1 has a crystal structure that is mainly rhombohedral (R phase), and in an X-ray diffraction pattern obtained by X-ray diffraction as viewed from the {100} oriented plane, the half-width of a composite peak consisting of diffractions from the (002) and (200) planes is 0.5° or more. Note that "piezoelectric ceramic 1 has a crystal structure that is mainly rhombohedral" means that at least 50% or more of the crystal structure of piezoelectric ceramic 1 is rhombohedral.

[0019] FIG. 2(a) shows the X-ray diffraction patterns of six types of piezoelectric ceramics with different compositions as viewed from the {100} oriented plane, and FIG. 2(b) shows an enlarged view of the diffraction peaks at an X-ray diffraction angle of about 45°. The diffraction peaks at an X-ray diffraction angle of about 45° shown in FIG. 2(b) show a composite peak consisting of diffractions from the (002) and (200) planes. In addition, in FIGS. 2(a) and (b), the six types of piezoelectric ceramic samples are referred to as samples S1 to S6 from the top. Samples S1 to S6 are unpolarized samples. In addition, in the case of a polarized element, it is preferable to measure the X-ray diffraction pattern after heating to above the Curie point and depolarizing it.

[0020] As shown in Figures 2(a) and (b), the diffraction pattern of sample S1 contains two peaks, one for the (002) plane and one for the (200) plane. On the other hand, the diffraction pattern of sample S6 contains a composite peak in which the diffraction peaks of the (002) plane and the (200) plane overlap. Note that while piezoelectric ceramic 1 has an MPB composition, the MPB composition is in the transition region between the R phase and the T phase, and microscopically there exists a region in which the lengths of the a-axis and c-axis of the crystal are different, so that a diffraction peak of the (002) plane and a diffraction peak of the (200) plane are observed.

[0021] The half-width of the composite peak formed by the diffraction of the (002) and (200) planes of sample S6 is 0.5° or more. The half-width of the composite peak formed by the diffraction of the (002) and (200) planes of samples S3 to S5 is also 0.5° or more. The height of the diffraction peak of the (200) plane of sample S2 is higher than half the height of the diffraction peak of the (002) plane, and the half-width of the composite peak formed by the diffraction of the (002) and (200) planes is 0.5° or more.

[0022] On the other hand, the height of the diffraction peak of the (200) plane of sample S1 is lower than half the height of the diffraction peak of the (002) plane. Therefore, the half-width of the composite peak consisting of the diffraction of the (002) plane and the (200) plane of sample S1 is less than 0.5°. Therefore, the piezoelectric ceramic of sample S1 cannot be the piezoelectric ceramic 1 of the piezoelectric element 10 of the present invention.

[0023] The piezoelectric element 10 of the present invention has high piezoelectric properties due to the above-mentioned structure, and can be used in various piezoelectric devices such as piezoelectric vibrators, piezoelectric filters, and piezoelectric actuators.

[0024] (Example) Powders of Pb3O4, TiO2, ZrO2, NiO, and Nb2O5 were prepared and weighed to obtain the desired composition, then mixed in a pot mill with water for 16 hours. The mixture was then dried and calcined at 900°C. The calcined powder was mixed with an aqueous binder solution, and the mixture was then milled and mixed in a pot mill for 16 hours to obtain a slurry.

[0025] The obtained slurry was applied to a sheet by doctor blade method, and a magnetic field of 10 T was applied in a direction parallel to the sheet until it dried, to produce a ceramic green sheet. The produced ceramic green sheet was cut to a specified size, and then stacked while aligning the orientation, and pressed at a pressure of 100 MPa to obtain a green body.

[0026] The obtained green body was degreased by heating in air at 350°C for 5 hours, and then fired in air at 1050°C for 2 hours to obtain a plate-shaped ceramic that is a piezoelectric ceramic.

[0027] Next, electrodes made of Ag were formed by sputtering on both main surfaces of the plate-shaped ceramic, i.e., the front and back surfaces, and then polarization treatment was performed under conditions of 80°C, 2 kV / mm, and 30 minutes. Finally, the plate was cut with a dicer so that the orientation direction was the longitudinal direction, and a rectangular parallelepiped piezoelectric element with a longitudinal direction of 13 mm, a lateral direction of 3 mm, and a thickness of 0.6 mm was obtained.

[0028] The obtained plate-shaped ceramic of the piezoelectric element contains a composite oxide having a perovskite crystal structure, specifically, PNN-PZT, as a main component.

[0029] In this piezoelectric element, the crystal axis of the plate-shaped ceramic, which is a piezoelectric ceramic, is oriented in {100}, and the orientation direction is perpendicular to the direction in which the pair of electrodes face each other, more specifically, the longitudinal direction of the piezoelectric element. The plate-shaped ceramic mainly has a rhombohedral crystal structure, and the half-width of the composite peak consisting of the diffraction of the (002) plane and the (200) plane in the X-ray diffraction pattern seen from the {100} oriented plane is 0.5° or more. The X-ray diffraction apparatus used was MiniFlex2 manufactured by Rigaku Corporation, and the measurements were performed using a Cu tube at a scan speed of 4° / min, a step of 0.02°, and a slit width of 1.25°, using the θ-2θ method. The measured data was analyzed using Jade 5.0 software to remove the Kα2 peak.

[0030] The relationship between the polarization axis of the plate-shaped ceramic and the orientation direction of the crystal axis is shown in Figure 3. In Figure 3, the direction of the polarization axis, which is the direction of spontaneous polarization, is the

[0111] direction, and the direction of the polarization treatment is the same as the direction of the applied electric field.

[0031] In addition, a plurality of piezoelectric elements with different orientation angles were fabricated by changing the direction of application of a magnetic field, and the piezoelectric constants of the fabricated piezoelectric elements were determined. FIG. 4 is a diagram showing the relationship between the electric field direction, the orientation direction of the plate-shaped ceramic, the polarization direction (direction of spontaneous polarization), and the vibration direction of the piezoelectric element when ideally 100% oriented. FIG. 4 shows the relationship between the directions when the orientation directions are 0°, 15°, 55°, 75°, and 90°. The angle of the orientation direction is the angle with respect to the electric field direction, i.e., the direction in which a pair of electrodes face each other. The orientation angle of the piezoelectric element of the present invention is 90°, and the orientation angle of the piezoelectric element described in Patent Document 1 is 0°.

[0032] Figure 4 also shows the polarization direction when viewed in the electric field direction when the orientation angle is 0°, 55°, and 90°. As shown in Figure 4, when the orientation angle is 0°, the polarization direction is distributed in the range indicated by the cone, and is uniformly distributed within the plane when viewed from above, but when it is 90°, the cone indicating the range in which the polarization direction can be distributed faces sideways, causing a deviation within the plane when viewed from above and causing it to be concentrated in a certain direction.

[0033] Fig. 5 is a diagram showing the relationship between the angle of the orientation direction and the piezoelectric constant. Fig. 6 is a diagram showing the relationship between the angle of the orientation direction and the coupling coefficient. The coupling coefficient is one of the parameters that indicates the magnitude of the piezoelectric effect, and the larger the value, the stronger the piezoelectric effect. In Figs. 5 and 6, the data shown by the dotted lines indicates the values ​​in the case of no orientation.

[0034] The notations of 31 mode, 32 mode, and t mode in Figures 5 and 6 respectively indicate vibration modes in different directions in the same sample, as shown in Figure 7. As shown in Figure 7, the 31 mode is a vibration mode in the longitudinal direction of the first surface on which the first electrode 2a is formed and the second surface on which the second electrode 2b is formed. Note that the orientation direction with an angle of 90° is adjusted to coincide with the longitudinal directions of the first surface and the second surface.

[0035] As shown in Fig. 5, the piezoelectric constant in the 31 mode was the largest when the angle of the orientation direction was 90°. In other words, the piezoelectric element 10 of the present invention, in which the crystal axis of the piezoelectric ceramic having a mainly rhombohedral crystal structure is oriented in {100} and the {100} orientation direction is perpendicular to the direction in which the first electrode 2a and the second electrode 2b face each other, has a higher piezoelectric constant and higher piezoelectric characteristics than a non-oriented piezoelectric element or a piezoelectric element oriented in the direction in which a pair of electrodes face each other, such as the piezoelectric element described in Patent Document 1. This is considered to be due to the polarization direction of the piezoelectric ceramic 1 being concentrated in the vibration direction.

[0036] Furthermore, even among the directions perpendicular to the opposing direction of the first electrode 2a and the second electrode 2b, a higher vibration effect can be obtained when the direction of the {100} orientation is the longitudinal direction of the first surface 1a and the second surface 1b of the piezoelectric ceramic 1. Therefore, it is preferable that the direction of the {100} orientation is the longitudinal direction of the first surface 1a and the second surface 1b of the piezoelectric ceramic 1.

[0037] It should be noted that the piezoelectric element described in Patent Document 1 controls the crystal orientation by utilizing crystal growth from the substrate, and therefore the crystal orientation can only be in the direction in which the pair of electrodes face each other.

[0038] However, the piezoelectric element 10 of the present invention does not use crystal growth from a substrate, so the orientation direction can be freely controlled. Also, unlike single crystals, it is relatively easy to put into industrial use in terms of composition control and ease of processing. Also, as in the above-mentioned embodiment, it is possible to obtain a piezoelectric element with a laminated structure by laminating ceramic green sheets.

[0039] The present invention is not limited to the above-described embodiment, and various applications and modifications are possible within the scope of the present invention. [Explanation of symbols]

[0040] 1 Piezoelectric ceramics 1a First Side 1b Second Side 2a First electrode 2b Second electrode 10 Piezoelectric element

Claims

1. a piezoelectric ceramic containing as a main component a composite oxide having a perovskite crystal structure; a first electrode provided on a first surface of the piezoelectric ceramic, and a second electrode provided on a second surface opposite to the first surface; Equipped with The piezoelectric ceramic has a predominantly rhombohedral crystal structure, The crystal axis of the piezoelectric ceramic is oriented in {100} direction. the direction of the {100} orientation is a direction perpendicular to the direction in which the first electrode and the second electrode face each other, A piezoelectric element, wherein the crystal axis of said piezoelectric ceramic is not oriented in a direction in which said first electrode and said second electrode face each other.

2. a piezoelectric ceramic containing as a main component a composite oxide having a perovskite crystal structure; a first electrode provided on a first surface of the piezoelectric ceramic, and a second electrode provided on a second surface opposite to the first surface; Equipped with The crystal axis of the piezoelectric ceramic is oriented in {100} direction. the direction of the {100} orientation is a direction perpendicular to the direction in which the first electrode and the second electrode face each other, A piezoelectric element, characterized in that the half-width of a composite peak consisting of diffractions from the (002) and (200) planes in an X-ray diffraction pattern viewed from a {100} oriented plane of said piezoelectric ceramic is 0.5° or more.

3. 3. The piezoelectric element according to claim 1, wherein the direction of the {100} orientation is a longitudinal direction of the first surface and the second surface.

4. 4. The piezoelectric element according to claim 1, wherein the composite oxide is PZT.

5. 4. The piezoelectric element according to claim 1, wherein the composite oxide is PNN-PZT.

6. 4. The piezoelectric element according to claim 1, wherein the composite oxide is PMN-PZT.

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