Piezoelectric element

Abstract

A piezoelectric element 1 of the present disclosure is obtained by laminating piezoelectric bodies 2 which are piezoelectric and electrodes in an alternating manner, wherein: at least one of the piezoelectric bodies 2 has a slit 6 on its own side surface; the outer edge of a cross section obtained by cutting, in a direction orthogonal to the lamination direction, a part of the piezoelectric element 1 having the slit 6 has a plurality of sides 20 and a plurality of stress relaxation units 30 which connect an adjacent pair of sides 20; and the stress relaxation units 30 are formed such that, when a point where respective extensions of the adjacent pair of sides 20 intersect is an imaginary vertex 22, the slit 6 is located further toward the center of the piezoelectric bodies 2 than the imaginary vertex 22.

Description

Piezoelectric element

[0001] The present disclosure relates to piezoelectric elements.

[0002] Traditionally, PZT (lead zirconate titanate) has been widely used as a ceramic that exhibits piezoelectricity. Piezoelectric materials made of PZT expand and contract in response to an applied voltage, and multi-layer piezoelectric actuator elements have been developed and put into practical use, with a structure in which piezoelectric materials and internal electrodes are alternately stacked in multiple layers. In multi-layer piezoelectric actuator elements, the portion of the piezoelectric material sandwiched between the internal electrodes becomes a polarized region, while the portion not sandwiched between the internal electrodes becomes a non-polarized region. As a result, the displacement distribution changes significantly at the boundary between the polarized and non-polarized regions, and stress concentrates in this area. This stress concentration increases the possibility of cracks occurring during long-term operation, reducing durability.

[0003] In order to relieve such stress, a multilayer piezoelectric actuator element is known in which slits are formed on the side surfaces of the laminate in a direction perpendicular to the lamination direction (parallel to the lamination plane). For example, the multilayer piezoelectric actuator element described in JP 2009-131138 A (Patent Document 1 listed below) is a columnar laminate formed by alternately laminating a plurality of piezoelectric layers and internal electrodes, and includes a laminate having a plurality of slits formed on opposing side surfaces of the laminate at arbitrary intervals extending into the piezoelectric layers and along the lamination direction of the laminate, and side electrodes formed on each opposing side surface of the laminate in a form separated by the slits and electrically connected to the internal electrodes.

[0004] JP 2009-131138 A

[0005] However, because PZT contains lead, its environmental impact has been a concern, and in recent years, development of lead-free piezoelectric ceramic materials has been progressing as an example of lead-free ceramic materials. However, because lead-free piezoelectric ceramic materials are less likely to deform and have greater rigidity than PZT, simply providing slits may not be sufficient to alleviate stress. In other words, there is a possibility that the stress in the portion of the piezoelectric element with the slits may not be fully alleviated.

[0006] The piezoelectric element of the present disclosure is a piezoelectric element in which piezoelectric bodies and electrodes are alternately stacked in multiple layers, at least one of the piezoelectric bodies has a slit on its side, and the outer edge of a cross section of the portion of the piezoelectric element having the slit cut in a direction perpendicular to the stacking direction has multiple sides and multiple stress relief portions that respectively connect adjacent pairs of the sides, and the stress relief portions are formed so that, when the point where the extensions of each of the adjacent pairs of sides intersect is defined as a virtual vertex, the slit is located closer to the center of the piezoelectric body than the virtual vertex.

[0007] According to the present disclosure, it is possible to relieve stress in the portion of the piezoelectric element having the slit.

[0008] FIG. 1 is a cross-sectional view schematically showing the configuration of a piezoelectric element according to an embodiment. FIG. 2 is a perspective view showing a portion of a laminate exploded in the stacking direction. FIG. 3 is a cross-sectional view showing an enlarged view of the periphery of a slit. FIG. 4 is a view showing a cross section of a portion of a piezoelectric element having a slit, cut in a direction perpendicular to the stacking direction. FIG. 5 is a cross-sectional view showing, by simulation, how stress is applied to a cross section passing through a slit. FIG. 6 is a graph showing the maximum stress applied to a vertex versus R / (L1 / 2). FIG. 7 is a graph showing the difference in stress applied to a vertex and an edge versus L1 / L2. FIG. 8 is a diagram showing a process flow for a piezoelectric element. FIG. 9 is a cross-sectional photograph of a slit.

[0009] [Summary of the Embodiments] First, embodiments of the present disclosure will be described. (1) A piezoelectric element of the present disclosure is a piezoelectric element in which piezoelectric bodies and electrodes are alternately stacked in multiple layers, at least one of the piezoelectric bodies having a slit on its side surface, and the outer edge of a cross section of the piezoelectric element cut in a direction perpendicular to the stacking direction at a portion having the slit has multiple sides and multiple stress relief portions connecting each pair of adjacent sides, and the stress relief portions are formed so that, when a virtual vertex is defined as a point where extensions of each pair of adjacent sides intersect, the slit is located closer to the center of the piezoelectric body than the virtual vertex. The piezoelectric body may be formed, for example, from a lead-free piezoelectric ceramic composition.

[0010] The portion of the piezoelectric body sandwiched between one electrode and the adjacent electrode is a polarized region, while the portion not sandwiched between the two electrodes is a non-polarized region. It is known that the displacement distribution changes significantly at the boundary between the polarized and non-polarized regions, and stress concentrates in this area. In particular, piezoelectric bodies formed from lead-free piezoelectric ceramic compositions are less likely to deform and have greater rigidity than PZT, so it is thought that simply forming slits cannot fully relieve stress. Therefore, with the above configuration, multiple stress relief sections are formed after forming slits, making it possible to relieve stress.

[0011] (2) The stress relaxation portion is preferably formed of a tapered C-surface, which makes it easier to distribute stress across the entire C-surface.

[0012] (3) The stress relaxation portion is preferably configured with a curved R-surface, which makes it easier to distribute stress across the entire R-surface.

[0013] (4) When the side connecting the adjacent virtual vertices is defined as a virtual side, the length of the virtual side is defined as L1, and the length of the region of the virtual side where the stress relaxation portion is formed is defined as R, it is preferable that R / (L1 / 2) is 15% or more and 100% or less. With the above configuration, it is possible to reduce the maximum stress acting on the stress relaxation portion.

[0014] (5) The piezoelectric element of the present disclosure is a piezoelectric element in which piezoelectric bodies and electrodes are alternately stacked in multiple layers, at least one of the piezoelectric bodies has a slit on its side surface, and the outer edge of a cross section of the portion of the piezoelectric element having the slit, cut in a direction perpendicular to the stacking direction, has a circular or elliptical shape. The piezoelectric body may be formed of, for example, a lead-free piezoelectric ceramic composition.

[0015] (6) It is preferable that a plurality of the slits are formed at arbitrary intervals in the stacking direction and every 35 layers or less.

[0016] [Details of the embodiment] Specific examples of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0017] 1 to 9, an embodiment of the present disclosure will be described. As shown in Fig. 1, a piezoelectric element 1 includes a laminate 5 formed by alternately laminating a piezoelectric body 2 formed of a lead-free piezoelectric ceramic composition and conductive internal electrodes 3, 4. Note that in Fig. 1, the number of layers in the laminate 5 is shown as a small number, but an actual piezoelectric element 1 will have a large number of layers, as shown in Fig. 3, for example.

[0018] [Piezoelectric body 2] Piezoelectric body 2 is a lead-free piezoelectric ceramic composition having a main phase formed of a first crystalline phase consisting of an alkali niobate-based perovskite oxide and a subphase including a second crystalline phase consisting of an M-Ti-O-based spinel compound.

[0019] In this specification, the term "spinel compound" includes both normal spinel compounds having a normal spinel crystal structure and inverse spinel compounds having an inverse spinel crystal structure. The element M in the M-Ti-O spinel compound is a monovalent to tetravalent metal element.

[0020] The ratio of the second crystalline phase in the lead-free piezoelectric ceramic composition is more than 0% by volume and not more than 10% by volume, with the remainder being the first crystalline phase. In this specification, the first crystalline phase is also referred to as the "main phase," and crystalline phases other than the main phase are referred to as "subphases."

[0021] The alkali niobate perovskite oxide of the first crystal phase is represented by the following composition formula (1).

[0022] (KaNabLicCd)e(DfEg)Oh (1) where the element C is at least one of Ca (calcium) and Ba (barium), the element D is at least one of Nb (niobium), Ti (titanium), and Zr (zirconium) containing at least Nb, and the element E is at least one of Fe (iron), Co (cobalt), Zn (zinc), and Mg (magnesium).

[0023] In the composition formula (1), K (potassium), Na (sodium), Li (lithium), and element C are arranged in the so-called A site of the perovskite structure, and elements D and E are arranged in the so-called B site of the perovskite structure.

[0024] The values ​​of the coefficients a, b, c, d, e, f, g, and h in the above composition formula (1) are selected from values ​​that establish a perovskite structure, and are preferred from the viewpoint of the electrical properties or piezoelectric properties (particularly the piezoelectric constant d33) of the lead-free piezoelectric ceramic composition, and are also preferred from the viewpoint of keeping the sintering temperature during production low.

[0025] Specifically, the sum of the coefficients a, b, c, and d of the A-site elements is 1 (that is, a+b+c+d=1).

[0026] The coefficients a, b, and c preferably satisfy the following relationships: 0≦a<1, 0≦b<1, and 0≦c<1, respectively. However, it is preferable that a=b=c=0 (i.e., a lead-free piezoelectric ceramic composition containing none of K, Na, or Li) does not hold. The coefficients a and b of K and Na typically satisfy the relationships: 0<a≦0.6, 0<b≦0.6. The coefficient c of Li may be 0 (zero), but is preferably 0<c≦0.2, and more preferably 0<c≦0.1.

[0027] The coefficient d of the element C may be 0 (zero), but is preferably 0<d≦0.2, and more preferably 0<d≦0.1.

[0028] The coefficient e for the entire A site may be any value as long as it does not impair the objective of the present disclosure. Note that the coefficient e is preferably 0.80≦e≦1.10, more preferably 0.84≦e≦1.08, and even more preferably 0.88≦e≦1.07.

[0029] The sum of the coefficients f and g of the elements D and E in the B site is 1 (i.e., f+g=1). Note that, unless the object of the present disclosure is impaired, it is preferable that the coefficient f of the element D is not 0 (zero), and the coefficient g of the element E may be 0 (zero).

[0030] The coefficient h of oxygen (O) is an arbitrary value that allows the first crystal phase to maintain a perovskite crystal structure. A typical value of the coefficient h is about 3, and 3.0≦h≦3.1 is preferable. The value of the coefficient h can be calculated from the electrical neutrality condition of the composition of the first crystal phase. However, a composition that slightly deviates from the electrical neutrality condition is also acceptable for the composition of the first crystal phase.

[0031] The alkali niobate perovskite oxide represented by the above composition formula (1) is an oxide containing K, Na, and Nb as main metal components, and is therefore called "KNN" or "KNN material." Such alkali niobate perovskite oxides have excellent piezoelectric properties, electrical properties, etc.

[0032] The M-Ti-O spinel compound of the second crystal phase is an oxide containing element M (a monovalent to tetravalent metal element) and Ti (titanium), and is represented, for example, by the following composition formula (2).

[0033] MxTiOy (2) where element M is a monovalent to tetravalent metal element. Specifically, element M is at least one element selected from the group consisting of Li, Fe, Co, Zn, Zr, and Mg.

[0034] The coefficients x and y are relative values ​​when the Ti content is set to 1. In order for the second crystal phase to form a spinel compound, the coefficient x preferably satisfies 0.5≦x≦5.0. The coefficient y may be any value that forms a spinel compound, but preferably satisfies, for example, 2≦y≦8.

[0035] The second crystal phase composed of a spinel compound stabilizes the structure of the first crystal phase, so that a lead-free piezoelectric ceramic composition having excellent piezoelectric properties can be obtained. ２ TiO ４ , or (M1, M2) TiO ４It is preferable to employ the second crystal phase represented by the following formula:

[0036] The second crystalline phase does not have piezoelectric properties, but its presence with the first crystalline phase improves the sinterability of the lead-free piezoelectric ceramic composition, improving its structural stability and piezoelectric properties. Specifically, the second crystalline phase fills voids formed between the crystals of the first crystalline phase. As a result, the crystals of the first crystalline phase are bonded together by the second crystalline phase, which is presumably why the structural stability and piezoelectric properties of the lead-free piezoelectric ceramic composition are improved.

[0037] [Internal electrodes 3, 4] As shown in Fig. 2, the internal electrodes 3, 4 are arranged alternately in the stacking direction, and one piezoelectric body 2 is sandwiched between the internal electrodes 3 and 4. The internal electrodes 3 are electrodes of the same polarity (e.g., positive poles), and the internal electrodes 4 are electrodes of the same polarity (e.g., negative poles) on the other hand. The internal electrodes 3, 4 of opposite polarities are arranged spaced apart in the stacking direction to prevent electrical short-circuiting.

[0038] One side edge (the left side edge in FIG. 1 ) of the internal electrode 3 is formed so as to be exposed on one side surface (the left side edge in FIG. 1 ) of the laminate 5. The other side edge (the right side edge in FIG. 1 ) of the internal electrode 3 is formed so as not to be exposed on the other side surface (the right side edge in FIG. 1 ) of the laminate 5.

[0039] One side edge (the right side edge in FIG. 1 ) of the internal electrode 4 is formed so as to be exposed on the other side surface (the right side edge in FIG. 1 ) of the laminate 5. The other side edge (the left side edge in FIG. 1 ) of the internal electrode 4 is formed so as not to be exposed on one side surface (the left side edge in FIG. 1 ) of the laminate 5.

[0040] By configuring the internal electrodes 3 and 4 in this manner, the internal electrodes 3 and 4 of different polarities are prevented from being electrically short-circuited to each other.

[0041] [Slits 6] Slits 6 are formed along the entire periphery of the outer side surface of the laminate 5, perpendicular to the stacking direction (parallel to the stacking surface) and extending from the outer side surface to a predetermined depth. As shown in FIG. 1, the depth of the slits 6 from the outer side surface of the laminate 5 is set to be deeper than the ends of the internal electrodes 3 and 4. FIG. 9 shows an actual cross-sectional photograph of the slits 6. A plurality of slits 6 are formed at arbitrary intervals in the stacking direction, and every 35 layers or less. These slits 6 are formed for the purpose of alleviating stress applied when the piezoelectric element 1 is driven.

[0042] [Side electrodes 7, 8] Side electrodes 7, 8 are formed on both side surfaces of the laminate 5. These side electrodes 7, 8 are formed, for example, by patterning a conductive paste using screen printing or the like, and are separated into blocks divided by slits 6 in the lamination direction.

[0043] [External electrodes 11, 12] Solder layers 9, 10 are formed on the surfaces of the side electrodes 7, 8. A pair of external electrodes 11, 12 is fixed to the side electrodes 7, 8 via these solder layers 9, 10. This ensures that the side electrodes 7, 8 of each block divided in the stacking direction by the slits 6 are electrically connected to each other. The external electrodes 11, 12 are made of a conductive material (e.g., copper). The external electrodes 11, 12 are formed, for example, in a mesh shape and are deformable in response to the expansion and contraction of the laminate 5.

[0044] [Lead electrodes 13, 14] Of the side electrodes 7, 8, those of the bottom block in Fig. 1 have lead electrodes 13, 14, which serve as voltage supply members for supplying voltage from the outside, fixed to them via solder layers 9, 10. Because the lead electrodes 13, 14 are fixed to the side electrodes 7, 8, the inertial weight of the lead electrodes 13, 14 will not cause breakage of the external electrodes 11, 12 even if the laminate 5 is vibrated at high speed for a long period of time.

[0045] The laminate 5 is constructed by alternately laminating multiple layers of piezoelectric bodies 2 and internal electrodes 3, 4, and is composed of polarized regions 50 that are displaced by applying a voltage to the internal electrodes 3, 4, and non-polarized regions 51 that are not displaced. The non-polarized regions 51 are arranged above, below, and on the outer periphery of the polarized regions 50.

[0046] 1, the lower side of the laminate 5 is the fixed end that is fixed and does not move, and the upper side is the movable end that moves. Lead electrodes 13 and 14 are fixed to side electrodes 7 and 8 of the block located at the end of the fixed end. In other words, lead electrodes 13 and 14 are fixed to side electrodes 7 and 8 on the fixed end side of slit 6, which is closest to the fixed end.

[0047] [Stress relaxation portion 30] Fig. 4 is a cross section of a portion of the laminate 5 having the slit 6, cut in a direction perpendicular to the stacking direction. The hatched portion in the center of Fig. 4 is the piezoelectric body 2 connecting the piezoelectric body 2 above the slit 6 and the piezoelectric body 2 below the slit 6, and will be referred to as a connecting portion 15 hereinafter.

[0048] The outer edge of the cross section of the connecting portion 15 has four sides 20 and four stress relief portions 30 that respectively connect pairs of adjacent sides 20. When the point where extensions 21 of pairs of adjacent sides 20 intersect is defined as a virtual vertex 22, the stress relief portions 30 are formed so that the slits 6 are located closer to the center of the piezoelectric body 2 than the virtual vertex 22. The cross section of the connecting portion 15 in this embodiment is generally square, but may also be generally triangular or generally polygonal with five or more sides.

[0049] Although the stress relief portion 30 in the embodiment is configured with a curved R-surface, it may be configured with a tapered C-surface. Also, although the outer edge of the connecting portion 15 in the embodiment is configured with a straight side 20 and a circular (quadrant) stress relief portion 30, an elliptical stress relief portion may be used instead of the circular stress relief portion 30.

[0050] [Example] The process flow for the piezoelectric element 1 is shown in Figure 8. First, multiple types of raw material powders necessary for forming the main phase were prepared, and these raw material powders were weighed out according to the values ​​of the coefficients a, b, c, d, e, f, and g in the composition formula of the main phase so as to obtain the desired composition. After weighing, each raw material powder was pulverized and mixed for 4 hours or more using a dry vibration mill to obtain a mixed powder. The obtained mixed powder was calcined, for example, in an air atmosphere at a temperature condition of 600 to 1200°C for 1 to 10 hours to obtain a powdered calcined product of the main phase.

[0051] Additionally, multiple types of raw material powders necessary for forming the subphase were prepared, and these raw material powders were weighed out according to the value of the coefficient x in the composition formula of the subphase so as to obtain the target composition. After weighing, each raw material powder was pulverized and mixed for 4 hours or more using a dry vibration mill to obtain a mixed powder. The obtained mixed powder was calcined, for example, in an air atmosphere at a temperature condition of 600 to 1200°C for 1 to 10 hours to obtain a powdered calcined product of the subphase (powder production).

[0052] Next, a dispersant, a binder, and an organic solvent (e.g., toluene) were added to the obtained main phase calcined product and subphase calcined product, and the wet mixture was pulverized and mixed to obtain a slurry. Thereafter, casting was performed to process the slurry into a sheet shape, thereby producing a ceramic green sheet (hereinafter simply referred to as "green sheet") of a predetermined thickness (sheet molding).

[0053] Next, the green sheet was punched out into a rectangle of 150 mm length x 150 mm width, and an electrode layer to become an internal electrode was formed on one side of the green sheet by, for example, screen printing using a conductive paste for an internal electrode (Pt paste) (internal electrode printing).

[0054] Thereafter, a predetermined number of green sheets (non-driving layers) without electrode layers printed thereon and green sheets (driving layers) with electrode layers printed thereon were stacked in order, and the sheets were pressure-laminated under heat and pressure, and then cut into small pieces of elements. For example, the pressure-laminated layers were stacked at a temperature of 40 to 80°C and a pressure of 5 to 100 MPa.

[0055] The elements cut into small pieces were subjected to a binder removal treatment (degreasing) by, for example, holding them in an air atmosphere at a temperature of 500 to 800° C. for 2 to 100 hours.

[0056] The element after the binder removal treatment was fired, for example, in an air atmosphere at a temperature of 900 to 1400° C. for 1 to 100 hours (firing).

[0057] Next, the four corners of the fired element were diced to a predetermined dimension (for example, a rectangle of 6 mm length x 6 mm width) to expose the internal electrodes. The top and bottom surfaces of the element were polished to adjust the thickness and process it to a predetermined parallelism. A slit was formed in the rectangular parallelepiped element from a direction perpendicular to the stacking direction using a laser (manufactured by COHERENT, UV, GREEN, IR wavelength). The slit was formed so that the radius of curvature of the stress relaxation portion was 0 mm to 0.2 mm and the length of one side was 1 mm to 5.4 mm (element processing).

[0058] Thereafter, electrodes were printed on the side surfaces of the laminate, and the laminate was baked and polarized at temperatures of 600 to 800° C. Four of the obtained elements were assembled using an adhesive, and the side electrodes of each element were connected with lead wires using solder, and the elements were sealed in a metal tube (assembly).

[0059] The evaluation process will be described below. The simulation was performed using ANSYS Workbench 2021R2.

[0060] As shown in Fig. 4, the side connecting adjacent virtual vertices 22 is defined as a virtual side, the length of the virtual side is defined as L1, and the length of the region of the virtual side where the stress relief portion 30 is formed is defined as R. The upper part of Fig. 5 is a cross-sectional view showing, by simulation, the maximum stress applied to the vertex (stress relief portion) of the connecting portion 15 when R / (L1 / 2) is changed in the range from 0% to 100%. The areas where stress is applied are shown in dark colors.

[0061] 5, at 0% and 5%, the stress is applied only to the connecting portion 15, whereas at 15% to 100%, the stress is applied to both the connecting portion 15 and the piezoelectric bodies 2 adjacent above and below the connecting portion 15. In other words, at 15% to 100%, the stress is widely distributed between the connecting portion 15 and the piezoelectric bodies 2, so the stress applied to the connecting portion 15 is alleviated and the maximum stress becomes smaller.

[0062] 6, when R / (L1 / 2) is 0% and 5% (when there is almost no R in the stress relaxation portion 30), the maximum stress is 75 MPa or more, whereas when R / (L1 / 2) is 100% (when there is sufficient R in the stress relaxation portion 30), the maximum stress decreases to 69 MPa. The maximum stress relative to R / (L1 / 2) is preferably 15% to 100%, more preferably 25% to 100%, more preferably 38% to 100%, and most preferably 100%.

[0063] As shown in Fig. 4, the length of one side of the piezoelectric body 2 adjacent to the top and bottom of the connecting portion 15 (the length of one side of the internal electrodes 3 and 4) is defined as L2. The lower part of Fig. 5 is a cross-sectional view showing the stress difference acting on the vertex (stress relaxation portion) and the side of the connecting portion 15 by simulation when L1 / L2 is changed in the range from 22% to 100%. At 100%, stress is concentrated at the connecting portion 15, but at 22% to 74%, the stress is widely dispersed along the outer edge of the connecting portion 15, so the stress acting on the connecting portion 15 is relaxed and the stress difference is reduced.

[0064] 7, the stress difference is 11 MPa when L1 / L2 is 100%, whereas the stress difference is reduced to 2 MPa or less when L1 / L2 is 22% to 74%. The stress difference relative to L1 / L2 is preferably 22% to 74%, more preferably 37% to 74%, and most preferably 56%.

[0065] [Effects of the embodiment] The piezoelectric element 1 is a piezoelectric element 1 in which piezoelectric bodies 2 formed of a lead-free piezoelectric ceramic composition having piezoelectricity and internal electrodes 3, 4 are alternately stacked in multiple layers, at least one of the piezoelectric bodies 2 has a slit 6 on its side surface, and the outer edge of a cross section of the portion of the piezoelectric element 1 having the slit 6 cut in a direction perpendicular to the stacking direction has four sides 20 and four stress relaxation portions 30 connecting each pair of adjacent sides 20, and the stress relaxation portions 30 are formed so that, when the point where portions 21 extended from each pair of adjacent sides 20 intersect is defined as a virtual vertex 22, the slit 6 is located closer to the center of the piezoelectric body 2 than the virtual vertex 22.

[0066] The portion of the piezoelectric body 2 sandwiched between the internal electrode 3 and the adjacent internal electrode 4 becomes the polarized region 50, and the portion not sandwiched between the electrodes 3, 4 becomes the non-polarized region 51 on the outer periphery. It is known that the displacement distribution changes significantly at the boundary between the polarized region 50 and the non-polarized region 51 on the outer periphery, and stress concentrates in this portion. In particular, since the piezoelectric body 2 formed from a lead-free piezoelectric ceramic composition is less likely to deform and has greater rigidity than PZT, it is thought that simply forming the slits 6 cannot sufficiently relieve stress. Therefore, with the above configuration, the slits 6 are formed and then multiple stress relief portions 30 are formed, making it possible to relieve stress.

[0067] Since the stress relaxation portion 30 is configured with a curved R-surface, stress can be easily dispersed over the entire R-surface.

[0068] If the side connecting the adjacent virtual vertices 22 is defined as a virtual side, the length of the virtual side is defined as L1, and the length of the region of the virtual side where the stress relaxation portion 30 is formed is defined as R, then R / (L1 / 2) is 15% or more and 100% or less. In this way, the maximum stress acting on the stress relaxation portion 30 can be reduced.

[0069] 1: Piezoelectric element 2: Piezoelectric body 3: Internal electrode 4: Internal electrode 5: Laminate 6: Slit 7: Side electrode 8: Side electrode 9: Solder layer 10: Solder layer 11: External electrode 12: External electrode 13: Lead electrode 14: Lead electrode 15: Connecting portion 20: Side 21: Portion obtained by extending each of a pair of adjacent sides 22: Virtual vertex 30: Stress relaxation portion 50: Polarized region 51: Non-polarized region

Claims

1. A piezoelectric element in which piezoelectric bodies having piezoelectric properties and electrodes are alternately stacked in multiple layers, at least one of the piezoelectric bodies has a slit on its side, the outer edge of a cross section of the piezoelectric element cut in a direction perpendicular to the stacking direction at a portion having the slit has a plurality of sides and a plurality of stress relief portions connecting each pair of adjacent sides, and the stress relief portions are formed so that, when the point where the extensions of each pair of adjacent sides intersect is defined as a virtual vertex, the slit is located closer to the center of the piezoelectric body than the virtual vertex.

2. The piezoelectric element according to claim 1, wherein the piezoelectric body is formed from a lead-free piezoelectric ceramic composition.

3. The piezoelectric element according to claim 1, wherein the stress relaxation portion is constituted by a tapered C-face.

4. The piezoelectric element according to claim 1, wherein the stress relaxation portion is configured with a curved R surface.

5. A piezoelectric element according to any one of claims 1 to 4, wherein, assuming that a side connecting adjacent virtual vertices is a virtual side, that the length of said virtual side is L1, and that the length of a region of said virtual side in which said stress relief portion is formed is R, R / (L1 / 2) is 15% or more and 100% or less.

6. A piezoelectric element in which piezoelectric bodies and electrodes are alternately stacked in multiple layers, at least one of the piezoelectric bodies has a slit on its side, and the outer edge of a cross section of the portion of the piezoelectric element having the slit cut in a direction perpendicular to the stacking direction is circular or elliptical.

7. The piezoelectric element according to claim 6, wherein the piezoelectric body is formed from a lead-free piezoelectric ceramic composition.

8. A piezoelectric element according to claim 1 or claim 6, wherein the slits are formed in a plurality at arbitrary intervals in the stacking direction and every 35 layers or less.

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