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

Technical Field

[0001] The present disclosure relates to piezoelectric elements.

Background Art

[0002] Conventionally, as ceramics exhibiting piezoelectricity, PZT (lead zirconate titanate) has been widely used. A piezoelectric body made of PZT expands and contracts in response to an applied voltage, and a laminated piezoelectric actuator element having a structure in which a plurality of piezoelectric bodies and internal electrodes are alternately laminated has been developed and put into practical use. In the laminated piezoelectric actuator element, the piezoelectric body in the portion sandwiched between the internal electrodes becomes a polarized region, and the portion not sandwiched between the internal electrodes becomes a non-polarized region. Therefore, the displacement distribution changes greatly at the boundary between the polarized region and the non-polarized region, and stress concentrates in this portion. Due to this stress concentration, the possibility of crack generation increases when driven for a long time, and the durability decreases.

[0003] In order to relieve such stress, a laminated piezoelectric actuator element in which slits are formed in a direction perpendicular to the lamination direction (parallel to the lamination surface) on the side surface of the laminate is known. For example, the laminated piezoelectric actuator element described in Japanese Patent Application Laid-Open No. 2009-131138 (Patent Document 1 below) is a columnar laminate in which a plurality of piezoelectric layers and internal electrodes are alternately laminated, and enters the inside of the piezoelectric layer on the opposing side surfaces of the laminate and is formed at an arbitrary interval along the lamination direction of the laminate. And a laminate having side electrodes formed on the opposing side surfaces of the laminate in a form separated by slits and electrically connected to the internal electrodes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, because PZT contains lead, its environmental impact is a concern, and in recent years, the development of lead-free piezoelectric ceramic materials has been progressing as an example of a lead-free ceramic material. However, lead-free piezoelectric ceramic materials are less deformable and have greater rigidity than PZT, so simply adding slits may not be sufficient to relieve stress. In other words, it may not be possible to adequately relieve the stress in the part of the piezoelectric element that has the slits. [Means for solving the problem]

[0006] The piezoelectric element of this disclosure is a piezoelectric element in which a plurality of piezoelectric bodies and electrodes are alternately stacked in multiple layers, wherein at least one of the piezoelectric bodies has a slit on its side surface, and the outer edge of the cross-section obtained by cutting the portion of the piezoelectric element having the slit in a direction perpendicular to the stacking direction has a plurality of sides and a plurality of stress-relieving portions that connect adjacent pairs of sides, respectively, and the stress-relieving portions are formed such that when the point where the extended portions of adjacent pairs of sides intersect is considered a virtual vertex, the slit is located closer to the center of the piezoelectric element than the virtual vertex. [Effects of the Invention]

[0007] According to this disclosure, the stress in the portion of the piezoelectric element having a slit can be relieved. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing the configuration of the piezoelectric element of the embodiment. [Figure 2] Figure 2 is a perspective view showing a portion of the laminated structure decomposed in the direction of the stacking. [Figure 3] Figure 3 is a cross-sectional view showing a magnified view of the area around the slit. [Figure 4] Figure 4 shows a cross-section of the piezoelectric element, specifically the portion with a slit, cut in a direction perpendicular to the stacking direction. [Figure 5]Figure 5 is a cross-sectional view showing the stress distribution in the cross-section passing through the slit, as determined by simulation. [Figure 6] Figure 6 is a graph showing the maximum stress at the apex with respect to R / (L1 / 2). [Figure 7] Figure 7 is a graph showing the stress difference between the vertices and edges relative to L1 / L2. [Figure 8] Figure 8 shows the process flow of a piezoelectric element. [Figure 9] Figure 9 is a cross-sectional photograph of the slit. [Modes for carrying out the invention]

[0009] [Summary of the Embodiment] First, embodiments of this disclosure will be listed and described. (1) The piezoelectric element of the present disclosure is a piezoelectric element in which a plurality of layers of piezoelectric materials and electrodes are alternately stacked, wherein at least one of the piezoelectric materials has a slit on its side surface, and the outer edge of the cross section obtained by cutting the portion of the piezoelectric element having the slit in a direction perpendicular to the stacking direction has a plurality of sides and a plurality of stress-relieving portions that connect adjacent pairs of sides, respectively, and the stress-relieving portions are formed such that when the point where the extended portions of adjacent pairs of sides intersect is considered a virtual vertex, the slit is located closer to the center of the piezoelectric element than the virtual vertex. The piezoelectric material may be made of, for example, a lead-free pressure electromagnetic composition.

[0010] The piezoelectric material sandwiched between two electrodes becomes a polarized region, while the portion not sandwiched between the two electrodes becomes 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 materials formed from lead-free pressure electromagnetic compositions are less deformable and have greater rigidity than PZT, so it is conceivable that stress cannot be sufficiently relieved by simply forming a slit. Therefore, with the above configuration, stress can be relieved by forming multiple stress-relieving sections in addition to forming a slit.

[0011] (2) Preferably, the stress relaxation portion is formed of a C-plane having a tapered shape. Since the stress relaxation portion is formed of the C-plane, it becomes easy to disperse the stress over the entire C-plane.

[0012] (3) Preferably, the stress relaxation portion is formed of an R-plane having a curved surface shape. Since the stress relaxation portion is formed of the R-plane, it becomes easy to disperse the stress over the entire R-plane.

[0013] (4) When the side connecting adjacent virtual vertices is defined as a virtual side, the length of the virtual side is L1, and the length of the region where the stress relaxation portion is formed among the virtual sides is R, it is preferable that R / (L1 / 2) is 15% or more and 100% or less. According to the above configuration, the maximum stress applied to the stress relaxation portion can be reduced.

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

[0015] (6) Preferably, the slits are formed at arbitrary intervals in the lamination direction and a plurality of slits are formed every 35 layers or less.

[0016] [Details of 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, and is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0017] <Embodiment> Embodiments of this disclosure will be described with reference to Figures 1 to 9. As shown in Figure 1, the piezoelectric element 1 comprises a laminate 5 formed by alternately stacking a piezoelectric body 2 made of a lead-free pressure electromagnetic composition having piezoelectric properties and conductive internal electrodes 3 and 4. In Figure 1, the number of layers of the laminate 5 is omitted and shown as a small number, but in an actual piezoelectric element 1, there are many layers, as shown in Figure 3, for example.

[0018] [Piezoelectric material 2] The piezoelectric element 2 is a lead-free pressure electromagnetic composition having a main phase formed of a first crystalline phase consisting of an alkali niobate perovskite oxide and a secondary phase including a second crystalline phase consisting of an M-Ti-O spinel compound.

[0019] In this specification, "spinel compound" includes both positive spinel compounds having a positive spinel crystal structure and inverse spinel compounds having an inverse spinel crystal structure. The element M in M-Ti-O spinel compounds is a 1- to 4-valent metallic element.

[0020] Furthermore, the proportion of the second crystalline phase in the lead-free pressure electromagnetic composition is greater than 0% by volume and less than or equal to 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 "sub-phases."

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

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

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

[0024] As the values of the coefficients a, b, c, d, e, f, g, h in the above compositional formula (1), among the values for which the perovskite structure is established, preferable values are selected from the viewpoints of the electrical properties or piezoelectric properties (particularly the piezoelectric constant d33) of the lead-free piezoelectric ceramic composition, and also from the viewpoint of keeping the sintering temperature low during manufacturing.

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

[0026] Regarding the coefficients a, b, c, it is preferable that 0 ≦ a < 1, 0 ≦ b < 1, 0 ≦ c < 1 respectively. However, it is preferable that a = b = c = 0 (that is, a lead-free piezoelectric ceramic composition containing neither K, Na, nor Li) does not hold. The coefficients a, b of K and Na are typically 0 < a ≦ 0.6, 0 < b ≦ 0.6. The coefficient c of Li may be 0 (zero), but 0 < c ≦ 0.2 is preferable, and 0 < c ≦ 0.1 is more preferable.

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

[0028] The coefficient e with respect to the entire A-site is an arbitrary value as long as it does not impair the object of the present disclosure. As the coefficient e, 0.80 ≦ e ≦ 1.10 is preferable, 0.84 ≦ e ≦ 1.08 is more preferable, and 0.88 ≦ e ≦ 1.07 is even more preferable.

[0029] The sum of the coefficients f, g of the elements D, E at the B-site is 1 (that is, f + g = 1). As long as it does not impair the object of the present disclosure, it is preferable that the coefficient f of element D is not 0 (zero), and the coefficient g of element E may be 0 (zero).

[0030] The coefficient h for oxygen (O) is any value that allows the first crystalline phase to maintain a perovskite-type crystalline structure. A typical value for the coefficient h is approximately 3, and 3.0 ≤ h ≤ 3.1 is preferred. The value of the coefficient h can be calculated from the electrical neutrality conditions of the composition of the first crystalline phase. However, compositions of the first crystalline phase that deviate slightly from the electrical neutrality conditions are also acceptable.

[0031] The alkali niobate perovskite oxide represented by the above compositional formula (1) is an oxide whose main metal components are K, Na, and Nb, 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 compounds of the second crystalline phase are oxides containing the elements M (a valent to tetravalent metallic element) and Ti (titanium), and are represented, for example, by the following compositional formula (2).

[0033] MxTiOy·····(2) Here, element M is a 1- to 4-valent metallic element. Specifically, element M consists of 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. For the second crystalline phase to form a spinel compound, it is preferable that the coefficient x satisfies 0.5 ≤ x ≤ 5.0. The coefficient y is any value that forms a spinel compound, but for example, it is preferable that 2 ≤ y ≤ 8 is satisfied.

[0035] The second crystalline phase, composed of a spinel compound, stabilizes the structure of the first crystalline phase, thus enabling the creation of a lead-free pressure electromagnetic composition with excellent piezoelectric properties. Furthermore, from the viewpoint of piezoelectric properties, it is preferable to use a second crystalline phase represented by the compositional formula M2TiO4 or (M1,M2)TiO4, which contains two divalent metal elements M.

[0036] The second crystalline phase does not possess piezoelectric properties, but by being mixed with the first crystalline phase, it improves the sinterability of the lead-free pressure electromagnetic composition, thereby improving its structural stability and piezoelectric properties. Specifically, the second crystalline phase fills the vacancies 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 presumed to improve the structural stability and piezoelectric properties of the lead-free pressure electromagnetic composition.

[0037] [Internal electrodes 3,4] As shown in Figure 2, the internal electrodes 3 and 4 are arranged alternately in the stacking direction, and one piezoelectric element 2 is sandwiched between the internal electrodes 3 and 4. The internal electrodes 3 together form one electrode of the same polarity (e.g., positive electrode), and the internal electrodes 4 together form the other electrode of the same polarity (e.g., negative electrode). The internal electrodes 3 and 4 of opposite polarity are spaced apart in the stacking direction to prevent electrical short circuits.

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

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

[0040] By configuring the internal electrodes 3 and 4 in this way, the internal electrodes 3 and 4 of opposite poles are prevented from being electrically short-circuited.

[0041] [Slit 6] Slits 6 are formed around the entire circumference of the outer periphery of the laminate 5, perpendicular to the lamination direction (parallel to the lamination surface), and extending to a predetermined depth from the outer periphery. As shown in Figure 1, the depth of the slits 6 from the outer periphery of the laminate 5 is set to be deeper than the ends of the internal electrodes 3 and 4. Figure 9 shows an actual cross-sectional photograph of the slits 6. Multiple slits 6 are formed at arbitrary intervals in the lamination direction, and at intervals of 35 layers or less. These slits 6 are formed to relieve the stress applied when the piezoelectric element 1 is driven.

[0042] [Side electrodes 7,8] Furthermore, side electrodes 7 and 8 are formed on both sides of the laminate 5. These side electrodes 7 and 8 are formed, for example, by patterning conductive paste using screen printing, and are separated for each block divided in the lamination direction by the slits 6.

[0043] [External electrodes 11,12] Solder layers 9 and 10 are formed on the surfaces of the side electrodes 7 and 8. A pair of external electrodes 11 and 12 are fixed to the side electrodes 7 and 8 via these solder layers 9 and 10. As a result, the side electrodes 7 and 8 of each block divided in the stacking direction by the slit 6 are electrically conductive. The external electrodes 11 and 12 are formed of a conductive material (for example, copper). The external electrodes 11 and 12 are formed, for example, in a mesh-like manner and are deformable in accordance with the expansion and contraction of the laminate 5.

[0044] [Lead electrodes 13, 14] Furthermore, of the side electrodes 7 and 8 mentioned above, lead electrodes 13 and 14, which serve as voltage supply members for supplying voltage from the outside, are fixed to the side electrodes 7 and 8 of the lowermost block in Figure 1 via solder layers 9 and 10. Since the lead electrodes 13 and 14 are fixed to the side electrodes 7 and 8, even if the laminate 5 is vibrated at high speed for a long period of time, the external electrodes 11 and 12 will not break due to the inertial weight of the lead electrodes 13 and 14.

[0045] The laminated body 5 described above is constructed by alternately stacking multiple layers of piezoelectric material 2 and internal electrodes 3 and 4, and consists of a polarized region 50 that displaces when a voltage is applied to the internal electrodes 3 and 4, and a non-polarized region 51 that does not displace. The non-polarized region 51 is located below, above, and on the outer periphery of the polarized region 50.

[0046] The laminate 5 has a fixed end at the bottom in Figure 1, which is fixed and does not move, and a movable end at the top, which is movable. The lead electrodes 13 and 14 are fixed to the side electrodes 7 and 8 of the block located at the end on the fixed end side. That is, the lead electrodes 13 and 14 are fixed to the side electrodes 7 and 8 on the fixed end side, which are closer to the fixed end side than the slit 6 closest to the fixed end side.

[0047] [Stress relaxation section 30] Figure 4 shows a cross-section of the laminated body 5, specifically the portion containing the slit 6, cut in a direction perpendicular to the lamination direction. The hatched portion in the center of Figure 4 is the piezoelectric element 2 connecting the piezoelectric element 2 above the slit 6 and the piezoelectric element 2 below the slit 6, and is hereinafter referred to as the connecting portion 15.

[0048] The outer edge of the cross-section of the connecting portion 15 has four sides 20 and four stress-relaxing portions 30 that connect adjacent pairs of sides 20. The stress-relaxing portions 30 are formed such that, when the point where the extended portions 21 of adjacent pairs of 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. The cross-section of the connecting portion 15 in this embodiment is substantially rectangular, but it may also be substantially triangular or a substantially polygonal shape with 5 or more sides.

[0049] The stress relief portion 30 in this embodiment is composed of a curved R-shaped surface, but it may also be composed of a tapered C-shaped surface. Furthermore, the outer edge of the connecting portion 15 in this embodiment is composed of a straight edge 20 and a circular (quarter-circular) stress relief portion 30, but the circular stress relief portion 30 may be replaced with an elliptical stress relief portion.

[0050] [Examples] Figure 8 shows the process flow of piezoelectric element 1. First, several types of raw material powders necessary for forming the main phase were prepared, and these raw material powders were weighed according to the values ​​of coefficients a, b, c, d, e, f, and g in the composition formula of the main phase to obtain the desired composition. After weighing, each raw material powder was crushed and mixed in a dry vibratory mill for more than 4 hours to obtain a mixed powder. The obtained mixed powder was calcined, for example, in an atmospheric environment at a temperature of 600 to 1200°C for 1 to 10 hours to obtain a powdered calcined main phase.

[0051] Furthermore, several types of raw material powders necessary for forming the subphase were prepared, and these raw material powders were weighed according to the value of the coefficient x in the composition formula of the subphase to achieve the desired composition. After weighing, each raw material powder was pulverized and mixed in a dry vibratory mill for more than 4 hours to obtain a mixed powder. The obtained mixed powder was calcined, for example, under atmospheric conditions at a temperature of 600 to 1200°C for 1 to 10 hours to obtain a powdered subphase calcined material (powder preparation).

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

[0053] Next, the green sheet was punched out into a rectangle measuring 150 mm x 150 mm, and an electrode layer, which would serve as the internal electrode, was formed on one side of the green sheet using conductive paste for internal electrodes (Pt paste), for example by screen printing (internal electrode printing).

[0054] Subsequently, a predetermined number of green sheets without printed electrode layers (non-driving layer) and green sheets with printed electrode layers (driving layer) were stacked in a specific order. After applying temperature and pressure, the layers were bonded together and then cut into small pieces. For example, the bonding was performed at a temperature of 40-80°C and a pressure of 5-100 MPa.

[0055] The elements, cut into small pieces, were debindered (degreased) by, for example, holding them in an atmospheric environment at a temperature of 500-800°C for 2-100 hours.

[0056] The elements after binder removal were fired, for example, by holding them 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 predetermined dimensions (for example, a 6mm x 6mm rectangle) to expose the internal electrodes. The top and bottom surfaces of the element were polished to adjust the thickness and process to achieve a predetermined degree of parallelism. Slits were then formed in the rectangular parallelepiped element using a laser (COHERENT, UV, GREEN, IR wavelengths) from a direction perpendicular to the stacking direction. The slits were formed so that the radius of curvature of the stress relaxation section ranged from 0mm to 0.2mm, and the length of each side ranged from 1mm to 5.4mm (element processing).

[0058] Subsequently, electrodes were printed onto the sides of the laminate, baked at a temperature of 600-800°C, and then subjected to polarization treatment. Four of the resulting elements were assembled using adhesive, the side electrodes of each element were connected with lead wires using solder, and then sealed in a metal cylinder (assembly).

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

[0060] As shown in Figure 4, the edges connecting adjacent virtual vertices 22 are defined as virtual edges, with L1 being the length of the virtual edge and R being the length of the region within the virtual edge where the stress relaxation area 30 is formed. The upper part of Figure 5 is a cross-sectional view showing the maximum stress applied to the vertices (stress relaxation areas) of the connecting section 15, as simulated when R / (L1 / 2) is varied from 0% to 100%. Areas where stress is applied are shown in darker colors.

[0061] As shown in the upper part of Figure 5, at 0% and 5%, the stress is applied only to the connecting portion 15, whereas from 15% to 100%, the stress is applied to both the connecting portion 15 and the piezoelectric elements 2 adjacent to the connecting portion 15 above and below. In other words, from 15% to 100%, the stress is widely distributed between the connecting portion 15 and the piezoelectric elements 2, thus relieving the stress on the connecting portion 15 and reducing the maximum stress.

[0062] As shown in Figure 6, the maximum stress is 75 MPa or more when R / (L1 / 2) is 0% and 5% (when there is almost no R in the stress relaxation section 30), whereas the maximum stress is reduced to 69 MPa when R / (L1 / 2) is 100% (when there is sufficient R in the stress relaxation section 30). The maximum stress with respect to R / (L1 / 2) is preferably 15% to 100%, more preferably 25% to 100%, even more preferably 38% to 100%, and most preferably 100%.

[0063] As shown in Figure 4, let L2 be the length of one side of the piezoelectric elements 2 adjacent to the top and bottom of the connecting portion 15 (the length of one side of the internal electrodes 3 and 4). The lower part of Figure 5 is a cross-sectional view showing the stress difference between the vertex (stress relaxation area) and the edges of the connecting portion 15, as simulated when L1 / L2 is varied from 22% to 100%. At 100%, stress is concentrated in the connecting portion 15, but from 22% to 74%, the stress is widely distributed along the outer edge of the connecting portion 15, thus relaxing the stress on the connecting portion 15 and reducing the stress difference.

[0064] As shown in Figure 7, the stress difference is 11 MPa when L1 / L2 is 100%, while the stress difference decreases to 2 MPa or less when L1 / L2 is between 22% and 74%. The stress difference relative to L1 / L2 is preferably between 22% and 74%, more preferably between 37% and 74%, and most preferably 56%.

[0065] [Effects of the Embodiment] The piezoelectric element 1 is formed by alternately stacking multiple layers of piezoelectric bodies 2 made of a lead-free pressure electromagnetic composition having piezoelectric properties and internal electrodes 3 and 4. At least one of the piezoelectric bodies 2 has a slit 6 on its side surface, and the outer edge of the 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-relieving portions 30 that connect adjacent pairs of sides 20, respectively. The stress-relieving portions 30 are formed such that, when the point where the portions 21 extended from adjacent pairs of 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 piezoelectric material 2 sandwiched between the internal electrode 3 and the adjacent internal electrode 4 becomes a polarized region 50, while the portion not sandwiched between the two electrodes 3 and 4 becomes a 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 that stress concentrates in this area. In particular, since the piezoelectric material 2 formed from a lead-free pressure electromagnetic composition is less deformable and has greater rigidity than PZT, it is conceivable that stress cannot be sufficiently relieved by simply forming a slit 6. Therefore, with the above configuration, stress can be relieved by forming a slit 6 and then forming multiple stress-relieving sections 30.

[0067] Since the stress-relaxing section 30 is composed of a curved R-shaped surface, it is easier to distribute the stress across the entire R-shaped surface.

[0068] When the edges connecting adjacent virtual vertices 22 are defined as virtual edges, with length L1 being the length of the virtual edge, and length R being the length of the region on the virtual edge where the stress relaxation section 30 is formed, then R / (L1 / 2) is between 15% and 100%. In this way, the maximum stress acting on the stress relaxation section 30 can be reduced. [Explanation of Symbols]

[0069] 1: Piezoelectric element 2: Piezoelectric material 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 part 20: Edge 21: Parts extended by a pair of adjacent edges 22: Virtual vertex 30: Stress relaxation section 50: Polarized region 51: Non-polarized region

Claims

1. A piezoelectric element comprising multiple layers of piezoelectric materials and electrodes stacked alternately, At least one of the piezoelectric elements has a slit on its side, The outer edge of the cross-section of the portion of the piezoelectric element having the slit, cut in a direction perpendicular to the stacking direction, has a plurality of sides and a plurality of stress-relaxing portions connecting adjacent pairs of sides, The stress-relieving portion is formed such that, when the point where the extended portions of a 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. The piezoelectric material is formed from a lead-free electromagnet composition. If we define a virtual edge as the edge connecting adjacent virtual vertices, define the length of the virtual edge as L1, and define the length of the region within the virtual edge where the stress relaxation portion is formed as R, A piezoelectric element in which R / (L1 / 2) is between 38% and 100%.

2. When the length of one side of the electrode is L2, The piezoelectric element according to claim 1, wherein L1 / L2 is 22% to 74%.

3. The piezoelectric element according to claim 1, wherein the stress-relieving portion is composed of a tapered C-surface.

4. The piezoelectric element according to claim 1, wherein the stress relaxation portion is composed of an R-shaped curved surface.

5. Multiple layers of the piezoelectric material and the electrode are alternately stacked to form a laminate, Side electrodes are formed on both sides of the laminate. The side electrodes are separated for each block divided in the stacking direction by the slits. External electrodes are arranged on the outside of the aforementioned side electrodes. The piezoelectric element according to any one of claims 1 to 4, wherein the side electrodes of each block divided in the stacking direction by the external electrode are electrically conductive.

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