Multilayer piezoelectric element

Abstract

To provide a lamination type piezoelectric element that does not contain lead in its component, can be manufactured by integrated burning with an internal electrode containing a large percentage of silver, and achieves both the long life and excellent piezoelectric characteristics.SOLUTION: A laminated type piezoelectric element 100 comprises: a plurality of piezoelectric ceramic layers 10 that contain alkali niobate having a perovskite-type structure as a main component, contain silver and at least one alkaline earth metal element selected from calcium, strontium, and barium, and contain 0.1 mole or more and 2.0 moles or less of lithium and 1.5 moles or more and 4.0 moles or less of silicon based on 100 moles of the main component in an amount such that the molar ratio of the lithium to the silicon Li / Si becomes 0.025 or more and less than 0.40; and internal electrodes 20 that are arranged between the plurality of piezoelectric ceramic layers 10 and are formed of a metal containing silver in an amount of 80 mass% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A piezoelectric element is an electronic component in which a piezoelectric ceramic (piezoelectric ceramic) is sandwiched between a pair of electrodes. Here, piezoelectricity refers to the property of being able to convert electrical energy and mechanical energy into each other.

[0003] Piezoelectric elements utilize the properties of piezoelectric ceramics mentioned above to convert the voltage applied between a pair of electrodes into mechanical energy such as pressure or vibration, thereby moving other objects or operating themselves. On the other hand, piezoelectric elements can also convert mechanical energy such as vibration or pressure into electrical energy and extract that electrical energy as a voltage between a pair of electrodes.

[0004] Piezoelectric elements have structures in which electrodes are formed only on the surface of the piezoelectric ceramic, as well as multilayer piezoelectric elements, which are constructed by alternately stacking multiple piezoelectric ceramic layers and internal electrode layers. Multilayer piezoelectric elements can be used in applications such as actuators because they allow for large displacement in the stacking direction of the piezoelectric ceramic layers. Multilayer piezoelectric elements are typically manufactured by simultaneously firing the piezoelectric ceramic layers and the internal electrode layers.

[0005] As piezoelectric ceramics constituting such piezoelectric elements, those containing lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) and solid solutions thereof as main components are widely used. Since PZT-based piezoelectric ceramics have a high Curie temperature, piezoelectric elements using the same can be used even in high-temperature environments. In addition, since PZT-based piezoelectric ceramics have a high electromechanical coupling coefficient, piezoelectric elements using the same can efficiently convert between electrical energy and mechanical energy. Furthermore, PZT-based piezoelectric ceramics can be fired at temperatures below 1000°C by selecting an appropriate composition, thereby reducing the manufacturing cost of piezoelectric elements. Particularly in the above-described multilayer piezoelectric elements, this allows the use of low-melting-point materials with a high silver content, in other words, a low content of expensive materials such as platinum and palladium, for internal electrodes that are co-fired with the piezoelectric ceramics, which produces a significant cost reduction effect.

[0006] However, PZT-based piezoelectric ceramics are regarded as problematic because they contain lead, which is a harmful substance, and lead-free piezoelectric ceramic compositions that can replace them are in demand.

[0007] To date, as lead-free piezoelectric ceramics, alkali niobate ((Li,Na,K)NbO₃)-based, bismuth sodium titanate ((Bi 0.5 Na 0.5 )TiO₃, BNT)-based, bismuth layered compound-based, tungsten bronze-based piezoelectric ceramics having various compositions have been reported. Among these, alkali niobate-based piezoelectric ceramics have attracted attention as alternatives to PZT-based materials because of their high Curie temperature and relatively large electromechanical coupling coefficient (Patent Document 1).

[0008] Attempts have been made to achieve low-temperature firing of these alkali niobate-based piezoelectric ceramics, enabling integral co-firing with internal electrodes having a high silver content, and reducing the manufacturing cost of multilayer piezoelectric elements.

[0009] For example, Patent Document 2 discloses a technical idea in which by allowing the composition of an alkali niobate-based piezoelectric ceramic to contain an alkaline earth metal and silver, co-firing with an internal electrode having a silver content of 50 mass% or more is enabled. And in Cited Document 2, Ag 0.7 Pd 0.3 a multilayer piezoelectric element that comprises the internal electrode, exhibits high electrical resistivity, and shows a large displacement when a voltage is applied is reported.

[0010] In addition, Patent Document 3 discloses a technical idea in which by allowing the composition of an alkali niobate-based piezoelectric ceramic to contain silver and a specific amount of calcium or barium, and allowing the piezoelectric ceramic layer to comprise sintered particles including silver segregation regions with a major axis of 10 nm or less, co-firing with an internal electrode formed of a metal having a silver content of 80 mass% or more is enabled. And in Cited Document 3, the composition formula is Li 0.064 Na 0.52 K 0.42 with respect to 100 mol% of alkali niobate that becomes NbO3, a piezoelectric ceramic layer obtained by adding 0.5 mol% of BaCO3, 0.4 mol% of LiCO3, 2.0 mol% of SiO2 and 0.5 mol% of MnO, as well as Ag 0.9 Pd 0.1 a multilayer piezoelectric element that comprises the internal electrode is reported. [Prior Art Documents] [Patent Documents]

[0011] [Patent Document 1] International Publication No. 2007 / 094115 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2017-163055 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2021-158249 [Summary of the Invention] [Problems to be Solved by the Invention]

[0012] Patent Document 2 states that the above-mentioned alkali niobate-based piezoelectric ceramics may contain Li2O and SiO2, which contribute to improved sinterability, and MnO, which contributes to improved electrical resistance. However, it has been found that depending on the content of these components, large amounts of conductive Li3NbO4 and lithium manganese oxide, which has lower electrical resistivity than alkali niobate salts, may be generated in the piezoelectric ceramics, leading to a decrease in electrical insulation during use of the device and potentially shortening its lifespan.

[0013] The multilayer piezoelectric element reported in Patent Document 3 has a long lifespan and excellent piezoelectric properties. However, there is a need for a multilayer piezoelectric element that achieves both long lifespan and excellent piezoelectric properties at an even higher level.

[0014] Therefore, the object of the present invention is to provide a multilayer piezoelectric element that does not contain lead in its constituent components, can be manufactured by integral firing with an internal electrode having a high silver content, and achieves both a long lifespan and excellent piezoelectric properties. [Means for solving the problem]

[0015] The inventors of the present invention conducted various studies to solve the aforementioned problems and found that the problems can be solved by adding lithium and silicon to alkali niobate in specific proportions when manufacturing a multilayer piezoelectric element, thereby making the piezoelectric ceramic layer contain a predetermined amount of Li2SiO3. This led to the completion of the present invention.

[0016] In other words, one aspect of the present invention for solving the above problems is that it mainly comprises an alkali niobate having a perovskite-type structure, and contains at least one alkaline earth metal element selected from calcium, strontium, and barium, and silver, and the main component is 100 moles % In contrast, 0.1 mole % Total of 2.0 moles %below Lithium and 1.5 moles % 4.0 moles %The following silicon is contained in an amount such that the molar ratio of lithium to silicon (Li / Si) is 0.025 or more and less than 0.40, and the strongest diffraction line intensity at 10.00°≦2θ≦50.00° when X-ray diffraction measurements using Cu-Kα rays are performed is I max The strongest diffraction line intensity at 26.50°≦2θ≦27.50° is I L2S The average value of the diffraction line intensity in the range 27.50°≦2θ≦29.00° is I BG When R1 = (I L2S -I BG ) / (I max -I BG ) × 100 ≥ 0.20 Furthermore, the strongest diffraction line intensity at 25.70°≦2θ≦26.00° is I L3N When R 2 =(I L3N -I BG ) / (I max -I BG ) × 100 ≤ 0.55 Multiple piezoelectric ceramic layers, and an internal electrode made of a metal having a silver content of 80% by mass or more, disposed between the multiple piezoelectric ceramic layers. The extreme It is a multilayer piezoelectric element. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a multilayer piezoelectric element that does not contain lead in its constituent components, can be manufactured by integral firing with an internal electrode containing a high proportion of silver, and achieves both a long lifespan and excellent piezoelectric properties. [Brief explanation of the drawing]

[0018] [Figure 1] Cross-sectional view (XZ plane) showing the structure of a multilayer piezoelectric element according to one aspect of the present invention. [Figure 2] Cross-sectional view (YZ plane) showing the structure of a multilayer piezoelectric element according to one aspect of the present invention. [Figure 3] Perspective view showing a unit cell model of a perovskite-type structure. [Modes for carrying out the invention]

[0019] The structure and effects of the present invention will be explained below, along with the technical concepts, with reference to the drawings. However, the mechanism of action is based on assumptions, and its validity does not limit the present invention.

[0020] [Multilayer piezoelectric element] A multilayer piezoelectric element 100 according to one aspect of the present invention (hereinafter sometimes simply referred to as "this aspect") comprises a piezoelectric ceramic layer 10, internal electrodes 20 disposed between the piezoelectric ceramic layers 10, and connecting conductors 30 that electrically connect the internal electrodes 20 every other layer, as schematically shown in the cross-sectional views in Figures 1 and 2. Note that among the internal electrodes 20 shown in Figures 1 and 2 and the connecting conductors 30 shown in Figure 1, those with the same letter ("a" or "b") indicate that they have the same polarity ("+" or "-"). Furthermore, in the multilayer piezoelectric element 100 shown in Figure 1, the connecting conductors 30 are formed on its surface, but the connecting conductors 30 may also be formed inside the multilayer piezoelectric element 100, penetrating the piezoelectric ceramic layer 10.

[0021] As shown in Figure 2, this side surface may have side margin portions 40 located between the Y-axis side surfaces and the internal electrode 20, and cover portions 50 located on the Z-axis top and bottom surfaces. Furthermore, this side surface may have terminal electrodes (not shown) formed on its surface to electrically connect the connecting conductor 30 and the drive circuit, or the connecting conductor 30 formed on the surface may also serve as the terminal electrodes.

[0022] The following describes in detail each component of the multilayer piezoelectric element 100.

[0023] (Piezoelectric ceramic layer) The piezoelectric ceramic layer 10 mainly consists of an alkali niobate having a perovskite-type structure.

[0024] The main component, alkali niobate, is an oxide having a perovskite structure, containing at least one alkali metal element selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), as well as niobium (Nb) as constituent elements. Here, the perovskite structure is a crystalline structure having A sites located at the vertices of the unit cell, O sites located at the face centers of the unit cell, and B sites located in an octahedron with the O sites as vertices, as shown in Figure 3. In the alkali niobate of this embodiment, alkali metal ions are located at the A sites, niobium ions at the B sites, and oxide ions at the O sites. In addition, each site may contain various ions other than those mentioned above.

[0025] Here, confirmation that the piezoelectric ceramic layer 10 mainly consists of an alkali niobate having a perovskite-type structure is performed by the following procedure. First, the diffraction line profile of the piezoelectric ceramic layer 10 exposed on the surface of the multilayer piezoelectric element 100, or the powder obtained by crushing the multilayer piezoelectric element 100, is measured using an X-ray diffraction (XRD) apparatus that uses Cu-Kα rays. The method for exposing the piezoelectric ceramic layer 10 on the surface of the multilayer piezoelectric element 100 is not particularly limited, and methods such as cutting or polishing the piezoelectric element can be employed. Furthermore, the means for crushing the multilayer piezoelectric element 100 is not particularly limited, and a hand mill (mortar and pestle) can be used. Next, when the ratio of the strongest diffraction line intensity in the diffraction profile derived from other structures to the strongest diffraction line intensity in the profile derived from the perovskite-type structure in the obtained diffraction line profile is 10% or less, it is determined that the piezoelectric ceramic layer 10 is mainly composed of a compound having a perovskite-type structure. At this time, if XRD measurement is performed on the powder obtained by crushing the multilayer piezoelectric element 100, peaks of the metal constituting the internal electrode 20 will also be detected, so these are excluded before comparing the diffraction line intensities as described above. Next, the piezoelectric ceramic layer 10, or the powder prepared therefrom, which is determined to mainly consist of a compound having a perovskite structure, is subjected to the measurement of the proportion of each element it contains using inductively coupled plasma (ICP) emission spectroscopy, ion chromatography, or XRF fluorescence analysis. Based on the measurement results, if the total content of alkali metal elements and the niobium content, expressed in mole percent (or atomic percent), are both greater than the content of other elements, it is determined that the main component, a compound having a perovskite structure, is an alkali niobate salt.

[0026] The piezoelectric ceramic layer 10 contains at least one alkaline earth metal element selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba), and silver (Ag). This results in a dense piezoelectric ceramic layer 10 with small sintered particle size, exhibiting excellent piezoelectric properties. The content of alkaline earth metal elements and silver in the piezoelectric ceramic layer 10 is not limited, but from the viewpoint of making the multilayer piezoelectric element excellent piezoelectric properties, the content of alkaline earth metal elements is preferably more than 0.2 mol%, more preferably 0.3 mol%, and even more preferably 0.5 mol%, when the content of elements (which are often in an ionic state) in the B site of the main component, alkali niobate, is taken as 100 mol%. Similarly, for silver, the content is preferably more than 0.5 mol%, more preferably 0.7 mol%, and even more preferably 1.0 mol%, relative to 100 mol% of the elements in the B site. On the other hand, in order to further improve the electrical insulation of the piezoelectric ceramic layer 10, enable use under high electric fields, and extend the lifespan of the element, the total content of the alkaline earth metal elements is preferably 5.0 mol% or less, more preferably 3.0 mol% or less, and even more preferably 1.0 mol% or less. Similarly, for the same reasons, the silver content is preferably 5.0 mol% or less, more preferably 4.0 mol% or less, and even more preferably 3.0 mol% or less. Furthermore, for the reasons mentioned above, regarding the total content of alkaline earth metal elements and the content of silver, it is preferable that the total content of alkaline earth metal elements is more than 0.2 mol% and 5.0 mol% or less, and the silver content is more than 0.5 mol% and 5.0 mol% or less, relative to 100 mol% of the elements in the B site; it is more preferable that the total content of alkaline earth metal elements is 0.3 mol% or more and 3.0 mol% or less, and the silver content is 0.7 mol% or more and 4.0 mol% or less; and it is even more preferable that the total content of alkaline earth metal elements is 0.5 mol% or more and 1.0 mol% or less, and the silver content is 1.0 mol% or more and 3.0 mol% or less.

[0027] The alkaline earth metal elements and silver contained in the piezoelectric ceramic layer 10 can form a solid solution at the A-site of alkali niobate, which is the main component. Further, when the piezoelectric ceramic layer 10 contains Ta or Sb, these elements can form a solid solution at the B-site of the alkali niobate. When these elements are dissolved in the alkali niobate as a solid solution, the alkali niobate having each of these elements dissolved therein as a solid solution becomes the main component of the piezoelectric ceramic layer 10.

[0028] From the viewpoints of allowing the main component to exhibit excellent piezoelectric properties and obtaining a device with a long service life when used under a high electric field, the main component is preferably one represented by the following composition formula (1). (Ag u M2 v (K 1-w-x Na w Li x ) 1-u-v ) a (Sb y Ta z Nb 1-y-z )O3 …(1) However, in the formula, M2 represents at least one alkaline earth metal element selected from the group consisting of calcium (Ca), strontium (Sr) and barium (Ba). Further, u, v, w, x, y, z and a are numerical values satisfying the respective inequalities represented by 0.005<u≦0.05, 0.002<v≦0.05, 0.007<u+v≦0.1, 0≦w≦1, 0.02<x≦0.1, 0.02<w+x≦1, 0≦y≦0.1, 0≦z≦0.4, and 1<a≦1.1, respectively.

[0029] Here, that the alkali niobate is represented by the above composition formula (1) is confirmed by the following procedure. First, the piezoelectric ceramic layer 10, or the powder prepared therefrom, which has been confirmed to mainly consist of an alkali niobate having a perovskite structure according to the procedure described above, is subjected to the measurement of the content of silver (Ag), calcium (Ca), strontium (Sr), barium (Ba), potassium (K), sodium (Na), lithium (Li), antimony (Sb), tantalum (Ta), and niobium (Nb) using high-frequency inductively coupled plasma (ICP) emission spectroscopy, ion chromatography, or XRF fluorescence analysis. However, when the measurement target is the powder prepared from the piezoelectric ceramic layer 10, a powder that does not contain components of the internal electrode is used to eliminate the influence of silver contained in the internal electrode. Next, the total number of moles of antimony, tantalum, and niobium is calculated, and the ratio of the number of moles of each of the aforementioned elements to this total is calculated. Then, if the proportions of each element obtained fall within the range of the above compositional formula (1), it is determined that the alkali niobate is represented by the above compositional formula (1).

[0030] The piezoelectric ceramic layer 10 contains 0.1 mol% to 2.0 mol% lithium and 1.5 mol% to 4.0 mol% silicon, relative to 100 mol% of the main component, in an amount such that the molar ratio of lithium to silicon (Li / Si) is 0.025 to less than 0.40. This ensures that the laminated piezoelectric element 100 achieves both a long lifespan and excellent piezoelectric properties even when fired at a temperature below the heat resistance temperature of the internal electrode 20, which will be described later. To achieve a higher level of long lifespan and excellent piezoelectric properties for the laminated piezoelectric element 100, the lithium content is preferably 0.2 mol% to 1.8 mol%, more preferably 0.3 mol% to 1.5 mol%, and even more preferably 0.4 mol% to 1.2 mol%, relative to 100 mol% of the main component. Furthermore, for similar reasons, the silicon content is preferably 1.8 mol% to 3.9 mol%, more preferably 2.0 mol% to 3.8 mol%, and even more preferably 2.2 mol% to 3.7 mol%, relative to 100 mol% of the main component mentioned above. Furthermore, for similar reasons, the Li / Si ratio is preferably 0.05 to 0.38, more preferably 0.08 to 0.36, and even more preferably 0.10 to 0.34. Although Li is also a constituent element of the main component mentioned above, the amount of Li described here does not include the Li in the main component. The amount of Li contained in the piezoelectric ceramic layer 10 that does not constitute the main component is calculated as the remainder obtained by subtracting the amount of Li that can be dissolved in the alkali niobate from the total amount of Li obtained as a result of the compositional analysis in the method for determining the compositional formula of the alkali niobate mentioned above.

[0031] The piezoelectric ceramic layer 10 has the strongest diffraction line intensity at 10.00°≦2θ≦50.00° when X-ray diffraction measurements using Cu-Kα rays are performed. max The strongest diffraction line intensity at 26.50°≦2θ≦27.50° is I L2S The average value of the diffraction line intensity in the range 27.50°≦2θ≦29.00° is I BG When R1 = (I L2S -I BG ) / (I max -I BGThe condition ) × 100 ≥ 0.20 is satisfied. This makes the multilayer piezoelectric element 100 able to achieve both a long lifespan and excellent piezoelectric characteristics. max In the piezoelectric ceramic layer 10, which has a perovskite-type structure and is mainly composed of alkali niobate, this corresponds to the main peak intensity of the alkali niobate, which is the main component. L2S This corresponds to the main peak intensity of Li2SiO3, and the above I BG This corresponds to the background X-ray intensity. Therefore, a large value of R1 means that the proportion of Li2SiO3 to the main component is high. Thus, it is presumed that including a certain proportion or more of Li2SiO3 relative to the main component contributes to extending the lifespan of the multilayer piezoelectric element 100 and improving its piezoelectric properties. In terms of achieving a higher level of long lifespan and excellent piezoelectric properties of the multilayer piezoelectric element 100, the value of R1 is preferably 0.23 or higher, more preferably 0.24 or higher, and even more preferably 0.25 or higher. The upper limit of R1 is not particularly limited as long as it can be obtained with the lithium and silicon content described above, but it is preferably 0.60 or lower, more preferably 0.50 or lower, and even more preferably 0.40 or lower. For the reasons mentioned above, the value of R1 is preferably 0.23 or more and 0.60 or lower, more preferably 0.24 or more and 0.50 or lower, and even more preferably 0.25 or more and 0.50 or lower.

[0032] The piezoelectric ceramic layer 10 has the strongest diffraction line intensity at 25.70°≦2θ≦26.00° when X-ray diffraction measurements using Cu-Kα rays are performed. L3N When this is done, then the aforementioned I max and I BG Between, R2=(I L3N -I BG ) / (I max -I BG It is preferable that the relationship ) × 100 ≤ 0.55 holds. This allows the multilayer piezoelectric element 100 to achieve a higher level of balance between long lifespan and excellent piezoelectric characteristics. L3NThis corresponds to the main peak intensity of Li3NbO4, and the value of R2 corresponds to the ratio of Li3NbO4 to the main component, alkali niobate. Therefore, a small value of R2 means that the ratio of Li3NbO4 to the main component is low. Since Li3NbO4 is a conductive compound, it is presumed that a low ratio of Li3NbO4 contributes to extending the lifespan of the multilayer piezoelectric element 100 and improving its piezoelectric properties. From the viewpoint of further extending the lifespan of the multilayer piezoelectric element 100 and obtaining even better piezoelectric properties, the value of R2 is more preferably 0.40 or less, and even more preferably 0.20 or less. A lower lower limit of R2 is preferable, but in measurements using a general-purpose X-ray diffractometer, the I L3N Even if it is not recognized as a peak, the value will still be around 0.05.

[0033] The X-ray diffraction measurements used to obtain the strongest diffraction line intensities described above can be performed in the same manner as the X-ray diffraction measurements used to confirm whether the piezoelectric ceramic layer 10 is mainly composed of an alkali niobate having a perovskite-type structure.

[0034] The piezoelectric ceramic layer 10 may also contain manganese (Mn) in addition to the components described above. This improves the electrical insulation of the piezoelectric ceramic layer 10, resulting in a long-life multilayer piezoelectric element 100. The manganese content is not particularly limited, but from the viewpoint of obtaining excellent electrical insulation, it is preferable to have a manganese content of 0.2 mol% or more, more preferably 0.3 mol% or more, and even more preferably 0.5 mol% or more, when the main component, alkali niobate, is considered to be 100 mol%. On the other hand, from the viewpoint of making the piezoelectric ceramic layer 10 excellent in piezoelectric properties, the manganese content is preferably 2.0 mol% or less, more preferably 1.5 mol% or less, and even more preferably 1.0 mol% or less, relative to 100 mol% of the main component. Furthermore, for the reasons mentioned above, the manganese content is preferably 0.2 mol% to 2.0 mol%, more preferably 0.3 mol% to 1.5 mol%, and even more preferably 0.5 mol% to 1.0 mol%, based on 100 mol% of the main component.

[0035] In addition to these components, the piezoelectric ceramic layer 10 may optionally contain at least one first transition element selected from Sc, Ti, V, Cr, Fe, Co, Ni, Cu, and Zn. By including these elements in appropriate amounts, it is possible to adjust the firing temperature of the multilayer piezoelectric element 100, control grain growth, and extend the lifespan at high electric fields.

[0036] Furthermore, the piezoelectric ceramic layer 10 may optionally contain at least one second transition element selected from Y, Zr, Mo, Ru, Rh, and Pd. By including these elements in appropriate amounts, it is possible to adjust the firing temperature of the multilayer piezoelectric element 100, control grain growth, and extend the lifespan at high electric fields.

[0037] Furthermore, the piezoelectric ceramic layer 10 may optionally contain at least one third transition element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Os, Ir, Pt, and Au. By including these elements in appropriate amounts, it is possible to adjust the firing temperature of the multilayer piezoelectric element 100, control grain growth, and extend the lifespan at high electric fields.

[0038] Of course, in this embodiment, the piezoelectric ceramic layer 10 can also contain multiple types of the aforementioned first transition elements, second transition elements, and third transition elements.

[0039] (internal electrode) The internal electrode 20 is formed from a metal having a silver content of 80% by mass or more. By having a silver content of 80% by mass or more, the amount of expensive metals such as platinum and palladium used can be reduced, thereby lowering the manufacturing cost of the element. In addition, as the proportion of silver, which has excellent conductivity, increases, the electrical resistivity of the internal electrode 20 decreases, and electrical losses when used as a piezoelectric element are reduced. Examples of metals with a silver content of 80% by mass or more include silver-palladium alloys and silver. The silver content in the metal constituting the internal electrode 20 is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0040] The silver content in the internal electrode 20 can be confirmed by performing elemental analysis of the internal electrode 20 using various measuring instruments and calculating the mass ratio of silver to all detected elements. Examples of measuring instruments that can be used include energy dispersive X-ray spectrometers (EDS) or wavelength dispersive X-ray spectrometers (WDS) attached to scanning electron microscopes (SEM) or transmission electron microscopes (TEM), electron probe microanalyzers (EPMA), and laser-irradiated inductively coupled plasma mass spectrometers (LA-ICP-MS).

[0041] (Connecting conductor) The connecting conductor 30 electrically connects the internal electrodes 20 every other layer. The material of the connecting conductor 30 is not particularly limited if it is formed on the surface of the multilayer piezoelectric element 100, as long as it has high conductivity and is physically and chemically stable under the polarization conditions and the operating environment of the element described later. Examples include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof. On the other hand, if the connecting conductor 30 is formed inside the multilayer piezoelectric element 100, penetrating the piezoelectric ceramic layer 10, it is preferable to use a metal with a silver content of 80% by mass or more, similar to the internal electrodes 20 described above.

[0042] (Side margin and cover section) The side margin portion 40 and the cover portion 50 function as protective parts that protect the piezoelectric ceramic layer 10 and the internal electrode 20.

[0043] The side margin portion 40 and the cover portion 50 are preferably formed from a sintered body mainly composed of alkali niobate, similar to the piezoelectric ceramic layer 10, from the viewpoint of the shrinkage rate during firing of the multilayer piezoelectric element 100 and the relaxation of internal stress within the multilayer piezoelectric element 100. However, the material forming the side margin portion 40 and the cover portion 50 does not have to be mainly composed of alkali niobate, as long as it is a material with high insulating properties.

[0044] (terminal electrode) The terminal electrodes have the function of electrically connecting the connecting conductor 30 and the drive circuit. Furthermore, if they are formed on a piezoelectric ceramic layer 10, they also have the function of applying voltage to it. The material of the terminal electrodes 30 is not particularly limited, as long as it has high conductivity and is physically and chemically stable under polarization conditions and in the operating environment of the piezoelectric element. Examples include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof.

[0045] [Method for manufacturing multilayer piezoelectric ceramics] The multilayer piezoelectric element relating to this aspect is manufactured by, for example, preparing a raw sheet containing an alkali niobate powder having a perovskite structure, one or more powders containing predetermined amounts of at least one alkaline earth metal element selected from calcium, strontium, and barium, lithium, and silicon, and a binder; placing an internal electrode precursor containing a metal with a silver content of 80% by mass or more on the raw sheet; stacking a predetermined number of raw sheets printed with the metal paste and pressing them together to obtain a manufactured form; removing the binder from the manufactured form and firing it to obtain a multilayer piezoelectric ceramic; applying a conductive paste to the surface of the multilayer piezoelectric ceramic where the internal electrodes are exposed and then firing it to form connecting conductors and terminal electrodes; and applying a high voltage between the terminal electrodes to perform polarization treatment of the piezoelectric ceramic layer. Each operation will be described in detail below.

[0046] (Preparation of alkaline niobate powder) Powders of alkali niobate salts having a perovskite structure can be obtained, for example, by mixing powders of compounds containing at least one alkali metal element selected from lithium, sodium, and potassium, and powders of compounds containing niobium, in a desired ratio, and then calcining (pre-sintering). Compounds containing elements other than alkali metals and niobium may be added to achieve the desired properties of the final piezoelectric ceramic product.

[0047] Examples of compounds used as raw materials include lithium carbonate (Li2CO3) and lithium fluoride (LiF) as lithium compounds, sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) as sodium compounds, potassium carbonate (K2CO3) and potassium bicarbonate (KHCO3) as potassium compounds, and niobium pentoxide (Nb2O5) as a niobium compound. In addition, although optional components, commonly used compounds include tantalum pentoxide (Ta2O5) as a tantalum compound and antimony trioxide (Sb2O3) as an antimony compound.

[0048] The method for mixing the raw material powders is not particularly limited as long as it ensures uniform mixing of each powder while minimizing the inclusion of impurities, and either dry mixing or wet mixing may be employed. When using wet mixing with a ball mill, for example, partially stabilized zirconia (PSZ) balls can be used, and the mixture can be stirred for 8 to 60 hours using a ball mill with an organic solvent such as ethanol as the dispersion medium, after which the organic solvent can be evaporated and dried.

[0049] The calcination conditions for the raw material mixture powder are not particularly limited, as long as the aforementioned compound powders react to obtain the desired alkali niobate. For example, calcination can be performed in air at a temperature of 700°C to 1000°C for 1 to 10 hours. The calcined powder may be used directly in the manufacture of piezoelectric ceramics, but it is preferable to crush it using a ball mill or stamp mill, etc., in order to improve its miscibility with the alkaline earth metal compound and organic binder described later, and to obtain a smooth raw sheet via a uniform slurry.

[0050] If commercially available alkali niobate powder is available, the mixing and calcination of the raw material powders described above may be omitted, and the subsequent operations may be performed on this powder instead.

[0051] (Preparation of raw sheets) A raw sheet comprising an alkali niobate powder, one or more powders containing predetermined amounts of at least one alkaline earth metal element selected from calcium, strontium, and barium, lithium, and silicon, and a binder can be obtained, for example, by adding one or more powders containing predetermined amounts of at least one alkaline earth metal element selected from calcium, strontium, and barium, lithium, and silicon to the aforementioned alkali niobate powder to prepare a mixed powder, mixing it with a binder and a dispersion medium to prepare a slurry, and then forming the slurry into a sheet.

[0052] Examples of powders containing alkaline earth metal elements include calcium carbonate (CaCO3), calcium metasilicate (CaSiO3), and calcium orthosilicate (Ca2SiO4) as those containing calcium, strontium carbonate (SrCO3) as those containing strontium, and barium carbonate (BaCO3) as those containing barium.

[0053] Examples of lithium-containing powders include lithium carbonate (Li2CO3), lithium fluoride (LiF), lithium metasilicate (Li2SiO3), and lithium orthosilicate (Li4SiO4).

[0054] Examples of silicon-containing powders include lithium metasilicate (Li2SiO3) and lithium orthosilicate (Li4SiO4) as mentioned above, as well as silicon dioxide (SiO2).

[0055] The binder used should be one that can maintain the shape of the raw sheet described later and volatilize without leaving any carbon residue after firing or a preceding binder removal process. Examples of usable binders include polyvinyl alcohol-based, polyvinyl butyral-based, cellulose-based, urethane-based, and vinyl acetate-based binders. The amount of binder used is not particularly limited, but since it will be removed in a later process, it is preferable to use as little as possible within the range where the desired moldability and shape retention can be obtained, in order to reduce raw material costs.

[0056] As the dispersion medium, one should be used that does not cause aggregation of the calcined powder and binder, and can be easily removed by volatilization or other means after the green sheet molding process described later. Examples of usable dispersion media include water and alcohol-based solvents.

[0057] Components that adjust the properties of the slurry, such as dispersants, plasticizers, and thickeners, may be added to the slurry.

[0058] The method for mixing the above mixed powder with a binder and dispersion medium is not particularly limited, as long as it ensures that each component is uniformly mixed while preventing the inclusion of impurities. One example is ball mill mixing.

[0059] Conventional methods such as the doctor blade method can be used to form the prepared slurry into a sheet and obtain a raw sheet.

[0060] (Arrangement of internal electrode precursors) The placement of the internal electrode precursor onto the raw sheet can be carried out, for example, by printing an internal electrode paste containing a metal with a silver content of 80% by mass or more onto the raw sheet. To improve the adhesion strength to the piezoelectric ceramic layer after firing, glass frit or a powder having a similar composition to the alkali niobate powder contained in the raw sheet may be added to the internal electrode paste.

[0061] When printing the paste for the internal electrodes onto a raw sheet, it is acceptable to leave a space that will become the side margin when the element is assembled into a multilayer piezoelectric element.

[0062] (Creation of the generated form) The resulting form can be obtained, for example, by stacking a predetermined number of raw sheets on which internal electrode precursors are arranged, and then pressing the raw sheets together. The stacking and pressing can be carried out by conventional methods, such as pressing the stacked raw sheets in the stacking direction while heating them, and then heat-pressing them together using the action of a binder.

[0063] During lamination and compression, raw sheets that will serve as cover portions when a laminated piezoelectric element is formed may be added to both ends in the lamination direction. In this case, the added raw sheets may have the same composition as the raw sheets on which the internal electrode precursors are placed, or a different composition. From the viewpoint of equalizing the shrinkage rate during firing, it is preferable that the composition of the added raw sheets is the same as or similar to the raw sheets on which the internal electrode precursors are placed.

[0064] (Fabrication of multilayer piezoelectric ceramics) Multilayer piezoelectric ceramics are obtained by firing the aforementioned generated form. Prior to firing, the binder may be removed from the generated form. In this case, binder removal and firing may be performed consecutively using the same firing apparatus. The conditions for binder removal and firing should be set appropriately considering the volatilization temperature and content of the binder, as well as the sinterability of the alkali niobate and the heat resistance of the metal contained in the internal electrode paste. Examples of conditions for binder removal include firing in an air atmosphere at a temperature of 300°C to 500°C for 5 to 20 hours. Examples of firing conditions include firing in an air atmosphere at 800°C to 1100°C for 1 to 5 hours. When obtaining multiple multilayer piezoelectric ceramics from a single generated form, the generated form may be divided into several blocks prior to firing.

[0065] During the aforementioned firing process, a sintered layer mainly composed of alkali niobate is formed from the raw sheet, and at the same time, internal electrodes are formed from the internal electrode precursors. At this time, silver diffuses from the internal electrodes into the sintered layer, causing the sintered layer to contain silver. Then, through the interaction of this silver with the alkaline earth metal elements added during the production of the raw sheet, the resulting sintered layer becomes dense, formed of fine sintered particles.

[0066] Furthermore, during the aforementioned firing process, the lithium and silicon added during the preparation of the raw sheet, along with the lithium component of the alkali niobate, react to produce Li2SiO3.

[0067] (Formation of connecting conductors and terminal electrodes) The connecting conductors and terminal electrodes can be formed, for example, by applying a conductive paste to the surface of the obtained multilayer piezoelectric ceramic and then baking it.

[0068] (Polarization treatment) Polarization is performed by applying a high voltage between the aforementioned terminal electrodes. The conditions for polarization are not particularly limited, as long as they can align the direction of spontaneous polarization in each piezoelectric ceramic layer without causing damage such as cracks to the multilayer piezoelectric ceramic. As an example, an electric field of 2kV / mm to 6kV / mm can be applied at a temperature of 100°C to 150°C. [Examples]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0070] (Example 1) As a powder of alkali niobate having a perovskite-type structure, the composition formula is Li 0.06 Na 0.52 K 0.42A calcined powder represented by NbO3 was prepared. To 100 mol% of this calcined powder, 0.6 mol% BaCO3, 0.4 mol% Li2CO3, 2.5 mol% SiO2, 0.8 mol% MnO, and a polyvinyl butyral-based binder were added and mixed using a wet ball mill. The resulting mixture slurry was formed using a doctor blade to obtain a raw sheet with a thickness of 80 μm. An Ag-Pd alloy paste (Ag / Pd mass ratio = 9 / 1) was screen printed onto this raw sheet to form an electrode pattern. Then, 11 layers of the raw sheet were stacked and pressed together under pressure of approximately 50 MPa while heating to obtain a laminate. After separating this laminate into individual pieces, a debinder treatment was performed in air, followed by firing in air at 970°C for 2 hours to obtain a fired body (layered piezoelectric ceramic). A conductive paste containing Ag was applied to the surface of the fired body, and the temperature was raised to 600°C to bake it, thereby forming a pair of connecting conductors and terminal electrodes. Finally, a polarization treatment was performed in a constant temperature bath at 100°C by applying an electric field of 3.0 kV / mm between the pair of terminal electrodes for 3 minutes to obtain the multilayer piezoelectric element according to Example 1.

[0071] (Examples 2 and 3) The laminated piezoelectric elements according to Examples 2 and 3 were obtained in the same manner as in Example 1, except that the amounts of Li2CO3 and SiO2 added to 100 mol% of calcined powder were 0.55 mol% Li2CO3 and 3.5 mol% SiO2 (Example 2), and 0.2 mol% Li2CO3 and 2.5 mol% SiO2 (Example 3), respectively.

[0072] (Comparative Example 1) A multilayer piezoelectric element according to Comparative Example 1 was obtained using the same method as in Example 1, except that the amounts of Li2CO3 and SiO2 added to 100 mol% of calcined powder were 0.65 mol% Li2CO3 and 1.3 mol% SiO2, and the calcination temperature was 990°C.

[0073] (Comparative Examples 2 to 4) Stacked piezoelectric elements according to Comparative Examples 2 to 4 were obtained using the same method as in Comparative Example 1, except that the amounts of Li2CO3 and SiO2 added to 100 mol% of calcined powder were 0.65 mol% Li2CO3 and 0.8 mol% SiO2 (Comparative Example 2), 2.5 mol% SiO2 added without Li2CO3 (Comparative Example 3), and 1.0 mol% Li2CO3 and 2.5 mol% SiO2 (Comparative Example 4), respectively.

[0074] Table 1 shows the molar percentages of lithium and silicon relative to the calcined powder, as well as the calcination temperature, for each of the above-described examples and comparative examples.

[0075] <Rating> [Calculation of R1 and R2] In each example and comparative example, the sintered body, including the internal electrodes, was pulverized into powder before the formation of the connecting conductor and terminal electrodes. X-ray diffraction measurements using Cu-Kα rays were then performed on this powder. The measurements were performed with an acceleration voltage of 40kV, a current of 40mA, and within the range of 10°≦2θ≦50° at 0.02° intervals, with a scan speed of 2° / min. As a result of the measurements, in addition to the peak of alkali niobate, the main component, a peak was observed in the range of 26.50°≦2θ≦27.50° in the powder prepared from each sintered body in the example, as well as from each sintered body in comparative examples 1, 3, and 4. In contrast, no such peak was observed in the powder prepared from the sintered body in comparative example 2. Furthermore, in the powders prepared from the calcined bodies of Example 1 and Comparative Examples 1, 2, and 4, peaks were observed within the range of 25.70°≦2θ≦26.00°, whereas in the powders prepared from the calcined bodies of Examples 2 and 3 and Comparative Example 3, the aforementioned peaks were not observed. Based on the measurement results, R1 and R2 were calculated using the above-described formula. The R1 and R2 values ​​obtained for each calcined body are shown in Table 1.

[0076] [Measuring elemental distribution within a piezoelectric ceramic layer] In each embodiment, the fired body before the formation of the connecting conductor and terminal electrodes was cut along a plane perpendicular to the piezoelectric ceramic layer and internal electrodes, and the elemental distribution of the piezoelectric ceramic layer in the exposed cross-section was measured by ToF-SIMS. As a result, it was confirmed that the silicon concentration was also high at locations where high concentrations of lithium were detected. Based on this result and the results of the X-ray diffraction measurements described above, it can be said that Li2SiO3 is present in the piezoelectric ceramic layer in the fired body according to each embodiment.

[0077] [Measurement of change in electrical insulation over time (average lifespan)] Each obtained multilayer piezoelectric element was placed in a 100°C constant temperature bath, and a DC electric field of 8 kV / mm was applied between the external electrodes. The time until the current flowing between the external electrodes reached 1 mA or more was measured. The average of this time for 10 elements was defined as the average lifetime. The average lifetimes obtained for each element are shown in Table 1 as a ratio to the average lifetime of the multilayer piezoelectric element in Comparative Example 1, which is set to 100.

[0078] [Evaluation of piezoelectric properties] The piezoelectric properties of each obtained multilayer piezoelectric element are defined by the displacement performance d * 33 The displacement was evaluated using (pm / V). First, a unipolar triangular wave with a maximum electric field of 6 kV / mm at approximately 100 Hz was injected into the multilayer piezoelectric ceramic, and the displacement of the multilayer piezoelectric element was measured using a laser Doppler displacement meter. Then, the obtained displacement of the multilayer piezoelectric element was divided by the thickness of the piezoelectric ceramic layer (distance between electrodes), the maximum voltage calculated from the maximum electric field, and the number of piezoelectric ceramic layers constituting the multilayer piezoelectric element to determine the displacement performance d per unit voltage of one piezoelectric ceramic layer. * 33 The displacement performance d obtained for each element was calculated. * 33 The displacement performance d of the multilayer piezoelectric element according to Comparative Example 1 * 33 The ratios are shown in Table 1, with the value set to 100.

[0079] [Table 1]

[0080] From these results, it can be said that by making the piezoelectric ceramic layer, which mainly consists of alkali niobate, contain alkaline earth metal elements and silver, as well as lithium and silicon in specific amounts, and also contain a predetermined amount of Li2SiO3, a multilayer piezoelectric element can be obtained that achieves both a long lifespan and excellent piezoelectric properties even when fired at low temperatures. [Industrial applicability]

[0081] According to the present invention, a multilayer piezoelectric element that achieves both long lifespan and excellent piezoelectricity, using piezoelectric ceramics mainly composed of alkali niobate, can be provided at low cost. Such a multilayer piezoelectric element is useful in that it does not contain lead in its constituent components and can be used for a long period of time, thereby reducing the environmental burden throughout its lifecycle. Furthermore, because the multilayer piezoelectric element has a high silver content in its internal electrodes, its electrical resistivity is low, which is also useful in that it reduces electrical losses during use. [Explanation of Symbols]

[0082] 100 Multilayer Piezoelectric Elements 10 Piezoelectric ceramic layer 20, 20a, 20b internal electrode 30, 30a, 30b connecting conductors 40 Side margin section 50 Cover section

Claims

1. It mainly consists of alkaliniobate salts having a perovskite-type structure, It contains at least one alkaline earth metal element selected from calcium, strontium, and barium, and silver. The above-mentioned main component is 100 mol%, and the product contains 0.1 mol% to 2.0 mol% lithium and 1.5 mol% to 4.0 mol% silicon in amounts such that the molar ratio of lithium to silicon (Li / Si) is 0.025 or more and less than 0.

40. The strongest diffraction line intensity at 10.00° ≤ 2θ ≤ 50.00° during X-ray diffraction measurements using Cu-Kα rays is defined as I. max The strongest diffraction line intensity at 26.50° ≤ 2θ ≤ 27.50° is I L2S The average value of the diffraction line intensity at 27.50° ≤ 2θ ≤ 29.00° is I BG When R 1 = (I L2S -I BG ) / (I max -I BG The following conditions must be met: ) × 100 ≥ 0.20, and when I L3N is the strongest diffraction line intensity at 25.70° ≤ 2θ ≤ 26.00°, then R2 = (I L3N - I BG) / (I max - I BG) × 100 ≤ 0.

55. Multiple piezoelectric ceramic layers, and Displaced between the plurality of piezoelectric ceramic layers, Formed from a metal with a silver content of 80% by mass or more. internal electrode A multilayer piezoelectric element equipped with [a specific feature].

2. The multilayer piezoelectric element according to claim 1, wherein the alkali niobate salt is represented by the following compositional formula. (A) u M2 v (K) 1-w-x Na w Li x ) 1-u-v ) a (S) y Ta z Nb 1-y-z )O 3 …(1) (However, M2 in the formula represents at least one alkaline earth metal selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba). Also, u, v, w, x, y, z, and a in the formula are numerical values ​​that satisfy the following inequalities, respectively: 0.005 < u ≤ 0.05, 0.002 < v ≤ 0.05, 0.007 < u + v ≤ 0.1, 0 ≤ w ≤ 1, 0.02 < x ≤ 0.1, 0.02 < w + x ≤ 1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.4, and 1 < a ≤ 1.1.)

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